on the effectiveness of whole spectral shape for vowel perception the formant hypothesis of vowel perception where the lowest two or three formant frequencies are essential cues for vowel quality perception is widely accepted there has however been some controversy suggesting that formant frequencies are not sufficient and that the whole spectral shape is necessary for perception three psychophysical experiments were performed to study this question in the first experiment the first or second formant peak of stimuli was suppressed as much as possible while still maintaining the original spectral shape the responses to these stimuli were not radically different from the ones for the unsuppressed control in the second experiment f2 suppressed stimuli whose amplitude ratios of high to low frequency components were systemically changed were used the results indicate that the ratio changes can affect perceived vowel quality especially its place of articulation in the third experiment the full formant stimuli whose amplitude ratios were changed from the original and whose f2 s were kept constant were used the results suggest that the amplitude ratio is equal to or more effective than f2 as a cue for place of articulation we conclude that formant frequencies are not exclusive cues and that the whole spectral shape can be crucial for vowel perception

factors affecting the use of noise band vocoders as acoustic models for pitch perception in cochlear implants although in a number of experiments noise band vocoders have been shown to provide acoustic models for speech perception in cochlear implants ci the present study assesses in four experiments whether and under what limitations noise band vocoders can be used as an acoustic model for pitch perception in ci the first two experiments examine the effect of spectral smearing on simulated electrode discrimination and fundamental frequency f0 discrimination the third experiment assesses the effect of spectral mismatch in an f0 discrimination task with two different vocoders the fourth experiment investigates the effect of amplitude compression on modulation rate discrimination for each experiment the results obtained from normal hearing subjects presented with vocoded stimuli are compared to results obtained directly from ci recipients the results show that place pitch sensitivity drops with increased spectral smearing and that place pitch cues for multi channel stimuli can adequately be mimicked when

the effect of spatial separation on informational and energetic masking of speech the effect of spatial separation of sources on the masking of a speech signal was investigated for three types of maskers ranging from energetic to informational normal hearing listeners performed a closed set speech identification task in the presence of a masker at various signal to noise ratios stimuli were presented in a quiet sound field the signal was played from 0 azimuth and a masker was played either from the same location or from 90 to the right signals and maskers were derived from sentences that were preprocessed by a modified cochlear implant simulation program that filtered each sentence into 15 frequency bands extracted the envelopes from each band and used these envelopes to modulate pure tones at the center frequencies of the bands in each trial the signal was generated by summing together eight randomly selected frequency bands from the preprocessed signal sentence three maskers were derived from the preprocessed masker sentences 1 different band sentence which was generated by summing together six randomly selected frequency bands out of the seven bands not present in the signal resulting in primarily informational masking 2 different band noise which was generated by convolving the different band sentence with gaussian noise and 3 same band noise which was generated by summing the same eight bands from the preprocessed masker sentence that were used in the signal sentence and convolving the result with gaussian noise resulting in primarily energetic masking results revealed that in the different band sentence masker the effect of spatial separation averaged 18 db at 51 correct while in the different band and same band noise maskers the effect was less than 10 db these results suggest that in these conditions the advantage due to spatial separation of sources is greater for informational masking than for energetic masking

an evaluation of semidefinite programming based approaches for discrete lot sizing problems abstract the present work is intended as a first step towards applying semidefinite programming models and tools to discrete lot sizing problems including sequence dependent changeover costs and times such problems can be formulated as quadratically constrained quadratic binary programs we investigate several semidefinite relaxations by combining known reformulation techniques recently proposed for generic quadratic binary problems with problem specific strengthening procedures developed for lot sizing problems our computational results show that the semidefinite relaxations consistently provide lower bounds of significantly improved quality as compared with those provided by the best previously published linear relaxations in particular the gap between the semidefinite relaxation and the optimal integer solution value can be closed for a significant proportion of the small size instances thus avoiding to resort to a tree search procedure the reported computation times are significant however improvements in sdp technology can still be expected in the future making sdp based approaches to discrete lot sizing more competitive

modulation spectra of natural sounds and ethological theories of auditory processing the modulation statistics of natural sound ensembles were analyzed by calculating the probability distributions of the amplitude envelope of the sounds and their time frequency correlations given by the modulation spectra these modulation spectra were obtained by calculating the two dimensional fourier transform of the autocorrelation matrix of the sound stimulus in its spectrographic representation since temporal bandwidth and spectral bandwidth are conjugate variables it is shown that the joint modulation spectrum of sound occupies a restricted space sounds cannot have rapid temporal and spectral modulations simultaneously within this restricted space it is shown that natural sounds have a characteristic signature natural sounds in general are low passed showing most of their modulation energy for low temporal and spectral modulations animal vocalizations and human speech are further characterized by the fact that most of the spectral modulation power is found only for low temporal modulation similarly the distribution of the amplitude envelopes also exhibits characteristic shapes for natural sounds reflecting the high probability of epochs with no sound systematic differences across frequencies and a relatively uniform distribution for the log of the amplitudes for vocalizations it is postulated that the auditory system as well as engineering applications may exploit these statistical properties to obtain an efficient representation of behaviorally relevant sounds to test such a hypothesis we show how to create synthetic sounds with first and second order envelope statistics identical to those found in natural sounds

speech perception based on spectral peaks versus spectral shape this study was designed to measure the relative contributions to speech intelligibility of spectral envelope peaks including but not limited to formants versus the detailed shape of the spectral envelope the problem was addressed by asking listeners to identify sentences and nonsense syllables that were generated by two structurally identical source filter synthesizers one of which constructs the filter function based on the detailed spectral envelope shape while the other constructs the filter function using a purposely coarse estimate that is based entirely on the distribution of peaks in the envelope viewed in the broadest terms the results showed that nearly as much speech information is conveyed by the peaks only method as by the detail preserving method just as clearly however every test showed some measurable advantage for spectral detail although the differences were not large in absolute terms

further development of the k enstrophy turbulence closure model the k model is extended to the study of two dimensional and three dimensional separated external e ows where morkovin s hypothesis is expected to hold the resulting model is free of damping and wall functions and is coordinate independent further all modeled correlations are tensorially consistent and galilean invariant applications include a variety of separated e ows over airfoils and a cylinder offset e are juncture comparisons are made with other turbulence models and experiment in general good agreement with experiment is indicated the results demonstrate that it is possible to develop a two equation turbulence model that is capable of predicting separated e ows without sacrie cing performance for free shear layers

speech recognition as a function of the number of channels in perimodiolar electrode recipients this study investigated the number of channels needed for maximum speech understanding and sound quality in 30 adult cochlear implant ci recipients with perimodiolar electrode arrays verified via imaging to be completely within scala tympani st performance was assessed using a continuous interleaved sampling cis strategy with 4 8 10 and 16 channels and n of m with 16 maxima listeners were administered auditory tasks of speech understanding monosyllables sentences quiet and 5 db signal to noise ratio snr vowels consonants spectral modulation detection as well as subjective estimates of sound quality results were as follows 1 significant performance gains were observed for speech in quiet monosyllables and sentences with 16 as compared to 8 channel cis 2 16 channels in a 16 of m strategy yielded significantly higher outcomes than 16 channel cis for sentences in noise percent correct and subjective sound quality and spectral modulation detection 3 16 channels in a 16 of m strategy yielded significantly higher outcomes as compared to 8 and 10 channel cis for monosyllables sentences quiet and noise consonants spectral modulation detection and subjective sound quality 4 16 versus 8 maxima yielded significantly higher speech recognition for monosyllables and sentences in noise using an n of m strategy and 5 the degree of benefit afforded by 16 versus 8 maxima was inversely correlated with mean electrode to modiolus distance these data demonstrate greater channel independence with perimodiolar electrode arrays as compared to previous studies with straight electrodes and warrant further investigation of the minimum number of maxima and number of channels needed for maximum auditory outcomes

a narrow band pattern matching model of vowel perception the purpose of this paper is to propose and evaluate a new model of vowel perception which assumes that vowel identity is recognized by a template matching process involving the comparison of narrow band input spectra with a set of smoothed spectral shape templates that are learned through ordinary exposure to speech in the present simulation of this process the input spectra are computed over a sufficiently long window to resolve individual harmonics of voiced speech prior to template creation and pattern matching the narrow band spectra are amplitude equalized by a spectrum level normalization process and the information bearing spectral peaks are enhanced by a flooring procedure that zeroes out spectral values below a threshold function consisting of a center weighted running average of spectral amplitudes templates for each vowel category are created simply by averaging the narrow band spectra of like vowels spoken by a panel of talkers in the present implementation separate templates are used for men women and children the pattern matching is implemented with a simple city block distance measure given by the sum of the channel by channel differences between the narrow band input spectrum level equalized and floored and each vowel template spectral movement is taken into account by computing the distance measure at several points throughout the course of the vowel the input spectrum is assigned to the vowel template that results in the smallest difference accumulated over the sequence of spectral slices the model was evaluated using a large database consisting of 12 vowels in hvd context spoken by 45 men 48 women and 46 children the narrow band model classified vowels in this database with a degree of accuracy 91 4 approaching that of human listeners

further experiments on supersonic turbulent flow development in a square duct the mean flow structure of supersonic turbulent adiabatic wall flow in a square duct is investigated experimentally over a development length x d 0 50 for a uniform flow mach 3 9 condition at the duct inlet the results show that a secondary flow cell structure develops which is similar to that for the incompressible case development of the primary flow is influenced by the combined effects of the secondary flow and the streamwise adverse pressure gradient total pressure axial mean velocity and mach number profiles are presented which show that the outer flow is sensitive primarily to the streamwise pressure gradient while flow in the near wall region is dominated by the secondary flow axial mean velocity profiles plotted in terms of van driest scaled variables show that a well defined log law region exists in the near wall layer this region exists in the presence of a secondary flow which continuously modifies spanwise wall shear stress behavior along the length of the duct

speech intelligibility as a function of the number of channels of stimulation for signal processors using sine wave and noise band outputs vowels consonants and sentences were processed through software emulations of cochlear implant signal processors with 2 9 output channels the signals were then presented as either the sum of sine waves at the center of the channels or as the sum of noise bands the width of the channels to normal hearing listeners for identification the results indicate as previous investigations have suggested that high levels of speech understanding can be obtained using signal processors with a small number of channels the number of channels needed for high levels of performance varied with the nature of the test material for the most difficult material vowels produced by men women and girls no statistically significant differences in performance were observed when the number of channels was increased beyond 8 for the least difficult material sentences no statistically significant differences in performance were observed when the number of channels was increased beyond 5 the nature of the output signal noise bands or sine waves made only a small difference in performance the mechanism mediating the high levels of speech recognition achieved with only few channels of stimulation may be the same one that mediates the recognition of signals produced by speakers with a high fundamental frequency i e the levels of adjacent channels are used to determine the frequency of the input signal the results of an experiment in which frequency information was altered but temporal information was not altered indicates that vowel recognition is based on information in the frequency domain even when the number of channels of stimulation is small

discrete lotsizing and scheduling by batch sequencing the discrete lotsizing and scheduling problem for one machine with sequence dependent setup times and setup costs is solved as a single machine scheduling problem which we term the batch sequencing problem the relationship between the lotsizing problem and the batch sequencing problem is analyzed the batch sequencing problem is solved with a branch bound algorithm which is accelerated by bounding and dominance rules the algorithm is compared with recently published procedures for solving variants of the dlsp and is found to be more efficient if the number of items is not large

multiscale model for turbulent flows a model is devised for computing general turbulent flows the model is an improvement over two equation turbulence models in a critically important manner that is the new model accounts for disalignment of the reynolds stress tensor and the mean strain rate tensor principal axes the improved representation of the reynolds stress tensor has been accomplished through the introduction of a multiscale description of the turbulence i e two energy scales are used corresponding to upper and lower partitions of the turbulence energy spectrum a novel feature of the formulation is that the differential equation for the reynolds stress tensor is of first order which in effect corresponds to what can be termed an algebraic stress model with convective terms as a consequence of its mathematical simplicity the model is very efficient and easy to implement computationally the model is applied to a wide range of turbulent flows including homogeneous turbulence compressible and incompressible two dimensional boundary layers and unsteady boundary layers including periodic separation and reattachment comparisons with corresponding experimental data show that the model reproducesall salient features of the flows considered perturbation analysis of the viscous sublayer shows that integration through the sublayer can be accomplished with no special viscous modifications to the closure coefficients appearing in the model

spectral integration of speech bands in normal hearing and hearing impaired listeners this investigation examined whether listeners with mild moderate sensorineural hearing impairment have a deficit in the ability to integrate synchronous spectral information in the perception of speech in stage 1 the bandwidth of filtered speech centered either on 500 or 2500 hz was varied adaptively to determine the width required for approximately 15 25 correct recognition in stage 2 these criterion bandwidths were presented simultaneously and percent correct performance was determined in fixed block trials experiment 1 tested normal hearing listeners in quiet and in masking noise the main findings were 1 there was no correlation between the criterion bandwidths at 500 and 2500 hz 2 listeners achieved a high percent correct in stage 2 approximately 80 and 3 performance in quiet and noise was similar experiment 2 tested listeners with mild moderate sensorineural hearing impairment the main findings were 1 the impaired listeners showed high variability in stage 1 with some listeners requiring narrower and others requiring wider bandwidths than normal and 2 hearing impaired listeners achieved percent correct performance in stage 2 that was comparable to normal the results indicate that listeners with mild moderate sensorineural hearing loss do not have an essential deficit in the ability to integrate across frequency speech information

wall normal free reynolds stress closure for three dimensional compressible separated flows a near wall reynolds stress closure that is independent of the distance from the wall and of the normal to the walldirection isdevelopedandvalidated particularattention wasgiven intheapplicabilityofthemodeltocomplex three dimensional e ows with shock waves and boundary layer separation in the separated e ow region measurements andmodelcomputations indicatethatthe e atnessparameter aoftheanisotropy tensor aij approaches unity therefore controlofseparation isachieved in themodel through theparticularfunctional dependenceoftherapid pressure strain isotropization of production model coefe cienton a echo termsaretreated by replacing geometric normalsanddistancesbyfunctionsofthegradientsofturbulencelengthscaleandanisotropytensorinvariants the modelisinitiallycomparedwithmeasurementsforcompressiblee at plateboundary layere ows itisthenvalidated by comparison with experimental data in a two dimensional compression corner oblique shock wave boundarylayer interaction at mach 3 finally the model is applied to the computation of the three dimensional interaction of a mach 1 5 1 8 strong shock wave with the boundary layers of a rectangular channel e tted with a swept bump on the lower wall and results are compared with measurements one important advantage of the proposed model is its robustness in complex three dimensional e ows a detailed discussion of therange of validity of the model and possible improvements is presented

the effect of enhanced spectral contrast on the internal representation of vowel shaped noise two steady state noise excited vowel sounds of 200 ms duration were synthesized one similar to a naturally produced whispered vowel the other with energy removed outside a nominal 50 hz band centered at each formant peak the threshold for a brief sinusoidal probe tone was measured at frequencies corresponding to the peaks and troughs in the vowel spectra in both forward and simultaneous masking the masking functions for a flat spectrum masker at each frequency were also measured so that the vowel masking patterns could be expressed in terms of the equivalent broadband masker level in the first experiment masking patterns for the two maskers were measured with three normal hearing subjects increasing spectral contrast was effective in increasing peak valley differences in the masking patterns up to 2 5 khz contrast was greater in forward than in simultaneous masking suggesting that the internal representation of a vowel may be enhanced by suppression in a second experiment masking patterns and flat spectrum masking functions were measured with three listeners with moderate sensorineural hearing impairments the enhancement produced by increasing spectral contrast was less than that obtained with normal hearing listeners but still present up to 2 5 khz a comparison of forward and simultaneous masking patterns again revealed an increase in peak valley differences suggesting that suppression mechanisms were still effective in these listeners the ability to enhance the internal representation of speechlike sounds in hearing impaired listeners may have implications for the design of signal processing hearing aids

modeling the judgment of vowel quality differences the hypothesis of this study is that the auditory cues relevant to listeners judgment of vowel quality are a spectral representation of loudness density versus pitch a model is described that generates such patterns for steady state vowels in addition to the nonlinear transformations underlying the loudness density and pitch scales it incorporates experimentally established characteristics associated with frequency resolution and masking such as the critical band concept this model is combined with a measure of auditory perceptual distance which operating on pairs of vowels treats each stimulus representation as a single spectral shape in order to test the distance metric and the model experimental data were gathered from listeners numerical estimates of quality differences between stimulus pairs which compared four formant and two formant vowels the correlation between experimental and theoretical results was 0 89 we interpret this value to indicate that the present definition of auditory cue and auditory distance can be said to account for the experimental behavior of our listeners only in a rather gross fashion on the other hand the theory was developed on the basis of rather conservative assumptions about the nature of auditory cues for instance the model ignores the possibility of temporal coding and certain nonlinear effects and it does not pay special attention to spectral peaks seen in that light the agreement between observed and predicted auditory distance is remarkably good

algebraic turbulence modeling for unstructured and adaptive meshes an algebraic turbulence model based on the baldwin lomax model has been implemented for use on unstructured grids the implementation is based on the use of local background turbulence meshes at each time step flow variables are interpolated from the unstructured mesh onto the background structured meshes the turbulence model is executed on these meshes and the resulting eddy viscosity values are interpolated back to the unstructured mesh modifications to the algebraic model were required to enable the treatment of more compli cated flows such as confluent boundary layers and wakes the model is used in conjunction with an efficient unstructured multigrid finite element navier stokes solver in order to compute compressible turbulent flows on fully unstructured meshes solutions about single and multiple element airfoils are obtained and compared with experimental data he use of unstructured mesh techniques for computa tional fluid dynamics cfd problems has become more widespread in recent years due to the flexibility they afford in discretizing arbitrarily complex geometries and due to the possibility they offer in resolving highly localized flow phenomena through the use of adaptive meshing however research on unstructured mesh techniques for cfd has con centrated almost exclusively on the solution of the euler equa tions in two or three dimensions for viscous flow calculations about nonsimple geometries hybrid meshes have generally been employed 1 3 where a thin structured mesh is placed in the boundary layer and wake regions and an unstructured mesh is constructed in the outer inviscid region of the flowfield besides leading to an increase in coding complexity this type of compromise limits the generality of the unstruc tured mesh approach in dealing with arbitrarily complex geometries such as multiple body geometries with close toler ances where confluent boundary layers or wakes may occur and complicates the task of performing adaptive meshing in the inviscid as well as viscous regions of flow it appears that the difficulties associated with generating highly stretched unstructured meshes which are required for efficiently resolv ing viscous shear layers as well as the efficient implementa tion of a turbulence model on such meshes has generally im peded the use of fully unstructured meshes for viscous flows the use of unstructured meshes throughout the entire flowfield is advocated in the present work previous work by the author has shown how a highly stretched unstructured mesh suitable for high reynolds number viscous flow calcula tions may be constructed4 and has also discussed the develop ment of an efficient unstructured navier stokes solver for laminar flows 5 this paper is thus concerned with the effi cient implementation of a turbulence model for computing high reynolds number turbulent flows using fully unstruc tured meshes

evaluating models of vowel perception there is a long standing debate concerning the efficacy of formant based versus whole spectrum models of vowel perception categorization data for a set of synthetic steady state vowels were used to evaluate both types of models the models tested included various combinations of formant frequencies and amplitudes principal components derived from excitation patterns and perceptually scaled lpc cepstral coefficients the stimuli were 54 five formant synthesized vowels that had a common f1 frequency and varied orthogonally in f2 and f3 frequency twelve speakers of american english categorized the stimuli as the vowels or results indicate that formant frequencies provided the best account of the data only if nonlinear terms in the form of squares and cross products of the formant values were also included in the analysis the excitation pattern principal components also produced reasonably accurate fits to the data although a wish to use the lowest dimensional representation would dicta

the use of acoustic cues for phonetic identification effects of spectral degradation and electric hearing although some cochlear implant ci listeners can show good word recognition accuracy it is not clear how they perceive and use the various acoustic cues that contribute to phonetic perceptions in this study the use of acoustic cues was assessed for normal hearing nh listeners in optimal and spectrally degraded conditions and also for ci listeners two experiments tested the tense lax vowel contrast varying in formant structure vowel inherent spectral change and vowel duration and the word final fricative voicing contrast varying in f1 transition vowel duration consonant duration and consonant voicing identification results were modeled using mixed effects logistic regression these experiments suggested that under spectrally degraded conditions nh listeners decrease their use of formant cues and increase their use of durational cues compared to nh listeners ci listeners showed decreased use of spectral cues like formant structure and formant change and consonant voicing and showed greater use of durational cues especially for the fricative contrast the results suggest that although nh and ci listeners may show similar accuracy on basic tests of word phoneme or feature recognition they may be using different perceptual strategies in the process

the discrete lot sizing and scheduling problem with sequence dependent setup costs abstract we consider the problem of scheduling several products on a single machine so as to meet the known dynamic demand and to minimize the sum of inventory costs and sequence dependent setup costs the planning interval is subdivided into many short periods e g shifts or days and any lot must last one or several full periods we formulate this problem as a travelling salesman problem with time windows and present a new procedure for determining lower bounds using lagrangean relaxation as well as a heuristic computational results for problems with up to 10 products and 150 periods are reported

fully polynomial approximation schemes for single item capacitated economic lot sizing problems np hard cases of the single item capacitated lot sizing problem have been the topic of extensive research and continue to receive considerable attention however surprisingly few theoretical results have been published on approximation methods for these problems to the best of our knowledge until now no polynomial approximation method is known that produces solutions with a relative deviation from optimality that is bounded by a constant in this paper we show that such methods do exist by presenting an even stronger result the existence of fully polynomial approximation schemes the approximation scheme is first developed for a quite general model which has concave backlogging and production cost functions and arbitrary monotone holding cost functions subsequently we discuss important special cases of the model and extensions of the approximation scheme to even more general models

simultaneous lotsizing and scheduling by combining local search with dual reoptimization abstract the contribution of this paper is twofold on the one hand the particular problem of integrating lotsizing and scheduling of several products on a single capacitated production line is modelled and solved taking into account sequence dependent setup times thereby continuous lotsizes meeting deterministic dynamic demands are to be determined and scheduled with the objective of minimizing inventory holding costs and sequence dependent setup costs on the other hand a new general algorithmic approach is presented a dual reoptimization algorithm is combined with a local search heuristic for solving a mixed integer programming problem this idea is applied to the above lotsizing and scheduling problem by embedding a dual network flow algorithm into threshold accepting and simulated annealing respectively computational tests show the effectiveness of the new solution method

critical evaluation of two equation models for near wall turbulence abstract a variety of two equation turbulence models including several versions of the k epsilon model as well as the k omega model are analyzed critically for near wall turbulent flows from a theoretical and computational standpoint it is shown that the k epsilon model has two major problems associated with it the lack of natural boundary conditions for the dissipation rate and the appearance of higher order correlations in the balance of terms for the dissipation rate at the wall in so far as the former problem is concerned either physically inconsistent boundary conditions have been used or the boundary conditions for the dissipation rate have been tied to higher order derivatives of the turbulent kinetic energy which leads to numerical stiffness the k omega model can alleviate these problems since the asymptotic behavior of w is known in more detail and since its near wall balance involves only exact viscous terms however the modeled form of the omega equation that is used in the literature is incomplete an exact viscous term is missing which causes the model to behave in an asymptotically inconsistent manner by including this viscous term and by introducing new wall damping functions with improved asymptotic behavior a new k tau model where tau 1 omega is turbulent time scale is developed it is demonstrated that this new model is computationally robust and yields improved predictions for turbulent boundary layers jhd

modeling formant frequency discrimination of female vowels the present investigations were designed to establish the features of vowel spectra that mediate formant frequency discrimination thresholds for detecting frequency shifts in the first and second formants of two steady state vowels were initially measured for conditions in which the amplitudes of all harmonics varied in accordance with a model of cascade formant synthesis in this model changes in formant frequency produce level variations in components adjacent to the altered formant as well as in harmonics spectrally remote from the shifted resonant frequency discrimination thresholds determined with the cascade synthesis procedure were then compared to difference limens dls obtained when the number of harmonics exhibiting level changes was limited to the frequency region surrounding the altered formant results indicated that amplitude variations could be restricted to one to three components near the shifted formant before significant increases in formant frequency dls were observed in a second

supersonic corner flow predictions using the quadratic constitutive relation a series of reynolds averaged navier stokes simulations is performed for a supersonic wall bounded turbulent corner flow these simulations are compared to a high order implicit large eddy simulation for the same geometry and flow conditions inclusion of the quadratic constitutive relation in the reynolds averaged navier stokes simulation results in significant improvement in qualitative agreement with the large eddy simulation specifically the presence of secondary flow a counter rotating vortex pair the range of valid values for the constant in the quadratic constitutive relation formulation is explored additionally the effects on this range from different turbulence models and momentum thickness reynolds numbers for the corner are also examined these effects of the quadratic constitutive relation are explored using both the finite difference fluid solver overflow and the finite volume fluid solver us3d the results indicate that the quadratic constitutive relation term directly affects the str

comparison of explicit and traditional algebraic stress models of turbulence a critical comparison of explicit vs traditional algebraic stress models of turbulence is made in an effort to clear up the confusion that appears to have been generated by the recently published literature on the subject in which disparate approaches are adopted the only way that general second order closures can formally lead to fully explicit algebraic stress models in a global sense is in the limit of equilibrium homogeneous turbulence when these fully explicit models are then applled to turbulent flows that are far from equilibrium a singularity can arise which can be removed by a systematic regularization when solved explicitly either analytically or numerically the traditional implicit algebraic stress models have either multiple solutions or singularities which tends to explain why they have had problems in applications to complex flows thus it is argued that traditional algebraic stress models are intrinsically ill behaved and should be abandoned in future applications in favor of regularized explicit algebraic stress models it is furthermore argued that these should be based on the homogeneous equilibrium hypothesis which allows for more general second order closures to be used to obtain single valued models

the discrete lot sizing and scheduling problem abstract the discrete lot sizing and scheduling problem consists in scheduling several products on a single machine so as to meet the known dynamic demand and to minimize the sum of inventory and setup cost the planning interval is phased into many short periods e g shifts or days and setups may occur only at the beginning of a period a branch and bound procedure is presented using lagrangean relaxation for determining both lower bounds and feasible solutions the relaxed problems are solved by dynamic programming computational results on a personal computer are reported for various examples from the literature with up to 12 products and 122 periods or 3 products and 250 periods the procedure yields optimal solutions or at least feasible solutions with tight lower bounds in a few minutes the results are compared with those obtained by solving the usual capacitated lot sizing problem

improvement of corner flow prediction using the quadratic constitutive relation this paper presents results of the implementation of spalart s quadratic constitutive relation into the reynolds averaged navier stokes equations on two applications encountered in applied aerodynamics these applications one in external flow and one in internal flow are intended to be representative of the problem of corner flow simulation with the corner separation size being generally overestimated by classical turbulence models the first application is the dlr f6 wing body configuration used in the drag prediction workshop where a separation occurs at the wing body junction in the case without fairing the second application is the shock induced separation in a rectangular duct it is shown that the quadratic constitutive relation greatly improves the accuracy of the junction flow simulation without worsening the quality of the solution elsewhere

prediction of nonequilibrium turbulent flows with explicit algebraic stress models an explicit algebraic stress equation developed by gatski and speziale is used in the framework of the k uj and k e formulations to predict two dimensional separated turbulent flows the nonequilibrium effects are modeled through coefficients that depend nonlinearly on both rotational and irrotational strains the proposed models were implemented in the courant friedrichs lewy three dimensional navier stokes code comparisons with the experimental data are presented which clearly demonstrate that explicit algebraic stress models improve the response of standard two equation models to nonequilibrium effects i introduction

implicit multiple grid solution of the compressible navier stokes equations using k epsilon turbulence closure in the present work an algorithm for the numerical solution of the two dimensional mass weighted ensemble averaged compressible navier stokes equations is presented turbulence closure for the reynolds stresses is obtained using a low reynolds n umber two equation k s model which includes near wall effects the same algorithm is used for the integration of both the navier stokes and the turbulence transport equations the algorithm consists of a basic explicit finite volume scheme whose convergence is accelerated using local time step ping and multiple grid techniques convergence is further enhanced by the use of an implicit residual smoothing technique applied both in the fine and the coarser grids the application of the numerical scheme to the solution of the k s equations is examined in detail comparisons of computations with experimental data are presented for three shock wave turbulent boundary layer interaction flows algorithm convergence rate and cpu time require ments are discussed he numerical solution of the navier stokes equations for the simulation of turbulent flowfields is a subject of intense research and code development work 1 interest is focused both on code applicability to variegated config urations and on computational rapidity although direct simulation of turbulent flows2 or large eddy numerical sim ulations using subgrid turbulence modeling 3 4 have appeared in the literature current status of algorithm development and computer power indicate that for practical applications the ensemble averaged navier stokes equations should be used in conjunction with transport equations for turbulence closure 5 7 algebraic or mixing length models may provide satisfactory results for relatively simple flow geometries8 but require the determination of the shear layer thickness and of the distance of each grid point from the solid boundary thus they lack both geometric invariance and locality which are highly desirable properties from a computational viewpoint when addressing complex flowfields with many interacting solid boundaries although research on reynolds stre ss transport closure appears quite promising 9 10 its extension to three dimensions involves considerable increase of the number of transport equations to be solved also further research con cerning wall effects is required the more so since the use of wall functions is considered inadequate 11 on the other hand the use of two equation closures such as a 12 14 is quite widespread notwithstanding the fact that the use of the boussinesq hypothesis15 introduces a question able simplification of the flow physics 16 the major drawback of the k s model is probably the near wall formulation which fails to reproduce correctly the effects of the solid boundary on turbulence several variants of the original jones launder model12 have been developed in an attempt to improve upon near wall modeling some ten such models have been thor oughly examined in a critical review article by patel et al 17 who concluded that the models of launder and sharma 14

spectral peak selection in spectral shape discrimination by normal hearing and hearing impaired listeners spectral shape discrimination thresholds were measured in the presence and absence of noise to determine whether normal hearing and hearing impaired listeners rely primarily on spectral peaks in the excitation pattern when discriminating between stimuli with different spectral shapes standard stimuli were the sum of 2 4 6 8 10 20 or 30 equal amplitude tones with frequencies fixed between 200 and 4000hz signal stimuli were generated by increasing and decreasing the levels of every other standard component the function relating the spectral shape discrimination threshold to the number of components n showed an initial decrease in threshold with increasing n and then an increase in threshold when the number of components reached 10 and 6 for normal hearing and hearing impaired listeners respectively the presence of a 50 db spl hz noise led to a 1 7db increase in threshold for normal hearing listeners and a 3 5db increase for hearing impaired listeners multichannel modeling and the relatively s

oblique shock wave boundary layer interaction using near wall reynolds stress models a synthesis is presented of the predictive capability of a family of near wall wall normal free reynolds stress models which are completely independent of wall topology i e of the distance fromthe wall and the normal to thewall orientation for oblique shock wave turbulent boundary layer interactions for the purpose of comparison results are also presented using a standard low turbulence reynolds number k e closure and a reynolds stress model that uses geometric wall normals and wall distances studied shock wave mach numbers are in the range msw 2 85 2 9 and incoming boundary layer thickness reynolds numbers are in the range re 0 1 2 106 computations were carefully checked for grid convergence comparison with measurements shows satisfactory agreement improving on results obtained using a k e model and highlights the relative importance of redistribution and diffusion closures indicating directions for future modeling work

forward masking as a function of frequency masker level and signal delay the forward masking of a sinusoidal signal by a sinusoid of the same frequency was investigated for frequencies ranging from 125 to 4000 hz forward masking in db is proportional to both masker level and log signal delay at each frequency more forward masking occurs at very low frequencies than at high frequencies given equal sensation level maskers and masked thresholds are greater at low frequencies than at high frequencies given equal spl maskers the data can be described equally well by assuming that the difference in forward masking as a function of frequency is due to a change in the time course of recovery from masking or to a change in the growth of masking at each signal delay the frequency effect is not large enough to change the interpretation of forward masking data in studies of suppression or psychophysical tuning curves

the perceptual relevance of locus equations identification curves were estimated for the english consonants b d g using five formant cv synthetic stimuli comprehensively sampling the f2 onset f2 vowel acoustic space in the vicinity of b d g locus equations h sussman et al j acoust soc am 90 1309 1325 1991 the stimuli included 10 english monophthongal vowel contexts 11 levels of f2 onset per vowel and 3 levels of f3 onset orthogonally varied with the f2 variables 10 vowels 11 f2 onsets 3 f3 onsets 330 stimuli after brief training each of six subjects three male and three female was presented eight trials of each of the stimuli one or two trials per day over a period of several days systems of identification curves were visualized as identification surfaces situated in locus equation acoustic space and were overlaid with acoustic data from five male speakers in order to judge the degree of correspondence between perception and acoustic data a chi square analysis was also performed in order to quantify the correspondence be

lotsizing and scheduling on parallel machines with sequence dependent setup costs industrial lotsizing and scheduling pose very difficult analytical problems we propose an unconventional model that deals with sequence dependent setup costs in a multiple machine environment the sequence splitting model splits an entire schedule into subsequences leading to tractable subproblems an optimization approach based on a column generation branch and bound methodology is developed and heuristically adapted to test problems including five real world problem instances gathered from industry

benefit of high rate envelope cues in vocoder processing effect of number of channels and spectral region in cochlear implants or vocoder simulations of cochlear implants the transmission of envelope cues at high rates related to voice fundamental frequency f0 may be limited by the widths of the filters used to form the channels and or by the cutoff frequency flp of the low pass filters used for envelope extraction the effect of varying flp in tone and noise vocoders was investigated for channel numbers n from 6 to 18 as n increased the widths of the channels decreased the value of flp was 45hz envelope or e filter or 180hz pitch or p filter the following combinations of cutoff frequencies were used for channels below and above 1500hz respectively ee pe ep and pp results from a competing talker task showed that the tone vocoder led to better intelligibility than the noise vocoder the pp condition led to the best intelligibility and the ee condition to the worst for n 6 intelligibility was better for condition pe than for condition ep for n 18 the reverse was true the results

evaluation of explicit algebraic reynolds stress models for separated supersonic flows high reynolds number supersonic e owe elds were generated numerically to assess the performance of three explicit algebraic reynolds stress turbulence models the cone gurations consist of a shock boundary layer interaction and a 24 deg compression ramp both of which exhibit an appreciable region of separated e ow solutions were also obtained using standard zero equation and k models details of the computations are summarized and the accuracy of numerical results is established via grid resolution studies comparisons are made with experimental data in terms of surface pressure and skin friction as well as off surface proe les of mean velocity and componentsofthereynolds stresstensor forthee owsconsidered here it isfound that thealgebraic stressmodels offer little improvement over existing closures

computation of oscillating airfoil flows with one and two equation turbulence models the ability of one and two quation turbulence models to predict unsteady separated flows over airfoils is evaluated an implicit factorized upwind biased numerical scheme is used for the integration of the compressible reynolds averaged navier stokes equations the turbulent eddy viscosity is obtained from the computed mean flowfield by integration of the turbulent field equations one and two equation turbulence models are first tested for a separated airfoil flow at fixed angle of incidence the same models are then applied to compute the unsteady flowfields about airfoils undergoing oscillatory motion at low subsonic mach numbers experimental cases where the flow has been tripped at the leading edge and where natural transition was allowed to occur naturally are considered the more recently developed turbulence models capture the physics of unsteady separated flow significantly better than the standard k e and k models however certain differences in the hysteresis effects are observed for an untripped high reynolds number flow it was found necessary to take into account the leading edge transitional flow region to capture the correct physical mechanism that leads to dynamic stall

near wall k e computation of transonic turbomachinery flows with tip clearance acomputational methodforthenumericalintegration ofthefavre reynolds averaged three dimensionalcompressible navier stokes equations in axial turbomachinery using the launder sharma near wall k turbulence closure is developed the mean e ow and turbulence transport equations are discretized using a e nite volume method based on muscl van leere ux vector splitting with van albada limiters and are integrated in time using a fully coupled approximately factored implicit backward euler method the resulting scheme is robust and was found stable for local time steps of courant friedrichs lewy number cfl 20 the computational domain is discretized using a basic h o h grid the tip clearance gap is discretized using a e ne o type grid the radial distribution ofnodeswithin thetip clearancegap is independent of theblade rowo grid and a bufferoverlap grid is used to convey information boundary conditions at periodicity boundaries and at domain interfaces are treated using e ve phantom nodes this procedure ensures stability at high cfl results are presented for the nasa 37 rotor at an operating point near surge computations are compared with measurements both for blade to blade mach number contours and pitchwise distributions and for radial distributions downstream of the blades results are obtained using three grids of 10 6 2 10 6 and 3 10 6 points with 21 31 and 41 radial stations within the tip clearancegap respectively demonstratingthatresultsaregridindependent comparisonwithmeasurementsis satisfactory with theexception of pressureratio overestimation due to unsatisfactory prediction ofe ow separation by the turbulence model

term by term analysis of near wall second moment closures highlighting the importance of the interaction between parts of the models the derived representations were then further assessed by comparison with experiments and existing models for various flows with mach numbers m 2 0 5 the flows considered include cases where separation or shockwave boundary layer interaction were present possible directions for further work for the improvement of near wall modeling are discussed

an efficient implementation of local search algorithms for constrained routing problems we investigate the implementation of local search algorithms for routing problems with various side constraints such as time windows on vertices and precedence relations between vertices the algorithms are based on the k exchange concept in the case of unconstrained routing problems a single k exchange can obviously be processed in constant time in the presence of side constraints feasibility problems arise testing the feasibility of a single solution requires an amount of time that is linear in the number of vertices we show how this effort can on the average still be reduced to a constant

a measure for predicting audibility discrimination thresholds for spectral envelope distortions in vowel sounds both in speech synthesis and in sound coding it is often beneficial to have a measure that predicts whether and to what extent two sounds are different this paper addresses the problem of estimating the perceptual effects of small modifications to the spectral envelope of a harmonic sound a recently proposed auditory model is investigated that transforms the physical spectrum into a pattern of specific loudness as a function of critical band rate a distance measure based on the concept of partial loudness is presented which treats detectability in terms of a partial loudness threshold this approach is adapted to the problem of estimating discrimination thresholds related to modifications of the spectral envelope of synthetic vowels data obtained from subjective listening tests using a representative set of stimuli in a 3ifc adaptive procedure show that the model makes reasonably good predictions of the discrimination threshold systematic deviations from the predicted thresholds may be related to individual differences in auditory filter selectivity the partial loudness measure is compared with previously proposed distance measures such as the euclidean distance between excitation patterns and between specific loudness applied to the same experimental data an objective test measure shows that the partial loudness measure and the euclidean distance of the excitation patterns are equally appropriate as distance measures for predicting audibility thresholds the euclidean distance between specific loudness is worse in performance compared with the other two

forward masked excitation patterns in multielectrode electrical stimulation across channel interactions in multi electrode cochlear implant patients may be critical to their performance in the natural auditory environment one measure of channel interaction can be obtained using forward masking the patterns of threshold shift were obtained as a function of the separation between masker and probe electrode pairs in four nucleus implanted patients with varying levels of speech recognition in the three subjects with better speech recognition n4 n7 and n13 the masking patterns showed the least parameter dependence in the subject with the lowest speech scores n3 the masking patterns showed the greatest dependence on masker level and on probe delay masking as a function of masker level also reflected these differences n3 s functions showed the greatest changes for different probe delays similar rates of recovery were observed in the three good performers time constant approximately 70 ms in contrast subject n3 s recovery function shows a more rapid recovery these data indicate that channel interaction is individually variable and parameter dependent both of which may play a role in the perception of dynamic stimuli in the natural auditory environment

use of psychometric function slopes for forward masked tones to investigate cochlear nonlinearity schairer et al 2003 effects of peripheral nonlinearity on psychometric functions for forward masked tones j acoust soc am 133 1560 1573 demonstrated that cochlear nonlinearity is reflected in psychometric function pf slopes for 4 khz forward masked tones the goals of the current study were to use pf slopes to compare the degree of compression between signal frequencies of 0 25 and 4 khz in listeners with normal hearing lnh and between lnh and listeners with cochlear hearing loss lhl forward masked thresholds were estimated in lnh and lhl using on and off frequency maskers and 0 25 and 4 khz signals in three experiments pfs were reconstructed from adaptive procedure data for each subject in each condition trends in pf slopes across conditions suggest comparable compression at 0 25 and 4 khz and potentially a wider bandwidth of compression in relative frequency at 0 25 khz this is consistent with other recent behavioral studies that revise earlier estimates of less compression at lower frequencies the preliminary results in lhl demonstrate that pf slopes are abnormally steep at frequencies with hl but are similar to those for lnh at frequencies with nh overall the results are consistent with the notion that pf slopes reflect degree of cochlear nonlinearity and can be used as an additional measure of compression across frequency

prediction of high lift flows using turbulent closure models the flow over two different multi element airfoil configurations is computed using linear eddy viscosity turbulence models and a nonlinear explicit algebraic stress model a subset of recently measured transition locations using hot film on a mcdonnell douglas configuration is presented and the effect of transition location on the computed solutions is explored deficiencies in wake profile computations are found to be attributable in large part to poor boundary layer prediction on the generating element and not necessarily inadequate turbulence modeling in the wake using measured transition locations for the main element improves the prediction of its boundary layer thickness skin friction and wake profile shape however using measured transition locations on the slat still yields poor slat wake predictions the computation of the slat flow field represents a key roadblock to successful predictions of multi element flows in general the nonlinear explicit algebraic stress turbulence model gives very similar results to the linear eddy viscosity models

missing data model of vowel identification vowel identity correlates well with the shape of the transfer function of the vocal tract in particular the position of the first two or three formant peaks however in voiced speech the transfer function is sampled at multiples of the fundamental frequency f0 and the short term spectrum contains peaks at those frequencies rather than at formants it is not clear how the auditory system estimates the original spectral envelope from the vowel waveform cochlear excitation patterns for example resolve harmonics in the low frequency region and their shape varies strongly with f0 the problem cannot be cured by smoothing lag domain components of the spectral envelope are aliased and cause f0 dependent distortion the problem is severe at high f0 s where the spectral envelope is severely undersampled this paper treats vowel identification as a process of pattern recognition with missing data matching is restricted to available data and missing data are ignored using an f0 dependent weighting functi

forward masking in patients with cochlear implants forward masking was measured in 12 patients with cochlear implants the amount of masking in microamps decreased linearly as a function of the logarithm of the signal delay from masker offset normalized forward masking recovery functions for cochlear implants were similar to normalized functions of normal hearing listeners indicating that the mechanism of psychophysical forward masking is retrocochlear these results indicate that the logarithm of acoustic amplitude should be mapped to microamps to produce normal forward masking in implanted patients despite the fact that the forward masking recovery functions were similar across all patients their performance with their speech processor varied widely

on the number of channels needed to understand speech recent studies have shown that high levels of speech understanding could be achieved when the speech spectrum was divided into four channels and then reconstructed as a sum of four noise bands or sine waves with frequencies equal to the center frequencies of the channels in these studies speech understanding was assessed using sentences produced by a single male talker the aim of experiment 1 was to assess the number of channels necessary for a high level of speech understanding when sentences were produced by multiple talkers in experiment 1 sentences produced by 135 different talkers were processed through n 2 n 16 number of channels synthesized as a sum of n sine waves with frequencies equal to the center frequencies of the filters and presented to normal hearing listeners for identification a minimum of five channels was needed to achieve a high level 90 of speech understanding asymptotic performance was achieved with eight channels at least for the speech material used in this study the outcome of experiment 1 demonstrated that the number of channels needed to reach asymptotic performance varies as a function of the recognition task and or need for listeners to attend to fine phonetic detail in experiment 2 sentences were processed through 6 and 16 channels and quantized into a small number of steps the purpose of this experiment was to investigate whether listeners use across channel differences in amplitude to code frequency information particularly when speech is processed through a small number of channels for sentences processed through six channels there was a significant reduction in speech understanding when the spectral amplitudes were quantized into a small number 8 of steps high levels 92 of speech understanding were maintained for sentences processed through 16 channels and quantized into only 2 steps the findings of experiment 2 suggest an inverse relationship between the importance of spectral amplitude resolution number of steps and spectral resolution number of channels

the recognition of sentences in noise by normal hearing listeners using simulations of cochlear implant signal processors with 6 20 channels sentences were processed through simulations of cochlear implant signal processors with 6 8 12 16 and 20 channels and were presented to normal hearing listeners at 2 db s n and at 2 db s n the signal processing operations included bandpass filtering rectification and smoothing of the signal in each band estimation of the rms energy of the signal in each band computed every 4 ms and generation of sinusoids with frequencies equal to the center frequencies of the bands and amplitudes equal to the rms levels in each band the sinusoids were summed and presented to listeners for identification at issue was the number of channels necessary to reach maximum performance on tests of sentence understanding at 2 db s n the performance maximum was reached with 12 channels of stimulation at 2 db s n the performance maximum was reached with 20 channels of stimulation these results in combination with the outcome that in quiet asymptotic performance is reached with five channels of stimulation demonstrate that more channels are needed in noise than in quiet to reach a high level of sentence understanding and that as the s n becomes poorer more channels are needed to achieve a given level of performance

some extensions of the discrete lotsizing and scheduling problem in this paper the discrete lotsizing and scheduling problem dlsp is considered dlsp relates to capacitated lotsizing as well as to job scheduling problems and is concerned with determining a feasible production schedule with minimal total costs in a single stage manufacturing process this involves the sequencing and sizing of production lots for a number of different items over a discrete and finite planning horizon feasibility of production schedules is subject to production quantities being within bounds set by capacity a problem classification for dlsp is introduced and results on computational complexity are derived for a number of single and parallel machine problems furthermore efficient algorithms are discussed for solving special single and parallel machine variants of dlsp

accurate numerical simulation of compressible transitional flows in turbomachinery an accurate and efe cient methodology is provided for computing turbulent and transitional e ows by solving the compressible reynolds averaged navier stokes equations with an explicit algebraic stress model and k turbulence closure the space discretization is based on a e nite volume method with roe s approximate riemann solver and formally second order accurate muscl extrapolation second order accuracy in time is achieved using a dual time stepping technique combined with an explicit runge kutta scheme and multigrid acceleration to converge the false transient at each physical time level the turbulence model has been validated computing the vortex shedding behind a two dimensional turbine cascade furthermore the transition model of mayle for separated e ow has been combined with such a turbulence model this methodology has been validated computing thee owthroughthet106low pressureturbinecascadewithseparated e owtransitionatthesuction sideboundary layer finally thethree dimensionale owthroughthet106linearcascadehasbeencomputedprovidingtheanalysis of the loss coefe cient distribution downstream of the cascade and the description of the interaction between the secondary e ow pattern and the suction side separation bubble

forward masking adaptation or integration the aim of this study was to attempt to distinguish between neural adaptation and persistence or temporal integration as possible explanations of forward masking thresholds were measured for a sinusoidal signal as a function of signal duration for conditions where the delay between the masker offset and the signal offset the offset offset interval was fixed the masker was a 200 ms broadband noise presented at a spectrum level of 40 db re 20 pa and the signal was a 4 khz sinusoid gated with 2 ms ramps the offset offset interval was fixed at various durations between 4 and 102 ms and signal thresholds were measured for a range of signal durations at each interval a substantial decrease in thresholds was observed with increasing duration for signal durations up to about 20 ms at short offset offset intervals the amount of temporal integration exceeded that normally found in quiet the results were simulated using models of temporal integration the temporal window model and adaptation for both models the inclusion of a peripheral nonlinearity similar to that observed physiologically in studies of the basilar membrane was essential in producing a good fit to the data both models were about equally successful in accounting for the present data however the temporal window model provided a somewhat better account of similar data from a simultaneous masking experiment using the same parameters this suggests that the linear time invariant properties of the temporal window approach are appropriate for modeling forward masking overall the results confirm that forward masking can be described in terms of peripheral nonlinearity followed by linear temporal integration at higher levels in the auditory system however the difference in predictions between the adaptation and integration models is relatively small meaning that influence of adaptation cannot be ruled out

improvements to the quadratic constitutive relation based on nasa juncture flow data modifications to the quadratic constitutive relations qcrs of spalart strategies for turbulence modelling and simulation international journal of heat and fluid flow vol 21 2000 pp 252 2

meta heuristics for dynamic lot sizing a review and comparison of solution approaches proofs from complexity theory as well as computational experiments indicate that most lot sizing problems are hard to solve because these problems are so difficult various solution techniques have been proposed to solve them in the past decade meta heuristics such as tabu search genetic algorithms and simulated annealing have become popular and efficient tools for solving hard combinatorial optimization problems we review the various meta heuristics that have been specifically developed to solve lot sizing problems discussing their main components such as representation evaluation neighborhood definition and genetic operators further we briefly review other solution approaches such as dynamic programming cutting planes dantzig wolfe decomposition lagrange relaxation and dedicated heuristics this allows us to compare these techniques understanding their respective advantages and disadvantages gives insight into how we can integrate elements from several solution approaches into more powerful hybrid algorithms finally we discuss general guidelines for computational experiments and illustrate these with several examples

using speech sounds to test functional spectral resolution in listeners with cochlear implants in this study spectral properties of speech sounds were used to test functional spectral resolution in people who use cochlear implants cis specifically perception of the ba da contrast was tested using two spectral cues formant transitions a fine resolution cue and spectral tilt a coarse resolution cue higher weighting of the formant cues was used as an index of better spectral cue perception participants included 19 ci listeners and 10 listeners with normal hearing nh for whom spectral resolution was explicitly controlled using a noise vocoder with variable carrier filter widths to simulate electrical current spread perceptual weighting of the two cues was modeled with mixed effects logistic regression and was found to systematically vary with spectral resolution the use of formant cues was greatest for nh listeners for unprocessed speech and declined in the two vocoded conditions compared to nh listeners ci listeners relied less on formant transitions and more on spectral tilt cue weighting results showed moderately good correspondence with word recognition scores the current approach to testing functional spectral resolution uses auditory cues that are known to be important for speech categorization and can thus potentially serve as the basis upon which ci processing strategies and innovations are tested

wall normal free reynolds stress model for rotating flows applied to turbomachinery a recently developed near wall wall normal free reynolds stress model is extended and applied to the computation of transonic three dimensional e ows in turbomachinery rotors with tip clearance the reynolds stress model used is completely independent of the distance from the wall and of the normal to the wall direction this is achieved by using a pseudonormal direction dee ned by the gradients of turbulence length scale and anisotropy tensor invariants in the pressure strain echo terms the effects of rotation are included through theexact coriolis termsin the reynolds stress transport equations and through the isotropization of absolute e ow production model used for the rapid pressure strain terms the model is initially validated by comparison with measurements in rotating fully developed plane channel e ows computational results obtained with the proposed reynolds stress model are compared with measurements and with k computations for various operating points of the nasa 37 rotor using a 3 10 6 multiblock computational grid with 41 radial stations within the tip clearance gap the proposed model substantially improves the agreement with measurements compared to existing algebraic and two equation models

the resolution of complex spectral patterns by cochlear implant and normal hearing listeners the differences in spectral shape resolution abilities among cochlear implant ci listeners and between ci and normal hearing nh listeners when listening with the same number of channels 12 was investigated in addition the effect of the number of channels on spectral shape resolution was examined the stimuli were rippled noise signals with various ripple frequency spacings an adaptive 41fc procedure was used to determine the threshold for resolvable ripple spacing which was the spacing at which an interchange in peak and valley positions could be discriminated the results showed poorer spectral shape resolution in ci compared to nh listeners average thresholds of approximately 3000 and 400 hz respectively and wide variability among ci listeners range of approximately 800 to 8000 hz there was a significant relationship between spectral shape resolution and vowel recognition the spectral shape resolution thresholds of nh listeners increased as the number of channels increased from 1 to 16 while the ci listeners showed a performance plateau at 4 6 channels which is consistent with previous results using speech recognition measures these results indicate that this test may provide a measure of ci performance which is time efficient and non linguistic and therefore if verified may provide a useful contribution to the prediction of speech perception in adults and children who use cis

near wall reynolds stress three dimensional transonic flow computation a computational method for the favre reynolds averaged three dimensional compressible navier stokes equations using near wall reynolds stress closure is described the near wall reynolds stress closure uses the launder shima formulation for the reynolds stresses and the jones launder sharma modified dissipation e equation the mean flow and turbulence transport equations are discretized using a finite volume method based on muscl van leer flux vector splitting with van albada limiters the mean flow and turbulence equations are integrated in time using a fully coupled approximately factored implicit backward euler method the resulting scheme is robust and achieves optimal convergence with local time step courant friedrichs lewy 50 the turbulence closure is validated by comparison with classic flat plate boundary layer data results are presented for the three dimensional delery transonic channel test case and compared with k e computations an analysis of the limitations of the closure is attempted and possible improvements are suggested

prediction of aerodynamic flows with a new explicit algebraic stress model we present an explicit algebraic stress model easm based on the more current pressure strain model of speziale et al the ssg model the ssg model represents a recent upgrade of the launder et al model that does not require wall reflection terms the ability of the proposed model to predict nonequilibrium flows over an airfoil and a wing will be established the isaac navier stokes code is used to simulate the flows considered

vowel identification and vowel masking patterns of hearing impaired subjects confusion matrices for seven synthetic steady state vowels were obtained from ten normal and three hearing impaired subjects the vowels were identified at greater than 96 accuracy by the normals and less accurately by the impaired subjects shortened versions of selected vowels then were used as maskers and vowel masking patterns vmps consisting of forward masked threshold for sinusoidal probes at all vowel masker harmonics were obtained from the impaired subjects and from one normal subject vowel masked probe thresholds were transformed using growth of masking functions obtained with flat spectrum noise vmps of the impaired subjects relative to those of the normal were characterized by smaller dynamic range poorer peak resolution and poorer preservation of the vowel formant structure these vmp characteristics however did not necessarily coincide with inaccurate vowel recognition vowel identification appeared to be related primarily to vmp peak frequencies rather than to the levels at the

predicting s duct flow using a composite algebraic stress model an incompressible composite algebraic stress model is presented that accounts for dissipation rate anisotropies and that is validated against s duct flow the component algebraic stress and algebraic anisotropic dissipation rate models have been developed previously and tested against homogeneous flow the composite model is developed for integration to the wall and is calibrated against high reynolds number plane channel flow data to ensure the correct log law behavior the model is validated and analyzed against turbulent flow in an s duct both predicted mean flow quantities and turbulence statistics are compared with experimental data as well as with an isotropic eddy viscosity model and an algebraic stress model with an isotropic dissipation rate the experimentally observed lag between the shear stress vector direction and the mean velocity gradient vector direction is qualitatively predicted the effects of anisotropic dissipation rate on the production of the dissipation term in the dissipation rate equation and on the scalar functions that multiply the linear and nonlinear terms in the tensor expansion are examined relative to the algebraic stress formulation with an isotropic eddy viscosity

lot sizing with start up times many practical applications of lot sizing and scheduling problems involve start up times operations research literature contains but few studies of lot sizing models that take start up times explicitly into account here we review some of these studies discuss the models and their complexity and we propose further models we consider in particular a single stage single mode multi item lot sizing model with continuous set ups and sequence independent start up times which we solve using an integer programming column generation algorithm and we develop a dynamic programming procedure for the single item subproblem that treats the initial stock as a decision variable we also use cutting planes developed by constantino for the multi item polyhedra by combining column and cut generation the lower bounds that we obtain before branching are on average less than 2 from an optimal solution our algorithm solves instances with 3 to 5 items and 24 periods in an average of 50 seconds on a modern workstation and problems with 36 periods in an average of 750 seconds solutions guaranteed to be within 2 of optimality are obtained in less than 75 of these times

coding of vowellike signals in cochlear implant listeners neural population interactions resulting from excitation overlap in multi channel cochlear implants ci may cause blurring of the internal auditory representation of complex sounds such as vowels in experiment i confusion matrices for eight german steady state vowellike signals were obtained from seven ci listeners identification performance ranged between 42 and 74 correct on the basis of an information transmission analysis across all vowels pairs of most and least frequently confused vowels were selected for each subject in experiment ii vowel masking patterns vmps were obtained using the previously selected vowels as maskers the vmps were found to resemble the electrical vowel spectra to a large extent indicating a relatively weak effect of neural population interactions correlation between vowel identification data and vmp spectral similarity measured by means of several spectral distance metrics showed that the ci listeners identified the vowels based on differences in the betwe

determination of length scales in algebraic turbulence models for navier stokes methods the algebraic turbulence models that are used in today s navier stokes methods have their origin in boundarylayer research the length scales in those models are the viscous layer thickness or other suitable boundary layer integral quantities which are not known a priori in navier stokes calculations bald win lorn ax first circumvented that problem by finding an alternative expression patterned after the cebeci smith model in the first part of the present paper the differences between the cebeci smith and the baldwin lomax turbulence model are discussed on a boundary layer basis a novel method to evaluate the turbulent length scale in navier stokes computations is described in the second part which first allows a direct use of the cebeci smith model or any other turbulence model based on boundary layer integral values and second presents the opportunity for a mesh adaption procedure this procedure guarantees a fixed number of mesh points inside the viscous layer and hence a controlled resolution of this area navier stokes results for both turbulence models in adapted and nonadapted meshes are compared to measurements on the rae 2822 airfoil nomenclature

performance of popular turbulence model for attached and separated adverse pressure gradient flows the performance of four popular eddy viscosity turbulence models under adverse pressure gradient conditions is investigated the baldwin lomax the johnson king the baldwin barth and the wilcox omega models have been implemented into the ins code which solves the incompressible reynolds averaged navier stokes equations results are shown for the well known samuel joubert flow and two new flowfields recently reported by d m driver 1991 the two new flowfields pose a stronger test of the models than the samuel joubert flow because of the more severe retardation of the boundary layer including separation in one case a detailed comparison of the numerical results and the experimental data is shown

a strong cutting plane algorithm for production scheduling with changeover costs changeover costs and times are central to numerous manufacturing operations these costs arise whenever work centers capable of processing only one product at a time switch from the manufacture of one product to another although many researchers have contributed to the solution of scheduling problems that include changeover costs due to the problem s combinatorial explosiveness optimization based methods have met with limited success in this paper we develop and apply polyhedral methods from integer programming for a dynamic version of the problem computational tests with problems containing one to five products and up to 225 integer variables show that polyhedral methods based upon a set of facet inequalities developed in this paper can effectively reduce the gap between the value of an integer programming formulation of the problem and its linear programming relaxation by a factor of 94 to 100 these results suggest the use of a combined cutting plane branch and bound procedure as a solution approach in a test with a five product problem this procedure when compared with a standard linear programming based branch and bound approach reduced computation time by a factor of seven

the effect of smoothing filter slope and spectral frequency on temporal speech information it is known that information contained within the filter skirts can provide cues important to speech intelligibility however the role of filter slope during temporal smoothing has received little attention in experiment 1 smoothing filter slope angle was found to have a large effect on the intelligibility of sentences represented by three amplitude modulated sinusoids in experiment 2 the use of temporal cues above 16hz was examined across various regions of the spectrum when increases in rate were presented to individual spectral bands intelligibility only increased when presented in the higher spectral region this result suggests a greater reliance on higher rate cues in this region however intelligibility was greatest when these cues were distributed across the spectrum indicating that their effective use is not restricted solely to this region

solving multi item capacitated lot sizing problems using variable redefinition mixed integer programming models are typically not used to solve realistic sized production scheduling problems because they require exorbitant solution times we impose a useful taxonomy on production scheduling problems and develop alternative formulations for a wide variety of problems within the taxonomy the linear programming relaxation of the new models is very effective in generating bounds we show that these bounds are equal to those that could be generated using lagrangian relaxation or column generation the linear programming bounds increase in effectiveness as the problems become larger perhaps of greatest significance is that practitioners can obtain our results using only standard off the shelf codes such as lindo or mpsx 370 we report computational experience in several computing environments hardware and software on problems with up to 200 products and 10 time periods 2000 0 1 variables

data parallel line relaxation method for the navier stokes equations the gauss seidel line relaxation method is modie ed for the simulation of viscous e ows on massively parallel computers the resulting data parallel line relaxation method is shown to have good convergence properties for a seriesoftestcases thenewmethodrequiressignie cantlymorememorythanthepreviouslydevelopeddata parallel relaxation methods but it reaches a steady state solution in much less time for all cases tested to date in addition the data parallel line relaxation method shows good convergence properties even on the high cell aspect ratio grids required to simulate high reynolds number e ows the new method is implemented using message passing on the cray t3e and the parallel performance of the method on this machine is discussed the data parallel line relaxation method combines the fast convergence of the gauss seidel line relaxation method with a high parallel efe ciency and thus shows promise for large scale simulation of viscous e ows

a stable and accurate convective modelling procedure based on quadratic upstream interpolation a convective modelling procedure is presented which avoids the stability problems of central differencing while remaining free of the inaccuracies of numerical diffusion associated with upstream differencing for combined convection and diffusion the number of operations at each grid point is comparable to that of standard upstream pluscentral differencing however highly accurate solutions can be obtained with a grid spacing much larger than that required by conventional methods for comparable accuracy with obvious practical advantaged in terms of both speed and storage the algorithm is based on a conservative control volume formulation with cell wall values of each field variable written in terms of a quadratic interpolation using in any one coordinate direction the two adjacent nodal values together with the value at the next upstream node this results in a convective differencing scheme with greater formal accuracy than central differencing while retaining the basic stable convective sensitivity property of upstream weighted schemes the consistent treatment of diffusion terms is equivalent to central differencing with careful modelling numerical boundary conditions are not troublesome some idealized problems are studied showing the practical advantages of the method over other schemes in comparison with exact solutions an application to a complex unsteady two dimensional flow is briefly discussed

features of stimulation affecting tonal speech perception implications for cochlear prostheses tone languages differ from english in that the pitch pattern of a single syllable word conveys lexical meaning in the present study dependence of tonal speech perception on features of the stimulation was examined using an acoustic simulation of a cis type speech processing strategy for cochlear prostheses contributions of spectral features of the speech signals were assessed by varying the number of filter bands while contributions of temporal envelope features were assessed by varying the low pass cutoff frequency used for extracting the amplitude envelopes ten normal hearing native mandarin chinese speakers were tested when the low pass cutoff frequency was fixed at 512 hz consonant vowel and sentence recognition improved as a function of the number of channels and reached plateau at 4 to 6 channels subjective judgments of sound quality continued to improve as the number of channels increased to 12 the highest number tested tone recognition i e recognition of the four mandarin tone patterns depended on both the number of channels and the low pass cutoff frequency the trade off between the temporal and spectral cues for tone recognition indicates that temporal cues can compensate for diminished spectral cues for tone recognition and vice versa an additional tone recognition experiment using syllables of equal duration showed a marked decrease in performance indicating that duration cues contribute to tone recognition a third experiment showed that recognition of processed fm patterns that mimic mandarin tone patterns was poor when temporal envelope and duration cues were removed

solving the discrete lotsizing and scheduling problem with sequence dependent set up costs and set up times using the travelling salesman problem with time windows abstract in this paper we consider the discrete lotsizing and scheduling problem with sequence dependent set up costs and set up times dlspsd dlspsd contains elements from lotsizing and from job scheduling and is known to be np hard an exact solution procedure for dlspsd is developed based on a transformation of dlspsd into a travelling salesman problem with time windows tsptw tsptw is solved by a novel dynamic programming approach due to dumas et al 1993 the results of a computational study show that the algorithm is the first one capable of solving dlspsd problems of moderate size to optimality with a reasonable computational effort