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 Journal of Signal and Information Processing (JSIP) , 2013, DOI: 10.4236/jsip.2013.42030 Abstract: An image super resolution reconstruction method was used to improve the spatial resolution of the thick pinhole imaging system and to mitigate the limitations of the image spatial resolution of the hardware of the image diagnostic system. The thick pinhole is usually applied into the diagnostics of the high energy neutron radiation image. Due to the impacts among its energy flux, spatial resolution and effective field of view, in dealing with the large area radiation source, the spatial resolution of the thick pinhole neutron image cannot meet the requirements for high precision modeling of the radiation source image. In this paper, the Lucy-Richardson image super resolution reconstruction method was used to simulate the thick pinhole imaging and super resolution image reconstruction. And the spatial resolution of the image could be increased by over three times after the image super resolution reconstruction. Besides, in dealing with the pseudo-noise, plum blossom shape appeared in the image super resolution reconstruction. The analysis of the source of the pseudo-noise was made based on the simulation of the image reconstruction under various conditions according to the characteristics of the thick pinhole image configuration.
 QiuSheng Dai Chinese Science Bulletin , 2011, DOI: 10.1007/s11434-011-4606-9 Abstract: The pinhole gamma camera is the basis of the newly developed method of high-resolution pinhole single photon emission computed tomography (SPECT). In this paper, a pinhole gamma camera system was examined using the channel model of information theory. The model pinhole gamma camera was simplified from a noisy, lossy channel to a noiseless, lossless channel by assuming a plane source. An approximate formula of average mutual information for the pinhole gamma camera was then derived from the model. Imaging experiments validated the applicability of the analytic formula. The findings demonstrated that the pinhole gamma camera can be adequately described using the channel model of information theory, and that average mutual information can be considered a figure of merit for the optimizing design of the pinhole gamma camera.
 Hajime Takami Physics , 2010, DOI: 10.1111/j.1365-2966.2011.18264.x Abstract: The respective contribution of disk and jet components to the total emission in low luminosity active galactic nuclei (LLAGNs) is an open question. This paper suggests that $\gamma$-rays emitted from electrons accelerated in jets could be a direct diagnostic tool for a jet component to the total emission. We demonstrate $\gamma$-ray flux from jets based on a synchrotron self-compton (SSC) model on the assumption that radio and X-rays are dominantly produced from jets in the case of a high state of a nearby LLAGN, NGC 4278. We also survey parameter space in the model. Observational properties of LLAGNs in radio and X-ray bands allow to constrain physical parameters in an emission region. The size of the emission region $R$ is limited to $10^{16}$ cm $\leq R \leq 10^{17.5}$ cm if the observed tight correlation between radio and X-ray emission originates from the same jet component. If the beaming factor of the emission region is close to the observed parsec scale jet of NGC 4278 and $R \sim 10^{16}$ cm, the $\gamma$-rays may be detected by Cherenkov Telescope Array, and the jet domination can be tested in the near future.
 Physics , 1994, Abstract: We analyse the propagation of particles in the narrow funnel of a thick accretion disk. It is assumed that: (1) the funnel walls emit black body radiation with temperature decreasing outwards; (2) the magnetic and electric fields are longitudinal in the funnel. Such a scenario is consistent with models in which a large potential drop is induced by a rotating massive black hole threaded by a magnetic field (Blandford & Znajek 1977, Macdonald & Thorne 1982). The interaction of relativistic protons with thermal photons from the funnel results in direct production of pairs and/or pions. We discuss the relative importance of these processes for different conditions in the funnel (temperature and electric field profiles). Injected pairs interact with thermal photons in the Thomson or Klein-Nishina regime. Under some conditions, a pair avalanche results, which we assume saturates in the production of stable bunches, containing almost equal numbers of electrons and positrons. As a consequence, highly collimated gamma-ray photons are produced. We obtain gamma-ray spectra from our model in order to test its applicability to the gamma-ray emitting AGNs recently reported by EGRET.
 物理学报 , 2012, Abstract: A figure of merit (FOM) for thick pinhole imaging and its formula are developed. The FOM can describe the total spatial resolution and sensitivity of thick pinhole imaging. Based on the penetration model, the root-mean-square of point spread function and the effective diameter at the center are derived. FOMs at the total and effective field of view are calculated. Based on the figures, the characteristics of thick pinhole imaging are discussed.
 Roberto Aloisio Physics , 2014, Abstract: We will review the main channels of gamma ray emission due to the acceleration and propagation of cosmic rays, discussing the cases of both galactic and extra-galactic cosmic rays and their connection with gamma rays observations.
 Roland Svensson Physics , 1997, Abstract: Various types of active galactic nuclei (AGN) are briefly discussed, with an emphasis on the theory of recent X-ray and $\gamma$-ray observations of the subclass, Seyfert 1 galaxies. The large radiation power from AGN is thought to originate from gravitational power released by matter accreting onto a supermassive black hole. The physical mechanisms responsible for the energy release and the geometry of the gaseous components are still uncertain in spite of three decades of observational and theoretical studies. The recent X-ray and gamma-ray observations, however, start to provide useful constraints on the models. This kind of interpretation of the observations is possible due to theoretical developments during the last decade of radiative transfer of X-rays in both optically thick and thin media of various geometries. Particular attention is paid to various accretion disk-corona models. Recent work on exact radiative transfer in such geometries are reviewed.
 E. Waxman Physics , 2003, DOI: 10.1038/423388a Abstract: The origin of energetic gamma-ray bursts is still unknown. But the detection of polarization of gamma-rays provides fresh insight into the mechanism driving these powerful explosions.
 M. Hernanz Physics , 2013, Abstract: Classical novae produce radioactive nuclei which are emitters of gamma-rays in the MeV range. Some examples are the lines at 478 and 1275 keV (from 7Be and 22Na) and the positron-electron annihilation emission (511 keV line and a continuum below this energy, with a cut-off at 20-30 keV). The analysis of gamma-ray spectra and light curves is a potential unique and powerful tool both to trace the corresponding isotopes and to give insights on the properties of the expanding envelope determining its transparency. Another possible origin of gamma-rays is the acceleration of particles up to very high energies, so that either neutral pions or inverse Compton processes produce gamma-rays of energies larger than 100 MeV. MeV photons during nova explosions have not been detected yet, although several attempts have been made in the last decades; on the other hand, GeV photons from novae have been detected in some particular novae, in symbiotic binaries, where the companion is a red giant with a wind, instead of a main sequence star as in the cataclysmic variables hosting classical novae. Both mechanisms of gamma-ray production in novae are reviewed, with more emphasis on the one related to radioactivities.
 R. Mukherjee Physics , 2000, DOI: 10.1016/S0920-5632(00)00978-6 Abstract: This article reviews the present status of high energy gamma-ray astronomy at energies above 30 MeV. Observations in the past decade using both space- and ground-based experiments have been primarily responsible for giving a tremendous boost to our knowledge of the high energy Universe. High energy gamma-rays have been detected from a wide range of Galactic and extragalactic astrophysical sources, such as gamma-ray bursters, pulsars, and active galaxies. These observations have established high energy gamma-ray astronomy as a vital and exciting field, that has a bright future. This review summarizes the experimental techniques, observations and results obtained with recent experiments, and concludes with a short description of future prospects.
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