Totally found 191673 items.

  • [学位] 多分散聚合物体系的统计热力学及其相图的理论计算
    成功地预测聚合物混合体系相行为,可以指导聚合物材料的设计和加工。从上个世纪四十年代开始,对聚合物混合体系相行为的研究就成为了高分子科学家们研究的热点之一。同时,由于多分散性是聚合物中普遍存在的特性,它对聚合物溶液或共混物体系的液-液相平衡行为有着显著的影响。因此,研究多分散性对聚合物体系相行为的影响有着重要的理论意义和现实应用价值。 典型的处理聚合物体系多分散性的方法主要有两种,即离散的多组分方法和连续的泛函方法。多组分方法是将多分散体系看作是一个由有限个亚组分组成的体系。基于经典的Gibbs统计热力学,通过求解行列式推导出多分散聚合物体系的Spinodal以及临界点表达式。对于含亚组分较少的体系,该方法比较适用,能够给出一些有意义的结果;但对于含有很多个亚组分的体系,不仅计算耗时,而且往往由于计算的截断误差而影响计算结果的精度。泛函方法是把多分散体系看作是由连续无限的单元组成的,聚合物的分子量分布通过某种连续函数表征。然而,聚合物的基本单元——单体是具有一定的尺寸的,因此该方法的可靠性还需要用离散方法来验证。但由于其数学上具有完备性,能够大大的缩短计算时间,也得到了很大的发展和应用。 本论文是在经典的Flory-Huggins(FH)格子理论基础上,通过引入FH相互作用参数对聚合物链长的依赖关系,分别采用上述两种方法系统地研究了多分散性对聚合物混合体系相行为的影响。 首先,我们用多组分处理方法,推导出了多分散聚合物-小分子溶剂体系Spinodal条件的通用表达式。计算了在不同链长及链长分布下模型体系的Spinodal曲线。结果表明:聚合物链长分布形式,数均、重均以及 均链长都对多分散聚合物溶液体系的Spinodal有影响,其中,重均链长的影响最为显著。随着链长分布的变宽,体系的相分离区域增大。当链长增加到一定程度时,多分散性对Spinodal的影响可以忽略。 其次,我们利用多组分方法计算了多分散聚合物溶液体系的临界点,并讨论了多分散性对它的影响。对于所研究的模型体系,聚合物链长具体分布,数均、重均以及 均链长都对多分散聚合物溶液体系的临界点有影响,其中数均链长的影响最弱。随着多分散指数的增加,体系的临界浓度增大。同样,当链长增加到一定程度时,多分散性对临界点的影响就可以忽略了。 此外,我们还运用多组分方法,研究了多分散性对聚合物共混体系Spinodal行为的影响。结果同样表明聚合物链长具体分布形式,数均、重均以及 均链长都对多分散聚合物共混
    关键词: Flory-Huggins理论;多分散性;Spinodal;临界点;多组分方法;泛函方法
  • [学位] 区域住宅地产投资环境综合评价方法研究——以重庆市为例
    房地产投资是一项时间长、资金需求量大、涉及对象多、风险大的活动,所以在进行投资前,投资者必须慎重把握投资环境,以制定正确的投资方案;政府必须采取措施改善当地房地产投资环境,以吸引更多投资者。我国区域房地产市场存在发展不均衡问题,且住宅地产因与人民生活紧密相关,而受到国家重点关注与调控,对区域住宅地产的投资环境研究具有实践意义。 论文结合区域投资环境与住宅地产二者的交叉点,对我国区域住宅地产投资环境进行研究。在界定研究对象相关概念、分析投资环境研究的理论基础之上,运用主成分分析法、熵权法、聚类分析法等进行复合分析。首先,在文献法梳理指标的基础上,利用主成分分析法剔除对结果影响不大的指标,进行指标归类,建立房地产投资环境指标体系;其次,利用主成分分析法和熵权法对各指标进行赋权,建立区域住宅地产投资环境评分体系,并对目标区域各区县的子环境和总体环境评分;最后,利用聚类分析法对区域住宅地产投资环境现状进行分类,并通过横向及纵向比较,分析投资环境相对变化情况。 通过以上过程构建区域住宅地产投资环境评价体系,并以重庆市为例对方法进行说明和验证。结论部分阐述了论文的研究结果。结果显示,首先,我国住宅地产发展不均衡,体现在不同区域发展不均衡和不同能级城市之间发展不均衡,前者将导致不同区域投资环境差距增大,后者将导致回波效应,两者均不利于我国城镇化发展的均衡稳定推进,应改善这种情况以促进住宅地产市场的发展,进而改善人民生活水平。其次,住宅地产投资环境研究不全面,在指标选取上有所偏颇、研究范围上有所缺失、研究体系上不够系统。应强化房地产投资环境研究的理论体系构建,以对其做出全面系统、科学合理的评价。最后,以重庆市为例对评价方法进行案例分析,说明方法在指标选取、指标赋权、体系构建等方面能够较为全面地还原和分析重庆市住宅地产投资环境,且能通过结果分析提出改善区域住宅地产投资环境的有效办法。 构建一套简单高效的区域住宅地产投资环境综合评价方法,有助于投资者充分了解区域投资环境,以选择合理区域并采取适当措施进行投资活动,也有助于政府充分把握投资环境现状,进而增强区域住宅开发市场的吸引力,以促进人民生活水平的提高,和我国城镇化的均衡稳定发展。
    关键词: 区域住宅地产;房地产市场;投资环境;主成分分析法;熵权法;均衡发展
  • [学位] 煤矿水灾害救治系统研究
    煤矿水灾害是我国煤矿建设和生产中的主要灾害之一,它严重威胁着职工的生命安全,同时还给国家和企业财产造成巨大损失。及时、高效、安全、可靠和经济性地对煤矿水灾害进行救治是国内外有关领域急需研究的重要课题。本文从管理学的角度出发,运用系统分析、系统集成和系统管理等理论和方法,对煤矿水灾害救治系统进行了深入的研究,旨在从整体上提高煤矿水灾害救治的效率、可靠性和经济性。 本文在以下方面进行了深入研究: 1、在对煤矿水灾害救治过程实体关系研究的基础上,提出了煤矿水灾害救治的系统模式,分析了该系统的目标、要素和特点,并把该系统和一般的生产系统进行比较,揭示了该系统的特殊性和复杂性。 2、在对现有煤矿水灾害救治流程分析和重组的基础上,将煤矿水灾害救治系统分为灾前准备子系统、灾情救治子系统和灾后处理子系统,并建立了煤矿水灾害救治系统的运作模型。 在灾前准备子系统中,本文提出建立专家信息库和社会救治资源信息库的设想,并运用客户关系管理(CRM)的理念,建立煤矿水灾害救治呼叫中心; 在分析库存成本的基础上,提出了煤矿水灾害救治能力水平的概念,并对其与库存成本的关系进行分析,对科学合理地储备救灾物资具有指导意义; 在灾后处理子系统中,提出了以人为本的灾害善后工作思路和基于知识积累的可持续救灾观。 3、建立了狭义煤矿水灾害救治系统的功能结构模型,将整个系统划分为主排水系统和辅助系统,对各功能模块进行了详细的分析研究。把主排水系统的供水系统作为一项单独的子系统来研究,发展了接力排水的思想,开发出了接力排水系统和斜井无轨道悬浮式排水系统,解决了无井底水窝及无轨道条件下的煤矿水灾害快速救治的难题。 4、提出煤矿水灾害救治系统集成的思想,分别对煤矿水灾害救治系统的管理和信息进行集成,设计了系统的信息集成模式和管理集成模式。在管理集成过程中,考虑了功能结构的实现和运作的实现。 5、对系统的可靠性进行研究,通过评价、优化,进一步提升系统的整体性能。运用特征线法对煤矿水灾害救治系统的主系统安全运行工况进行计算分析,从理论上对煤矿水灾害救治主系统停机时的水力过渡过程进行了描述,为实际工作中煤矿水灾害救治系统的设计和控制提供了理论依据,为评价抢险救灾系统的装备可靠度提供计算方法。特别地,由于水灾害救治系统的特殊需要,应用可拓评价方法对系统的可靠性进行评价。 6、对煤矿水灾害救治系统的经济性管理进行研究,提出了改善系统经济性的建设性意见。煤矿水灾害救治主系统的性能设计中有一个高效运行区,主系统在动态工况工作条件下的运行效率关乎煤矿水灾害救治系统的经济性,本文建立了煤矿水灾害救治主系统的运行数学模型,利用电算法对主系统不同工况条件下的运行经济性进行了仿真计算,得出了满意的结果。
    关键词: 煤矿水灾害;救治系统;集成模式;可靠性
  • [学位] Activated Carbon Preparation and Modification for Adsorption
    Butanol is considered a promising, infrastructure-compatible biofuel. Butanol has a higher energy content than ethanol and can be used in conventional gas engines without modifications. Unfortunately, the fermentation pathway for butanol production is restricted by its toxicity to the microbial strains used in the process. Butanol is toxic to the microbes, and this can slow fermentation rates and reduce butanol yields. Gas stripping technology can efficiently remove butanol from the fermentation broth as it is produced, thereby decreasing its inhibitory effects. Traditional butanol separation heavily depends on the energy intensive distillation method. One of the main issues in acetone-butanol-ethanol fermentation is that butanol concentrations in the fermentation broth are low, ranging from 1 to 1.2 percent in weight, because of its toxicity to the microorganisms. Therefore distillation of butanol is even worse than distillation of corn ethanol. Even new separation methods, such as solid- extraction methods involve adding substances, such as polymer resin and zeolite or activated carbon, to biobutanol fermentatioon broth did not achieve energy efficient separation of butanol due to low adsorption selectivity and fouling in broth. Gas-stripping - condensation is another new butanol recovery method, however, the butanol in gas-stripping stream is too low to be condensed without using expensive and energy intensive liquid nitrogen. Adsorption can then be used to recover butanol from the vapor phase. Activated carbon (AC) samples and zeolite were investigated for their butanol vapor adsorption capacities. Commercial activated carbon was modified via hydrothermal H2O2 treatment, and the specific surface area and oxygen-containing functional groups of activated carbon were tested before and after treatment. Hydrothermal H2O 2 modification increased the surface oxygen content, Brunauer-Emmett-Teller surface area, micropore volume, and total pore volume of active carbon. The adsorption capacities of these active carbon samples were almost three times that of zeolite. However, the un-modified active carbon had the highest adsorption capacity for butanol vapor (259.6 mg g-1), compared to 222.4 mg g-1 after 10% H2O2 hydrothermal treatment. Both modified and un-modified active carbon can be easily regenerated for repeatable adsorption by heating to 150 °C. Therefore, surface oxygen groups significantly reduced the adsorption capacity of active carbons for butanol vapor. In addition, original active carbon and AC samples modified by nitric acid hydrothermal modification were assessed for their ability to adsorb butanol vapor. The specific surface area and oxygen-containing functional groups of AC were tested before and after modification. The adsorption capacity of unmodified AC samples were the highest. Hydrothermal oxidation of AC with HNO3 increased the surface oxygen content, Brunauer-Emmett-Teller (BET) surface area, micropore, mesopore and total pore volume of AC. Although the pore structure and specific surface area were greatly improved after hydrothermal oxidization with 4 M HNO3, the increased oxygen on the surface of AC decreased the dynamic adsorption capacity. In order to get high adsorption capacity adsorbents, we used corn stalk as precursor to fabricate porous carbon. ACs were prepared through chemical activation of biochar from whole corn stalk (WCS) and corn stalk pith (CSP) at varying temperatures using potassium hydroxide as the activating agent. ACs were characterized via pore structural analysis and scanning electron microscopy (SEM). These adsorbents were then assessed for their adsorption capacity for butanol vapor. It was found that WCS activated at 900 °C for 1 h (WCS-900) had optimal butanol adsorption characteristics. The BET surface area and total pore volume of the WCS-900 were 2330 m2 g-1 and 1.29 cm3 g-1, respectively. The dynamic adsorption capacity of butanol vapor was 410.0 mg g-1, a 185.1 % increase compared to charcoal-based commercial AC (143.8 mg g -1). Based on the adsorption experiments of butanol vapor, we found the chemical properties of the AC surface play an important role in adsorbing molecules. The adsorption of creatinine on active carbons was also studied, which is a toxic compound generated by human. High levels of creatinine in the blood stream is normally caused by malfunction or failure of the kidneys. Activated carbons is taken by the patients orally to reduce creatinine level. In order to figure out whether chemical modification could increase the adsorption capacity of creatinine, AC samples modified by nitric acid hydrothermal modification were assessed for their ability to adsorb creatinine. The pore structure and surface properties of the AC samples were characterized by N 2 adsorption, temperature programmed desorption (TPD), Fourier Transform Infrared spectroscopy (FTIR), and X-ray photoelectron spectrometer (XPS). It indicated that 4M HNO3 hydrothermal modification with 180 °C was an efficient method in improvement of the creatinine adsorption. The improved adsorption capacity can be attributed mainly to an increase in the acidic oxygen-containing functional groups. The adsorption of creatinine over AC may involve an interaction with the acidic oxygen-containing groups on AC. Langmuir and Freundlich adsorption models were applied to describe the experimental isotherm and isotherm constants. Equilibrium data fitted very well to the Freundlich model in the entire saturation range (3.58-59.08 mg L-1 ). The maximum adsorption capacities of AC modified with 180 °C is 62.5 mg g-1 according to the Langmuir model. Pseudo first-order and second-order kinetic models were used to describe the kinetic data and the rate constants were evaluated. The experimental data fitted well to the second-order kinetic model, which indicates that the chemical adsorption was the rate-limiting step, instead of mass transfer. (Abstract shortened by ProQuest.). ProQuest Subject Headings: Chemical engineering, Materials science.
    关键词: Gas adsorption (major);Acetone;Activated carbon;Adsorption;Agricultural engineering;Charcoal;Chemical activation;Chemical engineering;Chemical modification;Coal tar;Distillation;Dyes;Energy efficiency;Ethanol;Fermentation;Fourier transform infrared spectroscopy;Isotherms;Kinetic parameters;Kinetic theory;Kinetics;Mass transfer;Materials science;Microorganisms;Microporosity;Nitric acid;Nitrogen;Oxygen;Pore structure;Porous materials;Rate constants;Reaction kinetics;Scanning electron microscopy;Separation;Specific surface area;Spectrometers;Temperature programmed desorption;Toxicity;Zeolites
  • [学位] DNA修复基因RAD51与MSH2合成致死作用研究——RI-1对MMR缺陷结直肠癌细胞的杀伤作用
    目的:探究同源重组修复蛋白RAD51抑制剂RI-1对错配修复基因MSH2缺陷结直肠癌细胞系的杀伤作用,并初步探索RAD51和MSH2二者之间的作用机制。 方法:采用Western blot法筛选MSH2差异表达的结直肠癌细胞系;MTT法检测不同结直肠癌细胞系对RI-1(10、20、30、40或50μmol/L)的敏感性;同时构建针对MSH2基因的重组shRNA慢病毒表达载体并感染HT29细胞,并采用MTT法检测MSH2敲降前后的结直肠癌细胞系对RI-1(10、20、30、40或50μmol/L)的敏感性。最后,选取40μmol/L RI-1处理MSH2差异表达的结直肠癌细胞,流式细胞术法或TUNEL法分析细胞凋亡的变化;单细胞凝胶电泳实验检测细胞内DNA损伤情况;细胞免疫荧光实验检测细胞内γ-H2AX foci的形成。 结果:一、HCT8细胞MSH2表达水平明显低于野生型HT29细胞,两者对RI-1的敏感性不同,且HCT8细胞在RI-1作用下发生明显的细胞凋亡现象(P<0.01);二、改变HT29细胞同源性MSH2表达水平,发现MSH2敲降的HT29shMSH2细胞与对照组相比对RI-1更敏感,且与对照组比较有明显的细胞凋亡现象;三、HCT8细胞和HT29shMSH2细胞尾部DNA含量、尾长和尾距及细胞内γ-H2AX foci的形成数量与对照组相比,均有显著性增加(P<0.05)。 结论:RAD51抑制剂RI-1对MSH2缺陷结直肠癌细胞具有杀伤作用,这种杀伤作用可能是通过增加细胞内DNA损伤发生的。
    关键词: 结直肠癌;重组蛋白A;错配修复基因;细胞凋亡
  • [学位] 有限流道内钝体-压电片系统能量转换特性实验研究
    钝体是在生活中随处可见的一种非流线型的结构体,钝体绕流是自然界中普遍存在的一种物理现象,这种看似简单的物理现象实际上包含了极其复杂的流动机理。当钝体的固定方式为弹性支撑或者允许发生形变的时候,钝体两侧因旋涡脱落而产生的脉动作用力会使钝体产生周期性的振动,振动的钝体会对其周围流场产生进一步的影响,这种流体与钝体之间相互影响和作用被称为流致振动(Flow-induced motion,FIM)。在工程领域中,结构体在流致振动的影响下持续受力产生振动进而出现疲劳破坏,同时也说明了这种现象本身具有较多可以利用的能量。由于流致振动及钝体绕流中旋涡脱落在低速来流条件下就会发生,如能利用旋涡脱落时引起的振动进行发电,相比传统的发电技术,这类装置中将不存在任何转动部件,没有滑动或滚动摩擦,更适合将装置微型化。 本文主要针对不同截面形状钝体和不同压电片参数的钝体-压电片系统进行了风洞实验研究,分析系统输出电压、输出电压频率及平均峰值电压曲线,了解钝体截面形状和压电片长度对钝体-压电片系统能量输出特性的影响,为利用钝体-压电片系统进行能量收集提供一定的理论依据。获得的主要结论如下: 首先针对不同长度压电片的方柱-压电片系统进行了风洞试验,研究了压电片长度对方柱-压电片系统能量收集特性的影响。实验发现来流速度对方柱-压电片系统的输出电压有直接影响。随着来流速度的增大,压电片自由端的振幅增加,振动频率减小。在压电片长度较短时,其振动频率与方柱尾涡脱落频率相近或相等时会出现共振现象,输出电压会急剧上升。随风速增加,在共振点之后会出现一个输出电压稳定的过渡区域。当压电片靠近固定端的部分开始参与振动时,标志着过渡阶段的结束,风速达到临界风速,输出电压再次出现快速增长。 然后,本文对前端钝体为三角柱、梯形柱和反向梯形柱的钝体-压电片系统进行了风洞实验,研究了前端钝体截面形状对系统输出电压的影响。研究结果表明钝体形状是钝体-压电片系统输出电压的重要影响因素。钝体形状发生改变时,钝体周围流动边界层发生分离以及旋涡脱落的位置都不尽相同。三角柱和梯形柱-压电片系统的流动边界层在背风面棱边处发生分离并脱落,且脱体旋涡不再受钝体影响而直接作用在压电片上。反向梯形柱和方柱-压电片系统的流动边界层都是在迎风封面处发生分离。由于反向梯形柱在迎风面后方垂直于钝体来流方向的宽度一直在减小,对在迎风面棱边处发生分离的边界层影响减弱,减少了对旋涡形成和脱落的阻碍,其电压输出表现强于方柱-压电片系统。 综合本文的研究结论,反向梯形柱-压电片系统电压输出在各个工况下的表现都比较好,尤其是在高风速下的表现尤为突出,最大平均峰值电压Vpeak=1.829V,此时输出功率为P=1.67μW。
    关键词: 钝体-压电片系统;流致振动;有限流道;能量转换;输出电压
  • [学位] Carbon Nanotubes-Based Lateral Flow Biosensor for Sensitive and Rapid Detection of DNA Sequence
    Sensitive detection for DNA has drawn great attention in plenty of different areas such as genetics therapy and basic discovery research. Recently, nucleic acid lateral flow biosensor (NALFB) has gained considerable attention for DNA analysis. Compared with the traditional immunoassays, NALFB has these advantages: short assay time and a low cost. In this thesis, we report a carbon nanotubes (CNTs)-based NALFB for rapid and sensitive detection of DNA. Amine-modified DNA detection probe was covalently immobilized on the CNTs via diimide-activated amidation between the carboxyl groups on the CNTs surface and amine groups on the detection DNA probes. Sandwich-type DNA hybridization reactions were performed and the captured MWCNTs on test zone and control zone produced the characteristic black bands. Based on the catalytic property of CNTs to enhance the Chemiluminescence intensity of the reaction between hydrogen peroxide and Lumigen APS-5, a rapid detection of DNA sequence with high sensitivity is achieved.
    关键词: Pure sciences
  • [学位] 不同覆盖方式对砂壤土水盐运移规律影响研究
    西北地区降雨稀少,蒸发强烈,土壤水分易通过大气蒸发而损失,水分难以保持。而土壤表面采用覆盖处理可避免土壤直接与空气接触,减小因蒸腾作用造成的水分损失,改变表层土壤的结构和理化性质,进而影响到土壤水分入渗、蒸发和盐分运移的过程。本研究拟通过室内外模拟实验,设覆砂(S)、覆膜+覆砂(MS)、覆砂+覆秸秆(SJ)、覆膜+覆秸秆(MJ)和无覆盖(CK)这5种方式,对不同覆盖方式下砂壤土水盐运移规律展开对比研究。主要内容有: (1)通过室内土柱模拟实验,对比研究了不同覆盖方式对砂壤土水分入渗规律的影响。结果表明:土壤表面采用覆盖处理会影响湿润锋推进距离与累积入渗量,抑制土壤水分的入渗能力,对水分入渗具有一定阻渗作用,其表现为覆膜+覆砂最强,覆膜+覆秸秆次之,其次为覆砂+覆秸秆,覆砂最弱。同时,土壤水分入渗形成湿润锋的推进距离与时间符合幂函数关系,相关系数介于0.9930~0.9991;土壤水分累积入渗量与时间符合Kostiakov入渗公式,相关系数介于0.9916~0.9980;湿润锋推进距离与累积入渗量符合线性关系,相关系数介于0.9991~0.9999。 (2)通过室外蒸发模拟实验,对比研究了不同覆盖方式对砂壤土水分蒸发规律的影响。结果表明:土壤表面采用覆盖处理的蒸发变化趋势和 CK的基本一致,只是覆盖处理的蒸发变化趋势较平缓,CK处理的蒸发变化趋势起伏较大。同时,覆盖处理的累积蒸发量均小于小于CK的,S、MS、SJ、MJ和CK处理的累积蒸发量分别为450.6g、375.1g、712.2g、473.3g和1823.6g,与CK相比,覆盖处理的累积蒸发量分别减小了75.30%、79.40%、60.90%、74.00%,表明土壤表面采用覆盖处理会对土壤水分的蒸发产生抑制作用。土壤水分累积蒸发量与时间符合对数关系,相关系数介于0.9243~0.9800。 (3)通过在5块面积均为1m2的正方形小区域内进行的室外模拟实验和室内土柱模拟实验,对比研究了不同覆盖方式对砂壤土水盐运移规律的影响。结果表明:土壤表面采用不同覆盖处理均具有明显的蓄水保墒效果,其保水效果为MS>SJ>S>MJ。同时,土壤表面采用的覆盖处理也能有效抑制土壤盐分向表层积聚,并对土壤盐分的垂向运移范围产生影响。有覆盖处理的土壤盐分的运移主要在0~20cm范围内发生,无覆盖处理的土壤盐分的运移主要在0~35cm范围内发生。这对改良盐渍化土壤和防治土壤的次生盐渍化有着重要的意义。 (4)通过室内外模拟实验,对比分析了土壤表面采用不同覆盖处理对土壤水分入渗、蒸发和盐分运移规律的影响,以及考虑到实验区气候特征和该地区砂石资源容易获取的特点,认为砂石覆盖方式是更适合西北地区的覆盖方式。
    关键词: 覆盖方式;砂壤土;水盐运移;水分入渗;理化性质
  • [学位] 基于动态背景下的运动目标检测与跟踪技术研究
    目标检测与跟踪是计算机视觉领域中一个热点课题,在交通情况监控、室内安全防护、公共安全预警等领域的应用极其广泛,该课题研究需要结合图像处理和模式识别相关知识。传统的检测与跟踪算法使用人工特征提取方法获取目标特征,但是由于实际应用中存在背景环境的复杂多变以及动态背景情况,上述算法存在诸多不足,极大限制了应用范围。 本文基于国内外目标检测与跟踪领域的研究现状,总结了目标检测与跟踪算法框架模型,针对传统目标检测与跟踪算法准确率低、鲁棒性较差的缺点,提出了一种基于深度神经网络的目标检测与跟踪方法。同时为了解决现有卷积神经网络目标检测与跟踪算法存在网络模型过于复杂以及训练时间长的缺陷,本文利用卷积神经网络和自编码神经网络,将目标检测和跟踪任务分为相互联系的两大步骤: (1)前景目标区域提取。 (2)前景目标识别与分类。在前景目标区域提取过程中,本文基于自编码神经网络提出一种目标区域提取网络,通过上述网络结构对视频序列中的每帧图像中的前景目标进行分割,得到一系列比较宽泛的前景目标区域。 而在前景目标识别与分类阶段,本文基于卷积神经网络结构和空间金字塔采样方法提出一种目标检测与跟踪方法,对(1)步骤中提取的目标区域利用已经训练好的网络模型进行分类识别,将目标检测与跟踪任务转换为目标分类识别任务,最终得到输入图像数据的前景目标的检测与跟踪结果。 为了验证本文所述算法的可行性和算法性能,本文使用斯坦福大学SBD数据集以及部分互联网数据作为训练数据集和测试数据集,通过人工标注前景目标,统计本文方法以及传统目标检测算法的检测结果,并且根据应用需求不同分别采用基于分类器评价标准和基于检测效果评价标准,对前景目标区域提取效果和前景目标识别与分类结果进行评价,可以得到本文算法相对于传统目标检测算法较大幅度提高了检测精度并且增强了系统的鲁棒性。而相对于现有卷积神经网络目标检测与跟踪算法大幅度缩减了模型训练时间,降低了系统的硬件环境要求,提高了系统运行速度,可以满足大部分应用场景对实时性的要求。
    关键词: 目标检测;动态跟踪;特征提取;卷积神经网络;自编码神经网络
  • [学位] Gendered pathways in higher education: Change and stability in the pursuit of a science degree
    This dissertation examines cohort changes in young women's and men's intentions to pursue science majors and achievements of a science degree between the 1970s and 1990s. The National Longitudinal Study of High School Seniors of 1972 (1972--1979) and the National Education Longitudinal Study 1988 (1992--2000) are used to test Jacobs' argument that young women's success in science majors is hampered by a life-long process of social control. Gender socialization teaches boys and girls to expect different rewards and responsibilities from work and family. Consequently, as young women and men make decisions about their educational and career pursuits, they do so in gender-specific ways (Jacobs 1989; 1995; 2003). I test Jacobs' social control hypothesis by examining changes in how adolescents' early valuation of family affects young women's and men's intentions to pursue science and achievement of a science degree in the 1970s and 1990s. In the 1970s, family commitment operated in a gender-specific way, hampering only young women's science intentions and achievements, but not significantly affecting men's. By the 1990s, both young men's and women's science intentions are dampened by their commitment to family. However, young women's science achievements continue to be hindered by their valuation of family, while men's science success is not similarly affected. My findings indicate some convergence in the effect of family commitment on young women's and men's plans to major in science, but also suggest the resilience of gender in shaping young adults' science achievements. The second part of this dissertation uses the NELS to examine social-psychological mechanisms that reproduce contemporary gender segregation of college majors. Competing explanations of gender segregation in academic majors are examined: the perceived competency (Correll) and social control (Jacobs) hypotheses. Specifically, I assess the influence of math efficacy and valuation of family on adolescents' intended college majors and their earned degrees. Majors are categorized as: traditionally female majors, non-physical sciences, social sciences, business, and physical science/engineering. My results suggest that math-efficacy promotes adolescents' science intentions and achievements, but does not explain the gender segregation of majors. Instead, early orientations toward family are essential to understanding contemporary gender segregation of academic majors.
    关键词: Sociology;Higher education;Womens studies
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