46 Search Results

In data-driven automated fault detection and diagnostics (AFDD) modeling for building energy systems, feature engineering is a critical process of extracting information from high-dimensional and noisy sensor measurement and turning it into informative and representative inputs or features for data-driven modeling. However, few studies specifically discuss the feature engineering, especially the interactions between feature extraction and feature selection in whole-building AFDD. We developed a systematic feature extraction and selection framework for whole-building AFDD. In this framework, features are aggressively extracted from raw sensor data using statistical feature extraction techniques with various window sizes and statistics. With many features extracted, amore » hybrid feature selection algorithm that combines the filter and wrapper method then selects the best feature set. The framework considers diversity in the duration of fault behavior among fault types in whole-building AFDD, thus achieving high model generalization. We implemented our developed framework in a virtual testbed calibrated with measured data from Oak Ridge National Laboratory's Flexible Research Platform designed to mimic the operation of a typical small commercial building. The AFDD model is trained by the simulation data generated from the virtual testbed. The results show that (1) the developed framework improves the generalization of the AFDD model by 10.7% compared with literature-reported feature extraction and selection methods and (2) features with diverse window sizes and statistics are selected, providing insight into physical systems beyond the current understanding of buildings and faults and improving the detection and diagnostics of multiple fault types.« less

Anionic oxygen redox has aroused great interests in developing high-capacity Li-ion battery cathode materials. The fundamental understanding of this concept, compared to cationic redox, has promoted extensive studies on lithium transition metal oxides including those of 4d and 5d transition metals. Lithium ruthenium oxide has been found to exhibit a reversible anionic redox upon cycling. However, lithium-rich layered oxide with anionic redox is still facing great challenges such as sluggish kinetics. Here we investigate the effect of cationic redox on the kinetics of anionic reaction when they are strongly coupled. We report the cobalt substituted lithium ruthenium oxide, where allmore » Ru, Co and O redox participate in the charge compensation mechanism in relatively defined voltage regions. Additionally, the improved anionic kinetics is attributed to the fast cationic Co redox process that serves as a redox mediator. Our work sheds light into the potential direction to address the commonly believed sluggish anionic kinetics in high-capacity oxygen-redox cathode materials.« less

Building energy modeling provides a fundamental tool to assess the potential for energy efficiency to contribute to reducing world energy consumption and global emissions. Occupancy-related operations are a key source of uncertainty for building energy analysis, particularly for aggregated building stocks. At a district or city level, it is critical to estimate aggregated power load profiles for sizing power grid infrastructure, power plant capacity allocation, and energy efficiency measures. The stochastic nature of behavior-related operations complicates the creation of models that accurately capture building load profiles for entire building stocks. This research introduces a new methodology called parametric schedules tomore » model occupancy-driven schedules for large and diverse building stocks. In contrast to computationally expensive methodologies proposed in the literature, our work does not use a recursive time-consuming step. Occupancy is estimated by the extrapolation of operation times directly from metered electric consumption data; occupancy-related schedules are stochastically assigned to each building model, guaranteeing diversity of operation times in the stock. Our procedure has been tested on a large, diversified data-set of 25,000 commercial buildings in Los Angeles, California. It proved to be able to adequately represent the stochastic schedules diversity of the stock and to refine the stock calibration process by 1%. This innovative approach represents a useful asset for utility companies, grid operators, urban planners, and balancing authorities, seeking to improve building stock modeling and better estimate the impact of energy conservation measures. – This work is part of a larger stock modeling tool called ComStock, which is under development by NREL.« less

This work focuses on the mechanisms of interfacial processes at the surface of amorphous silicon thin-film electrodes in organic carbonate electrolytes to unveil the origins of the inherent nonpassivating behavior of silicon anodes in Li-ion batteries. Attenuated total reflection Fourier-transform infrared spectroscopy, X-ray absorption spectroscopy, and infrared near-field scanning optical microscopy were used to investigate the formation, evolution, and chemical composition of the surface layer formed on Si upon cycling. Herein, we found that the chemical composition and thickness of the solid/electrolyte interphase (SEI) layer continuously change during the charging/discharging cycles. This SEI layer “breathing” effect is directly related tomore » the formation of lithium ethylene dicarbonate (LiEDC) and LiPF6 salt decomposition products during silicon lithiation and their subsequent disappearance upon delithiation. Furthermore, the detected appearance and disappearance of LiEDC and LiPF6 decomposition compounds in the SEI layer are directly linked with the observed interfacial instability and poor passivating behavior of the silicon anode.« less

Geological storage of CO₂ technologies has become an important and effective way to reduce the greenhouse gas emissions, especially when it is combined with CO₂ enhanced oil recovery (EOR), which can not only trap CO₂ but also enhance oil recovery. However, the risk of CO₂ leakage has always been a prominent issue. In this paper, the mechanisms and pathways of CO₂ leakage during geological storage in oil reservoirs were analyzed using fault tree analysis (FTR). Besides, monitoring technologies were discussed and deployed in a CO₂ EOR demonstration project. The analysis results showed that the sealing failures of oil producer andmore » CO2 injector wells, like well cement failure and casing failure, are the main reasons for the CO₂ leakage, which has been observed in the oil field monitoring project. The monitoring results indicated that there is no large-scale CO₂ leakage, while relatively high and abnormal CO₂ concentration in soil gas near some wellbores are observed, which indicates there is some leakage of CO₂ through incomplete cement ring and well casing string. FTR results provide guidelines for monitoring and preventing of CO₂ leakage during geological storage in oil reservoirs. Finally, the near-surface monitoring methods, especially the soil gas monitoring technologies, can effectively detect the leakage of CO₂, and are a proper method for CO₂ leakage monitoring.« less

Because of the high theoretical energy density of 2600Whkg^-1, lithium–sulfur (Li–S) batteries are regarded as one of the most promising energy storage technologies to meet the increasing requirement from personal devices to automobiles. However, the practical application of Li–S batteries is still challenging due to technical obstacles, such as low sulfur utilization and poor lifetime. Therefore, understanding the electrode reaction mechanism is of critical importance to further improve the battery performance and lifetime. Here, we review recent progress in the application of in situ and operando X-ray absorption spectroscopy in characterizing Li–S batteries. In this paper, we discuss in detailmore » how this advanced technique helps researchers understand the redox process of the electrode materials as well as the influence of polymer binder and electrolyte additive on the polysulfide shuttle effect, which provide valuable information for designing better Li–S batteries. A general conclusion and critical further research directions are also provided at the end.« less

Lithium-sulfur (Li-S) batteries have received extensive attention as one of the most promising next-generation energy storage systems, mainly because of their high theoretical energy density and low cost. Yet, the practical application of Li-S batteries has been hindered by technical obstacles arising from the polysulfide shuttle effect and poor electronic conductivity of sulfur and discharge products. Therefore, it is of critical significance for understanding the underlying reaction mechanism of Li-S batteries to circumvent these problems and improve the overall battery performance. Advanced characterization techniques, especially synchrotron-based X-ray techniques, have been widely applied to the mechanistic understanding of Li-S batteries. Specifically,more » in situ/operando synchrotron-based techniques allows chemical and structural evolution to be directly observed under real operation conditions. Here, current progress in the understanding of the operating principles of Li-S batteries based on in situ/operando synchrotron-based techniques, including X-ray absorption spectroscopy, X-ray diffraction, and X-ray microscopy, is reviewed. The aim of this progress report is to provide a comprehensive treatise on in situ/operando synchrotron-based techniques for mechanism understanding of Li-S batteries, and thereby provide guidance for optimizing their overall electrochemical performances.« less

A detailed understanding of the effects of surface chemical and geometric composition is essential for understanding the electrochemical performance of the perovskite (ABO₃) oxides commonly used as electrocatalysts in the cathodes of ceramic fuel cells. In this work, we report how the addition of submonolayer quantities of A- and B-site cations affect the rate of the Oxygen Reduction Reaction (ORR) of Sr-doped LaFeO₃ (LSF), LaMnO₃ (LSM), and LaCoO₃ (LSCo). Density functional theory (DFT) calculations were performed to determine the stability of different active sites on a collection of surfaces. With LSF and LSM, rates for ORR are significantly higher onmore » the A-site terminated surface, while surface termination is less important for LSCo. Our findings highlight the importance of tailoring the surface termination of the perovskite to obtain its ultimate ORR performance.« less

Influenza viruses antagonize key immune defence mechanisms via the virulence factor non-structural protein 1 (NS1). A key mechanism of virulence by NS1 is blocking nuclear export of host messenger RNAs, including those encoding immune factors; however, the direct cellular target of NS1 and the mechanism of host mRNA export inhibition are not known. Here, we identify the target of NS1 as the mRNA export receptor complex, nuclear RNA export factor 1–nuclear transport factor 2-related export protein 1 (NXF1–NXT1), which is the principal receptor mediating docking and translocation of mRNAs through the nuclear pore complex via interactions with nucleoporins. We determinedmore » the crystal structure of NS1 in complex with NXF1–NXT1 at 3.8 Å resolution. The structure reveals that NS1 prevents binding of NXF1–NXT1 to nucleoporins, thereby inhibiting mRNA export through the nuclear pore complex into the cytoplasm for translation. We demonstrate that a mutant influenza virus deficient in binding NXF1–NXT1 does not block host mRNA export and is attenuated. Here, this attenuation is marked by the release of mRNAs encoding immune factors from the nucleus. In sum, our study uncovers the molecular basis of a major nuclear function of influenza NS1 protein that causes potent blockage of host gene expression and contributes to inhibition of host immunity.« less

To date, Li₂S has drawn significant attention as a positive electrode active material for rechargeable lithium cells due to its high theoretical specific capacity and capability of pairing with a lithium-free anode which can obviate any safety concern of the lithium metal anode when using sulfur. In recent years, various approaches have been employed to develop Li/Li₂S rechargeable cells for commercialization that meet the performance goals for high energy/power applications. It is expected that high lithium sulfide-loading cells with long cycle life, an excellent capacity delivery and low electrolyte:sulfur weight ratio (E/S ratio) can be achieved. Here, we report amore » Li²S electrode comprised of a novel Li2S/KB@Cf nanocomposite which delivers an areal capacity of 7.56 mAh cm-2 and good cycling stability with a mass loading of 11.29 mg cm^-2 and a robust 3-dimensional (3D) aluminum foam current collector with a high open area. The high conductivity and scalability of the active material, the availability of 3D current collection for the active material and the control of the electrolyte/sulfur ratio offer the potential of realization of practical Li/S cells.« less