Analytical stress intensity solution for the Stable Poisson Loaded specimen

NASA Technical Reports Server (NTRS)

Ghosn, Louis J.; Calomino, Anthony M.; Brewer, David N.

1993-01-01

An analytical calibration of the Stable Poisson Loaded (SPL) specimen is presented. The specimen configuration is similar to the ASTM E-561 compact-tension specimen with displacement controlled wedge loading used for R-curve determination. The crack mouth opening displacements (CMODs) are produced by the diametral expansion of an axially compressed cylindrical pin located in the wake of a machined notch. Due to the unusual loading configuration, a three-dimensional finite element analysis was performed with gap elements simulating the contact between the pin and specimen. In this report, stress intensity factors, CMODs, and crack displacement profiles, are reported for different crack lengths and different contacting conditions. It was concluded that the computed stress intensity factor decreases sharply with increasing crack length thus making the SPL specimen configuration attractive for fracture testing of brittle, high modulus materials.

Application of computer assisted moire to the study of a crack tip

NASA Astrophysics Data System (ADS)

Sciammarella, C. A.; Albertazzi, A., Jr.; Mourikes, J.

The basic principles of computer assisted moire are discussed. The influence of the image sensor and its finite dimensions on the sampling theorem requirements is discussed. Criteria for the selection of grating pitch on the basis of the spatial bandwidth of the pattern to be observed and the requirements arising from sensitivity considerations are given. The method is used to analyze the strain field in the neighborhood of the crack tip of a standard ASTM compact tension specimen. From the displacements the strains are computed, and from the strains the stresses are obtained using the generalized Ramberg-Osgood stress strain relationship. The stresses are used to compute the values for the J-integral in several circuits surrounding the crack. Good agreement is obtained between the values of the stress intensity factors obtained by different methods. The plastic region surrounding the crack does not show a HRR field and thus the usual rationale to justify the J-integral methods must be re-evaluated.

Assessment of Cracks in Stress Concentration Regions with Localized Plastic Zones

DOE Office of Scientific and Technical Information (OSTI.GOV)

Friedman, E.

1998-11-25

Marty brittle fracture evaluation procedures include plasticity corrections to elastically computed stress intensity factors. These corrections, which are based on the existence of a plastic zone in the vicinity of the crack tip, can overestimate the plasticity effect for a crack embedded in a stress concentration region in which the elastically computed stress exceeds the yield strength of the material in a localized zone. The interactions between the crack, which acts to relieve the high stresses driving the crack, plasticity effects in the stress concentration region, and the nature and source of the loading are examined by formulating explicit flawmore » finite element models for a crack emanating from the root of a notch located in a panel subject to an applied tensile stress. The results of these calculations provide conditions under which a crack-tip plasticity correction based on the Irwin plastic zone size overestimates the plasticity effect. A failure assessment diagram (FAD) curve is used to characterize the effect of plasticity on the crack driving force and to define a less restrictive plasticity correction for cracks at notch roots when load-controlled boundary conditions are imposed. The explicit flaw finite element results also demonstrate that stress intensity factors associated with load-controlled boundary conditions, such as those inherent in the ASME Boiler and Pressure Vessel Code as well as in most handbooks of stress intensity factors, can be much higher than those associated with displacement-controlled conditions, such as those that produce residual or thermal stresses. Under certain conditions, the inclusion of plasticity effects for cracks loaded by displacement-controlled boundary conditions reduces the crack driving force thus justifying the elimination of a plasticity correction for such loadings. The results of this study form the basis for removing unnecessary conservatism from flaw evaluation procedures that utilize plasticity corrections.« less

Adaptive finite element methods for two-dimensional problems in computational fracture mechanics

NASA Technical Reports Server (NTRS)

Min, J. B.; Bass, J. M.; Spradley, L. W.

1994-01-01

Some recent results obtained using solution-adaptive finite element methods in two-dimensional problems in linear elastic fracture mechanics are presented. The focus is on the basic issue of adaptive finite element methods for validating the new methodology by computing demonstration problems and comparing the stress intensity factors to analytical results.

Fatigue crack growth in 2024-T3 aluminum under tensile and transverse shear stresses

NASA Technical Reports Server (NTRS)

Viz, Mark J.; Zehnder, Alan T.

1994-01-01

The influence of transverse shear stresses on the fatigue crack growth rate in thin 2024-T3 aluminum alloy sheets is investigated experimentally. The tests are performed on double-edge cracked sheets in cyclic tensile and torsional loading. This loading generates crack tip stress intensity factors in the same ratio as the values computed for a crack lying along a lap joint in a pressurized aircraft fuselage. The relevant fracture mechanics of cracks in thin plates along with the details of the geometrically nonlinear finite element analyses used for the test specimen calibration are developed and discussed. Preliminary fatigue crack growth data correlated using the fully coupled stress intensity factor calibration are presented and compared with fatigue crack growth data from pure delta K(sub I)fatigue tests.

Stresses Produced in Airplane Wings by Gusts

NASA Technical Reports Server (NTRS)

Kussner, Hans Georg

1932-01-01

Accurate prediction of gust stress being out of the question because of the multiplicity of the free air movements, the exploration of gust stress is restricted to static method which must be based upon: 1) stress measurements in free flight; 2) check of design specifications of approved type airplanes. With these empirical data the stress must be compared which can be computed for a gust of known intensity and structure. This "maximum gust" then must be so defined as to cover the whole ambit of empiricism and thus serve as prediction for new airplane designs.

Impact of surface coupling grids on tropical cyclone extremes in high-resolution atmospheric simulations

DOE PAGES

Zarzycki, Colin M.; Reed, Kevin A.; Bacmeister, Julio T.; ...

2016-02-25

This article discusses the sensitivity of tropical cyclone climatology to surface coupling strategy in high-resolution configurations of the Community Earth System Model. Using two supported model setups, we demonstrate that the choice of grid on which the lowest model level wind stress and surface fluxes are computed may lead to differences in cyclone strength in multi-decadal climate simulations, particularly for the most intense cyclones. Using a deterministic framework, we show that when these surface quantities are calculated on an ocean grid that is coarser than the atmosphere, the computed frictional stress is misaligned with wind vectors in individual atmospheric gridmore » cells. This reduces the effective surface drag, and results in more intense cyclones when compared to a model configuration where the ocean and atmosphere are of equivalent resolution. Our results demonstrate that the choice of computation grid for atmosphere–ocean interactions is non-negligible when considering climate extremes at high horizontal resolution, especially when model components are on highly disparate grids.« less

Effect of low-intensity resistance training with heat stress on the HSP72, anabolic hormones, muscle size, and strength in elderly women.

PubMed

Yoon, Sung Jin; Lee, Moon Jin; Lee, Hyo Min; Lee, Jin Seok

2017-10-01

Several recent studies have reported that heat stress stimulates the activation of heat shock protein 72 (HSP72), leading to an increase in muscle synthesis. Some studies suggested that low-intensity resistance training combined with heat stress could improve muscle size and strength. This study aimed to identify the effect of low-intensity resistance training with heat stress over 12 weeks on the HSP72, anabolic hormones, muscle size, and strength in elderly women. The subjects were physically healthy women of 65-75 years, who were randomly assigned to one of three groups: a low-intensity resistance training with heating sheet group (HRT group, n = 8), a moderate-intensity resistance training (RT group, n = 6), and a heating sheet group (HEAT group, n = 7). Computed tomography scans, 1-repetition maximum (1RM), and blood samples were taken pre- and post-training. The HSP72 did not vary significantly between the different groups and times. The IGF-1 and 1RM had significantly increased in all three groups after the training (respectively, p < 0.05). Moreover, the cross-sectional area (CSA) of the quadriceps showed a significantly greater increase in the HRT group than in the HEAT group (p < 0.05). We found that low-intensity training with heat stress stimulated the anabolic hormones of elderly women, improving their muscle strength and hypertrophy. We believe that low-intensity training with heat stress is an effective way to prevent muscle atrophy and to improve muscle strength in elderly women.

Stress studies in EFG

NASA Technical Reports Server (NTRS)

1983-01-01

Experimental work in support of stress studies in high speed silicon sheet growth has been emphasized in this quarter. Creep experiments utilizing four-point bending have been made in the temperature range from 1000 C to 1360 C in CZ silicon as well as on EFG ribbon. A method to measure residual stress over large areas using laser interferometry to map strain distributions under load is under development. A fiber optics sensor to measure ribbon temperature profiles has been constructed and is being tested in a ribbon growth furnace environment. Stress and temperature field modeling work has been directed toward improving various aspects of the finite element computing schemes. Difficulties in computing stress distributions with a very high creep intensity and with non-zero interface stress have been encountered and additional development of the numerical schemes to cope with these problems is required. Temperature field modeling has been extended to include the study of heat transfer effects in the die and meniscus regions.

Stress-intensity factors for small surface and corner cracks in plates

NASA Technical Reports Server (NTRS)

Raju, I. S.; Atluri, S. N.; Newman, J. C., Jr.

1988-01-01

Three-dimensional finite-element and finite-alternating methods were used to obtain the stress-intensity factors for small surface and corner cracked plates subjected to remote tension and bending loads. The crack-depth-to-crack-length ratios (a/c) ranged from 0.2 to 1 and the crack-depth-to-plate-thickness ratios (a/t) ranged from 0.05 to 0.2. The performance of the finite-element alternating method was studied on these crack configurations. A study of the computational effort involved in the finite-element alternating method showed that several crack configurations could be analyzed with a single rectangular mesh idealization, whereas the conventional finite-element method requires a different mesh for each configuration. The stress-intensity factors obtained with the finite-element-alternating method agreed well (within 5 percent) with those calculated from the finite-element method with singularity elements.

Numerical Analysis of Crack Tip Plasticity and History Effects under Mixed Mode Conditions

NASA Astrophysics Data System (ADS)

Lopez-Crespo, Pablo; Pommier, Sylvie

The plastic behaviour in the crack tip region has a strong influence on the fatigue life of engineering components. In general, residual stresses developed as a consequence of the plasticity being constrained around the crack tip have a significant role on both the direction of crack propagation and the propagation rate. Finite element methods (FEM) are commonly employed in order to model plasticity. However, if millions of cycles need to be modelled to predict the fatigue behaviour of a component, the method becomes computationally too expensive. By employing a multiscale approach, very precise analyses computed by FEM can be brought to a global scale. The data generated using the FEM enables us to identify a global cyclic elastic-plastic model for the crack tip region. Once this model is identified, it can be employed directly, with no need of additional FEM computations, resulting in fast computations. This is done by partitioning local displacement fields computed by FEM into intensity factors (global data) and spatial fields. A Karhunen-Loeve algorithm developed for image processing was employed for this purpose. In addition, the partitioning is done such as to distinguish into elastic and plastic components. Each of them is further divided into opening mode and shear mode parts. The plastic flow direction was determined with the above approach on a centre cracked panel subjected to a wide range of mixed-mode loading conditions. It was found to agree well with the maximum tangential stress criterion developed by Erdogan and Sih, provided that the loading direction is corrected for residual stresses. In this approach, residual stresses are measured at the global scale through internal intensity factors.

Solution-adaptive finite element method in computational fracture mechanics

NASA Technical Reports Server (NTRS)

Min, J. B.; Bass, J. M.; Spradley, L. W.

1993-01-01

Some recent results obtained using solution-adaptive finite element method in linear elastic two-dimensional fracture mechanics problems are presented. The focus is on the basic issue of adaptive finite element method for validating the applications of new methodology to fracture mechanics problems by computing demonstration problems and comparing the stress intensity factors to analytical results.

Determination of stress intensity factors for interface cracks under mixed-mode loading

NASA Technical Reports Server (NTRS)

Naik, Rajiv A.; Crews, John H., Jr.

1992-01-01

A simple technique was developed using conventional finite element analysis to determine stress intensity factors, K1 and K2, for interface cracks under mixed-mode loading. This technique involves the calculation of crack tip stresses using non-singular finite elements. These stresses are then combined and used in a linear regression procedure to calculate K1 and K2. The technique was demonstrated by calculating three different bimaterial combinations. For the normal loading case, the K's were within 2.6 percent of an exact solution. The normalized K's under shear loading were shown to be related to the normalized K's under normal loading. Based on these relations, a simple equation was derived for calculating K1 and K2 for mixed-mode loading from knowledge of the K's under normal loading. The equation was verified by computing the K's for a mixed-mode case with equal and normal shear loading. The correlation between exact and finite element solutions is within 3.7 percent. This study provides a simple procedure to compute K2/K1 ratio which has been used to characterize the stress state at the crack tip for various combinations of materials and loadings. Tests conducted over a range of K2/K1 ratios could be used to fully characterize interface fracture toughness.

Numerical simulation of stress amplification induced by crack interaction in human femur bone

NASA Astrophysics Data System (ADS)

Alia, Noor; Daud, Ruslizam; Ramli, Mohammad Fadzli; Azman, Wan Zuki; Faizal, Ahmad; Aisyah, Siti

2015-05-01

This research is about numerical simulation using a computational method which study on stress amplification induced by crack interaction in human femur bone. Cracks in human femur bone usually occur because of large load or stress applied on it. Usually, the fracture takes longer time to heal itself. At present, the crack interaction is still not well understood due to bone complexity. Thus, brittle fracture behavior of bone may be underestimated and inaccurate. This study aims to investigate the geometrical effect of double co-planar edge cracks on stress intensity factor (K) in femur bone. This research focuses to analyze the amplification effect on the fracture behavior of double co-planar edge cracks, where numerical model is developed using computational method. The concept of fracture mechanics and finite element method (FEM) are used to solve the interacting cracks problems using linear elastic fracture mechanics (LEFM) theory. As a result, this study has shown the identification of the crack interaction limit (CIL) and crack unification limit (CUL) exist in the human femur bone model developed. In future research, several improvements will be made such as varying the load, applying thickness on the model and also use different theory or method in calculating the stress intensity factor (K).

Stress intensities for cracks emanating from pin-loaded holes

NASA Technical Reports Server (NTRS)

Smith, C. W.; Jolles, M.; Peters, W. H.

1977-01-01

A series of stress freezing photoelastic experiments were conducted on large plates containing central holes with cracks emanating from the edge formed by the intersection of the hole with the plate surface. Loads were applied through rigid pins with neat fits in the holes. Stress-intensity factors (SIF) were estimated by a computer assisted least squares analysis of the photoelastic data taken from slices near the points of intersection of the flaw border with the hole boundary and the plate surface. Results indicate that the local mode of loading changes from Mode 1 near the hole boundary to mixed mode near the plate surface. The analysis is extended to include mixed mode loading, and results are compared with an existing approximate theory.

Stress generation in thermally grown oxide films. [oxide scale spalling from superalloy substrates

NASA Technical Reports Server (NTRS)

Kumnick, A. J.; Ebert, L. J.

1981-01-01

A three dimensional finite element analysis was conducted, using the ANSYS computer program, of the stress state in a thin oxide film thermally formed on a rectangular piece of NiCrAl alloy. The analytical results indicate a very high compressive stress in the lateral directions of the film (approximately 6200 MPa), and tensile stresses in the metal substrate that ranged from essentially zero to about 55 MPa. It was found further that the intensity of the analytically determined average stresses could be approximated reasonably well by the modification of an equation developed previously by Oxx for stresses induced into bodies by thermal gradients.

C deg continuity elements by Hybrid Stress method. M.S. Thesis, 1982 Final Report

NASA Technical Reports Server (NTRS)

Kang, David Sung-Soo

1991-01-01

An intensive study of the assumed variable distribution necessary for the Assumed Displacement Formulation, the Hellinger-Reissner Formulation, and the Hu-Washizu Formulation is made in a unified manner. With emphasis on physical explanation, a systematic method for the Hybrid Stress element construction is outlined. The numerical examples use four and eight node plane stress elements and eight and twenty node solid elements. Computation cost study indicates that the hybrid stress element derived using recently developed Uncoupled Stress Formulation is comparable in CPU time to the Assumed Displacement element. Overall, main emphasis is placed on providing a broader understanding of the Hybrid Stress Formulation.

Perceived competence in computer use as a moderator of musculoskeletal strain in VDU work: an ergonomics intervention case.

PubMed

Tuomivaara, S; Ketola, R; Huuhtanen, P; Toivonen, R

2008-02-01

Musculoskeletal strain and other symptoms are common in visual display unit (VDU) work. Psychosocial factors are closely related to the outcome and experience of musculoskeletal strain. The user-computer relationship from the viewpoint of the quality of perceived competence in computer use was assessed as a psychosocial stress indicator. It was assumed that the perceived competence in computer use moderates the experience of musculoskeletal strain and the success of the ergonomics intervention. The participants (n = 124, female 58%, male 42%) worked with VDU for more than 4 h per week. They took part in an ergonomics intervention and were allocated into three groups: intensive; education; and reference group. Musculoskeletal strain, the level of ergonomics of the workstation assessed by the experts in ergonomics and amount of VDU work were estimated at the baseline and at the 10-month follow-up. Age, gender and the perceived competence in computer use were assessed at the baseline. The perceived competence in computer use predicted strain in the upper and the lower part of the body at the follow-up. The interaction effect shows that the intensive ergonomics intervention procedure was the most effective among participants with high perceived competence. The interpretation of the results was that an anxiety-provoking and stressful user-computer relationship prevented the participants from being motivated and from learning in the ergonomics intervention. In the intervention it is important to increase the computer competence along with the improvements of physical workstation and work organization.

Frequency domain analysis of the random loading of cracked panels

NASA Technical Reports Server (NTRS)

Doyle, James F.

1994-01-01

The primary effort concerned the development of analytical methods for the accurate prediction of the effect of random loading on a panel with a crack. Of particular concern was the influence of frequency on the stress intensity factor behavior. Many modern structures, such as those found in advanced aircraft, are lightweight and susceptible to critical vibrations, and consequently dynamic response plays a very important role in their analysis. The presence of flaws and cracks can have catastrophic consequences. The stress intensity factor, K, emerges as a very significant parameter that characterizes the crack behavior. In analyzing the dynamic response of panels that contain cracks, the finite element method is used, but because this type of problem is inherently computationally intensive, a number of ways of calculating K more efficiently are explored.

Effect of crack curvature on stress intensity factors for ASTM standard compact tension specimens

NASA Technical Reports Server (NTRS)

Alam, J.; Mendelson, A.

1983-01-01

The stress intensity factors (SIF) are calculated using the method of lines for the compact tension specimen in tensile and shear loading for curved crack fronts. For the purely elastic case, it was found that as the crack front curvature increases, the SIF value at the center of the specimen decreases while increasing at the surface. For the higher values of crack front curvatures, the maximum value of the SIF occurs at an interior point located adjacent to the surface. A thickness average SIF was computed for parabolically applied shear loading. These results were used to assess the requirements of ASTM standards E399-71 and E399-81 on the shape of crack fronts. The SIF is assumed to reflect the average stress environment near the crack edge.

Anomolous Fatigue Crack Growth Phenomena in High-Strength Steel

NASA Technical Reports Server (NTRS)

Forth, Scott C.; James, Mark A.; Johnston, William M., Jr.; Newman, James C., Jr.

2004-01-01

The growth of a fatigue crack through a material is the result of a complex interaction between the applied loading, component geometry, three-dimensional constraint, load history, environment, material microstructure and several other factors. Previous studies have developed experimental and computational methods to relate the fatigue crack growth rate to many of the above conditions, with the intent of discovering some fundamental material response, i.e. crack growth rate as a function of something. Currently, the technical community uses the stress intensity factor solution as a simplistic means to relate fatigue crack growth rate to loading, geometry and all other variables. The stress intensity factor solution is a very simple linear-elastic representation of the continuum mechanics portion of crack growth. In this paper, the authors present fatigue crack growth rate data for two different high strength steel alloys generated using standard methods. The steels exhibit behaviour that appears unexplainable, compared to an aluminium alloy presented as a baseline for comparison, using the stress intensity factor solution.

surf3d: A 3-D finite-element program for the analysis of surface and corner cracks in solids subjected to mode-1 loadings

NASA Technical Reports Server (NTRS)

Raju, I. S.; Newman, J. C., Jr.

1993-01-01

A computer program, surf3d, that uses the 3D finite-element method to calculate the stress-intensity factors for surface, corner, and embedded cracks in finite-thickness plates with and without circular holes, was developed. The cracks are assumed to be either elliptic or part eliptic in shape. The computer program uses eight-noded hexahedral elements to model the solid. The program uses a skyline storage and solver. The stress-intensity factors are evaluated using the force method, the crack-opening displacement method, and the 3-D virtual crack closure methods. In the manual the input to and the output of the surf3d program are described. This manual also demonstrates the use of the program and describes the calculation of the stress-intensity factors. Several examples with sample data files are included with the manual. To facilitate modeling of the user's crack configuration and loading, a companion program (a preprocessor program) that generates the data for the surf3d called gensurf was also developed. The gensurf program is a three dimensional mesh generator program that requires minimal input and that builds a complete data file for surf3d. The program surf3d is operational on Unix machines such as CRAY Y-MP, CRAY-2, and Convex C-220.

Stress Intensity Factors for Part-Through Surface Cracks in Hollow Cylinders

NASA Technical Reports Server (NTRS)

Mettu, Sambi R.; Raju, Ivatury S.; Forman, Royce G.

1992-01-01

Flaws resulting from improper welding and forging are usually modeled as cracks in flat plates, hollow cylinders or spheres. The stress intensity factor solutions for these crack cases are of great practical interest. This report describes some recent efforts at improving the stress intensity factor solutions for cracks in such geometries with emphasis on hollow cylinders. Specifically, two crack configurations for cylinders are documented. One is that of a surface crack in an axial plane and the other is a part-through thumb-nail crack in a circumferential plane. The case of a part-through surface crack in flat plates is used as a limiting case for very thin cylinders. A combination of the two cases for cylinders is used to derive a relation for the case of a surface crack in a sphere. Solutions were sought which cover the entire range of the geometrical parameters such as cylinder thickness, crack aspect ratio and crack depth. Both the internal and external position of the cracks are considered for cylinders and spheres. The finite element method was employed to obtain the basic solutions. Power-law form of loading was applied in the case of flat plates and axial cracks in cylinders and uniform tension and bending loads were applied in the case of circumferential (thumb-nail) cracks in cylinders. In the case of axial cracks, the results for tensile and bending loads were used as reference solutions in a weight function scheme so that the stress intensity factors could be computed for arbitrary stress gradients in the thickness direction. For circumferential cracks, since the crack front is not straight, the above technique could not be used. Hence for this case, only the tension and bending solutions are available at this time. The stress intensity factors from the finite element method were tabulated so that results for various geometric parameters such as crack depth-to-thickness ratio (a/t), crack aspect ratio (a/c) and internal radius-to-thickness ratio (R/t) or the crack length-to-width ratio (2c/W) could be obtained by interpolation and extrapolation. Such complete tables were then incorporated into the NASA/FLAGRO computer program which is widely used by the aerospace community for fracture mechanics analysis.

Determination of the Fracture Parameters in a Stiffened Composite Panel

NASA Technical Reports Server (NTRS)

Lin, Chung-Yi

2000-01-01

A modified J-integral, namely the equivalent domain integral, is derived for a three-dimensional anisotropic cracked solid to evaluate the stress intensity factor along the crack front using the finite element method. Based on the equivalent domain integral method with auxiliary fields, an interaction integral is also derived to extract the second fracture parameter, the T-stress, from the finite element results. The auxiliary fields are the two-dimensional plane strain solutions of monoclinic materials with the plane of symmetry at x(sub 3) = 0 under point loads applied at the crack tip. These solutions are expressed in a compact form based on the Stroh formalism. Both integrals can be implemented into a single numerical procedure to determine the distributions of stress intensity factor and T-stress components, T11, T13, and thus T33, along a three-dimensional crack front. The effects of plate thickness and crack length on the variation of the stress intensity factor and T-stresses through the thickness are investigated in detail for through-thickness center-cracked plates (isotropic and orthotropic) and orthotropic stiffened panels under pure mode-I loading conditions. For all the cases studied, T11 remains negative. For plates with the same dimensions, a larger size of crack yields larger magnitude of the normalized stress intensity factor and normalized T-stresses. The results in orthotropic stiffened panels exhibit an opposite trend in general. As expected, for the thicker panels, the fracture parameters evaluated through the thickness, except the region near the free surfaces, approach two-dimensional plane strain solutions. In summary, the numerical methods presented in this research demonstrate their high computational effectiveness and good numerical accuracy in extracting these fracture parameters from the finite element results in three-dimensional cracked solids.

SURROGATE MODEL DEVELOPMENT AND VALIDATION FOR RELIABILITY ANALYSIS OF REACTOR PRESSURE VESSELS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hoffman, William M.; Riley, Matthew E.; Spencer, Benjamin W.

In nuclear light water reactors (LWRs), the reactor coolant, core and shroud are contained within a massive, thick walled steel vessel known as a reactor pressure vessel (RPV). Given the tremendous size of these structures, RPVs typically contain a large population of pre-existing flaws introduced in the manufacturing process. After many years of operation, irradiation-induced embrittlement makes these vessels increasingly susceptible to fracture initiation at the locations of the pre-existing flaws. Because of the uncertainty in the loading conditions, flaw characteristics and material properties, probabilistic methods are widely accepted and used in assessing RPV integrity. The Fracture Analysis of Vesselsmore » – Oak Ridge (FAVOR) computer program developed by researchers at Oak Ridge National Laboratory is widely used for this purpose. This program can be used in order to perform deterministic and probabilistic risk-informed analyses of the structural integrity of an RPV subjected to a range of thermal-hydraulic events. FAVOR uses a one-dimensional representation of the global response of the RPV, which is appropriate for the beltline region, which experiences the most embrittlement, and employs an influence coefficient technique to rapidly compute stress intensity factors for axis-aligned surface-breaking flaws. The Grizzly code is currently under development at Idaho National Laboratory (INL) to be used as a general multiphysics simulation tool to study a variety of degradation mechanisms in nuclear power plant components. The first application of Grizzly has been to study fracture in embrittled RPVs. Grizzly can be used to model the thermo-mechanical response of an RPV under transient conditions observed in a pressurized thermal shock (PTS) scenario. The global response of the vessel provides boundary conditions for local 3D models of the material in the vicinity of a flaw. Fracture domain integrals are computed to obtain stress intensity factors, which can in turn be used to assess whether a fracture would initiate at a pre-existing flaw. To use Grizzly for probabilistic analysis, it is necessary to have a way to rapidly evaluate stress intensity factors. To accomplish this goal, a reduced order model (ROM) has been developed to efficiently represent the behavior of a detailed 3D Grizzly model used to calculate fracture parameters. This approach uses the stress intensity factor influence coefficient method that has been used with great success in FAVOR. Instead of interpolating between tabulated solutions, as FAVOR does, the ROM approach uses a response surface methodology to compute fracture solutions based on a sampled set of results used to train the ROM. The main advantages of this approach are that the process of generating the training data can be fully automated, and the procedure can be readily used to consider more general flaw configurations. This paper demonstrates the procedure used to generate a ROM to rapidly compute stress intensity factors for axis-aligned flaws. The results from this procedure are in good agreement with those produced using the traditional influence coefficient interpolation procedure, which gives confidence in this method. This paves the way for applying this procedure for more general flaw configurations.« less

Analysis of crack propagation in roller bearings using the boundary integral equation method - A mixed-mode loading problem

NASA Technical Reports Server (NTRS)

Ghosn, L. J.

1988-01-01

Crack propagation in a rotating inner raceway of a high-speed roller bearing is analyzed using the boundary integral method. The model consists of an edge plate under plane strain condition upon which varying Hertzian stress fields are superimposed. A multidomain boundary integral equation using quadratic elements was written to determine the stress intensity factors KI and KII at the crack tip for various roller positions. The multidomain formulation allows the two faces of the crack to be modeled in two different subregions, making it possible to analyze crack closure when the roller is positioned on or close to the crack line. KI and KII stress intensity factors along any direction were computed. These calculations permit determination of crack growth direction along which the average KI times the alternating KI is maximum.

Comparison of mixed-mode stress-intensity factors obtained through displacement correlation, J-integral formulation, and modified crack-closure integral

NASA Astrophysics Data System (ADS)

Bittencourt, Tulio N.; Barry, Ahmabou; Ingraffea, Anthony R.

This paper presents a comparison among stress-intensity factors for mixed-mode two-dimensional problems obtained through three different approaches: displacement correlation, J-integral, and modified crack-closure integral. All mentioned procedures involve only one analysis step and are incorporated in the post-processor page of a finite element computer code for fracture mechanics analysis (FRANC). Results are presented for a closed-form solution problem under mixed-mode conditions. The accuracy of these described methods then is discussed and analyzed in the framework of their numerical results. The influence of the differences among the three methods on the predicted crack trajectory of general problems is also discussed.

Resolved shear stress intensity coefficient and fatigue crack growth in large crystals

NASA Technical Reports Server (NTRS)

Chen, Q.; Liu, H. W.

1988-01-01

Fatigue crack growth tests were carried out on large-grain Al 7029 aluminum alloy and the finite element method was used to calculate the stress field near the tip of a zigzag crack. The resolved shear stresses on all 12 slip systems were computed, and the resolved shear stress intensity coefficient (RSSIC) was defined. The RSSIC was used to analyze the irregular crack path and was correlated with the rate of single-slip-plane shear crack growth. Fatigue crack growth was found to be caused primarily by shear decohesion at a crack tip. When the RSSIC on a single-slip system was much larger than all the others, the crack followed a single-slip plane. When the RSSICs on two conjugate slip systems were comparable, a crack grew in a zigzag manner on these planes and the macrocrack-plane bisected the two active slip planes. The maximum RSSIC on the most active slip system is proposed as a parameter to correlate with the shear fatigue crack growth rate in large crystals.

Gear crack propagation investigations

NASA Technical Reports Server (NTRS)

Lewicki, David G.; Ballarini, Roberto

1996-01-01

Analytical and experimental studies were performed to investigate the effect of gear rim thickness on crack propagation life. The FRANC (FRacture ANalysis Code) computer program was used to simulate crack propagation. The FRANC program used principles of linear elastic fracture mechanics, finite element modeling, and a unique re-meshing scheme to determine crack tip stress distributions, estimate stress intensity factors, and model crack propagation. Various fatigue crack growth models were used to estimate crack propagation life based on the calculated stress intensity factors. Experimental tests were performed in a gear fatigue rig to validate predicted crack propagation results. Test gears were installed with special crack propagation gages in the tooth fillet region to measure bending fatigue crack growth. Good correlation between predicted and measured crack growth was achieved when the fatigue crack closure concept was introduced into the analysis. As the gear rim thickness decreased, the compressive cyclic stress in the gear tooth fillet region increased. This retarded crack growth and increased the number of crack propagation cycles to failure.

Stress Intensity Factor Plasticity Correction for Flaws in Stress Concentration Regions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Friedman, E.; Wilson, W.K.

2000-02-01

Plasticity corrections to elastically computed stress intensity factors are often included in brittle fracture evaluation procedures. These corrections are based on the existence of a plastic zone in the vicinity of the crack tip. Such a plastic zone correction is included in the flaw evaluation procedure of Appendix A to Section XI of the ASME Boiler and Pressure Vessel Code. Plasticity effects from the results of elastic and elastic-plastic explicit flaw finite element analyses are examined for various size cracks emanating from the root of a notch in a panel and for cracks located at fillet fadii. The results ofmore » these caluclations provide conditions under which the crack-tip plastic zone correction based on the Irwin plastic zone size overestimates the plasticity effect for crack-like flaws embedded in stress concentration regions in which the elastically computed stress exceeds the yield strength of the material. A failure assessment diagram (FAD) curve is employed to graphically c haracterize the effect of plasticity on the crack driving force. The Option 1 FAD curve of the Level 3 advanced fracture assessment procedure of British Standard PD 6493:1991, adjusted for stress concentration effects by a term that is a function of the applied load and the ratio of the local radius of curvature at the flaw location to the flaw depth, provides a satisfactory bound to all the FAD curves derived from the explicit flaw finite element calculations. The adjusted FAD curve is a less restrictive plasticity correction than the plastic zone correction of Section XI for flaws embedded in plastic zones at geometric stress concentrators. This enables unnecessary conservatism to be removed from flaw evaluation procedures that utilize plasticity corrections.« less

NASA/FLAGRO - FATIGUE CRACK GROWTH COMPUTER PROGRAM

NASA Technical Reports Server (NTRS)

Forman, R. G.

1994-01-01

Structural flaws and cracks may grow under fatigue inducing loads and, upon reaching a critical size, cause structural failure to occur. The growth of these flaws and cracks may occur at load levels well below the ultimate load bearing capability of the structure. The Fatigue Crack Growth Computer Program, NASA/FLAGRO, was developed as an aid in predicting the growth of pre-existing flaws and cracks in structural components of space systems. The earlier version of the program, FLAGRO4, was the primary analysis tool used by Rockwell International and the Shuttle subcontractors for fracture control analysis on the Space Shuttle. NASA/FLAGRO is an enhanced version of the program and incorporates state-of-the-art improvements in both fracture mechanics and computer technology. NASA/FLAGRO provides the fracture mechanics analyst with a computerized method of evaluating the "safe crack growth life" capabilities of structural components. NASA/FLAGRO could also be used to evaluate the damage tolerance aspects of a given structural design. The propagation of an existing crack is governed by the stress field in the vicinity of the crack tip. The stress intensity factor is defined in terms of the relationship between the stress field magnitude and the crack size. The propagation of the crack becomes catastrophic when the local stress intensity factor reaches the fracture toughness of the material. NASA/FLAGRO predicts crack growth using a two-dimensional model which predicts growth independently in two directions based on the calculation of stress intensity factors. The analyst can choose to use either a crack growth rate equation or a nonlinear interpolation routine based on tabular data. The growth rate equation is a modified Forman equation which can be converted to a Paris or Walker equation by substituting different values into the exponent. This equation provides accuracy and versatility and can be fit to data using standard least squares methods. Stress-intensity factor numerical values can be computed for making comparisons or checks of solutions. NASA/FLAGRO can check for failure of a part-through crack in the mode of a through crack when net ligament yielding occurs. NASA/FLAGRO has a number of special subroutines and files which provide enhanced capabilities and easy entry of data. These include crack case solutions, cyclic load spectrums, nondestructive examination initial flaw sizes, table interpolation, and material properties. The materials properties files are divided into two types, a user defined file and a fixed file. Data is entered and stored in the user defined file during program execution, while the fixed file contains already coded-in property value data for many different materials. Prompted input from CRT terminals consists of initial crack definition (which can be defined automatically), rate solution type, flaw type and geometry, material properties (if they are not in the built-in tables of material data), load spectrum data (if not included in the loads spectrum file), and design limit stress levels. NASA/FLAGRO output includes an echo of the input with any error or warning messages, the final crack size, whether or not critical crack size has been reached for the specified stress level, and a life history profile of the crack propagation. NASA/FLAGRO is modularly designed to facilitate revisions and operation on minicomputers. The program was implemented on a DEC VAX 11/780 with the VMS operating system. NASA/FLAGRO is written in FORTRAN77 and has a memory requirement of 1.4 MB. The program was developed in 1986.

Evaluation of stress intensity factors for bi-material interface cracks using displacement jump methods

NASA Astrophysics Data System (ADS)

Nehar, K. C.; Hachi, B. E.; Cazes, F.; Haboussi, M.

2017-12-01

The aim of the present work is to investigate the numerical modeling of interfacial cracks that may appear at the interface between two isotropic elastic materials. The extended finite element method is employed to analyze brittle and bi-material interfacial fatigue crack growth by computing the mixed mode stress intensity factors (SIF). Three different approaches are introduced to compute the SIFs. In the first one, mixed mode SIF is deduced from the computation of the contour integral as per the classical J-integral method, whereas a displacement method is used to evaluate the SIF by using either one or two displacement jumps located along the crack path in the second and third approaches. The displacement jump method is rather classical for mono-materials, but has to our knowledge not been used up to now for a bi-material. Hence, use of displacement jump for characterizing bi-material cracks constitutes the main contribution of the present study. Several benchmark tests including parametric studies are performed to show the effectiveness of these computational methodologies for SIF considering static and fatigue problems of bi-material structures. It is found that results based on the displacement jump methods are in a very good agreement with those of exact solutions, such as for the J-integral method, but with a larger domain of applicability and a better numerical efficiency (less time consuming and less spurious boundary effect).

3D multiscale crack propagation using the XFEM applied to a gas turbine blade

NASA Astrophysics Data System (ADS)

Holl, Matthias; Rogge, Timo; Loehnert, Stefan; Wriggers, Peter; Rolfes, Raimund

2014-01-01

This work presents a new multiscale technique to investigate advancing cracks in three dimensional space. This fully adaptive multiscale technique is designed to take into account cracks of different length scales efficiently, by enabling fine scale domains locally in regions of interest, i.e. where stress concentrations and high stress gradients occur. Due to crack propagation, these regions change during the simulation process. Cracks are modeled using the extended finite element method, such that an accurate and powerful numerical tool is achieved. Restricting ourselves to linear elastic fracture mechanics, the -integral yields an accurate solution of the stress intensity factors, and with the criterion of maximum hoop stress, a precise direction of growth. If necessary, the on the finest scale computed crack surface is finally transferred to the corresponding scale. In a final step, the model is applied to a quadrature point of a gas turbine blade, to compute crack growth on the microscale of a real structure.

Rural women, technology, and self-management of chronic illness.

PubMed

Weinert, Clarann; Cudney, Shirley; Hill, Wade G

2008-09-01

The objective of this study was to determine the differences in the psychosocial status of 3 groups of chronically ill rural women participating in a computer intervention. The 3 groups were: intense intervention, less-intense intervention, and control. At baseline and following the intervention, measures were taken for social support, self-esteem, empowerment, self-efficacy, depression, stress, and loneliness. ANCOVA results showed group differences for social support and self-efficacy among the overall group. The findings differed for a vulnerable subgroup, with significant between-group differences for social support and loneliness. It was concluded that a computer-delivered intervention can improve social support and self-efficacy and reduce loneliness in rural women, enhancing their ability to self-manage and adapt to chronic illness.

Fatigue crack growth behaviour of semi-elliptical surface cracks for an API 5L X65 gas pipeline under tension

NASA Astrophysics Data System (ADS)

Shaari, M. S.; Akramin, M. R. M.; Ariffin, A. K.; Abdullah, S.; Kikuchi, M.

2018-02-01

The paper is presenting the fatigue crack growth (FCG) behavior of semi-elliptical surface cracks for API X65 gas pipeline using S-version FEM. A method known as global-local overlay technique was used in this study to predict the fatigue behavior that involve of two separate meshes each specifically for global (geometry) and local (crack). The pre-post program was used to model the global geometry (coarser mesh) known as FAST including the material and boundary conditions. Hence, the local crack (finer mesh) will be defined the exact location and the mesh control accordingly. The local mesh was overlaid along with the global before the numerical computation taken place to solve the engineering problem. The stress intensity factors were computed using the virtual crack closure-integral method (VCCM). The most important results is the behavior of the fatigue crack growth, which contains the crack depth (a), crack length (c) and stress intensity factors (SIF). The correlation between the fatigue crack growth and the SIF shows a good growth for the crack depth (a) and dissimilar for the crack length (c) where stunned behavior was resulted. The S-version FEM will benefiting the user due to the overlay technique where it will shorten the computation process.

Direct restoration modalities of fractured central maxillary incisors: A multi-levels validated finite elements analysis with in vivo strain measurements.

PubMed

Davide, Apicella; Raffaella, Aversa; Marco, Tatullo; Michele, Simeone; Syed, Jamaluddin; Massimo, Marrelli; Marco, Ferrari; Antonio, Apicella

2015-12-01

To quantify the influence of fracture geometry and restorative materials rigidity on the stress intensity and distribution of restored fractured central maxillary incisors (CMI) with particular investigation of the adhesive interfaces. Ancillary objectives are to present an innovative technology to measure the in vivo strain state of sound maxillary incisors and to present the collected data. A validation experimental biomechanics approach has been associated to finite element analysis. FEA models consisted of CMI, periodontal ligament and the corresponding alveolar bone process. Three models were created representing different orientation of the fracture planes. Three different angulations of the fracture plane in buccal-palatal direction were modeled: the fracture plane perpendicular to the long axis in the buccal-palatal direction (0°); the fracture plane inclined bucco-palatally in apical-coronal direction (-30°); the fracture plane inclined palatal-buccally in apical-coronal direction (+30°). First set of computing runs was performed for in vivo FE-model validation purposes. In the second part, a 50N force was applied on the buccal aspect of the CMI models. Ten patients were selected and subjected to the strain measurement of CMI under controlled loading conditions. The main differences were noticed in the middle and incisal thirds of incisors crowns, due to the presence of the incisal portion restoration. The stress intensity in -30° models is increased in the enamel structure close to the restoration, due to a thinning of the remaining natural tissues. The rigidity of the restoring material slightly reduces such phenomenon. -30° model exhibits the higher interfacial stress in the adhesive layer with respect to +30° and 0° models. The lower stress intensity was noticed in the 0° models, restoration material rigidity did not influenced the interfacial stress state in 0° models. On the contrary, material rigidity influenced the interfacial stress state in +30° and -30° models, higher rigidity restoring materials exhibits lower interfacial stress with respect to low rigidity materials. Fracture planes inclined palatal-buccally in apical-coronal direction (+30°) reduce the interfacial stress intensity and natural tissues stress intensity with respect to the other tested configurations. Copyright © 2015 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Cyclic fatigue and fracture in pyrolytic carbon-coated graphite mechanical heart-valve prostheses: role of small cracks in life prediction.

PubMed

Dauskardt, R H; Ritchie, R O; Takemoto, J K; Brendzel, A M

1994-07-01

A fracture-mechanics based study has performed to characterize the fracture toughness and rates of cyclic fatigue-crack growth of incipient flaws in prosthetic heart-valve components made of pyrolytic carbon-coated graphite. Such data are required to predict the safe structural lifetime of mechanical heart-valve prostheses using damage-tolerant analysis. Unlike previous studies where fatigue-crack propagation data were obtained using through-thickness, long cracks (approximately 2-20 mm long), growing in conventional (e.g., compact-tension) samples, experiments were performed on physically small cracks (approximately 100-600 microns long), initiated on the surface of the pyrolytic-carbon coating to simulate reality. Small-crack toughness results were found to agree closely with those measured conventionally with long cracks. However, similar to well-known observations in metal fatigue, it was found that based on the usual computations of the applied (far-field) driving force in terms of the maximum stress intensity, Kmax, small fatigue cracks grew at rates that exceeded those of long cracks at the same applied stress intensity, and displayed a negative dependency on Kmax; moreover, they grew at applied stress intensities less than the fatigue threshold value, below which long cracks are presumed dormant. To resolve this apparent discrepancy, it is shown that long and small crack results can be normalized, provided growth rates are characterized in terms of the total (near-tip) stress intensity (incorporating, for example, the effect of residual stress); with this achieved, in principle, either form of data can be used for life prediction of implant devices. Inspection of the long and small crack results reveals extensive scatter inherent in both forms of growth-rate data for the pyrolytic-carbon material.

Effects of subcritical crack growth on fracture toughness of ceramics assessed in chevron-notched three-point bend tests

NASA Technical Reports Server (NTRS)

Chao, L. Y.; Singh, D.; Shetty, D. K.

1988-01-01

A numerical computational study was carried out to assess the effects of subcritical crack growth on crack stability in the chevron-notched three-point bend specimens. A power-law relationship between the subcritical crack velocity and the applied stress intensity were used along with compliance and stress-intensity relationships for the chevron-notched bend specimen to calculate the load response under fixed deflection rate and a machine compliance. The results indicate that the maximum load during the test occurs at the same crack length for all the deflection rates; the maximum load, however, is dependent on the deflection rate for rates below the critical rate. The resulting dependence of the apparent fracture toughness on the deflection rate is compared to experimental results on soda-lime glass and polycrystalline alumina.

Numerical calibration of the stable poisson loaded specimen

NASA Technical Reports Server (NTRS)

Ghosn, Louis J.; Calomino, Anthony M.; Brewer, Dave N.

1992-01-01

An analytical calibration of the Stable Poisson Loaded (SPL) specimen is presented. The specimen configuration is similar to the ASTM E-561 compact-tension specimen with displacement controlled wedge loading used for R-Curve determination. The crack mouth opening displacements (CMOD's) are produced by the diametral expansion of an axially compressed cylindrical pin located in the wake of a machined notch. Due to the unusual loading configuration, a three-dimensional finite element analysis was performed with gap elements simulating the contact between the pin and specimen. In this report, stress intensity factors, CMOD's, and crack displacement profiles are reported for different crack lengths and different contacting conditions. It was concluded that the computed stress intensity factor decreases sharply with increasing crack length, thus making the SPL specimen configuration attractive for fracture testing of brittle, high modulus materials.

Propagation of quasifracture in viscoelastic media under low-cycle repeated stressing

NASA Technical Reports Server (NTRS)

Liu, X. P.; Hsiao, C. C.

1985-01-01

The propagation of a craze as quasifracture under repeated cyclic stressing in polymeric systems has been under intensive investigation recently. Based upon a time-dependent crazing theory, the governing differential equation describing the propagation of a single craze as quasifracture in an infinite viscoelastic plate has been solved for sinusoidal stresses. Numerical methods have been employed to obtain the normalized craze length as a function of time. The computed results indicate that the length of a quasifracture may decelerate and decrease indicating that its velocity can reverse. This behavior may be consistent with the observed and much discussed craze healing and the enclosure model in fatigue and fracture of solids.

Analysis of flow patterns in a patient-specific aortic dissection model.

PubMed

Cheng, Z; Tan, F P P; Riga, C V; Bicknell, C D; Hamady, M S; Gibbs, R G J; Wood, N B; Xu, X Y

2010-05-01

Aortic dissection is the most common acute catastrophic event affecting the thoracic aorta. The majority of patients presenting with an uncomplicated type B dissection are treated medically, but 25% of these patients develop subsequent aneurysmal dilatation of the thoracic aorta. This study aimed at gaining more detailed knowledge of the flow phenomena associated with this condition. Morphological features and flow patterns in a dissected aortic segment of a presurgery type B dissection patient were analyzed based on computed tomography images acquired from the patient. Computational simulations of blood flow in the patient-specific model were performed by employing a correlation-based transitional version of Menter's hybrid k-epsilon/k-omega shear stress transport turbulence model implemented in ANSYS CFX 11. Our results show that the dissected aorta is dominated by locally highly disturbed, and possibly turbulent, flow with strong recirculation. A significant proportion (about 80%) of the aortic flow enters the false lumen, which may further increase the dilatation of the aorta. High values of wall shear stress have been found around the tear on the true lumen wall, perhaps increasing the likelihood of expanding the tear. Turbulence intensity in the tear region reaches a maximum of 70% at midsystolic deceleration phase. Incorporating the non-Newtonian behavior of blood into the same transitional flow model has yielded a slightly lower peak wall shear stress and higher maximum turbulence intensity without causing discernible changes to the distribution patterns. Comparisons between the laminar and turbulent flow simulations show a qualitatively similar distribution of wall shear stress but a significantly higher magnitude with the transitional turbulence model.

High-resolution computer-aided moire

NASA Astrophysics Data System (ADS)

Sciammarella, Cesar A.; Bhat, Gopalakrishna K.

1991-12-01

This paper presents a high resolution computer assisted moire technique for the measurement of displacements and strains at the microscopic level. The detection of micro-displacements using a moire grid and the problem associated with the recovery of displacement field from the sampled values of the grid intensity are discussed. A two dimensional Fourier transform method for the extraction of displacements from the image of the moire grid is outlined. An example of application of the technique to the measurement of strains and stresses in the vicinity of the crack tip in a compact tension specimen is given.

Characterization of Residual Stress Effects on Fatigue Crack Growth of a Friction Stir Welded Aluminum Alloy

NASA Technical Reports Server (NTRS)

Newman, John A.; Smith, Stephen W.; Seshadri, Banavara R.; James, Mark A.; Brazill, Richard L.; Schultz, Robert W.; Donald, J. Keith; Blair, Amy

2015-01-01

An on-line compliance-based method to account for residual stress effects in stress-intensity factor and fatigue crack growth property determinations has been evaluated. Residual stress intensity factor results determined from specimens containing friction stir weld induced residual stresses are presented, and the on-line method results were found to be in excellent agreement with residual stress-intensity factor data obtained using the cut compliance method. Variable stress-intensity factor tests were designed to demonstrate that a simple superposition model, summing the applied stress-intensity factor with the residual stress-intensity factor, can be used to determine the total crack-tip stress-intensity factor. Finite element, VCCT (virtual crack closure technique), and J-integral analysis methods have been used to characterize weld-induced residual stress using thermal expansion/contraction in the form of an equivalent delta T (change in local temperature during welding) to simulate the welding process. This equivalent delta T was established and applied to analyze different specimen configurations to predict residual stress distributions and associated residual stress-intensity factor values. The predictions were found to agree well with experimental results obtained using the crack- and cut-compliance methods.

Computer modeling of the stress-strain state of welded construction

NASA Astrophysics Data System (ADS)

Nurguzhin, Marat; Danenova, Gulmira; Akhmetzhanov, Talgat

2017-11-01

At the present time the maintenance of the welded construction serviceability over normative service life is provided by the maintenance system on the basis of the guiding documents according to the concept of "fail safe". However, technology factors relating to welding such as high residual stresses and significant plastic strains are not considered in the guiding documents. The design procedure of the stressed-strained state of welded constructions is suggested in the paper. The procedure investigates welded constructions during welding and the external load using the program ANSYS. In this paper, the model of influence of the residual stress strain state on the factor of stress intensity is proposed. The calculation method of the residual stressed-strained state (SSS) taking into account the phase transition is developed by the authors. Melting and hardening of a plate material during heating and cooling is considered. The thermomechanical problem of heating a plate by a stationary heat source is solved. The setup of the heating spot center on distance (190 mm) from the crack top in a direction of its propagation leads to the fact that the value of total factor of stress intensity will considerably decrease under action of the specified residual compressing stresses. It can lower the speed of the crack propagation to zero. The suggested method of survivability maintenance can be applied during operation with the purpose of increasing the service life of metal constructions up to running repair of technological machines.

Comparison of fatigue crack growth of riveted and bonded aircraft lap joints made of Aluminium alloy 2024-T3 substrates - A numerical study

NASA Astrophysics Data System (ADS)

Pitta, S.; Rojas, J. I.; Crespo, D.

2017-05-01

Aircraft lap joints play an important role in minimizing the operational cost of airlines. Hence, airlines pay more attention to these technologies to improve efficiency. Namely, a major time consuming and costly process is maintenance of aircraft between the flights, for instance, to detect early formation of cracks, monitoring crack growth, and fixing the corresponding parts with joints, if necessary. This work is focused on the study of repairs of cracked aluminium alloy (AA) 2024-T3 plates to regain their original strength; particularly, cracked AA 2024-T3 substrate plates repaired with doublers of AA 2024-T3 with two configurations (riveted and with adhesive bonding) are analysed. The fatigue life of the substrate plates with cracks of 1, 2, 5, 10 and 12.7mm is computed using Fracture Analysis 3D (FRANC3D) tool. The stress intensity factors for the repaired AA 2024-T3 plates are computed for different crack lengths and compared using commercial FEA tool ABAQUS. The results for the bonded repairs showed significantly lower stress intensity factors compared with the riveted repairs. This improves the overall fatigue life of the bonded joint.

Benchmarking Memory Performance with the Data Cube Operator

NASA Technical Reports Server (NTRS)

Frumkin, Michael A.; Shabanov, Leonid V.

2004-01-01

Data movement across a computer memory hierarchy and across computational grids is known to be a limiting factor for applications processing large data sets. We use the Data Cube Operator on an Arithmetic Data Set, called ADC, to benchmark capabilities of computers and of computational grids to handle large distributed data sets. We present a prototype implementation of a parallel algorithm for computation of the operatol: The algorithm follows a known approach for computing views from the smallest parent. The ADC stresses all levels of grid memory and storage by producing some of 2d views of an Arithmetic Data Set of d-tuples described by a small number of integers. We control data intensity of the ADC by selecting the tuple parameters, the sizes of the views, and the number of realized views. Benchmarking results of memory performance of a number of computer architectures and of a small computational grid are presented.

Fracture toughness of brittle materials determined with chevron notch specimens

NASA Technical Reports Server (NTRS)

Shannon, J. L., Jr.; Bursey, R. T.; Munz, D.; Pierce, W. S.

1980-01-01

The use of chevron-notch specimens for determining the plane strain fracture toughness (K sub Ic) of brittle materials is discussed. Three chevron-notch specimens were investigated: short bar, short rod, and four-point-bend. The dimensionless stress intensity coefficient used in computing K sub Ic is derived for the short bar specimen from the superposition of ligament-dependent and ligament-independent solutions for the straight through crack, and also from experimental compliance calibrations. Coefficients for the four-point-bend specimen were developed by the same superposition procedure, and with additional refinement using the slice model of Bluhm. Short rod specimen stress intensity coefficients were determined only by experimental compliance calibration. Performance of the three chevron-notch specimens and their stress intensity factor relations were evaluated by tests on hot-pressed silicon nitride and sintered aluminum oxide. Results obtained with the short bar and the four-point-bend specimens on silicon nitride are in good agreement and relatively free of specimen geometry and size effects within the range investigated. Results on aluminum oxide were affected by specimen size and chevron-notch geometry, believed due to a rising crack growth resistance curve for the material. Only the results for the short bar specimen are presented in detail.

Coupled Aerodynamic and Structural Sensitivity Analysis of a High-Speed Civil Transport

NASA Technical Reports Server (NTRS)

Mason, B. H.; Walsh, J. L.

2001-01-01

An objective of the High Performance Computing and Communication Program at the NASA Langley Research Center is to demonstrate multidisciplinary shape and sizing optimization of a complete aerospace vehicle configuration by using high-fidelity, finite-element structural analysis and computational fluid dynamics aerodynamic analysis. In a previous study, a multi-disciplinary analysis system for a high-speed civil transport was formulated to integrate a set of existing discipline analysis codes, some of them computationally intensive, This paper is an extension of the previous study, in which the sensitivity analysis for the coupled aerodynamic and structural analysis problem is formulated and implemented. Uncoupled stress sensitivities computed with a constant load vector in a commercial finite element analysis code are compared to coupled aeroelastic sensitivities computed by finite differences. The computational expense of these sensitivity calculation methods is discussed.

The role of fault surface geometry in the evolution of the fault deformation zone: comparing modeling with field example from the Vignanotica normal fault (Gargano, Southern Italy).

NASA Astrophysics Data System (ADS)

Maggi, Matteo; Cianfarra, Paola; Salvini, Francesco

2013-04-01

Faults have a (brittle) deformation zone that can be described as the presence of two distintive zones: an internal Fault core (FC) and an external Fault Damage Zone (FDZ). The FC is characterized by grinding processes that comminute the rock grains to a final grain-size distribution characterized by the prevalence of smaller grains over larger, represented by high fractal dimensions (up to 3.4). On the other hand, the FDZ is characterized by a network of fracture sets with characteristic attitudes (i.e. Riedel cleavages). This deformation pattern has important consequences on rock permeability. FC often represents hydraulic barriers, while FDZ, with its fracture connection, represents zones of higher permability. The observation of faults revealed that dimension and characteristics of FC and FDZ varies both in intensity and dimensions along them. One of the controlling factor in FC and FDZ development is the fault plane geometry. By changing its attitude, fault plane geometry locally alter the stress component produced by the fault kinematics and its combination with the bulk boundary conditions (regional stress field, fluid pressure, rocks rheology) is responsible for the development of zones of higher and lower fracture intensity with variable extension along the fault planes. Furthermore, the displacement along faults provides a cumulative deformation pattern that varies through time. The modeling of the fault evolution through time (4D modeling) is therefore required to fully describe the fracturing and therefore permeability. In this presentation we show a methodology developed to predict distribution of fracture intensity integrating seismic data and numerical modeling. Fault geometry is carefully reconstructed by interpolating stick lines from interpreted seismic sections converted to depth. The modeling is based on a mixed numerical/analytical method. Fault surface is discretized into cells with their geometric and rheological characteristics. For each cell, the acting stress and strength are computed by analytical laws (Coulomb failure). Total brittle deformation for each cell is then computed by cumulating the brittle failure values along the path of each cell belonging to one side onto the facing one. The brittle failure value is provided by the DF function, that is the difference between the computed shear and the strength of the cell at each step along its path by using the Frap in-house developed software. The width of the FC and the FDZ are computed as a function of the DF distribution and displacement around the fault. This methodology has been successfully applied to model the brittle deformation pattern of the Vignanotica normal fault (Gargano, Southern Italy) where fracture intensity is expressed by the dimensionless H/S ratio representing the ratio between the dimension and the spacing of homologous fracture sets (i.e., group of parallel fractures that can be ascribed to the same event/stage/stress field).

Electronic communication preferences among mothers in the neonatal intensive care unit.

PubMed

Weems, M F; Graetz, I; Lan, R; DeBaer, L R; Beeman, G

2016-11-01

Mobile communication with the medical-care team has the potential to decrease stress among parents of infants admitted to the neonatal intensive care unit (NICU). We assessed mobile use and communication preferences in a population of urban minority NICU mothers. A 30-question English language survey was administered to mothers of NICU patients. The survey was completed by 217 mothers, 75% were Black, and 75% reported annual household income below $20 000. Only 56% had a computer with Internet access at home, but 79% used smartphones. Most (79%) have searched the Internet for health information in the past year. Receiving electronic messages about their babies was viewed favorably, and text messaging was the preferred platform. The majority of mothers felt electronic messaging would improve communication but should not replace verbal communication. Mobile communication is used widely in this population of NICU mothers and could potentially improve provider-parent communication and reduce parental stress.

Calculation of stress intensity factors in an isotropic multicracked plate: Part 2: Symbolic/numeric implementation

NASA Technical Reports Server (NTRS)

Arnold, S. M.; Binienda, W. K.; Tan, H. Q.; Xu, M. H.

1992-01-01

Analytical derivations of stress intensity factors (SIF's) of a multicracked plate can be complex and tedious. Recent advances, however, in intelligent application of symbolic computation can overcome these difficulties and provide the means to rigorously and efficiently analyze this class of problems. Here, the symbolic algorithm required to implement the methodology described in Part 1 is presented. The special problem-oriented symbolic functions to derive the fundamental kernels are described, and the associated automatically generated FORTRAN subroutines are given. As a result, a symbolic/FORTRAN package named SYMFRAC, capable of providing accurate SIF's at each crack tip, was developed and validated. Simple illustrative examples using SYMFRAC show the potential of the present approach for predicting the macrocrack propagation path due to existing microcracks in the vicinity of a macrocrack tip, when the influence of the microcrack's location, orientation, size, and interaction are taken into account.

A mixed-mode crack analysis of isotropic solids using conservation laws of elasticity

NASA Technical Reports Server (NTRS)

Yau, J. F.; Wang, S. S.; Corten, H. T.

1980-01-01

A simple and convenient method of analysis for studying two-dimensional mixed-mode crack problems is presented. The analysis is formulated on the basis of conservation laws of elasticity and of fundamental relationships in fracture mechanics. The problem is reduced to the determination of mixed-mode stress-intensity factor solutions in terms of conservation integrals involving known auxiliary solutions. One of the salient features of the present analysis is that the stress-intensity solutions can be determined directly by using information extracted in the far field. Several examples with solutions available in the literature are solved to examine the accuracy and other characteristics of the current approach. This method is demonstrated to be superior in its numerical simplicity and computational efficiency to other approaches. Solutions of more complicated and practical engineering fracture problems dealing with the crack emanating from a circular hole are presented also to illustrate the capacity of this method

Stress Intensity Formulas for Three Dimensional Crack in the Vicinity of an Interface

NASA Astrophysics Data System (ADS)

Noda, Nao-Aki; Liang, Bin; Xu, Chunhui

2008-02-01

In this study, stress intensity factors are considered by using exact solutions available for cracks near an interface. The effect of crack shape on the stress intensity factors is studied with varying the aspect ratio of the cracks. Then, the stress intensity factors are expressed as formulas useful for engineering applications. The stress intensity factors for interface cracks and a crack in a functionally graded material are also discussed.

A Hybrid Multi-Scale Model of Crystal Plasticity for Handling Stress Concentrations

DOE PAGES

Sun, Shang; Ramazani, Ali; Sundararaghavan, Veera

2017-09-04

Microstructural effects become important at regions of stress concentrators such as notches, cracks and contact surfaces. A multiscale model is presented that efficiently captures microstructural details at such critical regions. The approach is based on a multiresolution mesh that includes an explicit microstructure representation at critical regions where stresses are localized. At regions farther away from the stress concentration, a reduced order model that statistically captures the effect of the microstructure is employed. The statistical model is based on a finite element representation of the orientation distribution function (ODF). As an illustrative example, we have applied the multiscaling method tomore » compute the stress intensity factor K I around the crack tip in a wedge-opening load specimen. The approach is verified with an analytical solution within linear elasticity approximation and is then extended to allow modeling of microstructural effects on crack tip plasticity.« less

A Hybrid Multi-Scale Model of Crystal Plasticity for Handling Stress Concentrations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, Shang; Ramazani, Ali; Sundararaghavan, Veera

Microstructural effects become important at regions of stress concentrators such as notches, cracks and contact surfaces. A multiscale model is presented that efficiently captures microstructural details at such critical regions. The approach is based on a multiresolution mesh that includes an explicit microstructure representation at critical regions where stresses are localized. At regions farther away from the stress concentration, a reduced order model that statistically captures the effect of the microstructure is employed. The statistical model is based on a finite element representation of the orientation distribution function (ODF). As an illustrative example, we have applied the multiscaling method tomore » compute the stress intensity factor K I around the crack tip in a wedge-opening load specimen. The approach is verified with an analytical solution within linear elasticity approximation and is then extended to allow modeling of microstructural effects on crack tip plasticity.« less

Study of the vortex conditions of wings with large sweepback by extrapolation of the Jones method

NASA Technical Reports Server (NTRS)

Hirsch, P.

1980-01-01

The pockets of separation originating on the leading edges are surrounded by vortex sheets. Their configuration and intensity were determined by four conditions with the JONES approximation, which is itself corrected by a simple logic. Field pressures and stresses were computed for different cases and are compared with test results (pure deltas, swallow tails, truncations, strakes, ducks, fuselage).

Extraversion and cardiovascular responses to recurrent social stress: Effect of stress intensity.

PubMed

Lü, Wei; Xing, Wanying; Hughes, Brian M; Wang, Zhenhong

2017-10-28

The present study sought to establish whether the effects of extraversion on cardiovascular responses to recurrent social stress are contingent on stress intensity. A 2×5×1 mixed-factorial experiment was conducted, with social stress intensity as a between-subject variable, study phase as a within-subject variable, extraversion as a continuous independent variable, and cardiovascular parameter (HR, SBP, DBP, or RSA) as a dependent variable. Extraversion (NEO-FFI), subjective stress, and physiological stress were measured in 166 undergraduate students randomly assigned to undergo moderate (n=82) or high-intensity (n=84) social stress (a public speaking task with different levels of social evaluation). All participants underwent continuous physiological monitoring while facing two consecutive stress exposures distributed across five laboratory phases: baseline, stress exposure 1, post-stress 1, stress exposure 2, post-stress 2. Results indicated that under moderate-intensity social stress, participants higher on extraversion exhibited lesser HR reactivity to stress than participants lower on extraversion, while under high-intensity social stress, they exhibited greater HR, SBP, DBP and RSA reactivity. Under both moderate- and high-intensity social stress, participants higher on extraversion exhibited pronounced SBP and DBP response adaptation to repeated stress, and showed either better degree of HR recovery or greater amount of SBP and DBP recovery after stress. These findings suggest that individuals higher on extraversion exhibit physiological flexibility to cope with social challenges and benefit from adaptive cardiovascular responses. Copyright © 2017 Elsevier B.V. All rights reserved.

Three dimensional finite-element analysis of finite-thickness fracture specimens

NASA Technical Reports Server (NTRS)

Raju, I. S.; Newman, J. C., Jr.

1977-01-01

The stress-intensity factors for most of the commonly used fracture specimens (center-crack tension, single and double edge-crack tension, and compact), those that have a through-the-thickness crack, were calculated using a three dimensional finite-element elastic stress analysis. Three-dimensional singularity elements were used around the crack front. The stress intensity factors along the crack front were evaluated by using a force method, developed herein, that requires no prior assumption of either plane stress or plane strain. The calculated stress-intensity factors from the present analysis were compared with those from the literature whenever possible and were generally found to be in good agreement. The stress-intensity factors at the midplane for all specimens analyzed were within 3 percent of the two dimensional plane strain values. The stress intensity factors at the specimen surfaces were considerably lower than at the midplanes. For the center-crack tension specimens with large thickness to crack-length ratios, the stress-intensity factor reached a maximum near the surface of the specimen. In all other specimens considered the maximum stress intensity occurred at the midplane.

Hydrodynamic optimization of membrane bioreactor by horizontal geometry modification using computational fluid dynamics.

PubMed

Yan, Xiaoxu; Wu, Qing; Sun, Jianyu; Liang, Peng; Zhang, Xiaoyuan; Xiao, Kang; Huang, Xia

2016-01-01

Geometry property would affect the hydrodynamics of membrane bioreactor (MBR), which was directly related to membrane fouling rate. The simulation of a bench-scale MBR by computational fluid dynamics (CFD) showed that the shear stress on membrane surface could be elevated by 74% if the membrane was sandwiched between two baffles (baffled MBR), compared with that without baffles (unbaffled MBR). The effects of horizontal geometry characteristics of a bench-scale membrane tank were discussed (riser length index Lr, downcomer length index Ld, tank width index Wt). Simulation results indicated that the average cross flow of the riser was negatively correlated to the ratio of riser and downcomer cross-sectional area. A relatively small tank width would also be preferable in promoting shear stress on membrane surface. The optimized MBR had a shear elevation of 21.3-91.4% compared with unbaffled MBR under same aeration intensity. Copyright © 2015 Elsevier Ltd. All rights reserved.

A boundary element alternating method for two-dimensional mixed-mode fracture problems

NASA Technical Reports Server (NTRS)

Raju, I. S.; Krishnamurthy, T.

1992-01-01

A boundary element alternating method, denoted herein as BEAM, is presented for two dimensional fracture problems. This is an iterative method which alternates between two solutions. An analytical solution for arbitrary polynomial normal and tangential pressure distributions applied to the crack faces of an embedded crack in an infinite plate is used as the fundamental solution in the alternating method. A boundary element method for an uncracked finite plate is the second solution. For problems of edge cracks a technique of utilizing finite elements with BEAM is presented to overcome the inherent singularity in boundary element stress calculation near the boundaries. Several computational aspects that make the algorithm efficient are presented. Finally, the BEAM is applied to a variety of two dimensional crack problems with different configurations and loadings to assess the validity of the method. The method gives accurate stress intensity factors with minimal computing effort.

Classification of oxidative stress based on its intensity

PubMed Central

Lushchak, Volodymyr I.

2014-01-01

In living organisms production of reactive oxygen species (ROS) is counterbalanced by their elimination and/or prevention of formation which in concert can typically maintain a steady-state (stationary) ROS level. However, this balance may be disturbed and lead to elevated ROS levels called oxidative stress. To our best knowledge, there is no broadly acceptable system of classification of oxidative stress based on its intensity due to which proposed here system may be helpful for interpretation of experimental data. Oxidative stress field is the hot topic in biology and, to date, many details related to ROS-induced damage to cellular components, ROS-based signaling, cellular responses and adaptation have been disclosed. However, it is common situation when researchers experience substantial difficulties in the correct interpretation of oxidative stress development especially when there is a need to characterize its intensity. Careful selection of specific biomarkers (ROS-modified targets) and some system may be helpful here. A classification of oxidative stress based on its intensity is proposed here. According to this classification there are four zones of function in the relationship between “Dose/concentration of inducer” and the measured “Endpoint”: I – basal oxidative stress (BOS); II – low intensity oxidative stress (LOS); III – intermediate intensity oxidative stress (IOS); IV – high intensity oxidative stress (HOS). The proposed classification will be helpful to describe experimental data where oxidative stress is induced and systematize it based on its intensity, but further studies will be in need to clear discriminate between stress of different intensity. PMID:26417312

Arithmetic Data Cube as a Data Intensive Benchmark

NASA Technical Reports Server (NTRS)

Frumkin, Michael A.; Shabano, Leonid

2003-01-01

Data movement across computational grids and across memory hierarchy of individual grid machines is known to be a limiting factor for application involving large data sets. In this paper we introduce the Data Cube Operator on an Arithmetic Data Set which we call Arithmetic Data Cube (ADC). We propose to use the ADC to benchmark grid capabilities to handle large distributed data sets. The ADC stresses all levels of grid memory by producing 2d views of an Arithmetic Data Set of d-tuples described by a small number of parameters. We control data intensity of the ADC by controlling the sizes of the views through choice of the tuple parameters.

Probabilistic finite elements for fracture mechanics

NASA Technical Reports Server (NTRS)

Besterfield, Glen

1988-01-01

The probabilistic finite element method (PFEM) is developed for probabilistic fracture mechanics (PFM). A finite element which has the near crack-tip singular strain embedded in the element is used. Probabilistic distributions, such as expectation, covariance and correlation stress intensity factors, are calculated for random load, random material and random crack length. The method is computationally quite efficient and can be expected to determine the probability of fracture or reliability.

Mimicking Natural Laminar to Turbulent Flow Transition: A Systematic CFD Study Using PAB3D

NASA Technical Reports Server (NTRS)

Pao, S. Paul; Abdol-Hamid, Khaled S.

2005-01-01

For applied aerodynamic computations using a general purpose Navier-Stokes code, the common practice of treating laminar to turbulent flow transition over a non-slip surface is somewhat arbitrary by either treating the entire flow as turbulent or forcing the flow to undergo transition at given trip locations in the computational domain. In this study, the possibility of using the PAB3D code, standard k-epsilon turbulence model, and the Girimaji explicit algebraic stresses model to mimic natural laminar to turbulent flow transition was explored. The sensitivity of flow transition with respect to two limiters in the standard k-epsilon turbulence model was examined using a flat plate and a 6:1 aspect ratio prolate spheroid for our computations. For the flat plate, a systematic dependence of transition Reynolds number on background turbulence intensity was found. For the prolate spheroid, the transition patterns in the three-dimensional boundary layer at different flow conditions were sensitive to the free stream turbulence viscosity limit, the reference Reynolds number and the angle of attack, but not to background turbulence intensity below a certain threshold value. The computed results showed encouraging agreements with the experimental measurements at the corresponding geometry and flow conditions.

The effects of acute foot shock stress on empathy levels in rats.

PubMed

Karakilic, Aslı; Kizildag, Servet; Kandis, Sevim; Guvendi, Guven; Koc, Basar; Camsari, Gamze B; Camsari, Ulas M; Ates, Mehmet; Arda, Sevil Gonenc; Uysal, Nazan

2018-09-03

Empathy defined as the ability to understand and the share the feelings, thoughts, and attitudes of another, is an important skill in survival and reproduction. Among many factors that affect empathy include psychological stress, anxiety states. The aim of this study was to investigate the impact of acute psychological stress on empathic behavior and its association with oxytocin and vasopressin levels in amygdala and prefrontal cortex. Rats were subjected to 0.2 mA (low) and 1.6 mA (high) intensity of foot shock stress for duration of 20 min. Empathic behavior was found to be improved as a response to low intensity stress, but not to high intensity stress. As a response to lower intensity stress, vasopressin was increased in prefrontal cortex and amygdala; oxytocin was increased in only prefrontal cortex, and corticosterone levels increased in general. Anxiety indicators did not change in low intensity stress group yet; high intensity stress group demonstrated a lesser degree of anxiety response. High intensity stress group stayed unexpectedly more active in middle area of elevated plus maze test equipment, which may support impaired executive decision making abilities in the setting of high anxiety states. Further research is needed to investigate gender effects, the role of dopaminergic system and other stress related pathways in acute stress. Copyright © 2018 Elsevier B.V. All rights reserved.

Preliminary weight and costs of sandwich panels to distribute concentrated loads

NASA Technical Reports Server (NTRS)

Belleman, G.; Mccarty, J. E.

1976-01-01

Minimum mass honeycomb sandwich panels were sized for transmitting a concentrated load to a uniform reaction through various distances. The form skin gages were fully stressed with a finite element computer code. The panel general stability was evaluated with a buckling computer code labeled STAGS-B. Two skin materials were considered; aluminum and graphite-epoxy. The core was constant thickness aluminum honeycomb. Various panel sizes and load levels were considered. The computer generated data were generalized to allow preliminary least mass panel designs for a wide range of panel sizes and load intensities. An assessment of panel fabrication cost was also conducted. Various comparisons between panel mass, panel size, panel loading, and panel cost are presented in both tabular and graphical form.

An animal-to-human scaling law for blast-induced traumatic brain injury risk assessment.

PubMed

Jean, Aurélie; Nyein, Michelle K; Zheng, James Q; Moore, David F; Joannopoulos, John D; Radovitzky, Raúl

2014-10-28

Despite recent efforts to understand blast effects on the human brain, there are still no widely accepted injury criteria for humans. Recent animal studies have resulted in important advances in the understanding of brain injury due to intense dynamic loads. However, the applicability of animal brain injury results to humans remains uncertain. Here, we use advanced computational models to derive a scaling law relating blast wave intensity to the mechanical response of brain tissue across species. Detailed simulations of blast effects on the brain are conducted for different mammals using image-based biofidelic models. The intensity of the stress waves computed for different external blast conditions is compared across species. It is found that mass scaling, which successfully estimates blast tolerance of the thorax, fails to capture the brain mechanical response to blast across mammals. Instead, we show that an appropriate scaling variable must account for the mass of protective tissues relative to the brain, as well as their acoustic impedance. Peak stresses transmitted to the brain tissue by the blast are then shown to be a power function of the scaling parameter for a range of blast conditions relevant to TBI. In particular, it is found that human brain vulnerability to blast is higher than for any other mammalian species, which is in distinct contrast to previously proposed scaling laws based on body or brain mass. An application of the scaling law to recent experiments on rabbits furnishes the first physics-based injury estimate for blast-induced TBI in humans.

Neoagarotetraose protects mice against intense exercise induced stress by modulating gut microbial composition and function

USDA-ARS?s Scientific Manuscript database

Exhaustive exercise stress has emerged as an important health issue, and gastrointestinal problems are a common concern during intense exercise. In this study, we investigated potential anti-fatigue effects of neoagarotetraose (NAT) in mice under intense exercise stress. Exhaustive exercise stress s...

Gaseous hydrogen-induced cracking of Ti-5Al-2.5Sn.

NASA Technical Reports Server (NTRS)

Williams, D. P.; Nelson, H. G.

1972-01-01

Study of the kinetics of hydrogen-induced cracking in the Ti-5Al-2.5Sn titanium alloy, which has a structure of acicular alpha platelets in a beta matrix. The crack-growth rate at low stress-intensity levels was found to be exponentially dependent on stress intensity but essentially independent of temperature. The crack-growth rate at intermediate stress-intensity levels was found to be independent of stress intensity but dependent on temperature in such a way that crack-growth rate was controlled by a thermally activated mechanism having an activation energy of 5500 cal/mole and varied as the square root of the hydrogen pressure. The crack-growth rate at stress-intensity levels very near the fracture toughness is presumed to be independent of environment. The results are interpreted to suggest that crack growth at high stress intensities is controlled by normal, bulk failure mechanisms such as void coalescence and the like. At intermediate stress-intensity levels the transport of hydrogen to some interaction site along the alpha-beta boundary is the rate-controlling mechanism. The crack-growth behavior at low stress intensities suggests that the hydrogen interacts at this site to produce a strain-induced hydride which, in turn, induces crack growth by restricting plastic flow at the crack tip.

Development of the NASA/FLAGRO computer program for analysis of airframe structures

NASA Technical Reports Server (NTRS)

Forman, R. G.; Shivakumar, V.; Newman, J. C., Jr.

1994-01-01

The NASA/FLAGRO (NASGRO) computer program was developed for fracture control analysis of space hardware and is currently the standard computer code in NASA, the U.S. Air Force, and the European Agency (ESA) for this purpose. The significant attributes of the NASGRO program are the numerous crack case solutions, the large materials file, the improved growth rate equation based on crack closure theory, and the user-friendly promptive input features. In support of the National Aging Aircraft Research Program (NAARP); NASGRO is being further developed to provide advanced state-of-the-art capability for damage tolerance and crack growth analysis of aircraft structural problems, including mechanical systems and engines. The project currently involves a cooperative development effort by NASA, FAA, and ESA. The primary tasks underway are the incorporation of advanced methodology for crack growth rate retardation resulting from spectrum loading and improved analysis for determining crack instability. Also, the current weight function solutions in NASGRO or nonlinear stress gradient problems are being extended to more crack cases, and the 2-d boundary integral routine for stress analysis and stress-intensity factor solutions is being extended to 3-d problems. Lastly, effort is underway to enhance the program to operate on personal computers and work stations in a Windows environment. Because of the increasing and already wide usage of NASGRO, the code offers an excellent mechanism for technology transfer for new fatigue and fracture mechanics capabilities developed within NAARP.

Development of a numerical procedure for mixed mode K-solutions and fatigue crack growth in FCC single crystal superalloys

NASA Astrophysics Data System (ADS)

Ranjan, Srikant

2005-11-01

Fatigue-induced failures in aircraft gas turbine and rocket engine turbopump blades and vanes are a pervasive problem. Turbine blades and vanes represent perhaps the most demanding structural applications due to the combination of high operating temperature, corrosive environment, high monotonic and cyclic stresses, long expected component lifetimes and the enormous consequence of structural failure. Single crystal nickel-base superalloy turbine blades are being utilized in rocket engine turbopumps and jet engines because of their superior creep, stress rupture, melt resistance, and thermomechanical fatigue capabilities over polycrystalline alloys. These materials have orthotropic properties making the position of the crystal lattice relative to the part geometry a significant factor in the overall analysis. Computation of stress intensity factors (SIFs) and the ability to model fatigue crack growth rate at single crystal cracks subject to mixed-mode loading conditions are important parts of developing a mechanistically based life prediction for these complex alloys. A general numerical procedure has been developed to calculate SIFs for a crack in a general anisotropic linear elastic material subject to mixed-mode loading conditions, using three-dimensional finite element analysis (FEA). The procedure does not require an a priori assumption of plane stress or plane strain conditions. The SIFs KI, KII, and KIII are shown to be a complex function of the coupled 3D crack tip displacement field. A comprehensive study of variation of SIFs as a function of crystallographic orientation, crack length, and mode-mixity ratios is presented, based on the 3D elastic orthotropic finite element modeling of tensile and Brazilian Disc (BD) specimens in specific crystal orientations. Variation of SIF through the thickness of the specimens is also analyzed. The resolved shear stress intensity coefficient or effective SIF, Krss, can be computed as a function of crack tip SIFs and the resolved shear stress on primary slip planes. The maximum value of Krss and DeltaKrss was found to determine the crack growth direction and the fatigue crack growth rate respectively. The fatigue crack driving force parameter, DeltaK rss, forms an important multiaxial fatigue damage parameter that can be used to predict life in superalloy components.

Effect of a Diffusion Zone on Fatigue Crack Propagation in Layered FGMs

NASA Astrophysics Data System (ADS)

Hauber, Brett; Brockman, Robert; Paulino, Glaucio

2008-02-01

Research into functionally graded materials (FGMs) has led to advances in our ability to analyze cracks. However, two prominent aspects remain relatively unexplored: 1) development and validation of modeling methods for fatigue crack propagation in FGMs, and 2) experimental validation of stress intensity models in engineered materials such as two phase monolithic and graded materials. This work addresses some of these problems for a limited set of conditions, material systems (e.g., Ti/TiB), and material gradients. Numerical analyses are conducted for single edge notch bend (SENB) specimens. Stress intensity factors are computed using the specialized finite element code I-Franc (Illinois Fracture Analysis Code), which is tailored for both homogeneous and graded materials, as well as Franc2DL and ABAQUS. Crack extension is considered by means of specified crack increments, together with fatigue evaluations to predict crack propagation life. Results will be used to determine linear material gradient parameters that are significant for prediction of fatigue crack growth behavior.

Quantitative stress measurement of elastic deformation using mechanoluminescent sensor: An intensity ratio model

NASA Astrophysics Data System (ADS)

Cai, Tao; Guo, Songtao; Li, Yongzeng; Peng, Di; Zhao, Xiaofeng; Liu, Yingzheng

2018-04-01

The mechanoluminescent (ML) sensor is a newly developed non-invasive technique for stress/strain measurement. However, its application has been mostly restricted to qualitative measurement due to the lack of a well-defined relationship between ML intensity and stress. To achieve accurate stress measurement, an intensity ratio model was proposed in this study to establish a quantitative relationship between the stress condition and its ML intensity in elastic deformation. To verify the proposed model, experiments were carried out on a ML measurement system using resin samples mixed with the sensor material SrAl2O4:Eu2+, Dy3+. The ML intensity ratio was found to be dependent on the applied stress and strain rate, and the relationship acquired from the experimental results agreed well with the proposed model. The current study provided a physical explanation for the relationship between ML intensity and its stress condition. The proposed model was applicable in various SrAl2O4:Eu2+, Dy3+-based ML measurement in elastic deformation, and could provide a useful reference for quantitative stress measurement using the ML sensor in general.

Psychological recovery after intensive care: Outcomes of a long-term quasi-experimental study of structured nurse-led follow-up.

PubMed

Jónasdóttir, Rannveig J; Jónsdóttir, Helga; Gudmundsdottir, Berglind; Sigurdsson, Gisli H

2018-02-01

To compare psychological recovery of patients receiving structured nurse-led follow-up and patients receiving usual care after intensive care discharge. Quasi-experimental study. Single centre, university hospital, mixed intensive care patient population. Symptoms of post-traumatic stress disorder, anxiety and depression measured three and four times over 12 months after intensive care discharge. Disturbing memories of the intensive care stay and psychological reactions (that one's life was in danger, threat to physical integrity, intense fear, helplessness, horror) three months after intensive care. A mixed effect model tested differences between the groups over time and regression model predicted post-traumatic stress at three months. The experimental group had significantly more symptoms of post-traumatic stress and anxiety than the control group over the 12 months. Patients from both groups had severe symptoms of post-traumatic stress. Patients with post-traumatic stress at three months had disturbing memories and psychological reactions. The structured nurse-led follow-up did not improve patients' measured outcomes of psychological recovery after intensive care. Patients with severe symptoms of post-traumatic stress are of concern. Emphasis needs to be placed on disturbing memories of the intensive care stay and psychological reactions when constructing intensive care nurse-led follow-up. Copyright © 2017 Elsevier Ltd. All rights reserved.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pritam Chakraborty; Michael R. Tonks; Giovanni Pastore

Grain boundary (GB) separation as a mechanism for fission gas release (FGR), complementary to gas bubble interlinkage, has been experimentally observed in irradiated light water reactor fuel. However there has been limited effort to develop physics-based models incorporating this mechanism for the analysis of FGR. In this work, a computational study is carried out to investigate GB separation in UO2 fuel under the effect of gas bubble pressure and hydrostatic stress. A non-dimensional stress intensity factor formula is obtained through 2D axisymmetric analyses considering lenticular bubbles and Mode-I crack growth. The obtained functional form can be used in higher length-scalemore » models to estimate the contribution of GB separation to FGR.« less

Development of an algebraic stress/two-layer model for calculating thrust chamber flow fields

NASA Technical Reports Server (NTRS)

Chen, C. P.; Shang, H. M.; Huang, J.

1993-01-01

Following the consensus of a workshop in Turbulence Modeling for Liquid Rocket Thrust Chambers, the current effort was undertaken to study the effects of second-order closure on the predictions of thermochemical flow fields. To reduce the instability and computational intensity of the full second-order Reynolds Stress Model, an Algebraic Stress Model (ASM) coupled with a two-layer near wall treatment was developed. Various test problems, including the compressible boundary layer with adiabatic and cooled walls, recirculating flows, swirling flows and the entire SSME nozzle flow were studied to assess the performance of the current model. Detailed calculations for the SSME exit wall flow around the nozzle manifold were executed. As to the overall flow predictions, the ASM removes another assumption for appropriate comparison with experimental data, to account for the non-isotropic turbulence effects.

A new procedure for investigating three-dimensional stress fields in a thin plate with a through-the-thickness crack

NASA Astrophysics Data System (ADS)

Yi, Dake; Wang, TzuChiang

2018-06-01

In the paper, a new procedure is proposed to investigate three-dimensional fracture problems of a thin elastic plate with a long through-the-thickness crack under remote uniform tensile loading. The new procedure includes a new analytical method and high accurate finite element simulations. In the part of theoretical analysis, three-dimensional Maxwell stress functions are employed in order to derive three-dimensional crack tip fields. Based on the theoretical analysis, an equation which can describe the relationship among the three-dimensional J-integral J( z), the stress intensity factor K( z) and the tri-axial stress constraint level T z ( z) is derived first. In the part of finite element simulations, a fine mesh including 153360 elements is constructed to compute the stress field near the crack front, J( z) and T z ( z). Numerical results show that in the plane very close to the free surface, the K field solution is still valid for in-plane stresses. Comparison with the numerical results shows that the analytical results are valid.

Plates and shells containing a surface crack under general loading conditions

NASA Technical Reports Server (NTRS)

Joseph, Paul F.; Erdogan, Fazil

1987-01-01

Various through and part-through crack problems in plates and shells are considered. The line-spring model of Rice and Levy is generalized to the skew-symmetric case to solve surface crack problems involving mixed-mode, coplanar crack growth. Compliance functions are introduced which are valid for crack depth to thickness ratios at least up to .95. This includes expressions for tension and bending as well as expressions for in-plane shear, out-of-plane shear, and twisting. Transverse shear deformation is taken into account in the plate and shell theories and this effect is shown to be important in comparing stress intensity factors obtained from the plate theory with three-dimensional solutions. Stress intensity factors for cylinders obtained by the line-spring model also compare well with three-dimensional solution. By using the line-spring approach, stress intensity factors can be obtained for the through crack and for part-through crack of any crack front shape, without recalculation integrals that take up the bulk of the computer time. Therefore, parameter studies involving crack length, crack depth, shell type, and shell curvature are made in some detail. The results will be useful in brittle fracture and in fatigue crack propagation studies. All problems considered are of the mixed boundary value type and are reducted to strongly singular integral equations which make use of the finite-part integrals of Hadamard. The equations are solved numerically in a manner that is very efficient.

Structural analysis of a reflux pool-boiler solar receiver

NASA Astrophysics Data System (ADS)

Hoffman, E. L.; Stone, C. M.

1991-06-01

Coupled thermal-structural finite element calculations of a reflux pool-boiler solar receiver were performed to characterize the operating stresses and to address issues affecting the service life of the receiver. Analyses performed using shell elements provided information for receiver material selection and design optimization. Calculations based on linear elastic fracture mechanics principles were performed using continuum elements to assess the vulnerability of a seam-weld to fatigue crack growth. All calculations were performed using ABAQUS, a general purpose finite element code, and elements specifically formulated for coupled thermal-structural analysis. Two materials were evaluated: 316L SS and Haynes 230 alloys. The receiver response was simulated for a combination of structural and thermal loads that represent the startup and operating conditions of the receiver. For both materials, maximum stresses in the receiver developed shortly after startup due to uneven temperature distribution across the receiver surface. The largest effective stress was near yield in the 316L SS receiver and below 39 percent of yield in the Haynes 230 receiver. The calculations demonstrated that stress reductions of over 25 percent could be obtained by reducing the aft dome thickness to one closer to the absorber. The fatigue calculations demonstrated that the stress distribution near the seam-weld notch depends primarily on the structural load created by internal pressurization of the receiver rather than the thermal, indicating that the thermal loads can be neglected when assessing the stress intensity near the seam-weld notch. The stress intensity factor, computed using the J-integral method and crack opening-displacement field equations, was significantly below the fatigue threshold for most steels. The calculations indicated that the weld notch was always loaded in compression, a condition which is not conducive to fatigue crack growth.

Thermomechanical analysis of fast-burst reactors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miller, J.D.

1994-08-01

Fast-burst reactors are designed to provide intense, short-duration pulses of neutrons. The fission reaction also produces extreme time-dependent heating of the nuclear fuel. An existing transient-dynamic finite element code was modified specifically to compute the time-dependent stresses and displacements due to thermal shock loads of reactors. Thermomechanical analysis was then applied to determine structural feasibility of various concepts for an EDNA-type reactor and to optimize the mechanical design of the new SPR III-M reactor.

Exposure to Acute Stress is Associated with Attenuated Sweet Taste

PubMed Central

al’Absi, Mustafa; Nakajima, Motohiro; Hooker, Stephanie; Wittmers, Larry; Cragin, Tiffany

2011-01-01

This study examined the effects of stress on taste perception. Participants (N = 38; 21 women) completed two laboratory sessions: one stress (public speaking, math, and cold pressor) and one control rest session. The taste perception test was conducted at the end of each session and included rating the intensity and pleasantness of sweet, salty, sour, and savory solutions at suprathreshold concentrations. Cardiovascular, hormonal, and mood measures were collected throughout the sessions. Participants showed the expected changes in cardiovascular, hormonal, and mood measures in response to stress. Reported intensity of the sweet solution was significantly lower on the stress day than on the rest day. Cortisol level post stress predicted reduced intensity of salt and sour, suggesting that stress-related changes in adrenocortical activity were related to reduced taste intensity. Results indicate that acute stress may alter taste perception, and ongoing research investigates the extent to which these changes mediate effects of stress on appetite. PMID:22091733

Effect of stress hyperglycemia and intensive rehabilitation therapy in non-diabetic hemorrhagic stroke: Korean Stroke Cohort for Functioning and Rehabilitation.

PubMed

Yoon, J A; Kim, D Y; Sohn, M K; Lee, J; Lee, S-G; Lee, Y-S; Han, E Y; Joo, M C; Oh, G-J; Han, J; Lee, S W; Park, M; Chang, W H; Shin, Y-I; Kim, Y-H

2016-11-01

We investigated the effect of stress hyperglycemia on the functional outcomes of non-diabetic hemorrhagic stroke. In addition, we investigated the usefulness of intensive rehabilitation for improving functional outcomes in patients with stress hyperglycemia. Non-diabetic hemorrhagic stroke patients were recruited and divided into two groups: intracerebral hemorrhage (ICH) (n = 165) and subarachnoid hemorrhage (SAH) (n = 156). Each group was divided into non-diabetics with or without stress hyperglycemia. Functional assessments were performed at 7 days and 3, 6 and 12 months after stroke onset. The non-diabetic with stress hyperglycemia groups were again divided into two groups who either received or did not receive intensive rehabilitation treatment. Serial functional outcome was compared between groups. For the ICH group, patients with stress hyperglycemia had worse modified Rankin Scale, National Institutes of Health Stroke Scale, Functional Ambulatory Category and Korean Mini-Mental State Examination scores than patients without stress hyperglycemia. For the SAH group, patients with stress hyperglycemia had worse scores on all functional assessments than patients without stress hyperglycemia at all time-points. After intensive rehabilitation treatment of patients with stress hyperglycemia, the ICH group had better scores on Functional Ambulatory Category and the SAH group had better scores on all functional assessments than patients without intensive rehabilitation treatment. Stress hyperglycemia affects the long-term prognosis of non-diabetic hemorrhagic stroke patients. Among stress hyperglycemia patients, intensive rehabilitation can enhance functional improvement after stroke. © 2016 EAN.

Analysis of mixed-mode crack propagation using the boundary integral method

NASA Technical Reports Server (NTRS)

Mendelson, A.; Ghosn, L. J.

1986-01-01

Crack propagation in a rotating inner raceway of a high speed roller bearing is analyzed using the boundary integral equation method. The method consists of an edge crack in a plate under tension, upon which varying Hertzian stress fields are superimposed. A computer program for the boundary integral equation method was written using quadratic elements to determine the stress and displacement fields for discrete roller positions. Mode I and Mode II stress intensity factors and crack extension forces G sub 00 (energy release rate due to tensile opening mode) and G sub r0 (energy release rate due to shear displacement mode) were computed. These calculations permit determination of that crack growth angle for which the change in the crack extension forces is maximum. The crack driving force was found to be the alternating mixed-mode loading that occurs with each passage of the most heavily loaded roller. The crack is predicted to propagate in a step-like fashion alternating between radial and inclined segments, and this pattern was observed experimentally. The maximum changes DeltaG sub 00 and DeltaG sub r0 of the crack extension forces are found to be good measures of the crack propagation rate and direction.

Mathematical model of a rotational bioreactor for the dynamic cultivation of scaffold-adhered human mesenchymal stem cells for bone regeneration

NASA Astrophysics Data System (ADS)

Ganimedov, V. L.; Papaeva, E. O.; Maslov, N. A.; Larionov, P. M.

2017-09-01

Development of cell-mediated scaffold technologies for the treatment of critical bone defects is very important for the purpose of reparative bone regeneration. Today the properties of the bioreactor for cell-seeded scaffold cultivation are the subject of intensive research. We used the mathematical modeling of rotational reactor and construct computational algorithm with the help of ANSYS software package to develop this new procedure. The solution obtained with the help of the constructed computational algorithm is in good agreement with the analytical solution of Couette for the task of two coaxial cylinders. The series of flow computations for different rotation frequencies (1, 0.75, 0.5, 0.33, 1.125 Hz) was performed for the laminar flow regime approximation with the help of computational algorithm. It was found that Taylor vortices appear in the annular gap between the cylinders in a simulated bioreactor. It was obtained that shear stress in the range of interest (0.002-0.1 Pa) arise on outer surface of inner cylinder when it rotates with the frequency not exceeding 0.8 Hz. So the constructed mathematical model and the created computational algorithm for calculating the flow parameters allow predicting the shear stress and pressure values depending on the rotation frequency and geometric parameters, as well as optimizing the operating mode of the bioreactor.

Caregiver stress and outcomes of children with pediatric feeding disorders treated in an intensive interdisciplinary program.

PubMed

Greer, Ashley J; Gulotta, Charles S; Masler, Elizabeth A; Laud, Rinita B

2008-07-01

This study investigated the impact of an intensive interdisciplinary feeding program on caregiver stress and child outcomes of children with feeding disorders across three categories. Children were categorized into either tube dependent, liquid dependent, or food selective groups. Outcomes for caregiver stress levels, child mealtime behaviors, weight, and calories were examined at admission and discharge for 121 children. Repeated measures ANOVAs were used to examine differences pre- and post-treatment and across feeding categories. Caregiver stress, child mealtime behaviors, weight, and caloric intake improved significantly following treatment in the intensive feeding program, regardless of category placement. Few studies have examined the impact of an intensive interdisciplinary approach on caregiver stress, as well as on child outcome variables with such a diverse population. This study provides support that regardless of a child's medical and feeding history, an intensive interdisciplinary approach significantly improves caregiver stress and child outcomes.

The Evolution of Stress Intensity Factors and the Propagation of Cracks in Elastic Media

NASA Astrophysics Data System (ADS)

Friedman, Avner; Hu, Bei; Velazquez, Juan J. L.

When a crack Γs propagates in an elastic medium the stress intensity factors evolve with the tip x(s) of Γs. In this paper we derive formulae which describe the evolution of these stress intensity factors for a homogeneous isotropic elastic medium under plane strain conditions. Denoting by ψ=ψ(x,s) the stress potential (ψ is biharmonic and has zero traction along the crack Γs) and by κ(s) the curvature of the crack at the tip x(s), we prove that the stress intensity factors A1(s), A2(s), as functions of s, satisfy: where , are stress intensity factors of the tangential derivative of in the polar coordinate system at x(s) with θ=0 in the direction of the crack at x(s). The case of antiplane shearing is also briefly considered; in this case ψ is harmonic.

Cortical encoding and neurophysiological tracking of intensity and pitch cues signaling English stress patterns in native and nonnative speakers.

PubMed

Chung, Wei-Lun; Bidelman, Gavin M

2016-01-01

We examined cross-language differences in neural encoding and tracking of intensity and pitch cues signaling English stress patterns. Auditory mismatch negativities (MMNs) were recorded in English and Mandarin listeners in response to contrastive English pseudowords whose primary stress occurred either on the first or second syllable (i.e., "nocTICity" vs. "NOCticity"). The contrastive syllable stress elicited two consecutive MMNs in both language groups, but English speakers demonstrated larger responses to stress patterns than Mandarin speakers. Correlations between the amplitude of ERPs and continuous changes in the running intensity and pitch of speech assessed how well each language group's brain activity tracked these salient acoustic features of lexical stress. We found that English speakers' neural responses tracked intensity changes in speech more closely than Mandarin speakers (higher brain-acoustic correlation). Findings demonstrate more robust and precise processing of English stress (intensity) patterns in early auditory cortical responses of native relative to nonnative speakers. Copyright © 2016 Elsevier Inc. All rights reserved.

The perception of sentence stress in cochlear implant recipients.

PubMed

Meister, Hartmut; Landwehr, Markus; Pyschny, Verena; Wagner, Petra; Walger, Martin

2011-01-01

Sentence stress is a vital attribute of speech since it indicates the importance of specific words within an utterance. Basic acoustic correlates of stress are syllable duration, intensity, and fundamental frequency (F0). Objectives of the study were to determine cochlear implant (CI) users' perception of the acoustic correlates and to uncover which cues are used for stress identification. Several experiments addressed the discrimination of changes in syllable duration, intensity, and F0 as well as stress identification based on these cues. Moreover, the discrimination of combined cues and identification of stress in conversational speech was examined. Both natural utterances and artificial manipulations of the acoustic cues were used as stimuli. Discrimination of syllable duration did not differ significantly between CI recipients and a control group of normal-hearing listeners. In contrast, CI users performed significantly worse on tasks of discrimination and stress identification based on F0 as well as on intensity. Results from these measurements were significantly correlated with the ability to identify stress in conversational speech. Discrimination performance for covarying F0 and intensity changes was more strongly correlated to identification performance than was found for discrimination of either F0 or intensity alone. Syllable duration was not related to stress identification in natural utterances. The outcome emphasizes the importance of both F0 and intensity for CI users' identification of sentence-based stress. Both cues were used separately for stress perception, but combining the cues provided extra benefit for most of the subjects.

Stress-intensity factor equations for cracks in three-dimensional finite bodies

NASA Technical Reports Server (NTRS)

Newman, J. C., Jr.; Raju, I. S.

1981-01-01

Empirical stress intensity factor equations are presented for embedded elliptical cracks, semi-elliptical surface cracks, quarter-elliptical corner cracks, semi-elliptical surface cracks at a hole, and quarter-elliptical corner cracks at a hole in finite plates. The plates were subjected to remote tensile loading. Equations give stress intensity factors as a function of parametric angle, crack depth, crack length, plate thickness, and where applicable, hole radius. The stress intensity factors used to develop the equations were obtained from three dimensional finite element analyses of these crack configurations.

Rapid insights from remote sensing in the geosciences

NASA Astrophysics Data System (ADS)

Plaza, Antonio

2015-03-01

The growing availability of capacity computing for atomistic materials modeling has encouraged the use of high-accuracy computationally intensive interatomic potentials, such as SNAP. These potentials also happen to scale well on petascale computing platforms. SNAP has a very general form and uses machine-learning techniques to reproduce the energies, forces, and stress tensors of a large set of small configurations of atoms, which are obtained using high-accuracy quantum electronic structure (QM) calculations. The local environment of each atom is characterized by a set of bispectrum components of the local neighbor density projected on to a basis of hyperspherical harmonics in four dimensions. The computational cost per atom is much greater than that of simpler potentials such as Lennard-Jones or EAM, while the communication cost remains modest. We discuss a variety of strategies for implementing SNAP in the LAMMPS molecular dynamics package. We present scaling results obtained running SNAP on three different classes of machine: a conventional Intel Xeon CPU cluster; the Titan GPU-based system; and the combined Sequoia and Vulcan BlueGene/Q. The growing availability of capacity computing for atomistic materials modeling has encouraged the use of high-accuracy computationally intensive interatomic potentials, such as SNAP. These potentials also happen to scale well on petascale computing platforms. SNAP has a very general form and uses machine-learning techniques to reproduce the energies, forces, and stress tensors of a large set of small configurations of atoms, which are obtained using high-accuracy quantum electronic structure (QM) calculations. The local environment of each atom is characterized by a set of bispectrum components of the local neighbor density projected on to a basis of hyperspherical harmonics in four dimensions. The computational cost per atom is much greater than that of simpler potentials such as Lennard-Jones or EAM, while the communication cost remains modest. We discuss a variety of strategies for implementing SNAP in the LAMMPS molecular dynamics package. We present scaling results obtained running SNAP on three different classes of machine: a conventional Intel Xeon CPU cluster; the Titan GPU-based system; and the combined Sequoia and Vulcan BlueGene/Q. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corp., for the U.S. Dept. of Energy's National Nuclear Security Admin. under Contract DE-AC04-94AL85000.

Recent Developments and Challenges Implementing New and Improved Stress Intensity Factor (K) Solutions in NASGRO for Damage Tolerance Analyses

NASA Technical Reports Server (NTRS)

Cardinal, Joseph W.; McClung, R. Craig; Lee, Yi-Der; Guo, Yajun; Beek, Joachim M.

2014-01-01

Fatigue crack growth analysis software has been available to damage tolerance analysts for many years in either commercial products or via proprietary in-house codes. The NASGRO software has been publicly available since the mid-80s (known as NASA/FLAGRO up to 1999) and since 2000 has been sustained and further developed by a collaborative effort between Southwest Research Institute® (SwRI®), the NASA Johnson Space Center (JSC), and the members of the NASGRO Industrial Consortium. Since the stress intensity factor (K) is the foundation of fracture mechanics and damage tolerance analysis of aircraft structures, a significant focus of development efforts in the past fifteen years has been geared towards enhancing legacy K solutions and developing new and efficient numerical K solutions that can handle the complicated stress gradients computed by today’s analysts using detailed finite element models of fatigue critical locations. This paper provides an overview of K solutions that have been recently implemented or improved for the analysis of geometries such as two unequal through cracks at a hole and two unequal corner cracks at a hole, as well as state-of-the-art weight function models capable of computing K in the presence of univariant and/or bivariant stress gradients and complicated residual stress distributions. Some historical background is provided to review how common K solutions have evolved over the years, including selective examples from the literature and from new research. Challenges and progress in rectifying discrepancies between older legacy solutions and newer models are reviewed as well as approaches and challenges for verification and validation of K solutions. Finally, a summary of current challenges and future research and development needs is presented. A key theme throughout the presentation of this paper will be how members of the aerospace industry have collaborated with software developers to develop a practical analysis tool that is used world-wide to support new design as well as the ongoing sustainment and airworthiness of commercial and military aircraft.

Effect of debond growth on stress-intensity factors in a cracked orthotropic sheet stiffened by a semi-infinite orthotropic sheet

NASA Technical Reports Server (NTRS)

Bigelow, C. A.

1986-01-01

Stress-intensity factors are determined for a cracked infinite sheet adhesively bonded to a stringer, and debonding of the adhesive layer is predicted. The stringer is modeled as a semi-infinite sheet. Adhesive nonlinearity is also included. Both the sheet and stringer are treated as homogeneous, orthotropic materials. A set of integral equations is formulated and solved to obtain the adhesive shear stresses and crack-tip stress-intensity factors. Adhesive debonding is predicted using a rupture criterion based on the combined adhesive stresses. When the crack is not under the stringer, the debond extends along the edge of the stringer. When the crack tip is beneath the stringer, the debond grows to the end of the crack, then along the edge of the stringer. Stress levels required for debond initiation decrease as the crack tip is moved beneath the stringer. With a nonlinear adhesive, the debond initiates at higher applied stress levels than in linear adhesive cases. Compared with the linear adhesive solution, modeling a nonlinear adhesive causes the stress-intensity factor to increase when the bond is assumed to remain intact but causes the stress-intensity factor to decrease when debonding is included.

Finite-element analysis of dynamic fracture

NASA Technical Reports Server (NTRS)

Aberson, J. A.; Anderson, J. M.; King, W. W.

1976-01-01

Applications of the finite element method to the two dimensional elastodynamics of cracked structures are presented. Stress intensity factors are computed for two problems involving stationary cracks. The first serves as a vehicle for discussing lumped-mass and consistent-mass characterizations of inertia. In the second problem, the behavior of a photoelastic dynamic tear test specimen is determined for the time prior to crack propagation. Some results of a finite element simulation of rapid crack propagation in an infinite body are discussed.

A simple method for determining stress intensity factors for a crack in bi-material interface

NASA Astrophysics Data System (ADS)

Morioka, Yuta

Because of violently oscillating nature of stress and displacement fields near the crack tip, it is difficult to obtain stress intensity factors for a crack between two dis-similar media. For a crack in a homogeneous medium, it is a common practice to find stress intensity factors through strain energy release rates. However, individual strain energy release rates do not exist for bi-material interface crack. Hence it is necessary to find alternative methods to evaluate stress intensity factors. Several methods have been proposed in the past. However they involve mathematical complexity and sometimes require additional finite element analysis. The purpose of this research is to develop a simple method to find stress intensity factors in bi-material interface cracks. A finite element based projection method is proposed in the research. It is shown that the projection method yields very accurate stress intensity factors for a crack in isotropic and anisotropic bi-material interfaces. The projection method is also compared to displacement ratio method and energy method proposed by other authors. Through comparison it is found that projection method is much simpler to apply with its accuracy comparable to that of displacement ratio method.

Flaw growth of 7075, 7475, 7050 and 7049 aluminum alloy plate in stress corrosion environments: 4-year marine atmosphere results

NASA Technical Reports Server (NTRS)

Hasse, K. R.; Dorward, R. C.

1981-01-01

After nearly 53 months of exposure to marine atmosphere, crack growth in SL DCB specimens from 7075, 7475, 7050, and 7049-T7X plate has slowed to the arbitrary 10 to the -10 power m/sec used to define threshold stress intensity. Because some specimens appear to be approaching crack arrest, the importance of self-loading from corrosion product wedging as a significant driving force for crack propagation in overaged materials is questioned. Crack length-time data were analyzed using a computer curve fitting program which minimized the effects of normal data scatter, and provided a clearer picture of material performance. Precracked specimen data are supported by the results of smooth specimen tests. Transgranular stress corrosion cracking was observed in TL DCB specimens from all four alloys. This process is extremely slow and is characterized by a striated surface morphology.

Micromechanical predictions of crack propagation and fracture energy in a single fiber boron/aluminum model composite

NASA Technical Reports Server (NTRS)

Adams, D. F.; Mahishi, J. M.

1982-01-01

The axisymmetric finite element model and associated computer program developed for the analysis of crack propagation in a composite consisting of a single broken fiber in an annular sheath of matrix material was extended to include a constant displacement boundary condition during an increment of crack propagation. The constant displacement condition permits the growth of a stable crack, as opposed to the catastropic failure in an earlier version. The finite element model was refined to respond more accurately to the high stresses and steep stress gradients near the broken fiber end. The accuracy and effectiveness of the conventional constant strain axisymmetric element for crack problems was established by solving the classical problem of a penny-shaped crack in a thick cylindrical rod under axial tension. The stress intensity factors predicted by the present finite element model are compared with existing continuum results.

Full Field Photoelastic Stress Analysis

NASA Technical Reports Server (NTRS)

Lesniak, Jon R. (Inventor)

2000-01-01

A structural specimen coated with or constructed of photoelastic material, when illuminated with circularly polarized light will, when stressed: reflect or transmit elliptically polarized light, the direction of the axes of the ellipse and variation of the elliptically light from illuminating circular light will correspond to and indicate the direction and magnitude of the shear stresses for each illuminated point on the specimen. The principles of this invention allow for several embodiments of stress analyzing apparatus, ranging from those involving multiple rotating optical elements, to those which require no moving parts at all. A simple polariscope may be constructed having two polarizing filters with a single one-quarter waveplate placed between the polarizing filters. Light is projected through the first polarizing filter and the one-quarter waveplate and is reflected from a sub-fringe birefringent coating on a structure under load. Reflected light from the structure is analyzed with a polarizing filter. The two polarizing filters and the one-quarter waveplate may be rotated together or the analyzer alone may be rotated. Computer analysis of the variation in light intensity yields shear stress magnitude and direction.

Probabilistic Simulation of Progressive Fracture in Bolted-Joint Composite Laminates

NASA Technical Reports Server (NTRS)

Minnetyan, L.; Singhal, S. N.; Chamis, C. C.

1996-01-01

This report describes computational methods to probabilistically simulate fracture in bolted composite structures. An innovative approach that is independent of stress intensity factors and fracture toughness was used to simulate progressive fracture. The effect of design variable uncertainties on structural damage was also quantified. A fast probability integrator assessed the scatter in the composite structure response before and after damage. Then the sensitivity of the response to design variables was computed. General-purpose methods, which are applicable to bolted joints in all types of structures and in all fracture processes-from damage initiation to unstable propagation and global structure collapse-were used. These methods were demonstrated for a bolted joint of a polymer matrix composite panel under edge loads. The effects of the fabrication process were included in the simulation of damage in the bolted panel. Results showed that the most effective way to reduce end displacement at fracture is to control both the load and the ply thickness. The cumulative probability for longitudinal stress in all plies was most sensitive to the load; in the 0 deg. plies it was very sensitive to ply thickness. The cumulative probability for transverse stress was most sensitive to the matrix coefficient of thermal expansion. In addition, fiber volume ratio and fiber transverse modulus both contributed significantly to the cumulative probability for the transverse stresses in all the plies.

Work stress, occupational burnout and depression levels: a clinical study of paediatric intensive care unit nurses in Taiwan.

PubMed

Lin, Tzu-Ching; Lin, Huey-Shyan; Cheng, Su-Fen; Wu, Li-Min; Ou-Yang, Mei-Chen

2016-04-01

This study aimed to examine the relationship between work stress and depression; and investigate the mediating effect of occupational burnout among nurses in paediatric intensive care units. The relationships among work stress, occupational burnout and depression level have been explored, neither regarding occupational burnout as the mediating role that causes work stress to induce depression nor considering the paediatric intensive care unit context. A cross-sectional correlational design was conducted. One hundred and forty-four female paediatric intensive care unit nurses from seven teaching hospitals in southern Taiwan were recruited as the participants. Data were collected by structured questionnaires including individual demographics, the Nurse Stress Checklist, the Occupational Burnout Inventory and the Taiwan Depression Questionnaire. The results indicated that after controlling for individual demographic variables, the correlations of work stress with occupational burnout, as well as work stress and occupational burnout with depression level were all positive. Furthermore, occupational burnout may exert a partial mediating effect on the relationship between work stress and depression level. This study provides information about work stress, occupational burnout and depression level, and their correlations, as well as the mediating role of occupational burnout among paediatric intensive care unit nurses. It suggests government departments and hospital administrators when formulating interventions to prevent work stress and occupational burnout. These interventions can subsequently prevent episodes of depression in paediatric intensive care unit nurses, thereby providing patients with a safe and high-quality nursing environment. © 2016 John Wiley & Sons Ltd.

Linear elastic fracture mechanics primer

NASA Technical Reports Server (NTRS)

Wilson, Christopher D.

1992-01-01

This primer is intended to remove the blackbox perception of fracture mechanics computer software by structural engineers. The fundamental concepts of linear elastic fracture mechanics are presented with emphasis on the practical application of fracture mechanics to real problems. Numerous rules of thumb are provided. Recommended texts for additional reading, and a discussion of the significance of fracture mechanics in structural design are given. Griffith's criterion for crack extension, Irwin's elastic stress field near the crack tip, and the influence of small-scale plasticity are discussed. Common stress intensities factor solutions and methods for determining them are included. Fracture toughness and subcritical crack growth are discussed. The application of fracture mechanics to damage tolerance and fracture control is discussed. Several example problems and a practice set of problems are given.

Stress-intensity factors and crack-opening displacements for round compact specimens. [fracture toughness of metallic materials

NASA Technical Reports Server (NTRS)

Newman, J. C., Jr.

1979-01-01

A two dimensional, boundary collocation stress analysis was used to analyze various round compact specimens. The influence of the round external boundary and of pin-loaded holes on stress intensity factors and crack opening displacements was determined as a function of crack-length-to-specimen-width ratios. A wide-range equation for the stress intensity factors was developed. Equations for crack-surface displacements and load-point displacements were also developed. In addition, stress intensity factors were calculated from compliance methods to demonstrate that load-displacement records must be made at the loading points and not along the crack line for crack-length-to-specimen-width ratios less than about 0.4.

Mathematical and computational aspects of nonuniform frictional slip modeling

NASA Astrophysics Data System (ADS)

Gorbatikh, Larissa

2004-07-01

A mechanics-based model of non-uniform frictional sliding is studied from the mathematical/computational analysis point of view. This problem is of a key importance for a number of applications (particularly geomechanical ones), where materials interfaces undergo partial frictional sliding under compression and shear. We show that the problem is reduced to Dirichlet's problem for monotonic loading and to Riemman's problem for cyclic loading. The problem may look like a traditional crack interaction problem, however, it is confounded by the fact that locations of n sliding intervals are not known. They are to be determined from the condition for the stress intensity factors: KII=0 at the ends of the sliding zones. Computationally, it reduces to solving a system of 2n coupled non-linear algebraic equations involving singular integrals with unknown limits of integration.

A mixed-mode crack analysis of rectilinear anisotropic solids using conservation laws of elasticity

NASA Technical Reports Server (NTRS)

Wang, S. S.; Yau, J. F.; Corten, H. T.

1980-01-01

A very simple and convenient method of analysis for studying two-dimensional mixed-mode crack problems in rectilinear anisotropic solids is presented. The analysis is formulated on the basis of conservation laws of anisotropic elasticity and of fundamental relationships in anisotropic fracture mechanics. The problem is reduced to a system of linear algebraic equations in mixed-mode stress intensity factors. One of the salient features of the present approach is that it can determine directly the mixed-mode stress intensity solutions from the conservation integrals evaluated along a path removed from the crack-tip region without the need of solving the corresponding complex near-field boundary value problem. Several examples with solutions available in the literature are solved to ensure the accuracy of the current analysis. This method is further demonstrated to be superior to other approaches in its numerical simplicity and computational efficiency. Solutions of more complicated and practical engineering problems dealing with the crack emanating from a circular hole in composites are presented also to illustrate the capacity of this method.

Influence of load interactions on crack growth as related to state of stress and crack closure

NASA Technical Reports Server (NTRS)

Telesman, J.

1985-01-01

Fatigue crack propagation (FCP) after an application of a low-high loading sequence was investigated as a function of specimen thickness and crack closure. No load interaction effects were detected for specimens in a predominant plane strain state. However, for the plane stress specimens, initially high FCP rates after transition to a higher stress intensity range were observed. The difference in observed behavior was explained by examining the effect of the resulting closure stress intensity values on the effective stress intensity range.

Crack growth induced by thermal-mechanical loading

NASA Astrophysics Data System (ADS)

John, R.; Hartman, G. A.; Gallagher, J. P.

1992-06-01

Advanced aerospace structures are often subjected to combined thermal and mechanical loads. The fracture-mechanics behavior of the structures may be altered by the thermal state existing around the crack. Hence, design of critical structural elements requires the knowledge of stress-intensity factors under both thermal and mechanical loads. This paper describes the development of an experimental technique to verify the thermal-stress-intensity factor generated by a temperature gradient around the crack. Thin plate specimens of a model material (AISI-SAE 1095 steel) were used for the heat transfer and thermal-mechanical fracture tests. Rapid thermal loading was achieved using high-intensity focused infrared spot heaters. These heaters were also used to generate controlled temperature rates for heat-transfer verification tests. The experimental results indicate that thermal loads can generate stress-intensity factors large enough to induce crack growth. The proposed thermal-stress-intensity factors appear to have the same effect as the conventional mechanical-stress-intensity factors with respect to fracture.

Strength evaluation of butt joint by stress intensity factor of small edge crack near interface edge

NASA Astrophysics Data System (ADS)

Sato, T.; Oda, K.; Tsutsumi, N.

2018-06-01

Failure of the bonded dissimilar materials generally initiates near the interface, or just from the interface edge due to the stress singularity at the interface edge. In this study, the stress intensity factor of an edge crack close to the interface between the dissimilar materials is analyzed. The small edge crack is strongly dominated by the singular stress field near the interface edge. The analysis of stress intensity factor of small edge crack near the interface in bi-material and butt joint plates is carried out by changing the length and the location of the crack and the region dominated by the interface edge is examined. It is found that the dimensionless stress intensity factor of small crack, normalized by the singular stress at the crack tip point in the bonded plate without the crack, is equal to 1.12, independent of the material combination and adhesive layer thickness, when the relative crack length with respect to the crack location is less than 0.01. The adhesive strength of the bonded plate with various adhesive layer thicknesses can be expressed as the constant critical stress intensity factor of the small edge crack.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oshima, M.; Port, S.C.; Ray, G.

Forty-two patients (pts) with 1VD(greater than or equal to 70% stenosis and no prior infarction) undergoing PTCA provide a model to study the efficacy with which non-invasive tests can a) detect stress induced ischemia and b) reflect the reduction in stress induced ischemia expected from arteriographically successful PTCA. The diseased coronary was the right in 12, the circumflex in 3 and the LAD in 27 pts. Pre- and post- PTCA paired data were available from treadmill (ETT), planar thallium (Qual-T1), 7 pinhole tomography and 1st pass radionuclide angiograms (RNA) in 29, 26, 31 and 25 pts. After tomographic images weremore » digitized and analyzed by a computer, the intensity (=area/range, a numerical index of the severity of a defect) served as a quantitative T1 (Quant-T1). Criteria for ischemia were: significant ST change on ETT, unequivocal stress defects on Qual-T1, Quant-T1 intensity greater than or equal to 2.0, and exercise ejection fraction (Ex EF) greater than or equal to 0.55 or a new wall motion abnormality on Ex RNA. Ex EF was .61 +- .13 pre- and .63 +- .10 post-PTCA (p=NS). Quant-T1 intensity was 9.5 +- 7.1 pre- and 4.0 +- 5.5 post-PTCA (p=.0003). T1 testing was the most sensitive for detecting ischemia pre-PTCA. However, given an ischemic response pre-PTCA, the RNA showed the greatest trend toward normalization post-PTCA. If one test must be chosen Quant-T1 seems most appropriate in the evaluation of pre- and post- PTCA pts with 1VD.« less

Direct Assessment of Wall Shear Stress by Signal Intensity Gradient from Time-of-Flight Magnetic Resonance Angiography

PubMed Central

Lee, Sang Hyuk; Ryu, Han Uk; Park, Se-Hyoung; Chung, Gyung-Ho; Cho, Young I.

2017-01-01

The aim of the study was to calculate the arterial wall signal intensity gradient (SIG) from time-of-flight MR angiography (TOF-MRA) and represent arterial wall shear stress. We developed a new algorithm that uses signal intensity (SI) of a TOF-MRA to directly calculate the signal intensity gradient (SIG). The results from our phantom study showed that the TOF-MRA SIG could be used to distinguish the magnitude of blood flow rate as high (mean SIG ± SD, 2.2 ± 0.4 SI/mm for 12.5 ± 2.3 L/min) and low (0.9 ± 0.3 SI/mm for 8.5 ± 2.6 L/min) in vessels (p < 0.001). Additionally, we found that the TOF-MRA SIG values were highly correlated with various flow rates (β = 0.96, p < 0.001). Remarkably, the correlation coefficient between the WSS obtained from the computational fluid dynamics (CFD) analysis and the TOF-MRA SIG was greater than 0.8 in each section at the carotid artery (p < 0.001 for all β values). This new technique using TOF-MRA could enable the rapid calculation of the TOF-MRA SIG and thereby the WSS. Thus, the TOF-MRA SIG can provide clinicians with an accurate and efficient screening method for making rapid decisions on the risk of vascular disease for a patient in clinical practice. PMID:28900625

Direct Assessment of Wall Shear Stress by Signal Intensity Gradient from Time-of-Flight Magnetic Resonance Angiography.

PubMed

Han, Kap-Soo; Lee, Sang Hyuk; Ryu, Han Uk; Park, Se-Hyoung; Chung, Gyung-Ho; Cho, Young I; Jeong, Seul-Ki

2017-01-01

The aim of the study was to calculate the arterial wall signal intensity gradient (SIG) from time-of-flight MR angiography (TOF-MRA) and represent arterial wall shear stress. We developed a new algorithm that uses signal intensity (SI) of a TOF-MRA to directly calculate the signal intensity gradient (SIG). The results from our phantom study showed that the TOF-MRA SIG could be used to distinguish the magnitude of blood flow rate as high (mean SIG ± SD, 2.2 ± 0.4 SI/mm for 12.5 ± 2.3 L/min) and low (0.9 ± 0.3 SI/mm for 8.5 ± 2.6 L/min) in vessels ( p < 0.001). Additionally, we found that the TOF-MRA SIG values were highly correlated with various flow rates ( β = 0.96, p < 0.001). Remarkably, the correlation coefficient between the WSS obtained from the computational fluid dynamics (CFD) analysis and the TOF-MRA SIG was greater than 0.8 in each section at the carotid artery ( p < 0.001 for all β values). This new technique using TOF-MRA could enable the rapid calculation of the TOF-MRA SIG and thereby the WSS. Thus, the TOF-MRA SIG can provide clinicians with an accurate and efficient screening method for making rapid decisions on the risk of vascular disease for a patient in clinical practice.

Exposure to acute stress is associated with attenuated sweet taste.

PubMed

Al'Absi, Mustafa; Nakajima, Motohiro; Hooker, Stephanie; Wittmers, Larry; Cragin, Tiffany

2012-01-01

This study examined the effects of stress on taste perception. Participants (N = 38; 21 women) completed two laboratory sessions: one stress (public speaking, math, and cold pressor) and one control rest session. The taste perception test was conducted at the end of each session and included rating the intensity and pleasantness of sweet, salty, sour, and savory solutions at suprathreshold concentrations. Cardiovascular, hormonal, and mood measures were collected throughout the sessions. Participants showed the expected changes in cardiovascular, hormonal, and mood measures in response to stress. Reported intensity of the sweet solution was significantly lower on the stress day than on the rest day. Cortisol level poststress predicted reduced intensity of salt and sour, suggesting that stress-related changes in adrenocortical activity were related to reduced taste intensity. Results indicate that acute stress may alter taste perception, and ongoing research investigates the extent to which these changes mediate effects of stress on appetite. Copyright © 2011 Society for Psychophysiological Research.

Mobile phone-based education and counseling to reduce stress among patients with diabetes mellitus attending a tertiary care hospital of India.

PubMed

Patnaik, Lipilekha; Joshi, Ashish; Sahu, Trilochan

2015-01-01

Stress among diabetic patients is much more as compared to normal individuals. A delayed recognition of stress undoubtedly worsens the prognosis for survival for many diabetic patients. Hence, this study was planned to develop an intervention model for the reduction of stress among diabetic patients and to evaluate the developed intervention model in the proposed group. This study was conducted in endocrinology outpatient department of a tertiary care hospital. Starting at random, the patients were allocated to control group and test group. Controls were given printed educational materials. Test group were counseled with intense lifestyle education using both printed materials and computers; they were contacted by telephones by the investigator every 3 weeks for 3 months and SMS were sent every week containing some educational tips. Mean age was 54 ± 11.5 years overall ranging from 30 years to 80 years. About two-third of participants were males with similar distribution in both the groups (intervention = 66%, control = 64%). Half (50%) of the participants lived in joint families, followed by nuclear families (40%). Most (83%) were married and with either graduate or above graduate education (n = 39%). No significant difference was observed in socio-demographic characteristics among both control and intervention groups (P > 0.05). The average stress scores were similar (18.9) at baseline for control and intervention arms. At 3-month follow-up, however, these scores reduced to 17.05 in the intervention arm while they increased to 20.7 in the control arm. At 3 months follow-up, higher proportion of stress reduction was seen in the intervention group. Intervention in the form of intensive lifestyle education and phone calls and SMS significantly decrease their stress score. Mobile-based education has great potential to improve their mental status and increase patient-provider communication, and to decrease stress.

Posttraumatic stress disorder in children and their parents following admission to the pediatric intensive care unit: a review.

PubMed

Nelson, Lara P; Gold, Jeffrey I

2012-05-01

To evaluate posttraumatic stress disorder in children who have been admitted to the pediatric intensive care unit and their families. Studies were identified through PubMed, MEDLINE, and Ovid. All descriptive, observational, and controlled studies with a focus on posttraumatic stress disorder and the pediatric intensive care unit were included. Posttraumatic stress disorder rates in children following admission to the pediatric intensive care unit were between 5% and 28%, while rates of posttraumatic stress disorder symptoms were significantly higher, 35% to 62%. There have been inconsistencies noted across risk factors. Objective and subjective measurements of disease severity were intermittently positively associated with development of posttraumatic stress disorder. There was a positive relationship identified between the child's symptoms of posttraumatic stress disorder and their parents' symptoms.The biological mechanisms associated with the development of posttraumatic stress disorder in children admitted to the pediatric intensive care unit have yet to be explored. Studies in children following burn or other unintentional injury demonstrate potential relationships between adrenergic hormone levels and a diagnosis of posttraumatic stress disorder. Likewise genetic studies suggest the importance of the adrenergic system in this pathway.The rates of posttraumatic stress disorder in parents following their child's admission to the pediatric intensive care unit ranged between 10.5% and 21%, with symptom rates approaching 84%. It has been suggested that mothers are at increased risk for the development of posttraumatic stress disorder compared to fathers. Objective and subjective measures of disease severity yielded mixed findings with regard to the development of posttraumatic stress disorder. Protective parental factors may include education or the opportunity to discuss the parents' feelings during the admission. Following admission to the pediatric intensive care unit, both children and their parents have high rates of trauma exposure, both personally and secondary exposure via other children and their families, and subsequently are reporting significant rates of posttraumatic stress disorder. To effectively treat our patients, we must recognize the signs of posttraumatic stress disorder and strive to mitigate the negative effects.

Building child trauma theory from longitudinal studies: a meta-analysis.

PubMed

Alisic, Eva; Jongmans, Marian J; van Wesel, Floryt; Kleber, Rolf J

2011-07-01

Many children are exposed to traumatic events, with potentially serious psychological and developmental consequences. Therefore, understanding development of long-term posttraumatic stress in children is essential. We aimed to contribute to child trauma theory by focusing on theory use and theory validation in longitudinal studies. Forty studies measuring short-term predictors and long-term posttraumatic stress symptoms were identified and coded for theoretical grounding, sample characteristics, and correlational effect sizes. Explicit theoretical frameworks were present in a minority of the studies. Important predictors of long-term posttraumatic stress were symptoms of acute and short-term posttraumatic stress, depression, anxiety, and parental posttraumatic stress. Female gender, injury severity, duration of hospitalization, and elevated heart rate shortly after hospitalization yielded small effect sizes. Age, minority status, and socioeconomic status were not significantly related to long-term posttraumatic stress reactions. Since many other variables were not studied frequently enough to compute effect sizes, existing theoretical frameworks could only be partially confirmed or falsified. Child trauma theory-building can be facilitated by development of encouraging journal policies, the use of comparable methods, and more intense collaboration. Copyright © 2011 Elsevier Ltd. All rights reserved.

Patient stress in intensive care: comparison between a coronary care unit and a general postoperative unit

PubMed Central

Dias, Douglas de Sá; Resende, Mariane Vanessa; Diniz, Gisele do Carmo Leite Machado

2015-01-01

Objective To evaluate and compare stressors identified by patients of a coronary intensive care unit with those perceived by patients of a general postoperative intensive care unit. Methods This cross-sectional and descriptive study was conducted in the coronary intensive care and general postoperative intensive care units of a private hospital. In total, 60 patients participated in the study, 30 in each intensive care unit. The stressor scale was used in the intensive care units to identify the stressors. The mean score of each item of the scale was calculated followed by the total stress score. The differences between groups were considered significant when p < 0.05. Results The mean ages of patients were 55.63 ± 13.58 years in the coronary intensive care unit and 53.60 ± 17.47 years in the general postoperative intensive care unit. For patients in the coronary intensive care unit, the main stressors were “being in pain”, “being unable to fulfill family roles” and “being bored”. For patients in the general postoperative intensive care unit, the main stressors were “being in pain”, “being unable to fulfill family roles” and “not being able to communicate”. The mean total stress scores were 104.20 ± 30.95 in the coronary intensive care unit and 116.66 ± 23.72 (p = 0.085) in the general postoperative intensive care unit. When each stressor was compared separately, significant differences were noted only between three items. “Having nurses constantly doing things around your bed” was more stressful to the patients in the general postoperative intensive care unit than to those in the coronary intensive care unit (p = 0.013). Conversely, “hearing unfamiliar sounds and noises” and “hearing people talk about you” were the most stressful items for the patients in the coronary intensive care unit (p = 0.046 and 0.005, respectively). Conclusion The perception of major stressors and the total stress score were similar between patients in the coronary intensive care and general postoperative intensive care units. PMID:25909309

Computer-assisted resilience training to prepare healthcare workers for pandemic influenza: a randomized trial of the optimal dose of training

PubMed Central

2010-01-01

Background Working in a hospital during an extraordinary infectious disease outbreak can cause significant stress and contribute to healthcare workers choosing to reduce patient contact. Psychological training of healthcare workers prior to an influenza pandemic may reduce stress-related absenteeism, however, established training methods that change behavior and attitudes are too resource-intensive for widespread use. This study tests the feasibility and effectiveness of a less expensive alternative - an interactive, computer-assisted training course designed to build resilience to the stresses of working during a pandemic. Methods A "dose-finding" study compared pre-post changes in three different durations of training. We measured variables that are likely to mediate stress-responses in a pandemic before and after training: confidence in support and training, pandemic-related self-efficacy, coping style and interpersonal problems. Results 158 hospital workers took the course and were randomly assigned to the short (7 sessions, median cumulative duration 111 minutes), medium (12 sessions, 158 minutes) or long (17 sessions, 223 minutes) version. Using an intention-to-treat analysis, the course was associated with significant improvements in confidence in support and training, pandemic self-efficacy and interpersonal problems. Participants who under-utilized coping via problem-solving or seeking support or over-utilized escape-avoidance experienced improved coping. Comparison of doses showed improved interpersonal problems in the medium and long course but not in the short course. There was a trend towards higher drop-out rates with longer duration of training. Conclusions Computer-assisted resilience training in healthcare workers appears to be of significant benefit and merits further study under pandemic conditions. Comparing three "doses" of the course suggested that the medium course was optimal. PMID:20307302

Fracture under combined modes in 4340 steel

NASA Technical Reports Server (NTRS)

Shah, R. C.

1974-01-01

An experimental investigation was conducted to study the interaction of combined modes of loading on crack instability in the presence of the opening and sliding modes of stress intensity factors, the opening and tearing modes of stress intensity factors, and all three modes of stress intensity factors. Through-cracked and surface-cracked flat and round specimens, and round notched bar specimens fabricated from high strength 4340 steel were used for the investigation. The results are evaluated to determine fracture criteria under the combined modes of stress intensity factors for the 4340 steel. These results are compared with the results of other investigators obtained for different materials.

A review of chevron-notched fracture specimens

NASA Technical Reports Server (NTRS)

Newman, J. C., Jr.

1984-01-01

The historical development of chevron notched fracture specimens is reviewed. Stress intensity factors and load line displacement solutions proposed for some of these specimens are compared. The original bend bar configurations up to the present day short rod and bar specimens are reviewed. The results of an analytical round robin that was conducted on chevron-notched specimens are presented. In the round robin, stress-intensity factors for either the chevron notched round rod or square bar specimens were calculated. The consensus stress intensity factor (compliance) solution for these specimens is assessed. The stress intensity factor solutions proposed for three and four point bend chevron notched specimens are reviewed.

Stress Intensity Factors of Semi-Circular Bend Specimens with Straight-Through and Chevron Notches

NASA Astrophysics Data System (ADS)

Ayatollahi, M. R.; Mahdavi, E.; Alborzi, M. J.; Obara, Y.

2016-04-01

Semi-circular bend specimen is one of the useful test specimens for determining fracture toughness of rock and geo-materials. Generally, in rock test specimens, initial cracks are produced in two shapes: straight-edge cracks and chevron notches. In this study, the minimum dimensionless stress intensity factors of semi-circular bend specimen (SCB) with straight-through and chevron notches are calculated. First, using finite element analysis, a suitable relation for the dimensionless stress intensity factor of SCB with straight-through crack is presented based on the normalized crack length and half-distance between supports. For evaluating the validity and accuracy of this relation, the obtained results are then compared with numerical and experimental results reported in the literature. Subsequently, by performing some experiments and also finite element analysis of the SCB specimen with chevron notch, the minimum dimensionless stress intensity factor of this specimen is obtained. Using the new equation for the dimensionless stress intensity factor of SCB with straight-through crack and an analytical method, i.e., Bluhm's slice synthesis method, the minimum (critical) dimensionless stress intensity factor of chevron notched semi-circular bend specimens is calculated. Good agreement is observed between the results of two mentioned methods.

The influence of water temperature and accelerometer-determined fight intensity on physiological stress and reflex impairment of angled largemouth bass.

PubMed

Brownscombe, Jacob W; Marchand, Kelsey; Tisshaw, Kathryn; Fewster, Victoria; Groff, Olivia; Pichette, Melissa; Seed, Marian; Gutowsky, Lee F G; Wilson, Alexander D M; Cooke, Steven J

2014-01-01

Release of fish captured by recreational anglers is a common practice due to angler conservation ethics or compliance with fisheries regulations. As such, there is a need to understand the factors that influence mortality and sub-lethal impairments to ensure that catch-and-release angling is a sustainable practice. Longer angling times generally contribute to increased stress and mortality in fish such that reducing these times putatively reduces stress and improves survival. However, the relative importance of fight intensity (rather than simply duration) on fish condition is poorly understood. The objective of this research was to examine the effects of fight intensity on physiological stress and reflex impairment of largemouth bass (Micropterus salmoides). The largemouth bass were angled using conventional recreational fishing gear in May (water temperature ∼12°C) and June (∼22°C) of 2014 in Lake Opinicon, Ontario, Canada. Fight intensity was quantified using tri-axial accelerometer loggers mounted on the tips of fishing rods. Upon capture, reflex impairment measures were assessed, and fish were held for 1 h prior to blood sampling for measurement of physiological stress (blood glucose and lactate concentrations and pH). Physiological stress values showed a negative trend with fight duration and total fight intensity, but a positive trend with average fight intensity. Water temperature emerged as the most important predictor of the stress response in largemouth bass, while fight duration and intensity were not strong predictors. Reflex impairment was minimal, but higher reflex impairment scores were associated with elevated blood glucose. Overall, the findings of this study suggest that angling for largemouth bass at colder temperatures (<15°C) causes greater physiological stress than at warmer temperatures (>20°C). Based on our findings, we conclude that fight intensity is likely not to be a major driver of physiological stress in this species using typical largemouth bass angling gear, owing to the relatively short fight times (i.e. <2 min).

Permeability of three-dimensional rock masses containing geomechanically-grown anisotropic fracture networks

NASA Astrophysics Data System (ADS)

Thomas, R. N.; Ebigbo, A.; Paluszny, A.; Zimmerman, R. W.

2016-12-01

The macroscopic permeability of 3D anisotropic geomechanically-generated fractured rock masses is investigated. The explicitly computed permeabilities are compared to the predictions of classical inclusion-based effective medium theories, and to the permeability of networks of randomly oriented and stochastically generated fractures. Stochastically generated fracture networks lack features that arise from fracture interaction, such as non-planarity, and termination of fractures upon intersection. Recent discrete fracture network studies include heuristic rules that introduce these features to some extent. In this work, fractures grow and extend under tension from a finite set of initial flaws. The finite element method is used to compute displacements, and modal stress intensity factors are computed around each fracture tip using the interaction integral accumulated over a set of virtual discs. Fracture apertures emerge as a result of simulations that honour the constraints of stress equilibrium and mass conservation. The macroscopic permeabilities are explicitly calculated by solving the local cubic law in the fractures, on an element-by-element basis, coupled to Darcy's law in the matrix. The permeabilities are then compared to the estimates given by the symmetric and asymmetric versions of the self-consistent approximation, which, for randomly fractured volumes, were previously demonstrated to be most accurate of the inclusion-based effective medium methods (Ebigbo et al., Transport in Porous Media, 2016). The permeabilities of several dozen geomechanical networks are computed as a function of density and in situ stresses. For anisotropic networks, we find that the asymmetric and symmetric self-consistent methods overestimate the effective permeability in the direction of the dominant fracture set. Effective permeabilities that are more strongly dependent on the connectivity of two or more fracture sets are more accurately captured by the effective medium models.

Computer-aided analysis of cutting processes for brittle materials

NASA Astrophysics Data System (ADS)

Ogorodnikov, A. I.; Tikhonov, I. N.

2017-12-01

This paper is focused on 3D computer simulation of cutting processes for brittle materials and silicon wafers. Computer-aided analysis of wafer scribing and dicing is carried out with the use of the ANSYS CAE (computer-aided engineering) software, and a parametric model of the processes is created by means of the internal ANSYS APDL programming language. Different types of tool tip geometry are analyzed to obtain internal stresses, such as a four-sided pyramid with an included angle of 120° and a tool inclination angle to the normal axis of 15°. The quality of the workpieces after cutting is studied by optical microscopy to verify the FE (finite-element) model. The disruption of the material structure during scribing occurs near the scratch and propagates into the wafer or over its surface at a short range. The deformation area along the scratch looks like a ragged band, but the stress width is rather low. The theory of cutting brittle semiconductor and optical materials is developed on the basis of the advanced theory of metal turning. The fall of stress intensity along the normal on the way from the tip point to the scribe line can be predicted using the developed theory and with the verified FE model. The crystal quality and dimensions of defects are determined by the mechanics of scratching, which depends on the shape of the diamond tip, the scratching direction, the velocity of the cutting tool and applied force loads. The disunity is a rate-sensitive process, and it depends on the cutting thickness. The application of numerical techniques, such as FE analysis, to cutting problems enhances understanding and promotes the further development of existing machining technologies.

Computer-Related Repetitive Stress Injuries

MedlinePlus

... for Educators Search English Español Computer-Related Repetitive Stress Injuries KidsHealth / For Parents / Computer-Related Repetitive Stress ... injuries and how to prevent them. About Repetitive Stress Injuries Repetitive stress injuries (RSIs) are conditions caused ...

Cumulative IT Use Is Associated with Psychosocial Stress Factors and Musculoskeletal Symptoms.

PubMed

So, Billy C L; Cheng, Andy S K; Szeto, Grace P Y

2017-12-08

This study aimed to examine the relationship between cumulative use of electronic devices and musculoskeletal symptoms. Smartphones and tablet computers are very popular and people may own or operate several devices at the same time. High prevalence rates of musculoskeletal symptoms associated with intensive computer use have been reported. However, research focusing on mobile devices is only just emerging in recent years. In this study, 285 persons participated including 140 males and 145 females (age range 18-50). The survey consisted of self-reported estimation of daily information technology (IT) exposure hours, tasks performed, psychosocial stress factors and relationship to musculoskeletal discomfort in the past 12 months. Total IT exposure time was an average of 7.38 h (±5.2) per day. The psychosocial factor of "working through pain" showed the most significant association with odds ratio (OR) ranging from 1.078 (95% CI = 1.021-1.138) for elbow discomfort, to 1.111 (95% CI = 1.046-1.180) for shoulder discomfort. Desktop time was also significantly associated with wrist/hand discomfort (OR = 1.103). These findings indicate only a modest relationship but one that is statistically significant with accounting for confounders. It is anticipated that prevalence rates of musculoskeletal disorders would rise in the future with increasing contribution due to psychosocial stress factors.

Application of a Reynolds stress turbulence model to the compressible shear layer

NASA Technical Reports Server (NTRS)

Sarkar, S.; Balakrishnan, L.

1990-01-01

Theoretically based turbulence models have had success in predicting many features of incompressible, free shear layers. However, attempts to extend these models to the high-speed, compressible shear layer have been less effective. In the present work, the compressible shear layer was studied with a second-order turbulence closure, which initially used only variable density extensions of incompressible models for the Reynolds stress transport equation and the dissipation rate transport equation. The quasi-incompressible closure was unsuccessful; the predicted effect of the convective Mach number on the shear layer growth rate was significantly smaller than that observed in experiments. Having thus confirmed that compressibility effects have to be explicitly considered, a new model for the compressible dissipation was introduced into the closure. This model is based on a low Mach number, asymptotic analysis of the Navier-Stokes equations, and on direct numerical simulation of compressible, isotropic turbulence. The use of the new model for the compressible dissipation led to good agreement of the computed growth rates with the experimental data. Both the computations and the experiments indicate a dramatic reduction in the growth rate when the convective Mach number is increased. Experimental data on the normalized maximum turbulence intensities and shear stress also show a reduction with increasing Mach number.

Fracture mechanics analyses of partial crack closure in shell structures

NASA Astrophysics Data System (ADS)

Zhao, Jun

2007-12-01

This thesis presents the theoretical and finite element analyses of crack-face closure behavior in shells and its effect on the stress intensity factor under a bending load condition. Various shell geometries, such as spherical shell, cylindrical shell containing an axial crack, cylindrical shell containing a circumferential crack and shell with double curvatures, are all studied. In addition, the influence of material orthotropy on the crack closure effect in shells is also considered. The theoretical formulation is developed based on the shallow shell theory of Delale and Erdogan, incorporating the effect of crack-face closure at the compressive edges. The line-contact assumption, simulating the crack-face closure at the compressive edges, is employed so that the contact force at the closure edges is introduced, which can be translated to the mid-plane of the shell, accompanied by an additional distributed bending moment. The unknown contact force is computed by solving a mixed-boundary value problem iteratively, that is, along the crack length, either the normal displacement of the crack face at the compressive edges is equal to zero or the contact pressure is equal to zero. It is found that due to the curvature effects crack closure may not always occur on the entire length of the crack, depending on the direction of the bending load and the geometry of the shell. The crack-face closure influences significantly the magnitude of the stress intensity factors; it increases the membrane component but decreases the bending component. The maximum stress intensity factor is reduced by the crack-face closure. The significant influence of geometry and material orthotropy on rack closure behavior in shells is also predicted based on the analytical solutions. Three-dimensional FEA is performed to validate the theoretical solutions. It demonstrates that the crack face closure occurs actually over an area, not on a line, but the theoretical solutions of the stress intensity factor and the FEA solutions are in good agreement, because the contact area is very small compared with the shell thickness.

Nursing staff stress in an intensive care unit.

PubMed

Lochoff, R V; Cane, R D; Buchanan, N; Cox, H J

1977-12-03

The stresses associated with nursing in an intensive care unit were assessed. A comparison was drawn between a group of Black and a group of White nurses. Proposals aimed at reducing the observed stress patterns are suggested.

Exposure to high stress in the intensive care unit may have negative effects on health-related quality-of-life outcomes after cardiac surgery.

PubMed

Schelling, Gustav; Richter, Markus; Roozendaal, Benno; Rothenhäusler, Hans-Bernd; Krauseneck, Till; Stoll, Christian; Nollert, Georg; Schmidt, Michael; Kapfhammer, Hans-Peter

2003-07-01

Up to 20% of patients do not show improvements in health-related quality of life (HRQL) after cardiac surgery, despite apparently successful surgical procedures. We sought to determine whether failed improvements in HRQL after cardiac surgery are associated with the development of traumatic memories and chronic stress states as a result of high perioperative stress exposure. Prospective cohort study. A 10-bed cardiovascular intensive care unit of a tertiary care university hospital. A total of 148 cardiac surgical patients. None. The patients were evaluated for traumatic memories from postoperative treatment in the cardiovascular intensive care unit (defined as the subjective recollection of pain, respiratory distress, anxiety/panic, and nightmares), symptoms of chronic stress, including those of posttraumatic stress disorder, and HRQL preoperatively (at baseline) and at 6 months after cardiac surgery. A state of chronic stress was defined as the development of posttraumatic stress disorder at 6 months after surgery. Factors predicting the decline in HRQL were determined by multivariable linear regression. Twenty-seven patients (18.2%) had posttraumatic stress disorder at 6 months after cardiac surgery; seven of these patients (4.8%) had evidence of preexisting posttraumatic stress disorder before undergoing cardiac surgery. Patients with new posttraumatic stress disorder at 6 months after cardiac surgery had a significantly higher number of traumatic memories from postoperative treatment in the cardiovascular intensive care unit (p =.01). A multiple regression model included the number of traumatic memories from the intensive care unit and stress symptom scores at 6 months after heart surgery as predictors for variations in physical HRQL outcome scores (R2 =.30, p <.04). Stress symptom scores were the most significant predictors of mental health HRQL outcomes (R2 =.52, p <.01). Exposure to high stress in the cardiovascular intensive care unit can have negative effects on HRQL outcomes of cardiac surgery.

Proficiency in English sentence stress production by Cantonese speakers who speak English as a second language (ESL).

PubMed

Ng, Manwa L; Chen, Yang

2011-12-01

The present study examined English sentence stress produced by native Cantonese speakers who were speaking English as a second language (ESL). Cantonese ESL speakers' proficiency in English stress production as perceived by English-speaking listeners was also studied. Acoustical parameters associated with sentence stress including fundamental frequency (F0), vowel duration, and intensity were measured from the English sentences produced by 40 Cantonese ESL speakers. Data were compared with those obtained from 40 native speakers of American English. The speech samples were also judged by eight native listeners who were native speakers of American English for placement, degree, and naturalness of stress. Results showed that Cantonese ESL speakers were able to use F0, vowel duration, and intensity to differentiate sentence stress patterns. Yet, both female and male Cantonese ESL speakers exhibited consistently higher F0 in stressed words than English speakers. Overall, Cantonese ESL speakers were found to be proficient in using duration and intensity to signal sentence stress, in a way comparable with English speakers. In addition, F0 and intensity were found to correlate closely with perceptual judgement and the degree of stress with the naturalness of stress.

Stress-intensity factors for a thick-walled cylinder containing an annular imbedded or external or internal surface crack

NASA Technical Reports Server (NTRS)

Erdol, R.; Erdogan, F.

1976-01-01

The elastostatic axisymmetric problem for a long thick-walled cylinder containing a ring-shaped internal or edge crack is considered. Using the standard transform technique the problem is formulated in terms of an integral equation which has a simple Cauchy kernel for the internal crack and a generalized Cauchy kernel for the edge crack as the dominant part. As examples the uniform axial load and the steady-state thermal stress problems have been solved and the related stress intensity factors have been calculated. Among other findings the results show that in the cylinder under uniform axial stress containing an internal crack the stress intensity factor at the inner tip is always greater than that at the outer tip for equal net ligament thicknesses and in the cylinder with an edge crack which is under a state of thermal stress the stress intensity factor is a decreasing function of the crack depth, tending to zero as the crack depth approaches the wall thickness.

Racial and gender differences on sources of acute stress and coping style among competitive athletes.

PubMed

Anshel, Mark H; Sutarso, Toto; Jubenville, Colby

2009-04-01

The authors examined racial and gender differences on sport-related sources of acute stress that competitive athletes perceived as highly intense and experienced during the competitive event. Athletes (N = 332, 176 men, 156 women; 59 African Americans: 27 men, 32 women; 232 Caucasians: 125 men, 107 women; and 41 Hispanics: 24 men, 17 women) who competed in sport on a high school or college team participated in this study. The sources of the acute stress and the coping style in sport scales, which M. H. Anshel and T. Sutarso (2007) developed, required the athletes to indicate their perceived stress intensity and their "typical" coping responses after experiencing the two stressors they perceived as most intense. A multivarite analysis of variance indicated that Caucasians experienced higher stress intensity more often than did African Americans on each of two sources of acute stress, and Caucasians tended to use an approach-behavior coping style. Women reported higher stress intensity for coach-related sources of acute stress and used approach-behavioral and avoidance-cognitive coping styles more often than did their male counterparts. Hispanic athletes did not differ from other groups on any measure. The authors conclude that race and gender influence the coping process in competitive sport.

A Database for Compounding Stress Intensity Factors.

DTIC Science & Technology

1985-04-01

8217"’.’’" . ." ’" " " " "".. .... .... .... . .. .... . : ,.’. .. MICROCOP RE O UT O ," EST CHART...8217 - .. . , ., . . ,. . .,\\ .- . , , . -, . .- . . . , * TR 85046 o UNLIMITED __ ROYAL AIRCRAFT ESTABLISHMENT O Technical Report 85046 April 1985 A DATABASE FOR COMPOUNDING STRESS INTENSITY FACTORS L W by...DATABASE FOR COMPOUNDING STRESS INTENSITY FACTORS by A. M. Prior . ..- - . .. _ D. P. Rooke D. J. Cartwright* SUMMARY . The compounding method enables

Early Detection of Salt Stress Damage by Biophotons in Red Bean Seedling

NASA Astrophysics Data System (ADS)

Ohya, Tomoyuki; Kurashige, Hideaki; Okabe, Hirotaka; Kai, Shoichi

2000-06-01

The optical detection of the stress damage to plants by NaCl solutions was attempted during germination of a seed and growth of a root. We compared the photon intensity of red beans before and after NaCl treatment and found that the photon intensity after NaCl treatment decreased as the NaCl concentration increased. For the saturated NaCl concentration (4.5 M), however, the observed photon intensity drastically increased, and the simultaneous destruction of cell membranes was observed. The intensity of biophoton emission from red beans showed characteristic change with salt concentrations. When the salt stress was applied to the red beans at an early growth stage, their root elongations were suppressed and photon intensity from the root decreased. This was not the case for the root at the late stage. This shows that biophoton intensity due to salt stress depends on not only NaCl concentration but also the growth stage of the plant. We may conclude that the extent of damage to roots by salt stress can be evaluated from biophoton response.

Probabilistic Structural Analysis Theory Development

NASA Technical Reports Server (NTRS)

Burnside, O. H.

1985-01-01

The objective of the Probabilistic Structural Analysis Methods (PSAM) project is to develop analysis techniques and computer programs for predicting the probabilistic response of critical structural components for current and future space propulsion systems. This technology will play a central role in establishing system performance and durability. The first year's technical activity is concentrating on probabilistic finite element formulation strategy and code development. Work is also in progress to survey critical materials and space shuttle mian engine components. The probabilistic finite element computer program NESSUS (Numerical Evaluation of Stochastic Structures Under Stress) is being developed. The final probabilistic code will have, in the general case, the capability of performing nonlinear dynamic of stochastic structures. It is the goal of the approximate methods effort to increase problem solving efficiency relative to finite element methods by using energy methods to generate trial solutions which satisfy the structural boundary conditions. These approximate methods will be less computer intensive relative to the finite element approach.

Facilitation as Attenuating of Environmental Stress among Structured Microbial Populations.

PubMed

Martins, Suzana Cláudia Silveira; Santaella, Sandra Tédde; Martins, Claudia Miranda; Martins, Rogério Parentoni

2016-01-01

There is currently an intense debate in microbial societies on whether evolution in complex communities is driven by competition or cooperation. Since Darwin, competition for scarce food resources has been considered the main ecological interaction shaping population dynamics and community structure both in vivo and in vitro. However, facilitation may be widespread across several animal and plant species. This could also be true in microbial strains growing under environmental stress. Pure and mixed strains of Serratia marcescens and Candida rugosa were grown in mineral culture media containing phenol. Growth rates were estimated as the angular coefficients computed from linearized growth curves. Fitness index was estimated as the quotient between growth rates computed for lineages grown in isolation and in mixed cultures. The growth rates were significantly higher in associated cultures than in pure cultures and fitness index was greater than 1 for both microbial species showing that the interaction between Serratia marcescens and Candida rugosa yielded more efficient phenol utilization by both lineages. This result corroborates the hypothesis that facilitation between microbial strains can increase their fitness and performance in environmental bioremediation.

Facilitation as Attenuating of Environmental Stress among Structured Microbial Populations

PubMed Central

Santaella, Sandra Tédde; Martins, Claudia Miranda; Martins, Rogério Parentoni

2016-01-01

There is currently an intense debate in microbial societies on whether evolution in complex communities is driven by competition or cooperation. Since Darwin, competition for scarce food resources has been considered the main ecological interaction shaping population dynamics and community structure both in vivo and in vitro. However, facilitation may be widespread across several animal and plant species. This could also be true in microbial strains growing under environmental stress. Pure and mixed strains of Serratia marcescens and Candida rugosa were grown in mineral culture media containing phenol. Growth rates were estimated as the angular coefficients computed from linearized growth curves. Fitness index was estimated as the quotient between growth rates computed for lineages grown in isolation and in mixed cultures. The growth rates were significantly higher in associated cultures than in pure cultures and fitness index was greater than 1 for both microbial species showing that the interaction between Serratia marcescens and Candida rugosa yielded more efficient phenol utilization by both lineages. This result corroborates the hypothesis that facilitation between microbial strains can increase their fitness and performance in environmental bioremediation. PMID:26904719

Optimum Material Composition for Minimizing the Stress Intensity Factor of Edge Crack in Thick-Walled FGM Circular Pipes Under Thermomechanical Loading

NASA Astrophysics Data System (ADS)

Sekine, Hideki; Yoshida, Kimiaki

This paper deals with the optimization problem of material composition for minimizing the stress intensity factor of radial edge crack in thick-walled functionally graded material (FGM) circular pipes under steady-state thermomechanical loading. Homogenizing the FGM circular pipes by simulating the inhomogeneity of thermal conductivity by a distribution of equivalent eigentemperature gradient and the inhomogeneity of Young's modulus and Poisson's ratio by a distribution of equivalent eigenstrain, we present an approximation method to obtain the stress intensity factor of radial edge crack in the FGM circular pipes. The optimum material composition for minimizing the stress intensity factor of radial edge crack is determined using a nonlinear mathematical programming method. Numerical results obtained for a thick-walled TiC/Al2O3 FGM circular pipe reveal that it is possible to decrease remarkably the stress intensity factor of radial edge crack by setting the optimum material composition profile.

Salivary Nerve Growth Factor Response to Intense Stress: Effect of Sex and Body Mass Index

DTIC Science & Technology

2014-01-01

the roles of age, sex, education, and BMI. sNGF increased 137% from baseline to intense stress. During recovery, sNGF remained elevated an average of...225 250 275 300 325 BASELI NE STRE SS RECOVERY sN G F (p g/ m L) *† * Figure 1 Effect of intense stress exposure on salivary nerve growth factor...neurotrophic responses to severe stress may play a role in the well docu- mented sex imbalance in these disorders. In particular, the failure to launch

Influence of psychological factors on acute exacerbation of tension-type headache: Investigation by ecological momentary assessment.

PubMed

Kikuchi, Hiroe; Yoshiuchi, Kazuhiro; Ando, Tetsuya; Yamamoto, Yoshiharu

2015-09-01

In this study, we investigated whether psychological factors were associated with subsequent acute exacerbation of tension-type headache (TTH) in a prospective and ecologically valid manner with computerized ecological momentary assessment. Eighteen women and five men with TTH wore watch-type computers that acted as an electronic diary for 1week. The subjects recorded momentary headache intensity, psychological stress, anxiety, and depressive mood with a visual analog scale of 0-100 approximately every 6h as well as when waking up, when going to bed, and at acute headache exacerbations. Multilevel logistic regression analysis with acute headache exacerbation occurrence as the outcome was conducted. Person-mean centering was applied to psychological factors to disaggregate between- and within-individual association. Momentary psychological stress was associated with subsequent increase in headache exacerbation within 3h [Odds Ratio (95% CI)=1.32 (1.07, 1.64) for 10-point increments] while the individual mean of psychological stress was not. These results support the possibility that psychological stress could trigger acute exacerbations of TTH. Copyright © 2015 Elsevier Inc. All rights reserved.

Intermittent fasting modulates IgA levels in the small intestine under intense stress: a mouse model.

PubMed

Lara-Padilla, Eleazar; Godínez-Victoria, Marycarmen; Drago-Serrano, Maria Elisa; Reyna-Garfias, Humberto; Arciniega-Martínez, Ivonne Maciel; Abarca-Rojano, Edgar; Cruz-Hernández, Teresita Rocío; Campos-Rodríguez, Rafael

2015-08-15

Intermittent fasting prolongs the lifespan and unlike intense stress provides health benefits. Given the role of the immunoglobulin A (IgA) in the intestinal homeostasis, the aim of this study was to assess the impact of intermittent fasting plus intense stress on secretory IgA (SIgA) production and other mucosal parameters in the duodenum and ileum. Two groups of six mice, with intermittent fasting or fed ad libitum for 12weeks, were submitted to a session of intense stress by a bout of forced swimming. Unstressed ad libitum fed or intermittently fasted groups were included as controls. After sacrifice, we evaluated intestinal SIgA and plasma adrenal hormones, lamina propria IgA+ plasma-cells, mRNA expression of polymeric immunoglobulin receptor, α- and J-chains in the liver and intestinal mucosa, as well as pro- (tumor necrosis factor-α, interleukin-6 and Interferon-γ) and anti- (interleukin-2, -4, -10 and transforming growth factor-β) inflammatory cytokines in mucosal samples. Under intense stress, intermittent fasting down- or up-modulated the levels of most parameters in the duodenum and ileum, respectively while up-regulated corticosterone levels without affecting epinephrine. Our data suggest intermittent fasting plus intense stress elicited neuroendocrine pathways that differentially controlled IgA and pIgR expression in duodenum and ileum. These findings provide experimental foundations for a presumable impact of intermittent fasting under intense stress on the intestinal homeostasis or inflammation by triggering or reducing the IgA production in ileum or duodenum respectively. Copyright © 2015 Elsevier B.V. All rights reserved.

The relation between intensity and complexity of coronary artery lesion and oxidative stress in patients with acute coronary syndrome.

PubMed

Turan, Turhan; Menteşe, Ümit; Ağaç, Mustafa Tarık; Akyüz, Ali Rıza; Kul, Selim; Aykan, Ahmet Çağrı; Bektaş, Hüseyin; Korkmaz, Levent; Öztaş Menteşe, Seda; Dursun, İhsan; Çelik, Şükrü

2015-10-01

Oxidative stress plays a major role in the development of atherosclerosis. However, the relationship between oxidative stress and complexity and intensity of coronary artery disease is less clear. The aim of this study is to assess the relationship between oxidative stress markers and the complexity and intensity of coronary artery disease in patients with acute coronary syndrome (ACS). Sixty-seven consecutive patients with an early phase of ACS (<3 h) were included in this single-centre, cross-sectional, prospective study. Syntax and Gensini scores were calculated based on angiographic findings. Patients were divided into two CAD complexity groups according to their Syntax scores: low SYNTAX score (<22) and moderate to high SYNTAX score (>=22). Likewise patients were divided into two CAD severity groups according to the median Gensini score of 64: less intensive CAD with Gensini score (<64) and intensive CAD with Gensini score >=64. Blood samples were taken in 1 hour within administration in order to measure total oxidative status (TOS) and total antioxidant capacity (TAC) levels determined by Erel method. Oxidative stress index (OSI) was calculated by TOS /TAC. There was no significant difference between the two SYNTAX groups for oxidative stress markers. Median TOS and OSI values were significantly high in the intensive CAD group (p=0.005, p=0.04, respectively). The Gensini score was positively correlated with TOS and OSI (p=0.003, p=0.02, respectively). Oxidative stress markers may be considered supportive laboratory parameters related to CAD intensity but not complexity in ACS patients.

Stress at the place of work and cognitive functions among women performing intellectual work during peri- and post-menopausal period.

PubMed

Gujski, Mariusz; Pinkas, Jarosław; Juńczyk, Tomasz; Pawełczak-Barszczowska, Adrianna; Raczkiewicz, Dorota; Owoc, Alfred; Bojar, Iwona

2017-10-06

The analysis of the relationship between stress at work and results of cognitive functions amongst women, at peri- and post-menopausal age, performing intellectual work. The study group included women, aged 45-66 years old, employed as intellectual workers. Research instruments were: the Montreal Cognitive Assessment; computer tests of the CNS Vital Signs; the Subjective Work Characteristics Questionnaire, and a questionnaire designed by the author. The results were statistically analyzed. Nearly a half of respondents experienced high stress at the place of work; 1/3 - on the average level, on a low level - every fifth. The largest number of respondents experienced stress caused by social contacts. Among a half of the women, stress was caused by the lack of awards at work, followed by the lack of support. Slightly fewer of them experienced stress caused by the feeling of psychological load related to the complexity of work or the feeling of uncertainty caused by the organization of work. Every third woman experienced stress due to the sense of responsibility or the lack of control. The smallest number experienced stress caused by physical arduousness, the sense of threat and unpleasant working conditions. The examined women obtained the best results with respect to simple attention, the worst results - with respect to the reaction time. The results concerning the remaining 9 cognitive functions were ranked in the middle of the aforementioned results. The intensity of stress at work and factors which caused this stress, negatively correlated with simple attention of women in the early peri-menopausal period, while positively correlating with the psychomotor and processing speed of women in the late peri-menopausal period. Among the post-menopausal women, negative correlations were observed between the majority of cognitive functions and the intensity of stress at work, and the majority of factors which caused this stress. Cognitive functions of the examined women remained within the range of average evaluations, and were correlated with stress-inducing factors at the place of work. Int J Occup Med Environ Health 2017;30(6):943-961. This work is available in Open Access model and licensed under a CC BY-NC 3.0 PL license.

Numerical simulation of fluid flow in a rotational bioreactor

NASA Astrophysics Data System (ADS)

Ganimedov, V. L.; Papaeva, E. O.; Maslov, N. A.; Larionov, P. M.

2017-10-01

Application of scaffold technology for the problem of bone tissue regeneration has great prospects in modern medicine. The influence of fluid shear stress on stem cells cultivation and its differentiation into osteoblasts is the subject of intensive research. Mathematical modeling of fluid flow in bioreactor allowed us to determine the structure of flow and estimate the level of mechanical stress on cells. The series of computations for different rotation frequencies (0.083, 0.124, 0.167, 0.2 and 0.233 Hz) was performed for the laminar flow regime approximation. It was shown that the Taylor vortices in the gap between the cylinders qualitatively change the distribution of static pressure and shear stress in the region of vortices connection. It was shown that an increase in the rotation frequency leads to an increase of the unevenness in distribution of the above mentioned functions. The obtained shear stress and static pressure dependence on the rotational frequency make it possible to choose the operating mode of the reactor depending on the provided requirements. It was shown that in the range of rotation frequencies chosen in this work (0.083 < f < 0.233 Hz), the shear stress does not exceed the known literature data (0.002 - 0.1 Pa).

Dynamic Failure of Materials: A Review

DTIC Science & Technology

2010-08-01

stress states . It is currently unknown how well the current trend of multi-scale modeling will impact dynamic failure; however... stress can exist in the necked region after a neck is formed due to the nonuniformity of the necked region. This triaxial stress state is extremely...7 into 8, the effective stress intensity factor (Keff) can be determined in terms of the stress intensity factor (K). Because the onset of

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

NASA Technical Reports Server (NTRS)

Tan, P. W.; Raju, I. S.; Shivakumar, K. N.; Newman, J. C., Jr.

1988-01-01

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.

Ignition Prediction of Pressed HMX based on Hotspot Analysis Under Shock Pulse Loading

NASA Astrophysics Data System (ADS)

Kim, Seokpum; Miller, Christopher; Horie, Yasuyuki; Molek, Christopher; Welle, Eric; Zhou, Min

The ignition behavior of pressed HMX under shock pulse loading with a flyer is analyzed using a cohesive finite element method (CFEM) which accounts for large deformation, microcracking, frictional heating, and thermal conduction. The simulations account for the controlled loading of thin-flyer shock experiments with flyer velocities between 1.7 and 4.0 km/s. The study focuses on the computational prediction of ignition threshold using James criterion which involves loading intensity and energy imparted to the material. The predicted thresholds are in good agreement with measurements from shock experiments. In particular, it is found that grain size significantly affects the ignition sensitivity of the materials, with smaller sizes leading to lower energy thresholds required for ignition. In addition, significant stress attenuation is observed in high intensity pulse loading as compared to low intensity pulse loading, which affects density of hotspot distribution. The microstructure-performance relations obtained can be used to design explosives with tailored attributes and safety envelopes.

Studies on laws of stress-magnetization based on magnetic memory testing technique

NASA Astrophysics Data System (ADS)

Ren, Shangkun; Ren, Xianzhi

2018-03-01

Metal magnetic memory (MMM) testing technique is a novel testing method which can early test stress concentration status of ferromagnetic components. Under the different maximum tensile stress, the relationship between the leakage magnetic field of at certain point of cold rolled steel specimen and the tensile stress was measured during the process of loading and unloading by repeated. It shows that when the maximum tensile stress is less than 610 MPa, the relationship between the magnetic induction intensity and the stress is linear; When the maximum tensile stress increase from 610 MPa to 653 MPa of yield point, the relationship between the magnetic induction intensity and the tensile becomes bending line. The location of the extreme point of the bending line will move rapidly from the position of smaller stress to the larger stress position, and the variation of magnetic induction intensity increases rapidly. When the maximum tensile stress is greater than the 653 MPa of yield point, the variation of the magnetic induction intensity remains large, and the position of the extreme point moves very little. In theoretical aspects, tensile stress is to be divided into ordered stress and disordered stress. In the stage of elastic stress, a microscopic model of the order stress magnetization is established, and the conclusions are in good agreement with the experimental data. In the plastic deformation stage, a microscopic model of disordered stress magnetization is established, and the conclusions are in good agreement with the experimental data, too. The research results can provide reference for the accurate quantitative detection and evaluation of metal magnetic memory testing technology.

Some remarks on elastic crack-tip stress fields.

NASA Technical Reports Server (NTRS)

Rice, J. R.

1972-01-01

It is shown that if the displacement field and stress intensity factor are known as functions of crack length for any symmetrical load system acting on a linear elastic body in plane strain, then the stress intensity factor for any other symmetrical load system whatsoever on the same body may be directly determined. The result is closely related to Bueckner's (1970) weight function, through which the stress intensity factor is expressed as a sum of work-like products between applied forces and values of the weight function at their points of application. An example of the method is given wherein the solution for a crack in a remotely uniform stress field is used to generate the expression for the stress intensity factor due to an arbitrary traction distribution on the faces of a crack. A corresponding theory is developed in an appendix for three-dimensional crack problems, although this appears to be directly useful chiefly for problems in which there is axial symmetry.

Evaluation of finite-element models and stress-intensity factors for surface cracks emanating from stress concentrations

NASA Technical Reports Server (NTRS)

Tan, P. W.; Raju, I. S.; Shivakumar, K. N.; Newman, J. C., Jr.

1990-01-01

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. 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. 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.

Skin temperature reveals the intensity of acute stress

PubMed Central

Herborn, Katherine A.; Graves, James L.; Jerem, Paul; Evans, Neil P.; Nager, Ruedi; McCafferty, Dominic J.; McKeegan, Dorothy E.F.

2015-01-01

Acute stress triggers peripheral vasoconstriction, causing a rapid, short-term drop in skin temperature in homeotherms. We tested, for the first time, whether this response has the potential to quantify stress, by exhibiting proportionality with stressor intensity. We used established behavioural and hormonal markers: activity level and corticosterone level, to validate a mild and more severe form of an acute restraint stressor in hens (Gallus gallus domesticus). We then used infrared thermography (IRT) to non-invasively collect continuous temperature measurements following exposure to these two intensities of acute handling stress. In the comb and wattle, two skin regions with a known thermoregulatory role, stressor intensity predicted the extent of initial skin cooling, and also the occurrence of a more delayed skin warming, providing two opportunities to quantify stress. With the present, cost-effective availability of IRT technology, this non-invasive and continuous method of stress assessment in unrestrained animals has the potential to become common practice in pure and applied research. PMID:26434785

Skin temperature reveals the intensity of acute stress.

PubMed

Herborn, Katherine A; Graves, James L; Jerem, Paul; Evans, Neil P; Nager, Ruedi; McCafferty, Dominic J; McKeegan, Dorothy E F

2015-12-01

Acute stress triggers peripheral vasoconstriction, causing a rapid, short-term drop in skin temperature in homeotherms. We tested, for the first time, whether this response has the potential to quantify stress, by exhibiting proportionality with stressor intensity. We used established behavioural and hormonal markers: activity level and corticosterone level, to validate a mild and more severe form of an acute restraint stressor in hens (Gallus gallus domesticus). We then used infrared thermography (IRT) to non-invasively collect continuous temperature measurements following exposure to these two intensities of acute handling stress. In the comb and wattle, two skin regions with a known thermoregulatory role, stressor intensity predicted the extent of initial skin cooling, and also the occurrence of a more delayed skin warming, providing two opportunities to quantify stress. With the present, cost-effective availability of IRT technology, this non-invasive and continuous method of stress assessment in unrestrained animals has the potential to become common practice in pure and applied research. Copyright © 2015 Elsevier Inc. All rights reserved.

The influence of water temperature and accelerometer-determined fight intensity on physiological stress and reflex impairment of angled largemouth bass

PubMed Central

Brownscombe, Jacob W.; Marchand, Kelsey; Tisshaw, Kathryn; Fewster, Victoria; Groff, Olivia; Pichette, Melissa; Seed, Marian; Gutowsky, Lee F. G.; Wilson, Alexander D. M.; Cooke, Steven J.

2014-01-01

Release of fish captured by recreational anglers is a common practice due to angler conservation ethics or compliance with fisheries regulations. As such, there is a need to understand the factors that influence mortality and sub-lethal impairments to ensure that catch-and-release angling is a sustainable practice. Longer angling times generally contribute to increased stress and mortality in fish such that reducing these times putatively reduces stress and improves survival. However, the relative importance of fight intensity (rather than simply duration) on fish condition is poorly understood. The objective of this research was to examine the effects of fight intensity on physiological stress and reflex impairment of largemouth bass (Micropterus salmoides). The largemouth bass were angled using conventional recreational fishing gear in May (water temperature ∼12°C) and June (∼22°C) of 2014 in Lake Opinicon, Ontario, Canada. Fight intensity was quantified using tri-axial accelerometer loggers mounted on the tips of fishing rods. Upon capture, reflex impairment measures were assessed, and fish were held for 1 h prior to blood sampling for measurement of physiological stress (blood glucose and lactate concentrations and pH). Physiological stress values showed a negative trend with fight duration and total fight intensity, but a positive trend with average fight intensity. Water temperature emerged as the most important predictor of the stress response in largemouth bass, while fight duration and intensity were not strong predictors. Reflex impairment was minimal, but higher reflex impairment scores were associated with elevated blood glucose. Overall, the findings of this study suggest that angling for largemouth bass at colder temperatures (<15°C) causes greater physiological stress than at warmer temperatures (>20°C). Based on our findings, we conclude that fight intensity is likely not to be a major driver of physiological stress in this species using typical largemouth bass angling gear, owing to the relatively short fight times (i.e. <2 min). PMID:27293678

Survey of Turbulence Models for the Computation of Turbulent Jet Flow and Noise

NASA Technical Reports Server (NTRS)

Nallasamy, N.

1999-01-01

The report presents an overview of jet noise computation utilizing the computational fluid dynamic solution of the turbulent jet flow field. The jet flow solution obtained with an appropriate turbulence model provides the turbulence characteristics needed for the computation of jet mixing noise. A brief account of turbulence models that are relevant for the jet noise computation is presented. The jet flow solutions that have been directly used to calculate jet noise are first reviewed. Then, the turbulent jet flow studies that compute the turbulence characteristics that may be used for noise calculations are summarized. In particular, flow solutions obtained with the k-e model, algebraic Reynolds stress model, and Reynolds stress transport equation model are reviewed. Since, the small scale jet mixing noise predictions can be improved by utilizing anisotropic turbulence characteristics, turbulence models that can provide the Reynolds stress components must now be considered for jet flow computations. In this regard, algebraic stress models and Reynolds stress transport models are good candidates. Reynolds stress transport models involve more modeling and computational effort and time compared to algebraic stress models. Hence, it is recommended that an algebraic Reynolds stress model (ASM) be implemented in flow solvers to compute the Reynolds stress components.

Postintensive care unit psychological burden in patients with chronic obstructive pulmonary disease and informal caregivers: A multicenter study.

PubMed

de Miranda, Sandra; Pochard, Frédéric; Chaize, Marine; Megarbane, Bruno; Cuvelier, Antoine; Bele, Nicolas; Gonzalez-Bermejo, Jesus; Aboab, Jérome; Lautrette, Alexandre; Lemiale, Virginie; Roche, Nicolas; Thirion, Marina; Chevret, Sylvie; Schlemmer, Benoit; Similowski, Thomas; Azoulay, Elie

2011-01-01

To determine the prevalence and risk factors of symptoms of anxiety, depression, and posttraumatic stress disorder-related symptoms in patients with chronic obstructive pulmonary disease and their relatives after an intensive care unit stay. Prospective multicenter study. Nineteen French intensive care units. One hundred twenty-six patients with chronic obstructive pulmonary disease who survived an intensive care unit stay and 102 relatives. None. Patients and relatives were interviewed at intensive care unit discharge and 90 days later to assess symptoms of anxiety and depression using Hospital Anxiety and Depression Scale (HADS) and posttraumatic stress disorder-related symptoms using the Impact of Event Scale (IES). At intensive care unit discharge, 90% of patients recollected traumatic psychological events in the intensive care unit. At day 90, we were able to conduct telephone interviews with 53 patients and 47 relatives. Hospital Anxiety and Depression Scale scores indicated symptoms of anxiety and depression in 52% and 45.5% of patients at intensive care unit discharge and in 28.3% and 18.9% on day 90, respectively. Corresponding prevalence in relatives were 72.2% and 25.7% at intensive care unit discharge and 40.4% and 14.9% on day 90, respectively. The Impact of Event Scale indicated posttraumatic stress disorder-related symptoms in 20.7% of patients and 29.8% of relatives on day 90. Peritraumatic dissociation assessed using the Peritraumatic Dissociative Experiences Questionnaire was independently associated with posttraumatic stress disorder-related symptoms in the patients and relatives. Previous intensive care unit experience and recollection of bothersome noise in the intensive care unit predicted posttraumatic stress disorder-related symptoms in the patients. Psychiatric symptoms were found to be common in a group of 126 patients with chronic obstructive pulmonary disease who survived an intensive care unit stay and their relatives at intensive care unit discharge and 90 days later. Peritraumatic dissociation at intensive care unit discharge was found to independently predict posttraumatic stress disorder-related symptoms in this sample of patients and relatives.

Complexity of cardiac signals for predicting changes in alpha-waves after stress in patients undergoing cardiac catheterization

NASA Astrophysics Data System (ADS)

Chiu, Hung-Chih; Lin, Yen-Hung; Lo, Men-Tzung; Tang, Sung-Chun; Wang, Tzung-Dau; Lu, Hung-Chun; Ho, Yi-Lwun; Ma, Hsi-Pin; Peng, Chung-Kang

2015-08-01

The hierarchical interaction between electrical signals of the brain and heart is not fully understood. We hypothesized that the complexity of cardiac electrical activity can be used to predict changes in encephalic electricity after stress. Most methods for analyzing the interaction between the heart rate variability (HRV) and electroencephalography (EEG) require a computation-intensive mathematical model. To overcome these limitations and increase the predictive accuracy of human relaxing states, we developed a method to test our hypothesis. In addition to routine linear analysis, multiscale entropy and detrended fluctuation analysis of the HRV were used to quantify nonstationary and nonlinear dynamic changes in the heart rate time series. Short-time Fourier transform was applied to quantify the power of EEG. The clinical, HRV, and EEG parameters of postcatheterization EEG alpha waves were analyzed using change-score analysis and generalized additive models. In conclusion, the complexity of cardiac electrical signals can be used to predict EEG changes after stress.

Complexity of cardiac signals for predicting changes in alpha-waves after stress in patients undergoing cardiac catheterization

PubMed Central

Chiu, Hung-Chih; Lin, Yen-Hung; Lo, Men-Tzung; Tang, Sung-Chun; Wang, Tzung-Dau; Lu, Hung-Chun; Ho, Yi-Lwun; Ma, Hsi-Pin; Peng, Chung-Kang

2015-01-01

The hierarchical interaction between electrical signals of the brain and heart is not fully understood. We hypothesized that the complexity of cardiac electrical activity can be used to predict changes in encephalic electricity after stress. Most methods for analyzing the interaction between the heart rate variability (HRV) and electroencephalography (EEG) require a computation-intensive mathematical model. To overcome these limitations and increase the predictive accuracy of human relaxing states, we developed a method to test our hypothesis. In addition to routine linear analysis, multiscale entropy and detrended fluctuation analysis of the HRV were used to quantify nonstationary and nonlinear dynamic changes in the heart rate time series. Short-time Fourier transform was applied to quantify the power of EEG. The clinical, HRV, and EEG parameters of postcatheterization EEG alpha waves were analyzed using change-score analysis and generalized additive models. In conclusion, the complexity of cardiac electrical signals can be used to predict EEG changes after stress. PMID:26286628

A theory for the fracture of thin plates subjected to bending and twisting moments

NASA Technical Reports Server (NTRS)

Hui, C. Y.; Zehnder, Alan T.

1993-01-01

Stress fields near the tip of a through crack in an elastic plate under bending and twisting moments are reviewed assuming both Kirchhoff and Reissner plate theories. The crack tip displacement and rotation fields based on the Reissner theory are calculated. These results are used to calculate the J-integral (energy release rate) for both Kirchhoff and Reissner plate theories. Invoking Simmonds and Duva's (1981) result that the value of the J-integral based on either theory is the same for thin plates, a universal relationship between the Kirchhoff theory stress intensity factors and the Reissner theory stress intensity factors is obtained for thin plates. Calculation of Kirchhoff theory stress intensity factors from finite elements based on energy release rate is illustrated. It is proposed that, for thin plates, fracture toughness and crack growth rates be correlated with the Kirchhoff theory stress intensity factors.

Fatigue crack growth under variable amplitude loading

NASA Astrophysics Data System (ADS)

Sidawi, Jihad A.

1994-09-01

Fatigue crack growth tests were conducted on an Fe 510 E C-Mn steel and a submerged arc welded joint from the same material under constant, variable, and random loading amplitudes. Paris-Erdogan's crack growth rate law was tested for the evaluation of m and C using the stress intensity factor K, the J-integral, the effective stress intensity factor K(sub eff), and the root mean square stress intensity factor K(sub rms) fracture mechanics concepts. The effect of retardation and residual stresses resulting from welding was also considered. It was found that all concepts gave good life predictions in all cases.

Evaluation of mean velocity and turbulence measurements with ADCPs

USGS Publications Warehouse

Nystrom, E.A.; Rehmann, C.R.; Oberg, K.A.

2007-01-01

To test the ability of acoustic Doppler current profilers (ADCPs) to measure turbulence, profiles measured with two pulse-to-pulse coherent ADCPs in a laboratory flume were compared to profiles measured with an acoustic Doppler velocimeter, and time series measured in the acoustic beam of the ADCPs were examined. A four-beam ADCP was used at a downstream station, while a three-beam ADCP was used at a downstream station and an upstream station. At the downstream station, where the turbulence intensity was low, both ADCPs reproduced the mean velocity profile well away from the flume boundaries; errors near the boundaries were due to transducer ringing, flow disturbance, and sidelobe interference. At the upstream station, where the turbulence intensity was higher, errors in the mean velocity were large. The four-beam ADCP measured the Reynolds stress profile accurately away from the bottom boundary, and these measurements can be used to estimate shear velocity. Estimates of Reynolds stress with a three-beam ADCP and turbulent kinetic energy with both ADCPs cannot be computed without further assumptions, and they are affected by flow inhomogeneity. Neither ADCP measured integral time scales to within 60%. ?? 2007 ASCE.

Sediment Dynamics in Shallow Tidal Landscapes: The Role of Wind Waves and Tidal Currents

NASA Astrophysics Data System (ADS)

Carniello, L.; D'Alpaos, A.

2014-12-01

A precise description of sediment dynamics (resuspension and re-distribution of sediments) is crucial when investigating the long term evolution of the different morphological entities characterizing tidal landscapes. It has been demonstrated that wind waves are the main responsible for sediment resuspension in shallow micro-tidal lagoons where tidal currents, which produce shear stresses large enough to carry sediments into suspension only within the main channels, are mainly responsible for sediment redistribution. A mathematical model has been developed to describe sediment entrainment, transport and deposition due to the combined effect of tidal currents and wind waves in shallow lagoons considering both cohesive and non-cohesive sediments. The model was calibrated and tested using both in situ point observations and turbidity maps obtained analyzing satellite images. Once calibrated the model can integrate the high temporal resolution of point observations with the high spatial resolution of remote sensing, overcoming the intrinsic limitation of these two types of observations. The model was applied to the specific test case of the Venice lagoon simulating an entire year (2005) which was shown to be a "representative" year for wind and tide characteristics. The time evolution of the computed total bottom shear stresses (BSS) and suspended sediment concentration (SSC) was analyzed on the basis of a "Peaks Over Threshold" method once a critical value for shear stress and turbidity were chosen. The analyses of the numerical results enabled us to demonstrate that resuspension events can be modeled as marked Poisson processes: interarrival time, intensity of peak excesses and duration being exponentially distributed random variable. The probability distributions of the interarrival time of overthreshold exceedances in both BSS and SSC as well as their intensity and duration can be used in long-term morphodynamic studies to generate synthetic series statistically equivalent to real sequences through which MonteCarlo realizations of relevant morphological evolutions can be computed.

A Programmable Optical Stimulator for the Drosophila Eye.

PubMed

Chen, Xinping; Leon-Salas, Walter D; Zigon, Taylor; Ready, Donald F; Weake, Vikki M

2017-10-01

A programmable optical stimulator for Drosophila eyes is presented. The target application of the stimulator is to induce retinal degeneration in fly photoreceptor cells by exposing them to light in a controlled manner. The goal of this work is to obtain a reproducible system for studying age-related changes in susceptibility to environmental ocular stress. The stimulator uses light emitting diodes and an embedded computer to control illuminance, color (blue or red) and duration in two independent chambers. Further, the stimulator is equipped with per-chamber light and temperature sensors and a fan to monitor light intensity and to control temperature. An ON/OFF temperature control implemented on the embedded computer keeps the temperature from reaching levels that will induce the heat shock stress response in the flies. A custom enclosure was fabricated to house the electronic components of the stimulator. The enclosure provides a light-impermeable environment that allows air flow and lets users easily load and unload fly vials. Characterization results show that the fabricated stimulator can produce light at illuminances ranging from 0 to 16000 lux and power density levels from 0 to 7.2 mW/cm 2 for blue light. For red light the maximum illuminance is 8000 lux which corresponds to a power density of 3.54 mW/cm 2 . The fans and the ON/OFF temperature control are able to keep the temperature inside the chambers below 28.17°C. Experiments with white-eye male flies were performed to assess the ability of the fabricated simulator to induce blue light-dependent retinal degeneration. Retinal degeneration is observed in flies exposed to 8 hours of blue light at 7949 lux. Flies in a control experiment with no light exposure show no retinal degeneration. Flies exposed to red light for the similar duration and light intensity (8 hours and 7994 lux) do not show retinal degeneration either. Hence, the fabricated stimulator can be used to create environmental ocular stress using blue light.

[Factors causing stress in patients in intensive care units].

PubMed

Pérez de Ciriza, A; Otamendi, S; Ezenarro, A; Asiain, M C

1996-01-01

Intensive care units have been considered stress generating areas. Knowing the causes why this happens will allow us to take specific measures to prevent or minimize it. This study has been performed with the aim to identify stress raising factors, as they are perceived by intensive care patients. The study has been performed in 49 patients most of whom were being attended in postoperatory control. The valuation of the degree of stress was performed using the "Scale of Environmental Stressors in Intensive Care" by Ballard in 1981, modified and adapted to our environment, with a result of 43 items distributed in six groups; Immobilization, Isolation, Deprivation of sleep, Time-spacial disorientation, Sensorial deprivation and overestimulation, and depersonalization and loss of autocontrol. The level of stress perceived by patients was low. The factors considered as most stressing were those related to physical aspects; presence of tubes in nose and mouth, impossibility to sleep and presence of noise, whereas those less stressing referred to Nursing attention. We conclude that patients perceive ICU as a little stressing place in spite of the excessive noise, remark the presence of invasive tubes and the difficulty to sleep as the most stressing factors, and in the same way, express a high degree of satisfaction about the attention received.

Stress intensity factors for surface and corner cracks emanating from a wedge-loaded hole

NASA Technical Reports Server (NTRS)

Zhao, W.; Sutton, M. A.; Shivakumar, K. N.; Newman, J. C., Jr.

1994-01-01

To assist analysis of riveted lap joints, stress intensity factors are determined for surface and corner cracks emanating from a wedge-loaded hole by using a 3-D weight function method in conjunction with a 3-D finite element method. A stress intensity factor equation for surface cracks is also developed to provide a closed-form solution. The equation covers commonly-encountered geometrical ranges and retains high accuracy over the entire range.

A Fatigue Life Prediction Method Based on Strain Intensity Factor

PubMed Central

Zhang, Wei; Liu, Huili; Wang, Qiang; He, Jingjing

2017-01-01

In this paper, a strain-intensity-factor-based method is proposed to calculate the fatigue crack growth under the fully reversed loading condition. A theoretical analysis is conducted in detail to demonstrate that the strain intensity factor is likely to be a better driving parameter correlated with the fatigue crack growth rate than the stress intensity factor (SIF), especially for some metallic materials (such as 316 austenitic stainless steel) in the low cycle fatigue region with negative stress ratios R (typically R = −1). For fully reversed cyclic loading, the constitutive relation between stress and strain should follow the cyclic stress-strain curve rather than the monotonic one (it is a nonlinear function even within the elastic region). Based on that, a transformation algorithm between the SIF and the strain intensity factor is developed, and the fatigue crack growth rate testing data of 316 austenitic stainless steel and AZ31 magnesium alloy are employed to validate the proposed model. It is clearly observed that the scatter band width of crack growth rate vs. strain intensity factor is narrower than that vs. the SIF for different load ranges (which indicates that the strain intensity factor is a better parameter than the stress intensity factor under the fully reversed load condition). It is also shown that the crack growth rate is not uniquely determined by the SIF range even under the same R, but is also influenced by the maximum loading. Additionally, the fatigue life data (strain-life curve) of smooth cylindrical specimens are also used for further comparison, where a modified Paris equation and the equivalent initial flaw size (EIFS) are involved. The results of the proposed method have a better agreement with the experimental data compared to the stress intensity factor based method. Overall, the strain intensity factor method shows a fairly good ability in calculating the fatigue crack propagation, especially for the fully reversed cyclic loading condition. PMID:28773049

Dynamic forces on agglomerated particles caused by high-intensity ultrasound.

PubMed

Knoop, Claas; Fritsching, Udo

2014-03-01

In this paper the acoustic forces on particles and agglomerates caused by high-intensity ultrasound in gaseous atmosphere are derived by means of computational fluid dynamics (CFD). Sound induced forces cause an oscillating stress scenario where the primary particles of an agglomerate are alternatingly pressed together and torn apart with the frequency of the applied wave. A comparison of the calculated acoustic forces with respect to the inter particle adhesion forces from Van-der-Waals and liquid bridge interactions reveals that the separation forces may reach the same order of magnitude for 80 μm sized SiO2-particles. Hence, with finite probability acoustically agitated gases may de-agglomerate/disperse solid agglomerate structures. This effect is confirmed by dispersion experiments in an acoustic particle levitation setup. Copyright © 2013 Elsevier B.V. All rights reserved.

Free radicals, reactive oxygen species, oxidative stress and its classification.

PubMed

Lushchak, Volodymyr I

2014-12-05

Reactive oxygen species (ROS) initially considered as only damaging agents in living organisms further were found to play positive roles also. This paper describes ROS homeostasis, principles of their investigation and technical approaches to investigate ROS-related processes. Especial attention is paid to complications related to experimental documentation of these processes, their diversity, spatiotemporal distribution, relationships with physiological state of the organisms. Imbalance between ROS generation and elimination in favor of the first with certain consequences for cell physiology has been called "oxidative stress". Although almost 30years passed since the first definition of oxidative stress was introduced by Helmut Sies, to date we have no accepted classification of oxidative stress. In order to fill up this gape here classification of oxidative stress based on its intensity is proposed. Due to that oxidative stress may be classified as basal oxidative stress (BOS), low intensity oxidative stress (LOS), intermediate intensity oxidative stress (IOS), and high intensity oxidative stress (HOS). Another classification of potential interest may differentiate three categories such as mild oxidative stress (MOS), temperate oxidative stress (TOS), and finally severe (strong) oxidative stress (SOS). Perspective directions of investigations in the field include development of sophisticated classification of oxidative stresses, accurate identification of cellular ROS targets and their arranged responses to ROS influence, real in situ functions and operation of so-called "antioxidants", intracellular spatiotemporal distribution and effects of ROS, deciphering of molecular mechanisms responsible for cellular response to ROS attacks, and ROS involvement in realization of normal cellular functions in cellular homeostasis. Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.

Spallation modeling in the Charring Material Thermal Response and Ablation (CMA) computer program

NASA Astrophysics Data System (ADS)

Sullivan, J. M.; Kobayashi, W. S.

1987-06-01

It has been observed during tests of certain laminated composite materials exposed to relatively high continuous wave laser irradiation, that the heated surface will spall. To model this phenomenon, the Charring Material Thermal Response and Ablation code has been updated. In addition to temperature response, in-depth decomposition, and surface recession, thermal and mechanical stresses are calculated. Spall is modeled as a discrete mass removal event occurring when the stresses exceed the ultimate strength of the char through a critical depth. Comparisons are made with test data for a carbon phenolic cylinder exposed to a shock tube environment and for a flat plate Kevlar epoxy test specimen exposed to high intensity laser irradiation. Good agreement is shown; however, the results indicate a requirement for more comprehensive elevated-temperature material properties for further validation.

Turbulence modelling of flow fields in thrust chambers

NASA Technical Reports Server (NTRS)

Chen, C. P.; Kim, Y. M.; Shang, H. M.

1993-01-01

Following the consensus of a workshop in Turbulence Modelling for Liquid Rocket Thrust Chambers, the current effort was undertaken to study the effects of second-order closure on the predictions of thermochemical flow fields. To reduce the instability and computational intensity of the full second-order Reynolds Stress Model, an Algebraic Stress Model (ASM) coupled with a two-layer near wall treatment was developed. Various test problems, including the compressible boundary layer with adiabatic and cooled walls, recirculating flows, swirling flows, and the entire SSME nozzle flow were studied to assess the performance of the current model. Detailed calculations for the SSME exit wall flow around the nozzle manifold were executed. As to the overall flow predictions, the ASM removes another assumption for appropriate comparison with experimental data to account for the non-isotropic turbulence effects.

Reactor Pressure Vessel Fracture Analysis Capabilities in Grizzly

DOE Office of Scientific and Technical Information (OSTI.GOV)

Spencer, Benjamin; Backman, Marie; Chakraborty, Pritam

2015-03-01

Efforts have been underway to develop fracture mechanics capabilities in the Grizzly code to enable it to be used to perform deterministic fracture assessments of degraded reactor pressure vessels (RPVs). Development in prior years has resulted a capability to calculate -integrals. For this application, these are used to calculate stress intensity factors for cracks to be used in deterministic linear elastic fracture mechanics (LEFM) assessments of fracture in degraded RPVs. The -integral can only be used to evaluate stress intensity factors for axis-aligned flaws because it can only be used to obtain the stress intensity factor for pure Mode Imore » loading. Off-axis flaws will be subjected to mixed-mode loading. For this reason, work has continued to expand the set of fracture mechanics capabilities to permit it to evaluate off-axis flaws. This report documents the following work to enhance Grizzly’s engineering fracture mechanics capabilities for RPVs: • Interaction Integral and -stress: To obtain mixed-mode stress intensity factors, a capability to evaluate interaction integrals for 2D or 3D flaws has been developed. A -stress evaluation capability has been developed to evaluate the constraint at crack tips in 2D or 3D. Initial verification testing of these capabilities is documented here. • Benchmarking for axis-aligned flaws: Grizzly’s capabilities to evaluate stress intensity factors for axis-aligned flaws have been benchmarked against calculations for the same conditions in FAVOR. • Off-axis flaw demonstration: The newly-developed interaction integral capabilities are demon- strated in an application to calculate the mixed-mode stress intensity factors for off-axis flaws. • Other code enhancements: Other enhancements to the thermomechanics capabilities that relate to the solution of the engineering RPV fracture problem are documented here.« less

Stress intensity factor in a tapered specimen

NASA Technical Reports Server (NTRS)

Xue-Hui, L.; Erdogan, F.

1985-01-01

The general problem of a tapered specimen containing an edge crack is formulated in terms of a system of singular integral equations. The equations are solved and the stress intensity factor is calculated for a compact and for a slender tapered specimen, the latter simulating the double cantilever beam. The results are obtained primarily for a pair of concentrated forces and for crack surface wedge forces. The stress intensity factors are also obtained for a long strip under uniform tension which contains inclined edge cracks.

The effect of psychosocial stress on muscle activity during computer work: Comparative study between desktop computer and mobile computing products.

PubMed

Taib, Mohd Firdaus Mohd; Bahn, Sangwoo; Yun, Myung Hwan

2016-06-27

The popularity of mobile computing products is well known. Thus, it is crucial to evaluate their contribution to musculoskeletal disorders during computer usage under both comfortable and stressful environments. This study explores the effect of different computer products' usages with different tasks used to induce psychosocial stress on muscle activity. Fourteen male subjects performed computer tasks: sixteen combinations of four different computer products with four different tasks used to induce stress. Electromyography for four muscles on the forearm, shoulder and neck regions and task performances were recorded. The increment of trapezius muscle activity was dependent on the task used to induce the stress where a higher level of stress made a greater increment. However, this relationship was not found in the other three muscles. Besides that, compared to desktop and laptop use, the lowest activity for all muscles was obtained during the use of a tablet or smart phone. The best net performance was obtained in a comfortable environment. However, during stressful conditions, the best performance can be obtained using the device that a user is most comfortable with or has the most experience with. Different computer products and different levels of stress play a big role in muscle activity during computer work. Both of these factors must be taken into account in order to reduce the occurrence of musculoskeletal disorders or problems.

Post-stress recovery of pituitary-adrenal hormones and glucose, but not the response during exposure to the stressor, is a marker of stress intensity in highly stressful situations.

PubMed

Márquez, Cristina; Belda, Xavier; Armario, Antonio

2002-02-01

Acute immobilization in male rats elicited the same ACTH, corticosterone and glucose response as foot shock when measured immediately after stress. However, post-stress recovery of plasma ACTH, corticosterone and glucose levels were delayed in immobilized versus shocked rats. Similarly, stress-induced anorexia was much greater in the former animals. All these data suggest that post-stress speed of recovery of some physiological variables is positively related to stressor intensity and could be used to evaluate it.

Comparison of measured temperatures, thermal stresses and creep residues with predictions on a built-up titanium structure

NASA Technical Reports Server (NTRS)

Jenkins, Jerald M.

1987-01-01

Temperature, thermal stresses, and residual creep stresses were studied by comparing laboratory values measured on a built-up titanium structure with values calculated from finite-element models. Several such models were used to examine the relationship between computational thermal stresses and thermal stresses measured on a built-up structure. Element suitability, element density, and computational temperature discrepancies were studied to determine their impact on measured and calculated thermal stress. The optimum number of elements is established from a balance between element density and suitable safety margins, such that the answer is acceptably safe yet is economical from a computational viewpoint. It is noted that situations exist where relatively small excursions of calculated temperatures from measured values result in far more than proportional increases in thermal stress values. Measured residual stresses due to creep significantly exceeded the values computed by the piecewise linear elastic strain analogy approach. The most important element in the computation is the correct definition of the creep law. Computational methodology advances in predicting residual stresses due to creep require significantly more viscoelastic material characterization.

Lexical stress contrast marking in fluent and non-fluent aphasia in Spanish: The relationship between acoustic cues and compensatory strategies.

PubMed

Baqué, Lorraine

2017-01-01

This study sought to investigate stress production in Spanish by patients with Broca's (BA) and conduction aphasia (CA) as compared to controls. Our objectives were to assess whether: a) there were many abnormal acoustic correlates of stress as produced by patients, b) these abnormalities had a phonetic component and c) ability for articulatory compensation for stress marking was preserved. The results showed abnormal acoustic values in both BA and CA's productions, affecting not only duration but also F0 and intensity cues, and an interaction effect of stress pattern and duration on intensity cubes in BA, but not in CA or controls. The results are interpreted as deriving from two different underlying phenomena: in BA, a compensatory use of intensity as a stress cue in order to avoid 'equal stress'; in CA, related to either a 'subtle phonetic deficit' involving abnormal stress acoustic cue-processing or to 'clear-speech' effects.

Three-dimensional stress intensity factor analysis of a surface crack in a high-speed bearing

NASA Technical Reports Server (NTRS)

Ballarini, Roberto; Hsu, Yingchun

1990-01-01

The boundary element method is applied to calculate the stress intensity factors of a surface crack in the rotating inner raceway of a high-speed roller bearing. The three-dimensional model consists of an axially stressed surface cracked plate subjected to a moving Hertzian contact loading. A multidomain formulation and singular crack-tip elements were employed to calculate the stress intensity factors accurately and efficiently for a wide range of configuration parameters. The results can provide the basis for crack growth calculations and fatigue life predictions of high-performance rolling element bearings that are used in aircraft engines.

Physiological Tolerance to Uncompensable Heat Stress: Effects of Exercise Intensity, Protective Clothing, and Climate

DTIC Science & Technology

1994-01-01

Physiological tolerance to uncompensable heat stress: effects of exercise intensity, protective clothing , and climate SCOTT J. MONTAIN, MICHAEL N...effects of exercise 26), there remains little information to predict the inci- intensity, protective clothing , and climate. J. AppL PhysioL dence of...that pre- exercise intensity, protective clothing level, and climate on dict the physiological responses and work capability dur- physiological tolerance

Stress Ratio Effects on Small Fatigue Crack Growth in Ti-6Al-4V (Preprint)

DTIC Science & Technology

2008-11-01

crack effect is observed in this alloy , consistent with previous observations, where small cracks grew at stress intensity factor ranges below the long...high stress intensity factor ranges, ΔK, on the order of 10 MPa√m or greater. A significant small crack effect is observed in this alloy , consistent...the behavior of small cracks under different stress ratios in Ti-6Al-4V, an alloy commonly used for fan airfoils. The effect of stress ratio on

The effect of lavender oil on stress, bispectral index values, and needle insertion pain in volunteers.

PubMed

Kim, Sioh; Kim, Hyun-Jae; Yeo, Jin-Seok; Hong, Sung-Jung; Lee, Ji-Min; Jeon, Younghoon

2011-09-01

The purpose of this study was to investigate whether lavender oil aromatherapy can reduce the bispectral index (BIS) values and stress and decrease the pain of needle insertion in 30 volunteers. Thirty (30) healthy volunteers were randomly allocated to 2 groups: the experimental group received oxygen with a face mask coated with lavender oil for 5 minutes, and the control group received oxygen through a face mask with no lavender oil for 5 minutes. The stress level (0=no stress, 10=maximum stress), BIS value, and pain intensity of needle insertion (0=no pain, 10=worst pain imaginable) were measured. There were no significant differences in age, sex, height, and weight between the two groups. Stress level, BIS value, and pain intensity of needle insertion before aromatherapy were similar between the two groups. However, the stress values (p<0.001) and BIS value (p<0.001) after aromatherapy were significantly reduced compared with the control. In addition, the pain intensity of needle insertion was significantly decreased after aromatherapy compared with the control (p<0.001). Lavender aromatherapy in volunteers provided a significant decrease in the stress levels and in the BIS values. In addition, it significantly reduced the pain intensity of needle insertion.

Effects of high intensity interval training versus moderate intensity continuous training on the reduction of oxidative stress in type 2 diabetic adult patients: CAT.

PubMed

Poblete Aro, Carlos Emilio; Russell Guzmán, Javier Antonio; Soto Muñoz, Marcelo Enrique; Villegas González, Bastián Eduardo

2015-08-13

Oxidative stress is caused by an imbalance between an excessive production of reactive oxygen species and/or a deficiency in the level of endogenous and exogenous antioxidant defenses. The presence of reactive oxygen species in large concentrations and for long periods is associated with the occurrence of various diseases, including type 2 diabetes mellitus. Exercise represents an effective means for the prevention and treatment of type 2 diabetes mellitus, and is also able to reduce long-term oxidative stress levels. High-intensity interval training has shown to be an efficient and viable option for type 2 diabetes mellitus control. In turn, high-intensity interval training seems to have positive effects on oxidative stress levels by increasing levels of endogenous antioxidants. To assess the validity and applicability of the results regarding the effectiveness of high-intensity interval training compared to moderate intensity continuous training to reduce oxidative stress in patients with type 2 diabetes mellitus and to answer the following question: In adults with type 2 diabetes mellitus, can the method of high-intensity interval training, compared to moderate intensity continuous training reduce oxidative stress levels? We performed a critical analysis of the article "Continuous training vs Interval training in glycemic control and macro and microvascular reactivity in patients with type 2 diabetes". No statistically significant differences were observed in concentrations of superoxide dismutase in any of the experimental groups. Only in the interval group a decrease in malondialdehyde regarding control group and baseline (p<0.05) was observed. In addition, only in the interval group there was an increase in glutathione peroxidase compared to the group of continuous aerobic training and baseline (p<0.05). Nitric oxide showed a significant increase regarding the control, continuous aerobic group and baseline (p<0.05) in the interval training group. Despite the fact that both training groups show improvements over markers of lipid profile and fitness, high intensity interval training has shown to be more effective in the normalization of oxidative stress, impacting positively on the concentration of pro-oxidant markers and antioxidants.

Visual and psychological stress during computer work in healthy, young females-physiological responses.

PubMed

Mork, Randi; Falkenberg, Helle K; Fostervold, Knut Inge; Thorud, Hanne Mari S

2018-05-30

Among computer workers, visual complaints, and neck pain are highly prevalent. This study explores how occupational simulated stressors during computer work, like glare and psychosocial stress, affect physiological responses in young females with normal vision. The study was a within-subject laboratory experiment with a counterbalanced, repeated design. Forty-three females performed four 10-min computer-work sessions with different stress exposures: (1) minimal stress; (2) visual stress (direct glare); (3) psychological stress; and (4) combined visual and psychological stress. Muscle activity and muscle blood flow in trapezius, muscle blood flow in orbicularis oculi, heart rate, blood pressure, blink rate and postural angles were continuously recorded. Immediately after each computer-work session, fixation disparity was measured and a questionnaire regarding perceived workstation lighting and stress was completed. Exposure to direct glare resulted in increased trapezius muscle blood flow, increased blink rate, and forward bending of the head. Psychological stress induced a transient increase in trapezius muscle activity and a more forward-bent posture. Bending forward towards the computer screen was correlated with higher productivity (reading speed), indicating a concentration or stress response. Forward bent posture was also associated with changes in fixation disparity. Furthermore, during computer work per se, trapezius muscle activity and blood flow, orbicularis oculi muscle blood flow, and heart rate were increased compared to rest. Exposure to glare and psychological stress during computer work were shown to influence the trapezius muscle, posture, and blink rate in young, healthy females with normal binocular vision, but in different ways. Accordingly, both visual and psychological factors must be taken into account when optimizing computer workstations to reduce physiological responses that may cause excessive eyestrain and musculoskeletal load.

Deformability analysis of sickle blood using ektacytometry.

PubMed

Rabai, Miklos; Detterich, Jon A; Wenby, Rosalinda B; Hernandez, Tatiana M; Toth, Kalman; Meiselman, Herbert J; Wood, John C

2014-01-01

Sickle cell disease (SCD) is characterized by decreased erythrocyte deformability, microvessel occlusion and severe painful infarctions of different organs. Ektacytometry of SCD red blood cells (RBC) is made difficult by the presence of rigid, poorly-deformable irreversibly sickled cells (ISC) that do not align with the fluid shear field and distort the elliptical diffraction pattern seen with normal RBC. In operation, the computer software fits an outline to the diffraction pattern, then reports an elongation index (EI) at each shear stress based on the length and width of the fitted ellipse: EI=(length-width)/(length+width). Using a commercial ektacytometer (LORCA, Mechatronics Instruments, The Netherlands) we have approached the problem of ellipse fitting in two ways: (1) altering the height of the diffraction image on a computer monitor using an aperture within the camera lens; (2) altering the light intensity level (gray level) used by the software to fit the image to an elliptical shape. Neither of these methods affected deformability results (elongation index-shear stress relations) for normal RBC but did markedly affect results for SCD erythrocytes: (1) decreasing image height by 15% and 30% increased EI at moderate to high stresses; (2) progressively increasing the light level increased EI over a wide range of stresses. Fitting data obtained at different image heights using the Lineweaver-Burke routine yielded percentage ISC results in good agreement with microscopic cell counting. We suggest that these two relatively simple approaches allow minimizing artifacts due to the presence of rigid discs or ISC and also suggest the need for additional studies to evaluate the physiological relevance of deformability data obtained via these methods.

Stress-intensity factors for a wide range of semi-elliptical surface cracks in finite-thickness plates

NASA Technical Reports Server (NTRS)

Raju, I. S.; Newman, J. C., Jr.

1979-01-01

Surface cracks are among the more common flaws in aircraft and pressure vessel components. Several calculations of stress-intensity factors for semi-elliptical surface cracks subjected to tension have appeared in the literature. However, some of these solutions are in disagreement by 50-100%. In this paper, stress-intensity factors for shallow and deep semi-elliptical surface cracks in plates subjected to tension are presented. To verify the accuracy of the three-dimensional finite-element models employed, convergence was studied by varying the number of degrees of freedom in the models from 1500 to 6900. The 6900 degrees of freedom used here were more than twice the number used in previously reported solutions. Also, the stress-intensity variations in the boundary-layer region at the intersection of the crack with the free surface were investigated.

Strain intensity factor approach for predicting the strength of continuously reinforced metal matrix composites

NASA Technical Reports Server (NTRS)

Poe, Clarence C., Jr.

1989-01-01

A method was previously developed to predict the fracture toughness (stress intensity factor at failure) of composites in terms of the elastic constants and the tensile failing strain of the fibers. The method was applied to boron/aluminum composites made with various proportions of 0 deg and +/- 45 deg plies. Predicted values of fracture toughness were in gross error because widespread yielding of the aluminum matrix made the compliance very nonlinear. An alternate method was develolped to predict the strain intensity factor at failure rather than the stress intensity factor because the singular strain field was not affected by yielding as much as the stress field. Far-field strains at failure were calculated from the strain intensity factor, and then strengths were calculated from the far-field strains using uniaxial stress-strain curves. The predicted strengths were in good agreement with experimental values, even for the very nonlinear laminates that contained only +/- 45 deg plies. This approach should be valid for other metal matrix composites that have continuous fibers.

Characterization of crack growth under combined loading

NASA Technical Reports Server (NTRS)

Feldman, A.; Smith, F. W.; Holston, A., Jr.

1977-01-01

Room-temperature static and cyclic tests were made on 21 aluminum plates in the shape of a 91.4x91.4-cm Maltese cross with 45 deg flaws to develop crack growth and fracture toughness data under mixed-mode conditions. During cyclic testing, it was impossible to maintain a high proportion of shear-mode deformation on the crack tips. Cracks either branched or turned. Under static loading, cracks remained straight if shear stress intensity exceeded normal stress intensity. Mixed-mode crack growth rate data compared reasonably well with published single-mode data, and measured crack displacements agreed with the straight and branched crack analyses. Values of critical strain energy release rate at fracture for pure shear were approximately 50% higher than for pure normal opening, and there was a large reduction in normal stress intensity at fracture in the presence of high shear stress intensity. Net section stresses were well into the inelastic range when fracture occurred under high shear on the cracks.

The role of emotions in the maintenance of cooperative behaviors

NASA Astrophysics Data System (ADS)

Zhang, Chunyan; Zhang, Jianlei; Weissing, Franz J.

2014-04-01

Our attention is focused on how individual emotions influence collective behaviors, which captures an aspect of reality missing from past studies: free riders may suffer some stress, which could adapt jointly with the individual stress intensity and size of the gaming group. With an evolutionary game theoretical approach, we gain the fixation probability for one mutant cooperator to invade and dominate the whole defecting population. When the stress intensity exceeds a threshold, natural selection favors cooperators replacing defectors in a finite population. We further infer that lower stress intensity is sufficient for one mutant cooperator to become fixed with an advantageous probability in a larger population. Moreover, when the gaming group is smaller than the population size, the more the return from the public goods, the lower the threshold of stress intensity required to facilitate the full dominance of cooperators. We hope our studies may show that individual sentiments or psychological activities will open up novel explanations for the puzzle of collective actions.

Growth characteristics of a plane crack subjected to three-dimensional loading. [based on stress intensity factors

NASA Technical Reports Server (NTRS)

Hartranft, R. J.; Sih, G. C.

1973-01-01

The closed form expressions for the stress intensity factors due to concentrated forces applied to the surfaces of a half plane crack in an infinite body are used to generate solutions for distributed loads in this geometry. The stress intensity factors for uniformly distributed loads applied over a rectangular portion of the crack surface are given in closed form. An example of non-uniformly distributed loads which can be treated numerically is also included. In particular, combinations of normal and shear stresses on the crack which simulate the case of loading at an angle to the crack front are considered. The resulting stress intensity factors are combined with the strain energy density fracture criterion for the purpose of predicting the most likely direction of crack propagation. The critical value of the energy density factor can then be used for determining the allowable load on a specimen with a crack front not perpendicular to the tensile axis.

Glucose and lactate as metabolic constraints on presynaptic transmission at an excitatory synapse.

PubMed

Lucas, Sarah J; Michel, Christophe B; Marra, Vincenzo; Smalley, Joshua L; Hennig, Matthias H; Graham, Bruce P; Forsythe, Ian D

2018-05-01

Synapses have high energy demands which increase during intense activity. We show that presynaptic terminals can utilise extracellular glucose or lactate to generate energy to maintain synaptic transmission. Reducing energy substrates induces a metabolic stress: presynaptic ATP depletion impaired synaptic transmission through a reduction in the number of functional synaptic vesicle release sites and a slowing of vesicle pool replenishment, without a consistent change in release probability. Metabolic function is compromised in many pathological conditions (e.g. stroke, traumatic brain injury and neurodegeneration). Knowledge of how synaptic transmission is constrained by metabolic stress, especially during intense brain activity, will provide insights to improve cognition following pathological insults. The synapse has high energy demands, which increase during intense activity. Presynaptic ATP production depends on substrate availability and usage will increase during activity, which in turn could influence transmitter release and information transmission. We investigated transmitter release at the mouse calyx of Held synapse using glucose or lactate (10, 1 or 0 mm) as the extracellular substrates while inducing metabolic stress. High-frequency stimulation (HFS) and recovery paradigms evoked trains of EPSCs monitored under voltage-clamp. Whilst postsynaptic intracellular ATP was stabilised by diffusion from the patch pipette, depletion of glucose increased EPSC depression during HFS and impaired subsequent recovery. Computational modelling of these data demonstrated a reduction in the number of functional release sites and slowed vesicle pool replenishment during metabolic stress, with little change in release probability. Directly depleting presynaptic terminal ATP impaired transmitter release in an analogous manner to glucose depletion. In the absence of glucose, presynaptic terminal metabolism could utilise lactate from the aCSF and this was blocked by inhibition of monocarboxylate transporters (MCTs). MCT inhibitors significantly suppressed transmission in low glucose, implying that lactate is a presynaptic substrate. Additionally, block of glycogenolysis accelerated synaptic transmission failure in the absence of extracellular glucose, consistent with supplemental supply of lactate by local astrocytes. We conclude that both glucose and lactate support presynaptic metabolism and that limited availability, exacerbated by high-intensity firing, constrains presynaptic ATP, impeding transmission through a reduction in functional presynaptic release sites as vesicle recycling slows when ATP levels are low. © 2018 The Authors. The Journal of Physiology © 2018 The Physiological Society.

Discrete crack growth analysis methodology for through cracks in pressurized fuselage structures

NASA Technical Reports Server (NTRS)

Potyondy, David O.; Wawrzynek, Paul A.; Ingraffea, Anthony R.

1994-01-01

A methodology for simulating the growth of long through cracks in the skin of pressurized aircraft fuselage structures is described. Crack trajectories are allowed to be arbitrary and are computed as part of the simulation. The interaction between the mechanical loads acting on the superstructure and the local structural response near the crack tips is accounted for by employing a hierarchical modeling strategy. The structural response for each cracked configuration is obtained using a geometrically nonlinear shell finite element analysis procedure. Four stress intensity factors, two for membrane behavior and two for bending using Kirchhoff plate theory, are computed using an extension of the modified crack closure integral method. Crack trajectories are determined by applying the maximum tangential stress criterion. Crack growth results in localized mesh deletion, and the deletion regions are remeshed automatically using a newly developed all-quadrilateral meshing algorithm. The effectiveness of the methodology and its applicability to performing practical analyses of realistic structures is demonstrated by simulating curvilinear crack growth in a fuselage panel that is representative of a typical narrow-body aircraft. The predicted crack trajectory and fatigue life compare well with measurements of these same quantities from a full-scale pressurized panel test.

Stressful life events and acute kidney injury in intensive and semi-intensive care unities.

PubMed

Diniz, Denise Para; Marques, Daniella Aparecida; Blay, Sérgio Luis; Schor, Nestor

2012-03-01

Several studies point out that pathophysiological changes related to stress may influence renal function and are associated with disease onset and evolution. However, we have not found any studies about the influence of stress on renal function and acute kidney injury. To evaluate the association between stressful life events and acute kidney injury diagnosis, specifying the most stressful classes of events for these patients in the past 12 months. Case-control study. The study was carried out at Hospital São Paulo, in Universidade Federal de São Paulo and at Hospital dos Servidores do Estado de São Paulo, in Brazil. Patients with acute kidney injury and no chronic disease, admitted to the intensive or semi-intensive care units were included. Controls included patients in the same intensive care units with other acute diseases, except for the acute kidney injury, and also with no chronic disease. Out of the 579 patients initially identified, 475 answered to the Social Readjustment Rating Scale (SRRS) questionnaire and 398 were paired by age and gender (199 cases and 199 controls). The rate of stressful life events was statistically similar between cases and controls. The logistic regression analysis to detect associated effects of the independent variables to the stressful events showed that: increasing age and economic classes A and B in one of the hospitals (Hospital São Paulo - UNIFESP) increased the chance of a stressful life event (SLE). This study did not show association between the Acute Kidney Injury Group with a higher frequency of stressful life events, but that old age, higher income, and type of clinical center were associated.

Dissociation During Intense Military Stress is Related to Subsequent Somatic Symptoms in Women

PubMed Central

Steffian, Lisa; Steffian, George; Doran, Anthony P.; Rasmusson, Ann M.; Morgan, CA

2007-01-01

Background: Research studies of the female response to intense stress are under-represented in the scientific literature; indeed, publications in female humans and animals number half those in male subjects. In addition, women have only recently entered more dangerous professions that were historically limited to men. The US Navy's survival course, therefore, offers a unique opportunity to examine, in a controlled manner, individual differences in the human female response to acute and realistic military stress. Method: The current study assessed the nature and prevalence of dissociative symptoms and other aspects of adaptive function in healthy female subjects experiencing acute, intense stress during US Navy survival training. Cognitive dissociation and previous exposure to traumatic events were assessed at baseline in 32 female service members prior to Navy survival training. At the conclusion of training, retrospectively rated levels of dissociation during peak training stress and current health symptoms were assessed. Results: Female subjects reported previous trauma (35%) and at least one symptom of dissociation at baseline prior to training (47%). Eighty-eight percent of subjects reported experiencing multiple symptoms of dissociation during peak training stress. Post-stress dissociation scores and stress-induced increases in dissociation, as well as prior cumulative exposure to potentially traumatic events, were significant predictors of post-stress health symptoms. Discussion: In this study, increases in dissociative symptoms during intense training stress, post-stress dissociation symptom levels, and prior cumulative exposure to stressful, potentially traumatic events predicted post-stress health symptoms in women. Prior studies in men have demonstrated correlations between neurobiological responses to stress and stress-associated levels of dissociation. Thus future studies in larger samples of women are needed to investigate the relationship between prior stress exposure, alterations in neurobiological responses to stress and potentially related alterations in neuropsychological and physical reactions to stress. PMID:20805901

Low intensity red laser action on Escherichia coli cultures submitted to stress conditions

NASA Astrophysics Data System (ADS)

Santos, J. N.; Roos, C.; Barboza, L. L.; Paoli, F.; Fonseca, A. S.

2014-12-01

Clinical applications of low intensity lasers are based on the biostimulation effect and considered to occur mainly at cells under stressful conditions. Also, although the cytochrome is a chromophore to red and near infrared radiations, there are doubts whether indirect effects of these radiations could occur on the DNA molecule by oxidative mechanisms. Thus, this work evaluated the survival, filamentation and morphology of Escherichia coli cultures proficient and deficient in oxidative DNA damage repair exposed to low intensity red laser under stress conditions. Wild type and endonuclease III deficient E. coli cells were exposed to laser (658 nm, 1 and 8 J cm-2) under hyposmotic stress and bacterial survival, filamentation and cell morphology were evaluated. Laser exposure: (i) does not alter the bacterial survival in 0.9% NaCl, but increases the survival of wild type and decreases the survival of endonuclease III deficient cells under hyposmotic stress; (ii) increases filamentation in 0.9% NaCl but decreases in wild type and increases in endonuclease III deficient cells under hyposmotic stress; (iii) decreases the area and perimeter of wild type, does not alter these parameters in endonuclease III deficient cells under hyposmotic stress but increases the area of these in 0.9% NaCl. Low intensity red laser exposure has different effects on survival, filamentation phenotype and morphology of wild type and endonuclease III deficient cells under hyposmotic stress. Thus, our results suggest that therapies based on low intensity red lasers could take into account physiologic conditions and genetic characteristics of cells.

French College Students’ Sports Practice and Its Relations with Stress, Coping Strategies and Academic Success

PubMed Central

Décamps, Greg; Boujut, Emilie; Brisset, Camille

2012-01-01

College students at university have to face several stress factors. Although sports practice has been considered as having beneficial effects upon stress and general health, few studies have documented its influence on this specific population. The aim of this comparative study was to determine whether the intensity of the college students’ sports practice (categorized into three groups: rare, regular, or intensive) would influence their levels of stress and self-efficacy, their coping strategies, and their academic success/failure. Three self-completion questionnaires were administered to 1071 French freshmen during their compulsory medical visit at the preventive medicine service of the university. Results indicated that students with intensive sport practice reported lower scores of general stress, academic stress, and emotion-focused coping strategies, and higher scores of self-efficacy than those with rare practice. However, the proportion of successful students did not differ significantly between the three groups of sports practice. PMID:22514544

Influence of precracked specimen configuration and starting stress intensity on the stress corrosion cracking of 4340 steel

NASA Technical Reports Server (NTRS)

Lisagor, W. B.

1984-01-01

Since the pioneer work of Brown (1966), precracked specimens and related fracture mechanics analyses have been extensively used to study stress corrosion cracking. Certain questions arose in connection with initial attempts to prepare standardized recommended practices by ASTM Committee G-1 on Corrosion of Metals. These questions were related to adequacy of test control as it pertains to acceptable limits of variability, and to validity of expressions for stress intensity and crack-surface displacements for both specimen configurations. An interlaboratory test program, was, therefore, planned with the objective to examine the validity of KIscc testing for selected specimen configurations, materials,and environmental systems. The results reported in the present paper include details of a single laboratory test program. The program was conducted to determine if the threshold value of stress intensity for onset and arrest of stress corrosion cracking was independent for the two specimen configurations examined.

Role of metabolic stress for enhancing muscle adaptations: Practical applications

PubMed Central

de Freitas, Marcelo Conrado; Gerosa-Neto, Jose; Zanchi, Nelo Eidy; Lira, Fabio Santos; Rossi, Fabrício Eduardo

2017-01-01

Metabolic stress is a physiological process that occurs during exercise in response to low energy that leads to metabolite accumulation [lactate, phosphate inorganic (Pi) and ions of hydrogen (H+)] in muscle cells. Traditional exercise protocol (i.e., Resistance training) has an important impact on the increase of metabolite accumulation, which influences hormonal release, hypoxia, reactive oxygen species (ROS) production and cell swelling. Changes in acute exercise routines, such as intensity, volume and rest between sets, are determinants for the magnitude of metabolic stress, furthermore, different types of training, such as low-intensity resistance training plus blood flow restriction and high intensity interval training, could be used to maximize metabolic stress during exercise. Thus, the objective of this review is to describe practical applications that induce metabolic stress and the potential effects of metabolic stress to increase systemic hormonal release, hypoxia, ROS production, cell swelling and muscle adaptations. PMID:28706859

Biomechanics of cervical tooth region and noncarious cervical lesions of different morphology; three-dimensional finite element analysis.

PubMed

Jakupović, Selma; Anić, Ivica; Ajanović, Muhamed; Korać, Samra; Konjhodžić, Alma; Džanković, Aida; Vuković, Amra

2016-01-01

The present study aims to investigate the influence of presence and shape of cervical lesions on biomechanical behavior of mandibular first premolar, subjected to two types of occlusal loading using three-dimensional (3D) finite element method (FEM). 3D models of the mandibular premolar are created from a micro computed tomography X-ray image: model of sound mandibular premolar, model with the wedge-shaped cervical lesion (V lesion), and model with saucer-shaped cervical lesion (U lesion). By FEM, straining of the tooth tissues under functional and nonfunctional occlusal loading of 200 (N) is analyzed. For the analysis, the following software was used: CTAn program 1.10 and ANSYS Workbench (version 14.0). The results are presented in von Mises stress. Values of calculated stress in all tooth structures are higher under nonfunctional occlusal loading, while the functional loading is resulted in homogeneous stress distribution. Nonfunctional load in the cervical area of sound tooth model as well as in the sub-superficial layer of the enamel resulted with a significant stress (over 50 [MPa]). The highest stress concentration on models with lesions is noticed on the apex of the V-shaped lesion, while stress in saucer U lesion is significantly lower and distributed over wider area. The type of the occlusal teeth loading has the biggest influence on cervical stress intensity. Geometric shape of the existing lesion is very important in the distribution of internal stress. Compared to the U-shaped lesions, V-shaped lesions show significantly higher stress concentrations under load. Exposure to stress would lead to its progression.

Stress state reconstruction and tectonic evolution of the northern slope of the Baikit anteclise, Siberian Craton, based on 3D seismic data

NASA Astrophysics Data System (ADS)

Moskalenko, A. N.; Khudoley, A. K.; Khusnitdinov, R. R.

2017-05-01

In this work, we consider application of an original method for determining the indicators of the tectonic stress fields in the northern Baikit anteclise based on 3D seismic data for further reconstruction of the stress state parameters when analyzing structural maps of seismic horizons and corresponded faults. The stress state parameters are determined by the orientations of the main stress axes and shape of the stress ellipsoid. To calculate the stress state parameters from data on the spatial orientations of faults and slip vectors, we used the algorithms from quasiprimary stress computation methods and cataclastic analysis, implemented in the software products FaultKinWin and StressGeol, respectively. The results of this work show that kinematic characteristics of faults regularly change toward the top of succession and that the stress state parameters are characterized by different values of the Lode-Nadai coefficient. Faults are presented as strike-slip faults with normal or reverse component of displacement. Three stages of formation of the faults are revealed: (1) partial inversion of ancient normal faults, (2) the most intense stage with the predominance of thrust and strike-slip faults at north-northeast orientation of an axis of the main compression, and (3) strike-slip faults at the west-northwest orientation of an axis of the main compression. The second and third stages are pre-Vendian in age and correlate to tectonic events that took place during the evolution of the active southwestern margin of the Siberian Craton.

Gaseous hydrogen embrittlement of high strength steels

NASA Technical Reports Server (NTRS)

Gangloff, R. P.; Wei, R. P.

1977-01-01

The effects of temperature, hydrogen pressure, stress intensity, and yield strength on the kinetics of gaseous hydrogen assisted crack propagation in 18Ni maraging steels were investigated experimentally. It was found that crack growth rate as a function of stress intensity was characterized by an apparent threshold for crack growth, a stage where the growth rate increased sharply, and a stage where the growth rate was unchanged over a significant range of stress intensity. Cracking proceeded on load application with little or no detectable incubation period. Gaseous hydrogen embrittlement susceptibility increased with increasing yield strength.

Improvement of mechanical properties and life extension of high reliability structural components by laser shock processing

NASA Astrophysics Data System (ADS)

Ocaña, J. L.; Morales, M.; Porro, J. A.; Iordachescu, D.; Díaz, M.; Ruiz de Lara, L.; Correa, C.

2011-05-01

Profiting by the increasing availability of laser sources delivering intensities above 109 W/cm2 with pulse energies in the range of several Joules and pulse widths in the range of nanoseconds, laser shock processing (LSP) is being consolidating as an effective technology for the improvement of surface mechanical and corrosion resistance properties of metals and is being developed as a practical process amenable to production engineering. The main acknowledged advantage of the laser shock processing technique consists on its capability of inducing a relatively deep compression residual stresses field into metallic alloy pieces allowing an improved mechanical behaviour, explicitly, the life improvement of the treated specimens against wear, crack growth and stress corrosion cracking. Following a short description of the theoretical/computational and experimental methods developed by the authors for the predictive assessment and experimental implementation of LSP treatments, experimental results on the residual stress profiles and associated surface properties modification successfully reached in typical materials (specifically Al and Ti alloys) under different LSP irradiation conditions are presented. In particular, the analysis of the residual stress profiles obtained under different irradiation parameters and the evaluation of the corresponding induced surface properties as roughness and wear resistance are presented.

Photoelastic Analysis of Cracked Thick Walled Cylinders

NASA Astrophysics Data System (ADS)

Pastramă, Ştefan Dan

2017-12-01

In this paper, the experimental determination of the stress intensity factor in thick walled cylinders subject to uniform internal pressure and having longitudinal non-penetrating cracks is presented. Photoelastic measurements were used together with the expressions of the stress field near the crack tip for Mode I crack extension and a specific methodology for stress intensity factor determination. Two types of longitudinal cracks - internal and external - were considered. Four plane models were manufactured and analyzed in a plane polariscope at different values of the applied internal pressure. The values of the normalized stress intensity factor were calculated and the results were compared to those reported by other authors. A good accuracy was noticed, showing the reliability of the experimental procedure.

Selection of finite-element mesh parameters in modeling the growth of hydraulic fracturing cracks

NASA Astrophysics Data System (ADS)

Kurguzov, V. D.

2016-12-01

The effect of the mesh geometry on the accuracy of solutions obtained by the finite-element method for problems of linear fracture mechanics is investigated. The guidelines have been formulated for constructing an optimum mesh for several routine problems involving elements with linear and quadratic approximation of displacements. The accuracy of finite-element solutions is estimated based on the degree of the difference between the calculated stress-intensity factor (SIF) and its value obtained analytically. In problems of hydrofracturing of oil-bearing formation, the pump-in pressure of injected water produces a distributed load on crack flanks as opposed to standard fracture mechanics problems that have analytical solutions, where a load is applied to the external boundaries of the computational region and the cracks themselves are kept free from stresses. Some model pressure profiles, as well as pressure profiles taken from real hydrodynamic computations, have been considered. Computer models of cracks with allowance for the pre-stressed state, fracture toughness, and elastic properties of materials are developed in the MSC.Marc 2012 finite-element analysis software. The Irwin force criterion is used as a criterion of brittle fracture and the SIFs are computed using the Cherepanov-Rice invariant J-integral. The process of crack propagation in a linearly elastic isotropic body is described in terms of the elastic energy release rate G and modeled using the VCCT (Virtual Crack Closure Technique) approach. It has been found that the solution accuracy is sensitive to the mesh configuration. Several parameters that are decisive in constructing effective finite-element meshes, namely, the minimum element size, the distance between mesh nodes in the vicinity of a crack tip, and the ratio of the height of an element to its length, have been established. It has been shown that a mesh that consists of only small elements does not improve the accuracy of the solution.

Objective measures, sensors and computational techniques for stress recognition and classification: a survey.

PubMed

Sharma, Nandita; Gedeon, Tom

2012-12-01

Stress is a major growing concern in our day and age adversely impacting both individuals and society. Stress research has a wide range of benefits from improving personal operations, learning, and increasing work productivity to benefiting society - making it an interesting and socially beneficial area of research. This survey reviews sensors that have been used to measure stress and investigates techniques for modelling stress. It discusses non-invasive and unobtrusive sensors for measuring computed stress, a term we coin in the paper. Sensors that do not impede everyday activities that could be used by those who would like to monitor stress levels on a regular basis (e.g. vehicle drivers, patients with illnesses linked to stress) is the focus of the discussion. Computational techniques have the capacity to determine optimal sensor fusion and automate data analysis for stress recognition and classification. Several computational techniques have been developed to model stress based on techniques such as Bayesian networks, artificial neural networks, and support vector machines, which this survey investigates. The survey concludes with a summary and provides possible directions for further computational stress research. Copyright © 2012 Elsevier Ireland Ltd. All rights reserved.

Development of advanced structural analysis methodologies for predicting widespread fatigue damage in aircraft structures

NASA Technical Reports Server (NTRS)

Harris, Charles E.; Starnes, James H., Jr.; Newman, James C., Jr.

1995-01-01

NASA is developing a 'tool box' that includes a number of advanced structural analysis computer codes which, taken together, represent the comprehensive fracture mechanics capability required to predict the onset of widespread fatigue damage. These structural analysis tools have complementary and specialized capabilities ranging from a finite-element-based stress-analysis code for two- and three-dimensional built-up structures with cracks to a fatigue and fracture analysis code that uses stress-intensity factors and material-property data found in 'look-up' tables or from equations. NASA is conducting critical experiments necessary to verify the predictive capabilities of the codes, and these tests represent a first step in the technology-validation and industry-acceptance processes. NASA has established cooperative programs with aircraft manufacturers to facilitate the comprehensive transfer of this technology by making these advanced structural analysis codes available to industry.

Computational Visual Stress Level Analysis of Calcareous Algae Exposed to Sedimentation

PubMed Central

Nilssen, Ingunn; Eide, Ingvar; de Oliveira Figueiredo, Marcia Abreu; de Souza Tâmega, Frederico Tapajós; Nattkemper, Tim W.

2016-01-01

This paper presents a machine learning based approach for analyses of photos collected from laboratory experiments conducted to assess the potential impact of water-based drill cuttings on deep-water rhodolith-forming calcareous algae. This pilot study uses imaging technology to quantify and monitor the stress levels of the calcareous algae Mesophyllum engelhartii (Foslie) Adey caused by various degrees of light exposure, flow intensity and amount of sediment. A machine learning based algorithm was applied to assess the temporal variation of the calcareous algae size (∼ mass) and color automatically. Measured size and color were correlated to the photosynthetic efficiency (maximum quantum yield of charge separation in photosystem II, ΦPSIImax) and degree of sediment coverage using multivariate regression. The multivariate regression showed correlations between time and calcareous algae sizes, as well as correlations between fluorescence and calcareous algae colors. PMID:27285611

Dynamic Tensile Properties of Iron and Steels for a Wide Range of Strain Rates and Strain

NASA Astrophysics Data System (ADS)

Kojima, Nobusato; Hayashi, Hiroyuki; Yamamoto, Terumi; Mimura, Koji; Tanimura, Shinji

The tensile stress-strain curves of iron and a variety of steels, covering a wide range of strength level, over a wide strain rate range on the order of 10-3 ~ 103 s-1, were obtained systematically by using the Sensing Block Type High Speed Material Testing System (SBTS, Saginomiya). Through intensive analysis of these results, the strain rate sensitivity of the flow stress for the large strain region, including the viscous term at high strain rates, the true fracture strength and the true fracture strain were cleared for the material group of the ferrous metals. These systematical data may be useful to develop a practical constitutive model for computer codes, including a fracture criterion for simulations of the dynamic behavior in crash worthiness studies and of work-pieces subjected to dynamic plastic working for a wide strain rate range.

Word-level prominence in Persian: An Experimental Study.

PubMed

Sadeghi, Vahid

2017-12-01

Previous literature on the phonetics of stress in Persian has reported that fundamental frequency is the only reliable acoustic correlate of stress, and that stressed and unstressed syllables are not differentiated from each other in the absence of accentuation. In this study, the effects of lexical stress on duration, overall intensity and spectral tilt were examined in Persian both in the accented and unaccented conditions. Results showed that syllable duration is consistently affected by stress in Persian in both the accented and unaccented conditions across all vowel types. Unlike duration, the results for overall intensity and spectral tilt were significant only in the accented condition, suggesting that measures of intensity are not a correlate of stress in Persian but they are mainly caused by the presence of a pitch movement. The findings are phonologically interpreted as suggesting that word-level prominence in Persian is typologically similar to 'stress accent' languages, in which multiple phonetic cues are used to signal the prominence contrast in the accented condition, and stressed and unstressed syllables are different from each other even when the word is not pitch-accented.

Critical assessment of precracked specimen configuration and experimental test variables for stress corrosion testing of 7075-T6 aluminum alloy plate

NASA Technical Reports Server (NTRS)

Domack, M. S.

1985-01-01

A research program was conducted to critically assess the effects of precracked specimen configuration, stress intensity solutions, compliance relationships and other experimental test variables for stress corrosion testing of 7075-T6 aluminum alloy plate. Modified compact and double beam wedge-loaded specimens were tested and analyzed to determine the threshold stress intensity factor and stress corrosion crack growth rate. Stress intensity solutions and experimentally determined compliance relationships were developed and compared with other solutions available in the literature. Crack growth data suggests that more effective crack length measurement techniques are necessary to better characterize stress corrosion crack growth. Final load determined by specimen reloading and by compliance did not correlate well, and was considered a major source of interlaboratory variability. Test duration must be determined systematically, accounting for crack length measurement resolution, time for crack arrest, and experimental interferences. This work was conducted as part of a round robin program sponsored by ASTM committees G1.06 and E24.04 to develop a standard test method for stress corrosion testing using precracked specimens.

Effect of Trailing Intensive Cooling on Residual Stress and Welding Distortion of Friction Stir Welded 2060 Al-Li Alloy

NASA Astrophysics Data System (ADS)

Ji, Shude; Yang, Zhanpeng; Wen, Quan; Yue, Yumei; Zhang, Liguo

2018-04-01

Trailing intensive cooling with liquid nitrogen has successfully applied to friction stir welding of 2 mm thick 2060 Al-Li alloy. Welding temperature, plastic strain, residual stress and distortion of 2060 Al-Li alloy butt-joint are compared and discussed between conventional cooling and trailing intensive cooling using experimental and numerical simulation methods. The results reveal that trailing intensive cooling is beneficial to shrink high temperature area, reduce peak temperature and decrease plastic strain during friction stir welding process. In addition, the reduction degree of plastic strain outside weld is smaller than that inside weld. Welding distortion presents an anti-saddle shape. Compared with conventional cooling, the reductions of welding distortion and longitudinal residual stresses of welding joint under intense cooling reach 47.7 % and 23.8 %, respectively.

Transverse shear effects on the stress-intensity factor for a circumferentially cracked, specially orthotropic cylindrical shell

NASA Technical Reports Server (NTRS)

Delale, F.; Erdogan, F.

1977-01-01

The problem of a cylindrical shell containing a circumferential through crack is considered by taking into account the effect of transverse shear deformations. The formulation is given for a specially orthotropic material within the confines of a linearized shallow shell theory. The particular theory used permits the consideration of all five boundary conditions regarding moment and stress resultants on the crack surface. Consequently, aside from multiplicative constants representing the stress intensity factors, the membrane and bending components of the asymptotic stress fields near the crack tip are found to be identical. The stress intensity factors are calculated separately for a cylinder under a uniform membrane load, and that under a uniform bending moment. Sample results showing the nature of the out-of-plane crack surface displacement and the effect of the Poisson's ratio are presented.

Initiation and growth of multiple-site damage in the riveted lap joint of a curved stiffened fuselage panel: An experimental and analytical study

NASA Astrophysics Data System (ADS)

Ahmed, Abubaker Ali

As part of the structural integrity research of the National Aging Aircraft Research Program, a comprehensive study on multiple-site damage (MSD) initiation and growth in a pristine lap-joint fuselage panel has been conducted. The curved stiffened fuselage panel was tested at the Full-Scale Aircraft Structural Test Evaluation and Research (FASTER) facility located at the Federal Aviation Administration William J. Hughes Technical Center. A strain survey test was conducted to verify proper load application. The panel was then subjected to a fatigue test with constant-amplitude cyclic loading. The applied loading spectrum included underload marker cycles so that crack growth history could be reconstructed from post-test fractographic examinations. Crack formation and growth were monitored via nondestructive and high-magnification visual inspections. Strain gage measurements recorded during the strain survey tests indicated that the inner surface of the skin along the upper rivet row of the lap joint experienced high tensile stresses due to local bending. During the fatigue loading, cracks were detected by eddy-current inspections at multiple rivet holes along the upper rivet row. Through-thickness cracks were detected visually after about 80% of the fatigue life. Once MSD cracks from two adjacent rivet holes linked up, there was a quick deterioration in the structural integrity of the lap joint. The linkup resulted in a 2.87" (72.9-mm) lead fatigue crack that rapidly propagated across 12 rivet holes and crossed over into the next skin bay, at which stage the fatigue test was terminated. A post-fatigue residual strength test was then conducted by loading the panel quasi-statically up to final failure. The panel failed catastrophically when the crack extended instantaneously across three additional bays. Post-test fractographic examinations of the fracture surfaces in the lap joint of the fuselage panel were conducted to characterize subsurface crack initiation and growth. Results showed evidence of fretting damage and crack initiation at multiple locations near the rivet holes along the faying surface of the skin. The subsurface cracks grew significantly along the faying surface before reaching the outer surface of the skin, forming elliptical crack fronts. A finite element model (FE) of the panel was constructed and geometrically-nonlinear analyses conducted to determine strain distribution under the applied loads. The FE model was validated by comparing the analysis results with the strain gage measurements recorded during the strain survey test. The validated FE model was then used to determine stress-intensity factors at the crack tips. Stress-intensity factor results indicated that crack growth in the lap joint was under mixed-mode; however, the opening-mode stress intensity factor was dominant. The stress-intensity factors computed from the FE analysis were used to conduct cycle-by-cycle integration of fatigue crack growth. In the cycle-by-cycle integration, the NASGRO crack growth model was used with its parameters selected to account for the effects of plasticity-induced crack closure and the test environment on crack growth rate. Fatigue crack growth predictions from cycle-by-cycle computation were in good agreement with the experimental measured crack growth data. The results of the study provide key insights into the natural development and growth of MSD cracks in the pristine lap joint. The data provided by the study represent a valuable source for the evaluation and validation of analytical methodologies used for predicting MSD crack initiation and growth.

Affective temperament, job stress and professional burnout in nurses and civil servants.

PubMed

Jaracz, Marcin; Rosiak, Izabela; Bertrand-Bucińska, Anna; Jaskulski, Maciej; Nieżurawska, Joanna; Borkowska, Alina

2017-01-01

The risk of professional burnout is constituted by job-related as well as individual factors. The latter involve affective temperament, which influences the perception of job-related stress. The aim of the present study was to assess the affective temperament, the level of job stress and professional burnout, as well as the relationships between these variables, in public servants and nurses. 100 civil servants and 100 nurses were enrolled in the study. Affective temperament and burnout were assessed by means of TEMPS-A and MBI questionnaires, respectively. To measure the level of job-related stress, we have designed a 6-item self-reported questionnaire, which considered stressors common for both professions. Compared to the civil servants, nurses showed higher rate of anxious temperament and experienced greater intensity of job-related stress. The groups did not differ in the intensity of burnout symptoms. The rates of cyclothymic and anxious temperaments correlated with the intensity of stress, and burnout symptoms in the group of nurses. Within the civil servants group, the level of stress correlated with intensity of burnout, however no correlations with affective temperament were observed. The regression analysis performed in both groups revealed the significant effect of stress and cyclothymic temperament on burnout, while the effect of anxious temperament was not significant. Cyclothymic and anxious temperaments are related to the level of experienced job stress and the risk of burnout. In professions like nursing, where employees show elevated rates of these temperaments, burnout prevention and stress management education is of particular importance.

Affective temperament, job stress and professional burnout in nurses and civil servants

PubMed Central

Jaracz, Marcin; Rosiak, Izabela; Borkowska, Alina

2017-01-01

Introduction The risk of professional burnout is constituted by job-related as well as individual factors. The latter involve affective temperament, which influences the perception of job-related stress. The aim of the present study was to assess the affective temperament, the level of job stress and professional burnout, as well as the relationships between these variables, in public servants and nurses. Material and methods 100 civil servants and 100 nurses were enrolled in the study. Affective temperament and burnout were assessed by means of TEMPS-A and MBI questionnaires, respectively. To measure the level of job-related stress, we have designed a 6-item self-reported questionnaire, which considered stressors common for both professions. Results Compared to the civil servants, nurses showed higher rate of anxious temperament and experienced greater intensity of job-related stress. The groups did not differ in the intensity of burnout symptoms. The rates of cyclothymic and anxious temperaments correlated with the intensity of stress, and burnout symptoms in the group of nurses. Within the civil servants group, the level of stress correlated with intensity of burnout, however no correlations with affective temperament were observed. The regression analysis performed in both groups revealed the significant effect of stress and cyclothymic temperament on burnout, while the effect of anxious temperament was not significant. Conclusions Cyclothymic and anxious temperaments are related to the level of experienced job stress and the risk of burnout. In professions like nursing, where employees show elevated rates of these temperaments, burnout prevention and stress management education is of particular importance. PMID:28586391

Applications in Data-Intensive Computing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shah, Anuj R.; Adkins, Joshua N.; Baxter, Douglas J.

2010-04-01

This book chapter, to be published in Advances in Computers, Volume 78, in 2010 describes applications of data intensive computing (DIC). This is an invited chapter resulting from a previous publication on DIC. This work summarizes efforts coming out of the PNNL's Data Intensive Computing Initiative. Advances in technology have empowered individuals with the ability to generate digital content with mouse clicks and voice commands. Digital pictures, emails, text messages, home videos, audio, and webpages are common examples of digital content that are generated on a regular basis. Data intensive computing facilitates human understanding of complex problems. Data-intensive applications providemore » timely and meaningful analytical results in response to exponentially growing data complexity and associated analysis requirements through the development of new classes of software, algorithms, and hardware.« less

The mechanics of delamination in fiber-reinforced composite materials. Part 2: Delamination behavior and fracture mechanics parameters

NASA Technical Reports Server (NTRS)

Wang, S. S.; Choi, I.

1983-01-01

Based on theories of laminate anisotropic elasticity and interlaminar fracture, the complete solution structure associated with a composite delamination is determined. Fracture mechanics parameters characterizing the interlaminar crack behavior are defined from asymptotic stress solutions for delaminations with different crack-tip deformation configurations. A numerical method employing singular finite elements is developed to study delaminations in fiber composites with any arbitrary combinations of lamination, material, geometric, and crack variables. The special finite elements include the exact delamination stress singularity in its formulation. The method is shown to be computationally accurate and efficient, and operationally simple. To illustrate the basic nature of composite delamination, solutions are shown for edge-delaminated (0/-0/-0/0) and (+ or - 0/+ or - 0/90/90 deg) graphite-epoxy systems under uniform axial extenstion. Three-dimensional crack-tip stress intensity factors, associated energy release rates, and delamination crack-closure are determined for each individual case. The basic mechanics and mechanisms of composite delamination are studied, and fundamental characteristics unique to recently proposed tests for interlaminar fracture toughness of fiber composite laminates are examined.

Dynamic tensile-failure-induced velocity deficits in rock

NASA Technical Reports Server (NTRS)

Rubin, Allan M.; Ahrens, Thomas J.

1991-01-01

Planar impact experiments were employed to induce dynamic tensile failure in Bedford limestone. Rock disks were impacted with aluminum and polymethyl methacralate (PMMA) flyer plates at velocities of 10 to 25 m/s. Tensile stress magnitudes and duration were chosen so as to induce a range of microcrack growth insufficient to cause complete spalling of the samples. Ultrasonic P- and S-wave velocities of recovered targets were compared to the velocities prior to impact. Velocity reduction, and by inference microcrack production, occurred in samples subjected to stresses above 35 MPa in the 1.3 microsec PMMA experiments and 60 MPa in the 0.5 microsec aluminum experiments. Using a simple model for the time-dependent stress-intensity factor at the tips of existing flaws, apparent fracture toughnesses of 2.4 and 2.5 MPa sq rt m are computed for the 1.3 and 0.5 microsec experiments. These are a factor of about 2 to 3 greater than quasi-static values. The greater dynamic fracture toughness observed may result from microcrack interaction during tensile failure. Data for water-saturated and dry targets are indistinguishable.

Flaw Growth of 6Al-4V Titanium in a Freon TF Environment

NASA Technical Reports Server (NTRS)

Tiffany, C. F.; Masters, J. N.; Bixler, W. D.

1969-01-01

The plane strain threshold stress intensity and sustained stress flaw growth rates were experimentally determined for 6AI-4V S.T.A. titanium forging and weldments in environments of Freon TF at room temperature. Sustained load tests of surface flawed specimens were conducted with the experimental approach based on linear elastic fracture mechanics. It was concluded that sustained stress flaw growth rates, in conjunction with threshold stress intensities, can be used in assessing the service life of pressure vessels.

Parenting stress reduces the effectiveness of early teaching interventions for autistic spectrum disorders.

PubMed

Osborne, Lisa A; McHugh, Louise; Saunders, Jo; Reed, Phil

2008-07-01

This community-based study examined the influence of early teaching interventions on children diagnosed with Autistic Spectrum Disorders, and the dynamics between the time intensity of the interventions and parenting stress, on child outcomes. Intellectual, educational, and adaptive behavior and social functioning were all measured. Sixty-five children were divided into four groups, based on the levels of time intensity of their intervention, and on their parents' stress levels. There were gains in intellectual, educational, and adaptive behavioral and social skills, and there was a positive relationship between the time intensity of the early teaching interventions and child outcome gains. More importantly, however, high levels of parenting stress counteracted the effectiveness of the early teaching interventions.

Stress-Intensity Factors along Three-Dimensional Elliptical Crack Fronts

DOT National Transportation Integrated Search

1998-05-01

The objective of the present investigation is to determine the mode I stress-intensity factors along two symmetric surface cracks emanating from a centrally located hole in a rectangular plate (the so-called Round Robin Problem) using the domain inte...

Development of a Wireless Computer Vision Instrument to Detect Biotic Stress in Wheat

PubMed Central

Casanova, Joaquin J.; O'Shaughnessy, Susan A.; Evett, Steven R.; Rush, Charles M.

2014-01-01

Knowledge of crop abiotic and biotic stress is important for optimal irrigation management. While spectral reflectance and infrared thermometry provide a means to quantify crop stress remotely, these measurements can be cumbersome. Computer vision offers an inexpensive way to remotely detect crop stress independent of vegetation cover. This paper presents a technique using computer vision to detect disease stress in wheat. Digital images of differentially stressed wheat were segmented into soil and vegetation pixels using expectation maximization (EM). In the first season, the algorithm to segment vegetation from soil and distinguish between healthy and stressed wheat was developed and tested using digital images taken in the field and later processed on a desktop computer. In the second season, a wireless camera with near real-time computer vision capabilities was tested in conjunction with the conventional camera and desktop computer. For wheat irrigated at different levels and inoculated with wheat streak mosaic virus (WSMV), vegetation hue determined by the EM algorithm showed significant effects from irrigation level and infection. Unstressed wheat had a higher hue (118.32) than stressed wheat (111.34). In the second season, the hue and cover measured by the wireless computer vision sensor showed significant effects from infection (p = 0.0014), as did the conventional camera (p < 0.0001). Vegetation hue obtained through a wireless computer vision system in this study is a viable option for determining biotic crop stress in irrigation scheduling. Such a low-cost system could be suitable for use in the field in automated irrigation scheduling applications. PMID:25251410

Crystallographic Orientation Identification in Multicrystalline Silicon Wafers Using NIR Transmission Intensity

NASA Astrophysics Data System (ADS)

Skenes, Kevin; Kumar, Arkadeep; Prasath, R. G. R.; Danyluk, Steven

2018-02-01

Near-infrared (NIR) polariscopy is a technique used for the non-destructive evaluation of the in-plane stresses in photovoltaic silicon wafers. Accurate evaluation of these stresses requires correct identification of the stress-optic coefficient, a material property which relates photoelastic parameters to physical stresses. The material stress-optic coefficient of silicon varies with crystallographic orientation. This variation poses a unique problem when measuring stresses in multicrystalline silicon (mc-Si) wafers. This paper concludes that the crystallographic orientation of silicon can be estimated by measuring the transmission of NIR light through the material. The transmission of NIR light through monocrystalline wafers of known orientation were compared with the transmission of NIR light through various grains in mc-Si wafers. X-ray diffraction was then used to verify the relationship by obtaining the crystallographic orientations of these assorted mc-Si grains. Variation of transmission intensity for different crystallographic orientations is further explained by using planar atomic density. The relationship between transmission intensity and planar atomic density appears to be linear.

Laplace-SGBEM analysis of the dynamic stress intensity factors and the dynamic T-stress for the interaction between a crack and auxetic inclusions

NASA Astrophysics Data System (ADS)

Kwon, Kibum

A dynamic analysis of the interaction between a crack and an auxetic (negative Poisson ratio)/non-auxetic inclusion is presented. The two most important fracture parameters, namely the stress intensity factors and the T-stress are analyzed by using the symmetric Galerkin boundary element method in the Laplace domain for three different models of crack-inclusion interaction. To investigate the effects of auxetic inclusions on the fracture behavior of composites reinforced by this new type of material, comparisons of the dynamic stress intensity factors and the dynamic T-stress are made between the use of auxetic inclusions as opposed to the use of traditional inclusions. Furthermore, the technique presented in this research can be employed to analyze for the interaction between a crack and a cluster of auxetic/non-auxetic inclusions. Results from the latter models can be employed in crack growth analysis in auxetic-fiber-reinforced composites.

Modeling of stress/strain behavior of fiber-reinforced ceramic matrix composites including stress redistribution

NASA Technical Reports Server (NTRS)

Mital, Subodh K.; Murthy, Pappu L. N.; Chamis, Christos C.

1994-01-01

A computational simulation procedure is presented for nonlinear analyses which incorporates microstress redistribution due to progressive fracture in ceramic matrix composites. This procedure facilitates an accurate simulation of the stress-strain behavior of ceramic matrix composites up to failure. The nonlinearity in the material behavior is accounted for at the constituent (fiber/matrix/interphase) level. This computational procedure is a part of recent upgrades to CEMCAN (Ceramic Matrix Composite Analyzer) computer code. The fiber substructuring technique in CEMCAN is used to monitor the damage initiation and progression as the load increases. The room-temperature tensile stress-strain curves for SiC fiber reinforced reaction-bonded silicon nitride (RBSN) matrix unidirectional and angle-ply laminates are simulated and compared with experimentally observed stress-strain behavior. Comparison between the predicted stress/strain behavior and experimental stress/strain curves is good. Collectively the results demonstrate that CEMCAN computer code provides the user with an effective computational tool to simulate the behavior of ceramic matrix composites.

Stress intensity factors for part-elliptical cracks emanating from dimpled rivet holes

NASA Astrophysics Data System (ADS)

Wang, Ailun; She, Chongmin; Lin, Gang; Zhou, You; Guo, Wanlin

2014-11-01

Detailed investigations on the stress intensity factors (SIFs) for corner cracks emanated from interference fitted dimpled rivet holes are conducted using three-dimensional finite element method. The influences of the crack length a, elliptical shape factor t, far-end stress S and interference magnitude δ on the stress intensity factors are systematically studied. The SIFs for corner cracks emanated from open holes are also investigated for comparisons. An empirical formula of the normalized SIF is proposed by use of the least square method for convenience of the engineering application, which is a function of the crack length a, elliptical shape factor t, far-end stress S, interference magnitude δ and the normalized elliptical centrifugal angle φn. Based on the empirical formula, a crack growth simulation for a rivet filled hole is conducted, which shows a good agreement with the test data.

The importance of physical activity and sleep for affect on stressful days: Two intensive longitudinal studies.

PubMed

Flueckiger, Lavinia; Lieb, Roselind; Meyer, Andrea H; Witthauer, Cornelia; Mata, Jutta

2016-06-01

We investigated the potential stress-buffering effect of 3 health behaviors-physical activity, sleep quality, and snacking-on affect in the context of everyday life in young adults. In 2 intensive longitudinal studies with up to 65 assessment days over an entire academic year, students (Study 1, N = 292; Study 2, N = 304) reported stress intensity, sleep quality, physical activity, snacking, and positive and negative affect. Data were analyzed using multilevel regression analyses. Stress and positive affect were negatively associated; stress and negative affect were positively associated. The more physically active than usual a person was on a given day, the weaker the association between stress and positive affect (Study 1) and negative affect (Studies 1 and 2). The better than usual a person's sleep quality had been during the previous night, the weaker the association between stress and positive affect (Studies 1 and 2) and negative affect (Study 2). The association between daily stress and positive or negative affect did not differ as a function of daily snacking (Studies 1 and 2). On stressful days, increasing physical activity or ensuring high sleep quality may buffer adverse effects of stress on affect in young adults. These findings suggest potential targets for health-promotion and stress-prevention programs, which could help reduce the negative impact of stress in young adults. (PsycINFO Database Record (c) 2016 APA, all rights reserved).

Stress-Intensity Factors for Elliptical Cracks Emanating from Countersunk Rivet Holes

DOT National Transportation Integrated Search

1998-04-01

Small cracks developing from rivet holes in lap joints of fuselage structure have been an issue of concern over the past decade. Stress-intensity factor solutions required to assess the structural integrity of such configurations are lacking. To addr...

Discrete element analysis is a valid method for computing joint contact stress in the hip before and after acetabular fracture.

PubMed

Townsend, Kevin C; Thomas-Aitken, Holly D; Rudert, M James; Kern, Andrew M; Willey, Michael C; Anderson, Donald D; Goetz, Jessica E

2018-01-23

Evaluation of abnormalities in joint contact stress that develop after inaccurate reduction of an acetabular fracture may provide a potential means for predicting the risk of developing post-traumatic osteoarthritis. Discrete element analysis (DEA) is a computational technique for calculating intra-articular contact stress distributions in a fraction of the time required to obtain the same information using the more commonly employed finite element analysis technique. The goal of this work was to validate the accuracy of DEA-computed contact stress against physical measurements of contact stress made in cadaveric hips using Tekscan sensors. Four static loading tests in a variety of poses from heel-strike to toe-off were performed in two different cadaveric hip specimens with the acetabulum intact and again with an intentionally malreduced posterior wall acetabular fracture. DEA-computed contact stress was compared on a point-by-point basis to stress measured from the physical experiments. There was good agreement between computed and measured contact stress over the entire contact area (correlation coefficients ranged from 0.88 to 0.99). DEA-computed peak contact stress was within an average of 0.5 MPa (range 0.2-0.8 MPa) of the Tekscan peak stress for intact hips, and within an average of 0.6 MPa (range 0-1.6 MPa) for fractured cases. DEA-computed contact areas were within an average of 33% of the Tekscan-measured areas (range: 1.4-60%). These results indicate that the DEA methodology is a valid method for accurately estimating contact stress in both intact and fractured hips. Copyright © 2017 Elsevier Ltd. All rights reserved.

Risk factors for the development of post-traumatic stress disorder and coping strategies in mothers and fathers following infant hospitalisation in the neonatal intensive care unit.

PubMed

Aftyka, Anna; Rybojad, Beata; Rosa, Wojciech; Wróbel, Aleksandra; Karakuła-Juchnowicz, Hanna

2017-12-01

The aim of this study was to identify the potential risk factors for the development of post-traumatic stress disorder in mothers and fathers following infant hospitalisation in the neonatal intensive care unit. The development of neonatal intensive care units has increased the survival rate of infants. However, one of the major parental problems is post-traumatic stress disorder. An observational study covered 125 parents (72 mothers and 53 fathers) of infants aged 3-12 months who were hospitalised in the neonatal intensive care unit during the neonatal period. Third-referral neonatal intensive care unit. Several standardised and self-reported research tools were used to estimate the level of post-traumatic stress symptoms (Impact Event Scale-Revised), perceived stress (Perceived Stress Scale) and coping strategies (COPE Inventory). The respondents also completed a Parent and Infant Characteristic Questionnaire. The mothers and fathers did not differ in their parental and infant characteristics. Post-traumatic stress disorder was present in 60% of the mothers and 47% of the fathers. Compared to the fathers, the mothers felt greater stress (p = .020) and presented a higher severity of post-traumatic stress disorder (p < .001). Previous miscarriages (p = .023) and the presence of chronic diseases (p = .032) were risk factors for post-traumatic stress disorder in the mothers. In the fathers, an Apgar test at 1 min after birth (p = .030) and a partner's post-traumatic stress disorder (p = .038) were related to post-traumatic stress disorder. The mothers compared to the fathers were more likely to use strategies such as: positive reinterpretation and growth, focusing on and venting of emotions, instrumental social support, religious coping and acceptance. In the fathers, the predictors included an Apgar score at 1 min after birth, a lack of congenital anomalies in the child and mental disengagement. Risk factors for post-traumatic stress disorder, as well as coping strategies, differ in women compare to men. Knowledge of risk factors for post-traumatic stress disorder, specific to men and women, may help identify the parents in whom probability of the occurrence of this disorder is increased. © 2017 John Wiley & Sons Ltd.

46 CFR 54.30-15 - Requirement for analysis and computation.

Code of Federal Regulations, 2010 CFR

2010-10-01

... PRESSURE VESSELS Mechanical Stress Relief § 54.30-15 Requirement for analysis and computation. (a) A stress... mechanical stress relief process. This analysis should include consideration of the local stresses in way of saddles or other supporting structure and additional bending stresses due to the weight of the...

46 CFR 54.30-15 - Requirement for analysis and computation.

Code of Federal Regulations, 2012 CFR

2012-10-01

... PRESSURE VESSELS Mechanical Stress Relief § 54.30-15 Requirement for analysis and computation. (a) A stress... mechanical stress relief process. This analysis should include consideration of the local stresses in way of saddles or other supporting structure and additional bending stresses due to the weight of the...

46 CFR 54.30-15 - Requirement for analysis and computation.

Code of Federal Regulations, 2014 CFR

2014-10-01

... PRESSURE VESSELS Mechanical Stress Relief § 54.30-15 Requirement for analysis and computation. (a) A stress... mechanical stress relief process. This analysis should include consideration of the local stresses in way of saddles or other supporting structure and additional bending stresses due to the weight of the...

46 CFR 54.30-15 - Requirement for analysis and computation.

Code of Federal Regulations, 2013 CFR

2013-10-01

... PRESSURE VESSELS Mechanical Stress Relief § 54.30-15 Requirement for analysis and computation. (a) A stress... mechanical stress relief process. This analysis should include consideration of the local stresses in way of saddles or other supporting structure and additional bending stresses due to the weight of the...

46 CFR 54.30-15 - Requirement for analysis and computation.

Code of Federal Regulations, 2011 CFR

2011-10-01

... PRESSURE VESSELS Mechanical Stress Relief § 54.30-15 Requirement for analysis and computation. (a) A stress... mechanical stress relief process. This analysis should include consideration of the local stresses in way of saddles or other supporting structure and additional bending stresses due to the weight of the...

Progressive delamination in polymer matrix composite laminates: A new approach

NASA Technical Reports Server (NTRS)

Chamis, C. C.; Murthy, P. L. N.; Minnetyan, L.

1992-01-01

A new approach independent of stress intensity factors and fracture toughness parameters has been developed and is described for the computational simulation of progressive delamination in polymer matrix composite laminates. The damage stages are quantified based on physics via composite mechanics while the degradation of the laminate behavior is quantified via the finite element method. The approach accounts for all types of composite behavior, laminate configuration, load conditions, and delamination processes starting from damage initiation, to unstable propagation, and to laminate fracture. Results of laminate fracture in composite beams, panels, plates, and shells are presented to demonstrate the effectiveness and versatility of this new approach.

Biomechanics of cervical tooth region and noncarious cervical lesions of different morphology; three-dimensional finite element analysis

PubMed Central

Jakupović, Selma; Anić, Ivica; Ajanović, Muhamed; Korać, Samra; Konjhodžić, Alma; Džanković, Aida; Vuković, Amra

2016-01-01

Objective: The present study aims to investigate the influence of presence and shape of cervical lesions on biomechanical behavior of mandibular first premolar, subjected to two types of occlusal loading using three-dimensional (3D) finite element method (FEM). Materials and Methods: 3D models of the mandibular premolar are created from a micro computed tomography X-ray image: model of sound mandibular premolar, model with the wedge-shaped cervical lesion (V lesion), and model with saucer-shaped cervical lesion (U lesion). By FEM, straining of the tooth tissues under functional and nonfunctional occlusal loading of 200 (N) is analyzed. For the analysis, the following software was used: CTAn program 1.10 and ANSYS Workbench (version 14.0). The results are presented in von Mises stress. Results: Values of calculated stress in all tooth structures are higher under nonfunctional occlusal loading, while the functional loading is resulted in homogeneous stress distribution. Nonfunctional load in the cervical area of sound tooth model as well as in the sub-superficial layer of the enamel resulted with a significant stress (over 50 [MPa]). The highest stress concentration on models with lesions is noticed on the apex of the V-shaped lesion, while stress in saucer U lesion is significantly lower and distributed over wider area. Conclusion: The type of the occlusal teeth loading has the biggest influence on cervical stress intensity. Geometric shape of the existing lesion is very important in the distribution of internal stress. Compared to the U-shaped lesions, V-shaped lesions show significantly higher stress concentrations under load. Exposure to stress would lead to its progression. PMID:27403064

Computational models of intergroup competition and warfare.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Letendre, Kenneth; Abbott, Robert G.

2011-11-01

This document reports on the research of Kenneth Letendre, the recipient of a Sandia Graduate Research Fellowship at the University of New Mexico. Warfare is an extreme form of intergroup competition in which individuals make extreme sacrifices for the benefit of their nation or other group to which they belong. Among animals, limited, non-lethal competition is the norm. It is not fully understood what factors lead to warfare. We studied the global variation in the frequency of civil conflict among countries of the world, and its positive association with variation in the intensity of infectious disease. We demonstrated that themore » burden of human infectious disease importantly predicts the frequency of civil conflict and tested a causal model for this association based on the parasite-stress theory of sociality. We also investigated the organization of social foraging by colonies of harvester ants in the genus Pogonomyrmex, using both field studies and computer models.« less

Simulation of the stress computation in shells

NASA Technical Reports Server (NTRS)

Salama, M.; Utku, S.

1978-01-01

A self-teaching computer program is described, whereby the stresses in thin shells can be computed with good accuracy using the best fit approach. The program is designed for use in interactive game mode to allow the structural engineer to learn about (1) the major sources of difficulties and associated errors in the computation of stresses in thin shells, (2) possible ways to reduce the errors, and (3) trade-off between computational cost and accuracy. Included are derivation of the computational approach, program description, and several examples illustrating the program usage.

Rock Burst Monitoring by Integrated Microseismic and Electromagnetic Radiation Methods

NASA Astrophysics Data System (ADS)

Li, Xuelong; Wang, Enyuan; Li, Zhonghui; Liu, Zhentang; Song, Dazhao; Qiu, Liming

2016-11-01

For this study, microseismic (MS) and electromagnetic radiation (EMR) monitoring systems were installed in a coal mine to monitor rock bursts. The MS system monitors coal or rock mass ruptures in the whole mine, whereas the EMR equipment monitors the coal or rock stress in a small area. By analysing the MS energy, number of MS events, and EMR intensity with respect to rock bursts, it has been shown that the energy and number of MS events present a "quiet period" 1-3 days before the rock burst. The data also show that the EMR intensity reaches a peak before the rock burst and this EMR intensity peak generally corresponds to the MS "quiet period". There is a positive correlation between stress and EMR intensity. Buckling failure of coal or rock depends on the rheological properties and occurs after the peak stress in the high-stress concentration areas in deep mines. The MS "quiet period" before the rock burst is caused by the heterogeneity of the coal and rock structures, the transfer of high stress into internal areas, locked patches, and self-organized criticality near the stress peak. This study increases our understanding of coal and rock instability in deep mines. Combining MS and EMR to monitor rock burst could improve prediction accuracy.

High intensity scenario training of military medical students to increase learning capacity and management of stress response.

PubMed

Mueller, Genevieve R; Moloff, Alan L; Wedmore, Ian S; Schoeff, Jonathan E; Laporta, Anthony J

2012-01-01

A delicate balance exists between a beneficial stress response that enhances memory and recall performance and a detrimental high stress response that impairs memory and learning. Repetitive training in stressful situations enables people to lower their stress levels from the detrimental range to a more beneficial one.1 This is particularly true for physicians in training as they seek to achieve advanced skills and knowledge in the fields of triage, emergency medicine, and surgery prior to graduation. This need is significant for medical students entering military service after graduation. We theorize that military medical students can advance their proficiencies through an Intensive Skills Week (ISW) prior to entering their third and forth year rotations. To test this theory, Rocky Vista University will hold a week long high-intensity first-responder, emergency medicine and surgical training course, facilitated by military medical physicians, to further students? skills and maximize training using the Human Worn Partial Surgical Task Simulator (Cut Suit). We also see the possible benefit to physician and non-physician military personnel, especially Special Operations Forces (SOF) medical personnel, from developing and implementing similar training programs when live tissue or cadaver models are unavailable or not feasible. Stress, cortisol, medical student, enhanced learning, scenario, high intensity. 2012.

EEG changes as heat stress reactions in rats irradiated by high intensity 35 GHz millimeter waves.

PubMed

Xie, Taorong; Pei, Jian; Cui, Yibin; Zhang, Jie; Qi, Hongxing; Chen, Shude; Qiao, Dengjiang

2011-06-01

As the application of millimeter waves for civilian and military use increases, the possibility of overexposure to millimeter waves will also increase. This paper attempts to evaluate stress reactions evoked by 35 GHz millimeter waves. The stress reactions in Sprague-Dawley (SD) rats were quantitatively studied by analyzing electroencephalogram (EEG) changes induced by overexposure to 35 GHz millimeter waves. The relative changes in average energy of the EEG and its wavelet decompositions were used for extracting the stress reaction indicators. Incident average power densities (IAPDs) of 35 GHz millimeter waves from 0.5 W cm(-2) to 7.5 W cm(-2) were employed to investigate the relation between irradiation dose and the stress reactions in the rats. Different stress reaction periods evoked by irradiation were quantitatively evaluated by EEG results. The results illustrate that stress reactions are more intense during the first part of the irradiation than during the later part. The skin temperature increase produced by millimeter wave irradiation is the principle reason for stress reactions and skin injuries. As expected, at the higher levels of irradiation, the reaction time decreases and the reaction intensity increases.

Strain intensity factor approach for predicting the strength of continuously reinforced metal matrix composites

NASA Technical Reports Server (NTRS)

Poe, C. C., Jr.

1988-01-01

A method was previously developed to predict the fracture toughness (stress intensity factor at failure) of composites in terms of the elastic constants and the tensile failing strain of the fibers. The method was applied to boron/aluminum composites made with various proportions of 0 to + or - 45 deg plies. Predicted values of fracture toughness were in gross error because widespread yielding of the aluminum matrix made the compliance very nonlinear. An alternate method was developed to predict the strain intensity factor at failure rather than the stress intensity factor because the singular strain field was not affected by yielding as much as the stress field. Strengths of specimens containing crack-like slits were calculated from predicted failing strains using uniaxial stress-strain curves. Predicted strengths were in good agreement with experimental values, even for the very nonlinear laminates that contained only + or - 45 deg plies. This approach should be valid for other metal matrix composites that have continuous fibers.

Normal compression wave scattering by a permeable crack in a fluid-saturated poroelastic solid

NASA Astrophysics Data System (ADS)

Song, Yongjia; Hu, Hengshan; Rudnicki, John W.

2017-04-01

A mathematical formulation is presented for the dynamic stress intensity factor (mode I) of a finite permeable crack subjected to a time-harmonic propagating longitudinal wave in an infinite poroelastic solid. In particular, the effect of the wave-induced fluid flow due to the presence of a liquid-saturated crack on the dynamic stress intensity factor is analyzed. Fourier sine and cosine integral transforms in conjunction with Helmholtz potential theory are used to formulate the mixed boundary-value problem as dual integral equations in the frequency domain. The dual integral equations are reduced to a Fredholm integral equation of the second kind. It is found that the stress intensity factor monotonically decreases with increasing frequency, decreasing the fastest when the crack width and the slow wave wavelength are of the same order. The characteristic frequency at which the stress intensity factor decays the fastest shifts to higher frequency values when the crack width decreases.

Effect of individually tailored biopsychosocial workplace interventions on chronic musculoskeletal pain, stress and work ability among laboratory technicians: randomized controlled trial protocol.

PubMed

Jay, Kenneth; Brandt, Mikkel; Sundstrup, Emil; Schraefel, Mc; Jakobsen, Markus D; Sjøgaard, Gisela; Andersen, Lars L

2014-12-18

Among laboratory technicians, the prevalence of neck and shoulder pain is widespread possibly due to typical daily work tasks such as pipetting, preparing vial samples for analysis, and data processing on a computer including mouse work - all tasks that require precision in motor control and may result in extended periods of time spent in static positions.In populations characterized by intense chronic musculoskeletal pain and diagnosed conditions in conjunction with psycho-physiological symptoms such as stress-related pain and soreness and other disabling conditions, multifactorial approaches applying a combination of individually tailored physical and cognitive strategies targeting the areas most needed, may be an effective solution to the physical and mental health challenges.The aim of this study is therefore to investigate the effect of an individually tailored biopsychosocial intervention strategy on musculoskeletal pain, stress and work disability in lab technicians with a history of musculoskeletal pain at a single worksite in Denmark. In this single-blind two-armed parallel-group randomized controlled trial with allocation concealment, participants receive either an individualized multifactorial intervention or "usual care" for 10 weeks at the worksite. 1) female laboratory technician (18-67 years of age) and 2) Pain intensity ≥ 3 (0-10 Visual Analogue Scale) lasting ≥3 months with a frequency of ≥ 3 days per week in one or more of the following regions: i) upper back i) low back iii) neck, iv) shoulder, v) elbow and/or vi) hand. 1) life-threatening disease and 2) pregnancy. Stress, as measured by Cohen´s perceived stress questionnaire is not an inclusion criteria, thus participants can participate regardless of their stress level.We will implement an individualized intervention addressing biopsychosocial elements of musculoskeletal pain with the following components; i) increasing physical capacity through strength- and motor control training; ii) lowering or preventing development of stress through mindfulness practice and learning de-catastrophizing pain management strategies through cognitive training.The primary outcome at 10-week follow-up is the between-group difference in intensity of perceived musculoskeletal pain during the last week (average value of back, neck, shoulder, elbow and hand) assessed by questionnaire (modified visual analogue scale 0-10). This study will provide experimental evidence to guide workplace initiatives designed towards reducing chronic musculoskeletal pain and stress. ClinicalTrials.gov NCT02047669.

Fracture Mechanics of Thin, Cracked Plates Under Tension, Bending and Out-of-Plane Shear Loading

NASA Technical Reports Server (NTRS)

Zehnder, Alan T.; Hui, C. Y.; Potdar, Yogesh; Zucchini, Alberto

1999-01-01

Cracks in the skin of aircraft fuselages or other shell structures can be subjected to very complex stress states, resulting in mixed-mode fracture conditions. For example, a crack running along a stringer in a pressurized fuselage will be subject to the usual in-plane tension stresses (Mode-I) along with out-of-plane tearing stresses (Mode-III like). Crack growth and initiation in this case is correlated not only with the tensile or Mode-I stress intensity factor, K(sub I), but depends on a combination of parameters and on the history of crack growth. The stresses at the tip of a crack in a plate or shell are typically described in terms of either the small deflection Kirchhoff plate theory. However, real applications involve large deflections. We show, using the von-Karman theory, that the crack tip stress field derived on the basis of the small deflection theory is still valid for large deflections. We then give examples demonstrating the exact calculation of energy release rates and stress intensity factors for cracked plates loaded to large deflections. The crack tip fields calculated using the plate theories are an approximation to the actual three dimensional fields. Using three dimensional finite element analyses we have explored the relationship between the three dimensional elasticity theory and two dimensional plate theory results. The results show that for out-of-plane shear loading the three dimensional and Kirchhoff theory results coincide at distance greater than h/2 from the crack tip, where h/2 is the plate thickness. Inside this region, the distribution of stresses through the thickness can be very different from the plate theory predictions. We have also explored how the energy release rate varies as a function of crack length to plate thickness using the different theories. This is important in the implementation of fracture prediction methods using finite element analysis. Our experiments show that under certain conditions, during fatigue crack growth, the presence of out-of-plane shear loads induces a great deal of contact and friction on the crack surfaces, dramatically reducing crack growth rate. A series of experiments and a proposed computational approach for accounting for the friction is discussed.

8-oxo-7,8-dihydroguanine level - the DNA oxidative stress marker - recognized by fluorescence image analysis in sporadic uterine adenocarcinomas in women.

PubMed

Postawski, Krzysztof; Przadka-Rabaniuk, Dorota; Piersiak, Tomasz

2013-01-01

In the case of carcinogenesis in human endometrium no information exists on tissue concentration of 8-oxo-7,8-dihydroguanine, the DNA oxidative stress marker This was the main reason to undertake the investigation of this DNA modification in human uterine estrogen-dependent tissue cancers. In order to estimate the level of oxidative damage, 8-oxo-7,8-dihydroguanine was determined directly in cells of tissue microscope slides using OxyDNA Assay Kit, Fluorometric. Cells were investigated under confocal microscope. Images of individual cells were captured by computer-interfaced digital photography and analyzed for fluorescence intensities (continuous inverted 8-bit gray-scale = 0 [black]-255 [white]). Fluorescence scores were calculated for each of 13 normal endometrial samples and 31 uterine adenocarcinoma specimens. Finally the level of the oxidative stress marker was also analyzed according to histological and clinical features of the neoplasms. The obtained data revealed that: 8-oxo-7,8-dihydroguanine levels were higher in uterine adenocarcinomas than in normal endometrial samples (48,32 vs. 38,64; p<0,001); in contrast to normal endometrium there was no correlation between age and DNA oxidative modification content in uterine cancer; highest mean fluorescence intensity was recognized in G2 endometrial adenocarcinomas; level of 8-oxo-7,8-dihydroguanine does not depend on Body Mass Index (BMI) and cancer uterine wall infiltration or tumor FIGO stage. Our study indicates that accumulation of the oxidized DNA base may contribute to the development of endometrial neoplasia, however oxidative DNA damage does not seem to increase with tumor progression.

Stressor-specific effects of sex on HPA axis hormones and activation of stress-related neurocircuitry.

PubMed

Babb, Jessica A; Masini, Cher V; Day, Heidi E W; Campeau, Serge

2013-11-01

Experiencing stress can be physically and psychologically debilitating to an organism. Women have a higher prevalence of some stress-related mental illnesses, the reasons for which are unknown. These experiments explore differential HPA axis hormone release in male and female rats following acute stress. Female rats had a similar threshold of HPA axis hormone release following low intensity noise stress as male rats. Sex did not affect the acute release, or the return of HPA axis hormones to baseline following moderate intensity noise stress. Sensitive indices of auditory functioning obtained by modulation of the acoustic startle reflex by weak pre-pulses did not reveal any sexual dimorphism. Furthermore, male and female rats exhibited similar c-fos mRNA expression in the brain following noise stress, including several sex-influenced stress-related regions. The HPA axis response to noise stress was not affected by stage of estrous cycle, and ovariectomy significantly increased hormone release. Direct comparison of HPA axis hormone release to two different stressors in the same animals revealed that although female rats exhibit robustly higher HPA axis hormone release after restraint stress, the same effect was not observed following moderate and high intensity loud noise stress. Finally, the differential effect of sex on HPA axis responses to noise and restraint stress cannot readily be explained by differential social cues or general pain processing. These studies suggest the effect of sex on acute stress-induced HPA axis hormone activity is highly dependent on the type of stressor.

Stress Management and Gifted Children

ERIC Educational Resources Information Center

Patel, Vidisha A.

2009-01-01

Stress can affect anyone, and gifted children are no exception. Giftedness can sometimes be the cause of the stress. Perfectionism, sensitivity, and intensity are characteristics of gifted children that may exacerbate stress. Stress can be constructive. Prolonged stress, however, with no time to recover becomes detrimental. Continued stress upsets…

The Fundamental Solutions for the Stress Intensity Factors of Modes I, II And III. The Axially Symmetric Problem

NASA Astrophysics Data System (ADS)

Rogowski, B.

2015-05-01

The subject of the paper are Green's functions for the stress intensity factors of modes I, II and III. Green's functions are defined as a solution to the problem of an elastic, transversely isotropic solid with a penny-shaped or an external crack under general axisymmetric loadings acting along a circumference on the plane parallel to the crack plane. Exact solutions are presented in a closed form for the stress intensity factors under each type of axisymmetric ring forces as fundamental solutions. Numerical examples are employed and conclusions which can be utilized in engineering practice are formulated.

Stress-intensity factors of r-cracks in fiber-reinforced composites under thermal and mechanical loading

NASA Astrophysics Data System (ADS)

Mueller, W. H.; Schmauder, S.

1993-02-01

The plane stress/plane strain problem of radial matrix cracking in fiber-reinforced composites, due to thermal mismatch and externally applied stress is solved numerically in the framework of linear elasticity, using Erdogan's integral equation technique. It is shown that, in order to obtain the results of the combined loading case, the solutions of purely thermal and purely mechanical loading can simply be superimposed. Stress-intensity factors are calculated for various lengths and distances of the crack from the interface for each of these loading conditions.

Psychoemotional stress of employees and workers in the public and real sectors of national economy in Bulgaria.

PubMed

Hristov, Zheliazko I

2009-01-01

Stress is a universal biologically based phenomenon that places adaptive demands on the changes in the environment. It is a set of non-specific mental, physiologic and behavioural responses of a human being to the impact of environmental stimuli. The effect of many of these environmental stimuli in Bulgaria has been intensified by the recent drastic changes (political, social, professional, and in the labour market). The severity and manifestation of stress changed as a result. To assess and measure these changes we conducted a nationwide study applying original methodological approach and using original quantitation parameters. To determine the type, duration and level (intensity) of stress; we attempted to determine the factors causing stress in seven major professions in the public and real sectors of economy. We studied stress and the factors causing it in a nationwide representative study which included 4892 employees and workers practicing seven different professions (physicians, teachers, office workers, miners, public transport drivers, metal workers, and train drivers). A battery of survey methods and original statistical and mathematical methods (including the method of weighted mean intensity of action and manifestation) were employed in the study to determine the type, manifestations, intensity and duration of stress and the stressogenic factors causing it. We found that 70.7% of the workers and employees exhibited symptoms of affective stress and 25.7%--of depressive stress. Affective stress was the most common type of stress in office workers (76.9%) and drivers (73.5%), and the least common--in physicians (65.9%) and teachers (63.3%). The level of stress was high and very high for 25.3% of the study contingent. Affective stress had the highest intensity in miners (0.5226) and drivers (0.4654), and the lowest - in physicians (0.3072). Affective stress was a permanent state in 24.12% of the people working in the public sector and 16.37% of those in the real sectors. Psychoemotional stress was transitory for 58% of the professions in the public sector and 31% of those in the real sector. The profession-related factors were assessed as the most stressful (0.6339), followed by those of social and economic nature (0.5982); the family-related factors and the factors associated with the organisation of the working process were the least stressful (0.5251 and 0.5730, respectively), There were statistically significant differences in the characteristics and intensity of psychoemotional stress between the different professions in both sectors of economy.in bth sctosofeconmy. The basic professions in Bulgarian economy are highly stressful, which comes as a corollary of the changed stressogenic situation in Bulgaria.

Cold pulse and rotation reversals with turbulence spreading and residual stress

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hariri, F.; Naulin, V.; Juul Rasmussen, J.

2016-05-15

Transport modeling based on inclusion of turbulence spreading and residual stresses shows internal rotation reversals and polarity reversal of cold pulses, with a clear indication of nonlocal transport effects due to fast spreading in the turbulence intensity field. The effects of turbulence spreading and residual stress are calculated from the gradient of the turbulence intensity. In the model presented in this paper, the flux is carried by the turbulence intensity field, which in itself is subject to radial transport effects. The pulse polarity inversion and the rotation profile reversal positions are close to the radial location of the stable/unstable transition.more » Both effects have no direct explanation within the framework of classical transport modeling, where the fluxes are related directly to the linear growth rates, the turbulence intensity profile is not considered and the corresponding residual stress is absent. Our simulations are in qualitative agreement with measurements from ohmically heated plasmas. Rotation reversal at a finite radius is found in situations not displaying saturated confinement, which we identify as situations where the plasma is nearly everywhere unstable. As an additional and new effect, the model predicts a perturbation of the velocity profile following a cold pulse from the edge. This allows direct experimental confirmation of both the existence of residual stress caused by turbulence intensity profiles and fundamental ideas of transport modeling presented here.« less

Resolved shear stress intensity coefficient and fatigue crack growth in large crystals

NASA Technical Reports Server (NTRS)

Chen, QI; Liu, Hao-Wen

1988-01-01

Fatigue crack growth in large grain Al alloy was studied. Fatigue crack growth is caused primarily by shear decohesion due to dislocation motion in the crack tip region. The crack paths in the large crystals are very irregular and zigzag. The crack planes are often inclined to the loading axis both in the inplane direction and the thickness direction. The stress intensity factors of such inclined cracks are approximated from the two dimensional finite element calculations. The plastic deformation in a large crystal is highly anisotropic, and dislocation motion in such crystals are driven by the resolved shear stress. The resolved shear stress intensity coefficient in a crack solid, RSSIC, is defined, and the coefficients for the slip systems at a crack tip are evaluated from the calculated stress intensity factors. The orientations of the crack planes are closely related to the slip planes with the high RSSIC values. If a single slip system has a much higher RSSIC than all the others, the crack will follow the slip plane, and the slip plane becomes the crack plane. If two or more slip systems have a high RSSIC, the crack plane is the result of the decohesion processes on these active slip planes.

Intensive cognitive therapy for post-traumatic stress disorder in routine clinical practice: A matched comparison audit.

PubMed

Murray, Hannah; El-Leithy, Sharif; Billings, Jo

2017-11-01

Intensive cognitive therapy for post-traumatic stress disorder (PTSD) has been shown to be as effective as weekly treatment in controlled trials. In this study, outcome data comparing standard and intensive treatments delivered in routine clinical practice were analysed. A consecutive case series of intensive treatment cases were compared to matched control cases who had completed weekly treatment. Both groups showed significant improvements on PTSD and depression measures. The intensive group showed larger PTSD symptomatic improvement. There were differences between the groups in age and time since trauma, suggesting selection biases in who is offered, and/or who chooses intensive treatment. For some individuals, an intensive format may be more effective than weekly treatment. © 2017 The British Psychological Society.

Delamination Analysis Of Composite Curved Bars

NASA Technical Reports Server (NTRS)

Ko, William L.; Jackson, Raymond H.

1990-01-01

Classical anisotropic elasticity theory used to construct "multilayer" composite semicircular curved bar subjected to end forces and end moments. Radial location and intensity of open-mode delamination stress calculated and compared with results obtained from anisotropic continuum theory and from finite element method. Multilayer theory gave more accurate predictions of location and intensity of open-mode delamination stress. Currently being applied to predict open-mode delamination stress concentrations in horse-shoe-shaped composite test coupons.

Relationships Between Stress, Negative Emotions, Resilience, and Smoking: Testing a Moderated Mediation Model.

PubMed

Wang, Yan; Chen, Xinguang; Gong, Jie; Yan, Yaqiong

2016-01-01

More effective tobacco prevention and cessation programs require in-depth understanding of the mechanism by which multiple factors interact with each other to affect smoking behaviors. Stress has long been recognized as a risk factor for smoking. However, the underlying mediation and moderation mechanisms are far from clear. The purpose of this study was to examine the role of negative emotions in mediating the link between stress and smoking and whether this indirect link was modified by resilience. Survey data were collected using audio computer-assisted self-interview (ACASI) from a large random sample of urban residents (n = 1249, mean age = 35.1, 45.3% male) in Wuhan, China. Perceived stress, negative emotions (anxiety, depression), resilience were measured with reliable instruments also validated in China. Self-reported smoking was validated with exhaled carbon monoxide. Mediation analysis indicated that two negative emotions fully mediated the link between stress and intensity of smoking (assessed by number of cigarettes smoked per day, effect =.082 for anxiety and.083 for depression) and nicotine dependence (assessed by DSM-IV standard, effect =.134 for anxiety and.207 for depression). Moderated mediation analysis demonstrated that the mediation effects of negative emotions were negatively associated with resilience. Results suggest resilience interacts with stress and negative emotions to affect the risk of tobacco use and nicotine dependence among Chinese adults. Further research with longitudinal data is needed to verify the findings of this study and to estimate the effect size of resilience in tobacco intervention and cessation programs.

Computational Methods for Frictional Contact With Applications to the Space Shuttle Orbiter Nose-Gear Tire

NASA Technical Reports Server (NTRS)

Tanner, John A.

1996-01-01

A computational procedure is presented for the solution of frictional contact problems for aircraft tires. A Space Shuttle nose-gear tire is modeled using a two-dimensional laminated anisotropic shell theory which includes the effects of variations in material and geometric parameters, transverse-shear deformation, and geometric nonlinearities. Contact conditions are incorporated into the formulation by using a perturbed Lagrangian approach with the fundamental unknowns consisting of the stress resultants, the generalized displacements, and the Lagrange multipliers associated with both contact and friction conditions. The contact-friction algorithm is based on a modified Coulomb friction law. A modified two-field, mixed-variational principle is used to obtain elemental arrays. This modification consists of augmenting the functional of that principle by two terms: the Lagrange multiplier vector associated with normal and tangential node contact-load intensities and a regularization term that is quadratic in the Lagrange multiplier vector. These capabilities and computational features are incorporated into an in-house computer code. Experimental measurements were taken to define the response of the Space Shuttle nose-gear tire to inflation-pressure loads and to inflation-pressure loads combined with normal static loads against a rigid flat plate. These experimental results describe the meridional growth of the tire cross section caused by inflation loading, the static load-deflection characteristics of the tire, the geometry of the tire footprint under static loading conditions, and the normal and tangential load-intensity distributions in the tire footprint for the various static vertical loading conditions. Numerical results were obtained for the Space Shuttle nose-gear tire subjected to inflation pressure loads and combined inflation pressure and contact loads against a rigid flat plate. The experimental measurements and the numerical results are compared.

Computational methods for frictional contact with applications to the Space Shuttle orbiter nose-gear tire: Comparisons of experimental measurements and analytical predictions

NASA Technical Reports Server (NTRS)

Tanner, John A.

1996-01-01

A computational procedure is presented for the solution of frictional contact problems for aircraft tires. A Space Shuttle nose-gear tire is modeled using a two-dimensional laminated anisotropic shell theory which includes the effects of variations in material and geometric parameters, transverse-shear deformation, and geometric nonlinearities. Contact conditions are incorporated into the formulation by using a perturbed Lagrangian approach with the fundamental unknowns consisting of the stress resultants, the generalized displacements, and the Lagrange multipliers associated with both contact and friction conditions. The contact-friction algorithm is based on a modified Coulomb friction law. A modified two-field, mixed-variational principle is used to obtain elemental arrays. This modification consists of augmenting the functional of that principle by two terms: the Lagrange multiplier vector associated with normal and tangential node contact-load intensities and a regularization term that is quadratic in the Lagrange multiplier vector. These capabilities and computational features are incorporated into an in-house computer code. Experimental measurements were taken to define the response of the Space Shuttle nose-gear tire to inflation-pressure loads and to inflation-pressure loads combined with normal static loads against a rigid flat plate. These experimental results describe the meridional growth of the tire cross section caused by inflation loading, the static load-deflection characteristics of the tire, the geometry of the tire footprint under static loading conditions, and the normal and tangential load-intensity distributions in the tire footprint for the various static vertical-loading conditions. Numerical results were obtained for the Space Shuttle nose-gear tire subjected to inflation pressure loads and combined inflation pressure and contact loads against a rigid flat plate. The experimental measurements and the numerical results are compared.

β-distribution for Reynolds stress and turbulent heat flux in relaxation turbulent boundary layer of compression ramp

NASA Astrophysics Data System (ADS)

Hu, YanChao; Bi, WeiTao; Li, ShiYao; She, ZhenSu

2017-12-01

A challenge in the study of turbulent boundary layers (TBLs) is to understand the non-equilibrium relaxation process after sep-aration and reattachment due to shock-wave/boundary-layer interaction. The classical boundary layer theory cannot deal with the strong adverse pressure gradient, and hence, the computational modeling of this process remains inaccurate. Here, we report the direct numerical simulation results of the relaxation TBL behind a compression ramp, which reveal the presence of intense large-scale eddies, with significantly enhanced Reynolds stress and turbulent heat flux. A crucial finding is that the wall-normal profiles of the excess Reynolds stress and turbulent heat flux obey a β-distribution, which is a product of two power laws with respect to the wall-normal distances from the wall and from the boundary layer edge. In addition, the streamwise decays of the excess Reynolds stress and turbulent heat flux also exhibit power laws with respect to the streamwise distance from the corner of the compression ramp. These results suggest that the relaxation TBL obeys the dilation symmetry, which is a specific form of self-organization in this complex non-equilibrium flow. The β-distribution yields important hints for the development of a turbulence model.

A comparison of parent and staff perceptions of setting-specific and everyday stressors encountered by parents with very preterm infants experiencing neonatal intensive care.

PubMed

Pritchard, Verena E; Montgomery-Hönger, Argène

2014-10-01

Stress responses among parents of premature infants experiencing the neonatal intensive care unit (NICU) environment are widely reported. However, less is known about how nurses perceive parents' experiences or how stressors relating to demands on family finances and practical challenges associated with infant hospitalization contribute to parental stress levels in the NICU. 1) To compare parent and staff perceptions of the stressors facing parents experiencing neonatal intensive care; and 2) to develop a scale suitable for identifying stressors outside the NICU setting. At infant 34 weeks, parents (n=21) of very preterm infants (≤ 32 weeks GA) and NICU nurses (n=23) completed the Parental Stressor Scale: NICU (PSS: NICU) and a custom-made External Stressor Scale (ESS: NICU). Nurses perceived parents to experience higher stress in the NICU than parents themselves (ps<0.00001), with parents reporting low-to-moderate stress and staff rating parental stress as moderate-to-high. Parents reported slightly lower levels of stress on the ESS: NICU, with nurses again overestimating the level of parental stress (ps<0.00001). Consideration of the extent of nurses' medical experience did not alter results. The ESS: NICU showed good internal reliability, with PCAs revealing all items to load onto a single component. Additional analyses demonstrated divergent validity, with no relation evident with stress responses on the PSS: NICU. Periodic reassessments of staff and parent perceptions should be encouraged along with research dedicated to a fuller understanding of the range of stressors facing parents experiencing neonatal intensive care in attempts to reduce stress levels and aid integration into the unit. Copyright © 2014 Elsevier Ltd. All rights reserved.

Modelling of the plastic deformation and primary creep of metals coupled with DC in terms of the synthetic theory of irrecoverable deformation

NASA Astrophysics Data System (ADS)

Rusinko, Andrew; Varga, Peter

2018-04-01

The paper deals with modelling of the plastic and creep deformation of metals coupled with current. The passage of DC manifests itself in the increase in creep deformation and leads to primary creep time shortening. With plastic deformation, a short electric impulse results in the step-wise decrease of stress (stress-drop) on the stress-strain diagram. To catch these phenomena, we utilize the synthetic theory of recoverable deformation. The constitutive equation of this theory is supplemented by a term taking into account the intensity of DC. Further, we introduce DC intensity into the function governing transient creep. As a result, we predict the parameters of transient creep and calculate the stress-drop as a function of current intensity. The model results show good agreement with experimental data.

A Computer Code for Dynamic Stress Analysis of Media-Structure Problems with Nonlinearities (SAMSON). Volume III. User’s Manual.

DTIC Science & Technology

NONLINEAR SYSTEMS, LINEAR SYSTEMS, SUBROUTINES , SOIL MECHANICS, INTERFACES, DYNAMICS, LOADS(FORCES), FORCE(MECHANICS), DAMPING, ACCELERATION, ELASTIC...PROPERTIES, PLASTIC PROPERTIES, CRACKS , REINFORCING MATERIALS , COMPOSITE MATERIALS , FAILURE(MECHANICS), MECHANICAL PROPERTIES, INSTRUCTION MANUALS, DIGITAL COMPUTERS...STRESSES, *COMPUTER PROGRAMS), (*STRUCTURES, STRESSES), (*DATA PROCESSING, STRUCTURAL PROPERTIES), SOILS , STRAIN(MECHANICS), MATHEMATICAL MODELS

Failure analysis of blots for diesel engine intercooler

NASA Astrophysics Data System (ADS)

Ren, Ping; Li, Zongquan; Wu, Jiangfei; Guo, Yibin; Li, Wanyou

2017-05-01

In diesel generating sets, it will lead to the abominable working condition if the fault couldn’t be recovered when the bolt of intercooler cracks. This paper aims at the fault of the blots of diesel generator intercooler and completes the analysis of the static strength and fatigue strength. Static intensity is checked considering blot preload and thermal stress. In order to obtain the thermal stress of the blot, thermodynamic of intercooler is calculated according to the measured temperature. Based on the measured vibration response and the finite element model, using dynamic load identification technique, equivalent excitation force of unit was solved. In order to obtain the force of bolt, the excitation force is loaded into the finite element model. By considering the thermal stress and preload as the average stress while the mechanical stress as the wave stress, fatigue strength analysis has been accomplished. Procedure of diagnosis is proposed in this paper. Finally, according to the result of intensity verification the fatigue failure is validation. Thereby, further studies are necessary to verification the result of the intensity analysis and put forward some improvement suggestion.

Kinetic studies of the stress corrosion cracking of D6AC steel

NASA Technical Reports Server (NTRS)

Noronha, P. J.

1975-01-01

The effect of load interactions on the crack growth velocity of D6AC steel under stress corrosion cracking conditions was determined. The environment was a 3.5 percent salt solution. The modified-wedge opening load specimens were fatigue precracked and subjected to a deadweight loading in creep machines. The effects of load shedding on incubation times and crack growth rates were measured using high-sensitivity compliance measurement techniques. Load shedding results in an incubation time, the length of which depends on the amount of load shed and the baseline stress intensity. The sequence of unloading the specimen also controls the subsequent incubation period. The incubation period is shorter when load shedding passes through zero load than when it does not if the specimen initially had the same baseline stress intensity. The crack growth rates following the incubation period are also different from the steady-state crack growth rate at the operating stress intensity. These data show that the susceptibility of this alloy system to stress corrosion cracking depends on the plane-strain fracture toughness and on the yield strength of the material.

Comparison of myocardial ischemia during intense mental stress using flight simulation in airline pilots with coronary artery disease to that produced with conventional mental and treadmill exercise stress testing.

PubMed

Doorey, Andrew; Denenberg, Barry; Sagar, Vidya; Hanna, Tracy; Newman, Jack; Stone, Peter H

2011-09-01

Mental stress increases cardiovascular morbidity and mortality. Although laboratory mental stress often causes less myocardial ischemia than exercise stress (ES), it is unclear whether mental stress is intrinsically different or differences are due to less hemodynamic stress with mental stress. We sought to evaluate the hemodynamic and ischemic response to intense realistic mental stress created by modern flight simulators and compare this response to that of exercise treadmill testing and conventional laboratory mental stress (CMS) testing in pilots with coronary disease. Sixteen airline pilots with angiographically documented coronary disease and documented myocardial ischemia during ES were studied using maximal treadmill ES, CMS, and aviation mental stress (AMS) testing. AMS testing was done in a sophisticated simulator using multiple system failures as stressors. Treadmill ES testing resulted in the highest heart rate, but AMS caused a higher blood pressure response than CMS. Maximal rate-pressure product was not significantly different between ES and AMS (25,646 vs 23,347, p = 0.08), although these were higher than CMS (16,336, p <0.0001). Despite similar hemodynamic stress induced by ES and AMS, AMS resulted in significantly less ST-segment depression and nuclear ischemia than ES. Differences in induction of ischemia by mental stress compared to ES do not appear to be due to the creation of less hemodynamic stress. In conclusion, even with equivalent hemodynamic stress, intense realistic mental stress induced by flight simulators results in significantly less myocardial ischemia than ES as measured by ST-segment depression and nuclear ischemia. Copyright © 2011 Elsevier Inc. All rights reserved.

Computation of stress on the surface of a soft homogeneous arbitrarily shaped particle.

PubMed

Yang, Minglin; Ren, Kuan Fang; Wu, Yueqian; Sheng, Xinqing

2014-04-01

Prediction of the stress on the surface of an arbitrarily shaped particle of soft material is essential in the study of elastic properties of the particles with optical force. It is also necessary in the manipulation and sorting of small particles with optical tweezers, since a regular-shaped particle, such as a sphere, may be deformed under the nonuniform optical stress on its surface. The stress profile on a spherical or small spheroidal soft particle trapped by shaped beams has been studied, however little work on computing the surface stress of an irregular-shaped particle has been reported. We apply in this paper the surface integral equation with multilevel fast multipole algorithm to compute the surface stress on soft homogeneous arbitrarily shaped particles. The comparison of the computed stress profile with that predicted by the generalized Lorenz-Mie theory for a water droplet of diameter equal to 51 wavelengths in a focused Gaussian beam show that the precision of our method is very good. Then stress profiles on spheroids with different aspect ratios are computed. The particles are illuminated by a Gaussian beam of different waist radius at different incidences. Physical analysis on the mechanism of optical stress is given with help of our recently developed vectorial complex ray model. It is found that the maximum of the stress profile on the surface of prolate spheroids is not only determined by the reflected and refracted rays (orders p=0,1) but also the rays undergoing one or two internal reflections where they focus. Computational study of stress on surface of a biconcave cell-like particle, which is a typical application in life science, is also undertaken.

Effect of mental stress on cold pain in chronic tension-type headache sufferers.

PubMed

Cathcart, Stuart; Winefield, Anthony H; Lushington, Kurt; Rolan, Paul

2009-10-01

Mental stress is a noted contributing factor in chronic tension-type headache (CTH), however the mechanisms underlying this are not clearly understood. One proposition is that stress aggravates already increased pain sensitivity in CTH sufferers. This hypothesis could be partially tested by examining effects of mental stress on threshold and supra-threshold experimental pain processing in CTH sufferers. Such studies have not been reported to date. The present study measured pain detection and tolerance thresholds and ratings of supra-threshold pain stimulation from cold pressor test in CTH sufferers (CTH-S) and healthy Control (CNT) subjects exposed to a 60-min stressful mental task, and in CTH sufferers exposed to a 60-min neutral condition (CTH-N). Headache sufferers had lower pain tolerance thresholds and increased pain intensity ratings compared to controls. Pain detection and tolerance thresholds decreased and pain intensity ratings increased during the stress task, with a greater reduction in pain detection threshold and increase in pain intensity ratings in the CTH-S compared to CNT group. The results support the hypothesis that mental stress contributes to CTH through aggravating already increased pain sensitivity in CTH sufferers.

[Factors influencing relocation stress syndrome in patients following transfer from intensive care units].

PubMed

Park, Jin-Hee; Yoo, Moon-Sook; Son, Youn-Jung; Bae, Sun Hyoung

2010-06-01

The purpose of this study was to identify the levels of relocation stress syndrome (RSS) and influencing the stress experienced by Intensive Care Unit (ICU) patients just after transfer to general wards. A cross-sectional study was conducted with 257 patients who transferred from the intensive care unit. Data were collected through self-report questionnaires from May to October, 2009. Data were analyzed using the Pearson correlation coefficient, t-test, one-way ANOVA, and stepwise multiple linear regression with SPSS/WIN 12.0. The mean score for RSS was 17.80+/-9.16. The factors predicting relocation stress syndrome were symptom experience, differences in scope and quality of care provided by ICU and ward nursing staffs, satisfaction with transfer process, length of stay in ICU and economic status, and these factors explained 40% of relocation stress syndrome (F=31.61, p<.001). By understanding the stress experienced by ICU patients, nurses are better able to provide psychological support and thus more holistic care to critically ill patients. Further research is needed to consider the impact of relocation stress syndrome on patients' health outcomes in the recovery trajectory.

Frequency and associated risk factors for neck pain among software engineers in Karachi, Pakistan.

PubMed

Rasim Ul Hasanat, Mohammad; Ali, Syed Shahzad; Rasheed, Abdur; Khan, Muhammad

2017-07-01

To determine the frequency of neck pain and its association with risk factors among software engineers. This descriptive, cross-sectional study was conducted at the Dow University of Health Sciences, Karachi, from February to March 2016, and comprised software engineers from 19 different locations. Non-probability purposive sampling technique was used to select individuals spending at least 6 hours in front of computer screens every day and having a work experience of at least 6 months. Data were collected using a self-administrable questionnaire. SPSS 21 was used for data analysis. Of the 185 participants, 49(26.5%) had neck pain at the time of data-gathering, while 136(73.5%) reported no pain. However, 119(64.32%) participants had a previous history of neck pain. Other factors like smoking, physical inactivity, history of any muscular pain and neck pain, uncomfortable workstation, and work-related mental stress and insufficient sleep at night, were found to be significantly associated with current neck pain (p<0.05 each). Intensive computer users are likely to experience at least one episode of computer-associated neck pain.

The relationship between psychosocial work factors, work stress and computer-related musculoskeletal discomforts among computer users in Malaysia.

PubMed

Zakerian, Seyed Abolfazl; Subramaniam, Indra Devi

2009-01-01

Increasing numbers of workers use computer for work. So, especially among office workers, there is a high risk of musculoskeletal discomforts. This study examined the associations among 3 factors, psychosocial work factors, work stress and musculoskeletal discomforts. These associations were examined via a questionnaire survey on 30 office workers (at a university in Malaysia), whose jobs required an extensive use of computers. The questionnaire was distributed and collected daily for 20 days. While the results indicated a significant relationship among psychosocial work factors, work stress and musculoskeletal discomfort, 3 psychosocial work factors were found to be more important than others in both work stress and musculoskeletal discomfort: job demands, negative social interaction and computer-related problems. To further develop study design, it is necessary to investigate industrial and other workers who have experienced musculoskeletal discomforts and work stress.

The Effect of the Laboratory Specimen on Fatigue Crack Growth Rate

NASA Technical Reports Server (NTRS)

Forth, S. C.; Johnston, W. M.; Seshadri, B. R.

2006-01-01

Over the past thirty years, laboratory experiments have been devised to develop fatigue crack growth rate data that is representative of the material response. The crack growth rate data generated in the laboratory is then used to predict the safe operating envelope of a structure. The ability to interrelate laboratory data and structural response is called similitude. In essence, a nondimensional term, called the stress intensity factor, was developed that includes the applied stresses, crack size and geometric configuration. The stress intensity factor is then directly related to the rate at which cracks propagate in a material, resulting in the material property of fatigue crack growth response. Standardized specimen configurations and experimental procedures have been developed for laboratory testing to generate crack growth rate data that supports similitude of the stress intensity factor solution. In this paper, the authors present laboratory fatigue crack growth rate test data and finite element analyses that show similitude between standard specimen configurations tested using the constant stress ratio test method is unobtainable.

[Mechanism of the dentino-enamel junction on the resist-crack propagation of human teeth by the finite element method].

PubMed

Jingjing, Zheng; Tiezhou, Hou; Hong, Tao; Xueyan, Guo; Cui, Wu

2014-10-01

This study aims to identify the crack tip stress intensity factor of the propagation process, crack propagation path, and the changes in the shape of the crack tip by the finite element method. The finite element model of dentino-enamel junction was established with ANSYS software, and the length of the initial crack in the single edge was set to 0.1 mm. The lower end of the sample was fixed. The tensile load of 1 MPa with frequency of 5 Hz was applied to the upper end. The stress intensity factor, deflection angle, and changes in the shape of the crack tip in the crack propagation were calculated by ANSYS. The stress intensity factor suddenly and continuously decreased in dentino-enamel junction as the crack extended. A large skewed angle appeared, and the stress on crack tip was reduced. The dentino-enamel junction on human teeth may resist crack propagation through stress reduction.

Normal and radial impact of composites with embedded penny-shaped cracks

NASA Technical Reports Server (NTRS)

Sih, G. C.

1979-01-01

A method is developed for the dynamic stress analysis of a layered composite containing an embedded penny-shaped crack and subjected to normal and radial impact. The material properties of the layers are chosen such that the crack lies in a layer of matrix material while the surrounding material possesses the average elastic properties of a two-phase medium consisting of a large number of fibers embedded in the matrix. Quantitatively, the time-dependent stresses near the crack border can be described by the dynamic stress intensity factors. Their magnitude depends on time, on the material properties of the composite and on the relative size of the crack compared to the composite local geometry. Results obtained show that, for the same material properties and geometry of the composite, the dynamic stress intensity factors for an embedded (penny-shaped) crack reach their peak values within a shorter period of time and with a lower magnitude than the corresponding dynamic stress intensity factors for a through-crack.

Stress intensity and crack displacement for small edge cracks

NASA Technical Reports Server (NTRS)

Orange, Thomas W.

1988-01-01

The weight function method was used to derive stress intensity factors and crack mouth displacement coefficients for small edge cracks (less than 20 percent of the specimen width) in common fracture specimen configurations. Contact stresses due to point application of loads were found to be small but significant for three-point bending and insignificant for four-point bending. The results are compared with available equations and numerical solutions from the literature and with unpublished boundary collocation results.

Internal and edge cracks in a plate of finite width under bending

NASA Technical Reports Server (NTRS)

Boduroglu, H.; Erdogan, F.

1983-01-01

Internal and edge cracks were studied by using Reissner's transverse shear theory. The effect of stress-free boundaries on the stress intensity factors in plates under bending were investigated. Among the results found, particularly interesting are those relating to the limiting cases of the crack geometries. The numerical results are given for a single internal crack, two collinear cracks, and two edge cracks. The effect of Poisson's ratio on the stress intensity factors was studied.

[The application of low-intensity electromagnetic radiation under immobilization stress conditions (an experimental study)].

PubMed

Korolev, Iu N; Bobrovnitskiĭ, I P; Nikoulina, L A; Mikhaĭlik, L V; Geniatulina, M S; Bobkova, A S

2014-01-01

The experiments carried out on outbred male white rats with the use of optical, electron-microscopic, biochemical, and radioimmunological methods have demonstrated that the application of low-intensity electromagnetic radiation (LI-EMR) with a flow density of 1 mcW/cm2 and a frequency of around 1,000 MHz both in the primary prophylaxis regime and as the therapeuticpreventive modality arrested the development of post-stress disorders in the rat testicles, liver, and thymus; moreover, it promoted activation of the adaptive, preventive, and compensatory processes. The data obtained provide a rationale for the application of low-intensity electromagnetic radiation to protect the organism from negative effects of stressful factors.

An internal crack parallel to the boundary of a nonhomogeneous half plane under thermal loading

NASA Astrophysics Data System (ADS)

Jin, Zhi-He; Noda, Naotake

1993-05-01

This paper considers the crack problem for a semi-infinite nonhomogeneous thermoelastic solid subjected to steady heat flux over the boundary. The crack faces are assumed to be insulated. The research is aimed at understanding the effect of nonhomogeneities of materials on stress intensity factors. By using the Fourier transform, the problem is reduced to a system of singular integral equations which are solved numerically. Results are presented illustrating the influence of the nonhomogeneity of the material on the stress intensity factors. Zero Mode I stress intensity factors are found for some groups of the material constants, which may be interesting for the understanding of compositions of advanced Functionally Gradient Materials.

Stress intensity and displacement coefficients for radially cracked ring segments subject to three-point bending

NASA Technical Reports Server (NTRS)

Gross, B.; Srawley, J. E.

1983-01-01

The boudary collocation method was used to generate Mode 1 stress intensity and crack mouth displacement coefficients for internally and externally radially cracked ring segments (arc bend specimens) subjected to three point radial loading. Numerical results were obtained for ring segment outer to inner radius ratios (R sub o/ R sub i) ranging from 1.10 to 2.50 and crack length to width ratios (a/W) ranging from 0.1 to 0.8. Stress intensity and crack mouth displacement coefficients were found to depend on the ratios R sub o/R sub i and a/W as well as the included angle between the directions of the reaction forces.

Occupational stress in human computer interaction.

PubMed

Smith, M J; Conway, F T; Karsh, B T

1999-04-01

There have been a variety of research approaches that have examined the stress issues related to human computer interaction including laboratory studies, cross-sectional surveys, longitudinal case studies and intervention studies. A critical review of these studies indicates that there are important physiological, biochemical, somatic and psychological indicators of stress that are related to work activities where human computer interaction occurs. Many of the stressors of human computer interaction at work are similar to those stressors that have historically been observed in other automated jobs. These include high workload, high work pressure, diminished job control, inadequate employee training to use new technology, monotonous tasks, por supervisory relations, and fear for job security. New stressors have emerged that can be tied primarily to human computer interaction. These include technology breakdowns, technology slowdowns, and electronic performance monitoring. The effects of the stress of human computer interaction in the workplace are increased physiological arousal; somatic complaints, especially of the musculoskeletal system; mood disturbances, particularly anxiety, fear and anger; and diminished quality of working life, such as reduced job satisfaction. Interventions to reduce the stress of computer technology have included improved technology implementation approaches and increased employee participation in implementation. Recommendations for ways to reduce the stress of human computer interaction at work are presented. These include proper ergonomic conditions, increased organizational support, improved job content, proper workload to decrease work pressure, and enhanced opportunities for social support. A model approach to the design of human computer interaction at work that focuses on the system "balance" is proposed.

Pain sensitivity mediates the relationship between stress and headache intensity in chronic tension-type headache.

PubMed

Cathcart, Stuart; Bhullar, Navjot; Immink, Maarten; Della Vedova, Chris; Hayball, John

2012-01-01

A central model for chronic tension-type headache (CTH) posits that stress contributes to headache, in part, by aggravating existing hyperalgesia in CTH sufferers. The prediction from this model that pain sensitivity mediates the relationship between stress and headache activity has not yet been examined. To determine whether pain sensitivity mediates the relationship between stress and prospective headache activity in CTH sufferers. Self-reported stress, pain sensitivity and prospective headache activity were measured in 53 CTH sufferers recruited from the general population. Pain sensitivity was modelled as a mediator between stress and headache activity, and tested using a nonparametric bootstrap analysis. Pain sensitivity significantly mediated the relationship between stress and headache intensity. The results of the present study support the central model for CTH, which posits that stress contributes to headache, in part, by aggravating existing hyperalgesia in CTH sufferers. Implications for the mechanisms and treatment of CTH are discussed.

Loss of parental role as a cause of stress in the neonatal intensive care unit.

PubMed

Bouet, Kary M; Claudio, Norma; Ramirez, Verónica; García-Fragoso, Lourdes

2012-01-01

Having a baby in the Neonatal Intensive Care Unit (NICU) is a major source of stress for parents. The barriers to parenting and reactions to the environment may negatively influence the parent-infant relationship. To identify NICU-related parental stress and associated factors. Parents (N = 156) of newborns admitted to NICU completed the Parental Stressor Scale. Most of the parents (46%) rated the experience to be extremely stressful. The principal cause of stress was the alteration in parental role and being separated from their baby. Stress was not associated to education, marital status, infants' birth weight, gestational age, congenital anomalies or if the parents expected the baby to be in the NICU. Identification of areas associated to higher levels of stress in parents may help the NICU staff to establish strategies to help parents cope with the stress caused by being unable to start their parenting role immediately after their babies' birth.

Three-dimensional finite-element analysis of chevron-notched fracture specimens

NASA Technical Reports Server (NTRS)

Raju, I. S.; Newman, J. C., Jr.

1984-01-01

Stress-intensity factors and load-line displacements were calculated for chevron-notched bar and rod fracture specimens using a three-dimensional finite-element analysis. Both specimens were subjected to simulated wedge loading (either uniform applied displacement or uniform applied load). The chevron-notch sides and crack front were assumed to be straight. Crack-length-to-specimen width ratios (a/w) ranged from 0.4 to 0.7. The width-to-thickness ratio (w/B) was 1.45 or 2. The bar specimens had a height-to-width ratio of 0.435 or 0.5. Finite-element models were composed of singularity elements around the crack front and 8-noded isoparametric elements elsewhere. The models had about 11,000 degrees of freedom. Stress-intensity factors were calculated by using a nodal-force method for distribution along the crack front and by using a compliance method for average values. The stress intensity factors and load-line displacements are presented and compared with experimental solutions from the literature. The stress intensity factors and load-line displacements were about 2.5 and 5 percent lower than the reported experimental values, respectively.

The stress intensity factors for a periodic array of interacting coplanar penny-shaped cracks

PubMed Central

Lekesiz, Huseyin; Katsube, Noriko; Rokhlin, Stanislav I.; Seghi, Robert R.

2013-01-01

The effect of crack interactions on stress intensity factors is examined for a periodic array of coplanar penny-shaped cracks. Kachanov’s approximate method for crack interactions (Int. J. Solid. Struct. 1987; 23(1):23–43) is employed to analyze both hexagonal and square crack configurations. In approximating crack interactions, the solution converges when the total truncation number of the cracks is 109. As expected, due to high density packing crack interaction in the hexagonal configuration is stronger than that in the square configuration. Based on the numerical results, convenient fitting equations for quick evaluation of the mode I stress intensity factors are obtained as a function of crack density and angle around the crack edge for both crack configurations. Numerical results for the mode II and III stress intensity factors are presented in the form of contour lines for the case of Poisson’s ratio ν =0.3. Possible errors for these problems due to Kachanov’s approximate method are estimated. Good agreement is observed with the limited number of results available in the literature and obtained by different methods. PMID:27175035

A Longitudinal Investigation of the Effects of Computer Anxiety on Performance in a Computing-Intensive Environment

ERIC Educational Resources Information Center

Buche, Mari W.; Davis, Larry R.; Vician, Chelley

2007-01-01

Computers are pervasive in business and education, and it would be easy to assume that all individuals embrace technology. However, evidence shows that roughly 30 to 40 percent of individuals experience some level of computer anxiety. Many academic programs involve computing-intensive courses, but the actual effects of this exposure on computer…

Physician work intensity among medical specialties: emerging evidence on its magnitude and composition.

PubMed

Horner, Ronnie D; Szaflarski, Jerzy P; Ying, Jun; Meganathan, Karthikeyan; Matthews, Gerald; Schroer, Brian; Weber, Debra; Raphaelson, Marc

2011-11-01

Similarities and differences in physician work intensity among specialties are poorly understood but have implications for quality of care, patient safety, practice organization and management, and payment. To determine the magnitude and important dimensions of physician work intensity for 4 specialties. Cross-sectional assessment of work intensity associated with actual patient care in the examination room or operating room. A convenience sample of 45 family physicians, 20 general internists, 22 neurologists, and 21 surgeons, located in Kansas, Kentucky, Maryland, Ohio, and Virginia. Work intensity measures included the National Aeronautics and Space Administration-Task Load Index (NASA-TLX), Subjective Work Assessment Technique (SWAT), and Multiple Resource Questionnaire. Stress was measured by the Dundee Stress State Questionnaire. Physicians reported similar magnitude of work intensity on the NASA-TLX and Multiple Resource Questionnaire. On the SWAT, general internists reported work intensity similar to surgeons but significantly lower than family physicians and neurologists (P=0.035). Surgeons reported significantly higher levels of task engagement on the stress measure than the other specialties (P=0.019), significantly higher intensity on physical demand (P < 0.001), and significantly lower intensity on the performance dimensions of the NASA-TLX than the other specialties (P=0.003). Surgeons reported the lowest intensity for temporal demand of all specialties, being significantly lower than either family physicians or neurologists (P=0.014). Family physicians reported the highest intensity on the time dimension of the SWAT, being significantly higher than either general internists or surgeons (P=0.008). Level of physician work intensity seems to be similar among specialties.

Characterization of stress-induced suppression of long-term potentiation in the hippocampal CA1 field of freely moving rats.

PubMed

Hirata, Riki; Togashi, Hiroko; Matsumoto, Machiko; Yamaguchi, Taku; Izumi, Takeshi; Yoshioka, Mitsuhiro

2008-08-21

Several lines of evidence have shown that exposure to stress impairs long-term potentiation (LTP) in the CA1 field of the hippocampus, but the detailed mechanisms for this effect remain to be clarified. The present study elucidated the synaptic mechanism of stress-induced LTP suppression in conscious, freely moving rats using electrophysiological approaches. Open field stress (i.e., novel environment stress) and elevated platform stress (i.e., uncontrollable stress) were employed. Basal synaptic transmission was significantly reduced during exposure to elevated platform stress but not during exposure to open field stress. LTP induction was blocked by elevated platform stress but not influenced by open field stress. Significant increases in serum corticosterone levels were observed in the elevated platform stress group compared with the open field stress group. Furthermore, LTP suppression induced by elevated platform stress was prevented by pretreatment with an anxiolytic drug diazepam (1 mg/kg, i.p.). These results suggest that stress-induced LTP suppression depends on the relative intensity of the stressor. The inhibitory synaptic response induced by an intense psychological stress, such as elevated platform stress, may be attributable to LTP impairment in the CA1 field of the hippocampus.

Fracture Growth Testing of Titanium 6AL-4V in AF-M315E

NASA Technical Reports Server (NTRS)

Sampson, Jeffrey W.; Martinez, Jonathan; McLean, Christopher

2015-01-01

The Green Propellant Infusion Mission (GPIM) will demonstrate the performance of AF-M315E monopropellant in orbit. Flight certification requires a safe-life analysis of the titanium alloy fuel tank to ensure inherent flaws will not cause failure during the design life. Material property inputs for this analysis require testing to determine the stress intensity factor for environmentally-assisted cracking (K (sub EAC)) of Ti 6Al-4V in combination with the AF-M315E monopropellant. Testing of single-edge notched specimens SE(B) representing the bulk tank membrane and weld material were performed in accordance with ASTM E1681. Specimens with fatigue pre-cracks were loaded into test fixtures so that the crack tips were exposed to the monopropellant at 50 degrees Centigrade for a duration of 1,000 hours. Specimens that did not fail during exposure were opened to inspect the crack surfaces for evidence of crack growth. The threshold stress intensity value, KEAC, is the highest applied stress intensity that produced neither a failure of the specimen during the exposure nor showed evidence of crack growth. The threshold stress intensity factor of the Ti 6Al-4V forged tank material when exposed to AF-M315E monopropellant was found to be at least 22.0 kilopounds per square inch. The stress intensity factor of the weld material was at least 31.3 kilopounds per square inch.

Measurement and interpretation of threshold stress intensity factors for steels in high-pressure hydrogen gas.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dadfarnia, Mohsen; Nibur, Kevin A.; San Marchi, Christopher W.

2010-07-01

Threshold stress intensity factors were measured in high-pressure hydrogen gas for a variety of low alloy ferritic steels using both constant crack opening displacement and rising crack opening displacement procedures. The sustained load cracking procedures are generally consistent with those in ASME Article KD-10 of Section VIII Division 3 of the Boiler and Pressure Vessel Code, which was recently published to guide design of high-pressure hydrogen vessels. Three definitions of threshold were established for the two test methods: K{sub THi}* is the maximum applied stress intensity factor for which no crack extension was observed under constant displacement; K{sub THa} ismore » the stress intensity factor at the arrest position for a crack that extended under constant displacement; and K{sub JH} is the stress intensity factor at the onset of crack extension under rising displacement. The apparent crack initiation threshold under constant displacement, K{sub THi}*, and the crack arrest threshold, K{sub THa}, were both found to be non-conservative due to the hydrogen exposure and crack-tip deformation histories associated with typical procedures for sustained-load cracking tests under constant displacement. In contrast, K{sub JH}, which is measured under concurrent rising displacement and hydrogen gas exposure, provides a more conservative hydrogen-assisted fracture threshold that is relevant to structural components in which sub-critical crack extension is driven by internal hydrogen gas pressure.« less

Measurement and interpretation of threshold stress intensity factors for steels in high-pressure hydrogen gas.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nibur, Kevin A.

2010-11-01

Threshold stress intensity factors were measured in high-pressure hydrogen gas for a variety of low alloy ferritic steels using both constant crack opening displacement and rising crack opening displacement procedures. The sustained load cracking procedures are generally consistent with those in ASME Article KD-10 of Section VIII Division 3 of the Boiler and Pressure Vessel Code, which was recently published to guide design of high-pressure hydrogen vessels. Three definitions of threshold were established for the two test methods: K{sub THi}* is the maximum applied stress intensity factor for which no crack extension was observed under constant displacement; K{sub THa} ismore » the stress intensity factor at the arrest position for a crack that extended under constant displacement; and K{sub JH} is the stress intensity factor at the onset of crack extension under rising displacement. The apparent crack initiation threshold under constant displacement, K{sub THi}*, and the crack arrest threshold, K{sub THa}, were both found to be non-conservative due to the hydrogen exposure and crack-tip deformation histories associated with typical procedures for sustained-load cracking tests under constant displacement. In contrast, K{sub JH}, which is measured under concurrent rising displacement and hydrogen gas exposure, provides a more conservative hydrogen-assisted fracture threshold that is relevant to structural components in which sub-critical crack extension is driven by internal hydrogen gas pressure.« less

Pubic Bone Osteomyelitis after Salvage High-Intensity Focused Ultrasound for Prostate Cancer

PubMed Central

Robison, Christopher M.; Gor, Ronak A.; Metro, Michael J.

2014-01-01

High-intensity focused ultrasound can be used for the primary treatment of prostate cancer and biochemical recurrence after radical prostatectomy or radiation. Complications of high-intensity focused ultrasound include urinary retention, urethral stenosis, stress incontinence, urinary tract infections, dysuria, impotence, and rarely, rectourethral or rectovesicular fistula. We describe a patient presenting with urinary retention, urinary tract infections and intermittent stress incontinence, later found to be associated with pubic bone osteomyelitis stemming from a prostatopubic fistula. PMID:24917777

Pseudoloma neurophilia infections in zebrafish Danio rerio: effects of stress on survival, growth, and reproduction.

USGS Publications Warehouse

Ramsay, J.M.; Watral, Virginia G.; Schreck, C.B.; Kent, M.L.

2009-01-01

Pseudoloma neurophilia (Microsporidia) is a common disease of zebrafish Danio rerio, including those used as research models. We conducted a study comprised of 4 separate experiments to determine the effects of husbandry stress on preexisting and experimental P. neurophilia infections and the subsequent effects on survival, infection onset and intensity, fish growth, and reproduction. In fish (AB strain) with preexisting infections, stress or feeding cortisol significantly increased mortality over 7 wk compared to no stress or cortisol treatment. In contrast, no mortality was observed in fish (TL strain) experimentally exposed to P. neurophilia over 10 wk. A third experiment involved experimental exposure of AB fish to P. neurophilia and exposure to crowding and handling stressors. No mortality was associated with P. neurophilia regardless of stress treatment over a period of 20 wk. However, the onset of infection occurred sooner in stress-treated fish. Stress significantly increased the mean intensity of infection (described as xenoma area/spinal cord area in histological sections) at Week 20 post-exposure (PE). In fish with preexisting infections, myositis was significantly greater in stressed and cortisol-treated fish than those not stressed. With experimental exposure of AB fish, stressed and infected groups weighed significantly less than the control group at Week 20 PE. Regarding fecundity, the number of larvae hatched at 5 d post fertilization was negatively associated with mean infection intensity among P. neurophilia-infected and stressed AB fish. These experiments are the first to show empirically that P. neurophilia can be associated with reduced weight and fecundity, and that stress can exacerbate the severity of the infection.

Responses to combined abiotic and biotic stress in tomato are governed by stress intensity and resistance mechanism

PubMed Central

Kissoudis, Christos; Sunarti, Sri; van de Wiel, Clemens; Visser, Richard G.F.; van der Linden, C. Gerard; Bai, Yuling

2016-01-01

Stress conditions in agricultural ecosystems can occur at variable intensities. Different resistance mechanisms against abiotic stress and pathogens are deployed by plants. Thus, it is important to examine plant responses to stress combinations under different scenarios. Here, we evaluated the effect of different levels of salt stress ranging from mild to severe (50, 100, and 150mM NaCl) on powdery mildew resistance and overall performance of tomato introgression lines with contrasting levels of partial resistance, as well as near-isogenic lines (NILs) carrying the resistance gene Ol-1 (associated with a slow hypersensitivity response; HR), ol-2 (an mlo mutant associated with papilla formation), and Ol-4 (an R gene associated with a fast HR). Powdery mildew resistance was affected by salt stress in a genotype- and stress intensity-dependent manner. In susceptible and partial resistant lines, increased susceptibility was observed under mild salt stress (50mM) which was accompanied by accelerated cell death-like senescence. In contrast, severe salt stress (150mM) reduced disease symptoms. Na+ and Cl− accumulation in the leaves was linearly related to the decreased pathogen symptoms under severe stress. In contrast, complete resistance mediated by ol-2 and Ol-4 was unaffected under all treatment combinations, and was associated with a decreased growth penalty. Increased susceptibility and senescence under combined stress in NIL-Ol-1 was associated with the induction of ethylene and jasmonic acid pathway genes and the cell wall invertase gene LIN6. These results highlight the significance of stress severity and resistance type on the plant’s performance under the combination of abiotic and biotic stress. PMID:27436279

Development of a screening measure of stress for parents of children hospitalised in a Paediatric Intensive Care Unit.

PubMed

Rodríguez-Rey, Rocío; Alonso-Tapia, Jesús

2016-08-01

Having a child admitted to intensive care is a highly stressful experience for parents; however there is a lack of screening instruments of parental stress in that context, which would be useful for both, research and clinical purposes. (1) To validate a brief measure of parental stress based on the Parental Stressor Scale: Paediatric Intensive Care Unit (PSS:PICU), (2) to study which environmental factors of the PICU are more stressful in a sample of Spanish parents, and (3) to study which variables are related to higher levels of stress among this group. 196 Spanish parents completed the Abbreviated PSS: PICU (A-PSS:PICU) and a general stress scale (the Perceived Stress Scale) upon their child's discharge to test the convergent validity of the tool. Three months later, they were assessed anxiety and depression using the Hospital Anxiety and Depression Scale, and posttraumatic stress with the Davidson Trauma Scale in order to test the predictive validity of the A-PSS:PICU. Two factors emerged from Confirmatory Factor Analyses, (1) stress due to child's condition and (2) stress related to PICU's staff. The A-PSS:PICU showed adequate reliability and convergent and predictive validity. The most stressful aspects were the behaviours and emotional responses of their child and the loss of their parental role. Age, gender, child's condition, length of admission, spiritual beliefs, and mechanical ventilation were associated to parental stress scores. The A-PSS:PICU is a reliable and valid measure. Parental stress should be screened during a child's PICU admission to identify parents at risk of post-discharge distress. Copyright © 2016 Australian College of Critical Care Nurses Ltd. Published by Elsevier Ltd. All rights reserved.

[Stress-induced hyperalgesia (SIH) as a consequence of emotional deprivation and psychosocial traumatization in childhood : Implications for the treatment of chronic pain].

PubMed

Egle, U T; Egloff, N; von Känel, R

2016-12-01

It is now widely recognized that in many chronic pain syndromes the intensity and severity of individually perceived pain does not correlate consistently with the degree of peripheral nervous system tissue damage or with the intensity of primary afferent or spinal nociceptive neurone activity. In particular, stress and anxiety exert modulatory influences on pain depending on the nature, duration and intensity of the stressor and developmental influences on the maturation of the stress as well as the pain system. In some chronic pain syndromes, e. g. fibromyalgia, TMD or somatoform disorders, no nociceptive or neuropathic input is detectable. We summarise the studies investigating the neural substrates and neurobiological mechanisms of stress-induced hyperalgesia (SIH) in animals and humans. The review provides new perspectives and challenges for the current and future treatment of chronic pain.

Post-traumatic stress disorder in intensive care unit patients.

PubMed

Caiuby, Andrea Vannini Santesso; Andreoli, Paola Bruno de Araújo; Andreoli, Sergio Baxter

2010-03-01

Post-traumatic stress disorder has been detected in patients after treatment in intensive care unit. The main goal of this study is to review the psychological aspects and therapeutic interventions on those patients after their treatment on intensive care unit. Thirty eight articles have been included. The prevalence of post-traumatic stress disorder has varied from 17% up to 30% and the incidence from 14% to 24%. The risk factors were: previous anxiety historic, depression or panic, having delusional traumatic memories (derived from psychic formations as dreams and delirium), belief effects, depressive behavior, stressing experiences and mechanical ventilation. High doses of opiates, symptoms caused by sedation or analgesia reduction and the use of lorazepam were related with the increase of delirium and delusional memory. The disorder sintomatology can be reduced with hydrocortisone administration, with daily sedation interruption. No other effectiveness psychological intervention study was found.

The effect of broken stringers on the stress intensity factor for a uniformly stiffened sheet containing a crack

NASA Technical Reports Server (NTRS)

Poe, C. C., Jr.

1973-01-01

A linear elastic stress analysis was made of a centrally cracked sheet stiffened by riveted, uniformly spaced and sized stringers. The stress intensity factor for the sheet and the load concentration factor for the most highly loaded stringer were determined for various numbers of broken stringers. A broken stringer causes the stress intensity factor to be very high when the crack tip is near the broken stringer, but causes little effect when the crack tip extends beyond several intact stringers. A broken stringer also causes an increase in the load concentration factor of the adjacent stringers. The calculated residual strengths and fatigue-crack-growth lives of a stiffened aluminum sheet with a broken stringer were only slightly less than a sheet with all intact stringers, and were still much higher than those of an unstiffened sheet.

Exercise intensity, redox homeostasis and inflammation in type 2 diabetes mellitus.

PubMed

Mallard, Alistair R; Hollekim-Strand, Siri Marte; Coombes, Jeff S; Ingul, Charlotte B

2017-10-01

To compare 12 weeks of exercise training at two intensities on oxidative stress, antioxidants and inflammatory biomarkers in patients with type 2 diabetes (T2D). Randomized trial. Thirty-six participants with T2D were randomized to complete either 12 weeks of treadmill based high-intensity interval training (HIIT) or moderate-intensity continuous training (MICT), followed by 40 weeks of home-based training at the same intensities. Plasma inflammation, oxidative stress and antioxidant biomarkers (total F2-isoprostanes, protein carbonyls, total antioxidant capacity, glutathione peroxidase activity, interleukin-10, interleukin-6, interleukin-8 and TNF-α) were measured at baseline, 12-weeks and 1-year. There were no significant changes (p>0.05) in oxidative stress and inflammation biomarkers from baseline to 12-weeks in either intervention. A decrease in total antioxidant capacity in the MICT group from baseline to 1-year by 0.05mmol/L (p=0.05) was observed. There was a significant difference (p<0.05) when groups were separated by sex with females in the MICT group having a 22.1% (p<0.05) decrease in protein carbonyls from baseline to 1-year. HIIT and MICT had no acute effect on oxidative stress and inflammatory biomarkers in patients with T2D. Copyright © 2017 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.

The mechanics of delamination in fiber-reinforced composite materials. II - The delamination behavior and fracture mechanics parameters

NASA Technical Reports Server (NTRS)

Wang, S. S.; Choi, I.

1983-01-01

Based on theories of laminate anisotropic elasticity and interlaminar fracture, the complete solution structure associated with a composite delamination is determined. Fracture mechanics parameters characterizing the interlaminar crack behavior are defined from asymptotic stress solutions for delaminations with different crack-tip deformation configurations. A numerical method employing singular finite elements is developed to study delaminations in fiber composites with any arbitrary combinations of lamination, material, geometric, and crack variables. The special finite elements include the exact delamination stress singularity in its formulation. The method is shown to be computationally accurate and efficient, and operationally simple. To illustrate the basic nature of composite delamination, solutions are shown for edge-delaminated (0/-0/-0/0) and (+ or - 0/+ or - 0/90/90 deg) graphite-epoxy systems under uniform axial extension. Three-dimensional crack-tip stress intensity factors, associated energy release rates, and delamination crack-closure are determined for each individual case. The basic mechanics and mechanisms of composite delamination are studied, and fundamental characteristics unique to recently proposed tests for interlaminar fracture toughness of fiber composite laminates are examined. Previously announced in STAR as N84-13222

A fracture mechanics study of the phase separating planar electrodes: Phase field modeling and analytical results

NASA Astrophysics Data System (ADS)

Haftbaradaran, H.; Maddahian, A.; Mossaiby, F.

2017-05-01

It is well known that phase separation could severely intensify mechanical degradation and expedite capacity fading in lithium-ion battery electrodes during electrochemical cycling. Experiments have frequently revealed that such degradation effects could be substantially mitigated via reducing the electrode feature size to the nanoscale. The purpose of this work is to present a fracture mechanics study of the phase separating planar electrodes. To this end, a phase field model is utilized to predict how phase separation affects evolution of the solute distribution and stress profile in a planar electrode. Behavior of the preexisting flaws in the electrode in response to the diffusion induced stresses is then examined via computing the time dependent stress intensity factor arising at the tip of flaws during both the insertion and extraction half-cycles. Further, adopting a sharp-interphase approximation of the system, a critical electrode thickness is derived below which the phase separating electrode becomes flaw tolerant. Numerical results of the phase field model are also compared against analytical predictions of the sharp-interphase model. The results are further discussed with reference to the available experiments in the literature. Finally, some of the limitations of the model are cautioned.

Transcriptomic Profiling of Soybean in Response to High-Intensity UV-B Irradiation Reveals Stress Defense Signaling

PubMed Central

Yoon, Min Young; Kim, Moon Young; Shim, Sangrae; Kim, Kyung Do; Ha, Jungmin; Shin, Jin Hee; Kang, Sungtaeg; Lee, Suk-Ha

2016-01-01

The depletion of the ozone layer in the stratosphere has led to a dramatic spike in ultraviolet B (UV-B) intensity and increased UV-B light levels. The direct absorption of high-intensity UV-B induces complex abiotic stresses in plants, including excessive light exposure, heat, and dehydration. However, UV-B stress signaling mechanisms in plants including soybean (Glycine max [L.]) remain poorly understood. Here, we surveyed the overall transcriptional responses of two soybean genotypes, UV-B-sensitive Cheongja 3 and UV-B-resistant Buseok, to continuous UV-B irradiation for 0 (control), 0.5, and 6 h using RNA-seq analysis. Homology analysis using UV-B-related genes from Arabidopsis thaliana revealed differentially expressed genes (DEGs) likely involved in UV-B stress responses. Functional classification of the DEGs showed that the categories of immune response, stress defense signaling, and reactive oxygen species (ROS) metabolism were over-represented. UV-B-resistant Buseok utilized phosphatidic acid-dependent signaling pathways (based on subsequent reactions of phospholipase C and diacylglycerol kinase) rather than phospholipase D in response to UV-B exposure at high fluence rates, and genes involved in its downstream pathways, such as ABA signaling, mitogen-activated protein kinase cascades, and ROS overproduction, were upregulated in this genotype. In addition, the DEGs for TIR-NBS-LRR and heat shock proteins are positively activated. These results suggest that defense mechanisms against UV-B stress at high fluence rates are separate from the photomorphogenic responses utilized by plants to adapt to low-level UV light. Our study provides valuable information for deep understanding of UV-B stress defense mechanisms and for the development of resistant soybean genotypes that survive under high-intensity UV-B stress. PMID:28066473

The interplay of stress and mowing disturbance for the intensity and importance of plant interactions in dry calcareous grasslands.

PubMed

Maalouf, Jean-Paul; Le Bagousse-Pinguet, Yoann; Marchand, Lilian; Touzard, Blaise; Michalet, Richard

2012-09-01

There is still debate regarding the direction and strength of plant interactions under intermediate to high levels of stress. Furthermore, little is known on how disturbance may interact with physical stress in unproductive environments, although recent theory and models have shown that this interplay may induce a collapse of plant interactions and diversity. The few studies assessing such questions have considered the intensity of biotic interactions but not their importance, although this latter concept has been shown to be very useful for understanding the role of interactions in plant communities. The objective of this study was to assess the interplay between stress and disturbance for plant interactions in dry calcareous grasslands. A field experiment was set up in the Dordogne, southern France, where the importance and intensity of biotic interactions undergone by four species were measured along a water stress gradient, and with and without mowing disturbance. The importance and intensity of interactions varied in a very similar way along treatments. Under undisturbed conditions, plant interactions switched from competition to neutral with increasing water stress for three of the four species, whereas the fourth species was not subject to any significant biotic interaction along the gradient. Responses to disturbance were more species-specific; for two species, competition disappeared with mowing in the wettest conditions, whereas for the two other species, competition switched to facilitation with mowing. Finally, there were no significant interactions for any species in the disturbed and driest conditions. At very high levels of stress, plant performances become too weak to allow either competition or facilitation and disturbance may accelerate the collapse of interactions in dry conditions. The results suggest that the importance and direction of interactions are more likely to be positively related in stressful environments.

Intensive skills week for military medical students increases technical proficiency, confidence, and skills to minimize negative stress.

PubMed

Mueller, Genevieve; Hunt, Bonnie; Wall, Van; Rush, Robert; Molof, Alan; Schoeff, Jonathan; Wedmore, Ian; Schmid, James; Laporta, Anthony

2012-01-01

The effects of stress induced cortisol on learning and memory is well documented in the literature.1-3 Memory and learning are enhanced at low levels while high levels are detrimental. Repetitive training in stressful situations enables management of the stress response4 as demonstrated by the high intensity training military members undergo to prepare for tactical situations. Appropriate management of one?s stress response is critical in the medical field, as the negative effects of stress can potentially hinder life-saving procedures and treatments. This also applies to physicians-in-training as they learn and practice triage, emergency medicine, and surgical skills prior to graduation. Rocky Vista University?s Military Medicine Honor?s Track (MMHT) held a week long high-intensity emergency medicine and surgical Intensive Skills Week (ISW), facilitated by military and university physicians, to advance students? skills and maximize training using the Human Worn Partial Surgical Task Simulator (Cut Suit). The short-term goal of the ISW was to overcome negative stress responses to increase confidence, technical and non-technical knowledge, and skill in surgery and emergency medicine in an effort to improve performance as third-year medical students. The long-term goal was to enhance performance and proficiency in residency and future medical practice. The metrics for the short-term goals were the focus of this pilot study. Results show an increase in confidence and decrease in perceived stress as well as statistically significant improvements in technical and non-technical skills and surgical instrumentation knowledge throughout the week. There is a correlative benefit to physician and non-physician military personnel, especially Special Operations Forces (SOF) medical personnel, from developing and implementing similar training programs when live tissue or cadaver models are unavailable or unfeasible. 2012.

Mixed-mode stress intensity factors for kink cracks with finite kink length loaded in tension and bending: application to dentin and enamel.

PubMed

Bechtle, Sabine; Fett, Theo; Rizzi, Gabriele; Habelitz, Stefan; Schneider, Gerold A

2010-05-01

Fracture toughness resistance curves describe a material's resistance against crack propagation. These curves are often used to characterize biomaterials like bone, nacre or dentin as these materials commonly exhibit a pronounced increase in fracture toughness with crack extension due to co-acting mechanisms such as crack bridging, crack deflection and microcracking. The knowledge of appropriate stress intensity factors which depend on the sample and crack geometry is essential for determining these curves. For the dental biomaterials enamel and dentin it was observed that, under bending and tensile loading, crack propagation occurs under certain constant angles to the initial notch direction during testing procedures used for fracture resistance curve determination. For this special crack geometry (a kink crack of finite length in a finite body) appropriate geometric function solutions are missing. Hence, we present in this study new mixed-mode stress intensity factors for kink cracks with finite kink length within samples of finite dimensions for two loading cases (tension and bending) which were derived from a combination of mixed-mode stress intensity factors of kink cracks with infinitely small kinks and of slant cracks. These results were further applied to determine the fracture resistance curves of enamel and dentin by testing single edge notched bending (SENB) specimens. It was found that kink cracks with finite kink length exhibit identical stress fields to slant cracks as soon as the kink length exceeds 0.15 times the initial straight crack or notch length. The use of stress intensity factor solutions for infinitely small kink cracks for the determination of dentin fracture resistance curves (as was done by other researchers) leads to an overestimation of dentin's fracture resistance of up to 30%. Copyright 2010 Elsevier Ltd. All rights reserved.

The effects of captivity survival training on mood, dissociation, PTSD symptoms, cognitive performance and stress hormones.

PubMed

Suurd Ralph, Cindy; Vartanian, Oshin; Lieberman, Harris R; Morgan, Charles A; Cheung, Bob

2017-07-01

In the Canadian Armed Forces (CAF), Conduct After Capture (CAC) training is a 4-day captivity survival course during which soldiers are exposed to increasing stress, and evaluated on their ability to accomplish military objectives. We hypothesized that: (a) compared to baseline, CAC training would cause significant, reversible perturbations in measures of psychological functioning and serum and salivary stress hormone levels relevant to models of stress hardiness and vulnerability; and (b) deviations from baseline would be maximal at the time point of most intense stress during training. CAF personnel were assessed at baseline, twice during training (immediately prior to a less challenging interrogation role-play scenario and again following another much more intense interrogation role-play scenario), and after completion of training. At each occasion, mood, fatigue, dissociation, PTSD symptoms, short-term and working memory, and salivary cortisol and dehydroepiandrosterone (DHEA) were assessed. As predicted, scores on all measures were degraded during CAC but recovered after completion of training, and almost all measures were most degraded at the more intense interrogation role-play scenario. Unexpectedly, memory performance was unaffected by training, suggesting that a short duration of intense stress might be insufficient for degrading it. Another unexpected finding was that mood assessed prior to training predicted successful completion of training, which bears important practical implications for increasing the success rate of training in similar environments. These results demonstrate that despite its relative brevity, CAC training nevertheless induces significant but reversible effects on psychological and physiological function-necessary preconditions for stress inoculation training. Copyright © 2017. Published by Elsevier B.V.

Experimental and Finite Element Modeling of Near-Threshold Fatigue Crack Growth for the K-Decreasing Test Method

NASA Technical Reports Server (NTRS)

Smith, Stephen W.; Seshadri, Banavara R.; Newman, John A.

2015-01-01

The experimental methods to determine near-threshold fatigue crack growth rate data are prescribed in ASTM standard E647. To produce near-threshold data at a constant stress ratio (R), the applied stress-intensity factor (K) is decreased as the crack grows based on a specified K-gradient. Consequently, as the fatigue crack growth rate threshold is approached and the crack tip opening displacement decreases, remote crack wake contact may occur due to the plastically deformed crack wake surfaces and shield the growing crack tip resulting in a reduced crack tip driving force and non-representative crack growth rate data. If such data are used to life a component, the evaluation could yield highly non-conservative predictions. Although this anomalous behavior has been shown to be affected by K-gradient, starting K level, residual stresses, environmental assisted cracking, specimen geometry, and material type, the specifications within the standard to avoid this effect are limited to a maximum fatigue crack growth rate and a suggestion for the K-gradient value. This paper provides parallel experimental and computational simulations for the K-decreasing method for two materials (an aluminum alloy, AA 2024-T3 and a titanium alloy, Ti 6-2-2-2-2) to aid in establishing clear understanding of appropriate testing requirements. These simulations investigate the effect of K-gradient, the maximum value of stress-intensity factor applied, and material type. A material independent term is developed to guide in the selection of appropriate test conditions for most engineering alloys. With the use of such a term, near-threshold fatigue crack growth rate tests can be performed at accelerated rates, near-threshold data can be acquired in days instead of weeks without having to establish testing criteria through trial and error, and these data can be acquired for most engineering materials, even those that are produced in relatively small product forms.

FASTRAN II - FATIGUE CRACK GROWTH STRUCTURAL ANALYSIS (UNIX VERSION)

NASA Technical Reports Server (NTRS)

Newman, J. C.

1994-01-01

Predictions of fatigue crack growth behavior can be made with the Fatigue Crack Growth Structural Analysis (FASTRAN II) computer program. As cyclic loads are applied to a selected crack configuration with an initial crack size, FASTRAN II predicts crack growth as a function of cyclic load history until either a desired crack size is reached or failure occurs. FASTRAN II is based on plasticity-induced crack-closure behavior of cracks in metallic materials and accounts for load-interaction effects, such as retardation and acceleration, under variable-amplitude loading. The closure model is based on the Dugdale model with modifications to allow plastically deformed material to be left along the crack surfaces as the crack grows. Plane stress and plane strain conditions, as well as conditions between these two, can be simulated in FASTRAN II by using a constraint factor on tensile yielding at the crack front to approximately account for three-dimensional stress states. FASTRAN II contains seventeen predefined crack configurations (standard laboratory fatigue crack growth rate specimens and many common crack configurations found in structures); and the user can define one additional crack configuration. The baseline crack growth rate properties (effective stress-intensity factor against crack growth rate) may be given in either equation or tabular form. For three-dimensional crack configurations, such as surface cracks or corner cracks at holes or notches, the fatigue crack growth rate properties may be different in the crack depth and crack length directions. Final failure of the cracked structure can be modelled with fracture toughness properties using either linear-elastic fracture mechanics (brittle materials), a two-parameter fracture criterion (brittle to ductile materials), or plastic collapse (extremely ductile materials). The crack configurations in FASTRAN II can be subjected to either constant-amplitude, variable-amplitude or spectrum loading. The applied loads may be either tensile or compressive. Several standardized aircraft flight-load histories, such as TWIST, Mini-TWIST, FALSTAFF, Inverted FALSTAFF, Felix and Gaussian, are included as options. FASTRAN II also includes two other methods that will help the user input spectrum load histories. The two methods are: (1) a list of stress points, and (2) a flight-by-flight history of stress points. Examples are provided in the user manual. Developed as a research program, FASTRAN II has successfully predicted crack growth in many metallic materials under various aircraft spectrum loading. A computer program DKEFF which is a part of the FASTRAN II package was also developed to analyze crack growth rate data from laboratory specimens to obtain the effective stress-intensity factor against crack growth rate relations used in FASTRAN II. FASTRAN II is written in standard FORTRAN 77. It has been successfully compiled and implemented on Sun4 series computers running SunOS and on IBM PC compatibles running MS-DOS using the Lahey F77L FORTRAN compiler. Sample input and output data are included with the FASTRAN II package. The UNIX version requires 660K of RAM for execution. The standard distribution medium for the UNIX version (LAR-14865) is a .25 inch streaming magnetic tape cartridge in UNIX tar format. It is also available on a 3.5 inch diskette in UNIX tar format. The standard distribution medium for the MS-DOS version (LAR-14944) is a 5.25 inch 360K MS-DOS format diskette. The contents of the diskette are compressed using the PKWARE archiving tools. The utility to unarchive the files, PKUNZIP.EXE, is included. The program was developed in 1984 and revised in 1992. Sun4 and SunOS are trademarks of Sun Microsystems, Inc. IBM PC is a trademark of International Business Machines Corp. MS-DOS is a trademark of Microsoft, Inc. F77L is a trademark of the Lahey Computer Systems, Inc. UNIX is a registered trademark of AT&T Bell Laboratories. PKWARE and PKUNZIP are trademarks of PKWare, Inc.

FASTRAN II - FATIGUE CRACK GROWTH STRUCTURAL ANALYSIS (IBM PC VERSION)

NASA Technical Reports Server (NTRS)

Newman, J. C.

1994-01-01

Predictions of fatigue crack growth behavior can be made with the Fatigue Crack Growth Structural Analysis (FASTRAN II) computer program. As cyclic loads are applied to a selected crack configuration with an initial crack size, FASTRAN II predicts crack growth as a function of cyclic load history until either a desired crack size is reached or failure occurs. FASTRAN II is based on plasticity-induced crack-closure behavior of cracks in metallic materials and accounts for load-interaction effects, such as retardation and acceleration, under variable-amplitude loading. The closure model is based on the Dugdale model with modifications to allow plastically deformed material to be left along the crack surfaces as the crack grows. Plane stress and plane strain conditions, as well as conditions between these two, can be simulated in FASTRAN II by using a constraint factor on tensile yielding at the crack front to approximately account for three-dimensional stress states. FASTRAN II contains seventeen predefined crack configurations (standard laboratory fatigue crack growth rate specimens and many common crack configurations found in structures); and the user can define one additional crack configuration. The baseline crack growth rate properties (effective stress-intensity factor against crack growth rate) may be given in either equation or tabular form. For three-dimensional crack configurations, such as surface cracks or corner cracks at holes or notches, the fatigue crack growth rate properties may be different in the crack depth and crack length directions. Final failure of the cracked structure can be modelled with fracture toughness properties using either linear-elastic fracture mechanics (brittle materials), a two-parameter fracture criterion (brittle to ductile materials), or plastic collapse (extremely ductile materials). The crack configurations in FASTRAN II can be subjected to either constant-amplitude, variable-amplitude or spectrum loading. The applied loads may be either tensile or compressive. Several standardized aircraft flight-load histories, such as TWIST, Mini-TWIST, FALSTAFF, Inverted FALSTAFF, Felix and Gaussian, are included as options. FASTRAN II also includes two other methods that will help the user input spectrum load histories. The two methods are: (1) a list of stress points, and (2) a flight-by-flight history of stress points. Examples are provided in the user manual. Developed as a research program, FASTRAN II has successfully predicted crack growth in many metallic materials under various aircraft spectrum loading. A computer program DKEFF which is a part of the FASTRAN II package was also developed to analyze crack growth rate data from laboratory specimens to obtain the effective stress-intensity factor against crack growth rate relations used in FASTRAN II. FASTRAN II is written in standard FORTRAN 77. It has been successfully compiled and implemented on Sun4 series computers running SunOS and on IBM PC compatibles running MS-DOS using the Lahey F77L FORTRAN compiler. Sample input and output data are included with the FASTRAN II package. The UNIX version requires 660K of RAM for execution. The standard distribution medium for the UNIX version (LAR-14865) is a .25 inch streaming magnetic tape cartridge in UNIX tar format. It is also available on a 3.5 inch diskette in UNIX tar format. The standard distribution medium for the MS-DOS version (LAR-14944) is a 5.25 inch 360K MS-DOS format diskette. The contents of the diskette are compressed using the PKWARE archiving tools. The utility to unarchive the files, PKUNZIP.EXE, is included. The program was developed in 1984 and revised in 1992. Sun4 and SunOS are trademarks of Sun Microsystems, Inc. IBM PC is a trademark of International Business Machines Corp. MS-DOS is a trademark of Microsoft, Inc. F77L is a trademark of the Lahey Computer Systems, Inc. UNIX is a registered trademark of AT&T Bell Laboratories. PKWARE and PKUNZIP are trademarks of PKWare, Inc.

Validation of Heart Rate Monitor Polar RS800 for Heart Rate Variability Analysis During Exercise.

PubMed

Hernando, David; Garatachea, Nuria; Almeida, Rute; Casajús, Jose A; Bailón, Raquel

2018-03-01

Hernando, D, Garatachea, N, Almeida, R, Casajús, JA, and Bailón, R. Validation of heart rate monitor Polar RS800 for heart rate variability analysis during exercise. J Strength Cond Res 32(3): 716-725, 2018-Heart rate variability (HRV) analysis during exercise is an interesting noninvasive tool to measure the cardiovascular response to the stress of exercise. Wearable heart rate monitors are a comfortable option to measure interbeat (RR) intervals while doing physical activities. It is necessary to evaluate the agreement between HRV parameters derived from the RR series recorded by wearable devices and those derived from an electrocardiogram (ECG) during dynamic exercise of low to high intensity. Twenty-three male volunteers performed an exercise stress test on a cycle ergometer. Subjects wore a Polar RS800 device, whereas ECG was also recorded simultaneously to extract the reference RR intervals. A time-frequency spectral analysis was performed to extract the instantaneous mean heart rate (HRM), and the power of low-frequency (PLF) and high-frequency (PHF) components, the latter centered on the respiratory frequency. Analysis was done in intervals of different exercise intensity based on oxygen consumption. Linear correlation, reliability, and agreement were computed in each interval. The agreement between the RR series obtained from the Polar device and from the ECG is high throughout the whole test although the shorter the RR is, the more differences there are. Both methods are interchangeable when analyzing HRV at rest. At high exercise intensity, HRM and PLF still presented a high correlation (ρ > 0.8) and excellent reliability and agreement indices (above 0.9). However, the PHF measurements from the Polar showed reliability and agreement coefficients around 0.5 or lower when the level of the exercise increases (for levels of O2 above 60%).

Oxidative stress does not influence local sweat rate during high-intensity exercise.

PubMed

Meade, Robert D; Fujii, Naoto; Poirier, Martin P; Boulay, Pierre; Sigal, Ronald J; Kenny, Glen P

2018-02-01

What is the central question of this study? We evaluated whether oxidative stress attenuates the contribution of nitric oxide to sweating during high-intensity exercise. What is the main finding and its importance? In contrast to our previous report of an oxidative stress-mediated reduction in nitric oxide-dependent cutaneous vasodilatation in this cohort during intense exercise, we demonstrated no influence of local ascorbate administration on the sweating response during moderate- (∼51% peak oxygen uptake) or high-intensity exercise (∼72% peak oxygen uptake). These new findings provide important mechanistic insight into how exercise-induced oxidative stress impacts sudomotor activity. Nitric oxide (NO)-dependent sweating is diminished during high- but not moderate-intensity exercise. We evaluated whether this impairment stems from increased oxidative stress during high-intensity exercise. On two separate days, 11 young (24 ± 4 years) men cycled in the heat (35°C) at a moderate [500 W; 52 ± 6% peak oxygen uptake (V̇O2 peak )] or high (700 W; 71 ± 5% V̇O2 peak ) rate of metabolic heat production. Each session included two 30 min exercise bouts separated by a 20 min recovery period. Local sweat rate was monitored at four forearm skin sites continuously perfused via intradermal microdialysis with the following: (i) lactated Ringer solution (Control); (ii) 10 mm ascorbate (Ascorbate; non-selective antioxidant); (iii) 10 mm N G -nitro-l-arginine methyl ester (l-NAME; NO synthase inhibitor); or (iv) 10 mm ascorbate plus 10 mm l-NAME (Ascorbate + l-NAME). During moderate exercise, sweat rate was attenuated at the l-NAME and Ascorbate + l-NAME sites (both ∼1.0 mg min -1  cm -2 ; all P < 0.05) but not at the Ascorbate site (∼1.1 mg min -1  cm -2 ; both P ≥ 0.28) in comparison to the Control site (∼1.1 mg min -1  cm -2 ). However, no differences were observed between treatment sites (∼1.4 mg min -1  cm -2 ; P = 0.75) during high-intensity exercise. We conclude that diminished NO-dependent sweating during intense exercise occurs independent of oxidative stress. © 2017 The Authors. Experimental Physiology © 2017 The Physiological Society.

Data intensive computing at Sandia.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wilson, Andrew T.

2010-09-01

Data-Intensive Computing is parallel computing where you design your algorithms and your software around efficient access and traversal of a data set; where hardware requirements are dictated by data size as much as by desired run times usually distilling compact results from massive data.

CT to Cone-beam CT Deformable Registration With Simultaneous Intensity Correction

PubMed Central

Zhen, Xin; Gu, Xuejun; Yan, Hao; Zhou, Linghong; Jia, Xun; Jiang, Steve B.

2012-01-01

Computed tomography (CT) to cone-beam computed tomography (CBCT) deformable image registration (DIR) is a crucial step in adaptive radiation therapy. Current intensity-based registration algorithms, such as demons, may fail in the context of CT-CBCT DIR because of inconsistent intensities between the two modalities. In this paper, we propose a variant of demons, called Deformation with Intensity Simultaneously Corrected (DISC), to deal with CT-CBCT DIR. DISC distinguishes itself from the original demons algorithm by performing an adaptive intensity correction step on the CBCT image at every iteration step of the demons registration. Specifically, the intensity correction of a voxel in CBCT is achieved by matching the first and the second moments of the voxel intensities inside a patch around the voxel with those on the CT image. It is expected that such a strategy can remove artifacts in the CBCT image, as well as ensuring the intensity consistency between the two modalities. DISC is implemented on computer graphics processing units (GPUs) in compute unified device architecture (CUDA) programming environment. The performance of DISC is evaluated on a simulated patient case and six clinical head-and-neck cancer patient data. It is found that DISC is robust against the CBCT artifacts and intensity inconsistency and significantly improves the registration accuracy when compared with the original demons. PMID:23032638

Posttraumatic Stress Disorder's Frequency and Intensity Ratings Are Associated with Factor Structure Differences in Military Veterans

ERIC Educational Resources Information Center

Elhai, Jon D.; Palmieri, Patrick A.; Biehn, Tracey L.; Frueh, B. Christopher; Magruder, Kathryn M.

2010-01-01

We examined possible differences in the factor structure of posttraumatic stress disorder (PTSD) on the basis of whether frequency or intensity symptom response formats were used to assess PTSD. Participants included 669 veterans recruited from an epidemiological study of four Veterans Affairs Medical Centers' primary care clinics in the…

Retinal flavoprotein autofluorescence as a measure of retinal health.

PubMed

Elner, Susan G; Elner, Victor M; Field, Matthew G; Park, Seung; Heckenlively, John R; Petty, Howard R

2008-01-01

To establish that increased autofluorescence of mitochondrial flavoproteins, an indicator of mitochondrial oxidative stress, correlates with retinal cell dysfunction. Retinal flavoprotein autofluorescence (FA) was imaged in humans with a fundus camera modified with 467DF8-nm excitation and 535-nm emission filters and a back-illuminated, electron-multiplying, charge-coupled device camera interfaced with a computer equipped with customized image capture software. Multiple digital images, centered on the fovea, were obtained from each eye. Histograms of pixel intensities in grayscale units were analyzed for average intensity and average curve width. Adults with diabetes mellitus, age-related macular degeneration (ARMD), central serous retinopathy, and retinal dystrophies, as well as healthy control volunteers, were imaged. Monolayers of cultured human retinal pigment epithelial (HRPE) cells, HRPE cells exposed to sublethal doses of H2O2, and HRPE cells exposed to H2O2 in the presence of antioxidants were imaged for FA using fluorescent photomicroscopy. Control patients demonstrated low levels of retinal FA, which increased progressively with age. Diabetics without visible retinopathy demonstrated increased FA levels compared to control volunteers (P < .001). Diabetics with retinopathy demonstrated significantly higher FA values than those without retinopathy (P < .04). Patients with ARMD, central serous retinopathy, or retinal dystrophies also demonstrated significantly increased FA. Compared to control RPE cells, cells oxidatively stressed with H2O2 had significantly elevated FA (P < .05), which was prevented by antioxidants (P < .05). Retinal FA is significantly increased with age and diseases known to be mediated by oxidative stress. Retinal FA imaging may provide a novel, noninvasive method of assessing retinal health and retinal dysfunction prior to retinal cell death.

Stress Analysis and Fracture in Nanolaminate Composites

NASA Technical Reports Server (NTRS)

Chamis, Christos C.

2008-01-01

A stress analysis is performed on a nanolaminate subjected to bending. A composite mechanics computer code that is based on constituent properties and nanoelement formulation is used to evaluate the nanolaminate stresses. The results indicate that the computer code is sufficient for the analysis. The results also show that when a stress concentration is present, the nanolaminate stresses exceed their corresponding matrix-dominated strengths and the nanofiber fracture strength.

HOLEGAGE 1.0 - Strain-Gauge Drilling Analysis Program

NASA Technical Reports Server (NTRS)

Hampton, Roy V.

1992-01-01

Interior stresses inferred from changes in surface strains as hole is drilled. Computes stresses using strain data from each drilled-hole depth layer. Planar stresses computed in three ways: least-squares fit for linear variation with depth, integral method to give incremental stress data for each layer, and/or linear fit to integral data. Written in FORTRAN 77.

Stresses In And Near A Bend In A Thin-Walled Duct

NASA Technical Reports Server (NTRS)

Min, J. B.; Aggarwal, P. K.

1995-01-01

Report describes computational study of distributions of stresses in and near 90 degrees bend in thin-walled duct subject to various applied loads. Purpose of study to help satisfy need for more accurate knowledge of local concentrations of stresses caused by loads: such knowledge makes possible to design light-weight ducts to survive reasonably foreseeable operating conditions with some degree of reliability. Also guides selection of locations for mounting strain gauges to measure local stresses for comparison with computed values, contributing to refinement of theoretical concepts and computational techniques.

The association between pregame snacks and exercise intensity, stress, and fatigue in children.

PubMed

Sacheck, Jennifer M; Rasmussen, Helen M; Hall, Meghan M; Kafka, Tamar; Blumberg, Jeffrey B; Economos, Christina D

2014-05-01

To investigate the association between pregame snacks varying in macronutrient content and exercise intensity, physiological stress, and fatigue in young soccer players. One hour before a 50-min soccer game, children (n = 79; 9.1 ± 0.8 y) were randomly assigned to consume a raisin-, peanut-butter-, or cereal-based snack. Body mass index, blood glucose, and salivary measures of stress (cortisol and immunoglobulin A-IgA) were measured pre- and post-game. Exercise intensity was measured by accelerometry. Self-administered questionnaires were used to assess diet quality and fatigue. Analysis of covariance was used to examine the relationship between pregame snacks and biochemical outcomes. Postgame glucose and cortisol increased [12.9 ± 21.3 mg/dL (p < .001) and 0.04 ± 0.10 μg/dL (p < .05), respectively] and IgA decreased (-2.3 ± 9.6 μg/mL; p < .001) from pregame values. The pregame snack was not associated with exercise intensity or post-game outcome; however, children consuming the cereal-based (high-sugar and high-glycemic index (GI)) snack exercised more intensely than the 2 lower-GI snack groups (p < .05). Children who consumed the high-sugar, high-GI snack also reported more symptoms of fatigue (p < .05). A high-sugar, high-GI pregame snack was associated with exercise intensity and fatigue but not changes in blood sugar or stress biomarkers following a soccer game in children.

On the measurement of the crack tip stress field as a means of determining Delta K(sub eff) under conditions of fatigue crack closure

NASA Technical Reports Server (NTRS)

Wallhead, Ian R.; Edwards, Lyndon; Poole, Peter

1994-01-01

The optical method of caustics has been successfully extended to enable stress intensity factors as low as 1MPa square root of m to be determined accurately for central fatigue cracks in 2024-T3 aluminium alloy test panels. The feasibility of using this technique to study crack closure, and to determine the effective stress intensity factor range, Delta K(sub eff), has been investigated. Comparisons have been made between the measured values of stress intensity factor, K(sub caus), and corresponding theoretical values, K(sub theo), for a range of fatigue cracks grown under different loading conditions. The values of K(sub caus) and K(sub theo) were in good agreement at maximum stress, where the cracks are fully open, while K(sub caus) exceeded K(sub theo) at minimum stress, due to crack closure. However, the levels of crack closure and values of Delta K(sub eff) obtained could not account for the variations of crack growth rate with loading conditions. It is concluded that the values of Delta K(sub eff), based on caustic measurements in a 1/square root of r stress field well outside the plastic zone, do not fully reflect local conditions which control crack tip behavior.

The Effects of Aromatherapy on Intensive Care Unit Patients' Stress and Sleep Quality: A Nonrandomised Controlled Trial

PubMed Central

Cho, Eun Hee; Lee, Mi-Young

2017-01-01

Background Stress has both physiological and psychological effects and can negatively impact patients' treatment and recovery. We examined whether the aromatherapy alleviated patients' stress and improved their sleep quality and provided data that can be utilized in clinical settings. Methods This was a nonrandomised controlled experimental study. Participants included lucid adult patients who were admitted to the intensive care unit and had spent more than two nights there. The experimental treatment required participants to engage in deep breathing with essential oils as part of the aromatherapy. The control group was instructed to go to sleep without receiving the lavender aroma oil. Results The experimental group and control group showed a significant difference in perceived stress (F = 60.11, p < .001), objective stress index (F = 25.65, p < .001), systolic blood pressure (F = 9.09, p < .001), diastolic blood pressure (F = 2.47, p = .046), heart rate (F = 5.71, p < .001), and sleep quality (F = 109.46, p < .001). Conclusions The results revealed that aromatherapy alleviated stress and improved sleep quality in intensive care unit patients after 2 days of the experimental treatment. These results demonstrate that aromatherapy affects stress and sleep quality, thus indicating its value in nursing interventions. This trial is registered with KCT0002344. PMID:29375641

Aqueous stress-corrosion cracking of high-toughness D6AC steel

NASA Technical Reports Server (NTRS)

Gilbreath, W. P.; Adamson, M. J.

1976-01-01

The crack growth behavior of D6AC steel as a function of stress intensity, stress and corrosion history, and test technique, under sustained load in filtered natural seawater, 3.3 per cent sodium chloride solution, and distilled water, was investigated. Reported investigations of D6AC were considered in terms of the present study with emphasis on thermal treatment, specimen configuration, fracture toughness, crack-growth rates, initiation period, and threshold. Both threshold and growth kinetics were found to be relatively insensitive to these test parameters. The apparent incubation period was dependent on technique, both detection sensitivity and precracking stress intensity level.

NICU admissions and maternal stress levels.

PubMed

Chourasia, Nitish; Surianarayanan, Pushkala; Adhisivam, B; Vishnu Bhat, B

2013-05-01

To determine the stress levels among mothers of babies admitted in Neonatal Intensive Care Unit (NICU) and to identify demographic parameters that influence their stress levels. Stress levels were assessed using Parental Stressor Scale: Neonatal Intensive Care Unit (PSS: NICU) questionnaire among 100 NICU mothers by doctors between 6 and 8 d of admission. Maternal stress was quantified using Likert scale as low (1-2.9), medium (3-3.9) and high (4-5). The data was analyzed using SPSS Ver.16. The mean scores for the subscales sights and sounds, looks and behaviour and alteration in the parental role were 2.55, 4.1 and 4.12 respectively. Increased maternal age, prematurity of baby, longer NICU stay and inability to directly breastfeed the baby were associated with higher stress levels. NICU mothers are under significant stress and appropriate counseling targeted towards specific stressors is required.

Paraheliotropism can protect water-stressed bean (Phaseolus vulgaris L.) plants against photoinhibition.

PubMed

Pastenes, Claudio; Porter, Victor; Baginsky, Cecilia; Horton, Peter; González, Javiera

2004-12-01

In order to estimate the importance of leaf movements on photosynthesis in well-watered and water-stressed field grown bean cultivars (Arroz Tuscola (AT), Orfeo INIA (OI), Bayos Titan (BT), and Hallados Dorado (HD)), CO2 assimilation, leaf temperature, and capacity for the maximum quantum yield recovery, measured as Fv/Fm, were assessed. Leaf water potential was lower in water-stressed compared to control plants throughout the day. Water status determined a decrease in the CO2 assimilation and stomatal conductance as light intensity and temperature increased up to maximal intensities at midday. Both parameters were lower in stressed compared to control plants. Even though high light intensity and water-stress induced stomatal closure is regarded as a photoinhibitory condition, the recovery of variable to maximal fluorescence (Fv/Fm) after 30min of darkness was nearly constant in both water regimes. In fact, higher values were observed in OI and AT when under stress. Photochemical and non-photochemical fluorescence quenching resulted in minor changes during the day and were similar between watered and stressed plants. It is concluded that paraheliotropism, present in the four bean cultivars, efficiently protects stressed plants from photoinhibition in the field and helps maintain leaf temperatures far below the ambient temperatures, however, it may also be responsible for low CO2 assimilation rates in watered plants.

[A study of relationship between occupational stress and diseases in secondary school teachers].

PubMed

Zhang, Yang; Zhu, Tao; Tang, Liu; Li, Jian; Lan, Yajia

2015-10-01

To analyze the relationship between occupational stress and diseases in secondary school teachers in a city of Sichuan Province, and to provide a basis for the evaluation of the long-term effects of occupational stress in teachers. With secondary school teachers as the target population, the stratified cluster sampling was adopted to conduct three studies among 780, 119, and 689 secondary school teachers in a city of Sichuan Province in 1999, 2005, and 2009, respectively. The Occupational Stress Inventory-Revised Edition (OSI-R) and working ability index (WAI) were used to investigate occupational stress and diseases in secondary school teachers. The variation of occupational stress in secondary school teachers was compared between different periods and the relationship between the intensity of stress and diseases was evaluated, on the basis of which the variation of the relationship over time was analyzed. There were significant differences in occupational stress in secondary school teachers between different periods (P<0.05). The incidence rates of medium and high physiological stress and psychological stress were significantly higher in 2009 than in 1999 (P<0.05). Compared with the year of 1999, the intensity of occupational stress in 2009 changed with cardiovascular, respiratory, and mental diseases. The incidence of abnormal psychological stress was a risk factor for all chronic, respiratory, and mental diseases (OR: 1.88, 2.25, and 5.91). The time dependence of odds ratio was only found in the risk of respiratory diseases: occupational stress resulted in a significant increase in the risk of respiratory diseases over time (P<0.05). Physiological stress was a risk factor for mental diseases (OR=2.31). The intensity of occupational stress in secondary school teachers changes over time. Occupational stress elevates the risks of certain diseases and has a time-dependent effect on the risk of respiratory diseases. Occupational stress in secondary school teachers needs more attention and effective prevention.

Relationships between stress, negative emotions, resilience, and smoking: Testing a moderated mediation model

PubMed Central

Wang, Yan; Chen, Xinguang; Gong, Jie; Yan, Yaqiong

2016-01-01

Objective More effective tobacco prevention and cessation programs require in-depth understanding of the mechanism by which multiple factors interact with each other to affect smoking behaviors. Stress has long been recognized as a risk factor for smoking. However, the underlying mediation and moderation mechanisms are far from clear. The purpose of this study was to examine the role of negative emotions in mediating the link between stress and smoking and whether this indirect link was modified by resilience. Methods Survey data were collected using audio computer assisted self-interview (ACASI) from a large random sample of urban residents (n=1249, mean age = 35.1, 45.3% male) in Wuhan, China. Perceived stress, negative emotions (anxiety, depression), resilience were measured with reliable instruments also validated in China. Self-reported smoking was validated with exhaled carbon monoxide. Results Mediation analysis indicated that two negative emotions fully mediated the link between stress and intensity of smoking (assessed by number of cigarettes smoked per day, effect = .082 for anxiety and .083 for depression) and nicotine dependence (assessed by DSM-IV standard, effect = .134 for anxiety and .207 for depression). Moderated mediation analysis demonstrated that the mediation effects of negative emotions were negatively associated with resilience. Conclusions Results suggest resilience interacts with stress and negative emotions to affect the risk of tobacco use and nicotine dependence among Chinese adults. Further research with longitudinal data is needed to verify the findings of this study and to estimate the effect size of resilience in tobacco intervention and cessation programs. PMID:26894428

Analysis of corner cracks at hole by a 3-D weight function method with stresses from finite element method

NASA Technical Reports Server (NTRS)

Zhao, W.; Newman, J. C., Jr.; Sutton, M. A.; Wu, X. R.; Shivakumar, K. N.

1995-01-01

Stress intensity factors for quarter-elliptical corner cracks emanating from a circular hole are determined using a 3-D weight function method combined with a 3-D finite element method. The 3-D finite element method is used to analyze uncracked configuration and provide stress distribution in the region where crack is to occur. Using this stress distribution as input, the 3-D weight function method is used to determine stress intensity factors. Three different loading conditions, i.e. remote tension, remote bending and wedge loading, are considered for a wide range in geometrical parameters. The significance in using 3-D uncracked stress distribution and the difference between single and double corner cracks are studied. Typical crack opening displacements are also provided. Comparisons are made with solutions available in the literature.

Stress management on underlying GaN-based epitaxial films: A new vision for achieving high-performance LEDs on Si substrates

NASA Astrophysics Data System (ADS)

Lin, Zhiting; Wang, Haiyan; Lin, Yunhao; Wang, Wenliang; Li, Guoqiang

2017-11-01

High-performance blue GaN-based light-emitting diodes (LEDs) on Si substrates have been achieved by applying a suitable tensile stress in the underlying n-GaN. It is demonstrated by simulation that tensile stress in the underlying n-GaN alleviates the negative effect from polarization electric fields on multiple quantum wells but an excessively large tensile stress severely bends the band profile of the electron blocking layer, resulting in carrier loss and large electric resistance. A medium level of tensile stress, which ranges from 4 to 5 GPa, can maximally improve the luminous intensity and decrease forward voltage of LEDs on Si substrates. The LED with the optimal tensile stress shows the largest simulated luminous intensity and the smallest simulated voltage at 35 A/cm2. Compared to the LEDs with a compressive stress of -3 GPa and a large tensile stress of 8 GPa, the improvement of luminous intensity can reach 102% and 28.34%, respectively. Subsequent experimental results provide evidence of the superiority of applying tensile stress in n-GaN. The experimental light output power of the LEDs with a tensile stress of 1.03 GPa is 528 mW, achieving a significant improvement of 19.4% at 35 A/cm2 in comparison to the reference LED with a compressive stress of -0.63 GPa. The forward voltage of this LED is 3.08 V, which is smaller than 3.11 V for the reference LED. This methodology of stress management on underlying GaN-based epitaxial films shows a bright feature for achieving high-performance LED devices on Si substrates.

Trivariate characteristics of intensity fluctuations for heavily saturated optical systems.

PubMed

Das, Biman; Drake, Eli; Jack, John

2004-02-01

Trivariate cumulants of intensity fluctuations have been computed starting from a trivariate intensity probability distribution function, which rests on the assumption that the variation of intensity has a maximum entropy distribution with the constraint that the total intensity is constant. The assumption holds for optical systems such as a thin, long, mirrorless gas laser amplifier where under heavy gain saturation the total output approaches a constant intensity, although intensity of any mode fluctuates rapidly over the average intensity. The relations between trivariate cumulants and central moments that were needed for the computation of trivariate cumulants were derived. The results of the computation show that the cumulants have characteristic values that depend on the number of interacting modes in the system. The cumulant values approach zero when the number of modes is infinite, as expected. The results will be useful for comparison with the experimental triavariate statistics of heavily saturated optical systems such as the output from a thin, long, bidirectional gas laser amplifier.

Application of a linked stress release model in Corinth Gulf and Central Ionian Islands (Greece)

NASA Astrophysics Data System (ADS)

Mangira, Ourania; Vasiliadis, Georgios; Papadimitriou, Eleftheria

2017-06-01

Spatio-temporal stress changes and interactions between adjacent fault segments consist of the most important component in seismic hazard assessment, as they can alter the occurrence probability of strong earthquake onto these segments. The investigation of the interactions between adjacent areas by means of the linked stress release model is attempted for moderate earthquakes ( M ≥ 5.2) in the Corinth Gulf and the Central Ionian Islands (Greece). The study areas were divided in two subareas, based on seismotectonic criteria. The seismicity of each subarea is investigated by means of a stochastic point process and its behavior is determined by the conditional intensity function, which usually gets an exponential form. A conditional intensity function of Weibull form is used for identifying the most appropriate among the models (simple, independent and linked stress release model) for the interpretation of the earthquake generation process. The appropriateness of the models was decided after evaluation via the Akaike information criterion. Despite the fact that the curves of the conditional intensity functions exhibit similar behavior, the use of the exponential-type conditional intensity function seems to fit better the data.

Memory in Posttraumatic Stress Disorder: Properties of voluntary and involuntary, traumatic and non-traumatic autobiographical memories in people with and without PTSD symptoms

PubMed Central

Rubin, David C.; Boals, Adriel; Berntsen, Dorthe

2008-01-01

One-hundred-fifteen undergraduates screened for PTSD symptom severity rated 15 word-cued memories and their 3 most-negatively-stressful, 3 most-positive, and 7 most-important events, and completed tests of personality and depression. Eighty-nine also recorded involuntary memories online for one week. We compared 1) memories of stressful to control events and 2) involuntary to voluntary memories 3) in people high versus low in PTSD symptom severity, providing the first three-way comparisons needed to test existing theories. Stressful versus control memories in all participants and high PTSD symptom severity in all memories produced memories with more emotional intensity and more frequent voluntary and involuntary retrieval, but not more fragmentation. Involuntary memories had more emotional intensity and less centrality to the life story than voluntary memories. Meeting the diagnostic criteria for traumatic events had no effect, the emotional responses to events did. Correlations among measures were replicated and the Negative-Intensity factor of the Affect Intensity Measure correlated with PTSD symptom severity in 533 undergraduates. No special trauma mechanisms were needed to account for the results, which are summarized by the Autobiographical Memory Theory of PTSD. PMID:18999355

Creep crack growth by grain boundary cavitation under monotonic and cyclic loading

NASA Astrophysics Data System (ADS)

Wen, Jian-Feng; Srivastava, Ankit; Benzerga, Amine; Tu, Shan-Tung; Needleman, Alan

2017-11-01

Plane strain finite deformation finite element calculations of mode I crack growth under small scale creep conditions are carried out. Attention is confined to isothermal conditions and two time histories of the applied stress intensity factor: (i) a monononic increase to a plateau value subsequently held fixed; and (ii) a cyclic time variation. The crack growth calculations are based on a micromechanics constitutive relation that couples creep deformation and damage due to grain boundary cavitation. Grain boundary cavitation, with cavity growth due to both creep and diffusion, is taken as the sole failure mechanism contributing to crack growth. The influence on the crack growth rate of loading history parameters, such as the magnitude of the applied stress intensity factor, the ratio of the applied minimum to maximum stress intensity factors, the loading rate, the hold time and the cyclic loading frequency, are explored. The crack growth rate under cyclic loading conditions is found to be greater than under monotonic creep loading with the plateau applied stress intensity factor equal to its maximum value under cyclic loading conditions. Several features of the crack growth behavior observed in creep-fatigue tests naturally emerge, for example, a Paris law type relation is obtained for cyclic loading.

Internal and edge cracks in a plate of finite width under bending

NASA Technical Reports Server (NTRS)

Boduroglu, H.; Erdogan, F.

1983-01-01

In this paper the title problem is studied by using Reissner's transverse shear theory. The main purpose of the paper is to investigate the effect of stress-free boundaries on the stress intensity factors in plates under bending. Among the results found particularly interesting are those relating to the limiting cases of the crack geometries. The numerical results are given for a single internal crack, two collinear cracks, and two edge cracks. Also studied is the effect of Poisson's ratio on the stress intensity factors.

A note on the effect of bending stiffness of stringers attached to a plate with a crack

NASA Technical Reports Server (NTRS)

Arin, K.

1974-01-01

An infinite stringer partially bonded to a plate through a layer of adhesive is considered. The stringer had bending as well as longitudinal stiffness. The effect of the stringer's bending rigidity on the stress intensity factor at the tip of the crack is illustrated. Shear stress distribution between the plate and the stringer and the stress intensity factors are obtained from the solution of a system of Fredholm integral equations. The continuity of displacements along the line of bond is represented by the equations.

Pain sensitivity mediates the relationship between stress and headache intensity in chronic tension-type headache

PubMed Central

Cathcart, Stuart; Bhullar, Navjot; Immink, Maarten; Della Vedova, Chris; Hayball, John

2012-01-01

BACKGROUND: A central model for chronic tension-type headache (CTH) posits that stress contributes to headache, in part, by aggravating existing hyperalgesia in CTH sufferers. The prediction from this model that pain sensitivity mediates the relationship between stress and headache activity has not yet been examined. OBJECTIVE: To determine whether pain sensitivity mediates the relationship between stress and prospective headache activity in CTH sufferers. METHOD: Self-reported stress, pain sensitivity and prospective headache activity were measured in 53 CTH sufferers recruited from the general population. Pain sensitivity was modelled as a mediator between stress and headache activity, and tested using a nonparametric bootstrap analysis. RESULTS: Pain sensitivity significantly mediated the relationship between stress and headache intensity. CONCLUSIONS: The results of the present study support the central model for CTH, which posits that stress contributes to headache, in part, by aggravating existing hyperalgesia in CTH sufferers. Implications for the mechanisms and treatment of CTH are discussed. PMID:23248808

Very preterm birth: maternal experiences of the neonatal intensive care environment.

PubMed

Woodward, L J; Bora, S; Clark, C A C; Montgomery-Hönger, A; Pritchard, V E; Spencer, C; Austin, N C

2014-07-01

Examine sources, predictors and child outcomes associated with neonatal intensive care unit (NICU)-related stress for mothers of infants born very preterm (VPT). Participants were 133 mothers of VPT infants admitted to a regional level-III NICU. At term equivalent, mothers completed the Parental Stressor Scale: NICU and were interviewed about their psychological well-being and family circumstances. Infant clinical data were also collected. At corrected age 4 years, 49 children were assessed for cognition, language and socio-emotional development. Mothers reported moderate to low stress, with parental role alteration considered most stressful and parent-staff communications least stressful. Predictors of overall stress included maternal educational underachievement, stressful life events, postnatal depression and infant unsettled-irregular behavior. NICU-related stress was associated with child anxiety and poorer language development. Parental well-being is an important focus of care in the neonatal setting. Strategies are needed to optimize early engagement and reduce stress levels to assist improved child outcomes.

Design of Test Articles and Monitoring System for the Characterization of HIRF Effects on a Fault-Tolerant Computer Communication System

NASA Technical Reports Server (NTRS)

Torres-Pomales, Wilfredo; Malekpour, Mahyar R.; Miner, Paul S.; Koppen, Sandra V.

2008-01-01

This report describes the design of the test articles and monitoring systems developed to characterize the response of a fault-tolerant computer communication system when stressed beyond the theoretical limits for guaranteed correct performance. A high-intensity radiated electromagnetic field (HIRF) environment was selected as the means of injecting faults, as such environments are known to have the potential to cause arbitrary and coincident common-mode fault manifestations that can overwhelm redundancy management mechanisms. The monitors generate stimuli for the systems-under-test (SUTs) and collect data in real-time on the internal state and the response at the external interfaces. A real-time health assessment capability was developed to support the automation of the test. A detailed description of the nature and structure of the collected data is included. The goal of the report is to provide insight into the design and operation of these systems, and to serve as a reference document for use in post-test analyses.

Determination of stresses in gas-turbine disks subjected to plastic flow and creep

NASA Technical Reports Server (NTRS)

Millenson, M B; Manson, S S

1948-01-01

A finite-difference method previously presented for computing elastic stresses in rotating disks is extended to include the computation of the disk stresses when plastic flow and creep are considered. A finite-difference method is employed to eliminate numerical integration and to permit nontechnical personnel to make the calculations with a minimum of engineering supervision. Illustrative examples are included to facilitate explanation of the procedure by carrying out the computations on a typical gas-turbine disk through a complete running cycle. The results of the numerical examples presented indicate that plastic flow markedly alters the elastic-stress distribution.

Simulation Analysis of the Mutual Influence of the Stress Intensity Factor on the Multiple Blisters Caused by Hydrogen Induced Damage

NASA Astrophysics Data System (ADS)

Ji, Congwei; Zhang, Shaojie; Wang, Hehui

2018-03-01

Hydrogen blisters are taken as the research object by using the finite element software ABAQUS. The stress intensity factors of blister cracks are numerically calculated at varying depths and different edge distances for established three-dimensional finite element models of single-blister and double-blisters, respectively. The mutual influence of the stress intensity factors of the multiple blisters is obtained. It shows that the blister crack is easier to expand when the crack is closer to inner wall of the cylinder. What’s more, the crack growth rate increases firstly and then decreases as the increasing of the distance between two blisters cracks. The investigated result is of great reference value for predicting the trend of blister crack growth.

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

NASA Technical Reports Server (NTRS)

Mcgowan, J. J.; Smith, C. W.

1974-01-01

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.

Higher-order ice-sheet modelling accelerated by multigrid on graphics cards

NASA Astrophysics Data System (ADS)

Brædstrup, Christian; Egholm, David

2013-04-01

Higher-order ice flow modelling is a very computer intensive process owing primarily to the nonlinear influence of the horizontal stress coupling. When applied for simulating long-term glacial landscape evolution, the ice-sheet models must consider very long time series, while both high temporal and spatial resolution is needed to resolve small effects. The use of higher-order and full stokes models have therefore seen very limited usage in this field. However, recent advances in graphics card (GPU) technology for high performance computing have proven extremely efficient in accelerating many large-scale scientific computations. The general purpose GPU (GPGPU) technology is cheap, has a low power consumption and fits into a normal desktop computer. It could therefore provide a powerful tool for many glaciologists working on ice flow models. Our current research focuses on utilising the GPU as a tool in ice-sheet and glacier modelling. To this extent we have implemented the Integrated Second-Order Shallow Ice Approximation (iSOSIA) equations on the device using the finite difference method. To accelerate the computations, the GPU solver uses a non-linear Red-Black Gauss-Seidel iterator coupled with a Full Approximation Scheme (FAS) multigrid setup to further aid convergence. The GPU finite difference implementation provides the inherent parallelization that scales from hundreds to several thousands of cores on newer cards. We demonstrate the efficiency of the GPU multigrid solver using benchmark experiments.

A test procedure for determining the influence of stress ratio on fatigue crack growth

NASA Technical Reports Server (NTRS)

Fitzgerald, J. H.; Wei, R. P.

1974-01-01

A test procedure is outlined by which the rate of fatigue crack growth over a range of stress ratios and stress intensities can be determined expeditiously using a small number of specimens. This procedure was developed to avoid or circumvent the effects of load interactions on fatigue crack growth, and was used to develop data on a mill annealed Ti-6Al-4V alloy plate. Experimental data suggest that the rates of fatigue crack growth among the various stress ratios may be correlated in terms of an effective stress intensity range at given values of K max. This procedure is not to be used, however, for determining the corrosion fatigue crack growth characteristics of alloys when nonsteady-state effects are significant.

Axisymmetric elastodynamic response from normal and radial impact of layered composites with embedded penny-shaped cracks

NASA Technical Reports Server (NTRS)

Sih, G. C.; Chen, E. P.

1980-01-01

A method is developed for the dynamic stress analysis of a layered composite containing an embedded penny-shaped crack and subjected to normal and radial impact. Quantitatively, the time-dependent stresses near the crack border can be described by the dynamic stress intensity factors. Their magnitude depends on time, on the material properties of the composite and on the relative size of the crack compared to the composite local geometry. Results obtained show that, for the same material properties and geometry of the composite, the dynamic stress intensity factors for an embedded (penny-shaped) crack reach their peak values within a shorter period of time and with a lower magnitude than the corresponding dynamic stress factors for a through-crack.

Predator stress-induced persistent emotional arousal is associated with alterations of plasma corticosterone and hippocampal steroid receptors in rat.

PubMed

Wang, Qingsong; Yu, Ke; Wang, Jun; Lin, Hang; Wu, Yuxian; Wang, Weiwen

2012-04-21

To investigate the long-term effects of psychological stress on emotionality, the emotional arousal of rats in 4 months after predator stress was assessed in both an open field environment and elevated plus maze. We also assessed the levels of plasma corticosterone (CORT) by radioimmunoassay, the distributions of brain glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) by immunohistochemistry, and the expressions of GR and MR by Western blot. The results showed that intense predator stress, which was adjusted to ensure consistent stressor intensity using rat tonic immobility behavior, successfully induced lasting decreased locomotor activity and habituation to novel environments, suppressed exploratory behavior, and increased anxiety-like behavior. The plasma CORT levels dramatically increased 1h after stress, then returned to basal levels at 1wk, decreased 1 month later, and remained significantly lower than control levels 4 months after exposure to stress. Immunohistochemical analysis showed that GR was markedly increased in the hippocampus and frontal cortexes of stressed rats and that the changes in the hippocampus were more pronounced. In contrast, MR expression was significantly decreased in both brain regions. Western analysis confirmed these dramatically elevated levels of GR expression and lower levels of MR expression in the hippocampus 4 months after stress. We conclude that acute severe psychological stress may induce long-term emotional behavioral changes, and that different patterns in plasma CORT, alterations in brain corticoid receptors, and increased hippocampal vulnerability to the effects of predator stress may play important roles in the persistent emotional arousal induced by intense psychological stress. Copyright © 2012 Elsevier B.V. All rights reserved.

Mixed-mode crack tip loading and crack deflection in 1D quasicrystals

NASA Astrophysics Data System (ADS)

Wang, Zhibin; Scheel, Johannes; Ricoeur, Andreas

2016-12-01

Quasicrystals (QC) are a new class of materials besides crystals and amorphous solids and have aroused much attention of researchers since they were discovered. This paper presents a generalized fracture theory including the J-integral and crack closure integrals, relations between J1, J2 and the stress intensity factors as well as the implementation of the near-tip stress and displacement solutions of 1D QC. Different crack deflection criteria, i.e. the J-integral and maximum circumferential stress criteria, are investigated for mixed-mode loading conditions accounting for phonon-phason coupling. One focus is on the influence of phason stress intensity factors on crack deflection angles.

Improvement in surface fatigue life of hardened gears by high-intensity shot peening

NASA Astrophysics Data System (ADS)

Townsend, Dennis P.

1992-04-01

Two groups of carburized, hardened, and ground spur gears that were manufactured from the same heat vacuum induction melted vacuum arc melted (VIM VAR) AISI 9310 steel were endurance tested for surface fatigue. Both groups were manufactured with a standard ground 16 rms surface finish. One group was subjected to a shot peening (SP) intensity of 7 to 9A, and the second group was subjected to a SP intensity of 15 to 17A. All gears were honed after SP to a surface finish of 16 rms. The gear pitch diameter was 8.89 cm. Test conditions were a maximum Hertz stress of 1.71 GPa, a gear temperature of 350 K, and a speed of 10000 rpm. The lubricant used for the tests was a synthetic paraffinic oil with an additive package. The following results were obtained: The 10 pct. surface fatigue (pitting) life of the high intensity (15 to 17A) SPed gears was 2.15 times that of the medium intensity (7 to 9A) SPed gears, the same as that calculated from measured residual stress at a depth of 127 microns. The measured residual stress for the high intensity SPed gears was 57 pct. higher than that for the medium intensity SPed gears at a depth of 127 microns and 540 pct. higher at a depth of 51 microns.

Improvement in surface fatigue life of hardened gears by high-intensity shot peening

NASA Technical Reports Server (NTRS)

Townsend, Dennis P.

1992-01-01

Two groups of carburized, hardened, and ground spur gears that were manufactured from the same heat vacuum induction melted vacuum arc melted (VIM VAR) AISI 9310 steel were endurance tested for surface fatigue. Both groups were manufactured with a standard ground 16 rms surface finish. One group was subjected to a shot peening (SP) intensity of 7 to 9A, and the second group was subjected to a SP intensity of 15 to 17A. All gears were honed after SP to a surface finish of 16 rms. The gear pitch diameter was 8.89 cm. Test conditions were a maximum Hertz stress of 1.71 GPa, a gear temperature of 350 K, and a speed of 10000 rpm. The lubricant used for the tests was a synthetic paraffinic oil with an additive package. The following results were obtained: The 10 pct. surface fatigue (pitting) life of the high intensity (15 to 17A) SPed gears was 2.15 times that of the medium intensity (7 to 9A) SPed gears, the same as that calculated from measured residual stress at a depth of 127 microns. The measured residual stress for the high intensity SPed gears was 57 pct. higher than that for the medium intensity SPed gears at a depth of 127 microns and 540 pct. higher at a depth of 51 microns.

Subgrid or Reynolds stress-modeling for three-dimensional turbulence computations

NASA Technical Reports Server (NTRS)

Rubesin, M. W.

1975-01-01

A review is given of recent advances in two distinct computational methods for evaluating turbulence fields, namely, statistical Reynolds stress modeling and turbulence simulation, where large eddies are followed in time. It is shown that evaluation of the mean Reynolds stresses, rather than use of a scalar eddy viscosity, permits an explanation of streamline curvature effects found in several experiments. Turbulence simulation, with a new volume averaging technique and third-order accurate finite-difference computing is shown to predict the decay of isotropic turbulence in incompressible flow with rather modest computer storage requirements, even at Reynolds numbers of aerodynamic interest.

Computational Psychometrics for Modeling System Dynamics during Stressful Disasters.

PubMed

Cipresso, Pietro; Bessi, Alessandro; Colombo, Desirée; Pedroli, Elisa; Riva, Giuseppe

2017-01-01

Disasters can be very stressful events. However, computational models of stress require data that might be very difficult to collect during disasters. Moreover, personal experiences are not repeatable, so it is not possible to collect bottom-up information when building a coherent model. To overcome these problems, we propose the use of computational models and virtual reality integration to recreate disaster situations, while examining possible dynamics in order to understand human behavior and relative consequences. By providing realistic parameters associated with disaster situations, computational scientists can work more closely with emergency responders to improve the quality of interventions in the future.

Real-time visualization of oxidative stress in a floating macrophyte Lemna minor L. exposed to cadmium, copper, menadione, and AAPH.

PubMed

Razinger, Jaka; Drinovec, Luka; Zrimec, Alexis

2010-12-01

An ultra-sensitive digital imaging system was employed to visualize oxidative stress in intact L. minor plants exposed to Cd, Cu, menadione, AAPH, and ascorbate in real time. The increase of ROS production was assessed by measuring the rate of fluorescence intensity increases of the test medium supplemented with a fluorescing probe (dichlorofluorescein diacetate). The addition of 100 μM CdCl₂ or 100 μM CuSO₄ to the growth medium resulted in a significant increase of medium fluorescence. Additionally, CuSO₄ caused a significantly higher fluorescence intensity than CdCl₂ did. A strong positive correlation (R² = 0.99) between menadione concentration and fluorescence intensity was observed. The positive correlation between AAPH concentration and fluorescence intensity was not as strong as in the case of menadione (R² = 0.81). Menadione induced a stronger oxidative stress than similar concentration of AAPH. The addition of 100 μM ascorbate to L. minor treated with 50 μM menadione significantly reduced the fluorescence intensity increase. A linear trend of the fluorescence increase was observed in all treatments, indicating that chemical-induced oxidative stress is a gradual process and that the applied concentrations of the chemicals caused a constant increased production of ROS with different intensities, depending on the treatment. This is the combined result of a gradual diminishing of antioxidant reserves and accumulating oxidative damage. The observed rates of ROS production were slower than those in the studies using cell cultures. Copyright © 2009 Wiley Periodicals, Inc.

A small randomized pilot study of a workplace mindfulness-based intervention for surgical intensive care unit personnel: effects on salivary α-amylase levels.

PubMed

Duchemin, Anne-Marie; Steinberg, Beth A; Marks, Donald R; Vanover, Kristin; Klatt, Maryanna

2015-04-01

To determine whether a workplace stress-reduction intervention decreases reactivity to stress among personnel exposed to a highly stressful occupational environment. Personnel from a surgical intensive care unit were randomized to a stress-reduction intervention or a waitlist control group. The 8-week group mindfulness-based intervention included mindfulness, gentle yoga, and music. Psychological and biological markers of stress were measured 1 week before and 1 week after the intervention. Levels of salivary α-amylase, an index of sympathetic activation, were significantly decreased between the first and second assessments in the intervention group with no changes in the control group. There was a positive correlation between salivary α-amylase levels and burnout scores. These data suggest that this type of intervention could decrease not only reactivity to stress but also the risk of burnout.

Correlation between the local stress and the grain misorientation in the polycrystalline Al2O3 measured by near-field luminescence spectroscopy

NASA Astrophysics Data System (ADS)

Tomimatsu, Toru; Takigawa, Ryo

2018-06-01

Owing to its high spatial resolution, near-field spectroscopy is a useful method for sensing the stress in a narrow region of submicron order. Here, on the basis of the highly resolved images obtained by near-field luminescence spectroscopy, we propose a statistical method of analyzing grain anisotropy-induced stress in polycrystalline Al2O3. We focus on two characteristics of a spectra: the intensity ratio and peak shift of luminescence of two lines (R1 and R2) from Al2O3 to discuss crystal orientation and stress, respectively. By incorporating the concept of the crystal misorientation parameter using intensity ratio, an apparent correlation between the magnitude of stress and the misorientation is found. This correlation analysis provides an important insight for the investigation of local thermal stress in Al2O3.

Affect-laden imagery and risk taking: the mediating role of stress and risk perception.

PubMed

Traczyk, Jakub; Sobkow, Agata; Zaleskiewicz, Tomasz

2015-01-01

This paper investigates how affect-laden imagery that evokes emotional stress influences risk perception and risk taking in real-life scenarios. In a series of three studies, we instructed participants to imagine the consequences of risky scenarios and then rate the intensity of the experienced stress, perceived risk and their willingness to engage in risky behavior. Study 1 showed that people spontaneously imagine negative rather than positive risk consequences, which are directly related to their lower willingness to take risk. Moreover, this relationship was mediated by feelings of stress and risk perception. Study 2 replicated and extended these findings by showing that imagining negative risk consequences evokes psychophysiological stress responses observed in elevated blood pressure. Finally, in Study 3, we once again demonstrated that a higher intensity of mental images of negative risk consequences, as measured by enhanced brain activity in the parieto-occipital lobes, leads to a lower propensity to take risk. Furthermore, individual differences in creating vivid and intense negative images of risk consequences moderated the strength of the relationship between risk perception and risk taking. Participants who created more vivid and intense images of negative risk consequences paid less attention to the assessments of riskiness in rating their likelihood to take risk. To summarize, we showed that feelings of emotional stress and perceived riskiness mediate the relationship between mental imagery and risk taking, whereas individual differences in abilities to create vivid mental images may influence the degree to which more cognitive risk assessments are used in the risk-taking process.

Affect-Laden Imagery and Risk Taking: The Mediating Role of Stress and Risk Perception

PubMed Central

2015-01-01

This paper investigates how affect-laden imagery that evokes emotional stress influences risk perception and risk taking in real-life scenarios. In a series of three studies, we instructed participants to imagine the consequences of risky scenarios and then rate the intensity of the experienced stress, perceived risk and their willingness to engage in risky behavior. Study 1 showed that people spontaneously imagine negative rather than positive risk consequences, which are directly related to their lower willingness to take risk. Moreover, this relationship was mediated by feelings of stress and risk perception. Study 2 replicated and extended these findings by showing that imagining negative risk consequences evokes psychophysiological stress responses observed in elevated blood pressure. Finally, in Study 3, we once again demonstrated that a higher intensity of mental images of negative risk consequences, as measured by enhanced brain activity in the parieto-occipital lobes, leads to a lower propensity to take risk. Furthermore, individual differences in creating vivid and intense negative images of risk consequences moderated the strength of the relationship between risk perception and risk taking. Participants who created more vivid and intense images of negative risk consequences paid less attention to the assessments of riskiness in rating their likelihood to take risk. To summarize, we showed that feelings of emotional stress and perceived riskiness mediate the relationship between mental imagery and risk taking, whereas individual differences in abilities to create vivid mental images may influence the degree to which more cognitive risk assessments are used in the risk-taking process. PMID:25816238

Thermotolerance and heat stress responses of Douglas-fir and ponderosa pine seedling populations from contrasting climates

Treesearch

Danielle E. Marias; Frederick C. Meinzer; David R. Woodruff; Katherine A. McCulloh; David Tissue

2016-01-01

Temperature and the frequency and intensity of heat waves are predicted to increase throughout the 21st century. Germinant seedlings are expected to be particularly vulnerable to heat stress because they are in the boundary layer close to the soil surface where intense heating occurs in open habitats. We quantified leaf thermotolerance and whole-plant physiological...

Serotonin Transporter Gene ("SLC6A4") Methylation Associates with Neonatal Intensive Care Unit Stay and 3-month-old Temperament in Preterm Infants

ERIC Educational Resources Information Center

Montirosso, Rosario; Provenzi, Livio; Fumagalli, Monica; Sirgiovanni, Ida; Giorda, Roberto; Pozzoli, Uberto; Beri, Silvana; Menozzi, Giorgia; Tronick, Ed; Morandi, Francesco; Mosca, Fabio; Borgatti, Renato

2016-01-01

Preterm birth and Neonatal Intensive Care Unit (NICU) stay are early adverse stressful experiences, which may result in an altered temperamental profile. The serotonin transporter gene ("SLC6A4"), which has been linked to infant temperament, is susceptible to epigenetic regulation associated with early stressful experience. This study…

Fermilab computing at the Intensity Frontier

DOE PAGES

Group, Craig; Fuess, S.; Gutsche, O.; ...

2015-12-23

The Intensity Frontier refers to a diverse set of particle physics experiments using high- intensity beams. In this paper I will focus the discussion on the computing requirements and solutions of a set of neutrino and muon experiments in progress or planned to take place at the Fermi National Accelerator Laboratory located near Chicago, Illinois. In addition, the experiments face unique challenges, but also have overlapping computational needs. In principle, by exploiting the commonality and utilizing centralized computing tools and resources, requirements can be satisfied efficiently and scientists of individual experiments can focus more on the science and less onmore » the development of tools and infrastructure.« less

Effect of the low- versus high-intensity exercise training on endoplasmic reticulum stress and GLP-1 in adolescents with type 2 diabetes mellitus.

PubMed

Lee, Sung Soo; Yoo, Jae Ho; So, Yong Seok

2015-10-01

[Purpose] The primary objective of this study was to investigate the effect of low-intensity exercise training compare with high-intensity exercise training on endoplasmic reticulum stress and glucagon-like peptide-1 in adolescents with type 2 diabetes mellitus. [Subjects and Methods] The low-intensity exercise training group performed aerobic exercise training at an intensity of ≤ 45% of the heart rate reserve. The high-intensity interval exercise training group performed interval exercise training at an intensity of ≥ 80% of the heart rate reserve. The exercise-related energy consumption was determined for both groups on a per-week basis (1,200 kcal/week). [Results] Both groups showed improvement in the glucose-regulated protein 78 and dipeptidyl peptidase-4, but the size of the between-group effect was not statistically significant. The high-intensity interval exercise training group showed a significant reduction in percentage body fat. The C-peptide level increased after the 12-weeks programs and was significantly different, between the groups. Fasting glucose, insulin resistance in the fasting state according to homeostasis model assessment, and leptin decreased after the 12-weeks exercise program and were significantly different between the groups, and glucagon-like peptide-1 increased after the 12-week exercise programs and was significantly different between the groups. [Conclusion] In conclusion high-intensity interval exercise training, as defined in this study, may lead to improvements in body composition, glycemic control, endoplasmic reticulum stress, and the glucagon-like peptide-1 in adolescents with type 2 diabetes mellitus.

Effect of the low- versus high-intensity exercise training on endoplasmic reticulum stress and GLP-1 in adolescents with type 2 diabetes mellitus

PubMed Central

Lee, Sung Soo; Yoo, Jae Ho; So, Yong Seok

2015-01-01

[Purpose] The primary objective of this study was to investigate the effect of low-intensity exercise training compare with high-intensity exercise training on endoplasmic reticulum stress and glucagon-like peptide-1 in adolescents with type 2 diabetes mellitus. [Subjects and Methods] The low-intensity exercise training group performed aerobic exercise training at an intensity of ≤ 45% of the heart rate reserve. The high-intensity interval exercise training group performed interval exercise training at an intensity of ≥ 80% of the heart rate reserve. The exercise-related energy consumption was determined for both groups on a per-week basis (1,200 kcal/week). [Results] Both groups showed improvement in the glucose-regulated protein 78 and dipeptidyl peptidase-4, but the size of the between-group effect was not statistically significant. The high-intensity interval exercise training group showed a significant reduction in percentage body fat. The C-peptide level increased after the 12-weeks programs and was significantly different, between the groups. Fasting glucose, insulin resistance in the fasting state according to homeostasis model assessment, and leptin decreased after the 12-weeks exercise program and were significantly different between the groups, and glucagon-like peptide-1 increased after the 12-week exercise programs and was significantly different between the groups. [Conclusion] In conclusion high-intensity interval exercise training, as defined in this study, may lead to improvements in body composition, glycemic control, endoplasmic reticulum stress, and the glucagon-like peptide-1 in adolescents with type 2 diabetes mellitus. PMID:26644644

[Effects of Ca2+ on nitric oxide-induced adventitious rooting in cucumber under drought stress].

PubMed

Li, Chun Lan; Niu, Li Juan; Hu, Lin Li; Liao, Wei Biao; Chen, Yue

2017-11-01

Cucumber (Cucumis sativus L. 'Xinchun 4') was used to explore the relationship between nitric oxide (NO) and calcium (Ca 2+ ) during adventitious rooting under drought stress. Rooting parameters, endogenous Ca 2+ fluorescent intensity and the antioxidant enzymes activity (SOD, CAT and APX) in cucumber explants under drought stress were investigated. The results showed that treatment with 200 μmol·L -1 CaCl 2 and 0.05% PEG significantly improved the number and length of adventitious root in cucumber explants under drought stress, while the application of Ca 2+ chelating agent (EGTA) and channel inhibitor (BAPTA/AM) significantly decreased NO-induced number and length of adventitious root under drought stress. Under drought stress, the fluorescence intensity of Ca 2+ in hypocotyls treated with NO and CaCl 2 was improved, however, the Ca 2+ fluorescence intensity in the hypocotyls treated with NO scavenger (cPTIO) was significantly lower than that in the hypocotyls treated with NO. Under drought stress, the activities of antioxidant enzymes in the cucumber explants were significantly promoted by the treatments with NO and CaCl 2 , however, Ca 2+ chelating agent and channel inhibitor significantly decreased the activity of antioxidant enzymes induced by NO. In conclusion, Ca 2+ might be involved in the process of NO-adjusted antioxidant enzymes activity during adventitious rooting under drought stress, which alleviated the negative effects of drought on the adventitious rooting and promoted the formation of adventitious roots.

Impact of composite plates: Analysis of stresses and forces

NASA Technical Reports Server (NTRS)

Moon, F. C.; Kim, B. S.; Fang-Landau, S. R.

1976-01-01

The foreign object damage resistance of composite fan blades was studied. Edge impact stresses in an anisotropic plate were first calculated incorporating a constrained layer damping model. It is shown that a very thin damping layer can dramatically decrease the maximum normal impact stresses. A multilayer model of a composite plate is then presented which allows computation of the interlaminar normal and shear stresses. Results are presented for the stresses due to a line impact load normal to the plane of a composite plate. It is shown that significant interlaminar tensile stresses can develop during impact. A computer code was developed for this problem using the fast Fourier transform. A marker and cell computer code were also used to investigate the hydrodynamic impact of a fluid slug against a wall or turbine blade. Application of fluid modeling of bird impact is reviewed.

Stress-intensity factor calculations using the boundary force method

NASA Technical Reports Server (NTRS)

Tan, P. W.; Raju, I. S.; Newman, J. C., Jr.

1987-01-01

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.

The effects of castration, preslaughter stress and zeranol implants on beef: Part 2-Cooking properties and flavor of loin steaks from bovine males.

PubMed

Jeremiah, L E; Newman, J A; Tong, A K; Gibson, L L

1988-01-01

A total of 144 male crossbred calves were allocated to four castration or implant treatments (unimplanted bulls; unimplanted steers; bulls implanted with zeranol at 100 days of age and reimplanted at intervals of 69, 93 and 56 days thereafter; bulls implanted with zeranol at 168 days of age and reimplanted at intervals of 93 and 56 days thereafter) and two preslaughter shipping treatments (minimum preslaughter stress, with cattle shipped and slaughtered within 4 h of leaving the feedlot pen; normal preslaughter stress, with cattle mixed, trucked 160 km, and slaughtered up to 24 h after leaving the feedlot pen). These cattle were slaughtered and striploin steaks were removed after 6 days of post-mortem aging. Evaluations of these steaks were then conducted using both an experienced laboratory taste panel and a highly trained professional flavor profile panel. Results indicated that: (1) steaks from bulls had higher cooking losses than their counterparts from steers, when minimum preslaughter stress was applied; and required longer cooking times under both preslaughter handling treatments; (2) steaks from unimplanted bulls had greater cooking losses and required longer cooking times than their counterparts from implanted bulls under normal preslaughter stress, but not under minimum preslaughter stress; (3) higher proportions of bull steaks than steer steaks contained inappropriate flavor character notes, under both minimum and normal levels of preslaughter stress; (4) both castration and preslaughter handling affected the intensity and order of appearance of specific flavor character notes; (5) the level of preslaughter stress significantly influenced the detection of specific flavor character notes in steaks from both bulls and steers; (6) steaks from steers under minimum preslaughter stress were rated significantly higher in flavor amplitude than their counterparts from bulls when under normal preslaughter stress, and steaks from steers under minimum preslaughter stress received higher flavor desirability scores than steaks from bulls under both minimum and normal preslaughter stress; (7) zeranol implants influenced the appearance and the order of appearance of specific flavor character notes under both minimum and normal levels of preslaughter stress; (8) both zeranol implants and the length of time animals were implanted appeared to increase the intensity of certain inappropriate character notes, and to decrease the intensity of certain appropriate character notes; (9) steaks from implanted bulls received lower flavor amplitude ratings than their counterparts from unimplanted bulls under normal preslaughter stress, but not under minimum preslaughter stress; (10) the level of preslaughter stress influenced both the appearance and order of appearance of specific flavor character notes in both implanted and unimplanted bull steaks; (11) the intensities of certain flavor character notes were influenced by differences in the level of preslaughter stress in both implanted and unimplanted bull steaks, and higher levels usually resulted in inappropriate character notes being more intense; (12) steaks from bulls in both implant groups received lower flavor amplitude ratings when normal preslaughter stress was applied, clearly indicating the deleterious effect of the combination of zeranol implants and normal preslaughter stress on bull beef flavor; and (13) the deleterious effect of the combination of zeranol implants and normal preslaughter stress on bull beef flavor could not be explaind on the basis of greater production of 'dark cutting' beef. Copyright © 1988. Published by Elsevier Ltd.

The effect of massage therapy on occupational stress of Intensive Care Unit nurses.

PubMed

Nazari, Fateme; Mirzamohamadi, Mojtaba; Yousefi, Hojatollah

2015-01-01

One of the main causes of stress in the lives of people is their jobs. Occupational stress is causing a wide range of significant issues in health and community services. Nursing is the most stressful profession in the health services. Massage therapy is one way of coping with stress. This study was conducted to determine the effect of massage therapy on stress in nurses. This study was a clinical trial on 66 male and female nurses working in intensive care units (dialysis, ICU, and CCU) of Isfahan University of Medical Sciences, Iran, in 2013. Participants were selected according to the aims and inclusion criteria of the study. Then, they were randomly divided into experimental and control groups. The Occupational Stress Inventory (OSI) (Osipow and Spokane, 1987) was completed by participants of the two groups before, immediately after, and 2 weeks after the intervention. General Swedish massage was performed on participants of the experimental group for 25 min in each session, twice a week for 4 weeks. Data were analyzed by descriptive and inferential statistics [Chi-square, t-test, and repeated measures analysis of variance (ANOVA)] using SPSS software. Results showed that the difference in overall mean occupation stress scores between experimental and control groups 2 weeks after the intervention was significant (P < 0.001). According to the results, it is recommended that massage, as a valuable noninvasive method, be used for nurses in intensive care units to reduce their stress, promote mental health, and prevent the decrease in quality of nursing work life.

Stressed Out! A National Study of Women and Men Journalism and Mass Communication Faculty, Their Uses of Technology, and Levels of Professional and Personal Stress.

ERIC Educational Resources Information Center

Ogan, Christine; Chung, Deborah

2003-01-01

Examines gender differences as they manifest themselves when journalism educators use computers and computer-based technologies in their teaching and research. Notes that gender differences have been found in overall stress levels and for a variety of types of stress. Concludes that the strongest relationship in the study was not between…

The interplay of stress and mowing disturbance for the intensity and importance of plant interactions in dry calcareous grasslands

PubMed Central

Maalouf, Jean-Paul; Le Bagousse-Pinguet, Yoann; Marchand, Lilian; Touzard, Blaise; Michalet, Richard

2012-01-01

Background and Aims There is still debate regarding the direction and strength of plant interactions under intermediate to high levels of stress. Furthermore, little is known on how disturbance may interact with physical stress in unproductive environments, although recent theory and models have shown that this interplay may induce a collapse of plant interactions and diversity. The few studies assessing such questions have considered the intensity of biotic interactions but not their importance, although this latter concept has been shown to be very useful for understanding the role of interactions in plant communities. The objective of this study was to assess the interplay between stress and disturbance for plant interactions in dry calcareous grasslands. Methods A field experiment was set up in the Dordogne, southern France, where the importance and intensity of biotic interactions undergone by four species were measured along a water stress gradient, and with and without mowing disturbance. Key Results The importance and intensity of interactions varied in a very similar way along treatments. Under undisturbed conditions, plant interactions switched from competition to neutral with increasing water stress for three of the four species, whereas the fourth species was not subject to any significant biotic interaction along the gradient. Responses to disturbance were more species-specific; for two species, competition disappeared with mowing in the wettest conditions, whereas for the two other species, competition switched to facilitation with mowing. Finally, there were no significant interactions for any species in the disturbed and driest conditions. Conclusions At very high levels of stress, plant performances become too weak to allow either competition or facilitation and disturbance may accelerate the collapse of interactions in dry conditions. The results suggest that the importance and direction of interactions are more likely to be positively related in stressful environments. PMID:22782241

The reciprocity law concerning light dose relationships applied to BisGMA/TEGDMA photopolymers: theoretical analysis and experimental characterization.

PubMed

Wydra, James W; Cramer, Neil B; Stansbury, Jeffrey W; Bowman, Christopher N

2014-06-01

A model BisGMA/TEGDMA unfilled resin was utilized to investigate the effect of varied irradiation intensity on the photopolymerization kinetics and shrinkage stress evolution, as a means for evaluation of the reciprocity relationship. Functional group conversion was determined by FTIR spectroscopy and polymerization shrinkage stress was obtained by a tensometer. Samples were polymerized with UV light from an EXFO Acticure with 0.1wt% photoinitiator. A one-dimensional kinetic model was utilized to predict the conversion-dose relationship. As irradiation intensity increased, conversion decreased at a constant irradiation dose and the overall dose required to achieve full conversion increased. Methacrylate conversion ranged from 64±2% at 3mW/cm(2) to 78±1% at 24mW/cm(2) while the final shrinkage stress varied from 2.4±0.1MPa to 3.0±0.1MPa. The ultimate conversion and shrinkage stress levels achieved were dependent not only upon dose but also the irradiation intensity, in contrast to an idealized reciprocity relationship. A kinetic model was utilized to analyze this behavior and provide theoretical conversion profiles versus irradiation time and dose. Analysis of the experimental and modeling results demonstrated that the polymerization kinetics do not and should not be expected to follow the reciprocity law behavior. As irradiation intensity is increased, the overall dose required to achieve full conversion also increased. Further, the ultimate conversion and shrinkage stress that are achieved are not dependent only upon dose but rather upon the irradiation intensity and corresponding polymerization rate. Copyright © 2014 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Peak Stress Intensity Factor Governs Crack Propagation Velocity In Crosslinked UHMWPE

PubMed Central

Sirimamilla, P. Abhiram; Furmanski, Jevan; Rimnac, Clare

2013-01-01

Ultra high molecular weight polyethylene (UHMWPE) has been successfully used as a bearing material in total joint replacement components. However, these bearing materials can fail as a result of in vivo static and cyclic loads. Crack propagation behavior in this material has been considered using the Paris relationship which relates fatigue crack growth rate, da/dN (mm/cycle) versus the stress intensity factor range, ΔK (Kmax-Kmin, MPa√m). However, recent work suggests that the crack propagation velocity of conventional UHMWPE is driven by the peak stress intensity (Kmax), not ΔK. The hypothesis of this study is that the crack propagation velocity of highly crosslinked and remelted UHMWPE is also driven by the peak stress intensity, Kmax, during cyclic loading, rather than by ΔK. To test this hypothesis, two highly crosslinked (65 kGy and 100 kGy) and remelted UHMWPE materials were examined. Frequency, waveform and R-ratio were varied between test conditions to determine the governing factor for fatigue crack propagation. It was found that the crack propagation velocity in crosslinked UHMWPE is also driven by Kmax and not ΔK, and is dependent on loading waveform and frequency in a predictable quasi-static manner. The current study supports that crack growth in crosslinked UHMWPE materials, even under cyclic loading conditions, can be described by a relationship between the velocity of crack growth, da/dt and the peak stress intensity, Kmax. The findings suggest that stable crack propagation can occur as a result of static loading only and this should be taken into consideration in design of UHMWPE total joint replacement components. PMID:23165898

RNA-seq analysis of stress response in rainbow trout

USDA-ARS?s Scientific Manuscript database

Fish under intensive rearing conditions experience various stress conditions, which have negative impacts on survival, growth and fillet quality. Understanding the molecular mechanisms underlying stress responses will facilitate improvement of animal welfare and production efficiency. Our objective ...

Impact of isotropic constitutive descriptions on the predicted peak wall stress in abdominal aortic aneurysms.

PubMed

Man, V; Polzer, S; Gasser, T C; Novotny, T; Bursa, J

2018-03-01

Biomechanics-based assessment of Abdominal Aortic Aneurysm (AAA) rupture risk has gained considerable scientific and clinical momentum. However, computation of peak wall stress (PWS) using state-of-the-art finite element models is time demanding. This study investigates which features of the constitutive description of AAA wall are decisive for achieving acceptable stress predictions in it. Influence of five different isotropic constitutive descriptions of AAA wall is tested; models reflect realistic non-linear, artificially stiff non-linear, or artificially stiff pseudo-linear constitutive descriptions of AAA wall. Influence of the AAA wall model is tested on idealized (n=4) and patient-specific (n=16) AAA geometries. Wall stress computations consider a (hypothetical) load-free configuration and include residual stresses homogenizing the stresses across the wall. Wall stress differences amongst the different descriptions were statistically analyzed. When the qualitatively similar non-linear response of the AAA wall with low initial stiffness and subsequent strain stiffening was taken into consideration, wall stress (and PWS) predictions did not change significantly. Keeping this non-linear feature when using an artificially stiff wall can save up to 30% of the computational time, without significant change in PWS. In contrast, a stiff pseudo-linear elastic model may underestimate the PWS and is not reliable for AAA wall stress computations. Copyright © 2018 IPEM. Published by Elsevier Ltd. All rights reserved.

A study of creep crack growth in 2219-T851

NASA Astrophysics Data System (ADS)

Bensussan, Philippe L.; Jablonski, David A.; Pelloux, Regis M.

1984-01-01

Creep crack growth rates were measured in high strength 2219-T851 aluminum alloy with a computerized fully automated test procedure. Crack growth tests were performed on CT specimens with side grooves. The experimental set-up is described. During a test, the specimen is cyclically loaded on a servohydraulic testing machine under computer control, maintained at maximum load for a given hold time at each cycle, unloaded, and then reloaded. Crack lengths are obtained from compliance measurements recorded during each unloading. It is shown that the measured crack growth rates per cycle do represent creep crack growth rates per unit time for hold times longer than 10 seconds. The validity of LEFM concepts for side-grooved specimens is reviewed, and compliance and stress intensity factor calibrations for such specimens are reported. For the range of testing conditions of this study, 2219-T851 is shown to be creep brittle in terms of concepts of fracture mechanics of creeping solids. It is found that, under these testing conditions, a correlation exists between the creep crack growth rates under plane strain conditions and the stress intensity factor ( da/dt = A K 3.8 at 175 °C) for simple K histories in a regime of steady or quasi-steady state crack growth. The micromechanisms of fracture are determined to be of complex nature. The fracture mode is observed to be mixed inter- and transgranular, the relative amount of intergranular fracture decreasing as K and da/dt increase.

Correlative analysis of head kinematics and brain's tissue response: a computational approach toward understanding the mechanisms of blast TBI

NASA Astrophysics Data System (ADS)

Sarvghad-Moghaddam, H.; Rezaei, A.; Ziejewski, M.; Karami, G.

2017-11-01

Upon impingement of blast waves on the head, stress waves generated at the interface of the skull are transferred into the cranium and the brain tissue and may cause mild to severe blast traumatic brain injury. The intensity of the shock front, defined by the blast overpressure (BoP), that is, the blast-induced peak static overpressure, significantly affects head kinematics as well as the tissue responses of the brain. While evaluation of global linear and rotational accelerations may be feasible, an experimental determination of dynamic responses of the brain in terms of intracranial pressure (ICP), maximum shear stress (MSS), and maximum principal strain (MPS) is almost impossible. The main objective of this study is to investigate possible correlations between head accelerations and the brain's ICP, MSS, and MPS. To this end, three different blasts were simulated by modeling the detonation of 70, 200, and 500 g of TNT at a fixed distance from the head, corresponding to peak BoPs of 0.52, 1.2, and 2 MPa, respectively. A nonlinear multi-material finite element algorithm was implemented in the LS-DYNA explicit solver. Fluid-solid interaction between the blast waves and head was modeled using a penalty-based method. Strong correlations were found between the brain's dynamic responses and both global linear and rotational accelerations at different blast intensities (R^{2 }≥98%), implying that global kinematic parameters of the head might be strong predictors of brain tissue biomechanical parameters.

Quantification of Protein Biomarker Using SERS Nano-Stress Sensing with Peak Intensity Ratiometry

NASA Astrophysics Data System (ADS)

Goh, Douglas; Kong, Kien Voon; Jayakumar, Perumal; Gong, Tianxun; Dinish, U. S.; Olivo, Malini

We report a surface enhanced Raman spectroscopy (SERS) ratiometry method based on peak intensity coupled in a nano-stress sensing platform to detect and quantify biological molecules. Herein, we employed an antibody-conjugated p-aminothiophenol (ATP) functionalized on a bimetallic-film-over-nanosphere (BMFON) substrate as a sensitive SERS platform to detect human haptoglobin (Hp) protein, which is an acute phase protein and a biomarker for various cancers. Correlation between change in the ATP spectral characteristics and concentration of Hp protein was established by examining the peak intensity ratio at 1572cm-1 and 1592cm-1 that reflects the degree of stress experienced by the aromatic ring of ATP during Hp protein-antibody interaction. Development of this platform shows the potential in developing a low-cost and sensitive SERS sensor for the pre-screening of various biomarkers.

Stress intensity factors in bonded half planes containing inclined cracks and subjected to antiplane shear loading

NASA Technical Reports Server (NTRS)

Bassani, J. L.; Erdogan, F.

1979-01-01

The antiplane shear problem for two bonded dissimilar half planes containing a semi-infinite crack or two arbitrarily located collinear cracks is considered. For the semi-infinite crack the problem is solved for a concentrated wedge load and the stress intensity factor and the angular distribution of stresses are calculated. For finite cracks the problem is reduced to a pair of integral equations. Numerical results are obtained for cracks fully imbedded in a homogeneous medium, one crack tip touching the interface, and a crack crossing the interface for various crack angles.

The fracture of boron fibre-reinforced 6061 aluminium alloy

NASA Technical Reports Server (NTRS)

Wright, M. A.; Welch, D.; Jollay, J.

1979-01-01

The fracture of 6061 aluminium alloy reinforced with unidirectional and cross-plied 0/90 deg, 0/90/+ or - 45 deg boron fibres has been investigated. The results have been described in terms of a critical stress intensity, K(Q). Critical stress intensity factors were obtained by substituting the failure stress and the initial crack length into the appropriate expression for K(Q). Values were obtained that depended on the dimensions of the specimens. It was therefore concluded that, for the size of specimen tested, the values of K(Q) did not reflect any basic materials property.

Biomedical equipment in the neonatal intensive care unit: is it a stressor?

PubMed

Gibbons, C; Geller, S; Glatz, E

1998-12-01

The objective of this research was to learn more about nurses' perceptions of the sources of stress in a neonatal intensive care unit and based on the results, to initiate programs to combat stressors. Nurses were asked to complete a demographic sheet and stress audit. Thirty-three (52%) nurses responded and reported that their greatest source of stress was centered on bio-medical equipment--specifically on access, storage, design, and function issues. Nurses reported their least sources were advanced positions, stable infants, and routine procedures. Plans are underway to remedy equipment issues--primarily to inform and collaborate with others.

Crack growth in bonded elastic half planes

NASA Technical Reports Server (NTRS)

Goree, J. G.

1975-01-01

Two solutions were developed for the two dimensional problem of bonded linearly elastic half-planes. For each solution, numerical results are presented for the stress intensity factors, strain energy release rate, stresses, and displacements. The behavior predicted by the studies was investigated experimentally using polymers for the material pairs. Close agreement was found for the critical stress intensity factor at fracture for the perpendicular crack near the interface. Fracture along the interface proved to be inconclusive due to difficulties in obtaining a brittle bond. Some interesting and predictable behavior regarding the potential for the crack to cross the interface was observed and is discussed.

Stress intensity factors in bonded half planes containing inclined cracks and subjected to antiplane shear loading

NASA Technical Reports Server (NTRS)

Bassani, J. L.; Erdogan, F.

1978-01-01

The antiplane shear problem for two bonded dissimilar half planes containing a semi-infinite crack or two arbitrarily located collinear cracks was considered. For the semi-infinite crack the problem was solved for a concentrated wedge load and the stress intensity factor and the angular distribution of stresses were calculated. For finite cracks the problem was reduced to a pair of integral equations. Numerical results were obtained for cracks fully imbedded in a homogeneous medium, one crack tip touching the interface, and a crack crossing the interface for various crack angles.

Fatigue and fracture assessment of cracks in steel elements using acoustic emission

NASA Astrophysics Data System (ADS)

Nemati, Navid; Metrovich, Brian; Nanni, Antonio

2011-04-01

Single edge notches provide a very well defined load and fatigue crack size and shape environment for estimation of the stress intensity factor K, which is not found in welded elements. ASTM SE(T) specimens do not appear to provide ideal boundary conditions for proper recording of acoustic wave propagation and crack growth behavior observed in steel bridges, but do provide standard fatigue crack growth rate data. A modified versions of the SE(T) specimen has been examined to provide small scale specimens with improved acoustic emission(AE) characteristics while still maintaining accuracy of fatigue crack growth rate (da/dN) versus stress intensity factor (ΔK). The specimens intend to represent a steel beam flange subjected to pure tension, with a surface crack growing transverse to a uniform stress field. Fatigue test is conducted at low R ratio. Analytical and numerical studies of stress intensity factor are developed for single edge notch test specimens consistent with the experimental program. ABAQUS finite element software is utilized for stress analysis of crack tips. Analytical, experimental and numerical analysis were compared to assess the abilities of AE to capture a growing crack.

A tailored relocation stress intervention programme for family caregivers of patients transferred from a surgical intensive care unit to a general ward.

PubMed

Lee, Seul; Oh, HyunSoo; Suh, YeonOk; Seo, WhaSook

2017-03-01

To develop and examine a relocation stress intervention programme tailored for the family caregivers of patients scheduled for transfer from a surgical intensive care unit to a general ward. Family relocation stress syndrome has been reported to be similar to that exhibited by patients, and investigators have emphasised that nurses should make special efforts to relieve family relocation stress to maximise positive contributions to the well-being of patients by family caregivers. A nonequivalent control group, nonsynchronised pretest-post-test design was adopted. The study subjects were 60 family caregivers of patients with neurosurgical or general surgical conditions in the surgical intensive care unit of a university hospital located in Incheon, South Korea. Relocation stress and family burden were evaluated at three times, that is before intervention, immediately after transfer and four to five days after transfer. This relocation stress intervention programme was developed for the family caregivers based on disease characteristics and relocation-related needs. In the experimental group, relocation stress levels significantly and continuously decreased after intervention, whereas in the control group, a slight nonsignificant trend was observed. Family burden levels in the control group increased significantly after transfer, whereas burden levels in the experimental group increased only marginally and nonsignificantly. No significant between-group differences in relocation stress or family burden levels were observed after intervention. Relocation stress levels of family caregivers were significantly decreased after intervention in the experimental group, which indicates that the devised family relocation stress intervention programme effectively alleviated family relocation stress. The devised intervention programme, which was tailored to disease characteristics and relocation-related needs, may enhance the practicality and efficacy of relocation stress management and make meaningful contribution to the relief of family relocation stress, promote patient recovery and enhance the well-being of patients and family caregivers. © 2016 John Wiley & Sons Ltd.

Reconstruction of structural damage based on reflection intensity spectra of fiber Bragg gratings

NASA Astrophysics Data System (ADS)

Huang, Guojun; Wei, Changben; Chen, Shiyuan; Yang, Guowei

2014-12-01

We present an approach for structural damage reconstruction based on the reflection intensity spectra of fiber Bragg gratings (FBGs). Our approach incorporates the finite element method, transfer matrix (T-matrix), and genetic algorithm to solve the inverse photo-elastic problem of damage reconstruction, i.e. to identify the location, size, and shape of a defect. By introducing a parameterized characterization of the damage information, the inverse photo-elastic problem is reduced to an optimization problem, and a relevant computational scheme was developed. The scheme iteratively searches for the solution to the corresponding direct photo-elastic problem until the simulated and measured (or target) reflection intensity spectra of the FBGs near the defect coincide within a prescribed error. Proof-of-concept validations of our approach were performed numerically and experimentally using both holed and cracked plate samples as typical cases of plane-stress problems. The damage identifiability was simulated by changing the deployment of the FBG sensors, including the total number of sensors and their distance to the defect. Both the numerical and experimental results demonstrate that our approach is effective and promising. It provides us with a photo-elastic method for developing a remote, automatic damage-imaging technique that substantially improves damage identification for structural health monitoring.

Stat5 Signaling Specifies Basal versus Stress Erythropoietic Responses through Distinct Binary and Graded Dynamic Modalities

PubMed Central

Porpiglia, Ermelinda; Hidalgo, Daniel; Koulnis, Miroslav; Tzafriri, Abraham R.; Socolovsky, Merav

2012-01-01

Erythropoietin (Epo)-induced Stat5 phosphorylation (p-Stat5) is essential for both basal erythropoiesis and for its acceleration during hypoxic stress. A key challenge lies in understanding how Stat5 signaling elicits distinct functions during basal and stress erythropoiesis. Here we asked whether these distinct functions might be specified by the dynamic behavior of the Stat5 signal. We used flow cytometry to analyze Stat5 phosphorylation dynamics in primary erythropoietic tissue in vivo and in vitro, identifying two signaling modalities. In later (basophilic) erythroblasts, Epo stimulation triggers a low intensity but decisive, binary (digital) p-Stat5 signal. In early erythroblasts the binary signal is superseded by a high-intensity graded (analog) p-Stat5 response. We elucidated the biological functions of binary and graded Stat5 signaling using the EpoR-HM mice, which express a “knocked-in” EpoR mutant lacking cytoplasmic phosphotyrosines. Strikingly, EpoR-HM mice are restricted to the binary signaling mode, which rescues these mice from fatal perinatal anemia by promoting binary survival decisions in erythroblasts. However, the absence of the graded p-Stat5 response in the EpoR-HM mice prevents them from accelerating red cell production in response to stress, including a failure to upregulate the transferrin receptor, which we show is a novel stress target. We found that Stat5 protein levels decline with erythroblast differentiation, governing the transition from high-intensity graded signaling in early erythroblasts to low-intensity binary signaling in later erythroblasts. Thus, using exogenous Stat5, we converted later erythroblasts into high-intensity graded signal transducers capable of eliciting a downstream stress response. Unlike the Stat5 protein, EpoR expression in erythroblasts does not limit the Stat5 signaling response, a non-Michaelian paradigm with therapeutic implications in myeloproliferative disease. Our findings show how the binary and graded modalities combine to generate high-fidelity Stat5 signaling over the entire basal and stress Epo range. They suggest that dynamic behavior may encode information during STAT signal transduction. PMID:22969412

High-Intensity Exercise Induced Oxidative Stress and Skeletal Muscle Damage in Postpubertal Boys and Girls: A Comparative Study.

PubMed

Pal, Sangita; Chaki, Biswajit; Chattopadhyay, Sreya; Bandyopadhyay, Amit

2018-04-01

Pal, S, Chaki, B, Chattopadhyay, S, and Bandyopadhyay, A. High-intensity exercise induced oxidative stress and skeletal muscle damage in post-pubertal boys and girls: a comparative study. J Strength Cond Res 32(4): 1045-1052, 2018-The purpose of this study was to examine the sex variation in high-intensity exercise induced oxidative stress and muscle damage among 44 sedentary postpubertal boys and girls through estimation of postexercise release pattern of muscle damage markers like creatine kinase, lactate dehydrogenase (LDH), alanine aminotransferase (ALT), aspartate aminotransferase (AST) and oxidative stress markers like extent of lipid peroxidation (thiobarbituric acid-reactive substances) and catalase activity. Muscle damage markers like creatine kinase, LDH, ALT, and AST were measured before, immediately after, and 24 and 48 hours after high-intensity incremental treadmill running. Oxidative stress markers like thiobarbituric acid-reactive substances and catalase activity were estimated before and immediately after the exercise. Lipid peroxidation and serum catalase activity increased significantly in both groups after exercise (p < 0.001) with postexercise values and percentage increase significantly higher in postpubertal boys as compared to girls (p < 0.001). Creatine kinase and LDH activity also increased significantly above pre-exercise level at 24 and 48 hours after exercise in both the sexes, (p < 0.001) with values significantly higher for boys than the girls (p < 0.001). Although ALT and AST increased significantly in both the groups after exercise, the pattern of postexercise release of these markers were found to be similar in both the groups. Accordingly, it has been concluded from the present investigation that high-intensity exercise induces significant oxidative stress and increases indices of skeletal muscle damage in both postpubertal girls and boys. However, postpubertal girls are relatively better protected from oxidative stress and muscle damage as compared to the boys of similar age and physical activity level. It is further evident that sex difference may not be apparent for all the biomarkers of muscle damage in this age group.

Assessment of Reynolds stress components and turbulent pressure loss using 4D flow MRI with extended motion encoding.

PubMed

Haraldsson, Henrik; Kefayati, Sarah; Ahn, Sinyeob; Dyverfeldt, Petter; Lantz, Jonas; Karlsson, Matts; Laub, Gerhard; Ebbers, Tino; Saloner, David

2018-04-01

To measure the Reynolds stress tensor using 4D flow MRI, and to evaluate its contribution to computed pressure maps. A method to assess both velocity and Reynolds stress using 4D flow MRI is presented and evaluated. The Reynolds stress is compared by cross-sectional integrals of the Reynolds stress invariants. Pressure maps are computed using the pressure Poisson equation-both including and neglecting the Reynolds stress. Good agreement is seen for Reynolds stress between computational fluid dynamics, simulated MRI, and MRI experiment. The Reynolds stress can significantly influence the computed pressure loss for simulated (eg, -0.52% vs -15.34% error; P < 0.001) and experimental (eg, 306 ± 11 vs 203 ± 6 Pa; P < 0.001) data. A 54% greater pressure loss is seen at the highest experimental flow rate when accounting for Reynolds stress (P < 0.001). 4D flow MRI with extended motion-encoding enables quantification of both the velocity and the Reynolds stress tensor. The additional information provided by this method improves the assessment of pressure gradients across a stenosis in the presence of turbulence. Unlike conventional methods, which are only valid if the flow is laminar, the proposed method is valid for both laminar and disturbed flow, a common presentation in diseased vessels. Magn Reson Med 79:1962-1971, 2018. © 2017 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.

Edge delamination in angle-ply composite laminates, part 5

NASA Technical Reports Server (NTRS)

Wang, S. S.

1981-01-01

A theoretical method was developed for describing the edge delamination stress intensity characteristics in angle-ply composite laminates. The method is based on the theory of anisotropic elasticity. The edge delamination problem is formulated using Lekhnitskii's complex-variable stress potentials and an especially developed eigenfunction expansion method. The method predicts exact orders of the three-dimensional stress singularity in a delamination crack tip region. With the aid of boundary collocation, the method predicts the complete stress and displacement fields in a finite-dimensional, delaminated composite. Fracture mechanics parameters such as the mixed-mode stress intensity factors and associated energy release rates for edge delamination can be calculated explicity. Solutions are obtained for edge delaminated (theta/-theta theta/-theta) angle-ply composites under uniform axial extension. Effects of delamination lengths, fiber orientations, lamination and geometric variables are studied.

Stress intensity factors for bonded orthotropic strips with cracks

NASA Technical Reports Server (NTRS)

Delale, F.; Erdogan, F.

1978-01-01

The elastostatic problem for a nonhomogeneous plane which consists of two sets of periodically arranged dissimilar orthotropic strips is considered. It is assumed that the plane contains a series of collinear cracks perpendicular to the interfaces and is loaded in tension away from and perpendicular to the cracks. Cracks fully imbedded into the homogenous strips were analyzed as well as the singular behavior of the stresses for two special crack geometries. The analysis of cracks crossing interfaces indicates that, for certain orthotropic material combinations, the stress state at the point of intersection of a crack and an interface may be bounded. A number of numerical examples are worked out in order to separate the primary material parameters influencing the stress intensity factors and the powers of stress singularity, and to determine the trends regarding the influence of the secondary parameters.

Children's Post-Traumatic Stress and the Role of Memory Following Admission to Intensive Care: A Review

ERIC Educational Resources Information Center

Dow, Belinda; Kenardy, Justin; Long, Deborah; Le Brocque, Robyne

2012-01-01

Although our understanding of children's psychological outcomes following intensive care lags significantly behind advances in medicine, there is a growing awareness that intensive care admission impacts children beyond the boundaries of physical well-being. Intensive care presents a variety of disease-related, treatment-related, and…

[The ultrastructure of Leydig cells under the influence of drinking mineral water and electromagnetic radiation under the stress conditions in the rats].

PubMed

Geniatulina, M S; Korolev, Yu N; Nikulina, L A

The objective of the present study was elucidate the peculiar features of low-intensity electromagnetic radiation (LI EMR) and mineral water (MW) on the ultrastructure of rat Leydig cells under conditions of immobilization stress. The experiments were carried out on outbred male rats with the use of electron microscopy. It has been demonstrated that the prophylactic consumption of drinking sulfate-containing mineral water and the application low-intensity electromagnetic radiation (with the flow power density of 1 mcW/cm2 and frequency around 1,000 Hz) or the combination of these two modalities under conditions of immobilization stress reduced the degree of ultrastructural derangement in the rat Leydig cells and stimulated the development of regenerative processes. In the cases of the single-factor impact, drinking mineral water exerted more pronounced action than low-intensity electromagnetic radiation on mitochondrial regeneration. In case of the simultaneous application of the two factors their protective action on the Leydig cells was much more conspicuous than that of either of them applied alone. It is concluded that drinking sulfate-containing mineral water in combination with the application of low-intensity electromagnetic radiation enhances resistance of the rat Leydig cells to stress.

Stress-intensity factors for circumferential surface cracks in pipes and rods under tension and bending loads

NASA Technical Reports Server (NTRS)

Raju, I. S.; Newman, J. C., Jr.

1985-01-01

The purpose of this paper is to present stress-intensity factors for a wide range of nearly semi-elliptical surface cracks in pipes and rods. The configurations were subjected to either remote tension or bending loads. For pipes, the ratio of crack depth to crack length (a/c) ranged from 0.6 to 1; the ratio of crack depth to wall thickness (a/t) ranged from 0.2 to 0.8; and the ratio of internal radius to wall thickness (R/t) ranged from 1 to 10. For rods, the ratio of crack depth to crack length also ranged from 0.6 to 1; and the ratio of crack depth to rod diameter (a/D) ranged from 0.05 to 0.35. These particular crack configurations were chosen to cover the range of crack shapes (a/c) that have been observed in experiments conducted on pipes and rods under tension and bending fatigue loads. The stress-intensity factors were calculated by a three-dimensional finite-element method. The finite-element models employed singularity elements along the crack front and linear-strain elements elsewhere. The models had about 6500 degrees of freedom. The stress-intensity factors were evaluated using a nodal-force method.

The effect of contact stresses in four-point bend testing of graphite/epoxy and graphite/PMR-15 composite beams

NASA Technical Reports Server (NTRS)

Binienda, Wieslaw K.; Roberts, Gary D.; Papadopoulos, Demetrios S.

1992-01-01

The results of in-plane four-point bend experiments on unidirectionally reinforced composite beams are presented for graphite/epoxy (T300/934) and graphite/polyimide (G30-500/PMR-15) composites. The maximum load and the location of cracks formed during failure were measured for testpieces with fibers oriented at various angles to the beam axis. Since most of the beams failed near one or more of the load points, the strength of the beams was evaluated in terms of a proposed model, for the local stress distribution. In this model, an exact solution to the problem of a localized contact force acting on a unidirectionally reinforced half plane is used to describe the local stress field. The stress singularity at the load points is treated in a manner similar to the stress singularity at a crack tip in fracture mechanisms problems. Using this approach, the effect of fiber angle and elastic material properties on the strength of the beam is described in terms of a load intensity factor. For fiber angles less than 45 deg from the beam axis, a single crack is initiated near one of the load points at a critical value of the load intensity factor. The critical load intensity factor decreases with the increasing fiber angle. For larger fiber angles, multiple cracks occur at locations both near and away from the load points, and the load intensity factor at failure increases sharply with increasing fiber angle.

Effect of contact stresses in four-point bend testing of graphite/epoxy and graphite/PMR-15 composite beams

NASA Technical Reports Server (NTRS)

Binienda, W. K.; Roberts, G. D.; Papadopoulos, D. S.

1992-01-01

The results of in-plane four-point bend experiments on unidirectionally reinforced composite beams are presented for graphite/epoxy (T300/934) and graphite/polyimide (G30-500/PMR-15) composites. The maximum load and the location of cracks formed during failure were measured for testpieces with fibers oriented at various angles to the beam axis. Since most of the beams failed near one or more of the load points, the strength of the beams was evaluated in terms of a proposed model for the local stress distribution. In this model, an exact solution to the problem of a localized contact force acting on a unidirectionally reinforced half plane is used to describe the local stress field. The stress singularity at the load points is treated in a manner similar to the stress singularity at a crack tip in fracture mechanisms problems. Using this approach, the effect of fiber angle and elastic material properties on the strength of the beam is described in terms of a load intensity factor. For fiber angles less than 45 deg from the beam axis, a single crack is initiated near one of the load points at a critical value of the load intensity factor. The critical load intensity factor decreases with increasing fiber angle. For larger fiber angles, multiple cracks occur at locations both near and away from the load points, and the load intensity factor at failure increases sharply with increasing fiber angle.

Computational Psychometrics for Modeling System Dynamics during Stressful Disasters

PubMed Central

Cipresso, Pietro; Bessi, Alessandro; Colombo, Desirée; Pedroli, Elisa; Riva, Giuseppe

2017-01-01

Disasters can be very stressful events. However, computational models of stress require data that might be very difficult to collect during disasters. Moreover, personal experiences are not repeatable, so it is not possible to collect bottom-up information when building a coherent model. To overcome these problems, we propose the use of computational models and virtual reality integration to recreate disaster situations, while examining possible dynamics in order to understand human behavior and relative consequences. By providing realistic parameters associated with disaster situations, computational scientists can work more closely with emergency responders to improve the quality of interventions in the future. PMID:28861026

Expedited patient-specific assessment of contact stress exposure in the ankle joint following definitive articular fracture reduction.

PubMed

Kern, Andrew M; Anderson, Donald D

2015-09-18

Acute injury severity, altered joint kinematics, and joint incongruity are three important mechanical factors linked to post-traumatic osteoarthritis (PTOA). Finite element analysis (FEA) was previously used to assess the influence of increased contact stress due to joint incongruity on PTOA development. While promising agreement with PTOA development was seen, the inherent complexities of contact FEA limited the numbers of subjects that could be analyzed. Discrete element analysis (DEA) is a simplified methodology for contact stress computation, which idealizes contact surfaces as a bed of independent linear springs. In this study, DEA was explored as an expedited alternative to FEA contact stress exposure computation. DEA was compared to FEA using results from a previously completed validation study of two cadaveric human ankles, as well as a previous study of post-operative contact stress exposure in 11 patients with tibial plafond fracture. DEA-computed maximum contact stresses were within 19% of those experimentally measured, with 90% of the contact area having computed contact stress values within 1MPa of those measured. In the 11 fractured ankles, maximum contact stress and contact area differences between DEA and FEA were 0.85 ± 0.64 MPa and 22.5 ± 11.5mm(2). As a predictive measure for PTOA development, both DEA and FEA had 100% concordance with presence of OA (KL grade ≥ 2) and >95% concordance with KL grade at 2 years. These results support DEA as a reasonable alternative to FEA for computing contact stress exposures following surgical reduction of a tibial plafond fracture. Copyright © 2015 Elsevier Ltd. All rights reserved.

Visualizing stressful aspects of repetitive motion tasks and opportunities for ergonomic improvements using computer vision.

PubMed

Greene, Runyu L; Azari, David P; Hu, Yu Hen; Radwin, Robert G

2017-11-01

Patterns of physical stress exposure are often difficult to measure, and the metrics of variation and techniques for identifying them is underdeveloped in the practice of occupational ergonomics. Computer vision has previously been used for evaluating repetitive motion tasks for hand activity level (HAL) utilizing conventional 2D videos. The approach was made practical by relaxing the need for high precision, and by adopting a semi-automatic approach for measuring spatiotemporal characteristics of the repetitive task. In this paper, a new method for visualizing task factors, using this computer vision approach, is demonstrated. After videos are made, the analyst selects a region of interest on the hand to track and the hand location and its associated kinematics are measured for every frame. The visualization method spatially deconstructs and displays the frequency, speed and duty cycle components of tasks that are part of the threshold limit value for hand activity for the purpose of identifying patterns of exposure associated with the specific job factors, as well as for suggesting task improvements. The localized variables are plotted as a heat map superimposed over the video, and displayed in the context of the task being performed. Based on the intensity of the specific variables used to calculate HAL, we can determine which task factors most contribute to HAL, and readily identify those work elements in the task that contribute more to increased risk for an injury. Work simulations and actual industrial examples are described. This method should help practitioners more readily measure and interpret temporal exposure patterns and identify potential task improvements. Copyright © 2017. Published by Elsevier Ltd.

Laser-Induced Thermal-Mechanical Damage Characteristics of Cleartran Multispectral Zinc Sulfide with Temperature-Dependent Properties

NASA Astrophysics Data System (ADS)

Peng, Yajing; Jiang, Yanxue; Yang, Yanqiang

2015-01-01

Laser-induced thermal-mechanical damage characteristics of window materials are the focus problems in laser weapon and anti-radiation reinforcement technology. Thermal-mechanical effects and damage characteristics are investigated for cleartran multispectral zinc sulfide (ZnS) thin film window materials irradiated by continuous laser using three-dimensional (3D) thermal-mechanical model. Some temperature-dependent parameters are introduced into the model. The temporal-spatial distributions of temperature and thermal stress are exhibited. The damage mechanism is analyzed. The influences of temperature effect of material parameters and laser intensity on the development of thermal stress and the damage characteristics are examined. The results show, the von Mises equivalent stress along the thickness direction is fluctuant, which originates from the transformation of principal stresses from compressive stress to tensile stress with the increase of depth from irradiated surface. The damage originates from the thermal stress but not the melting. The thermal stress is increased and the damage is accelerated by introducing the temperature effect of parameters or the increasing laser intensity.

Vision-Based UAV Flight Control and Obstacle Avoidance

DTIC Science & Technology

2006-01-01

denoted it by Vb = (Vb1, Vb2 , Vb3). Fig. 2 shows the block diagram of the proposed vision-based motion analysis and obstacle avoidance system. We denote...structure analysis often involve computation- intensive computer vision tasks, such as feature extraction and geometric modeling. Computation-intensive...First, we extract a set of features from each block. 2) Second, we compute the distance between these two sets of features. In conventional motion

Uncertainties in obtaining high reliability from stress-strength models

NASA Technical Reports Server (NTRS)

Neal, Donald M.; Matthews, William T.; Vangel, Mark G.

1992-01-01

There has been a recent interest in determining high statistical reliability in risk assessment of aircraft components. The potential consequences are identified of incorrectly assuming a particular statistical distribution for stress or strength data used in obtaining the high reliability values. The computation of the reliability is defined as the probability of the strength being greater than the stress over the range of stress values. This method is often referred to as the stress-strength model. A sensitivity analysis was performed involving a comparison of reliability results in order to evaluate the effects of assuming specific statistical distributions. Both known population distributions, and those that differed slightly from the known, were considered. Results showed substantial differences in reliability estimates even for almost nondetectable differences in the assumed distributions. These differences represent a potential problem in using the stress-strength model for high reliability computations, since in practice it is impossible to ever know the exact (population) distribution. An alternative reliability computation procedure is examined involving determination of a lower bound on the reliability values using extreme value distributions. This procedure reduces the possibility of obtaining nonconservative reliability estimates. Results indicated the method can provide conservative bounds when computing high reliability. An alternative reliability computation procedure is examined involving determination of a lower bound on the reliability values using extreme value distributions. This procedure reduces the possibility of obtaining nonconservative reliability estimates. Results indicated the method can provide conservative bounds when computing high reliability.

From cosmos to connectomes: the evolution of data-intensive science.

PubMed

Burns, Randal; Vogelstein, Joshua T; Szalay, Alexander S

2014-09-17

The analysis of data requires computation: originally by hand and more recently by computers. Different models of computing are designed and optimized for different kinds of data. In data-intensive science, the scale and complexity of data exceeds the comfort zone of local data stores on scientific workstations. Thus, cloud computing emerges as the preeminent model, utilizing data centers and high-performance clusters, enabling remote users to access and query subsets of the data efficiently. We examine how data-intensive computational systems originally built for cosmology, the Sloan Digital Sky Survey (SDSS), are now being used in connectomics, at the Open Connectome Project. We list lessons learned and outline the top challenges we expect to face. Success in computational connectomics would drastically reduce the time between idea and discovery, as SDSS did in cosmology. Copyright © 2014 Elsevier Inc. All rights reserved.

The influence of anesthesia and fluid-structure interaction on simulated shear stress patterns in the carotid bifurcation of mice.

PubMed

De Wilde, David; Trachet, Bram; De Meyer, Guido; Segers, Patrick

2016-09-06

Low and oscillatory wall shear stresses (WSS) near aortic bifurcations have been linked to the onset of atherosclerosis. In previous work, we calculated detailed WSS patterns in the carotid bifurcation of mice using a Fluid-structure interaction (FSI) approach. We subsequently fed the animals a high-fat diet and linked the results of the FSI simulations to those of atherosclerotic plaque location on a within-subject basis. However, these simulations were based on boundary conditions measured under anesthesia, while active mice might experience different hemodynamics. Moreover, the FSI technique for mouse-specific simulations is both time- and labor-intensive, and might be replaced by simpler and easier Computational Fluid Dynamics (CFD) simulations. The goal of the current work was (i) to compare WSS patterns based on anesthesia conditions to those representing active resting and exercising conditions; and (ii) to compare WSS patterns based on FSI simulations to those based on steady-state and transient CFD simulations. For each of the 3 computational techniques (steady state CFD, transient CFD, FSI) we performed 5 simulations: 1 for anesthesia, 2 for conscious resting conditions and 2 more for conscious active conditions. The inflow, pressure and heart rate were scaled according to representative in vivo measurements obtained from literature. When normalized by the maximal shear stress value, shear stress patterns were similar for the 3 computational techniques. For all activity levels, steady state CFD led to an overestimation of WSS values, while FSI simulations yielded a clear increase in WSS reversal at the outer side of the sinus of the external carotid artery that was not visible in transient CFD-simulations. Furthermore, the FSI simulations in the highest locomotor activity state showed a flow recirculation zone in the external carotid artery that was not present under anesthesia. This recirculation went hand in hand with locally increased WSS reversal. Our data show that FSI simulations are not necessary to obtain normalized WSS patterns, but indispensable to assess the oscillatory behavior of the WSS in mice. Flow recirculation and WSS reversal at the external carotid artery may occur during high locomotor activity while they are not present under anesthesia. These phenomena might thus influence plaque formation to a larger extent than what was previously assumed. Copyright © 2016 Elsevier Ltd. All rights reserved.

Methods of Stress Calculation in Rotating Disks

NASA Technical Reports Server (NTRS)

Tumarkin, S.

1944-01-01

The paper describes nethods of computing the stresses in disks of a given profile as well as methods of choosing the disk profiles for a given stress distribution for turhines, turbo blowers, and so forth. A new method of in tegrating the differential equations of Stodola leads to a simplification of the computation for disks of hyperbolic profile.

Finite Element Analysis of Osteocytes Mechanosensitivity Under Simulated Microgravity

NASA Astrophysics Data System (ADS)

Yang, Xiao; Sun, Lian-Wen; Du, Cheng-Fei; Wu, Xin-Tong; Fan, Yu-Bo

2018-04-01

It was found that the mechanosensitivity of osteocytes could be altered under simulated microgravity. However, how the mechanical stimuli as the biomechanical origins cause the bioresponse in osteocytes under microgravity is unclear yet. Computational studies may help us to explore the mechanical deformation changes of osteocytes under microgravity. Here in this paper, we intend to use the computational simulation to investigate the mechanical behavior of osteocytes under simulated microgravity. In order to obtain the shape information of osteocytes, the biological experiment was conducted under simulated microgravity prior to the numerical simulation The cells were rotated by a clinostat for 6 hours or 5 days and fixed, the cytoskeleton and the nucleus were immunofluorescence stained and scanned, and the cell shape and the fluorescent intensity were measured from fluorescent images to get the dimension information of osteocytes The 3D finite element (FE) cell models were then established based on the scanned image stacks. Several components such as the actin cortex, the cytoplasm, the nucleus, the cytoskeleton of F-actin and microtubules were considered in the model. The cell models in both 6 hours and 5 days groups were then imposed by three magnitudes (0.5, 10 and 15 Pa) of simulating fluid shear stress, with cell total displacement and the internal discrete components deformation calculated. The results showed that under the simulated microgravity: (1) the nuclear area and height statistically significantly increased, which made the ratio of membrane-cortex height to nucleus height statistically significantly decreased; (2) the fluid shear stress-induced maximum displacements and average displacements in the whole cell decreased, with the deformation decreasing amplitude was largest when exposed to 1.5Pa of fluid shear stress; (3) the fluid shear stress-induced deformation of cell membrane-cortex and cytoskeleton decreased, while the fluid shear stress-induced deformation of nucleus increased. The results suggested the mechanical behavior of whole osteocyte cell body was suppressed by simulated microgravity, and this decrement was enlarged with either the increasing amplitude of fluid shear stress or the duration of simulated microgravity. What's more, the mechanical behavior of membrane-cortex and cytoskeleton was suppressed by the simulated microgravity, which indicated the mechanotransduction process in the cell body may be further inhibited. On the contrary, the cell nucleus deformation increased under simulated microgravity, which may be related to either the decreased amount of cytoskeleton or the increased volume occupied proportion of nucleus in whole cell under the simulated microgravity. The numerical results supported our previous biological experiments, and showed particularly affected cellular components under the simulated microgravity. The computational study here may help us to better understand the mechanism of mechanosensitivity changes in osteocytes under simulated microgravity, and further to explore the mechanism of the bone loss in space flight.

A NUMERICAL SCHEME FOR SPECIAL RELATIVISTIC RADIATION MAGNETOHYDRODYNAMICS BASED ON SOLVING THE TIME-DEPENDENT RADIATIVE TRANSFER EQUATION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ohsuga, Ken; Takahashi, Hiroyuki R.

2016-02-20

We develop a numerical scheme for solving the equations of fully special relativistic, radiation magnetohydrodynamics (MHDs), in which the frequency-integrated, time-dependent radiation transfer equation is solved to calculate the specific intensity. The radiation energy density, the radiation flux, and the radiation stress tensor are obtained by the angular quadrature of the intensity. In the present method, conservation of total mass, momentum, and energy of the radiation magnetofluids is guaranteed. We treat not only the isotropic scattering but also the Thomson scattering. The numerical method of MHDs is the same as that of our previous work. The advection terms are explicitlymore » solved, and the source terms, which describe the gas–radiation interaction, are implicitly integrated. Our code is suitable for massive parallel computing. We present that our code shows reasonable results in some numerical tests for propagating radiation and radiation hydrodynamics. Particularly, the correct solution is given even in the optically very thin or moderately thin regimes, and the special relativistic effects are nicely reproduced.« less

Computational simulation of matrix micro-slip bands in SiC/Ti-15 composite

NASA Technical Reports Server (NTRS)

Mital, S. K.; Lee, H.-J.; Murthy, P. L. N.; Chamis, C. C.

1992-01-01

Computational simulation procedures are used to identify the key deformation mechanisms for (0)(sub 8) and (90)(sub 8) SiC/Ti-15 metal matrix composites. The computational simulation procedures employed consist of a three-dimensional finite-element analysis and a micromechanics based computer code METCAN. The interphase properties used in the analysis have been calibrated using the METCAN computer code with the (90)(sub 8) experimental stress-strain curve. Results of simulation show that although shear stresses are sufficiently high to cause the formation of some slip bands in the matrix concentrated mostly near the fibers, the nonlinearity in the composite stress-strain curve in the case of (90)(sub 8) composite is dominated by interfacial damage, such as microcracks and debonding rather than microplasticity. The stress-strain curve for (0)(sub 8) composite is largely controlled by the fibers and shows only slight nonlinearity at higher strain levels that could be the result of matrix microplasticity.

From monsoon to marine productivity in the Arabian Sea: insights from glacial and interglacial climates

NASA Astrophysics Data System (ADS)

Le Mézo, Priscilla; Beaufort, Luc; Bopp, Laurent; Braconnot, Pascale; Kageyama, Masa

2017-07-01

The current-climate Indian monsoon is known to boost biological productivity in the Arabian Sea. This paradigm has been extensively used to reconstruct past monsoon variability from palaeo-proxies indicative of changes in surface productivity. Here, we test this paradigm by simulating changes in marine primary productivity for eight contrasted climates from the last glacial-interglacial cycle. We show that there is no straightforward correlation between boreal summer productivity of the Arabian Sea and summer monsoon strength across the different simulated climates. Locally, productivity is fuelled by nutrient supply driven by Ekman dynamics. Upward transport of nutrients is modulated by a combination of alongshore wind stress intensity, which drives coastal upwelling, and by a positive wind stress curl to the west of the jet axis resulting in upward Ekman pumping. To the east of the jet axis there is however a strong downward Ekman pumping due to a negative wind stress curl. Consequently, changes in coastal alongshore stress and/or curl depend on both the jet intensity and position. The jet position is constrained by the Indian summer monsoon pattern, which in turn is influenced by the astronomical parameters and the ice sheet cover. The astronomical parameters are indeed shown to impact wind stress intensity in the Arabian Sea through large-scale changes in the meridional gradient of upper-tropospheric temperature. However, both the astronomical parameters and the ice sheets affect the pattern of wind stress curl through the position of the sea level depression barycentre over the monsoon region (20-150° W, 30° S-60° N). The combined changes in monsoon intensity and pattern lead to some higher glacial productivity during the summer season, in agreement with some palaeo-productivity reconstructions.

The surface and through crack problems in layered orthotropic plates

NASA Technical Reports Server (NTRS)

Erdogan, Fazil; Wu, Binghua

1991-01-01

An analytical method is developed for a relatively accurate calculation of Stress Intensity Factors in a laminated orthotropic plate containing a through or part-through crack. The laminated plate is assumed to be under bending or membrane loading and the mode 1 problem is considered. First three transverse shear deformation plate theories (Mindlin's displacement based first-order theory, Reissner's stress-based first-order theory, and a simple-higher order theory due to Reddy) are reviewed and examined for homogeneous, laminated and heterogeneous orthotropic plates. Based on a general linear laminated plate theory, a method by which the stress intensity factors can be obtained in orthotropic laminated and heterogeneous plates with a through crack is developed. Examples are given for both symmetrically and unsymmetrically laminated plates and the effects of various material properties on the stress intensity factors are studied. In order to implement the line-spring model which is used later to study the surface crack problem, the corresponding plane elasticity problem of a two-bonded orthotropic plated containing a crack perpendicular to the interface is also considered. Three different crack profiles: an internal crack, an edge crack, and a crack terminating at the interface are considered. The effect of the different material combinations, geometries, and material orthotropy on the stress intensity factors and on the power of stress singularity for a crack terminating at the interface is fully examined. The Line Spring model of Rice and Levy is used for the part-through crack problem. The surface crack is assumed to lie in one of the two-layered laminated orthotropic plates due to the limitation of the available plane strain results. All problems considered are of the mixed boundary value type and are reduced to Cauchy type of singular integral equations which are then solved numerically.

Association between objectively measured physical activity, chronic stress and leukocyte telomere length.

PubMed

von Känel, Roland; Bruwer, Erna J; Hamer, Mark; de Ridder, J Hans; Malan, Leoné

2017-10-01

Physical activity (PA) attenuates chronic stress and age-related and cardiovascular disease risks, whereby potentially slowing telomere shortening. We aimed to study the association between seven-day objectively measured habitual PA, chronic stress and leukocyte telomere length. Study participants were African (N.=96) and Caucasian (N.=107) school teachers of the Sympathetic activity and Ambulatory Blood Pressure in Africans study. All lifestyle characteristics (including PA) were objectively measured. The general health questionnaire and serum cortisol were assessed as psychological and physical measures of chronic stress. Leukocyte telomere length was measured using the quantitative real-time polymerase chain reaction. Africans had significantly shorter telomeres (P<.0001) and greater psychological distress (P=0.001) than Caucasians, whereas no group difference was seen for cortisol levels. Higher age (ß=-0.28 [-0.40, -0.16, P≤0.000), higher alcohol consumption (ß=-0.21 [-0.36, -0.08], P=0.003) and increased central obesity (ß=-0.17 [-0.30, -0.03], P=0.017) were all significantly associated with shorter telomeres. Habitual PA of different intensity was not significantly associated with markers of chronic stress or telomere length. However, more time spent with light intensity PA time was significantly and independently correlated with lower waist circumference (r=-0.21, P=0.004); in turn, greater waist circumference was significantly associated shorter telomeres (β=-0.17 [-0.30, -0.03], P=0.017). Habitual PA of different intensity was not directly associated with markers of chronic stress and leukocyte telomere length in this biethnic cohort. However, our findings suggest that light intensity PA could contribute to lowered age-related disease risk and healthy ageing by facilitating maintenance of a normal waist circumference.

Modeling Tidal Stresses on Satellites Using an Enhanced SatStressGUI

NASA Astrophysics Data System (ADS)

Patthoff, D. A.; Pappalardo, R. T.; Li, J.; Ayton, B.; Kay, J.; Kattenhorn, S. A.

2015-12-01

Icy and rocky satellites of our solar system display a wide range of geological deformation on their surfaces. Some are old and heavily cratered while other are observed to be presently active. Many of the potential sources of stress which can deform satellites are tied to the tidal deformation the moons experience as they orbit their parent planets. Other plausible sources of global-scale stress include a change in orbital parameters, nonsynchronous rotation, or volume change induced by the melting or freezing of a subsurface layer. We turn to computer modeling to correlate observed geologic features to the possible stresses that created them. One model is the SatStress open-source program developed by Z. Selvans (Wahr et al.,2009) to compute viscoelastic diurnal and nonsynchronous rotation stresses using a four-layer viscoelastic satellite model. Kay and Katternhorn (2010) expanded on this work by developing SatStressGUI, which integrated SatStress's original features into a graphical user interface. SatStressGUI computes stress vectors and Love numbers, and generates stress plots and lineaments. We have expanded on SatStressGUI by adding features such as the ability to generate cycloid-style lineaments, calculate stresses resulting from obliquity, and more efficient batch the processing of data. Users may also define their own Love numbers to propagate through further calculations. Here we demonstrate our recent enhancements to SatStressGUI and its abilities, by comparing observed features on Enceladus and Europa to modeled diurnal, nonsynchronous, and obliquity stresses.

Perceptions of webcams in the neonatal intensive care unit: here's looking at you kid!

PubMed

Hawkes, Gavin A; Livingstone, Vicki; Ryan, C Anthony; Dempsey, Eugene Michael

2015-02-01

Many tertiary neonatal units employ a restricted visiting policy. Webcams have previously been implemented in the neonatal unit setting in several countries. This study aims to determine the views from parents, physicians, and nursing staff before implementation of a webcam system. A questionnaire-based study. There were 101 responses. Parental computer usage was 83%. The majority of parents indicated that they would use the webcam system. Parents felt that a webcam system would reduce stress. Members of the nursing staff were most concerned about privacy risks (68%), compared with parents who were confident in the security of these systems (92%, p-value < 0.001). Seventy two percent of nurses felt that a webcam system would increase the stress levels of staff as compared with less than 20% of the physicians (p-value < 0.001). The majority of parents who completed the questionnaire have positive attitudes toward implementation of a webcam system in the NICU. Education of health care staff is required before implementation. Thieme Medical Publishers 333 Seventh Avenue, New York, NY 10001, USA.

Study of inducer load and stress, volume 2

NASA Technical Reports Server (NTRS)

1972-01-01

A program of analysis, design, fabrication and testing has been conducted to develop computer programs for predicting rocket engine turbopump inducer hydrodynamic loading, stress magnitude and distribution, and vibration characteristics. Methods of predicting blade loading, stress, and vibration characteristics were selected from a literature search and used as a basis for the computer programs. An inducer, representative of typical rocket engine inducers, was designed, fabricated, and tested with special instrumentation selected to provide measurements of blade surface pressures and stresses. Data from the tests were compared with predicted values and the computer programs were revised as required to improve correlation. For Volume 1 see N71-20403. For Volume 2 see N71-20404.

Meta-Analysis of Stress Myocardial Perfusion Imaging

ClinicalTrials.gov

2017-06-06

Coronary Disease; Echocardiography; Fractional Flow Reserve, Myocardial; Hemodynamics; Humans; Magnetic Resonance Imaging; Myocardial Perfusion Imaging; Perfusion; Predictive Value of Tests; Single Photon Emission Computed Tomography; Positron Emission Tomography; Multidetector Computed Tomography; Echocardiography, Stress; Coronary Angiography

Simulation of Stress-Strain State of Shovel Rotary Support Kingpin

NASA Astrophysics Data System (ADS)

Khoreshok, A. A.; Buyankin, P. V.; Vorobiev, A. V.; Dronov, A. A.

2016-04-01

The article presents the sequence of computational simulation of stress-strain state of shovel’s rotary support. Computation results are analyzed, the kingpin is specified as the most loaded element, maximum stress zones are identified. Kingpin design modification such as enhancement of fillet curvature radius to 25 mm and displacement of eyebolt holes on the diameter of 165 mm are proposed, thus diminishing impact of stress concentrators and improving reliability of the rotary support.

Stress-related cortisol responsivity modulates prospective memory.

PubMed

Glienke, K; Piefke, M

2017-12-01

It is known that there is inter-individual variation in behavioural and physiological stress reactions to the same stressor. The present study aimed to examine the impact of cortisol responsivity on performance in a complex real life-like prospective memory (PM) paradigm by a re-analysis of data published previously, with a focus on the taxonomy of cognitive dimensions of PM. Twenty-one male subjects were stressed with the Socially Evaluated Cold Pressor Test (SECPT) before the planning of intentions. Another group of 20 males underwent a control procedure. Salivary cortisol was measured to assess the intensity of the biological stress response. Additionally, participants rated the subjective experience of stress on a 5-point rating scale. Stressed participants were post-hoc differentiated in high (n = 11) and low cortisol responders (n = 10). Cortisol niveau differed significantly between the two groups, whereas subjective stress ratings did not. PM performance of low cortisol responders was stable across time and the PM performance of controls declined. High cortisol responders showed a nominally weaker PM retrieval across the early trails and significantly improved only on the last trial. The data demonstrate for the first time that participants with a low cortisol responsivity may benefit from stress exposure before the planning phase of PM. PM performance of high cortisol responders shows a more inconsistent pattern, which may be interpreted in the sense of a recency effect in PM retrieval. Alternatively, high cortisol responses may have a deteriorating effect on PM retrieval, which disappeared on the last trials of the task as a result of the decrease of cortisol levels across time. Importantly, the data also demonstrate that the intensity of cortisol responses does not necessarily correspond to the intensity of the mental experience of stress. © 2017 British Society for Neuroendocrinology.

Effects of Computer-Based Practice on the Acquisition and Maintenance of Basic Academic Skills for Children with Moderate to Intensive Educational Needs

ERIC Educational Resources Information Center

Everhart, Julie M.; Alber-Morgan, Sheila R.; Park, Ju Hee

2011-01-01

This study investigated the effects of computer-based practice on the acquisition and maintenance of basic academic skills for two children with moderate to intensive disabilities. The special education teacher created individualized computer games that enabled the participants to independently practice academic skills that corresponded with their…

Noise levels in fitness classes are still too high: evidence from 1997-1998 and 2009-2011.

PubMed

Beach, Elizabeth Francis; Nie, Valerie

2014-01-01

Fitness instructors routinely use high music volumes that may be harmful to hearing. This study assessed noise levels during 35 low-intensity and 65 high-intensity fitness classes in 1997-1998 and 2009-2011. Questionnaires examined instructors' and clients' preferred music volumes and whether they found loud music "stressful" or "motivating." Noise levels in 1997-1998 and 2009-2011 were similar, frequently exceeding 90 dB(A). Although noise levels in low-intensity classes dropped from 88.9 to 85.6 dB(A), they remained high for high-intensity classes, averaging 93.1 dB(A). In 2009-2011, instructors preferred significantly higher volumes than clients for high-intensity classes. In both time periods, about 85% of instructors found loud music motivating, whereas about one fifth of clients found it stressful. The results suggest that noise exposure from fitness classes, particularly high-intensity classes, continues to pose a potential risk to hearing.

Composite Repairs of Cracked Metallic Airframe Structures

DTIC Science & Technology

1993-05-01

painting of the surface of composites. Therefore, repairs on external surfaces of aircraft should be painted prior to service. 30 2. ANALITICAL AND...tends to decrease the ’apparent’ stress intensity factor. These factors have to be taken into account when comparing the analytical predictions with the...analytical predictions . The fatigue crack growth data for one of the specimens appears in Figure 2-46Zhe ’Inferred’ stress-intensity factor [from the

The surface crack problem in an orthotropic plate under bending and tension

NASA Technical Reports Server (NTRS)

Wu, Bing-Hua; Erdogan, F.

1987-01-01

The elasticity problem for an infinite orthotropic flat plate containing a series of through and part through cracks and subjected to bending and tension loads is considered. The problem is formulated by using Reissner's plate bending theory and considering three-dimensional material orthotropy. The Line-spring model developed by Rice and Levy is used to formulate the surface crack problem in which a total of nine material constants were used. The effects of material orthotropy on the stress intensity factors was determined, the interaction between two asymmetrically arranged collinear cracks was investigated, and extensive numerical results regarding the stress intensity factors are provided. The problem is reduced to a system of singular integral equations which is solved by using the Gauss-Chebyshev quadrature formulas. The calculated results show that the material orthotropy does have a significant effect on the stress intensity factor.

The surface crack problem in an orthotropic plate under bending and tension

NASA Technical Reports Server (NTRS)

Wu, B. H.; Erdogan, F.

1986-01-01

The elasticity problem for an infinite orthotropic flat plate containing a series of through and part-through cracks and subjected to bending and tension loads is considered. The problem is formulated by using Reissner's plate bending theory and considering three dimensional materials orthotropy. The Line-spring model developed by Rice and Levy is used to formulate the surface crack problem in which a total of nine material constants has been used. The main purpose of this study is to determine the effect of material orthotropy on the stress intensity factors, to investigate the interaction between two asymmetrically arranged collinear cracks, and to provide extensive numerical results regarding the stress intensity factors. The problem is reduced to a system of singular integral equations which is solved by using the Gauss-Chebyshev quadrature formulas. The calculated results show that the material orthotropy does have a significant effect on the stress intensity factor.

Strain Measurements within Fibre Boards. Part II: Strain Concentrations at the Crack Tip of MDF Specimens Tested by the Wedge Splitting Method

PubMed Central

Sinn, Gerhard; Müller, Ulrich; Konnerth, Johannes; Rathke, Jörn

2012-01-01

This is the second part of an article series where the mechanical and fracture mechanical properties of medium density fiberboard (MDF) were studied. While the first part of the series focused on internal bond strength and density profiles, this article discusses the fracture mechanical properties of the core layer. Fracture properties were studied with a wedge splitting setup. The critical stress intensity factors as well as the specific fracture energies were determined. Critical stress intensity factors were calculated from maximum splitting force and two-dimensional isotropic finite elements simulations of the specimen geometry. Size and shape of micro crack zone were measured with electronic laser speckle interferometry. The process zone length was approx. 5 mm. The specific fracture energy was determined to be 45.2 ± 14.4 J/m2 and the critical stress intensity factor was 0.11 ± 0.02 MPa.

Low intensity aerobic exercise and oxidative stress markers in older adults.

PubMed

Bouzid, Mohamed A; Hammouda, Omar; Matran, Régis; Robin, Sophie; Fabre, Claudine

2014-10-01

This comparative study examined the effects of regular low intensity aerobic exercise on oxidative stress markers in older adults. The study was carried out on 15 sedentary subjects (age: 65.1 ± 3.5 years) versus 18 subjects performing fitness exercises (age: 65.8 ± 3.3 years). Before and after an incremental exercise test, oxidative stress markers were assessed. Superoxide dismutase was higher at rest and at the recovery for the physically active subjects compared with sedentary subjects (p < .05). At recovery, glutathione peroxidase and α -Tocopherol increased significantly above the resting values only in the active group (p < .05). Malondialdehyde had increased in both groups (p < .01), associated with a higher level in the sedentary group (p < .05) at the recovery. These data suggest that low intensity aerobic exercise may be useful to prevent the decline of antioxidants linked with aging.

A study of spectrum fatigue crack propagation in two aluminum alloys. 1: Spectrum simplification

NASA Technical Reports Server (NTRS)

Telesman, J.; Antolovich, S. D.

1985-01-01

The fatigue crack propagation behavior of two commercial Al alloys was studied using spectrum loading conditions characteristics of those encountered at critical locations in high performance fighter aircraft. A tension dominated (TD) and tension compression (TC) spectrum were employed for each alloy. Using a mechanics-based analysis, it was suggested that negative loads could be eliminated for the TC spectrum for low to intermediate maximum stress intensities. The suggestion was verified by subsequent testing. Using fractographic evidence, it was suggested that a further similification in the spectra could be accomplished by eliminating low and intermediate peak load points resulting in near or below threshold maximum peak stress intensity values. It is concluded that load interactions become more important at higher stress intensities and more plasticity at the crack tip. These results suggest that a combined mechanics/fractographic mechanisms approach can be used to simplify other complex spectra.

Effect of stress and attention on startle response and prepulse inhibition.

PubMed

De la Casa, Luis Gonzalo; Mena, Auxiliadora; Ruiz-Salas, Juan Carlos

2016-10-15

The startle reflex magnitude can be modulated when a weak stimulus is presented before the onset of the startle stimulus, a phenomenon termed prepulse inhibition (PPI). Previous research has demonstrated that emotional processes can modulate PPI and startle intensity, but the available evidence is inconclusive. In order to obtain additional evidence in this domain, we conducted two experiments intended to analyze the effect of induced stress and attentional load on PPI and startle magnitude. Specifically, in Experiment 1 we used a between subject strategy to evaluate the effect on startle response and PPI magnitude of performing a difficult task intended to induce stress in the participants, as compared to a group exposed to a control task. In Experiment 2 we evaluated the effect of diverting attention from the acoustic stimulus on startle and PPI intensity. The results seem to indicate that induced stress can reduce PPI, and that startle reflex intensity is reduced when attention is directed away from the auditory stimulus that induces the reflex. Copyright © 2016 Elsevier Inc. All rights reserved.

Mental and Physical Workload, Salivary Stress Biomarkers and Taste Perception: Mars Desert Research Station Expedition

PubMed Central

Rai, Balwant; Kaur, Jasdeep

2012-01-01

Background: Very few studies have been conducted on the effects of simulation of Mars conditions on taste. Aims: This study was planned to find the effects of physical and mental workload on taste sensitivity and salivary stress biomarkers. Materials and Methods: Twelve crew members were selected. Taste reactions and intensity of the taste sensations to quinine sulfate, citric acid, and sucrose were tested before and after mental and physical tasks for one hour. Also, psychological mood states by profile of mood state, salivary, salivary alpha amylase and cortisol, and current stress test scores were measured before and after mental and physical tasks. Results: Average time intensity evaluation showed that after the mental and physical tasks, the perceived duration of bitter, sour, and sweet taste sensations was significantly shortened relative to control group. There were good correlations between average time intensity of sweetness, bitterness, sourness and cortisol levels. Conclusions: Taste alterations due to stress can have an effect on the health and confidence of astronauts in long- term space missions. Thus, this issue remains one of the important issues for future human explorations. PMID:23181230

Application verification research of cloud computing technology in the field of real time aerospace experiment

NASA Astrophysics Data System (ADS)

Wan, Junwei; Chen, Hongyan; Zhao, Jing

2017-08-01

According to the requirements of real-time, reliability and safety for aerospace experiment, the single center cloud computing technology application verification platform is constructed. At the IAAS level, the feasibility of the cloud computing technology be applied to the field of aerospace experiment is tested and verified. Based on the analysis of the test results, a preliminary conclusion is obtained: Cloud computing platform can be applied to the aerospace experiment computing intensive business. For I/O intensive business, it is recommended to use the traditional physical machine.

A Fast Synthetic Aperture Radar Raw Data Simulation Using Cloud Computing.

PubMed

Li, Zhixin; Su, Dandan; Zhu, Haijiang; Li, Wei; Zhang, Fan; Li, Ruirui

2017-01-08

Synthetic Aperture Radar (SAR) raw data simulation is a fundamental problem in radar system design and imaging algorithm research. The growth of surveying swath and resolution results in a significant increase in data volume and simulation period, which can be considered to be a comprehensive data intensive and computing intensive issue. Although several high performance computing (HPC) methods have demonstrated their potential for accelerating simulation, the input/output (I/O) bottleneck of huge raw data has not been eased. In this paper, we propose a cloud computing based SAR raw data simulation algorithm, which employs the MapReduce model to accelerate the raw data computing and the Hadoop distributed file system (HDFS) for fast I/O access. The MapReduce model is designed for the irregular parallel accumulation of raw data simulation, which greatly reduces the parallel efficiency of graphics processing unit (GPU) based simulation methods. In addition, three kinds of optimization strategies are put forward from the aspects of programming model, HDFS configuration and scheduling. The experimental results show that the cloud computing based algorithm achieves 4_ speedup over the baseline serial approach in an 8-node cloud environment, and each optimization strategy can improve about 20%. This work proves that the proposed cloud algorithm is capable of solving the computing intensive and data intensive issues in SAR raw data simulation, and is easily extended to large scale computing to achieve higher acceleration.

The crack problem in bonded nonhomogeneous materials

NASA Technical Reports Server (NTRS)

Erdogan, Fazil; Kaya, A. C.; Joseph, P. F.

1988-01-01

The plane elasticity problem for two bonded half planes containing a crack perpendicular to the interface was considered. The effect of very steep variations in the material properties near the diffusion plane on the singular behavior of the stresses and stress intensity factors were studied. The two materials were thus, assumed to have the shear moduli mu(o) and mu(o) exp (Beta x), x=0 being the diffusion plane. Of particular interest was the examination of the nature of stress singularity near a crack tip terminating at the interface where the shear modulus has a discontinuous derivative. The results show that, unlike the crack problem in piecewise homogeneous materials for which the singularity is of the form r/alpha, 0 less than alpha less than 1, in this problem the stresses have a standard square-root singularity regardless of the location of the crack tip. The nonhomogeneity constant Beta has, however, considerable influence on the stress intensity factors.

The crack problem in bonded nonhomogeneous materials

NASA Technical Reports Server (NTRS)

Erdogan, F.; Joseph, P. F.; Kaya, A. C.

1991-01-01

The plane elasticity problem for two bonded half planes containing a crack perpendicular to the interface was considered. The effect of very steep variations in the material properties near the diffusion plane on the singular behavior of the stresses and stress intensity factors were studied. The two materials were thus, assumed to have the shear moduli mu(o) and mu(o) exp (Beta x), x=0 being the diffusion plane. Of particular interest was the examination of the nature of stress singularity near a crack tip termination at the interface where the shear modulus has a discontinuous derivative. The results show that, unlike the crack problem in piecewise homogeneous materials for which the singularity is of the form r/alpha, 0 less than alpha less than 1, in this problem the stresses have a standard square-root singularity regardless of the location of the crack tip. The nonhomogeneity constant Beta has, however, considerable influence on the stress intensity factors.

Unit Reconstitutions: Combat Stress as an Indicator of Unit Effectiveness

DTIC Science & Technology

2014-06-13

Soldier and unit readiness by- A. Enhancing adaptive stress reactions. B. Preventing maladaptive stress reactions. 8 C. Assisting Soldiers with......and intensity of the most recent combat experience. 4. Physical condition of the soldiers. This includes their nutritional status, number and status

Objective Versus Subjective Measurement of Stress and Social Support: Combat-Related Reactions.

ERIC Educational Resources Information Center

Solomon, Zahava; And Others

1987-01-01

Studied combat intensity, social support, and related stress reactions among soldiers who fought in the 1982 Israeli-Lebanon War, comparing those who experienced combat stress reaction (N=382) and those who did not (N=344). Subjective indicators were found to be stronger predictors than were objective indicators. Combat stress reaction was clearly…

Analysis of intensity variability in multislice and cone beam computed tomography.

PubMed

Nackaerts, Olivia; Maes, Frederik; Yan, Hua; Couto Souza, Paulo; Pauwels, Ruben; Jacobs, Reinhilde

2011-08-01

The aim of this study was to evaluate the variability of intensity values in cone beam computed tomography (CBCT) imaging compared with multislice computed tomography Hounsfield units (MSCT HU) in order to assess the reliability of density assessments using CBCT images. A quality control phantom was scanned with an MSCT scanner and five CBCT scanners. In one CBCT scanner, the phantom was scanned repeatedly in the same and in different positions. Images were analyzed using registration to a mathematical model. MSCT images were used as a reference. Density profiles of MSCT showed stable HU values, whereas in CBCT imaging the intensity values were variable over the profile. Repositioning of the phantom resulted in large fluctuations in intensity values. The use of intensity values in CBCT images is not reliable, because the values are influenced by device, imaging parameters and positioning. © 2011 John Wiley & Sons A/S.

Autobiographical Memory for Stressful Events: The Role of Autobiographical Memory in Posttraumatic Stress Disorder

PubMed Central

Rubin, David C.; Dennis, Michelle F.; Beckham, Jean C.

2011-01-01

To provide the three-way comparisons needed to test existing theories, we compared 1) most-stressful memories to other memories and 2) involuntary to voluntary memories 3) in 75 community dwelling adults with and 42 without a current diagnosis of posttraumatic stress disorder (PTSD). Each rated their 3 most-stressful, 3 most-positive, 7 most-important and 15 word-cued autobiographical memories, and completed tests of personality and mood. Involuntary memories were then recorded and rated as they occurred for two weeks. Standard mechanisms of cognition and affect applied to extreme events accounted for the properties of stressful memories. Involuntary memories had greater emotional intensity than voluntary memories, but were not more frequently related to traumatic events. The emotional intensity, rehearsal, and centrality to the life story of both voluntary and involuntary memories, rather than incoherence of voluntary traumatic memories and enhanced availability of involuntary traumatic memories, were the properties of autobiographical memories associated with PTSD. PMID:21489820

A Small Randomized Pilot Study of a Workplace Mindfulness-Based Intervention for Surgical Intensive Care Unit Personnel: Effects on Salivary α-Amylase Levels

PubMed Central

Duchemin, Anne-Marie; Steinberg, Beth A.; Marks, Donald R.; Vanover, Kristin; Klatt, Maryanna

2015-01-01

Objective To determine if a workplace stress-reduction intervention decreases reactivity to stress among personnel exposed to a highly stressful occupational environment. Methods Personnel from a surgical intensive care unit (SICU) were randomized to a stress reduction intervention or a wait-list control group. The 8-week group mindfulness-based intervention (MBI) included mindfulness, gentle yoga and music. Psychological and biological markers of stress were measured one week before and one week after the intervention. Results Levels of salivary α-amylase, an index of sympathetic activation, were significantly decreased between the 1st and 2nd assessments in the intervention group with no changes in the control group. There was a positive correlation between salivary α-amylase levels and burnout scores. Conclusions These data suggest that this type of intervention could not only decrease reactivity to stress, but also decrease the risk of burnout. PMID:25629803

Extremity movements help occupational therapists identify stress responses in preterm infants in the neonatal intensive care unit: a systematic review.

PubMed

Holsti, Liisa; Grunau, Ruth E

2007-06-01

Accurate assessment and treatment of pain and stress in preterm infants in neonatal intensive care units (NICU) is vital because pain and stress responses have been linked to long-term alterations in development in this population. To review the evidence of specific extremity movements in preterm infants as observed during stressful procedures. Five on-line databases were searched for relevant studies. For each study, levels of evidence were determined and effect size estimates were calculated. Each study was also evaluated for specific factors that presented potential threats to its validity. Eighteen studies were identified and seven comprised the review. The combined sample included 359 preterm infants. Six specific movements were associated with painful and intrusive procedures. A set of specific extremity movements, when combined with other reliable biobehavioural measures of pain and stress, can form the basis for future research and development of a clinical stress scale for preterm infants.

Human Milk Management Redesign: Improving Quality and Safety and Reducing Neonatal Intensive Care Unit Nurse Stress.

PubMed

Settle, Margaret Doyle; Coakley, Amanda Bulette; Annese, Christine Donahue

2017-02-01

Human milk provides superior nutritional value for infants in the neonatal intensive care unit and is the enteral feeding of choice. Our hospital used the system engineering initiative for patient safety model to evaluate the human milk management system in our neonatal intensive care unit. Nurses described the previous process in a negative way, fraught with opportunities for error, increased stress for nurses, and the need to be away from the bedside and their patients. The redesigned process improved the quality and safety of human milk management and created time for the nurses to spend with their patients.

Integral flange design program. [procedure for computing stresses

NASA Technical Reports Server (NTRS)

Wilson, J. F.

1974-01-01

An automated interactive flange design program utilizing an electronic desk top calculator is presented. The program calculates the operating and seating stresses for circular flanges of the integral or optional type subjected to internal pressure. The required input information is documented. The program provides an automated procedure for computing stresses in selected flange geometries for comparison to the allowable code values.

A wind-tunnel investigation of the effects of thrust-axis inclination on propeller first-order vibration

NASA Technical Reports Server (NTRS)

Gray, W H; Hallissy, J M , Jr

1950-01-01

Data on the aerodynamic excitation of first-order vibration occurring in a representative three-blade propeller having its thrust axis inclined to the air stream at angles of 0 degrees, 4.55 degrees, and 9.8 degrees are included in this paper. For several representative conditions the aerodynamic excitation has been computed and compared with the measured values. Blade stresses also were measured to permit the evaluation of the blade stress resulting from a given blade aerodynamic excitation. It was concluded that the section aerodynamic exciting force of a pitched propeller may be computed accurately at low rotational speeds. As section velocities approach the speed of sound, the accuracy of computation of section aerodynamic exciting force is not always so satisfactory. First-order blade vibratory stresses were computed with satisfactory accuracy from untilted-propeller loading data. A stress prediction which assumes a linear relation between first-order vibratory stress and the product of pitch angle and dynamic pressure and which is based on stresses at low rotational speeds will be conservative when the outer portions of the blade are in the transonic and low supersonic speed range.

Physical validation of a patient-specific contact finite element model of the ankle.

PubMed

Anderson, Donald D; Goldsworthy, Jane K; Li, Wendy; James Rudert, M; Tochigi, Yuki; Brown, Thomas D

2007-01-01

A validation study was conducted to determine the extent to which computational ankle contact finite element (FE) results agreed with experimentally measured tibio-talar contact stress. Two cadaver ankles were loaded in separate test sessions, during which ankle contact stresses were measured with a high-resolution (Tekscan) pressure sensor. Corresponding contact FE analyses were subsequently performed for comparison. The agreement was good between FE-computed and experimentally measured mean (3.2% discrepancy for one ankle, 19.3% for the other) and maximum (1.5% and 6.2%) contact stress, as well as for contact area (1.7% and 14.9%). There was also excellent agreement between histograms of fractional areas of cartilage experiencing specific ranges of contact stress. Finally, point-by-point comparisons between the computed and measured contact stress distributions over the articular surface showed substantial agreement, with correlation coefficients of 90% for one ankle and 86% for the other. In the past, general qualitative, but little direct quantitative agreement has been demonstrated with articular joint contact FE models. The methods used for this validation enable formal comparison of computational and experimental results, and open the way for objective statistical measures of regional correlation between FE-computed contact stress distributions from comparison articular joint surfaces (e.g., those from an intact versus those with residual intra-articular fracture incongruity).

Psychology of computer use: XXIV. Computer-related stress among technical college students.

PubMed

Ballance, C T; Rogers, S U

1991-10-01

Hudiburg's Computer Technology Hassles Scale, along with a measure of global stress and a scale on attitudes toward computers, were administered to 186 students in a two-year technical college. Hudiburg's work with the hassles scale as a measure of "technostress" was affirmed. Moderate, but statistically significant, correlations among the three scales are reported. No relationship between the hassles scale and achievement as measured by GPA was detected.

Examining the uniqueness of frequency and intensity symptom ratings in posttraumatic stress disorder assessment.

PubMed

Elhai, Jon D; Lindsay, Brenda M; Gray, Matt J; Grubaugh, Anouk L; North, Terry C; Frueh, B Christopher

2006-12-01

Data from two studies are presented, investigating the relative effectiveness of posttraumatic stress disorder (PTSD) symptom frequency and intensity rating dimensions, in assessing overall PTSD severity and diagnosis. We assessed frequency and intensity ratings using 1) the Modified PTSD Symptom Scale with 298 trauma-exposed college students, and 2) the Clinician-Administered PTSD Scale with 130 combat-exposed military veterans. Results demonstrated little empirical justification for separating frequency and intensity ratings when measuring PTSD. Large overlaps in variance were evidenced between the dimensions (suggesting construct redundancy), with little meaningful contribution to diagnosing PTSD using one dimension over the other. Implications for future PTSD clinical and research assessment are discussed, including the potential to decrease administration time for these commonly used PTSD measures, given their time-consuming nature.

Ongoing exposure versus intense periodic exposure to military conflict and terror attacks in Israel.

PubMed

Lahad, Mooli; Leykin, Dmitry

2010-12-01

The manifestation of posttraumatic stress disorder (PTSD) symptoms in two clinical samples in Israel (N = 212) was examined. Individuals suffering ongoing exposure to shelling were compared with subjects exposed to intense periodic exposure. Elevated arousal and avoidance symptoms, but not intrusion were reported in the ongoing exposure group. When compared by age, young participants in the ongoing exposure group had significantly lower PTSD scores, whereas no differences were found between participants among the intense periodic exposure age groups. No gender differences in symptoms were found among participants from intense periodic exposure, whereas in the other ongoing group the difference was in avoidance. Results are discussed in light of past research on exposure to terrorism. Copyright © 2010 International Society for Traumatic Stress Studies.

ASR4: A computer code for fitting and processing 4-gage anelastic strain recovery data

DOE Office of Scientific and Technical Information (OSTI.GOV)

Warpinski, N.R.

A computer code for analyzing four-gage Anelastic Strain Recovery (ASR) data has been modified for use on a personal computer. This code fits the viscoelastic model of Warpinski and Teufel to measured ASR data, calculates the stress orientation directly, and computes stress magnitudes if sufficient input data are available. The code also calculates the stress orientation using strain-rosette equations, and its calculates stress magnitudes using Blanton's approach, assuming sufficient input data are available. The program is written in FORTRAN, compiled with Ryan-McFarland Version 2.4. Graphics use PLOT88 software by Plotworks, Inc., but the graphics software must be obtained by themore » user because of licensing restrictions. A version without graphics can also be run. This code is available through the National Energy Software Center (NESC), operated by Argonne National Laboratory. 5 refs., 3 figs.« less

An analytical approach for the calculation of stress-intensity factors in transformation-toughened ceramics

NASA Astrophysics Data System (ADS)

Müller, W. H.

1990-12-01

Stress-induced transformation toughening in Zirconia-containing ceramics is described analytically by means of a quantitative model: A Griffith crack which interacts with a transformed, circular Zirconia inclusion. Due to its volume expansion, a ZrO2-particle compresses its flanks, whereas a particle in front of the crack opens the flanks such that the crack will be attracted and finally absorbed. Erdogan's integral equation technique is applied to calculate the dislocation functions and the stress-intensity-factors which correspond to these situations. In order to derive analytical expressions, the elastic constants of the inclusion and the matrix are assumed to be equal.

Geometric effects in microfluidics on heterogeneous cell stress using an Eulerian-Lagrangian approach.

PubMed

Warren, K M; Mpagazehe, J N; LeDuc, P R; Higgs, C F

2016-02-07

The response of individual cells at the micro-scale in cell mechanics is important in understanding how they are affected by changing environments. To control cell stresses, microfluidics can be implemented since there is tremendous control over the geometry of the devices. Designing microfluidic devices to induce and manipulate stress levels on biological cells can be aided by computational modeling approaches. Such approaches serve as an efficient precursor to fabricating various microfluidic geometries that induce predictable levels of stress on biological cells, based on their mechanical properties. Here, a three-dimensional, multiphase computational fluid dynamics (CFD) modeling approach was implemented for soft biological materials. The computational model incorporates the physics of the particle dynamics, fluid dynamics and solid mechanics, which allows us to study how stresses affect the cells. By using an Eulerian-Lagrangian approach to treat the fluid domain as a continuum in the microfluidics, we are conducting studies of the cells' movement and the stresses applied to the cell. As a result of our studies, we were able to determine that a channel with periodically alternating columns of obstacles was capable of stressing cells at the highest rate, and that microfluidic systems can be engineered to impose heterogenous cell stresses through geometric configuring. We found that when using controlled geometries of the microfluidics channels with staggered obstructions, we could increase the maximum cell stress by nearly 200 times over cells flowing through microfluidic channels with no obstructions. Incorporating computational modeling in the design of microfluidic configurations for controllable cell stressing could help in the design of microfludic devices for stressing cells such as cell homogenizers.

Relocation stress in critical care: a review of the literature.

PubMed

McKinney, Aidín A; Melby, Vidar

2002-03-01

1. Transfer to the ward following a period in intensive care may cause stress for patients. 2. A review of the literature reveals that this phenomenon has been described in a number of different ways, such as transfer stress, transfer anxiety, translocation syndrome and, more recently, relocation stress. 3. This paper reviews the various concepts before arriving at a more operational definition of the phenomenon. 4. It attempts to reveal what causes this phenomenon and to what extent it exists. 5. Patients' responses to transfer are identified and the physical and psychological problems that have been associated with discharge from intensive care are discussed. 6. Lists of interventions that the literature suggests may reduce or prevent this phenomenon from occurring are reviewed. 7. Recommendations for practice development and further research are made.

Bonded orthotropic strips with cracks

NASA Technical Reports Server (NTRS)

Delale, F.; Erdogan, F.

1978-01-01

The elastostatic problem for a nonhomogeneous plane which consists of two sets of periodically arranged dissimilar orthotropic strips is considered. First, the problem of cracks fully imbedded into the homogeneous strips is considered. Then, the singular behavior of the stresses for two special crack geometries is studied in some detail. The first is the case of a broken laminate in which the crack tips touch the interfaces. The second is the case of cracks crossing the interfaces. A number of numerical examples are worked out in order to separate the primary material parameters influencing the stress intensity factors and the powers of stress singularity, and to determine the trends regarding the influence of the secondary parameters. Finally, some numerical results are given for the stress intensity factors in certain basic crack geometries and for typical material combinations.

Stress intensity factors in a cracked infinite elastic wedge loaded by a rigid punch

NASA Technical Reports Server (NTRS)

Erdogan, F.; Civelek, M. B.

1978-01-01

A plane elastic wedge-shaped solid was split through the application of a rigid punch. It was assumed that the coefficient of friction on the the contact area was constant, and the problem had a plane of symmetry with respect to loading and geometry, with the crack in the plane of symmetry. The problem was formulated in terms of a system of integral equations with the contact stress and the derivative of the crack surface displacement as the unknown functions. The solution was obtained for an internal crack and for an edge crack. The results include primarily the stress intensity factors at the crack tips, and the measure of the stress singularity at the wedge apex, and at the end points of the contact area.

Navier-Stokes Computations With One-Equation Turbulence Model for Flows Along Concave Wall Surfaces

NASA Technical Reports Server (NTRS)

Wang, Chi R.

2005-01-01

This report presents the use of a time-marching three-dimensional compressible Navier-Stokes equation numerical solver with a one-equation turbulence model to simulate the flow fields developed along concave wall surfaces without and with a downstream extension flat wall surface. The 3-D Navier- Stokes numerical solver came from the NASA Glenn-HT code. The one-equation turbulence model was derived from the Spalart and Allmaras model. The computational approach was first calibrated with the computations of the velocity and Reynolds shear stress profiles of a steady flat plate boundary layer flow. The computational approach was then used to simulate developing boundary layer flows along concave wall surfaces without and with a downstream extension wall. The author investigated the computational results of surface friction factors, near surface velocity components, near wall temperatures, and a turbulent shear stress component in terms of turbulence modeling, computational mesh configurations, inlet turbulence level, and time iteration step. The computational results were compared with existing measurements of skin friction factors, velocity components, and shear stresses of the developing boundary layer flows. With a fine computational mesh and a one-equation model, the computational approach could predict accurately the skin friction factors, near surface velocity and temperature, and shear stress within the flows. The computed velocity components and shear stresses also showed the vortices effect on the velocity variations over a concave wall. The computed eddy viscosities at the near wall locations were also compared with the results from a two equation turbulence modeling technique. The inlet turbulence length scale was found to have little effect on the eddy viscosities at locations near the concave wall surface. The eddy viscosities, from the one-equation and two-equation modeling, were comparable at most stream-wise stations. The present one-equation turbulence model is an effective approach for turbulence modeling in the near solid wall surface region of flow over a concave wall.

On the Representation of Turbulent Stresses for Computing Blood Damage

PubMed Central

Hund, Samuel J.; Antaki, James F.; Massoudi, Mehrdad

2011-01-01

Computational prediction of blood damage has become a crucial tool for evaluating blood-wetted medical devices and pathological hemodynamics. A difficulty arises in predicting blood damage under turbulent flow conditions because the total stress is indeterminate. Common practice uses the Reynolds stress as an estimation of the total stress causing damage to the blood cells. This study investigates the error introduced by making this substitution, and further shows that energy dissipation is a more appropriate metric of blood trauma. PMID:21318093

Stress, coping and burnout among Intensive Care Unit nursing staff: associated factors.

PubMed

Andolhe, Rafaela; Barbosa, Ricardo Luis; Oliveira, Elaine Machado de; Costa, Ana Lúcia Siqueira; Padilha, Katia Grillo

2015-02-01

Objective To investigate emotional stress, coping and burnout among nursing staff and their association with biosocial factors and characteristics of work in Intensive Care Units (ICU). Method This was a cross-sectional study, conducted in eight ICUs at a teaching hospital in the city of São Paulo, Brazil, in October 2012. Biosocial data and information about the professionals' work was gathered, and they were given the Scale of Occupational Stress, Scale of Occupational Coping, List of Signs and Symptoms of Stress and the Maslach Burnout Inventory. Results The study sample consisted of 287 subjects, predominately women, with partners and children. Most professionals presented moderate stress levels and control as a coping strategy (74.47% and 79.93%, respectively), and burnout was present among 12.54%. Factors associated with stress were related to working conditions. The most prevalent protective factors were having a partner, working in the clinical ICU and liking work, while adequate amount of sleep was a protective factor for burnout. Conclusion Control of the working environment and adequate sleep are decisive and protective factors in dealing with situations of occupational stress.

Lifestyle Intervention Is Associated With Lower Prevalence of Urinary Incontinence

PubMed Central

Brown, Jeanette S.; Wing, Rena; Barrett-Connor, Elizabeth; Nyberg, Leroy M.; Kusek, John W.; Orchard, Trevor J.; Ma, Yong; Vittinghoff, Eric; Kanaya, Alka M.

2006-01-01

OBJECTIVE Diabetes is associated with increased urinary incontinence risk. Weight loss improves incontinence, but exercise may worsen this condition. We examined whether an intensive lifestyle intervention or metformin therapy among overweight pre-diabetic women was associated with a lower prevalence of incontinence. RESEARCH DESIGN AND METHODS We analyzed data from the Diabetes Prevention Program, a randomized controlled trial in 27 U.S. centers. Of the 1,957 women included in this analysis, 660(34%) were randomized to intensive lifestyle therapy, 636(32%) to metformin, and 661 (34%) to placebo with standard lifestyle advice. The main outcome measure was incontinence symptoms by frequency and type by a validated questionnaire completed at the end-of-trial visit (mean 2.9 years). RESULTS The prevalence of total (stress or urge) weekly incontinence was lower among women in the intensive lifestyle group (38.3%) than those randomized to metformin (48.1%) or placebo (45.7%). This difference was most apparent among women with stress incontinence (31.3% for intensive lifestyle group vs. 39.7% for metformin vs. 36.7% for placebo, P = 0.006). Changes in weight accounted for most of the protective effect of the intensive lifestyle intervention on stress incontinence. CONCLUSIONS Less-frequent urinary incontinence may be a powerful motivator for women to choose lifestyle modification to prevent diabetes. PMID:16443892

HammerCloud: A Stress Testing System for Distributed Analysis

NASA Astrophysics Data System (ADS)

van der Ster, Daniel C.; Elmsheuser, Johannes; Úbeda García, Mario; Paladin, Massimo

2011-12-01

Distributed analysis of LHC data is an I/O-intensive activity which places large demands on the internal network, storage, and local disks at remote computing facilities. Commissioning and maintaining a site to provide an efficient distributed analysis service is therefore a challenge which can be aided by tools to help evaluate a variety of infrastructure designs and configurations. HammerCloud is one such tool; it is a stress testing service which is used by central operations teams, regional coordinators, and local site admins to (a) submit arbitrary number of analysis jobs to a number of sites, (b) maintain at a steady-state a predefined number of jobs running at the sites under test, (c) produce web-based reports summarizing the efficiency and performance of the sites under test, and (d) present a web-interface for historical test results to both evaluate progress and compare sites. HammerCloud was built around the distributed analysis framework Ganga, exploiting its API for grid job management. HammerCloud has been employed by the ATLAS experiment for continuous testing of many sites worldwide, and also during large scale computing challenges such as STEP'09 and UAT'09, where the scale of the tests exceeded 10,000 concurrently running and 1,000,000 total jobs over multi-day periods. In addition, HammerCloud is being adopted by the CMS experiment; the plugin structure of HammerCloud allows the execution of CMS jobs using their official tool (CRAB).

Ecophysiological evaluation of the potential invasiveness of Rhus typhina in its non-native habitats.

PubMed

Zhang, Zhanjiang; Jiang, Chuangdao; Zhang, Jinzheng; Zhang, Huijin; Shi, Lei

2009-11-01

Rhus typhina L. (staghorn sumac) is a clonal woody species that is considered potentially invasive in its non-native habitats. It is slow growing as seedlings, but grows fast once established. Its growth in the early stages is limited by many abiotic factors, including light intensity. To evaluate its potential of becoming invasive in areas it has been introduced into, we conducted a field experiment to investigate the effects of light intensity on the physiology and growth of R. typhina. Two-month-old R. typhina seedlings were examined under five light levels, that is, 100% full sunlight (unlimited light), moderate stress (50% or 25% of full sunlight) and severe stress (10% or 5% of full sunlight), for 60 days in Hunshandak Sandland, China. Net photosynthetic rate (PN) was reduced significantly under severe light stress, but PN of the moderately stressed seedlings was unaffected. Light stress also led to a reduction in saturated light intensity of the moderately stressed seedlings by 20% and of the severely stressed seedlings by 40%, although the light saturation points were as high as 800 and 600 micromol m(-2) s(-1) for the moderately and severely stressed seedlings, respectively. Under severe light stress, the maximum quantum yield of Photosystem II (Fv/Fm) decreased significantly, but the minimal fluorescence yield (F0) increased compared to that of the control plants. The number of newly produced leaves and the stem height, however, decreased as the light intensity became lower. Root length and leaf area decreased, whereas specific leaf area significantly increased as light became increasingly lower. Biomass production was significantly reduced by light stress, but the allocation pattern was unaffected. Our results demonstrated that R. typhina seedlings can survive low light and grow well in other light conditions. The physiology and growth of R. typhina will likely enable it to acclimate to varying light conditions in Hunshandak Sandland, where R. typhina has been widely cultivated for sand stabilization and other purposes. Because of its ability to tolerate low light and to compete aggressively for light resource once established, that is, becoming invasive, we urge caution when it comes to introducing R. typhina into its non-native habitats, despite its many ecological benefits.

The perception of prosody and associated auditory cues in early-implanted children: the role of auditory working memory and musical activities.

PubMed

Torppa, Ritva; Faulkner, Andrew; Huotilainen, Minna; Järvikivi, Juhani; Lipsanen, Jari; Laasonen, Marja; Vainio, Martti

2014-03-01

To study prosodic perception in early-implanted children in relation to auditory discrimination, auditory working memory, and exposure to music. Word and sentence stress perception, discrimination of fundamental frequency (F0), intensity and duration, and forward digit span were measured twice over approximately 16 months. Musical activities were assessed by questionnaire. Twenty-one early-implanted and age-matched normal-hearing (NH) children (4-13 years). Children with cochlear implants (CIs) exposed to music performed better than others in stress perception and F0 discrimination. Only this subgroup of implanted children improved with age in word stress perception, intensity discrimination, and improved over time in digit span. Prosodic perception, F0 discrimination and forward digit span in implanted children exposed to music was equivalent to the NH group, but other implanted children performed more poorly. For children with CIs, word stress perception was linked to digit span and intensity discrimination: sentence stress perception was additionally linked to F0 discrimination. Prosodic perception in children with CIs is linked to auditory working memory and aspects of auditory discrimination. Engagement in music was linked to better performance across a range of measures, suggesting that music is a valuable tool in the rehabilitation of implanted children.

Measurement of salivary cortisol as a marker of stress in newborns in a neonatal intensive care unit.

PubMed

Cabral, Débora Macedo; Antonini, Sonir Roberto Rauber; Custódio, Rodrigo José; Martinelli, Carlos Eduardo; da Silva, Carlos Antonio Bruno

2013-01-01

The study was designed to evaluate the newborn (NB) stress response during the inpatient time in the neonatal intensive care unit. A quantitative, prospective, observational study was conducted with two NB groups. The first group consisted of 12 NB patients in the neonatal intensive care unit as the experimental group (EG), and the second included 43 NBs who were sent to their own homes and were considered the control group (CG). The EG's salivary cortisol concentration was measured on the 2nd day (D2) and 9th day (D9) of life. The CG's salivary cortisol concentration was measured on the 14th day of life at the child's own home. The salivary cortisol concentration levels for the EG on D2 and D9 and for the CG were 4.3151 ± 2.6492, 1.826 ± 1.2252, and 1.0166 ± 0.8300 ng/dl, respectively. These findings indicated the presence of an adrenal response to stress during the first inpatient days. The salivary cortisol concentration is an accurate method to indicate neonatal stress. The glucocorticoids frequently used in the prenatal period suppress the adrenal glands and interfere with the stress response. Copyright © 2013 S. Karger AG, Basel.

The effects of climate change associated abiotic stresses on maize phytochemical defenses

USDA-ARS?s Scientific Manuscript database

Reliable large-scale maize production is an essential component of global food security; however, sustained efforts are needed to ensure optimized resilience under diverse crop stress conditions. Climate changes are expected to increase the frequency and intensity of both abiotic and biotic stress. ...

Numerical Evaluation of Mode 1 Stress Intensity Factor as a Function of Material Orientation For BX-265 Foam Insulation Material

NASA Technical Reports Server (NTRS)

Knudsen, Erik; Arakere, Nagaraj K.

2006-01-01

Foam; a cellular material, is found all around us. Bone and cork are examples of biological cell materials. Many forms of man-made foam have found practical applications as insulating materials. NASA uses the BX-265 foam insulation material on the external tank (ET) for the Space Shuttle. This is a type of Spray-on Foam Insulation (SOFI), similar to the material used to insulate attics in residential construction. This foam material is a good insulator and is very lightweight, making it suitable for space applications. Breakup of segments of this foam insulation on the shuttle ET impacting the shuttle thermal protection tiles during liftoff is believed to have caused the space shuttle Columbia failure during re-entry. NASA engineers are very interested in understanding the processes that govern the breakup/fracture of this complex material from the shuttle ET. The foam is anisotropic in nature and the required stress and fracture mechanics analysis must include the effects of the direction dependence on material properties. Material testing at NASA MSFC has indicated that the foam can be modeled as a transversely isotropic material. As a first step toward understanding the fracture mechanics of this material, we present a general theoretical and numerical framework for computing stress intensity factors (SIFs), under mixed-mode loading conditions, taking into account the material anisotropy. We present mode I SIFs for middle tension - M(T) - test specimens, using 3D finite element stress analysis (ANSYS) and FRANC3D fracture analysis software, developed by the Cornel1 Fracture Group. Mode I SIF values are presented for a range of foam material orientations. Also, NASA has recorded the failure load for various M(T) specimens. For a linear analysis, the mode I SIF will scale with the far-field load. This allows us to numerically estimate the mode I fracture toughness for this material. The results represent a quantitative basis for evaluating the strength and fracture properties of anisotropic foam insulation material.

Caprock Integrity during Hydrocarbon Production and CO2 Injection in the Goldeneye Reservoir

NASA Astrophysics Data System (ADS)

Salimzadeh, Saeed; Paluszny, Adriana; Zimmerman, Robert

2016-04-01

Carbon Capture and Storage (CCS) is a key technology for addressing climate change and maintaining security of energy supplies, while potentially offering important economic benefits. UK offshore, depleted hydrocarbon reservoirs have the potential capacity to store significant quantities of carbon dioxide, produced during power generation from fossil fuels. The Goldeneye depleted gas condensate field, located offshore in the UK North Sea at a depth of ~ 2600 m, is a candidate for the storage of at least 10 million tons of CO2. In this research, a fully coupled, full-scale model (50×20×8 km), based on the Goldeneye reservoir, is built and used for hydro-carbon production and CO2 injection simulations. The model accounts for fluid flow, heat transfer, and deformation of the fractured reservoir. Flow through fractures is defined as two-dimensional laminar flow within the three-dimensional poroelastic medium. The local thermal non-equilibrium between injected CO2 and host reservoir has been considered with convective (conduction and advection) heat transfer. The numerical model has been developed using standard finite element method with Galerkin spatial discretisation, and finite difference temporal discretisation. The geomechanical model has been implemented into the object-oriented Imperial College Geomechanics Toolkit, in close interaction with the Complex Systems Modelling Platform (CSMP), and validated with several benchmark examples. Fifteen major faults are mapped from the Goldeneye field into the model. Modal stress intensity factors, for the three modes of fracture opening during hydrocarbon production and CO2 injection phases, are computed at the tips of the faults by computing the I-Integral over a virtual disk. Contact stresses -normal and shear- on the fault surfaces are iteratively computed using a gap-based augmented Lagrangian-Uzawa method. Results show fault activation during the production phase that may affect the fault's hydraulic conductivity and its connection to the reservoir rocks. The direction of growth is downward during production and it is expected to be upward during injection. Elevated fluid pressures inside faults during CO2 injection may further facilitate fault activation by reducing normal effective stresses. Activated faults can act as permeable conduits and potentially jeopardise caprock integrity for CO2 storage purposes.

Thermal stresses in composite tubes using complementary virtual work

NASA Technical Reports Server (NTRS)

Hyer, M. W.; Cooper, D. E.

1988-01-01

This paper addresses the computation of thermally induced stresses in layered, fiber-reinforced composite tubes subjected to a circumferential gradient. The paper focuses on using the principle of complementary virtual work, in conjunction with a Ritz approximation to the stress field, to study the influence on the predicted stresses of including temperature-dependent material properties. Results indicate that the computed values of stress are sensitive to the temperature dependence of the matrix-direction compliance and matrix-direction thermal expansion in the plane of the lamina. There is less sensitivity to the temperature dependence of the other material properties.

Effects of stress management program on the quality of nursing care and intensive care unit nurses

PubMed Central

Pahlavanzadeh, Saied; Asgari, Zohreh; Alimohammadi, Nasrollah

2016-01-01

Background: High level of stress in intensive care unit nurses affects the quality of their nursing care. Therefore, this study aimed to determine the effects of a stress management program on the quality of nursing care of intensive care unit nurses. Materials and Methods: This study is a randomized clinical trial that was conducted on 65 nurses. The samples were selected by stratified sampling of the nurses working in intensive care units 1, 2, 3 in Al-Zahra Hospital in Isfahan, Iran and were randomly assigned to two groups. The intervention group underwent an intervention, including 10 sessions of stress management that was held twice a week. In the control group, placebo sessions were held simultaneously. Data were gathered by demographic checklist and Quality Patient Care Scale before, immediately after, and 1 month after the intervention in both groups. Then, the data were analyzed by Student's t-test, Mann–Whitney, Chi-square, Fisher's exact test, and analysis of variance (ANOVA) through SPSS software version 18. Results: Mean scores of overall and dimensions of quality of care in the intervention group were significantly higher immediately after and 1 month after the intervention, compared to pre-intervention (P < 0.001). The results showed that the quality of care in the intervention group was significantly higher immediately after and 1 month after the intervention, compared to the control group (P < 0.001). Conclusions: As stress management is an effective method to improve the quality of care, the staffs are recommended to consider it in improvement of the quality of nursing care. PMID:27186196

Measurement of Kirchhoff's stress intensity factors in bending plates

NASA Astrophysics Data System (ADS)

Bäcker, D.; Kuna, M.; Häusler, C.

2014-03-01

A measurement method of the stress intensity factors defined by KIRCHHOFF's theory for a crack in a bending plate is shown. For this purpose, a thin piezoelectric polyvinylidene fluoride film (PVDF) is attached to the surface of the cracked plate. The measured electrical voltages are coupled with the load type and the crack tip position relative to the sensor film. Stress intensity factors and the crack tip position can be determined by solving the non-linear inverse problem based on the measured signals. To guarantee solvability of the problem, more measuring electrodes on the film have to be taken in to account. To the developed sensor concept the KIRCHHOFF's plate theory has been applied. In order to connect the electrical signals and the stress intensity factors the stresses near the crack tip have to be written in eigenfunctions (see WILLIAMS [1]). The presented method was verified by means of the example of a straight crack of the length 2a in an infinite isotropic plate under all- side bending. It was found that the positioning of the electrodes is delimited by two radii. On one hand, the measurement points should not be too close to the crack tip. In this area, the Kirchhoff's plate theory cannot be used effectively. On the other hand, the measuring electrodes should be placed at a smaller distance to each other and not too far from the crack tip regarding the convergence radius of the WILLIAMS series expansion. Test calculations on a straight crack in an infinite isotropic plate showed the general applicability of the measurement method.

Lifetime prediction for the subsurface crack propagation using three-dimensional dynamic FEA model

NASA Astrophysics Data System (ADS)

Yin, Yuan; Chen, Yun-Xia; Liu, Le

2017-03-01

The subsurface crack propagation is one of the major interests for gear system research. The subsurface crack propagation lifetime is the number of cycles remaining for a spall to appear, which can be obtained through either stress intensity factor or accumulated plastic strain analysis. In this paper, the heavy loads are applied to the gear system. When choosing stress intensity factor, the high compressive stress suppresses Mode I stress intensities and severely reduces Mode II stress intensities in the heavily loaded lubricated contacts. Such that, the accumulated plastic strain is selected to calculate the subsurface crack propagation lifetime from the three-dimensional FEA model through ANSYS Workbench transient analysis. The three-dimensional gear FEA dynamic model with the subsurface crack is built through dividing the gears into several small elements. The calculation of the total cycles of the elements is proposed based on the time-varying accumulated plastic strain, which then will be used to calculate the subsurface crack propagation lifetime. During this process, the demonstration from a subsurface crack to a spall can be uncovered. In addition, different sizes of the elements around the subsurface crack are compared in this paper. The influences of the frictional coefficient and external torque on the crack propagation lifetime are also discussed. The results show that the lifetime of crack propagation decreases significantly when the external load T increasing from 100 N m to 150 N m. Given from the distributions of the accumulated plastic strain, the lifetime shares no significant difference when the frictional coefficient f ranging in 0.04-0.06.

Computational modeling for prediction of the shear stress of three-dimensional isotropic and aligned fiber networks.

PubMed

Park, Seungman

2017-09-01

Interstitial flow (IF) is a creeping flow through the interstitial space of the extracellular matrix (ECM). IF plays a key role in diverse biological functions, such as tissue homeostasis, cell function and behavior. Currently, most studies that have characterized IF have focused on the permeability of ECM or shear stress distribution on the cells, but less is known about the prediction of shear stress on the individual fibers or fiber networks despite its significance in the alignment of matrix fibers and cells observed in fibrotic or wound tissues. In this study, I developed a computational model to predict shear stress for different structured fibrous networks. To generate isotropic models, a random growth algorithm and a second-order orientation tensor were employed. Then, a three-dimensional (3D) solid model was created using computer-aided design (CAD) software for the aligned models (i.e., parallel, perpendicular and cubic models). Subsequently, a tetrahedral unstructured mesh was generated and flow solutions were calculated by solving equations for mass and momentum conservation for all models. Through the flow solutions, I estimated permeability using Darcy's law. Average shear stress (ASS) on the fibers was calculated by averaging the wall shear stress of the fibers. By using nonlinear surface fitting of permeability, viscosity, velocity, porosity and ASS, I devised new computational models. Overall, the developed models showed that higher porosity induced higher permeability, as previous empirical and theoretical models have shown. For comparison of the permeability, the present computational models were matched well with previous models, which justify our computational approach. ASS tended to increase linearly with respect to inlet velocity and dynamic viscosity, whereas permeability was almost the same. Finally, the developed model nicely predicted the ASS values that had been directly estimated from computational fluid dynamics (CFD). The present computational models will provide new tools for predicting accurate functional properties and designing fibrous porous materials, thereby significantly advancing tissue engineering. Copyright © 2017 Elsevier B.V. All rights reserved.

The Silent Enemy. Combat Stress Reaction.

DTIC Science & Technology

1986-04-01

intense anxiety, thus the term "shell shock." Such men were thought to have brain damage resulting from the concussion of high explosive shell blasts...French casualties returning to combat. (23:989) Upon the entrance of United States forces into World War I, Thomas W. Salmon, who held the job as...that battle stress is directly related to battle intensity. This was clearly 9 Shown in the Battle of Metz from September to November, 1944. The 5th

Stress Potentiates Early and Attenuates Late Stages of Visual Processing

DTIC Science & Technology

2011-01-19

threat (M 6.5, SD 20.0) than during safety (M 19.3, SD 11.6), t(31) 6.7, p 0.001. They also expressed more intense negative emotion on their...threats increase risk assessment (Kava- liers and Choleris, 2001), and fearful facial expressions enhance sensory intake (Susskind et al., 2008). These...visual analog scales to rate the intensity of their emotional experience (anxious, happy, safe, or stressed) during safety and threat blocks. To minimize

Tibial stress fracture after computer-navigated total knee arthroplasty.

PubMed

Massai, F; Conteduca, F; Vadalà, A; Iorio, R; Basiglini, L; Ferretti, A

2010-06-01

A correct alignment of the tibial and femoral component is one of the most important factors determining favourable long-term results of a total knee arthroplasty (TKA). The accuracy provided by the use of the computer navigation systems has been widely described in the literature so that their use has become increasingly popular in recent years; however, unpredictable complications, such as displaced or stress femoral or tibial fractures, have been reported to occur a few weeks after the operation. We present a case of a stress tibial fracture that occurred after a TKA performed with the use of a computer navigation system. The stress fracture, which eventually healed without further complications, occurred at one of the pinhole sites used for the placement of the tibial trackers.

Fracture Mechanics Testing of Titanium 6AL-4V in AF-M315E

NASA Technical Reports Server (NTRS)

Sampson, J. W.; Martinez, J.; McLean, C.

2016-01-01

The Green Propellant Infusion Mission (GPIM) will demonstrate the performance of AF-M315E monopropellant on orbit. Flight certification requires a safe-life analysis of the titanium alloy fuel tank to ensure inherent processing flaws will not cause failure during the design life of the tank. Material property inputs for this analysis require testing to determine the stress intensity factor for environment-assisted cracking (KEAC) of Ti 6Al-4V in combination with the AF-M315E monopropellant. Testing of single-edge notched, or SE(B), specimens representing the bulk tank membrane and weld material were performed in accordance with ASTM E1681. Specimens with fatigue pre-cracks were loaded into test fixtures so that the crack tips were exposed to AF-M315E at 50 C for a duration of 1,000 hours. Specimens that did not fail during exposure were opened to inspect the crack surfaces for evidence of crack growth. The threshold stress intensity value, KEAC, is the highest applied stress intensity that produced neither a failure of the specimen during the exposure nor showed evidence of crack growth. The threshold stress intensity factor for environment-assisted cracking of the Ti 6Al-4V forged tank material was found to be at least 22 ksivin and at least 31 ksivin for the weld material when exposed to AF-M315E monopropellant.

Effect of Exercise Intensity on Neurotrophic Factors and Blood-Brain Barrier Permeability Induced by Oxidative-Nitrosative Stress in Male College Students.

PubMed

Roh, Hee-Tae; Cho, Su-Youn; Yoon, Hyung-Gi; So, Wi-Young

2017-06-01

We investigated the effects of aerobic exercise intensity on oxidative-nitrosative stress, neurotrophic factor expression, and blood-brain barrier (BBB) permeability. Fifteen healthy men performed treadmill running under low-intensity (LI), moderate-intensity (MI), and high-intensity (HI) conditions. Blood samples were collected immediately before exercise (IBE), immediately after exercise (IAE), and 60 min after exercise (60MAE) to examine oxidative-nitrosative stress (reactive oxygen species [ROS]; nitric oxide [NO]), neurotrophic factors (brain-derived neurotrophic factor [BDNF]; nerve growth factor [NGF]), and blood-brain barrier (BBB) permeability (S-100β; neuron-specific enolase). ROS concentration significantly increased IAE and following HI (4.9 ± 1.7 mM) compared with that after LI (2.8 ± 1.4 mM) exercise (p < .05). At 60MAE, ROS concentration was higher following HI (2.5 ± 1.2 mM) than after LI (1.5 ± 0.5 mM) and MI (1.4 ± 0.3 mM) conditions (p < .05). Plasma NO IAE increased significantly after MI and HI exercise (p < .05). Serum BDNF, NGF, and S-100b levels were significantly higher IAE following MI and HI exercise (p < .05). BDNF and S-100b were higher IAE following MI (29.6 ± 3.4 ng/mL and 87.1 ± 22.8 ng/L, respectively) and HI (31.4 ± 3.8 ng/mL and 100.6 ± 21.2 ng/L, respectively) than following LI (26.5 ± 3.0 ng/mL and 64.8 ± 19.2 ng/L, respectively) exercise (p < .05). 60MAE, S-100b was higher following HI (71.1 ± 14.5 ng/L) than LI (56.2 ± 14.7 ng/L) exercise (p < .05). NSE levels were not significantly different among all intensity conditions and time points (p > .05). Moderate- and/or high-intensity exercise may induce higher oxidative-nitrosative stress than may low-intensity exercise, which can increase peripheral neurotrophic factor levels by increasing BBB permeability.

Lamination residual stresses in hybrid composites, part 1

NASA Technical Reports Server (NTRS)

Daniel, I. M.; Liber, T.

1976-01-01

An experimental investigation was conducted to study lamination residual stresses for various material and loading parameters. The effects of hybridization on residual stresses and residual properties after thermal cycling under load were determined in angle-ply graphite/Kevlar/epoxy and graphite/S-glass/epoxy laminates. Residual strains in the graphite plies are not appreciably affected by the type and number of hybridizing plies. Computed residual stresses at room temperature in the S-glass plies reach values up to seventy-five percent of the transverse strength of the material. Computed residual stresses in the graphite plies exceed the static strength by approximately ten percent. In the case of Kevlar plies, computed residual stresses far exceed the static strength indicating possible early failure of these plies. Static testing of the hybrids above indicates that failure is governed by the ultimate strain of the graphite plies. In thermally cycled hybrids, in general, residual moduli were somewhat lower and residual strengths were higher than initial values.

Thermal stress analysis of reusable surface insulation for shuttle

NASA Technical Reports Server (NTRS)

Ojalvo, I. U.; Levy, A.; Austin, F.

1974-01-01

An iterative procedure for accurately determining tile stresses associated with static mechanical and thermally induced internal loads is presented. The necessary conditions for convergence of the method are derived. An user-oriented computer program based upon the present method of analysis was developed. The program is capable of analyzing multi-tiled panels and determining the associated stresses. Typical numerical results from this computer program are presented.

Mobile computing device configured to compute irradiance, glint, and glare of the sun

DOEpatents

Gupta, Vipin P; Ho, Clifford K; Khalsa, Siri Sahib

2014-03-11

Described herein are technologies pertaining to computing the solar irradiance distribution on a surface of a receiver in a concentrating solar power system or glint/glare emitted from a reflective entity. A mobile computing device includes at least one camera that captures images of the Sun and the entity of interest, wherein the images have pluralities of pixels having respective pluralities of intensity values. Based upon the intensity values of the pixels in the respective images, the solar irradiance distribution on the surface of the entity or glint/glare corresponding to the entity is computed by the mobile computing device.

Influence of computer work under time pressure on cardiac activity.

PubMed

Shi, Ping; Hu, Sijung; Yu, Hongliu

2015-03-01

Computer users are often under stress when required to complete computer work within a required time. Work stress has repeatedly been associated with an increased risk for cardiovascular disease. The present study examined the effects of time pressure workload during computer tasks on cardiac activity in 20 healthy subjects. Heart rate, time domain and frequency domain indices of heart rate variability (HRV) and Poincaré plot parameters were compared among five computer tasks and two rest periods. Faster heart rate and decreased standard deviation of R-R interval were noted in response to computer tasks under time pressure. The Poincaré plot parameters showed significant differences between different levels of time pressure workload during computer tasks, and between computer tasks and the rest periods. In contrast, no significant differences were identified for the frequency domain indices of HRV. The results suggest that the quantitative Poincaré plot analysis used in this study was able to reveal the intrinsic nonlinear nature of the autonomically regulated cardiac rhythm. Specifically, heightened vagal tone occurred during the relaxation computer tasks without time pressure. In contrast, the stressful computer tasks with added time pressure stimulated cardiac sympathetic activity. Copyright © 2015 Elsevier Ltd. All rights reserved.

Energy intensity of computer manufacturing: hybrid assessment combining process and economic input-output methods.

PubMed

Williams, Eric

2004-11-15

The total energy and fossil fuels used in producing a desktop computer with 17-in. CRT monitor are estimated at 6400 megajoules (MJ) and 260 kg, respectively. This indicates that computer manufacturing is energy intensive: the ratio of fossil fuel use to product weight is 11, an order of magnitude larger than the factor of 1-2 for many other manufactured goods. This high energy intensity of manufacturing, combined with rapid turnover in computers, results in an annual life cycle energy burden that is surprisingly high: about 2600 MJ per year, 1.3 times that of a refrigerator. In contrast with many home appliances, life cycle energy use of a computer is dominated by production (81%) as opposed to operation (19%). Extension of usable lifespan (e.g. by reselling or upgrading) is thus a promising approach to mitigating energy impacts as well as other environmental burdens associated with manufacturing and disposal.

Low intensity microwave radiation induced oxidative stress, inflammatory response and DNA damage in rat brain.

PubMed

Megha, Kanu; Deshmukh, Pravin Suryakantrao; Banerjee, Basu Dev; Tripathi, Ashok Kumar; Ahmed, Rafat; Abegaonkar, Mahesh Pandurang

2015-12-01

Over the past decade people have been constantly exposed to microwave radiation mainly from wireless communication devices used in day to day life. Therefore, the concerns over potential adverse effects of microwave radiation on human health are increasing. Until now no study has been proposed to investigate the underlying causes of genotoxic effects induced by low intensity microwave exposure. Thus, the present study was undertaken to determine the influence of low intensity microwave radiation on oxidative stress, inflammatory response and DNA damage in rat brain. The study was carried out on 24 male Fischer 344 rats, randomly divided into four groups (n=6 in each group): group I consisted of sham exposed (control) rats, group II-IV consisted of rats exposed to microwave radiation at frequencies 900, 1800 and 2450 MHz, specific absorption rates (SARs) 0.59, 0.58 and 0.66 mW/kg, respectively in gigahertz transverse electromagnetic (GTEM) cell for 60 days (2h/day, 5 days/week). Rats were sacrificed and decapitated to isolate hippocampus at the end of the exposure duration. Low intensity microwave exposure resulted in a frequency dependent significant increase in oxidative stress markers viz. malondialdehyde (MDA), protein carbonyl (PCO) and catalase (CAT) in microwave exposed groups in comparison to sham exposed group (p<0.05). Whereas, levels of reduced glutathione (GSH) and superoxide dismutase (SOD) were found significantly decreased in microwave exposed groups (p<0.05). A significant increase in levels of pro-inflammatory cytokines (IL-2, IL-6, TNF-α, and IFN-γ) was observed in microwave exposed animal (p<0.05). Furthermore, significant DNA damage was also observed in microwave exposed groups as compared to their corresponding values in sham exposed group (p<0.05). In conclusion, the present study suggests that low intensity microwave radiation induces oxidative stress, inflammatory response and DNA damage in brain by exerting a frequency dependent effect. The study also indicates that increased oxidative stress and inflammatory response might be the factors involved in DNA damage following low intensity microwave exposure. Copyright © 2015 Elsevier Inc. All rights reserved.

Synergistic effects of abiotic stresses in plants: a case study of nitrogen limitation and saturating light intensity in Arabidopsis thaliana.

PubMed

Cohen, Itay; Rapaport, Tal; Chalifa-Caspi, Vered; Rachmilevitch, Shimon

2018-05-22

Under natural conditions, plants are regularly exposed to combinations of stress factors. A common example is the conjunction between nitrogen (N) deficiency and excess light. The combined effect of stress factors is often ignored in studies using controlled conditions, possibly resulting in misleading conclusions. To address this issue, the current study examined the physiological behavior of Arabidopsis thaliana under the effect of varying nitrogen levels and light intensities. The joint influence of low N and excess light had an adverse effect on plant growth, chlorophyll and anthocyanin concentrations, photochemical capacity, and the abundance of proteins involved in carbon assimilation and anti-oxidative metabolism. In contrast, no adverse physiological responses were observed for plants under either nitrogen limitation or high light intensity conditions (i.e., single stress). The underline mechanisms for the increased growth in conditions of high light and sufficient nitrogen was due to a combination of chlorophyll accumulation and an increased number of proteins involved in C3 carbon assimilation, amino acids biosynthesis and chloroplast development. In contrast, combined stress conditions caused anthocyanin accumulation and increased number proteins involved in catabolism of lipids and amino acids as energy substrates. Ultimately switching plants from growth to survival. Our results suggest that an assessment of the physiological response to the combined effect of multiple stresses cannot be directly extrapolated from the physiological response to a single stress. Specifically, the synergistic interaction between N deficiency and saturating light in Arabidopsis plants could not have been modeled via only one of the stress factors. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.

Feasibility and validity of animal-based indicators for on-farm welfare assessment of thermal stress in dairy goats

NASA Astrophysics Data System (ADS)

Battini, Monica; Barbieri, Sara; Fioni, Luna; Mattiello, Silvana

2016-02-01

This investigation tested the feasibility and validity of indicators of cold and heat stress in dairy goats for on-farm welfare assessment protocols. The study was performed on two intensive dairy farms in Italy. Two different 3-point scale (0-2) scoring systems were applied to assess cold and heat stress. Cold and heat stress scores were visually assessed from outside the pen in the morning, afternoon and evening in January-February, April-May and July 2013 for a total of nine sessions of observations/farm. Temperature (°C), relative humidity (%) and wind speed (km/h) were recorded and Thermal Heat Index (THI) was calculated. The sessions were allocated to three climatic seasons, depending on THI ranges: cold (<50), neutral (50-65) and hot (>65). Score 2 was rarely assessed; therefore, scores 1 and 2 were aggregated for statistical analysis. The amount of goats suffering from cold stress was significantly higher in the cold season than in neutral ( P < 0.01) and hot ( P < 0.001) seasons. Signs of heat stress were recorded only in the hot season ( P < 0.001). The visual assessment from outside the pen confirms the on-farm feasibility of both indicators: No constraint was found and time required was less than 10 min. Our results show that cold and heat stress scores are valid indicators to detect thermal stress in intensively managed dairy goats. The use of a binary scoring system (presence/absence), merging scores 1 and 2, may be a further refinement to improve the feasibility. This study also allows the prediction of optimal ranges of THI for dairy goat breeds in intensive husbandry systems, setting a comfort zone included into 55 and 70.

Probabilistic Fatigue Damage Program (FATIG)

NASA Technical Reports Server (NTRS)

Michalopoulos, Constantine

2012-01-01

FATIG computes fatigue damage/fatigue life using the stress rms (root mean square) value, the total number of cycles, and S-N curve parameters. The damage is computed by the following methods: (a) traditional method using Miner s rule with stress cycles determined from a Rayleigh distribution up to 3*sigma; and (b) classical fatigue damage formula involving the Gamma function, which is derived from the integral version of Miner's rule. The integration is carried out over all stress amplitudes. This software solves the problem of probabilistic fatigue damage using the integral form of the Palmgren-Miner rule. The software computes fatigue life using an approach involving all stress amplitudes, up to N*sigma, as specified by the user. It can be used in the design of structural components subjected to random dynamic loading, or by any stress analyst with minimal training for fatigue life estimates of structural components.

Analysis of differential gene expression in response to handling and confinement stress in rainbow trout using whole transcriptome RNA-seq

USDA-ARS?s Scientific Manuscript database

Fish under intensive rearing conditions experience various stress conditions, which have negative impacts on survival, growth and fillet quality. Understanding the molecular mechanisms underlying stress responses will facilitate improvement of animal welfare and production efficiency. Our objective ...

Written Disclosure Treatment for Posttraumatic Stress Disorder in Substance Use Disorder Inpatients

ERIC Educational Resources Information Center

Bragdon, Rodney A.; Lombardo, Thomas W.

2012-01-01

Comprehensive exposure-based approaches to treating posttraumatic stress disorder (PTSD) are effective, but they are time intensive and not widely used because of factors such as client noncompliance and fears of iatrogenic effects. Exposure by writing disclosure (WD), modeled after Pennebaker's brief stress-reduction procedure, may circumvent…

Academic Expectations as Sources of Stress in Asian Students

ERIC Educational Resources Information Center

Tan, Joyce Beiyu; Yates, Shirley

2011-01-01

Education is highly valued in Confucian Heritage Culture (CHC) countries such as China, Taiwan, Singapore, Hong Kong, Japan and Korea but the expectations of parents, teachers and students themselves to excel academically can also be a source of intense stress for many students. The "Academic Expectations Stress Inventory" (AESI),…

Large Eddy Simulation of Turbulent Flow in a Ribbed Pipe

NASA Astrophysics Data System (ADS)

Kang, Changwoo; Yang, Kyung-Soo

2011-11-01

Turbulent flow in a pipe with periodically wall-mounted ribs has been investigated by large eddy simulation with a dynamic subgrid-scale model. The value of Re considered is 98,000, based on hydraulic diameter and mean bulk velocity. An immersed boundary method was employed to implement the ribs in the computational domain. The spacing of the ribs is the key parameter to produce the d-type, intermediate and k-type roughness flows. The mean velocity profiles and turbulent intensities obtained from the present LES are in good agreement with the experimental measurements currently available. Turbulence statistics, including budgets of the Reynolds stresses, were computed, and analyzed to elucidate turbulence structures, especially around the ribs. In particular, effects of the ribs are identified by comparing the turbulence structures with those of smooth pipe flow. The present investigation is relevant to the erosion/corrosion that often occurs around a protruding roughness in a pipe system. This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2010-0008457).

Mechanical Behaviour of Light Metal Alloys at High Strain Rates. Computer Simulation on Mesoscale Levels

NASA Astrophysics Data System (ADS)

Skripnyak, Vladimir; Skripnyak, Evgeniya; Meyer, Lothar W.; Herzig, Norman; Skripnyak, Nataliya

2012-02-01

Researches of the last years have allowed to establish that the laws of deformation and fracture of bulk ultrafine-grained and coarse-grained materials are various both in static and in dynamic loading conditions. Development of adequate constitutive equations for the description of mechanical behavior of bulk ultrafine-grained materials at intensive dynamic influences is complicated in consequence of insufficient knowledge about general rules of inelastic deformation and nucleation and growth of cracks. Multi-scale computational model was used for the investigation of deformation and fracture of bulk structured aluminum and magnesium alloys under stress pulse loadings on mesoscale level. The increment of plastic deformation is defined by the sum of the increments caused by a nucleation and gliding of dislocations, the twinning, meso-blocks movement, and grain boundary sliding. The model takes into account the influence on mechanical properties of alloys an average grains size, grain sizes distribution of and concentration of precipitates. It was obtained the nucleation and gliding of dislocations caused the high attenuation rate of the elastic precursor of ultrafine-grained alloys than in coarse grained counterparts.

A Fast Synthetic Aperture Radar Raw Data Simulation Using Cloud Computing

PubMed Central

Li, Zhixin; Su, Dandan; Zhu, Haijiang; Li, Wei; Zhang, Fan; Li, Ruirui

2017-01-01

Synthetic Aperture Radar (SAR) raw data simulation is a fundamental problem in radar system design and imaging algorithm research. The growth of surveying swath and resolution results in a significant increase in data volume and simulation period, which can be considered to be a comprehensive data intensive and computing intensive issue. Although several high performance computing (HPC) methods have demonstrated their potential for accelerating simulation, the input/output (I/O) bottleneck of huge raw data has not been eased. In this paper, we propose a cloud computing based SAR raw data simulation algorithm, which employs the MapReduce model to accelerate the raw data computing and the Hadoop distributed file system (HDFS) for fast I/O access. The MapReduce model is designed for the irregular parallel accumulation of raw data simulation, which greatly reduces the parallel efficiency of graphics processing unit (GPU) based simulation methods. In addition, three kinds of optimization strategies are put forward from the aspects of programming model, HDFS configuration and scheduling. The experimental results show that the cloud computing based algorithm achieves 4× speedup over the baseline serial approach in an 8-node cloud environment, and each optimization strategy can improve about 20%. This work proves that the proposed cloud algorithm is capable of solving the computing intensive and data intensive issues in SAR raw data simulation, and is easily extended to large scale computing to achieve higher acceleration. PMID:28075343

Eigen Spreading

DTIC Science & Technology

2008-02-27

between the PHY layer and for example a host PC computer . The PC wants to generate and receive a sequence of data packets. The PC may also want to send...the testbed is quite similar. Given the intense computational requirements of SVD and other matrix mode operations needed to support eigen spreading a...platform for real time operation. This task is probably the major challenge in the development of the testbed. All compute intensive tasks will be

3D J-Integral Capability in Grizzly

DOE Office of Scientific and Technical Information (OSTI.GOV)

Spencer, Benjamin; Backman, Marie; Chakraborty, Pritam

2014-09-01

This report summarizes work done to develop a capability to evaluate fracture contour J-Integrals in 3D in the Grizzly code. In the current fiscal year, a previously-developed 2D implementation of a J-Integral evaluation capability has been extended to work in 3D, and to include terms due both to mechanically-induced strains and due to gradients in thermal strains. This capability has been verified against a benchmark solution on a model of a curved crack front in 3D. The thermal term in this integral has been verified against a benchmark problem with a thermal gradient. These developments are part of a largermore » effort to develop Grizzly as a tool that can be used to predict the evolution of aging processes in nuclear power plant systems, structures, and components, and assess their capacity after being subjected to those aging processes. The capabilities described here have been developed to enable evaluations of Mode- stress intensity factors on axis-aligned flaws in reactor pressure vessels. These can be compared with the fracture toughness of the material to determine whether a pre-existing flaw would begin to propagate during a pos- tulated pressurized thermal shock accident. This report includes a demonstration calculation to show how Grizzly is used to perform a deterministic assessment of such a flaw propagation in a degraded reactor pressure vessel under pressurized thermal shock conditions. The stress intensity is calculated from J, and the toughness is computed using the fracture master curve and the degraded ductile to brittle transition temperature.« less

Automated generation of influence functions for planar crack problems

NASA Technical Reports Server (NTRS)

Sire, Robert A.; Harris, David O.; Eason, Ernest D.

1989-01-01

A numerical procedure for the generation of influence functions for Mode I planar problems is described. The resulting influence functions are in a form for convenient evaluation of stress-intensity factors for complex stress distributions. Crack surface displacements are obtained by a least-squares solution of the Williams eigenfunction expansion for displacements in a cracked body. Discrete values of the influence function, evaluated using the crack surface displacements, are curve fit using an assumed functional form. The assumed functional form includes appropriate limit-behavior terms for very deep and very shallow cracks. Continuous representation of the influence function provides a convenient means for evaluating stress-intensity factors for arbitrary stress distributions by numerical integration. The procedure is demonstrated for an edge-cracked strip and a radially cracked disk. Comparisons with available published results demonstrate the accuracy of the procedure.

Fracture mechanics in fiber reinforced composite materials, taking as examples B/A1 and CRFP

NASA Technical Reports Server (NTRS)

Peters, P. W. M.

1982-01-01

The validity of linear elastic fracture mechanics and other fracture criteria was investigated with laminates of boron fiber reinforced aluminum (R/A1) and of carbon fiber reinforced epoxide (CFRP). Cracks are assessed by fracture strength Kc or Kmax (critical or maximum value of the stress intensity factor). The Whitney and Nuismer point stress criterion and average stress criterion often show that Kmax of fiber composite materials increases with increasing crack length; however, for R/A1 and CFRP the curve showing fracture strength as a function of crack length is only applicable in a small domain. For R/A1, the reason is clearly the extension of the plastic zone (or the damage zone n the case of CFRP) which cannot be described with a stress intensity factor.

A comparison of constant-load and constant-deflection stress-corrosion tests on precracked DCB specimens. [Double Cantilever Beam

NASA Technical Reports Server (NTRS)

Dorward, R. C.; Hasse, K. R.

1978-01-01

A comparison is made between measurements of stress-corrosion crack propagation made by a constant-load procedure and by a constant-deflection procedure. Precracked double cantilever beam specimens from 7075 aluminum alloy plate were used. The specimens were oriented in such a way that cracking would begin in the short-transverse plane and would propagate in the rolling direction. The specimens were subjected to a buffered salt-chromate solution and a 3.6% synthetic sea salt solution. The measurements were made optically with a binocular microscope. Stress intensities and crack lengths were calculated and crack velocities were obtained. Velocity was plotted against the average calculated stress intensity. Good agreement between the two methods was found for the salt-chromate solution, although some descrepancies were noted for the artificial sea salt solution.