Chemically and enzymatically catalyzed synthesis of C6–C10 alkyl benzoates

The esterification of benzoic acid with n‐hexanol, n‐octanol, 2‐ethyl hexanol and n‐decanol was investigated in detail. An analysis of the reaction kinetics of esterification in the presence of different commercially available chemical catalysts was carried out. The effects of catalyst type and loading on the reaction rate were studied. Although the considered reaction is bimolecular, it showed a first‐order behavior, and a linear dependence with respect to the catalyst concentration was observed. Hence, a new approach is presented to describe the reaction kinetics accurately over a wide range. The application of biotechnological synthesis applying different enzymes as catalysts offers an interesting alternative besides chemical synthesis. Especially an esterase from Bacillus subtilis immobilized on Sepabeads EC‐EP showed high stability and was applied for 2 days in the synthesis of hexyl benzoate. Nevertheless, the chemical reaction route remains superior with respect to the catalyst activities under the applied conditions, which were 25 kU/g for the chemical reaction and 0.7 kU/g for the best enzymatic conversion.     

Dealuminated Y Zeolite for Water-Driven Adsorption Heat Pumps: Hydrothermal Stability

Silica gel or zeolites AlPO-5 and SAPO-34 are recommended as adsorbents in water-driven heat pumps because of their selective water uptake. Secondary energy, like solar energy, can be used for regeneration of loaded adsorbers. In case of the availability of only low energy levels, the use of dealuminated Y zeolite (DAY) is the better choice because of the infinitely variation of its hydrophilic properties by tailoring of the framework Si/Al ratio. Actual data on the hydrothermal stability of DAY are lacking. Thus, we report on the long-term behavior of DAY zeolites with different Si/Al ratios.     

Tropfenbewegung und Stofftransport in technischen Flüssig/flüssig-Systemen. Teil 2: Auswirkung von Grenzflächeneffekten und Verunreinigungen

The design of a liquid/liquid contact apparatus necessitates the knowledge of fluid dynamics and mass transfer in the dispersion. Prediction of process parameters is challenging due to swarm and interfacial effects. Single drop investigations are suitable to enable a sophisticated dimensioning based on few simple experiments combined with published theories and correlations. In the first part of this article, the fundamentals of fluid dynamics and mass transfer in absence of interfacial effects were explained. Here, an overview of relevant interfacial phenomena and the influence of different substances typically occurring in technical applications as impurities or accompanying components is given.     

Development, fabrication, and test of a modular eddy current micro sensor on a flexible polymer foil

This paper describes the development and fabrication of a modular eddy current micro sensor on a flexible polymer foil. Due to handling purposes during the micro sensor fabrication process the modular eddy current micro sensors are fabricated on a temporary Si substrate. To enable a release of the micro sensors at the end of the fabrication process, initial investigations concentrated on the proof of principle applying a deep reactive-ion etching (DRIE) process to structure the Si wafer. The DRIE process was used to structure Si frames, which serve as carriers for the modular micro sensors. For the evaluation of the fabricated eddy current micro sensors, electrical resistance measurements were accomplished with the integrated anisotropic magneto-resistance (AMR) sensor. The aim of these investigations was to evaluate the influence of the substrate material on the characteristics of the AMR sensor. The electrical output signal of these micro sensors were subsequently compared to electrical resistance measurements of identical AMR sensors fabricated on a Si substrate and served as reference. To prove the capability of the completed eddy current micro sensors, a defect in form of a scratch was created on the surface of a Cu probe and investigated by eddy current testing. The electrical output signal of the eddy current micro sensor was subsequently compared to an optical measurement of the surface profile of this scratch. There is a high correlation between the optical measurements and the signal of the eddy current micro sensor.     

Deepening our understanding of bioactive glass crystallization using TEM and 3D nano-CT

One key issue influencing a broader application of Bioglass 45S5 in tissue engineering is its inherent crystallization tendency, severely limiting the mechanical strength of 3D porous scaffolds. Despite numerous studies, Bioglass 45S5 crystallization is not yet fully understood with regard to the mechanisms involved or morphology of the crystal phases forming. Here we show how two cutting-edge imaging techniques, state-of-the-art transmission electron microscopy (TEM) with image correction including energy dispersive X-ray spectroscopy and X-ray nano-computed tomography (nano-CT), allowed us to visualize changes in microstructure from near-nucleation to almost full crystallization in bulk Bioglass 45S5. At early times of heat treatment at 660 °C the formation of phase-separated nano-droplets within the glassy matrix was observed. Later, besides surface crystallization, bulk crystallization of combeite spheres was predominant. The formation of the first combeite spheres, their coarsening with time and finally their merging at near full crystallization were recorded by in situ high-temperature optical microscopy videos. The 3D nature of these spheres was confirmed by nano-CT, while TEM showed that their internal structure was composed of sub-micron grains. X-ray diffraction analysis at early time points showed a much higher crystalline fraction in bulk samples compared to powder samples, highlighting the influence of processing and sample morphology. These results show the importance of using complementary techniques for gaining insight into the crystallization process in the volume. In addition, we show that TEM and nano-CT are suitable characterization techniques to visualize the crystallization even in fast crystallizing systems, such as bioactive glasses.     

Asymptotic integration of nonoscillatory differential equations: a unified approach

We consider the equation [r(t)x′]′ + f(t)x = 0 as a perturbation of the equation [r(t)y′]′ + g(t)y = 0, where the latter is assumed to be nonoscillatory at infinity. The functions r and g are real-valued, r is positive, and f is complex-valued. The problem of the asymptotic integration of the perturbed equation in comparison with solutions of the unperturbed equation has been studied by many mathematicians, including Hartman and Wintner, Trench, ˇSimˇsa, Chen, and Chernyavskaya and Shuster. Here we apply a unified approach. Working in a matrix setting, we use preliminary and so-called conditioning transformations to bring the system in the form [(z)\vec] = [ L (t) + R(t) ][(z)\vec] \vec{z} = \left[ {\Lambda (t) + R(t)} \right]\vec{z} , where Λ is a certain diagonal matrix and R is an absolutely integrable perturbation. This allows us to use Levinson’s fundamental theorem to find the asymptotic behavior of solutions and, in addition, to estimate the error involved. This method allows us to derive these known results in a more unified setting and to weaken the hypotheses in some instances.     

Computer-algebra calculations and measurements on AB spin systems for double-spin-echo sequences

The time evolution of the density operator of an AB spin system during a double-spin-echo pulse sequence is evaluated analytically by a computer-algebra system. The computer-algebra system allows one to generate the extensive formulas describing the density operator and yields an expression for the integral of the spectral signals. The simulation of spectra for arbitrary sequence timings can be easily performed by this new tool without risking errors that might occur in conventional calculations. The computer-algebra method can be extended straightforward to other pulse angles and types of sequences. The double-spin-echo pulse sequence is used in the point-resolved spectroscopy (PRESS) method which is often applied for volume selective examinationsin vivo. For verification of the results generated by the computer-algebra system,¹H spectra from a half-liter spherical sample with an aqueous solution that was 0.1 M in sodium citrate and 0.1 M in sodium acetate were recorded after 90°-180°-180° double-spin-echo pulse sequences on a 1.5-T whole-body unit. The measured behavior of the citrate AB spin system corresponds very well with the theoretical predictions. Thus, the theory provides the basis for the optimization of sequence timings for double-spin-echo measurements with high signal gain from AB systems as, for example, citrate. In addition, the theoretically predicted signal modulations could be fitted to the experimental data, providing the transverse relaxation time of the AB-coupled protons.     

AudioBrowser: a mobile browsable information access for the visually impaired

Although a large amount of research has been conducted on building interfaces for the visually impaired that allows users to read web pages and generate and access information on computers, little development addresses two problems faced by the blind users. First, sighted users can rapidly browse and select information they find useful, and second, sighted users can make much useful information portable through the recent proliferation of personal digital assistants (PDAs). These possibilities are not currently available for blind users. This paper describes an interface that has been built on a standard PDA and allows its user to browse the information stored on it through a combination of screen touches coupled with auditory feedback. The system also supports the storage and management of personal information so that addresses, music, directions, and other supportive information can be readily created and then accessed anytime and anywhere by the PDA user. The paper describes the system along with the related design choices and design rationale. A user study is also reported.