Scale-dependent three-dimensional charged black holes in linear and non-linear electrodynamics

In the present work we study the scale dependence at the level of the effective action of charged black holes in Einstein–Maxwell as well as in Einstein–power-Maxwell theories in \((2+1)\)-dimensional spacetimes without a cosmological constant. We allow for scale dependence of the gravitational and electromagnetic couplings, and we solve the corresponding generalized field equations imposing the null energy condition. Certain properties, such as horizon structure and thermodynamics, are discussed in detail.     

Optimizing the source distribution in fluid mixing

A passive scalar is advected by a velocity field, with a nonuniform spatial source that maintains concentration inhomogeneities. For example, the scalar could be temperature with a source consisting of hot and cold spots, such that the mean temperature is constant. Which source distributions are best mixed by this velocity field? This question has a straightforward yet rich answer that is relevant to real mixing problems. We use a multiscale measure of steady-state enhancement to mixing and optimize it by a variational approach. We then solve the resulting Euler-Lagrange equation for a perturbed uniform flow and for simple cellular flows. The optimal source distributions have many broad features that are as expected: they avoid stagnation points, favour regions of fast flow, and their contours are aligned such that the flow blows hot spots onto cold and vice versa. However, the detailed structure varies widely with diffusivity and other problem parameters. Though these are model problems, the optimization procedure is simple enough to be adapted to more complex situations.     

The cohomology groups of a special Einstein manifold

Summary We consider a compact orientable Einstein manifold of even dimension n=2m, which is k-pinched. If k>[m(m−1) ₂ (2m−1) ₂ (2m−1)+3], then there exists no element, different from zero of the H ₂ (M,R) such that its exterior m-power belongs to a zero class. This result has some applications to the topological product of manifold. Entrata in Redazione il 27 settembre 1977.     

Bestimmung der organischen Bestandteile von Aerosolpartikeln aus Reinluft

Zusammenfassung Das für die Untersuchung der organischen Bestandteile von Reinluft-Aerosolteilchen entwickelte Analysenverfahren beruht auf der Kombination von klassischen Trennmethoden mit Verfahren der Dünnschicht- und der Gas-Chromatographie bzw. der Gas-Chromatographie/Massenspektrometrie. Im Gegensatz zu älteren Verfahren werden alle vorkommenden organischen Verbindungen, soweit sie äther-löslich sind bzw. in eine äther-lösliche Form überführt werden können, erfaßt. Die verfahrensbedingten Substanzverluste sind so gering, daß schon 100 mg Aerosolteilchen ausreichend sind für die Analyse der organischen Bestandteile (bei ca. 10% organischer Substanz). Ein Anwendungsbeispiel für das Analysenverfahren wird gegeben. Best. von Organ. Substanzen in Luft; Chromatographie, Dünnschicht/Chromatographie, Gas/Massenspektrometrie; Aerosolbestandteile in Reinluft.

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Determination of the organic constituents of aerosol particles from clean air

The method developed for analysing the organic matter of atmospheric particles from clean air is based on the combination of classical separation procedures and thinlayer chromatography together with gas chromatography and gas chromatography/mass spectrometry, respectively. In contrast to methods published earlier, all organic compounds present can be detected (if they are or can be converted to compounds soluble in ether). The loss of organic matter inherent in the analytical procedure is small enough to allow the determination of the organic constituents of 100 mg of aerosol particles (with about 10% organic matter). An example for the application of the analytical method is presented.

     

Green's function of radial inhomogeneous spheres excited by internal sources

Green's function in the interior of penetrable bodies with inhomogeneous compressibility by sources placed inside them is evaluated through a Schwinger-Lippmann volume integral equation. In the case of a radial inhomogeneous sphere, the radial part of the unknown Green's function can be expanded in a double Dini's series, which allows analytical evaluation of the involved cumbersome integrals. The simple case treated here can be extended to more difficult situations involving inhomogeneous density as well as to the corresponding electromagnetic or elastic problem. Finally, numerical results are given for various inhomogeneous compressibility distributions.     

A Heterogeneous Multiscale Dynamic Model for Simulation of Catalytic Reforming Reactors

The present work aims to establish a generic reforming reaction scheme to evaluate the performance of catalytic reforming systems with the aid of a one‐dimensional heterogeneous dynamic model. The novelty of the numerical model stems from the direct inclusion of interphase (fluid‐to‐particle surface), intraparticle (within particle), and intrareactor heat and mass transport resistances under transient conditions. The developed model accounts for the multicomponent gas mixture physicochemical properties and correlations for calculating mass and heat transfer coefficients. Effective macroscopic properties within the particle are calculated by incorporating diffusivities and conductivities of the porous network characteristics accounting for Knudsen and molecular transport as well as tortuosity and porosity of the overall porous path. The industrial case of a steam‐methane reforming multitubular reactor was studied as the most representative case of the generic reaction scheme, with all mass/energy resistances present under severe pressure and temperature conditions. It was shown that there are notable diffusional limitations within the particle, whereas there are also temperature and partial pressure gradients due to the heat and mass transport resistances in the particle film layer. It is further demonstrated that the proposed model can be utilized as a versatile design tool for catalytic reactor development and optimization.     

“Gluelump” spectrum and adjoint source potential in lattice QCD3

We calculate the potential between “quarks” which are in the adjoint representation of SU(2) color in the three-dimensional lattice theory. We work in the scaling region of the theory and at large quark separations R. We also calculate the masses M_Qg of color-singlet bound states formed by coupling an adjoint quark to adjoint glue (“gluelumps”). Good scaling behavior is found for the masses of both magnetic (angular momentum J = 0) and electric (J = 1) gluelumps, and the magnetic gluelump is found to be the lowest-lying state. It is naively expected that the potential for adjoint quarks should saturate above a separation R_scr where it becomes energetically favorable to produce a pair of gluelumps. We obtain a good estimate of the naive screening distance R_scr. However we find little evidence of saturation in the potential out to separations R of about 1.5R_scr.     

Singular Ricci Solitons and Their Stability under the Ricci Flow

We introduce certain spherically symmetric singular Ricci solitons and study their stability under the Ricci flow from a dynamical PDE point of view. The solitons in question exist for all dimensions n + 1 ≥ 3, and all have a point singularity where the curvature blows up; their evolution under the Ricci flow is in sharp contrast to the evolution of their smooth counterparts. In particular, the family of diffeomorphisms associated with the Ricci flow “pushes away” from the singularity causing the evolving soliton to open up immediately becoming an incomplete (but non-singular) metric. The main objective of this paper is to study the local-in time stability of this dynamical evolution, under spherically symmetric perturbations of the singular initial metric. We prove a local well-posedness result for the Ricci flow in suitably weighted Sobolev spaces, which in particular implies that the “opening up” of the singularity persists for the perturbations as well.     

Combining evolutionary and stochastic gradient techniques for system identification

In the present contribution, a novel method combining evolutionary and stochastic gradient techniques for system identification is presented. The method attempts to solve the AutoRegressive Moving Average (ARMA) system identification problem using a hybrid evolutionary algorithm which combines Genetic Algorithms (GAs) and the Least Mean Squares LMS algorithm. More precisely, LMS is used in the step of the evaluation of the fitness function in order to enhance the chromosomes produced by the GA. Experimental results demonstrate that the proposed method manages to identify unknown systems, even in cases with high additive noise. Furthermore, it is observed that, in most cases, the proposed method finds the correct order of the unknown system without using a lot of a priori information, compared to other system identification methods presented in the literature. So, the proposed hybrid evolutionary algorithm builds models that not only have small MSE, but also are very similar to the real systems. Except for that, all models derived from the proposed algorithm are stable.