2,031 research outputs found
Hard x-ray broad band Laue lenses (80 - 600 keV): building methods and performances
We present the status of the laue project devoted to develop a technology for
building a 20 meter long focal length Laue lens for hard x-/soft gamma-ray
astronomy (80 - 600 keV). The Laue lens is composed of bent crystals of Gallium
Arsenide (GaAs, 220) and Germanium (Ge, 111), and, for the first time, the
focusing property of bent crystals has been exploited for this field of
applications. We show the preliminary results concerning the adhesive employed
to fix the crystal tiles over the lens support, the positioning accuracy
obtained and possible further improvements. The Laue lens petal that will be
completed in a few months has a pass band of 80 - 300 keV and is a fraction of
an entire Laue lens capable of focusing X-rays up to 600 keV, possibly
extendable down to 20 - 30 keV with suitable low absorption crystal materials
and focal length. The final goal is to develop a focusing optics that can
improve the sensitivity over current telescopes in this energy band by 2 orders
of magnitude
A focal plane detector design for a wide-band Laue-lens telescope
The energy range above 60 keV is important for the study of many open
problems in high energy astrophysics such as the role of Inverse Compton with
respect to synchrotron or thermal processes in GRBs, non thermal mechanisms in
SNR, the study of the high energy cut-offs in AGN spectra, and the detection of
nuclear and annihilation lines. Recently the development of high energy Laue
lenses with broad energy bandpasses from 60 to 600 keV have been proposed for a
Hard X ray focusing Telescope (HAXTEL) in order to study the X-ray continuum of
celestial sources. The required focal plane detector should have high detection
efficiency over the entire operative range, a spatial resolution of about 1 mm,
an energy resolution of a few keV at 500 keV and a sensitivity to linear
polarization. We describe a possible configuration of the focal plane detector
based on several CdTe/CZT pixelated layers stacked together to achieve the
required detection efficiency at high energy. Each layer can operate both as a
separate position sensitive detector and polarimeter or work with other layers
to increase the overall photopeak efficiency. Each layer has a hexagonal shape
in order to minimize the detector surface required to cover the lens field of
view. The pixels would have the same geometry so as to provide the best
coupling with the lens point spread function and to increase the symmetry for
polarimetric studies.Comment: 10 pages, 9 figure
Stress-Free Two-Way Shape Memory Effect of Poly(ethylene glycol)/ Poly(epsilon-caprolactone) Semicrystalline Networks
In this work, poly(ethylene glycol) (PEG)/poly(epsilon- caprolactone) (PCL) semicrystalline networks were prepared by photo-cross-linking of methacrylated macromonomers with different molecular weights and in different proportions to obtain amphiphilic materials capable of displaying properly designed shape memory effects. Networks based on PCL 10 kDa and PEG 3 kDa showed suitable thermal and mechanical properties with well-separated crystallization and melting regions to achieve a self-standing two-way shape memory effect. Particularly, after the application of a specific thermomechanical history, these materials are capable of cyclically changing their shape between two configurations upon cooling-heating cycles in the absence of any external load applied. The effect of the composition of the networks and of the employed thermomechanical parameters, such as the applied strain and the actuation temperature, was investigated to shed light on the shape memory mechanism for this class of materials, which are considered promising for applications in the biomedical field and as reversible actuators for soft robotics
The gamma-ray burst monitor for Lobster-ISS
Lobster-ISS is an X-ray all-sky monitor experiment selected by ESA two years
ago for a Phase A study (now almost completed) for a future flight (2009)
aboard the Columbus Exposed Payload Facility of the International Space
Station. The main instrument, based on MCP optics with Lobster-eye geometry,
has an energy passband from 0.1 to 3.5 keV, an unprecedented daily sensitivity
of 2x10^{-12} erg cm^{-2}s$^{-1}, and it is capable to scan, during each orbit,
the entire sky with an angular resolution of 4--6 arcmin. This X-ray telescope
is flanked by a Gamma Ray Burst Monitor, with the minimum requirement of
recognizing true GRBs from other transient events. In this paper we describe
the GRBM. In addition to the minimum requirement, the instrument proposed is
capable to roughly localize GRBs which occur in the Lobster FOV (162x22.5
degrees) and to significantly extend the scientific capabilities of the main
instrument for the study of GRBs and X-ray transients. The combination of the
two instruments will allow an unprecedented spectral coverage (from 0.1 up to
300/700 keV) for a sensitive study of the GRB prompt emission in the passband
where GRBs and X-Ray Flashes emit most of their energy. The low-energy spectral
band (0.1-10 keV) is of key importance for the study of the GRB environment and
the search of transient absorption and emission features from GRBs, both goals
being crucial for unveiling the GRB phenomenon. The entire energy band of
Lobster-ISS is not covered by either the Swift satellite or other GRB missions
foreseen in the next decade.Comment: 6 pages, 4 figures. Paper presented at the COSPAR 2004 General
Assembly (Paris), accepted for publication in Advances in Space Research in
June 2005 and available on-line at the Journal site
(http://www.sciencedirect.com/science/journal/02731177), section "Articles in
press
Reversible Stress-Driven and Stress-Free Two-Way Shape Memory Effect in a Sol-Gel Crosslinked Polycaprolactone
The two-way shape memory effect is the ability of a material to change its shape between two configurations upon application and removal of a stimulus, and, among shape memory polymers, it is featured only by few systems, such as semicrystalline networks. When studied under tensile conditions, it consists of elongation-contraction cycles along cooling and heating across the crystallization and melting region, typically under the application of a constant load. However, recent studies on crosslinked semicrystalline co-polymers demonstrate that also a completely stress-free, or self-sustained, two-way effect may be achieved through specific thermomechanical cycles. This effect is currently regarded with interest for the development of intrinsically reversible sensors and actuators, and it may also be displayed by simpler materials, as homopolymer-based semicrystalline networks. Only seldom articles investigate this possibility, therefore in this work the two-way shape memory behavior is studied on a poly(e-caprolactone) system, crosslinked by means of a sol-gel approach. The effect is studied both under stress-driven and stress-free condition, by applying properly set-up thermo-mechanical histories. The results allow to describe the effect as a function of temperature, to reveal the dependence on specific testing parameters and to compare the extent of the reversible strain variation under these two conditions
Poster Session II, July 14th 2010 â Abstracts Improvements in the design of a kayak-ergometer using a sliding footrest-seat complex
AbstractAs observed previously in rowing, kayaking an ergometer becomes more and more popular. Nowadays, indoor kayak championships are organized performed on ergometer designed with a fixed footrest-seat complex. The main goal when one designs ergometers is to reproduce as closest as possible the on-water conditions. The reliability with on-water condition is usually assessed using both physiological and kinematics parameters. The previous studies of our research group have shown that the dynamics of the in situ movement has also to be reproduced. In other words, major muscular groups (who generated the joint torque and by the way the contact forces) involved in kayaking should be recruit with the same timing during on-water and ergometer kayaking. At the 7th ISEA conference, our research group presented a method based on numerical optimization to design a kayak ergometer equipped with a sliding footrest-seat complex that reproduces the acceleration generated in flatwater kayak. Based on these preliminary results, we have constructed a new ergometer. Then, the purpose of this study was to present the last developments performed on this ergometer and preliminary 3D kinematics analysis from elite kayakers. The characteristics (stiffness and damping) of the bungee cord linking the back of the frame with the trolley were determined using our previous results. An air brake, composed of a flywheel with a heavy wheel and two freewheel-pulleys on a shaft, simulated the water drag on the blades. However, a magnetic brake was added for specific training sessions. The paddle was linked to the pulleys by two ropes. Each side of the frame is equipped with one slide (1 dof in translation) in order to always keep the directions of the ropes parallel to the long axis of the ergometer whatever the instant of the cycle. First trials performed with elite athlete showed the robustness of all the mechanisms developed. 3D kinematic analysis showed the relevance of the adding slides when compared with on-water paddle trajectories observed during the propulsion phase. An instrumentation (3D force sensors at each contact) coupled with a specific interface that allows real time feedback is under development. This innovative ergometer will be used to collect dynamic and kinematic parameters. They will serve as input data of our simulator in order to carry out intra-athlete comparisons and to still improve the design of kayak ergometers
Potentialities of High-Resolution 3-D CZT Drift Strip Detectors for Prompt Gamma-Ray Measurements in BNCT
Recently, new high-resolution cadmiumâzincâtelluride (CZT) drift strip detectors for room temperature gamma-ray spectroscopic imaging were developed by our group. The CZT detectors equipped with orthogonal anode/cathode collecting strips, drift strips and dedicated pulse processing allow a detection area of 6 Ă 20 mm2 and excellent room temperature spectroscopic performance (0.82% FWHM at 661.7 keV). In this work, we investigated the potentialities of these detectors for prompt gamma-ray spectroscopy (PGS) in boron neutron capture therapy (BNCT). The detectors, exploiting the measurement of the 478 keV prompt gamma rays emitted by 94%7Li nuclides from the10B(n, α)7Li reaction, are very appealing for the development of single-photon emission computed tomography (SPECT) systems and Compton cameras in BNCT. High-resolution gamma-ray spectra from10B samples under thermal neutrons were measured at the T.R.I.G.A. Mark II research nuclear reactor of the University of Pavia (Italy)
Opening the path to hard X-/soft gamma-ray focussing: The ASTENA-pathfinder mission
Hard X-/soft gamma-ray astronomy is a crucial field for transient, nuclear and multimessenger astrophysics. However, the spatial localization, imaging capabilities and sensitivity of the measurements are strongly limited for the energy range >70keV. To overcome these limitations, we have proposed a mission concept, ASTENA, submitted to ESA for its program âVoyage 2050â. We will report on a pathfinder of ASTENA, that we intend to propose to ASI as an Italian mission with international participation. It will be based on one of the two instruments aboard ASTENA: a Laue lens with 20m focal length, able to focus hard X-rays in the 50â700keV passband into a 3-d position sensitive focal plane spectrometer. The combination of the focussing properties of the lens and of the localization properties of the detector will provide unparalleled imaging and spectroscopic capabilities, thus enabling studies of phenomena such as gamma-ray bursts afterglows, supernova explosions, positron annihilation lines and many more
Development status of a Laue lens project for gamma-ray astronomy
We report the status of the HAXTEL project, devoted to perform a design study
and the development of a Laue lens prototype. After a summary of the major
results of the design study, the approach adopted to develop a Demonstration
Model of a Laue lens is discussed, the set up described, and some results
presented.Comment: 11 pages, 11 figures, 2007 SPIE Conference on Optics for EUV, X-Ray,
and Gamma-Ray Astronomy II
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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