2,311 research outputs found
Near-field antenna testing using the Hewlett Packard 8510 automated network analyzer
Near-field antenna measurements were made using a Hewlett-Packard 8510 automated network analyzer. This system features measurement sensitivity better than -90 dBm, at measurement speeds of one data point per millisecond in the fast data acquisition mode. The system was configured using external, even harmonic mixers and a fiber optic distributed local oscillator signal. Additionally, the time domain capability of the HP8510, made it possible to generate far-field diagnostic results immediately after data acquisition without the use of an external computer
Indirect measures of learning transfer between real and virtual environments
This paper reports on research undertaken to determine the effectiveness of a 3D simulation environment used to train mining personnel in emergency evacuation procedures, designated the Fires in Underground Mines Evacuation Simulator (FUMES). Owing to the operational constraints of the mining facility, methods for measuring learning transfer were employed which did not require real world performance evaluation. Transfer measures that examined simulator performance relative to real world experience, fidelity assessment, and appraisal of the training value of the platform were utilised. Triangulation of results across all three measures indicated the presence of learning transfer, suggesting the viability of indirect measures in instances where real world performance testing is not possible. Furthermore, these indirect measures of learning transfer also provided some insight as to the strengths and weaknesses of the simulation design, which could be used to inform the development of future versions of the product
A Fresh Catch of Massive Binaries in the Cygnus OB2 Association
Massive binary stars may constitute a substantial fraction of progenitors to
supernovae and gamma-ray bursts, and the distribution of their orbital
characteristics holds clues to the formation process of massive stars. As a
contribution to securing statistics on OB-type binaries, we report the
discovery and orbital parameters for five new systems as part of the Cygnus OB2
Radial Velocity Survey. Four of the new systems (MT070, MT174, MT267, and MT734
(a.k.a. VI Cygni #11) are single-lined spectroscopic binaries while one (MT103)
is a double-lined system (B1V+B2V). MT070 is noteworthy as the longest period
system yet measured in Cyg OB2, with P=6.2 yr. The other four systems have
periods ranging between 4 and 73 days. MT174 is noteworthy for having a
probable mass ratio q<0.1, making it a candidate progenitor to a low-mass X-ray
binary. These measurements bring the total number of massive binaries in Cyg
OB2 to 25, the most currently known in any single cluster or association.Comment: Accepted for publication in the Astrophysical Journa
Statistical methods for automated drug susceptibility testing: Bayesian minimum inhibitory concentration prediction from growth curves
Determination of the minimum inhibitory concentration (MIC) of a drug that
prevents microbial growth is an important step for managing patients with
infections. In this paper we present a novel probabilistic approach that
accurately estimates MICs based on a panel of multiple curves reflecting
features of bacterial growth. We develop a probabilistic model for determining
whether a given dilution of an antimicrobial agent is the MIC given features of
the growth curves over time. Because of the potentially large collection of
features, we utilize Bayesian model selection to narrow the collection of
predictors to the most important variables. In addition to point estimates of
MICs, we are able to provide posterior probabilities that each dilution is the
MIC based on the observed growth curves. The methods are easily automated and
have been incorporated into the Becton--Dickinson PHOENIX automated
susceptibility system that rapidly and accurately classifies the resistance of
a large number of microorganisms in clinical samples. Over seventy-five studies
to date have shown this new method provides improved estimation of MICs over
existing approaches.Comment: Published in at http://dx.doi.org/10.1214/08-AOAS217 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Space Power Facility Reverberation Chamber Calibration Report
This document describes the process and results of calibrating the Space Environmental Test EMI Test facility at NASA Plum Brook Space Power Facility according to the specifications of IEC61000-4-21 for susceptibility testing from 100 MHz to 40 GHz. The chamber passed the field uniformity test, in both the empty and loaded conditions, making it the world's largest Reverberation Chamber
Multi-source self-calibration: Unveiling the microJy population of compact radio sources
Context. Very Long Baseline Interferometry (VLBI) data are extremely
sensitive to the phase stability of the VLBI array. This is especially
important when we reach {\mu}Jy r.m.s. sensitivities. Calibration using
standard phase referencing techniques is often used to improve the phase
stability of VLBI data but the results are often not optimal. This is evident
in blank fields that do not have in-beam calibrators. Aims. We present a
calibration algorithm termed Multi-Source Self-Calibration (MSSC) which can be
used after standard phase referencing on wide-field VLBI observations. This is
tested on a 1.6 GHz wide-field VLBI data set of the Hubble Deep Field-North and
the Hubble Flanking Fields. Methods. MSSC uses multiple target sources detected
in the field via standard phase referencing techniques and modifies the
visibili- ties so that each data set approximates to a point source. These are
combined to increase the signal to noise and permit self-calibration. In
principle, this should allow residual phase changes caused by the troposphere
and ionosphere to be corrected. By means of faceting, the technique can also be
used for direction dependent calibration. Results. Phase corrections, derived
using MSSC, were applied to a wide-field VLBI data set of the HDF-N comprising
of 699 phase centres. MSSC was found to perform considerably better than
standard phase referencing and single source self-calibration. All detected
sources exhibited dramatic improvements in dynamic range. Using MSSC, one
source reached the detection threshold taking the total detected sources to
twenty. 60% of these sources can now be imaged with uniform weighting compared
to just 45% with standard phase referencing. The Parseltongue code which
implements MSSC has been released and made publicly available to the
astronomical community (https://github.com/jradcliffe5/multi_self_cal).Comment: 7 pages, 4 figures, accepted to A&
Petrology and Geochemistry of Volcanic Rocks from the South Kauaʻi Swell Volcano, Hawaiʻi: Implications for the Lithology and Composition of the Hawaiian Mantle Plume
The South Kauaʻi Swell (SKS) volcano was sampled during four JASON dives and three dredge hauls recovering rocks that range from fresh pillow lavas to altered volcanic breccias. Two geochemical groups were identified: shield-stage tholeiites (5·4–3·9 Ma) and rejuvenation-stage alkalic lavas (1·9–0·1 Ma). The young SKS ages and the coeval rejuvenated volcanism along a 400km segment of the Hawaiian Islands (Maui to Niʻihau) are inconsistent with the timing and duration predictions by the flexure and secondary plume melting models for renewed volcanism. The SKS tholeiites are geochemically heterogeneous but similar to lavas from nearby Kauaʻi, Niʻihau and Waiʻanae volcanoes, indicating that their source regions within the Hawaiian mantle plume sampled a well-mixed zone. Most SKS tholeiitic lavas exhibit radiogenic Pb isotope ratios (208Pb*/206Pb*) that are characteristic of Loa compositions (>0·9475), consistent with the volcano’s location on the west side of the Hawaiian Islands. These results document the existence of the Loa component within the Hawaiian mantle plume prior to 5 Ma. Loa trend volcanoes are thought to have a major pyroxenite component in their source. Calculations of the pyroxenitic component in the parental melts for SKS tholeiites using high-precision olivine analyses and modeling of trace element ratios indicate a large pyroxenite proportion (≥50%), which was predicted by recent numerical models. Rejuvenation-stage lavas were also found to have a significant pyroxenite component based on olivine analyses (40–60%). The abundance of pyroxenite in the source for SKS lavas may be the cause of this volcano’s extended period of magmatism (>5 Myr). The broad distribution of the Loa component in the northern Hawaiian Island lavas coincides with the start of a dramatic magma flux increase (300%) along the Hawaiian Chain, which may reflect a major structural change in the source of the Hawaiian mantle plume
Growth dynamics of a Bose-Einstein condensate in a dimple trap without cooling
We study the formation of a Bose-Einstein condensate in a cigar-shaped
three-dimensional harmonic trap, induced by the controlled addition of an
attractive "dimple" potential along the weak axis. In this manner we are able
to induce condensation without cooling due to a localized increase in the phase
space density. We perform a quantitative analysis of the thermodynamic
transformation in both the sudden and adiabatic regimes for a range of dimple
widths and depths. We find good agreement with equilibrium calculations based
on self-consistent semiclassical Hartree-Fock theory describing the condensate
and thermal cloud. We observe there is an optimal dimple depth that results in
a maximum in the condensate fraction. We also study the non-equilibrium
dynamics of condensate formation in the sudden turn-on regime, finding good
agreement for the observed time dependence of the condensate fraction with
calculations based on quantum kinetic theory.Comment: v1: 9 pages, 7 figures, submitted to Phys. Rev. A; v2: 10 pages, 8
figures, fixed typos, added references, additional details on experimental
procedure, values of phase-space density, new figure and discussion on
effects of three-body loss in Appendix B (replaced with published version
Characterization of MOS Sensors for R-32 and R-454B Leaks
Owing to concerns about climate change, many jurisdictions are phasing out high global warming potential refrigerants in HVAC&R systems. Their near-term replacements are class A2L (mildly-flammable) refrigerants. Area monitoring detectors will be required for most future residential, commercial, and industrial HVAC systems that use these refrigerants. UL Standard 60335-2-40 requires these detectors to have a set-point of 25% of the lower flammability limit (LFL) and to detect the set-point within 10 s when exposed to a gas mixture at the LFL. Inexpensive detectors that meet these requirements do not exist, which has delayed the adoption of A2L refrigerants. A technology with good potential is based on metal-oxide semiconductors (MOS). MOS detectors are tested here, considering their response to leaks of R-32 and R-454B. They are characterized here for their sensitivity, response time, false alarms from contaminants, and poisoning. The sensors have good sensitivity with a steady-state output that is linear with respect to the logarithm of concentration. The sensors fail narrowly to meet the 10 s response time requirement for both R-32 and R-454B. The sensors do not alarm when exposed to the contaminants in the standard. However, several of the contaminants do poison the sensors, at least temporarily
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