Quasi-stationary Conditions Research Articles

INFLUENCE OF FUEL PROPERTIES ON THE DIESEL INJECTION PROCESS IN NONVAPORIZING CONDITIONS

This paper presents an experimental investigation of the influence of fuel density, viscosity, and surface tension on the diesel injection process (spray development and droplet size distribution) in non-vaporizing conditions. The spray development was captured in a pressurized vessel with a high-speed camera in order to obtain the penetration length and the spray angle. The droplet size distributions were measured by laser diffraction. A fuel matrix of eight fuels was designed including independent variations of fuel density, viscosity, and surface tension. Experimental conditions, such as injection pressure and air density, were varied according to current diesel engine conditions. The analysis focuses mainly on the quasi-stationary phase of the injection event. Results indicate that viscosity and to a lesser extent fuel density affect the spray characteristics. Increasing fuel density and viscosity by, respectively, 100 kg/m3 and 6.5 mm2/s induces longer spray tip penetration (up to 7%) with a narrower spray angle (drop of up to 3 deg) in quasi-stationary conditions. An increase in the Sauter mean diameter (up to 23% or 3 µm) was also observed. An increase in surface tension from 18 to 30 mN/m did not induce any significant modifications in the droplet size or in the spray development. Correlations, some of which are based on existing ones, are proposed to estimate the spray cone angle, the spray tip penetration, the SMD (Sauter mean diameter) and the drop size distribution considering the experimental conditions and the fuel properties.

Ecological state equation

The direct equivalence between ecology and thermodynamics has not been attained despite accepted thermodynamic features of the ecosystem. This article explores the homeomorphism between ecology and statistical mechanics by analysis of ruderal vegetation. In conventional thermostatistical algorithm, the pro-kinetic effect of temperature on molecules was replaced by the anti-kinetic effect of species diversity on biological individuals. The existence of an ecological equivalent of the thermodynamic Boltzmann constant was empirically verified. From the relationship of this constant with biocenological variables, we derived a probable ecological equation of state under stationary and quasi-stationary conditions. This equation of state is homeomorphic with regard to the ideal gas state equation, and it is useful to infer the value of some biocenological parameters whose direct measurement is difficult, as biomass, energy and dispersal. According to these results, ecosystem assessment from conventional thermostatistics is plausible and empirically verifiable. This approach offers useful analytical tools for the conservation and restoration of ecosystems.

Radiation Heat Transfer and Its Impact on Stability Against Quench of a Superconductor

Stability functions are an important analytical/numerical tool for appropriate design of conductor geometry and dimensions to prevent conductor losses under a transport current. While standard stability calculations following the Stekly, adiabatic, or dynamic stability models apply purely solid thermal conduction mechanism and derive results under (quasi) stationary conditions, the present paper investigates if, and to which extent, also radiation heat transfer, in addition to solid conduction, can exert impacts on conductor stability. Further, the full transient conductor temperature evolution after a disturbance is calculated. The analysis applies an interplay between Monte Carlo radiative transfer calculations, to describe absorption of heat pulses and their distribution in the conductor, and a rigorous finite element method to calculate the resulting temperature field and stability functions. The results show that radiative heat transfer cannot be neglected in particular if periodic disturbances have to be considered that can arise, e.g., in a flux flow fault current limiter.

Bayesian on-line spectral change point detection: a soft computing approach for on-line ASR

Current automatic speech recognition (ASR) works in off-line mode and needs prior knowledge of the stationary or quasi-stationary test conditions for expected word recognition accuracy. These requirements limit the application of ASR for real-world applications where test conditions are highly non-stationary and are not known a priori. This paper presents an innovative frame dynamic rapid adaptation and noise compensation technique for tracking highly non-stationary noises and its application for on-line ASR. The proposed algorithm is based on a soft computing model using Bayesian on-line inference for spectral change point detection (BOSCPD) in unknown non-stationary noises. BOSCPD is tested with the MCRA noise tracking technique for on-line rapid environmental change learning in different non-stationary noise scenarios. The test results show that the proposed BOSCPD technique reduces the delay in spectral change point detection significantly compared to the baseline MCRA and its derivatives. The proposed BOSCPD soft computing model is tested for joint additive and channel distortions compensation (JAC)-based on-line ASR in unknown test conditions using non-stationary noisy speech samples from the Aurora 2 speech database. The simulation results for the on-line AR show significant improvement in recognition accuracy compared to the baseline Aurora 2 distributed speech recognition (DSR) in batch-mode.

Multiple electron cyclotron power deposition location tracking by break-in-slope analysis in TCV plasmas

Modulation of the amplitude of externally injected electron cyclotron (EC) power is a frequent method used to determine the radial power deposition profile in fusion plasmas. There are many tools to analyze the plasma response to the power modulations under quasi-stationary conditions. This paper focuses on the unique ability of the break-in-slope (BIS) method to retrieve a quasi-instantaneous estimate of the power deposition profile at each power step in the modulation, an outcome particularly relevant to track the power deposition location under non-stationary conditions. Here, the BIS analysis method is applied to the signals of a fast and high radial resolution wire-chamber soft x-ray camera in the Tokamak à Configuration Variable (TCV) where the plasma magnetic configuration and thus the EC resonance location are varied during the plasma discharge. As a step to validate this technique before real-time control experiments, the time-varying EC power deposition location of a single beam is successfully monitored by off-line BIS analysis. Simultaneous tracking of deposition locations of two EC beams gives promising results.

Initiation of a reactive material by a radiation beam absorbed by optical heterogeneities of the material

The heating dynamics and thermal ignition of a condensed transparent material by a radiation pulse absorbed by optical micro-heterogeneities present in the material were studied numerically and approximately analytically over a wide range of pulse durations. For quasistationary heating conditions of micro-heterogeneities, an analytical dependence of the radiation power density critical for ignition on the formal kinetic parameters of the chemical process and the radius of the particle absorbing the radiation was obtained. The critical energy characteristics of ignition are compared with experimental data on the initiation threshold of lead azide by laser pulses of different duration.

Triplet–Triplet Annihilation in a Series of Poly(p-phenylene) Derivatives

We have studied the temperature dependence of phosphorescence (Ph) and delayed fluorescence (DF) in two series of poly(p-phenylene) derivatives within a temperature range from 10 to 300 K under quasi-stationary conditions. One set of materials consists of the dimer, trimer, and polymer of ethylhexyl-substituted poly(fluorene) (PF2/6) and thus allows us to assess the effects of oligomer length. The second series addresses the influence of energetic disorder and conjugation length by being composed of the polymers alkoxy-substituted poly(p-phenylene) (DOO-PPP), poly(indenofluorene) (PIF), and ladder-type poly(p-phenylene) (MeLPPP). Under low light intensities, the DF features a maximum at a certain temperature T(max). For the dimer and trimer, the T(max) coincides with the temperature at which the phosphorescence has decayed to 1/2 of the value at 10 K, while T(max) shifts to lower temperature values along the series DOO-PPP, PIF, and MeLPPP and approaches T = 0 K for MeLPPP. By applying conventional kinetic equations we show that the occurrence of a maximum in the DF intensity is the consequence of generalized thermally activated triplet exciton transport toward quenching sites. We find the quenching rates at 0 K to be in the range of 1 s(-1) for the polymers, while they are more than an order of magnitude lower for the oligomers.

Validating LES-based flow and dispersion models

Validating LES-based flow and dispersion models for the purpose of predicting transient flow and dispersion phenomena is more demanding than validating RANS-based codes. Since the model output is no longer related to stationary or quasi-stationary boundary conditions, and since the model results are not meant to be used for predicting mean flow and dispersion patterns, an evaluation of the model based on mean results is not meaningful for most of the model-specific applications. A more sophisticated but also more complex validation approach based on statistically representative ensembles is required. By comparing frequency/probability distributions of flow and dispersion results with qualified reference data the reliability of complex models can be evaluated. Based on a careful comparison of FAST3D-CT simulation results with corresponding systematic wind tunnel data from the JU2003 experiments, an example for an application specific evaluation procedure for instantaneous puff dispersion modeling is given.

Flame Stabilization Mechanisms in Lifted Flames

Flame stabilization and the mechanisms that govern the dynamics at the flame base of lifted flames have been subject to numerous studies in recent years. A combined Large Eddy Simulation-Conditional Moment Closure (LES-CMC) approach has been successful in predicting flame ignition and stabilization by auto-ignition, but accurate modelling of the competition between turbulent quenching and laminar and turbulent flame propagation at the anchor point had not been demonstrated. This paper will consolidate LES-CMC results by analysing a wide range of lifted flame geometries with different prevailing stabilization mechanisms. The simulations allow a clear distinction of these mechanisms. It is corroborated that LES-CMC accurately predicts the competition between turbulence and chemistry during the auto-ignition process, the dynamics of turbulent flame propagation can be captured, however, the dynamics of the extinction process are not approximated well under certain conditions. The averaging process inherent in the CMC methods does not allow for an instant response of the transported conditionally averaged reactive species to the changes in the flow conditions and any response of the scalars will therefore be delayed. The dimensionality of the CMC implementation affects the solution and higher dimensionality does no necessarily improve results. Stationary or quasi-stationary conditions, however, can be well predicted for all flame configurations.

Modelling and validation of robust partial thawing of frozen convenience foods during distribution in the cold chain

In collaboration with two commercial distributors we have tested a new concept for distribution, where convenience products for the food service industry are prepared, frozen and packed in cardboard boxes, but distributed in the chill chain at +5°C instead of in the frost chain. This will lead to a partial thawing before reaching the end user. The high thermal buffering capacity of the product under thawing ensures that the product temperature remains stable at subzero temperatures, also in cases of temperature abuse for some hours. To investigate and validate the concept, cardboard boxes packed with small blocks of a frozen model food (23 pct. Tylose® gel) and quipped with temperature loggers were distributed by trucks operating in the cold chain. In addition, controlled storage and temperature abuse experiments were conducted. To predict the product temperature–time relationship we developed a new thawing model for the slow thawing of food pieces packed in a box. The model is based on enthalpy balances under quasi-stationary conditions; a condition that is fulfilled in the practical distribution experiments. The experiments confirmed the model predictions that the products were still partially frozen even after two days or more of distribution at +5oC, and that the temperatures inside the product and in the middle of the box were quite stable against the normal oscillations of the ambient temperature in the cold chain. The product temperature was also robust against temperature abuse, as predicted. The new distribution method not only has the potential of prolonging product shelf life but also gives the distributors an increased flexibility in the distribution chain.

Theory of Repeating Nucleation in Point Contact Reactions between Nanowires

Modification of the classical Zeldovich nucleation theory for nonstationary conditions is presented. It is applied to the recently discovered repeating nucleation events in point contact reactions between metal and silicon nanowires to form epitaxial silicides; the nucleation provides the reproducible quasi-stationary conditions satisfying the fundamental suppositions of the modified theory. The modified theory enables us to predict the rate of repeating nucleation at nanoscale level by developing a theory of the incubation time. The understanding is extremely important for the design and applications of nanoheterostructures.

The dilemma of when to neuter

Long distance dispersal (LDD) of airborne aerosol of foot-and-mouth disease (FMD) virus was extensively modeled in the literature. Most studies modeled this aerosol in simplistic approach as a passive tracer, neglecting physical and biological mechanisms that affect bio-aerosols such as the FMD aerosol. This approach was justified either because under persistent wind these mechanisms lower the extant of downwind hazard or on the grounds that the effect of some of the physical mechanisms on particles as small as the FMD particles (0.015–20 μm) is supposed to be negligible compared to the effect of atmospheric turbulence. Even when the FMD aerosol was treated as aerosol, it was assumed that it is monodisperse, i.e., all its particles are of the same size. The aim of the study is to examine whether these simplistic approaches are indeed justified when dealing with LDD of a bio-aerosol under actual atmospheric conditions. In order to do so, the influence of a more realistic modeling of the FMD aerosol as a polydisperse aerosol was compared to passive tracer and to monodisperse aerosol. The comparison refers to a case of a widespread FMD outbreak that occurred in 2012 in Egypt. This outbreak involved the emergence of a new serotype in Egypt, SAT2 and concern was raised that this serotype will advance further to Asia and Europe. Israel is located on the land bridge between Africa, Asia and Europe, and shares a long desert border with Egypt as well as a long Mediterranean shore adjacent to Egypt's shore. This unique location as well as the fact that Israel does not have any cattle trade with its neighboring countries make Israel an interesting test case for the examination of the necessary conditions for the long distance dispersal (LDD) of a new FMD strains from Africa to Europe. The analysis in this study shows that under quasi-stationary wind conditions modeling FMD dispersal as a passive tracer results in a significantly longer hazard distance. Under non-stationary conditions this modeling assumption results in an under-estimation of the hazard distance in comparison to the results of polydisperse aerosol. In these conditions modeling the FMD dispersal as a monodisperse aerosol results in similar under-estimation. The implications of such under-estimation may be severe because it may lead authorities in a threatened area to refrain from taking the necessary protective measures. Therefore, the modeling of the FMD aerosol as a polydisperse aerosol is preferable, leading to realistic estimation both under non-stationary and stationary wind conditions.

Activation Energies of the Electrooxidation of Formic Acid on Pt(100)

The electrooxidation of small organic molecules on platinum surfaces usually involves different structure-dependent steps that include adsorption and desorption of various species and multiple reaction pathways. Because temperature plays a decisive role on each individual step, understanding its global influence on the reaction mechanism is often a difficult task, especially when the system is studied under far from equilibrium conditions in the presence of kinetic instabilities. Aiming at contributing to unravel this problem, herein, we report an experimental study of the role played by temperature on the electrooxidation of formic acid on a Pt(100) electrode. The system was investigated under both close and far from equilibrium conditions, and apparent activation energies were estimated using different strategies. Overall, comparable activation energies were estimated under oscillatory and quasi-stationary conditions, at high potentials. At low potentials, the poisoning process associated with the formic acid dehydration step presented a negligible dependence with temperature and, therefore, zero activation energy. On the basis of our experimental findings, we suggest that formic acid dehydration is the main, but maybe not the unique, step that differentiates the temperature dependence of the oscillatory electrooxidation of formic acid on Pt(100) with that on polycrystalline platinum.

Identification of an Equivalent-Source System for Magnetic Stray Field Evaluation

The aim of this paper is to propose an approximate technique for the reconstruction of magnetic-field distribution in the proximity of unknown sources. The method is based on two nested optimization algorithms-the external one is responsible for the definition of the geometry of the equivalent-source system, while an internal procedure based on least-square minimization is used to identify the currents of the sources. The goal is to minimize the deviation between the reconstructed and actual field. It is shown that under magnetic quasi stationary conditions, the proposed approach is able to reconstruct the field distribution of a complex 3-D environment as medium-voltage/low-voltage substations. The main limitation is the availability of magnitude and phase of the measured magnetic field. This information is not usually provided by standard probes but can be obtained by a proper measurement setup. The proposed technique allows accurate reconstruction of the magnetic field even in the case of many sources without requiring their accurate geometrical description and is suitable for the evaluation of stray fields and the design of magnetic shielding.

Optimization of boundary conditions for a distributed control system on the growing of crystals

Boundary conditions for a distributed system simulating the temperature distribution in a growing crystal and the heat exchange with the environment under nonlinear boundary conditions have been optimized by the example of a garnet crystal grown by the Czochralski method. Quasi-stationary conditions for the temperature distribution in a growing crystal have been used. The obtained results allow the optimization of technological parameters for the growth of crystals with a high degree of structure perfection.

The Freezing Precipitation over the Middle-Lower Reaches of the Yangtze River during February-March 2009

In this paper, the authors analyze the quasistationary fronts, surface conditions, and atmospheric stratification processes associated with a freezing precipitation event over the middle-lower reaches of the Yangtze River, especially in the Dabie mountain during February-March 2009. The long duration of freezing precipitation was primarily caused by stationary and anomalous synoptic weather patterns, such as a blocking high pressure in the northern branch and a trough in the southern branch of the westerlies, which resulted in the encounter cold air from northern China and warm moisture from the south. The east-west-oriented, quasi-stationary front (or shear line) found in central China was mostly responsible for producing the precipitation. The warm layer and nearsurface frozen layer were located in the lower troposphere along the front zone. Although the warm layer ( 0oC) existed along the whole front, a surface temperature less than 0oC appeared only over the lower-middle reaches of the Yangtze River, especially in the Dabie mountain. Therefore, the surface temperature was the main influencing factor, as the freezing precipitation only happened over the Dabie mountain.

RELATIONSHIP BETWEEN CURRENT DENSITY AND MASS DENSITY FOR OHMIC TOKAMAK PLASMAS

The relation between current density and mass density in the plasma has been derived based on the assumption that the magnetic entropy is constant in time. Over the entire range of quasi-stationary ohmic conditions, it is obtained [Formula: see text]. Here j0 and ρ0 are the central values of j and ρ with j0 ≈ cB/2πR0 (this corresponds to a value q ≈ 1 of the safety factor near the minor axis).

Osteogenic differentiation of human mesenchymal stem cells on chip: A comparison between two nutrient feeding methods

Osteogenic differentiation of human mesenchymal stem cells (hMSCs) on chip was studied by using two types of nutrient feeding methods. The first one was with a hydraulic pressure which allows controlling the flow rate with a large dynamic range. The second one was with integrated reservoirs of relative large volumes, providing a quasi stationary culture condition (regular medium change has to be done once per day). In both cases, cells survived for several weeks but showed different behaviors of cell proliferation and differentiation. In hydraulic pressure controlled chambers, cells grow fast but the formation of calcium nodes is less efficient. Under quasi stationary conditions with an optimal initial cell density between 20 and 40 k cells/cm 2, both morphology and Alizarin Red staining images show a better osteogenic differentiation.

In vivo dynamics of glycolysis in Escherichia coli shows need for growth‐rate dependent metabolome analysis

Metabolomics emerges to become an important profiling technique in bio(techno)logical systems. In addition to intracellular metabolite concentrations at (quasi) stationary conditions, stimulus-response experiments provide information on the dynamic behavior of metabolic pathways. These data are relevant for bioprocess analysis on the level of metabolism and for application of metabolic engineering principles aiming at a metabolic redesign of producer cells. However, even for the well-studied bacteria Escherichia coli only limited growth-rate dependent intracellular metabolite information is currently available, thereby impeding comprehensive metabolome analysis. Here, we present intracellular metabolite concentration data of representative glycolytic intermediates in E. coli cultivated in glucose-limited chemostats, (i) at systematic variation of growth-rate (D = 0.1, 0.2, 0.3, and 0.4 h(-1)) and (ii) at both steady-state and after a glucose pulse applying a recently introduced integrated sampling procedure and LC-MS analytical method. Whereas intracellular steady-state concentrations of upper part glycolytic intermediates FBP and DHAP+GAP increased 2.3-fold, respectively 2.8-fold, when specific growth-rate is raised from micro = 0.1 h(-1) to micro = 0.4 h(-1), the opposite trend was observed for 2PG+3PG and PEP pools with a decrease by a factor of 2.1, respectively 1.9. In glucose pulse experiments FBP and DHAP+GAP showed a 3.3 (1.8)-fold, respectively 2.8 (2.0)-fold, increase relative to the steady-state level at micro = 0.1 (0.4) h(-1). Also, the dynamics changed with growth-rate for these two metabolite pools. In contrast, 2PG+3PG and PEP were characterized by decreased concentrations in response to a glucose pulse and the relative changes related to steady-state values were significantly smaller compared with FBP and DHAP+GAP. The observed growth-rate dependency of our data clearly indicates the necessity for metabolome studies covering a broader range of physiological growth conditions.

Approach to calculation time-dependent moisture diffusivity for thin layered biological materials

A method is presented to determine the effective diffusivity from experimental drying kinetics as a time-dependent parameter. The method combines an analytical solution of Fick's equation in which the Fourier number is approximated using the empirical coefficients a and b with a semi-theoretical equation derived for quasi-stationary conditions. The resulting equation has been applied to calculate the effective diffusivity from literature data on the drying of tobacco lamina and sliced celery. The applicability of the method was confirmed by good agreement of calculated and experimental data. It was found that the effective diffusivity for tobacco lamina rises sharply from practically zero at the beginning of drying to a maximum of 9·10 − 10 m 2/s at 89 s, and then gradually decays with time of drying. The same trend was found for sliced celery, but the maximum of the effective diffusivity (1.6·10 − 7 m 2/min) was attained at 56 s. The exact definition of the effective diffusivity vs. drying time identifies two phases of drying: the first phase was characterized by the rising intensity of drying with the maximum at the end of this phase, followed by the phase of slow decrease in the intensity of moisture removal. The rising intensity of drying observed during the initial phase of the process can be explained by warming up of the dried material during the initial phase of drying.