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排序方式: 共有262条查询结果,搜索用时 306 毫秒
41.
Alkynyl ruthenium colorimetric sensors: optimizing the selectivity toward fluoride anion 总被引:1,自引:0,他引:1
Fillaut JL Andriès J Perruchon J Desvergne JP Toupet L Fadel L Zouchoune B Saillard JY 《Inorganic chemistry》2007,46(15):5922-5932
We report on the synthesis of alkynyl ruthenium colorimetric sensors whose receptors are constituted by thiazolidinedione, rhodanine, or barbituric heads as recognition centers for anions. As modifications in the charge density at these recognition centers affect the whole molecule, through the alkynyl ligand acting as a communicating wire, the effects of hydrogen-bonding interactions with the anions were observed with the naked eye and monitored by UV-vis absorption spectrometry. The selectivity of the sensors was improved through electronic modifications of the alkynyl ruthenium subunit: the higher the electron density at the receptor head, the higher the selectivity is. TD-DFT calculations rationalize the long-range electronic communication as a main characteristic of the alkynyl ruthenium species and as a key to improve the selectivity of alkynyl ruthenium-based sensors toward anions. 相似文献
42.
In this work, we study the effect of concentration, host medium, PH and phase states on the fluorescence emission from the
laser dye Rhodamine B pumped by UV laser as exited source. The polymethylmethacrylate PMMA is used as a host medium in case
of solid phase samples while, ethanol and Tetrahydrofuran (THF) are used in case of a liquid one. Laser Induced Fluorescence
(LIF) technique was used to study the fluorescence properties of both cases of liquid and thin film solid-state samples. In
addition, the Dual Thermal Lens (DTL) technique was used to study the quantum yield of these samples. The concentrations of
Rhodamine B in ethanol as solvent between 2 × 10−2 M and 5 × 10−6 M were studied. The maximum fluorescence emission is observed at concentration of Rhodamine B C = 3 × 10−4 M. Comparison studies were investigated for different host medium such as ethanol, THF, PMMA in liquid phase state and PMMA
in solid phase state. The measurements revealed that, the behavior of both phases state was analogous. Rhodamine B/PMMA thin
film sample by ratio of 4:1 and thickness 0.12 mm was found to have the best photostability sample with a quantum yield about
≈0.82. 相似文献
43.
A. Assani El. M. Lotfi P. Bourson M. Aillerie B. Lahbabi M. Zriouil B. Elouadi 《Journal of Physics and Chemistry of Solids》2009,70(3-4):755-764
We have characterized by Raman spectroscopy the disorder and the local modifications of cation environment in the lithium tantalate structure resulting from the incorporation of bivalent cations Co2+ and Mn2+ as potential substitutes for Li and/or Ta ions. Frequency and damping of the E(TO1), E(TO6) and E(TO8) phonon modes of ceramic powders are studied along seven lines in the ternary phase diagrams Li2O–Ta2O5–(M′O)2 with M′=Mn and Co, and compared to those of the pure stoichiometric LiTaO3. Raman spectroscopy is found to be very sensitive to the substitution ions and defects generated in the lattice vibration. Dopants occupy primarily the Li site in the region of lithium oxide excess. The site of Ta becomes progressively implicated in the substitution process when the concentration of dopant increases. In the Li-poor region of the ternary-phase diagram, corresponding to under-stoichiometric compositions, we retain the charge compensation mechanism involving both Li and Ta site according to: 3Li++Ta5+→4M′2+ with M′2+=Mn2+ or Co2+. 相似文献
44.
This paper presents a new numerical model to investigate the vibro-acoustic behaviour of two laminated glass plates enclosing a thin viscothermal fluid cavity. The aim of this work is to develop an original five layer (two skins plies, two adhesive films and a core ply) laminated plate finite element by mixing Kirchhoff and Mindlin plate’s theory. The formulation is based on the theory that accounts for the transverse shear in the adhesive films and in the core. The acousto-elastic model is established in dimensionless appropriate form including the effects of viscosity and thermal conductivity of fluid and by taking into account the fluid-structure interaction. The discretization of the energy functional by finite element method gives after minimisation a symmetrical coupled matrix system in which the acoustic matrices are frequency dependent. Therefore, an iterative procedure is derived to determine the eigenmodes of the coupled system. The modal approach is adopted to determine the vibro-acoustic system’s response. Then, the validation of the new laminate finite element model is achieved by comparing the sandwich plate results against data obtained from literature. Subsequently, predicted responses, such as the vibration transmissibility and the transmission loss of the coupled system, for a given laminated double glazing under an imposed homogeneous pressure are presented and discussed. Numerical results show the importance of both lamination and viscothermal fluid effects on double glazing vibro-acoustic behaviour. 相似文献
45.
F. Hosseinzadeh Lotfi T. Allahviranloo M. Alimardani Jondabeh L. Alizadeh 《Applied Mathematical Modelling》2009
This paper discusses full fuzzy linear programming (FFLP) problems of which all parameters and variable are triangular fuzzy numbers. We use the concept of the symmetric triangular fuzzy number and introduce an approach to defuzzify a general fuzzy quantity. For such a problem, first, the fuzzy triangular number is approximated to its nearest symmetric triangular number, with the assumption that all decision variables are symmetric triangular. An optimal solution to the above-mentioned problem is a symmetric fuzzy solution. Every FLP models turned into two crisp complex linear problems; first a problem is designed in which the center objective value will be calculated and since the center of a fuzzy number is preferred to (its) margin. With a special ranking on fuzzy numbers, the FFLP transform to multi objective linear programming (MOLP) where all variables and parameters are crisp. 相似文献
46.
Production of natural fruity aroma by Geotrichum candidum 总被引:3,自引:0,他引:3
Mdaini N Gargouri M Hammami M Monser L Hamdi M 《Applied biochemistry and biotechnology》2006,128(3):227-235
Based on its aromatic potential, Geotrichum candidum isolated from olive vegetation water was tested for the production of volatile compounds. When G. candidum was cultivated on media with glucose as the carbon source, flavor volatile compounds were produced and accumulated in the
broth. Fruity flavoring compounds (pineapple-like) such as esters and alcohols were analyzed by gas chromatography coupled
to mass spectrometry, including ethyl esters of acetic acid and butyric acid, methyl-3-butan-1-ol, and methyl-2-propan-1-ol.
Their synthesis corresponded to the stationary growth phase of the strain. Production of the volatile compounds reached 9.5
g/L of 2-hexanoic acid ethyl ester and 1.6 g/L of benzaldehyde as the main concentrated molecules. Ethyl alcohol seems to
be an intermediate metabolite in this pathway. 相似文献
47.
Asymmetric Cycloaddition: An Efficient Synthesis of Enantiopure Isoxazolines Substituted with Carbohydrate Analogues 下载免费PDF全文
Omar K. Al‐Duaij Naoufel Ben Hamadi Lotfi Khezemi 《Journal of heterocyclic chemistry》2016,53(2):408-413
A simple and convenient method for the synthesis of heterocycles substituted with carbohydrate analogs is described. The chiral optically pure five‐membered glycoconjugates containing the isoxazoline unit were obtained by an aromatic nitrile oxides cycloaddition with 1‐phenyl‐1,2‐dihydro‐pyridazine‐3,6‐dionyl N‐glycoside derivatives. 相似文献
48.
Localized proton spectroscopy without water suppression: removal of gradient induced frequency modulations by modulus signal selection 总被引:1,自引:0,他引:1
Serrai H Clayton DB Senhadji L Zuo C Lenkinski RE 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2002,154(1):53-59
Most Magnetic Resonance Spectroscopy (MRS) localization methods can generate gradient vibrations at acoustic frequencies and/or magnetic field oscillation, which can cause a time-varying magnetic field superimposed onto the static one. This effect can produce frequency modulations of the spectral resonances. When localized MRS data are acquired without water suppression, the associated frequency modulations are manifested as a manifold of spurious peaks, called sidebands, which occur symmetrically around the water resonance. These sidebands can be larger than the small metabolite resonances and can present a problem for the quantitation of the spectra, especially at short echo times. Furthermore, the resonance lineshapes may be distorted if any low frequency modulations are present. A simple solution is presented which consists of selecting the modulus of the acquired Free Induction Decay (FID) signal. Since the frequency modulations affect only the phase of the FID signal, the obtained real spectrum of the modulus is free from the spurious peaks where quantitative results may be directly obtained. Using this method, the distortions caused by the sidebands are removed. This is demonstrated by processing proton MRS spectra acquired without water suppression collected from a phantom containing metabolites at concentrations comparable to those in human brain and from a human subject using two different localization methods (PRESS and Chemical Shift Imaging PRESS-(CSI)). The results obtained illustrate the ability of this approach to remove the spurious peaks. The corrected spectra can then be fit accurately. This is confirmed by the results obtained from both the relative and the absolute metabolites concentrations in phantoms and in vivo. 相似文献
49.
Influences of nanoparticles and chain length on thermodynamic and electrical behavior of fluorine liquid crystals 下载免费PDF全文
Ines Ben Amor Lotfi Saadaoui Abdulaziz N. Alharbi Talal M. Althagafi and Taoufik Soltani 《中国物理 B》2022,31(10):104202-104202
Hydrogen-bonded polar nematic liquid crystal series with the general formula nOBAF (n = 7—12) is studied. The mesomorphic characterization is demonstrated through differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The complexes with short alkyl chains (n=7, 8) present a wide nematic range and monotropic smectic F mesophase, whereas the longer alkyl chain (n=10—12) analogues show high melting and low clearing mesomorphic liquid crystals. The thermal range of the mesophase and the birefringence increase with chain length decreasing. Furthermore, the effect of the nanoparticles (LiNbO3) on the thermal and the electrical behavior of 8OBAF are investigated. The presence of LiNbO3 nanoparticles increases the conductivity and reduces the resistivity of the complex. 相似文献
50.
Samir Meskaldji Abdelmalik Belkhiri Lotfi Belkhiri Abdou Boucekkine Michel Ephritikhine 《Comptes Rendus Chimie》2012,15(2-3):184-191
Magnetic exchange coupling between uranium U(V) ions, in the case of the two para- and meta-imido diuranium complexes, respectively [(C5H5)3U]2(μ-1,4-N2C6H4) and [(C5H5)3U]2(μ-1,3-N2C6H4) exhibiting the 5f1-5f1 configuration, have been investigated using relativistic DFT calculations, combined with the broken symmetry (BS) approach. Using the B3LYP functional, the singlet BS state of the para complex has been found of lower energy than the high spin (HS) triplet one, in agreement with the observed antiferromagnetic character of the complex. On the contrary the BP86 functional fails to predict this magnetic property. The spin density distributions and MO analysis explain well the antiferromagnetic character of the para complex and clarify the failure of the BP86 functional. The effective participation of the 5f metal orbitals in bonding with the imido ligand plays a key role for electronic and magnetic communication between the two active U(V) 5f1 electrons. The same technique led us to explain the ferromagnetic character of the meta isomer in agreement with experiment. For both isomers the spin polarization mechanism explains well their observed magnetic behaviour. 相似文献