近20年塔里木河干流生态环境变化遥感监测分析

针对塔里木河流域综合治理后生态环境的变化状况及植被的恢复状况等热点问题,基于遥感时空变化分析方法从土地利用、地表水体和植被覆盖度的时空变化方面分析了近20年来塔里木河干流生态环境的变化状况。结果表明:(1)塔里木河干流土地利用受到人类活动的影响显著,自2000年以来,塔里木河干流耕地面积增加显著,净增2 229 km~2,草地面积整体下降,萎缩3 157 km~2;(2)综合治理以来,下游河段2009—2018时段水体出现频率明显高于2000—2008时段,水体出现频率提高约15%;(3)2000年以来,塔里木河流域的植被覆盖度持续增加,特别是下游河段植被覆盖度增加明显,覆盖度增加18%。但中、上游流域的植被覆盖度的增加趋势主要贡献来源于耕地,中上游地区耕地的增加仍会对塔里木河流域的生态保护和恢复造成一定的影响。     

基于MODIS数据的浙江省植被覆盖度时空变化分析

以浙江省为研究区,基于2009—2018年MODIS_NDVI数据,采用MVC最大值合成法获取逐月NDVI值,利用改进的像元二分模型估算2009—2018年植被覆盖度,结合DEM数据及《浙江省林地保护利用规划》(2010—2020年)中的林地分区,分析浙江省植被覆盖度的时空变化情况。结果表明:①2009—2018年浙江省植被覆盖度总体处于高盖度级别,存在缓慢降低的趋势。②2009年和2018年的植被覆盖度空间格局基本一致,即浙南山地区、浙西山地丘陵区>浙中丘陵盆地区、浙东沿海丘陵海岛区>浙北平原区;植被覆盖度变化以稳定为主,占总面积的62.79%,退化区域面积大于改善区域面积,退化趋势以浙北平原区最为严重,占总面积的6.73%,改善趋势以浙南山地区最为明显,占总面积的4.87%。③各地形因子范围内的植被覆盖度变化均相对稳定;不同高程范围内,明显退化区域在高程100 m以下,明显改善区域在高程200 m以上;不同坡度范围内,退化最明显区域为坡度[0°,5°)范围,明显改善区域为坡度15°以上;不同坡向间,植被变化的差异并不明显。研究成果可为该地区的生态环境建设和水土流失防治提供理论依据。     

基于EEMD方法的区域降水事件特征分析——以京津冀地区为例

区域降水事件特征影响水循环,进而对社会经济各个方面有着深远的影响。京津冀地区是我国的政治、经济、文化中心,水旱灾害频发,亟需全面了解该地区区域降水事件特征。以京津冀地区173个气象站1989—2018年间逐日降水数据为基础,共识别出552次区域降水事件,采用集合经验模态分解(EEMD)等方法,从持续时间、覆盖范围、降水强度3个要素对京津冀地区区域降水事件特征及时空分布情况展开研究。结果表明:①区域降水事件发生频率有随持续时间、覆盖范围增大而减小的趋势,减小趋势逐渐变缓,区域降水事件的降水强度在10 mm附近频率最高,区域降水事件的3个要素均与综合性强度有着明显的正相关关系;②京津冀地区区域降水事件综合性强度年际变化呈现出10 a左右的周期,但长期趋势性不明显;③京津冀地区区域降水事件沿地形呈“西北少、中部多”的空间分布规律。研究成果可为当地水资源规划、防灾减灾等提供技术支撑。     

Population effect of a large‐scale stream restoration effort on Chinook salmon in the Pahsimeroi River,Idaho

Stream habitat restoration is an important tool for fisheries management in impaired lotic systems. Although small‐scale benefits of stream habitat restoration are commonly investigated, it is difficult to demonstrate population effects. The Pahsimeroi River Chinook salmon Oncorhynchus tshawytscha population was previously restricted to the lower portion of the river by multiple irrigation structures. To address fish passage issues, a combination of restoration projects was initiated including barrier removals, instream flow enhancements and installation of fish screens on diversions. The largest barrier was removed in 2009, more than doubling the amount of accessible linear habitat. We hypothesized restoration efforts would expand the distribution of spawning salmon in the Pahsimeroi River watershed, leading to a broader distribution of juveniles. We also hypothesized a broader juvenile distribution would have population effects by reducing the prevalence of density‐dependent growth and survival. Redds were documented in newly accessible habitat immediately following barrier removal and accounted for a median of 42% of all redds in the Pahsimeroi River watershed during 2009–2015. Snorkel surveys also documented juvenile rearing in newly accessible habitat. Juvenile productivity increased from a median of 64 smolts/female spawner for brood years 2002–2008 to 99 smolts/female spawner for brood years 2009–2014. Overall, results suggested increased habitat accessibility in the Pahsimeroi River broadened the distribution of spawning adult and rearing juvenile salmon and reduced the effects of density‐dependent survival. Large‐scale stream restoration efforts can have a population effect. Despite the large‐scale effort and response, habitat restoration alone is likely not sufficient to restore this population.     

煤矿井下便携式电子设备电源设计要点

针对便携式电子设备的电源性能影响设备稳定运行的问题,探讨了便携式电子设备电源设计要点:介绍了电池类型的选择,指出选择锂电池作为后备电池较为理想;分析了电源安全栅的保护方式,指出先限流后截止的安全栅保护方式可有效提高电源的抗干扰能力;针对电池Boost升压电路中出现的振铃问题,给出了优化Boost变换器关键环路的解决方法,有效减小了电源纹波。     

栅栏覆盖最大化生存周期调度算法

栅栏覆盖是近年来无线传感器网络的研究热点之一,如何延长生存周期是无线传感器网络研究的一个重要问题。针对无线传感器网络的栅栏覆盖应用,设计了两种最大化网络生存周期的调度算法:集中式的Greedy调度算法和分布式的DBCS调度算法。仿真实验表明:两种算法显著地延长了网络的生存周期;在较稀疏的网络中,DBCS算法与Greedy算法性能接近,分布式的DBCS算法适合应用于大规模传感器网络。     

Chemical composition and bond structure of carbon-nitride films deposited by CH4/N2 dielectric barrier discharge

Carbon nitride films have been deposited by dielectric barrier discharge with a CH₄/N₂ gas mixture at different conditions. Fourier Transform Infrared (FTIR) spectroscopy, X-ray photo electron spectroscopy (XPS), Raman spectroscopy, Atomic force microscopy (AFM) and ellipsometry were used to systematically study chemical composition, bond structure and surface morphology of deposited films. Various bonds between carbon, nitrogen, hydrogen, and also oxygen were observed.     

Cutting Edge of the Pathogenesis of Atopic Dermatitis: Sphingomyelin Deacylase,the Enzyme Involved in Its Ceramide Deficiency,Plays a Pivotal Role

Atopic dermatitis (AD) is characterized clinically by severe dry skin and functionally by both a cutaneous barrier disruption and an impaired water-holding capacity in the stratum corneum (SC) even in the nonlesional skin. The combination of the disrupted barrier and water-holding functions in nonlesional skin is closely linked to the disease severity of AD, which suggests that the barrier abnormality as well as the water deficiency are elicited as a result of the induced dermatitis and subsequently trigger the recurrence of dermatitis. These functional abnormalities of the SC are mainly attributable to significantly decreased levels of total ceramides and the altered ceramide profile in the SC. Clinical studies using a synthetic pseudo-ceramide (pCer) that can function as a natural ceramide have indicated the superior clinical efficacy of pCer and, more importantly, have shown that the ceramide deficiency rather than changes in the ceramide profile in the SC of AD patients plays a central role in the pathogenesis of AD. Clinical studies of infants with AD have shown that the barrier disruption due to the ceramide deficiency is not inherent and is essentially dependent on postinflammatory events in those infants. Consistently, the recovery of trans-epidermal water loss after tape-stripping occurs at a significantly slower rate only at 1 day post-tape-stripping in AD skin compared with healthy control (HC) skin. This resembles the recovery pattern observed in Niemann–Pick disease, which is caused by an acid sphingomyelinase (aSMase) deficiency. Further, comparison of ceramide levels in the SC between before and after tape-stripping revealed that whereas ceramide levels in HC skin are significantly upregulated at 4 days post-tape-stripping, their ceramide levels remain substantially unchanged at 4 days post-tape-stripping. Taken together, the sum of these findings strongly suggests that an impaired homeostasis of a ceramide-generating process may be associated with these abnormalities. We have discovered a novel enzyme, sphingomyelin (SM) deacylase, which cleaves the N-acyl linkage of SM and glucosylceramide (GCer). The activity of SM deacylase is significantly increased in AD lesional epidermis as well as in the involved and uninvolved SC of AD skin, but not in the skin of patients with contact dermatitis or chronic eczema, compared with HC skin. SM deacylase competes with aSMase and β-glucocerebrosidase (BGCase) to hydrolyze their common substrates, SM and GCer, to yield their lysoforms sphingosylphosphorylcholine (SPC) and glucosylsphingosine (GSP), respectively, instead of ceramide. Consistently, those reaction products (SPC and GSP) accumulate to a greater extent in the involved and uninvolved SC of AD skin compared with chronic eczema or contact dermatitis skin as well as HC skin. Successive chromatographies were used to purify SM deacylase to homogeneity with a single band of ≈43 kDa and with an enrichment of >14,000-fold. Analysis of a protein spot with SM deacylase activity separated by 2D-SDS-PAGE using MALDI-TOF MS/MS allowed its amino acid sequence to be determined and to identify it as the β-subunit of acid ceramidase (aCDase), an enzyme consisting of α- and β-subunits linked by amino-bonds and a single S-S bond. Western blotting of samples treated with 2-mercaptoethanol revealed that whereas recombinant human aCDase was recognized by antibodies to the α-subunit at ≈56 and ≈13 kDa and the β-subunit at ≈43 kDa, the purified SM deacylase was detectable only by the antibody to the β-subunit at ≈43 kDa. Breaking the S-S bond of recombinant human aCDase with dithiothreitol elicited the activity of SM deacylase with an apparent size of ≈40 kDa upon gel chromatography in contrast to aCDase activity with an apparent size of ≈50 kDa in untreated recombinant human aCDase. These results provide new insights into the essential role of SM deacylase as the β-subunit aCDase that causes the ceramide deficiency in AD skin.     

The Neurovascular Unit Dysfunction in Alzheimer’s Disease

Alzheimer’s disease (AD) is the most common neurodegenerative disease worldwide. Histopathologically, AD presents with two hallmarks: neurofibrillary tangles (NFTs), and aggregates of amyloid β peptide (Aβ) both in the brain parenchyma as neuritic plaques, and around blood vessels as cerebral amyloid angiopathy (CAA). According to the vascular hypothesis of AD, vascular risk factors can result in dysregulation of the neurovascular unit (NVU) and hypoxia. Hypoxia may reduce Aβ clearance from the brain and increase its production, leading to both parenchymal and vascular accumulation of Aβ. An increase in Aβ amplifies neuronal dysfunction, NFT formation, and accelerates neurodegeneration, resulting in dementia. In recent decades, therapeutic approaches have attempted to decrease the levels of abnormal Aβ or tau levels in the AD brain. However, several of these approaches have either been associated with an inappropriate immune response triggering inflammation, or have failed to improve cognition. Here, we review the pathogenesis and potential therapeutic targets associated with dysfunction of the NVU in AD.