In recent years, it has become increasingly clear that the critical issue in gradient methods is the choice of the step length, whereas using gradient as the search direction may lead to very ...effective algorithms, whose surprising behaviour has only been partially explained, mostly in terms of the spectrum of the Hessian matrix. On the other hand, the convergence of the classical Cauchy steepest descent (SD) method has been analysed extensively and related to the spectral properties of the Hessian matrix, but the connection with the spectrum of the Hessian has not been exploited much to modify the method in order to improve its behaviour. In this work, we show how, for convex quadratic problems, moving from some theoretical properties of the SD method, second-order information provided by the step length can be exploited to dramatically improve the usually poor practical behaviour of this method. This allows us to achieve computational results comparable with those of the Barzilai and Borwein algorithm, with the further advantage of monotonic behaviour.
We invented (2007) the VSiPMT, a novel, high-gain, photo detector device and we publically proposed this idea in an International Conference for the first time at the 11 super(th) Topical Seminar on ...Innovative Particle and Radiation Detectors (IPRD08) in Siena, triggering deep discussions on the feasibility of the device itself and on the convenience of such a solution. After several years spent in designing, evaluation, tests and eventually negotiations with some suppliers, we finally got a couple of prototypes of the Vacuum Silicon Photo Multiplier Tube (VSiPMT) made under our specifications by Hamamatsu. We present in this paper the most important results of characterization tests of the first prototypes of the VSiPMT.
Mobile-Dose has been designed for a very innovative use: the integration in a robotic machinery for automatic preparation of radioactive doses, to be injected to patients in Nuclear Medicine ...Departments, with real time measurement of the activity under preparation. Mobile-Dose gives a constant measurement of the dose during the filling of vials or syringes, triggering the end of the filling process based on a predefined dose limit. Several applications of Mobile-Dose have been delivered worldwide, from Italian hospitals and clinics to European and Japanese ones. The design of such an instrument and its integration in robotic machineries, was required by an Italian company specialised in radiation protection tools for nuclear applications, in the period 2001-2003. At the time of its design, apparently no commercial instruments with a suitable interfacing capability to the external world existed: we designed it in order to satisfy all the strict requirements coming from the medical aspects (precision within 10%, repeatability, stability, time response) and from the industrial conceiving principles that are mandatory to ensure a good reliability in such a complicated environment. The instrument is suitable to be used in standalone mode too, thanks to its portability and compactness and to the intelligent operator panel programmed for this purpose.
Using RPC Detectors as Cosmic Rays Monitor de Asmundis, R.; Avella, P.; Toglia, F.
IEEE transactions on nuclear science,
06/2007, Letnik:
54, Številka:
3
Journal Article
Recenzirano
We have measured the cosmic ray absolute flux and its variations caused by the ldquoday-nightrdquo and the ldquobarometricrdquo effects, by using a telescope of resistive plate chamber (RPC) ...detectors. Because of the high sensitivity needed for this measure, the RPC behaviour must be very well controlled and all the influences induced by the environmental parameters, must be compensated. For this purpose we introduced, among others features, an alternative method for the stabilization of the RPC working point. We present here all the results for both aspects: the cosmic ray flux measurements, the barometric effect and a description of the RPC stabilization method used.
We describe a system test of the ATLAS muon spectrometer performed at the H8 beam line of the CERN Super-Proton-Synchrotron (SPS) during 2003. The setup includes one barrel tower made of six ...Monitored Drift Tube chambers equipped with an alignment system and four Resistive Plate Chambers, and one end-cap octant consisting of six end-cap MDT equipped with an alignment system and one triplet and two doublets of Thin Gap Chambers. Many system aspects of the muon spectrometer have been studied with this setup, from the performance of the precision and trigger chambers to the capability to align the precision chambers at the level of a few tens of micrometers and to operate the muon trigger at the crossing frequency of the LHC.
In order to ensure that the resistive plate chambers used in the ATLAS experiment will not show, during their operation, any abnormal aging effect which could degrade their performances, an aging ...test is being performed at X5-GIF, CERN's gamma irradiation facility. In this paper, the latest results are presented, together with an example of successful damage recovery technique.
Ageing test of the ATLAS RPCs at X5-GIF Aielli, G.; Alviggi, M.; Ammosov, V. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
11/2004, Letnik:
533, Številka:
1-2
Journal Article
Recenzirano
Odprti dostop
An ageing test of three ATLAS production RPC stations is in course at X5-GIF, the CERN irradiation facility. The chamber efficiencies are monitored using cosmic rays triggered by a scintillator ...hodoscope. Higher statistics measurements are made when the X5 muon beam is available. We report here the measurements of the efficiency versus operating voltage at different source intensities, up to a maximum counting rate of about 700Hz/cm2. We describe the performance of the chambers during the test up to an overall ageing of 4 ATLAS equivalent years corresponding to an integrated charge of 0.12C/cm2, including a safety factor of 5.
The proton-proton beam crossing at the LHC accelerator at CERN will have a rate of 40 MHz at the project luminosity. The ATLAS Trigger System has been designed in three levels in order to select only ...interesting physics events reducing from that rate of 40 MHz to the foreseen storage rate of about 200 Hz. The First Level reduces the output rate to about 100 kHz. The ATLAS Muon Spectrometer has been designed to perform stand-alone triggering and measurement of Muon transverse momentum up to 1 TeV/c with good resolution (from 3% at 10 GeV/c up to 10% at 1 TeV/c). In the Barrel region of the Muon Spectrometer the Level-1 trigger is given by means of three layers of resistive plate chamber detectors (RPC): a gaseous detector working in avalanche mode composed by two plates of high-resistivity bakelite and two orthogonal planes of read-out strips. The logic of the Level-1 barrel Muon trigger is based on the search of patterns of RPC hits in the three layers consistent with a high transverse momentum Muon track originated from the interaction vertex. The associated trigger electronics is based on dedicated processors, the Coincidence Matrix boards, performing space coincidences and time gates and providing the RPC readout as well. A detailed simulation of the ATLAS Experiment and of both the hardware components and the logic of the Level-1 Muon Trigger in the barrel of the Muon Spectrometer has been performed. This simulation has been used not only to evaluate the performances of the system but also to define the hardware set-up such as the cabling of both the trigger detectors and the trigger electronics modules. A description of both the Level-1 Muon Trigger system in the barrel and the RPC detectors, with their cosmic rays quality tests, will be presented together with the trigger performances and rates calculations evaluated for Muons over a wide range of p T and preliminary studies on the impact of accidental triggers due to low energy background particles in the experimental area
RPC ageing studies Aielli, G; Camarri, P; Cardarelli, R ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
02/2002, Letnik:
478, Številka:
1
Journal Article
Recenzirano
Odprti dostop
A 15-month ageing test of an ATLAS module “0” RPC has been performed at the GIF X5 CERN irradiation facility. The aged RPC performances largely fulfilled the ATLAS requirements. However, the test ...showed a significant reduction of the RPC maximum rate capability, from almost
2
kHz
cm
−2
to a few hundred
Hz
cm
−2
, due to the total charge integrated during the test. The reasons for this ageing phenomenon are found to be related to an increase of the total electrode plates resistance as it was already pointed out in previous tests on smaller prototypes. This is found to be not only due to a possible increase of the plate resistivity but mainly to a degradation of the graphite coating.
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