948 research outputs found
κ Velorum: Another variable interstellar sightline?
We present ultra-high-resolution (R = 900 000) observations of interstellar Na i and K i absorption lines towards κ Vel (HD 81188) which show clear evidence for temporal variation between 1994 and 2000. Specifically, the column densities of K0 and Na0 in the main velocity component have increased by 40 and 16 per cent, respectively, over this period. Earlier work had suggested that this component actually consists of two unresolved sub-components; this result is confirmed here, and the overall line profile is found to be consistent with only one of these sub-components having increased in strength since 1994. We argue that this variation is consistent with the line of sight gradually probing a cold, dense interstellar filament of the kind recently proposed by Heiles to explain other observations of small-scale structure in the interstellar medium
FORECASTING URBAN EXPANSION BASED ON NIGHT LIGHTS
Forecasting urban expansion models are a very powerful tool in the hands of urban planners in order to anticipate and mitigate future
urbanization pressures. In this paper, a linear regression forecasting urban expansion model is implemented based on the annual
composite night lights time series available from National Oceanic and Atmospheric Administration (NOAA). The product known as
'stable lights' is used in particular, after it has been corrected with a standard intercalibration process to reduce artificial year-to-year
fluctuations as much as possible. Forecasting is done for ten years after the end of the time series. Because the method is spatially
explicit the predicted expansion trends are relatively accurately mapped. Two metrics are used to validate the process. The first one is
the year-to-year Sum of Lights (SoL) variation. The second is the year-to-year image correlation coefficient. Overall it is evident that
the method is able to provide an insight on future urbanization pressures in order to be taken into account in planning. The trends are
quantified in a clear spatial manner
A postmortem investigation of the Type IIb supernova 2001ig
We present images taken with the GMOS instrument on Gemini-South, in
excellent (<0.5 arcsec) seeing, of SN 2001ig in NGC 7424, ~1000 days after
explosion. A point source seen at the site of the SN is shown to have colours
inconsistent with being an H II region or a SN 1993J-like remnant, but can be
matched to a late-B through late-F supergiant with A_V<1. We believe this
object is the massive binary companion responsible for periodic modulation in
mass loss material around the Wolf-Rayet progenitor which gave rise to
significant structure in the SN radio light curve.Comment: 5 pages, 3 figures. Accepted for publication in MNRAS Letters. Fig. 1
resolution degraded to meet size limitations; full resolution version
available from http://www.aao.gov.au/local/www/sdr/pubs/sn2001ig_gmos.ps.g
Accelerating Quantum Computer Simulation via Parallel Eigenvector Computation
Quantum-dot cellular automata (QDCA) hold great potential to produce the next generation of computer hardware, but their development is hindered by computationally intensive simulations. Our research therefore focuses on rewriting one such simulation to run parallel calculations on a graphics processing unit (GPU). We have decreased execution time from 33 hours 11 minutes to 1 hour 39 minutes, but current progress has shown that further gains are possible. The calculation of eigenvectors holds particular promise for acceleration. Our research has two components: testing MATLAB’s algorithm for these calculations and creating a C-based algorithm to improve on MATLAB’s execution time. MATLAB requires 0.2352 +/- 0.0074 seconds to execute this function, while our function requires 0.0674 +/- 0.0143 seconds. Further, our function’s iterative and many-threaded nature makes it ideal for parallel implementation in the CUDA language, which is expected to further increase execution speed. At the time of this writing, implementation is ongoing. Our presentation shall focus on our functions’ efficiency increases over their MATLAB counterparts, and the application of GPUs’ immense computational power to QDCA device simulation
RF Roaming System Locator: A Modular Omnidirectional Antenna System
Drones are increasingly common in everything from entertainment to delivery services. Currently, GPS and wireless triangulation are the two main methods of tracking drones and collision avoidance. The main problem with these two methods are accuracy and mobility. This thesis goes into building a system that is able to solve the two main drawbacks, by using a completely contained antenna system. The system is robust and can work in a variety of environments and situations. While the thesis focuses on drone tracking, the system is built with modularity in mind and can be adapted to track other RF signals with proper RF down conversion modules. This thesis will go in depth in how this aforementioned system was conceptualized, designed, built, and evaluated
Forecasting Price Spikes in Electricity Markets
Electricity markets are considered to be the most volatile amongst commodity markets. The non-storability of electricity and the need for instantaneous balancing of demand and supply can often cause extreme short-lived fluctuations in electricity prices. These fluctuations are termed price spikes. In this paper, we employ a multiclass Support Vector Machine (SVM) model to forecast the occurrence of price spikes in the German intraday electricity market. As price spikes, we define the prices that lie above the 95th quantile estimated by fitting a Generalized Pareto distribution in the innovation distribution of an AR-EGARCH model. The generalization ability of the model is tested in an out-of-the-sample dataset consisting of 4080 hours. Furthermore, we compare the performance of our best SVM model against Neural Networks (NNs) and Gradient Boosted Machines (GBMs)
Productivity in construction : an issue of analysis and measurement
Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Civil Engineering, 1988.Includes bibliographical references.by Nicholas Stathakis.M.S
Radial velocity variations of the pulsating subdwarf B star PG 1605+072
We present an analysis of high-speed spectroscopy of the pulsating subdwarf B
star PG 1605+072. Periodic radial motions are detected at frequencies similar
to those reported for photometric variations in the star, with amplitudes of up
to 6 km/s. Differences between relative strengths for given frequency peaks for
our velocity data and previously measured photometry are probably a result of
shifting of power between modes over time. Small differences in the detected
frequencies may also indicate mode-shifting. We report the detection of
line-shape variations using the moments of the cross correlation function
profiles. It may be possible to use the moments to identify the star's
pulsation modes.Comment: 5 pages, 6 figure
Photometric Variability and Astrometric Stability of the Radio Continuum Nucleus in the Seyfert Galaxy NGC 5548
The NRAO VLA and VLBA were used from 1988 November to 1998 June to monitor
the radio continuum counterpart to the optical broad line region (BLR) in the
Seyfert galaxy NGC 5548. Photometric and astrometric observations were obtained
at 21 epochs. The radio nucleus appeared resolved, so comparisons were limited
to observations spanning 10-60 days and 3-4 yr, and acquired at matched
resolutions of 1210 mas = 640 pc (9 VLA observations), 500 mas = 260 pc (9 VLA
observations), or 2.3 mas = 1.2 pc (3 VLBA observations). The nucleus is
photometrically variable at 8.4 GHz by % and % between VLA
observations separated by 41 days and 4.1 yr, respectively. The 41-day changes
are milder (%) at 4.9 GHz and exhibit an inverted spectrum (, ) from 4.9 to 8.4 GHz. The nucleus
is astrometrically stable at 8.4 GHz, to an accuracy of 28 mas = 15 pc between
VLA observations separated by 4.1 yr and to an accuracy of 1.8 mas = 0.95 pc
between VLBA observations separated by 3.1 yr. Such photometric variability and
astrometric stability is consistent with a black hole being the ultimate energy
source for the BLR, but is problematic for star cluster models that treat the
BLR as a compact supernova remnant and, for NGC 5548, require a new supernova
event every 1.7 yr within an effective radius 42 mas = 22 pc. A deep
image at 8.4 GHz with resolution 660 mas = 350 pc was obtained by adding data
from quiescent VLA observations. This image shows faint bipolar lobes
straddling the radio nucleus and spanning 12 arcsec = 6.4 kpc. These
synchrotron-emitting lobes could be driven by twin jets or a bipolar wind from
the Seyfert 1 nucleus.Comment: with 9 figures, to appear in the Astrophysical Journal, 2000 March
10, volume 53
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