bluuebunny/crossref_metadata_2025 huggingface dataset:
The Stability of an Elastic Rotor in Journal Bearings With Flexible, Damped Supports
Authors: Lund Jorgen W.
Published: October 2011

A theoretical analysis is presented investigating the stability (fractional frequency whirl, “oil whip”) of a symmetrical, flexible rotor supported in journal bearings. The bearings are mounted in flexible, damped supports. The analysis determines the rotor speed at which instability sets in as affected by rotor stiffness, the dynamic properties of the bearing film, and the flexibility and damping of the bearing supports. The analysis is based on the fact that the bearing can be represented by frequency-dependent spring and damping coefficients, and the method by which the coefficients are obtained is described with emphasis on the gas-lubricated bearing. The conclusions are: (a) Rotor and support flexibility by themselves lower the speed at onset of instability; (b) when the bearing support possesses damping in addition to flexibility, the speed at onset of instability can be raised significantly above the threshold speed of a rotor in rigidly mounted bearings. Numerical results are presented in the form of graphs for the plain cylindrical gas bearing.
Fluid-Particle Motion During Rotary Sloshing
Authors: Hutton R. E.
Published: October 2011

This paper presents the results of a theoretical and experimental investigation of fluid-particle motion in a partially filled cylindrical tank. The body of fluid is assumed to have a steady-state motion consisting of first nonsymmetric sloshing mode only (lowest J1 mode), which gives rise to a free-surface wave that rotates around the tank at the sloshing natural frequency. It was found that theory predicts a net transport motion of the fluid particles in the direction of the free-surface waves when nonlinear terms are retained in differential equations that describe the fluid-particle displacements. Experimental measurements of the particle motion are compared with theoretical predictions. Fluid angular momentum was computed using the theoretical fluid motion and compared with the angular momentum that the fluid would possess if the fluid moved as a rigid body at the same rate as the free-surface waves. It was found that an upper bound to the ratio of the transport angular momentum to the rigid-body angular momentum was equal to 0.8 (η/a)2, where η is the peak wave height of the free surface waves and a is the tank radius.
Laminar Free-Convection Wake Above a Heated Vertical Plate
Authors: Yang Kwang-Tzu
Published: October 2011

The development of momentum and energy fields in the laminar-wake region above a heated finite vertical plate is studied analytically. Detailed velocity and temperature profiles in the immediate neighborhood of the trailing edge of the plate are calculated for two Prandtl numbers by means of asymptotic series expansions. These results are then continued to the rest of the wake region by an integral solution. It is found that the spreading of the boundary layers is rather gradual.
On the Disintegration of Bodies of (Granular) Materials Governed by the Coulomb Rule
Authors: Bleich H. H.
Published: October 2011

For the purposes of analysis, granular materials are frequently idealized by stating that slip will occur when the stresses satisfy a relation depending on the angle of internal friction and cohesion. States of stress violating this rule are not permitted. From a simple mechanical model it is concluded that in dynamic problems the possibility of disintegration of the body must be considered, and that disintegration, if it occurs, is a boundary-layer phenomenon.
Buckling of a Very Thin Cylindrical Shell Due to an Impulsive Pressure
Authors: Lindberg H. E.
Published: October 2011

This paper shows that when very thin cylindrical shells are subjected to an external impulsive pressure, the interaction between the radial, purely extensional mode and the flexural modes is sufficient to precipitate permanent wrinkles. The theory predicts that these wrinkles occur at a wavelength which depends on the magnitude of the pressure pulse as well as on the cylinder parameters; experiments on cylindrical shells and thin strips confirm this prediction. Framing camera photographs showing the formation of wrinkles of this type are also presented.
The Dynamic Response of a Solid, Viscoelastic Sphere to Translational and Rotational Excitation
Authors: Christensen R. M. , Gottenberg W. G.
Published: October 2011

A solution is presented for the dynamic response of a solid sphere of linear viscoelastic material bonded to a mating, rigid spherical cavity which undergoes harmonic excitation. The dynamic response in the form of complex mechanical impedance is obtained in exact analytic form for two types of excitation of the rigid spherical boundary; rotation about a diameter and translation along a diameter. For the purpose of showing the usefulness of this system for experimentally determining the general stress-strain characteristics of the linear viscoelastic material, the sensitivity of the complex mechanical impedance of the sphere in each mode of excitation is examined relative to variations in the complex dynamic shear modulus and complex dynamic Poisson’s ratio of the material.
Shaft Whirl Induced by Rotor Internal Damping
Authors: Ehrich F. F.
Published: October 2011

An analysis is made of the instability in rotating systems induced by internal damping in the rotor. The stability boundary is defined in terms of the ratio of the external damping of the system to the internal damping in the shaft. It is shown that the induced-whirl mode is not necessarily the fundamental mode. For various damping conditions, a particular whirl mode is induced. It is shown that, in general, the whirl mode induced at the instability boundary occurs in the mode whose whirling speed is approximately one half the rotational speed.
An Equation for the Critical Mass Velocity of Homogeneous Vapor-Liquid Mixtures at Low Pressures
Authors: Goldmann K. , Hankel R. , Stein R. P.
Published: October 2011

Equations have been developed expressing the critical mass velocity, (Gc)s, and the isentropic expansion coefficient, k, of a single-component, homogeneous vapor-liquid mixture at low pressures in terms of tabulated thermodynamic properties. With these parameters, two-phase flow relations can be developed which are analogous to the relations governing the flow of single-phase compressible fluids, most readily formulated in terms of Mach numbers. The computed values of k for saturated steam agree favorably with those reported in the literature of steam-turbine design.
An Analysis of Axially Symmetric Coupled Tube Sheets
Authors: Cook R. D.
Published: October 2011

The purpose of this paper is to present an analysis and a discussion of the design of axially symmetric coupled tube sheets of constant thickness, subject to mechanical and thermal loads. The basic strain-energy expressions and differential equations of the problem are derived. Methods of analysis and design, including a solution of the differential equations and the resulting expressions for bending moments, stress, and so on, are developed. The behavior of the system and its similarity to a sandwich plate are discussed.
Elastic and Viscoelastic Foundation Models
Authors: Kerr Arnold D.
Published: October 2011

The present paper contains a critical study of a number of foundation models as well as a further development of some of the ideas involved. Among others it is shown that the Pasternak foundation is a mechanical model for the so-called “generalized” foundation. It is also demonstrated that the kernel for the Pasternak foundation in plane stress or plane strain is identical with Wieghardt’s exponential kernel, and that for the three-dimensional case the kernel is a modified Bessel function. It is also shown that the “non solvability” of the problem of a finite beam or plate resting on a continuous foundation as posed by Wieghardt and further elaborated by Pflanz is not correct, and that problems of this type are solvable for any load distribution permissible in classical plate theory. Throughout the paper, emphasis is placed on the proper mathematical formulation of the physical problems in question.
On the Unstable Vibrations of a Shaft Carrying an Unsymmetrical Rotor
Authors: Yamamoto Toshio , O¯ta Hiroshi
Published: October 2011

In a rotating shaft system carrying an unsymmetrical rotor, there is always one unstable region in the neighborhood of the rotating speed at which the sum of two natural frequencies of the system is equal to twice the rotating speed of the shaft. In this unstable region two unstable lateral vibrations with frequencies P1 and P2 take place simultaneously and grow up steadily. Generally, frequencies P1 and P2 are not equal to the rotating speed ω of the shaft and the sum of these P1 + P2 is always equal to 2ω. Of course there are other unstable regions which appear at the major critical speeds.
Flexible Disk Rotating on a Gas Film Next to a Wall
Authors: Pelech Ivan , Shapiro Ascher H.
Published: October 2011

The flow generated by the rotation of a flexible disk next to a wall is analyzed for small Reynolds numbers. A nonlinear differential equation for the radial variation of the pressure and the gap width is solved simultaneously with the equation governing the deflection of a spinning circular membrane under axial pressure load. Optical methods are used to measure the gap width experimentally. The theory agrees well with the measurements.
Stability of Flow Between Arbitrarily Spaced Concentric Cylindrical Surfaces Including the Effect of a Radial Temperature Gradient
Authors: Walowit J. , Tsao S. , DiPrima R. C.
Published: October 2011

The stability of Couette flow and flow due to an azimuthal pressure gradient between arbitrarily spaced concentric cylindrical surfaces is investigated. The stability problems are solved by using the Galerkin method in conjunction with a simple set of polynomial expansion functions. Results are given for a wide range of spacings. For Couette flow, in the case that the cylinders rotate in the same direction, a simple formula for predicting the critical speed is derived. The effect of a radial temperature gradient on the stability of Couette flow is also considered. It is found that positive and negative temperature gradients are destabilizing and stabilizing, respectively.
Stresses in Curved, Circular Thin-Wall Tubes
Authors: Utecht E. A.
Published: October 2011

Curves are presented which give stress intensification factors for curved, thin-walled circular tubes under various combinations of in-plane and out-of-plane bending moments.
The Theory of Pulsating Flow in Conical Nozzles
Authors: Elrod H. G.
Published: October 2011

A knowledge of the dynamic characteristics of nozzles and orifices is important in many control and stability analyses of engineering devices. It is usual to assume that the instantaneous flowrate, for a given set of inlet conditions and outlet pressure, is the same as the nontransient value for the same operating conditions. Recently, in connection with the stability analysis of an externally pressurized thrust bearing, the validity of this assumption was questioned. The analysis presented in this paper was undertaken to provide an answer. The present analysis applies to any fluid, liquid, or gas flowing into a simple conical nozzle. The amplitude and phase of the mass-flux response to a sinusoidally time-varying pressure fluctuation at the nozzle exit are determined. An approximate formula is given for these quantities in terms of the nozzle throat area, the solid angle subtended by the cone, the velocity of the fluid at the nozzle throat, the acoustic velocity at the throat, and the frequency of the pressure fluctuation.
Linear Bending Theory of Laminated Cylindrical Shells Under Axisymmetric Load
Authors: Paul B.
Published: October 2011

The linear bending theory of laminated elastic cylindrical shells under axisymmetric loading is developed from first principles. It is shown that a spontaneous “beam-column” type of deformation may develop even in the absence of end loads. Generally, however, this effect is shown to be small for metallic cylinders, in which case the laminated shell deforms in the same manner as a homogeneous shell, where the effective flexural rigidity and effective extensional rigidity are both shown to have a simple dependence upon the “elasticity distribution” throughout the wall thickness. The influence of edge loads on a pressurized semi-infinite shell are determined and applied to find the stresses in a titanium shell with a steel reinforcing band.
Stability of Two Planar Loop Elasticas
Authors: Zajac E. E.
Published: October 2011

This paper considers the stability of two planar forms of the elastica: (1) A twisted circular hoop and (2) the classical noninflectional plane elastica. By means of the Kirchhoff thin-rod theory, the critical loads at which the planar forms become unstable and tend to “pop out” into spatial forms are determined. The results are related to the problems of coiling and kinking of submarine cable.
A General Solution for the Elastoplastic Thermal Stresses in a Strain-Hardening Plate With Arbitrary Material Properties
Authors: Mendelson A. , Spero S. W.
Published: October 2011

A general method is presented for obtaining the elastoplastic stress and strain distributions in a thermally stressed plate of a strain-hardening material with temperature-varying modulus, yield point, and coefficient of thermal expansion. It is shown that for linear strain-hardening the solution can often be obtained in closed form. It is indicated that the error due to neglecting strain-hardening may sometimes be appreciable. The assumption that the total strain remains the same as that computed elastically (strain invariance) often leads to smaller errors than the neglect of strain-hardening.
Physical Interpretation of Fictitious Nodes Encountered in the Node Method of Vibration Analysis
Authors: Best G. C.
Published: October 2011

A method of interpreting apparently meaningless solutions of the system of equations encountered when solving a vibration problem by the node method is presented in this paper. These solutions are associated with fictitious nodes connected to the structure by a device called a structural doublet. An illustrative problem is solved.
Magnetohydrodynamic Flow and Heat Transfer About a Rotating Disk
Authors: Sparrow E. M. , Cess R. D.
Published: October 2011

The effects of an axial magnetic field on the flow and heat transfer about a rotating disk have been analyzed. It is found that the presence of the magnetic field significantly decreases the flow velocities; but increases the torque required to maintain steady rotation of the disk. The heat transfer is also decreased by the magnetic field, with greater redutions occurring for low Prandtl number fluids.
Resonant Oscillations of a Beam-Pendulum System
Authors: Struble R. A. , Heinbockel J. H.
Published: October 2011

The resonance phenomena and energy transfer associated with a set of coupled nonlinear differential equations are analyzed using asymptotic methods. The equations describe the motion of a beam-pendulum system which exhibits autoparametric excitation. Precise conditions under which resonant or nonresonant oscillations arise, are obtained. These conditions not only depend upon the physical parameters of the system but also upon the energy of the oscillations (i.e., initial conditions). In general, the envelopes of the resonant oscillations are periodic of long period and there is intermittent energy transfer between the pendulum and beam modes.
Extension of Iteration Method for Determining Strain Distributions to the Uniformly Stressed Plate With a Hole
Authors: Davis E. A.
Published: October 2011

The iterative method for determining strain distributions is applied to a uniformly stressed plate with a hole at the center. The method is not limited to incompressible materials; the load can be raised in incremental amounts; and strain-hardening of the material can be taken into consideration.
On the Parametric Excitation of a Dynamic System Having Multiple Degrees of Freedom
Authors: Hsu C. S.
Published: October 2011

A dynamical system having multiple degrees of freedom and under parametric excitation is governed by a system of ordinary differential equations with periodic coefficients. In this paper a first-approximation analysis is carried out and criteria for instability are derived explicitly.
A Comparison of Five Methods of Calculating Aerodynamic Stagnation-Point Heat Transfer at Velocities of 25,000 to 40,000 fps
Authors: Schreier Stefan
Published: October 2011

Five methods of calculating aerodynamic stagnation-point heat transfer at velocities of 25,000 to 40,000 fps are considered. Three of these methods are simple extrapolations of techniques previously developed for calculations below 25,000 fps. The other two are methods especially developed for velocities above 25,000 fps. The five methods are: The method of Fay and Riddell [1]; the method of Scala [2]; the reference enthalpy method [3]; the method of Adams [4]; and the method of Cohen [5]. Methods [4] and [5] are the methods developed for the higher velocities. The results are presented in graphical form. It is found that the extrapolation of the reference enthalpy method and the correlation formula of Fay and Riddell yield results so close to those of Cohen that, in view of the uncertainties involved in the latter method, using the former two methods over the range of values considered in the present paper yields results at least as satisfactory as those of Cohen for equilibrium flow. Furthermore it is found that extrapolation of the formula of Fay and Riddell for frozen flow yields results sufficiently close to those obtained by the method of Adams that, in view of the uncertainties of the latter method, the advantage of its use over the former in the range of values under consideration is questionable.
Turbulent Wakes in Pressure Gradients
Authors: Hill P. G. , Schaub U. W. , Senoo Y.
Published: October 2011

The application of moderate pressure gradients can exercise a large influence on the decay of wakes produced by obstructions in a flow field. In fact, a positive pressure gradient may arrest completely the decay process and cause the relative wake size to grow rapidly. This phenomenon could exist in any diffusing passage whose entrance flow has a wake-type distortion. Such a nonuniformity, due to a blade or a strut or other cause of stagnation-pressure variation in the stream, could lead to diffuser stall, as has been demonstrated experimentally. An analytical study of the problem has been made on the basis of measurements made in the M.I.T. Gas Turbine Laboratory. Theoretical considerations have led to a very convenient calculation formula which shows quite acceptable agreement with experimental data. The methods employ momentum integral equations and an “eddy viscosity” which is uniform across the wake and proportional to the product of the local free-stream velocity and the momentum thickness.
Information Theory as the Basis for Thermostatics and Thermodynamics
Authors: Tribus Myron
Published: October 2011

Information theory described in Part 1 provides a meaning for the concept of entropy independent of the field of thermodynamics. Using this meaning (uncertainty) it is possible to derive all of statistical and classical thermodynamics in a direct and simple way. Many of the concepts and definitions of classical thermodynamics are given a new interpretation. Using information theory as a basis for a statistical description of an open system, in Part 2, the laws and theorems of thermodynamics are seen to follow in a simple way. The coupling of irreversible flows (Onsager’s relation) is seen as a natural connection between thermostatics and thermodynamics if the functions introduced by Massieu are used instead of those introduced by Gibbs.
The Propagation of an Impulse Into a Viscous-Locking Medium
Authors: Miles J. W.
Published: October 2011

A viscous-locking medium is defined by the compressive stress-strain relation p = f(ε) + μεt, where f(ε) = 0 for ε < εc and f′(εc) = ∞; it behaves as a viscous liquid until the compressive strain attains the value εc, after which it behaves as a rigid solid. A general solution is given for the disturbance produced by a pressure p0(t) acting on an inviscid (μ = 0) half space, in which case the transition from viscous to rigid phases occurs through a shock wave. It is found that the stress falls off inversely as the square of the depth of penetration and that it may be approximated (asymptotically) by the disturbance produced by a concentrated impulse. A similarity solution then is given for a concentrated impulse acting on a viscous half space. It is concluded that viscosity reduces the peak pressure at all depths, even though the disturbance is diffused into the viscous phase and may achieve its peak value in that phase.
The Bending Stress Distribution at the Base of a Stationary Crack
Authors: Williams M. L.
Published: October 2011

Extending an earlier paper dealing with extensional stress distributions, this study considers the stresses around a crack point owing to bending loads. It is found first that the stresses possess the characteristic inverse square-root singularity in terms of distance from the crack point. Along the crack prolongation direction the symmetric principal stresses are of opposite sign and in the ratio (1 − ν)/(3 + ν), in contrast to the extensional situation where they are identically equal. This leads to the observation that more yielding might be expected as the percentage of bending to extension stress at the crack increases. In the antisymmetrical loading, the shear stress is a maximum ±90 deg to the side of the crack, where the distortion energy is also a maximum. Interesting reciprocity relationships are also shown to exist between the symmetrical and antisymmetrical loading conditions for the isochromatic fringe lines and the stress trajectories. Finally, the results are discussed in connection with the combined extensional and bending loading.
Random Vibration of Beams
Authors: Crandall S. H. , Yildiz Asim
Published: October 2011

The calculated response of a uniform beam to stationary random excitation depends greatly on the dynamical model postulated, on the damping mechanism assumed, and on the nature of the random excitation process. To illustrate this, the mean square deflections, slopes, bending moments, and shear forces have been compared for four different dynamical models, with three different damping mechanisms, subjected to a distributed transverse loading process which is uncorrelated spacewise and which is either ideally “white” timewise or band-limited with an upper cut-off frequency. The dynamic models are the Bernoulli-Euler beam, the Timoshenko beam, and two intermediate models, the Rayleigh beam, and a beam which has the shear flexibility of the Timoshenko beam but not the rotatory inertia. The damping mechanisms are transverse viscous damping, rotatory viscous damping, and Voigt viscoelasticity. It is found that many of the mean-square response quantities are finite when the excitation is ideally white (i.e., when the input has infinite mean square); however, some of the responses are unbounded. For these cases the rate of growth of the response as the cut-off frequency of the excitation is increased is obtained.
Green’s Functions for Axially Symmetric Elastic Waves in Unbounded Inhomogeneous Media Having Constant Velocity Gradients
Authors: Hook J. F.
Published: October 2011

This paper treats the propagation of elastic waves in one class of inhomogeneous media. The properties of the media are proportional to powers of the Cartesian co-ordinate z in such a way that Poisson’s ratio remains constant and the velocities of propagation of P and S waves are proportional to z. Exact expressions are obtained for the P, SV, and SH displacements generated by impulsive point sources buried in unbounded media of this class. The sources are taken to be symmetric about the z axis. Separation of the vector-wave equation is achieved by use of a potential representation that is a generalization of the familiar Stokes-Helmholtz representation; the P, SV, and SH displacement vectors are expressed in terms of scalar potentials that satisfy independent second-order wave equations. The SH displacement is solenoidal, but it is found that the products of the P and SV displacement vectors with appropriate weighting functions, rather than the displacement vectors themselves, are irrotational and solenoidal, respectively. The media are found to be dispersive, with the result that decaying tails follow the advancing wave fronts.
Dynamical Stress Concentration in an Elastic Plate
Authors: Pao Yih-Hsing
Published: October 2011

Stress concentrations around a circular cavity in an infinitely extended, thin elastic plate, during passage of plane compressional waves, are discussed. The dynamical stress concentration factors are found to be dependent on the incident wave length and Poisson’s ratio for the plate, and, at certain wave lengths, they are larger than those encountered under statical loading.
Characteristics of the Flow of an Ionized Perfect Gas Through a Magnetic Field
Authors: Carabateas E. N. , Hatsopoulos G. N.
Published: October 2011

The problem of the compressible flow of a perfect gas with constant fractional ionization through a magnetic field is considered. The Joulean heat dissipation is assumed to be taken out of the gas so that the flow can be treated as isentropic. The present analysis differs slightly from others previously reported in the literature [1, 2, 3, 4] mainly in that the entire conductivity tensor and the variation of its elements with gas properties are taken into account. It is felt that the somewhat unrealistic condition of isentropic flow is much less restrictive than the assumption of a scalar constant conductivity. Under these conditions, a relatively simple integration of the flow equations is possible. The assumption of isentropic flow implies that the difference in stagnation enthalpies at the entrance and exit of the magnetic field region is equal to the electrical output plus the Joulean heat. Therefore the ratio of the output power to the difference in stagnation enthalpies gives a measure of the Joulean heat dissipation and hence of the efficiency of the device.
Large-Deflection Analysis of Buckling of a Cylinder Under Bending
Authors: Yao J. C.
Published: October 2011

A theoretical study is made on the local ovaling of a relatively thick tube of low modulus caused by bending. Use is made of modified Donnell’s large-deflection theory [3] and the principle of minimum potential energy in the solution. It is found that tubes with small radius-thickness ratio tend to buckle by local ovaling rather than by the small wave pattern since the former yields lower buckling moment than the latter.
Experimental Solution of Elastic-Plastic Plane-Stress Problems
Authors: Theocaris P. S.
Published: October 2011

The paper presents an experimental method for the solution of the plane state of stress of an elastic-plastic, isotropic solid that obeys the Mises yield condition and the associated flow rule. The stress-strain law is an incremental type law, determined by the Prandtl-Reuss stress-strain relations. The method consists in determining the difference of principal strains in the plane of stress by using birefringent coatings cemented on the surface of the tested solid. A determination of relative retardation using polarized light at normal incidence, complemented by a determination in two oblique incidences at 45 deg along with the tracing of isoclinics, procures enough data for obtaining the principal strains all over the field. The calculation of the elastic and plastic components of strains is obtained in a step-by-step process of loading. It is assumed that during each step the Cartesian components of stress and strain remain constant. The stress increments and the stresses can be found thereafter by using the Prandtl-Reuss stress-strain relations and used for the evaluation of the components of strains and their increments in the next step. The method can be used with any material having any arbitrary stress-strain curve, provided that convenient formulas are established relating the stress and strain components and their increments at each point of the loading path. The method is applied to an example of contained plastic flow in a notched tensile bar of an elastic, perfectly plastic material under conditions of plane stress.
Application of the Point-Matching Method to Shallow-Spherical-Shell Theory
Authors: Conway H. D. , Leissa A. W.
Published: October 2011

Using Reissner’s [1] theory of the bending of shallow spherical shells, two unsymmetrical problems are investigated by the method of point-matching. The first is a uniformly loaded spherical shell clamped on a square base, numerical values of the moments and membrane forces being obtained and compared with the corresponding values for the case of a clamped circular base. The second problem is a spherical shell with a rigid elliptical insert, the latter carrying a central radial load. This gives information concerning the problem of a spherical shell which is pierced at an angle by a relatively rigid circular pipe.
On the Dynamic Behavior of a Frank-Read Source
Authors: Campbell J. D. , Simmons J. A. , Dorn J. E.
Published: October 2011

The equation of motion for a curved dislocation moving at high velocities in a slip plane is solved for a dislocation half-mill. It is found that the angular velocity of a dislocation half-mill about the pinning point is constant for constant stress. The solution is applied to a Frank-Read source to give the shape of the nucleating source and the time of activation. For Al, the time of nucleation of a Frank-Read source is about 9 × 10−10 sec when the stress on the source is 5 × 10−4G.
Dynamics of Nonholonomic Systems
Authors: Kane T. R.
Published: October 2011

A general method for obtaining the differential equations governing motions of a class of nonholonomic systems is presented. Several supplementary theorems are stated, and the use of the method is illustrated by means of two examples.
Viscoelastic Effects in Birefringent Coatings
Authors: Theocaris P. S. , Mylonas C.
Published: October 2011

The method of birefringent coatings for the determination of elastic and plastic surface strains of opaque bodies like metals assumes perfect elasticity of the coating material. In reality the coating, assumed much softer than the metal, presents the problem of a general viscoelastic layer under prescribed boundary displacements (at the metal-plastic interface). As already shown, this problem is greatly simplified for isotropic linear viscoelastic coatings, for small strains, for a linear law of strain birefringence, and for interface displacements expressed as a product of a function of space co-ordinates by a time function. The obviously advantageous stress-strain-optical linearity was experimentally verified in pure and in plasticized epoxy resins which make the best coatings. Tests were carried out in uniaxial loading and in shear, in creep, as well as in relaxation. The main conclusion is that the pure epoxy resins show negligible inelasticity, and the plasticized have a linear photo-viscoelastic behavior. Explicit laws were fitted to the creep and relaxation curves. Tests were also carried out with deeply notched coated steel bars deformed in the plastic range. The variation of fringe pattern with time was found to be negligible for the pure epoxy resins and to diminish slightly and proportionally with time throughout the model for the plasticized resins.
APENELOPE‐based system for the automated Monte Carlo simulation of clinacs and voxelized geometries—application to far‐from‐axis fields
Authors: Sempau Josep , Badal Andreu , Brualla Lorenzo
Published: October 2011

Purpose:

Two new codes,PENEASYandPENEASYLINAC, which automate the Monte Carlo simulation of Varian Clinacs of the 600, 1800, 2100, and 2300 series, together with their electron applicators and multileaf collimators, are introduced. The challenging case of a relatively small and far‐from‐axis field has been studied with these tools.

Methods:

PENEASYis a modular, general‐purpose main program for thePENELOPEMonte Carlo system that includes various source models, tallies and variance‐reduction techniques (VRT). The code includes a new geometry model that allows the superposition of voxels and objects limited by quadric surfaces. A variant of the VRT known as particle splitting, called fan splitting, is also introduced.PENEASYLINAC, in turn, automatically generates detailed geometry and configuration files to simulate linacs withPENEASY. These tools are applied to the generation of phase‐space files, and of the corresponding absorbed dose distributions in water, for two 6 MV photon beams from a Varian Clinac 2100 C/D: a 40 × 40 cm2centered field; and a 3 × 5 cm2field centered at (4.5, −11.5) cm from the beam central axis. This latter configuration implies the largest possible over‐traveling values of two of the jaws. Simulation results for the depth dose and lateral profiles at various depths are compared, by using the gamma index, with experimental values obtained with a PTW 31002 ionization chamber. The contribution of several VRTs to the computing speed of the more demanding off‐axis case is analyzed.

Results:

For the 40 × 40 cm2field, the percentages γ1and γ1.2of voxels with gamma indices (using 0.2 cm and 2% criteria) larger than unity and larger than 1.2 are 0.2% and 0%, respectively. For the 3 × 5 cm2field, γ1 = 0%. These figures indicate an excellent agreement between simulation and experiment. The dose distribution for the off‐axis case with voxels of 2.5 × 2.5 × 2.5 mm3and an average standard statistical uncertainty of 2% (1σ) is computed in 3.1 h on a single core of a 2.8 GHz Intel Core 2 Duo processor. This result is obtained with the optimal combination of the tested VRTs. In particular, fan splitting for the off‐axis case accelerates execution by a factor of 240 with respect to standard particle splitting.

Conclusions:

PENEASYandPENEASYLINACcan simulate the considered Varian Clinacs both in an accurate and efficient manner. Fan splitting is crucial to achieve simulation results for the off‐axis field in an affordable amount of CPU time. Work to include Elekta linacs and to develop a graphical interface that will facilitate user input is underway.
Extended-Spectrum-β-Lactamase-Producing Escherichia coli as a Cause of Pediatric Infections: Report of a Neonatal Intensive Care Unit Outbreak Due to a CTX-M-14-Producing Strain
Authors: Oteo Jesús , Cercenado Emilia , Fernández-Romero Sara , Saéz David , Padilla Belén , Zamora Elena , Cuevas Oscar , Bautista Verónica , Campos José
Published: October 2011

Little information is available about pediatric infections caused by extended-spectrum-β-lactamase (ESBL)-producing
Escherichia coli
. We characterized an outbreak caused by a CTX-M-14-producing
E. coli
isolate in a neonatal intensive care unit (NICU) and studied other infections caused by ESBL-producing
E. coli
in non-NICU pediatric units. All children ≤4 years old who were infected or colonized by ESBL-producing
E. coli
isolates between January 2009 and September 2010 were included. Molecular epidemiology was studied by phylogroup analysis, pulsed-field gel electrophoresis (PFGE), and multilocus sequence typing. Antibiotic resistance genes were analyzed by PCR and sequencing. Plasmids were studied by PFGE with S1 nuclease digestion and by incompatibility group analysis using a PCR-based replicon-typing scheme. Of the ESBL-producing
E. coli
isolates colonizing or infecting the 30 newborns, identical PFGE results were observed for 21 (70%) isolates, which were classified as CTX-M-14-producing
E. coli
of ST23 phylogroup A.
bla
CTX-M-14a
was linked to IS
Ecp1
and was carried on an ∼80-bp IncK plasmid. A smaller ongoing outbreak due to SHV-12-producing ST131
E. coli
was also identified in the same NICU. Fifteen additional infections with ESBL-producing
E. coli
were identified in non-NICU pediatric units, but none was caused by the CTX-M-14-producing
E. coli
epidemic clone. Overall, CTX-M-14 (71.1%), CTX-M-15 (13.3%), and SHV-12 (13.3%) were the most important ESBLs causing pediatric infections in this study. Infections of newborns with CTX-M-14-producing
E. coli
were caused by both clonal and nonclonal isolates.
Loss of Function of the GdpP Protein Leads to Joint β-Lactam/Glycopeptide Tolerance in Staphylococcus aureus
Authors: Griffiths J. M. , O'Neill A. J.
Published: October 2011

The genetic basis of tolerance to inhibitors of peptidoglycan biosynthesis in
Staphylococcus aureus
was investigated by generating tolerant mutants
in vitro
and characterizing them by comparative genome sequencing. Two independently selected tolerant mutants harbored nonsynonymous mutations in
gdpP
, a gene encoding a putative membrane-located signaling protein. Insertional inactivation of
gdpP
also conferred tolerance. Our findings further implicate altered signal transduction as a route to antibiotic tolerance in
S. aureus
.
ICE
Sp2905
, the
erm
(TR)-
tet
(O) Element of Streptococcus pyogenes, Is Formed by Two Independent Integrative and Conjugative Elements
Authors: Giovanetti Eleonora , Brenciani Andrea , Tiberi Erika , Bacciaglia Alessandro , Varaldo Pietro Emanuele
Published: October 2011

In ICE
Sp2905
, a widespread
erm
(TR)- and
tet
(O)-carrying genetic element of
Streptococcus pyogenes
, the two resistance determinants are contained in separate fragments inserted into a scaffold of clostridial origin. ICE
Sp2905
(∼65.6 kb) was transferable not only in its regular form but also in a defective form lacking the
erm
(TR) fragment (ICE
Sp2906
, ∼53.0 kb). The
erm
(TR) fragment was also an independent integrative and conjugative element (ICE) (ICE
Sp2907
, ∼12.6 kb). ICE
Sp2905
thus results from one ICE (ICE
Sp2907
) being integrated into another (ICE
Sp2906
).
Estimating the biomass of woodland caribou forage lichens
Authors: McMullin Richard Troy , Thompson Ian D. , Lacey Brian W. , Newmaster Steven G.
Published: October 2011

Lichens are an important winter food source for woodland caribou ( Rangifer tarandus caribou ), but quantifying their abundance is difficult. Here, we present an efficient method for assessing lichen biomass at the stand level in boreal forests. We measured lichens occurring in high enough abundance to serve as a winter food source for woodland caribou in 51 boreal forest stands. Samples of each species or genus were collected from each stand and a mean abundance (cover) to biomass ratio was established. The method does not require samples to be collected or weighed, due to this predetermined relationship, and it also accounts for the variation in biomass among lichen species that are equally abundant. The variation in lichen growth between stands was assessed by means of five lichen abundance classes. The proposed method was tested in 34 stands with a wide range of ages and stem densities. The average time to complete a lichen biomass assessment was approximately 2 h. This method is an efficient and accurate tool that can assist forest managers and researchers with ecological studies on lichens or with monitoring changes in lichen biomass over time and with habitat assessments for organisms for which lichens are important, such as woodland caribou.
Modeling annualized occurrence, frequency, and composition of ingrowth using mixed-effects zero-inflated models and permanent plots in the Acadian Forest Region of North America
Authors: Li Rongxia , Weiskittel Aaron R. , Kershaw John A.
Published: October 2011

Forest tree ingrowth is a highly variable and largely stochastic process. Consequently, predicting occurrence, frequency, and composition of ingrowth is a challenging task but of great importance in long-term forest growth and yield model projections. However, ingrowth data often require different statistical techniques other than traditional Gaussian regression, because these data are often bounded, skewed, and non-normal and commonly contain a large fraction of zeros. This study presents a set of regression models based on discrete Poisson and negative binomial probability distributions for ingrowth data collected from permanent sample plots in the Acadian Forest Region of North America. Models considered here include regular Poisson, zero-inflated Poisson (ZIP), zero-altered Poisson (ZAP; hurdle Poisson), regular negative binomial (NB), zero-inflated negative binomial (ZINB), and zero-altered negative binomial (ZANB; hurdle NB). Plot-level random effects were incorporated into each of these models. The ZINB model with random effects was found to provide the best fit statistics for modeling annualized occurrence and frequency of ingrowth. The key explanatory variables were stand basal area per hectare, percentage of hardwood basal area, number of trees per hectare, a measure of site quality, and the minimum measured diameter at breast height of each plot. A similar model was developed to predict species composition. All models showed logical behavior despite the high variability observed in the original data.
Fire history from three species on a central Appalachian ridgetop
Authors: Hessl Amy E. , Saladyga Tom , Schuler Thomas , Clark Peter , Wixom Joshua
Published: October 2011

The impact of settlement era fires on Appalachian forests was substantial, but whether these fires affected the extent of fire-adapted ridgetop plant communities is poorly understood. Here we present fire history and stand structure of an Appalachian ridgetop (Pike Knob, West Virginia) based on fire scars from three species (Pinus pungens Lamb., Pinus resinosa Soland., and Quercus rubra L.) and stand structure from two species (P. pungens and P. resinosa). Our research objectives are to determine (i) the degree to which the fire frequency on Pike Knob was affected by European American settlement (~1780–1900) and (ii) how the history of fire on Pike Knob shaped the current age structure of P. resinosa and P. pungens. All three species documented fire activity beginning in the mid- to late 1800s and continuing into the middle of the 20th century, when pasture lands were most active. The majority of P. pungens and P. resinosa established during or shortly after the ~85-year period of fires (1868–1953), suggesting a strong influence of past land use on current forest composition. Ridgetop pine communities have been resilient to both the absence of fire and frequent fire, indicating that pine communities will also be resilient to modern fire management, whether fire is excluded or re-introduced.
Forecasting the response of spruce budworm defoliation to climate change in Ontario
Authors: Candau Jean-Noël , Fleming Richard A.
Published: October 2011

Predicting the effect of climate change on insect populations is critical to improve the reliability of forest management plans, wood supply projections, and pest protection programs. In this study, we use an empirical model to relate the spatial distribution of past defoliation by spruce budworm ( Choristoneura fumiferana Clem.) in Ontario to bioclimatic variables. We then apply data from six climate change scenarios to this model to project potential changes in the distribution of defoliation for 2011–2040. The spatial distribution of historical defoliation was found to be related to winter maximum and minimum temperatures, forest content in balsam fir ( Abies balsamea (L.) Mill.) and white spruce ( Picea glauca (Moench) Voss), and spring and summer minimum temperatures. All six climate change scenarios project broadly similar changes in the spatial patterns of defoliation: (i) an extension of the northern limit of defoliation as far as available data go or close to it, (ii) a decrease in the frequency of defoliation in the center of the historical defoliation belt, and (iii) a persistence of the southern limit of defoliation. This leads to a projected increase of the total area defoliated of between 22.8% and 25.5%, while the mean frequency of defoliation, calculated over the whole study area, would slightly increase (+1%) or decrease (–17.7% to –2.9%).
CONDITIONALLY MONOTONE INDEPENDENCE I: INDEPENDENCE, ADDITIVE CONVOLUTIONS AND RELATED CONVOLUTIONS
Authors: HASEBE TAKAHIRO
Published: October 2011

We define a product of algebraic probability spaces equipped with two states. This product is called a conditionally monotone product. This product is a new example of independence in noncommutative probability theory and unifies the monotone and Boolean products, and moreover, the orthogonal product. Then we define the associated cumulants and calculate the limit distributions in central limit theorem and Poisson's law of small numbers. We also prove a combinatorial moment-cumulant formula using monotone partitions. We investigate some other topics such as infinite divisibility for the additive convolution and deformations of the monotone convolution. We define cumulants for a general convolution to analyze the deformed convolutions.
A software process engineering approach to improving software team productivity using socioeconomic mechanism design
Authors: Yilmaz Murat , O'Connor Rory V.
Published: October 2011

Software development is a knowledge and human intensive activity. At the social level, the interactions of these participants and their ability to cooperate are important for improving the productivity of teams and organizations. It is therefore not surprising to discover that recent contributions in software development have repeatedly asserted the critical role of people in software development efforts. However, existing approaches to software development fail to fully exploit the importance of social and intellectual capital that has been highlighted in the fields of economics and sociology. We propose that leveraging the existing approaches from economics and sociology and applying to software development can assist software organizations in maximizing their return on investment. For example, by applying one such approach, mechanism design, we can improve and model the organization's total productivity based on social aspects affecting productivity (i.e. social productivity). This paper will discuss the vision and progress for applying the concept of mechanism design for optimizing software development teams.
Electroless Deposition for New Challenges in Nanoelectronics and Microelectronics
Authors: Khoperia Teimuraz
Published: October 2011

The proposed patentable nanomethod is much more advantageous and simpler than other expensive and complicated methods such as e-beam and X-ray lithography or fabrication of nano-sized elements by light phase shift photomasks. The proposed method allows us to eliminate surface treatment by e-beam. It can save about $4 000 000 (the price of e-beam lithography exposure equipment). It also eliminates the application of X-ray masks with gold masking elements. The proposed patentable nanomethods for the first time allow one to produce nano-sized adjacent elements of different thickness made of various materials (e.g. Si) by single optical UV photolithography. These advantages significantly extend the functional capabilities of the devices and simplify the removal of undesirable gases and heat dissipation.
A Research of Corrosion for Generated Condensate at Intercooler in Emission Recirculation Engine System
Authors: Yoon Yeo Seong , Oh Mee Hye , Oh Kwang Chul , Kim Ah Young , Ko Sang Chul
Published: October 2011

Because of environmental pollution caused by automobile exhaust gas regulations have been strengthened. Engine development has already progressed a lot. Thus, in recently, exhaust gas recirculation system is being developed in industry. Exhaust gas recirculation can be satisfied the emission regulations. However, engine related parts are changed environment. When the exhaust gas recirculation, corrosive elements are recycled into the gas phase. Depending on the temperature of the gas condensate composition and concentration is changing. Containing NO3- condensate can cause corrosion for metal parts. In this study, the exhaust gas emissions to satisfy the circular engine intercooler parts of the system in the circulation of the condensate corrosion due to gas condensate were investigated.