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排序方式: 共有428条查询结果,搜索用时 15 毫秒
21.
Vikram Basava Broc Flores Matthew Giovine Thomas Licisyn Katelyn Walck Walter Boyko 《Journal of carbohydrate chemistry》2013,32(7):389-400
The addition of benzenesulfinic acid to glycals was investigated under various conditions, and optimized yields of the glycosyl phenylsulfone products were obtained in the presence of tin tetrachloride as a catalyst. Double bond shift (Ferrier rearrangement) occurred in all cases except amicetal, which lacks a substituent at the allylic carbon. Glycosylation of benzenesulfinic acid with 1,2-dibromides was carried out using silver triflate as the promoter, and gave sulfinate esters as products by reaction at oxygen rather than at sulfur. The sulfinate esters were obtained as mixtures of stereoisomers at the stereogenic sulfur atom. Trapping of the sulfinates with carboxylate nucleophiles was observed during attempted oxidation with MCPBA. 相似文献
22.
Vikram Kestens Guy Auclair Katarzyna Drozdzewska Andrea Held Gert Roebben Thomas Linsinger 《Journal of Thermal Analysis and Calorimetry》2010,99(1):245-261
In this study, the use of differential scanning calorimetry (DSC) is demonstrated as a powerful technique that can provide
accurate thermodynamic property values of environmental contaminants such as polycyclic aromatic hydrocarbons (PAHs). In total,
47 high purity PAH certified reference materials were selected and analysed by DSC. Their onset melting temperature, enthalpy
of fusion and eutectic purity were calculated from the obtained melting endotherms. In addition, the entropy of fusion, which
was calculated from the onset melting temperature and enthalpy of fusion, is presented. All measurements were evaluated in
a metrologically rigorous manner, including measurement uncertainties. 相似文献
23.
24.
Vikram Kestens Gert Roebben Thomas Linsinger 《Accreditation and quality assurance》2010,15(5):269-281
Based on a standard test method for purity by differential scanning calorimetry (DSC), ASTM E 928, a purity determination
method for highly pure polycyclic aromatic hydrocarbons (PAHs) has been developed and validated. The robustness of the developed
method was investigated by determining, under varying measurement conditions, the purity of two PAH certified reference materials
(CRMs), benzo[c]phenanthrene and dibenzo[a,h]anthracene. The repeatability and intermediate precision of the developed method was determined by analysing the purity of
benzo[c]phenanthrene and dibenzo[a,h]anthracene and PAH candidate CRMs indeno[1,2,3-c,d]pyrene, 6-methylchrysene and benzo[a]pyrene. The trueness of the method was studied using the same (candidate) CRMs and a series of 42 other PAH CRMs. For each
of the five (candidate) CRMs, a full measurement uncertainty budget was developed. Also for PAH materials for which the DSC
purity determination method has not been explicitly validated, the relative expanded measurement uncertainty was estimated. 相似文献
25.
The effect of resonant fluorescent enhancement from a photonic crystal surface upon the fluorescent photobleaching rate of
Cyanine-5 labeled protein has been investigated. We show that the enhanced excitation mechanism for photonic crystal enhanced
fluorescence, in which the device surface resonantly couples light from an excitation laser, accelerates photobleaching in
proportion to the coupling efficiency of the laser to the photonic crystal. We also show that the enhanced extraction mechanism,
in which the photonic crystal directs emitted photons approximately normal to the surface, does not play a role in the rate
of photobleaching. We show that the photobleaching rate of dye molecules on the photonic crystal surface is accelerated by
30x compared to an ordinary glass surface, but substantial signal gain is still evident, even after extended periods of continuous
illumination at the resonant condition. 相似文献
26.
Resonance width, shift in resonance frequency, relaxation time and activation energy of 5CB nematic liquid crystal are measured
using microwave cavity technique under the influence of an external magnetic field at 9 GHz and at different temperatures.
The dielectric response in liquid crystal at different temperatures and the effects of applied magnetic field on transition
temperatures are studied in the present work. The technique needs a small quantity (< 0.001 cm3) of the sample and provides fruitful information about the macroscopic structure of the liquid crystal. 相似文献
27.
PRASHANT SINGH RUDRA BANERJEE MOSHIOUR RAHAMAN A V RUBAN BIPLAB SANYAL ABHIJIT MOOKERJEE 《Pramana》2011,76(4):639-656
We study the electronic structure and a mean-field phase analysis based on the pair–pair energies derived from first-principles
electronic structure calculations of AuFe and NiMo alloys. We have used the tight-binding linear muffin-tin orbitals-based
augmented space recursion (TB-LMTO-ASR) method to do so. We investigate different behaviours of the two alloy systems by mapping
the problems onto equivalent Ising models and then discuss the magnetic phase diagrams using the calculated pair energies.
All three phases: paramagnetic, random ferromagnetic and spin glass, have been studied. 相似文献
28.
Primordial black holes evaporate due to Hawking radiation. We find that the evaporation times of primordial black holes increase
when accretion of radiation is included. Thus, depending on accretion efficiency, more primordial black holes are existing
today, which strengthens the conjecture that the primordial black holes are the proper candidates for dark matter. 相似文献
29.
We study the interplay of topology and dynamics of excitable nodes on random networks. Comparison is made between systems
grown by purely random (Erdős–Rényi) rules and those grown by the Achlioptas process. For a given size, the growth mechanism
affects both the thresholds for the emergence of different structural features as well as the level of dynamical activity
supported on the network. 相似文献
30.
Vikram Jha 《Designs, Codes and Cryptography》2014,72(3):675-686
To each non-square integer \(2^{2N+1}\ge 2^5\) there correspond semifields \(D\) of order of \(2^{2N+1}\) that contain \(\text{ GF}(4)\) . Hence there exist affine planes for each non-square order \(2^{2N+1}\ge 2^{5}\) that contain subaffine planes of order \(2^2\) . Moreover, there also exists semifields \(D_1\) and \(D_2\) , with \(|D_1|= |D_2| =|D|\) such that \(D_1\) is commutative and \(D_2\) is non-commutative but neither \(D_1\) nor \(D_2\) contains \(\text{ GF}(4)\) . 相似文献