2,755 research outputs found
Design and development of a smart panel with five decentralised control units for the reduction of vibration and sound radiation
This Technical Report discusses the design and the construction of a smart panel with five decentralised direct velocity feedback control units in order to reduce the vibration of the panel dominated by well separated low frequency resonances. Each control unit consists of an accelerometer sensor and a piezoelectric patch strain actuator. The integrated accelerometer signal is fed back to the actuator via a fixed negative control gain. In this way the actuator generates a control excitation proportional and opposite to the measured transverse velocity of the panel so that it produces active damping on the panel. First the open loop frequency response function between the sensor and the actuator of a single channel has been studied and an analogue controller has been designed and tested in order to improve the stability of this control system. Following the stability of all five control units has been assessed using the generalised Nyquist criterion. Finally the performances of the smart panel have been tested with reference to the reduction of the vibrations at the error positions and with reference to the reduction of the radiated sound. Finally in appendix to this Report, a parametric study is presented on the properties of sensor-actuator FRFs measured with different types of piezoelectric patch actuators. The results of this parametric study have been used in order to choose the actuators to be used for the construction of the smart pane
A Fast Chi-squared Technique For Period Search of Irregularly Sampled Data
A new, computationally- and statistically-efficient algorithm, the Fast
algorithm, can find a periodic signal with harmonic content in
irregularly-sampled data with non-uniform errors. The algorithm calculates the
minimized as a function of frequency at the desired number of
harmonics, using Fast Fourier Transforms to provide performance.
The code for a reference implementation is provided.Comment: Source code for the reference implementation is available at
http://public.lanl.gov/palmer/fastchi.html . Accepted by ApJ. 24 pages, 4
figure
The ECLAIRs telescope onboard the SVOM mission for gamma-ray burst studies
The X- and gamma-ray telescope ECLAIRs onboard the future mission for
gamma-ray burst studies SVOM (Space-based multi-band astronomical Variable
Objects Monitor) is foreseen to operate in orbit from 2013 on. ECLAIRs will
provide fast and accurate GRB triggers to other onboard telescopes, as well as
to the whole GRB community, in particular ground-based follow-up telescopes.
With its very low energy threshold ECLAIRs is particularly well suited for the
detection of highly redshifted GRB. The ECLAIRs X- and gamma-ray imaging camera
(CXG), used for GRB detection and localization, is combined with a soft X-ray
telescope (SXT) for afterglow observations and position refinement. The CXG is
a 2D-coded mask imager with a 1024 cm detection plane made of 8080
CdTe pixels, sensitive from 4 to 300 keV, with imaging capabilities up to about
120 keV and a localization accuracy better than 10 arcmin. The CXG permanently
observes a 2 sr-wide field of the sky and provides photon data to the onboard
science and triggering unit (UTS) which detects GRB by count-rate increases or
by the appearance of a new source in cyclic sky images. The SXT is a mirror
focusing X-ray telescope operating from 0.3 to 2 keV with a sensitivity of 1
mCrab for 100 s observations. The spacecraft slews within 3 min in
order to place the GRB candidate into the 2323 arcmin field of view
of the SXT, after which it refines the GRB position to about 10 arcsec. GRB
alerts are transmitted to ground-observers within tens of seconds via a VHF
network and all detected photons are available hours later for detailed
analysis. In this paper we present the ECLAIRs concepts, with emphasis on the
expected performances.Comment: on behalf of the ECLAIRs collaboration. Proceedings of Gamma-Ray
Bursts 2007 conference, Santa Fe, USA, 5-9 November 2007. Published in AIP
conf. proc. 1000, 581-584 (2008
Strong spectral evolution during the prompt emission of GRB 070616
Swift has revealed features in GRB early light curves, such as steep decays
and X-ray flares, whose properties are consistent with an internal origin
though they are far from understood. The steep X-ray decay is often explained
using the curvature effect; however a significant number of GRBs display strong
spectral evolution during this phase, and a new mechanism must be invoked to
explain this. Of particular interest are the longest duration GRBs in which the
early emission can be studied in most detail. Here we present data for GRB
070616, in which the prompt emission shows a complex multipeaked structure,
leading to one of the longest prompt emission durations ever recorded. We take
advantage of extensive coverage of such a long burst by all Swift instruments.
Combining data from Swift and Suzaku we study the evolution of the prompt
emission spectrum, following the temporal variability of the peak energy and
spectral slope.Comment: 4 pages, 2 figures (Fig 1 in colour), contributed talk, submitted to
the proceedings of Gamma Ray Bursts 2007, Santa Fe, New Mexico, November 5-9
200
GRB-triggered searches for gravitational waves in LIGO data
The LIGO gravitational wave detectors have recently reached their design
sensitivity and finished a two-year science run. During this period one year of
data with unprecedented sensitivity has been collected. I will briefly describe
the status of the LIGO detectors and the overall quality of the most recent
science run. I also will present results of a search for inspiral waveforms in
gravitational wave data coincident with the short gamma ray burst detected on
1st February 2007, with its sky location error box overlapping a spiral arms of
M31. No gravitational wave signals were detected and a binary merger in M31 can
be excluded at the 99% confidence level.Comment: 5 pages, 3 figures, contributed talk, submitted to the proceedings of
Gamma Ray Bursts 2007, Santa Fe, New Mexico, November 5-9 200
Diversity, Recognition, Respect: Embedding Indigenous Services at the State Library of New South Wales, Australia
The State Library of New South Wales (NSW) holds significant collections of material relating to the history and experiences of Indigenous people in Australia. These collections are a vital resource for Indigenous people and communities, particularly in relation to language and cultural revitalisation. As Australia’s oldest library, with its origins dating back to 1826, the State Library aims to inform, educate and inspire with the services it provides online, on site and on tour. In 2014, the Library renewed its focus and commitment to Aboriginal and Torres Strait Islander people and communities by establishing a team dedicated to developing Indigenous services for the Library. This paper provides a case study of the Library developing a Business Plan (2014) for Indigenous services. It will describe the research and engagement process undertaken to develop the plan and to progress Indigenous priorities as core business of the Library. The building of long-term and meaningful relationships with Indigenous people and communities, through ongoing consultation will be discussed. Speakers will share information on strategies for embedding Indigenous library services through a respectful recognition of Indigenous culture and history. In doing this the paper will aim to promote a two-way learning process - where libraries can engage in ongoing capacity building for staff to feel competent and empowered
Quantum dynamics of a high-finesse optical cavity coupled with a thin semi-transparent membrane
We study the quantum dynamics of the cavity optomechanical system formed by a
Fabry-Perot cavity with a thin vibrating membrane at its center. We first
derive the general multimode Hamiltonian describing the radiation pressure
interaction between the cavity modes and the vibrational modes of the membrane.
We then restrict the analysis to the standard case of a single cavity mode
interacting with a single mechanical resonator and we determine to what extent
optical absorption by the membrane hinder reaching a quantum regime for the
cavity-membrane system. We show that membrane absorption does not pose serious
limitations and that one can simultaneously achieve ground state cooling of a
vibrational mode of the membrane and stationary optomechanical entanglement
with state-of-the-art apparatuses.Comment: 14 pages, 7 figure
Afterglows of Gamma-Ray Bursts: Short vs. Long GRBs
We compiled a large sample of Swift-era photometric data on long (Type II)
and short (Type I) GRB afterglows. We compare the luminosity and energetics of
the different samples to each other and to the afterglows of the pre-Swift era.
Here, we present the first results of these studies.Comment: Conference Proceedings, "Gamma-Ray Bursts 2007", Santa Fe, shortened
poster presentation; 4 pages, 3 figures; for full updated papers, go here to
arXiv:0712.2186 and also here to arXiv:0804.195
Functional biases in GRB's spectral parameter correlations
Gamma Ray Bursts (GRBs) show evidence of different spectral shapes, light
curves, duration, host galaxies and they explode within a wide redshift range.
However, the most of them seems to follow very tight correlations among some
observed quantities relating to their energetic. If true, these correlations
have significant implications on burst physics, giving constraints on
theoretical models. Moreover, several suggestions have been made to use these
correlations in order to calibrate GRBs as standard candles and to constrain
the cosmological parameters. We investigate the cosmological relation between
low energy index in GRBs prompt spectra and the redshift . We
present a statistical analysis of the relation between the total isotropic
energy and the peak energy (also known as Amati relation) in
GRBs spectra searching for possible functional biases. Possible implications on
the vs relation of the vs correlation are
evaluated. We used MonteCarlo simulations and the boostrap method to evaluate
how large are the effects of functional biases on the vs . We
show that high values of the linear correlation coefficent, up to about 0.8, in
the vs relation are obtained for random generated samples of
GRBs, confirming the relevance of functional biases. Astrophysical consequences
from vs relation are then to be revised after a more accurate
and possibly bias free analysis.Comment: 6 pages, 6 figures, conference poster session: "070228: The Next
Decade of Gamma-Ray Burst Afterglows", Amsterdam, March 2007, MNRAS submitte
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