Taking "Galton's problem" Seriously : Towards a Theory of Policy Diffusion

This article builds on the recent policy diffusion literature and attempts to overcome one of its major problems, namely the lack of a coherent theoretical framework. The literature defines policy diffusion as a process where policy choices are interdependent, and identifies several diffusion mechanisms that specify the link between the policy choices of the various actors. As these mechanisms are grounded in different theories, theoretical accounts of diffusion currently have little internal coherence. In this article we put forward an expected-utility model of policy change that is able to subsume all the diffusion mechanisms. We argue that the expected utility of a policy depends on both its effectiveness and the payoffs it yields, and we show that the various diffusion mechanisms operate by altering these two parameters. Each mechanism affects one of the two parameters, and does so in distinct ways. To account for aggregate patterns of diffusion, we embed our model in a simple threshold model of diffusion. Given the high complexity of the process that results, strong analytical conclusions on aggregate patterns cannot be drawn without more extensive analysis which is beyond the scope of this article. However, preliminary considerations indicate that a wide range of diffusion processes may exist and that convergence is only one possible outcome.

Diffusion dynamics on multiplex networks

We study the time scales associated with diffusion processes that take place on multiplex networks, i.e., on a set of networks linked through interconnected layers. To this end, we propose the construction of a supra-Laplacian matrix, which consists of a dimensional lifting of the Laplacian matrix of each layer of the multiplex network. We use perturbative analysis to reveal analytically the structure of eigenvectors and eigenvalues of the complete network in terms of the spectral properties of the individual layers. The spectrum of the supra-Laplacian allows us to understand the physics of diffusionlike processes on top of multiplex networks.

Mobile Communications within the European Union: The Role of Location in the Evolution and Forecasting of the Diffusion Process

In the European Union, the importance of mobile communications was realized early on. The process of mobile communications becoming ubiquitous has taken time, as the innovation of mobile communications diffused into the society. The aim of this study is to find out how the evolution and spatial patterns of the diffusion of mobile communications within the European Union could be taken into account in forecasting the diffusion process. There is relatively lot of research of innovation diffusion on the individual (micro) andthe country (macro) level, if compared to the territorial level. Territorial orspatial diffusion refers either to the intra-country or inter-country diffusionof an innovation. In both settings, the dif- fusion of a technological innovation has gained scarce attention. This study adds knowledge of the diffusion between countries, focusing especially on the role of location in this process. The main findings of the study are the following: The penetration rates of the European Union member countries have become more even in the period of observation, from the year 1981 to 2000. The common digital GSM system seems to have hastened this process. As to the role of location in the diffusion process, neighboring countries have had similar diffusion processes. They can be grouped into three, the Nordic countries, the central and southern European countries, and the remote southern European countries. The neighborhood effect is also domi- nating in thegravity model which is used for modeling the adoption timing of the countries. The subsequent diffusion within a country, measured by the logistic model in Finland, is af- fected positively by its economic situation, and it seems to level off at some 92 %. Considering the launch of future mobile communications systemsusing a common standard should implicate an equal development between the countries. The launching time should be carefully selected as the diffusion is probably delayed in economic downturns. The location of a country, measured by distance, can be used in forecasting the adoption and diffusion. Fi- nally, the result of penetration rates becoming more even implies that in a relatively homoge- nous set of countries, such as the European Union member countries, the estimated final pene- tration of a single country can be used for approximating the penetration of the others. The estimated eventual penetration of Finland, some 92 %, should thus also be the eventual level for all the European Union countries and for the European Union as a whole.

On the design of customized risk measures in insurance, the problem of capital allocation and the theory of fluctuations for L��vy processes

Dans cette th��se, nous ��tudions quelques probl��mes fondamentaux en math��matiques financi��res et actuarielles, ainsi que leurs applications. Cette th��se est constitu��e de trois contributions portant principalement sur la th��orie de la mesure de risques, le probl��me de l���allocation du capital et la th��orie des fluctuations. Dans le chapitre 2, nous construisons de nouvelles mesures de risque coh��rentes et ��tudions l���allocation de capital dans le cadre de la th��orie des risques collectifs. Pour ce faire, nous introduisons la famille des "mesures de risque entropique cumulatifs" (Cumulative Entropic Risk Measures). Le chapitre 3 ��tudie le probl��me du portefeuille optimal pour le Entropic Value at Risk dans le cas o�� les rendements sont mod��lis��s par un processus de diffusion �� sauts (Jump-Diffusion). Dans le chapitre 4, nous g��n��ralisons la notion de "statistiques naturelles de risque" (natural risk statistics) au cadre multivari��. Cette extension non-triviale produit des mesures de risque multivari��es construites �� partir des donn��es financi��res et de donn��es d���assurance. Le chapitre 5 introduit les concepts de "drawdown" et de la "vitesse d�����puisement" (speed of depletion) dans la th��orie de la ruine. Nous ��tudions ces concepts pour des modeles de risque d��crits par une famille de processus de L��vy spectrallement n��gatifs.

A traceable physical calibration of the vertical advection-diffusion equation for modelling ocean heat uptake

The classic vertical advection-diffusion (VAD) balance is a central concept in studying the ocean heat budget, in particular in simple climate models (SCMs). Here we present a new framework to calibrate the parameters of the VAD equation to the vertical ocean heat balance of two fully-coupled climate models that is traceable to the models��� circulation as well as to vertical mixing and diffusion processes. Based on temperature diagnostics, we derive an effective vertical velocity w��� and turbulent diffusivity k��� for each individual physical process. In steady-state, we find that the residual vertical velocity and diffusivity change sign in mid-depth, highlighting the different regional contributions of isopycnal and diapycnal diffusion in balancing the models��� residual advection and vertical mixing. We quantify the impacts of the time-evolution of the effective quantities under a transient 1%CO2 simulation and make the link to the parameters of currently employed SCMs.

Speziation von Plutonium bei der Sorption und Diffusion in Opalinuston

Die vorliegende Arbeit wurde im Rahmen des BMWi-Verbundprojektes Wechselwirkung und Transport von Aktiniden im nat��rlichen Tongestein unter Ber��cksichtigung von Huminstoffen und Tonorganika ��� Wechselwirkung von Neptunium und Plutonium mit nat��rlichem Tongestein��� durchgef��hrt. Um die langfristige Sicherheit der nuklearen Endlager beurteilen zu k��nnen, muss eine m��gliche Migration der radiotoxischen Abf��lle in die Umwelt betrachtet werden. Wegen seiner langen Halbwertszeit (24000 a) leistet Pu-239 einen wesentlichen Beitrag zur Radiotoxizit��t abgebrannter Kernbrennstoffe in einem Endlager. Das redox-sensitive Pu tritt in L��sung unter umweltrelevanten Bedingungen in den Oxidationsstufen +III bis +VI auf und kann nebeneinander in bis zu vier Oxidationsstufen vorliegen. Tonsteinformationen werden als m��gliches Wirtsgestein f��r Endlager hoch-radioaktiver Abf��lle betrachtet. Deshalb sind ausf��hrliche Informationen zur Mobilisierung und Immobilisierung des Pu durch/in das Grundwasser aus einem Endlager von besonderer Bedeutung. In dieser Arbeit wurden neue Erkenntnisse ��ber die Wechselwirkung zwischen Pu und dem nat��rlichen Tongestein Opalinuston (OPA, Mont Terri, Schweiz) mit Hinblick auf die Endlagerung w��rmeentwickelnder radioaktiver Abf��lle in einem geologischen Tiefenlager gewonnen.rnDer Fokus der Arbeit lag dabei auf der Bestimmung der Speziation von Pu an der Mineraloberfl��che nach Sorptions- und Diffusionsprozessen mittels verschiedener synchrotronbasierter Methoden (��-XRF, ��-XANES/EXAFS, ��-XRD, XANES/EXAFS). rnDie Wechselwirkung zwischen Pu und OPA wurde zun��chst in Batch- und Diffusionsexperimenten in Abh��ngigkeit verschiedener experimenteller Parameter (u.a. pH, Pu-Oxidationsstufe) untersucht. In Sorptionsexperimenten konnte gezeigt werden, dass einige Parameter (z.B. Temperatur, Humins��ure) einen deutlichen Einfluss auf die Sorption von Pu haben.rnDie Speziationsuntersuchungen wurden zum einen an Pulverproben aus Batchexperimenten und zum anderen an OPA-D��nnschliffen bzw. Diffusionsproben in Abh��ngigkeit verschiedener experimenteller Parameter durchgef��hrt. Die EXAFS-Messungen an der Pu LIII-Kante der Pulverproben ergaben, dass eine innersph��riche Sorption von Pu(IV) an Tongestein unabh��ngig von dem Ausgangsoxidationszustand des Plutoniums in L��sung stattgefunden hat. Durch die Kombination der ortsaufgel��sten Methoden wurde erstmalig mittels ��-XRF die Verteilung von Pu und anderen in OPA enthaltenen Elementen bestimmt. ��-XANES-Spektren an Pu-Anreicherungen auf OPA-D��nnschliffen und in Diffusionsproben best��tigen, dass das weniger mobile Pu(IV) die dominierende Spezies nach den Sorptions- und Diffusionsprozessen ist. Dar��ber hinaus wurde zum ersten Mal ein Diffusionsprofil von Pu in OPA mittels ��-XRF gemessen. Die Speziationsuntersuchungen mittels ��-XANES zeigten, dass das eingesetzte Pu(V) entlang seines Diffusionspfades zunehmend zu Pu(IV) reduziert wird. Mit ��-XRD wurde Illit als dominierende Umgebung, in der Pu angereichert wurde, identifiziert und Siderit als eine redoxaktive Phase auftreten kann. Die Ergebnisse dieser Arbeit zeigen, dass die Sicherheit von OPA als Wirtsgestein eines Endlagers hoch-radioaktiver Abf��lle positiv zu bewerten ist. rn

Diffusion transport of water in basalts

Studying diffusive transport in porous rocks is of fundamental importance in understanding a variety of geochemical processes including: element transfer, primary mineral dissolution kinetics and precipitation of secondary phases. Here we report new findings on the relationship between diffusive transport and textural characteristics of the pore systems on the example of mid-oceanic ridge basalts having different degree of alteration but very similar bulk pore volume. Diffusion processes in porous basalts were studied in situ using H2O -> D2O exchange experiments. The effective diffusion coefficients of water molecules increase systematically from 5.05*10**-11 to 1.19*10**-10 m**2/s for fresh and moderately altered basalts and from 2.40*10**-11 to 6.72*10**-11 m**2/s for completely altered basalt as temperature increases from 5 to 50 ��C. The activation energy of the diffusion process increases from 12.29 �� 0.71 kJ/mol for fresh and moderately altered basalts to 14.3 �� 1.33 kJ/mol for completely altered basalt. The results indicate that neither the bulk porosity nor the degree of alteration can be used as proxies for the efficiency of element transport during MORB-water interaction. The formation of secondary phases that replace primary minerals and fill the pore space in the rock leads to the formation of tiny pores and phases with large specific surface area. These factors might have a dominant control on the transport properties of altered basaltic rocks.

Diffusion of Zn into GaAs and AlGaAs from isothermal Liquid-phase epitaxy solutions

In this work we present results of zinc diffusion in GaAs using the liquid phase epitaxy technique from liquid solutions of Ga���As���Zn and Ga���As���Al���Zn. Using silicon���doped n���GaAs substrates, working at a diffusion temperature of 850�����C, and introducing a dopant concentration ranging 1018���1019 cm���3, the most important findings regarding the diffusion properties are as follows: (a) zinc concentration in the solid depends on the square root of zinc atomic fraction in the liquid; (b) the diffusion is dominated by the interstitial���substitutional process; (c) the diffusivity D varies as about C3 in the form D=2.9��10���67C3.05; (d) aluminum plays the role of the catalyst of the diffusion process, if it is introduced in the liquid solution, since it is found that D varies as (��AsXlAs)���1; (e) the zinc interstitial is mainly doubly ionized (Zn++i); (f) the zinc diffusion coefficient in Al0.85 Ga0.15 As is about four times greater than in GaAs; (g) by means of all these results, it is possible to control zinc diffusion processes in order to obtain optimized depth junctions and doping levels in semiconductor device fabrication.

Lifetime improvement after phosphorous diffusion gettering on upgraded metallurgical grade silicon

Wide experimental evidence of the phosphorus diffusion gettering beneficial effect on solar grade silicon is found by measuring electron effective lifetime and interstitial iron concentration in as-grown and post processed samples from two ingots of upgraded metallurgical grade silicon produced by Ferrosolar. Results after two different P-diffusion processes are compared: P emitter diffusion at 850��C followed by fast cool-down (called ���standard process���) or followed by slow cool-down (called ���extended process���). It is shown that final lifetimes of this low cost material are in the range of those obtained with conventional material. The extended process can be beneficial for wafers with specific initial distribution and concentration of iron, e.g. materials with high concentration of big Fe precipitates, while for other cases the standard process is enough efficient. An analysis based on the comparison of measured lifetime and dissolved iron concentration with theoretical calculations helps to infer the initial iron distribution and concentration, and according to that, choose the more effective type of gettering.

Effects of adsorbed phase on diffusion of subcritical hydrocarbons in activated carbon at low pressures

Diffusions of free and adsorbed molecules of subcritical hydrocarbons in activated carbon were investigated to study the influence of adsorbed molecules on both diffusion processes at low pressures. A collision reflection factor, defined as the fraction of molecules undergoing collision to the solid surface over reflection from the surface, is incorporated into Knudsen diffusivity and surface diffusivity in meso/macropores. Since the porous structure of activated carbon is bimodal in nature, the diffusion of adsorbed molecules is contributed by that of weakly adsorbed molecules on the meso/macropore surfaces and that of strongly adsorbed molecules in the small confinement of micropores. The mobility of adsorbed molecules on the meso/macropore surface is characterized by the surface diffusivity D-mu 2, while that in the micropore is characterized by D-mu 1. In our study with subcritical hydrocarbons, we have found that the former increases almost linearly with pressure, while the latter exhibits a sharp increase at a very low-pressure region and then decreases beyond a critical pressure. This critical pressure is identified as a pressure at which the micropores are saturated.

Ionic and molecular diffusion in cementitious materials

The work described in this thesis is an attempt to provide improved understanding of the effects of several factors affecting diffusion in hydrated cement pastes and to aid the prediction of ionic diffusion processes in cement-based materials. Effect of pore structure on diffusion was examined by means of comparative diffusion studies of quaternary ammonium ions with different ionic radii. Diffusivities of these ions in hydrated pastes of ordinary portland cement with or without addition of fly ash were determined by a quasi-steady state technique. The restriction of the pore geometry on diffusion was evaluated from the change of diffusivity in response to the change of ionic radius. The pastes were prepared at three water-cement ratios, 0.35, 0.50 and 0.65. Attempts were made to study the effect of surface charge or the electrochemical double layer at the pore/solution interface on ionic diffusion. An approach was to evaluate the zeta potentials of hydrated cement pastes through streaming potential measurements. Another approach was the comparative studies of the diffusion kinetics of chloride and dissolved oxygen in hydrated pastes of ordinary portland cement with addition of 0 and 20% fly ash. An electrochemical technique for the determination of oxygen diffusivity was also developed. Non-steady state diffusion of sodium potassium, chloride and hydroxyl ions in hydrated ordinary portland cement paste of water-cement ratio 0.5 was studied with the aid of computer-modelling. The kinetics of both diffusion and ionic binding were considered for the characterization of the concentration profiles by Fick's first and second laws. The effect of the electrostatic interactions between ions on the overall diffusion rates was also considered. A general model concerning the prediction of ionic diffusion processes in cement-based materials has been proposed.

Opinion leaders' role in innovation diffusion:a simulation study

This study investigates the critical role that opinion leaders (or influentials) play in the adoption process of new products. Recent existing reseach evidence indicates a limited effect of opinion leaders on diffusion processes, yet these studies take into account merely the network position of opinion leaders without addressing their influential power. Empirical findings of our study show that opinion leaders, in addition to having a more central network position, possess more accurate knowledge about a product and tend to be less susceptible to norms and more innovative. Experiments that address these attributes, using an agent-based model, demonstrate that opinion leaders increase the speed of the information stream and the adoption process itself. Furthermore, they increase the maximum adoption percentage. These results indicate that targeting opinion leaders remains a valuable marketing strategy.

Discrete Models of Time-Fractional Diffusion in a Potential Well

Mathematics Subject Classification: 26A33, 45K05, 60J60, 60G50, 65N06, 80-99.

Quasi-Likelihood Estimation for Ornstein-Uhlenbeck Diffusion Observed at Random Time Points

2000 Mathematics Subject Classification: 60J60, 62M99.

Latent Space and Social Psychological Models of Diffusion

<p>The problem of social diffusion has animated sociological thinking on topics ranging from the spread of an idea, an innovation or a disease, to the foundations of collective behavior and political polarization. While network diffusion has been a productive metaphor, the reality of diffusion processes is often muddier. Ideas and innovations diffuse differently from diseases, but, with a few exceptions, the diffusion of ideas and innovations has been modeled under the same assumptions as the diffusion of disease. In this dissertation, I develop two new diffusion models for "socially meaningful" contagions that address two of the most significant problems with current diffusion models: (1) that contagions can only spread along observed ties, and (2) that contagions do not change as they spread between people. I augment insights from these statistical and simulation models with an analysis of an empirical case of diffusion - the use of enterprise collaboration software in a large technology company. I focus the empirical study on when people abandon innovations, a crucial, and understudied aspect of the diffusion of innovations. Using timestamped posts, I analyze when people abandon software to a high degree of detail. </p><p>To address the first problem, I suggest a latent space diffusion model. Rather than treating ties as stable conduits for information, the latent space diffusion model treats ties as random draws from an underlying social space, and simulates diffusion over the social space. Theoretically, the social space model integrates both actor ties and attributes simultaneously in a single social plane, while incorporating schemas into diffusion processes gives an explicit form to the reciprocal influences that cognition and social environment have on each other. Practically, the latent space diffusion model produces statistically consistent diffusion estimates where using the network alone does not, and the diffusion with schemas model shows that introducing some cognitive processing into diffusion processes changes the rate and ultimate distribution of the spreading information. To address the second problem, I suggest a diffusion model with schemas. Rather than treating information as though it is spread without changes, the schema diffusion model allows people to modify information they receive to fit an underlying mental model of the information before they pass the information to others. Combining the latent space models with a schema notion for actors improves our models for social diffusion both theoretically and practically. </p><p>The empirical case study focuses on how the changing value of an innovation, introduced by the innovations' network externalities, influences when people abandon the innovation. In it, I find that people are least likely to abandon an innovation when other people in their neighborhood currently use the software as well. The effect is particularly pronounced for supervisors' current use and number of supervisory team members who currently use the software. This case study not only points to an important process in the diffusion of innovation, but also suggests a new approach -- computerized collaboration systems -- to collecting and analyzing data on organizational processes.</p>