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排序方式: 共有4713条查询结果,搜索用时 9 毫秒
61.
Sébastien Hentz Laurent Daudeville Frédéric V. Donzé 《Canadian Metallurgical Quarterly》2004,130(6):709-719
The use of a three-dimensional discrete element method (DEM) is proposed to study concrete structures submitted to dynamic loading. The aim of this paper is to validate the model first in the quasistatic domain, and second in dynamic compression, at the sample scale. A particular growing technique is used to set a densely packed assembly of arbitrarily sized spherical particles interacting together, representing concrete. An important difference from classical DEMs where only contact interactions are considered, is the use of an interaction range. First, the correct identification of parameters of the DEM model to simulate elastic and nonlinear deformation including damage and rupture is made through quasistatic uniaxial compression and tension tests. The influence of the packing is shown. The model produces a quantitative match of strength and deformation characteristics of concrete in terms of Young’s modulus, Poisson’s coefficient, and compressive and tensile strengths. Then, its validity is extended through dynamic tests. The simulations exhibit complex macroscopic behaviors of concrete, such as strain softening, fractures that arise from extensive microcracking throughout the assembly, and strain rate dependency. 相似文献
62.
63.
Natacha Kalline de Oliveira Lucyene Miguita Tais Helena Costa Salles Marcos Akira d’Ávila Márcia Martins Marques Maria Cristina Zindel Deboni 《Journal of Materials Science》2018,53(23):15757-15768
The aim of this study was to analyze the influence of nanoporous structure of polymeric biomaterials on the in vitro osteogenic induction of human stem cells. An electronic search in three databases (MEDLINE, SCOPUS, and Web of Science) was performed for articles that were published before May 2018. In vitro studies were included if they met the following criteria: (1) the use of polymeric scaffolds (natural or synthetic); (2) the co-culture of human stem cells with the scaffold; and (3) cell viability, proliferation, and osteogenic differentiation assays. The main characteristics of the published studies were summarized, and a quality assessment tool was used to analyze methodological features. Eighty-eight potential articles were firstly retrieved. Thirteen were eligible for qualitative analysis. Only three studies characterized cell stemness. Nanostructure of the scaffolds showed a significant influence on viability, proliferation, and osteogenic differentiation of human stem cells. Combination of porosity between 72 and 93% and a large range diameter between 50 and 224 μm resulted in more remarkable cellular proliferation and differentiation. Porous polymeric scaffolds can be functionalized by stem cells leading to osteogenic induction. High standards of laboratory practice and accurate methodological reporting are essential for the credibility of the results. 相似文献
64.
65.
Elena Bonetti Giovanna Bonfanti Frédéric Lebon 《Computers & Mathematics with Applications》2019,77(11):2906-2916
In this paper we introduce a model describing a layered structure composed by two thermoelastic adherents and a thin adhesive subject to a degradation process. By an asymptotic expansion method, we derive a model of imperfect interface coupling damage and temperature evolution. Moreover, assuming that the behaviour of the adhesive is ruled by two different regimes, one in traction and one in compression, we derive a second limit model where unilateral contact conditions on the interface are also included. 相似文献
66.
Maciej Dulewicz Agnieszka Kulczyska-Przybik Piotr Mroczko Johannes Kornhuber Piotr Lewczuk Barbara Mroczko 《International journal of molecular sciences》2022,23(15)
Alzheimer’s disease (AD) is a progressive condition and the most common cause of dementia worldwide. The neuropathological changes characteristic of the disorder can be successfully detected before the development of full-blown AD. Early diagnosis of the disease constitutes a formidable challenge for clinicians. CSF biomarkers are the in vivo evidence of neuropathological changes developing in the brain of dementia patients. Therefore, measurement of their concentrations allows for improved accuracy of clinical diagnosis. Moreover, AD biomarkers may provide an indication of disease stage. Importantly, the CSF biomarkers of AD play a pivotal role in the new diagnostic criteria for the disease, and in the recent biological definition of AD by the National Institute on Aging, NIH and Alzheimer’s Association. Due to the necessity of collecting CSF by lumbar puncture, the procedure seems to be an important issue not only from a medical, but also a legal, viewpoint. Furthermore, recent technological advances may contribute to the automation of AD biomarkers measurement and may result in the establishment of unified cut-off values and reference limits. Moreover, a group of international experts in the field of AD biomarkers have developed a consensus and guidelines on the interpretation of CSF biomarkers in the context of AD diagnosis. Thus, technological advancement and expert recommendations may contribute to a more widespread use of these diagnostic tests in clinical practice to support a diagnosis of mild cognitive impairment (MCI) or dementia due to AD. This review article presents up-to-date data regarding the usefulness of CSF biomarkers in routine clinical practice and in biomarkers research. 相似文献
67.
Mateusz Sypniewski Zbigniew J. Krl Joanna Szyda Elbieta Kaja Magdalena Mroczek Tomasz Suchocki Adrian Lejman Maria Stpie Piotr Topolski Maciej Dbrowski Krzysztof Kotlarz Angelika Aplas Micha Wasiak Marzena Wojtaszewska Pawe Zawadzki Agnieszka Pawlak Robert Gil Paula Dobosz Joanna Stojak 《International journal of molecular sciences》2022,23(15)
Background: Severe outcomes of COVID-19 account for up to 15% of all cases. The study aims to check if any gene variants related to cardiovascular (CVD) and pulmonary diseases (PD) are correlated with a severe outcome of COVID-19 in a Polish cohort of COVID-19 patients. Methods: In this study, a subset of 747 samples from unrelated individuals collected across Poland in 2020 and 2021 was used and whole-genome sequencing was performed. Results: The GWAS analysis of SNPs and short indels located in genes related to CVD identified one variant significant in COVID-19 severe outcome in the HADHA gene, while for the PD gene panel, we found two significant variants in the DRC1 gene. In this study, both potentially protective and risk variants were identified, of which variants in the HADHA gene deserve the most attention. Conclusions: This is the first study reporting the association between the HADHA and DRC1 genetic variants and COVID-19 severe outcome based on the cohort WGS analysis. Although all the identified variants are localised in introns, they may be correlated and therefore inherited along with other risk variants, potentially causative to severe outcome of COVID-19 but not discovered yet. 相似文献
68.
Product development involves many experts collaborating to the same design goal. Every expert has his own formalisms and tools leading to a high heterogeneity of information systems supporting design activities. Interoperability became a major challenge to avoid information incompatibility along the product life cycle. To synchronise heterogeneous representations of product will be a major step to integrate expert activities. In this paper, the authors propose a meta-model framework to connect together heterogeneous design models. This meta-model framework is used to formalise possible interactions between heterogeneous representations. Interaction formalisation is considered as a key point to synchronise heterogeneous models and to provide more interoperability between various computer assisted systems. The synchronisation loop is also presented as a major sequence of activities to manage collaborative design. Tools to support synchronisation are proposed. However, through a basic case study, authors highlight what can be automated and where human intervention is still expected. 相似文献
69.
T. Czyżewski 《Wear》1975,34(2):201-214
The rolling contact fatigue life of modified NU 209 roller bearing inner races subjected to tensile stress mechanically induced in the contact zone, has been investigated using the four-contact fatigue machine.A high tensile stress of 80 MN/m2 by a clamp pressure, acting on the inner surface of the specimen, has a catastrophic effect on fatigue life; all specimens burst earlier than pitting failure would have occurred at a near zero tensile stress level.A theoretical study of the influence of the axi-symmetrical stress field, induced by the steady pressure applied inside the hollow rotating cylinder on the stress distribution in the e.h.d. contact zone of cylinders showed a significant increase of the resultant shear stresses caused by tension. The pure shear stress state may exist in the contact zone when the tensile stress level is high. 相似文献
70.
Anna Ciechanowska Ilona M. Gora Stanislawa Sabalinska Piotr Ladyzynski 《International journal of molecular sciences》2022,23(12)
Diabetes mellitus causes endothelial dysfunction. The aim of this study was to investigate the effect of normal (5 mmol/L), high (20 mmol/L), and fluctuating (5 and 20 mmol/L changed every day) glucose concentration in the culture medium on the viability of human umbilical vein endothelial cells (HUVECs) co-cultured with human umbilical artery smooth muscle cells (HUASMCs). The cultures were conducted on semi-permeable flat polysulfone (PSU) fibronectin-coated membranes immobilized in self-made inserts. The insert contained either HUVECs on a single membrane or HUASMCs and HUVECs on two membranes close to each other. Cultures were conducted for 7 or 14 days. Apoptosis, mitochondrial potential, and the production of reactive oxygen species and lactate by HUVECs were investigated. The results indicate that fluctuations in glucose concentration have a stronger negative effect on HUVECs viability than constant high glucose concentration. High and fluctuating glucose concentrations slow down cell proliferation compared to the culture carried out in the medium with normal glucose concentration. In conclusion, HUASMCs affect the viability of HUVECs when both types of cells are co-cultured in medium with normal or variable glucose concentration. 相似文献