bluuebunny/crossref_metadata_2025 huggingface dataset:
MAGNETIC RESONANCE IMAGING FEATURES OF INTRACRANIAL ASTROCYTOMAS AND OLIGODENDROGLIOMAS IN DOGS
Authors: YOUNG BENJAMIN D. , LEVINE JONATHAN M. , PORTER BRIAN F. , CHEN‐ALLEN ANNIE V. , ROSSMEISL JOHN H. , PLATT SIMON R. , KENT MARC , FOSGATE GEOFFREY T. , SCHATZBERG SCOTT J.
Published: November 2010

Astrocytomas and oligodendrogliomas represent one third of histologically confirmed canine brain tumors. Our purpose was to describe the magnetic resonance (MR) imaging features of histologically confirmed canine intracranial astrocytomas and oligodendrogliomas and to examine for MR features that differentiate these tumor types. Thirty animals with confirmed astrocytoma (14) or oligodendroglioma (16) were studied. All oligodendrogliomas and 12 astrocytomas were located in the cerebrum or thalamus, with the remainder of astrocytomas in the cerebellum or caudal brainstem. Most (27/30) tumors were associated with both gray and white matter. The signal characteristics of both tumor types were hypointense on T1‐weighted images (12 each) and hyperintense on T2‐weighted images (11/14 astrocytomas, 12/16 oligodendrogliomas). For astrocytomas and oligodendrogliomas, respectively, common findings were contrast enhancement (10/13, 11/15), ring‐like contrast enhancement (6/10, 9/11), cystic regions within the mass (7/14, 12/16), and hemorrhage (4/14, 6/16). Oligodendrogliomas were significantly more likely to contact the brain surface (meninges) than astrocytomas (14/16, 7/14, respectively, P=0.046). Contact with the lateral ventricle was the most common finding, occurring in 13/14 astrocytomas and 14/16 oligodendrogliomas. No MR features were identified that reliably distinguished between these two tumor types. Contrast enhancement was more common in high‐grade tumors (III or IV) than low‐grade tumors (II, P=0.008).
“How Can You Just Cut Off a Whole Side of the Family and Say Move On?” The Reshaping of Paternal Grandparent‐Grandchild Relationships Following Divorce or Separation in the Middle Generation
Authors: Doyle Martha , O’Dywer Ciara , Timonen Virpi
Published: November 2010

On the basis of a qualitative study of 31 grandparents, this article highlights how separation in the middle generation can result in an erosion of trust and quality of paternal grandparent‐grandchild relationships. Notwithstanding these changes, grandparents endeavor to support and remain involved in the lives of their grandchildren by, inter alia, compensating for a perceived lack of their sons' parenting skills, affirming their grandchild's position in the paternal kin network, and acting as a mediator between the separated couple to ensure continued contact with grandchildren. The findings suggest that the actions of paternal grandparents can potentially have important future implications not only for the grandparent‐grandchild relationship, but also the relationship trajectories of their adult son and child in the post‐separation family.
Through the Eyes of the Beholder: The Mediating Role of Relationship Acceptance in the Impact of Partner Behavior
Authors: South Susan C. , Doss Brian D. , Christensen Andrew
Published: November 2010

Integrative Behavioral Couple Therapy (IBCT) posits that emotional reactions to a partner's behavior can be as important to the relationship as the behavior itself. This study examined whether acceptance (a) is distinct from relationship sentiment, (b) mediates the link between a partner's behavioral frequency and own relationship satisfaction, and (c) mediates the association between frequency of partner behavior and frequency of one's own behavior. Both members of 307 married couples (N = 614 persons) completed self‐ and spouse‐report measures of frequency and acceptability of positive and negative behaviors. Acceptance was distinct from satisfaction and mediated both relations for all types of relationship behaviors. Findings support IBCT's model of emotional‐cognitive acceptance of partner behaviors as a key source of relationship distress.
Perceived Helpfulness of Four Different Types of Marriage Preparation Interventions
Authors: Duncan Stephen F. , Childs Geniel R. , Larson Jeffry H.
Published: November 2010

As evidence of the benefits of marriage preparation continues to mount, so does the importance of investigating the characteristics of the interventions that are most helpful and for whom. In a sample of 1,409 individuals, this study compares perceived helpfulness of four marriage preparation interventions: class, community/church sponsored workshop, counseling, and self‐directed. All interventions were perceived as helpful, but class and self‐directed learning were rated more highly than counseling and workshops, independent of gender. Class and self‐directed learning participants had the highest improvement scores overall, with women reporting greater positive change than men. Implications for marriage preparation interventions are discussed.
MANAGING DIVERSITY: HOW ORGANIZATIONAL EFFORTS TO SUPPORT DIVERSITY MODERATE THE EFFECTS OF PERCEIVED RACIAL DISCRIMINATION ON AFFECTIVE COMMITMENT
Authors: TRIANA MARÍA del CARMEN , GARCÍA MARÍA FERNANDA , COLELLA ADRIENNE
Published: November 2010

Using the interactional model of cultural diversity, we examined whether the negative effects of perceived racial discrimination on affective commitment can be mitigated by perceived organizational efforts to support diversity. Across 3 studies, we found that perceptions of workplace racial discrimination are negatively related to affective commitment. In 2 out of 3 studies, this negative relationship was attenuated as employees perceived more organizational efforts to support diversity. Studies 1 (mostly Whites) and 2 (mostly Hispanics) showed that organizational efforts to support diversity attenuate the negative effects of perceived racial discrimination on affective commitment. However, in Study 3 (African Americans), results showed that when organizational efforts to support diversity are high, the negative relationship between perceived racial discrimination and affective commitment became stronger. Studies 2 and 3 also extended these results by showing that the interaction of perceived racial discrimination and organizational efforts to support diversity indirectly influences turnover intent.
Intensity‐dependent Direct Solar Radiation‐ and UVA‐induced Radical Damage to Human Skin and DNA, Lipids and Proteins
Authors: Haywood Rachel , Andrady Carima , Kassouf Nick , Sheppard Nick
Published: November 2010

Skin can be exposed to high‐intensity UV‐radiation in hot countries and during sunbed use; however, the free‐radical damage at these intensities is unknown. We used electron spin resonance spectroscopy to measure free‐radical generation in ex vivo human skin/substitutes +/− the spin‐trap 5,5 dimethyl‐1‐pyrroline N‐oxide (DMPO) exposed to solar‐irradiation equivalent to Mediterranean sunlight. Skin‐substitutes, model DNA‐photosensitizer systems, lipids and proteins were also irradiated with low‐intensity UVA/visible light. Without DMPO a broad singlet was detected (using both irradiations) in skin/substitutes, nail‐keratin, tendon‐collagen, phospholipid and DNA + melanin or riboflavin. In addition to lipid‐derived (tentatively tert‐alkoxyl/acyl‐) and protein radicals detected with DMPO at lower intensities, isotropic carbon‐, additional oxygen‐ and hydrogen‐adducts were detected in solar‐irradiated skin/substitutes at higher intensities. Carbon‐adducts were detected in UVA‐irradiated human skin cells, DNA + melanin or riboflavin and soybean‐phospholipid. Anisotropic protein‐adducts, comparable to adducts in solar‐irradiated tendon‐collagen, were absent in UVA‐irradiated skin fibroblasts suggesting the trapping of extracellular collagen radicals. Absence of hydrogen‐adducts in fibroblasts implies formation in the extracellular compartment. We conclude damage at high intensities is part cellular (carbon‐ and oxygen‐radicals) and part extracellular (protein‐ and hydrogen/H+ + e−), and skin substitutes are suitable for sunscreen testing. While UVA absorption and lipid‐oxidation is direct, DNA and protein‐oxidation require photosensitisation.
Trapeze-Flap Plasty: An Effective Technique for Postburn Edge Elbow Contracture Elimination
Authors: Grishkevich Viktor M.
Published: November 2010

Background

Scar flexion elbow contracture is a common complication of burns that restricts upper limb function and requires surgical elimination. In spite of the many surgical techniques that have been suggested, the contracture reconstruction still presents a challenge for surgeons.

Methods

One hundred and twenty-six patients with 174 edge elbow contractures were operated on. Edge elbow contracture, comprising 70% of all elbow contractures, is characterized by the presence of the fold located on the medial or/and lateral edge of cubital fossa. A crescent-shaped fold consists of a lateral sheet, comprising scars; the medial sheet and cubital fossa consists of healthy skin. The fold's crest is the edge of the scar sheet. The contracture is caused by the scar sheet's surface deficit in length; the scar's surface deficit is present all the way from the fold's crest to the joint rotation axis, and possesses a trapezoid shape. The best tissue for scar sheet deficit compensation and contracture elimination the comprises healthy skin of the cubital fossa and medial fold sheet. After fold sheet division, scar sheet dissection and joint extension, the trapeze-shaped wound is formed as a rule. The adipose-cutaneous trapezoid flap, which includes all the cubital fossa and medial fold sheet surface, is elevated. The flap advances on the wound with tension. As a result of flap tension, the adjacent skin of the contralateral side and the back surfaces of the elbow are displaced towards the cubital fossa, participating in donor wound coverage and contracture elimination.

Results

Mild edge elbow contractures were eliminated with a single trapezoid flap. In the case of moderate and severe contractures, additional trapezoid adipose-scar flaps were elevated from the scar sheet in order to cover the donor wound on the sides of the main flap. The adipose-cutaneous and adipose-scar trapezoid flaps are large, have no acute angles, do not undergo rotation and have steady blood circulation. Contractures were eliminated completely in 166 cases. Local flap end necrosis of the adipose-scar flap occurred in eight cases. The extended healthy flap's skin continued to grow. Full range of flexion and extension was achieved in all cases, except for eight cases with articular changes; there was no contracture recurrence and no re-operations were needed. The cubital fossa as the donor site preserved a normal shape as a result of growth of the stretched skin.

Conclusion

The single-staged trapeze-flap technique using cubital fossa flap is easy to plan and perform; edge elbow contractures of different severity were eliminated in full and definitively without skin grafting, pedicled and free flaps.
Healing of Arthroscopic Portals in Shoulder Surgery: A Randomized Controlled Trial Comparing Different Methods of Closure
Authors: Loveridge Jeremy M. , Gardner Richard , Barnett Andrew , Davis Nicky , Dunkley Alan
Published: November 2010

Background

Suturing of portals following arthroscopic shoulder surgery is the standard method of closure, but may be unnecessary. We carried out a randomised controlled trial to compare patients whose arthroscopic portals were closed by suturing and those that were covered by a simple dressing. We randomised 60 patients undergoing diagnostic shoulder arthroscopy, arthroscopic subacromial decompression and arthroscopic acromioclavicular joint excision.

Methods

At 10 to 12 days following surgery, patients attended the GP surgery for a wound check and removal of sutures as required. At 3 weeks and 3 months every patient was reviewed by a designated, blinded, observer and the wounds assessed. The patients completed a questionnaire including visual analogue scores to determine their satisfaction with wound appearance and any complications such as infection.

Results

At 3 weeks and 3 months no patients had needed antibiotics with no wound erythema or signs of infection. The number of dressings needed was comparable in both groups (p=0.73). The difference in the level of patient satisfaction was not statistically significant in either group (p=0.46). The wound cosmesis score was not statistically different in either group (p=0.66).

Conclusion

We conclude that both closure techniques were equivalent but the non-suture technique is cheaper with lower morbidity. From our study there is no need to suture shoulder arthroscopy portal wounds.
Accuracy of High-Resolution Ultrasonography in the Diagnosis of Articular-Sided Partial Thickness Rotator Cuff Tears
Authors: Modi Chetan S. , Smith Christopher D. , Ho Kevin , Karthikeyan Shanmugam , Rai Santosh , Boer Ronald , Drew Steven J.
Published: November 2010

Background

The present study aimed to assess the accuracy of high-resolution ultrasonography in the detection of articular-sided partial thickness rotator cuff tears.

Methods

Two-hundred and forty-six shoulders of 245 patients underwent ultrasonography and subsequent shoulder arthroscopy. All scans were performed by an experienced specialist musculoskeletal radiologist and arthroscopies were carried out by a single surgeon.

Results

Fifty-eight partial thickness tears (of which 56 were articular-sided) were found at arthroscopy. Of the remaining shoulders, 90 had full thickness tears and 98 had intact rotator cuffs. Ultrasonography correctly identified 21 of 56 articular-sided tears as partial thickness tears. It had a sensitivity of 7%, a specificity of 98% and an accuracy of 74% for the diagnosis of articular-sided partial thickness tears. If a full thickness tear was considered as a true positive, the sensitivity increased to 89%, specificity to 98% and accuracy to 96%.

Discussion

Ultrasonography is not sufficiently accurate to diagnose articular-sided partial thickness tears. A higher accuracy can be achieved if a full thickness tear is considered a positive finding. Ultrasonography should not be considered a first line investigation for a clinically suspected partial thickness rotator cuff tear. An articular-sided partial thickness rotator cuff tear should be considered in all patients undergoing an arthroscopic rotator cuff procedure.
Clinical Commentary and Literature Review: Diagnosis, Conservative and Surgical Management of Adhesive Capsulitis
Authors: Manske Robert C. , Prohaska Daniel
Published: November 2010

Adhesive capsulitis is a painful musculoskeletal condition of the glenohumeral joint causing limitation of motion and pain. To date the aetiology of adhesive capsulitis remains somewhat of a mystery. Standard of care generally consists of conservative management which can be followed by surgical intervention if adequate function is not attained. Conservative treatment can often be a long and frustrating course. Patience and persistence usually prevail with a functional return following either conservative or surgical intervention.
On Analysis of Cable Network Vibrations Using Galerkin’s Method
Authors: Soler A. I. , Afshari H.
Published: November 2010

Built-up systems consisting of rectangular cable networks covered by or embedded in a membrane matrix are considered; small oscillations about an initially flat, pretensioned state are studied. By employing Dirac delta functions to aid in representation of preload and weight distribution acting on the system, the system response is shown to be given by a generalized version of the equation for a vibrating membrane. A solution of the field equation is effected using Galerkin’s method and approximating functions are suggested for a wide class of boundary shapes. As an illustration of the method a rectangular boundary shape is considered and results are obtained for typical values of preload, cable distribution, etc. Results are compared with previous analyses of similar systems, and advantages of the present approach are discussed.
On the Structure of Stress-Strain Relations for Time-Dependent Plastic Deformation in Metals
Authors: Rice J. R.
Published: November 2010

The paper is concerned with the structure of multiaxial stress-strain relations in time-dependent metal plasticity, as for transient creep and rate sensitive yielding. First, a general kinematical relation is developed between the macroscopic inelastic strain tensor and microstructural slip displacements, as modeled either by continuum shearing on crystallographic planes of individual grains or by the motion of discrete dislocation lines. It is assumed that at any given slipped state, the rate of slipping on a particular system is governed by the resolved shear stress on that system (or by the local “forces” on dislocation lines). This leads to the primary result of the paper: Components of the macroscopic inelastic strain rate tensor are derivable, at each instant in the course of deformation, from a potential function of stress. General features of the flow potential surfaces in stress space are discussed, and some specific functional forms are examined. Linear viscoelasticity and time-independent plasticity are developed as limiting cases of the flow potential formulation, and the appropriateness of a potential function for stationary creep is discussed.
An Analysis of Primary Creep of Nickel-Base Superalloy Single Crystals
Authors: Paslay P. R. , Wells C. H. , Leverant G. R.
Published: November 2010

The orientation and stress dependence of the primary creep rate in single crystals of a nickel-base superalloy is predicted from crystallographic deformation mechanisms. An experimentally determined relationship between the deformation rate and applied stress is employed to calculate the independent contributions of each of the possible slip systems to the strain rate. Calculations were made for single crystals of a nickel-base superalloy tested in tensile creep at 1400 deg F, at which temperature the active slip planes are known to be {111}, and the slip directions either 〈110〉 or 〈112〉 at high or low strain rates, respectively. Comparison with measured primary creep rates showed the 〈110〉 contribution to be negligible and that while semi-quantitative agreement with the 〈112〉 analysis was obtained, an accurate prediction of creep rates may require inclusion of strain hardening in the analysis.
Low-Gravity Fuel Sloshing in an Arbitrary Axisymmetric Rigid Tank
Authors: Chu Wen-Hwa
Published: November 2010

Solutions to free and forced oscillations have been found in terms of an auxiliary set of eigenfunctions through the use of a modified Galerkin procedure. The slosh force and moment for an arbitrary axisymmetric rigid tank at arbitrary Bond number have been derived for both pitching and translation, and expressed in terms of characteristics of an equivalent spring-mass system. Numerical examples have been constructed which which compare favorably with available theories and experiments.
A Load Accelerating on the Surface of an Acoustic Half Space
Authors: Stronge W. J.
Published: November 2010

The problem of a pressure, distributed as a step function, which moves across the surface of an acoustic half space is discussed. The pressure is suddenly applied and thereafter the step moves as any prescribed continuous function of time. This results in a problem in plane flow. An analytical solution for the pressure and displacements throughout the half space is obtained in terms involving only single integrals. It is shown that if the step moves with the sonic speed for a finite time the displacements beneath the step are discontinuous. This displacement discontinuity increases in proportion with time. (Displacements remain continuous at every point below the surface.) However, if the step accelerates through the sonic speed no displacement discontinuities occur. After the step is moving supersonically, two wave fronts develop. The pressure increases across the leading wave front and decreases across the trailing one.
Biaxial Plastic Simple Waves With Combined Kinematic and Isotropic Hardening
Authors: Goel R. P. , Malvern L. E.
Published: November 2010

The study of one-dimensional combined longitudinal and torsional plastic wave propagation in a thin-walled cylindrical tube of isotropic-hardening material was first carried out by Clifton. In this paper, the same problem is studied for a combined kinematic and isotropic hardening material. Simple wave solutions are obtained. In some cases, a discontinuity in shear stress occurs, propagating at the elastic shear-wave speed c2, followed by a slow plastic simple wave.
Dynamic Stability of Hovercraft in Heave
Authors: Davies H. J. , Poland G. A.
Published: November 2010

The regimes of flow governing the dynamic behavior of a two-dimensional mathematical model of an edge-jet Hovercraft in heaving motion are described and the equations associated with such regimes derived. Both the free and forced-oscillation characteristics are studied. The nonlinear nature of the system manifests itself, in the case of the forced oscillations, as a shift in the dynamic equilibrium position resulting in a loss of mean hoverheight.
Laminar Swirling Flow in a Tube With Surface Mass Transfer
Authors: Kinney R. B. , Sparrow E. M.
Published: November 2010

The decay of swirl and the associated axial and radial velocity perturbations are analyzed for laminar tube flow with surface mass transfer. The initial swirl distribution is that corresponding to a fully developed flow characterized by injection or withdrawal of fluid having both circumferential and radial components of velocity. Consideration is also given to swirling flows in impermeable tubes, and new results are obtained by specializing the general solution for the case of surface mass transfer. Numerical results are presented for a range of values of the mass transfer Reynolds number. Among the findings, it is observed that at the higher rates of fluid injection, the decay of the swirl requires a much longer length of run than does the decay of the axial and radial velocity perturbations.
Load Transfer Problem for an Embedded Shaft in Torsion
Authors: Keer L. M. , Freeman N. J.
Published: November 2010

This paper deals with the axially symmetric torsion of a semi-infinite cylinder embedded into an elastic half space, where the cylinder is allowed to protrude by a finite amount. The problem is formulated to include the case of the protruding portion of the cylinder when it is a different material and partially bonded to the embedded portion. With the use of integral transforms and Dini series, the problem is reduced to the determination of the solution of an integral equation. Stress singularities of a fractional order are noted and computed at the juncture, when all members are perfectly bonded. A numerical solution of the integral equation is obtained for the case of a homogeneous cylinder. The bond stress on the cylinder—half space interface and the torque-twist (and consequently, strain energy) for the entire system are computed for different values of the elastic constants.
Role of Elastic Constants in Certain Contact Problems
Authors: Dundurs J. , Stippes M.
Published: November 2010

The dependence of stresses on the elastic constants is explored in frictionless contact problems principally for the case when the contacting bodies are made of the same material and the deformations are induced by prescribed surface tractions. The strongest results can be obtained for problems with contacts that either recede or remain stationary upon loading. In such problems, the stresses are proportional to the applied tractions and the extent of contact is independent of the level of loading. Furthermore, it is shown that the Michell result regarding the dependence of stresses on Poisson’s ratio carries over to plane contact problems with receding and stationary contacts. In three and two-dimensional problems with advancing contacts, it is possible to establish certain rules for scaling displacements and stresses.
Axisymmetric Elasticity Solutions of Spherical Shell Segments
Authors: Levine H. S. , Klosner J. M.
Published: November 2010

A series solution for the stresses and displacements of a spherical segment subjected to arbitrary axisymmetric surface tractions and edge boundary conditions is presented. A least-square point-matching technique is used to satisfy the specified edge conditions. The general solution for the axisymmetric case has been obtained by utilizing two sets of functions, namely, the Lure´ homogeneous functions and the full sphere functions used by Sternberg, Eubanks, and Sadowsky. In particular, solutions to the following problems have been obtained: (a) the spherical segment with a stress free edge subjected to a centrifugal force field; (b) the spherical segment subjected to an external pressure varying as cos2N θ supported on a rigid surface with no shear resistance; and (c) the hemisphere having zero traction on its spherical surfaces subjected to edge shear stresses. The results are presented in graphic form, which demonstrate the boundary-layer effect. Heretofore solutions to these types of problems have been obtained by using shell theory approximations.
The Propagation of Radially Symmetric Stress Waves in Anisotropic Nonhomogeneous Elastic Media
Authors: Greif R. , Chou S.-C.
Published: November 2010

A study is made of the transient response of a thick-walled cylinder (plane-strain) or plate (plane-stress) subjected to an axially symmetric time-dependent pressure (or velocity) at an internal or external surface. The material of the structure is orthotropic with cylindrical anisotropy and, in addition, is continuously inhomogeneous with mechanical properties varying along the radius. The curvilinear characteristics in the space-time plane are transformed into straight lines of equal slope so that numerical errors can be minimized. The problem is then solved using numerical integration of the characteristic equations in the transformed space-time plane and incorporates the exact jump conditions across discontinuous wave fronts.
A General Nonlinear Relaxation Iteration Technique for Solving Nonlinear Problems in Mechanics
Authors: Perrone N. , Kao R.
Published: November 2010

The nonlinear relaxation method, an iterative approach used in conjunction with finite-difference approximations, is illustrated via the solution to a very simple problem. Subsequently, the method is used to solve three geometrically nonlinear problems in mechanics: finite bending of a circular thin walled tube, the large deflection membrane response of a spherical cap, and finite deformations of a uniformly loaded circular membrane. Formulations for the three problems are quite different but this difference does not inhibit the use of the nonlinear relaxation technique. Solutions were obtained in approximately one man day per problem including the total time devoted to examining, planning, programming, debugging, etc. Solutions compare very favorably with results found elsewhere in the literature. The essential and important advantages of the nonlinear relaxation technique are (a) versatility and ease of application, (b) efficiency with respect to people and computer time utilized, (c) insensitivity to starting values as far as convergence is concerned, and (d) simplicity of logic that makes it a trivial task to learn how to employ it.
A Mathematical Programming Method for Design of Elastic Bodies in Contact
Authors: Conry T. F. , Seireg A.
Published: November 2010

This study deals with the development of a programming procedure for the analysis and design of general problems of elastic bodies in contact. The procedure utilizes a simplex-type algorithm. The technique is applied to Hertzian-type contacts, and contacts of beams on elastic foundations. The selection of initial separations in the latter case for the optimal load distribution is considered as an example for the design scheme. The technique gives an effective and relatively inexpensive means of treating this class of problems.
A Modified Linear Membrane Theory for the Pressurized Toroid
Authors: Tielking J. T. , McIvor I. K. , Clark S. K.
Published: November 2010

A modified linear membrane theory for the pressurized toroid is presented for which the displacement field is nonsingular. The derivation rests on a nonlinear formulation, but the equations are linearized by exploiting the insensitivity of the meridional stress resultant to the deformation. The resulting equilibrium equations are not statically determinate, containing two geometric variables. Two compatability equations complete the formulation. It is possible to construct a quadratic functional such that its vanishing first variation generates the derived boundary-value problem. Approximate solutions are then obtained by direct methods of the variational calculus. The results are compared with previously published nonlinear solutions and show very good agreement for a wide range of the load parameter. The present formulation readily permits generalization to orthotropic toroids.
On the Initial Speed of Elastic-Plastic Boundaries in Longitudinal Wave Propagation in a Rod
Authors: Ting T. C. T.
Published: November 2010

A study is given of elastic-plastic boundaries which start at the end x = 0 of a rod in one-dimensional wave propagation. The initial speed of the elastic-plastic boundaries at x = 0 and at any time, say t = t0, is determined analytically for all possible combinations of the time derivative σt of the stress σ(0, t) before and after t = t0. If σt at x = 0 is continuous and vanishes at t = t0, all possible combinations of σtt before and after t = t0 are considered. The analysis also gives the number of regions involved, the derivatives in each region, and distinguishes elastic regions from plastic regions. These are useful guides for a numerical solution of general initial and boundary-value problems.
Normal Impact of an Infinite Elastic Beam by a Semi-Infinite Elastic Rod
Authors: Ranganath S.
Published: November 2010

Solutions are obtained by the method of Laplace transformation for the problem of normal impact of an infinite elastic beam by a semi-infinite elastic rod. The Timoshenko beam theory is used to describe the waves in the beam and elementary one-dimensional bar theory is used to describe the waves in the rod. Numerical results are presented for the velocity and the bending moment. These results are shown to agree well with experimental observations, except at early times.
Crack Propagation in a Linearly Viscoelastic Strip
Authors: Mueller H. K. , Knauss W. G.
Published: November 2010

The tip velocity of a crack propagating through a viscoelastic material depends on geometry, applied load and its history, and material properties. A consideration of the work done by the unloading tractions at the crack tip shows that, for a large crack propagating through an infinitely long strip under constant lateral strain, the rate of propagation can be calculated from a knowledge of the intrinsic fracture energy (a material constant), the material creep compliance, and an additional size parameter. This parameter vanishes from the analysis if the material is elastic, and the familiar instability criterion is obtained in this case. Comparison with experimental data is provided and the consequences of step loadings are examined.
Free Vibrations of Viscoelastic Timoshenko Beams
Authors: Huang T. C. , Huang C. C.
Published: November 2010

The correspondence principle has been applied to derive the differential equations of viscoelastic Timoshenko beams with external viscous damping. These equations are solved by Laplace transform and boundary conditions are applied to obtain complex frequency equations and mode shapes for beams of any combination of end conditions. For beams without external damping, the correspondence principle can be applied directly to the available solutions of elastic Timoshenko beams. Numerical illustration is given.
Resonance Classification in a Cubic System
Authors: Ness D. J.
Published: November 2010

A weakly nonlinear, single-degree-of-freedom cubic system subject simultaneously to a time-varying force and parametric excitation is considered. The various types of resonance phenomena exhibited by the system are classified and a detailed stability analysis is presented for one case of particular interest.
The Unsteady Wake of an Oscillating Cylinder at Low Reynolds Number
Authors: Griffin O. M.
Published: November 2010

A great deal of consideration has been given to flow-bluff body interactions because of the practical need to know the fluid forces acting on bodies immersed in a flowing stream. A flow regime exists where forced and fluid-induced transverse vibrations of a cylinder synchronize the vortex shedding and cylinder frequencies, and interact with the flow to control the wake formation process. Measurements have been made with a hot-wire anemometer for Reynolds numbers between 120 and 350, where cylinder vibrations at, and near, the natural shedding frequency both synchronize the wake and suppress the initiation of turbulence. Data are presented for the changes induced in the vortex formation by different conditions of forced excitation, and it is shown that the formation region length is reduced by as much as 50 percent from its value behind the stationary cylinder. A detailed study is made of fluctuating velocities between 1–9 dia downstream at a Reynolds number of 200, and the paths of the early vortices after formation are inferred from the fluctuating velocity profiles. The formation length is shown to be a suitable scale for displaying the velocity distribution in the synchronized wake, and the mechanics of the formation process are discussed in terms of the present experimental results. Wake correlation effects and the onset of turbulence are also discussed in light of the hot-wire measurements.
On Aerodynamic Disturbances Caused by Single Hot-Wire Probes
Authors: Comte-Bellot G. , Strohl A. , Alcaraz E.
Published: November 2010

The disturbances which result from the different parts of single hot-wire probes (stem, prongs, wire sheath if any) are experimentally investigated by means of an auxiliary “reference” probe and are compared with evaluations derived from a potential flow scheme. Our findings suggest that the disturbances created by the prongs are usually 2–4 times greater than that produced by the stem, and that the wire sheath has a negligible effect. The global disturbance, closely equalling the sum of the separate ones, shows up as a velocity decrease when the probe is aligned with the mean flow (8 percent or less depending on the probe’s geometry) and shows up as a velocity increase when the probe is normal to the mean flow (11 percent or less, again depending on the probe’s geometry).
Displacement and Plastic Distortion Fields Produced by Dislocations in Anisotropic Media
Authors: Mura T.
Published: November 2010

The fundamental relations among dislocation density tensors, plastic distortion tensors, and dislocation flux tensors are introduced by the Fourier integral method. The proposed method is analytical rather than geometrical and powerful for further analysis of elastic fields. This method is applied to find displacement and plastic distortion fields for a given distribution of dislocations in anisotropic media. Since these quantities are not state quantities, the unique solution is obtained by designating a history of creation of the dislocations. In this paper the history is given in terms of the direction of motion in which the dislocations are introduced in the material from infinity with infinitely small uniform velocity.
Determination of the Unloading Boundary in Longitudinal Elastic-Plastic Stress Wave Propagation
Authors: Tuschak P. A. , Schultz A. B.
Published: November 2010

For several types of excitation of one-dimensional elastic-plastic stress waves in a rod, unloading waves propagate which interact with the loading waves. The moving boundary at which this interaction occurs is the unloading boundary. A knowledge of the location of this boundary and the behavior exhibited on it is necessary for the solution of wave-propagation problems of this kind. A technique is presented to obtain an arbitrary number of terms in series expressions describing the response in semi-infinite rods. Several examples, including finite mass impact of the rod, are given to illustrate the use of the technique. The technique will determine the initial portion of the boundary in a finite length rod.
The Elastic Strip With Prescribed End Displacements
Authors: Torvik P. J.
Published: November 2010

The stresses and displacements in an elastic strip arising from displacements prescribed over one end are determined in terms of the eigenfunctions of the strip, with the coefficients being determined through a variational principle. Certain elementary solutions are included to account for the resultant force and moment induced by an arbitrarily prescribed displacement. Stresses and displacements resulting from pressing a strip against rough flat and parabolic surfaces were determined as were the deflections of a two-dimensional beam with one end built-in and the other subjected to a moment or a shear force. Differences between the results obtained and the predictions of elementary formulas are small.
Microstructure Theory for a Composite Beam
Authors: Sun C.-T.
Published: November 2010

A continuum model with microstructure is constructed for laminated beams. In deriving equations, each constituent layer is considered as a Timoshenko beam. With a certain kinematical assumption regarding the deformations of the composite beam the kinetic and strain energies, as well as the variation of the work done by external forces, are computed. The energy and work expressions are “smoothed out” by a smoothing operation, thus transforming the laminated structuring into microstructure of a macro-homogeneous beam. Subsequent application of Hamilton’s principle yields the equations of motion and the boundary conditions. The equations thus obtained are employed to investigate free flexural waves in a composite beam. It is found that the dispersion curves according to the present theory agree very well with the curves obtained according to an exact analysis. Results according to the effective modulus theory are presented for comparison. Two simplified versions of the microstructure beam theory are also developed and discussed.
On the Behavior of Acceleration Waves in Deformed Elastic Nonconductors
Authors: Chen P. J.
Published: November 2010

In this paper, we consider one-dimensional acceleration waves propagating in an elastic nonconductor of heat which is at rest in a nonhomogeneous configuration. We show that there exists a number called the critical initial amplitude which either vanishes or is finite depending on the nature of the strain field just ahead of the waves and the material properties, and that under various physically reasonable circumstances the behavior of the waves can be quite different.
An Experiment on Laser-Generated Stress Waves in a Circular Elastic Ring
Authors: Hartman W. F. , Forrestal M. J. , Bushnell J. C.
Published: November 2010

A circular, magnesium fluoride ring was irradiated with a Q-switched, neodymium-doped glass laser. The sudden absorption of laser energy by the ring produced an internal temperature distribution which could be closely approximated by a cosine function over half the circumference of the ring. The ensuing membrane strains were measured with semiconductor strain gages. Measured strain-time histories were found to be in close agreement with theoretical predictions.
Stresses Emanating From the Supports of a Cylindrical Shell Produced by a Lateral Pressure Pulse
Authors: Forrestal M. J. , Sliter G. E. , Sagartz M. J.
Published: November 2010

A semi-infinite, elastic, circular cylindrical shell is subjected to two uniform, radial pressure pulses, one a step pulse and the other a short-duration, rectangular pulse. Solutions for the stresses emanating from both a clamped support and a simple support are presented for a Timoshenko-type shell theory and a shell bending theory. Results from the Timoshenko-type theory are obtained using the method of characteristics, and results from the shell bending theory are obtained using integral transform techniques. Numerical results from both shell theories are presented for the bending stress and the shear stress resultant. Results show that the effects of rotary inertia and shear deformation are important only in the vicinity of the wave fronts. However, if the duration of the pressure pulse is short, maximum stresses can occur in the vicinity of the wave fronts where a Timoshenko-type shell theory is required for realistic response predictions.
Acoustic Diffraction by a Rigid Annular Spherical Cap
Authors: Jain D. L. , Kanwal R. P.
Published: November 2010

The problem of the diffraction of time-harmonic axially symmetric acoustic waves by a perfectly rigid annular spherical cap is solved approximately by an integral equation technique. Formulas are derived for the far-field amplitude as well as the scattering cross section when the incident wave is a plane wave traveling along the polar axis. By taking appropriate limits, the solutions for the corresponding problems for an annular circular disk and a whole spherical cap are also presented.
On the Buckling and Initial Postbuckling Behavior of Shallow Spherical and Conical Sandwich Shells
Authors: Akkas N.
Published: November 2010

The boundary-value problems associated with the axisymmetrical, asymmetrical, and initial postbuckling behavior of the clamped shallow conical sandwich shell under a uniform pressure are developed for face sheets of the same material and equal thicknesses. The numerical results presented show that the buckling and initial postbuckling behavior of the sandwich cap is similar to that of the conical homogeneous cap. The effects of the thickness and material parameters on the axisymmetric snap-through buckling behavior of the clamped shallow spherical and conical sandwich shells are also studied. For one material parameter considered the axisymmetric buckling behavior of the sandwich shells is similar to that of the corresponding homogeneous shells; so it is suggested that, without any further analysis, the asymmetric buckling and the initial postbuckling behavior of the sandwich cap can be obtained by conjecture. For the other material parameters considered, the axisymmetric buckling behavior of the sandwich caps is different from the axisymmetric buckling behavior of the corresponding homogeneous caps.
The Part-Through Surface Crack in an Elastic Plate
Authors: Rice J. R. , Levy N.
Published: November 2010

An elastic analysis is presented for the tensile stretching and bending of a plate containing a surface crack penetrating part-through the thickness, Fig. 1. The treatment is approximate, in that the two-dimensional generalized plane stress and Kirchhoff-Poisson plate bending theories are employed, with the part-through cracked section represented as a continuous line spring. The spring has both stretching and bending resistance, its compliance coefficients being chosen to match those of an edge cracked strip in plane strain. The mathematical formulation reduces finally to two-coupled integral equations for the thickness averaged force and moment per unit length along the cracked section. These are solved numerically for the case of a semi-elliptical part-through crack, with results compared to a simple but approximate closed-form solution. Extensive results are given for the stress intensity factor at the midpoint of the part-through crack for both remote tensile and bending loads on the plate. These results indicate that the stress-intensity factor is substantially lower, in general, than for a similarly loaded strip in plane strain with a crack of the same depth.
Parametric Stability of Thin-Walled Beams of Open Section
Authors: Ghobarah A. A. , Tso W. K.
Published: November 2010

A study is made on the parametric stability of open thin-walled beams under axial load. A set of nonlinear equations of stability and the appropriate boundary conditions are obtained using the energy approach. The derived equations are applicable to thin-walled open section of any shape. The effect of longitudinal deformation is taken into account in the derived theory. Using the nonlinear theory, the torsional parametric stability of a beam of a symmetrical 1 section is studied. The principal region of torsional instability is determined. The steady-state amplitude of torsional oscillation when the system is parametrically excited is found. Finally, the transient growth of the torsional motion from the onset of instability to the steady-state oscillation is computed. The effect of viscous damping on the steady-state and transient response is also included in the analysis.
Pressurization of a Solidifying Sphere
Authors: Hsiao K. H. , Cox J. E. , Hedgcoxe P. G. , Witte L. C.
Published: November 2010

The pressurization in a solidifying sphere of molten material (initially at a uniform melting temperature) immersed in an infinite cooling medium is presented. The steady-state approximate solution applied to the heat-conduction problem with change of phase (the Stefan problem) provides the temperature distribution in the shell and rate of solidification, which can be employed in the evaluation of the pressurization stress and thermal stress distributions in the solid shell. Stress distributions are evaluated and plotted in dimensionless form. Additional results are presented for the specific case of aluminum alloy.
An Experimental Study of Dispersion of Stress Waves in a Fiber-Reinforced Composite
Authors: Tauchert T. R. , Guzelsu A. N.
Published: November 2010

An ultrasonic pulse technique was used to investigate the dispersive behavior of plane harmonic waves in a boron-epoxy composite. The dependence of group velocity upon frequency is determined for longitudinal and transverse waves propagating either parallel or perpendicular to the fibers. The static elastic moduli for the composite are also obtained, and to a first approximation the material is found to be tetragonal.
Numerical Computation of Spherical Waves in Two Viscoelastic Media
Authors: Tsay L. J.
Published: November 2010

By applying the correspondence principle, the Laplace transform solutions of spherical waves in viscoelastic model are derived in this study. The numerical inversion of Laplace transform developed by Bellman is introduced to invert the transform solution of spherical waves into time domain. A modification of the numerical inversion is particularly shown to enable one to obtain the viscoelastic waves adequately. The accuracy of the numerical inversion is proven by comparing the results calculated from series solution and Papoulis’ method. The efficiency of the numerical inversion is demonstrated by studying the wave parameters in 6-element and 5-element models. By examining the behavior of wave responses in time domain, it is found that the 5-element model behaves as a viscous liquid and the 6-element model as a solid.
Elastic Analysis of Cylindrical Configurations With Stress Singularities
Authors: Zak A. R.
Published: November 2010

The problem of stress analysis of a circular cylinder is considered under conditions which give rise to stress singularities. Such stresses can be produced by circular boundary discontinuities or when boundaries are subject to mixed displacement and force conditions. General solutions are obtained using transformation of the cylindrical coordinates and these solutions converge in the singular region. The results predict exactly the singular behavior and the analysis generates solutions which can be used over a finite region of the cylinder. A numerical example is given showing the application of this analysis to a circular cylinder completely clamped at one end and loaded axially at the other. In this example the stresses and displacements from the present solution are matched with the corresponding quantities obtained from a finite-element analysis. The matching is performed at a finite distance from the stress singularity. Good agreement is obtained between the two solutions.