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  • Springer  (339,256)
  • Nature Publishing Group  (12,082)
  • 1995-1999  (351,338)
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  • 101
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    Bulletin of mathematical biology 61 (1999), S. 207-208 
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
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  • 102
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    Bulletin of mathematical biology 61 (1999), S. 601-623 
    ISSN: 1522-9602
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    Topics: Biology , Mathematics
    Notes: Abstract In this paper a mathematical model is developed to describe the migration of labelled particles within a multicell spheroid. In the model, spatial variations in cell proliferation and death create an internal velocity field which leads to redistribution of the labelled and unlabelled cells. By applying a range of numerical and analytical techniques to the model equations, it is possible to show that, whilst the speed with which the labelled cells migrate through the tumour is independent of the type of cells that are labelled, their limiting distribution depends crucially on whether inert polystyrene microspheres or live tumour cells are labelled. These predictions are shown to be in good qualitative agreement with independent experimental results.
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  • 103
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    Bulletin of mathematical biology 61 (1999), S. 1009-1013 
    ISSN: 1522-9602
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  • 104
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    Bulletin of mathematical biology 61 (1999), S. 935-947 
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract Human T-cell lymphotropic virus type I (HTLV-I) infection in humans causes a chronic infection of CD4+ T cells, and is associated with various disease outcomes, among them with the development of adult T-cell leukemia (ATL). The T-cell dynamics after HTLV-I infection can be described in a mathematical model with coupled differential equations. The infection process is modeled assuming cell-to-cell infection of CD4+ T cells. The model allows for CD4+ T cell subsets of susceptible, latently infected and actively infected cells as well as for leukemia cells. Latently infected T cells may harbor the virus for several years until they become activated and able to infect susceptible T cells. Uncontrolled proliferation of CD4+ T cells with monoclonal DNA-integration of HTLV-I results in the development of ATL. The model describes basic features that characterize HTLV-I infection; the chronic infection of CD4+ T cells, the increasing number of abnormal cells and the possible progression to ATL.
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  • 105
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    Bulletin of mathematical biology 61 (1999), S. 949-961 
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract A neighbourhood-based competition model for plant individuals is studied to evaluate how a hierarchical structure related to size may emerge in plant communities. It is shown by numerical simulations and linear stability analysis that many stable states exist in the hierarchical structure when both the total number of individuals and the degree of asymmetry of competition are high. When the hierarchical structures are self-organized by the dynamic instability of the homogeneous state due to non-linearity of competition, it is proved that these states are always locally stable. The relevance of the results to size structures in real plant communities (boreal forests vs tropical and temperate forests) is discussed. This is suggested to be the mechanism responsible for the coexistence of species in plant communities.
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  • 106
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    Bulletin of mathematical biology 61 (1999), S. 141-155 
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract Phenomenological models represent a simplified approach to the study of complex systems such as host-parasitoid interactions. In this paper we compare the dynamics of three phenomenological models for host-parasitoid interactions developed by May (1978), May and Hassell (1981) and May et al. (1981). The essence of the paper by May and Hassell (1981) was to define a minimum number of parameters that would describe the interactions, avoiding the technical difficulties encountered when using models that involve many parameters, yet yielding a system of equations that could capture the essence of real world interactions in patchy environments. Those studies dealt primarily with equilibrium and coexistence phenomena. Here we study the dynamics through bifurcation analysis and phase portraits in a much wider range of parameter values, carrying the models beyond equilibrium states. We show that the dynamics can be either stable or chaotic depending on the location of a damping term in the equations. In the case of the stable system, when host density dependence acts first, a stable point is reached, followed by a closed invariant curve in phase space that first increases then decreases, finally returning to an asymptotically stable point. Chaos is not seen. On the other hand, when parasitoid attack occurs before host density dependence, chaos is inevitably apparent. We show, as did May et al. (1981) and stated earlier byWang and Gutierrez (1980), that the sequence of events in host-parasitoid interactions is crucial in determining their stability. In a chaotic state the size of the host (e.g., insect pests) population becomes unpredictable, frequently becoming quite large, a biologically undesirable outcome. From a mathematical point of view the system is of interest because it reveals how a strategically placed damping term can dramatically alter the outcome. Our study, reaching beyond equilibrium states, suggests a strategy for biological control different from that of May et al. (1981).
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  • 107
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    Bulletin of mathematical biology 61 (1999), S. 179-205 
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract In this paper we study the uniform persistence (UP) of an association of two competing host species sharing a directly transmitted macroparasite. Like predators, parasites can regulate UP while the hosts are either coexisting or in a dominance relationship without any infections, but cannot regulate UP in case the hosts are in bistability. The regulatory mechanism depends on the relationships between the parameters, such as host intrinsic growth rate, host carrying capacity, susceptibility, parasite pathogenicity and the magnitude of parasite aggregation. In the case of coexistence the parametric space for UP is more than that for global stability of the host-parasite equilibrium, but is less than that for UP in the case of dominance. In the case of dominance, the parasites can alter the competitive outcome locally or can enhance the local exclusion of the inferior competitor and thus, unlike the predation, parasitism has an beneficial effect over competition. We derive explicitly the range of the values of ratios of the rates of reproduction and survivorship of the hosts, and also of the values of the degree of aggregations, with which macroparasites are not effective in maintaining its beneficial effect over competition. Finally our results support the body-size hypothesis of Price et al. (1988), with possible explanations of certain exceptional examples of the hypothesis.
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  • 108
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    Bulletin of mathematical biology 61 (1999), S. 209-220 
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract The representation of the shape of a biconcave erythrocyte by a set of three parametric equations was achieved by using the expressions that transform the curvilinear coordinates from the disc-cyclide coordinate system [denoted J2R; Moon and Spencer (1988), Field Theory Handbook, Springer-Verlag, Berlin] to Cartesian coordinates. The equations are products of elliptic functions, so the challenge was to relate the three major ’shape-defining’ measurements of the human erythrocyte in Cartesian coordinates to three parameters in the new curvilinear coordinates, to give a realistic representation of the shape of the membrane-surface. The relationships between the coefficients of the Cartesian degree-4 surface that describes the discocyte and the coordinate transformation equations were derived with the aid of Mathematica; and the membrane-surface of the cell was drawn using the ParametricPlot3D function in this ‘package’. By having the erythrocyte shape expressed in its new form it is readily amenable to further transformations that might be used to model those changes in shape that are seen when the cells are immersed in media of various osmolalities, or when they change metabolic ’states’. On the other hand, the relationship between the coefficients of the Cartesian expression for the disc-cyclide surface is relevant to image analysis of erythrocytes, as determined by physical methods that rely on Cartesian imaging ’slices’. These methods include confocal microscopy and various nuclear magnetic resonance microimaging procedures.
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  • 109
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    Bulletin of mathematical biology 61 (1999), S. 239-272 
    ISSN: 1522-9602
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    Topics: Biology , Mathematics
    Notes: Abstract A coupled model is presented for simulating physical and biological dynamics in fresh water lakes. The physical model rests upon the assumption that the turbulent kinetic energy in a water column of the lake is fully contained in a mixed layer of variable depth. Below this layer the mechanical energy content is assumed to vanish. Additionally, the horizontal currents are ignored. This one-dimensional two-layered model describes the internal conversion of the mechanical and thermal energy input from the atmosphere into an evolution of the mixed layer depth by entrainment and detrainment mechanisms. It is supposed to form the physical domain in which the simulation of the biological processes takes place. The biological model describes mathematically the typical properties of phyto-and zooplankton, their interactions and their response to the physical environment. This description then allows the study of the behaviour of Lagrangian clusters of virtual plankton that are subjected to such environments. The essence of the model is the dynamical simulation of an arbitrary number of nutrient limited phytoplankton species and one species of zooplankton. The members of the food web above and below affect the model only statically. The model is able to reproduce the typical progression of a predator-prey interaction between phyto-and zooplankton as well as the exploitative competition for nutrients between two phytoplankton species under grazing pressure of Daphnia. It suggests that the influence of the biological system on the physical system results in a weak increase of the surface temperature for coupled simulations, but a considerably higher seasonal thermocline in spring and a lower one in autumn.
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  • 110
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    Bulletin of mathematical biology 61 (1999), S. 303-339 
    ISSN: 1522-9602
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    Topics: Biology , Mathematics
    Notes: Abstract We investigate the dynamical behaviour of a simple plankton population model, which explicitly simulates the concentrations of nutrient, phytoplankton and zooplankton in the oceanic mixed layer. The model consists of three coupled ordinary differential equations. We use analytical and numerical techniques, focusing on the existence and nature of steady states and unforced oscillations (limit cycles) of the system. The oscillations arise from Hopf bifurcations, which are traced as each parameter in the model is varied across a realistic range. The resulting bifurcation diagrams are compared with those from our previouswork, where zooplankton mortality was simulated by a quadratic function—here we use a linear function, to represent alternative ecological assumptions. Oscillations occur across broader ranges of parameters for the linear mortality function than for the quadratic one, although the two sets of bifurcation diagrams show similar qualitative characteristics. The choice of zooplankton mortality function, or closure term, is an area of current interest in the modelling community, and we relate our results to simulations of other models.
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  • 111
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    Bulletin of mathematical biology 61 (1999), S. 355-363 
    ISSN: 1522-9602
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    Topics: Biology , Mathematics
    Notes: Abstract The bayesian decomposition of posterior distribution was used to develop a likelihood function to correct bias in the estimates of population parameters from data collected randomly with size-specific selectivity. Positive distributions with time as a parameter were used for parametrization of growth data. Numerical illustrations are provided. The alternative applications of the likelihood to estimate selectivity parameters are discussed.
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  • 112
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    Bulletin of mathematical biology 61 (1999), S. 1015-1016 
    ISSN: 1522-9602
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  • 113
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    Topics: Biology , Mathematics
    Notes: Abstract We present a model for the formation of parallel rows of scale cells in the developing adult wing of moths and butterflies. Precursors of scale cells differentiate throughout each epithelial monolayer and migrate into rows that are roughly parallel to the body axis. Grafting experiments have revealed what appears to be a gradient of adhesivity along the wing. What is more, cell adhesivity character is maintained after grafting. Thus we suggest that it is a cell’s location prior to migration that determines its interactions during migration. We use nonlinear bifurcation analysis to show that differential origin-dependent cell adhesion can result in the stabilization of rows over spots.
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  • 114
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    Bulletin of mathematical biology 61 (1999), S. 1065-1091 
    ISSN: 1522-9602
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    Topics: Biology , Mathematics
    Notes: Abstract Critical to epithelial cell viability is the homeostasis of cell volume and composition during changes in transcellular transport. In this study, two previously developed mathematical models (principal cell of the collecting duct and proximal tubule cell) are approximated by their linearizations about a reference condition. This yields matrices which estimate cell volume, cell composition, and transcellular fluxes in response to perturbations of bath conditions and membrane transporter activity. These approximations are themselves extended with the inclusion of linear dependence of membrane transport coefficients on cell variables (e.g., volume, solute concentrations, or electrical potential). This provides cell models with variable permeabilities, which may be homeostatic, and which can be examined systematically: sequentially testing each membrane permeability and its controlling cell variable. In the proximal tubule approximation, volume-mediated increases in peritubular K—Cl or Na—3HCO3 cotransport, and volume-mediated decreases in Na,K-ATPase activity are homeostatic; modulation of peritubular K permeability has little impact. In the principal cell model, volume homeostasis is afforded by volume-sensitive peritubular Na/H exchange or Cl− conductance. Predictions from the linear analysis are confirmed in the full models. This approach yields a systematic examination of homeostasis in an epithelial model, and identifies candidate control parameters.
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  • 115
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    Circuits, systems and signal processing 18 (1999), S. 17-25 
    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract A complete analytic characterization and solution construction (done either explicitly or by recursion) for the minimax control problem using optimal rate feedback is given for the case when the plant consists of a known fixed set of coupled oscillators of cardinality not exceeding three. When this is not the case, the problem appears to be analytically intractable, and suboptimal solutions based on numerical techniques are currently the only recourse.
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  • 116
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    Circuits, systems and signal processing 18 (1999), S. 1-16 
    ISSN: 1531-5878
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The task of constructing an energy function is essential for direct stability analysis of electric power systems. This paper presents a general procedure for constructing analytical energy functions for detailed lossless network-reduction power system stability models. This paper primarily (i) develops canonical representations for lossless networkreduction power system models and shows that such canonical representations cover existing stability models, (ii) derives theoretical results regarding the existence of analytical energy functions for the canonical representations, and (iii) presents a systematic procedure to construct corresponding energy functions.
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  • 117
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    Circuits, systems and signal processing 18 (1999), S. 89-110 
    ISSN: 1531-5878
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The problem of finding all the DC solutions of a certain class of piecewise-linear electronic circuits containing locally passive and locally active one-ports is considered in this paper. An effective method enabling us to locate the solutions is developed. The method constitutes the crucial point of an algorithm based on the idea of successive contraction, division, and elimination that is capable of determining all the solutions. Several numerical examples are given, and some comparison analyses are performed confirming the usefulness of the proposed approach.
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  • 118
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    Circuits, systems and signal processing 18 (1999), S. 269-290 
    ISSN: 1531-5878
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The controllability and observability properties of a singular system are extensively studied. The definitions of controllability,R-controllability, and impulse controllability are introduced via characteristics of the original state vector. Analogous definitions are presented for the case of observability. The criteria established for controllability and observability are simple rank criteria related to the Markov parameters from the inputs to the states and from the initial conditions to the outputs, respectively. The present results can be considered as the direct extension of Kalman's controllability and observability criteria to the case of singular systems. Finally, the controllability and observability subspaces are derived from the image and the kernel of the controllability and the observability matrices, respectively.
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  • 119
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Given a stationary time seriesX and another stationary time seriesY (with a different power spectral density), we describe an algorithm for constructing a stationary time series Z that contains exactly the same values asX permuted in an order such that the power spectral density ofZ closely resembles that ofY. We call this methodspectral mimicry. We prove (under certain restrictions) that, if the univariate cumulative distribution function (CDF) ofX is identical to the CDF ofY, then the power spectral density ofZ equals the power spectral density ofY. We also show, for a class of examples, that when the CDFs ofX andY differ modestly, the power spectral density ofZ closely approximates the power spectral density ofY. The algorithm, developed to design an experiment in microbial population dynamics, has a variety of other applications.
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  • 120
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    Circuits, systems and signal processing 18 (1999), S. 479-487 
    ISSN: 1531-5878
    Keywords: Cramér-Rao bounds ; direction-of-arrival estimation ; unknown noise
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The deterministic and stochastic direction estimation Cramér-Rao bounds (CRBs) are studied in the presence of one signal and spatially uncorrelated sensor noise with unknown nonequal variances in array sensors. The explicit CRB expressions are obtained, and their relationship is studied showing some typical properties inherent in the nonidentical noise case.
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  • 121
    ISSN: 1531-5878
    Keywords: Nonlinear circuit theory ; co-content ; functional minimization ; image processing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The solutions of many physical-mathematical problems can be obtained by minimizing proper functionals. In the literature, some methods for the synthesis of analog circuits (mainly cellular neural networks) are presented that find the solution of some of these problems by implementing the discretized Euler-Lagrange equations associated with the pertinent functionals. In this paper, we propose a method for defining analog circuits that directly minimize (in a parallel way) a class of discretized functionals in the frequently occurring case where the solution depends on two spatial variables. The method is a generalization of the one presented in Parodi et al.,Internat. J. Circuit Theory Appl., 26, 477–498, 1998. The analog circuits consist of both a (nonlinear) resistive part and a set of linear capacitors, whose steady-state voltages represent the discrete solution to the problem. The method is based on the potential (co-content) functions associated with voltage-controlled resistive elements. es an example, we describe an application in the field of image processing: the restoration of color images corrupted by additive noise.
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  • 122
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    The journal of Fourier analysis and applications 5 (1999), S. 159-184 
    ISSN: 1531-5851
    Keywords: Primary 65T20 ; secondary 42C10 ; 33C55 ; spherical harmonics ; fast transforms ; associated Legendre functions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract Spherical harmonics arise on the sphere S2 in the same way that the (Fourier) exponential functions {eikθ}k∈ℤ arise on the circle. Spherical harmonic series have many of the same wonderful properties as Fourier series, but have lacked one important thing: a numerically stable fast transform analogous to the Fast Fourier Transform (FFT). Without a fast transform, evaluating (or expanding in) spherical harmonic series on the computer is slow—for large computations probibitively slow. This paper provides a fast transform. For a grid ofO(N2) points on the sphere, a direct calculation has computational complexityO(N4), but a simple separation of variables and FFT reduce it toO(N3) time. Here we present algorithms with timesO(N5/2 log N) andO(N2(log N)2). The problem quickly reduces to the fast application of matrices of associated Legendre functions of certain orders. The essential insight is that although these matrices are dense and oscillatory, locally they can be represented efficiently in trigonometric series.
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  • 123
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    The journal of Fourier analysis and applications 5 (1999), S. v 
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    Topics: Mathematics
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  • 124
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    Transformation groups 4 (1999), S. i 
    ISSN: 1531-586X
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    Topics: Mathematics
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  • 125
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    The journal of Fourier analysis and applications 5 (1999), S. v 
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  • 126
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    Transformation groups 4 (1999), S. 3-24 
    ISSN: 1531-586X
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    Topics: Mathematics
    Notes: Abstract Weakly symmetric homogeneous spaces were introduced by A. Selberg in 1956. We prove that, for a real reductive algebraic group, they can be characterized as the spaces of real points of affine spherical homogeneous varieties of the complexified group. As an application, under the same assumption on the transitive group, we show that weakly symmetric spaces are precisely the homogeneous Riemannian manifolds with commutative algebra of invariant differential operators.
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  • 127
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    Transformation groups 4 (1999), S. 53-95 
    ISSN: 1531-586X
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    Topics: Mathematics
    Notes: Abstract We study the modificationA→A′ of an affine domainA which produces another affine domainA′=A[I/f] whereI is a nontrivial ideal ofA andf is a nonzero element ofI. First appeared in passing in the basic paper of O. Zariski [Zar], it was further considered by E. D. Davis [Da]. In [Ka1] its geometric counterpart was applied to construct contractible smooth affine varieties non-isomorphic to Euclidean spaces. Here we provide certain conditions (more general than those in [Ka1]) which guarantee preservation of the topology under a modification. As an application, we show that the group of biregular automorphisms of the affine hypersurfaceX⊂C k+2, given by the equationuv=(p(x 1,...,xk) wherep∈C[x 1,...,x k ],k≥2, actsm-transitively on the smooth part regX ofX for anym∈N. We present examples of such hypersurfaces diffeomorphic to Euclidean spaces.
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    Transformation groups 4 (1999), S. 273-300 
    ISSN: 1531-586X
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    Topics: Mathematics
    Notes: Abstract The symmetric varieties considered in this paper are the quotientsG/H, whereG is an adjoint semi-simple group over a fieldk of characteristic ≠ 2, andH is the fixed point group of an involutorial automorphism ofG which is defined overk. In the casek=C, De Concini and Procesi (1983) constructed a “wonderful” compactification ofG/H. We prove the existence of such a compactification for arbitraryk. We also prove cohomology vanishing results for line bundles on the compactification.
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    Transformation groups 4 (1999), S. 303-327 
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    Topics: Mathematics
    Notes: Abstract The Yang-Baxter equation admits two classes of elliptic solutions, the vertex type and the face type. On the basis of these solutions, two types of elliptic quantum groups have been introduced (Foda et al. [FIJKMY1], Felder [Fe]). Frønsdal [Fr1, Fr2] made a penetrating observation that both of them are quasi-Hopf algebras, obtained by twisting the standard quantum affine algebraU q(g). In this paper we present an explicit formula for the twistors in the form of an infinite product of the universalR matrix ofU q(g). We also prove the shifted cocycle condition for the twistors, thereby completing Frønsdal's findings. This construction entails that, for generic values of the deformation parameters, the representation theory forU q(g) carries over to the elliptic algebras, including such objects as evaluation modules, highest weight modules and vertex operators. In particular, we confirm the conjectures of Foda et al. concerning the elliptic algebraA q,p ( $$\widehat{\mathfrak{s}\mathfrak{l}}_2 $$ ).
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    Transformation groups 4 (1999), S. 375-404 
    ISSN: 1531-586X
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    Topics: Mathematics
    Notes: Abstract In this survey we shall prove a convexity theorem for gradient actions of reductive Lie groups on Riemannian symmetric spaces. After studying general properties of gradient maps, this proof is established by (1) an explicit calculation on the hyperbolic plane followed by a transfer of the results to general reductive Lie groups, (2) a reduction to a problem on abelian spaces using Kostant's Convexity Theorem, (3) an application of Fenchel's Convexity Theorem. In the final section the theorem is applied to gradient actions on other homogeneous spaces and we show, that Hilgert's Convexity Theorem for moment maps can be derived from the results.
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  • 131
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    Circuits, systems and signal processing 18 (1999), S. i 
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    Topics: Electrical Engineering, Measurement and Control Technology
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  • 132
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    Circuits, systems and signal processing 18 (1999), S. 111-130 
    ISSN: 1531-5878
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The cumulants defined in terms of moments are basic to the study of higher-order statistics (HOS) of a stationary stochastic process. This paper presents a concurrent systolic array system for the computation of higher-order moments. The system allows for the simultaneous computation of the second-, third-, and fourth-order moments. The architecture achieves good speedup through its excellent exploitation of parallelism, pipelining, and reusability of some intermediate results. The computational complexity and system performance issues related to the architecture are discussed. The concurrent system is designed with the CMOS VLSI technology and is capable of operating at 3.9 MHz.
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    Circuits, systems and signal processing 18 (1999), S. 183-187 
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Necessary and sufficient conditions for the invertibility of a (not necessarily linear) operatorN between normed linear spaces are given. It is shown thatN is invertible precisely if a certain operator associated withN is a contraction.
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  • 134
    ISSN: 1539-6924
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
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  • 135
    ISSN: 1539-6924
    Keywords: Environment ; equity ; coke ; oil ; history ; risk
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Facility-specific information on pollution was obtained for 36 coke plants and 46 oil refineries in the United States and matched with information on populations surrounding these 82 facilities. These data were analyzed to determine whether environmental inequities were present, whether they were more economic or racial in nature, and whether the racial composition of nearby communities has changed significantly since plants began operations. The Census tracts near coke plants have a disproportionate share of poor and nonwhite residents. Multivariate analyses suggest that existing inequities are primarily economic in nature. The findings for oil refineries are not strongly supportive of the environmental inequity hypothesis. Rank ordering of facilities by race, poverty, and pollution produces limited (although not consistent) evidence that the more risky facilities tend to be operating in communities with above-median proportions of nonwhite residents (near coke plants) and Hispanic residents (near oil refineries). Over time, the racial makeup of many communities near facilities has changed significantly, particularly in the case of coke plants sited in the early 1900s. Further risk-oriented studies of multiple manufacturing facilities in various industrial sectors of the economy are recommended.
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    Risk analysis 19 (1999), S. 231-247 
    ISSN: 1539-6924
    Keywords: Health risk assessment ; hazard characterization ; Acceptable Daily Intake ; Reference Dose ; paradigm ; practices ; cancer ; non-cancer ; Bayesian ; default options
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract We investigated the way results of human health risk assessments are used, and the theory used to describe those methods, sometimes called the “NAS paradigm.” Contrary to a key tenet of that theory, current methods have strictly limited utility. The characterizations now considered standard, Safety Indices such as “Acceptable Daily Intake,” “Reference Dose,” and so on, usefully inform only decisions that require a choice between two policy alternatives (e.g., approve a food additive or not), decided solely on the basis of a finding of safety. Risk is characterized as the quotient of one of these Safety Indices divided by an estimate of exposure: a quotient greater than one implies that the situation may be considered safe. Such decisions are very widespread, both in the U. S. federal government and elsewhere. No current method is universal; different policies lead to different practices, for example, in California's “Proposition 65,” where statutory provisions specify some practices. Further, an important kind of human health risk assessment is not recognized by this theory: this kind characterizes risk as likelihood of harm, given estimates of exposure consequent to various decision choices. Likelihood estimates are necessary whenever decision makers have many possible decision choices and must weigh more than two societal values, such as in EPA's implementation of “conventional air pollutants.” These estimates can not be derived using current methods; different methods are needed. Our analysis suggests changes needed in both the theory and practice of human health risk assessment, and how what is done is depicted.
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    Risk analysis 19 (1999), S. 249-259 
    ISSN: 1539-6924
    Keywords: Reliability ; Monte Carlo simulation ; hazardous waste treatment ; safety factor ; packed tower ; activated sludge
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract The reliability of a treatment process is addressed in terms of achieving a regulatory effluent concentration standard and the design safety factors associated with the treatment process. This methodology was then applied to two aqueous hazardous waste treatment processes: packed tower aeration and activated sludge (aerobic) biological treatment. The designs achieving 95 percent reliability were compared with those designs based on conventional practice to determine their patterns of conservatism. Scoping-level treatment costs were also related to reliability levels for these treatment processes. The results indicate that the reliability levels for the physical/chemical treatment process (packed tower aeration) based on the deterministic safety factors range from 80 percent to over 99 percent, whereas those for the biological treatment process range from near 0 percent to over 99 percent, depending on the compound evaluated. Increases in reliability per unit increase in treatment costs are most pronounced at lower reliability levels (less than about 80 percent) than at the higher reliability levels (greater than 90 percent, indicating a point of diminishing returns. Additional research focused on process parameters that presently contain large uncertainties may reduce those uncertainties, with attending increases in the reliability levels of the treatment processes.
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    Risk analysis 19 (1999), S. 321-321 
    ISSN: 1539-6924
    Source: Springer Online Journal Archives 1860-2000
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    Risk analysis 19 (1999), S. 295-308 
    ISSN: 1539-6924
    Keywords: Noncancer risk assessment ; uncertainty analysis ; systematic error ; calibration ; censoring ; relative potency ; safety factor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract The prominent role of animal bioassay evidence in environmental regulatory decisions compels a careful characterization of extrapolation uncertainties. In noncancer risk assessment, uncertainty factors are incorporated to account for each of several extrapolations required to convert a bioassay outcome into a putative subthreshold dose for humans. Measures of relative toxicity taken between different dosing regimens, different endpoints, or different species serve as a reference for establishing the uncertainty factors. Ratios of no observed adverse effect levels (NOAELs) have been used for this purpose; statistical summaries of such ratios across sets of chemicals are widely used to guide the setting of uncertainty factors. Given the poor statistical properties of NOAELs, the informativeness of these summary statistics is open to question. To evaluate this, we develop an approach to “calibrate” the ability of NOAEL ratios to reveal true properties of a specified distribution for relative toxicity. A priority of this analysis is to account for dependencies of NOAEL ratios on experimental design and other exogenous factors. Our analysis of NOAEL ratio summary statistics finds (1) that such dependencies are complex and produce pronounced systematic errors and (2) that sampling error associated with typical sample sizes (50 chemicals) is non-negligible. These uncertainties strongly suggest that NOAEL ratio summary statistics cannot be taken at face value; conclusions based on such ratios reported in well over a dozen published papers should be reconsidered.
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  • 140
    ISSN: 1539-6924
    Keywords: Cancer risk ; in vivo doses ; linear multiplicative model ; ethylene oxide ; relative potency ; butadiene ; acrylamide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract A mechanistic model and associated procedures are proposed for cancer risk assessment of genotoxic chemicals. As previously shown for ionizing radiation, a linear multiplicative model was found to be compatible with published experimental data for ethylene oxide, acrylamide, and butadiene. The validity of this model was anticipated in view of the multiplicative interaction of mutation with inherited and acquired growth-promoting conditions. Concurrent analysis led to rejection of an additive model (i.e. the model commonly applied for cancer risk assessment). A reanalysis of data for radiogenic cancer in mouse, dog and man shows that the relative risk coefficient is approximately the same (0.4 to 0.5 percent per rad) for tumours induced in the three species. Doses in vivo, defined as the time-integrated concentrations of ultimate mutagens, expressed in millimol × kg−1 × h (mMh) are, like radiation doses given in Gy or rad, proportional to frequencies of potentially mutagenic events. The radiation dose equivalents of chemical doses are, calculated by multiplying chemical doses (in mMh) with the relative genotoxic potencies (in rad × mMh−1) determined in vitro. In this way the relative cancer incidence increments in rats and mice exposed to ethylene oxide were shown to be about 0.4 percent per rad-equivalent, in agreement with the data for radiogenic cancer. Our analyses suggest that values of the relative risk coefficients for genotoxic chemicals are independent of species and that relative cancer risks determined in animal tests apply also to humans. If reliable animal test data are not available, cancer risks may be estimated by the relative potency. In both cases exposure dose/target dose relationships, the latter via macromolecule adducts, should be determined.
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    Risk analysis 19 (1999), S. 585-598 
    ISSN: 1539-6924
    Keywords: uncertainty ; threatened plants ; risk ; conservation ; rule sets ; IUCN
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Australian state and federal agencies use a broad range of methods for setting conservation priorities for species at risk. Some of these are based on rule sets developed by the International Union for the Conservation of Nature, while others use point scoring protocols to assess threat. All of them ignore uncertainty in the data. In this study, we assessed the conservation status of 29 threatened vascular plants from Tasmania and New South Wales using a variety of methods including point scoring and rule-based approaches. In addition, several methods for dealing with uncertainty in the data were applied to each of the priority-setting schemes. The results indicate that the choice of a protocol for setting priorities and the choice of the way in which uncertainty is treated may make important differences to the resulting assessments of risk. The choice among methods needs to be rationalized within the management context in which it is to be applied. These methods are not a substitute for more formal risk assessment.
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  • 142
    ISSN: 1539-6924
    Keywords: MeHg ; pharmacokinetics ; PBPK model ; variability ; risk assessment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract An analysis of the uncertainty in guidelines for the ingestion of methylmercury (MeHg) due to human pharmacokinetic variability was conducted using a physiologically based pharmacokinetic (PBPK) model that describes MeHg kinetics in the pregnant human and fetus. Two alternative derivations of an ingestion guideline for MeHg were considered: the U.S. Environmental Protection Agency reference dose (RfD) of 0.1 μg/kg/day derived from studies of an Iraqi grain poisoning episode, and the Agency for Toxic Substances and Disease Registry chronic oral minimal risk level (MRL) of 0.5 μg/kg/day based on studies of a fish-eating population in the Seychelles Islands. Calculation of an ingestion guideline for MeHg from either of these epidemiological studies requires calculation of a dose conversion factor (DCF) relating a hair mercury concentration to a chronic MeHg ingestion rate. To evaluate the uncertainty in this DCF across the population of U.S. women of child-bearing age, Monte Carlo analyses were performed in which distributions for each of the parameters in the PBPK model were randomly sampled 1000 times. The 1st and 5th percentiles of the resulting distribution of DCFs were a factor of 1.8 and 1.5 below the median, respectively. This estimate of variability is consistent with, but somewhat less than, previous analyses performed with empirical, one-compartment pharmacokinetic models. The use of a consistent factor in both guidelines of 1.5 for pharmacokinetic variability in the DCF, and keeping all other aspects of the derivations unchanged, would result in an RfD of 0.2 μg/kg/day and an MRL of 0.3 μg/kg/day.
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    Risk analysis 19 (1999), S. 577-584 
    ISSN: 1539-6924
    Keywords: risk assessment ; exposure point concentration ; bootstrapping ; gamma distribution ; lognormal
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract The U.S. Environmental Protection Agency (EPA) recommends the use of the one-sided 95% upper confidence limit of the arithmetic mean based on either a normal or lognormal distribution for the contaminant (or exposure point) concentration term in the Superfund risk assessment process. When the data are not normal or lognormal this recommended approach may overestimate the exposure point concentration (EPC) and may lead to unecessary cleanup at a hazardous waste site. The EPA concentration term only seems to perform like alternative EPC methods when the data are well fit by a lognormal distribution. Several alternative methods for calculating the EPC are investigated and compared using soil data collected from three hazardous waste sites in Montana, Utah, and Colorado. For data sets that are well fit by a lognormal distribution, values for the Chebychev inequality or the EPA concentration term may be appropriate EPCs. For data sets where the soil concentration data are well fit by gamma distributions, Wong's method may be used for calculating EPCs. The studentized bootstrap-t and Hall's bootstrap-t transformation are recommended for EPC calculation when all distribution fits are poor. If a data set is well fit by a distribution, parametric bootstrap may provide a suitable EPC.
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  • 144
    ISSN: 1539-6924
    Keywords: risk perception ; air quality ; environmental justice ; community health survey
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract This paper describes a multi-stakeholder process designed to assess the potential health risks associated with adverse air quality in an urban industrial neighborhood. The paper briefly describes the quantitative health risk assessment conducted by scientific experts, with input by a grassroots community group concerned about the impacts of adverse air quality on their health and quality of life. In this case, rather than accept the views of the scientific experts, the community used their powers of perception to advantage by successfully advocating for a professionally conducted community health survey. This survey was designed to document, systematically and rigorously, the health risk perceptions community members associated with exposure to adverse air quality in their neighborhood. This paper describes the institutional and community contexts within which the research is situated as well as the design, administration, analysis, and results of the community health survey administered to 402 households living in an urban industrial neighborhood in Hamilton, Ontario, Canada. These survey results served to legitimate the community's concerns about air quality and to help broaden operational definitions of ‘health.’ In addition, the results of both health risk assessment exercises served to keep issues of air quality on the local political agenda. Implications of these findings for our understanding of the environmental justice process as well as the ability of communities to influence environmental health policy are discussed.
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  • 145
    ISSN: 1539-6924
    Keywords: risk perception ; risk characteristics ; outrage factors ; rbGH ; ordered probit
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract This study estimates the effect risk characteristics, described as outrage factors by Hadden, have on consumers' risk perceptions toward the food-related biotechnology, recombinant bovine growth hormone (rbGH). The outrage factors applicable to milk from rbGH treated herds are involuntary risk exposure, unfamiliarity with the product's production process, unnatural product characteristics, lack of trust in regulator's ability to protect consumers in the marketplace, and consumers' inability to distinguish milk from rbGH treated herds compared to milk from untreated herds. An empirical analysis of data from a national survey of household food shoppers reveals that outrage factors mediate risk perceptions. The results support the inclusion of outrage factors into the risk perception model for the rbGH product, as they add significantly to the explanatory power of the model and therefore reduce bias compared to a simpler model of attitudinal and demographic factors. The study indicates that outrage factors which have a significant impact on risk perceptions are the lack of trust in the FDA as a food-related information source, and perceiving no consumer benefits from farmers' use of rbGH. Communication strategies to reduce consumer risk perceptions therefore could utilize agencies perceived as more trustworthy and emphasize the benefits of rbGH use to consumers.
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  • 146
    ISSN: 1539-6924
    Keywords: risk perceptions ; psychometric paradigm ; multilevel modeling ; random coefficient models
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Psychometric data on risk perceptions are often collected using the method developed by Slovic, Fischhoff, and Lichtenstein, where an array of risk issues are evaluated with respect to a number of risk characteristics, such as how dreadful, catastrophic or involuntary exposure to each risk is. The analysis of these data has often been carried out at an aggregate level, where mean scores for all respondents are compared between risk issues. However, this approach may conceal important variation between individuals, and individual analyses have also been performed for single risk issues. This paper presents a new methodological approach using a technique called multilevel modelling for analysing individual and aggregated responses simultaneously, to produce unconditional and unbiased results at both individual and aggregate levels of the data. Two examples are given using previously published data sets on risk perceptions collected by the authors, and results between the traditional and new approaches compared. The discussion focuses on the implications of and possibilities provided by the new methodology.
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    Risk analysis 19 (1999), S. 739-749 
    ISSN: 1539-6924
    Keywords: probabilistic forecasting ; uncertainty quantification ; Bayesian method ; Monte-Carlo simulation ; decision making
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Rational decision making requires that the total uncertainty about a variate of interest (a predictand) be quantified in terms of a probability distribution, conditional on all available information and knowledge. Suppose the state-of-knowledge is embodied in a deterministic model, which is imperfect and outputs only an estimate of the predictand. Fundamentals are presented of two Bayesian methods for producing a probabilistic forecast via any deterministic model. The Bayesian Processor of Forecast (BPF) quantifies the total uncertainty in terms of a posterior distribution, conditional on model output. The Bayesian Forecasting System (BFS) decomposes the total uncertainty into input uncertainty and model uncertainty, which are characterized independently and then integrated into a predictive distribution. The BFS is compared with Monte Carlo simulation and “ensemble forecasting” technique, none of which can alone produce a probabilistic forecast that quantifies the total uncertainty, but each can serve as a component of the BFS.
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    Risk analysis 19 (1999), S. 759-761 
    ISSN: 1539-6924
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
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  • 149
    ISSN: 1539-6924
    Keywords: regulation ; radioactive waste ; performance assessment ; risk assessment ; regulatory assessment ; bias evaluation ; international collaboration ; underground disposal ; quantitative risk analysis ; public debate ; decision process
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Much has been written about the development and application of quantitative methods for estimating under uncertainty the long-term radiological performance of underground disposal of radioactive wastes. Until recently, interest has been focused almost entirely on the technical challenges regardless of the role of the organization responsible for these analyses. Now the dialogue between regulators, the repository developer or operator, and other interested parties in the decision-making process receives increasing attention, especially in view of some current difficulties in obtaining approvals to construct or operate deep facilities for intermediate or high-level wastes. Consequently, it is timely to consider the options for regulators' review and evaluation of safety submissions, at the various stages in the site selection to repository closure process, and to consider, especially, the role for performance assessment (PA) within the programs of a regulator both before and after delivery of such a submission. The origins and broad character of present regulations in the European Union (EU) and in the OECD countries are outlined and some regulatory PA reviewed. The issues raised are discussed, especially in regard to the interpretation of regulations, the dangers from the desire for simplicity in argument, the use of regulatory PA to review and challenge the PA in the safety case, and the effects of the relationship between proponent and regulator. Finally, a very limited analysis of the role of PA in public hearings is outlined and recommendations are made, together with proposals for improving the mechanisms for international collaboration on technical issues of regulatory concern.
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    Risk analysis 19 (1999), S. 23-32 
    ISSN: 1539-6924
    Keywords: Software failures ; software hazard analysis ; safety-critical systems ; risk assessment ; context
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract As the use of digital computers for instrumentation and control of safety-critical systems has increased, there has been a growing debate over the issue of whether probabilistic risk assessment techniques can be applied to these systems. This debate has centered on the issue of whether software failures can be modeled probabilistically. This paper describes a “context-based” approach to software risk assessment that explicitly recognizes the fact that the behavior of software is not probabilistic. The source of the perceived uncertainty in its behavior results from both the input to the software as well as the application and environment in which the software is operating. Failures occur as the result of encountering some context for which the software was not properly designed, as opposed to the software simply failing “randomly.” The paper elaborates on the concept of “error-forcing context” as it applies to software. It also illustrates a methodology which utilizes event trees, fault trees, and the Dynamic Flowgraph Methodology (DFM) to identify “error-forcing contexts” for software in the form of fault tree prime implicants.
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    Risk analysis 19 (1999), S. 47-68 
    ISSN: 1539-6924
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    Topics: Energy, Environment Protection, Nuclear Power Engineering
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  • 152
    ISSN: 1539-6924
    Keywords: Variability ; uncertainty ; maximum likelihood ; bootstrap simulation ; Monte Carlo simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Variability arises due to differences in the value of a quantity among different members of a population. Uncertainty arises due to lack of knowledge regarding the true value of a quantity for a given member of a population. We describe and evaluate two methods for quantifying both variability and uncertainty. These methods, bootstrap simulation and a likelihood-based method, are applied to three datasets. The datasets include a synthetic sample of 19 values from a Lognormal distribution, a sample of nine values obtained from measurements of the PCB concentration in leafy produce, and a sample of five values for the partitioning of chromium in the flue gas desulfurization system of coal-fired power plants. For each of these datasets, we employ the two methods to characterize uncertainty in the arithmetic mean and standard deviation, cumulative distribution functions based upon fitted parametric distributions, the 95th percentile of variability, and the 63rd percentile of uncertainty for the 81st percentile of variability. The latter is intended to show that it is possible to describe any point within the uncertain frequency distribution by specifying an uncertainty percentile and a variability percentile. Using the bootstrap method, we compare results based upon use of the method of matching moments and the method of maximum likelihood for fitting distributions to data. Our results indicate that with only 5–19 data points as in the datasets we have evaluated, there is substantial uncertainty based upon random sampling error. Both the boostrap and likelihood-based approaches yield comparable uncertainty estimates in most cases.
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  • 153
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    Risk analysis 19 (1999), S. 159-169 
    ISSN: 1539-6924
    Keywords: Trust ; geography ; personality ; environment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract A sample of 323 residents of New Jersey stratified by neighborhood quality (excellent, good, fair, poor) was gathered to determine if trust in science and technology to protect public health and environment at the societal scale was associated with trust of the local officials, such as the mayor, health officer, developers, mass media, and legislators who are guardians of the local environment. Societal (trust of science and technology) and neighborhood (mayor, health officer) dimensions of trust were found. These societal and neighborhood trust dimensions were weakly correlated. Respondents were divided into four trust-of-authority groups: high societal–high neighborhood, low societal–low neighborhood, high societal–low neighborhood, and low societal–high neighborhood. High societal–high neighborhood trust respondents were older, had lived in the neighborhoods for many years, were not troubled much by neighborhood or societal environmental threats, and had a strong sense of control over their environment. In strong contrast, low societal–low neighborhood trust respondents were relatively young, typically had lived in their present neighborhood for a short time, were troubled by numerous neighborhood and societal environmental threats, did not practice many personal public health practices, and felt little control over their environment.
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  • 154
    ISSN: 1539-6924
    Keywords: Risk ; fishing ; ethnicity ; perception ; toxics ; consumption
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Recreational and subsistence angling are important aspects of urban culture for much of North America where people are concentrated near the coasts or major rivers. Yet there are fish and shellfish advisories for many estuaries, rivers, and lakes, and these are not always heeded. This paper examines fishing behavior, sources of information, perceptions, and compliance with fishing advisories as a function of ethnicity for people fishing in the Newark Bay Complex of the New York–New Jersey Harbor. We test the null hypothesis that there were no ethnic differences in sources of information, perceptions of the safety of fish consumption, and compliance with advisories. There were ethnic differences in consumption rates, sources of information about fishing, knowledge about the safety of the fish, awareness of fishing advisories or of the correct advisories, and knowledge about risks for increased cancer and to unborn and young children. In general, the knowledge base was much lower for Hispanics, was intermediate for blacks, and was greatest for whites. When presented with a statement about the potential risks from eating fish, there were no differences in their willingness to stop eating fish or to encourage pregnant women to stop. These results indicate a willingness to comply with advisories regardless of ethnicity, but a vast difference in the base knowledge necessary to make informed risk decisions about the safety of fish and shellfish. Although the overall median income level of the population was in the $25,000–34,999 income category, for Hispanics it was on the border between $15,000–24,999 and $25,000–34,999.
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    The journal of Fourier analysis and applications 5 (1999), S. 545-562 
    ISSN: 1531-5851
    Keywords: 42C15 ; Weyl-Heisenberg frame ; dual window ; spline
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract We present a simple proof of Ron and Shen's frame bounds estimates for Gabor frames. The proof is based on the Heil and Walnut's representation of the frame operator and shows that it can be decomposed into a continuous family of infinite matrices. The estimates then follow from a simple application of Gershgorin's theorem to each matrix. Next, we show that, if the window function has exponential decay, also the dual function has some exponential decay. Then, we describe a numerical method to compute the dual function and give an estimate of the error. Finally, we consider the spline of order 2; we investigate numerically the region of the time-frequency plane where it generates a frame and we compute the dual function for some values of the parameters.
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    The journal of Fourier analysis and applications 5 (1999), S. 575-588 
    ISSN: 1531-5851
    Keywords: 42C15 ; 94A12 ; sampling ; multiresolution analysis ; Gibbs phenomenon
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    Topics: Mathematics
    Notes: Abstract We deal with the maximum Gibbs ripple of the sampling wavelet series of a discontinuous function f at a point t ∈R, for all possible values of a satisfyingf(t)=αf(t−0)+(1−a)f(t+0). For the Shannon wavelet series, we make a complete description of all ripples, for any a in [0,1]. We show that Meyer sampling series exhibit Gibbs Phenomenon for α〈0.12495 and α〉0.306853. We also give Meyer sampling formulas with maximum overshoots shorter than Shannon's for several α in [0,1].
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    The journal of Fourier analysis and applications 5 (1999), S. v 
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    Topics: Mathematics
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    The journal of Fourier analysis and applications 5 (1999), S. 127-157 
    ISSN: 1531-5851
    Keywords: Primary 30D10 ; 42C30 ; Secondary 40G99 ; 41A58 ; 94A12
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract It is well known that Gabor expansions generated by a lattice of Nyquist density are numerically unstable, in the sense that they do not constitute frame decompositions. In this paper, we clarify exactly how “bad” such Gabor expansions are, we make it clear precisely where the edge is between “enough” and “too little,” and we find a remedy for their shortcomings in terms of a certain summability method. This is done through an investigation of somewhat more general sequences of points in the time-frequency plane than lattices (all of Nyquist density), which in a sense yields information about the uncertainty principle on a finer scale than allowed by traditional density considerations. An important role is played by certain Hilbert scales of function spaces, most notably by what we call the Schwartz scale and the Bargmann scale, and the intrinsically interesting fact that the Bargmann transform provides a bounded invertible mapping between these two scales. This permits us to turn the problems into interpolation problems in spaces of entire functions, which we are able to treat.
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    Transformation groups 4 (1999), S. 35-52 
    ISSN: 1531-586X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract LetG be a classical algebraic group defined over an algebraically closed field. We classify all instances when a parabolic subgroupP ofG acts on its unipotent radicalP u , or onp u , the Lie algebra ofP u , with only a finite number of orbits. The proof proceeds in two parts. First we obtain a reduction to the case of general linear groups. In a second step, a solution for these is achieved by studying the representation theory of a particular quiver with certain relations. Furthermore, for general linear groups we obtain a combinatorial formula for the number of orbits in the finite cases.
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    The journal of Fourier analysis and applications 5 (1999), S. 331-345 
    ISSN: 1531-5851
    Keywords: 26B35 ; 42B05 ; 42B99 ; chirp ; oscillating function
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract We show that the trace of an indefinitely oscillating function on a subspace of ℝd is not always indefinitely oscillating. In the periodic case, the number of oscillations of the trace depends on the regularity of the function. In the general case, we exhibit a definitive counter-example.
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    The journal of Fourier analysis and applications 5 (1999), S. 385-408 
    ISSN: 1531-5851
    Keywords: Primary: 45E05, 47A10 ; Secondary: 35J25, 42B20 ; layer potentials ; spectral radius ; polyhedra ; Lipschitz domains
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract By producing a L2 convergent Neumann series, we prove the invertibility of the elastostatics and hydrostatics boundary layer potentials on arbitrary Lipschitz domains with small Lipschitz character and 3D polyhedra with large dihedral angles.
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    The journal of Fourier analysis and applications 5 (1999), S. 431-447 
    ISSN: 1531-5851
    Keywords: Eigenfunction expansions ; localization ; Primary: 42C14 ; Secondary: 42B08
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    Topics: Mathematics
    Notes: Abstract We state a localization principle for expansions in eigenfunctions of a self-adjoint second order elliptic operator and we prove an equiconvergence result between eigenfunction expansions and trigonometric expansions. We then study the Gibbs phenomenon for eigenfunction expansions of piecewise smooth functions on two-dimensional manifolds.
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    The journal of Fourier analysis and applications 5 (1999), S. 523-544 
    ISSN: 1531-5851
    Keywords: primary 62H05 ; 60E10 ; secondary 32E25 ; Cauchy type integral ; characteristic function ; completely monotonicity ; Liouville numbers ; Plemelj-Sokhotskii formula ; unimodality
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    Topics: Mathematics
    Notes: Abstract The function $$\varphi _\alpha ^\theta (t) = \frac{1}{{1 + e^{ - i\theta \operatorname{s} gnt} \left| t \right|^\alpha }},\alpha \in (0,2),\theta \in ( - \pi ,\pi ]$$ , is a characteristic function of a probability distribution iff $$\left| \theta \right| \leqslant \min (\tfrac{{\pi \alpha }}{2},\pi - \tfrac{{\pi \alpha }}{2})$$ . This distribution is absolutely continuous; for θ=0 it is symmetric. The latter case was introduced by Linnik in 1953 [13] and several applications were found later. The case θ≠0 was introduced by Klebanov, Maniya, and Melamed in 1984 [9], while some special cases were considered previously by Laha [12] and Pillai [18]. In 1994, Kotz, Ostrovskii and Hayfavi [10] carried out a detailed investigation of analytic and asymptotic properties of the density of the distribution for the symmetric case θ=0. We generalize their results to the non-symmetric case θ≠0. As in the symmetric case, the arithmetical nature of the parameter α plays an important role, but several new phenomena appear.
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    The journal of Fourier analysis and applications 5 (1999), S. 589-597 
    ISSN: 1531-5851
    Keywords: 42C15 ; 39B99 ; multivariate ; nonhomogeneous ; refinement
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    Topics: Mathematics
    Notes: Abstract We give necessary and sufficient conditions for the existence and uniqueness of compactly supported distribution solutionsf=(f 1,...,f r)T of nonhomogeneous refinement equations of the form $$f(x) = h(x) + \sum\limits_{\alpha \in A} {c_\alpha f(2x - \alpha )(x \in R^s )} $$ , where h=(h1,...,hr)Tis a compactly supported vector-valued multivariate distribution, A⊂Z+ s has compact support, and the coefficientsc α are real-valued r×r matrices. In particular, we find a finite dimensional matrix B, constructed from the coefficientsc α of the equation (I−B)q=p, where the vectorp depends on h. Our proofs proceed in the time domain and allow us to represent each solution regardless of the spectral radius of P(0):=2−s∑c α , which has been a difficulty in previous investigations of this nature.
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    The journal of Fourier analysis and applications 5 (1999), S. 599-615 
    ISSN: 1531-5851
    Keywords: 41A25 ; 42C15 ; 47B35 ; 15A99 ; shift-invariant systems ; finite section method ; block Toeplitz matrices ; Laurent operator ; Gabor frame ; filter banks ; band matrices
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    Topics: Mathematics
    Notes: Abstract A shift-invariant system is a collection of functions {gm,n} of the form gm,n(k)=gm(k−an). Such systems play an important role in time-frequency analysis and digital signal processing. A principal problem is to find a dual system γm,n(k)=γm(k−an) such that each functionf can be written asf= ∑〈f, γm,n〉gm,n. The mathematical theory usually addresses this problem in infinite dimensions (typically in L2 (ℝ) or ℓ2(ℤ)), whereas numerical methods have to operate with a finite-dimensional model. Exploiting the link between the frame operator and Laurent operators with matrix-valued symbol, we apply the finite section method to show that the dual functions obtained by solving a finite-dimensional problem converge to the dual functions of the original infinite-dimensional problem in ℓ2(ℤ). For compactly supported gm, n (FIR filter banks) we prove an exponential rate of convergence and derive explicit expressions for the involved constants. Further we investigate under which conditions one can replace the discrete model of the finite section method by the periodic discrete model, which is used in many numerical procedures. Again we provide explicit estimates for the speed of convergence. Some remarks on tight frames complete the paper.
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    Transformation groups 4 (1999), S. 25-34 
    ISSN: 1531-586X
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    Topics: Mathematics
    Notes: Abstract We consider actions of compact real Lie GroupsK on complex spacesX such that the associated reducedK-space admits a semistable quotient, e.g.X is a Stein space. We show that there is a complex spaceX c endowed with a holomorphic action of the universal complexificationG ofK that containsX as an openK-stable subset. As our main result, we prove that every coherentK-sheaf onX extends uniquely to a holomorphicG-sheaf onX c .
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    Transformation groups 4 (1999), S. 97-101 
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    Topics: Mathematics
    Notes: Abstract A characterization of the complexity of a homogeneous space $$\mathcal{O}$$ of a reductive groupG is given in terms of the mutual position of the tangent Lie algebra of the stabilizer of a generic point of $$\mathcal{O}$$ and the (−1)-eigenspace of a Weyl involution of $$\mathcal{O}$$ .
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    Transformation groups 4 (1999), S. 119-125 
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    Transformation groups 4 (1999), S. 219-272 
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    Topics: Mathematics
    Notes: Abstract In this paper we classifyℤ-graded transitive Lie superalgebras with prescribed nonpositive parts listed in [K2]. The classification of infinite-dimensional simple linearly compact Lie superalgebras given in [K2] is based on this result. We also study the structure of the exceptionalℤ-graded transitive Lie superalgebras and give their geometric realization.
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    Transformation groups 4 (1999), S. 329-353 
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    Topics: Mathematics
    Notes: Abstract We determine the covolumes of all hyperbolic Coxeter simplex reflection groups. These groups exist up to dimension 9. the volume computations involve several different methods according to the parity of dimension, subgroup relations and arithmeticity properties.
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    Circuits, systems and signal processing 18 (1999), S. 315-329 
    ISSN: 1531-5878
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract In earlier studies a multiclass vector quantization (MVQ)-based neural network design was explored for pattern classification. We reconsider that design here in the context of function emulation. With proper adjustment, the MVQ design demonstrates excellent performance. Moreover, the design algorithms sense discontinuities in the data and replicate them in the network.
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    Circuits, systems and signal processing 18 (1999), S. 365-376 
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract In earlier studies the concept of a fast form was generalized to a format that unified such discrete transform examples as the FFT, the FCT, the FST, and the FHT. In this study we consider the approximation of arbitrary linear maps by fast forms. Using simulation we evaluate the approximation capabilities of the generalized fast form.
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    Circuits, systems and signal processing 18 (1999), S. 377-393 
    ISSN: 1531-5878
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract On-line running spectral analysis is of considerable interest in many electrophysiological signals, such as the EEG (electroencephalograph). This paper presents a new method of implementing the fast Fourier transform (FFT) algorithm. Our “real-time FFT algorithm” efficiently utilizes computer time to perform the FFT computation while data acquisition proceeds so that local butterfly modules are built using the data points that are already available. The real-time FFT algorithm is developed using the decimation-in-time split-radix FFT (DIT sr-FFT) butterfly structure. In order to demonstate the synchronization ability of the proposed algorithm, the authors develop a method of evaluating the number of arithmetic operations that it requires. Both the derivation and the experimental result show that the real-time FFT algorithm is superior to the conventional whole-block FFT algorithm in synchronizing with the data acquisition process. Given that the FFT sizeN=2 r , real-time implementation of the FFT algorithm requires only 2/r the computational time required by the whole-block FFT algorithm.
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    Circuits, systems and signal processing 18 (1999), S. 523-523 
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    Circuits, systems and signal processing 18 (1999), S. 539-551 
    ISSN: 1531-5878
    Keywords: H 2 deconvolution filter ; envelope-constrained filter ; finite impulse response filter ; linear matrix inequality
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract In this paper, we consider an envelope-constrained (EC)H 2 optimal finite impulse response (FIR) filtering problem. Our aim is to design a filter such that theH 2 norm of the filtering error transfer function is minimized subject to the constraint that the filter output with a given input to the signal system is contained or bounded by a prescribed envelope. The filter design problem is formulated as a standard optimization problem with linear matrix inequality (LMI) constraints. Furthermore, by relaxing theH 2 norm constraint, we propose a robust ECFIR filter design algorithm based on the LMI approach.
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    Circuits, systems and signal processing 18 (1999), S. 565-585 
    ISSN: 1531-5878
    Keywords: Two-dimensional system ; model conversion ; Roesser's model
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract This paper presents a geometric-series method for finding two-dimensional (2D) discrete-time (continuous-time) state-space models from 2D continuous-time (discretetime) systems. This method allows the use of well-developed theorems and algorithms in the 2D discrete-time (continuous-time) domain to indirectly carry out analysis and design of hybrid 2D composite systems.
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    Circuits, systems and signal processing 18 (1999), S. 505-521 
    ISSN: 1531-5878
    Keywords: Multirate systems ; multirate signal processing ; filter banks ; optimal design
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The design of general nonuniform filter banks is studied. Contrary to uniform filter banks, in nonuniform filter banks, it may not be possible to achieve perfect reconstruction, but in some cases by using optimization techniques, we can design acceptable filter banks. Here, the initial finite impulse response (FIR) analysis filters are designed according to the characteristics of the input. By the design procedure, the FIR synthesis filters are found so that theH-norm of an error system is minimized over all synthesis filters that have a prespecified order. Then, the synthesis filters obtained in the previous step are fixed, and the analysis filters are found similarly. By iteration, theH-norm of the error system decreases until it converges to its final value. At each iteration, the coefficients of the analysis or synthesis filters are obtained by finding the least squares solution of a system of linear equations. If necessary, the frequency characteristics of the filters can be altered by adding penalty terms to the objective function.
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    Circuits, systems and signal processing 18 (1999), S. 617-617 
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    Circuits, systems and signal processing 18 (1999), S. 43-57 
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract We consider multirate digital control systems that consist of an interconnection of a continuous-time nonlinear plant (described by ordinary differential equations) and a digital lifted controller (described by ordinary difference equations). The input to the digital controller consists of the multirate sampled output of the plant, and the input to the continuous-time plant consists of the multirate hold output of the digital controller. In this paper we show that when quantizer nonlinearities are neglected, then under reasonable conditions (which exclude the critical cases), the stability properties (in the Lyapunov sense) of the trivial solution of the nonlinear multirate digital control system can be deduced from the stability properties of the trivial solution of its linearization. We also point out that certain results involving quantization effects and stabilizing controllers can be established which are in the spirit of some existing results.
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    Circuits, systems and signal processing 18 (1999), S. 59-73 
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Chaotic systems provide a simple means of generating deterministic signals that resemble white noise. It is this noise-like property that provides the potential for applying chaotic systems in communications. In this work, we report a detailed study of the logistic map for use as direct-sequence spread-spectrum (DS/SS) codes. The advantages of the chaotic DS/SS codes are the almost unlimited number of distinct sequences of arbitrary lengths, the ease of generating these sequences, and the increased privacy afforded by the noise-like appearance of these sequences. Some design criteria are provided from the correlation properties of these sequences, and bit-error rate (BER) results are generated by Monte Carlo simulations.
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    Circuits, systems and signal processing 18 (1999), S. 75-84 
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The asymptotic behavior of block floating-point and floating-point digital filters is analyzed. As a result, mantissa wordlength conditions are derived guaranteeing the absence of limit cycles in the regular dynamic range. Explicitly, the requirements are given for block floating-point state space filters with different quantization formats. Although these conditions are only sufficient, examples are given in which they are also necessary. In most cases the conditions are easily satisfied.
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    Circuits, systems and signal processing 18 (1999), S. 85-85 
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    Circuits, systems and signal processing 18 (1999), S. 87-88 
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    Circuits, systems and signal processing 18 (1999), S. 189-190 
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    Circuits, systems and signal processing 18 (1999), S. 169-181 
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract In this paper the Cramér-Rao bound (CRB) for a general nonparametric spectral estimation problem is derived under a local smoothness condition (more exactly, the spectrum is assumed to be well approximated by a piecewise constant function). Further-more, it is shown that under the aforementioned condition the Thomson method (TM) and Daniell method (DM) for power spectral density (PSD) estimation can be interpreted as approximations of the maximum likelihood PSD estimator. Finally the statistical efficiency of the TM and DM as nonparametric PSD estimators is examined and also compared to the CRB for autoregressive moving-average (ARMA)-based PSD estimation. In particular for broadband signals, the TM and DM almost achieve the derived nonparametric performance bound and can therefore be considered to be nearly optimal.
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    Circuits, systems and signal processing 18 (1999), S. 149-168 
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The issue of stability of higher-order, single-stage Sigma-Delta (ΣΔ) modulators is addressed using a method from nonlinear system theory. As a result, theoretical bounds for the quantizer input of the modulators are derived. A new method for stabilizing the ΣΔ modulators is then presented. It uses the quantizer input bound for possible instability detection. Upon detection of such a state, the highest-order integrator is cut off, effectively reducing the order of the modulator, and thus resulting in a stable system. The method is easily implemented and results in a very good signal-to-noise ratio (SNR) and fast return to normal operation compared to other stabilization methods.
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    Circuits, systems and signal processing 18 (1999), S. 225-239 
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The uncorrelated component analysis (UCA) of a stationary random vector process consists of searching for a linear transformation that minimizes the temporal correlation between its components. Through a general analysis we show that under practically reasonable and mild conditions UCA is a solution for blind source separation. The theorems proposed in this paper for UCA provide useful insights for developing practical algorithms. UCA explores the temporal information of the signals, whereas independent component analysis (ICA) explores the spatial information; thus UCA can be applied for source separation in some cases where ICA cannot. For blind source separation, combining ICA and UCA may give improved performance because more information can be utilized. The concept of single UCA (SUCA) is also proposed, which leads to sequential source separation.
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    Circuits, systems and signal processing 18 (1999), S. i 
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    Circuits, systems and signal processing 18 (1999), S. 331-350 
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract This paper analyzes the nonlinear phenomenon of rotating stall via the methods of projection [Elementary Stability and Bifurcation Theory, G. Iooss and D. D. Joseph, Springer-Verlag, 1980] and Lyapunov [J.-H. Fu,Math. Control Signal Systems, 7, 255–278, 1994]. A compressor model of Moore and Greitzer is adopted in which rotating stall dynamics are associated with Hopf bifurcations. Local stability for each pair of the critical modes is studied and characterized. It is shown that local stability of individual pairs of the critical modes determines collectively local stability of the compressor model. Explicit conditions are obtained for local stability of rotating stall which offer new insight into the design, and active control of axial flow compressors.
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    Circuits, systems and signal processing 18 (1999), S. 407-429 
    ISSN: 1531-5878
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract We describe herein a new means of training dynamic multilayer nonlinear adaptive filters, orneural networks. We restrict our discussion to multilayer dynamic Volterra networks, which are structured so as to restrict their degrees of computational freedom, based on a priori knowledge about the dynamic operation to be emulated. The networks consist of linear dynamic filters together with nonlinear generalized single-layer subnets. We describe how a Newton-like optimization strategy can be applied to these dynamic architectures and detail a newmodified Gauss-Newton optimization technique. The new training algorithm converges faster and to a smaller value of cost than backpropagation-through-time for a wide range of adaptive filtering applications. We apply the algorithm to modeling the inverse of a nonlinear dynamic tracking system. The superior performance of the algorithm over standard techniques is demonstrated.
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    Circuits, systems and signal processing 18 (1999), S. 445-455 
    ISSN: 1531-5878
    Keywords: Linear-phase digital filters ; FIR integrators
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract In many signal processing situations, the desired (ideal) magnitude response of the filter is a rational function: $$\tilde H(\omega ) = |1/\omega |$$ (a digital integrator). The requirements of a linear phase response and guaranteed stable performance limit the design to a finite impulse response (FIR) structure. In many applications we require the FIR filter to yield a highly accurate magnitude response for a narrow band of frequencies with maximal flatness at an arbitrary frequencyω 0 in the spectrum (0, π). No techniques for meeting such requirements with respect to approximation of $$\tilde H(\omega )$$ are known in the literature. This paper suggests a design by which the linear phase magnitude response $$|\tilde H(\omega )|$$ can be approximated by an FIR configuration giving a maximally flat (in the Butterworth sense) response at an arbitrary frequency ω0, 0〈ω0〈π*. A technique to compute exact weights for the design has also been given.
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    Circuits, systems and signal processing 18 (1999), S. 524-524 
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    Circuits, systems and signal processing 18 (1999), S. 525-537 
    ISSN: 1531-5878
    Keywords: Random sampling, digital signal processing ; spectral estimation ; computational algorithm
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Random sampling is one of the methods used to achieve sub-Nyquist sampling. This paper proposes a novel algorithm to evaluate the circular autocorrelation of a randomly sampled sequence, from which its power density spectrum can be obtained. With uniform sampling, the size of each lag (the step size) for computing an autocorrelation of a sequence is the same as the sampling period. When random sampling is adopted, the step size should be chosen such that the highest-frequency component of interest contained in a sequence can be accommodated. To find overlaps between a time sequence and its shifted version, an appropriate window is opened in one of the time sequences. To speed up the process, a marker is set to limit the range of searching for overlaps. The proposed method of estimating the power spectrum via autocorrelation is comparable in terms of accuracy and signal-to-noise ratio (SNR) to the conventional point rule. The techniques introduced can also apply to other operations for randomly sampled sequences.
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    Circuits, systems and signal processing 18 (1999), S. 587-609 
    ISSN: 1531-5878
    Keywords: Transfinite graphs ; infinite electrical networks ; current flows through infinity
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Transfinite electrical networks of ranks larger than 1 have previously been defined by arbitrarily joining together various infinite extremities through transfinite nodes that are independent of the networks' resistance values. Thus, some or all of those transfinite nodes may remain ineffective in transmitting current “through infinity.” In this paper, transfinite nodes are defined in terms of the paths that permit currents to ”reach infinity.” This is accomplished by defining a suitable metricd v on the node setN S v of eachv-sectionS v, av-section being a maximal subnetwork whose nodes are connected by two-ended paths of ranks no larger thanv. Upon taking the completion ofN S v under that metricd v, we identify those extremities (now calledv-terminals) that are accessible to current flows. These are used to define transfinite nodes that combine such extremities. The construction is recursive and is carried out through all the natural number ranks, and then through the first arrow rank ω and the first limit-ordinal rank ω. The recursion can be carried still further. All this provides a more natural development of transfinite networks and indeed simplifies the theory of electrical behavior for such networks.
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  • 195
    ISSN: 1539-6924
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    Topics: Energy, Environment Protection, Nuclear Power Engineering
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  • 196
    ISSN: 1539-6924
    Keywords: Cancer dose–response modeling ; multistage model ; two-stage model ; hazard functions ; carcinogenesis ; Benzene ; Dieldrin ; Ethylene Thiourea ; Trichloroethylene ; Vinyl Chloride
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract We compare the regulatory implications of applying the traditional (linearized) and exact two-stage dose–response models to animal carcinogenic data. We analyze dose–response data from six studies, representing five different substances, and we determine the “goodness-of-fit” of each model as well as the 95% confidence lower limit of the dose corresponding to a target excess risk of 10−5 (the target risk dose TRD). For the two concave datasets, we find that the exact model gives a substantially better fit to the data than the traditional model, and that the exact model gives a TRD that is an order of magnitude lower than that given by the traditional model. In the other cases, the exact model gives a fit equivalent to or better than the traditional model. We also show that although the exact two-stage model may exhibit dose–response concavity at moderate dose levels, it is always linear or sublinear, and never supralinear, in the low-dose limit. Because regulatory concern is almost always confined to the low-dose region extrapolation, supralinear behavior seems not to be of regulatory concern in the exact two-stage model. Finally, we find that when performing this low-dose extrapolation in cases of dose–response concavity, extrapolating the model fit leads to a more conservative TRD than taking a linear extrapolation from 10% excess risk. We conclude with a set of recommendations.
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    Risk analysis 19 (1999), S. 69-81 
    ISSN: 1539-6924
    Keywords: Parameters ; probability distributions ; validity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract In any model the values of estimates for various parameters are obtained from different sources each with its own level of uncertainty. When the probability distributions of the estimates are obtained as opposed to point values only, the measurement uncertainties in the parameter estimates may be addressed. However, the sources used for obtaining the data and the models used to select appropriate distributions are of differing degrees of uncertainty. A hierarchy of different sources of uncertainty based upon one's ability to validate data and models empirically is presented. When model parameters are aggregated with different levels of the hierarchy represented, this implies distortion or degradation in the utility and validity of the models used. Means to identify and deal with such heterogeneous data sources are explored, and a number of approaches to addressing this problem is presented. One approach, using Range/Confidence Estimates coupled with an Information Value Analysis Process, is presented as an example.
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  • 198
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    Electronic Resource
    Springer
    Risk analysis 19 (1999), S. 1-2 
    ISSN: 1539-6924
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Type of Medium: Electronic Resource
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  • 199
    ISSN: 1539-6924
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Type of Medium: Electronic Resource
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  • 200
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    Electronic Resource
    Springer
    Risk analysis 19 (1999), S. 33-42 
    ISSN: 1539-6924
    Keywords: Uncertainty ; model uncertainty ; epistemic uncertainty ; integrated assessment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract The characterization and treatment of uncertainty poses special challenges when modeling indeterminate or complex coupled systems such as those involved in the interactions between human activity, climate and the ecosystem. Uncertainty about model structure may become as, or more important than, uncertainty about parameter values. When uncertainty grows so large that prediction or optimization no longer makes sense, it may still be possible to use the model as a “behavioral test bed” to examine the relative robustness of alternative observational and behavioral strategies. When models must be run into portions of their phase space that are not well understood, different submodels may become unreliable at different rates. A common example involves running a time stepped model far into the future. Several strategies can be used to deal with such situations. The probability of model failure can be reported as a function of time. Possible alternative “surprises” can be assigned probabilities, modeled separately, and combined. Finally, through the use of subjective judgments, one may be able to combine, and over time shift between models, moving from more detailed to progressively simpler order-of-magnitude models, and perhaps ultimately, on to simple bounding analysis.
    Type of Medium: Electronic Resource
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