Rethinking Out-of-distribution (OOD) Detection: Masked Image Modeling is All You Need

The core of out-of-distribution (OOD) detection is to learn the in-distribution (ID) representation, which is distinguishable from OOD samples. Previous work applied recognition-based methods to learn the ID features, which tend to learn shortcuts instead of comprehensive representations. In this work, we find surprisingly that simply using reconstruction-based methods could boost the performance of OOD detection significantly. We deeply explore the main contributors of OOD detection and find that reconstruction-based pretext tasks have the potential to provide a generally applicable and efficacious prior, which benefits the model in learning intrinsic data distributions of the ID dataset. Specifically, we take Masked Image Modeling as a pretext task for our OOD detection framework (MOOD). Without bells and whistles, MOOD outperforms previous SOTA of one-class OOD detection by 5.7%, multi-class OOD detection by 3.0%, and near-distribution OOD detection by 2.1%. It even defeats the 10-shot-per-class outlier exposure OOD detection, although we do not include any OOD samples for our detectionComment: This paper is accepted by CVPR2023 and our codes are released here: https://github.com/JulietLJY/MOO

Automatic Course Website Discovery from Search Engine Results

With the rapid development of Internet Technology, the forms of education have been undergoing drastic changes. Instructors are used to posting teaching materials on course websites and setting them publicly accessible. Thus large amounts of course resources have been well organized and shared, which also provide possibilities for building knowledge graphs for a specific domain. However, so far no specific method has been developed for collecting online course resources. In this paper, we propose a method to identify course websites by filtering search results from a general search engine. Experiment results show that the proposed method could achieve good performances on both within-domain and cross-domain tasks, which lays a solid foundation for further work on mining and integrating the online educational resources

Underestimated ecosystem carbon turnover time and sequestration under the steady state assumption: a perspective from long‐term data assimilation

It is critical to accurately estimate carbon (C) turnover time as it dominates the uncertainty in ecosystem C sinks and their response to future climate change. In the absence of direct observations of ecosystem C losses, C turnover times are commonly estimated under the steady state assumption (SSA), which has been applied across a large range of temporal and spatial scales including many at which the validity of the assumption is likely to be violated. However, the errors associated with improperly applying SSA to estimate C turnover time and its covariance with climate as well as ecosystem C sequestrations have yet to be fully quantified. Here, we developed a novel model-data fusion framework and systematically analyzed the SSA-induced biases using time-series data collected from 10 permanent forest plots in the eastern China monsoon region. The results showed that (a) the SSA significantly underestimated mean turnover times (MTTs) by 29%, thereby leading to a 4.83-fold underestimation of the net ecosystem productivity (NEP) in these forest ecosystems, a major C sink globally; (b) the SSA-induced bias in MTT and NEP correlates negatively with forest age, which provides a significant caveat for applying the SSA to young-aged ecosystems; and (c) the sensitivity of MTT to temperature and precipitation was 22% and 42% lower, respectively, under the SSA. Thus, under the expected climate change, spatiotemporal changes in MTT are likely to be underestimated, thereby resulting in large errors in the variability of predicted global NEP. With the development of observation technology and the accumulation of spatiotemporal data, we suggest estimating MTTs at the disequilibrium state via long-term data assimilation, thereby effectively reducing the uncertainty in ecosystem C sequestration estimations and providing a better understanding of regional or global C cycle dynamics and C-climate feedback

Do Native Parasitic Plants Cause More Damage to Exotic Invasive Hosts Than Native Non-Invasive Hosts? An Implication for Biocontrol

Field studies have shown that native, parasitic plants grow vigorously on invasive plants and can cause more damage to invasive plants than native plants. However, no empirical test has been conducted and the mechanism is still unknown. We conducted a completely randomized greenhouse experiment using 3 congeneric pairs of exotic, invasive and native, non-invasive herbaceous plant species to quantify the damage caused by parasitic plants to hosts and its correlation with the hosts' growth rate and resource use efficiency. The biomass of the parasitic plants on exotic, invasive hosts was significantly higher than on congeneric native, non-invasive hosts. Parasites caused more damage to exotic, invasive hosts than to congeneric, native, non-invasive hosts. The damage caused by parasites to hosts was significantly positively correlated with the biomass of parasitic plants. The damage of parasites to hosts was significantly positively correlated with the relative growth rate and the resource use efficiency of its host plants. It may be the mechanism by which parasitic plants grow more vigorously on invasive hosts and cause more damage to exotic, invasive hosts than to native, non-invasive hosts. These results suggest a potential biological control effect of native, parasitic plants on invasive species by reducing the dominance of invasive species in the invaded community

AlphaTracker: a multi-animal tracking and behavioral analysis tool

Computer vision has emerged as a powerful tool to elevate behavioral research. This protocol describes a computer vision machine learning pipeline called AlphaTracker, which has minimal hardware requirements and produces reliable tracking of multiple unmarked animals, as well as behavioral clustering. AlphaTracker pairs a top-down pose-estimation software combined with unsupervised clustering to facilitate behavioral motif discovery that will accelerate behavioral research. All steps of the protocol are provided as open-source software with graphic user interfaces or implementable with command-line prompts. Users with a graphical processing unit (GPU) can model and analyze animal behaviors of interest in less than a day. AlphaTracker greatly facilitates the analysis of the mechanism of individual/social behavior and group dynamics

Confection et caractérisation de revêtements d'oxydes métalliques semi-conducteurs par projection thermique, à partir de solutions des éléments précurseurs (techniques "SPTS").

Les procédés de photodégradation, de conversion photocatalytique du CO2 et la technologie des supercondensateurs représentent des options intéressantes pour palier aux problèmes environnementaux et pour apporter des réponses à la crise énergétique. Dans ces trois domaines, les matériaux à base d'oxydes métalliques sont très prometteurs. Cependant, les voies classiques (c'est-à-dire par voies hydrothermales ou de sol-gels) présentent un certain nombre d’inconvénients tels que leur longues durées de préparation et leurs rendements limités. En outre, la mise en oeuvre de nanopoudres suppose une opération de post-filtration dans les procédés de photodégradation et l’utilisation supplémentaire d’un liant dans la confection d’électrodes de supercondensateurs, ce qui non seulement réduit les performances respectives de ces deux procédés mais entrave également leur développement au niveau industriel. Dans cette thèse, les technologies SPPS (Solution Precursor Plasma Spray) et SPFS (Solution Precursor Flame Spray) ont été introduites pour préparer des films d'oxydes métalliques à base de ZnO, en bénéficiant des avantages de rapidité et simplicité de ces techniques de formation de dépôts. Les films ainsi obtenues ont ensuite été testés dans des expériences de photodégradation, de conversion photocatalytique du CO2 et sous forme de supercondensateurs. Tout d'abord, à notre connaissance, c'est la première fois que l'on synthétise directement des nanostructures de ZnO (par exemple des nanotubes ou des nanofils) par des procédés SPPS. Ces films nanostructurés et hiérarchisés présentent non seulement une croissance préférentielle le long du plan cristallin (002), mais contiennent aussi des lacunes d'oxygène dans leurs réseaux. La mise en œuvre de simulations DFT a permis de proposer un mécanisme possible de croissance des nanostructures de ZnO lors de leur synthèse par la voie SPPS. Deuxièmement, divers films “composites”, constitués de ZnO et d’un second oxide “MO” ont également été préparés par SPPS afin de réduire les bandes d'énergie interdites. Dans cette partie de la thèse, nous avons étudié l’effet du rapport molaire MO/ZnO sur la structure des films MO/ZnO obtenus (M = Mn et Cu); nous avons aussi préparé, par cette nouvelle méthode, des films fins CuO/ZnO et CeO2/ZnO ainsi que des films de ZnO “décorés”. Troisièmement, des films mettant en œuvre des structures du type spinelle (tels que les oxydes mixtes ZnFe2O4, NiCo2O4, ZnCo2O4 et Co3O4) ont également été synthétisés et déposés à l’aide des techniques SPPS et SPFS, ceci en raison de leur grand intérêt pour les applications susmentionnées. Il a été constaté que les structures obtenues sont très sensibles aux rapports MO/ZnO et que les morphologies de surface dépendent davantage des paramètres d'injection des solutions. En outre, la puissance de la torche joue un rôle plus critique dans la synthèse in situ de la phase spinelle binaire que la température de préchauffage du substrat. Enfin, la voie de préparation par SPPS favorise la formation de dépôts de textures floconneuses, notamment dans le cas des films de NiCo2O4 et Co3O4, tandis que des particules de formes sphériques ont été plutôt observées dans les échantillons préparés par la voie SPFS...The fields of research dealing with photodegradation, photocatalytic conversion of CO2 and supercapacitors are important to address environmental problems and respond to the energy crisis. Metal oxides are promising materials in these three domains. However, the conventional routes (i.e. hydrothermal, sol-gel) suffer from major deficiencies, namely their multi-step natures, their long preparation duration and small-scaled yields. Moreover, the usage of nanopowders implies a post-filtration operation at the end of the photodegradation processes and requires an additional binder in supercapacitor electrodes. In this thesis, “Solution Precursor Plasma Spray” (SPPS) and “Solution Precursor Flame Spray” (SPFS) technologies have been introduced to develop metal oxide films in view of the three aforementioned applications, benefiting from the facility and rapidity advantages of this one-step process.Firstly, to our best knowledge, it is the first time that films composed by ZnO nanostructures (e.g. nanorods, nanowires) are directly synthesized via a SPPS process. These hierarchical ZnO nanostructured films not only exhibit preferential orientation growth along the (002) crystal plane, but also feature in-situ oxygen vacancies. As a result, a possible growth mechanism of ZnO nanostructures via SPPS route was proposed.Secondly, various metal oxides composite films containing ZnO and a second metal oxide were also prepared by SPPS in an effort to narrow the energy bandgaps. In this work, not only the effect of the molar CuO/ZnO and MnO/ZnO ratio was investigated, but also laminated CuO/ZnO and CeO2/ZnO films and CuO, Co3O4 and Fe2O3 decorated ZnO nanorods films were pioneeringly deposited via this novel route.Thirdly, films involving spinel-type materials (including ZnFe2O4, NiCo2O4, ZnCo2O4 and Co3O4) were also synthesized and deposited by the SPPS and SPFS technologies, owing to their high-interest in the aforementioned applications. We found that the phase compositions are more sensitive to the Fe/Zn and Ni/Co ratios and that the surface morphologies are more dependent on the patterns of the solution injection. In addition, the power of the torch plays a more critical role on the in-situ synthesis of binary spinel phase. Besides, the SPPS route promotes the formation of flake-like particles both in the NiCo2O4 and Co3O4 films, while sphere-like particles were observed in the SPFS-prepared samples.Finally, some as-prepared films were selected to evaluate their performances within the three applications. On the one hand, Orange II was successfully (100%) degraded within 2h under UV irradiation and about 85% was removed within 6h under visible light irradiation. On the other hand, Co3O4 samples exhibited specific capacitances up to 1190 F g−1 with a retention capacity of 136% after 2500 cycles at a 20 mV/s scanning rate in 2 M KOH electrolyte. Finally, when using ZnCo2O4 as photocatalyst, CO2 was converted into CO by visible light irradiation with a maximum turnover number as high as 61.38 and a selectivity as high as 90.5 %.Overall, this work not only improves the performances of the three studied processes thanks to the use of novel, fast preparation methods, but also suggests that “Solution Precursor Thermal Spray” should be a highly promising technology for further, alternative functional applications that involve finely structured metal oxides film

Study on working condition of 750 kV AC filter breaker in ± 1100 kV UHVDC system

In this article, the Changji-Guquan ± 1100 kV ultra-high voltage direct current (UHVDC) system has been established by PSCAD software, especially for the arc of the circuit breakers. The AC filter groups and the control strategy have been analysed based on the reactive power demand of this system, AC system voltage amplitude, and harmonic limit. This article mainly studies inrush currents and overvoltage, especially recovery voltage caused by switching circuit breaker of AC filter in the different working conditions. Simulation results show that the currents through circuit breakers are capacitive and contain a variety of harmonics. There will be a high inrush current when a circuit breaker of AC filter is closing, which can be suppressed by phase selection switch device and appropriate closing resistance. A higher DC transmission power and a less short circuit both make the recovery voltage of circuit breakers higher when the AC filters are removed. The maximum transient recovery voltage of circuit breakers of AC filters can be suppressed by adding the parallel opening resistors. In a certain range, higher resistance of opening resistor makes a better suppression effect on recovery voltage

Identification Method for Pulse Wave Resulted From Fault Transient of Overhead Transmission Line

This paper presents a simple and effective method to extract the identification quantity of transient pulse waveform produced by the overhead transmission line short-circuit fault. This method employs the second-order time harmonic equation of the power frequency component to convert the fault full-wave data. After the conversion, only the identification quantity remains. This method can amplify high-frequency spectral content by the times of the square of the angular frequency, and hence improve the sensitivity of identifying fault transient. Using the identification quantity, one can clearly observe the arrival time and relative intensity of fault transient. A three-phase half wavelength transmission line of 50Hz/3000km is simulated with PSCAD to illuminate the effectiveness of this method. The effects of fault type, soil resistivity, fault resistance, power frequency fluctuation, sampling rate, transposition length, fault inception angle and white noise are analyzed. Calculated results show that this method can distinguish different fault type and can work effectively at low sampling rate down to 10kHz. This method is helpful for improving the performance of the traveling-wave based fault location method