12,054 research outputs found
Hdo And SO2 Thermal Mapping On Venus: Evidence For Strong SO2 Variability
We have been using the TEXES high-resolution imaging spectrometer at the NASA Infrared Telescope Facility to map sulfur dioxide and deuterated water over the disk of Venus. Observations took place on January 10-12, 2012. The diameter of Venus was 13 arcsec, with an illumination factor of 80%. Data were recorded in the 1344-1370 cm(-1) range (around 7.35 mu m) with a spectral resolving power of 80 000 and a spatial resolution of about 1.5 arcsec. In this spectral range, the emission of Venus comes from above the cloud top (z = 60-80 km). Four HDO lines and tens of SO2 lines have been identified in our spectra. Mixing ratios have been estimated from HDO/CO2 and SO2/CO2 line depth ratios, using weak neighboring transitions of comparable depths. The HDO maps, recorded on Jan. 10 and Jan. 12, are globally uniform with no significant variation between the two dates. A slight enhancement of the HDO mixing ratio toward the limb might be interpreted as a possible increase of the D/H ratio with height above the cloud level. The mean H2O mixing ratio is found to be 1.5 +/-0.75 ppm, assuming a D/H ratio of 0.0312 (i.e. 200 times the terrestrial value) over the cloud deck. The SO2 maps, recorded each night from Jan. 10 to Jan. 12, show strong variations over the disk of Venus, by a factor as high as 5 to 10. In addition, the position of the maximum SO2 mixing ratio strongly varies on a timescale of 24 h. The maximum SO2 mixing ratio ranges between 75 +/-25 ppb and 125 +/-50 ppb between Jan. 10 and Jan. 12. The high variability of sulfur dioxide is probably a consequence of its very short photochemical lifetime.NASA NNX-08AE38A, NNX08AW33G S03NSF AST-0607312, AST-0708074Astronom
Raman signatures of classical and quantum phases in coupled dots: A theoretical prediction
We study electron molecules in realistic vertically coupled quantum dots in a
strong magnetic field. Computing the energy spectrum, pair correlation
functions, and dynamical form factor as a function of inter-dot coupling via
diagonalization of the many-body Hamiltonian, we identify structural
transitions between different phases, some of which do not have a classical
counterpart. The calculated Raman cross section shows how such phases can be
experimentally singled out.Comment: 9 pages, 2 postscript figures, 1 colour postscript figure, Latex 2e,
Europhysics Letters style and epsfig macros. Submitted to Europhysics Letter
Storms in the tropics of Titan
Methane clouds, lakes and most fluvial features on Saturn's moon Titan have been observed in the moist high latitudes while the tropics have been nearly devoid of convective clouds and have shown an abundance of wind-carved surface features like dunes. The presence of small-scale channels and dry riverbeds near the equator observed by the Huygens probe at latitudes thought incapable of supporting convection (and thus strong rain) has been suggested to be due to geological seepage or other mechanisms not related to precipitation. Here we report the presence of bright, transient, tropospheric clouds in tropical latitudes. We find that the initial pulse of cloud activity generated planetary waves that instigated cloud activity at other latitudes across Titan that had been cloud-free for at least several years. These observations show that convective pulses at one latitude can trigger short-term convection at other latitudes, even those not generally considered capable of supporting convection, and may also explain the presence of methane-carved rivers and channels near the Huygens landing site
Inference for bounded parameters
The estimation of signal frequency count in the presence of background noise
has had much discussion in the recent physics literature, and Mandelkern [1]
brings the central issues to the statistical community, leading in turn to
extensive discussion by statisticians. The primary focus however in [1] and the
accompanying discussion is on the construction of a confidence interval. We
argue that the likelihood function and -value function provide a
comprehensive presentation of the information available from the model and the
data. This is illustrated for Gaussian and Poisson models with lower bounds for
the mean parameter
Evaluation of Euler Fluxes for Hypersonic Flow Computations
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76462/1/AIAA-33735-324.pd
Step Position Distributions and the Pairwise Einstein Model for Steps on Crystal Surfaces
The Pairwise Einstein Model (PEM) of steps not only justifies the use of the
Generalized Wigner Distribution (GWD) for Terrace Width Distributions (TWDs),
it also predicts a specific form for the Step Position Distribution (SPD),
i.e., the probability density function for the fluctuations of a step about its
average position. The predicted form of the SPD is well approximated by a
Gaussian with a finite variance. However, the variance of the SPD measured from
either real surfaces or Monte Carlo simulations depends on , the
length of step over which it is calculated, with the measured variance
diverging in the limit . As a result, a length scale
can be defined as the value of at which the measured and
theoretical SPDs agree. Monte Carlo simulations of the terrace-step-kink model
indicate that , where is the correlation
length in the direction parallel to the steps, independent of the strength of
the step-step repulsion. can also be understood as the length over
which a {\em single} terrace must be sampled for the TWD to bear a "reasonable"
resemblence to the GWD.Comment: 4 pages, 3 figure
Propane on Titan
We present the first observations of propane (CH) on Titan that
unambiguously resolve propane features from other numerous stratospheric
emissions. This is accomplished using a
spectrometer (TEXES) to observe propane's rotation-vibration band
near 748 cm. We find a best-fit fractional abundance of propane in
Titan's stratosphere of in the altitude range to
which we are sensitive (90-250 km or 13-0.24 mbar).Comment: accepted to ApJL 18 September 2003; See also:
http://www.gps.caltech.edu/~hroe/propane2003
A New Technique for Finding Needles in Haystacks: A Geometric Approach to Distinguishing Between a New Source and Random Fluctuations
We propose a new test statistic based on a score process for determining the
statistical significance of a putative signal that may be a small perturbation
to a noisy experimental background. We derive the reference distribution for
this score test statistic; it has an elegant geometrical interpretation as well
as broad applicability. We illustrate the technique in the context of a model
problem from high-energy particle physics. Monte Carlo experimental results
confirm that the score test results in a significantly improved rate of signal
detection.Comment: 5 pages, 4 figure
Gaseous argon time projection chamber with electroluminescence enhanced optical readout
Systematic uncertainties in accelerator oscillation neutrino experiments
arise mostly from nuclear models describing neutrino-nucleus interactions. To
mitigate these uncertainties, we can study neutrino-nuclei interactions with
detectors possessing enhanced hadron detection capabilities at energies below
the nuclear Fermi level. Gaseous detectors not only lower the particle
detection threshold but also enable the investigation of nuclear effects on
various nuclei by allowing for changes in the gas composition. This approach
provides valuable insights into the modelling of neutrino-nucleus interactions
and significantly reduces associated uncertainties. Here, we discuss the design
and first operation of a gaseous argon time projection chamber optically read.
The detector operates at atmospheric pressure and features a single stage of
electron amplification based on a thick GEM. Here, photons are produced with
wavelengths in the vacuum ultraviolet regime. In an optical detector the
primary constraint is the light yield. This study explores the possibility of
increasing the light yield by applying a low electric field downstream of the
ThGEM. In this region, called the electroluminescence gap, electrons propagate
and excite the argon atoms, leading to the subsequent emission of photons. This
process occurs without any further electron amplification, and it is
demonstrated that the total light yield increases up to three times by applying
moderate electric fields of the order of 3~kV/cm. Finally, an indirect method
is discussed for determining the photon yield per charge gain of a ThGEM,
giving a value of 18.3 photons detected per secondary electron
Spin Path Integrals and Generations
The spin of a free electron is stable but its position is not. Recent quantum
information research by G. Svetlichny, J. Tolar, and G. Chadzitaskos have shown
that the Feynman \emph{position} path integral can be mathematically defined as
a product of incompatible states; that is, as a product of mutually unbiased
bases (MUBs). Since the more common use of MUBs is in finite dimensional
Hilbert spaces, this raises the question "what happens when \emph{spin} path
integrals are computed over products of MUBs?" Such an assumption makes spin no
longer stable. We show that the usual spin-1/2 is obtained in the long-time
limit in three orthogonal solutions that we associate with the three elementary
particle generations. We give applications to the masses of the elementary
leptons.Comment: 20 pages, 2 figures, accepted at Foundations of Physic
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