bluuebunny/crossref_metadata_2025 huggingface dataset:
Vibration Response of Linear Damped Complex Systems
Authors: Plunkett Robert
Published: October 2011

Hahnkamm has found the changes in the amplitudes of each of the two maxima of the unit vibration response of a two-degree-of-freedom linear system as the strength of the single linear dashpot is changed. This paper develops two approximate expressions for the change in all of the response maxima of a multidegree or continuous system as the dashpot constant of the single linear damper is changed. One of these approximations is derived from a perturbation solution around the minimax values, and the other is derived from an expansion in normal modes. These expressions are useful in determining the sensitivity of the maximum response value to small changes in the damping constant.
Analysis of U-Shaped Expansion Joints
Authors: Laupa A. , Weil N. A.
Published: October 2011

An elastic analysis of U-shaped expansion joints under axial loads and internal or external pressure is presented. The analysis employs the energy method for the toroidal sections, and the theory of symmetrical bending of circular plates augmented by thickwalled cylinder analysis for the annular plate connecting the two toroidal sections. The general solution permits the investigation of any U-shaped expansion joint falling in the range of thin shells, for any arbitrary combination of axial force and pressure loading. Different forming radii may be assigned to the inner and outer toroidal sections, and it is permissible to vary the average thicknesses of the two toroidal sections and the interconnecting annular plate independently. Expressions are given for the load-extension and load-stress characteristics of U-shaped expansion joints, and a numerical example is presented comparing the present solution with results of existing approximate analyses. The method presented here lends itself readily to programming on an electronic computer.
Application of Reissner’s Variational Principle to Cantilever Plate Deflection and Vibration Problems
Authors: Plass H. J. , Gaines J. H. , Newsom C. D.
Published: October 2011

A variational principle due to E. Reissner has been rewritten in a form which is applicable to small deflection problems for thin plates. The modified principle is used to obtain approximations to static deflection and vibration problems of square and skew cantilever plates of uniform thickness.
Slow Viscous Flow Between Rotating Concentric Infinite Cylinders With Axial Roughness
Authors: Citron S. J.
Published: October 2011

This paper presents the solution to the problem of determining the velocity field and the moment necessary to sustain the motion of a viscous incompressible fluid between two concentric infinite cylinders, rotating with constant but different angular velocities, when the radii of the cylinders vary axially. The solution is obtained for cases when the equations of slow motion govern the problem. The roughness of each cylinder is assumed small compared to the smooth radius; the roughness need not be small compared to the spacing between the cylinders. Results are explicitly obtained for the case of sinusoidal roughness.
A Single Axiom for Classical Thermodynamics
Authors: Hatsopoulos G. N. , Keenan J. H.
Published: October 2011

The definitions employed in classical thermodynamics are revised and a single axiom is stated from which all the relations of classical thermodynamics can be deduced. A detailed discussion of the meaning of the terms, system, possible variation, equilibrium, and thermodynamic system is followed by a statement of the axiom of stable equilibrium. The zeroth, first, and second laws and the state principle are then derived as theorems. Unambiguous definitions of heat, work, and temperature are deduced. The objective is to avoid the redundancies and implied hypotheses that may be found in previous treatments and to provide a rigorous and unambiguous base for exposition of all the classical aspects and the recent developments of thermodynamics.
Laminar Flow in a Uniformly Porous Tube
Authors: White F. M.
Published: October 2011

A solution is given in power series form to the problem of fully developed laminar flow in a uniformly porous tube. Although the general analysis is similar to a previous solution for a porous channel, the present tube results exhibit marked instabilities for wall suction, in contrast to the well-behaved channel results. A physical reason for the instabilities has been given in a recent paper by Weissberg, whose analysis of the inlet region indicates a breakdown in the assumption of fully developed flow.
On Vibrations of Pretwisted Rectangular Plates
Authors: Nordgren R. P.
Published: October 2011

This paper contains an analysis of the free vibrations of uniformly pretwisted rectangular plates, utilizing the exact equations of classical shallow-shell theory. Specifically, solutions are given (a) for two opposite edges simply supported and the other two free, and (b) for all four edges simply supported. Numerical results obtained for case (b) are compared with previous results for the torsional vibrations of pretwisted beams. A simple frequency equation is obtained for case (b), permitting a detailed study of the effects of both pretwist and longitudinal inertia.
Displacement and Strain-Energy Distribution in a Longitudinally Vibrating Cylindrical Rod With a Viscoelastic Coating
Authors: Hertelendy P.
Published: October 2011

A numerical solution by R. M. Davies of the Pochhammer frequency equation is used to determine the displacement and strain-energy distribution across the cross section of an infinite elastic circular cylindrical rod for a number of wave lengths of the first, second, and third modes of symmetrical longitudinal wave propagation. With these results the effect of a thin uniform layer of viscoelastic material is investigated. The four viscoelastic parameters of the coating are reduced to one in the definition and computation of upper and lower bounds of the loss factor, and the application of results to experimental work is discussed.
The Dispersion of Flexural Waves in an Elastic, Circular Cylinder—Part 2
Authors: Pao Yih-Hsing
Published: October 2011

In the first part of this paper, a method was developed for the construction of the branches of Pochhammer’s frequency equation for flexural waves in a circular cylinder. The method was applied to the portions of the branches with real propagation constants. The method is now extended and applied to those portions having imaginary propagation constants.
The Normal Modes of Nonlinear n-Degree-of-Freedom Systems
Authors: Rosenberg R. M.
Published: October 2011

A system of n masses, equal or not, interconnected by nonlinear “symmetric” springs, and having n degrees of freedom is examined. The concept of normal modes is rigorously defined and the problem of finding them is reduced to a geometrical maximum-minimum problem in an n-space of known metric. The solution of the geometrical problem reduces the coupled equations of motion to n uncoupled equations whose natural frequencies can always be found by a single quadrature. An infinite class of systems, of which the linear system is a member, has been isolated for which the frequency amplitude can be found in closed form.
Bending Deflection of a Circular Shaft Terminating in a Semi-Infinite Body
Authors: Brown J. M. , Hall A. S.
Published: October 2011

Consider a semi-infinite, elastic body with its boundary a plane except for a solid circular cylinder which has its longitudinal axis perpendicular to the boundary plane. This paper contains an approximate solution for the effective rotation of the semi-infinite body when a bending moment is applied to the cylinder. The applied stress is assumed to vary linearly with the distance from the bending axis. In addition, the rotation was determined experimentally and is compared with the analytical solution. The maximum difference between the rotation obtained analytically and experimentally is 18 per cent. Since some of the experimental values were greater and some were less than the analytical values and since the experimental techniques employed may have produced results which are in error by the amount of the variation between the specimens, the analytical equation should be regarded as correct within the accuracy of available test data.
A Generalized Minimum Principle and Its Application to the Vibration of a Wedge With Rotatory Inertia and Shear
Authors: Lee H. C.
Published: October 2011

The minimum principle and step-by-step iteration method are generalized for coupled simultaneous differential equations in order to obtain an approximate solution for the flexural vibration frequencies of a wedge with rotatory inertia and shear effects. This procedure avoids the difficulty of solving the nonself-adjoint equation which results when the simultaneous equations for bending slope and displacement are combined into a single differential equation. The upper and lower bounds of the first two eigenvalues are established and a comparison is made with the classical Kirchhoff solution where the rotatory inertia and shear are neglected.
Analysis of Plastic Shallow Conical Shells
Authors: Lance R. H. , Onat E. T.
Published: October 2011

The paper is concerned with simply supported shallow conical shells loaded through a central boss. The shell material is rigid-plastic and the relevant stress resultants are subject to a nonlinear yield condition. The critical load intensity at which the shell will begin to deform and the associated fields of stress resultants and plastic flow are to be determined. For this purpose, a problem concerned exclusively with stress resultants is formulated by using the equation of stress compatibility. The resulting nonlinear problem is solved, with the help of a digital computer, in cases where the yield-point state of stress is controlled, over the pertinent intervals covering the entire shell, by three distinct yield conditions, each corresponding to a given face of the appropriate four-dimensional nonlinear yield surface.
Flexure by a Concentrated Force of the Infinite Plate on a Circular Support
Authors: Dundurs J. , Lee Tung-Ming
Published: October 2011

Treated is the flexure of an infinite plate which is simply supported on a circle and subjected to a concentrated force at an arbitrary point. The portion of the plate inside the circular support is allowed to have elastic properties that are different from those of the outside part. The solution is exact within the framework of the classical theory of thin elastic plates and is in the form of a uniformly convergent series. Several previously known solutions appear as limiting cases of the results given here.
Thermal Radiation Absorption in Rectangular-Groove Cavities
Authors: Sparrow E. M. , Jonsson V. K.
Published: October 2011

The amount of energy absorbed when a stream of external radiation enters a rectangular-groove cavity has been calculated for a variety of surface conditions, cavity depths, and incident energy distributions. The surfaces of the cavity are either diffuse reflectors or specular reflectors, and a wide range of reflectivity values has been considered. The incoming radiation is either diffusely distributed across the cavity opening or else arrives in a bundle of parallel rays. The results show that for diffuse incoming radiation, a specular cavity absorbs more effectively than does a diffuse cavity. For incoming radiation in a parallel ray bundle, the comparison depends on the angle of inclination of the rays.
Longitudinal Impact of a Semi-Infinite Elastic Cylindrical Shell
Authors: Berkowitz H. M.
Published: October 2011

The axially symmetric pressure signal produced by the longitudinal impact of a semi-infinite elastic cylindrical shell upon a rigid obstacle is determined by using membrane theory. Using this simplified theory, it is possible to obtain not only the leading term of an asymptotic expansion for large values of time, but also additional terms.
Crushing of a Tube Between Rigid Plates
Authors: DeRuntz John A. , Hodge P. G.
Published: October 2011

The load-deformation curve is obtained for a thin tube crushed between two parallel, rigid plates. It is found that the influence of geometry changes after initial yield results in increased load-carrying capacity. In addition, the effects on the yield condition due to direct stress and shear are quantitatively discussed.
Strength of Stress Singularities at Crack Tips for Flexural and Torsional Problems
Authors: Sih G. C.
Published: October 2011

Continuing a series of studies on the fracture analysis of elastic bodies, the present paper provides a complex variable method for evaluating the strength of stress singularities at crack tips encountered in the flexure and torsion of cylindrical bars. As a result of the complex flexure functions being sectionally holomorphic for crack problems, the singular character of the shearing stresses is found to be of the type r−1/2, where r is radial distance from the crack point. Crack-tip stress-intensity-factor solutions are given for problems involving both imbedded and surface cracks in bars. The results suggest the possibility of extending the Griffith-Irwin theory of static fracture to flexural and torsional problems.
On the Choice of Coordinates Used to Describe Thermoelectric and Thermomagnetic Generators
Authors: Osterle J. F. , Angrist S. W.
Published: October 2011

It is demonstrated that the form of the energy-dissipation equation which describes thermoelectric and thermomagnetic generators is greatly dependent on the choice of dependent variables in the coupled equations used to describe the devices. If “natural” coordinates are chosen, the energy dissipation will always contain two terms—the Fourier conduction term and Joulean heating term. If “unnatural” coordinates are chosen, the energy-dissipation equation will contain three terms. A brief solid-state consideration demonstrates how a bound on the figure-of-merit temperature product can arise in terms of fundamental physical parameters.
Steady-State Flow of a Gelling Material Between Rotating Concentric Cylinders
Authors: Slibar Alfred , Paslay P. R.
Published: October 2011

In a previous paper the authors proposed constitutive equations for the analytical description of gelling incompressible materials. This set of equations is used to predict the steady-state Couette-type flow between concentric cylinders under relative rotation. The solution for the thixotropic material is given in terms of five material parameters accounting for the phenomena of “breakdown” and “recovery” in rigidity. Analysis shows that dependence of the solution on the loading history occurs if a certain inequality is satisfied by the five material parameters.
The Generation of Secondary Vorticity in an Incompressible Fluid
Authors: Marris A. W.
Published: October 2011

A general equation for the development of secondary vorticity in a homogeneous incompressible fluid is developed by extending the analysis of Hawthorne [1]. It is shown that secondary vorticity can be generated not only through the action of a nonuniform flow field on curved streamlines, but also whenever the flow kinetics are such that the vector curl (V × Ω) has a component in the flow-wise direction. Applied to the problem of the skewed boundary layer along a plane wall the general result partially explains the experimentally observed attenuation of skewing in the viscous sublayer region. The equation is applied to the problem of secondary flow generation in sharply curved passages of appreciable depth where the deep curved channel flow configuration dominates the secondary flow. Finally, one discusses the implication of secondary vorticity development from the vector curl (V × Ω) to the problem of laminar boundary-layer instability resulting in the occurrence of a system of longitudinal vortices.
Thermoelastic Dissipation in Vibrating Plates
Authors: Tasi J.
Published: October 2011

The thermal dissipation associated with the natural modes of free vibration of a thermoelastic medium is obtained as an integral formula involving the mode of vibration and the temperature produced in the mode. The integral formula for dissipation is applied to an infinite isotropic plate, and numerical results are given for the three lowest, real, symmetric branches of the spectrum. Finally, it is shown that low-frequency extensional vibrations of plates can be adiabatic or isothermal, depending on whether adiabatic or isothermal boundary conditions are specified on the faces of the plate.
Concentrated Force in an Elastically Embedded Disk
Authors: Dundurs J.
Published: October 2011

This paper deals with the concentrated force in a disk which is embedded in an unbounded elastic plane with different properties. The disk with its edge free of tractions and subjected to concentrated forces and moments is also discussed.
Diffraction of Steady Elastic Waves by Surfaces of Arbitrary Shape
Authors: Banaugh Robert P. , Goldsmith Werner
Published: October 2011

The diffraction of steady-state elastic waves from arbitrarily shaped inclusions in an infinite medium is described by means of simultaneous singular integral equations expressed in terms of a set of displacement potentials. In contrast to some other formulations, this procedure permits the incorporation of the boundary conditions without approximation and the possibility of discontinuities in the surface of the diffracting object, such as cusps and corners, in the solution of the problem. The solution of the integral equations yields the potential functions at the interface which, in turn, are employed to derive the field potentials by surface integration. The formulation is presented for the two-dimensional case for an inclusion fixed in space which may be a void, a rigid body, or another elastic medium. The equations are solved by means of finite-difference approximations to the contour integrals. The resulting scattered field was found to be in excellent agreement with that obtained from a series solution of the diffraction of a plane compression wave from a rigid circular cylinder. Solutions of other two-dimensional configurations of interest involving rigid bodies are also presented. The corresponding acoustic cases, which have previously been examined, can be analyzed in an identical manner and numerical values established with a substantially lower level of computational effort.
Dynamic Stresses and Displacements Around Cylindrical Discontinuities Due to Plane Harmonic Shear Waves
Authors: Mow C. C. , Mente L. J.
Published: October 2011

The problem of dynamic stresses and displacements around a cavity and rigid inclusion of arbitrary density is examined for an elastic medium during the passage of a plane shear wave. In the cavity case, the dynamic stresses and displacements are found to be dependent upon the incident wave number and Poisson’s ratio of the medium. In the rigid-inclusion case it is found that dynamic stresses and the rigid-body rotation and translation are dependent upon the incident wave numbers, the Poisson’s ratio, and the density ratio of the medium and the insert. Close coupling is observed between the stresses and the rigid-body motion of the insert.
Heat Conduction in Deformed Initially Isotropic Materials
Authors: Sih G. C. , Smith G. F.
Published: October 2011

A generalization of the Fourier heat-conduction law appropriate for heat flow in a deformed incompressible initially isotropic material is considered and applied to the determination of the temperature distribution in a uniformly extended plate and in thick-walled circular cylinders subjected to torsion and shear.
On the Response of Linear Systems to Time-Dependent, Multidimensional Loadings
Authors: Beer F. P.
Published: October 2011

The concept of frequency response, which has long been used by communication engineers to predict the response of a linear system to a periodic, nonperiodic, or random input, is extended to the general case of a linear mechanical system subjected to a time-dependent, multidimensional loading. Various possible methods for determining the transfer function of a given system are examined. One method is given special attention; it is based on the cross correlation in space and time of the response of the given system to a multidimensional random load field with the response of another system to the same field.
A New Approach to the Analysis of the Deflection of Thin Cantilevers
Authors: Frisch-Fay R.
Published: October 2011

The paper proposes a new method for the calculation of large deflections. Slender bars under point loads are traced back to the strut problem, thus bypassing the solution of nonlinear differential equations.
A Note on a New Stability Method for the Linear Modes of Nonlinear Two-Degree-of-Freedom Systems
Authors: Porter Jack , Atkinson C. P.
Published: October 2011

This paper presents a method for analyzing the stability of the linearly related modes of nonlinear two-degree-of-freedom oscillatory systems. For systems described by the coupled equations x¨1 = f(x1, x2) and x¨2 = g(x1, x2) there exist solutions related by the linear modal restraint x1 = cx2 where c is a constant. Such oscillations are not always stable. The method of this paper allows the prediction of the stability of the modes in terms of the amplitudes of the oscillations and the parameters of the equations of motion. Analog-computer results are presented which confirm the theoretical predictions.
Similitude in Package Cushioning
Authors: Soper W. G. , Dove R. C.
Published: October 2011

Buckingham’s theorem is applied to impulsively loaded cushion systems and the dimensionless response is found to be a function of two variables. These results point out a method for presenting experimental response data which is valid for any cushioning material, regardless of the complexity of its dynamic behavior.
Shear Deformation in Beams on Elastic Foundations
Authors: Essenburg F.
Published: October 2011

The importance of the effect of transverse shear deformation in the flexure of an elastic beam of symmetric cross section, constrained by a Winkler-type elastic foundation, is found to depend upon both the elastic properties of the beam and the foundation and the geometry of the beam cross section. Under certain conditions the form of the solution is substantially altered and the periodic character predicted by the classical treatment is not present. The practical significance of these modifications is illustrated by means of the specific examples of an infinite beam under concentrated load and an infinite beam under concentrated couple.
The Axially Loaded Circular Cylinder
Authors: Conway H. D.
Published: October 2011

Commencing with Kelvin’s closed-form solution to the problem of a concentrated force acting at a given point in an indefinitely extended solid, a Fourier transform method is used to obtain an exact solution for the case when the force acts along the axis of a circular cylinder. Numerical values are obtained for the maximum direct stress on cross sections at various distances from the force. These are then compared with the corresponding stresses from the solution for an infinitely long strip, and in both cases it is observed that the stresses are practically uniform on cross sections greater than a diameter or width from the point of application of the load.
On the Buckling of Truncated Conical Shells in Torsion
Authors: Seide Paul
Published: October 2011

The problem of the buckling of thin circular conical frustums in pure torsion is solved in a manner similar to that employed previously by the author for buckling under uniform hydrostatic pressure. Synthesis of the numerical results indicates that the critical torsion of a truncated cone is equal to that of an equivalent cylinder whose length and thickness are the axial length and wall thickness of the cone and whose radius is a function of the semivertex angle and the taper ratio of the cone. Curves and equations to aid in the analysis of conical frustums are given. It is shown that a previous recommendation for the analysis of truncated cones in torsion may be seriously unconservative in some cases.
Bending of Plates on an Elastic Foundation
Authors: Pister K. S. , Westmann R. A.
Published: October 2011

This paper discusses a two-dimensional elastostatic plate theory in which effects of both transverse shearing strain and normal strain are retained. The governing system of equations is deduced as a limiting case of results obtained for thin shells by Naghdi. As an example of a class of problems for which such effects are significant, axisymmetric bending of an infinite plate resting on an elastic half space is discussed. Illustrative numerical results are included.
The Influence of Molecular Vibration on Brayton-Cycle Performance
Authors: Jacobs T. A. , Lloyd J. R.
Published: October 2011

By means of the harmonic-oscillator approximation, the influence of molecular vibration on Brayton-cycle performance is demonstrated.
Dynamic Stresses Created by a Moving Crack
Authors: Baker B. R.
Published: October 2011

A solution is obtained for the case in which a sem-infinite crack suddenly appears and grows at constant velocity in a stretched elastic body. The problem, one of mixed boundary values on a half plane, is solved by transform methods including the Weiner-Hopf and Cagniard techniques. Among the graphical results presented is the time variation of the transverse stress at a fixed point on the line of fracture as the tip of the crack approaches. Asymptotic forms for the stresses near the crack tip are also obtained and are compared with results of other studies in crack propagation.
Flexure of a Circular Plate With a Ring of Holes
Authors: Kraus H.
Published: October 2011

The problem of the moment distribution resulting from a uniform pressure load acting over the surface of a circular plate containing a ring of equally spaced circular holes with, and without, a central circular hole is solved within the framework of the Poisson-Kirchhoff theory of plates. A general boundary condition is applied at the outer rim of the plate to make the solution valid for a range of conditions from the simply supported case to the clamped case. The edges of the perforations are allowed to be either free or to have a net shear force acting. Numerical results in the form of curves are given for typical cases, and the results of a photoelastic test are also presented.
The Stress Field Produced by Localized Plastic Slip at a Free Surface
Authors: Lin T. H. , Tung T. K.
Published: October 2011

Uniform plastic slip is assumed to occur in a cubic region embedded at the free surface of a semi-infinite elastic solid. The slip plane and slip direction are both inclined at 45 deg to the free surface and to two opposite interior faces of the cube. The stress field produced by the slip is the same as that produced by equivalent uniform tractions acting on the faces of the cube. Closed-form solutions are obtained for all stress components by employing Papkovitch functions to calculate the effects of the equivalent surface tractions. Calculated numerical results for the distribution of stress components are shown graphically. Certain stress components are found to be discontinuous across the boundary surface of the region of plastic slip.
Hot-Wire Measurements of Turbulence Correlations in a Triangular Duct
Authors: Cremers C. J. , Eckert E. R. G.
Published: October 2011

Previous studies by flow visualization have indicated that the flow through a duct of triangular cross section is in its characteristics quite different from flow through a duct with circular cross section. They revealed among others that purely laminar flow exists in the corners of the duct even though the bulk of the fluid moves in turbulent motion. Heat-transfer measurements in such a duct appear to indicate that the turbulent transport in the direction of the height of the duct is considerably smaller than expected from circular tube measurements. The present paper reports the measurements of turbulent correlations for turbulent flow through such a duct. These measurements have been made with hot wires of very small dimensions. They again reveal the existence of a laminar corner region. In the bulk of the fluid, the differences of the correlations to those in a round tube turned out to be smaller than originally suspected.
Minimum-Weight Proportions of Pressure-Vessel Heads
Authors: Hoffman G. A.
Published: October 2011

This paper derives the minimum-weight shapes of head closures for cylindrical pressure vessels. Head configurations, weights, and membrane stresses are obtained for thin-shell heads of isotropic materials with uniform internal pressure by restricting the knuckle shear stresses to constant values where possible and by minimizing the weight of prescribed-shape heads. Torispherical, ellipsoidal, and Biezeno-type heads with constant and varying thickness (neglecting the effects of bending) are investigated. Enclosed-volume constancy and supporting structures are also considered. Certain highly efficient shapes are obtained that weigh up to 11 per cent less than the corresponding hemispherical capping closure.
Triangular Plates Analyzed by Point Matching
Authors: Conway H. D.
Published: October 2011

This brief note analyzes uniformly loaded triangular plates with either clamped or simply supported edges using a special adaptation of the point-matching technique, the functions satisfying the differential equation, also being chosen to satisfy exactly the boundary conditions on one edge. Numerical results are tabulated for three geometries.
On the Probability Densities of the Output of Some Random Systems
Authors: Kozin Frank
Published: October 2011

The probability density, mean, and variance of the displacement of simple linear one-degree-of-freedom systems are investigated when the spring constants and the initial conditions are random variables. The ensemble mean motion is found to be considerably different from the “mean” motion obtained by first averaging over the spring constants. Furthermore, it is found that only the first and second moments of the initial conditions affect the first and second moments of the displacement.
On Transient Thermal Stresses in Viscoelastic Materials With Temperature-Dependent Properties
Authors: Muki Rokuro , Sternberg Eli
Published: October 2011

This paper deals with the quasi-static analysis of transient thermal stresses in the linear theory of viscoelastic solids with temperature-dependent properties. The underlying constitutive law rests on the temperature-time equivalence hypothesis. Following an exposition of the theoretical framework exact solutions to two specific problems are deduced: The first concerns the thermal stresses in a slab of infinite extent, generated by a temperature field that depends arbitrarily on the thickness co-ordinate and time; the second application concerns the stresses produced in a sphere by an arbitrary time-dependent radially symmetric temperature distribution. The numerical illustrations of the results obtained include a quantitative study based on actual test data for a polymethyl methacrylate.
On Classical Plate Theory and Wave Propagation
Authors: Medick M. A.
Published: October 2011

The purpose of this investigation is to assess the applicability of classical plate theory in describing the response of a flat plate of large radius to a sharp, transient loading applied over a small surface area by evaluating its predictions and comparing them with some preliminary experiments.
On Normal Vibrations of a General Class of Nonlinear Dual-Mode Systems
Authors: Rosenberg R. M.
Published: October 2011

Free vibrations in normal modes are examined for a system consisting of two unequal (or equal) masses, interconnected by a nonlinear coupling spring, and each mass connected by nonlinear unequal (or equal) anchor springs to fixed points. All spring forces are odd functions, and proportional to the k’th power, of the spring deflections, where k is a real, positive number. The frequency-amplitude relations for the in and out-of-phase modes are derived without approximation, the stability of these modes is analyzed, and several numerical examples are worked out. A surprising feature of these systems is that they may have a greater number of normal modes than they have degrees of freedom.
The Bending, Buckling, and Flexural Vibration of Simply Supported Polygonal Plates by Point-Matching
Authors: Conway H. D.
Published: October 2011

The bending by uniform lateral loading, buckling by two-dimensional hydrostatic pressure, and the flexural vibrations of simply supported polygonal plates are investigated. The method of meeting the boundary conditions at discrete points, together with the Marcus membrane analog [1], is found to be very advantageous. Numerical examples include the calculation of the deflections and moments, and buckling loads of triangular square, and hexagonal plates. A special technique is then given, whereby the boundary conditions are exactly satisfied along one edge, and an example of the buckling of an isosceles, right-angled triangle plate is analyzed. Finally, the frequency equation for the flexural vibrations of simply supported polygonal plates is shown to be the same as that for buckling under hydrostatic pressure, and numerical results can be written by analogy. All numerical results agree well with the exact solutions, where the latter are known.
Mixing of Compressible Fluids
Authors: Kennedy E. D.
Published: October 2011

The problem of the mixing of two streams of the same compressible fluid in a constant-area duct is solved by applying certain dimensionless parameters first used by Kiselev. The extension to dissimilar fluids or to more than two streams is straightforward. Although the analysis is unrestricted, detailed results are given only for the case where one stream is sonic or supersonic and the other sonic or subsonic at the origin of mixing. For this case, the second law of thermodynamics indicates that, of the two solutions of the conservation equations, the subsonic one is always permitted while some of the supersonic solutions are thermodynamically impossible. Upon examination of experimental data, it is further concluded that of the admissible supersonic solutions, only one may be expected to occur. The establishment of this supersonic solution with its relatively high stagnation pressure leads to the conclusion that when the initial temperatures are sufficiently different, there exist thermodynamically possible solutions with a stagnation pressure higher than that of either of the two initial streams.
The Laminar Boundary Layer on a Hot Cylinder Fixed in a Fluctuating Stream
Authors: Gribben R. J.
Published: October 2011

The equations for nonsteady, two-dimensional low-speed compressible flow in the laminar boundary layer are solved approximately by use of the Pohlhausen technique with the assumption of quartic profiles for the velocity and temperature. The external flow considered is of the form of a steady basic velocity with a superimposed small amplitude oscillation such as may arise, for example, when a sound wave is present in a uniform incident stream. The analysis is then applicable to the case of a hot cylinder fixed in such a stream. Terms of the order of the incident stream Mach number are neglected in the expressions for external flow quantities (whereas the low-speed boundary-layer equations involve errors of the order of only the square of this Mach number). Two special cases are worked out—the flow over a flat plate for which there is fair agreement with available exact calculations, and the flow over a circular cylinder.
Combined Stresses in an Orthotropic Plate Having a Finite Crack
Authors: Ang D. D. , Williams M. L.
Published: October 2011

Using a formulation in integral equations, a solution for the combined extension-classical bending stress and displacement solution is presented for the case of an infinite orthotropic flat plate containing a finite crack. While the solution can be expressed in closed form for the entire field, primary emphasis is placed upon the stresses near the crack point. Qualitatively, no major difference in behavior due to orthotropy was found although certain quantitative features are noted, mainly as a function of the characteristic rigidity ratio (Ex/Ey)1/2. The inverse square-root character of the isotropic stress bending and extension is not changed by orthotropy, although amplitudes and distribution are affected. Account is taken of recent important work by Knowles and Wang dealing with Reissner bending of the plate which shows that the extensional and surface bending stresses are identical in singular character and circumferential distribution. A bending-extension interaction curve for fracture initiation is derived and shown to be linear when based upon the more exact bending theory.
Bending of a Cantilever Plate Supported From an Elastic Half Space
Authors: Small N. C.
Published: October 2011

A solution is obtained for an infinitely long cantilever plate supported from an elastic half space. The junction conditions between the elasticity approach for the half space and the classical plate theory (no-shear) approach for the plate are based upon the use of assumed equilibrium surface tractions for the half space. The formal Fourier integral results for the example of a concentrated free-edge load are evaluated using an IBM 704 computer. The correlation with the deflection results of a steel model test is shown to be very good. The small deviations from the theoretical values are primarily due to shear effects in the model. It is also shown that, except for very stubby plates, it is sufficiently accurate to neglect the shear effects along the half space, and to assume that the rotation is proportional to the moment in the conventional “Winkler” sense.
Dynamic Membrane Stresses in a Circular Elastic Shell
Authors: Payton R. G.
Published: October 2011

The dynamic membrane stress for a thin, infinitely long, circular, elastic shell is obtained for a point impulse, a distributed impulse, and a moving pressure load. These solutions, based on a method due principally to Friedlander, give new solutions to the problems mentioned.
Bending of a Thin Cylindrical Shell Subjected to a Line Load Around a Circumference
Authors: Meck H. R.
Published: October 2011

An analysis is developed for bending of a thin circular cylindrical shell under a varying radial line load distributed around the circumference at the center section. The problem is solved by reducing the eighth-order differential equation of thin-shell theory to two approximate fourth-order equations. Deflections, bending stresses, and membrane stresses are evaluated. Both simply supported and clamped ends are considered.
On the Occurrence of Nodal Patterns of Nonparallel Form in Rectangular Orthotropic Plates
Authors: Huffington N. J.
Published: October 2011

This note provides a demonstration that an anomalous type of flexural vibration mode, previously discussed only for square isotropic plates, may be expected to occur for rectangular orthotropic plates having a certain ratio of length to width.
The Hump Deformation Preceding a Moving Load on a Layer of Soft Material
Authors: Abrahamson G. R. , Goodier J. N.
Published: October 2011

When a load, for instance a heavy roller, moves slowly along the surface of a solid mass of soft material, a “hump” deformation is often observed to precede it. The process of formation from an initially level surface, and the final form of hump established, are investigated analytically for a purely viscous material, in two-dimensional motion. It becomes evident that a material showing nonlinear creep, or a viscoelastic material, would show qualitatively similar behavior, the simple viscous model being adequate to exhibit the essential qualitative features.
Automated temporal tracking and segmentation of lymphoma on serial CT examinations
Authors: Xu Jiajing , Greenspan Hayit , Napel Sandy , Rubin Daniel L.
Published: October 2011

Purpose:

It is challenging to reproducibly measure and compare cancer lesions on numerous follow‐up studies; the process is time‐consuming and error‐prone. In this paper, we show a method to automatically and reproducibly identify and segment abnormal lymph nodes in serial computed tomography (CT) exams.

Methods:

Our method leverages initial identification of enlarged (abnormal) lymph nodes in the baseline scan. We then identify an approximate region for the node in the follow‐up scans using nonrigid image registration. The baseline scan is also used to locate regions of normal, non‐nodal tissue surrounding the lymph node and to map them onto the follow‐up scans, in order to reduce the search space to locate the lymph node on the follow‐up scans. Adaptive region‐growing and clustering algorithms are then used to obtain the final contours for segmentation. We applied our method to 24 distinct enlarged lymph nodes at multiple time points from 14 patients. The scan at the earlier time point was used as the baseline scan to be used in evaluating the follow‐up scan, resulting in 70 total test cases (e.g., a series of scans obtained at 4 time points results in 3 test cases). For each of the 70 cases, a “reference standard” was obtained by manual segmentation by a radiologist. Assessment according to response evaluation criteria in solid tumors (RECIST) using our method agreed with RECIST assessments made using the reference standard segmentations in all test cases, and by calculating node overlap ratio and Hausdorff distance between the computer and radiologist‐generated contours.

Results:

Compared to the reference standard, our method made the correct RECIST assessment for all 70 cases. The average overlap ratio was 80.7 ± 9.7% s.d., and the average Hausdorff distance was 3.2 ± 1.8 mm s.d. The concordance correlation between automated and manual segmentations was 0.978 (95% confidence interval 0.962, 0.984). The 100% agreement in our sample between our method and the standard with regard to RECIST classification suggests that the true disagreement rate is no more than 6%.

Conclusions:

Our automated lymph node segmentation method achieves excellent overall segmentation performance and provides equivalent RECIST assessment. It potentially will be useful to streamline and improve cancer lesion measurement and tracking and to improve assessment of cancer treatment response.
Load-Induced Modulation of Signal Transduction Networks
Authors: Jiang Peng , Ventura Alejandra C. , Sontag Eduardo D. , Merajver Sofia D. , Ninfa Alexander J. , Del Vecchio Domitilla
Published: October 2011

The presence of downstream partners that interact with enzymatically modified or unmodified signaling proteins changes the dynamics of signal transduction.
Science Signaling
Podcast: 11 October 2011
Authors: De Robertis Edward M. , VanHook Annalisa M.
Published: October 2011

Phosphorylation of the transcription factor Mad determines whether it mediates Wingless or BMP signaling.
Fear No More
Authors: Gough Nancy R.
Published: October 2011

Insulin-like growth factor 2 contributes to fear extinction.
Calming the Gut
Authors: Foley John F.
Published: October 2011

Interleukin-37 protects against inflammatory bowel disease in mice by inhibiting the production of proinflammatory cytokines.
Evaluation of Pharmacokinetic/Pharmacodynamic Relationships of PD-0162819, a Biotin Carboxylase Inhibitor Representing a New Class of Antibacterial Compounds, Using
In Vitro
Infection Models
Authors: Ogden Adam , Kuhn Michael , Dority Michael , Buist Susan , Mehrens Shawn , Zhu Tong , Xiao Deqing , Miller J. Richard , Hanna Debra
Published: October 2011

The present study investigated the pharmacokinetic/pharmacodynamic (PK/PD) relationships of a prototype biotin carboxylase (BC) inhibitor, PD-0162819, against
Haemophilus influenzae
3113 in static concentration time-kill (SCTK) and one-compartment chemostat
in vitro
infection models.
H. influenzae
3113 was exposed to PD-0162819 concentrations of 0.5 to 16× the MIC (MIC = 0.125 μg/ml) and area-under-the-curve (AUC)/MIC ratios of 1 to 1,100 in SCTK and chemostat experiments, respectively. Serial samples were collected over 24 h. For efficacy driver analysis, a sigmoid maximum-effect (
E
max
) model was fitted to the relationship between bacterial density changes over 24 h and corresponding PK/PD indices. A semimechanistic PK/PD model describing the time course of bacterial growth and death was developed. The AUC/MIC ratio best explained efficacy (
r
2
= 0.95) compared to the peak drug concentration (
C
max
)/MIC ratio (
r
2
= 0.76) and time above the MIC (
T
>MIC) (
r
2
= 0.88). Static effects and 99.9% killing were achieved at AUC/MIC values of 500 and 600, respectively. For time course analysis, the net bacterial growth rate constant, maximum bacterial density, and maximum kill rate constant were similar in SCTK and chemostat studies, but PD-0162819 was more potent in SCTK than in the chemostat (50% effective concentration [EC
50
] = 0.046 versus 0.34 μg/ml). In conclusion, basic PK/PD relationships for PD-0162819 were established using
in vitro
dynamic systems. Although the bacterial growth parameters and maximum drug effects were similar in SCTK and the chemostat system, PD-0162819 appeared to be more potent in SCTK, illustrating the importance of understanding the differences in preclinical models. Additional studies are needed to determine the
in vivo
relevance of these results.
In Vitro
Analyses of the Effects of Heparin and Parabens on Candida albicans Biofilms and Planktonic Cells
Authors: Miceli Marisa H. , Bernardo Stella M. , Ku T. S. Neil , Walraven Carla , Lee Samuel A.
Published: October 2011

Infections and thromboses are the most common complications associated with central venous catheters. Suggested strategies for prevention and management of these complications include the use of heparin-coated catheters, heparin locks, and antimicrobial lock therapy. However, the effects of heparin on
Candida albicans
biofilms and planktonic cells have not been previously studied. Therefore, we sought to determine the
in vitro
effect of a heparin sodium preparation (HP) on biofilms and planktonic cells of
C. albicans
. Because HP contains two preservatives, methyl paraben (MP) and propyl paraben (PP), these compounds and heparin sodium without preservatives (Pure-H) were also tested individually. The metabolic activity of the mature biofilm after treatment was assessed using XTT [2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide] reduction and microscopy. Pure-H, MP, and PP caused up to 75, 85, and 60% reductions of metabolic activity of the mature preformed
C. albicans
biofilms, respectively. Maximal efficacy against the mature biofilm was observed with HP (up to 90%) compared to the individual compounds (
P
< 0.0001). Pure-H, MP, and PP each inhibited
C. albicans
biofilm formation up to 90%. A complete inhibition of biofilm formation was observed with HP at 5,000 U/ml and higher. When tested against planktonic cells, each compound inhibited growth in a dose-dependent manner. These data indicated that HP, MP, PP, and Pure-H have
in vitro
antifungal activity against
C. albicans
mature biofilms, formation of biofilms, and planktonic cells. Investigation of high-dose heparin-based strategies (e.g., heparin locks) in combination with traditional antifungal agents for the treatment and/or prevention of
C. albicans
biofilms is warranted.