Dispersion Characteristics Research Articles

Longitudinal thermoelastic guided waves in functionally graded hollow cylinders with Green–Naghdi thermoelastic theory

Abstract At present, functional gradient material (FGM) pipelines are widely used in high-temperature environments, and the need for online inspection of such pipelines is becoming more and more urgent. Ultrasonic guided wave is undoubtedly one of the most promising methods for detection, but research on the propagation characteristics of thermoelastic guided wave in high-temperature FGM pipelines is still limited. In this paper, based on Green–Naghdi thermoelastic theory, a theoretical model of longitudinal thermoelastic guided wave in a hollow cylinder of FGM considering temperature effect is established by using the Voigt model, and the governing equations of thermoelastic guided wave are solved by the Legendre series method. The dispersion, displacement, and temperature distribution curves of guided waves in a hollow cylinder of FGM are plotted. The convergence of the method and the influence of the coupling of thermodynamic equations on the dispersion characteristics of guided waves are discussed. The influence of circumferential order, ratio of radius to thickness, gradient index, and temperature change on the dispersion characteristics of guided waves is analyzed. This study provides a theoretical basis for nondestructive testing and evaluation of high-temperature FGM pipelines.

Spatiotemporal migration of dust pollution during the tunnel mucking process and development of dust removal trolley based on computational fluid dynamics technology

ABSTRACT During tunnel construction, the protracted mucking phase poses significant occupational health risks, particularly from dust exposure. This study delves into comprehensive numerical simulations to examine the spatiotemporal dynamics of dust particles during the mucking process. A distinct ‘bimodal pattern’ was characterized by higher concentrations in the mucking area (0-30 m) and the inverted arch area (60-110 m), where concentrations exceed 30 mg/m3 under all conditions. To address this issue, a novel dust removal system has been developed. Integrating six dust collectors and one air curtain device, a dust removal trolley is strategically positioned at z = 70 m to locally purify the air. The extracted wind speed of the dust collectors ( V inlet 1 ) and the air curtain’s wind speed ( V inlet 2 ) are optimized based on ventilation conditions and dust dispersion characteristics. This system effectively reduces dust mass concentrations to below 4.8 mg/m3 at six worker locations.

Effect of pulsation intensity on flow and dispersion characteristics of single-pulsed dual parallel plane jets

The effect of pulsation intensity on flow and dispersion characteristics of single-pulsed dual parallel plane jets was experimentally investigated in this study. A single jet from a pair of dual jets was pulsed by a loudspeaker. The flow evolution processes were examined using the laser-light sheet-assisted smoke flow visualization method. The visual spread of the jet flow was measured using the binary boundary edge detection technique. A hotwire anemometer was used to detect the instantaneous velocities, mean velocities, turbulence intensities, Lagrangian integral time, and length scales. The dispersion capabilities of the jet fluid were evaluated employing the tracer-gas concentration detection technique. Two characteristic flow modes, namely the coherent vortices and vortex breakup, could be classified based on pulsation intensity. At Ip < 1.0, the flow was characterized by coherent vortices, which maintained coherence within one excitation cycle. At Ip > 1.0, vortex breakup occurred, where vortices deformed, lost coherence, and transformed into puff-shaped vortical structures within one excitation cycle. The vortices emerging from the pulsed jet undergo deformation, evolving into puff-shaped vortices, and subsequently fragment into smaller turbulent eddies more quickly than the synchronized vortices from the non-pulsed jet. This leads to significant penetration and velocity fluctuations in the trajectory of the pulsed jet. Consequently, the overall spread width and concentration reduction index of the single-pulsed dual parallel plane jets exceed those of the non-pulsed dual parallel plane jets.

Dispersion analysis of grounded dielectric slab coated with double positive (DPS) / double negative (DNG) material

The present work investigates the dispersion characteristics both for TM and TE modes in a grounded dielectric slab coated with double positive (DPS) material and double negative (DNG) material. The outermost dielectric layer is assumed to be free space. By employing proper boundary conditions at interfaces, dispersion relations for the aforementioned structure for both TM and TE modes are derived. Additionally, surface waves at the interface of free space and DPS/DNG coating are investigated. Existence of mode degeneracy for DNG/DPS combination has been discussed based on dispersion analysis.

Small-signal model for inhomogeneous helix traveling-wave tubes using transfer matrices

We introduce a practical method for modeling the small-signal behavior of frequency-dispersive and inhomogeneous helix-type traveling-wave tube (TWT) amplifiers based on a generalization of the one-dimensional (1D) Pierce model. Our model is applicable to both single-stage and multi-stage TWTs. Like the Pierce model, we assume that electrons flow linearly in one direction, parallel and in proximity to a slow-wave structure (SWS) that guides a single dominant electromagnetic mode. Realistic helix TWTs are modeled with position-dependent and frequency-dependent SWS characteristics, such as loss, phase velocity, plasma frequency reduction factor, interaction impedance, and the coupling factor that relates the SWS modal characteristic impedance to the interaction impedance. For the multi-stage helix TWTs, we provide a simple lumped element circuit model for combining the stages separated by a sever, or gap, which attenuates the guided circuit mode while allowing the space-charge wave on the beam to pass freely to the next stage. The dispersive SWS characteristics are accounted for using full-wave eigenmode simulations for a realistic helix SWS supported by dielectric rods in a metal barrel, all of which contribute to the distributed circuit loss. We compare our computed gain vs frequency, computed using transfer matrices, to results found through particle-in-cell simulations and the 1D TWT code LATTE to demonstrate the accuracy of our model. Furthermore, we demonstrate the ability of our model to reproduce gain ripple due to mismatches at the input and output ports of the TWT.

Application of some cationic pullulan and curdlan derivatives as flocculants in fungicides-containing wastewater purification

The ability of some cationic pullulan (TMAPx-P) and curdlan (TMAP0.4-C) derivative to remove different fungicide particles from synthetic wastewater has been studied. Commercial fungicides formulations of different type, Bordeaux mixture (BM), Dithan M45 (Dt) and Melody Compact49 WG (MC) have been used. The influence of some parameters related to the dispersion characteristics (suspension pH and salinity) and the polysaccharide derivatives (polymer dose, the ionic groups content, flexibility) on the separation process have been assessed. All the polysaccharide samples revealed a good removal efficiency (RE%) for the fungicide formulations prepared in saltless aqueous solutions, namely between 94 and 98 % for BM, 81.5–85 % for Dt, 88–91 % for MC. Slightly higher residual fungicides absorbance percent values for the suspensions prepared in the presence of salts (up to 7 %) than those prepared in water have been noticed. Less amount of BM and MC particles were removed in acidic pH than in water and basic pH, while contrary results were recorded in case of Dt ones, irrespective of the flocculant used. However, the RE% values were located between 79 % and 98 % over the entirely suspension pH investigated. Both zeta potential and floc size measurements indicated the charge patch flocculation mechanism for the fungicide particles separation.

Modelling of EM Wave Propagation in Distorted Conventional Optical Fiber to Multilayer Hollow Bragg Fiber

Present investigation deals with the electromagnetic (EM) wave propagation through the asymmetrical (distorted) conventional optical fiber and extended the investigation for the distorted multilayered hollow Bragg Fiber. For this purposed theoretical and mathematical are well connected to investigate and further discuss the wave propagation through such distorted structure so that further many useful parameters like optical power, different losses, dispersion analysis, etc. can be computed easily by the researchers in the same area. In present study, the dispersion properties of an optical fiber with a little one-sided flattening are modelled using a straightforward mathematical approach that relies on coordinate transformation. In order to derive the modal eigenvalue equation, we provide the boundary condition under a weak guiding condition and choose new orthogonal coordinates that are suitable for the suggested waveguide construction. Further, a distorted Bragg fiber with a little flattened distortion is anticipated to have dispersion characteristics by comparing the fields at different boundaries.

The Behavior and Dispersion Characteristics of Microparticles under Reservoir Flipping

The Behavior and Dispersion Characteristics of Microparticles under Reservoir Flipping

Rheology-dependent surface wave characteristics in an advanced geomaterial flexoelectric plate with viscoelastic coating

Abstract This study investigates the transmission of seismic surface waves in a composite framework comprising a viscoelastic layer overlying a flexoelectric material. The study focuses on understanding the impact of different viscoelastic models (Maxwell, Newtonian, and Kelvin-Voigt) and interface conditions (smooth and welded contact) on the damping and dispersion characteristics of these waves.To achieve this, the study employs a variable-separable technique and appropriate boundary conditions to derive complex frequency relations for electrically open and short circuits scenarios. These relations are subsequently divided into real and imaginary parts to examine the dispersion and dampening properties, respectively. Numerical simulations are conducted to analyze the response of flexoelectric coefficient, viscoelastic layer thickness, and bonding parameter on phase velocity and dampening coefficient.The research findings indicate that the attenuation properties of the Maxwell and Newtonian models are lower compared to the Kelvin-Voigt model. Graphical comparisons highlight the influence of viscoelastic models and interface characteristics on wave propagation.This research can help in the development of sensors, energy harvesters, and wave manipulation devices that employ flexoelectric materials with viscoelastic coatings. Knowledge of surface wave dynamics in these structures is vital for their optimal performance.&amp;#xD;

Beyond two-octave coherent OAM supercontinuum generation in air-core Ge-doped ring fiber

Orbital angular momentum (OAM) has emerged as a revolutionary technology for communication networks due to its ability to significantly increase the channel capacity. However, traditional optical fibers present significant hurdles to harnessing OAM’s full potential, including dispersion and limited bandwidth, which facilitates investigations on supercontinuum (SC) generation for OAM beams. In this paper, an air-core Ge-doped ring fiber is proposed and designed to support high-order OAM mode up to |l| = 24. To achieve this, the fiber has a high refractive index difference between the ring core and the cladding, enabling stable transmission of high-order OAM modes. A key feature of this design is the OAM24,1 mode, which exhibits near-zero and flat dispersion. This characteristic translates into high coherence and a remarkably broad SC generation. The generated SC spans over two octaves (2336 nm) within the infrared wavelength range (764 nm to 3100 nm) at a power level of −40 dB. Furthermore, by optimizing the structural parameters, we ensure near-zero and flat dispersion characteristics for the other OAM modes (|l| < 24), along with broad SC generation exceeding two octaves. This fiber design holds significant promise for future advancements in OAM beam transmission within the infrared spectrum.

The energy dispersion of magnetic Rossby waves in the quasi-geostrophic shallow water magnetohydrodynamic theory

Abstract This research firstly comprehensively investigates the energy dispersion of magnetic Rossby waves in zonally non-uniform basic states by applying the quasi-geostrophic (QG) shallow water magnetohydrodynamic (SWMHD) equations. The eddy momentum and heat flux transported by magnetic Rossby waves, which can be described by the group velocity vector, have significant impacts on the large-scale dynamics of various celestial bodies. The findings suggest that the energy dispersion paths, also called rays, are curves and restricted in limited regions in the non-uniform basic states, in contrast with straight lines in the uniform basic states. Furthermore, the limited propagative regions are influenced by three important meridional locations, which are defined as the symmetric turning location, the asymmetric turning location, and the critical location. The first two reflect rays and the third one acts as an asymptote. The propagative region that is enclosed by a turning location and a critical location is more general. Besides, the occurrence of the asymmetric turning location, which is mainly depended on the distribution of the zonal basic flow, is a quite new feature of the energy dispersion for magnetic Rossby waves since there is no asymmetric turning location for Rossby waves on the Earth’s atmosphere and ocean. The results have important applications in illustrating interactions between magnetic Rossby waves and zonally basic states and in explaining the maintenance of the zonal flow and meridional circulation of various celestial bodies.

Unit Cell Optimization of Groove Gap Waveguide for High Bandwidth Microwave Applications

Recently, groove gap waveguides (GGWs) have shown significant potential in power handling and bandwidth enhancement compared to conventional waveguides. In this research work, we designed and developed an innovative mushroom-unit-cell-based groove gap waveguide (MGGW) that has shown improved bandwidth compared to conventional GGW structures. The dispersion characteristics of the MGGW were analyzed through the eigenmode solver feature of Microwave Studio CST, which showed that the bandwidth was improved by 8% compared to conventional unit cells in the microwave spectrum. To validate our proposed method for the physical dimensions of unit cell structures, we developed an MGGW structure for the S band, which shows similar trends aligning with the simulation results. The measurement results are promising as a reflection coefficient of less than −20 dB was achieved over the entire band for the WR284 Electronic Industries Alliance (EIA) standard waveguide adapter. The proposed MGGW structure with improved bandwidth will open new doors for researchers to develop ultra-wide bandwidth microwave applications, i.e., filters, transmission lines, resonators, attenuators, etc.

Collagen and chitosan-based biogenic sprayable gel of silver nanoparticle for advanced wound care.

Silver nanoparticles have gained significant attention recently due to their unique antibacterial properties, making them promising candidates for wound care applications. This study proposes a novel approach for advanced wound care using a silver nanoparticle-impregnated biogenic spray hydrogel supplemented with collagen and chitosan. Silver nanoparticles were incorporated into the hydrogel (optimized by a QbD approach) to impart antimicrobial activity, crucial for combating wound infections and promoting faster healing. The study assessed the physical and chemical properties of the biogenic hydrogel, including its viscosity, pH, and nanoparticle dispersion characteristics. In vitro, antimicrobial efficacy against common wound pathogens and in vivo studies using chronic wound models in small animals portrayed the immense potential of the developed biogenic hydrogel in effectively reducing the bacterial load of broad-spectrum pathogens. The hydrogel exhibited excellent biocompatibility, supporting cell proliferation and tissue repair without toxic effects. It accelerated wound healing, improved collagen deposition, and enhanced tissue regeneration in the tested animals by reducing proinflammatory cytokines, ROS, and NF-kb levels. Overall, this innovative silver nanoparticle-impregnated biogenic spray hydrogel of collagen and chitosan presents a uniform spray pattern that proved efficient, showing a promising solution for advanced wound care. Its biocompatibility, safety, anti-inflammatory, antimicrobial efficacy, and wound healing properties hold great potential for improving the management of complex wounds, opening new avenues in wound care and regenerative medicine.

Impact of CaO-Modified γ-Al2O3 Support on CO Oxidation Activity of Pt/LaFeO3 Catalyst.

In this study, we prepared Pt/29.3 wt % LaFeO3 on a commercial carrier of γ-Al2O3 by inserting a CaO interlayer between LaFeO3 and γ-Al2O3 (i.e., Pt/LaFeO3/CaO/γ-Al2O3) via atomic layer deposition. With the interaction between CaO and LaFeO3, the Pt supported on LaFeO3/CaO/γ-Al2O3 demonstrated diverse dispersion characteristics, with regions showing well-dispersed Pt particles of approximately 2 nm, while others displayed some larger Pt nanoparticles. Interestingly, after redox treatments, the CO adsorption over Pt/LaFeO3/CaO/γ-Al2O3 was significantly attenuated, and high-resolution transmission electron microscope analysis on the Pt surface revealed the presence of FeOx layers covering the Pt. Postoxidation, a thick FeOx layer was generated on Pt, leading to the inertness of the catalyst toward CO oxidation. However, after reduction, a thinner FeOx layer (approximately two atomic layers) developed on Pt, which facilitated the oxidation of CO through the Pt-FeOx interface.

Reflection phenomena of thermoelastic plane waves on a rigid surface within a size-dependent elastic media

The current investigation aims to comprehend the spread of time-harmonic thermoelastic plane waves in an isotropic and homogeneous nonlocal elastic material without bounds, within the framework of the Lord–Shulman model and Eringen’s nonlocal stress model. Our analysis reveals two sets of coupled longitudinal waves and one independent shear-type wave. The coupled longitudinal waves experience dispersion and damping over time due to the dissipative nature of the L-S model. In contrast, the vertically shear-type waves exhibit dispersion characteristics due to the presence of nonlocality in the medium. Furthermore, we observe that the shear-type wave encounters a critical frequency, while the coupled longitudinal waves may face critical frequency conditions under certain circumstances. We explore the reflection of thermoelastic waves at a rigid, thermally insulated, and isothermal boundary of a thermoelastic half-space, particularly in the case of an incident coupled longitudinal thermoelastic wave. We determine the amplitude ratios of the reflected waves to the incident wave through analytical methods. For a specific model, we generate various graphs to analyze the behavior of phase speeds, attenuation coefficients, and reflection coefficients. To assess the impact of the elastic nonlocal parameter on the variations of phase speeds, attenuation coefficients, and amplitude ratios of the reflected waves, we present graphical representations. Notably, our observations indicate that all waves are influenced by the nonlocality of the medium. Longitudinal waves exhibit sensitivity to thermal parameters, whereas the shear-type wave remains independent of thermal effects. Furthermore, the presence of elastic nonlocality results in a reduction in the classical shear-type wave speed.

Multi-octave two-color soliton frequency comb in integrated chalcogenide microresonators

Mid-infrared (MIR) Kerr microcombs are of significant interest for portable dual-comb spectroscopy and precision molecular sensing due to strong molecular vibrational absorption in the MIR band. However, achieving a compact, octave-spanning MIR Kerr microcomb remains a challenge due to the lack of suitable MIR photonic materials for the core and cladding of integrated devices and appropriate MIR continuous-wave (CW) pump lasers. Here, we propose a novel slot concentric dual-ring (SCDR) microresonator based on an integrated chalcogenide glass chip, which offers excellent transmission performance and flexible dispersion engineering in the MIR band. This device achieves both phase-matching and group velocity matching in two separated anomalous dispersion regions, enabling phase-locked, two-color solitons in the MIR region with a commercial 2-μm CW laser as the pump source. Moreover, the spectral locking of the two-color soliton enhances pump wavelength selectivity, providing precise control over soliton dynamics. By leveraging the dispersion characteristics of the SCDR microresonator, we have demonstrated a multi-octave-spanning, two-color soliton microcomb, covering a spectral range from 1156.07 to 5054.95 nm (200 THz) at a −40 dB level, highlighting the versatility and broad applicability of our approach. And the proposed multi-octave MIR frequency comb is relevant for applications such as dual-comb spectroscopy and trace-gas sensing.Graphical

Perforated plate ventilation system and dynamics of infectious respiratory particle transmission

AbstractWith the removal of indoor pollutants and the assurance of air quality emerging as critical research topics, the optimization of the internal environment in offices, where people stay for extended periods, is essential for controlling the spread of infectious respiratory particles. Frequent movements of personnel and the operation of doors and windows within offices significantly impact the mechanisms of droplet transmission, warranting further investigation. This study employs computational fluid dynamics simulations to explore the droplet dispersion characteristics and pollutant removal efficiency of the simplified model of perforated plate ventilation system (PPVS) (the diameter of the air supply openings has been reasonably simplified and uniformly set to 0.02 m) in office settings, as well as the impact of dynamic door operation scenarios on droplet spread and concentrations in breathing zones. To optimize the ventilation system's pollutant removal efficiency, airflow velocities (2.86, 3.18, and 5.00 m/s) are varied, with simulations conducted at the optimal velocity of 3.18 m/s. The effects of continuous door operations, door‐opening directions (towards the office and towards the isolation room), and opening speeds (π/4, π/6, π/8, and π/10 rad/s) are also examined, revealing significant impacts on droplet spread. Results indicate that PPVS effectively reduces indoor pollutant concentrations at all tested airflow velocities, with the optimal speed identified as 3.18 m/s. Additionally, door‐opening direction and speed can significantly influence droplet spread. Opening doors towards isolation rooms at smaller angles (less than 30°) effectively reduces droplet concentrations in personnel breathing zones, thereby mitigating the risk of droplet transmission. Faster door‐opening speeds also contribute to lower droplet concentrations in these zones. This innovative study explores the impacts of PPVS and dynamic door operation dynamics on droplet transmission during respiratory disease outbreaks, providing valuable theoretical insights and technical support for disease prevention and indoor air quality improvement.

Experimental investigation of natural gas leakage and dispersion characteristics in utility tunnels under the effects of real facility layout and forced ventilation

Natural gas leakage occurring in underground utility tunnels usually poses a significant threat to public safety. In order to prevent unexpected fires and explosions, the evolution mechanism of natural gas leakage and dispersion in utility tunnels is urgently needed. In this study, an experimental apparatus was built to facilitate the understanding of leakage and dispersion dynamics in utility tunnels. Methane with a purity of 99.9% is used as a surrogate for natural gas. A schlieren imaging system with a Z-shaped optical path was designed to visualize the high-speed gas jet. The concentration distribution, alarm time, dilution efficiency, and gas jet image were analyzed under the effect of various facility layouts, ventilation, and leakage rates. The results show that the gas leakage and dispersion process can be divided into three zones: upwind zone, leak zone, and downwind zone, characterized by complicated airflow collision, high-speed get jets, and stable dilution dispersion respectively. Scenario analysis highlights the significance of key facilities, such as cable brackets, in experimental and numerical modeling due to their impact on dispersion trajectories. Higher ventilation rates prove beneficial in reducing peak concentration, hazardous areas, and enhancing purge efficiency. Conversely, higher leakage rates exacerbate the likelihood and severity of gas explosions. Alarm time exhibits a V-shaped distribution relative to the leak point, while purge time correlates positively with sensor positions. These findings are of practical importance in enhancing quantitative risk assessment and designing mitigation strategies for gas leakage accidents, which helps to improve the safety-risk-control capabilities of utility tunnels.

Computational Fluid Dynamics Analysis and Optimization of a Doublesuction Turbine Agitator

Background: As one of the essential pieces of chemical equipment, a reactor provides the necessary reaction space and conditions for the materials involved in the reaction during the stirring process. However, under typical operating conditions, issues such as uneven gas distribution, suboptimal gas-liquid mixing, and low product yield often arise in gas-liquid phase reactors. Purpose: To address the issues prevalent in current stirred reactors, a new design for a stirred reactor equipped with a double-suction turbine agitator was developed. Method: In this paper, a stirred reactor equipped with a double-suction turbine agitator was designed, and its three-dimensional modeling was conducted using SolidWorks. Computational Fluid Dynamics (CFD) simulations, based on the Euler-Euler two-phase approach with the RNG k −ε turbulence model, were performed to assess variables such as stirring speed, installation height, blade diameter and agitator inner diameter. The dispersion characteristics and flow field behaviors of the gas-liquid two-phase under varying conditions were comparatively analyzed. Optimizations were conducted across various parameters to enhance the gas mixing efficiency in the liquid phase. Result: The results show that a diameter of 370mm for the double-suction turbine agitator, an installation height of 640mm, a blade diameter of 500mm, and an inner hole diameter of 200mm yield optimal gas-liquid two-phase mixing performance. This configuration results in a broad and uniform gas distribution within the reactor, maintaining a desired high level of gas holdup at specific positions. Conclusion: The double suction turbine agitator is a type of radial agitator. During operation, it induces significant centrifugal forces in the liquid, exerts a robust shear effect, and enhances the mixing of the gas-liquid phases, thereby increasing the production efficiency of the product.

Radiomics Features from Positron Emission Tomography with [18F] Fluorodeoxyglucose Can Help Predict Cervical Nodal Status in Patients with Head and Neck Cancer.

Background: Detecting pathological lymph nodes (LNs) is crucial for establishing the proper clinical approach in patients with head and neck cancer (HNC). Positron emission tomography with [18F] fluorodeoxyglucose (FDG PET) has high diagnostic value, although it can yield false positives since FDG-avid LNs can also occur from non-cancerous diseases. Objectives: To explore if radiomics features from FDG PET can enhance the identification of pathological lymph nodes in head and neck cancer. Materials and methods: This study was carried out on n=51 cervical lymph nodes (26 negative, 25 positive) from a cohort of n=27 subjects, and the standard of reference was fine needle aspiration cytology or excisional biopsy. An initial set of 54 IBSI-compliant radiomics features, which was subsequently reduced to 31 after redundancy elimination, was considered for the analysis. Mann-Whitney U tests were performed to compare each feature between positive and negative LNs. Classification models based on two sets of features, PETBase (SUVmax, MTV and TLG) and PETRad (radiomics features), respectively, were trained using logistic regression, support vector machines and Gaussian naïve Bayes, and their performance was compared. Accuracy was estimated via leave-one-out cross-validation. Results: We identified via univariate analysis 21 features that were statistically different between positive and negative LNs. In particular, dispersion features indicated that positive LNs had higher uptake non-uniformity than the negative ones. AUC, sensitivity, specificity and accuracy obtained with logistic regression were, respectively, 0.840, 68.0%, 89.5% and 80.4% for PETBase and 0.880, 72.0%, 90.0% and 82.4% for PETRad. The other classification models showed the same trend. Conclusions: Radiomics features from FDG PET can improve the diagnostic accuracy of LN status in HNC.