信号流图求解部分分式展开     

马洪明  杨玲 《成都信息工程学院学报》1996,(4)

含有多重极点的有理真分式展开为部分分式，不需要计算低阶导数。列出被求函数的各阶导数的关系式，画出各阶导数作为节点的信号流图。该图无环路，既直观表现出各高阶导数的相互关系及影响的单向性，也使求节点增益的梅森公式特别简便。该方法将求高阶导数问题简化为代数运算，特别适合于编制成计算机程序  相似文献   

射电喷流中湍动阿耳芬波对相对论电子的加速     

马春玉 《天文学报》1996,37(1):28-34

本文通过数值求解带电粒子与Ａｌｆｖｅｎ波湍动相互作用的动力学方程，得到了相对论电子在射电喷流中被加速随时间演化的解．高能电子可以加速到Ｌｏｒｅｎｔｚ因子γｙ～１０６，且形成稳态的幂律谱，尽管其谱指数Ｓ≈ｌ比观测值小，但粒子加速时间约为１０１２－１０１４秒，小于射电斑的寿命１０７年．粒子能谱指数几乎与Ａｌｆｖｅｎ波谱指数和能量损失函数无关．能量损失对加速上限有较大影响．  相似文献   

Dissipationless mergers of elliptical galaxies and the evolution of the fundamental plane     

Michael Boylan-Kolchin  Chung-Pei Ma  Eliot Quataert 《Monthly notices of the Royal Astronomical Society》2005,362(1):184-196

We carry out numerical simulations of dissipationless major mergers of elliptical galaxies using initial galaxy models that consist of a dark matter haloes and a stellar bulge with properties consistent with the observed fundamental plane. By varying the density profile of the dark matter haloes [standard Navarro, Frenk & White (NFW) profile versus adiabatically contracted NFW profile], the global stellar to dark matter mass ratio and the orbit of the merging galaxies, we are able to assess the impact of each of these factors on the structure of the merger remnant. Our results indicate that the properties of the remnant bulge depend primarily on the angular momentum and energy of the orbit; for a cosmologically motivated orbit, the effective radius and velocity dispersion of the remnant bulge remain approximately on the fundamental plane. This indicates that the observed properties of elliptical galaxies are consistent with significant growth via late dissipationless mergers. We also find that the dark matter fraction within the effective radius of our remnants increases after the merger, consistent with the hypothesis that the tilt of the fundamental plane from the virial theorem is due to a varying dark matter fraction as a function of galaxy mass.  相似文献   

地球化学景观吸引子的发现及其意义     

李长江  麻土华  徐有浪 《浙江国土资源》1995,(1)

勘查地球化学对异常评价的最大不确定性源于对地球化学景观特性的认识不够。我们应用构造相空间的方法分析了浙江儒岙幅（1:5万）水系沉积物测量的Ag含量数据，揭示了地球化学景观是具有低维吸引子（DZ≈2．9）的混饨系统。这一发现将对勘查地球化学中采样密度的选择、地球化学场模拟、异常评价等根本性问题产生重大影响。  相似文献   

Cosmological implications of BL Lac objects     

G. Z. Xie  F. K. Liu  Y. Y. Zhu  J. H. Fan  R. W. Lu 《Astrophysics and Space Science》1991,179(2):321-329

It has become clear in recent years that relativistic beaming is a good explanation for the BL Lac phenomenon. Of studies based on the relativistic beaming model of BL Lac objects, we note that the orientation of jet's axis to the line-of-sight is very small and, therefore, the observed flux emitted from a rapidly moving source is orders of magnitude higher than the flux in its rest-frame:F _obs = ^{3 +} F _intr, where is the bulk relativistic Doppler factor. Then the observed apparent magnitudem _v must be corrected for this effect. For our 39 samples, the corrected apparent magnitudem _v ^corr and logZ have a good correlation.  相似文献   

Palaeoenvironmental significance of Late Permian palaeosols in the South‐Eastern Iberian Ranges,Spain     

RAÚL DE LA HORRA  Ma ISABEL BENITO  JOSE LÓPEZ‐GÓMEZ  ALFREDO ARCHE  JOSÉ F. BARRENECHEA  JAVIER LUQUE 《Sedimentology》2008,55(6):1849-1873

The Late Permian (Wuchiapingian) Alcotas Formation in the SE Iberian Ranges consists of one red alluvial succession where abundant soil profiles developed. Detailed petrographical and sedimentological studies in seven sections of the Alcotas Formation allow six different types of palaeosols, with distinctive characteristics and different palaeogeographical distribution, to be distinguished throughout the South‐eastern Iberian Basin. These characteristics are, in turn, related to topographic, climatic and tectonic controls. The vertical distribution of the palaeosols is used to differentiate the formation in three parts from bottom to top showing both drastic and gradual vertical upwards palaeoenvironmental changes in the sections. Reconstruction of palaeoenvironmental conditions based on palaeosols provides evidence for understanding the events that occurred during the Late Permian, some few millions of years before the well‐known Permian‐Triassic global crisis.  相似文献   

Impact evaluation on groundwater of the infiltration of an urban wastewater geopurification system placed over a detrital aquifer in a semiarid region (Spain)     

L. Moreno  J. J. Durán  M. A. Casermeiro  J. R. Quintana  Ma A. Fernández 《Environmental Geology》2008,54(3):465-477

Over a period of 4 years and 4 months, the geopurification installations at Dehesas de Guadix (Granada, Spain) were monitored to determine the impact on soil and groundwater of the controlled discharge of urban wastewater, and also to identify the best indicators of the entry of the recharged water into the aquifer. The installations are located in an area where the climate is Mediterranean sub-arid, with an average precipitation of less than 287 mm/year, and a rate of evapotranspiration that is almost three times greater. The system was controlled by determining the balance of majority nutrients and boron in the soil and in the groundwater, both at the points affected directly by the wastewater discharge and at others. The quantity of mass discharged was relatively large (COD 14,656 g/m², NO₃ 85 g/m², NO₂ 4 g/m², NH₄ 2,425 g/m², PO₄ 1,143 g/m², K 1,531 g/m², B 63 g/m²). It was observed that the elimination of nutrients within the soil (COD 97.5%, PO₄ 94.4%, K 59.17%, N _total 18.8%, B 12.69%) was very efficient except for the nitrogen, which nevertheless did not reach the groundwater, as it was eliminated at deep levels of the unsaturated zone. Only 12.69% of the boron was removed, and appreciable, increasing amounts of this element did reach the groundwater. Unexpectedly, none of the majority nutrients behaved as a reliable indicator of the impact on groundwater; despite this, the boron and the bicarbonate did clearly reflect the arrival of the recharged water, and are proposed as the best indicators.  相似文献   

Experimental investigation on thermochemical sulfate reduction by H₂S initiation   总被引：1，自引：0，他引：1  

Tongwei Zhang  Alon Amrani  Qisheng Ma 《Geochimica et cosmochimica acta》2008,72(14):3518-3530

Hydrogen sulfide (H₂S) is known to catalyze thermochemical sulfate reduction (TSR) by hydrocarbons (HC), but the reaction mechanism remains unclear. To understand the mechanism of this catalytic reaction, a series of isothermal gold-tube hydrous pyrolysis experiments were conducted at 330 °C for 24 h under a constant confining pressure of 24.1 MPa. The reactants used were saturated HC (sulfur-free) and CaSO₄ in the presence of variable H₂S partial pressures at three different pH conditions. The experimental results showed that the in-situ pH of the aqueous solution (herein, in-situ pH refers to the calculated pH of aqueous solution under the experimental conditions) can significantly affect the rate of the TSR reaction. A substantial increase in the TSR reaction rate was recorded with a decrease in the in-situ pH value of the aqueous solution involved. A positive correlation between the rate of TSR and the initial partial pressure of H₂S occurred under acidic conditions (at pH ∼3-3.5). However, sulfate reduction at pH ∼5.0 was undetectable even at high initial H₂S concentrations. To investigate whether the reaction of H₂S_(aq) and occurs at pH ∼3, an additional series of isothermal hydrous pyrolysis experiments was conducted with CaSO₄ and variable H₂S partial pressures in the absence of HC at the same experimental temperature and pressure conditions. CaSO₄ reduction was not measurable in the absence of paraffin even with high H₂S pressure and acidic conditions. These experimental observations indicate that the formation of organosulfur intermediates from H₂S reacting with hydrocarbons may play a significant role in sulfate reduction under our experimental conditions rather than the formation of elemental sulfur from H₂S reacting with sulfate as has been suggested previously (Toland W. G. (1960) Oxidation of organic compounds with aqueous sulphate. J. Am. Chem. Soc.82, 1911-1916).Quantification of labile organosulfur compounds (LSC), such as thiols and sulfides, was performed on the products of the reaction of H₂S and HC from a series of gold-tube non-isothermal hydrous pyrolysis experiments conducted at about pH 3 from 300 to 370 °C and a 0.1-°C/h heating rate. Incorporation of sulfur into HC resulted in an appreciable amount of thiol and sulfide formation. The rate of LSC formation positively correlated with the initial H₂S pressure. Thus, we propose that the LSC produced from H₂S reaction with HC are most likely the reactive intermediates for H₂S initiation of sulfate reduction. We further propose a three-step reaction scheme of sulfate reduction by HC under reservoir conditions, and discuss the geological implications of our experimental findings with regard to the effect of formation water and oil chemistry, in particular LSC content.  相似文献   

Formation and abundance of doubly-substituted methane isotopologues (CH₃D) in natural gas systems     

Qisheng Ma 《Geochimica et cosmochimica acta》2008,72(22):5446-5456

Formation of the Carbon-13 (¹³C) and deuterium (D) doubly-substituted methane isotopologues (¹³CH₃D) in natural gases is studied utilizing both first-principle quantum mechanism molecular calculation and direct FTIR laboratorial measurements of specifically synthesized high isotope concentration methane gas. For ¹³CH₃D, the symmetrically breathing mode A₀ emerges as IR-detectable attributed to the molecular symmetry lowering to C_3v from T_d of the non-isotopic methane (CH₄), along with a large vibrational frequency shift from ∼3000 to ∼2250 cm⁻¹. Our studies also indicate that the concentration of ¹³CH₃D is dependent on the environmental temperature through isotope exchanges among methane isotopologues; and the Gibbs’ Free Energy difference due to Quantum Mechanics Zero-Point vibrational motions has the major contribution to this temperature dependency. Potential geologic applications of the ¹³CH₃D measurement to natural gas exploration and assessments are also discussed. In order to detect the ¹³CH₃D concentration change of each 50 °C in the natural gas system, a 10⁻⁹ resolution is desirable. Such a measurement could provide important add-on information to distinguish natural gas origin and distribution.  相似文献   

Identifying China’s leading world city: a network approach   总被引：3，自引：0，他引：3  

Xiulian Ma  Michael F. Timberlake 《GeoJournal》2008,71(1):19-35

This paper reports our research on China’s world cities. Formal network analysis of air passenger linkages for recent years among China’s most populous cities and among many of the world’s largest cities allows us to identify the country’s leading world city from among the leading Mainland candidates, Beijing, Shanghai and Guangzhou. We theorize our findings about China’s world cities in relation to both global forces (and China’s increasing entanglement with them) and the policies and actions of the national state. We examine the national and global urban network through a longitudinal, two-level analysis of airline passenger travel for four time points between about 1990 and 2005. We show that Beijing was China’s leading world city at the beginning of the time period, a status it lost nationally in as early as 1995, and then globally 10 years later. On the other hand Shanghai became China’s leading world city, and it acquired this status first nationally in 2000, and then globally in 2005. The changing status of the Chinese capital corresponds to the country’s increasing involvement with the capitalist world economy. Shanghai’s ascendance as the leading world city in China may indicate that global forces have come to play an increasingly important role relative to that of the developmental state.

Michael F. TimberlakeEmail:

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