Dispersed Distribution Research Articles

A universal and ultrafast method for fabricating a library of nanocellulose-supported metal nanoparticles

Using nanocatalysts to catalyze water electrolysis for hydrogen production is an ideal solution to address the energy crisis. The most well-adopted fabrication methods for nanocatalysts are tube furnace annealing, Hydrothermal method, etc., hardly satisfying the trade-off among coarsening, dispersity, and particle size due to mutual restrictions. Herein, a universal, ultrafast and facile cellulose nanometer whiskers-high temperature shock (CNW-HTS) method was reported for fabricating a library of ultrafine metal nanoparticles with uniform dispersion and narrow size distribution. The metal-anchor functional groups in CNW (i.e., –OH and –COOH) and the characteristics of the HTS method for ultrafast heating and powerful quenching synergistically contribute to the successful synthesis of metal nanoparticles. As an initial demonstration, the as-prepared Pt nanocatalyst (η10 ​mA ​cm−2 ​= ​51.8 ​mV) shows more excellent catalytic hydrogen evolution reaction (HER) performance than the Pt catalyst prepared in the tubular furnace (η10 ​mA ​cm−2 ​= ​169.4 ​mV). This rapid and universal CNW-HTS method can pave the way for nanomanufacturing to produce high-quality metal nanoparticles, thereby expanding applications of energy conversion and electrocatalysis.

Research on the spatial allocation of national fitness resources at the street scale—taking Fuzhou city as an example

To explore the spatial allocation of national fitness resources at different spatial scales in Fuzhou city to provide useful references for optimizing and enhancing the spatial allocation of national fitness resources and urban planning. The equity, spatial distribution characteristics, accessibility and supply-demand balance of national fitness resources in Fuzhou city are analysed in depth by using the two-step mobile search method of multiple travel modes, the Gini coefficient, and exploratory spatial data analysis methods. The results show that the overall spatial allocation of national fitness resources is in a balanced state, but there are serious inequities and spatial mismatches in each district (county); the spatial distribution of national fitness resources is characterized by centralized agglomeration and surface dispersion, being dense in the south and sparse in the north. Areas with insufficient resources per capita have an agglomeration-type scattering distribution; areas with sufficient resources per capita have a dispersed patch distribution. Access to national fitness resources and the relationship between their supply and demand are characterized by positive spatial concentration; however, the layout of the national fitness resources planned for the old urban areas urgently needs to be optimized, with the Chating and Antai streets serving as centres, to increase the effective supply. Finally,we suggestions that Top-level design should be strengthened, the communalization of sports public services should be promoted, the service capacity and utilization efficiency of national fitness resources should be enhanced, and the construction of national fitness resources in new urban areas and new industrial agglomerations should be accelerated.

A Lignin Silver Nanoparticles/Polyvinyl Alcohol/Sodium Alginate Hybrid Hydrogel with Potent Mechanical Properties and Antibacterial Activity.

Antibacterial hydrogels have attracted significant attention due to their diverse applications, efficient antimicrobial properties, and adaptability to various environments and requirements. However, their relatively fragile structure, coupled with the potential for environmental toxicity when exposed to their surroundings for extended periods, may significantly limit their practical application potential. In this work, a composite hydrogel was synthesized with outstanding mechanical features and antibacterial capability. The hydrogel was developed through the combination of the eco-friendly and enduring antibacterial agent, lignin silver nanoparticles (Lig-Ag NPs), with polyvinyl alcohol (PVA) and sodium alginate (SA), in varying proportions. The successful synthesis of the hydrogel and the dispersed distribution of Lig-Ag NPs within the hydrogel were confirmed by various analytical techniques, including field emission scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), mercury intrusion porosimetry (MIP), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The formation of multiple hydrogen bonds between Lig-Ag NPs and the composites contributed to a more stable and dense network structure of the hydrogel, consequently enhancing its mechanical properties. Rheological tests revealed that the hydrogel exhibited an elastic response and demonstrated outstanding self-recovery properties. Significantly, the antibacterial hydrogel demonstrated effectiveness against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), achieving a <5% survival of bacteria within 12 h. This study presented a green and straightforward synthetic strategy for the application of antibacterial composite hydrogels in various fields.

Spatial Pattern and Driving Mechanism of Urban Taxi Fares in China

Taxi fare is related to the daily life of residents. Reasonable taxi fare not only meets the travel demand of residents but also improves the income of drivers and promotes employment. The spatial variation of taxi fares exists between different regions and cities. Previous studies on taxi fares have been conducted mostly in individual cities, and there has been no study on the spatial differentiation pattern of taxi fares on a national scale. Taking 336 cities across China as the research object, a multiple linear regression model of taxi fares was established by demonstrating the spatial variation pattern of taxi fares, the global differentiation index, spatial autocorrelation analysis, and kernel density analysis, etc. The significance of the study is to explore the law of spatial differentiation of taxi fares in China and to provide a stenographic record of taxi fare adjustment. The results show that: (1) the spatial variation of taxi fares across the country is significant, with the starting taxi fare range being between RMB 4 and RMB 14. (2) The global differentiation index of taxi fares is large, with two low-low clusters and three high-high clusters appearing spatially, and the results of the kernel density analysis surface a dispersion distribution centered on provincial capitals. (3) The divergence pattern of taxis nationwide is influenced by several factors. A multiple linear regression model is selected to establish a multiple linear regression model of urban disposable income per capita, regional GDP, urbanization rate, and urban population density, which shows that urban disposable income per capita has the greatest influence on taxi fares. The model shows that urban disposable income per capita has the greatest influence on taxi fares, and the fare of a 5 km taxi ride is 6.07. Taxi fares have a clear pattern of spatial differentiation in China and are most affected by urban disposable income per capita. Through this study, we can gain a deeper understanding of the variation in taxi fares across the country and provide data and theoretical support for the rationality of taxi fare adjustments.

Compact homogeneous Si/SiC/C in-situ nanocomposite microspheres as anode materials for lithium-ion batteries

Compact homogeneous Si/SiC/C in-situ nanocomposite microspheres are synthesized by a procedure consisted of sol-gel, air calcination and magnesiothermic reduction processes. The components of Si, C, and SiC are all generated in situ and have the advantages of high dispersion and uniform distribution at the nanoscale level, which can maximize the conductivity and structural stability of nanocomposite microspheres when used as the anode materials for lithium-ion batteries. A series of samples with different compositions and morphologies are obtained by controlling the temperature in the air calcination step. Electrochemical tests reveal that the sample with the best comprehensive performance delivers an initial coulombic efficiency of 79.1 %, a reversible specific capacity of 1513 mAh g−1, and a capacity retention of 87.8 % after 200 cycles. The significantly enhanced electrochemical performance relative to the pure Si sample composed of irregular nanoparticles confirms that the method of synthesizing compact homogeneous materials through in-situ means is highly effective and promising for the fabrication of high-performance electrode materials.

On the properties of free floating planets originating in circumbinary planetary systems

Abstract Free-floating planets are a new class of planets recently discovered. These planets don’t orbit within stellar systems, instead living a nomadic life within the galaxy. How such objects formed remains elusive. Numerous works have explored mechanisms to form such objects, but have not yet provided predictions on their distributions that could differentiate between formation mechanisms. In this work we form these objects within circumbinary systems, where these planets are readily formed and ejected through interactions with the central binary stars. We find significant differences between planets ejected through planet-planet interactions and those by the binary stars. The main differences that arise are in the distributions of excess velocity, where binary stars eject planets with faster velocities. These differences should be observable amongst known free-floating planets in nearby star-forming regions. We predict that targeted observations of directly imaged free-floating planets in these regions should be able to determine their preferred formation pathway, either by planet formation in single or multiple stellar systems, or through processes akin to star formation. Additionally the mass distributions of free-floating planets can yield important insights into the underlying planet populations. We find that for planets more massive than 20 M⊕, their frequencies are similar to those planets remaining bound and orbiting near the central binaries. This similarity allows for effective and informative comparisons between mass distributions from microlensing surveys, to those of transit and radial velocities. Ultimately, by observing the velocity dispersion and mass distribution of free-floating planets, it will be possible to effectively compare with predictions from planet formation models, and to further understand the formation and evolution of these exotic worlds.

Modulating surface microenvironment based on Ag-adorned CuO flower-liked nanospheres for strengthening C-‍C coupling during CO2RR

Modulating the surface microenvironment is crucial in strengthening CC coupling, leading to increasing selectivity in the production of multi-carbon (C2+) products during CO2 electroreduction. Herein, we have concentrated on investigating how to control the effect of surface distribution of active components of a series of Ag-decorated CuO, denoted as xAg/yCuO. These catalysts with similar chemical elements and morphology are designed, but they exhibit different selectivity in the CO2 electroreduction process. As a result, the Ag particles in 3Ag/CuO aggregates, while the Ag in 2Ag/2CuO and Ag/3CuO is uniformly distributed on the flower-like CuO nanosphere. Besides, 3Ag/CuO has the highest Faraday efficiency (FE) of CO with a value of 30.9 % at 0.8 V vs. RHE, demonstrating rich-Ag catalysts are beneficial to produce CO. 2Ag/2CuO shows excellent FEC2H4 of 51.4 % at -1.2 V vs. RHE due to the highly dispersed distribution of Ag on the flower-like CuO and higher vacancy O. Ag/3CuO exhibits higher FEH2 compared to other catalysts across a wide potential range, and its minimal impedance is attributed to its exceptional performance in the hydrogen evolution reaction. The proposed reaction pathway for the most effective catalysts 2Ag/2CuO, as determined by in-situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS), involves the following steps: CO2 →*CO2−→ *COOH → *CO→ *CHO→ *OCHCHO→ *OCHCH2→ C2H4. These findings demonstrate that controlling the surface structure can influence the local environment to enhance the efficiency of CO2 electroreduction.

Cytogenomic Characterization of Transposable Elements and Satellite DNA in Passiflora L. Species.

The species Passiflora alata, P. cincinnata, and P. edulis have great economic value due to the use of their fruits for human consumption. In this study, we compared the repetitive genome fractions of these three species. The compositions of the repetitive DNA of these three species' genomes were analyzed using clustering and identification of the repetitive sequences with RepeatExplorer. It was found that repetitive DNA content represents 74.70%, 66.86%, and 62.24% of the genome of P. alata, P. edulis, and P. cincinnata, respectively. LTR Ty3/Gypsy retrotransposons represent the highest genome proportions in P. alata and P. edulis, while Ty1/Copia comprises the largest proportion of P. cincinnata genome. Chromosomal mapping by Fluorescent In Situ Hybridization (FISH) showed that LTR retrotransposons have a dispersed distribution along chromosomes. The subtelomeric region of chromosomes is where 145 bp satellite DNA is located, suggesting that these elements may play important roles in genome structure and organization in these species. In this work, we obtained the first global characterization of the composition of repetitive DNA in Passiflora, showing that an increase in genome size is related to an increase in repetitive DNA, which represents an important evolutionary route for these species.

Method for predicting the size of Ni1/3Mn1/3Co1/3(OH)2 particles precipitated in a stirred-tank semi-batch crystallizer using CFD and particle agglomeration models

NixMnyCoz(OH)2 is widely used as a precursor for the cathode active material LiNixMnyCozO2 in lithium ion batteries, and the precursor size, which determines the size of the active cathode material, affects the characteristics of lithium-ion batteries. This paper proposes a method for predicting the particle size of Ni1/3Mn1/3Co1/3(OH)2 precipitated by semi-batch reaction crystallization. The distribution of supersaturated components formed in the reactor varies with the reactor scale, feed conditions of the raw material solution, and agitation conditions. Therefore, the method presented in this paper considers the effects of these conditions on particle growth. First, to identify the turbulent dispersion and concentration distribution of the supersaturated components formed in the reaction crystallizer, a computational fluid dynamics (CFD) model was constructed consisting of the governing equations of hydrodynamics and the mass balance equations of the supersaturated components considering the production by neutralization and consumption by precipitation. Next, a model of agglomeration was constructed that focused on the balance of the binding and breaking up energies for the particle pairs. The binding energy was quantified based on the bridging between particle pairs by surface deposition. The breaking up-energy was quantified based on the hydrodynamic forces when the agglomerate passes through the impeller. These models were fitted using experimental results for the final average size of the Ni1/3Mn1/3Co1/3(OH)2 secondary aggregate, which was precipitated in a small-scale stirred-tank type semi-batch reaction crystallizer. The models predicted the experimental results of the final average size in a large-scale crystallizer, with the feeding conditions of the raw material solution and stirring conditions as experimental parameters, within ±20%. The models may be used to analyze semi-batch reaction crystallization systems of NixMnyCoz(OH)2 of any composition by adjusting the model parameters according to the procedure developed in this study.

Interpreting and modelling the daily extreme sediment events in karst mountain watersheds

Increasingly frequent extreme rainfall as a result of climate change is strongly damaging the global soil and water environment. However, few studies have focused on daily extreme sediment events (DESE) in heterogeneous karst watersheds based on long-term in-situ observations. This study quantitatively assessed the time effect of DESE on rainfall response, decoupled the impact of environmental factors on DESE by using structural equation modelling, and finally explored the modelling scheme of DESE based on the hybrid model. The results showed that DESE had the highest frequency of occurrence in May–July, with dispersed distribution in the value domain. Rainfall with a time lag of 1 day and a time accumulation of 2 or 3 days was an important contribution to DESE (P < 0.01, R = 0.47–0.68). Combined effects of environmental factors explained 53.6 %–64.1 % of the variation in DESE. Runoff and vegetation exerted the strongest direct and indirect effects on DESE, respectively (β = 0.66/−0.727). Vegetation was the dominant driver of DESE in Dabanghe and Yejihe (β = −0.725/−0.758), while the dominant driver in Tongzhihe was climate (β = 0.743). In the future, the risk of extreme sediments should be prevented and resolved through the comprehensive regulation of multiple paths, such as runoff and vegetation. Hybrid models significantly improved the modelling performance of machine learning models. Generalized additive model-Extreme gradient boost had the best performance, while Partial least squares regression-Extreme gradient boost was the most valuable when considering performance and input data cost. Two methods can be used as recommended solutions for DESE modelling. This study provides new and in-depth insights into DESE in karst watersheds and helps the region develop forward-looking soil and water management models to cope with future extreme erosion hazards.

Numerical analysis of coarse particle two-phase flow in deep-sea mining vertical pipe transport with forced vibration

Exploring the dynamics and flow characteristics of coarse particles within vertical lifting pipes is essential to ensure safe and efficient pipeline transportation. This study combines computational fluid dynamics (CFD) and the discrete element method (DEM) to investigate the behavior of coarse particle solid–liquid two-phase flow in a vertical pipe utilized for deep-sea mining under forced vibration and compares it with that in stationary pipes. This study examined the effects of pipe amplitude, vibration frequency, and initial internal flow velocity separately. The amplitude values tested were 0D (static), 1D, 2D, 3D, and 4D, where D represents pipe diameter. The vibration frequencies of 0 Hz (static), 0.25 Hz, 0.5 Hz, 1 Hz, and 2 Hz were tested, respectively. Finally, initial velocities of 1 m/s, 2 m/s, 3 m/s, and 4 m/s were tested. Compared with stationary pipes, particle-induced turbulence gradually disrupts the flow field, leading to a more dispersed particle volume distribution during pipe vibration. An increase in the amplitude and vibration frequency of the pipe results in an augmentation of the pressure drop within the pipe. By comparing the results of the vibrating pipe with those of the stationary pipe, the effect of the pipe vibration gradually weakened as the initial velocity increased.

The effects of stress ultrasonic rolling on the surface integrity and fatigue properties of TiB2/7050 Al composite

In the present work, a new surface mechanical strengthening (SMS) technique named stress ultrasonic rolling (SUR), which is ultrasonic rolling (UR) assisted with a uniaxial tensile elastic stress field, was reported and successfully conducted on 5 % wt TiB2/7050Al composite. Based on the experimental analysis and numerical simulation, the effects of SUR on surface integrity and fatigue performance of the composite were comprehensively investigated. Compared with ordinary UR, SUR further enhanced the fatigue strength at 106 cycles of the composite by 5 % and prolonged the fatigue life of the composite under the stress level of 532.8 MPa by 1.8 to 3.3 times, which are attributed to the comprehensive effect of excellent surface finish, larger and deeper compressive residual stress (RSc) layer, dispersed TiB2 particles distribution in the surface, and superficial nanocrystalline structures. Besides, the assistance of uniaxial tensile elastic stress field did not increase the amount of surface plastic deformation, which indicates the RSc generated by SUR should have similar mechanical and thermal stability to that produced by ordinary UR treatment.

Effect of Ti content on microstructure and mechanical properties of TaMoNbCrTix refractory high-entropy alloy

Refractory high entropy alloys (RHEAs) hold great promise for applications requiring high-temperature resistance. In this study, TaMoNbCrTix (x = 0, 0.25. 0.5, 0.75, 1) RHEAs were fabricated through mechanical alloying (MA) and spark plasma sintering (SPS). The effect of Ti content on the microstructure and mechanical properties of TaMoNbCrTix RHEAs was investigated. The results revealed that the alloys consisted of a body-centred cubic (BCC) matrix and Laves phase, with the addition of Ti promoting the formation of the Ti(O, N) phase. By employing severe deformation of the ball-milled powder, short sintering time, and the inhibition of precipitated phases on grain growth, the resulting RHEAs exhibited ultrafine grains measuring less than 1 μm. As the Ti content increased, the volume fraction of the Laves phase decreased, transitioning from a reticulated to a dispersed distribution. This shift had a positive influence on the ductility of the alloys. Among the studied compositions, TaMoNbCrTi0.75 displayed desirable comprehensive mechanical properties with yield strength, compressive strength, and fracture strain of 2696 MPa, 3098 MPa, and 16.8%, respectively. Notably, the ductility exhibited by TaMoNbCrTi0.75 at room temperature surpassed that of most Cr-containing RHEAs.

Effect of Yttria-Stabilized Zirconia addition along with Cu in development of titanium based metal matrix composite via FSP technique for the application in biomedical devices

ABSTRACT The present study investigated the effect of incorporating Yttria-Stabilized Zirconia (YSZ) and copper (Cu) in the development of Titanium-Based Metal Matrix Composites (TMCs) using the Friction Stir Processing (FSP) technique. The macrostructure of the TMCs, after adding 5% YSZ and 2% Cu, displayed a defect-free, crack-free, and porosity-free surface, indicating the precision of the FSP method. Microstructure analysis revealed a uniform distribution of reinforcement particles and proper dispersion of grains, key for enhancing mechanical properties. The interfacial bonding between titanium and YSZ was exceptionally strong, devoid of cracks and porosity, attributed to the copper additive’s role. The increase in the number of grains per square inch for the Ti/5% YSZ/2% Cu composite (1176.26 grains per square inch at 500×) signified finer grain structure, contributing to a remarkable 48.04% improvement in tensile strength compared to pure titanium. The uniform distribution of reinforcement and strong bonding between titanium and YSZ are the driving forces behind the 46.34% increased in hardness. Additionally, the wear resistance of the composite improved by approximately 76.66%, a vital characteristic for applications facing abrasive conditions. The corrosion testing demonstrated an 8.33% enhancement in corrosion resistance with the Ti/5% YSZ/2% Cu composite.

Corrosion characteristics of in situ hybrid (Al3Ni + Al2O3)/Al composites synthesized by the solid-state combustion

Abstract In this study, in situ hybrid (Al3Ni + Al2O3)/Al composites were prepared successfully by the solid-state combustion via Al–NiO system. The effects of Al3Ni + Al2O3 on the corrosion features of composites were analyzed using potentiodynamic polarization, electrochemical impedance spectroscopy, and immersion corrosion in 3.5 wt% NaCl solution. The results show that with the increase of NiO addition, the corrosion resistance of composites is improved, and the corrosion resistance of 15 % NiO–Al composite is almost comparable to the Al matrix. The increased quantity and dispersive distribution of Al3Ni and Al2O3 particles can effectively prevent the occurrence of corrosion and the movement of free electrons. Besides, more fine Al2O3 particles distributed in grain boundaries can increase the impedance and hinder the electrochemical corrosion preferentially starting at the boundary. Also, in the composite with high NiO addition, a better and compact interface bonding can be formed due to reduction of large size Al3Ni particles and improvement in the dispersion of particles, thereby inhibiting interface damage. This study has advanced understanding of corrosion.

Spatial and temporal assessment of snake encounters in urban Delhi, India

Delhi, the capital city of India is, highly urbanized and surrounded by remnant forest, farms, ridges, and other green areas experience regular snake encounters in and around residential, institutional, and industrial areas. A total of 41 months of sampling from January 2019 to May 2022 was conducted wherein we, studied the snake assemblage in Delhi to determine the species composition, encounter frequency, seasonal activity patterns, and probable encounter sites in an urban setup. We documented 372 individuals belonging to 15 species from seven families out of 23 species found in Delhi. Snakes were found inside forests, public parks, homes, drain networks, streets, office buildings, and even in school-college buildings. The most recorded species being Ptyas mucosa (37.37%, n = 139), Naja naja (19.62%, n = 73), and Lycodon aulicus (13.44%, n = 50). The highest numbers of incidents were reported in the month of July (22.04%, n = 82) and August (19.89%, n = 74) during the peak monsoon season, for identifying high encounter sites, we used a geostatistical modeling tool, Ordinary kriging to identify places having more snake occurrences. We further used a statistical spatial method called average nearest neighbor distance to detect the pattern distribution of snake species. Spatial interpolation done through Ordinary kriging highlighted two areas having concentrated snake encounters. The results of the average nearest neighbor distance analysis showed three species having clustered and two species having dispersed distribution. The incidence of snake encounters was found to be highly seasonal and appeared to be associated mainly with monthly rainfall, temperature, and humidity. The findings of this study on snakes’ distribution patterns provide valuable insights into the conservation of these species. Understanding their habitat preferences and spatial distribution is crucial for the implementation of effective conservation strategies.

The effects of interfacial layers on dielectric properties of an acrylic co-polymer containing polymer-grafted reduced graphene oxide

In this study, the influence of interfacial layers, in addition to other effective parameters, on the dielectric efficiency of polymer nanocomposites in the rubbery state is presented. For this purpose, reduced graphene oxide (rGO) was grafted by poly (butyl acrylate) chains (rGO-PBA) via surface-initiated atom transfer radical polymerization (SI-ATRP) and incorporated into an acrylic co-polymer matrix with the glass-transition temperature (Tg) well below room temperature. The rGO exhibited poor dispersion and uneven distribution in acrylic co-polymer, whereas polymer grafted-rGO showed excellent dispersion. The grafted chains can penetrate and form entropic interactions with the matrix chains, which results in a strong interfacial region. The immobilized interfacial layer was characterized by DSC and dielectric measurements. The dielectric measurements in different temperatures provided the means to evaluate the contribution of the interfacial layers on dielectric properties. The findings confirmed that there exists an optimum chain mobility in which the chain polarization shows a major contribution to the dielectric properties of polymer nanocomposites. Reduction of temperature to a certain degree exhibited more rise in the dielectric properties of polymer/rGO-PBA nanocomposites than pure matrix which can be correlated to the interfacial region.

Tailoring the formability and planar anisotropy of Al-Mg-Si-Cu-Zn alloys via cross hot rolling and two-stage cold rolling

Al-Mg-Si-(Cu) alloys have shown great potential in responding to the growing demand for automotive lightweight, but the limited formability and high planar anisotropy have always hindered their application. The present study designs a novel method for simultaneously improving the formability and planar anisotropy of Al-Mg-Si-Cu-Zn alloys by coupling cross hot rolling and two-stage cold rolling. The results have shown that the multi-scale distribution of secondary particles and strong Brass{011}<112> and S{123}<634> texture are induced by the designed cross hot rolling process, which weakens the recrystallization texture after solution treatment, especially Cube{001}<100> orientation. Meanwhile, the designed two-stage cold rolling process (intermediate cold rolling process with high reduction + final cold rolling process with low reduction) promotes the precipitation of unstable precipitates (Mg2Si and Q phase), and inhibits the formation of Copper{112}<111> orientation, which further weakens the recrystallization texture and results in the dispersion distribution of recrystallization texture. Accordingly, the formability and planar anisotropy of the Al-Mg-Si-Cu-Zn alloy are simultaneously improved without strength loss by coupling the designed cross hot rolling with two-stage cold rolling, and the influence mechanism of texture on r value has been analyzed by Visco-Plastic Self-Consistent (VPSC) model.

Dispersion and Spatial Distribution of Air Voids or Microspheres in Assessing Frost Resistance of Concrete

Abstract The standard spacing factor developed by Powers is typically used to evaluate the quality of the air void system in hardened concrete, but it does not always correlate with durability of the concrete. Several air void spacing equations, which are also applicable when polymeric microspheres are used in place of air entrainment, have been proposed because of the need for a more robust and comprehensive basis to evaluate the quality of the air void system. However, the spacing parameters provided by the various proposed equations, when used as sole measures in predicting the frost resistance of concrete, do not seem to do any better than the standard spacing factor. Dispersion and spatial distribution have been shown to be effective ways of describing air void or microsphere systems in hardened concrete because they have been quantified to establish criteria to assess the frost resistance of concrete. In this paper, dispersion and distribution factors are further elaborated upon to explain how they characterize zones that are protected by air voids or microspheres in the concrete. Criteria to assess the durability of concrete under rapid cycles of freezing and thawing based on the dispersion and distribution factors are linked to the exposure classes defined in the ACI 318 Code and in the recently proposed Unified Durability Guidance in ACI Committee Documents.

Non-informative Bayesian estimation in dispersion models

The estimation of parameters for a distribution function is a significant and prominent field within statistical inference. This particular problem holds great relevance in various domains, including industries, stock markets, image processing, and reliability studies. There are two recognized approaches to estimation: point estimation and interval estimation, also known as confidence intervals. In this study, our primary focus lies in the point estimation of parameters associated with an exponential dispersion distribution function. In this process, we consider one of the parameters as a random variable that requires estimation. To tackle this, we adopt a Bayesian inference approach utilizing a one-parameter dispersion distribution. We explore non-informative priors, such as uniform and Jeffrey's priors, and provide evidence of the effectiveness of our method through simulation studies.