Gas permeation in silicon-oxide/polymer (SiOx/PET) barrier films: role of the oxide lattice, nano-defects and macro-defects

We propose a model for permeation in oxide coated gas barrier films. The model accounts for diffusion through the amorphous oxide lattice, nano-defects within the lattice, and macro-defects. The presence of nano-defects indicate the oxide layer is more similar to a nano-porous solid (such as zeolite) than silica glass with respect to permeation properties. This explains why the permeability of oxide coated polymers is much greater, and the activation energy of permeation much lower, than values expected for polymers coated with glass. We have used the model to interpret permeability and activation energies measured for the inert gases (He, Ne and Ar) in evaporated SiOx films of varying thickness (13-70 nm) coated on a polymer substrate. Atomic force and scanning electron microscopy were used to study the structure of the oxide layer. Although no defects could be detected by microscopy, the permeation data indicate that macro-defects (>1 nm), nano-defects (0.3-0.4 nm) and the lattice interstices (<0.3 nm) all contribute to the total permeation. (C) 2002 Elsevier Science B.V. All rights reserved.

Embryogenesis and metamorphosis in a haplosclerid demosponge: gastrulation and transdifferentiation of larval ciliated cells to choanocytes

Early development and metamorphosis of Reniera sp., a haplosclerid demosponge, have been examined to determine how gastrulation occurs in this species, and whether there is an inversion of the primary germ layers at metamorphosis. Embryogenesis occurs by unequal cleavage of blastomeres to form a solid blastula consisting micro- and macromeres; multipolar migration of the micromeres to the surface of the embryo results in a bi-layered embryo and is interpreted as gastrulation. Polarity of the embryo is determined by the movement of pigment-containing micromeres to one pole of the embryo; this pole later becomes the posterior pole of the swimming larva. The bi-layered larva has a fully differentiated monociliated outer cell layer, and a solid interior of various cell types surrounded by dense collagen. The pigmented cells at the posterior pole give rise to long cilia that are capable of responding to environmental stimuli. Larvae settle on their anterior pole. Fluorescent labeling of the monociliated outer cell layer with a cell-lineage marker (CMFDA) demonstrates that the monociliated cells resorb their cilia, migrate inwards, and transdifferentiate into the choanocytes of the juvenile sponge, and into other amoeboid cells. The development of the flagellated choanocytes and other cells in the juvenile from the monociliated outer layer of this sponge's larva is interpreted as the dedifferentiation of fully differentiated larval cells-a process seen during the metamorphosis of other ciliated invertebrate larvae-not as inversion of the primary germ layers. These results suggest that the sequences of development in this haplosclerid demosponge are not very different than those observed in many cnidarians.

Immunity to malaria after administration of ultra-low doses of red cells infected with Plasmodium falciparum

Background The ability of T cells, acting independently of antibodies, to control malaria parasite growth in people has not been defined. If such cell-mediated immunity was shown to be effective, an additional vaccine strategy could be pursued. Our aim was to ascertain whether or not development of cell-mediated immunity to Plasmodium falciparum blood-stage infection could be induced in human beings by exposure to malaria parasites in very low density. Methods We enrolled five volunteers from the staff at our research institute who had never had malaria. We used a cryopreserved inoculum of red cells infected with P falciparum strain 3D7 to give them repeated subclinical infections of malaria that we then cured early with drugs, to induce cell-mediated immune responses. We tested for development of immunity by measurement of parasite concentrations in the blood of volunteers by PCR of the multicopy gene STEVOR and by following up the volunteers clinically, and by measuring antibody and cellular immune responses to the parasite. Findings After challenge and a extended period without drug cure, volunteers were protected against malaria as indicated by absence of parasites or parasite DNA in the blood, and absence of clinical symptoms. Immunity was characterised by absence of detectable antibodies that bind the parasite or infected red cells, but by the presence of a proliferative T-cell response, involving CD4+ and CD8+ T cells, a cytokine response, consisting of interferon gamma but not interleukin 4 or interleukin 10, induction of high concentrations of nitric oxide synthase activity in peripheral blood mononuclear cells, and a drop in the number of peripheral natural killer T cells. Interpretation People can be protected against the erythrocytic stage of malaria by a strong cell-mediated immune response, in the absence of detectable parasite-specific antibodies, suggesting an additional strategy for development of a malaria vaccine.

Platelet inhibitory effects of the nitric oxide donor drug MAHMA NONOate in vivo in rats

The platelet inhibitory effects of the nitric oxide (NO) donor drug MAHMA NONOate ((Z-1-{N-methyl-N-[6-(N-methylammoniohexyl)amino] diazen-1-ium-1,2-diolate) were examined in anaesthetised rats and compared with those of S-nitrosoglutathione (GSNO; an S-nitrosothiol). Bolus administration of the aggregating agent ADP dose-dependently reduced the number of circulating free platelets. Intravenous infusions of MAHMA NONOate (3-30 nmol/kg/min) dose-dependently inhibited the effect of 0.3 mumol/kg ADP. MAHMA NONOate was approximately 10-fold more potent than GSNO. MAHMA NONOate (0.3-10 nmol/kg/min) also reduced systemic artery pressure and was again 10-fold more potent than GSNO. Thus MAHMA NONOate has both platelet inhibitory and vasodepressor effects in vivo. The dose ranges for these two effects overlapped, although blood pressure was affected at slightly lower doses. The platelet inhibitory effects compared favourably with those of GSNO, even though NONOates generate free radical NO which, in theory, could have been scavenged by haemoglobin. Therefore platelet inhibition may be a useful therapeutic property of NONOates. (C) 2003 Elsevier B.V. All rights reserved.

N-aminopyrroledione-hydrazonoketene-pyrazolium oxide-pyrazolone rearrangements and pyrazolone tautomerism

Flash vacuum thermolysis (FVT) of 1-(dimethylamino)pyrrole-2,3-diones 5 causes extrusion of CO with formation of transient hydrazonoketenes 7. The transient ketenes 7 are observable in the form of weak bands at 2130 (7a) or 2115 cm(-1) (7b) in the Ar matrix IR spectra resulting from either FVT or photolysis of either 5 or 1,1- dimethylpyrazolium-5- oxides 8, and these absorptions are in excellent agreement with B3LYP/6-31G* frequency calculations. Under FVT conditions the ketenes 7 cyclize to pyrazolium oxides 8, which undergo 1,4-migration of a methyl group to yield 1,4-dimethyl-3-phenylpyrazole-5(4H)-one 9a and 1,4,4-trimethyl-3-phenylpyrazole-5(4H)-one 9b. All three tautomers of 9a have been characterized, viz. the CH form 9a (most stable form in the gas phase, the solid state and solvents of low polarity), the OH form 9a' (metastable solid at room temperature) and the NH form 9a (stable in aprotic dipolar solvents). The isomeric 1,4-dimethyl-5-phenylpyrazole-3(2H)-one 12 tautomerizes to the 3-hydroxypyrazole 12'. The crystal structure of the hydrochloride 14 of 9a'/9a is reported, representing the first structurally characterised example of a protonated 5-hydroxypyrazole.

Transport properties in microcrystalline silicon solar cells under AM1.5 illumination analysed by two-dimensional numerical simulation

Microcrystalline silicon is a two-phase material. Its composition can be interpreted as a series of grains of crystalline silicon imbedded in an amorphous silicon tissue, with a high concentration of dangling bonds in the transition regions. In this paper, results for the transport properties of a mu c-Si:H p-i-n junction obtained by means of two-dimensional numerical simulation are reported. The role played by the boundary regions between the crystalline grains and the amorphous matrix is taken into account and these regions are treated similar to a heterojunction interface. The device is analysed under AM1.5 illumination and the paper outlines the influence of the local electric field at the grain boundary transition regions on the internal electric configuration of the device and on the transport mechanism within the mu c-Si:H intrinsic layer.

Boron-doped nanocrystalline silicon thin films for solar cells

This article reports on the structural, electronic, and optical properties of boron-doped hydrogenated nanocrystalline silicon (nc-Si: H) thin films. The films were deposited by plasma-enhanced chemical vapour deposition (PECVD) at a substrate temperature of 150 degrees C. Crystalline volume fraction and dark conductivity of the films were determined as a function of trimethylboron-to-silane flow ratio. Optical constants of doped and undoped nc-Si: H were obtained from transmission and reflection spectra. By employing p(+) nc-Si: H as a window layer combined with a p' a-SiC buffer layer, a-Si: H-based p-p'-i-n solar cells on ZnO:Al-coated glass substrates were fabricated. Device characteristics were obtained from current-voltage and spectral-response measurements. (C) 2011 Elsevier B. V. All rights reserved.

Study on the use of MgAl hydrotalcites as solid heterogeneous catalysts for biodiesel production

This paper, reports experimental work on the use of new heterogeneous solid basic catalysts for biodiesel production: double oxides of Mg and Al, produced by calcination, at high temperature, of MgAl lamellar structures, the hydrotalcites (HT). The most suitable catalyst system studied are hydrotalcite Mg:Al 2:1 calcinated at 507 degrees C and 700 degrees C, leading to higher values of FAME also in the second reaction stage. One of the prepared catalysts resulted in 97.1% Fatty acids methyl esters (FAME) in the 1st reaction step, 92.2% FAME in the 2nd reaction step and 34% FAME in the 3rd reaction step. The biodiesel obtained in the transesterification reaction showed composition and quality parameters within the limits specified by the European Standard EN 14214. 2.5% wt catalyst/oil and a molar ratio methanol:oil of 9:1 or 12:1 at 60 -65 degrees C and 4 h of reaction time are the best operating conditions achieved in this study. This study showed the potential of Mg/Al hydrotalcites as heterogeneous catalysts for biodiesel production. (C) 2011 Elsevier Ltd. All rights reserved.

Iron oxide/gold core/shell nanomagnetic probes and CdS biolabels for amplified electrochemical immunosensing of Salmonella typhimurium

There is an imminent need for rapid methods to detect and determine pathogenic bacteria in food products as alternatives to the laborious and time-consuming culture procedures. In this work, an electrochemical immunoassay using iron/gold core/shell nanoparticles (Fe@Au) conjugated with anti-Salmonella antibodies was developed. The chemical synthesis and functionalization of magnetic and gold-coated magnetic nanoparticles is reported. Fe@Au nanoparticles were functionalized with different self-assembled monolayers and characterized using ultraviolet-visible spectrometry, transmission electron microscopy, and voltammetric techniques. The determination of Salmonella typhimurium, on screen-printed carbon electrodes, was performed by square-wave anodic stripping voltammetry through the use of CdS nanocrystals. The calibration curve was established between 1×101 and 1×106 cells/mL and the limit of detection was 13 cells/mL. The developed method showed that it is possible to determine the bacteria in milk at low concentrations and is suitable for the rapid (less than 1 h) and sensitive detection of S. typhimurium in real samples. Therefore, the developed methodology could contribute to the improvement of the quality control of food samples.

Study of Annealed Indium Tin Oxide-Films prepared by RF Reactive Magnetron Sputtering

Tin doped indium oxide (ITO) films were deposited on glass substrates by rf reactive magnetron sputtering using a metallic alloy target (In-Sn, 90-10). The post-deposition annealing has been done for ITO films in air and the effect of annealing temperature on the electrical, optical and structural properties of ITO films was studied. It has been found that the increase of the annealing temperature will improve the film electrical properties. The resistivity of as deposited film is about 1.3 x 10(-1) Omega*cm and decreases down to 6.9 x 10(-3) Omega*cm as the annealing temperature is increased up to 500 degrees C. In addition, the annealing will also increase the film surface roughness which can improve the efficiency of amorphous silicon solar cells by increasing the amount of light trapping.

Cu2ZnSnS4 solar cells prepared with sulphurized dc-sputtered stacked metallic precursors

In the present work we report the details of the preparation and characterization results of Cu2ZnSnS4 (CZTS) based solar cells. The CZTS absorber was obtained by sulphurization of dc magnetron sputtered Zn/Sn/Cu precursor layers. The morphology, composition and structure of the absorber layer were studied by scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction and Raman scattering. The majority carrier type was identified via a hot point probe analysis. The hole density, space charge region width and band gap energy were estimated from the external quantum efficiency measurements. A MoS2 layer that formed during the sulphurization process was also identified and analyzed in this work. The solar cells had the following structure: soda lime glass/Mo/CZTS/CdS/i-ZnO/ZnO:Al/Al grid. The best solar cell showed an opencircuit voltage of 345 mV, a short-circuit current density of 4.42 mA/cm2, a fill factor of 44.29% and an efficiency of 0.68% under illumination in simulated standard test conditions: AM 1.5 and 100 mW/cm2.

Solid-State bipolar Marx modulator modeling

A mathematical model that simulates the operation of a solid-state bipolar Marx modulator topology, including the influence of parasitic capacitances is presented and discussed as a tool to analyze the circuit behavior and to assist the design engineer to select the semiconductor components and to enhance the operating performance. Simulations show good agreement with experimental results, considering a four stage circuit assembled with 1200 V isolated gate bipolar transistors and diodes, operating at 1000 V dc input voltage and 1-kHz frequency, giving 4 kV and 10-mu s output pulses into several resistive loads. Results show that parasitic capacitances between Marx cells to ground can significantly load the solid-state switches, adding new operating circuit conditions.

Non-enzymatic assay for glucose by using immobilized whole-cells of E. coli containing glucose binding protein fused to fluorescent proteins

Glucose monitoring in vivo is a crucial issue for gaining new understanding of diabetes. Glucose binding protein (GBP) fused to two fluorescent indicator proteins (FLIP) was used in the present study such as FLIP-glu- 3.2 mM. Recombinant Escherichia coli whole-cells containing genetically encoded nanosensors as well as cell-free extracts were immobilized either on inner epidermis of onion bulb scale or on 96-well microtiter plates in the presence of glutaraldehyde. Glucose monitoring was carried out by Förster Resonance Energy Transfer (FRET) analysis due the cyano and yellow fluorescent proteins (ECFP and EYFP) immobilized in both these supports. The recovery of these immobilized FLIP nanosensors compared with the free whole-cells and cell-free extract was in the range of 50–90%. Moreover, the data revealed that these FLIP nanosensors can be immobilized in such solid supports with retention of their biological activity. Glucose assay was devised by FRET analysis by using these nanosensors in real samples which detected glucose in the linear range of 0–24 mM with a limit of detection of 0.11 mM glucose. On the other hand, storage and operational stability studies revealed that they are very stable and can be re-used several times (i.e. at least 20 times) without any significant loss of FRET signal. To author's knowledge, this is the first report on the use of such immobilization supports for whole-cells and cell-free extract containing FLIP nanosensor for glucose assay. On the other hand, this is a novel and cheap high throughput method for glucose assay.

25 kV bipolar solid-state Marx generator for industrial food applications

The preliminary results from a bipolar industrial solidstate based Marx generator, developed for the food industry, capable of delivering 25 kV/250 A positive and negative pulses with 12 kW average power, are presented and discussed. This modular topology uses only four controlled switches per cell, 27 cells in total that can be charged up to 1000V each, the two extra cells are used for droop compensation. The triggering signals for all the switches are generated by a FPGA. Considering that biomaterials are similar to resistive type loads, experimental results from this new bipolar 25 kV modulator into resistive loads are presented and discussed.

Preparation and characterization of dye-sensitized TiO2 nanorod solar cells

TiO2 nanorodswere prepared by DC reactive magnetron sputtering technique and applied to dye-sensitized solar cells (DSSCs). The length of the TiO2 nanorods was varied from 1 μm to 6 μm. The scanning electronmicroscopy images showthat the nanorods are perpendicular to the substrate. Both the X-ray diffraction patterns and Raman scattering results show that the nanorods have an anatase phase; no other phase has been observed. (101) and the (220) diffraction peaks have been observed for the TiO2 nanorods. The (101) diffraction peak intensity remained constant despite the increase of nanorod length, while the intensity of the (220) diffraction peak increased almost linearly with the nanorod length. These nanorods were used as the working electrodes in DSSCs and the effect of the nanorod length on the conversion efficiency has been studied. An optimumphotoelectric conversion efficiency of 4.8% has been achieved for 4 μm length nanorods.