1,154 research outputs found
Canonical time-frequency, time-scale, and frequency-scale representations of time-varying channels
Mobile communication channels are often modeled as linear time-varying
filters or, equivalently, as time-frequency integral operators with finite
support in time and frequency. Such a characterization inherently assumes the
signals are narrowband and may not be appropriate for wideband signals. In this
paper time-scale characterizations are examined that are useful in wideband
time-varying channels, for which a time-scale integral operator is physically
justifiable. A review of these time-frequency and time-scale characterizations
is presented. Both the time-frequency and time-scale integral operators have a
two-dimensional discrete characterization which motivates the design of
time-frequency or time-scale rake receivers. These receivers have taps for both
time and frequency (or time and scale) shifts of the transmitted signal. A
general theory of these characterizations which generates, as specific cases,
the discrete time-frequency and time-scale models is presented here. The
interpretation of these models, namely, that they can be seen to arise from
processing assumptions on the transmit and receive waveforms is discussed. Out
of this discussion a third model arises: a frequency-scale continuous channel
model with an associated discrete frequency-scale characterization.Comment: To appear in Communications in Information and Systems - special
issue in honor of Thomas Kailath's seventieth birthda
An assessment of ring seine fishery in Kerala through surplus production model
Outboard ring seine is one of the major gears operated in Kerala which
contributes about 37% of the total landings in the State. Oil sardine (Sardinella
longiceps) and Indian mackerel (Rastrelliger kanagurta) are the two species that
account for about 84% of the ring seine catch. The ring seine fishery began in
the State by mid eighties and grown into a major fishery over the years. An
assessment of the ring seine fishery in the state through nonequilibrium surplus
production model was made in this study by using time series data on catch and
effort of ring seine in Kerala during 1986-2004. An index of relative biomass at
and an index of net production rate mt were computed, apart from fishing
mortality rates Ft, maximum sustainable yield (MSY), effort corresponding to
MSY and biomass corresponding to MSY. Results revealed that the ring seine
fishery in Kerala is close to the state of equilibrium. Behaviour of mt and Ft were
almost similar showing characteristics of fully developed fishery and the pattern
of their difference mt-Ft indicated that the status of ring seine fishery in Kerala
is close to the optimal level at present
Bayesian evidence for two companions orbiting HIP 5158
We present results of a Bayesian analysis of radial velocity (RV) data for
the star HIP 5158, confirming the presence of two companions and also
constraining their orbital parameters. Assuming Keplerian orbits, the
two-companion model is found to be e^{48} times more probable than the
one-planet model, although the orbital parameters of the second companion are
only weakly constrained. The derived orbital periods are 345.6 +/- 2.0 d and
9017.8 +/- 3180.7 d respectively, and the corresponding eccentricities are 0.54
+/- 0.04 and 0.14 +/- 0.10. The limits on planetary mass (m \sin i) and
semimajor axis are (1.44 +/- 0.14 M_{J}, 0.89 +/- 0.01 AU) and (15.04 +/- 10.55
M_{J}, 7.70 +/- 1.88 AU) respectively. Owing to large uncertainty on the mass
of the second companion, we are unable to determine whether it is a planet or a
brown dwarf. The remaining `noise' (stellar jitter) unaccounted for by the
model is 2.28 +/- 0.31 m/s. We also analysed a three-companion model, but found
it to be e^{8} times less probable than the two-companion model.Comment: 5 pages, 4 figures, 3 tables. Added a couple of figures showing the
residuals after one and two companion fits. Accepted for publication in MNRAS
Letter
Fish Trend at major mechnised centres
During the last two decades the marine fish
landings in India by the mechanised sedtor have
been steadily increasing. Presently, ttiey form
about 60% of the total landings
Marine Fish Trend at major mechanised centres
During the last two decades the marine fish
landings in India by the mechanised sector 4iave
been steadily increasing. Presently, they form
about 60% of the total landings
Fish Trend at major marine mechanised centres
During the last two decades the marine fish
landings in India by the mechanised sector have,
been steadily increasing. Presently, they form
about 60% of the total landings
Gaining insight into exclusive and common transcriptomic features linked with biotic stress responses in Malus
Identifying key information in transcriptomic data is very important, especially when the “omic” study deals with plant responses to stresses in field conditions where a high number of variables and disturbing factors may affect the analysis. In this meta-analysis we collected 12 transcriptomic works in Malus in order to identify which key genes, proteins, gene categories are involved in general plant pathological conditions and those features linked with exclusive biotic stress responses. Those genes that are only related with molecular responses to pathogen attacks and those linked with other plant physiological processes were identified. A pipeline composed by pathway and gene set enrichment analysis, protein-protein interaction networks and gene visualization tools was employed. A total of 13,230 genes of the 12 studies were analyzed with functional data mining tools: 5,215 were upregulated, 8,015 were downregulated. Gene set enrichment analysis pointed out that photosynthesis was inhibited by Erwinia amylovora and fungal pathogens. Different hormonal crosstalk was linked with responses to different pathogens. Gibberellin-related pathways, ABA-related were mostly repressed by fungal pathogens. Relating to transcription factors, genes encoding MYBs and WRKY2 were downregulated by fungal pathogens and 12 WRKYs were commonly regulated by different biotic stresses The protein-protein interaction analysis discovered the presence of several proteins affected by more than one biotic stress including a WRKY40 and some highly interactive proteins such as heat shock proteins. This study represents a first preliminary curated meta-analysis of apple transcriptomic responses to biotic stresses
A Uniformly Derived Catalogue of Exoplanets from Radial Velocities
A new catalogue of extrasolar planets is presented by re-analysing a
selection of published radial velocity data sets using EXOFIT (Balan & Lahav
2009). All objects are treated on an equal footing within a Bayesian framework,
to give orbital parameters for 94 exoplanetary systems. Model selection
(between one- and two-planet solutions) is then performed, using both a visual
flagging method and a standard chi-square analysis, with agreement between the
two methods for 99% of the systems considered. The catalogue is to be made
available online, and this 'proof of concept' study may be maintained and
extended in the future to incorporate all systems with publicly available
radial velocity data, as well as transit and microlensing data.Comment: 16 pages, 6 figures, 6 table
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