Schnelle Löser für Partielle Differentialgleichungen

The workshop Schnelle Löser für partielle Differentialgleichungen, organised by Randolph E. Bank (La Jolla), Wolfgang Hackbusch (Leipzig), and Gabriel Wittum (Frankfurt am Main), was held May 22nd–May 28th, 2011. This meeting was well attended by 54 participants with broad geographic representation from 7 countries and 3 continents. This workshop was a nice blend of researchers with various backgrounds

On the direct detection of 229mTh

Measurements are described that have led to the direct detection of the isomeric first excited state of the thorium-229 nucleus

1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface

A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance

Beam scanning by liquid-crystal biasing in a modified SIW structure

A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium

Ionization and Triggered Star Formation in Turbulent Molecular Clouds

Einige der spektakulärsten Beobachtungen unserer Milchstrasse zeigen die filamentären Strukturen in der Umgebung von heissen massereichen O-Sternen. Sobald diese Sterne beginnen zu leuchten, ionisiert ihre ultraviolette Strahlung das umgebende Gas und erzeugt eine heisse HII-Region. Das erhitzte Gas expandiert in die umgebende kalte Molekülwolke. Die dabei entstehende Schockwelle komprimiert das kalte Gas in die auffälligen Strukturen. An den Spitzen dieser Strukturen entstehen neue, masseärmere Sterne. Bis heute ist die präzise Entstehung dieser Regionen nicht vollständig verstanden. Ziel dieser Arbeit ist die Simulation dieser Entwicklung anhand hydrodynamischer Methoden. Dazu wird ionisierende Strahlung in einen Smoothed Particle Hydrodynamics (SPH) Code namens VINE, der vollständig OpenMP-parallelisiert ist, implementiert. Für die Berechnung der Ionisation wird angenommen, dass die betrachtete Region so weit von dem Stern entfernt ist, dass die Strahlung näherungsweise plan-parallel eintrifft. Zunächst wird die Eintrittsfläche in gleich grosse Strahlen unterteilt. Dann wird die Ionisation entlang dieser Strahlen propagiert. Die neue Implementation ist vollständig parallelisiert und trägt den Namen iVINE. Zuerst wird anhand mehrerer Tests die Übereinstimmung von iVINE mit bekannten analytischen Lösungen gezeigt. Danach wird der durch Ionisation induzierte gravitative Kollaps einer marginal stabilen Sphäre untersucht. In allen drei simulierten Fällen mit unterschiedlichem einfallenden ionisierenden Fluss kollabiert die Sphäre. Zusätzlich kann die beobachtete Tendenz, dass jüngere Sterne weiter entfernt von der Quelle der Ionisation entstehen, bestätigt werden. Desweiteren werden Simulationen über den Einfluss ionisierender Strahlung auf turbulente Molekülwolken durchgeführt. Hier zeigt sich, dass die beobachteten, komplexen Strukturen durch die Kombination von Ionisation, Hydrodynamik und Gravitation reproduziert werden können. An den Spitzen der Strukturen wird das Gas stark komprimiert und kollabiert unter dem Einfluss seiner Eigengravitation, genau wie beobachtet. Gleichzeitig treibt die ionisierende Strahlung die Turbulenz im kalten Gas weit stärker als bisher angenommen. Anhand von einer Parameterstudie folgt, dass die entstehenden Strukturen kritisch von dem jeweiligen Anfangsstadium der Wolke zur Zeit der Zündung des O-Sterns abhängen. Dies ergibt die einmalige Gelegenheit, zusätzliche Informationen über Molekülwolken, die ansonsten schwierig zu beobachten sind, in den von O-Sternen stark illuminierten Regionen zu erhalten. Die Implementation ionisierender Strahlung im Rahmen dieser Doktorarbeit ermöglicht die Untersuchung der Einwirkung massereicher Sterne auf ihre Umgebung in bislang Unerreichter Genauigkeit. Die durchgeführten Simulationen vertiefen unser Verständnis der Wechselwirkung von Turbulenz und Gravitation im Rahmen der Sternentstehung. Weitere erstrebenswerte Schritte wären die genauere Berücksichtigung der Kühlprozesse innerhalb der Molekülwolke und die Implementation der Winde massereicher O-Sterne

Passive Planar Microwave Devices

The aim of this book is to highlight some recent advances in microwave planar devices. The development of planar technologies still generates great interest because of their many applications in fields as diverse as wireless communications, medical instrumentation, remote sensing, etc. In this book, particular interest has been focused on an electronically controllable phase shifter, wireless sensing, a multiband textile antenna, a MIMO antenna in microstrip technology, a miniaturized spoof plasmonic antipodal Vivaldi antenna, a dual-band balanced bandpass filter, glide-symmetric structures, a transparent multiband antenna for vehicle communications, a multilayer bandpass filter with high selectivity, microwave planar cutoff probes, and a wideband transition from microstrip to ridge empty substrate integrated waveguide

Isomotive dielectrophoresis for enhanced analyses of cell subpopulations.

As the relentless dream of creating a true lab-on-a-chip device is closer to realization than ever before, which will be enabled through efficient and reliable sample characterization systems. Dielectrophoresis (DEP) is a term used to describe the motion of dielectric particles/ cells, by means of a non-uniform electric field (AC or DC). Cells of different dielectric properties (i.e., size, interior properties, and membrane properties) will act differently under the influence of dielectrophoretic force. Therefore, DEP can be used as a powerful, robust, and flexible tool for cellular manipulation, separation, characterization, and patterning. However, most recent DEP applications focus on trapping, separation, or sorting particles. The true value of DEP lies in its analytical capabilities which can be achieved by utilizing isomotive dielectrophoresis (isoDEP). In isoDEP, the gradient of the electric field-squared is constant, hence, upon the application of electric field, all particles/cells that share the same dielectric properties will feel the same constant dielectrophoretic force i.e., translate through the micro-channel at the same velocity. However, DEP is not the only acting force upon particles inside an isoDEP device, other electrokinetics, including but not limited to electrothermal hydrodynamics, might act on particles simultaneously. Within this dissertation, electrothermal-based experiments have been conducted to assess the effect of such undesired forces. Also, to maximize the relative DEP force over other forces for a given cell/particle size, design parameters such as microchannel width, height, fabrication materials, lid thickness, and applied electric field must be properly tuned. In this work, scaling law analyses were developed to derive design rules that relate those tunable parameters to achieve the desired dielectrophoretic force for cell analysis. Initial results indicated that for a particle suspended in 10 mS/m media, if the channel width and height are below 10 particle diameters, the electrothermal-driven flow is reduced by ∼ 500 times compared to the 500 µm thick conventional isoDEP device. Also, Replacing glass with silicon as the device’s base for an insulative-based isoDEP, reduces the electrothermal induced flow by ∼ 20 times. Within this dissertation, different device designs and fabrication methods were attempted in order to achieve an isoDEP platform that can characterize and differentiate between live and dead phytoplankton cells suspended in the same solution. Unfortunately, unwanted electrokinetics (predicted by the previously mentioned scaling law analysis) prevented comprehensive isoDEP analysis of phytoplankton cells. Due to isoDEP device limitations and other complications, other techniques were pursued to electrically characterize phytoplankton cells in suspension. An electrochemical-based platform utilizing impedance spectroscopy measurements was used to extract the electrical properties of phytoplankton cells in suspension. Impedance spectroscopy spectra were acquired, and the single-shell model was applied to extract the specific membrane capacitance, cytoplasm permittivity, and conductivity of assumingly spherical cells in suspension utilizing Maxwell’s mixture theory of a controlled volume fraction of cells. The impedance of suspensions of algae were measured at different frequencies ranging from 3 kHz to 10 MHz and impedance values were compared to investigate differences between two types of cells by characterizing their change in cytoplasm permittivity and membrane capacitance. Differentiation between healthy control and nitrogen-depleted cultured algae was attempted. The extracted specific membrane capacitances of Chlamydomonas and Selenastrum were 15:57 ± 3:62 and 40:64 ± 12:6 mF/m2 respectively. Successful differentiation based on the specific membrane capacitance of different algae species was achieved. However, no significant difference was noticed between nitrogen abundant and nitrogen depleted cultures. To investigate the potential of isoDEP for cell analysis, a comparison to existing dielectrophoresis-based electrokinetic techniques was encouraged, including electrorotation (ROT) microfluidic platforms. The ROT microfluidic chip was used to characterize M17, HEK293, T-lymphocytes, and Hela single cells. Through hands-on experience with ROT, the advantages and disadvantages of this approach and isoDEP are apparent. IsoDEP proves to be a good characterization tool for subpopulation cell analysis with potential higher throughput compared to ROT while maintaining simple fabrication and operation processes. To emphasize the role of dielectrophoresis in biology, further studies utilizing the 3DEP analytical system were used to determine the electrical properties of Drosophila melanogaster (Kc167) cells ectopically expressing Late embryogenesis abundant (LEA) proteins from the anhydrobiotic brine shrimp, Artemia franciscana. Dielectrophoretic-based characterization data demonstrates that single expression of two different LEA proteins, AfrLEA3m and AfrLEA6, both increase cytoplasmic conductivity of Kc167 cells to a similar extend above control values. The extracted DEP data supported previously reported data suggesting that AfrLEA3m can interact directly with membranes during water stress. This hypothesis was strengthened using scanning electron microscopy, where cells expressing AfrLEA3m were found to retain their spherical morphology during desiccation, while control cells exhibited a larger variety of shapes in the desiccated state

Navigating Healthcare Science Student Learning and Engagement Through Implementation of a Virtual Classroom

Objective. This study explored whether virtual classrooms can be utilized to facilitate student learning and engagement. Background. University students and their learning approaches undergo constant changes, mainly due to advances in technology. Therefore, student expectations are continuously shifting. Although technology allows easier access to learning material, students still depend on a structured learning environment facilitated by an instructor to receive and process the correct information. Methods. A virtual classroom developed and housed in Second Life was used to deliver a week-long course on health promotion. Thirty students from different healthcare science programs participated in the study. After a 15-minute live orientation session, participants explored the classroom for a week, completed a short quiz, and described their experience using a survey. The quiz was completed via Canvas while Qualtrics was used to capture student experience. SPSS v.26.0 was utilized to run correlation and cluster analyses. Results. Hierarchical cluster analysis was completed in order to identify groups of students that had similar characteristics. The results partitioned students into three clusters characterized by quiz score, belief in difficulty of the content and technology. Correlation analysis revealed that students who perceived the course content as challenging also expressed that the control devices interfered with performance within the virtual classroom; r(22)=0.473, pConclusion. 82% of the participants believed that the Second Life platform can serve as an alternative to supplement occasional live student engagement and learning. Grants. This study was funded by the HPD Research Grant at Nova Southeastern University