598 research outputs found
Electrical transport and optical studies of ferromagnetic Cobalt doped ZnO nanoparticles exhibiting a metal-insulator transition
The observed correlation of oxygen vacancies and room temperature
ferromagnetic ordering in Co doped ZnO1-o nanoparticles reported earlier (Naeem
et al Nanotechnology 17, 2675-2680) has been further explored by transport and
optical measurements. In these particles room temperature ferromagnetic
ordering had been observed to occur only after annealing in forming gas. In the
current work the optical properties have been studied by diffuse reflection
spectroscopy in the UV-Vis region and the band gap of the Co doped compositions
has been found to decrease with Co addition. Reflections minima are observed at
the energies characteristic of Co+2 d-d (tethrahedral symmetry) crystal field
transitions, further establishing the presence of Co in substitutional sites.
Electrical transport measurements on palletized samples of the nanoparticles
show that the effect of a forming gas is to strongly decrease the resistivity
with increasing Co concentration. For the air annealed and non-ferromagnetic
samples the variation in the resistivity as a function of Co content are
opposite to those observed in the particles prepared in forming gas. The
ferromagnetic samples exhibit an apparent change from insulator to metal with
increasing temperatures for T>380K and this change becomes more pronounced with
increasing Co content. The magnetic and resistive behaviors are correlated by
considering the model by Calderon et al [M. J. Calderon and S. D. Sarma, Annals
of Physics 2007 (Accepted doi: 10.1016/j.aop.2007.01.010] where the
ferromagnetism changes from being mediated by polarons in the low temperature
insulating region to being mediated by the carriers released from the weakly
bound states in the higher temperature metallic region.Comment: 7 pages, 6 figure
Altered collecting duct adenylyl cyclase content in collecting duct endothelin-1 knockout mice
<p>Abstract</p> <p>Background</p> <p>Endothelin-1 (ET-1) inhibition of vasopressin (AVP)-stimulated water reabsorption by the inner medullary collecting duct (IMCD) is associated with reduced cAMP accumulation. To determine the effect of ET-1 deficiency, AVP-stimulated cAMP responsiveness was assessed in IMCD from mice with collecting duct-specific deletion of ET-1 (CD ET-1 KO) and from control animals.</p> <p>Methods</p> <p>Cyclic AMP production, adenylyl cyclase (AC) mRNA, and AC protein were measured in acutely isolated IMCD.</p> <p>Results</p> <p>CD ET-1 KO IMCD had enhanced AVP-stimulated cAMP accumulation. Inhibition of calcium-stimulated AC using BAPTA did not prevent enhanced AVP responsiveness in CD ET-1 KO IMCD. Factors known to be modified by ET-1, including nitric oxide, cyclooxygenase metabolites, and superoxide did not affect the increased AVP responsiveness of CD ET-1 KO IMCD. Differential V2 receptor or G-protein activity was not involved since CD ET-1 KO IMCD had increased cAMP accumulation in response to forskolin and/or cholera toxin. CD ET-1 KO did not affect mRNA or protein levels of AC3, one of the major known collecting duct AC isoforms. However, the other known major collecting duct AC isoform (AC5/6) did have increased protein levels in CD ET-1 KO IMCD, although AC5 (weak signal) and 6 mRNA levels were unchanged.</p> <p>Conclusion</p> <p>ET-1 deficiency increases IMCD AC5/6 content, an effect that may synergize with acute ET-1 inhibition of AVP-stimulated cAMP accumulation.</p
First-principles study of As interstitials in GaAs: Convergence, relaxation, and formation energy
Convergence of density-functional supercell calculations for defect formation
energies, charge transition levels, localized defect state properties, and
defect atomic structure and relaxation is investigated using the arsenic split
interstitial in GaAs as an example. Supercells containing up to 217 atoms and a
variety of {\bf k}-space sampling schemes are considered. It is shown that a
good description of the localized defect state dispersion and charge state
transition levels requires at least a 217-atom supercell, although the defect
structure and atomic relaxations can be well converged in a 65-atom cell.
Formation energies are calculated for the As split interstitial, Ga vacancy,
and As antisite defects in GaAs, taking into account the dependence upon
chemical potential and Fermi energy. It is found that equilibrium
concentrations of As interstitials will be much lower than equilibrium
concentrations of As antisites in As-rich, -type or semi-insulating GaAs.Comment: 10 pages, 5 figure
The origin of human chromosome 2 analyzed by comparative chromosome mapping with a DNA microlibrary
Fluorescencein situ hybridization (FISH) of microlibraries established from distinct chromosome subregions can test the evolutionary conservation of chromosome bands as well as chromosomal rearrangements that occurred during primate evolution and will help to clarify phylogenetic relationships. We used a DNA library established by microdissection and microcloning from the entire long arm of human chromosome 2 for fluorescencein situ hybridization and comparative mapping of the chromosomes of human, great apes (Pan troglodytes, Pan paniscus, Gorilla gorilla, Pongo pygmaeus) and Old World monkeys (Macaca fuscata andCercopithecus aethiops). Inversions were found in the pericentric region of the primate chromosome 2p homologs in great apes, and the hybridization pattern demonstrates the known phylogenetically derived telomere fusion in the line that leads to human chromosome 2. The hybridization of the 2q microlibrary to chromosomes of Old World monkeys gave a different pattern from that in the gorilla and the orang-utan, but a pattern similar to that of chimpanzees. This suggests convergence of chromosomal rearrangements in different phylogenetic lines
Metallic foreign body in middle ear: an unusual cause of hearing loss
This is a rare case report of a foreign metallic body found in the middle ear. During the use of an electric welding by a metalworker, a glowing drop of dissolved metal overrun, burning the skin of his external auditory meatus, perforated the tympanic membrane and finally was implanted around the ossicles as a foreign body. Due to difficulty of the physical examination and the moderate symptoms (hearing loss and sense of fullness), the foreign body was detected six months after the incident, by CT scanning and it was removed by a transcanal approach under general anesthesia. A successful ossiculoplasty-tympanoplasty was followed four weeks later
Ocupaciones tempranas (ca. 3200-2200 A.P.) en el Alero Morro Blanco (Barrancas, Jujuy, Argentina): resultados preliminares
Se presentan los primeros resultados de la investigaciĂłn abordada en el sitio Alero del Morro Blanco de la localidad de Barrancas (AbdĂłn Castro Tolay) en la Puna de Jujuy. Este sitio es un alero con representaciones rupestres fechado radiocarbĂłnicamente entre 3200-2200 AP (3400-2200 cal. AP). Los estudios se enfocaron en el análisis de las tecnologĂas lĂtica y cerámica y en el análisis faunĂstico y del arte rupestre. Asimismo, las investigaciones incluyen un estudio polĂnico local y una sĂntesis paleoambiental regional. Los datos obtenidos cotejados con los antecedentes arqueolĂłgicos regionales permiten concluir que se tratarĂa de una ocupaciĂłn pastoril, con un aprovisionamiento de bienes alĂłctonos obtenidos mediante el tráfico caravanero.This article presents the preliminary results of research at the Alero Morro Blanco site located at Barrancas (AbdĂłn Castro Tolay) in the puna of Jujuy. This site is a shelter with rock art, radiocarbon dated to between 3200-2200 years AP (3400-2200 cal AP). The results presented here focus on an analysis of lithic and ceramic technologies, and on faunal and rock art analysis. Also, the investigation included a local pollen study and a regional paleoenvironmental synthesis. The data obtained are discussed within the regional archaeological background, which allows us to conclude that it would be a pastoral occupation with a supply of allochthonous goods obtained through caravan traffic.Nous prĂ©sentons ici les premiers rĂ©sultats des recherches effectuĂ©es sur le site Abri de Morro Blanco dans la localitĂ© de Barrancas (AbdĂłn Castro Tolay) dans la Puna de Jujuy. Il s’agit d’un site avec motifs rupestres datĂ© radiocarbonicamente entre ca. 3200 et 2200 ans BP (ca. 3400 et 2200 ans cal. BP). Les Ă©tudes ont Ă©tĂ© centrĂ©es sur les technologies lithiques et cĂ©ramiques, sur l’analyse faunistique et sur l’art rupestre. Les recherches incluent Ă©galement une Ă©tude pollinique locale et une synthèse palĂ©oenvironnementale rĂ©gionale. Les donnĂ©es obtenues mises en comparaison avec l’historique des recherches archĂ©ologiques rĂ©gionales permettent de conclure qu’il s’agirait d’une occupation pastorale, avec un approvisionnement de biens allochtones obtenu Ă travers le trafic des caravanes de lamas
The Effect of Lattice Vibrations on Substitutional Alloy Thermodynamics
A longstanding limitation of first-principles calculations of substitutional
alloy phase diagrams is the difficulty to account for lattice vibrations. A
survey of the theoretical and experimental literature seeking to quantify the
impact of lattice vibrations on phase stability indicates that this effect can
be substantial. Typical vibrational entropy differences between phases are of
the order of 0.1 to 0.2 k_B/atom, which is comparable to the typical values of
configurational entropy differences in binary alloys (at most 0.693 k_B/atom).
This paper describes the basic formalism underlying ab initio phase diagram
calculations, along with the generalization required to account for lattice
vibrations. We overview the various techniques allowing the theoretical
calculation and the experimental determination of phonon dispersion curves and
related thermodynamic quantities, such as vibrational entropy or free energy. A
clear picture of the origin of vibrational entropy differences between phases
in an alloy system is presented that goes beyond the traditional bond counting
and volume change arguments. Vibrational entropy change can be attributed to
the changes in chemical bond stiffness associated with the changes in bond
length that take place during a phase transformation. This so-called ``bond
stiffness vs. bond length'' interpretation both summarizes the key phenomenon
driving vibrational entropy changes and provides a practical tool to model
them.Comment: Submitted to Reviews of Modern Physics 44 pages, 6 figure
Treatment with class a CpG oligodeoxynucleotides in cats with naturally occurring feline parvovirus infection: A prospective study
Feline parvovirus (FPV) causes severe gastroenteritis and leukopenia in cats; the outcome is poor. Information regarding specific treatments is lacking. Class A CpG oligodeoxynucleotides (CpG-A) are short single-stranded DNAs, stimulating type I interferon production. In cats, CpG-A induced an antiviral response in vivo and inhibited FPV replication in vitro. The aim was to prospectively investigate the effects of CpG-A on survival, clinical score, hematological findings, antiviral response (cytokines), viremia, and fecal shedding (real-time qPCR) in cats naturally infected with FPV. Forty-two FPV-infected cats were randomized to receive 100 g/kg of CpG-A (n = 22) or placebo (n = 20) subcutaneously, on admission and after 48 h. Blood and fecal samples were collected on admission, after 1, 3, and 7 days. All 22 cats showed short duration pain during CpG-A injections. The survival rate, clinical score, leukocyte and erythrocyte counts, viremia, and fecal shedding at any time-point did not differ between cats treated with CpG-A (50%) and placebo (40%). Antiviral myxovirus resistance (Mx) gene transcription increased in both groups from day 1 to 3 (p = 0.005). Antibodies against FPV on admission were associated with survival in cats (p = 0.002). In conclusion, CpG-A treatment did not improve the outcome in cats with FPV infection. FPV infection produced an antiviral response
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