512 research outputs found
A revised uncertainty budget for measuring the Boltzmann constant using the Doppler Broadening Technique on ammonia
We report on our on-going effort to measure the Boltzmann constant, kB, using
the Doppler Broadening Technique. The main systematic effects affecting the
measurement are discussed. A revised error budget is presented in which the
global uncertainty on systematic effects is reduced to 2.3 ppm. This
corresponds to a reduction of more than one order of magnitude compared to our
previous Boltzmann constant measurement. Means to reach a determination of kB
at the part per million accuracy level are outlined
A widely tunable 10-m quantum cascade laser phase-locked to a state-of-the-art mid-infrared reference for precision molecular spectroscopy
We report the coherent phase-locking of a quantum cascade laser (QCL) at
10-m to the secondary frequency standard of this spectral region, a CO2
laser stabilized on a saturated absorption line of OsO4. The stability and
accuracy of the standard are transferred to the QCL resulting in a line width
of the order of 10 Hz, and leading to our knowledge to the narrowest QCL to
date. The locked QCL is then used to perform absorption spectroscopy spanning 6
GHz of NH3 and methyltrioxorhenium, two species of interest for applications in
precision measurements.Comment: 5 pages, 4 figure
Rotation Measure Synthesis of Galactic Polarized Emission with the DRAO 26-m Telescope
Radio polarimetry at decimetre wavelengths is the principal source of
information on the Galactic magnetic field. The diffuse polarized emission is
strongly influenced by Faraday rotation in the magneto-ionic medium and
rotation measure is the prime quantity of interest, implying that all Stokes
parameters must be measured over wide frequency bands with many frequency
channels. The DRAO 26-m Telescope has been equipped with a wideband feed, a
polarization transducer to deliver both hands of circular polarization, and a
receiver, all operating from 1277 to 1762 MHz. Half-power beamwidth is between
40 and 30 arcminutes. A digital FPGA spectrometer, based on commercially
available components, produces all Stokes parameters in 2048 frequency channels
over a 485-MHz bandwidth. Signals are digitized to 8 bits and a Fast Fourier
Transform is applied to each data stream. Stokes parameters are then generated
in each frequency channel. This instrument is in use at DRAO for a Northern sky
polarization survey. Observations consist of scans up and down the Meridian at
a drive rate of 0.9 degree per minute to give complete coverage of the sky
between declinations -30 degree and 90 degree. This paper presents a complete
description of the receiver and data acquisition system. Only a small fraction
of the frequency band of operation is allocated for radio astronomy, and about
20 percent of the data are lost to interference. The first 8 percent of data
from the survey are used for a proof-of-concept study, which has led to the
first application of Rotation Measure Synthesis to the diffuse Galactic
emission obtained with a single-antenna telescope. We find rotation measure
values for the diffuse emission as high as approximately 100 rad per square
metre, much higher than recorded in earlier work.Comment: Accepted for publication in The Astronomical Journa
Radio polarimetric imaging of the interstellar medium: magnetic field and diffuse ionized gas structure near the W3/W4/W5/HB3 complex
We have used polarimetric imaging to study the magneto-ionic medium of the
Galaxy, obtaining 1420 MHz images with an angular resolution of 1' over more
than 40 square-degrees of sky around the W3/W4/W5/HB3 HII region/SNR complex in
the Perseus Arm. Features detected in polarization angle are imposed on the
linearly polarized Galactic synchrotron background emission by Faraday rotation
arising in foreground ionized gas having an emission measure as low as 1
cm^{-6} pc. Several new remarkable phenomena have been identified, including:
mottled polarization arising from random fluctuations in a magneto-ionic screen
that we identify with a medium in the Perseus Arm, probably in the vicinity of
the HII regions themselves; depolarization arising from very high rotation
measures (several times 10^3 rad m^{-2}) and rotation measure gradients due to
the dense, turbulent environs of the HII regions; highly ordered features
spanning up to several degrees; and an extended influence of the HII regions
beyond the boundaries defined by earlier observations. In particular, the
effects of an extended, low-density ionized halo around the HII region W4 are
evident, probably an example of the extended HII envelopes postulated as the
origin of weak recombination-line emission detected from the Galactic ridge.
Our polarization observations can be understood if the uniform magnetic field
component in this envelope scales with the square-root of electron density and
is 20 microG at the edge of the depolarized region around W4, although this is
probably an over-estimate since the random field component will have a
significant effect.Comment: 18 pages, 8 figures (7 jpeg and 1 postscript), accepted for
publication in the Astrophysical Journa
Absorption line shape recovery beyond the detection bandwidth limit: application to the precision spectroscopic measurement of the Boltzmann constant
22 pagesInternational audienceA theoretical model of the influence of detection bandwidth properties on observed line shapes in laser absorption spectroscopy is described. The model predicts artificial frequency shifts, extra broadenings and line asymmetries which must be taken into account in order to obtain accurate central frequencies and other spectroscopic parameters. This reveals sources of systematic effects most probably underestimated so far potentially affecting spectroscopic measurements. This may impact many fields of research, from atmospheric and interstellar physics to precision spectroscopic measurements devoted to metrological applications, tests of quantum electrodynamics or other fundamental laws of nature. Our theoretical model is validated by linear absorption experiments performed on H2O and NH3 molecular lines recorded by precision laser spectroscopy in two distinct spectral regions, near- and mid-infrared. Possible means of recovering original line shape parameters or experimental conditions under which the detection bandwidth has a negligible impact, given a targeted accuracy, are proposed. Particular emphasis is put on the detection bandwidth adjustments required to use such high-quality molecular spectra for a spectroscopic determination of the Boltzmann constant at the 1 ppm level of accuracy
Is rs34861192 or rs1862513 a more promising variant for determining plasma resistin in an aged Japanese population?
Replication Study of Candidate Genes Associated With Type 2 Diabetes Based On Genome-Wide Screening
OBJECTIVE—The present study was conducted to confirm possible associations between candidate genes from genome-wide association studies and type 2 diabetes in Japanese diabetic patients and a community-based general population. A total of 11 previously reported single-nucleotide polymorphisms (SNPs) from the TCF7L2, CDKAL1, HHEX, IGF2BP2, CDKN2A/B, SLC30A8, and KCNJ11 genes were analyzed
Radio Loud and Radio Quiet Active Galactic Nuclei
We generated a sample of 409 AGNs for which both the radio luminosity at 5
GHz and the line luminosity in [OIII] 5007 have been measured. The radio
luminosity spans a range of ten orders of magnitude, and the [OIII] line
luminosity spans a range of eight orders of magnitude --- both considerably
larger than the ranges in previous studies. We show that these two quantities
are correlated in a similar way for both radio-loud and radio-quiet AGNs. We
demonstrate that the observed correlation can be explained in terms of a model
in which jets are accelerated and collimated by a vertical magnetic field.Comment: 45 pages inc. 7 figures, 1 table of 15 pages in ps-format. Accept to
AJ September 199
Radio spectra and polarisation properties of radio-loud Broad Absorption Line Quasars
We present multi-frequency observations of a sample of 15 radio-emitting
Broad Absorption Line Quasars (BAL QSOs), covering a spectral range between 74
MHz and 43 GHz. They display mostly convex radio spectra which typically peak
at about 1-5 GHz (in the observer's rest-frame), flatten at MHz frequencies,
probably due to synchrotron self-absorption, and become steeper at high
frequencies, i.e., >~ 20 GHz. VLA 22-GHz maps (HPBW ~ 80 mas) show unresolved
or very compact sources, with linear projected sizes of <= 1 kpc. About 2/3 of
the sample look unpolarised or weakly polarised at 8.4 GHz, frequency in which
reasonable upper limits could be obtained for polarised intensity. Statistical
comparisons have been made between the spectral index distributions of samples
of BAL and non-BAL QSOs, both in the observed and the rest-frame, finding
steeper spectra among non-BAL QSOs. However constraining this comparison to
compact sources results in no significant differences between both
distributions. This comparison is consistent with BAL QSOs not being oriented
along a particular line of sight. In addition, our analysis of the spectral
shape, variability and polarisation properties shows that radio BAL QSOs share
several properties common to young radio sources like Compact Steep Spectrum
(CSS) or Gigahertz-Peaked Spectrum (GPS) sources.Comment: 18 pages, 11 Postscript figures, 12 Tables. Accepted for publication
in MNRA
In C. elegans, High Levels of dsRNA Allow RNAi in the Absence of RDE-4
C. elegans Dicer requires an accessory double-stranded RNA binding protein, RDE-4, to enact the first step of RNA interference, the cleavage of dsRNA to produce siRNA. While RDE-4 is typically essential for RNAi, we report that in the presence of high concentrations of trigger dsRNA, rde-4 deficient animals are capable of silencing a transgene. By multiple criteria the silencing occurs by the canonical RNAi pathway. For example, silencing is RDE-1 dependent and exhibits a decrease in the targeted mRNA in response to an increase in siRNA. We also find that high concentrations of dsRNA trigger lead to increased accumulation of primary siRNAs, consistent with the existence of a rate-limiting step during the conversion of primary to secondary siRNAs. Our studies also revealed that transgene silencing occurs at low levels in the soma, even in the presence of ADARs, and that at least some siRNAs accumulate in a temperature-dependent manner. We conclude that an RNAi response varies with different conditions, and this may allow an organism to tailor a response to specific environmental signals
- …