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Layer Composition (layer + composition)
Selected AbstractsLong-wavelength (, , 1.3 µm) InGaAlAs,InP vertical-cavity surface-emitting lasers for applications in optical communication and sensingPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 14 2006Markus-Christian Amann Abstract In this paper we present an overview of the properties and applications of long-wavelength vertical-cavity surface-emitting lasers (VCSELs) based on the InGaAlAs,InP material system. With respect to significant temperature sensitivity of active material gain as well as insufficient thermal conductivity of InP-based epitaxial compound layers, the effective thermal heat management appears as a major issue for application suitable device performance. In this context, the incorporation of a buried tunnel junction (BTJ) in connection with improved heat sinking resembles a breakthrough for long-wavelength VCSELs. With the utilization of n-type spreading layers and consequently ultralow series resistances, BTJ-VCSELs exhibit sharply reduced excess heat generation. Furthermore, the BTJ-approach enables self-aligned optical and current confinement. A hybrid dielectric stack with Au-coating yields an improved thermal heatsinking. The current status of BTJ-VCSELs encompasses a number of superior performance values. At 1.55 µm wavelength, this includes room temperature single- and multimode continuous wave (cw) output powers of more than 3 mW and 10 mW, respectively, laser operation for heat sink temperatures well exceeding 100 °C, and optical data transmission rates up to 10 Gbit/s. The versatility of compound layer composition enables arbitrary emission wavelengths within a broad range of 1.3 and 2 µm. With respect to sensing applications, BTJ-VCSELs appear as ideal components for optical detection of infrared active gases. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Optimisation of surface passivation for highly reliable angular AMR sensorsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2010M. Isler Abstract For state-of-the-art angular sensors based on the anisotropic magnetoresistive (AMR) effect in NiFe layers, the angular accuracy over time is limited by a drift of the offset voltage of the Wheatstone bridge configuration. It is shown that the interaction of the passivation layer and the magnetic permalloy is crucial for the drift of the offset voltage. By investigating the time and temperature dependence, the offset drift is attributed to stress relief of the PECVD passivation layer due to microstructural changes. Hydrogen outdiffusion from the passivation layer is involved in the observed stress evolution. It is demonstrated that optimising the passivation layer composition as well as the time of the subsequent annealing is beneficial for stress stabilisation of the permalloy-passivation layer system. With this optimised passivation layer a significant offset drift reduction of the NiFe Wheatstone bridge has been achieved resulting in highly accurate and long-term stable angular AMR sensors. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Wood/plastic composites co-extruded with multi-walled carbon nanotube-filled rigid poly(vinyl chloride) cap layerPOLYMER INTERNATIONAL, Issue 5 2010Shan Jin Abstract Wood/plastic composites (WPCs) can absorb moisture in a humid environment due to the hydrophilic nature of the wood in the composites, making products susceptible to microbial growth and loss of mechanical properties. Co-extruding a poly(vinyl chloride) (PVC)-rich cap layer on a WPC significantly reduces the moisture uptake rate, increases the flexural strength but, most importantly, decreases the flexural modulus compared to uncapped WPCs. A two-level factorial design was used to develop regression models evaluating the statistical effects of material compositions and a processing condition on the flexural properties of co-extruded rigid PVC/wood flour composites with the ultimate goal of producing co-extruded composites with better flexural properties than uncapped WPCs. Material composition variables included wood flour content in the core layer and carbon nanotube (CNT) content in the cap layer of the co-extruded composites, with the processing temperature profile for the core layer as the only processing condition variable. Fusion tests were carried out to understand the effects of the material compositions and processing condition on the flexural properties. Regression models indicated all main effects and two powerful interaction effects (processing temperature/wood flour content and wood flour content/CNT content interactions) as statistically significant. Factors leading to a fast fusion of the PVC/wood flour composites in the core layer, i.e. low wood flour content and high processing temperature, were effective material composition and processing condition parameters for improving the flexural properties of co-extruded composites. Reinforcing the cap layer with CNTs also produced a significant improvement in the flexural properties of the co-extruded composites, insensitive to the core layer composition and the processing temperature condition. Copyright © 2009 Society of Chemical Industry [source] Anatomicohistological Characteristics of the Female Genital Organs of the White-lipped Peccary (Tayassu pecari) in the Peruvian AmazonANATOMIA, HISTOLOGIA, EMBRYOLOGIA, Issue 6 2009P. Mayor Summary This study examined the anatomical and histological characteristics of the genital organs of the female white-lipped peccary in the wild in different reproductive stages, collected by rural hunters in the North-eastern Peruvian Amazon. Mean ovulation rate was 2.12 ± 0.83 follicles and litter size was 1.78 ± 0.41 embryos or fetuses per pregnant female, resulting in a low rate of reproductive wastage, averaging 0.33 ± 0.66 (16.04%) oocytes or embryos per pregnancy. The ovulation rate and the anatomical performance of the uterus could limit the prolificacy of this species. Females in follicular phase showed follicular waves suggesting the synchronous growth of a cohort of follicles. Different uterine and vaginal epithelium features changed in accordance with the reproductive state of the female. Pregnant females and females in the luteal phase presented a significant proliferation of endometrial uterine glands, characterized by hyperplasia and branching of endometrial glands, and increase in the proportion of cervical epithelial cells with periodic acid-schiff (PAS)-positive granules compared with that in females in the follicular phase. Females in the follicular phase showed a more developed vaginal epithelium (in thickness and in layer composition) than females in the luteal phase and pregnant females. [source] Herb layer changes (1954-2000) related to the conversion of coppice-with-standards forest and soil acidificationAPPLIED VEGETATION SCIENCE, Issue 2 2009Lander Baeten Abstract Question: Did the composition of the herb layer of a deciduous forest on loamy soils sensitive to soil acidification change between 1954 and 2000? How are these change related to the abandonment of traditional coppice-with-standards forest management and increased soil acidification? Location: Central Belgium (Europe). Methods: Twenty semi-permanent phytosociological quadrats from an ancient deciduous forest (Meerdaal forest) were carefully selected out of a total of 70 plots dating from 1954 and were revisited in 2000. Species composition and soil pH H2O were recorded using an analogous methodology. The studied period coincides with a period of forest conversion from coppice-with-standards towards a high forest structure and with an increase in acidifying and eutrophying deposition. Results: Between 1954 and 2000, species composition of the herb layer changed significantly. Redundancy analysis pointed to increased shade resulting from shifts in cover and species composition of the shrub and tree layer as the main driving force. Soil acidity increased and the majority of plots entered the aluminium buffer range, which potentially affected herb layer composition. Observations at the species level, especially a strong decrease in cover of the vernal species Anemone nemorosa supported this hypothesis. Conclusions: Our results show significant shifts in the forest herb layer in less than five decades. These shifts were related to an alteration in the traditional forest management regime and increased soil acidity. Whereas the effect of a changed management regime can be mitigated, soil acidification is less reversible. Testing the generality of these patterns on more extensive data sets is certainly needed. [source] Impact of storm-burning on Melaleuca viridiflora invasion of grasslands and grassy woodlands on Cape York Peninsula, AustraliaAUSTRAL ECOLOGY, Issue 2 2009GABRIEL CROWLEY Abstract This paper examines invasion of grasslands on Cape York Peninsula, Australia, by Melaleuca viridiflora and other woody species, and the role of storm-burning (lighting fires after the first wet season rains) in their maintenance. Trends in disturbance features, fuel characteristics, ground layer composition, and woody plants dynamics under combinations of withholding fire and storm-burning over a 3-year period were measured on 19 plots in three landscape settings. Population dynamics of M. viridiflora are described in detail and 20-year population projections based on transition matrices under different fire regimes generated. Numerous M. viridiflora suckers occurred within the grass layer, increasing each year regardless of fire regime, and were rapidly recruited to the canopy in the absence of fire. Storm-burning had little impact on fuel, ground layer or woody plant composition, but maintained open vegetation structure by substantially reducing recruitment of M. viridiflora suckers to the sapling layer, and by reducing the above-grass-layer abundance of several other invasive woody species. Population projections indicated that withholding fire for 20 years could cause a sevenfold increase of M. viridiflora density on Ti-tree flats, and that annual to triennial storm-burning should be effective at maintaining a stable open vegetation structure. These findings argue against vegetation thickening being an inevitable consequence of climate change. We conclude that a fire regime that includes regular storm-burning can be effective for maintaining grasslands and grassy woodlands being invaded by M. viridiflora. [source] | |||||||||||||