番茄褪绿病毒的进化动态与适应性进化特征

【目的】番茄褪绿病毒(tomato chlorosis virus,ToCV)是长线形病毒科(Closteroviridae)毛形病毒属(Crinivirus)成员,现已成为我国番茄和其他蔬菜作物上最为常见的病毒之一。研究旨在查明ToCV的进化历史,尤其是该病毒何时何地传入我国,并阐明其适应性进化机制。【方法】根据ToCV外壳蛋白(coat protein,CP)基因两侧保守区设计1对特异性引物,对随机抽取的13个ToCV分离物进行扩增克隆,将测序获得的新序列与GenBank下载的含有采样时间和地理信息的序列合并得到103条ToCV CP基因序列,采用日期随机化检验(date-randomization test,DRT)检测数据集中的时间信号,并应用贝叶斯谱系动力学框架重建该病毒的进化动态。同时,应用系统发育与性状关联分析(phylogeny-trait association analysis)评估地理因素对ToCV适应性进化的影响。【结果】13个ToCV分离物均成功扩增出预期大小(约800 bp)的特异性片段,核苷酸序列与已报道的ToCV不同分离物CP基因序列一致性均在98%以上...     

不同种植年限苜蓿草地昆虫种群及群落的发生规律

苜蓿是我国西北重要的牧草,明确苜蓿多年种植情况下害虫-天敌生态演变规律,对宁夏南部山区畜牧产业结构调整、持续发展牧草种植和提高防治水平有着重要意义。在研究区域,针对不同种植年限的苜蓿草地昆虫种群数量进行调查,通过对其发生规律和群落结构分析,结果表明:种植5年以内的苜蓿草地中,昆虫总个体数以及害虫的危害较轻,昆虫总个体数比较稳定,没有明显的变化,但种植年限5年以上的苜蓿草地中害虫逐步开始发生严重,尤其是地下害虫。因此苜蓿草业发展应当注意合理安排种植规模和时间,充分利用害虫-天敌发展的生态规律进行控害增产,进入持续发展的良性轨道。     

Femtosecond phase-coherent two-dimensional spectroscopy

Femtosecond phase-coherent two-dimensional (2D) spectroscopy has been experimentally demonstrated as the direct optical analog of 2D nuclear magnetic resonance. An acousto-optic pulse shaper created a collinear three-pulse sequence with well-controlled and variable interpulse delays and phases,which interacted with a model atomic system of rubidium vapor. The desired nonlinear polarization was selected by phase cycling (coadding experimental results obtained with different interpulse phases). This method may enhance our ability to probe the femtosecond structural dynamics of macromolecules.     

Femtosecond clocking of the chemical bond

When a chemical bond is broken in a direct dissociation reaction, the process is so rapid that it has generally been considered instantaneous and thus unmeasurable. However, the bond does persist for times on the order of 10(-13) seconds after the photon has been absorbed. Femtosecond (10(-15) second) laser techniques can be used to directly clock this process, which describes the dynamics of the chemical bond. The time required to break the chemical bond in an elementary reaction has been measured and the characteristic repulsion length for the potential governing fragment separation has been obtained.     

Femtosecond infrared spectroscopy of bacteriorhodopsin chromophore isomerization

The vibrational dynamics of the retinal chromophore all-trans-to-13-cis photoisomerization in bacteriorhodopsin has been studied with mid-infrared absorption spectroscopy at high time resolution (about 200 femtoseconds). After photoexcitation of light-adapted bacteriorhodopsin, the transient infrared absorption was probed in a broad spectral region, including vibrations with dominant C-C, C=C, and C=NH stretching mode amplitude. All photoproduct modes, especially those around 1190 reciprocal-centimeters that are indicative for a 13-cis configuration of the chromophore, rise with a time constant of approximately 0.5 picosecond. The results presented give direct vibrational-spectroscopic evidence for the isomerization taking place within 0.5 picosecond, as has been suggested by previous optical femtosecond time-resolved experiments but questioned recently by picosecond time-resolved vibrational spectroscopy experiments.     

Femtosecond multidimensional imaging of a molecular dissociation

The coupled electronic and vibrational motions governing chemical processes are best viewed from the molecule's point of view-the molecular frame. Measurements made in the laboratory frame often conceal information because of the random orientations the molecule can take. We used a combination of time-resolved photoelectron spectroscopy, multidimensional coincidence imaging spectroscopy, and ab initio computation to trace a complete reactant-to-product pathway-the photodissociation of the nitric oxide dimer-from the molecule's point of view, on the femtosecond time scale. This method revealed an elusive photochemical process involving intermediate electronic configurations.     

Femtosecond dynamics of electron localization at interfaces

The dynamics of two-dimensional small-polaron formation at ultrathin alkane layers on a silver(111) surface have been studied with femtosecond time- and angle-resolved two-photon photoemission spectroscopy. Optical excitation creates interfacial electrons in quasi-free states for motion parallel to the interface. These initially delocalized electrons self-trap as small polarons in a localized state within a few hundred femtoseconds. The localized electrons then decay back to the metal within picoseconds by tunneling through the adlayer potential barrier. The energy dependence of the self-trapping rate has been measured and modeled with a theory analogous to electron transfer theory. This analysis determines the inter- and intramolecular vibrational modes of the overlayer responsible for self-trapping as well as the relaxation energy of the overlayer molecular lattice. These results for a model interface contribute to the fundamental picture of electron behavior in weakly bonded solids and can lead to better understanding of carrier dynamics in many different systems, including organic light-emitting diodes.     

Femtosecond resolution of soft mode dynamics in structural phase transitions

The microscopic pathway along which ions or molecules in a crystal move during a structural phase transition can often be described in terms of a collective vibrational mode of the lattice. In many cases, this mode, called a "soft" phonon mode because of its characteristically low frequency near the phase transition temperature, is difficult to characterize through conventional frequency-domain spectroscopies such as light or neutron scattering. A femtosecond time-domain analog of light-scattering spectroscopy called impulsive stimulated Raman scattering (ISRS) has been used to examine the soft modes of two perovskite ferroelectric crystals. The low-frequency lattice dynamics of KNbO(3) and BaTiO(3) are clarified in a manner that permits critical evaluation of microscopic models for their ferroelectric transitions. The results illustrate the advantages of ISRS over conventional Raman spectroscopy of low-frequency, heavily damped soft modes.     

Femtosecond pulse sequences used for optical manipulation of molecular motion

Optical control over elementary molecular motion is enhanced with timed sequences of femtosecond (10(-15) second) pulses produced by pulse-shaping techniques. Appropriately timed pulse sequences are used to repetitively drive selected vibrations of a crystal lattice, in a manner analogous to repetitively pushing a child on a swing with appropriate timing to build up a large oscillation amplitude. This process corresponds to repetitively "pushing" molecules along selected paths in the lattice. Amplification of selected vibrational modes and discrimination against other modes are demonstrated. Prospects for more extensive manipulation of molecular and collective behavior and structure are clearly indicated.     

Parametric Generation of Tunable Light from Continuous-Wave to Femtosecond Pulses

By exploiting nonlinear optical effects, a technology of unprecedented flexibility for the production of tunable coherent light has been developed. Referred to as optical parametric generation, it provides sources with spectral coverage extending all the way from the ultraviolet to the mid-infrared, and with temporal coverage extending over all time domains from the femtosecond pulse to the continuous wave. Such sources generate coherent light of outstanding optical quality and are now finding wide-ranging applications.     

红花尔基樟子松林国家级自然保护区松鼠的种群动态

[目的]研究松鼠种群动态特征及其对食物因素的响应机制。[方法]2007～2012春、秋季分别在红花尔基樟子松林国家级自然保护区用样线法开展松鼠种群调查,同时收集樟子松结实量数据。[结果]樟子松结实量对松鼠春季种群密度有显著影响。红花尔基保护区松鼠的种群密度处于持续下降中。[结论]食物资源变化对松鼠的种群密度有显著影响,需要对松鼠种群密度动态开展持续的监测和研究。     

飞秒激光处理对水稻种子发芽和苗期生长的影响

以水稻品种龙稻5号种子为试材,以波长800 nm、光斑半径2 mm、功率650 mw、频率1000 Hz的飞秒激光分别辐照3、5、7、9、11和13 s后,研究飞秒激光辐照处理对水稻种子发芽和苗期生长的影响.结果表明:飞秒激光辐照处理可以刺激水稻发芽和幼苗的生长.3～9 s飞秒激光辐照处理,水稻发芽势和发芽率增高,而随...     

溴虫腈在稻田环境中的消解动态研究

通过田间试验,采用气相色谱法分析研究了溴虫腈在湖南和浙江两地稻田土壤、稻田水和水稻植株中的消解动态。结果表明:溴虫腈在水稻土壤、稻田水和水稻植株中的平均添加回收率分别为90.0%~108.0%、96.2%~105.0%和87.9%~105.0%;溴虫腈在稻田环境中的消解动态符合一级动力学指数模型,在两试验地稻田土壤中的平均半衰期为11.17 d;稻田水中的平均半衰期为5.17 d;水稻植株中的平均半衰期为6.27 d。     

动态法研究苯酚在土壤中吸附的动力学

用动态法研究了饱水细沙土柱中含酚废水在垂直流动情况下，土壤颗粒对苯酚的吸附传质过程。实验结果表明，吸附速率、“准平衡”吸附量等均与溶液浓度、流动速度有关。溶液浓度、流速提高，吸附速率常数及“准平衡”吸附量随之加大。根据吸附动力学曲线及由实验数据计算出的流体与颗粒间的对流传质系数可判断，其间的对流传质不可能是吸附过程的控制步骤，过程由颗粒内扩散控制，符合一级反应动力学方程。