Littérature scientifique sur le sujet « Fast diffusion line »

This paper develops the notion and properties of the generalized principal eigenvalue for an elliptic system coupling an equation in a plane with one on a line in this plane, together with boundary conditions that express exchanges taking place between the plane and the line. This study is motivated by the reaction–diffusion model introduced by Berestycki, Roquejoffre and Rossi [The influence of a line with fast diffusion on Fisher–KPP propagation, J. Math. Biol. 66(4–5) (2013) 743–766] to describe the effect on biological invasions of networks with fast diffusion imbedded in a field. Here we study the eigenvalue associated with heterogeneous generalizations of this model. In a forthcoming work [Influence of a line with fast diffusion on an ecological niche, preprint (2018)] we show that persistence or extinction of the associated nonlinear evolution equation is fully accounted for by this generalized eigenvalue. A key element in the proofs is a new Harnack inequality that we establish for these systems and which is of independent interest.

Our goal in this work is to explain an unexpected feature of the expanding level sets of the solutions of a system where a half-plane in which reaction-diffusion phenomena occur exchanges mass with a line having a large diffusion of its own. The system was proposed by H. Berestycki, L. Rossi, and the second author as a model of enhancement of biological invasions by a line of fast diffusion. It was observed numerically by A.-C. Coulon that the leading edge of the front, rather than being located on the line, was in the lower half-plane. We explain this behavior for a closely related free boundary problem. We construct travelling waves for this problem, and the analysis of their free boundary near the line confirms the predictions of the numerical simulations.

We propose a new model of accelerating fronts, consisting of one equation with nonlocal diffusion on a line, coupled via the boundary condition with a reaction–diffusion equation in the upper half-plane. The underlying biological question is to understand how transportation networks may enhance biological invasions. We show that the line accelerates the propagation in the direction of the line and enhances the overall propagation in the plane and that the propagation is directed by diffusion on the line, where it is exponentially fast in time. We also describe completely the invasion in the upper half-plane. This work is a nonlocal version of the model introduced in Ref. 15, where the line had a strong but local diffusion described by the classical Laplace operator.

Just after formation, optical fibres are wetted stably with acrylate at capillary numbers routinely exceeding 1000. It is hypothesized that this is possible because of dissolution of air into the liquid coating. A lubrication/boundary integral analysis that includes gas diffusion and solubility is developed. It is applied using conservatively estimated solubility and diffusivity coefficients and solutions are found that are consistent with industry practice and with the hypothesis. The results also agree with the claim of Deneka, Kar & Mensah (1988) that the use of high-solubility gases to bathe a wetting line allows significantly greater wetting speeds. The solutions indicate a maximum speed of wetting which increases with gas solubility and with reduction in wetting-channel diameter.

AbstractWe use ultrafast coherent two-dimensional electronic spectroscopy (2DES) to study the ultrafast spectral diffusion dynamics of colloidal CdSe quantum dots (QDs) and CdSe nanoplatelets (NPLs). The Center Line Slope (CLS) and Nodal Line Slope (NLS) techniques were employed to analyse the 2DES spectra. We show that no spectral diffusion dynamics occurs for the CdSe QDs. On the other hand, spectral diffusion was observed in the CdSe 5 mono-layers NPLs heavy-hole transition. The normalized Frequency Fluctuation Correlation Function (FFCF) of the CdSe NPLs heavy-hole transition was measured to have a major fast decay component at 140 fs.

The main topic of this thesis is the analysis of evolution equations reflecting issues in ecology and population dynamics. In mathematical modelling, the impact of environmental elements and the interaction between species is read into the role of heterogeneity in equations and interactions in coupled systems. In this direction, we investigate three separate problems, each corresponding to a chapter of this thesis. The first problem addresses the evolution of a single population living in a periodic medium with a fast diffusion line; this corresponds to the study of a reaction-diffusion system with equations in different dimensions. We derive results on asymptotic behaviour through the study of some generalised principal eigenvalues. We find that the road has no impact on the survival chances of the population, despite the deleterious effect expected from fragmentation. The second investigation regards a model describing the competition between two populations in a situation of asymmetrically aggressive interactions; this consists of a system of two ODEs. The evolution progresses through two possible scenarios, where only one population survives. Then, the interpretation of one of the parameters as the aggressiveness of the attacker population naturally raises questions of controllability. We characterise the set of initial conditions leading to the victory of the attacker through a suitable (possibly time-dependant) strategy. The third and last part of this thesis analyses the time decay of some evolution equations with classical and fractional time derivatives. Depending on the type of derivative and some degree of non-degeneracy of the spatial operator, quantitative polynomial or exponential estimates are entailed.

Despite significant efforts have been directed toward reducing waste generation and encouraging alternative waste management strategies, landfills still remain the main option for Municipal Solid Waste (MSW) disposal in many countries. Hence, landfills and related impacts on the surroundings are still current issues throughout the world. Actually, the major concerns are related to the potential emissions of leachate and landfill gas into the environment, that pose a threat to public health, surface and groundwater pollution, soil contamination and global warming effects. To ensure environmental protection and enhance landfill sustainability, modern sanitary landfills are equipped with several engineered systems with different functions. For instance, the installation of containment systems, such as bottom liner and multi-layers capping systems, is aimed at reducing leachate seepage and water infiltration into the landfill body as well as gas migration, while eventually mitigating methane emissions through the placement of active oxidation layers (biocovers). Leachate collection and removal systems are designed to minimize water head forming on the bottom section of the landfill and consequent seepages through the liner system. Finally, gas extraction and utilization systems, allow to recover energy from landfill gas while reducing explosion and fire risks associated with methane accumulation, even though much depends on gas collection efficiency achieved in the field (range: 60-90% Spokas et al., 2006; Huitric and Kong, 2006). Hence, impacts on the surrounding environment caused by the polluting substances released from the deposited waste through liquid and gas emissions can be potentially mitigated by a proper design of technical barriers and collection/extraction systems at the landfill site. Nevertheless, the long-term performance of containment systems to limit the landfill emissions is highly uncertain and is strongly dependent on site-specific conditions such as climate, vegetative covers, containment systems, leachate quality and applied stress. Furthermore, the design and operation of leachate collection and treatment systems, of landfill gas extraction and utilization projects, as well as the assessment of appropriate methane reduction strategies (biocovers), require reliable emission forecasts for the assessment of system feasibility and to ensure environmental compliance. To this end, landfill simulation models can represent an useful supporting tool for a better design of leachate/gas collection and treatment systems and can provide valuable information for the evaluation of best options for containment systems depending on their performances under the site-specific conditions. The capability in predicting future emissions levels at a landfill site can also be improved by combining simulation models with field observations at full-scale landfills and/or with experimental studies resembling landfill conditions. Indeed, this kind of data may allow to identify the main parameters and processes governing leachate and gas generation and can provide useful information for model refinement. In view of such need, the present research study was initially addressed to develop a new landfill screening model that, based on simplified mathematical and empirical equations, provides quantitative estimation of leachate and gas production over time, taking into account for site-specific conditions, waste properties and main landfill characteristics and processes. In order to evaluate the applicability of the developed model and the accuracy of emissions forecast, several simulations on four full-scale landfills, currently in operative management stage, were carried out. The results of these case studies showed a good correspondence of leachate estimations with monthly trend observed in the field and revealed that the reliability of model predictions is strongly influenced by the quality of input data. In particular, the initial waste moisture content and the waste compression index, which are usually data not available from a standard characterisation, were identified as the key unknown parameters affecting leachate production. Furthermore, the applicability of the model to closed landfills was evaluated by simulating different alternative capping systems and by comparing the results with those returned by the Hydrological Evaluation of Landfill Performance (HELP), which is the most worldwide used model for comparative analysis of composite liner systems. Despite the simplified approach of the developed model, simulated values of infiltration and leakage rates through the analysed cover systems were in line with those of HELP. However, it should be highlighted that the developed model provides an assessment of leachate and biogas production only from a quantitative point of view. The leachate and biogas composition was indeed not included in the forecast model, as strongly linked to the type of waste that makes the prediction in a screening phase poorly representative of what could be expected in the field. Hence, for a qualitative analysis of leachate and gas emissions over time, a laboratory methodology including different type of lab-scale tests was applied to a particular waste material. Specifically, the research was focused on mechanically biologically treated (MBT) wastes which, after the introduction of the European Landfill Directive 1999/31/EC (European Commission, 1999) that imposes member states to dispose of in landfills only wastes that have been preliminary subjected to treatment, are becoming the main flow waste landfilled in new Italian facilities. However, due to the relatively recent introduction of the MBT plants within the waste management system, very few data on leachate and gas emissions from MBT waste in landfills are available and, hence, the current knowledge mainly results from laboratory studies. Nevertheless, the assessment of the leaching characteristics of MBT materials and the evaluation of how the environmental conditions may affect the heavy metals mobility are still poorly investigated in literature. To gain deeper insight on the fundamental mechanisms governing the constituents release from MBT wastes, several leaching experiments were performed on MBT samples collected from an Italian MBT plant and the experimental results were modelled to obtain information on the long-term leachate emissions. Namely, a combination of experimental leaching tests were performed on fully-characterized MBT waste samples and the effect of different parameters, mainly pH and liquid to solid ratio (L/S,) on the compounds release was investigated by combining pH static-batch test, pH dependent tests and dynamic up-flow column percolation experiments. The obtained results showed that, even though MBT wastes were characterized by relatively high heavy metals content, only a limited amount was actually soluble and thus bioavailable. Furthermore, the information provided by the different tests highlighted the existence of a strong linear correlation between the release pattern of dissolved organic carbon (DOC) and several metals (Co, Cr, Cu, Ni, V, Zn), suggesting that complexation to DOC is the leaching controlling mechanism of these elements. Thus, combining the results of batch and up-flow column percolation tests, partition coefficients between DOC and metals concentration were derived. These data, coupled with a simplified screening model for DOC release, allowed to get a very good prediction of metal release during the experiments and may provide useful indications for the evaluation of long-term emissions from this type of waste in a landfill disposal scenario. In order to complete the study on the MBT waste environmental behaviour, gas emissions from MBT waste were examined by performing different anaerobic tests. The main purpose of this study was to evaluate the potential gas generation capacity of wastes and to assess possible implications on gas generation resulting from the different environmental conditions expected in the field. To this end, anaerobic batch tests were performed at a wide range of water contents (26-43 %w/w up to 75 %w/w on wet weight) and temperatures (from 20-25 °C up to 55 °C) in order to simulate different landfill management options (dry tomb or bioreactor landfills). In nearly all test conditions, a quite long lag-phase was observed (several months) due to the inhibition effects resulting from high concentrations of volatile fatty acids (VFAs) and ammonia that highlighted a poor stability degree of the analysed material. Furthermore, experimental results showed that the initial waste water content is the key factor limiting the anaerobic biological process. Indeed, when the waste moisture was lower than 32 %w/w the methanogenic microbial activity was completely inhibited. Overall, the obtained results indicated that the operative conditions drastically affect the gas generation from MBT waste, in terms of both gas yield and generation rate. This suggests that particular caution should be paid when using the results of lab-scale tests for the evaluation of long-term behaviour expected in the field, where the boundary conditions change continuously and vary significantly depending on the climate, the landfill operative management strategies in place (e.g. leachate recirculation, waste disposal methods), the hydraulic characteristics of buried waste, the presence and type of temporary and final cover systems.

AbstractWhile most of our tissues appear static, in fact, cell motion comprises an important facet of all life forms, whether in single or multicellular organisms. Amoeboid cells navigate their environment seeking nutrients, whereas collectively, streams of cells move past and through evolving tissue in the development of complex organisms. Cell motion is powered by dynamic changes in the structural proteins (actin) that make up the cytoskeleton, and regulated by a circuit of signaling proteins (GTPases) that control the cytoskeleton growth, disassembly, and active contraction. Interesting mathematical questions we have explored include (1) How do GTPases spontaneously redistribute inside a cell? How does this determine the emergent polarization and directed motion of a cell? (2) How does feedback between actin and these regulatory proteins create dynamic spatial patterns (such as waves) in the cell? (3) How do properties of single cells scale up to cell populations and multicellular tissues given interactions (adhesive, mechanical) between cells? Here I survey mathematical models studied in my group to address such questions. We use reaction-diffusion systems to model GTPase spatiotemporal phenomena in both detailed and toy models (for analytic clarity). We simulate single and multiple cells to visualize model predictions and study emergent patterns of behavior. Finally, we work with experimental biologists to address data-driven questions about specific cell types and conditions.

The mobile Internet is a fast-growing technology that provides access to the traditional stationary (fixed-line) Internet from devices connected to mobile communication networks. It is predicted that the convergence between mobile networks and the fixed-line Internet will be a core feature in the next generation network architecture, achieving fast ‘anywhere’ Internet access and global mobility management. Applying a case study approach, this paper reviews the New Zealand mobile Internet market mix, competition, and mobile service provision. The key mobile Internet deployment requirements are determined and analyzed in order to identify a set of mobile Internet critical success factors and to investigate the impact of the shift from fixed-line to mobile and wireless Internet data communication infrastructure.

This article aims to investigate how information-sharing mechanisms in online communities favor activities of ignorance distribution on their platforms, such as fake data, biased beliefs, and inaccurate statements. In brief, the authors claim that online communities provide more ways to connect the users to one another rather than to control the quality of the data they share and receive. This, in turn, diminishes the value of fact-checking mechanisms in online news-consumption. The authors contend that while digital environments can stimulate the interest of groups of students and amateurs in scientific and political topics, the diffusion of false, poor, and un-validated data through digital media contributes to the formation of bubbles of shallow understanding in the digitally informed public. In brief, the present article is a philosophical research that applies the virtual niche construction theory to the cognitive behavior of internet users, as it is described by the current psychological, sociological, and anthropological literature.

This chapter identifies an important inbuilt difference between the two paradigms with respect to innovation diffusion. The difference springs from the fact that, unlike producers, free innovators do not protect their innovations from free adoption, and they do not sell them. As a result, benefits that free-riding adopters may gain are not systematically shared with free innovators—there is no market link between these parties. This chapter thus presents evidence for the systematic shortfall in free innovators' incentives to invest in the diffusion of free innovations, and then argues that it is caused by the absence of a market link between free innovators and free-riding adopters. The chapter then concludes with suggested ways for addressing this situation.

This chapter is an extension of our discussion on transport in chapters 7 to 10. Our goal here is to explore a few aspects of the transport problem which are unique to variably saturated soils. The heterogeneity of soils affects transport of solutes in the vadose zone in different ways. It leads to irregular and hard-to-predict spreading of the solutes. The solutes may be channeled through highly conductive flow channels where diffusion plays only a minor role. This may lead to concentrations which are high and travel times which are fast compared to what one may anticipate by assuming that the medium is homogeneous. Evidence for such behavior was found in field experiments (cf. Wierenga et al., 1991; Ellsworth et al., 1991; Ritsema et al., 1998; Sassner et al., 1994) and in large-scale laboratory experiments (Dagan et al., 1991). Hence, the effects of heterogeneity must be recognized and modeled. The effects of heterogeneity can be modeled by employing the stochastic concepts discussed in earlier chapters. The approach for modeling contaminant transport which is the least restrictive in terms of assumptions introduced is the MC simulation. This approach will be reviewed briefly in section 12.1. Modeling of the mean concentration along our discussion in chapter 8 is computationally less demanding compared to MC simulations, yet is less informative since the concentration in the field can hardly be expected to be equal to its expected value. Applications along that line are limited since deriving the macrodispersion coefficients needed for such an undertaking is difficult. Nonetheless, we shall discussed this approach in section 12.2, for the insight into the transport processes it provides. A few simple models are available for gravitational flow through shallow depths. These methods are of course limited in applications, yet they are less demanding in terms of data requirements and the computational efforts involved. Such methods are the focus of the last section in this chapter. The concept of MC simulation was discussed in earlier chapters.

Clearly, the internet and its applications are pivotal in facilitating the economic activities of nations as well as significantly influencing an individual's work and life. However, the fact is that the internet diffusion rates remain vastly uneven across nations. Why? This chapter attempts to identify some of the key economic, political, cultural, technological, and individual factors that influence the diffusion rates of the internet across the nations of the world. Support for the stated factors is provided by citing existing research studies conducted across many nations. Further, a comprehensive understanding of the factors germane to the diffusion of the internet is essential in formulating and implementing policies that spur the availability and usage of the internet.

Clearly, the Internet and its applications are pivotal in facilitating the economic activities of nations as well as significantly influencing an individual's work and life. However, the fact is, the Internet diffusion rates remain vastly uneven across nations. Why? This paper attempts to identify some of the key economic, political, cultural, technological, and individual factors that influence the diffusion rates of the Internet across the nations of the world. Support for the stated factors is provided by citing existing research studies conducted across many nations. Further, a comprehensive understanding of the factors germane to the diffusion of the Internet is essential in formulating and implementing policies that spur the availability and usage of the Internet.

Imagination is an often-overlooked integral element of human progress, in general, and innovations, in particular. In this chapter, it is argued that the examination of the diffusion and evolution of imaginations and their manifestation as innovations can help to understand the imaginative roots of innovations and to create a responsibly chosen path into a sustainable future. Science fiction as a specific area of manifested imagination is used to show how manifested imaginations influence the social imagination in general and certain individuals like scientists and innovators in particular. It is even used to sell ideas (or make them stick) and give them heritage, again influencing the social imagination. And the accelerated fusion, development, and progress of technologies in the wake of the digitalization is enabling fast and vast diffusion and distribution of imaginations, creating a need to explore, understand, and responsibly utilize imaginations.

Employers want workers to be as healthy as possible, to reduce absenteeism and to boost productivity. The challenge is getting employees to adopt healthy behaviors, a daunting task in our obesogenic society, which promotes a sedentary lifestyle and a diet high in saturated fat, sodium, and sugar. We are seeing an epidemic of obesity and type 2 diabetes, two preventable diseases that impair quality of life and increase healthcare costs. Rogers' Diffusions of Innovations (DOI) theory explains how and why people adopt new behaviors. Rogers observed how some workers were resistant to change. He categorized people according to how long it took them to adopt an innovation. He found that certain attributes were characteristic of early adopters, the opinion leaders that organizations need to win over to facilitate acceptance of an innovation. This chapter explores how DOI theory can be applied to the workplace to promote healthy behaviors.

The QSR (quick service restaurants) industry in the emerging economies such as India is undergoing a wave of disruption and re-engineering. Many global brands in QSR food servicing have resorted to technology and innovation in one or more aspects of their value chain in order to maintain leadership positions in a market that is facing some fast-growing competition from various channels, especially with the penetration that service aggregators like Zomato, Swiggy, and Uber Eats have managed to gain. This study aims to establish a general direction towards which the QSR industry is progressing in India by examining not only the current trends in India but also the trends that are prevalent worldwide and which have the potential of diffusion to emerging economies like India.

Persistent hole burning yields a spectral resolution of the order of the homogeneous linewidth, which, especially in the case of amorphous materials, greatly improved the utility of optical spectroscopy. However, the homogeneous linewidth itself can in general not be measured in a hole-burning experiment, since in virtually all disordered solids the hole width is affected by spectral diffusion [1,2]. The time [3] and temperature [4] dependence of spectral diffusion, on the other hand, can be investigated by fast hole-burning measurements and by thermal cycling, respectively. During a thermal cycle, spectral diffusion gives rise to an additional irreversible inhomogeneous broadening component of a hole spectrum because at a higher excursion temperature more tunneling states or TLS of the glassy matrix are in thermal equilibrium than at the burning temperature. This irreversible broadening yields information on the activation energies of the TLS [4,5].

A calculation of the radiative source term in combustion processes is an important part of the simulation process, because high temperatures are involved and the coupling of radiation to chemistry affects the overall flame characteristics. While relatively simple gas absorption coefficient models have been used in the recent past, it is becoming clearer that more accurate gas models alter the distribution of radiative sources in the flame. To accurately evaluate the radiative losses, it is necessary to use gas models in which the gas absorption coefficient is wavelength dependent. Such analyses can be computationally expensive depending on the particular treatment of the spectral dependence. It is important to understand the relative costs and benefits of different treatment of these effects. In this work, the divergence of the radiative heat flux is calculated for a two-dimensional cylindrical axisymmetric chamber using four different models: a simple gray gas model, the weighted-sum-of-gray-gases (WSGG) model, the spectral line-based weighted-sum-of-gray-gases (SLW) model, and the cumulative wavenumber (CW) model. The gray gas model and the WSGG model are widely used in recent studies and in most commercial software, because they are simple to implement and provide fast results. In general, however, they are not able to accurately predict the radiative losses. On the other hand, the SLW and CW models detail the variations of the absorption coefficient with the wavelength, and can give more accurate answers for the radiative source term, but require bigger computational effort. The divergence of the radiative flux predictions are compared with these four models, using temperature and concentration fields obtained from previous numerical simulations. The overall differences in radiation properties and in the overall cost of computations are detailed.

High temperature diffusion brazing is a very important technology for filling cracks in components from single-crystalline nickel-base superalloys as used in aircraft engines and stationary gas turbines: alloys, which are similar to the base material, are enhanced by a fast diffusing melting-point depressant (MPD) like boron or silicon, which causes solidification by diffusing into the base material. Generally, epitaxial solidification of single-crystalline materials can be achieved by use of conventional braze alloys, however, very long hold times are necessary to provide a complete diffusion of the MPD out of the braze gap. If the temperature is lowered before diffusion is completed, brittle secondary phases precipitate, which serve as nucleation sites for stray grains and, therefore, lead to deteriorating mechanical properties. It was demonstrated in earlier works that nickel-manganese-based braze alloys are appropriate systems for the braze repair of particularly wide gaps in the range of more than 200 μm, which allow a significant shortening of the required hold times. This is caused by the complete solubility of manganese in nickel: epitaxial solidification can be controlled by cooling in addition to diffusion. In this work, it will be shown that the nickel-manganese-based systems can be enhanced by chromium and aluminium, which is with regard to high-temperature applications a very important aspect. Furthermore, it will be demonstrated that silicon, which could be identified as appropriate secondary MPD in recent works, can be replaced by titanium, as this element has additionally a γ′ stabilizing effect. Several braze alloys containing nickel, manganese, chromium, aluminium and titanium will be presented. Previously, the influence of the above mentioned elements on the nickel-manganese-based systems will be visualized by thermodynamic simulations. Afterwards, different compositions in combination with a heat treatment, which is typical for nickel-base superalloys, will be discussed: a microstructure, which is very similar to that within the base material can be presented.

Semiconductor diode lasers represent an important spectroscopic tool for performing high resolution measurements of spectral lines, from which plasma state parameters can be deduced. It is easy to obtain a fast scanning of the emission frequency of the laser so that the kinetics of the plasma can be followed with a high temporal resolution. The plasma that we want to analyse is produced in a mag- netoplasmadynamic (MPD) thruster, which consists of a coaxial cylindrical Lorentz force accelerator. A pulse of Argon (4 gr/sec) of the length of few msec is injected in the thruster and excited by a current pulse, roughly rectangular, with a typical duration of about 1 msec and an intensity of several KA. A diffusion pump keeps the vacuum at a value of the order of 10−5 torr. The experimental apparatus is shown in Fig. 1. The used diode laser was a Mitsubishi ML64114R. Operational wavelength, corresponding to transition starting from metastable level, was chosen by tuning the temperature of the diode through a Peltier module and the injection current. The laser emission frequency was quickly scanned, every 26 µs over the transition line. The laser output was sent into the vacuum chamber using an optical fiber (200 µm of core). The radiation was collimated into a parallel beam of about 1 cm of diameter through the plasma and finally focused on a fast silicon detector. A beamsplitter sent a fraction of the laser radiation into a low pressure, room temperature d.c. discharge in argon, whose transmission was simultaneously recorded and used as a reference. A typical recording is shown in Fig. 2. A sequence of single frequency sweeps, alternatively forwards and backwards, scanning the transmission profiles of the 1s5−2p8 transition (801.479 nm), are simultaneously observed through the plasma (orthogonal to the thruster axis) and a low pressure argon discharge. We extract from the experimental data the frequency dependent optical thickness. The lineshapes were fit to a Gauss, Lorentz, or Voigt profile to infer atomic density, temperature, and velocity. Two types of measurement were carried out in different points and in two directions (orthogonal and transversal). Figure 3 shows atomic density evolution at 12 cm from thruster anode. Further measurements are in progress. Two crossing beams will be used to obtain the bidimensional velocity profile.

This paper presents a numerical methodology and simulation for three-dimensional transonic flow in Safety Relief Valves. Simulation of safety relief valve flows is very challenging due to complex flow paths, high pressure variation, supersonic flow with shock and expansion waves, boundary layers, etc. The 3D unsteady Reynolds averaged Navier-Stokes (URANS) equations with one-equation Spalart-Allmaras turbulence model is used. A fifth order WENO scheme for the inviscid flux and a second order central differencing for the viscous terms are employed to discretize the Navier-Stokes equations. The low diffusion E-CUSP scheme used as the approximate Riemann solver suggested by Zha et al. is utilized with the WENO scheme to evaluate the inviscid fluxes. Implicit time marching method with 2nd order temporal accuracy using Gauss-Seidel line relaxation is employed to achieve a fast convergence rate. Parallel computing is implemented to save wall clock simulation time. The valve flows with air under different inlet pressures and temperatures are successfully simulated for the full geometry with all the fine leakage channels. A 3D mesh topology is generated for the complex geometry. Detailed simulations of air flow are accomplished with inlet gauge pressure 0.5MPa and 2.1MPa. The simulated air mass flow rate agrees excellently with the experimental results with an error of 0.26% for the inlet pressure of 0.5Mpa, and an error of 2.5% for the inlet pressure of 2.1MPa. The shock waves and expansion waves downstream of the orifice are very well resolved.

This paper describes a model used for the prediction of the formation of nitrogen oxides in modifications of an industrial diffusion flame, natural gas fueled can combustor. The flow field inside the modified combustors is calculated using a Navier-Stokes solver. A fast chemistry assumption is used for modeling the heat release. Calculated turbulence parameters are then used for the calculation of the NOx formation rate in the post-processing mode with the aid of a flamelet model. The flamelet model permits the use of detailed kinetics with only minimal computational expense. The dependence of the NOx formation rate on the mixture fraction and scalar dissipation is calculated separately for each given condition. The validation of the model predictions is based on field test data taken earlier on several low NOx modifications recently applied to an industrial, reverse flow can type combustor. The reduced level of NOx emissions was achieved in these modifications by changes in the air distribution within the combustor liner. A comparison of the predicted and measured NOx emission levels shows good potential of the flamelet model.

In this first part of a two part paper, an axisymmetric multi-disciplinary optimization approach for compressors is presented and applied to the design of a three stage booster. The booster has been chosen because its optimization gets little attention in the literature, it has low rotational speed and high curvature, and is also a component with only a few stages to test the capabilities of the approach. Optimization of compressors using a meanline approach have been done in the past, but a mean-line code cannot easily deal with complex curvature effects that are accentuated in a booster. An axisymmetric flow solver with a coupled boundary layer and compressor loss models is used for the aerodynamics, and an axisymmetric disk analysis code is used to generate weight-optimum disks for every rotor. The process is driven by the DAKOTA optimization package available from Sandia Labs. A genetic optimizer is used to create the Pareto front for a multi-objective function that includes efficiency, weight, length and number of airfoils. Following the genetic algorithm, a gradient based algorithm is also used. The design space is specified using physical parameters that completely define the multistage compressor. A booster made of titanium is presented in addition to two design studies. One design study explores using carbon-carbon composites and another design study explores restricting the last stage stator to 10 blades to understand if an integrated strut concept is feasible. Several optimum results along the Pareto front are described, and they are not intuitive. The optimizer has found solutions that have very high reactions in the last stage. The near-wall streamlines at the edge of the boundary layer are used as the resulting flowpath for the design. The benefit of the high stage reaction is to keep the rotor at a high tip radius, and have high turning in the following stator with very low diffusion as it matches to a lower radius high pressure compressor. The optimization process is fast enough to replace a meanline approach and explores a large design space to create a novel design.

Achieving the fast mixing requirements posed by the chemical, biological, and life science community for confined microchannel flows remains an engineering challenge. The viscous and surface tension forces that dominate conventional micro-flows undermine fast, efficient mixing. By increasing the collisional velocity of reagent droplets, inertia can be exploited to increase mixing rates. This paper experimentally investigates inertial droplet mixing in micro flows. A high speed, gaseous flow is used to detach, transport, and collide droplets of nanoliter-size volumes in standard T and Y-junction microchannel geometries. Mixing rates are quantified using differential fluorescent optical diagnostics. Measured droplet mixing times are compared to the characteristic time scales for mass and viscous diffusion and bulk convection. Results show that mixing times are decreased as the droplet inertia is increased, indicating the potential benefit of inertia-driven mixing.

The fruit of pepper (Capsicum annuum) commonly wilts (or shrivels) during postharvest storage due to rapid water loss, a condition that greatly reduces its shelf life and market value. The fact that pepper fruit are hollow, and thus have limited water content, only exacerbates this problem in pepper. The collaborators on this project completed research whose findings provided new insight into the genetic, physiological, and biochemical basis for water loss from the fruits of pepper (Capsicum annuum and related Capsicum species). Well-defined genetic populations of pepper were used in this study, the first being a series of backcross F₁ and segregating F₂, F₃, and F₄ populations derived from two original parents selected for having dramatic differences in fruit water loss rate (very high and very low water loss). The secondly population utilized in these studies was a collection of 50 accessions representing world diversity in both species and cultivar types. We found that an unexpectedly large amount of variation was present in both fruit wax and cutin composition in these collections. In addition, our studies revealed significant correlations between the chemical composition of both the fruit cuticular waxes and cutin monomers with fruit water loss rate. Among the most significant were that high alkane content in fruit waxes conferred low fruit water loss rates and low permeability in fruit cuticles. In contrast, high amounts of terpenoids (plus steroidal compounds) were associated with very high fruit water loss and cuticle permeability. These results are consistent with our models that the simple straight chain alkanes pack closely together in the cuticle membrane and obstruct water diffusion, whereas lipids with more complex 3-dimensional structure (such as terpenoids) do not pack so closely, and thus increase the diffusion pathways. The backcross segregating populations were used to map quantitative trait loci (QTLs) associated with water loss (using DART markers, Diversity Arrays Technology LTD). These studies resulted in identification of two linked QTLs on pepper’s chromosome 10. Although the exact genetic or physiological basis for these QTLs function in water loss is unknown, the genotypic contribution in studies of near-isogenic lines selected from these backcross populations reveals a strong association between certain wax compounds, the free fatty acids and iso-alkanes. There was also a lesser association between the water loss QTLs with both fruit firmness and total soluble sugars. Results of these analyses have revealed especially strong genetic linkages between fruit water loss, cuticle composition, and two QTLs on chromosome 10. These findings lead us to further speculate that genes located at or near these QTLs have a strong influence on cuticle lipids that impact water loss rate (and possibly, whether directly or indirectly, other traits like fruit firmness and sugar content). The QTL markers identified in these studies will be valuable in the breeding programs of scientists seeking to select for low water loss, long lasting fruits, of pepper, and likely the fruits of related commodities. Further work with these newly developed genetic resources should ultimately lead to the discovery of the genes controlling these fruit characteristics, allowing for the use of transgenic breeding approaches toward the improvement of fruit postharvest shelf life.