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This article proposes an optimization framework, based on genetic algorithms (GA), to calibrate the constitutive law of von Wolffersdorff. This constitutive law, known as Sand Hypoplasticity (SH), allows for robust and accurate modelling of the soil behaviour but requires a complex calibration involving eight parameters. The proposed optimization can automatically fit these parameters from the results of an oedometric and a triaxial drained compression test, by combining the GA with a numerical solver that integrates the SH in the test conditions. By repeating the same calibration several times, the stochastic nature of the optimizer enables the uncertainty quantification of the calibration parameters and allows studying their relative importance on the model prediction. After validating the numerical solver on the ExCalibre-Laboratory software from the SoilModels’ website, the GA calibration is tested on a synthetic dataset to analyse the convergence and the statistics of the results. In particular, a correlation analysis reveals that two couples of the eight model parameters are strongly correlated. Finally, the calibration procedure is tested on the results from von Wolffersdorff, 1996, and Herle and Gudehus, 1999, on the Hochstetten sand. The model parameters identified by the GA optimization improves the matching with the experimental data and hence lead to a better calibration.

Plasma jets naturally develop hydrodynamic instabilities originating from thermal and momentum exchanges with the cold and quiescent surrounding fluid. This work investigates the hydrodynamic instabilities of a simulated plasma jet using multiscale data-driven modal analysis. The investigated conditions are representative of the flow produced in the Plasmatron facility at the von Karman Institute, designed to simulate the harsh environment encountered during an atmospheric entry. Two aspects were investigated. First, we demonstrate the multiscale Proper Orthogonal Decomposition (mPOD) capabilities to extract the main structures in the plasma jet flow from highly resolved thermal fields of the flow. To this end, we analyzed DNS simulations of the plasma jet with characteristic outlet velocity и = 146 m s-1, a temperature T = 10 665 K, and diameter d = 0.16 m. Second, we investigate the experimental observability of these patterns using a high-speed recording. To this end, we simulated the image acquisition process of a High-Speed Camera (HSC) and generated synthetic videos by rebuilding the light emission from the DNS temperature field. The analysis of the synthetic grayscale images was performed on two light intensity ranges commonly employed to record the plasma flow of the VKI Plasmatron. The decomposition of the thermal field reveals travelling wave patterns belonging to different frequency ranges and evolving in the shear layer of the jet. The analysis of the synthetic grayscale images shows that much of the relevant information on the frequency content and scales of the leading travelling waves is retained, but the associated spatial structures are severely altered.

This work discusses an approach to compute pressure fields from planar PIV measurement using standard CFD tools. In particular, we propose a combination of interpolation and mesh adaptation to import the PIV measurements on a grid that is morphed around objects, and is fine enough to solve the Poisson equation accurately. The whole process of meshing, interpolation and pressure computation is carried out using the popular open-source solver OpenFoam®. The method is tested and validated on a classic benchmark test case, namely, the unsteady flow past a cylinder. A 3D multiphase flow simulation is used to generate the reference data and analyze the impact of both, the PIV interrogation and the interpolation on the morphed grid. The simulation uses an Euler-Lagrangian one-way coupling approach to simulate the flow field and the dynamics of seeding particles. The analysis compares the pressure field from the 3D CFD simulation with the solution of a 2D Poisson equation based on the 2D velocity field obtained by either down-sampling the CFD data or by PIV interrogation of synthetic images built from the CFD data. Finally, we challenge the proposed method with the pressure reconstruction in a TR-PIV experiment in similar conditions.

This second part of a two-part article on the stability of the jet wiping process focuses on the interaction between the impinging gas jet and the coating liquid film. Using a simplified laboratory model, the first part of the study (Gosset et al., 2019) has shown that this coating process is unstable and leads to wavy coating films. The scaling laws of the problem suggest that this coating nonuniformity does not originate from the liquid coating stability itself, but from a hydrodynamic feedback between the liquid and the impinging jet. This hydrodynamic feedback is herein investigated by combining several optical techniques and data processing methods. Time-Resolved Light Absorption (LAbs) technique is used for the 3D characterization of the coating layer thickness downstream the wiping region, while Time-Resolved Particle Image Velocimetry (TR-PIV) is used to analyze the dynamics of the impinging gas jet, in combination with liquid interface tracking via image processing and Laser Induced Fluorescence (LIF). A link between the frequency content in the liquid film and the jet flow is established. Specifically, the dynamics of the gas jet is analyzed via Multiscale Proper Orthogonal Decomposition (mPOD) of the TR-PIV data and reveals large-scale oscillations which are coupled with waves in the liquid film upstream the wiping, referred to as runback flow. The interaction between the flow structures responsible for the oscillation and the runback liquid film is discussed, showing how this self-sustained mechanism is potentially responsible for the nonuniformity of the final coating.

Data-driven decompositions are becoming essential tools in fluid dynamics, allowing for tracking the evolution of coherent patterns in large datasets, and for constructing low order models of complex phenomena. In this work, we analyze the main limits of two popular decompositions, namely the Proper Orthogonal Decomposition (POD) and the Dynamic Mode Decomposition (DMD), and we propose a novel decomposition which allows for enhanced feature detection capabilities. This novel decomposition is referred to as Multiscale Proper Orthogonal Decomposition (mPOD) and combines Multiresolution Analysis (MRA) with a standard POD. Using MRA, the mPOD splits the correlation matrix into the contribution of different scales, retaining non-overlapping portions of the correlation spectra; using the standard POD, the mPOD extracts the optimal basis from each scale. After introducing a matrix factorization framework for data-driven decompositions, the MRA is formulated via 1D and 2D filter banks for the dataset and the correlation matrix respectively. The validation of the mPOD, and a comparison with the Discrete Fourier Transform (DFT), DMD and POD are provided in three test cases. These include a synthetic test case, a numerical simulation of a nonlinear advection-diffusion problem, and an experimental dataset obtained by the Time-Resolved Particle Image Velocimetry (TR-PIV) of an impinging gas jet. For each of these examples, the decompositions are compared in terms of convergence, feature detection capabilities, and time-frequency localization., submitted to Journal of Fluid Mechanics

The jet wiping process is a continuous coating method that uses impinging gas jets to control the thickness of a liquid layer dragged by a moving substrate. This first part of a two-part article on the analysis of the process stability presents an experimental characterization of the achievable coating uniformity as a function of various design and operating parameters, including the nozzle opening width, stand-off distance, tilt angle and stagnation pressure, substrate speed and liquid properties. The process is reproduced on a dedicated laboratory model, instrumented with a Light Absorption (LAbs) test section for the 3D time-dependent reconstruction of the final coating film thickness. Several types of wave patterns are observed on the final coating film and characterized in terms of peak to peak wave amplitude and dominant frequency. The results are nondimensionalized following the scaling laws derived from the classical ‘one-way coupling’ analysis of the process. This approach, which assumes that the wiping capabilities of the jet flow are not influenced by the dynamics of the impinged liquid, is proven successful for the prediction of the average film thickness but inadequate for the scaling of the coating non-uniformity. This suggests that the dynamics of the final coat is mostly governed by the interaction of the liquid with the gas jet, investigated in the second part of the article.

The Koopman decomposition of the Burgers' flow is explicitly derived, the frequencies and the coefficients of this decomposition are identified as eigenvalues and eigenfunctionals of the Koopman operator, and the convergence of the Koopman decomposition is proven for $tg0$ for small Cauchy data, and up to $t=0$ for regular Cauchy data.

In the era of the Big Data revolution, methods for the automatic discovery of regularities in large datasets are becoming essential tools in applied sciences. This article presents an open software package, named MODULO (MODal mULtiscale pOd), to perform the Multiscale Proper Orthogonal Decomposition (mPOD) of numerical and experimental data. This novel decomposition combines Multi-resolution Analysis (MRA) and standard Proper Orthogonal Decomposition (POD) to allow for the optimal compromise between decomposition convergence and spectral purity of its modes. The software is equipped with a Graphical User Interface (GUI) and enriched by numerous examples and video tutorials (see Youtube channel MODULO mPOD). The MATLAB source codes and an executable for Windows users can be downloaded at \url{https://github.com/mendezVKI/MODULO/releases}; a collection of exercises in Matlab and Python are provided in \url{https://github.com/mendezVKI/MODULO}, submitted to Software X

Oscillating impinging gas jets are encountered in many flow configurations, including fluidic devices, jet flow discharges into cavities and jet impinging onto deformable interfaces. For an incompressible flow, the self-sustained mechanism is referred to as hydrodynamic feedback and it is linked to the interaction between the flow field and its geometric confinement. This work presents an experimental characterization of the flow structures responsible for the hydrodynamic feedback, considering both a steady confinement and a pulsing confinement. The selected configuration consists of a planar gas jet impinging on an asymmetric interface consisting of a flat wall on one side of the stagnation region and bidimensional bump on the other. This bump is fixed in the steady condition and pulses in the unsteady conditions. Jet oscillation and interface tracking are carried out by means of high-speed flow visualization and image processing, combined with a time-frequency analysis in the Fourier and Wavelet spaces. The flow field is characterized via Time-Resolved Particle Image Velocimetry (TR-PIV) and analyzed with a novel modal decomposition, referred to as multi-scale Proper Orthogonal Decomposition (mPOD). This decomposition uses multiresolution analysis (MRA) on the correlation matrix to produce a set of PODs at multiple scales. Two physical mechanisms of the hydrodynamic feedback have been captured at largely different scales and the dynamic of their characteristic flow structures is presented. The first, referred to as fluidic mode, consists of a self-sustained oscillation of the impinging jet; the second, referred to as coupled mode, consists of a periodic downward deflection of the impinging jet, at the frequency of the interface pulsation.

Low Kapitza liquids, such as mineral or vegetable oils, have a low surface tension and a high viscosity. In these liquids, capillary forces and extensional viscous dissipation play an equal role in damping interface deformation, resulting in a configuration which challenges the long wavelength assumption at the origin of low-dimensional models for falling films. This paper presents time-resolved 2D thickness measurements of a vertical falling film of Dipropilene Glycol ( Ka = 3.7 ± 2 % ) using the light absorption technique. The test cases are in the low Reynolds number regime ( Re = 1 – 6 ), with a flow rate pulsing at frequencies in the range f p = 12 – 24 Hz . Different liquid film responses to the perturbation are reported, including growing waves, fully developed traveling waves and sinusoidal waves under period doubling instability. For the fully developed waves, simple dimensionless correlations for wave celerity, wavelength and wave profiles are proposed using the Skhadov scaling. The wave characteristics are compared to those of 2D waves in high Kapitza liquid films, as described by Nosoko’s correlation (Nosoko et al., 1996).

Data-driven decompositions of Particle Image Velocimetry (PIV) measurements are widely used for a variety of purposes, including the detection of coherent features (e.g., vortical structures), filtering operations (e.g., outlier removal or random noise mitigation), data reduction and compression. This work presents the application of a novel decomposition method, referred to as Multiscale Proper Orthogonal Decomposition ( Mendez J Fluid Mech 870:988-1036, 2019) to Time-Resolved PIV (TR-PIV) measurement. This method combines Multiresolution Analysis (MRA) and standard Proper Orthogonal Decomposition (POD) to achieve a compromise between decomposition convergence and spectral purity of the resulting modes. The selected test case is the flow past a cylinder in both stationary and transient conditions, producing a frequency-varying Karman vortex street. The results of the mPOD are compared to the standard POD, the Discrete Fourier Transform (DFT) and the Dynamic Mode Decomposition (DMD). The mPOD is evaluated in terms of decomposition convergence and time-frequency localization of its modes. The multiscale modal analysis allows for revealing beat phenomena in the stationary cylinder wake, due to the three-dimensional nature of the flow, and to correctly identify the transition from various stationary regimes in the transient test case., Article submitted to Meas Sci Tech

The jet wiping process is a cost-effective coating technique that uses impinging gas jets to control the thickness of a liquid layer dragged along a moving strip. This process is fundamental in various coating industries (mainly in hot-dip galvanizing) and is characterized by an unstable interaction between the gas jet and the liquid film that results in wavy final coating films. To understand the dynamics of the wave formation, we extend classic laminar boundary layer models for falling films to the jet wiping problem, including the self-similar integral boundary layer and the weighted integral boundary layer models. Moreover, we propose a transition and turbulence model to explore modelling extensions to larger Reynolds numbers and to analyse the impact of the modelling strategy on the liquid film dynamics. The validity of the long-wave formulation was first analysed on a simpler problem, consisting of a liquid film falling over an upward-moving wall, using volume of fluid simulations. This validation proved the robustness of the integral formulation in conditions that are well outside their theoretical limits of validity. Finally, the three models were used to study the response of the liquid coat to harmonic and non-harmonic oscillations and pulsations in the impinging jet. The impact of these disturbances on the average coating thickness and wave amplitude is analysed, and the range of dimensionless frequencies yielding maximum disturbance amplification is presented., SCOPUS: ar.j, info:eu-repo/semantics/published

While PIV allows the extraction of instantaneous streamlines, the availability of typically thousands of patterns hampers a statistical understanding of the underlying flow topology. A particular application is oscillating gas jets, encountered in scientific and industrial studies dealing with mass transfer and flow control. Multiple methods, such as statistical moments (including mean, variance, skewness, and kurtosis), proper orthogonal decomposition (POD), and Hartigan’s dip test are common post-processing methodologies. However, as demonstrated in this paper, they do not provide sufficient in-depth information from a statistical perspective to attribute probabilities to potential flow topologies. In this work, a novel approach to describe probability distributions based on extracted streamline patterns is proposed. Based on the available streamline patterns, the convolution with adaptive Gaussian kernels reveals the probability density function of the flow topology. The proposed methodology, as well as more traditional post-processing approaches, are assessed on the basis of synthetic flow fields and experimental PIV data of oscillating impinging gas jets, demonstrating the added value of the streamline probability map in characterising the scrutinised flow.

We analyze the flow of a planar gas jet impinging on a thin film dragged by a vertical moving wall. In the coating industry, this configuration is known as jet wiping, a process in which impinging jets control the thickness of liquid coatings on flat plates withdrawn vertically from a coating bath. We present three-dimensional (3D) two-phase flow simulations combining large eddy simulation (LES) and volume of fluid techniques. Three wiping configurations are simulated and the results are validated with experimental data from previous works. Multiscale modal analysis is used to analyze the dynamic interaction between the gas flow and the liquid film. In particular, we present a combination of multiscale Proper Orthogonal Decomposition (mPOD) and correlation analysis. The mPOD is used to identify the dominant traveling wave pattern in the liquid film flow, and the temporal structures are used to determine the most correlated flow features in the gas jet. This allows for revealing a two-dimensional mechanism for wave formation in the liquid coat. Finally, we use the numerical results to analyze the validity of some of the critical assumptions underpinning the derivation of integral film models of jet wiping.

Cavitation phenomena, produced when a flow is accelerated through a restriction, are of fundamental importance because of the large pressure oscillation they induce on pipelines. This paper presents an experimental investigation of various cavitation regimes produced at the exit of an orifice and its downstream propagation and attenuation. A cylindrical and a conical orifice are investigated over a range of cavitation number σ = 0.2 - 1 , keeping the ratio between saturation pressure ( P sat ) and downstream pressure ( P dw ) at two different values ξ = P sat / P dw = 0.05 , 0.3 . The range of operating conditions allows to investigate cavitation from the inception to the cloud, the developed, and the super-cavitation regime. For each configuration, the experimental analysis includes flow rate measurements, pressure signals via fast pressure transducers, and high-speed videos. The videos are analyzed using Multiscale Proper Orthogonal Decomposition (mPOD), to extract the coherent patterns that arise during the cloud cavitation and the developed cavitation regimes. The simultaneous analysis of the high-speed video in the proximity of the orifice and the time-resolved downstream pressure signal allows highlighting the effect of the cavitation intensity on the downstream evolution of these fundamental flows.

State-of-art preprocessing methods for Particle Image Velocimetry (PIV) are severely challenged by time dependent light reflections and strongly non-uniform background. In this work, a novel image preprocessing method is proposed. The method is based on the Proper Orthogonal Decomposition (POD) of the image recording sequence and exploits the different spatial and temporal coherence of background and particles. After describing the theoretical framework, the method is tested on synthetic and experimental images, and compared with well-known pre-processing techniques in terms of image quality enhancement, improvements in the PIV interrogation and computational cost. The results show that, unlike existing techniques, the proposed method is robust in the presence of significant background noise intensity, gradients, and temporal oscillations. Moreover, the computational cost is one to two orders of magnitude lower than conventional image normalization methods. A downloadable version of the preprocessing toolbox has been made available at http://seis.bris.ac.uk/similar to aexrt/PIVPODPreprocessing/. Miguel Alfonso Mendez is supported by a FRIA grant from the Belgian FNRS. Marco Raiola, Stefano Discetti, and Andrea Ianiro have been partially supported by grant TRA2013-41103-P of the Spanish Ministry of Economy and Competitiveness, which includes FEDER funding. The authors wish to thank Mr. Carlos Cobos for contributing in the realization of the flapping wing experimental setup, and Eigenmann & Veronelli Iberica SL for kindly providing the polyamide particles used as PIV seeding tracers.

We propose a novel data-driven decomposition referred to as Multi-scale Proper Orthogonal Decomposition (mPOD). This decomposition combines Multi-resolution Analysis (MRA) via Discrete Wavelet Transform (DWT) and Proper Orthogonal Decomposition (POD). Using MRA analysis, the mPOD decomposes the correlation matrix into the contribution of different scales, each retaining a non-overlapping portion of the correlation spectra and each leading to a POD constrained to a limited frequency bandwidth. The MRA analysis of the correlation matrix is presented both in terms of frequency response and eigenvalue spectra, in order to link the POD to the Fourier spectra. Finally, the decomposition is tested on a nonlinear advection-diffusion problem and compared to standard Proper Orthogonal Decomposition (POD), Dynamic Mode Decomposition (DMD) and Spectral Proper Orthogonal Decomposition (SPOD) in terms of feature extraction capabilities, residual decay versus the number of modes, and time-frequency localization.

In this paper, the most relevant characteristics of the substrate noise spectrum for mixed-signal integrated circuits (ICs) are derived using a simple analytical model. These characteristics are related to parameters of the digital circuit, the package + printed circuit board parasitics, and other elements of the mixed-signal IC. The model used to derive the substrate noise spectral characteristics includes the statistical properties of the digital switching current waveform and the coupling transfer function between the digital power supply nodes and the substrate node of the victim circuitry. The results of the work are validated experimentally on a mixed-signal prototype

This paper presents an experimental characterization of the jet wiping process, used in continuous coating applications to control the thickness of a liquid coat using an impinging gas jet. Time Resolved Particle Image Velocimetry (TR-PIV) is used to characterize the impinging gas flow, while an automatic interface detection algorithm is developed to track the liquid interface at the impact. The study of the flow interaction is combined with time resolved 3D thickness measurements of the liquid film remaining after the wiping, via Time Resolved Light Absorption (TR-LAbs). The simultaneous frequency analysis of liquid and gas flows allows to correlate their respective instability, provide an experimental data set for the validation of numerical studies and allows for formulating a working hypothesis on the origin of the coat non-uniformity encountered in many jet wiping processes.

The coverage dependence of the local adsorption structure of potassium on Ni(100) is investigated by means of diffuse LEED in the poorly ordered low coverage regime θ ⩽ 1 4 . We apply a diffuse intensity analysis whereby diffuse intensities are measured as functions of energy for constant values of the surface parallel momentum transfer. The resulting DI( E ) spectra are analyzed using conventional LEED computer programs. The adsorption height of potassium seems to decrease slightly by about 0.07 A when the coverage increases from θ = 0.08 to 0.25, though this behavior is still within the limits of error.

Alkali adsorbates on transition metals have traditionally given poor R factors for LEED theory/experiment comparison. In this paper we postulate that at least part of the remaining discrepancy is due to the non-spherical potential caused by a dipole moment on the alkali atom. Inclusion of a dipole in the fitting procedure gives a reasonable magnitude for the dipole, and a location not far from the centre of the alkali. The R factor shows a substantial improvement.

The current status of reconstruction of real-space images from diffuse LEED (DLEED) intensity distributions is described. We show by reconstruction of images from measured data that reliable images cannot be obtained from single energy diffraction maps. This holds also when intensities for electron energies even up to the order of 1000 eV are used, and we propose a new method to measure such higher energy data by sampling the diffuse intensity distribution through conventional LEED spot intensities. In order to show the reasons for the failure of the holographic interpretation of single energy diffuse maps we break up the various dynamical diffraction processes in the surface into its relevant constituents. This allows the demonstration that multiple diffraction makes the reference wave generally ill defined and the weight of the object wave too large. However, by inclusion of multiple energy data and proper phased averaging of intensities the disturbing influence of multiple diffraction seems to degrade and much more reliable and sharp images can result. This gives LEED and DLEED holography a high potential for its use in surface crystallography.

A recently published interpretation of diffuse LEED patterns as electron holograms as well as the subsequent reconstruction of real-space images is extended to use conventional LEED spot intensities. The procedure is based on the fact that ordered adsorbates produce superstructure spots which sample the diffuse intensity distribution appearing in the case of disordered adsorption. This circumvents experimental difficulties in measuring diffuse (i.e. low-level) intensities, particularly at higher energies. It also opens up the application of electron holography to ordered structures. Using experimental data the authors show that laterally resolved images can be reconstructed from the spot intensities. However, atomic positions can be displaced and vertical cut images are of insufficient quality.

The p(√3 × √3)R30 ° structure formed by oxygen adsorption on Ni(111) at coverage θ = 0.33 was investigated by LEED intensity measurements and their full dynamical analysis. Oxygen is found to reside on threefold coordinated fcc hollow sites at height 1.08 ± 0.02 A above the substrate with a Ni-O bondlength of 1.80 ± 0.02 A. Compared to the unrelaxed clean surface, which was also analysed, the topmost nickel layer spacing is slightly expanded to 2.05 ± 0.02 A (bulk value: 2.03 A) whereas the second to third interlayer spacing is practically unrelaxed (2.02 ± 0.02 A). A lateral reconstruction of the first substrate layer as found for the p(2 × 2) phase can be ruled out, i.e., lateral atomic shifts must be smaller than the error limit of 0.03 A. Vertical buckling in the first substrate layer is excluded by symmetry. This means that the reconstruction of the p(2 × 2) phase is lifted in the transition p(2 × 2)→ p(√3 × √3)R30°, i.e., by a coverage increase from θ = 0.25 to θ = 0.33. The quality and reliability of the structure determinations are mirrored by a Pendry R -factor of R = 0.16 for both the clean and oxygen-covered surface.

This paper presents film thickness measurement over a vertical falling liquid film, carried out with Light Absorption (LAbs) and a 2D laser tomography techniques known as Level Detection and Recording (LeDaR). The presented test cases are in the low Reynolds regime (Re = 1 - 8) and include undisturbed conditions, i.e. constant flow rate, and inlet-forced conditions, i.e. flow rate pulsing at frequencies in the range fp = 12-18Hz. The liquid used is Dipropilene Glycol (DPG), with Kapitza number Ka = 4.6. The results include average film thickness in the steady case, wave celerity and wave profile in the forced conditions. All the measurements are scaled using the Skhadov scaling, to facilitate the comparison with analytical low-dimensional models. Both LAbs and LeDaR techniques are presented in detail, including calibration, uncertainties and data processing aspects., SCOPUS: cp.p, info:eu-repo/semantics/published

© 2006 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. This paper presents the effects of noise generated by realistic digital circuits on RF voltage controlled oscillators (VCO) integrated in the same silicon die. The digital noise is coupled through the common substrate and generates both phase noise and sideband spurs at the VCO output. The noise coupling and impact mechanisms, and their dependence on the VCO operating conditions (control voltage, gain and bias current) are investigated.

This work presents an experimental investigation about the relation between specific characteristics of a digital circuit (clock frequency and architecture) and the substrate noise spectrum that it generates. Both the discrete impulse train term and the continuous term of the substrate noise spectrum are investigated. The results indicate that the continuous term sets an upper bound to the substrate noise reduction that may be obtained by changing the digital frequency or by staggering the simultaneous activity of the circuit, two techniques that have been proposed in the literature to reduce substrate noise.

The present work addresses the investigation of phase noise degradation of LC-tank VCOs due to realistic digitally originated substrate noise. The dominant mechanisms by which this noise is coupled to the output of the oscillator due to the substrate and the package are analyzed, indicating that both noise at low frequencies and at high frequencies around the oscillation fundamental significantly degrade phase noise.

© 2005 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. This paper presents a simplified analytical model of the substrate noise generated by digital circuitry that captures the most relevant frequency domain characteristics and relates them with parameters of the digital circuit and the package. Simulations and experimental results are used to validate the analytical model.

The recent suggestion that a diffuse low-energy-electron-diffraction pattern from a disordered layer of adsorbate atoms on a crystal surface may be interpreted as a Fraunhofer hologram, from which crystallographic information may be extracted directly, is put to a practical test in the case of O/Ni(100). Holographic reconstruction yields an image of the Ni atoms closest to the O adsorbates. The image resolution appears sufficient for its use as a starting point for more established crystallographic techniques, to discriminate, in a preliminary search, between very different models

Atrial natriuretic peptide (ANP) plays an important role in blood pressure regulation, electrolyte and water balance. ANP has direct hypotensive effects (Borenstein et al., 1983; Cantin & Genest, 1985; Garcia et al., 1985; Marin Grez et al., 1985) decreasing the peripheric vascular resistance through vasodilatation and circulating blood volume through natriuretic and diuretic mechanisms (Cantin & Genest, 1985; De Bold et al., 1981; Nushiro et al., 1987; Trippodo et al., 1983; Winquist, 1985).

Recent developments to reconstruct real space atomic images from diffuse LEED intensities generated by disordered adsorbates ask for data at higher electron energies in order to improve resolution. However, at energies above ∼ 500 eV increasing thermal diffuse and Kikuchi scattering as well as crowding of substrate spots make the direct measurement of such data practically impossible. Therefore, we describe a new procedure to measure diffuse intensity distributions: we show both experimentally and theoretically that conventional superstructure spots of ordered adsorbates sample the diffuse distribution when the local adsorption geometry is the same. So, diffuse intensity distributions can be obtained by conventional spot measurements. Diffuse patterns resulting from this sampling procedure may be input to holographic reconstruction techniques particularly when data of different energies are needed.

In contrast to the considerable infomation obtained on the intestinal handling of calcium in healthy human subjects as well as in disease states (1), there are few data concerning the gastrointestinal absorption of phosphate.

While the radioactivity distribution varies in the longitudinal and vertical directions, the efficiency of each spectral energy band in a Whole Body Counter, changes. Two experiments were carried out varying the longitudinal distribution of radioactivity and increasing the depth of the absorption media. The optimum scatter window to measure 47Ca in a Whole Body Counter was determined by the method proposed by Gibbs et al. Results show that: 1. (i) the energy band corresponding to 0·37-·073 MeV is the best to measure 47Ca. 2. (ii) estimated accuracy when a patient is measured using the optimum energy band is 7 per cent.