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71.
While isobutyl vinyl ketone reacts with α-acetyl-α'-methyl succinate to give a normal Michael adduct, the Mannich base or its quaternary derivative as a source of vinylketonc gives the butenolide derivative 8a. Isobutyl cyclohexenoneacetic acid (1b) previously stated to be the reaction product was present only as a by-product. When α-acetyl-α'-methyl succinate is treated with acrylic acid derivatives only butenolides 8c–8f were obtained. 相似文献
72.
We report on a new random laser phenomenon that gives rise to narrow emission modes without requiring optical cavities. Sharp emission peaks are observed experimentally over a broad range of scattering strengths and analyzed in numerical calculations. We find that the introduction of exponential gain in a multiple light scattering process strongly increases the importance of very long light paths. Such long paths are rare and often neglected in passive disordered materials but we show that they can dominate the emission spectrum from an amplifying disordered system. 相似文献
73.
Mariana Voicescu Marilena VasilescuTitus Constantinescu Aurelia Meghea 《Journal of luminescence》2002,97(1):60-67
Luminol solution in DMSO in the presence of [18C6…K]+ O2− supramolecular complex (achieved from KO2 and 18-Crown-6 (18C6)-ether) is chemiluminescent, and its intensity depends on the complex concentration. Using fluorescein (Fl) as an energy acceptor in this system, the luminescence energy transfer process from chemically excited species, aminophtalate dianion, to Fl could be evidenced. On the basis of Förster theory, the critical energy transfer distance, for both fluorescence and chemiluminescence, has been determined. The values are comparable: 22.41 Å (for chemiluminescence) and 20.88 Å (for fluorescence). 相似文献
74.
Models of inflation in which non-Gaussianity is generated outside the horizon, such as curvaton models, generate distinctive higher-order correlation functions in the cosmic microwave background and other cosmological observables. Testing for violation of the Suyama-Yamaguchi inequality τ(NL) ≥ (6/5f (NL))(2), where f(NL) and f(NL) denote the amplitude of the three-point and four-point functions in certain limits, has been proposed as a way to distinguish qualitative classes of models. This inequality has been proved for a wide range of models, but only weaker versions have been proved in general. In this Letter, we give a proof that the Suyama-Yamaguchi inequality is always satisfied. We discuss scenarios in which the inequality may appear to be violated in an experiment such as Planck and how this apparent violation should be interpreted. 相似文献
75.
Bogdan Frecus Corneliu I. Oprea Petre Panait Marilena Ferbinteanu Fanica Cimpoesu Mihai A. Gîrţu 《Theoretical chemistry accounts》2014,133(5):1-17
We report quantum chemical calculations providing the exchange coupling constants of the V[TCNE]2 model system, describing the amorphous room temperature molecular magnet V[TCNE] x (TCNE = tetracyanoethylene, x ~ 2). The geometry is optimized for the ideal lattice using density functional theory (DFT) calculations with periodic boundary conditions. Broken-symmetry DFT calculations indicate antiparallel spin alignment resulting in ferrimagnetic ordering, but heavily overestimate the value of the exchange coupling. Better estimates of the exchange coupling parameters between the V(II) ion and the [TCNE]? anionic radical are obtained by means of multiconfigurational calculations performed on smaller molecular models cut from the optimized crystal lattice. Complete active space self-consistent field and multireference second-order perturbation theory calculations provide the sign and the strength of the nearest-neighbor as well as next-nearest-neighbor interactions along all three crystallographic directions. We are able to explain also intuitively the mechanism for antiferromagnetic spin coupling in terms of the superexchange pathways, discussing the role of the main four types of contributions to superexchange. Moreover, we clarify the influence of the transition metal ion on the strength of the exchange interaction and on the critical temperature for long-range ferrimagnetic ordering. 相似文献
76.
Melchior Andrea Lanas Sara Gràcia Valiente Manuel Tolazzi Marilena 《Journal of Thermal Analysis and Calorimetry》2018,134(2):1261-1266
Journal of Thermal Analysis and Calorimetry - The adsorption of Pt(IV) by iron oxide (Fe3O4) superparamagnetic nanoparticles (SPION) functionalized with 3-mercaptopropionic acid (3-MPA) is... 相似文献
77.
Jeffrey K. S. Wan Marilena Radoiu Ivan Kalatchev M. Catherine Depew 《Research on Chemical Intermediates》2000,26(9):931-939
Since the granting of our first US patent on microwave induced catalytic decomposition of PCBs some 18 years ago, microwave
technology has slowly begun to attract some industrial attention in the last few years. There was no doubt that microwaves
had been applied to facilitate the conventional bleaching process of wood pulps in the past but with little or no success.
The myth that microwaves can be regarded and manipulated as a rapid heat source probably caused most of the failures of unsuccessful
microwave applications. It is therefore necessary to understand the real potential of microwaves as an energy source and to
identify the many critical electromagnetic properties of the load (chemical systems), before a final choice of a proper microwave
system be designed and installed. In this preliminary report, we demonstrate the real potential of pulsed microwave radiation
for non-alkaline bleaching of mechanical pulps. Typically, very high consistency TMP up to 93% can be treated by pulsed microwave
in the order of 90 seconds with an average increase of 20 to 25 points in brightness. 相似文献
78.
Bioremediation of toluene and naphthalene in liquid cultures of bacteria grown in the presence of these aromatic compounds as unique sources of carbon was investigated by gas chromatography (GC). For this purpose, a method based on the use of GC with flame ionization detection was developed and validated. Validation was carried out in terms of limit of detection (LOD), limit of quantitation (LOQ), linearity, precision and trueness. In the case of naphthalene, LOD and LOQ values of 0.43 and 0.72 mg kg(-1) were achieved. Linearity was established over one order of magnitude in the range of interest, i.e. 10-100 mg kg(-1). Excellent precision was obtained both in terms of intra-day repeatability and between-day precision on two concentration levels (RSD% lower than 0.5%). A recovery of 97.9 +/- 0.2% (n=3) was calculated by addition of 640 mg kg(-1) of naphthalene to the Bushnell & Haas mineral salts basal solution containing the micro-organisms. Findings clearly showed a reduction of the naphthalene content equal to 50% and 75% after two and four weeks of contact with the micro-organisms, whereas a lower degradation was shown in the case of toluene. Finally bioremediation activity was ascribed to two different microbial populations, Bordetella Petrii and Bacillus Sphericus, which survived in the polluted medium. 相似文献
79.
Toma L Toma LM Lescouëzec R Armentano D De Munno G Andruh M Cano J Lloret F Julve M 《Dalton transactions (Cambridge, England : 2003)》2005,(8):1357-1364
The binuclear complex NiII2L(H2O)2(ClO4)2(1) and the neutral tetranuclear bimetallic compounds [{M(III)(phen)(CN)4}2{NiII2L(H2O)2}].2CH3CN with M=Fe (2) and Cr (3)[H2L=11,23-dimethyl-3,7,15,19-tetraazatricyclo[19.3.1.1(9,13)]hexacosa-2,7,9,11,13(26),14,19,21(25),22,24-decaene-25,26-diol] have been synthesized and the structures of and determined by single crystal X-ray diffraction. and are isostructural compounds whose structure is made up of centrosymmetric binuclear cations [Ni2(L)(H2O)2]2+ and two peripheral [M(phen)(CN)4]- anions [M=Fe (2) and Cr (3)] acting as monodentate ligands towards the nickel atoms through one of their four cyanide nitrogen atoms. The environment of the metal atoms in 2 and 3 is six-coordinated: two phen-nitrogen and four cyanide-carbon atoms at the iron and chromium atoms and a water molecule, one cyanide-nitrogen and two phenolate-oxygens and two imine-nitrogens from the binucleating ligand L2- at the nickel atom build distorted octahedral surroundings. The values of the FeNi and CrNi separations through the single cyanide bridge are 5.058(1) and 5.174(2)A respectively, whereas the Ni-Ni distances across the double phenolate bridge are 3.098(2)(2) and 3.101(1) A (3). The magnetic properties of have been investigated in the temperature range 1.9-290 K. The magnetic behaviour of corresponds to that of an antiferromagnetically coupled nickel(II) dimer with J=-61.0(1) cm-1, the Hamiltonian being defined as H=-J S(A).S(B). An overall antiferromagnetic behaviour is observed for and with a low-lying singlet spin state. The values of the intramolecular magnetic couplings are J(Fe-Ni)=+17.4(1) cm-1 and J(Ni-Ni(a))=-44.4(1) cm-1 for and J(Cr-Ni)=+11.8(1) cm-1 and J(Ni-Ni(a))=-44.6(1) cm-1 for [H=-J(M-Ni)(S(M).S(Ni)+S(Ma).S(Nia))-J(Ni-Nia)S(Ni)S(Nia)]. Theoretical calculations using methods based on density functional theory (DFT) have been employed on in order to analyze the efficiency of the exchange pathways involved and also to substantiate the exchange coupling parameters. 相似文献
80.