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Abrupt climate change and collapse of ancient civilizations at 2200BC-2000BC

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Progress in Natural Science:Materials International 2005年第10期15卷 46-52页

作者： WANG Shaowu (Department of Atmospheric Science, school of physics, peking university, beijing 100871, China) Department of Atmospheric Science School of Physics Peking University Beijing 100871 China

Plentiful evidence of historical, archaeological and palaeoclimatic studies proved that an abrupt change from wetter to drier climate occurred over the Nile Valley,the Mesopotamia, the Indus Valley and Huanghe River Valley at 2200BC-2000BC. The abrupt change was developed based on the general lowering of temperature in the middle latitudes, and was a strong cold event since the beginning of the Megathermal (8.5-3.0 kaBP). Collapse of Nile civilization appeared at the First Intermediate Period (2181BC-2040BC). Civilization of Mesopotamia began collapse following the disintegration of Akkadian Empire. This process lasted to the foundation of Babylon Kingdom from 2200BC to 1900BC. Indus civilization abruptly fell off at 1800BC. A widespread alternation of archaeological cultures happened in China at ca. 2000BC except only in its central part. Longsheng culture was replaced by the Erlitou culture, which is now acknowledged in China as Xia Culture. Foundation of Xia Dynasty at 2070BC opened a new chapter in the development of Chinese civilization. Studies indicated that abrupt climate change may be caused by the weakening of the Thermohaline Circulation (THC).

关键词： 2200BC-2000BC abrupt climate change collapse of ancient civilization.

INFINITE ELEMENT METHOD FOR THE EXTERIOR PROBLEMS OF THE HELMHOLTZ EQUATIONS

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Journal of Computational Mathematics 2000年第6期18卷 657-672页

作者： Lung-an Ying (school of Mathematical Sciences, peking university, beijing 100871, China) 北京大学北京 100871

There are two cases of the exterior problems of the Helmholtz equation. If λ ≥ 0 the bilinear form is coercive, and if λ < 0 it is the scattering problem. We give a new approach of the infinite element method, which enables us to solve these exterior problems as well as corner problems. A numerical example of the scattering problem is given. [ABSTRACT FROM AUTHOR]

关键词： Helmholtz equation exterior problem infinite element method

Probability parametric imaging with DCE-MRI data to identify prostate cancer in the peripheral zone

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Progress in Natural Science:Materials International 2006年第9期16卷 948-953页

作者： HUANG Xinrui, WANG Qiang, XU Yufeng, WANG Xiaoying and BAO Shanglian ( The Key Laboratory of Medical physics and Engineering, peking university, beijing 100871, China The Medical {3. of peking university, beijing 100083. China 3. The First Hospital of peking university, beijing 10003., China) Key Laboratory of Medical physics and Engineering Peking University Beijing 100871 China Medical school of peking university Beijing 100083 China First Hospital of peking university Beijing 100034 China

To quantitatively analyze prostate dynamic contrast-enhanced magnetic resonance images (DCE-MRI), a retrospective study was carried out to construct a mathematical model to predict whether a lesion is cancerous or not. With known diagnosis of 52 re-gions-of-interest (10 malignant, 26 benign and 16 normal) in peripheral zone (PZ) of prostate from 18 patients undergoing needle biopsy and 8 normal volunteers, we combined feature parameters (k1, k2 and tp) from the linear-slope model with logistic regression to determine the statistical probability model. Prostate cancerous probability maps were derived using the model on each subject to examine the correlation between the model-based prediction and the known diagnosis. Compared the model prediction results of 52 regions-of-interest with the histopathologic results, the total agreement rate was 90.4 % ; the agreement rate was 60 % for the malignant and 97. 6 % for the nonmalignant. The diagnostic results only referencing the probability maps by two radiologists showed a high agreement in tissue characteristics and lesion location with the combining results from other diagnostic techniques such as PSA (prostate specific antigen) level and MRS (magnetic resonance spectroscopy) .

关键词： time-intensity curve prostate DCE-MRI logistic regression probability parametric image.

|m| Partial wave treatment for two-dimensional Coulomb-scattering and Regge pole

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Science China(physics,Mechanics & Astronomy) 2004年第6期47卷 676-684页

作者： WANG Jing & ZENG Jinyan Department of physics,Tsinghua university,beijing 100084,China {3.,peking university,beijing 100871,China Department of physics Tsinghua University Beijing 100084 China school of physics Peking University Beijing 100871 China

The symmetry and |m| partial-wave analysis for two-dimensional (2D) Coulomb-scattering is investigated. As a function of energyE, the |m| partial-wave scattering amplitudef |m|(θ) is analytically continuated to the, negativeE (complexk) plane, and it is found that the bound state energy eigenvalues (E<0) are just located at the poles off |m|(θ) on the positive imaginaryk axis as is expected. In addition, as a function of |m|,f |m|(θ) is analytically continuated to the complex |m| plane, the bound state energy eigenvalues are just located at the poles off |m|(θ) on the positive real |m| axis.

关键词： two-dimensional Coulomb scattering, |m| partial-wave, Regge pole.

Inclination of Broad Line Region in Narrow Line and Broad Line Seyfert 1 Galaxies

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Chinese Journal of Astronomy and Astrophysics 2002年第6期2卷 487-500页

作者： Tian-Zhi Zhang and Xue-Bing WuDepartment of Astronomy, school of physics, peking university, beijing 100871 Department of Astronomy School of Physics Peking University Beijing 100871

The sizes of the Broad Line Region (BLR) of some Seyfert 1 galaxies and nearby quasars can be determined by the reverberation mapping method. Combining with the observed FWHM of Hbeta emission line and assuming that the motion of BLR clouds is virialized, the black hole masses of these objects have been estimated. However, this method strongly depends on the poorly-understood geometry and inclination of the BLR. On the other hand, a tight correlation between the black hole mass and the bulge velocity dispersion was recently found for both active and nearby inactive galaxies. This may provide another method, independent of the BLR geometry, for estimating the black hole mass. Using this method for estimating the black hole mass and combining with the measured BLR size and FWHM of Hbeta emission line, we derived the BLR inclination angles for 20 Seyfert 1 galaxies under the assumption that the BLR is disk-like. The derived inclination angles agree well with those derived previously by fitting the UV continuum and Hbeta emission line profiles. Adopting a relation between the FWHMs of [OIII]lambda5007 forbidden line and the stellar velocity dispersion, we also estimated the BLR inclinations for 50 narrow line Seyfert 1 galaxies (NLS1s). We found that the inclinations of broad Line Seyfert 1 galaxies (BLS1s) axe systematically greater than those of NLS1s, which seldom exceed 3.degrees. This may be an important factor that leads to the differences between NLS1s and BLS1s if the BLR of NLS1s is really disk-like.

关键词： galaxies : active galaxies : nuclei galaxies : Seyfert

Kinetic characteristics of continuous flow polymerase chain reaction chip: A numerical investigation

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Science China(Technological Sciences) 2010年第7期53卷 1967-1972页

作者： WANG ShiYing1 & WANG Wei2,3.1 school of physics, peking university, beijing 100871, China 2 Institute of Microelectronics, peking university, beijing 100871, China 3.National Key Laboratory of Science and Technology on Micro/Nano Fabrication, beijing 100871, China school of physics Peking University Beijing China Institute of Microelectronics Peking University Beijing China National Key Laboratory of Science and Technology on Micro/Nano Fabrication Beijing China

Continuous flow PCR (polymerase chain reaction) chip holds impressive advantages compared to micro chamber PCR chip. In order to have better understanding of kinetic characteristics of continuous flow PCR chip, a comprehensive mathematical model is presented in this paper, including melting, annealing and extension phases of a typical PCR process which has the essence of a convection-diffusion-reaction system. Using this model, we can simulate the PCR process in series of reaction cycles. Numerical results show that the average sample velocity plays a significant role in affecting the amplification efficiency. Also, appropriate combination of the PCR mixture is important for high-quality DNA amplification. Giving a large initial DNA concentration range, the continuous flow PCR scheme holds excellent real-time detection ability theoretically. The present numerical model bridges the temperature distribution to the real DNA amplification, and thereby is able to successfully predict continuous flow PCR properties which are important for the chip design.

关键词： continuous flow PCR chip numerical simulation convection-diffusion-reaction system

Genetic and logic networks with the signal-inhibitor-activator structure are dynamically robust

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Progress in Natural Science:Materials International 2006年第12期16卷 1329-1336页

作者： LI Fangting** and TAN Ning(school of physics and Centre for Theoretical Biology, peking university, beijing 100871, China) school of physics and Centre for Theoretical Biology Peking University Beijing 100871 China

The proteins, DNA and RNA interaction networks govern various biological functions in living cells, these networks should be dynamically robust in the intracellular and environmental fluctuations. Here, we use Boolean network to study the robust structure of both genetic and logic networks. First, SOS network in bacteria E. coli, which regulates cell survival and repair after DNA damage, is shown to be dynamically robust. Comparing with cell cycle network in budding yeast and flagella network in E. coli, we find the signal-inhibitor-activator (SIA) structure in transcription regulatory networks. Second, under the dynamical rule that inhibition is much stronger than activation, we have searched 3.node non-self-loop logical networks that are dynamically robust, and that if the attractive basin of a final attractor is as large as seven, and the final attractor has only one active node, then the active node acts as inhibitor, and the SIA and signal-inhibitor (SI) structures are fundamental architectures of robust networks. SIA and SI networks with dynamic robustness against environment uncertainties may be selected and maintained over the course of evolution, rather than blind trial-error testing and being an accidental consequence of particular evolutionary history. SIA network can perform a more complex process than SI network, and SIA might be used to design robust artificial genetic network. Our results provide dynamical support for why the inhibitors and SIA/SI structures are frequently employed in cellular regulatory networks.

关键词： genetic network signal-inhibitor-activator (SIA) structure Boolean network model dynamical robust.

The regular representation and regular covariant representation of crossed products of Woronowicz C^(*)-algebras

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Science China Mathematics 2005年第9期48卷 1245-1259页

作者： ZHANG Xiaoxia~(1,2) & GUO Maozheng~(1,3. 1. school of Mathematical Sciences,peking university,beijing 100871,China 2. Department of Mathematics,Yantai {3.,Yantai 264005,China 3. LMAM,peking university,beijing 100871,China school of Mathematical Sciences Peking University Beijing China Department of Mathematics Yantai University Yantai China LMAM Peking University Beijing China

In this paper,it is shown that the regular representation and regular covariant representation of the crossed products A×α G correspond to the twisted multiplicative unitary operators,where A is a Woronowicz C~*-algebra acted upon by a discrete group ***,it is also shown that the regular covariant C~*-algebra is the Woronowicz C~*-algebra which corresponds to a multiplicative ***,an explicit description of the multiplicative unitary operator for C(SU_q(2) )×α (?) is given in terms of those of the Woronowicz C~*-algebra C(SU_q(2) ) and the discrete group G.

关键词： multiplicative unitary operator, Woronowicz C*-algebra, crossed product.

REGULARITY OF SOLUTIONS TO THE DIRICHLET PROBLEM FOR DEGENERATE ELLIPTIC EQUATION

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Chinese Annals of Mathematics,Series B 2003年第4期24卷 529-540页

作者： CHEN YEMIN school of Mathematics, peking university, beijing 100871, China. school of Mathematics Peking University Beijing 100871

In this paper, the author studies the regularity of solutions to the Dirichlet problem forequation Lu = f, where L is a second order degenerate elliptic operator in divergence form inΩ, a bounded open subset of Rn (n... 详细信息

关键词： Regularity Dirichlet problem Degenerate Weighted spaces