用SY87721实现城域网波分复用系统的多业务接入

为了使城域网的DWDM（密集波分复用）系统可以接入多种信号速率和格式，以满足用户的要求，首先介绍了一种波长转换板的设计方法，使用SY87721自适应提取28Mbit／s～2.7Gbit/s之间任意速率信号的时钟，其次介绍了SY87721提取时钟的工作原理、与单片机和CPLD（复杂可编程逻辑器件）的接口方式、对寄存器的配置和读出方式。最后介绍了使用参考时钟测量接入信号频率的方法，这会在系统维护时带来较大的方便。     

The opacity coefficient method—nongray determination of inhomogeneous atmospheric extinction

The computation of radiation transmittance in nongray, inhomogeneous atmospheric models is frequently complicated by complex bands of line spectra which range in value over many orders of magnitudes and depend strongly on either or both of pressure and temperature. We present here a new opacity sampling technique which is shown to determine correctly the wavelength-averaged extinction due to path-dependent realizations of banded line spectra. The technique is easy to implement computationally and is applicable to a wide variety of atmospheric problems in which frequent iteration of the radiative transfer model is required. We consider two such instances: modeling of solar flux attenuation for use in a time-dependent planetary ionosphere model and retrieval from nadir measurements of backscattered solar irradiance. The power of the new method lies in its straightforward analytical treatment of both atmospheric inhomogeneity and spectral complexity. It is thus relevant for both retrieval and radiative transfer modeling purposes.     

北京同步辐射装置3B1B生物光谱实验站

本文介绍北京同步辐射装置（ＢＳＲＦ）３Ｂ１Ｂ光束线、生物光谱实验站和圆二色谱仪的基本情况。报道北京正负电子对撞机（ＢＥＰＣ）同步辐射专用光期间，我们在站测量了１１种手征性生物和药物样品的圆二色（ＣＤ）谱，首次在国内利用同步辐射光获取了Ｄ－苯丙氨酸等样品的ＣＤ谱和Ｄ－及Ｌ－亮氨酸对称的ＣＤ曲线。     

Field Measurements with a 5.25 GHz Broadband MIMO-OFDM Communication System

Theoretical capacity calculations and corresponding simulations show significant capacity/throughput gains from MIMO systems. Whether these gains are achievable in a real system, deployed in a practical environment, depends on a variety of factors, such as the choice of the communication algorithms, analog impairments and the "quality" of the wireless channel to sustain MEMO communications. In this paper, a 5.25 GHz broadband MIMO-OFDM testbed is described along with field measurements conducted with it. The MIMO-OFDM communication algorithms and also the impact of analog impairments on the performance of the system are described. Detailed system calibration results are described which serve as a baseline for results of field measurements. The results of wireless measurements are compared with the theoretical capacity, computed with the channel estimates obtained during the demodulation process. The average achievable capacity in the indoor wireless environment is shown to be 9.97 bps/Hz (bits per sec per Hz) while the capacity loss due to analog impairments and the choice of algorithms is about 2.33 bps/Hz. Also, field measurements conducted with the system in various environments are presented comparing the average throughput/capacity achieved in each of these environments.     

电子碰撞诱导原子从低激态向高激态弛豫

本文根据空心阴极放电中电子能量分布的物理图象,分析了原子从低激态向高激态弛豫的可能途径。建立高低激态集居数密度增量的关系。讨论高激态集居数密度增量获得可观量的条件。根据此条件分别选取钠原子的基态3s~2S_(1/2)和铜原子的亚稳态4s~2D_(3/2)为与激光共振的下能级,并激发具有较大自发发射几率的3s~2S_(1/2)→3p~2P°_(1/2)(和3p~2P°_(3/2))和4s~2D_(3/2)→4p~2P°_(1/2)跃迁,在远离上能级的高激态上观测到敏化荧光,并精确测得这些态的自发发射系数比值,而在更高激态上没有观测到敏化荧光,表明讨论中提出的条件是合理的。     

Theoretical analysis on waveform structures of pulse propagating in shallow water with an ideal thermocline

I.IntroductionDuetospatia1andtemporalvariabilityoftheocean-acousticenvironment,especially,theeffectsofboundaryaswel1asmediumonpropagationofacousticwavesinshal1owwater,theacousticpropagationisextrcmelycomp1icatcd.Multipathtransmissionisthebasiccharacteris-hcsofunderwatersoundchannels.Undctcrminedmultipathstructurescangreatlylimittheperformanceofunderwateracousticdetcction.However,ifthemultipathcharacteristicsofacousticpropagationinunderwatcrsoundchanne1sareknown,spaee-timeresolutionandpro-cess…     

Electrochemical formation and clevage of bis-imidazolyls

Bis-(2,4,5-triphenylimidazolyls) result from the dimerization of 2,4,5-triphenylimidazolyls and from the nucleophilic attack of 2,4,5-triphenylimidazole anions upon 2,4,5-triphenylimidazolylium cations. The isomeric bis-imidazolyls consist of imidazole and isoimidazole systems. Imidazoles undergo only anodic oxidation, isoimidazoles only cathodic reduction. Therefore the bis-imidazolyls may be analyzed from their electrochemical behaviour. Bis-(2,4,5-triphenylimidazolyl)-1,2′ and bis-(2,4,5-triphenylimidazolyl)-1,4′ undergo reductive bond cleavage in an ē.c?.ē. mechanism from which 2,4,5-triphenyl-imidazole anions result. The electrochemical properties of one of the bis-imidazolyls agree with that of 1,4,5-triphenyl-2-(2,4,5-triphenylisoimidazolyl-4)-imidazole and not with that of bis-(2,4,5-triphenylimidazolyl)-2,4′ as reported in literature.