18,493 research outputs found
Precise measurements of inflationary features with 21 cm observations
Future observations of 21~cm emission using HI intensity mapping will enable
us to probe the large scale structure of the Universe over very large survey
volumes within a reasonable observation time. We demonstrate that the
three-dimensional information contained in such surveys will be an extremely
powerful tool in searching for features that were imprinted in the primordial
power spectrum and bispectrum during inflation. Here we focus on the "resonant"
and "step" inflation models, and forecast the potential of upcoming 21~cm
experiments to detect these inflationary features in the observable power- and
bispectrum. We find that the full scale Tianlai experiment and the Square
Kilometre Array (SKA) have the potential to improve on the sensitivity of
current Cosmic Microwave Background (CMB) experiments by several orders of
magnitude.Comment: 7 pages, 3 figures, replaced with revised versio
The orbital periods of subdwarf B binaries produced by the first stable Roche overflow channel
Long-orbital-period subdwarf B (sdB) stars with main-sequence companions are
believed to be the product of stable Roche Lobe overflow (RLOF), a scenario
challenged by recent observations. Here we represent the results of a
systematic study of the orbital-period distribution of sdB binaries in this
channel using detailed binary evolution calculations. We show that the observed
orbital-period distribution of long-period sdB binaries can be well explained
by this scenario. Furthermore, we find that, if the progenitors of the sdB
stars have initial masses below the helium flash mass, the sdB binaries
produced from stable RLOF follow a unique mass -- orbital period relation for a
given metallicity ; increasing the orbital period from to \,d corresponds to increasing the mass of the sdB star from to
for . We suggest that the longest sdB binaries
(with orbital period \,d) could be the result of atmospheric RLOF. The
mass -- orbital period relation can be tested observationally if the mass of
the sdB star can be determined precisely, e.g.\ from asteroseismology. Using
this relation, we revise the orbital period distribution of sdB binaries
produced by the first stable RLOF channel for the best fitting model of Han et
al (2003), and show that the orbital period has a peak around 830\,d.Comment: 8 pages, 2 figures, accepted for publication in MNRA
Representing fuzzy decision tables in a fuzzy relational database environment.
In this paper the representation of decision tables in a relational database environment is discussed. First, crisp decision tables are defined. Afterwards a technique to represent decision tables in a relational system is presented. Next, fuzzy extensions are made to crisp decision tables in order to deal with imprecision and uncertainty. As a result, with crisp decision tables as special cases fuzzy decision tables are defined which include fuzziness in the conditions as well as in the actions. Analogous to the crisp case, it is demonstrated how fuzzy decision tables can be stored in a fuzzy relational database environment. Furthermore, consultation of these tables is discussed using fuzzy queries.Decision making;
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