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The emergence of elevated concentrations of bromate, classified as a 2B type carcinogen, in drinking water following the treatment of water supplies with ozonation and other oxidation methods has underscored the importance of developing methods for reliable and rapid screening of drinking water. In this work, we report the use of electro activated riboflavin (RF) impregnated Ketjen black (KB) modified screen-printed electrode (el RF@KB-SPE) for the determination of bromate. The sensing surfaces were subjected to morphological and structural characterization using scanning electron microscopy and Raman spectroscopy. These analyses confirmed the successful modification of the electrode with an extended el RF@KB porous coating. Based on cyclic voltammetry (CV) and electrochemical impedance spectroscopy measurements, the response of el RF@KB-SPE towards bromate can be described through a dual mechanism involving i) an autocatalytic chemical/electrochemical process that predominantly occurs in the finite length pores of KB, and ii) an RF-mediated electrocatalytic process. Notably, the data demonstrated that the advanced electrocatalytic properties of the otherwise electrocatalytically inactive absorbed RF molecules are endowed after a simple electro activation process (three CV scans). Amperometric measurements at −0.05 V vs. Ag/AgCl revealed a linear relationship between the current response and the concentration of bromates over the concentration range 0.50−18.0 μM, achieving a limit of detection (3 σ /slope) of 0.04 μM. The interference effect of various electroactive species was investigated demonstrating that el RF@KB-SPE is highly selective to bromate. The analytical utility of the method was evaluated in spiked tap water samples. Recoveries were 91.2 − 106.4 %. [Display omitted] • Bromate sensing in electroactivated riboflavin impregnated carbon black (KB) SPE. • CV and EIS data support a dual autocatalytic redox mediation mechanism. • Electrocatalysis occurs in a finite-length diffusion regime within the pores of KB. • Impregnation of riboflavin in KB porous promotes the electroanalysis of bromate. • Data demonstrated high selectivity and analytical utility in water samples. [ABSTRACT FROM AUTHOR]

Copyright of Caderno Brasileiro de Ensino de Física is the property of Caderno Brasileiro de Ensino de Fisica and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The linear stability of plane Poiseuille flow through a finite-length channel is studied. A weakly divergence-free basis finite element method with streamline upwind Petrov-Galerkin (SUPG) stabilization is used to formulate the weak form of the problem. The linear stability characteristics are studied under three possible inlet-outlet boundary conditions, and the corresponding perturbation kinetic energy transfer mechanisms are investigated. Active transfer of perturbation kinetic energy at the channel inlet and outlet, energy production due to convection and dissipation at the flow bulk provide a new perspective in understanding the distinct stability characteristics of plane Poiseuille flow under various boundary conditions. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Direct numerical simulation (DNS) is performed to investigate the modes of shedding of the wake of a wall-mounted finite-length square cylinder with an aspect ratio (AR) of 7 for six different boundary layer thicknesses (0.0-0.30) at a Reynolds number of 250. For all the cases of wall boundary layer considered in this study, two modes of shedding, namely, anti-symmetric and symmetric modes of shedding, were found to coexist in the cylinder wake with symmetric one occurring intermittently for smaller time duration. The phase-averaged flow field revealed that the symmetric modes of shedding occur only during instances when the near wake experiences the maximum strength of upwash/downwash flow. The boundary layer thickness seems to have a significant effect on the area of dominance of both downwash and upwash flow in instantaneous and time-averaged flow field. It is observed that the near-wake topology and the total drag force acting on the cylinder are significantly affected by the bottom-wall boundary layer thickness. The overall drag coefficient is found to decrease with thickening of the wall boundary layer thickness. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Vibration Engineering is the property of Nanjing University of Aeronautics & Astronautics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Strain growth is a phenomenon observed in the elastic response of containment vessels subjected to internal blast loading. The local dynamic response of a containment vessel may become larger in a later stage than its response in the earlier stage. In order to understand the possible mechanisms of the strain growth phenomenon in a cylindrical vessel, dynamic elastic responses of a finite-length cylindrical shell with different boundary conditions subjected to internal pressure pulse are studied by finite-element simulation using LS-DYNA. It is found that the strain growth in a finite-length cylindrical shell with sliding-sliding boundary conditions is caused by nonlinear modal coupling. Strain growth in a finite-length cylindrical shell with free-free or simply supported boundary conditions is primarily caused by the linear modal superposition, possibly enhanced by the nonlinear modal coupling. The understanding of these strain growth mechanisms can guide the design of cylindrical containment vessels. [ABSTRACT FROM AUTHOR]

Wake characteristics of the flow over a finite square prism at different incidence angles were experimentally investigated using an open-loop wind tunnel. A finite square prism with a width D - 15 mm and a height H=1D was vertically mounted on a horizontal flat plate. The Reynolds number was varied from 6.5×103 to 28.5×103 and the incidence angle α was changed from 0° to 45°. The ratio of boundary layer thickness to the prism height was about δ/H= 7%. The time-averaged velocity, turbulence intensity and the vortex shedding frequency were obtained through a single-component hotwire probe. Power spectrum of the streamwise velocity fluctuations revealed that the tip and base vortices shed at the same frequency as that of spanwise vortices. Furthermore, the results showed that the critical incidence angle corresponding to the maximum Strouhal number and minimum wake width occurs at αcr = 15° which is equal to that reported for an infinite prism. There is a reduction in the size of the wake region along the height of the prism when moving away from the ground plane towards the free end. [ABSTRACT FROM AUTHOR]

A general hydraulic loss coefficient correlation for perpendicular, cylindrical, finite length dividing pipe junctions is developed and implemented in a discrete dividing-flow manifold model. Dividing-flow manifolds are used in several technical appliances, e.g., in water and wastewater treatment, swimming pool technology, air engineering, and polymer processing. Ensuring uniform flow distribution is a major goal of a flow manifold system design, whose accuracy is usually determined by the accuracies of applied flow coefficients. Coefficient of turning losses is calculated by a computational fluid dynamics (CFD)-based approach applying a nonlinear fit. In the case of a single-phase flow, the loss coefficient depends on four dimensionless parameters: the Reynolds number, the ratio of port and header flow velocities, the diameter ratio, and the ratio of the port length and the diameter of the pipe. Instead of experimentally covering this fourdimensional parameter space, more than 1000 judiciously chosen three-dimensional simulations were run to determine the loss coefficient for the parameter range most used in engineering practice. Validated results of our novel resistance formula show that the velocity and port length to header diameter ratios have a significant effect on the turning loss coefficient, while the diameter ratio and Reynolds number dependency are weaker in the investigated parameter ranges. [ABSTRACT FROM AUTHOR]

An analytical investigation is presented to study the unsteady peristaltic transport of nanofluids. Three different geometries of nanoparticle viz bricks, cylinder and platelets are considered in our analysis. The flow geometry is taken as nonuniform channel of finite length to explore our model for wide range of biomedical applications. Exact solutions are obtained for the non-dimensional governing equations subject to physically realistic boundary conditions. The effects of nanoparticle shapes on effective thermal conductivity, axial velocity, transverse velocity, temperature, and pressure difference distributions along the length of non-uniform channel with variation of different flow parameters are discussed with the help of graphical illustrations. It is observed that platelet shaped nanoparticles carry maximum velocity whereas brick shaped nanoparticles are the best to enhance the thermal conductivity. An inherent property of peristaltic transport i.e. trapping is also discussed. This model is applicable in drugs delivery system where different geometries of drugs are delivered and it is also applicable to design a microperistaltic pump for transportation of nanofluids. [ABSTRACT FROM AUTHOR]

Finite-length line contact conditions, existing in applications such as gears or roller hearings, lead to subsurface stress distribution influenced by the free boundaries. This paper presents a semi-analytical method (SAM) for the finite-length line contact problem, based on the overlapping concept and matrix formation, to consider the effect of two free-end surfaces. In order to obtain two free surfaces, three half-spaces with mirrored loads to be solved are overlapped to cancel out the stresses at expected surfaces. The error introduced by this method is analyzed and proven to be negligible. The conjugate gradient method (CGM) is used to solve the pressure distribution, and the fast Fourier transform (FFT) is used to speed up the elastic deformation and stress-related calculation. The model is verified by finite element method (FEM) and shows a high conformity and efficiency. Besides, the line contact situations are discussed to explore the effect of free surfaces. [ABSTRACT FROM AUTHOR]

In this paper a new 2D-FGM material model based on Mori-Tanaka scheme and third-order transition function has been developed for a thick hollow cylinder of finite length. Elastic mechanical stress analysis is performed by utilizing the finite element method. The corresponding material, displacement and stress distributions are evaluated for different values of n r and n z . Moreover, the effects of different material property distributions on the effective stress with respect to the metallic phase volume fraction are investigated. It is demonstrated that the increase in n r and V m leads to a significant reduction in the effective stress. Finally, it is shown that the ceramic phase rich cylinder wall has lower maximum effective stresses of which the lowest value of effective stress has been evaluated for n r = 20 and n z = 5. This minimum value is about half the maximum effective stress which has been evaluated for the non-FGM cylinder case ( n r = n z =0.1). [ABSTRACT FROM AUTHOR]

Feedback stabilization of inviscid and high Reynolds number, axisymmetric, swirling flows in a long finite-length circular pipe using active variations of pipe geometry as a function of the evolving inlet radial velocity is studied. The complicated dynamics of the natural flow requires that any theoretical mode! that attempts to control vortex stability must include the essential nonlinear dynamics of the perturbation modes. In addition, the control methodology must establish a stable desired state with a wide basin of attraction. The present approach is built on a weakly nonlinear model problem for the analysis of perturbation dynamics on near-critical swirling flows in a slightly area-varying, long, circular pipe with unsteady changes of wall geometry. In the natural case with no control, flows with incoming swirl ratio above a critical level are unstable and rapidly evolve to either vortex breakdown states or accelerated flow states. Following an integration of the model equation, a perturbation kinetic-energy identity is derived, and an active feedback control methodology to suppress perturbations from a desired columnar state is proposed. The stabilization of both inviscid and high-Re flows is demonstrated for a wide range of swirl ratios above the critical swirl for vortex breakdown and for large-amplitude initial perturbations. The control gain for the fastest decay of perturbations is found to be a function of the swirl level. Large gain values are required at near-critical swirl ratios while lower gains provide a successful control at swirl levels away from critical. This feedback control technique cuts the feed-forward mechanism between the inlet radial velocity and the growth of perturbation's kinetic energy in the bulk and thereby enforces the decay of perturbations and eliminates the natural explosive evolution of the vortex breakdown process. The application of this proposed robust active feedback control method establishes a branch of columnar states with a wide basin of attraction for swirl ratios up to at least 50% above the critical swirl. This study provides guidelines for future flow control simulations and experiments. However, the present methodology is limited to the control of high-Reynolds number (nearly inviscid), axisymmetric, weakly nonparallel flows in long pipes. [ABSTRACT FROM AUTHOR]

The three-lobe bearings widely used in rotating machinery follow the design data evaluated using numerical methods for the solution of the Reynolds equation. This paper defines exact and approximate analytical solutions of the Reynolds equation for the case of three-lobe bearings with finite length. Dynamic characteristics are provided analytically with closed-form expressions for laminar regimes of operation, using an approximate analytical solution that proves to be reliable and of low cost of evaluation time. The results for eccentricity ratio, equilibrium locus, stiffness and damping coefficients are presented for a range of Sommerfeld number and different cases of load orientation and compared with theoretical and experimental data from the literature. [ABSTRACT FROM AUTHOR]

Line contact is common in many machine components, such as various gears, roller and needle bearings, and cams and followers. Traditionally, line contact is modeled as a two-dimensional (2D) problem when the surfaces are assumed to be smooth or treated stochastically. In reality, however, surface roughness is usually three-dimensional (3D) in nature, so that a 3D model is needed when analyzing contact and lubrication deterministically. Moreover, contact length is often finite, and realistic geometry may possibly include a crowning in the axial direction and round corners or chamfers at two ends. In the present study, plasto-elastohydrodynamic lubrication (PEHL) simulations for line contacts of both infinite and finite length have been conducted, taking into account the effects of surface roughness and possible plastic deformation, with a 3D model that is needed when taking into account the realistic contact geometry and the 3D surface topography. With this newly developed PEHL model, numerical cases are analyzed in order to reveal the PEHL characteristics in different types of line contact. [ABSTRACT FROM AUTHOR]

Taylor- Couette flow (TCF) is an important template for studying various mechanisms of the laminarturbulent transition of rotating fluid in enclosed cavity. It is also relevant to engineering applications like bearings, fluid mixing and filtration. Furthermore, this flow system is of potential importance for development of bio-separators employing Taylor vortices for enhancement of mass transfer. The fluid flowing in the annular gap between two rotating cylinders has been used as paradigm for the hydrodynamic stability theory and the transition to turbulence. In this paper, the fluid in an annulus between short concentric cylinders is investigated numerically for a three dimensional viscous and incompressible flow. The inner cylinder rotates freely about a vertical axis through its centre while the outer cylinder is held stationary and oscillating radially. The main purpose is to examine the effect of a pulsatile motion of the outer cylinder on the onset of Taylor vortices in the vicinity of the threshold of transition, i.e., from the laminar Couette flow to the occurrence of Taylor vortex flow. The numerical results obtained here show significant topological changes on the Taylor vortices. In addition, the active control deeply affects the occurrence of the first instability. It is established that the appearance of the Taylor vortex flow is then substantially delayed with respect to the classical case; flow without control. [ABSTRACT FROM AUTHOR]

This paper investigates the use of finite 1:1 dimer chains to mitigate the transmission of shock disturbances. Dimer chains consist of alternating light and heavy masses with interconnecting compliance. Changing the mass ratio has provided interesting results in previous research. In particular, in the case of Hertzian contacts with zero-preload, certain mass ratios have revealed minimal levels of transmitted force. This paper examines this phenomenon from the perspective of utilizing it in practical isolation systems. The zero-preload Hertzian contact case is contrasted with chains connected by linear or cubic springs. Through numerical simulations, tradeoffs are examined between displacement and transmitted force. Parametric studies are conducted to examine how isolation performance changes with mass ratio, stiffness, and different chain lengths. [ABSTRACT FROM AUTHOR]

The spanwise characteristics of flow passing a yawed finite circular cylinder are numerical investigated at the yaw angle of 30°, aspect ratio of 9 and Reynolds number of 3900 using Large Eddy Simulation. The wake vortical structure and streamlines manifest that the regular Karman vortex street breaks down and there exists axial flow along the cylinder axis. To get further insight into the spanwise characteristics, the cylinder is virtually divided into nine equal-spaced sections along the cylinder span, and the drag and lift force coefficients of each section are monitored. By comparing the drag coefficients of these nine cylinder sections, it is found that the anti-clockwise torque is imposed on the cylinder. Furthermore, the FFT analyses of these nine fluctuating lift coefficients are carried out to reveal the characteristics in the frequency domain. It is shown that the nine spectra demonstrate different behaviours, by which the wake vortical structure is identified spanwise as three regions, two end-plate regions and the midspan region. In the downstream end-plate region, the vortex-shedding is well organized, whereas in the upstream end-plate region the wake vortex structure manifests itself stronger three-dimensional and severely irregular. And in the midspan region, the peak of frequency spectra is broadband and the regular Karman vortex street is not yet noticeable to identify. [ABSTRACT FROM AUTHOR]

Peristaltic transport due to a sinusoidal wave traveling on the boundary of a tube filled with an incompressible fluid is presented. Solution is obtained under infinite wavelength and zero Reynolds number in a finite length tube which extends the study of Li and Brasseur (1993, "Non-Steady Peristaltic Transport in Finite-Length Tubes," J. Fluid Mech., 248, pp. 129-151). Boundary conditions are changed to include wall permeability. Analysis of pressure profile is described. [ABSTRACT FROM AUTHOR]

A new method for determining a closed-form expression for the hydrodynamic forces in finite-length plain journal bearings is introduced. The method is based on applying correction functions to the force models of the infinitely long (IL) or infinitely short (IS) bearing approximation. The correction functions are derived by modeling the ratio between the forces from the numerical integration of the two-dimensional Reynolds equation and the forces from either the IL or IS bearing approximation. Low-order polynomial models, dependent on the eccentricity ratio and aspect ratio, are used for the correction functions. A comparative computational study is presented for the steady-state behavior of the bearing system under static and unbalance loads. The results show the proposed models outperforming the standard limiting approximations as well as a model based on the finite-length impedance method. [ABSTRACT FROM AUTHOR]

This paper describes a predictive model for breakout noise from an elliptical duct or shell of finite length. The transmission mechanism is essentially that of "mode coupling", whereby higher structural modes in the duct walls get excited because of non-circularity of the wall. Effect of geometry has been taken care of by evaluating Fourier coefficients of the radius of curvature. The noise radiated from the duct walls is represented by that from a finite vibrating length of a semi infinite cylinder in a free field. Emphasis is on understanding the physics of the problem as well as analytical modeling. The analytical model is validated with 3-D FEM. Effects of the ovality, curvature, and axial terminations of the duct have been demonstrated. [ABSTRACT FROM AUTHOR]

Abstract: The transient thermal response of a thick orthotropic hollow cylinder with finite length is studied by a high order shell theory. The radial and axial displacements are assumed to have quadratic and cubic variations through the thickness, respectively. It is important that the radial stress is approximated by a cubic expansion satisfying the boundary conditions at the inner and outer surfaces, and the corresponding strain should be least-squares compatible with the strain derived from the strain-displacement relation. The equations of motion are derived from the integration of the equilibrium equations of stresses, which are solved by precise integration method (PIM). Numerical results are obtained, and compared with FE simulations and dynamic thermo-elasticity solutions, which indicates that the high order shell theory is capable of predicting the transient thermal response of an orthotropic (or isotropic) thick hollow cylinder efficiently, and for the detonation tube of actual pulse detonation engines (PDE) heated continuously, the thermal stresses will become too large to be neglected, which are not like those in the one time experiments with very short time. [Copyright &y& Elsevier]

The article presents a study on semi-infinite-spatial-domain wave equation modeling of the real-world problem of longitudinal waves propagating along a slender, homogeneous elastic rod-pump gas wells of finite length. It found that precision of the downhole-pump card can be increased by improving the accuracy of the friction law in the wave equation. The authors also discussed the Gibb's theorem and illustrated its validity with an existing well. It is noted that the supposition of validity comes from Gibb's conjecture, which states that downhole conditions can be derived from surface measurements if a correct law of rod friction is known.

This article extends the perturbation method introduced by Wang (2008, A Novel Method for Analyzing the Global Stability of Inviscid Columnar Swirling Flow in a Finite Pipe," Phys. Fluids, 20(7), p. 074101) to determine the global stability of a swirling flow in a straight circular pipe with specified inlet and outlet boundary conditions. To accurately compute the flow stability characteristics, a general procedure to treat the complexity arising from high-order terms is developed. It extends the previous fourth-order method to an eighth-order method. The technique is first applied to the benchmark case of a solid-body rotation flow with a uniform axial speed. It is demonstrated that the eighth-order method is sufficient to construct the growth rate curve between the first and second critical swirls of this flow. Note that this range of swirl is crucial for the study of the vortex breakdown phenomenon since the base flow is unstable and starts the initial stage of transition to a breakdown state. The method is then applied to the Lamb-Oseen vortex to construct the growth rate curve between the first and second critical swirls of this flow. Calculated results are compared with the growth rate curve computed from direct numerical simulations and an overall agreement between the two computations is found. This demonstrates that the Wang and Rusak (1996, "On the Stability of an Axisymmetric Rotating Flow in a Pipe," Phys. Fluids, 8(4), pp. 1007-1076) instability mechanism captures quantitatively the initial growth of disturbance, which eventually evolves into a breakdown state. [ABSTRACT FROM AUTHOR]