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First Layer (first + layer)
Selected AbstractsAtomistic simulation of the self-diffusion in Mg (001) surfaceCRYSTAL RESEARCH AND TECHNOLOGY, Issue 9 2008Jian-Min Zhang Abstract Both the formation energies and the intra- and inter-layer diffuse activation energies of a vacancy in the first six lattice planes of Mg (001) surface have been calculated by combining the modified analytical embedded-atom method (MAEAM) with molecular dynamics (MD). The results show that the effect of the surface on the formation and migration of the vacancy is only down to the third-layer. It is easer for a single vacancy to form and to migrate in the first layer. Furthermore, the vacancy in the second layer is favorable to migrate to the first layer. This is in agreement with the experimental results that the first layer has the highest concentration of the vacancy. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Joint full-waveform analysis of off-ground zero-offset ground penetrating radar and electromagnetic induction synthetic data for estimating soil electrical propertiesGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2010D. Moghadas SUMMARY A joint analysis of full-waveform information content in ground penetrating radar (GPR) and electromagnetic induction (EMI) synthetic data was investigated to reconstruct the electrical properties of multilayered media. The GPR and EMI systems operate in zero-offset, off-ground mode and are designed using vector network analyser technology. The inverse problem is formulated in the least-squares sense. We compared four approaches for GPR and EMI data fusion. The two first techniques consisted of defining a single objective function, applying different weighting methods. As a first approach, we weighted the EMI and GPR data using the inverse of the data variance. The ideal point method was also employed as a second weighting scenario. The third approach is the naive Bayesian method and the fourth technique corresponds to GPR,EMI and EMI,GPR sequential inversions. Synthetic GPR and EMI data were generated for the particular case of a two-layered medium. Analysis of the objective function response surfaces from the two first approaches demonstrated the benefit of combining the two sources of information. However, due to the variations of the GPR and EMI model sensitivities with respect to the medium electrical properties, the formulation of an optimal objective function based on the weighting methods is not straightforward. While the Bayesian method relies on assumptions with respect to the statistical distribution of the parameters, it may constitute a relevant alternative for GPR and EMI data fusion. Sequential inversions of different configurations for a two layered medium show that in the case of high conductivity or permittivity for the first layer, the inversion scheme can not fully retrieve the soil hydrogeophysical parameters. But in the case of low permittivity and conductivity for the first layer, GPR,EMI inversion provides proper estimation of values compared to the EMI,GPR inversion. [source] Solution-Deposited Zinc Oxide and Zinc Oxide/Pentacene Bilayer Transistors: High Mobility n-Channel, Ambipolar, and Nonvolatile Devices,ADVANCED FUNCTIONAL MATERIALS, Issue 12 2008Bhola Nath Pal Abstract A solution processed n-channel zinc oxide (ZnO) field effect transistor (FET) was fabricated by simple dip coating and subsequent heat treatment of a zinc acetate film. The field effect mobility of electrons depends on ZnO grain size, controlled by changing the number of coatings and zinc acetate solution concentration. The highest electron mobility achieved by this method is 7.2,cm2 V,1 s,1 with On/Off ratio of 70. This electron mobility is higher than for the most recently reported solution processed ZnO transistor. We also fabricated bilayer transistors where the first layer is ZnO, and the second layer is pentacene, a p-channel organic which is deposited by thermal evaporation. By changing the ZnO grain size (or thickness) this type of bilayer transistor shows p-channel, ambipolar and n-channel behavior. For the ambipolar transistor, well balanced electron and hole mobilities are 7.6,×,10,3 and 6.3,×,10,3,cm2 V,1 s,1 respectively. When the ZnO layer is very thin, the transistor shows p-channel behavior with very high reversible hysteresis. The nonvolatile tuning function of this transistor was investigated. [source] Enhancement of Interconnectivity in the Channels of Pentacene Thin-Film Transistors and Its Effect on Field-Effect Mobility,ADVANCED FUNCTIONAL MATERIALS, Issue 14 2006S. Lee Abstract With the aim of improving the field-effect mobility of transistors by promoting the interconnectivity of the grains in pentacene thin films, deposition conditions of the pentacene molecules using one-step (total thickness of layer 50,nm: 0.1,Å,s,1) and two-step (first layer 10,nm: 0.1,Å,s,1, second layer 40,nm: 4.0,Å,s,1) depositions are controlled. Significantly, it is found that the continuities of the pentacene thin films vary with the deposition conditions of the pentacene molecules. Specifically, a smaller number of voids is observed at the interface for the two-step deposition, which results in field-effect mobilities as high as 1.2,cm2,V,1,s,1; these are higher by more than a factor of two than those of the pentacene films deposited in one step. This remarkable increase in field-effect mobility is due in particular to the interconnectivity of the pentacene grains near the insulator substrate. [source] Observation of Unusual Homoepitaxy in Ultrathin Pentacene Films and Correlation with Surface Electrostatic PotentialADVANCED MATERIALS, Issue 30 2009Vivek Kalihari Pentacene second layer grows with a twist (,76,°) on the first layer, while the third and subsequent layers show commensurism with their respective underlayers. The preferred twisting of the second layer on the first layer gives rise to epitaxial and non-epitaxial domains which also reflect in the surface electrostatic potential measurements. [source] Retinal pigment epithelial cells promote spatial reorganization and differentiation of retina photoreceptorsJOURNAL OF NEUROSCIENCE RESEARCH, Issue 16 2008Olga L. German Abstract Retina differentiation involves the acquisition of a precise layered arrangement, with RPE cells in the first layer in intimate contact with photoreceptors in the second layer. Here, we developed an in vitro coculture model, to test the hypothesis that RPE cells play a pivotal role in organizing the spatial structure of the retina. We cocultured rat retinal neurons with ARPE-19 epithelial cells under various experimental conditions. Strikingly, when seeded over RPE cells, photoreceptors attached to their apical surfaces and proceeded with their development, including the increased synthesis of rhodopsin. Conversely, when we seeded RPE cells over neurons, the RPE cells rapidly detached photoreceptors from their substrata and positioned themselves underneath, thus restoring the normal in vivo arrangement. Treatment with the metalloproteinase inhibitor TIMP-1 blocked this reorganization, suggesting the involvement of metalloproteinases in this process. Reorganization was highly selective for photoreceptors because 98% of photoreceptors but very few amacrine neurons were found to redistribute on top of RPE cells. Interestingly, RPE cells were much more efficient than other epithelial or nonepithelial cells in promoting this reorganization. RPE cells also promoted the growth of photoreceptor axons away from them. An additional factor that contributed to the distal arrangement of photoreceptor axons was the migration of photoreceptor cell bodies along their own neurites toward the RPE cells. Our results demonstrate that RPE and photoreceptor cells interact in vitro in very specific ways. They also show that in vitro studies may provide important insights into the process of pattern formation in the retina. © 2008 Wiley-Liss, Inc. [source] Formation process of three-dimensional arrays from silica spheresAICHE JOURNAL, Issue 5 2003Keiji Ishikawa Elucidating the formation process of 3-D arrays from submicrometer-sized particles is a key to creating an optimal fabrication process of photonic crystals. In this research, the spontaneous sedimentation of silica spheres is imaged by in situ confocal laser scanning microscopy, and the dynamics is studied. When the pH is 7.0 and 10, the rate of the formation process of a hexagonal structure is attributed to the transport of spheres in the early stage of precipitation, and can be reproduced by a simple equation for Langmuir-type adsorption, ignoring the desorption part. In a later stage, however, the rate becomes smaller. In the first layer, even after drying, the nearest two spheres are separated, while maintaining a hexagonal structure. From the results, the formation process of three-dimensional arrays from silica spheres is illustrated. [source] Influence of buffer layers on the texture and magnetic properties of Co/Pt multilayers with perpendicular anisotropyPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 12 2007J. Kanak Abstract A study on the buffer layer dependence of film texture, surface roughness, and magnetization reversal mechanism in Co/Pt multilayers is presented. Four different buffers are used: (A) 10 nm Cu, (B) 5 nm Ta/10 nm Cu, (C) 5 nm Ta/10 nm Cu/5 nm Ta, and (D) 5 nm Ta/10 nm Cu/5 nm Ta/10 nm Cu. The growth of [2 nm Pt/0.5 nm Co]5/2 nm Pt on top of these buffer layers results in a large variation of film textures and surface morphologies. Samples with a Cu buffer (A) exhibit a low degree of film texture and are relatively rough. MOKE and MFM measurements on these films reveal that the magnetization reverses by the nucleation of numerous small domains due to a large dispersion of the activation energy barrier. Buffer layer structures where the first layer consists of Ta, on the other hand, result in (111)-textured Co/Pt multilayers with a more regular surface morphology. In these samples, magnetization reversal proceeds by fast domain wall movement. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Glutamate receptor-mediated ischemic injury of premyelinated central axons,ANNALS OF NEUROLOGY, Issue 5 2009James J.P. Alix Objective Ischemic injury of axons is a feature of periventricular leukomalacia, a pathological correlate of cerebral palsy. Recent evidence suggests that axons are damaged before they receive the first layer of compact myelin. Here we examine the cellular mechanisms underlying ischemic-type injury of premyelinated central axons. Methods Two-thirds of axons in the postnatal day 10 (P10) rat optic nerve are small premyelinated axons (<0.4,m in diameter), and one-third have undergone radial expansion in preparation for glial contact and the onset of myelination. Compound action potential recording and quantitative electron microscopy were used to examine the effect of modeled ischemia (oxygen-glucose deprivation) upon these two axon populations. Glutamate receptor (GluR) expression was investigated using polymerase chain reaction (PCR) and immunostaining approaches at the confocal light and ultrastructural levels. Results Oxygen-glucose deprivation produced action potential failure and focal breakdown of the axolemma of small premyelinated axons at sites of contact with oligodendrocyte processes, which were also disrupted. The resulting axon loss was Ca2+ -dependent, Na+ - and Cl, -independent, and required activation of N -methyl-D-aspartic acid (NMDA) and non-NMDA GluRs. NMDA receptor expression was localized to oligodendrocyte processes at sites of contact with premyelinated axons, in addition to expression within compact myelin. No periaxonal NMDA receptor expression was observed on oligodendrocyte processes ensheathing large premyelinated axons and no protective effect of GluR block was observed in these axons. Interpretation NMDA receptor-mediated injury to oligodendrocyte processes navigating along small premyelinated axons precedes damage to the underlying axon, a phenomena that is lost following radial expansion and subsequent oligodendrocyte ensheathment. Ann Neurol 2009;66:682,693 [source] Possible Pathways of CVD Processes Leading to III,V Semiconductors via a Two-Dimensional Growth,CHEMPHYSCHEM, Issue 4 2005Hans-Jörg Himmel Priv.-Doz. Abstract Quantum-chemical calculations were carried out to shed more light upon possible first intermediates formed during chemical vapour deposition (CVD) processes leading to III,V semiconductors. Information about possible structures of intermediates and about thermodynamic properties in dependence of the temperature were collected. Because some of the systems calculated herein contain a substantial number of atoms (up to 144), it is limited to intermediates on the way to solid AlN. According to our suggestion, the first intermediates are species with the overall formula AlNH2, Al2N2H4, Al3N3H6, Al5N5H8, Al7N7H, and Al9N9H, Al12N12H12. In further calculations the growth of a second layer, on top of the first layer, which is modelled by the Al12N12H12 cluster, is simulated. The Al12N12H12 "surface" offers two places for the attachment of an Al3N3H6 ring. At temperatures of 1000 K, the ,G value for this attachment is only slightly negative, which suggests that the molecules can move relatively freely on the surface. This might be of importance for a defect-free growth process. Up to four layers are built on top of the first Al12N12H12 layer leading to Al24N24H24 (two layers), Al36N36H36 (three layers) and Al48N48H48 (four layers). The structures are compared with that of solid AlN in its most stable Wurzit-type structure. [source] Magnetic Materials: X-Ray Magnetic Circular Dichroism Picks out Single-Molecule Magnets Suitable for Nanodevices (Adv. Mater.ADVANCED MATERIALS, Issue 2 20092/2009) The surface sensitivity of X-ray magnetic circular dichroism in extreme conditions has been exploited to investigate the first layers of bulk single-molecule magnets (SMMs), as reported by Roberta Sessoli and co-workers on p. 167. Striking differences have emerged between two classes of SMM having different structural constraints, thus highlighting the importance of molecular design in the realization of molecular spintronic devices. [source] X-Ray Magnetic Circular Dichroism Picks out Single-Molecule Magnets Suitable for NanodevicesADVANCED MATERIALS, Issue 2 2009Matteo Mannini The surface sensitivity of X-ray Magnetic Circular Dichroism in extreme conditions is exploited to investigate the first layers of bulk single-molecule magnets (SMM). Striking differences emerge between two classes of SMM with different structural constraints, thus highlighting the importance of molecular design in the realization of molecular spintronic devices [source] Epidermal differentiation in embryos of the tuatara Sphenodon punctatus (Reptilia, Sphenodontidae) in comparison with the epidermis of other reptilesJOURNAL OF ANATOMY, Issue 1 2007L. Alibardi Abstract Studying the epidermis in primitive reptiles can provide clues regarding evolution of the epidermis during land adaptation in vertebrates. With this aim, the development of the skin of the relatively primitive reptile Sphenodon punctatus in representative embryonic stages was studied by light and electron microscopy and compared with that of other reptiles previously studied. The dermis organizes into a superficial and deep portion when the epidermis starts to form the first layers. At embryonic stages comparable with those of lizards, only one layer of the inner periderm is formed beneath the outer periderm. This also occurs in lizards and snakes so far studied. The outer and inner periderm form the embryonic epidermis and accumulate thick, coarse filaments (25,30 nm thick) and sparse alpha-keratin filaments as in other reptiles. Beneath the embryonic epidermis an oberhautchen and beta-cells form small horny tips that represent overlapping borders along the margin of beta-cells that overlap other beta-cells (in a tile-like arrangement). The tips resemble those of agamine lizards but at a small scale, forming a lamellate-spinulated pattern as previously described in adult epidermis. The embryonic epidermis matures by the dispersion of coarse filaments among keratin at the end of embryonic development and is shed around hatching. The presence of these matrix organelles in the embryonic epidermis of this primitive reptile further indicates that amniote epidermis acquired interkeratin matrix proteins early for land adaptation. Unlike the condition in lizards and snakes, a shedding complex is not formed in the epidermis of embryonic S. punctatus that is like that of the adult. Therefore, as in chelonians and crocodilians, the epidermis of S. punctatus also represents an initial stage that preceded the evolution of the shedding complex for moulting. [source] Ablative heat transfer in a shrinking packed-bed of ZnO undergoing solar thermal dissociationAICHE JOURNAL, Issue 7 2009L. O. Schunk Abstract A transient heat transfer model is formulated for a shrinking packed-bed of reacting ZnO particles exposed to concentrated solar irradiation. The model combines conduction, convection, and radiation heat transfer with simultaneous sintering and reaction kinetics. Validation is accomplished in terms of temperatures and dissociation rates experimentally measured using a solar-driven thermogravimeter with ZnO packed-bed samples subjected to solar flux concentration ratios in the range 1225,2133 suns and surface temperatures in the range 1834,2109 K. Operating conditions are typical of an ablation regime controlled by the rate of radiative heat transfer to the first layers of ZnO undergoing endothermic dissociation. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] | |||||||||||||||||||