bluuebunny/crossref_metadata_2025 huggingface dataset:
Punishment has a lasting impact on error‐related brain activity
Authors: Riesel Anja , Weinberg Anna , Endrass Tanja , Kathmann Norbert , Hajcak Greg
Published: October 2011

The current study examined whether punishment has direct and lasting effects on error‐related brain activity, and whether this effect is larger with increasing trait anxiety. Participants were told that errors on a flanker task would be punished in some blocks but not others. Punishment was applied following 50% of errors in punished blocks during the first half of the experiment (i.e., acquisition), but never in the second half (i.e., extinction). The ERN was enhanced in the punished blocks in both experimental phases—this enhancement remained stable throughout the extinction phase. More anxious individuals were characterized by larger punishment‐related modulations in the ERN. The study reveals evidence for lasting, punishment‐based modulations of the ERN that increase with anxiety. These data suggest avenues for research to examine more specific learning‐related mechanisms that link anxiety to overactive error monitoring.
Antiangiogenic effects of β2‐adrenergic receptor blockade in a mouse model of oxygen‐induced retinopathy
Authors: Martini Davide , Monte Massimo Dal , Ristori Chiara , Cupisti Elena , Mei Sara , Fiorini Patrizio , Filippi Luca , Bagnoli Paola
Published: October 2011

J. Neurochem. (2011) 10.1111/j.1471‐4159.2011.07530.x

Oxygen‐induced retinopathy (OIR) is a model for human retinopathy of prematurity. In mice with OIR, beta‐adrenergic receptor (β‐AR) blockade with propranolol has been shown to ameliorate different aspects of retinal dysfunction in response to hypoxia. In the present study, we used the OIR model to investigate the role of distinct β‐ARs on retinal proangiogenic factors, pathogenic neovascularization and electroretinographic responses. Our results demonstrate that β2‐AR blockade with ICI 118,551 decreases retinal levels of proangiogenic factors and reduces pathogenic neovascularization, whereas β1‐ and β3‐AR antagonists do not. Determination of retinal protein kinase A activity is indicative of the fact that β‐AR blockers are indeed effective at the receptor level. In addition, the specificity of ICI 118,551 on retinal angiogenesis has been demonstrated by the finding that in mouse retinal explants, β2‐AR silencing prevents ICI 118,551 effects on hypoxia‐induced vascular endothelial growth factor accumulation. In OIR mice, ICI 118,551 is effective in increasing electroretinographic responses suggesting that activation of β2‐ARs constitutes an important part of the retinal response to hypoxia. Lastly, immunohistochemical studies demonstrate that β2‐ARs are localized to several retinal cells, particularly to Müller cells suggesting the possibility that β2‐ARs play a role in regulating vascular endothelial growth factor production by these cells. The present results suggest that pathogenic angiogenesis, a key change in many hypoxic/ischemic vision‐threatening retinal diseases, depends at least in part on β2‐AR activity and indicate that β2‐AR blockade can be effective against retinal angiogenesis.
Mothers’ experiences of peer support via an Internet discussion forum after the death of a child
Authors: Aho Anna Liisa , Paavilainen Erja , Kaunonen Marja
Published: October 2011

Scand J Caring Sci; 2012; 26; 417–426

Mothers’ experiences of peer support via an Internet discussion forum after the death of a child

The aim of this study was to describe mothers’ experiences of peer support via an Internet discussion group for mothers who have a child died. A longitudinal qualitative study design was used. The research data were collected from four (n = 4) bereaved mothers from a private Internet support group titled ‘angel baby’ during the period 2001–2006. The data included 631 messages. Content analysis was used to examine the data. Peer support on an Internet discussion forum included giving and receiving emotional, cognitive and community support among bereaved mothers. The Internet discussion forum was a viable alternative to peer support after the death of a child. A strong sense of communality and lasting friendships was formed between the bereaved mothers who had similar experiences.
Hypoxic hepatitis
Authors: Henrion Jean
Published: October 2011

Hypoxic hepatitis (HH), an acute liver injury also known as ‘ischaemic hepatitis’ or ‘shock liver’, is frequently observed in intensive care units. HH is heralded by a massive but transient rise in serum aminotransferase activities caused by anoxic necrosis of centrilobular liver cells. Cardiac failure, respiratory failure and toxic‐septic shock are the main underlying conditions accounting for more than 90% of cases, but HH may also occur in other circumstances. Until recently, liver ischaemia, i.e. a drop in hepatic blood flow, was considered the leading, and even the sole, hemodynamic mechanism responsible for HH, and it was generally held that a shock state was required. In reality, other hemodynamic mechanisms of hypoxia, such as passive congestion of the liver, arterial hypoxaemia and dysoxia, play an important role while a shock state is observed in only 50% of cases. Accordingly, ‘ischaemic hepatitis’ and ‘shock liver’ are misnomers. Therapy of HH depends primarily on the nature of the underlying condition. The prognosis is poor, with more than half of patients dying during the hospital stay.
The Information Content of REIT Short Interest: Investment Focus and Heterogeneous Beliefs
Authors: Chen Honghui , Downs David H. , Patterson Gary A.
Published: October 2011

This article examines real estate investment trusts (REITs) to determine the correspondence between short interest and subsequent prices. The theoretical basis for our tests comes from the overvaluation conditions created by a combination of costly short selling and heterogeneous beliefs. This article exploits the unique characteristics of REITS as they are similar with respect to high dividend payouts and differentiated by underlying real asset investments. An innovative aspect of the methodology involves partitioning firms based on investment focus as a proxy for transparency and as a determinant of heterogeneous beliefs regarding valuation. The findings (i) affirm the information content of REIT short interest and (ii) highlight the importance of investment focus in resolving the divergence in investor opinions of value. Overvaluation conditions exist among REITs with greater short interest and less transparency, whereas such valuation conditions do not appear among transparent REITs, regardless of the level of short selling.
Co‐movements and Correlations Across Asian Securitized Real Estate and Stock Markets
Authors: Hiang Liow Kim
Published: October 2011

We find conditional real estate‐stock correlations at the local, regional and global levels are time varying and asymmetric in some cases for our sample of eight Asian securitized real estate markets over 1995–2009. Real estate–global stock correlations co‐move significantly and positively with real estate–regional stock correlations and real estate–local stock correlations. They are also influenced significantly by relative (real estate/stock) volatilities and their lags at three integration levels. Furthermore, real estate and stock volatilities, covariances and correlations increased from the preglobal financial crisis period to the crisis period. However, real estate and stock volatility are more important than correlation in causing the changes in covariance during both the precrisis and crisis periods. Finally, exchange rate volatility appears to have played a relatively less important role in these cross real estate–stock correlations.
Emotions and Opportunities: The Interplay of Opportunity Evaluation, Fear, Joy, and Anger as Antecedent of Entrepreneurial Exploitation
Authors: Welpe Isabell M. , Spörrle Matthias , Grichnik Dietmar , Michl Theresa , Audretsch David B.
Published: October 2011

This research examines the interplay of opportunity evaluation and emotions as determinants of entrepreneurial exploitation using affect–as–information theory and the affective processing principle as conceptual bases. Three central assumptions are confirmed across two studies. The first is that the effects of opportunity characteristics on exploitation are mediated by evaluation. The second is that emotions influence exploitation decisions in addition to evaluation. Fear reduces exploitation, whereas joy and anger increase it. The third is that fear, joy, and anger influence evaluation's effect on exploitation with higher levels of fear reducing and higher levels of joy and anger increasing the positive impact of evaluation on exploitation.
Radiation
Authors: WINTHER J. F. , ULBAK K. , DREYER L. , PUKKALA E. , ØSTERLIND A.
Published: October 2011

Exposure to solar and ionizing radiation increases the risk for cancer in humans. Some 5% of solar radiation is within the ultraviolet spectrum and may cause both malignant melanoma and nonmelanocytic skin cancer; the latter is regarded as a benign disease and is accordingly not included in our estimation of avoidable cancers. Under the assumption that the rate of occurrence of malignant melanoma of the buttocks of both men and women and of the scalp of women would apply to all parts of the body in people completely unexposed to solar radiation, it was estimated that approximately 95% of all malignant melanomas arising in the Nordic populations around the year 2000 will be due to exposure to natural ultraviolet radiation, equivalent to an annual number of about 4700 cases, with 2100 in men and 2600 in women, or some 4% of all cancers notified. Exposure to ionizing radiation in the Nordic countries occurs at an average effective dose per capita per year of about 3 mSv (Iceland, 1.1 mSv) from natural sources, and about 1 mSv from man‐made sources. While the natural sources are primarily radon in indoor air, natural radionuclides in food, cosmic radiation and gamma radiation from soil and building materials, the man‐made sources are dominated by the diagnostic and therapeutic use of ionizing radiation. On the basis of measured levels of radon in Nordic dwellings and associated risk estimates for lung cancer derived from well‐conducted epidemiological studies, we estimated that about 180 cases of lung cancer (1% of all lung cancer cases) per year could be avoided in the Nordic countries around the year 2000 if indoor exposure to radon were eliminated, and that an additional 720 cases (6%) could be avoided annually if either radon or tobacco smoking were eliminated. Similarly, it was estimated that the exposure of the Nordic populations to natural sources of ionizing radiation other than radon and to medical sources will each give rise to an annual total of 2120 cancers at various sites. For all types of ionizing radiation, the annual total will be 4420 cancer cases, or 3.9% of all cancers arising in the Nordic populations, with 3.4% in men and 4.4% in women.
A self‐fulfilling prophecy: linking belief to behavior
Authors: Sternberg Esther
Published: October 2011

The intriguing title “A self‐fulfilling prophecy: linking belief to behavior” can be viewed from either philosophical or biological perspectives. This brief overview addresses the concept of self‐fulfilling prophecy from the point of view of a neurobiologist‐immunologist and shows how self‐fulfilling prophecies might trigger behaviors that play a role in healing.
Experimental sward islets: the effect of dung and fertilisation on Hemiptera and Araneae
Authors: DITTRICH ALEX D. K. , HELDEN ALVIN J.
Published: October 2011

Abstract. 1. Cattle avoid grazing around their dung. This pattern persists after the decomposition of the initial dung patch leading to the formation of taller grass patches, termed islets. It is known that islets hold a disproportionate amount of the arthropods in grazed grasslands.

2. An experimental manipulation was set up to investigate the relative effects of vegetation structure and nutrient input on arthropod distributions. Herbivorous bugs (Hemiptera) and predatory spiders (Araneae) were sampled in artificially generated islets treated with dung, fertiliser, a cutting regime to mimic grazing and a fallow control.

3. The densities of both Hemiptera and Araneae were affected by the presence of increased nutrient input through dung and fertiliser. The densities of different herbivore taxonomic families were influenced by food plant quality and the predators by the subsequent increase in prey density.

4. Delphacidae (Hemiptera) showed a preference for taller more nutrient rich swards treated with fertiliser, whereas Cicadellidae (Hemiptera) were more abundant in those swards treated with dung. Lycosidae (Araneae) were more common in dung‐treated swards, whereas Linypiidae (Araneae) were more common in the taller fertiliser‐treated swards.

5. Higher Hemiptera species richness was found in the fertiliser‐ and dung‐treated swards. It is believed that this effect was because of nutrient availability.

6. It is likely that the presence of cattle dung islets in grazed grassland plays an important role in the maintenance of biodiversity, through increasing structural heterogeneity.
Idealism and Scepticism
Authors: BRUECKNER ANTHONY
Published: October 2011

It is argued that contrary to appearances, Berkeleyan Idealism lacks anti‐sceptical force. The problem stems from the way in which the idealist draws the appearance/reality distinction.
Synaptically evoked Ca2+ release from intracellular stores is not influenced by vesicular zinc in CA3 hippocampal pyramidal neurones
Authors: Evstratova Alesya , Tóth Katalin
Published: October 2011

Non‐technical summary  The hippocampus plays a key role in memory formation. Cortical information is conveyed to the hippocampus via specialized axons of the dentate granule cells. These axon terminals contain a high concentration of zinc. Recently vesicular zinc was suggested to be a key modulator of postsynaptic calcium signals. We explored this possibility using fluorescence calcium imaging and electrophysiological recordings. We eliminated endogenous zinc with pharmacological and genetic tools, and found that none of these manipulations altered postsynaptic calcium signals. Our data suggest that the main function of vesicular zinc is not the control of postsynaptic calcium signalling during synaptic interactions.
Thermal Shock on a Finite Disk Due to an Instantaneous Point Heat Source
Authors: Hsu T. R.
Published: October 2011

This paper contains an exact solution for the transient temperature distribution and the associated quasi-static thermal stresses and deformations which arise in a finite circular disk subjected to an instantaneous point heat source acting on its periphery. The solutions given are in the form of double infinite series, and extensive illustrative numerical results are included. The solutions are pertinent to problems which occur in welding engineering and in modern nuclear technology.
Shock Propagation in a Strain-Hardening Material
Authors: Rausch P. J.
Published: October 2011

Weak shock theory is used to analyze the propagation of the stress waves which are induced by nonuniform, instantaneous, internal heating of a nonlinearly elastic, semi-infinite solid. The material nonlinearity considered is caused by the increase in bulk modulus which occurs as the hydrodynamic stress component increases. Heating is assumed to occur instantaneously. Since the shock is assumed to be weak, the entropy change across it is negligible, and therefore the wave form both behind and in front of the shock is found by using a coordinate perturbation method to solve the nonlinear equations for constant entropy. This solution predicts a multivalued material state in the vicinity of the shock front without locating the front itself. The location of the shock front is found separately by using the principle of momentum conservation. If the front is then inserted at this location, a wave form is obtained for which the material state is everywhere single-valued. The results and conclusions which are presented are based on a comparison of the perturbation solution found in this paper, and a simple wave solution and on an assessment of shock strength.
On the Stability of a Differential Equation With Application to the Vibrations of a Particle in the Plane
Authors: Rand Richard H. , Tseng Shoei-Fu
Published: October 2011

The stability of the equation Z¨ + f(t)Z = 0, where f(t) = (δ − ε cos2t)/(1 − ε cos2t), is studied by using Floquet theory, Fourier analysis and perturbations. The results are used to study the stability of the vibrations of a particle constrained to a plane and restrained by two identical linear springs with initial stress.
A Simple Description of the Motion of a Spherical Pendulum
Authors: Johansen K. F. , Kane T. R.
Published: October 2011

Hamilton-Jacobi theory is used to obtain an approximate solution of the equations of motion of a spherical pendulum. By reference to this solution, the motion is then described in simple geometric terms.
Experiments on Dispersive Pulse Propagation in Laminated Composites and Comparison With Theory
Authors: Whittier J. S. , Peck J. C.
Published: October 2011

Transient stress-wave experiments on laminated composites are described, and the results are compared with theoretical predictions. The composites are laminated from alternating layers of high and low-modulus material, which cause a high degree of geometric dispersion of waves propagating in the composite. Experiments were conducted in which waves propagated parallel to the laminations. Flat plates were subjected on one face to a uniform pressure with step-function time dependence induced by a gas-dynamic shock wave. Under this loading, the central portion of the specimen initially responds as if it were laterally unbounded. The average velocity over a 3/8-in-dia area of the backface of the plate was measured with a capacitance gauge. The results are in good agreement with theoretical predictions made with a long-time asymptotic approximation called the head-of-the-pulse approximation. The theory isolates the dominant character of the response and predicts timing and amplitude of oscillations in normalized rear surface velocity within a few percent.
On Elastic Filament Reinforcement of a Viscoelastic Cylinder
Authors: Huang N. C. , Lee E. H.
Published: October 2011

The strengthening of a hollow viscoelastic cylinder by elastic, helically wound, reinforcing wires is considered. The theoretical basis for stress analysis is developed, and applied to the cylinder subjected to internal pressure and additionally supported by an elastic casing on the exterior cylindrical surface. Solutions for various choices of parameters are evaluated, and the variation of the resulting stress fields is discussed. The conclusions include the importance of varying the density of the distribution of reinforcing wires for maximum effectiveness.
Numerical Solutions of Transients in Pneumatic Networks: Part 3—Network Problems With Branching
Authors: Tsao S. , Rodgers W.
Published: October 2011

This paper investigates the mathematical problem of fluid flow at a junction. It is shown that the junction pressure at a given time can be expressed approximately in terms of the known pressures and flow rates at and near the junction at an earlier time. After the junction pressure is determined, it serves as a boundary condition for all the transmission lines meeting at the junction. Several junction networks are computed for illustrative purposes.
In-Plane Flexural Vibrations of Circular Rings
Authors: Rao S. S. , Sundararajan V.
Published: October 2011

An equation of motion governing the free, in-plane vibrations of a circular ring is developed to include the effects of shear deformation and rotatory inertia. This equation is solved to find the natural frequencies of vibration of free rings and stiffened rings and the results compared with those given by a classical formula. The frequencies for a free ring are found to compare well with the experimental values of Kuhl [5]. Natural frequencies of circular arcs are calculated from the classical equation with hinged and fixed end conditions and the results compared with the approximate values given by Den Hartog [8, 9].
The Linearization of the Prebuckling State and Its Effect on the Determined Instability Loads
Authors: Kerr A. D. , Soifer M. T.
Published: October 2011

The effect of the linearization of the prebuckled state upon the determined buckling loads is studied first on an elastic system of two degrees of freedom and then on a shallow arch subjected to a uniform lateral load; structures that exhibit a nontrivial state of stress, an upper buckling load, a lower buckling load, and a bifurcation load. For each case the exact solution of the nonlinear formulation is discussed first. Then, using the perturbation analysis, the instability loads are determined again using the exact and the linearized prebuckled state, respectively. The paper concludes with a comparison of the obtained buckling loads and a discussion of relevant problems. It was found that the usual “adjacent equilibrium” argument presented in the literature, according to which only the displacements are perturbed, is not applicable for the determination of the bifurcation pressures of the shallow arch. A proper argument is presented and then used to determine the bifurcation and limit points.
On Obtaining Solutions in Nonlinear Viscoelasticity
Authors: Christensen R. M.
Published: October 2011

A derivation is given of a particular form of the isothermal nonlinear stress constitutive relation for materials with fading memory. This particular derivation results in a form for the constitutive relations that is well suited for application in solving boundary-value problems. The resulting forms are applied to obtain the exact quasi-static solution for the torsion of a right circular isotropic viscoelastic cylinder. Several effects due to the nonlinearity of the problem are discussed.
Magnetoelastic Buckling of a Thin Plate
Authors: Moon F. C. , Pao Yih-Hsing
Published: October 2011

The instability of a column under axial load is well known. A similar phenomenon is discussed in this paper for a beam-plate in a transverse magnetic field. Experiments show that the beam may buckle (in the sense of an Euler column) when the uniform magnetic field strength reaches a critical value. A mathematical model is proposed with distributed magnetic torques along the plate. A nontrivial adjacent equilibrium configuration satisfying the magnetostatic field equations is shown to exist for characteristic values of the external magnetic field. Results as predicted from this model compare favorably with experiments.
Buckling and Initial Postbuckling Behavior of Oval Cylindrical Shells Under Axial Compression
Authors: Hutchinson J. W.
Published: October 2011

Buckling and initial postbuckling behavior is determined for thin, elastic cylindrical shells of elliptical cross section. This study complements the buckling and advanced postbuckling calculations reported by Kempner and Chen on a similar class of shells. The initial postbuckling analysis indicates that, like compressed circular cylinders, the oval cylinders will be highly sensitive to small geometrical imperfections and may buckle at loads well below the predictions for the perfect shell. On the other hand, buckling will not necessarily result in complete collapse. A series of simple tests has been performed which provide qualitative verification of the major features of the theory.
A Path Independent Integral and the Approximate Analysis of Strain Concentration by Notches and Cracks
Authors: Rice J. R.
Published: October 2011

A line integral is exhibited which has the same value for all paths surrounding the tip of a notch in the two-dimensional strain field of an elastic or deformation-type elastic-plastic material. Appropriate integration path choices serve both to relate the integral to the near tip deformations and, in many cases, to permit its direct evaluation. This averaged measure of the near tip field leads to approximate solutions for several strain-concentration problems. Contained perfectly plastic deformation near a crack tip is analyzed for the plane-strain case with the aid of the slip-line theory. Near tip stresses are shown to be significantly elevated by hydrostatic tension, and a strain singularity results varying inversely with distance from the tip in centered fan regions above and below the tip. Approximate estimates are given for the strain intensity, plastic zone size, and crack tip opening displacement, and the important role of large geometry changes in crack blunting is noted. Another application leads to a general solution for crack tip separations in the Barenblatt-Dugdale crack model. A proof follows on the equivalence of the Griffith energy balance and cohesive force theories of elastic brittle fracture, and hardening behavior is included in a model for plane-stress yielding. A final application leads to approximate estimates of strain concentrations at smooth-ended notch tips in elastic and elastic-plastic materials.
Semilinear Random Vibrations in Discrete Systems
Authors: Foster E. T.
Published: October 2011

Random vibration problems are discussed for weakly nonlinear, multidegree-of-freedom discrete systems subjected to zero-mean, stationary random excitation. The semilinear solution technique developed involves substituting an optimum linear set of equations of motion for the actual nonlinear equations of motion. Parameters of this optimum linear system are selected on the basis of the system output so that a cyclic solution occurs. The cycles require parameter selection and response analysis until a convergence occurs in the sense that the answers from cycle to cycle are similar.
Deviations From the Cosine Law for Yawed Cylindrical Anemometer Sensors
Authors: Friehe C. A. , Schwarz W. H.
Published: October 2011

A new relation is presented to describe the deviations from the cosine law for cylindrical anemometer sensors inclined to the flow direction. The formula correlates the data for both hot-wire and hot-film sensors. One experimentally determined parameter, depending on the length-to-diameter ratio of the sensor, is used. The resulting corrections to the use of the cosine law for turbulent velocity correlations are also presented.
Conditions for Symmetry of Multiply Separated Positions in Coplanar Motion
Authors: Tesar D. , Sparks J. W.
Published: October 2011

A generalized treatment for combinations of infinitesimally and finitely separated coplanar positions is presented for four, five, and six positions lying symmetrically about an axis in the reference plane. Symmetry of the first and second kind are shown to be distinct because of the constraint system and not due to the form of the motion specification. The solution for the Burmester points is represented by the intersection of the Bottema conics. This development is supported by an algorithm for synthesizing five multiply separated positions in coplanar motion.
Numerical Methods for the Limit Analysis of Plates
Authors: Hodge P. G. , Belytschko T.
Published: October 2011

The determination of upper and lower bounds on the yield-point loads of plates are formulated as mathematical programming problems by using finite element representations for the velocity and moment fields. Results are presented for a variety of square and rectangular plate problems and are compared to other available solutions.
Linear and Nonlinear Analyses of Skewed Plates
Authors: Kennedy J. B. , Ng Simon
Published: October 2011

The perturbation method is used to analyze small and large-deflection problems of clamped skewed plates under uniform pressure. The results are improved by successive approximations to the three displacement components of a point on the middle plane of the plate. Numerical and graphical results are presented. Comparisons are made with existing results for skewed plates with small deflections as well as with results for rectangular plates with small and large-deflection behavior; good agreement is shown. The effects of skew and aspect ratio on plates with large deflections are investigated. The ratios of maximum center deflection to thickness of plate at which linear and nonlinear theories start deviating significantly from each other are obtained for different aspect ratios and skew angles. It is shown that the center deflection decreases with increase in skew and aspect ratio, and that the maximum resultant stress occurs along the longer edges of the plates and is displaced toward the obtuse corners.
On the Stability of the Equilibrium of Nonconservative Continuous Systems With Slight Damping
Authors: Nemat-Nasser S.
Published: October 2011

The stability of the equilibrium configuration of a linearly elastic solid (with or without internal damping) subjected to partial follower surface tractions (nonconservative loading) is studied. Proportional loading is considered and it is proved that the flutter (oscillations with increasing amplitude) load parameter of the undamped system is an upper bound for that of the system with slight damping. The necessary and sufficient condition for stability of the equilibrium state with respect to flutter-type motions, and sufficiency conditions for stability with respect to both divergence (or buckling) and flutter, are established. Based on energy considerations, an approximate method of stability analysis is suggested which reduces to the usual energy criterion for the cases of conservative loading.
Dynamic Force Analysis of Spatial Linkages
Authors: Uicker J. J.
Published: October 2011

The matrix method of linkage analysis is extended to the analysis of the bearing forces and torques which result from the inertia of the moving links when a single-loop, single-degree-of-freedom linkage is driven with known input velocity and acceleration. The method is well suited to digital computation and has been tested on several examples of spatial linkages, one of which is presented. A 4 × 4 “inertia matrix” is defined to describe the mass distributions of the links, and a matrix expression is derived for their kinetic energy. The dynamic bearing reactions are found by using the Lagrange equations with a varying constraint.
Experimental and Theoretical Studies of Liquid Sloshing at Simulated Low Gravity
Authors: Dodge F. T. , Garza L. R.
Published: October 2011

Analyses and experimental comparisons are given for liquid sloshing in a rigid cylindrical tank under conditions of moderately small axial accelerations; in particular, the theory is valid for Bond numbers larger than 10. The analytical results are put in the form of an equivalent mechanical model, and it is shown that the sloshing mass and the natural frequency of the first mode, for a liquid having a 0 deg contact angle at the tank walls, are smaller than for high-g conditions. The experimental data, obtained by using several small-diameter tanks and three different liquids, are compared to the predictions of the mechanical model; good correlation is found in most cases for the sloshing forces and natural frequency as a function of Bond number.
Buckling of Microfibers
Authors: Sadowsky M. A. , Pu S. L. , Hussain M. A.
Published: October 2011

Most composites are fabricated at elevated temperatures and cooled to room temperature. The difference in coefficients of thermal expansion of the fiber and matrix may cause buckling of the slender-shaped microfibers. This would greatly reduce the initial strength of the composites. The primary objective of this paper is to explain qualitatively the basic phenomenon of buckled microfibers in a composite and to present some numerical results in certain ranges of elastic parameters. Our analysis is based on assumptions that (a) the volume percentage of fibers is small so that the mutual interference of fibers is negligible and the matrix surrounding a fiber may be considered as infinitely large; (b) the diameter of the fiber is very small in comparison to its length so that the fiber may be treated as a linear fiber with infinite length; (c) the constituents are homogeneous and isotropic and the classical linear theory of elasticity may be applied; and, (d) in the process of cooling, the fiber is subjected to compression but not twisting moment by the surrounding matrix. The analysis leads to a relation between the pertinent elastic and thermal characteristics of the matrix and microfiber and the compressive force along the axis of the microfiber at the critical moment of incipient buckling. With the knowledge of that relation, it is now possible to know in advance whether or not buckling is to be expected and to avoid such manufacturing methods in which a threat of having buckled microfibers is present.
Stress Concentration in a Rubber Sheet Under Axially Symmetric Stretching
Authors: Yang Wei Hsuin
Published: October 2011

A class of axially symmetric problems, concerning a highly elastic, circular rubber sheet with (a) a centered circular hole, (b) a rigid circular inclusion under outward radial loading at outer boundary, and (c) a rigid outer boundary and a concentric hole under inward radial loading around the hole, is solved. The solution of (a) has been obtained by Rivlin and Thomas [1] by solving simultaneously a set of differential equations numerically. In this paper, their equations are reduced to a single second-order differential equation governing the deformation function ρ(r). This is further reduced to two decoupled first-order equations after introducing the phase plane (λ1 – λ2 plane). The solutions are obtained conveniently in the phase plane by Picard’s method and by straightforward numerical integration.
Application of Fracture Mechanics to Anisotropic Plates
Authors: Wu E. M.
Published: October 2011

The conditions necessary for the application of fracture mechanics to anisotropic materials were examined and verified experimentally on orthotropic plates. It was observed that crack extension, by opening and forward sliding, occurred independently and the associated stress-intensity factors at the state of incipient fracture are material constants. An empirical relation (k1/k1c) + (k2/k2c)2 = 1 was found to be a fracture criterion for both balsa wood and fiber-glass-reinforced plastic plates, inferring the existence of a general law of fracture for orthotropic materials.
A Unified Approach to Cylindrical and Spherical Elastic Waves by Method of Characteristics
Authors: Chou Pei Chi , Koenig H. A.
Published: October 2011

A set of generalized equations is presented which governs the propagation of plane, cylindrical, and spherical dilatation waves in elastic media. The corresponding characteristic equations are then derived, including the propagation of abrupt changes (discontinuous wave fronts). Procedures of numerical integration along the characteristic directions are established and carried out for several examples on a digital computer. The solutions of four of the specific examples calculated show excellent agreement with existing solutions by other methods.
Strain-Gradient Effects Around Cylindrical Inclusions and Cavities in a Field of Cylindrically Symmetric Tension
Authors: Weitsman Y.
Published: October 2011

In this work, it is assumed that the potential energy of an elastic body depends on its strains and strain gradients. Such a potential energy will give rise to both classical and higher-order stress terms. The constitutive law of the body will therefore incorporate additional elastic constants whose dimensions differ from those of the classical moduli by the square of length. A solution to the problem of a cylindrical inclusion and cavity in a field of cylindrically symmetric tension is presented to illustrate some of the new effects contained in the strain-gradient theory.
Experimental Studies of Turbulent Flow in a Porous Circular Tube With Uniform Fluid Injection Through the Tube Wall
Authors: Olson Reuben M. , Eckert E. R. G.
Published: October 2011

Fully developed turbulent flow of air at Re = 28,000 to 82,000 entered a porous tube with circular cross section. Air was injected uniformly through the tube wall for 18 diameters at various ratios of mass velocity through the tube wall to the average mass velocity at the entrance cross section of the tube, ranging from 0.00246 to 0.0584. Tests were also made with zero entrance velocity at the upstream end of the porous tube so that the flow developed in the tube exclusively as a result of the uniform mass injection through the tube wall. Most of the change in the shape of the velocity profiles, in the internal and wall shear, in the momentum flux factor, and in the friction factor occurred within the first 10 to 12 diameters of the tube length. Some changes even persisted further downstream, caused by the fact that mass is continuously injected along the porous tube. The parameters mentioned above, however, become independent of axial position for normalized distances downstream from the entrance cross section larger than x/D = 10 to 12, when they are considered as function of the ratio of injection velocity to average main flow velocity at the specific axial location. Eddy diffusivity values agreed in this presentation reasonably with the results of measurements in turbulent tube flow without injection. Normalized friction factors agreed with values measured in external flow. Properly normalized velocity defect profiles with injection agreed with those for flow without injection.
Experimental Buckling Modes of Clamped Shallow Shells Under Concentrated Load
Authors: Penning F. A.
Published: October 2011

Elastic stability of clamped shallow spherical shells subjected to a small finite-area load at the apex is studied experimentally. Upper and lower critical buckling loads and prebuckled and postbuckled deflections are found for λ between 10 and 17. Buckling modes have been observed and defined. Nonaxisymmetric deformations are noted. Shells for λ less than 8 1/2 exhibit plastic behavior and do not buckle.
Transient Response of a Circular Cylinder of Arbitrary Thickness, in an Elastic Medium, to a Plane Dilatational Wave
Authors: Garnet Hyman , Crouzet-Pascal Jacques
Published: October 2011

The response of a hollow cylinder of arbitrary thickness, embedded in an elastic medium, to a transient plane pressure wave is presented. The solution is valid within the scope of the linear theory of elasticity. The technique for obtaining the solutions relies upon (a) the construction of a train of incident pulses from steady-state components, where each pulse represents the time history of the transient stress in the incident wave, and (b) the existence of a physical mechanism which, between pulses, restores the disturbed particles of the cylinder and the surrounding medium to an unstrained state of rest. The validity of the technique is demonstrated by (a) comparisons with published data for limiting cases and (b) results obtained for a broad range of values of cylinder and surrounding medium parameters. The influence on the cylinder response of liner thickness and cylinder-medium impedance mismatch, when the incident wave is a step pulse, is investigated.
An Arc Crack Around a Circular Elastic Inclusion
Authors: England A. H.
Published: October 2011

The problem of a circular elastic inclusion bonded to a different elastic material except over an arc crack is considered. It is found that the solution yields an oscillation phenomenon near the ends of the crack of a form found previously by several authors, indicating that linear elasticity may not be used to predict the stresses and displacements in these regions.
Momentum Transfer in Turbulent Separated Flow Past a Rectangular Cavity
Authors: Haugen R. L. , Dhanak A. M.
Published: October 2011

This paper presents results of an analytical and experimental investigation aimed at describing the turbulent momentum transfer mechanism in the separated-flow region of a rectangular cavity facing an oncoming turbulent boundary layer. A flow model of the mixing region in the slot postulated on the basis of eddy diffusion in free jets gives values of velocities and drag in good agreement with the measurements. The results further point to the significant effects exerted by the oncoming boundary layer on transfer rates from the slot. Flow-visualization pictures show some interesting vortex patterns inside the cavity when height-to-width ratio is varied between values of 1 and 3.
Axisymmetrical Turbulent Swirling Natural-Convection Plume: Part 1—Theoretical Investigation
Authors: Lee Shao-Lin
Published: October 2011

A theoretical investigation is made of the behavior of an axisymmetrical turbulent swirling natural-convection plume in an otherwise motionless ambient fluid. With the introduction of the assumption of similar axial and swirling velocity profiles and similar buoyancy profile, and the assumption of lateral entrainment of ambient fluid, the order of the governing differential equations is reduced by one after the initial integration following the von Karman integral method. The behavior of the swirling plume is found to depend solely on two physical parameters associated with the source characteristics, the source Fronde number, and the source swirling velocity parameter. A series solution developed in the vicinity of the source of the swirling plume is obtained for any values of these two physical parameters. Numerical solutions for extended range of axial distance from the source of the swirling plume and for wide ranges of selected representative values of these two physical parameters are obtained with the use of a digital electronic computer. The behavior of the swirling plume is found to approach that of a nonswirling jet, a swirling jet, or a nonswirling plume when these two physical parameters are assigned values approaching those designating each of the aforementioned simpler, boundary situations.
Peripheral Jets in Proximity of the Ground
Authors: Cohen M. J.
Published: October 2011

The problem of the performance of a two-dimensional lifting unit with peripheral jet distribution in proximity of the ground is considered fully from a theoretical standpoint but with design considerations in view. The parametral dependence of the lift augmentation characteristic of the unit on a set of three basic parameters—namely, jet thickness, height from the ground, and jet curtain inclination—is examined fully. The effect of raking the jet nozzle exit line on lift is also considered. Compressibility effects in the case of a high-speed jet are briefly commented upon, and overall design guidance lines are suggested. The extension of this analysis to the problem of the peripheral jet with axial symmetry can be performed easily by means of the geometric transformation first suggested by H. R. Chaplin.
Dynamic Vibrations and Stresses in Elastic Cylinders and Spheres
Authors: Cinelli G.
Published: October 2011

A new finite Hankel transform [1] is used to find the transient displacement and stresses in thick elastic cylinders and spheres when the surfaces are subjected to dynamic loads for the following problems: (a) Pure radial and torsional motion of an infinitely long circular cylindrical shell; (b) radially symmetric motion of a spherical shell. The loads applied to both surfaces of the cylindrical and spherical shells are completely arbitrary functions of space (for the torsional case) and time. Employing the solutions obtained for the arbitrary loads, the spatial and temporal positions of these loads are then specialized to standard forms, such as a line load, band load, impulse, and so on, and the corresponding motion and stresses are found.
The Elastic Cylindrical Shell Under Radial Impulse
Authors: McIvor I. K.
Published: October 2011

In the motion of an elastic cylindrical shell following impulsive pressure, marked deviations from linear theory may occur through interaction of circumferential membrane force with flexural curvature. Energy is transferred to flexural modes of rather high order. The resulting flexural stress is significantly higher than that given by linear theory.
Axially Symmetric Motions of a Two-Layered Timoshenko-Type Cylindrical Shell
Authors: Jones J. P. , Whittier J. S.
Published: October 2011

A Timoshenko-type theory is presented for the dynamics of a cylindrical shell whose two layers are joined by a perfect bond. An assessment of the accuracy of the theory is obtained by solving the problem of axial propagation of an infinite train of axially symmetric waves and comparing the results with those obtained from the three-dimensional elasticity theory. Frequencies of the four lowest modes are accurately predicted by the shell theory for sufficiently long wavelengths and low frequencies. Preliminary comparisons of displacement distributions indicate that the shell-theory displacements are accurate in a more restricted frequency-wavelength regime. Timoshenko shear coefficients are determined by matching simple thickness-shear cutoff frequencies rather than by matching the lower Rayleigh wave speed. This is found preferable by consideration of the shapes of the first-mode phase velocity versus wave-number curves for the two theories.
The Contact Stresses Between a Rigid Indenter and a Viscoelastic Half-Space
Authors: Ting T. C. T.
Published: October 2011

The Hertz problem for a rigid spherical indenter on a viscoelastic half-space was studied by Lee and Radok [1] in which the radius a(t) of the contact area is a monotonically increasing function of time t. Later, Hunter [2] studied the rebound of a rigid sphere on a viscoelastic half-space so that the contact radius a(t) increases monotonically to a maximum and then decreases to zero monotonically. The contact problem in which a(t) increases for the second time and decreases again does not seem to have been studied; nor has the contact problem in which a(t) is nonzero initially and decreases monotonically been studied. In this paper, a method is introduced so that the contact problem can be solved for arbitrary a(t). The rigid indenter is assumed to be smooth and axisymmetric but otherwise arbitrary. The viscoelastic solutions are expressed in terms of the associated elastic solutions. A means for measuring the viscoelastic Poisson’s ratio is suggested.
Exact and Variational Solutions to a General Viscoelasto-Kinetic Problem
Authors: Valanis K. C.
Published: October 2011

Exact and variational methods of analysis are proposed which reduce a general elastic wave-propagation problem to a static problem plus an eigenvalue problem. The methods are shown to be immediately applicable to linear viscoelastic materials with constant Poisson’s ratio. The viscoelastic wave problem is thus reduced to an elastic wave problem plus an integral equation of the Volterra type involving time only.
The Effect of a Stringer on the Stress in a Cracked Sheet
Authors: Greif Robert , Sanders J. L.
Published: October 2011

An infinite stringer is assumed to be continuously attached to a sheet along a line perpendicular to a finite crack. At a great distance from the crack, the sheet is under a uniform tensile stress parallel to the stringer. The plane-stress solution for this problem is carried out by using the complex variable approach of Muskhelishvili to derive an integral equation which is then solved numerically on the IBM 7090 computer. In particular, the effect of the stringer on the strength of the stress singularity at the crack tip, and the maximum load-concentration factor in the stringer are found.
Two-Dimensional Wave Propagation in Realistic Viscoelastic Materials
Authors: Arenz R. J.
Published: October 2011

A solution method using realistic (broad-band) viscoelastic response characteristics covering approximately ten decades of logarithmic time is presented for wave propagation in two-dimensional geometries. A Dirichlet series representation of the viscoelastic mechanical properties and a numerical collocation inversion procedure overcome many of the computational difficulties associated with the Laplace-transform approach to dynamic linear viscoelasticity and also afford a complete time solution. Stress distributions are given for two complementary cases, (a) the viscoelastic half-space subjected on the upper surface to the steady motion of a step pressure load moving supersonically relative to any wave speed in the material, and (b) the semi-infinite thin plate similarly loaded on its edge.