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Now showing items 1 - 16 of 88383

  • Z型光催化体系中存在的电荷转移机理问题(英文)


    <正>Photocatalysis is a sunrise technology with great potential for hydrogen production [1,2], carbon dioxide reduction [3], and so on. However, a single-component photocatalyst often exhibits severely limited activity due to rapid photogenerated carrier recombination and weak redox abilities.
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  • 弹幕闯进年轻人的生活:超八成Z世代享受弹幕狂欢(英文)

    <正>Huang Xiaobei is a university student in south China’s Guangxi Zhuang Autonomous Region. She first came into contact with bullet-screen (弹幕) comments when she was watching a Chinese movie. At that time, she couldn’t close the comments on the web page, so she was forced to watch them. However, after this experience, Huang Xiaobei considered this form of interaction to be very interesting. Like Huang Xiaobei, many college students find themselves interested in bullet-screen comments when watching videos.
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  • 可见光诱导Z型V2O5/g-C3N4异质结催化未活化烯烃串联反应

    桂清文   吴一帆   农志彬   杨龙汐   阳天宝   何卫民  

    半导体光催化剂是一种极具前景的绿色催化剂,广泛用于污染物降解、水解制氢和有机合成等领域,有望利用太阳能来解决能源和环境问题,是当前的研究前沿和热点.然而,单组分半导体光催化剂的光生电子和空穴容易复合,导致量子效率差和光催化效率低.近年人们发现,将两种或多种催化材料结合,构建异质结光催化体系可有效促进光生电子-空穴分离.但传统的异质结体系中光生电子的还原性和光生空穴的氧化性通常在电荷转移后变弱,因此,很难同时具备高电荷转移效率和强氧化还原能力.研究发现,构建Z型异质结光催化体系不仅可以减少本体电子-空穴的复合,使其在不同半导体材料上实现空间分离,具有光谱响应宽、电荷分离效率高和稳定性高等优势,而且能保持良好的氧化还原能力.在半导体材料领域,石墨相氮化碳(g-C3N4)作为一种无金属聚合物半导体,具有良好的热化学稳定性、电学和光学特性,但存在量子效率低和适用范围窄等局限性.而五氧化二钒(V2O5)是一种重要的过渡金属氧化物半导体,由于具有良好的电学和光学性能被广泛用于锂离子电池、气敏传感器和光电器件.V2O5能带间隙(~2.19 eV)窄,具有合适的能量频带边缘(ECB=0.81 eV,EVB=3.0 eV),可以与g-C3N4(ECB=1.14 eV,EVB=1.59 eV)很好地匹配,形成稳定状态的Z型光催化体系,并提高光催化有机合成反应的效率.本文以三聚氰胺和偏钒酸铵为原料,采用热处理法分别制备g-C3N4和V2O5,采用水热法制备Z型V2O5/g-C3N4二元复合材料.X射线衍射(XRD)、傅里叶变换红外光谱(FTIR)、扫描电子显微镜(SEM)、X射线光电子能谱(XPS)和紫外-可见光吸收光谱(UV-Vis)等结果表明,成功制备了Z型V2O5/g-C3N4.UV-Vis结果表明,V2O5/g-C3N4具有较宽的光吸收范围,从而提高了复合半导体材料的光学性能.在温和条件下,以未活化烯烃修饰的喹唑啉酮和芳基氧膦为反应物,V2O5/g-C3N4为多相光催化剂,进行膦酰化自由基偶联反应,制得一系列环合的膦酰化喹唑啉酮,收率为63%-83%.该反应具有原料易得、条件温和、底物范围广、产品收率及区域选择性良好等优点,同时催化剂循环使用性能良好.值得注意的是,不同吸电子取代基、供电子取代基修饰的喹唑啉酮和非对称结构的芳基氧膦均能兼容于该反应体系,并以中等至良好的收率得到了各种膦酰化喹唑啉酮化合物.本文采用的合成策略同样适用于三氟甲基化、二氟烷基化和芳基磺酰化等自由基串联环化反应,且具有良好的催化性能.机理研究结果表明,V2O5/g-C3N4被光激发后,V2O5导带(CB)上的光生电子与g-C3N4价带(VB)上的光生空穴迅速复合,导致g-C3N4的导带上无法与本体空穴复合的电子发生单电子转移(SET)过程,且与分子氧(空气中)反应生成超氧阴离子自由基(O2·-).V2O5价带上的空穴氧化芳基氧膦产生自由基阳离子,去质子化产生氧膦自由基,随后加成到未活化烯烃生成新的自由基物种,最后发生分子内环化反应,得到目标产物.V2O5/g-C3N4成本较低,且该光催化反应策略可实现克级制备,循环使用5次后催化活性保持不变.综上,本文可为光催化自由基串联环化反应,杂环化合物合成研究和Z型异质结的光催化应用提供参考.
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  • 聚焦Z世代信贷成瘾


    <正>借贷有风险,监管要给力。花钱不量力,后悔又伤悲。难词探意At one point in June last year, Zeng Jinpeng was more than 10,000 yuan in debt to a smartphone app. The 23-year-old Shanghai resident pays for his online purchases with Huabei, a virtual credit card that’s part of Alibaba Group Holding Ltd.’s sprawling stable of e-commerce properties.
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  • Z-meatoplasty technique of the external auditory canal; Z形成術を用いた外耳道入口部拡大法;

    Minami, Shujiro   Yamamoto, Nobuko  

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  • Ma铆z, papas y carro帽a: la 鈥渋dentidad”alimenticia del 鈥渋ndio”de Huasipungo

    Gustavo V. García  

    Huasipungo by Jorge Icaza is considered one of the primary texts of the Latin American social criticism novels because it denounces the exploitation of the Andean indigenous peoples of Ecuador. This judgement, however, ignores descriptions that show “Indians” as degraded, animal-like and lacking culture, especially when it is time to “devour” the “food” that is attributed to them: corn, low-quality potatoes and carrion. These textual ambiguities are in conflict with the social objectives of Huasipungo, since they prolong the vision of an inferior “Indian,” lacking rights and therefore, an object of exploitation and “natural” extermination on the part of the landowning oligarchy in the name of “progress” for the nation.
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  • 鈥濴icht, Liebe, Leben鈥擶as z盲hlt”BR>Deutscher Orthop盲denkongress, Berlin 21.”3.10.2004 (Teil聽2)

    S. Hunt A1 A2  

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  • Search for top quark FCNC couplings in Z”models at聽the聽LHC聽and聽CLIC

    O. Çakır   I. T. Çakır   A. Senol and A. T. Tasci  

    The top quark is the heaviest particle to date discovered, with a mass close to the electroweak symmetry breaking scale. It is expected that the top quark would be sensitive to the new physics at the TeV scale. One of the most important aspects of the top quark physics can be the investigation of the possible anomalous couplings. Here, we study the top quark flavor changing neutral current (FCNC) couplings via the extra gauge boson Z′ at the Large Hadron Collider (LHC) and the Compact Linear Collider (CLIC) energies. We calculate the total cross sections for the signal and the corresponding Standard Model (SM) background processes. For an FCNC mixing parameter x=0.2 and the sequential Z′ mass of 1 TeV, we find the single top quark FCNC production cross sections 0.38(1.76) fb at the LHC with 脰{spp}=7(14)\sqrt{s_{pp}}=7(14) TeV, respectively. For the resonance production of sequential Z′ boson and decays to single top quark at the Compact Linear Collider (CLIC) energies, including the initial state radiation and beamstrahlung effects, we find the cross section to be 27.96(0.91) fb at 脰{se+e-}=1(3)\sqrt{s_{e^{+}e^{-}}}=1(3) TeV, respectively. We make the analysis to investigate the parameter space (mixing-mass) through various Z′ models. It is shown that the results benefit from the flavor tagging.
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  • 鈥濴icht, Liebe, Leben鈥擶as z盲hlt”BR>Deutscher Orthop盲denkongress, Berlin 21.”3.10.2004, Teil 1

    S. Hunt A1 A2  

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  • Sh?nanzan no hen\"y?-Ch? T? bungaku ronsh? 終南山の変程裕- 中唐文學諭集by Kawai K?z? 川合康三

    Review by: William H. Nienhauser   Jr.  

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  • Li, Maozeng 李茂增, The Beauty Beyond Words: A Critical Biography of Z\r hu Guangqian 無言之美: 朱光潛評傳

    Sun   Weimin  

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  • Z”/sup> boson signal at Fermilab-Tevatron and CERN-LHC in聽a聽331聽model

    J. G. Dueñas   N. Gutierrez   R. Martínez and F. Ochoa  

    We analyse the possibilities to detect a new Z ′ boson in di-electron events at Tevatron and LHC in the framework of the 331 model with right-handed neutrinos. We also study other fermions and Higgs events as final state at LHC. Using p[`(p)]p\bar{p} collision data collected by the CDF II detector at Fermilab Tevatron, we find that the 331 Z ′ boson is excluded with masses below 920 GeV. For an integrated luminosity of 100 fb−1 at LHC, and considering a central value MZ垄=1500M_{Z^{\prime}}=1500 GeV, we obtain the invariant-mass distribution in the process pp→Z ′→e + e −, where a huge peak, corresponding to 800 signal events/(20 GeV), is found above the SM background. The number of di-electron events vary from 50000 to 2400 in the mass range of MZ垄=800M_{Z^{\prime}}=800 –2000 GeV. We also obtain branching ratios and cross sections in other fermion and Higgs channels at LHC, where a heavy top quark T exhibits the biggest ratio with m T =300 GeV.
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  • In response to 鈥渃urrent approach to seronegative myasthenia”by Z. Argov

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  • The M emission spectra of the heavy rare earth elements 67 鈮?Z 鈮?71

    Jan Dellith and Michael Wendt  

    The M emission spectra of the heavy rare earth elements 67Ho, 68Er, 69Tm, 70Yb, and 71Lu were reinvestigated using wavelength dispersive spectrometry with a TAP crystal as the dispersing element. In order to resolve weak lines, which are near to the strong α and β lines/bands, the regions around these lines were additionally measured using the second order reflection. In this manner in total 54 M lines were observed of which only 19 are contained in Bearden’s compilation. A difference between the line positions of metals and oxides was observed only for the Mα line of 70Yb. This observation agrees with an earlier report of Fischer and Baun. The observed dependencies of the intensity ratios Mβ/Mα and Mζ/Mα on the atomic number Z reflect the increasing filling of the N7 subshell with increasing Z.
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  • Electron Excited L X-Ray Spectra of the Elements 24 鈮?Z 鈮?33

    Andrea Aßmann   Jan Dellith and Michael Wendt  

    A reinvestigation was undertaken in order to obtain reliable data of the relative intensities of the L spectra for the elements 24 ≤ Z ≤ 33. A TAP crystal with a periodicity of 25.757 脜 was used as the dispersing element. With this crystal one is able to resolve the lines/bands Ll = L3M1, Lη = L2M1, Lα1,2 = L3M4,5, Lβ1 = L2M4, and Lβ3,4 = L1M2,3. Among the investigated elements 33As is the only one for which the energy of the lines Lα1,2 and Lβ1 is below the L3 absorption edge. For all the other elements the lines Ll, Lη, and Lα1,2 are below the L3 edge, whereas Lβ1 and Lβ3,4 are above this edge. This difference leads to effects of differential absorption, where the absorption is stronger for decreasing line energy. For the net peak height ratio β1/α we obtained results which are of the same order of magnitude as those given by White and Johnson (W&J) in their popular tables. But for l/α and β3,4/β1 our results show an atomic number dependence which is completely different from those given by W&J.
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  • Z boson as 鈥渢he standard candle”for high-precision W boson physics at LHC

    M.W. Krasny   F. Fayette   W. Płaczek and A. Siódmok  

    In this paper we propose a strategy for measuring the inclusive W boson production processes at LHC. This strategy exploits simultaneously the unique flexibility of the LHC collider in running variable beam particle species at variable beam energies, and the configuration flexibility of the LHC detectors. We propose their concrete settings for a precision measurement of the standard model parameters. These dedicated settings optimise the use of the Z boson and Drell–Yan-pair production processes as “the standard reference candles”. The presented strategy allows one to factorise and to directly measure those of the QCD effects that affect differently the W and Z production processes. It reduces to a level of O(10-4)\mathcal{O}(10^{-4}) the impact of uncertainties in the partonic distribution functions (PDFs) and in the transverse momentum of the quarks on the measurement precision. Last but not the least, it reduces by a factor of 10 the impact of systematic measurement errors, such as the energy scale and the measurement resolution, on the W boson production observables.
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