期刊文献+
共找到32,560篇文章
< 1 2 250 >
每页显示 20 50 100
Upsilon Constants and Their Usefulness in Planck Scale Quantum Cosmology
1
作者 Eugene Terry Tatum 《Journal of Modern Physics》 2024年第2期167-173,共7页
This paper introduces the two Upsilon constants to the reader. Their usefulness is described with respect to acting as coupling constants between the CMB temperature and the Hubble constant. In addition, this paper su... This paper introduces the two Upsilon constants to the reader. Their usefulness is described with respect to acting as coupling constants between the CMB temperature and the Hubble constant. In addition, this paper summarizes the current state of quantum cosmology with respect to the Flat Space Cosmology (FSC) model. Although the FSC quantum cosmology formulae were published in 2018, they are only rearrangements and substitutions of the other assumptions into the original FSC Hubble temperature formula. In a real sense, this temperature formula was the first quantum cosmology formula developed since Hawking’s black hole temperature formula. A recent development in the last month proves that the FSC Hubble temperature formula can be derived from the Stephan-Boltzmann law. Thus, this Hubble temperature formula effectively unites some quantum developments with the general relativity model inherent in FSC. More progress towards unification in the near-future is expected. 展开更多
关键词 Quantum Cosmology Hubble Constant Planck Scale Upsilon Constant Flat Space Cosmology Black Holes CMB Temperature ΛCDM Cosmology Quantum Gravity Unification
下载PDF
Unity Formulas for the Coupling Constants and the Dimensionless Physical Constants
2
作者 Stergios Pellis 《Journal of High Energy Physics, Gravitation and Cosmology》 CAS 2023年第1期245-294,共50页
In this paper in an elegant way will be presented the unity formulas for the coupling constants and the dimensionless physical constants. We reached the conclusion of the simple unification of the fundamental interact... In this paper in an elegant way will be presented the unity formulas for the coupling constants and the dimensionless physical constants. We reached the conclusion of the simple unification of the fundamental interactions. We will find the formulas for the Gravitational constant. It will be presented that the gravitational fine-structure constant is a simple analogy between atomic physics and cosmology. We will find the expression that connects the gravitational fine-structure constant with the four coupling constants. Perhaps the gravitational fine-structure constant is the coupling constant for the fifth force. Also will be presented the simple unification of atomic physics and cosmology. We will find the formulas for the cosmological constant and we will propose a possible solution for the cosmological parameters. Perhaps the shape of the universe is Poincare dodecahedral space. This article will be followed by the energy wave theory and the fractal space-time theory. 展开更多
关键词 Fine-Structure Constant Proton To Electron Mass Ratio Dimensionless Physical constants Coupling Constant Gravitational Constant Avogadro’s Number Fundamental Interactions Gravitational Fine-Structure Constant Cosmological Constant
下载PDF
Fundamental Physical Constants and Primary Physical Parameters
3
作者 Vladimir S. Netchitailo 《Journal of High Energy Physics, Gravitation and Cosmology》 CAS 2023年第1期190-209,共20页
Every four years the Committee on Data for Science and Technology (CODATA) supplies a self-consistent set of values of the basic constants and conversion factors of physics recommended for international use. In 2013, ... Every four years the Committee on Data for Science and Technology (CODATA) supplies a self-consistent set of values of the basic constants and conversion factors of physics recommended for international use. In 2013, the World-Universe Model (WUM) proposed a principally different depiction of the World as an alternative to the picture of the Big Bang Model. This article: 1) Gives the short history of Classical Physics before Special Relativity;2) Calculates Fundamental Physical Constants based on experimentally measured Rydberg constant, Electrodynamic constant, Electron Charge-to-Mass Ratio, and Planck constant;3) Discusses Electrodynamic constant and Speed of Light;4) Considers Dimensionless Fundamental Parameters (Dirac Large Number Q and Dimensionless Rydberg Constant α);5) Calculates Newtonian Constant of Gravitation based on the Inter-connectivity of Primary Physical Parameters;6) Makes a detailed analysis of the Self-consistency of Fundamental Physical Constants and Primary Physical Parameters through the prism of WUM. The performed analysis suggests: 1) Discontinuing using the notion “Vacuum” and its characteristics (Speed of Light in Vacuum, Characteristic Impedance of Vacuum, Vacuum Magnetic Permeability, Vacuum Electric Permittivity);2) Accepting the exact numerical values of Electrodynamic constant, Planck constant, Elementary charge, and Dimensionless Rydberg Constant α. WUM recommends the predicted value of Newtonian Constant of Gravitation in 2018 to be considered in CODATA Recommend Values of the Fundamental Physical Constants 2022. 展开更多
关键词 Classical Physics Fundamental Physical constants Electrodynamic Constant Speed of Light Dirac Large Number Dimensionless Rydberg Constant Newtonian Constant of Gravitation Self-Consistency of Fundamental Physical constants
下载PDF
On the Fine Structure and the Other Coupling Constants at the Planck Scale
4
作者 Paolo Christillin 《Journal of Modern Physics》 CAS 2023年第5期666-669,共4页
It is shown that the fine structure constant at Planck times tends to one as well as those of the weak and strong interactions. This results by constraining them at the Planck force. That seems to provide interesting ... It is shown that the fine structure constant at Planck times tends to one as well as those of the weak and strong interactions. This results by constraining them at the Planck force. That seems to provide interesting new results which confirm that at the beginning of space time (Planck scale) all fundamental forces converge to the same unit value. 展开更多
关键词 Fine Structure Constant Fundamental Interactions Coupling constants Unification at Planck Scale
下载PDF
Precise measurement of 171Yb magnetic constants for 1S_(0)–3P_(0) clock transition
5
作者 张昂 田聪聪 +5 位作者 朱强 王兵 熊德智 熊转贤 贺凌翔 吕宝龙 《Chinese Physics B》 SCIE EI CAS CSCD 2023年第2期184-188,共5页
We present a precise measurement of171Yb magnetic constants for 1S_(0)-3P_(0) clock transition. The background magnetic field is firstly compensated to < 1 m Gs(1 Gs = 10^(-4)T) through measuring the splitting of t... We present a precise measurement of171Yb magnetic constants for 1S_(0)-3P_(0) clock transition. The background magnetic field is firstly compensated to < 1 m Gs(1 Gs = 10^(-4)T) through measuring the splitting of two π transitins of171Yb clock transition at different compensation coils currents. Then, the splitting ratios of the π and σ components of171Yb clock transition at different bias magnetic fields are measured, and the first-order Zeeman coefficient is determined to beα = 199.49(5) Hz/Gs. The second-order Zeeman shifts at various bias magnetic fields are also measured through interleaved self-comparison in which the bias magnetic fields are modulated between high and low values. The second-order Zeeman coefficient is fitted to be β =-6.09(3) Hz/m T^(2), which is consistent with the result of NIST group. 展开更多
关键词 optical lattice clock ytterbium atoms Zeeman effects magnetic constants
下载PDF
Effects of heavy metal ions Cu^(2+)/Pb^(2+)/Zn^(2+)on kinetic rate constants of struvite crystallization
6
作者 Guangyuan Chen Tong Zhou +5 位作者 Meng Zhang Zhongxiang Ding Zhikun Zhou Yuanhui Ji Haiying Tang Changsong Wang 《Chinese Journal of Chemical Engineering》 SCIE EI CAS CSCD 2023年第5期10-16,共7页
Struvite(MAP)crystallization technology is widely used to treat ammonia nitrogen in waste effluents of its simple operation and good removal efficiency.However,the presence of heavy metal ions in the waste effluents c... Struvite(MAP)crystallization technology is widely used to treat ammonia nitrogen in waste effluents of its simple operation and good removal efficiency.However,the presence of heavy metal ions in the waste effluents causes problems such as slow crystallization rate and small crystal size,limiting the recovery rate and economic value of the MAP.The present study was conducted to investigate the effects of concentrations of three heavy metal ions(Cu^(2+),Zn^(2+),and Pb^(2+))on the crystal morphology,crystal size,average growth rate,and crystallization kinetics of MAP.A relationship was established between the kinetic rate constant Ktcalculated by the chemical gradient model and the concentrations of heavy metal ions.The results showed that low concentrations of heavy metal ions in the solution created pits on the MAP surface,and high level of heavy metal ions generated flocs on the MAP surface,which were composed of metal hydroxides,thus inhibiting crystal growth.The crystal size,average growth rate,MAP crystallization rate,and kinetic rate constant Ktdecreased with the increase in heavy metal ion concentration.Moreover,the Ktdemonstrated a linear relationship with the heavy metal concentration ln(C/C~*),which provided a reference for the optimization of the MAP crystallization process in the presence of heavy metal ions. 展开更多
关键词 STRUVITE CRYSTALLIZATION Heavy metal ions KINETICS Kinetic modeling Kinetic rate constant
下载PDF
Variable Physical Constants and Beyond
7
作者 Qinghua Cui 《Journal of High Energy Physics, Gravitation and Cosmology》 CAS 2023年第1期116-123,共8页
We previously revealed that the speed of light in vacuum c, the gravitational constant G, the vacuum permittivity ε, and the vacuum permeability μ can be defined by the temperature T (or the expected average frequen... We previously revealed that the speed of light in vacuum c, the gravitational constant G, the vacuum permittivity ε, and the vacuum permeability μ can be defined by the temperature T (or the expected average frequency f) of cosmic microwave background (CMB) radiation. Given that CMB is continuously cooling, that is, T is continuously decreasing, we proposed that the above “constants” are variable and their values at some space-time with CMB temperature T (c<sub>T</sub>, G<sub>T</sub>, ε<sub>T</sub>, and μ<sub>T</sub>) can be described using their values (c<sub>0</sub>, G<sub>0</sub>, ε<sub>0</sub>, and μ<sub>0</sub>) and the temperature (T<sub>0</sub>) of CMB at present space-time. Based on the above observation, a number of physical equations related with these constants are re-described in this study, including relativity equation, mass-energy equation, and Maxwell’s equations, etc. 展开更多
关键词 Speed of Light in Vacuum Gravitational Constant Vacuum Permittivity Vacuum Permeability Cosmic Microwave Background
下载PDF
Autonomous Robot with Artificial Intelligence for Taking Health Constants
8
作者 Ababacar Sadikh Faye Ousmane Sow +4 位作者 Mame Andallah Diop Youssou Traore Jupiter Ndiaye Mamour Gueye Abdoulaye Diop 《Open Journal of Applied Sciences》 2023年第7期963-975,共13页
Health facilities are generally short-staffed and overworked. This has a significant impact on the reliability of the acquisition of health constants required at the start of diagnosis. Manual acquisition and transmis... Health facilities are generally short-staffed and overworked. This has a significant impact on the reliability of the acquisition of health constants required at the start of diagnosis. Manual acquisition and transmission of these constants and other data leads to delays in the execution of successive care-related tasks. What’s more, the quality of service is sometimes compromised by a lack of communication between patients and staff. In pediatrics, this is compounded by the difficulty of diagnosis in the face of children’s silence, intimidated by the hospital environment. Technological assistance would relieve healthcare staff of the need to perform certain repetitive tasks. The solution proposed in this document studies a robot, based on electrical, electronic, computer and artificial intelligence resources, with human-machine interaction for taking vitals and health data in health facilities. This system enables height, mass and temperature to be taken autonomously and without contact. The algorithm we’ve developed uses artificial intelligence to check the conditions for correct measurements, both bareheaded and barefoot. This solution also alerts you to epidemic trends such as obesity. This health data is made available in the healthcare facility on terminals such as tablets, smartphones and computers used by nursing staff. This work will help healthcare staff to take automatic health vitals without contact, and to acquire and circulate data via a computer network. 展开更多
关键词 Health constants INSTRUMENTATION MECHATRONICS ARDUINO CLOUD AI
下载PDF
恒力支吊架性能指标研究及标准修改建议
9
作者 康豫军 吴晓俊 +5 位作者 程勇明 安付立 祝俭 彭天星 曹燕东 陈冰峰 《热力发电》 CAS CSCD 北大核心 2024年第3期177-182,共6页
高温汽水管道是发电厂的重要部件,由于管道垂直高差和水平跨距较大,为协调管道热膨胀和降低管道热胀应力,在管道设计时配置了较多恒力弹簧支吊架(恒力吊架)。由于存在转轴摩擦力矩等原因,恒力吊架并非恒力,其荷载偏差会造成管道运行时... 高温汽水管道是发电厂的重要部件,由于管道垂直高差和水平跨距较大,为协调管道热膨胀和降低管道热胀应力,在管道设计时配置了较多恒力弹簧支吊架(恒力吊架)。由于存在转轴摩擦力矩等原因,恒力吊架并非恒力,其荷载偏差会造成管道运行时偏离设计冷态、热态线及管道应力升高。为控制恒力支吊架质量,国内相关标准中有恒定度和荷载偏差度2个质量性能控制指标。分析研究荷载偏差度可得:由于存在摩擦力矩等,恒力吊架在测试荷载偏差度时,不同加载方向测得的拔销荷载差异较大,导致其荷载偏差度差异较大,因此拔销荷载不宜作为代表性参数;平均荷载可表征位移-荷载曲线的位置,是恒力支吊架的代表性参数,并给出了新的平均荷载偏差度计算公式。建议对相关标准进行修订,提高恒力吊架性能。 展开更多
关键词 恒力弹簧支吊架 恒定度 平均荷载偏差度
下载PDF
弹簧支吊架荷载变化系数的选取与汽水管道支吊架优化设计
10
作者 康豫军 安付立 +3 位作者 吴晓俊 程勇明 孙克学 彭钰君 《热力发电》 CAS CSCD 北大核心 2024年第2期192-198,共7页
目前,我国火力发电厂汽水管道设计标准规定,弹簧吊架荷载变化系数不应大于25%,据此设计的管道系统恒力吊架比例过高,其荷载“非法”转移会造成管道偏离设计线运行,应力升高。分析了恒力吊架恒定度与荷载变化系数的关系并给出了优化设计... 目前,我国火力发电厂汽水管道设计标准规定,弹簧吊架荷载变化系数不应大于25%,据此设计的管道系统恒力吊架比例过高,其荷载“非法”转移会造成管道偏离设计线运行,应力升高。分析了恒力吊架恒定度与荷载变化系数的关系并给出了优化设计案例,研究结果表明,在汽水管道设计中适当增大弹簧吊架荷载变化系数,可增大弹簧吊架配置占比,减少管道膨胀异常现象的发生。 展开更多
关键词 弹簧吊架 荷载变化系数 恒力吊架 恒定度 管道支吊架优化设计
下载PDF
恒压下GIS固体绝缘界面气隙缺陷放电严重程度评估 被引量:2
11
作者 唐志国 李阳 《高压电器》 CAS CSCD 北大核心 2024年第2期62-68,77,共8页
为了研究GIS绝缘子界面气隙缺陷的放电发展过程,文中设计了空洞气隙缺陷模型,搭建了一套GIS气隙缺陷放电长期测试平台。基于缺陷模型的击穿电压对带有缺陷的试品施加90%Ub、60%Ub、30%Ub的交流恒压,使用UHF检测系统采集放电数据直至试... 为了研究GIS绝缘子界面气隙缺陷的放电发展过程,文中设计了空洞气隙缺陷模型,搭建了一套GIS气隙缺陷放电长期测试平台。基于缺陷模型的击穿电压对带有缺陷的试品施加90%Ub、60%Ub、30%Ub的交流恒压,使用UHF检测系统采集放电数据直至试品击穿。提取放电次数、放电幅值、放电时间间隔分析放电状态特征,发现GIS气隙缺陷放电发展过程存在两个阶段,前期放电幅值缓慢增大,放电脉冲逐渐稀疏,放电发展较为平稳;后期放电幅值急剧减小,放电脉冲密集,放电发展剧烈,采用k⁃means聚类算法及BP神经网络建立了气隙缺陷局放发展阶段的划分规则。研究表明,放电次数、放电幅值、放电时间间隔3种统计参量呈现阶段式单调性的趋势,可以用3种统计参量前向差分绝对值作为特征参量来评估GIS气隙放电严重程度;对GIS恒压试验进行聚类分析将放电过程划分为平稳劣化阶段和加速劣化阶段,随着外施电压水平的降低,平稳劣化阶段被压缩,加速劣化阶段占比升高。 展开更多
关键词 GIS绝缘子 气隙放电 恒压法 状态划分 评估
下载PDF
基于变频重构S/SP拓扑的无线电能传输系统恒流恒压研究
12
作者 李中启 张晨曦 +2 位作者 王建斌 王忠美 黄守道 《电工技术学报》 EI CSCD 北大核心 2024年第15期4718-4732,共15页
针对电动汽车无线充电系统耦合系数和负载变化导致系统输出电流和电压剧烈波动的问题,提出一种由交错叠放式线圈结构和变频重构控制策略组成的无线电能传输系统,通过重构补偿拓扑,并切换工作频率,实现了系统的恒流恒压输出。首先,分析... 针对电动汽车无线充电系统耦合系数和负载变化导致系统输出电流和电压剧烈波动的问题,提出一种由交错叠放式线圈结构和变频重构控制策略组成的无线电能传输系统,通过重构补偿拓扑,并切换工作频率,实现了系统的恒流恒压输出。首先,分析了拓扑重构前后系统的恒流、恒压输出特性和零相角特性,对比恒流恒压工作模式下补偿电容的大小,给出了系统参数调整方法。其次,剖析了交错叠放式线圈结构模型,提出基于耦合系数波动最小原则的线圈结构优化策略。所提出的系统补偿元件较少,两个工作频率点符合国际标准。最后,搭建一套500 W的实验样机,验证系统的可行性和有效性。实验结果表明,交错叠放式线圈在X轴方向偏移发射线圈外径的55%(187mm)或Y轴方向偏移120mm时,耦合系数波动率小于5%。系统在恒流模式下电流波动率为3.58%,在恒压模式下电压波动率为4.83%,满足无线充电系统恒流恒压需求。 展开更多
关键词 无线电能传输 变频重构 恒流 恒压 零相角
下载PDF
基于偏航机动的常推力定点着陆制导方法
13
作者 李骥 张洪华 +1 位作者 张晓文 关轶峰 《深空探测学报(中英文)》 CSCD 北大核心 2024年第1期47-55,共9页
实现定点着陆终端位置速度六分量控制通常需要发动机推力可调。提出了一种通过偏航机动实现固定推力下的定点着陆制导方法。该方法通过偏转航向角,调节发动机输出在下降轨迹平面内的分量,从而实现航程控制;为了消除推力方向偏转产生的... 实现定点着陆终端位置速度六分量控制通常需要发动机推力可调。提出了一种通过偏航机动实现固定推力下的定点着陆制导方法。该方法通过偏转航向角,调节发动机输出在下降轨迹平面内的分量,从而实现航程控制;为了消除推力方向偏转产生的横向位置、速度偏差,设计了偏转角符号调整策略,使得着陆器在水平面内呈“之”字形运动,以一定推进剂为代价,最终保证了下降着陆终端位置、速度的全部可控。仿真表明,所提方法简单有效,易于工程实施。 展开更多
关键词 动力下降 定点着陆 常推力 显式制导
下载PDF
恒流源三侧向电阻率测井模块研制及应用 被引量:1
14
作者 冯延强 刘富强 +2 位作者 布和 于怀远 邵帅 《世界核地质科学》 CAS 2024年第1期23-32,共10页
为进一步提高砂岩型铀矿地层电阻率参数在测井解释中的应用效果,尤其是对泥砂泥交互薄层的精细测量与识别,研究了基于OPA547放大器的恒流源三侧向电阻率测井模块,通过设计以OPA547为恒流激励源的数字激励控制电路,实现了正弦激励信号的... 为进一步提高砂岩型铀矿地层电阻率参数在测井解释中的应用效果,尤其是对泥砂泥交互薄层的精细测量与识别,研究了基于OPA547放大器的恒流源三侧向电阻率测井模块,通过设计以OPA547为恒流激励源的数字激励控制电路,实现了正弦激励信号的恒流输出;设计了正弦检测信号的恒流反馈电路,实现恒流源的负反馈稳定输出;设计了交流电压检测电路,实现了交流信号的低通滤波与信号半波整流;最后,在实验室利用标准刻度器进行了研制模块的系数刻度,且在砂岩型铀矿钻孔进行了实际测井应用对比。经对比分析,研制的恒流源三侧向电阻率测井模块能够与砂岩铀矿综合测井中的其他参数组合使用,输出激励电流可调,对岩性及岩性界面具有较高的识别能力,对于交互薄层、钙质夹层等地层岩性变化的响应显示明显。 展开更多
关键词 恒流源 三侧向电阻率 OPA547 地球物理测井
下载PDF
基于改进型ZVT Buck电路的IPT充电系统设计
15
作者 刘雪莉 徐睿 +3 位作者 李阳 汪学亮 寇苏雅 孟航 《天津工业大学学报》 CAS 北大核心 2024年第1期64-73,共10页
为了避免在感应式无线电能传输系统的耦合机构中增加多余的开关器件以及额外的无源元件,同时减小系统工作在高频率、大功率时全控型开关器件存在的开关损耗,提出基于改进型ZVT Buck电路闭环控制的方法实现对电池的恒流、恒压充电,通过... 为了避免在感应式无线电能传输系统的耦合机构中增加多余的开关器件以及额外的无源元件,同时减小系统工作在高频率、大功率时全控型开关器件存在的开关损耗,提出基于改进型ZVT Buck电路闭环控制的方法实现对电池的恒流、恒压充电,通过分析改进型ZVT Buck电路的工作模态以及对电路参数的设计,确保在整个充电过程中DC-DC变换器均工作在软开关状态,最后搭建充电电流为35 A、充电电压为370 V的实验平台验证该方法的可行性。结果表明:该方法控制简单,并且降低了系统电路结构的复杂度,传输效率相对较高,能够满足恒流恒压充电需求。 展开更多
关键词 感应式无线电能传输 改进型ZVT Buck电路 恒流恒压充电 软开关
下载PDF
基于频率切换实现恒流/恒压输出的电场耦合无线电能传输系统
16
作者 苏玉刚 颜志琼 +3 位作者 胡宏晟 孙跃 刘哲 刘书柏杨 《中国电机工程学报》 EI CSCD 北大核心 2024年第4期1553-1564,I0025,共13页
电场耦合无线电能传输(electric-field coupled wireless power transfer,EC-WPT)技术的实际应用中,有些用电设备需要系统具有不同的恒定输出特性(恒流/恒压),即系统输出电压或输出电流与负载解耦,此外,系统还需具备在恒流、恒压模式间... 电场耦合无线电能传输(electric-field coupled wireless power transfer,EC-WPT)技术的实际应用中,有些用电设备需要系统具有不同的恒定输出特性(恒流/恒压),即系统输出电压或输出电流与负载解耦,此外,系统还需具备在恒流、恒压模式间按需切换的功能。针对该需求,基于LC-CLC谐振网络提出1种具有恒流/恒压输出特性的EC-WPT系统,分析LC-CLC谐振网络特性,推导恒流/恒压输出特性的实现条件以及恒流频率和恒压频率的计算方法,并给出系统参数设计方法,分析系统对工作频率的敏感性。最后通过仿真和实验验证所提出的EC-WPT系统恒流/恒压输出特性及其参数设计方法的正确性和有效性。实验结果表明所提出的系统在输入电压恒定的不同负载工况下分别实现2 A的恒流输出以及96 V的恒压输出,其最大传输效率分别为87.83%及88.17%。 展开更多
关键词 电场耦合无线电能传输系统 频率切换 恒流 恒压 谐振网络
下载PDF
子宫内膜癌增强MRI定量参数变化与临床特征的关系及对预后的预测价值分析
17
作者 杨川桦 姜萍 谢刚 《中国CT和MRI杂志》 2024年第3期148-151,共4页
目的 探究子宫内膜癌(EC)增强MRI定量参数变化与临床特征关系,分析其对预后的预测价值。方法 选取2019年3月~2022年3月本院收治的EC患者98例作为研究组,另选同期子宫内膜良性病变患者98例作为对照组。比较两组增强MRI定量参数[速率常数(... 目的 探究子宫内膜癌(EC)增强MRI定量参数变化与临床特征关系,分析其对预后的预测价值。方法 选取2019年3月~2022年3月本院收治的EC患者98例作为研究组,另选同期子宫内膜良性病变患者98例作为对照组。比较两组增强MRI定量参数[速率常数(K_(ep))、容量转移常数(K^(trans))、血管外细胞外间隙容积比(V_(e))]。比较研究组不同临床特征患者增强MRI定量参数,分析其与临床特征相关性。比较研究组不同预后患者增强MRI定量参数,分析其对预后的预测价值。结果 研究组K_(ep)、K^(trans)、V_(e)高于对照组(P<0.05);K_(ep)、K^(trans)、V_(e)病理分期、淋巴结转移、宫颈间质累及情况、子宫肌层浸润深度呈正相关,而与分化程度呈负相关(p<0.05)预后不良者K_(ep)、K^(trans)、V_(e)高于预后良好者,且与预后不良显著相关(P<0.05);K_(ep)、K^(trans)、V_(e)联合预测预后不良的AUC大于各参数独独预测(P<0.05)。结论 EC患者增强MRI定量参数K_(ep)、K^(trans)、V_(e)升高,且与临床特征、预后密切相关,联合检测各参数对预后不良具有一定预测价值。 展开更多
关键词 子宫内膜癌 增强MRI 临床特征 预后 预测 速率常数 容量转移常数 血管外细胞外间隙容积比
下载PDF
过渡态理论对Arrhenius公式的诠释——以硝酸异丙酯与自由基反应为例
18
作者 孙翠红 许保恩 +2 位作者 刘迎 杨静 吕立强 《大学化学》 CAS 2024年第1期320-324,共5页
大学物理化学教学中,Arrhenius公式阐述了反应的速率常数与温度及活化能的关系,但是,单纯从公式的表达式进行讲解,难免枯燥乏味,不利于学生理解和掌握。本文以硝酸异丙酯与Cl原子、OH和NO_(3)自由基反应为例,基于反应的势能面,用过渡态... 大学物理化学教学中,Arrhenius公式阐述了反应的速率常数与温度及活化能的关系,但是,单纯从公式的表达式进行讲解,难免枯燥乏味,不利于学生理解和掌握。本文以硝酸异丙酯与Cl原子、OH和NO_(3)自由基反应为例,基于反应的势能面,用过渡态理论计算不同温度下反应的速率常数,直观形象地分析了在不同反应能垒时,反应速率常数随温度的变化情况,以期帮助学生从本质上理解Arrhenius公式,拓宽他们的知识面,培养其科学探究的意识和能力。 展开更多
关键词 动力学 势能面 速率常数 温度
下载PDF
千米深井切顶卸压自成巷支护技术及应用 被引量:1
19
作者 郭志飚 王程中 +2 位作者 尹松阳 杨东山 张帅 《煤炭工程》 北大核心 2024年第5期58-62,共5页
为了解决深部复杂条件下的切顶卸压自成巷难题,以红阳三矿703工作面运输巷道为研究对象,从恒阻大变形锚索超前支护、切顶巷内支护、切顶巷旁支护三个方面研究了切顶卸压沿空成巷支护技术,并对现场试验巷道顶板受力以及巷道围岩变形量进... 为了解决深部复杂条件下的切顶卸压自成巷难题,以红阳三矿703工作面运输巷道为研究对象,从恒阻大变形锚索超前支护、切顶巷内支护、切顶巷旁支护三个方面研究了切顶卸压沿空成巷支护技术,并对现场试验巷道顶板受力以及巷道围岩变形量进行了监测。结果表明:在超前工作面实施爆破切顶能够极大降低巷道所受应力,成巷区巷道顶板整体下沉量较小,巷中顶板最大下沉量约385 mm,平均下沉量约280 mm,巷中底鼓最大值545 mm,碎石巷帮无明显侧鼓现象,实体煤帮无明显片帮现象,满足安全和使用要求,巷道围岩变形在可控范围内,留巷效果良好。 展开更多
关键词 千米深井 切顶卸压 沿空留巷 恒阻大变形锚索
下载PDF
基于微波透射法的谷物粉相对介电常数检测装置设计
20
作者 白雪 倪利华 徐雷钧 《微波学报》 CSCD 北大核心 2024年第2期40-45,50,共7页
针对谷物属性的快速测量需求,设计了一种小型化的谷物粉相对介电常数快速检测装置。创新性地提出了一种双外差混频结构,并基于自由空间法建立了微波相移量与谷物粉相对介电常数的关系。通过对米粉、大麦粉和糯米粉在4.5 GHz~11.5 GHz频... 针对谷物属性的快速测量需求,设计了一种小型化的谷物粉相对介电常数快速检测装置。创新性地提出了一种双外差混频结构,并基于自由空间法建立了微波相移量与谷物粉相对介电常数的关系。通过对米粉、大麦粉和糯米粉在4.5 GHz~11.5 GHz频率范围内进行测量,计算出相对介电常数,采用随机森林算法进行种类鉴别。实验结果表明,相对介电常数平均相对误差不超过3.5%,样品预测正确率为96.7%,检测装置具有良好的可重复性和实用性。 展开更多
关键词 微波 谷物粉 介电常数 随机森林
下载PDF
上一页 1 2 250 下一页 到第
使用帮助 返回顶部