Effects of the magneto-crystalline anisotropy on the magnetic properties of Fe/Cr/Fe (110) trilayer

Using a variational procedure based on Lee-Low-Pines and Huybrechts canonical transformations, we study the stability region of two-dimensional bipolarons confined in a parabolic quantum dot, subject to a uniform magnetic field. In the framework of our approach, we calculate the ground-state energy for two-dimensional magnetobipolarons, together with the free polaron ground-state energy, by performing a self consistent calculation. We then obtain the binding energy for two-dimensional magnetobipolarons, in the usual way, to explore the properties of bipolaron formation in two-dimensional quantum dot structures. The stability region is found to be very sensitive to the confinement length of the parabolic potential and to the magnetic field strength, as well as to the material parameters and . The stability region is also found to be remarkably enhanced by increasing the degree of spatial confinement and magnetic field. Our results are both in qualitative and quantitative agreement with those found in the literature.Received: 11 December 2003, Published online: 9 April 2004PACS: 71.38.Fp Large or Fröhlich polarons - 63.20.Kr Phonon-electron and phonon-phonon interactions     

On the kinetics of oxygen desorption of57Fe: YBa2Cu3O7−d superconducting oxides

We report on “in situ” high temperature⁵⁷Fe Mössbauer measurements on several⁵⁷Fe: YBaCuO samples under vacuum and various controlled temperatures. The results obtained allowed us to get information about the mechanism of oxygen desorption under various annealing heating conditions.     

Raman validity for crystallite size La determination on reticulated vitreous carbon with different graphitization index

The graphitization index provided by X-ray diffraction (XRD) and Raman spectrometry for reticulated vitreous carbon (RVC) substrates, carbonized at different heat treatment temperatures (HTT), is investigated. A systematic study of the dependence between the disorder-induced D and G Raman bands is presented. The crystallite size L_a was obtained for both X-ray diffraction and Raman spectrometry techniques. Particularly, the validity for L_a determination, from Raman spectra, is pointed out comparing the commonly used formula based on peaks amplitude ratio (I_D/I_G) and the recent proposed equation that uses the integrated intensities of D and G bands. The results discrepancy is discussed taken into account the strong contribution of the line broadening presented in carbon materials heat treated below 2000 °C.     

On a Class of Supersoluble Groups

This paper identifies a class of supersoluble groups, called finitely generated hallsoging groups. The main result states that the product of a normal finitely generated hall-soging subgroup and a subnormal supersoluble subgroup is always supersoluble.AMS Subject Classification (1991): 20F16, 20F19, 20E25.     

Capillary electrophoresis-mass spectrometry of citrus endophytic bacteria siderophores

CE-ESI-MS with a liquid sheath interface and IT mass analyzer was used for analysis of siderophores from different strains of Methylobacterium spp. citrus endophyte extracts. Three Methylobacterium strains were investigated according to positive bioassay tests. Bacteria cultures were grown under Fe(III) absence (siderophore producing cultures) and under Fe(III) presence (control cultures). Siderophores were extracted from culture supernatant with polystyrene resins. BGE and sheath-liquid composition were optimized, respectively, in order to assure both, best peak resolution and ESI-MS sensitivity. The best analysis conditions were obtained with 100 mmol/L ammonium bicarbonate at pH 8 as BGE and methanol:H(2)O 25:75 + 0.05% formic acid as sheath liquid. CZE-ESI-MS analysis revealed two possible siderophores, according to bacterium species, presenting M(r) of 1004.3 and 798.3 Da.     

Attachment of water-soluble proteins to the surface of (magnetizable) phospholipid colloids via NeutrAvidin-derivatized phospholipids

The present work describes the incorporation of a functionalized phospholipid derivative into the phospholipid bilayer of both classical small unilamellar vesicles and recently developed magnetoliposomes, resulting in unique biocolloid structures onto which peripheral water-soluble enzymes can be immobilized on the surfaces. In the first part of this work, a synthesis protocol is outlined for a universal membrane anchor for water-soluble proteins. Dioleoylphosphatidylethanolamine-N-dodecanyl was used as the starting lipid molecule. After activation of the terminal -COOH group, alpha,omega-diamino-poly(ethylene glycol), used as a hydrophilic, flexible spacer arm, was coupled covalently. Subsequently, NeutrAvidin was bound, after blocking the free -NH(2) groups with citraconic anhydride. In the second part, the resulting lipid-NeutrAvidin derivative was incorporated into small unilamellar vesicles comprised of dimyristoylphosphatidylglycerol. FPLC with Superdex 200 as the column matrix clearly showed that biotinylated alkaline phosphatase, which served as a representative model of water-soluble proteins, was attached to the vesicles. Furthermore, magnetoliposomes, constructed of the same type of phospholipid molecules, were presented as interesting colloids to assess the degree of enzyme immobilization in a rapid and elegant manner. Potential applications that can emerge from this study are briefly discussed.     

57Fe and119Sn Mössbauer studies on La1.25Nd0.6Sr0.15CuO4

⁵⁷Fe- and¹¹⁹Sn Mössbauer effect studies on 0.5 at %⁵⁷Fe (or¹¹⁹Sn) dopednon-superconducting La_1.25Nd_0.6Sr_0.15CuO₄ in the temperature region 300 K T4.2 K reveal an onset of local magnetic ordering occurring atT _m 32 K for both⁵⁷Fe—as well as¹¹⁹Sn-doped samples. The local magnetic ordering shows up in the presence of a very large transferred hyperfine field ofB _thf 11.0(5)T at the¹¹⁹Sn nuclei. Since such a large field is neither present in antiferromagnetic La₂CuO₄, nor in superconducting La_1.85Sr_0.15CuO₄ or overdoped La_2–xSr_xCuO₄ (x=0.4), the occurrence of such local spin correlations seems to be a signature of the non-superconducting low temperature tetragonal phase of La_1.25Nd_0.6Sr_0.15CuO₄.     

Synthesis and application of a new thiazolylazo reagent for cloud point extraction and determination of cobalt in pharmaceutical preparations

The synthesis and characterization of the reagent 2-(5-bromothiazolylazo)-4-chlorophenol and its application in the development of a preconcentration procedure for cobalt determination using flame atomic absorption spectrometry after cloud point extraction is presented. This procedure is based on cobalt complexing and entrapment of the metal chelates into micelles of a surfactant-rich phase of Triton X-114. The preconcentration procedure was optimized by using a response surface methodology through the application of the Box-Behnken matrix. Under optimum conditions, the procedure determined the presence of cobalt with an LOD of 2.8 microg/L and LOQ of 9.3 microg/L. The enrichment factor obtained was 25. The precision was evaluated as the RSD, which was 5.5% for 10 microg/L cobalt and 6.9% for 30 microg/L. The accuracy of the procedure was assessed by comparing the results with those found using inductively coupled plasma-optical emission spectrometry. After validation, the procedure was applied to the determination of cobalt in pharmaceutical preparation samples containing cobalamin (vitamin B12).