It has been shown elsewhere that infrared (IR) spectroscopy can be successfully employed for the on-line monitoring of bio-processes. A horizontal attenuated total reflection (ATR) unit connected to ...a portable IR-cube was used here to measure the IR absorption spectra of supernatant and microorganisms separately. The common problem of bio-film formation on the ATR was addressed before, e.g. by chemical means. We present a novel method employing the principles of ultrasonic particle manipulation to avoid and potentially remove this coating brought about by the use of fermentation broth. A novel flow cell for a horizontal ATR was developed that decreases measurement time and the undesired formation of bio-films on the ATR surface. An ultrasonic standing wave (/spl sim/2 MHz) is built up between a horizontal transducer and the ATR crystal. Yeast cells in suspension were agglomerated within certain regions by the ultrasound field and therefore settled about 3-4 times faster on the ATR when the field was switched off compared to the slow sedimentation of freely dispersed cells. After the IR spectrum had been measured, the same sound field was used to actively lift the settled material from the optical sensitive surface which therefore could be rinsed away more effectively.
•Six Galactic open clusters (five of them younger than 40 Myr) were investigated for variable stars of all kinds.•About 26 000 individual CCD frames of more than 312 h of photometry were analyzed.•A ...detailed time-series analysis was performed resulting in 11 new variables.•Several different types of variable stars, such as eclipsing binaries, pulsating, and rotational induced variables were detected.•A detailed membership probability study helped to estimate the ages of these variables.
Variables in open cluster (known distance, age, and metallicity) fields play an important role in stellar astrophysics because they allow to investigate the interior of stars. Therefore, six Galactic open clusters were selected to search for new variables and to complement data for already known variables. As five of these clusters are younger than 40 Myr, we aim at finding variable high-mass stars such as β Cephei and Slowly Pulsating B-type stars as well as classical pulsating stars within the instability strip. About 26 000 images (312 h) photometric images were taken at the 0.8 m (Vienna, Austria) and 1.0 m (Hvar, Croatia) telescope using V and I filters. The differential light curves were analyzed with standard time series analysis methods. In total, 11 variables were found in all investigated clusters. For nine of them, we were able to determine their nature and period. In addition, the membership probabilities from the literature were analyzed.
