检索结果-南通市图书馆

Photocatalytic syngas synthesis from CO_(2) and H_(2)O using ultrafine CeO_(2)-decorated layered double hydroxide nanosheets under visible-light up to 600 nm

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Frontiers of Chemical Science and Engineering 2021年第1期15卷 99-108页

作者： Ling Tan kipkorir peter Jing Ren Baoyang Du Xiaojie Hao Yufei Zhao Yu-Fei Song State Key Laboratory of Chemical Resource Engineering Beijing University of Chemical TechnologyBeijing 100029China

The rational design of photocatalyst that can effectively reduce CO_(2) under visible light(l>400 nm),and simultaneously precise control of the products syngas(CO/H2)ratio is highly desirable for the Fischer-Tropsch *** this work,we synthesized a series of CeO_(2)-decorated layered double hydroxides(LDHs,Ce-x)samples for photocatalytic CO_(2) *** was found that the selectivity and productivity of CO and H_(2) from photoreduction of CO_(2) in conjunction with Ru-complex as photosensitizer performed an obvious“volcano-like”trend,with the highest point at Ce-0.15 and the CO/H_(2) ratio can be widely tunable from 1/7.7 to 1/***,compared with LDH,Ce-0.15 also drove photocatalytic CO_(2) to syngas under 600 nm *** implied that an optimum amount of CeO_(2) modifying LDH promoted the photoreduction of CO_(2) to *** report gives the way to fully utilize the rare earth elements and provides a promising route to enhance the photo-response ability and charge injection efficiency of LDH-based photocatalysts in the synthesis of syngas with a tunable ratio under visible light irradiation.

关键词： visible light catalysis CO_(2)conversion layered double hydroxide rare earth elements

采用插层和掺杂策略改性水滑石及其光催化还原CO2性能研究

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

采用插层和掺杂策略改性水滑石及其光催化还原CO2性能研究

作者： kipkorir peter 北京化工大学

学位级别：硕士

在化石燃料资源短缺和环境污染两大问题的威胁之下,可持续能源的开发和减少温室气体排放日益迫切。利用CO2作为原料,采用光催化还原CO2生产高附加值化学品,实现碳循环,是一条符合经济利益的可行道路。由于具有类似的氧化还原电位和高的... 详细信息

在化石燃料资源短缺和环境污染两大问题的威胁之下,可持续能源的开发和减少温室气体排放日益迫切。利用CO2作为原料,采用光催化还原CO2生产高附加值化学品,实现碳循环,是一条符合经济利益的可行道路。由于具有类似的氧化还原电位和高的热力学稳定性,CO2催化还原反应和H2O裂解反应存在着激烈的竞争。此外,光催化反应的效率往往受到低的电荷传输、快速的载流子复合和有限的光捕获能力等因素的限制。进一步地,光催化CO2还原反应过程还涉及水分子活化和多电子转移,其产物的选择性不易控制。因此,亟需发展一种高效的CO2还原光催化剂。在已报道的光催化剂中,水滑石具有优异的性能,有望在光催化反应中展现出广阔的应用前景。水滑石的结构和水镁石(Mg(OH)2)类似,具有典型的二维层状结构、可调变的主体层板元素和层间客体阴离子等结构特征。通过调变其主体层板和层间阴离子可以提高其稳定性、光性能、电性能,从而为设计和构筑CO2还原光催化剂提供了一条有效途径。本论文利用独特的改性水滑石作为光催化剂,在可见光下实现C02还原制备高附加值化学品。具体的研究内容如下:第一章对CO2性质和还原过程的基本原理、LDHs性质、结构、合成、表征和应用进行了综述。第二章发展了一系列硝酸根和碳酸根插层的NiAl-LDH,CoAl-LDH和MgAl-LDH。首次深入研究了 LDHs的层间改性对C02光催化还原性能的影响。与CO32-阴离子插层的水滑石相比,NO3-阴离子插层的水滑石的光催化性能有所提高。其中,NiAl-NO3对CH4和CO的选择性分别为6.07%和83%,而对NiAl-C03对CH4和CO的选择性分别为0.49%和66%。原因有可能归结于,N03-阴离子插层后水滑石层间的高度增高,暴露了更多的表面羟基基团和活性金属位点,打破反应底物和产物的扩散限制。XAS和UV-Vis DRS等多种表征证实经过层间改性后,氧空位的浓度和可见光吸收能力提高,并证实N03-阴离子插层的水滑石在光催化CO2还原中的优越性。本工作通过拓宽水滑石层间高度和层间阴离子的改性,提高光催化CO2还原性能,为拓宽光催化剂打开了新的思路。第三章探讨了水滑石主体层板掺杂稀土元素对光催化CO2还原性能的影响。稀土元素具有连续填充的f轨道,强的配位能力,独特的电学、光学和磁学特性,在催化领域具有广泛的应用。在本章的工作中,我们使用共沉淀法在MgAl-LDH主体层板上掺杂不同含量的Ce,并探讨不同掺杂量的水滑石的光催化C02还原性能。和未掺杂的水滑石相比,掺杂量为 7.5%的水滑石(Mg6Al1.85Ce0.15-LDH,记为 Ce-0.15 LDH)对 CO 的选择性从11.5%提升到41.5%。由于稀土元素本身具有强的离域电子及由此带来的强的电性能,Ce的掺杂提高了水滑石载流子的传输效率、提高催化剂在可见光区域对光的吸收,从而提高光催化C02还原性能。值得注意的是,Ce的掺杂量为7.5%时达到性能最优,原因可能是在该催化剂中载流子的传输和复合率达到了一个平衡。本章工作为开发低成本的高效光催化CO2还原催化剂提供了借鉴。

关键词：二氧化碳光还原水滑石层间修饰稀土元素掺杂

Factors associated with financial support in old age for young and middle-aged rural residents in China

同方学位论文库评论

在线全文

同方学位论文库

学校读者我要写书评

暂无评论

Chinese Journal of Population,Resources and Environment 2015年第2期13卷 169-176页

作者： Suyan Shen Fang Li John kipkorir Tanui College of Public Administration Nanjing Agricultural University Department of Agricultural Economics Moi University

This study examined the factors associated with financial support in old age from three primary mechanisms-personal savings,family support,and social insurance-to explore the implications for the future development of China's rural social welfare ***-sectional surveys of 1392 young and middle-aged rural residents were conducted in July and *** results showed that while social insurance was increasingly acceptable,personal savings and family support still had fundamental *** the three mechanisms,the rural old-age welfare system presented nontraditional ***'s new rural endowment insurance is discussed as a means to address the need for financial support among the rural aging population.

关键词： old-age financial support young and middle-aged rural residents personal savings family support social insurance

Diabetes and skin cancers: Risk factors, molecular mechanisms and impact on prognosis

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

World Journal of Clinical Cases 2022年第31期10卷 11214-11225页

作者： Elena-Codruta Dobrică Madalina Laura Banciu Vincent kipkorir Mohammad Amin Khazeei Tabari Madeleine Jemima Cox L V Simhachalam Kutikuppala Mihnea-Alexandru Găman Doctoral School University of Medicine and Pharmacy of CraiovaCraiova 200349Romania Department of Dermatology "Elias"University Emergency HospitalBucharest 011461Romania Department of Human Anatomy University of NairobiCollege of Health SciencesNairobi 00100Kenya USERN Office Mazandaran University of Medical SciencesSari 48175-866Iran University of New South Wales University of New South WalesSydney 2052Australia Dr NTR University of Health Sciences VijayawadaAndhra Pradesh 520008India Faculty of Medicine "Carol Davila"University of Medicine and PharmacyBucharest 050474Romania

Diabetes and skin cancers have emerged as threats to public health ***,their association has been less intensively *** this narrative review,we explore the common risk factors,molecular mechanisms,and prognosis of the association between cutaneous malignancies and ***,oxidative stress,low-grade chronic inflammation,genetic,lifestyle,and environmental factors partially explain the crosstalk between skin cancers and this metabolic *** addition,diabetes and its related complications may interfere with the appropriate management of cutaneous *** medication seems to exert an antineoplastic effect,however,future large,observation studies with a prospective design are needed to clarify its impact on the risk of malignancy in *** for diabetes in skin cancers,as well as close follow-up for the development of cutaneous malignancies in subjects suffering from diabetes,is warranted.

关键词： Diabetes Skin cancers Squamous cell carcinoma Melanoma Basocellular carcicoma

异构多媒体无线网络中基于QoE的MIH的性能评价

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

异构多媒体无线网络中基于QoE的MIH的性能评价

作者： Sang Eli kipkorir 中南大学

学位级别：硕士

大量的移动设备如个人数字助理（PDAs）、智能电话、笔记本电脑、甚至是视频游戏控制台等,在硬件和软件方面都取得了巨大的进展。这些设备集成了多个有线或无线接口,如蜂窝网络,WiFi, WiMAX以及蓝牙等,正朝着下一代网络形态（超3G）迈进... 详细信息

大量的移动设备如个人数字助理（PDAs）、智能电话、笔记本电脑、甚至是视频游戏控制台等,在硬件和软件方面都取得了巨大的进展。这些设备集成了多个有线或无线接口,如蜂窝网络,WiFi, WiMAX以及蓝牙等,正朝着下一代网络形态（超3G）迈进。3G技术支持更高的数据传输率,更好的区域移动性,更低的延迟和更好的QoS要求,从而能为广大用户提供高清晰（HD）的多媒体应用服务。然而,由于用户总是希望能在任何时间、任何地点都获得最佳的连接,因此下一代网络应着眼于超越同构网络技术的透明移动性以及异构网络技术的无缝移动性。随着越来越多的网络技术用于移动设备,现在的重点是：在尽可能降低成本的情况下,持续提供最佳可用的网络服务。于是带来了切换的问题：即当MN从一个无线接入技术切换到另一个技术时,要能维持与CN之间的通信。因此,IEEE制定了IEEE 802.21媒体交接服务标准（MIH）,专用于异构网络的切换。本文中,将以QoE（用户感知）的方式对802.21协议进行性能评估。我们通过从CN到MN的视频流来实现QoE性能评估。而视频流的选取时机是在WiFi与WiMAX网络进行垂直切换的时候,这种垂直切换是在802.21协议的辅助下实现的。我们使用峰值信噪比（PSNR）作为客观性的评价指标,此外,为了分析对视频质量的主观感受,将峰值信噪比（PSNR）转换为平均意见分（MOS）。同时,为研究QoS与QoE之间的关系,使用端到端的QoS延迟参数,吞吐量以及包丢失率来决定QoE的垂直切换。最后,使用NS2进行了模拟。从实验结果中可以看出,原始视频流在通过垂直切换后,其质量发生了明显的变化,最终接收到的视频质量的MOS得分只有5.然而,在模拟中产生大量的背景流量时,视频质量也会明显下降。我们还观察到,包的丢失数量随着断线率（Link Going Down ratio）的增加而减少。因此,在QoE与断线率（Link Going Down ratio）之间存在某种相关性。

关键词： QoE MIH 切换质量无缝的 WiFi WiMAX

同方学位论文库评论

在线全文

同方学位论文库

学校读者我要写书评

暂无评论

电信客户流失预测的研究

电信客户流失预测的研究

作者： Clement kipkorir Kirui 中南大学

学位级别：硕士

客户流失是许多商业部门都极其反感的问题。每个行业都渴望建立和保持一个忠实的客户群。在无线通信行业中,有许多因素会导致客户较容易地流失到竞争对手,这些因素包括激烈的竞争、新技术的出现、低转向成本、新竞争对手的引入。使获得... 详细信息

客户流失是许多商业部门都极其反感的问题。每个行业都渴望建立和保持一个忠实的客户群。在无线通信行业中,有许多因素会导致客户较容易地流失到竞争对手,这些因素包括激烈的竞争、新技术的出现、低转向成本、新竞争对手的引入。使获得新客户的成本增高的这一实际情况进一步加剧了客户流失问题。电信数据集通常有数百个描述电话详单和和客户资料的属性。然而,并不是所有的属性都具有重要的预测意义,因此有必要选择最佳的流失预测器,以便提高预测模型的性能。此外,流失通常是一个稀有事件,即正类样本是少数类。在这项研究中使用的数据集中,例如,流失客户占总客户的5.6%,其余都是非流失客户。提出了类不平衡问题,这削弱了一些像决策树的数据挖掘算法的学习。在这项工作中,针对不同的特征子集对客户流失预测的影响进行了研究。数据集包含电话详单、客户资料。完整的属性集被分解成多个子集,这些子集分别是网内电话、国际电话、网外电话、增值业务服务电话、客户通话活动信息、、客户资料。然后评估这些属性子集,来确定他们对预测的重要性。接下来,派生出新的属性分为三类：合同的相关属性、电话模式属性、电话模式变化属性。这样的分类为理解这些属性提供了一个简单的框架。合同相关属性描述的特征是指客户与公司的各种协议或合同,这类属性中派生了“任期”属性,它说明了客户使用该公司服务的时间。电话模式属性所描述的特征是指客户通话模式的趋势,这类属性集包含总呼叫持续时间、总电话数量和总语音电话数。假设当总电话数越高,呼叫持续时间越长,客户就不太可能会流失。电话模式变化属性所描述的特征是指客户电话模式的变化。这类属性包含使用分钟的变化,使用频率的变化,影响范围的变化,用户活动的改变,呼叫网外电话持续时间的改变,呼叫网外电话所占的百分比,语音电话打出的百分比。客户呼叫模式的改变量可以是正或是负。对于一些属性如使用频率的变化,如果改变量是正的,这说明用户在后续的月份中有比较多的电话,因此不太可能在短期内流失。另一方面,对于影响范围的变化,如果改变量是负的,这意味着用户在后续的月份中电话数比较少,,因此客户可能早晚会流失。提取了属性之后,将他们组合起来形成一个子集被称为“新属性”,并将它添加到原始数据集中。然后对所有的子集进行评估。在第一组实验中,将所有的子集进行测试并比较它们的预测性能。在第二组实验中,对修改后的数据集和原始数据集中的所有子集进行测试,以确定是否添加新属性后的流失预测率会比原始数据集的流失预测高。由于每个子集的属性维数比较高,所以采用信息增益滤波器的方法来给每个子集的属性按重要性进行排序,每个子集选择排在前面的60个属性。采用C4.5、朴素贝叶斯分类器和贝叶斯网络三种预测技术通过十倍交叉验证来评价属性。在这种技术下,数据集在每一次迭代中被分为十份,数据集中的九份用作训练集来构建预测模型,剩余的一份作为测试集,执行十次迭代。在每种预测技术下,采用TPR和FPR的平均值来生成ROC曲线。从ROC曲线中计算出AUC值,用它作为评价标准选出流失预测的最好的特征子集。实验结果表明,提出的属性的预测性能比原始属性子集要好。为了解决类不平衡的问题,本论文研究了两种抽样方法。在第一个实验中,采用了欠抽样,方法的原理是将训练集中的多数类进行剔除直到得到理想的样子数量。在保持少数类数量不变的情况下,对多数类从它的10%到100%进行抽样。在第二组实验中,运用SMOTH方法对少数类样本进行过抽样,SMOTE是对少数类进行合成,形成训练集,从而对少数类进行过采样控制。在这组实验中,少数类样本以100%到1000%进行过抽样来产生连续的数据点。在第三组实验中,在抽样从100%到1000%的各个样本大小下,将SMOTH与欠抽样方法结合。在三组实验中,均采用C4.5决策树和朴素贝叶斯分类器通过10倍交叉验证进行性能的评估。对于这二种预测技术,记录TPR和FPR的值来生成ROC曲线,并从中计算出AUC值,实验结果表明,欠抽样下的SMOTE方法能够更好地处理类不平衡问题。

关键词：客户流失数据挖掘属性集选择预测类不平衡

Institutional Structures and Sustainability of Projects in Nyangores River Sub-Catchment Basin in Bomet County, Kenya

同方学位论文库评论

在线全文

同方学位论文库

学校读者我要写书评

暂无评论

Journal of Geoscience and Environment Protection 2022年第12期10卷 331-353页

作者： Kirui kipkorir Charles Mallans Rambo George Muhua Faculty of Business and Management Sciences University of Nairobi Nairobi Kenya Faculty of Mathematics University of Nairobi Nairobi Kenya

Integrated basin management approach has been applied in Nyangores River sub-catchment basin, since the year 2009 but with minimal success. Sub catchment degradation, organizational weakness, the flow and quality of water had started to diminish, creating challenges for local livelihoods, wildlife in the Maasai Mara Game Reserve, and in maintaining biodiversity and healthy ecosystem functioning. Water resources can be successfully managed only if the natural, social, economic and political environments, in which water occurs and used, are taken fully into consideration. The aim of this study is to determine the influence of institutional structures influence on sustainability of projects in Nyagores river sub-catchment basin in Bomet County, Kenya. The research designs used were descriptive survey and correlational research design. Stepwise and purposive sampling formed the sampling procedure. The results are presented descriptively using Tables while for qualitative data, narrative statements were used. Questionnaires, Interview guide and document analysis were used for data collection. The sample size was 371, from a targeted a population of 56,508 household heads and 10 informants, purposively selected from the water concerned institutions and ministries of Water and Agriculture. Total of 371 questionnaires were given out to the respondents and only 321, were duly filled and returned representing (86.5%). The objective was to establish the extent to which institutional structures influence sustainability of projects in Nyangores River sub-catchment Basin. The results indicated that there was a positive correlation r = 0.552, (p is was rejected and concluded that there is a significant relationship between the institutional structures and sustainability of projects in Nyangores river sub-catchment basin. R2 was 0.304;hence, 30.4% of changes in sustainability of projects are explained by institutional structures. Recommendations are;ensure a stringent po

关键词： Institutional Structures Sustainability of Projects River Sub-Catchment Basin

Acute myocardial infarction in myeloproliferative neoplasms

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

World Journal of Cardiology 2023年第11期15卷 571-581页

作者： Muhammad Romail Manan Vincent kipkorir Iqra Nawaz Maryann Wanjiku Waithaka Bahadar Singh Srichawla Amelia Maria Găman Camelia Cristina Diaconu Mihnea-Alexandru Găman Services Institute of Medical Sciences Lahore 54000Pakistan Department of Human Anatomy and Physiology University of NairobiNairobi 00100Kenya Quaid-e-Azam Medical College Bahawalpur 63100Pakistan Department of Neurology University of Massachusetts Chan Medical SchoolWorcesterMA 01655United States Department of Pathophysiology University of Medicine and Pharmacy of CraiovaCraiova 200143Romania Clinic of Hematology Filantropia City HospitalCraiova 200143Romania Department of Internal Medicine Faculty of Medicine“Carol Davila”University of Medicine and PharmacyBucharest 050474Romania Internal Medicine Clinic Clinical Emergency Hospital of BucharestBucharest 105402Romania Faculty of Medicine “Carol Davila”University of Medicine and PharmacyBucharest 050474Romania Department of Hematology Center of Hematology and Bone Marrow TransplantationFundeni Clinical InstituteBucharest 022328Romania Department of Cellular and Molecular Pathology Stefan S.Nicolau Institute of VirologyRomanian AcademyBucharest 030304Romania

Myeloproliferative neoplasms(MPNs)are a heterogeneous group of hematologic malignancies characterized by an abnormal proliferation of cells of the myeloid *** individuals are at increased risk for cardiovascular and thrombotic *** infarction(MI)may be one of the earliest clinical manifestations of MPNs or may be a thrombotic complication that develops during the natural course of the *** the present review,we examine the epidemiology,pathogenesis,clinical presentation,and management of MI in MPNs based on the available ***,we review potential biomarkers that could mediate the MI-MPNs crosstalk,from classical biochemical tests,e.g.,lactate dehydrogenase,creatine kinase and troponins,to pro-inflammatory cytokines,oxidative stress markers,and clonal hematopoiesis.

关键词： Myeloproliferative neoplasms Polycythemia vera Essential thrombocythemia Myelofibrosis Myocardial infarction Acute coronary syndrome Biomarker Clonal hematopoiesis

Vehicle Discrimination Using a Combined Multiple Features Based on Vehicle Face

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Vehicle Discrimination Using a Combined Multiple Features Ba...