1,256 research outputs found
Detection of CO in Triton's atmosphere and the nature of surface-atmosphere interactions
Triton possesses a thin atmosphere, primarily composed of nitrogen, sustained
by the sublimation of surface ices. The goal is to determine the composition of
Triton's atmosphere and to constrain the nature of surface-atmosphere
interactions. We perform high-resolution spectroscopic observations in the
2.32-2.37 m range, using CRIRES at the VLT. From this first spectroscopic
detection of Triton's atmosphere in the infrared, we report (i) the first
observation of gaseous methane since its discovery in the ultraviolet by
Voyager in 1989 and (ii) the first ever detection of gaseous CO in the
satellite. The CO atmospheric abundance is remarkably similar to its surface
abundance, and appears to be controlled by a thin, CO-enriched, surface veneer
resulting from seasonal transport and/or atmospheric escape. The CH partial
pressure is several times larger than inferred from Voyager. This confirms that
Triton's atmosphere is seasonally variable and is best interpreted by the
warming of CH-rich icy grains as Triton passed southern summer solstice in
2000. The presence of CO in Triton's atmosphere also affects its temperature,
photochemistry and ionospheric composition. An improved upper limit on CO in
Pluto's atmosphere is also reported.Comment: 11 pages, including 4 figures and 2 on-line figures Astronomy and
Astrophysics, in press (accepted March 13, 2010
Financial Markets Analysis by Probabilistic Fuzzy Modelling
For successful trading in financial markets, it is important to develop financial models where one can identify different states of the market for modifying one???s actions. In this paper, we propose to use probabilistic fuzzy systems for this purpose. We concentrate on Takagi???Sugeno (TS) probabilistic fuzzy systems that combine interpretability of fuzzy systems with the statistical properties of probabilistic systems. We start by recapitulating the general architecture of TS probabilistic fuzzy rule-based systems and summarize the corresponding reasoning schemes. We mention how probabilities can be estimated from a given data set and how a probability distribution can be approximated by a fuzzy histogram. We apply our methodology for financial time series analysis and demonstrate how a probabilistic TS fuzzy system can be identified, assuming that a linguistic term set is given. We illustrate the interpretability of such a system by inspecting the rule bases of our models.time series analysis;data-driven design;fuzzy reasoning;fuzzy rule base;probabilistic fuzzy systems
Exploring the spatial, temporal, and vertical distribution of methane in Pluto's atmosphere
High-resolution spectra of Pluto in the 1.66 um region, recorded with the
VLT/CRIRES instrument in 2008 (2 spectra) and 2012 (5 spectra), are analyzed to
constrain the spatial and vertical distribution of methane in Pluto's
atmosphere and to search for mid-term (4 year) variability. A sensitivity study
to model assumptions (temperature structure, surface pressure, Pluto's radius)
is performed. Results indicate that (i) no variation of the CH4 atmospheric
content (column-density or mixing ratio) with Pluto rotational phase is present
in excess of 20 % (ii) CH4 column densities show at most marginal variations
between 2008 and 2012, with a best guess estimate of a ~20 % decrease over this
time frame. As stellar occultations indicate that Pluto's surface pressure has
continued to increase over this period, this implies a concomitant decrease of
the methane mixing ratio (iii) the data do not show evidence for an
altitude-varying methane distribution; in particular, they imply a roughly
uniform mixing ratio in at least the first 22-27 km of the atmosphere, and high
concentrations of low-temperature methane near the surface can be ruled out.
Our results are also best consistent with a relatively large (> 1180 km) Pluto
radius. Comparison with predictions from a recently developed global climate
model GCM indicates that these features are best explained if the source of
methane occurs in regional-scale CH4 ice deposits, including both low latitudes
and high Northern latitudes, evidence for which is present from the rotational
and secular evolution of the near-IR features due to CH4 ice. Our "best guess"
predictions for the New Horizons encounter in 2015 are: a 1184 km radius, a 17
ubar surface pressure, and a 0.44 % CH4 mixing ratio with negligible
longitudinal variations.Comment: 21 pages, 6 figure
Non-commutative desingularization of determinantal varieties, I
We show that determinantal varieties defined by maximal minors of a generic
matrix have a non-commutative desingularization, in that we construct a maximal
Cohen-Macaulay module over such a variety whose endomorphism ring is
Cohen-Macaulay and has finite global dimension. In the case of the determinant
of a square matrix, this gives a non-commutative crepant resolution.Comment: 52 pages, 3 figures, all comments welcom
Financial Markets Analysis by Probabilistic Fuzzy Modelling
For successful trading in financial markets, it is important to develop financial models where one can identify different states of the market for modifying one???s actions. In this paper, we propose to use probabilistic fuzzy systems for this purpose. We concentrate on Takagi???Sugeno (TS) probabilistic fuzzy systems that combine interpretability of fuzzy systems with the statistical properties of probabilistic systems. We start by recapitulating the general architecture of TS probabilistic fuzzy rule-based systems and summarize the corresponding reasoning schemes. We mention how probabilities can be estimated from a given data set and how a probability distribution can be approximated by a fuzzy histogram. We apply our methodology for financial time series analysis and demonstrate how a probabilistic TS fuzzy system can be identified, assuming that a linguistic term set is given. We illustrate the interpretability of such a system by inspecting the rule bases of our models
Swift X-ray Observations of Classical Novae
The new gamma-ray burst mission Swift has obtained pointed observations of
several classical novae in outburst. We analyzed all the observations of
classical novae from the Swift archive up to 30 June, 2006. We analyzed usable
observations of 12 classical novae and found 4 non-detections, 3 weak sources
and 5 strong sources. This includes detections of 2 novae exhibiting spectra
resembling those of Super Soft X-ray binary Source spectra (SSS) implying
ongoing nuclear burning on the white dwarf surface. With these new Swift data,
we add to the growing statistics of the X-ray duration and characteristics of
classical novae.Comment: Accepted for ApJ; this version contains additional material: 18
pages, 16 figure
Probabilistic and Statistical Fuzzy Set Foundations of Competitive Exception Learning
Recently, a Competitive Exception Learning Algorithm (CELA) was introduced [1, 2]. This algorithm establishes an optimal mapping from a (continuous) M-dimensional input sample space to an N-dime
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