Quantitative and depth-resolved deep level defect distributions in InGaN/GaN light emitting diodes
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solar (photovoltaic), solid state lighting, phonon↗
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A two-level stochastic collocation method for semilinear elliptic equations with random coefficients
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Chen, Luoping↗
A bi-level advanced control framework for large-scale control of buildings with system-level impact
Increased electricity consumption combined with new forms of generation is testing the reliability of our grid infrastructure. This work describes a method to improve the reliability of the grid through large-scale advanced building control. This paper develops a bi-level distributed control framework to shift the load of 153 buildings to achieve a system-level objective of tracking a power reference signal. This bi-level control is based on the previously-developed ANPV-MPC, a predictive controller that uses a Bayesian neural network to generate an accurate control model and adapt to changing conditions over time. By shifting the building electricity demand to better match the available power, the grid system supplying the buildings is more reliable as evidenced by the analysis of node voltages across an IEEE 13-bus distribution system. The proposed bi-level control framework tracks the system-level power reference with enough accuracy to regulate node voltages across the IEEE 13-bus distribution system within ANSI limits of ±5%. Additionally, the adaptive nature of ANPV-MPC allows each building across the system to adapt to changing conditions, further amplifying the system-level reliability.
32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
Promoting system-level learning from project-level lessons
A growing number of low and middle income nations (LMCs) have adopted some sort of system for environmental impact assessment (EIA). However, generally many of these EIA systems are characterised by a low performance in terms of timely information dissemination, monitoring and enforcement after licencing. Donor actors (such as the World Bank) have attempted to contribute to a higher performance of EIA systems in LMCs by intervening at two levels: the project level (e.g. by providing scoping advice or EIS quality review) and the system level (e.g. by advising on EIA legislation or by capacity building). The aims of these interventions are environmental protection in concrete cases and enforcing the institutionalisation of environmental protection, respectively. Learning by actors involved is an important condition for realising these aims. A relatively underexplored form of learning concerns learning at EIA system-level via project level donor interventions. This 'indirect' learning potentially results in system changes that better fit the specific context(s) and hence contribute to higher performances. Our exploratory research in Ghana and the Maldives shows that thus far, 'indirect' learning only occurs incidentally and that donors play a modest role in promoting it. Barriers to indirect learning are related to the institutional context rather than to individual characteristics. Moreover, 'indirect' learning seems to flourish best in large projects where donors achieved a position of influence that they can use to evoke reflection upon system malfunctions. In order to enhance learning at all levels donors should thereby present the outcomes of the intervention elaborately (i.e. discuss the outcomes with a large audience), include practical suggestions about post-EIS activities such as monitoring procedures and enforcement options and stimulate the use of their advisory reports to generate organisational memory and ensure a better information dissemination.
54 ENVIRONMENTAL SCIENCES↗
Impact of Inverter-Interfaced Renewable Generation on Transient Stability at Varying Levels of Penetration: Preprint
The transient dynamics of conventional power systems are dominated by synchronous generators, and low-inertia inverters serve as the primary interface between power systems and renewable energy resources. Increasing penetration levels of inverter-interfaced generation are impacting the transient dynamics of power systems. In this paper, we attempt to quantify these impacts at different penetration levels. An elementary system including one inverter, one synchronous generator, and one load is studied under different parameter variations to assess the transient dynamics of the system. To quantify transient stability, the post-fault regions of attraction of the system are estimated by the sample-based basin stability approach with parallel computing technology. The simulation results suggest that different inverter penetration levels, inertias of the generator, inverter controller gains, and phase-locked loop controller gains have a clear impact on the regions of attraction as well as on the transient dynamics of proposed systems.
24 POWER TRANSMISSION AND DISTRIBUTION↗
Adaptive nonlocal means filtering based on local noise level for CT denoising
Purpose: To develop and evaluate an image-domain noise reduction method based on a modified nonlocal means (NLM) algorithm that is adaptive to local noise level of CT images and to implement this method in a time frame consistent with clinical workflow. Methods: A computationally efficient technique for local noise estimation directly from CT images was developed. A forward projection, based on a 2D fan-beam approximation, was used to generate the projection data, with a noise model incorporating the effects of the bowtie filter and automatic exposure control. The noise propagation from projection data to images was analytically derived. The analytical noise map was validated using repeated scans of a phantom. A 3D NLM denoising algorithm was modified to adapt its denoising strength locally based on this noise map. The performance of this adaptive NLM filter was evaluated in phantom studies in terms of in-plane and cross-plane high-contrast spatial resolution, noise power spectrum (NPS), subjective low-contrast spatial resolution using the American College of Radiology (ACR) accreditation phantom, and objective low-contrast spatial resolution using a channelized Hotelling model observer (CHO). Graphical processing units (GPU) implementation of this noise map calculation and the adaptive NLM filtering were developed to meet demands of clinical workflow. Adaptive NLM was piloted on lower dose scans in clinical practice. Results: The local noise level estimation matches the noise distribution determined from multiple repetitive scans of a phantom, demonstrated by small variations in the ratio map between the analytical noise map and the one calculated from repeated scans. The phantom studies demonstrated that the adaptive NLM filter can reduce noise substantially without degrading the high-contrast spatial resolution, as illustrated by modulation transfer function and slice sensitivity profile results. The NPS results show that adaptive NLM denoising preserves the shape and peak frequency of the noise power spectrum better than commercial smoothing kernels, and indicate that the spatial resolution at low contrast levels is not significantly degraded. Both the subjective evaluation using the ACR phantom and the objective evaluation on a low-contrast detection task using a CHO model observer demonstrate an improvement on low-contrast performance. The GPU implementation can process and transfer 300 slice images within 5 min. On patient data, the adaptive NLM algorithm provides more effective denoising of CT data throughout a volume than standard NLM, and may allow significant lowering of radiation dose. After a two week pilot study of lower dose CT urography and CT enterography exams, both GI and GU radiology groups elected to proceed with permanent implementation of adaptive NLM in their GI and GU CT practices. Conclusions: This work describes and validates a computationally efficient technique for noise map estimation directly from CT images, and an adaptive NLM filtering based on this noise map, on phantom and patient data. Both the noise map calculation and the adaptive NLM filtering can be performed in times that allow integration with clinical workflow. The adaptive NLM algorithm provides effective denoising of CT data throughout a volume, and may allow significant lowering of radiation dose.
62 RADIOLOGY AND NUCLEAR MEDICINE↗
A system-level mathematical model for evaluation of power train performance of load-leveled electric-vehicles
The power train performance of load leveled electric vehicles can be compared with that of nonload leveled systems by use of a simple mathematical model. This method of measurement involves a number of parameters including the degree of load leveling and regeneration, the flywheel mechanical to electrical energy fraction, and efficiencies of the motor, generator, flywheel, and transmission. Basic efficiency terms are defined and representative comparisons of a variety of systems are presented. Results of the study indicate that mechanical transfer of energy into and out of the flywheel is more advantageous than electrical transfer. An optimum degree of load leveling may be achieved in terms of the driving cycle, battery characteristics, mode of mechanization, and the efficiency of the components. For state of the art mechanically coupled flyheel systems, load leveling losses can be held to a reasonable 10%; electrically coupled systems can have losses that are up to six times larger. Propulsion system efficiencies for mechanically coupled flywheel systems are predicted to be approximately the 60% achieved on conventional nonload leveled systems.
Purohit, G. P.↗
Comparison of level-1 and level-2 buckling and postbuckling solutions
The accuracy of the solutions obtained with the Level-1 computational modules of DISDECO (Delft Interactive Shell Design Code) are investigated by comparing them with solutions obtained with ANILISA, a Level-2 computational module. Whereas the Level-1 solutions are based on the use of trigonometric functions to represent the out-of-plane displacement W and involve Galerkin type approximations to reduce the governing partial differential equations to simple algebraic expressions, the Level-2 solutions employ a truncated Fourier expansion in the circumferential direction and solve the resulting ordinary differential equations forming a nonlinear eigenvalue problem by a Stodola like technique. This involves the numerical integration of the set of ordinary differential equations, which in turn makes it possible to satisfy the specified boundary conditions exactly. It is shown that in many applications the Level-1 predictions concerning the critical buckling load of the perfect structure and its imperfection sensitivity are quite accurate and reliable. For those cases where this is not true, it is shown how the pre and postprocessing facilities of DISDECO can be used efficiently to arrive at a reliable prediction. This involves always the use of the Level-2 computational module ANILISA with its rigorous prebuckling solution and its feature which makes it possible to satisfy the specified boundary conditions exactly.
Arbocz, J.↗
Acceptor levels in ZnMgO:N probed by deep level optical spectroscopy
A combination of deep level optical spectroscopy and lighted capacitance voltage profiling has been used to analyze the effect of N into the energy levels close to the valence band of Zn{sub 0.9}Mg{sub 0.1}O. Three energy levels at E{sub V} + 0.47 eV, E{sub V} + 0.35 eV, and E{sub V} + 0.16 eV are observed in all films with concentrations in the range of 10{sup 15}–10{sup 18} cm{sup −3}. The two shallowest traps at E{sub V} + 0.35 eV and E{sub V} + 0.16 eV have very large concentrations that scale with the N exposure and are thus potential acceptor levels. In order to correctly quantify the deep level concentrations, a metal-insulator-semiconductor model has been invoked, explaining well the resulting capacitance-voltage curves.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
A novel method for measuring ultra-trace levels of U and Th in Au, Pt, Ir, and W matrices using ICP-QQQ-MS employing an O 2 reaction gas
A mass shift method using ICP-MS/MS with O 2 reaction gas is used for ultra-trace determinations of U and Th in samples containing W, Ir, Pt, and Au derived polyatomic interferants without the need for extensive chemical sample preprocessing.
Harouaka, Khadouja↗
Line shape of a transition between two levels in a three-level {Lambda} configuration
We report on our study of the line shape of a transition between two levels in a three-level {Lambda} configuration. By using Poisson statistics under the assumption that the atom stays in a two-level steady state before it is optically pumped to the reservoir state, we arrive at a simple analytic expression for the line shape of a three-level atom. This expression reveals a new type of saturation in the time domain, which is conceptually different from that of power-broadening in a two-level atom. It can also be used as a basis for more complicated situations of Doppler-broadened gaseous samples or pump-and-probe spectroscopy. We tested the theory experimentally in an ideal situation of slow pulsed {sup 85}Rb atoms and found excellent agreement. Application to measurements of a branching ratio or a Franck-Condon factor of a diatomic molecule is discussed.
74 ATOMIC AND MOLECULAR PHYSICS↗
Metabolic engineering of seeds can achieve levels of omega-7 fatty acids comparable to the highest levels found in natural plant sources
Plant oils containing {omega}-7 fatty acids (FAs; palmitoleic 16:1{Delta}{sup 9} and cis-vaccenic 18:1{Delta}{sup 11}) have potential as sustainable feedstocks for producing industrially important octene via metathesis chemistry. Engineering plants to produce seeds that accumulate high levels of any unusual FA has been an elusive goal. We achieved high levels of {omega}-7 FA accumulation by systematic metabolic engineering of Arabidopsis (Arabidopsis thaliana). A plastidial 16:0-ACP desaturase has been engineered to convert 16:0 to 16:1{Delta}{sup 9} with specificity >100-fold than that of naturally occurring paralogs, such as that from cat's claw vine (Doxantha unguis-cati). Expressing this engineered enzyme (Com25) in seeds increased {omega}-7 FA accumulation from <2% to 14%. Reducing competition for 16:0-ACP by down-regulating the {beta}-ketoacyl-ACP synthase II 16:0 elongase further increased accumulation of {omega}-7 FA to 56%. The level of 16:0 exiting the plastid without desaturation also increased to 21%. Coexpression of a pair of fungal 16:0 desaturases in the cytosol reduced the 16:0 level to 11% and increased {omega}-7 FA to as much as 71%, equivalent to levels found in Doxantha seeds.
59 BASIC BIOLOGICAL SCIENCES↗
Improving Self-Driving Labs: Quantifying System-Level Experiment Repeatability and Broadening Instrument-Level Compatibility
Modular Autonomous Research System (MARS) is a self-driving laboratory (SDL) which performs wet-lab science with peptide-lanthanide combinations in an automated and, ultimately, an autonomous manner to aid in soil analysis for domestic lithium mining. Autonomous experimentation involves automated experimentation, experiment planning, and active learning. MARS consists of a 6-axis robotic arm (UR5e) on a linear rail, pipette robots (Opentrons 2), and microplate readers. These components transport, operate on, and collect data with chemical solutions in standard labware. For effective autonomy, MARS must perform system-level labware operations repeatably, plan experiments autonomously, and be portable between research-domains. Repeatability is evaluated by labware placement precision, such that future operations can properly locate labware, as well as the elapsed time, so that low variance mean estimates of experiment duration can inform high-level researcher decision making. Autonomous experiment planning is the next step to decouple experimentation from human management; however, there is a conflict between the ideal system-level experiment goals and the constraints imposed by instruments’ limitations. Sub-domain portability is a long-term goal to extend MARS’ research beyond the chemistry of peptide-lanthanide binding to other sub-domains without having to invest significant overhead to system retrofitting. To address these goals, we manually trained the robotic arm labware placement and modelled statistical failurerate and uncertainty Additionally, we benchmarked the duration and variance of each experiment sub-operation as a heuristic for research decision making. Next, we use a parameterized geometric program (PGP) approach to design experiments that optimize system-level objectives and satisfy instrument-level constraints. Lastly, we proposed a Python framework to maximize MARS’ extensibility to other scientific sub-domains through a JSON-based experiment specification.
36 MATERIALS SCIENCE↗
Impacts on High-level Systems-of-Systems Figures of Merit due to Integrated Architecture Sizing and Technology Evaluation at the Subsystem-Level
Understanding the impacts on high-level system-of-systems (SOS) figures of merit (FOMs) due to the design of architectures and technologies is critical in providing decision makers sufficient information in selecting suitable alternatives in an effort to reduce costly financial and schedule overruns. Several techniques exist within academia and industry for performing SOS architecture design and technology evaluation. However, these techniques fail to solve the problem in an integrated fashion when defined at the subsystem-level. In order to understand the impacts on high-level SOS FOMs due to integrated architecture sizing and technology evaluation, a general concept exploration process is utilized to perform a notional 2033 manned Mars fly by study. The notional study draws out observation with regard to specific FOMs traditionally used during the subsystem-level sizing and technology evaluation processes which can result in misleading conclusions regarding the overall SOS design. Furthermore, these observations suggest that selection of FOMs for the subsystems of an architecture should be influenced by the desired objectives of the high-level SOS objectives and FOMs.
Trent, Douglas J.↗
Taking Risk Assessment and Management to the Next Level: Program-Level Risk Analysis to Enable Solid Decision-Making on Priorities and Funding
A multi-level (facility and programmatic) risk assessment was conducted for the facilities in the Nevada National Security Site (NNSS) Readiness in Technical Base and Facilities (RTBF) Program and results were included in a new Risk Management Plan (RMP), which was incorporated into the fiscal year (FY) 2010 Integrated Plans. Risks, risk events, probability, consequence(s), and mitigation strategies were identified and captured, for most scope areas (i.e., risk categories) during the facilitated risk workshops. Risk mitigations (i.e., efforts in addition to existing controls) were identified during the facilitated risk workshops when the risk event was identified. Risk mitigation strategies fell into two broad categories: threats or opportunities. Improvement projects were identified and linked to specific risks they mitigate, making the connection of risk reduction through investments for the annual Site Execution Plan. Due to the amount of that was collected, analysis to be performed, and reports to be generated, a Risk Assessment/ Management Tool (RAMtool) database was developed to analyze the risks in real-time, at multiple levels, which reinforced the site-level risk management process and procedures. The RAMtool database was developed and designed to assist in the capturing and analysis of the key elements of risk: probability, consequence, and impact. The RAMtool calculates the facility-level and programmatic-level risk factors to enable a side-by-side comparison to see where the facility manager and program manager should focus their risk reduction efforts and funding. This enables them to make solid decisions on priorities and funding to maximize the risk reduction. A more active risk management process was developed where risks and opportunities are actively managed, monitored, and controlled by each facility more aggressively and frequently. risk owners have the responsibility and accountability to manage their assigned risk in real-time, using the RAMtool database.
Nelson, J. G.↗
Carrier Density and Compensation in Semiconductors with Multi Dopants and Multi Transition Energy Levels: The Case of Cu Impurity in CdTe: Preprint
Doping is one of the most important issues in semiconductor physics. The charge carrier generated by doping can profoundly change the properties of semiconductors and their performance in optoelectronic device applications, such as solar cells. Using detailed balance theory and first-principles calculated defect formation energies and transition energy levels, we derive general formulae tocalculate carrier density for semiconductors with multi dopants and multi transition energy levels. As an example, we studied CdTe doped with Cu, in which VCd, CuCd, and Cui are the dominant defects/impurities. We show that in this system, when Cu concentration increases, the doping properties of the system can change from a poor p-type, to a poorer p-type, to a better p-type, and then to a poorp-type again, in good agreement with experimental observation of CdTe-based solar cells.
14 SOLAR ENERGY↗
Evaluation of Computed Tomography Techniques for Material Identification in Low Level and Intermediate Level Waste - 16648
Measures required to assure long term safe storage of Low-level and intermediate-level short-lived (LIL/SL) waste generated by the nuclear-power industry in France include the characterization of the waste and identification of materials within the waste. Digital Radiography (DR) techniques using x-ray at energies in the 6 MeV range have been shown to be effective for validation of the integrity of the concrete containers, and it was considered that the use of this technique together with the addition of Computed Tomography (CT) techniques could effectively identify materials within the waste. This paper describes the initial evaluation of two DR imaging techniques and two CT techniques using x-ray energy spectra up to 9 MeV to inspect a surrogate waste package, which comprised an outer concrete cylindrical container of 1400 mm diameter with 148 mm wall thickness, and an overall volume of 2 meters cubed, within which a 200 liter drum containing representative heterogeneous inactive waste, was placed in the center and the annulus between the 200 liter drum and the outer cylindrical package was filled with cement grout. The surrogate waste within the 200 liter drum comprised three separate layers of high density, medium density and low density mixed materials. The equipment used was a linear accelerator producing high energy spectra at either 6 MeV or 9 MeV and a high-precision CT manipulator with X, Y, Z and rotation motions, which were common to all techniques investigated. Two different digital detectors were used in the DR and CT performance evaluations, a Digital Detector Array (DDA) comprising a columnar Thallium-doped Cesium-Iodide scintillator screen in intimate contact with a 2 k by 2 k array of amorphous silicon detectors, 200 μm x 200 μm in area, and a Linear Diode Array (LDA) comprising a line of Cadmium-Tungstate columns, 1 cm thick and 400 μm x 400 μm in area. The work comprised evaluations of linear accelerator spectra and the attenuation effects of the waste container and contents, image acquisition performance of each detector, and CT techniques using area detector and linear detector. The results presented in this paper include mathematical evaluation of the two CT techniques, and analysis of measurement data, digital images, CT reconstruction images, and estimated material densities. The data was compared with recorded details and photographs of the actual configuration of materials within the surrogate waste. The Digital Detector Array can generate CT inspection volumes with considerable resolution and detail for the low-density and medium-density sections of the surrogate waste, however, the high-density sections were not imaged with sufficient detail and the images contained a large number of artifacts mainly due to the detectors lack of high energy photon stopping power. Materials identification with the Digital Detector Array, while possible for certain materials, for materials in the steel to plastic density range the attenuation values of the voxels in the reconstruction are too similar and difficult to resolve from the artifacts present. The Linear Diode Array can generate CT inspection volumes of regions of interest of the low-density and medium-density sections with considerable resolution and contrast, and potentially acceptable levels of resolution and contrast of the high-density section of the waste. While a few artifacts were present in the reconstructions, the majority are not due to the fundamental properties of the detector and are considered to be correctable. Materials identification with the LDA inspection data appear to be viable, with steel, copper, and higher-density metals being readily be distinguished from other materials on the basis of voxel value. Future work is needed to obtain a better definition of optimum spatial resolution and inspection speed, and to develop a system of 'calibration rods' which would consist of a series of 50 mm diameter cylinders of 7 materials; Plastic, Teflon, Concrete, Aluminum, Copper, Tungsten and Lead. The cylinders will be distributed at a certain radius in the surrogate waste and will be used as reference points in the evaluation and demonstration of the contrastive performance for the low, medium and high-density cases. The ability to identify the materials within a sealed waste container, by nondestructive examination, enables the verification of waste acceptance criteria without the need to open the waste containers. This eliminates the need for complex and expensive equipment to open and remotely handle the intermediate level waste, avoids potential hazards and risk of personnel dose uptake, and does not increase the volume of waste caused by repackaging of materials after examination and the decontamination or disposal of equipment used.
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗