Table of contents

The application of digital image processing to mass screening for breast cancer is demonstrated in the context of adaptive spatial filtering. Experimental results for feature extraction by texture analysis and grey level thresholding reveal there is significant potential for computer-aided mass screening as an adjunct to radiological examination. Digital image processing can improve the visibility of image features, such as neoplasms or tumours, providing also speed and automation of inspection, whilst saving the radiologist time which is otherwise spent on checking clear samples (which represent the majority of screening cases).

Zusammenfassung.Die Anwendung ziffernmäßiger Bildbearbeitung zur Massenabblendung für Brustkrebs wird im Zusammenhang mit räumlichem Filtern demonstriert. Experimentresultate für Besonderheiten-Extraktion im Falle von Gewebeanalyse und Grau-Niveaubegrenzung enthüllen, daß hier eine bedeutende Möglichkeit für computer-unterstützte Massenabblendung als ein Zusatz zur radiologischen Untersuchung besteht. Ziffernmäßige Bildbearbeitung kann die Sichtbarkeit von Bildmerkmalen, wie Neoplasmen und Tumoren, verbessern, außerdem Geschwindigkeit und Automation der Inspektion bietend, während dem Radiologen Zeit ersparend, die andernfalls zur Überprüfung klarer Muster verwendet würde (was für die Mehrzahl der Abschirmfälle zutrifft).

Experiments on matter wave interference involving up to four beams have been realized using a holographic electron microscope equipped with two electrostatic biprisms. The experimental results obtained for parallel biprisms are presented and discussed.

Zusammenfassung.Mit einem holographischen Electronenmikroskop, das mit zwei elektronischen Biprismen ausgestattet ist, wurden Electroneninterferenzexperimente mit bis zu vier beteiligten Strahlen durchgeführt. Die experimentellen Resultate für parallele Biprismen werden dargestellt und diskutiert.

The general motion of a flexible chain sliding from a horizontal surface is analysed. It is shown that the introduction of friction produces no new features in the solution if a suitable coordinate transformation is affected. Indeed a universal function is introduced which gives the sliding time of any chain from a horizontal surface for all surfaces and initial conditions.

We discuss the general conditions under which reversible thermodynamic work, like reversible heat, admits an integrating factor. We present simple examples in which work does and does not admit an integrating factor, and briefly comment on the significance of this integrating factor if it exists.

Resumen.Analizamos las condiciones generales bajo las cuales el trabajo termodinámico reversible, como ocurre con el calor reversible, admite un factor integrante. Damos ejemplos sencillos en los que el trabajo reversible admite un factor integrante, y ejemplos en los que el factor integrante no existe. También comentamos brevemente el significado, cuando existe, de dicho factor integrante.

The voltage sensitivity and the measurement uncertainty due to the finite resolution in multi-decade and slide wire DC Wheatstone bridges have been reviewed and analysed in detail. The use of the term `precision' is discussed, and a criterion for maximum resolution with minimum power dissipation is shown.

Resumen.Se examina en detalle la Sensibilidad (respecto del voltaje) y la incertidumbre de las mediciones debida a la resolución finita en el puente de Wheatstone de corriente continua de `hilo' y del tipo multi-década. Se discute el uso del término `precisión' y se muestra un criterio de máxima resolución con mínima disipación de potencia.

We review the thermodynamics of interference as developed by Max von Laue. Laue applied Planck's concept of electromagnetic entropy of radiation to the phenomenon of interference of light beams, and showed that the total entropy after interference decreases. This fact stood in sharp contrast to Planck's conclusion that whenever there is a splitting of a light beam the entropy must increase.

Zusammenfassung.Ein überblic über die Thermodynamik der Interferenz durch von Laue eingeführt, ist hier gegeben. Von Laue benutzte Planck's konzept der elektromagnetische Entropie um zu zeigen daß bei Interferenzerscheinungen von Lichtstrahlen die Gesamtentropie abnimmt! Diese Tatsache widerspricht ganz dem Planckschen Schluß, daß bei jeder Lichtstrahlaufspaltung die Entropie sich vermehrt.

An experiment on laser-induced fluorescence of the iodine dimer is reported. The experiment, meant for an advanced undergraduate physics laboratory, requires relatively simple and inexpensive apparatus yet it introduces students to essential laser spectroscopy methods. Observation of the molecular spectrum demonstrates basic principles of quantum mechanics. Molecular parameters such as bond length, force constant, anharmonicity of the interatomic potential etc may be obtained from the analysis of the data. Finer phenomena, such as intensity distribution of spectral lines or collisional energy transfer between rotational levels, can also be studied. Apparatus, specific results and various stages of data analysis are described in the paper.

Streszczenie (In Polish).Przedstawiamy doswiadczenie dotyczace badania widma czasteczki przez obserwacje fluorescencji wzbudzonej swiatlem laserowym. Doswiadczenie to, przeznaczone dla pracowni dydaktycznych, zapoznaje studentów z metodami spektroskopii laserowej, mimo ze wymaga stosunkowo prostej i taniej aparatury. Obserwowane widmo czasteczkowe unaocznia podstawowe zasady mechaniki kwantowej. Analiza wyników doswiadczenia pozwala wyznaczyc takie parametry czasteczki jak dlugosc wiazania, stala silowa, anharmonicznosc potencjalu czasteczkowego itd. Mozliwa jest tez obserwacja subtelniejszych zjawisk, takich jak rozklad natezen linii widmowych lub zderzeniowy przekaz energii wzbudzenia miedzy poziomami rotacyjnymi. Artyku przedstawia uklad doswiadczalny, przykladowe wyniki pomiarów oraz kolejne etapy analizy otrzymanych rezultatów.

The Casimir effect is presented through an easy analytically solvable problem in which the vacuum field energy changes in a prismatic constant volume cavity are calculated. The cubic cavity is found to be a stable form under the Casimir force.

Resumen.El efecto Casimir se aborda a través de un problema resoluble analí ticamente, en el cual se calculan los cambios de energía en una cavidad prismática deformable a volumen constante. La cavidad cúbica resulta ser estable bajo la fuerza de Casimir y, en ella se produce una transición de fase en el campo.

Using the method of multiple scales we derive the effective-mass equation for a particle in a perturbed periodic potential. This approach uses a single smallness parameter , the ratio between the lattice constant a and the length scale L over which typical variations in the perturbing potential take place.

Sammendrag.Via multiple-skala metoden utleder vi effektiv-masse likningen for en partikkel i et perturbert periodisk potensial. Denne metoden trenger kun én litenhetsparameter , der a er gitterkonstanten og L er lengdeskalaen for typiske variasjoner i det perturberende potensialet.

Starting from a single rod, and then a single conducting layer, into either of which a test charge is introduced, a straightforward method is presented for calculating the electrostatic potential due to the test charge outside the rod or the layer in question.

A relationship is then set up for the plasma frequency using a modification of a simple harmonic equation of motion describing small oscillations of the electron density around the ground-state value, for a three-dimensional (3D) electron gas. The Langmuir (plasma) frequency is the first term and a quadratic dispersion is exhibited. It is stressed that, on lowering the dimensionality to 2D and 1D, it is the Langmuir term that already contains the dispersion, the plasma frequency going to zero in the long wavelength limit.

To make the above quantitative, a relation is then displayed between plasma frequency and effective electron - electron interaction: a result valid from 1D to 3D. This is the basis for directly connecting plasmon dispersion with electrostatic potentials.

Riassunto.Si presenta anzitutto un metodo semplice per calcolare il potenziale elettrostatico esterno ad un filo conduttore o ad una lamina conduttrice nei quali sia stata inserita una carica di prova.

Un'espressione per la frequenza di plasma nel gas di elettroni in tre dimensioni (3D) è poi ottenuta da un'equazione che descrive piccole oscillazioni della densità elettronica attorno allo stato fondamentale. In tale espressione il primo termine è la frequenza di Langmuir e il secondo mostra dispersione quadratica. Il termine di Langmuir già contiene dispersione quando la dimensionalità si riduca a 2D o 1D.

Si mostra infine una relazione tra la frequenza di plasma e l'interazione elettrone - elettrone. Questa è valida anche in dimensionalità ridotta e permette una connessione diretta tra dispersione del plasmone e potenziali elettrostatici.

Volume 6 of The Collected Papers of Albert Einstein includes Einstein's writings during 1914 - 1917, his first three years in Berlin. Einstein moved to Berlin in April 1914 from Zurich where he had been a Professor at his old undergraduate school, The Federal Institute of Technology, since February 1912. In the spring of 1913, Max Planck and Walther Nernst journeyed from Berlin to visit Einstein in Zurich in order to make him an offer that, in the end, he could not refuse: a professorship with no teaching obligations and the directorship of the fledgling Kaiser Wilhelm Institute for Physics. Soon after their arrival in Berlin, the Einsteins separated. Mileva departed for Zurich with their sons Hans Albert and Eduard. At this point Einstein's relationship with his cousin Elsa Löwenthal deepened further. Thus, as the editors put so well, in the period covered in this volume, `Einstein's life and career entered a new phase'.

Amongst the key documents in Volume 6 are publications from 1914 in which Einstein concluded that gravitational field equations `cannot possibly be generally covariant'. After having realized his errors, Einstein returned to the theme of general covariance and, in 1915, published three papers in succession in which he developed the generalized theory of relativity. The third paper, published on 25 November 1915 and entitled `The Field Equations of Gravitation', is the capstone of the trio, correcting as it does errors in the previous two. A week prior to its publication Einstein published a result of his new theory: the calculation from the new generally covariant field equations of Mercury's perihelion motion of 43 seconds of arc per century, in agreement with observation. Some time later, Einstein told his former collaborator Adriaan Fokker that upon seeing the result emerge he had heart palpitations. On 8 February 1917 Einstein essentially started the field of modern cosmology with the publication of `Cosmological Considerations in the General Theory of Relativity'. One of the many points of interest in this pioneering paper is Einstein's modification of his field equations with the so-called `cosmological constant' in order to incorporate, as best he could, Machian ideas on effects of distant rotating masses.

Besides tidying up general relativity theory with his review paper of 1916, Einstein made new and far reaching contributions to the quantum theory of radiation. In two papers of 1916 he published his A and B coefficients and went on to conclude that atoms need not emit radiation in spherical waves, but in light quanta with a specific direction and definite momentum. The presence of probability in this theory was to Einstein a `weakness'.

The eclectic set of publications in Volume 6 include ones on molecular currents in magnets, book reviews, contributions to Bohr's atomic theory and statements on the war, as well as documents relating to Einstein's participation as an expert witness in a patent dispute between the German firm Anschütz & Co. and the American Sperry Gyroscope Company. In the end the court chose to follow the former patent clerk's report and decided to prohibit Sperry Gyroscope from manufacturing gyrocompasses that incorporated methods patented by Anschütz.

In summary there is something for everyone in this fascinating collection of papers published by Einstein during 1914 - 1917 and assembled in what we have come to expect as a meticulous scholarly presentation replete with an up to date listing of secondary studies and informative footnotes. We eagerly await further volumes of this truly historic project.

Dear Reader,

During the past year European Journal of Physics gained the subtitle `The European voice of physics teachers in higher education'. I believe that this subtitle will be of great value in giving the right impression of the journal. The subtitle will very clearly inform readers and future authors that the journal is not intended for basic research articles but scholarly studies of interest to physics teachers in university education.

Some examples of papers recently published in the journal can be observed from the electronic journal's home page on the IOPP WWW server (http://www.iop.org); these articles will be updated approximately every three months.

An analysis of submissions to European Journal of Physics indicates that an average of around 20 papers and 2 or 3 communications (short items) are received every month, while the acceptance rate is reasonably constant at about one third of this. High proportions of articles received during 1995 originated from the USA, South America and Spain, but acceptances were more widely spread. The subtitle of the journal and the examples of good papers freely available electronically on the IOPP WWW server will, we hope, be of great assistance in improving the acceptance rate of papers of interest to teachers in physics higher education.

In the Editorial at the start of 1996 I gave details of the intention of the Editorial Board to produce a special issue on the theme of the centenary of the discovery of the electron. However, we have discovered that it can be difficult to find authors for enough papers to fill a whole issue on one topic, so the special papers will appear as a feature in a regular journal issue in 1997 instead. The idea of publishing special issues will not be lost, however, and many new proposals have been put forward:

• the acoustics of musical instruments (perhaps in the form of `mini-reviews' of different instruments),

• astronomy education,

• explanations of complicated physics issues (advanced topics in four-year courses),

• large scale quantum effects,

• melting, both in the context of liquids and of solids,

• neural networks,

• solid state physics, especially of semiconductors,

• unresolved problems in physics (such as were outlined in Physics World September 1996).

The refereeing process for the journal is very important and all members of the Editorial Board are involved. Due to the limited resources available for rewriting articles submitted in poor English, we must ask all our authors to have their papers checked thoroughly before despatching them to the Editorial Office. Articles should additionally fulfil the requirements laid down by the journal's subtitle, and should not contain too specialized a content or be uninteresting. However, papers dealing in a more general way with new research may be accepted if the physics involved has already been accepted by the physics community.

We look forward to receiving your contributions to the journal in the coming months, therefore.

With best wishes

Lennart Samuelsson