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THE TAOS PROJECT: RESULTS FROM SEVEN YEARS OF SURVEY DATA
Zhang, Z.-W.,Lehner, M. J.,Wang, J.-H.,Wen, C.-Y.,Wang, S.-Y.,King, S.-K.,Granados, Á,. P.,Alcock, C.,Axelrod, T.,Bianco, F. B.,Byun, Y.-I.,Chen, W. P.,Coehlo, N. K.,Cook, K. H.,de Pater, I.,Kim American Institute of Physics 2013 The Astronomical journal Vol.146 No.1
<P>The Taiwanese-American Occultation Survey (TAOS) aims to detect serendipitous occultations of stars by small (~1 km diameter) objects in the Kuiper Belt and beyond. Such events are very rare (<10<SUP>–3</SUP> events per star per year) and short in duration (~200 ms), so many stars must be monitored at a high readout cadence. TAOS monitors typically ~500 stars simultaneously at a 5 Hz readout cadence with four telescopes located at Lulin Observatory in central Taiwan. In this paper, we report the results of the search for small Kuiper Belt objects (KBOs) in seven years of data. No occultation events were found, resulting in a 95% c.l. upper limit on the slope of the faint end of the KBO size distribution of q = 3.34-3.82, depending on the surface density at the break in the size distribution at a diameter of about 90 km.</P>
UPPER LIMITS ON THE NUMBER OF SMALL BODIES IN SEDNA-LIKE ORBITS BY THE TAOS PROJECT
Wang, J.-H.,Lehner, M. J.,Zhang, Z.-W.,Bianco, F. B.,Alcock, C.,Chen, W.-P.,Axelrod, T.,Byun, Y.-I.,Coehlo, N. ,K.,Cook, K. H.,Dave, R.,de Pater, I.,Porrata, R.,Kim, D.-W.,King, S.-K.,Lee, T.,Lin, American Institute of Physics 2009 The Astronomical journal Vol.138 No.6
<P>We present the results of a search for occultation events by objects at distances between 100 and 1000 AU in light curves from the Taiwanese-American Occultation Survey. We searched for consecutive, shallow flux reductions in the stellar light curves obtained by our survey between 2005 February 7 and 2006 December 31 with a total of ~4.5 × 10<SUP>9</SUP> three-telescope simultaneous photometric measurements. No events were detected, allowing us to set upper limits on the number density as a function of size and distance of objects in Sedna-like orbits, using simple models.</P>
Probabilistic time-dependent sensitivity analysis of HPC bridge deck exposed to chlorides
Pratanu Ghosh,Petr Konečný,Petr Lehner,Paul J. Tikalsky 사단법인 한국계산역학회 2017 Computers and Concrete, An International Journal Vol.19 No.3
A robust finite element based reinforced concrete bridge deck corrosion initiation model is applied for time-dependent probabilistic sensitivity analysis. The model is focused on uncertainties in the governing parameters that include variation of high performance concrete (HPC) diffusion coefficients, concrete cover depth, surface chloride concentration, holidays in reinforcements, coatings and critical chloride threshold level in several steel reinforcements. The corrosion initiation risk is expressed in the form of probability over intended life span of the bridge deck. Conducted study shows the time-dependent sensitivity analysis to evaluate the significance of governing parameters on chloride ingress rate, various steel reinforcement protection and the corrosion initiation likelihood. Results from this probabilistic analysis provide better insight into the effect of input parameters variation on the estimate of the corrosion initiation risk for the design of concrete structures in harsh chloride environments.
Temperature and Structural Analysis of Omega Clip
Jakub Flodr,Martin Krejsa,Petr Lehner 한국강구조학회 2019 International Journal of Steel Structures Vol.19 No.4
Cold-formed thin-walled cross sections are very frequently and effi ciently used as secondary construction elements as well as self-supporting cladding systems. Typically, they are used on hall-type buildings and other lightweight structures. The primary advantage of thin-walled cross sections is their ratio between self-weight and load bearing capacity. Another important factor is their easy installation. The main disadvantage of thin-walled cross sections is their low resistance to fi re. Their low weight and thin cross section can cause higher temperature increase in the element compared with hot-rolled or welded cross sections. This is undesirable with respect to the load bearing capacity. The article deals with numerical modelling of thin-walled omega clip under temperature and force load. Two calculations—heat passage by radiation and structural analysis using temperature analysis outputs—are combined. The temperature values as input data for the temperature analysis are sourced from the physical experiments conducted.
Bianco, F. B.,Zhang, Z.-W.,Lehner, M. J.,Mondal, S.,King, S.-K.,Giammarco, J.,Holman, M. J.,Coehlo, N. ,K.,Wang, J.-H.,Alcock, C.,Axelrod, T.,Byun, Y.-I.,Chen, W. P.,Cook, K. H.,Dave, R.,de Pater, American Institute of Physics 2010 The Astronomical journal Vol.139 No.4
<P>We have analyzed the first 3.75 years of data from the Taiwanese American Occultation Survey (TAOS). TAOS monitors bright stars to search for occultations by Kuiper Belt objects (KBOs). This data set comprises 5 × 10<SUP>5</SUP> star hours of multi-telescope photometric data taken at 4 or 5 Hz. No events consistent with KBO occultations were found in this data set. We compute the number of events expected for the Kuiper Belt formation and evolution models of Pan & Sari, Kenyon & Bromley, Benavidez & Campo Bagatin, and Fraser. A comparison with the upper limits we derive from our data constrains the parameter space of these models. This is the first detailed comparison of models of the KBO size distribution with data from an occultation survey. Our results suggest that the KBO population is composed of objects with low internal strength and that planetary migration played a role in the shaping of the size distribution.</P>
Ishioka, R.,Wang, S.-Y.,Zhang, Z.-W.,Lehner, M. J.,Alcock, C.,Axelrod, T.,Bianco, F. B.,Byun, Y.-I.,Chen, W. P.,Cook, K. H.,Kim, D.-W.,King, S.-K.,Lee, T.,Marshall, S. L.,Protopapas, P.,Rice, J. A.,Sc American Institute of Physics 2014 The Astronomical journal Vol.147 No.4
<P>The Taiwanese-American Occultation Survey project is designed for the detection of stellar occultations by small-size Kuiper Belt Objects, and it has monitored selected fields along the ecliptic plane by using four telescopes with a 3 deg<SUP>2</SUP> field of view on the sky since 2005. We have analyzed data accumulated during 2005-2012 to detect variable stars. Sixteen fields with observations of more than 100 epochs were examined. We recovered 85 variables among a total of 158 known variable stars in these 16 fields. Most of the unrecovered variables are located in the fields observed less frequently. We also detected 58 variable stars which are not listed in the International Variable Star Index of the American Association of Variable Star Observers. These variable stars are classified as 3 RR Lyrae, 4 Cepheid, 1 δ Scuti, 5 Mira, 15 semi-regular, and 27 eclipsing binaries based on the periodicity and the profile of the light curves.</P>
Kim, D.-W.,Protopapas, P.,Alcock, C.,Byun, Y.-I.,Kyeong, J.,Lee, B.-C.,Wright, N. J.,Axelrod, T.,Bianco, F. B.,Chen, W.-P.,Coehlo, N. K.,Cook, K. H.,Dave, R.,King, S.-K.,Lee, T.,Lehner, M. J.,Lin, H.- American Institute of Physics 2010 The Astronomical journal Vol.139 No.2
<P>We analyzed data accumulated during 2005 and 2006 by the Taiwan-American Occultation Survey (TAOS) in order to detect short-period variable stars (periods of <img entity='lsim' SRC='http://ej.iop.org/icons/Entities/lsim.gif' ALT='lsim' ALIGN='BASELINE' />1 hr) such as δ Scuti. TAOS is designed for the detection of stellar occultation by small-size Kuiper Belt Objects and is operating four 50 cm telescopes at an effective cadence of 5 Hz. The four telescopes simultaneously monitor the same patch of the sky in order to reduce false positives. To detect short-period variables, we used the fast Fourier transform algorithm (FFT) in as much as the data points in TAOS light curves are evenly spaced. Using FFT, we found 41 short-period variables with amplitudes smaller than a few hundredths of a magnitude and periods of about an hour, which suggest that they are low-amplitude δ Scuti stars. The light curves of TAOS δ Scuti stars are accessible online at the Time Series Center Web site (http://timemachine.iic.harvard.edu).</P>