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

Modelling selective activation of small myelinated nerve fibres using a monopolar point electrode

The aim of this study is to investigate theoretically the possibility for activation of small myelinated nerve fibres without activating larger ones when stimulating a nerve fibre bundle using a monopolar point electrode. Therefore, the sensitivity of excitation and blocking threshold currents of nerve fibres to fibre diameter, electrode-fibre distance and pulse duration has been simulated by a computer model. A simple infinite, homogeneous volume conductor and a cathodal point source were used in combination with a model representing the electrical properties of a myelinated nerve fibre. The results show that selective activation of small myelinated fibres may be possible in a region at some distance from the electrode

Campylobacter cuniculorum sp nov., from rabbits

Eight strains of an unknown thermotolerant Campylobacter species were isolated from the caecal contents of rabbits (Oryctolagus cuniculus). All strains were initially identified as belonging to the genus Campylobacter by means of genus-specific PCR, but none were identified using species-specific PCR for known thermophilic species. Cells were spiral shaped with bipolar unsheathed flagella, with no periplasmic fibres, and appeared coccoid after 10-12 days of incubation. Phylogenetic analyses based on 16S rRNA gene, rpoB and groEL sequences revealed that all strains formed a robust clade that was very distinct from recognized Campylobacter species. 16S rRNA gene sequence pairwise comparisons of strain 150B(T) with the type strains of other Campylobacter species revealed that the nearest phylogenetic neighbour was Campylobacter helveticus NCTC 12470(T), with 96.6% similarity. The uniqueness of these rabbit isolates was confirmed by whole-cell protein electrophoresis. Taken together, these data indicate that the strains belong to a novel Campylobacter species for which the name Campylobacter cuniculorum sp. nov. is proposed, with 150B(T) (=LMG 24588(T) =CCUG 56289(T)) as the type strain

Nuclear transparencies in relativistic A(e,e'p) models

Relativistic and unfactorized calculations for the nuclear transparency extracted from exclusive A(e,e'p) reactions for 0.3 \leq Q^2 \leq 10 (GeV/c)^2 are presented for the target nuclei C, Si, Fe and Pb. For Q^2 \geq 0.6 (GeV/c)^2, the transparency results are computed within the framework of the recently developed relativistic multiple-scattering Glauber approximation (RMSGA). The target-mass and Q^2 dependence of the RMSGA predictions are compared with relativistic distorted-wave impulse approximation (RDWIA) calculations. Despite the very different model assumptions underlying the treatment of the final-state interactions in the RMSGA and RDWIA frameworks, they predict comparable nuclear transparencies for kinematic regimes where both models are applicable.Comment: 15 pages, 4 figure

A Framework for Decision-based Consistencies

International audienceConsistencies are properties of constraint networks that can be enforced by appropriate algorithms to reduce the size of the search space to be explored. Recently, many consistencies built upon taking decisions (most often, variable assignments) and stronger than (general- ized) arc consistency have been introduced. In this paper, our ambition is to present a clear picture of decision-based consistencies. We identify four general classes (or levels) of decision-based consistencies, denoted by S∆φ, E∆φ, B∆φ and D∆φ, study their relationships, and show that known consistencies are particular cases of these classes. Interestingly, this gen- eral framework provides us with a better insight into decision-based con- sistencies, and allows us to derive many new consistencies that can be directly integrated and compared with other ones

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