20 research outputs found
Selbstorganisierte Strukturen in planaren Gasentladungssystemen mit dielektrischer Barriere
In dieser Arbeit wird ein planares, dielektrisches Barrierenentladungssystem untersucht, dessen laterale Ausdehnung groß gegenüber dem Entladungsabstand ist. In solchen Systemen wird eine laterale, selbstorganisierte Strukturierung
der Stromdichte beobachtet. Der erste Teil der Arbeit gibt einen Überblick über die bisher gefundenen Strukturen. Die experimentellen Untersuchungen, die im zweiten Teil der Arbeit vorgestellt werden, befassen sich mit der Strukturierung des homogenen Entladungsgebietes, mit der Dynamik einzelner Filamente und mit Turing-artigen Bifurkationen. Außderdem werden ein Aufbau zur ortsaufgelösten Messung von Oberflächenladungen in der laufenden Entladung
beschrieben und die erhaltenen Ergebnisse vorgestellt. Der dritte Teil der Arbeit zeigt numerischen Untersuchungen, die auf zwei- und dreidimensionalem Grundgebiet durchgeführt werden. Es können die Strukturierung der Entladung und der Mechanismus zur Stabilisierung eines Filamentes nachvollzogen werden
Phase-resolved measurement of the spatial surface charge distribution in a laterally patterned barrier discharge
Abstract
The presented experimental system is a barrier discharge system with plane parallel electrodes. The lateral surface charge distribution being deposited on the dielectric layer during each breakdown is observed optically using the well known electro-optic effect (Pockels effect). The temporal resolution of the surface charge measurement has been increased to 200 ns, and so for the first time it is possible to resolve the charge transfer to the dielectric surface in a single breakdown. In the present measurements, a patterned glow-like barrier discharge is investigated. It is found that the charge reversal in a single discharge spot (microdischarge) starts in the centre and then grows outwards. These experimental findings verify previously unconfirmed predictions from earlier numerical calculations and thereby contribute to a better understanding of the interaction between the plasma and the electrical charge on the electrodes
Quantized Compressed Sensing by Rectified Linear Units
This work is concerned with the problem of recovering high-dimensional
signals which belong to a convex set of
low-complexity from a small number of quantized measurements. We propose to
estimate the signals via a convex program based on rectified linear units
(ReLUs) for two different quantization schemes, namely one-bit and uniform
multi-bit quantization. Assuming that the linear measurement process can be
modelled by a sensing matrix with i.i.d. subgaussian rows, we obtain for both
schemes near-optimal uniform reconstruction guarantees by adding well-designed
noise to the linear measurements prior to the quantization step. In the one-bit
case, we show that the program is robust against adversarial bit corruptions as
well as additive noise on the linear measurements. Further, our analysis
quantifies precisely how the rate-distortion relationship of the program
changes depending on whether we seek reconstruction accuracies above or below
the noise floor. The proofs rely on recent results by Dirksen and Mendelson on
non-Gaussian hyperplane tessellations. Finally, we complement our theoretical
analysis with numerical experiments which compare our method to other
state-of-the-art methodologies.Comment: 40 pages, 5 figure
Theoretical and experimental analysis of scan angle-depending pulse front tilt in optical systems for laser scanners
For realising fast and highly dynamical laser-based material processing, scanner systems are already utilised for many different industrial applications. Furthermore, ultra-short pulsed (<1 ps) laser sources provide possibilities of processing most different materials with highest accuracy. Owing to the large spectral bandwidth of ultra-short laser pulses, dispersion in optical components becomes relevant. The dispersion in optical systems for laser scanners may lead to scan angle-depending pulse properties as, for example, pulse front tilt. The investigation of these effects is not state of the art today but absolutely necessary to exploit the full potential of laser scanners for ultra-short pulse applications. By means of an exemplary focusing lens, the simulation and experimental analysis of scan angle-depending pulse front tilt is presented for the first time
Quantitation of bacterial adhesion to polymer surfaces by bioluminescence
Quantitation of microbes adhering to a surface is commonly used in studies of microbial adhesion to different surfaces. We have quantified different staphylococcal strains adhering to polymer surfaces by measuring bacterial ATP (adenosine triphosphate) by bioluminescence. The method is sensitive, having a detection limit of 104 bacterial cells. Viable counting of bacterial cells may yield falsely low results due to the presence of 'dormant' and adherent bacteria. By using bioluminescence, this can be avoided. Cells of different bacterial species and cells of strains of the same species were shown to differ significantly in their basal ATP content (8.7 x 10-13 - 5.2 x 10-22 MATP). The size of adherent and planktonic bacteria decreased with time (0.7 μm → 0.3 μm, 20 days). During incubation in nutrient-poor buffer ('starvation'), the ATP content of adherent bacteria decreased after 24-96 h whereas that of planktonic bacteria was stable over 20 days. The presence of human serum or plasma did not interfere significantly with the test results. Since the ATP concentration of bacterial strains of different species varies and is also influenced by the growth conditions of bacteria (solid or liquid culture medium), a species-specific standard curve has to be established for bacteria grown under the same culture conditions. We conclude that the method is a sensitive tool to quantify adherent bacteria during experiments lasting for less than 6 h and constitutes a valuable method to be used in conjunction with different microscopical techniques
Correlation of phase resolved current, emission and surface charge measurements in an atmospheric pressure helium jet
The interaction of an atmospheric pressure plasma jet with two different surfaces (conducting and dielectric) is investigated using a setup with two ring electrodes around a dielectric capillary. For diagnostics, phase resolved ICCD-imaging, current measurements and surface charge measurements are applied. The results show the correlation of plasma dynamics with the deposition of surface charge and electrical current signals. Further, the influence of the distance between surface and jet capillary on the surface charge distribution is presented. A complex discharge dynamic is found with a dielectric barrier discharge between the ring electrodes and back-and-forth bullet propagation outside the capillary. A conducting channel connecting the jet nozzle and the surface is found. This correlates well with the observed charge exchange on the surface. The number of formed channels and the average deposited charge density on the surface is found to be strongly sensitive to the jet distance from the surface
Molecularly imprinted polymers in biological applications.
Molecularly imprinted polymers (MIPs) are currently widely used and further developed for biological applications. The MIP synthesis procedure is a key process, and a wide variety of protocols exist. The templates that are used for imprinting vary from the smallest glycosylated glycan structures or even amino acids to whole proteins or bacteria. The low cost, quick preparation, stability and reproducibility have been highlighted as advantages of MIPs. The biological applications utilizing MIPs discussed here include enzyme-linked assays, sensors, in vivo applications, drug delivery, cancer diagnostics and more. Indeed, there are numerous examples of how MIPs can be used as recognition elements similar to natural antibodie