Varying Collimation for Dark-Field Extraction

Although x-ray imaging is widely used in biomedical applications, biological soft tissues have small density changes, leading to low contrast resolution for attenuation-based x-ray imaging. Over the past years, x-ray small-angle scattering was studied as a new contrast mechanism to enhance subtle structural variation within the soft tissue. In this paper, we present a detection method to extract this type of x-ray scattering data, which are also referred to as dark-field signals. The key idea is to acquire an x-ray projection multiple times with varying collimation before an x-ray detector array. The projection data acquired with a collimator of a sufficiently high collimation aspect ratio contain mainly the primary beam with little scattering, while the data acquired with an appropriately reduced collimation aspect ratio include both the primary beam and small-angle scattering signals. Then, analysis of these corresponding datasets will produce desirable dark-field signals; for example, via digitally subtraction. In the numerical experiments, the feasibility of our dark-field detection technology is demonstrated in Monte Carlo simulation. The results show that the acquired dark field signals can clearly reveal the structural information of tissues in terms of Rayleigh scattering characteristics

LCOGT Network Observatory Operations

We describe the operational capabilities of the Las Cumbres Observatory Global Telescope Network. We summarize our hardware and software for maintaining and monitoring network health. We focus on methodologies to utilize the automated system to monitor availability of sites, instruments and telescopes, to monitor performance, permit automatic recovery, and provide automatic error reporting. The same jTCS control system is used on telescopes of apertures 0.4m, 0.8m, 1m and 2m, and for multiple instruments on each. We describe our network operational model, including workloads, and illustrate our current tools, and operational performance indicators, including telemetry and metrics reporting from on-site reductions. The system was conceived and designed to establish effective, reliable autonomous operations, with automatic monitoring and recovery - minimizing human intervention while maintaining quality. We illustrate how far we have been able to achieve that.Comment: 13 pages, 9 figure

Real-time monitoring and diagnostics of crystal-based collimation of particle accelerator beams

The beam collimation represents one of the important items for the future upgrade of the Large Hadron Collider (LHC) at CERN. An effective collimation system is particularly required at higher beam intensities, as even a relatively small number of particles impinging on the superconducting magnets can cause quenching (a sudden loss of superconducting condition). Although the currently used collimation system at CERN is working properly, it presents some limitations which can be overcome by future upgrades. One of these limitations is due the particle diffraction from heavy absorbers. An alternative option to the current collimation system at CERN is represented by the use of bent crystals. These latter are expected to be very effective in beam collimation. In fact, they have the advantage to guide halo particles of the beam on a single absorber. This allows the improvements to the cleaning performance as well as to the impedance of the collider as compared to the multi-stage collimation systems, consisting of large blocks made of amorphous material, placed around the beam. In this framework, UA9 Experiment at CERN is carrying on since many years an R&D on various types of crystals. The aim is to find the best solution to overcome the limitations of the currently used collimation system at CERN, in view of future upgrades of the collider. The first part of this PhD work has been devoted, within the UA9 collaboration, to the characterization of some new crystals to be used in LHC and in the Super Proton Synchrotron (SPS) for collimation. The radiation hardness for high energy neutrons were also tested for these crystals. Beam collimation monitoring is performed in the UA9 crystal based system using a Cherenkov detector for high energy protons going through the fused silica. Presently, classical PMTs are in use to collect the Cherenkov light, but its dark count rate is directly affected by the high intensity radiation. With the aim to face this limitation, the second part of this PhD project focused on the characterization of ZnO material, which resulted to be very promising for realizing alternative photodetectors. In this respect, Cherenkov detector/setup used in UA9 could be updated with more functional sensor systems which are radiation resistant and compatible with vacuum requirements in the beam pipe. Another important aspect in collimation systems is the real time monitoring of collimated beams inside the accelerators, especially when using a crystal based collimation system as in UA9. A good approach to face this aspect is to develop a machine learning based real time framework to analyze the signal and detect the faults. The last aim of this work is to present a preliminary study of data acquisition as a starting point to develop a real time framework to be built in the future. This work has been carried out using a SiPM sensor (which competes with the PMTs) with a fast ADC digitizer in real time

Two-component magnetohydrodynamical outflows around young stellar objects Interplay between stellar magnetospheric winds and disc-driven jets

We present the first-ever simulations of non-ideal magnetohydrodynamical (MHD) stellar magnetospheric winds coupled with disc-driven jets where the resistive and viscous accretion disc is self-consistently described. These innovative MHD simulations are devoted to the study of the interplay between a stellar wind (having different ejection mass rates) and an MHD disc-driven jet embedding the stellar wind. The transmagnetosonic, collimated MHD outflows are investigated numerically using the VAC code. We first investigate the various angular momentum transports occurring in the magneto-viscous accretion disc. We then analyze the modifications induced by the interaction between the two components of the outflow. Our simulations show that the inner outflow is accelerated from the central object's hot corona thanks to both the thermal pressure and the Lorentz force. In our framework, the thermal acceleration is sustained by the heating produced by the dissipated magnetic energy due to the turbulence. Conversely, the outflow launched from the resistive accretion disc is mainly accelerated by the magneto-centrifugal force.}{The simulations show that the MHD disc-driven outflow extracts angular momentum more efficiently than do viscous effects in near-equipartition, thin-magnetized discs where turbulence is fully developed. We also show that, when a dense inner stellar wind occurs, the resulting disc-driven jet has a different structure, namely a magnetic structure where poloidal magnetic field lines are more inclined because of the pressure caused by the stellar wind. This modification leads to both an enhanced mass-ejection rate in the disc-driven jet and a larger radial extension that is in better agreement with the observations, besides being more consistent.Comment: 16 pages, Accepted in A&A 04/08/200

Pulsar-driven Jets in Supernovae, Gamma-Ray Bursts, and the Universe

The bipolarity of Supernova 1987A can be understood through its very early light curve observed from the CTIO 0.4-m telescope and IUE FES, and following speckle observations of the `Mystery Spot' by two groups. These indicate a highly directional beam/jet of light/particles, with initial collimation factors in excess of 10,000 and velocities in excess of 0.95 c, as an impulsive event of up to 1e-5 solar masses interacting with circumstellar material. These can be produced by a model proposed in 1972, by Bolotovskii and Ginzburg, which employs pulsar emission from polarization currents induced/(modulated faster than c) beyond the pulsar light cylinder by the periodic electromagnetic field (supraluminally induced polarization currents -- SLIP). SLIP accounts for the disruption of progenitors in supernova explosions and their anomalous dimming at cosmological distances, jets from Sco X-1 and SS 433, the lack/presence of intermittent pulsations from the high/low luminosity low mass X-ray binaries, long/short gamma-ray bursts and predicts that their afterglows are the pulsed optical/near infrared emission associated with these pulsars. SLIP may also account for the TeV e+/e- results from PAMELA and ATIC, the WMAP `Haze'/Fermi `Bubbles', and the r-process. SLIP jets from SNe of the first stars may allow galaxies to form without dark matter, and explain the peculiar, non-gravitational motions observed from pairs of distant galaxies by GALEX.Comment: This article has been published in the open source journal, Advances in Astronomy: http://www.hindawi.com/journals/aa/2012/898907 This arXiv version is out of date. arXiv admin note: substantial text overlap with arXiv:0909.2604 (Note: but less so by v2, Also Brook Sandford in Ackn. -JM