Finite element modeling of microstructural changes in dry and cryogenic machining of AZ31B magnesium alloy

Unsatisfactory corrosion resistance is one of the major disadvantages of magnesium alloys that impede their wide application. Microstructural changes, especially grain sizes, of Mg alloys have significant influence on their corrosion resistance. Cryogenic machining was reported to effectively induce grain refinement on Mg alloys and has a potential to improve their corrosion resistance. It is important to model these changes so that proper machining conditions can be found to enhance the corrosion rate of Mg alloys. In this paper, a preliminary study was conducted to model the microstructural changes of AZ31B Mg alloy during dry and cryogenic machining using the finite element (FE) method and a user subroutine based on the dynamic recrystallization (DRX) mechanism of Mg alloys. Good agreement in terms of grain size and affected layer thickness was found between experimental and predicted results. A numerical study was conducted using this model to investigate the influence of rake angle on microstructural changes after cryogenic machining.     

县级土地利用动态变化及驱动力分析——以郑州市中牟县为例

以郑州市中牟县为例,利用土地详查和统计数据等资料,建立土地利用动态变化模型,分析了中牟县1996-2008年土地利用数量、速度、程度、区域差异等变化,揭示中牟县土地利用变化特征.同时,采用主成分分析法得出城镇化进程和收入水平提高是影响中牟县土地利用变化的主要驱动因素.     

内蒙古地区近25年植被对气温和降水变化的影响

利用1982—2006年内蒙古地区GIMMS-NDVI和降水量、气温数据,分析了不同植被类型对气温和降水变化趋势的影响。结果表明：近25年来内蒙古地区气温整体上呈上升趋势,降水量呈微弱降低趋势,西部荒漠区呈暖湿化趋势,中东部草原、森林等植被类型区呈暖干化趋势;从不同植被类型NDVI与平均气温和降水量的变化趋势率相关分析表明,NDVI值越低,升温趋势越明显,其中春季和秋季各植被类型间NDVI与季均气温升高趋势率呈显著和较显著的相关,夏、冬季关系不明显;植被NDVI越高,降水量减少趋势越明显。基于栅格的NDVI与气温升高幅度、降水变化趋势相关分析表明,年均气温升高幅度基本随NDVI的增加而降低,其中春、夏和秋季的季均气温升高幅度均随NDVI的增加而显著降低,冬季趋势不明显;而年降水量减小趋势率随植被NDVI的增加而显著增加,其中春季和冬季NDVI变化对降水的变化几乎没有影响;夏季和秋季均表现为随NDVI的增加,降水减小趋势率呈增加趋势。     

近40 a 长江源各拉丹冬冰川进退变化研究

在近几十年气候变暖的背景下,地球上的冰川迅速消融,我国的山地冰川也发生了剧烈变化。山地冰川变化会直接或间接影响地球的生态环境及人类的生活环境,因此对山地冰川的变化进行监测至关重要。各拉丹东冰川的伸缩变化非常明显地揭示了当地乃至青藏高原和全球气候的变迁,极具科研价值。论文在总结国内外研究现状的同时结合所学知识,采用多达5 个时相的陆地资源卫星以及中国冰川目录等有效资料,利用冰雪指数和监督分类方法提取冰川信息,对提取的冰川范围利用空间分析技术进行冰川变化监测。统计分析1973—1986、1986—1992、1992—2004、2004—2009 年4 个时间段以及1973—2009 年整个36 a 间的冰川前进及后退信息,并计算冰川进退变化速率, 对其中5 条变化较大的冰川进行详细的分析统计。结果表明：从1973 年至2009 年近40 a 时间里,各拉丹冬地区既有退缩冰川也有前进冰川, 其中冰川退缩面积为118.64 km², 前进面积为62.66 km²,冰川总体面积持续退缩。根据相关资料,近40 a 来“三江源”地区气温普遍升高是导致各拉丹冬冰川总体面积持续退缩的关键因素。     

广东省近18年粮食生产区域格局变化及成因分析

在分析建国以来广东省粮食生产历程及其阶段性特征的基础上，利用广东省1987～2004年分县统计数据，采用数理统计、区域差异定量分析与GIS空间分析等方法，研究了广东省近18年来粮食生产区域格局变化，并探讨了其影响因素，以期为进一步制定粮食宏观政策、保障广东省粮食安全提供参考依据。研究结果表明：1980年以来，广东省人均粮食占有量与全国人均粮食占有量之间的差距在逐渐增大；1987-2004年，广东省粮食生产中心逐渐北移；珠江三角洲粮食产量出现严重滑坡，粤东粤西地区处于低水平的相对稳定的粮食生产状态，而北部山区粮食产量经历了明显先升后降的过程，但在全省粮食生产的地位逐渐提升；珠江三角洲和粤东地区各县市区地域绝对差异和相对差异较大，18年间波动幅度也较大，而北部山区与粤西地区各县市区地域绝对差异和相对差异较小，变化幅度也较小；影响广东省粮食生产区域格局变化的主要因素包括工业化和城市化的迅速发展、种粮比较收益低下、粮食作物播种面积与产值构成的大幅下降以及经济体制的转型。     

Potential of Marine Reserves to Cause Community-Wide Changes beyond Their Boundaries

Abstract:  Fishing and other human activities can alter the abundances, size structure, and behavior of species playing key roles in shaping marine communities (e.g., keystone predators), which may in turn cause ecosystem shifts. Despite extensive evidence that cascading trophic interactions can underlie community-wide recovery inside no-take marine reserves by protecting high-level predators, the spatial extent of these effects into adjacent fished areas is unknown. I examined the potential for community-wide changes (i.e., the transition from overgrazed coralline barrens to macroalgal beds) in temperate rocky reefs within and around a no-take marine reserve. For this purpose I assessed distribution patterns of predatory fishes, sea urchins, and barrens across the reserve boundaries. Predatory fishes were significantly more abundant within the reserve than in adjacent locations, with moderate spillover across the reserve edges. In contrast, community-wide changes of benthic assemblages were apparent well beyond the reserve boundaries, which is consistent with temporary movements of predatory fishes (e.g., foraging migration) from the reserve to surrounding areas. My results suggest that no-take marine reserves can promote community-wide changes beyond their boundaries.     

Population Dynamics of Forest Voles (Clethrionomys,Rodentia) in Northern European Russia

Long-term data sets on the population dynamics of forest voles in northern European Russia were analyzed. Eastward and northward trends in changes of the ratio between model species and the degree of their dominance were revealed. In virtually all sites studied, the numbers of the northern red-backed and bank voles changed synchronously; however, the population dynamics became less synchronous as the distance between study areas increased.     

不同气候情景下甘肃草地碳收支时空模拟与预测

在碳达峰、碳中和的背景下,草地碳汇是实现碳中和的关键路径.基于第六次国际耦合模式比较计划（CMIP6）气候情景数据,运用Daycent模型对甘肃草地2015~2100年碳收支进行模拟,并利用趋势分析法研究未来78 a草地碳收支的时空变化规律.结果表明,SSP245未来气候情景下,净生态系统生产力（NEP）呈不显著波动下降趋势,速率（以C计,下同）达-0.20 g ·（m² ·a）^-1,且该情景下草地碳汇处于下降状态;SSP585未来气候情景下,草地NEP以1.36 g ·（m² ·a）^-1的速率呈显著波动上升趋势,草地碳汇逐渐增加;草地碳收支的空间分布由西北向东南递增;SSP585气候情景下的温度和降水的增幅高于SSP245的气候情景,且草地碳收支与降水量的变动具有一致性,与温度的变化呈反向关系.研究明确了在不同气候情景下甘肃草地的碳汇强度,对有效固碳有参考和促进作用.     

2015~2019年南京北郊碳质气溶胶组成变化

碳质气溶胶是大气细颗粒物的重要组成,对空气质量、人体健康和气候变化有着重要影响.为了探究碳质气溶胶在减排背景下的长期变化,本研究测定了南京北郊5 a（2014年12月17日至2020年1月5日） PM_2.5样品的有机碳（OC）和元素碳（EC）浓度.结果表明,ρ（OC）和ρ（EC）5a平均值分别为（10.2±5.3）μg·m^-3和（1.6±1.1）μg·m^-3,其中OC占PM_2.5的31.1%,EC占PM_2.5的5.2%.OC和EC均呈现出冬高夏低的季节特征.通过非参数的Mann-Kendall检验和Sen’s斜率发现,OC和PM_2.5的浓度整体呈显著下降趋势[OC:P<0.000 1,-0.79μg·（m³·a）^-1,-0.29%·a^-1; PM_2.5:P<0.000 1,-4.59μg·（m³·a）^-1,-1.5...     

Sub-chronic exposure to carbendazim induces biochemical and hematological alterations in male goats

The present investigation reports the effect of repeated (90 days) administration of carbendazim on the biochemical and hematological parameters in male goats. Carbendazim administered orally at a daily dose of 50 mg kg^?1 body weight for 90 consecutive days resulted in increased plasma concentration of aspartate aminotransferase (AST), alanine aminotransferase (ALT), lactate dehydrogenase (LDH), gamma-glutamyl transferase (GGT), creatinine and albumin, while alkaline phosphatase (ALP) and glucose levels were decreased. Decrease in total leukocyte (TLC) and neutrophil count and increase in lymphocyte count was observed in the treatment group. The findings of the present investigation indicate that sub-chronic exposure to carbendazim in male goats causes hepatic and slight kidney dysfunctions.