Modeling evaporation effects in conditional moment closure for spray autoignition

Simulations of an n-heptane spray autoigniting under conditions relevant to a diesel engine are performed using two-dimensional, first-order conditional moment closure (CMC) with full treatment of spray terms in the mixture fraction variance and CMC equations. The conditional evaporation term in the CMC equations is closed assuming interphase exchange to occur at the droplet saturation mixture fraction values only. Modeling of the unclosed terms in the mixture fraction variance equation is done accordingly. Comparison with experimental data for a range of ambient oxygen concentrations shows that the ignition delay is overpredicted. The trend of increasing ignition delay with decreasing oxygen concentration, however, is correctly captured. Good agreement is found between the computed and measured flame lift-off height for all conditions investigated. Analysis of source terms in the CMC temperature equation reveals that a convective–reactive balance sets in at the flame base, with spatial diffusion terms being important, but not as important as in lifted jet flames in cold air. Inclusion of droplet terms in the governing equations is found to affect the mixture fraction variance field in the region where evaporation is the strongest, and to slightly increase the ignition delay time due to the cooling associated with the evaporation. Both flame propagation and stabilization mechanisms, however, remain unaffected.     

Poly(caprolactone‐co‐lactide)/perfluoropolyether block copolymers: Synthesis,thermal, and surface characterization

Poly[(caprolactone‐co‐lactide)‐b‐perfluoropolyether‐b‐(caprolactone‐co‐lactide)] copolymers (TXCLLA) were prepared by ring‐opening polymerization of D ,L ‐dilactide (LA2) and caprolactone (CL) in the presence of α,ω‐hydroxy terminated perfluoropolyether (Fomblin Z‐DOL TX) as macroinitiator and tin(II) 2‐ethylexanoate as catalyst. ¹H NMR analysis showed that LA2 is initially incorporated into the copolymer preferentially with respect to CL. A blocky structure of the polyester segment was also indicated by the sequence distribution analysis of the monomeric units. Differential scanning calorimetry analysis showed the compatibility between poly(lactide) (PLA) and poly(caprolactone) (PCL) blocks inside the amorphous phase with glass‐transition temperature values increasing from ?60 to ?15 °C by increasing the PLA content. Copolymers with high average length of CL blocks were semicrystalline with a melting temperature ranging from +35 to +47 °C. Surface analysis showed a high surface activity of TXCLLA copolymers with values of surface tension independent from the PLA/PCL content and very close to those of pure TX. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3588–3599, 2005     

Cooperative Behavior of Kinetically Constrained Lattice Gas Models of Glassy Dynamics

Kinetically constrained lattice models of glasses introduced by Kob and Andersen (KA) are analyzed. It is proved that only two behaviors are possible on hypercubic lattices: either ergodicity at all densities or trivial non-ergodicity, depending on the constraint parameter and the dimensionality. But in the ergodic cases, the dynamics is shown to be intrinsically cooperative at high densities giving rise to glassy dynamics as observed in simulations. The cooperativity is characterized by two length scales whose behavior controls finite-size effects: these are essential for interpreting simulations. In contrast to hypercubic lattices, on Bethe lattices KA models undergo a dynamical (jamming) phase transition at a critical density: this is characterized by diverging time and length scales and a discontinuous jump in the long-time limit of the density autocorrelation function. By analyzing generalized Bethe lattices (with loops) that interpolate between hypercubic lattices and standard Bethe lattices, the crossover between the dynamical transition that exists on these lattices and its absence in the hypercubic lattice limit is explored. Contact with earlier results are made via analysis of the related Fredrickson--Andersen models, followed by brief discussions of universality, of other approaches to glass transitions, and of some issues relevant for experiments.     

Large time behaviour of solutions to Penrose–Fife phase change models

A non‐conserved phase transition model of Penrose–Fife type is considered where Dirichlet boundary conditions for the temperature are taken. A sketch of the proof of existence and uniqueness of the solution is given. Then, the large time behaviour of such a solution is studied. By using the Simon–?ojasiewicz inequality it is shown that the whole solution trajectory converges to a single stationary state. Due to the non‐coercive character of the energy functional, the main difficulty in the proof is to control the large values of the temperature. This is achieved by means of non‐standard a priori estimates. Copyright © 2005 John Wiley & Sons, Ltd.     

High-order Levi curvatures and classification results

In this paper we write some differential formulas involving the high-order Levi curvatures of a real hypersurface in a complex space form. As application we get a classification result under suitable assumptions.     

Determination of volatile organic compounds in the dried leaves of Salvia species by solid-phase microextraction coupled to gas chromatography mass spectrometry

Salvia spp. are used throughout the world both for food and pharmaceutical purposes. In this study, a method involving headspace solid-phase microextraction combined with gas chromatography–mass spectrometry was developed, to establish the volatiles profile of dried leaves of four Iranian Salvia spp.: Salvia officinalis L., Salvia leriifolia Benth, Salvia macrosiphon Boiss. and two ecotypes of Salvia reuterana Boiss. A total of 95 volatiles were identified from the dried leaves of the five selected samples. Specifically, α-thujone was the main component of S. officinalis L. and S. macrosiphon Boiss. (34.40 and 17.84%, respectively) dried leaves, S. leriifolia Benth was dominated by β-pinene (27.03%), whereas α-terpinene was the major constituent of the two ecotypes of S. reuterana Boiss. (21.67 and 13.84%, respectively). These results suggested that the proposed method can be considered as a reliable technique for isolating volatiles from aromatic plants, and for plant differentiation based on the volatile metabolomic profile.     

Post-buckling behaviour of graphite/epoxy stiffened panels with initial imperfections subjected to eccentric biaxial compression loading

The post-buckling behaviour of anisotropic stiffened panels with initial imperfections is investigated. Since buckling of the skin between the stiffeners often occurs first, a non-linear analysis is developed for symmetric panels under biaxial compression in order to obtain the out-of-plane panel deflection in the post-buckling range. The non-linear differential equations are expressed in terms of the out-of-plane displacement and the Airy function. They are solved with the Galerkin method for various boundary conditions by imposing an edge displacement control. The theoretical and experimental results obtained by the present analysis show that the transverse load can greatly influence the buckling loads and halfwave number. Since no experimental results have been found in the literature, several tests have been carried out on graphite/epoxy blade stiffened panels 900 mm long and 620 mm wide applying simultaneously biaxial compression loads with several combined ratios. An eccentricity results between longitudinal and transverse load, because the longitudinal compression is applied along the centroidal axes of the stiffened section while the transverse compression is applied to the skin panel. The correlation between the experimental and analytical results has been quite good; the experimental results demonstrate the influence of eccentricity of the transverse load on panel deflection in the pre- and post-buckling range.     

A Modular Synthesis of Modified Phosphoanhydrides

Phosphoanhydrides (P‐anhydrides) are ubiquitously occurring modifications in nature. Nucleotides and their conjugates, for example, are among the most important building blocks and signaling molecules in cell biology. To study and manipulate their biological functions, a diverse range of analogues have been developed. Phosphate‐modified analogues have been successfully applied to study proteins that depend on these abundant cellular building blocks, but very often both the preparation and purification of these molecules are challenging. This study discloses a general access to P‐anhydrides, including different nucleotide probes, that greatly facilitates their preparation and isolation. The convenient and scalable synthesis of, for example, ¹⁸O labeled nucleoside triphosphates holds promise for future applications in phosphoproteomics.     

Creep damage and rupture in AISI 310 austenitic steel

Summary We recall two approaches for dealing with creep damage in metals: the metallurgical — one which consists in measuring creep cavitation and the phenomenological — one with Kachanov's damage laws.For the first type we refer papers which deal particularly with the measure of density variation in order to compair them with the results of the present work where this technique is applied to AISI 310 steel. A wide statistical analysis, which consists in using Fisher's function and which is applied to damage laws with different numbers of indipendent variables, points out that strain is the variable which density variation strictly depends on for AISI 310 steel in the employed test conditions.We obtain the connection between tension stresses and creep rupture times by the density variation law and the constitutive law compairing it with experimental results.At the end we compair our results with Kachanov's law in order to prove that density variation is equal to damage factor for the steel which here we deal with and to compute Kachanov's rupture parameters.

---

Sommario Si richiamano i due modi di affrontare il problema del danneggiamento a scorrimento viscoso dei materiali metallici: quello di tipo metallurgico che consiste nella misura della cavitazione e quello fenomenologico ingegneristico con leggi di danno del tipo di quella del Kachanov.Per il primo tipo si sono ricercati i lavori che trattano in particolare della misura di variazione di densità per confrontarli con i risultati di questa nota in cui la tecnica è stata applicata all'acciaio tipo AISI 310. Un'ampia indagine statistica che consiste nell'uso della funzione del Fisher e che è svolta su leggi di danno con differente numero di variabili indipendenti rileva che, per l'acciaio qui considerato, la variazione di densità dipende in modo molto stretto dalla deformazione.Si determinano il legame carichi tempi di rottura a trazione per lo scorrimento viscoso per mezzo della legge di variazione di densità e la legge costitutiva confrontandoli con i risultati sperimentali.Si confrontano infine i risultati con la legge del Kachanov al fine di provare l'uguaglianza tra la variazione densità ed il fattore di danno per l'acciaio qui considerato e di determinare i valori delle costanti del Kachanov.

---

Research partially supported by C.N.R. grant N. CT 76.00645.07 and M.P.I. research grant (1976) and in the framework of the Nuclear Reactor Safety Program of Ispra.