Photon beam asymmetry Sigma for eta and eta ' photoproduction from the proton

Measurements of the linearly-polarized photon beam asymmetry $\Sigma$ for photoproduction from the proton of $\eta$ and $\eta^\prime$ mesons are reported. A linearly-polarized tagged photon beam produced by coherent bremsstrahlung was incident on a cryogenic hydrogen target within the CEBAF Large Acceptance Spectrometer. Results are presented for the $\gamma p \to \eta p$ reaction for incident photon energies from 1.070 to 1.876 GeV, and from 1.516 to 1.836 GeV for the $\gamma p \to \eta^\prime p$ reaction. For $\gamma p \to \eta p$, the data reported here considerably extend the range of measurements to higher energies, and are consistent with the few previously published measurements for this observable near threshold. For $\gamma p \to \eta^\prime p$, the results obtained are consistent with the few previously published measurements for this observable near threshold, but also greatly expand the incident photon energy coverage for that reaction. Initial analysis of the data reported here with the Bonn-Gatchina model strengthens the evidence for four nucleon resonances -- the $N(1895)1/2^-$, $N(1900)3/2^+$, $N(2100)1/2^+$ and $N(2120)3/2^-$ resonances -- which presently lack the "four-star" status in the current Particle Data Group compilation, providing examples of how these new measurements help refine models of the photoproduction process.Comment: 10 pages, 3 figure

On molecular modelling and continuum concepts

Continuum concepts and field values are related to local (scale-dependent) spacetime atomistic averages. Spatial averaging is effected by both weighting function and cellular localisation procedures, and resulting forms of linear momentum balance are compared. The former yields a local balance directly, with several candidate interaction stress fields. The latter results in a global balance involving a traction field expressible in terms of an interaction stress tensor field. In both approaches the Cauchy stress incorporates distinct interaction and thermokinetic contributions. Inter alia are addressed physically-distinguished choices of weighting function; the scale-dependence of the boundary of a body, its motion and material points thereof; physical interpretations of various candidate interaction stress tensors; temporal averaging and material systems whose content changes with time; and the possible relevance of the latter to investigating a molecular context for configurational forces

Some fundamental aspects of surface modelling

Attention is drawn to four aspects of surface modelling: (1) delineation of the (scale-dependent) geometrical boundary of a body via molecular considerations, (2) identification of the highly inhomogeneous interfacial region between a body and its exterior, and its modelling as a bidimensional continuum involving interfacial excess quantities, (3) the utility of co-ordinate-free notation for surfaces, and (4) the importance of surface effects for small-scale bodies exemplified within a thermoelastic context

On the identification of continuum concepts and fields with molecular variables

The need to explore a molecular foundation for continuum mechanics is here motivated by recognition of the scale dependence of mass density and boundaries of solid bodies. Modelling molecules as interacting point masses, continuum fields are defined via local spatial averaging using a scale-dependent weighting function. Local balances of linear and angular momentum, and of energy, are established directly, rather than as localised versions of integral relations. Attention is drawn to the non-uniqueness of stress, couple-stress, and heat flux, and to the physical interpretations thereof. A conservation relation for a local measure of inhomogeneity is derived and related to generalised (i.e. tensor valued) moment of momentum. Remarks are made on the scale dependence of the notions of ‘material point’ and ‘boundary’, choices of weighting function, and how further temporal averaging can be implemented, with particular reference to systems whose molecular content changes with time

Fluid flow in porous media: continuum modelling based upon microscopic considerations

The main objective of the course was to provide the participants with fundamental knowledge in the field of modelling of coupled physical phenomena in saturated porous materials. The problems of upscaling, continual description of flow and transport, and coupled poroelastic processesin saturaetd porous media have been discussed. In addition experimental methods useful in studies of basic structural and mechanical properties of porous materials were introduced and presented. The course was dedicated to Ph.D. students and young researchers working in different areas of applications of models of porous media including biomechanics, civil and environmental engineering, earth science, engineering of materials, etc

On criticism of the nature of objectivity in classical continuum physics

Murdoch (J. Elasticity 60, 233-242, 2000) showed that restrictions imposed upon response functions by material frame-indifference are the consequences of five distinct aspects of observer agreement (that is, of objectivity) and involve only proper orthogonal tensors. Accordingly it is unnecessary to invoke the principle of invariance under superposed rigid motions (in the sense of one observer, two motions), which imposes a restriction upon nature. Liu (Continuum Mech. Thermodyn. 16, 177-183, 2003, and Continuum Mech. Thermodyn. 17, 125-133, 2005) has challenged, misinterpreted and misrepresented the content of both Murdochs work and this work. Here all criticisms of Liu are answered, his counter-examples are used to amplify the tenets of Murdochs work, and a key modelling issue in the controversy is indicated. Further, the response function restrictions for a given observer, derived on the basis of considering other observers, are shown to be independent of possible differences in the scales of mass, length, and time employed by other observers

Foundations of continuum modelling: a microscopic perspective with applications

This book contains Lectures on Continuum Mechanics with emphasis on its physical and mathematical foundations. The lectures are directed towards anyone who wishes to understand fundamental assumptions implicit in the continuum modelling of physical phenomena, and are intended to be of interest to mathematicians, physicists, and engineers

Objectivity in classical continuum physics : a rationale for discarding the 'principle of invariance under superposed rigid body motions' in favour of purely objective considerations

Individual aspects of observer consensus are discussed in the context of classical continuum physics. These are shown to be sufficient to mandate standard restrictions upon response functions employed in constitutive relations by any given observer. No a priori assumption is made that observers should employ the same response functions, and restrictions are shown to involve only proper orthogonal tensors. Since the 'principle of material invariance under superposed rigid motions' (interpreted in the sense of 'one observer, two motions') is not needed to establish such restrictions, and imposes a requirement upon Nature that kinetic theory has shown to be questionable, this 'principle' serves no useful purpose and should be discarded