A new Large-Acceptance Forward Angle Spectrometer [Super Bigbite Spectrometer (SBS)], is under development for the upcoming experiments in Hall A at the Thomas Jefferson National Accelerator Facility (Virginia, USA), where a longitudinally polarized electron beam up to 12 GeV energy is now available. The excellent beam intensity (up to 100), combined with innovative polarized targets, will provide luminosity up to , opening interesting opportunities to investigate unexplored aspects of the inner structure of the nucleons. In one of the most demanding configuration, the new spectrometer will consist of a dipole magnet, one front charged particle tracker, two identical proton polarimeters with related back trackers and a segmented hadron calorimeter.The front tracker, placed just after the dipole magnet, consists of up to six layers of large area GEM (Gas Electron Multiplier) chambers; each chamber is made by three adjacent GEM modules of active rectangular area (18 modules as a total).We have chosen the GEM technology in order to optimize spatial resolution (approximate to 80mm), high hit rate, cost/performance and high radiation hardness.We present the main features of the SBS front tracker and its GEM detectors and, finally, we discuss the ongoing tracker commissioning at JLab and show some representative test results.

Experimental results on proton and charged pion detection obtained from a study of the +np+- reaction are reported in detail. Data have been collected using the tagged and linearly polarized photon beam, impinging on a deuterium target, and the large solid angle apparatus of the GRAAL facility in Grenoble (France). The energy of the charged particles was measured using a BGO calorimeter. A comparison of the experimental data with a GEANT3-based simulation is also presented.

The study of meson photoproduction on the nucleon is a very important tool to complete the puzzle of baryon excited states. GRAAL aim is the measurement of cross sections and of beam asymmetries for all the photonuclear reactions accessible in the energy range from 600 MeV up to 1.5 GeV. In the following preliminary results of the Sigma beam asymmetry for omega photoproduction on the free proton in Hydrogen and on the quasi-free nucleon in Deuterium are shown. GRAAL is the first experiment in which both the charged and the radiative decay of omega meson are studied. Since the beam asymmetry is independent of the decay mode, the comparison of the results from the two channel allows an important check on data consistency. Results on the free proton are in good agreement with theoretical prediction from Zhao model and confirm the presence of P(13)(1720) state. The analysis performed for the radiative decay is applied to the process of. photoproduction on the quasi free nucleon in Deuterium.

We present the analysis of data performed in order to identify the events of the gamma + n -> pi(-) + p reaction obtained by bombarding a liquid Deuterium target with a polarised. beam of 0.55-1.5 GeV at the Graal-experiment. We show the effect of different kinematic and hardware constraints used to reduce the contamination coming from the concurrent reaction channels. By the simulation we estimate the contamination degree due to the other reaction channels so we can test the reliability of our method. We describe a new three-dimensional cut based on the Fermi momentum reconstruction and its effect on the suppression of the concurrent double charged pion photoproduction. We present the preliminary beam asymmetry Sigma of the pi(-) fotoproduction off quasi-free neutron up to about theta(c.m.), (pi-) = 165 degrees together with some theoretical multipolar analysis. For a comparison we also report the data present in literature on the same reaction for E(gamma) -850-1740 MeV and theta(c.m.), (pi-) <= 105 degrees.

The gamma p -> eta'p reaction was studied near the threshold, in the 1.44 GeV > E(gamma) < 1.55GeV energy range with the tagged photons of the former GRAAL experiment. The two neutral decays gamma gamma(Gamma(i)/Gamma = 2.10 +/- 0.12%) and pi(0)pi(0)eta(Gamma(i)/Gamma = 20.7 +/- 1.2%) were analized and preliminary results of the beam asymmetry were extracted together with the invariant masses.

The Sigma beam asymmetry in the photoproduction of neutral pions from quasi-free nucleons in a deuteron target was measured for the first time between 0.60 and 1.50 GeV, with the GRAAL polarized and tagged photon beam. The asymmetry values from the quasi-free proton were found equal to the ones extracted from a pure proton target. The asymmetries from quasi-free proton and quasi-free neutron were found equal up to 0.82 GeV and substantially different at higher energies. The results are compared with recent partial-wave analyses.

The preliminary results obtained by the GRAAL collaboration for the pi(0)pi(+) photoproduction on the free and quasi-free proton (deuteron) at E(gamma) = 0.7-1.5 GeV are presented. The total cross section of the gamma p -> pi(0)pi(+)n reaction and invariant mass spectra for the pi(+)pi(0), pi(+)n and pi(0)n systems are presented in the photon energy range from 0.7 to 1.5 GeV. These results are in good agreement with the 2 pi-MAID calculations.

Recently multiserver queues with setup times have been extensively studied because they have applications in power-saving data centers. A challenging model is the M/M/c/Setup queue where a server is turned off when it is idle and is turned on if there are some waiting jobs. Recently, Gandhi et al. (in: Proceedings of the ACM SIGMETRICS, pp. 153-166, ACM, 2013; Queueing Syst. 77(2):177-209, 2014) obtain the generating function of the number of jobs in the system, as well as the Laplace transform of the response time using the recursive renewal reward approach and the distributional Little's law (Keilson and Servi in Oper Res Lett 7(5):223- 227, 1988). In this paper, we derive exact solutions for the joint stationary queue length distribution of the same model using two alternative methodologies: generating function approach and matrix analytic method. The generating function approach yields exact closed form expressions for the joint stationary queue length distribution and the conditional decomposition formula. On the other hand, the matrix analytic approach leads to an exact recursive algorithm to calculate the joint stationary distribution and performance measures so as to provide some application insights.

This paper considers stationary MAP/M/c and M/PH/c queues with constant impatience times. In those queues, waiting customers leave the system without receiving their services if their elapsed waiting times exceed a predefined deterministic threshold. For the MAP/M/c queue with constant impatience times, Choi et al. (Math Oper Res 29:309-325, 2004) derive the virtual waiting time distribution, from which the loss probability and the actual waiting time distribution are obtained. We first refine their result for the virtual waiting time and then derive the stationary queue length distribution. We also discuss the computational procedure for performance measures of interest. Next we consider the stationary M/PH/c queue with constant impatience times and derive the loss probability, the waiting time distribution, and the queue length distribution. Some numerical results are also provided.

Overtaking events can occur in parallel processing systems when customers are served simultaneously by multiple servers. We say that one customer overtakes another when the customer leaves the system after having been served ahead of another customer(s) who arrived earlier. Overtaking events are an important issue in flexible assembly systems or packet switched communication networks, Although materials-(or packets) can be processed by different servers simultaneously, there is a designated order for the assembly of final products (or data). If overtaking occurs, then additional time and money may be required to rearrange materials (or packets) to the original order (called resequencing). We investigate overtaking in an M/M/c queueing system. Two distributions were considered to describe the amount of overtaking: the number of customers that an arbitrary (tagged) customer overtakes and the number of customers who overtake the tagged customer. Explicit forms of these distributions are provided for some cases. Finally, we apply our results to. practical issues in flexible assembly systems and telecommunication systems. (C) 2016 Elsevier Ltd. All rights reserved.

In this paper we study the spectral properties of (m, C)-isometric operators. In particular, if is (m, C)-isometric operators, then the power of (m, C)-isometric operators is also (m, C)-isometric operators. Moreover, if has the single-valued extension property, then T has the single-valued extension property. Finally, we investigate conditions for (m, C)-isometric operators to be (1, C)-isometric operators.