@phdthesis{6179, abstract = {In the first part of this thesis we consider large random matrices with arbitrary expectation and a general slowly decaying correlation among its entries. We prove universality of the local eigenvalue statistics and optimal local laws for the resolvent in the bulk and edge regime. The main novel tool is a systematic diagrammatic control of a multivariate cumulant expansion. In the second part we consider Wigner-type matrices and show that at any cusp singularity of the limiting eigenvalue distribution the local eigenvalue statistics are uni- versal and form a Pearcey process. Since the density of states typically exhibits only square root or cubic root cusp singularities, our work complements previous results on the bulk and edge universality and it thus completes the resolution of the Wigner- Dyson-Mehta universality conjecture for the last remaining universality type. Our analysis holds not only for exact cusps, but approximate cusps as well, where an ex- tended Pearcey process emerges. As a main technical ingredient we prove an optimal local law at the cusp, and extend the fast relaxation to equilibrium of the Dyson Brow- nian motion to the cusp regime. In the third and final part we explore the entrywise linear statistics of Wigner ma- trices and identify the fluctuations for a large class of test functions with little regularity. This enables us to study the rectangular Young diagram obtained from the interlacing eigenvalues of the random matrix and its minor, and we find that, despite having the same limit, the fluctuations differ from those of the algebraic Young tableaux equipped with the Plancharel measure.}, author = {Schröder, Dominik J}, issn = {2663-337X}, pages = {375}, publisher = {Institute of Science and Technology Austria}, title = {{From Dyson to Pearcey: Universal statistics in random matrix theory}}, doi = {10.15479/AT:ISTA:th6179}, year = {2019}, } @article{6182, abstract = {We consider large random matrices with a general slowly decaying correlation among its entries. We prove universality of the local eigenvalue statistics and optimal local laws for the resolvent away from the spectral edges, generalizing the recent result of Ajanki et al. [‘Stability of the matrix Dyson equation and random matrices with correlations’, Probab. Theory Related Fields 173(1–2) (2019), 293–373] to allow slow correlation decay and arbitrary expectation. The main novel tool is a systematic diagrammatic control of a multivariate cumulant expansion.}, author = {Erdös, László and Krüger, Torben H and Schröder, Dominik J}, issn = {2050-5094}, journal = {Forum of Mathematics, Sigma}, publisher = {Cambridge University Press}, title = {{Random matrices with slow correlation decay}}, doi = {10.1017/fms.2019.2}, volume = {7}, year = {2019}, } @article{6186, abstract = {We prove that the local eigenvalue statistics of real symmetric Wigner-type matrices near the cusp points of the eigenvalue density are universal. Together with the companion paper [arXiv:1809.03971], which proves the same result for the complex Hermitian symmetry class, this completes the last remaining case of the Wigner-Dyson-Mehta universality conjecture after bulk and edge universalities have been established in the last years. We extend the recent Dyson Brownian motion analysis at the edge [arXiv:1712.03881] to the cusp regime using the optimal local law from [arXiv:1809.03971] and the accurate local shape analysis of the density from [arXiv:1506.05095, arXiv:1804.07752]. We also present a PDE-based method to improve the estimate on eigenvalue rigidity via the maximum principle of the heat flow related to the Dyson Brownian motion.}, author = {Cipolloni, Giorgio and Erdös, László and Krüger, Torben H and Schröder, Dominik J}, issn = {2578-5885}, journal = {Pure and Applied Analysis }, number = {4}, pages = {615–707}, publisher = {MSP}, title = {{Cusp universality for random matrices, II: The real symmetric case}}, doi = {10.2140/paa.2019.1.615}, volume = {1}, year = {2019}, } @inproceedings{7479, abstract = {Multi-exit architectures, in which a stack of processing layers is interleaved with early output layers, allow the processing of a test example to stop early and thus save computation time and/or energy. In this work, we propose a new training procedure for multi-exit architectures based on the principle of knowledge distillation. The method encourage searly exits to mimic later, more accurate exits, by matching their output probabilities. Experiments on CIFAR100 and ImageNet show that distillation-based training significantly improves the accuracy of early exits while maintaining state-of-the-art accuracy for late ones. The method is particularly beneficial when training data is limited and it allows a straightforward extension to semi-supervised learning,i.e. making use of unlabeled data at training time. Moreover, it takes only afew lines to implement and incurs almost no computational overhead at training time, and none at all at test time.}, author = {Bui Thi Mai, Phuong and Lampert, Christoph}, booktitle = {IEEE International Conference on Computer Vision}, isbn = {9781728148038}, issn = {1550-5499}, location = {Seoul, Korea}, pages = {1355--1364}, publisher = {IEEE}, title = {{Distillation-based training for multi-exit architectures}}, doi = {10.1109/ICCV.2019.00144}, volume = {2019-October}, year = {2019}, } @article{22454, abstract = {Direct quantification of terrestrial biosphere responses to global change is crucial for projections of future climate change in Earth system models. Here, we synthesized ecosystem carbon-cycling data from 1,119 experiments performed over the past four decades concerning changes in temperature, precipitation, CO2 and nitrogen across major terrestrial vegetation types of the world. Most experiments manipulated single rather than multiple global change drivers in temperate ecosystems of the USA, Europe and China. The magnitudes of warming and elevated CO2 treatments were consistent with the ranges of future projections, whereas those of precipitation changes and nitrogen inputs often exceeded the projected ranges. Increases in global change drivers consistently accelerated, but decreased precipitation slowed down carbon-cycle processes. Nonlinear (including synergistic and antagonistic) effects among global change drivers were rare. Belowground carbon allocation responded negatively to increased precipitation and nitrogen addition and positively to decreased precipitation and elevated CO2. The sensitivities of carbon variables to multiple global change drivers depended on the background climate and ecosystem condition, suggesting that Earth system models should be evaluated using site-specific conditions for best uses of this large dataset. Together, this synthesis underscores an urgent need to explore the interactions among multiple global change drivers in underrepresented regions such as semi-arid ecosystems, forests in the tropics and subtropics, and Arctic tundra when forecasting future terrestrial carbon-climate feedback.}, author = {Song, Jian and Wan, Shiqiang and Piao, Shilong and Knapp, Alan K. and Classen, Aimée T. and Vicca, Sara and Ciais, Philippe and Hovenden, Mark J. and Leuzinger, Sebastian and Beier, Claus and Kardol, Paul and Xia, Jianyang and Liu, Qiang and Ru, Jingyi and Zhou, Zhenxing and Luo, Yiqi and Guo, Dali and Adam Langley, J. and Zscheischler, Jakob and Dukes, Jeffrey S. and Tang, Jianwu and Chen, Jiquan and Hofmockel, Kirsten S. and Kueppers, Lara M. and Rustad, Lindsey and Liu, Lingli and Smith, Melinda D. and Templer, Pamela H. and Quinn Thomas, R. and Norby, Richard J. and Phillips, Richard P. and Niu, Shuli and Fatichi, Simone and Wang, Yingping and Shao, Pengshuai and Han, Hongyan and Wang, Dandan and Lei, Lingjie and Wang, Jiali and Li, Xiaona and Zhang, Qian and Li, Xiaoming and Su, Fanglong and Liu, Bin and Yang, Fan and Ma, Gaigai and Li, Guoyong and Liu, Yanchun and Liu, Yinzhan and Yang, Zhongling and Zhang, Kesheng and Miao, Yuan and Hu, Mengjun and Yan, Chuang and Zhang, Ang and Zhong, Mingxing and Hui, Yan and Li, Ying and Zheng, Mengmei}, issn = {2397-334X}, journal = {Nature Ecology & Evolution}, number = {9}, pages = {1309--1320}, publisher = {Springer Nature}, title = {{A meta-analysis of 1,119 manipulative experiments on terrestrial carbon-cycling responses to global change}}, doi = {10.1038/s41559-019-0958-3}, volume = {3}, year = {2019}, } @article{22442, abstract = {Mountainous running water ecosystems are vulnerable to climate change with major changes coming from warming temperatures. Species distribution will be affected and some species are anticipated to be winners (increasing their range) or losers (at risk of extinction). Climate change vulnerability is seldom integrated when assessing threat status for lists of species at risk (Red Lists), even though this might appear an important addition in the current context. The main objective of our study was to assess the potential vulnerability of Ephemeroptera (E), Plecoptera (P) and Trichoptera (T) species to global warming in a Swiss mountainous region by supplementing Species Distribution Models (SDMs) with a trait-based approach, using available historical occurrence and environmental data and to compare our outcomes with the Swiss National Red List. First, we used nine different modelling techniques and topographic, land use, climatic and hydrological variables as predictors of EPT species distribution. The shape of the response curves of the species for the environmental variables in the nine modelling techniques, together with three biological and ecological traits were used to assess the potential vulnerability of each species to climate change. The joint use of SDMs and trait approach appeared complementary and even though discrepancies were highlighted between SDMs and trait analyses, groups of potential “winners” and “losers” were raised out. Plecoptera appeared as the most vulnerable group to global warming. Divergences between current threat status of species and our results pointed out the need to integrate climate change vulnerability in Red List assessments.}, author = {Besacier Monbertrand, Anne-Laure and Timoner, Pablo and Rahman, Kazi and Burlando, Paolo and Fatichi, Simone and Gonseth, Yves and Moser, Frédéric and Castella, Emmanuel and Lehmann, Anthony}, issn = {2073-4441}, journal = {Water}, keywords = {Species Distribution Models, ensemble forecasting, Swiss Alps, climate change, red lists}, number = {4}, publisher = {MDPI}, title = {{Assessing the vulnerability of aquatic macroinvertebrates to climate warming in a mountainous watershed: Supplementing presence-only data with species traits}}, doi = {10.3390/w11040636}, volume = {11}, year = {2019}, } @inproceedings{6677, abstract = {The Fiat-Shamir heuristic transforms a public-coin interactive proof into a non-interactive argument, by replacing the verifier with a cryptographic hash function that is applied to the protocol’s transcript. Constructing hash functions for which this transformation is sound is a central and long-standing open question in cryptography. We show that solving the END−OF−METERED−LINE problem is no easier than breaking the soundness of the Fiat-Shamir transformation when applied to the sumcheck protocol. In particular, if the transformed protocol is sound, then any hard problem in #P gives rise to a hard distribution in the class CLS, which is contained in PPAD. Our result opens up the possibility of sampling moderately-sized games for which it is hard to find a Nash equilibrium, by reducing the inversion of appropriately chosen one-way functions to #SAT. Our main technical contribution is a stateful incrementally verifiable procedure that, given a SAT instance over n variables, counts the number of satisfying assignments. This is accomplished via an exponential sequence of small steps, each computable in time poly(n). Incremental verifiability means that each intermediate state includes a sumcheck-based proof of its correctness, and the proof can be updated and verified in time poly(n).}, author = {Choudhuri, Arka Rai and Hubáček, Pavel and Kamath Hosdurg, Chethan and Pietrzak, Krzysztof Z and Rosen, Alon and Rothblum, Guy N.}, booktitle = {Proceedings of the 51st Annual ACM SIGACT Symposium on Theory of Computing - STOC 2019}, isbn = {9781450367059}, location = {Phoenix, AZ, United States}, pages = {1103--1114}, publisher = {ACM}, title = {{Finding a Nash equilibrium is no easier than breaking Fiat-Shamir}}, doi = {10.1145/3313276.3316400}, year = {2019}, } @article{22571, abstract = {Urban heat islands (UHIs) exacerbate the risk of heat-related mortality associated with global climate change. The intensity of UHIs varies with population size and mean annual precipitation, but a unifying explanation for this variation is lacking, and there are no geographically targeted guidelines for heat mitigation. Here we analyse summertime differences between urban and rural surface temperatures (ΔTs) worldwide and find a nonlinear increase in ΔTs with precipitation that is controlled by water or energy limitations on evapotranspiration and that modulates the scaling of ΔTs with city size. We introduce a coarse-grained model that links population, background climate, and UHI intensity, and show that urban–rural differences in evapotranspiration and convection efficiency are the main determinants of warming. The direct implication of these nonlinearities is that mitigation strategies aimed at increasing green cover and albedo are more efficient in dry regions, whereas the challenge of cooling tropical cities will require innovative solutions.}, author = {Manoli, Gabriele and Fatichi, Simone and Schläpfer, Markus and Yu, Kailiang and Crowther, Thomas W. and Meili, Naika and Burlando, Paolo and Katul, Gabriel G. and Bou-Zeid, Elie}, issn = {1476-4687}, journal = {Nature}, pages = {55--60}, publisher = {Springer Nature}, title = {{Magnitude of urban heat islands largely explained by climate and population}}, doi = {10.1038/s41586-019-1512-9}, volume = {573}, year = {2019}, } @article{22527, abstract = {Mountain ecosystems are experiencing rapid warming resulting in ecological changes worldwide. Projecting the response of these ecosystems to climate change is thus crucial, but also uncertain due to complex interactions between topography, climate, and vegetation. Here, we performed numerical simulations in a real and a synthetic spatial domain covering a range of contrasting climatic conditions and vegetation characteristics representative of the European Alps. Simulations were run with the mechanistic ecohydrological model Tethys–Chloris to quantify the drivers of ecosystem functioning and to explore the vulnerability of Alpine ecosystems to climate change. We correlated the spatial distribution of ecohydrological responses with that of meteorological and topographic attributes and computed spatially explicit sensitivities of net primary productivity, transpiration, and snow cover to air temperature, radiation, and water availability. We also quantified how the variance in several ecohydrological processes, such as transpiration, quickly diminishes with increasing spatial aggregation, which highlights the importance of fine spatial resolution for resolving patterns in complex topographies. We conducted controlled numerical experiments in the synthetic domain to disentangle the effect of catchment orientation on ecohydrological variables, such as streamflow. Our results support previous studies reporting an altitude threshold below which Alpine ecosystems are water‐limited in the drier inner‐Alpine valleys and confirm that the wetter areas are temperature‐limited. High‐resolution simulations of mountainous areas can improve our understanding of ecosystem functioning across spatial scales. They can also locate the areas that are the most vulnerable to climate change and guide future measurement campaigns.}, author = {Mastrotheodoros, Theodoros and Pappas, Christoforos and Molnar, Peter and Burlando, Paolo and Hadjidoukas, Panagiotis and Fatichi, Simone}, issn = {1936-0592}, journal = {Ecohydrology}, keywords = {Alpine ecohydrology, Climate change, Ecosystem sensitivity, Numerical modelling, Spatialheterogeneity}, number = {1}, publisher = {Wiley}, title = {{Ecohydrological dynamics in the Alps: Insights from a modelling analysis of the spatial variability}}, doi = {10.1002/eco.2054}, volume = {12}, year = {2019}, } @article{22544, abstract = {The Bayesian weighted averaging (BWA) method is commonly used to integrate over multi-model ensembles of climate series. This method relies on two criteria to assign weights to individual outputs: model skill in reproducing historical observations, and inter-model agreement in simulating future period. Observations are generally thought to be relevant for correcting biases in model outputs in the BWA framework. However, they concurrently may introduce unpredictable impacts in the context of the downscaling process, in particular, when model output on precipitation is of interest. Specifically, the posterior distribution may excessively depend on few ‘outlier models’ being close to the observation, when all other models fail to capture observation of the historical period—a common situation for precipitation metrics. Another issue emerges for climates with very dry months: the inclusion of observation in BWA may result in a significant spread of the posterior distribution into the negative region. To address these problems, a modified version of the BWA method that removes observations in the initial phase of downscaling (computation of Factors of Change) and adds them in the estimation of posterior distributions is explored in this work. Comparisons of simulation results for the locations of Miami (FL), Fresno (CA), and Flint (MI) between the modified BWA and the traditional BWA demonstrate consistent outcomes with regards to the effect of observation in the Bayesian framework. Further, the modified BWA approach generally reduces uncertainty, as compared to ‘simple averaging’ in the Bayesian context, which assigns equal weights to all model outputs.}, author = {Xu, Donghui and Ivanov, Valeriy Y. and Kim, Jongho and Fatichi, Simone}, issn = {1436-3259}, journal = {Stochastic Environmental Research and Risk Assessment}, keywords = {Bayesian weighted averaging, Multi-model ensemble, Weighting skill, Model bias, Observations, Factor of change}, pages = {1923--1937}, publisher = {Springer Nature}, title = {{On the use of observations in assessment of multi-model climate ensemble}}, doi = {10.1007/s00477-018-1621-2}, volume = {33}, year = {2019}, } @article{22522, abstract = {The increase in atmospheric CO2 in the future is one of the most certain projections in environmental sciences. Understanding whether vegetation carbon assimilation, growth, and changes in vegetation carbon stocks are affected by higher atmospheric CO2 and translating this understanding in mechanistic vegetation models is of utmost importance. This is highlighted by inconsistencies between global-scale studies that attribute terrestrial carbon sinks to CO2 stimulation of gross and net primary production on the one hand, and forest inventories, tree-scale studies, and plant physiological evidence showing a much less pronounced CO2 fertilization effect on the other hand. Here, we review how plant carbon sources and sinks are currently described in terrestrial biosphere models. We highlight an uneven representation of complexity between the modelling of photosynthesis and other processes, such as plant respiration, direct carbon sinks, and carbon allocation, largely driven by available observations. Despite a general lack of data on carbon sink dynamics to drive model improvements, ways forward toward a mechanistic representation of plant carbon sinks are discussed, leveraging on results obtained from plant-scale models and on observations geared toward model developments.}, author = {Fatichi, Simone and Pappas, Christoforos and Zscheischler, Jakob and Leuzinger, Sebastian}, issn = {1469-8137}, journal = {New Phytologist}, keywords = {Ecosystem modelling, Nonstructural carbohydrates, Carbon cycle, Photosynthesis, Plant growth, respiration}, number = {2}, pages = {652--668}, publisher = {Wiley}, title = {{Modelling carbon sources and sinks in terrestrial vegetation}}, doi = {10.1111/nph.15451}, volume = {221}, year = {2019}, } @article{22549, abstract = {The time that rainfall takes to reach the outlet of a catchment as discharge (transit time) is a fundamental and integrated measure of catchment hydrological processes and solute transport mechanisms. As such, many efforts have been dedicated to its understanding and quantification. However, defining and ranking which factors, internal and external to the system, control the distributions of transit time is still an open challenge. Here, we develop a two-stage approach to explore climate and topography controls on transit time, using a fully distributed hydrological model coupled with a transport component. Specifically, we apply the model to two synthetic topographies under five observed climate regimes. With this setup, water fluxes from two years of daily rainfall events are singularly tracked across the catchments to then derive the distributions of transit time and fraction of young water for each combination of topography and climate. Results highlight a considerable variability of transit times in all climates and a pronounced effect of topography within a given climate. They further reveal that for wet climates it is possible to define a curve describing water transit time as a function of cumulative discharge that only depends on topographic properties. On the contrary, in dry climates the variability of transit time and young water fraction is much larger and not amenable to a simple summary. Despite simplifications, quantitative model-based inferences of transit time distributions are useful to better understand how climate and topography affect catchment functioning.}, author = {Remondi, Federica and Botter, Martina and Burlando, Paolo and Fatichi, Simone}, issn = {1879-2707}, journal = {Journal of Hydrology}, keywords = {Transit time distributions, Young water, Climate, Topography, Distributed hydrological modelling}, pages = {37--50}, publisher = {Elsevier}, title = {{Variability of transit time distributions with climate and topography: A modelling approach}}, doi = {10.1016/j.jhydrol.2018.11.011}, volume = {569}, year = {2019}, } @article{22551, abstract = {Exploring the effects of climate change on the hydrological response at the local scale requires climate data at high spatial and temporal resolutions. This is best achieved by generating downscaled ensembles of future climate variables derived from climate models. For this purpose we present a methodology to re-parameterize the AWE-GEN-2d model (Advanced WEather GENerator for a two-dimensional grid). The model simulates key meteorological variables needed by hydrological models and is particularly suitable to explore the effects of stochastic (natural) climatic uncertainty, which is fundamental for hydrological applications, especially at sub-kilometer and hourly scales. Factors of change for different climate statistics are calculated from climate model simulations of present and future climates and subsequently applied to the statistics derived from observations to re-parameterize AWE-GEN-2d. The model abilities in generating an ensemble of future climate variables for the transient period 2020–2089 is presented with examples of precipitation and near-surface air temperature fields from hourly to multi-annual scales for a small mountainous region in the Swiss Alps. The stochastic uncertainty is examined for present and future periods and for spatial scales from the RCM scale (12-km, daily) to 2-km demonstrating the potential use of AWE-GEN-2d outputs. At the RCM scale, model results yield a small increase in annual precipitation (4%) which is within the stochastic uncertainty range for present and future periods (7%). At the fine scale of 2-km, the increase in annual precipitation can exceed the stochastic uncertainty, but for less than 10% of the domain area. On the contrary, changes in annual near-surface air temperature exceed stochastic uncertainty both at the RCM and finer scales. Stochastic climate uncertainty was concluded to be very similar when comparing present and future periods and 12-km and 2-km scales. The benefits of using AWE-GEN-2d in hydrological climate change impact assessments are finally discussed.}, author = {Peleg, Nadav and Molnar, Peter and Burlando, Paolo and Fatichi, Simone}, issn = {1879-2707}, journal = {Journal of Hydrology}, keywords = {Weather generator, Stochastic downscaling, Climate change, Internal climate variability, Climate uncertainty, High-resolution rainfall model}, pages = {627--641}, publisher = {Elsevier}, title = {{Exploring stochastic climate uncertainty in space and time using a gridded hourly weather generator}}, doi = {10.1016/j.jhydrol.2019.02.010}, volume = {571}, year = {2019}, } @article{22507, abstract = {Present gaps in the representation of key soil biogeochemical processes such as the partitioning of soil organic carbon among functional components, microbial biomass and diversity, and the coupling of carbon and nutrient cycles present a challenge to improving the reliability of projected soil carbon dynamics. We introduce a new soil biogeochemistry module linked with a well‐tested terrestrial biosphere model T&C. The module explicitly distinguishes functional soil organic carbon components. Extracellular enzymes and microbial pools are differentiated based on the functional roles of bacteria, saprotrophic, and mycorrhizal fungi. Soil macrofauna is also represented. The model resolves the cycles of nitrogen, phosphorus, and potassium. Model simulations for 20 sites compared favorably with global patterns of litter and soil stoichiometry, microbial and macrofaunal biomass relations with soil organic carbon, soil respiration, and nutrient mineralization rates. Long‐term responses to bare fallow and nitrogen addition experiments were also in agreement with observations. Some discrepancies between predictions and observations are appreciable in the response to litter manipulation. Upon successful model reproduction of observed general trends, we assessed patterns associated with the carbon cycle that were challenging to address empirically. Despite large site‐to‐site variability, fine root, fungal, bacteria, and macrofaunal respiration account for 33%, 40%, 24%, and 3% on average of total belowground respiration, respectively. Simulated root exudation and carbon export to mycorrhizal fungi represent on average about 13% of plant net primary productivity. These results offer mechanistic and general estimates of microbial biomass and its contribution to respiration fluxes and to soil organic matter dynamics.}, author = {Fatichi, Simone and Manzoni, Stefano and Or, Dani and Paschalis, Athanasios}, issn = {1944-9224}, journal = {Global Biogeochemical Cycles}, number = {6}, pages = {620--648}, publisher = {American Geophysical Union}, title = {{A mechanistic model of microbially mediated soil biogeochemical processes: A reality check}}, doi = {10.1029/2018gb006077}, volume = {33}, year = {2019}, } @article{10874, abstract = {In this article we prove an analogue of a theorem of Lachaud, Ritzenthaler, and Zykin, which allows us to connect invariants of binary octics to Siegel modular forms of genus 3. We use this connection to show that certain modular functions, when restricted to the hyperelliptic locus, assume values whose denominators are products of powers of primes of bad reduction for the associated hyperelliptic curves. We illustrate our theorem with explicit computations. This work is motivated by the study of the values of these modular functions at CM points of the Siegel upper half-space, which, if their denominators are known, can be used to effectively compute models of (hyperelliptic, in our case) curves with CM.}, author = {Ionica, Sorina and Kılıçer, Pınar and Lauter, Kristin and Lorenzo García, Elisa and Manzateanu, Maria-Adelina and Massierer, Maike and Vincent, Christelle}, issn = {2363-9555}, journal = {Research in Number Theory}, keywords = {Algebra and Number Theory}, publisher = {Springer Nature}, title = {{Modular invariants for genus 3 hyperelliptic curves}}, doi = {10.1007/s40993-018-0146-6}, volume = {5}, year = {2019}, } @article{6310, abstract = {An asymptotic formula is established for the number of rational points of bounded anticanonical height which lie on a certain Zariskiopen subset of an arbitrary smooth biquadratic hypersurface in sufficiently many variables. The proof uses the Hardy–Littlewood circle method.}, author = {Browning, Timothy D and Hu, L.Q.}, issn = {1090-2082}, journal = {Advances in Mathematics}, pages = {920--940}, publisher = {Elsevier}, title = {{Counting rational points on biquadratic hypersurfaces}}, doi = {10.1016/j.aim.2019.04.031}, volume = {349}, year = {2019}, } @article{6835, abstract = {We derive the Hasse principle and weak approximation for fibrations of certain varieties in the spirit of work by Colliot-Thélène–Sansuc and Harpaz–Skorobogatov–Wittenberg. Our varieties are defined through polynomials in many variables and part of our work is devoted to establishing Schinzel's hypothesis for polynomials of this kind. This last part is achieved by using arguments behind Birch's well-known result regarding the Hasse principle for complete intersections with the notable difference that we prove our result in 50% fewer variables than in the classical Birch setting. We also study the problem of square-free values of an integer polynomial with 66.6% fewer variables than in the Birch setting.}, author = {Destagnol, Kevin N and Sofos, Efthymios}, issn = {0007-4497}, journal = {Bulletin des Sciences Mathematiques}, number = {11}, publisher = {Elsevier}, title = {{Rational points and prime values of polynomials in moderately many variables}}, doi = {10.1016/j.bulsci.2019.102794}, volume = {156}, year = {2019}, } @article{175, abstract = {An upper bound sieve for rational points on suitable varieties isdeveloped, together with applications tocounting rational points in thin sets,to local solubility in families, and to the notion of “friable” rational pointswith respect to divisors. In the special case of quadrics, sharper estimates areobtained by developing a version of the Selberg sieve for rational points.}, author = {Browning, Timothy D and Loughran, Daniel}, issn = {1088-6850}, journal = {Transactions of the American Mathematical Society}, number = {8}, pages = {5757--5785}, publisher = {American Mathematical Society}, title = {{Sieving rational points on varieties}}, doi = {10.1090/tran/7514}, volume = {371}, year = {2019}, } @article{6620, abstract = {This paper establishes an asymptotic formula with a power-saving error term for the number of rational points of bounded height on the singular cubic surface of ℙ3ℚ given by the following equation 𝑥0(𝑥21+𝑥22)−𝑥33=0 in agreement with the Manin-Peyre conjectures. }, author = {De La Bretèche, Régis and Destagnol, Kevin N and Liu, Jianya and Wu, Jie and Zhao, Yongqiang}, issn = {1674-7283}, journal = {Science China Mathematics}, number = {12}, pages = {2435–2446}, publisher = {Springer}, title = {{On a certain non-split cubic surface}}, doi = {10.1007/s11425-018-9543-8}, volume = {62}, year = {2019}, } @article{22582, abstract = {Rising atmospheric carbon dioxide concentration should stimulate biomass production directly via biochemical stimulation of carbon assimilation, and indirectly via water savings caused by increased plant water-use efficiency. Because of these water savings, the CO2 fertilization effect (CFE) should be stronger at drier sites, yet large differences among experiments in grassland biomass response to elevated CO2 appear to be unrelated to annual precipitation, preventing useful generalizations. Here, we show that, as predicted, the impact of elevated CO2 on biomass production in 19 globally distributed temperate grassland experiments reduces as mean precipitation in seasons other than spring increases, but that it rises unexpectedly as mean spring precipitation increases. Moreover, because sites with high spring precipitation also tend to have high precipitation at other times, these effects of spring and non-spring precipitation on the CO2 response offset each other, constraining the response of ecosystem productivity to rising CO2. This explains why previous analyses were unable to discern a reliable trend between site dryness and the CFE. Thus, the CFE in temperate grasslands worldwide will be constrained by their natural rainfall seasonality such that the stimulation of biomass by rising CO2 could be substantially less than anticipated.}, author = {Hovenden, Mark J. and Leuzinger, Sebastian and Newton, Paul C. D. and Fletcher, Andrew and Fatichi, Simone and Lüscher, Andreas and Reich, Peter B. and Andresen, Louise C. and Beier, Claus and Blumenthal, Dana M. and Chiariello, Nona R. and Dukes, Jeffrey S. and Kellner, Juliane and Hofmockel, Kirsten and Niklaus, Pascal A. and Song, Jian and Wan, Shiqiang and Classen, Aimée T. and Langley, J. Adam}, issn = {2055-0278}, journal = {Nature Plants}, number = {2}, pages = {167--173}, publisher = {Springer Nature}, title = {{Globally consistent influences of seasonal precipitation limit grassland biomass response to elevated CO2}}, doi = {10.1038/s41477-018-0356-x}, volume = {5}, year = {2019}, }