Homogeneous Path Research Articles

Flame propagation of combustible dusts: A Mallard-Le Chatelier inspired model

In this work, a three-layers Mallard-Le Chatelier inspired theoretical model is developed to fully characterise the steps occurring during the flame propagation of combustible dusts/air. The model is based on the hypothesis that the dust flame propagation follows a homogeneous path: the dust-air mixture is pre-heated up to the volatile point (VP), at which production of volatiles occurs, thanks to the back-diffusion of heat from the combustion zone of the flame to the colder zones. The volatiles produced are then heated up to the ignition temperature and enter in the combustion zone. The flame burning velocity is the results of the coupling between heating rate, pyrolysis and/or evaporation/sublimation rate and volatiles combustion rate. The rate of formation of volatiles was measured by means of TG/DSC analysis. The laminar burning velocity of gases was computed by simulating the gas flame propagation in a tube starting from the measured gas compositions (by literature data or FTIR analysis).

A bio-inspired heterogeneous catalyst for the transformation of limonene from orange peel waste biomass into value-added products

The kinetic study of limonene oxidation using an iron hexadecachlorinated phthalocyanine immobilized on modified silica catalyst (FePcCl16-NH2-SiO2) with the oxidizing agent t-butyl hydroperoxide (TBHP) is developed. Experimental reaction rates from a batch reactor were fitted with the kinetic expression based on Langmuir-Hinshelwood-Hougen-Watson (LHHW) mechanisms with the adsorption of both reactants and the main reaction products (carvone, limonene 1,2-epoxide and carveol) on the surface of the phthalocyanine with 99% accuracy. A similar kinetic expression fitted the carveol oxidation to carvone with a 96% exactness. Limonene conversion of 74% was obtained after 23h with a carvone selectivity of 10% and apparent activation energy of 38.6kJmol−1; whereas at 78% carveol conversion the selectivity to carvone was 87% after 10h. The catalyst can be recycled up to seven times without losing neither limonene conversion nor carvone selectivity and these results do not depend on the treatment of the catalyst before reusing. Leaching of the active species was not observed at the reaction conditions and the influence of liquid-phase free-radicals was demonstrated, concluding that the reaction includes heterogeneous and homogeneous paths.

Zeons, Orthozeons, and Graph Colorings

Nilpotent adjacency matrix methods have proven useful for counting self-avoiding walks (paths, trails, cycles, and circuits) in finite graphs. In the current work, these methods are extended for the first time to problems related to graph colorings. Nilpotent-algebraic formulations of graph coloring problems include necessary and sufficient conditions for k-colorability, enumeration (counting) of heterogeneous and homogeneous paths, trails, cycles, and circuits in colored graphs, and a matrix-based greedy coloring algorithm. Introduced here also are the orthozeons and their application to counting monochromatic self-avoiding walks in colored graphs. The algebraic formalism easily lends itself to symbolic computations, and Mathematica-computed examples are presented throughout.

SU‐E‐T‐42: A Method to Determine the Optimal Proton Scanned Beam Angle to Ensure Robust Treatment Planning

Purpose:The ability of pencil beam scanning (PBS) to deliver highly conformal dose distributions may be affected by patient‐ and physics‐related uncertainties. In clinical practice, selection of proton beam angles is determined qualitatively. This study investigates whether an optimal proton PBS beam angle could be quantitatively determined to ensure robust planning for pelvic targets.Methods:PBS beam angles were optimized based on two independent criteria; shortest and most homogeneous path from the patient surface to the distal edge of the target. The beam angle optimization criteria for gantry angles between 90°‐270° were quantified in 10° increments for each ray, calculated as the straight line distance from the surface of the skin to the CTV's distal edge. The goal was to minimize the path length of a proton PBS beam from the patient surface to the distal edge of the CTV, relative to the entry point, while minimizing HU inhomogeneity along the ray. HU homogeneity (i.e. HU variation) was quantitatively defined as the standard deviation of the average intra‐ray HU intensity distribution of the rays comprising a single beam. This method was validated relative to inter‐fraction changes on ten consecutive, locally advanced, rectal cancer patients, who underwent an average 4 verification CTs. The displacement of the 95–98% isodose lines was determined from forward calculated dose distributions on verification CTs.Results:The posterior beam (180°) had the average shortest path length, 132.7±17.2mm, and the most homogenous path, 31.9±4.3HU. The 95–98% isodose lines from all plans verified our path length to within 2.3±1.2% and HU homogeneity to within 1.2±0.5%.Conclusion:The proposed optimization algorithm determined the posterior beam dose distribution as the most robust relative to inter‐fraction variation for large pelvic targets treated with PBS and was validated via verification CT for our patient cohort. Future work will focus on further algorithm development.

Pseudo-path connected homogeneous continua

The main result of this paper states that every homogeneous pseudo-path connected continuum is weakly chainable, or equivalently, every homogeneous continuum connected by continuous images of the pseudo-arc is itself a continuous image of the pseudo-arc. We notice that even though there exist homogeneous path connected continua that are not continuous images of an arc (Prajs, 2002), they all are continuous images of the pseudo-arc.

Reconnecting Disconnected Youth: Examining the Development of Productive Engagement

Little is known about the developmental process of disconnected youth reengaging in more productive aspects of life. For this study, we examined the process of developing productive engagement among 38 disconnected youth who are either gang‐affiliated, involved with juvenile justice, or (and) homeless. These youth were reengaging into educational and workforce experiences through a comprehensive youth development center. Using a dynamic systems analytic strategy, we categorized upwards of 24 monthly assessments for each youth to determine their development of productive engagement. We found productive engagement does not develop along a homogeneous path. Instead, we found four different pathways. All youth had dips in their engagement, but those along more positive paths rebounded and continued on to graduation from the program.

The Stability of Self-Control: A Group-Based Approach

In A General Theory of Crime (1990), Gottfredson and Hirschi argue that self-control, fully developed in the early stage of life (around age 8 to 10), is a primary explanatory factor of deviance. Research consistently supports the relationship between self-control and deviance, while only limited studies have examined whether self-control is stable after age 10. Using a longitudinal national sample of South Korean youths from age 10 to 14, this study provides a rigorous test of three assumptions of the self-control stability thesis: first, if the development of self-control follows a homogenous process among individuals; second, if within-individual level of self-control stay unchanged over time (absolute stability); and third, if the age and self-control relationships parallel across individuals (relative stability). Both attitudinal and behavioral measures of self-control were used to investigate whether different measures yielded different results in the stability thesis. The results indicated that among individuals multiple developmental paths of self-control existed instead of a homogeneous path. The findings also showed different measures yielded divergent results in the stability thesis. While the analysis of the attitudinal measure revealed strong absolute stability for 50% of the sample, and strong relative stability for 99.7%, the analysis of the behavioral measure showed strong absolute and relative stabilities for 88.6% of the sample.

FPT algorithms for path-transversal and cycle-transversal problems

We study the parameterized complexity of several vertex- and edge-deletion problems on graphs, parameterized by the number p of deletions. The first kind of problems are separation problems on undirected graphs, where we aim at separating distinguished vertices in a graph. The second kind of problems are feedback set problems on group-labelled graphs, where we aim at breaking nonnull cycles in a graph having its arcs labelled by elements of a group. We obtain new FPT algorithms for these different problems, relying on a generic O ∗ ( 4 p ) algorithm for breaking paths of a homogeneous path system.

Formation of controllable sequence of radio pulses at the ionospheric path

The influence of dispersion distortions on a decameter-band radio pulse with amplitude-frequency modulation, which propagates along a homogeneous ionospheric path, has been considered. It is demonstrated that the specially selected frequency modulation law can give rise to the transformation of a radiated pulse into a sequence of pulses. The possibility of controlling the parameters of a formed sequence via the selection of monopulse characteristics is justified.

A resequencing model for high-speed packet-switching networks

In this paper, we propose a framework to study the resequencing mechanism in high-speed networks. This framework allows us to estimate the packet resequencing delay and the resequencing buffer occupancy distributions when data traffic is dispersed on multiple disjoint paths. In contrast to most existing work, the end-to-end path delay distribution is decoupled from the resequencing model. Thus, once the end-to-end path delay distribution is obtained, such as from historical data, our model may be used. In this paper, we illustrate our proposed model with Gaussian distributed path delays. Our results show that the packet resequencing delay and the resequencing buffer occupancy drop when the traffic is spread over a larger number of homogeneous paths, although the network performance improvement quickly saturates when the number of paths increases. We find that the number of paths used in multipath routing should be small, say, up to three.

Introduction to Discrete Event Systems, Second Edition (Cassandras, C.G. et al.; 2008) [Bookshelf

This book covers, in a progressively refined manner, concepts, theories, and methods for modeling, control, and performance analysis of discrete event systems. The book contains two complete instructional paths: chapters 2-5 for deterministic discrete event systems and chapters 6-11 for stochastic discrete event systems. Two appendices are included: "Review of Probability Theory" and "IPA Estimator." The presentation of the material is both intuitive and formal. It follows along a homogeneous path of progressively refined models of discrete event systems, from untimed to timed and from deterministic to stochastic. The logic development is clear, mathematically rigorous, and supplied with a wide range of examples. This is among the best books for both instructional and research purposes.

Callus patterns in femur lengthening using a monolateral external fixator

We studied the callus pattern seen in femoral lengthening using monolateral external fixator to determine whether callus types and shapes can predict the final outcome of the procedure. The radiographs of 41 cases of femoral lengthening (33 unilateral and 8 bilateral) in 33 patients with a mean age 11.9 years (range 4-22 years) were retrospectively analysed by four observers and classified into different shapes and types in concordance with the Ru Li classification. The classification was tested for concurrence and reproducibility by inter-observer studies. An average of 6.2 cm of lengthening (range 3-10.8) was achieved with an external fixator index of 36.5 (range 20.9-55.3). The fusiform type of callus (fixator index 32.04, maturation index 21.6) showed the best result followed by the cylinder type of callus (fixator index 35.7, maturation index 22.3) and the lateral type of callus (fixator index 33.2, maturation index 21.5). However, the concave type of callus showed poor results with a fixator index of 49.4 and a maturation index of 37.1. The homogeneous path showed the best results (fixator index 30.4, maturation index 18.6). The heterogeneous path also showed good results (fixator index 36.4, maturation index 23.9). The mixed path (fixator index 42.5, maturation index 30.8) and the lucent path (fixator index 45.1, maturation index 32.8) showed poor results. Analysis of the callus pattern helps the surgeon to predict the outcome of the procedure and guide him in planning any additional interventions if necessary.

Three-dimensional radial anisotropic structure of the North American upper mantle from inversion of surface waveform data

Seismic anisotropy provides insight into palaeo and recent deformation processes and, therefore, mantle dynamics. In a first step towards a model for the North American upper mantle with anisotropy characterized by a symmetry axis of arbitrary orientation, aimed at filling the gap between global tomography and SKS splitting studies, we inverted long period waveform data simultaneously for perturbations in the isotropic S-velocity structure and the anisotropic parameter , in the framework of normal mode asymptotic coupling theory (NACT). The resulting 2-D broad-band sensitivity kernels allow us to exploit the information contained in long period seismograms for fundamental and higher mode surface waves at the same time. To ensure high quality of the retrieved regional upper-mantle structure, accurate crustal corrections are essential. Here, we follow an approach which goes beyond the linear perturbation approximation and split the correction into a linear and non-linear part. The inverted data set consists of more than 40 000 high quality three component fundamental and overtone surface waveforms, recorded at broad-band seismic stations in North America from teleseismic events and provides a fairly homogeneous path and azimuthal coverage. The isotropic part of our tomographic model shares the large-scale features of previous regional studies for North America. We confirm the pronounced difference in the isotropic velocity structure between the western active tectonic region and the central/eastern stable shield, as well as the presence of subducted material (Juan de Fuca and Farallon Plate) at transition zone depths. The new regional 3-D radial anisotropic model indicates the presence of two distinct anisotropic layers beneath the cratonic part of the North American continent: a deep asthenospheric layer, consistent with present day mantle flow, and a shallower lithospheric layer, possibly a record of ancient tectonic events.

Basic Evaluation of the Catalytic Pattern of the CuCeOx System in the Wet Oxidation of Phenol with Oxygen

The working mechanism of a ceria-supported Cu (Cuat:Ceat = 1:10) system in the Catalytic Wet Oxidation (CWO) of phenol with O2 (TR, 130–170 °C; PO2, 7 atm) has been thoroughly assessed. Basic relationships amongst pH, extent of leaching and rate of phenol and TOC conversion prove the major contribution of a homogeneous catalytic path by Cu ions on the peculiar CWO pattern of supported copper catalyst. In addition, gas-phase reduction/oxidation tests signal the lack of reversibility of the redox cycle of the CuCeO x system under typical reaction conditions.

Acylation and carbanilation of cellulose in ionic liquids

Ionic liquids (ILs) namely 1-N-butyl-3-methylimidazolium chloride ([C4mim]+Cl−), 1-N-ethyl-3-methylimidazolium chloride ([C2mim]+Cl−), 1-N-butyldimethylimidazolium chloride ([C4dmim]+Cl−) and 1-N-allyl-2,3-dimethylimidazolium bromide ([Admim]+Br−) were investigated as solvent for the homogeneous acylation and carbanilation of the biopolymer cellulose. Cellulose acetates with a degree of substitution (DS) in the range from 2.5 to 3.0 are accessible within 2 h at 80 °C in a complete homogeneous procedure. The acylation of cellulose with the fatty acid chloride lauroyl chloride leads to cellulose laurates with DS from 0.34 to 1.54. The reaction starts homogeneously and continues heterogeneously. The synthesis of cellulose carbanilates succeeds in the ionic liquid [C4mim]+Cl− without any catalyst. The new homogeneous path gives pure cellulose carbanilates. All reactions are carried out under mild conditions, low excess of reagent and a short reaction time. The reaction media applied can be easily recycled and reused.

Local structure of condensed zinc oxide

The high-pressure local structure of zinc oxide has been studied at room temperature using combined energy-dispersive x-ray-diffraction and x-ray-absorption spectroscopy experiments. The structural parameter u and the lattice-parameter ratio $c/a$ of the wurtzite phase is given as a function of pressure and compared with results from ab initio calculations based on a plane-wave pseudopotential method within the density-functional theory. It is shown that an accurate study of ZnO requires the explicit treatment of the d electrons of Zn as valence electrons. In good agreement with present calculations, our experimental data do not show any variation of $u(P)$ in the low-pressure wurtzite phase between 0 and 9 GPa, pressure at which the phase transition to the rocksalt phase occurs. Moreover, no dramatic modification of the r-phase K-edge position up to $\ensuremath{\sim}20\mathrm{GPa}$ is observed, indicating the absence of metallization. In view of all these results, theoretical models identifying the wurtzite-to-rocksalt transition as an homogeneous path are discussed.

PREDICTION OF SELF-ABSORPTION IN OPPOSED FLOW DIFFUSION AND PARTIALLY PREMIXED FLAMES USING A WEIGHTED SUM OF GRAY GASES MODEL (WSGGM)-BASED SPECTRAL MODEL

A weighted sum of gray gases model (WSGGM)-based low-resolution spectral model for calculating radiation transfer in combustion gases is applied to estimate self-absorption of radiation energy in one-dimensional opposed-flow flames. Development of such a model is necessary in order to enable detailed chemistry-radiation interaction calculations including self-absorption. A database of band model parameters which can be applied to various one-dimensional opposed-flow diffusion and partially premixed flames is created. This in-situ flame property-based database is necessary for the application of the WSGGM to real flames, since previously developed databases were only for homogeneous and isothermal radiation paths. For the validation of the model and database, low-resolution spectral intensities leaving the flat flame in a direction normal to the fuel exit plane are calculated and compared with the results of a narrow-band model based on the Curtis-Godson approximation. Good agreement has been found between them. The resulting radiation model is coupled to the OPPDIF code to calculate the self-absorption of radiant energy and compared with the results of an optically thin calculation and the results of a discrete ordinates calculation in conjunction with the statistical narrow-band model. Significant self-absorption of radiation is found for the flames considered here, particularly on the fuel side of the reaction zone. However, the self-absorption does not have significant effects on the flame structure in this case. Even in the cases of low-velocity diffusion flame and a partially premixed flame having a low equivalence ratio, the effects of self-absorption of radiation on the flame temperature and the production of minor species are not significant.

Zero actions and energy functions for perfect crystals

We give a combinatorial description of the action of the crystal operators \tilde e_0 , \tilde f_0 on certain perfect crystals of U'_q(C_n^{(1)}) , U'_q(D_n^{(1)}) and U'_q(D_{n+1}^{(2)}) , by means of Dynkin diagram automorphisms and Schensted column insertion. Also, for certain level 1 perfect crystals of these algebras we give a definition of a combinatorial “charge” related to the energy function on homogeneous paths in such crystals.

Source prebiasing for improved second harmonic bubble-response imaging

The use of the second harmonic bandwidth in order to improve the contrast enhancement of vascular space provided by microbubble echo contrast is well established. A significant obstacle to improving on the contrast advantage of the second harmonic bandwidth arises from the linear response of tissue to the finite amplitude distortion produced second harmonic in the beam. A scheme in which the source wave contains a second harmonic component designed to cancel out the second harmonic produced by finite amplitude distortion in the focal region was computationally investigated. This prebiasing scheme was found to offer significant reductions in the amplitude of the second harmonic in the focal region. These reductions were found in both the homogeneous tissue path case and in the inhomogeneous tissue path case. The resulting clinical potential of source prebiasing is discussed. Also, it was observed that the inhomogeneous focusing of the finite amplitude distortion-produced second harmonic was significantly better than that of a same frequency fundamental with an identical homogeneous path focal profile.

Homogeneous reonomic contact transformations and path reparametrization in functional integrals with respect to quasimeasures

Homogeneous reonomic contact transformations and path reparametrizations in functional integrals with respect to quasimeasures are considered for linear fourth-order parabolic differential equations with coefficients explicitly depending on time. An integral relation between the Green’s functions is found for fourth-order differential equations that correspond to each other. In a special case, the differential operator of the transformed equation coincides with the Bol conformally covariant operator, which is well known in exactly integrable and conformal models.