Academic literature on the topic 'Universal exposition, EXPO'

In the social sciences, there is an emerging interest in process tracing as a method for improving rigour and transparency in within-case inferences. Recently, the method has been proposed as a possible enhancement of theory-based approaches to evaluation, but applications of the method remain rare. In an attempt to fill this gap, process tracing was used to evaluate the Universal Exposition held in Milano in 2015 (EXPO2015). Mega-events of this kind are perfect candidates for ‘testing’ the method; although their effects have been widely discussed in the relevant literature, claims about the causal contribution of mega-events are not straightforward, and a number of ambiguities complicate any clear assessment of their consequences. Two in-depth case studies of projects related to EXPO2015 – the East External Highway and Refettorio Ambrosiano – demonstrate the advantages and feasibility of process tracing and of the application of Bayesian logic to evidence search, collection and assessment. In particular, case study results show that Bayesian scrutiny may reveal unexpected weakness in apparently obvious inferences and increase reliability in assessing less straightforward causal attributions.

Universal expositions, referred to as Expo, are events organised every five years, during which usually about 150 countries strive to present their distinctive qualities and achievements in an attractive manner – devoting special attention to natural values, culture and science. However, expositions should not only focus on exhibitors’ unique features, but they should also comply with the main topic of an Expo event. Therefore, the aim of this paper is to examine – based on observation conducted during the exhibition event held in Milan – performances given by countries in the context of referring to the main motto of the Expo. In 2015, the slogan used for the event in question was: “Feeding the Planet, Energy for Life”, and it directly referred to the idea of sustainable development. The observation made it possible to distinguish four groups of national exhibitions. Pavilions of selected countries were classified under those groups, and if there were displays that clearly referred to the central theme of the Expo, as well as strongly emphasised national distinctive qualities, a detailed description was provided.

Brisbane will never be the same after Expo — shopping hours, outdoor eating, the greening of the city, our attitudes to hospitality … all these things will permanently transform our city. (Edwards, quoted in Robson 1988: 54)While food historians have begun to focus attention on world's fairs, Vaccaro's detailed study of food at the 1904 World Fair in St Louis (2004) is at the vanguard of publishing in this area. Similarly, although the intense interest in culinary matters that is now identified as ‘foodie’ culture was developing in Australia in the 1980s, little attention has concentrated on this aspect of Brisbane's World Expo '88 (also widely known simply as ‘Expo '88’), which was staged from April to October 1988 as part of the national Bicentennial celebrations. Expo '88 dominated local headlines and became a part of the national imagination during the bicentennial year but, although commentators at the time predicted that it would ‘doubtless be a focus of research for a long time to come’ (Day 1988: iv), other matters have since dominated reflection about this period of recent Australian history. Yet food was specified in the ‘Cultural and Entertainment’ category of one of the three exposition's official sub-themes of ‘Leisure: The Universal Pastime’, and did play a number of important roles in and at Expo '88. Moreover, Robinson has identified Expo '88 as one of the ‘plethora of social, economic, cultural and political determinants’ that explains the diversity of cuisines available in Brisbane today (2007: 71).

Alongside the robots, rockets, kitchen appliances, and other technical wonders displayed at the great expositions and world’s fairs of the late-19th and early-20th centuries, visitors frequently found deceptively staid demonstrations of banal bureaucratic tools: cards, fiches, and files. Yet these technologies of information management were aestheticized and presented as integral to the generation and pursuit of the fairs’ ambitious ‘world projects’: global networks, universal intelligences, efficient cities, colonized galaxies. The small, moving parts of information functioned as critical tools for city- and world-building. In this article we begin with the 1964–5 World’s Fair, where bits and fragments of information fueled (or generated?) space-age visions, then trace those mid-century imaginaries back to the 1939–40 World’s Fair and a constellation of expos at the turn of the century, to see how the small, moving parts of information management ‘scale up’ to generate grand fantasies, and, at the same time, how they serve to index their own particular political and cultural milieux.

De conformidad con la resolutión nº 10, aprobada por el Consejo de Delegados en su reunión del 27 de noviembre de 1987, celebrada en Río de Janeiro, se decidió que el Movimiento International de la Cruz Roja y de la Media Luna Roja participaría en la Expositóon Universal que tendría lugar en Sevilla, decisión que ese mismo organo confirmó dos años más tarde. Se pensaba que esa manifestatión international, que contaria con la participatión de más de 100 países, unas 20 organizaciones internacionales y un elevado número de empresas multinacionales, atraería a unos 18 millones de visitantes. Sena una ocasión excepcional para difundir, durante seis meses, el mensaje y la actión humanitaria del Movimiento, ofreciendo, además, un marco en el que cobraría esplendor la conmemoración del Día Mundial de la Cruz Roja y de la Media Luna Roja, el 8 de mayo de 1992.

The aim of our Ph.D. Research Program was to improve the knowledge and test the implementation in the real world of that combination of procedures, methods and tools defined as Health Impact Assessment (HIA), whose aim is to assess the impact that the construction of industrial plants, infrastructures, housing, transport, energy plants and, broadly, any policy, plan and project in diverse economic sectors may cause on the health of the general population. An HIA procedure was applied to the world exposition “EXPO 2015” (Milan, Italy), focusing on three different phases. The analysis on the PRE-CONSTRUCTION period (ante-operam) allowed us to estimate the effects of exposure to particulate matter with aerodynamic diameter ≤ 10µm (PM10) and nitrogen dioxide (NO2) on the health of the study population, before the opening of the construction site (2007-2011). The effect estimates were expressed as percent variations in the frequency of expected health events in the population (deaths and hospitalizations) per 10µg/m3 increase in the pollutants concentration. Those estimates (i.e. concentration-response functions, CRF) were obtained by applying Poisson regression models to the daily counts of health events, and were then used to estimate the impact that the exposure to the same pollutants would have entailed during the subsequent CONSTRUCTION phase (January 2013 – April 2015). The impact was thus quantified in terms of deaths and hospital admissions attributable to the difference between the mean PM10 and NO2 annual concentrations estimated for the study period and the mean PM10 and NO2 annual concentrations corresponding to selected counterfactual scenarios. Our reference scenario was represented by the mean PM10 and NO2 annual concentrations measured by the network of air pollution monitoring stations of the regional environmental protection agency (ARPA Lombardia) in the last year of the PRE-CONTRUCTION phase (2011). In the CONSTRUCTION phase, we estimated 0.54 natural deaths and 0.70 hospitalizations (due to cardiac, cerebrovascular, and respiratory causes) attributable to PM10 levels exceeding the mean concentrations of the PRE-CONSTRUCTION period, in one year. As regards NO2, we estimated 0.36 and 0.56 additional deaths and hospitalizations, respectively. During the second year of the Ph.D. Program the HIA procedure was applied to the EVENT phase (May-October 2015). We obtained estimates of the traffic flow expected during the opening of the exhibition site. Such estimates were then inputted into dispersion models to obtain maps of the ground fallout of PM10 and NO2 emitted by the traffic due to the exhibition. We observed a mild contribution of the EXPO-related traffic flow to the air pollutants concentration averages in the investigated area. The ground fallout levels (annual means) ranged between 0.019 and 0.067µg/m3 for PM10 and between 0.270 and 0.684µg/m3 for NO2. Deaths and hospital admissions data were updated with information from the local health authorities. We were thus able to estimate, on a historical basis, the baseline number of health events we could have expected in our population during the study period. Using the CRFs obtained for the PRE-CONSTRUCTION phase and up-to-date exposure and health data, we estimated, for the EVENT phase, 0.11 natural deaths and 0.15 hospitalizations (due to cardiac, cerebrovascular, and respiratory causes) attributable to PM10 levels exceeding the mean concentrations of the PRE-CONSTRUCTION period, in one year. As regards NO2, we estimated 1.45 and 2.33 additional deaths and hospitalizations, respectively. The HIA methodology was subsequently applied to another study, conducted within the ESSIA project (Effetti Sulla Salute degli Inquinanti Aerodispersi in regione Lombardia: Health Effects of Air Pollutants in Lombardy). The project has been ongoing for several years and quantified the association between air pollutants and population health (effect and impact), based on Lombardy specific characteristics (see Baccini et al., 2011. Am J Epidemiol. 174, 1396-405 and Baccini et al., 2015. Environ Health Perspect. 123, 27-33). The published investigations focused on particulate matter exposure and all-cause mortality, taking into account between-city commuting as well. During the second year of our Ph.D. Program, we expanded the investigated exposures and health events and verified whether the reduction in air pollution levels observed in Lombardy in the last ten years paralleled a decrease in the number of health events. We considered exposure to PM10 and NO2, mortality and hospitalization data for a non-opportunistic sample of the most polluted and densely populated areas of the region (years 2003-2006). We obtained area-specific effect estimates for PM10 and NO2 applying Poisson regression models to the daily count of all-cause deaths and cause-specific hospitalizations (cardiac, cerebrovascular, and respiratory causes). Area-specific estimates were then combined in a random-effect Bayesian meta-analysis. For cardiovascular and respiratory mortality, we applied a case-crossover analysis. Effect estimates were expressed as percent variation of deaths and hospital admissions per 10µg/m3 increase in PM10 or NO2 concentrations. Natural mortality was positively associated with both pollutants (0.30%, 90% Credibility Interval [CrI]: -0.21; 0.70 for PM10; 0.70%, 90%CrI: 0.20; 1.18 for NO2). Cardiovascular deaths were more strongly associated to NO2 (1.12%, 90% Confidence Interval [CI]: 0.30; 1.95), while respiratory mortality was highest in association with PM10 (1.64%, 90%CI: 0.56; 2.72). The effect of both pollutants was more evident in the summer season and a trend in mortality with increasing age classes was apparent for PM10 only. Air pollution was also associated to hospitalizations, the highest variations being 0.77% (90%CrI: 0.31; 1.32) for respiratory diseases and PM10, and 1.70% (90%CrI: 0.60; 2.66) for cerebrovascular diseases and NO2. The effect of PM10 on respiratory hospital admissions increased with age. For both pollutants, effects on cerebrovascular hospitalizations were more evident in subjects aged less than 75 years. In a sub-analysis on all-cause mortality, we evaluated how the mortality burden due to PM10 exposure estimated for the period 2003-2006 (see Baccini et al., 2011. Am J Epidemiol. 174, 1396-405) varied when considering its concentrations in 2014. Assuming our study population and its mortality rates remained constant over time and applying the previously estimated CRFs, we quantified the number of deaths attributable to exposure levels exceeding the threshold of 20µg/m3 for PM10 annual average (WHO Air Quality Guidelines, 2005). The difference between attributable deaths estimated in 2003-2006 and 2014 represents the variation of the mortality burden between the two periods or, in other words, the number of deaths “avoided” thanks to the reduction in PM10 concentrations measured in the last decade. In 2014 we estimated 162 natural deaths less than in the period 2003-2006 (CrI80%: 24.2; 311.6) attributable to PM10 levels exceeding the WHO threshold. As expected, the bigger impact was observed in the capital city of Milan, with a difference between the two periods of 116 deaths due to natural causes (CrI80%: 65; 176).

The diploma thesis is focused on the media reflection of the Czech pavilion from the recent EXPO in Czech and Italian print. The research sample comprised of 12 daily newspapers (Hospodářské noviny, Lidové noviny, Mladá fronta DNES, Právo, E15, Deník, Corriere della Sera, la Repubblica, La Stampa, Il Giornale, Il Messaggero, Il Sole 24 Ore) that were monitored from 1. 3. 2015 until 30. 11. 2015. Firstly, the content analysis of 137 articles was performed on the individual level for both states. Subsequently, the media reflections in Czech and Italian print were compared to each other. The research found out for both countries that the highest number of media outputs was in May and that one particular journal was dominant in each country. On the contrary, the primary differentiation point was the extent of interest of the media outcomes. As the focus range of the articles differed (the Czech pavilion only in contrast to multiple national pavilions), other distinctions imply, such as the main subject of the articles or the most accented news values.

Abstract The complex interaction between the turbulent flow, combustion and the acoustic field in gas turbine engines often results in thermoacoustic instability that produces ruinously high-amplitude pressure oscillations. These self-sustained periodic oscillations may result in a sudden failure of engine components and associated electronics, and increased thermal and vibra-tional loads. Estimating the amplitude of the limit cycle oscillations (LCO) that are expected during thermoacoustic instability helps in devising strategies to mitigate and to limit the possible damages due to thermoacoustic instability. We propose two methodologies to estimate the amplitude using only the pressure measurements acquired during stable operation. First, we use the universal scaling relation of the amplitude of the dominant mode of oscillations with the Hurst exponent to predict the amplitude of the LCO. We also present a methodology to estimate the amplitudes of different modes of oscillations separately using ‘spectral measures’ which quantify the sharpening of peaks in the amplitude spectrum. The scaling relation enables us to predict the peak amplitude at thermoacoustic instability, given the data during the safe operating condition. The accuracy of prediction is tested for both methods, using the data acquired from a laboratory-scale turbulent combustor. The estimates are in good agreement with the actual amplitudes.

Abstract The flow inside a gas turbine engine has unique complexities. One of the important characteristics of such flow field is the existence of periodic unsteady wakes, originating from stator–rotor interaction. The unsteady wakes, with their highly vortical core, impinge on the downstream blade surfaces and cause an intermittent transition of the boundary layer from laminar to turbulent. The relative intermittency value corresponding to the wake vortical core and the calm region outside the wake, irrespective of freestream turbulence intensity and wake frequency, exhibits a universal behavior which is best described by the universal intermittency function of Chakka and Schobeiri [1, 2]. This study aims at introducing a new physics-based universal intermittency function that in conjunction with the current turbulence models accurately predicts the unsteady behavior of an intermittent flow. For that reason, a transport equation for turbulence intermittency was proposed based on this function and was integrated into a RANS based solver with k-ω turbulence model. The model was tested for reliability. Experimental aerodynamics and heat transfer measurements conducted at Turbomachinery Performance and Flow research Lab (TPFL) at Texas A&M University, were used as benchmark tests. For experimental measurements, an unsteady linear cascade facility in TPFL was used to produce the periodic unsteady flow condition. Moving wakes, originating from upstream blades, were simulated in this facility by rods attached to two parallel timing belts in front of the turbine blades. Heat transfer measurements along the suction surface were conducted utilizing a specially manufactured blade with an internal heater core, instrumented with liquid crystal. All Measurements and calculations were conducted at Reynolds number of 264,000. The computational results, obtained from implementing the new enhanced intermittency transport equation into the solver, are compared with (a) experimental measurements and (b) with the computational results from RANS that incorporates Langtry-Menter [3, 4] method.

Acceptance tests on large fans to prove the performance (efficiency and total pressure rise) to the customer are expensive and sometimes even impossible to perform. Hence there is a need for the manufacturer to reliably predict the performance of fans from measurements on down-scaled test fans. The commonly used scale-up formulas give satisfactorily results only near the design point, where inertia losses are small in comparison to frictional losses. At part- and overload the inertia losses are dominant and the scale-up formulas used so far fail. In 2013 Pelz and Stonjek introduced a new scaling method which fullfills the demands ( [1], [2]). This method considers the influence of surface roughness and geometric variations on the performance. It consists basically of two steps: Initially, the efficiency is scaled. Efficiency scaling is derived analytically from the definition of the total efficiency. With the total derivative it can be shown that the change of friction coefficient is inversely proportional to the change of efficiency of a fan. The second step is shifting the performance characteristic to a higher value of flow coefficient. It is the task of this work to improve the scaling method which was previously introduced by Pelz and Stonjek by treating the rotor/impeller and volute/stator separately. The validation of the improved scale-up method is performed with test data from two axial fans with a diameter of 1000 mm/250mm and three centrifugal fans with 2240mm/896mm/224mm diameter. The predicted performance characteristics show a good agreement to test data.

Abstract This paper presents the universal method of assessing the Vaneless Diffuser Rotating Stall (VDRS) cells’ size with the use of the Particle Image Velocimetry (PIV) technique. Two different cell dimensions’ definitions were introduced: Radial Cell Size (RCS) and Circumferential Cell Size (CCS). The step-by-step instructions for the calculation of both cell sizes are provided. Also, potential issues that readers may encounter while calculating the VDRS cell’s size are presented followed by examples of their solutions. The presented method for cell size assessment is universal and can be used not only with PIV measurements but with any technique allowing flow field reconstruction inside the diffuser or in numerical research. Such an analysis provides information regarding the most crucial zones inside the diffuser for anti-VDRS systems. Based on the results it is possible to increase the efficiency and applicability of the already developed and future VDRS prevention systems. Additionally, this method allows further understanding of the VDRS development by means of the cell growth study. Results of such an analysis may be used to improve compressor design resulting in better performance and wider operation range.

Efficiency and performance of gas turbine engines are affected by the flow field around the blades. The flow field inside a gas turbine engine is very complex. One of the characteristics of the flow inside an engine is existence of periodic unsteady wakes, originating from the upstream stator blades. The unsteady wakes, with their highly vortical core, impinge on the downstream blade surfaces and cause an intermittent transition of the flow regime from laminar to turbulent. This study aims at investigating and modeling the behavior and development of the boundary layer along the suction surface of a highly loaded low-pressure turbine blade under steady and unsteady inlet flow condition. The current paper includes results of a computational work substantiated by the experimental verifications. For the experimental investigations, the linear cascade facility in Turbomachinery Performance and Flow research Lab (TPFL) at Texas A&M University was used to simulate the periodic unsteady flow condition inside gas turbine engine. Moving wakes, originating from upstream blades, were simulated in this facility by moving rods attached to two parallel timing belts. Measurements and calculations were conducted at Reynolds number of 110,000. This Reynolds number pertains to cruise condition of a low-pressure turbine. At this Reynolds number, the flow around the blades is transitional and highly susceptible to flow separation. Aerodynamics experiments include measuring the boundary layer, locating its transition, separation and finally re-attachment using miniature hot wire probes. Heat transfer measurements along the suction and pressure surfaces were conducted utilizing a specially designed heat transfer blade that was instrumented with liquid crystal coating. To numerically simulate the transitional behavior of the boundary layer under periodic unsteady flow condition, a new intermittency function is developed which is based on the universal intermittency function developed by Chakka and Schobeiri [1]. Accurate prediction of the boundary layer behavior under the above conditions requires minimum and the maximum intermittency functions. These functions were developed inductively using the experimental results that were obtained in the absence of flow separation. In the current investigation the impact of the separation on the minimum and maximum intermittency are accounted for. The enhanced minimum and maximum intermittency functions along with the universal intermittency are implemented in a RANS based solver for computational simulation. The computational results are compared with (a) experimental ones and (b) with the computational results from RANS that involves Langtry-Menter [2, 3] method.

Abstract Probabilistic failure risk assessment is becoming important in the field of airworthiness. In the fracture mechanics module of probabilistic failure risk assessment, it is important to efficiently and accurately calculate the stress intensity factors (SIFs). At present, the weight function method (WFM), especially the universal weight functions (UWFs) proposed by Glinka and Shen, has been adopted to calculate SIFs with high accuracy and computational efficiency. However, the concrete coefficients in the universal weight functions remain unknown, and the rules of the geometry parameters and these coefficients have not yet been summarized, which hinders their subsequent use. In this article, the specific type of embedded crack-central crack is under discussion, and the derivation of the UWF is introduced. The response surface method (RSM), as a means of database establishment, is used to construct the relations between the geometric parameters including the length and thickness of a three-dimensional finite plate and coefficients in the UWF. The errors of the SIF calculation between the UWF and finite element results are less than 2 MPa m within a certain range. For the evaluation of the boundary effect on central cracks, the difference between finite and infinite plates is discussed. In addition, considering the complexity of the general off-centre crack, an approximation method has been proposed to transform the off-centre crack to the central crack. The results show that the method can be applied with high precision in specific situations and stresses the necessity of follow-up research on general off-centre cracks.

Streamline curvature technique for inverse through-flow modeling of turbomachinery is still one of the most prevalent alternatives in design. Even though the subject has been studied in numerous aspects over many years, open literature on fully coupled split-flow turbomachinery system design which is encountered in turbofan engines, is still limited. The principal method, viable for analysis mode, may easily give rise to undesired streamline distortion near the splitter leading edge whilst operating in design mode. Besides, spanwise discontinuity of flow properties along the stagnation streamline prior to final solution convergence may be another outcome. The present study is geared towards eliminating these potential drawbacks by developing an alternative generally-applicable split-flow scheme incorporated in a recently developed streamline curvature software. This new scheme disposes the need to define a stagnation streamline, while preserving full coupling between the main and split ducts. This is achieved through removal of by-pass ratio restriction, which makes local velocity vector always perfectly aligned with the splitter leading edge without any limit on fan-splitter axial distance. A two-step validation strategy is followed: Firstly, 2D split-flow solutions of the developed method for representative duct geometries having design by-pass ratios ranging between 0.25 and 6.5, but without turbomachinery, are compared with a commercial CFD software; Secondly, the method is compared with 3D viscous CFD solution of NASA Rotor 37 geometry, whose flowpath is modified to include a downstream flowpath splitter. It is shown that the proposed scheme can be used as a practical alternative to the conventional treatment that promises minimal effort to implement to an existing compressor streamline curvature methodology.

Three particle impact models have been evaluated to determine their ability to predict particle material properties and restitution coefficients using experimental data for the coefficient of restitution of particles impacting a 410 stainless steel plate. The particles consisted of PMMA and three coal fly ashes: JBPS, Bituminous, and Lignite. Particle speeds ranged from approximately 20 to 120 meters per second, and the nominal impact angle was approximately 85 degrees. Flow temperatures for the ash particulate experiments were set at 295 K and 395 K. The impact models were applied to the experimental data via curve fitting to evaluate the yield stress of the particulate, which was known for the PMMA. For the ash particulate, a linear law of mixtures was used to approximate the modulus of elasticity and Poisson’s ratio for use in the yield stress determination. A Hertzian mechanics model was shown to over-predict the yield stress of the PMMA particulate, indicating that, for known material properties, they would under-predict the coefficient of restitution. A Plastic-JKR model and a finite element based model by Wu et al. showed good agreement between the calculated yield stress and known range of yield stress values for the PMMA particulate, indicating that the model would accurately predict restitution coefficients for particulate with known material properties (or could be used to accurately determine the material properties from experimental coefficient of restitution data). However, some questions remain as to the ability of these models to be used for non-spherical, conglomerate type particulate. A thorough overview of the impact process is provided, and the application of the results of the study to the development of a physics-based universal impact and deposition model is presented.

Numerous experimental and numerical studies were performed in the past by various authors to reduce the leakage of labyrinth seals and thus increase the performance of turbo machines. Based on the experience of more than 20 years of research activities in this area at the ITS, the authors aim to improve the prediction quality for labyrinth seal performance by combining experimental, numerical and data mining methods. Special emphasis in this work lies on more complex and also worn labyrinth geometries and thus on a more universal optimization tool for labyrinth seals incorporating more realistic engine running conditions as well as wear mechanisms. Better understanding of labyrinth seal behavior based on the new correlations and models will thus lead to optimized geometries and improved designs. The paper contains the results of experiments to determine the discharge coefficients of different straight-through labyrinth seals with three and five fins and two different fin geometries over a large range of pressure ratios as well as results from a stepped labyrinth seal with six fins in convergent and divergent flow direction. The collected data extends an existing data base of labyrinth seal performance already presented in the paper of Pychynski et al. [1]. This data base is used to create models to calculate labyrinth seal performance depending on up to 25 input parameters. The resulting models will be used as a basis for a universal optimization tool for labyrinth seals. In the paper the new and versatile test rig for various kinds of labyrinth and gap seals is presented and an analysis of measurement accuracy will be given. The results of a first set of experiments performed with new (i.e. unworn) geometries are compared to experimental data of similar labyrinth geometries from previous investigations, showing an excellent agreement. The results are then interpreted using Data Mining Methods to identify correlations between different input parameters and the labyrinth seal discharge coefficient. The paper will show that a data based approach can yield similar quality relations as empirical studies but is much less time consuming and more versatile. Several models with different sets of input parameters will be presented and compared as to their applicability in automated geometry optimization using a newly developed optimization tool.

A new model is proposed for predicting particle rebound and deposition in environments relevant for gas turbine engines. The model includes the following physical phenomena: elastic deformation, plastic deformation, adhesion, and shear removal. It also incorporates material property sensitivity to temperature and tangential-normal rebound velocity cross-dependencies observed in experiments. The model is well-suited for incorporation in CFD simulations of complex gas turbine flows due to its algebraic (explicit) formulation. Model predictions are compared to coefficient of restitution data available in the open literature as well as deposition results from two different high temperature turbine deposition facilities. While the model comparisons with experiments are in many cases promising, several key aspects of particle deposition remain elusive. The simple phenomenological nature of the model allows for parametric dependencies to be evaluated in a straightforward manner. It is hoped that this feature of the model will aid in identifying and resolving the remaining stubborn holdouts that prevent a universal model for particle deposition.