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The injection of fully developed turbulent heated air from a tube into a cooler turbulent duct flow is examined as a analogy to film-cooled turbine blades. An implicit large-eddy simulation numeric...

International audience; Probability density function methods for characterizing various fluctuating quantities in the reacting gas phase of turbulent spray flames are presented, for the development of which E.E. O'Brien has been a pioneer. Balance equations for two-phase flows considered as a piecewise continuous medium are first presented, with the interface conditions containing the vaporization-condensation equilibrium. From these, the equation for the joint probability density function of temperature and composition in the gas phase is derived, in which specific terms related to vaporization are identified. The terms needing modeling are then highlighted. The first one is the classical micromixing term, which has to include all the features already discussed for single phase reacting flows, but adaptation to two phase flow has to be questioned. And, mainly, several unclosed terms are dealing with vaporization, needing a specific attention. It is shown that proposals for their modeling can be obtained on the same bases as in the socalled Eulerian-Lagrangian models, which will directly induce changes of the shape of the probability density function. We finally discuss the model presented herein and comment its connection with recently published literature for this subject. Specific attention is devoted to the combustion regimes and to the presence of diffusion flamelets surrounding fuel droplets or groups of droplets. The proposals presented here go one step further compared to the recent studies, and they have now to be compared with well defined experiments, numerical experiments with direct numerical simulations or real experiments in conveniently controlled conditions.

Major surgery is associated with intraoperative and postoperative bleeding, generally treated with homologous blood transfusions, which carry the risk of infection, allergic reactions, or incompatibility as well as a number of organizational and economic problems. Transfusion strategies and steps to minimize perioperative bleeding are needed. Another resource is drugs; human recombinant erythropoietin, aprotinin, and some analogues of lysine have been used to reduce the rate of allogenic transfusions in the perioperative period. The safest method is autologous blood transfusions through predeposits and hemodilution; however, it can only be used for elective surgery. Autologous transfusion techniques include blood collection, both intraoperatively, as described by Orr, and postoperatively, as introduced by Borghi in 1984, which enables the continuous monitoring of postoperative bleeding. Blood collection can also be performed during emergency surgery, reducing the rate and costs of homologous transfusions.

A theoretical analysis for the evaluation of the probability of error occurring in resampling a noise-like band-limited Gaussian signal with flat power spectrum available through its digitized samples, is presented. The analysis assumes the use of an ideal sine-based interpolation algorithm for the digitized signal reconstruction, which is proved to be optimum for the considered class of signals and quantization functions. The particular case of lowest order, i.e., 1 bit, quantization function, is fully treated in analytical terms and a theoretical prediction for the error probability is derived. Validation of the presented analysis is made through a comparison with numerical simulations.

A transport equation for scalar flux in turbulent premixed flames was modelled on the basis of DNS databases. Fully developed turbulent premixed flames were obtained for three different density ratios of flames with a single-step irreversible reaction, while the turbulent intensity was comparable to the laminar burning velocity. These DNS databases showed that the countergradient diffusion was dominant in the flame region. Analyses of the Favre-averaged transport equation for turbulent scalar flux proved that the pressure related terms and the velocity–reaction rate correlation term played important roles on the countergradient diffusion, while the mean velocity gradient term, the mean progress variable gradient term and dissipation terms suppressed it. Based on these analyses, modelling of the combustion-related terms was discussed. The mean pressure gradient term and the fluctuating pressure term were modelled by scaling, and these models were in good agreement with DNS databases. The dissipation terms ...

This work deals with the numerical simulation on an unstructured mesh of the ignition and burning in an oxidizing atmosphere of a fuel droplet heated on one side. This is relevant for studying the ignition of droplets in a spray when they are crossing a flame zone stabilized in it. The droplet here is replaced by a porous cylinder, and the flame by a hot solid wall. The reaction is assumed to be described by a single step, A + νB → P. The cell-centred finite volume scheme considered here uses a generalized Roe's approximate Riemann solver with the monotonic upwind scheme for conservative laws (MUSCL) technique for the convective part and Green–Gauss type interpolation for the viscous part. The thinness of the reaction zone is taken into account by using an adaptive refinement–unrefinement procedure. It has been found that the process of droplet ignition takes place by means of a propagation of a triple flame around the ‘droplet’ when the chemical reaction is sufficiently fast with respect to the molecular...

This publication represents one of the components of Mutual Heritage, a project that is part of the Euro-Mediterranean Euromed Heritage 4 programme and which aims to extend the base of proactive stakeholders on issues concerning heritage in the Mediterranean area. One of the possible strategies to reach this objective, is to facilitate the involvement of players who have the impression that they are less concerned in these issues and to help them to become active agents of the new, complex and modern dynamics around the enhancement of architectural heritage. This practical handbook provides information as added value for existing buildings and sites. It will help a number of potential players in the domain of heritage tourism to become proactive agents who will rise to the challenge of enhancing heritage - a sphere of activity that engenders cultural and economic growth.

Turbulent combustion within sprays has been studied. Experiment and theory predict that the presence of fuel droplets leads to an increase in the fluctuations of temperature and equivalence ratio, and that these fluctuations must be considered to correctly estimate the mean reaction rate. A convenient way to describe the fluctuations of the medium is to compute the probability density function of all the fluctuating variables for the gas and liquid phases. The method used to derive the probability density function (PDF) equations in a pure gaseous medium was extended to two-phase flows by using the local equations written in terms of distribution functions. The PDF for the liquid phase contained complex unclosed terms representing dispersion and atomization. Instead of modeling these terms, we have used a stochastic Lagrangian simulation of the liquid droplets which employs classical atomization models and assumes spherical droplets. This method is used to close the vaporization terms which appear in the PDF equation for the gas. The PDF equation for the gas-phase could be solved by using a Monte-Carlo method but here we have used a more tractable model based on a presumed PDF shape for the mixture fraction. The effects of finite rate chemistry were taken into account by using the MIL model. Finally, the complete model was used to simulate auto-ignition and the establishment of a flame in a diesel type experiment. The auto-ignition delay and the shape of the flame were well simulated. The importance of taking into account the influence of the droplets on the fluctuations is demonstrated by testing the model with and without the corresponding terms.

A turbulent combustion model based an the probability density function (PDF) approach has been extended for the spray combustion computations under simulated diesel engine conditions. This approach accounts for the effects of turbulence and of random dynamics of evaporating droplets on the mean rate of chemistry. The paper begins with formulation of the equation for the joint PDF for the gaseous mixture variables where evaporating droplets are viewed as point sources. Then the modified micromixing model that involves evaporation process is described and details of a Monte-Carlo modeling of PDF-equation are given. After that, the results of numerical studies dealing with diesel spray combustion are discussed. Three different examples are considered. First, the computations of the evaporating spray injected into heated nitrogen atmosphere are carried out. The contribution of evaporating droplets dynamics to the mean and variance distributions of temperature and vapor concentration is demonstrated. Next, the...

A recently proposed algorithm for the determination of the modal power distribution inside a stable multimode laser cavity is applied to the case of a flat-topped transverse intensity beam profile. We show that such a technique leads to closed-form expressions for the modal weights and for the M/sup 2/ factor of the output beam. Comparisons with experimental results present in literature are also reported.

The principle of a sample model for atomisation and vaporisation in two-phase flows is developed and presented. It is based on use of two quantities which are the average liquid mass fraction and the average area of the gas-liquid interface, both taken per unit mass of two-phase media. This model can easily be used in combustion modelling when the chemistry is very fast that is when the atomisation, vaporisation and the micro-scale turbulent mixing are the controlling phenomena. The practical use of this model needs the values of a few constants which are determined from the comparison with the experiments.

The modelling of micromixing in premixed turbulent combustion is reviewed for a moderately fast chemistry and existing probabilistic closures for small scale mixing term are presented, discussed and tested. The numerical study is made on a statistically homogeneous and isotropic decaying turbulent premixed medium where, at initial time, pockets of burnt gases are randomly placed, to initiate the reaction. The comparisons between closure models using the probability density function and the direct numerical simulation for turbulent combustion were performed to assess the sensibility and prediction capabilities of these models; in particular, the binomial model of Dopazo and Valin¯o, compared to other tested models, yields a good quantitative as well as qualitative behavior. More interestingly, the study has shown that the classical assumption that the micromixing time scale is proportional to the turbulence integral time scale was not at all convenient in the investigated case. This suggest that a...

The structure of dialkoxy disulfides ROSSOR has been established by single-crystal X-ray diffraction of 1, ArCH2OSSOCH2Ar (Ar = 4-nitrophenyl). The gauche conformation (OSSO dihedral angle = 85.4°) observed in the solid state entails the existence of M and P enantiomers that were actually detected in solution, in the case of MeOSSOMe, t-BuOSSOBu-t, and t-BuOSSOMe (3, 4, 5, respectively), by means of NMR spectroscopy in a chiral environment. The activation parameters (ΔG⧧, ΔH⧧, and ΔS⧧) for the stereomutation of this type of enantiomers, brought about by the S−S bond rotation at high temperature (50−110 °C), were measured by computer line shape simulation of the dynamic NMR spectra of appropriate derivatives bearing alkyl substituents with potentially diastereotopic geminal groups. The free energies of activation for such a process (18−19 kcal mol-1, depending on the compound) were found to be much higher than for the corresponding disulfides (RSSR), owing to the larger S−S double-bond character, as indica...

A quasi-automatic quantitative analysis of electro-optic holography images is proposed. The phase information is extracted by means of the Fourier transform method. The phase map is unwrapped by an algorithm based on no-path-following scheme and fast cosine transform. On propose une analyse quantitative quasi-automatique d'images d'holographie electro-optique. L'information de phase est extraite par une methode de transformation de Fourier. La carte de phase est racolle grâce a un algorithme base sur un schema iteratif et une transformee en cosinus rapide.

An analysis of a quasi-optical launcher of lower hybrid plasma waves powered by an incident Gaussian beam is performed. This study, based on the solution for the scattering by an array of conducting cylinders with parallel axes close and parallel to a plane interface, is presented together with numerical results. An experimental configuration that gives high values of the coupled power is proposed.

A simple two-equation model is proposed for soot formation and oxidation. It is based on measurements of the maximum soot volume fraction, experimentally observed in all premixed hydrocarbon-air laminar flames, and depends on the fuel composition. The model is validated on laminar diffusion flames, and then introduced in an Eulerian-Lagrangian approach to predict turbulent flames. The proposed set of constants has been adapted to ethylene-air atmospheric flames, although the newly developed approach may be applied to any hydrocarbon-air diffusion flame. The major parameters have been tested and the present study emphasizes the effects of turbulent fluctuations on the soot yield. The comparison of the computed results and experimental published data shows good agreement with the predictive trends provided.

Gas Electron Multiplier based detectors have been recently used for neutron measurement at spallation sources and for fusion relevant applications. The present work is meant to characterize the detector sensitivity to γ-ray background which often can represent the main background source associated to neutron measurements. The γ-ray sensitivity has been measured as a function of detector gain and it has been found to be lower than 10 -7at the typical gain used for neutrons detection. Coincidence measurements, giving the possibility to select mono-energetic photons and to suppress background events, allowed to measure the absolute sensitivity at a well defined γ-ray energy and at low interaction rates. The mechanism of interaction and energy deposition of γ-rays in the detector has been studied using MCNPX Monte Carlo simulations.© 2013 IOP Publishing Ltd and Sissa Medialab srl

BACKGROUND: Chronic low back pain (LBP) and sciatica can occur without obvious structural causes and are often resistant to conventional analgesic drugs. The effect of periradicular injection of meloxicam on LBP with or without a radicular component was assessed. A secondary objective of this prospective observational study was to assess the effect of meloxicam on functional recovery. METHODS: Seventy-two patients (30 men, 42 women) with LBP and/or sciatica were followed for 90 days to six years after injecting 10 mg meloxicam in 10 mL saline at each of the involved dermatomal levels. A standard verbal rating scale (VRS) from 0=no pain to 10=severe pain was used for assessing LBP before the injection of meloxicam (at baseline) and at 1, 5, 10, 30 and 60 min, and 1, 5, 15, 30 and 90 days intervals after the injection. The meloxicam injection was repeated only if the VRS score remained >3. Rescue analgesic requirements and functional activity levels were also assessed from 30-90 days after the last injection of meloxicam. RESULTS: The mean baseline LBP score was 8.60 ± 1.50 (SD) despite the use of multi-modal analgesic regimens (NSAIDs, glucocorticosteroids, paracetamol, oral opioids, gabapentanoid compounds, epidural or periradicular steroid and/or local anesthetics) as well as laser treatments and physical therapy. The majority of patients reported that their pain intensity decreased by ~50% 1-2 min after the meloxicam injection was completed. Thirty-six patients (50%) required no further injections, 25 patients (35%) required a second injection after seven days, and 11 patients (15%) required a total of three injections. After the meloxicam treatment(s), only 10 patients (14%) required "rescue" analgesia with oral NSAIDs. All patients were able to increase their level of functional activity after the meloxicam treatment(s). CONCLUSION: Periradicular injections of meloxicam (10 mg) appear to be a useful alternative to opioid and non-opiod analgesics for patients with intractable LBP due to nerve root inflammation.

The addition of several photochemically generated aryl and fluoroalkyl radicals to fullerene C70 was studied by electron spin resonance and the results were compared with those obtained with C60. While simple alkyl radicals afford only three of the five expected RC70• regioisomers, the more reactive aryl and fluoroalkyl radicals give rise to four, except for the trifluoromethyl radical which yielded for the first time the ESR spectra of all five expected isomers. Semiempirical MO calculations and density functional theory calculations were carried out for HC60• and for the five HC70• regioisomers as models for the corresponding alkyl, aryl, and fluoroalkyl analogs in order to describe the unpaired electron distribution in these radical species and as an aid in the assignment of the observed spectra to specific RC70• regioisomers.

Photolysis of dialkoxy disulfides ROSSOR (R = Me, Et, i-Pr, t-Bu, i-PrCH2, t-BuCH2) yields the radicals RO•, ROS•, and ROS•O that were identified on the basis of product analysis and spin trapping techniques. It has been shown that only the alkoxy radicals RO•, produced from ROSSOR, add to the sphere of fullerene C60 in steady state conditions to yield the RO−C60• adducts which can be detected by ESR spectroscopy. The different trend of the hydrogen splitting constants in the RO−C60• with respect to the corresponding RS−C60• adducts previously reported has been interpreted as a consequence of the different C−O and C−S bond lengths.

The addition of several photochemically generated organic radicals (H[sup [sm bullet]], CH[sub 3][sup [sm bullet]], C[sub 6]H[sub 5][sup [sm bullet]], CF[sub 3][sup [sm bullet]], and C[sub 2]F[sub 5][sup [sm bullet]]) to ellipsoidal C[sub 70] was studied by electron spin resonance. Three of the five possible isomers of RC[sub 70] were detected with R = H, CH[sub 3] and four with R = C[sub 6]H[sub 5], CF[sub 3], C[sub 2]F[sub 5]. Arguments based on relative abundances and on comparisons of hyperfine interactions and g factors of the RC[sub 70] isomers and of their C[sub 60] analogs allowed to place the isomers in homologous series and to identify the sites of radical addition on the C[sub 70] surface leading to each isomer. 30 refs., 4 figs., 1 tab.

The ignition of a droplet simulated as a porous cylindrical wall is addressed numerically. This ‘model droplet’ is located in a constant volume chamber, in the vicinity of a heated planar wall. Despite the restrictive assumptions that are made on the chemical process, the flow around the droplet, strongly influenced by the heat release, is rigorously computed by means of the full Navier-Stokes equations. The transient of the phenomenon is captured and the numerical method based on a nine points upwind differencing scheme, is proved to be relevant for this physical problem.

The present study is a new step in the development of a lagrangian turbulent combustion model devotedto the prediction of non-premixed flames in which kinetic effects occur. Taking into account, in a refined manner, the interaction between chemical reaction and turbulence, the model includes a spectrum of turbulent timescales instead of a single mean timescale. The more recent improvement of the model consists in including a library of chemical delay times derived from a six-step reduced reaction mechanism for methane-air combustion, which is valid over a wide range of equivalence ratio. The predictions of the combustion model in which the library was implemented were compared with experimental data on turbulent jet diffusion flames near extinction. These calculations were performed with a finite volume technique devoted to variable density Navier-Stokes equations. A standard two-equations turbulence model was used and provided reliable results for dynamic variables (mean velocity and kinetic energy of turbulence). Comparisons between computed and measured mean mixture fraction and mixture fraction root mean square (rms) are quite satisfactory, proving that scalar transport is correctly modeled. The more salient point is the prediction of partial extinction and reignition phenomena, in agreement with experiments. This result clearly demonstrates the ability of the turbulent combustion model to simulate the interaction between turbulence and chemical reactions, which occurs in flames displaying kinetic effects.

The addition of several photochemically generated aryl and fluoroalkyl radicals to fullerene C70 was studied by electron spin resonance and the results were compared with those obtained with C60. While simple alkyl radicals afford only three of the five expected RC70• regioisomers, the more reactive aryl and fluoroalkyl radicals give rise to four, except for the trifluoromethyl radical which yielded for the first time the ESR spectra of all five expected isomers. Semiempirical MO calculations and density functional theory calculations were carried out for HC60• and for the five HC70• regioisomers as models for the corresponding alkyl, aryl, and fluoroalkyl analogs in order to describe the unpaired electron distribution in these radical species and as an aid in the assignment of the observed spectra to specific RC70• regioisomers.

The combustion of dense sprays of droplets mixed with a gaseous reactant is studied by means of a numerical simulation. The simulation algorithm is similar to a “cellular automaton,” and involves models for the interaction of diffusion flamelets in the vicinity of droplets and for the ignition of these flamelets by heat from already burning droplets. The realism of the elementary models has been checked, qualitatively and quantitatively, with existing experiments. The results of the simulation show the importance of the interactions between droplets, which depend on the parameter nr F 1/2 (where r F is the radius of the flame around a single droplet whose diameter is the mean “mass-weighted” diameter and n the number of droplets per unit of surface of the two-dimensional spray). The depletion of gaseous reactant by the combustion itself, which influences r F , is also a phenomenon that modifies strongly the mean consumption rate. The ignition of flamelets around droplets or groups of droplets allows for the increase of the consumption rate from the initial state and is influenced by the mean temperature of the gas. This simulation can give mean consumption rates of the droplets in the case of statistically homogeneous combustion; it could give mean “flame” propagation and mean “flame thickness” in the case of a propagating combustion zone.

The exact closed-form expression of the eigenmodes of a closed waveguide resonator terminated with small-curvature cylindrical mirrors is presented. The results obtained are compared with those recently obtained through the use of the WKB approximation. Plots of the spatial structure of the transverse modes inside the resonator are also shown.

The prediction of turbulent combustion is classically performed by numerical integration of “modeled” equations. For each existing approach, a crucial quantity is a time scale for the destruction of temperature (or concentration) fluctuations. Usually, this time scale is simply taken as proportional to the corresponding time scale for velocity fluctuations, but the question of the influence of the reaction on this scale arises, and has already been discussed. We discuss here this point in the particular case of wrinkled premixed flames. Algebraic closure formulas, as well as closures based on the so-called ϵy equation, or on the equation for the flame surface by unit of volume of Marble and Broadwell, are proposed and discussed. It is found, in particular, that in the case of wrinkled flames with infinite Damkohler and Reynolds numbers the reaction does not play any direct role on the time scale.

The universal gadget recently proposed by Simon and Mukunda to synthesize any non-absorbing optical element acting on the polarization of a wave is explained by elementary means. This different approach also leads to alternative synthesis procedures. Le gadget universel, propose recemment par Simon et Mukunda pour synthetiser chaque element optique pas-absorbent qui agit sur la polarisation d'une onde, est explique par des moyens elementaires. Cette differente approche conduit aussi a des procedes alternatifs de synthese.

The authors report ESR studies of three regioisomers of the MeS-C{sub 70}{center_dot} adduct formed by photolysis. A 1:3:3:1 splitting pattern was observed for each regioisomer. A methoxy adduct of C{sub 70} was formed by photolysis of di-tert butyl peroxide in the presence of C{sub 70}, but the ESR spectra were too complicated for interpretation. Photolysis of MeOSSOMe generates an MeO{center_dot} radical which adds to C{sub 60} forming MeO-C{sub 60}{center_dot} which was studied by ESR spectrometry. 11 refs., 3 figs., 1 tab.

A new model for Diesel injection is developed in order to be able to predict the break-up of the liquid core and the evolution of the dense spray. The formulation is based on a set of equations representing the liquid/gas mixture evolution in the Diesel combustion chamber. A generalized turbulence model is applied due to the high density ratio mixture. For the break-up part of the model, a new equation for the surface density of liquid is derived. A switch is used to go back to the usual Lagrangian formulation when the spray is diluted. The goal of this study is to show the need for such a model and to present the mathematical formulation, of which the first is used in a 3D industrial code such as KIVA [2].

A 3D Eulerian model has been developed to improve the primary break-up of an atomizing jet. The model is divided in three parts and is implemented in a modified version of KIVA II. The first part focuses mainly on the liquid dispersion, the second on the atomizing process itself, and the third on the adaptation of the model's mathematical formulation to the physics of the flow. Since the spray close to the injector is dense, an Eulerian formulation is thus chosen. However, when the spray is diluted, a Lagrangian formulation should then be applied. Different computations have been carried out using this new model and will be thoroughly discussed in this paper. The first calculation serves as a validation of the model. Those which follow demonstrate the importance of the internal liquid flow inside the injector on the spray development. They also manifest an influence of the air-co-flow, which assists the atomization of the spray. Last but not least, we observe the appropriate trends from the model when the pressure is increased inside the combustion chamber. The ensemble of these calculations displays the principal advantage of such a model, which enables us to follow the development of the spray upon entry into the combustion chamber, in other words, during the entire atomization process- both the primary break-up and after the secondary break-up. Beyond this point, no more initial cone angle nor initial droplet size distribution are further mandatory.