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991.
The origin of life on Earth remains a fascinating mystery in spite of many theories existing on this subject. However, it seems that simple prebiotic molecules could play an essential role in the formation of more complex organisms. In our experiment, we synthesized a class of these molecules (quinones) bombarding frozen anthracene containing water with low energy hydrogen ions. This experiment roughly simulated the astrophysical conditions which one can find in the solar system. Thus, we can hypothesize that prebiotic molecules could be created by interaction of the solar wind with interplanetary dust grains. The delivery of these molecules to early Earth may have contributed to the generation of life on our planet. 相似文献
992.
Micromachining bulk glass by use of femtosecond laser pulses with nanojoule energy 总被引:13,自引:0,他引:13
Using tightly focused femtosecond laser pulses of just 5 nJ, we produce optical breakdown and structural change in bulk transparent materials and demonstrate micromachining of transparent materials by use of unamplified lasers. We present measurements of the threshold for structural change in Corning 0211 glass as well as a study of the morphology of the structures produced by single and multiple laser pulses. At a high repetition rate, multiple pulses produce a structural change dominated by cumulative heating of the material by successive laser pulses. Using this cumulative heating effect, we write single-mode optical waveguides inside bulk glass, using only a laser oscillator. 相似文献
993.
Molina-Terriza G Torner L Wright EM García-Ripoll JJ Pérez-García VM 《Optics letters》2001,26(20):1601-1603
We predict that vortex dipoles nested in light beams trapped in graded-index media can undergo closed Berry trajectories, yielding periodic vortex annihilations and revivals along the light-propagation direction. The vortex revivals from vortex-free wave fronts are mediated by Freund stationary point bundles that carry the necessary Poincaré-Hopf indices. Vortex spiraling and spontaneous generation of circular-edge dislocations are also found to occur. 相似文献
994.
1 INTRODUCTION In recent years, chemists have paid their attention to the design and construction of extended metal- organic framework solids with potential applications, such as catalysts, nonlinear optical devices, ion ex- change, adsorption, sensors etc.[1, 2]. As one kind of polydentate ligands, isonicotinic acid has been exte- nsively employed to synthesize transition metal coo- rdination polymers[3, 4] with one-[5~8], two-[9~12] and three- dimensional[13~21] extended frameworks b… 相似文献
995.
1 INTRODUCTION In the last decades, metal carboxylate complexes have become a particularly important subject in mo- dern coordination chemistry owing to their fascina- ting structural diversity and potential applications as functional materials[1~3]. The generation of supramo- lecular architectures relies on the combination of se- veral factors, such as the coordination geometry of metals, bonding of the ligands and reaction condi- tions[4, 5]. In relation to the ligands, the judicious c… 相似文献
996.
HUA Guo-Pinga ZHANG Xiao-Jingb TU Shu-Jiangb② ZHU Song-Leib LI Tuan-Jieb ZHU Xiao-Tongb ZHANG Jin-Pengb a 《结构化学》2005,24(4):399-402
1 INTRODUCTION Since the discovery of pharmacological effectsof 1,4-dihydropyridine (1,4-DHPs) as calcium mo-dulators[1], a great deal of work has been directedtowards the synthesis of 1,4-DHPs acting as cal-cium antagonists[2]. The chemical modifications onthe DHP ring, such as the introduction of differentsubstituents on heteroatoms[3], have allowed theexpansion of researches on structure-activity rela-tionship to have new insight into the molecularinteractions at the receptor l… 相似文献
997.
YANG Jian-Guoa PAN Fu-Youb② a 《结构化学》2005,24(12):1403-1407
1 INTRODUCTION 2. 1 Physical measurements Azole derivatives, such as pyrazole, imidazole, All solvent and chemicals were commercial rea- triazole(including benzotriazole), tetrazole and indole, gents and used without further purification. Ele- have extensive biological activities. They have be- mental analyses were performed on a PE 1700 CHN come the central focus of studies for agricultural che- auto elemental analyzer. IR spectra were recorded on micals, medicines, plant growth regul… 相似文献
998.
HUANG Lia ZHOU Ya-Jua YE De-Yonga① CHEN Min-Qinb a 《结构化学》2005,24(8):945-951
1 INTRODUCTION The success of strategies for total synthesis con-tinues to depend on high levels of stereoselectivityobserved in substrate-directed diastereoselective re-actions[1]. In this context, one of the most widelyused processes is diastereoselective epoxidation ofcyclic alkenes with allylic O- and N-directing group,which is very useful in building stereodefined syn-thetic blocks[2, 3] .However, in some circumstances,the assignment of resulting epoxides is not straight-forward[4~8… 相似文献
999.
1 INTRODUCTIONResearchonSHGeffecthasbeenonaremarkablepositioninorganicnonlinearoptical(NLO)materialsfield.Theconjugateddelocalizedπelectronspossiblyresultinthesecond-orderNLOpropertyoforganiccompounds,soanumberofnitroanilinederivatives,suchas2-methyl… 相似文献
1000.
María Natividad Pérez-Camacho Jehad Abu-Dahrieh Alexre Goguet Kening Sun David Rooney 《催化学报》2014,(8)
Gas-to-liquid processes are generally used to convert natural gas or other gaseous hydrocarbons into liquid fuels via an intermediate syngas stream. This includes the production of liquid fuels from biomass‐derived sources such as biogas. For example, the dry reforming of methane is done by reacting CH4 and CO2, the two main components of natural biogas, into more valuable products, i.e.,CO and H2. Nickel containing perovskite type catalysts can promote this reaction, yielding good conversions and selectivities; however, they are prone to coke laydown under certain operating conditions. We investigated the addition of high oxygen mobility dopants such as CeO2, ZrO2, or YSZ to reduce carbon laydown, particularly using reaction conditions that normally result in rapid cok‐ing. While doping with YSZ, YDC, GDC, and SDC did not result in any improvement, we show that a Ni perovskite catalyst (Na0.5La0.5Ni0.3Al0.7O2.5) doped with 80.9 ZrO2 15.2 CeO2 gave the lowest amount of carbon formation at 800 °C and activity was maintained over the operating time. 相似文献