Stress intensity factors for deep cracks emanating from the corner formed by a hole intersecting a plate surface

A technique consisting of freezing photo-elasticity and a numerical method was used to obtain stress intensity factors for natural cracks emanating from the corner at which a hole intersects a plate surface. Geometries studied were: (1) crack depth to thickness ratios of approximately 0.2, (2) 0.5 and 0.75; (3) crack depth to crack length ratios of approximately 1.0 to 2.0; and (4) crack length to hole radius ratios of about 0.5 to 2.0. All final crack geometries were grown under monotonic loading and growth was not self similar, with most of the growth occuring through the thickness under remote extension. Stress intensity factors were determined at the intersection of the flaw border

Stress intensity factors for deep cracks emanating from the corner formed by a hole intersecting a plate surface

A technique consisting of a marriage between stress freezing photoelasticity and a numerical method was used to obtain stress intensity factors for natural cracks emanating from the corner at which a hole intersects a plate surface. Geometrics studied were: crack depth to thickness ratios of approximately 0.2, 0.5, and 0.75; crack depth to crack length ratios of approximately 1.0 to 2.0. All final crack geometries were grown under monotonic loading and growth was not self similar with most of the growth occurring through the thickness under remote extension. Stress intensity plate surface K sub s factors were determined at the intersection of the flaw border with the plate surface K sub s and with the edge of the hole K sub h. Results showed that for the relatively shallow flaws K sub h approximately equal to 1.5 K sub s, for the moderately deep flaws K sub h approximately equal to K sub s, and for the deep flaws K sub h approximately equal to 0.5 K sub s, revealing a severe sensitivity of K to flaw geometry

A plane strain analysis of the blunted crack tip using small strain deformation plasticity theory

A deformation plasticity analysis of the tip region of a blunted crack in plane strain is presented. The power hardening material is incompressible both elastically and plastically, in order to simulate behavior of a stress freezing material above critical temperature. Stress and displacement fields surrounding the crack tip are presented. The results indicate that the maximum stress seen at the crack tip is indeed limited and is determined by the tensile properties; however, the scale over which the stresses act is dependent on the loading. Comparisons are good between the forward crack tip displacement and micro-fractographic measurments of stretch zones observed in plane strain fracture toughness tests

Refusing to Endorse. A must Explanation for Pejoratives.

In her analysis of pejoratives, Eva Picardi rejects a too sharp separation between descriptive and expressive content. I reconstruct some of her arguments, endorsing Eva’s criticism of Williamson’s analysis of Dummett and developing a suggestion by Manuel Garcia Carpintero on a speech act analysis of pejoratives. Eva’s main concern is accounting for our instinctive refusal to endorse an assertion containing pejoratives because it suggests a picture of reality we do not share. Her stance might be further developed claiming that uses of pejoratives not only suggest, but also promote a wrong picture of reality. Our refusal to endorse implies rejecting not only a wrong picture of reality but also a call for participation to what that picture promotes

Leading-edge slat optimization for maximum airfoil lift

A numerical procedure for determining the position (horizontal location, vertical location, and deflection) of a leading edge slat that maximizes the lift of multielement airfoils is presented. The structure of the flow field is calculated by iteratively coupling potential flow and boundary layer analysis. This aerodynamic calculation is combined with a constrained function minimization analysis to determine the position of a leading edge slat so that the suction peak on the nose of the main airfoil is minized. The slat position is constrained by the numerical procedure to ensure an attached boundary layer on the upper surface of the slat and to ensure negligible interaction between the slat wake and the boundary layer on the upper surface of the main airfoil. The highest angle attack at which this optimized slat position can maintain attached flow on the main airfoil defines the optimum slat position for maximum lift. The design method is demonstrated for an airfoil equipped with a leading-edge slat and a trailing edge, single-slotted flap. The theoretical results are compared with experimental data, obtained in the Ames 40 by 80 Foot Wind Tunnel, to verify experimentally the predicted slat position for maximum lift. The experimentally optimized slat position is in good agreement with the theoretical prediction, indicating that the theoretical procedure is a feasible design method

Dynamics of leg muscle function in tammar wallabies (M. eugenii) during level versus incline hopping

The goal of our study was to examine whether the in vivo force-length behavior, work and elastic energy savings of distal muscle-tendon units in the legs of tammar wallabies (Macropus eugenii) change during level versus incline hopping. To address this question, we obtained measurements of muscle activation (via electromyography), fascicle strain (via sonomicrometry) and muscle-tendon force (via tendon buckles) from the lateral gastrocnemius (LG) and plantaris (PL) muscles of tammar wallabies trained to hop on a level and an inclined (10°, 17.4% grade) treadmill at two speeds (3.3 m s^(-1) and 4.2 m s^(-1)). Similar patterns of muscle activation, force and fascicle strain were observed under both level and incline conditions. This also corresponded to similar patterns of limb timing and movement (duty factor, limb contact time and hopping frequency). During both level and incline hopping, the LG and PL exhibited patterns of fascicle stretch and shortening that yielded low levels of net fascicle strain [LG: level, -1.0±4.6% (mean ± s.e.m.) vs incline, 0.6±4.5%; PL: level, 0.1±1.0% vs incline, 0.4±1.6%] and muscle work (LG: level, -8.4±8.4 J kg^(-1) muscle vs incline, -6.8±7.5 J kg^(-1) muscle; PL: level, -2.0±0.6 J kg^(-1) muscle vs incline, -1.4±0.7 J kg^(-1) muscle). Consequently, neither muscle significantly altered its contractile dynamics to do more work during incline hopping. Whereas electromyographic (EMG) phase, duration and intensity did not differ for the LG, the PL exhibited shorter but more intense periods of activation, together with reduced EMG phase (P<0.01), during incline versus level hopping. Our results indicate that design for spring-like tendon energy savings and economical muscle force generation is key for these two distal muscle-tendon units of the tammar wallaby, and the need to accommodate changes in work associated with level versus incline locomotion is achieved by more proximal muscles of the limb

Conformational Plasticity of an Enzyme during Catalysis: Intricate Coupling between Cyclophilin A Dynamics and Substrate Turnover

Enzyme catalysis is central to almost all biochemical processes, speeding up rates of reactions to biological relevant timescales. Enzymes make use of a large ensemble of conformations in recognizing their substrates and stabilizing the transition states, due to the inherent dynamical nature of biomolecules. The exact role of these diverse enzyme conformations and the interplay between enzyme conformational dynamics and catalysis is, according to the literature, not well understood. Here, we use molecular dynamics simulations to study human cyclophilin A (CypA), in order to understand the role of enzyme motions in the catalytic mechanism and recognition. Cyclophilin A is a tractable model system to study using classical simulation methods, because catalysis does not involve bond formation or breakage. We show that the conformational dynamics of active site residues of substrate-bound CypA is inherent in the substrate-free enzyme. CypA interacts with its substrate via conformational selection as the configurations of the substrate changes during catalysis. We also show that, in addition to tight intermolecular hydrophobic interactions between CypA and the substrate, an intricate enzyme-substrate intermolecular hydrogen-bonding network is extremely sensitive to the configuration of the substrate. These enzyme-substrate intermolecular interactions are loosely formed when the substrate is in the reactant and product states and become well formed and reluctant to break when the substrate is in the transition state. Our results clearly suggest coupling among enzyme-substrate intermolecular interactions, the dynamics of the enzyme, and the chemical step. This study provides further insights into the mechanism of peptidyl-prolyl cis/trans isomerases and the general interplay between enzyme conformational dynamics and catalysis

Self-organization of intrinsically disordered proteins with folded N-termini

Thousands of human proteins lack recognizable tertiary structure in most of their chains. Here we hypothesize that some use their structured N-terminal domains (SNTDs) to organise the remaining protein chain via intramolecular interactions, generating partially structured proteins. This model has several attractive features: as protein chains emerge, SNTDs form spontaneously and serve as nucleation points, creating more compact shapes. This reduces the risk of protein degradation or aggregation. Moreover, an interspersed pattern of SNTD-docked regions and free loops can coordinate assembly of sub-complexes in defined loop-sections and enables novel regulatory mechanisms, for example through posttranslational modifications of docked regions