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Spatial structure and scale feature of the atmospheric pollution source impact of city agglomeration

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Science China Earth Sciences 2005年第Z2期48卷 1-24页

作者： XU Xiangde ZHOU Xiuji SHI Xiaohui State Key Laboratory of Severe Weather Chinese Academy of Meteorological Sciences Beijing 100081 China State Key Laboratory of Severe Weather Chinese Academy of Meteorological Sciences Beijing 100081 China State Key Laboratory of Severe Weather Chinese Academy of Meteorological Sciences Beijing 100081 China

The spatial structure and multi-scale feature of the atmospheric pollution influence domain of Beijing and its peripheral areas (a rapidly developed city agglomeration) is dissected and analyzed in this paper on the basis of the atmospheric pollution dynamic-chemical process observation data of the urban building ensemble boundary layer of the Beijing City Air Pollution Observation Experiment (BECAPEX) in winter (February) and summer (August) 2003, and relevant meteorological elements and satellite retrieval aerosol optical depth (AOD), etc. comprehensive data with the dynamic-statistical integrated analysis of 'point-surface' spatial structure. Results show that there existed significant difference in the contribution of winter/summer different pollution emission sources to the component character of atmospheric pollution, and the principal component analysis (PCA) results of statistical model also indicate that SO2 and NOx dominated in the component structure of winter aerosol particle; instead, CO and NOxdominated in summer. Surface layer atmospheric dynamic and thermal structures and various pollutant species at the upper boundary of building ensembles at urban different observational sites of Beijing in winter and summer showed an 'in-phase' variation and its spatial scale feature of 'influence domain'. The power spectrum analysis (PSA) shows that the period spectrum of winter/summer particle concentration accorded with those of atmospheric wind field: the longer period was dominative in winter, but the shorter period in summer, revealing the impact of the seasonal scale feature of winter/summer atmospheric general circulation on the period of atmospheric pollution variations. It is found that from analyzing urban area thermal heterogeneity that the multi-scale effect of Beijing region urban heat island (UHI) was associated with the heterogeneous expansion of tall buildings area. In urban atmospheric dynamical and thermal characteristic spatial structures, the

关键词： atmospheric pollution source, contribution rate, boundary layer structure, multi-scale, backward trajec- tory, correlation vector, climatic effect, interaction of water, soil and atmosphere.

Whirl Interaction of a Drill Bit with the Bore-Hole Bottom

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Modern Mechanical Engineering 2015年第3期5卷 41-60页

作者： Nabil W. Musa V. I. Gulyayev L. V. Shevchuk Hasan Aldabas Department of Mechanical Engineering Philadelphia University Amman Jordan Department of Mathematics National Transport University Kyiv Ukraine

This paper deals with the theoretic simulation of a drill bit whirling under conditions of its contact interaction with the bore-hole bottom rock plane. The bit is considered to be an absolutely rigid ellipsoidal body with uneven surface. It is attached to the lower end of a rotating elastic drill string. In the perturbed state, the bit can roll without sliding on the bore-hole bottom, performing whirling vibrations (the model of dynamic equilibrium with pure rolling when maximum cohesive force does not exceed the ultimate Coulombic friction). To describe these motions, a nonholonomic dynamic model is proposed, constitutive partial differential equations are deduced. With their use, the whirling vibrations of oblong and oblate ellipsoidal bits are analyzed, the functions of cohesive (frictional) forces are calculated. It is shown that the system of elastic drill string and ellipsoidal bit can acquire stable or unstable whirl modes with approaching critical Eulerian values by the parameters of axial force, torque and angular velocity. The analogy of the found modes of motions with ones of the Celtic stones is established. It is shown that the ellipsoidal bits can stop their whirling vibrations and change directions of their circumferential motions in the same manner as the ellipsoidal Celtic stones do. As this takes place, the trajectories of the oblate ellipsoidal bits are characterized by more complicated paths and irregularities.

关键词： Deep Drilling Ellipsoidal Bits Nonholonomic Dynamics Celtic Stones Instability Forward and backward Whirling Motions

Electromagnetic Wave Propagation in Waveguide Loaded by Split Ring Resonator of Negative Permeability

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Journal of Electromagnetic Analysis and Applications 2017年第8期9卷 113-121页

作者： Abd El Moneim M. Alaa Mostafa El Said Samir F. Mahmoud Electronics and Communications Department Faculty of Engineering Cairo University Cairo Egypt

This paper aims to study and analyze the electromagnetic propagation in media with negative transverse permeability and how this leads into some physical phenomena such as the appearance of backward waves and the propagation below cutoff. This study is done through the use of metamaterials of split ring resonators. It is shown that the waveguide dimensions needed to transmit a certain frequency band, can be miniaturized to half its dimension. The analytical determination of the propagation inside a waveguide in the presence of two slabs with dielectric permittivity and negative transverse permeability is derived. Finally it is shown by simulation, how to obtain a backward wave with lower loss than reported earlier in the literature.

关键词： Negative Transverse Permeability Metamaterials backward Waves Miniaturization of Waveguide Propagation Below Cutoff

The “Chinese Dream ”in a World of Nightmares

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International Understanding 2014年第1期 52-54页

作者： Angel E.Pino Tri-continental magazine the delegation of the Organization of Solidarity of the Peoples of Africa

Those who visit China with some frequency usually exclaim,in a mixture of surprise and admiration,that it is a country that changes with each passing *** and development have lightening speed here,and it is a phenomenon that exceeds the observation or simple perception of the *** one of the planet’s poorest and most backward countries。

关键词： perception backward surprise planet perceived Chin

Speech at the High-level Dialogue

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Peace 2014年第4期 9-10页

作者： Yu Hongjun CPAPD

The commemoration of 2014 International Day of Peace,themed with"A More Secure Asia Aspired by People"is highly *** begin with,I would like to share 3 points on Asian security with ***,problems in the realm of traditional security are *** security perspectives and security systemic structures left by the cold war are threatening Asian peace and development,yet some countries still believe in backward

关键词： Peace backward realm begin peace threatening coope

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The Nature of Time

语言教育 1994年第2期 40-41页

作者：白永康

Scientists have debated for many years about the nature of *** does time seem to flow the past to the future? why does it never flow in the opposite direction-from the

关键词： never opposite Nature older backward 少典 stand stars

An Implicit-Explicit Computational Method Based on Time Semi-Discretization for Pricing Financial Derivatives with Jumps

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Open Journal of Statistics 2018年第2期8卷 334-344页

作者： Yang Wang School of Economic Jinan University Guangzhou China

This paper considers pricing European options under the well-known of SVJ model of Bates and related computational methods. According to the no-arbitrage principle, we first derive a partial differential equation that the value of any European contingent claim should satisfy, where the asset price obeys the SVJ model. This equation is numerically solved by using the implicit- explicit backward difference method and time semi-discretization. In order to explain the validity of our method, the stability of time semi-discretization scheme is also proved. Finally, we use a simulation example to illustrate the efficiency of the method.

关键词： SVJ Model of Bates Time Semi-Discretization Stability No-Arbitrage Principle Implicit-Explicit backward Difference Method

Matrix Padé-Type Method for Computing the Matrix Exponential

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Applied Mathematics 2011年第2期2卷 247-253页

作者： Chunjing Li Xiaojing Zhu Chuanqing Gu 不详

Matrix Padé approximation is a widely used method for computing matrix functions. In this paper, we apply matrix Padé-type approximation instead of typical Padé approximation to computing the matrix exponential. In our approach the scaling and squaring method is also used to make the approximant more accurate. We present two algorithms for computing and for computing with many espectively. Numerical experiments comparing the proposed method with other existing methods which are MATLAB’s functions expm and funm show that our approach is also very effective and reliable for computing the matrix exponential . Moreover, there are two main advantages of our approach. One is that there is no inverse of a matrix required in this method. The other is that this method is more convenient when computing for a fixed matrix A with many t ≥ 0.

关键词： Matrix Padé-Type Approximation Matrix Exponential Scaling and Squaring backward Er-ror

On Transient Simulation of Field Equations

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Applied Mathematics 2019年第9期10卷 719-727页

作者： Peter Chen School of Mechanical and Manufacturing Engineering University of New South Wales Sydney Australia

We investigate under what conditions transient simulation could be used to integrate backward in time so that the initial field could be recovered from later histories. In this paper we use realistic examples and find that, in long histories, traces of the initial field would be present only in the exact analytical solutions. We conclude that the recovery of initial field is possible only if the equations could be solved analytically or only short time periods are involved. In practice, it is not possible to detect those traces by measurements or observations. If numerical procedures are used, truncation and discretization errors are always present. Fine-tuning of system parameters used or transforming time into another pseudo time frame may allow numerical integration to be carried out backward in time. But numerical instability is still a problem. Large spurious increases found by numerical procedures are most likely due to numerical inaccuracy and instability.

关键词： Solution of Differential Equations Transient Simulation Numerical Instability Mathematical Modelling backward Time Integration