塔里木河下游植被和景观格局变化及其驱动力分析

利用RS和GIS手段相结合的方法研究了塔里木河下游的植被和景观变化，并分析了由于历史时期塔里木河水流量的变化而导致的地下水位变化、环境因子和人类活动对植被及景观格局的影响。 对环境因子与植被覆盖变化关系的分析结果发现： ⑴在1987年至2004年占研究区总面积26％的景观发生变化；而植被和水体的变化最大；植被的变化中荒漠化和转化为农田是其主要的变化类型。1987年至2004年，仅有占总面积39％的植被没有发生变化，而发生荒漠化和盐碱化的植被仅有少数能够恢复。 ⑵在选取的环境因子中，植被缀块的起始NDVI和植被缀块距河道的距离对植被变化的影响最大，其次为海拔、坡度、缀块形状和缀块距离居民点的距离；而坡向和缀块面积与植被变化的关系较小。发生荒漠化的植被缀块距离河道较远且自身的NDVI较低，表明这些植被缀块的变化主要是受到水资源的限制；而转化为农田的植被缀块自身的NDVI较高且距河道较近，表明人类的开垦活动主要在植被生长较好的地区进行。研究期间内能够保持的植被距河道较近且NDVI较低，这与能够保留的植被主要是较稀疏的胡杨林有关。 ⑶植被缀块距河道的距离在1987年至1999年间与植被的变化显著相关，而在1999年至2004年相关不显著，这表明影响植被变化的影响环境因子随时间变化。 ⑷虽然所选取的环境因子对植被变化的解释力偏低，但在某些时间段对植被变化的解释力可以达到40％。如果增加环境因子，使用梯度分析的方法可以较好的解释环境及其它因子对植被变化的影响。 对地下水位变化对植被及景观时空格局变化的研究结果发现： ⑴在地下水水位剧烈下降的1986年至1999年，植被面积减少30％，距离河道最近的区域减少最多，植被占总面积的比例和植被的减少随距离河道距离的增加而减小；平均NDVI降低；荒漠面积增加4.8％，年均增加1338公顷；盐碱地面积增加。由于生态应急输水工程的实施，1999年至2004年期间沿塔里木河道地下水位回升，植被面积增加48％，距离河道最近的区域面积增加最明显，植被面积增加的增幅随距离河道距离的增加而减小；荒漠面积减少8.3％，年均减少6280公顷；平均NDVI升高；荒漠面积减少；盐碱地面积在某些区段增加，某些区段减少。 ⑵1986年至1999年胡杨林、柽柳灌丛和盐生草甸缀块密度增加，植被趋于破碎化；总体上胡杨林、柽柳灌丛和盐生草甸的缀块形状变得规则，而盐生草甸在某些区段趋于不规则；景观的聚集度在河道左侧增加而右侧减小；景观多样性和均匀性均下降。1999年至2004年，总体上胡杨林、柽柳灌丛和盐生草甸的缀块密度减小，植被趋于整合；胡杨林、柽柳灌丛和盐生草甸缀块形状变得不规则，但盐生草甸在某些区段变得相对规则；景观聚集度指数变化没有明显的规律；景观多样性和均匀性均增加。 ⑶除植被占总面积的比例在沿河道由上段到中断到下段方向上呈现减少的趋势，其它植被及景观特性在沿河道纵向上变化规律不明显；而在沿河道垂直方向上，植被及景观特性的变化表现出与距离河道的距离相关，表明该地区的植被及景观特性是受到地下水控制的。 ⑷在塔里木河实施的生态应急输水工程对当地植被的恢复起到了一定的作用，但主要局限在沿河道附近的区域。对于干旱区植物的保护，合理使用径流水资源，保证水资源的供应畅通是更好和更长远的发展策略。 对人类活动对景观的影响的研究发现： ⑴1987年至1999年，农田面积增加4240公顷，年均增加353公顷；植被面积减少4884公顷，年均减少407公顷。1999年至2004年，农田面积增加4568公顷，年均增加913公顷；植被面积减少8487公顷，年均减少1697公顷，远大于农田面积的增加。 ⑵农田平均缀块面积和农田最大缀块面积从1987年至1999年至2004年增加；聚集度指数在1987年至1999年降低，而1999年至2004年升高。最大植被缀块面积、平均形状指数和聚集指数从1987年至1999年至2004年均下降；其它植被及农田景观指数在1987年至1999年和1999年至2004年间变化不一致。在距河道1km的范围内，农田缀块数、农田面积、最大农田缀块面积、平均缀块面积、平均形状指数以及聚集度指数在从1987年至1999年至2004年一直升高；距河道1km范围内的景观多样性和均匀度指数和平均形状指数在1987年至1999年至2004年增加，而聚集度指数和最大缀块指数在1987年至1999年至2004年一直减小。 ⑶研究结果表明人类活动-主要是开垦农田-导致了当地植被面积的减少，并导致植被破碎化。受到径流来水量减少的影响，人类开垦活动正在逐渐向距离河道近的区域转移，并导致植被向退化的方向发展，河道附近的区域是塔里木河下游植被分布的主要区域，这对该地区植被的维持和保护非常不利。 在塔里木河下游，地下水位的下降和人类活动都导致植被趋于退化，人工输水虽然能够恢复植被，但其效应主要集中在河道附近的地区，对于该生态关键地区植被的保护，合理的使用水资源并适当的进行人类活动才是植被及生态保护的根本。

Origin and evolution of new exons in the rodent zinc finger protein 39 gene

The origin of new structures and functions is an important process in evolution. In the past decades, we have obtained some preliminary knowledge of the origin and evolution of new genes. However, as the basic unit of genes, the origin and evolution of exons remain unclear. Because young exons retain the footprints of origination, they can be good materials for studying origin and evolution of new exons. In this paper, we report two young exons in a zinc finger protein gene of rodents. Since they are unique sequences in mouse and rat genome and no homologous sequences were found in the orthologous genes of human and pig, the young exons might originate after the divergence of primates and rodents through exonization of intronic sequences. Strong positive selection was detected in the new exons between mouse and rat, suggesting that these exons have undergone significant functional divergence after the separation of the two species. On the other hand, population genetics data of mouse demonstrate that the new exons have been subject to functional constraint, indicating an important function of the new exons in mouse. Functional analyses suggest that these new exons encode a nuclear localization signal peptide, which may mediate new ways of nuclear protein transport. To our knowledge, this is the first example of the origin and evolution of young exons.

Upconversion emission of a Er3+-doped glass microsphere under 633 nm excitation (vol 35, pg 353, 2004)

　

1-mm gate periphery AlGaN/AIN/GaN HEMTs on SiC with output power of 9.39 W at 8 GHz

AlGaN/AlN/GaN high electron mobility transistor (HEMT) structures with high mobility GaN channel layer were grown on 50 min diameter semi-insulating (SI) 6H-SiC substrates by metalorganic chemical vapor deposition and large periphery HEMT devices were fabricated and characterized. High two-dimensional electron gas mobility of 2215 cm(2)/V s at room temperature with sheet electron concentration of 1.044 x 10(13)/cm(2) was achieved. The 50 mm diameter HEMT wafer exhibited a low average sheet resistance of 251.0 Omega/square, with the resistance uniformity of 2.02%. Atomic force microscopy measurements revealed a smooth AlGaN surface with a root-mean-square roughness of 0.27 nm for a scan area of 5 mu mi x 5 pm. The 1-mm gate width devices fabricated using the materials demonstrated a very high continuous wave output power of 9.39 W at 8 GHz, with a power added efficiency of 46.2% and power gain of 7.54 dB. A maximum drain current density of 1300 mA/mm, an extrinsic transconductance of 382 mS/mm, a current gain cutoff frequency of 31 GHz and a maximum frequency of oscillation 60 GHz were also achieved in the same devices. (C) 2007 Elsevier Ltd. All rights reserved.

结构因子相角的代数解法及K_8H_5[La(SiWMo_(10)O_(39))(SiW_3Mo_8O_(39))]·nH_2O的晶体结构

一 结构因子相角的代数解法晶体结构研究中的相角问题，一直是晶体学工作者努力探求的基本问题。几十年来，关于相角问题的研究已经取得了巨大的进展，直接法的成熟和普遍应用就是这个进展的显著标志。在直接法相角问题研究中，历来存在两种基本方法，即概率法和代数法。当前直接法的迅猛发展，则主要以概率法为基础，其应用的基本公式即是来自∑关系中的∑_2关系和由此发展出的TANGENT公式，并结合一系列的基本理论和辅助公式，从而使直接法的发展一直呈方兴未艾之势。与此形成鲜明对照的是，相角问题的代数法研究则有日趋下降之势，尤其近十年来则显著落后了。作者从近年来的∑关系研究中，看到要解决相角问题，代数法仍然有其潜在的应作价值，并认为在概率法可以得到应用的许多方面，在代数法那里都应找到对应的类似内容，而代数法在研究和应用中所表现出的不同于概率法的那些方面也正是在相角问题研究中最令人感兴趣的问题，这就是我们进行代数法研究的目的和出发点。（一）1.5和2.5阶代数式的提出及对±2~(II)型相角的估算。（二）一般类型相角的估算（三）结构相角通用代数式的推导。代数法不仅可用于结构半不变量O，π型相角的计算，而且可用于非结构半不变量的种种类型相角的估算，其中包括型和一般类型相角，而且其应用效果完全可以和概率法相比拟，在机时利用上前者有一定优势。通用代数式的获得将为代数法的普遍应用和计算机计算创造了方便条件。二稀土杂多酸根配合物K_8H_5[La(SiWMo_(10)O_(39))(SiW_3Mo_8O_(39))]·nH_2O的晶体结构采用低温技术，在-90 ℃的干燥氮气保护下，收集晶体衍射数据，以直接法解出结构。a = 17.485(5), b = 27.096(6), c = 21.642(5)A, β = 107.79(2)°, z = 4。最后的R值为0.097。中心离子La(III)同两个杂多酸根提供的8 个氧配合。而其中的W、Mo同氧的配位情况基本相同，者是与氧六配位，形成变形配位八面体。

无介体双室微生物燃料电池产电性能初步研究

本文对无介体双室微生物燃料电池的产电性能进行了初步研究，并根据不同运行阶段产电性能的优劣，对其中微生物的差异性进行了比较分析。全文分为两个部分： 第一部分：以乙酸钠为阳极原料构建双室微生物燃料电池（MFC），研究不同阴极受体、外接电阻、乙酸钠浓度和pH等因素对电池产电性能的影响，研究结果表明：在500mL的阴阳极反应体系中，选用乙酸钠作为阳极底物，质量浓度为6.46 g/L， pH 7.0，接入500Ω外电阻，阴极电子受体选择高锰酸钾的情况下，微生物燃料电池产电性能最好，最大电功率密度达到294.72 mW/m2，库伦效率能达到25.87%。在确定最适外接电阻阻值的同时对MFC内阻进行测定，阻值为871.87Ω。 第二部分：微生物燃料电池运行中，比较以厌氧污泥作为接种源的第一阶段和只接入附着有大量微生物电极的第二阶段的产电性能，得出第二阶段产电性能优于第一阶段，最大电功率密度达到353.57mW/m2，比第一阶段提高58.85 mW/m2；库伦效率为39.35%，增幅达52％左右；针对微生物燃料电池运行过程中，底物CH3COONa可能存在其它的代谢途径，本实验进行了第二阶段产电性能与CH3COONa消耗率关系以及阳极液面上方气体成分和含量的研究，发现第二阶段50h前CH3COONa的大量消耗主要用于微生物的生长，在整个运行过程中，阳极液面上方含有CH4和CO2；对气体测定的同时还发现，振荡能增强电功率密度的输出；通过对电极上和污泥中微生物差异性分析得出，δ-变形菌纲、β-变形菌纲和拟杆菌门的菌种更适应微生物燃料电池的运行环境，能在电极上大量富集，提高电池的产电性能，只接入附着有大量微生物的电极能有效降低热袍菌纲的菌种数量，降低了CH3COONa的无为消耗，有效提高了电池的库伦效率。 Electricity production in the mediator-less two-chambered microbial fuel cell(MFC) was researched. Based on the result in the different operation phase in the MFC, the microbial diversity was analysed. The paper involved two parts: Part 1: A two-chambered microbial fuel cell (MFC) was constructed with high-concentration sodium acetate as fuel in the anode. The influence of different electron acceptors in the cathode, external resistance value, pH value and concentration of sodium acetate on electricity generation in MFC was investigated. The result showed that the maximum power density of 294.72 mW/m2 and the coulombic efficiency of 25.87% was achieved at sodium acetate concentration of 6.46 g/L, pH 7.0, external resistance 500Ωin the anode and when using potassium permanganate as electron acceptor in the cathode. While decided the value of resistor, we found that shaking has effect on electricity production in the MFC. Part 2: Comparing the electricity production in different operation phases when using anaerobic sludge as inoculum in the first phase and microbes in the anodic electrode as inoculum in the second phase, the result showed that electricity production in the second phase was more than that in the first phase, the maximum power density of 353.57 mW/m2 and the coulombic efficiency of 39.35% was achieved, 58.85 mW/m2 and 52％ more than that in the first phase, respectively. According to the fact that CH3COONa might be metabolized in other pathway in the running process in the MFC, we determining the relationship between electricity production and CH3COONa consumption, and the gas content in the anode, we found that CH3COONa was mainly used for microbe growth before 50h, and the anode contained CH4 and CO2. At the same time, we found that shaking could improve power density. The analysis on diversity of microbe in the anodic electrode and anaerobic sludge showed that δ-proteobacterium, β-proteobacterium and Bacteroidetes adapted themselves to the running environment of MFC. The anode could enrich them to improve the electricity production while reduced the quantity of Thermotogales, which were obligately anaerobic organotrophs with a fermentative metabolism, to increase the coulombic efficiency effectively.

Measurement of the isospin-filtering dd → 4He K+K- reaction at Q = 39 MeV

The total cross-section for the dd → 4HeK+K− reaction has been measured at a beam momentum of 3.7GeV/c, corresponding to an excess energy of 39MeV, which is the maximum possible atthe Cooler Synchrotron COSY-Jülich. A deuterium cluster-jet target and the ANKE forward magnetic spectrometer, placed inside the storage ring, have been employed in this investigation. We find a total cross-section of σtot < 14 pb, which brings into question the viability of investigating the dd → 4He a0(980)reaction as a means of studying isospin violation.

用CR-39对空间重离子的鉴别模型(英文)

根据重离子在CR39中能量损失率公式,建立了一个鉴别空间重离子的数学模型LET=cZdRb.通过传能线密度与剩余射程之间的关系曲线,获得了该模型的系数.在实验中发现的CR39蚀刻率与离子有限传能线密度的关系VT=A·(REL)BE<350,被用来与该数学模型相关联,并得到一等式R=A0.0455Z3.18V-1T.最终,借助于标定实验得到了离子鉴别公式Z3.18=64541.08+2.53(dR/dV-1T).

Syntheses and properties of polyimides derived from diamines containing 2,5-disubstituted pyridine group

A Series of novel homo- and copolyimides containing pyridine units were prepared from the heteroaromatic diamines, 2,5-bis (4-aminophenyl) pyridine and 2-(4aminophenyl)-5-aminopyridine, with pyromelltic dianhydride (PMDA), and 3,3',4,4'-biphenyl tertracarboxylic dianhydride (BPDA) via a conventional two-step thermal imidizaton method. The poly(amic acid) precursors have inherent viscosities of 1.60-9.64 dL/g (c = 0.5 g/dL in DMAC, 30 degrees C) and all of them can be cast and thermally converted into flexible and tough polyimide films. All of the polyimides show excellent thermal stability and mechanical properties. The polyimides have 10% weight loss temperature in the range of 548-598 degrees C in air. The glass transition temperatures of the PMDA-based samples are in the range of 395-438 degrees C, while the BPDA-based polyimides show two glass transition temperatures (T(g)1 and T(g)2), ranging from 268 to 353 degrees C and from 395 to 418 degrees C, respectively. The flexible films possess tensile modulus in the range of 3.42-6.39 GPa, strength in the range of 112-363 MPa and an elongation at break in the range of 1.2-69%. The strong reflection peaks in the wide-angle X-ray diffraction patterns indicate that the polyimides have a high packing density and crystallinity.

Isothermal crystallization of poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

Isothermal crystallization behavior of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) was investigated by means of differential scanning calorimetry and polarized optical microscopy (POM). The Avrami analysis can be used successfully to describe the isothermal crystallization kinetics of PHBV, which indicates that the Avrami exponent n = 3 is good for all the temperatures investigated. The spherulitic growth rate, G, was determined by POM. The result shows that the G has a maximum value at about 353 K. Using the equilibrium melting temperature (448 K) determined by the Flory equation for melting point depression together with U-* = 1500 cal mol(-1), T-infinity = 30 K and T-g = 278 K, the nucleation parameter K-g was determined, which was found to be 3.14+/-0.07 x 10(5) (K-2), lower than that for pure PHB. The surface-free energy sigma = 2.55 x 10(-2) J m(-2) and sigma(e) = 2.70+/-0.06 x 10-2 J m(-2) were estimated and the work of chain-folding (q = 12.5+/-0.2 kJ mol(-1)) was derived from sigma(e), and found to be lower than that for PHB. This implies that the chains of PHBV are more flexible than that of PHB.