27,468 research outputs found
Is FIRST J102347.6+003841 Really a Cataclysmic Binary?
The radio source FIRST J102347.6+003841 was presented as the first
radio-selected cataclysmic. In the discovery paper, Bond et al. (2002) show a
spectrum consistent with a magnetic AM Her-type system and a light curve with
rapid, irregular flickering. In contrast, Woudt, Warner, and Pretorius (2004)
found a smoothly-varying light curve with a period near 4.75 h and one minimum
per orbit, indicating a dramatic change. We present time-resolved spectra
showing a superficially normal, mid-G type photosphere, with no detectable
emission lines. The absorption-line radial velocity varies sinusoidally, with
semi-amplitude 268 +- 4 km/s, on the orbital period, which is refined to
0.198094(2) d. At this orbital period the secondary's spectral type is
atypically early, suggesting an unusual evolutionary history. We also obtained
BVI photometry around the orbit. The light curve resembles that given by Woudt
et al., and the color modulation is consistent with a heating effect. A simple
illumination model matches the observations strikingly well with a Roche-lobe
filling secondary near 5650 kelvin being illuminated by a primary giving out
around 2 solar luminosities. The modest amplitude of the observed modulation
constrains the orbital inclination to be less than about 55 deg, unless the
gravity darkening is artificially reduced. The resulting primary star mass is
above the Chandrasekhar limit (assuming conventional gravity darkening). We
examine the possibility that the compact object in this system is not a white
dwarf, in which case this is not actually a cataclysmic variable. On close
examination, FIRST J102347.6+003841 defies easy classification.Comment: 24 pages, 5 postscript and two JPG figures; Astronomical Journal,
accepte
An application of multivariable design techniques to the control of the national transonic facility
The digital versions of optimal linear regulator theory and eigenvalue placement theory are applied to the Mach number control loop of the National Transonic Facility cryogenic wind tunnel. The control laws developed are evaluated on a nonlinear simulation of the tunnel process for a typical est condition and are found to significantly reduce the open loop time required to achieve a Mach number set point
Robust model-based controller synthesis for the SCOLE configuration
The design of a robust compensator is considered for the SCOLE configuration using a frequency-response shaping technique based on the LQG/LTR algorithm. Results indicate that a tenth-order compensator can be used to meet stability-performance-robustness conditions for a 26th-order SCOLE model without destabilizing spillover effects. Since the SCOLE configuration is representative of many proposed spaceflight experiments, the results and design techniques employed potentially should be applicable to a wide range of large space structure control problems
Low temperature catalytic ignition of hydrogen and oxygen
Catalyst composed of 32 percent iridium metal supported on granular alumina is most active and most stable of platinum metal catalysts. Catalyst consistently induces reactions at temperatures as low as 78 K
Development of Hydrogen-Oxygen Catalysts Final Report
Catalysts of improved activity and thermal stability for low temperature ignition of oxygen- hydrogen mixtur
LISA Science Results in the Presence of Data Disturbances
Each spacecraft in the Laser Interferometer Space Antenna houses a proof mass
which follows a geodesic through spacetime. Disturbances which change the proof
mass position, momentum, and/or acceleration will appear in the LISA data
stream as additive quadratic functions. These data disturbances inhibit signal
extraction and must be removed. In this paper we discuss the identification and
fitting of monochromatic signals in the data set in the presence of data
disturbances. We also present a preliminary analysis of the extent of science
result limitations with respect to the frequency of data disturbances
Enhancing the work of the Islington Integrated Gangs Team: A pilot study on the response to serious youth violence in Islington
This report is the result of research conducted by the Centre for City Criminology at City, University of London, in partnership with Islington’s Integrated Gangs Team (IGT) and the Metropolitan Police Service (MPS). The research was co-funded by MPS and the School of Arts and Social Sciences, City, University of London. Following a collaborative research event in October 2017, City Criminologists were commissioned to carry out a small-scale research project to capture the work of the IGT and to make recommendations regarding its operations, coherence, effectiveness and sustainability. The research team conducted semi-structured interviews over several months with 23 practitioners across the services that constitute the IGT. This report presents the findings and recommendations
Weakly bound states of polar molecules in bilayers
We investigate a system of two polarized molecules in a layered trap. The
molecules reside in adjacent layers and interact purely via the dipole-dipole
interaction. We determine the properties of the ground state of the system as a
function of the dipole moment and polarization angle. A bound state is always
present in the system and in the weak binding limit the bound state extends to
a very large distance and shows universal behavior.Comment: Presented at the 21st European Conference on Few-Body Problems in
Physics, Salamanca, Spain, 30 August - 3 September 201
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