Connection between electrical conductivity and diffusion coefficient of a conductive porous material filled with electrolyte

The paper focuses on the cross-property connection between the effective electrical conductivity and the overall mass transfer coefficient of a two phase material. The two properties are expressed in terms of the tortuosity parameter which generalized to the case of a material with two conductive phases. Elimination of this parameter yields the cross-property connection. The theoretical derivation is verified by comparison with computer simulation

Effect of spherical pores coalescence on the overall conductivity of a material

The problem about steady-state temperature distribution in a homogeneous isotropic medium containing a pore or an insulating inhomogeneity formed by two coalesced spheres of the same radius, under arbitrarily oriented uniform heat flux, is solved analytically. The limiting case of two touching spheres is analyzed separately. The solution is obtained in the form of converged integrals that can be calculated using Gauss-Laguerre quadrature rule. The temperature on the inhomogeneity’s surface is used to determine components of the resistivity contribution tensor for the insulating inhomogeneity of the mentioned shape. An interesting observation is that the extreme values of these components are achieved when the spheres are already slightly coalesce

Effective thermal conductivity of oolitic rocks using the Maxwell homogenization method

International audienceThe present work focuses on effective thermal conductivity of oolitic lime-stones, characterized by an assemblage of porous grains (oolites), mesopores and solid grains. Two distinct scales of pores, micropores or intra oolitic pores and mesopores or inter oolitic pores are taken into account. At the first step, micropores are homogenized inside the oolites by using self consistent homogenization scheme. The second homogenization step describing transition from the mesoscale to the macroscale, is performed by using a recent reformulation of the Maxwell homogenization scheme (see [1]). At the mesoscale, porous oolitic inclusions are quasi spherical whereas two families of mesopores are considered according to analysis of photomicrographs: (1) randomly oriented oblate spheroidal pores and (2) concave pores. The proposed model is compared to a simplified one when all the pores are of ellipsoidal shape. The relevancy of the ellipsoidal approximation is then evaluated. In particular, the influence of the shape of the mesopores on the overall thermal conductivity is discussed. Comparisons between multi-scale model based on Maxwell homogenization method and experimental data show that effects of porosity and saturating fluids on overall conductivity are correctly predicted when concave pores are taken into account

Effective properties of ageing linear viscoelastic media with spheroidal inhomogeneities

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Maxwell homogenization scheme for piezoelectric composites with arbitrarily-oriented spheroidal inhomogeneities

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Development and examination of high-performance fluidised bed vibration drier for processing food production waste

Drying and processing wet particulate food production waste, such as distillery dreg, brewer's grains, beet pulp, spent coffee and barley slurry etc. for their further use as cattle fodder or fuel is an important and topical problem, which needs effective solutions. As a solution of the problem, the authors have developed improved equipment and a fluidised bed vibration drier, which ensures reaching the required output of the work process and final moisture content in the waste at a minimum power and material intensity and features the combination of the high feasibility with the high reliability of design. In order to validate the improved drying work process together with the optimum parameters of the vibration drier, theoretical investigations based on the mathematical model of the process developed by the authors have been carried out. The process of the vibration drier’s frame oscillating together with the waste has been examined, which has resulted in the generation of the differential equation that analytically describes the said process. The work process under consideration has been researched into from the thermophysical point of view using the specific initial data typical for the specific food producer. The research has resulted in obtaining the following design and process parameters of the vibration drier, in particular, for its heating pipes: diameter rt = 0.1 m; length lt = 5 m; number nt = 20, heat-transfer factor Kp = 30 and the final temperature of the dried food production waste to2 = 80 °C. The listed parameters provide for reaching the required final moisture content in the dried food production waste. Also, new relations have been generated for determining the principal process parameters of the improved drier (productive capacity, heat consumption, mass of heat carrier, waste conveyance speed, sizes and masses of the drier’s actuating elements). The obtained relations can be applied in the further theoretical and experimental research on the drier as well as the development of standard methods for its design and calculation

Effect of Saturation on the Viscoelastic Properties of Dentin

This paper focuses on the analysis and quantitative characterization of the effect of saturation on the viscoelastic properties of human root dentin. Uniaxial compression tests under creep conditions have been performed on root molar dentin with tubules fully saturated with a viscous physiological fluid, as well as samples with non-saturated tubules (dry dentin samples). Blair-Rabotnov (BR) fraction-exponential model is used to characterize the overall viscoelastic properties of dentin and correlate them to the level of saturation. Experimental data are compared with theoretical predictions that interrelate the viscoelastic properties of saturated and dry specimens. The results show that saturation increases the viscous creep strains of dentin, which indicates a reduced capacity for stress relief. The uniaxial compression test under creep conditions, in combination with the BR kernel model, allows us to analyze the creep-relaxation behavior of dentin. © 2020 Elsevier Ltd.TC, SS, and IS gratefully acknowledge financial support from National Institute of Health (USA), grant 2R25GM061222-18 . DZ, PP, and MYG gratefully acknowledge financial support from Russian Foundation for Basic Research (Russia), research project No. 18-38-20097

Connecting Diffraction Based Strain with Macroscopic Stresses in Laser Powder Bed Fused Ti 6Al 4V

The laser powder bed fusion LPBF production process often results in large residual stress RS in the parts. Nondestructive techniques to determine RS are badly needed. However, a reliable quantification of macro RS i.e., stress at the component level by means of diffraction based techniques is still a great challenge, because the link between diffraction based strain and macro RS is not trivial. In this study, we experimentally determine by means of in situ synchrotron radiation diffraction this link for LPBF Ti 6Al 4V. We compare our results with commonly used models to determine the so called diffraction elastic constants DECs . We show that LPBF materials possess different DECs than wrought alloys, simply because their microstructural and mechanical properties are different. We also show that the existing models can be used to calculate DECs only if high accuracy of the RS values is not required. If the peculiarities of the microstructure have to be taken into account as is the case of additively manufactured materials , a radically new approach is desirabl

ВЛИЯНИЕ АЛЛОГЕННЫХ МУЛЬТИПОТЕНТНЫХ МЕЗЕНХИМАЛЬНЫХ СТРОМАЛЬНЫХ КЛЕТОК КОСТНОГО МОЗГА НА ФОРМИРОВАНИЕ ПРОТИВОИШЕМИЧЕСКОЙ РЕЗИСТЕНТНОСТИ ПОЧЕК

Аim of this work was to study the influence of intravenous injection times of bone marrow allogeneic multipotent mesenchymal stromal cells (BM MMSCs) on kidney function and morphology in modeled ischemicreperfusion injury of kidney (IRIK). Materials and methods. The study was conducted on 90 male Wistar rats. On the original IRI model of a single kidney (60 min, warm ischemia) 4 groups of experiments were performed: in the first group the dose of 5 × 106 of BM MMSCs was administered intravenously 14 days before IRIK modeling; in the second group, the same dose of BM MMSCs was administered 7 days before IRIK; in the third group, the same dose of BM MMSCs was administered during kidney reperfusion after IRIK modeling; the fourth group served as the control group (IRIK without BM МMSCs). The study duration was 21 days since the start of IRIK modeling. In all groups the nitrogen secretory function of kidneys was examined and the histological condition of kidneys during the entire recovery period was evaluated. Besides, blood of rats of the first and the fourth groups was examined for proand anti-inflammatory cytokine levels and phagocytosis indices using the suspension of inactivated St. aureus. The significance of differences in these two groups was evaluated by Student's test at p < 0.05. Results. It has been demonstrated that the pretreatment with BM MMSCs (1 and 2 weeks before IRIK modeling) increased the anti-ischemic resistance of kidney while the administration of BM MMSCs on the day of IRIK modeling (during reperfusion) enhanced kidney damage, characterized by increased mortality, elevated levels of urea and creatinine in blood and structural injury of renal tissue, as compared to other groups. The comparative analysis of the first and fourth groups shows that BM MMSCs decrease the levels of pro-inflammatory cytokines and increase the levels of anti-inflammatory cytokines, as well as enhance potential of antimicrobial protection. Conclusion. Intravenous injection of BM MMSCs 1–2 weeks prior to IRIK modeling increases the kidney resistance to ischemia, reduces the severity of the systemic inflammatory response as well as the risk of infectious complications. However, considering the possibility of the summation of the injuring influence of ischemia and the stress of the adapting doses of BM MMSCs on ischemic kidney tissue during reperfusion, the search for the optimal concentrations of BM MMSCs needs to be continued. Цель работы – изучить влияние сроков внутривенного введения аллогенных мультипотентных мезенхимальных стромальных клеток костного мозга (ММСК КМ) на функциональное и морфологическое состояние почки при моделировании ишемически-реперфузионного повреждения почки (ИРПП). Материалы и методы. Исследование выполнено на 90 крысах – самцах породы Вистар. На модели ИРП единственной почки (60 мин тепловой ишемии) выполнено 4 группы опытов: в 1-й группе – за 14 сут до ИРПП внутривенно вводили ММСК КМ в дозе 5 × 106 клеток; во 2-й группе ММСК КМ в той же дозе вводили за 7 сут до ИРПП; в 3-й группе ММСК КМ в той же дозе вводили во время реперфузии почки после моделирования ИРПП; 4-я группа служила контролем (ИРПП без ММСК КМ). Продолжительность эксперимента – 21 сут с момента начала моделирования ИРПП. Во всех группах опытов исследовали азотовыделительную функцию почек и оценивали их гистологическое состояние в течение всего восстановительного периода. Кроме того, у крыс 1-й и 4-й групп в сыворотке крови исследовали уровень прои противовоспалительных цитокинов и показатели фагоцитоза с помощью взвеси нежизнеспособных St. aureus. Достоверность различий в сравниваемых группах оценивали по критерию Стьюдента при р < 0,05. Результаты. Показано, что предварительное введение ММСК КМ (за 1–2 нед. до моделирования ИРПП) повышает противоишемическую резистентность почки, тогда как введение ММСК КМ в день моделирования ИРПП (на этапе реперфузии) усиливает процессы повреждения почки: повышает летальность, содержание креатинина и мочевины в крови и деструкцию почечной ткани по сравнению с другими группами. Из сравнительного анализа 1-й и 4-й группы животных следует, что ММСК КМ снижают уровень провоспалительных и повышают уровень противовоспалительных цитокинов, а также повышают потенциал противомикробной защиты организма. Выводы. Внутривенное введение ММСК КМ в организм за 1–2 нед. до моделирования ИРПП повышает резистентность почки к ишемии, снижает выраженность системной воспалительной реакции, а также опасность развития инфекционных осложнений. Однако, учитывая возможность суммации повреждающего воздействия ишемии и стрессорного воздействия адаптирующих доз ММСК КМ на ткань ишемизированной почки в реперфузионном периоде, поиск оптимальных концентраций ММСК КМ для обеспечения противоишемической резистентности почки на этапе реперфузии должен быть продолжен.