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101.
Kok Chung Chin Chee Kok Poh Ghee Lee Chong Jianyi Lin Chorng Haur Sow Andrew Thye Shen Wee 《Applied Physics A: Materials Science & Processing》2008,90(4):623-627
We demonstrate an improved and rapid method to synthesize uniform two-dimensional ZnO nanosheets at low temperature. These
nanosheets can be prepared within an hour. The compositions and morphologies of the nanosheets produced were characterized
by SEM, XRD, Raman and photoluminescence analysis. The nanosheets showed reasonably strong electron field emission properties
with good reliability. Emission current density close to 0.3 mA/cm2 was obtained. The effects of dimensions and morphologies on the field emission performance of the nanosheets are also discussed.
PACS 62.23.Kn; 79.70.+q; 81.16.Be 相似文献
102.
Wee Chew 《Journal of Raman spectroscopy : JRS》2011,42(1):36-47
A methodology of multivariate chemometric techniques based on the information‐theoretic approach was applied for elucidating chemical reaction information from a Raman data array R m×ν that arises from in situ reaction monitoring. This reaction‐induced dynamic dataset R m×ν can be contaminated by random cosmic ray spikes found in the midst of characteristic spectral variations associated with the disappearance or emergence of Raman active reactants, intermediates and products. Such spurious cosmic spikes were identified and removed using a novel and fast numerical approach based on maximum and minimum spectral entropy principles while preserving the genuine reaction‐induced spectral variations. Subsequently, the band‐target entropy minimization (BTEM) algorithm, a minimum spectral entropy based self‐modeling curve resolution technique, was applied to recover the pure component spectra of Raman active chemical species. Information gain through the chemometric analyses was calculated using information entropies with base 2 logarithm. This sequence of information‐theoretic chemometric analyses (or transinformations) was successfully tested on the reaction spectral data obtained from alcoholysis of acetic anhydride, which contains four Raman active chemical species. It is envisioned that this series of multivariate statistical analyses will be useful in chemical reaction studies and process analytical technology (PAT) applications that utilize in situ Raman spectroscopy to monitor transient dynamic changes in chemical concentrations, and also in Raman microscopy/imaging data containing spatial variations. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
103.
Let VI be the category whose objects are the finite dimensional vector spaces over a finite field of order q and whose morphisms are the injective linear maps. A VI-module over a ring is a functor from the category VI to the category of modules over the ring. A VI-module gives rise to a sequence of representations of the finite general linear groups. We prove that the sequence obtained from any finitely generated VI-module over an algebraically closed field of characteristic zero is representation stable - in particular, the multiplicities which appear in the irreducible decompositions eventually stabilize. We deduce as a consequence that the dimension of the representations in the sequence {V n } obtained from a finitely generated VI-module V over a field of characteristic zero is eventually a polynomial in q n . Our results are analogs of corresponding results on representation stability and polynomial growth of dimension for FI-modules (which give rise to sequences of representations of the symmetric groups) proved by Church, Ellenberg, and Farb. 相似文献
104.
Zhaofu Fei Dr. Dun‐Ru Zhu Prof. Xue Yang Dr. Lingjie Meng Dr. Qinghua Lu Prof. Wee Han Ang Dr. Rosario Scopelliti Dr. Christian G. Hartinger Dr. Paul J. Dyson Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(22):6473-6481
A series of fluorescent imidazolium‐based salts containing the cation [AnCH2MeIm]+ (in which An=anthracene and Im=the imidazolium cation) with Cl?, BF4?, PF6?, SO3CF3?, [N(CN)2]?, [N(SO2CF3)2]?, or PhBF3? anions have been prepared and characterized. X‐ray diffraction analysis of four of the salts reveals a number of C? H???X‐type (X=O, N, F) hydrogen bonds between the hydrogen atoms from the imidazolium ring and in some cases from the anthracene ring with the electronegative atoms of the anions. Additionally, C? H???π interactions can be found in all the salts analyzed by X‐ray diffraction, whereas π–π stacking is observed only in the salt containing the phenyltrifluoroborate anion. Fluorescence emission analysis in acetonitrile shows that the fluorescence of these salts varies significantly according to the nature of the anion, and correlates to the extent of ion pairing present in solution. Photodimerization of these salts was observed, and in one case a dimer has been isolated and characterized by X‐ray crystallography. 相似文献
105.
Effects of intermolecular interactions on the occupied electronic structure of amorphous solid of a carbazole-based material were investigated under an assumption that the organic solid consists of randomly oriented assemblies of dimers. The electronic energy states were calculated on the ensemble of large number of random dimers, of which geometries are relaxed using semiempirical van der Waals density functional theory. Intermolecular interactions result in splitting of energy level, and further disorders occur by aggregation of randomly orientated molecules. As a result, frontier occupied energy states can be represented by a superposition of Gaussian distributions, including (i) a main distribution with full width at half maximum of 80-110 meV, depending on the methods of relaxation and (ii) shoulders separated from the center of the main distribution with a value as large as 150 meV. A possible origin for the appearance of these shoulders was ascribed to the presence of molecular assemblies consisting of more tightly bound dimers compared with the others. 相似文献
106.
J. H. Moon M. Ebihara B. F. Ni B. Arporn P. Setyo R. M. Theresia B. S. Wee N. A. Abd. Salim P. C. B. Pabroa 《Journal of Radioanalytical and Nuclear Chemistry》2012,291(1):217-221
Since 2000, collaborative studies for applying NAA have been performed through the Forum for Nuclear Cooperation in Asia (FNCA)
sponsored by the Japanese Government. White rice is a main food for Asians and thus was selected as a common target sample
for a collaborative study in 2008. Seven Asian countries including China, Indonesia, Japan, Korea, Malaysia, Philippines and
Thailand, are greatly concerned about the composition of arsenic, heavy metals, and essential trace elements and took part
in this study. Rice samples were purchased and prepared by following a protocol that had been proposed for this study. Samples
were analyzed by their own NAA systems. In each country, more than 10 elements were examined and the results were compared.
These data will be very useful in the monitoring of the levels of food contamination and to evaluate the nutritional status
for people living in Asia. 相似文献
107.
Tian Q Wong W Xu Y Chan Y Ho HK Pastorin G Ang WH 《Chemical communications (Cambridge, England)》2012,48(44):5467-5469
A sensitive and versatile detection scheme based on quantum dot immobilisation on a solid support through bio-orthogonal PCR amplification and labelling has been developed for detection and quantification of gene targets in complex DNA mixtures. 相似文献
108.
The Rh(II)- and Cu(II)-catalyzed reactions of N-bis(trimethylsilyl)methyl, N-(2-indolyl)methyl α-diazoamides are investigated to delineate how conformational, steric and electronic factors influence the site- and chemoselectivity of the metallocarbenoid reaction. The N-bis(trimethylsilyl)methyl (N-BTMSM) group is found to be essential in promoting the metallocarbenoid reaction at the N-(2-indolyl)methyl moiety as well as providing subtle but effective conformational influence about the amide N-C(α) sigma bond in diazoamides carrying an N-C(α) alkoxymethyl side-chain, to afford excellent site- and chemoselectivity. In general, the metal-catalyzed reactions are found to favor metallocarbenoid addition to the indole C(2)-C(3) double bond over C-H insertion to give cyclopropanated products (tetracyclic γ-lactams); however, chemoselectivity is also affected by steric effects, as revealed in the N-[2-(3-methylindolyl)]methyl diazoamides, and to some extent by the nature of the catalyst employed, as seen in the N-C(α)-alkoxymethyl diazoamides. The tetracyclic γ-lactams are found to rearrange to give good to high yields of the tricyclic indole derivatives under the metallocarbenoid reaction conditions or under acidic conditions. The propensity of the tetracyclic γ-lactams to undergo rearrangement is found to be dependent on the nature of the α-substituent on the original diazo carbon and the indole N-substituent. 相似文献
109.
Feyyaz Durap Nermin Biricik Bahattin Gümgüm Saim Özkar Wee Han Ang Zhaofu Fei Rosario Scopelliti 《Polyhedron》2008
N,N-Bis(diphenylphosphino)ethylaniline compounds, [Ph2P]2N-C6H4-C2H5, with ethyl groups at the ortho- and para-positions have been synthesized. Oxidation of the aminophosphines with hydrogen peroxide, elemental sulfur and selenium gave the corresponding oxides, sulfides and selenides [Ph2P(E)]2N-C6H4-C2H5 (E = O, S, Se). Complexes [MCl2{(Ph2P)2N-C6H4-(C2H5)}] (M = Pd, Pt) and [Cu{(Ph2P)2N-C6H4-C2H5}2]PF6 were obtained by the reaction of N,N-bis(diphenylphosphino)ethylaniline with [MCl2(COD)] (M = Pd, Pt) and [Cu(MeCN)4]PF6. The new compounds were characterized by NMR, IR spectroscopy and microanalysis. In addition, representative solid-state structures of the palladium and platinum complexes were determined using single crystal X-ray diffraction analyses. 相似文献
110.
Unprecedented Acid‐Promoted Polymerization and Gelation of Acrylamide: A Serendipitous Discovery 下载免费PDF全文
Siew Yin Chan Dr. Shermin S. Goh Dr. Qingqing Dou Benjamin Qi Yu Chan Dr. Wee Sim Choo Prof. David James Young Prof. Xian Jun Loh 《化学:亚洲杂志》2018,13(14):1797-1804
Dilute acid polymerizes degassed, aqueous acrylamide with concomitant gelation, without the need for added free radical initiator or cross‐linking agent. This reaction is accelerated by sonication or UV irradiation, but inhibited by adventitious oxygen or the addition of a free radical inhibitor, suggesting an acid‐accelerated free radical process. The resulting hydrogels are thixotropic in nature and partially disrupted by the addition of chaotropic agents, indicating the importance of hydrogen bonding to the 3D network. This discovery was made while trying to prepare pectin‐polyacrylamide hydrogels. We observed that pectin initiated the gelation of acrylamide, but only if the aqueous pectin samples had a pH lower than ca. 5. 相似文献