Probing the cosmic distance-duality relation with the Sunyaev-Zel'dovich effect, X-ray observations and supernovae Ia

Context. The angular diameter distances toward galaxy clusters can be determined with measurements of Sunyaev-Zel'dovich effect and X-ray surface brightness combined with the validity of the distance-duality relation, D-L(z)(1 + z)(2)/D-A(z) = 1, where D-L(z) and D-A(z) are, respectively, the luminosity and angular diameter distances. This combination enables us to probe galaxy cluster physics or even to test the validity of the distance-duality relation itself. Aims. We explore these possibilities based on two different, but complementary approaches. Firstly, in order to constrain the possible galaxy cluster morphologies, the validity of the distance-duality relation (DD relation) is assumed in the Lambda CDM framework (WMAP7). Secondly, by adopting a cosmological-model-independent test, we directly confront the angular diameters from galaxy clusters with two supernovae Ia (SNe Ia) subsamples (carefully chosen to coincide with the cluster positions). The influence of the different SNe Ia light-curve fitters in the previous analysis are also discussed. Methods. We assumed that eta is a function of the redshift parametrized by two different relations: eta(z) = 1 +eta(0)z, and eta(z) = 1 + eta(0)z/(1 + z), where eta(0) is a constant parameter quantifying the possible departure from the strict validity of the DD relation. In order to determine the probability density function (PDF) of eta(0), we considered the angular diameter distances from galaxy clusters recently studied by two different groups by assuming elliptical and spherical isothermal beta models and spherical non-isothermal beta model. The strict validity of the DD relation will occur only if the maximum value of eta(0) PDF is centered on eta(0) = 0. Results. For both approaches we find that the elliptical beta model agrees with the distance-duality relation, whereas the non-isothermal spherical description is, in the best scenario, only marginally compatible. We find that the two-light curve fitters (SALT2 and MLCS2K2) present a statistically significant conflict, and a joint analysis involving the different approaches suggests that clusters are endowed with an elliptical geometry as previously assumed. Conclusions. The statistical analysis presented here provides new evidence that the true geometry of clusters is elliptical. In principle, it is remarkable that a local property such as the geometry of galaxy clusters might be constrained by a global argument like the one provided by the cosmological distance-duality relation.

Suitability of distance metrics as indexes of home-range size in tropical rodent species

Estimators of home-range size require a large number of observations for estimation and sparse data typical of tropical studies often prohibit the use of such estimators. An alternative may be use of distance metrics as indexes of home range. However, tests of correlation between distance metrics and home-range estimators only exist for North American rodents. We evaluated the suitability of 3 distance metrics (mean distance between successive captures [SD], observed range length [ORL], and mean distance between all capture points [AD]) as indexes for home range for 2 Brazilian Atlantic forest rodents, Akodon montensis (montane grass mouse) and Delomys sublineatus (pallid Atlantic forest rat). Further, we investigated the robustness of distance metrics to low numbers of individuals and captures per individual. We observed a strong correlation between distance metrics and the home-range estimator. None of the metrics was influenced by the number of individuals. ORL presented a strong dependence on the number of captures per individual. Accuracy of SD and AD was not dependent on number of captures per individual, but precision of both metrics was low with numbers of captures below 10. We recommend the use of SD and AD instead of ORL and use of caution in interpretation of results based on trapping data with low captures per individual.

Heuristics for minimizing the maximum within-clusters distance

The clustering problem consists in finding patterns in a data set in order to divide it into clusters with high within-cluster similarity. This paper presents the study of a problem, here called MMD problem, which aims at finding a clustering with a predefined number of clusters that minimizes the largest within-cluster distance (diameter) among all clusters. There are two main objectives in this paper: to propose heuristics for the MMD and to evaluate the suitability of the best proposed heuristic results according to the real classification of some data sets. Regarding the first objective, the results obtained in the experiments indicate a good performance of the best proposed heuristic that outperformed the Complete Linkage algorithm (the most used method from the literature for this problem). Nevertheless, regarding the suitability of the results according to the real classification of the data sets, the proposed heuristic achieved better quality results than C-Means algorithm, but worse than Complete Linkage.

Kinetic of water diffusion and color stability of a resin composite as a function of the curing tip distance

The influence of curing tip distance and storage time in the kinetics of water diffusion (water sorption-W SP, solubility-W SB, and net water uptake) and color stability of a composite were evaluated. Composite samples were polymerized at different distances (5, 10, and 15 mm) and compared to a control group (0 mm). After desiccation, the specimens were stored in distilled water to evaluate the water diffusion over a 120-day period. Net water uptake was calculated (sum of WSP and WSB). The color stability after immersion in a grape juice was compared to distilled water. Data were submitted to three-way ANOVA/Tukey's test (α = 5%). The higher distances caused higher net water uptake (p < 0.05). The immersion in the juice caused significantly higher color change as a function of curing tip distance and the time (p < 0.05). The distance of photoactivation and storage time provide the color alteration and increased net water uptake of the resin composite tested.

Intelligent tutoring system for distance education

This study aims to develop and implement a tool called intelligent tutoring system in an online course to help a formative evaluation in order to improve student learning. According to Bloom et al. (1971,117) formative evaluation is a systematic evaluation to improve the process of teaching and learning. The intelligent tutoring system may provide a timely and high quality feedback that not only informs the correctness of the solution to the problem, but also informs students about the accuracy of the response relative to their current knowledge about the solution. Constructive and supportive feedback should be given to students to reveal the right and wrong answers immediately after taking the test. Feedback about the right answers is a form to reinforce positive behaviors. Identifying possible errors and relating them to the instructional material may help student to strengthen the content under consideration. The remedial suggestion should be given in each answer with detaileddescription with regards the materials and instructional procedures before taking next step. The main idea is to inform students about what they have learned and what they still have to learn. The open-source LMS called Moodle was extended to accomplish the formative evaluation, high-quality feedback, and the communal knowledge presented here with a short online financial math course that is being offered at a large University in Brazil. The preliminary results shows that the intelligent tutoring system using high quality feedback helped students to improve their knowledge about the solution to the problems based on the errors of their past cohorts. The results and suggestion for future work are presented and discussed.

CID: an efficient complexity-invariant distance for time series

The ubiquity of time series data across almost all human endeavors has produced a great interest in time series data mining in the last decade. While dozens of classification algorithms have been applied to time series, recent empirical evidence strongly suggests that simple nearest neighbor classification is exceptionally difficult to beat. The choice of distance measure used by the nearest neighbor algorithm is important, and depends on the invariances required by the domain. For example, motion capture data typically requires invariance to warping, and cardiology data requires invariance to the baseline (the mean value). Similarly, recent work suggests that for time series clustering, the choice of clustering algorithm is much less important than the choice of distance measure used.In this work we make a somewhat surprising claim. There is an invariance that the community seems to have missed, complexity invariance. Intuitively, the problem is that in many domains the different classes may have different complexities, and pairs of complex objects, even those which subjectively may seem very similar to the human eye, tend to be further apart under current distance measures than pairs of simple objects. This fact introduces errors in nearest neighbor classification, where some complex objects may be incorrectly assigned to a simpler class. Similarly, for clustering this effect can introduce errors by “suggesting” to the clustering algorithm that subjectively similar, but complex objects belong in a sparser and larger diameter cluster than is truly warranted.We introduce the first complexity-invariant distance measure for time series, and show that it generally produces significant improvements in classification and clustering accuracy. We further show that this improvement does not compromise efficiency, since we can lower bound the measure and use a modification of triangular inequality, thus making use of most existing indexing and data mining algorithms. We evaluate our ideas with the largest and most comprehensive set of time series mining experiments ever attempted in a single work, and show that complexity-invariant distance measures can produce improvements in classification and clustering in the vast majority of cases.

Rich media content adaptation in e-learning systems

The wide use of e-technologies represents a great opportunity for underserved segments of the population, especially with the aim of reintegrating excluded individuals back into society through education. This is particularly true for people with different types of disabilities who may have difficulties while attending traditional on-site learning programs that are typically based on printed learning resources. The creation and provision of accessible e-learning contents may therefore become a key factor in enabling people with different access needs to enjoy quality learning experiences and services. Another e-learning challenge is represented by m-learning (which stands for mobile learning), which is emerging as a consequence of mobile terminals diffusion and provides the opportunity to browse didactical materials everywhere, outside places that are traditionally devoted to education. Both such situations share the need to access materials in limited conditions and collide with the growing use of rich media in didactical contents, which are designed to be enjoyed without any restriction. Nowadays, Web-based teaching makes great use of multimedia technologies, ranging from Flash animations to prerecorded video-lectures. Rich media in e-learning can offer significant potential in enhancing the learning environment, through helping to increase access to education, enhance the learning experience and support multiple learning styles. Moreover, they can often be used to improve the structure of Web-based courses. These highly variegated and structured contents may significantly improve the quality and the effectiveness of educational activities for learners. For example, rich media contents allow us to describe complex concepts and process flows. Audio and video elements may be utilized to add a “human touch” to distance-learning courses. Finally, real lectures may be recorded and distributed to integrate or enrich on line materials. A confirmation of the advantages of these approaches can be seen in the exponential growth of video-lecture availability on the net, due to the ease of recording and delivering activities which take place in a traditional classroom. Furthermore, the wide use of assistive technologies for learners with disabilities injects new life into e-learning systems. E-learning allows distance and flexible educational activities, thus helping disabled learners to access resources which would otherwise present significant barriers for them. For instance, students with visual impairments have difficulties in reading traditional visual materials, deaf learners have trouble in following traditional (spoken) lectures, people with motion disabilities have problems in attending on-site programs. As already mentioned, the use of wireless technologies and pervasive computing may really enhance the educational learner experience by offering mobile e-learning services that can be accessed by handheld devices. This new paradigm of educational content distribution maximizes the benefits for learners since it enables users to overcome constraints imposed by the surrounding environment. While certainly helpful for users without disabilities, we believe that the use of newmobile technologies may also become a fundamental tool for impaired learners, since it frees them from sitting in front of a PC. In this way, educational activities can be enjoyed by all the users, without hindrance, thus increasing the social inclusion of non-typical learners. While the provision of fully accessible and portable video-lectures may be extremely useful for students, it is widely recognized that structuring and managing rich media contents for mobile learning services are complex and expensive tasks. Indeed, major difficulties originate from the basic need to provide a textual equivalent for each media resource composing a rich media Learning Object (LO). Moreover, tests need to be carried out to establish whether a given LO is fully accessible to all kinds of learners. Unfortunately, both these tasks are truly time-consuming processes, depending on the type of contents the teacher is writing and on the authoring tool he/she is using. Due to these difficulties, online LOs are often distributed as partially accessible or totally inaccessible content. Bearing this in mind, this thesis aims to discuss the key issues of a system we have developed to deliver accessible, customized or nomadic learning experiences to learners with different access needs and skills. To reduce the risk of excluding users with particular access capabilities, our system exploits Learning Objects (LOs) which are dynamically adapted and transcoded based on the specific needs of non-typical users and on the barriers that they can encounter in the environment. The basic idea is to dynamically adapt contents, by selecting them from a set of media resources packaged in SCORM-compliant LOs and stored in a self-adapting format. The system schedules and orchestrates a set of transcoding processes based on specific learner needs, so as to produce a customized LO that can be fully enjoyed by any (impaired or mobile) student.

Relationships between running economy and mechanics in middle-distance runners

Running economy (RE), i.e. the oxygen consumption at a given submaximal speed, is an important determinant of endurance running performance. So far, investigators have widely attempted to individuate the factors affecting RE in competitive athletes, focusing mainly on the relationships between RE and running biomechanics. However, the current results are inconsistent and a clear mechanical profile of an economic runner has not been yet established. The present work aimed to better understand how the running technique influences RE in sub-elite middle-distance runners by investigating the biomechanical parameters acting on RE and the underlying mechanisms. Special emphasis was given to accounting for intra-individual variability in RE at different speeds and to assessing track running rather than treadmill running. In Study One, a factor analysis was used to reduce the 30 considered mechanical parameters to few global descriptors of the running mechanics. Then, a biomechanical comparison between economic and non economic runners and a multiple regression analysis (with RE as criterion variable and mechanical indices as independent variables) were performed. It was found that a better RE was associated to higher knee and ankle flexion in the support phase, and that the combination of seven individuated mechanical measures explains ∼72% of the variability in RE. In Study Two, a mathematical model predicting RE a priori from the rate of force production, originally developed and used in the field of comparative biology, was adapted and tested in competitive athletes. The model showed a very good fit (R2=0.86). In conclusion, the results of this dissertation suggest that the very complex interrelationships among the mechanical parameters affecting RE may be successfully dealt with through multivariate statistical analyses and the application of theoretical mathematical models. Thanks to these results, coaches are provided with useful tools to assess the biomechanical profile of their athletes. Thus, individual weaknesses in the running technique may be identified and removed, with the ultimate goal to improve RE.

Tactile perception - Perception of tactile distance changes with body site: a neural network modelling study.

La distorsione della percezione della distanza tra due stimoli puntuali applicati sulla superfice della pelle di diverse regioni corporee è conosciuta come Illusione di Weber. Questa illusione è stata osservata, e verificata, in molti esperimenti in cui ai soggetti era chiesto di giudicare la distanza tra due stimoli applicati sulla superficie della pelle di differenti parti corporee. Da tali esperimenti si è dedotto che una stessa distanza tra gli stimoli è giudicata differentemente per diverse regioni corporee. Il concetto secondo cui la distanza sulla pelle è spesso percepita in maniera alterata è ampiamente condiviso, ma i meccanismi neurali che manovrano questa illusione sono, allo stesso tempo, ancora ampiamente sconosciuti. In particolare, non è ancora chiaro come sia interpretata la distanza tra due stimoli puntuali simultanei, e quali aree celebrali siano coinvolte in questa elaborazione. L’illusione di Weber può essere spiegata, in parte, considerando la differenza in termini di densità meccano-recettoriale delle differenti regioni corporee, e l’immagine distorta del nostro corpo che risiede nella Corteccia Primaria Somato-Sensoriale (homunculus). Tuttavia, questi meccanismi sembrano non sufficienti a spiegare il fenomeno osservato: infatti, secondo i risultati derivanti da 100 anni di sperimentazioni, le distorsioni effettive nel giudizio delle distanze sono molto più piccole rispetto alle distorsioni che la Corteccia Primaria suggerisce. In altre parole, l’illusione osservata negli esperimenti tattili è molto più piccola rispetto all’effetto prodotto dalla differente densità recettoriale che affligge le diverse parti del corpo, o dall’estensione corticale. Ciò, ha portato a ipotizzare che la percezione della distanza tattile richieda la presenza di un’ulteriore area celebrale, e di ulteriori meccanismi che operino allo scopo di ridimensionare – almeno parzialmente – le informazioni derivanti dalla corteccia primaria, in modo da mantenere una certa costanza nella percezione della distanza tattile lungo la superfice corporea. E’ stata così proposta la presenza di una sorta di “processo di ridimensionamento”, chiamato “Rescaling Process” che opera per ridurre questa illusione verso una percezione più verosimile. Il verificarsi di questo processo è sostenuto da molti ricercatori in ambito neuro scientifico; in particolare, dal Dr. Matthew Longo, neuro scienziato del Department of Psychological Sciences (Birkbeck University of London), le cui ricerche sulla percezione della distanza tattile e sulla rappresentazione corporea sembrano confermare questa ipotesi. Tuttavia, i meccanismi neurali, e i circuiti che stanno alla base di questo potenziale “Rescaling Process” sono ancora ampiamente sconosciuti. Lo scopo di questa tesi è stato quello di chiarire la possibile organizzazione della rete, e i meccanismi neurali che scatenano l’illusione di Weber e il “Rescaling Process”, usando un modello di rete neurale. La maggior parte del lavoro è stata svolta nel Dipartimento di Scienze Psicologiche della Birkbeck University of London, sotto la supervisione del Dott. M. Longo, il quale ha contribuito principalmente all’interpretazione dei risultati del modello, dando suggerimenti sull’elaborazione dei risultati in modo da ottenere un’informazione più chiara; inoltre egli ha fornito utili direttive per la validazione dei risultati durante l’implementazione di test statistici. Per replicare l’illusione di Weber ed il “Rescaling Proess”, la rete neurale è stata organizzata con due strati principali di neuroni corrispondenti a due differenti aree funzionali corticali: • Primo strato di neuroni (il quale dà il via ad una prima elaborazione degli stimoli esterni): questo strato può essere pensato come parte della Corteccia Primaria Somato-Sensoriale affetta da Magnificazione Corticale (homunculus). • Secondo strato di neuroni (successiva elaborazione delle informazioni provenienti dal primo strato): questo strato può rappresentare un’Area Corticale più elevata coinvolta nell’implementazione del “Rescaling Process”. Le reti neurali sono state costruite includendo connessioni sinaptiche all’interno di ogni strato (Sinapsi Laterali), e connessioni sinaptiche tra i due strati neurali (Sinapsi Feed-Forward), assumendo inoltre che l’attività di ogni neurone dipenda dal suo input attraverso una relazione sigmoidale statica, cosi come da una dinamica del primo ordine. In particolare, usando la struttura appena descritta, sono state implementate due differenti reti neurali, per due differenti regioni corporee (per esempio, Mano e Braccio), caratterizzate da differente risoluzione tattile e differente Magnificazione Corticale, in modo da replicare l’Illusione di Weber ed il “Rescaling Process”. Questi modelli possono aiutare a comprendere il meccanismo dell’illusione di Weber e dare così una possibile spiegazione al “Rescaling Process”. Inoltre, le reti neurali implementate forniscono un valido contributo per la comprensione della strategia adottata dal cervello nell’interpretazione della distanza sulla superficie della pelle. Oltre allo scopo di comprensione, tali modelli potrebbero essere impiegati altresì per formulare predizioni che potranno poi essere verificate in seguito, in vivo, su soggetti reali attraverso esperimenti di percezione tattile. E’ importante sottolineare che i modelli implementati sono da considerarsi prettamente come modelli funzionali e non intendono replicare dettagli fisiologici ed anatomici. I principali risultati ottenuti tramite questi modelli sono la riproduzione del fenomeno della “Weber’s Illusion” per due differenti regioni corporee, Mano e Braccio, come riportato nei tanti articoli riguardanti le illusioni tattili (per esempio “The perception of distance and location for dual tactile pressures” di Barry G. Green). L’illusione di Weber è stata registrata attraverso l’output delle reti neurali, e poi rappresentata graficamente, cercando di spiegare le ragioni di tali risultati.

Tactile Perception - Perception of tactile distance on a single skin surface changes with stimulus orientation: a neuronal network modelling study

L’interazione che abbiamo con l’ambiente che ci circonda dipende sia da diverse tipologie di stimoli esterni che percepiamo (tattili, visivi, acustici, ecc.) sia dalla loro elaborazione per opera del nostro sistema nervoso. A volte però, l’integrazione e l’elaborazione di tali input possono causare effetti d’illusione. Ciò si presenta, ad esempio, nella percezione tattile. Infatti, la percezione di distanze tattili varia al variare della regione corporea considerata. Il concetto che distanze sulla cute siano frequentemente erroneamente percepite, è stato scoperto circa un secolo fa da Weber. In particolare, una determinata distanza fisica, è percepita maggiore su parti del corpo che presentano una più alta densità di meccanocettori rispetto a distanze applicate su parti del corpo con inferiore densità. Oltre a questa illusione, un importante fenomeno osservato in vivo è rappresentato dal fatto che la percezione della distanza tattile dipende dall’orientazione degli stimoli applicati sulla cute. In sostanza, la distanza percepita su una regione cutanea varia al variare dell’orientazione degli stimoli applicati. Recentemente, Longo e Haggard (Longo & Haggard, J.Exp.Psychol. Hum Percept Perform 37: 720-726, 2011), allo scopo di investigare come sia rappresentato il nostro corpo all’interno del nostro cervello, hanno messo a confronto distanze tattili a diverse orientazioni sulla mano deducendo che la distanza fra due stimoli puntuali è percepita maggiore se applicata trasversalmente sulla mano anziché longitudinalmente. Tale illusione è nota con il nome di Illusione Tattile Orientazione-Dipendente e diversi risultati riportati in letteratura dimostrano che tale illusione dipende dalla distanza che intercorre fra i due stimoli puntuali sulla cute. Infatti, Green riporta in un suo articolo (Green, Percpept Pshycophys 31, 315-323, 1982) il fatto che maggiore sia la distanza applicata e maggiore risulterà l’effetto illusivo che si presenta. L’illusione di Weber e l’illusione tattile orientazione-dipendente sono spiegate in letteratura considerando differenze riguardanti la densità di recettori, gli effetti di magnificazione corticale a livello della corteccia primaria somatosensoriale (regioni della corteccia somatosensoriale, di dimensioni differenti, sono adibite a diverse regioni corporee) e differenze nella dimensione e forma dei campi recettivi. Tuttavia tali effetti di illusione risultano molto meno rilevanti rispetto a quelli che ci si aspetta semplicemente considerando i meccanismi fisiologici, elencati in precedenza, che li causano. Ciò suggerisce che l’informazione tattile elaborata a livello della corteccia primaria somatosensoriale, riceva successivi step di elaborazione in aree corticali di più alto livello. Esse agiscono allo scopo di ridurre il divario fra distanza percepita trasversalmente e distanza percepita longitudinalmente, rendendole più simili tra loro. Tale processo assume il nome di “Rescaling Process”. I meccanismi neurali che operano nel cervello allo scopo di garantire Rescaling Process restano ancora largamente sconosciuti. Perciò, lo scopo del mio progetto di tesi è stato quello di realizzare un modello di rete neurale che simulasse gli aspetti riguardanti la percezione tattile, l’illusione orientazione-dipendente e il processo di rescaling avanzando possibili ipotesi circa i meccanismi neurali che concorrono alla loro realizzazione. Il modello computazionale si compone di due diversi layers neurali che processano l’informazione tattile. Uno di questi rappresenta un’area corticale di più basso livello (chiamata Area1) nella quale una prima e distorta rappresentazione tattile è realizzata. Per questo, tale layer potrebbe rappresentare un’area della corteccia primaria somatosensoriale, dove la rappresentazione della distanza tattile è significativamente distorta a causa dell’anisotropia dei campi recettivi e della magnificazione corticale. Il secondo layer (chiamato Area2) rappresenta un’area di più alto livello che riceve le informazioni tattili dal primo e ne riduce la loro distorsione mediante Rescaling Process. Questo layer potrebbe rappresentare aree corticali superiori (ad esempio la corteccia parietale o quella temporale) adibite anch’esse alla percezione di distanze tattili ed implicate nel Rescaling Process. Nel modello, i neuroni in Area1 ricevono informazioni dagli stimoli esterni (applicati sulla cute) inviando quindi informazioni ai neuroni in Area2 mediante sinapsi Feed-forward eccitatorie. Di fatto, neuroni appartenenti ad uno stesso layer comunicano fra loro attraverso sinapsi laterali aventi una forma a cappello Messicano. E’ importante affermare che la rete neurale implementata è principalmente un modello concettuale che non si preme di fornire un’accurata riproduzione delle strutture fisiologiche ed anatomiche. Per questo occorre considerare un livello astratto di implementazione senza specificare un’esatta corrispondenza tra layers nel modello e regioni anatomiche presenti nel cervello. Tuttavia, i meccanismi inclusi nel modello sono biologicamente plausibili. Dunque la rete neurale può essere utile per una migliore comprensione dei molteplici meccanismi agenti nel nostro cervello, allo scopo di elaborare diversi input tattili. Infatti, il modello è in grado di riprodurre diversi risultati riportati negli articoli di Green e Longo & Haggard.

Complexes of polyelectrolytes with defined charge distance and different dendrimer counterions

Complexes of polyelectrolytes with defined charge distance and different dendrimer counterions Magdalena Chelmecka Max Planck Institute for Polymer Research; Ackermannweg 10; D-55128 Mainz ; Tel.: (+49) 06131- 379 – 226 A study of complexes in solution is of interest to investigate whether the formation of well-defined assemblies like in classical surfactant systems is possible. Aim of this thesis is to investigate the electrostatic self-assembly of linear polycations of varying charge distance with “large” counterions of varying architecture. We especially investigate the morphology of objects formed, but also their stability under salt free condition and after low molecular mass salt addition. As polycations, Poly(dialkylimino)-alkylene salts (Ionenes) I65MeBr and I25MeBr were chosen. Ionenes are synthesized via Menschutkin reaction and characterized by standard methods. Counterions are Polyamidoamine (PAMAM) dendrimers of generations G2.5, G5.5, G7.5 with -COONa surface groups and shape-persistent, Polyphenylene dendrimers of generation G1 with surface -COOH groups. A complex interplay of interactions is expected to direct the self assembly via electrostatic interaction, geometric factors, hydrophobic interaction or hydrogen bonds. Methods used for the investigation of complexes are: UV-spectroscopy, pH-metric techniques, dynamic and static light scattering, small angle neutron scattering,  potential measurements and potentiometric titration. Under certain conditions, (i.e. charge ratio of compounds, charge density of ionene and dendrimer also concentration of sample) polyelectrolyte systems composed of ionenes and dendrimers build complexes in solution. System compounds are typical polyelectrolytes, but structures which they build behave not usual for typical polyelectrolytes. In a one diffusion mode regime aggregates of about 100 nm hydrodynamic radius have been found. Such aggregates are core-shell or anisotropic core shell structures in the case of ionenes/PAMAM dendrimers complexes. These complexes are stable even at high ionic strength. In case of ionenes with poly(phenylene) dendrimers, hard sphere-like objects or spherical objects with hairy-like surface have been found in a one diffusion mode regime. Their stability at high ionic strength is lower. For the ionenes/poly(phenylene) dendrimers systems one transition point has been found from one to two diffusion processes, towards increasing ionene concentration, i.e. for the samples with fixed dendrimer concentration towards increasing ionic strength. For the diffusion profile of ionene/PAMAM dendrimers in most cases two transition regimes are observed. One at very low ionene concentration, the second one at high ionene concentrations, which again means for the samples with fixed dendrimer concentration, also at higher ionic strength. Both two mode regimes are separated by the one mode regime. As was confirmed experimentally, the one diffusion mode regime is caused by the motion of well defined assemblies. The two diffusion mode regimes are caused by the movement of different sized species in solution, large aggregates and middle-size aggregates (oligoaggregates). The location and also the number of transition points in the diffusion profiles is dependent on the ionene to dendrimer charge ratio, charge density of the compounds and concentration. No influence of the molecular mass of the ionene has been found. The aggregates are found to be charged on the surface, however this surface charge does not significantly influence the diffusion properties of the system.

Internationalization intentions: micro-foundations and psychological distance perceptions in immigrant and non-immigrant entrepreneurs

This dissertation project aims at shedding light on the micro-foundations of international entrepreneurship, focusing on the pre-internationalization phase and taking an individual-level perspective. Three research questions are investigated building on a cognitive model of internationalization intentions. First, what are the antecedents to internationalization intentions, i.e. desirability and feasibility, and how they interact with psychological distance towards internationalization options. Second, what is the role of previous entrepreneurs’ experience on such antecedents, in particular for immigrant vs. non-immigrant entrepreneurs. Third, how are these antecedent elements influenced by entrepreneurs’ individual-level motivations and goals. Using a new data set from 140 independent, non-internationalized, high-tech SMEs and their 169 owners, a variety of analytical techniques are used to investigate the research questions, such as structural equation modeling, hierarchical regression and a "laddering" technique. This project advances our theoretical understanding of internationalization and international entrepreneurship and has relevant implications for entrepreneurs and policy-makers.