177 research outputs found
Новое семейство преобразователей напряжения с низким уровнем гармонических искажений с использованием соединенных индуктивностей
У даній статті представлений новий підхід до багатоімпульсних перетворювачів напруги, зокрема інверторів напруги і матричних перетворювачів на основі кількох типових ідентичних модулів, з'єднаних паралельно з використанням Inductive Current Splitters/Mergers. Такі механізми призводить до зниження напруги спотворення при низькій частоті перемикання. Пропоновані нові механізми була підтверджені за допомогою моделювання. Лабораторні моделі 18- і 24-імпульсних 3-рівневих перетворювачів напруги були також досліджені експериментально. Результати моделювання і лабораторних випробувань експериментальних моделей представлені в роботі.This paper presented a novel approach to the multipulse voltage converters (VC), especially voltage source inverters (VSI) and matric converters (MC) based on several typical identical modules connected in parallel using Inductive Current Splitters/Mergers. Such arrangements resulting in lower voltage distortions at extremely low switching frequency. Proposed new arrangements was validated by simulation. Laboratory models of 18- and 24-pulse 3-level VSI arrangements was also investigated experimentally. Results of simulation and laboratory tests of experimental models are presented in the paper.В данной статье представлен новый подход к многоимпульсным преобразователям напряжения, в том числе инверторам напряжения и матричным преобразователям на основе нескольких типовых идентичных модулей, соединенных параллельно с использованием Inductive Current Splitters / Mergers. Такие механизмы приводит к снижению напряжения искажения при низкой частоте переключения. Предлагаемые новые механизмы были подтверждены с помощью моделирования. Лабораторные модели 18- и 24-импульсных 3-уровневый преобразователей напряжения были также исследованы экспериментально. Результаты моделирования и лабораторных испытаний экспериментальных моделей представлены в работе
System Response Kernel Calculation for List-mode Reconstruction in Strip PET Detector
Reconstruction of the image in Positron Emission Tomographs (PET) requires
the knowledge of the system response kernel which describes the contribution of
each pixel (voxel) to each tube of response (TOR). This is especially important
in list-mode reconstruction systems, where an efficient analytical
approximation of such function is required. In this contribution, we present a
derivation of the system response kernel for a novel 2D strip PET.Comment: 10 pages, 2 figures; Presented at Symposium on applied nuclear
physics and innovative technologies, Cracow, 03-06 June 201
A novel method for calibration and monitoring of time synchronization of TOF-PET scanners by means of cosmic rays
All of the present methods for calibration and monitoring of TOF-PET scanner
detectors utilize radioactive isotopes such as e.g. Na or Ge,
which are placed or rotate inside the scanner. In this article we describe a
novel method based on the cosmic rays application to the PET calibration and
monitoring methods. The concept allows to overcome many of the drawbacks of the
present methods and it is well suited for newly developed TOF-PET scanners with
a large longitudinal field of view. The method enables also monitoring of the
quality of the scintillator materials and in general allows for the continuous
quality assurance of the PET detector performance.Comment: 10 pages, 7 figure
Beam profile investigation of the new collimator system for the J-PET detector
Jagiellonian Positron Emission Tomograph (J-PET) is a multi-purpose detector
which will be used for search for discrete symmetries violations in the decays
of positronium atoms and for investigations with positronium atoms in
life-sciences and medical diagnostics. In this article we present three methods
for determination of the beam profile of collimated annihilation gamma quanta.
Precise monitoring of this profile is essential for time and energy calibration
of the J-PET detector and for the determination of the library of model signals
used in the hit-time and hit-position reconstruction. We have we have shown
that usage of two lead bricks with dimensions of 5x10x20 cm^3 enables to form a
beam of annihilation quanta with Gaussian profile characterized by 1 mm FWHM.
Determination of this characteristic is essential for designing and
construction the collimator system for the 24-module J-PET prototype.
Simulations of the beam profile for different collimator dimensions were
performed. This allowed us to choose optimal collimation system in terms of the
beam profile parameters, dimensions and weight of the collimator taking into
account the design of the 24 module J-PET detector.Comment: 14 pages, 9 figure
Application of Compressive Sensing Theory for the Reconstruction of Signals in Plastic Scintillators
Compressive Sensing theory says that it is possible to reconstruct a measured
signal if an enough sparse representation of this signal exists in comparison
to the number of random measurements. This theory was applied to reconstruct
signals from measurements of plastic scintillators. Sparse representation of
obtained signals was found using SVD transform.Comment: 7 pages, 3 figures; Presented at Symposium on applied nuclear physics
and innovative technologies, Cracow, 03-06 June 201
Searches for discrete symmetries violation in ortho-positronium decay using the J-PET detector
In this paper we present prospects for using the J-PET detector to search for
discrete symmetries violations in a purely leptonic system of the positronium
atom. We discuss tests of CP and CPT symmetries by means of ortho-positronium
decays into three photons. No zero expectation values for chosen correlations
between ortho-positronium spin and momentum vectors of photons would imply the
existence of physics phenomena beyond the Standard Model. Previous measurements
resulted in violation amplitude parameters for CP and CPT symmetries consistent
with zero, with an uncertainty of about 10-3. The J-PET detector allows to
determine those values with better precision thanks to a unique time and
angular esolution combined with a high geometrical acceptance. Achieving the
aforementioned is possible due to application of polymer scintillators instead
of crystals as detectors of annihilation quanta.Comment: in Nukleonika 201
Studies of unicellular micro-organisms Saccharomyces cerevisiae by means of Positron Annihilation Lifetime Spectroscopy
Results of Positron Annihilation Lifetime Spectroscopy (PALS) and microscopic
studies on simple microorganisms: brewing yeasts are presented. Lifetime of
ortho - positronium (o-Ps) were found to change from 2.4 to 2.9 ns (longer
lived component) for lyophilised and aqueous yeasts, respectively. Also
hygroscopicity of yeasts in time was examined, allowing to check how water -
the main component of the cell - affects PALS parameters, thus lifetime of o-Ps
were found to change from 1.2 to 1.4 ns (shorter lived component) for the dried
yeasts. The time sufficient to hydrate the cells was found below 10 hours. In
the presence of liquid water an indication of reorganization of yeast in the
molecular scale was observed.
Microscopic images of the lyophilised, dried and wet yeasts with best
possible resolution were obtained using Inverted Microscopy (IM) and
Environmental Scanning Electron Microscopy (ESEM) methods. As a result visible
changes to the surface of the cell membrane were observed in ESEM images.Comment: Nukleonika (2015
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