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111.
Thermally stimulated current (TSC) measurements performed in the 100 K–400 K temperature range on Bi4Ti3O12 (BiT) thin films annealed at 550 °C and 700 °C had revealed two trapping levels having activation energies of 0.55 eV and 0.6 eV. The total trap concentration was estimated at 1015 cm−3 for the samples annealed at 550 °C and 3×1015 cm−3 for a 700 °C annealing and the trap capture cross-section was estimated about 10−18 cm2. From the temperature dependence of the dark current in the temperature range 20 °C–120 °C the conduction mechanism activation energy was found to be about 0.956–0.978 eV. The electrical conductivity depends not only on the sample annealing temperature but also whether the measurement is performed in vacuum or air. The results on the dark conductivity are discussed considering the influence of oxygen atoms and oxygen vacancies. Received: 28 January 1998 / Accepted: 8 January 1999 / Published online: 5 May 1999  相似文献   
112.
BaTiO3 nanofibers (BT NFs), prepared by electrospinning, were used as a filler for electrospun poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) nanocomposite mats. The phase structure and the effect of poling conditions on the piezoelectric properties of PVDF-TrFE/BT nanocomposites were investigated. The results showed an improved degree of crystallinity (78.6%) and a high β-crystal phase (up to 98.3%) in all electrospun samples, independent of the nanofiber content. The two-step poling method, applying electric fields of opposite polarity, led to significantly improved piezoelectric constants d33 (−31.7 pC N−1), strongly dependent on the added BaTiO3 nanofibers. The inclusion of piezoelectric ceramic nanofibers into a polymer matrix, easily carried out by means of electrospinning, followed by an ad hoc optimized poling treatment, allowed to develop flexible materials with enhanced piezoelectric properties, potentially exploitable in innovative conversion systems used in wearable and sensing devices.  相似文献   
113.
Pristine high-density bulk disks of MgB2 with added hexagonal BN (10 wt.%) were prepared using spark plasma sintering. The BN-added samples are machinable by chipping them into desired geometries. Complex shapes of different sizes can also be obtained by the 3D printing of polylactic acid filaments embedded with MgB2 powder particles (10 wt.%). Our present work aims to assess antimicrobial activity quantified as viable cells (CFU/mL) vs. time of sintered and 3D-printed materials. In vitro antimicrobial tests were performed against the bacterial strains Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853, Staphylococcus aureus ATCC 25923, Enterococcus faecium DSM 13590, and Enterococcus faecalis ATCC 29212; and the yeast strain Candida parapsilosis ATCC 22019. The antimicrobial effects were found to depend on the tested samples and microbes, with E. faecium being the most resistant and E. coli the most susceptible.  相似文献   
114.
Moderate or intense low oxygen dilution (MILD) combustion has been the focus of a range of fundamental experimental and numerical studies. Reasonable agreement between experimental and numerical investigations, however, requires finite-rate chemistry models and, often, ad hoc model adjustment. To remedy this, an adaptive eddy dissipation concept (EDC) combustion model has previously been developed to target conditions encountered in MILD combustion; however, this model relies on a simplified, pre-defined assumption about the combustion chemistry. The present paper reports a generalised version of the modified EDC model without the need for an assumed, single-step chemical reaction or ad hoc coefficient tuning. The results show good agreement with experimental measurements of two CH4/H2 flames in hot coflows, showing improvements over the standard EDC model as well as the previously published modified EDC model. The updated version of the EDC model also demonstrates the capacity to reproduce the downstream transition in flame structure of a MILD jet flame seen experimentally, but which has previously proven challenging to capture computationally. Analyses of the previously identified dominant heat-release reactions provide insight into the structural differences between a conventional autoignitive flame and a flame in the MILD combustion regime, whilst highlighting the requirement for a generalised EDC combustion model.  相似文献   
115.
116.
Since the discovery of symplesite mineral in the late 19th century, a number of structural studies were performed. The crystal symmetry of this mineral was debated to be either monoclinic or triclinic. Even though this debate has ended, agreeing on the triclinic symmetry, no detailed crystal structure was reported so far. In the present contribution, we report on the crystal structure of symplesite. The crystal structure was solved and refined from high‐resolution laboratory X‐ray powder diffraction data, collected on a natural sample. Symplesite is shown to be isostructural to metavivianite (and possibly to ferrostrunzite).  相似文献   
117.
Periodica Mathematica Hungarica - In this paper we consider individual stability for linear skew-product semiflows over semiflows by using the standard Perron’s method. To our knowledge, in...  相似文献   
118.
For simple mechanical systems, bifurcating branches of relative equilibria with breaking symmetry from a given set of relative equilibria with toral symmetry are found. Lyapunov stability conditions along these branches are given.  相似文献   
119.
Additives to MgB2 can improve the superconducting functional characteristics, such as critical current density (J c) and irreversibility field (H irr). Recently, we have shown that repagermanium (C6H10Ge2O7) is an effective additive, enhancing both J c and H irr. To look into details of the processes taking place during the reactive sintering, a thermal analysis study (0.167 K s?1, in Ar) is reported. We used differential scanning calorimetry between 298 and 863 K and simultaneous thermogravimetric—differential thermal analysis between 298 and 1233 K. Samples were mixtures of powders with composition 97 mol% MgB2 and 3 mol% C6H10Ge2O7. Up to 863 K, repagermanium decomposes by multiple steps and forms amorphous phases. A reaction with MgB2 is not observed. Above this temperature, partial decomposition of MgB2 occurs. Crystalline Ge and MgO are detected before formation of Mg2Ge and MgB4, when temperature approaches the melting point of Ge (1211 K). Carbon substitution for boron in the crystal lattice of MgB2 is observed for samples heated above 863 K. The amount of substitutional C does not significantly change with temperature.  相似文献   
120.
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