Induced Nucleon Polarization and Meson-Exchange Currents in (e,e'p) Reactions

Nucleon recoil polarization observables in $(e,e'\vec{p})$ reactions are investigated using a semi-relativistic distorted-wave model which includes one- and two-body currents with relativistic corrections. Results for the induced polarization asymmetry are shown for closed-shell nuclei and a comparison with available experimental data for $^{12}$C is provided. A careful analysis of meson exchange currents shows that they may affect significantly the induced polarization for high missing momentum.Comment: 7 pages, 9 figures. Revised version with small changes, new curve in Fig. 3. To be published in PR

Spin-orbit final state interaction in the framework of Glauber theory for (e,e'p) reactions

We investigate the reactions D(e,e'p)n and D(\vec e,e'p)n at GeV energies and discuss the opportunities to distinguish between different models for the nuclear ground state by measuring the response functions. In calculating the final-state interaction (FSI) we employ Glauber theory, and we also include relativistic effects in the electromagnetic current. We include not only the central FSI, but also the spin-orbit FSI which is usually neglected in (e,e'p) calculations within the Glauber framework and we show that this contribution plays a crucial role for the fifth response function. All of the methods developed here can be applied to any target nucleus.Comment: 20 pages, 12 figures, minor change in figures 3 and 4 (changed beam energy), correction of error in figure 4 in the previous replacemen

Meson Exchange Currents in (e,e'p) recoil polarization observables

A study of the effects of meson-exchange currents and isobar configurations in $A(\vec{e},e'\vec{p})B$ reactions is presented. We use a distorted wave impulse approximation (DWIA) model where final-state interactions are treated through a phenomenological optical potential. The model includes relativistic corrections in the kinematics and in the electromagnetic one- and two-body currents. The full set of polarized response functions is analyzed, as well as the transferred polarization asymmetry. Results are presented for proton knock-out from closed-shell nuclei, for moderate to high momentum transfer.Comment: 44 pages, 18 figures. Added physical arguments explaining the dominance of OB over MEC, and a summary of differences with previous MEC calculations. To be published in PR

A review of diagnostic and functional imaging in headache

The neuroimaging of headache patients has revolutionised our understanding of the pathophysiology of primary headaches and provided unique insights into these syndromes. Modern imaging studies point, together with the clinical picture, towards a central triggering cause. The early functional imaging work using positron emission tomography shed light on the genesis of some syndromes, and has recently been refined, implying that the observed activation in migraine (brainstem) and in several trigeminal-autonomic headaches (hypothalamic grey) is involved in the pain process in either a permissive or triggering manner rather than simply as a response to first-division nociception per se. Using the advanced method of voxel-based morphometry, it has been suggested that there is a correlation between the brain area activated specifically in acute cluster headache — the posterior hypothalamic grey matter — and an increase in grey matter in the same region. No structural changes have been found for migraine and medication overuse headache, whereas patients with chronic tension-type headache demonstrated a significant grey matter decrease in regions known to be involved in pain processing. Modern neuroimaging thus clearly suggests that most primary headache syndromes are predominantly driven from the brain, activating the trigeminovascular reflex and needing therapeutics that act on both sides: centrally and peripherally

Support for Multi-Level Security Policies in DRM Architectures

Digital rights management systems allow copyrighted content to be commercialized in digital format without the risk of revenue loss due to piracy. Making such systems secure is no easy task, given that content needs to be protected while accessed through electronic devices in the hands of potentially malicious end-users; in this context, intrusion tolerance becomes a very useful system property. In this paper we point out a limitation shared by all current DRM architectures, namely their weakness in reacting to possible device compromise and confining the damage caused by such a compromise. As a solution, we propose a paradigm shift - moving from the original DRM system model where all devices are equally trustworthy and have discretionary control over all protected content, to a new model where information flow is controlled through a multi-level security policy that differentiates between devices based on their tamper-resistance properties. We show that besides improved intrusion-tolerance, supporting such policies has other advantages, such as the ability to define more flexible business models for supplying content. We also show that for a given DRM architecture, the type authentication protocol used when accepting new devices in the system has a big impact on how well multi-level security policies can be supported, and that a number of protocols currently being considered are not very well suited for this job. © 2005 ACM