Transmission, reflection and localization in a random medium with absorption or gain

We study reflection and transmission of waves in a random tight-binding system with absorption or gain for weak disorder, using a scattering matrix formalism. Our aim is to discuss analytically the effects of absorption or gain on the statistics of wave transport. Treating the effects of absorption or gain exactly in the limit of no disorder, allows us to identify short- and long lengths regimes relative to absorption- or gain lengths, where the effects of absorption/gain on statistical properties are essentially different. In the long-lengths regime we find that a weak absorption or a weak gain induce identical statistical corrections in the inverse localization length, but lead to different corrections in the mean reflection coefficient. In contrast, a strong absorption or a strong gain strongly suppress the effect of disorder in identical ways (to leading order), both in the localization length and in the mean reflection coefficient.Comment: Important revisions and expansion caused by a crucial property of $\hat Q

Stratigraphic and taxonomic considerations on the late Cretaceous rudist fauna of Aksai Chin (Western Tibet, China) from the De Filippi collection

The rudist fauna collected in western Tibet in the Aksai Chin area by the DE FILIPPI expedition in 1914 has been reprised and redescribed. This fauna is composed of Radiolites cf. lusitanicus, Radiolites sp., Gorjanovicia cf. endrissi, ? Sauvagesia sp., Sphaerulites sp., Durania sp., and Gyropleu-ra sp. The rudist-bearing beds belong to the Tielongtan Group of the Tianshuihai terrane. The Turo-nian-? Coniacian Xiloqzung Formation (Fm.) bear the older rudists (Radiolites cf. lusitanicus, Radiolites sp., Sphaerulites sp., Durania sp.), whereas younger ages have been determined through microfossil analysis which, compared with the western Neotethys records, suggests an early-mid Campanian age. This allowed to ascribe the younger rudists of the collection (Gorjanovicia cf. endrissi, ? Sauvagesia sp., Gyropleura sp., Radiolites sp.) to the Dongloqzung Formation. Our data confirm that rudist-bea-ring facies in the Tielongtan Group extend at least up to the middle Campanian. The Aksai Chin rudist assemblage should belong to the Southwestern Asian assemblage of the Eastern Mediterranean Sub-province

Metabolic network analysis reveals microbial community interactions in anammox granules.

Microbial communities mediating anaerobic ammonium oxidation (anammox) represent one of the most energy-efficient environmental biotechnologies for nitrogen removal from wastewater. However, little is known about the functional role heterotrophic bacteria play in anammox granules. Here, we use genome-centric metagenomics to recover 17 draft genomes of anammox and heterotrophic bacteria from a laboratory-scale anammox bioreactor. We combine metabolic network reconstruction with metatranscriptomics to examine the gene expression of anammox and heterotrophic bacteria and to identify their potential interactions. We find that Chlorobi-affiliated bacteria may be highly active protein degraders, catabolizing extracellular peptides while recycling nitrate to nitrite. Other heterotrophs may also contribute to scavenging of detritus and peptides produced by anammox bacteria, and potentially use alternative electron donors, such as H2, acetate and formate. Our findings improve the understanding of metabolic activities and interactions between anammox and heterotrophic bacteria and offer the first transcriptional insights on ecosystem function in anammox granules

Comparison of Numerical Simulations and Analytical Theories for Elastic Wave Scattering within Polycrystalline Materials

Understanding the propagation and scattering of ultrasonic waves within polycrystalline materials is relevant to both material characterisation and flaw detection NDE. Validating analytical theories of scattering however has historically been hampered by the difficulty of obtaining sufficiently reliable experimental data where the statistical properties of the grains within the volume of the material are known well enough. Instead, this presentation exploits important recent progress in numerical modelling, which for the first time enables accurate three-dimensional simulations of wave propagation and scattering in polycrystals. The presentation reports work using such a model to compare and validate 3D numerical simulations of wave scattering against existing analytical theories. A wide range of wavenumber to grain size ratios, ka, are considered such that scattering within the Rayleigh, transitional, and stochastic regimes are compared. The numerical calculations are based on an established Voronoi algorithm to generate statistically representative random materials. An explicit Finite Element scheme (Pogo) running on an array of graphics processors is used to solve the time-domain wave propagation problem. It is found that near perfect agreement exists with the generalized second order theories (type of Stanke-Kino) for attenuation coefficient when these theories are implemented with properly fitted second order material statistics

Fluctuations of radiation from a chaotic laser below threshold

Radiation from a chaotic cavity filled with gain medium is considered. A set of coupled equations describing the photon density and the population of gain medium is proposed and solved. The spectral distribution and fluctuations of the radiation are found. The full noise is a result of a competition between positive correlations of photons with equal frequencies (due to stimulated emission and chaotic scattering) which increase fluctuations, and a suppression due to interaction with a gain medium which leads to negative correlations between photons. The latter effect is responsible for a pronounced suppression of the photonic noise as compared to the linear theory predictions.Comment: 7 pages, 5 figures; expanded version, to appear in Phys. Rev.

First-principles thermal equation of state and thermoelasticity of hcp Fe at high pressures

We investigate the equation of state and elastic properties of hcp iron at high pressures and high temperatures using first principles linear response linear-muffin-tin-orbital method in the generalized-gradient approximation. We calculate the Helmholtz free energy as a function of volume, temperature, and volume-conserving strains, including the electronic excitation contributions from band structures and lattice vibrational contributions from quasi-harmonic lattice dynamics. We perform detailed investigations on the behavior of elastic moduli and equation of state properties as functions of temperature and pressure, including the pressure-volume equation of state, bulk modulus, the thermal expansion coefficient, the Gruneisen ratio, and the shock Hugoniot. Detailed comparison has been made with available experimental measurements and theoretical predictions.Comment: 33 pages, 12 figure

Local edge modes in doped cuprates with checkerboard polaronic heterogeneity

We study a periodic polaronic system, which exhibits a nanoscale superlattice structure, as a model for hole-doped cuprates with checkerboard-like heterogeneity, as has been observed recently by scanning tunneling microscopy (STM). Within this model, the electronic and phononic excitations are investigated by applying an unrestricted Hartree-Fock and a random phase approximation (RPA) to a multiband Peierls-Hubbard Hamiltonian in two dimensions

A Contour Integral Representation for the Dual Five-Point Function and a Symmetry of the Genus Four Surface in R6

The invention of the "dual resonance model" N-point functions BN motivated the development of current string theory. The simplest of these models, the four-point function B4, is the classical Euler Beta function. Many standard methods of complex analysis in a single variable have been applied to elucidate the properties of the Euler Beta function, leading, for example, to analytic continuation formulas such as the contour-integral representation obtained by Pochhammer in 1890. Here we explore the geometry underlying the dual five-point function B5, the simplest generalization of the Euler Beta function. Analyzing the B5 integrand leads to a polyhedral structure for the five-crosscap surface, embedded in RP5, that has 12 pentagonal faces and a symmetry group of order 120 in PGL(6). We find a Pochhammer-like representation for B5 that is a contour integral along a surface of genus five. The symmetric embedding of the five-crosscap surface in RP5 is doubly covered by a symmetric embedding of the surface of genus four in R6 that has a polyhedral structure with 24 pentagonal faces and a symmetry group of order 240 in O(6). The methods appear generalizable to all N, and the resulting structures seem to be related to associahedra in arbitrary dimensions.Comment: 43 pages and 44 figure

Labour Market and Social Policy in Italy: Challenges and Changes. Bertelsmann Policy Brief #2016/02

vEight years after the outbreak of the financial crisis, Italy has still to cope with and overcome a plethora of economic and social challenges. On top of this, it faces an unfavourable demographic structure and severe disparities between its northern and southern regions. Some promising reforms have recently been enacted, specifically targeting poverty and social exclusion. However, much more remains to be done on the way towards greater economic stability and widely shared prosperity

BiOX (X = Cl, Br, I) photocatalysts prepared using NaBiO 3 as the Bi source: Characterization and catalytic performance

The Bismuth oxyhalides, crystalline BiOX (X = Cl, Br, I) were prepared via a facile method, using NaBiO 3 and HX aqueous solutions as the raw materials for the first time. The systematic microstructure and optical property characterizations of the BiOX photocatalysts demonstrated the reliability of this new and facile preparation approach. The photocatalytic activity on the degradation of typical phenolic endocrine disrupting chemicals over BiOX and P25 were evaluated under Xenon-light irradiation and the initial photocatalytic mechanism was discussed based on the band edge potential analysis. © 2009.postprin