EDDINGTON'S “Internal Constitution of the Stars” was published in 1926 and gives what now ranks as a classical account of his own researches and of the general state of the theory at that time. Since then, a tremendous amount of work has appeared. Much of it has to do with the construction of stellar models with different equations of state applying in different zones. Other parts deal with the effects of varying chemical composition, with pulsation and tidal and rotational distortion of stars, and with the precise relations between the interior and the atmosphere of a star. The striking feature of all this work is that so much can be done without assuming any particular mechanism of stellar energy-generation. Only such very comprehensive assumptions are made about the distribution and behaviour of the energy sources that we may expect future knowledge of their mechanism to lead mainly to more detailed results within the framework of the existing general theory. An Introduction to the Study of Stellar Structure By S. Chandrasekhar. (Astrophysical Monographs sponsored by The Astrophysical Journal.) Pp. ix+509. (Chicago: University of Chicago Press; London: Cambridge University Press, 1939.) 50s. net.

An Introduction to the Study of Stellar Structure

It is a fundamental assumption of statistical mechanics that a closed system with many degrees of freedom ergodically samples all equal energy points in phase space. To understand the limits of this assumption, it is important to find and study systems that are not ergodic, and thus do not reach thermal equilibrium. A few complex systems have been proposed that are expected not to thermalize because their dynamics are integrable. Some nearly integrable systems of many particles have been studied numerically, and shown not to ergodically sample phase space. However, there has been no experimental demonstration of such a system with many degrees of freedom that does not approach thermal equilibrium. Here we report the preparation of out-of-equilibrium arrays of trapped one-dimensional (1D) Bose gases, each containing from 40 to 250 (87)Rb atoms, which do not noticeably equilibrate even after thousands of collisions. Our results are probably explainable by the well-known fact that a homogeneous 1D Bose gas with point-like collisional interactions is integrable. Until now, however, the time evolution of out-of-equilibrium 1D Bose gases has been a theoretically unsettled issue, as practical factors such as harmonic trapping and imperfectly point-like interactions may compromise integrability. The absence of damping in 1D Bose gases may lead to potential applications in force sensing and atom interferometry.

A quantum Newton's cradle

J. M. Ziman London: Cambridge University Press. 1964. Pp. 360. Price 45s. This book is essentially an account of the consequences of the lattice periodicity in solids. Much of the ground was well tilled in the author's treatise Electrons and Phonons (Oxford: The Clarendon Press, 1962) but, as a textbook, the new work covers a larger area while being less rigorous.

http://iopscience.iop.org/article/10.1088/0031-9112/16/7/012/pdf

Principles of the Theory of Solids

It is a fundamental assumption of statistical mechanics that a closed system with many degrees of freedom ergodically samples all equal energy points in phase space. To understand the limits of this assumption, it is important to find and study systems that are not ergodic, and thus do not reach thermal equilibrium. A few complex systems have been proposed that are expected not to thermalize because their dynamics are integrable. Some nearly integrable systems of many particles have been studied numerically, and shown not to ergodically sample phase space. However, there has been no experimental demonstration of such a system with many degrees of freedom that does not approach thermal equilibrium. Here we report the preparation of out-of-equilibrium arrays of trapped one-dimensional (1D) Bose gases, each containing from 40 to 250 87Rb atoms, which do not noticeably equilibrate even after thousands of collisions. Our results are probably explainable by the well-known fact that a homogeneous 1D Bose gas with point-like collisional interactions is integrable. Until now, however, the time evolution of out-of-equilibrium 1D Bose gases has been a theoretically unsettled issue, as practical factors such as harmonic trapping and imperfectly point-like interactions may compromise integrability. The absence of damping in 1D Bose gases may lead to potential applications in force sensing and atom interferometry.

http://absimage.aps.org/image/DAMOP06/MWS_DAMOP06-2006-000603.pdf

Translational motion in solution, either diffusion or fluid flow, is at the heart of chemical and biochemical reactivity. Nuclear Magnetic Resonance (NMR) provides a powerful non-invasive technique for studying the phenomena using magnetic field gradient methods. Describing the physical basis of measurement techniques, with particular emphasis on diffusion, balancing theory with experimental observations and assuming little mathematical knowledge, this is a strong, yet accessible, introduction to the field. A detailed discussion of magnetic field gradient methods applied to Magnetic Resonance Imaging (MRI) is included, alongside extensive referencing throughout, providing a timely, definitive book to the subject, ideal for researchers in the fields of physics, chemistry and biology.

/pdf/nmr-studies-of-translational-motion-1y45lcz4az.pdf

NMR Studies of Translational Motion

The chemical potential is a quantity for which students hardly have an intuitive feeling in contrast to other intensive quantities like pressure or temperature. Some students may believe that this is not really an insufficiency because the chemical potential seems to be essentially a quantity for chemists. We will try to show that the chemical potential does not merit its reputation as a difficult to understand quantity. Not only is it easy to grasp, it is a particularly intelligible quantity for which even the layman can develop a feeling. Moreover, this quantity is not only important for chemists. It is just as useful for describing physical phenomena and processes, such as phase transitions, the stratification of gases in a gravitational field and electric currents in semi-conductor junctions and nuclear reactions, to mention just a few.

/pdf/chemical-potential-a-quantity-in-search-of-recognition-2umbrh78ip.pdf

Chemical potential—a quantity in search of recognition

The Karlsruhe Physics Course is an attempt to modernize the physics syllabus by eliminating obsolete concepts, restructuring the contents and extensively applying a new model, the substance model. The course has been used, tested and improved for several years, and we believe that the time has come to make it known to a wider public. We introduce the structure which underlies the course and discuss some consequences for the teaching of various subfields of physics.

https://iopscience.iop.org/article/10.1088/0143-0807/21/1/308/pdf

The Karlsruhe Physics Course

Pictures of the energy density and the energy flow in distributions of incoherent light for various two-dimensional situations are shown and discussed. Rules are introduced that allow one to sketch and to interpret such pictures.

Which way does the light go

“What is heat?” was the title of a 1954 article by Freeman J. Dyson, published in Scientific American. Apparently, it was appropriate to ask this question at that time. The answer is given in the very first sentence of the article: heat is disordered energy. We will ask the same question again, but with a different expectation for its answer. Let us imagine that all the thermodynamic knowledge is already available: both the theory of phenomenological thermodynamics and that of statistical thermodynamics, including quantum statistics, but that the term “heat” has not yet been attributed to any of the variables of the theory. With the question “What is heat?” we now mean: which of the physical quantities deserves this name? There are several candidates: the quantities Q, H, Etherm and S. We can then formulate a desideratum, or a profile: What properties should such a measure of the quantity or amount of heat ideally have? Then, we evaluate all the candidates for their suitability. It turns out that the winner is the quantity S, which we know by the name of entropy. In the second part of the paper, we examine why entropy has not succeeded in establishing itself as a measure for the amount of heat, and we show that there is a real chance today to make up for what was missed.

Which Physical Quantity Deserves the Name “Quantity of Heat”?

The Poynting vector field of a transformer with two separated coils and long, parallel arms has the same distribution as that of a pair of parallel electric conductors. The magnetic field between the arms of a transformer plays the same important role for the energy transport in a transformer as does the electric field for the transport of energy between the conductors of a conductor pair. In the latter case, the energy current (=power) P is given by the familiar expression P=UI, where U  is the electric tension between the conductors and I the electric charge current through them. In the former case, we find an analogous expression P=UmIm for the energy current in a transformer. Here Um is the magnetic tension Um=∫ dr H between the arms of the transformer (H=magnetic field vector) and Im=−∫ dA B is the Hertz magnetic current (B=the time derivative of the magnetic induction B) through them. An experiment will be described which shows that the energy loss in a transformer is related to a magnetic potenti...

The Poynting vector field and the energy flow within a transformer

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