Stokes flow due to infinite arrays of stokeslets in three dimensions

Infinite periodic arrays of stokeslets in three dimensions are summed up by obtaining various rapidly converging infinite series. The three cases treated here are: 1. Identical stokeslets distributed at constant intervals on a line parallel to a plate, 2. An array of identical stokeslets distributed on a two-dimensional periodic lattice on a plane parallel to a plate, 3. The same array, but parallel to and in between two plates. Computational results are shown and comparisons with previously averaged expressions are made.     

Modelling cracks in finite bodies by distributed dislocation dipoles

The method of continuous distribution of dislocations is extended here to model cracks in finite geometries. The cracks themselves are still modelled by distributed dislocations, whereas the finite boundaries are represented by a continuous distribution of dislocation dipoles. The use of dislocation dipoles, instead of dislocations, provides a unified formulation to treat both simple and arbitrary boundaries in a numerical solution. The method gives a set of singular integral equations with Cauchy kernels, which can be readily solved using Gauss–Chebyshev quadratures for finite bodies of simple shapes. When applied to arbitrary geometries, the continuous distribution of infinitesimal dislocation dipoles is approximated by a discrete distribution of finite dislocation dipoles. Both the stress intensity factor and the T -stress are evaluated for some well-known crack problems, in an attempt to assess the performance of the methods and to provide some new engineering data.     

Interpretation of single-particle negative polarization at intermediate scattering angles

We study the interrelation of the internal field of irregular particles to the far-field scattering characteristics by modifying the internal field of dipole groups. In this paper, we concentrate on the longitudinal component, i.e., the internal-field component parallel to the incident wave vector. We use the discrete-dipole approximation to determine the internal field and switch off the longitudinal component from the dipoles that have the highest energy density above a preset cutoff value. We conclude that only a relatively small number of core dipoles, about 5% of all dipoles, contribute to the negative linear polarization at intermediate scattering angles. These core dipole groups are located at the forward part of the particles. The number of core dipoles in the group becomes greater as particle asphericity increases. We find that the interference between the scattered waves from the core dipole groups, which was studied previously for spherical particles, is preserved to a large extent for nonspherical particles.     

Helical distributions of stokeslets

Helical distributions of stokeslets can valuably model microbial locomotion through a fluid, and also the flow field generated, wherever a flagellum actively executes helical undulations (as in many single-celled algae and protozoa) or where (as in many bacteria) the action of rotary motors causes a passive structure of helical shape (which may be a flagellum or else the cell body itself) to rotate. Here, previous biomechanical studies of such modes of locomotion are extended to include analyses of three-dimensional flow fields. In some cases, a rotlet field (curl of a stokeslet) needs to be incorporated in the models. For example, spirochete swimming is modelled by combined helical distributions of stokeslets and rotlets; the computed flow field being confined to within distances of less than twice the radius of the cell body's helical shape from its axis, while including a powerful jet-like interior flow through the coils of the swimming spirochete.     

Concentrated ring loading in a nonlocal elastic medium

Assuming an appropriate nonlocal modulus and using the Boussinesq–Galerkin vector representation of the nonlocal stress field the stress distribution in a nonlocal elastic medium has been found under the concentrated ring normal and shear loadings and force dipoles. The nonlocal modulus used in the paper is the Green function of the diffusion equation. To solve the corresponding boundary-value problem the Laplace transform with respect to the nonlocal parameter and the Hankel transform with respect to the radial coordinate are used. The Laplace transform is inverted analytically; inverting the Hankel transform the oscillatory integrals containing products of Bessel functions have been changed into integrands which decay exponentially, thus producing a solution more amenable to numerical quadrature. All classical singularities for stresses are eliminated.     

Centreline defects in strips produced through thin slab casting and rolling

Segregation in conventional slabs has been the topic of multiple researches; the centreline segregation in thin slabs has not been explicitly reported in published literature. However, a centreline band (defect) is invariably observed on macroetching high-manganese (>1?wt-%) strips from thin slab casting and rolling route of TATA Steel, Jamshedpur. A study was conducted to establish the exact nature of centreline defects and correlate with observation in the corresponding slab. Presence of second phases at the centreline due to heavy manganese enrichment was observed to be the source of defect band. In summary, this paper establishes a direct correlation between defects in hot-rolled strips and macrosegregation in thin slabs and highlights countermeasures taken to address the defect.     

Flexibility of bacterial flagella in external shear results in complex swimming trajectories

Many bacteria use rotating helical flagella in swimming motility. In the search for food or migration towards a new habitat, bacteria occasionally unbundle their flagellar filaments and tumble, leading to an abrupt change in direction. Flexible flagella can also be easily deformed by external shear flow, leading to complex bacterial trajectories. Here, we examine the effects of flagella flexibility on the navigation of bacteria in two fundamental shear flows: planar shear and Poiseuille flow realized in long channels. On the basis of slender body elastodynamics and numerical analysis, we discovered a variety of non-trivial effects stemming from the interplay of self-propulsion, elasticity and shear-induced flagellar bending. We show that in planar shear flow the bacteria execute periodic motion, whereas in Poiseuille flow, they migrate towards the centre of the channel or converge towards a limit cycle. We also find that even a small amount of random reorientation can induce a strong response of bacteria, leading to overall non-periodic trajectories. Our findings exemplify the sensitive role of flagellar flexibility and shed new light on the navigation of bacteria in complex shear flows.     

The effectiveness of audio-tactile lane-marking in reducing various types of crash: A review of evidence, template for evaluation, and preliminary findings from Australia

Audio-tactile lane-marking (ATLM) is designed to alert inattentive drivers when they deviate from their lane. Most commonly used previously to mark the edges of divided freeways, it is increasingly used to mark the edge and/or centre of two-lane undivided roads. We present a detailed review of ATLM evaluations to demonstrate that although both edge- and centreline ATLM appear to be effective, evaluations have been flawed insofar as they have (1) often not controlled adequately for variations due to extraneous factors known to affect crash incidence; (2) often focussed on total crashes, or on inattention-related crashes, and failed to address the possibility that ATLM increases some crash-types (particularly crashes involving two-wheeled vehicles, out-of-control crashes, or crashes on the opposite side of the lane to which the ATLM is installed); (3) almost always related to the milled-in “rumble strips” employed in the US rather than the raised profile lane-marking (PLM) that is employed in Australia. The present Empirical Bayes analysis aimed to evaluate PLM by comparing treated and untreated sections of the same roads both before and after the date of treatment in terms a range of crash types (some separately for roads with only edgeline-PLM, with only centreline-PLM, and with both edgeline- and centreline-PLM). Although some of the above issues could not be addressed due to insufficient data, the analysis provides a useful template for future researchers. The results provide evidence that both edgeline and centreline (alone or in combination) reduce targeted (same-side) crashes. Although there is no evidence that edgeline and centreline alone increase opposite side crashes, only edgeline and centreline together produced a net reduction in total crashes. Thus, the present results suggest that installing PLM on both edgeline and centreline is preferable to installing either alone.     

Heat flow visualization for thermal bridge problems

A method for the plotting of heat-flow intensity to provide an effective visual representation of heat flows in solid matter is proposed in this report. The heat-flow intensities are defined as the heat gain and the heat loss per volume. Two-dimensional steady-state simulation of heat flow in a structure was carried out under two conditions and the results were represented as plots of the temperatures and the heat-flow intensities. This representation of heat flow provides a stronger emphasis on the heat flows through good conductors than does the temperature distribution; the proposed method thus helps us to effectively visualize the effects of thermal bridges.     

Segregation and eutectic formation in solidification of Fe-1C-1 5-Cr steel

Abstract

The microstructure and solute segregation have been investigated in a continuously cast bloom and laboratory cast ingot of Fe–1C–1.5Cr (wt-%) steel. Eutectic carbide formation was observed only in the centreline region in the continuously cast bloom. In both specimens, the maximum chromium level detected was 3% in the columnar and 5% in the equiaxed region, while the minimum remained at 1.2% in both regions. The corresponding segregation ratios (C _max/C _min) were 2.5 and 5, in agreement with many previous studies. By numerical modelling of microsegregation it has been shown that the equilibrium partition coefficient of chromium k _Cr, which changes with carbon content, has a significant effect on chromium distribution during solidification. The carbon distribution may be taken to be in equilibrium during solidification, while that of chromium develops a concentration gradient in the solid. Numerical predictions of segregation behaviour, assuming local equilibrium at the liquid/solid interface, backdiffusion in the solid and complete mixing in the residual liquid, are consistent with experimental results in the columnar and equiaxed regions. The conclusion that eutectic carbide observed in the centreline region must have resulted from macrosegregation is supported by an estimate of the composition of the enriched liquid.     

碳税约束的城市冷链物流配送网络设计

为了减轻即将出台的碳税政策对城市冷链物流配送活动所带来的成本压力,建立了一个考虑碳税成本,且冷库能力受限的冷链物流配送网络拓展模型。通过合理设计输入参数,设定碳税范围在0.01~0.10元/kg CO_2eq（二氧化碳当量）之间变化,并基于在YALMIP工具箱中建模,借助优化套件对模型进行精确求解,得到了不同碳税率条件下,配送网络的节点和产品流向设计方案。研究结果表明：递进型的碳税率政策实施后,冷链配送企业可以通过网络微调策略,实现最大30%的碳排放缩减,而对应的总体运营成本仅仅增加了不到10%。最后得出结论：应用所提出的优化模型及精确求解方案,可以从运营优化角度,找到城市冷链配送网络的最佳设计方案,部分抵消碳税成本压力,为企业前瞻性的运营决策提供依据。     

Inverse and centreline segregation formation in twin roll cast AZ31 magnesium alloy

Two microstructure defects formed in the twin roll cast AZ31 strips were investigated: inverse and centreline segregations. A two-dimensional finite element thermal–fluid–stress model was employed to study the thermomechanical response of the AZ31 strip during twin roll casting process. The results showed that the key parameter for centreline segregation is the mushy zone thickness at centreline. For inverse segregation, the interaction between the yy peak stress at the centreline in the mushy zone and the solidified shell on the roll surface is the determinant parameter. The modelling results suggested increasing the setback distance decreases the risk of both defects. Moreover, scaling up the caster reduces the propensity to inverse segregation but appears to have a minor effect for centreline segregation formation.     

On first integrals of second-order ordinary differential equations

Here we discuss first integrals of a particular representation associated with second-order ordinary differential equations. The linearization problem is a particular case of the equivalence problem together with a number of related problems such as defining a class of transformations, finding invariants of these transformations, obtaining the equivalence criteria, and constructing the transformation. The relationship between the integral form, the associated equations, equivalence transformations, and some examples are considered as part of the discussion illustrating some important aspects and properties.     

Axial temperature distribution in vertical jet fires

The behaviour of vertical commercial propane jet fires (flame lengths of up to 8 m) was studied experimentally. The temperatures along the jet fire centreline were measured using a set of thermocouples and the flame contour was determined from infra-red (IR) images. The results show that temperature increases from the bottom of the flame, reaches a maximum value and decreases again at the top zone. A second-degree polynomial expression describes fairly well the variation of temperature as a function of the position on the flame centreline. The temperature along the centreline was found to increase for Q values lower than 7 MW and to decrease at higher values.     

Residual stress and strain in MIG butt welds in 5083-H321 aluminium: As-welded and fatigue cycled

This paper presents single-line residual stress profiles for 8 mm 5083-H321 aluminium plates joined by gas metal arc (MIG) welding. The data were obtained by synchrotron diffraction strain scanning. Weld metal stresses (up to ～7 mm either side of the centreline) are quite scattered and unreliable because of the large epitaxial grain size in the fusion zone. Peak magnitude of the transverse stresses varies between +50 MPa (19% of parent plate proof strength) at the HAZ boundary to ?150 MPa (57% of PP proof strength) at the weld centreline. Equivalent values for longitudinal stresses are +90 MPa (34% of PP proof strength) some 22 mm from the weld centreline to ?120 MPa (45% of PP proof strength) at the weld centreline. Plate-to-plate variation in the as-welded transverse and longitudinal residual stress values across the weld toe region is around 40 MPa. The effect on residual stress and strain values of a sequence of applied fatigue loads was also considered and reported.     

Technical foundations of TANDEM-STRAIGHT,a speech analysis,modification and synthesis framework

This article presents comprehensive technical information about STRAIGHT and TANDEM-STRAIGHT, a widely used speech modification tool and its successor. They share the same concept: the periodic excitation found in voiced sounds is an efficient mechanism for transmitting underlying smooth time–frequency representation. The tools are also based on the perceptual equivalence of two sets of independent Gaussian random signals. This equivalence makes it possible to discard input phase information intentionally and enables flexible manipulation of parameters.     

A front remeshing technique for a Lagrangian description of moving interfaces in two‐fluid flows

The numerical analysis of two‐fluid flows involves the treatment of a discontinuity that appears at the separating interface. Classical Lagrangian schemes applied to update the front position between two immiscible incompressible fluids have been long recognized to provide a sharp representation of the interface. However, the main drawback of these approaches is the progressive distortion in the distribution of the markers used to identify the material front. To avoid this problem, an interface remeshing algorithm based on the diffuse approximation of the interface curvature is proposed in this work. In addition, the remeshed front is enforced to preserve the global volume. These new aspects are incorporated in an existing fluid dynamics formulation for the analysis of two‐fluid flows problems. The resulting formulation is called in this work as the moving Lagrangian interface remeshing technique (MLIRT). Copyright © 2005 John Wiley & Sons, Ltd.     

A graphical representation for a statistical test of average equivalence and variance comparison with process data

This paper provides a graphical approach for presenting results of a statistical test of average equivalence with process data. In addition, a graphical representation of process change in variance is presented. An example from the biopharmaceutical industry is provided to illustrate the information contained in the chart. Copyright © 2010 John Wiley & Sons, Ltd.     

The effects of an edgeline on speed and lateral position: a meta-analysis

This paper presents a meta-analysis of studies that have evaluated the effects of an edgeline on speed and lateral position of motorised road users. Together with many other study characteristics, 41 estimates of the effects of an edgeline on speed and 65 on lateral position were extracted from the studies. The results of the evaluation studies show a great variety in effects. Both negative and positive effects on speed and lateral position were found; amongst others, increases in speed up to 10.6 km/h, as well as decreases in speed up to 5.0 km/h, and shifts of the lateral position towards the centre of the road up to 30 cm, as well as shifts towards the edge of the road up to 35 cm. Further analyses resulted in the determination of study characteristics that influence the effects of an edgeline on speed and lateral position. It is concluded that the effects of an edgeline on speed are related to the presence of a centreline. Applying an edgeline to a road without a centreline increases the speed of road users, and replacing a centreline by an edgeline decreases the speed. Results with respect to adding an edgeline to a road with a centreline were unclear. Another conclusion is that shoulder width and road environment contribute to the effects of an edgeline on lateral position. In combination with wide shoulders or buildings and/or trees next to the road, edgelines lead to shifts of the lateral position towards the edge of the road, and in combination with narrow shoulders or open fields, edgelines lead to shifts towards the centre of the road.