Analysis of the additional modulation of semiconductor lasers using optical heterodyne techniques

In this letter, the power spectrum of a cooled distributed feedback laser module is measured using the self-heterodyne technique. Periodical oscillation peaks have been observed in the measurement. Further investigation shows that the additional modulation signal is coupled from the thermal electric cooler (TEC) controller to the laser driver, and then applied to the laser diode. The additional modulation can be eliminated by properly isolating the laser driving source from the TEC controller.

84.5MeV~(12)C~(4+)离子诱发金属靶原子发射的Kβ与Kα-X射线强度比值的研究

本实验是在中国科学院兰州近代物理研究所,国家实验室的重离子加速器上完成的.实验用OR-TEC公司生产的HPGe X射线探测器测量了84.5 MeV的12C4+离子轰击Cu,Mo,Ag,Cd,In,Sn,W和Au金属靶产生的K壳层特征X射线谱,计算了Kβ与Kα-X射线强度的比值,并将结果与Scofield用Hartree-Fock-Slater模型计算出的理论值与用其它方法(如:衰变幅射,用光子,电子,质子等粒子与靶相互作用)得到的实验值进行了比较.比较结果表明用84.5 MeV的12C4+离子轰击Cu,Mo,Ag,Cd,In,Sn,W和Au金属靶产生的Kβ与K-αX射线强度比值比理论值和其它实验值要大许多.

黄土高原旱地连续施用锰肥的土壤效应研究

采用连续浸提形态分级方法,研究了连续施用锰肥17 a后锰的土壤化学特性变化。结果表明:经过长期连续施用锰肥,土壤全锰和DTPA-Mn含量增加不多。土壤DTPA-Mn含量随试验时间的延长呈增加趋势,施锰土壤有效锰提高不多,土壤DTPA-Mn含量只增加了0.4~1.7 mg kg-1。土壤中的锰主要以矿物态存在,占土壤全锰含量的比例为87.3%~91.8%。碳酸盐态、氧化锰态和紧结有机态锰占全锰的比例相当,土壤中各形态锰按含量大致呈矿物态>碳酸盐态>氧化锰态>紧结有机态>松结有机态>交换态的顺序。施入土壤的锰肥有91.1%~98.6%进入碳酸盐结合态、氧化锰结合态、紧结有机态和矿物态,只有很少一部分仍留在有效态锰库中。交换态和松结有机态锰对土壤锰的有效性起着主要作用,可以反映土壤锰的供给状况,碳酸盐态和紧结有机态锰不能反映土壤锰的有效性。

资源流动的环境效应(英文)

21世纪,中国的人口和经济的持续增长面临着资源短缺和生态脆弱的限制。提高资源利用效率和消减资源利用引起的环境影响是学术界和决策者面临的新课题。本文从资源流动的视角研究资源利用过程及其引起的环境影响。我们把资源流动过程分解为开采、加工、转化、消费等几个关键环节,评价其资源利用效率和环境影响,并寻求改善的途径。因其资源消耗量大、生态环境影响严重,我们选取了林木、煤炭及石油研究其资源与产品流动及其环境影响。林木产品的产量、进出口量和消费量数据来自中国森林统计年鉴(1949-2001)。煤炭、石油的开采量、进出口

Thermal barrier coating of lanthanum-zirconium-cerium composite oxide made by electron beam-physical vapor deposition

Lanthanum-zirconium-cerium composite oxide (La-2(Zr0.7Ce0.3)(2)O-7, LZ7C3) as a candidate material for thermal barrier coatings (TBCs) was prepared by electron beam-physical vapor deposition (EB-PVD). The composition, crystal structure, thermophysical properties, surface and cross-sectional morphologies and cyclic oxidation behavior of the LZ7C3 coating were studied. The results indicated that LZ7C3 has a high phase stability between 298 K and 1573 K, and its linear thermal expansion coefficient (TEC) is similar to that of zirconia containing 8 wt% yttria (8YSZ). The thermal conductivity of LZ7C3 is 0.87 W m(-1) K-1 at 1273 K, which is almost 60% lower than that of 8YSZ. The deviation of coating composition from the ingot can be overcome by the addition of excess CeO2 and ZrO2 during ingot preparation or by adjusting the process parameters.

Neodymium-cerium oxide as new thermal barrier coating material

Neodymium-cerium oxide (Nd2Ce2O7) was proposed as a new thermal barrier coating material in this work. Monolithic Nd2Ce2O7 powder was prepared by the solid-state reaction at 1400 degrees C. The phase composition, thermal stability and thermophysical properties of Nd2Ce2O7 were investigated. Nd2Ce2O7 with fluorite structure was thermally stable in the temperature range of interest for TBC applications. The results indicated that the thermal expansion coefficient (TEC) of Nd2Ce2O7 was higher than that of YSZ (6-8 Wt-% Y2O3 + ZrO2) and even more interesting was the TEC change as a function of temperature paralleling that of the superalloy bond coat. Moreover, the thermal conductivity of Nd2Ce2O7 is 30% lower than that of YSZ, which was discussed based on the theory of heat conduction. Thermal barrier coating of Nd2Ce2O7 was produced by atmospheric plasma spraying (APS) using the spray-dried powder. The thermal cycling was performed with a gas burner test facility to examine the thermal stability of the as-prepared coating.

电离层行进式扰动的GPS台网监测研究

In this dissertation, we investigated two types of traveling ionospheric disturbances (TIDs)/gravity waves (GWs) triggered separately by auroral energy input during super geomagnetic storms and solar terminator (ST) under quiet geomagnetic conditions (kp<3+) using TEC measurements from the global network of GPS receivers. Research into the generation and propagation of TIDs/GWs during storms greatly enhance our understandings on the evolution processes of energy transportation from the high-latitude’s magnetosphere to the low-latitude ionosphere and the conjugated effect of TIDs propagation between the northern and southern hemispheres. Our results revealed that the conjugacy of propagation direction between the northern and southern hemispheres was subject to the influence of Coriolis force. We also figure out the evolution processes of ionospheric disturbances at the global scale. These are important topics that had not been well addressed previously. In addition, we also obtained thee wave structures of medium scale TIDs excited by the solar terminator (ST) moving over the northern America and physical mechanisms involved. Our observations confirm that the ST is a stable and repetitive source of ionospheric wave disturbances and the evidence of solar terminator generated disturbances has been demonstrated experimentally via the GPS TEC measurement. The main researches and results of this dissertation are as follows. First, the global traveling ionospheric disturbances (TIDs) during the drastic magnetic storms of October 29–31, 2003 were analyzed using the Global Position System (GPS) total electron content (TEC) data observed in the Asian-Australian, European and North American sectors. We collected the most comprehensive set of the TEC data from more than 900 GPS stations on the International GNSS Services (IGS) website and introduce here a strategy that combines polynomial fitting and multi-channel maximum entropy spectral analysis to obtain TID parameters. Moreover, in collaboration with my thesis advisor, I have developed an imaging technique of 2-dimensional map of TIDs structures to obtain spatial and temporal maps of large scale traveling ionospheric disturbances (LSTIDs). The clear structures of TEC perturbations map during the passage of TIDs were displayed. The results of our study are summarized as follows: (1) Large-scale TIDs (LSTIDs) and medium-scale TIDs (MSTIDs) were detected in all three sectors after the sudden commencement (SC) of the magnetic storm, and their features showed longitudinal and latitudinal dependences. The duration of TIDs was longer at higher latitudes than at middle latitudes, with a maximum of about 16 h. The TEC variation amplitude of LSTIDs was larger in the North American sector than in the two other sectors. At the lower latitudes, the ionospheric perturbations were more complicated, and their duration and amplitude were relatively longer and larger. (2) The periods and phase speeds of TIDs were different in these three sectors. In Europe, the TIDs propagated southward; in North America and Asia, the TIDs propagated southwestward; in the near-equator region, the disturbances propagated with the azimuth (the angle of the propagation direction of the LSTIDs measured clockwise from due north with 0°) of 210° showing the influence of Coriolis force; in the Southern Hemisphere, the LSTIDs propagated conjugatedly northwestward. Both the southwestward and northeastward propagating LSTIDs are found in the equatorial region. These results mean that the Coriolis effect cannot be ignored for the wave propagation of LSTIDs and that the propagation direction is correlated with the polar magnetic activity. (3) The day (day of year: 301) before the SC (sudden commencement) of magnetic storm, we observed a sudden TEC skip disturbances (±10 TECU). It should be a response for the high flux of proton during the solar flare event, but not the magnetic storms. Next, the most comprehensive and dense GPS network’s data from North-America region were used in this paper to analyze the medium scale traveling ionospheric disturbances (MSTIDs) which were generated by the moving solar terminator during the quiet days in 2005. We applied the multi-channel maximum entropy spectral analysis to calculated TID parameters, and found that the occurrence of ST-MSTIDs depends on the seasonal variations. The results of our study are summarized as follows: (1) MSTIDs stimulated by the moving ST (ST-MSTIDs) are detected at mid-latitudes after the passage of the solar terminator with the life time of 2～3 hours and the variation amplitude of 0.2～0.8 TECU. Spectral analysis indicated that the horizontal wavelength, average period, horizontal phase velocity of the MSTIDs are around 300±150 km，150±80 m/s and 25±15 min, respectively. In addition, ST-MSTIDs have wave fronts elongating the moving ST direction and almost parallel to ST. (2) The statistical results demonstrate that the dusk MSTIDs stimulated by ST is more obvious than the dawn MSTIDs in summer. On the contrary, the more-pronounced dawn MSTIDs occurs in winter. (3) Further analysis indicates that the seasonal variations of ST-MSTIDs occurrence frequency are most probably related to the seasonal differences of the variations of EUV flux in the ionosphere region and recombination process during sunrise and sunset period at mid-latitudes. Statistical study of occurrence characteristics of TIDs using the GPS network in North-American and European during solar maximum, In conclusion, statistical studies of the propagation characteristics of TIDs, which excited by the two common origins including geomagnetic storms and moving solar terminator, were involved with global GPS TEC databasein this thesis. We employed the multichannel maximum entropy spectral analysis method to diagnose the characteristics of propagation and evolvement of ionospheric disturbances, also, the characteristics of their regional distribution and climatological variations were revealed by the statistic analysis. The results of these studies can improve our knowledge about the energy transfer in the solar-terrestrial system and the coupling process between upper and lower atmosphere (thermosphere-ionosphere-mesosphere). On the other hand, our results of the investigation on TIDs generated by particular linear origin such as ST are important for developing ionospheric irregularity physics and modeling the transionosphere radio wave propagation. Besides, the GPS TEC representation of the ST-generated ionospheric structure suggests a better possibility for investigating this phenomenon. Subsequently, there are scientific meaning of the result of this dissertation to deeply discuss the energy transfer and coupling in the ionosphere, as well as realistic value to space weather forecast in the ionosphere region.

中高层大气对低层大气声重波响应的分析

Acoustic Gravity waves (AGW) play an important role in balancing the atmospheric energy and momentum budget. Propagation of gravity wave in the atmosphere is one of the important factors of changing middle and upper atmosphere and ionosphere. The purpose of this dissertation is to study the propagation of gravity wave in a compression atmosphere whit means of numerical simulation and to analyze the response of middle and upper atmosphere to pulse disturbance from lower atmosphere. This work begins with the establishment of 2-D fully nonlinear compressible atmospheric dynamic model in polar coordinate, which is used ton numerically study gravity wave propagation. Then the propagation characteristics of acoustic gravity wave packets are investigated and discussed. We also simulate the response of middle and upper atmosphere to pulse disturbance of lower atmosphere in background winds or without background winds by using this model and analyze the data we obtained by using Fourier Transform (FT), Short-time Fourier Transform (STFT) and Empirical Mode Decomposition (EMD) method which is an important part of Hilbert-Huang Transform (HHT). The research content is summarized in the following: 1. By using a two-dimensional full-implicit-continuous-Eulerian (FICE) scheme and taking the atmospheric basic motion equations as the governing equations, a numerical model for nonlinear propagation of acoustic gravity wave disturbance in two-dimensional polar coordinates is solved. 2. Then the propagation characteristics of acoustic gravity wave packets are investigated and discussed. Results of numerical simulation show that the acoustic gravity wave packets propagate steadily upward and keep its shape well after several periods. 3. We simulate the response of middle and upper atmosphere to pulse disturbance of lower atmosphere in background winds or without background winds by using this model, and obtain the distribution of a certain physical quantity in time and space from earth’s surface to 300km above. The results reveal that the response of ionosphere occurs at a large horizontal distance from the source and the disturbance becomes greater with increasing of height. The situation when the direction of the background wind is opposite to or the same as the direction of disturbed velocity of gravity-wave is studied. The results show that gravity wave propagating against winds is easier than those propagating along winds and the background wind can accelerate gravity wave propagation. Just upon the source, an acoustic wave component with period of 6 min can be found. These images of simulation are similar to observations of the total electron content (TEC) disturbances caused by the great Sumatra-Andaman earthquake on December 26 in 2004. 4. Using the EMD method the disturbed velocity data of a certain physical quantity in time and space can be decomposed into a series of intrinsic mode function (IMF) and a trend mode respectively. The results of EMD reveal impact of the gravity wave frequency under the background winds.

太阳耀斑和日食期间电离层行为的统计和模拟研究

The ionosphere is the ionized component of the Earth's upper atmosphere. Solar EUV radiation is the source of ionospheric ionization. Thus the ionosphere is affected strongly by the variations in solar radiation. Solar flares and solar eclipses can induce remarkable short time changes in solar radiation: the solar radiation would increase suddenly during solar flares and decrease significantly during solar eclipses. Solar flare and eclipse events not only affect directly the photochemical processes, but also affect the dynamic processes, and even affect the neutral atmosphere, which is strongly coupled with the ionosphere. The study on the ionospheric response to solar flares and eclipses can advance our knowledge on the ionosphere and its photochemical and dynamic processes and help us to evaluate the ionospheric parameters (such as ion loss coefficients). In addition, the study on the ionospheric responses to solar flares and eclipses is an important part of the ionospheric space weather, which can provide guides for space weather monitoring. This thesis devotes to the study on the ionospheric responses to solar flares and solar eclipses. I have developed two models to simulate the variations of solar EUV radiation during solar flares and solar eclipses, and involved in developing a 2D mid- and low-latitude ionospheric model. On the basis of some observed data and the ionospheric model, I study the temporal and spatial variations of the ionosphere during solar flares and eclipses, and investigate the influences of solar activity, solar zenith angle, neutral gas density, and magnetic dip angle on the ionospheric responses to solar flares and solar eclipses. The main points of my works and results are summarized as follows. 1. The ionospheric response to the X17.2 solar flare on October 28, 2003 was modeled via using a one-dimension theoretical ionospheric model. The simulated variation of TEC is in accordance with the observations, though there are some differences in the amplitude of the variation. Then I carried out a series of simulations to explore the local time and seasonal dependences of the ionospheric responses to solar flares. These calculations show that the ionospheric responses are largely related with the solar zenith angle (SZA). During the daytime (small SZA), most of the increases in electron density occur at altitudes below 300 km with a peak at around 115 km; whereas around sunrise and sunset (SZA>90°), the strongest ionospheric responses occur at much higher altitudes. The TEC increases slower at sunrise than at sunset, which is caused by the difference in the evolution of SZA at sunrise and sunset: SZA decreases with time at sunrise and increase with time at sunset. The ionospheric response is largest in summer and smallest in winter, which is also related to the seasonal difference of SZA. 2. Based on the observations from the ionosondes in Europe and the ionospheric model, I investigated the differences of the ionosphere responses to solar eclipses between the E-layer and F1-layer. Both the observation and simulation show that the decrease in foF1 due to the solar eclipses is larger than that in foE. This effect is due to that the F1 region locates at the transition height between the atomic ion layer and the molecular ion layer. With the revised model of solar radiation during solar flares, our model calculates the radiations from both the inside and outside of photosphere. Large discrepancy can be found between the observations and the calculations with an unrevised model, while the calculations with the revised model consist with the observations. 3. I also explore the effects of the F2-layer height, local time, solar cycle, and magnetic dip angle on the ionospheric responses to solar eclipses via using an ionospheric model and study on the solar zenith angle and the dip dependences by analyzing the data derived from 23 ionosonde stations during seven eclipse events. Both the measured and simulated results show that these factors have significant effect on the ionospheric response. The larger F2-layer height causes the smaller decrease in foF2, which is because that the electron density response decreases with height. The larger dip results in the smaller eclipse effect on the F2 layer, because the larger dip would cause the more diffusion from the top ionosphere which can make up for the plasma loss. The foF2 response is largest at midday and decreases with the increasing SZA. The foF2 response is larger at high solar activity than at low solar activity. The simulated results show that the local time and solar activity discrepancy of the eclipse effect mainly attribute to the difference of the background neutral gas density. 4. I carried out a statistical study on the latitudinal dependence of the ionospheric response to solar eclipses and modeled this latitudinal dependence by the ionospheric model. Both the observations and simulations show that the foF2 and TEC responses have the same latitudinal dependence: the eclipse effects on foF2 and TEC are smaller at low latitudes than at middle latitudes; at the middle latitudes (>40°), the eclipse effect decreases with increasing latitude. In addition, the simulated results show the change in electron temperature at the heights of above 300 km of low latitudes is much smaller than that at the same heights of middle latitudes. This is due to the smaller decrease in photoelectron production rate at its conjugate low heights. 5. By analyzing the observed data during the October 3, 2005 solar eclipse, I find some significant disturbances in the conjugate region of the eclipse region, including a decrease in Te, an increase in foF2 and TEC, and an uprising in hmF2. I also simulated the ionosphere behavior during this eclipse using a mid-low latitude ionospheric model. The simulations reproduce the measured ionospheric disturbances mentioned above in the conjugated hemisphere. The simulations show that the great loss of arriving photoelectron heat from the eclipse region is the principal driving source for the disturbances in the conjugate hemisphere.

红枫湖有机氯污染物的生物地球化学

本研究以红枫湖为主要研究对象，对环境各介质中PCBs和OCPs进行了研究，讨论了理化因素TOC、粒度、SPM、微生物等对于PCBs和OCPs的影响，对各介质中PCBs和OCPs的组成进行了分析，讨论了红枫湖地区PCBs和OCPs的来源，并对其污染水平进行了评价，得到以下几点认识： 1、对红枫湖水体和沉积物的理化性质进行了分析，和洱海进行了对比。湖泊沉积物有机质含量和C/N比值表明红枫湖沉积物有机质主要来源于河流输入和湖泊内部，洱海主要以湖泊内源为主，与后面PCBs和OCPs分析结果相符。湖泊沉积物有机质及DNA呈现同一规律，表层是有机质和DNA的含量较高的区域，表层至底层整体呈逐渐降低的趋势，表明表层是微生物量和活性最高的层段，有机质的降解主要发生在此区域。湖泊沉积物粒度与有机质和DNA变化趋势一致，暗示了有机质的降解过程主要发生在表层，SRI和SRB的分析表明微生物在有机质降解过程中起着至关重要的作用。 2、红枫湖沉积物中7种PCBs的含量范围在3.2～31.6ng/g之间，主要以PCB28和PCB52为主。其中PCB28的含量范围在0.5～4.6ng/g，平均为1.8ng/g， PCB52含量在0.4～28.1ng/g。PCB28和PCB52低氯取代的PCBs占PCBs总量的60%以上。各点沉积物中PCBs的组成基本一致，其含量的变化主要与其输入来源和环境条件相关。沉积物中PCBs随深度整体呈现降低的趋势，但表层含量比次表层低，表明近年PCBs的输入降低。PCBs与TOC和粒径呈现较显著的正相关关系，与其自身的理化性质相关，PCBs具有较高的憎水性，倾向于在颗粒态中分布，也暗示了其来源。 3、红枫湖沉积物中13种OCPs的组成主要以HCHs和DDTs为主。其中HCHs的含量范围1.6～8.9ng/g，平均值为3.2ng/g，沉积物柱均值表现为HW>DB>HE>JJD；DDTs的含量范围在0.9～25.7ng/g，平均值为7.8ng/g，沉积物柱均值表现为HW>HE>DB>JJD。HCHs按其组成来看，以β-HCH和γ-HCH为主，DDTs以p,p’-DDE和p,p’-DDT为主。α-HCH/γ-HCH的比值在范围在0.1~3.0之间，表明HCH在环境中发生了改变，而且林丹的用量高于混合HCHs。DDT/DDE+DDD的比值基本都小于1，暗示DDTs在环境中发生了较长期的变化，β-HCH和p,p’-DDE的高含量也暗示了大气来源可能也是红枫湖地区OCPs的主要来源之一。 4、红枫湖湖水、汇入汇出河流及其周边土壤中PCBs和OCPs的分析，显示PCBs和OCPS在过滤后水中含量较低，主要分配在悬浮颗粒物中，悬浮颗粒物中的PCBs和OCPs组成与周边土壤中的组成基本一致。HCHs和DDTs的组成和α-HCH/γ-HCH、DDT/DDE+DDD的比值暗示水中悬浮颗粒物及其PCBs和OCPs主要来源于周边土壤和大气沉降。 5、 红枫湖后五鱼体内PCBs主要以4～6氯取代的PCBs的同系物为主，OCPs以HCHs和DDTs为主。鱼体内PCBs和OCPs对于水体的富集系数达到102～105。PCBs富集系数随氯取代数目的增加而增加，表明其生物有效性随氯取代数目的增加而增加，高氯取代的PCBs更容易通过食物链在高营养级生物体内富集，对人体造成危害。 6、 大气总悬浮颗粒物TSP中及背景区土壤中PCBs和OCPs的分析，与其它环境介质中结果基本一致。红枫湖地区大气、水、沉积物、生物和土壤各环境介质中PCBs和OCPs的组成基本一致，表明其来源具有一致性。α-HCH/γ-HCH和 DDT/DDE+DDD的值，及β-HCH、p,p’-DDE的高的比例，暗示红枫湖地区OCPs在环境中经历了较长时间的变化，而且大气长距离传输对于该区OCPs和PCBs的来源具有一定的贡献。从各因子的分析可以得出，红枫湖为该地区PCBs和OCPs的汇。 7、我国PCBs和DDTs、HCHs的含量除了典型区外，在国内外都处于较低和中等污染水平，红枫湖地区整体处于较低污染水平。根据Long和Chapman等对沉积物中POPs的评价方法，红枫湖沉积物中PCBs只有一个样品处于ERL和ERM之间，其它都低于ERL值，表明PCBs对生物造成不利影响的可能性较低；DDTs的值大部分处于ERL和ERM值之间，对生物造成不利影响的可能性较大；γ-HCH的值都低于TEC值，对生物的潜在影响较小。

Metodologia para avaliação experimental da atividade da fauna bentônica.

2007

Integração lavoura-pecuária: alternativa para diversificação e redução do impacto ambiental do sistema produtivo no Vale do Rio Xingu.

2010

In situ high temperature X-ray diffraction studies of mixed ionic and electronic conducting perovskite-type membranes

Phase structure and stability of three typical mixed ionic and electronic conducting perovskite-type membranes, SrCo0.8Fe0.2O3-delta (SCF), Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCF) and BaCo0.4Fe0.4Zr0.2O3-delta (BCFZ) were studied by in situ high temperature X-ray diffraction at temperatures from 303 to 1273 K and under different atmospheres (air, 2% O-2 in Ar and pure Ar) at 1173 K. By analyzing their lattice parameters the thermal expansion coefficients (TECs) of BSCF, SCF and BCZF are obtained to be 11.5 x 10(-6) K-1, 17.9 x 10(-6) K-1 and 10.3 x 10(-6) K-1, respectively. A relationship between phase stability and TEC was proposed: the higher is the TEC, the lower is the operation stability of the perovskite materials. (C) 2005 Elsevier B.V. All rights reserved.

Sobre el teorema de Liouville para funciones enteras

La idea del artículo es presentar las pruebas del teorema de Liouville sobre funciones enteras. En este trabajo recalcamos dos importantes aplicaciones, una en la demostración del teorema fundamental del álgebra y otra en el área de las aplicaciones conformes. El presente contiene una breve nota histórica de la vida de Joseph Liouville y su trabajo. También contiene la version del teorema de Liouville para funciones doblemente periódicas, funciones armónicas y aplicaciones cuasiconformes.