The shell effect on the room temperature photoluminescence from ZnO/MgO core/shell nanowires: exciton-phonon coupling and strain

The room temperature photoluminescence from ZnO/MgO core/shell nanowires (NWs) grown by a simple two-step vapor transport method was studied for various MgO shell widths (w). Two distinct effects induced by the MgO shell were clearly identified. The first one, related to the ZnO/MgO interface formation, is evidenced by strong enhancements of the zero-phonon and first phonon replica of the excitonic emission, which are accompanied by a total suppression of its second phonon replica. This effect can be explained by the reduction of the band bending within the ZnO NW core that follows the removal of atmospheric adsorbates and associated surface traps during the MgO growth process on one hand, and a reduced exciton-phonon coupling as a result of the mechanical stabilization of the outermost ZnO NW monolayers by the MgO shell on the other hand. The second effect is the gradual increase of the excitonic emission and decrease in the defect related emission by up to two and one orders of magnitude, respectively, when w is increased in the ∼3-17 nm range. Uniaxial strain build-up within the ZnO NW core with increasing w, as detected by x-ray diffraction measurements, and photocarrier tunneling escape from the ZnO core through the MgO shell enabled by defect-states are proposed as possible mechanisms involved in this effect. These findings are expected to be of key significance for the efficient design and fabrication of ZnO/MgO NW heterostructures and devices.

Electronic structure of MgS and MgYb2S4: Electron Energy-Loss Spectroscopy and self-consistent multiple scattering calculations

The electronic structure of MgS and MgYb2S4 have been studied using the fine structure of the Mg-K, S-K, Mg-L2,3, S-L2,3 and Yb-N5 edges measured by electron energy-loss spectroscopy (EELS). Our experimental results are compared with real-space full multiple scattering calculations as incorporated in the FEFF9.6 code. All edges are very well reproduced. Total and partial densities of states have been calculated. The calculated densities of states of Mg and S are similar in both compounds. The energy distribution of these states suggests a covalent nature for both materials. For MgYb2S4 a band gap smaller than for MgS is predicted. In this compound the top of the valence band and the bottom of the conduction band are dominated by Yb states.

Exploring the benefits of electron tomography to characterize the precise morphology of core-shell Au@Ag nanoparticles and its implications on their plasmonic properties

In the design and engineering of functional core-shell nanostructures, material characterization at small length scales remains one of the major challenges. Here we show how electron tomography in high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) mode can be applied successfully to perform nano-metrological characterization of Au@Ag core-shell nanostructures. This work stresses the benefits of HAADF-STEM tomography and its use as a novel and rigorous tool for understanding the physical-chemical properties of complex 3D core-shell nanostructures. The reconstructed Au@Ag core-shell architecture was used as an input for discrete dipole approximation (DDA)-based electrodynamics simulations of the optical properties of the nanostructures. The implications of localized surface plasmon spectroscopy as well as Raman-enhanced spectroscopy are analysed.

Improved route for the synthesis of colloidal NaYF4 nanocrystals and electron spin resonance of Gd3+ local probe

This paper presents the synthesis and characterization of colloidal NaYF4 and NaYF4:20% Gd lanthanide nanocrystals. The nanoparticles were prepared by chemical route using co-thermolysis of Na(CF3COO), Y(CF3COO)3 and Gd(CF3COO)3 precursor in oleylamine surfactant/phenylether at Ts = 250 degrees C. By tuning the precursor/surfactant molar ratio during the process, it was possible to control the crystalline phase, chemical order and size of the nanocrystals. The nanocrystals were characterized by Transmission Electron Microscopy, Small Angle X-ray Scattering, powder X-ray Diffraction, dc-magnetization and Electron Spin Resonance (ESR) techniques. The ESR experiments show the so called U-spectrum for the Gd3+ ions in bulk counterpart materials, where characteristic powder spectra of cubic and lower crystal field symmetries were observed.

Intestinal and haematic parasitism in the birds of the Almuñecar (Granada, Spain) ornithological garden

Birds from the Almuñecar ornithological garden (Granada, Spain) were surveyed from June 2006 to May 2007 to establish programmes to prevent, control, and treat intestinal and haematic parasites. A total of 984 faecal samples and 41 samples of blood were collected from Psittacidae, Cacatuidae, Phasianidae, and Anatidae. One or more intestinal parasites were identified in 51.6% of the samples. Blood parasites were found in 26.8% of the birds examined. The most frequent pathogenic endoparasites were coccidians, such as Cyclospora sp. (4.5%), Eimeria sp. (4.1%) and Isospora sp. (2%) and helminths such as Capillaria sp. (10. 1%), Ascaridia sp. (4.9%) and Heterakis gallinarum (4.9%). All the parasites varied with season but the most were found year round. Multiple parasitic infections by intestinal parasites were common, with 196 of 984 faecal samples having 2-5 intestinal parasites. The most frequent cases of multiple parasitism were Blastocystis plus Entamoeba sp. and Blastocystis plus Cyclospora sp. The haematic protozoa detected were Haemoproteus sp. (17%) and Plasmodium sp. (7.3%). Multiple parasitism by Haemoproteus sp. and Plasmodium sp. was detected in 1 sample of Gallus gallus. After each sampling, some of the affected animals were treated according to our results, and the corresponding programmes of prevention and control were designed.

Fourier-ratio deconvolution and its Bayesian equivalent

We discuss how an inner-shell electron energy-loss spectrum can be processed using Bayesian (maximum-entropy or maximum-likelihood) deconvolution to simultaneously remove plural scattering and improve the energy resolution. As in Fourier-ratio deconvolution, a low-loss spectrum (recorded from the same area of specimen) is used as a kernel or resolution function. This procedure avoids the need to record the zero-loss peak in the absence of a specimen and uncertainties related to the width of the zero-loss peak. Unlike the case of Fourier-ratio deconvolution, we find that core-loss data do not require pre-edge background subtraction and extrapolation towards zero intensity; simply matching the intensity at both ends of the region is usually sufficient to avoid oscillatory artifacts. Using the low-loss spectrum as both data and kernel yields a zero-loss peak whose width provides an indication of the energy resolution as a function of the number of iterations. Finally, we argue that Fourier-ratio deconvolution or its Bayesian equivalent is the correct way to remove the substrate or matrix contribution to an energy-loss spectrum recorded from a particle on a substrate or embedded in a matrix.

More productive in vitro culture of Cryptosporidium parvum for better study of the intra- and extracellular phases

The great difficulties in treating people and animals suffering from cryptosporidiosis have prompted the development of in vitro experimental models. Due to the models of in vitro culture, new extracellular stages of Cryptosporidium have been demonstrated. The development of these extracellular phases depends on the technique of in vitro culture and on the species and genotype of Cryptosporidium used. Here, we undertake the molecular characterization by polymerase chain reaction-restriction fragment length polymorphism of different Cryptosporidium isolates from calves, concluding that all are C. parvum of cattle genotype, although differing in the nucleotide at positions 472 and 498. Using these parasites, modified the in vitro culture technique for HCT-8 cells achieving greater multiplication of parasites. The HCT-8 cell cultures, for which the culture had not been renewed in seven days, were infected with C. parvum sporozoites in RPMI-1640 medium with 10% IFBS, CaCl2 and MgCl2 1 mM at pH 7.2. Percentages of cell parasitism were increased with respect to control cultures (71% at 48 h vs 14.5%), even after two weeks (47% vs 1.9%). Also, the percentage of extracellular stages augmented (25.3% vs 1.1% at 96 h). This new model of in vitro culture of C. parvum will enable easier study of the developmental phases of C. parvum in performing new chemotherapeutic assays.

Practical aspects of electron energy-loss spectroscopy (EELS) calculations using FEFF8

We discuss the application of the ab initio program FEFF8 to calculations of electron energy-loss spectroscopy (EELS), focusing in particular on core-loss spectra. FEFF8 is based on a self-consistent, real space multiple scattering formalism. We focus on issues relevant to practical simulations, including the construction of well-converged potentials, the treatment of inelastic losses and exchange-correlation potentials and the core-hole. We also discuss how to account for experimental conditions, for example, sample orientation and finite temperature effects such as Debye-Waller factors. Finally we discuss the interpretation of the spectra in terms of electronic structure and local projected density of states (LDOS). As an explicit example, we illustrate various features of the code by application to the ionization edges of GaN.

Extracellular like-gregarine stages of Cryptosporidium parvum

The present study confirms the existence of extracellular stages of Cryptosporidiumparvum during in vitro culture on MDCK, HCT 8 and Vero cells as well as alveolar macrophages, by optic, Nomarski and transmission electron microscopy images. Extracellular trophozoite/gamont, stages in syzygy, zygotes and spores with eight sporozoites were seen in the supernatant of the cultures. The first ultrastructural images of extracellular stages of C. parvum are shown in this study. The morphology of these stages, which have characteristics similar to those of some gregarines, support the contention that Cryptosporidium has closer affinity with gregarines. It also supports the necessity of reconsidering the life cycle of Cryptosporidium and the classification within the coccidia.

Catabolite repression mediated by the CcpA protein in Bacillus subtilis: novel modes of regulation revealed by whole-genome analyses

Previous studies have shown that the CcpA protein of Bacillus subtilis is a major transcription factor mediating catabolite repression. We report here whole-transcriptome analyses that characterize CcpA-dependent, glucose-dependent gene expression and correlate the results with full-genome computer analyses of DNA binding (CRE) sites for CcpA. The data obtained using traditional approaches show good agreement with those obtained using the transcriptome approach. About 10% of all genes in B. subtilis are regulated > 3x by glucose, with repressed genes outnumbering activated genes three to one. Eighty per cent of these genes depend on CcpA for regulation. Classical approaches have provided only evidence for CcpA-mediated, glucose-dependent activation or repression. We show here that CcpA also mediates glucose-independent activation or repression, and that glucose may alter either the direction or the intensity of either effect. Computer analyses revealed the presence of CRE sites in most operons subject to CcpA-mediated glucose repression, but not in those subject to glucose activation, suggesting that either secondary transcription factors regulate the latter genes or activation by CcpA involves a dissimilar binding site. Operons encoding the constituents of ABC-type transporters that are subject to CcpA-mediated glucose regulation show two distinct patterns: either all genes in the operon are regulated in parallel (the minor class) or the gene encoding the extracytoplasmic solute-binding receptor is preferentially regulated (the major class). Genes subject to CcpA-independent catabolite repression are primarily concerned with sporulation. Several transcription factors were identified that are themselves regulated by CcpA at the transcriptional level. Representative data with functionally characterized genes are presented to illustrate the novel findings. The comprehensive transcriptome data are available on our website: www.biology.uesd.edu/~MSAIER/regulation/ and also on http://www.blackwell-science.com/ products/journals/suppmat/MMI/MMI2328/MMI2328sm.htm

[Basilar artery migraine]

Basilar artery migraine is a rare headache characterized by attacks preceded and/or accompanied by transitory focal neurologic symptoms that point to dysfunction in the region irrigated by the basilar artery and its branches. Clinical variation in presentation can complicate differential diagnosis. We review the clinical characteristics, diagnostic criteria, complementary tests and most frequent results, as well as the differential diagnoses to be taken into consideration. We also suggest possible prophylactic and therapeutic measures based on recent genetic studies.

Sequence analysis of the phs operon in Salmonella typhimurium and the contribution of thiosulfate reduction to anaerobic energy metabolism

The phs chromosomal locus of Salmonella typhimurium is essential for the dissimilatory anaerobic reduction of thiosulfate to hydrogen sulfide. Sequence analysis of the phs region revealed a functional operon with three open reading frames, designated phsA, phsB, and phsC, which encode peptides of 82.7, 21.3, and 28.5 kDa, respectively. The predicted products of phsA and phsB exhibited significant homology with the catalytic and electron transfer subunits of several other anaerobic molybdoprotein oxidoreductases, including Escherichia coli dimethyl sulfoxide reductase, nitrate reductase, and formate dehydrogenase. Simultaneous comparison of PhsA to seven homologous molybdoproteins revealed numerous similarities among all eight throughout the entire frame, hence, significant amino acid conservation among molybdoprotein oxidoreductases. Comparison of PhsB to six other homologous sequences revealed four highly conserved iron-sulfur clusters. The predicted phsC product was highly hydrophobic and similar in size to the hydrophobic subunits of the molybdoprotein oxidoreductases containing subunits homologous to phsA and phsB. Thus, phsABC appears to encode thiosulfate reductase. Single-copy phs-lac translational fusions required both anaerobiosis and thiosulfate for full expression, whereas multicopy phs-lac translational fusions responded to either thiosulfate or anaerobiosis, suggesting that oxygen and thiosulfate control of phs involves negative regulation. A possible role for thiosulfate reduction in anaerobic respiration was examined. Thiosulfate did not significantly augment the final densities of anaerobic cultures grown on any of the 18 carbon sources tested. on the other hand, washed stationary-phase cells depleted of ATP were shown to synthesize small amounts of ATP on the addition of the formate and thiosulfate, suggesting that the thiosulfate reduction plays a unique role in anaerobic energy conservation by S typhimurium.

Monoamine oxidase in adult Hymenolepis diminuta (Cestoda)

A membrane-bound monoamine oxidase (EC 1.4.3.4) was demonstrated in homogenates of Hymenolepis diminuta. The enzyme oxidized a variety of biologically active amines (in decreasing order: dopamine, adrenaline, noradrenaline, tryptamine, tyramine, octopamine), there was, however, no activity with 5-hydroxytryptamine or benzylamine. No diamine oxidase (EC 1.4.3.6.) could be detected in H. diminuta (using histamine, cadaverine or putrescine as substrates). The monoamine oxidase from H. diminuta was not inhibited by azide, hydroxylamine or semicarbazide, but was inhibited by cupferron, alpha-alpha dipyridyl and iodoacetamide, and by the specific monoamine oxidase inhibitors pargyline, nialamide and iproniazid. Several anthelmintics were also found to be inhibitors of monoamine oxidase. The possible roles of monoamine oxidase in H. diminuta are discussed.