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91.
We show that closed Chen-Willmore rotational hypersurfaces of nonnegative curved real space forms are shaped on closed hyperelastic
curves of the hyperbolic plane. Then, we study the variational problem associated to this class of curves, proving that there
exist a rationally dependent family of closed solutions. They give rise to the first non-trivial examples of Chen-Willmore
hypersurfaces in real space forms.
Research partially supported by a MCYT-FEDER grant No. BFM2001-2871-C04 and by a UPV grant 9/UPV00127.310-13574/01. 相似文献
92.
Alcindo A. Dos Santos Jefferson L. Princival Simone M.G. de Barros 《Tetrahedron》2007,63(24):5167-5172
1,4-C,O-dianions have been generated through concomitant acid/base and tellurium/lithium exchange reactions. The di-lithium salts were transmetallated with cerium chloride to the corresponding di-cerium salts and subsequently reacted with lactones and carboxylic acid anhydrides to yield the respective spiroketals. The di-lithium entities were also converted into the corresponding cyanocuprates that add in a 1,4-manner to 2-cyclohexen-1-one to form 1,6-dioxygenated compounds. 相似文献
93.
Marcos Ghislandi Luis Antonio Sanchez de A. Prado Alejandra de la Vega Oyerviedes Hans Wittich Karl Schulte Ana Barros‐Timmons 《Journal of polymer science. Part A, Polymer chemistry》2008,46(10):3326-3335
Vapor‐grown carbon nanofibers (CNFs) were oxidized and functionalized for atom transfer radical polymerization (ATRP) of tert‐butyl acrylate (t‐BA) from the surface of the CNFs. The materials were characterized by solubility tests, Fourier‐transform infrared (FTIR) spectroscopy, Raman spectroscopy, thermogravimetric analysis (TGA), X‐ray diffraction (XRD), and scanning electron microscopy. The FTIR and electron microscopy results suggest that ATRP process was successfully used to graft poly(tert‐butyl acrylate) (poly(t‐BA)) chains from the surface of the fibers. Raman results strongly indicate the partial degradation of the graphitic layer of CNFs because of the chemical treatments. TGA results suggest that the presence of poly(t‐BA) leads to a decrease of the initial degradation temperature of the fibers. XRD and electron microscopy results indicate that the microstructure of fibers was not destroyed because of the oxidation and functionalization processes. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3326–3335, 2008 相似文献
94.
Marcionilo de Barros Lins C. G. B. Frischkorn J. Krusche D. Unterlugauer H. Kohler 《Fresenius' Journal of Analytical Chemistry》1979,295(5):375-379
Summary The thermolabile isomeric acetylenes and allenes were separated from reaction mixtures of the base-catalysed isomerisation of 1,1-diethoxy-hexa-2,5-diyne by preparative HSLC in milligram to gram amounts. This allows a fast and reliable identification by spectroscopic methods. By using fine particle silica (5 m) for both separations, the analytical one on small columns and the preparative separation on columns with large diameters, the analytical conditions of separation may be transferred to the preparative scale without any difficulty.
Isolierung und Identifizierung thermolabiler Reaktionsprodukte einer Allen-Acetylen-Umlagerung mit der schnellen Flüssigkeits-Chromatographie (HSLC)
Zusammenfassung Die thermolabilen isomeren Acetylene und Allene lassen sich aus Reaktionsgemischen der basenkatalysierten Umlagerung von 1,1-Diäthoxyhexa-2,5-diin durch präparative HSLC leicht und ohne Sekundärreaktionen in ausreichender Menge für eine anschließende sichere spektroskopische Identifizierung im Milligramm- bis Grammbereich trennen. Bei Verwendung von feinkörnigem Kieselgel (5 m) kann die an analytischen Säulen ausgearbeitete Trennung problemlos auf präparativen Maßstab übertragen werden.相似文献
95.
96.
The Mossbauer spectrum of 151Eu3Ti2O7 reveals a ferrimagnetic ordering below (8 ± 0.3) K with two inequivalent sites in ratio 2: 1, and with exchange constants nearly equal to those of EuTiO3 and of Eu2TiO4. The sublattice magnetizations are explained in terms of these constants. 相似文献
97.
In a recent paper (Barros, Sousa in: Kodai Math. J. 2009) the authors proved that closed oriented non-totally geodesic minimal hypersurfaces of the Euclidean unit sphere have index of stability greater than or equal to n + 3 with equality occurring at only Clifford tori provided their second fundamental forms A satisfy the pinching: |A|2 ≥ n. The natural generalization for this pinching is ?(r + 2)S r+2 ≥ (n ? r)S r > 0. Under this condition we shall extend such result for closed oriented hypersurface Σ n of the Euclidean unit sphere ${\mathbb{S}^{n+1}}$ with null S r+1 mean curvature by showing that the index of r-stability, ${Ind_{\Sigma^n}^{r}}$ , also satisfies ${Ind_{\Sigma^n}^{r}\ge n+3}$ . Instead of the previous hypothesis if we consider ${\frac{S_{r+2}}{{S_r}}}$ constant we have the same conclusion. Moreover, we shall prove that, up to Clifford tori, closed oriented hypersurfaces ${\Sigma^{n}\subset \mathbb{S}^{n+1}}$ with S r+1 = 0 and S r+2 < 0 have index of r-stability greater than or equal to 2n + 5. 相似文献
98.
Thais Francine Ribeiro Alves Cecília Torqueti Barros Denicezar Baldo Venâncio Alves Amaral Mirella Sever Carolina Santos 《Journal of Dispersion Science and Technology》2019,40(4):546-554
The aim of the present study was to improve the solubility and dissolution rate of ibuprofen and to evaluate, ex vivo, the intestinal permeation. Solid dispersions (SD) were prepared with Kollicoat IR® by solvent evaporation technique in different drug:carrier ratios. The permeation intestinal of ibuprofen was evaluated by inverted intestinal sac method. The SD was characterized by solubility equilibrium, FT-IR, DSC, PXRD, SEM, and dissolution rate. The solubility, dissolution rate, and permeability were significantly greater for SD 1:2. The PXRD, SEM and DSC indicated a partial change in the crystalline state of ibuprofen. The solubility equilibrium of SD (1:2) was approximately 15 times greater than the solubility of ibuprofen. Dissolution rate enhancement was attributed to the decreased crystallinity of the ibuprofen, and increase of wettability and decrease of particle size. In conclusion, dissolution rate and intestinal permeability of ibuprofen were enhanced by the use of Kollicoat IR® carrier in the SD formulation. 相似文献
99.
Aharmim B Ahmed SN Amsbaugh JF Anthony AE Banar J Barros N Beier EW Bellerive A Beltran B Bergevin M Biller SD Boudjemline K Boulay MG Bowles TJ Browne MC Bullard TV Burritt TH Cai B Chan YD Chauhan D Chen M Cleveland BT Cox-Mobrand GA Currat CA Dai X Deng H Detwiler J DiMarco M Doe PJ Doucas G Drouin PL Duba CA Duncan FA Dunford M Earle ED Elliott SR Evans HC Ewan GT Farine J Fergani H Fleurot F Ford RJ Formaggio JA Fowler MM Gagnon N Germani JV Goldschmidt A Goon JT Graham K Guillian E 《Physical review letters》2008,101(11):111301
The Sudbury Neutrino Observatory (SNO) used an array of 3He proportional counters to measure the rate of neutral-current interactions in heavy water and precisely determined the total active (nu_x) 8B solar neutrino flux. This technique is independent of previous methods employed by SNO. The total flux is found to be 5.54_-0.31;+0.33(stat)-0.34+0.36(syst)x10(6) cm(-2) s(-1), in agreement with previous measurements and standard solar models. A global analysis of solar and reactor neutrino results yields Deltam2=7.59_-0.21;+0.19x10(-5) eV2 and theta=34.4_-1.2;+1.3 degrees. The uncertainty on the mixing angle has been reduced from SNO's previous results. 相似文献
100.
Sebastião da Costa Paolinelli Marco Antônio da Cunha André Barros Cota 《Journal of magnetism and magnetic materials》2008
The presence of shear bands in the deformed material before final annealing is very important for Goss and Cube textures formation in silicon steel [S.C. Paolinelli, M.A. Cunha, J. Magn. Magn. Mater. 255 (2003) pp. 379. [1]; J.T. Park, J.A. Szpunar, Acta Mater., 51 (2003) 3037. [2]]. The increase of the hot-band grain size can increase the number of shear bands, which favor the nucleation of these orientations. In this work, the effect of the hot band grain size variation, promoted by varying the hot rolling finishing temperature, on final structure and magnetic properties was investigated for 3% Si alloy. It was found that the increase of the hot-band grain size increases the occurrence of shear bands and promotes an increase of η fiber fraction and a reduction of γ fiber fraction, improving the magnetic induction. On the other hand, the final grain size is reduced when the hot-band grain size is larger than 190 μm, deteriorating the core loss values in spite of the texture benefits. The reduction of final grain size was explained by the increase of the number of nuclei at the beginning of the recrystallization caused by the increase of shear bands in the deformed material. 相似文献