Search Results (119)

The success of acid stimulation in tight carbonate reservoirs relies on the formation of non-uniform etching on fracture walls. However, existing research on the influence of the fracture surface morphology on non-uniform etching and fracture conductivity predominantly employed non-replicable tensile fracture surfaces. Previous studies were unable to use identical fracture surfaces to conduct single-factor analysis and clarify the impact of roughness. This study utilized digital engraving technology to fabricate multiple artificial carbonate rock samples with a homogeneous lithology and completely consistent fracture surface morphology. Using the Triangular Prism Method (TPM), the initial fracture roughness of the rock samples was decomposed into large-scale waviness and small-scale unevenness. Through controlled injection parameters, single-factor acid etching experiments were conducted. For the first time, the effects of large-scale waviness and small-scale unevenness on acid etching were investigated, along with the influences of the acid injection rate and injection time. The existence of an optimal injection rate and an optimal injection time was clarified. The results demonstrate that the engraved carbonate samples’ surfaces exhibit good consistency with the original natural fracture surfaces. The acid solution acts to shave the “peaks” and deepen the “valleys” of rough fractures. The large-scale waviness characteristics of the initial rough surfaces determine the overall post-etching morphology, leading to poor surface contact within the fracture. This is the primary reason for the high fluid flow capacity of acid-etched fractures under low closure stresses. However, the small-scale unevenness characteristics of the initial rough surfaces determine the formation and the distribution of small protruding support points on the post-etching surface. This is the primary reason for the retention of high conductivity in acid-etched fractures under high closure stresses. An increase in the acid injection rate or acid injection time does not lead to a linear decrease in linear roughness, surface mismatch, or fracture aperture. A critical acid injection rate or critical acid injection time exists. Optimizing the injection rate or time can achieve an ideal etching morphology—the protrusions formed by punctate etching enable the fractures to maintain a certain level of conductivity even under a high closure stress of 55.2 MPa, while channel etching can increase the conductivity under high closure stress by 20–25%, providing a key direction for optimizing acid etching effects. Full article

Accurate characterization of river channel geometry is essential for hydrological and hydraulic analyses, yet the increasing use of unmanned aerial vehicle (UAV) photogrammetry introduces challenges related to uneven point density, shadow-induced data gaps, and spurious outliers. This study proposed a novel approach for reconstructing 3D river channels from UAV-derived point clouds, emphasizing K-nearest neighbor local regression (KLR), and compared it with the LOWESS model. Method performance was examined through controlled simulations of trapezoidal, triangular, and U-shaped synthetic channels, where KLR consistently preserved morphological fidelity and produced lower RMSE than LOWESS, particularly at channel bends and bed undulations, while a neighborhood selection heuristic approach demonstrated robust results across varying data densities. Synthetic channel experiments show that the proposed K-nearest-neighbor local linear regression (KLR) method achieves RMSE values below 0.06 all tested geometries. In contrast, LOWESS produces substantially larger errors, with RMSE values exceeding 0.9 across all channel shapes. Subsequent application to two South Korean field sites reinforced these findings. In the data-scarce Migok-cheon stream, KLR effectively interpolated missing surfaces while maintaining geomorphic realism, whereas LOWESS generated over-smoothed representations. Within the dense Ogsan Bridge dataset, KLR retained small-scale bed features critical for hydraulic simulations and cross-sectional delineation, while LOWESS obscured local variability. Conclusively, the results demonstrate that KLR provides a more reliable and computationally efficient framework for UAV-based 3D river channel reconstruction, with clear implications for hydraulic modeling, flood risk management, and the advancement of digital-twin systems in operational hydrology. Full article

This study presents a Design for Additive Manufacturing (DfAM)–driven redesign of an industrial robot vacuum gripper for Fused Deposition Modeling (FDM), focusing on the systematic transformation of a multi-part, machined aluminum assembly into a lightweight, support-minimized polymer component suitable for continuous industrial operation. Beyond a practical redesign, the work contributes a geometry-centered DfAM methodology that links internal channel topology, overhang control, and functional interfaces to manufacturability, vacuum performance, and cost efficiency. The development follows three iterative design revisions, progressing from a geometry-adapted baseline toward a fully DfAM-optimized solution. A key innovation is the introduction of support-free internal vacuum channels with triangular cross-sections, enabling complete elimination of soluble support material within enclosed cavities. This redesign reduces the internal vacuum volume by 44%, leading to faster vacuum response while maintaining functional suction performance. The optimized overhang angles, filleted load paths, and DfAM-compliant suction cup seats significantly reduce post-processing requirements and improve structural robustness. Experimental validation under industrial operating conditions confirms that the final design achieves reliable vacuum performance and mechanical durability. Compared to the original configuration, the optimized gripper demonstrates a substantial reduction in manufacturing complexity, with printing time reduced by approximately 50% and total part cost decreased by 26%, primarily due to eliminated tooling, reduced support material, and simplified post-processing. The presented results demonstrate that DfAM principles, when applied systematically at both global and internal geometry levels, can yield quantifiable functional and economic benefits. The findings provide transferable design guidelines for support-free internal channels and functional interfaces in FDM-manufactured vacuum components, offering practical reference points for researchers and practitioners developing end-use additive manufacturing solutions in industrial automation. Full article

This work presents an experimental evaluation of a high-speed analog-to-digital conversion method based on passive reference waveform crossings combined with time-to-digital converter (TDC) time-tagging. Unlike conventional level-crossing event-driven analog-to-digital converters (ADCs) that require dynamically updated digital-to-analog converters (DACs), the proposed architecture compares the input waveform against a broadband periodic sampling function without active threshold control. Crossing instants are detected by a high-speed comparator and converted into rising and falling edge timestamps using a multi-channel TDC. A commercial ScioSense GPX2-based time-tagger with 30 ps single-shot precision was used for validation. A range of test signals—including 5 MHz sine, sawtooth, damped sine, and frequency-modulated chirp waveforms—were acquired using triangular, sinusoidal, and sawtooth sampling functions. Stroboscopic sampling was demonstrated using reference frequencies lower than the signal of interest, enabling effective undersampling of periodic radio frequency (RF) waveforms. The method achieved effective bandwidths approaching 100 MHz, with amplitude reconstruction errors of 0.05–0.30 RMS for sinusoidal signals and 0.15–0.40 RMS for sawtooth signals. Timing jitter showed strong dependence on the relative slope between the acquired waveform and sampling function: steep regions produced jitter near 5 ns, while shallow regions exhibited jitter up to 20 ns. The study has several limitations, including the bandwidth and dead-time constraints of the commercial TDC, the finite slew rate and noise of the comparator front-end, and the limited frequency range of the generated sampling functions. These factors influence the achievable timing precision and reconstruction accuracy, especially in low-gradient signal regions. Overall, the passive waveform-crossing method demonstrates strong potential for wideband, sparse, and rapidly varying signals, with natural scalability to multi-channel systems. Potential application domains include RF acquisition, ultra-wideband (UWB) radar, integrated sensing and communication (ISAC) systems, high-speed instrumentation, and wideband timed antenna arrays. Full article

This paper investigates bearing-based formation control of multiple unmanned aerial vehicles (UAVs) flying in low-altitude wind fields. In such environments, time-varying wind disturbances can distort the formation geometry, enlarge bearing errors, and even induce potential collisions among neighboring UAVs, yet they also contain components that can be beneficial for the formation motion. Conventional disturbance compensation methods treat wind as a purely harmful factor and aim to reject it completely, which may sacrifice responsiveness and energy efficiency. To address this issue, we propose a pure bearing-based formation control framework with Conditional Disturbance Utilization (CDU). First, a real-time disturbance observer is designed to estimate the wind-induced disturbances in both translational and rotational channels. Then, based on the estimated disturbances and the bearing-dependent potential function, CDU indicators are constructed to judge whether the current disturbance component is beneficial or detrimental with respect to the formation control objective. These indicators are embedded into the bearing-based formation controller so that favorable wind components are exploited to accelerate formation convergence, whereas adverse components are compensated. Using an angle-rigid formation topology and a Lyapunov-based analysis, we prove that the proposed CDU-based controller guarantees global asymptotic stability of the desired formation. Simulation results on triangular and hexagonal formations under complex wind disturbances show that the proposed method achieves faster convergence and improved responsiveness compared with traditional disturbance observer-based control, while preserving formation stability and safety. Full article

A two-dimensional D2Q9 lattice Boltzmann (LBM) model with a sinusoidal pressure inlet boundary condition is implemented to study pulsatile flow through pseudo-periodic porous channels. Simulations in MATLAB are performed for geometries containing periodically arranged rectangular, circular, and elliptic obstacles to represent simplified porous media. Grid- and time-step-independence tests, together with the verification of small pressure and density variations, ensure low-Mach-number, weakly compressible flow and numerical stability. The study focuses on the coupling between the oscillation frequency and spatial periodicity of the structure. The results reveal distinct resonance effects, where the cycle-averaged flow rate exceeds the steady-state value by up to 40–50% at optimal frequencies. A dimensionless response function, $R\left(\omega \right)={\bar{Q}}_{\mathrm{p}\mathrm{u}\mathrm{l}\mathrm{s}}/Q_{\mathrm{s}\mathrm{t}\mathrm{e}\mathrm{a}\mathrm{d}\mathrm{y}}$, is introduced to quantify flow enhancement. The response amplitude and bandwidth depend strongly on obstacle shape and porosity—circular and elliptical obstacles produce the largest enhancement due to smoother streamline transitions, whereas rectangular and triangular ones show weaker responses. The frequency dependence of $R\left(\omega \right)$ follows a resonance-type trend consistent with Womersley theory, reflecting the interaction between temporal forcing and spatial periodicity. These findings provide quantitative insights into pulsation-induced flow enhancement and establish physically grounded boundary and outlet conditions for reliable LBM modeling of unsteady transport in microfluidic, biological, and enhanced oil recovery systems. Full article

This study uses the finite element (FE) software ABAQUS V 6.14to develop detailed, comprehensive numerical models of the behaviour of restrained structural subassemblies of corrugated web steel beams (SBCW) connected to concrete-filled tubular columns (CFTC) via reverse channel connection. Four different types of web corrugation profiles—trapezoidal (Trap), rectangular (Rec), sinusoidal (Sin), and triangular (Tria)—are numerically modelled and analyzed to evaluate the significance of their influence on structural behaviour. In addition, the effects of flange stiffeners at the point load and web slenderness are examined. Moreover, this study investigates the effects of using four different joint types of reverse channel connection: extended endplate, flush endplate, flexible endplate, and hybrid extended/flexible endplate on the behaviour of SBCW. It is concluded that, by means of corrugated webs for enhancing beam deformation capacity and strength, it is feasible for the beams to achieve a higher load-carrying capacity. The ultimate load of the beams with Trap and Rec corrugated web was higher than that for the flat web beam by about 22% and 18%, respectively, and with the same increase of 10.5% for Tria and Sin corrugation profiles. However, providing the corrugated web beams with flange stiffeners at the point load had a limited effect (+0.7% to +5.1% depending on profile). Moreover, increasing the web thickness to reduce the slenderness ratio (hw/tw) from 250 to 200 can be an effective solution to prolong their load-carrying capacity. In addition, using an extended or flush endplate gave the best behaviour of SBCW connected to concrete-filled tubular columns (CFTC) with an increase of (5.3–31.7%) and (25–30.9%) for flush endplate and extended endplate, respectively, compared to flexible endplate, depending on the web corrugation profile. Full article

In this study, two types of gas sensors—silicone-based interdigital electrode and silicon micropillar sensors based on rGO and rGO/SnO₂—were fabricated. Their gas-sensing performance was investigated at room temperature. First, interdigital electrodes of different channel widths were fabricated to investigate the impact of the channel width parameter. Subsequently, the rGO/SnO₂ doping ratio in the composite material was varied to identify the optimal composition for gas sensitivity. Additionally, triangular and square-arrayed silicon micropillar substrates were fabricated via photolithography and inductively coupled plasma etching. The rGO/SnO₂-based gas sensor on a silicon micropillar substrate exhibited an ultra-high specific surface area. The triangular micropillar arrangement of rGO/SnO₂-160 demonstrates the best performance, showing approximately 14% higher response and a 106 s reduction in response time compared with interdigital electrode sensors spray-coated with the same concentration of rGO/SnO₂ when tested at room temperature under 250 ppm NO₂. The optimized sensor achieves a detection limit as low as 5 ppm and maintains high responsiveness, even in conditions of 60% relative humidity (RH). Additionally, the repeatability, selectivity, and stability of the sensor were evaluated. Finally, structural and morphological characterization was conducted using XRD, SEM, TEM, and Raman spectroscopy, which confirmed the successful modification of rGO with SnO₂. Full article

Compact nuclear reactor systems usually use helium–xenon (He-Xe) mixtures as coolants. Tight-lattice rod-bundled channels, serving as primary core configurations in compact nuclear reactor designs, exhibit quasi-triangular cross-sections where fluid dynamics substantially deviate from circular tube behavior. This study evaluates the applicability of turbulence models and turbulent Prandtl number (Pr_t) models in quasi-triangular channels through systematic numerical simulations. The results demonstrate that the Transition SST model accurately resolves flow dynamics and turbulence development in helium–xenon mixtures, while implementing Pr_t models significantly enhances temperature prediction accuracy. Among the evaluated models, the Weigand model achieves optimal performance by dynamically adapting Pr_t values across flow regimes. Further refinements targeting parameters governing near-wall Pr_t distribution are identified as critical pathways for improving numerical simulation precision of low-Prandtl-number fluids in geometrically complex nuclear systems. Full article

The most widely used nanowire channel architecture for creating state-of-the-art high-performance transistors is the nanowire wrap-gate transistor, which offers low power consumption, high carrier mobility, large electrostatic control, and high-speed switching. The frequency-dependent capacitance and conductance measurements of triangular-shaped GaN nanowire wrap-gate transistors are measured in the frequency range of 1 kHz–1 MHz at room temperature to investigate carrier trapping effects in the core and at the surface. The performance of such a low-dimensional device is greatly influenced by its surface traps. With increasing applied frequency, the calculated trap density promptly decreases, from 1.01 × 10¹³ cm⁻² eV⁻¹ at 1 kHz to 8.56 × 10¹² cm⁻²eV⁻¹ at 1 MHz, respectively. The 1/f-noise features show that the noise spectral density rises with applied gate bias and shows 1/f-noise behavior in the accumulation regime. The fabricated device is controlled by 1/f-noise at lower frequencies and 1/f²-noise at frequencies greater than ~ 0.2 kHz in the surface depletion regime. Further generation–recombination (G-R) is responsible for the 1/f²-noise characteristics. This process is primarily brought on by electron trapping and detrapping via deep traps situated on the nanowire’s surface depletion regime. When the device works in the deep-subthreshold regime, the cut-off frequency for the 1/f²-noise characteristics further drops to a lower frequency of 30 Hz–10⁴ Hz. Full article

The relationship between concentration and discharge (C/Q) is widely studied to understand the behavior of solute transport in complex natural media during storm events. The causes of C/Q hysteresis are due to the delay between the signals of C and Q at a given observation point. Many indices are used to characterize the C/Q hysteresis curve, like the hysteresis index (HI) and the flushing index (FI). The limitation of relating C/Q hysteresis relationships or indices to storm event parameters is because, in real-world situations, we ignore and do not control storm event parameters. This paper is the first attempt to study the variability of C/Q relationships under a well-known storm event on a controlled experimental channel. We tested nine scenarios where the storm event consisted of a triangular input signal with a constant peak and a variable duration. The main parameter of this study is the storm event duration. We calculated known indices, like the hysteresis index (HI) and the flushing index (FI), and we introduced the following two new indices: the saturation index (SI) and the bisector index (BI). Then we related all calculated indices to the storm duration parameter. The importance of our study is that it presents, for the first time, a quantitative description of how the magnitude of the hysteresis indices varies with the storm duration parameter. We found that the most popular HI index does not follow a monotonic behavior for increasing storm duration. Conversely, the FI index and the two newly introduced indices (SI and BI) follow a monotonic behavior for increasing storm duration according to a Fermi-type function. The SI varies between 0.11 and 0.93, while the BI varies between 1 and 0.32 for an increasing storm event duration. Full article

Continuous multi-day extremely low or high new energy outputs have posed significant challenges in relation to power supply and new energy accommodations. Conventional reservoir hydropower, with the advantage of controllability and the storage ability of reservoirs, can represent a reliable and low-carbon flexibility resource to safeguard against continuous extreme new energy fluctuations. This paper proposes a mid-term scheduling method for reservoir hydropower to enhance our ability to regulate continuous extreme new energy fluctuations. First, a data-driven scenario generation method is proposed to characterize the continuous extreme new energy output by combining kernel density estimation, Monte Carlo sampling, and the synchronized backward reduction method. Second, a two-stage stochastic hydropower–new energy complementary optimization scheduling model is constructed with the reservoir water level as the decision variable, ensuring that reservoirs have a sufficient water buffering capacity to free up transmission channels for continuous extremely high new energy outputs and sufficient water energy storage to compensate for continuous extremely low new energy outputs. Third, the mathematical model is transformed into a tractable mixed-integer linear programming (MILP) problem by using piecewise linear and triangular interpolation techniques on the solution, reducing the solution complexity. Finally, a case study of a hydropower–PV station in a river basin is conducted to demonstrate that the proposed model can effectively enhance hydropower’s regulation ability, to mitigate continuous extreme PV outputs, thereby improving power supply reliability in this hybrid renewable energy system. Full article

In urban environments, the highly complex communication environment often leads to blockages in the link between ground users (GUs) and unmanned aerial vehicles (UAVs), resulting in poor communication quality. Although traditional reconfigurable intelligent surfaces (RISs) can improve wireless channel quality, they can only provide reflection services and have limited coverage. For this reason, we study a novel simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR–RIS)–assisted UAV–mobile edge computing (UAV–MEC) network, which can serve multiple users residing in the transmission area and reflection area, and switch between reflection and transmission modes according to the relative positions of the UAV, GUs, and STAR–RIS, providing users with more flexible and efficient services. The system comprehensively considers user transmit power, time slot allocation, UAV flight trajectory, STAR–RIS mode selection, and phase angle matrix, achieving long–term energy consumpution minimization while ensuring stable task backlog queue. Since the proposed problem is a long–term stochastic optimization problem, we use the Lyapunov method to transform it into three deterministic online optimization subproblems and iteratively solve them alternately. Specifically, we firstly use the Lambert function to solve for the closed-form solution of the transmit power; then, use Lagrange duality and the Karush–Kuhn–Tucker conditions to solve time slot allocation; finally, successive convex approximation is used to obtain trajectory planning for UAVs with lower complexity, and triangular inequalities are used to solve the STAR–RIS phase shift. The simulation results show that the proposed scheme has better performance than other benchmark schemes in maintaining queue stability and reducing energy consumption. Full article

Adding blockages to the gas flow channels in the bipolar plates has a significant effect on the performance of the proton exchange membrane fuel cell (PEMFC). The design parameters of the gas flow channels with blockages mainly include the blockage shape (S), blockage number (N), blockage height (H), and channel–rib width ratio (CRWR) value. This paper systematically examines the combined effects of S, N, H, and CRWR value on current density (I), pressure drop (ΔP), net output power (W_net), and non-uniformity of oxygen distribution (NU) of PEMFC through the application of the orthogonal experimental method (OEM). To provide a comprehensive optimization strategy, a novel multi-criteria decision framework is introduced, which integrates the analytic hierarchy process (AHP) and entropy weight method (EWM) to balance different evaluation objectives. Results from the AHP-EWM analysis reveal that the weight values of I, ΔP, W_net, and NU are 0.415, 0.08, 0.325, and 0.18, respectively. The CRWR value exhibits the greatest effect on the comprehensive performance of PEMFC, followed by H, N, and S. The optimal design parameter combination identified in this paper is a triangular blockage with nine blockages, a height of 0.8 mm, and a CRWR value of 0.25, corresponding to the highest comprehensive score of 31.8306 among the 25 groups of orthogonal experiments. This paper provides a new optimization perspective and certain guidance for the performance optimization direction of PEMFC. Full article

The core subunits of the K_V7.2, K_V7.3, and K_V7.5 channels, encoded by the KCNQ2, KCNQ3, and KCNQ5 genes, are expressed across various cell types and play a key role in generating the M-type K⁺ current (I_K(M)). This current is characterized by an activation threshold at low voltages and displays slow activation and deactivation kinetics. Variations in the amplitude and gating kinetics of I_K(M) can significantly influence membrane excitability. Notably, I_K(M) demonstrates distinct voltage-dependent hysteresis when subjected to prolonged isosceles-triangular ramp pulses. In this review, we explore various small-molecule modulators that can either inhibit or enhance the amplitude of I_K(M), along with their perturbations on its gating kinetics and voltage-dependent hysteresis. The inhibitors of I_K(M) highlighted here include bisoprolol, brivaracetam, cannabidiol, nalbuphine, phenobarbital, and remdesivir. Conversely, compounds such as flupirtine, kynurenic acid, naringenin, QO-58, and solifenacin have been shown to enhance I_K(M). These modulators show potential as pharmacological or therapeutic strategies for treating certain disorders linked to gain-of-function or loss-of-function mutations in M-type K⁺ (K_V7x or KCNQx) channels. Full article