Relativistic eikonal approximation in high-energy A(e,e'p) reactions

A fully relativistic model for the description of exclusive (e,e'p) reactions off nuclear targets at high energies and momentum transfers is outlined. It is based on the eikonal approximation for the ejectile scattering wave function and a relativistic mean-field approximation to the Walecka model. Results for ^{12}C(e,e'p) and ^{16}O(e,e'p) differential cross sections and separated structure functions are presented for four-momenta in the range 0.8 \leq Q^{2} \leq 20 (GeV/c)^{2}. The regions of applicability of the eikonal approximation are studied and observed to be confined to proton knockout in a relatively small cone about the momentum transfer. A simple criterium defining the boundaries of this cone is determined. The Q^2 dependence of the effect of off-shell ambiguities on the different (e,e'p) structure functions is addressed. At sufficiently high values of Q^2 their impact on the cross sections is illustrated to become practically negligible. It is pointed out that for the whole range of Q^2 values studied here, the bulk of the relativistic effects arising from the coupling between the lower components in the wave functions, is manifesting itself in the longitudinal-transverse interference term.Comment: 13 pages,11 figure

Bridging Two Ways of Describing Final-State Interactions in A(e,e'p) Reactions

We outline a relativistic and unfactorized framework to treat the final-state interactions in quasi-elastic A(e,e'p) reactions for four-momentum transfers Q$^{2} \gtrsim 0.3$ (GeV/c)$^{2}$. The model, which relies on the eikonal approximation, can be used in combination with optical potentials, as well as with the Glauber multiple-scattering method. We argue that such a model can bridge the gap between a typical ``low'' and ``high-energy'' description of final-state interactions, in a reasonably smooth fashion. This argument is made on the basis of calculated structure functions, polarization observables and nuclear transparencies for the target nuclei $^{12}$C and $^{16}$O.Comment: revised versio

Impact of lens distrortions on strain measurements obtained with digital image correlation

The determination of strain fields based on displacements obtained via DIC at the micro-strain level is still a cumbersome task. In particular when high-strain gradients are involved, e.g. in composite materials with multidirectional fibre reinforcement, uncertainties in the experimental setup and errors in the derivation of the displacement fields can substantially hamper the strain identification process. In this contribution, the aim is to investigate the impact of lens distortions on strain measurements. To this purpose, we first perform pure rigid body motion experiments, revealing the importance of precise correction of lens distortions. Next, a uni-axial tensile test on a textile composite with spatially varying high strain gradients is performed, resulting in very accurate determined strains along the fibers of the materia

Persistent neuronal Ube3a expression in the suprachiasmatic nucleus of Angelman syndrome model mice

Mutations or deletions of the maternal allele of the UBE3A gene cause Angelman syndrome (AS), a severe neurodevelopmental disorder. The paternal UBE3A/Ube3a allele becomes epigenetically silenced in most neurons during postnatal development in humans and mice; hence, loss of the maternal allele largely eliminates neuronal expression of UBE3A protein. However, recent studies suggest that paternal Ube3a may escape silencing in certain neuron populations, allowing for persistent expression of paternal UBE3A protein. Here we extend evidence in AS model mice (Ube3am–/p+) of paternal UBE3A expression within the suprachiasmatic nucleus (SCN), the master circadian pacemaker. Paternal UBE3A-positive cells in the SCN show partial colocalization with the neuropeptide arginine vasopressin (AVP) and clock proteins (PER2 and BMAL1), supporting that paternal UBE3A expression in the SCN is often of neuronal origin. Paternal UBE3A also partially colocalizes with a marker of neural progenitors, SOX2, implying that relaxed or incomplete imprinting of paternal Ube3a reflects an overall immature molecular phenotype. Our findings highlight the complexity of Ube3a imprinting in the brain and illuminate a subpopulation of SCN neurons as a focal point for future studies aimed at understanding the mechanisms of Ube3a imprinting

The role of hyperon resonances in p(gamma,K+)Lambda processes

We discuss the role of hyperon resonances in the u-channel when modeling p (gamma,K+)Lambda processes in an effective Lagrangian approach. Without the introduction of hyperon resonances, one is forced to use soft hadronic form factors with a cutoff mass which is at best two times the kaon mass. After inclusion of the hyperon resonances in the u-channel, we obtain a fair description of the data with a cutoff mass of the order of 1.8 GeV.Comment: 7 pages, 7 eps figures, submitted to Eur. Phys. J.

Comparison of organic and conventional dairy farm economic and environmental performances throughout North West Europe

From an environmental point of view, organic farming (OF) systems have been identified as beneficial thanks to a system allowing fewer losses of nitrogen (N) per ha and lower green house gases (GHG) emissions per ha and per ton of milk (TM). From an economic point of view, milk coming from these OF systems is sold at a higher prize. However, incomes provided by both systems are similar (for similar amount of milk produced). This may be explained by higher input costs per unit of product for OF systems and by more incomes coming from sold crops for conventional farming (CF) systems. Therefore, on the one hand CF systems may improve their environmental performances by reducing the amount of inputs brought into the system, for example through a better forage and fertilisation management. On the other hand, the valorisation of milk through a differentiated production or market (price premium due to a label and/or on-farm transformation and/or sale) may bring them higher incomes. OF system may increase their incomes by selling one cash crop destined for human consumption and by finding the good balance between intensivity and extensivity in order to better valorise the inputs brought into the system

Kaon photoproduction: background contributions, form factors and missing resonances

The photoproduction p(gamma, K+)Lambda process is studied within a field-theoretic approach. It is shown that the background contributions constitute an important part of the reaction dynamics. We compare predictions obtained with three plausible techniques for dealing with these background contributions. It appears that the extracted resonance parameters drastically depend on the applied technique. We investigate the implications of the corrections to the functional form of the hadronic form factor in the contact term, recently suggested by Davidson and Workman (Phys. Rev. C 63, 025210). The role of background contributions and hadronic form factors for the identification of the quantum numbers of ``missing'' resonances is discussed.Comment: 11 pages, 7 eps figures, submitted to Phys. Rev.