检索结果-内蒙古大学图书馆

POLARIMETRIC RADAR STUDIES OF ATMOSPHERIC ICE PARTICLES

IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING 1994年第1期32卷 1-10页

作者： VIVEKANANDAN, J BRINGI, VN HAGEN, M MEISCHNER, P DEUTSCH FORSCHUNGSANSTALT LUFT & RAUMFAHRT INST ATMOSPHER PHYSDIV CLOUD PHYSOBERPFAFFENHOFENGERMANY COLORADO STATE UNIV DEPT ELECT ENGNFT COLLINSCO 80523

Single scattering properties of ice crystals are described at microwave frequencies using discrete dipole approximations and Rayleigh scattering techniques. For a given shape, the average bulk densities of ice crystals can be estimated using the ratio of the copolarized radar signal in a linear (horizontal, vertical) polarization basis. Reflectivity depends on the ice content (g . m-3), and also on both size distribution parameters and average bulk density of the scatterers. Differential propagation phase is primarily a function of shape, ice water content, and is independent of size distribution parameters. Thus, by using a combination of polarimetric radar measurements, average ice content, bulk density, and shape of distributed scatterers can be inferred. These techniques become quite complex in the case of a winter storm where scatterers can exist with varying shape and bulk densities. Polarimetric radar properties of such complex distributed scatterers are modeled. Physical variations in the relation among ice water content, reflectivity, and differential propagation phase are considered with respect to change in the shape of size distribution, bulk density, and average shape of the scatterers. Also, simultaneous polarimetric radar observations and in situ aircraft measurements are shown to demonstrate practical applicability of the techniques.

关键词： single scattering RADAR SIGNALS Ice Water Radar polarimetry ice contents WINTER STORMS Microwave frequencies Ice Crystals Bulk density distributed parameter

来源：评论

学校读者我要写书评

暂无评论

Statistical analysis of low-voltage electron emission from nanocarbon cathodes

引用

JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS 2003年第6期97卷 1240-1245页

作者： Zakhidov, AA Obraztsov, AN Volkov, AP Lyashenko, DA Moscow MV Lomonosov State Univ Moscow 119992 Russia

The current-voltage (I-V) characteristics of low-voltage electron emission from nanocarbon (nC) film cathodes consisting of carbon nanotubes and/or nanosized graphite crystallites is analyzed. It is shown that an adequate qualitative description of the I-V characteristics can be obtained within the classical Fowler-Nordheim (FN) theory with regard to the normal statistical distribution of the parameters of emission sites situated on the cathode surface. However, the application of this classical theory to obtain quantitative estimates leads to a considerable discrepancy between the results obtained and experimental data. A quantitative agreement between experimental data and theoretical results can be achieved under the assumption that the effective areas of emission sites increase at the expense of the lateral surfaces of nC structures. (C) 2003 MAIK "Nauka/Interperiodica".

关键词： Experimental data Statistical analysis Gaussian distribution Electron emission Low voltage distributed parameter Statistical methods

来源：评论

学校读者我要写书评

暂无评论

Dynamic modeling and characteristic analysis of natural gas network with hydrogen injections

引用

INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 2022年第78期47卷 33209-33223页

作者： Zhou, Dengji Wang, Chen Yan, Siyun Yan, Yuan Guo, Youyou Shao, Tiemin Li, Taotao Jia, Xingyun Hao, Jiarui Shanghai Jiao Tong Univ Key Lab Power Machinery Engn Educ Minist Shanghai 200240 Peoples R China Shanghai Jiao Tong Univ Sichuan Res Inst Sichuan 610231 Peoples R China China Natl Oil & Gas Explorat & Dev Corp Beijing 100034 Peoples R China China Oil & Gas Pipeline Network Corp Beijing 100010 Peoples R China

With the transformation of energy structure, the proportion of renewable energy in the power grid continues to increase. However, the power grid's capacity to absorb renewable is limited. In view of this, converting the excess renewable energy into hydrogen and injecting it into natural gas network for transportation can not only increase the absorption capacity of renewable energy but also reduce the transportation cost of hydrogen. While this can lead to the problem that hydrogen injection will make the dynamic characteristics of the pipeline more complicated, and hydrogen embrittlement of pipeline may occur. It is of great significance to simulate the dynamic characteristics of gas pipeline with hydrogen injection, especially the hydrogen mixture ratio. In this paper, the cell segmentation method is used to solve each natural gas pipeline model, the gas components are recal-culated in each cell and the parameters of partial differential equation are updated. Additionally, the dynamic simulation model of natural gas network with hydrogen in-jections is established. Simulation results show that for a single pipeline, when the inlet hydrogen ratio changes, whether or not hydrogen injection has little influence on the pressure and flow. The propagation speed of hydrogen concentration is far less than that of the pressure and flow rate, and it takes about 1.2 x 105 s for the 100 km pipeline hydrogen ratio to reach the steady state again.(c) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

关键词： Natural gas network Dynamic modeling Hydrogen injection Power to gas (P2G) distributed parameter characteristics

来源：评论

学校读者我要写书评

暂无评论

Problems and Constructive Methods of Applied Control Theory for the Technical Systems with distributed parameters

Problems and Constructive Methods of Applied Control Theory ...

引用

International Conference on Complex Systems: Control and Modeling Problems

作者： Edgar Rapoport Yuliya Pleshivtseva Samara State Technical University ICCS RASSamaraRussia

The approaches and methods for further development of applied theory of systems with distributed parameters are suggested to solve problems of open-loop controllability, construction of program optimization, a wide ra... 详细信息

关键词： control system synthesis controllability distributed parameter systems open loop systems optimal control optimisation vectors Open loop systems control system synthesis distributed parameter systems Optimal control controllability distributed parameter Control Theory Systems Theory program optimization

来源：评论

学校读者我要写书评

暂无评论

Accurate closed-form approximations to generalised-K sum distributions and applications in the performance analysis of equal-gain combining receivers

引用

IET COMMUNICATIONS 2011年第7期5卷 982-989页

作者： Peppas, K. P. Natl Ctr Sci Res Demokritos Inst Informat & Telecommun Lab Mobile Commun Athens 15310 Greece

In this study, highly accurate closed-form approximations to the probability density function of the sum of independent identically distributed (i.i.d.) generalised-K fading envelopes are derived. These approximations are valid for a wide range of values of the distribution parameters and number of summands. Based on the previously derived formulas, simple precise approximations for the outage probability and the average bit error probability of equal-gain combining receivers operating on i.i.d. generalised-K fading channels are proposed. Extensive numerically evaluating and computer simulation results are presented to demonstrate the proposed analysis.

关键词： ABER sums Receivers Task Performance and Analysis Probability density function distributed parameter system performance analysis Suppliers files

来源：评论

学校读者我要写书评

暂无评论

Bayesian uncertainty assessment of flood predictions in ungauged urban basins for conceptual rainfall-runoff models

引用

HYDROLOGY AND EARTH SYSTEM SCIENCES 2012年第4期16卷 1221-1236页

作者： Sikorska, A. E. Scheidegger, A. Banasik, K. Rieckermann, J. Eawag Swiss Fed Inst Aquat Sci & Technol Dept Urban Water Management CH-8600 Dubendorf Switzerland Warsaw Univ Life Sci SGGW Dept Hydraul Engn PL-02787 Warsaw Poland

Urbanization and the resulting land-use change strongly affect the water cycle and runoff-processes in watersheds. Unfortunately, small urban watersheds, which are most affected by urban sprawl, are mostly ungauged. This makes it intrinsically difficult to assess the consequences of urbanization. Most of all, it is unclear how to reliably assess the predictive uncertainty given the structural deficits of the applied models. In this study, we therefore investigate the uncertainty of flood predictions in ungauged urban basins from structurally uncertain rainfall-runoff models. To this end, we suggest a procedure to explicitly account for input uncertainty and model structure deficits using Bayesian statistics with a continuous-time autoregressive error model. In addition, we propose a concise procedure to derive prior parameter distributions from base data and successfully apply the methodology to an urban catchment in Warsaw, Poland. Based on our results, we are able to demonstrate that the autoregressive error model greatly helps to meet the statistical assumptions and to compute reliable prediction intervals. In our study, we found that predicted peak flows were up to 7 times higher than observations. This was reduced to 5 times with Bayesian updating, using only few discharge measurements. In addition, our analysis suggests that imprecise rainfall information and model structure deficits contribute mostly to the total prediction uncertainty. In the future, flood predictions in ungauged basins will become more important due to ongoing urbanization as well as anthropogenic and climatic changes. Thus, providing reliable measures of uncertainty is crucial to support decision making.

关键词： Model structures Flood forecasting error model water circulation Runoff Urbanization Bayesian Statistics Uncertainty distributed parameter

来源：评论

学校读者我要写书评

暂无评论

A diffusion model of roundtrip time

引用

COMPUTATIONAL STATISTICS & DATA ANALYSIS 2004年第1期45卷 25-50页

作者： Bohacek, S Rozovskii, B Univ Delaware Dept Elect & Comp Engn Newark DE 19716 USA Univ So Calif Dept Math Los Angeles CA 90089 USA

A diffusion model of the roundtrip time experienced by packets on the Internet is developed. The parameters of the diffusion system are modeled as Markov processes. The transition probabilities of the parameters are modeled with a mixture of Laplace distributions. The stationary distributions of the parameters are modeled as Normal distributions. The results show that the model is able to reproduce the probabilities observed in the Internet. (C) 2003 Elsevier B.V. All rights reserved.

关键词： Internets Packet parameters Laplace DIFFUSION MODELS Gaussian distribution Markov chain distributed parameter TRANSITION PROBABILITIES

来源：评论

学校读者我要写书评

暂无评论

Simulation and experiment on bridge-shaped nonlinear piezoelectric vibration energy harvester

引用

SMART MATERIALS AND STRUCTURES 2019年第4期28卷

作者： Qin, Yi Wei, Tiantian Zhao, Yue Chen, Haizhou Chongqing Univ State Key Lab Mech Transmiss Chongqing 400044 Peoples R China Qingdao Univ Sci & Technol Coll Electromech Engn Qingdao 266061 Peoples R China

There is abundant of vibration energy in environment. Using piezoelectric energy harvesters to power ultra-low power wireless sensors has become a hot topic in recent years. Most piezoelectric energy harvesters have satisfactory output only at one resonant frequency, while once the external excitation frequency deviates from the resonant frequency, the voltage output will drop significantly. Therefore, this paper proposes a bridge-shaped piezoelectric energy harvester to broaden the frequency band for energy harvesting, and the harvester can adaptively adjust the natural frequency of the system to match the external excitation. Based on the two-dimensional nonlinear Euler-Bernoulli beam hypothesis and the Hamilton principle, the distributed-parameter dynamic model of the nonlinear energy harvesting system is set up. By use of variation operator and nondimensionalization, we derive the dimensionless electromechanical coupling equations. With the harmonic balance method, the approximate equations for calculating voltage amplitude and average power are derived. And then the model is numerically solved and analyzed by considering the influence of excitation frequency, excitation amplitude, mass position and load on the output performance of the bridge-type piezoelectric energy harvester. Finally, various comprehensive experiments are performed to verify the results of simulation, and the dynamic effects of the moving mass on the output characteristics are studied. It can be noted that the moving mass can improve the voltage output of the bridge type energy harvester by changing the resonant frequency of the bridge-type piezoelectric energy harvester and impacting the piezoelectric beam. The proposed vibration energy collection device can adaptively tune the resonant frequency and has practical value in engineering.

关键词： nonlinear piezoelectric energy harvesting distributed parameter band widening adaptive frequency tuning

来源：评论

学校读者我要写书评

暂无评论

Maximizing the lift-drag ratio of wing airfoils with a turbulent boundary layer: Exact solutions and approximations

引用

DOKLADY PHYSICS 2008年第4期53卷 221-227页

作者： Elizarov, A. M. Kazan VI Lenin State Univ Chebotarev Res Inst Math & Mech Kazan 420008 Russia

The problem under consideration pertains to the class of variational inverse boundary-value problems of aero-hydrodynamics (IBVPA) [1] and is related to both the optimum design problems (see, e.g., [2]) and the optimization problems for systems with distributed parameters [3]. It has been demonstrated previously [1,4, 5] that, using methods of the IBVPA theory [6], it is possible to formulate this problem in terms of the classical calculus of variations, while employing the inviscid incompressible-fluid and boundary-layer models allows one to write the optimized functional and the optimization constraints in an explicit form. In this study, the exact solution was obtained using an apparatus developed previously [4,5].

关键词： Constrained optimization Calculus of variation Wings design problems Airfoils approximation EXACT SOLUTIONS distributed parameter turbulent boundary layer Exact

来源：评论

学校读者我要写书评

暂无评论

Response of SiCf/Si3N4 composites under static and cyclic loading - An experimental and statistical analysis

引用

JOURNAL OF ENGINEERING MATERIALS AND TECHNOLOGY-TRANSACTIONS OF THE ASME 1997年第2期119卷 186-193页

作者： Mahfuz, H Maniruzzaman, M Vaidya, U Brown, T Jeelani, S ***

Monotonic tensile and fatigue response of continuous silicon carbide fiber reinforced silicon nitride (SiCf/Si3N4) composites has been investigated The monotonic tensile tests have been performed at room and elevated temperatures. Fatigue tests have been conducted at room temperature (RT), at a stress ratio, R = 0.1 and a frequency of 5 Hz. It is observed during the monotonic tests that the composites retain only 30 percent of its room temperature strength at 1600 degrees C suggesting a substantial chemical degradation of the matrix at that temperature. The softening of the matrix at elevated temperature also causes reduction in tensile modulus, and the total reduction in modulus is around 45 percent. Fatigue data have been generated at three load levels and the fatigue strength of the composite has been found to be considerably high;about 75 percent of its ultimate room temperature strength. Extensive statistical analysis has been performed to understand the degree of scatter in the fatigue as well as in the static test data. Weibull shape factors and characteristic values have been determined for each set of tests and their relationship with the response of the composites has been discussed. A statistical fatigue life prediction method developed from the Weibull distribution is also presented. Maximum Likelihood Estimator with censoring techniques and data pooling schemes has been employed to determine the distribution parameters for the statistical analysis. These parameters have been used to generate the S-N diagram with desired level of reliability Details of the statistical analysis and the discussion of the static and fatigue behavior of the composites are presented in this paper.

关键词： Environmental Temperature Percent Fatigue Statistical analysis Weibull distribution Composites Statistical methods SiC fiber maximum likelihood estimation Room temperature Monotonic distributed parameter TENSILE MODULUS Data analysis Fatigue strength

来源：评论

学校读者我要写书评

暂无评论

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案：

请选择收藏分类：

通借通还

建议与咨询 留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案： 新增检索档案 确定 取消

请选择收藏分类： 新增自定义分类 确定 取消

通借通还

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

请选择保存的检索档案：

请选择收藏分类：