Die politische Differenz und die Kontingenz der Ordnung

The distinction between politics (as practice of institutions) and the political (as the interruption of the practice of the former) has recently received greater attention in political theory. Whereas, on one side, five types of this distinction can be made, on the other, a problem persists: the question whether this distinction means to make a hierarchical differentiation between “mere politics” and the “real event” of the political. To this extent, it might help to see the political difference through the lens of Waldenfels’ distinction between (contingent) order and the extra-ordinary. The main idea is that the excess of the extraordinary is only to be found in politics and not outside of it. By means of this interpretation it could be argued that the gap between politics and the political could be reduced without being completely bridged

Transnationalism fading? Elderly Mexican migrants in Chicago and shifting notions of belonging

Transnationalism fading? Elderly Mexican migrants inChicago and shifting notions of belongin

The origin of interstellar asteroidal objects like 1I/2017 U1 'Oumuamua

We study the origin of the interstellar object 1I/2017 U1 'Oumuamua by juxtaposing estimates based on the observations with simulations. We speculate that objects like 'Oumuamua are formed in the debris disc as left over from the star and planet formation process, and subsequently liberated. The liberation process is mediated either by interaction with other stars in the parental star-cluster, by resonant interactions within the planetesimal disc or by the relatively sudden mass loss when the host star becomes a compact object. Integrating backward in time in the Galactic potential together with stars from the Gaia-TGAS catalogue we find that about 1.3Myr ago 'Oumuamua passed the nearby star HIP 17288 within a mean distance of $1.3$pc. By comparing nearby observed L-dwarfs with simulations of the Galaxy we conclude that the kinematics of 'Oumuamua is consistent with relatively young objects of $1.1$--$1.7$Gyr. We just met 'Oumuamua by chance, and with a derived mean Galactic density of $\sim 3\times 10^{5}$ similarly sized objects within 100\,au from the Sun or $\sim 10^{14}$ per cubic parsec we expect about 2 to 12 such visitors per year within 1au from the Sun.Comment: MNRAS (in press

Development of Ultrathin Niobium Nitride and Niobium Titanium Nitride Films for THz Hot-Electron Bolometers

The main focus of this work is the development of ultrathin NbN and NbTiN films. A reproducible and reliable deposition process for ultrathin NbN and NbTiN films for the use in phonon-cooled HEB devices was established. The ultrathin films were deposited on silicon (Si) substrates and on 2µm Si3N4 membranes by DC reactive magnetron sputtering. A method for the precise control of the nitrogen partial pressure by monitoring the target voltage has been introduced to deposit high quality, ultrathin NbN (3-4nm, Tc=8.5 K) and NbTiN (4-5nm, Tc=8K) films. Substrate heating of at least 600°C during the deposition is essential for the fabrication of ultrathin NbN and NbTiN films on Si substrates and Si3N4 membranes. The fabrication process required for HEB devices to be used in a quasi-optical mixer was developed. The ultrathin film was patterned by electron beam lithography (EBL), resulting in bolometer devices that measure areas of about 0.4 µm x 4 µm. The nature of the contact determines the interface transparency between the bolometer and the contact structure. Different cleaning processes have been performed and the influence on the contact resistance has been instigated. A better interface transparency gives less RF losses and could improve the HEB sensitivity and local oscillator (LO) requirement. A better control of the interface transparency also leads to a better reproducibility in values of the normal state resistance of the HEB devices. Heterodyne measurements were performed at 0.8 THz and 1.6 THz. For the NbTiN HEB devices, the double sideband (DSB) receiver noise temperature at 0.8 THz was found to be 2500 K for at 1.2 GHz IF. The main problem with HEB mixers is the limitation in the IF bandwidth. The measured noise bandwidth was about 1.5 GHz. The DSB receiver noise temperature at 1.6 THz LO frequency measured at Chalmers University, Sweden, was found to be 1600 K at 1.5 GHz IF. This result shows that the noise of these NbTiN HEB devices is comparable with the NbN HEB mixers fabricated at the Chalmers University. For the NbN HEB devices the DSB receiver noise temperature Trec was 1344 K at 0.8 THz with an absorbed LO power of 55 nW, estimated using the isothermal method. This receiver noise temperature is higher than the state-of-the-art receiver noise temperature at this frequency. This is possibly due to the losses in the optics. It was not possible to determine the noise bandwidth of this device, because the noise temperature did not increase by the factor of two in the bandwidth of the isolator. But the noise bandwidth is estimated to be about than 1.8 GHz. Although the true bandwidth of the NbTiN and NbN HEB devices could only be measured with an appropriate IF system, the combination of these results show that NbTiN is possibly inferior in bandwidth to NbN used for the HEB fabrication

Thermo-mechanical characterization of polymer samples using nanoindentation - From bulk characterization to thin film properties

Polymer films for the use of coating or structuring applications for small scale devices are widely used. For the raw bulk material the thermal and mechanical data are easily accessible and often supplied by the manufacturer. For the final use as a thin film, the verification of these properties is more difficult. Nanoindentation techniques can be used for the characterization of thin film due to the small-scaled mechanical stress field of the nanoindenter tip. Studies comparing nanoindentation data on bulk polymer samples with conventional DMA data show a good agreement in storage and in loss modulus [1]. Since thermal properties of polymers are often important, indentation tests at non-ambient temperatures are required. By using an actively heated tip, we are able to study these properties under isothermal conditions. We will show results on heated polymer samples for semiconductor applications and discuss the influence of the heating method to the results

Nanoindentation tests using flat punch indenter ‐ Contact formation and tilt correction

Flat punch indenters are commonly used as probes for Nanoindentation due to the fact that contact area is easy to define. Furthermore the contact area with the sample is usually much larger compared to conical or pyramidal geometries. The larger contact area extends the field of applications to softer materials like soft polymers or gels. The contact formation between flat punch indenter and a flat sample surface is depending on the tilt angle between both normal directions. Above a certain depth or load the flat punch forms a “full contact” with the sample. Depending on the actual tilt and the sample thickness, this can be a limitation for the measurements. Strategies for evaluating the tilt and for tilt compensation are presented and discussed

Scalable Distributed DNN Training using TensorFlow and CUDA-Aware MPI: Characterization, Designs, and Performance Evaluation

TensorFlow has been the most widely adopted Machine/Deep Learning framework. However, little exists in the literature that provides a thorough understanding of the capabilities which TensorFlow offers for the distributed training of large ML/DL models that need computation and communication at scale. Most commonly used distributed training approaches for TF can be categorized as follows: 1) Google Remote Procedure Call (gRPC), 2) gRPC+X: X=(InfiniBand Verbs, Message Passing Interface, and GPUDirect RDMA), and 3) No-gRPC: Baidu Allreduce with MPI, Horovod with MPI, and Horovod with NVIDIA NCCL. In this paper, we provide an in-depth performance characterization and analysis of these distributed training approaches on various GPU clusters including the Piz Daint system (6 on Top500). We perform experiments to gain novel insights along the following vectors: 1) Application-level scalability of DNN training, 2) Effect of Batch Size on scaling efficiency, 3) Impact of the MPI library used for no-gRPC approaches, and 4) Type and size of DNN architectures. Based on these experiments, we present two key insights: 1) Overall, No-gRPC designs achieve better performance compared to gRPC-based approaches for most configurations, and 2) The performance of No-gRPC is heavily influenced by the gradient aggregation using Allreduce. Finally, we propose a truly CUDA-Aware MPI Allreduce design that exploits CUDA kernels and pointer caching to perform large reductions efficiently. Our proposed designs offer 5-17X better performance than NCCL2 for small and medium messages, and reduces latency by 29% for large messages. The proposed optimizations help Horovod-MPI to achieve approximately 90% scaling efficiency for ResNet-50 training on 64 GPUs. Further, Horovod-MPI achieves 1.8X and 3.2X higher throughput than the native gRPC method for ResNet-50 and MobileNet, respectively, on the Piz Daint cluster.Comment: 10 pages, 9 figures, submitted to IEEE IPDPS 2019 for peer-revie

"We don't have a Culture" - Being coloured in Namibia als Konstruktion und Praxis

Frau Bedorfs Magisterarbeit, betreut von Professor Michael Bollig, wurde im Kontext des Sonderforschungsbereichs 389 "Kultur- und Landschaftswandel im ariden Afrika" und hier insbesondere innerhalb des Teilprojektes C11, in dem es um urbane Identitäten im postkolonialen Namibia ging, erarbeitet. Die im Fokus der Arbeit stehende Gruppe der sogenannten Coloureds ist ein Produkt der Segregations- und Apartheidspolitik des 20. Jahrhunderts. Bereits in der deutschen Kolonialzeit marginalisierte und diskriminierte die kolonisierende weiße Bevölkerung Nachkommen, die aus Verbindungen weißer Siedler, Verwalter und Soldaten mit einheimischen Frauen hervorgingen. Sie verweigerte ihnen, wie auch der übrigen einheimischen Bevölkerung, Grundrechte und schloss sie von der politischen Partizipation weitestgehend aus. Gleichzeitig räumten die weißen Kolonialherren den Coloureds aber mehr Rechte als der schwarzen Bevölkerung ein und in der Apartheidszeit (1948-1989) wurden für sie getrennte Stadtteile angelegt. In dem zu Windhoek, der Hauptstadt Namibias, gehörenden, Anfang der 1960er Jahre eingerichteten coloured Stadtteil Khomasdal hat Franziska Bedorf eine zweimonatige Feldarbeit zu der Thematik �Identitätskonstruktionen und soziale Praxis� durchgeführt. Im Fokus der Arbeit steht die Frage, wie die Kategorie des being coloured seit Ende des 19. Jahrhunderts in Namibia entstanden ist, welchen Einfluss sie auf das Leben, insbesondere die sozialen Beziehungen, der so kategorisierten Menschen hat und inwieweit sich Inhalt und Bedeutung des Attributs seit der Unabhängigkeit des Namibias 1990 gewandelt haben. Frau Bedorfs Arbeit zu den Coloureds Namibias ist eine der ersten sozial und kulturwissenschaftlichen Arbeiten zu dieser sozialen Gruppe. Mittels einer auf Befragungen, teilnehmender Beobachtung, Archivarbeit und Netzwerkanalyse beruhenden Herangehensweise gelingt es Franziska Bedorf, die historisch gewachsenen Ambiguitäten aber auch die zentralen Markierungen einer coloured Identität kenntnisreich zu beschreiben und zu analysieren

New Tools to solve known problems at critical nanoindentation measurements

The nanoindentation measurement process is a widely used in material science. It delivers very useful information about the mechanical properties with high spatial resolution. Nevertheless the knowledge of the exact contact mechanic with its geometrical conditions of indenter tip and sample surface in the contact area is essential for the accuracy of the results. Because the indenter geometry is not free of tolerances as well the sample surface is not in the accurate position to the indenter – so corrections are necessary to solve this incorrectness. The detailed analysis of flat punch force-displacement curves allows to correct the incorrectness of the contact surfaces by aligning the sample surface parallel to the real flat punch surface. Please click Additional Files below to see the full abstract

Transnationalism fading? Elderly Mexican migrants in Chicago and shifting notions of belonging

Transnationalism fading? Elderly Mexican migrants inChicago and shifting notions of belongin