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Diffusion kurtosis imaging of microstructural changes in brain tissue affected by acute ischemic stroke in different locations 预览
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作者 Liu-Hong Zhu Zhong-Ping Zhang +2 位作者 Fu-Nan Wang Qi-Hua Cheng Gang Guo 《中国神经再生研究:英文版》 SCIE CAS CSCD 2019年第2期272-279,共8页
The location of an acute ischemic stroke is associated with its prognosis. The widely used Gaussian model-based parameter, apparent diffusion coefficient (ADC), cannot reveal microstructural changes in different locat... The location of an acute ischemic stroke is associated with its prognosis. The widely used Gaussian model-based parameter, apparent diffusion coefficient (ADC), cannot reveal microstructural changes in different locations or the degree of infarction. This prospective observational study was reviewed and approved by the Institutional Review Board of Xiamen Second Hospital, China (approval No. 2014002). Diffusion kurtosis imaging (DKI) was used to detect 199 lesions in 156 patients with acute ischemic stroke (61 males and 95 females), mean age 63.15 ± 12.34 years. A total of 199 lesions were located in the periventricular white matter (n = 52), corpus callosum (n = 14), cerebellum (n = 29), basal ganglia and thalamus (n = 21), brainstem (n = 21) and gray-white matter junctions (n = 62). Percentage changes of apparent diffusion coefficient (ΔADC) and DKI-derived indices (fractional anisotropy [ΔFA], mean diffusivity [ΔMD], axial diffusivity [ΔDa], radial diffusivity ΔDr, mean kurtosis [ΔMK], axial kurtosis [ΔKa], and radial kurtosis [ΔKr]) of each lesion were computed relative to the normal contralateral region. The results showed that (1) there was no significant difference in ΔADC, ΔMD, ΔDa or ΔDr among almost all locations. (2) There was significant difference in ΔMK among almost all locations (except basal ganglia and thalamus vs. brain stem; basal ganglia and thalamus vs. gray-white matter junctions; and brainstem vs. gray-white matter junctions. (3) The degree of change in diffusional kurtosis in descending order was as follows: corpus callosum > periventricular white matter > brainstem > gray-white matter junctions > basal ganglia and thalamus > cerebellum. In conclusion, DKI could reveal the differences in microstructure changes among various locations affected by acute ischemic stroke, and performed better than diffusivity among all groups. 展开更多
关键词 nerve REGENERATION APPARENT DIFFUSION coefficient DIFFUSION weighted IMAGING DIFFUSION KURTOSIS IMAGING acute ischemic stroke mean KURTOSIS microstructure changes white matter 1.5 TESLA magnetic resonance system neural REGENERATION
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中尺度煤块中煤层气多尺度扩散系数随时间依赖的实验及模型
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作者 李志强 彭建松 成墙 《煤炭技术》 CAS 2019年第1期86-88,共3页
为探究煤层气含气量(和储量)测定过程中混有中尺度(厘米级)煤块的影响,开展了不同煤种的毫米-厘米级中等尺度煤块在不同压力下的煤层气扩散实验。实验发现,扩散前期实验扩散率大于经典模型的理论扩散率,扩散后期实验扩散率小于经典模型... 为探究煤层气含气量(和储量)测定过程中混有中尺度(厘米级)煤块的影响,开展了不同煤种的毫米-厘米级中等尺度煤块在不同压力下的煤层气扩散实验。实验发现,扩散前期实验扩散率大于经典模型的理论扩散率,扩散后期实验扩散率小于经典模型的理论值。全时扩散过程中扩散系数并非一个常数,而是随时间延长而衰减的函数。提出了能精确描述不同气压下不同煤种中尺度煤块的煤层气扩散全过程的动扩散系数新模型。与以往实验相比,中尺度煤块的初始扩散系数比粉煤大1~2个数量级,而扩散系数衰减系数比粉煤小1~2个数量级,原因是中尺度煤块包含了更大的孔裂隙,而其孔径级差较小。 展开更多
关键词 煤层气 扩散 扩散系数 模型
Traumatic axonal injury of the cingulum in patients with mild traumatic brain injury:a diffusion tensor tractography study 预览
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作者 Sung Ho Jang Seong Ho Kim Han Do Lee 《中国神经再生研究:英文版》 SCIE CAS CSCD 2019年第9期1556-1561,共6页
The cingulum,connecting the orbitofrontal cortex to the medial temporal lobe,involves in diverse cognition functions including attention,memory,and motivation.To investigate the relationship between the cingulum injur... The cingulum,connecting the orbitofrontal cortex to the medial temporal lobe,involves in diverse cognition functions including attention,memory,and motivation.To investigate the relationship between the cingulum injury and cognitive impairment in patients with chronic mild traumatic brain injury,we evaluated the integrity between the anterior cingulum and the basal forebrain using diffusion tensor tractography in 73 patients with chronic mild traumatic brain injury(39 males,34 females,age 43.29±11.42 years)and 40 healthy controls(22 males,18 females,age 40.11±16.81 years).The patients were divided into three subgroups based on the integrity between the anterior cingulum and the basal forebrain on diffusion tensor tractography:subgroup A(n=19 patients)– both sides of the anterior cingulum were intact;subgroup B(n=36 patients)– either side of the anterior cingulum was intact;and subgroup C(18 patients)– both sides of the anterior cingulum were discontinued.There were significant differences in total Memory Assessment Scale score between subgroups A and B and between subgroups A and C.There were no significant differences in diffusion tensor tractography parameters(fractional anisotropy,apparent diffusion coefficient,and fiber volume)between patients and controls.These findings suggest that the integrity between the anterior cingulum and the basal forebrain,but not diffusion tensor tractography parameter,can be used to predict the cognitive function of patients with chronic mild traumatic brain injury.This study was approved by Yeungnam University Hospital Institutional Review Board(approval No.YUMC-2014-01-425-010)on August 16,2017. 展开更多
关键词 mild traumatic BRAIN injury BRAIN trauma DIFFUSION TENSOR TRACTOGRAPHY DIFFUSION TENSOR imaging cognitive impairment CINGULUM memory Glasgow COMA Scale neural regeneration
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Application of interface material and effects of oxygen gradient on the performance of single-chamber sediment microbial fuel cells (SSMFCs)
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作者 Chin-Tsan Wang Thangavel Sangeetha +5 位作者 Wei-Mon Yan Wen-Tong Chong Lip-Huat Saw Feng Zhao Chung-Ta Chan Chen-Hao Wang 《环境科学学报:英文版》 SCIE EI CAS CSCD 2019年第1期163-168,共6页
Single-chamber sediment microbial fuel cells (SSMFCs) have received considerable attention nowadays because of their unique dual-functionality of power generation and enhancement of wastewater treatment performance.Th... Single-chamber sediment microbial fuel cells (SSMFCs) have received considerable attention nowadays because of their unique dual-functionality of power generation and enhancement of wastewater treatment performance.Thus,scaling up or upgrading SSMFCs for enhanced and efficient performance is a highly crucial task.Therefore,in order to achieve this goal,an innovative physical technique of using interface layers with four different pore sizes embedded in the middle of SSMFCs was utilized in this study. Experimental results showed that the performance of SSMFCs employing an interface layer was improved regardless of the pore size of the interface,material,compared to those without such layers.The use of an interface layer resulted in a positive and significant effect on the performance of SSMFCs because of the effective prevention of oxygen diffusion from the cathode to the anode.Nevertheless,when a smaller pore size interface was utilized,better power performance and COD degradation were observed.A maximum power density of 0.032mW/m^2 and COD degradation of 47.3% were obtained in the case of an interface pore size of 0.28μm.The findings in this study are of significance to promote the future practical application of SSMFCs in wastewater treatment plants. 展开更多
关键词 Single sediment MICROBIAL fuel cells INTERFACE layer Dissolved OXYGEN PORE size OXYGEN DIFFUSION DIFFUSION coefficient
扩散峰度成像在轻度认知功能障碍患者额叶前皮质微结构变化中的应用分析 预览
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作者 刘东涛 李坤 +3 位作者 卜乔 潘振宇 周立春 胡文立 《中国脑血管病杂志》 CAS CSCD 北大核心 2019年第3期123-128,共6页
目的 探讨MR扩散峰度成像(DKI)技术在轻度认知功能障碍(MCI)患者额叶前皮质微结构变化的应用价值。方法 回顾性连续纳入2018年1月至12月于首都医科大学附属北京朝阳医院神经内科脑小血管病住院患者79例,经头部MRI和MR血管成像证实,并采... 目的 探讨MR扩散峰度成像(DKI)技术在轻度认知功能障碍(MCI)患者额叶前皮质微结构变化的应用价值。方法 回顾性连续纳入2018年1月至12月于首都医科大学附属北京朝阳医院神经内科脑小血管病住院患者79例,经头部MRI和MR血管成像证实,并采用蒙特利尔认知评估(MoCA)量表对总体认知功能进行评估。根据是否存在MCI,将79例患者分为MCI组(46例)和无MCI组(33例)。记录并分析两组患者一般临床资料;神经心理学测评结果,包括MoCA量表、汉密尔顿抑郁量表(HAMD)、汉密尔顿焦虑量表(HAMA);常规MR形态学及DKI扫描结果。选择患者额叶前皮质为感兴趣区,即双侧背外侧额上回、内侧额上回、前扣带和旁扣带脑回;测量兴趣区的DKI相关参数,包括平均扩散率(MD)、扩散各向异性分数(FA)、轴向扩散峰度(AK)、平均扩散峰度(MK)和径向扩散峰度(RK)。对多个兴趣区的多次比较应用Bonferroni方法校正P值,校正P值以P <0. 008为差异有统计学意义。结果 (1) MCI组患者MoCA量表评分低于无MCI组,组间差异有统计学意义[20(19,22)分比27(25,28)分,Z=-6. 836,P <0. 01];年龄、性别、受教育年限、HAMD评分、HAMA评分的组间差异均无统计学意义(均P> 0. 05)。(2)在右侧前扣带和旁扣带脑回,MCI组患者FA、AK、MK值均低于无MCI组,组间差异均有统计学意义(0. 16±0. 03比0. 18±0. 03、0. 64±0. 08比0. 70±0. 06、0. 67±0. 09比0. 73±0. 06,均P <0. 008),MD、RK值的组间差异均无统计学意义(均P> 0. 008);在左侧前扣带和旁扣带脑回,MD、FA、AK、MK、RK值的组间差异均无统计学意义(均P> 0. 008)。(3) MD、FA、AK、MK及RK值在双侧背外侧额上回、双侧内侧额上回的组间差异均无统计学意义(均P> 0. 008)。结论 DKI技术可尝试用于MCI患者额叶前皮质微结构改变的观察,DKI相关参数在MCI患者临床影像学评估中具有一定的价值。 展开更多
关键词 认知障碍 磁共振成像 弥散 扩散峰度成像 额叶前皮质
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A comprehensive assessment on the durability of gas diffusion electrode materials in PEM fuel cell stack
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作者 Arunkumar JAYAKUMAR 《能源前沿:英文版》 CSCD 2019年第2期325-338,共14页
Polymer electrolyte membrane (PEM) fuel cell is the most promising among the various types of fuel cells. Though it has found its applications in numerous fields, the cost and durability are key barriers impeding the ... Polymer electrolyte membrane (PEM) fuel cell is the most promising among the various types of fuel cells. Though it has found its applications in numerous fields, the cost and durability are key barriers impeding the commercialization of PEM fuel cell stack. The crucial and expensive component involved in it is the gas diffusion electrode (GDE) and its degradation, which limits the performance and life of the fuel cell stack. A critical analysis and comprehensive understanding of the struc-tural and functional properties of various materials involved in the GDE can help us to address the related durability and cost issues. This paper reviews the key GDE components, and in specific, the root causes influencing the durability. It also envisages the role of novel materials and provides a critical recommendation to improve the GDE durability. 展开更多
关键词 PEM FUEL CELL GAS DIFFUSION electrode(GDE) GAS DIFFUSION layer(GDL) membrane ELECTRODE assembly DURABILITY FUEL CELL catalyst
多发性骨髓瘤患者全身扩散加权成像的表现与临床检查结果的相关性
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作者 黄文阳 杨咪 +7 位作者 隋伟薇 邓书会 刘薇 冀晓东 邹德慧 郝牧 邱录贵 夏爽 《中华医学杂志》 CAS CSCD 北大核心 2019年第9期664-668,共5页
目的探讨多发性骨髓瘤患者全身扩散加权成像的表现与临床检查结果的相关性。方法回顾性收集2015年5月至2017年5月于天津市第一中心医院进行全身扩散加权成像(WBDWI)的多发性骨髓瘤患者共43例纳入本研究。其中男29例、女14例,年龄36-73岁... 目的探讨多发性骨髓瘤患者全身扩散加权成像的表现与临床检查结果的相关性。方法回顾性收集2015年5月至2017年5月于天津市第一中心医院进行全身扩散加权成像(WBDWI)的多发性骨髓瘤患者共43例纳入本研究。其中男29例、女14例,年龄36-73岁,中位年龄54岁。将患者按照WBDWI的表现分为异常组和正常组,比较两组患者的临床资料,表观扩散系数(ADC)值差异有无统计学意义。比较WBDWI表现异常组初诊和治疗后临床资料差异。结果43例患者中,WBDWI表现正常组10例,男7例、女3例,年龄(59±9)岁;异常组33例,男22例、女11例,年龄(57±10)岁,两组间年龄、性别差异均无统计学意义(均P>0.05)。WBDWI异常组、正常组患者的浆细胞比例分别为50.0%(14.0%,78.0%)、5.0%(2.5%, 15.0%)β2微球蛋白浓度中位数分别为4.8(2.7,7.7)、2.4(2.0,3.7)mg/L, WBDWI异常组显著高于正常组(P<0.05)。WBDWI全身扩散表现异常组的肋骨、胸骨、锁骨、胸椎、腰椎、骨盆、肱骨近端、股骨近端、股骨干、胫骨干、胫骨近端ADC值分别为(0.66±0.15)×10^-3、(0.71±0.20)×10^-3、(0.67±0.17)×10^-3、(0.63±0.17)×10^-3、(0.69±0.20)×10^-3、(0.83±0.36)×10^-3、(0.76±0.13)×10^-3、(0.64±0.17)×10^-3、(0.70±0.22)×10^-3、(0.97±0.18)×10^-3、(0.83±0.18)×10^-3 mm^2/s,均显著高于正常组(均P<0.05): WBDWI异常组患者治疗后的白蛋白浓度升高,两组间差异有统计学意义(P<0.05),余临床结果差异均无统计学意义(均P>0.05)。结论WBDWI的不同影像学表现,能够反映临床的严重程度,当WBDWI表现正常时,临床症状较轻,当WBDWI表现异常时,虽然经过治疗后白蛋白浓度升高,但患者临床症状仍较重。 展开更多
关键词 磁共振成像 多发性骨髓瘤 扩散 表观扩散系数
Differentiating between Alzheimer’s disease, amnestic mild cognitive impairment, and normal aging via diffusion kurtosis imaging 预览
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作者 Guo-Ping Song Ting-Ting Yao +1 位作者 Dan Wang Yue-Hua Li 《中国神经再生研究:英文版》 SCIE CAS CSCD 2019年第12期2141-2146,共6页
Diffusion kurtosis imaging can be used to assess pathophysiological changes in tissue structure and to diagnose central nervous system diseases. However, its sensitivity in assessing hippocampal differences between pa... Diffusion kurtosis imaging can be used to assess pathophysiological changes in tissue structure and to diagnose central nervous system diseases. However, its sensitivity in assessing hippocampal differences between patients with Alzheimer’s disease and those with amnestic mild cognitive impairment has not been characterized. Here, we examined 20 individuals with Alzheimer’s disease (11 men and 9 women, mean 73.2 ± 4.49 years), 20 with amnestic mild cognitive impairment (10 men and 10 women, mean 71.55 ± 4.77 years), and 20 normal controls (11 men and 9 women, mean 70.45 ± 5.04 years). We conducted diffusion kurtosis imaging, using a 3.0 T magnetic resonance scanner, to compare hippocampal differences among the three groups. The results demonstrated that the right hippocampal volume and bilateral mean kurtosis were remarkably smaller in individuals with Alzheimer’s disease compared with those with amnestic mild cognitive impairment and normal controls. Further, the mean kurtosis was lower in the amnestic mild cognitive impairment group compared with the normal control group. The mean diffusion in the left hippocampus was lower in the Alzheimer’s disease group than in the amnestic mild cognitive impairment and normal control groups, while the mean diffusion in the right hippocampus was lower in the Alzheimer’s disease group than in the normal control group. Fractional anisotropy was similar among the three groups. These results verify that bilateral mean kurtosis and mean diffusion are sensitive to the diagnosis of Alzheimer’s disease and amnestic mild cognitive impairment. This study was approved by the Ethics Review Board of Affiliated Sixth People’s Hospital of Shanghai Jiao Tong University, China on May 4, 2010 (approval No. 2010(C)-6). 展开更多
关键词 nerve REGENERATION magnetic resonance IMAGING DIFFUSION KURTOSIS IMAGING hippocampus amnestic mild cognitive impairment Alzheimer's disease mean KURTOSIS mean DIFFUSION fractional anisotropy neural REGENERATION
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厂内液氨钢瓶泄漏对应急集合点影响研究 预览
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作者 张小良 宋慧娟 +1 位作者 刘晓晨 刘婷婷 《工业安全与环保》 2019年第4期23-26,共4页
为防止液氨泄漏时造成严重影响,以上海某公司液氨泄漏事故为例,利用Aloha软件对液氨钢瓶在不同风速、泄漏孔径和质量条件下泄漏的扩散范围及规律进行模拟分析,找出厂内应急集合点安全的临界条件和最危险情况下新的应急集合点。结果表明... 为防止液氨泄漏时造成严重影响,以上海某公司液氨泄漏事故为例,利用Aloha软件对液氨钢瓶在不同风速、泄漏孔径和质量条件下泄漏的扩散范围及规律进行模拟分析,找出厂内应急集合点安全的临界条件和最危险情况下新的应急集合点。结果表明,泄漏扩散面积随着风速的增大先减小后逐渐趋于定值;随着钢瓶内液氨储量的增多而持续增大;随着泄漏孔径的增大而增大后逐渐趋于定值;应急集合点只有在风速小于1 m/s时才会受到影响,在最危险情况下,新应急集合点应设在原来应急集合点的北侧105 m。 展开更多
关键词 液氨泄漏 扩散应急集合点
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Effect of Interconnect Linewidth on Evolution of Intragranular Microcracks Due to Electromigration Analyzed by Finite Element Method 预览
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作者 HE Dingni HUANG Peizhen 《南京航空航天大学学报:英文版》 EI CSCD 2019年第2期290-297,共8页
The effect of interconnect linewidth on the evolution of intragranular microcracks due to surface diffusion induced by electromigration is analyzed by finite element method.The numerical results indicate that there ex... The effect of interconnect linewidth on the evolution of intragranular microcracks due to surface diffusion induced by electromigration is analyzed by finite element method.The numerical results indicate that there exists critical values of the linewidth hc,the electric fieldχc and the aspect ratioβc.When h>hc,χ<χc orβ<βc,the microcrack will evolve into a stable shape as it migrates along the interconnect line.When h≤hc,χ≥χc orβ≥βc,the microcrack will split into two smaller microcracks.The critical electric field,the critical aspect ratio and the splitting time have a stronger dependence on the linewidth when h≤6.In addition,the decrease of the linewidth,the increase of the electric field or the aspect ratio is beneficial to accelerate microcrack splitting,which may delay the open failure of the interconnect line. 展开更多
关键词 finite element method surface diffusion ELECTROMIGRATION LINEWIDTH MICROCRACK EVOLUTION
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甲基磺酸溶液中二价锡离子在玻碳电极上的初期沉积行为 预览
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作者 孔德龙 王紫玉 +1 位作者 黎德育 李宁 《电镀与涂饰》 CAS CSCD 北大核心 2019年第7期289-296,共8页
采用循环伏安法和计时电流法对甲基磺酸溶液中二价锡离子在玻碳电极上的初期沉积行为进行研究,考察了二价锡离子浓度、pH、温度和添加剂对二价锡离子初期沉积行为的影响。结果表明:二价锡离子在甲基磺酸溶液中的电沉积按连续成核及受扩... 采用循环伏安法和计时电流法对甲基磺酸溶液中二价锡离子在玻碳电极上的初期沉积行为进行研究,考察了二价锡离子浓度、pH、温度和添加剂对二价锡离子初期沉积行为的影响。结果表明:二价锡离子在甲基磺酸溶液中的电沉积按连续成核及受扩散影响生长的机理进行,该沉积机理不受上述因素的影响。 展开更多
关键词 甲基磺酸 二价锡离子 玻碳电极 电沉积 连续成核 扩散
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On a new modified fractional analysis of Nagumo equation
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作者 Khaled M.Saad Sinan Deniz Dumitru Baleanu 《生物数学学报:英文版》 2019年第3期191-205,共15页
In this work, a new modified fractional form of the Nagumo equation has been presented and deeply analyzed. Using the Caputo–Fabrizio and Atangana–Baleanu time-fractional derivatives, classical Nagumo model is trans... In this work, a new modified fractional form of the Nagumo equation has been presented and deeply analyzed. Using the Caputo–Fabrizio and Atangana–Baleanu time-fractional derivatives, classical Nagumo model is transformed to a new fractional version. The modified equation has been solved by using the homotopy analysis transform method. The convergence analysis has been also examined with the help of the so-called hh-curves and average residual error. Comparing the obtained approximate solution with the exact solution leaves no doubt believing that the proposed technique is very efficient and converges toward the exact solution very rapidly. 展开更多
关键词 Nagumo equation nonlinear diffusion and CONVECTION HOMOTOPY ANALYSIS TRANSFORM method Caputo-Fabrizio-Caputo derivative Atangana-Baleanu-Caputo time-fractional derivatives
噻吩、吡咯、呋喃在H-FAU分子筛中吸附和扩散行为的分子模拟 预览
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作者 党宇 杨晓东 +2 位作者 刘熠斌 冯翔 杨朝合 《石油学报(石油加工)》 EI CAS CSCD 北大核心 2019年第5期911-919,共9页
采用蒙特卡洛方法(GCMC)和分子动力学方法(MD),研究了在823 K、100~1000 kPa条件下噻吩、吡咯和呋喃3种典型的杂原子分子在H-FAU分子筛中吸附和扩散性能,分析了3种分子在H-FAU分子筛中的概率密度分布、分子扩散动力学和径向分布函数(RDF... 采用蒙特卡洛方法(GCMC)和分子动力学方法(MD),研究了在823 K、100~1000 kPa条件下噻吩、吡咯和呋喃3种典型的杂原子分子在H-FAU分子筛中吸附和扩散性能,分析了3种分子在H-FAU分子筛中的概率密度分布、分子扩散动力学和径向分布函数(RDF)。单组分吸附模拟的结果表明,噻吩的饱和吸附量和吸附热最大,吡咯居中,呋喃最小。三元混合组分的吸附模拟表明:噻吩的吸附强度明显大于吡咯和呋喃;3种分子在分子筛的超笼和SOD笼中均有分布,且噻吩在超笼中更加集中;3种分子在孔道中扩散阻力的大小依次为噻吩、吡咯、呋喃;噻吩、吡咯和呋喃主要通过分子环区的离域电子及杂原子与孔道表面H质子进行作用。 展开更多
关键词 杂原子分子 八面沸石(FAU)分子筛 吸附 扩散 分子模拟
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基于Bass模型的4G用户数扩散研究 预览
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作者 李华丽 《科技创新与应用》 2019年第30期11-12,15共3页
目前4G仍是我国主流的通信技术,但随着5G正式商用的启动,4G可能会逐步进入产品生命周期的后半程,需要预测4G用户规模未来几年的发展状况,以便更好的制定市场策略。文章采用Bass扩散模型对4G用户扩散过程进行了参数估计,并根据模型模拟... 目前4G仍是我国主流的通信技术,但随着5G正式商用的启动,4G可能会逐步进入产品生命周期的后半程,需要预测4G用户规模未来几年的发展状况,以便更好的制定市场策略。文章采用Bass扩散模型对4G用户扩散过程进行了参数估计,并根据模型模拟了我国4G用户的扩散过程,判断出目前4G用户数发展的速度开始下降,用户数增量有限,已进入存量经营阶段,预测结果也为今后5G用户扩散过程的研究提供了参考。 展开更多
关键词 BASS模型 4G用户 扩散 研究
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河北邢台市连续重污染天气维持与消散成因分析 预览
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作者 齐佳慧 郝巨飞 +1 位作者 王丛梅 杨允凌 《沙漠与绿洲气象》 2019年第1期122-129,共8页
利用环境监测数据、气象常规观测数据及NCEP的GDAS气象数据与HYSPLIT后向轨迹模式结合,通过对天气形势、垂直与水平输送、降水因子及污染物来源等因素进行分析,探讨了2016年12月16日—2017年1月9日河北省邢台市连续重污染天气维持及消... 利用环境监测数据、气象常规观测数据及NCEP的GDAS气象数据与HYSPLIT后向轨迹模式结合,通过对天气形势、垂直与水平输送、降水因子及污染物来源等因素进行分析,探讨了2016年12月16日—2017年1月9日河北省邢台市连续重污染天气维持及消散阶段的成因。结果表明:此次连续重污染过程在静稳的大气层结与地面均压场下,污染物容易积累,大气混合层高度与AQI值呈负相关,AQI<200时,大气混合层平均高度为1305m,AQI>200时,大气混合层平均高度为763m,最低降到437m;地面风场的辐合、强的逆温层结、高湿和静小风是重污染天气过程维持的关键,连续重污染过程中,小风(风速<3m/s)日数达22d(占比85%),平均逆温层厚度443m、强度1.83℃/100m,平均相对湿度82.6%,导致污染物极易生成又不容易向高空扩散;降水与冷空气活动对污染物的消散起到一定作用,降水量>3mm时,清除率可达40%以上,降水量<1mm时,污染物浓度反而会增加;结合污染物来源分析,在空气重污染维持阶段50%以上的气团来自距邢台市200km以内的局地输送,高空远距离干洁空气的输送对污染物的消散起到有效的作用。 展开更多
关键词 天气形势 气象条件 重污染 维持 消散
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MCrAlY涂层对单晶中γ'相消耗及TCP相生成影响的模拟研究 预览
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作者 原慷 于月光 +1 位作者 刘建明 章德铭 《热喷涂技术》 2019年第1期23-29,共7页
高温下,MCrAlY涂层与高温合金单晶基材之间会发生元素互扩散,引起显微组织结构变化,往往造成单晶中具有析出强化作用的γ'相的消耗和对力学性能有害的拓扑密堆(Topological closed packed,TCP)相的生成。本研究采用扩散模拟计算的方... 高温下,MCrAlY涂层与高温合金单晶基材之间会发生元素互扩散,引起显微组织结构变化,往往造成单晶中具有析出强化作用的γ'相的消耗和对力学性能有害的拓扑密堆(Topological closed packed,TCP)相的生成。本研究采用扩散模拟计算的方法,设计了 6种 MCrAlY模型涂层,分析 Co、Cr、Al主元素对 DD6单晶基材显微组织的影响规律。研究结果表明,基材中γ'相消耗区在靠近涂层-基材界面处形成,该区的形成主要与 Co、Cr元素内扩散相关。基材中 TCP相则在更深位置的γ'相富集区内生成,γ'相富集区与 Al元素内扩散有关。另外,本文着重分析了涂层成分对γ'相消耗区深度及 TCP相生成含量与深度的影响。 展开更多
关键词 单晶 扩散 γ'相消耗 TCP相
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Effect of Deposition Time on Thickness and Corrosion Behavior of Zn-Fe Coating
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作者 刘丽 于思荣 《上海交通大学学报:英文版》 EI 2019年第3期395-401,共7页
Zn-Fe coatings on Q235 steel are prepared by pack cementation process at 390 ℃ for 2,4,6,8 and10 h to investigate the effects of the deposition time on the thickness and corrosion behavior of the Zn-Fe coatings.The t... Zn-Fe coatings on Q235 steel are prepared by pack cementation process at 390 ℃ for 2,4,6,8 and10 h to investigate the effects of the deposition time on the thickness and corrosion behavior of the Zn-Fe coatings.The thickness of the coating increases with the increase of the deposition time.The coating is composed of a thick outer layer and a thin inner layer.The formation of the coating depends on the inward diffusion of Zn atoms and the outward diffusion of Fe atoms.The outer layer is composed of Fe11 Zn40 and FeZn10 phases.The corrosion behavior of the Zn-Fe coatings is evaluated by immersion test and polarization test.The results show that the Zn-Fe coatings can effectively prevent the Q235 steel from corrosion.The corrosion resistance of the coating is proportional to the deposition time. 展开更多
关键词 Zn PACK CEMENTATION thickness DIFFUSION corrosion resistance
熔融沉积3D打印材料粘接强度及模量预测研究 预览
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作者 张黎 王新宇 +3 位作者 李征 谷俊峰 阮诗伦 申长雨 《化工学报》 EI CAS CSCD 北大核心 2019年第7期2727-2736,F0004共11页
主要介绍了一种用于预测熔融沉积模型(FDM)层间粘接强度的扩散修复模型。根据流变数据确定温度相关扩散模型,基于一维瞬态热分析预测FDM部件层间的扩散。将温度历史上的扩散系数对时间积分得到界面分子总扩散,进而得到层间粘接强度预测... 主要介绍了一种用于预测熔融沉积模型(FDM)层间粘接强度的扩散修复模型。根据流变数据确定温度相关扩散模型,基于一维瞬态热分析预测FDM部件层间的扩散。将温度历史上的扩散系数对时间积分得到界面分子总扩散,进而得到层间粘接强度预测模型。结果表明:不同打印条件下预测结果与测得的粘合强度结果的吻合度较好,且该模型经修正后也适用于FDM部件弹性模量的预测。通过三点弯曲实验与数值模拟的结果对比,验证了粘接强度及模量预测模型的可用性。因此,可以作为FDM打印件承载性能预测的有效模型。 展开更多
关键词 聚合物 熔融沉积成型 层间粘接性能预测 扩散 数值模拟
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基于CFD的埋地天然气管道泄漏扩散数值分析 预览
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作者 张伯扬 马贵阳 +2 位作者 王凯 黄梦杰 陈树军 《辽宁石油化工大学学报》 CAS 2019年第1期39-43,共5页
受地质灾害、腐蚀缺陷、第三方破坏等因素的影响,油气管道在安全运输方面存在诸多隐患,因此研究埋地天然气管道泄漏扩散规律对泄漏点预测定位、应急预案制定具有重要的现实意义。通过对埋地天然气管道泄漏扩散过程进行数值模拟,分析了... 受地质灾害、腐蚀缺陷、第三方破坏等因素的影响,油气管道在安全运输方面存在诸多隐患,因此研究埋地天然气管道泄漏扩散规律对泄漏点预测定位、应急预案制定具有重要的现实意义。通过对埋地天然气管道泄漏扩散过程进行数值模拟,分析了泄漏速度、风速以及环境温度对CH4体积分数的影响,总结了扩散规律。研究结果可为埋地天然气管道泄漏点准确定位及应急预案提供理论支撑。 展开更多
关键词 埋地管道 泄漏 扩散 数值分析
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低渗气藏CO2驱与埋存的数值模拟 预览
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作者 郭平 李雪弘 +2 位作者 孙振 王少飞 杜建芬 《科学技术与工程》 北大核心 2019年第23期68-76,共9页
为揭示低渗气藏中注CO2提高气藏采收率和CO2埋存(carbon sequestration with enhanced gas recovery,CSEGR)技术的效果,以苏里格气田召10区块为例,开展了注CO2驱气的长岩心实验,并使用数值模拟的研究手段,分析了该区块采用CSEGR技术的... 为揭示低渗气藏中注CO2提高气藏采收率和CO2埋存(carbon sequestration with enhanced gas recovery,CSEGR)技术的效果,以苏里格气田召10区块为例,开展了注CO2驱气的长岩心实验,并使用数值模拟的研究手段,分析了该区块采用CSEGR技术的可行性,并重点研究了扩散、吸附、天然裂缝、井型对于CO2突破时间、气藏采收率及CO2埋存的影响。模拟结果表明:采用面积为3.2km^2的平行四边形“二注七采”井网,在气藏衰竭开采至12MPa后注CO2,在CO2突破时能够提高采收率14.26%,共能实现3.8×10^6t的CO2埋存;在废弃压力3MPa时注入CO2采收率仅能增加2.2%,但CO2埋存量可提高至1.44倍;在低渗气藏中扩散和吸附对于CO2驱的影响不大;随着扩散系数增大,CO2突破越快,提高采收率效果越差;吸附滞后现象会略微降低提高采收率的效果;天然裂缝的存在会使气窜现象严重,突破时间大大提前,且裂缝渗透率越高,提高采收率效果越差,但依然可以实现CO2安全稳定埋存;与直井相比,采用水平井注气将使提高采收率效果降低6%~8%,但对埋存有利。 展开更多
关键词 注CO2 低渗气藏 扩散 吸附 吸附滞后 天然裂缝 井型
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