Monitoring of Cell Layer Integrity with a Current-Driven Organic Electrochemical Transistor

The integrity of CaCo-2 cell barriers is investigated by organic electrochemical transistors (OECTs) in a current-driven configuration. Ion transport through cellular barriers via the paracellular pathway is modulated by tight junctions between adjacent cells. Rupturing its integrity by H2O2 is monitored by the change of the output voltage in the transfer characteristics. It is demonstrated that by operating the OECT in a current-driven configuration, the sensitive and temporal resolution for monitoring the cell barrier integrity is strongly enhanced as compared to the OECT transient response measurement. As a result, current-driven OECTs are useful tools to assess dynamic and critical changes in tight junctions, relevant for clinical applications as drug targeting and screening

Excitation and detection of vibrations of micromechanical structures using a dielectric thin film

A new technique is introduced for both the excitation and the detection of vibrations of micromechanical structures. This makes use of a dielectric thin film, sandwiched between lower and upper electrodes, on top of the vibrating structure. The excitation is based on electrostatic forces between the charged electrodes, causing deformation of the dielectric film and bending of the multilayer structure. The detection of the vibration is capacitive, based on the fluctuation of the capacitance due to the deformation of the dielectric film. Experimental results for a stoichiometric silicon nitride dielectric film on top of a silicon cantilever agree well with predicted values. The yield of the electrostatic excitation as well as of the capacitive detection are satisfactory

Axially linear slopes of composition for “delta” crystals

“Delta” crystals are solid solutions of miscible materials with large lattice parameter differences which contain high concentration gradients in one direction (parallel to a lattice plane strongly diffracting X-rays). The system GaSb-InSb has been chosen as suitable for study. By means of a “gradient projection method”, the growth of nearly linear composition profiles with relatively steep slopes of the lattice parameter (up to (Δa/ ) / Δz = 8.3% cm-1), adjustable by the temperature gradient, have been performed. However, the grown ingots were not monocrystalline due to the use of too high a growth rate

Device operation of organic tandem solar cells

A generalized methodology is developed to obtain the current-voltage characteristic of polymer tandem solar cells by knowing the electrical performance of both sub cells. We demonstrate that the electrical characteristics of polymer tandem solar cells are correctly predicted for both the series and parallel connection of the sub cells. The agreement with experiments allows us to investigate the effect of a reduced open-circuit voltage, short-circuit current or fill factor in one of the sub cells on the performance of the tandem cell. A low fill factor in one of the sub cells leads to a stronger reduction of the efficiency in a series configuration as compared to the parallel tandem device. (C) 2008 Elsevier B.V. All rights reserved

Rapid Induction of Ageing Character in Brandy Products – Part I. Effects of Extraction Media and Preparation Conditions

The purpose of this study was to investigate the use of different wood types and treatments, and extraction mediato induce rapid ageing of brandy. Extracts were prepared from American and French oak, specially preparedand supplied by a cooper, and from commercially obtained oak; both representative of different toasting levels,including untoasted, light, medium and heavy toasted. To extract the wood components, wood chips in either 55%(v/v) neutral wine spirits or water media were boiled under reflux. Distillation was followed by either open (higherboiling temperature) or closed (vacuum or reduced pressure – lower boiling temperature) concentration of thedecanted solvent by 45, 65 and 85% (v/v). The concentrated extracts were fortified. Screened extracts were addedto unmatured pot-still brandy and aged for eight months at room temperature in glass containers. Controls werestored below 0°C. Matured and unmatured (control) pot-still brandy samples were analyzed for wood-derivedcongeners by means of HPLC and GC. This article focuses on the effects of the extraction media, and on level andmethod of concentration (open and reduced pressure) on sensory quality and chemical composition. The treatmentsthat gave acceptable extracts, and the best overall quality pot-still brandy were those that entailed (1) using ethanolinstead of water as extraction medium, and (2) levels of concentration above 45% (v/v). Open and reduced-pressureconcentrations showed little difference in the quality of the products yielded. Treatments yielding the most acceptableextracts and best overall quality pot-still brandy generally also contained higher concentrations of volatile andless volatile wood-derived congeners. Multivariate data analysis was conducted on the pot-still brandy samplesrepresenting the different treatments. Discriminate analysis provided better separation of samples than principalcomponent analysis

Trap-limited electron transport in disordered semiconducting polymers

The electron transport in diodes of poly(dialkoxy-p-phenylene vinylene) (PPV) derivatives is strongly reduced as compared to the hole transport. A recent reexamination [M. M. Mandoc , Phys. Rev. B 73, 155205 (2006)] revealed that the room-temperature electron current shows the fingerprints of trap-limited transport with a distribution of traps in energy. Here, we report on the measured temperature dependence of the electron current in these PPV derivatives. This dependence is weak and seems to be in contradiction with existing trap-limited models. We demonstrate that the presence of a Gaussian density of states (DOS) for the mobile carriers, being characteristic for disordered semiconductors, reduces the temperature dependence of the trap-limited charge transport. The reduction is governed by the width of the Gaussian DOS and originates from the equilibrium concentrations of the mobile and trapped carriers