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THE UFFO SLEWING MIRROR TELESCOPE FOR EARLY OPTICAL OBSERVATION FROM GAMMA RAY BURSTS
NAM, JIWOO,AHMAD, S.,AHN, K.,BARRILLON, P.,BRANDT, S.,BUDTZ-JØRGENSEN, C.,CASTRO-TIRADO, A. J.,CHANG, S.-H.,CHEN, C.-R.,CHEN, P.,CHOI, Y. J.,CONNELL, P.,DAGORET-CAMPAGNE, S.,EYLES, C.,GROSSAN, B.,HUAN World Scientific 2013 Modern physics letters A Vol.28 No.2
<P> While some space born observatories, such as SWIFT and FERMI, have been operating, early observation of optical after grow of GRBs is still remained as an unexplored region. The Ultra-Fast Flash Observatory (UFFO) project is a space observatory for optical follow-ups of GRBs, aiming to explore the first 60 seconds of GRBs optical emission. Using fast moving mirrors to redirect our optical path rather than slewing the entire spacecraft, UFFO is utilized to catch early optical emissions from GRB within 1 sec. We have developed the UFFO Pathfinder Telescope which is going to be on board of the Lomonosov satellite and launched in middle of 2012. We will discuss about scientific potentials of the UFFO project and present the payload development status, especially for Slewing Mirror Telescope which is the key instrument of the UFFO-pathfinder mission. </P>
Mancini, L.,Giacobbe, P.,Littlefair, S. P.,Southworth, J.,Bozza, V.,Damasso, M.,Dominik, M.,Hundertmark, M.,Jørgensen, U. G.,Juncher, D.,Popovas, A.,Rabus, M.,Rahvar, S.,Schmidt, R. W.,Skottfelt, J.,S EDP Sciences 2015 Astronomy and astrophysics Vol.584 No.-
<P>Context. Photometric monitoring of the variability of brown dwarfs can provide useful information about the structure of clouds in their cold atmospheres.The brown-dwarf binary system Luhman16AB is an interesting target for such a study, because its components stand at the L/T transition and show high levels of variability. Luhman16AB is also the third closest system to the solar system, which allows precise astrometric investigations with ground-based facilities. Aims. The aim of the work is to estimate the rotation period and study the astrometric motion of both components. Methods. We have monitored Luhman16AB over a period of two years with the lucky-imaging camera mounted on the Danish 1.54m telescope at La Silla, through a special i + z long-pass filter, which allowed us to clearly resolve the two brown dwarfs into single objects. An intense monitoring of the target was also performed over 16 nights, in which we observed a peak-to-peak variability of 0.20±0.02mag and 0.34±0.02mag for Luhman16A and 16B, respectively. Results. We used the 16-night time-series data to estimate the rotation period of the two components. We found that Luhman16B rotates with a period of 5.1 ±0.1h, in very good agreement with previous measurements. For Luhman16A, we report that it rotates more slowly than its companion, and even though we were not able to get a robust determination, our data indicate a rotation period of roughly 8h. This implies that the rotation axes of the two components are well aligned and suggests a scenario in which the two objects underwent the same accretion process. The 2-year complete data set was used to study the astrometric motion of Luhman16AB. We predict a motion of the system that is not consistent with a previous estimate based on two months of monitoring, but cannot confirm or refute the presence of additional planetary-mass bodies in the system.</P>
UFFO/Lomonosov: The Payload for the Observation of Early Photons from Gamma Ray Bursts
Park, I. H.,Panasyuk, M. I.,Reglero, V.,Chen, P.,Castro-Tirado, A. J.,Jeong, S.,Bogomolov, V.,Brandt, S.,Budtz-Jørgensen, C.,Chang, S.-H.,Chang, Y. Y.,Chen, C.-R.,Chen, C.-W.,Choi, H. S.,Connell, P.,E Springer-Verlag 2018 Space science reviews Vol.214 No.1
Chang, Y.-Y.,Chen, C.R.,Chen, P.,Huang, J.-J.,Huang, M.A.,Liu, T.-C.,Nam, J.W.,Wang, M.-Z.,Bogomolov, V.,Brandt, S.,Budtz-Jørgensen, C.,Castro-Tirado, A.J.,Choi, H.S.,Connell, P.H.,Eyles, C.,Jeong, S. Elsevier 2015 Nuclear Instruments & Methods in Physics Research. Vol.771 No.-
<P><B>Abstract</B></P> <P>In this paper we present the Inverted-Conical light guide designed for optical crosstalk reduction in the scintillator-MAPMT assemblies. The research was motivated by the 30% crosstalk observed in <I>UFFO</I> X-ray telescope, <I>UBAT</I>, during the preliminary calibration with MAPMTs of 64 2.88 × 2.88 mm<SUP>2</SUP> pixels and identically gridded YSO crystal matrices. We began the study with the energy and crosstalk calibrations of the detector, then we constructed a GEANT4 simulation with the customized metallic film model as the MAPMT photocathode. The simulation reproduced more than 70% of the crosstalk and explained it as a consequence of the total reflection produced by the photocathode. The result indicated that the crosstalk mechanism could be a common case in most of the contact-assembled scintillation detectors. The concept of the Inverted-Conical light guide was to suppress the total reflection by contracting the incident angle of the scintillation. We optimized the design in the simulation and fabricated a test sample. The test sample reduced 52% crosstalk with a loss of 6% signal yield. The idea of the Inverted-Conical light guide can be adapted by scintillation detectors multi-pixel, imaging-purpose scintillation detectors such as the ultra-fast GRB observatory <I>UFFO-UBAT</I>, whose performances are sensitive to responding time, image resolution, and geometrical modifications.</P>
On the nonlinear structural analysis of wind turbine blades using reduced degree-of-freedom models
K. Holm-Jørgensen,J.W. Stærdahl,S.R.K. Nielsen 국제구조공학회 2008 Structural Engineering and Mechanics, An Int'l Jou Vol.28 No.1
Wind turbine blades are increasing in magnitude without a proportional increase of stiffness for which reason geometrical and inertial nonlinearities become increasingly important. Often these effects are analysed using a nonlinear truncated expansion in undamped fixed base mode shapes of a blade, modelling geometrical and inertial nonlinear couplings in the fundamental flap and edge direction. The purpose of this article is to examine the applicability of such a reduced-degree-of-freedom model in predicting the nonlinear response and stability of a blade by comparison to a full model based on a nonlinear co-rotating FE formulation. By use of the reduced-degree-of-freedom model it is shown that under strong resonance excitation of the fundamental flap or edge modes, significant energy is transferred to higher modes due to parametric or nonlinear coupling terms, which influence the response and stability conditions. It is demonstrated that the response predicted by such models in some cases becomes instable or chaotic. However, as a consequence of the energy flow the stability is increased and the tendency of chaotic vibrations is reduced as the number of modes are increased. The FE model representing the case of infinitely many included modes, is shown to predict stable and ordered response for all considered parameters. Further, the analysis shows that the reduced-degree-of-freedom model of relatively low order overestimates the response near resonance peaks, which is a consequence of the small number of included modes. The qualitative erratic response and stability prediction of the reduced order models take place at frequencies slightly above normal operation. However, for normal operation of the wind turbine without resonance excitation 4 modes in the reduced-degree-of-freedom model perform acceptable.
Slewing mirror telescope of the UFFO-pathfinder: first report on performance in space
Gaikov, G.,Jeong, S.,Agaradahalli, V. G.,Park, I. H.,Budtz-Jørgensen, C.,Castro-Tirado, A. J.,Chen, P.,Jeong, H. M.,Kim, J. E.,Kim, M. B.,Kim, S. W.,Lee, J.,Leonov, V.,Nam, J. W.,Panasyuk, M. I.,Petro The Optical Society 2017 Optics express Vol.25 No.23