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1.
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 Bi0.88Sb0.12 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.  相似文献   

2.
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.  相似文献   

3.
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.  相似文献   

4.
We have investigated the structural and magnetic properties of CaMn1 − xFexO3 − 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 CaMn1 − xFexO3 − 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 CaMn1 − xFexO3 − 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.  相似文献   

5.
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 BaCe0.9Y0.1O3 and BaZr0.85Y0.15O3 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 BaCe0.9Y0.1O3 and BaZr0.85Y0.15O3 against water and carbon dioxide has been investigated, and it was found that BaZr0.85Y0.15O3 materials showed a better chemical compatibility.  相似文献   

6.
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 Ce1−xTbxO2−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.  相似文献   

7.
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.  相似文献   

8.
We report synthesis, structure and dielectric properties of double perovskite-type Ba3−xKxCaNb2O9−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, Ba1.75K1.25CaNb2O9−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.  相似文献   

9.
针对分数阶PIλDμ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PIλ控制器和分数阶PDμ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。  相似文献   

10.
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.  相似文献   

11.
The structure, morphology, and magnetic properties of the mechanically alloyed iron manganese phosphides (Fe1?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 (Fe1?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.  相似文献   

12.
We present a new method to improve the oxygen flux properties and stability of Ba0.5Sr0.5Co0.8Fe0.2O3 − δ tube membrane using a thin layer of La0.6Sr0.4Ti0.3Fe0.7O3 − δ as protective coatings. The first relevant result is that the La0.6Sr0.4Ti0.3Fe0.7O3 − δ protective layer had an extraordinary positive effect on improving the oxygen permeation flux of the tubular Ba0.5Sr0.5Co0.8Fe0.2O3 − δ membranes. La0.6Sr0.4Ti0.3Fe0.7O3 − δ-coated Ba0.5Sr0.5Co0.8Fe0.2O3 − 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.  相似文献   

13.
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 Bi1.6Pb0.5Sr2−xDyxCa1.1Cu2.1O8+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 (TC) and critical current density (JC) at self-field of the Dy-doped samples enhance considerably at optimum doping levels. Maximum TC of 92.3 K (for x = 0.4) and JC 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.  相似文献   

14.
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.  相似文献   

15.
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.  相似文献   

16.
The phase transitions that take place in Sr1 + xCo0.8Fe0.2O3 − 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, Sr1 + xCo0.8Fe0.2O3 − δ (x = − 0.2, 0, 0.1), used as oxygen-permeable membranes were investigated. The phase transitions in Sr1 + xCo0.8Fe0.2O3 − δ (x = − 0.2, 0) have also been detected in differential scanning calorimetry (DSC) profiles.  相似文献   

17.
Nanocrystalline Pr1−xZrxO2−δ (0 ≤ x ≤ 1) and Pr1−xyPdyZrxO2−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 Pr1−xZrxO2−δ (0.0 ≤ x ≤ 0.8) solid solutions have been investigated by temperature-programmed reduction (TPR) and are compared with those of Ce1−xZrxO2. Pr1−xZrxO2−δ exhibited H2 uptake and CO oxidation at a lower temperature than Ce1−xZrxO2. Small amount of Pd ion (y = 0.02) substitution was found to bring down the temperature of oxygen release-storage significantly.  相似文献   

18.
The polycrystalline samples with nominal compositions Nd0.5Sr0.5Mn1−xCuxO3 (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 (TCO) at 240 K in Nd0.5Sr0.5Mn03 sample. The Neel temperature (TN) 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 TN are observed for the oxygen annealed samples. Furthermore, oxygen annealing enhances the magnetization of the samples. It is also found that TC increases and TN 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.  相似文献   

19.
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.  相似文献   

20.
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