19,554 research outputs found
Test program to demonstrate the stability of hydrazine in propellant tanks
A 24-month coupon test program to evaluate the decomposition of propellant tanks is reported. The propellant fuel evaluated was monopropellant-grade hydrazine (N2H4), which is normally a colorless, fuming, corrosive, strongly reducing liquid. The degree of hydrazine decomposition was determined by means of chemical analyses of the liquid and evolved gases at the end of the test program. The experimental rates of hydrazine decomposition were determined to be within acceptable limits. The propellant tank materials and material combinations were not degraded by a 2-year exposure to hydrazine propellant. This was verified using change-of-weight determinations and microscopic examination of the specimen surface before and after exposure, and by posttest chemical analyses of hydrazine liquid for residual metal content
Galaxy Clusters Selected via the SunyaevâZel'dovich Effect in the SPTpol 100-square-degree Survey
We present a catalog of galaxy cluster candidates detected in 100 square degrees surveyed with the SPTpol receiver on the South Pole Telescope. The catalog contains 89 candidates detected with a signal-to-noise ratio greater than 4.6. The candidates are selected using the SunyaevâZel'dovich effect at 95 and 150 GHz. Using both space- and ground-based optical and infrared telescopes, we have confirmed 81 candidates as galaxy clusters. We use these follow-up images and archival images to estimate photometric redshifts for 66 galaxy clusters and spectroscopic observations to obtain redshifts for 13 systems. An additional two galaxy clusters are confirmed using the overdensity of near-infrared galaxies only and are presented without redshifts. We find that 15 candidates (18% of the total sample) are at redshift z â„ 1.0, with a maximum confirmed redshift of z_(max) = 1.38±0.10. We expect this catalog to contain every galaxy cluster with M_(500c) > 2.6Ă10ÂčâŽMâhâ»Âčââ and z > 0.25 in the survey area. The mass threshold is approximately constant above z = 0.25, and the complete catalog has a median mass of approximately M_(500c) > 2.7Ă10ÂčâŽMâhâ»Âčââ. Compared to previous SPT works, the increased depth of the millimeter-wave data (11.2 and 6.5 ÎŒK-arcmin at 95 and 150 GHz, respectively) makes it possible to find more galaxy clusters at high redshift and lower mass
Constraints on Cosmological Parameters from the 500 degÂČ SPTPOL Lensing Power Spectrum
We present cosmological constraints based on the cosmic microwave background (CMB) lensing potential power spectrum measurement from the recent 500 degÂČ SPTPOL survey, the most precise CMB lensing measurement from the ground to date. We fit a flat ÎCDM model to the reconstructed lensing power spectrum alone and in addition with other data sets: baryon acoustic oscillations (BAO), as well as primary CMB spectra from Planck and SPTPOL. The cosmological constraints based on SPTPOL and Planck lensing band powers are in good agreement when analyzed alone and in combination with Planck full-sky primary CMB data. With weak priors on the baryon density and other parameters, the SPTPOL CMB lensing data alone provide a 4% constraint on ÏâΩ^(0.25)_m = 0.593 ± 0.025. Jointly fitting with BAO data, we find Ïâ = 0.779±0.023, Ω_m = 0.368^(+0.032)_(â0.037), and Hâ = 72.0^(+2.1)_(â2.5)kmsâ»Âč Mpcâ»Âč, up to 2Ï away from the central values preferred by Planck lensing + BAO. However, we recover good agreement between SPTPOL and Planck when restricting the analysis to similar scales. We also consider single-parameter extensions to the flat ÎCDM model. The SPTPOL lensing spectrum constrains the spatial curvature to be Ω_K = â0.0007±0.0025 and the sum of the neutrino masses to be âm_Îœ < 0.23 eV at 95% C.L. (with Planck primary CMB and BAO data), in good agreement with the Planck lensing results. With the differences in the signal-to-noise ratio of the lensing modes and the angular scales covered in the lensing spectra, this analysis represents an important independent check on the full-sky Planck lensing measurement
Orbital periods of the binary sdB stars PG0940+068 and PG1247+554
We have used the radial velocity variations of two sdB stars previously
reported to be binaries to establish their orbital periods. They are
PG0940+068, (P=8.33d) and PG1247+554 (P=0.599d). The minimum masses of the
unseen companions, assuming a mass of 0.5 solar masses for the sdB stars, are
0.090 +/- 0.003 solar masses for PG1247+554 and 0.63 +/- 0.02 solar masses for
PG0940+068. The nature of the companions is not constrained further by our
data.Comment: 5 pages, 2 figure
DSP-based ionospheric radiolink using DS-CDMA and on-line channel estimation
In this paper, a new blind multiuser detection algorithm is presented. It can both cancel multiuser interference and estimate the multipath channel response in a blind way. The method has been specially conceived for low coherence bandwidth channels such as the ionospheric channel and exhibits very low computational requirements. Real-time measurements from a fully digital HF radio-link are presented that confirm the reliability of the method for the ionospheric channel.Peer ReviewedPostprint (published version
Detection of solvents using a distributed fibre optic sensor
A fibre optic sensor that is capable of distributed detection of liquid solvents is presented. Sensor interrogation using optical time domain reflectometry (OTDR) provides the capability of locating solvent spills to a precision of ±2 m over a total sensor length that may extend to 20 km
Voter models on weighted networks
We study the dynamics of the voter and Moran processes running on top of
complex network substrates where each edge has a weight depending on the degree
of the nodes it connects. For each elementary dynamical step the first node is
chosen at random and the second is selected with probability proportional to
the weight of the connecting edge. We present a heterogeneous mean-field
approach allowing to identify conservation laws and to calculate exit
probabilities along with consensus times. In the specific case when the weight
is given by the product of nodes' degree raised to a power theta, we derive a
rich phase-diagram, with the consensus time exhibiting various scaling laws
depending on theta and on the exponent of the degree distribution gamma.
Numerical simulations give very good agreement for small values of |theta|. An
additional analytical treatment (heterogeneous pair approximation) improves the
agreement with numerics, but the theoretical understanding of the behavior in
the limit of large |theta| remains an open challenge.Comment: 21 double-spaced pages, 6 figure
Polarized Broad H-alpha Emission from the LINER Nucleus of NGC 1052
Optical spectropolarimetry of the nucleus of the LINER NGC 1052, obtained at
the Keck Observatory, reveals a rise in polarization in the wings of the
H-alpha line profile. The polarization vector of H-alpha is offset by 67
degrees from the parsec-scale radio axis and by 83 degrees from the
kiloparsec-scale radio axis, roughly in accord with expectations for scattering
within the opening cone of an obscuring torus. The broad component of H-alpha
has FWHM ~ 2100 km/s in total flux and FWHM ~ 5000 km/s in polarized light.
Scattering by electrons is the mechanism most likely responsible for this
broadening, and we find T_e ~ 10^5 K for the scattering medium, similar to
values observed in Seyfert 2 nuclei. This is the first detection of a polarized
broad emission line in a LINER, demonstrating that unified models of active
galactic nuclei are applicable to at least some LINERs.Comment: 6 pages, 2 figures, prepared using the emulateapj style file,
accepted for publication in The Astrophysical Journal Letter
ââThereâs so much more to it than what I initially thoughtââ: Stepping into researchersâ shoes with a class activity in a first year psychology survey course
In psychology, it is widely agreed that research methods, although central to the discipline, are particularly challenging to learn and teach, particularly at introductory level. This pilot study explored the potential of embedding a student-conducted research activity in a one-semester undergraduate Introduction to Psychology survey course, with the aims of (a) engaging students with the topic of research methods; (b) developing studentsâ comprehension and application of research methods concepts; and (c) building studentsâ ability to link research with theory. The research activity explored shoe ownership, examining gender differences and relationships with age, and linking to theories of gender difference and of consumer identity. The process of carrying out the research and reflecting on it created a contextualized, active learning environment in which students themselves raised many issues that research methods lectures seek to cover. Students also wrote richer assignments than standard first year mid-term essay
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