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RISS 인기검색어
- 검색키워드
- 저자 : Ruiz-Bustos, R. (검색결과 4 건)
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Substitutions at the gadolinium and the strontium sites in the RuSr2GdCu2O8 magnetic superconductor
R. Ruiz-Bustos,M. H. Aguirre,E. Mor?n,R. Saez-Puche,M. ?. Alario-Franco 한국물리학회 2002 Current Applied Physics Vol.2 No.6
The coexistence of superconductivity and magnetic order seems to take place in the so called ruthenate-cuprates. Previous workhas mainly focused on RuSr2GdCu 2O8 where a magnetic transition is observed at 133 K and superconductivity has been claimedbelow Tc . 46 K.At room pressure, Sm, Eu and Gd seem to be the only RE elements that accept to enter into the structure of RuSr2GdCu 2O8.However high pressures and temperatures allows one to replace gadolinium by other lanthanide cations, although it is dicult to getpure samples.In order to better understand this, rather unusual behaviour, we have performed some substitutions in the title compound.The synthesis at high pressures (. 60 kbar) and high temperatures (. 1100 .C) of the title new ruthenates has been achieved andthe materials compared to the gadolinium analogue. The structure remains tetragonal (Space group: P 4/mmmrameters linearly decrease following the lanthanide contraction.We have succeeded in replacing Gd by Tb, Dy, Y, Ho and Er, magnetic susceptibility measurements reveal the existence ofinteresting phenomena. The microstructure of these compounds has been studied by high-resolution electron microscopy.Also, at room pressure, we have replaced up to 10% calcium for strontium and observed that, in consonance with the dierence inionic radii, the unit cell contracts. On the other hand, the calcium-doped sample shows a positive magnetic susceptibility at 5 K.. 2002 Elsevier Science B.V. All rights reserved.
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Antibacterial and Antifungal Activities of Some Mexican Medicinal Plants
E. Ruiz-Bustos,C. Velazquez,A. Garibay-Escobar,Z. García,M. Plascencia-Jatomea,M.O. Cortez-Rocha,J. Hernandez-Martínez,R.E. Robles-Zepeda 한국식품영양과학회 2009 Journal of medicinal food Vol.12 No.6
In Mexico about 4,000 plant species have some medicinal use. The aim of this work was to evaluate the antimicrobial activity of six Mexican medicinal plants against fungi and Gram-positive and Gram-negative bacteria. Methanolic extracts were prepared from the Mexican medicinal plants Amphypteringium adstrigens, Castella tortuosa, Coutarea latiflora, Ibervillea sonorae, Jatropha cuneata, and Selaginella lepidophylla. The antibacterial and antifungal activities of the plants were determined by the broth microdilution method and the radial growth inhibition assay, respectively. All Mexican plants tested showed antimicrobial activity. Among the six plant extracts analyzed, J. cuneata showed the highest growth-inhibitory activity against fungi, Gram-positive and Gram-negative bacteria (J. cuneata > A. adstrigens > C. latiflora > C. tortuosa > I. sonorae ≈ S. lepidophylla). Shigella flexneri and Staphylococcus aureus were the most susceptible bacteria to plant extracts. Complete inhibition of S. flexneri growth was observed with J. cuneata methanolic extract at 90μg/mL. This plant extract also showed the strongest antifungal activity against Fusarium verticillioides and Aspergillus niger. Our data suggest that the medicinal plants tested have important antimicrobial properties. This is the first report describing the antimicrobial activities of several of the Mexican medicinal plants used in this study.
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Induced quadrupolar singlet ground state of praseodymium in a modulated pyrochlore
van Duijn, J.,Kim, K. H.,Hur, N.,Ruiz-Bustos, R.,Adroja, D. T.,Bridges, F.,Daoud-Aladine, A.,Fernandez-Alonso, F.,Wen, J. J.,Kearney, V.,Huang, Q. Z.,Cheong, S.-W.,Perring, T. G.,Broholm, C. American Physical Society 2017 Physical Review B Vol.96 No.9
<P>The complex structure and magnetism of Pr2-xBixRu2O7 was investigated by neutron scattering and extended x-ray absorption fine structure. Pr has an approximate doublet ground state and the first excited state is a singlet. While the B-site (Ru) is well ordered throughout, this is not the case for the A-site (Pr/Bi). A broadened distribution for the Pr-O-2 bond length at low temperature indicates the Pr environment varies from site to site even for x = 0. The environment about the Bi site is highly disordered ostensibly due to the 6s lone pairs on Bi3+. Correspondingly, we find that the non-Kramers doublet ground-state degeneracy, otherwise anticipated for Pr in the pyrochlore structure, is lifted so as to produce a quadrupolar singlet ground statewith a spatially varying energy gap. For x = 0, below TN, the Ru sublattice orders antiferromagnetically, with propagation vector k = (0,0,0) as forY(2)Ru(2)O(7). No ordering associated with the Pr sublattice is observed down to 100 mK. The low-energy magnetic response of Pr2-xBixRu2O7 features a broad spectrum of magnetic excitations associated with inhomogeneous splitting of the Pr quasidoublet ground state. For x = 0 (x = 0.97), the spectrum is temperature dependent (independent). It appears disorder associated with Bi alloying enhances the inhomogeneous Pr crystal-field level splitting so that intersite interactions become irrelevant for x = 0.97. The structural complexity for the A-site may be reflected in the hysteretic uniform magnetization of B-site ruthenium in the Neel phase.</P>
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Antimicrobial Activity of Northwestern Mexican Plants Against Helicobacter pylori
Ramón E. Robles-Zepeda,Carlos A. Velázquez-Contreras,Adriana Garibay-Escobar,Juan C. Gálvez-Ruiz,Eduardo Ruiz-Bustos 한국식품영양과학회 2011 Journal of medicinal food Vol.14 No.10
Helicobacter pylori is the major etiologic agent of such gastric disorders as chronic active gastritis and gastric carcinoma. Over the past few years, the appearance of antibiotic-resistant bacteria has led to the development of better treatments, such as the use of natural products. This study evaluated the anti–H. pylori activity of 17 Mexican plants used mainly in the northwestern part of Mexico (Sonora) for the empirical treatment of gastrointestinal disorders. The anti–H. pylori activity of methanolic extracts of the plants was determined by using the broth microdilution method. The 50% minimum inhibitory concentrations ranged from less than 200 to 400 μg/mL for Castella tortuosa, Amphipterygium adstringens, Ibervillea sonorae, Pscalium decompositum, Krameria erecta, Selaginella lepidophylla, Pimpinella anisum, Marrubium vulgare, Ambrosia confertiflora, and Couterea latiflora and were greater than 800 μg/mL for Byophyllum pinnatum, Tecoma stans linnaeus, Kohleria deppena, Jatropha cuneata, Chenopodium ambrosoides, and Taxodium macronatum. Only Equisetum gigantum showed no activity against H. pylori. This study suggests the important role that these plants may have in the treatment of gastrointestinal disorders caused by H. pylori. The findings set the groundwork for further characterization and elucidation of the active compounds responsible for such activity.
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