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Top Layer (top + layer)

Distribution by Scientific Domains

Polymers and Materials Science	20%
Engineering	20%
Earth and Environmental Science	20%
Chemistry	20%
Physics and Astronomy	10%
Life Sciences	6%

Selected Abstracts

Influence of top layer geometries on the electronic properties of pentacene and diindenoperylene thin films

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 3 2008
M. Scharnberg
Abstract Top layers have a pronounced influence on the electronic properties of molecular organic thin films. Here, we report about the changes induced by metallic and polymeric top layers and contacts. As test structures, model systems of diindenoperylene and pentacene crystalline molecular organic thin films are used. A very sensitive radiotracer technique is introduced to study the details of metal penetration during top contact formation. The influence of temperature, evaporation time, adhesion promoter and grain size of the organic film were examined. The electric currents passing through metal top contacts were found to vary by more than a factor of three, depending on the preparation conditions of the metal contact. Furthermore, the series resistance of chemically identical contacts that only differed in the morphology of the interface were found to show pronounced asymmetric conductivity behaviour. We also show that with the help of electret top layers, based on the Teflon-AF fluropolymer, the threshold voltage of an organic field effect transistor can be tuned by several volts. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Identification of structural and soil properties from vibration tests of the Hualien containment model

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 1 2005
J. Enrique Luco
Abstract Measurements of the response of the ¼-scale reinforced concrete Hualien (Taiwan) containment model obtained during forced vibration tests are used to identify some of the characteristics of the superstructure and the soil. In particular, attempts are made to determine the fixed-base modal frequencies, modal damping ratios, modal masses and participation factors associated with translation and rocking of the base. The shell superstructure appears to be softer than could have been predicted on the basis of the given geometry and of test data for the properties of concrete. Estimates of the shear-wave velocity and damping ratio in the top layer of soil are obtained by matching the observed and theoretical system frequency and peak amplitude of the response at the top of the structure. The resulting models for the superstructure and the soil lead to theoretical results for the displacement and rotations at the base and top of the structure which closely match the observed response. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Effect of temperature and moisture on rates of carbon mineralization in a Mediterranean oak forest soil under controlled and field conditions

EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 5 2005
A. Rey
Summary We examined the relationship between carbon mineralization (Cmin), moisture and temperature in a Mediterranean forest soil under controlled and field conditions. We studied the following. 1,The temperature sensitivity at three soil depths: soil samples were incubated at 4, 10, 20 and 30°C at optimal water content of 60% of water holding capacity (WHC). Values of Cmin of the top layer were more than 12 times faster than those measured in deeper layers. We found a temperature sensitivity factor (Q10) of 3.3, 2.7 and 2.2 for the 0,5 cm, 5,10 cm and 10,20 cm layers, respectively. 2,The relationship between Cmin, moisture and temperature (top layer). The sensitivity of Cmin to fluctuating moisture depended on temperature. However, the Q10 was not significantly affected by soil moisture. We fitted a multiple polynomial model that predicted Cmin as a multiplicative function of temperature and moisture (R2 > 0.99). 3,The response of Cmin of soil to rewetting after 1 and 24 hours. In all cases, the response was rapid. The soil incubated at 60% WHC or less responded positively to a sudden increase in water content, with the largest increase in the 20% WHC treatment. The model predicted Cmin in the field well when rewetting effects were taken into account (R2 > 0.81). These results indicate that sudden changes in soil moisture can lead to increased carbon mineralization during the dry summer. It is necessary to include such responses in models as they may represent a substantial loss of carbon in the overall carbon balance of Mediterranean ecosystems. [source]

Are environmental conditions recorded by the organic matrices associated with precipitated calcium carbonate in cyanobacterial microbialites?

GEOBIOLOGY, Issue 2 2006
P. GAUTRET
ABSTRACT The amino acid composition of organic matrices associated with calcium carbonate precipitates in microbialites built by different Phormidium species (cyanobacteria) has been compared for samples recovered in lagoonal settings from two regions of the Southern Tropical Pacific separated by more than 4000 km: New Caledonia (Nouméa lagoon) and French Polynesia (Tikehau atoll). Calcium carbonate precipitation in these microbial structures was observed mainly in the interior of the domes and clearly separated from the photosynthetically active surface layer. This study focuses on the hydrolysable amino acid composition of the associated organic matrices that are typically rich in cysteine, leucine, alanine and arginine in New Caledonia, whereas they are particularly rich in dicarboxylic amino acids in French Polynesia. This striking difference is seemingly related to different environmental conditions that characterize the two reef settings. The high cysteine content suggests an origin from metallothioneins produced by the cyanobacteria and/or by epiphytic diatoms that were observed on the top layer, as the result of the input of metals from terrestrial origin in the Nouméa lagoon. In addition, we analysed the bulk organic matter of the photosynthetically active surface layer and of the interior of the domes. The former showed remarkable variations of amino acid composition throughout the year 2001, which may potentially reflect the impact of climatological events (e.g. cyclones) and/or a much stronger seasonality in New Caledonia than in French Polynesia. Although the mechanisms behind the differences remain elusive, our study clearly shows that environmental conditions can be reflected by amino acid compositions, particularly for the organic matrices associated with carbonate precipitates. [source]

Artificial neural network inversion of magnetotelluric data in terms of three-dimensional earth macroparameters

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2000
Vjacheslav Spichak
The possibility of solving the three-dimensional (3-D) inverse problem of geoelectrics using the artificial neural network (ANN) approach is investigated. The properties of a supervised ANN based on the back-propagation scheme with three layers of neurons are studied, and the ANN architecture is adjusted. A model class consisting of a dipping dyke in the basement of a two-layer earth with the dyke in contact with the overburden is used for numerical experiments. Six macroparameters of the 3-D model, namely the thickness of the top layer, which coincides with the depth of the dyke (D), the conductivity ratio between the first and second layers (C1,/C2,), the conductivity contrast of the dyke (C/C2,), and the width (W ), length (L ) and dip angle of the dyke (A), are used. Various groups of magnetotelluric field components and their transformations are studied in order to estimate the effect of the data type used on the ANN recognition ability. It is found that use of only the xy - and yx -components of impedance phases results in reasonable recognition errors for all unknown parameters (D: 0.02 per cent, C1/C2: 8.4 per cent, C/C2: 26.8 per cent, W : 0.02 per cent, L : 0.02 per cent, A: 0.24 per cent). The influence of the size and shape of the training data pool (including the ,gaps in education' and ,no target' effects) on the recognition properties is studied. Results from numerous ANN tests demonstrate that the ANN possesses good enough interpolation and extrapolation abilities if the training data pool contains a sufficient number of representative data sets. The effect of noise is estimated by means of mixing the synthetic data with 30, 50 and 100 per cent Gaussian noise. The unusual behaviour of the recognition errors for some of the model parameters when the data become more noisy (in particular, the fact that an increase in error is followed by a decrease) indicates that the use of standard techniques of noise reduction may give an opposite result, so the development of a special noise treatment methodology is required. Thus, it is shown that ANN-based recognition can be successfully used for inversion if the data correspond to the model class familiar to the ANN. No initial guess regarding the parameters of the 3-D target or 1-D layering is required. The ability of the ANN to teach itself using real geophysical (not only electromagnetic) data measured at a given location over a sufficiently long period means that there is the potential to use this approach for interpreting monitoring data. [source]

Chitosan Hydrogel-Capped Porous SiO2 as a pH Responsive Nano-Valve for Triggered Release of Insulin

ADVANCED FUNCTIONAL MATERIALS, Issue 5 2009
Jianmin Wu
Abstract A pH responsive, chitosan-based hydrogel film is used to cap the pores of a porous SiO2 layer. The porous SiO2 layer is prepared by thermal oxidation of an electrochemically etched Si wafer, and the hydrogel film is prepared by reaction of chitosan with glycidoxypropyltrimethoxysilane (GPTMS). Optical reflectivity spectroscopy and scanning electron microscopy (SEM) confirm that the bio-polymer only partially infiltrates the porous SiO2 film, generating a double layer structure. The optical reflectivity spectrum displays Fabry,Pérot interference fringes characteristic of a double layer, which is characterized using reflective interferometric Fourier transform spectroscopy (RIFTS). Monitoring the position of the RIFTS peak corresponding to the hydrogel layer allows direct, real-time observation of the reversible volume phase transition of the hydrogel upon cycling of pH in the range 6.0,7.4. The swelling ratio and response time are controlled by the relative amount of GPTMS in the hydrogel. The pH-dependent volume phase transition can be used to release insulin trapped in the porous SiO2 layer underneath the hydrogel film. At pH 7.4, the gel in the top layer effectively blocks insulin release, while at pH 6.0 insulin penetrates the swollen hydrogel layer, resulting in a steady release into solution. [source]

Cover Picture: A Novel Method to Orient Semiconducting Polymer Films (Adv. Funct.

ADVANCED FUNCTIONAL MATERIALS, Issue 7 2005
Mater.
Abstract A new technique for orienting thin polymer semiconductor films is reported by Österbacka and co-workers on p.,1095. The technique uses the mechanical force of a shrinking polymer transferred through a polymer multilayer structure. The orientation is obtained using three polymer layers, where the uppermost layer shrinks resulting in orientation of the semiconductor film beneath the intermediate layer. The topmost and intermediate polymer films are removed to reveal the oriented surface. The cover shows a crossed-polarizer microscopy image of an oriented regio-regular poly(3-hexylthiophene) film. We present a new technique for orienting polymer semiconductor thin films. In our technique, polymer chains are rigorously oriented without using any mechanical tools and with minimal risk of film contamination. The technique is based on the mechanical force resulting from the in-plane shrinkage exerted by a shrinker (top layer) that is used to orient the semiconductor beneath an intermediate layer; the latter acting as a force mediator. The chain orientation is demonstrated by several techniques such as crossed-polarizer microscopy, atomic force microscopy, grazing-incidence X-ray diffraction, and polarized absorption. The orientation geometry is controlled by the shrinking process and the shrinker area. The semiconductivity of the film only stems from the transistor device structures under study, and the method can therefore be generalized. [source]

Primary Cell Adhesion on RGD-Functionalized and Covalently Crosslinked Thin Polyelectrolyte Multilayer Films,

ADVANCED FUNCTIONAL MATERIALS, Issue 1 2005
C. Picart
Abstract Polyelectrolyte multilayers (PEMs) are now widely used for biomedical applications. In this work, we investigated the primary osteoblast adhesion properties of PEMs of poly(L -lysine) (PLL), poly(L -glutamic acid) (PGA), poly(alginic acid) (Palg), and poly(galacturonic acid) (Pgal). In order to compensate for the poor adhesion of the as-synthesized films, two kinds of film modifications were achieved: a purely physical modification by film crosslinking, and a chemical modification by grafting a arginine,glycine,aspartic acid (RGD) peptide to PGA. Crosslinking was performed using a water-soluble carbodiimide in combination with N -hydroxysulfosuccinimide (sulfo-NHS) to induce amide formation. This reaction was followed by Fourier-transform IR spectroscopy. For film functionalization, a 15-amino-acid peptide was grafted to PGA and deposited as the top layer of the film. PLL/PGA, PLL/Palg, and PLL/Pgal films were crosslinked or functionalized. The films were tested for both short-term adhesion properties and long-term proliferation of primary osteoblasts. Whereas the effect of film crosslinking on short-term adhesion was moderate, it was much more important for the RGD-functionalized films. On the other hand, the long-term proliferation was the same or even higher for the crosslinked films as compared with the functionalized films. This effect was particularly enhanced for the PLL/Palg and PLL/Pgal films. Finally, we functionalized PLL/PGA that had been crosslinked prior to PGA-RGD deposition. These architectures exhibited even higher short-term adhesion and proliferation. These results clearly show the important role of the physical properties of the films, besides their chemical properties, for the modulation of primary cell-adhesion behavior. [source]

Madelung Strain in Cuprate Superconductors , A Route to Enhancement of the Critical Temperature

ADVANCED MATERIALS, Issue 36 2009
Vladimir Y. Butko
"Madelung Strain" in cuprate films containing metal (M,=,La1.56Sr0.44CuO4) and insulator (I,=,La2CuO4) layers: X-ray diffraction shows that, unexpectedly, the volume of unit cell of the top layer adjusts to that of the bottom layer. The effect is due to long-range Coulomb forces; it affects interfacial superconductivity because the critical temperature scales with the unit-cell height. [source]

Miniaturization of a Laser Doppler Blood Flow Sensor by System-in-Package Technology: Fusion of an Optical Microelectromechanical Systems Chip and Integrated Circuits

IEEJ TRANSACTIONS ON ELECTRICAL AND ELECTRONIC ENGINEERING, Issue 2 2010
Wataru Iwasaki Member
Abstract We have developed the first and the smallest blood flow sensor composed of integrated circuits (ICs) fused with an optical microelectromechanical systems (MEMS) chip using system-in-package (SiP) technologies for application in a healthcare monitoring system. The probe of this blood flow sensor consists of three layers, and the optical MEMS chip is stacked as the top layer. Through silicon via (TSV), vertical-cavity surface-emitting laser (VCSEL) and cavities enable wafer-level packaging of the optical MEMS chip. The other two layers consisting of ICs are highly densified by SiP technology, and the volume of the probe is miniaturized to about one-sixth of our previously reported integrated laser Doppler blood flowmeter, an MEMS blood flow sensor to which SiP technology was not applied. Copyright © 2010 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [source]

On optimization of bio-probes

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 6 2004
N. L. Pedersen
Abstract The present paper deals with the modelling and optimization of small bio-probes that can be used for biological sensing; the bio-probes can be classified as MicroElectroMechnical Systems (MEMS). The objective is to optimize the structure of the bio-probes in order to maximize the sensing sensitivity. A biological coating results in a prestress on the sensing cantilever when certain molecules are present in the surrounding medium. The mechanical deformation due to the biological material is modelled by applying a prestress in the top layer of the bio-probes. Topology optimization is used to improve the design. In the present work it is necessary to use an interpolation scheme different from the SIMP (power law) approach which is usually used in topology optimization. In calculating the sensitivities, needed for the optimization, complications due to the prestress occur, but also due to the coupling between the elastic field and the electric field which both must be used in an integrated model. These complications are dealt with and analytically obtained sensitivities are presented. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Tailoring surface properties of cellulose acetate membranes by low-pressure plasma processing

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2010
Chun Huang
Abstract The aim of this study was to tailor the surface properties of cellulose acetate membranes using low-pressure plasma processing. Argon (Ar) plasma and Difluoromethane (CH2F2) plasma were used to control the surface wettabilities of cellulose acetate membranes. Optical emission spectroscopy was used to examine the various chemical species of low-pressure plasma processing. In this investigation, the plasma-treated surfaces were analyzed by X-ray photoelectron spectroscopy, while changes in morphology and surface roughness were determined with confocal laser scanning microscopy. Ar plasma activation resulted in hydrophilic surface. CH2F2 plasma deposited hydrophobic layer onto the cellulose acetate membrane because of strong fluorination of the top layer. The results reveal low-pressure plasma processing is an effective method to control the surface properties of cellulose acetate membranes. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source]

Skin hydration and possible shunt route penetration in controlled estradiol delivery from ultradeformable and standard liposomes

JOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 10 2001
Gamal M. M. El Maghraby
Human skin delivery of estradiol from ultradeformable and traditional liposomes was explored, comparing occlusive and open application, with the aim of examining the role of skin hydration. Partially hydrated epidermis was used for open hydration, but fully hydrated membranes were used for occluded studies. In addition, we developed a novel technique to investigate the role of shunt route penetration in skin delivery of liposomal estradiol. This compared delivery through epidermis with that through a stratum corneum (SC)/epidermis sandwich from the same skin with the additional SC forming the top layer of the sandwich. This design was based on the fact that orifices of shunts only occupy 0.1% of skin surface area and thus for SC/epidermis sandwiches there will be a negligible chance for shunts to superimpose. The top SC thus blocks most shunts available on the bottom membrane. If shunts play a major role then the delivery through sandwiches should be much reduced compared with that through epidermis, taking into consideration the expected reduction owing to increased membrane thickness. After open application, both ultradeformable and traditional liposomes improved estradiol skin delivery, with the ultradeformable liposomes being superior. Occlusion reduced the delivering efficiency of both vesicle types, supporting the theory that a hydration gradient provides the driving force. Shunt route penetration was found to play only a very minor role in liposomal delivery. In conclusion, full hydration of skin reduces estradiol delivery from liposomes and the shunt route is not the main pathway for this delivery. [source]

The highly specialized secretory epithelium in the buccal cavity of the alkalinity adapted Lake Magadi cichlid, Oreochromis alcalicus grahami (Teleostei: Cichlidae): a scanning and transmission electron microscope study

JOURNAL OF ZOOLOGY, Issue 4 2000
J. N. Maina
Abstract Oreochromis alcalicus grahami is a small cichlid fish that lives in the hot, highly alkaline, highly saline peripheral lagoons of Lake Magadi, Kenya. The fish faces profound diurnal oscillations of oxygen concentration. During the day, from photosynthetic activity of cyanobacteria (blue-green algae), the water is supersaturated with oxygen but after sunset when photosynthetic activity stops the water is virtually anoxic as a result of bacterial respiration. During the night and after explosive exercise, O. a. grahami characteristically skims the surface of the water with the mouth agape, suggesting that the buccal cavity is used as a gas-exchange organ. Contrary to expectation, however, the buccal cavity was found to be conspicuously non-vascularized: the surface epithelial lining was fundamentally of a mucus secretory type. In addition, certain cells in the deeper layers showed extensive lateral labyrinths similar to the epithelium of the renal tubules. These morphological features respectively indicated roles of secreting a protective film and regulation of ions taken across the epithelial lining of the buccal cavity. The allocation of gas-exchange to the gills and the air-bladder, osmoregulation essentially to the gills, and mucus secretion/protection to the buccal cavity displays an adaptive trade-off process in an elite animal. Effective use of the buccal cavity as a gas-exchanger would entail air-gulping followed by brief retention of it in the cavity to allow oxygen uptake. During such interval, both the gills and the air-bladder would of necessity be rendered temporarily non-functional. Skimming the top layer of water with the mouth open ensures that the gills are passively ventilated with well aerated water and the air-bladder is simultaneously used for gas-exchange, a strategy that should enhance oxygen acquisition, especially at higher ambient temperatures. [source]

An intact soil-core microcosm method to evaluate the survival and vertical dispersal of Trichoderma atroviride SC1

LETTERS IN APPLIED MICROBIOLOGY, Issue 5 2009
C.M.O. Longa
Abstract Aim:, To develop an intact soil-core microcosm method to study the survival and vertical dispersal of an experimental biocontrol agent (Trichoderma atroviride SC1) applied to the soil surface. Methods and Results:, The soil for the microcosms was collected using iron pipes with perforations corresponding to different soil layers. The tool was inserted into the soil and gently removed with the soil core inside. Trichoderma atroviride SC1 was mixed with the top layer of soil in the pipe. The experiment was performed in 2006 and 2007, and data from the microcosms were compared with results obtained under field conditions in the locations in which, the microcosms were collected, in the same periods. The concentrations of T. atroviride SC1 in the soil were estimated immediately after treatment, and 1, 5, 9 and 18 weeks after treatment at both the soil surface and the above-mentioned depths. The development of T. atroviride SC1 populations in the microcosms during the 18 weeks of monitoring was similar to that observed under field conditions. The dispersal of conidia was affected by the application of water to the soil. Conclusions:, Results demonstrate that this microcosm prototype can be used to model the behaviour of T. atroviride SC1 in soil. Significance and Impact of the Study:, The intact soil-core microcosm is a reliable, easy-to-use, fast and cheap method that could also be used in studies of similar filamentous fungi to study their probable fate in the soil prior to their being introduced into the environment. [source]

Tribological characterisation of hard coatings with and without DLC top layer in fretting tests

LUBRICATION SCIENCE, Issue 1 2006
D. KlaffkeArticle first published online: 14 DEC 200
Abstract The potential of coatings to protect components against wear and to reduce friction has led to a large variety of protective coatings. In order to check the success of coating modifications and to find solutions for different purposes, initial tests with laboratory tribometers are usually done to give information about the performance of a coating. Different Ti-based coatings (TiN, Ti(C,N), and TiAlN) and NiP were tested in comparison to coatings with an additional diamond-like carbon (DLC) top coating. Tests were done in laboratory air at room temperature with oscillating sliding (gross slip fretting) with a ball-on-disc arrangement against a ceramic ball (Al2O3). Special attention was paid to possible effects of moisture (relative humidity). The coefficient of friction was measured on line, and the volumetric wear at the disc was determined after the test from microscopic measurements of the wear scar and additional profiles. The friction and wear behaviour is quite different for the different coatings and depends more or less on the relative humidity. The DLC coating on top of the other coatings reduces friction and wear considerably. In normal and in moist air the coefficient of wear of the DLC top-layer coating is significantly less than 10,6,mm3/Nm and the coefficient of friction is below 0.1. In dry air, however, there is a certain tendency to high wear and high friction. Copyright © 2006 John Wiley & Sons, Ltd. [source]

C-shaped ultra-wideband bandpass filter with WLAN notch band

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 5 2010
Pai-Yi Hsiao
Abstract A compact bandpass filter (BPF) embedded with 5.8 GHz wireless-LAN notch is presented for 3.1,10.6 GHz ultra-wideband (UWB) systems. The proposed UWB-BPF based on a defect-grounded structure is implemented with an FR4 board. Two open-loop resonators on the top layer provide a narrow notch band whose center frequency can be easily adjusted by varying the sizes of the open-loop. A simple C-shaped slot on the bottom ground layer is adopted to improve the bandwidth performance. The characteristics of UWB-BPF are analyzed and simulated using a circuit model of LC lump elements. The size of the filter is at least 34% less than those filters with the same specification. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1215,1218, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25153 [source]

A combined imaging, microthermal and spectroscopic study of a multilayer packaging system

PACKAGING TECHNOLOGY AND SCIENCE, Issue 3 2004
I. Woodward
Abstract The effectiveness of a packaging solution for the pharmaceutical and food industry is dependent on the integrity of the constituent layers and the interfaces formed between them. The deconvolution and analysis of the many intimate layers found in packaging is analytically challenging, requiring techniques capable of identifying sub-micron regions. Here we have characterized the chemical and physical nature of the layers in a multilayer packaging system along with the interfaces, using a combination of high-resolution atomic force microscopy (AFM), microthermal analysis using scanning thermal microscopy (SThM), and Fourier transform infrared (FT-IR) spectroscopy. In particular, localized thermal analysis is shown to reveal the thermal transitions of the individual layers, but it was found that care must be exercised when melting through one layer to the next, as this can result in overestimates of melting temperatures of the underlying layer due to excess power loss from the SThM probe to the already molten top layer surrounding the probe. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Photoluminescence and TEM characterization of (AlyGa1,y)1,xInxP layers grown on graded buffers

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2007
J. Novak
Abstract Composition, crystallographic quality and low temperature photoluminescence of AlGaInP quaternary layers were studied. These layers were grown on the InGaP/GaP graded buffers by metalorganic vapour phase epitaxy. Final composition of the graded buffer top layer was xIn = 0.24. Incorporation of the small amount Al into quaternary led to a substantial improvement of the surface morpohology and crystallographic quality observed in cross-sectional TEM view. Incorporation of higher amount of Al (above 1%) led to the increase of lattice mismatch, decrease of In content in the alloy and to the indirect band gap. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

The decline of metallophyte vegetation in floodplain grasslands: Implications for conservation and restoration

APPLIED VEGETATION SCIENCE, Issue 1 2009
Esther C.H.E.T. Lucassen
Abstract Question: Which biogeochemical processes are responsible for the decline of endemic metallophyte vegetation in floodplain grasslands? Location: Floodplain grasslands along the River Geul (the Netherlands) and metalliferous mine spoils near the River Geul (Belgium). Methods: In order to find factors and soil processes that have caused a decline of metallophytes and an increase of pseudo-metallophytes in floodplain grasslands, a soil study was done at locations currently and formerly dominated by metallophytes. In addition, changes in soil chemistry in recent decades in floodplain grasslands were investigated. Finally, a 2-year plant growth experiment was performed in the field, to test the effects of improving soil conditions by topsoil removal. Results: Metallophytes only occur on acidic floodplain soils (pH-H2O 5.0-5.5) with relatively high Zn availability (total Zn >40 ,mol g,1; Zn/Ca>0.8; Zn-H2O>59 ,mol kg,1) combined with low phosphate availability (Olsen-P,1250 ,mol kg,1). The Olsen-P and total Ca concentrations were relatively high in topsoil (0-20 cm), while total Zn was high throughout the soil profile (0-50 cm). Removal of topsoil led to recovery of P and Zn availability. Under the new soil conditions there was almost no growth and expansion of pseudo-metalliferous grasses in time, wheras metallophytes easily established, maintained and reproduced with significant increases in cover over time. Conclusions: On a global scale, metallophyte vegetation types are increasingly under threat of extinction. Our study shows that factors leading to higher soil alkalinity inhibit Zn availability at the expense of the metallophyte vegetation. Factors leading to a higher Olsen-P concentration stimulate the growth of more competitive pseudo-metallophyte grasses. Both eutrophication and alkalinisation have contributed to the decline of metallophyte vegetation in floodplains of the River Geul. Removal of the alkaline- and phosphate-enriched soil top layer restores the original soil chemistry and enables re-colonisation by the metallophyte vegetation. The results can be applied in conservation and restoration strategies for such sites. [source]

Synthesis of mesoporous alumina,titania membranes by the sol-gel method

ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2010
A. Bottino
Abstract Ceramic tubular membranes with alumina,titania top layers were prepared using the dipping procedure and a mixed sol composed of both boehmite and titania. The influence of the Ti/Al ratio, the amount of an organic additive (namely hydroxypropylcellulose), the dip-time, the number of depositions and drying,calcination conditions on the membrane morphology and transport properties were investigated. The conditions for the formation of a defect-free and homogeneous top layer were individuated. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source]

Transdermal drug delivery by coated microneedles: geometry effects on drug concentration in blood

ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 6 2009
Barrak Al-Qallaf
Abstract Drug administration through transdermal delivery is restricted by the top layer of skin, the stratum corneum. One possible solution to overcome the barrier function of the stratum corneum is to employ microneedle arrays. However, detailed theoretical models relating drug-coated microneedles and their geometry to the drug concentration in the blood are limited. This article aims to address this issue by examining the blood concentration profiles for a model drug, insulin, that has been administered via coated microneedles. A mathematical model is introduced and applied to predict theoretical blood concentrations. Furthermore, the insulin concentration in blood is calculated for a range of different microneedle shapes and dimensions to identify the most effective geometry. The results indicate that the optimum microneedle geometry in terms of maximizing insulin concentration was a rocket-shaped needle with a constant tip angle of 90°. Also, it has been found that the number of microneedles in an array is the most significant factor in determining maximum insulin concentration in the blood (Cb, max). Penetration depth of the microneedle, centre-to-centre spacing and microneedle thickness had a less significant effect on the maximum insulin concentration in the blood. It is envisaged that the current study will help in designing microneedles of optimum size and shape for transdermal drug delivery. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source]

Formation of submarginal and proglacial end moraines: implications of ice-flow mechanism during the 1963,64 surge of Brúarjökull, Iceland

BOREAS, Issue 3 2009
ÍVAR ÖRN BENEDIKTSSON
The morphology, sedimentology and architecture of an end moraine formed by a ,9 km surge of Brúarjökull in 1963,64 are described and related to ice-marginal conditions at surge termination. Field observations and accurate mapping using digital elevation models and high-resolution aerial photographs recorded at surge termination and after the surge show that commonly the surge end moraine was positioned underneath the glacier snout by the termination of the surge. Ground-penetrating radar profiles and sedimentological data reveal 4,5 m thick deformed sediments consisting of a top layer of till overlying gravel and fine-grained sediments, and structural geological investigations show that the end moraine is dominated by thrust sheets. A sequential model explaining the formation of submarginal end moraines is proposed. The hydraulic conductivity of the bed had a major influence on the subglacial drainage efficiency and associated porewater pressure at the end of the surge, thereby affecting the rates of subglacial deformation. High porewater pressure in the till decreased its shear strength and raised its strain rate, while low porewater pressure in the underlying gravel had the opposite effect, such that the gravel deformed more slowly than the till. The principal velocity component was therefore located within the till, allowing the glacier to override the gravel thrust sheets that constitute the end moraine. The model suggests that the processes responsible for the formation of submarginal end moraines are different from those operating during the formation of proglacial end moraines. [source]

Physico-Chemical Characterization of Nanofiltration Membranes

CHEMPHYSCHEM, Issue 3 2007
Katleen Boussu
Abstract This study presents a methodology for an in-depth characterization of six representative commercial nanofiltration membranes. Laboratory-made polyethersulfone membranes are included for reference. Besides the physical characterization [molecular weight cut-off (MWCO), surface charge, roughness and hydrophobicity], the membranes are also studied for their chemical composition [attenuated total reflectance Fourier spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS)] and porosity [positron annihilation spectroscopy (PAS)]. The chemical characterization indicates that all membranes are composed of at least two different layers. The presence of an additional third layer is proved and studied for membranes with a polyamide top layer. PAS experiments, in combination with FIB (focused ion beam) images, show that these membranes also have a thinner and a less porous skin layer (upper part of the top layer). In the skin layer, two different pore sizes are observed for all commercial membranes: a pore size of 1.25,1.55 Å as well as a pore size of 3.20,3.95 Å (both depending on the membrane type). Thus, the pore size distribution in nanofiltration membranes is bimodal, in contrast to the generally accepted log-normal distribution. Although the pore sizes are rather similar for all commercial membranes, their pore volume fraction and hence their porosity differ significantly. [source]

Phase Separation of Polyfluorene-Based Blend Films and Its Influence on Device Operations,

ADVANCED MATERIALS, Issue 11 2006
Y. Xia
Vertical phase separations have been found in blend films (TFB:F8BT) of polymer light-emitting diodes, giving rise to better device performances. A TFB wetting layer is present over most of the bottom interface with the substrate, as evidenced by the fluorescent microscopy images after top layers are etched away by oxygen plasma (see figure). [source]

Yield, Boll Distribution and Fibre Quality of Hybrid Cotton (Gossypium hirsutum L.) as influenced by Organic and Modern Methods of Cultivation

JOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 4 2006
D. Blaise
Abstract India is the largest cotton-growing country (8.9 million hectares) in the world and most of the area is rain-dependent. Large amount of pesticides are used for the control of sucking pests and lepidopterans. Increasing demand for clean organic fibre has led to an interest in organic cotton. However, information on the effects of organic cultivation on fibre quality is limited. Seed cotton yield and fibre quality (length, strength, micronaire and uniformity) were determined for an organic and modern method of cultivation during 3 years (2002,2003 to 2004,2005) of a 11-year (1994,1995 to 2004,2005) study. Vertical and horizontal distribution of bolls on a cotton plant was also determined in 2003,2004 and 2004,2005. At the end of year 11, soil samples were collected and analysed for soil organic carbon content, water-stable aggregates (%), and mean weight diameter. Averaged over 3 years, an additional 94 kg seed cotton ha,1 was produced in the organic over the modern method of cultivation and the difference was significant. The year × treatment interaction was significant. Seed cotton yield in the organic plots was significantly greater than the modern method of cultivation plots in 2003,2004 because of a well-distributed normal rainfall and low pest incidence. The main stem nodes 13,22 accounted for the largest numbers of bolls present on the plant. Plants of the organic plots had significantly (37,71 %) more bolls on nodes 13,27 than those for the plants of the modern method of cultivation. Lateral distribution of bolls on a sympodial (fruiting) branch, was noticed up to fruiting point 11. However, treatment differences were not significant. With regard to fibre quality (length, strength, fineness and uniformity), differences between years were significant. Inferior quality fibre was produced in 2004,2005 because of delayed planting and early cessation of rain. On average, cotton grown under organic conditions compared with the modern method of cultivation had significantly better fibre length (25.1 vs. 24.0 mm) and strength (18.8 vs. 17.9 g tex,1). Soil samples of the organic plots had significantly greater C content, water-stable aggregates and mean weight diameter than the modern method of cultivation plots. Differences were restricted to the top layers (0,0.1 and 0.1,0.2 m). Yield benefits of growing cotton in an organic system over the modern method of cultivation are expected to be greater in years receiving normal rainfall and having low pest incidence. [source]

Transient fluidization and segregation of binary mixtures of particles

AICHE JOURNAL, Issue 11 2000
A. Marzocchella
Fluidization of binary mixtures of particles belonging to group B of the Geldart classification of powders was studied. Beds tested were prepared by mixing in different proportions particles with almost equal density (,2,500 kg/m3) and dissimilar size (125 ,m silica sand and 500 ,m glass beads). Experiments were carried out using a segmented fluidization column equipped with multiple pressure transducers. Experimental procedures included continuous monitoring of pressure drop at different locations along the bed during quasi-steady or stepwise changes of gas superficial velocity, and characterization of particle-size distributions in each segment of the fluidization column after fluidization of the bed for given times. Three ranges of gas superficial velocity were recognized for each solids mixture. At low velocity the bed behaves as a fixed bed. At high velocity, it is fully and steadily fluidized. In an intermediate velocity range, transient fluidization takes place: an initially uniform fluidized bed eventually undergoes segregation, giving rise to a defluidized bottom layer rich in the coarser solids and to a "supernatant" fluidized layer where finer particles prevail. The thresholds between these velocity ranges are rather sharp and were characterized as functions of initial bed composition. Rates at which the defluidized solids layer builds up from initially uniform beds, and the ultimate compositions of the defluidized bottom and fluidized top layers are characterized for beds with different compositions at variable gas superficial velocity. [source]