Photoassociation and coherent transient dynamics in the interaction of ultracold rubidium atoms with shaped femtosecond pulses - I. Experiment

We experimentally investigate various processes present in the photoassociative interaction of an ultracold atomic sample with shaped femtosecond laser pulses. We demonstrate the photoassociation of pairs of rubidium atoms into electronically excited, bound molecular states using spectrally cut femtosecond laser pulses tuned below the rubidium D1 or D2 asymptote. Time-resolved pump-probe spectra reveal coherent oscillations of the molecular formation rate, which are due to coherent transient dynamics in the electronic excitation. The oscillation frequency corresponds to the detun-ing of the spectral cut position to the asymptotic transition frequency of the rubidium D1 or D2 lines, respectively. Measurements of the molecular photoassociation signal as a function of the pulse energy reveal a non-linear dependence and indicate a non-perturbative excitation process. Chirping the association laser pulse allowed us to change the phase of the coherent transients. Furthermore, a signature for molecules in the electronic ground state is found, which is attributed to molecule formation by femtosecond photoassociation followed by spontaneous decay. In a subsequent article [A. Merli et al., submitted] quantum mechanical calculations are presented, which compare well with the experimental data and reveal further details about the observed coherent transient dynamics

Aufbereitung von optischen Messdaten zur Analyse der asymmetrischen inkrementellen Blechumformung (AIBU)

Ziel unseres Projektes ist die statistische Analyse der bisher wenig erforschten asymmetrischen inkrementellen Blechumformung (AIBU). Ein elementares Problem hierbei ist die Quanti zierung der Qualität eines gefertigten Bauteils. Da der AIBU-Prozess ein inkrementeller Prozess ist, spielt die Qualität der gesamten dreidimensionalen Geometrie des Fertigteils eine Rolle. Nur wenn sie gänzlich quanti ziert werden kann, ist eine Untersuchung der Prozessdynamik möglich. Die dreidimensionale Vermessung des Fertigteils ist jedoch mit den herkömmlichen (taktilen) Messmethoden nur schwer möglich, daher stellen wir in diesem Diskussionspapier ein Verfahren zur Aufbereitung von optischen Messdaten vor, welches eine solche Analyse ermöglicht. Hierbei wird die Geometrie der Bauteile zunächst optisch komplett vermessen. Aufbauend auf diesen Messungen werden in einem mehrstu figen Ansatz die Messdaten mittels statistischer Methoden aufbereitet, um Artefakte heraus zu filtern, Ober- und Unterseiten zu trennen und schließlich auch die Wandstärken zu bestimmen. Kennt man die exakte Geometrie des Fertigteils und dessen Wandstärke über die gesamte Oberfläche, können hieraus leicht Qualitätskennzahlen errechnet werden. In Kapitel 2 werden zunächst die prozesstechnischen Grundlagen der AIBU und deren Prozessparameter und Einflussfaktoren eingeführt. In Kapitel 3 wird das in diesem Papier verwendete Experiment und die Messmethodik erklärt. Das Kapitel 4 befasst sich dann detailliert mit den einzelnen Schritten der Messdatenaufbereitung. Das letzte Kapitel diskutiert die Reproduzierbarkeit und Verlässlichkeit der vorgestellten Methode

REactor Safety Analysis ToolboX RESA-TX

The REactor Safety Analysis ToolboX RESA-TX is a software and data package in development that combines the automatisation of all established procedures for deterministic safety analysis (DSA), the integration of expert know-how and a large database including the most relevant information required for conducting a DSA. In the current state of the art, DSA is a complex and thus error-prone process that is highly time-consuming and repetitive. The reliability of the result is strongly dependent on the availability of plant data and expert know-how. The idea of developing the RESA-TX toolbox arose at GRS to cope with these conditions. The innovative approach proposes an automated and standardised procedure, supported by a large database of plant design characteristics, plant behaviour, regulatory rules and DSA expert knowledge incorporated within the tool. Its application allows the end user to automatically generate and verify an input deck, as well as conduct design basis accident (DBA) calculations for a certain design with highly reduced manual intervention. The databases can be extended depending on available information or other boundary conditions. A heuristic approach is integrated into the model generation process, where users often suffer from a lack of information about the facility under consideration. These heuristics can be replaced when higher information quality is available or enhanced over time, which can lead to more reliable results with increasing usage of the tool. As a result, the application of RESA-TX could highly increase the efficiency of the DSA process, reducing both repetitiveness as well as user-induced errors. This in return will lead to an improvement in the quality of the analysis and reliability of the results. In consequence, RESA-TX will allow for a DSA to be conducted more frequently in situations where time or budget was a limitation before, thereby contributing to an increase in reactor safety

Graphitizability of Polymer Thin Films: An In Situ TEM Study of Thickness Effects on Nanocrystalline Graphene/Glassy Carbon Formation

Polymer pyrolysis has emerged as a versatile method to synthesize graphenoid (graphene like) materials with varying thickness and properties. The morphology of the thin film, especially the thickness, greatly affects the graphitizability and the properties of the graphenoid material. Using in situ current annealing inside a transmission electron microscope (TEM), the thickness-dependent structural evolution of the polymer film with a special focus on thickness effects is followed. At high temperatures, thin samples form large graphene layers oriented parallel to the substrate, whereas in thick samples multi-walled cage-like structures are formed. Moleclar Dynamics (MD) simulations reveal a film thickness of 40 Å below which, the carbonized layers align parallel to the surface. For thicker samples, the orientation of the layers becomes increasingly misoriented starting from the surface to the center. This structural change can be attributed to the formation of bonded multi-layers from the initially unsaturated activated edges. The resulting cage-like structures are stable even during simulated annealing at temperatures as high as 3500 K. An atomistic understanding of the formation of these structures is presented. The results clearly indicate the critical effect of thickness on the graphitizability of polymers and provide a new understanding of the structural evolution during pyrolysis

Sensing Molecules with Metal–Organic Framework Functionalized Graphene Transistors

Graphene is inherently sensitive to vicinal dielectrics and local charge distributions, a property that can be probed by the position of the Dirac point in graphene field‐effect transistors. Exploiting this as a useful sensing principle requires selectivity; however, graphene itself exhibits no molecule‐specific interaction. Complementarily, metal–organic frameworks can be tailored to selective adsorption of specific molecular species. Here, a selective ethanol sensor is demonstrated by growing a surface‐mounted metal–organic framework (SURMOF) directly onto graphene field‐effect transistors (GFETs). Unprecedented shifts of the Dirac point, as large as 15 V, are observed when the SURMOF/GFET is exposed to ethanol, while a vanishingly small response is observed for isopropanol, methanol, and other constituents of the air, including water. The synthesis and conditioning of the hybrid materials sensor with its functional characteristics are described and a model is proposed to explain the origin, magnitude, and direction of the Dirac point voltage shift. Tailoring multiple SURMOFs to adsorb specific gases on an array of such devices thus generates a versatile, selective, and highly sensitive platform for sensing applications

Fin whale (Balaenoptera physalus) mitogenomics: A cautionary tale of defining sub-species from mitochondrial sequence monophyly

The advent of massive parallel sequencing technologies has resulted in an increase of studies based upon complete mitochondrial genome DNA sequences that revisit the taxonomic status within and among species. Spatially distinct monophyly in such mitogenomic genealogies, i.e., the sharing of a recent common ancestor among con-specific samples collected in the same region has been viewed as evidence for subspecies. Several recent studies in cetaceans have employed this criterion to suggest subsequent intraspecific taxonomic revisions. We reason that employing intra-specific, spatially distinct monophyly at non-recombining, clonally inherited genomes is an unsatisfactory criterion for defining subspecies based upon theoretical (genetic drift) and practical (sampling effort) arguments. This point was illustrated by a re-analysis of a global mitogenomic assessment of fin whales, Balaenoptera physalus spp., published by Archer et al. (2013), which proposed to further subdivide the Northern Hemisphere fin whale subspecies, B. p. physalus. The proposed revision was based upon the detection of spatially distinct monophyly among North Atlantic and North Pacific fin whales in a genealogy based upon complete mitochondrial genome DNA sequences. The extended analysis conducted in this study (1676 mitochondrial control region, 162 complete mitochondrial genome DNA sequences and 20 microsatellite loci genotyped in 380 samples) revealed that the apparent monophyly among North Atlantic fin whales reported by Archer et al. (2013) to be due to low sample sizes. In conclusion, defining sub-species from monophyly (i.e., the absence of para- or polyphyly) can lead to erroneous conclusions due to relatively 'trivial' aspects, such as sampling. Basic population genetic processes (i.e., genetic drift and migration) also affect the time to the most recent common ancestor and hence the probability that individuals in a sample are monophyletic