21,482 research outputs found
On a functional equation appearing in characterization of distributions by the optimality of an estimate
Let be a second countable locally compact Abelian group containing no
subgroup topologically isomorphic to the circle group . Let
be a probability distribution on such that its characteristic function
does not vanish and for some satisfies the
equation Then is a
convolution of a Gaussian distribution and a distribution supported in the
subgroup of generated by elements of order 2
Synchronizing to the Environment: Information Theoretic Constraints on Agent Learning
We show that the way in which the Shannon entropy of sequences produced by an
information source converges to the source's entropy rate can be used to
monitor how an intelligent agent builds and effectively uses a predictive model
of its environment. We introduce natural measures of the environment's apparent
memory and the amounts of information that must be (i) extracted from
observations for an agent to synchronize to the environment and (ii) stored by
an agent for optimal prediction. If structural properties are ignored, the
missed regularities are converted to apparent randomness. Conversely, using
representations that assume too much memory results in false predictability.Comment: 6 pages, 5 figures, Santa Fe Institute Working Paper 01-03-020,
http://www.santafe.edu/projects/CompMech/papers/stte.htm
New insight into the physical state of solar system objects
The application of IUE to observations of solar system objects is summarized and a brief survey of discoveries made during the first two years of IUE operation is given
A study of the feasibility of ultraviolet spectrometry for cometary missions
Ultraviolet spectra fo the comet West obtained by sounding rocket experiments in 1976 are reproduced and interpreted in order to estimate the expected brightness of the emission features and determine the spatial extent of these features for the proposed Halley Flyby/Tempel 2 rendezvous and the possible Halley or Encke flybys close to perihelion. A coma model was constructed and evaluated for the physical condition of candidate targets such as heliocentric distance, gas production, and composition. In addition to brightness profiles, the neutral and ion densities of the principal species are also dervied. The brightness profiles can be used to determine the feasibility of utilizing the space telescope to provide supporting observations during the mission. Basic parameters identified are spectral range, wavelength resolution, spatial resolution, sensitivity and dynamic range, rejection of scattered light, and integration or accumulation time
Rocket and laboratory studies in aeronomy and astronomy
Data extracted from semi-annual status reports presented include: a list of all sounding rocket launches performed under NASA sponsorship; a list of Ph.D. and M.A. degrees awarded to students who worked in these programs; a summary bibliography of all publications through 1983; the most recent list of the publications from the IUE program; a summary of instrument development supported by the Johns Hopkins sounding rocket program; and a list of faculty and post-doctoral research associates whose work was supported by this grant
Rocket and laboratory studies in aeronomy and astrophysics
Progress from March 1, 1986 to August 31, 1986 is covered and includes the work performed in response to a proposal entitled A Spartan Payload for Spatially Resolved Spectroscopy of Extended Faint Sources in the Extreme Ultraviolet (EUV). During this period, one rocket was launched, the reflight of the payload to observe Halley's comet on March 13, 1986. Most of the effort during this period was concentrated on detailed mechanical and electronic design of a Spartan payload and on the reduction and analysis of the data from the two Halley rocket flights and from the UVX experiment which flew on STS-61C in January 1986
A Rigorous Proof of Fermi Liquid Behavior for Jellium Two-Dimensional Interacting Fermions
Using the method of continuous constructive renormalization group around the
Fermi surface, it is proved that a jellium two-dimensional interacting system
of Fermions at low temperature remains analytic in the coupling constant
for where is some numerical constant
and is the temperature. Furthermore in that range of parameters, the first
and second derivatives of the self-energy remain bounded, a behavior which is
that of Fermi liquids and in particular excludes Luttinger liquid behavior. Our
results prove also that in dimension two any transition temperature must be
non-perturbative in the coupling constant, a result expected on physical
grounds. The proof exploits the specific momentum conservation rules in two
dimensions.Comment: 4 pages, no figure
The Temperature and Density Structure of the Solar Corona. I. Observations of the Quiet Sun with the EUV Imaging Spectrometer (EIS) on Hinode
Measurements of the temperature and density structure of the solar corona
provide critical constraints on theories of coronal heating. Unfortunately, the
complexity of the solar atmosphere, observational uncertainties, and the
limitations of current atomic calculations, particularly those for Fe, all
conspire to make this task very difficult. A critical assessment of plasma
diagnostics in the corona is essential to making progress on the coronal
heating problem. In this paper we present an analysis of temperature and
density measurements above the limb in the quiet corona using new observations
from the EUV Imaging Spectrometer (EIS) on \textit{Hinode}. By comparing the Si
and Fe emission observed with EIS we are able to identify emission lines that
yield consistent emission measure distributions. With these data we find that
the distribution of temperatures in the quiet corona above the limb is strongly
peaked near 1 MK, consistent with previous studies. We also find, however, that
there is a tail in the emission measure distribution that extends to higher
temperatures. EIS density measurements from several density sensitive line
ratios are found to be generally consistent with each other and with previous
measurements in the quiet corona. Our analysis, however, also indicates that a
significant fraction of the weaker emission lines observed in the EIS
wavelength ranges cannot be understood with current atomic data.Comment: Submitted to Ap
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