[en] Purpose: To compare IMRT QA pass rates before and after an in-house MLC leaf calibration procedure. Methods: The MLC leaves and backup jaws on four Elekta linear accelerators with MLCi2 heads were calibrated using the EPID-based RIT Hancock Test as the means for evaluation. The MLCs were considered to be successfully calibrated when they could pass the Hancock Test with criteria of 1 mm jaw position tolerance, and 1 mm leaf position tolerance. IMRT QA results were collected pre- and postcalibration and analyzed using gamma analysis with 3%/3mm DTA criteria. AAPM TG-119 test plans were also compared pre- and post-calibration, at both 2%/2mm DTA and 3%/3mm DTA. Results: A weighted average was performed on the results for all four linear accelerators. The pre-calibration IMRT QA pass rate was 98.3 ± 0.1%, compared with the post-calibration pass rate of 98.5 ± 0.1%. The TG-119 test plan results showed more of an improvement, particularly at the 2%/2mm criteria. The averaged results were 89.1% pre and 96.1% post for the C-shape plan, 94.8% pre and 97.1% post for the multi-target plan, 98.6% pre and 99.7% post for the prostate plan, 94.7% pre and 94.8% post for the head/neck plan. Conclusion: The patient QA results did not show statistically significant improvement at the 3%/3mm DTA criteria after the MLC calibration procedure. However, the TG-119 test cases did show significant improvement at the 2%/2mm level.

[en] Applications of arc plasma processing to high-temperature chemistry of Group V nitrides and Si and Ge alloys are studied. The transition metal nitrides 4f-VN, 4f-NbN, and 4f-TaN are directly synthesized in a dc argon-nitrogen plasma from powders of the metals. A large excess of N₂ is required to form stoichiometric 4f-VN, while the Nb and Ta can only be synthesized with a substoichiometric N content. In a dc argon plasma the alloys V₃Si, VSi₂, NbSi₂, NbGe₂, Cr₃Si, and Mo₃Si are obtained from powder mixtures of the corresponding elements. The compounds are identified by x-ray diffraction patterns and particle shape and size are studied by electron microscopy

[en] Chemical reactions which occur in a thermal plasma between fine powders of tungsten and graphite and between powdered tungsten and methane have been studied. When using a commercial d.c. torch and a standard reactor design, the conversion to tungsten carbide is relatively poor. With a specially designed reactor operating in a transferred-arc mode, nearly complete conversion to carbide results when operating at the same power level and with methane as a reactant. Crystal structures and particle morphologies have been studied with electron microscopy and X-ray diffraction. Several initial stages of the particle-particle and particle-gas reactions have been determined. A number of interesting composite particles corresponding to intermediate reaction steps has been observed. (author)

[en] Fuel cell power systems are emerging as promising means of electrical power generation on account of the associated clean electricity generation process, as well as their suitability for use in a wide range of applications. During the design stage, the development of a computer model for simulating the behaviour of a system under development can facilitate the experimentation and testing of that system's performance. Since the electrical power output of a fuel cell stack is seldom at a suitable fixed voltage, conditioning circuits and their associated controllers must be incorporated in the design of the fuel cell power system. This paper presents a MATLAB/Simulink model that simulates the behaviour of a Proton Exchange Membrane (PEM) fuel cell, conditioning circuits and their controllers. The computer modelling of the PEMFC was based on adopted mathematical models that describe the fuel cell's operational voltage, while accounting for the irreversibilities associated with the fuel cell stack. The conditioning circuits that are included in the Simulink model are a DC-DC converter and DC-AC inverter circuits. These circuits are the commonly utilized power electronics circuits for regulating and conditioning the output voltage from a fuel cell stack. The modelling of the circuits is based on relationships that govern the output voltage behaviour with respect to their input voltages, switching duty cycle and efficiency. In addition, this paper describes a Fuzzy Logic Controller (FLC) design that is aimed at regulating the conditioning circuits to provide and maintain suitable electrical power for a wide range of applications. (author)

[en] INFN-CNAF is the central computing facility of INFN: it is the Italian Tier-1 for the experiments at LHC, but also one of the main Italian computing facilities for several other experiments such as BABAR, CDF, SuperB, Virgo, Argo, AMS, Pamela, MAGIC, Auger etc. Currently there is an installed CPU capacity of 100,000 HS06, a net disk capacity of 9 PB and an equivalent amount of tape storage (these figures are going to be increased in the first half of 2012 respectively to 125,000 HS06, 12 PB and 18 PB). More than 80,000 computing jobs are executed daily on the farm, managed by LSF, accessing the storage, managed by GPFS, with an aggregate bandwidth up to several GB/s. The access to the storage system from the farm is direct through the file protocol. The interconnection of the computing resources and the data storage is based on 10 Gbps technology. The disk-servers and the storage systems are connected through a Storage Area Network allowing a complete flexibility and easiness of management; dedicated disk-servers are connected, also via the SAN, to the tape library. The INFN Tier-1 is connected to the other centers via 3×10 Gbps links (to be upgraded at the end of 2012), including the LHCOPN and to the LHCONE. In this paper we show the main results of our center after 2 full years of run of LHC.

[en] In a Plasma Focus device the plasma collapses into the pinch where it reaches thermonuclear conditions for a few tens of nanoseconds, becoming a multi-radiation source. The nature of the radiation generated depends on the gas filling the chamber and the device working parameters. The self-collimated electron beam generated in the backward direction with respect to the plasma motion is one of the main radiation sources of interest also for medical applications. The electron beam may be guided against a high Z material target to produce an X-ray beam. This technique offers an ultra-high dose rate source of X-rays, able to deliver during the pinch a massive dose (up to 1 Gy per discharge for the PFMA-3 test device), as measured with EBT3 Gafchromicâ’¸film tissue equivalent dosimeters. Given the stochastic behavior of the discharge process, a reliable on-line estimate of the dose-delivered is a very challenging task, in some way preventing a systematic application as a potentially interesting therapy device. This work presents an approach to linking the dose registered by the EBT3 Gafchromicâ’¸films with the information contained in the signal recorded during the current discharge process. Processing the signal with the Wigner-Ville distribution, a spectrogram was obtained, displaying the information on intensity at various frequency scales, identifying the band of frequencies representative of the pinch events and define some patterns correlated with the dose.