Elevated-temperature application of the IITRI compression test fixture for graphite/polyimide filamentary composites

Seventy-nine graphite/polyimide compression specimens were tested to investigate experimentally the IITRI test method for determining compressive properties of composite materials at room and elevated temperatures (589 K (600 F)). Minor modifications were made to the standard IITRI fixture and a high degree of precision was maintained in specimen fabrication and load alignment. Specimens included four symmetric laminate orientations. Various widths were tested to evaluate the effect of width on measured modulus and strength. In most cases three specimens of each width were tested at room and elevated temperature and a polynomial regression analysis was used to reduce the data. Scatter of replicate tests and back-to-back strain variations were low, and no specimens failed by instability. Variation of specimen width had a negligible effect on the measured ultimate strengths and initial moduli of the specimens. Measured compressive strength and stiffness values were sufficiently high for the material to be considered a usable structural material at temperatures as high as 589 K (600 F)

Stress-intensity factor calculations using the boundary force method

The Boundary Force Method (BFM) was formulated for the three fundamental problems of elasticity: the stress boundary value problem, the displacement boundary value problem, and the mixed boundary value problem. Because the BFM is a form of an indirect boundary element method, only the boundaries of the region of interest are modeled. The elasticity solution for the stress distribution due to concentrated forces and a moment applied at an arbitrary point in a cracked infinite plate is used as the fundamental solution. Thus, unlike other boundary element methods, here the crack face need not be modeled as part of the boundary. The formulation of the BFM is described and the accuracy of the method is established by analyzing a center-cracked specimen subjected to mixed boundary conditions and a three-hole cracked configuration subjected to traction boundary conditions. The results obtained are in good agreement with accepted numerical solutions. The method is then used to generate stress-intensity solutions for two common cracked configurations: an edge crack emanating from a semi-elliptical notch, and an edge crack emanating from a V-notch. The BFM is a versatile technique that can be used to obtain very accurate stress intensity factors for complex crack configurations subjected to stress, displacement, or mixed boundary conditions. The method requires a minimal amount of modeling effort

Radiative Damping and Functional Differential Equations

We propose a general technique to solve the classical many-body problem with radiative damping. We modify the short-distance structure of Maxwell electrodynamics. This allows us to avoid runaway solutions as if we had a covariant model of extended particles. The resulting equations of motion are functional differential equations (FDEs) rather than ordinary differential equations. Using recently developed numerical techniques for stiff FDEs, we solve these equations for the one-body central force problem with radiative damping with a view to benchmark our new approach. Our results indicate that locally the magnitude of radiation damping may be well approximated by the standard third-order expression but the global properties of our solutions are dramatically different. We comment on the two body problem and applications to quantum field theory and quantum mechanics.Comment: (v1) 6 pages, version of Nov 22, 2007 (v2) 24 pages double-spaced. calculations and results unchanged, explanations elaborate

Boundary force method for analyzing two-dimensional cracked bodies

The Boundary Force Method (BFM) was formulated for the two-dimensional stress analysis of complex crack configurations. In this method, only the boundaries of the region of interest are modeled. The boundaries are divided into a finite number of straight-line segments, and at the center of each segment, concentrated forces and a moment are applied. This set of unknown forces and moments is calculated to satisfy the prescribed boundary conditions of the problem. The elasticity solution for the stress distribution due to concentrated forces and a moment applied at an arbitrary point in a cracked infinite plate are used as the fundamental solution. Thus, the crack need not be modeled as part of the boundary. The formulation of the BFM is described and the accuracy of the method is established by analyzing several crack configurations for which accepted stress-intensity factor solutions are known. The crack configurations investigated include mode I and mixed mode (mode I and II) problems. The results obtained are, in general, within + or - 0.5 percent of accurate numerical solutions. The versatility of the method is demonstrated through the analysis of complex crack configurations for which limited or no solutions are known

Management of infected supracondylar femoral nonunion with bone loss by primary knee arthrodesis with hybrid Ilizarov frame: a study of 10 cases

Background: Most of infected nonunion supracondylar femur with bone loss is a challenge to orthopedicians, where amputation is one of the choice. Opinions are divided on the appropriate management of infected nonunion supracondylar femur with bone loss. Evidence supports for both, osteosynthesis with or without salvaging knee joint and above knee amputation.Methods: 10 consecutive patients at Nizam’s Institute of Medical Sciences, from Jan 2013 to December 2016, who underwent limb salvage with knee arthrodesis for infected nonunion supracondylar femur with bone loss were evaluated and followed till union. Treatment option in the form of osteosynthesis with knee arthrodesis was achieved with hybrid Ilizarov fine wire fixator. The hybrid Ilizarov frame comprised of conventional two ring tibial frame and one ring and one Italian arch in the femoral segment with half treaded pins, this construct was chosen because of less weight, less cumbersome without compromising the stability and basic features.Results: All patients went for solid knee arthrodesis in functional position, with a mean fusion time of 22.4 ± 4.97 weeks. The time interval between primary surgery and definitive treatment was 15.6 ± 6.37 weeks. The mean shortening of lower limb was 3.1±1.19 cms. To achieve arthrodesis quickly, it’s necessary to have light weight, compact Ilizarov frame, have good bone to bone contact and allow early full weight bearing. Conclusions: Osteosynthesis with knee arthrodesis in cases of infected nonunion supracondylar femur with bone loss is a viable option in select cases where the patient is physiologically young, has undergone several procedures around the knee and the knee is stiff. Fusion of the knee enables quick restoration of the patient to his work place

A re-evaluation of finite-element models and stress-intensity factors for surface cracks emanating from stress concentrations

A re-evaluation of the 3-D finite-element models and methods used to analyze surface crack at stress concentrations is presented. Previous finite-element models used by Raju and Newman for surface and corner cracks at holes were shown to have ill-shaped elements at the intersection of the hole and crack boundaries. These ill-shaped elements tended to make the model too stiff and, hence, gave lower stress-intensity factors near the hole-crack intersection than models without these elements. Improved models, without these ill-shaped elements, were developed for a surface crack at a circular hole and at a semi-circular edge notch. Stress-intensity factors were calculated by both the nodal-force and virtual-crack-closure methods. Both methods and different models gave essentially the same results. Comparisons made between the previously developed stress-intensity factor equations and the results from the improved models agreed well except for configurations with large notch-radii-to-plate-thickness ratios. Stress-intensity factors for a semi-elliptical surface crack located at the center of a semi-circular edge notch in a plate subjected to remote tensile loadings were calculated using the improved models. The ratio of crack depth to crack length ranged form 0.4 to 2; the ratio of crack depth to plate thickness ranged from 0.2 to 0.8; and the ratio of notch radius to the plate thickness ranged from 1 to 3. The models had about 15,000 degrees-of-freedom. Stress-intensity factors were calculated by using the nodal-force method

Protective effect of ethanolic leaf extract of Alphonsea sclerocarpa against ethylene glycol induced urolithiasis in rats

Alphonsea sclerocarpa Thwaites belonging to the family Annonaceae is a small tree, which grows up to 10-15 m tall the leaves are simple and alternate. Despite its medicinal properties the plant seems to be less explored and hence this research aims at exploring the antiurolithiatic activity of ethanolic leaf extract of A. sclerocarpa on ethylene glycol induced urolithiasis in rats. A. sclerocarpa leaf powder was extracted using ethanol. The effect of ethanolic leaf extract of A. sclerocarpa (250 and 500 mg/kg, p.o.) was studied in experimentally induced renal stone in rats by in vivo model. Ethylene glycol model (0.75% in drinking water, for 28 days) was used for renal stone induction. The blood, urine and kidney samples were used for various parameters. The concentration of calcium, oxalate, phosphorus, creatinine and blood urea nitrogen was observed in each group. The phytochemical analysis was carried out to detect the presence of secondary metabolites like saponins and flavonoids in the ethanolic extract of A. sclerocarpa leaf extract. In ethylene glycol (0.75% v/v) treated animal model ethanolic extract of A. sclerocarpa leaf extract showed significant results on stone promoters (calcium oxalate, inorganic phosphate and sodium), kidney function parameters (uric acid, blood urea nitrogen, creatinine). On the basis of biochemical parameters and histopathological study it was confirmed that A. sclerocarpa leaf extract protected the renal cells from oxidative stress and injury induce by calcium oxalate crystals. The investigation of ethanolic extract of A. sclerocarpa leaf has shown promising antiurolithiatic activity and support folklore claims of these plants as antiurolithiatic. The mechanism of action of these plants for antiurolithiatic is apparently related to increased diuresis and lowering of urinary concentrations of stone-forming constituents, though it should be confirmed by the extensive exploratory studies

Dufour and Thermal Radiation Effects of Kuvshinski Fluid on Double Diffusive and Convective MHD Heat and Mass Transfer Flow Past a Porous Vertical Plate in the Presence of Radiation Absorption, Viscous Dissipation and Chemical Reaction

In this paper an analysis is presented to investigate the influence of diffusion thermo, thermal radiation, radiation absorption, chemical reaction and viscous dissipation on hydro magnetic free convective heat and mass transfer flow of Kuvshinski fluid past a porous vertical plate. A uniform magnetic field of is applied in the direction of the flow field.  Analytical solutions for velocity, temperature and concentration are obtained by using a Perturbation technique. Skin friction, rate of heat and mass transfer coefficients are also derived. The results have been analyzed graphically and numerically for various values of the flow parameters

Counting Giant Gravitons in AdS_3

We quantize the set of all quarter BPS brane probe solutions in global AdS_3 \times S^3 \times T^4/K3 found in arxiv:0709.1168 [hep-th]. We show that, generically, these solutions give rise to states in discrete representations of the SL(2,R) WZW model on AdS_3. Our procedure provides us with a detailed description of the low energy 1/4 and 1/2 BPS sectors of string theory on this background. The 1/4 BPS partition function jumps as we move off the point in moduli space where the bulk theta angle and NS-NS fields vanish. We show that generic 1/2 BPS states are protected because they correspond to geodesics rather than puffed up branes. By exactly quantizing the simplest of the probes above, we verify our description of 1/4 BPS states and find agreement with the known spectrum of 1/2 BPS states of the boundary theory. We also consider the contribution of these probes to the elliptic genus and discuss puzzles, and their possible resolutions, in reproducing the elliptic genus of the symmetric product.Comment: 47 pages; (v2) references and minor clarifications adde