499 research outputs found
Bayesians Can Learn From Old Data
In a widely-cited paper, Glymour (Theory and Evidence, Princeton, N. J.: Princeton University Press, 1980, pp. 63-93) claims to show that Bayesians cannot team from old data. His argument contains an elementary error. I explain exactly where Glymour went wrong, and how the problem should be handled correctly. When the problem is fixed, it is seen that Bayesians, just like logicians, can indeed learn from old data.Astronom
Orbital theories of outer planet satellites
An analytical theory of Mimas and Tethys was developed, retaining terms which produce perturbations of the order of + or - 10 km. The theory uses a novel set of variables, and was developed with the Hori-Lie algorithm, using the algebraic manipulation language TRIGMAN. the perturbations were implemented by means of FORTRAN subroutines produced by the computer
Equivalence of the perturbation theories of Hori and Deprit
Equivalence of perturbation theories of Hori and Deprit, based on Poisson brackets, and computer calculations through sixth orde
IGDS/TRAP Interface Program (ITIP). Detailed Design Specification (DDS)
The software modules which comprise the IGDS/TRAP Interface Program are described. A hierarchical input processing output (HIPO) chart for each user command is given. The description consists of: (1) function of the user command; (2) calling sequence; (3) moduls which call this use command; (4) modules called by this user command; (5) IGDS commands used by this user command; and (6) local usage of global registers. Each HIPO contains the principal functions performed within the module. Also included with each function are a list of the inputs which may be required to perform the function and a list of the outputs which may be created as a result of performing the function
Vacuum Energy: Cosmological Constant or Quintessence?
For a flat universe presently dominated by smooth energy, either cosmological
constant (LCDM) or quintessence (QCDM), we calculate the asymptotic collapsed
mass fraction as function of the present ratio of smooth energy to matter
energy . Identifying the normalized collapsed fraction as a
conditional probability for habitable galaxies, we observe that the observed
present ratio is likely in LCDM, but more likely in QCDM.
Inverse application of Bayes' Theorem makes the Anthropic Principle a
predictive scientific principle: the data implies that the prior probability
for must be essentially flat over the anthropically allowed
range. Interpreting this prior as a distribution over {\em theories} lets us
predict that any future theory of initial conditions must be indifferent to
. This application of the Anthropic Principle does not demand the
existence of other universes.Comment: 17 pages AAS LATEX, including 2 tables, 3 figures (Postscript
Detection of a Third Planet in the HD 74156 System Using the Hobby-Eberly Telescope
We report the discovery of a third planetary mass companion to the G0 star HD
74156. High precision radial velocity measurements made with the Hobby-Eberly
Telescope aided the detection of this object. The best fit triple Keplerian
model to all the available velocity data yields an orbital period of 347 days
and minimum mass of 0.4 M_Jup for the new planet. We determine revised orbital
periods of 51.7 and 2477 days, and minimum masses of 1.9 and 8.0 M_Jup
respectively for the previously known planets. Preliminary calculations
indicate that the derived orbits are stable, although all three planets have
significant orbital eccentricities (e = 0.64, 0.43, and 0.25). With our
detection, HD 74156 becomes the eighth normal star known to host three or more
planets. Further study of this system's dynamical characteristics will likely
give important insight to planet formation and evolutionary processes.Comment: 24 pages, 4 tables, 6 figures. Accepted for publication in ApJ. V2
fixed table 4 page overrun. V3 added reference
Type Ia Supernovae, Evolution, and the Cosmological Constant
We explore the possible role of evolution in the analysis of data on SNe Ia
at cosmological distances. First, using a variety of simple sleuthing
techniques, we find evidence that the properties of the high and low redshift
SNe Ia observed so far differ from one another. Next, we examine the effects of
including simple phenomenological models for evolution in the analysis. The
result is that cosmological models and evolution are highly degenerate with one
another, so that the incorporation of even very simple models for evolution
makes it virtually impossible to pin down the values of and
, the density parameters for nonrelativistic matter and for the
cosmological constant, respectively. Moreover, we show that if SNe Ia evolve
with time, but evolution is neglected in analyzing data, then, given enough SNe
Ia, the analysis hones in on values of and which
are incorrect. Using Bayesian methods, we show that the probability that the
cosmological constant is nonzero (rather than zero) is unchanged by the SNe Ia
data when one accounts for the possibility of evolution, provided that we do
not discriminate among open, closed and flat cosmologies a priori. The case for
nonzero cosmological constant is stronger if the Universe is presumed to be
flat, but still depends sensitively on the degree to which the peak
luminosities of SNe Ia evolve as a function of redshift. The estimated value of
, however, is only negligibly affected by accounting for possible
evolution.Comment: 45 pages, 15 figures; accepted for publication in The Astrophysical
Journal. Minor revisions and clarifications made including addition of recent
reference
Bayesian Analysis of Two Stellar Populations in Galactic Globular Clusters II: NGC 5024, NGC 5272, and NGC 6352
We use Cycle 21 Hubble Space Telescope (HST) observations and HST archival
ACS Treasury observations of Galactic Globular Clusters to find and
characterize two stellar populations in NGC 5024 (M53), NGC 5272 (M3), and NGC
6352. For these three clusters, both single and double-population analyses are
used to determine a best fit isochrone(s). We employ a sophisticated Bayesian
analysis technique to simultaneously fit the cluster parameters (age, distance,
absorption, and metallicity) that characterize each cluster. For the
two-population analysis, unique population level helium values are also fit to
each distinct population of the cluster and the relative proportions of the
populations are determined. We find differences in helium ranging from
0.05 to 0.11 for these three clusters. Model grids with solar
-element abundances ([/Fe] =0.0) and enhanced -elements
([/Fe]=0.4) are adopted.Comment: ApJ, 21 pages, 14 figures, 7 table
An m sin i = 24 Earth Mass Planetary Companion To The Nearby M Dwarf GJ 176
We report the detection of a planetary companion with a minimum mass of m sin
i = 0.0771 M_Jup = 24.5 M_Earth to the nearby (d = 9.4 pc) M2.5V star GJ 176.
The star was observed as part of our M dwarf planet search at the Hobby-Eberly
Telescope (HET). The detection is based on 5 years of high-precision
differential radial velocity (RV) measurements using the
High-Resolution-Spectrograph (HRS). The orbital period of the planet is 10.24
d. GJ 176 thus joins the small (but increasing) sample of M dwarfs hosting
short-periodic planets with minimum masses in the Neptune-mass range. Low mass
planets could be relatively common around M dwarfs and the current detections
might represent the tip of a rocky planet population.Comment: 13 pages preprint, 3 figures, submitted to Ap
High-Frequency network activity, global increase in Neuronal Activity, and Synchrony Expansion Precede Epileptic Seizures In Vitro
How seizures start is a major question in epilepsy research. Preictal EEG changes occur in both human patients and animal models, but their underlying mechanisms and relationship with seizure initiation remain unknown. Here we demonstrate the existence, in the hippocampal CA1 region, of a preictal state characterized by the progressive and global increase in neuronal activity associated with a widespread buildup of low-amplitude high-frequency activity (HFA) (100 Hz) and reduction in system complexity.HFAis generated by the firing of neurons, mainly pyramidal cells, at much lower frequencies. Individual cycles ofHFAare generated by the near-synchronous (within 5 ms) firing of small numbers of pyramidal cells. The presence of HFA in the low-calcium model implicates nonsynaptic synchronization; the presence of very similar HFA in the high-potassium model shows that it does not depend on an absence of synaptic transmission. Immediately before seizure onset, CA1 is in a state of high sensitivity in which weak depolarizing or synchronizing perturbations can trigger seizures. Transition to seizure is haracterized by a rapid expansion and fusion of the neuronal populations responsible for HFA, associated with a progressive slowing of HFA, leading to a single, massive, hypersynchronous cluster generating the high-amplitude low-frequency activity of the seizure
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