ALBERT

Description: This paper presents a novel energy management strategy for a hybridized power source small urban electric vehicle (EV). First, an analysis of load requirements for typical urban driving cycles is presented. Thereafter, the energy and power management issues are addressed for a multisource EV to define an improved management architecture. A dynamically restricted search space strategy coupled with a simulated annealing technique is exploited to accomplish the global optimization of the energy management system (EMS). The control of the dc/dc converter operations based on this EMS is also presented. The multiple sources have been simulated using an overall model implemented in Matlab/Simulink. A reduced-scale prototype has been built to analyze the performance of the energy management strategy. The results obtained show that energy management has been enhanced leading to an increase of the vehicle performance with reduced size embarked sources.

Description: Prediction intervals (PIs) are a promising tool for quantification of uncertainties associated with point forecasts of wind power. However, construction of PIs using parametric methods is questionable, as forecast errors do not follow a standard distribution. This paper proposes a nonparametric method for construction of reliable PIs for neural network (NN) forecasts. A lower upper bound estimation (LUBE) method is adapted for construction of PIs for wind power generation. A new framework is proposed for synthesizing PIs generated using an ensemble of NN models in the LUBE method. This is done to guard against NN performance instability in generating reliable and informative PIs. A validation set is applied for short listing NNs based on the quality of PIs. Then, PIs constructed using filtered NNs are aggregated to obtain combined PIs. Performance of the proposed method is examined using data sets taken from two wind farms in Australia. Simulation results indicate that the quality of combined PIs is significantly superior to the quality of PIs constructed using NN models ranked and filtered by the validation set.

Description: This paper presents a supervisory control unit (SCU) combined with short-term ahead wind speed prediction for proper and effective management of the stored energy in a small capacity flywheel energy storage system (FESS) which is used to mitigate the output power fluctuations of an aggregated wind farm. Wind speed prediction is critical for a wind energy conversion system since it may greatly influence the issues related to effective energy management, dynamic control of wind turbine, and improvement of the overall efficiency of the power generation system. In this study, a wind speed prediction model is developed by artificial neural network (ANN) which has advantages over the conventional prediction schemes including data error tolerance and ease in adaptability. The proposed SCU-based control would help to reduce the size of the energy storage system for minimizing wind power fluctuation taking the advantage of prediction scheme. The model for prediction using ANN is developed in MATLAB/Simulink and interfaced with PSCAD/EMTDC. Effectiveness of the proposed control system is illustrated using real wind speed data in various operating conditions.

Description: Due to its reduced communication overhead and robustness to failures, distributed energy management is of paramount importance in smart grids, especially in microgrids, which feature distributed generation (DG) and distributed storage (DS). Distributed economic dispatch for a microgrid with high renewable energy penetration and demand-side management operating in grid-connected mode is considered in this paper. To address the intrinsically stochastic availability of renewable energy sources (RES), a novel power scheduling approach is introduced. The approach involves the actual renewable energy as well as the energy traded with the main grid, so that the supply–demand balance is maintained. The optimal scheduling strategy minimizes the microgrid net cost, which includes DG and DS costs, utility of dispatchable loads, and worst-case transaction cost stemming from the uncertainty in RES. Leveraging the dual decomposition, the optimization problem formulated is solved in a distributed fashion by the local controllers of DG, DS, and dispatchable loads. Numerical results are reported to corroborate the effectiveness of the novel approach.

Description: The present paper investigates the effect of high penetration of photovoltaic (PV) systems on the small signal stability of a large power system. Reduced system inertia and altered power flow patterns as a result of the addition of the utility scale and residential rooftop PVs that replace a portion of conventional generation resources, may lead to decreased damping of the critical modes of the system. To identify the critical modes of the system and the effect of the high PV penetration on these modes, eigenvalue analysis is carried out on the aforementioned system under various PV penetration levels. To substantiate the results observed from the small signal analysis, transient analysis is carried out on the system under various PV penetration levels. The simulation results effectively identify the impact of high PV penetration on small signal stability of the studied system.

Description: A speed exclusion zone algorithm to prevent the rotor rotational frequency from exciting the side-side tower mode in a variable-speed wind turbine was designed. The algorithm was first tested on a simple wind turbine model developed in Simulink and then implemented and tested on an experimental test rig. Different speed exclusion zone widths were tested to observe how the performance of the wind turbine is affected. Results obtained from both simulations and experiments showed the effectiveness of the speed exclusion zone algorithm in preventing excitation of tower resonance. Results from different speed exclusion zone widths showed that with a wider exclusion zone, the tower mode is excited less at the expense of a larger power loss.

Description: A control strategy for the quasi-Z-source inverter (qZSI) with a battery-based photovoltaic (PV) power conversion system is proposed. A battery-assisted qZSI can buck/boost PV panel voltage by introducing shoot-through states, and make full use of PV power by the energy-stored battery paralleled to the quasi-Z-source capacitor. A dynamic small-signal model of the battery-assisted qZSI is established to design a closed-loop controller for regulating shoot-through duty ratio and managing the battery's energy storage. A modified space vector modulation (SVM) technique for the qZSI is applied to achieve low harmonics, high voltage utilization, and high efficiency. A P-Q decoupled grid-tie power injection is fulfilled with the maximum power capture from PV panels and the unity power factor. The validity of the proposed PV system is proved by experimental results, showing an efficient method for the energy-stored PV power generation.

Description: Doubly-fed induction generator (DFIG)-based wind turbines (WTs) are reported to suffer reliability problems due to the presence of slip-rings, brushes, and the gearbox. These disadvantages encouraged several research groups to investigate the viability of employing single or double-frame brushless cascade DFIGs (BCDFIGs) in grid-connected multimegawatt WTs especially offshore and in solar chimney power plants. In this regard, this paper tackles three main issues. Initially, the expected reduction in gear ratio when BCDFIGs are used instead of DFIGs is examined from a steady state perspective. A reduction would lead to less frequent maintenance and an improved return on investment. Next, a detailed comparison between DFIG-WTs and BCDFIG-WTs under unbalanced grid voltage is presented. Finally, the extent to which a multimegawatt BCDFIG-WT is grid code compliant in terms of fault ride-through capability is studied. This is illustrated by comparing and quantifying the response of a DFIG-WT and a BCDFIG-WT to a severe three-phase voltage dip. Simulation and experimental results indicate promising behavior for BCDFIGs during disturbances.

Description: We analyze the potential benefits of colocating wind and concentrating solar power (CSP) plants in the southwestern U.S. Using a location in western Texas as a case study, we demonstrate that such a deployment strategy can improve the capacity factor of the combined plant and the associated transmission investment. This is because of two synergies between wind and CSP: 1) the negative correlation between real-time wind and solar resource availability and 2) the use of low-cost high-efficiency thermal energy storage in CSP. The economic tradeoff between transmission and system performance is highly sensitive to CSP and transmission costs. We demonstrate that a number of deployment configurations, which include up to 67% CSP, yield a positive net return on investment.

Description: Renewable energy resources, especially wind power, are expected to provide a considerable portion of the world energy requirements in the near future. Large-scale wind power penetration impacts the electricity industry in many aspects and raises a number of technical challenges for the electricity network. A day-ahead network-constrained market clearing formulation is proposed which considers demand side resources. The proposed approach can provide flexible load profile and reduce the need for ramp up/down services by the conventional generators. This method can potentially facilitate a large penetration of wind power by shifting the wind power generation from the off-peak periods to the high-peak hours. The validity of the proposed approach has been verified using the IEEE 30 bus and 57 bus test systems.

Description: The small generation units including cogeneration units and renewables have been widely spread during the last decades. These units raise several questions regarding the power system, e.g., their integration into power system control or their role on the supply-side of smart grids. A multiagent model was established in order to facilitate the investigations of the emerged questions. Several viewpoints are taken into account and built into the model considering technical specifications, proper wind-speed and temperature simulations, constraints of heating service, fuel consumption, legal regulation, outages, and services. A state-based method is elaborated in order to generalize different technologies. The different aspects of operation control are represented by agent strategies. Applying these methods resulted in an easy-to-follow and flexible model. This paper is dealing with the developed multiagent-based model applied to study the distributed generation system from many viewpoints like power system balance, virtual power plant, or smart grid scheduling.

Description: The trend towards multimegawatt (multi-MW) wind turbines and the increasing interest in direct-drive variable-speed wind energy systems have made multilevel converters a promising candidate for large wind energy conversion systems. This paper presents a new hybrid modular multilevel converter for interfacing a full-scale, permanent magnet synchronous generator (PMSG)-based direct-drive variable-speed wind energy conversion system (WECS). The proposed hybrid converter, which is used on the grid side of the system, consists of a three-level modular multilevel converter (MMC) in series connection with three H-bridge modules. The generator-side converter is based on a conventional three-level neutral-point-clamped converter. The proposed hybrid converter, as opposed to the existing full-scale multilevel converter-based wind energy systems, provides structural modularity and a higher dc-bus voltage utilization. This paper formulates and analyzes the internal dynamics of the proposed hybrid converter including the circulating currents and the capacitor voltage ripples. The ac components of the circulating currents, if not properly reduced, increase the amplitude of the capacitor voltage ripples, rating values of the converter components, and losses. Based on the analysis, closed-loop circulating current and capacitor voltage ripple reduction techniques are developed. The reduction of capacitor voltage ripples help reduce the capacitor value. A mathematical model is also developed for the overall WECS. Performance of the overall WECS, under the proposed multilevel converter-based topology and controls, is evaluated based on time domain simulations in the PSCAD/EMTDC environment.

Description: Electric vehicles (EVs) are likely to have a continued presence in the light-vehicle market in the next few decades. As a result, EV charging will put an extra burden on the distribution grid and adjustments need to be made in some cases. On the other hand, EVs have the potential to support the grid as well. This paper presents a single-phase bidirectional charger topology which pairs up a photovoltaic (PV) source with an EV charger resulting in production cost reduction. The presented topology is then used for vehicle-to-grid (V2G) services. The main focus of this paper is on power quality services which only slightly discharge the battery. Among these services, it studies the possibility of local reactive injection of EVs connected to the grid through a single-phase charger to compensate for voltage drops caused by motor startup or inductive loads. It also studies the possibility of active power injection of EVs for short time periods during PV transients in cloudy weather to keep the system stable. It also studies the potential of EVs to help during low voltage ride-through of the PV sources. The studies are performed using Simulink simulations and a real-time implementation in Real Time Digital Simulator (RTDS). The results demonstrate the effectiveness of power quality V2G services with small wear on the EV battery.

Description: The short-term wind power scenarios have a significant impact on the operation cost and power system reliability due to the stochastic generation scheduling of wind-integrated power systems. In order to obtain the scenarios containing the information of forecast error distribution and fluctuation distribution for short-term wind power, a scenario generation method is proposed. This paper characterizes forecast error via empirical distributions of a set of forecast bins and assumes that wind power fluctuations over unit interval follow $t$ location-scale distribution. An inverse transform sampling from a multivariate normal distribution is adopted to generate a large number of wind power scenarios. The covariance matrix of the multivariate normal distribution is estimated to fit the distribution of historical wind power fluctuations. The proposed scenario generation method is applied to the actual aggregate wind power data in the whole regions of Ireland's Power System. The results indicate that the variability of wind power scenarios can be adjusted by estimating the key range parameter in the exponential covariance structure of a multivariate normal distribution.

Description: A fuzzy fault-tolerant control (FFTC) framework is proposed for wind-diesel-hybrid systems (WDHS) with time-varying bounded sensor faults. The algorithm utilizes fuzzy systems based on “Takagi–Sugeno” (TS) fuzzy models to represent nonlinear systems. A fuzzy proportional-integral estimation observer (FPIEO) design is proposed to achieve fault estimation of TS models with abrupt sensor faults. Sufficient conditions are derived for robust stabilization in the sense of Lyapunov asymptotic stability and are formulated in the format of linear matrix inequalities (LMIs) to obtain controller gains and observer gains. The proposed algorithm maximizes the produced power, minimizes the voltage ripple, and is able to maintain the system's stability during the sensor faults. A physical model of the WDHS is presented and transformed into a TS model. Then, an FFTC algorithm is developed and applied to a WDHS to demonstrate the effectiveness of this method.

Description: Modeling wind speed time series (WSTS) is an essential part of network planning studies in order to generate synthetic wind power time series (WPTS). Hence, this paper proposes a methodology to equip planners with accurate simulation of wind speed and power variations as well as complete temporal dependence structure based on the copula theory. Unlike traditional autoregressive and Markov chain methods, the suggested technique is well-prepared to deal with “nonlinear long-memory temporal dependence” and “non-Gaussian empirical probability distributions” of the WSTS. Meanwhile, the proposed statistical modeling framework is compatible with the scenario-based analysis of active networks as well. Furthermore, a case study for optimal sizing of an autonomous wind/photovoltaic/battery system is presented. The purpose of the presented study is to fully examine the accuracy and effectiveness of the copula-based model of wind generation for planning nonmemoryless power systems. Among a list of commercially available system devices, the optimal number and type of units are calculated ensuring both a minimum 20-year round total system cost and a perfect reliability. The genetic algorithm is used in four wind generation scenarios consisting of real and simulated WPTS. Then, considering the corresponding optimal solutions, the autoregressive moving average (ARMA), nonparametric Markov and proposed copula-based simulations are compared against real data.

Description: This paper presents series grid interface topologies for enhancing the fault ride-through (FRT) performance of doubly-fed induction generator (DFIG)-based wind turbines (WTs). Two voltage booster schemes, 1) dynamic voltage restorer (DVR) and 2) resistive type high temperature superconducting fault current limiter (HTS-FCL), are designed and implemented. The test system represents a WT connected to an electric grid with alternatively employing DVR and HTS-FCL. Both schemes provide fast mitigation of voltage dip that maintains the nominal operating conditions for DFIG-WT. To achieve a flexible control solution for balanced and unbalanced fault conditions, the DVR employs positive and negative sequence controllers while the HTS-FCL is designed to perform fast quenching for each phase individually. The potential of the two booster schemes is evaluated and analyzed in positive and negative sequence reference frames. Comprehensive simulation studies are presented to verify the capability of the series grid interface schemes for ensuring the normal operation and smooth wind power evacuation with effective isolation from grid faults. Furthermore, the grid code requirements of reactive current support are evaluated for both schemes at various fault scenarios.

Description: This paper presents a real-time mechanism to tolerate faults occurring in a wind turbine (WT) system. This system is a FAST coded simulator designed by the U.S. National Renewable Energy Laboratory's (NREL's) National Wind Turbine Center. The demonstrated mechanism lies under the taxonomy of active fault-tolerant control (AFTC) systems, namely the projection-based approach. In the proposed approach, we do not use any a priori information about the model of the turbine in real-time. In fact, we use the online measurements generated by WT. Based on the given control objectives, and the observed measurements, an occurring fault is accommodated by reconfiguring the controller such that the turbine generates the rated power even under faulty conditions. Second, no use of an explicit fault-diagnosis module is seen in this approach. Therefore, the fault accommodation delay in the proposed AFTC structure is smaller than the delay as experienced in the traditional structure of AFTC systems.

Description: Conventionally operated full power converter wind plants show high short-term power output variability caused by variable winds, and does not contribute to the power system inertia due to the decoupled generator speed and grid frequency. There is, however, abundant inertial resources in wind plant rotors for both smoothing of output power and for synthetic inertia contribution. Together with added frequency controlling functionality, this could facilitate inclusion of wind power in islanding systems, enabling greater system loads and enhancing power system stability. This paper describes modeling of power smoothing and frequency controlling wind plants and assesses different control strategies as well as the grid frequency performance gains achievable over hydro powered islanding systems and over islanding systems incorporating both hydro power and conventional wind plants. The results show that wind plant power output could be smoothed in the short time frame, and support frequency in both primary and secondary frequency control timescales including droop functionality.

Description: This paper deals principally with the grid connection problem of a kite-based system, named the “Kite Generator System (KGS).” It presents a control scheme of a closed-orbit KGS, which is a wind power system with a relaxation cycle. Such a system consists of a kite with its orientation mechanism and a power transformation system that connects the previous part to the electric grid. Starting from a given closed orbit, the optimal tether's length rate variation (the kite's tether radial velocity) and the optimal orbit's period are found. The trajectory-tracking problem is not considered in this paper; only the kite's tether radial velocity is controlled via the electric machine rotation velocity. The power transformation system transforms the mechanical energy generated by the kite into electrical energy that can be transferred to the grid. A Matlab/simulink model of the KGS is employed to observe its behavior, and to insure the control of its mechanical and electrical variables. In order to improve the KGS's efficiency in case of slow changes of wind speed, a maximum power point tracking (MPPT) algorithm is proposed.

Description: To maximize the revenue from selling energy, photovoltaic systems (PVs) in general operate in the so-called maximum power point tracking mode. However, the increasing penetration of renewable energy sources in power systems has motivated the design of innovative control to provide ancillary services. The focus of this paper is to develop a new control strategy that enables PVs to adjust the active power outputs and provide frequency regulation to power systems. In this strategy, two different modes are designed: 1) the frequency droop control mode for PVs to provide primary frequency support to power systems, and 2) the emergency control mode to prevent system frequency collapse and, therefore, to prevent too much generation tripping after fault. Based on a detailed PV dynamic model, simulation results show the effectiveness of the proposed control strategy in improving the frequency stability.

Description: Standalone microgrids with renewable sources and battery storage play an important role in solving power supply problems in remote areas such as islands. To achieve reliable and economic operations of a standalone microgrid, in addition to the consideration of utilization of renewable resources, the lifetime characteristics of a battery energy storage system also need to be fully investigated. In this paper, in order to realize the economic operation of a recently developed standalone microgrid on Dongfushan Island in China, an optimization model including battery life loss cost, operation and maintenance cost, fuel cost, and environmental cost is established to obtain a set of optimal parameters of operation strategy. Considering the lifetime characteristics of lead–acid batteries, a multiobjective optimization to minimize power generation cost and to maximize the useful life of lead–acid batteries has been achieved via the nondominated sorting genetic algorithm (NSGA-II). The results show that the proposed method can optimize the system operations under different scenarios and help users obtain the optimal operation schemes of the actual microgrid system.

Description: Plug-in electric vehicles in the future will possibly emerge widely in city areas. Fleets of such vehicles in large numbers could be regarded as considerable stochastic loads in view of the electrical grid. Moreover, they are not stabled in unique positions to define their impact on the grid. Municipal parking lots could be considered as important aggregators letting these vehicles interact with the utility grid in certain positions. A bidirectional power interface in a parking lot could link electric vehicles with the utility grid or any storage and dispersed generation. Such vehicles, depending on their need, could transact power with parking lots. Considering parking lots equipped with power interfaces, in more general terms, parking-to-vehicle and vehicle-to-parking are propose here instead of conventional grid-to-vehicle and vehicle-to-grid concepts. Based on statistical data and adopting general regulations on vehicles (dis)charging, a novel stochastic methodology is presented to estimate total daily impact of vehicles aggregated in parking lots on the grid. Different scenarios of plug-in vehicles' penetration are suggested in this paper and finally, the scenarios are simulated on standard grids that include several parking lots. The results show acceptable penetration level margins in terms of bus voltages and grid power loss.

Description: It is demonstrated that a physical-based equivalent electrical circuit could be developed based on electrochemical impedance spectroscopy (EIS) to describe electrochemical performance of a commercial $hbox{Li}_{1-{x}}hbox{PO}_{4}$ -cathode, Li-ion cell. This model uses only EIS modeling and Fourier transform techniques to provide reasonably accurate voltage performance characteristics while providing insight into the physical processes at work in the cell.

Description: The demand for reducing fossil fuel consumption and carbon emissions has stimulated the development and deployment of electric vehicles (EVs). The reliability of power systems will be significantly influenced by the increasing penetration of EVs. Currently, there are mainly two potential modes for EVs charging: 1) plug-in mode and 2) battery exchange (BE) mode. There have been many papers studying the impact of EVs using plug-in mode. However, research on BE mode is still only limited. This paper aims at estimating the reliability impact caused by EVs using BE mode. First, the behavior of EV users under BE mode are extracted from two reliable databases. The behavior extraction method is developed specifically for BE mode, which is modified based on a method originally designed for plug-in mode. Afterwards, power system reliability is studied from the viewpoint of both the power system and the EV users by introducing a new reliability index named User Demand Not Satisfied (UDNS). The algorithm for reliability assessment is developed based on an algorithm designed for energy storage system (ESS) integration. The numerical results demonstrate the integration of EVs using BE mode can greatly benefit the reliability performances of power systems.

Description: As increasing number of nations, industries, and individuals are involved in the carbon mitigation initiative, it becomes significant to answer what amount of carbon emissions social entities are responsible for, especially from electricity service. In this paper, a carbon flow tracing method is presented to determine carbon emissions obligation from electricity consumption. The method traces energy sources of electricity consumption across the electricity network to determine the indirect carbon emissions caused. From a “generation-to-consumption” perspective, the transmission characteristic of electricity supply and locational energy mix are reflected. The method is employed to address two important issues uniformly, i.e., carbon accounting at the regional level and locational carbon intensity assessment at the user level, respectively. Test results from two examples show that the method is a preferable choice to solve the two problems. Additionally, the method may contribute to carbon reduction cooperation and end user participation in carbon mitigation.

Description: This paper presents an intelligent economic operation of smart grid environment facilitating an advanced quantum evolutionary method. The proposed method models the wind generation (WG) and photovoltaic (PV) generation as renewable power generation sources as a measure of global warming effect. Thermal generators (TGs) are included in this model to provide the maximum amount of energy to meet consumers' demand. On the other hand, plug-in hybrid electric vehicles (PHEVs) are capable of reducing CO $_2$ , NO $_x$ , and gradually becoming an integral part of smart-grid infrastructure. Such integration introduces uncertainties into the system that are addressed by fuzzy-logic-based formulations. Demanded load, wind speed, solar radiation, and number of involved PHEVs are taken under fuzzy formulations. An intelligent quantum inspired evolutionary algorithm (IQEA) is proposed and applied in this model to perform the intelligent economic scheduling operation concerning scheduling and dispatching TG, WG, PV, and PHEV. IQEA features intelligent operators such as sophisticated rotation operator, differential operator, etc. The method is tested on a hypothetical power system with 10 thermal units, equivalent number of PHEVs, equivalent solar and wind farm. The simulation results will show the effectiveness of IQEA that provides excellent operational resource scheduling while reducing the production cost and emission.

Description: Often voltage rise along low voltage (LV) networks limits their capacity to accommodate more renewable energy (RE) sources. This paper proposes a robust and effective approach to coordinate customers' resources and control voltage rise in LV networks, where photovoltaics (PVs) are considered as the RE sources. The proposed coordination algorithm includes both localized and distributed control strategies. The localized strategy determines the value of PV inverter active and reactive power, while the distributed strategy coordinates customers' energy storage units (ESUs). To verify the effectiveness of proposed approach, a typical residential LV network is used and simulated in the PSCAD-EMTC platform.

Description: It is well known that control systems, which can modulate the power takeoff force of a wave energy device, have the capability of extending the effective device bandwidth and thereby improve energy capture. For an array of wave energy devices, there is the additional complication that each device is subject to radiated waves from other devices, which are a function of the device motion and, hence, an indirect function of each of the device controllers. This gives the possibility of enhancing the energy harvesting properties of the wave farm as a whole, by giving each controller information about the motion of other devices and employing a global performance function which allows coordinated control for the overall benefit of the farm. This paper examines the possibilities of using such coordinated control and makes conclusions on the types of devices, and types of arrays, that might benefit from such coordinated control. In addition, the overall benefit of a global array control strategy, compared to independent control of each device, is assessed against the added complexity of a coordinated control strategy.

Description: Novel fabrication methods for cost-effective and large-volume production of important lanthanide halide scintillators are currently being explored.

Description: Positron emission tomography (PET) detectors based on continuous scintillation crystals can achieve very good performance and have a number of practical advantages compared to detectors based on a pixelated array of crystals. Our goal is to develop a thick continuous detector with high energy and spatial resolution, along with high $gamma$ -photon capture efficiency. We examine the performance of two crystal blocks: a 46 $,times,$ 46 $,times,$ 14 mm $^{3}$ and a 48 $,times,$ 48 $,times,$ 25 mm $^{3}$ block of LYSO (Lutetium Yttrium Orthosilicate). Using Maximum Likelihood (ML) positioning based upon the light response function (LRF) in the 14 mm thick crystal, we measure a spatial resolution of 3 mm in the central region of the crystal with degradation near the edges due to reflections off the crystal sides. We also show that we can match the spatial resolution achieved using a 14 mm thick crystal by using a 25 mm thick crystal with slots cut into the gamma entrance surface to narrow the LRF. We also find that we can improve the spatial resolution performance near the detector edges by reducing the reflectivity of the crystal sides, albeit with some loss in energy resolution.

Description: We demonstrate a new scintillator material that has a one-dimensional eutectic structure and optical light-guiding properties. Our light propagation calculations predicted that a structure where high refractive index luminescence cylinders are embedded in a matrix should show effective light-guiding properties. An inverse structure where a high refractive index luminescence matrix contains low refractive index cylinders was also predicted to possess light-guiding properties. A CsI—NaCl:Tl eutectic phase, which contained NaCl cylinders in a CsI matrix, was grown by a one-dimensional solidification method. This material showed high spatial resolution because of the difference in the refractive indices of NaCl and CsI.

Description: We are proposing a novel design for a module with depth of interaction (DOI) capability for gamma rays by measuring the pulse-height ratio of double-sided Multi-Pixel Photon Counters (MPPCs) coupled at both ends of a scintillation crystal block. Thanks to newly developed monolithic MPPC arrays consisting of 4 $times$ 4 channels with a three-side buttable package, the module is very thin and compact, thereby enabling less dead space between each module when arranged into a fully designed gantry. To demonstrate our concept of a DOI measuring technique, we first made a 1-D crystal array consisting of five Ce-doped ${rm Gd}_{3}{rm Al}_{2}{rm Ga}_{3}{rm O}_{12}$ (Ce:GAGG) cubic crystals measuring $3times 3times 3 {rm mm}^{3}$ in size, separated by a layer of air approximately 10 $mu{rm m}$ -thick. When the light signals output from both ends are read with the $3times 3 {rm mm}^{2}$ MPPCs, the position of each crystal is clearly distinguished. The same measurements were also made using Ce-doped $({rm Lu},{rm Y})_{2}({rm SiO}_{4}){rm O}$ (Ce:LYSO), achieving a similarly good separation. We then fabricated thin Ce:GAGG 2-D crystal arrays consisting of two types: [A] 4 $times$ 4 matrix of $3times 3times 3 {rm mm}^{3}$ pixels, and [B] 10 $times$ 10 matrix of $0.8times 0.8times 5 {rm mm}^{3}$ pixe- s, with each pixel divided by a ${rm BaSO}_{4}$ reflector 0.2 mm-thick. Then four arrays are laid on top of each other facing the DOI direction through a layer of air 10 $mu{rm m}$ -thick. We demonstrated that the 3-D position of each Ce:GAGG pixel is clearly distinguished in both the 2-D and DOI directions for type A and B when illuminated by 662 keV gamma rays. Average energy resolutions of 9.8 $pm$ 0.8% and 11.8 $pm$ 1.3% were obtained for types A and B, respectively. These results suggest that our proposed method is simple and offers promise in achieving both excellent spatial and energy resolutions for future medical imaging, particularly in positron emission tomography (PET).

Description: We developed SPECT imaging capability on a LabPET animal scanner to provide an integrated PET/SPECT dual-modality imaging system. The add-on SPECT sub-system was enabled by 1) mechanically integrating a multiple-pinhole collimator in the PET detector ring, and 2) configuring the detectors to acquire singles events in the 120–160 keV range. We report on the design parameters, data acquisition protocols and initial performance assessment of this cost-effective SPECT imaging solution. Phantom and animal images demonstrating the relevance of the system for various imaging tasks in preclinical research are presented.

Description: Collimation can improve both the spatial resolution and sampling properties compared to the same scanner without collimation. Spatial resolution improves because each original crystal can be conceptually split into two (i.e., doubling the number of in-plane crystals) by masking half the crystal with a high-density attenuator (e.g., tungsten); this reduces coincidence efficiency by 4 $times$ since both crystals comprising the line of response (LOR) are masked, but yields 4 $times$ as many resolution-enhanced (RE) LORs. All the new RE LORs can be measured by scanning with the collimator in different configurations.

Description: Images taken with time-of-flight (TOF) positron emission tomography (PET) scanners are of improved quality compared to equivalent non-TOF images. This improvement is dependent on the scanner time resolution. The present generation of commercial TOF scanners has a time resolution in the range of 500–600 ps full width half maximum. In this work we investigate how the image characteristics will improve for future generations of TOF PET. We performed a Geant4 simulation of a 30-cm uniform cylinder containing hot spheres, with time resolution ranging from 600 to 200 ps. Data were reconstructed using TOF filtered back projection (FBP) and TOF ordered subsets expectation maximization (OSEM), with nonTOF reconstruction as a reference. Images were compared in terms of contrast recovery and variance in the image. The TOF gain was evaluated for both reconstruction methods. The TOF gain was also evaluated vs. counts in the scan, in order to understand the behavior of such gain at very low statistics. Using TOF FBP, it was shown that the TOF gain can be used as a sensitivity amplifier, reducing (according to the expected TOF gain) the number of counts necessary to produce an image of the same characteristics. Some limitations in the TOF gain were observed at very low counts, particularly if using iterative methods.

Description: We investigate the capability to perform K-edge imaging with the newly developed micro-CT PIXSCAN based on the XPAD3 hybrid pixel detector. The XPAD3 detector surface of $8~{rm cm} times 11~{rm cm}$ makes it possible to perform whole body mouse imaging. We present a proof of principle of K-edge imaging of mouse-size phantoms filled with Silver and Iodine solutions. Results are compared with standard X-ray absorption tomography for several solution densities.

Description: We are currently investigating the feasibility of using highly pixelated Cadmium Zinc Telluride (CdZnTe) detectors for sub-500 $mu$ m resolution PET imaging applications. A 20 mm $,times,$ 20 mm $,times,$ 5 mm CdZnTe substrate was fabricated with 350 $mu$ m pitch pixels (250 $mu$ m anode pixels with 100 $mu$ m gap) and coplanar cathode. Charge sharing among the pixels of a 350 $mu$ m pitch detector was studied using collimated 122 keV and 511 keV gamma ray sources. For a 350 $mu$ m pitch CdZnTe detector, scatter plots of the charge signal of two neighboring pixels clearly show more charge sharing when the collimated beam hits the gap between adjacent pixels. Using collimated Co-57 and Ge-68 sources, we measured the count profiles and estimated the intrinsic spatial resolution of 350 $mu$ m pitch detector biased at ${-}1000$ V. Depth of interaction was analyzed based on two methods, i.e., cathode/anode ratio and electron drift time, in both 122 keV and 511 keV measurements. For single-pixel photopeak events, a linear correlation between cathode/anode ratio and electron drift time was shown, which would be useful for estimating the DOI information and preserving image resolution in CdZnTe PET imaging applications.

Description: This article describes a compact single-photon emission computed tomography (SPECT) system that consists of a high-resolution detector combined with a lofthole collimator. The detector is based on a NaI(Tl) scintillator, a position sensitive photomultiplier (PSPMT), dedicated read-out electronics that digitize all PSPMT anodes and finally, a maximum likelihood algorithm for position estimation. The collimator has a new pinhole geometry, called the lofthole. Our choice of magnification (1.06 for the mouse setup, 0.63 for the rat setup) results in a small system with a footprint of 45 cm $,times,$ 25 cm.

Description: The redundancy in 3D time-of-flight (TOF) PET data can be exploited to reduce data storage or to estimate unmeasured data samples caused by defective or missing detectors. Mathematically, redundancy is expressed by consistency conditions which can be expressed either in terms of the 3D Fourier transform of the data or as a pair of partial differential equations (PDE). The benefit of the latter is that the PDEs are local and therefore can be applied even if some data samples are missing.

Description: While the performance of most current commercially available PET scanners is sufficient for many standard clinical applications, some specific tasks likely require specialized imaging systems. The goal of this project is to explore the capabilities and limitations of a small, high-resolution prototype system for obtaining PET images. The scanner consists of a tandem of detectors. One is a small detector consisting of a 20 $,times,$ 20 array of $0.7times 0.7times 3~{hbox {mm}}^{3}$ (pitch 0.8 mm) LYSO elements. The scintillator array is coupled to an array of silicon photomultipliers. The second detector is a 96 $,times,$ 72 array of $2times 2times 15~{hbox {mm}}^{3}~({rm pitch}=2.1~{hbox {mm}})$ LYSO elements coupled to PSPMTs. Separation between the two devices is 180 mm. The detectors are operated in coincidence with each other. Image reconstruction is performed using a limited angle, Maximum Likelihood Expectation Maximization (MLEM) algorithm. Evaluation of the device included measurements of spatial resolution and detection sensitivity as a function of distance. The transaxial radial and tangential spatial resolution of the system ranged from 0.6 mm to 0.9 mm FWHM; axial resolution ranged from 2.7 mm to 4.6 mm FWHM. Detection sensitivity ranged from 0.05 to 0.28%. Spatial resolution and field-of-view vary as a function of distance from the small detector. The tandem detector insert permitted differentiation of the smallest (1 mm diameter) rods in a mini-hot rod phantom. The results indicate that a tandem PET imaging scheme can be potentially employed in applications where high-resolution images over a small region are required.

Description: Positron Emission Tomography (PET) is an imaging method affected by artifacts caused by patient motion. PET-MR simultaneous acquisition may provide the means to correct for the effects of motion. This study investigates the creation of a deformable PVA cryogel phantom for motion correction purposes in PET-MR. This phantom has to contain the appropriate concentration of PVA and a sufficient amount of radioactive tracer along with gadolinium contrast agent. The effect of modifying the standard PVA cryogel process were assessed by measuring differences in the Young's modulus and also the diffusion of radiotracer inside the phantom. The alteration of the freeze-thaw cycle decreased the Young's modulus up to 50% by comparison with the standard MRI cryogel phantom. The diffusion speed on the other hand was found to be at 2 mm h $^{-1}$ inside a 10% p.w. cryogel. The results are demonstrated with a simultaneous PET-MR experiment. The new approach of cryogel preparation provides the opportunity to create a PET and MR visible phantom with structural complexity and customized shape, which is capable of reproducible deformations when reproducible pressure is applied. The methodology to build the phantom can be used in other simultaneous or sequential imaging modalities such as SPECT and ultrasound.

Description: Most of the regularized iterative reconstruction schemes employed in emission tomography (such as penalized maximum-likelihood, PML) usually require the adjustment of a scalar parameter $beta$ that determines the strength of the a priori information regarding the studied object. Empirical selection of $beta$ remains hazardous since its optimal value depends on the morphological structure of the reconstructed image and the data signal to noise ratio (SNR), which explains partly the scarce utilization of penalized reconstruction in clinical routine. In this paper, we derive a simple optimization criterion for $beta$ that relies on a statistical description of the noise propagation when iteratively updating the image estimate and on a surrogate algebraic formulation holding for both PML and expectation-maximization-smooth (EMS) iterative reconstruction. When incorporated into each iteration step, the statistic-algebraic tuning optimization (SATO) yields two new optimized regularized iterative methods: SATO-PML and SATO-EMS. These methods are compared with classical MLEM reconstruction followed by optimal Gaussian post-filtering (ML-opt) through Monte-Carlo experiments involving the Hoffman brain phantom and the Shepp-Logan phantom. It is shown that, whatever the studied object and the count rate, SATO-PML and SATO-EMS are convergent in terms of $beta$ and produce images with bias, variance and contrast properties that are at least as good as those of the ML-opt images. The two proposed algorithms are also evaluated using realistic PET data from a Hoffman phantom produced using the GATE platform in order to demonstrate the feasibility of our SATO scheme with actual data.

Description: Currently, radiotherapy with electrons and photons beams is the most common approach in health care facilities; it allows widespread use of technology. Only a fast and accurate verification of the dose characteristics of the beams provides a safe and effective use of the methodology. We have designed, built and tested a new instrument based on a layer of square scintillating fibers of 0.5 mm thickness that can run a scan of the beam. The system provides the dosage profiles, related to a plane orthogonal to the beam axis at a fixed depth. The device was tested with a photon beam of 6 MV delivered by a linear accelerator Varian Clinac DHX 2100. The data collected were processed for the tomographic reconstruction of the dose by means of the FBP (filtered back projection) algorithm with different filters. An iterative reconstruction algorithm was also tested. In this paper, the results are presented and suggestions for future developments are made.

Description: We describe a GPU-accelerated framework that efficiently models spatially (shift) variant system response kernels and performs forward- and back-projection operations with these kernels for the DIRECT (Direct Image Reconstruction for TOF) iterative reconstruction approach. Inherent challenges arise from the poor memory cache performance at non-axis aligned TOF directions. Focusing on the GPU memory access patterns, we utilize different kinds of GPU memory according to these patterns in order to maximize the memory cache performance. We also exploit the GPU instruction-level parallelism to efficiently hide long latencies from the memory operations. Our experiments indicate that our GPU implementation of the projection operators has slightly faster or approximately comparable time performance than FFT-based approaches using state-of-the-art FFTW routines. However, most importantly, our GPU framework can also efficiently handle any generic system response kernels, such as spatially symmetric and shift-variant as well as spatially asymmetric and shift-variant, both of which an FFT-based approach cannot cope with.

Description: The spatial resolution in positron emission tomography (PET) can be improved by the addition of depth-of-interaction (DOI) information. This can be achieved by using the phoswich approach in which depth identification relies on differences in scintillation decay time and pulse shape discrimination techniques. In this paper we have looked at a special phoswich combination LuAP/LSO or LuYAP/LSO. This combination of scintillators is especially interesting since LuAP and LuYAP have emission in the excitation band of LSO, which may have an impact on the timing resolution of the detector. As will be shown in this paper, the phoswich concept based on these two scintillators can be utilized, however, with some limitations. This paper is an extension of our previous phoswich investigation .

Description: Maximum Likelihood (ML) reconstruction estimators are non biased and achieve the lowest variance, called the Cramer-Rao lower bound (CRLB), in the asymptotic regime, which in positron emission tomography (PET) or in single photon emission tomography (SPECT) corresponds to measuring an infinite number of counts. At finite number of counts or iterations, practical reconstruction algorithms are however biased, and nothing guarantees that the minimum variance expressed by the CRLB is achieved. We study the two dimensional Ordered Subsets Expectation Maximization (2D OSEM) algorithm with a finite number of counts and iterations, and investigate the question: given its bias, does this algorithm achieve the minimum variance predicted by the biased Cramer-Rao lower bound?

Description: Stationary small-animal SPECT systems are being developed for rapid dynamic imaging from limited angular views. This work quantified, through simulations, the performance of Maximum Likelihood Expectation Maximization (MLEM) for reconstructing a time-activity curve (TAC) with uptake duration of a few seconds from a stationary, three-camera multi-pinhole SPECT system. The study also quantified the benefits of a heuristic method of initializing the reconstruction with a prior image reconstructed from a conventional number of views, for example from data acquired during the late-study portion of the dynamic TAC. We refer to MLEM reconstruction initialized by a prior-image initial guess (IG) as ${rm MLEM}_{ig}$ . The effect of the prior-image initial guess on the depiction of contrast between two regions of a static phantom was quantified over a range of angular sampling schemes. A TAC was modeled from the experimentally measured uptake of $^{99m}{rm Tc}$ -hexamethylpropyleneamine oxime (HMPAO) in the rat lung. The resulting time series of simulated images was quantitatively analyzed with respect to the accuracy of the estimated exponential washin and washout parameters. In both static and dynamic phantom studies, the prior-image initial guess improved the spatial depiction of the phantom, for example improved definition of the cylinder boundaries and more accurate quantification of relative contrast between cylinders. For example in the dynamic study, there was ${sim}50%$ error in relative contrast for MLEM reconstructions compared to ${sim}{25}$ -30% error for ${rm MLEM}_{ig}$ . In the static phantom study, the benefits of the initial gues- decreased as the number of views increased. The prior-image initial guess introduced an additive offset in the reconstructed dynamic images, likely due to biases introduced by the prior image. MLEM initialized with a uniform initial guess yielded images that faithfully reproduced the time dependence of the simulated TAC; there were no statistically significant differences in the mean exponential washin/washout parameters estimated from MLEM reconstructions compared to the true values. Washout parameters estimated from ${rm MLEM}_{ig}$ reconstructions did not differ significantly from the true values, however the estimated washin parameter differed significantly from the true value in some cases. Overall, MLEM reconstruction from few views and a uniform initial guess accurately quantified the time dependance of the TAC while introducing errors in the spatial depiction of the object. Initializing the reconstruction with a late-study initial guess improved spatial accuracy while decreasing temporal accuracy in some cases.

Description: Task-based assessments of image quality constitute a rigorous, principled approach to the evaluation of imaging system performance. To conduct such assessments, it has been recognized that mathematical model observers are very useful, particularly for purposes of imaging system development and optimization. One type of model observer that has been widely applied in the medical imaging community is the channelized Hotelling observer (CHO). Since estimates of CHO performance typically include statistical variability, it is important to control and limit this variability to maximize the statistical power of image-quality studies. In a previous paper, we demonstrated that by including prior knowledge of the image class means, a large decrease in the bias and variance of CHO performance estimates can be realized. The purpose of the present work is to present refinements and extensions of the estimation theory given in our previous paper, which was limited to point estimation with equal numbers of images from each class. Specifically, we present and characterize minimum-variance unbiased point estimators for observer signal-to-noise ratio (SNR) that allow for unequal numbers of lesion-absent and lesion-present images. Building on this SNR point estimation theory, we then show that confidence intervals with exactly-known coverage probabilities can be constructed for commonly-used CHO performance measures. Moreover, we propose simple, approximate confidence intervals for CHO performance, and we show that they are well-behaved in most scenarios of interest.

Description: Positron emission tomography (PET) images suffer from low spatial resolution. To improve the spatial resolution, we previously proposed a sinogram-based super-resolution (SR) algorithm for a whole-body PET scanner, by assuming space invariant blur. However, since the spatial resolution of a sinogram varies along the radial direction due to parallax error, this algorithm is not appropriate for providing a high-resolution sinogram with reduction of parallax error. In this paper, we propose a novel and efficient sinogram-based SR algorithm that is suitable even for a small animal PET scanner by using space variant blur matrices. In the algorithm, we estimate the space variant blur matrices through a Monte Carlo simulation and use them for the SR process to obtain a high-resolution sinogram. Using a Derenzo phantom and a line source, we demonstrate in a real PET scanner, microPET R4, that the proposed SR algorithm noticeably improves the spatial resolution while alleviating its space variance. By applying the proposed SR algorithm, the full width at half-maximum (FWHM) value reaches 1.2 mm at the system center and 1.63 mm with a considerable parallax error reduction at a radial position of 4 cm.

Description: To reduce the radiation dose in dental computed tomography (CT), backprojection-filtration (BPF) algorithm is the preferred choice as it can reconstruct images from truncated data within limited scanning angle, thereby reducing radiation dose and avoiding irradiation to the brain. However, the integral interval of backprojection is variable for every PI-line which causes the calculation efficiency and parallel performance to be low. In this paper, the tent BPF method (T-BPF) was developed, which was performed by firstly rearranging the cone-beam data to tent-like parallel-beam data, and then applying the proposed BPF-type algorithm to reconstruct images from the rearranged data. T-BPF turns the variable integral interval of backprojection into fixed integral interval, which means the reconstruction efficiency and the parallel performance of T-BPF are improvements over those of the original BPF algorithm. The experiments of numerical simulation and real data reconstruction show that the reconstruction efficiency of T-BPF is faster than the original BPF algorithm and the FDK algorithm in the case of comparable reconstruction quality. The results demonstrate that the proposed T-BPF is good at achieving fast low-dose reconstruction from truncated projection data in dental CT.

Description: A high resolution x-ray imaging system designated the solid state x-ray image intensifier (SSXII) is being developed as a potential replacement of conventional lower-resolution x-ray detectors for neurovascular interventions. The SSXII consists of a CsI(Tl) phosphor to convert x-rays to light, a fiber optic taper to extend the field-of-view and to couple the phosphor to an Electron-Multiplying CCD (EMCCD) which has a built-in gain to boost the signal above the read-out noise floor. A parallel cascade linear-system model is explored and applied to quantitatively analyze the signal and noise transfer at each stage, and optimize the detector performance. The modulation transfer function (MTF), detective quantum efficiency (DQE) and frequency dependent instrumentation noise equivalent exposure (INEE) can be obtained from the theoretical model and experimental measurement. Agreement of these results validates the effectiveness of the model. Finally, compared with the traditional flat-panel detector (FPD), the SSXII exhibits better performance with higher spatial resolution, higher DQE and lower INEE.

Description: Most efforts at developing time-of-flight (TOF) positron emission tomography (PET) instruments have focused on improving their time resolution, which is affected by many factors. The aim of this study was to evaluate the performance of two new fast photomultiplier tubes (PMT) (Hamamatsu R9800 and R11194) for use as a TOF-PET detector, and to investigate the correlation of time resolution with time discrimination methods, the properties of the PMTs, the locations of the scintillation crystal on the PMT, and the size of the scintillation crystal. The PMTs evaluated in this study have fast rise time and short time jitter. The performance evaluation of the PMTs was conducted using a LYSO scintillation crystal. A $^{22}{rm Na}$ source was placed between the testing detector and a reference detector (with a time resolution of 200 ps), and data were acquired by using the coincidence trigger of the two detectors. To determine the optimal time discrimination method, time resolutions were obtained using a leading-edge discriminator (LED) with various thresholds and a constant-fraction discriminator (CFD) with various CFD delays. The effects on time resolution of PMT properties, the crystal position on the PMT, and the size of the crystal were observed. Based on the comparison of time resolutions obtained by various time discrimination setups, the optimal setup was determined to be CFD with 1.0 ns CFD delay. When these PMTs were coupled with $4~{rm mm}times 4~{rm mm}times 10~{rm mm}$ LYSO crystal and CFD with 1.0 ns delay was used for time discrimination, the average time resolution (FWHM) for 7 R9800 was 200.5 ps and for 7 R11194 was 227.8 ps. The average energy resolutions were 11.1% and 11.8%, respectively. Time resolutions at the edge of the PMT were degraded due to light collection loss and worse transit time jitter. Time resolutions w- re inversely proportional to the square root of the numbers of photoelectrons per pulse. The numbers of photoelectrons increased proportionately with the blue sensitivity of individual PMTs. Time resolutions have a distinct dependence as a function of the length and cross-section of the crystal. The new fast PMT coupled with LYSO crystals allow for the improvement of timing performance in TOF-PET detectors. The results of this study will be of value as a guideline for optimizing the TOF-PET detector design using the fast PMTs.

Description: In the framework of the Joint Instrumentation Laboratory (LCI), gathering resources from SCK-CEN (Belgium) and CEA (France), we are developing an optical sensor in order to accurately measure radiation-induced elongation of material placed in the core of a Material Testing Reactor (MTR). This extensometer displays common advantages of Fibre Optic (FO) sensors: high resolution, easy remote sensing and multiplexing, and also compact size which is of particular interest for in pile experiments with little room available. In addition, light weight reduces gamma heating hence limiting the thermal effect. In accordance with the specifications, the sensor has preferably two fixing points defining a gauge length of 10 to 15 mm. The diameter is less than 2 mm. Intense gamma and neutron irradiation as well as high temperatures are the most difficult environment conditions to withstand. Reactor radiation produces huge losses in common optical fibre. The losses can be limited by selecting the fibres, the wavelength range (800–1200 nm), and a measurement based on interferometry (largely insensitive to losses in the fibre thanks to the wavelength encoding of the useful signal). Heavy neutron—mainly—and gamma flux such as in MTR, also produce compaction of silica, resulting in a significant drift and preventing the use of commercial FO sensors in such environment. Knowing this issue we revised the basic scheme of Extrinsic Fabry Perot Interferometer (EFPI) in order to limit the effects of compaction. A first sensor prototype fixed on a stainless steel support is tested with the Smirnof test facility in the BR2 MTR in Mol (Belgium). The support is subject to a constant mechanical and thermal stress, and then his dimensions are not supposed to vary. This test shows a very low drift of the revisited EPFI design under high irradiation field in comparison with a commercial EFPI. This result has to be confirmed with second generation sensors with an increased ro- ustness. The other difficulty to face is high temperature. Fibre optics with metal coating allow safe operation under temperatures up to 400 $^{circ}{rm C}$ and even higher. But differential dilatation between silica and typical metallic material produces differential elongation in the range of 0.7 $10^{-2}$ i.e 5000 $muvarepsilon$ for an increase in temperature of 400 $^{circ}{rm C}$ . Such large elongation has to be considered carefully in the sensor design and its fixing on the sample. We are currently implementing metal-coated fibre and we are preparing the next in pile irradiation on the BR2 reactor scheduled for end of 2011. Other applications of the sensor can be considered.

Description: A transient waveform capture and digitization circuit with continuous synchronous 2-GHz sampling capability and real-time programmable windowed trigger generation has been fabricated and tested. Designed in 0.25 $mu{rm m}$ CMOS, the digitizer contains a circular array of 128 sample and hold circuits for continuous sample acquisition, and attains 2-GHz sample speeds with over 800-MHz analog bandwidth. Sample clock generation is synchronous, combining a phase-locked loop for high-speed clock generation and a high-speed fully-differential shift register for distributing clocks to all 128 sample circuits. Using two comparators per sample, the sampled voltage levels are compared against two reference levels, a high threshold and a low threshold, that are set via per-comparator digital to analog converters (DACs). The 256 per-comparator 5-bit DACs compensate for comparator offsets and allow for fine reference level adjustment. The comparator results are matched in 8-sample-wide windows against up to 72 programmable patterns in real time using an on-chip programmable logic array. Each 8-sample trigger window is equivalent to 4 ns of acquisition, overlapped sample by sample in a circular fashion through the entire 128-sample array. The 72 pattern-matching trigger criteria can be programmed to be any combination of High—above the high threshold, Low—below the low threshold, Middle—between the two thresholds, or “Don't Care”—any state is accepted. A trigger pattern of “HLHLHLHL,” for example, watches for a waveform that is oscillating at about 1 GHz given the 2-GHz sample rate. A trigger is flagged in under 20 ns if there is a match, after which sampling is stopped, and on-chip digitization can proceed via 128 parallel 10-bit converters, or off-chip conversion can proceed via an analog readout. The chip exceeds 11 bits of dynamic range, nets ov- r 800-MHz $-$ 3-dB bandwidth in a realistic system, and jitter in the PLL-based sampling clock has been measured to be about 1 part per million, RMS.

Description: Caliste HD is a recently developed micro-camera designed for X and gamma-ray astronomy, based on a $1times 1 {rm cm}^{2}$ CdTe Schottky pixelated detector. Its entire surface is composed of 256 pixels, disposed on a 16 $times$ 16 pixel array. This spectrometer is buttable on its 4 sides and can be used to create a large focal plane. It is also designed for space environment. Its IDeF-X front-end electronics has low power consumption, excellent noise performance and a wide dynamic range, from 2 keV to 1 MeV. Moreover, electronic noise performances of this device were optimized to set the low level energy threshold lower than 2 keV.

Description: For given arbitrary electromagnetic fields, an analytical method to obtain transfer coefficients up to the third order in phase-space coordinates is described in this paper. The method is based on numerical tracking of a number of representative particles followed by the least-square minimization. The result is applied to an arbitrary beamline consisting of linear and nonlinear beam-optical elements and favorably compared with the numerical particle tracking. Transfer coefficients obtained with our method are also compared with those obtained from an existing computer code.

Description: A pixel-level 8-bit 5-MS/s Wilkinson-type analog-to-digital converter was designed and fabricated in the IBM 8M1P 130-nm CMOS technology. The pixel blocks are implemented with a core area of 130 $mu {rm m}$ by 140 $mu {rm m}$ , consuming about 560 $mu {rm W}$ at 1.2 V. Taking the measured dynamic range of 0.86 V into account, a signal-to-noise ratio above 65 dB was achieved for small signal amplitudes. The maximum differential and integral nonlinearity remains well below 0.4 LSB and 0.5 LSB, respectively. The conversion time is 160 ns, and the energy per conversion step 470 fJ. The digitizer permits the trimming of gain and offset.

Description: This work presents the experimental results from the characterization of the second prototype of a high accuracy (in terms of linearity, mismatch and noise) injection circuit to be used for in-pixel calibration of a large sensor matrix. The circuit was designed for the calibration of the pixel cell unit of a hybrid pixel device, the DEPFET Sensor with Signal Compression (DSSC) chip, for the large format imager at the European X-ray Free Electron Laser (XFEL), but, in principle, it can be used also for other kinds of detectors, e.g., deep N-well monolithic CMOS sensors. In the case of hybrid pixels, the injection circuit is particularly useful to test the functionality of the readout electronics already at the chip level, when no sensor is connected to the chip. Two injection techniques have been investigated: one for a charge sensitive amplification and the other for a transresistance readout channel. The aim of the paper is to describe the architecture of the calibration circuit, which has been implemented in a 130-nm CMOS technology, and to present the results from the characterization of the second prototype.

Description: An Integrated Circuit (IC) for processing the signals from CdTe/CdZnTe X-ray detectors in the 5–100 keV energy range is presented. The IC, named CCA, is designed to operate in a capsule for colon 3D-imaging as a diagnostic tool for cancer prevention. The CCA is composed of a low-power consumption analog and a digital sections for counting photons within two energy windows to a maximum of $130times 10 ^{3}$ photons per second. The analog section consists of a preamplifier optimized for detectors with 8 pF capacitance, a pulse shaper with 4 shaping times selectable between $0.5 ~mu{rm s}$ and $2 ~mu{rm s}$ , a peak stretcher and an analog buffer able to drive up to 15 pF load. The digital section is composed of a two energy windows discriminator fully configurable in the 8.5–120 keV range with 7 bits energy thresholds resolution, two 12 bits counters, two memory registers and an SPI interface for IC configuration and data transfer. The CCA guarantees stable spectroscopic-grade performance allowing for supply voltage variations between 3.1 V to 2.5 V, as is the case of the battery powered capsule during its operation; this feature has been achieved with no voltage regulator for power saving.

Description: Networked control has been attempted for a wide variety of plants using memory-less State Feedback controllers. Networked Control Systems (NCSs) have also been mooted for PHWRs and implemented in practical systems e.g. a Reactor Regulating System (RRS) of the Indian PHWRs. While existing approaches using State Feedback controllers guarantee stability under data loss and variable delay which are inherent in real time communications, they cannot be extended to discrete PID controllers which involve a memory element. In this paper, a switched system formulation has been used to analyze the stability of a nuclear reactor with networked discrete PID controllers in the RRS under specified data loss and variable delay. The results have been verified using MATLAB xPC target based Real-time Simulation involving multiple simulation nodes integrated over switched Ethernet. A Distributed Network Analyzer (DNA) has been used to log actual network traffic to establish the credibility of the assumptions related to data loss and variable delay in communication.

Description: Pressurized water reactor (PWR) is the most widely used nuclear fission reactor, and the renaissance of fission energy industry needs the safe, stable and efficient operation of PWRs. Power-level control technique which strengthens the closed-loop stability and dynamic performance is meaningful to build a strong operation strategy for PWRs. In this paper, after extending the shifted-ectropy of thermodynamic systems to that of transport systems, a proportional-differential (PD) power-level controller is proposed for PWRs based on the physically-based approach. A sufficient condition for this PD controller to provide the globally asymptotic stability of those reactor state variables is established. Numerical simulation results not only verify the correctness of the theoretic results but also illustrate the relationship between the control performance and controller parameters. The meaning of this result is giving a theoretic explanation to why the simple PD control is effective for PWR power-level regulation practically.

Description: Complementary metal oxide semiconductor (CMOS) active pixel sensor (APS) prototypes made using 0.18 $mu{rm m}$ technology process have been developed for the Extreme Ultraviolet Imager of the Solar Orbiter mission. Backside illuminated CMOS APS devices, i.e., 256 $times$ 256 pixels area, 10 $mu{rm m}$ pixel pitch with different pixel designs have been fully characterized in the visible and in EUV wavelengths. A set of irradiation tests were carried out to investigate the degradation of the devices expected in the space environment conditions of Solar Orbiter. Total ionizing dose effects from grounded measurements are presented up to 150 ${rm krad}[{rm SiO}_{2}]$ . The prototype sensors show the immunity to single-event latch up at linear energy transfer's of 67.7 ${rm MeV} {rm cm}^{2}/{rm mg}$ but were observed to suffer from strong degradations after proton irradiation test (with a cumulated fluence up to $4times 10^{11} {rm protons/cm}^{2}$ ) and from single event functional interrupt.

Description: New, multi-pixel, air-filled ionization chamber for beam monitoring was constructed. For processing of 400 input signals, it utilizes a dedicated, homemade ASIC. Device parameters: sensitivity, resolution, dynamic range, etc. are discussed together with results from the particle beam tests.

Description: A CMOS sensor chip for charged particle detection has been developed and submitted for fabrication in a 0.18 $mu$ m Quadruple-Well (N&P-Wells, Deep N&P-Wells) CMOS Image Sensor (CIS) process. Improvement of the radiation hardness, the power dissipation and the readout speed of the mainstream CMOS sensors is expected with the exploration of this process. In order to ensure better charge collection and neutron tolerance, wafers with high-resistivity epitaxial layer have been chosen. In this paper a digital CMOS sensor prototype developed in order to validate the key analog blocks (from sensing element to 1-bit digital conversion) of a binary Monolithic Active Pixel Sensor (MAPS) in this process will be presented. The digital sensor prototype comprises four different sub-arrays of 20 $mu$ m pitch 64 $,times,$ 32 pixels, 128 column-level auto-zeroed discriminators, a sequencer and an output digital multiplexer. Laboratory tests results including the charge-to-voltage conversion factor, the charge collection efficiency, the temporal noise and the fixed-pattern noise are presented in details. Some irradiation results will also be given.

Description: The objective of this paper is to propose a predictive analysis based on MUSCA SEP3 including statistic properties, and to demonstrate the relevance of this approach if compared to real operational results. The method was validated by comparison with ground test results and statistical analyses were applied to in-flight data issued from the ICARE equipment (SAC-C satellite). In an operational context, results show that confidence level SEU-risk is relevant when conventional average calculations are deficient. This is particularly accurate when the solar flare is characterized by medium or low flux level.

Description: The robustness of commercial power metal–oxide semiconductor field-effect transistors to combined gamma-heavy ion irradiation has been investigated, evidence that the degradation of the gate oxide caused by the $gamma$ irradiation can severely corrupt the robustness to single-event effects and drastically modify the physical behavior of the device under test after the impact of a heavy ion. A decrease of the critical voltages at which destructive burnouts and gate ruptures for heavy ion impact appear, has been detected in the devices under test, which were previously irradiated with $gamma$ rays. In addition, the amount of critical voltage reduction is strictly related to the amount of the absorbed $gamma$ -ray dose. Furthermore, at the failure voltage, the behavior of the device is affected by the conduction of a current through the gate oxide. Moreover, the single-event gate rupture” of the device appears at lower voltages because of the reduction of the Fowler–Nordheim limit in the $gamma$ -irradiated devices.

Description: The present article presents technology, required for repeatable manufacturing of the 1.5 and 2 inch crystal rods of (Cd, Mn)Te is discussed. In order to obtain semiinsultaing crystals, compensation and annealing in Cd-vapours was used. Vanadium was mainly used as the compensating dopant. The resistivity of the obtained monocrystalline plates was around $10^{9}$ $Omega$ cm, and the $mu tau$ -product was about $10^{-3}$ cm $^{2}$ /V. Mapping of the resistivity was performed on both as-grown crystals and the crystals annealed in the saturated Cd vapour. As-grown (undoped) crystals were inhomogeneous and their resistivities were in the range $10^{5} -10^{6} Omega$ cm. After annealing resistivity increased up to $1 hbox{--}2 cdot 10^{9} Omega$ cm and better homogeneity could be seen. Annealing in saturated Cd-vapours had influence on tellurium inclusions/precipitates. It was studied by IR transmission microscopy. For as-grown samples the density of Te inclusions ( ${〉} 1 mu$ m) was ${approx} 3 cdot 10^{5}$ cm $^{-3}$ but for annealed samples was ${approx} 10^{4}$ cm $^{-3}$ . The concentrations (measured by SIMS) of the unintentional impurities Na, Ca, and Ga were in the regio- $10^{15} hbox{--} 10^{16}$ cm $^{-3}$ , corresponding well with the purity (6N) of the elements used for crystallization of our (Cd, Mn)Te. The low temperature photoluminescence (PL) measurements indicated significantly lowered concentrations of acceptors after annealing. Nearly ohmic contacts to the high resistivity (Cd, Mn)Te plates were obtained by deposition of the amorphous layers of heavily doped semiconductor (ZnTe:Sb). We undertook the present work to show that low vanadium doping level and proper annealing conditions are sufficient to obtain detector grade material.

Description: The various crystal growing methods (Low Pressure Bridgman, High Pressure Bridgman, Horizontal Bridgman, Physical Vapor Transport, Travelling Heater Method—THM) and the subsequent bulk and surface treatments can greatly affect the performances of CdTe as well as CdZnTe based X-ray detectors. For this investigation THM was chosen as a low temperature growth process where the crystals have relatively low number of defects and less impurity incorporation from the crucible. Surface (i.e., electrode and electrode-bulk material interface) characteristics have been already investigated , , aiming at understanding the effects of annealing on the electrode deposition. Here bulk effects, including an analysis of the Te inclusion distribution, on CdTe wafers obtained starting from as-grown or subsequently annealed standard or large area ingots have been investigated by IR imaging, resistivity and electron mobility mappings as well as spectroscopic characterization. The results of these measurements are presented and correlated with the detector performances of hundreds of samples. The main observed effects of the annealing are a reduction of the large size ( ${〉} 10 mu$ m) Te inclusions and a peaking of the resistivity and electron mu-tau products, though in this last case around worse average values, over the entire wafers, that lead to a significant reduction of the spread in the electron transit times, and at the end to better spectroscopic performances.

Description: A conventional master-slave flip-flop is very sensitive to particle strike that causes an SEU. When the clock is high, an SEU may upset the logic state of the master latch resulting in a faulty output of this flip-flop, and the erroneous value will also be locked in the slave latch when clock is low. When the clock is low, an SEU may also upset the logic state of the slave latch, resulting in a faulty output of this flip-flop. This paper presents an SEU hardened flip-flop that can mitigate SEU using an error detection circuit and a multiplexer. When the clock is high or low, an SEU in the master or slave latch of a flip-flop can be detected by the error detection circuit using dynamic logic. The multiplexer selects a correct output according to the error indication signal. The proposed flip-flop has small area, power and delay overheads and good radiation hardening capabilities.

Description: Digital detectors based on complementary metal-oxide-semiconductors (CMOS) active pixel sensor (APS) technology have been introduced recently in many scientific applications. This work is focused on the X-ray performance evaluation of a novel CMOS APS detector in low energy medical imaging applications using monochromatic synchrotron radiation (i.e., 17–35 keV), which also allows studying how the performance varies with energy. The CMOS sensor was coupled to a Thallium-activated structured cesium iodide (CsI:Tl) scintillator and the detector's X-ray performance evaluation was carried out in terms of sensitivity, presampling modulation transfer function (pMTF), normalized noise power spectrum (NNPS) and the resulting detective quantum efficiency (DQE). A Monte Carlo simulation was used to validate the experimentally measured low frequency DQE. Finally, the effect of iodine's secondary generated K-fluorescence X-rays on pMTF and DQE results was evaluated. Good agreement (within 5%) was observed between the Monte Carlo and experimentally measured low frequency DQE results. A CMOS APS detector was characterized for the first time over a wide range of low energies covering the mammographic spectra. The detector's performance is limited mainly by the detectability of the scintillator. Finally, we show that the current data could be used to calculate the detector's pMTF, NNPS and DQE for any mammographic spectral shape within the investigated energies.

Description: Radiation imaging has many applications ranging from health care to homeland security and defense, and source motion is present in many of these applications. When the motion profile of the source is known or otherwise estimated, one can use motion-compensation techniques to reduce blur in the reconstructed image. In this paper, we present a model-based source-intensity reconstruction in the energy and spatial domains using list-mode data. The model includes separate parameterization for objects moving with known motion that is independent of the stationary backdrop. This approach corrects for object motion without smearing stationary sources in the backdrop space. The goal is to simultaneously obtain an estimate of the incident energy and spatial distribution of the radiation field for the stationary backdrop and for each moving object. Experimental Compton-imaging results using an 18-detector array of 3-D-position-sensitive CdZnTe detectors show that the method can successfully reconstruct the source intensity of moving objects while also revealing stationary sources in the backdrop. Also, by modeling the possibility of partial photon energy deposition in the detector, the incident energy spectrum is reconstructed more accurately.

Description: There is a need for radiation spectrometers that are able to work in sustained high-count-rate environments. This work presents the results obtained with a discrete component charge-sensitive amplifier and shaper combination designed to be the front end for a diamond spectrometer. A system with a rise time of 2.12ns, FWHM of 3.75ns and an ENC of $293{hbox{e}} ^{-}$ RMS was developed and a high gain of $147~{rm mV/fC}$ was achieved with return to baseline within 20 ns. Instantaneous count rates of 50MHz and sustained count-rates of 20MHz were made possible through the use of a fast preamplifier and differentiating shaper.

Description: A technique for increasing light extraction out of scintillation crystals has been developed by introducing a uniform surface taper at the exit boundary of thin YAP:Ce scintillators. This taper was introduced by precision machining pyramidal structures on the scintillator's surface on a scale significantly larger than the scale typical of surface roughness. Light extraction out of the crystal is increased because the surface modification significantly reduces the chance that light can be incident on the crystal's exit boundary at an angle greater than the critical angle for total internal reflection. For the best case, a factor of 4.8 increase in light collection was measured without optical coupling, relative to the same crystal with a normal, polished exit boundary. The characteristics of the etched surfaces were precisely quantified, and measured increases in light collection relative to a polished surface are presented. Gains in light extraction are interpreted through detailed light transport simulations, and good agreement between predicted and measured light collection was observed.

Description: This paper presents an algorithm to calculate gamma dose rates intended for virtual reality (VR) applications. It dynamically adapts the method to cope with both accuracy and time requirements. Given the real-time constraints imposed by VR applications, more accurate, but computationally intensive stochastic algorithms (e.g., Monte Carlo) are not suited to this task. On the opposite end, a Point Kernel (PK) method can be effective in some cases with as little as one point (mono PK) to define a source, in contrast with the millions of points that Monte Carlo computes. Simple mono PK codes may lack the desired accuracy in some circumstances, requiring a more detailed source representation. In this work, a novel method is presented which automatically estimates the appropriate level of detail for a source's volumetric representation, then generates a non-regular mesh model and subsequently computes the dose rate via a PK method, performing this three-step process in real time.

Description: This paper investigates the effects of boron and calcium co-doping on the measured energy resolution of Gd $_{3}$ Ga $_{3}$ Al $_{2}$ O $_{12}$ :Ce (GGAG: Ce). For this study, three samples of GAGG were grown using the Czochralski method. The first sample was doped with Ce $^{3+}$ and was used as a reference for comparison. The next two samples were additionally doped with either B $^{3+}$ or Ca $^{2+}$ . The boron co-doped sample was found to have an overall improved performance when compared to the reference sample. The light output of the GGAG:Ce,B was measured to be 10% greater than the reference sample. In addition, the sample was found to have less charge trapping and a more linear relative light yield response. These factors led to an observed improvement in energy resolution from 9% in the reference sample to 7.8% in the B $^{3+}$ co-doped sample. Co-doping with Ca $^{2+}$ led to an overall reduction in charge trapping; however, the sample suffered a 30% reduction in light output, and it was found to have a less linear relative light yield than the reference sample. Its energy resolution was measured to be 10.1%. The relationship between the measured energy resolution and the other measured properties in these samples is discussed.

Description: Thallium bromide (TlBr) has been regarded as candidate detector materials for the gamma-ray spectrometers operating at room temperature. In this study, a simple and rapid method, the filter method, was performed to purify a raw TlBr material used for fabrication of TlBr detectors. The material was loaded on shards of crashed quartz and installed in a Pyrex tube, and was melted using a furnace. A purified material passing through interspaces of the shards of quartz was collected in a quartz ampoule located at the outlet of the Pyrex tube. After the purification, impurities colored black extracted from the raw material remained. TlBr crystals were then grown by the travelling molten zone method both from the raw material and the purified material. TlBr detectors were fabricated from the grown crystals, and were characterized by measuring mobility-lifetime products $(mu tau)$ for carriers and gamma-ray spectra ( $^{137}$ Cs) at room temperature. $mu tau$ for electrons of a TlBr detector fabricated from the purified material was around 5 times higher than that of a detector fabricated from the raw material.

Description: A new method for the absolute radioactivity measurement of radionuclides using a liquid scintillation detector comprising three photomultipliers has been described. The method does not contain any a priori model of the photomultiplier detection efficiency and uses a modified Compton Coincidence technique, therefore it has been named the Zero Model By using Coincidence Scintillation (ZoMBieS) method. Validation measurements of the activity of a $^{63} $ Ni source against the Triple to Double Coincidence Ratio method are presented and the results agree within their standard uncertainties.

Description: At the NIST Neutron Imaging Facility, we collect neutron projection data for both the dry and wet states of a Proton-Exchange-Membrane (PEM) fuel cell. Transmitted thermal neutrons captured in a scintillator doped with lithium-6 produce scintillation light that is detected by an amorphous silicon detector. Based on joint analysis of the dry and wet state projection data, we reconstruct a residual neutron attenuation image with a Penalized Likelihood method with an edge-preserving Huber penalty function that has two parameters that control how well jumps in the reconstruction are preserved and how well noisy fluctuations are smoothed out. The choice of these parameters greatly influences the resulting reconstruction. We present a data-driven method that objectively selects these parameters, and study its performance for both simulated and experimental data. Before reconstruction, we transform the projection data so that the variance-to-mean ratio is approximately one. For both simulated and measured projection data, the Penalized Likelihood method reconstruction is visually sharper than a reconstruction yielded by a standard Filtered Back Projection method. In an idealized simulation experiment, we demonstrate that the cross validation procedure selects regularization parameters that yield a reconstruction that is nearly optimal according to a root-mean-square prediction error criterion.

Description: Effects of oxide-trapped charge and interface traps induced by ionizing radiation, on the degradation of the electrical properties in NPN bipolar junction transistors (BJTs), are identified in this paper. Ionization traps in 3DG110 NPN BJTs are caused by 110 keV electron irradiations for various fluences, and the key electrical parameters are measured in situ during irradiation. In order to separate the effects of the interface traps and oxide charge on the radiation response in BJTs, the isochronal and isothermal annealing are performed after irradiations. Behavior of the radiation-induced defects is detected by DLTS after the irradiation and the postirradiation annealing. Measurement results indicate that when the change in reciprocal of the gain $(Delta (1/ beta))$ tends to level off, the concentration of oxide-trapped charge increases with increasing irradiation fluence, while that of the interface traps keeps unchangeable. A comparison of DLTS signals with changes in excess base current $(Delta I_{B})$ versus base-emitter voltage $(V_{rm BE})$ is conducted to show the role of oxide-trapped charge and interface traps on the excess base current, illustrating that the DLTS analysis is suitable to separate the ionization traps in BJTs.

Description: We report on noise measurements performed on the n-side of double-sided, AC-coupled, punch-through biased silicon strip detectors. The noise has been measured over a wide range of peaking times and bias voltages, allowing the disentanglement of two excess noise terms, one related to the p-stops surrounding the strips and the other related to the electron accumulation layer at the Si/ ${hbox {SiO}}_{2}$ interface.

Description: This paper presents an improved version of our previous gamma radiation sensor based on a floating gate MOSFET whose output current is changed by the total ionizing dose. Both versions exhibit zero bias operation and reprogramming capabilities. They have been designed in a standard CMOS technology, require little silicon area, and exhibit low power consumption. Sensitivity to radiation dose is ${-}11.4 mu$ A/krad, dose range over 3.6 krad, and lowest detectable dose lower than 2 rad. The new version features much higher linearity and supply voltage rejection and much lower sensitivity to ambient temperature.

Description: With the source and detector kept stationary while an inspected object moves between them, straight-line-trajectory-based tomographic imaging (SLTTI) has the capability to provide both digital radiologic images and tomographic images simultaneously, at high speed and with low-cost equipment. It has a promising future for fast security inspection for air cargo examinations. In order to fully investigate the feasibility of this approach, an experimental SLTTI platform has been developed. In this work, the system design is first presented. Then, a hybrid image reconstruction algorithm is proposed to obtain high quality tomographic images from the system to solve the limited-angle problem it represents. In the proposed algorithm, an initial reconstruction using either a direct filtered-backprojection (FBP) -type algorithm or the linogram technique is followed by a Gerchberg-Papoulis (GP) extrapolation to compensate for missing data. The GP extrapolation is implemented by the linogram technique, and constrained by a total variation (TV) minimization. By taking advantage of the FBP, the linogram and the TV techniques, we establish a fast and stable iterative reconstruction for the SLTTI. Finally, numerical simulations and realistic experiments are given, through which our proposals are validated to be feasible and effective. In the numerical examples, our algorithm can reduce the reconstruction inaccuracies for both high contrast and low contrast objects by factors of more than 15 and can generate nearly artifact free images as if complete projection data were available. A realistic experiment on a CatPhan©600 phantom suggests that high quality tomographic images can be achieved from 120-deg of source fan-beam angle with undersampled data. For a group of explosive simulacra using 90 projection views over 120-deg of source fan-beam angle, the reconstruction inaccuracy can be reduced to lower than 4%.

Description: This paper presents a general and efficient method for geometrical calibration of industrial X-ray tomography systems without the use of any phantom. In the field of nondestructive testing (NDT), an accurate numerical model of the object is usually available. By extending the classical volume-to-image registration framework, the method estimates both the parameters related to the position of the object, and those related to the positions and the orientations of the X-ray source, the detector and the rotation axis. Only using the projections data and the numerical model of the object, the values of the geometrical parameters are estimated with a good accuracy. Numerical experiments show that the method provides good results, even if the initialization of the process is far from the real values.

Description: One-dimensional fiber-bundle arrays may prove useful in a number of radiation sensing applications where radiation detection over large areas is needed. Tests have been performed to evaluate the light generation and transmission characteristics of 15-meter long, 10-fiber bundles of BCF-10, BCF-12, and BCF-20 scintillating fibers (Saint Gobain) exposed to collimated gamma-ray sources. The test set-up used one R9800 (Hamamatsu) photomultiplier tube (PMT) at each end, with a high-speed waveform digitizer to collect data. Time constraints were imposed on the waveform data to perform time-of-flight analysis of the events in the fiber bundles, eliminating spurious noise pulses in the high gain PMTs and also allowing 1-dimensional localization of interactions along the lengths of the fiber bundles. Measurements show that the spatial response of these three fibers is linear over at least 15-m lengths and that, with the equipment used here, the spatial resolution for events irradiating 1 cm of fiber (using a collimated source) ranges from 50 cm to 60 cm over the entire length of the bundles. The efficiency for detecting events varies along the length of the arrays, with the sensitivity at the midpoint (half of the distance) of an array ranging from $sim $ 2X to $sim$ 3X the efficiency at the ends, depending on the length of the fiber-bundle array and the self-absorption factor for each fiber's scintillation light. Compared to prior work, a 20-fold improvement in detection sensitivity has been shown for this technique, most likely due to improved optical coupling and improved signal analysis.

Description: Provides a listing of current staff, committee members and society officers.

Description: A photovoltaic (PV) plant model is presented. It is based on a detailed electrothermal description of the panels forming strings that, in turn, form the power plant. It accounts for environmental working conditions, such as temperature and wind speed, and specific plant configuration, such as plant topology and power losses due to interconnections. The input variables of the model are the ambient temperature, irradiance, and wind speed. The model derives the working temperature of the panel taking into account also the power conversion performed by the panel; the electrical operating point is determined by simulating the actions done by the maximum power point tracker that operates at plant level. This model has been tested using a large database of experimental data from industrial PV plants characterized by power levels ranging from 250 kW to 1 MW. As shown, the model is capable to predict power production when “fed” by forecast irradiance, ambient temperature, and wind speed data.