Smooth transonic flow in an array of counter-rotating vortices

Numerical solutions to the steady two-dimensional compressible Euler equations corresponding to a compressible analogue of the Mallier & Maslowe (Phys. Fluids, vol. A 5, 1993, p. 1074) vortex are presented. The steady compressible Euler equations are derived for homentropic flow and solved using a spectral method. A solution branch is parameterized by the inverse of the sound speed at infinity, $c_{\infty}^{-1}$, and the mass flow rate between adjacent vortex cores of the corresponding incompressible solution, $\epsilon$. For certain values of the mass flux, the solution branches followed numerically were found to terminate at a finite value of $c_{\infty}^{-1}$. Along these branches numerical evidence for the existence of extensive regions of smooth steady transonic flow, with local Mach numbers as large as 1.276, is presented

Dipole lasing phase transitions in media with singularities in polarizabilities

We show that a divergence in the optical polarizability of a heterogeneous medium with nonlinear amplification and a strong dipole-dipole interaction between particles can lead to a phase transition, for which the dipole momentum of the particles or the dipole radiation rate can be taken as order parameters. The "dipole laser" (Phys. Rev. A 71, 063812 (2005)) can be used both as a simple example of such a second-order phase transition and to provide a recipe for its analysis. We show that similar phase transitions may be possible for a nanoparticle on the surface of an optically active medium and at the "Clausius-Mossotti" catastrophe in a bulk heterogeneous medium

Agronomic performance of acid-based liquid fertilisers on winter wheat.

End of Project ReportIn the early 90’s, a new and novel means (liquid Flex system) of crop fertilisation was launched on the Irish market which was capable of supplying the crop’s total nitrogen, phosphorus, potassium and trace element requirement in liquid form, formulated to meet specific crop requirements. This system included novel chemistry, untested under Irish conditions and with little specific reference in the scientific literature. The chemistry of the liquid Flex system consists of an acid-based material. Stable compounds i.e. urea sulphate, urea phosphate and urea-metal complexes are formed by the reaction of urea with sulphuric acid, phosphoric acid and metal salts, respectively. Interest in these materials has been generated because they possess a number of physical and chemical characteristics, which, in theory, should be beneficial. However, the ability of the Flex system to effectively supply nutrients to the plant has not been researched. A field and greenhouse experimental programme was carried out over the three seasons, 1996-1998 to compare acid-base/urea-metal complexes with conventional fertilisers and to investigate whether this unconventional chemistry could lead to increased biological efficiency. The trial programme evaluated the Flex system, both as individual components and as a complete fertiliser. In field comparisons, formulation of P as urea phosphate gave similar results to conventional granular superphosphate in terms of grain yield, recovery of P by the crop and grain quality, regardless of soil type. This was supported by the results from the greenhouse experiment. In field comparisons of the main soil-applied liquid Flex source of N, i.e. N24 (urea with the addition of a standard level of acid and metal salts) with conventional N formulations, N24 gave poorer performance than CAN and granular urea in warm dry conditions due to insufficient inhibition to substantially reduce ammonia volatilisation. In wet conditions, the slow release of N from inhibited urea may have reduced the potential loss from leaching or denitrification, and led to a better performance than CAN or urea. The additional product of the Flex system, i.e. liquid Flex urea - N18 (urea with the addition of metal salts), applied as a foliar spray, was no more efficient than liquid urea as a late N source. The Flex urea had the disadvantage that it gave higher scorch levels than conventional liquid urea. When flag leaf scorch was excessive, grain yield was affected and quality suffered, with reduced grain and hectolitre weights. Where early application of P may have been critical to obtain maximum response, the N that accompanied the early application of P as urea phosphate was most likely lost through leaching. The application of large quantities of K in any one application with the liquid system was restricted due to solubility problems, which ultimately resulted in delayed application in soils with low K levels. The Flex system does not lead to increased biological efficiency. However, as farms get bigger and greater emphasis is placed on the reduction of water and air pollution, the liquid Flex system may become attractive because of its practical advantages in handling, storage and application and the ability to tailor-make specific formulations for given crop requirements

Probing the causes of thermal hysteresis using tunable N-agg micelles with linear and brush-like thermoresponsive coronas

Self-assembled thermoresponsive polymers in aqueous solution have great potential as smart, switchable materials for use in biomedical applications. In recent years, attention has turned to the reversibility of these polymers’ thermal transitions, which has led to debate over what factors influence discrepancies in the transition temperature when heating the system compared to the temperature obtained when cooling the system, known as the thermal hysteresis. Herein, we synthesize micelles with tunable aggregation numbers (Nagg) whose cores contain poly(n-butyl acrylate-co-N,N-dimethylacrylamide) (p(nBA-co-DMA)) and four different thermoresponsive corona blocks, namely poly(N-isopropylacrylamide) (pNIPAM), poly(N,N-diethylacrylamide) (pDEAm), poly(diethylene glycol monomethyl ether methacrylate) (pDEGMA) and poly(oligo(ethylene glycol) monomethyl ether methacrylate) (pOEGMA). By studying their thermoresponsive behavior, we elucidate the effects of changing numerous important characteristics both in the thermoresponsive chain chemistry and architecture, and in the structure of their self-assemblies. Our findings demonstrate large deviations in the reversibility between the self-assemblies and the corresponding thermoresponsive homopolymers; specifically we find that micelles whose corona consist of polymers with a brush-like architecture (pDEGMA and pOEGMA) exhibit irreversible phase transitions at a critical chain density. These results lead to a deeper understanding of stimuli-responsive self-assemblies and demonstrate the potential of tunable Nagg micelles for uncovering structure–property relationships in responsive polymer systems

Comparison of photo- and thermally initiated polymerization-induced self-assembly : a lack of end group fidelity drives the formation of higher order morphologies

Polymerization-induced self-assembly (PISA) is an emerging industrially relevant technology, which allows the preparation of defined and predictable polymer self-assemblies with a wide range of morphologies. In recent years, interest has turned to photoinitiated PISA processes, which show markedly accelerated reaction kinetics and milder conditions, thereby making it an attractive alternative to thermally initiated PISA. Herein, we attempt to elucidate the differences between these two initiation methods using isothermally derived phase diagrams of a well-documented poly(ethylene glycol)-b-(2-hydroxypropyl methacrylate) (PEG-b-HPMA) PISA system. By studying the influence of the intensity of the light source used, as well as an investigation into the thermodynamically favorable morphologies, the factors dictating differences in the obtained morphologies when comparing photo- and thermally initiated PISA were explored. Our findings indicate that differences in a combination of both reaction kinetics and end group fidelity led to the observed discrepencies between the two techniques. We find that the loss of the end group in photoinitiated PISA drives the formation of higher order structures and that a morphological transition from worms to unilamellar vesicles could be induced by extended periods of light and heat irradiation. Our findings demonstrate that PISA of identical block copolymers by the two different initiation methods can lead to structures that are both chemically and morphologically distinct

Dipole nanolaser

A "dipole" laser is proposed consisting of a nanoparticle and a two-level system with population inversion. If the threshold conditions are fulfilled, the dipole interaction between the two-level system and the nanoparticle leads to coherent oscillations in the polarization of the particles, even in the absence of an external electromagnetic field. The emitted radiation has a dipolar distribution. It does not need an optical cavity, and has a very small volume, 0.1 mu m(3), which can be important for applications in microelectronics. Estimates of the threshold conditions are carried out for a dipole laser composed of a quantum dot and a silver nanoparticle

Revista de Indias y Anuario de Estudios Americanos. Visibilidad y uso de la edición electrónica

Una década americanista en línea, 2010, [En línea], Puesto en línea el 25 mayo 2010[EN] In this article we analyze the online visibility and content usage of two Americanist Journals published by CSIC, Revista de Indias and Anuario de Estudios Americanos. The online edition dates back to 2007; contents are comparable in terms of accessible documents, and both Journals are published in Open Access, with a 6-months embargo. We also discuss some methodological issues in terms of the need of a data normalization allowing the measurement of genuine downloads assimilable to document reading. Both Journals registered close to 500,000 normalized downloads along 2008 and 2009, most coming from Latin America and the United States (70%). Data show a high degree of repeated downloads of the same document from the same user (25% of total downloads) and indexation downloads (25% of normalized downloads), and also the lack of correlation between Journal’s visibility (webpage visits) and content usage (document downloads). Access restriction has a negative effect, as evidenced by the low downloading of embargoed documents[ES] En este artículo analizamos los datos de visibilidad y uso de las dos revistas de temática americanista editadas por el CSIC, Revista de Indias y Anuario de Estudios Americanos. La edición electrónica de ambas data de 2007, y su contenido en artículos accesibles es comparable; ambas se publican en Acceso Abierto (OA) con un embargo de acceso de 6 meses. También analizamos cuestiones metodológicas relativas al análisis de descargas, en el sentido de la necesidad de una normalización de los datos que permita determinar las descargas reales, asimilables a una lectura del documento. Durante los años 2008 y 2009, ambas revistas han recibido cerca de 500.000 descargas normalizadas, que provienen en su mayoría de Latinoamérica y Estados Unidos (70%). Los datos muestran el elevado número de descargas repetidas de documentos en periodos cortos de tiempo por el mismo usuario (25% de las totales registradas) y de descargas de indización (25% de las descargas normalizadas), y también la falta de correlación entre visibilidad de las revistas (visitas a páginas web) y uso de los contenidos (descarga de documentos). La restricción de acceso tiene un efecto perjudicial, evidenciado por el bajo nivel de descarga de los documentos sometidos a embargoPeer reviewe