63 research outputs found
The 1998 November 14 Occultation of GSC 0622-00345 by Saturn. II. Stratospheric Thermal Profile, Power Spectrum, and Gravity Waves
On 1998 November 14, Saturn and its rings occulted the star GSC 0622-00345.
The occultation latitude was 55.5 degrees S. This paper analyzes the 2.3 {\mu}m
light curve derived by Harrington & French. A fixed-baseline isothermal fit to
the light curve has a temperature of 140 +/- 3 K, assuming a mean molecular
mass of 2.35 AMU. The thermal profile obtained by numerical inversion is valid
between 1 and 60 {\mu}bar. The vertical temperature gradient is >0.2 K/km more
stable than the adiabatic lapse rate, but it still shows the
alternating-rounded-spiked features seen in many temperature gradient profiles
from other atmospheric occultations and usually attributed to breaking gravity
(buoyancy) waves. We conduct a wavelet analysis of the thermal profile, and
show that, even with our low level of noise, scintillation due to turbulence in
Earth's atmosphere can produce large temperature swings in light-curve
inversions. Spurious periodic features in the "reliable" region of a wavelet
amplitude spectrum can exceed 0.3 K in our data. We also show that gravity-wave
model fits to noisy isothermal light curves can lead to convincing wave
"detections". We provide new significance tests for localized wavelet
amplitudes, wave model fits, and global power spectra of inverted occultation
light curves by assessing the effects of pre- and post-occultation noise on
these parameters. Based on these tests, we detect several significant ridges
and isolated peaks in wavelet amplitude, to which we fit a gravity wave model.
We also strongly detect the global power spectrum of thermal fluctuations in
Saturn's atmosphere, which resembles the "universal" (modified Desaubies) curve
associated with saturated spectra of propagating gravity waves on Earth and
Jupiter.Comment: LaTeX/emulateapj, 13 pages, 7 figure
Is the Machine Smarter than the Theorist: Deriving Formulas for Particle Kinematics with Symbolic Regression
We demonstrate the use of symbolic regression in deriving analytical
formulas, which are needed at various stages of a typical experimental analysis
in collider phenomenology. As a first application, we consider kinematic
variables like the stransverse mass, , which are defined
algorithmically through an optimization procedure and not in terms of an
analytical formula. We then train a symbolic regression and obtain the correct
analytical expressions for all known special cases of in the
literature. As a second application, we reproduce the correct analytical
expression for a next-to-leading order (NLO) kinematic distribution from data,
which is simulated with a NLO event generator. Finally, we derive analytical
approximations for the NLO kinematic distributions after detector simulation,
for which no known analytical formulas currently exist.Comment: 15 pages, 13 figures, 8 table
Searching for Novel Chemistry in Exoplanetary Atmospheres using Machine Learning for Anomaly Detection
The next generation of telescopes will yield a substantial increase in the
availability of high-resolution spectroscopic data for thousands of exoplanets.
The sheer volume of data and number of planets to be analyzed greatly motivate
the development of new, fast and efficient methods for flagging interesting
planets for reobservation and detailed analysis. We advocate the application of
machine learning (ML) techniques for anomaly (novelty) detection to exoplanet
transit spectra, with the goal of identifying planets with unusual chemical
composition and even searching for unknown biosignatures. We successfully
demonstrate the feasibility of two popular anomaly detection methods (Local
Outlier Factor and One Class Support Vector Machine) on a large public database
of synthetic spectra. We consider several test cases, each with different
levels of instrumental noise. In each case, we use ROC curves to quantify and
compare the performance of the two ML techniques.Comment: Submitted to AAS Journals, 30 pages, 14 figure
Identifying the Group-Theoretic Structure of Machine-Learned Symmetries
Deep learning was recently successfully used in deriving symmetry
transformations that preserve important physics quantities. Being completely
agnostic, these techniques postpone the identification of the discovered
symmetries to a later stage. In this letter we propose methods for examining
and identifying the group-theoretic structure of such machine-learned
symmetries. We design loss functions which probe the subalgebra structure
either during the deep learning stage of symmetry discovery or in a subsequent
post-processing stage. We illustrate the new methods with examples from the
U(n) Lie group family, obtaining the respective subalgebra decompositions. As
an application to particle physics, we demonstrate the identification of the
residual symmetries after the spontaneous breaking of non-Abelian gauge
symmetries like SU(3) and SU(5) which are commonly used in model building.Comment: 10 pages, 8 figures, 2 table
Discovering Sparse Representations of Lie Groups with Machine Learning
Recent work has used deep learning to derive symmetry transformations, which
preserve conserved quantities, and to obtain the corresponding algebras of
generators. In this letter, we extend this technique to derive sparse
representations of arbitrary Lie algebras. We show that our method reproduces
the canonical (sparse) representations of the generators of the Lorentz group,
as well as the and families of Lie groups. This approach is
completely general and can be used to find the infinitesimal generators for any
Lie group.Comment: 14 pages, 6 figure
Midlatitude and highâlatitude electron density profiles in the ionosphere of Saturn obtained by Cassini radio occultation observations
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95024/1/jgra19781.pd
Cassini radio occultations of Saturn's ionosphere: Model comparisons using a constant water flux
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94688/1/grl22099.pd
Upper atmospheres and ionospheres of planets and satellites
The upper atmospheres of the planets and their satellites are more directly
exposed to sunlight and solar wind particles than the surface or the deeper
atmospheric layers. At the altitudes where the associated energy is deposited,
the atmospheres may become ionized and are referred to as ionospheres. The
details of the photon and particle interactions with the upper atmosphere
depend strongly on whether the object has anintrinsic magnetic field that may
channel the precipitating particles into the atmosphere or drive the
atmospheric gas out to space. Important implications of these interactions
include atmospheric loss over diverse timescales, photochemistry and the
formation of aerosols, which affect the evolution, composition and remote
sensing of the planets (satellites). The upper atmosphere connects the planet
(satellite) bulk composition to the near-planet (-satellite) environment.
Understanding the relevant physics and chemistry provides insight to the past
and future conditions of these objects, which is critical for understanding
their evolution. This chapter introduces the basic concepts of upper
atmospheres and ionospheres in our solar system, and discusses aspects of their
neutral and ion composition, wind dynamics and energy budget. This knowledge is
key to putting in context the observations of upper atmospheres and haze on
exoplanets, and to devise a theory that explains exoplanet demographics.Comment: Invited Revie
Jupiter Thermospheric General Circulation Model (JTGCM): Global structure and dynamics driven by auroral and Joule heating
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94793/1/jgre1837.pd
Processes of auroral thermal structure at Jupiter: Analysis of multispectral temperature observations with the Jupiter Thermosphere General Circulation Model
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95248/1/jgre2561.pd
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