bluuebunny/crossref_metadata_2025_split huggingface dataset:
Tunneling Current in Polycrystalline Organic Thin‐Film Transistors
Authors: Horowitz G. 
Published: February 2003

AbstractSeveral recent papers have demonstrated that charge‐carrier mobility in organic field‐effect transistors made of vacuum‐evaporated films may become temperature‐independent at low temperature. To account for this behavior, we developed a model based on the polycrystalline nature of these films, where charge transport is mostly limited by grain boundaries. The free‐carrier density in the intergrain regions is controlled by traps, which leads to the formation of back‐to‐back Schottky barriers at each side of the grain boundaries. The height and width of these barriers is estimated from solving Poisson’s equation using the graded‐channel approximation. It is shown that in most cases the barrier width is negligibly small as compared to the physical size of the grain boundaries. In the high‐temperature regime, the conducting channel can be simply described by grains and grain boundaries connected in series, so that the overall resistance reduces to that of the grain boundaries. At low temperatures, tunneling through the barrier becomes predominant, leading to temperature‐independent mobility. A complete two‐dimensional model for charge tunneling through the barriers is developed. A quantitative check of the model is made by least‐squares fitting of the gate voltage‐dependent current measured on an octithiophene transistor at low temperature, which gives a reasonable determination of the trap density and size of the grain boundaries.
Surfactant‐Assisted Synthesis of Alumina with Hierarchical Nanopores
Authors: Deng W. , Toepke M.W. , Shanks B.H. 
Published: February 2003

AbstractUsing surfactant‐assisted synthesis, aluminas with hierarchical nanopores are produced. The hierarchical structures are composed of mesopores of 4 nm diameter, and macropores with diameters of about 300 nm. The structures were found to be stable to the thermal removal of the surfactant. Synthesis factors affecting the appearance of the hierarchically structured alumina material are presented. A potential mechanism for the formation of the uniquely structured aluminas is proposed.
Controlling the Morphology of Nanocrystal–Polymer Composites for Solar Cells
Authors: Huynh W.U. , Dittmer J.J. , Libby W.C. , Whiting G.L. , Alivisatos A.P. 
Published: February 2003

AbstractWe have shown recently that the use of high‐aspect‐ratio inorganic nanorods in conjunction with conjugated polymers is a route to obtaining efficient solar cells processed from solution. Here, we demonstrate that the use of binary solvent mixtures in which one of the components is a ligand for the nanocrystals is effective in controlling the dispersion of nanocrystals in a polymer. By varying the concentration of the solvent mixture, phase separation between the nanocrystal and polymer could be tuned from micrometer scale to nanometer scale. In addition, we can achieve nanocrystal surfaces that are free of surfactant through the use of weak binding ligands that can be removed through heating. When combined, the control of film morphology together with surfactant removal result in nanorod–polymer blend photovoltaic cells with a high external quantum efficiency of 59 % under 0.1 mW cm–2 illumination at 450 nm.
Selective Growth of Carbon Nanotubes for Nanoscale Transistors
Authors: Choi W.B. , Cheong B.‐H. , Kim J.J. , Chu J. , Bae E. 
Published: February 2003

AbstractThe selective growth of vertically aligned carbon nanotubes (CNTs) and their application as field‐effect transistors (FETs) are demonstrated. Vertically aligned carbon nanotubes were selectively grown in nanoholes formed in an anodized aluminum oxide (AAO) template. Each device element is formed on a vertical carbon nanotube attached to bottom (source) and upper (drain) electrodes and a gate electrode, which can be integrated in large arrays with the potential for tera‐level density (1012 cm–2). Simulation of the potential distribution shows that the direction of potential formation would depend on the polarity of the gate bias, which is consistent with an experimental result of CNT‐FET operation.
Novel Nanostructures of Functional Oxides Synthesized by Thermal Evaporation
Authors: Dai Z.R. , Pan Z.W. , Wang Z.L. 
Published: February 2003

AbstractFunctional oxides are the fundamentals of smart devices. This article reviews novel nanostructures of functional oxides, including nanobelts, nanowires, nanosheets, and nanodiskettes, that have been synthesized in the authors’ laboratory. Among the group of ZnO, SnO2, In2O3, Ga2O3, CdO, and PbO2, which belong to different crystallographic systems and structures, a generic nanobelt structure has been synthesized. The nanobelts are single crystalline and dislocation‐free, and their surfaces are atomically flat. The oxides are semiconductors, and have been used for fabrication of nanodevices such as field‐effect transistors and gas sensors. Taking SnO2 and SnO as examples, other types of novel nanostructures are illustrated. Their growth, phase transformation, and stability are discussed. The nanobelts and related nanostructures are a unique group that is likely to have important applications in electronic, optical, sensor, and optoelectronic nanodevices.
Grundzüge der Sensorik Höherer Pflanzen
Authors: Weiler Elmar W. 
Published: February 2003

AbstractPflanzen reagieren auf eine Vielzahl unterschiedlicher Reize aus ihrem Körperinneren und ihrer Umgebung. Unser Wissen um die sensorischen Fähigkeiten von Pflanzen hat gerade in den letzten zehn Jahren enorm zugenommen. Dies liegt einerseits an dem konsequenten Einsatz molekulargenetischer Verfahren, andererseits daran, daß weltweit viele Kräfte auf eine einzige, repräsentative Höhere Pflanze konzentriert werden, auf Arabidopsis thaliana, die Acker‐Schmalwand. Dieser Aufsatz konzentriert sich eher auf die Prinzipien als auf Details und beschränkt sich auf solche Systeme, die funktional eindeutig identifiziert sind. Höhere Pflanzen sind hinsichtlich ihrer sensorischen Fähigkeiten um nichts weniger faszinierend, nicht weniger komplex, nicht weniger empfindlich als Tiere oder sogar der Mensch. Pflanzen überwachen dauernd ihre Umgebung und den Zustand in ihrem Inneren mit Hilfe eines erstaunlichen Aufgebots sensorischer Systeme, die sich von denen der Tiere oder des Menschen unterscheiden.
Recent Developments in Protein Microarray Technology
Authors: Wilson David S. , Nock Steffen 
Published: February 2003

AbstractThe sequencing of the human genome and the advent of DNA chips and sophisticated bioinformatics platforms have enabled molecular biologists to take a more global view of biological systems and to analyze naturally occurring genetic variation. Microarrays of antibodies can measure the concentrations of many proteins quickly and simultaneously. Microarrays of genomically encoded proteins allow scientists to screen entire genomes for proteins that interact with particular factors, catalyze particular reactions, or act as substrates for protein‐modifying enzymes or as targets of autoimmune responses. The new protein microarray platforms will prove invaluable to basic biological research, and will dramatically accelerate the pace of discovery of drug targets and diagnostic biomarkers.
One Century of Aryne Chemistry
Authors: Wenk Hans Henning , Winkler Michael , Sander Wolfram 
Published: February 2003

AbstractArynes, which are formally derived from aromatic rings by abstraction of two hydrogen atoms, have been a focus of organic chemistry for 100 years. In contrast to ortho‐benzyne, which is mentioned in almost every introductory textbook on organic reaction mechanisms as a reactive intermediate of nucleophilic aromatic substitution, the meta and para isomers were regarded as rather exotic until recently. This situation has changed dramatically with the discovery of the enediyne antibiotics, a promising new class of antitumor drugs, and has aroused the interest of research groups from all branches of chemistry. Nowadays, arynes and related compounds are among the most intensively studied systems in chemistry. However, many aspects of the chemistry of these reactive intermediates are not well understood yet. In this review we outline the historical developement with an emphasis on recent progress in this challenging field of research.
Development of a novel process for the biological conversion of H2S and methanethiol to elemental sulfur
Authors: Sipma Jan , Janssen Albert J. H. , Hulshoff Pol Look W. , Lettinga Gatze 
Published: February 2003

AbstractThe feasibility of anaerobic treatment of wastewater containing methanethiol (MT), an extremely volatile and malodorous sulfur compound, was investigated in lab‐scale bioreactors. Inoculum biomass originating from full‐scale anaerobic wastewater treatment facilities was used. Several sludges, tested for their ability to degrade MT, revealed the presence of organisms capable of metabolizing MT as their sole source of energy. Furthermore, batch tests were executed to gain a better understanding of the inhibition potential of MT. It was found that increasing MT concentrations affected acetotrophic organisms more dramatically than methylotrophic organisms. Continuous reactor experiments, using two lab‐scale upflow anaerobic sludge bed (UASB) reactors (R1 and R2), aimed to determine the maximal MT load and the effect of elevated sulfide concentrations on MT conversion. Both reactors were operated at a hydraulic retention time (HRT) of about 7 hours, a temperature of 30°C, and a pH of between 7.3 and 7.6. At the highest influent MT concentration applied, 14 mM in R1, corresponding to a volumetric loading rate of about 50 mM MT per day, 87% of the organic sulfur was recovered as hydrogen sulfide (12.2 mM) and the remainder as volatile organic sulfur compounds (VOSCs). Upon decreasing the HRT to 3.5 to 4.0 h at a constant MT loading rate, the sulfide concentration in the reactor decreased to 8 mM and MT conversion efficiency increased to values near 100%. MT conversion was apparently inhibited by the high sulfide concentrations in the reactor. The specific MT degradation rate, as determined after 120 days of operation in R1, was 2.83 ± 0.27 mmol MT g VSS−1 day−1. During biological desulfurization of liquid hydrocarbon phases, such as with liquefied petroleum gas (LPG), the combined removal of hydrogen sulfide and MT is desired. In R2, the simultaneous addition of sodium sulfide and MT was therefore studied and the effect of elevated sulfide concentrations was investigated. The addition of sodium sulfide resulted in enhanced disintegration of sludge granules, causing significant washout of biomass. Additional acetate, added to stimulate growth of methanogenic bacteria to promote granulation, was hardly converted at the termination of the experimental period. © 2003 Wiley Periodicals, Inc. Biotechnol Bioeng 82: 1–11, 2003.
A reversible hydrogel membrane for controlling the delivery of macromolecules
Authors: Tang M. , Zhang R. , Bowyer A. , Eisenthal R. , Hubble J. 
Published: February 2003

AbstractGlucose‐sensitive hydrogel membranes have been synthesized and characterized for their rate‐of‐delivery of macromolecules. The mechanism for changing this rate is based on variable displacement of the affinity interaction between dextran and concanavalin A (con A). Our main objective was to characterize the diffusion of model proteins (insulin, lysozyme, and BSA) through the membrane, in response to changes in environmental glucose concentrations. Membranes were constructed from crosslinked dextrans to which con A was coupled via a spacer arm. Changes in the porosity of the resulting hydrogel in the presence of glucose led to changes in the diffusion rate observed for a range of proteins. Gels of specified thickness were cast around to nylon gauze support (pore size, 0.1 mm) to improve mechanical strength. Diffusion of proteins through the gel membrane was determined using a twin‐chamber diffusion cell with the concentrations being continuously monitored using a UV‐spectrophotometer. Changes in the transport properties of the membranes in response to glucose were explored and it was found that, while 0.1M D‐glucose caused a substantial, but saturateable, increase in the rates of diffusion of both insulin and lysozyme, controls using glycerol or L‐glucose (0.1M) had no significant effect. Sequential addition and removal of external glucose in a stepwise manner showed that permeability changes were reversible. As expected, diffusion rates were inversely proportional to membrane thickness. A maximum increase in permeability was observed at pH 7.4 and at 37°C. The results demonstrate that this hydrogel membrane functions as a smart material allowing control of solute delivery in response to specific changes in its external environment. © 2003 Wiley Periodicals, Inc. Biotechnol Bioeng 82: 47–53, 2003.
Theory of pH‐stat titration
Authors: Ficara Elena , Rozzi Alberto , Cortelezzi Paola 
Published: February 2003

AbstractInnovative techniques are being studied to assess the activity of bioreactors and to improve the performance and operational stability of biological processes. Among these techniques, the pH‐stat titration is applicable to any bioreaction involving pH variations. Up to now, the main application of the pH‐stat titration has been for nitrification monitoring. In this article, we present a theoretical model of pH‐stat titration, which predicts the response to any reaction involving the production or consumption of protons, hydroxyl ions, or inorganic carbon chemical species (CO2, HCO3−, CO3=). This model is a useful tool to understand pH‐stat titrations, to define their applicability and limits, and to select the best experimental conditions for specific applications. Tests have been performed to compare experimental pH‐stat titration rates in the presence of carbon dioxide and HCO3− producing reactions to the values predicted by the model and a very satisfying correspondence was found. © 2003 Wiley Periodicals, Inc. Biotechnol Bioeng 82: 28–37, 2003.
Outdoor helical tubular photobioreactors for microalgal production: Modeling of fluid‐dynamics and mass transfer and assessment of biomass productivity
Authors: Hall David O. , Acién Fernández F. G. , Guerrero E. Cañizares , Rao K. Krishna , Grima E. Molina 
Published: February 2003

AbstractThe production of the microalga Phaeodactylum tricornutum in an outdoor helical reactor was analyzed. First, fluid dynamics, mass‐transfer capability, and mixing of the reactor was evaluated at different superficial gas velocities. Performance of the reactor was controlled by power input per culture volume. A maximum liquid velocity of 0.32 m s−1 and mass transfer coefficient of 0.006 s−1 were measured at 3200 W m−3. A model of the influence of superficial gas velocity on the following reactor parameters was proposed: gas hold‐up, induced liquid velocity, and mass transfer coefficient, with the accuracy of the model being demonstrated. Second, the influence of superficial gas velocity on the yield of the culture was evaluated in discontinuous and continuous cultures. Mean daily values of culture parameters, including dissolved oxygen, biomass concentration, chlorophyll fluorescence (Fv/Fm ratio), growth rate, biomass productivity, and photosynthetic efficiency, were determined. Different growth curves were measured when the superficial gas velocity was modified—the higher the superficial gas velocity, the higher the yield of the system. In continuous mode, biomass productivity increased by 35%, from 1.02 to 1.38 g L−1 d−1, when the superficial gas velocity increased from 0.27 to 0.41 m s−1. Maximal growth rates of 0.068 h−1, biomass productivities up to 1.4 g L−1 d−1, and photosynthetic efficiency of up to 15% were obtained at the higher superficial gas velocity of 0.41 m s−1. The fluorescence parameter, Fv/Fm, which reflects the maximal efficiency of PSII photochemistry, showed that the cultures were stressed at average irradiances within the culture higher than 280 μE m−2 s−1 at every superficial gas velocity. For nonstressed cultures, the yield of the system was a function of average irradiance inside the culture, with the superficial gas velocity determining this relationship. When superficial gas velocity was increased, higher growth rates, biomass productivities, and photosynthetic efficiencies were obtained for similar average irradiance values. The higher the superficial gas velocity, the higher the liquid velocity, with this increase enhancing the movement of the cells inside the culture. In this way the efficiency of the cells increased and higher biomass concentrations and productivities were reached for the same solar irradiance. © 2003 Wiley Periodicals, Inc. Biotechnol Bioeng 82: 62–73, 2003.
Enhancement of 2‐phenylethanol productivity by Saccharomyces cerevisiae in two‐phase fed‐batch fermentations using solvent immobilization
Authors: Serp D. , von Stockar U. , Marison I. W. 
Published: February 2003

AbstractThe bioconversion of L‐phenylalanine to 2‐phenylethanol by Saccharomyces cerevisiae in fed‐batch experiments has shown that concentrations of 2‐phenylethanol of >2.9 g/L have a negative impact on the oxidative capacity of the yeast. Without tight control on ethanol production, and hence on the feed rate, ethanol rapidly accumulates in the culture media, resulting in complete inhibition of cell growth before the maximal 2‐phenylethanol concentration of 3.8 g/L, obtained in the absence of ethanol production, could be achieved. This effect was attributed to a cumulative effect of ethanol and 2‐phenylethanol, which reduced the tolerance of the cells for these two products. To enhance the productivity of the bioconversion, a novel in situ product recovery strategy, based on the entrapment of an organic solvent (dibutylsebacate) into a polymeric matrix of polyethylene to form a highly absorbent and chemically and mechanically stable composite resin, was developed. Immobilization of the organic solvent successfully prevented phase toxicity of the solvent and allowed for an efficient removal of 2‐phenylethanol from the bioreactor without the need for prior cell separation. The use of the composite resin increased the volumetric productivity of 2‐phenylethanol by a factor 2 and significantly facilitated downstream processing, because no stable emulsion was formed. The 2‐phenylethanol could be backextracted from the composite resin, yielding a concentrated and almost cell‐free solution. In comparison to two‐phase extractive fermentations with cells immobilized in alginate‐reinforced chitosan beads, the use of a composite resin was extremely inexpensive and simple. In addition, the composite resin was found to be insensitive to abrasion and chemically stable, such that sterilization with 2 M NaOH or heat was possible. Finally, the composite resin could be produced on a large scale using commercially available equipment. © 2003 Wiley Periodicals, Inc. Biotechnol Bioeng 82: 103–110, 2003.
Quantification of a novel h‐shaped ultrasonic resonator for separation of biomaterials under terrestrial gravity and microgravity conditions
Authors: Böhm Hannes , Briarty Lewis G. , Lowe Kenneth C. , Power J. Brian , Benes Ewald , Davey Michael R. 
Published: February 2003

AbstractA novel, h‐shaped ultrasonic resonator was used to separate biological particulates. The effectiveness of the resonator was demonstrated using suspensions of the cyanobacterium,Spirulina platensis. The key advantages of this approach were improved acoustic field homogeneity, flow characteristics, and overall separation efficiency (σ = 1 − ratio of concentration in cleared phase to input), monitored using a turbidity sensor. The novel separation concept was also effective under microgravity conditions; gravitational forces influenced overall efficiency. Separation ofSpirulinaat cleared flow rates of 14 to 58 L/day, as assessed by remote video recording, was evaluated under both microgravity (≤0.05g) and terrestrial gravity conditions. The latter involved a comparison with 5‐ and 24‐μm‐diameter polystyrene microspheres. Influences of gravity on σ were evaluated by varying the relative inclination angle (within a range of 120°) between the resonator and the gravitational vector. Cells ofSpirulinabehaved in a manner comparable to that of the 5‐μm‐diameter polystyrene microspheres, with a significant decrease in mean (±SE, n = 3) σ from 0.97 ± 0.03 and 0.91 ± 0.02 at a flow rate of 14 L/day, to corresponding values of 0.53 ± 0.05 and 0.57 ± 0.03 (P< 0.05) at 58 L/day, respectively. During a typical microgravity period of ca. 22 s, achieved during the 29th ESA Parabolic Flight Campaign, σ was unchanged at a flow rate of 14 L/day, compared with terrestrial gravity conditions; with increased flow rates, σ was significantly reduced. Overall, these results demonstrate that, for optimum resonator performance under the relatively short microgravity period utilized in this study, flow rates of ca. 14 L/day were preferred. These data provide a baseline for exploiting noninvasive, compact, ultrasonic separation systems for manipulating biological particulates under microgravity conditions. © 2003 Wiley Periodicals, Inc. Biotechnol Bioeng 82: 74–85, 2003.
Inactivation of bacteria and spores by pulse electric field and high pressure CO2 at low temperature
Authors: Spilimbergo Sara , Dehghani Fariba , Bertucco Alberto , Foster Neil R. 
Published: February 2003

AbstractThe common methods for inactivation of bacteria involve heating or exposure to toxic chemicals. These methods are not suitable for heat‐sensitive materials, food, and pharmaceutical products. Recently, a complete inactivation of many microorganisms was achieved with high‐pressure carbon dioxide at ambient temperature and in the absence of organic solvent and irradiation. The inactivation of spores with CO2 required long residence time and high temperatures, such as 60°C. In this study the synergistic effect of pulsed electric field (PEF) in combination with high‐pressure CO2 for inactivation was investigated. The bacteria Escherichia coli, Staphylococcus aureus, and Bacillus cereus were suspended in glycerol solution and treated in the first step with PEF (up to 25 KV/cm) and then with high‐pressure CO2 not higher than 40°C and 200 bar. The inactivation efficiency was determined by counting the colony formation units of control and sample. Samples of the cells subjected to PEF treatment alone and in combination with CO2 treatment were examined by scanning electron microscopy to determine the effect of the processes on the cell wall. Experimental results indicate that the viability decreased with increasing electrical field strength and number of pulses. A further batch treatment with supercritical CO2 lead to complete inactivation of bacterial species and decreased the count of the spores by at least three orders of magnitude, the inactivation being enhanced by an increase of contact time between CO2 and the sample. A synergistic effect between the pulsed electric field and the high‐pressure CO2 was evident in all the species treated. The new low temperature process is an alternative for pasteurization of thermally labile compounds such as protein and plasma and minimizes denaturation of important nutrient compounds in the liquid media. © 2003 Wiley Periodicals, Inc. Biotechnol Bioeng 82: 118–125, 2003.
Numerical Simulations of the Direct Shear Test
Authors: Thornton C. , Zhang L. 
Published: February 2003

AbstractNumerical simulations of the direct shear test have been performed under constant normal stress conditions, using the Discrete Element Method. Results are presented to show how the average shear to normal stress ratio acting on the shear band compares with the force data at the boundaries. From the calculations of the stress tensor inside the shear band the corresponding Mohr’s circles are obtained and the principal stress directions identified. The principal directions of stress and strain‐rate are shown to be coaxial under steady‐state conditions. Using the state of stress and strain in the shear band, the interpretation of direct shear test data is discussed in the context of traditional experimental measurements.