5,860 research outputs found
Detection of volcanic, solar and greenhouse gas signals in paleo-reconstructions of Northern Hemispheric temperature
Enabling science with Gaia observations of naked-eye stars
ESA's Gaia space astrometry mission is performing an all-sky survey of
stellar objects. At the beginning of the nominal mission in July 2014, an
operation scheme was adopted that enabled Gaia to routinely acquire
observations of all stars brighter than the original limit of G~6, i.e. the
naked-eye stars. Here, we describe the current status and extent of those
observations and their on-ground processing. We present an overview of the data
products generated for G<6 stars and the potential scientific applications.
Finally, we discuss how the Gaia survey could be enhanced by further exploiting
the techniques we developed.Comment: 16 pages, 8 figures. Submitted for the proceedings of the 2016 SPIE
Astronomical Instrumentation and Telescopes conference (SPIE 9904
Highly-functionalised difluorinated cyclohexane polyols via the Diels–Alder reaction : regiochemical control via the phenylsulfonyl group
A difluorinated dienophile underwent cycloaddition reactions with a range of furans to afford cycloadducts whichcould be processed regio- and stereoselectively via episulfonium ions, generated by the reaction between their alkenyl groups and phenylsulfenyl chloride. The oxabicyclic products were oxidised to the phenylsulfonyl level and ring opened via E1CB or reductive desulfonative pathways to afford, ultimately, difluorinated cyclohexene or cyclohexane polyols
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Detection of human influence on a new, validated 1500-Year temperature reconstruction
Climate records over the last millennium place the twentieth-century warming in a longer historical context. Reconstructions of millennial temperatures show a wide range of variability, raising questions about the reliability of currently available reconstruction techniques and the uniqueness of late-twentieth-century warming. A calibration method is suggested that avoids the loss of low-frequency variance. A new reconstruction using this method shows substantial variability over the last 1500 yr. This record is consistent with independent temperature change estimates from borehole geothermal records, compared over the same spatial and temporal domain. The record is also broadly consistent with other recent reconstructions that attempt to fully recover low-frequency climate variability in their central estimate. High variability in reconstructions does not hamper the detection of greenhouse gas-induced climate change, since a substantial fraction of the variance in these reconstructions from the beginning of the analysis in the late thirteenth century to the end of the records can be attributed to external forcing. Results from a detection and attribution analysis show that greenhouse warming is detectable in all analyzed high-variance reconstructions (with the possible exception of one ending in 1925), and that about a third of the warming in the first half of the twentieth century can be attributed to anthropogenic greenhouse gas emissions. The estimated magnitude of the anthropogenic signal is consistent with most of the warming in the second half of the twentieth century being anthropogenic
Advanced modulation technology development for earth station demodulator applications
The purpose of this contract was to develop a high rate (200 Mbps), bandwidth efficient, modulation format using low cost hardware, in 1990's technology. The modulation format chosen is 16-ary continuous phase frequency shift keying (CPFSK). The implementation of the modulation format uses a unique combination of a limiter/discriminator followed by an accumulator to determine transmitted phase. An important feature of the modulation scheme is the way coding is applied to efficiently gain back the performance lost by the close spacing of the phase points
A tradeoff in simultaneous quantum-limited phase and loss estimation in interferometry
Interferometry with quantum light is known to provide enhanced precision for
estimating a single phase. However, depending on the parameters involved, the
quantum limit for the simultaneous estimation of multiple parameters may not
attainable, leading to trade-offs in the attainable precisions. Here we study
the simultaneous estimation of two parameters related to optical
interferometry: phase and loss, using a fixed number of photons. We derive a
trade-off in the estimation of these two parameters which shows that, in
contrast to single-parameter estimation, it is impossible to design a strategy
saturating the quantum Cramer-Rao bound for loss and phase estimation in a
single setup simultaneously. We design optimal quantum states with a fixed
number of photons achieving the best possible simultaneous precisions. Our
results reveal general features about concurrently estimating Hamiltonian and
dissipative parameters, and has implications for sophisticated sensing
scenarios such as quantum imaging.Comment: 9 pages, 6 figure
Digging supplementary buried channels: investigating the notch architecture within the CCD pixels on ESA's Gaia satellite
The European Space Agency (ESA) Gaia satellite has 106 CCD image sensors
which will suffer from increased charge transfer inefficiency (CTI) as a result
of radiation damage. To aid the mitigation at low signal levels, the CCD design
includes Supplementary Buried Channels (SBCs, otherwise known as `notches')
within each CCD column. We present the largest published sample of Gaia CCD SBC
Full Well Capacity (FWC) laboratory measurements and simulations based on 13
devices. We find that Gaia CCDs manufactured post-2004 have SBCs with FWCs in
the upper half of each CCD that are systematically smaller by two orders of
magnitude (<50 electrons) compared to those manufactured pre-2004 (thousands of
electrons). Gaia's faint star (13 < G < 20 mag) astrometric performance
predictions by Prod'homme et al. and Holl et al. use pre-2004 SBC FWCs as
inputs to their simulations. However, all the CCDs already integrated onto the
satellite for the 2013 launch are post-2004. SBC FWC measurements are not
available for one of our five post-2004 CCDs but the fact it meets Gaia's image
location requirements suggests it has SBC FWCs similar to pre-2004. It is too
late to measure the SBC FWCs onboard the satellite and it is not possible to
theoretically predict them. Gaia's faint star astrometric performance
predictions depend on knowledge of the onboard SBC FWCs but as these are
currently unavailable, it is not known how representative of the whole focal
plane the current predictions are. Therefore, we suggest Gaia's initial
in-orbit calibrations should include measurement of the onboard SBC FWCs. We
present a potential method to do this. Faint star astrometric performance
predictions based on onboard SBC FWCs at the start of the mission would allow
satellite operating conditions or CTI software mitigation to be further
optimised to improve the scientific return of Gaia.Comment: Accepted for publication in MNRAS, 16 pages, 19 figure
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