分类： 核科学技术 >> 核材料与工艺技术 提交时间： 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要： In light of the problem of radiolysis of the solvent system in PUREX (plutonium uranium recovery by extraction) process, and irradiation stabilities of tributylphosphate (TBP)/n-dodecane/nitric acid system were studied using 60Co -rays and particles from 238Pu. The main degradation products, dibutyl phosphate (HDBP) and monobutyl phosphate (H2MBP) were detected by the gas chromatography-mass spectrometry (GC-MS), and the degradation products that could not be easily removed by the washing procedure were measured by the Pu retention. Effects of the absorbed dose, the HNO3 concentration, and the cumulative dose on the irradiation stability of the systems were investigated. The yields of HDBP, H2MBP and the Pu retention increased with the absorbed dose. The HNO3 concentration affected significantly on the yield of HDBP, but had little impact on the output of H2MBP and Pu retention. For a similar absorbed dose, the Pu retention of the solvent by alpha irradiation is larger than that by gamma irradiation.
分类： 核科学技术 >> 核材料与工艺技术 提交时间： 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
Norzita Yacob
Maznah Mahmud
Norhashidah Talip
Kamaruddin Hashim
Abdul Rahim Harun
Khairul Zaman
Hj Dahlan
摘要： A variety of techniques including chemical and enzymatic hydrolysis, and radiation degradation processes can be used to prepare low molecular weight chitosan. Degradation of chitosan by radiation can be carried out in solid state and liquid state. Radiation degraded polysaccharides has been reported to exhibit growth-stimulating activity like phytohormones thatinduce the promotion in germination, shoot and root elongation in variety of plants. In this study, the chitosan was irradiated in solid state (powder form) by gamma rays within the dose range of 25‒75 kGy. And the irradiated chitosan was then irradiated in solution form in the presence of hydrogen peroxide. The effects of irradiation on the molecular weight and viscosity of the chitosan were investigated using Ubbelohde Capillary Viscometer. The molecular weight and viscosity of the chitosan decreased with increment of absorbed doses. In the presence of hydrogen peroxide, the molecular weight of chitosan could be further decreased. The effect of radiation degraded chitosan on the growth promotion of rice was investigated and it was shown during seedling period of 15 days for transplanting whereby the growth is 15%‒20% faster than using chemicals growth promoters.
分类： 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间： 2017-05-02
Pang, YY [Pang, Yongyan][ 1,2 ]
Watson, SS [Watson, Stephanie S.][ 2 ]
Sung, LP [Sung, Li-Piin][ 2 ]
摘要： The objective of this study was to investigate the effect of nanoparticle dispersion on surface morpho- logical changes and degradation process in polymeric coatings during exposure to ultraviolet (UV) ra- diation. Three types of nano-titanium dioxide (nano-TiO2) were selected and dispersed into acrylic urethane (AU) coating to generate degrees of nanoparticle dispersion states. Two accelerated exposure conditions: wet (30 C and 75% relative humidity (RH)) and dry (30 C and 0% RH), were selected. Attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) was used to monitor surface chemical degradation. Laser scanning confocal microscopy (LSCM) was used to characterize nanoparticle dispersion and surface/subsurface morphological changes in the AU coatings during UV exposure. For a given nanoparticle, similar surface morphological changes of the coatings indicated the similar degradation processes under the wet and dry conditions, but the degradation was faster under the wet condition. Surface morphological changes were closely related to the nanoparticle dispersion in three coatings, and the heterogeneity in nanoparticle dispersion significantly affects the degradation process and dominates the degradation patterns.
分类： 地球科学 >> 地理学 提交时间： 2022-02-21 合作期刊: 《干旱区科学》
Carlos R PINHEIRO JUNIOR
Conan A SALVADOR
Tiago R TAVARES
Marcel C ABREU
Hugo S FAGUNDES
Wilk S ALMEIDA
Eduardo C SILVA NETO
Lúcia H C ANJOS
Marcos G PEREIRA
摘要： Soils (Leptosols or Epileptic Regosols) with lithic contact at a depth of 50 cm occupy almost 20% of the Brazilian semi-arid region. These lithic soils are susceptible to erosion due to faster saturation of water-holding capacity during rainfall, which accelerates the beginning of runoff. However, erosion traits of lithic soils in the semi-arid region of Brazil are less studied. The aim of this study was to characterize the soil and landscape attributes in areas with Neossolos Litlicos (Entisols) in the Ca atinga biome to identify region of high susceptibility to erosion. Results showed that the soils were characterized by a sandy texture, soil structure with poor development and low content of organic carbon. These attributes increase susceptibility to erosion and reduce water storage capacity, especially in the states of Cear and Sergipe. In these states, the content of rock fragments in the soil reaches 790 g/kg. High contents of silt and fine sand, high silt/clay ratio, predominance of Leptosols and strong rainfall erosivity were observed in Piau and northwestern Cear. A very high degree of water erosion was observed in the states of Pernambuco and Paraba. Despite the low degree of erosion observed in the state of Bahia, it is highly susceptible to erosion due to the predominance of very shallow soils, rugged relief and high values of rainfall erosivity. Lower vulnerability was observed in the state of Alagoas because of its more smoothed relief, greater effective soil depth, thicker A horizon of soil and lower rainfall erosivity. In general, the characteristics that intensify the susceptibility to erosion in the Caatinga biome are those soil structures with poor development or without aggregation, low contents of organic carbon, high contents of silt and fine sand, high values of silt/clay ratio and rugged relief in some regions. This study collected information contributing to a better characterization of soils with lithic contact in the semi-arid region of Brazil. In addition, regions with a higher susceptibility to erosion were identified, revealing insights that could help develop strategies for environmental risk mitigation.
分类： 化学 >> 物理化学 提交时间： 2017-11-05 合作期刊: 《结构化学》
WANG Dao-Hua
LIN Xiao-Yan
WANG Yu-Kang
ZHANG Wen-Ting
SONG Kai-Yue
LIN Heng
LI Hao-Hong
CHEN Zhi-Rong
摘要： A new iodiplumbate/organic hybrid constructed from asymmetric viologen and polyiodides, (PBPY-H2)2[PbI4(I3)2] (1, PBPY = N-(propionate)-4,4΄-bipyridinium), has been synthesized via solvothermal reaction and structurally determined by X-ray diffraction method. Compound 1 crystallizes in monoclinic system, space group P21/c with Mr = 1936.72, a = 11.622(2), b = 14.839(3), c = 13.372(2) Å, β = 109.447(3)°, V = 2174.6(7) Å3, Z = 2, Dc = 2.958 g/cm3, F(000) = 1712, μ(MoKα) = 11.011 mm–1, the final R = 0.0389 and wR = 0.0854 for 3866 observed reflections with I > 2σ(I). [PbI4(I3)2]4- mononuclear cluster of 1 features a seldom example of coordinated I3- donors for the lead center. Intermolecular hydrogen bonds between [PbI4(I3)2]4- clusters and (PBPY-H)24+ dimmers contribute to the formation of a 2-D layer. Its absorption spectrum was investigated, and lower energy band gap of 1.42 eV was explained by DFT calculation. Interestingly, 1 exhibits photocatalytic activity for the degradation of rhodamine B.
分类： 生物学 >> 生物物理学 >> 生物物理、生物化学与分子生物学 提交时间： 2016-05-12
Reddy, Pradeep
Ocampo, Alejandro
Suzuki, Keiichiro
Luo, Jinping
Sugawara, Atsushi
Okamura, Daiji
Wu, Jun
Lam, David
Esteban, Concepcion Rodriguez
Sancho-Martinez, Ignacio
Belmonte, Juan Carlos Izpisua
Bacman, Sandra R.
Williams, Sion L.
Moraes, Carlos T.
Tsunekawa, Yuji
Xiong, Xiong
Zhao, Huimin
Montserrat, Nuria
Liu, Guang-Hui
Liu, Guang-Hui
摘要： Mitochondrial diseases include a group of maternally inherited genetic disorders caused by mutations in mtDNA. In most of these patients, mutated mtDNA coexists with wild-type mtDNA, a situation known as mtDNA heteroplasmy. Here, we report on a strategy toward preventing germline transmission of mitochondrial diseases by inducing mtDNA heteroplasmy shift through the selective elimination of mutated mtDNA. As a proof of concept, we took advantage of NZB/BALB heteroplasmic mice, which contain two mtDNA haplotypes, BALB and NZB, and selectively prevented their germline transmission using either mitochondria-targeted restriction endonucleases or TALENs. In addition, we successfully reduced human mutated mtDNA levels responsible for Leber's hereditary optic neuropathy (LHOND), and neurogenic muscle weakness, ataxia, and retinitis pigmentosa (NARP), in mammalian oocytes using mitochondria-targeted TALEN (mito-TALENs). Our approaches represent a potential therapeutic avenue for preventing the trans-generational transmission of human mitochondrial diseases caused by mutations in mtDNA.
分类： 地球科学 >> 地理学 提交时间： 2023-07-17 合作期刊: 《干旱区科学》
摘要：Since there are some signs of land degradation and desertification showing how soil sustainability is threatened, it is crucial to create a soil quality index (SQI) model in the semi-arid Çorum Basin, situated between the Black Sea and Anatolia Region, Central Turkey. The primary aims of the study are: (1) to determine SQI values of the micro-basin in terms of land degradation and desertification. Moreover, the best-worst method (BWM) was used to determine the weighting score for each parameter; (2) to produce the soils' spatial distribution by utilizing different geostatistical models and GIS (geographic information system) techniques; and (3) to validate the obtained SQI values with biomass reflectance values. Therefore, the relationship of RE-OSAVI (red-edge optimized soil-adjusted vegetation index) and NDVI (normalized difference vegetation index) generated from Sentinel-2A satellite images at different time series with soil quality was examined. Results showed that SQI values were high in the areas that had almost a flat and slight slope. Moreover, the areas with high clay content and thick soil depth did not have salinity problems, and were generally distributed in the middle parts of the basin. However, the areas with a high slope, poor vegetation, high sand content, and low water holding capacity had low SQI values. Furthermore, a statistically high positive correlation of RE-OSAVI and NDVI indices with soil quality was found, and NDVI had the highest correlative value for June (R2=0.802) compared with RE-OSAVI.
分类： 环境科学技术及资源科学技术 >> 环境学 提交时间： 2022-03-15 合作期刊: 《干旱区科学》
Mona KARAMI
Mehdi HEYDARI
Ali SHEYKHOLESLAMI
Majid ESHAGH NIMVARI
Reza OMIDIPOUR
YUAN Zuoqiang
Bernard PREVOSTO
摘要： The relationships between different aspects of diversity (taxonomic, structural and functional) and the aboveground biomass (AGB) as a major component of global carbon balance have been studied extensively but rarely under the simultaneous influence of forest dieback and management. In this study, we investigate the relationships between taxonomic, functional and structural diversity of woody species (trees and shrubs) and AGB along a gradient of dieback intensity (low, moderate, high and no dieback as control) under two contrasted management conditions (protection by central government vs. traditional management by natives) in a semi-arid oak (Quercus brantii Lindl.) forest ecosystem. AGB was estimated and taxonomic diversity, community weighted average (CWM) and functional divergence indices were produced. We found that the aerial biomass was significantly higher in the intensively used area (14.57 (1.60) t/hm2) than in the protected area (8.70 (1.05) t/hm2) due to persistence of some large trees but with decreasing values along the dieback intensity gradient in both areas. CWM of height (H), leaf nitrogen content (LNC) and leaf dry matter content (LDMC) were also higher in the traditional managed area than in the protected area. In contrast, in the protected area, the woody species diversity was higher and the inter-specific competition was more intense, explaining a reduced H, biomass and LDMC. Contrary to the results of CWM, none of the functional diversity traits (FDvar) was affected by dieback intensity and only FDvar values of LNC, leaf phosphorus content (LPC) and LDMC were influenced by management. We also found significantly positive linear relationships of AGB with CWM and FDvar indices in the protected area, and with taxonomic and structural diversity indices in the traditional managed area. These results emphasize that along a dieback intensity gradient, the leaf functional traits are efficient predictors in estimating the AGB in protected forests, while taxonomic and structural indices provide better results in forests under a high human pressure. Finally, species identity of the dominant species (i.e., Brant's oak) proves to be the main driver of AGB, supporting the selection effect hypothesis.
分类： 化学 >> 物理化学 提交时间： 2017-11-05 合作期刊: 《结构化学》
摘要： Uniform and well-dispersed ZnS nanospheres have been successfully synthesized via a facile chemical route. The crystal structure, morphology, surface area燼nd爌hotocatalytic properties of the爏ample were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) and ultraviolet-visible (UV-vis) spectrum. The results of characterizations indicate that the products are identified as mesoporous zinc-blende ZnS nanospheres with an average diameter of 200 nm, which are comprised of nanoparticles with the crystallite size of about 3.2 nm calculated by XRD. Very importantly, photocatalytic燿egradation爋f爉ethylene blue (MB)爏hows that the as-prepared ZnS nanospheres exhibit excellent photocatalytic activity with nearly 100% of MB decomposed after UV-light irradiation for 25 min. The excellent photocatalytic activity of ZnS nanospheres can be ascribed to the large specific surface area and hierarchical mesoporous structure.
分类： 生物学 >> 生物物理学 >> 生物物理、生物化学与分子生物学 提交时间： 2016-05-18
Wu, Yanwei
Wu, Yanwei
Cheng, Shiya
Zou, Wei
Wang, Xiaochen
Zhao, Hongyu
Zhang, Hong
Yoshina, Sawako
Mitani, Shohei
Yoshina, Sawako
Mitani, Shohei
摘要： Autophagosome formation is promoted by the PI3 kinase complex and negatively regulated by myotubularin phosphatases, indicating that regulation of local phosphatidylinositol 3-phosphate (PtdIns3P) levels is important for this early phase of autophagy. Here, we show that the Caenorhabditis elegans myotubularin phosphatase MTM-3 catalyzes PtdIns3P turnover late in autophagy. MTM-3 acts downstream of the ATG-2/EPG-6 complex and upstream of EPG-5 to promote autophagosome maturation into autolysosomes. MTM-3 is recruited to autophagosomes by PtdIns3P, and loss of MTM-3 causes increased autophagic association of ATG-18 in a PtdIns3P-dependent manner. Our data reveal critical roles of PtdIns3P turnover in autophagosome maturation and/or autolysosome formation.
分类： 地球科学 >> 地理学 提交时间： 2020-11-25 合作期刊: 《干旱区科学》
摘要： Understanding the effects of degradation on belowground biomass (BGB) is essential for assessment of carbon budget of the alpine meadow ecosystem on the Tibetan Plateau, China. This ecosystem has been undergoing serious degradation owing to climate change and anthropogenic activities. This study examined the response of the vertical distribution of plant BGB to degradation and explored the underlying mechanisms in an alpine meadow on the Tibetan Plateau. A field survey was conducted in an alpine meadow with seven sequential degrees of degradation in the Zoige Plateau on the Tibetan Plateau during the peak growing season of 2018. We measured aboveground biomass (AGB), BGB, soil water content (SWC), soil bulk density (SBD), soil compaction (SCOM), soil organic carbon (SOC), soil total nitrogen (STN), soil total phosphorus (STP), soil available nitrogen (SAN), and soil available phosphorus (STP) in the 0–30 cm soil layers. Our results show that degradation dramatically decreased the BGB in the 0–10 cm soil layer (BGB0–10) but slightly increased the subsoil BGB. The main reason may be that the physical-chemical properties of surface soil were more sensitive to degradation than those of subsoil, as indicated by the remarked positive associations of the trade-off value of BGB0–10 with SWC, SCOM, SOC, STN, SAN, and STP, as well as the negative correlation between the trade-off value of BGB0–10 and SBD in the soil layer of 0–10 cm. In addition, an increase in the proportion of forbs with increasing degradation degree directly affected the BGB vertical distribution. The findings suggest that the decrease in the trade-off value of BGB0–10 in response to degradation might be an adaptive strategy for the degradation-induced drought and infertile soil conditions. This study can provide theoretical support for assessing the effects of degradation on the carbon budget and sustainable development in the alpine meadow ecosystem on the Tibetan Plateau as well as other similar ecosystems in the world.
分类： 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间： 2018-04-24 合作期刊: 《干旱区科学》
摘要： The main purpose of this study was to explore the dynamic changes of greenhouse gas (GHG) from grasslands under different degradation levels during the growing seasons of Inner Mongolia, China. Grassland degradation is associated with the dynamics of GHG fluxes, e.g., CO2, CH4 and N2O fluxes. As one of the global ecological environmental problems, grassland degradation has changed the vegetation productivity as well as the accumulation and decomposition rates of soil organic matter and thus will influence the carbon and nitrogen cycles of ecosystems, which will affect the GHG fluxes between grassland ecosystems and the atmosphere. Therefore, it is necessary to explore how the exchanges of CO2, CH4 and N2O fluxes between soil and atmosphere are influenced by the grassland degradation. We measured the fluxes of CO2, CH4 and N2O in lightly degraded, moderately degraded and severely degraded grasslands in Inner Mongolia of China during the growing seasons from July to September in 2013 and 2014. The typical semi-arid grassland of Inner Mongolia plays a role as the source of atmospheric CO2 and N2O and the sink for CH4. Compared with CO2 fluxes, N2O and CH4 fluxes were relatively low. The exchange of CO2, N2O and CH4 fluxes between the grassland soil and the atmosphere may exclusively depend on the net exchange rate of CO2 in semi-arid grasslands. The greenhouse gases showed a clear seasonal pattern, with the CO2 fluxes of –33.63–386.36 mg/(m•h), CH4 uptake fluxes of 0.113–0.023 mg/(m•h) and N2O fluxes of –1.68–19.90 µg/(m•h). Grassland degradation significantly influenced CH4 uptake but had no significant influence on CO2 and N2O emissions. Soil moisture and temperature were positively correlated with CO2 emissions but had no significant effect on N2O fluxes. Soil moisture may be the primary driving factor for CH4 uptake. The research results can be in help to better understand the impact of grassland degradation on the ecological environment.
分类： 地球科学 >> 地球科学史 提交时间： 2017-12-18 合作期刊: 《干旱区科学》
摘要： The causes of land degradation in the African drylands have been shown to vary. Some researchers consider climate to be the major contributor to degradation, with anthropogenic factors playing a minor role. Others reverse the significance of these two factors. A third group attributes land degradation to climate and anthropogenic factors equally. This study was undertaken to establish the factors influencing land degradation in a semi-arid environment in southeastern Kenya and the rate of change in vegetation types for a period of 35 years (1973–2007). The reduction in grassland cover was used as an indicator of land degradation. Causes of land degradation were determined by a multiple regression analysis. A log-linear regression analysis was used to establish the rate of vegetation change. The multiple and log-linear regression analyses showed: (1) woody vegetation, livestock population and cultivated area to be the main contributors of reduction in grassland cover in the area, and (2) an increase in undesirable woody species, livestock population and cultivated area had a significant (P<0.05) negative effect on grassland vegetation. Increased human population, low amounts of rainfall and drought showed no significant negative effect on grassland vegetation cover. In conclusion, human and livestock population growth and increased agricultural land have contributed to intensive crop cultivation and overgrazing in the semi-arid lands. This overuse of the semi-arid rangelands has worsened the deterioration of the natural grassland vegetation.
分类： 生物学 >> 生态学 提交时间： 2023-12-20 合作期刊: 《干旱区科学》
摘要： Grassland degradation can alter the structure and function of ecosystem and soil seed bank. Therefore, estimating the role of soil seed bank in vegetation regeneration of degraded grasslands is crucial. We selected grasslands with three levels of degradation, namely non-degraded (ND), mildly degraded (MD), and heavily degraded (HD) to analyze the effect of grassland degradation on soil seed bank, as well as the role of soil seed bank on vegetation regeneration of the alpine grasslands, China. Soil samples from each level were collected in May, before seedling emergence, in August, after completion of transient seed bank germination, and in December, after seed dispersal, to determine the seed density and species composition through germination experiment. Result showed that a total of 35 plant species was identified, including 15 species observed in both soil seed bank and above-ground vegetation. A total of 19, 15, and 14 species of soil seed bank were identified in December, May, and August, respectively. The most abundant species in soil seed bank were Compositae (5 species), followed by Poaceae (4 species), and Cyperaceae (3 species). Degradation level has no significant impact on species richness and Shannon- Wiener index of soil seed bank. In addition, sampling month and grassland degradation affected soil seed bank density, in which December>May>August, and ND>MD>HD, indicating that density of transient seed bank was greater than persistent seed bank. Soil seed bank density of surface layer (05 cm) accounting for 42%72% of the total density, which was significantly higher than that of deep layer (510 cm). Similarity of species composition between vegetation and soil seed bank was low, and it increased with degradation level (ranged from 0.14 to 0.69). We concluded that grassland degradation affects soil seed bank density more than species diversity, and soil seed bank contributed slightly to vegetation regeneration of degraded alpine grassland. Therefore, it is unlikely that degraded alpine meadow can be restored solely through soil seed bank.
分类： 地球科学 >> 地球科学史 提交时间： 2020-10-20 合作期刊: 《干旱区科学》
摘要： Land degradation has a major impact on environmental and socio-economic sustainability. Scientific methods are necessary to monitor the risk of land degradation. In this study, the environmental sensitive area index (ESAI) was utilized to assess land degradation sensitivity and convergence analysis in Korla, a typical oasis city in Xinjiang of China, which is located on the northeast border of the Tarim Basin. A total of 18 indicators depicting soil, climate, vegetation, and management qualities were used to illustrate spatial-temporal patterns of land degradation sensitivity from 1994 to 2018. We investigated the causes of spatial convergence and divergence based on the Ordinary Least Squares (OLS) and Geographically Weighted Regression (GWR) models. The results show that the branch of the Tianshan Mountains and oasis plain had a low sensitivity to land degradation, while the Tarim Basin had a high risk of land degradation. More than two-thirds of the study area can be categorized as "critical" sensitivity classes. The largest percentage (32.6%) of fragile classes was observed for 2006. There was no significant change in insensitive or low-sensitivity areas, which accounted for less than 0.4% of the entire observation period. The ESAI of the four time periods (1994–1998, 1998–2006, 2006–2010, and 2010–2018) formed a series of convergence patterns. The convergence patterns of 1994–1998 and 1998–2006 can be explained by the government's efforts to "Returning Farmland to Forests" and other governance projects. In 2006–2010, the construction of afforested work intensified, but industrial development and human activities affected the convergence pattern. The pattern of convergence in most regions between 2010 and 2018 can be attributed to the government's implementation of a series of key ecological protection projects, which led to a decrease in sensitivity to land degradation. The results of this study altogether suggest that the ESAI convergence analysis is an effective early warning method for land degradation sensitivity.
分类： 地球科学 >> 水文学 提交时间： 2018-07-05 合作期刊: 《干旱区科学》
BELALA, Fahima
HIRCHE, Azziz
MULLER, Serge D
Mahmoud, TOURKI
SALAMANI, Mostefa
GRANDI, Mohamed
AIT HAMOUDA, Tahar
Madjid, BOUGHANI
摘要： Since 1960, the steppe regions of North Africa have been subject to an increasing desertification, including the degradation of traditional pastures. The initially dominant species (Artemisia herba-alba, Lygeum spartum and Stipa tenacissima) declined and were progressively replaced by other species (Atractylis serratuloides and Salsola vermiculata) that are more tolerant to the new conditions. It is not clear whether these changes are due to anthropogenic reasons or climatic determinism. We have carried out a statistical analysis of the climate to detect putative rainfall changes during the 20th century in the Algerian steppes based on data from 9 meteorological stations, including 2 Saharan stations (El Oued and Touggourt), 3 pre-Saharan stations (Biskra, Laghouat and Ain Sefra) and 4 steppe stations (Djelfa, Saida, Mchria and El-Bayadh) located in the arid high plains, which represent the bioclimate diversities of the region. Previous studies suggested that significant rainfall changes for the 20th century only had records in the south of the Oran region. Most of the studies, however, looked at restricted territories over limited periods, and did not integrate the rainiest period 20042014. Our work is designed to integrate all the longest time series of meteorological data available for the steppe regions of Algeria. Our results confirm the spatial rainfall distribution (significant rainfall changes only recorded in the southwestern region) evidenced by previous studies, and reveal a decreasing rainfall gradient from northeastern to southwestern Algeria. Moreover, the results reveal a trend of significant decrease of rainfall in the southern Oran region, marked by two drought periods in 19801985 and 19992003. However, with the exception of the southwestern region, rainfall overall has not declined since the beginning of the 20th century. While less marked in other regions, the drought appear to have affected all territories of the Algerian steppe. Consequently, our study implies that the climate was not a leading influence in the on-going degradation of the vegetation cover of steppe landscapes. Such a vegetation evolution thus appears to be have been determined more by human activities than by climate forcing.
分类： 生物学 >> 植物学 >> 应用植物学 提交时间： 2020-05-31 合作期刊: 《干旱区科学》
摘要： Land cover in the Chinese Loess Plateau has undergone dramatic changes since the late 1980s. Revealing the trend in land cover change and eco-environmental quality response of different geomorphic units in this stage is a realistic requirement for promoting sustainable development of the Chinese Loess Plateau. Based on the data of geomorphic units and land cover in 1990, 2000, 2010 and 2018 of the Chinese Loess Plateau, we studied the trend of land cover change and eco-environmental quality response of different geomorphic units by using a significance index of land cover change, a proportion index of land cover change and an eco-environmental response model. The results indicated that from 1990 to 2018, the areas of forestland and construction land substantially increased, whereas those of cropland, grassland, wetland and unused land considerably decreased. Land cover change exhibited large geomorphic differences, and the main conversion of land cover was from cropland into other land types. Unstable trend of land cover change in the loess tablelands and sandy loess hills declined, whereas the unstable trends in the other geomorphic units enhanced. Eco-environmental quality varied among different geomorphic units. The expansion of construction land and degradation of forestland, grassland and wetland resulted in the deterioration of eco-environmental quality. The conversion of cropland and unused land into forestland and grassland, and the conversion of grassland into forestland were the main factors that drove the improvement of eco-environmental quality. The findings of this study may provide theoretical reference and support decision making for the optimization of land use structure and the improvement of eco-environmental quality on the Chinese Loess Plateau.
分类： 生物学 >> 生物物理学 提交时间： 2016-05-11
Mi, Zeyun
Ding, Jiwei
Zhang, Quan
Ma, Ling
Shan, Guangzhi
Li, Xiaoyu
Zhou, Jinming
Cen, Shan
Mi, Zeyun
Ding, Jiwei
Zhang, Quan
Ma, Ling
Shan, Guangzhi
Li, Xiaoyu
Zhou, Jinming
Cen, Shan
Zhao, Jianyuan
Wei, Tao
Liu, Zhenlong
Liang, Chen
摘要： Human BST-2 inhibits HIV-1 replication by tethering nascent virions to the cell surface. HIV-1 codes Vpu that counteracts BST-2 by down-regulating this restriction factor from the cell surface. This important function makes Vpu a potential therapeutic target. Yet, no agents have been reported to block Vpu from antagonizing BST-2. In this study, we report a small molecule compound IMB-LA that abrogates the function of Vpu and thereby strongly suppresses HIV-1 replication by sensitizing the virus to BST-2 restriction. Further studies revealed that IMB-LA specifically inhibits Vpu-mediated degradation of BST-2 and restores the expression of BST-2 at the cell surface. Although IMB-LA does not prevent Vpu from interacting with BST-2 or beta-TrCP2-containing ubiquitin E3 ligase, sorting of BST-2 into lysosomes in Vpu-expressing cells is blocked by IMB-LA. Most importantly, HIV-1 release and infection is inhibited by IMB-LA only in BST-2-expressing cells. In summary, results herein demonstrated that IMB-LA could specifically inhibit the degradation of BST-2 induced by Vpu, and impair HIV-1 replication in a BST-2 dependent manner, suggesting the feasibility of utilizing small molecule compounds to disable the antagonist function of Vpu and thereby expose HIV-1 to the restriction by BST-2.
分类： 生物学 >> 生物物理学 提交时间： 2016-05-11
摘要： CouR from Rhodopseudomonas palustris is a member of the MarR transcriptional regulator family. It regulates the expression of CouA and CouB, enzymes that are involved in the degradation of p-coumarate. In vivo, CouR binds to a DNA fragment containing the couAB promoter and suppresses the expression of CouA and CouB, while binding of p-coumaroyl-CoA attenuates its affinity towards DNA and activates the expression of CouA and CouB. Here, the crystallization and X-ray diffraction analyses of CouR alone and in complex with p-coumaroyl-CoA are reported. Apo and ligand-complexed CouR crystals diffracted to 2.5 and 3.3 angstrom resolution, respectively. The crystals of apo CouR belonged to space group P22(1)2(1), with unit-cell parameters a = 62.78, b = 76.15, c = 87.38 angstrom, whereas the crystals of the CouR-ligand complex belonged to space group P2(1)2(1)2(1), with unit-cell parameters a = 61.37, b = 69.82, c = 70.32 angstrom. The crystals were predicted to contain two CouR molecules or CouR-ligand complexes per asymmetric unit.
分类： 生物学 >> 生物物理学 >> 生物物理、生物化学与分子生物学 提交时间： 2016-05-05
Wu, R.
Chen, H.
Ma, J.
He, Q.
Yuan, Z.
Wu, R.
Ma, J.
He, Q.
Yuan, Z.
Chen, H.
Yuan, Z.
Huang, Q.
Li, M.
Huang, Q.
Li, M.
Liu, Q.
摘要： Oxidative stress is a major cause of sporadic Parkinson's disease (PD). Here, we demonstrated that c-Abl plays an important role in oxidative stress-induced neuronal cell death. C-Abl, a nonreceptor tyrosine kinase, was activated in an 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine hydrochloride (MPTP)-induced acute PD model. Conditional knockout of c-Abl in neurons or treatment of mice with STI571, a c-Abl family kinase inhibitor, reduced the loss of dopaminergic neurons and ameliorated the locomotive defects induced by short-term MPTP treatment. By combining the SILAC (stable isotope labeling with amino acids in cell culture) technique with other biochemical methods, we identified p38 alpha as a major substrate of c-Abl both in vitro and in vivo and c-Abl-mediated phosphorylation is critical for the dimerization of p38 alpha. Furthermore, p38 alpha inhibition mitigated the MPTP-induced loss of dopaminergic neurons. Taken together, these data suggested that c-Abl-p38 alpha signaling may represent a therapeutic target for PD.
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