Femtosecond laser and FIB: A revolutionary approach in rapid micro- mechanical sample preparation

The established Focused Ion Beam (FIB) technique usually poses a bottleneck in the preparation of samples for micro-mechanical experiments. This is due to its limited material removal rate. Especially for tungsten, the sputter yield of the Ga+ ion beam is very low. Therefore the practical sample size is restricted to dimensions of a few micrometers. On the contrary a femtosecond laser offers ablation rates 4-6 orders of magnitude higher compared to a Ga+ FIB [1] and therefore allows a rapid fabrication of specimens on the meso-scale. A prototype, which combines both methods, has been developed on the basis of the Zeiss Auriga Laser platform [2]. This system consists of the main chamber, where the FIB milling is conducted, and a separated airlock chamber for the femtosecond laser ablation. This setup prevents the contamination of the main chamber with laser ablated material and allows laser processing under atmospheric, inert gas or vacuum conditions. Fracture toughness experiments on single crystal tungsten in the micro-regime [3] exhibit a different behavior compared to specimens on the macro-scale [4]. The rapid processing of specimens with the novel laser system allows to sample the transition region from a discrete flow behavior of the micro-sized cantilevers to macroscopic plasticity. An analysis of fracture experiments for sample sizes ranging from 20 x 20 x 100 µm^3 to 200 x 200 x 1000 µm^3 is conducted. In addition to that, the quality of the laser processed samples is analyzed regarding the influence of processing parameters. Please click Additional Files below to see the full abstract

Small scale mechanical testing of nanoporous tungsten tailored by reverse phase dissolution

Nanoporous metals possess a number of positive attributes such as light weight, large surface area, excellent thermal properties, and energy absorption capability, making them a good candidate as future radiation shielding materials [1]. Tungsten seems to be ideally suited as the base material for such a foam, as it is commonly used in nuclear facilities, medical diagnosis systems and a number of other circumstances in order to protect personnel and sensitive equipment from radiation [2]. Therefore, it is of great value and interest to tailor such novel nanoporous tungsten, in order to combine the beneficial properties of tungsten with the positive attributes of nanoporous foams. In this work, nanoporous tungsten foams with relative densities ranging from 20 to 50 % were created on a bulk scale through a unique route involving severe plastic deformation of a coarse-grained tungsten-copper composite, followed by the selective dissolution of the nobler copper phase. Scanning electron microscopy and high-resolution transmission electron microscopy were utilized for characterizing the microstructural evolution and analyzing the way the etching solutions affect the resulting nanoporous structures. The mechanical properties, which are an important consideration in fusion reactor applications, were investigated by employing nanoindentation and other small-scale testing techniques in situ in the SEM. Based on this, the elemental plasticity mechanisms governing the mechanical behavior were elucidated. This work for the first time provides an innovative and adaptive approach to create bulk nanoporous tungsten. The developed reverse phase dissolution method is generally applicable and can be transferred to other refractory metal materials in the future. The promising mechanical results of nanoporous tungsten will serve as foundation for forthcoming related scientific studies and engineering applications. [1] S. Xu. M. Bourham, A. Rabiei. A novel ultra-light structure for radiation shielding. Materials & Design. 31 (2010), 2140-2146. [2] S. Kobayashi, N. Hosoda, R. Takashima. W alloys as radiation protection materials. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. 390 (1997), 426-430

“Ich habe mich noch nicht mit Pollux beschäftigt” - eine Zufriedenheits- und Bedarfsanalyse des Fachinformationsdienstes Politikwissenschaft

Der Fachinformationsdienst Politikwissenschaft Pollux hat im Juni 2020 unter den Politik­wissenschaftler*innen in Deutschland eine Online-Umfrage durchgeführt. Ziel der Umfrage war es, die Bedarfe und die Zufriedenheit der Zielgruppe mit dem Angebot von Pollux zu ermitteln. Es wurden Fragen aus den Bereichen Literaturrecherche, Open-Access-Publizieren, Forschungsdaten­management und Kommunikation gestellt. Ziele aus den Ergebnissen der Umfrage sind, dass Pollux bekannter gemacht werden muss, die Kernservices weiter ausgebaut und stetig zu verbessern sind sowie künftig auch über Open-Access-Publizieren und Forschungsdatenmanagement informiert und beraten werden soll.In June 2020, the Specialised Information Service for Political Science Pollux conducted an online survey among political scientists in Germany. The aim of the survey was to determine the needs and satisfaction with the services offered by Pollux. Questions were asked in the areas of literature research, open access publishing, research data management and communication. The key outcomes from the survey are that Pollux needs to be better known, that the main services of Pollux should be further expanded and continuously improved, and that in the future, information and advice on open access publishing and research data management should also be provided

M-Library

Keine andere Technologie wurde jemals zuvor so schnell und in so großem Umfang angenommen, wie die mobile Kommunikation. Mittlerweile besitzen 3,3 Milliarden Menschen weltweit (das ist jeder Zweite) einen Mobiltelefonvertrag. In Deutschland sind es über 100 Millionen (mehr Telefone als Einwohner). Mobile Geräte, wie Apples iPhone, Googles G1 und andere Smartphones, werden aufgrund erhöhter Bandbreite und Usability immer populärer. Auf ihnen fließen die Funktionen eines Computers, Audio-Players, Fotoapparats und Mobiletelefons zusammen. In Zusammenhang mit diesen neuen Technologien nimmt die mobile Nutzung des Internets drastisch zu. So nutzen in Deutschland bereits 35% das mobile Internet. Bis 2015 wird von einem Anstieg um 300% ausgegangen. Besonders die jüngere Generation (90%), NetGeneration, oder auch Digital Natives genannt, besitzen ein Mobiltelefon das völlig in ihr Alltagsleben integriert ist. Zudem nutzen sie ein breites Spektrum an Web 2.0 Software, mit der sie Inhalte schaffen, teilen und kommentieren können. Oftmals agieren sie in informellen Netzwerken wie StudiVZ, Facebook oder MySpace. Die meisten dieser Dienste, aber auch Tageszeitungen und Nachschlagewerke wie Wikipedia, Suchmaschinen und weitere kommerzielle Anbieter haben bereits mobile Websites, bzw. speziell für das Mobiltelefon entwickelte Anwendungen (z.B. Amazons Kindle für das iPhone). Durch die permanente Verbundenheit zum eigenen E-Mail Account, sozialen Netzwerken, zu Blogs usw. vermischt sich das soziale, berufliche und Freizeitleben, wodurch sich auch Konzepte von Raum und Zeit verändern. Dies stellt auch an Bibliotheken die Herausforderung, ihre Dienstleistungen in die virtuelle Umgebung einzubetten und Inhalte und Dienste mobilen Nutzern anzubieten. Mobile Technologie kann für verschiedene Bibliotheksdienste genutzt werden: mobile Interfaces, Lokalisierungsdienste, visuelle Suche, Multi-Media-Führungen und SMS-Benachrichtigungen. Während in Deutschland mobile Dienste in Bibliotheken eine noch unbedeutende Rolle spielen, nutzen US-amerikanische Bibliotheken bereits ein breites Spektrum. In diesem Vortrag sollen die verschiedenen mobilen Bibliotheksdiensteistungen vorgestellt und ausgewertet werden

Fracture mechanics of microsamples

Fracture mechanics has been developed to avoid catastrophic failures of structures. It is nowadays the basic tool for damage tolerant design. From materials science point of view the development of materials with improved fracture resistance has become an important topic. The developed standards to determine the fracture mechanics parameters are adapted to sample sizes from centimetre to meter. The standards are designed to generate materials specific data and not size dependent parameters. The transferability of this testing procedure to dimensions of micrometers is important but not straight forward. The fracture mechanical properties of materials in small dimensions have become an important research area in materials science. A driving force is the growing industrial importance of micro-electronic and micro-electromechanical systems and new down sized devices, for example for medical applications. The load bearing capacity and life time of such micro sized components are determined by the mechanical properties of the material with the corresponding dimensions. Another reason for the development of mechanical tests with samples in the micro range is the evaluation of individual properties of microstructural elements like grain boundaries or individual phases, which have typical dimensions in the micrometer and submicrometer regime. The main goal of the paper will be devoted to: - limits of the application of fracture mechanic tests to microsized samples, - when do fracture mechanic parameters remain size independent and when not, - what can we learn from micromechanical tests about fracture of materials in general, - can we solve fracture problems with microsamples which cannot be generated from conventional fracture mechanics tests

The value of diversifying uncertain renewable generation through the transmission system

A study published by the ISE estimates transmission-related benefits attributable to the geographic diversification of variable renewable generation and loads. The analysis indicates that the benefits of transmission expansion between areas with diverse renewable generation resources are greater than typically estimated, with significant reductions in system-wide costs and renewable generation curtailments in both hourly day-ahead and intra-hour power market operations. The benefits are substantial and yet often not accounted for because they are more difficult to model. The key findings of the study include the following: 1. For renewable generation levels from 10% to 60% of annual energy consumption, interconnecting two power market sub-regions with different wind regimes through transmission investments can reduce annual production costs by between 2% and 23% and annual renewable curtailments by 45% to 90%. 2. When real-time uncertainties of renewable generation and loads relative to their day-ahead forecasts are taken into consideration, the benefit of geographic diversification through the transmission grid are 2 to 20 times higher than benefits typically quantified based only on “perfect forecasts.” The findings of the study highlight the important role transmission expansion can play in successfully integrating large-scale renewable generation under both forecasted day-ahead and real-time market conditions. The authors also emphasize the need for transmission benefit-cost analyses to go beyond deterministic hourly simulations and begin taking into account both forecasting uncertainty and intra-hour system conditions to fully capture the regional and inter-regional renewable generation diversification benefits of the transmission system