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61.
Anaí Duarte Wilson Cunico Claudio M.P. Pereira Alex F.C. Flores Rogério A. Freitag Geonir M. Siqueira 《Ultrasonics sonochemistry》2010,17(2):281-283
An ultrasound-enhanced method has been developed for the synthesis of a variety of thioesters from benzoyl chlorides and 2-mercaptobenzoxa(thia)zoles. Applying this methodology, 14 compounds were synthesized in excellent yields. 相似文献
62.
We explore two- and three-state Markov models driven out of thermal equilibrium by non-potential forces, to demonstrate basic properties of the steady heat capacity based on the concept of quasistatic excess heat. It is shown that large enough driving forces can make the steady heat capacity negative. For both the low- and high-temperature regimes we propose an approximative thermodynamic scheme in terms of “dynamically renormalized” effective energy levels. 相似文献
63.
New eight lanthanide metal complexes were prepared. These complexes were characterized by elemental analysis, molar conductivity measurements, spectral analysis (1H NMR, FT-IR, UV–vis), luminescence and thermal gravimetric analysis. All Ln(III) complexes were 1:1 electrolytes as established by their molar conductivities. The microanalysis and spectroscopic analysis revealed eight-coordinated environments around lanthanide ions with two nitrate ligands behaving in a bidentate manner. The other four positions were found to be occupied with tetradentate LIII ligand. Tb–LIII and Sm–LIII complexes exhibited characteristic luminescence emissions of the central metal ions and this was attributed to efficient energy transfer from the ligand to the metal center. The LIII and Ln–LIII complexes showed antibacterial activity against a number of pathogenic bacteria. 相似文献
64.
Magnetic resonance imaging (MRI) technique enables non-invasive analysis of the human vocal tract during phonation. Creation of MR images of the vocal tract is accompanied by simultaneous recording of the produced speech. The paper analyzes and compares spectral properties of an acoustical noise produced by mechanical vibration of the gradient coils during scanning in the open-air MRI equipment working in a weak magnetic field with low B0 up to 0.2 T. This noise exhibits harmonic character, so it is suitable to analyze its properties in the spectral domain. Obtained results of spectral analysis will be used to devise a new cepstral-based filtering method for noise suppression of recorded speech. 相似文献
65.
García-Meca C Hurtado J Martí J Martínez A Dickson W Zayats AV 《Physical review letters》2011,106(6):067402
We experimentally demonstrate a low-loss multilayered metamaterial exhibiting a double-negative refractive index in the visible spectral range. To this end, we exploit a second-order magnetic resonance of the so-called fishnet structure. The low-loss nature of the employed magnetic resonance, together with the effect of the interacting adjacent layers, results in a figure of merit as high as 3.34. A wide spectral range of negative index is achieved, covering the wavelength region between 620 and 806 nm with only two different designs. 相似文献
66.
Elzain M. Al Rawas A. Yousif A. Gismelseed A. Rais A. Al-Omari I. Bouziane K. Widatallah H. 《Hyperfine Interactions》2004,158(1-4):205-209
Time differential perturbed γ-γ angular correlation technique was used to measure the magnetic hyperfine field (MHF) at Tb
sites in the intermetallic compound Tb3In5 using the 140La → 140Ce nuclear probe. The measurements were carried out in the temperature range of 8 to 295 K. Two different temperature dependent
magnetic frequencies were observed below 30 K, which were assigned as 140Ce substituting the two inequivalent Tb sites in the orthorhombic structure of Tb3In5. The temperature dependence of MHF also shows a possible deviation from an expected Brillouin-like behavior for temperatures
below 18 K. A Néel transition at 27 K was observed from magnetization measurements in the samples. The magnetization as a
function of the applied magnetic field was measured at two temperatures, 5 and 40 K, and the results show antiferromagnetic
and a typical paramagnetic behavior, respectively. In both cases it was not observed saturation under high magnetic field. 相似文献
67.
G. M. Abramova A. M. Vorotynov G. A. Petrakovskii N. I. Kiselev D. A. Velikanov A. F. Bovina R. F. Al’mukhametov R. A. Yakshibaev É. V. Gabitov 《Physics of the Solid State》2004,46(12):2225-2228
Electrical, resonant, and magnetic properties of intercalated copper chromium disulfide CuCrS2 are studied. It is established that CuCrS2 is an antiferromagnetic semiconductor with Néel temperature TN=40.7 K and an effective magnetic moment of 4.3µB. Anomalies in the electrical, magnetic, and resonant properties of CuCrS2 are found at Tc=110 K, which suggest an electron transition accompanied by alteration of the valences of the 3d-metal ions. 相似文献
68.
Motivated by the ongoing discussion about a seeming asymmetry in the performance of fermionic and bosonic replicas, we present an exact, nonperturbative approach to both fermionic and bosonic zero-dimensional replica field theories belonging to the broadly interpreted beta=2 Dyson symmetry class. We then utilize the formalism developed to demonstrate that the bosonic replicas do correctly reproduce the microscopic spectral density in the QCD-inspired chiral Gaussian unitary ensemble. This disproves the myth that the bosonic replica field theories are intrinsically faulty. 相似文献
69.
70.
V. I. Al’shits V. N. Lyubimov A. Radowicz 《Journal of Experimental and Theoretical Physics》2005,101(1):107-119
The conditions of existence of the zero components of electric field E and electric induction D accompanying a volume acoustic wave propagating in a piezoelectric medium have been studied. General equations describing the positions of the zero-field lines E(m) = 0 and the zero-induction points m0, such that D(m0) = 0 on the unit sphere (m2 = 1) of the wave propagation directions, are obtained. General theorems determining the conditions ensuring the existence of such lines and points, even in triclinic crystals, are formulated. The relationship between such directions and various elements of the crystal symmetry is analyzed. The vector fields D(m), which are always orthogonal to the wave normals m, in the vicinity of the zero-induction points m0 exhibit certain orientational singularities characterized by the Poincaré indices n = 0, ±1, ±2. The general analytical expressions are obtained for the n values in crystals with arbitrary anisotropy and specified for a number of crystals belonging to various symmetry classes. The conditions of stability of the orientational singularities with respect to small perturbations of the material moduli and a change in the crystal symmetry are considered. 相似文献