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In order to solve the shortcoming that Boost converter can obtain high voltage gain under the limit duty cycle, a new type of high-gain converter is proposed on the basis of the traditional Sepic converter. The converter retains the advantages of the continuous input current of the Sepic converter, by introducing a passive clamp circuit, the voltage stress of the switch tube is reduced, at the same time, the leakage inductance and the capacitor in the circuit have a resonance process, effectively reducing the impact of the diode reverse recovery problem. The working process of the converter in each switching mode was analyzed in detail, the voltage gain expression of the converter was deduced, and the voltage stress of the switching device were calculated. A 100 W experimental prototype was made, and the correctness of the theoretical analysis is verified through experiments.

The Tibetan Plateau (TP) hosts a variety of vegetation types, ranging from broadleaved and needle-leaved forests at the lower altitudes and in mesic areas to alpine grassland at the higher altitudes and in xeric areas. Accurate and detailed mapping of the vegetation distribution on the TP is essential for an improved understanding of climate change effects on terrestrial ecosystems. Yet, existing land cover datasets for the TP are either provided at a low spatial resolution or have insufficient vegetation types to characterize certain unique TP ecosystems, such as the alpine scree. Here, we produced a 10 m resolution TP land cover map with 12 vegetation classes and 3 non-vegetation classes for the year 2022 (referred to as TP_LC10-2022) by leveraging state-of-the-art remote-sensing approaches including Sentinel-1 and Sentinel-2 imagery, environmental and topographic datasets, and four machine learning models using the Google Earth Engine platform. Our TP_LC10-2022 dataset achieved an overall classification accuracy of 86.5 % with a kappa coefficient of 0.854. Upon comparing it with four existing global land cover products, TP_LC10-2022 showed significant improvements in terms of reflecting local-scale vertical variations in the southeast TP region. Moreover, we found that alpine scree, which is ignored in existing land cover datasets, occupied 13.99 % of the TP region, and shrublands, which are characterized by distinct forms (deciduous shrublands and evergreen shrublands) that are largely determined by the topography and are missed in existing land cover datasets, occupied 4.63 % of the TP region. Our dataset provides a solid foundation for further analyses which need accurate delineation of these unique vegetation types in the TP. TP_LC10-2022 and the sample dataset are freely available at 10.5281/zenodo.8214981 and 10.5281/zenodo.8227942 , respectively. Additionally, the classification map can be viewed at https://cold-classifier.users.earthengine.app/view/tplc10-2022 (last access: 6 June 2024). [ABSTRACT FROM AUTHOR]

Alpine treelines are considered ecological monitors recording the impacts of climate change on trees and forests. To date, most treeline research has focused on how climate change drives treeline dynamics. However, little is known about how biotic interactions mediate treeline shifts, particularly in the case of tree recruitment, a bottleneck of treeline dynamics. We hypothesized that inter- and intraspecific facilitation determined the establishment and survival of tree seedlings at alpine treelines. To test this hypothesis, 630 Abies georgei var. smithii seedlings with different ages (4–6, 7–9 and 10–15 years old) were transplanted into three growth habitats (canopy-in, canopy-out and meadow) across the alpine treeline ecotone (4300–4500 m) in the Sygera Mountains, on the southeastern Qinghai-Tibetan Plateau. Microclimate, height growth, mortality rates and leaf functional traits of transplanted seedlings were measured over 3 years. We found that the variations in leaf functional traits were driven by microclimate. After the transplantation, the leaf concentrations of soluble sugars and starch and C:P ratio increased, whereas leaf size decreased. The resource use of seedlings gradually shifted to a more conservative strategy as indicated by changes in non-structural carbohydrates and nutrient concentrations. Radiation, temperature and moisture conditions, mediated by plant interactions, influenced seedling mortality and annual growth by affecting leaf morphological traits. Our findings illustrate how facilitation plays a crucial role in altering solar radiation and leaf trait functioning, determining seedling survival and growth at alpine treelines. We provide new insights into the underlying mechanisms for tree establishment and alpine treeline shifts in response to climate change. [ABSTRACT FROM AUTHOR]

During our biodiversity investigations in Tibet, China, typical Cytospora canker symptoms were observed on branches of hosts Myricaria paniculate, Prunus cerasifera and Sibiraea angustata. Samples were studied, based on morphological features coupled with multigene phylogenetic analyses of ITS , act , rpb2 , tef1 and tub2 sequence data, which revealed two new species (Cytospora myricicola sp. nov. and C. sibiraeicola sp. nov.) and a known species (C. populina). In addition, Cytospora populina is newly discovered on the host Prunus cerasifera and in Tibet. [ABSTRACT FROM AUTHOR]

Abies georgei var. smithii (Abies George I varsmithorr. II (Viguie et Gaussen) Cheng et l.) belongs to Abies of Pinaceae, which is distributed in the southeast of Tibet, southwest of Sichuan and northwest of Yunnan. In this study, Abies georgei var. smithii in Sejila Mountain of southeastern Tibet was studied, the contents of Malondialdehyde (MDA), proline (pro), hydrogen peroxide (H2O2), soluble sugar and chlorophyll as well as the activities of superoxide dismutase (SOD) and superoxide dismutase (SOD) in the leaves, twigs, tree stems and roots of Abies georgei var. smithii were measured at different altitudes in the growing and non-growing seasons, single factor analysis of variance and multiple comparison were used to process the data. The results showed that the contents of Malondialdehyde (MDA), proline (pro) and hydrogen peroxide (H2O2) in the roots of Abies georgei var. smithii were significantly higher than those of other tissues in both growing and non-growing seasons, the content of chlorophyll in the leaves increased at first and then decreased with the elevation gradient, on the contrary, the ratio of chlorophyll a/b (CHLA/CHLB) increased with the elevation gradient. The activities of Peroxidase (POD) and superoxide dismutase (SOD) were the lowest. When the altitude was more than 4300m, the activities of POD and SOD decreased. The results showed that the physiological resistance of Abies georgei var. smithii decreased when the elevation was over 3900m, which was not beneficial to the growth and development of Abies georgei var. smithii, therefore, the distribution of Abies georgei var. smithii along the higher elevation gradient was limited by the unfavorable environmental factors at high altitude.

Knowledge of altitudinal patterns in soil C, N and P distribution is important for understanding biogeochemical processes in mountainous forests, yet the influence of slope aspects on soil stoichiometry has been largely neglected in previous studies. In this paper, a total number of 150 topsoil samples at four altitudes (3700, 3900, 4100, 4380 m a.s.l.) on sunny and shady slopes of Sygera mountains in the Southeastern Tibet were collected. Soil C, N and P contents, and pH, were measured. Soil temperature, moisture and richness of plant species were investigated at each sampling site. The results showed that: 1) in sunny slope, soil C, N and P concentrations increased with the increase in altitude, whereas soil C:N, C:P, and N:P decreased along the altitudinal gradient on s. Soil moisture was the main regulator of soil nutrition and stoichiometric ratios. 2) In shady slope, soil C and N contents had no significant difference along the altitudinal gradient except the higher values at low altitude, whereas soil P increased first and then decreased. Soil C:N increased with the increase in altitude, whereas C:P and N:P decreased first and then increased. Soil temperature and species richness were the main factors influencing soil nutrition and stoichiometric ratios. 3) Decoupling of soil C:N:P stoichiometry was observed in shady slope owing to changes in soil pH and temperature. 4) The rich contents of soil C and P were observed at two slopes along the altitudinal gradient, and high capacity of N supply existed at the topsoil in shady slope. These results suggested that slope aspect plays an important role in shaping the altitudinal pattern of soil C:N:P stoichiometry in mountainous forests.