Browsing by Subject "OPTICS"

Sort by: Order: Results:

Now showing items 1-2 of 2
  • Wysokinski, Tomasz W.; Renier, Michel; Suortti, Pekka; Belev, George; Rousset, Leo; Adam, Madison; Miller, Denise; Huber, Norman; Chapman, L. Dean (2018)
    The research program at the biomedical imaging facility requires a high-flux hard-X-ray monochromator that can also provide a wide beam. A wide energy range is needed for standard radiography, phase-contrast imaging, K-edge subtraction imaging and monochromatic beam therapy modalities. The double-crystal Laue monochromator, developed for the BioMedical Imaging and Therapy facility, is optimized for the imaging of medium- and large-scale samples at high energies with the resolution reaching 4 mu m. A pair of 2mm-thick Si(111) bent Laue-type crystals were used in fixed-exit beam mode with a 16mm vertical beam offset and the first crystal water-cooled. The monochromator operates at energies from 25 to 150keV, and the measured size of the beam is 189mm (H)x8.6mm (V) at 55m from the source. This paper presents our approach in developing a complete focusing model of the monochromator. The model uses mechanical properties of crystals and benders to obtain a finite-element analysis of the complete assembly. The modeling results are compared and calibrated with experimental measurements. Using the developed analysis, a rough estimate of the bending radius and virtual focus (image) position of the first crystal can be made, which is also the real source for the second crystal. On the other hand, by measuring the beam height in several points in the SOE-1 hutch, the virtual focus of the second crystal can be estimated. The focusing model was then calibrated with measured mechanical properties, the values for the force and torque applied to the crystals were corrected, and the actual operating parameters of the monochromator for fine-tuning were provided.
  • Silva, José Filipe (2017)
    By the end of the thirteenth century several models of visual perception were available in the Latin West, differing according to their influences - Aristotelian, Augustinian, Avicennian - and their interpretations. One such model was that of perspectivist optics, as espoused by Alhacen and popularized by Roger Bacon. While the general structure of this theory is well-known, until recently scholars have paid less attention to the issue of discrimination - distinction, comparison, judgment - by a higher cognitive faculty (the virtus distinctiva) of incoming sensory information. In my paper, I specifically examine what role this discriminative faculty, as proposed by Alhacen, plays in the works of later perspectivi such as Roger Bacon, John Pecham, and Blasius of Parma, proceeding from the assumption that the best way to understanding the influence of any given theory is by understanding the authors influenced by it. My focus is on two aspects of this power: what exactly its functions are, and whether its nature is rational or sensory. Building on this last aspect, I consider whether this nature is better suited for passive or active accounts of perception.