bluuebunny/crossref_metadata_2025 huggingface dataset:
Vertical Height Loss: An Investigation of Four Restorative Materials Opposing Enamel
Authors: Ramp Merrie H. , Ramp Lance C. , Suzuki Shiro
Published: March 2005

Purpose

The objective of this in vitro investigation was to compare the vertical wear produced by cone‐shaped styli of three ceramic restorative materials and a Type III gold alloy opposing flattened human enamel. Vertical wear was measured as enamel height loss, material stylus height loss, and total vertical height loss (the sum of the enamel height loss and the restorative material height loss).

Materials and Methods

Ten cone‐shaped styli were fabricated from each of four restorative materials, which included two machined ceramics, a pressed ceramic, and a Type III gold alloy. To maintain the standardized shape, styli were not polished or glazed. Specimens were subjected to wear in the presence of water for 100,000 cycles at 1.2 Hz under a load of 75 N using a wear simulation device. Enamel wear was evaluated by profilometry, and stylus wear was evaluated by computer imaging. Vertical wear was reported as enamel height loss, material stylus height loss, and total vertical height loss (the sum of the enamel height loss and material height loss). Data were compared using one‐way analysis of variance and Scheffe's analysis (α= 0.05).

Results

Significant differences existed among materials based on material height loss (p= .0001), enamel height loss (p= .0001), and total vertical height loss (p= .0118). No significant difference among the three ceramics was found in mean total height loss, which ranged from 0.280 to 0.305 mm. However, the Type III gold exhibited less mean total wear (0.231 ± 0.082) than the pressed and one machineable ceramic. This machined ceramic exhibited the most material height loss (0.249 ± 0.044 mm). With the other ceramics, mean enamel wear was significantly more (0.211 and 0.216 mm, respectively).

Conclusions

During wear simulation, pressed or machineable ceramics opposing flattened enamel exhibited a similar degree of total vertical height loss. One machined ceramic material wore significantly more than the other materials. The other machineable ceramic and the pressed ceramic wore the opposing enamel significantly more.
Tooth fragment embedded in the lower lip after dental trauma: case reports
Authors: Da Silva Alessandro Costa , De Moraes Márcio , Bastos Eider Guimarães , Moreira Roger William Fernandes , Passeri Luis Augusto
Published: March 2005

Abstract –  Dental traumas are reasonably common, especially in children and adolescents. This report describes two cases in which dental fragments were embedded in the lip soft tissue. Radiographs confirmed the presence of this foreign‐body, which were surgically removed under a local anesthesia. Early diagnosis and surgical removal of theses fragments could prevent undesirable foreign‐body reaction and scarring. The need in such cases for taking routine facial soft tissue radiographs and chest rx‐ray before stating treatment is emphasized.
Method and Apparatus for Soft Tissue Material Parameter Estimation Using Tissue Tagged Magnetic Resonance Imaging
Authors: Augenstein Kevin F. , Cowan Brett R. , LeGrice Ian J. , Nielsen Poul M. F. , Young Alistair A.
Published: March 2005

We describe an experimental method and apparatus for the estimation of constitutive parameters of soft tissue using Magnetic Resonance Imaging (MRI), in particular for the estimation of passive myocardial material properties. MRI tissue tagged images were acquired with simultaneous pressure recordings, while the tissue was cyclically deformed using a custom built reciprocating pump actuator. A continuous three-dimensional (3D) displacement field was reconstructed from the imaged tag motion. Cavity volume changes and local tissue microstructure were determined from phase contrast velocity and diffusion tensor MR images, respectively. The Finite Element Method (FEM) was used to solve the finite elasticity problem and obtain the displacement field that satisfied the applied boundary conditions and a given set of material parameters. The material parameters which best fit the FEM predicted displacements to the displacements reconstructed from the tagged images were found by nonlinear optimization. The equipment and method were validated using inflation of a deformable silicon gel phantom in the shape of a cylindrical annulus. The silicon gel was well described by a neo-Hookian material law with a single material parameter C1=8.71±0.06 kPa, estimated independently using a rotational shear apparatus. The MRI derived parameter was allowed to vary regionally and was estimated as C1=8.80±0.86 kPa across the model. Preliminary results from the passive inflation of an isolated arrested pig heart are also presented, demonstrating the feasibility of the apparatus and method for isolated heart preparations. FEM based models can therefore estimate constitutive parameters accurately and reliably from MRI tagging data.
Changes in the Mechanical Environment of Stenotic Arteries During Interaction With Stents: Computational Assessment of Parametric Stent Designs
Authors: Holzapfel Gerhard A. , Stadler Michael , Gasser Thomas C.
Published: March 2005

Clinical studies have identified factors such as the stent design and the deployment technique that are one cause for the success or failure of angioplasty treatments. In addition, the success rate may also depend on the stenosis type. Hence, for a particular stenotic artery, the optimal intervention can only be identified by studying the influence of factors such as stent type, strut thickness, geometry of the stent cell, and stent–artery radial mismatch with the wall. We propose a methodology that allows a set of stent parameters to be varied, with the aim of evaluating the difference in the mechanical environment within the wall before and after angioplasty with stenting. Novel scalar quantities attempt to characterize the wall changes in form of the contact pressure caused by the stent struts, and the stresses within the individual components of the wall caused by the stent. These quantities are derived numerically and serve as indicators, which allow the determination of the correct size and type of the stent for each individual stenosis. In addition, the luminal change due to angioplasty may be computed as well. The methodology is demonstrated by using a full three-dimensional geometrical model of a postmortem specimen of a human iliac artery with a stenosis using imaging data. To describe the material behavior of the artery, we considered mechanical data of eight different vascular tissues, which formed the stenosis. The constitutive models for the tissue components capture the typical anisotropic, nonlinear and dissipative characteristics under supra-physiological loading conditions. Three-dimensional stent models were parametrized in such a way as to enable new designs to be generated simply with regard to variations in their geometric structure. For the three-dimensional stent–artery interaction we use a contact algorithm based on smooth contact surfaces of at least C1-continuity, which prevents numerical problems known from standard facet-based contact algorithm. The proposed methodology has the potential to provide a scientific basis for optimizing treatment procedures and stent geometries and materials, to help stent designers examine new stent designs “virtually,” and to assist clinicians in choosing the most suitable stent for a particular stenosis.
Trabecular Bone Contributes to Strength of the Proximal Femur Under Mediolateral Impact in the Avian
Authors: Passi N. , Gefen A.
Published: March 2005

Background: Osteoporosis in long bones involves loss of cortical thickness and of the trabecular microarchitecture. Deterioration and weakening of trabecular bone tissue during osteoporosis imposes greater physiological loads on the cortical shell. However, it is unclear whether trabecular bone significantly contributes to the strength of whole bones under non-physiological impact loads. Method of Approach: We hypothesize that trabecular tissue in epiphyses of long bones contributes to resisting and distributing impact loads. To test this hypothesis, we caused artificial trabecular bone loss in proximal femora of adult hens but did not alter the bone cortex. Subsequently, we compared the energy required to fracture the proximal part of femora with missing trabecular tissue with the energy required to fracture control femora, by means of a Charpy test. Results: Extensive loss of trabecular bone in hens (over 0.50 grams or ∼71% weight fraction) significantly reduced the energy required to fracture the whole proximal femur in mediolateral impacts (from ∼0.37 joule in controls to ∼0.20 joule after extraction of core trabecular tissue). Conclusions: These findings indicate that trabecular bone in the proximal femur is important for distributing impact loads applied to the cortex, and support the concept that in treating osteoporosis to prevent hip fractures, it is just as important to prevent trabecular bone loss as it is important to prevent loss of cortical thickness.
Review of Wall Turbulence as Described by Composite Expansions
Authors: Panton Ronald L.
Published: March 2005

This article reviews the literature on the theory of wall turbulence and the correlation of data from the viewpoint of composite expansions. As an interpretive tool, composite expansions have been used explicitly since the time of the introduction of the wake law. Nevertheless, the articles of the pioneer turbulence researchers, Prandtl and von Ka´rma´n for example, can be interpreted in this more contemporary light. Although the review begins with the work of the founding fathers, it is comprehensive and includes the modern high-quality experiments, “direct numerical simulations,” and analyses that have been published in this century. Additionally, this review organizes and consolidates the theory as it offers a unifying way to think about wall turbulence. There are 119 reference cited.
Determining Dual Euler Angles of the Ankle Complex in vivo Using “Flock of Birds” Electromagnetic Tracking Device
Authors: Ying Ning , Kim Wangdo
Published: March 2005

The dual Euler angles method has been proposed as an alternative approach to describe the general spatial human joint motion. In this study, the dual Euler angles method was applied to study the three-dimensional motion of the ankle complex. The methodology for obtaining dual Euler angles of the ankle complex was developed by using a “Flock of Birds” electromagnetic tracking device. The repeatability of the methodology was studied based on the intertester and intratester variability analysis. Finally kinematic coupling characteristics of the ankle complex during dorsiflexion–plantarflexion, eversion–inversion, and abduction–adduction were analyzed according to the parameters of the dual Euler angles.
Wigner’s rotation revisited
Authors: Ben-Menahem Ari
Published: March 2005

The separation of Wigner’s rotation from the three-dimensional representation of two successive Lorentz transformations is effected naturally via three-space tensor algebra. An alternative derivation is afforded by means of Gibbs’s addition law of spin vectors. The explicit dependence of the Wigner rotation operator on the intrinsic parameters of the two partaking boosts is derived. Applications are given to the Thomas precession and the Lorentz-invariant helicity of a massless particle.
Breit–Wigner resonance and the delta++
Authors: Haskins J. Richard
Published: March 2005

Pion–proton cross-section data from the literature are used to illustrate how the delta++ resonance is analyzed to obtain the rest mass energy of 1232 MeV and the width of 112 MeV. This example illustrates the approximate nature of the Breit–Wigner resonance formula with its corresponding Lorentzian shape. Also, the way in which the wavelength of the bombarding particle, which appears in the resonance formula, should be determined for a relativistic situation such as this is discussed.
Carnot and the Universal Heat Death
Authors: Bailyn M.
Published: March 2005

The relation between Kelvin’s Heat Death and Carnot’s prohibition of perpetual motion machines is traced. The link between them is that Carnot’s proposition implies a perpetual destruction machine, whereas Kelvin’s implies a perpetual degradation machine, the one historically evolving into the other.
General kinematics of winding processes
Authors: McKelvey J. P.
Published: March 2005

Processes which trace, scan, or otherwise generate an Archimedian spiral are referred to as winding processes. A general theory of the kinematics of these processes is presented, in which the linear velocity with which the spiral is generated is assumed to be an arbitrary function of time, controlled by external mechanisms. Explicit formulas for radius, angular velocity, arc length, angular displacement, and angular acceleration are obtained. These quantities all exhibit a nonlinear time dependence, with the magnitude of the nonlinearity critically dependent upon certain physical parameters, which are identified and discussed. The results are directly applicable to many problems in metals, textiles, and paper processing, and also to the technology of audio and video recording processes.
In what frame is a current-carrying conductor neutral?
Authors: Peters P. C.
Published: March 2005

A current-carrying conductor is often used as an example to illustrate the transformation laws of the electric and magnetic fields. The conductor is generally assumed to be neutral in the rest frame of the lattice of positive ions, in which frame the free-electrons have a drift velocity v. A reexamination of this question, taking into account a self-induced Hall effect, shows that the bulk of the conductor is negatively charged in this frame. The bulk of the conductor is neutral, however, in the frame in which the free-electrons are at rest, just the opposite of what is usually assumed for this system. A simple ring circuit driven by an induced emf is used to understand the role of surface charge densities on the conductor, and implications for more general circuits are discussed.
Individual atoms and molecules as dielectric media
Authors: Zangwill A. , Levine Zachary H.
Published: March 2005

A clear physical connection is made between the optical response of atoms and molecules and elementary textbook discussions of the electrostatics of dielectric media. Electrons within atoms and molecules are shown to respond to the Coulomb fields of neighboring electrons in just the same way as the dipole moment of an atom responds to the fields established by dipoles on neighboring atoms. In the presence of a uniform static electric field, a nonuniform internal effective field within the electronic system can be displayed explicitly. Both screening and antiscreening of the external field are found. At finite frequency, the dielectric properties of atoms and molecules are reflected in the photoelectric cross section. The effective field at finite frequency is presented in a pictorial fashion, which helps elucidate the physics of the photoelectric emission process. Calculations of the cross section using the dielectric approach yield extremely accurate values when compared to experiment.
Extra dimensions to remove singularities and determine fundamental constants
Authors: Rau A. R. P.
Published: March 2005

The structure of atoms in an intense magnetic field (≂1012 G) is analyzed as a problem of ‘‘compactification’’ of dimensions. The motion of the electrons is reduced effectively to one dimension, with the dimensions transverse to the field direction frozen at small values. The analysis shows how a reduction in dimensions accounts for the removal of seeming singularities in the structure of atoms and for the occurrence of what appear to be fundamental constants that govern this structure. Thereby, this elementary problem of nonrelativistic quantum mechanics provides analogs of similar studies now being pursued in supergravity and other unified field theories.
Experimental studies of potential problems in quantum mechanics using nonlinear transmission line
Authors: Yazaki T. , Fukushima K.
Published: March 2005

The experimental method for solving the potential problem in quantum mechanics is demonstrated using the nonlinear transmission line equivalent to the Korteweg–de Vries equation (K–dV equation) Ut−6UUx+Uxxx=0. An input voltage pulse corresponding to the potential is observed to dissolve into a finite train of solitons propagating along the line. The signal voltage consisting of solitons is compared with the solution of the initial-value problem for the K–dV equation, which is exactly solved by the theory called the ‘‘inverse scattering method.’’ Consequently, it is shown that the number of bound states and discrete energy levels for one-dimensional potentials (square well potential, −U0 sech2 αx potential, and the Kronig–Penny potential) are determined by observing the signal waveform without calculations.
Fourier analysis for vibrating string’s profile using optical detection
Authors: Sandoval J. L. , Porta A. V.
Published: March 2005

In this paper, we describe an experimental method to analyze the vibration of a string fixed at both ends using the symmetry between time and space behavior. An optoelectronic sensor detects the motion of a point directly displayed on an oscilloscope. The plot of this motion as a function of time is associated with the space behavior of the whole string. The Fourier spectrum of the obtained shape is used to compare experimental results with theoretical predictions. This detection method may also be used to analyze damping effects. The experimental part is intended for intermediate and sophomore university students, but it may be realized for high school students just as a demonstrative experiment.
When can we treat identical particles as distinguishable? An unfamiliar classical limit
Authors: Ingraham R. L.
Published: March 2005

Consider a system of N identical particles having an internal degree of freedom α whose energy enters additively. In statistical mechanics the question arises, ‘‘When can we compute the equilibrium properties related to α as if the system were a collection of N noninteracting distinguishable particles?’’ Most texts leave the student very unclear about this. Consider the case α=intrinsic spin. Then for a paramagnetic solid the answer is ‘‘for any density, temperature, or B field.’’ For an ideal gas we find the general answer ‘‘if and only if 〈nr〉 ≪1, all single particle states r, that is, degeneracy effects are negligible.’’ It is well known that this criterion is necessary for the so-called ‘‘classical limit’’ of low densities or high temperatures. However, it is not equivalent to it; this generalized classical regime can hold for arbitrary densities or temperatures, and lead to unfamiliar magnetic properties, if the B field is strong enough. In other words, very strong B fields can inhibit degeneracy even for high densities or low temperatures. Neutron stars are briefly considered.
Repeated potentials in one dimension and Lorentz transformations
Authors: da Costa R. C. T.
Published: March 2005

It is shown that Lorentz transformations in two spatial dimensions provide a representation for the group of transference matrices of one-dimensional short-range potentials. This gives rise to the possibility of obtaining the quantum-mechanical properties of a chain of localized potentials through the behavior of the product of the corresponding Lorentz transformations. As an example, it is shown that to the energy gaps of a periodic potential correspond an infinite sequence of Lorentz transformations whose final velocity tend ultimately to the velocity of light.
Population explosion in the vacuum
Authors: Hartmann K. M.
Published: March 2005

We show in a simple calculation that, for sufficiently strong electrostatic fields, the vacuum containing charged particles has a lower energy than the vacuum containing no particles at all. Further, the ‘‘empty’’ vacuum in a sufficiently strong gravitational field becomes degenerate with the vacuum containing particle–antiparticle pairs.
Time-energy uncertainty relation and Lorentz covariance
Authors: Hussar P. E. , Kim Y. S. , Noz Marilyn E.
Published: March 2005

The uncertainty relations applicable to space and time separations between the quarks in a hadron are discussed. It is pointed out that the time-energy uncertainty relation between the time and energy separations is the same as the relationship between the widths and lifetimes of unstable states. It is then shown that this relation can be combined with Heisenberg’s position-momentum uncertainty relation to give the uncertainty principle in a covariant form. It is pointed out that this effect manifests itself in Feynman’s parton picture.
Lorentz-transformation properties for energy and momentum in electromagnetic systems
Authors: Boyer Timothy H.
Published: March 2005

The Lorentz-transformation properties of the energy and momentum in electromagnetic systems are illustrated in simple examples involving systems of two point charges. For systems free of external forces the total energy and momentum consisting of mechanical and electromagnetic contributions are seen to transform as a Lorentz four-vector. The examples reveal the roles played by time nonsimultaneity between inertial frames and by electromagnetic forces of one part of the system upon the other in maintaining the four-vector behavior in special relativity. For systems experiencing external forces the mechanical plus electromagnetic energy and momentum do not transform as a Lorentz four-vector; the actual transformation properties can be understood from descriptions for the assembly of the system as viewed in two different inertial frames.
Relativistic one-dimensional hydrogen atom
Authors: Spector Harold N. , Lee Johnson
Published: March 2005

The problem of the one-dimensional hydrogen atom has evoked interest because of its relevance to the behavior of hydrogeniclike atoms in the presence of strong magnetic fields and of hydrogenic impurities confined in quantum-well wire structures. The binding energy of the one-dimensional nonrelativistic hydrogen atom has been found to be infinite in its ground state. We have solved the relativistic hydrogen atom problem for the one-dimensional case using the Klein–Gordon equation. We find that the binding energy in the ground state for the one-dimensional relativistic hydrogen atom is finite and is of order of the rest mass energy of the electron. Therefore a relativistic treatment removes the infinite binding energy found for the ground state for the one-dimensional nonrelativistic hydrogen atom.
Smoke generation in a nuclear war
Authors: Broyles A. A.
Published: March 2005

Simple formulas are derived and calculations are presented to illustrate the procedure for estimating the smoke generated in a nuclear war and the penetration of sunlight through this smoke. Calculations with these formulas for a war in which essentially all the urban areas in theU. S. and Soviet Union burn show that the attenuation of sunlight by the smoke cloud can vary from a decrease of 12% or less of the light to 100% depending upon the input data assumed. Uncertainties in the input data are shown to make these numbers very uncertain. A temperature drop of 27° at the Earth’s surface would result under reasonable assumptions if the sunlight is 100% cut off by the top of a smoke cloud 9 km high.
Application of classical physics to electronic devices
Authors: Guy A. G.
Published: March 2005

Recent publications by the author have employed classical physics (especially electromagnetic theory and phenomenological thermodynamics) to analyze quantitatively the behavior of conduction electrons in metals and semiconductors. The topics discussed here include enthalpy of electrons, electronic heat capacity, departure from Ohm’s law for semiconductors, implications for junction theory, and an extension of Maxwell’s equations. These applications suggest that complex electronic devices can be analyzed more effectively by (nonmechanistic) classical physics than by present electron theories based on quantum mechanics.
Evaluation of a discussion technique used for both classroom instruction and grade assignment
Authors: Long Dale D. , Bedard Jo C.
Published: March 2005

This paper reports the evaluation of a discussion technique used in a one-quarter conceptual physics course. The plan included not only specific guidelines for classroom discussion but also a quantitative method for assigning grades for discussion contributions. The technique was evaluated using questionnaires, written comments by students, and student records of study habits. An analysis of this evaluation indicates an overall favorable response from students.
Momentum flow in the electromagnetic field
Authors: Herrmann F. , Schmid G. Bruno
Published: March 2005

Newton’s second law is equivalent to the continuity equation for momentum in integral form. This insight provides an alternative picture of forces in terms of momentum currents. In such a picture, the forces exerted on an object via a field are completely described locally in terms of the momentum current density of the field. The momentum current picture leads to a representation of Maxwell’s stress tensor which is easy to visualize and to sketch quantitatively. Computer sketches of the momentum current distributions for a few simple examples are presented. In particular, it is shown that two like charges are ‘‘pulled apart’’ by their common electric field and that two parallel wires carrying electric currents in the same direction are ‘‘pushed together’’ by their common magnetic field.
Bridge between particle and fluid kinematics
Authors: Schwalm William A. , Schwalm Mizuho K.
Published: March 2005

Fluid kinematics is developed in a natural way, like particle kinematics, through differentiation rather than by applying the divergence theorem. Dynamical equations are obtained for densities and current densities defined as sums of delta functions. The delta function’s operational properties provide a simple, unified conceptual framework. For a charged fluid interacting with the electromagnetic field, the Poynting theorem and Maxwell stress relation are obtained as fundamental energy and momentum transport equations. Fluid and field are treated symmetrically in the development, account being taken of the stresses and fluxes for each. Then, a microscopic energy transport equation is derived in a similar way for a fluid whose particles interact pairwise through instantaneous forces. The requirement of form invariance under a Galilean transformation yields both the continuity equation and the momentum transport equation. The macroscopic continuum equations are derived by way of simple, spatial averaging, without reference to ensembles, virial theorems, or phase space. The development is tailored for presentation to advanced undergraduate students and assumes no previous exposure to continuum mechanics.
Analyzing students’ reasoning: Tendencies in interpretation
Authors: Viennot L.
Published: March 2005

This paper points out some general tendencies of physics experts in analyzing students’ mistakes. We illustrate these tendencies with two instances in the field of mechanics. It is shown that frequently in interpreting students’ comments, experts proceed in terms of the accepted theory, and thus may fail to discern some important aspects of spontaneous reasoning. These aspects are illustrated with results obtained at college level.
Teaching simulation with a ‘‘digital’’ analog computer
Authors: Bold Gary E. J. , Tan S. M.
Published: March 2005

A hybrid approach to system simulation is proposed in which a digital computer is used to simulate an analog computer, which is then programmed by the user. This retains the simplicity of the analog computer approach but removes the limitations imposed by analog electronics. It is shown how a ‘‘virtual’’ analog computer can be simulated in BASIC using Runge–Kutta integration procedures. Quite complicated systems involving coupled, nonlinear differential equations, which would be intractable on a ‘‘real’’ analog computer, can be readily simulated. Several such simulations are illustrated and discussed.
Experimental analysis of the work done by a variable force
Authors: Sherman Joel F.
Published: March 2005

The work done in moving a mass at the end of a string through an arc, under the influence of a variable horizontal force, is measured by pre-engineering students in a general physics laboratory. The experiment is designed to illustrate the concept of work done by a force as the area under a force–distance curve and to demonstrate the relation between the work done by forces on a system and resulting changes in the system’s mechanical energy. The student finds that an experimental approximation to the integration process may yield reasonably good results using finite intervals over which the work is calculated.
Systems of equations versus extended reference sets in dimensional analysis
Authors: Supplee James M.
Published: March 2005

Dimensional analysis yields the most informative results when the largest possible number of independent reference dimensions is used. This paper gives examples to illustrate that separately analyzing various ‘‘component equations’’ that enter the problem is equivalent to the standard method of using ‘‘extended’’ reference sets. Using the component equations method may also be more convenient since the origin of the additional information is usually more transparent.
Simple examples of correlations in error propagation
Authors: Taylor John R.
Published: March 2005

This paper offers two simple examples of pairs of variables which are correlated, and whose covariance is easily evaluated. Examples are given of error propagation in which these correlations play an important role.
Spontaneous symmetry breaking in a simple mechanical model
Authors: Drugowich de Felício J. R. , Hipólito Oscar
Published: March 2005

A very simple mechanical system which exhibits spontaneous symmetry breaking similar to that appearing in a ferroelectric material is presented. This model can be used to introduce the phase transition mechanism and related concepts such as universality classes and critical exponents in an elementary fashion. It can be easily understood by students of an introductory course in statistical physics.
Stark effect in a one-dimensional model atom
Authors: Fernández Francisco M. , Castro Eduardo A.
Published: March 2005

A very simple one-dimensional, quantum-mechanical analog of the second-order Stark effect in hydrogen is proposed. Its only resonance is found to be a complex root of an algebraic relation among the Airy functions and their derivatives. The Rayleigh–Schrödinger perturbation series is shown to arise from the real part of the resonance. The nonperturbative nature of the resonance width is stressed.
Evaluation of Feynman path integrals by Monte Carlo methods
Authors: MacKeown P. K.
Published: March 2005

Details of a project suitable for an advanced undergraduate course in computational physics, involving the evaluation of functional integrals, are presented. The square of the ground state wavefunction for a simple system may be formulated as a Feynman path integral, and such path integrals evaluated using Monte Carlo methods on a microcomputer. Application to a system interacting through a Morse potential or through a simple harmonic potential is described, while the possible employment of over-relaxation in the latter case is explained.
Charge density in circuits
Authors: Moreau W. R. , Ryan S. G. , Beuzenberg S. J. , Syme R. W. G.
Published: March 2005

It is argued that in the teaching of electric circuits more emphasis needs to be placed on the basic physical ideas introduced earlier in electrostatics. Two lecture demonstrations are described which illustrate the point that electrical potential in a circuit is the same function of charge density distribution as it is in electrostatics.
Use of the ‘‘Welch’’ scattering apparatus
Authors: Price Robert I.
Published: March 2005

Atomic or nuclear collisions can be modeled using the ‘‘Welch’’ scattering apparatus. The student obtains and analyzes ‘‘macroscopic’’ data from a scattering experiment in order to ascertain ‘‘microscopic’’ properties (orientation and shape) of a hidden target. The procedure described emphasizes the analysis of data that are analogous to the data obtained in atomic or nuclear collision studies. The student finds that the position of a cluster of scattered projectiles indicates the orientation of the scattering surface while the density of the cluster indicates the shape (radius of curvature) of the scattering surface.
Relativistic and nonrelativistic Kronig–Penney models
Authors: Domínguez-Adame F.
Published: March 2005

The wavefunction and the Kronig–Penney dispersion relation of an electron moving in a one-dimensional periodic array of delta potentials are found, in the relativistic as well as in the nonrelativistic case. The Green’s function method and Bloch’s theorem are used in a simple form.
Evaluation of chemical potential and energy for an ideal Fermi–Dirac gas
Authors: Kiess E.
Published: March 2005

A method for evaluation of chemical potential and energy of an ideal Fermi–Dirac gas is presented. Additional terms in the series expressions for chemical potential and energy are given.
A general expression for the multipole moments of the quantum harmonic oscillator
Authors: Namias Victor
Published: March 2005

Multipole moments for the harmonic oscillator as well as for other familiar quantum systems can be obtained without knowledge of the wavefunction by means of simple recursion relations. The third-order differential equation satisfied by the probability density is first obtained and from it, the recursion relation for the moments is directly deduced. A general and presumably novel formula giving all the multipole moments is obtained by solving the finite difference equation generated by the recursion relation.
The dynamic shear modulus and internal friction of a fiber vibrating in the torsional mode
Authors: Simpson H. M. , Fortner B. E.
Published: March 2005

A torsional pendulum consisting of an 8-mil boron–tungsten fiber and inertial member is described. The torsional oscillations are excited electrostatically and detected by a frequency modulation technique. Both the dynamic shear modulus and the internal friction can be measured. In addition, this system exhibits the resonance behavior characteristic of a high Q oscillator.
A computer-managed undergraduate physics laboratory
Authors: Kalman C. S.
Published: March 2005

Seventeen one-semester undergraduate laboratory courses are managed by a microcomputer system at Concordia University. Students may perform experiments at any time during operating hours. The computer administers pre- and post-tests. Considerable savings in manpower costs is achieved. The system also provides many pedagogical advantages.
The lateral force on a spinning sphere: Aerodynamics of a curveball
Authors: Watts Robert G. , Ferrer Ricardo
Published: March 2005

The lateral force on a spinning baseball in a wind tunnel has been measured. The magnitude of the force is nearly independent of the orientation of the seams of the ball. The drag coefficient appears to be at most weakly dependent on Reynolds number and to be principally a function of the ratio of the rotational speed of the equator of the ball to the wind tunnel speed. This is to be compared to the work of Briggs, which implies a strong effect of Reynolds number on the drag coefficient.
Entropic versus kinetic viewpoints in rubber elasticity
Authors: Weiner J. H.
Published: March 2005

The role of entropy change as the basic cause of the restoring force in a piece of stretched rubber has been understood for some time. The less-utilized kinetic view, in which the restoring force is the time average of the dynamical forces due to the interaction of thermal motion and the covalent constraints, provides a clearer physical picture. The equivalence of the two viewpoints is demonstrated.
Is mixing a thermodynamic process?
Authors: Ben-Naim A.
Published: March 2005

Mixing processes exist with positive entropy change and negative free energy change. However, the idea that the irreversibility of the mixing processes is responsible for the so-called free energy and entropy of mixing is faulty. The mixing, as well as the demixing processes may be associated with either reversible or irreversible phenomena, depending on the particular conditions. For ideal gases, the word ‘‘mixing’’ in the terms ‘‘mixing entropy’’ and ‘‘mixing free energy’’ may sometimes be used descriptively but never causatively. The quantity −∑ Ni R ln Xi, usually referred to as ‘‘mixing entropy,’’ has nothing to do with the mixing phenomenon. Therefore the terms ‘‘mixing entropy’’ and ‘‘mixing free energy’’ are essentially misconceptions. In fact, it is shown that the process of mixing of ideal gases has, by itself, no relevance to any thermodynamic quantity. Therefore, in a thermodynamical sense, it is a nonprocess. The concepts of assimilation and deassimilation are introduced. It is shown that the ‘‘deassimilation process is essentially irreversible.’’ This should replace the traditional principle that ‘‘the mixing process is essentially irreversible.’’
On the quality of knowledge in the field of electricity and magnetism
Authors: Ferguson-Hessler Monica G. M. , de Jong Ton
Published: March 2005

Problem solving in physics requires a certain quantity of knowledge of the subject matter: principles, procedures, etc. In addition, the problem solver must be able to access these principles and procedures in a given situation. Investigations have shown that failure in problem solving is often caused by lack of availability of knowledge, and also that availability is closely related to the organization of knowledge in memory. Opinions differ, however, on whether the optimal form of this organization should be centered around problem types or arranged in a hierarchical way. In this study two concrete examples of knowledge structures in the field of electricity and magnetism are compared. An experiment is also described, in which the actual knowledge structure of beginning students was studied. The outcome indicates that students with good results in problem solving organize their knowledge more in accordance with problem types than do students with poor results. The results of the experiment are discussed in the light of the two knowledge structures described. The possible role of these structures in physics teaching is treated in the final paragraph.
When did the universe begin?
Authors: Rosen Joe
Published: March 2005

The conceptual basis of assigning a beginning and an age to the universe is discussed, especially with regard to big bang scenarios.
The light-scattering Mueller matrix elements for Rayleigh, Rayleigh–Gans, and Mie spheres
Authors: Bickel William S. , Watkins Arleen J. , Videen Gordon
Published: March 2005

The four nonzero light-scattering matrix element curves for spheres near the Rayleigh and Rayleigh–Gans limit are calculated using Mie theory and compared as the respective limits are approached by a large, high-refractive-index Mie sphere.
The operation of Maxwell’s demon in a low entropy system
Authors: Rex A. F.
Published: March 2005

The problem of Maxwell’s sorting demon traditionally has been studied for the case in which the hot and cold regions differ very little in temperature. In this article a solution is presented for the case in which the temperature difference is great so that the total entropy is lower. Calculations indicate that in this case the demon must use a large number of photons to observe the proper kinds of particles. This causes an increase in entropy which more than offsets the decrease caused by an exchange of particles.
The static effectiveness mass of a slinkyTM
Authors: Mak S. Y.
Published: March 2005

The static elongation of a loaded spring is derived taking into account its own weight and the fact that a finite nonzero force is required to pull the spring apart. A simple experiment is described to verify that the static effective mass is equal to half of the total mass of the spring using a slinky. The experimental result is in good agreement with the theory.
In memoriam J. Jaumann: A direct demonstration of the drift velocity in metals
Authors: Klein W.
Published: March 2005

Moving a Hall specimen perpendicular to the magnetic field and in the opposite direction to the drift motion of carriers with exactly the drift velocity results in a compensation of the Hall voltage. Thus a drift velocity of, e.g., 0.6 mm s−1 in Cu can be directly observed.
Comparative Genomic Hybridizations ofEntamoebaStrains Reveal Unique Genetic Fingerprints That Correlate with Virulence
Authors: Shah Preetam H. , MacFarlane Ryan C. , Bhattacharya Dhruva , Matese John C. , Demeter Janos , Stroup Suzanne E. , Singh Upinder
Published: March 2005

Variable phenotypes have been identified forEntamoebaspecies.Entamoeba histolyticais invasive and causes colitis and liver abscesses but only in ∼10% of infected individuals; 90% remain asymptomatically colonized.Entamoeba dispar, a closely related species, is avirulent. To determine the extent of genetic diversity amongEntamoebaisolates and potential genotype-phenotype correlations, we have developed anE. histolyticagenomic DNA microarray and used it to genotype strains ofE. histolyticaandE. dispar. On the basis of the identification of divergent genetic loci, all strains had unique genetic fingerprints. Comparison of divergent genetic regions allowed us to distinguish betweenE. histolyticaandE.dispar, identify novel genetic regions usable for strain and species typing, and identify a number of genes restricted to virulent strains. Among the fourE. histolyticastrains, a strain with attenuated virulence was the most divergent and phylogenetically distinct strain, raising the intriguing possibility that genetic subtypes ofE. histolyticamay be partially responsible for the observed variability in clinical outcomes. This microarray-based genotyping assay can readily be applied to the study ofE. histolyticaclinical isolates to determine genetic diversity and potential genotypic-phenotypic associations.
Detection of and Response to Signals Involved in Host-Microbe Interactions by Plant-Associated Bacteria
Authors: Brencic Anja , Winans Stephen C.
Published: March 2005

Diverse interactions between hosts and microbes are initiated by the detection of host-released chemical signals. Detection of these signals leads to altered patterns of gene expression that culminate in specific and adaptive changes in bacterial physiology that are required for these associations. This concept was first demonstrated for the members of the familyRhizobiaceaeand was later found to apply to many other plant-associated bacteria as well as to microbes that colonize human and animal hosts. The familyRhizobiaceaeincludes various genera of rhizobia as well as species ofAgrobacterium. Rhizobia are symbionts of legumes, which fix nitrogen within root nodules, whileAgrobacterium tumefaciensis a pathogen that causes crown gall tumors on a wide variety of plants. The plant-released signals that are recognized by these bacteria are low-molecular-weight, diffusible molecules and are detected by the bacteria through specific receptor proteins. Similar phenomena are observed with other plant pathogens, includingPseudomonas syringae, Ralstonia solanacearum, andErwiniaspp., although here the signals and signal receptors are not as well defined. In some cases, nutritional conditions such as iron limitation or the lack of nitrogen sources seem to provide a significant cue. While much has been learned about the process of host detection over the past 20 years, our knowledge is far from being complete. The complex nature of the plant-microbe interactions makes it extremely challenging to gain a comprehensive picture of host detection in natural environments, and thus many signals and signal recognition systems remain to be described.
Being at the Right Place, at the Right Time, for the Right Reasons—Plant Pathology
Authors: Webster Robert K.
Published: March 2005

This article relates some personal history and influences leading to becoming a plant pathologist. Next a summary of my research experiences on rice and barley diseases and the effect of regulatory changes on efforts to manage rice diseases in California. I conclude with an invitation to consider the opportunities and obligations of plant pathologists to return to the field and for individual introspection regarding attitudes and behavior toward colleagues and factors affecting our profession.
Ambulatory Blood Pressure and Mortality
Authors: Hansen Tine Willum , Jeppesen Jørgen , Rasmussen Susanne , Ibsen Hans , Torp-Pedersen Christian
Published: March 2005

The relationship between ambulatory blood pressure and mortality in a general Western population is unknown. Therefore, we conducted this prospective study of a random sample of 1700 Danish men and women, aged 41 to 72 years, without major cardiovascular diseases. At baseline, ambulatory blood pressure, office blood pressure, and other risk factors were recorded. After a mean period of 9.5 years, 174 had died: 63 were cardiovascular deaths. In multivariate proportional hazards models, adjusted for other risk factors of significance, the relative risk of cardiovascular mortality (95% confidence interval) associated with 10 mm Hg increments in systolic and 5 mm Hg increments in diastolic ambulatory blood pressure were 1.51 (1.28 to 1.77) and 1.43 (1.26 to 1.61). The corresponding figures for all cause mortality were 1.18 (1.06 to 1.31) and 1.18 (1.09 to 1.28). The relative risks of cardiovascular mortality were lower for office blood pressure, and office blood pressure did not predict all cause mortality. When ambulatory and office blood pressures were entered in the same multivariate models, only the ambulatory blood pressures were significant predictors of all cause mortality and cardiovascular mortality. The relationship between ambulatory blood pressures and risk of mortality was log-linear, with no indication of a threshold. The absolute risk of mortality was also dependent on age and smoking status, and an upper “acceptable” ambulatory blood pressure based on risk of mortality could only be defined when other risk factors were taken into account. In conclusion, ambulatory blood pressure provided prognostic information on mortality above and beyond that of office blood pressure.
Managerial Resourcefulness: The Construct and Its Measurement
Authors: Kanungo R. N. , Menon S. T.
Published: March 2005

This paper attempts to operationalise the construct of managerial resourcefulness. The construct was first proposed by Kanungo and Misra 1 who suggested that managerial resourcefulness is a constellation of three generic competencies—affective, intellectual and action-oriented, which helps the manager deal with the non-routine, non-programmable aspects of the managerial role. The present study involving 485 managers, develops a psychometrically sound measure of managerial resourcefulness and tests a nomothetic network for the construct. Analysis also revealed an underlying three-factor structure.
Parallel Compositional Reservoir Simulation on Clusters of PCs
Authors: Abate Jason , Wang Peng , Sepehrnoori Kamy
Published: March 2005

The authors have ported a fully implicit equation-of-state (EOS) compositional parallel reservoir simulator to run on clusters of PCs. They report on the performance of the code on two clusters, both in terms of scalability and in absolute performance relative to an IBM SP. The simulator scales well through 16 processors on the clusters and is comparable in execution time with the SP.