bluuebunny/crossref_metadata_2025 huggingface dataset:
Mothers in the making? Exploring liminality in cyber/space
Authors: Madge Clare , O'Connor Henrietta
Published: March 2005

This paper makes a case for cyberspace and geographical space coexisting simultaneously as an interconnected dyadic cyber/space combining the virtually real and the actually real. Based on empirical evidence from a study examining the role of the Internet in the life of new mothers, we investigate the simultaneity of online/onsite experiences through an exploration of cyberspace as a performative liminal space, one where the women ‘tried out’ different versions of motherhood. We suggest that liminality, as a concept that can denote both a space and time of ‘betweenness’, is a useful tool in the virtual geographers ‘conceptual handbag’ as it enables a more lively understanding of cyberspace. But although cyberspace can result in the production of new selves, these selves have residual attachments to embodied experiences and practices. This suggests that new theorizing about cyber/space must combine a consideration of liminality with everyday corporeality.
Inter‐instrumental variation of skin capacitance measured with the Corneometer®
Authors: O'goshi Ken‐ichiro , Serup Jørgen
Published: March 2005

Background/purpose: Measurement of skin surface and stratum corneum (SC) hydration during clinical and/or experimental trials needs devices with acceptable reproducibility and sensitivity under conditions ranging from increased and normal to low hydration. A previous study comparing Corneometer® instruments (European group for Efficacy Measurement of Cosmetics and Other products – EEMCO) used for measurement of electrical capacitance of skin indicated a major difference among Corneometer® instruments. The aim of this study was to assess threee inter‐instrumental similar Corneometer® instruments (two pieces of CM820 and one CM810) in normal skin. We named them CM‐A(CM820), CM‐B(CM820), and CM‐C(CM810).

Methods: The hydration state of SC measured as electrical capacitance of six body sites were measured in 53 subjects with three Corneometer® instruments.

Result: We found that the Corneometer® instruments displayed close capacitance levels. When one Corneometer® was plotted against another the regression line indicated a good correlation among instruments albeit a major and random disagreement could appear in individual sites as an exception.

Conclusion: Three Corneometer® instruments evaluated in this study gave close measurements and correlated well. Nevertheless, pretest validation of instruments should be undertaken in multicenter studies where capacitance data are compared or pooled, and concordance among instruments should be documented prior to study.
Skin irritation due to repetitive application of adhesive tape: the influence of adhesive strength and seasonal variability
Authors: Tokumura Fumio , Umekage Kazuo , Sado Masashi , Otsuka Saburo , Suda Shin , Taniguchi Masaharu , Yamori Akira , Nakamura Atsushi , Kawai Jun , Oka Keiji
Published: March 2005

Background/purpose: Influence of the repetitive application of pressure‐sensitive adhesive tapes on skin was evaluated.

Methods: Two kinds of tapes with different adhesive strengths were repetitively applied to the inside of the forearm of six volunteers in winter and summer, in order to examine the dermal peeling force, the amount of stripped corneocytes, transepidermal water loss (TEWL), hydration and deepened skin furrows (changes in skin surface topography) in the epidermal stratum corneum.

Results and conclusion: As adhesive tapes were applied repetitively, dermal peeling force gradually increased while the amount of stripped corneocytes decreased. As the cumulative amount of stripped corneocytes increased with repetitive applications, the skin irritation worsened as measured by increased destruction of the skin surface topography and TEWL. These phenomena were more marked with the stronger adhesive tape, and there was seasonal variability.
Pressure ulcer‐like presacral gummata in a patient with tertiary syphilis
Authors: Wollina Uwe , Koch André , Abdel‐Naser Mohammed Badawy , Schönlebe Jacqueline
Published: March 2005

Pressure ulcers are common among elderly patients. Here, we describe a case of tertiary syphilis with ulcerated gummata, appearing as a possible pressure ulcer. In such a case, wound management has to be accompanied by specific antibiosis to achieve healing.
Case series of use of Manuka honey in leg ulceration
Authors: Gethin Georgina , Cowman Seamus
Published: March 2005

The historical and current literature reports the successful use of honey to manage a diversity of wound aetiologies. However, only in the last 40 years is research on its mode of action and contribution to wound healing being investigated. The challenge of managing chronic non healing wounds generated interest in researching non standard therapies. The aims of the study were to gain insight into the practical use of Manuka honey in wound management. The objective was to test the feasibility of further rigorous research into the use of honey in the management of chronic wounds. Instrumental case series were used to examine the use of Manuka honey in eight cases of leg ulceration. To collect the necessary data, photographs, acetate tracings, data monitoring and patient comments and observations were used to add greater reliability and validity to the findings. The wounds were dressed weekly with Manuka honey. The results obtained showed three males and five females with ulceration of different aetiologies were studied. A mean initial wound size for all wounds of 5·62 cm2 was obtained. At the end of four‐week treatment period, the mean size was 2·25 cm2. Odour was eliminated and pain reduced. The conclusions drawn were that the use of Manuka honey was associated with a positive wound‐healing outcome in these eight cases. Arterial wounds showed minimal improvement only.
The ‘‘mystery’’ of the quadratic Mandelbrot set
Authors: Metzler Wolfgang
Published: March 2005

Numerical simulations suggest that the Mandelbrot set for binary numbers z=x+γy with x, y∈R and γ2=α+γβ (α,β∈R given) is a simple filled-in square in the perplex case, i.e., α=1, β=0. The paper gives a proof of this experimental result.
Electrostatic orrery for celestial mechanics
Authors: Biewer Ted , Alexander David , Robertson Scott , Walch Bob
Published: March 2005

A device is described in which negatively charged submillimeter particles are trapped in orbits about a rod with a positive potential. Hollow glass microspheres about 50 μm in diameter are dropped past an emitting filament and accumulate a charge of approximately 5×105 electrons. The microspheres fall into a Kingdon trap (concentric cylinders with end caps) and are trapped by a rising potential of order 10 kV. The orbital decay time is determined by molecular drag and is about 40 min or 105 revolutions at 2×10−6 Torr. Orbiting particles are visible to the unaided eye and may be recorded photographically with a CCD camera. Possible applications from celestial mechanics include experiments on orbital resonances, Kirkwood gaps, and planetary ring phenomena.
Geometrical derivation of Lagrange’s equations for a system of particles
Authors: Casey James
Published: March 2005

A concise but general derivation of Lagrange’s equations is given for a system of finitely many particles subject to holonomic and nonholonomic constraints. Based directly on Newton’s second law, it takes advantage of an inertia-based metric to obtain a geometrically transparent statement of Lagrange’s equations in configuration space. Illustrative examples are included.
Comparing problem solving performance of physics students in inquiry-based and traditional introductory physics courses
Authors: Thacker Beth , Kim Eunsook , Trefz Kelvin , Lea Suzanne M.
Published: March 2005

Performance of students in an introductory inquiry-based physics class is compared with that of students in three other introductory physics courses on two different examination problems. One problem is a qualitative problem, typical of those used in inquiry-based physics. The second problem is a quantitative problem, similar to those found in a standard introductory physics text. The students in the inquiry-based physics course were all elementary education majors. They performed significantly better than the engineering students and as well as the honors physics students on the two problems used.
Analytical ground state wave functions for an infinite family of one-dimensional potentials
Authors: Casas M. , Plastino A.
Published: March 2005

We present an infinite family of one-dimensional potentials, of a rather general aspect, whose ground-state energies and wave functions can be expressed in an exact, analytic fashion.
Light exchange in an expanding universe in fixed coordinates
Authors: Fletcher Robert C.
Published: March 2005

The standard model of light exchange in the expanding universe is usually expressed in the Robertson–Walker (RW) proper distance as a function of RW cosmic time, a standard time which is the same for all points on the expanding spatial coordinates. In these coordinates, light like the cosmic microwave background emitted early in the universe close to the origin recedes before it approaches the earth, taking about one-third of the universe’s age, t0, to achieve a maximum distance of about ct0/2, traveling outward an average velocity (maximum distance divided by elapsed cosmic time) about 50% greater than c, the normal speed of light in the absence of gravity. This paper examines this light exchange in fixed spatial coordinates rather than the RW comoving coordinates both because it provides a graceful transition from special relativity and because it is an interesting exercise by itself. For this the array of noninertial observers at fixed distances from the origin must have peculiar velocities, moving towards the origin from the inertial observers on the RW comoving coordinates in order to keep their distances fixed. This peculiar velocity, V, plays a very similar role to that of two inertial systems moving at a velocity of V with respect to each other.

When V approaches the velocity of light, the fixed observer encounters a singular point, earlier than which the time on her clock is not defined since she cannot move faster than light. This is the same point where the RW distance for approaching light is at a maximum. Near this point the fixed observer measurements show dilations of time and radial distance proportional to 1−(V/C)2, instead of the square root of this quantity which is characteristic of the Lorentz transform. This can be shown by a transform from RW coordinates to the fixed coordinates, using for radius any of three distance measures: the Euclidean distance, the RW proper distance, or the light distance (sometimes called the radar distance). In spite of the difficulties with the singularity occurring with these fixed coordinates, for all three assumptions of distance and for a range of densities from 0 to twice the critical density, a fairly simple picture of light exchange in fixed coordinates emerges; light arriving at the origin at the present time, t0, which was emitted early in the universe travels out to a maximum distance of close to ct0/2 in a time close to t0/2, and comes back to the origin, traveling in both directions close to the normal speed of light, c. For the last half of the universe’s history, this is close to the picture derived from special relativity for zero gravity.
What potentials permit a uniqueness theorem
Authors: Bartlett D. F. , Su Y.
Published: March 2005

We show that the Yukawa and Coulomb potentials are the only two real, central, analytic potentials that permit a uniqueness theorem in all bounded geometries. Only for point potentials of the form U(r)=(α/r)cosh(kr)+(β/r)sinh(kr) is it possible to construct a potential V(r) everywhere within any bounded region given V at every point on the boundary (Dirichlet conditions). The replacement of the hyperbolic by trigonometric functions gives a class of ‘‘sinusoidal’’ potentials. These generally have an associated uniqueness theorem, but fail to do so when the boundary forms a resonant cavity for the particular k.
Classical analogy to quantum mechanical level repulsion
Authors: Frank Winfried , von Brentano Peter
Published: March 2005

The frequency repulsion in coupled harmonic oscillators can be treated as a classical analogy to the quantum mechanical level repulsion. As an example the inductively coupled LC circuit will be discussed.
Electric charge on the wire connecting two spheres
Authors: Tong Guo-ping
Published: March 2005

In some textbooks, the case of two charged conducting spheres connected by a wire is used to explain the effect of a sharp point on a conductor. Because the wire is a part of the system, there must be charge on it. In this paper, the wire is modeled by a chain of small conducting spheres, making it possible to calculate the charge on the wire.
Antilinear operators in Dirac’s bra–ket notation
Authors: Royer Antoine
Published: March 2005

A notation is introduced which makes the manipulation of antilinear operators within Dirac’s bra–ket notation as efficient as that of linear operators.
Wave front relativity
Authors: Moreau William
Published: March 2005

A complete picture of the relativity of wave fronts, heretofore lacking, is presented in the context of an expanding spherical light wave as recorded in two Lorentz frames in relative motion.
Resource Letter: GW-1: Global warming
Authors: Firor John W.
Published: March 2005

This Resource Letter provides a guide to the literature on the possibility of a human-induced climate change—a global warming. Journal articles and books are cited for the following topics: the Greenhouse Effect, sources of infrared-trapping gases, climate models and their uncertainties, verification of climate models, past climate changes, and economics, ethics, and politics of policy responses to climate change. [The letter E after an item indicates elementary level or material of general interest to persons becoming informed in the field. The letter I, for intermediate level, indicates material of somewhat more specialized nature, and the letter A indicates rather specialized or advanced material.]
Classical orbits in power-law potentials
Authors: Grant Aaron K. , Rosner Jonathan L.
Published: March 2005

The motion of bodies in power-law potentials of the form V(r)=λrα has been of interest ever since the time of Newton and Hooke. Aspects of the relation between powers α and ᾱ, where (α+2)(ᾱ+2)=4, are derived for classical motion and the relation to the quantum-mechanical problem is given. An improvement on a previous expression for the WKB quantization condition for nonzero orbital angular momenta is obtained. Relations with previous treatments, such as those of Newton, Bertrand, Bohlin, Fauré, and Arnold, are noted, and a brief survey of the literature on the problem over more than three centuries is given.
Acoustic resonators with variable nonuniformity
Authors: Denardo Bruce , Alkov Steven
Published: March 2005

In a novel set of acoustic resonators, alterations of the nonuniformity in cross-sectional area are utilized to change the resonance frequency. Each resonator is designed to yield two, three, or four frequencies whose differences correspond to musical intervals. The apparatus have a simple piecewise-uniform geometry that can easily be changed, and are useful as educational demonstrations of an effect of nonuniformity on waves. The shifts in frequency can be accurately calculated by imposing boundary conditions on solutions of the wave equation in the uniform regions. The phenomenon can be physically understood with the energy method of Rayleigh, or more generally with the method of adiabatic invariance. The latter methods yield the shift in resonance frequency for arbitrary but small nonuniformity.
Time’s arrow: A numerical experiment
Authors: Fowles G. Richard
Published: March 2005

The dependence of time’s arrow on initial conditions is illustrated by a numerical example in which plane waves produced by an initial pressure pulse are followed as they are multiply reflected at internal interfaces of a layered medium. Wave interactions at interfaces are shown to be analogous to the retarded and advanced waves of point sources. The model is linear and the calculation is exact and demonstrably time reversible; nevertheless the results show most of the features expected of a macroscopically irreversible system, including the approach to the Maxwell–Boltzmann distribution, ergodicity, and concomitant entropy increase.
Symmetry and the derivation of invariant vectors for planar motions
Authors: Sivardière Jean
Published: March 2005

Symmetry considerations are used to simplify the derivation of time-invariant vectors for the Kepler motion, the harmonic motion, and the motion of an electric charge in a magnetic field.
Hooke, orbital motion, and Newton’s Principia
Authors: Nauenberg Michael
Published: March 2005

A detailed analysis is given of a 1685 graphical construction by Robert Hooke for the polygonal path of a body moving in a periodically pulsed radial field of force. In this example the force varies linearly with the distance from the center. Hooke’s method is based directly on his original idea from the mid-1660s that the orbital motion of a planet is determined by compounding its tangential velocity with a radial velocity impressed by the gravitational attraction of the sun at the center. This hypothesis corresponds to the second law of motion, as formulated two decades later by Newton, and its geometrical implementation constitutes the cornerstone of Newton’s Principia. Hooke’s diagram represents the first known accurate graphical evaluation of an orbit in a central field of force, and it gives evidence that he demonstrated that his resulting discrete orbit is an approximate ellipse centered at the origin of the field of force. A comparable calculation to obtain orbits for an inverse square force, which Hooke had conjectured to be the gravitational force, has not been found among his unpublished papers. Such a calculation is carried out here numerically with the Newton–Hooke geometrical construction. It is shown that for orbits of comparable or larger eccentricity than Hooke’s example, a graphical approach runs into convergence difficulties due to the singularity of the gravitational force at the origin. This may help resolve the long-standing mystery why Hooke never published his controversial claim that he had demonstrated that an attractive force, which is ‘‘...in a duplicate proportion to the Distance from the Center Reciprocall...’’ implies elliptic orbits.
Suppression and restoration of constants
Authors: Desloge Edward A.
Published: March 2005

Given a set of physical equations containing one or more positive dimensionally independent constants, one can suppress the constants by setting them equal to unity, operate mathematically with the resulting simplified equations, and at the end restore the constants in the final equations. A simple explanation of how and why this method works, and six examples of the application of this method are given. The first example clarifies certain details of the mechanism behind the method. The remaining examples illustrate the utility of the method in the determination of the orbits of a particle in an inverse square attractive force field, the effect of the Coriolis force on the motion of a freely falling particle, the vertical ascent of a rocket in a uniform gravitational field, the nature of a plane electromagnetic wave propagating in a medium of constant permeability and permittivity, and the motion of an electron in a Bohr atom.
Computer modeling of resonance scattering in the time domain
Authors: Greenhow R. C.
Published: March 2005

Microcomputer generation of motion pictures illustrating solutions of Schrödinger’s time-dependent equation is described. The technique is used to model the resonance scattering of a Gaussian wave packet by a spherical step-potential well. The formation of transient resonance states is observed, and the decay times correlated with the widths of the resonances.
Nonrelativistic calculation of the radiation emitted by a pair of identical particles
Authors: Cordes J. G.
Published: March 2005

The calculation of the electromagnetic radiation produced by a pair of nonrelativistic charged particles presents an interesting difficulty in the case where the net dipole moment of the system vanishes. One apparently attractive method of solution fails dramatically for the classic problem of two electrons in relative circular motion. The reason for the failure is explained, for this and other systems.
Compton scattering, the electron mass, and relativity: A laboratory experiment
Authors: Jolivette P. L. , Rouze N.
Published: March 2005

Compton scattering in a semiconductor detector is used to ‘‘discover’’ the relativistic relation between energy and momentum and to demonstrate the dependence of p, E and γ on β. The motivation is to measure the (rest) mass of the electron, and this can be done to within 1 keV with a commonly available set of gamma ray sources. To determine precisely where the Compton edge occurs in a spectrum, a Monte Carlo calculation of detector response is described which also helps the student to understand the physics of the detection process.
Bell’s theorem and quantum mechanics
Authors: Rosen Nathan
Published: March 2005

Bell showed that assuming locality leads to a disagreement with quantum mechanics. Here the nature of the nonlocality that follows from quantum mechanics is investigated. Note by the Editor—Readers will recognize Professor Rosen, author of this paper, as one of the co-authors of the famous EPR paper, Albert Einstein, Boris Podolsky, and Nathan Rosen, ‘‘Can Quantum-Mechanical Description of Physical Reality be considered Complete?’’, Phys. Rev. 47, 770–780 (1935). Robert H. Romer, Editor
‘‘Ruler physics:’’ Thirty-four demonstrations using a plastic ruler
Authors: Ehrlich Robert
Published: March 2005

A collection of 34 demonstrations is described which use only a plastic ruler and other simple items. Many of the demonstrations have a quantitative component, making them suitable for student experiments or at-home exercises. Although most are appropriate to introductory physics courses, a few involve more advanced concepts.
Simple mechanical forced damped oscillator with electronic output
Authors: Moore G. Ian
Published: March 2005

An inverted meter movement with weighted pointer is used as an electromagnetically driven damped oscillator. The meter coil serves as both the driving and sensing transducer and electronic output of displacement, velocity and forcing function allow amplitude and phase relationships to be displayed using an oscilloscope. Resonance phenomena are easily observed over a range of Q’s adjustable by simple mechanical means. Step and impulse responses, excited either mechanically or electronically, can be digitized and recorded with appropriate computer interfacing. The apparatus is low cost and is easily replicated for hands-on experiments in larger classes.
Free particle nonenergy eigenfunctions of a transformed momentum operator using classical solution variables
Authors: Fradkin David M.
Published: March 2005

The classical solution is used to provide appropriate variables for the quantum-mechanical free particle time-dependent Schrödinger wave equation, which then becomes separable giving nonenergy eigenfunctions of closed form. Solutions derived in this fashion may fail to satisfy the homogeneous Schrödinger wave equation at one point in space/time; if this should occur, an inhomogeneous term is produced and a corresponding restricted solution reduces to the free particle propagator. In general, it is shown that the nonenergy eigenfunctions may also be interpreted as eigenfunctions of a time-independent transformed momentum operator. The similarity transformation, by means of which is constructed the transformed momentum operator, the transformed position operator, and the transformed Hamiltonian, are explicitly determined. The relationship of the nonenergy eigenfunctions to the energy eigenfunctions is also exhibited.
Compact complex expressions for the electric field of two-dimensional elliptical charge distributions
Authors: Furman Miguel A.
Published: March 2005

We present a formula for the analytic calculation of the electric field in complex form for two-dimensional charge distributions with elliptical contours, in the absence of boundary conditions except at infinity. The formula yields compact and practical expressions for a significant class of distributions. The fact that the electric field vanishes inside an elliptical shell follows as a straightforward consequence of Cauchy’s theorem. The known expressions for the field inside and outside a uniformly charged ellipse are recovered in simple, concise form. Similarly, the expression for the field of a Gaussian distribution is found in a straightforward way as a special case of the more general formula. We also present a brief discussion of more complicated distributions.
Electromagnetism in Euclidean four space: A discussion between God and the Devil
Authors: Heras José A.
Published: March 2005

In this paper we reexamine the known argument by which Maxwell’s equations are ‘‘derived’’ from the gauge invariance of quantum mechanics, or alternatively, from the gauge invariance of classical mechanics. We point out that this argument is ambiguous in the sense that it may lead us equally to another theory different from that of Maxwell, namely, an electromagnetic theory in Euclidean four space. We attempt to enliven our discussion by presenting it as a dialogue between God and the Devil.
Electric field of a slowly moving rectangular current loop: A microscopic approach
Authors: Blackford B. L.
Published: March 2005

The electric field on the axis of a slowly (v≪c) moving rectangular current loop is calculated using two concepts from introductory level physics textbooks; (1) Lorentz-contraction induced charge density, and (2) relativistic flattening of the electric field pattern of a point charge moving with constant velocity. The correct field, proportional to vI/c2, on the axis of the moving loop is obtained only when both effects are considered and applied separately to the ions and electrons of the loop. Effect (1) is important only for the longitudinal sections of the loop, whereas effect (2) must be considered for all sections of the loop. The latter point is often overlooked in textbooks.
Collinear H+H–H reaction. Computer simulation of quasiclassical trajectories
Authors: Grivet J.-P.
Published: March 2005

An undergraduate computer project, suitable for a computational physics or applied numerical analysis course, is presented. The equations of motion for the three H atoms of the collinear H+H–H system are set up in the Hamiltonian formalism. They are then solved numerically, using the analytical Porter–Karplus potential energy function and the Runge–Kutta algorithm. The program is used to illustrate several types of motion: nonlinear oscillations of the H2 molecule, atom–molecule inelastic collisions, reactive collisions. Results are displayed either as internuclear distances versus time or as the motion of a point in configuration space.
The equivalence principle in the Schwarzschild geometry
Authors: Moreau William , Neutze Richard , Ross D. K.
Published: March 2005

Written in its standard form the Schwarzschild line element obscures the equivalence principle which is hidden in its geometrical structure. Through a coordinate transformation we re-express the line element in a form composed of terms of two different types: (1) terms that correspond to a line element in a uniformly accelerated reference frame in flat space–time, and (2) terms that correspond to curvature and are related to geodesic deviation. The dissection of the Schwarzschild line element into two parts, one corresponding to acceleration and the other to curvature, provides a good specific example of Einstein’s equivalence principle.
Infrared divergence, Thomson scattering, and Lamb shift
Authors: Khriplovich I. B. , Milstein A. I. , Yelkhovsky A. S.
Published: March 2005

The logarithmic part of the Lamb shift in hydrogen is related to the usual infrared divergence and can be obtained immediately from the corresponding radiative correction to the Coulomb scattering amplitude. By a simple generalization of Welton’s arguments we get one of the recoil contributions. To complete the recoil calculation one has to include an elementary iteration of the Thomson amplitude. In this way we derive also the logarithmic part of the Lamb-shift operator in positronium and many-electron atoms.
When Newton’s cooling law doesn’t hold
Authors: Tarnow Eugen
Published: March 2005

What is the fastest way to cool something? If the object is macroscopic it is to lower the surrounding temperature as much as possible and let Newton’s cooling law take effect. If we enter the microscopic world where quantum mechanics rules, this procedure may no longer be the best. This is shown in a simple example where we calculate the optimum cooling rate for an asymmetric two-state system.
Entropy of measurement and erasure: Szilard’s membrane model revisited
Authors: Leff Harvey S. , Rex Andrew F.
Published: March 2005

It is widely believed that measurement is accompanied by irreversible entropy increase. This conventional wisdom is based in part on Szilard’s 1929 study of entropy decrease in a thermodynamic system by intelligent intervention (i.e., a Maxwell’s demon) and Brillouin’s association of entropy with information. Bennett subsequently argued that information acquisition is not necessarily irreversible, but information erasure must be dissipative (Landauer’s principle). Inspired by the ensuing debate, we revisit the membrane model introduced by Szilard and find that it can illustrate and clarify (1) reversible measurement, (2) information storage, (3) decoupling of the memory from the system being measured, and (4) entropy increase associated with memory erasure and resetting.
Polygons of unequal resistors
Authors: Sidhu Satinder S.
Published: March 2005

Consider an N-sided polygon made of resistors such that the resistances connected between the vertices are 2G times those connected between the center and each vertex. Effective resistance between the center and a vertex of such a polygon is obtained by a recursive procedure. The limiting value of the resistance for large N is found to be a fraction that is not always irrational. The method developed is suitable even for cases where resistances making up the polygon are of arbitrary values so that conventional symmetry arguments would not be applicable. The results are applied to a uniform wire shaped into a circular wheel with evenly spaced spokes, and other wire frame structures.
Superconductivity: A guide to alternating current susceptibility measurements and alternating current susceptometer design
Authors: Nikolo Martin
Published: March 2005

Since the arrival of high temperature superconductivity in 1987, the measurement of ac susceptibility has gradually become more popular as a large number of laboratories around the world have either already acquired an ac susceptometer or are in the process of doing so. Its advantage over other techniques is that it is an inductive, noncontact measurement that screens an entire volume of the sample. Here it is explained why this seemingly simple technique is very useful and the principle of measurement is explained in full detail. It is shown how to design and construct a low-cost susceptometer and how to interpret the data when applied to high temperature bulk superconductors.
Data analysis in the undergraduate nuclear laboratory
Authors: Curry Byron , Riggins Dave , Siegel P. B.
Published: March 2005

Experiments for introducing data analysis techniques in the undergraduate nuclear laboratory are presented. In particular, data from gamma spectroscopy using NaI detectors are ideal for teaching curve fitting and chi-square analysis. An experiment well suited for error analysis is the measurement of the half-life of a radioisotope, since the uncertainties are primarily statistical and can be determined by a well-defined procedure. All software used in our experiments was written by students as special projects.
Resource letter: LC-1: Liquid crystals: Physics and applications
Authors: Ondris-Crawford Renate J. , Crawford Gregory P. , Doane J. William
Published: March 2005

This Resource Letter provides a list of references on liquid crystalline materials emphasizing both their fundamental properties and their practical uses in flat-panel displays and electro-optic applications. We have labeled those articles that can be used by students with little or no physics background and no prior knowledge of liquid crystals with an E (elementary), those that require a physics background but can be read by undergraduates with an I (intermediate), and the articles geared towards graduate students and researchers in the field with an A (advanced).
An elementary account of the factor of 4/3 in the electromagnetic mass
Authors: Moylan Patrick
Published: March 2005

It is known that elementary and nonrelativistic electromagnetic considerations lead to a value for the mass of a spherical electrical distribution that is 4/3 times larger than its value obtained from a relativistic treatment. We have obtained a very simple account of this discrepancy, which makes use only of Coulomb’s law and the Biot–Savart law together with the well-known formulas for the energy densities of the electrostatic and magnetic fields. The resolution of this discrepancy, of course, involves the correct (relativistically covariant) definitions for the momentum and energy of an electromagnetic field. This example shows the necessity for relativistic considerations even in nonrelativistic treatments of electromagnetism.
Intrinsic optical bistability in a semiconductor doped glass filter
Authors: Pereira F. , Salcedo J. R. , Belsley M.
Published: March 2005

We present a simple experiment which demonstrates the main features of intrinsic optical bistability obtained through thermally induced shifts in the band edge of semiconductor particles embedded in a glass matrix. This readily demonstrates how nonlinear optical effects can be used to transmit information, providing an instructive introduction to the main concepts of optical computing. Several possible extensions of the experiment suitable for advanced independent research projects are discussed.
Special relativity and length contraction
Authors: Graham John R.
Published: March 2005

Students often have difficulty understanding the relationship between length contraction, the Lorentz transformation of spacetime coordinates, and the relativistic addition of velocities. The following one-dimensional example uses all of these in calculating the length of a stick as measured by two different inertial frame observers. Use of this example as a teaching aid reinforces the concept that the proper length is the maximum length an observer will ever measure.
Determination of the half-life of 212Po
Authors: Ruddick Keith
Published: March 2005

A gas lantern mantle provides a safe radioactive thorium source in an undergraduate laboratory. We describe its use in an experiment to measure the 300 ns half-life of 212Po which occurs in the natural thorium decay chain.
Resource Letter QIMS–1: Quantum interference in macroscopic samples
Authors: Das Sarma S. , Kawamura T. , Washburn S.
Published: March 2005

This Resource Letter provides a guide to the literature on quantum interference in macroscopic systems. The main topics included are weak localization, interference-induced fluctuations, Aharonov–Bohm effect, ballistic transport, and numerical methods. Our compilation of references is intended to help the nonspecialist who wishes to study the main topics covered. [The letter E after an item indicates elementary level or material of general interest to persons becoming informed in the field. The letter I, for intermediate level, indicates material of somewhat more specialized nature; and the letter A indicates rather specialized or advanced material.]
Fizeau’s experiment and the Aharonov–Bohm effect
Authors: Cook Richard J. , Fearn Heidi , Milonni Peter W.
Published: March 2005

The electromagnetic wave equations in a moving medium may be approximated by a form similar to that of the Schrödinger equation for a particle in an electromagnetic field, with the velocity v of the medium and the vorticity ∇×v playing the roles of the vector potential and magnetic field, re- spectively. A purely classical optical analogue of the Aharonov–Bohm effect follows by consider- ation of the interference pattern produced by two beams, each of which propagates in a region with zero vorticity, but such that the flux of the vorticity through the closed loop defined by the optical paths does not vanish. Fizeau’s experiment (1851) on the velocity of light in moving media may be regarded as an example of such a situation.
Macroscopic motion in systems at thermal equilibrium
Authors: Ghosh Amit , Mukhopadhyay Partha
Published: March 2005

A theorem regarding the macroscopic motion of systems states that under thermal equilibrium the only possible motions are those of a rigid body. We show that this is true even for relativistic movements of the system. However for systems like superfluids relative motions between different components (superfluid and normal components) can take place even while maintaining thermal equilibrium. The existing theorem contradicts this. We generalize the theorem so as to eliminate this inconsistency.
Vacuum catastrophe: An elementary exposition of the cosmological constant problem
Authors: Adler Ronald J. , Casey Brendan , Jacob Ovid C.
Published: March 2005

Quantum field theory predicts a very large energy density for the vacuum, and this density should have large gravitational effects. However these effects are not observed, and the discrepancy between theory and observation is an incredible 120 orders of magnitude. There is no generally accepted explanation for this discrepancy, although numerous papers have been written about it. As usually stated the problem requires a knowledge of quantum field theory and general relativity, topics not normally studied by undergraduates. We have tried to make the problem accessible to undergraduates by using only the simplest ideas of quantum theory, such as the uncertainty principle and the theory of the harmonic oscillator, and classical gravitational theory. We believe that such simplification is not only an amusing pedagogical exercise but clarifies how basic is the conflict between quantum theory and gravitational theory. We do not here discuss various proposed solutions to the problem, beyond the trivial and unsatisfactory one of assuming an ad hoc canceling term in the Hamiltonian or field equations.
The flow of electromagnetic energy in the decay of an electric dipole
Authors: Schantz Hans Gregory
Published: March 2005

In a typical dipole decay, the induction magnetic field and the radiation magnetic field are in opposing directions. The former is dominant close to the decay, and the latter is dominant far away. Thus, there exists a surface on which these two components cancel each other, so that the magnetic field reverses direction. Because the magnetic field changes direction, so also will the Poynting vector field, provided the electric field is reasonably well behaved. This defines a ‘‘causal surface,’’ within which electromagnetic energy will collapse, and outside which the electromagnetic energy will radiate away. I present a simple example, the decay of a point electric dipole, to argue that the radiated energy comes, not necessarily from the accelerating charges themselves, but from the energy stored in the far field.
The principle of relativity as applied to motional electromagnetic induction
Authors: Valverde J. Guala , Mazzoni P.
Published: March 2005

We describe the behavior of a unipolar generator that is an obvious variant of the Faraday disk. The behavior of our device, if properly interpreted, is in agreement with the principle of relativity. ‘‘For nearly a century after its discovery by Faraday in 1832 the unipolar generator was a conundrum for the theory of electromagnetism.’’—D. F. Bartlett et al. Phys. Rev. D 16(12), 3459–3463 (1977).
Undergraduate laboratory demonstration of aspects of phase transitions using Curie temperature determination in amorphous ferromagnetic materials
Authors: Fisher David G. , Franz William T.
Published: March 2005

Traditionally, Curie temperature measurements have been performed using a vibrating sample magnetometer, an expensive piece of equipment not readily available to all undergraduate physics laboratories. This article describes an alternative measurement technique requiring only equipment stocked in most undergraduate physics departments. The device was originally constructed for data collection as part of a graduate-level research program in radiation damage effects in amorphous Fe–Ni–P–B ferromagnetic alloys, but can be used for lecture demonstration purposes or as an undergraduate laboratory experiment.
Radiation from a suddenly moving sheet of charge
Authors: Holstein Barry R.
Published: March 2005

Apparent paradoxes associated with Feynman’s picture of plane wave radiation arising from a uniform sheet of surface charge which is suddenly placed into motion are pointed out and resolved.
Resource Letter: TFM-1: Time and frequency measurement
Authors: Hackman Christine , Sullivan Donald B.
Published: March 2005

This Resource Letter is a guide to the literature on time and frequency measurement. Journal articles and books are cited for the following topics: frequency standards; methods of characterizing performance of clocks and oscillators; time scales, clock ensembles, and algorithms; international time scales; frequency and time distribution; and applications. [The letter E after an item indicates elementary level or material of general interest. The letter I, for intermediate level, indicates material of somewhat more specialized nature, and the letter A indicates rather specialized or advanced material. The designations E/I and I/A are used to indicate that the article contains material at both levels, so that at least part of the article is written at the lower of the two levels.]
Gravitational collapse in a single coordinate system
Authors: Gautreau Ronald , Cohen Jeffrey M.
Published: March 2005

We formulate the problem of a gravitationally collapsing body in terms of a single set of coordinates that are employed both in the vacuum region outside the body and inside the body where there is a zero pressure perfect fluid. The spatial coordinate R is the usual Schwarzschild radial coordinate, while the time coordinate t is measured by radially falling geodesic clocks. It is possible to follow the collapse of the body entirely on a single (R,t) space–time diagram. We give analytical expressions for the metrics in the interior and exterior regions which join smoothly and naturally at the surface of the collapsing body. Other features such as apparent and event horizons are also described.
Chaotic pendulum based on torsion and gravity in opposition
Authors: Peters Randall D.
Published: March 2005

An unconventional driven torsion pendulum influenced by gravity has been studied for chaos. Through the use of a symmetric differential capacitive sensor and a galvanometer, phase-space trajectories were generated with an x–y recorder. These were then later compared against output from a computer model of the system which has been further used to generate Poincaré sections, Fourier transforms, and time records. Sensitive dependence on initial conditions as a function of frequency and drive amplitude was demonstrated.
Off-axis illumination and its relation to partial coherence
Authors: Young Matt , Hale Paul D.
Published: March 2005

We calculate the partially coherent images of an edge in one dimension by the method of adding intensities, that is, by modeling the illumination as an array of mutually incoherent plane waves incident over a range of angles. In order to visualize the transition between coherent and incoherent imaging, we display images that result from such off-axis plane waves; these images change considerably as the angle of illumination changes. The calculations are easily carried out on a microcomputer with a high-level mathematics program. The results shed light on off-axis and dark-field illumination as well. Finally, we elucidate a distinction between imaging with the aperture stop in the transform plane and imaging with the aperture stop distant from the transform plane.
Thermodynamic insights from a one-particle gas
Authors: Leff Harvey S.
Published: March 2005

Fundamentals of thermodynamics are introduced and illuminated using a model ‘‘gas’’ consisting of a single particle of mass m and kinetic energy E in a one-dimensional box of length L. Constancy of the classical action, 𝒜=2√2mE L under slow, mechanically reversible changes in L reflects the symmetry of reversibility. Heat is defined in terms of work using adiabatic paths to connect an arbitrary pair of states. The ensemble average of 𝒜 increases for many irreversible mechanical processes that break the reversibility symmetry, and entropy can be linked to ln(𝒜). Although not strictly ‘‘thermodynamic,’’ this model helps clarify the statistical nature of the second law of thermodynamics and illuminates the very essence of thermodynamics, namely, the invisible mixing of energy within systems.
Inexpensive diode laser microwave modulation for atom trapping
Authors: Feng Paul , Walker Thad
Published: March 2005

We describe a simple modification to a grating-stabilized diode laser intended for use in neutral atom cooling and trapping. Modulation of the laser diode’s driving current at microwave frequencies induces sidebands in the laser’s spectrum that eliminate the need for a second laser in a trapping apparatus, yielding a considerable savings in effort and cost. A detailed description of the process for selection and assembly of microwave components is given. In an appendix we list the hardware used, with vendor and pricing information.
Effect of in-class student–student interaction on the learning of physics in a college physics course
Authors: Samiullah Mohammad
Published: March 2005

The effectiveness of in-class student–student interaction on the learning of physics in an algebra-based college physics course is investigated. The student–student interaction leads to an improvement of attitudes of the students toward the course, improves the academic environment of the class, and makes students feel better about the material they are learning. However, it is also found that these qualitative improvements in the class do not lead to a significant change in the test scores on either the classroom tests or the Halloun–Hestenes’s mechanics diagnostics test. The correlation between the performances of students on the classroom tests with the performance on the Halloun–Hestenes test used as a pretest is also investigated and it is found that this correlation is less for students with cooperative learning than for students without cooperative learning.
Conceptual questions in computer-assisted assignments
Authors: Kashy E. , Gaff S. J. , Pawley N. H. , Stretch W. L. , Wolfe S. L. , Morrissey D. J. , Tsai Y.
Published: March 2005

The computer-assisted personalized assignment system has been used to prepare and present conceptual, qualitative questions to students in large introductory classes. The questions appear to be effective in helping students to grasp concepts, as they stimulate dialogue and discussion among the students while they are seeking correct solutions, and provide the instructor with feedback on difficulties students encounter with certain concepts. No formal evaluation of the effectiveness of these questions has been made. Many conceptual, qualitative questions for introductory physics have been written with this system and used in assignments. Several examples are given and briefly discussed.