Distinguishing the direct and indirect products of a gas-surface reaction

It has long been postulated that gas-surface chemical reactions can occur by means of two distinct mechanisms: direct reaction on a single gas-surface encounter or reaction between two adsorbed species. It is shown here that these mechanisms have distinct dynamical signatures, as illustrated by the reaction of hydrogen with chlorine on gold(111). The direct reaction product leaves the surface with a high kinetic energy in a narrow angular distribution that displays a "memory" of the direction and energy of the incident hydrogen atom. The indirect reaction product has a near-thermal energy distribution and an angular distribution that is close to that of a cosine function.     

Watching vibrational energy transfer in liquids with atomic spatial resolution

Ultrafast spectroscopy was used to study vibrational energy transfer between vibrational reporter groups on different parts of a molecule in a liquid. When OH stretching vibrations of different alcohols were excited by mid-infrared laser pulses, vibrational energy was observed to move through intervening CH2 or CH groups, taking steps up and down in energy, ending up at terminal CH3 groups. For each additional CH2 group in the path between OH and CH3, the time for vibrational energy transfer increased by about 0.4 picosecond.     

能源植物石栗ISSR-PCR体系的建立与优化

对能源植物石栗种质资源的遗传多样性进行研究,建立了其ISSR-PCR分子标记体系.应用CTAB法提取石栗叶片基因组DNA,用正交设计和单因素水平优化的方法对ISSR-PCR反应程序中的一些重要参数进行筛选和优化.结果表明,25 μLISSR-PCR反应体系的最优条件为:DNA模板20 ng、Mg2+ 1.5 mmol/L,Taq DNA聚合酶1.5 U,引物0.40μmol/L,dNTP 200 μmol/L.     

Conformational dynamics in a dipeptide after single-mode vibrational excitation

The dynamics of conformational isomerization are explored in a methyl-capped dipeptide, N-acetyl-tryptophan methyl amide (NATMA), using infrared-ultraviolet (IR-UV) hole-filling and IR-induced population transfer spectroscopies. IR radiation selectively excites individual NH stretch vibrational fundamentals of single conformations of the molecule in the early portions of a gas-phase expansion, and then this excited population is collisionally recooled into its conformational minima for subsequent conformation-specific detection. Efficient isomerization is induced by the IR excitation that redistributes population between the same conformations that have population in the absence of IR excitation. The quantum yields for transfer of the population into the various conformational minima depend uniquely on which conformation is excited and on which NH stretch vibration is excited within a given conformation.     

Tunable field control over the binding energy of single dopants by a charged vacancy in GaAs

Local manipulation of electric fields at the atomic scale may enable new methods for quantum transport and creates new opportunities for field control of ferromagnetism and spin-based quantum information processing in semiconductors. We used a scanning tunneling microscope to position charged arsenic (As) vacancies in the gallium arsenide 110 [GaAs(110)] surface with atomic precision, thereby tuning the local electrostatic field experienced by single manganese (Mn) acceptors. The effects of this field are quantified by measuring the shift of an acceptor state within the band gap of GaAs. Experiments with varying tip-induced band-bending conditions suggest a large binding energy for surface-layer Mn, which is reduced by direct Coulomb repulsion when the As vacancy is moved nearby.     

Ethanol for a sustainable energy future

Renewable energy is one of the most efficient ways to achieve sustainable development. Increasing its share in the world matrix will help prolong the existence of fossil fuel reserves, address the threats posed by climate change, and enable better security of the energy supply on a global scale. Most of the "new renewable energy sources" are still undergoing large-scale commercial development, but some technologies are already well established. These include Brazilian sugarcane ethanol, which, after 30 years of production, is a global energy commodity that is fully competitive with motor gasoline and appropriate for replication in many countries.     

昆虫对冬季显花植物蜜粉组合的选择偏好

为探明昆虫的授粉行为与不同粉蜜组合模式植物间的关系,采用野外考察法研究冬季昆虫对油菜(含大量花蜜与适量花粉)、芥蓝(含大量花蜜与少量花粉)、蚕豆(含少量花蜜和大量花粉)等不同花蜜和花粉组合模式显花植物的选择偏好。结果表明:相同条件下,昆虫对油菜的访花频次为(591±11.83)只/d,显著高于蚕豆的(127±1.90)只/d和芥蓝的(180±2.53)只/d。蜜粉组合方式(油菜)比仅提供粉源(蚕豆)更能吸引授粉者。优势访花昆虫1d的最大访花量及其出现时间存在差异,中蜂和食蚜蝇的最大访花量分别为(34±9.80)只和(14±0.56)只,出现在12:00~13:00;意蜂为(39±9.17)只,出现在12:30~14:30;家蝇为(12±1.34)只,出现在16:00~18:00。最大访花量及其出现时间的差异能减少授粉者间的取食竞争,提高显花植物的授粉率。     

Electronic Characterization of Solid Surfaces: Determination of the energy levels of electrons at surfaces is now possible over a wide energy range

At this point it would be presumptuous to suggest either that we understand very much about the electronic structure of solid surfaces or that we can specify in detail exactly what each of our tools for studying such structure is telling us. I think it is fair to say, however, that FES, UPS, and INS do make it possible for us to determine energy level spectra which can with some confidence be ascribed to the resonances of electrons in surface orbitals. It is true that INS is the more surface-selective of the two electron spectroscopies capable of producing data over at least a 10-ev energy range. We have seen intriguing differences between INS and UPS which, when we come to understand them, will most certainly reveal important characteristics of surface electronic structure and greatly expand our ability to distinguish electronic states in the surface from those in the selvedge. Possibly it is not too much to hope that the combined use of INS and UPS with incidence angle as an independent variable will give us information on the geometrical extent of surface orbitals, as well as the net electrical charge and the electric potential gradient in the region of the surface in which the orbitals lie.     

Photoinduction of fast, reversible translational motion in a hydrogen-bonded molecular shuttle

A rotaxane is described in which a macrocycle moves reversibly between two hydrogen-bonding stations after a nanosecond laser pulse. Observation of transient changes in the optical absorption spectrum after photoexcitation allows direct quantitative monitoring of the submolecular translational process. The rate of shuttling was determined and the influence of the surrounding medium was studied: At room temperature in acetonitrile, the photoinduced movement of the macrocycle to the second station takes about 1 microsecond and, after charge recombination (about 100 microseconds), the macrocycle shuttles back to its original position. The process is reversible and cyclable and has properties characteristic of an energy-driven piston.     

混凝土局部破损梁损伤诊断的振动检测方法

为对钢筋混凝土梁进行动力破损评估，建立了钢筋混凝土梁的分离式有限元模型，推导了四节点矩形粘结单元的刚度矩阵。采用该模型计算了健康和局部破损梁的振动特性参数，计算结果与实际测试结果相吻合；计算及实际测试结果均表明。固有频率是进行钢筋混凝土梁损伤定性辨识的重要指标；曲率模态振型和应变模态振型对于钢筋混凝土梁的局部损伤较位移模态振型敏感。基于曲率模态振型和应变模态振型可以进行钢筋混凝土梁的局部损伤诊断。     

山西矿区农业持续发展的择抉:矿区生态重建

基于山西采煤引发的大量地表塌陷、废弃岩土压占土地、人为水土流失加剧、区域性水破坏和污染等严峻的现实，提出：借助于现代采矿业的经济实力和运用现代生态工程技术，进行矿区生态重建（ＥｃｏｌｏｇｉｃａｌＲｅｃｏｎｓｔｒｕｃｔｉｏｎ），是扭转山西长期以来“输出资源、留下污染”、“捧着金碗讨饭吃”的唯一选择。本文围绕矿区生态重建中的核心问题——土地复垦（ＬａｎｄＲｅｃｌａｍａｔｉｏｎ），分析了山西矿区生态重建的现状和问题，论述了山西矿区生态重建的迫切性、必要性和可能性，提出了进行山西矿区生态重建的战略框架     

A microRNA as a translational repressor of APETALA2 in Arabidopsis flower development

Plant microRNAs (miRNAs) show a high degree of sequence complementarity to, and are believed to guide the cleavage of, their target messenger RNAs. Here, I show that miRNA172, which can base-pair with the messenger RNA of a floral homeotic gene, APETALA2, regulates APETALA2 expression primarily through translational inhibition. Elevated miRNA172 accumulation results in floral organ identity defects similar to those in loss-of-function apetala2 mutants. Elevated levels of mutant APETALA2 RNA with disrupted miRNA172 base pairing, but not wild-type APETALA2 RNA, result in elevated levels of APETALA2 protein and severe floral patterning defects. Therefore, miRNA172 likely acts in cell-fate specification as a translational repressor of APETALA2 in Arabidopsis flower development.     

行为偏好下的海南文笔峰景区景观情境感知分析

选择道教文化场地海南文笔峰景区作为研究场地,研究游客对道教文化景观情境感知与行为偏好之间的关系。于2019?04?26—04?30,通过现场调查、分发问卷,5 d共获得186份调查问卷,并进行量化分析。结果表明:1）道教文化景观情境感知与行为偏好之间的确存在着数量关系,通过特定的行为活动可以获得景观情境感知;2）游客对修仙情境感知受学习性活动影响;3）游客对自然情境感知随学习性活动、游赏性活动而变化,且游赏性活动比学习性活动产生的影响更大;4）游客对美学情境感知随学习性活动、游赏性活动和宗教性活动而变化,其中,学习性活动并未能增加对美学情境感知;5）游客对孝善情境感知随学习性活动、宗教性活动而变化,且宗教性活动比学习性活动产生的影响更大。     

Charge separation in a reaction center incorporating bacteriochlorophyll for photoactive bacteriopheophytin

Site-directed mutagenic replacement of M subunit Leu214 by His in the photosynthetic reaction center (RC) from Rhodobacter sphaeroides results in incorporation of a bacteriochlorophyll molecule (BChl) in place of the native bacteriopheophytin (BPh) electron acceptor. Evidence supporting this conclusion includes the ground-state absorption spectrum of the (M)L214H mutant, pigment and metal analyses, and time-resolved optical experiments. The genetically modified RC supports transmembrane charge separation from the photoexcited BChl dimer to the primary quinone through the new BChl molecule, but with a reduced quantum yield of 60 percent (compared to 100 percent in wild-type RCs). These results have important implications for the mechanism of charge separation in the RC, and rationalize the choice of (bacterio)pheophytins as electron acceptors in a variety of photosynthetic systems.     

Mode-specific energy disposal in the four-atom reaction OH + D2 --> HOD + D

Experiments, employing crossed molecular beams, with vibrational state resolution have been performed on the simplest four-atom reaction, OH + D2 --> HOD + D. In good agreement with the most recent quantum scattering predictions, mode-specific reaction dynamics is observed, with vibration in the newly formed oxygen-deuterium bond preferentially excited to v = 2. This demonstrates that quantum theoretical calculations, which in the past decade have achieved remarkable accuracy for three-atom reactions involving three dimensions, have progressed to the point where it is now possible to accurately predict energy disposal in four-atom reactions involving six dimensions.     

林业有害生物薇甘菊化学防除优选药剂研究

[目的]解决林地薇甘菊规模化防除药剂优选问题。[方法]以①18%2,4-D微乳剂∶水=1∶700;②75%甲嘧磺隆可湿性粉剂∶水=1∶800;③50%草甘膦可溶性粉剂∶85%2,4-D钠盐∶水=35∶1∶12 500;④41%草甘膦异丙胺盐水剂∶水=1∶200 4种药剂对薇甘菊盖度变化和药效作用进行了研究。[结果]4种药剂均可用于薇甘菊防治,①（18%2,4-D微乳剂）略优于其他药剂,90 d补防1次后,防效可达（97.75±1.01）%。[结论]草甘膦类除草剂添加2,4-D钠盐后能增效防除薇甘菊。