1,602 research outputs found
The Extended-window Channel Estimator For Iterative Channel-and-symbol Estimation
The application of the expectation-maximization (EM) algorithm to channel estimation results in a well-known iterative channel-and-symbol estimator (ICSE). The EM-ICSE iterates between a symbol estimator based on the forward-backward recursion (BCJR equalizer) and a channel estimator, and may provide approximate maximum-likelihood blind or semiblind channel estimates. Nevertheless, the EM-ICSE has high complexity, and it is prone to misconvergence. In this paper, we propose the extended-window (EW) estimator, a novel channel estimator for ICSE that can be used with any soft-output symbol estimator. Therefore, the symbol estimator may be chosen according to performance or complexity specifications. We show that the EW-ICSE, an ICSE that uses the EW estimator and the BCJR equalizer, is less complex and less susceptible to misconvergence than the EM-ICSE. Simulation results reveal that the EW-ICSE may converge faster than the EM-ICSE. © 2005 Hindawi Publishing Corporation.200529299Barry, J.R., Lee, E.A., Messerschmitt, D.G., (2003) Digital Communications, , Kluwer Academic Publishers, Norwell, Mass, USA, 3rd editionAyadi, J., De Carvalho, E., Slock, D.T.M., Blind and semi-blind maximum likelihood methods for FIR multichannel identification (1998) Proc. IEEE International Conference on Acoustics, Speech, Signal Processing (ICASSP'98), 6, pp. 3185-3188. , Seattle, Wash, USA, MayFeder, M., Catipovic, J.A., Algorithms for joint channel estimation and data recovery-application to equalization in underwater communications (1991) IEEE J. Oceanic Eng., 16 (1), pp. 42-55Kaleh, G.K., Vallet, R., Joint parameter estimation and symbol detection for linear or nonlinear unknown channels (1994) IEEE Trans. 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Commun., 50 (5), pp. 754-767Lopes, R.R., Barry, J.R., Soft-output decision-feedback equalization with a priori information (2003) IEEE Global Communications Conference (GLOBECOM'03), 3, pp. 1705-1709. , San Francisco, Calif, USA, DecemberPoor, H.V., (1994) An Introduction to Signal Detection and Estimation, , Springer-Verlag, New York, NY, USA, 2nd editionMontemayor, C.A., Flikkema, P.G., Near-optimum iterative estimation of dispersive multipath channels (1998) IEEE 48th Vehicular Technology Conference (VTC'98), 3, pp. 2246-2250. , Ottawa, ON, Canada, MaySandell, M., Luschi, C., Strauch, P., Yan, R., Iterative channel estimation using soft decision feedback (1998) IEEE Global Communications Conference (GLOBECOM'98), 6, pp. 3728-3733. , Sydney, NSW, Australia, Novembe
Application of nanotechnology in the agro-food sector
Nanotechnology is an emerging field of research that has been widely applied in different scientific and engineering areas. The agro-food sector is not an exception, which
considers its applicability in several areas of major interest for both consumers and producers. This review considers major concepts related to nanostructures and nano-based instruments used in the food sector, as well as their applications in agro-food products. Food
safety through the use of nanosensors for pathogen detection, smart packaging, and valorisation of food products by nanoencapsulation/nanodelivery of food ingredients (e.g. flavours) are examples of important areas of nanotechnology. Consumers' apprehension regarding food stability and safety issues is also considered.info:eu-repo/semantics/publishedVersio
Walls of Marginal Stability and Dyon Spectrum in N=4 Supersymmetric String Theories
The spectrum of quarter BPS dyons in N=4 supersymmetric string theories can
change as the asymptotic moduli cross walls of marginal stability on which the
dyon can break apart into a pair of half BPS states. In this paper we classify
these marginal stability walls and examine this phenomenon in the context of
exact dyon spectrum found in a class of N=4 supersymmetric string theories. We
argue that the dyon partition functions in different domains separated by
marginal stability walls are the same, but the choice of integration contour
needed for extracting the degeneracies from the partition function differ in
these different regions. We also find that in the limit of large charges the
change in the degeneracy is exponentially suppressed compared to the leading
contribution. This is consistent with the fact that in the computation of black
hole entropy we do not encounter any change as the asymptotic moduli fields
move across the walls of marginal stability. Finally we carry out some tests of
S-duality invariance in the theory.Comment: LateX file, 1 figure, 42 pages; v2 more tests of S-duality added with
complete proof for all N<7; v3: minor change
Effect of soil grain size distribution on the mechanical damage of nonwoven geotextiles under repeated loading
Installation processes (which induce mechanical damage) may cause undesirable changes on the properties of geosynthetics, affecting their performance. This work evaluates the effect of mechanical damage on the short-term tensile behaviour of two nonwoven geotextiles (with different masses per unit area). The geotextiles were damaged in laboratory using a standardised procedure and an artificial aggregate (corundum) and eight other soils. The damage induced was characterized using wide-width tensile tests. Results showed reductions of the tensile strength of both geotextiles, which depended on the grain size distribution and uniformity of the soils and on the mass per unit area of the geotextiles. The reduction in tensile strength provoked by corundum was higher than the decreases caused by most of the other soils. The mechanical damage tests also led to a reduction of elongation at maximum load and an increase of stiffness
On the dyon partition function in N=2 theories
We study the entropy function of two N =2 string compactifications obtained
as freely acting orbifolds of N=4 theories : the STU model and the FHSV model.
The Gauss-Bonnet term for these compactifications is known precisely. We apply
the entropy function formalism including the contribution of this four
derivative term and evaluate the entropy of dyons to the first subleading order
in charges for these models. We then propose a partition function involving the
product of three Siegel modular forms of weight zero which reproduces the
degeneracy of dyonic black holes in the STU model to the first subleading order
in charges. The proposal is invariant under all the duality symmetries of the
STU model. For the FHSV model we write down an approximate partition function
involving a Siegel modular form of weight four which captures the entropy of
dyons in the FHSV model in the limit when electric charges are much larger than
magnetic charges.Comment: 48 page
Three String Junction and N=4 Dyon Spectrum
The exact spectrum of dyons in a class of N=4 supersymmetric string theories
gives us information about dyon spectrum in N=4 supersymmetric gauge theories.
This in turn can be translated into prediction about the BPS spectrum of three
string junctions on a configuration of three parallel D3-branes. We show that
this prediction agrees with the known spectrum of three string junction in
different domains in the moduli space separated by walls of marginal stability.Comment: LaTeX file, 14 page
Rare Decay Modes of Quarter BPS Dyons
The degeneracy of quarter BPS dyons in N=4 supersymmetric string theories is
known to jump across walls of marginal stability on which a quarter BPS dyon
can decay into a pair of half BPS dyons. We show that as long as the electric
and magnetic charges of the original dyon are primitive elements of the charge
lattice, the subspaces of the moduli space on which a quarter BPS dyon becomes
marginally unstable against decay into a pair of quarter BPS dyons or a half
BPS dyon and a quarter BPS dyon are of codimension two or more. As a result any
pair of generic points in the moduli space can be connected by a path avoiding
these subspaces and there is no jump in the spectrum associated with these
subspaces.Comment: LaTeX file, 9 pages; v2: a minor logical error corrected with no
change in the result
Two Centered Black Holes and N=4 Dyon Spectrum
The exact spectrum of dyons in a class of N=4 supersymmetric string theories
is known to change discontinuously across walls of marginal stability. We show
that the change in the degeneracy across the walls of marginal stability can be
accounted for precisely by the entropy of two centered small black holes which
disappear as we cross the walls of marginal stability.Comment: LaTeX file, 12 pages; v3: added footnote 2 regarding overall sign of
the index, expanded footnote 3, added reference
Dyon Spectrum in Generic N=4 Supersymmetric Z_N Orbifolds
We find the exact spectrum of a class of quarter BPS dyons in a generic N=4
supersymmetric Z_N orbifold of type IIA string theory on K3\times T^2 or T^6.
We also find the asymptotic expansion of the statistical entropy to first
non-leading order in inverse power of charges and show that it agrees with the
entropy of a black hole carrying same set of charges after taking into account
the effect of the four derivative Gauss-Bonnet term in the effective action of
the theory.Comment: LaTeX file, 39 pages; minor change
Dying Dyons Don't Count
The dyonic 1/4-BPS states in 4D string theory with N=4 spacetime
supersymmetry are counted by a Siegel modular form. The pole structure of the
modular form leads to a contour dependence in the counting formula obscuring
its duality invariance. We exhibit the relation between this ambiguity and the
(dis-)appearance of bound states of 1/2-BPS configurations. Using this insight
we propose a precise moduli-dependent contour prescription for the counting
formula. We then show that the degeneracies are duality-invariant and are
correctly adjusted at the walls of marginal stability to account for the
(dis-)appearance of the two-centered bound states. Especially, for large black
holes none of these bound states exists at the attractor point and none of
these ambiguous poles contributes to the counting formula. Using this fact we
also propose a second, moduli-independent contour which counts the "immortal
dyons" that are stable everywhere.Comment: 27 pages, 2 figures; one minus sign correcte
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