2,825 research outputs found
The European Large Area ISO Survey - ISOPHOT results using the MPIA-pipeline
The European Large Area ISO Survey (ELAIS) will provide Infrared observations
of 4 regions in the sky with ISO. Around 2000 Infrared sources have been
detected at 7 and 15 microns (with ISOCAM), 90 and 175 microns (with ISOPHOT))
over 13 square degrees of the sky. We present the source extraction pipeline of
the 90 microns ISOPHOT observations, describe and discuss the results obtained
and derive the limits of the ELAIS observational strategy.Comment: 4 pages, 5 figures, to appear in the ISO conference "The Universe as
seen by ISO", 1998, UNESCO, Pari
High accuracy measure of atomic polarizability in an optical lattice clock
Despite being a canonical example of quantum mechanical perturbation theory,
as well as one of the earliest observed spectroscopic shifts, the Stark effect
contributes the largest source of uncertainty in a modern optical atomic clock
through blackbody radiation. By employing an ultracold, trapped atomic ensemble
and high stability optical clock, we characterize the quadratic Stark effect
with unprecedented precision. We report the ytterbium optical clock's
sensitivity to electric fields (such as blackbody radiation) as the
differential static polarizability of the ground and excited clock levels:
36.2612(7) kHz (kV/cm)^{-2}. The clock's fractional uncertainty due to room
temperature blackbody radiation is reduced an order of magnitude to 3 \times
10^{-17}.Comment: 5 pages, 3 figures, 2 table
An atomic clock with instability
Atomic clocks have been transformational in science and technology, leading
to innovations such as global positioning, advanced communications, and tests
of fundamental constant variation. Next-generation optical atomic clocks can
extend the capability of these timekeepers, where researchers have long aspired
toward measurement precision at 1 part in . This milestone will
enable a second revolution of new timing applications such as relativistic
geodesy, enhanced Earth- and space-based navigation and telescopy, and new
tests on physics beyond the Standard Model. Here, we describe the development
and operation of two optical lattice clocks, both utilizing spin-polarized,
ultracold atomic ytterbium. A measurement comparing these systems demonstrates
an unprecedented atomic clock instability of after
only hours of averaging
Estimated glomerular filtration rate is a poor predictor of the concentration of middle molecular weight uremic solutes in chronic kidney disease
Background: Uremic solute concentration increases as Glomerular Filtration Rate (GFR) declines. Weak associations were demonstrated between estimated GFR (eGFR) and the concentrations of several small water-soluble and protein-bound uremic solutes (MW500Da).
Materials and Methods: In 95 CKD-patients (CKD-stage 2-5 not on dialysis), associations between different eGFR-formulae (creatinine, CystatinC-based or both) and the natural logarithm of the concentration of several LMWP's were analyzed: i.e. parathyroid hormone (PTH), Cystatin C (CystC), interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-alpha), leptin, retinol binding protein (RbP), immunoglobin light chains kappa and lambda (Ig-kappa and Ig-lambda), beta-2-microglobulin (beta M-2), myoglobin and fibroblast growth factor-23 (FGF-23)).
Results: The regression coefficients (R-2) between eGFR, based on the CKD-EPI-Crea-CystC-formula as reference, and the examined LMWP's could be divided into three groups. Most of the LMWP's associated weakly (R-2 0.7). Almost identical R-2-values were found per LMWP for all eGFR-formulae, with exception of CystC and beta M-2 which showed weaker associations with creatinine-based than with CystC-based eGFR.
Conclusion: The association between eGFR and the concentration of several LMWP's is inconsistent, with in general low R-2-values. Thus, the use of eGFR to evaluate kidney function does not reflect the concentration of several LMWP's with proven toxic impact in CKD
Hyper-Ramsey Spectroscopy of Optical Clock Transitions
We present non-standard optical Ramsey schemes that use pulses individually
tailored in duration, phase, and frequency to cancel spurious frequency shifts
related to the excitation itself. In particular, the field shifts and their
uncertainties of Ramsey fringes can be radically suppressed (by 2-4 orders of
magnitude) in comparison with the usual Ramsey method (using two equal pulses)
as well as with single-pulse Rabi spectroscopy. Atom interferometers and
optical clocks based on two-photon transitions, heavily forbidden transitions,
or magnetically induced spectroscopy could significantly benefit from this
method. In the latter case these frequency shifts can be suppressed
considerably below a fractional level of 10^{-17}. Moreover, our approach opens
the door for the high-precision optical clocks based on direct frequency comb
spectroscopy.Comment: 5 pages, 4 figure
Sub-femtosecond absolute timing precision with a 10 GHz hybrid photonic-microwave oscillator
We present an optical-electronic approach to generating microwave signals
with high spectral purity. By circumventing shot noise and operating near
fundamental thermal limits, we demonstrate 10 GHz signals with an absolute
timing jitter for a single hybrid oscillator of 420 attoseconds (1Hz - 5 GHz)
Determination of the cosmic far-infrared background level with the ISOPHOT instrument
The cosmic infrared background (CIRB) consists mainly of the integrated light
of distant galaxies. In the far-infrared the current estimates of its surface
brightness are based on the measurements of the COBE satellite. Independent
confirmation of these results is still needed from other instruments. In this
paper we derive estimates of the far-infrared CIRB using measurements made with
the ISOPHOT instrument aboard the ISO satellite. The results are used to seek
further confirmation of the CIRB levels that have been derived by various
groups using the COBE data. We study three regions of very low cirrus emission.
The surface brightness observed with the ISOPHOT instrument at 90, 150, and 180
um is correlated with hydrogen 21 cm line data from the Effelsberg radio
telescope. Extrapolation to zero hydrogen column density gives an estimate for
the sum of extragalactic signal plus zodiacal light. The zodiacal light is
subtracted using ISOPHOT data at shorter wavelengths. Thus, the resulting
estimate of the far-infrared CIRB is based on ISO measurements alone. In the
range 150 to 180 um, we obtain a CIRB value of 1.08+-0.32+-0.30 MJy/sr quoting
statistical and systematic errors separately. In the 90 um band, we obtain a
2-sigma upper limit of 2.3 MJy/sr. The estimates derived from ISOPHOT
far-infrared maps are consistent with the earlier COBE results.Comment: Accepted for publication in A&A, 17 page
A Deep VLA survey at 20cm of the ISO ELAIS survey regions
We have used the Very Large Array(VLA) in C configuration to carry out a
sensitive 20cm radio survey of regions of sky that have been surveyed in the
Far Infra-Red over the wavelength range 5-200 microns with ISO as part of the
European Large Area ISO Survey(ELAIS). As usual in surveys based on a
relatively small number of overlapping VLA pointings the flux limit varies over
the area surveyed. The survey has a flux limit that varies from a 5
limit of 0.135mJy over an area of 0.12deg to a 5 limit of 1.15mJy
or better over the whole region covered of 4.22 deg. In this paper we
present the radio catalogue of 867 sources. These regions of sky have
previously been surveyed to shallow flux limits at 20cm with the VLA as part of
the VLA D configuration NVSS(FWHM=45 arcsec) and VLA B configuration
FIRST(FWHM=5 arcsec) surveys. We have carried out a a detailed comparison of
the reliability of our own survey and these two independent surveys in order to
assess the reliability and completeness of each survey.Comment: 19 pages, 24 figures, submitted to MNRAS, also available in
http://www.ast.cam.ac.uk/~ciliegi/elais/paper
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