Kinetic Study of the Photoexcited Triplet State of Free Base Porphyrins by EPR

An electron paramagnetic resonance (EPR) study of the photoexcited triplet state of four free base porphyrins is presented. The zero field splitting parameters (ZFS) |D| and |E| were calculated from the EPR spectra of the porphyrins dissolved in n-octane matrices at 80°K. |D| = 0.0359 cm^?1, |E| = 0.0079 cm^?1 for tetra phenyl porphyrin (H₂ TPP), |D| = 0.0432 cm^?1, |E| = 0.0037 cm^?1 for tetra (per-fluoro) phenyl porphyrin H₂T (per-F) PP, |D| = 0.0366 cm^?1, |E| = 0.0078 cm^?1 for tetra (para-chloro) phenyl porphyrin H₂T(P-Cl)PP, |D| = 0.0369 cm^?1, |E| = 0.0076 cm^?1 for tetra (para-methyl) phenyl porphyrin H₂T(P-Me)PP. The transient behavior of the EPR signal intensities in the last two porphyrins is discussed. The depopulation rate constants of the triplet sublevels k_p, the ratio between the population rate constants A_p (at zero field, p = x,y,z), and the spin lattice relaxation rate W within the triplet manifold, were calculated. k_x = (12 ± 2) × 10² sec^?1, k_y = (0.5 ± 0.1) × 10² sec^?1, k_z = (1.2 ± 0.4) × 10² sec^?1, A_x:A_y:A_z ? 0.63:0.01:0.33, W = (0.4 ± 0.1) × 10⁴ sec^?1 for H₂T(P-Cl)PP, k_x = (7 ± 2) × 10² sec^?1, k_y = (4 ± 1) × 10² sec^?1, k_z = (1.5 ± 0.5) × 10² sec^?1, A_x:A_y:A_z ? 0.56:0.31:0.13, W = (1.7 ± 0.4) × 10³ sec^?1 for H₂T(P-Me)PP.     

Long-range hydrodynamic response of particulate liquids and liquid-laden solids

In viscous particulate liquids, such as suspensions and polymer solutions, the large-distance steady-state flow due to a local disturbance is commonly described in terms of hydrodynamic screening—beyond a correlation length ξ the response drops from that of the pure solvent, characterized by its viscosity η₀, to that of the macroscopic liquid with viscosity η > η₀ For cases where η >> η₀ we show, based on general conservation arguments, that this screening picture, while being asymptotically correct, should be refined in an essential way. The crossover between the microscopic and macroscopic behaviors occurs gradually over a wide range of distances, ξ < r < (η / η₀)^1/2 ξ In liquid-laden solids, such as colloidal glasses, gels, and liquid-filled porous media, where η → ∞, this intermediate behavior takes over the entire large-distance response. The intermediate flow field, arising from the effect of mass displacement rather than momentum diffusion, has several unique characteristics: (i) It has a dipolar shape with l/r ³ spatial decay, negative transverse components, and vanishing angular average. (ii) Its amplitude depends on the liquid properties through η₀ and ξ alone; thus, in cases where ξ is fixed by geometry (e.g., for particulate liquids tightly confined in solid matrices), the large-distance response is independent of particle concentration. (iii) The intermediate field builds up non-diffusively, with a distance-independent relaxation rate, making it dominant at large distances before steady state has been reached. We demonstrate these general properties in three model systems.     

Rethinking cities in the Middle East: political economy, planning, and the lived space

Urbanisation is an economic, political, and socio-cultural complexity, and so is its interaction with cityscapes. However, this truism rarely finds an expression in academic research. It is obvious that economic transitions would determine the quality and volume of the built environment. Municipal and state decision making further shape the nature of urban spaces, and socio-cultural transformations influence perceived notions of the lived space and, in turn, reshape the physical landscape itself. Nevertheless, research on cities in the Middle East and elsewhere remains fairly limited in scope, with little cross-discipline 'conversation' among scholars in different fields which attempts to account for such complexity. This is all the more surprising as life in cities has become, over the past half century or so, the most significant form of human collective dwelling; in the Middle East over half the population currently lives in urban settings and the numbers are forecast to grow in the future.1

This review article is the result of a dialogue between an architect and an economic historian in response to the foregoing. We have united in an attempt to offer a more integrative approach to Middle East urbanism, accounting for the interactions of the political economy of this region, planning, and the lived space. The key questions on which we focus are why and how do state transformation and economic structural change impact upon urban space. In seeking the answers we examine the long-term trajectory of cities as they went through the first period of globalisation under imperial intervention and/or direct colonial rule; gradually came under independent, inward-looking, national regimes; and presently experience the second wave of globalisation and the opening of local economies to international markets. Such a narrative explores common themes in the historical trajectories of cities' lives.

Our long-term, geographically extensive overview (Map 1) is bound to miss some specific developments that have made a significant impact on the transformations of cities in the region; our aim is not to totalise Middle East experiences and reduce a variety of narratives to a simplistic linear model of change. Even more so, our study of the Middle East is mostly focused on Egypt, the Asian Arab countries (the mashraq), Israel/Palestine, and Turkey, the geographical unit which roughly corresponded with the Ottoman Empire, the last state to control the Middle East before the age of nations. We acknowledge that any bird's eye view perspective is bound to do some injustice to historically specific contexts, and city transitions that occurred in such contexts. We would welcome any future work that brings our suggestion here, namely to integrate political economy with the study of urban development and city life, to bear on more specific research on urbanism in the Middle East.     

Experimental Investigation of Convective Heat Transfer Between Silicon-Melt and Solidification Front

Convective heat transfer between silicon melt and solidification front during Bridgman-type solidification process in a ceramic crucible has been investigated by means of heat balance analysis of the crucible during the process. The effect of aspect ratio on the Rayleigh and Nusselt numbers has been investigated. For a large crucible size (with inner diameter of about 0.50-m), the dependence correlates well with the empiric formula Nu?=?0.303 Ra^0.279. For a small crucible size (with inner diameter of about 0.20-m), the dependence correlates well with the empiric formula Nu?=?0.181 Ra^0.285. The experimental data obtained were compared with the available literature experimental and numerical simulation data.

     

General control charts for attributes

Traditional Shewhart-type control charts ignore the skewness of the plotted statistic. Occasionally, the skewness is too large to be ignored, and in such cases the classical Shewhart chart ceases to deliver satisfactory performance. In this paper, we develop a general framework for constructing Shewhart-like control charts for attributes based on fitting a quantile function that preserves all first three moments of the plotted statistic. Furthermore, these moments enter explicitly into the formulae for calculating the limits. To enhance the accuracy of these limits the value of the skewness measure used in the calculations is inflated by 44%. This inflation rate delivers accurate control limits for diversely-shaped attribute distributions like the binomial, the Poisson, the geometric and the negative binomial. A new control chart for the M/M/S queueing model is developed and its performance evaluated.     

Mesh insensitive formulation for initiation and growth of shear bands using mixed finite elements

An Implicit Nonlinearly Consistent (INC) numerical solution of a partial differential equation (PDE) model for shear bands, which includes a thermo-visco-plastic flow rule and finite thermal conductivity, is presented, and is found to be insensitive to mesh size. Insensitivity is achieved through the use of finite thermal conductivity in the PDE model in conjunction with the INC numerical solver. Finite thermal conductivity gives rise to an inherent physical length scale in the PDE model, governed by competition between shear heating and diffusion. This length scale serves as a localization limiter and will regularize the problem in the strain softening regime. This occurs since diffusion removes heat from the shearband more quickly as localization becomes more severe (i.e. as temperature gradients steepen). The INC solver leaves no splitting error at the end of a time step and is accurate even during phases for which the solution is evolving very rapidly. A key point in this paper is the analytical derivation of the system Jacobian by differentiation of the weak form of the PDE model, thus avoiding the use of numerical approximation formulas. In contrast, solution of the same continuous model using an operator split solution scheme is seen to lead to unreasonably slow convergence. One and two dimensional implementations of the algorithm are presented. For two dimensions, a mixed quadrilateral using discontinuous bilinear functions for plastic strain, and the interpolants associated with the Pian-Sumihara element for the stress is implemented.     

Effect of Congeneric Chemical Signals of Different Ages on Foraging Response and Food Choice in the Field by Golden Spiny Mice (Acomys russatus)

The common spiny mice Acomys dimidiatus and golden spiny mice Acomys russatus coexist in the extreme warm and dry parts of the Rift Valley in Israel. However, they are temporally segregated in that the former is nocturnal, whereas the latter is diurnal. Daily rhythms of physiological and behavioral variables in A. russatus responded to semiochemical signals released by A. dimidiatus (in the urine and feces). Both species feed upon the same food items but at different times of the 24-hr cycle. The main aim of the present study was to test under field conditions the foraging response of A. russatus to odors of different ages released by A. dimidiatus. Various feeding and behavioral variables were compared in three groups of A. russatus. The results show that fresh semiochemical signals released by A. dimidiatus decrease the feeding efficiency and increase the rate of smelling from a distance in A. russatus. These results support the idea that temporal segregation between the two coexisting species is at least partly through semiochemicals present in the urine and feces.     

Numerical Study of Particle Motion in Jet Milling

Jet mills are common devices used in industry for fine milling of dry particulate materials. The size reduction is caused by repeated events of impacts between particles. Although many parameters affect the performance of a jet mill, only a few of them were investigated. Particles' motions in a jet mill have great influence on the comminution process and energy consumption. Therefore, as a first step for a full simulation of the jet-mill process, it was decided to investigate the particle motion inside the jet mill by neglecting particle-particle interaction and particle breakage. In this way, the numerical simulations provide a better understanding of the classification process. In the present study, three-dimensional numerical simulations of particle motion in an industrial full-scale jet mill were conducted. The predictions of the numerical simulations were compared with experimental data and used to analyze the flow field characteristics.