bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Unique Crystal Structure of the Triclinic Samarium(III) Oxoselenate(IV) Sm2[SeO3]3
Authors: Krügermann Ina , Wickleder Mathias S. , Wontcheu Joseph , Schleid Thomas 
Published: March 2006

AbstractPale yellow, needle‐shaped single crystals of Sm2[SeO3]3 were obtained by heating stoichiometric mixtures of Sm2O3 and SeO2 (molar ratio: 1:3) along with substantial amounts of CsCl as fluxing agent in evacuated sealed silica tubes at 830 °C for one week. According to X‐ray single‐crystal diffraction data, Sm2[SeO3]3 crystallizes triclinic (space group: $P{\bar 1}$ ) with two formula units per unit cell of the dimensions a = 698.62(7), b = 789.71(8), c = 910.34(9) pm, α = 96.693(5), β = 104.639(5), γ = 115.867(5)°. Its crystal structure contains two crystallographically distinct Sm3+ cations in eight‐ and ninefold coordination with oxygen atoms arranged as distorted uncapped or capped square antiprisms (d(Sm3+−O2−) = 232−271 pm). These [(Sm1)O8] and [(Sm2)O9] polyhedra share opposite edges and faces to form zigzag chains along [100] with discrete pyramidal [SeO3]2− anions bridging units. Further linkage by [SeO3]2− anions in [010] direction leads to a three‐dimensional network, which exhibits almost rectangular channels along [111]. These tunnels offer width enough to incorporate the free non‐bonding electron pairs („lone pairs”︁) at the Se4+ cations, since all nine different Ψ1‐tetrahedral [SeO3]2− groups (d(Se4+−O2−) = 165−173 pm, ∢(O–Se–O) = 94 – 108°) exhibit a pronounced stereochemical „lone‐pair”︁ activity. For not being isotypic with neither triclinic Er2[SeO3]3 (CN(Er3+) = 7 and 8) nor the remainder rare‐earth metal(III) oxoselenates(IV) of the composition M2[SeO3]3 (≡ M2Se3O9; M = Sc, Y, La, Ce – Lu), Sm2[SeO3]3 claims a unique crystal structure among them.
Negotiation, email, and Internet reverse auctions: How sourcing mechanisms deployed by buyers affect suppliers’ trust
Authors: Gattiker Thomas F. , Huang Xiaowen , Schwarz Joshua L. 
Published: March 2006

AbstractThe Internet has made a wealth of new tools available to the industrial buyer. However, researchers have suggested that computer‐mediated interaction with suppliers may not be conducive to strong supplier relationships in general and to trust in particular. This paper compares two computer‐mediated sourcing tools (email negotiation and Internet reverse auctions) with face‐to‐face negotiation. Information richness theory suggests that the different media will produce different impacts relating to sellers’ trust in buyers. Data are generated with a simulation experiment using 117 subjects. We found that information richness affects seller–buyer trust: Sellers who used face‐to‐face negotiation, the richest medium in the study, always reported higher trust in their buyer counterparts than did sellers using Internet reverse auctions. There were also some trust advantages of face‐to‐face negotiation over email and limited advantages of email over reverse auctions. We also found that procurement complexity influences the relationship between information richness and trust. As hypothesized, when face‐to‐face negotiation is used, procurement complexity has no effect on seller trust. When reverse auctions are utilized, the greater the complexity of the purchase, the less the seller trust. However, when email is used, greater procurement complexity is associated with greater seller trust, and there are no differences in trust between the email and face‐to‐face channels. Finally, we found that sellers’ trust in buyers is positively associated with sellers’ desire for future dealings with the buyer.
Color Doppler Ultrasonography is a Reliable Predictor of Free Tissue Transfer Outcomes in Head and Neck Reconstruction
Authors: Khalid Ayesha N. , Quraishi Sadeq A. , Zang William A. , Chadwick Johnathan L. , Stack Brendan C. 
Published: March 2006

OBJECTIVEThe purpose of our investigation was to report our experience with a color flow doppler (CFD) ultrasonography for postoperative monitoring of free tissue transfers.METHODSA retrospective analysis of head and neck free tissue transfers at a single institution between 2000 and 2005 (n = 84; 80 successful, 4 failures). CFD measured blood flow velocity (cm/sec) and resistance to flow in the pedicle vein and artery on postoperative days 1, 3, and 7.RESULTSAnalysis of artery/vein ratio revealed vascular congestion by postoperative day 3 which later resolved. In flap failures, there was a significant reduction (P < 0.05) in venous blood flow by postoperative day 3. Waveform morphology representing vascular resistance and origin of donor flap did not correlate with flap outcome (r2 = 0.23 and 0.44 respectively).CONCLUSIONPostoperative monitoring of free tissue transfers may allow for detection of poor perfusion. CFD is an objective method of studying blood flow postoperatively.
On the rise of small air bubbles in water
Authors: Saffman P. G. 
Published: March 2006

This paper is concerned with the motion in water of air bubbles whose equivalent spherical radii are in the range 0.5-4.0 mm. These bubbles are not spherical but are, approximately, oblate spheroids; and they may rise steadily in a vertical straight line, or along a zig-zag path, or in a uniform spiral. The rectilinear motion occurs when the radius is less than about 0.7 mm, and the other motions occur for larger bubbles. There is disagreement in the literature as to whether it is the zig-zag or the spiral motion that occurs. It was found experimentally that, when the bubbles are produced in the manner described in this paper, only the zig-zag motion occurs when the radius of the bubble is less than about 1 mm, but bubbles of larger radius either zig-zag or spiral depending upon various factors.The spiralling bubble is treated theoretically by assuming that the flow near the front of the bubble is inviscid (the Reynolds number of the motion is several hundred) and considering the distribution of pressure over the front surface. Equations are obtained relating the geometrical parameters of the spiral, the shape of the bubble and the velocity of rise. The analysis is simplified by assuming that the pitch of the spiral is large compared with its radius, and the velocity of rise and shape of the bubble are determined as functions of the radius. The experimental and theoretical values are compared, and fair agreement found. Reasons to account for the disagreement are proposed.A modification of the theory is proposed to take account of the presence of impurities or surface-active substances in the water, and the velocities of rise thus predicted are in agreement with the experimental observations.The zig-zag motion is treated in a similar way, and the analysis leads to an equation which determines the stability of the rectilinear motion. The value of the Weber number at which the rectilinear motion. The value of the Weber number at which the rectilinear motion becomes unstable is deduced, and is found to be in fair agreement with experiment. The experimental evidence on the wake behind solid bodies is described briefly, and reasons are given for suggesting that the zig-zag motion is due to an interaction between the instability of the rectilinear motion and a periodic oscillation of the wake.
Steady wave patterns on a non-uniform steady fluid flow
Authors: Ursell F. 
Published: March 2006

A steady slightly non-uniform flow with a free surface is subject to a concentrated surface pressure which gives rise to a pattern of surface waves. (For gravity waves on deep water this is the well-known Kelvin ship-wave pattern.) The motion is assumed inviscid, and the waves are assumed small. A theory is developed for the wave pattern, based on the following assumptions:
The stream velocity component normal to a wave crest is equal to the phase velocity based on the local wavelength;the separation between consecutive crests is equal to the local wave-length.
These assumptions are expressed in mathematical form, and the existence of a set of characteristic curves (associated with the group velocity) is deduced from them. These characteristics are not identical with the crests. Let the additional assumption be made thatthe characteristics all pass through the point disturbance; the characteristics are then completely defined and may be constructed by a step-by-step process starting at the point disturbance. The same construction gives the direction of the wave crests at all points. The wave crests can then be deduced.Assumptions of the same type as (1) and (2) have long been familiar in various applications of ray tracing. For uniform flows the present theory gives the same pattern as the method of stationary phase.
One-dimensional magnetogasdynamics in oblique fields
Authors: Shercliff J. A. 
Published: March 2006

Earlier work on the dynamics of a perfectly conductive gas in situations where all variables depend on one space co-ordinate only is extended to the case where the magnetic field has a component in the direction of variation. The theory is developed for an arbitrary gas in equilibrium, subject only to certain reasonable restrictions.The first main section studies the variation of the transverse field component in slow and fast simple waves and the tendency of compressive waves in which the transverse field does not change sign to steepen into shocks.The next section develops a symmetrical treatment of the Rayleigh, Fanno and other processes of ordinary steady one-dimensional gasdynamics, generalized to allow for electromagnetic effects. The slow, fast and Alfvén wave speeds are critical. A particular case of this analysis is a generalization of ordinary gasdynamics which allows for the effect of transverse forces such as occur in turbo-machinery.The final section is an exhaustive study of shocks in the presence of a field component normal to the shock front. From the generalized Rayleigh line it is established that there are up to six different types of shocks, all compressive and distinguishable by the relative magnitudes of the upstream and downstream normal velocities in comparison with the local slow, fast and Alfvén wave speeds.Some aspects of shock structure are discussed briefly.
The motion of a thin oil sheet under the steady boundary layer on a body
Authors: Squire L. C. 
Published: March 2006

A solution is obtained for the motion of a thin oil sheet, of non-uniform thickness, under a boundary layer. The following points are deduced: (a) The oil flows in the direction of the boundary-layer skin-friction, except near separation, where the oil tends to indicate separation too early. These conclusions are independent of oil viscosity. (b) The effect of the oil flow on the boundary-layer motion is very small.The application of the results to the interpretation of oil-flow patterns is briefly considered.
An experimental investigation of the oscillating lift and drag of a circular cylinder shedding turbulent vortices
Authors: Gerrard J. H. 
Published: March 2006

The oscillating lift and drag on circular cylinders are determined from measurements of the fluctuating pressure on the cylinder surface in the range of Reynolds number from 4 × 103 to just above 105.The magnitude of the r.m.s. lift coefficient has a maximum of about 0.8 at a Reynolds number of 7 × 104 and falls to about 0.01 at a Reynolds number of 4 × 103. The fluctuating component of the drag was determined for Reynolds numbers greater than 2 × 104 and was found to be an order of magnitude smaller than the lift.
The characteristics of the turbulence in the mixing region of a round jet
Authors: Davies P. O. A. L. , Fisher M. J. , Barratt M. J. 
Published: March 2006

Measurements in the mixing region of a 1 in. diameter cold air jet are described for Mach numbers ranging from 0.2 to 0.55. The statistical characteristics of the turbulence in the first few diameters of the flow may be expressed in terms of simple kinematic similarity relationships. These are based on the jet diameter and the distance downstream from the jet orifice as length-scales, and the inverse of the local shear as a time-scale. The experiments show that the integral time scale of the turbulence in a frame convected with the maximum energy of the turbulent motion is inversely proportional to the local shear.The most interesting result obtained is that the local intensity of the turbulence is equal to 0.2 times the shear velocity. This velocity is defined as the product of the local integral length-scale of the turbulence with the local shear. The local intensity is defined as the R.M.S. value of the local velocity fluctuations divided by the jet efflux velocity. It was found that the length-scale is proportional to the distance from the jet orifice, while the maximum shear is also related to this distance as well as to the jet efflux velocity. These two similarity relations break down close to the jet orifice and change beyond the first six or so diameters downstream. The convection velocity is not equal to the local mean velocity but varies slowly over the region of maximum shear when it is just over half the jet efflux velocity. The measurements of other observers fit the relationships obtained quite well. From these relationships it is possible to calculate the noise generated by the mixing region of a given jet directly, using expressions derived by Lilley (1958).
Some general theorems concerning the finite motion of a shallow rotating liquid lying on a paraboloid
Authors: Ball F. K. 
Published: March 2006

The motion of a bounded shallow liquid, initially of arbitrary shape, in an arbitrary state of motion and lying on a paraboloid of revolution (including a level surface as a special case) can always be separated into three parts:
the motion of the centre of gravity, which is entirely independent of the other motions and is governed by a pair of simple ordinary linear differential equations;an isotropic two-dimensional dilatation and rotation which are also governed by a simple linear differential equation;the motions that remain after removal of the velocity fields associated with the preceding motions; these will be called additional motions.The additional motions exert a ‘pressure’, determined by their total energy, which tends to increase the spread of the liquid. If the spread does increase then the additional motions lose energy which then appears as energy associated with the dilatation.The effect of the dilatation and rotation on the additional motions can be described by transformation into a co-ordinate system that rotates and dilates with the liquid. In these co-ordinates, with a properly adjusted time scale, the additional motions satisfy equations that are isomorphic with the original equations of motion; however, the liquid now appears to be lying on a parabola that is always concave upwards.
Magnetohydrodynamic flow in rectangular ducts
Authors: Hunt J. C. R. 
Published: March 2006

The paper presents an analysis of laminar motion of a conducting liquid in a rectangular duct under a uniform transverse magnetic field. The effects of the duct having conducting walls are investigated. Exact solutions are obtained for two cases, (i) perfectly conducting walls perpendicular to the field and thin walls of arbitrary conductivity parallel to the field, and (ii) non-conducting walls parallel to the field and thin walls of arbitrary conductivity perpendicular to the field.The boundary layers on the walls parallel to the field are studied in case (i) and it is found that at high Hartmann number (M), large positive and negative velocities of order MVc are induced, where Vc is the velocity of the core. It is suggested that contrary to previous assumptions the magnetic field may in some cases have a destabilizing effect on flow in ducts.
On some aspects of fully-developed turbulent flow in rectangular channels
Authors: Gessner F. B. , Jones J. B. 
Published: March 2006

For fully-developed turbulent flow in straight channels of non-circular cross-section, there exists a transverse mean flow superimposed upon the axial mean flow. This transverse flow, commonly known as secondary flow, interacts with the axial mean flow and turbulence structure in a complex manner. In this paper several heretofore unexplored aspects of this type of secondary flow are discussed on the basis of results of an extensive experimental programme which was conducted for steady, incompressible, fully-developed turbulent air flow in both square and rectangular channels. Specifically, the following aspects are examined: (a) the Reynolds-number effect on secondary flow, (b) the directional characteristics of local wall shear stress, (c) the orientation of Reynolds-stress principal planes in a plane normal to the axial flow direction, and (d) the Reynolds equation along a secondary-flow streamline.Within the Reynolds-number range of the investigation, the results indicate that secondary-flow velocities, when non-dimensionalized with either the bulk velocity or the axial mean-flow velocity at the channel centreline, decrease for an increase in Reynolds number. Also, the greatest skewness of local wall shear-stress vectors is shown to occur in the near vicinity of corners where secondary flow is maximum. In addition, it is shown that in planes normal to the axial flow direction, traces of Reynolds stress principal planes are not tangent and normal to lines of constant axial mean-flow velocity. This behaviour is in contrast to that for less complicated turbulent flows, for example, two-dimensional channel flow or circular-pipe flow where such traces are always tangent and normal to lines of constant axial mean-flow velocity in accordance with symmetry considerations. Finally, through experimental evaluation of terms in a momentum balance along a typical secondary-flow streamline, it is shown that secondary flow is the result of small differences in magnitude of opposing forces exerted by the Reynolds stresses and static pressure gradients in planes normal to the axial flow direction.
Equilibrium turbulent boundary layers
Authors: Mellor G. L. , Gibson D. M. 
Published: March 2006

Empirical information is extracted from constant-pressure flows and, on this basis alone, the equations of motion are solved for flows where the pressure gradient parameter, β = δ*(dp/dx)/τ0 is held constant. The experimental defect profiles of Clauser and the near-separating profile of Stratford are predicted quite well.The present work is an extension of the work of Clauser and Townsend in that a particular form for an effective or eddy viscosity is hypothesized. Here, however, a continuous, and analytically precise family of defect profiles are calculated for the entire range, −0·5 ≤ β ≤ ∞. The solutions span the whole profile with the exception of the viscous sublayer.A detailed consideration of the viscous sublayer and a comparative examination of various eddy viscosity hypotheses are included in a companion paper.
The large-scale structure of homogeneous turbulence
Authors: Saffman P. G. 
Published: March 2006

A field of homogeneous turbulence generated at an initial instant by a distribution of random impulsive forces is considered. The statistical properties of the forces are assumed to be such that the integral moments of the cumulants of the force system all exist. The motion generated has the property that at the initial instant\[ E(\kappa) = C\kappa^2 + o(\kappa^2), \]whereE(k) is the energy spectrum function,kis the wave-number magnitude, andCis a positive number which is not in general zero. The corresponding forms of the velocity covariance spectral tensor and correlation tensor are determined. It is found that the terms in the velocity covarianceRij(r) areO(r−3) for large values of the separation magnituder.An argument based on the conservation of momentum is used to show thatCis a dynamical invariant and that the forms of the velocity covariance at large separation and the spectral tensor at small wave number are likewise invariant. For isotropic turbulence, the Loitsianski integral diverges but the integral\[ \int_0^{\infty} r^2R(r)dr = \frac{1}{2}\pi C \]exists and is invariant.
The slow motion of a flat plate in a viscous stratified fluid
Authors: Martin Seelye , Long Robert R. 
Published: March 2006

The existence of a ‘wake’ upstream of an obstacle moving slowly through a stratified fluid has been known for some time. The present study shows that a thin, flat plate moving slowly and horizontally through a linearly stratified salt-water mixture has, in addition, a boundary layer over the plate whose thickness increases upstream from thebackof the plate.The theory assumes that the ratio of diffusivity to viscosity is small, and that the plate moves so slowly that inertia forces are negligible; under these conditions, a similarity solution is derived describing the boundary layer over the plate. The study also shows that salt diffusion is important in a second, thinner boundary layer whose thickness increases from the front of the plate.In the experiment, a plate was towed through a tank of linearly stratified salt water. From streak photographs of the boundary layer over the plate, it was possible to confirm quantitatively the similarity solution and to infer at very slow velocities the presence of the thin diffusion boundary layer.
The unstable thermal interface
Authors: Elder J. W. 
Published: March 2006

The motion which develops in a deep layer of a viscous, thermally conducting fluid initially hot below and cold above some horizontal plane, so that the system is gravitationally unstable, is studied by laboratory and numerical experiments. Three cases are considered: (i) the flow which occurs in a porous medium when the interface is the lower boundary of the system; (ii) a similar study in a viscous fluid; (iii) an interface distant from the confining horizontal boundaries, in a viscous fluid. In all cases the initial development of the flow—assuming an initial source of noise, for example as temperature fluctuations—occurs within the thermal interface between the hot and cold fluid. The scale of the motion is set by the thickness of the interface.The development of the disturbances in the interface involves: a period of local thickening and induced, damped motions in which the diffusion of heat and vorticity dominate; a period of gestation, involving rapid amplification, with the disturbance imbedded in the interface and diminishing importance of the role of diffusion of heat; a period of emergence of the disturbances from the interface, during which the accelerations are sufficiently rapid for molecular processes to be unimportant, entrainment being the dominant process, and the gravitational energy accumulated locally in the interface is largely removed; and finally a period of adjustment of the large eddies. The amplification process is adequately described by the linearized equations of motion.
The propagation upward of the shock wave from a strong explosion in the atmosphere
Authors: Hayes Wallace D. 
Published: March 2006

A method is established for the calculation of the trajectories of shocks moving upward in the atmosphere, on the basis of the assumption that they are of the self-propagating type. The results of calculations for self-similar motions are given, and these are used to establish a propagation law based upon the concepts of the Chisnell, Chester and Whitham (CCW) approximation. This propagation law enters a characteristics law based upon that proposed by Whitham, but reformulated for the computation of axisymmetric shocks with varying density.An asymptotic self-preserving shock shape is investigated, and is computed for the case γ = 1·4. A parabolic approximation scheme suggested by the self-preserving solution is developed, in which the solution near the axis is reduced to the solution of a system of ordinary differential equations. Finally, the governing equation for the general case without axial symmetry (but without winds) is presented.