Effects of Reflection and Refraction of Ultrasonic Waves on the Angle Beam Inspection of Anisotropic Composite Material

Nondestructive testing of composite materials by ultrasonic techniques has several specific features resulting from strong material anisotropy and inhomogeneity. This requires reexamination of old testing methodologies and development of new ones. The latest developments in this direction were recently reviewed by Henneke and Duke [1] and by Bar-Cohen [2]

Modeling for Ultrasonic Health Monitoring of Foams with Embedded Sensors

In this report analytical and numerical methods are proposed to estimate the effective elastic properties of regular and random open-cell foams. The methods are based on the principle of minimum energy and on structural beam models. The analytical solutions are obtained using symbolic processing software. The microstructure of the random foam is simulated using Voronoi tessellation together with a rate-dependent random close-packing algorithm. The statistics of the geometrical properties of random foams corresponding to different packing fractions have been studied. The effects of the packing fraction on elastic properties of the foams have been investigated by decomposing the compliance into bending and axial compliance components. It is shown that the bending compliance increases and the axial compliance decreases when the packing fraction increases. Keywords: Foam; Elastic properties; Finite element; Randomnes

Effect of multiaxial forging on microstructure and mechanical properties of Mg-0.8Ca alloy

It was shown that multiaxial forging with continuous decrease of temperature from 450°C to 250°C turns coarse structure of the Mg-0.8Ca alloy in homogenized state with grain size of several hundreeds μm into fine structure with average grain size of about 2.1 μm. Refinement of structure is accompanied by drastic increase of mechanical properties: tensile yield strength increases from 50 MPa to 193 MPa, ultimate tensile strength increases from 78 to 308 MPa and elongation to fracture increases from 3.0% to 7.2%. The microstructural evolution during multiaxial forging is studied using optical microscopy, scanning electron microscopy and EBSD analysis. The mechanisms responsible for refinement of microstructure are discusse

Anomalous absorption of bulk shear sagittal acoustic waves in a layered structure with viscous fluid

It is demonstrated theoretically that the absorptivity of bulk shear sagittal waves by an ultra-thin layer of viscous fluid between two different elastic media has a strong maximum (in some cases as good as 100%) at an optimal layer thickness. This thickness is usually much smaller than the penetration depths and lengths of transverse and longitudinal waves in the fluid. The angular dependencies of the absorptivity are demonstrated to have significant and unusual structure near critical angles of incidence. The effect of non-Newtonian properties and non-uniformities of the fluid layer on the absorptivity is also investigated. In particular, it is shown that the absorption in a thin layer of viscous fluid is much more sensitive to non-zero relaxation time(s) in the fluid layer than the absorption at an isolated solid-fluid interface.Comment: 14 pages, 8 figure

Scattering in flatland: Efficient representations via wave atoms

This paper presents a numerical compression strategy for the boundary integral equation of acoustic scattering in two dimensions. These equations have oscillatory kernels that we represent in a basis of wave atoms, and compress by thresholding the small coefficients to zero. This phenomenon was perhaps first observed in 1993 by Bradie, Coifman, and Grossman, in the context of local Fourier bases \cite{BCG}. Their results have since then been extended in various ways. The purpose of this paper is to bridge a theoretical gap and prove that a well-chosen fixed expansion, the nonstandard wave atom form, provides a compression of the acoustic single and double layer potentials with wave number $k$ as $O(k)$-by-$O(k)$ matrices with $O(k^{1+1/\infty})$ nonnegligible entries, with a constant that depends on the relative $\ell_2$ accuracy \eps in an acceptable way. The argument assumes smooth, separated, and not necessarily convex scatterers in two dimensions. The essential features of wave atoms that enable to write this result as a theorem is a sharp time-frequency localization that wavelet packets do not obey, and a parabolic scaling wavelength $\sim$ (essential diameter)${}^2$. Numerical experiments support the estimate and show that this wave atom representation may be of interest for applications where the same scattering problem needs to be solved for many boundary conditions, for example, the computation of radar cross sections.Comment: 39 page

Complexity Analysis of a Fast Directional Matrix-Vector Multiplication

We consider a fast, data-sparse directional method to realize matrix-vector products related to point evaluations of the Helmholtz kernel. The method is based on a hierarchical partitioning of the point sets and the matrix. The considered directional multi-level approximation of the Helmholtz kernel can be applied even on high-frequency levels efficiently. We provide a detailed analysis of the almost linear asymptotic complexity of the presented method. Our numerical experiments are in good agreement with the provided theory.Comment: 20 pages, 2 figures, 1 tabl

Computational Physics on Graphics Processing Units

The use of graphics processing units for scientific computations is an emerging strategy that can significantly speed up various different algorithms. In this review, we discuss advances made in the field of computational physics, focusing on classical molecular dynamics, and on quantum simulations for electronic structure calculations using the density functional theory, wave function techniques, and quantum field theory.Comment: Proceedings of the 11th International Conference, PARA 2012, Helsinki, Finland, June 10-13, 201

Novel HTS Strategy Identifies TRAIL-Sensitizing Compounds Acting Specifically Through the Caspase-8 Apoptotic Axis

Tumor Necrosis Factor-Related Apoptosis-Inducing Ligand (TRAIL) is potentially a very important therapeutic as it shows selectivity for inducing apoptosis in cancer cells whilst normal cells are refractory. TRAIL binding to its cognate receptors, Death Receptors-4 and -5, leads to recruitment of caspase-8 and classical activation of downstream effector caspases, leading to apoptosis. As with many drugs however, TRAIL's usefulness is limited by resistance, either innate or acquired. We describe here the development of a novel 384-well high-throughput screening (HTS) strategy for identifying potential TRAIL-sensitizing agents that act solely in a caspase-8 dependent manner. By utilizing a TRAIL resistant cell line lacking caspase-8 (NB7) compared to the same cells reconstituted with the wild-type protein, or with a catalytically inactive point mutant of caspase-8, we are able to identify compounds that act specifically through the caspase-8 axis, rather than through general toxicity. In addition, false positive hits can easily be “weeded out” in this assay due to their activity in cells lacking caspase-8-inducible activity. Screening of the library of pharmacologically active compounds (LOPAC) was performed as both proof-of-concept and to discover potential unknown TRAIL sensitizers whose mechanism is caspase-8 mediated. We identified known TRAIL sensitizers from the library and identified new compounds that appear to sensitize specifically through caspase-8. In sum, we demonstrate proof-of-concept and discovery of novel compounds with a screening strategy optimized for the detection of caspase-8 pathway-specific TRAIL sensitizers. This screen was performed in the 384-well format, but could easily be further miniaturized, allows easy identification of artifactual false positives, and is highly scalable to accommodate diverse libraries

Extrafocal transcutaneous transpedicular fixation as the stage of surgical treatment of inflammatory diseases of the spine

Trachelokyphosis and hematogenous osteomielitis of the spine are common and crippling diseases, in most cases leading to disability. Surgical treatment of inflammatory diseases of the spine is a rather complicated problem due to the fact that often in the postoperative period, an increase in spinal deformity, fracture and resorption of the transplants, festering in the area of plastics. The basis of modern surgical treatment of tuberculosis spondylitis (Pott's disease) is a radical reconstruction of the spine, including the complete removal of the damaged vertebral body abscesses, anterior decompression of the spinal cord and anterior spinal fusion The goal was to analyze the short - and long-term results of open and minimally invasive transpedicular fixation of thoracic and lumbar spine in inflammatory diseases of the spine.The material of this work based on 65 cases with tuberculosis spondylitis (Pott's disease) and nonspecific spondylitis of thoracic and lumbar segments of spine, operated in 2008-2010. In to the main group 35 patients were involved with single and double lower thoracic spine and lumbar spine lesions at the age of 25 to 70 years after surgery with minimally invasive transcutaneous transpedicular fixation (TTF). The control group included 30 patients with tuberculosis spondylitis (Pott's disease) of the thoracic and lumbar segments of spine with conventional open transpedicular internal fixation (TIF). Conclusion. Minimally invasive technology can reduce the period of preparation for surgery in patients with concomitant somatic pathology, reduce operational manuals and traumatic blood loss, trauma of a large array of soft tissue, to provide early mobilization patients despite the severity of degradation of the spine and to ensure good quality of life for a period of prolonged antibiotic and / or anti-tuberculosis therapy.Туберкулезный спондилит и гематогенный остеомиелитпозвоночника до настоящего времени остаются распространенными и калечащими заболеваниями, в большинстве случаев ведущими к инвалидности. Хирургическое лечение воспалительных заболеваний позвоночника до настоящего времени представляет достаточно сложную проблему в связи с тем, что нередко в послеоперационном периоде наблюдается увеличение деформации позвоночника, резорбция и перелом трансплантатов, нагноение в зоне пластики. Основу современного хирургического лечения туберкулезного спондилита составляет радикальная реконструкция позвоночника, включающая полное удаление разрушенных тел позвонков, абсцессов, переднюю декомпрессию спинного мозга и передний спондилодез.Цель исследования: анализ ближайших и отдаленных результатов применения открытой и малоинвазивной транспедикулярной фиксации грудного и поясничного отделов позвоночника при воспалительных заболеваниях позвоночника. Материалом для настоящей работы послужили исследования историй болезней 65 пациентов с туберкулезным и неспецифическим спондилитом грудных и поясничных сегментов, оперированных в период с 2008 по 2010 годы. В основную группу включены 35 больных с одно- и двухсегментарным поражением нижнегрудного и поясничного отделов позвоночника в возрасте от 25 до 70 лет, оперированных с применением минимально-инвазивной транскутанной транспедикулярной фиксации (ТТФ). В группу контроля включены 30 пациентов с туберкулезным спондилитом грудных и поясничных сегментов с применением традиционной открытой внутренней транспедикулярной фиксацией (ОТФ).Заключение. Минимально-инвазивная технология позволяет сократить период подготовки к операции у пациентов с сопутствующей соматической патологией, снизить травматичность оперативного пособия и кровопотерю.травматизацию большого массива мягких тканей, обеспечить раннюю активизацию пациента несмотря на выраженность деструкции позвоночника и обеспечить приемлемое качество жизни на период длительной антибактериальной и/или противотуберкулёзной терапии