bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanical behavior and oxidation resistance of Cr(Al)N coatings
Authors: Sánchez-López J. C. , Martínez-Martínez D. , López-Cartes C. , Fernández A. , Brizuela M. , García-Luis A. , Oñate J. I.
Published: September 2005

Nanocrystalline chromium nitride and ternary chromium aluminium nitride thin films were deposited by reactive magnetron sputtering of Cr and Al targets in argon/nitrogen atmosphere varying the sputtering power and gas composition. The coatings were characterized in terms of crystal phase, chemical composition, microstructure, and mechanical properties by x-ray diffraction, x-ray photoelectron spectroscopy, including x-ray-induced Auger electron spectroscopy, transmission electron microscopy, selected-area electron diffraction, electron energy-loss spectroscopy, cross-sectional scanning electron microscopy, and ultramicrohardness tester. The incorporation of Al in the composition of the films produces an increase in the mechanical properties (hardness and reduced Young’s modulus) and an increased thermal resistance against oxidation in comparison to the pure CrN composition. The hardness behavior was attributed mainly to a reduction of the CrN crystallite size according to a Hall–Petch relationship. The oxidation resistance was evaluated after annealing both types of coatings in air up to 800°C. The oxygen content and the crystallite size appear almost unaltered in the CrAlN in contrast to the pure CrN films where the oxidation and grain growth is very noticeable at 800°C. This improvement in thermal stability in air is explained by the formation of a nanocomposite structure of small CrN crystals embedded in an amorphous aluminum oxide or oxinitride matrix that prevents the CrN phase from crystal growth and further oxidation.
Tailored stoichiometries of silicon carbonitride thin films prepared by combined radio frequency magnetron sputtering and ion beam synthesis
Authors: Bruns M. , Geckle U. , Trouillet V. , Rudolphi M. , Baumann H.
Published: September 2005

Homogenous Si–C–N films of 120 nm thickness have been successfully fabricated by means of rf magnetron sputtering combined with ion implantation. These means are capable of producing various tailored stoichiometries of so far unequaled nitrogen concentration and high purity (O<0.2at.%, H<0.5at.%). The achieved compounds Si2CN4,SiCN2, and SiC2N2.2 consist of SiN4 tetrahedron layers interconnected by carbodiimid bridges. Stoichiometry, chemical binding states, and homogeneity of these layers as well as the reproducibility have been investigated by means of x-ray photoelectron spectroscopy, Fourier transform infrared, non-Rutherford back scattering spectroscopy, and resonant nuclear reaction analyses. Furthermore, sputter induced effects on the Si–C–N system during surface analytical characterization using Ar+ ions at 250 and 3250 eV for sputter cleaning have been studied carefully.
Electron heating in capacitively coupled discharges and reactive gases
Authors: Franz Gerhard , Klick Michael
Published: September 2005

The effective collision frequency νeff of electrons in capacitively driven discharges of Ar∕Kr, Cl2 and BCl3 has been investigated using self-excited electron resonance spectroscopy. The most prominent features are the steep increase of νeff at low power inputs in all three gases and a slight but systematic decrease of νeff versus p for Ar∕Kr and BCl3 over the whole pressure range investigated. At medium pressures, the effective collision rate νeff in Cl2 increases by 2 orders of magnitude which is a clear manifestation for the transition from stochastic to ohmic heating. These features have been correlated with data gained with a V(I) probe. The dependence of the ohmic discharge resistance is mainly determined by the drastic change of νeff rather than by the variation of electron density ne.
The case of the curious curl
Authors: McKelvey J. P.
Published: September 2005

Some important, though rarely discussed, aspects of the geometry of the curl of a vector field are investigated. In particular, the direction of the vector ∇ × A with respect to A itself is considered. Ordinarily, the vector A and its curl are neither perpendicular nor parallel. For vector fields with real components, it is shown in general that ∇ × A is orthogonal to A only on a specific surface, while ∇ × A and A are parallel (or antiparallel) only at points lying on a specific curve. Specific examples of vector fields wherein the field vector and its curl are everywhere orthogonal are frequently encountered in physics and engineering. Conditions under which this may occur are investigated. It is shown that when the field direction coincides everywhere with that of any of the unit vectors of a general system of orthogonal coordinates, the field vector and its curl will be everywhere orthogonal. The question of whether there exist vector fields wherein A and ∇ × A are everywhere parallel or antiparallel is also considered. It is shown that such fields can be constructed, and some physical examples are exhibited and discussed.
Simple aspects of post-Newtonian gravitation
Authors: Frisch David H.
Published: September 2005

The physical ideas that are unified in general relativity have been separated out and their effects introduced as separate perturbations of Newtonian mechanics. Compression of space and proportional dilation of time contribute the main parts of all observed and expected quasistatic first-order post-Newtonian gravitational phenomena. In this approach, tests measuring trajectories are variants on a single refraction-in-a-nonuniform-medium experiment; their similarity has been obscured by the few small contributions from special relativity (in only the DeSitter and perihelion precessions) and from gravitation by the gravitational field (in only the perihelion precession).
The power radiated by a slowly moving accelerated acoustic point dipole
Authors: Sporre M.
Published: September 2005

This article considers the acoustic analog of a nonrelativistic accelerated point dipole. Having derived the source density of an acoustic point dipole, the velocity potential is calculated to find the energy flux contributing to the radiated power. A low-speed approximation simplifies the calculations considerably, and the radiated power is obtained. The result is finally applied to the special case of a small rigid body and to simple harmonic oscillations of a sphere.
The transport of momentum theorem
Authors: Lindgren E. Rune
Published: September 2005

The dynamics of mechanical systems with transport of momentum across their boundaries is analyzed by elementary methods as motivated by some misunderstandings on the subject due to the occasional arbitrariness of a physical event that may occur in its mathematical model formulation. The analysis demonstrates the need for careful consideration of circumstances for the generation of momentum flux leaving or entering a dynamic system, resulting in the specification of rules for the design of system boundaries. Reference is made to the so-called ‘‘sprinkler problem’’ to which Richard Feynman has drawn attention in his biography. Rules for the application of momentum flux dynamics presented in this article have been verified by comprehensive experimental checks.
Electromagnetic energy and momentum balance for surface charge distributions
Authors: Ragusa S.
Published: September 2005

The energy and momentum balance, which are usually derived for volume charge distributions, are obtained for surface charge distributions by direct calculation.
Unusual solutions of the Laplace equation
Authors: Harp G. R. , Sorbello R. S.
Published: September 2005

Standard textbook treatments of electrostatic boundary-value problems in 2-D polar coordinates and 3-D spherical polar coordinates do not consider angular and radial coordinates on an equal basis. Series solutions are traditionally expressed in terms of oscillating angular functions and monotonic radial functions, but it is also possible to choose oscillating radial functions and monotonic angular functions. This unusual choice of functions is useful for the class of boundary-value problems where the potential is specified along the radial coordinate. Examples of such boundary-value problems are worked out.
Observations on efficiency of heat engines operating at maximum power
Authors: Gordon J. M.
Published: September 2005

The behavior of the efficiency of a general class of cyclic endoreversible heat engines at maximum power point is considered. The functional temperature dependence of heat transfer is considered as a variable, and its physical significance is addressed. It is shown that a broader spectrum of solutions emerges for efficiency at maximum power, as a function of the relevant system parameters, than originally realized. Specifically, it is proved that efficiency at maximum power is in general not independent of the heat-transfer coefficients, and that a type of ‘‘symmetry’’ exists relative to the functional temperature dependence of Newtonian heat conduction. The ‘‘Curzon–Ahlborn efficiency’’ of finite-time thermodynamics is shown not to be a fundamental upper limit on the efficiency of an endoreversible engine at maximum power point. Rather, this upper limit depends both on the functional temperature dependence of the heat transfer and on the relative value of the hot- and cold-side heat-transfer coefficients.
Yukawa potential approach to the nuclear binding energy formula
Authors: Gauthier N.
Published: September 2005

The volume and surface contributions to the nuclear binding energy of a nucleus are calculated from first principles. Yukawa’s meson theory of the nucleon–nucleon interaction is used to show that the potential energy contains a volume term that is linear in the nucleon number A and a surface term that varies as A2/3, for A sufficiently large. The kinetic energy contribution is accounted for in the usual way. The results are used to estimate the strong force coupling constant. The present approach could be used to discuss the binding energy of a nucleus in terms that are more fundamental than the customary analogy with the case of a drop of liquid.
Measurement of thermal conductivity and heat capacity in an undergraduate physics laboratory
Authors: Talpe J. H. , Bekeris V. I. , Acha C. E.
Published: September 2005

An undergraduate laboratory course experiment on thermal properties of low diffusivity materials is fully described. The experimental setup is of simple construction, not requiring the use of vacuum techniques nor temperature controllers. From the transient regime data, thermal conductivity as well as specific heat capacity can be determined.
Water flow demonstration in the rotating frame
Authors: Daw Harold A.
Published: September 2005

This article deals with fluid flow in a rotating coordinate frame and how to make the characteristics of the flow visible to lecture-demonstration-size audiences. This is a sequel to an earlier article [H. A. Daw, Am. J. Phys. 55, 1010–1014 (1987)] dealing with a rolling ball in the rotating frame. Basically, the same apparatus is used. The path of the fluid flow in a uniformly rotating system in two dimensions is made visible using food coloring, and observation is made by using a video camera. A simple derivation of the flow path is given. The article concludes with the description of a demonstration showing the formation of whirlpools.
If Coulomb’s law were not inverse square: The charge distribution inside a solid conducting sphere
Authors: Spencer Ross L.
Published: September 2005

The distribution of charge between concentric conducting shells has been at the heart of the most sensitive tests of the exponent in Coulomb’s law since the days of Henry Cavendish. But it appears that no one has ever answered the question of how an excess of charge would distribute itself throughout the interior of a solid conductor if Coulomb’s law were other than inverse square. Spherically symmetric solutions to this problem have been found under the assumption that the potential of a point charge varies either as e−kr/r or as 1/rn.
Momentum transfer in a transmission line
Authors: Whatley M. C.
Published: September 2005

The impulse delivered to the end of an electromagnetic transmission line is calculated explicitly, using techniques of university sophomore-level physics and calculus. The result is obtained for the open-circuit end, the shorted end, and for arbitrary resistive termination, and without solving for the fringing electric field or the current density distribution in the terminating resistor. Equating impulse to momentum transfer yields the relationship E=pc for electromagnetic propagation of energy.
Feynman’s proof of the Maxwell equations
Authors: Dyson Freeman J.
Published: September 2005

Feynman’s proof of the Maxwell equations, discovered in 1948 but never published, is here put on record, together with some editorial comments to put the proof into its historical context.
Second law: Sears–Kestin statement and Clausius inequality
Authors: Muschik W.
Published: September 2005

The Sears–Kestin statement represents a formulation of the second law of thermodynamics, restricted to adiabatic processes, which links equilibrium states and which is cyclic in the work variables (generalized displacements). Two conditions, formulated as axioms, are specified which, together with the Sears–Kestin statement, are necessary and sufficient to derive the Clausius inequality. Because these two additional axioms relate to reversible processes and to compound systems—general items not affecting the second law—the status of the Sears–Kestin statement among all the formulations of the second law is strengthened.
Cameron–Martin–Wiener expansions and one-electron quantum transport
Authors: Radzihovsky L. , Nettel S.
Published: September 2005

In 1946 Cameron and Martin concluded a paper [‘‘The orthogonal development of non-linear functionals in series of Fourier–Hermite functionals,’’ Ann. Math. 48, 385–392 (1947)] by saying: ‘‘This paper opens up the whole set of techniques of Orthogonal Developments...for use...in the study of non-linear functionals... .’’ Here, the Cameron–Martin–Wiener expansion is developed with mathematics familiar to physicists, and its use is illustrated and applied to a quantum theory of electron transport.
An approximate image solution method for the electrostatic quadrupole lens
Authors: Cederberg James , Thomas Richard , Bartz David
Published: September 2005

While no simple image method exists that yields an exact solution for the potential around the parallel conducting cylinders of a quadrupole electrostatic lens, we have found that using two line image charges in each cylinder makes an excellent approximation. Graphs are presented of the equipotentials and contours of electric field squared for different rod spacing.
A communication on electrical charge relaxation in metals
Authors: Bochove Erik J. , Walkup John F.
Published: September 2005

The correction of an erroneous textbook derivation on electrical charge relaxation in conductors is discussed. The actual decay in a good conductor is damped oscillatory instead of the simple exponential decay that is often claimed, while short wavelength disturbances spread through the medium much like particles of mass m=ℏωp/〈v2〉, where ωp is the plasmon frequency and 〈v2〉 is the mean-square electron velocity.
Nuclear magnetic resonance: Free-induction decay and spin echoes in a 0.05-T magnetic field
Authors: Klein W.
Published: September 2005

NMR-absorption signals in a 2-cm3 sample of glycerol can be observed in a small permanent magnet producing a field of 50 mT. Observing the beat frequency between the marginal oscillator used as spin detector and the Larmor frequency of the spin system after excitation with 10- to 20- μs high-frequency pulses, the free-induction decay and spin echoes can be detected. The experiment is capable of demonstrating the principles of NMR tomography, e.g., the Carr–Purcell sequence, inversion recovery, and image formation in a field gradient.
Error analysis for parameters determined in nonlinear least-squares fits
Authors: Burrell Keith H.
Published: September 2005

This article presents a calculation of the error in parameters derived from the least-squares method of fitting nonlinear models to experimental data. The formula reduces to the well-known result for the case of a linear least-squares fit. It differs, however, from a method for calculating the error that is often employed for the nonlinear case. The difference between the current result and that method’s is illustrated with examples from least-squares fits to spectroscopic data.
A simple way to assess the structure of red giants
Authors: Celnikier Ludwik M.
Published: September 2005

A simple semianalytical calculation is used to study how a star reacts when its central stock of hydrogen is exhausted and before the next fusion reaction based on helium begins.
Laboratory observation of elastic waves in solids
Authors: Rossing Thomas D. , Russell Daniel A.
Published: September 2005

Compressional, torsional, and bending waves in bars and plates can be studied with simple apparatus in the laboratory. Although compressional and torsional waves show little or no dispersion, bending waves propagate at a speed proportional to (f)1/2. Reflections at boundaries lead to standing waves that determine the vibrational mode shapes and mode frequencies. Boundary conditions include free edges, simply supported edges, and clamped edges. Typical mode shapes and mode frequencies for rectangular bars, circular plates, and square plates are described.
A hydrogenic atom in d-dimensions
Authors: Andrew Keith , Supplee James
Published: September 2005

The laws of physics in d spatial dimensions are interesting and often lead to insights concerning the laws of physics in three spatial dimensions. A hydrogenic bound system in d-dimensions is investigated where d is any real positive number, not necessarily an integer, and where a d-dimensional radial Schrödinger equation is defined by the analytic continuation of the Schrödinger equation used in integer dimensions, with a d-dimensional potential defined by Gauss’ law. The fundamental constants and physical relationships in d dimensions are arrived at by assuming the electric flux obeys a Gausslike law in d dimensions. This fixes the potential and makes it possible to write down the d-dimensional Schrödinger equation. This equation is then solved numerically for the ground-state energy eigenvalues, for several different dimensions, using a fourth-order Runge–Kutta predictor algorithm. The solutions to this equation are compared to the analogous Bohr model energies in d dimensions and to the results obtained by others at well-known integer dimensions. There is good qualitative agreement between the two theories in all dimensions. In addition, the wave functions for the Schrödinger equation are numerically determined and normalized in order to locate the most probable orbital radius. These values are compared to the d-dimensional Bohr radii.
The two-dimensional hydrogen atom with a logarithmic potential energy function
Authors: Eveker K. , Grow D. , Jost B. , Monfort C. E. , Nelson K. W. , Stroh C. , Witt R. C.
Published: September 2005

Recently, a ‘‘shooting’’ method has been used to obtain exact expressions for eigenvalues and eigensolutions of the two-dimensional hydrogen atom. This paper shows that the shooting method is easy for undergraduate students to understand and implement numerically. The highly accurate approximations for both eigenvalues and eigensolutions are then used to contrast the two-dimensional and three-dimensional hydrogen atoms. Finally, previous methods for solving the two-dimensional hydrogen atom are compared with the shooting method.
Newton’s first two laws of motion are not definitions
Authors: Anderson James L.
Published: September 2005

Newton’s first two laws of motion are often taken to be a definition of force. It is argued that they are true laws in that they make statements about the nature of the physical world. In particular, the first law can be viewed as asserting the existence of an ensemble of trajectories in a four-dimensional space along which force-free bodies, if they exist, would move. Such an ensemble, together with Newton’s absolute time, constitute the essential ingredients of the underlying geometrical structure of Newtonian space-time. If this view is accepted, it is a relatively simple matter to describe how special and general relativity differ from Newtonian mechanics.
Precise calculation of the electrostatic force between charged spheres including induction effects
Authors: Soules Jack A.
Published: September 2005

The method of images is applied iteratively to compute precisely the electrostatic force between charged spheres. The results are compared to the experimental results reported by Coulomb and show that Coulomb overlooked induction effects revealed in his data.
Quantum mechanical study of particles in ‘‘softened’’ potential boxes and wells
Authors: Salter Lewis S.
Published: September 2005

The ground-state energies and wave functions of a particle moving in one-dimensional potentials of the form V(x)=x2p, p=1,2,..., are obtained nearly exactly by iterative solution of the Schrödinger equation. These solutions are used as the ‘‘experimental benchmark’’ against which approximate solutions for the general case are tested. Both finite depth wells and infinitely deep wells are studied, as is the three-dimensional version (spherical symmetry, angular momentum quantum number l=0). The approach is aimed at student exploration of the physics of the family of potential wells, with emphasis upon connecting the familiar extreme cases, V(x)=x2 (simple harmonic oscillator) and the limiting case xk, k→∞ (square well).
Cyclotron resonance effects in a fluorescent lamp plasma
Authors: Orr Julie , Wolfson Richard
Published: September 2005

A plasma physics experiment is described, which is suitable for undergraduate courses in electromagnetism as well as for independent projects. Using the plasma of a fluorescent lamp inside a conducting cavity that is immersed in a magnetic field, the experiment shows the effect of electron cyclotron motion of plasma electrons on the resonant modes of the cavity. An added benefit of the magnetic field is the ability to measure the plasma density through a frequency shift technique, but without having to know the mode frequencies in the absence of plasma. Density measurements made using this technique are consistent with those described in an earlier article on the unmagnetized fluorescent lamp plasma, and with the literature on fluorescent lamps and gas discharges. Understanding the experiment described here will give the advanced undergraduate experience in the theory of electromagnetic wave propagation in magnetized plasma, in the theory of resonant cavities, and in microwave and instrumentation techniques.
Macroscopic motion of a totally isolated system in statistical equilibrium
Authors: Diu Bernard , Guthmann Claudine , Lederer Danielle , Roulet Bernard
Published: September 2005

The conditions for macroscopic motion to be compatible with statistical equilibrium are reviewed for a totally isolated macroscopic system (fixed energy, momentum, and angular momentum). The analysis clarifies the general definition of internal energy, the implications of macroscopic motion on the chemical potential, and the status of momentum and angular momentum conservation in statistical mechanics. Two important consequences follow: The temperature is necessarily positive, and the microcanonical ensemble (equiprobability of all accessible microstates) can be applied, as it is usually done, to systems that are only partially isolated (constant energy, but not momentum or angular momentum).
The exactly solvable Thomas–Fermi atom in two dimensions
Authors: Bhaduri R. K. , Das Gupta S. , Lee S. J.
Published: September 2005

The mathematical model of the two-dimensional Thomas–Fermi atom is solved analytically. The electrons interact with each other and with the nucleus through logarithmic potentials that have at least one arbitrary length parameter that sets the zero of energy. The most stable configuration of the system is shown to be a positive ion.
A tricritical point in the dimerized Ising chain phase diagram
Authors: Zaspel C. E.
Published: September 2005

The free energy of the elastic Ising chain with a dimerizing distortion in an external magnetic field is obtained exactly. With the lattice distortion as an order parameter it is shown that the phase diagram in the external field, temperature plane contains a tricritical point. This is probably the simplest known system that exhibits a tricritical point.
Modeling some two-dimensional relativistic phenomena using an educational interactive graphics software
Authors: Sastry G. P. , Ravuri Tushar R.
Published: September 2005

This paper describes several relativistic phenomena in two spatial dimensions that can be modeled using the collision program of Spacetime Software. These include the familiar aberration, the Doppler effect, the headlight effect, and the invariance of the speed of light in vacuum, in addition to the rather unfamiliar effects like the dragging of light in a moving medium, reflection at moving mirrors, Wigner rotation of noncommuting boosts, and relativistic rotation of shrinking and expanding rods. All these phenomena are exhibited by tracings of composite computer printouts of the collision movie. It is concluded that an interactive educational graphics software with pleasing visuals can have considerable investigative power packed within it.
The study of alpha-particle decay schemes of heavy nuclei
Authors: Desmarais D. , Duggan J. L.
Published: September 2005

A nuclear experiment has been designed for use in the undergraduate laboratory. Following a theoretical treatment of alpha barrier penetration and the kinematics and Q value of alpha decay, a semiclassical calculation is made for the half-life for alpha decay, followed by a more exact quantum mechanical result. The decay schemes of three commercially available sources are studied. The branching ratios to various excited states in the residual nuclei are measured along with the precise energies of the decay. The absolute activity of one source (241Am) is determined from its measured alpha activity, and from its gamma activity as measured by a low-energy photon detector.
Quantum mechanics made transparent
Authors: Henry Richard C.
Published: September 2005

This article is a ‘‘sampler,’’ which shows how quantum mechanics may be presented to students in a way that makes apparent how natural quantum mechanics is as a description of the world. The mathematical machinery of Hilbert space, the idea of representing observables by operators, the Schrödinger equation, and the position-momentum uncertainty relation all follow from natural assumptions that students can readily accept. The basic ideas of quantum mechanics are developed from intuitive first principles to the point where one can connect with more traditional treatments of quantum mechanics.
An experiment to study localized excitations—Nonpropagating hydrodynamic solitons
Authors: Winkler Erik , Wu Junru
Published: September 2005

A simple experiment designed to study nonpropagating hydrodynamic solitons of (0, 1) and (0,2) modes is discussed. A brief review of the properties of the soliton is provided.
Why l(l+1) instead of l2?
Authors: Milonni P. W.
Published: September 2005

By considering the allowed values of the z−component of the quantum mechanical angular momentum operator, a simple explanation is given for the term l(l+1). (AIP)
Slinky-whistler dispersion relation from ‘‘scaling’’
Authors: Crawford Frank S.
Published: September 2005

Slinkies come in two sizes, ‘‘regular’’ and ‘‘junior.’’ Using 61% of the total length of the regular slinky, a whistler is obtained that sounds to the ear exactly like that obtained using the total length of the junior. That agrees with the proposed (approximate) dispersion relation ω=ck2r. If n is taken to be unknown in an assumed dispersion relation ω=ck(kr)n, then, by ear, with no equipment, it is found out n=0.83±0.17, in reasonable agreement with the proposed n=1.0.
Geometric interpretation of a nonlinear gauge
Authors: Schweizer Martin Andreas
Published: September 2005

A large gauge class is presented in which the electromagnetic vector potential Aμ does allow for direct geometric interpretation. The gauge condition is quadratic in Aμ and the integral curves generated by the vector field Aμ turn out to be classical particle trajectories in this case.
An inductorless double scroll chaotic circuit
Authors: Weldon Thomas P.
Published: September 2005

The chaotic behavior of a simple electronic circuit that exhibits a double scroll attractor at audio frequencies is described. No inductors are used in the circuit. The necessary inductive reactance is implemented as an active inductor composed of resistors, capacitors, and an amplifier. The chaotic behavior of the circuit is verified by computer simulation on a personal computer and by experimental measurements on a circuit breadboard. The simulation and experimental results are shown to agree with each other and with the results of previous investigators.
Aberration and Doppler shift: The cosmic background radiation and its rest frame
Authors: Greber T. , Blatter H.
Published: September 2005

An individual observer located at one position in space collecting information from the retarded light cone is confronted with aberration and Doppler shift, but also with a shift in intensity and pressure of the observed radiation. The latter are derived using the photon hypothesis and are applied to the cosmic microwave background. The interaction of matter with the cosmic background radiation tends to bring the matter to rest in a preferred frame in which the radiation is isotropic.
The diffraction grating under nonuniform illumination
Authors: Mendelson Kenneth S. , Karioris Frank G.
Published: September 2005

A grating illuminated by a beam with a spatial distribution of intensity produces a diffraction pattern that appears to consist of copies of the incident beam. The copies are centered at the classical diffraction angles given by nλ=d sin φ. In this article, this is indeed shown to be the case if the incident beam has a very narrow spread in wavelength and direction. If the incident beam has a very narrow spread in direction, but not in wavelength, only the zeroth-order diffracted beam is a copy of the incident beam. The higher-order diffracted beams are spread out in wavelength. A black-and-white lantern slide projected through a grating shows the picture in black and white in zeroth-order and as colored images in higher orders.
Newton’s law of cooling—A critical assessment
Authors: O’Sullivan Colm T.
Published: September 2005

The regime of applicability of Newton’s law of cooling is considered in some detail. Three distinct models of the cooling of hot bodies under laboratory conditions are compared experimentally. A model found to be applicable over a reasonably wide range of temperatures and cooling conditions is presented.
Less is more: Experiments with an individual atomic particle at rest in free space
Authors: Dehmelt Hans
Published: September 2005

This article surveys experiments with individual closely confined atomic particles since their beginning in 1973. Such experiments have improved information on the size of an elementary particle on the same level as a quark, the electron, by at least three orders of magnitude. Their extension to the optical region promises atomic clocks of a reproducibility improved up to 100 000 times. The most important of the techniques developed for continuously detecting, cooling, and spin-state analyzing a permanently confined individual electron are described in some detail. The electron, trapped in ultrahigh vacuum at liquid helium temperature, is profitably viewed as a man-made atom, geonium.
The Richtmyer Memorial Lecture (January 1989): Novel magnetic phenomena and high-temperature superconductivity in lamellar copper oxides
Authors: Birgeneau Robert J.
Published: September 2005

The discovery of high-temperature superconductivity in lamellar copper oxide materials is one of the most dramatic and unexpected events in physics in the last several decades. In this paper, which is the text of the 48th Richtmyer Lecture, the basic physics of this new phenomenon is discussed and it is explained why the problem is proving to be so difficult in spite of the unprecedented assault on it by many thousands of physicists, chemists, and materials scientists.
Moments to remember—The conditions for equating torque and rate of change of angular momentum
Authors: Zypman Fredy R.
Published: September 2005

It is a well-known but frequently forgotten fact that the net external torque on a system of particles is equal to the rate of change of angular momentum only if the point about which moments are taken satisfies certain stringent conditions: The point must have zero acceleration, or it must be the center of mass, or its instantaneous acceleration must be directly toward or away from the center of mass. A simple problem in rigid-body mechanics has been solved by Crawford, taking moments about the center of mass. It is shown here that the problem may also be solved using a point that does not satisfy any of these conditions, in which case a more general equation is required. An external fixed point may also be used for calculating moments. When carefully executed, all correct approaches yield the same solution.
Functional integrals and the BCS theory of superconductivity
Authors: Fletcher G.
Published: September 2005

As an example of the application of functional integral techniques to condensed matter physics, the partition function for the BCS model for superconductivity is derived. The pairing term in the Hamiltonian is linearized by applying the Hubbard–Stratonovich transformation. It is shown that the standard result for the gap equation can be obtained by making a saddle-point approximation to the functional integral.
The bipolar motor: A simple demonstration of deterministic chaos
Authors: Ballico M. J. , Sawley M. L. , Skiff F.
Published: September 2005

A simple and inexpensive mechanical model for the demonstration of chaos in a nonlinear deterministic system is described. Periodic, period-doubled, and chaotic motions are exhibited by the model in agreement with the solutions of its governing differential equation. The model is sufficiently free from long-term drifts to enable experimental Poincaré plots to be easily constructed. Such a simple mechanical model is shown to be ideal for use as a lecture room demonstration, as well as for a student laboratory.
On the surface charge density of a moving sphere
Authors: Torres M. , González J. M. , Martín A. , Pastor G. , Ferreiro A.
Published: September 2005

It is shown that the surface charge density on a spherical conductor (spherical in the lab frame) is uniform, regardless of its velocity.
A computer-assisted experiment in single-slit diffraction and spatial filtering
Authors: Bennett C. A.
Published: September 2005

An intermediate-level experiment examines Fraunhofer diffraction and its implications for the image formation of a coherently illuminated object. A commercially available software package is used to provide an environment that allows interactive data acquisition and subsequent numerical and graphical analysis.
Simple proof of the symmetrization postulate in quantum mechanics
Authors: Tikochinsky Yoel , Shalitin Dan
Published: September 2005

With the assumption that n complete single-particle measurements αi uniquely determine the n-identical-particle state ‖α1,α2,...,αn〉, the wavefunction ψ(α1,α2,...,αn) =〈α1,α2,...,αn‖ψ〉 is shown to be either symmetric or antisymmetric under any permutation of its arguments.
A simple device to illustrate angular momentum conservation and instability
Authors: Kalotas T. M. , Lee A. R.
Published: September 2005

An inexpensive and easily constructed spring-loaded dumbbell that illustrates both angular momentum conservation and mechanical instability is described.
Wind chime physics
Authors: Forinash Kyle , Richie John P. , Jones Tim
Published: September 2005

The construction of a set of wind chimes tuned to specific pitches is described. A method for the determination of Young’s modulus based on the measured frequencies of vibration of the sample is employed in the construction of the chimes. Some complications dealing with the perception of musical pitch are also discussed.
Simulation of wave propagation in dispersive media using FFT
Authors: Albareda A. , Toribio E. , Gorri J. A. , Pérez R.
Published: September 2005

A method to show the temporal evolution of wavefunctions in linear lossless media is developed by using the inverse fast Fourier transform. Sequential images of the wave patterns are obtained by assuming simple phase functions for different dispersion relations, and for any given kind of spectra. The evolution of a wave packet shows the different group and phase velocities, and the deformation and spreading of the envelope in several dispersive media.
The gravitational red shift in a uniform field
Authors: Desloge Edward A.
Published: September 2005

When a photon is transmitted from a source S through a uniform gravitational field for which the acceleration due to gravity is g to a detector D located a distance h above S, the frequency νD of the photon measured at the detector is less than the frequency νS measured at the source. The various assumptions and approximations employed in textbook analyses of this phenomenon are considered. The exact dependence of νD on νS, g, and h is then determined first on the conventional assumption that the frequency shift in a uniform gravitational field is the same as the frequency shift in a uniformly accelerating reference frame in field-free space and, second, on the more valid assumption that space-time is curved in a uniform gravitational field and the frequency shift in the field is a consequence of the space-time curvature. The expressions obtained depend not only on which of the above assumptions is made but also on the exact interpretation of the quantities g and h.
Learning motion concepts using real-time microcomputer-based laboratory tools
Authors: Thornton Ronald K. , Sokoloff David R.
Published: September 2005

Microcomputer-based laboratory (MBL) tools have been developed which interface to Apple II and Macintosh computers. Students use these tools to collect physical data that are graphed in real time and then can be manipulated and analyzed. The MBL tools have made possible discovery-based laboratory curricula that embody results from educational research. These curricula allow students to take an active role in their learning and encourage them to construct physical knowledge from observation of the physical world. The curricula encourage collaborative learning by taking advantage of the fact that MBL tools present data in an immediately understandable graphical form. This article describes one of the tools—the motion detector (hardware and software)—and the kinematics curriculum. The effectiveness of this curriculum compared to traditional college and university methods for helping students learn basic kinematics concepts has been evaluated by pre- and post-testing and by observation. There is strong evidence for significantly improved learning and retention by students who used the MBL materials, compared to those taught in lecture.
Optical fiber sensor experiments for the undergraduate physics laboratory
Authors: Bunch R. M.
Published: September 2005

Two experiments, suitable for a 3-h undergraduate laboratory period, employing optical fibers as position sensors are described. These two experiments are based on microbending losses in the fiber and on an external moving reflector, respectively. For each case a model that characterizes the behavior of the transmitted light output from the sensor is given. A knowledge of the model and subsequent analysis for each sensor provide natural experiments suitable for an undergraduate physics/optics laboratory.
A very simple stabilized single-mode He–Ne laser for student laboratories and wave meters
Authors: Ståhlberg B. , Jungner P. , Fellman T.
Published: September 2005

The principle and the construction of an intensity and a frequency-stabilized single-mode internal mirror He–Ne 633-nm laser are described. An intensity stability better than 10−3 and a frequency stability better than 10−8 are obtained. The design is very simple, and the system is recommended for student laboratories and for laser-wavelength meters.
Collapse of wavefunctions and probability densities
Authors: Keller Joseph B.
Published: September 2005

Three facts related to the collapse of quantum mechanical wavefunctions following measurements or observations are presented and explained. They are (1) in all stochastic theories, both classical and quantum mechanical, probability densities collapse following observations; (2) the laws of probability determine the probability density just after an observation in terms of that just before the observation and the result of the observation; (3) the wavefunction just after an observation can be found from that just before the observation by using the result of the observation, the laws of probability, and the assumption that immediate repetition of an observation yields the same result and does not change the wavefunction except for an arbitrary phase factor.
A dynamic method of measuring the charge induced on a conductor
Authors: MacLatchy Cyrus S. , Chipman Hugh A.
Published: September 2005

A simple method of measuring the charge induced on a conductor is presented. The method is based on the idea that a charged projectile passing near a conducting object will cause surface charges to be dynamically induced on its surface. By suitably arranging a detector in the surface of the object, the charge drawn onto the conductor during the passage of the charged projectile can be measured and related to the induced surface charge density. The charge is computed by integrating the current waveform. The concept has been used to design a detector that measures the charge induced on a high-speed projectile such as a pellet fired from an air rifle, the charge induced on a raised hemispherical boss by a uniform electric field, and the surface charge induced on a flat plate by a point charge.
The Bohr–Einstein ‘‘weighing-of-energy’’ debate and the principle of equivalence
Authors: Hughes Richard J.
Published: September 2005

The Bohr–Einstein debate over the ‘‘weighing of energy’’ and the validity of the time–energy uncertainty relation is reexamined in the context of gravitation theories that do not respect the equivalence principle. Bohr’s use of the equivalence principle is shown to be sufficient, but not necessary, to establish the validity of this uncertainty relation in Einstein’s ‘‘weighing-of-energy’’ gedanken experiment. The uncertainty relation is shown to hold in any energy-conserving theory of gravity, and so a failure of the equivalence principle does not engender a failure of quantum mechanics. The relationship between the gravitational redshift and the equivalence principle is reviewed.
Oscillations of a dipole in a magnetic field: An experiment
Authors: Bisquert Juan , Hurtado Emilia , Mafé Salvador , Pina José
Published: September 2005

The small oscillations of a parallelepidal magnet along the axis of a circular coil carrying an electric current have been analyzed theoretically and experimentally. The study of this system (a particular case of a magnetic dipole in motion in a nonuniform magnetic field) involves basic ideas from both mechanics and electromagnetism, and the equipment used in the experiment is very common in an undergraduate laboratory. Comparison with the experiment shows that a very simple theoretical approach gives good results. It is also shown how the introduction of some refinements in the physical model can improve the agreement between theory and experiment, though the theoretical analysis becomes more involved in this case. The use of the principle of superposition to calculate magnetic fields is emphasized throughout the article.
A perspective on teacher preparation in physics and other sciences: The need for special science courses for teachers
Authors: McDermott Lillian C.
Published: September 2005

This article proceeds from the premise that one of the major reasons for the perceived crisis in science education is the failure of our colleges and universities to provide the type of preparation that precollege teachers need to teach science effectively. The perspective taken is based on many years of teaching physics and physical science to prospective and practicing teachers at all grade levels. The inadequacy of the present system of preparing teachers is examined and an argument is presented for offering special physics courses for teachers. Experience at the University of Washington provides the basis for a discussion of the type of intellectual objectives and instructional methods that should characterize such courses.
The New Mexico State University motion room
Authors: Daw Harold A.
Published: September 2005

This article describes the construction and operation of a totally enclosed motion room capable of carrying four students. The room is used for studying motion in a rotating frame. The rotation rate can be varied from 0 to above 20 rpm. Unique features of this motion room are the 60-in. searchlight frame used for the mount and electrical connections and the two cattle watering troughs used for the motion room proper. The room, built a number of years ago, has not previously been described in the literature.
Einstein’s opposition to the quantum theory
Authors: Deltete Robert , Guy Reed
Published: September 2005

Einstein’s opposition to the quantum theory is well known to physicists, but his reasons for being dissatisfied are not. Einstein regarded the theory as not only incomplete, but as fundamentally inadequate. He believed that the only reasonable interpretation of the quantum formalism was an ‘‘ensemble interpretation,’’ but he also thought that this interpretation and others were incomplete and irremediably inadequate, because they failed to describe the objective, real states of individual systems. He hoped, and expected, that a better theory would be developed—one expressed in terms of individuals having their own real states and from which the quantum theory could be recovered as an approximation.
Bell’s theorem: Local realism versus quantum mechanics
Authors: Ferrero M. , Marshall T. W. , Santos E.
Published: September 2005

Realism and locality are defined emphasizing the fundamental character of both principles. From this, the well-known expression proposed by Bell for calculating correlations is derived. Starting from this expression, the theorem of incompatibility is proved between local realism and quantum mechanics. An analysis is made of the experiments performed by Aspect and others, and it is concluded that, because photomultipliers and polarizing filters are not perfectly efficient, it is necessary to make subsidiary assumptions about how they operate in order to rule out local realism. It is argued that the subsidiary assumptions are not logically necessary and, consequently, local realism has not yet been refuted empirically.
Gravitational scattering of quantum particles
Authors: Golowich Eugene , Gribosky Philip S. , Pal Palash B.
Published: September 2005

Instead of taking the usual geometrical approach, the phenomenon of light bending is treated as a quantum scattering problem. This treatment is instructive and straightforward considered when the gravitational field is weak, and can be easily applied even for massive particles, as is demonstrated with the example of a massive spinless particle.
A rotating U-tube experiment
Authors: Denardo Bruce , Wright William , Barber Brad , Folley Chris
Published: September 2005

A rotating U-tube experiment is described in which the axis of rotation lies between a vertical arm and the axis of symmetry of the tube. As the rotational frequency is slowly varied, the equilibrium position of the liquid in the tube can abruptly change, resulting in a hysteresis loop. The effect is not due to friction, which causes a much smaller amount of hysteresis. The data agree well with the theory.