An alternative approach to analyze the nonrelativistic quantum dynamics of a rigid and extended charged particle taking into account the radiation reaction is discussed with detail. Interpretation of the field operators as annihilation and creation ones, theory of perturbations and renormalization are not used. The analysis is carried out in the Heisenberg picture with the electromagnetic field expanded in a complete orthogonal basis set of functions which allows the electromagnetic field to satisfy arbitrary boundary conditions. The corresponding coefficients are the (...) field operators which satisfy the usual commutation relations. A nonlinear equation of motion for the charged particle is obtained. A careful consideration of the quantum effects allows the derivation of a linear equation of motion which is free of both runaway solutions and preacceleration, even for a point charge. Also, the electromagnetic mass, which is defined as the coefficient of the acceleration operator, vanishes for a point particle. However, this does not mean that the results are free of ambiguities which are exhibited and discussed. (shrink)

In this paper the analysis of the classical dynamics of a charged particle is carried out without considering that the electromagnetic field necessarily goes to zero at infinity. A quite general non-linear equation of motion is obtained for an extended charged particle valid for any distribution of charge in the particle and for an electromagnetic field satisfying any boundary conditions. Some common approximations are analyzed with detail to determine how the usual difficulties arise.

In order to understand the rise of runaway solutions in the radiation reaction problem a mechanical model is used. An alternative demonstration of Daboul’s theorem, through Hurwitz’s criterion, is given. The origin of runaway solutions in electrodynamics is discussed. They arise when the particle has a negative mechanical mass or when approximations are used in the equation of motion. In the 1-dimensional mechanical model an exact and linear equation of motion for the particle is obtained, the corresponding exact solution is (...) again runaway when the mechanical mass is negative. The exact solution is not runaway when the mechanical mass is positive. However, the use of approximations leads to an equation of motion which has runaway solutions. It is exhibited that the use of approximations in the 3-dimensional mechanical model is completely necessary because the general equation of motion for the particle is non-linear. The analysis of this case proceeds in a very similar way to the one carried out in electrodynamics. This means that the number of dimensions also plays an important role in the analysis. (shrink)

A new translation of the Pensées, presented here in the order of the Copy made by Pascal's literary executors, which is the order in which Pascal left them. Since Pascal never did complete the job of ordering and classifying, it does not follow, as the cover of the book insinuates, that this edition enables us to appreciate the workings of Pascal's mind better than others, which are marred by the intrusions of editors. Krailsheimer also translates fragments not found in the (...) Copy, including those recently discovered by Mesnard. The translation is a good one, and a definite improvement over other paperback editions.—A. E. J. (shrink)

Shoemaker's book can be divided into two main sections; the first five chapters, which consist of somewhat tedious criticisms of some classical and semi-classical positions, and Chapter Six, "How is Self-Knowledge Possible?" Of particular interest in the latter are his claims that we have non-criterial knowledge of personal identity and that "sincere and confident perceptual and memory statements" are necessarily generally true. The book is an outgrowth of Shoemaker's doctoral dissertation and retains a dissertorial style. The influence of Malcolm is (...) evident throughout.—A. E. J. (shrink)

Garnett attempts to defend realism while accepting much of what sense-data theorist have had to say. He does this by tracing the origin of our belief in external objects to the finding of "centres of resistance" in the experience of effort and resistance, these centres being symbolized by sensory qualia. Since the centres are found in experience they are not unknowable Lockean substances, and since the resistance is something over and above sensations of pressure they are not phenomenalistic patterns of (...) sense-data. Though a great deal of the book is devoted to the "refutation" of particular arguments of Ryle and Austin, Garnett seems oblivious to the thrust of recent criticism of traditional accounts of the role of sense qualia in perception. All too often he allows assertion to replace argument.—A. E. J. (shrink)

Objectives To evaluate whether the requirement of “minimal risk and burden” for paediatric research without direct benefit to the subjects compromises the ability to obtain data necessary for improving paediatric care. To provide evidence-based reflections on the EU recommendation that allows for a higher level of risk. Design and setting Systematic analysis of the approval/rejection decisions made by the Dutch Central Committee on Research involving Human Subjects (CCMO). Review methods The analysis included 165 proposals for paediatric research without direct benefit (...) that were reviewed by the CCMO between January, 2000, and July, 2007. A separate, in-depth analysis of all drug studies included 18 early phase drug studies and nine other drug studies without direct benefit. Results 11 out of 165 studies were definitively rejected because the CCMO did not regard the risk and/or burden to be minimal. In three of these 11 cases (including two early phase drug studies) the requirement of minimal risk and burden was cited as the only reason for rejection. Four other early phase drug studies also involved risks and/or burdens that were not regarded to be minimal but were nevertheless approved. Conclusions The requirement of minimal risk and burden, aiming to protect research subjects, occasionally leads to rejection of protocols. Early phase drug studies relatively often do not comply with the requirement. Committees may find ways to approve important studies that formally should be rejected, but that is not a desirable solution. The regulatory framework should be revised to make such occasional exceptions to the requirement legitimate and transparent. (shrink)

It's an achievement of the last couple of decades that people who work in linguistic semantics and people who work in the philosophy of language have arrived at a friendly, de facto agreement as to their respective job descriptions. The terms of this agreement are that the semanticists do the work and the philosophers do the worrying. The semanticists try to construct actual theories of meaning (or truth theories, or model theories, or whatever) for one or another kind of expression (...) in one or another natural language; for example, they try to figure out how the temperature could be rising compatibly with the substitutivity of identicals. The philosophers, by contrast, keep an eye on the large, foundational issues, such as: what's the relation between sense and denotation; what's the relation between thought and language; whether translation is determinate; and whether life is like a fountain. Every now and then the philosophers and the semanticists are supposed to get together and compare notes on their respective progress. Or lack thereof. (shrink)

We examine “de Broglie-Bohm” causal trajectories for the two electrons in a nonrelativistic helium atom, taking into account the spin-dependent momentum terms that arise from the Pauli current. Given that this many-body problem is not exactly solvable, we examine approximations to various helium eigenstates provided by a low-dimensional basis comprised of tensor products of one-particle hydrogenic eigenstates.First to be considered are the simplest approximations to the ground and first-excited electronic states found in every introductory quantum mechanics textbook. For example, the (...) trajectories associated with the simple 1s(1)1s(2) approximation to the ground state are, to say the least, nontrivial and nonclassical.We then examine higher-dimensional approximations, i.e., eigenstates Ψ α of the Hamiltonian in this truncated basis, and show that ∇ i S α =0 for both particles, implying that only the spin-dependent momentum term contributes to electronic motion. This result is independent of the size of the truncated basis set, implying that the qualitative features of the trajectories will be the same, regardless of the accuracy of the eigenfunction approximation.The electronic motion associated with these eigenstates is quite specialized due to the condition that the spins of the two electrons comprise a two-spin eigenfunction of the total spin operator. The electrons either (i) remain stationary or (ii) execute circular orbits around the z-axis with constant velocity. (shrink)

Tom Andersen’s reflecting team process, which allowed families to witness and respond to the talk of professionals during therapy sessions, has been described as revolutionary in the field of family therapy. Reflecting teams are prominent in a number of family therapy approaches, more recently in narrative and dialogical therapies. This way of working is considered more a philosophy than a technique, and has been received positively by both therapists and service users. This paper describes how dialogical therapists conceptualise the reflective (...) process, how they work to engage families in reflective dialogues and how this supports change. We conducted semi-structured, reflective interviews with 12 dialogical therapists with between 2 and 20 years of experience. Interpretative Phenomenological analysis of transcribed interviews identified varying conceptualisations of the reflecting process and descriptions of therapist actions that support reflective talk among network members. We adopted a dialogical approach to interpretation of this data. In this sense, we did not aim to condense accounts into consensus but instead to describe variations and new ways of understanding dialogical reflecting team practices. Four themes were identified: Lived experience as expertise; Listening to the self and hearing others; Relational responsiveness and fostering connection; and Opening space for something new. We applied these themes to psychotherapy process literature both within family therapy literature and more broadly to understand more about how reflecting teams promote helpful and healing conversations in practice. (shrink)

The essays collected together in this volume, many of them written by leading scholars in the field, explore the commonsensical fact that our presence as..

Graph polynomials are graph parameters invariant under graph isomorphisms which take values in a polynomial ring with a fixed finite number of indeterminates. We study graph polynomials from a model theoretic point of view. In this paper we distinguish between the graph theoretic (semantic) and the algebraic (syntactic) meaning of graph polynomials. Graph polynomials appear in the literature either as generating functions, as generalized chromatic polynomials, or as polynomials derived via determinants of adjacency or Laplacian matrices. We show that these (...) forms are mutually incomparable, and propose a unified framework based on definability in Second Order Logic. We show that this comprises virtually all examples of graph polynomials with a fixed finite set of indeterminates. Finally we show that the location of zeros and stability of graph polynomials is not a semantic property. The paper emphasizes a model theoretic view. It gives a unified exposition of classical results in algebraic combinatorics together with new and some of our previously obtained results scattered in the graph theoretic literature. (shrink)

The diffusion of technology in the US has taken place in an environment of both regulation and free enterprise. Each has been subject to manipulation by doctors and medical administrators that has fostered unprecedented ethical dilemmas and legal challenges. Understanding these developments and historical precedents may allow a more rational diffusion policy for medical technology in the future.