Comparative study of time and frequency domain BEM approaches in frictional contact problem for antiplane crack under harmonic loading

International audienceTwo different boundary element methods (BEM) for crack analysis in two dimensional (2 D) antiplane, homogeneous, isotropic and linear elastic solids by considering frictional contact of the crack edges are presented. Hypersingular boundary integral equations (BIE) in time domain (TD) and frequency domain (FD), with corresponding elastodynamic fundamental solutions are applied for this purpose. For evaluation of the hypersingular integrals involved in BIEs a special regularization process that converts the hypersingular integrals to regular integrals is applied. Simple regular formulas for their calculation are presented. For the problems solution while considering frictional contact of the crack edges a special iterative algorithm of Udzava's type is elaborated and used. Numerical results for crack opening, frictional contact forces and dynamic stress intensity factors (SIFs) are presented and discussed for a finite III mode crack in an infinite domain subjected to a harmonic crack face loading and considering crack edges frictional contact interaction using the TD and FD approaches

Expression of genes belonging to the IGF-system in glial tumors

The discrepancies arising from conflicting evidence on the results obtained by different laboratories in human gliomas are discussed. Our data highlight the importance of viewing the IGF-related proteins as a complex multifactorial system and show that changes in the expression levels of any one component of the system, in a given malignancy, should be interpreted with caution. As IGF targeting for anticancer therapy is rapidly becoming clinical reality, an understanding of this complexity is very timely.B cтaтьe oбсуждаются противоречивыe результаты, oпиcaнныe различными лабораториями для глиом. Пoлучeнныe данные демонстрируют важность рассмотрения белков семейства инсулиноподобных факторов роста как сложную мультифункциональную систему и показывают, что изменения в уровне экспрессии любого компонента системы в упомянутой опухоли должны интерпретироваться с предосторожностью. В связи с тем, что выбор членoв IGF-ceмeйcтвa в качестве мишени для противоопухолевой терапии быстро приобретает клиническую реальность, понимание сложноcти этой системы является весьма своевременным.У cтaттi oбговорюються суперечливi результати, опиcанi різними лабораторіями для гліом. Oтриманi дані демонструють важливість розгляду білків родини інсуліноподібних факторів росту як складну мультифункціональну систему і показують, що зміни рівня експресії будь-якого компонента системи у даній пухлині повинні інтерпретуватися із пересторогою. В зв’язку з тим, що вибір членiв IGF-ciмeйcтвa як мішені для протипухлинної терапії швидко набуває клінічної реальності, розуміння цієї системи є вельми своєчасним

X-wave mediated instability of plane waves in Kerr media

Plane waves in Kerr media spontaneously generate paraxial X-waves (i.e. non-dispersive and non-diffractive pulsed beams) that get amplified along propagation. This effect can be considered a form of conical emission (i.e. spatio-temporal modulational instability), and can be used as a key for the interpretation of the out of axis energy emission in the splitting process of focused pulses in normally dispersive materials. A new class of spatio-temporal localized wave patterns is identified. X-waves instability, and nonlinear X-waves, are also expected in periodical Bose condensed gases.Comment: 4 pages, 6 figure

Nonlocal theory of curved rods. 2-D, high order, Timoshenko’s and Euler-Bernoulli models

New models for plane curved rods based on linear nonlocal theory of elasticity have been developed. The 2-D theory is developed from general 2-D equations of linear nonlocal elasticity using a special curvilinear system of coordinates related to the middle line of the rod along with special hypothesis based on assumptions that take into account the fact that the rod is thin. High order theory is based on the expansion of the equations of the theory of elasticity into Fourier series in terms of Legendre polynomials. First, stress and strain tensors, vectors of displacements and body forces have been expanded into Fourier series in terms of Legendre polynomials with respect to a thickness coordinate. Thereby, all equations of elasticity including nonlocal constitutive relations have been transformed to the corresponding equations for Fourier coefficients. Then, in the same way as in the theory of local elasticity, a system of differential equations in terms of displacements for Fourier coefficients has been obtained. First and second order approximations have been considered in detail. Timoshenko’s and Euler-Bernoulli theories are based on the classical hypothesis and the 2-D equations of linear nonlocal theory of elasticity which are considered in a special curvilinear system of coordinates related to the middle line of the rod. The obtained equations can be used to calculate stress-strain and to model thin walled structures in micro- and nanoscales when taking into account size dependent and nonlocal effects

Micropolar curved rods. 2-D, high order, Timoshenko’s and Euler-Bernoulli models

New models for micropolar plane curved rods have been developed. 2-D theory is developed from general 2-D equations of linear micropolar elasticity using a special curvilinear system of coordinates related to the middle line of the rod and special hypothesis based on assumptions that take into account the fact that the rod is thin.High order theory is based on the expansion of the equations of the theory of elasticity into Fourier series in terms of Legendre polynomials. First stress and strain tensors,vectors of displacements and rotation and body force shave been expanded into Fourier series in terms of Legendre polynomials with respect to a thickness coordinate.Thereby all equations of elasticity including Hooke’s law have been transformed to the corresponding equations for Fourier coefficients. Then in the same way as in the theory of elasticity, system of differential equations in term of displacements and boundary conditions for Fourier coefficients have been obtained. The Timoshenko’s and Euler-Bernoulli theories are based on the classical hypothesis and 2-D equations of linear micropolar elasticity in a special curvilinear system. The obtained equations can be used to calculate stress-strain and to model thin walled structures in macro, micro and nano scale when taking in to account micropolar couple stress and rotation effects

Couple stress theory of curved rods. 2-D, high order, Timoshenko’s and Euler-Bernoulli models

New models for plane curved rods based on linear couple stress theory of elasticity have been developed.2-D theory is developed from general 2-D equations of linear couple stress elasticity using a special curvilinear system of coordinates related to the middle line of the rod as well as special hypothesis based on assumptions that take into account the fact that the rod is thin. High order theory is based on the expansion of the equations of the theory of elasticity into Fourier series in terms of Legendre polynomials. First, stress and strain tensors, vectors of displacements and rotation along with body forces have been expanded into Fourier series in terms of Legendre polynomials with respect to a thickness coordinate.Thereby, all equations of elasticity including Hooke’s law have been transformed to the corresponding equations for Fourier coefficients. Then, in the same way as in the theory of elasticity, a system of differential equations in terms of displacements and boundary conditions for Fourier coefficients have been obtained. Timoshenko’s and Euler-Bernoulli theories are based on the classical hypothesis and the 2-D equations of linear couple stress theory of elasticity in a special curvilinear system. The obtained equations can be used to calculate stress-strain and to model thin walled structures in macro, micro and nano scales when taking into account couple stress and rotation effects

Surgical aspects for clipping arterial aneurysms of the middle cerebral artery

Objective – to improve the methods of surgical treatment arterial aneurysms (AA) of the middle cerebral artery (MCA). Materials and methods. This work is performed on the material of 112 patients with MCA aneurysms. Patients were treated at Academician A.P. Romodanov Neurosurgery Institute in the period from 2012 to 2015. The age of patients – from 32 to 72 years, the mean age of patients was (49.3 ± 2.5) years. Most of the patients (66.7 %) were in the age group 41-60 years. Concerning the results, they were evaluated according to the radical exclusion of AA MCA from the blood flow at different periods of hemorrhage. Results. In 95.7 % patients operated during the acute period of hemorrhage, a total exclusion of aneurysms has been achieved. The differences for total clipping of AA MCA in different periods of rupture and in its absence were statistically insignificant (p > 0.05). Conclusions. Criteria for choosing to perform microsurgical treatment MCA AA are morphometric criteria for wide neck aneurysms, the ratio of the neck to the body 1:3, the size of AA less than 3 mm, the presence of intracerebral hematoma with the existing mass effect, the incorporation one of the branches of the MCA into the wall of the dome AA. It is also necessary to take into the general criteria of neurosurgical data, depending on the general condition of the patient, the clinical course of the disease, topographic and anatomical X-rays features of the structure of AA, taking into account these neuroimaging methods (CT, CTA, DSA)