一种频标变换的方法

对基准频率进行变换通常采用锁相环路或频率搬移电路，前者作为一个环路电路肯定复杂，调试难度增加，后者由于需要混频器或乘法器也存在类似问题．该文介绍的基准频率变换方法实质上是一种频率搬移法。采用MOTOROLA公司生产的MC14011、CMOS与门非电路及模块化晶体带通滤波器可使电路大大简化．调试十分方便。实验结果表明，具有工作可靠、稳定度高、体积小等特点。文中还讨论了工作原理和设计要点。     

Structures and properties of metal-free and magnesium tetrathieno[2,3-b]porphyrazine investigated using density functional theory

Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculation were adopted to study the structures and properties of metal-free and magnesium tetrathieno[2,3-b]porphyrazine (TTPPzH₂ and TTPPzMg) using B3LYP method with the 6–31G(d) basis set. A comparison of the geometrical structures, atomic charges, molecular orbitals, UV-vis spectra and infrared (IR) spectra among tetrathieno[2,3-b]porphyrazine (TTPPzH₂), phthalocyanine (H₂Pc) and porphyrazine (H₂Pz) compounds was performed. The substituent effect of the thiophene heterocycle for electron-donating on the structures and properties of these compounds has been discussed. Compared with other atoms, the charge distribution of C_β atoms adjacent to the sulfur atom is significantly influenced by the thiophene heterocycle substituents. The enlargement of the HOMO-LUMO gaps from H₂Pc and MgPc to TTPPzH₂ and TTPPzMg is at the origin of the observed blue shift of the Q band when moving from H₂Pc to TTPPzH₂ compounds. Special emphasis has been devoted to the strongest B bands for TTPPzH₂ compounds which show red shift due to the large destabilization of the lower lying occupied orbitals compared with the corresponding B bands of H₂Pc compounds. With the assistance of animated pictures produced on the basis of the normal coordinates, the significant peaks and vibration modes in the IR spectra of all the compounds were assigned and analyzed.     

Palaeogeothermal response and record of the effusing of Emeishan basalts in the Sichuan basin

Thermal history of the Sichuan basin is reconstructed based on vitrinite reflectance from boreholes in the basin using a paleo-heat flow method.The results show that the Sichuan basin experienced a relatively low heat flow period in the Early Paleozoic,and an elevated paleo-heat flow,ranging 60-80 mW/m2 with a maximum as high as 100 mW/m2 around 259 Ma,from the beginning of the Late Paleozoic to the end of the early Permian,and a decreased paleo-heat flow from the late Permian to the late Triassic,and then ...     

Estimation of wind erosion rates by using 137Cs tracing technique: A case study in Tariat-Xilin Gol transect, Mongolian Plateau

Wind erosion is one of the major environmental problems in semi-arid and arid regions. Here we established the Tariat-Xilin Gol transect from northwest to southeast across the Mongolian Plateau, and selected seven sampling sites along the transect. We then estimated the soil wind erosion rates by using the 137Cs tracing technique and examined their spatial dynamics. Our results showed that the 137Cs inventories of sampling sites ranged from 265.63=44.91 to 1279.54=166.53 Bq. m-2, and the wind erosion rates varied from 64.58 to 419.63 t. km-2. a-~ accordingly. In the Mongolia section of the transect （from Tariat to Sainshand）, the wind erosion rate increased gradually with vegetation type and climatic regimes; the wind erosion process was controlled by physical factors such as annual precipitation and vegetation coverage, etc., and the impact of human activities was negligible. While in the China section of the transect （Inner Mongolia）, the wind erosion rates of Xilin Hot and Zhengxiangbai Banner were thrice as much as those of Bayannur of Mongolia, although these three sites were all dominated by typical steppe. Besides the physical factors, higher population density and livestock carrying level should be responsible for the higher wind erosion rates in these two regions of Inner Mongolia.     

Using 137Cs tracing technique to estimate wind erosion rates in the typical steppe region,northern Mongolian Plateau

Wind erosion is one of the major factors of land degradation in the typical steppe region, northern Mongolian Plateau. Using ^137Cs tracing technique, we estimated the wind erosion rates of different pastures and abandoned farmland at Bayannur and Karakorum in Mongolia. The pastures and cutting grassland at Bayannur were slightly eroded by wind, with the rates of 64.58-169.07 t·km^-2.a^-1. The abandoned farmland in Karakorum, however, was strongly eroded by wind, with annual surface soil loss of 4.05 mm. a^-1, and wind erosion rates up to 6723.06 t· km^-2. a^-1. The total loss of surface soil due to wind erosion has been 17.4 cm since the cultivation of the steppe land in the 1960s. The wind ero- sion rate at the abandoned farmland was much higher than that at the typical steppe sites, showing that the cultivation led to serious wind erosion in the typical steppe region, northern Mongolian Plateau. By contrast, traditional livestock grazing resulted in less disturbance to the surface soil, and did not induce to devastating wind erosion, which plays an important role in maintaining the stability of the steppe ecosystem in the northern Mongolian Plateau.     

Theoretical study on stability and nonlinear optical properties of tetrahydropyrrole diradical and its isoelectronic systems in different electronic states

The polarizabilities and hyperpolarizabilities of the tetrahydropyrrole diradical in different electronic states have been investigated using ab initio and density functional theory(DFT) methods combined with the finite field(FF) approach.The polarizability average value αs is a maximum for the singlet state,while that for the closed-shell is a minimum.The trend in second hyperpolarizability average value γ is in good agreement with that for αs.The γ values of the singlet and triplet states are,respectively...     

The unified ideal model of mean motion resonance of artificial satellites due to geopotential perturbations

From Kaula’s Earth gravitational potential written in classical orbital elements, the unified ideal model of mean motion resonance of artificial satellites due to geopotential perturbations is developed in this paper first, through a suitable sequence of canonical transformations constructed by implicit functions. This unified ideal orbital resonance model is valid for all the commensurabilities between the rotational angular velocity of the Earth and the angular velocities of mean orbital motion of artificial satellites with arbitrary inclination and small eccentricity, and can be also transformed into Garfinkel’s general expression of ideal resonance problem. Then 1/1 resonance of the 24-hour satellite with arbitrary inclination and small eccentricity is analyzed under the effect of harmonics of J2 and J 22 of the geopotential, based on the unified ideal model of mean motion resonance. The analytical expressions of the libration period and libration half width of the 1/1 resonance of the 24-hour satellite with arbitrary inclination and small eccentricity are presented.     

Quantum chemical studies on tuning the second-order nonlinear optical molecular switching of triarylborane derivatives

In this work, density functional theory (DFT) combined with the finite field (FF) method has been adopted to analyze the second-order nonlinear optical (NLO) properties of the triarylborane (TAB) derivatives obtained by introducing different inductive electron groups into the phenylene ring of the TAB (RTAB, where R=2-C6H5-C2B10H10(1),R=F(2), R=Me(3),R=NO2(4),R=NH2(5)). The static first hyperpolarizabilities (βtot) of the RTAB molecules can be switched by binding one F- to the boron center (RTAB′) or one-electron reduction (RTAB"). The DFT-FF calculations show that the βtot values of 2′, 3′ and 5′ decrease while those of 1′ and 4′ increase compared with the values of their neutral molecules, which was attributed to the fact that the charge transfers of 2, 3 and 5 become smaller and those of 1 and 4 become larger by binding one F- ion to the boron center, according to time-domain DFT (TD-DFT) analysis. However, the incorporation of one electron enhances the second-order NLO properties of the RTAB molecules remarkably, especially for system 1. It is notable that the βtot value of reduced form 1″ is 508.69×10-30 esu, i.e. about 578 times larger than that of system 1. Frontier molecular orbital (FMO) and natural bond orbital (NBO) analyses suggest that the reversal of the charge distribution between the neutral molecules and their reduced forms leads to low HOMO-LUMO energy gaps (E0) and thus large βtot values for the reduced forms.     

Numerical studies on flow and thermal fields in MOCVD reactor

A systematic study has been performed to investigate the flow and thermal patterns of vertical rotating Thomas Swan MOCVD reactor at low pressure,using 2-D dynamic modeling.By varying and calculating the several important process parameters of the reactor,the optimized conditions of the uniform distributions of velocity and temperature profiles in steady state have been obtained.Then,time-dependent models with the step response perturbation of the total gas rate can help identify the visual transient behavi...     

DFT study on second-order nonlinear optical properties of Pt(II) complexes with different chromophores

DFT B3LYP/LANL2DZ method was employed to calculate electron properties and the second-order nonlinear optical (NLO) respond of platinum (II) complexes which have been synthesized by Weinstein group. 4,7-diphenyl-1,10-phenanthroline shows the ability to push electron in these complexes. Metal Pt plays a balancing charge role. Comparing complex 1b–6b with complex a, the β_vec value of complex 1b–5b is larger than one of complex a, while the β_vec value of complex 6b is smaller than one of complex a. In these seven complexes, the β_vec values of complexes increase with decreasing of the energy difference between HOMO and LUMO. Moreover, the electron transfers from deeper layer occupied orbitals to empty orbitals have a distinct contribution to second-order NLO coefficient. Supported by Program for Changjiang Scholars and Innovative Research Team in University, the Foundation of Jilin Provincial Excellent Youth (Grant No. 20050107) and Youth Science Foundation of Northeast Normal University (Grant No. 111494117)