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1
Jancar, Josef, Klara Zarybnicka, Jan Zidek, and Frantisek Kucera. "Effect of Porosity Gradient on Mechanical Properties of Cellular Nano-Composites." Polymers 12, no. 3 (March 19, 2020): 681. http://dx.doi.org/10.3390/polym12030681.
Анотація:
With their hierarchical architectures incorporating gradients in composition, porosity, and orientation, natural materials have evolved optimized balance of mechanical properties. Deciphered from the structure of bamboo, we prepared cellular solids with convex and/or concave porosity gradient and investigated their static mechanical and impact properties. Non-monotonous porosity dependences of tensile, crush, and impact strength were related to the shape of porosity gradient rather than to the properties of the wall material alone. Our results provide experimental evidence, that novel mechanically robust low density additively fabricated cellular nano-composites with convex porosity gradient satisfy the structural requirements of lightweight engineering parts. Moreover, novel functions, such as reduced flammability or electrical conductivity, can easily be introduced by selecting the type and spatial organization of nanoparticles and cellular structure of the cellular micro-particles (CMPs).
2
Lei, Chuan, Jinglan Luo, Xiong Pang, Chi Li, Jiang Pang, and Yongkun Ma. "Impact of Temperature and Geothermal Gradient on Sandstone Reservoir Quality: the Baiyun Sag in the Pearl River Mouth Basin Study Case (Northern South China Sea)." Minerals 8, no. 10 (October 15, 2018): 452. http://dx.doi.org/10.3390/min8100452.
Анотація:
Deep-water areas have become a hotspot for global hydrocarbon exploration. In the deep-water area of the Northern South China Sea, a complete set of source rocks, reservoir rocks, and caprock represents a good oil and gas exploration prospect. The Pearl River Mouth basin, an important exploration target in this area, has a wide range of geothermal gradients. However, the mechanism by which the geothermal gradient influences reservoir quality remains unclear, which severely restricts future exploration. We observed that the reduction rates in the porosity and permeability with increasing burial depth and stratum temperature are more rapid in high geothermal gradient areas. The stratum temperature affects the process of diagenesis and the reservoir quality by changing the grain compressive strength, solubility, and precipitation of minerals and clay minerals transformations. With a comparison the crustal extensional thinning histories of different geothermal gradient areas, this study elucidates the comprehensive factors controlling the decreases rates of reservoir porosity and permeability. These findings explain the different evolutions of reservoirs in areas with different geothermal gradients.
3
Martina, A. Della, and J. G. Hilborn. "Gradient porosity poly(dicyclopentadiene)." Journal of Materials Research 16, no. 7 (July 2001): 2045–52. http://dx.doi.org/10.1557/jmr.2001.0280.
Анотація:
This article describes the preparation of gradient porosity thermoset polymers. The technique used is based on polymerizing a solution of cross-linkable dicyclopentadiene and 2-propanol. The forming polymer being insoluble in 2-propanol, phase separation occurs. Subsequent drying of the 2-propanol gives porosities up to 80%. An apparatus was built to produce a gradient in 2-propanol concentration in a flask, resulting in polymerized gradient porosity rods. The resulting materials have been characterized by scanning electron microscopy (SEM) and density measurements. A mathematical model which allows prediction of the gradient produced is also presented.
4
Liu, Chong, and Nathaniel L. Rosi. "Ternary gradient metal–organic frameworks." Faraday Discussions 201 (2017): 163–74. http://dx.doi.org/10.1039/c7fd00045f.
Анотація:
Gradient MOFs contain directional gradients of either structure or functionality. We have successfully prepared two ternary gradient MOFs based on bMOF-100 analogues, namely bMOF-100/102/106 and bMOF-110/100/102, via cascade ligand exchange reactions. The cubic unit cell parameter discrepancy within an individual ternary gradient MOF crystal is as large as ∼1 nm, demonstrating the impressive compatibility and flexibility of the component MOF materials. Because of the presence of a continuum of unit cells, the pore diameters within individual crystals also change in a gradient fashion from ∼2.5 nm to ∼3.0 nm for bMOF-100/102/106, and from ∼2.2 nm to ∼2.7 nm for bMOF-110/100/102, indicating significant porosity gradients. Like previously reported binary gradient MOFs, the composition of the ternary gradient MOFs can be easily controlled by adjusting the reaction conditions. Finally, X-ray diffraction and microspectrophotometry were used to analyse fractured gradient MOF crystals by comparing unit cell parameters and absorbance spectra at different locations, thus revealing the profile of heterogeneity (i.e. gradient distribution of properties) and further confirming the formation of ternary gradient MOFs.
5
Lynn, Heloise Bloxsom, and Bill Goodway. "Azimuthal P-P prestack amplitudes in the presence of oil-filled aligned porosity (fracture porosity)." Interpretation 8, no. 4 (October 14, 2020): SP109—SP133. http://dx.doi.org/10.1190/int-2020-0035.1.
Анотація:
A 3D P-P high-fold full-azimuth full-offset reflection survey was acquired and processed to characterize a naturally fractured carbonate reservoir. The reservoir is a thick carbonate, which will flow commercial oil with a sufficient fracture network. Extensive calibration data include (1) a horizontal borehole’s resistivity image log, (2) the first 24 months cumulative oil produced, by stage, as known from chemical frac tracer data, (3) pre- and postfrac job instantaneous shut-in pressures, (4) microseismic, and (5) wireline log data. We used the cumulative oil production to document the spatially varying amount of aligned vertical porosity (aligned compliance or fracture porosity) connected to the stage borehole location. The stages of high oil production exhibited, for the fracture-perpendicular azimuth, the more positive amplitude variation with angle (AVA) gradients, and dimmer near-angle (6°–15° angles of incidence) amplitudes, compared to the fracture-parallel azimuth. The azimuthal variation of the AVA gradient fit the cos 2θ curve well, indicating the presence of one set of vertical aligned fractures dominating the azimuthal amplitude signature. In a similar fashion, the azimuthal variation of the mathematical intercept, physically the near-angle amplitudes, also fit the cos 2θ curve well. We have constructed crossplots of the azimuthal near-angle amplitude versus the AVA gradient on a bin-by-bin basis: we observed a straight line at bins with elevated oil production (elevated fracture density). A straight line crossplot of the (AVA gradient, mathematical intercept) is the signature of change of the (sensed) porosity, as long as the lithology and pore fluid are held constant. In accord with industry knowledge, we found that porosity affects the P impedance and thus the near-angle amplitudes: the aligned porosity yields azimuthal P impedance (measured at the 6°–15° angles of incidence). Legacy high-fold 3D P-P surveys rich in the 6°–20° angles of incidence should be considered for reprocessing and reinterpretation using these techniques.
6
Lootsik, M. D., N. O. Manko, R. O. Bilyy, M. M. Lutsyk (Jr.), and R. S. Stoika. "Analysis of chitosan molecular weight profile by electrophoresis in a porosity step gradient polyacrylamide gel." Ukrainian Biochemical Journal 94, no. 2 (July 11, 2022): 76–84. http://dx.doi.org/10.15407/ubj94.02.076.
Анотація:
Chitosan is biocompatible and biodegradable natural biopolymer widely applied in various fields of biology, medicine, and pharmacy, however, its effects significantly depend on the degree of polymerization (DP) and the degree of deacetylation (DDA) of polymer chains. Evaluation of the chitosan chain diversity by DP requires the use of a highly expensive method of high-performance size exclusion chromatography. The aim of our study was to determine the molecular weight profile of chitosan specimens by the use of electrophoresis in a porosity step gradient polyacrylamide gel and to evaluate the efficacy of this method in monitoring the purification of chitosan fragments and its derivatives. Two types of step gradient porosity gels were used: 1) gels of layers with acrylamide concentration 2.5, 3.5, 5.0, 10.0, 15.0, 20.0 % w/v for native chitosan or its high molecular fragments; 2) gels of layers with acrylamide concentration 2.5, 5.0, 10.0, 15.0, 20.0, 25.0 % w/v for low molecular chitosan fragments. The main amount of molecules from the chitosan pool was localized in the type 1 gel in the region of 550-40 kDa and distributed among three bands, which in different samples differed significantly in percentage. Electrophoresis of chitosan fragments fractionated by gel permeation chromatography provided a clear separation of medium molecular weight fragments (50–400 kDa) in type 1 gel and of low molecular weight fragments (3–40 kDa) in type 2 gel. Thus the method of chitosan electrophoresis in a step-gradient porosity of polyacrylamide gel was developed which permits to characterize the molecular weight profile of chitosan specimens polymer chains and is effective in monitoring the isolation of chitosan fragments by gel penetration chromatography of molecular weights from 3 to 400 kDa.
7
Pradewa, Mohammad Resalto, Retno Gumilang Dewi, and Ucok W. R. Siagian. "Simulasi aliran fluida pada proses enhanced coalbed methane." Jurnal Teknik Kimia Indonesia 10, no. 3 (October 2, 2018): 157. http://dx.doi.org/10.5614/jtki.2011.10.3.7.
Анотація:
Fluid flow simulation on enhanched coalbed methane systemThe Enhanced Coalbed Methane (ECBM) process can be applied as a carbon capture and storage (CCS) technology for the mitigation of greenhouse gases emissions, by transferring CO2 emitted by stationary sources into ECBM field reservoirs. This CCS-ECBM integration is a novel technology that is aimed at reducing CO2 emission while simultaneously improving the energy supply security in Indonesia. This research studies the fluid flow in fractures/cleats in CBM reservoirs, which is a laminar flow under pressure gradient in accordance to Darcy's law. The objective of this research is to understand the mechanism of the integration between CCS and ECBM process via computer simulations. Gas components considered in the simulation include CH4 and CO2. Fluid flow variables in this research are permeability (k), porosity (ϕ), and gas saturation (S). Simulations are done using the FlexPDE version 5 software package. Simulation results indicate that all three variables influence the fluid flow mechanism in fractures/cleats during the injection of CO2 in ECBM process. Simulations which are run for 100 days predict that methane recovery is inversely proportional to porosity, with a recovery of 97.88% at a porosity of 0.017, and 37.16% at a porosity of 0.63.Keywords: greenhouse gases, CCS, ECBM, fractures, cleats Abstrak Proses Enhanced Coalbed Methane (ECBM) dapat diterapkan sebagai salah satu teknologi penangkapan dan penyimpanan karbon (Carbon Capture and Storage atau CCS) untuk mitigasi emisi gas rumah kaca, dengan cara menyalurkan CO2 dari sumber emisi stasioner ke dalam reservoir lapangan ECBM. Integrasi CCS-ECBM ini merupakan teknologi baru yang diharapkan mampu mengurangi emisi CO2 sekaligus meningkatkan ketahanan pasokan energi Indonesia. Penelitian ini mempelajari aliran fluida pada retakan (fractures/cleats) di dalam reservoir CBM yang merupakan aliran laminer di bawah gradien tekanan yang mengikuti hukum Darcy. Penelitian ini bertujuan memahami mekanisme integrasi CCS dengan proses ECBM melalui pendekatan simulasi komputer. Senyawa-senyawa yang ditinjau adalah CH4 dan CO2. Variabel-variabel aliran yang diperhitungkan dalam model mencakup permeabilitas (k), porositas (ϕ), dan saturasi gas (S). Simulasi dilakukan menggunakan perangkat lunak FlexPDE versi 5. Hasil simulasi menunjukkan bahwa mekanisme aliran dalam retakan dengan injeksi CO2 pada proses ECBM dipengaruhi oleh ketiga variabel yang ditinjau. Simulasi yang dijalankan selama 100 hari menunjukkan bahwa perolehan metana berbanding terbalik secara linier terhadap porositas, dengan perolehan sebesar 97,88% pada porositas 0,017 dan 37,16% pada porositas 0,63.Kata kunci: gas rumah kaca, CCS, ECBM, retakan, cleats
8
Wang, Hao, Guogang Yang, Qiuwan Shen, Shian Li, Fengmin Su, Ziheng Jiang, Jiadong Liao, Guoling Zhang, and Juncai Sun. "Effects of Compression and Porosity Gradients on Two-Phase Behavior in Gas Diffusion Layer of Proton Exchange Membrane Fuel Cells." Membranes 13, no. 3 (March 4, 2023): 303. http://dx.doi.org/10.3390/membranes13030303.
Анотація:
Water management within the gas diffusion layer (GDL) plays an important role in the performance of the proton exchange membrane fuel cell (PEMFC) and its reliability. The compression of the gas diffusion layer during fabrication and assembly has a significant impact on the mass transport, and the porosity gradient design of the gas diffusion layer is an essential way to improve water management. In this paper, the two-dimensional lattice Boltzmann method (LBM) is applied to investigate the two-phase behavior in gas diffusion layers with different porosity gradients under compression. Compression results in an increase in flow resistance below the ribs, prompting the appearance of the flow path of liquid water below the channel, and liquid water breaks through to the channel more quickly. GDLs with linear, multilayer, and inverted V-shaped porosity distributions with an overall porosity of 0.78 are generated to evaluate the effect of porosity gradients on the liquid water transport. The liquid water saturation values within the linear and multilayer GDLs are significantly reduced compared to that of the GDL with uniform porosity, but the liquid water within the inverted V-shaped GDL accumulates in the middle region and is more likely to cause flooding.
9
Mulsow, Sandor, Bernard P. Boudreau, and John A. Smith. "Bioturbation and porosity gradients." Limnology and Oceanography 43, no. 1 (January 1998): 1–9. http://dx.doi.org/10.4319/lo.1998.43.1.000i.
10
Mulsow, Sandor, Bernard P. Boudreau, and John N. Smith. "Bioturbation and porosity gradients." Limnology and Oceanography 43, no. 1 (1998): l—9. http://dx.doi.org/10.4319/lo.1998.43.1.000l.
11
Zhang, Xiang, Minghao Zhang, Chenping Zhang, Tian Zhou, Xuncheng Wu, and Xuezheng Yue. "Prediction and Numerical Study of Thermal Performance of Gradient Porous Structures Based on Voronoi Tessellation Design." Materials 15, no. 22 (November 14, 2022): 8046. http://dx.doi.org/10.3390/ma15228046.
Анотація:
Porous [d=per]materials arematerial is a new type of engineering material with both functional and structural properties. Compared with regular porous [d=per]structures and random porous structures, a gradientstructure and the random porous structure, gradient porous structure is a porous structure with a spatial variation mechanism, which can adjust the layout of the structure by changing its own load and boundary conditions according to different situations, thus obtaining better performance. In this paper, three spatial Voronoi structures with different spatial gradients are designed [d=per]using theby spatial Voronoi tessellation method. The differences in thermal protection [d=per]performancesperformance between the Voronoi spatial gradient structure and the regular structure and the effects of porosity, gradient direction and heat flow density on the three-dimensional Voronoi stochastic gradient structure were investigated [d=per]viaby data simulation. The results show that the effective thermal conductivity of the Voronoi spatial gradient structure is lower than that of the regular structure. The effective thermal conductivity of the structure gradually decreases with increasing porosity. Taking the gradient Voronoi structure consisting of 3×3×3 units as an example, when the porosity increases from 83% to 94.98%, its effective thermal conductivity decreases from 0.586 to 0.149 Wm−1K−1. The anisotropy of the random structure leads to effective thermal conductivity errors of more than 5% in all three gradient directions. In addition, according to the principle of thermal resistance superposition, we designed a battery pack set for calculating the effective thermal [d=per]conductivitiesconductivity of pillar-based porous materials, including three-dimensional Voronoi gradient random porous materials on the Grasshopper platform. In this way, the effective thermal conductivity of a pillar-based porous material can be predicted more accurately. The predicted calculation results and the simulation results basically agree with each other, and the relative errors of both are within 10%.
12
Zhou, Gang, Lei Qiu, Wenzheng Zhang, and Jiao Xue. "Simulation Analysis on Water’s Micro Seepage Laws under Different Pressure Gradients Using Computed Tomography Method." Advances in Civil Engineering 2018 (September 6, 2018): 1–26. http://dx.doi.org/10.1155/2018/3401341.
Анотація:
The aim of this paper was to develop a model that can characterize the actual micropore structures in coal and gain an in-depth insight into water’s seepage rules in coal pores under different pressure gradients from a microscopic perspective. To achieve this goal, long-flame coals were first scanned by an X-ray 3D microscope; then, through a representative elementary volume (REV) analysis, the optimal side length was determined to be 60 μm; subsequently, by using Avizo software, the coal’s micropore structures were acquired. Considering that the porosity varies in the same coal sample, this study selected four regions in the sample for an in-depth analysis. Moreover, numerical simulations on water’s seepage behaviors in coal under 30 different pressure gradients were performed. The results show that (1) the variation of the simulated seepage velocity and pressure gradient accorded with Forchheimer’s high-velocity nonlinear seepage rules; (2) the permeability did not necessarily increase with the increase of the effective porosity; (3) in the same model, under different pressure gradients, the average seepage pressure decreased gradually, while the average seepage velocity and average mass flow varied greatly with the increase of the seepage length; and (4) under the same pressure gradient, the increase of the average mass flow from the inlet to the outlet became more significant under a higher inlet pressure.
13
Wen, Cui E., Yasuo Yamada, A. Nouri, and Peter D. Hodgson. "Porous Titanium with Porosity Gradients for Biomedical Applications." Materials Science Forum 539-543 (March 2007): 720–25. http://dx.doi.org/10.4028/www.scientific.net/msf.539-543.720.
Анотація:
Highly porous titanium and titanium alloys with an open cell structure are promising implant materials due to their low elastic modulus, excellent bioactivity, biocompatibility and the ability for bone regeneration. However, the mechanical strength of the porous titanium decreases dramatically with increasing porosity, which is a prerequisite for the ingrowth of new bone tissues and vascularization. In the present study, porous titanium with porosity gradients, i.e. solid core with highly porous outer shell was successfully fabricated using a powder metallurgy approach. Satisfactory mechanical properties derived from the solid core and osseointegration capacity derived from the outer shell can be achieved simultaneously through the design of the porosity gradients of the porous titanium. The outer shell of porous titanium exhibited a porous architecture very close to that of natural bone, i.e. a porosity of 70% and pore size distribution in the range of 200 - 500 μm. The peak stress and the elastic modulus of the porous titanium with a porosity gradient (an overall porosity 63%) under compression were approximately 152 MPa and 4 GPa, respectively. These properties are very close to those of natural bone. For comparison, porous titanium with a uniform porosity of 63% was also prepared and characterised in the present study. The peak stress and the elastic modulus were 109 MPa and 4 GPa, respectively. The topography of the porous titanium affected the mechanical properties significantly.
14
Armstrong, J., and W. Armstrong. "A physical model involving Nuclepore membranes to investigate the mechanism of humidity-induced convection in Phragmites australis." Proceedings of the Royal Society of Edinburgh. Section B. Biological Sciences 102 (1994): 529–39. http://dx.doi.org/10.1017/s026972700001455x.
Анотація:
SynopsisNuclepore membranes of known pore size and porosity, attached to small glass chambers were used to investigate the mechanism of humidity-induced convection found in Phragmites and other species. The convective flow of gases and the development of static pressures were studied in relation to a variety of conditions imposed on opposite sides of the membrane. Data were obtained in relation to pore size (0.015 to 3 μm diameter) and porosity, temperature and humidity gradients, membrane area and resistance to venting.A humidity gradient across the Nuclepore membranes was far more effective than a temperature gradient per se for inducing flow; also pores of the order 0.2 μm diameter were the most effective. With a steep enough humidity gradient, however, significant flows could also be induced across pores as large as 2 μm diameter. The results accord with previous experiments and observations on Phragmites and with the mathematical treatment of the mechanism. It is concluded that humidity-induced convection should play a greater role than thermal transpiration (thermo-osmosis) in effecting convections in Phragmites and other non-floating-leaved species.
15
Dalwadi, M. P., I. M. Griffiths, and M. Bruna. "Understanding how porosity gradients can make a better filter using homogenization theory." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 471, no. 2182 (October 2015): 20150464. http://dx.doi.org/10.1098/rspa.2015.0464.
Анотація:
Filters whose porosity decreases with depth are often more efficient at removing solute from a fluid than filters with a uniform porosity. We investigate this phenomenon via an extension of homogenization theory that accounts for a macroscale variation in microstructure. In the first stage of the paper, we homogenize the problems of flow through a filter with a near-periodic microstructure and of solute transport owing to advection, diffusion and filter adsorption. In the second stage, we use the computationally efficient homogenized equations to investigate and quantify why porosity gradients can improve filter efficiency. We find that a porosity gradient has a much larger effect on the uniformity of adsorption than it does on the total adsorption. This allows us to understand how a decreasing porosity can lead to a greater filter efficiency, by lowering the risk of localized blocking while maintaining the rate of total contaminant removal.
16
Brigaud, F., G. Vasseur, and G. Caillet. "Thermal state in the north Viking Graben (North Sea) determined from oil exploration well data." GEOPHYSICS 57, no. 1 (January 1992): 69–88. http://dx.doi.org/10.1190/1.1443190.
Анотація:
We can deduce thermal conductivities and thermal gradients from extensively available oil exploration data: geophysical well logs, cores, cuttings, formation thicknesses and temperatures. Thermal conductivity is predicted at three significant scales. First, it is computed at the scale of well‐log electrofacies (thicknesses from 1 to 10 m) using a geometric mean model calibrated on laboratory measurements made on the main sedimentary rocks—the electrofacies conductivity is calculated as a function of the mineralogy, the porosity and the saturating fluids. Second, it is estimated at formation scale at each well site (thicknesses from 100 to a few thousand meters) using a serial model that accounts for the anisotropy due to sediment stacking and for temperature effects. Finally, for each formation (thicknesses on the order of 1 km), the average conductivity field is mapped at basin scale (extent on the order of 100 km) using a geostatistical treatment accounting for lateral facies and/or porosity changes. For thermal gradient field reconstruction, the systematic errors associated with the drilling history are removed from temperatures (bottom‐hole temperatures) using various techniques depending on data quality. The formation thermal gradient fields are then estimated using a stochastic inversion for temperatures and thicknesses, considering lateral correlations between thermal gradients at well sites. The technique is applied to the Norwegian Viking Graben, a multistage rift basin in the North Sea, where previous studies indicate large lateral and vertical variations in thermal conductivity and thermal gradient fields.
17
Centea, T., G. Peters, K. Hendrie, and SR Nutt. "Effects of thermal gradients on defect formation during the consolidation of partially impregnated prepregs." Journal of Composite Materials 51, no. 28 (October 16, 2017): 3987–4003. http://dx.doi.org/10.1177/0021998317733317.
Анотація:
We describe the effects of thermal gradients on the consolidation of partially impregnated prepregs. Laminates were cured on a heated tool in isothermal and nonisothermal conditions. Key process parameters were varied, including thermal gradient magnitude, air evacuation direction, and vacuum quality. Laminate quality was assessed using microscopy of polished cross-sections and X-ray computed tomography, and interpreted relative to the evolution of resin and prepreg properties during cure. The results show that thermal gradients influenced the rate of impregnation of the prepreg and the rate of gas transport, and affected the amount and distribution of porosity when air was not fully evacuated. Temperature distributions that led to cold regions at the ply boundaries were advantageous, typically exhibiting lower porosity than isothermal baselines. Conversely, gradients resulting in hotter-than-average part perimeters effectively sealed air within the laminate, degrading quality. The results clarify fundamental defect formation mechanisms for partially impregnated prepregs and other processes reliant on air evacuation through an unsaturated preform and provide guidelines for part, tool, and process design.
18
Wubie, Mesfin Anteneh, and Mohammed Assen. "Effects of land cover changes and slope gradient on soil quality in the Gumara watershed, Lake Tana basin of North–West Ethiopia." Modeling Earth Systems and Environment 6, no. 1 (October 21, 2019): 85–97. http://dx.doi.org/10.1007/s40808-019-00660-5.
Анотація:
Abstract This study evaluated land cover change and slope gradient on selected soil quality parameters in the Gumara watershed, northwestern Ethiopia. 36 soil samples were collected from 0- to 20-cm depth under four land cover types across three slope gradients. The collected soil samples were analyzed for selected soil quality parameters. Result indicated that the bulk density of the soil is different (P < 0.001) in the watershed because of land cover change and slope gradient. Cultivated land and steeper slopes have the highest bulk density and lowest total porosity. On the other hand, the forestland and gentler slopes have lowest bulk density and high total porosity. Intensive cultivation accompanied by continuous conversion of forestland to cultivated land caused high bulk density and low total porosity. Cation exchange capacity, exchangeable magnesium total nitrogen, available phosphorus and potassium negatively correlated with slope gradient. Conversion of forestland to cultivated land contributed to changes in pH (P < 0.05) exchangeable calcium (P < 0.01), potassium (P < 0.001), available phosphorus (P < 0.01) and nitrogen (P < 0.01) content. The soil degradation index results showed that soil organic carbon, nitrogen, available phosphorus and exchangeable potassium contents declined and bulk density increased because of the land cover change. This negative effect on agricultural development and environmental health of the watershed makes an integrated land resource management approach vital for sustaining agricultural productivity and the environment health of the Gumara watershed.
19
Rodríguez-Parra, Jesús, Rodrigo Moreno, and Isabel Nieto. "Effect of cooling rate on the microstructure and porosity of alumina produced by freeze casting." Journal of the Serbian Chemical Society 77, no. 12 (2012): 1775–85. http://dx.doi.org/10.2298/jsc121018132r.
Анотація:
Freeze casting is a well-known shaping technique to produce materials with directional porosity. One of the major problems is the difficulty to control the cooling rate thus leading to gradients in pore size and homogeneity. This work deals with the manufacture of alumina ceramics with directional porosity by freeze casting of aqueous suspensions. An experimental set-up was prepared in order to apply different cooling rates. Freeze casting tests were done with an aqueous alumina suspension after optimization of its rheological behavior. The porosity and microstructural features of sintered bodies produced under different experimental conditions were studied and analyzed. It is concluded that the cooling rate influences the microstructure while final temperature has a much lower influence. Also, the microstructural analysis shows that there is a gradient in the directionality of pores, being lower at the bottom and the top and higher in the central region of the specimens.
20
Andertová, Jana, Jiří Havrda, and Radek Tláskal. "Functional Gradient Alumina Ceramics with Controlled Porosity." Key Engineering Materials 333 (March 2007): 223–26. http://dx.doi.org/10.4028/www.scientific.net/kem.333.223.
Анотація:
The work deals with preparation of functional gradient alumina ceramics with controlled porosity by slip casting method of aqueous alumina suspension containing pore-generating agent. The sol-gel transition of AlO(OH) was employed to stabilize pore-generating agent in the suspension. The composite bodies with layers of variable porosity were prepared. Based on dilatometer measurement the admission difference of irreversible dilatation changes #αirr between compounded layers was determined in order to prepare defect free bi-layer bodies. The dependence of physical and mechanical properties of as fired composite bodies on the porosity value was expressed.
21
Heidenau, Frank, Harald Schmidt, Frauke Stenzel, and Günter Ziegler. "Sol-Gel-Dervied Titania with Gradient Porosity." Key Engineering Materials 161-163 (July 1998): 115–16. http://dx.doi.org/10.4028/www.scientific.net/kem.161-163.115.
22
Yang, Jian, Jie Xiong, Guanyi Wang, Wenquan Lu, and Qingliu Wu. "Gradient Porosity Electrode for Fast Charging Batteries." ECS Meeting Abstracts MA2021-02, no. 4 (October 19, 2021): 474. http://dx.doi.org/10.1149/ma2021-024474mtgabs.
23
Zeschky, Jürgen, Thomas Höfner, Claudia Arnold, Rudolf Weißmann, Djamila Bahloul-Hourlier, Michael Scheffler, and Peter Greil. "Polysilsesquioxane derived ceramic foams with gradient porosity." Acta Materialia 53, no. 4 (February 2005): 927–37. http://dx.doi.org/10.1016/j.actamat.2004.10.039.
24
Zhang, Wen Bin, and Da Da Wang. "Design of New MEA Structure for Mciro Direct Methanol Fuel Cell." Advanced Materials Research 694-697 (May 2013): 1565–68. http://dx.doi.org/10.4028/www.scientific.net/amr.694-697.1565.
Анотація:
A novel double-catalyst layer MEA using CCM-GDE (Catalyst Coated Membrane,CCM;Gas Diffusion Electrode,GDE) fabrication method is provided. The double-catalyst layer is formed with an inner catalyst layer (in anode side: PtRu black as catalyst, in cathode side: Pt black as catalyst) and an outer catalyst layer (in anode side: PtRu/C as catalyst, in cathode side: Pt/C as catalyst). By study of the catalyst loading in the double-catalyst layer, an optimization of the catalyst layer structure is obtained, that is the cell may perform best when the ratio of the inner catalyst and outer catalyst is 1:1 (both in inner and outer catalyst layer, the catalyst loading is 1.5mg/cm2). As the hydrophilicity and pore structure are important to the MEA performance, they are optimized by adding pore former and Nafion in the GDL and outer catalyst layer, respectively. Thus three gradients from the PEM to the GDL are formed in the novel MEA: catalyst concentration gradient, porosity gradient and hydrophilicity gradient. These gradients may increase the mass transfer and quicken the electrochemistry reaction in MEA. The CCM-GDE technology may enhance the contact properties between the catalyst and PEM, and increase the electrode reaction areas, resulted in increasing the performance of the μDMFC.
25
Wang, Yingmei, Jie Liu, Wenze Jiao, Yadong Teng, Jing Zhan, and Peng Zhang. "Determination and Application of Archie Model Parameters in Hydrate Formation under Different Temperature Gradients." Energies 16, no. 14 (July 21, 2023): 5517. http://dx.doi.org/10.3390/en16145517.
Анотація:
To investigate the impact of geothermal gradient on the distribution and reserves of hydrate in permafrost regions, it is crucial to utilize the Archie formula to compute hydrate saturation and adjust parameters to enhance the model’s precision under varying temperature gradient conditions. This study formed methane hydrate under four temperature gradients of 0.02 °C/cm, 0.07 °C/cm, 0.11 °C/cm and 0.18 °C/cm, and two sand particle ratios. The values of porosity index (m) and saturation index (n) were fitted according to different conditions. The water saturation and hydrate saturation were then calculated and contrasted with experimental results. Findings indicate that the influence of temperature gradient on the values of m and n is intricate, with n decreasing gradually and m fluctuating with an increase in temperature gradient. The discrepancies between the optimized Archie model and the actual calculated hydrate saturation values ranged from 0.8% to 2.5%, with average errors of less than 3%, proving its applicability. Finally, the optimized Archie model was used to investigate the hydrate saturation and its distribution in different layers, which confirmed the significant effect of temperature gradient on the assessment of hydrate storage and distribution by Archie’s equation.
26
Liu, Miaomiao, Dan Yao, Zhigang Liu, Jingfeng Guo, and Jing Chen. "An Improved Adam Optimization Algorithm Combining Adaptive Coefficients and Composite Gradients Based on Randomized Block Coordinate Descent." Computational Intelligence and Neuroscience 2023 (January 10, 2023): 1–14. http://dx.doi.org/10.1155/2023/4765891.
Анотація:
An improved Adam optimization algorithm combining adaptive coefficients and composite gradients based on randomized block coordinate descent is proposed to address issues of the Adam algorithm such as slow convergence, the tendency to miss the global optimal solution, and the ineffectiveness of processing high-dimensional vectors. The adaptive coefficient is used to adjust the gradient deviation value and correct the search direction firstly. Then, the predicted gradient is introduced, and the current gradient and the first-order momentum are combined to form a composite gradient to improve the global optimization ability. Finally, the random block coordinate method is used to determine the gradient update mode, which reduces the computational overhead. Simulation experiments on two standard datasets for classification show that the convergence speed and accuracy of the proposed algorithm are higher than those of the six gradient descent methods, and the CPU and memory utilization are significantly reduced. In addition, based on logging data, the BP neural networks optimized by six algorithms, respectively, are used to predict reservoir porosity. Results show that the proposed method has lower system overhead, higher accuracy, and stronger stability, and the absolute error of more than 86% data is within 0.1%, which further verifies its effectiveness.
27
Kuo, Yeong Sant. "Study of Thermal Gradient on Porosity Formation in A201 Aluminum Alloy Plate Castings." Applied Mechanics and Materials 248 (December 2012): 9–13. http://dx.doi.org/10.4028/www.scientific.net/amm.248.9.
Анотація:
This study is to with system change the riser size and the casting geometry to find out the relation between thermal gradient and porosity formation in A201 aluminum alloy plate casting, which is discussed in this study. The results show that the porosity content was found to be relevant to the thermal gradient and riser system. The larger the thermal gradient (G), the lower the porosity content was found in this study.
28
Kuo, Yeong Sant. "Influences of Thermal Gradient and Solidus Velocity on Porosity Content in A201 Aluminum Alloy Castings." Applied Mechanics and Materials 496-500 (January 2014): 255–58. http://dx.doi.org/10.4028/www.scientific.net/amm.496-500.255.
Анотація:
With systematic change in the riser size, together with variation of thickness and length, A201 aluminum alloys were cast in 100% silica sand molds. The higher the thermal gradient, the lower the porosity content was measured in the A201 aluminum alloy plate casting. And the faster the solidus velocity, the more the porosity content in this study. The porosity content of A201 aluminum alloy was influenced by both of thermal gradient and solidus velocity at same time in this study. Basically, high thermal gradient with slow solidus velocity seems get lower porosity content in A201 aluminum alloy castings.
29
Sathujoda, Prabhakar, Aneesh Batchu, Bharath Obalareddy, Giacomo Canale, Angelo Maligno, and Roberto Citarella. "Free Vibration Analysis of a Thermally Loaded Porous Functionally Graded Rotor–Bearing System." Applied Sciences 10, no. 22 (November 19, 2020): 8197. http://dx.doi.org/10.3390/app10228197.
Анотація:
The present work deals with natural and whirl frequency analysis of a porous functionally graded (FG) rotor–bearing system using the finite element method (FEM). Stiffness, mass and gyroscopic matrices are derived for porous and non-porous FG shafts by developing a novel two-noded porous FG shaft element using Timoshenko beam theory (TBT), considering the effects of translational inertia, rotatory inertia, gyroscopic moments and shear deformation. A functionally graded shaft whose inner core is comprised of stainless steel (SS) and an outer layer made of ceramic (ZrO2) is considered. The effects of porosity on the volume fractions and the material properties are modelled using a porosity index. The non-linear temperature distribution (NLTD) method based on the Fourier law of heat conduction is used for the temperature distribution in the radial direction. The natural and whirl frequencies of the porous and non-porous FG rotor systems have been computed for different power law indices, volume fractions of porosity and thermal gradients to investigate the influence of porosity on fundamental frequencies. It has been found that the power law index, volume fraction of porosity and thermal gradient have a significant influence on the natural and whirl frequencies of the FG rotor–bearing system.
30
Tychsen, Jörn, and Joachim Rösler. "Investigation of the Porosity Gradient in Thickness Direction Formed by Cold Rolling in Porous Aluminum." Metals 13, no. 4 (March 30, 2023): 681. http://dx.doi.org/10.3390/met13040681.
Анотація:
To adapt porous material for its application as low noise trailing edge, a special rolling process, using a time-varied rolling gap, was used in previous research to produce a porosity gradient in the direction of rolling. Investigations suggest that a gradient in porosity may also be produced in the thickness direction of the material, i.e., in the rolling gap direction, without using a specialized rolling mill. Such a gradient may help to further increase acoustic efficiency of porous materials. The aim of this study was to analyze the dependency of such a gradient on the rolling parameters, and to clarify which stress components are significantly responsible for an increased near-surface compaction. Experiments using different relative compressed lengths were performed to analyze shear-dominated and friction-dominated rolling. The material was characterized using compression tests, computed tomography and flow resistance measurements. It is shown that the compressed length is an important parameter for adjusting a porosity gradient. Rolling with small values of compressed length during all rolling passes leads to increased compaction of near-surface regions, compared to interior ones. The difference in porosity achieved was up to 15%. Furthermore, the results suggested that a gradient in hydrostatic stress is responsible for the porosity gradient. Validation of the results by FE simulation is forthcoming, but not part of this publication.
31
Kuo, Y. S. "Effects of Thermal Gradient and Solidification Time on Porosity Content of A201 Aluminum Alloy Castings." Advanced Materials Research 503-504 (April 2012): 597–600. http://dx.doi.org/10.4028/www.scientific.net/amr.503-504.597.
Анотація:
The purpose of the present study was to discuss the effects of local solidification time and thermal gradient on porosity content in long solidification range A201 aluminum alloy plate castings. With systematic change in the riser size, together with variation of thickness and length, were cast in different kinds of molds. The sand molds with end chill for the plate castings were made of 100% silica sand. The porosity content of A201 aluminum alloy was affected by the local solidification time and thermal gradient at same time in this study. The correlation between porosity content and any individual thermal parameter is found to be split into 2 bands, each being associated with one of the two thicknesses of plate castings. The higher the thermal gradient, the lower the porosity content was measured in the A201 aluminum alloy plate casting. And high thermal gradient with short solidification time will get lower porosity content in aluminum alloy castings
32
Li, Qiang, Jing Yuan Yu, Er Yong Zheng, Ze Sun, and Yu Shan Zeng. "Study on Preparation of Gradient Porous Ti by Powder Metallurgy Method." Advanced Materials Research 490-495 (March 2012): 3589–93. http://dx.doi.org/10.4028/www.scientific.net/amr.490-495.3589.
Анотація:
Gradient porous Ti was prepared by powder metallurgy method using NH4HCO3 as pore former. The effect of content and distribution of NH4HCO3 and sintering temperature on pore characteristic, sintering shrinkage, flexural property was studied. Stress-strain curves of gradient and uniform porous Ti material were compared. The results show the porosity, sintering shrinkage rate and flexural strength vary from 51.8% to 41.3%, from 23.5% to 28.7%, and from 145.7 MPa to 221.6 MPa when the distribution of NH4HCO3 varying form uniformity to gradient. Additionally, with the increase of sintering temperature, the porosity of gradient samples first increases and then decreases. When sintered at 1573K for 2h, the porosity of gradient porous Ti has the maximum of 45.6%. Moreover, there is pseudo yield phenomenon according to the test curve of three points bending of the gradient porous Ti with three layers structure.
33
Song, Kaifang, Chi Zhang, Naifang Hu, Xiangkun Wu, and Lan Zhang. "High performance thick cathodes enabled by gradient porosity." Electrochimica Acta 377 (May 2021): 138105. http://dx.doi.org/10.1016/j.electacta.2021.138105.
34
Kim, K. H., T. W. Kim, S. Y. Yoon, B. K. Kim, and H. C. Park. "Porous mullite/alumina layered composites with gradient porosity." Materials Research Innovations 18, sup2 (May 2014): S2–225—S2–228. http://dx.doi.org/10.1179/1432891714z.000000000625.
35
Koizumi, M., and M. Niino. "Overview of FGM Research in Japan." MRS Bulletin 20, no. 1 (January 1995): 19–21. http://dx.doi.org/10.1557/s0883769400048867.
Анотація:
Space planes require high-performance heat-resistant materials which can withstand ultrahigh temperatures and extremely large temperature gradients. To meet these needs, functionally gradient materials (FGMs) were proposed about 10 years ago in Japan.Figure 1 shows a conceptual diagram of functionally gradient materials, taking into account the relaxation of thermal stress. For the surface that contacts high-temperature gases at thousands of degrees, ceramics are used to provide adequate heat resistance. For the surface that provides cooling, metallic materials are used to furnish the necessary thermal conductivity and mechanical strength. In addition, the composition of these materials is formulated to provide optimum distribution of composition, structure, and porosity to effectively relax thermal stress.Since fiscal 1987, an R&D project entitled “Research on Fundamental Techniques to Develop Functionally Gradient Materials for Relaxation of Thermal Stress,” which aimed to develop ultra heat-resistant materials, had been carried out with special coordination funds from the Science and Technology Agency. The five-year project had two phases; Phase I was carried out from 1987 to 1989, and Phase II from 1990 to 1991.
36
Romanitan, Cosmin, Pericle Varasteanu, Daniela C. Culita, Alexandru Bujor, and Oana Tutunaru. "X-ray scattering profiles: revealing the porosity gradient in porous silicon." Journal of Applied Crystallography 54, no. 3 (May 25, 2021): 847–55. http://dx.doi.org/10.1107/s1600576721003484.
Анотація:
Porous silicon layers with different porosities were prepared by adjusting the anodization current density of the electrochemical etching process, starting from highly doped p-type crystalline silicon wafers. The microstructural parameters of the porous layers were assessed by high-resolution X-ray diffraction, total external reflection, scanning electron microscopy and nitrogen adsorption–desorption analysis. Furthermore, both the surface porosity and the mean porosity for the entire volume of the samples were estimated by employing total external reflection measurements and X-ray reciprocal-space mapping, respectively. The results clearly indicate that the surface porosity is different from the mean porosity, and the presence of a depth porosity gradient is suggested. To evaluate the porosity gradient in a nondestructive way, a new laboratory method using the grazing-incidence X-ray diffraction technique is reported. It is based on the analysis of the X-ray scattering profiles of the porous layers to obtain the static Debye–Waller factors. In this way, a description of the porosity gradient in a quantitative framework becomes possible, and, as a result, it was shown that the porosity increases exponentially with the X-ray penetration depth. Moreover, a strong dependence between the porosity gradient and the anodization current was demonstrated. Thus, in the case of the lowest anodization current (e.g. 50 mA cm−2) a variation of only 15% of the porosity from the surface to the interface is found, but when applying a high anodization current of 110 mA cm−2 the porosity close to the bulk interface is almost three times higher than at the surface.
37
Deng, Ying Er, Jing Yu, and Xin Peng. "Evolution Characteristics of Permeability and Porosity of Mudding Weak Permeability Media with Nonlinear Flow." Applied Mechanics and Materials 580-583 (July 2014): 893–96. http://dx.doi.org/10.4028/www.scientific.net/amm.580-583.893.
Анотація:
Concepts of flow permeability, flow permeability coefficient and flow porosity were presented to investigate changes of permeability and porosity of mudding weak permeability media with nonlinear flow. Formulas of flow permeability, flow permeability coefficient and flow porosity were presented to study the evolution characteristics. Results show that permeability and porosity of mudding weak permeability media nonlinear flow increase with pressure gradient or hydraulic gradient of nonlinear flow, while permeability and porosity of high permeability media Darcy flow are constant. The results can provide a test and calculation of micro porosity with a new method and can provide engineering safety of mudding weak permeability media nonlinear flow with scientific basis.
38
Liu, Rui Liang, Wei Zhou, Wei Song Ling, Shuang Li Li, and Ping He. "Thermal Conductivity Measurements of Novel Porous Copper Fiber Sintered Sheet." Materials Science Forum 933 (October 2018): 159–68. http://dx.doi.org/10.4028/www.scientific.net/msf.933.159.
Анотація:
In this work, a porous copper fiber sintered sheet (PCFSS) is fabricated by using a low-temperature solid-phase sintering method. Copper fiber is a raw material that is produced by a cutting method with a multi-tooth tool. A novel reference plate method (RPM) with a steady state heat transfer process is introduced to measure the thermal conductivity of PCFSS. The study involves experimentally investigating the effects of reference plate materials as well as the porosity and porosity gradients of PCFSS on thermal conductivity. The findings indicate that reasonable measurement results of thermal conductivity of PCFSS are obtained when 304 stainless steel is selected as a reference plate material when compared with that in the case of a red copper plate. The thermal conductivity increases with a decrease in the porosities of PCFSS in the approximate range of 70%–90%. With respect to the approximate measuring temperature range of 34°C~58°C, the thermal conductivities of PCFSSs with 70%, 80% and 90% porosities correspond to 25.35 W/(m·°C), 15.01 W/(m·°C) and 11.24 W/(m·°C), respectively. The thermal conductivity of PCFSS with 70%-80%-90% gradient porosity corresponds to 13.43 W/(m·°C), and this value is between 80% and 90% porosity of PCFSS.
39
Zubko, Pavol, Ivan Zahornacký, Dora Kroisová, Marek Vojtko, and Ladislav Pešek. "Structure and Properties of Selected Natural Materials." Key Engineering Materials 635 (December 2014): 66–70. http://dx.doi.org/10.4028/www.scientific.net/kem.635.66.
Анотація:
This paper deals with description of properties of selected natural materials mainly theirs shelter function. The investigated materials are horsetail and walnut shell. Both natural materials have porous shell/tubular structure. Walnut shell provides natural shield cover for fruit with gradient distribution of porosity and membrane function. In case of horse tail, except the gradient distribution of porosity there is also the gradient change of chemical composition along the cross-section.
40
Li, Mengmeng, Gang Bi, Jie Zhan, Liangbin Dou, and Hailong Xu. "A Semianalytical Two-Phase Imbibition Model in Dual-Porosity and Dual-Permeability Reservoirs." Geofluids 2021 (April 5, 2021): 1–14. http://dx.doi.org/10.1155/2021/5589936.
Анотація:
The pressure transient behavior of water injection well has been extensively investigated under single-phase flow conditions. However, when water is injected into formation, there are saturation gradients within the water flooded area. Additionally, water imbibition is essentially important for oil displacement in dual-porosity and dual-permeability (DPDP) reservoirs. In this work, a novel semianalytical two-phase flow DPDP well test model considering both saturation gradient and water imbibition has been developed. The model was solved by the Laplace transform finite difference method. Type curves were generated, and flow regimes were identified by the model. The model features and effect of parameters were analyzed. Results show that water imbibition reduces the advancing speed of water drive front in the fracture system and slows down the water cut raising rate and the expansion speed of the two-phase zone in the fracture system. Therefore, the fluid exchange between the fracture and matrix systems becomes more sufficient and more oil will be recovered from the DPDP reservoir. The shape of pressure curves is similar for the single-phase and two-phase flow DPDP model, but the position of the proposed model is above the curves of the single-phase model. Shape factor mainly influences the interporosity period of the pressure derivatives. Water imbibition has a major effect on the whole system radial flow period of the curves. The findings of this study can help for better understanding of the oil/water two-phase flow pressure transient behavior in DPDP reservoirs considering saturation gradients and water imbibition.
41
Mikheeva, O. V., A. V. Kravchuk, and S. S. Orlova. "Methodology of influence of free porosity and water loss on the processes occuring in the soils of irrigation channel with an earth bed." Prirodoobustrojstvo, no. 1 (2024): 12–17. http://dx.doi.org/10.26897/1997-6011-2024-1-12-17.
Анотація:
Purpose of the research: to consider the influence of free porosity and water loss on the filtration of water from channels with an earthen bed. Explore existing calculation methods taking into account the parameters of free porosity and fluid loss. Collect calculation material that can form the basis of a program for calculating the filtration of channels with an earthen bed, taking into account the factors influencing the first and second stages of filtration in the channels. Materials and research methods: The work used theoretical methods for calculating filtration in channels with an earthen bed, presented the calculation of the loss of flow rate Qf for filtration per 1 km of length with a steady free surface for different types of channel cross-sections, considered the basic formulas proving that water supply changes with changes in transverse cross-section of the canal, the change in the stability of the canal slopes is shown, a test calculation of the canal for filtration strength according to the maximum pressure gradients is presented, the need to compare the excess of the critical filtration pressure gradient with the permissible pressure gradient is considered. Results and its discussion. The relationship between the total, capillary and minimum moisture capacity and water yield in the thickness of soils is presented, the dependence of free porosity on the groundwater level, and the change in water permeability of soils over time are considered. As a result of the research, material was collected on the influence of free porosity and water loss on the movement of water in soils and the influence on the increase in groundwater levels in the zone of influence of canals, a methodology was presented for the influence of free porosity and water loss on the processes occurring in the soils of irrigation canals in an earthen channel, which will allow its use for modeling these processes on a computer.
42
Ogban, P. I., M. I. Ibotto, U. E. Utin, O. A. Essien, and G. J. Arthur. "Effect of slope curvature and gradient on soil properties affecting erodibility of coastal plain sands in Akwa Ibom State, Nigeria." Agro-Science 21, no. 2 (June 20, 2022): 12–23. http://dx.doi.org/10.4314/as.v21i2.2.
Анотація:
A study was conducted to assess the effect of slope curvature and gradient on soil properties affecting erodibility of coastal plain sands in Akwa Ibom State. Twelve locations comprising six each of concave (CC) and convex (CV) slopes, and three slope gradients, namely, gentle (GS), moderate (MS) and steep slopes (SS) in CC and CV were identified for the study. Bulk and core soil samples were collected from the top 30 cm soil depth at three slope positions of slope curvature and gradient categories for physical and chemical characterization, and derivation of microaggregate stability indices and erodibility factor, K. Results showed that coarse sand (CS), fine sand (FS), bulk density (Bd), total porosity (TP) and saturated hydraulic conductivity (Ksat) were significantly (p ≤ 0.05) higher on CC than CV, and among the slope gradients, GS > MS > SS. The interaction of slope curvature and gradients was significantly higher on CC than CV. A similar pattern of differences was also observed inorganic matter (SOM), calcium (Ca), magnesium (Mg), and other exchangeable cations, but the effect of slope curvature and gradients interaction was not significant. The microaggregate stability indices, water dispersible clay (WDC), water dispersible silt (WDS), dispersion ratio (DR), clay dispersion ratio (CDR), modified clay ratio (MCR), clay flocculation index (CFI), aggregated silt + clay (ASC) and aggregated clay (AC) were significantly higher on CV than CC, and differences among slope gradients and interaction of slope curvature and gradients were not significant. The erodibility factor, K, was significantly higher on CV than CC, while the slope gradients were similar in their effects on K. Linear regression analysis showed that K-factor was highly significantly related to CS, FS, Si, Cl, Bd, TP and Ksat, as well as WDC, WDS, CDR, DR, CR, MCR, CFI, ASC and AC. However, CS, Si, Ksat, Cl, ASC and WDS which explained > 40% of the variability in Kfactor could be relied upon as indices of soil erodibility in the coastal plain sands in Akwa Ibom State.
43
Fogliatto, Aloysio Arthur Becker, Carlos Henrique Ahrens, Paulo Antônio Pereira Wendhausen, Edson Costa Santos, and Daniel Rodrigues. "Correlation between porosity and permeability of stainless steel filters with gradient porosity produced by SLS/SLM." Rapid Prototyping Journal 26, no. 1 (January 6, 2020): 73–81. http://dx.doi.org/10.1108/rpj-09-2018-0224.
Анотація:
Purpose Porous structures have been widely used in filtration, medical implants and aerospace field. In the filtration field, the study of permeability of the porous structures is of great importance. This paper aims to study the influence of selective laser sintering/melting (SLS/SLM) process parameters on porosity and permeability of stainless steels filters with gradient porosity (FGM). Design/methodology/approach AISI 316L stainless steel powder was used to manufacture FGM filters by varying the hatch distance while other process parameters were fixed. The relationship between porosity and permeability of such FGM filters was investigated by means of Archimedes’ and Forchheimer’s laws. The gradient of porosity was also analyzed by means of micro-computed tomography. Findings The results have confirmed the ability of SLS/SLM in controlling porosity of the final product by varying the hatch distance. Further, the results allow to assume that FGM filters will have particle retention capacity related to lowest porosity value (which in turn is associated with the lowest hatch distance value used), while it will work at lower pressure drops – or at higher flow rates for equal pressure drop – when compared to a filter without gradient porosity. Originality/value Some research found in recent literature has showed the relationship between SLS/SLM process parameters and permeability of stainless steel porous structures. However, this paper fulfils the need to understand the relationship between SLS/SLM process parameters, porosity and permeability behavior of functionally graded porous structures (FGM filters).
44
Li, X. B., H. Y. Wang, H. X. Gu, J. Wang, W. J. Zhang, and T. G. Wang. "Preparation of gradient Ni-SDC anode by tape casting and co-sintering." Science of Sintering 42, no. 2 (2010): 153–59. http://dx.doi.org/10.2298/sos1002153l.
Анотація:
Gradient Ni-SDC anode and anode-supported SDC electrolyte were produced by tape casting method with laminating and co-sintering process. The best co-sintering temperature of gradient Ni-SDC anode and SDC electrolyte was 1300?C for 3 h. The open porosity of gradient Ni-SDC anode sintered at 1300oC was 36%, which offered sufficient open porosity of more than 30%. By adjusting the composition of Ni in gradient anode, the thermal expansion coefficient (TEC) of Ni-SDC anode could be adjusted close to that of SDC electrolyte, which improve the compatibility of anode and electrolyte. The bending strength of gradient Ni-SDC anode was 134 MPa. The electrical conductivity of gradient Ni-SDC anode was better than that of non-gradient Ni-SDC anode at 650 - 800?C.
45
Lu, Xia, Sun, Bian, Qiu, Lu, Luo, and Cai. "Permeability Evolution at Various Pressure Gradients in Natural Gas Hydrate Reservoir at the Shenhu Area in the South China Sea." Energies 12, no. 19 (September 26, 2019): 3688. http://dx.doi.org/10.3390/en12193688.
Анотація:
The sediment of the hydrate reservoir in the Shenhu Area is mainly clayey silt. Its characteristic small particles and poor cementation challenge the quantification of the reservoir permeability during gas production. An accurate description of the seepage mechanism of the clayey-silt reservoir is the basis, and also a difficulty, of effective development of gas in the South China Sea. In this study, four sets of water seepage experiments under different pressure gradients are carried out using the clayey-silt reservoir sediments, in which the fourth sample was subjected to computed tomographic (CT) scans. The experimental results shows that the clayey-silt reservoir has a compression of the pore structure and decreasing permeability with the increasing pressure gradient. CT images are used to show the reduction of pore spaces for fluid flow. When the pressure gradient is less than 3 MPa per meter, the pore structure of the reservoir has minor changes. When the pressure gradient is greater than this value, the pore structure of the reservoir will be quickly compressed. This leads to a rapid decrease in permeability, and the process of permeability reduction is irreversible. The decrease of permeability can be predicted directly by establishing a power law model with the change of porosity. Our experimental results preliminarily reveal the dynamic evolution law of pore structure and permeability of clayey-silt reservoir in the process of gas hydrate exploitation via depressurization. The permeability evolution law at various pressure gradients provides a scientific and reasonable basis of a productivity control system for clayey-silt gas hydrate in depressurized gas production.
46
Niksiar, Pooya, Frances Su, Michael Frank, Taylor Ogden, Steven Naleway, Marc Meyers, Joanna McKittrick, and Michael Porter. "External Field Assisted Freeze Casting." Ceramics 2, no. 1 (March 24, 2019): 208–34. http://dx.doi.org/10.3390/ceramics2010018.
Анотація:
Freeze casting under external fields (magnetic, electric, or acoustic) produces porous materials having local, regional, and global microstructural order in specific directions. In freeze casting, porosity is typically formed by the directional solidification of a liquid colloidal suspension. Adding external fields to the process allows for structured nucleation of ice and manipulation of particles during solidification. External control over the distribution of particles is governed by a competition of forces between constitutional supercooling and electromagnetism or acoustic radiation. Here, we review studies that apply external fields to create porous ceramics with different microstructural patterns, gradients, and anisotropic alignments. The resulting materials possess distinct gradient, core–shell, ring, helical, or long-range alignment and enhanced anisotropic mechanical properties.
47
Niedzialek, Scott E., Gregory C. Stangle, and Yoshinari Kaieda. "Combustion-synthesized functionally gradient refractory materials." Journal of Materials Research 8, no. 8 (August 1993): 2026–34. http://dx.doi.org/10.1557/jmr.1993.2026.
Анотація:
Functionally Gradient Materials (FGM's) are soon to be used in a variety of important commercial applications; joining and thermal barrier coatings are two of the most widely studied. FGM's of the TiC/NiAl and the TiC/Ni3Al systems were fabricated using a one-step, self-propagating high-temperature synthesis (SHS) and densification method. It was observed that ignition of the starting mixture for these two systems was affected by the initial sample temperature and the external pressure that was applied to the sample during the ignition stage. Quality of the final product (e.g., porosity, grain size, cracking and microcracking, etc.) depends on a number of factors during this one-step operation. Reaction temperature control is important and is necessary to minimize residual porosity of the final product. Particle size of reactant powders, as well as applied pressure, also has an effect on the resulting microstructure. If careful reaction temperature control is achieved, along with optimum reactant powder size and applied pressure, an FGM of minimal porosity is obtained without residual macrocracks. Further, this method can easily be used to fabricate an FGM with a highly precise composition and material properties gradient. Finally, this process results in FGM's of similar quality when compared to those prepared by existing fabrication methods at only a fraction of the cost. Most importantly, it is expected that this process can be scaled up with relative ease.
48
Huang, Shufeng, Chuanshun Long, Zhihan Hu, Yingshuai Xu, Bin Zhang, and Changjian Zhi. "Thermal Performance of Heat Sink Filled with Double-Porosity Porous Aluminum Skeleton/Paraffin Phase Change Material." Micromachines 15, no. 6 (June 20, 2024): 806. http://dx.doi.org/10.3390/mi15060806.
Анотація:
Phase change materials (PCMs) are used to cool high-power-density electronic devices because of their high latent heat and chemical stability. However, their low thermal conductivity limits the application of PCMs. To solve this problem, a double-porosity porous aluminum skeleton/paraffin phase change materials (DPAS/PCM) was prepared via additive manufacturing and the water-bath method. The thermal performance of the DPAS/PCM heat sink (HS) was experimentally investigated to examine the effects of the positive- and reverse-gradient porosity structures of the DPAS/PCM. The results show that a positive-gradient porosity arrangement is more conducive to achieving a low-temperature cooling target for LED operation. In particular, the temperature control time for the positive gradient porosity structure increased by 4.6–13.7% compared with the reverse gradient porosity structure. Additionally, the thermal performances of uniform porous aluminum skeleton/paraffin (UAS) and DPAS/PCMs were investigated. The temperature control effect of the DPAS/PCM was better than that of the UAS/PCM HS at high critical temperatures. Compared with the UAS/PCM HS, the temperature control time of the DPAS/PCM HS is increased by 7.8–12.5%. The results of this work show that the prepared DPAS/PCM is a high-potential hybrid system for thermal management of high-power electronic devices.
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Sotov, Anton, Artem Kantyukov, Anatoliy Popovich, and Vadim Sufiiarov. "A Review on Additive Manufacturing of Functional Gradient Piezoceramic." Micromachines 13, no. 7 (July 17, 2022): 1129. http://dx.doi.org/10.3390/mi13071129.
Анотація:
Functionally graded piezoceramics are a new generation of engineering materials whose final properties are determined by a chemical composition gradient (volume distribution), material microstructure, or design characteristics. This review analyzes possible ways to create a functionally graded piezoceramic material (gradient chemical composition, gradient porosity—controlled and disordered porosity) by additive manufacturing methods, to control such materials’ functional characteristics. An analysis of the creation of gradient piezoceramics using binder jetting technology is presented in more detail. The review shows that today, the creation of functional gradient piezoceramics by additive manufacturing is a poorly-studied but promising research area, due to the rapid development of the additive manufacturing market and their unique features in shaping parts.
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Al-Shuhail, Abdullatif A. "Fracture-porosity inversion from P-wave AVOA data along 2D seismic lines: An example from the Austin Chalk of southeast Texas." GEOPHYSICS 72, no. 1 (January 2007): B1—B7. http://dx.doi.org/10.1190/1.2399444.
Анотація:
Vertical aligned fractures can significantly enhance the horizontal permeability of a tight reservoir. Therefore, it is important to know the fracture porosity and direction in order to develop the reservoir efficiently. P-wave AVOA (amplitude variation with offset and azimuth) can be used to determine these fracture parameters. In this study, I present a method for inverting the fracture porosity from 2D P-wave seismic data. The method is based on a modeling result that shows that the anisotropic AVO (amplitude variation with offset) gradient is negative and linearly dependent on the fracture porosity in a gas-saturated reservoir, whereas the gradient is positive and linearly dependent on the fracture porosity in a liquid-saturated reservoir. This assumption is accurate as long as the crack aspect ratio is less than 0.1 and the ratio of the P-wave velocity to the S-wave velocity is greater than 1.8 — two conditions that are satisfied in most naturally fractured reservoirs. The inversion then uses the fracture strike, the crack aspect ratio, and the ratio of the P-wave velocity to the S-wave velocity to invert the fracture porosity from the anisotropic AVO gradient after inferring the fluid type from the sign of the anisotropic AVO gradient. When I applied this method to a seismic line from the oil-saturated zone of the fractured Austin Chalk of southeast Texas, I found that the inversion gave a median fracture porosity of 0.21%, which is within the fracture-porosity range commonly measured in cores from the Austin Chalk.