10,478 research outputs found
Permanent structures for irrigation farms
With the close of the irrigation season many farmers have put away their shovels with sighs of relief. Now no doubt they have forgotten, due to the passage of time, the many battles with unruly water. Perhaps they have even forgotten the arduous hours of shovelling and the attendant backaches
Meta-Learning for Phonemic Annotation of Corpora
We apply rule induction, classifier combination and meta-learning (stacked
classifiers) to the problem of bootstrapping high accuracy automatic annotation
of corpora with pronunciation information. The task we address in this paper
consists of generating phonemic representations reflecting the Flemish and
Dutch pronunciations of a word on the basis of its orthographic representation
(which in turn is based on the actual speech recordings). We compare several
possible approaches to achieve the text-to-pronunciation mapping task:
memory-based learning, transformation-based learning, rule induction, maximum
entropy modeling, combination of classifiers in stacked learning, and stacking
of meta-learners. We are interested both in optimal accuracy and in obtaining
insight into the linguistic regularities involved. As far as accuracy is
concerned, an already high accuracy level (93% for Celex and 86% for Fonilex at
word level) for single classifiers is boosted significantly with additional
error reductions of 31% and 38% respectively using combination of classifiers,
and a further 5% using combination of meta-learners, bringing overall word
level accuracy to 96% for the Dutch variant and 92% for the Flemish variant. We
also show that the application of machine learning methods indeed leads to
increased insight into the linguistic regularities determining the variation
between the two pronunciation variants studied.Comment: 8 page
Scaling Laws for Advection Dominated Flows: Applications to Low Luminosity Galactic Nuclei
We present analytical scaling laws for self-similar advection dominated
flows. The spectra from these systems range from 10 - 10 Hz, and
are determined by considering cooling of electrons through synchrotron,
bremsstrahlung, and Compton processes. We show that the spectra can be quite
accurately reproduced without detailed numerical calculations, and that there
is a strong testable correlation between the radio and X-ray fluxes from these
systems. We describe how different regions of the spectrum scale with the mass
of the accreting black hole, , the accretion rate of the gas, , and
the equilibrium temperature of the electrons, . We show that the universal
radio spectral index of 1/3 observed in most elliptical galaxies (Slee et al.
1994) is a natural consequence of self-absorbed synchrotron radiation from
these flows. We also give expressions for the total luminosity of these flows,
and the critical accretion rate, , above which the advection
solutions cease to exist. We find that for most cases of interest the
equilibrium electron temperature is fairly insensitive to , , and
parameters in the model. We apply these results to low luminosity black holes
in galactic nuclei. We show that the problem posed by Fabian & Canizares (1988)
of whether bright elliptical galaxies host dead quasars is resolved, as pointed
out recently by Fabian & Rees (1995), by considering advection-dominated flows.Comment: 30 pages, 5 postscript files. Accepted to ApJ. Also available
http://cfa-www.harvard.edu/~rohan/publications.htm
Self-interacting dark matter and Higgs bosons in the SU(3)_C x SU(3)_L x U(1)_N model with right-handed neutrinos
We investigate the possibility that dark matter could be made from CP-even
and CP- odd Higgs bosons in the SU(3)_C X SU(3)_L X U(1)_N (3-3-1) model with
right-handed neutrinos. This self-interacting dark matters are stable without
imposing of new symmetry and should be weak-interacting.Comment: 7 pages, Latex, To appear in Europhys. Let
Optical vernier technique for in-situ measurement of the length of long Fabry-Perot cavities
We propose a method for in-situ measurement of the length of kilometer size
Fabry-Perot cavities in laser gravitational wave detectors. The method is based
on the vernier, which occurs naturally when the laser incident on the cavity
has a sideband. By changing the length of the cavity over several wavelengths
we obtain a set of carrier resonances alternating with sideband resonances.
From the measurement of the separation between the carrier and a sideband
resonance we determine the length of the cavity. We apply the technique to the
measurement of the length of a Fabry-Perot cavity in the Caltech 40m
Interferometer and discuss the accuracy of the technique.Comment: LaTeX 2e, 12 pages, 4 figure
Galaxy Groups in the SDSS DR4: II. halo occupation statistics
We investigate various halo occupation statistics using a large galaxy group
catalogue constructed from the SDSS DR4 with an adaptive halo-based group
finder. The conditional luminosity function (CLF) is measured separately for
all, red and blue galaxies, as well as in terms of central and satellite
galaxies. The CLFs for central and satellite galaxies can be well modelled with
a log-normal distribution and a modified Schechter form, respectively. About
85% of the central galaxies and about 80% of the satellite galaxies in halos
with masses M_h\ga 10^{14}\msunh are red galaxies. These numbers decrease to
50% and 40%, respectively, in halos with M_h \sim 10^{12}\msunh. For halos of
a given mass, the distribution of the luminosities of central galaxies, ,
has a dispersion of about 0.15 dex. The mean luminosity (stellar mass) of the
central galaxies scales with halo mass as
() for halos with masses M\gg 10^{12.5}\msunh, and
both relations are significantly steeper for less massive halos. We also
measure the luminosity (stellar mass) gap between the first and second
brightest (most massive) member galaxies, (). These gap statistics, especially in halos with M_h \la
10^{14.0}\msunh, indicate that the luminosities of central galaxies are
clearly distinct from those of their satellites. The fraction of fossil groups,
defined as those groups with , ranges from for groups with M_h\sim 10^{14}\msunh to 18-60% for groups with
M_h\sim 10^{13}\msunh. Finally, we measure the fraction of satellites, which
changes from for galaxies with \rmag\sim -22.0 to for
galaxies with \rmag\sim -17.0. (abridged)Comment: 16 pages, 11 figures. Accepted for publication in Ap
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