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Material Quality (material + quality)
Selected AbstractsBone material quality in transiliac bone biopsies of postmenopausal osteoporotic women after 3 years of strontium ranelate treatmentJOURNAL OF BONE AND MINERAL RESEARCH, Issue 4 2010Paul Roschger Abstract Strontium ranelate (SrR) is a relatively new treatment for osteoporosis. In this study we investigated its potential impact on human bone material quality in transiliac bone biopsies from postmenopausal osteoporotic women treated 3 years with calcium and vitamin D plus either 2,g SrR per day or placebo. Bone mineralization density distribution (BMDD), strontium (Sr) concentration, collagen cross-link ratio, and indentation modulus were analyzed by quantitative backscattered electron imaging, electron-induced X-ray fluorescence analysis, synchrotron radiation induced micro X-ray fluorescence elemental mapping, Fourier transform infrared imaging, and nanoindentation, respectively. The BMDD of SrR-treated patients was shifted to higher atomic numbers (Zmean +1.5%, p,<,.05 versus placebo). We observed Sr being preferentially incorporated in bone packets formed during SrR treatment up to 6% atom fraction [Sr/(Sr,+,Ca)] depending on the SrR serum levels of the individuals (correlation r,=,0.84, p,=,.018). Collagen cross-link ratio was preserved in SR-treated bone. The indentation modulus was significantly decreased in younger versus older bone packets for both placebo- (,20.5%, p,<,.0001) and SrR-treated individuals (,24.3%, p,<,.001), whereas no differences were found between the treatment groups. In conclusion, our findings indicate that after SrR treatment, Sr is heterogeneously distributed in bone and preferentially present in bone packets formed during treatment. The effect of SrR on BMDD seems to be due mainly to the uptake of Sr and not to changes in bone calcium content. Taken together, these data provide evidence that the investigated bone quality determinants at tissue level were preserved in postmenopausal osteoporotic women after 3-year treatment with 2,g SrR per day plus calcium and vitamin D. © 2010 American Society for Bone and Mineral Research [source] How do implementation efforts relate to program adherence? examining the role of organizational, implementer, and program factorsJOURNAL OF COMMUNITY PSYCHOLOGY, Issue 6 2008Jacinda K. Dariotis Widespread replications of evidence-based prevention programs (EBPPs) prompt prevention scientists to examine program implementation adherence in real world settings. Based on Chen's model (1990), we identified five key factors of the implementation system and assessed which characteristics related to program adherence. The sample included 32 EBPPs and results indicate that target recipient responsivity, program material quality, implementer prioritization, community collaborative system support, and parental support significantly relate to program adherence. Several differences reached statistical significance, thereby highlighting the importance of these variables and the need for future studies with larger sample sizes to identify factors related to program adherence adequately. © 2008 Wiley Periodicals, Inc. [source] Three-dimensionally structured silicon as a substrate for the MOVPE growth of GaN nanoLEDsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2009Sönke Fündling Abstract Three-dimensionally patterned Si(111) substrates are used to grow GaN based heterostructures by metalorganic vapour phase epitaxy, with the goal of fabricating well controlled, defect reduced GaN-based nanoLEDs. In contrast to other approaches to achieve GaN nanorods, we employed silicon substrates with deep etched nanopillars to control the GaN nanorods growth by varying the size and distance of the Si pillars. The small footprint of GaN nanorods grown on Si pillars minimise the influence of the lattice mismatched substrate and improve the material quality. For the Si pillars an inductively coupled plasma dry-etching process at cryogenic temperature has been developed. An InGaN/GaN multi quantum well (MQW) structure has been incorporated into the GaN nanorods. We found GaN nanostructures grown on top of the silicon pillars with a pyramidal shape. This shape results from a competitive growth on different facets as well as from surface diffusion of the growth species. Spatially resolved optical properties of the structures are analysed by cathodoluminescence. Strongly spatial-dependent MQW emission spectra indicate the growth rate differences on top of the rods. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Deep ultraviolet light-emitting diodesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2006X. Hu Abstract We report on the development of AlGaN-based deep UV light emitting diodes (LEDs) with emission wavelengths from 254 to 340 nm, focusing on the improvement of 280 nm LEDs efficiency. Under optimal device structure the UV LEDs efficiency was found to strongly depend on the AlGaN material quality. Milliwatt-power level LEDs were demonstrated for the 254,340 nm spectral range, and for 280 nm LEDs powers reaching 2.5 mW was achieved at 20 mA DC. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Modeling of spatially inhomogeneous solar cells by a multi-diode approachPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 15 2005P. O. Grabitz Abstract An equivalent circuit model consisting of parallel connected diodes with different electronic quality simulates the electronic properties of solar cells with spatially inhomogeneous material quality. Variations of the local saturation current density result in a degradation of the open circuit voltage, the fill factor and, in consequence, of the overall power conversion efficiency. However, a local series resistance introduced into this network limits this degradation by preventing areas with high saturation current density to dominate the electronic losses of the entire device. Analyzing the integral current/voltage-curves of the networks shows the diode ideality larger than unity to result from resistive limitations to the spatially inhomogeneous current flow. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Projective techniques for the growth of compound semiconductor nanostructuresPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2003T. Schallenberg Abstract We investigate the geometric deposition of compound semiconductors through shallow shadow masks as a means to obtain 3D nanostructures in situ. A high spatial resolution in the order of 10 nm and good material quality are achieved by epitaxy with directed molecular beams through stationary masks. Based on our study of growth dynamics new processes were tailored for the deposition of compound semiconductors. These expand the degrees of freedom of directional shadow growth. We would like to give an overview of this alternative technology, and present late results from experiments with an optimised molecular beam epitaxy (MBE) set-up. Projective techniques are demonstrated with sample structures. We discuss their respective potential and limitations. An outlook shows the perspective of further increase of the complexity of feasible structures by increasing the complexity of the masks (3D nanostructured). [source] The origin of the high ideality factor in AlGaN-based quantum well ultraviolet light emitting diodesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 7 2010K. B. Lee Abstract The ideality factor of AlGaN-based quantum well ultraviolet light emitting diodes (LEDs) is found to be dependent on both material quality and the presence of electron blocking layer (EBL). The ideality factor of the 340,nm LEDs decreases from 6.9 to 4.9 in the low bias regime (1,,,V,,,2) as the structural dislocation density reduces from 5,×,109 to 9,×,108,cm,2. Moreover, the ideality factor of the 310,nm LEDs decreases with increasing thickness of the AlGaN EBL which is placed between the barrier after the QW and the p-type layer. The slope of the I,V characteristics is temperature independent, indicating that the carrier tunneling is the dominant mechanism. The characteristic tunneling energy extracted from the I,V characteristics decreases from the order of 200 to around 100,meV as the dislocation density in the LED is reduced and with the insertion of a 10,nm EBL. This is attributed to the suppression of deep level states assisted electron tunneling into p-type layer. [source] High-performance nanoparticle-enhanced tunnel junctions for photonic devicesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2010Adam M. Crook Abstract We describe GaAs-based tunnel junctions that are compatible with photonic devices, including long-wavelength vertical-cavity surface-emitting lasers and multi-junction solar cells. Tunneling was enhanced with semimetallic ErAs nanoparticles, particularly when grown at reduced substrate temperatures. Additionally, we present the first direct measurement of the quality of III-V layers grown above ErAs nanoparticles. Photoluminescence measurements indicate that III-V material quality does not degrade when grown above ErAs nanoparticles, despite the mismatch in crystal structures. These findings validate these tunnel junctions as attractive candidates for GaAs-based photonic devices (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Mechanical behavior of recycled reinforced polyamide railway fastenersPOLYMER COMPOSITES, Issue 7 2010José Antonio Casado Modern railway tracks use short-fiber glass reinforced polyamide to inject insulating and mechanically resistant fasteners to connect the rails to the sleepers. Some of this material is later withdrawn, due either to defective production or to breakage in service. The recovery of the material for its later re-use would lead to a great saving, from both an environmental and an economic viewpoint. Mechanical recycling is a simple, economic process that only requires the crushing of the material and its subsequent molding, without the need for any chemical treatments. However, it has some drawbacks; as with any kind of recycling, there is a certain loss of material quality with some degradation of its properties. In this work, the physical and mechanical results for fasteners injected with recycled material are compared to others injected with pure material. The results show that the use of recycled fasteners is limited in-service by working conditions that increase the thermoplastic material temperature above its critical glass transition temperature, Tg. POLYM. COMPOS., 31:1142,1149, 2010. © 2009 Society of Plastics Engineers [source] 8% Efficient thin-film polycrystalline-silicon solar cells based on aluminum- induced crystallization and thermal CVDPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 7 2007I. Gordon Abstract A considerable cost reduction could be achieved in photovoltaics if efficient solar cells could be made from polycrystalline-silicon (pc-Si) thin films on inexpensive substrates. We recently showed promising solar cell results using pc-Si layers obtained by aluminum-induced crystallization (AIC) of amorphous silicon in combination with thermal chemical vapor deposition (CVD). To obtain highly efficient pc-Si solar cells, however, the material quality has to be optimized and cell processes different from those applied for standard bulk-Si solar cells have to be developed. In this work, we present the different process steps that we recently developed to enhance the efficiency of pc-Si solar cells on alumina substrates made by AIC in combination with thermal CVD. Our present pc-Si solar cell process yields cells in substrate configuration with efficiencies so far of up to 8·0%. Spin-on oxides are used to smoothen the alumina substrate surface to enhance the electronic quality of the absorber layers. The cells have heterojunction emitters consisting of thin a-Si layers that yield much higher Voc values than classical diffused emitters. Base and emitter contacts are on top of the cell in interdigitated finger patterns, leading to fill factors above 70%. The front surface of the cells is plasma textured to increase the current density. Our present pc-Si solar cell efficiency of 8% together with the fast progression that we have made over the last few years indicate the large potential of pc-Si solar cells based on the AIC seed layer approach. Copyright © 2007 John Wiley & Sons, Ltd. [source] High-rate deposition of epitaxial layers for efficient low-temperature thin film epitaxial silicon solar cellsPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 5 2001Lars Oberbeck Low,temperature deposition of Si for thin-film solar cells has previously been hampered by low deposition rates and low material quality, usually reflected by a low open-circuit voltage of these solar cells. In contrast, ion-assisted deposition produces Si films with a minority-carrier diffusion length of 40,,m, obtained at a record deposition rate of 0.8,,m/min and a deposition temperature of 650°C with a prebake at 810°C. A thin-film Si solar cell with a 20-,m-thick epitaxial layer achieves an open-circuit voltage of 622,mV and a conversion efficiency of 12.7% without any light trapping structures and without high-temperature solar cell process steps. Copyright © 2001 John Wiley & Sons, Ltd. [source] | ||||||||||