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Multilevel approach for the local nanobuckling analysis of CNT-based composites
Silvestre, N.,Faria, B.,Duarte, A. Techno-Press 2012 Coupled systems mechanics Vol.1 No.3
In the present paper, a multilevel approach for the local nanobuckling analysis of carbon nanotube (CNT) based composite materials is proposed and described. The approach comprises four levels, all of them at nanoscale. The first level aims to propose the potential that describes the interatomic forces between carbon atoms. In the second level, molecular dynamics simulations are performed to extract the elastic properties of the CNT. The third level aims to determine the stiffness of the material that surrounds the CNT (matrix), using the annular membrane analysis. In the fourth level, finite strip analysis of the CNT elastically restrained by the matrix is performed to calculate the critical strain at which the CNT buckles locally. In order to achieve accurate results and take the CNT-matrix interaction into account, the $3^{rd}$ and $4^{th}$ steps may be repeated iteratively until convergence is achieved. The proposed multilevel approach is applied to several CNTs embedded in a cylindrical representative volume element and illustrated in detail. It shows that (i) the interaction between the CNT and the matrix should be taken into account and (ii) the buckling at nanoscale is sensitive to several types of local buckling modes.
Distortional buckling formulae for cold-formed steel rack-section members
N. Silvestre,D. Camotim 국제구조공학회 2004 Steel and Composite Structures, An International J Vol.4 No.1
The paper derives, validates and illustrates the application of GBT-based formulae to estimate distortional critical lengths and bifurcation stress resultants in cold-formed steel rack-section columns, beams and beam-columns with arbitrarily inclined mid-stiffeners and four support conditions. After a brief review of the Generalised Beam Theory (GBT) basics, the main concepts and procedures employed to obtain the formulae are addressed. Then, the GBT-based estimates are compared with exact results and, when possible, also with values yielded by formulae due to Lau and Hancock, Hancock and Teng et al. A few remarks on novel aspects of the rack-section beam-column distortional buckling behaviour, unveiled by the GBT-based approach, are also included.
Antonio Silvestre,Fernando Almeida,Pablo Renovell,Elena Morante,Raúl López 대한정형외과학회 2013 Clinics in Orthopedic Surgery Vol.5 No.3
Background: A two-stage revision remains as the “gold standard” treatment for chronically infected total knee arthroplasties. Methods: Forty-five septic knee prostheses were revised with a minimum follow-up of 5 years. Static antibiotic-impregnated cement spacers were used in all cases. Intravenous antibiotics according to sensitivity test of the culture were applied during patients' hospital stay. Oral antibiotics were given for another 5 weeks. Second-stage surgery was undertaken after control of infection with normal erythrocyte sedimentation rate and C-reactive protein values. Extensile techniques were used if needed and metallic augments were employed for bone loss in 32 femoral and 29 tibial revisions. Results: The average interval between the first-stage resection and reimplantation was 4.4 months. Significant improvement was obtained with respect to visual analog scale pain and clinical and functional scores, and infection was eradicated in 95.6% of cases following a two-stage revision total knee arthroplasty. Radiographic evaluation showed suitable alignment without signs of mechanical loosening. Conclusions: This technique is a reasonable procedure to eradicate chronic infection in knee arthroplasty and provides proper functional and clinical results. However, it sometimes requires extensile surgical approaches that could imply arduous surgeries. Metallic augments with cementless stems available in most of the knee revision systems are a suitable alternative to handle bone deficiencies, avoiding the use of bone allografts with its complications.
Tests for Cointegration, Cobreaking and Cotrending in a System of Trending Variables
Josep Lluis Carrion-i-Silvestre,김덕파 서강대학교 지암남덕우경제연구원 2018 시장경제연구 Vol.47 No.1
We consider a set of variables with a deterministic trend and a stochastic trend. The deterministic trend is allowed to have changes in the intercept and slope. We develop three tests, a cointegration test, a joint test for cointegration and cobreaking, and a joint test for cointegration and cotrending. Our analysis in this paper is complementary to Carrion-i-Silvestre and Kim(2017), which deals with deterministic trends with intercept shifts only.