6,821 research outputs found
Computationally efficient algorithms for the two-dimensional Kolmogorov-Smirnov test
Goodness-of-fit statistics measure the compatibility of random samples against some theoretical or reference probability distribution function. The classical one-dimensional Kolmogorov-Smirnov test is a non-parametric statistic for comparing two empirical distributions which defines the largest absolute difference between the two cumulative distribution functions as a measure of disagreement. Adapting this test to more than one dimension is a challenge because there are 2^d-1 independent ways of ordering a cumulative distribution function in d dimensions. We discuss Peacock's version of the Kolmogorov-Smirnov test for two-dimensional data sets which computes the differences between cumulative distribution functions in 4n^2 quadrants. We also examine Fasano and Franceschini's variation of Peacock's test, Cooke's algorithm for Peacock's test, and ROOT's version of the two-dimensional Kolmogorov-Smirnov test. We establish a lower-bound limit on the work for computing Peacock's test of
Omega(n^2.lg(n)), introducing optimal algorithms for both this and Fasano and Franceschini's test, and show that Cooke's algorithm is not a faithful implementation of Peacock's test. We also discuss and evaluate parallel algorithms for Peacock's test
Exploring the inner region of Type 1 AGNs with the Keck interferometer
The exploration of extragalactic objects with long-baseline interferometers
in the near-infrared has been very limited. Here we report successful
observations with the Keck interferometer at K-band (2.2 um) for four Type 1
AGNs, namely NGC4151, Mrk231, NGC4051, and the QSO IRAS13349+2438 at z=0.108.
For the latter three objects, these are the first long-baseline interferometric
measurements in the infrared. We detect high visibilities (V^2 ~ 0.8-0.9) for
all the four objects, including NGC4151 for which we confirm the high V^2 level
measured by Swain et al.(2003). We marginally detect a decrease of V^2 with
increasing baseline lengths for NGC4151, although over a very limited range,
where the decrease and absolute V^2 are well fitted with a ring model of radius
0.45+/-0.04 mas (0.039+/-0.003 pc). Strikingly, this matches independent radius
measurements from optical--infrared reverberations that are thought to be
probing the dust sublimation radius. We also show that the effective radius of
the other objects, obtained from the same ring model, is either roughly equal
to or slightly larger than the reverberation radius as a function of AGN
luminosity. This suggests that we are indeed partially resolving the dust
sublimation region. The ratio of the effective ring radius to the reverberation
radius might also give us an approximate probe for the radial structure of the
inner accreting material in each object. This should be scrutinized with
further observations.Comment: accepted for publication in A&A Letter
Direct evaporative cooling of 41K into a Bose-Einstein condensate
We have investigated the collisional properties of 41K atoms at ultracold
temperature. To show the possibility to use 41K as a coolant, a Bose-Einstein
condensate of 41K atoms in the stretched state (F=2, m_F=2) was created for the
first time by direct evaporation in a magnetic trap. An upper bound of three
body loss coefficient for atoms in the condensate was determined to be 4(2)
10^{-29} cm -6 s-1. A Feshbach resonance in the F=1, m_F=-1 state was observed
at 51.42(5) G, which is in good agreement with theoretical prediction.Comment: 4 pages, 4 figure
Statistical description of turbulent transport for flux driven toroidal plasmas
A novel methodology to analyze non-Gaussian probability distribution
functions (PDFs) of intermittent turbulent transport in global full-f
gyrokinetic simulations is presented. In this work, the Auto-Regressive
Integrated Moving Average (ARIMA) model is applied to time series data of
intermittent turbulent heat transport to separate noise and oscillatory trends,
allowing for the extraction of non-Gaussian features of the PDFs. It was shown
that non-Gaussian tails of the PDFs from first principles based gyrokinetic
simulations agree with an analytical estimation based on a two fluid model.Comment: arXiv admin note: text overlap with arXiv:1008.321
Mapping the radial structure of AGN tori
We present mid-IR interferometric observations of 6 type 1 AGNs at multiple
baseline lengths of 27--130m, reaching high angular resolutions up to
lambda/B~0.02 arcseconds. For two of the targets, we have simultaneous near-IR
interferometric measurements as well. The multiple baseline data directly probe
the radial distribution of the material on sub-pc scales. Within our sample,
which is small but spans over ~2.5 orders of magnitudes in the UV/optical
luminosity L of the central engine, the radial distribution clearly and
systematically changes with luminosity. First, we show that the brightness
distribution at a given mid-IR wavelength seems to be rather well described by
a power law, which makes a simple Gaussian or ring size estimation quite
inadequate. Here we instead use a half-light radius R_1/2 as a representative
size. We then find that the higher luminosity objects become more compact in
normalized half-light radii R_1/2 /R_in in the mid-IR, where R_in is the dust
sublimation radius empirically given by the L^1/2 fit of the near-IR
reverberation radii. This means that, contrary to previous studies, the
physical mid-IR emission size (e.g. in pc) is not proportional to L^1/2, but
increases with L much more slowly, or in fact, nearly constant at 13 micron.
Combining the size information with the total flux specta, we infer that the
radial surface density distribution of the heated dust grains changes from a
steep ~r^-1 structure in high luminosity objects to a shallower ~r^0 structure
in those of lower luminosity. The inward dust temperature distribution does not
seem to smoothly reach the sublimation temperature -- on the innermost scale of
~R_in, a relatively low temperature core seems to co-exist with a slightly
distinct brightness concentration emitting roughly at the sublimation
temperature.Comment: accepted for publication in A&
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