A management and control architecture for providing IPdifferentiated services in MPLS-based networks

As the Internet evolves toward the global multiservice network of the future, a key consideration is support for services with guaranteed quality of service. The proposed differentiated services framework is seen as the key technology to achieve this. DiffServ currently concentrates on control/data plane mechanisms to support QoS, but also recognizes the need for management plane aspects through the bandwidth broker. In this article we propose a model and architectural framework for supporting DiffServ-based end-to-end QoS in the Internet, assuming underlying MPLS-based explicit routed paths. The proposed integrated management and control architecture will allow providers to offer both quantitative and qualitative services while optimizing the use of underlying network resources     

Torsional surface waves in a gradient-elastic half-space

The present work deals with torsional wave propagation in a linear gradient-elastic half-space. More specifically, we prove that torsional surface waves (i.e. waves with amplitudes exponentially decaying with distance from the free surface) do exist in a homogeneous gradient-elastic half-space. This finding is in contrast with the well-known result of the classical theory of linear elasticity that torsional surface waves do not exist in a homogeneous half-space. The weakness of the classical theory, at this point, is only circumvented by modeling the half-space as having material properties variable with depth (E. Meissner, Elastische Oberflachenwellen mit Dispersion in einem inhomogenen Medium, Vierteljahrsschrift der Naturforschenden Gesellschaft in Zurich 66 (1921) 181–195; I. Vardoulakis, Torsional surface waves in inhomogeneous elastic media, Internat. J. Numer. Anal. Methods Geomech. 8 (1984) 287–296; G.A. Maugin, Shear horizontal surface acoustic waves on solids, in: D.F. Parker, G.A. Maugin (Eds.), Recent Developments in Surface Acoustic Waves, Springer Series on Wave Phenomena, vol. 7, Springer, Berlin, 1988, pp. 158–172), as a layered structure (Maugin, 1988; E. Reissner, Freie und erzwungene Torsionsschwingungen des elastischen Halbraumes, Ingenieur-Archiv 8 (1937) 229–245) or by considering couplings with electric and magnetic fields for different types of materials (Maugin, 1988). The theory employed here is the simplest possible version of Mindlin’s (R.D. Mindlin, Micro-structure in linear elasticity, Arch. Rat. Mech. Anal. 16 (1964) 51–78) generalized linear elasticity. A simple wave-propagation analysis based on Hankel transforms and complex-variable theory was done in order to determine the conditions for the existence of the torsional surface motions and to derive dispersion curves and cut-off frequencies. Also, we notice that, up to date, no other generalized linear continuum theory (including the integral-type non-local theory) has successfully been proposed to predict torsional surface waves in a homogeneous half-space.     

Velocity measurements of flow through a step stenosis using Magnetic Resonance Imaging

 Magnetic resonance imaging (MRI) is a versatile noninvasive tool for achieving full-field quantitative visualization of complex fluid flows. The MRI signal results from the interaction of radio-frequency (RF) pulses with nuclear spins exposed to a strong static magnetic field. The two main techniques of MRI velocimetry are time-of-flight and phase contrast techniques. Time-of- flight techniques involve tagging and tracking a material volume of fluid, whereas phase contrast techniques use magnetic field gradients to encode velocity information into the phase of the MRI signal. In this study, both techniques are used to probe the pressure-driven steady flow of water in a pipe with a step stenosis. The velocity measurements were then compared with computational results obtained using the FIDAP software package. The experiments show that the phase contrast method gives more accurate results, with 90% of the measurements within 10% of the local computational fluid dynamics (CFD) velocity predictions at Re = 100 and 94% of the measurements within 10% of the local CFD predictions at Re = 258. Although the time-of-flight experiments were not as accurate, they provide a good qualitative image of the flow field. Sources of the discrepancies between the MRI data and the CFD results are also discussed, including acceleration and spin flow-through artifacts. Received: 7 April 1999/Accepted: 20 December 1999     

AN EVALUATION OF THE BOUNCE-BACK BOUNDARY CONDITION FOR LATTICE BOLTZMANN SIMULATIONS

The bounce-back boundary condition for lattice Boltzmann simulations is evaluated for flow about an infinite periodic array of cylinders. The solution is compared with results from a more accurate boundary condition formulation for the lattice Boltemann method and with finite difference solutions. The bounce-back boundary condition is used to simulate boundaries of cylinders with both circular and octagonal cross-sections. The convergences of the velocity and total drag associated with this method are slightly sublinear with grid spacing. Error is also a function of relaxation time, increasing exponentially for large relaxation times. However, the accuracy does not exhibit a trend with Reynolds number between 0·1 and 100. The square lattice Boltzmann grid conforms to the octagonal cylinder but only approximates the circular cylinder, and the resulting error associated with the octagonal cylinder is half the error of the circular cylinder. The bounce-back boundary condition is shown to yield accurate lattice Boltzmann simulations with reduced computational requirements for computational grids of 170×170 or finer, a relaxation time less than 1·5 and any Reynolds number from 0·1 to 100. For this range of parameters the root mean square error in velocity and the relative error in drag coefficient are less than 1 per cent for the octagonal cylinder and 2 per cent for the circular cylinder. © 1997 John Wiley & Sons, Ltd.     

Novel capsule phase microextraction in combination with high performance liquid chromatography with diode array detection for rapid monitoring of sulfonamide drugs in milk

Capsule phase microextraction is introduced herein for the first time to determine four sulfonamide residues in milk samples (sulfanilamide, sulfadiazine, sulfamethizole, and sulfathiazole). The technique eloquently integrates filtration and stirring mechanism into the extraction device, as such no filtration of the sample is needed prior to introducing the extraction device into the sample, and when placed on a magnetic stirrer, the device spins itself in order to diffuse the sample, resulting in faster extraction equilibrium. Microextraction capsules consist of three main parts; a magnet, a cellulose fiber substrate coated with high performance sol‐gel hybrid organic‐inorganic sorbent, and a porous membrane. Various encapsulated sol‐gel sorbents were tested in standard solutions prepared in deionized water and milk samples under different operational conditions. Analyte extraction time and elution time, type of sol‐gel sorbent, elution solvent, as well as the ratio of the sorbent to the elution solvent were among the optimized conditions. The protocols that yielded the best absolute recovery rates were subsequently tested in various milk samples. Method validation was performed in terms of linearity, accuracy and precision, reusability and ruggedness using the Youden test. The examined sulfonamides were subsequently analysed by reversed phase high performance liquid chromatography with diode array detection.     

Sh surface Waves in a Homogeneous Gradient-Elastic Half-Space with Surface Energy

The existence of SH surface waves in a half-space homogeneous material (i.e. anti-plane shear wave motions which decay exponentially with the distance from the free surface) is shown to be possible within the framework of the generalized linear continuum theory of gradient elasticity with surface energy. As is well-known such waves cannot be predicted by the classical theory of linear elasticity for a homogeneous half-space, although there is experimental evidence supporting their existence. Indeed, this is a drawback of the classical theory which is only circumvented by modelling the half-space as a layered structure (Love waves) or as having non-homogeneous material properties. On the contrary, the present study reveals that SH surface waves may exist in a homogeneous half-space if the problem is analyzed by a continuum theory with appropriate microstructure. This theory, which was recently introduced by Vardoulakis and co-workers, assumes a strain-energy density expression containing, besides the classical terms, volume strain-gradient and surface-energy gradient terms. This revised version was published online in August 2006 with corrections to the Cover Date.     

The Boussinesq problem in dipolar gradient elasticity

The three-dimensional axisymmetric Boussinesq problem of an isotropic half-space subjected to a concentrated normal quasi-static load is studied within the framework of dipolar gradient elasticity involving linear constitutive relations and small strains. Our main concern is to determine possible deviations from the predictions of classical linear elastostatics when a more refined theory is employed to attack the problem. Of special importance is the behavior of the new solution near to the point of application of the load where pathological singularities exist in the classical solution. The use of the theory of gradient elasticity is intended here to model the response of materials with microstructure in a manner that the classical theory cannot afford. A linear version of this theory (as regards both kinematics and constitutive response) results by considering a linear isotropic expression for the strain-energy density that depends on strain gradient terms, in addition to the standard strain terms appearing in classical elasticity and by considering small strains. Through this formulation, a microstructural material constant is introduced, in addition to the standard Lamé constants. The solution method is based on integral transforms and is exact. The present results show significant departure from the predictions of classical elasticity. Indeed, continuous and bounded displacements are predicted at the points of application of the concentrated load. Such a behavior of the displacement field is, of course, more natural than the singular behavior exhibited in the classical solution.     

Bounds on the delay distribution of window random-access algorithms

A method for analyzing the delay distribution of window random-access algorithms is presented. The window size is allowed to vary during the operation of the algorithm. It is shown that the quantities of interest in the computation of the delay distribution can be related to the solution of appropriate infinite systems of linear equations. Once the constants and the coefficients of the unknowns of the system are determined, bounds on the solution can be developed by applying previously developed methodologies. The method is applied to the delay distribution analysis of the Capetanakis window random-access algorithm and the part-and-try algorithm, both under binary feedback     

Pattern Nulling in Coupled Oscillator Antenna Arrays

An optimization method is presented for constrained beam steering with null formation in linear coupled oscillator arrays. The method is based on a perturbation model of the far field of the array that includes both amplitude and phase perturbations, to accommodate prescribed nulls. Moreover, it takes into account the array nonlinear dynamics through a first-order approximation model of the array steady state. The optimization results are verified by harmonic balance simulations. Also, the stability of the optimized solutions is examined by perturbing the steady state solution and is verified with envelope transient. Design examples are used to demonstrate the validity and limitations of the proposed method     

Pseudodifferential operators on mixed‐norm Besov and Triebel–Lizorkin spaces

We prove boundedness of pseudodifferential operators on anisotropic mixed‐norm Besov and Triebel–Lizorkin spaces. Our proof relies only on general maximal function estimates and provides a new perspective even in the case of spaces without mixed norms. Moreover, we cover the case of Fourier multipliers on the above mentioned spaces. As application we establish boundedness of pseudodifferential operators and Fourier multipliers on anisotropic mixed‐norm Sobolev spaces.