The preferential path effect
220050193
Coupled effect of flow velocity and structural heterogeneity on transport and release of kaolinite colloids in saturated porous media
Understanding the behavior and fate of clay colloids in water saturated porous media is critical to assess its environmental impact and potential risk since clay is commonly a carrier of many contaminants. Column experiments with four packing configurations were designed to understand the coupled effects of column structural heterogeneity and the flow velocity on the transport and fate of kaolinite colloids in the saturated porous media. The results showed that the structural heterogeneity could have facilitated the transport of kaolinite colloids in saturated porous media. For the columns with strong heterogeneity, the preferential flow paths led to an early breakthrough of kaolinite. Only few kaolinite colloids were released with slow flow rate; however, the released peak concentration and release percentage of kaolinite colloids had further increased with the high flow velocity. In the layered column, there was significant kaolinite's retention at the interface where water passed from fine to coarse quartz sand. All results indicated that both flow rates and media characteristics played an important role in controlling kaolinite's fate and transport in porous media. A thorough understanding of these processes had an important significance for pollution control in subsurface natural environment where heterogeneous soil and variation in flow pattern are usually common.
Environmental Science and Pollution Research
Mengting Mao Xiaoli Zheng Chong Chen Kang Zhao Chaorui Yan Prabhakar Sharma Jianying Shang
225544341
Non Fickian Solute Transport in Rough Walled Fractures: The Effect of Contact Area
The influence of contact area, caused by normal deformation, on fluid flow and solute transport through three dimensional (3D) rock fractures is investigated. Fracture surfaces with different Hurst exponents (H) were generated numerically using the modified successive random addition (SRA) method. By applying deformations normal to the fracture surface (Du) a series of fracture models with different aperture distributions and contact area ratios (c) were simulated. The results show that the contact area between the two fracture surfaces increases and more void spaces are reduced as deformation (Du) increases. The streamlines in the rough walled fractures show that the contact areas result in preferential flow paths and fingering type transport. The non Fickian characteristics of the "early arrival" and "long tail" in all of the breakthrough curves (BTCs) for fractures with different deformation (Du) and Hurst parameters (H) were determined. The solute concentration distribution index (CDI) which quantifies the uniformity of the concentration distribution within the fracture, decreases exponential as deformation (Du) and/or contact area ratios (c) increase, indicating that increased contact area can result in a larger delay rate of mass exchange between the immobile zone around the contact areas and the main flow channel, thus, resulting in a longer time for the solute to fill the entire fracture. The BTCs were analyzed using the continuous time random walk (CTRW) inverse model. The inverse modeling results show that the dispersion exponent b decreases from 1.92 to 0.81 as c increases and H decreases, suggesting that the increase in contact area and fracture surfaces enhance the magnitude of the non Fickian transport.
Liang-tong Zhan Zuyang Ye
213653725
Effect of excavation stress condition on hydraulic fracture behaviour
Abstract The fracture behaviour of single and multi stage hydraulic fracturing (HF) under varying excavation stress conditions was studied using a flow coupled discrete element method (DEM) Conventional HF theories and analytical solutions for excavation stress redistribution are used to verify the numerical model. The numerical simulation results indicated that for the single stage HF, both the in situ stresses and injection location have major influences on the HF propagation path, caused by the redistributions of the local maximum and minimum principal stresses under excavation conditions. Fractures generally propagate perpendicular to the local minimum principal stress s min and also propagate preferentially towards the area with lower s min Hydraulic fractures propagation is dominated by tensile failure, and the generation of fracture branches is disfavored because of the high local compressive stress field induced by the HF process itself. As for multi stage HF, different excavation stress conditions may cause different fracture development performances because of alterations of the preferred fracture orientation, blunting of propagating fractures, or creating a more complex fracture geometry in the affected zone. Therefore, when using high pressure HF for preconditioning the rock mass to assist mechanical excavation in hard rock mining, performance can be enhanced by understanding the impact of stress changes and careful selection of appropriate HF methods depending on the in situ stress.
Zhenghong Chen Xibing Li Maurice B Dusseault Lei Weng
85512079
APPROXIMATION BY THE FINITE ELEMENT METHOD TO THE PREFERENTIAL CHLORIDE DIFFUSION THROUGH INTERFACIAL TRANSITION ZONE IN CONCRETE
Chloride diffusion in concrete is a main aspect of reinforced concrete durability. It de fines the time required for reinforcement corrosion in marine structures. Concrete porosity is one of the main concerns involved in the process of chloride ingress from the environment into concrete. How ever, concrete can hardly be considered homogene ous in the meso level. Natural coarse aggregates are usually less porous than the cementitious matrix, whereas interfacial zones between aggregates and the matrix are the most porous phase in concrete. This aspect is difficult to be experimentally studied, as very small samples need to be collected and ana lyzed. As an approach, the diffusion process can be simulated with the Finite Element Method (FEM) In this paper, chloride diffusion into concrete is simu lated with a 2D FEM model, distinguishing three phases with different porosities in the material. In terfacial zone is identified as preferential path for chloride ingress. The study reveals a significant in fluence of particle inclusion on the chloride diffusion into concrete, and the effect of the particle shape.
Yury Andres Villagran Zaccardi V L Taus
230568179
Path dependent rheology of carbon particle hydroxyethylcellulose fluids
Abstract Polymeric fluids with tunable viscosity find application in different sectors, ranging from enhanced oil recovery to environmental remediation. This study investigates polymeric fluids obtained with hydroxyethylcellulose (HEC) and biocarbon particles prepared at low (6500C, LM) and high (9000C, HM) temperature of pyrolization. High pyrolization temperatures increased the hydrophobicity of biocarbon particles. In the absence of HEC, HM particles partitioned preferentially in non polar solvents (e.g. toluene, rather than in water) Without particles, the shear loss (G" and storage (G' moduli of aqueous hydroxyethylcellulose solutions slowly increased over time, due to HEC hydration. The progressive increase in molecular crowding and microviscosity due to the hydration of HEC was demonstrated using steady state fluorescence spectroscopy with the molecular rotor 9 (dicyanovinyl)julolidine (DCVJ) as a probe. Particles added to HEC increased the viscoelastic moduli of HEC solutions only slightly (i.e. less than doubled them) when HEC was pre hydrated, and significantly when HEC was not pre hydrated. Specifically, addition of LM and HM particles (1 30 g/L) to non hydrated HEC (16 g/L) increased the viscoelastic moduli of HEC solutions in water from below detection to G">9 Pa and G'>6 Pa (in the whole range of biocarbon particle concentrations analyzed) Our study investigates for the first time the effect of path dependence of the preparation method on the rheology of HEC carbon particle fluids. The viscoelastic moduli increase of HEC is ascribed to hydrophobic interactions between biocarbon particles and non hydrated HEC. The preferential particle partitioning in aqueous HEC solutions (rather than in toluene) is also attributed to these interactions. Such interactions were attributed to the partially hydrophobic nature of HEC, which partitioned at the air water interface (rather than exclusively in bulk water) lowering the interfacial tension and producing interfacial films with compressional rigidity. HEC interfacial film rigidity changed upon particle addition, supporting the hypothesis of HEC particle interactions. Compression isotherms modelled using the theory by Marczak et al. were used here for the first time as an indirect tool to gain insights regarding HEC carbon particle interactions. Partial HEC hydrophobicity was also indicated by the higher viscosity measured in ethanol water solutions than in water, which showed that ethanol water was a better solvent than pure water. Steady state fluorescence measurements confirmed that the amount of HEC bound solvent was greater in ethanol water mixtures than in pure water. Biocarbon particles mixed with non hydrated HEC were well dispersed. Instead, biocarbon particles aggregated when they were mixed with hydrated HEC, indicating that the magnitude of attractive forces between particles and HEC decreased when HEC was hydrated. Compression isotherms measured at the air water interface with non hydrated HEC alone and with non hydrated HEC biocarbon particle mixtures differed, indicating HEC particle co adsorption at the air water interface and the formation of HEC particle aggregates.
Tatianna Marshall Alejandro G Marangoni Maria G Corradini Arturo Rodriguez-Uribe Manjusri Misra Amar Kumar Mohanty Braulio Macias Rodriguez Erica Pensini
230534955
The effect of Mo on microstructure and mechanical properties of Nb 22Ti 16Si alloy additively manufactured via laser directed energy deposition
Abstract Alloying process and processing optimization are most effective methods to modify the microstructure and mechanical properties of Nb Si based alloys. In this work, Nb 22Ti 16Si xMo(x=5 20 at. alloys were successfully fabricated by a laser directed energy deposition additive manufacture with elemental powder mixtures. The effect of Mo on the microstructure, micro hardness, nano hardness and fracture toughness of Nb 22Ti 16Si xMo alloy were investigated. The results indicated that the addition of Mo in Nb 22Ti 16Si alloy is promoting the formation of Ti(Nb)5Si3 and b Nb5Si3 phases and inhibiting the formation of Nb3Si phase. Mo was preferentially enriched in the niobium solid solution (Nbss) phase. The volume fraction of Nbss phase first increases then slightly decrease, while Ti(Nb)5Si3 phase was increased with Mo content, especially Nbss matrix also become more continuous. The solidification path of Nb 22Ti 16Si xMo alloys show a certain deviate from the prediction by the Scheil solidification models. Mo alloying in Nb 22Ti 16Si alloy also lead to the increase in the young's modulus and nano hardness of Nbss and b Nb5Si3 phases. The fracture toughness of Nb 22Ti 16Si xMo(x=5 20 at. alloys first increases to 12.2 MPa*m1/2 when Mo content increases to 10 at. then decreases with further increases in Mo content, while their micro hardness shows the opposite trend.
Yunlong Li Xin Lin Yunlong Hu Jun Hua Yu Hongbiao Dong Fencheng Liu Weidong Huang
226984899
Translational genetics: a challenging but important path
Hair disorders can be difficult to address in clinic, not least because our current understanding of molecular mechanisms and targeted therapies remains limited. Loose anagen syndrome (OMIM 600628) is reportedly rare, although cases may remain undiagnosed because the condition is usually selflimiting. A genetic predisposition with dominant inheritance has been observed and the shed hairs may be thinner and longitudinally grooved. It has therefore been suggested that variation in KRT75 (OMIM *609025) encoding a keratin of the inner root sheath companion layer, may account for loose anagen and unruly hair. Onoufriadis et al. propose a genetically determined enzyme abnormality to account for loose anagen occurring with hypotrichosis. Recessive mutations in TKFC, the gene encoding an enzyme named triokinase and flavin mononucleotide cyclase, were detected in one compound heterozygous case, from a total of 15 families studied. This gene product has not previously been implicated in skin or hair disorders and the protein structure has not been determined by crystallization. The conclusion that TKFC plays a role in loose anagen syndrome therefore required a sequence of work from genetic analysis to functional assessment of enzyme variants (Figure 1) Whole exome sequencing (WES) has been used to identify genes responsible for a range of dermatological disorders, but sequence analysis data must be carefully interpreted and various assumptions are required to make sense of the large number of variants detected. Onoufriadis et al. applied WES to 15 families with children showing features of loose anagen. The pattern of inheritance was assumed to represent a new dominant mutation or recessive mutations, the variant(s) should be rare (present in 0 5% of individuals in available databases) and variant(s) should have a deleterious effect on the protein product, based on biochemical structure or function predictions. The team were lucky in that only one gene met all of these criteria, because multiple plausible mutations can be detected even in apparently healthy individuals, each requiring detailed characterization. Modelling in silico and functional analyses in vitro were next used to confirm the effects of compound heterozygous mutations in TKFC on enzyme function. Onoufriadis and colleagues are to be congratulated on completing this detailed and technically challenging work. Further steps towards a therapeutic intervention are clearly a possibility. Questions remain unanswered in this path from phenotype to genotype to molecular mechanisms. Why is hair on the scalp preferentially affected by this metabolic defect and why is loose anagen a self limiting disorder? To what extent does TKFC contribute to the hypotrichosis seen in this patient in addition to loose anagen? Why were TKFC variants not found in any of the other families with a similar hair phenotype? These observations indicate that functional variants in TKFC are likely to be a rare cause even within a rare disorder, thereby limiting wider therapeutic use. The authors acknowledge that other TKFC variants cause multisystem disease without a hair disorder; genetic variation in or near TKFC may also contribute to the control of skin and hair pigmentation in African populations. It is plausible that different mutations give rise to different phenotypes, or the transient effects of loose anagen may simply have been overlooked. Despite these unanswered questions, the work by Onoufriadis and colleagues is an exemplar for translational genetics. It demonstrates the important opportunity to identify previously unexpected molecular mechanisms of dermatological disease for future therapeutic targeting.
The British journal of dermatology
S J Brown
213672919
Effect of spatial arrangement on breakdown characteristics of synthetic particle in high voltage pulse breakage
Abstract The performance of high voltage pulse breakage (HVPB) is largely determined by the properties of ore particles coupled with the characteristics of electrical breakdown. In this study, the effects of spatial arrangement (electrode gap and particle dimension/location) on the breakdown characteristics (channel path and electrical parameters) of synthetic particle in HVPB were investigated. The test results indicated that the channel of breakdown developed preferentially inside tested particle when the electrode gap was completely filled by the particle. Moving particle away from the centre of electrode gap or leaving water gap between electrode and particle would increase the occurrence probability of "flashover" along particle surface and deteriorate the size reduction effect of HVPB. The negative effect of moving particle away from the centre was more severe when electrode gap was small. Electrical parameters of the breakdown voltage (Vbkd) and the breakdown delay time (Td) in pre breakdown phase, as well as the total energy transferred into breakdown channel (Echt) the averaged channel resistance (Rchavg) and the proportion of energy transferred efficiently (Ete) in channel phase were determined according to the pulse wave forms of voltage and current. Generally, all of these electrical parameters increased with the increase of electrode gap when the electrode gap was completely filled by the tested particle. At the same electrode gap, higher values of Vbkd and Td were observed in the tests having water gap between rod electrode and tested particle. By contrast, the effect of water gap on the value of Echt was less significant. The existence of water gap could also reduce the value of Rchavg if breakdown channel had to pass through water before reaching particle. Linear models were developed to describe the relations of Vbkd to Td and Echt to Rchavg in this study. In addition, exponential relation between Ete and Rchavg was developed. Based on the observations in this study, the size reduction effect of HVPB can be optimized by: (1) using larger electrode gap, provided the electrical field strength is high enough to cause breakdown; (2) filling the electrode gap completely with feed particles.
Weiran Zuo Zeming He Fengnian Shi Feng Rao Bao Guo Rongdong Deng
202949473
Effect of build orientation on fracture and tensile behavior of A357 Al alloy processed by Selective Laser Melting
Abstract Selective Laser Melting (SLM) is an additive manufacturing technology that allows producing components through local melting of a metallic powder bed using high power laser beam in accordance with 3D digital CAD models. Cast Al Si Mg alloys are broadly used due to their good processability by SLM and mechanical properties. This work investigates the mechanical behavior of A357 aluminum alloy produced by SLM in the as built and artificially aged conditions. In particular, the tensile properties and fracture toughness of the alloy were investigated according to different specimen orientations on the build plate in the first case and different crack propagation planes in the second. In addition, microstructural and fractographic analyses were performed in order to investigate crack propagation paths and fracture mechanisms. The results showed that building orientation has a strong influence on material response, mainly with regards to the fracture toughness. The melt pool boundaries act as preferential paths for crack propagation and lead to a marked drop in fracture toughness of samples with cracks perpendicular to the building direction.
Materials Science and Engineering: A
Joao Teixeira Oliveira de Menezes Enrique Mariano Castrodeza Riccardo Casati
95389177
The combined effect of sodium and vanadium contamination upon the catalytic performance of USY zeolite in the cracking of n butane: Evidence of path dependent behavior in Constable Cremer plots
Abstract NaCl and [VO(C 5 H 7 O 2 2 were impregnated on a commercial ultra stabilized Y zeolite (USY) Samples were calcined in dry air at 700 degC and examined by X ray diffraction (XRD) N 2 adsorption, isopropylamine decomposition and the n butane cracking reaction. Sodium concentration was kept constant but in excess related to a variable vanadium concentration. Dry thermal treatment in the presence of metal contamination was found to induce framework destruction by sodium but not by vanadium. Vanadium was found to neutralize preferentially the Bronsted acid sites (BASs) responsible for alkane cracking. Selectivity to dehydrogenation increases with vanadium loading due to its intrinsic redox activity. No evidence of a vanadium sodium compound was found; sodium reacts preferentially with the framework than with vanadium. Arrhenius plots rendered quite linear relations, and isokinetic behavior was established for cracking and dehydrogenation reactions. The findings clearly show that the slopes in Constable Cremer plots are sensitive to the reaction mechanism.
Luis-Ernesto Sandoval-Diaz Jose-Manuel Martinez-Gil Carlos Alexander Trujillo