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Extreme droughts generally decrease productivity in grassland ecosystems1,2,3 with negative consequences for nature’s contribution to people4,5,6,7. The extent to which this negative effect varies among grassland types and over time in response to multi-year extreme drought remains unclear. Here, using a coordinated distributed experiment that simulated four years of growing-season drought (around 66% rainfall reduction), we compared drought sensitivity within and among six representative grasslands spanning broad precipitation gradients in each of Eurasia and North America—two of the Northern Hemisphere’s largest grass-dominated regions. Aboveground plant production declined substantially with drought in the Eurasian grasslands and the effects accumulated over time, while the declines were less severe and more muted over time in the North American grasslands. Drought effects on species richness shifted from positive to negative in Eurasia, but from negative to positive in North America over time. The differing responses of plant production in these grasslands were accompanied by less common (subordinate) plant species declining in Eurasian grasslands but increasing in North American grasslands. Our findings demonstrate the high production sensitivity of Eurasian compared with North American grasslands to extreme drought (43.6% versus 25.2% reduction), and the key role of subordinate species in determining impacts of extreme drought on grassland productivity. 

Synthetic traffic generation can produce sufficient data for model training of various traffic analysis tasks for IoT networks with few costs and ethical concerns. However, with the increasing functionalities of the latest smart devices, existing approaches can neither customize the traffic generation of various device functions nor generate traffic that preserves the sequentiality among packets as the real traffic. To address these limitations, this paper proposes IoTGemini, a novel framework for high-quality IoT traffic generation, which consists of a Device Modeling Module and a Traffic Generation Module. In the Device Modeling Module, we propose a method to obtain the profiles of the device functions and network behaviors, enabling IoTGemini to customize the traffic generation like using a real IoT device. In the Traffic Generation Module, we design a Packet Sequence Generative Adversarial Network (PS-GAN), which can generate synthetic traffic with high fidelity of both per-packet fields and sequential relationships. We set up a real-world IoT testbed to evaluate IoTGemini. The experiment result shows that IoTGemini can achieve great effectiveness in device modeling, high fidelity of synthetic traffic generation, and remarkable usability to downstream tasks on different traffic datasets and downstream traffic analysis tasks. 

An experimental research is being conducted at the Yale University Beam Physics Laboratory, aiming to confirm fundamental aspects of an as-yet untested two-beam collinear electron accelerator concept employing a detuned bimodal cavity structure. The features of this novel beam-driven accelerator concept include (i) interleaving of bunches of the low-current accelerated beam with bunches of the high-current drive beam, while both beams move along the same central axis in the structure; (ii) excitation by the drive beam of two modes of each cavity in the structure, with the frequency of the higher mode equal to three times the frequency of the fundamental TM010mode; and (iii) detuning of the cavity modes away from the frequency of the accelerated and drive beam bunches, and their third harmonic. Advantages that are anticipated from this approach include (a) operation at higher acceleration gradient with lower breakdown and pulsed heating rates than for a structure of single-mode cavities at the same acceleration gradient, due to the unconventional spatiotemporal field distributions in the bimodal cavities; (b) realization of a transformer ratio well above two, due to the detuning of the cavity modes; and (c) greater system simplicity and lower cost than for a two-beam accelerator with separate drive and accelerated beam-lines. The recent R&D; progress is presented.