Two-way coupling of FENE dumbbells with a turbulent shear flow

We present numerical studies for finitely extensible nonlinear elastic (FENE) dumbbells which are dispersed in a turbulent plane shear flow at moderate Reynolds number. The polymer ensemble is described on the mesoscopic level by a set of stochastic ordinary differential equations with Brownian noise. The dynamics of the Newtonian solvent is determined by the Navier-Stokes equations. Momentum transfer of the dumbbells with the solvent is implemented by an additional volume forcing term in the Navier-Stokes equations, such that both components of the resulting viscoelastic fluid are connected by a two-way coupling. The dynamics of the dumbbells is given then by Newton's second law of motion including small inertia effects. We investigate the dynamics of the flow for different degrees of dumbbell elasticity and inertia, as given by Weissenberg and Stokes numbers, respectively. For the parameters accessible in our study, the magnitude of the feedback of the polymers on the macroscopic properties of turbulence remains small as quantified by the global energy budget and the Reynolds stresses. A reduction of the turbulent drag by up to 20% is observed for the larger particle inertia. The angular statistics of the dumbbells shows an increasing alignment with the mean flow direction for both, increasing elasticity and inertia. This goes in line with a growing asymmetry of the probability density function of the transverse derivative of the streamwise turbulent velocity component. We find that dumbbells get stretched referentially in regions where vortex stretching or bi-axial strain dominate the local dynamics and topology of the velocity gradient tensor.Comment: 20 pages, 10 Postscript figures (Figures 5 and 10 in reduced quality

Some recent rural radio talks

Current experiments with vegetable crops - By T. WACHTEL, Agricultural Adviser, Horticultural Division Pedigree seed planting - By H. G. CARISS, B.Sc. (Agric), Regional Agricultural Adviser The Ruakura round farrowing house - By P. BECK, Field Assistant, Dairying Division How the random sample laying test could affect the poultry industry - By R. H. MORRIS, Officer-in-Charge, Poultry Branch Feeding the milking goat - By K. NEEDHAM, Dairy Cattle Husbandry Officer Fertilisers for vegetables in summer months - By J. P. FALLON, Senior Adviser (Vegetables), Horticultural Division Pastures and their carrying capacity - By H. G. ELLIOTT, Assistant Superintendent of Dairying Pollination - By J. CRIPPS, Adviser, Horticultural Division Aeroplanes and insect pest control - By P. N. FORTE, Senior Entomologist Kill those flies - By H. MASLIN, Dairy Instructor, Busselton Grazing for pigs - By P. BECK, Field Assistant, Dairying Division Feed flavours in cream - By an officer of the Dairying Division. Those old milk and cream cans - By D. C. MICKLE, Dairy Instructor, Bunbury Overrun in butter making and quality in home-made butter - By A. H. HOBBS, Dairy Produce Inspector Milk flow indicators - By G. W. SCOTT, Dairy Instructor, Head Offic

Notes on Conformal Invisibility Devices

As a consequence of the wave nature of light, invisibility devices based on isotropic media cannot be perfect. The principal distortions of invisibility are due to reflections and time delays. Reflections can be made exponentially small for devices that are large in comparison with the wavelength of light. Time delays are unavoidable and will result in wave-front dislocations. This paper considers invisibility devices based on optical conformal mapping. The paper shows that the time delays do not depend on the directions and impact parameters of incident light rays, although the refractive-index profile of any conformal invisibility device is necessarily asymmetric. The distortions of images are thus uniform, which reduces the risk of detection. The paper also shows how the ideas of invisibility devices are connected to the transmutation of force, the stereographic projection and Escheresque tilings of the plane

The Speed of Fronts of the Reaction Diffusion Equation

We study the speed of propagation of fronts for the scalar reaction-diffusion equation $u_t = u_{xx} + f(u)$\, with $f(0) = f(1) = 0$. We give a new integral variational principle for the speed of the fronts joining the state $u=1$ to $u=0$. No assumptions are made on the reaction term $f(u)$ other than those needed to guarantee the existence of the front. Therefore our results apply to the classical case $f > 0$ in $(0,1)$, to the bistable case and to cases in which $f$ has more than one internal zero in $(0,1)$.Comment: 7 pages Revtex, 1 figure not include

The origins of the Selden map of China: scientific analysis of the painting materials and techniques using a holistic approach

Since the 'rediscovery' of the Selden map of China, an early seventeenth century map of Asia, in the Bodleian Library in Oxford, the importance of the map in our understanding of globalisation in the early seventeenth century has been recognised. One of the unresolved questions is the origin of the map. This paper addresses the question through material evidence provided by a holistic approach using a suite of complementary analytical techniques. The map was examined in situ and non-invasively by a remote spectral imaging instrument (PRISMS) modified for close range imaging, which was followed by a range of complementary techniques applied to a number of detached fragments, though most of the techniques are non-invasive and can be applied to the map directly in the future. The binding medium was found to be a gum, almost certainly gum Arabic, rather than the animal glue commonly used in Chinese paintings. Some of the pigments and their usage were found to be at odds with the common practice in paintings from China. The detection of gum Arabic, a binding medium used by the Europeans, South and West Asians and the use of a mixture of orpiment and indigo, commonly found in European, South and West Asian paintings gives further evidence on the unusual origins of this map. The likely detection of a basic copper chloride, such as atacamite, in the green areas suggests an influence from the South and West Asian rather than the European tradition. Detailed analysis of the various spectral bands of the spectral image cube along with visual inspection of the large scale colour image showed that the map was not fully planned at the beginning but rather painted in stages, at times by trial and error and that it was unfinished. A new hypothesis for the origin of the Selden map in Aceh Sumatra is proposed based on the new evidences

Oral tolerance to cancer can be abrogated by T regulatory cell inhibition

Oral administration of tumour cells induces an immune hypo-responsiveness known as oral tolerance. We have previously shown that oral tolerance to a cancer is tumour antigen specific, non-cross-reactive and confers a tumour growth advantage. We investigated the utilisation of regulatory T cell (Treg) depletion on oral tolerance to a cancer and its ability to control tumour growth. Balb/C mice were gavage fed homogenised tumour tissue – JBS fibrosarcoma (to induce oral tolerance to a cancer), or PBS as control. Growth of subcutaneous JBS tumours were measured; splenic tissue excised and flow cytometry used to quantify and compare systemic Tregs and T effector (Teff) cell populations. Prior to and/or following tumour feeding, mice were intraperitoneally administered anti-CD25, to inactivate systemic Tregs, or given isotype antibody as a control. Mice which were orally tolerised prior to subcutaneous tumour induction, displayed significantly higher systemic Treg levels (14% vs 6%) and faster tumour growth rates than controls (p<0.05). Complete regression of tumours were only seen after Treg inactivation and occurred in all groups - this was not inhibited by tumour feeding. The cure rates for Treg inactivation were 60% during tolerisation, 75% during tumour growth and 100% during inactivation for both tolerisation and tumour growth. Depletion of Tregs gave rise to an increased number of Teff cells. Treg depletion post-tolerisation and post-tumour induction led to the complete regression of all tumours on tumour bearing mice. Oral administration of tumour tissue, confers a tumour growth advantage and is accompanied by an increase in systemic Treg levels. The administration of anti-CD25 Ab decreased Treg numbers and caused an increase in Teffs. Most notably Treg cell inhibition overcame established oral tolerance with consequent tumor regression, especially relevant to foregut cancers where oral tolerance is likely to be induced by the shedding of tumour tissue into the gut

Evidence for a null entropy of extremal black holes

We present some arguments in support of a {\it zero} entropy for {\it extremal} black holes. These rely on a combination of both quantum, thermodynamic, and statistical physics arguments. This result may shed some light on the nature of these extreme objects. In addition, we show that within a {\it quantum} framework the capture of a particle by an initially extremal black hole always results with a final nonextremal black hole.Comment: 11 page