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Contribution of on-site Coulomb repulsion energy to structural, electronic and magnetic properties of SrCoO3 for different space groups: first-principles study

Abstract

We report structural, electronic, and magnetic properties of SrCoO3 in Pm3̅m and P4/mbm space groups, which are calculated by using generalized gradient approximation corrected with on-site Coulomb repulsion U and exchange energies J. The cubic lattice parameter a and local magnetic moments of Co (μCo) are optimized by varying U at Co 3d site. Employing ultrasoft pseudopotential, the values of U = 8 eV and J = 0.75 eV are the best choice for Pm3̅m space group. We found the value of μCo = 2.56 μB, which is consistent with the previous results. It was also found that Co 3d, hybridized with O 2p, is the main contributor to ferromagnetic metallic properties. Besides, norm-conserving pseudopotential promotes a, which is in good agreement with experimental result. However, it is not suitable for P4/mbm space group. By using ultrasoft pseudopotential, the value of U = 3 eV (J = 0.75) is the most suitable for P4/mbm group. Ferromagnetic metallic properties, Jahn-Teller distortion, and reasonable lattice parameters have been obtained. This study shows that U has significant contribution to the calculated properties and also points out that P4/mbm space group with US-PP is suitable to describe experimental results.

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Structural and optical characterization of annealed As30Te60Ga10 thin films prepared by thermal evaporation technique

Abstract

Effect of annealing temperature on the structural and optical properties of As30Te60Ga10 thin film was studied using various techniques such as differential scanning calorimetry (DSC), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The DSC analysis revealed that the As30Te60Ga10 glass has a single glass transition and crystallization peak while XRD results confirmed that the as-prepared and annealed films have crystalline nature. The coexistence of the crystalline phases in the investigated films could be attributed to the formation of orthorhombic As, hexagonal Ga7Te10, and monoclinic As2Te3 phases. It was found that the average crystallite size and optical parameters of the studied films depend on the annealing temperature. For example, the optical band gap decreased from 1.54 eV to 1.11 eV as the annealing temperature increased from 300 K to 433 K.

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Influence of magnetron powering mode on various properties of TiO2 thin films

Abstract

In this paper, comparative studies on the structural, surface, optical, mechanical and corrosion properties of titanium dioxide (TiO2) thin films deposited by continuous and sequential magnetron sputtering processes were presented. In case of continuous process, magnetron was continuously supplied with voltage for 90 min. In turn, in sequential process, the voltage was supplied for 1 s alternately with 1 s break, therefore, the total time of the process was extended to 180 min. The TiO2 thin films were crack free, exhibited good adherence to the substrate and the surface morphology was homogeneous. Structural analysis showed that there were no major differences in the microstructure between coatings deposited in continuous and sequential processes. Both films exhibited nanocrystalline anatase structure with crystallite sizes of ca. 21 nm. Deposited coatings had high transparency in the visible wavelength range. Significant differences were observed in porosity (lower for sequential process), scratch resistance (better for sequential process), mechanical performance, i.e. hardness:elastic modulus ratio (higher for sequential process) and corrosion resistance (better for sequential process).

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A geometric approach to structural model matching by output feedback in linear impulsive systems

Abstract

This paper provides a complete characterization of solvability of the problem of structural model matching by output feedback in linear impulsive systems with nonuniformly spaced state jumps. Namely, given a linear impulsive plant and a linear impulsive model, both subject to sequences of state jumps which are assumed to be simultaneous and measurable, the problem consists in finding a linear impulsive compensator that achieves exact matching between the respective forced responses of the linear impulsive plant and of the linear impulsive model, by means of a dynamic feedback of the plant output, for all the admissible input functions and for all the admissible sequences of jump times. The solution of the stated problem is achieved by reducing it to an equivalent problem of structural disturbance decoupling by dynamic feedforward. Indeed, this latter problem is formulated for the so-called extended linear impulsive system, which consists of a suitable connection between the given plant and a modified model. A necessary and sufficient condition for the solution of the structural disturbance decoupling problem is first shown. The proof of sufficiency is constructive, since it is based on the synthesis of the compensator that solves the problem. The proof of necessity is based on the definition and the geometric properties of the unobservable subspace of a linear impulsive system subject to unequally spaced state jumps. Finally, the equivalence between the two structural problems is formally established and proven.

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Use of MgO to Promote the Oxyethylation Reaction of Lauryl Alcohol

Abstract

Synthesis of magnesium hydroxide was performed by the precipitation method with the use of magnesium sulfate and sodium hydroxide. The infiuence of temperature and ratio of reagents was studied. Magnesium hydroxides, and the magnesium oxides obtained from them by thermal decomposition, were analyzed to determine their bulk density, polydispersity and particle size. The magnesium oxide with the largest surface area was tested as a catalyst in the oxyethylation of lauryl alcohol, and shown to be selective but poorly reactive in comparison with commercially available catalysts. Further studies are needed to improve its reactivity.

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Anomalous structural properties of some RCu2Ge2 compounds (R = La, Gd-Tm)

Abstract

In this paper, we address the issue of possible quadrupole ordering in RCu2Ge2 compounds. In the literature, there are reports on anomalous behaviour of lattice parameters, however, lack of high quality data makes the relevant analysis dubious. Therefore, we attempt to perform precise, non-ambient XRD measurements within 12–300 K temperature range. Our results confirm peculiar temperature behaviour of the c-lattice parameter that exhibits a well defined minimum at about 60–120 K for majority of investigated compounds. However, in contrast to the literature, the anomalous behaviour does not exhibit discontinuities. On the other hand, such behaviour has been evidenced for La-based compounds (LaCu2Ge2 and LaNi2Ge2), where the 4f orbitals are unoccupied.

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Synthesis and study of structural properties of Sn doped ZnO nanoparticles

Abstract

Pure and Sn-doped ZnO nanostructures were synthesized by simple chemical solution method. In this method we used zinc nitrate and NaOH as precursors. Sn doping content in ZnO was taken with the ratio 0, 5, 10, 15 and 20 percent by weight. Physical properties of Sn-doped ZnO powder were studied by XRD analysis which revealed that Sn doping had a significant effect on crystalline quality, grain size, intensity, dislocation density and strain. The calculated average grain size of pure ZnO was 21 nm. The best crystalline structure was found for 0 wt.%, 5 wt.% and 10 wt.% Sn doping as observed by FESEM and XRD. However, higher Sn-doping (> 10 wt.%) degraded the crystallinity and the grain size of 27.67 nm to 17.76 nm. The structures observed in FESEM images of the samples surfaces were irregular and non-homogeneous. EDX depicted no extra peak of impurity and confirmed good quality of the samples.

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Intelligence via ultrafilters: structural properties of some intelligence comparators of deterministic Legg-Hutter agents

Abstract

Legg and Hutter, as well as subsequent authors, considered intelligent agents through the lens of interaction with reward-giving environments, attempting to assign numeric intelligence measures to such agents, with the guiding principle that a more intelligent agent should gain higher rewards from environments in some aggregate sense. In this paper, we consider a related question: rather than measure numeric intelligence of one Legg-Hutter agent, how can we compare the relative intelligence of two Legg-Hutter agents? We propose an elegant answer based on the following insight: we can view Legg-Hutter agents as candidates in an election, whose voters are environments, letting each environment vote (via its rewards) which agent (if either) is more intelligent. This leads to an abstract family of comparators simple enough that we can prove some structural theorems about them. It is an open question whether these structural theorems apply to more practical intelligence measures.

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Annealing and Ni content effects on EPR and structural properties of Zn1–xNixO aerogel nanoparticles

Abstract

Zn1-xNixO aerogel nanopowders with nickel concentration in the range of 0.05 ≤ x ≤ 0.25, were synthesized by the sol-gel processing technique and post-annealed in air at 500 °C. Structural, vibrational, thermal and magnetic properties of the as-prepared and annealed Zn1-xNixO powdered samples were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman scattering, thermal gravimetric analysis (TGA) and electron paramagnetic resonance (EPR) spectroscopy. In addition to the ZnNiO phase, XRD analysis revealed the formation of a secondary NiO phase when the Ni content was greater than or equal to 10 %. The TEM images confirm that the particle size is in the range of 20 nm to 40 nm, in accordance with XRD results, and the particles are well dispersed. Raman scattering measurements confirm the wurtzite structure of the synthesized Zn1-xNixO nanopowders and show that intrinsic host-lattice defects are activated when Ni2+ ions are substituted to the Zn sites. Room temperature ferromagnetic order was observed in all of the samples and was strongly dependent on the Ni content and thermal annealing. These results indicate that the observed room temperature ferromagnetism in ZnNiO may be attributed to the substitutional incorporation of Ni at Zn sites.

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Test signal generation for service diagnosis based on local structural properties

Test signal generation for service diagnosis based on local structural properties

The paper presents a new approach to the generation of test signals used in service diagnosis. The tests make it possible to isolate faults, which are isolable only if the system is brought into specific operating points. The basis for the test signal selection is a structure graph that represents the couplings among the external and internal signals of the system and the fault signals. Graph-theoretic methods are used to identify edges that disappear under certain operating conditions and prevent a fault from changing the system behavior at this operating point. These operating conditions are identified by validuals, which are indicators obtained during the graph-theoretic analysis. The test generation method is illustrated by a process engineering example.

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