Thermoelectric properties of the welded Cu/Bi<Subscript>0.88</Subscript> Sb<Subscript>0.12</Subscript> /Cu composites in the temperature region from 193 K to 298 K

The resultant thermoelectric properties of Cu/T/Cu composites welded with alloy were measured in the temperature range from T = 193 K to 298 K and compared with those calculated as a function of x by treating these composites as an electrical and thermal circuit, where x is the ratio of thickness of Bi–Sb alloy to the interval between two thermocouples. Consequently, the resultant electrical resistivities ρ of composites coincided closely with the calculated ρ values as a function of x, while the resultant Seebeck coefficients α were enhanced significantly in the range from x=0.076 to 0.61. In the x range from 0.16 to 1.0, the x-dependence of the resultant thermoelectric power factor P was found to be explained roughly at every temperature by the simple model proposed here when an enhancement factor in α was taken into the calculation. However, the maximum resultant P appeared at a small x of 0.076. The resultant P at x = 0.076 increases with a decrease of T and reached a surprisingly great value of 128.3 mW/K² m at 193 K, which is 15.5 times larger than 8.29 mW/K² m obtained for Bi_0.88Sb_0.12 alloy. On the other hand, its resultant ZT also increases monotonically with a decrease of T and has a great value of 0.54 at 193 K, which is 31% higher than 0.41 at 193 K for Bi–Sb alloy. The significant enhancement in the resultants P and ZT at low temperatures is owing predominantly to the increase in α due to the boundary effect.     

Revisiting the concept of the ‘problem young driver’ within the context of the ‘young driver problem’: Who are they?

For decades there have been two young driver concepts: the ‘young driver problem’ where the driver cohort represents a key problem for road safety; and the ‘problem young driver’ where a sub-sample of drivers represents the greatest road safety problem. Given difficulties associated with identifying and then modifying the behaviour of the latter group, broad countermeasures such as graduated driver licensing (GDL) have generally been relied upon to address the young driver problem. GDL evaluations reveal general road safety benefits for young drivers, yet they continue to be overrepresented in fatality and injury statistics. Therefore it is timely for researchers to revisit the ‘problem young driver’ concept to assess its potential countermeasure implications. This is particularly relevant within the context of broader countermeasures that have been designed to address the ‘young driver problem’ Personal characteristics, behaviours and attitudes of 378 Queensland novice drivers aged 17–25 years were explored during their pre-, Learner and Provisional 1 (intermediate) licence as part of a larger longitudinal project. Self-reported risky driving was measured by the Behaviour of Young Novice Drivers Scale (BYNDS), and five subscale scores were used to cluster the drivers into three groups (high risk n = 49, medium risk n = 163, low risk n = 166). High risk ‘problem young drivers’ were characterised by greater self-reported pre-Licence driving, unsupervised Learner driving, and speeding, driving errors, risky driving exposure, crash involvement, and offence detection during the Provisional period. Medium risk drivers were also characterised by more risky road use than the low risk group. Interestingly problem young drivers appear to have some insight into their high-risk driving, since they report significantly greater intentions to bend road rules in future driving. The results suggest that tailored intervention efforts may need to target problem young drivers within the context of broad countermeasures such as GDL which address the young driver problem in general. Experiences such as crash-involvement could be used to identify these drivers as a preintervention screening measure.     

Experimental investigation on the influence of the presence of alkali compounds on the performance of a commercial Pt–Pd/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> diesel oxidation catalyst

Experimental investigation was conducted on the influence of the presence of alkali compounds such as K and Na present in biofuels on catalytic behaviors of a commercial diesel oxidation catalyst (Pt/Pd/Al₂O₃) in the monolith form. Doping of different alkali metal components on carrots of monolith was performed. These carrots were physicochemically characterized, and the catalytic tests consisted of series of temperature-programmed surface reactions with representative exhaust gas mixtures from diesel combustion. The aim of the present study is to reveal the effect of the alkali metal on overall catalytic activity of diesel oxidation catalyst (DOC) and more particularly to show their influence on the reactions involving CO, hydrocarbons, NO, and NO₂. Potassium and sodium lead to different catalytic properties. A promotion effect was found in the presence of K, whereas an inhibiting effect was evidenced in the presence of Na or when both Na and K were doped onto the DOC.     

Structural transformation and magnetic properties of CaMn1 − xFexO3 − δ (0.0 ≤ x ≤ 0.5)

We have investigated the structural and magnetic properties of CaMn_1 − xFe_xO_3 − δ (0.0 ≤ x ≤ 0.5). Solid state method is used for the synthesis of these samples. Sintering of these compositions at 1300 °C stabilizes higher ionic radii Fe^+ 3 (0.645 Å) at Mn^+ 4 (0.53 Å) site in CaMn_1 − xFe_xO_3 − δ. Structural transformation from orthorhombic to tetragonal to pseudo cubic crystal system and the increase in lattice parameters have been observed with the substitution of Fe at Mn site in CaMn_1 − xFe_xO_3 − δ (0.0 ≤ x ≤ 0.5). The magnetization data show the transformation of G type of antiferromagnetic arrangement of Mn^+ 4 electrons spins in CaMnO₃ into paramagnetic spin type arrangement with the substitution of Fe at Mn site. The compositions x = 0.05, x = 0.1and x = 0.2 show a small kink ~ 100 K in the magnetization data, which resulted due to the competition between antiferromagnetic and paramagnetic states with the Fe substitution.     

Study on the chemical stability of Y-doped BaCeO3 − δ and BaZrO3 − δ films deposited by aerosol deposition

Barium cerate (BaCeO₃) has high proton conductivity but rather poor chemical stability in CO₂-containing atmospheres. Barium zirconate (BaZrO₃), in contrast, is a rather stable material, but exhibits poor sinterability. In the present work, powders of Y-doped BaCeO₃ and BaZrO₃ were synthesized via the solid solution reaction method, and dense ceramic membranes with BaCe_0.9Y_0.1O₃ and BaZr_0.85Y_0.15O₃ were prepared by the aerosol deposition method at room temperature. Aerosol deposition method is a technique that enables the fabrication of ceramic films at room temperature with a high deposition rate as well as strong adhesion to the substrate. The powders and aerosol-deposited membranes were characterized by X-ray diffraction, particle size analysis, scanning electron microscopy, and X-ray elemental mapping. The chemical stability of powders and aerosol-deposited membranes with BaCe_0.9Y_0.1O₃ and BaZr_0.85Y_0.15O₃ against water and carbon dioxide has been investigated, and it was found that BaZr_0.85Y_0.15O₃ materials showed a better chemical compatibility.     

Microstructural characterization of Ce1−xTbxO2−δ (0.60 ≤ x ≤ 0.90) sintered samples

To understand the secondary phase formation in ceria based oxide, the microstructure need to be studied in a wide compositional range. However, in most previous studies, the doping concentration is lower than 50 at.%. In this work, the microstructure of Ce_1−xTb_xO_2−δ sintered samples with Tb concentrations of 0.60 ≤ x ≤ 0.90 were investigated by using X-ray diffraction (XRD) and transmission electron microscopy (TEM). Besides the fluorite-structured matrix, a secondary phase with a superstructure formed from a structural modulation of the fluorite structure along [1 1 0] and [0 0 1] directions was observed, whose amount and size reached a maximum at x = 0.90. It has a cubic structure with a lattice constant twice as large as that of the fluorite-structured matrix.     

The systematic errors of the measurement of the parameters of low-frequency noise with a 1/<Emphasis Type="Italic">f</Emphasis><Superscript>γ</Superscript> spectrum

Recommendations are made for choosing the optimum parameters of a procedure for measuring the spectral power density of noise G(f) for problems of the nondestructive quality control of electronic equipment as regards the parameters of low-frequency noise. Expressions are derived for the systematic error in determining the exponent in the frequency dependence G(f) from single measurements of the noise at two frequencies. Translated from Izmeritel’naya Tekhnika, No. 10, pp. 51–53, October, 2008.     

Dielectric properties of Ba3−xKxCaNb2O9−δ (0.5 < x < 1.25) (KBCN) double perovskites

We report synthesis, structure and dielectric properties of double perovskite-type Ba_3−xK_xCaNb₂O_9−δ (x = 0.5, 0.75, 1, 1.25) (KBCN). Powder X-ray diffraction (XRD) confirmed the formation of double perovskite-type structure and lattice constant decreases with increasing K in KBCN. AC impedance study showed a single semicircle over the investigated temperatures and frequencies in dry H₂, H₂ + 3% H₂O, 3% H₂O + N₂, while two semicircles were observed at low temperatures in air, which could be attributed to bulk and grain-boundary contributions. Unlike un-doped BCN, KBCN exhibits negligible grain-boundary and electrode effects to the total electrical properties and is consistent with perovskite-type K-doped BaZrO₃. The bulk dielectric constant and dielectric loss were found to increase with increasing K content in KBCN and also found to change with sintering temperature. Among the samples investigated, Ba_1.75K_1.25CaNb₂O_9−δ sintered at 1100 °C showed the highest dielectric constant of 65 at 10⁶ Hz and dielectric loss of 0.14 at 400 °C in air. Isothermal dielectric constant and electrical conductivity at 1 MHz were found to be independent at elevated temperatures, while vary at low-frequency and low temperatures. Below 700 °C, dielectric constant and dielectric loss decreases with increasing frequency, whereas an opposite trend was observed for the electrical conductivity.     

分数阶PIλDμ控制器参数λ和μ分析

针对分数阶PI^λD^μ控制器的积分阶次λ和微分阶次μ在0<λ,μ<2的范围内变化时,对分数阶控制系统的影响进行了频率特性和阶跃响应分析,给出了阶次取值的合理范围。首先采用分数阶微积分方程的数值解法,对分数阶闭环控制系统进行数值计算,且其中的分数阶微积分算子用近似计算公式来代替。然后分别采用分数阶PI^λ控制器和分数阶PD^μ控制器当积分阶次λ和微分阶次μ变化时,利用Bode图从频率特性和单位阶跃响应两方面分别对其性能进行分析,频率特性分析与实际阶跃响应的结果一致,表明分数阶PIλDμ控制器的积分阶次λ和微分阶次μ均有一较佳的取值范围。     

The mechanism of the failure of the dispersion-strengthened Cu–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanosystem

The method of “in situ tensile testing in SEM” is suitable for investigations of fracture mechanisms because it enables to observe and document deformation processes directly, thank to which the initiation and development of plastic deformation and fracture can be reliably described. The deformation and fracture mechanisms of Cu–Al₂O₃ nanomaterials with 5 vol.% of Al₂O₃ phase has been analyzed using technique of the “in situ tensile testing in SEM.” It has been shown that the deformation process causes break-up of large Al₂O₃ particles and decohesion of smaller ones. The final fracture path is influenced also by boundaries of nanograins, through which the principal crack propagates towards the sample exterior surface. Based on the experimental observations, a model of damage and/or fracture mechanisms has been proposed.     

Effect of the Mn/Fe Ratio on the Microstructure and Magnetic Properties in the Powder Form (Fe<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>)<Subscript>2</Subscript>P System

The structure, morphology, and magnetic properties of the mechanically alloyed iron manganese phosphides (Fe_1?x Mn _x )₂P with 0.15 ≤ x ≤ 0.75 (Mn/Fe ratio = 0.17, 0.33, 0.66, and 3) have been studied by means of X-ray diffraction, scanning electron microscopy coupled with energy-dispersive X-ray spectrometry, and BS1 and BS2 magnetometry. The powder form (Fe_1?x Mn _x )₂P compounds exhibit multiphase structures that contain Fe(Mn)-type solid solution and Fe₂P-type, Mn₂P-type, Fe₃P-type, and MnP/FeP-type phosphides. The magnetization versus temperature reveals the existence of multiple magnetic phase transitions. The saturation magnetization, coercivity, and squarness M _r/M _s ratio values are discussed as a function of both the Mn content and the temperature. From the approach to saturation magnetization studies, several fundamental magnetic parameters were extracted. The local magnetic anisotropy constant K ₁ was determined.     

Significant improvement of the oxygen permeation flux of tubular Ba0.5Sr0.5Co0.8Fe0.2O3 − δ membranes covered by a thin La0.6Sr0.4Ti0.3Fe0.7O3 − δ layer

We present a new method to improve the oxygen flux properties and stability of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3 − δ tube membrane using a thin layer of La_0.6Sr_0.4Ti_0.3Fe_0.7O_3 − δ as protective coatings. The first relevant result is that the La_0.6Sr_0.4Ti_0.3Fe_0.7O_3 − δ protective layer had an extraordinary positive effect on improving the oxygen permeation flux of the tubular Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3 − δ membranes. La_0.6Sr_0.4Ti_0.3Fe_0.7O_3 − δ-coated Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3 − δ tubular membrane showed the highest oxygen permeability with the flux reaching ~ 3 ml cm⁻² min⁻¹ (oxygen purity > 99%) at 950 °C in static atmospheric pressure through a 1.0 mm thick membrane.     

Properties of superconducting, polycrystalline dysprosium-doped Bi1.6Pb0.5Sr2−xDyxCa1.1Cu2.1O8+δ (0 ≤ x ≤ 0.5)

The structural and superconducting properties of dysprosium (Dy) doped (Bi,Pb)-2212 superconductor have been studied. Dy concentration is varied from x = 0.0 to 0.5 in a general stoichiometry of Bi_1.6Pb_0.5Sr_2−xDy_xCa_1.1Cu_2.1O_8+δ. It is found that the Dy atoms enter into the crystal structure by replacing Sr atoms and induce significant change in lattice parameter, microstructure, hole-concentration and normal state conductivity of the system. The critical temperature (T_C) and critical current density (J_C) at self-field of the Dy-doped samples enhance considerably at optimum doping levels. Maximum T_C of 92.3 K (for x = 0.4) and J_C of 1390 A/cm² at 64 K (for x = 0.2) are observed for doped samples as against 79.4 K and 127 A/cm², respectively, for the pure sample. The results are discussed on the basis of the change in hole-concentration due to Dy-doping at Sr-site of (Bi,Pb)-2212 superconductor.     

High-temperature heat capacity of the oxide compounds in the Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–V<Subscript>2</Subscript>O<Subscript>5</Subscript> system

The compounds BiVO₄, Bi₄V₂O₁₁, and Bi₁₂V₂O₂₃ have been prepared by solid-state synthesis using stoichiometric mixtures of Bi₂O₃ and V₂O₅. The effect of temperature on the heat capacity of the synthesized bismuth vanadates has been studied by differential scanning calorimetry in the range 350–950 K. The C _p (T) curves have extrema at 531.7 K for BiVO₄ and at 725.2 and 852.8 K for Bi₄V₂O₁₁, which are due to polymorphic transformations of these compounds.     

Phase transitions in Sr1 + xCo0.8Fe0.2O3 − δ oxides

The phase transitions that take place in Sr_1 + xCo_0.8Fe_0.2O_3 − δ (− 0.2 ≤ x ≤ 0.1) oxides are reported here. Thermogravimetric analysis (TGA) showed that the oxides with − 0.2 ≤ x ≤ 0 were prone to undergo oxygen-vacancy disorder-order phase transitions, while others with x = 0.05, 0.1 had more stable crystal structures during oxygen-desorption processes in nitrogen. These results were further confirmed by high-temperature in-situ X-ray techniques. The changes in activation energies of three typical oxides, Sr_1 + xCo_0.8Fe_0.2O_3 − δ (x = − 0.2, 0, 0.1), used as oxygen-permeable membranes were investigated. The phase transitions in Sr_1 + xCo_0.8Fe_0.2O_3 − δ (x = − 0.2, 0) have also been detected in differential scanning calorimetry (DSC) profiles.     

Effect of the ZrO<Subscript>2</Subscript> concentration on the crystallization behavior and the mechanical properties of high-strength MgO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> glass–ceramics

High-strength, colorless glass–ceramics in the MgO/Al₂O₃/SiO₂ system with high concentrations of ZrO₂ and a great potential for technical application, e.g., as high-performance hard disc substrates, are investigated. ZrO₂ concentrations from 6 to 9 mol% are added to a stoichiometric cordierite glass to investigate the influence of the concentration of the nucleating agent on the crystallization behavior and the mechanical properties. The phase formation and the microstructure of the glass–ceramics are studied using X-ray diffraction and scanning electron microscopy including electron backscatter diffraction. It is shown that the volume crystallization of ZrO₂, a low-/high-quartz solid solution (low-/high-QSS), and spinel is accompanied by the surface crystallization of indialite. This phase offers a much smaller coefficient of thermal expansion than the other crystal phases, which may induce high compressive stresses in the surface layer of the glass–ceramics after cooling and seems to result in excellent mechanical properties of the material. Biaxial flexural strengths of up to 1 GPa were measured. Higher ZrO₂ concentrations reduce the surface crystallization of indialite and decrease the mean size of the crystals resulting in a higher translucency. The volume-crystallizing phases and the mechanical properties of the glass–ceramics do not seem to be significantly affected by the analyzed ZrO₂ concentrations.     

Synthesis, structure and oxygen-storage capacity of Pr1−xZrxO2−δ and Pr1−x−yPdyZrxO2−δ

Nanocrystalline Pr_1−xZr_xO_2−δ (0 ≤ x ≤ 1) and Pr_1−x−yPd_yZr_xO_2−δ (x = 0.50, y = 0.02) solid solutions have been synthesized by a single step solution combustion method. The whole range of solid solution compositions crystallize in cubic fluorite structure. The lattice parameter ‘a’ linearly varied up to x = 1.0. Oxygen-storage capacity (OSC) and redox properties of Pr_1−xZr_xO_2−δ (0.0 ≤ x ≤ 0.8) solid solutions have been investigated by temperature-programmed reduction (TPR) and are compared with those of Ce_1−xZr_xO₂. Pr_1−xZr_xO_2−δ exhibited H₂ uptake and CO oxidation at a lower temperature than Ce_1−xZr_xO₂. Small amount of Pd ion (y = 0.02) substitution was found to bring down the temperature of oxygen release-storage significantly.     

Effect of Cu doping and oxygen-annealing on the magnetic properties of Nd0.5Sr0.5Mn1−xCuxO3−δ (x = 0.0, 0.01, 0.03, 0.05 and 0.10)

The polycrystalline samples with nominal compositions Nd_0.5Sr_0.5Mn_1−xCu_xO₃ (x = 0.0, 0.01, 0.03, 0.05 and 0.10) have been synthesized with the aim to study the change in the structural, magnetic and electrical properties due to substitution of Cu for Mn and oxygen-annealing. The temperature dependence magnetization measurement shows a charge ordering transition (T_CO) at 240 K in Nd_0.5Sr_0.5Mn0₃ sample. The Neel temperature (T_N) increases with increasing the Cu doping content but changes induced by even 0.1 Cu doping are quite small. As compared to the air sintered samples, higher values of T_N are observed for the oxygen annealed samples. Furthermore, oxygen annealing enhances the magnetization of the samples. It is also found that T_C increases and T_N decreases with increase in the applied magnetic-?eld. The value of resistivity decreases with the increasing Cu content from x = 0.0 to x = 0.03 and afterwards it increases with increasing value of x up to 0.10 for both air and oxygen sintered samples. It is also found that oxygen annealed samples exhibit higher resistivity than the air sintered samples. In the present paper the results are discussed according to the change of magnetic exchange interaction caused by Cu-doping. It is also found that the amount of Mn⁴⁺ appears to be the main variable which in?uences the physical properties.     

Influence of the Substrate Layer on the Lightning Current Performance of YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7−δ</Subscript> Tapes

In a power grid, the superconducting power devices might also experience lightning impulse current except for the common over-currents. However, the study of the performance of YBCO tapes suffering a lightning current is scarcely reported. This paper mainly focuses on the influence of the substrate layer on the thermal stability of YBCO tapes suffering a lightning current. A numerical model which took into account both the thermal and the electromagnetic aspects was proposed. The validity of this model was verified by experiment. Based on this model, the influence of the dimension and material type of thesubstrate layer on the thermal stability were investigated in detail. The simulated results showed that the substrate layer could affect the temperature distribution on different layers, and stainless steel substrate layer is a more desired choice for decreasing the maximum temperature. Moreover, a theoretical explanation based on a simplified equivalent circuit was also used to study the influence of the substrate layer.