光纤通信系统中的色散补偿研究

光纤色散特性是光纤通信系统的决定性因素.利用光学傅立叶变换(OFT)和变换受限(TL)脉冲可以实现色散的补偿,该色散补偿方案以傅立叶变换受限脉冲信号传输时的无畸变频谱为基础,在输出端利用光学傅立叶变换把这个无畸变的频谱转化成时域中的波形,这个波形和初始脉冲信号的波形在时域上是无失真变化的.然后用这个方案对三阶色散的补偿进行了分析研究,数值模拟结果和理论结果相符.     

昆嵛山泰礴顶次生木本植物资源的调查及分析

昆嵛山区属暖温带季风型气候,原生植被为暖温带落叶阔叶林,但原生植被受到很大破坏,现已形成天然次生林.通过对昆嵛山泰礴顶森林植被的次生木本植物资源的调查,初步分析了植被的林分组成及结构,以期对山东的植被恢复与重建提供相关理论指导和具体建议.     

Does flagship species tourism benefit conservation? A case study of the golden snub-nosed monkey in Shennongjia National Nature Reserve

Tourism has been widely used as a conservation strategy that directly compensates local people or management authorities, thereby contributing to development and creating incentives to preserve the landscape. Reserves or parks that are inhabited by flagship species may be able to generate more revenue through tourism than those without such species because flagship species have great potential for raising funds and creating publicity for conservation goals. In this paper, we examine flagship species tourism...     

Preliminary regional estimation of carbon sink flux by carbonate rock corrosion: A case study of the Pearl River Basin

The formation of carbonate rocks has had a dramatic sink effect on atmospheric CO2 throughout geological time.The wide global distribution of carbonate rocks and their strong sensitivity to climate change mean that carbonate rock corrosion consuming air/soil CO2 can play an important role in the global carbon cycle.The carbon sink accounts for 12.00%-35.29% of the missing carbon in the global carbon cycle.Using the Pearl River Basin as a case study,we analyzed comprehensively the factors impacting karstific...     

Premixed jet flame characteristics of syngas using OH planar laser induced fluorescence

Lean premixed flame characteristics of several typical low calorific value (LCV) syngases (basis CO/H2/CH4/CO2/N2),including bituminous coal,wood residue,corn core,and wheat straw gasification syngas,were investigated using OH planar laser induced fluorescence (PLIF) technology.OH radical distributions within the turbulent flame were measured for different turbulence intensities.Flame structures of syngases were analyzed and characterized with respect to burnt and unburnt regions,flame curvature (sharp cusp),local extinction (holes and penetration),OH reaction layer thickness,wrinkling,and other features,with OH-PLIF instantaneous images and statistical analysis.Results show that H2 content,LCV,and turbulence intensity are the most effective factors influencing the OH radical intensity and thickness of OH radical layers.The bituminous coal gasification syngas with relatively higher LCV and H2 content tends to burn out easily.Through changes in thickness of the OH radical layers and signal intensities,the reaction layer can be compressed by intensifying turbulence and thereby the combustion processes of syngas.     

Phase field simulation of interatomic potentials for double phase competition during early stage precipitation

Phase field model was employed to study the variations of interatomic potentials of Ni 3 Al (L1 2 phase) and Ni 3 V (DO 22 phase) as a function of temperature and concentration. The long-range order (LRO) parameter related interatomic potentials equations formulated by Khachaturyan were utilized to establish the inversion equations for L1 2 and DO 22 phases, with which interatomic potentials could be calculated. The interatomic potentials of Ni-Al and Ni-V exhibited approximately linear increases and decreases, individually, with enhanced Al concentration. Substituting the inverted interatomic potentials into the microscopic phase field equations led to three cases of precipitation sequence: the DO 22 phase preceded L1 2 phase precipitating at the interatomic potentials of Ni-V > Ni-Al; the vice cases; and two phases precipitated simultaneously at interatomic potentials of Ni-V and Ni-Al were equal.     

The effects of the guide field on the structures of electron density depletions in collisionless magnetic reconnection

Two-dimensional particle-in-cell simulations are performed to investigate the formation of electron density depletions in collisionless magnetic reconnection.In anti-parallel reconnection,the quadrupole structures of the out-of-plane magnetic field are formed,and four symmetric electron density depletion layers can be found along the separatrices due to the effects of magetic mirror.With the increase of the initial guide field,the symmetry of both the out-of-plane magnetic field and electron density depletion layers is distorted.When the initial guide field is sufficiently large,the electron density depletion layers along the lower left and upper right separatrices disappear.The parallel electric field in guide field reconnection is found to play an important role in forming such structures of the electron density depletion layers.The structures of the out-of-plane magnetic field By and electron depletion layers in anti-parallel and guide field reconnection are found to be related to electron flow or in-plane currents in the separatrix regions.In anti-parallel reconnection,electrons flow towards the X line along the separatrices,and are directed away from the X line along the magnetic field lines just inside the separatrices.In guide field reconnection,electrons can only flow towards the X line along the upper left and lower right separatrices due to the existence of the parallel electric field in these regions.     

Sea surface temperature records of core ZY2 from the central mud area in the South Yellow Sea during last 6200 years and related effect of the Yellow Sea Warm Current

Sea surface temperature (SST) records in the South Yellow Sea during the last 6200 years are reconstructed by the unsaturation index of long-chain alkenones (K 37 U ’) in sediment core ZY2 from the central mud area.The SST records varied between 14.1 and 16.5°C (15.6°C on average),with 3 phases:(1) A high SST phase at 6.2-5.9 cal ka BP;(2) A low and intensely fluctuating SST phase at 5.9-2.3 cal ka BP;and (3) A high and stable SST phase since 2.3 cal ka BP.Variation of the SST records is similar to intensity of the Kuroshio Current (KC),and corresponds well in time to global cold climate events.However,the amplitude of the SST response to cooling events was significantly different in different phases.The SST response to global cooling event was weak while the KC was strong;and the SST response was strong while the KC was weak.The difference in amplitude of the SST response is possibly caused by the modulation effect of the Yellow Sea Warm Current which acts as a shelf branch of the KC and a compensating current induced by the East Asia winter monsoon.The warm waters brought by the Yellow Sea Warm Current cushion the SST decrease induced by climate cooling,and both the Kuroshio and East Asian winter monsoon play important roles in the modulation mechanism.The SST records display a periodicity of 1482 years.The same period was found in the KC records,indicating that variation of the SST records in the central South Yellow Sea is strongly affected by KC intensity.The same period was also found in Greenland ice cores and North Atlantic and Arabian Sea sediment cores,showing a regional response of marine environmental variability in the East China Seas to that in the global oceans.     

A small difference in nuclear mass could make a big impact in the cosmos

In a recent paper [1] published in Physical Review Letters, scientists at the Institute of Modern Physics, Chinese Academy of Sciences, have reported their first results from the Cooler Storage Ring at the Heavy Ion Research Facility, a newly-constructed major scientific facility in Lanzhou, China. As a part of an international collaboration including colleagues from Europe, USA and Japan, they were able to identify in experiments the very     

Reverberation nulling and echo enhancement at low frequency using waveguide invariance

Based on the fact that the transfer function vector between a source receiver array and the dominant scatterer of boundary reverberation at a range can be obtained from the corresponding reverberations scattered from this range cell, a reverberation nulling concept using time reversal processing has been proposed. However, current reverberation nulling methods have certain limitations when applied into practice, which would null boundary reverberation and target echo simultaneously. As a solution, a passive reverberation nulling and echo enhancement method at low frequency using waveguide invariance is proposed in this paper. In this method, the reverberation subspace for the target range cell is not obtained directly from the return signals scattered by the target range cell but from the return signals scattered by a range cell located before the target using waveguide invariance, so as to suppress the reverberation embodied in the target echo by passive reverberation nulling. Besides, a range-dependent optimal weighting vector rather than conventional projector matrix is deduced to null the reverberation component meanwhile maximizing the target echo, thereby enhancing the echo-to-reverberation ratio furthest. Numerical simulations in typical range-independent shallow water environment demonstrate the efficacy and the improved performance of the proposed method for echo-to-reverberation enhancement.