Optimal treatment of stratified Carreau and Casson nanofluids flows in Darcy-Forchheimer porous space over porous matrix

A comparative three-dimensional(3D)analysis for Casson-nanofluid and Carreau-nanofluid flows due to a flat body in a magnetohydrodynamic(MHD)stratified environment is presented.Flow is estimated to be suspended in a Darcy-Forchheimer medium.Soret and Dufour responses are also accommodated in the flow field.A moving(rotating)coordinate system is exercised to examine the bidirectionally stretched flow fields(flow,heat transfer,and mass transfer).Nanofluid is compounded by taking ethylene glycol/sodium alginate as base fluid and ferric-oxide(Fe3O4)as nanoparticles.Governing equations are handled by the application of optimal homotopy asymptotic method(OHAM),where convergence parameters are optimized through the classical least square procedure.The novel mechanism(hidden physics)due to appearing parameters is explored with the assistance of tabular and graphical expositions.Outcomes reveal the double behavior state for temperature field with thermal stratification/Dufour number,and for concentration field with Soret number due to the presence of turning points.

Processing and performance of 2D fused-silica fiber reinforced porous Si_3N_4 matrix composites

Two-dimension （2D） fused-silica fiber reinforced porous silicon nitride matrix composites were fabricated using slurry impregnation and cyclic infiltration with colloidal silica sol. The microstructure and fracture surface were characterized by SEM, the mechanical behavior was investigated by three-point bending test, and the dielectric constant was also measured by impedance analysis. The microstructure showed that the fiber and the matrix had a physical bonding, forming a clearance interface. The mechanical behavior suggested that the porous matrix acted as crack deflection, and the fracture surface had a lot of fiber pull-out. However, the interlaminar shear strength was not so good. The dielectric constant of the composites at room temperature was about 2.8-3.1. The relatively low dielectric constant and non-catastrophic failure indicated the potential application in the radome materials field. 2008 University of Science and Technology Beijing. All rights reserved.

Effects of Solid Matrix and Porosity of Porous Medium on Heat Transfer of Marangoni Boundary Layer Flow Saturated with Power-Law Nanofluids

The effect of the solid matrix and porosity of the porous medium are first introduced to the study of power-law nanofluids, and the Marangoni boundary layer flow with heat generation is investigated. Two cases of solid matrix of porous medium including glass balls and aluminum foam are considered. The governing partial differential equations are simplified by dimensionless variables and similarity transformations, and are solved numerically by using a shooting method with the fourth-fifth-order Runge-Kutta integration technique. It is indicated that the increase of the porosity leads to the enhancement of heat transfer in the surface of the Marangoni boundary layer flow.

Determination of elastic moduli of composite medium containing bimaterial matrix and non-uniform inclusion concentrations

Reservoir porous rocks usually consist of more than two types of matrix materials, forming a randomly heterogeneous material. The determination of the bulk modulus of such a medium is critical to the elastic wave dispersion and attenuation. The elastic moduli for a simple matrix-inclusion model are theoretically analyzed. Most of the efforts assume a uniform inclusion concentration throughout the whole single-material matrix. However, the assumption is too strict in real-world rocks. A model is developed to estimate the moduli of a heterogeneous bimaterial skeleton, i.e., the host matrix and the patchy matrix. The elastic moduli, density, and permeability of the patchy matrix differ from those of the surrounding host matrix material. Both the matrices contain dispersed particle inclusions with different concentrations. By setting the elastic constant and density of the particles to be zero, a double-porosity medium is obtained. The bulk moduli for the whole system are derived with a multi-level effective modulus method based on Hashin＇s work. The proposed model improves the elastic modulus calculation of reservoir rocks, and is used to predict the kerogen content based on the wave velocity measured in laboratory. The results show pretty good consistency between the inversed total organic carbon and the measured total organic carbon for two sets of rock samples.

Template-assisted formation of atomically dispersed iron anchoring on nitrogen-doped porous carbon matrix for efficient oxygen reduction

Isolated active metal atoms anchored on nitrogen-doped carbon matrix have been developed as the efficient catalyst for accelerating sluggish reaction kinetics of oxygen reduction reaction(ORR).The facile rational structure engineering with abundant isolated active metal atoms is highly desirable but challenging.Herein,we demonstrate that atomically dispersed Fe sites(Fe-N4 moieties)on the hierarchical porous nitrogen-doped carbon matrix(Fe-SA-PNC)for high ORR activity can be achieved by a dual-template assisted strategy.By thermal decomposition of NH_(4)Cl template,the nitrogen-doped carbon matrix is generated based on the interaction with carbon precursor of citric acid.Meanwhile,the introduction of NaCl template facilitates the formation of hierarchical porous structures,which enable more active sites exposed and improve the mass transfer.Interestingly,the dual-template strategy can inhibit the formation of iron carbide nanoparticles(NPs)by generating porous structures and avoiding of the rapid loss of nitrogen during pyrolysis.The as-made Fe-SA-PNC catalysts with well-defined Fe-N_(4)active sites exhibit highly efficient ORR activity with a half-wave potential of 0.838 V versus the reversible hydrogen electrode,as well as good stability and methanol tolerance,outperforming the commercial Pt/C.The zinc-air battery(ZAB)constructed by Fe-SA-PNC also shows a higher peak power density and specific discharging capacity than that of Pt-based ZAB.The present work provides the facile strategy for tailoring nitrogen doping and porous structures simultaneously to prevent the formation NPs for achieving the well-dispersed and accessible single-atom active sites,paving a new way to design efficient electrocatalysts for ORR in fuel cells.

Ultrasmall CoS nanoparticles embedded in heteroatom-doped carbon for sodium-ion batteries and mechanism explorations via synchrotron X-ray techniques

Transition metal sulfides have been regarded as promising anode materials for sodium-ion batteries(SIB).However,they face the challenges of poor electronic conductivity and large volume change,which result in capacity fade and low rate capability.In this work,a composite containing ultrasmall CoS(~7 nm)nanoparticles embedded in heteroatom(N,S,and O)-doped carbon was synthesized by an efficient one-step sulfidation process using a Co(Salen)precursor.The ultrasmall CoS nanoparticles are beneficial for mechanical stability and shortening Na-ions diffusion pathways.Furthermore,the N,S,and O-doped defect-rich carbon provides a robust and highly conductive framework enriched with active sites for sodium storage as well as mitigates volume expansion and polysulfide shuttle.As anode for SIB,CoS@HDC exhibits a high initial capacity of 906 mA h g^(-1)at 100 mA g^(-1)and a stable long-term cycling life with over 1000 cycles at 500 mA g^(-1),showing a reversible capacity of 330 mA h g^(-1).Meanwhile,the CoS@HDC anode is proven to maintain its structural integrity and compositional reversibility during cycling.Furthermore,Na-ion full batteries based on the CoS@HDC anode and Na_(3)V_(2)(PO_(4))_(3)cathode demonstrate a stable cycling behavior with a reversible specific capacity of~200 m A h g^(-1)at least for 100 cycles.Moreover,advanced synchrotron operando X-ray diffraction,ex-situ X-ray absorption spectroscopy,and comprehensive electrochemical tests reveal the structural transformation and the Co coordination chemistry evolution of the CoS@HDC during cycling,providing fundamental insights into the sodium storage mechanism.

Amorphous silica fiber matrix biomaterials:An analysis of material synthesis and characterization for tissue engineering

Silica biomaterials including Bioglass offer great biocompatibility and bioactivity but fail to provide pore and degradation features needed for tissue engineering.Herein we report on the synthesis and characterization of novel amorphous silica fiber matrices to overcome these limitations.Amorphous silica fibers were fused by sintering to produce porous matrices.The effects of sacrificial polymer additives such as polyvinyl alcohol(PVA)and cellulose fibers(CF)on the sintering process were also studied.The resulting matrices formed between sintering temperatures of 1,350-1,550◦C retained their fiber structures.The matrices presented pores in the range of 50-200μm while higher sintering temperatures resulted in increased pore diameter.PVA addition to silica significantly reduced the pore diameter and porosity compared with silica matrices with or without the addition of CF.The PVA additive morphologically appeared to fuse the silica fibers to a greater extent and resulted in significantly higher compressive modulus and strength than the rest of the matrices synthesized.These matrices lost roughly 30%of their original mass in an in vitro degradation study over 40 weeks.All matrices absorbed 500 wt%of water and did not change in their overall morphology,size,or shape with hydration.These fiber matrices supported human mesenchymal stem cell adhesion,proliferation,and mineralized matrix production.Amorphous silica fiber biomaterials/matrices reported here are biodegradable and porous and closely resemble the native extracellular matrix structure and water absorption capacity.Extending the methodology reported here to alter matrix properties may lead to a variety of tissue engineering,implant,and drug delivery applications.

成层多孔粘弹性地基在轴对称荷载作用下的解

给出一种有效的解析方法求解成层多孔粘弹性地基在轴对称荷载作用下的固结问题。通过关于时间t的拉普拉斯变换和关于半径r的亨克尔变换，将控制偏微分方程转化为常微分方程，从而得到用常微分矩阵方程形式表示的控制方程。基于矩阵常微分方程的解以及拉普拉斯、亨克尔逆变换，可得到该固结问题的解。该方法理论及计算简捷。通过算例比较了该方法的精度，并研究了地基的粘弹性特性对固结过程的影响。

Flow and heat transfer of composite porous medium saturated with nanofluid

The present article is concerned with the heat transfer of nanofluid saturated with porous medium sandwiched between clear viscous fluid filled in a vertical channel.The model is developed to analyze the behavior of nanofluids taking into account the solid volume fraction.The governing equations are obtained based on the Darcy's law for the porous medium and Tiwari and Das model to define the nanofluid.The viscous and Darcy dissipation terms are included in the energy equation.The transformed dimensionless governing equations are solved analytically using regular perturbation.Investigations are carried out on the flow characteristics for different values of Grashof number,Brinkman number,solid volume fraction and porous parameter using water as base fluid and copper as nanoparticle.Flow and heat transfer are also observed using five different types of nanoparticles.It is found that the maximum value of Nusselt number is obtained for silver nanoparticle.

Recent progress in Li-S and Li-Se batteries

Li–S and Li–Se batteries have attracted tremendous attention during the past several decades, as the energy density of Li–S and Li–Se batteries is high（several times higher than that of traditional Li-ion batteries）.Besides, Li–S and Li–Se batteries are low cost and environmental benign. However, the commercial applications of Li–S and Li–Se batteries are hindered by the dissolution and shuttle phenomena of polysulfide（polyselenium）, the low conductivity of S（Se）, etc. To overcome these drawbacks, scientists have come up with various methods, such as optimizing the electrolyte, synthesizing composite electrode of S/polymer, S/carbon, S/metal organic framework（MOF） and constructing novelty structure of battery.In this review, we present a systematic introduction about the recent progress of Li–S and Li–Se batteries, especially in the area of electrode materials, both of cathode material and anode material for Li–S and Li–Se batteries. In addition, other methods to lead a high-performance Li–S and Li–Se batteries are also briefly summarized, such as constructing novelty battery structure, adopting proper charge–discharge conditions, heteroatom doping into sulfur molecules, using different kinds of electrolytes and binders. In the end of the review, the developed directions of Li–S and Li–Se batteries are also pointed out. We believe that combining proper porous carbon matrix and heteroatom doping may further improve the electrochemical performance of Li–S and Li–Se batteries. We also believe that Li–S and Li–Se batteries will get more exciting results and have promising future by the effort of battery community.