1,190 research outputs found
Validating delta-filters for resonant bar detectors of improved bandwidth foreseeing the future coincidence with interferometers
The classical delta filters used in the current resonant bar experiments for
detecting GW bursts are viable when the bandwidth of resonant bars is few Hz.
In that case, the incoming GW burst is likely to be viewed as an impulsive
signal in a very narrow frequency window. After making improvements in the
read-out with new transducers and high sensitivity dc-SQUID, the
Explorer-Nautilus have improved the bandwidth ( Hz) at the sensitivity
level of . Thus, it is necessary to reassess this
assumption of delta-like signals while building filters in the resonant bars as
the filtered output crucially depends on the shape of the waveform. This is
presented with an example of GW signals -- stellar quasi-normal modes, by
estimating the loss in SNR and the error in the timing, when the GW signal is
filtered with the delta filter as compared to the optimal filter.Comment: 7 pages, presented in Amaldi6, accepted for publication in Journal of
Physics: Conference Serie
What can we learn about GW Physics with an elastic spherical antenna?
A general formalism is set up to analyse the response of an arbitrary solid
elastic body to an arbitrary metric Gravitational Wave perturbation, which
fully displays the details of the interaction antenna-wave. The formalism is
applied to the spherical detector, whose sensitivity parameters are thereby
scrutinised. A multimode transfer function is defined to study the amplitude
sensitivity, and absorption cross sections are calculated for a general metric
theory of GW physics. Their scaling properties are shown to be independent of
the underlying theory, with interesting consequences for future detector
design. The GW incidence direction deconvolution problem is also discussed,
always within the context of a general metric theory of the gravitational
field.Comment: 21 pages, 7 figures, REVTeX, enhanced Appendix B with numerical
values and mathematical detail. See also gr-qc/000605
An Effective Search Method for Gravitational Ringing of Black Holes
We develop a search method for gravitational ringing of black holes. The
gravitational ringing is due to complex frequency modes called the quasi-normal
modes that are excited when a black hole geometry is perturbed. The detection
of it will be a direct confirmation of the existence of a black hole. Assuming
that the ringdown waves are dominated by the fundamental mode with least
imaginary part, we consider matched filtering and develop an optimal method to
search for the ringdown waves that have damped sinusoidal wave forms.
When we use the matched filtering method, the data analysis with a lot of
templates required. Here we have to ensure a proper match between the filter as
a template and the real wave. It is necessary to keep the detection efficiency
as high as possible under limited computational costs.
First, we consider the white noise case for which the matched filtering can
be studied analytically. We construct an efficient method for tiling the
template space. Then, using a fitting curve of the TAMA300 DT6 noise spectrum,
we numerically consider the case of colored noise. We find our tiling method
developed for the white noise case is still valid even if the noise is colored.Comment: 17 pages, 9 figures. Accepted to Phys. Rev. D, Note correction to Eq.
(3-25), A few comments added and minor typos correcte
The mathematical theory of resonant transducers in a spherical gravity wave antenna
The rigoruos mathematical theory of the coupling and response of a spherical
gravitational wave detector endowed with a set of resonant transducers is
presented and developed. A perturbative series in ascending powers of the
square root of the ratio of the resonator to the sphere mass is seen to be the
key to the solution of the problem. General layouts of arbitrary numbers of
transducers can be assessed, and a specific proposal (PHC), alternative to the
highly symmetric TIGA of Merkowitz and Johnson, is described in detail.
Frequency spectra of the coupled system are seen to be theoretically recovered
in full agreement with experimental determinations.Comment: 31 pages, 7 figures, LaTeX2e, \usepackage{graphicx,deleq
Stochastic Background Search Correlating ALLEGRO with LIGO Engineering Data
We describe the role of correlation measurements between the LIGO
interferometer in Livingston, LA, and the ALLEGRO resonant bar detector in
Baton Rouge, LA, in searches for a stochastic background of gravitational
waves. Such measurements provide a valuable complement to correlations between
interferometers at the two LIGO sites, since they are sensitive in a different,
higher, frequency band. Additionally, the variable orientation of the ALLEGRO
detector provides a means to distinguish gravitational wave correlations from
correlated environmental noise. We describe the analysis underway to set a
limit on the strength of a stochastic background at frequencies near 900 Hz
using ALLEGRO data and data from LIGO's E7 Engineering Run.Comment: 8 pages, 2 encapsulated PostScript figures, uses IOP class files,
submitted to the proceedings of the 7th Gravitational Wave Data Analysis
Workshop (which will be published in Classical and Quantum Gravity
Search for astro-gravity correlations
A new approach in the gravitational wave experiment is considered. In
addition to the old method of searching for coincident reactions of two
separated gravitational antennae it was proposed to seek perturbations of the
gravitational detector noise background correlated with astrophysical events
such as neutrino and gamma ray bursts which can be relaibly registered by
correspondent sensors. A general algorithm for this approach is developed. Its
efficiency is demonstrated in reanalysis of the old data concerning the
phenomenon of neutrino-gravity correlation registered during of SN1987A
explosion.Comment: 29 pages (LaTeX), 4 figures (EPS
Detection, Localization and Characterization of Gravitational Wave Bursts in a Pulsar Timing Array
Efforts to detect gravitational waves by timing an array of pulsars have
focused traditionally on stationary gravitational waves: e.g., stochastic or
periodic signals. Gravitational wave bursts --- signals whose duration is much
shorter than the observation period --- will also arise in the pulsar timing
array waveband. Sources that give rise to detectable bursts include the
formation or coalescence of supermassive black holes (SMBHs), the periapsis
passage of compact objects in highly elliptic or unbound orbits about a SMBH,
or cusps on cosmic strings. Here we describe how pulsar timing array data may
be analyzed to detect and characterize these bursts. Our analysis addresses, in
a mutually consistent manner, a hierarchy of three questions: \emph{i}) What
are the odds that a dataset includes the signal from a gravitational wave
burst? \emph{ii}) Assuming the presence of a burst, what is the direction to
its source? and \emph{iii}) Assuming the burst propagation direction, what is
the burst waveform's time dependence in each of its polarization states?
Applying our analysis to synthetic data sets we find that we can \emph{detect}
gravitational waves even when the radiation is too weak to either localize the
source of infer the waveform, and \emph{detect} and \emph{localize} sources
even when the radiation amplitude is too weak to permit the waveform to be
determined. While the context of our discussion is gravitational wave detection
via pulsar timing arrays, the analysis itself is directly applicable to
gravitational wave detection using either ground or space-based detector data.Comment: 43 pages, 13 figures, submitted to ApJ
Final analysis of colorectal cancer patients treated with irinotecan and 5-fluorouracil plus folinic acid neoadjuvant chemotherapy for unresectable liver metastases
We have previously reported that neoadjuvant therapy with modified FOLFIRI enabled nearly a third of patients with metastatic colorectal cancer (mCRC) to undergo surgical resection of liver metastases. Here, we present data from the long-term follow-up of these patients. Forty patients received modified FOLFIRI: irinotecan 180 mg m−2, day 1; folinic acid, 200 mg m−2; and 5-fluorouracil: as a 400 mg m−2 bolus, days 1 and 2, and a 48-h continuous infusion 1200 mg m−2, from day 1. Treatment was repeated every 2 weeks, with response assessed every six cycles. Resected patients received six further cycles of chemotherapy postoperatively. Nineteen (47.5%) of 40 patients achieved an objective response; 13 (33%) underwent resection. After a median follow-up of 56 months, median survival for all patients was 31.5 months: for non-resected patients, median survival was 24 months and was not reached for resected patients. Median time to progression was 14.3 and 5.2 months for all and non-resected patients, respectively. Median disease-free (DF) survival in resected patients was 52.5 months. At 2 years, all patients were alive (8 DF), and at last follow-up, eight were alive (6 DF). Surgical resection of liver metastases after neoadjuvant treatment with modified FOLFIRI in CRC patients achieved favourable survival times
Testing the performance of a blind burst statistic
In this work we estimate the performance of a method for the detection of
burst events in the data produced by interferometric gravitational wave
detectors. We compute the receiver operating characteristics in the specific
case of a simulated noise having the spectral density expected for Virgo, using
test signals taken from a library of possible waveforms emitted during the
collapse of the core of Type II Supernovae.Comment: 8 pages, 6 figures, Talk given at the GWDAW2002 worksho
A GFP-Tagged Gross Deletion on Chromosome 1 Causes Malignant Peripheral Nerve Sheath Tumors and Carcinomas in Zebrafish
Malignant peripheral nerve sheath tumors (MPNSTs) are highly aggressive soft-tissue sarcomas, characterized by complex karyotypes. The molecular bases of such malignancy are poorly understood and efficient targeted molecular therapies are currently lacking. Here we describe a novel zebrafish model of MPNSTs, represented by the transgenic mutant line Tg(-8.5nkx2.2a:GFP)ia2. ia2 homozygous animals displayed embryonic lethality by 72 hpf, while the heterozygotes develop visible tumor masses with high frequency in adulthood. Histological and immunohistochemical examination revealed aggressive tumors with either mesenchymal or epithelial features. The former (54% of the cases) arose either in the abdominal cavity, or as intrathecal/intraspinal lesions and is composed of cytokeratin-negative spindle cells with fascicular/storiform growth pattern consistent with zebrafish MPNSTs. The second histotype was composed by polygonal or elongated cells, immunohistochemically positive for the pan-cytokeratin AE1/AE3. The overall histologic and immunohistochemical features were consistent with a malignant epithelial neoplasm of possible gastrointestinal/pancreatic origin. With an integrated approach, based on microsatellite (VNTR) and STS markers, we showed that ia2 insertion, in Tg(-8.5nkx2.2a:GFP)ia2 embryos, is associated with a deletion of 15.2 Mb in the telomeric portion of chromosome 1. Interestingly, among ia2 deleted genes we identified the presence of the 40S ribosomal protein S6 gene that may be one of the possible drivers for the MPNSTs in ia2 mutants.Thanks to the peculiar features of zebrafish as animal model of human cancer (cellular and genomic similarity, transparency and prolificacy) and the GFP tag, the Tg(-8.5nkx2.2a:GFP)ia2 line provides a manageable tool to study in vivo with high frequency MPNST biology and genetics, and to identify, in concert with the existing zebrafish MPNST models, conserved relevant mechanisms in zebrafish and human cancer development
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