174 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
Synthesis, Analytical and Theoretical Studies of (Z)-4-amino-3-hydroxy-2-((4-(N-(5-methylisoxazol-3-yl)Sulfamoyl)Phenyl)Diazenyl)Naphthalene-1-Sulfonic Acid
New azodye that characterize (Z)-4-amino-3-hydroxy-2-((4-(N-(5-methylisoxazol-3-yl) sulfamoyl) phenyl)diazenyl)naphthalene-1-sulfonic acid (1) was synthesized. The azodye has been characterized by IR, visible spectra and elemental (CHN) analysis. The results of visible spectra which recorded in the range (360-6540) nm were showed that the maximum wave length (λmax) of azodye was 500 nm. Analytical studies carried on the dye, the results of the solvent effect were showed high solubility in ethanol and water. But, the results of the pH effect in a range of buffer solution were gave three isopestic points. The ionization constant (pKa) and protonation constant (pKb) were calculated by using the half height method. The results were showed that the pKp1 and pKp2 of each nitrogen atom and pKa of OH-group were equal to 2.5, 4.5 and 8.5 respectively. Theoretical studies also carried on azodye (1). The actual and optimal bonds length of -N=N- was equal to 1.248 in each. Though, internal coordinate mechanics (ICM) of (1) was showed that the angle type in most of atoms was dihedral. But, the R and S configuration were observed in other atoms in the structure of azodye. The results also indicated that the torsion angles (ψ) of (1) were variable. High close contacts of atoms were observed in the structure of azodye. The molecular mechanics (MM2) properties was intended for (1), the results showed that the stretch, bend, stretch-bend, torsion, non-1,4 VDW, 1,4 VDW and the total energy were equal to 61.0809, 627.0240, -1.6517, 179.0634, 4686.8146, 33.0379 and 5585.3692 kcal/mol respectively. High VDW interactions of this molecule was observed, due to the results of dipole/dipole were not computed. Thus, the result of MM2 minimization for azodye (1) was showed high VDW interactions of this molecule higher than before the minimization, due to the result of dipole/dipole was also not computed. The high steric energy (1235.782) was affecting the results of minimization. However, the results of the molecular mechanics force field (MMFF94) energy and gradient for azodye (1) were showed that the total energy and RMS gradient were equal to 26223.422 kcal/ mol and 9113.745 respectively. Further, the results of MMFF94 minimization and MMFF94 minimization/sampling of azodye (1) were showed that the minimization was attended successfully using this method. Keywords: Internal coordinate, Molecular mechanics, Azodye
Overview of the CLEF-2019 Checkthat! LAB: Automatic identification and verification of claims. Task 2: Evidence and factuality
We present an overview of Task 2 of the second edition of the CheckThat! Lab at CLEF 2019. Task 2 asked (A) to rank a given set of Web pages with respect to a check-worthy claim based on their usefulness for fact-checking that claim, (B) to classify these same Web pages according to their degree of usefulness for fact-checking the target claim, (C) to identify useful passages from these pages, and (D) to use the useful pages to predict the claim's factuality. Task 2 at CheckThat! provided a full evaluation framework, consisting of data in Arabic (gathered and annotated from scratch) and evaluation based on normalized discounted cumulative gain (nDCG) for ranking, and F1 for classification. Four teams submitted runs. The most successful approach to subtask A used learning-to-rank, while different classifiers were used in the other subtasks. We release to the research community all datasets from the lab as well as the evaluation scripts, which should enable further research in the important task of evidence-based automatic claim verification
Magnetic response of core-shell cobalt ferrite nanoparticles at low temperature
Cobaltferritenanoparticles (size: 26±4nm) have been synthesized by coprecipitation route. The coercivity of nanoparticles follows a simple model of thermal activation of particle moments over the anisotropy barrier in the temperature range of 30–300K in accordance with Kneller’s law; however, at low temperatures
EveTAR: Building a Large-Scale Multi-Task Test Collection over Arabic Tweets
This article introduces a new language-independent approach for creating a
large-scale high-quality test collection of tweets that supports multiple
information retrieval (IR) tasks without running a shared-task campaign. The
adopted approach (demonstrated over Arabic tweets) designs the collection
around significant (i.e., popular) events, which enables the development of
topics that represent frequent information needs of Twitter users for which
rich content exists. That inherently facilitates the support of multiple tasks
that generally revolve around events, namely event detection, ad-hoc search,
timeline generation, and real-time summarization. The key highlights of the
approach include diversifying the judgment pool via interactive search and
multiple manually-crafted queries per topic, collecting high-quality
annotations via crowd-workers for relevancy and in-house annotators for
novelty, filtering out low-agreement topics and inaccessible tweets, and
providing multiple subsets of the collection for better availability. Applying
our methodology on Arabic tweets resulted in EveTAR , the first
freely-available tweet test collection for multiple IR tasks. EveTAR includes a
crawl of 355M Arabic tweets and covers 50 significant events for which about
62K tweets were judged with substantial average inter-annotator agreement
(Kappa value of 0.71). We demonstrate the usability of EveTAR by evaluating
existing algorithms in the respective tasks. Results indicate that the new
collection can support reliable ranking of IR systems that is comparable to
similar TREC collections, while providing strong baseline results for future
studies over Arabic tweets
Effect of Reducing Atmosphere on the Magnetism of Zn1-xCoxO Nanoparticles
We report the crystal structure and magnetic properties of Zn1-xCoxO
nanoparticles synthesized by heating metal acetates in organic solvent. The
nanoparticles were crystallized in wurtzite ZnO structure after annealing in
air and in a forming gas (Ar95%+H5%). The X-ray diffraction and X-ray
photoemission spectroscopy (XPS) data for different Co content show clear
evidence for the Co+2 ions in tetrahedral symmetry, indicating the substitution
of Co+2 in ZnO lattice. However samples with x=0.08 and higher cobalt content
also indicate the presence of Co metal clusters. Only those samples annealed in
the reducing atmosphere of the forming gas, and that showed the presence of
oxygen vacancies, exhibited ferromagnetism at room temperature. The air
annealed samples remained non-magnetic down to 77K. The essential ingredient in
achieving room temperature ferromagnetism in these Zn1-xCoxO nanoparticles was
found to be the presence of additional carriers generated by the presence of
the oxygen vacancies.Comment: 11 pages, 6 figures, submitted to Nanotechnology IO
Synthesis and Biological Activity of Three Novel Azo Dyes
The azo dyes that named, (E)-4-((2-nitrophenyl) diazenyl) benzene-1,3-diol (1), (E)-4- ((3-nitrophenyl) diazenyl) benzene-1,3-diol (2) and (E)-4-((4-nitrophenyl) diazenyl) benzene-1,3-diol (3) were synthesized and then characterized using IR, UV-visible spectrum. These results were compared with that obtained by ChemBio 3D Ultra - [Chem3D XML] Gaussian Interface and were seems to be identical. Then, the antimicrobial activity of each azo dye was carried out against two bacterial strains: Staphylococcus aureus NCTC 6571, and Escherichia coli ATCC 25922, and fungal strains of Candida albicans using Agar-well diffusion method. The results were showed that the three azo dyes were biologically active and the best reactivity was observed in (2). Though, the biological activity of (1) with NO2 group in ortho- position remained reasonable against Candida albicans. But, the effect of (1) was resisted by Staphylococcus aureus and Escherichia coli. However, the (2) and (3) with substituted NO2 group in meta- and para- positions respectively were showed better reactivity’s than (1) towered Candida albicans and Staphylococcus aureus. Further, the Gaussian interface properties and the conformational analysis of (1), (2) and (3) were intended. The results were indicated that the variations in the properties of each azo dye and their conformational energies of generated conformers can affect their biological activity afterward. Keywords: key words, Azo dyes, Staphylococcus aureus, Escherichia coli, Candida albicans, Agar-well diffusion method, Antimicrobial activit
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