Electron dynamics and harmonics emission spectra due to electron oscillation driven by intense laser pulses

The dynamics and harmonics emission spectra due to electron oscillation driven by intense laser pulses have been investigated considering a single electron model. The spectral and angular distributions of the harmonics radiation are numerically analyzed and demonstrate significantly different characteristics from those of the low-intensity field case. Higher-order harmonic radiation is possible for a sufficiently intense driving laser pulse. A complex shifting and broadening structure of the spectrum is observed and analyzed for different polarization. For a realistic pulsed photon beam, the spectrum of the radiation is redshifted for backward radiation and blueshifted for forward radiation, and spectral broadening is noticed. This is due to the changes in the longitudinal velocity of the electron during the laser pulse. These effects are much more pronounced at higher laser intensities giving rise to even higher-order harmonics that eventually leads to a continuous spectrum. Numerical simulations have further shown that broadening of the high harmonic radiation can be limited by increasing the laser pulse width. The complex shifting and broadening of the spectra can be employed to characterize the ultrashort and ultraintense laser pulses and to study the ultrafast dynamics of the electrons. (c) 2006 American Institute of Physics.

Laser conditioning and multi-shot laser damage accumulation effects of HfO2/SiO2 antireflective coatings

Laser conditioning effects of the HfO2/SiO2 antireflective (AR) coatings at 1064 nm and the accumulation effects of multishot laser radiation were investigated. The HfO2/SiO2 AR coatings were prepared by E-beam evaporation (EBE). The singleshot and multi-shot laser induced damage threshold was detected following ISO standard 11254-1.2, and the laser conditioning was conducted by three-step raster scanning method. It was found that the single-shot LIDT and multi-shot LIDT was almost the same. The damage mostly > 80% occurred in the first shot under multi-shot laser radiation, and after that the damage occurring probability plummeted to < 5%. There was no obvious enhancement of the laser damage resistance for both the single-shot and multi-shot laser radiation of the AR coatings after laser conditioning. A Nomarski microscope was employed to map the damage morphology, and it found that the damage behavior is defect-initiated for both unconditioned and conditioned samples. © 2004 Elsevier B.V. All rights reserved.

Molecular phylogenetics and biogeography of Lepus in Eastern Asia based on mitochondrial DNA sequences

In spite of several classification attempts among taxa of the genus Lepus, phylogenetic relationships still remain poorly understood. Here, we present molecular genetic evidence that may resolve some of the current incongruities in the phylogeny of the leporids. The complete mitochondrial cytb, 12S genes, and parts of ND4 and control region fragments were sequenced to examine phylogenetic relationships among Chinese hare taxa and other leporids throughout the World using maximum parsimony, maximum likelihood, and Bayesian phylogenetic reconstruction approaches. Using reconstructed phylogenies, we observed that the Chinese hare is not a single monophyletic group as originally thought. Instead, the data infers that the genus Lepus is monophyletic with three unique species groups: North American, Eurasian, and African. Ancestral area analysis indicated that ancestral Lepus arose in North America and then dispersed into Eurasia via the Bering Land Bridge eventually extending to Africa. Brooks Parsimony analysis showed that dispersal events followed by subsequent speciation have occurred in other geographic areas as well and resulted in the rapid radiation and speciation of Lepus. A Bayesian relaxed molecular clock approach based on the continuous autocorrelation of evolutionary rates along branches estimated the divergence time between the three major groups within Lepus. The genus appears to have arisen approximately 10.76 MYA (+/- 0.86 MYA), with most speciation events occurring during the Pliocene epoch (5.65 +/- 1.15 MYA similar to 1.12 +/- 10.47 MYA). (c) 2005 Elsevier Inc. All rights reserved.

Coherent laser control in attosecond sum-frequency polarization beats using twin noisy driving fields

Based on the phase-conjugate polarization interference between two-pathway excitations, we obtained an analytic closed form for the second-order or fourth-order Markovian stochastic correlation of the V three-level sum-frequency polarization beat (SFPB) in attosecond scale. Novel interferometric oscillatory behavior is exposed in terms of radiation-radiation, radiation-matter, and matter-matter polarization beats. The phase-coherent control of the light beams in the SFPB is subtle. When the laser has broadband linewidth, the homodyne detected SFPB signal shows resonant-nonresonant cross correlation, a drastic difference for three Markovian stochastic fields, and the autocorrelation of the SFPB exhibits hybrid radiation-matter detuning terahertz damping oscillation. As an attosecond ultrafast modulation process, it can be extended intrinsically to any sum frequency of energy levels. It has been also found that the asymmetric behaviors of the polarization beat signals due to the unbalanced controllable dispersion effects between the two arms of interferometer do not affect the overall accuracy in case using the SFPB to measure the Doppler-free energy-level sum of two excited states.

Investigation on the N-eff reverse annealing effect using TSC/I-DLTS: Relationship between neutron induced microscopic defects and silicon detector electrical degradations

Neutron induced defect levels in high resistivity silicon detectors have been studied using a current-based macroscopic defect analysis system: thermally stimulated current (TSC) and current deep level transient spectroscopy (I-DLTS). These studies have been correlated to the traditional C-V, I-V, and transient current and charge techniques (TCT/TChT) after neutron radiation and subsequent thermal anneals. It has been found that the increases of the space charge density, N-eff, in irradiated detectors after thermal anneals (N-eff reverse anneal) correspond to the increases of deep levels in the silicon bandgap. In particular, increases of the double vacancy center (V-V and V-V-- -) and/or C-i-O-i level have good correlations with the N-eff reverse anneal. It has also been observed that the leakage current of highly irradiated (Phi(n) > 10(13) n/cm(2)) detectors increases after thermal anneals, which is different from the leakage current annealing behavior of slightly irradiated (Phi(n) < 10(13) n/cm(2)) detectors. It is apparent that V-V center and/or C-i-O-i level play important roles in both N-eff and leakage current degradations for highly irradiated high resistivity silicon detectors.

Survivin expressions in human hepatoma HepG2 cells exposed to ionizing radiation of different LET

Survivin is a member of the inhibitors of apoptosis (IAP) protein family that interferes with post-mitochondrial events including activation of caspases. To examine the regulation of survivin expression in response to irradiation with different linear energy transfer (LET), human hepatoma HepG2 cells were irradiated in vitro with X-rays and carbon ions. Cellular sensitivities to low- and high-LET radiation were determined by colony formation. Survivin expression at mRNA and protein level were measured with RT-PCR and Western blot analyses, respectively. Radiation-induced cell cycle arrest and apoptosis were investigated with flow cytometry. We found that low-LET X-rays induced dose-dependent increases in survivin expression. After exposure to high-LET carbon ions, survivin expression gradually increased from 0 to 4 Gy, and then declined at 6 Gy. More pronounced survivin expression, stronger G(2)/M phase arrest was observed after exposure to carbon ions in comparison with X-rays at doses from 0 to 4 Gy. These observations indicate that there is a differential survivin expression in response to different LET radiations and the cycle arrest mechanism may be associated with it. In addition, our data on induction of apoptosis are compatible with the assumption that survivin expression induced by low-LET X-rays radiation may play a critical role in inhibiting apoptosis. However, after irradiation with ions, an anti-apoptotic function of survivin is not evident, possibly because of the serious damage produced by densely ionizing radiation.

Correlation between initial chromatid damage and survival of various cell lines exposed to heavy charged particles

The biophysical characteristics of heavy ions make them a rational source of radiation for use in radiotherapy of malignant tumours. Prior to radiotherapy treatment, a therapeutic regimen must be precisely defined, and during this stage information on individual patient radiosensitivity would be of very great medical value. There are various methods to predict radiosensitivity, but some shortfalls are difficult to avoid. The present study investigated the induction of chromatid breaks in five different cell lines, including one normal liver cell line (L02), exposed to carbon ions accelerated by the heavy ion research facility in Lanzhou (HIRFL), using chemically induced premature chromosome condensation (PCC). Previous studies have reported the number of chromatid breaks to be linearly related to the radiation dose, but the relationship between cell survival and chromatid breaks is not clear. The major result of the present study is that cellular radiosensitivity, as measured by D-0, is linearly correlated with the frequency of chromatid breaks per Gy in these five cell lines. We propose that PCC may be applied to predict radiosensitivity of tumour cells exposed to heavy ions.

Stress Resistance and Disease Resistance in Seaweeds:The Role of Reactive Oxygen Metabolism

It has become clear that the last 15-20 years that the immediate effect of a wide range of environmental stresses,and of infection,on vascular plants is to increase the information of reactive oxygen species(ROS) and to impose oxidative stress on the cells.Since 1994,sufficient examples similar responses in a broad range of marine macroalgae have been decribed to show that reactive oxygen metabolism also underlies the mechanisms by which seaweeds respond(and become resistant) to stress and infection.Desiccation,freezing,low temperatures,high light,ultraviolet radiation,and heavy metals all tend to result in a gradual and continued buildup of ROS because photosynthesis is inhibited and excess energy results in the formation of singlet oxygen.The response to other stresses (infection or oligosaccharides which signal that infection is occurring,mechanical stress,hyperosmotic shock) is quite different-a more rapid and intence,but short-lived production of ROS ,discribed as an "oxidative burst"-which is attributed to activation of NADPHoxidases in the plasma membrane.Seaweed species that are able to survive such stresses or resist infection have the capacity to remove the ROS through a high cellular content of antioxidant compounds,or a high activity of antioxidant enzymes.

Vulcanization of polybutadiene latex induced by Co-60 gamma radiation

Polybutadiene latex (PBL) vulcanization induced by Co-60 radiation and the influence of dose on crosslinking were investigated. Morphology and particle size distribution were examined by AFM and a particle size analyzer. The casting films were characterized for their swelling and mechanical properties as a function of dose.

Radiation-induced crystallization of polyamide-1010 containing heterogeneous nuclei

Radiation-induced crystallization of polyamide-1010 (PA1010) or nylon-1010 containing heterogeneous nuclei (neodymium oxide, Nd2O3) is discussed in this paper by Wide Angle X-ray Diffraction (WAXD) and Differential Scanning Calorimetry (DSC). The results show that at low dosage the crystallinities of the irradiated specimens increase, while crystallite size (L(hkl)) decreases, indicating that some new crystallites are produced in the course of irradiation. The new centers were brought about in the fold surface of the lamellae. Copyright (C) 1997 Elsevier Science Ltd

Alteration of metallothionein mRNA in bay scallop Argopecten irradians under cadmium exposure and bacteria challenge

Metallothionein (MT) is a superfamily of cysteine-rich proteins contributing to metal metabolism, detoxification of heavy metals, and immune response such as protecting against ionizing radiation and antioxidant defense. A metallothionein (designated AiMT2) gene was identified and cloned from bay scallop, Argopecten irradians. The full length cDNA of AiMT2 consisted of an open reading frame (ORF) of 333 bp encoding a protein of 110 amino acids. with nine characteristic Cys-X-Cys, five Cys-X-X-Cys, five Cys-X-X-X-Cys and two Cys-Cys motif arrangements and a conserved structural pattern Cys-x-Cys-x(3)-Cys-Tyr-x(3)Cys-x-Cys-x(3)-Cys-x-Cys-Arg at the C-terminus. The cloned ANT showed about 50% identity in the deduced amino acid sequence with previously published MT sequences of mussels and oysters. The conserved structural pattern and the close phylogenetic relationship of AiMT2 shared with MTs from other mollusc especially bivalves indicated that AiMT2 was a new member of molluscan MT family. The mRNA transcripts in hemolymph of AiMT2 under cadmium (Cd) exposure and bacteria challenge were examined by real-time RT-PCR. The mRNA expression of AiMT2 was up-regulated to 3.99-fold at 2 h after Listonella anguillarum challenge, and increased drastically to 66.12-fold and 126.96-fold at 16 and 32 h post-challenge respectively. Cadmium ion exposure could induce the expression of AiMT2, and the expression level increased 2.56-fold and 6.91-fold in hemolymph respectively after a 10-day exposure of 100 mu g L-1 and 200 mu g L-1 CdCl2. The sensitivity of AiMT2 to bacteria challenge and cadmium stress indicated it was a new Cd-dependent MT in bay scallop and also regulated by an immune challenge. The changes in the expression of AiMT2 could be used as an indicator of exposure to metals in pollution monitoring programs and oxidative stress, and bay scallop as a potential sentinel organism for the cadmium contamination in aquatic environment. (C) 2008 Elsevier Inc. All rights reserved.

A new species of Saussurea (Asteraceae) from Tibet and its systematic position based on ITS sequence analysis

A new species of Saussurea, S. erecta S. W Liu, J. T Pan A J. Q. Liu sp. nov., is described from Tibet. It resembles S. kingii but may be distinguished by having distinct stems and glabrous achenes. Saussurea kingii was placed in sect. Pseudoeriocoryne of subgen. Eriocoryne; this section was circumscribed by acaulescence and an inflorescence with congested capitula surrounded by a rosette of leaves. The discovery of S. erecta with distinct stems, cauline leaves and corymbose capitula blurred the delimitation of sect. Pseudoeriocoryne and suggested that the section may be polyphyletic. Both the close relationship and the significant difference between S. erecta and S. kingii were confirmed by analyses of nrDNA ITS sequences. The resulting phylogenies based on ITS data further suggest that Saussurea sect. Pseudoeriocoryne, as traditionally defined, does not constitute a monophyletic group. The rapid radiation and speciation of Saussurea in the Qinghai-Tibetan Plateau, as inferred from ITS phylogeny, are discussed. (c) 2005 The Linnean Society of London.

高寒草甸生态系统陆地生物圈模式研究及应用

改进了适合于高寒草甸生态系统的陆地生态圈模式，分析了模式中温度变化与水分运动分层的物理原因，说明了气候状况对地表面能量交换的影响，给出了净辐射和蒸散量新的计算方法，提出了有很差分计算中具有二阶精度的Euler隐式格式，介绍了中国科学院海北高寒草甸生态站的气候概况和野外观测情况。最后利用本模式对高寒草甸生态站地区的土壤-植被-大气间水热交换过程进行了数值模拟，模拟值与实测值吻合较好。

横断山区马先蒿属的形态分化与分子进化

半寄生植物马先蒿属（Pedicularis）是列当科（Orobanchaceae）中最大的属，也是北温带被子植物最大的属之一。该属至少有500种植物，主要分布在北半球的高山、亚高山地区或高纬度地区，其中超过一半的种类分布在东喜马拉雅至横断山区，构成该地区高山植物区系的主要成分。马先蒿属花部器官的强烈分化程度在被子植物中极为罕见，导致这种分化发生的机制仍是难解之谜。马先蒿属下系统非常混乱，迄今为止该属属下分类系统不下10个。关于该属的起源时间、地点及迁移散布过程只是基于一些间接证据的推测。针对以上问题，本文通过大量的标本查阅、野外考察、传粉生物学观察以及分子系统学研究，得出了一些初步的结果。 　　1．形态学 通过大量的野外考察及标本观察，发现马先蒿属花部器官变异非常复杂，是区分近缘种的主要性状依据，但是花部器官存在明显的平行进化现象，不适合作为划分群、组等属下高级分类单元的主要依据;而营养性状比较保守，可作为划分群、组的主要依据。通过考证，发现直管群万叶系的德钦马先蒿（P. deqinensis）实属轮枝群纤细系多枝马先蒿（P. ramosissima）的异名。同时发现一个新种，即折喙马先蒿（P. inflexirostris），该种属于直管群的万叶系。 　　2.传粉生物学 对27种马先蒿的昆虫传粉行为进行了初步的观察。发现横断山区的马先蒿主要靠熊蜂进行有效的传粉。昆虫的传粉方式有两种，即背触式（Nototribic）和腹触式（Sternotribic）。不同花冠类型的马先蒿属植物中，昆虫的传粉方式也有所区别。对短管、无喙、无花蜜的马先蒿，昆虫主要以腹触式完成传粉;对短管、无喙、具花蜜的马先蒿，昆虫既可以通过背触式也可以通过腹触式完成传粉;而对短管、具喙和长管、具喙的马先蒿，昆虫都以腹触式完成传粉。没有发现鳞翅目的昆虫访问长管类型的马先蒿。不同花冠类型传粉方式的不同说明马先蒿花部形态结构和传粉媒介的行为之间存在协同进化关系。 3.核rDNA ITS分析 对12个群的42种马先蒿的核rDNA ITS序列进行了分析。基于ITS序列构建的基因树和经典的属下分类系统很不一致，基因树上的大部分分支和经典系统中的高级分类单元不相吻合，原因可能是马先蒿属花部器官发生了平行进化，而经典的分类系统过于权重这些花部形态性状。此外，发现在横断山区这一相对狭小的地域范围内，nrDNA ITS序列在马先蒿种间存在很大差异。造成此差异的原因可能有两个方面：一方面是马先蒿属的起源和分化的时间可能较早，不同的支系从其他地域先后多次迁入横断山区;另一方面可能是由于半寄生植物马先蒿中快速的分子进化造成的。 4.叶绿体基因组trnT-F区序列分析 对8个群的11种马先蒿的trnT-F区序列进行了分析，发现种间存在大量的插入/缺失序列，其中甘肃马先蒿（P. kansuensis）和大王马先蒿（P. rex）分别在trnT-trnL（UAA）和trnL–trnF基因间区发生了长达228bp和303bp碱基序列缺失，说明半寄生植物的叶绿体基因组也可能存在大量基因丢失现象。 5. GLOBOSA-like MADS-box基因的研究 对11种马先蒿属植物（8个群）中控制花瓣发育的GLOBOSA（PGLO）基因的部分片段进行了分离、克隆和测序，发现该基因在种间发生了明显的分化，但是碱基的变异主要发生在非编码区或非结构域，基因的同义突变率远高于非同义突变率，说明PGLO基因的进化受到强烈的功能制约。PGLO基因在马先蒿种间的明显分化表明：在辐射分化类群中，调节基因也可能发生了快速分化。对11种马先蒿属植物的PGLO基因树、nrDNA ITS基因树以及trnT-F基因树的比较发现：三个树图在结构上既有一致、也有相互矛盾之处，推测可能是因为这些基因具有不同的遗传体系或经历了不同的进化历史所致，另一方面说明GLOBOSA基因在探讨近缘类群系统发育关系方面的价值有待进一步验证。

冬小麦抗寒性和光合作用对增强UV-B辐射与温度交互作用的响应

人类活动产生的氯氟烃化合物破坏了大气臭氧层，导致了到达地球表面的UV-B辐射大幅度增加。UV-B辐射增强可以影响到植物的生长、形态与发育等各个方面，因此有关增强UV-B辐射对植物的影响，及其与许多环境因子复合作用的研究都已经广泛开展。但是增强UV-B辐射与温度，特别是与低温的相互作用的研究报道很少。在北半球的晚秋至早春这段时期里，一些越冬生长的植物将面临着UV-B辐射增强和低温的双重胁迫，因此，迫切需要进行UV-B辐射和低温生长环境下植物的响应及其机制的研究。 以人工气候生长室中生长的冬小麦(Triticum aestivum)幼苗为试验材料，研究了低剂量（4.2 kJ m-2 d-1 UV-BBE，LUVB）和较高剂量（7.0 kJ m-2 d-1 UV-BBE，HUVB）UV-B辐射处理对20/16℃条件下幼苗抗寒力的交叉适应性及其抗氧化系统的反应;同时还研究了在两种生长温度（25/20℃和10/5℃）条件下，低剂量（4.2 kJ m-2 d-1 UV-BBE，LUVB）和超高剂量（10.3 kJ m-2 d-1 UV-BBE，SHUVB）UV-B辐射处理幼苗的生长速率、光合与荧光参数、叶黄素循环色素、抗氧化系统、以及抗寒性和酚类物质等生理反应，以期阐明不同温度条件下生长的冬小麦对UV-B辐射的生长、光合作用以及抗寒性响应与适应机制。主要结果如下： 1.在LUVB辐射处理下，在20/16℃和25/20℃条件下生长的冬小麦幼苗LT50值都显著降低，HUVB辐射处理对在20/16℃条件下生长的幼苗LT50值也可以显著降低，而SHUVB辐射对25/20℃条件下生长的幼苗LT50值没有显著影响。但是，LUVB和SHUVB辐射处理都导致了10/5℃条件下生长的幼苗LT50值的显著增加。表明适当的UV-B辐射能增强较高温度（20/16℃或25/20℃）条件下冬小麦幼苗的抗寒力，即表现出对冷冻低温的交叉适应性，但低温（10/5℃）生长条件却削弱了UV-B辐射下冬小麦的抗寒能力。 2.在20/16℃条件下接受UV-B辐射预处理的幼苗在-6℃条件下冷冻胁迫6 h再缓慢恢复6 h后，与未进行UV-B辐射处理的对照相比，其叶片过氧化氢酶（CAT）、愈创木酚过氧化物酶（GPX）、谷胱甘肽还原酶（GR）活性，谷胱甘肽氧化还原比例（GSH/GSSG）都显著提高，而由硫代巴比妥酸反应物质（TBARS）代表的膜质过氧化程度显著低于对照。此外，UV-B辐射期间处理幼苗的H2O2含量较对照显著增加，而冷冻恢复以后却明显低于对照。表明UV-B辐射诱导的抗寒力的提高应该与冷冻恢复后植株体内抗氧化系统的上调表达有关，H2O2可能参与了UV-B辐射对低温的交叉适应的信号传导。 3.除25/20℃生长条件下的LUVB处理的小麦幼苗外，UV-B辐射显著降低幼苗的相对生长速率（RGR）、净光合速率（Pn）、光系统II最大量子产量（Fv/Fm）、光系统II实际量子产量（(F΄m−Fs)/F΄m）以及光化学淬灭（qP），但是UV-B辐射并不影响叶片胞间CO2浓度（Ci），而且冬小麦幼苗生长和光合作用的抑制被增加的UV-B辐射剂量和降低的温度加强。UV-B辐射引起的光抑制由非气孔限制所导致，而且主要与PS II光化学效率降低有关。 4.UV-B辐射显著增加了两个温度条件（20/16℃或25/20℃）下生长的冬小麦幼苗叶黄素循环过程中紫黄素（V）的合成，但抑制了V向玉米黄质（Z）的转化，从而造成了对照与LUVB辐射处理幼苗之间的叶片中脱环氧化比例（DEPS）和NPQ无显著性差异，但SHUVB辐射处理幼苗叶片中DEPS和NPQ显著降低。因此，在本试验条件下，增强UV-B辐射处理的冬小麦可能并不通过热耗散形式形成光保护机制，光抑制形成的过剩激发能的耗散可能更多地通过代谢途径来实现。 5.UV-B辐射处理提高了在25/20℃条件下幼苗的超氧化物歧化酶（SOD）、抗坏血酸过氧化物酶（APX）和GR等活性，以及抗坏血酸氧化还原比例（AsA/DHA）和GSH/GSSG;但是在10/5℃下，UV-B辐射除了导致SOD和CAT活性升高之外，对APX活性和AsA/DHA并不产生明显影响，但GPX和GSH/GSSG则显著降低。说明UV-B辐射幼苗的抗氧化系统在较高生长温度下显著地增强，而在低温10/5℃下被严重地削弱或降低，即低温阻止了代谢途径的光保护机制的正常运转。 6.多酚物质在UV-B辐射或低温10/5℃条件下都能显著地累积，且在UV-B辐射和低温复合作用下增加尤其显著，表明多酚物质在两个温度生长条件下特别是低温条件下都参与了对UV-B辐射幼苗的保护。 7.在高温条件下仅仅SHUVB处理的幼苗TBARS含量显著增加，而低温10/5℃条件下两个UV-B辐射处理都非常显著地上升，说明与高温生长条件相比较，低温加重了UV-B辐射引起的氧化胁迫，低温10/5℃条件下幼苗多酚的增加以及抗氧化系统的部分增强都没有能阻止UV-B辐射对幼苗的伤害。