160 research outputs found
A genetic algorithm to design Laue lenses with optimal performance for focusing hard X- and gamma-rays
In order to focus hard X- and gamma-rays it is possible to make use of a Laue
lens as a concentrator. With this optical tool it would be possible to improve
the detection of radiation for several applications, spanning from the
observation of the most violent phenomena in the sky to nuclear medicine
applications, for diagnostic and therapeutic purposes. A code named LaueGen,
based on a genetic algorithm and aimed to designing optimized Laue lenses, has
been implemented. The genetic algorithm was selected because the optimization
of a Laue lens is a complex and discretized problem. The output of the code
consists in the design of a Laue lens composed of diffracting crystals selected
and arranged in such a way to maximize the performance of the lens. The code
allows one to manage crystals of any material and crystallographic orientation.
The program is structured in such a way that the user can control all the
initial parameters of the lens. As a result, LaueGen is highly versatile and
can be used for the design of very small lens, e.g. for nuclear medicine, to
very large lens, e.g. for satellite-borne astrophysical missions.Comment: 18 pages, 4 figure
Homogeneous self-standing curved monocrystals, obtained using sandblasting, to be used as manipulators of hard X-rays and charged particle beams
Carbon source dependent promoters in yeasts
Budding yeasts are important expression hosts for the production of recombinant proteins. The choice of the right promoter is a crucial point for efficient gene expression, as most regulations take place at the transcriptional level. A wide and constantly increasing range of inducible, derepressed and constitutive promoters have been applied for gene expression in yeasts in the past; their different behaviours were a reflection of the different needs of individual processes. Within this review we summarize the majority of the large available set of carbon source dependent promoters for protein expression in yeasts, either induced or derepressed by the particular carbon source provided. We examined the most common derepressed promoters for Saccharomyces cerevisiae and other yeasts, and described carbon source inducible promoters and promoters induced by non-sugar carbon sources. A special focus is given to promoters that are activated as soon as glucose is depleted, since such promoters can be very effective and offer an uncomplicated and scalable cultivation procedure
Curved crystals as optical elements for focusing X- and γ rays in a Laue lens
Curved crystals as optical elements for
focusing X- and γ rays in a Laue lens
Abstract
This thesis is devoted to achieve a method to realize bent crystals in order to diffract hard X- and γ
rays with high-efficiency. A simple and economical method that would lead to the production of
accurate and homogeneous bent samples is presented. In fact, a homogeneous curvature is a necessary
condition for the diffraction of the radiation with high efficiency and resolution. Furthermore, an
appropriate physical model is given, to foresee the curvature of the samples as a function of the
production parameters. Several silicon and germanium samples were bent and pre-characterized at the
Sensor and Semiconductor Laboratory (SSL) of Ferrara, Italy. The focusing capabilities of the crystals
were tested with monochromatic and polychromatic X- and γ rays at the European Synchrotron
Radiation Facility (ESRF) and at the Institut Laue-Langevin (ILL) in Grenoble, France. Investigations
and experimental validations of diffraction with unusual crystal configurations are described.
Furthermore, two proposals of Laue lens are given. Such proposals were theoretical obtained with
LaueGen, a genetic algorithm written for this purpose. Finally, the performance of these simulated
Laue lenses are shown and compared with the data available in the literature.
The work of thesis was carried out within the Laue project, which is a project financed by the Italian
Space Agency (ASI). The final aim of the Laue project was the realization of a prototype of Laue lens
composed of germanium and gallium arsenide bent crystals. In particular, the realization and the precharacterization
of the germanium samples were performed during this Ph.D. period
Experimental study on grooved Si and Ge crystals for Laue lens application
An experimental study on the method of indentations for bent crystals to realize a hard X-ray Laue lens has been done. We tested the diffraction properties of indented Si and Ge crystalline plates at European Synchrotron Radiation
Facility (Grenoble, France). The samples were analyzed by diffraction of their (111) planes with hard X-rays from 150 to 600 keV. Crystals have shown significantly high diffraction efficiency, i.e. a Si crystal has exhibited up to 80% at 300 keV. A Ge crystal has confirmed the observation for a Si one, though the diffraction efficiency
was about 60%. In both cases rocking curves showed flat-toped rectangular shapes, which demonstrates that the method of indentations evenly bends the crystals. Moreover, measured angular spread was always very close to the morphological curvature of the sample under investigation, showing that this method offers high reproducibility and, thus, easy control of diffraction properties of the crystals
Experimental evidence of planar channeling in a periodically bent crystal
The usage of a Crystalline Undulator (CU) has been identified as a promising
solution for generating powerful and monochromatic -rays. A CU was
fabricated at SSL through the grooving method, i.e., by the manufacturing of a
series of periodical grooves on the major surfaces of a crystal. The CU was
extensively characterized both morphologically via optical interferometry at
SSL and structurally via X-ray diffraction at ESRF. Then, it was finally tested
for channeling with a 400 GeV/c proton beam at CERN. The experimental results
were compared to Monte Carlo simulations. Evidence of planar channeling in the
CU was firmly observed. Finally, the emission spectrum of the positron beam
interacting with the CU was simulated for possible usage in currently existing
facilities
Genome-scale metabolic reconstruction and in silico analysis of methylotrophic yeast Pichia pastoris for strain improvement
<p>Abstract</p> <p>Background</p> <p><it>Pichia pastoris </it>has been recognized as an effective host for recombinant protein production. A number of studies have been reported for improving this expression system. However, its physiology and cellular metabolism still remained largely uncharacterized. Thus, it is highly desirable to establish a systems biotechnological framework, in which a comprehensive <it>in silico </it>model of <it>P. pastoris </it>can be employed together with high throughput experimental data analysis, for better understanding of the methylotrophic yeast's metabolism.</p> <p>Results</p> <p>A fully compartmentalized metabolic model of <it>P. pastoris </it>(<it>iPP</it>668), composed of 1,361 reactions and 1,177 metabolites, was reconstructed based on its genome annotation and biochemical information. The constraints-based flux analysis was then used to predict achievable growth rate which is consistent with the cellular phenotype of <it>P. pastoris </it>observed during chemostat experiments. Subsequent <it>in silico </it>analysis further explored the effect of various carbon sources on cell growth, revealing sorbitol as a promising candidate for culturing recombinant <it>P. pastoris </it>strains producing heterologous proteins. Interestingly, methanol consumption yields a high regeneration rate of reducing equivalents which is substantial for the synthesis of valuable pharmaceutical precursors. Hence, as a case study, we examined the applicability of <it>P. pastoris </it>system to whole-cell biotransformation and also identified relevant metabolic engineering targets that have been experimentally verified.</p> <p>Conclusion</p> <p>The genome-scale metabolic model characterizes the cellular physiology of <it>P. pastoris</it>, thus allowing us to gain valuable insights into the metabolism of methylotrophic yeast and devise possible strategies for strain improvement through <it>in silico </it>simulations. This computational approach, combined with synthetic biology techniques, potentially forms a basis for rational analysis and design of <it>P. pastoris </it>metabolic network to enhance humanized glycoprotein production.</p
Enhancement of the Inelastic Nuclear Interaction Rate in Crystals via Antichanneling
The interaction rate of a charged particle beam with the atomic nuclei of a target varies significantly if the target has a crystalline structure. In particular, under specific orientations of the target with respect to the incident beam, the probability of inelastic interaction with nuclei can be enhanced with respect to the unaligned case. This effect, which can be named antichanneling, can be advantageously used in the cases where the interaction between beam and target has to be maximized. Here we propose to use antichanneling to increase the radioisotope production yield via cyclotron. A dedicated set of experimental measurements was carried out at the INFN Legnaro Laboratories with the AN2000 and CN accelerators to prove the existence of the antichanneling effect. The variation of the interaction yield at hundreds of keV to MeV energies was observed by means of sapphire and indium phosphide crystals, achieving an enhancement of the interaction rate up to 73% and 25%, respectively. Such a result may pave the way to the development of a novel type of nozzle for the existing cyclotrons, which can exploit crystalline materials as targets for radioisotope production, especially to enhance the production rate for expensive prime materials with minor upgrades of the current instrumentation
Development status of the LAUE project
We present the status of LAUE, a project supported by the Italian Space
Agency (ASI), and devoted to develop Laue lenses with long focal length (up to
100 meters), for hard X--/soft gamma--ray astronomy (80-600 keV). Thanks to
their focusing capability, the design goal is to improve the sensitivity of the
current instrumention in the above energy band by 2 orders of magnitude, down
to a few times photons/(cm s keV).Comment: 9 pages, 9 figures, presented at the Space Telescopes and
Instrumentation Symposium in Amsterdam, 2012: Ultraviolet to Gamma Ray
Conference. Published in the Proceedings of the SPIE, Volume 8443, id.
84430B-84430B-9 (2012
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