a maximum likelihood time delay estimator in a multipath environment using importance sampling in this paper we present a new implementation of the maximum likelihood criterion for the estimation of the time delays in a multipath environment and then extend it to the estimation of the time difference of arrival when the transmitted signal is unknown the new technique implements the concept of importance sampling is to find the global maximum of the compressed likelihood function in a modest computational manner it thereby avoids traditional complex multidimensional grid search or initialization dependent iterative methods indeed one of the most interesting features is that it transforms the multi dimensional search inherent to multipath propagation into a much simpler one dimensional optimization problem in the delays dimension moreover it guarantees convergence to the global maximum contrarily to the popular iterative implementation of the maximum likelihood criterion by the well known expectation maximization em algorithm comparisons with some other methods such as the em algorithm music and accelerated random search ars demonstrates the superiority of the proposed is based multipath delay estimator in terms of estimation performance and complexity

time delay estimation from low rate samples a union of subspaces approach time delay estimation arises in many applications in which a multipath medium has to be identified from pulses transmitted through the channel previous methods for time delay recovery either operate on the analog received signal or require sampling at the nyquist rate of the transmitted pulse in this paper we develop a unified approach to time delay estimation from low rate samples this problem can be formulated in the broader context of sampling over an infinite union of subspaces although sampling over unions of subspaces has been receiving growing interest previous results either focus on unions of finite dimensional subspaces or finite unions the framework we develop here leads to perfect recovery of the multipath delays from samples of the channel output at the lowest possible rate even in the presence of overlapping transmitted pulses and allows for a variety of different sampling methods the sampling rate depends only on the number of multipath components and the transmission rate but not on the bandwidth of the probing signal this result can be viewed as a sampling theorem over an infinite union of infinite dimensional subspaces by properly manipulating the low rate samples we show that the time delays can be recovered using the well known esprit algorithm combining results from sampling theory with those obtained in the context of direction of arrival estimation we develop sufficient conditions on the transmitted pulse and the sampling functions in order to ensure perfect recovery of the channel parameters at the minimal possible rate

estimation of multipath channels with long impulse response at low snr via an mcmc method this paper addresses the estimation of multipath channels with long impulse response at low signal to noise ratio snr the channel sparseness impulse response is modeled by means of a bernoulli gaussian process then the optimization of the resulting posterior distribution resorts to monte carlo markov chain mcmc simulation techniques special attention is devoted to noise correlation involved by matched filtering taking this correlation into account in the algorithm derivation leads to significantly improved performance for both amplitude and time delay estimation the method is also extended to cope with doppler frequency offsets in particular simultaneous paths with different doppler offsets can be estimated crameacuter rao lower bounds crlbs are derived and presented together with simulation results

fuzzy normal subgroups and fuzzy cosets abstract we introduce here the notion of 1 i a fuzzy normal subgroup and 2 ii a fuzzy coset we prove that for a group g a fuzzy subgroup is fuzzy normal if and only if it is constant on the conjugate classes of g further we show that the level subgroups of a fuzzy normal subgroup are all normal we obtain several results which are analogs of some basic theorems of group theory in particular a fuzzy version of lagrange s theorem is established

fuzzy topological vector spaces over r in this paper the concepts of fuzzy vector fuzzy vector space and fuzzy topological vector space are investigated a topology called sendograph topology which is compatible with the algebraic structure is given

large eddy simulation of an equilibrium three dimensional turbulent boundary layer large eddy simulation has been applied to prediction of an equilibrium three dimensional turbulent boundary layer tbl subgrid scale stresses were parameterized using a lagrangian dynamic mixed model the predicted mean velocities and second order statistics are in good agreement with direct numerical simulation results single point statistics are also generally similar to those found in other equilibrium three dimensional tbls such as the flow over a rotating disk and the turbulent ekman layer the modification of shear stress producing structure by mean flow three dimensionality was also investigated

on fuzzy ideals of a ring 1 abstract the aim of this paper is to study fuzzy ideals of a ring to characterise regular rings and noetherian rings by fuzzy ideals and to determine all fuzzy prime ideals of the ring z of integers

fuzzy ideals and fuzzy prime ideals of a ring abstract besides obtaining certain ring theoretic analogues some peculiarities of the fuzzy setting are also discussed in particular a study of i the conditions under which a given fuzzy ideal can or cannot be expressed as a union of two proper fuzzy ideals ii the algebraic nature of images and preimages of fuzzy prime ideals under homomorphisms and iii the ring of all the fuzzy cosets of a fuzzy prime fuzzy maximal ideal is carried out

the basic equations for the large eddy simulation of turbulent flows in complex geometry abstract the equations for large eddy simulation les of turbulent flows are derived by applying a filtering operation to the navier stokes equations les of inhomogeneous turbulent flows requires the use of filters with variable filter width the use of such filters invalidates the standard derivation of the basic equations for the filtered fields since the filtering operation in general does not commute with the operation of differentiation in this paper an alternate definition of the filtering operation based on the mapping function of the nonuniform grid is introduced it is shown that with this modified definition the filtering and differentiation operations commute up to an error which is second order in the filter width it is also shown that the commutation error can be expressed in terms of the filtered field and its derivatives as an asymptotic series in the square of the filter width these results are then applied to the navier stokes equations to derive the basic equations satisfied by the filtered fields

prediction of the three dimensional turbulent boundary layer over a swept bump large eddy simulation les and reynolds averaged navier stokes rans computations have been used for prediction of a spatially developing three dimensional turbulent boundary layer over a bump swept at 45 deg with respect to the upstream flow subgrid scale stresses in the les were parameterized using the dynamic eddy viscosity model reynolds stresses in the rans calculations were closed using the v 2 f model and spalart allmaras one equation model in the calculations a zero pressure gradient statistically two dimensional boundary layer at momentum thickness reynolds number 3 8x10 3 is introduced one half chord length upstream of the onset of curvature the flow is statistically homogeneous along the coordinate parallel to the bump axis and is subject to combined perturbations in streamwise pressure gradient spanwise pressure gradient and surface curvature the turning angle of the wall shear stress measured with respect to the upstream flow changes sign twice due to the alternating spanwise pressure gradient with a maximum of more than 45 deg near the trailing edge no slip conditions were imposed on solid boundaries in rans whereas algebraic approximate boundary conditions were applied in the les to model the near wall flow

on fuzzy ideals and fuzzy bi ideals in semigroups abstract in this paper we give some properties of fuzzy ideals and fuzzy bi ideals of semigroups and characterize semigroups that are left duo left simple and semilattices of subsemigroups in terms of fuzzy ideals and fuzzy bi ideals

on the direct product of fuzzy subgroups abstract anthony and sherwood 1979 1980 redefined the fuzzy subgroup the idea introduced by rosenfeld 1971 foster 1979 introduced the concept of product fuzzy subgroups using rosenfeld s definition in this paper the product fuzzy subgroups will be redefined according to anthony and sherwood s definition

level subgroups and union of fuzzy subgroups abstract in this paper we investigate the conditions under which a given fuzzy subgroup of a given group can or can not be realized as a union of two proper fuzzy subgroups moreover we formulate the notion of fuzzy subgroup generated by a given fuzzy subset by level subgroups we also give characterizations of fuzzy conjugate subgroups and fuzzy characteristic subgroups by their level subgroups also we discuss the relationship between level subgroups of a given fuzzy subgroup and the level subgroups of its homomorphic image

active high resolution time delay estimation for large bt signals two different high resolution time delay estimation hrtde methods a temporal method and a frequency method specially adapted to large bandwidth duration bt product time resolvent signals are described the performance gain of these methods is shown to be about four times better in comparison with the classical time delay resolution methods the frequency hrtde method is applied to real data obtained from an ocean acoustic experiment although classic methods cannot distinguish close signal components the method presented yields estimates of the delay differences and the attenuation associated with each propagation path

fuzzy prime ideals of rings abstract the notions of fuzzy ideal and fuzzy prime ideal of a ring with truth values in a complete lattice satisfying the infinite meet distributive law are introduced which generalize the existing notions with truth values in the unit interval of real numbers a procedure to construct any fuzzy ideal from a family of ideals with certain conditions is established all fuzzy prime maximal ideals of a given ring are determined by establishing a one to one correspondence between fuzzy prime maximal ideals and the pairs p where p is a prime maximal ideal of the ring and is a prime element dual atom in the complete lattice

fuzzy invariant subgroups and fuzzy ideals abstract the purpose of this paper is to introduce some basic concepts of fuzzy algebra as fuzzy invariant subgroups fuzzy ideals and to prove some fundamental properties in particular it will give a characteristic of a field by a fuzzy ideal

fuzzy semiprime ideals in semigroups abstract in this paper we shall introduce the notion of fuzzy semiprimality in a semigroup which is an extension of semiprimality in it and characterize a semigroup that is a semilattice of simple semigroups in terms of fuzzy semiprimality

separated flow computations with the k e v2 model tlirbulent separated flows over a backstep in a plane diffuser and around a triangular cylinder are computed with the k e v2 model these provide examples of massive separation of smooth separation and of unsteady vortex shedding it is shown that to accurately predict the time averaged properties of bluff body flow it is necessary to resolve the coherent vortex shedding the near wall treatment of the v2 22 system of equations is able to cope with both the massive and smooth separations good agreement between experiment and prediction is found in all

the dual of a fuzzy subspace abstract the concept of the dual of a fuzzy subspace is defined double dual fuzzy subspaces and linear maps of fuzzy subspaces are also studied

prime l fuzzy ideals and primary l fuzzy ideals abstract in this paper the concepts of a primary l fuzzy ideal and a prime l fuzzy ideal and p primary are introduced and some fundamental propositions proved in particular a structural theorem for a primary l fuzzy ideal belonging to a prime l fuzzy ideal is given

prediction of the high reynolds number flow over a two dimensional bump large eddy simulation les has been applied to prediction of the high reynolds number boundary layer flowing over a bump approximate boundary conditions were used in the les to model the wall layer in which the instantaneous wall stress is correlated with the velocity at the first layer of grid points two formulations of the approximate boundary conditions were employed in the first formulation a constrained relation was used in which the mean wall shear stress is specified a priori either from experimental measurements or from a separate solution of the reynolds averaged navier stokes rans equations in the second formulation an unconstrained relation which is based on an instantaneous power law velocity profile was used calculations were also performed in which the wall stress was computed directly i e as if the near wall flow were resolved in the region resolved by the les the strong distortions of the mean flow stream wise fluctuations and turbulent shear stress are reasonably well predicted and the relatively rapid recovery downstream of the trailing edge is also captured however neither les nor rans reproduces the plateau in skin friction measured upstream of the bump summit attributed to early relaminarization in the experiments les predictions of the mean flow and turbulence intensities using the dynamic eddy viscosity model are relatively insensitive to the particular formulation of approximate boundary conditions however in calculations without a subgrid model les predictions exhibit large errors compared to experiments and the quantitative levels of such errors are also sensitive to the choice of wall layer model

fuzzy vector spaces and fuzzy cosets abstract a fuzzy subspace is characterized by its level subspaces the algebraic nature of fuzzy subspaces under homomorphisms is studied certain conditions are obtained under which a given fuzzy subspace can or cannot be realized as a union of two fuzzy subspaces such that none is contained in the other the construction of a fuzzy subspace generated by a given fuzzy subset of a vector space is given the set of all the fuzzy cosets of a fuzzy subspace is shown to be a vector space and the dimension of the same is obtained a fuzzy quotient space is defined and an analogue of a consequence of the fundamental theorem of homomorphisms is obtained

fuzzy hv submodules abstract in this paper we define the concept of fuzzy h v submodule of an h v module and study a few results in this respect we also consider the fundamental relation e defined on an h v module m and prove a fundamental theorem concerning the module m e

fuzzy vector spaces under triangular norms abstract the object of this paper is to redefine fuzzy subspaces using the notion of a t norm and to obtain several results some of which are generalisations of the results of katsaras and liu 3