Recent developments in the field of the metal-insulator transition in two dimensions

We review the latest developments in the field of the metal-insulator transition in strongly-correlated two-dimensional electron systems. Particular attention is given to recent discoveries of a sliding quantum electron solid and interaction-induced spectrum flattening at the Fermi level in high-quality silicon-based structures.Comment: As publishe

Electron-electron interaction at decreasing kFlk_Fl

The contribution of the electron-electron interaction to conductivity is analyzed step by step in gated GaAs/InGaAs/GaAs heterostructures with different starting disorder. We demonstrate that the diffusion theory works down to $k_F l\simeq 1.5-2$, where $k_F$ is the Fermi quasimomentum, $l$ is the mean free paths. It is shown that the e-e interaction gives smaller contribution to the conductivity than the interference independent of the starting disorder and its role rapidly decreases with $k_Fl$ decrease.Comment: 5 pages, 6 figure

Global transpiration data from sap flow measurements : the SAPFLUXNET database

Plant transpiration links physiological responses of vegetation to water supply and demand with hydrological, energy, and carbon budgets at the land-atmosphere interface. However, despite being the main land evaporative flux at the global scale, transpiration and its response to environmental drivers are currently not well constrained by observations. Here we introduce the first global compilation of whole-plant transpiration data from sap flow measurements (SAPFLUXNET, https://sapfluxnet.creaf.cat/, last access: 8 June 2021). We harmonized and quality-controlled individual datasets supplied by contributors worldwide in a semi-automatic data workflow implemented in the R programming language. Datasets include sub-daily time series of sap flow and hydrometeorological drivers for one or more growing seasons, as well as metadata on the stand characteristics, plant attributes, and technical details of the measurements. SAPFLUXNET contains 202 globally distributed datasets with sap flow time series for 2714 plants, mostly trees, of 174 species. SAPFLUXNET has a broad bioclimatic coverage, with woodland/shrubland and temperate forest biomes especially well represented (80 % of the datasets). The measurements cover a wide variety of stand structural characteristics and plant sizes. The datasets encompass the period between 1995 and 2018, with 50 % of the datasets being at least 3 years long. Accompanying radiation and vapour pressure deficit data are available for most of the datasets, while on-site soil water content is available for 56 % of the datasets. Many datasets contain data for species that make up 90 % or more of the total stand basal area, allowing the estimation of stand transpiration in diverse ecological settings. SAPFLUXNET adds to existing plant trait datasets, ecosystem flux networks, and remote sensing products to help increase our understanding of plant water use, plant responses to drought, and ecohydrological processes. SAPFLUXNET version 0.1.5 is freely available from the Zenodo repository (https://doi.org/10.5281/zenodo.3971689; Poyatos et al., 2020a). The "sapfluxnetr" R package - designed to access, visualize, and process SAPFLUXNET data - is available from CRAN.Peer reviewe

Age-Effect on Intra-Annual δ13C-Variability within Scots Pine Tree-Rings from Central Siberia

Intra-annual tree-ring parameters are increasingly used in dendroecology thanks to their high temporal resolution. To better understand the nature of intra-ring proxy signals, we compared old and young trees according to the different ways in which they respond to climate. The study was carried out in central Siberia (Russia, 60°75′ N, 89°38′ E) in two even-aged Pinus sylvestris L. stands of different ages (20 and 220 years). Ring width, cell size, and intra-annual δ¹³С were measured for 4 to 27 tree rings, depending on age group (young vs. old) and tree-ring parameter. Wood formation was monitored to link tree-ring position to its time of formation. Results indicated more distinct intra-annual δ¹³С patterns at both the beginning and end of the ring of young trees compared to old ones. Older trees showed a stronger significant correlation between δ¹³С across the ring border, indicating a stronger carry-over effect of the previous year’s growing conditions on current year wood production. This suggests that tree age/size influences the magnitude of the transfer of mobile carbon reserves across the years

Seasonal Sap Flow Dynamics in Larix sibirica Trees Growing in the Krasnoyarsk Forest-Steppe

Проведен анализ сезонной динамики сокодвижения от корней к кроне у деревьев лиственницы сибирской (Larix sibirica Ledeb.), различающихся по скорости радиального роста, произрастающих на территории опорно-экспедиционного пункта ИЛ СО РАН (ОЭП) «Погорельский бор» (Красноярская лесостепь, 56.36° с.ш., 92.95° в.д.). Непрерывные измерения интенсивности стволового сокодвижения в вегетационные сезоны 2014 и 2015 гг. энергобалансовым (THB) методом проведены на двух одновозрастных деревьях, произрастающих на расстоянии 3 м друг от друга, примерно одинаковой высоты, но разного диаметра. Показано, что сезонная динамика интенсивности сокодвижения у деревьев в общем для них временном интервале в пределах сезона роста характеризуется высокой синхронностью (R=0.77–0.94) при значительной разнице абсолютных значений. С применением эколого-физиологической BS- модели, верифицированной по динамике сокодвижения, была рассчитана суточная и сезонная динамика транспирации. Количество транспортируемой воды в день, приходящееся на дерево, транспирация в день, приходящаяся на единицу листовой поверхности, дефицит влажности воздуха (VPD) и количество осадков в течение сезона роста меняются синхронно, в то же время связь перечисленных показателей с влажностью почвы выражена не столь определенно. Предполагается, что влажность почвы – не определяющий динамику сокодвижения в стволах исследуемых деревьев в означенном месте произрастания фактор, и этим фактором является VPD. На примере двух сезонов вегетации 2014 и 2015 гг. показано, что непрерывные синхронные автоматические измерения интенсивности сокодвижения позволяют исследовать в древостое феноциклы у деревьев с разными скоростями роста и четко устанавливать точные даты начала и окончания их сезона вегетацииSeasonal dynamics of sap flow in the stems of two Siberian larch trees (Larix sibirica Ledeb.) with different radial growth rates were analyzed. The trees grew nearby Pogorelsky Bor research station of Institute of Forest, SB RAS (Krasnoyarsk forest-steppe, 56.36°N, 92.95°E). Intensity of stem sap flow was measured continuously during the vegetation seasons of 2014 and 2015 using the tissue heat balance (THB) method on two individual trees of the same age and height that grew three meters apart and differed in stem diameter (DBH) only. Seasonal dynamics of sap flow intensity of these trees were synchronous (R = 0.77-0.94) within the common vegetation period while the absolute diurnal values differed considerably. The eco-physiological BS-model verified by the data of sap flow measurements allowed to calculate daily and seasonal transpiration dynamics. Seasonal dynamics of sap flow intensity per tree and transpiration per day, and vapor pressure deficit (VPD) as well as seasonal precipitation during the vegetation period were all synchronous. Soil moisture, however, did not show clear correlation with these parameters, thus it may be concluded that it is VPD, but not soil moisture that is the main factor responsible for sap flow intensity in the observed vegetation conditions. The data obtained from the seasons of 2014 and 2015 suggest that continuous automatic measurements of sap flow intensity allow to study phenocycles in trees with various growth rates as well as to determine very precisely the start and the end of their vegetation seaso

Titanium Complex Containing a Saligenin Ligand - New Universal Post-Metallocene Polymerization Catalyst: Copolymerization of Ethylene with Higher α-Olefins

Copolymerization reactions of ethylene with three α-olefins, 1-hexene, 1-octene and 1-decene, were carried out with a new post-metallocene catalyst based on Ti complex with a bidentate saligenin-type ligand I and two co catalysts, MAO and a combination of AlEt2Cl and MgBu2. Ability of the I - AlEt2Cl - MgBu2 system to copolymerize α-olefins with ethylene is far superior to that of the I - MAO system. Reactivity of α-olefins in copolymerization reactions with ethylene decreases in the sequence: 1-hexene>1-octene>1-decene. Both catalyst systems, I - MAO and I - AlEt2Cl - MgBu2, contain several populations of active centers that greatly differs both in the average molecular weights and in composition of the copolymer molecules they produce. Active centers in both catalytic systems show significant tendency to alternate monomer units in copolymer chains