4,442 research outputs found
Cournot Versus Supply Functions: What does the Data Tell us?
The liberalization of the electricity sector increases the need for realistic and robust models of the oligopolistic interaction of electricity firms. This paper compares the two most popular models: Cournot and the Supply Function Equilibrium (SFE), and tests which model describes the observed market data best. Using identical demand and supply specifications, both models are calibrated to the German electricity market by varying the contract cover of firms. Our results show that each model explains an identical fraction of the observed price variation. We therefore suggest using Cournot models for short term analysis, as more market details, such as network constraints, can be accommodated. As the SFE model is less sensitive to the choice of the calibration parameters, it might be more appropriate for long term analysis, such as the study of a merger.supply function equilibrium;Cournot competition;electricity markets
Cournot versus Supply Functions: What Does the Data tell us?
The liberalization of the electricity sector increases the need for realistic and robust models of the oligopolistic interaction of electricity firms. This paper compares the two most popular models: Cournot and the Supply Function Equilibrium (SFE), and tests which model describes the observed market data best. Using identical demand and supply specifications, both models are calibrated to the German electricity market by varying the contract cover of firms. Our results show that each model explains an identical fraction of the observed price variation. We therefore suggest using Cournot models for short term analysis, as more market details, such as network constraints, can be accommodated. As the SFE model is less sensitive to the choice of the calibration parameters, it might be more appropriate for long term analysis, such as the study of a merger.supply function equilibrium;Cournot competition;electricity markets
Bit-interleaved coded modulation in the wideband regime
The wideband regime of bit-interleaved coded modulation (BICM) in Gaussian
channels is studied. The Taylor expansion of the coded modulation capacity for
generic signal constellations at low signal-to-noise ratio (SNR) is derived and
used to determine the corresponding expansion for the BICM capacity. Simple
formulas for the minimum energy per bit and the wideband slope are given. BICM
is found to be suboptimal in the sense that its minimum energy per bit can be
larger than the corresponding value for coded modulation schemes. The minimum
energy per bit using standard Gray mapping on M-PAM or M^2-QAM is given by a
simple formula and shown to approach -0.34 dB as M increases. Using the low SNR
expansion, a general trade-off between power and bandwidth in the wideband
regime is used to show how a power loss can be traded off against a bandwidth
gain.Comment: Submitted to IEEE Transactions on Information Theor
Bit-Interleaved Coded Modulation Revisited: A Mismatched Decoding Perspective
We revisit the information-theoretic analysis of bit-interleaved coded
modulation (BICM) by modeling the BICM decoder as a mismatched decoder. The
mismatched decoding model is well-defined for finite, yet arbitrary, block
lengths, and naturally captures the channel memory among the bits belonging to
the same symbol. We give two independent proofs of the achievability of the
BICM capacity calculated by Caire et al. where BICM was modeled as a set of
independent parallel binary-input channels whose output is the bitwise
log-likelihood ratio. Our first achievability proof uses typical sequences, and
shows that due to the random coding construction, the interleaver is not
required. The second proof is based on the random coding error exponents with
mismatched decoding, where the largest achievable rate is the generalized
mutual information. We show that the generalized mutual information of the
mismatched decoder coincides with the infinite-interleaver BICM capacity. We
also show that the error exponent -and hence the cutoff rate- of the BICM
mismatched decoder is upper bounded by that of coded modulation and may thus be
lower than in the infinite-interleaved model. We also consider the mutual
information appearing in the analysis of iterative decoding of BICM with EXIT
charts. We show that the corresponding symbol metric has knowledge of the
transmitted symbol and the EXIT mutual information admits a representation as a
pseudo-generalized mutual information, which is in general not achievable. A
different symbol decoding metric, for which the extrinsic side information
refers to the hypothesized symbol, induces a generalized mutual information
lower than the coded modulation capacity.Comment: submitted to the IEEE Transactions on Information Theory. Conference
version in 2008 IEEE International Symposium on Information Theory, Toronto,
Canada, July 200
Superconducting phase formation in random neck syntheses: a study of the Y-Ba-Cu-O system by magneto-optics and magnetometry
Magneto-optical imaging and magnetization measurements were applied to
investigate local formation of superconducting phase effected by a random neck
synthesis in Y-Ba-Cu-O system. Polished pellets of strongly inhomogeneous
ceramic samples show clearly the appearance of superconducting material in the
intergrain zones of binary primary particles reacted under different
conditions. Susceptibility measurements allows evaluation of superconducting
critical temperature, which turned out to be close to that of optimally doped
YBCO.Comment: 6 pages, 11 figure
Op zoek naar een alternatief voor de ChangeMirror: een onderzoek binnen Atrium MC naar betekenisgeving binnen sociale netwerken tijdens organsiatieverandering
in deze scriptie wordt verslag gedaan van een onderzoek naar de vraag in hoeverre de onderzoeksmethode van Rentsch een adequaat alternatief is voor de ChangeMirror bij het meten van betekenisgeving in netwerken tijdens organisatieveranderingen
On upscaling heat conductivity for a class of industrial problems
Calculating effective heat conductivity for a class of industrial problems is discussed. The considered composite materials are glass and metal foams, fibrous materials, and the like, used in isolation or in advanced heat exchangers. These materials are characterized by a very complex internal structure, by low volume fraction of the higher conductive material (glass or metal), and by a large volume fraction of the air. The homogenization theory (when applicable), allows to calculate the effective heat conductivity of composite media by postprocessing the solution of special cell problems for representative elementary volumes (REV). Different formulations of such cell problems are considered and compared here. Furthermore, the size of the REV is studied numerically for some typical materials. Fast algorithms for solving the cell problems for this class of problems, are presented and discussed
Saprolegnia diclina IIIA and S. parasitica employ different infection strategies when colonizing eggs of Atlantic salmon, Salmo salar L.
Acknowledgements The work has been funded by the European Commission through the EU Marie Curie ITN project SAPRO (238550) (MMS, AW). We would also like to acknowledge support from the BBSRC and the University of Aberdeen (PvW) and Landcatch and AquaGen for providing salmon eggs. Elin Rolen's assistance with sequencing of the strains is highly appreciated.Peer reviewedPublisher PD
WASP-33: The first delta Scuti exoplanet host star
We report the discovery of photometric oscillations in the host star of the
exoplanet WASP-33 b (HD 15082). The data were obtained in the R band in both
transit and out-of-transit phases from the 0.3-m telescope and the Montcabrer
Observatory and the 0.8-m telescope at the Montsec Astronomical Observatory.
Proper fitting and subsequent removal of the transit signal reveals stellar
photometric variations with a semi-amplitude of about 1 mmag. The detailed
analysis of the periodogram yields a structure of significant signals around a
frequency of 21 cyc per day, which is typical of delta Scuti-type variable
stars. An accurate study of the power spectrum reveals a possible
commensurability with the planet orbital motion with a factor of 26, but this
remains to be confirmed with additional time-series data that will permit the
identification of the significant frequencies. These findings make WASP-33 the
first transiting exoplanet host star with delta Sct variability and a very
interesting candidate to search for star-planet interactions.Comment: 5 pages, 6 figures. Revised version accepted for publication in A&A
Letter
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