Recovery blocks for communicating systems

In many practical applications of real-time computing (avionics, switching systems) a message-passing inter-processes communication approach is adopted for both modularity and reliability aims. In the present paper, the problem of adding fault-tolerance in a message passing multiprocesses environment is examined. Recovery blocks implementation schemes for both asynchronous and synchronous communications are proposed, with the aim of avoiding domino-effects and exploiting the message oriented system structure. When a sender process produces a message, an acceptance test is performed on the message by system procedures, which in sequence: i) transfer the message on the receiving process working memory, ii) save present process status, or in case of error, restore some previous process status, and iii) discard no longer needed status informations

Self-Assembly of Polyhedral Hybrid Colloidal Particles

We have developed a new method to produce hybrid particles with polyhedral shapes in very high yield (liter quantities at up to 70% purity) using a combination of emulsion polymerization and inorganic surface chemistry. The procedure has been generalized to create complex geometries, including hybrid line segments, triangles, tetrahedra, octahedra, and more. The optical properties of these particles are tailored for studying their dynamics and self-assembly. For example, we produce systems that consist of index-matched spheres allowing us to define the position of each elementary particle in three-dimensional space. We present some preliminary studies on the self-assembly of these complex shaped systems based on electron and optical microscopy.Engineering and Applied SciencesPhysic

The GRAAL high resolution BGO calorimeter and its energy calibration and monitoring system

We describe the electromagnetic calorimeter built for the GRAAL apparatus at the ESRF. Its monitoring system is presented in detail. Results from tests and the performance obtained during the first GRAAL experiments are given. The energy calibration accuracy and stability reached is a small fraction of the intrinsic detector resolution.Comment: 19 pages, 14 figures, submitted to Nuclear Instruments and Method

ep → ep π⁰ Reaction Studied in the Δ(1232) Mass Region Using Polarization Asymmetries

Measurements of the angular distributions of target and double-spin asymmetries for the Δ+(1232) in the exclusive channel → p(→e,e\u27p)π0 obtained at the Jefferson Lab in the Q2 range from 0.5 to 1.5 GeV2/c2 are presented. Results of the asymmetries are compared with the unitary isobar model [D. Drechsel , Nucl. Phys. A645, 145 (1999)], dynamical models [T. Sato and T. S. Lee, Phys. Rev. C 54, 2660 (1996); S. S. Kamalov , Phys. Lett. B 27, 522 (2001)], and the effective Lagrangian theory [R. M. Davidson , Phys. Rev. D 43, 71 (1991)]. Sensitivity to the different models was observed, particularly in relation to the description of background terms on which the target asymmetry depends significantly

Exclusive Electroproduction of ᵠ Mesons at 4.2 GeV

We studied the exclusive reaction ep → e\u27 p\u27 ᵠ using the ᵠ →K+K- decay mode. The data were collected using a 4.2 GeV incident electron beam and the CEBAF Large Acceptance Spectrometer (CLAS) at the Thomas Jefferson National Accelerator Facility. Our experiment covers the range in Q2 from 0.7 to 2.2 GeV2and W from 2.0 to 2.6 GeV. Taken together with all previous data, we find a consistent picture of ᵠ production on the proton. Our measurement shows the expected decrease of the t slope with the vector-meson formation time c Δ t below 2 fm. At c Δ t = 0.6 fm, we measure bɸ = 2.27 ± 0.42 GeV-2. The cross section dependence on W as W0.2 ±0.1 at Q2, 1.3 GeV2 was determined by comparison with ɸ production at HERA after correcting for threshold effects. This is the same dependence as observed in photoproduction

Corrected Article: Exclusive Electroproduction of ᵠ Mesons at 4.2 GeV [Physical. Rev. C 63, 065205, (2001)]

We studied the exclusive reaction ep → e\u27 p\u27 ᵠ using the ᵠ →K+K- decay mode. The data were collected using a 4.2 GeV incident electron beam and the CEBAF Large Acceptance Spectrometer (CLAS) at the Thomas Jefferson National Accelerator Facility. Our experiment covers the range in Q2 from 0.7 to 2.2 GeV2and W from 2.0 to 2.6 GeV. Taken together with all previous data, we find a consistent picture of ᵠ production on the proton. Our measurement shows the expected decrease of the t slope with the vector-meson formation time c Δ t below 2 fm. At c Δ t = 0.6 fm, we measure bɸ = 2.27 ± 0.42 GeV-2. The cross section dependence on W as W0.2 ±0.1 at Q2, 1.3 GeV2 was determined by comparison with ɸ production at HERA after correcting for threshold effects. This is the same dependence as observed in photoproduction

Kinematically Complete Measurement of the Proton Structure Function F₂ in the Resonance Region and Evaluation of its Moments

We measured the inclusive electron-proton cross section in the nucleon resonance region (W \u3c2.5 GeV) at momentum transfers Q2 below 4.5 (GeV/c)2 with the CLAS detector. The large acceptance of CLAS allowed the measurement of the cross section in a large, contiguous two-dimensional range of Q2 and x, making it possible to perform an integration of the data at fixed Q2 over the significant x interval. From these data we extracted the structure function F2 and, by including other world data, we studied the Q2 evolution of its moments, Mn(Q2), in order to estimate higher twist contributions. The small statistical and systematic uncertainties of the CLAS data allow a precise extraction of the higher twists and will require significant improvements in theoretical predictions if a meaningful comparison with these new experimental results is to be made

Measurement of Inclusive Spin Structure Functions of the Deuteron

We report the results of a new measurement of spin structure functions of the deuteron in the region of moderate momentum transfer [Q2 = 0.27-1.3 (GeV/c)2] and final hadronic state mass in the nucleon resonance region (W=1.08-2.0 GeV). We scattered a 2.5 GeV polarized continuous electron beam at Jefferson Lab off a dynamically polarized cryogenic solid state target (15ND3) and detected the scattered electrons with the CEBAF large acceptance spectrometer. From our data, we extract the longitudinal double spin asymmetry A∥ and the spin structure function g1d. Our data are generally in reasonable agreement with existing data from SLAC where they overlap, and they represent a substantial improvement in statistical precision. We compare our results with expectations for resonance asymmetries and extrapolated deep inelastic scaling results. Finally, we evaluate the first moment of the structure function g1d and study its approach to both the deep inelastic limit at large Q2 and to the Gerasimov-Drell-Hearn sum rule at the real photon limit (Q2→ 0). We find that the first moment varies rapidly in the Q2 range of our experiment and crosses zero at Q2 between 0.5 and 0.8 (GeV/c)2, indicating the importance of the Delta resonance at these momentum transfers

Measurement of ep → e \u27 p π⁺π⁻ and Baryon Resonance Analysis

The cross section for the reaction ep→ e\u27pπ+π- was measured in the resonance region for 1.4 2 \u3c 1.5 GeV2/c2using the CLAS detector at Jefferson Laboratory. The data show resonant structures not visible in previous experiments. The comparison of our data to a phenomenological prediction using available information on N* and Δ states shows an evident discrepancy. A better description of the data is obtained either by a sizable change of the properties of the P13(1720) resonance or by introducing a new baryon state, not reported in published analyses