Reducing dielectric loss in Na0.5Bi0.5TiO3 based high temperature capacitor material

The demand for capacitors exhibiting low sensitivity towards temperature changes and high power peaks has increased significantly. Recently, Na_0.5Bi_0.5TiO₃ (NBT) based ceramics became excellent candidates for such extreme temperature capacitors. The dielectric loss of these materials is, however, difficult to control because of the complex defect chemistry of NBT based ceramics. Therefore, it is the limiting factor for high temperature applications. In this work, we present a strategy to increase the upper temperature limit for low dielectric loss. The addition of BiAlO₃ to Na_0.5Bi_0.5TiO₃-BaTiO₃-CaZrO₃ reduces the loss and sensitivity towards Bi evaporation during synthesis. For unmodified samples, the relative permittivity (ε_r = 581, at 1 kHz) varies less than 15 %, while the dielectric loss stays below 0.02 between -68 and 368 °C. With the addition of BiAlO₃, the temperature range of low loss extends from -68 to 391 °C at even higher permittivity (ε_r = 628, at 1 kHz).     

Effect of target peak power density on the phase formation,microstructure evolution,and mechanical properties of Cr2AlC MAX-phase coatings

The applicability of Cr₂AlC MAX-phases as protective coatings in energy conversion or aerospace applications requires a dense, single-phase structure. Therefore, we study the effect of target power density and substrate bias on phase formation, microstructure evolution, and mechanical properties of Cr₂AlC coatings utilizing direct current (DCMS) and high-power pulsed magnetron sputtering (HPPMS). Generally, HPPMS results in coatings with superior density and hence larger elastic moduli compared to DCMS, indicating that ion bombardment by ionized film-forming species is beneficial. However, decreasing the substrate bias to ?200 V for DCMS and ?100 V for HPPMS favors the ion bombardment induced formation of the disordered (Cr,Al)₂C_x solid solution. It is evident that there is an optimum moderate ion energy for the formation of dense Cr₂AlC coatings. Too low energy results in the formation of under-dense coatings. Too high energy yields the formation of (Cr,Al)₂C_x in addition to Cr₂AlC.     

ZnO-based single crystal-polycrystal structures for piezotronic applications

Electrostatic potential barriers at doped ZnO-ZnO interfaces can be modified by stress-induced polarization charges. This concept was enhanced by preparing ZnO-based single crystal-polycrystal-single crystal structures by diffusion bonding. Increasing time for epitaxial solid-state transformation results in structures with a decreasing thickness of residual polycrystalline material in between two well-oriented single crystals. Microstructural and electrical analysis quantifies the influence of high-temperature treatment during epitaxial growth on the stress sensitivity of the prepared structures. The orientation of the single crystals is defined to maximize the interaction between stress-induced polarization charges and the potential barriers at doped ZnO-ZnO interfaces. With decreasing thickness of residual polycrystalline material, the percentage of grain boundaries with favorably aligned polarization vectors is increased resulting in a higher stress sensitivity. This effect is compensated by an adverse effect of the high-temperature treatment on the initial potential barrier height. Hence, a maximum in stress sensitivity can be observed for intermediate times of epitaxial growth. The prepared structures close the gap between the varistor piezotronics based on bulk ceramics with random orientation of the polarization vector and the bicrystal piezotronics with perfect orientation of the polarization vector, demonstrating the capability of microstructural engineering for varistor-based piezotronic devices.     

Pentoxifylline inhibits experimental bleomycin-induced fibrosing alveolitis

Therapy of idiopathic pulmonary fibrosis (IPF) is directed at 1) inhibition of alveolitis and tissue damage, and 2) inhibition of matrix deposition. We and others have identified pentoxifylline (POF) as a promising drug in achieving these aims. For further clarification, we established a model of bleomycin-induced fibrosing alveolitis. Fisher 344 rats (n = 7 per group) were given bleomycin intratracheally once (0.7 U/100 g bw) and treated with POF (1.5 or 3 mg/kg bw per day i.p.), prednisolone (15 mg/kg bw i.m. per day), or sodium chloride solution (NaCL). The extent of inflammatory reactions was determined after 8 days by differentiation of cells of broncho-alveolar lavage (BAL) and by quantification of proliferating cells in lung interstitium subsequent to staining of the Ki-67 antigen. POF inhibited neutrophil alveolitis in BAL and reduced the amount of proliferating cells in the lungs significantly while prednisolone and NaCL did not. Both POF and prednisolone exerted a positive influence on postoperative weight loss as well as on lung weight increase subsequent to bleomycin instillation. The postoperative body weight loss and the lung weight increase after bleomycin instillation are most likely due to an inflammatory reaction subsequent to operation and bleomycin deposition. Tumor necrosis factor alpha (TNF-alpha) has been shown to be a key cytokine in bleomycin-induced fibrosing alveolitis as well as in IPF; it also exerts catabolizing effects. Since both POF and prednisolone are known to effectively inhibit proinflammatory cytokines and, among those, TNF-alpha, nonspecific antiinflammatory effects probably explain the benefits. Additionally, however, this study proved POF to be more effective in inhibition of BAL neutrophils and number of proliferating cells in lung interstitium. Further, it has been shown that POF, but not prednisolone, inhibits activation of neutrophil granulocytes and formation of reactive oxygen species. Thus we believe that the mechanism of action of xanthines might contribute to therapy of IPF. For further clarification, a prospective clinical study of POF in IPF therapy has been initiated.     

The reverse voltage limit of planarpn-junctions with field-plates

Contents High Voltagepn-Junctions are often equipped with a fieldplate to improve the blocking capability. The upper limit for this improvement, however, is still unknown. In this paper the upper limit for the blocking capability of field-plate structures is calculated, using an analytical model and two-dimensional numerical simulation. Based on scaled ionization integrals it is shown, that the ratio of the blocking voltage of a field-plate structure and the abrupt plane junction depends on a set of normalized geometrical parameters and a set of normalized physical parameters. Moreover it is found, that the blocking voltage can be calculated in scaled units. The results can be applied to a wide range of doping concentrations of the substrate layer.

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Die Sperrspannungsgrenze planarerpn-Übergänge mit Feldplatten

Übersicht Um die Sperrfähigkeit hochsperrenderpn-Übergänge zu verbessern, werden oftmals Feldplattenstrukturen eingesetzt. Ziel dieses Beitrages ist es, unter Verwendung analytischer Modelle und numerischer Simulation, die Sperrspannungsgrenze für Feldplattenstrukturen zu bestimmen. Ausgehend von einem skalierten Ionisierungsintegral wird gezeigt, daß das Verhältnis aus der Durchbruchspannung einer Feldplattenstruktur und der Durchbruchspannung des abrupten planparallelenpn-Übergangs von einer Anzahl normierter geometrischer und materialspezifischer Parameter abhängt. Durch die Einführung normierter Größen sind die Ergebnisse in einem weiten Bereich der Substratdotierung anwendbar.

     

Morphological changes in chest radiographs of patients with acute respiratory distress syndrome (ARDS)

The value of ultrasonography (US), magnetic resonance imaging (MRI), computed tomography (CT) and plain radiography (PR) in detecting bone erosions on the humeral head was evaluated in a study of 26 in-patients (26 shoulders) with rheumatoid arthritis (RA). MRI depicted humeral erosions in 25 (96%), US in 24 (92%), CT in 20 (77%) and PR in 19 (73%) of the 26 shoulders. MRI and US were superior to CT in detecting small erosions. US was the most sensitive method to show surface erosions on the greater tuberosity. US, CT and MRI detected large erosions quite similarly. PR frequently missed small erosions. In the evaluation of early erosions in the rheumatoid shoulder, US and MRI are more sensitive methods than the traditionally used PR. US and MRI are suitable for the evaluation of soft-tissue involvement in the rheumatoid shoulder, but also for the detection of bone erosions of the humeral head.     

Asymptotic S/N results for an adaptive polyspectral canceller usingsample matrix inversion

An adaptive polyspectral canceller configuration is defined, whereby auxiliary canceller channels are formed using distinct monomial expressions of the auxiliary sensor channels. If noises in the auxiliary canceller channels are correlated with the noise in a main channel, then improvement in output signal-to-noise (S/N) power ratio is possible by cancelling in linear fashion the correlated auxiliary canceller channels with the main channel. The convergence performance of the polyspectral canceller is analyzed. A simple expression is derived for the asymptotic S/N efficiency of the adaptive polyspectral canceller as a function of the number of independent input sample vectors used to calculate the adaptive canceller weights and other canceller/noise model parameters. It is shown by simulation for low-order polyspectral cancellers of a specific form with Gaussian inputs that this asymptotic expression is a good approximation of the actual S/N efficiency for a moderate number of input sample vectors. However, for moderate-to-high order polyspectral cancellers, the asymptotic expression is a poor indicator of performance