Dispersion Effects Research Articles

Simulation-based analysis of impact of CNT dispersion on hydration of cement paste

Dispersion of carbon nanotubes (CNTs) is one of the key factors determining the mechanical properties of cement composites. This study analyzed impact of CNT dispersion on hydration of cement paste. An image analysis method based on optical microscopy images was proposed to quantitatively consider the CNT dispersion. To quantify CNT dispersion, this paper proposed PCNT, which is the percentage of a 1 μm2 space containing CNTs within entire water volume. To investigate CNT dispersion effect, the same amount of CNT was classified into six steps (S1, S5, S15, S30, S50, and S100) according to PCNT. The relationship between CNT dispersion and the hydration, porosity, and compressive strength of the cement paste was analyzed using a CEMHYD3D considered CNT effect. The optimal CNT dispersion for 0.1 wt% CNT reinforcement in a cement paste with water-to-cement ratio of 0.3 was found to be 15 % PCNT. The improvement in CNT dispersion resulted in acceleration of hydration of cement paste, improvement in compressive strength, and densified microstructure.

Estimating heterogeneous effects: Applications to labor economics

A growing number of applications involve settings where, in order to infer heterogeneous effects, a researcher compares various units. Examples of research designs include children moving between different neighborhoods, workers moving between firms, patients migrating from one city to another, and banks offering loans to different firms. We present a unified framework for these settings, based on a linear model with normal random coefficients and normal errors. Using the model, we discuss how to recover the mean and dispersion of effects, other features of their distribution, and to construct predictors of the effects. We provide moment conditions on the model’s parameters, and outline various estimation strategies. A main objective of the paper is to clarify some of the underlying assumptions by highlighting their economic content, and to discuss and inform some of the key practical choices.

Low-Power Field-Deployable Interdigital Transducer-Based Scanning Laser Doppler Vibrometer for Wall-Thinning Detection in Plates

Lamb waves have become a focal point in ultrasonic testing owing to their potential for long-range and inaccessible detection. However, accurately estimating the flaws in plates using Lamb waves remains challenging because of scattering, mode conversion, and dispersion effects. Recent advances in laser ultrasonic wave techniques have introduced innovative visualization methods that exploit the dispersion effect of Lamb waves to visualize defects via, for example, acoustic wavenumber spectroscopy. In this study, we developed an interdigital transducer (IDT)-based scanning laser Doppler vibrometer (SLDV) system without a power amplifier using a low-power IDT fabricated from lead magnesium niobate–lead zirconate titanate single crystals. To validate the proposed low-power IDT-based SLDV, four different defective plates were measured for defects. A comparison between a conventional IDT-based SLDV, a dry-coupled IDT-based SLDV, and the proposed method demonstrated that the latter is highly reliable for measuring thin plate defects.

Optimization of a Groundwater Pollution Monitoring Well Network Using a Backpropagation Neural Network-Based Model

Selecting representative groundwater monitoring wells in polluted areas is crucial to comprehensively assess groundwater pollution, thereby ensuring effective groundwater remediation. However, numerous factors can affect the effectiveness of groundwater monitoring well network optimizations. A local sensitivity analysis method was used in this study to analyze the hydrogeological parameters of a simulation groundwater solute transport model. The results showed a strong effect of longitudinal dispersion and transverse dispersion on the output results of the simulation model, and a good fit between the backpropagation neural network (BPNN)-based alternative model’s results and those obtained using the solute transport simulation model, accurately reflecting the input and output relationship of the simulation model. The optimized groundwater monitoring layout scheme consisted of four groundwater monitoring wells, namely no. 7, no. 16, no. 23, and no. 24. These wells resulted in a groundwater fluoride pollution rate of 98.44%, which was substantially higher than that obtained using the random layout scheme. In addition, statistical analysis of the fluoride groundwater pollution results obtained using the Monte Carlo random simulation highlighted continuous and high groundwater fluoride levels in the second and third pollution sources and their downstream groundwater. Therefore, more attention should be devoted to these sources to ensure the effective remediation of groundwater pollution in the study area.

Noise Study Auralization of an Open-Rotor Engine

Based on the performance and acoustic data files of reduced-size open-rotor engines in low-speed wind tunnels, the static sound pressure level was derived by converting the 1-foot lossless spectral density into sound-pressure-level data, the background noise was removed, and the results were corrected according to the environmental parameters of the low-speed wind tunnels. In accordance with the requirements of Annex 16 of the Convention on International Civil Aviation Organization and Part 36 of the Civil Aviation Regulations of China on noise measurement procedures, the takeoff trajectory was physically modeled; the static noise source was mapped onto the takeoff trajectory to simulate the propagation process of the noise during takeoff; and the 24 one-third-octave center frequencies that corresponded to the SPL data were corrected for geometrical dispersion, atmospheric absorption, and Doppler effects, so that the takeoff noise could be corrected to represent a real environment. In addition, the audible processing of noise data with a 110° source pointing angle was achieved, which can be useful for enabling practical observers to analyze the noise characteristics.

In situ/operando method for energy stability measurement of synchrotron radiation.

A novel in situ/operando method is introduced to measure the photon beam stability of synchrotron radiation based on orthogonal diffraction imaging of a Laue crystal/analyzer, which can decouple the energy/wavelength and Bragg angle of the photon beam using the dispersion effect in the diffraction process. The method was used to measure the energy jitter and drift of the photon beam on BL09B and BL16U at the Shanghai Synchrotron Radiation Facility. The experimental results show that this method can provide a fast way to measure the beam stability of different light sources including bending magnet and undulator with meV-level energy resolution and ms-level time response.

Modeling the effects of trap crop attraction strength, patch dispersion, and biological control on pest suppression

Modeling the effects of trap crop attraction strength, patch dispersion, and biological control on pest suppression

Synthetic Microwave Focusing Techniques for Medical Imaging: Fundamentals, Limitations, and Challenges.

Synthetic microwave focusing methods have been widely adopted in qualitative medical imaging to detect and localize anomalies based on their electromagnetic scattering signatures. This paper discusses the principles, challenges, and limitations of synthetic microwave-focusing techniques in medical applications. It is shown that the various focusing techniques, including time reversal, confocal imaging, and delay-and-sum, are all based on the scalar solution of the electromagnetic scattering problem, assuming the imaged object, i.e., the tissue or object, is linear, reciprocal, and time-invariant. They all aim to generate a qualitative image, revealing any strong scatterer within the imaged domain. The differences among these techniques lie only in the assumptions made to derive the solution and create an image of the relevant tissue or object. To get a fast solution using limited computational resources, those methods assume the tissue is homogeneous and non-dispersive, and thus, a simplified far-field Green's function is used. Some focusing methods compensate for dispersive effects and attenuation in lossy tissues. Other approaches replace the simplified Green's function with more representative functions. While these focusing techniques offer benefits like speed and low computational requirements, they face significant ongoing challenges in real-life applications due to their oversimplified linear solutions to the complex problem of non-linear medical microwave imaging. This paper discusses these challenges and potential solutions.

Study of Styrene Butadiene Rubber Reinforced by Polybutadiene Liquid Rubber-Modified Silica.

The dispersion of silica in rubber systems and its interaction with rubber are two key factors in the preparation of rubber composites with excellent properties. In view of this, silica modified with terminal isocyanate-based polybutadiene liquid rubber (ITPB) is used to improve the dispersion effect of silica in rubber and enhance its interaction with the rubber matrix to improve the rubber's performance. The impact of different modification conditions on the dispersion of silica and the properties of modified silica-filled rubber composites were studied by changing the amount of ITPB and the modification method of silica, including blending and chemical grafting. The experimental results show that ITPB is successfully grafted onto silica, and the use of modified silica improves the cross-linking density of rubber, promotes the rate of rubber vulcanization, and overcomes the shortcomings of the delayed vulcanization of silica itself. When the ratio of ITPB liquid rubber to silica equals 1:20, the comprehensive performance of rubber is the best, the ITPB-modified silica has a better dispersion effect in rubber, and the rolling resistance is slightly improved, with tensile strength reaching 12.6 MPa. The material demonstrates excellent overall performance and holds promise for applications in the rail, automotive, and electrical fields.

Effects of chromatic dispersion on single-photon temporal wave functions in quantum communications

In this study, we investigate the effects of chromatic dispersion on single-photon temporal wave functions (TWFs) in the context of quantum communications. Departing from classical beam analysis, we focus on the temporal shape of single photons, specifically exploring generalized Gaussian modes. From this foundation, we introduce chirped and unchirped Gaussian TWFs, demonstrating the impact of the chirp parameter in mitigating chromatic dispersion effects. Furthermore, we extend our investigation to time-bin qubits, a topic of ongoing research relevance. By exploring the interplay of dispersion effects on qubit interference patterns, we contribute essential insights to quantum information processing. This comprehensive analysis considers various parameters, introducing a level of complexity not previously explored in the context of dispersion management. We demonstrate the relationships between different quantities and their impact on the spreading of TWFs. Our results not only deepen the theoretical understanding of single-photon TWFs but also offer practical guidelines for system designers to optimize symbol rates in quantum communications.

Assessment of compatibility of dextran/PEMA blends by thermal, topologic and viscoelastic analysis

In this study, the compatibility of polymer blends of dextran (DEX) and poly(ethylene-alt-maleic anhydride) (PEMA) was evaluated with their enhanced thermal and dynamic mechanical properties as well as structural and topological properties. Blends were prepared in various ratios via solution casting method. The effects of composition and dispersion on interactions, thermal, viscoelastic and topological properties of the blends were investigated using thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), atomic force microscopy (AFM) and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy and X-ray diffraction (XRD) analysis. TGA results indicated that blends exhibited higher thermal stability than the individual polymers, with residue percentages increasing from 13.57 % and 11.43 % for DEX and PEMA, respectively, to 27.42 %–16.86 % for the blends at 605 °C. DMA results showed that all blends remained intact at higher temperatures compared to the polymers, with higher Tg values due to the H-bonding interactions confirmed by ATR-FTIR. AFM phase imaging enabled the visualization of miscibility distinctions, revealing that the 30/70 DEX/PEMA blend had a uniform phase distribution and minimal phase shifts, suggesting improved miscibility. In contrast, other blends exhibited more heterogeneous miscibility. These findings highlight that DEX/PEMA blends, with their enhanced thermal and dynamic mechanical properties, have significant potential for various applications.

Evaluation of a novel non-ionic graft starch-based antiscalant in reduction of CaSO4 scaling by static and reverse osmosis test

A novel nonionic starch-based antiscalant (St-g-GMA) was designed and obtained by graft copolymerization of starch and glycidyl methacrylate (GMA). St-g-GMA not only achieved an obvious reduction of CaSO4 scaling in static test, but also effectively mitigated the flux decrease in dynamic reverse osmosis (RO) system. This improvement is ascribed to the grafted poly(GMA) chains on St-g-GMA. A suitable grafting ratio of this starch-based antiscalant achieve a high performance cost in control of CaSO4 scaling. Combination of the apparent antiscaling performance, observation under scanning electron microscopy, energy dispersive x-ray spectroscopy unit, x-ray diffraction pattern, conductivity measurement, and dispersion experiment, the scale-inhibition mechanism of St-g-GMA was investigated and mainly attributed to chelation, dispersion and lattice distortion effects. The oxygen-containing groups on poly(GMA) chains such as epoxy groups can chelate with Ca2+, causing the induction time of crystallization prolonged; St-g-GMA with the distinct branched chain configuration can well disperse the formed microcrystal of CaSO4. Moreover, molecular dynamics simulations confirmed that the grafted poly(GMA) chains well bind to the crystal surfaces and the oxygen-containing groups could even enter the crystal lattice to inhibit the crystal growth and change the morphologies. St-g-GMA still mitigated the flux decrease notably in treatment of a synthetic seawater during a 24-h RO measurement. This study provided an efficient, environmentally-friendly and low-cost antiscalant with high application potentials.

A machine learning model for predicting the mechanical strength of cement-based materials filled with waste rubber modified by PVA

As demand for sustainable building materials rises, the use of waste rubber in civil engineering is gaining attention. This study proposes a method to modify waste rubber using polyvinyl alcohol (PVA) to enhance its material properties and expand its applications. A dataset was created focusing on the mechanical strength of cementitious materials incorporating PVA-modified waste rubber, and multiple machine learning methods were used to develop regression prediction models, particularly evaluating the support vector regression (SVR) model. Results show that the SVR model outperforms others, achieving mean squared errors of 1.21 and 0.33, and mean absolute errors of 2.06 and 0.15. Analysis indicates a negative correlation between waste rubber content and the water-to-cohesive ratio (w/c) with strength indexes, while a positive correlation exists between curing age and PVA. Notably, waste rubber content significantly affects strength. The mechanical strength of cementitious materials was notably enhanced by PVA-modified waste rubber, likely due to PVA's dispersion and bridging effects. This study presents a novel approach to sustainably recycle waste rubber, highlighting its potential in construction materials.

Review on road congestion pricing: a long-term land use effect perspective

Road congestion pricing (RCP) is an important way of controlling traffic congestion from the perspective of traffic demand management. This paper introduces the concept and four main types of applications of RCP, summarises the development of RCP theory, reveals the first- and second-order effects of RCP on transportation systems and land use, and analyses the long-term impact of RCP on the spatial location structure of land use. Relevant research progress considering land use effects is systematically and comprehensively reviewed from three research perspectives: demand modelling (pre-RCP), monitoring and analysis (post-RCP) and modelling methods (integration models and other models). The results showed that RCP will affect residents’ travel behaviour in the short term and will lead to changes in spatial location decisions in the long run, thus creating new travel demands and travel modes, affecting the transportation system and urban spatial patterns again. Implementing cordon charges has an agglomeration effect on the population in city centres. Cordon charges also have a significant negative impact on businesses in the toll area and a dispersive effect on jobs. Combined with appropriate strategies for shared autonomous vehicles, RCP can simultaneously improve transportation efficiency and regional accessibility.

Octave-wide broadening of ultraviolet dispersive wave driven by soliton-splitting dynamics

Coherent dispersive wave emission, as an important phenomenon of soliton dynamics, manifests itself in multiple platforms of nonlinear optics from fibre waveguides to integrated photonics. Limited by its resonance nature, efficient generation of coherent dispersive wave with ultra-broad bandwidth has, however, proved difficult to realize. Here, we unveil a new regime of soliton dynamics in which the dispersive wave emission process strongly couples with the splitting dynamics of the driving pulse. High-order dispersion and self-steepening effects, accumulated over soliton self-compression, break the system symmetry, giving rise to high-efficiency generation of coherent dispersive wave in the ultraviolet region. Simultaneously, asymmetric soliton splitting results in the appearance of a temporally-delayed ultrashort pulse with high intensity, overlapping and copropagating with the dispersive wave pulse. Intense cross-phase modulations lead to octave-wide broadening of the dispersive wave spectrum, covering 200–400 nm wavelengths. The highly-coherent, octave-wide ultraviolet spectrum, generated from the simple capillary fibre set-up, is in great demand for time-resolved spectroscopy, ultrafast electron microscopy and frequency metrology applications, and the critical role of the secondary pulse in this process reveals some new opportunities for all-optical control of versatile soliton dynamics.

The broad-spectrum biocide triclosan trigonal crystal: Experimental and DFT-calculated structural, electronic and optical properties

Triclosan, a member of the broad-spectrum biocide class, has seen widespread usage in various household and healthcare-related products worldwide over the past 35 years. However, its extensive use has raised concerns regarding health and environmental impacts. Notably, there is a notable gap in our understanding of the solid-state properties of triclosan, encompassing both experimental aspects, such as optical absorption, and theoretical insights. Expanding upon the established trigonal crystal structure of triclosan, this study employs experimental techniques including X-ray and photoacoustic-based optical absorption, alongside density functional theory (DFT) calculations, to elucidate its structural, electronic, and optical characteristics. Employing the generalized gradient approximation (GGA) DFT exchange-correlation functional and accounting for dispersion effects, optimal lattice parameters were determined with small deviations from experimental measurements (<∼2.2%). The calculations predict that the triclosan trigonal crystal has very close direct band gaps of about 3.44 eV, almost identical to the value of 3.45 eV derived from photoacoustic optical absorption measurements. Analysis of the calculated optical absorption and complex dielectric function underscores the optical isotropy of solid state triclosan. Furthermore, effective mass computations, in conjunction with the band gap results, suggest that triclosan displays electronic characteristics akin to those of a wide direct gap semiconductor.

Innovative strategies for time-release PCE design and cement paste flowability control

Extending the retention time of cement paste flowability with the addition of admixtures containing slow-release components is standard practice for ensuring the continued building quality of cement-based materials. This study aims to control the release rate of PCE and enhance its time-varying dispersion effect in fresh cement paste by utilizing Time-dependent Release PCEs (TRPCEs) with varying side-chain structures. The structural characterization of the synthesized TRPCEs was investigated using GPC (Gel Permeation Chromatography), FTIR (Fourier Transform Infrared Spectroscopy), and 1H NMR (Proton Nuclear Magnetic Resonance) techniques. Furthermore, experiments were carried out on time-varying flowability with different dosages of TRPCEs to investigate the flowability changes under the time-varying release effect. The influence of TRPCEs on cement hydration was examined using isothermal calorimetry by measuring the early hydration heat of cement paste. The time-dependent adsorption behaviors of TRPCEs were also examined using a TOC (Total Organic Carbon) analyzer. The findings show that TRPCEs have a minor effect on the cement hydration process's rapid reaction period but little effect on its induction and acceleration periods because of variations in the initial dispersion effect. Additionally, the adsorption behaviors of TRPCEs on cement particles vary significantly due to the hydrolysis of slow-release groups. The varying adsorption and consumption of TRPCEs on cement particles and hydration products in different hydration phases are key controlling factors for the time-varying flowability changes in cement paste. Finally, this innovative approach offers a novel perspective for designing and preparing new types of PCEs with a strong capability for time-varying flowability retention.

Evolving Trainee Participation in Radiologists’ Workload: A National Medicare-Focused Analysis From 2008 to 2020

PurposeIncreasing volumes and productivity expectations, along with practice type consolidation, may be impacting trainees’ roles in the work effort of radiologists involved in education. We assessed temporal shifts in trainee participation in radiologists’ workload nationally. MethodsAll US radiologists interpreting noninvasive diagnostic imaging for Medicare fee-for-service beneficiaries were identified from annual 5% Research Identifiable Files from 2008 to 2020 (n = 35,595). Teaching radiologists were defined as those billing services using Medicare’s GC modifier, indicating trainee supervision. Billed work relative value units were used to determine the percentage of teaching radiologists’ total workload with trainee participation. Mean trainee participation in workload was calculated for teaching radiologists overall and stratified by radiologist and practice characteristics determined using National Downloadable Files. ResultsThe percentage of radiologists involved in teaching increased from 13.6% (2008) to 20.4% (2020). Among teaching radiologists, mean total workload increased 7% from 2008 to 2019 and decreased in 2020 to 2% below 2008’s level; mean teaching workload decreased 19% from 2008 to 2019 and decreased in 2020 to 31% below 2008’s level. Mean trainee participation in teaching radiologists’ total workload decreased from 35.3% (2008) to 26.3% (2019) and 24.5% (2020). Teaching radiologists showed decreased mean trainee participation when stratified by gender, experience, subspecialty, geography, practice type, and practice size. ConclusionsThe percentage of US radiologists involved in resident teaching has increased, likely reflecting academic practice expansion and academic-community practice consolidation. However, a declining percentage of teaching radiologists’ total workload involves trainees; this dispersion effect could have implications for education quality.

Deposition, microstructure and hardness of AlCoCrFeNi2.1 eutectic high entropy alloy coatings by cold spray, HVOF, and plasma spray

Eutectic high entropy alloys (EHEAs) are reported to exhibit excellent mechanical properties which are useful for coating applications. In this study, we have produced AlCoCrFeNi2.1 EHEA coatings using the cold spray, high velocity oxygen-fuel (HVOF), and plasma spray techniques and compared their bonding characteristics, microstructure and hardness. We observe body-centered cubic (bcc) to face-centered cubic (fcc) phase transformations in all the types of coatings. The high processing temperatures in HVOF and plasma sprays lead to the segregation and depletion of Al from Ni-and Al-rich bcc/B2 regions and form Al2O3. In the cold sprayed coatings, we observe that a fraction of lamellar microstructure is preserved after cold spraying. Regarding the hardness, the cold sprayed coatings exhibit hardness in the range of 440–498 HV due to high work hardening and low oxygen content below 4 at.%; the HVOF coatings show the hardness in the range of 380–556 HV due to the effects of oxide dispersion strengthening with 13–28 at.% oxygen; The plasma sprayed coatings exhibit the hardness in the range 208–258 HV and 6.1–13.4 at.% oxygen. This study demonstrates the feasibility to produce thick and dense EHEA coatings using the above spray techniques, and the cold sprayed coatings exhibit relatively high hardness and low oxygen levels.

Cellulose nanofibers-based UV resistant and hydrophobic wood coatings

Wood and wood-based products are regarded as sustainable building materials, nonetheless, they frequently need the addition of protective coatings due to their susceptibility to abiotic and biotic degrading elements. Among the coating systems, water-borne coatings are a better choice since the majority of popular wood coatings are solvent-based and release volatile organic chemicals (VOCs). In this study, cellulose nanofibers (CNFs) were isolated from eucalyptus wood pulp using a chemo-mechanical method and used as the base substrate for wood coatings. The effect of CNF dispersion with varying concentrations (0.5 and 1 wt.%) of zinc oxide (ZnO) nanoparticles on UV-resistance of Pinus radiata and Hevea brasiliensis after 500 hrs of exposure was assessed. Wood surfaces without coating exhibited severe discolouration after 500 hrs of UV exposure. Only CNF-coating results in slight protection of wood surfaces from weathering but significantly increased water wettability of the surface. The incorporation of ZnO nanoparticles significantly reduced the colour change of the wood surfaces. As the concentration of ZnO increased, the colour stability and hydrophobicity of both the wood increased.