bluuebunny/crossref_metadata_2025 huggingface dataset:
Large-scale structures in a forced turbulent mixing layer
Authors: Gaster M. , Kit E. , Wygnanski I.
Published: April 2006

The large-scale structures that occur in a forced turbulent mixing layer at moderately high Reynolds numbers have been modelled by linear inviscid stability theory incorporating first-order corrections for slow spatial variations of the mean flow. The perturbation stream function for a spatially growing time-periodic travelling wave has been numerically evaluated for the measured linearly diverging mean flow. In an accompanying experiment periodic oscillations were imposed on the turbulent mixing layer by the motion of a small flap at the trailing edge of the splitter plate that separated the two uniform streams of different velocity. The results of the numerical computations are compared with experimental measurements.

When the comparison between experimental data and the computational model was made on a purely local basis, agreement in both the amplitude and phase distribution across the mixing layer was excellent. Comparisons on a global scale revealed, not unexpectedly, less good accuracy in predicting the overall amplification.
The self-induced motion of vortex sheets
Authors: Higdon J. J. L. , Pozrikidis C.
Published: April 2006

A method is presented for following the self-induced motion of vortex sheets. In this method, we use a piecewise analytic representation of the sheet consisting of circular arcs with trigonometric polynomials for the circulation. The procedure is used to study the evolution of the motion in two special cases: a circular vortex sheet with sinusoidal circulation distribution and an infinite plane vortex sheet subject to periodic disturbances. The first problem was studied by Baker (1980) as a test of the method of Fink & Soh (1978), while the second has been studied by a number of authors, notably Meiron, Baker & Orszag (1982). In each case, we follow the motion of the sheet up to the appearance of a singularity at a finite time. The singularity takes the form of an exponential spiral with the simultaneous development of singularities in the curvature and in the circulation distribution. In the final stages of the calculations, up to 155 marker points are used to specify the position of the sheet. If it were possible to execute a stable calculation with equally spaced point vortices, approximately 106 points would be required to achieve the same resolution. Problems with instabilities have been reduced, but not entirely eliminated, and prevent a rigorous verification of the results obtained.
The structure of a steady high-speed deflagration with a finite origin
Authors: Kassoy D. R. , Clarke J. F.
Published: April 2006

A theoretical study is made of the structure of a steady planar deflagration downstream of a specific origin location from which a compressible reactive gas flow emanates. The chemistry is modelled by a high-activation-energy Arrhenius reactionrate law without the introduction of an ignition temperature. Chemically derived heat addition is significant relative to the initial thermal energy of the flow. Perturbation methods, based on the limit of high activation energy, are used to construct solutions for sub- and supersonic values of the Mach number [ ] at the origin. With the exception of a thin layer adjacent to the origin in which very small changes occur, the structure of the deflagration is determined by a fundamental balance of convection, reaction and compressibility effects. Transport processes have an insignificant effect on the energetics of the flow. The upstream portion of the deflagration is dominated by an ignition event reminiscent of the induction period of an adiabatic thermal explosion. Subsequently in the neighbourhood of a well-defined ignition delay (or explosion) location a very rapid reaction takes place with order-unity changes in all the dependent variables. Compressibility effects are shown to be the source of basic limitations on the maximum temperature rise permitted in a flow with a particular value of [ ]. Chapman–Jouguet deflagrations are found to appear when the chemical heat addition is maximized for a given [ ]. Subsonic combustion is shown to exist for fairly general initial conditions at the origin. In contrast, a purely supersonic reaction is found to be possible only for specifically defined values of the initial strain rate and temperature gradient which would be difficult to control in the experimental environment.
A numerical study of water-wave modulation based on a higher-order nonlinear Schrödinger equation
Authors: Lo Edmond , Mei Chiang C.
Published: April 2006

In existing experiments it is known that the slow evolution of nonlinear deep-water waves exhibits certain asymmetric features. For example, an initially symmetric wave packet of sufficiently large wave slope will first lean forward and then split into new groups in an asymmetrical manner, and, in a long wavetrain, unstable sideband disturbances can grow unequally to cause an apparent downshift of carrier-wave frequency. These features lie beyond the realm of applicability of the celebrated cubic Schrödinger equation (CSE), but can be, and to some extent have been, predicted by weakly nonlinear theories that are not limited to slowly modulated waves (i.e. waves with a narrow spectral band). Alternatively, one may employ the fourth-order equations of Dysthe (1979), which are limited to narrow-banded waves but can nevertheless be solved more easily by a pseudospectral numerical method. Here we report the numerical simulation of three cases with a view to comparing with certain recent experiments and to complement the numerical results obtained by others from the more general equations.
Determining modes and fractal dimension of turbulent flows
Authors: Constantin P. , Foias C. , Manley O. P. , Temam R.
Published: April 2006

Research on the abstract properties of the Navier–Stokes equations in three dimensions has cast a new light on the time-asymptotic approximate solutions of those equations. Here heuristic arguments, based on the rigorous results of that research, are used to show the intimate relationship between the sufficient number of degrees of freedom describing fluid flow and the bound on the fractal dimension of the Navier–Stokes attractor. In particular it is demonstrated how the conventional estimate of the number of degrees of freedom, based on purely physical and dimensional arguments, can be obtained from the properties of the Navier–Stokes equation. Also the Reynolds-number dependence of the sufficient number of degrees of freedom and of the dimension of the attractor in function space is elucidated.
Far-field noise of a subsonic jet under controlled excitation
Authors: Zaman K. B. M. Q.
Published: April 2006

The phenomena of excitation-induced suppression and amplification of broadband jet noise have been experimentally investigated in an effort to understand the mechanisms, especially in relation to the near flow-field large-scale structure dynamics. Suppression is found to occur only in jets at low speeds with laminar exit boundary layers, the optimum occurring for excitation at Stθ ≈ 0.017, where Stθ is the Strouhal number based on the initial shear-layer momentum thickness. The suppression mechanism is linked to an initial-condition effect on the large-scale structure dynamics. The interaction and evolution of laminar-like structures at low jet speeds produce more (normalized) noise and turbulence, compared to asymptotically lower levels at high speeds when the initial shear layer is no longer laminar. The effect of initial condition has been demonstrated by tripped versus untripped jet data. The excitation at Stθ ≈ 0.017 results in a quick roll-up and transition of the laminar shear-layer vortices, yielding coherent structures which are similar to those at high speeds. Thus, the broadband noise and turbulence are suppressed, but at the most to the asymptotically lower levels. When at the asymptotic level, the broadband jet noise can only be amplified by the excitation; the amplification is found to be maximum for excitation in the StD range of 0.65–0.85, StD being the Strouhal number based on the jet diameter. Excitation in this StD range also produces strongest vortexpairing activity. From spectral analysis of the flow-field and the near sound-pressure field, it is inferred that the pairing process induced by the excitation is at the origin of the broadband noise amplification.
Bifurcation in steady laminar mixed convection flow in horizontal ducts
Authors: Nandakumar K. , Masliyah Jacob H. , Law Hin-Sum
Published: April 2006

The fully developed laminar mixed-convection flow in horizontal ducts of rectangular, circular and semicircular cross-sections has been studied using a numerical model of the governing equations of motion, subject to the Boussinesq approximation and an axially uniform heat-flux condition. Dual solutions with a two- and a four-vortex flow pattern have been observed in all cases. The rectangular geometry, with its aspect ratio and Grashof number as parameters, is posed as a two-parameter problem. In this parameter-space, the critical points where the transition between the two- and the four-vortex pattern occur, follow a tilted cusp. This is akin to the phenomenon in the Taylor problem which has been thoroughly investigated by Benjamin and co-workers in a general study of bifurcation phenomena for viscous flow problems. The bifurcation phenomenon in circular ducts, which is essentially a one-parameter problem, has features similar to that observed for the Dean problem, by Nandakumar and Masliyah.
Resonant reflection of surface water waves by periodic sandbars
Authors: Mei Chiang C.
Published: April 2006

One of the possible mechanisms of forming offshore sandbars parallel to a coast is the wave-induced mass transport in the boundary layer near the sea bottom. For this mechanism to be effective, sufficient reflection must be present so that the waves are partially standing. The main part of this paper is to explain a theory that strong reflection can be induced by the sandbars themselves, once the so-called Bragg resonance condition is met. For constant mean depth and simple harmonic waves this resonance has been studied by Davies (1982), whose theory, is however, limited to weak reflection and fails at resonance. Comparison of the strong reflection theory with Heathershaw's (1982) experiments is made. Furthermore, if the incident waves are slightly detuned or slowly modulated in time, the scattering process is found to depend critically on whether the modulational frequency lies above or below a threshold frequency. The effects of mean beach slope are also studied. In addition, it is found for periodically modulated wave groups that nonlinear effects can radiate long waves over the bars far beyond the reach of the short waves themselves. Finally it is argued that the breakpoint bar of ordinary size formed by plunging breakers can provide enough reflection to initiate the first few bars, thereby setting the stage for resonant reflection for more bars.
The large-scale coherent structure in the intermittent region of the self-preserving round free jet
Authors: Komori Satoru , Ueda Hiromasa
Published: April 2006

Large-scale coherent structure in a round free jet injected into a low-speed, co-flowing stream was experimentally investigated using laser-Doppler and cold-wire techniques. Particular attention was paid to the coherent structures in the outer intermittent region of the jet in an almost self-preserving state. Velocity fluctuations u (axial) and v (radial) and temperature fluctuations θ were measured simultaneously at two positions: a reference position and a moving position. In order to clarify the pattern of coherent motion, a pattern-averaging technique was adopted and the characteristics of the turbulent fluctuations were conditionally averaged. The results show that a large-scale coherent structure exists even in the self-preserving region of a round free jet, as well as in the near field. It has a vortical structure which consists of strong outward turbulent motion from inside the jet, turbulent reverse flow and inflow in the irrotational ambient region (entrainment). In the coherent structure, the negative pattern-averaged Reynolds stress occurs at two locations: one in the irrotational ambient region outside the turbulent/irrotational interface and the other in the turbulent jet inside the interface. The former is instantaneously produced in the irrotational inflow outside the interface when the vortical motion is accelerated, and it changes even the sign of conventionally averaged Reynolds stress. The latter is instantaneously produced in the turbulent flow near the high-shear region when the turbulent motion is more strongly directed by the acceleration of the vortical motion towards the centre of the vortical structure than the averaged motion.
Steady flows inside and around a fluid sphere at low Reynolds numbers
Authors: Oliver D. L. R. , Chung J. N.
Published: April 2006

The effects of internal circulation in bubbles and droplets have been analysed by means of a semi-analytical series-truncation method. The equations of motion are transformed into a series of coupled, ordinary, nonlinear differential equations by use of orthogonal sets. These infinite-series equations are then truncated adequately and solved numerically. Using this series-truncation method, we have evaluated the effects of different ratios (between the continuous and dispersed phases) of both density and viscosity for the flows of low Reynolds numbers. For all the density ratios investigated, the density difference has almost no effect on the drag coefficient at low Reynolds numbers. The shear stress and the drag coefficient increase with increasing viscosity ratio of droplet to ambience and decrease with increasing Reynolds number.
Experiments on fluid flow induced by melting around a migrating heat source
Authors: Moallemi M. K. , Viskanta R.
Published: April 2006

A series of melting experiments with a moving horizontal cylindrical heat source at constant surface heat flux have been performed. The heat source was designed in such a way that it could descend under its weight while melting the phase-change material (n-octadecane) surrounding it. The heat-source velocity was measured and the motion and shape of the solid–liquid interface were determined photographically. The effects of the surface heat flux, the density and initial position of the heat source, and the initial subcooling of the solid were investigated and are discussed. Conduction was found to be the dominant heat-transfer mechanism around the lower stagnation point and controlled the terminal velocity of the source. The fluid motion in the melt pool above the heat source was mainly induced by the descent of the source, while natural convection played only a relatively minor role in the motion.
Finite-difference simulation of nonlinear ship waves
Authors: Miyata Hideaki , Nishimura Shinichi
Published: April 2006

A finite-difference solution method for nonlinear wave generation in the near field of ships of arbitrary three-dimensional configuration is developed. Momentum equations of finite-difference form in a fixed rectangular cell system are solved by a time-marching scheme. The exact inviscid free-surface condition is approximately satisfied at the actual location of the free surface, and the free-slip body boundary condition is implemented by use of approximation of the body configuration and a special pressure computation in body boundary cells. The degree of accuracy is raised by employing a variable-mesh system in the vertical direction. Computed results are presented for three hull forms: a mathematical and two practical hull forms. Agreement with experiment seems to be fairly good. In particular, the computed wave profiles and contour maps of bow waves show excellent resemblance to the measured ones, having some typical characteristics of nonlinear ship waves.
On the enhancement of centrifugal separation
Authors: Greenspan H. P. , Ungarish M.
Published: April 2006

We consider the two-phase flow of a suspension in a rotating cylinder with inclined endplates for which inertial and viscous effects are small. It is shown that, when the Coriolis force is dominant, flow in the core is essentially unaffected by geometry. If a fluid particle can make a complete circuit about the rotation axis, the sedimentation velocity cannot be augmented by geometrical effects as it can in gravitational settling. However, with the insertion of a complete meridional barrier to block movement around the centre, separation becomes more sensitive to the shape of the container walls. In this case, behaviour similar to that in a gravitational field is possible once again.
Developing turbulent boundary layers with system rotation
Authors: Watmuff J. H. , Witt H. T. , Joubert P. N.
Published: April 2006

Measurements are presented for low-Reynolds-number turbulent boundary layers developing in a zero pressure gradient on the sidewall of a duct. The effect of rotation on these layers is examined. The mean-velocity profiles affected by rotation are described in terms of a common universal sublayer and modified logarithmic and wake regions.

The turbulence quantities follow an inner and outer scaling independent of rotation. The effect appears to be similar to that, of increased or decreased layer development. Streamwise-energy spectra indicate that, for a given non-dimensional wall distance, it is the low-wavenumber spectral components alone that are affected by rotation.

Large spatially periodic spanwise variations of skin friction are observed in the destabilized layers. Mean-velocity vectors in the cross-stream plane clearly show an array of vortex-like structures which correlate strongly with the skin-friction pattern. Interesting properties of these mean-flow structures are shown and their effect on Reynolds stresses is revealed. Near the duct centreline, where we have measured detailed profiles, the variations are small and there is a reasonable momentum balance.

Large-scale secondary circulations are also observed but the strength of the pattern is weak and it appears to be confined to the top and bottom regions of the duct. The evidence suggests that it has minimally affected the flow near the duct centreline where detailed profiles were measured.
Asymmetric flow above a rotating disk
Authors: Lai C.-Y. , Rajagopal K. R. , Szeri A. Z.
Published: April 2006

In this paper we generalize the von Kármán solution for flow above a single rotating disk, to include non-axisymmetric solutions. These solutions contain an arbitrary parameter; for zero value of the parameter the asymmetric flow degenerates into the classical von Kármán solution. Thus the classical solution is never isolated when considered within the scope of the full Navier–Stokes equations; there are asymmetric solutions in every neighbourhood of the von Kármán solution. Calculations are reported here for s = 0, 0.02 and 0.06, where s represents the ratio of angular velocity of the fluid at infinity to the angular velocity of the disk. A subset of the solutions obtained here corresponds to flow induced by the rotation of a disk when the latter is placed in a fluid that is moving with a constant uniform velocity.
The dynamics of waves at the interface between a viscoelastic coating and a fluid flow
Authors: Duncan J. H. , Waxman A. M. , Tulin M. P.
Published: April 2006

The dynamics of two-dimensional uniform wavetrains on the interface between a viscoelastic compliant coating and a boundary-layer flow are explored theoretically. The coating is treated as a single-layer isotropic Voigt material of finite thickness that is bonded to a rigid half-space. The flow is modelled first by potential theory and then modified to incorporate pressure phase shifts and magnitudes found in boundary-layer flow over wavy walls. The consideration of viscoelastic effects has led to an important dimensionless damping parameter γt = Ct τt/d (where τt is the strain relaxation time, Ct is the elastic shear-wave speed and d is the layer depth) that seems to have been overlooked by experimentalists. The flow and the damping are found to have dramatic effects on wave propagation. Using flow pressure and material-damping parameters typical of experiments, the results show that both upstream- and downstream-propagating waves exist at low flow speeds. At higher flow speeds, shorter waves can no longer propagate upstream. At still higher velocities, two instabilities, ‘static divergence’ and ‘flutter’, are found. Static divergence occurs for flow speeds above 2.86Ct and consists of slow waves moving with speeds of about 0.02Ct. These results compare fairly well with published experimental data. Static divergence is found to be a damping instability for these coating systems. When the flow speed is increased further, the flutter instability appears consisting of waves with phase speeds about equal to Ct.
Experimental study of the oscillations of a rotating drop
Authors: Annamalai P. , Trinh E. , Wang T. G.
Published: April 2006

Two- and three-lobed oscillations of a rotating liquid drop immersed in an immiscible fluid of comparable density and the same angular velocity were studied experimentally. Using acoustically suspended drops, it has been found that the relative change in the resonance frequencies of the axisymmetric drop-shape oscillations Δωl/ωl(0) is proportional to the square of the normalized angular speed (Ω/ωl(0))2 when ωl > 2Ω. This is in agreement with a recent analytical study of the same problem. Some preliminary results regarding the effect of rotation on the free-decay rate of the two-lobed oscillations are also presented.
Influence of rotation on the near-wake development behind an impulsively started circular cylinder
Authors: Coutanceau Madeleine , Ménard Christian
Published: April 2006

The early phase of the establishment of the flow past a circular cylinder started impulsively into rotation and translation is investigated by visualizing the flow patterns with solid tracers and by analysing qualitatively (flow topology) and quantitatively (velocity distributions and singular-point trajectories) the corresponding photographs. The range considered corresponds to moderate Reynolds numbers (Re [les ] 1000). The rotating-to-translating-speed ratio α increases from 0 to 3.25 and the motion covers a period during which the cylinder translates 4.5 or even 7 times its diameter. The details of the mechanisms of the near-wake formation are considered in particular and the increase of the flow asymmetry with increase in rotation is pointed out. Thus the existence of two regimes has been confirmed with the creation or non-creation of alternate eddies after an initial one E1 Furthermore, the new phenomena of saddle-point transposition and intermediate-eddy coalescence have been identified in the formation or shedding of respectively the odd and even subsequent eddies Ei (i = 2,3,…) when they exist. The very good agreement between these experimental data and the numerical results of Badr & Dennis (1985), obtained by solving the Navier-Stokes equations and presented in a parallel paper, confirms their respective validity and permits the determination of the flow characteristics not accessible, or accessible only with difficulty, to the present experiments. These flow properties such as drag and vorticity are capable of providing information on the Magnus effect for the former property and on unsteady separated flows for the latter.
Finite-amplitude steady waves in plane viscous shear flows
Authors: Milinazzo F. A. , Saffman P. G.
Published: April 2006

Computations of two-dimensional solutions of the Navier–Stokes equations are carried out for finite-amplitude waves on steady unidirectional flow. Several cases are considered. The numerical method employs pseudospectral techniques in the streamwise direction and finite differences on a stretched grid in the transverse direction, with matching to asymptotic solutions when unbounded. Earlier results for Poiseuille flow in a channel are re-obtained, except that attention is drawn to the dependence of the minimum Reynolds number on the physical constraint of constant flux or constant pressure gradient. Attempts to calculate waves in Couette flow by continuation in the velocity of a channel wall fail. The asymptotic suction boundary layer is shown to possess finite-amplitude waves at Reynolds numbers orders of magnitude less than the critical Reynolds number for linear instability. Waves in the Blasius boundary layer and unsteady Rayleigh profile are calculated by employing the artifice of adding a body force to cancel the spatial or temporal growth. The results are verified by comparison with perturbation analysis in the vicinity of the linear-instability critical Reynolds numbers.
Laminar flow over unsteady humps: the formation of waves
Authors: Duck P. W.
Published: April 2006

Both the incompressible and supersonic laminar flow over a small, unsteady hump are considered. The Reynolds number is assumed large, and the analysis is based upon triple-deck theory. In the incompressible case disturbances tend to grow downstream, as a result of triggering the Tollmien–Schlichting mode of instability. For the supersonic case the flow disturbances tend to decay downstream across the entire frequency spectrum. However, for sufficiently large humps a seemingly catastrophic failure of the governing equations may occur, our results suggesting that this is caused by an inviscid, short-scale, Rayleigh type of instability.
Climate change hot‐spots
Authors: Giorgi F.
Published: April 2006

A Regional Climate Change Index (RCCI), is developed based on regional mean precipitation change, mean surface air temperature change, and change in precipitation and temperature interannual variability. The RCCI is a comparative index designed to identify the most responsive regions to climate change, or Hot‐Spots. The RCCI is calculated for 26 land regions from the latest set of climate change projections by 20 global climate models for the A1B, A2 and B1 IPCC emission scenarios. The Mediterranean and North Eastern European regions emerge as the primary Hot‐Spots, followed by high latitude northern hemisphere regions and by Central America, the most prominent tropical Hot‐Spot. The main African Hot‐Spots are Southern Equatorial Africa and the Sahara. Eastern North America is the prominent Hot‐Spot over the continental U.S. Different factors over different regions contribute to the magnitude of the RCCI, which is in fact greater than 0 for all regions.
Hierarchical synchronization in complex networks with heterogeneous degrees
Authors: Zhou Changsong , Kurths Jürgen
Published: April 2006

We study synchronization behavior in networks of coupled chaotic oscillators with heterogeneous connection degrees. Our focus is on regimes away from the complete synchronization state, when the coupling is not strong enough, when the oscillators are under the influence of noise or when the oscillators are nonidentical. We have found a hierarchical organization of the synchronization behavior with respect to the collective dynamics of the network. Oscillators with more connections (hubs) are synchronized more closely by the collective dynamics and constitute the dynamical core of the network. The numerical observation of this hierarchical synchronization is supported with an analysis based on a mean field approximation and the master stability function.
Synchronized state of coupled dynamics on time-varying networks
Authors: Amritkar R. E. , Hu Chin-Kun
Published: April 2006

We consider synchronization properties of coupled dynamics on time-varying networks and the corresponding time-average network. We find that if the different Laplacians corresponding to the time-varying networks commute with each other then the stability of the synchronized state for both the time-varying and the time-average topologies are approximately the same. On the other hand for noncommuting Laplacians the stability of the synchronized state for the time-varying topology is in general better than the time-average topology.
Spatiotemporal dynamics of networks of excitable nodes
Authors: Steele Aaron J. , Tinsley Mark , Showalter Kenneth
Published: April 2006

A network of excitable nodes based on the photosensitive Belousov-Zhabotinsky reaction is studied in experiments and simulations. The addressable medium allows both local and nonlocal links between the nodes. The initial spread of excitation across the network as well as the asymptotic oscillatory behavior are described. Synchronization of the spatiotemporal dynamics occurs by entrainment to high-frequency network pacemakers formed by excitation loops. Analysis of the asymptotic behavior reveals that the dynamics of the network is governed by a subnetwork selected during the initial transient period.
On the electron leak problem in orbital-free embedding calculations
Authors: Dułak Marcin , Wesołowski Tomasz A.
Published: April 2006

Computer simulation methods using orbital level of description only for a selected part of the larger systems are prone to the artificial charge leak to the parts which are described without orbitals. The absence of orbitals in one of the subsystems makes it impossible to impose explicitly the orthogonality condition. Using the subsystem formulation of density functional theory, it is shown that the absence of explicit condition of orthogonality between orbitals belonging to different subsystems, does not cause any breakdown of this type of description for the chosen intermolecular complexes (F−H2O and Li+H2O), for which a significant charge-leak problem could be a priori expected.
Vibrational quenching of CO2(010) by collisions with O(P3) at thermal energies: A quantum-mechanical study
Authors: de Lara-Castells M. P. , Hernández Marta I. , Delgado-Barrio G. , Villarreal P. , López-Puertas M.
Published: April 2006

The CO2(010)–O(P3) vibrational energy transfer (VET) efficiency is a key input to aeronomical models of the energy budget of the upper atmospheres of Earth, Venus, and Mars. This work addresses the physical mechanisms responsible for the high efficiency of the VET process at the thermal energies existing in the terrestrial upper atmosphere (150K⩽T⩽550K). We present a quantum-mechanical study of the process within a reduced-dimensionality approach. In this model, all the particles remain along a plane and the O(P3) atom collides along the C2v symmetry axis of CO2, which can present bending oscillations around the linear arrangement, while the stretching C–O coordinates are kept fixed at their equilibrium values. Two kinds of scattering calculations are performed on high-quality ab initio potential energy surfaces (PESs). In the first approach, the calculations are carried out separately for each one of the three PESs correlating to O(P3). In the second approach, nonadiabatic effects induced by spin-orbit couplings (SOC) are also accounted for. The results presented here provide an explanation to some of the questions raised by the experiments and aeronomical observations. At thermal energies, nonadiabatic transitions induced by SOC play a key role in causing large VET efficiencies, the process being highly sensitive to the initial fine-structure level of oxygen. At higher energies, the two above-mentioned approaches tend to coincide towards an impulsive Landau-Teller mechanism of the vibrational to translational (V-T) energy transfer.
Quantifying the hydration status of lambs in relation to carcass characteristics
Authors: Jacob R. H. , Pethick D. W. , Clark P. , D'Souza D. N. , Hopkins D. L. , White J.
Published: April 2006

An experiment was undertaken to determine the physiological effects of water deprivation on lambs before slaughter. The aim of this experiment was to develop a method for quantifying the hydration status of lambs in relation to any subsequent effects on carcass and meat characters. Forty-eight crossbred lambs were subjected to 1 of 4 treatments: (i) normal ambient air temperature with access to water; (ii) normal ambient with no access to water; (iii) high ambient air temperature with access to water; and (iv) high ambient air temperature with no access to water. The treatments were imposed for a period of 48 h, after which the lambs were slaughtered. Food was withheld from all lambs during this 48 h period. Serum and urine were collected from each lamb at 0, 24 and 48 h and the concentrations of a range of analytes measured. Muscle, viscera and gastrointestinal tract were sampled immediately after slaughter. Water deprivation for a period of 48 h caused an increase in liveweight loss but no change in hot carcass weight or dressing percentage. Water deprivation caused an increase in muscle dry matter concentration and osmolality. The concentrations of protein, β-hydroxybutyrate, glucose, creatinine, potassium or albumin in serum were not affected by water deprivation. The concentration of sodium and chloride ions in serum and urine increased with feed deprivation time in lambs which had no access to water, but did not change for lambs that had access to water. Interactions occurred between water access and ambient air temperature for some but not all parameters. A significant relationship was found between muscle dry matter concentration, serum sodium concentration and urine specific gravity. It was concluded that urine specific gravity is a sensitive indicator of water consumption. Serum sodium concentration and urine specific gravity used together may be useful to predict the muscle hydration status of lambs.
Sustainable grazing systems for the Central Tablelands of New South Wales. 4. Soil water dynamics and runoff events for differently-managed pasture types
Authors: Hughes J. D. , Packer I. J. , Michalk D. L. , Dowling P. M. , King W. McG. , Brisbane S. , Millar G. D. , Priest S. M. , Kemp D. R. , Koen T. B.
Published: April 2006

Soil water, runoff amount and quality, pasture production and environmental data were measured for a pastoral prime lamb enterprise in the Central Tablelands of New South Wales from 1998 to 2002. There were 4 pasture treatments: fertilised and sown chicory (CH), fertilised and sown introduced pastures (SP), fertilised naturalised pastures (FN) and unfertilised naturalised pastures (UN). Two grazing management regimes, tactically grazed (TG) and continuously grazed (CG) were imposed on the SP, FN and UN treatments. The CH treatment was rotationally grazed.
To compare pasture and grazing system water use, maximum soil water deficit values (SWDMax) were calculated from neutron moisture meter data. SWDMax was influenced by both environmental and management factors. Management factors that influenced SWDMax were herbage mass of perennials, degree of perenniality, and the perennial species present. Environmental factors accounted for >50% of the variation in SWDMax. Inclusion of management factors (perennial herbage mass of C3 and C4 species and percentage perennial herbage mass), accounted for an additional 16% of variation. While the influence of pasture management appears to be relatively small, importantly, management is the only avenue available to land managers for influencing SWDMax. The UNTG and all sown treatments, with greater perennial herbage mass or greater C4 herbage mass consistently produced the highest SWDMax.
Runoff amount and quality data are presented for ground cover percentages which generally exceeded 80% for the experimental period. Runoff as a proportion of rain received during the experiment was <3%. Environmental factors explained 47% of variation in runoff, while pasture herbage mass and ground cover percentage explained an additional 2% of variation. Water quality was monitored on 3 treatments (SPTG, FNTG and UNCG) for total nitrogen (N), total phosphorus (P) and total suspended solids (TST) over a 6-month period. The mean values for total N and P were below the acceptable contaminant concentration for agricultural irrigation water. An important outcome of this research is the concept of a practical Targeted Water Management Plan (TWMP) which devises a framework for optimum water usage and productivity at a landscape scale.
On and Off Membrane Dynamics of the Endoplasmic Reticulum–Golgi Tethering Factor p115 In Vivo
Authors: Brandon Elizabeth , Szul Tomasz , Alvarez Cecilia , Grabski Robert , Benjamin Ronald , Kawai Ryoichi , Sztul Elizabeth
Published: April 2006

The mechanisms regulating membrane recruitment of the p115 tethering factor in vivo are unknown. Here, we describe cycling of p115 between membranes and cytosol and document the effects of Golgi matrix proteins, Rab1, and soluble N-ethylmaleimide-sensitive factor (NSF) attachment protein (SNAP) receptors (SNAREs) on this process. Rapid membrane/cytosol exchange is shown by swift (t1/2∼20 s) loss of Golgi-localized p115-green fluorescent protein (GFP) after repeated photobleaching of cell periphery and rapid (t1/2∼13 s) fluorescence recovery after photobleaching Golgi-localized p115-GFP. p115 mutant missing the GM130/giantin binding site exhibits analogous fluorescence recovery after photobleaching (FRAP) (t1/2∼13 s), suggesting that GM130 and giantin are not major determinants of p115 membrane dynamics. In contrast, p115-GFP exchanges more rapidly (t1/2∼8 s) in cells expressing the inactive Rab1/N121I mutant, indicating that p115 cycling is influenced by Rab1. p115-GFP dynamics is also influenced by the assembly status of SNAREs. In cells expressing an ATPase-deficient NSF/E329Q mutant that inhibits SNARE complex disassembly, the cycling kinetics of p115-GFP are significantly slower (t1/2∼21 s). In contrast, in cells incubated at reduced temperature (10°C) that inhibits vesicular traffic, the cycling kinetics of p115-GFP are faster (t1/2∼7 s). These data suggest that p115-binding sites on the membrane are provided by unassembled SNAREs. In agreement, biochemical studies show increased p115 recruitment to membranes in the presence of NSF and α-SNAP. Our data support a model in which recruitment of tethers is directly regulated by the assembly status of SNAREs.
Desulfovibrio alkalitolerans sp. nov., a novel alkalitolerant, sulphate-reducing bacterium isolated from district heating water
Authors: Abildgaard Lone , Nielsen Marie Bank , Kjeldsen Kasper Urup , Ingvorsen Kjeld
Published: April 2006

A novel alkalitolerant, sulphate-reducing bacterium (strain RT2T) was isolated from alkaline district heating water. Strain RT2T was a motile vibrio (0.5–0.8 μm wide and 1.4–1.9 μm long) and grew at pH 6.9–9.9 (optimum at pH 9.0–9.4) and at 16–47 °C (optimum at 43 °C). The genomic DNA G+C content was 64.7 mol%. A limited number of compounds were used as electron donors with sulphate as electron acceptor, including lactate, pyruvate, formate and hydrogen/acetate. Sulphite and thiosulphate also served as electron acceptors. Based on physiological and genotypic properties, the isolate was considered to represent a novel species of the genus Desulfovibrio, for which the name Desulfovibrio alkalitolerans sp. nov. is proposed. The type strain is RT2T (=DSM 16529T=JCM 12612T). The strain is the first alkali-tolerant member of the genus Desulfovibrio to be described.
The best and worst aspects of the ICU research coordinator role
Authors: Roberts Brigit L , Rickard Claire M , Foote Jonathon , McGrail Matthew R
Published: April 2006

Background : The Research Coordinator (RC) role is a relative new addition to staffing profiles in Australasian Intensive Care Units (ICUs). The RC plays a pivotal role in conducting ethically and scientifically sound research. There have been anecdotal reports of the RC role in various speciality areas. However, limited research has been undertaken into the role, and only one study has been published from the intensive care setting.Aim : To evaluate which factors the RC found to be the best and worst attributes of the role.Methods : A cross‐sectional web‐based cohort study was conducted in 2004 collecting free text information from RCs in ICUs in Australia and New Zealand.Results : Forty‐nine participants (71%) completed the study with 273 entries into the two categories of ‘best’ (60%) and ‘worst’ (40%) aspects of the role. We identified four thematic clusters in both categories: (1) ‘How the job was structured’ (2) ‘The worth of the job’ (3) ‘What the work involves’ and (4) ‘Who I work with’. Both categories received proportionally the same number of responses in each theme with (1) the most frequent and (4) the least number of entries.Conclusion : There is much variation between RCs in almost every descriptor of the role. The Australasian Intensive Care RC values autonomy, respect and intellectual stimulation with the scope for extending the role to suit the individual and finds isolation, under‐recognition and workload, often not sufficiently compensated, to be the worst aspects of the position.
Partnership working between a Higher Education Institution and NHS TRUSTS: developing an acute and critical care module
Authors: Rattray Janice E , Paul Fiona , Tully Vicki
Published: April 2006

The underpinning philosophy of preparing nurses to work within a modern National Health Service (NHS) is to ensure patient safety and quality of clinical care. There is increasing recognition that post‐registration education should become more clinically focused and adopt a more work‐based approach. Critical to the success of such an approach is partnership working between education providers and NHS Trusts. Changes in the delivery of acute care in the NHS have resulted in an increased number of highly dependent patients in both critical and non‐critical care areas. This article describes a partnership approach between a Higher Education Institution (HEI) and two NHS Trusts to deliver a degree level module to address the subsequent educational implications of these changes. This approach ensured module credibility and clinical focus. Student feedback confirms the clinical relevance of the module. Staff from the NHS had the opportunity to develop teaching skills by preparing teaching materials, delivering teaching sessions and receiving feedback on these. Areas of good practice were identified and there was sharing of skills, knowledge and expertise between both institutions. Joint working can enhance clinical relevance of educational provision and ensure consistency between theory and practice. In addition, there were a number of wider benefits to both institutions that resulted from this initiative.
General practitioners’ ranking of evidence‐based prescribing quality indicators: a comparative study with a prescription database
Authors: Okechukwu Ifeanyi , Bennett Kathleen , Feely John
Published: April 2006

Background

To ensure that indicators for assessing prescribing quality are appropriate and relevant, physicians should be involved in their development. How general practitioners (GPs) rank these indicators is not fully understood.

Aims

(i) To determine how GPs in Ireland rank a set of evidence‐based prescribing quality indicators in order of importance and relevance to their practice, and (ii) to compare the GPs’ ranking of the defined set of indicators with actual prescribing practice using a prescription database.

Methods

A postal questionnaire was sent to 105 GPs, who were asked to rank a set of 11 prescribing quality indicators, identified from the literature from most to least important. The results were aggregated and a weighted score for each indicator determined. These same prescribing indicators were then applied to a prescription database to compare the ranking provided with actual prescribing practice.

Results

Eighty‐six GPs (82%) returned the completed questionnaire. The higher ranks were for quality issues—use of inhaled corticosteroids, statins and benzodiazepines. Actual prescribing data showed prolonged use of benzodiazepines in over half of the prescriptions dispensed (n = 18 171), 52.48% (95% confidence interval 51.95, 53.01) and low usage of generic drugs, 17.78% (17.70, 17.90) despite their high ranking by the GPs.

Conclusion

While GPs have diverse views about the value of different prescribing quality indicators, the results suggest that they do rank evidence‐based guidelines on patient management highly, but those based on costs and less evidence the lowest. There was considerable divergence between theory and practice in the application of quality indices.
Long‐term results of an ultra low‐dose cytarabine‐based regimen for the treatment of acute megakaryoblastic leukaemia in children with Down syndrome
Authors: Al‐Ahmari Ali , Shah Niketa , Sung Lillian , Zipursky Alvin , Hitzler Johann
Published: April 2006

Children with acute megakaryoblastic leukaemia (AMKL) and Down syndrome (DS) show a favourable response to chemotherapy, probably due to increased sensitivity of the leukaemic blasts to cytarabine. In contrast, dose‐intensive approaches have resulted in disproportionate treatment‐related mortality in this group. The survival of children with AMKL and DS was retrospectively compared following treatment with a low‐dose chemotherapy protocol, consisting of cytarabine (10 mg/m2/dose), retinylpalmitate and vincristine or standard chemotherapy. Event‐free (67 ± 11%) and overall survival (77 ± 10%) at 5 years were not significantly different in both groups. Further reduction of treatment intensity in AMKL of children with DS, therefore, appears feasible.
Costly melanin ornaments: the importance of taxon?
Authors: STOEHR A. M.
Published: April 2006

Experimental work in vertebrates shows that different forms of coloration – particularly carotenoid‐based vs melanin‐based ornaments – are differentially sensitive to stressors such as diet manipulations and parasitic infections. Comparative work also shows that historical patterns of ornament evolution depend on the proximate mechanisms of colour production.

Based on the results from vertebrates, it has been argued that melanin‐based ornaments may not be good indicators of quality because, unlike carotenoid‐based ornaments, melanin pigments can be synthesized from amino acid precursors, and therefore melanin synthesis is unlikely to be costly.

However, there is evidence for costly melanin synthesis in insects, which use melanin in some ways that vertebrates do not. Differences across taxa in the costs of melanin synthesis challenge the generality of the hypotheses relevant to these ornaments.

In general, all pigment‐based ornaments are a function of precursor intake and processing. Differences in costs of melanin synthesis across taxa may reflect differences in one or both of these parameters.

I urge communication between researchers working on related questions in disparate taxa (vertebrates and invertebrates). This should facilitate the discovery of the most fundamental aspects of colour ornament evolution.