Structural, Optical, and Electrical Properties of Nb-Doped ZnO Thin Films Prepared by Spray Pyrolysis Method

Niobium (Nb) doping (0 at.% to 3 at.%) in ZnO thin films prepared by the chemical spray pyrolysis method at a substrate temperature of 400°C enhances the optical and electrical properties but deteriorates the structural quality of the films. The films are polycrystalline with hexagonal structure having a preferential orientation along the (002) crystallographic direction. The film doped with 3 at.% Nb demonstrates a maximum average transmittance of ~83% in the visible region. A strong blue emission is recorded for both pure and doped films, and the intensity is substantially enhanced with Nb doping due to interface and valence-band transitions. Vacuum annealing at 400°C for 60 min improves the electrical characteristics of the films, and the highest mobility of 71 cm²/V s is achieved for the 1 at.% Nb-doped ZnO films.     

Influence of crack tip constraint on void growth in pressure sensitive plastic solids - I: 2D analysis

In this work, the effect of constraint on void growth near a notch tip under mode-I loading is investigated in materials exhibiting pressure sensitive yielding and plastic dilatancy. To this end, large deformation elastic-plastic finite element analyses are performed using a two-dimensional (2D) plane strain, modified boundary layer formulation by prescribing the elastic K − T field as remote boundary conditions. The analyses are conducted for different values of K (or J) and T-stress. The material is assumed to obey a finite strain, Extended Drucker-Prager yield condition. The roles of pressure sensitivity, plastic dilatancy and yield locus shape on the interaction between the notch and a nearby void are studied by examining the distribution of hydrostatic stress and plastic strain in the ligament connecting them as well as the growth of notch and the void. The results show that void growth with respect to J is enhanced due to pressure sensitivity, and more so when the plastic flow is non-dilatational. By contrast, irrespective of pressure sensitivity, loss of crack tip constraint can significantly retard void growth.     

Experiments and modeling of propane combustion with vitiation

The chemical species composition of a vitiated oxidizer stream can significantly affect the combustion processes that occur in many propulsion and power generation systems. Experiments were performed to investigate the chemical kinetic effects of vitiation on ignition and flame propagation of hydrocarbon fuels using propane. Atmospheric-pressure flow reactor experiments were performed to investigate the effect of NO_x on propane ignition delay time at varying O₂ levels (14–21 mol%) and varying equivalence ratios (0.5–1.5) with reactor temperatures of 875 K and 917 K. Laminar flame speed measurements were obtained using a Bunsen burner facility to investigate the effect of CO₂ dilution on flame propagation at an inlet temperature of 650 K. Experimental and modeling results show that small amounts of NO can significantly reduce the ignition delay time of propane in the low- and intermediate-temperature regimes. For example, 755 ppmv NOx in the vitiated stream reduced the ignition delay time of a stoichiometric propane/air mixture by 75% at 875 K. Chemical kinetic modeling shows that H-atom abstraction reaction of the fuel molecule by NO₂ plays a critical role in promoting ignition in conjunction with reactions between NO and less reactive radicals such as HO₂ and CH₃O₂ at low and intermediate temperatures. Experimental results show that the presence of 10 mol% CO₂ in the vitiated air reduces the peak laminar flame speed by up to a factor of two. Chemical kinetic effects of CO₂ contribute to the reduction in flame speed by suppressing the formation of OH radicals in addition to the lower flame temperature caused by dilution. Overall, the detailed chemical kinetic mechanism developed in the current work predicts the chemical kinetic effects of vitiated species, namely NO_x and CO₂, on propane combustion reasonably well. Moreover, the reaction kinetic scheme also predicts the negative temperature coefficient (NTC) behavior of propane during low-temperature oxidation.     

Alkaline protease from Bacillus cereus VITSN04: Potential application as a dehairing agent

The objective of this work is to use protease enzyme as an ecofriendly alternative to chemicals in dehairing. An alkaline protease producing bacterium was isolated from protein-rich soil sample. The bacterium was identified as Bacillus cereus VITSN04 by 16S rRNA gene sequencing method. Growth characteristics and protease activity were studied in yeast, malt, beef, nutrient broth and soybean casein digest media and the enzyme secretion was found to correspond with growth. Maximum protease production was obtained in soybean casein digest medium at 16h with the activity of 200.1±0.68U/ml and a correlation coefficient of 0.965 between growth and enzyme production. The crude enzyme was found to have maximum activity at 30°C and pH 8.0. The protease was purified by ammonium sulphate precipitation, Sephadex G-50 and G-100 gel filtration chromatography. The purified protease was homogeneous on non-denaturing PAGE and its molecular weight was estimated to be 32kDa. The purified protease was of the serine type as it was inhibited by phenylmethylsulphonyl fluoride. The crude enzyme preparation was found to be effective in dehairing goat skins in leather processing.     

SiRNA drug delivery by biodegradable polymeric nanoparticles

RNA interference (RNAi) is an emerging technology in which the introduction of double-stranded RNA (dsRNA) into a diverse range of organisms and cell types causes degradation of the complementary mRNA. It offers a broad spectrum of applications in both biological and medical research. Small interference RNA (siRNA) was recently explored for its therapeutical potential. However, the drug delivery of siRNA oligos is very novel and is in great need of future research. To this end, a biodegradable poly(D,L-lactide-co-glycolide) (PLGA) nanoparticle drug carrier system was prepared to load siRNA oligos with desired physicochemical properties. The nanoparticles were characterized by scanning electron microscopy and laser diffraction particle sizer. The delivery of siRNA into the targeted 293T cells was observed using fluorescent-labeled double-stranded Cy3-oligos. The model siRNA oligos, si-GFP-RNA, were also successfully loaded into PLGA nanoparticles and delivered in 293T cells. The gene silencing effect and the inhibition of GFP expression were investigated using fluorescent microscopy. Both positive and negative controls were used to compare with the new siRNA nanoparticle delivery system. It was found that nanoparticles offered both effective delivery of siRNA and prominent GFP gene silencing effect. Compared to conventional carrier systems, the new biodegradable polymeric nanoparticle system may also offer improved formulation stability, which is practically beneficial and may be used in the future clinical studies of siRNA therapeutics.     

Electrochemical characterization of oxide formed on chromium containing mild steel alloys in LiOH medium

Flow accelerated corrosion leads to wall thinning of outlet-feeder pipes in the primary heat transport system of pressurized heavy water reactors and can even necessitate enmasse feeder replacement. Replacement of carbon steel 106-grade-B (CS) with chromium containing carbon steel reduces the risk of this failure. This paper discusses the role of small additions of chromium in modifying the properties of the oxide film. CS and chromium containing mild steels viz., A333, 2.25Cr–1Mo and modified 9Cr–1Mo alloy were exposed to primary heat transport (PHT) system chemistry conditions. The oxide films formed were characterized by electrochemical and surface characterization techniques. Mott–Schottky analysis showed donor type of defects. The densities of defects in the oxides of chromium containing alloys were 3–15 times less than that in CS. In presence of ∼200 ppb of dissolved oxygen, the oxides formed were hematite with two orders of magnitude smaller concentration of defects as compared to that formed under reducing conditions. These results suggest that the presence of chromium lowers the defect density of the oxide film and thus ensures a reduced corrosion rate.     

Tissue-specific activation of the osmotin gene by ABA, C2H4 and NaCl involves the same promoter region

The gene encoding the antifungal protein osmotin is induced by several hormonal and environmental signals. In this study, tissue-specific and inducer-mediated expression of the reporter gene beta-glucuronidase (uidA) fused to different fragment lengths of the osmotin promoter was evaluated in transgenic tobacco (Nicotiana tabacum). The region of the promoter between -248 to -108 (Fragment A) was found to be essential and sufficient for inducer (abscisic acid (ABA), C2H4 and NaCl)-mediated expression of the reporter gene. Expression of the reporter gene was developmentally regulated and increased with maturity of leaves, stem and flowers. Expression also was tissue-specific being most highly expressed in epidermis and vascular parenchyma of the stem. The regulators ABA, C2H4 and NaCl exhibited tissue-specific induction of this promoter. The promoter was specifically responsive to C2H4 in flowers at virtually all stages of development, but not responsive in these tissues to ABA or NaCl. Conversely, ABA and NaCl were able to induce reporter gene activity using promoter Fragment A in specific tissues of root where C2H4 was unable to induce activity. Further dissection of the promoter Fragment A into fragments containing either the conserved GCC element (PR); PR/AT; or G/AT sequences, and subsequent testing of these fragments fused to GUS in transgenic plants was performed. These experiments revealed that the promoter fragment containing PR element alone, although required, was barely able to allow responsiveness to C2H4. However, significant C2H4-induced activity was obtained with a promoter fragment containing the AT and PR elements together.     

Risikobasierter Ansatz zur Bewertung der Robustheit von Bauwerken

Ziel des vorliegenden Beitrages ist es, einen Überblick über die aktuellen Entwicklungen im Bereich der Bewertung und der Quantifizierung der Robustheit von Bauwerken zu geben. In diesem Sinne ist eine Zusammenstellung von Ansätzen und Ergebnissen aktueller Veröffentlichungen enthalten. Ein umfassender entscheidungstheoretischer Ansatz für die Berechnung und das Management der Robustheit wird vorgestellt. Dieser beinhaltet die Definition der Robustheit als eine Qualität eines Systems, welches das Bauwerk beinhaltet, d. h. eine Qualität, die auf der Grundlage einer Risikoanalyse bewertet werden kann. Um eine umfassende Risikoanalyse zu ermöglichen, wird ein szenarienbasierter Modellansatz eingeführt, welcher zwei Arten von Konsequenzen im System unterscheidet: direkte Konsequenzen (in Verbindung mit Schäden einzelner Komponenten des Systems) und indirekte Konsequenzen (in Verbindung mit einem Versagen des Systems). Die Definition des Systems spielt deshalb für die Risikoanalyse eine wichtige Rolle, und es wird diskutiert, wie die Robustheit für verschiedene Definitionen zu unterschiedlichen Ergebnissen und Erkenntnissen im Sinne des Managements der Integrität des Bauwerks im gesamten Lebenszyklus unter Berücksichtigung seiner Funktionalität führt. Weiterhin werden wichtige Aspekte der Standardisierung der Robustheitsanalyse, wie auch Anforderungen an die Robustheit, diskutiert und Vorschläge zum Umgang mit diesen Aspekten unterbreitet. Auf der Grundlage der vorgestellten Ansätze zur Berechnung der Robustheit eines Bauwerks wird beschrieben, wie Entscheidungen in Bezug auf den Entwurf, die Zustandsbewertung, auf Inspektionen und Wartung sowie in Bezug auf die Überwachung von Bauwerken, in Hinblick auf das Management der Risiken in allen Phasen des Lebenszyklus, optimiert werden können. Risk based approach for the assessment of the robustness of structures. The present paper serves as an overview of recent developments by the author on the assessment and quantification of robustness of structures; the paper aims in this sense not to present any new results but collects approaches and results from previous publications. A general decision theoretical approach to the assessment and management of structural robustness is outlined. Structural robustness is introduced as a quality of the system comprising the structure; a quality which can be assessed by means of risk assessments. To facilitate an appropriate risk assessment for structural systems a scenario based model approach is outlined which differentiates consequences into two different types: direct (related to damages to individual components) and indirect (related to collapse failures). The definition of the “structural system” thus plays an important role in the risk assessment and it is discussed how the robustness assessed according to different definitions of the structural system will lead to different results and insights of relevance for the lifecycle management of the structural integrity. Furthermore, the important aspects of standardization of robustness assessments as well as requirements to robustness are discussed and suggestions for the treatment of these are proposed. Based on the presented approach to the assessment of structural robustness it is outlined how decisions on design, condition assessment, inspection and maintenance as well as monitoring activities for structures can be optimized for the purpose of managing structural risks over all phases of the life‐cycle of structures.     

Convection-assisted intra-vitreous drug delivery in human eye: An experimental investigation

We report an in vitro transient experimental study of the human eye to determine the effects of convection on the transport of drugs from the point of injection to the retinal surface through the fluid in the vitrectomized eye. The human eye is modeled as a glass orb of realistic proportions, and water and silicone oil mimic the vitreous fluid. In a series of experiments, the dye that is used to mimic the drug is injected at two different spots in the vitreous chamber, and its transport through the vitreous fluid mimic to the retinal surface is recorded under conditions of simple diffusion and convection-assisted diffusion. The drug concentrations at two different spots on the retinal surface at different times are monitored. It is shown that the drug reaches all parts of the retinal surface much faster during convection-assisted diffusion than during pure diffusion, irrespective of where it is injected in the cavity. In a snapshot, it is seen that the dye concentration reaches $12.95\mathrm{\mu g}∕\mathrm{mL}$ at the target central retinal pigmented epithelium spot in just 12 min (0.2 h) with convection-assisted diffusion as against 12 h in pure diffusion. The steady-state average drug concentration at the target retinal region is seen to be 56.25 times greater for the convection-assisted drug transport than for the pure diffusion case. The results show that applying mild heat to the retinal surface by methods such as laser irradiation can induce convection-based transport of the drug in the vitreous fluid. This method makes the drug available much faster at the target retinal region than drug transport by pure diffusion. The faster transport of the drug within the cavity can expedite the drug's effect and prevent drug loss due to delays.