ALBERT

Beschreibung: The results of a search for gluino and squark pair production with the pairs decaying via the lightest charginos into a final state consisting of two W bosons, the lightest neutralinos ($$ilde{chi }^0_1$$ χ ~ 1 0 ), and quarks, are presented: the signal is characterised by the presence of a single charged lepton ($$e^{pm }$$ e ± or $$mu ^{pm }$$ μ ± ) from a W boson decay, jets, and missing transverse momentum. The analysis is performed using 139 fb$$^{-1}$$ - 1 of proton–proton collision data taken at a centre-of-mass energy $$sqrt{s}=13$$ s = 13   delivered by the Large Hadron Collider and recorded by the ATLAS experiment. No statistically significant excess of events above the Standard Model expectation is found. Limits are set on the direct production of squarks and gluinos in simplified models. Masses of gluino (squark) up to 2.2  (1.4 ) are excluded at 95% confidence level for a light $$ilde{chi }^0_1$$ χ ~ 1 0 .

Beschreibung: A correction to this paper has been published: 10.1140/epjc/s10052-021-09344-w

Beschreibung: The COVID-19 pandemic is impacting human activities, and in turn energy use and carbon dioxide (CO2) emissions. Here we present daily estimates of country-level CO2 emissions for different sectors based on near-real-time activity data. The key result is an abrupt 8.8% decrease in global CO2 emissions (-1551 Mt CO2) in the first half of 2020 compared to the same period in 2019. The magnitude of this decrease is larger than during previous economic downturns or World War II. The timing of emissions decreases corresponds to lockdown measures in each country. By July 1st, the pandemic's effects on global emissions diminished as lockdown restrictions relaxed and some economic activities restarted, especially in China and several European countries, but substantial differences persist between countries, with continuing emission declines in the U.S. where coronavirus cases are still increasing substantially.

Beschreibung: We summarise the discussions at a virtual Community Workshop on Cold Atoms in Space concerning the status of cold atom technologies, the prospective scientific and societal opportunities offered by their deployment in space, and the developments needed before cold atoms could be operated in space. The cold atom technologies discussed include atomic clocks, quantum gravimeters and accelerometers, and atom interferometers. Prospective applications include metrology, geodesy and measurement of terrestrial mass change due to, e.g., climate change, and fundamental science experiments such as tests of the equivalence principle, searches for dark matter, measurements of gravitational waves and tests of quantum mechanics. We review the current status of cold atom technologies and outline the requirements for their space qualification, including the development paths and the corresponding technical milestones, and identifying possible pathfinder missions to pave the way for missions to exploit the full potential of cold atoms in space. Finally, we present a first draft of a possible road-map for achieving these goals, that we propose for discussion by the interested cold atom, Earth Observation, fundamental physics and other prospective scientific user communities, together with the European Space Agency (ESA) and national space and research funding agencies.

Beschreibung: A detailed and extensive empirical study of dynamic selection (DS) and random under-sampling (RUS) for the class imbalance problem is conducted in this paper. Total 20 state of the art DS methods are compared on 54 datasets. The empirical results clearly answer the following six key research questions in this direction, (1) how performances of ensembles with and without RUS compare with respect to different DS and static ensemble (SE) methods (2) how whether RUS is used affects performances of ensembles with respect to different DS/SE methods (3) how performances of different DS/SE methods compare with respect to ensembles with and without RUS (4) whether DS methods perform better than SE methods no matter whether RUS is used and what types of ensembles are used (5) how numbers of base classifiers affect how performances of ensembles with and without RUS compare with respect to different DS/SE methods (6) how numbers of base classifiers affect how performances of different DS/SE methods compare with respect to ensembles with and without RUS. The answers to the six research questions based on the experimental results in this study and the experimental findings are the main contributions of this work.

Beschreibung: The focus of the paper is to use a single weibo from a user to predict whether the user account is verified, referred to as verified account prediction, on Sina Weibo. To the best of our knowledge, verified account prediction on Sina Weibo has not been studied. For better understanding of the prediction problem, a comprehensive data analysis of weibos related to verified accounts is conducted first. Then, verified account prediction is formulated as a sequence learning problem. Specifically, a weibo from a user is represented as a sequence of feature values by feature hashing and whether the user account is verified is the corresponding label to predict. A deep learning approach is proposed for solving verified account prediction in this formulation. The proposed approach significantly outperforms the shallow learning methods in the comparisons in terms of accuracy and F1 by large margins in the experiments.

Beschreibung: We present observations of three-dimensional magnetic power spectra in wavevector space to investigate the anisotropy and scalings of sub-Alfvénic solar wind turbulence at magnetohydrodynamic (MHD) scale using the Magnetospheric Multiscale spacecraft. The magnetic power distributions are organized in a new coordinate determined by wavevectors (k) and background magnetic field (b_0). This study utilizes two approaches to determine wavevectors: the singular value decomposition method and multispacecraft timing analysis. The combination of the two methods allows an examination of the properties of magnetic field fluctuations in terms of mode compositions without any spatiotemporal hypothesis. Observations show that fluctuations (δB⊥1) in the direction perpendicular to k and b_0 prominently cascade perpendicular to b_0, and such anisotropy increases with wavenumbers. The reduced power spectra of δB⊥1 follow Goldreich–Sridhar scalings. In contrast, fluctuations within the kb0 plane show isotropic behaviors: perpendicular power distributions are approximately the same as parallel distributions. Their reduced power spectra follow the scalings P(k⊥)∝k⊥^-3/2 and P(k∥)∝k∥^-3/2. Comparing frequency–wavevector spectra with theoretical dispersion relations of MHD modes, we find that δB⊥1 are probably associated with Alfvén modes. On the other hand, magnetic field fluctuations within the kb_0 plane more likely originate from fast modes based on their isotropic behaviors. The observations of anisotropy and scalings of different magnetic field components are consistent with the predictions of current compressible MHD theory. Moreover, for the Alfvénic component, the ratio of cascading time to the wave period is found to be a factor of a few, consistent with critical balance in the strong turbulence regime.

Beschreibung: As the result of changes in ice dynamics and weather-driven changes on the surface, surface elevation changes over ice sheets are sensitive to climate forcing. Thus, long-term surface elevation changes over ice sheets of Greenland and Antarctica are of essential to assess the impact of climate change. Here, a dataset of monthly surface elevation time series over ice sheets of Greenland and Antarctica at 5km grid resolution using ERS-1, ERS-2, Envisat, and CryoSat-2 radar altimeter observations from August 1991 to December 2020. An updated plane-fitting least-squares regression strategy and Empirical orthogonal function (EOF) reconstruction were applied to ensure the accuracy and self-consistency of the merged elevation time series in the data processing. In addition, the cross-comparison with the IceBridge airborne laser altimeter observations confirmed that our merged dataset is reliable. Benefiting from its high temporal and spatial resolutions, the evolution processes on multiple temporal (up to 30 years) of ice loss from the main outflow glaciers in Greenland and Antarctica can be derived in detail. The spatiotemporal patterns of accelerating or decelerating surface elevation changes over ice sheet related to ENSO (for the Antarctic Ice sheet) and NAO (for the Greenland Ice sheet) indicated that climate forcing shifts oceanic forcing or atmospheric forcing in some way to affect ice sheet changes. Our merged time series provide a vital dataset for exploring the processes of climate forcing driving ice sheet change.

Beschreibung: China is one of the countries where extreme precipitation events occur frequently. In recent years, extreme precipitation events have increased significantly in both intensity and volume. It is urgent to find areas that are vulnerable to extreme precipitation and formulate more reasonable measures to reduce the risk of extreme precipitation. In this study, we comprehensively characterize land surface vulnerability by selecting gross domestic product (GDP), population, nighttime light (NTL), normalized difference vegetation index (NDVI), runoff depth (RD), and relief degree of land surface (RDLS) data. The 90%, 95% and 99% precipitation quantiles and their occurrence times in the historical and future periods were selected as exposure factors. The risk of extreme precipitation faced by different regions of China is calculated according to the risk calculation formula. The research results show that the Qinghai-Tibet Plateau in western China, where the natural environment is relatively fragile, and the urbanized areas with dense economic population are high-value extreme precipitation risk areas. The precipitation simulated by the selected BCC-CSM2-MR global climate model (GCM) is relatively small, but it can basically reflect the actual spatial distribution characteristics of precipitation. Under the four climate scenarios in the future, the joint occurrence probability of extreme precipitation will decrease, and the high-value areas of extreme precipitation risk will still be in the Qinghai-Tibet Plateau and urbanized areas. This study systematically analyzes the spatial distribution characteristics of extreme precipitation risk under different historical and future scenarios, and provides theoretical support for formulating more reasonable extreme precipitation risk prevention measures.