Being able to determine the provenience of statements is a fundamental step in any SW trust modeling. We propose a methodology that allows signing of small groups of RDF statements. Groups of statements signed with this methodology can be safely inserted into any existing triple store without the loss of provenance information since only standard RDF semantics and constructs are used. This methodology has been implemented and is both available as open source library and deployed in a SW P2P project.Authorship authentication and signing of RDF graphs is still in its infancy. The most relevant work is certainly [1] by J. Carroll which illustrates a nondeterministic, but relatively simple and efficient, procedure for providing a "canonical serialization" for (entire) RDF graphs. The canonical serialization is needed to digitally sign RDF as the same graph could be serialized in a very large number of model equivalent ways. The same author then argues that a mechanism for trust is "naming" graphs [2]; the two things when combined would work by associating a graph with its signature, which would remain external to the graph. This is similar to what has been informally proposed for signing FOAF files [3]. In this work we present a methodology to attach digital signatures closer to the individual statement and using only the standard RDF semantic [4]. This brings the following advantages:• triples all lie in the same model (i.e. Computational space) so that they can all be conveniently considered at the same time when performing a query • no need for special, non standardized, implementations (named graphs, quadruples) • a graph can safely be split into minimal subsets of statements that nevertheless conserve the ability to verify the digital signature. 2.Definitions and propertiesLet's first define what is the minimum "standalone" fragment of an RDF model. As blank nodes are not addressable from outside a graph, they must always be considered together with all surrounding statements, i.e. stored and transfered together. This is of course unless they have an IFP (Inverse Functional Property), which effectively makes them as addressable as URI nodes. We will here give a formal definition of MSG (Minimum Selfcontained Graph) and will prove some simple properties laying the base for MSG signing. Definition 3.Given an RDF statement s, the Minimum Selfcontained Graph (MSG) containing that statement, written MSG (s), is the set of RDF statements comprised of the following: 1.The statement in question; 2.Recursively, for all the blank nodes involved by statements included in the description so far, the MSG of all the statements involving such blank nodes; This definition recursively build the MSG from a particular starting statement; we now show however that the choice of the starting statement is arbitrary and this leads to an unique decomposition of the an RDF graph into MSGs. Proposition 1. The MSG of a ground statement is the statement itself. Theorem 1. If s and t are distinct statements and t belong to MSG (s), then MSG(...

A theoretical study is presented concerning the diffraction characteristics of curved monochromators for X-ray synchrotron radiation used at the laboratories of Hamburg, Orsay and Stanford. The investigation was performed by extending to the X-ray case a simple model recently developed and fruitfully employed to describe the neutron diffraction properties of curved monochromators. Several diffraction patterns were obtained corresponding to different monochromator materials (Ge, Si) used by the different laboratories, for different reflecting planes (111), (220). asymmetry angles, X-ray wavelengths (Mo K:~, Cu K:~, Cr K~) and curvature radii. The results are discussed in physical terms and their implications on the design of curved monochromators for synchrotron radiation are presented. In particular, the study shows that all the monochromators used in the different laboratories should behave practically as perfect crystals and therefore should have a very low integrated reflectivity corresponding to an optimized wavelength passband A2/2 ~ 10-4. The gain that can be obtained by increasing the curvature, by introducing a gradient in the lattice spacing or by any other kind of imperfection is quite limited and much lower than the desirable value. The adopted model can help in obtaining a possible moderate gain in intensity by also taking into consideration other parameters, such as crystal material, reflecting plane, asymmetry of the reflection and X-ray wavelength.

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The Taupin dynamical theory of X‐ray diffraction by deformed crystals which was previously extended to the neutron diffraction by curved crystals in the Bragg geometry, is applied to calculate neutron diffraction patterns in the Laue geometry. The theoretical results are compared with experimental data on curved silicon crystals. The agreement is quite satisfactory. In the second part a simple model recently presented to describe neutron diffraction properties in the Bragg case is extended to the Laue case. The predictions of such a model are in satisfactory agreement with the rigorous theory and the experimental results.