Search results for "SPECTRA"
showing 10 items of 3542 documents
X-Ray Spectral Variability of 3C273
1985
3C273 has been monitored by EXOSAT over the period December 1983 to June 1984 in 4 observations. In the December observation the flux was high and the spectrum showed a power law index of 1.5 changing to 0.9 at~8 keV. In subsequent observations the flux dropped to~40% of its original value and the hard tail disappeared. In the last observation the LE flux increased by a factor of 2 with no accompanying ME flux increase.
Non-stationary spectral moments of base excited MDOF systems
1988
The paper deals with the evaluation of non-stationary spectral moments of multi-degree-of-freedom (MDOF) line systems subjected to seismic excitations. The spectral moments of the response are evaluated in incremental form solution by means of an unconditionally stable step-by-step procedure. As an application, the statistics of the largest peak of the response are also evaluated.
Measurement of the Spectral Shape of the β -Decay of Xe137 to the Ground State of Cs137 in EXO-200 and Comparison with Theory
2020
We report on a comparison between the theoretically predicted and experimentally measured spectra of the first-forbidden nonunique β-decay transition ^{137}Xe(7/2^{-})→^{137}Cs(7/2^{+}). The experimental data were acquired by the EXO-200 experiment during a deployment of an AmBe neutron source. The ultralow background environment of EXO-200, together with dedicated source deployment and analysis procedures, allowed for collection of a pure sample of the decays, with an estimated signal to background ratio of more than 99 to 1 in the energy range from 1075 to 4175 keV. In addition to providing a rare and accurate measurement of the first-forbidden nonunique β-decay shape, this work constitut…
Truncated thermalization of incoherent optical waves through supercontinuum generation in photonic crystal fibers
2013
We revisit the process of optical wave thermalization through supercontinuum generation in photonic crystal fibers. We report theoretically and numerically a phenomenon of `truncated thermalization': The incoherent optical wave exhibits an irreversible evolution toward a Rayleigh-Jeans thermodynamic equilibrium state characterized by a compactly supported spectral shape. The theory then reveals the existence of a frequency cut-off which regularizes the ultraviolet catastrophe inherent to ensembles of classical nonlinear waves. This phenomenon sheds new light on the mechanisms underlying the formation of bounded supercontinuum spectra in photonic crystal fibers.
Spectral analysis of two-dimensional Bose-Hubbard models
2016
One-dimensional Bose-Hubbard models are well known to obey a transition from regular to quantum-chaotic spectral statistics. We are extending this concept to relatively simple two-dimensional many-body models. Also in two dimensions a transition from regular to chaotic spectral statistics is found and discussed. In particular, we analyze the dependence of the spectral properties on the bond number of the two-dimensional lattices and the applied boundary conditions. For maximal connectivity, the systems behave most regularly in agreement with the applicability of mean-field approaches in the limit of many nearest-neighbor couplings at each site.
The rotational gas-phase spectrum of trans- and cis-HSSOH at 100GHz
2009
Abstract We present the first pure rotational spectra of the two most stable conformers of oxatrisulfane, trans- and cis-HSSOH, in their vibrational ground state. For both conformers a-, b-, and c-type transitions have been recorded in the range from 75 to 120 GHz using an all solid-state spectrometer. More than 200 lines have been assigned for each conformer, most of them belonging to the r Q 2 - and the r Q 3 -branch of the perpendicular spectra. The least-squares fit analysis using a semirigid rotor Hamiltonian in S-reduction yields precise values for the ground-state rotational constants A 0 = 21 145.93422 ( 66 ) , B 0 = 4479.92301 ( 21 ) , C 0 = 3828.34269 ( 21 ) for cis-HSSOH, and A 0…
Hyperfine structure study of atomic niobium with enhanced sensitivity of Fourier transform spectroscopy
2011
In an experimental setup with a high-resolution Fourier transform (FT) spectrometer and a hollow-cathode discharge, bandpass interference filters are used to enhance the sensitivity. This extension leads to an improvement of the signal-to-noise ratio in the spectrum of atomic niobium by a factor of up to 10 compared to FT spectra measured previously without filters (see Kroger et al 2010 Astron. Astrophys. 516 A70). Several additional spectral lines with low intensity have been observed. Additionally, in some intense lines, blends become visible due to the better signal-to-noise ratio. The hyperfine structure of 51 lines recorded in the wavelength range from 415 to 670 nm is analysed or re-…
The Cryogenic Anticoincidence Detector for ATHENA-XMS
2012
The TES cryogenic detectors, due to their high spectral resolution and imaging capability in the soft X-ray domain, are the reference devices for the next proposed space missions whose aims are to characterize the spectra of faint or diffuse sources. ATHENA is the re-scoped IXO mission, and one of its focal plane instrument is the X-ray Microcalorimeter Spectrometer (XMS) working in the energy range 0.3-10 keV. XMS will be able to achieve the proposed scientific goals if a background lower than 0.02 cts/cm2/s/keV is guaranteed. The studies performed by GEANT4 simulations depict a scenario where it is mandatory to use an active Anti-Coincidence (AC) to reduce the expected background in the L…
Gas-phase detection of discharge-generated DSOD
2003
Abstract We report the first spectroscopic detection of perdeuterated 1-oxadisulfane, DSOD, generated in a radio-frequency plasma of D2S and D2O. The chain molecule DSOD produces a perpendicular-type spectrum, with well-known spectral features encountered in previous studies of geometrically related molecules, such as compact Q-branches, which are clearly recognizable. The arrangement of the transitions shaping the Q-branches usually provides sufficient proof for a clear-cut detection of a chain molecule such as DSOD. Guided by quantum chemical calculations, we have located the band center of the r Q 2 -branch of DSOD in the frequency region near 466.5 GHz using the Cologne terahertz spectr…
A ten-fold divided total absorption Ge(Li) gamma-ray detector
1976
Abstract We have constructed a split-crystal total absorption Ge(Li) gamma-ray spectrometer and special logic electronics for rejecting Compton continuum in spectra. A 10 cm3 planar detector was divided into ten electrically separated detectors by grinding nine parallel slots on the n-surface of the detector. In operation both the n- and p-contacts are isolated from the ground. Using capacitive sharing, most of the released electrical charge is taken from the p-contact into an ordinary pulse amplifier line and analyzed. A small fraction of the charge collected at the n-strips is observed with voltage-sensitive FET-preamplifiers. The following logic electronics provides a gate pulse for the …