frame time hopping patterns in multirate optical cdma networks using conventional and multicode schemes a class of generalized optical orthogonal codes oocs namely frame time hopping fth patterns with an extremely large cardinality are studied for implementing multirate and multiservice mr ms optical cdma ocdma networks conventional mr ms methods namely variable spreading rate and parallel mapping are considered using fth patterns the problem of low ooc code cardinality in conventional mr ms schemes is removed moreover several new multicode methods using subcode concatenation scheme are proposed for mr ms ocdma the proposed multicode schemes present flexibility for supporting mr ms applications such as lower implementation complexity and cost less need for service synchronization and finally lower link power budget multiple access performances of the systems are evaluated using saddle point approximation methods considering photodetector shot noise dark current and circuit thermal noise the results show that the conventional parallel mapping outperforms the other schemes in high received powers and the proposed multicode method using walsh subcode along with difference modulation presents the best performance in low received powers for the cases considered

control of the vorticity mode in the linearized euler equations for hybrid aeroacoustic prediction the issue of vorticity mode perturbation in linearized euler equations lee is addressed in this paper we chose to tackle this question by the point of view of source term formulation it is numerically shown that the use of a rotational free acoustic source term significantly reduces the development of the hydrodynamic mode in accordance with the theory the proposed source term lead to a quasi total absence of vorticity mode in a spatially uniform mean flow and a strong reduction in a sheared mean flow

frame time hopping fiber optic code division multiple access using generalized optical orthogonal codes a new spreading technique for intensity modulation direct detection fiber optic code division multiple access fo cdma communication systems is proposed this new spreading technique is based on generalized optical orthogonal codes ooc with large cardinality and minimal degradation in performance when compared with a more optimum system namely an optical cdma system using ooc with autocorrelation and cross correlation value bounded by one i e ooc spl lambda 1 to obtain the performance of such systems we use a communication scheme namely frame time hopping fth cdma with random coding systems with generalized ooc patterns and random time hopping coding are close in structure and performance furthermore the performance of such systems is near the performance of optical cdma with optimum but low cardinality ooc spl lambda 1 which further renders the practicality of the proposed technique with very large cardinality two new receiver structures for fo cdma namely chip level detector with optimum comparator threshold and correlation receiver with an electrical hard limiter are also proposed the performance analysis for a binary pulse position fth fo cdma network is considered for the correlation receiver chip level detector correlation receiver with an optical hard limiter optimum receiver and the two newly proposed receiver structures the results also show that a chip level detector with optimum comparator threshold is superior to a chip level detector for received low signal powers and predict that the performance of the correlation receiver with an electrical hard limiter is superior to all other considered receiver structures e g requiring one third of transmission power to achieve a desired bit error rate when compared with other receiver structures

simultaneous confidence intervals for all distances from the best in practice comparisons with the best are often the ones of primary interest in this paper parametric and nonparametric simultaneous upper confidence intervals for all distances from the best are derived under the location model their improvement upon the results of bechhofer 1954 gupta 1956 1965 fabian 1962 and desu 1970 in the parametric case is discussed in the nonparametric case no comparable confidence statements were available previously

optimization of time integration schemes coupled to spatial discretization for use in caa applications in this paper errors arising from spatial and temporal discretization are discussed a new formulation to optimize time integration schemes is proposed the new optimization also takes the errors coming from the spatial discretization into account which leads to a minimization of the total errors it is applicable to central and upwind type spatial discretizations a six stage runge kutta scheme is optimized for central and upwind spatial discretizations its efficiency is demonstrated on a one dimensional convection equation and on a linearized euler problem the results indicate an important improvement

graphical procedures for multiple comparisons under general dependence abstractit has been more than half a century since tukey first introduced graphical displays that relate nonoverlap of confidence intervals to statistically significant differences between parameter estimates in this article we show how tukey s graphical overlap procedure can be modified to accommodate general forms of dependence within and across samples we also develop a procedure that can be used to more effectively resolve rankings within the tails of the distributions of parameter values thereby generalizing existing methods for multiple comparisons with the best we show that these new procedures retain the simplicity of tukey s original procedure while maintaining asymptotic control of the familywise error rate under very general conditions simple examples are used throughout to illustrate the procedures supplementary materials for this article are available online

numerical simulation of sound generated by vortex pairing in a mixing layer a numerical code solving the filtered navier stokes equations is developed using special techniques of computational aeroacoustics this approach allows a direct determination of the compressible field on a computational domain including the acoustic far field a two dimensional mixing layer between two flows at m 1 0 12 and m 2 0 48 is simulated the reynolds number built up from the initial vorticity thickness and the velocity difference across the mixing layer is re 1 28 x 10 4 an appropriate forcing of the mixing layer is defined to have only one pairing in the computational domain at a fixed location the sound generation pattern for a single pairing displays a double spiral structure corresponding to the rotating quadrupole associated to two corotative vortices successive pairings produce an acoustic radiation at the frequency of this mechanism the directly computed far field sound is then compared to the prediction of lighthill s acoustic analogy lighthill m j on sound generated aerodynamically i general theory proceedings of the royal society of london vol 211 series a 1107 1952 pp 564 587 based on the aerodynamic fluctuations provided by the large eddy simulation code two integral formulations of the analogy based on spatial derivatives and time derivatives respectively are tested results are in good qualitative agreement with the results of direct simulation the accuracy is however greater with the formulation using time derivatives instead of spatial derivatives

direct computation of the noise radiated by a subsonic cavity flow and application of integral methods abstract the goal of this paper is to investigate the acoustic field generated by the flow over a cavity using two different and complementary numerical methods first a direct numerical simulation of the 2 d compressible navier stokes equations is performed to obtain directly the radiated noise the results of the acoustic and aerodynamic fields are compared to the experimental data in the literature second this reference solution is compared to solutions provided by hybrid methods using the flowfield computed inside the cavity combined with an integral formulation to evaluate the far field noise numerical issues of three integral methods are studied the ffowcs williams and hawkings analogy that extends lighthill s theory to account for solid boundaries and two wave extrapolation methods from a control surface the kirchhoff and porous ffowcs williams and hawkings methods all methods show a good agreement with the direct numerical simulation but the first one is more expensive owing to an additional volume integral however the analogy can help in the analysis of wave patterns by separating the direct waves from the reflected ones the wave extrapolation methods from a surface are more efficient and provide a complementary tool to extend computational aeroacoustics near field to the very far field

second order correctness of the blockwise bootstrap for stationary observations we show that the blockwise bootstrap approximation for the distribution of a studentized statistic computed from dependent data is second order correct provided we choose an appropriate variance estimator we also show how to adapt the bc a confidence interval of efron to the dependent case for the proofs we extend the results of gotze and hipp on the validity of the formal edgeworth expansion for a sum to the studentized mean

performance analysis of fiber optic bppm cdma systems with single parity check product codes the application of a family of single parity check spc product codes in the fiber optic code division multiple access cdma systems with binary pulse position modulation bppm is considered in this paper we evaluate the bit error probabilities of the coded systems taking into account the photodetector noise thermal noise and the multiple access interference in this paper the performance of the employed coding schemes over a binary input output symmetric channel is analyzed based on the density evolution approach the validity of the analytically obtained bit error rates bers over binary symmetric channels bscs for each of the decoding iterations is verified by the system simulation it is then shown that the application of these coding schemes in the optical bppm cdma communication system which can be modeled as a bsc significantly improves the system performance particularly for a certain ber less than 10 7 and bandwidth the coded systems not only permit a higher number more than twice of active users compared with the uncoded systems but also can operate at higher channel bit rate up to four times with more than 10 energy saving furthermore by increasing the number of code dimensions less power less than 40 is required to achieve the desired performance

computation of flow noise using source terms in linearized euler s equations an acoustic analogy using linearized euler s equations lee forced with aerodynamic source terms is investigated to computetheacousticfare eld thishybridmethod isappliedto threemodelproblemssimulatedby solving navier stokes equations in this way its validity is estimated by comparing the predicted acoustic e eld with the reference solution given directly by the navier stokes equations the noise radiated by two corotating vortices is studied e rst in a medium at rest and second in a mean sheared e ow with no convection velocity then the sound e eld generated by vortex pairings in a subsonic mixing layer is investigated in this case a simplie ed formulation of lee is proposed to prevent the exponential growth of instability waves the acoustic e elds obtained by solving lee are in good agreement with the reference solution this study shows that the source terms introduced into the lee are appropriate for free sheared e ows and that acoustic mean e ow interactions are properly taken into account in the wave operator nomenclature b half width of the monopolar source c sound velocity e f h vectors in linearized euler s equations lee f frequency f0 fundamental frequency of the mixing layer k complex wave number kr ciki m mach number p pressure re reynolds number rc vortex core radius r0 initial half distance between the two vortices s sound source vector in lee si source terms in the momentum equations t period tij lighthill s tensor t time u unknown vector in lee u1 slow stream velocity of the mixing layer u2 rapid stream velocity of the mixing layer u velocity vector u1 u2 v initial tangential velocity of vortices

a controllable canonical form implementation of time domain impedance boundary conditions for broadband aeroacoustic computation a new method which can be effectively and efficiently applied in the simulations of broadband noise problems is proposed for time domain impedance boundary condition implementations by using the so called controllable canonical form that is well known in linear system usually the impedance boundary condition can be defined in frequency domain as a rational polynomial function with poles in the negative half of the complex plane to guarantee stability otherwise causality might be violated in the corresponding time domain implementation to address this issue various methodologies have been proposed previously that usually lead to complicated polynomials whose numerical implementations are often indirect and intricate the proposed method with a controllable canonical form on the other hand directly transforms the frequency domain transfer function a quotient of rational polynomials to an equivalent state space model which consists of a series of first order ordinary differential equations that can be numerically implemented in a straightforward way the proposed method is demonstrated by using two benchmark problems a two dimensional gaussian pulse propagating in a uniform flow with a lined wall and the test cases from the nasa langley grazing incidence tube experiments good agreements demonstrate the potential of the proposed computational method

constrained simultaneous confidence intervals for multiple comparisons with the best for comparing k treatment effects 01 02 ok often the parameters of primary interest are 0i maxeioi0 i 1 k in this article we develop constrained 100p two sided simultaneous confidence intervals for 0i maxj i0j which we refer to as constrained mcb intervals it turns out that the lower bounds of the intervals imply indifference zone selection inference and the upper bounds of these intervals imply subset selection inference each given at the same confidence level 100p as mcb we also extend our

acoustic source terms for the linearized euler equations in conservative form a rather novel approach to predict jet noise is the stochastic noise generation and radiation sngr method the sngr method uses the linear euler equations as an acoustic analogy together with source terms which are modeled in other studies the euler equations on primitive form are used in the present work the linear euler equations on conservative form are used due to this new source terms have to be derived for the conservative set of equations a formal derivation of the correct source terms for the linear euler equations on conservative form is presented simplified versions of the derived source terms are also developed to validate the derived source terms a direct simulation of a forced 2d mixing layer is carried out the solutions to the linearized euler equations with source terms are compared to the solution of the direct simulation and show a good agreement all simulations are performed using tam and webb s fourth order drp scheme and a four step fourth order runge kutta time marching technique artificial selective damping introduced through the numerical scheme is used to avoid spurious waves absorbing boundary conditions based on characteristic variables engquist and majda are used at the free boundaries and a buffer layer is added at the outflow

short note straightforward high order numerical dissipation via the viscous term for direct and large eddy simulation in this short note we show how to use a highly accurate finite difference scheme to compute second derivatives in the navier stokes equations while ensuring targeted numerical dissipation this approach essentially non conservative is shown to be close to an upwind method and is straightforward to implement with a negligible computational extra cost the benefit offered by the resulting discrete operator is illustrated for the direct computation of sound in aeroacoustics and in the more general context of large eddy simulation through connections with hyperviscosity and spectral vanishing viscosity

numerical modeling of sound diffraction at a half plane trailing edge the problem of sound propagation in the presence of a rigid semi infinite plate and a double stream sheared mean flow is solved numerically by means of a linearized lilley s equation this is discretized in the frequency domain by using a green function discretization gfd scheme leading to a very ecient numerical method it is demonstrated that the present approach is able to tackle the edge diraction problem without any additional treatment of the vortex sheet and that it provides results that are in close agreement with the analytical solution for a uniform base flow in addition it is shown that the results obtained by considering a piecewise constant base flow and a mixing layer base flow compare favourably with the solutions obtained by solving the linearized euler equations using a discontinuous galerkin method

numerical study of sound generation due to a spinning vortex pair a numerical approach for the calculation of an acoustic field is applied to the case of a spinning vortex pair to investigate the sound generation by quadrupole sources in unsteady vortical flows based on the unsteady hydrodynamic information from the known incompressible flowfield the perturbed compressible acoustic terms derived from the euler equations are calculated nonreflecting boundary conditions are developed to obtain highly stable solutions calculated results are compared with analytical solutions obtained by the method of matched asymptotic expansions the possibility of predicting the effect of convective mean flow is also tested it is concluded that the sound generated by the quadrupole sources of unsteady vortical flows without a sound generating body or surface can be calculated by using the source terms of hydrodynamic flow fluctuations

numerical simulation of sound generation in a mixing layer by the finite difference lattice boltzmann method we simulated aerodynamic sound in a two dimensional mixing layer using the finite difference lattice boltzmann method fdlbm we introduced a finite difference scheme called the dispersion relation preserving drp scheme into the fdlbm to carry out an accurate simulation of aerodynamic problems the scheme is designed such that the dispersion relation of the finite difference scheme is the same as that of the original partial differential equations and is useful for acoustic simulations a turbulent flow field was simulated by large eddy simulation les using the smagorinsky model and the results were compared with those from a direct simulation based on the navier stokes equations to confirm the usefulness of this method the combination of the fdlbm and the drp scheme was shown to be very effective for direct simulations of aerodynamic sound

controlling the false discovery rate a practical and powerful approach to multiple testing summary the common approach to the multiplicity problem calls for controlling the familywise error rate fwer this approach though has faults and we point out a few a different approach to problems of multiple significance testing is presented it calls for controlling the expected proportion of falsely rejected hypotheses the false discovery rate this error rate is equivalent to the fwer when all hypotheses are true but is smaller otherwise therefore in problems where the control of the false discovery rate rather than that of the fwer is desired there is potential for a gain in power a simple sequential bonferronitype procedure is proved to control the false discovery rate for independent test statistics and a simulation study shows that the gain in power is substantial the use of the new procedure and the appropriateness of the criterion are illustrated with examples

a family of low dispersive and low dissipative explicit schemes for flow and noise computations explicit numerical methods for spatial derivation filtering and time integration are proposed they are developed with the aim of computing flow and noise with high accuracy and fidelity all the methods are constructed in the same way by minimizing the dispersion and the dissipation errors in the wavenumber space up to k x 2 corresponding to four points per wavelength they are shown to be more accurate and also more efficient numerically than most of the standard explicit high order methods for uniform and slowly non uniform grids two problems involving long range sound propagation are resolved to illustrate their respective precisions remarks about their practical applications are then made especially about the connection with the boundary conditions finally their relevance for the simulation of turbulent flows is emphasized

on compressibility assumptions in aeroacoustic integrals a numerical study with subsonic mixing layers two assumptions commonly made in predictions based on lighthill s formalism are investigated a constant density in the quadrupole expression and the evaluation of the source quantity from incompressible simulations numerical predictions of the acoustic field are conducted in the case of a subsonic spatially evolving two dimensional mixing layer at re 400 published results of the direct noise computation dnc of the flow are used as reference and input for hybrid approaches before the assumptions on density are progressively introduced divergence free velocity fields are obtained from an incompressible simulation of the same flow case exhibiting the same hydrodynamic field as the dnc for the tested values of the mach number hybrid predictions reproduce correctly the reference acoustic field validating both assumptions in the source region however in the observer region the inclusion of flow effects in the lighthill source term is not preserved which is illustrated through a comparison with the kirchhoff wave extrapolation formalism and with the use of a convected green function in the integration process