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131.
In this paper, we report the effects of the substitution of Sr by Eu on the properties of Bi-2201 ceramics. Samples with nominal compositions of Bi2Sr2?xEuxCuOy (x = 0–0.4) are elaborated in air by solid state reaction. They are characterized by means of X ray diffraction (XRD), scanning electron microscopy (SEM), magnetic and resistivity measurements. The undoped sample (x = 0) is monophasic and its structure belongs to phase A. No trace of superconductivity is observed down to 2 K for this sample and the variation of resistivity with temperature shows a semiconducting behaviour. As Eu is added and for x ≥ 0.2, the samples convert totally to B or Raveau phase and become superconducting. The highest Tc, obtained from both magnetic and resistivity measurements, is observed for x = 0.3. In the normal state, all the samples exhibit a semiconducting character which decreases as well as resistivity when the Eu content increases. The refinement of cell parameters is done with considering the structural modulation. The study shows that the substitution of Sr2+ by Eu3+ leads to an increase of a and b parameters, while c decreases similarly to those of the La doped phases. The a axis component of the modulation is observed to be independent of Eu content, while the c axis one increases slightly as this content increases. The XRD analysis has also revealed that the limit solubility of the used Eu2O3 oxide is situated between x = 0.3 and 0.4 of Eu content. The SEM micrographs show that the undoped sample consists of poorly connected grains with a random distribution. A quite different microstructure is obtained for the doped samples. The grains are more connected and have a flat shape which is characteristic of the Bi-based superconductors. 相似文献
132.
133.
Abasi R Markley L Eleftheriades GV 《The Journal of the Acoustical Society of America》2011,130(6):EL405-EL409
A linear array of closely spaced sound transducers is presented that can produce a subwavelength-focused intensity profile at a distance of a quarter wavelength. This work is related to research on super-resolution using metamaterials in both the acoustic and optical domains. It is designed using the principle of shifted beams, a near-field antenna array theory developed for the subwavelength focusing of electromagnetic waves. Once the spatial sound pattern is characterized for each source, the optimal weights for a minimum beam width can be calculated. An experiment operating at 4 kHz was able to successfully construct a super-focused beam. 相似文献
134.
Haïat G Naili S Ba Vu M Desceliers C Soize C 《The Journal of the Acoustical Society of America》2011,129(4):EL114-EL120
Cortical bone is a viscoelastic heterogeneous medium which may be assessed with axial transmission. This work aims at evaluating the average depth investigated by the lateral wave for radial variations of material properties in relatively thick cortical bone. The equivalent contributing depth (ECD) is derived from the finite element simulation results for spatial variations of a viscoelastic coefficient (η(11)) and of porosity. A value of ECD equal to around 1.6 mm is obtained for a spatial variation of η(11). The method fails to predict accurate values of the ECD for a spatial variation of porosity, because all parameters vary simultaneously. 相似文献
135.
Mohamed Saïdi 《Mathematische Zeitschrift》2014,277(1-2):361-372
We show the existence of group-theoretic sections of the “étale-by-geometrically abelian” quotient of the arithmetic fundamental group of hyperbolic curves over $p$ -adic local fields relative to a proper and flat model which are non-geometric, i.e., which do not arise from rational points. 相似文献
136.
Pierre-Loïc Méliot 《Potential Analysis》2014,40(4):427-509
In this paper, we prove the cut-off phenomenon in total variation distance for the Brownian motions traced on the classical symmetric spaces of compact type, that is to say:
- the classical simple compact Lie groups: special orthogonal groups SO(n), special unitary groups SU(n) and compact symplectic groups USp(n);
- the real, complex and quaternionic Grassmannian varieties (including the real spheres, and the complex or quaternionic projective spaces when q?=?1): SO(p?+?q)/(SO(p)×SO(q)), SU(p?+?q)/S(U(p)×U(q)) and USp(p?+?q)/(USp(p)×USp(q));
- the spaces of real, complex and quaternionic structures: SU(n)/SO(n), SO(2n)/ U(n), SU(2n)/USp(n) and USp(n)/UU(n).
137.
Haïm Brezis 《Comptes Rendus Mathematique》2011,349(5-6):269-271
In this Note I discuss some assertions made by L. Ma and X. Xu (2009) [6] and L. Ma (2010) [5], which need to be corrected and supplemented with additional references. 相似文献
138.
139.
The encapsulation of seed polymer particles coated by anionic iron oxide nanoparticles has been investigated using N-isopropylacrylamide as a main monomer, N,N-methylene bisacrylamide as a crosslinking agent, itaconic acid as a functional monomer and potassium persulfate as an anionic
initiator. The magnetic latexes obtained have been characterized with regard to particle size, iron oxide content and electrophoretic
mobility. All these properties have been examined by varying several polymerization parameters: reaction medium, monomer(s)
and crosslinking agent concentrations, nature of seed latexes and type of polymerization (batch versus shot process). The
magnetic content in the polymer microspheres strongly depends on the polymerization procedure (i.e., encapsulation process)
and varies between 6 and 23 wt%, and monodisperse magnetic polymer particles were obtained.
Received: 28 December 1999 Accepted in revised form: 15 June 1999 相似文献
140.
Interaction of the general volatile anesthetic Enflurane with bacteriorhodopsin-DPPC proteoliposomes
Nathalie Hauet Maïté Paternostre Danny Létourneau François Boucher 《Journal of Thermal Analysis and Calorimetry》2009,98(1):39-45
Thermal decomposition of dried crystalline powder obtained from titanium(IV) bis(acetylacetonate) diisopropoxide (75% solution
in 2-propanol) (1) was monitored by simultaneous TG/DTA, EGA-FTIR and EGA-MS measurements and the results were compared with those of amorphous
powder obtained by gelling of acetylacetonate-modified titanium(IV) tetra-isopropoxide at molar ratio of 1:2 in boiling 2-methoxyethanol
(2). Thermal degradation of 1 in the temperature range of 25–700°C consists of 5 steps with a total mass loss of 62.5%. EGA by FTIR and MS revealed the
release of H2O below 120°C; followed by an intensive evolution of acetylacetone around 245°C. The release of acetone and acetic acid occurs
up to 270°C and that of CO and CO2 up to 530°C. 相似文献