Active suspension design for a Large Space Structure ground test facility

The expected future high performance requirements for Large Space Structures (LSS) enforce technology innovations such as active vibration damping techniques e.g., by means of structure sensors and actuators. The implementation of new technologies like that requires an interactive and integrated structural and control design with an increased effort in hardware validation by ground testing. During the technology development phase generic system tests will be most important covering verification and validation aspects up to the preparation and definition of relevant space experiments. For many applications using advanced designs it is deemed necessary to improve existing testing technology by further reducing disturbances and gravity coupling effects while maintaining high performance reliability. A key issue in this context is the improvement of suspension techniques. The ideal ground test facility satisfying these requirements completely will never be found. The highest degree of reliability will always be obtained by passive suspension methods taking into account severe performance limitations such as non-zero rigid body modes, restriction of degrees of freedom of motion and frequency response limitations. Passive compensation mechanisms, e.g., zero-spring-rate mechanisms, either require large moving masses or they are limited with respect to low-frequency performance by friction, stiction or other non-linear effects. With active suspensions these limitations can be removed to a large extent thereby increasing the range of applications. Despite an additional complexity which is associated with a potential risk in reliability their development is considered promising due to the amazing improvement of real-time control technology which is still continuing

Tool Wear Segmentation in Blanking Processes with Fully Convolutional Networks based Digital Image Processing

The extend of tool wear significantly affects blanking processes and has a decisive impact on product quality and productivity. For this reason, numerous scientists have addressed their research to wear monitoring systems in order to identify or even predict critical wear at an early stage. Existing approaches are mainly based on indirect monitoring using time series, which are used to detect critical wear states via thresholds or machine learning models. Nevertheless, differentiation between types of wear phenomena affecting the tool during blanking as well as quantification of worn surfaces is still limited in practice. While time series data provides partial insights into wear occurrence and evolution, direct monitoring techniques utilizing image data offer a more comprehensive perspective and increased robustness when dealing with varying process parameters. However, acquiring and processing this data in real-time is challenging. In particular, high dynamics combined with increasing strokes rates as well as the high dimensionality of image data have so far prevented the development of direct image-based monitoring systems. For this reason, this paper demonstrates how high-resolution images of tools at 600 spm can be captured and subsequently processed using semantic segmentation deep learning algorithms, more precisely Fully Convolutional Networks (FCN). 125,000 images of the tool are taken from successive strokes, and microscope images are captured to investigate the worn surfaces. Based on findings from the microscope images, selected images are labeled pixel by pixel according to their wear condition and used to train a FCN (U-Net)

Dust-temperature of an isolated star-forming cloud: Herschel observations of the Bok globule CB244

We present Herschel observations of the isolated, low-mass star-forming Bok globule CB244. It contains two cold sources, a low-mass Class 0 protostar and a starless core, which is likely to be prestellar in nature, separated by 90 arcsec (~ 18000 AU). The Herschel data sample the peak of the Planck spectrum for these sources, and are therefore ideal for dust-temperature and column density modeling. With these data and a near-IR extinction map, the MIPS 70 micron mosaic, the SCUBA 850 micron map, and the IRAM 1.3 mm map, we model the dust-temperature and column density of CB244 and present the first measured dust-temperature map of an entire star-forming molecular cloud. We find that the column-averaged dust-temperature near the protostar is ~ 17.7 K, while for the starless core it is ~ 10.6K, and that the effect of external heating causes the cloud dust-temperature to rise to ~ 17 K where the hydrogen column density drops below 10^21 cm^-2. The total hydrogen mass of CB244 (assuming a distance of 200 pc) is 15 +/- 5 M_sun. The mass of the protostellar core is 1.6 +/- 0.1 M_sun and the mass of the starless core is 5 +/- 2 M_sun, indicating that ~ 45% of the mass in the globule is participating in the star-formation process.Comment: Accepted for A&A Herschel Special Issue; 5 pages, 2 figure

Implementation of a Modelica library for simulation of electromechanical actuators for aircraft and helicopters

The goal of the A2015 library presented in this paper is to develop a Modelica based, tool-independent standard for electromechanical actuators (EMA). This will contribute to the establishment of a “common language” throughout the development of EMAs for aircraft and helicopters and through the supply chain. All stages of the design and validation process (conceptual design, specification, development and validation) are covered. The modeling approach addresses specific aspects of the EMA design process not covered by existing tools. The library scope, engineering need and implementation are described. Modeling of selected EMA components is discussed in more detail. An application example of the library is given (linear actuator, A320 aileron

The mentor-mentee relationship between student teachers and their mentors

Bestehende Forschungen zu Schulpraktika konzentrieren sich vor allem auf die Gruppe der Studierenden. Befunde zu den Betreuungspersonen und zur Interaktion beider Gruppen fehlen bisher und stellen ein Desiderat dar. Dem folgend diskutieren in der vorliegenden Studie Studierende im Praktikum und ihre betreuenden Lehrkräfte Bedingungen einer gelingenden Beziehung und Zusammenarbeit. Diese geben auch Aufschluss darüber, welche Konzeptionen von Beziehung und welche Rollengefüge beide Seiten als förderlich für ihre Interaktion wahrnehmen. Die Stichprobe umfasst 57 Studierende und 99 Praktikumslehrkräfte aus Grund- und Mittelschulen, rekrutiert im Rahmen eines Praktikums, das sich über ein Schuljahr verteilt. Die Auswertung der 21 Gruppendiskussionen erfolgte inhaltsanalytisch. Ein zentrales alle Kategorien übergreifend charakterisierendes Ergebnis ist, dass die Gelingensbedingungen aus Sicht von Studierenden und Lehrkräften eine Auflösung tradierter Meister-Lehrlings-Modelle widerspiegeln. Sie sind an einer symmetrischen Beziehungsgestaltung orientiert und beruhen auf reziprokem Agieren und einer gemeinsamen Verantwortung aller Akteur:innen. Hierarchische Abstufungen zeigen sich dort überholt, wo Studierende ihren Mentor:innen kritisches Feedback geben dürfen und sollen bzw. wo Mentor:innen ihren eigenen Unterricht zur Diskussion stellen und bereit sind, von Studierenden zu lernen. Die kollegiale Zusammenarbeit auf Augenhöhe ist allerdings an Erwartungen der Mentor:innen hinsichtlich des Verhaltens der Studierenden gebunden. Abschließend werden Desiderate der praktischen Implementierung und der wissenschaftlichen Evaluierung diskutiert. (DIPF/Orig.)Existing research on school practicum focuses mainly on the group of student teachers. Findings on the mentor teachers and even more on the interaction of both groups are missing. In the present study, student teachers and mentor teachers discuss the conditions for a successful relationship and collaboration. These conditions provide information about the conceptions of relationship and the role structures both sides perceive as beneficial for their interaction. The sample consists of 57 student teachers and 99 mentor teachers from primary and lower secondary schools. The participants were part of a one-school-year teacher practicum. The 21 group discussions were analyzed using content analysis. A central result across all categories is that conditions of success reflect the dissolution of traditional master-apprenticeship models from both the perspective of student teachers and mentor teachers. Instead, they are orientated towards a symmetrical relationship as well as reciprocal action and shared responsibility. Hierarchies appear to be outdated where teacher students are allowed and expected to give critical feedback to their mentor teachers, where mentor teachers are willing to discuss with and learn from student teachers. However, collegial collaboration on an equal basis is linked to mentors’ expectations of mentees’ behavior. Finally, desiderata for the practical implementation and scientific evaluation are discussed. (DIPF/Orig.

90 GHz Continuum Observations of Messier 66

Radio emission at around 90 GHz from star-forming galaxies is expected to be strongly dominated by the free-free component due to ionising radiation from massive, short-lived, stars. We present high surface-brightness sensitivity observations at 90 GHz of the nearby star-forming galaxy Messier 66 with resolution of about 9 arcsec (corresponding to a physical scale of about 500 pc) and analyse these observations in combination with archival lower frequency radio and mid-infrared measurements. For the four regions for which the observations support our models we find that the free-free component indeed dominates the emission at 90 GHz, making up 76--90 per cent of the luminosity at this frequency but with the data also consistent with all of the emission being due to free-free. The estimates of free-free luminosities are also consistent, within measurement and decomposition errors, with star-formation rates derived from lower radio frequencies and mid-infrared observations. In our analysis we consider both power-law and curved spectra for the synchrotron component but do not find evidence to support the curved model in preference to the power-law.Comment: 7 pages, 5 figures. Submitted to MNRAS. Further information, plots, links to software are available at http://www.mrao.cam.ac.uk/~bn204/galevol/2012-90ghz-m66.htm

AMI observations of Lynds Dark Nebulae: further evidence for anomalous cm-wave emission

Observations at 14.2 to 17.9 GHz made with the AMI Small Array towards fourteen Lynds Dark Nebulae with a resolution of 2' are reported. These sources are selected from the SCUBA observations of Visser et al. (2001) as small angular diameter clouds well matched to the synthesized beam of the AMI Small Array. Comparison of the AMI observations with radio observations at lower frequencies with matched uv-plane coverage is made, in order to search for any anomalous excess emission which can be attributed to spinning dust. Possible emission from spinning dust is identified as a source within a 2' radius of the Scuba position of the Lynds dark nebula, exhibiting an excess with respect to lower frequency radio emission. We find five sources which show a possible spinning dust component in their spectra. These sources have rising spectral indices in the frequency range 14.2--17.9 GHz. Of these five one has already been reported, L1111, we report one new definite detection, L675, and three new probable detections (L944, L1103 and L1246). The relative certainty of these detections is assessed on the basis of three criteria: the extent of the emission, the coincidence of the emission with the Scuba position and the likelihood of alternative explanations for the excess. Extended microwave emission makes the likelihood of the anomalous emission arising as a consequence of a radio counterpart to a protostar or a proto-planetary disk unlikely. We use a 2' radius in order to be consistent with the IRAS identifications of dark nebulae (Parker 1988), and our third criterion is used in the case of L1103 where a high flux density at 850 microns relative to the FIR data suggests a more complicated emission spectrum.Comment: submitted MNRA

The type IIb SN 2008ax: spectral and light curve evolution

We present spectroscopy and photometry of the He-rich supernova (SN) 2008ax. The early-time spectra show prominent P-Cygni H lines, which decrease with time and disappear completely about two months after the explosion. In the same period He I lines become the most prominent spectral features. SN 2008ax displays the ordinary spectral evolution of a type IIb supernova. A stringent pre-discovery limit constrains the time of the shock breakout of SN 2008ax to within only a few hours. Its light curve, which peaks in the B band about 20 days after the explosion, strongly resembles that of other He-rich core-collapse supernovae. The observed evolution of SN 2008ax is consistent with the explosion of a young Wolf-Rayet (of WNL type) star, which had retained a thin, low-mass shell of its original H envelope. The overall characteristics of SN 2008ax are reminiscent of those of SN 1993J, except for a likely smaller H mass. This may account for the findings that the progenitor of SN 2008ax was a WNL star and not a K supergiant as in the case of SN 1993J, that a prominent early-time peak is missing in the light curve of SN 2008ax, and that Halpha is observed at higher velocities in SN 2008ax than in SN 1993J.Comment: 10 pages, including 8 figures and 4 tables. Accepted for publication in MNRA

GRB 071028B, a burst behind large amounts of dust in an unabsorbed galaxy

We report on the discovery and properties of the fading afterglow and underlying host galaxy of GRB 071028B, thereby facilitating a detailed comparison between these two. Observations were performed with the Gamma-ray Burst Optical and Near-infrared Detector at the 2.2 m telescope on the La Silla Paranal Observatory in Chile. We conducted five observations from 1.9 d to 227.2 d after the trigger and obtained deep images in the g'r'i'z' and JHKs bands. Based on accurate seven-channel photometry covering the optical to near-infrared wavelength range, we derive a photometric redshift of z = 0.94 +0.05 -0.10 for the unabsorbed host galaxy of GRB 071028B. In contrast, we show that the afterglow with an intrinsic extinction of AV(SB) = (0.70 +/- 0.11) mag is moderately absorbed and requires a relatively flat extinction curve. According to the reported Swift/BAT observations, the energetics yield an isotropic energy release of E(gamma,iso.,rest) = (1.4 +2.4 -0.7) x 10^51 erg.Comment: 8 pages, 5 figures, accepted for publication in A&

On the nature of the extremely fast optical rebrightening of the afterglow of GRB 081029

Context. After the launch of the Swift satellite, the Gamma-Ray Burst (GRB) optical light-curve smoothness paradigm has been questioned thanks to the faster and better sampled optical follow-up, which has unveiled a very complex behaviour. This complexity is triggering the interest of the whole GRB community. The GROND multi-channel imager is used to study optical and near-infrared (NIR) afterglows of GRBs with unprecedented optical and near-infrared temporal and spectral resolution. The GRB 081029 has a very prominent optical rebrightening event and is an outstanding example of the application of the multi-channel imager to GRB afterglows. Aims. Here we exploit the rich GROND multi-colour follow-up of GRB 081029 combined with XRT observations to study the nature of late-time rebrightenings that appear in the optical-NIR light-curves of some GRB afterglows. Methods. We analyse the optical and NIR observations obtained with the seven-channel Gamma-Ray burst Optical and Near-infrared Detector (GROND) at the 2.2 m MPI/ESO telescope and the X-ray data obtained with the XRT telescope on board the Swift observatory. The multi-wavelength temporal and spectral evolution is discussed in the framework of different physical models. Results. The extremely steep optical and NIR rebrightening observed in GRB 081029 cannot be explained in the framework of the standard forward shock afterglow model. The absence of a contemporaneous X-ray rebrightening and the evidence of a strong spectral evolution in the optical-NIR bands during the rise suggest two separate components that dominate in the early and late-time lightcurves, respectively. The steepness of the optical rise cannot be explained even in the framework of the alternative scenarios proposed in the literature unless a late-time activity of the central engine is assumed.Comment: 9 pages, 7 figures, accepted for publication in Astronomy and Astrophysic