Dispersal Mechanisms Research Articles

Spatial distributions of Tribrachidium, Rugoconites, and Obamus from the Ediacara Member (Rawnsley Quartzite), South Australia

AbstractThe spatial distribution of in situ sessile organisms, including those from the fossil record, provides information about life histories, such as possible dispersal and/or settlement mechanisms, and how taxa interact with one another and their local environments. At Nilpena Ediacara National Park (NENP), South Australia, the exquisite preservation and excavation of 33 fossiliferous bedding planes from the Ediacara Member of the Rawnsley Quartzite reveals in situ communities of the Ediacara Biota. Here, the spatial distributions of three relatively common taxa, Tribrachidium, Rugoconites, and Obamus, occurring on excavated surfaces were analyzed using spatial point pattern analysis. Tribrachidium have a variable spatial distribution, implying that settlement or post-settlement conditions/preferences had an effect on populations. Rugoconites display aggregation, possibly related to their reproductive methods in combination with settlement location availability at the time of dispersal and/or settlement. Additionally, post-settlement environmental controls could have affected Rugoconites on other surfaces, resulting in lower populations and densities. Both Tribrachidium and Rugoconites also commonly occur as individuals or in low numbers on a number of beds, thus constraining possible reproductive strategies and environmental/substrate preferences. The distribution of Obamus is consistent with selective settlement, aggregating near conspecifics and on substrates of mature microbial mat. This dispersal process is the first example of substrate-selective dispersal among the Ediacara Biota, thus making Obamus similar to numerous modern sessile invertebrates with similar dispersal and settlement strategies.

Scaling up the fabrication of wafer-scale Ni-MoS2/WS2 nanocomposite moulds using novel intermittent ultrasonic-assisted dual-bath micro-electroforming

In the scale-up fabrication process for electroformed Ni-MoS2/WS2 composite moulds, the formulation of nanosheets is critical, since the size, charge, and their distribution can largely affect the hardness, surface morphology and tribological properties of the moulds. Additionally, the long-term dispersion of hydrophobic MoS2/WS2 nanosheets in a nickel sulphamate solution is problematic. In this work, we studied the effect of ultrasonic power, processing time, surfactant types and concentrations on the properties of nanosheets to elaborate their dispersion mechanism and control their size and surface charge in divalent nickel electrolyte. The formulation of MoS2/WS2 nanosheets was optimized for effective electrodeposition along with nickel ions. A novel strategy of intermittent ultrasonication in the dual bath was proposed to resolve the problem of long-term dispersion, overheating, and deterioration of 2D material deposition under direct ultrasonication. Such strategy was then validated by electroforming 4-inch wafer-scale Ni-MoS2/WS2 nanocomposite moulds. The results indicated that the 2D materials were successfully co-deposited into composite moulds without any defects, along with the mould microhardness increasing by ∼2.8 times, the coefficient of friction reducing by two times against polymer materials, and the tool life increasing up to 8 times. This novel strategy will contribute to the industrial manufacturing of 2D material nanocomposites under ultrasonication process.

Passive transport of a zebra mussel attached to a freshwater fish: A novel Dreissena dispersal mechanism?

Passive transport of a zebra mussel attached to a freshwater fish: A novel Dreissena dispersal mechanism?

Non‐reproductive dispersal: an important driver of migratory range dynamics and connectivity

Dispersal is the primary ecological process underpinning spatial dynamics in motile species by generating flux in reproductive locations over time. In migratory species, dispersal can also occur around non‐breeding ranges, but this form currently lacks a unifying theoretical framework. We present a novel conceptual model for dispersal in migrants that builds upon existing literature, differentiating ‘reproductive' dispersal (i.e. changes in breeding locations) from ‘non‐reproductive' dispersal, which we define as movements resulting in inter‐annual or inter‐generational changes in non‐breeding locations. Crucially, unlike reproductive dispersal where movement outcomes are naturally propagated between generations, the outcomes of non‐reproductive dispersal can be non‐heritable. We use simulations of a solo‐migrant population with a genetically encoded migratory programme to illustrate how variation in this heritability exerts a strong influence on both migratory connectivity and range shift propensity. When exposed to spatially uncoupled shifts in habitable ranges (i.e. seasonal climate niches shifting at different rates), long‐term persistence of simulated populations required changes in migratory programmes to arise through heritable forms of non‐reproductive dispersal (e.g. mutations in migratory gene complexes). By contrast, non‐heritable dispersal mechanisms (e.g. navigation errors) cannot drive long‐term shifts in non‐breeding ranges, despite being a major component of realised dispersal and migratory connectivity patterns. Migratory connectivity metrics conflate these heritable and non‐heritable drivers of non‐reproductive dispersal, and therefore have limited power in predicting population responses to environmental change. Our models provide a framework for improving our understanding of spatial dynamics in migratory populations, and highlight the importance of teasing apart the mechanisms that drive migratory variability in order to evaluate and predict range plasticity in migrants.

Dispersal Mechanisms of Trace Metal Elements in the Environment: The Case of Mineral Wastes Stored in Tshamilemba District of the City of Lubumbashi, DR Congo

Since 2001, the Tshamilemba quarter, located in the City of Lubumbashi (DRC), has been home to copper- and cobalt-producing plants, which generate great amounts of mineral waste, the storage of which has resulted in environmental pollution. Previous studies conducted in the Tshamilemba district have identified the weathering process of stored mineral wastes as the main source of trace metal elements (TMEs) involved in the contamination of soil and well water, and have highlighted the population exposure to cobalt. This study strives to identify or establish the dispersal mechanisms of pollutants in the environment that contaminate soil, surface water and edible plants. This study measured major physicochemical parameters, determined TME concentrations in samples (soil, water and edible plants) and established, based on data from soil sample analysis mathematically processed using Matlab 7.1 software, the spatial distributions of TMEs, in both the upper and deep soil (20 cm). The soil sample analysis revealed an average pH of 7.69 and a value of 9.1 for the near-white crusts collected at some spots. In the soil, TMEs were present in upper layers (Co, Cu, Zn and Fe) and the deep layers (Co, Cu, Pb, Zn and Fe) at phytotoxic concentrations. TMEs were observed in water samples at concentrations (Cu, Co, Mn, Zn and Pb) surpassing the quality standards for drinking water. This also applies to edible plant samples of Saccharum officinarum (Co, Cd, Ni, Mg and Pb) and Musa acuminate (Cd, Co, Pb, Zn, Mn and Ni). TMEs disperse in the environment as airborne particles from aerial erosion and as dissolved species in run-off water, mixed with acidic, metal-rich waters spreading from the weathering of stored mineral waste. TMEs contaminate the surrounding soil near to the surface water and build up in edible plants. Therefore, fear among the population about the environment pollution in Tshamilemba is well justified. Understanding the dispersal mechanisms of TMEs is of paramount importance to better control and to contain mineral pollution and design strategies for minimizing the effects on human health.

A Comprehensive Analysis of Fatigue and Healing Capacity of Sasobit Polymer-Modified Asphalt from Two Perspectives: Binder and FAM

Wax-based Sasobit synthetic hard wax can be designed for producing asphalt with less energy consumption and lower carbon emissions in the pavement industry. This study investigated the effectiveness of Sasobit synthetic hard wax on microscopic properties, fatigue-fracture behavior, and healing potential of polymer-modified asphalt (PMA) from two perspectives: asphalt binder and fine aggregate matrix (FAM). First, microscopic morphology, dispersion mechanism, and thermal stability of styrene-butadiene-styrene (SBS)– and crumb rubber (CR)–modified asphalt binders under the influence of Sasobit synthetic hard wax were characterized. Second, linear viscoelastic properties and evolution law of fatigue life of Sasobit synthetic hard wax/polymer-modified asphalt binders and FAM with and without healing interval were assessed under the framework of the simplified viscoelastic continuum damage (S-VECD) model. Third, the correlation between properties of the modified asphalt binder and FAM was statistically analyzed by radar chart. Thermodynamic analysis indicated that Sasobit synthetic hard wax enhanced the thermal stability of PMA but slightly reduced the low-temperature performance. Morphological observations showed that Sasobit synthetic hard wax had limited effectiveness on the dispersion of the polymer particles in PMA. Dynamic modulus master curves and fatigue and healing tests demonstrated that Sasobit synthetic hard wax contributes to the stiffness, fatigue resistance, and self-healing capability of the asphalt binder and mixture. Finally, statistical analysis revealed that the asphalt binder performance lacked a close correlation with the FAM owing to the complex composition system.

Bearing capacity of concentric anchorage zones in post-tensioned members: A stress field solution

The post-tensioned anchorage zones are generally subdivided into local and general zones, which are treated with semi-empirical approaches and strut-and-tie models separately in many design codes. Even with their functions that look different, the two adjacent zones are intrinsically related in terms of the compression dispersion mechanism. Holding this view, this paper intends to present a mechanical model to integrate their combined actions. Firstly, two confinement effects in anchorage zones are studied: the local confinement under the bearing plate and the passive confinement by bursting reinforcement. Then, a discontinuous stress field model for concentric anchorage zones is proposed, which allows for a triaxial state of compression stresses in the local zone and the contribution of bursting reinforcement in the general zone simultaneously. After that, an explicit bearing capacity formula for anchorage zones is derived, in which the ultimate failure can be attributed to either the yielding of the distributed tension subfield or the crushing of fan subfields. The prediction of bearing capacity is in fairly good agreement with the collected test results.

Invasion history of Gyraulus chinensis (Gastropoda: Planorbidae) in Europe: a molecular and literature-based approach

AbstractInvasion of alien species is one of the major environmental problems in the globalised world. Therefore, identifying pathways for the introduction and spread of alien species can help to mitigate their impact on invaded ecosystems. This study focused on the freshwater snail Gyraulus chinensis, which invades Europe from eastern Eurasia, where it is native. It was first recorded in Europe about 50 years ago and has since expanded its distribution. However, its origin and the mechanisms of its spread have not yet been studied. Therefore, we performed molecular identification and estimated its origin and dispersal mechanisms based on a literature review, molecular phylogenetics, and population genetics. We found that the haplotypes of G. chinensis in Europe are closely related to southern East Asia, namely Hong Kong, Taiwan, and the Ryukyu Islands. The results also suggest multiple introductions, mainly due to the diversity of haplotypes detected in European G. chinensis populations. Currently, the distribution and invasion of the species in the outdoor environments are concentrated in southern Europe, probably due to thermal constraints. However, the species has been recorded in many indoor habitats in the northern part of Europe, indicating a high potential for its spread in the warmer world.

Nonlinear optical limiting effect of porous graphene dispersions at 1064 nm.

This work presents a new, to the best of our knowledge, porous graphene dispersion in ethanol that can achieve a good nonlinear optical limiting (NOL) effect at the wavelength of 1064nm. Using the Z-scan system, the nonlinear absorption coefficient of the porous graphene dispersion with a concentration of 0.01mg/mL was measured as 9.69×10-9 c m/W. The NOL of the porous graphene dispersions in ethanol under three different concentrations (0.01, 0.02, and 0.03mg/mL) were measured. Among them, the 1-cm-thick porous graphene dispersion with a concentration of 0.01mg/mL has the best optical limiting effect, in which the linear transmittance is 76.7%, and the lowest transmittance is 24.9%. By using the pump-probe technique, we detected the formation and annihilation times of the scatter when the suspension interacts with the pump light. The analysis shows that the NOL mechanisms of the novel porous graphene dispersion are mainly nonlinear scattering and nonlinear absorption.

Isotope geochemistry as a natural tag of fish in Patagonian freshwater environments: The invasive Chinook salmon case

Patagonian aquatic environments have been invaded since the end of the last century by different species of salmonids. Knowing the natal origin and homing/straying rate of the salmonids in colonised environments is essential to understanding the dispersal mechanisms and developing management plans. In the last two decades, Chinook salmon Oncorhynchus tshawytscha showed the greatest natural dispersal capacity in Patagonia. The main goal of this study was to evaluate the environmental strontium isotope ratio (87Sr/86Sr) as a potential natural tag to infer the natal origin and ontogenetic habitat use of salmonids in Patagonia, specifically Chinook salmon. 87Sr/86Sr ratio was determined in water samples from 26 sites distributed in 14 Atlantic and Pacific basins in low and high water seasons. Environmental 87Sr/86Sr showed greater spatial than temporal variation, revealing great potential as a tool to infer the natal origin and life history of several migratory fish species in Patagonia. Otolith core-to-edge 87Sr/86Sr profiles were also analysed in 108 Chinook salmon from six basins. A cluster analysis based on the Unweighted Pair Group method (UPGMA) and Euclidean distances without prior classification grouped the sampled rivers into five main groups with significantly different (p < 0.05) isotopic ratios, sometimes integrated basins with different slopes (Atlantic or Pacific). The cluster analysis based on the natal 87Sr/86Sr period in otolith (∼natal origin) showed clear segregation between the Atlantic and Pacific samples. A mismatch between water and otolith natal 87Sr/86Sr ratio was detected in some Atlantic basins (e.g. De las Vueltas River in Santa Cruz Basin) and Pacific (e.g. Liquiñe Basin) and, which could be explained either by straying behaviours or by large geochemical variability between tributaries, within river systems. Our results showed that 87Sr/86Sr is a useful natural tag to trace the life history of migratory fishes in Patagonia, especially for invasive species such as Chinook salmon.

Study on two-phase cloud dispersion from liquefied CO2 release

The knowledge of two-phase cloud dispersion mechanism from HLG (hazardous liquefied gas) release is the prerequisite for accurate assessment and precise rescue of such accidents. In this paper, an experiment of two-phase cloud dispersion from liquefied CO2 hole release is performed. The source terms, such as vapour mass fraction, release velocity and mean droplet diameter, are calculated based on thermodynamic theory. Taking phase transition of CO2 droplets to gas into account, CFD (computational fluid dynamics) model for two-phase cloud dispersion is established. The predicted cloud temperatures at the downstream agree well with the experimental data, with the maximum relative error of 5.8% and average relative error of 2.3%. The consequence distances in the downstream direction and in the crosswise direction calculated through two-phase model are larger than those through single-phase model, with the relative differences of 57.8% and 53.6% respectively. CO2 concentration calculated by two-phase model is smaller in the vicinity of release hole, and larger beyond 0.135 m downstream. A smaller leakage rate results in a lower CO2 concentration and a higher cloud temperature.

Experimental transport of Trichomanes speciosum spores on Azorean woodpigeon feathers as a possible explanation for interisland dispersal

AbstractTrichomanes speciosum is a protected fern whose sporophyte generation is abundant on the island of Terceira (Azores archipelago, Portugal) but whose dispersal mechanism has never been directly documented. Based on its distribution, bird‐mediated epizoochory is a likely mechanism for spore dispersal, but there is no evidence to support this hypothesis. Laboratory experiments were performed to test the transportability of T. speciosum spores by the woodpigeon (Columba palumbus azorica), by observing the persistence of artificially added spores to feather samples that had been exposed to treatments of different wind speeds (2, 4, 6, and 8.25 m s−1) to simulate flight. The spores attached readily to the woodpigeon feathers, and 47% of the spores, on average, were lost after applying the maximum wind speed of the experiment. Spore loss was significantly related to wind speed but not to time of exposure. These findings suggest that if a fern spore adheres to the feathers of a woodpigeon, it has a probability of around 53% to remain there during flight and to eventually be dropped away from its origin. This study not only sheds new light on the possibility of T. speciosum spores being dispersed by woodpigeons, but also provides mechanistic evidence for spore retention on bird surfaces more generally.

Role of carboxymethyl cellulose binder and its effect on the preparation process of anode slurries for Li-ion batteries

We systematically investigate the role of carboxymethyl cellulose (CMC) and show how it affects the slurry dispersion according to the slurry preparation process. We find that CMC plays various roles as a dispersant, thickener, and gelling agent in the anode slurry depending on its content. CMC acts as a dispersant at lower content than the optimum graft density at which the two particles (carbon black, graphite) are adsorbed and saturated. When the CMC content increases above the optimum graft density, the adsorbed CMC still acts as a dispersant, but the extra free CMC acts as a thickener or a gelling agent depending on the content. In the meanwhile, CMC shows similar adsorption and dispersion mechanism for the two particles. Therefore, at a CMC content lower than the optimum graft density, the adsorption selectivity of CMC for both particles is significantly affected by the mixing sequence of CMC and two particles, resulting in a significant difference in slurry dispersion. On the other hand, at higher CMC content, the slurry dispersion is rarely affected by the CMC mixing sequence as both particles are eventually adsorbed and saturated in the final mixing stage. This study reports for the first time that the adsorption selectivity of the binder for the two particles can be controlled through the slurry preparation process, and that the slurry dispersion can be differently affected by the preparation process depending on the binder content.

Surface Effects on the Frequency Dispersion of Flexural Waves in Timoshenko Nanobeams

The surface effects play an important role in nanobeams. Based on a recently developed theory of surface elastodynamics, a model of the flexural wave propagation in Timoshenko nanobeams is established, in which the surface effects characterized by surface energy and surface inertia are introduced. It is found that when the size of a beam is comparable with nanometers, the surface energy effect would enhance the wave speed, while the surface inertial one would reduce it. An interesting phenomenon discovered is that with an increasing wave frequency, the dominant role transits from the surface energy effect to the surface inertial effect. The two kinds of surface effects exhibit a frequency-dependent competitive mechanism. In contrast to the macroscopic beams, due to the surface effects, the frequency dispersion of flexural waves in nanobeams becomes size-dependent. Furthermore, a comparison of the Timoshenko nanobeam and the Euler one indicates that the shear deformation effect and rotary inertial one cannot be neglected for a large wave number, which would prominently decrease the wave speed. Besides, when the size of the beam is large enough, the surface effects can be neglected and the present results can degenerate to the classical Timoshenko ones. The present results should be helpful not only for deep understanding of the dispersive mechanism of flexural waves in nanobeams, but also for optimal design of nanobeam-based acoustic wave devices.

Stable dispersions of double-walled carbon nanotubes for carbon nanotube/copper co-deposition

This work explores a novel approach to disperse purified double-walled carbon nanotubes in high ionic strength aqueous media, i.e. a copper ion solution to further prepare double-walled carbon nanotubes/Cu composites by co-electrodeposition. Firstly, the metal catalyst impurities in the tube samples are selectively removed by a one-pot gas-phase purification treatment. Two non-ionic (Triton X-100 and Pluronic-P123) and one anionic (sodium dodecyl sulfate) surfactant were used to disperse the purified samples by varying the carbon nanotubes/surfactant ratio and the surfactant content. Triton X-100 is a poly(ethylene glycol) in which one of the terminal hydroxy groups has been converted into the corresponding p-(2,4,4-trimethylpentan-3-yl)phenyl ether. Pluronic-P123 is a triblock copolymer comprising poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) leading to PEO-PPO-PEO. Sodium dodecyl sulfate of chemical formula C12H25OSO2ONa possesses a sulfate head and a hydrocarbon tail. The capability of each surfactant to disperse the double-walled carbon nanotubes in the copper ion solution is analyzed and later discussed based on the nature of the inter-tube forces. Among the employed surfactants, Pluronic-P123 exhibits the best dispersive level since stable and homogenous suspensions of double-walled carbon nanotubes are obtained. The dispersion mechanism proposes that the hydrophobic nature of Pluronic-P123 promotes efficient steric repulsions allowing the stable dispersion in the copper electrolyte. The samples dispersed by this way are successfully co-deposited and they form well-distributed double-walled carbon nanotubes within the copper matrix. The obtained results are an important step on the way to achieving an efficient double-walled carbon nanotubes/Cu composite synthesized by electrodeposition means.

Trace metal element pollution in media from the abandoned Pb and Zn mine of Lakhouat, Northern Tunisia

This study aimed to determine the contamination status, dispersion mechanisms, and ecological and health risks associated with trace elements in environmental media collected from the abandoned lead and zinc mine of Lakhouat, Northern Tunisia. A total of 41 samples, including 3 mine tailings, 21 stream sediments and 17 soils were collected and analysed for some potentially toxic elements (As, Pb, Hg, Cd, Cr, Co, Ni, Cu, Zn and Zr). Among 10 potentially toxic elements that were analysed, As, Cd, Hg, Pb and Zn exhibited considerably high concentrations in mine tailings and stream sediments. The Spearman rho correlation coefficient and principal component analysis showed that mining activities mainly controlled As, Cd, Hg, Pb and Zn. At the same time, natural sources strongly governed Co, Cr, Cu, Ni and Zr. Pollution indices revealed a very contaminated area with an essential risk to ecosystems and human health. Ecological risk assessment suggested that the potentially toxic elements in mine tailings and stream sediments induced significant ecological risks, mainly mediated by Cd. The health risk assessment revealed that oral ingestion was the primary exposure pathway to potentially toxic elements in the stream sediments and mine tailings, and children were more susceptible to adverse health effects. Pb and As had high non-carcinogenic risks for an individual potentially toxic element, and Cd and As presented intolerable carcinogenic risks. Overall, the results indicated the need for epidemiological studies to outline the extent of the occurrence of diseases related to mining activities in the region.

The effects of meteorological conditions on allergenic airborne pollen in arid Northwest China

Understanding the variations in temporal allergenic airborne pollen (AAP) distribution and the mechanisms of pollen release and dispersal during pollen season is fundamental for predicting respiratory allergies, as well as assessing the effects of meteorological conditions on vegetation. In this paper, we described the seasonal variations of in situ AAP for dominant taxa in samples obtained from 11 May 2019 to 31 March 2022, with uninterrupted quasi-monthly sampling time intervals (22–48 days). We also discussed how meteorological factors drive pollen variations in an arid region of Northwest China through correlation analysis and the HYSPLIT model. Results showed: (1) The three most prevalent AAP taxa were Artemisia (65.1% by average), Amaranthaceae (13.5% by average), and Poaceae (6.5% by average), with a high cumulative pollen concentration (CPC) value during July–September period. (2) The duration and total CPC in pollen season were shorter and lower in 2020 than that in 2019 and 2021, which were attributed to the lower precipitation and higher temperature from July to September 2020. In contrast, the wind was the dominant factor influencing each sample's CPC in the non-pollen season. (3) Both the predominant potential source area (PSA) and short transport pathways suggested AAP mainly comes from the local and regional areas. (4) There would be a serious risk of allergy to the three AAP types, especially Artemisia. Our results reveal that precipitation and temperature during July–September have an immediate effect on the characteristics of the AAP pollen season in arid regions.

A thick reaction zone model for premixed flames in two-dimensional channels

Direct interactions between the flow field and the chemical reaction in premixed flames occur when the reaction zone thickness is comparable to, or greater than flow length scales. To study such interactions, a laminar model is considered that has direct bearings to steadily propagating deflagrations in a Hele-Shaw channel with a background plane Poiseuille flow. The study employs asymptotic analyses, pertaining to large activation energy and lubrication theories and considers a distinguished limit where the channel width is comparable to the reaction zone thickness, with account being taken of thermal-expansion and heat-loss effects. The reaction zone structure and burning rates depend on three parameters, namely, the Peclet number, , the Lewis number, and the ratio of channel half-width to reaction zone thickness, . In particular, when the parameter is small wherein the reaction zone is thick, transport processes are found to be controlled by Taylor's dispersion mechanism and an explicit formula for the effective burning speed is obtained. The formula indicates that for , which interestingly coincides with a recent experimental prediction of the turbulent flame speed in a highly turbulent jet flame. The results suggest that the role played by differential diffusion effects is significant both in the laminar and turbulent cases. The reason for the peculiar dependence can be attributed, at least in our laminar model, to Taylor dispersion. Presumably, this dependence may be attributed to a similar but more general mechanism in the turbulent distributed reaction zone regime, rather than to diffusive-thermal curvature effects. The latter effects play however an important role in determining the effective propagation speed for thinner reaction zones, in particular, when is large in our model. It is found that the magnitude of heat losses at extinction, which directly affects the mixture flammability limits, is multiplied by a factor in comparison with those corresponding to the no-flow case in narrow channels.

Unraveling the dispersion mechanism of carbon nanotubes in aluminum powder particles during high energy ball milling by FIB-TEM study

For the development of high-performance aluminum (Al) matrix composites reinforced with carbon nanotubes (CNTs), high energy ball milling (HEBM) is the most prevalent method to disperse CNTs in Al powder. However, the dispersion mechanism of CNTs in Al powder is still unclear, mainly because it is difficult to characterize CNTs when they are buried inside Al powder particles. Herein, focused-ion-beam-assisted transmission electron microscopy observation of CNTs in Al powder via HEBM with various milling times was conducted. Results showed that with increasing HEBM time, CNTs clusters were firstly broken up to be dispersed shorter-lengthed CNTs on the surface of Al flakes with gradually reduced thickness. Afterward, cold-welding of Al flakes was the predominant phenomenon, which resulted in re-spheroidization of Al powders and homogeneously dispersed CNTs. This study may provide guidance for controlling and optimizing the HEBM process to disperse CNTs in Al matrix towards the development of high-performance CNTs/Al composites.

An insight into the temperature-dependent dielectric dispersion and conduction mechanisms in BaTiO3 modified bismuth borate glass-ceramic system

Dielectric characteristics of BaTiO3-modified bismuth borate glass-ceramics have been analyzed at temperatures ranging from 623 to 703 K and a frequency range of 1 Hz–1 MHz. Dielectric permittivity and tan δ have been found to increase with the temperature and BaTiO3 (BT) content. The sharp and intense peak in Z” signifies the presence of grain boundary contributions. R-C and R-CPE models have been employed to analyze the experimentally obtained impedance data of glass-ceramic samples. A theoretical non-exponential Kohlrausch-Williams-Watts (KWW) function has been used to fit experimental data of the imaginary part of the electric modulus. The values of activation energy obtained from impedance and electric modulus are in close agreement with each other and also increase with an increase in BaTiO3. Stretched coefficient (β) is found to be temperature and composition-dependent. The obtained values of β are less than 1, suggesting the nature of relaxation in the samples to be of purely non-Debye type.