How predictable : patterns of human economic behavior in the wild

Thesis (S.M.)--Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 40-41).Shopping is driven by needs (to eat, to socialize, to work), but it is also a driver of where we go. I examine the transaction records of 80 million customers and find that while our economic choices predict mobility patterns overall, at the small scale we transact unpredictably. In particular, we bundle together multiple store visits, and interleave the order in which we frequent those stores. Individual predictability also varies with income level. I end with a description of how merchant composition emerges in US cities, as seen through the lens of credit card swipes.by Katherine (Coco) Krumme.S.M

Tidal and diel dynamics in a nursery area: Patterns in fish migration in a mangrove in north Brazil

Mangroves are considered important as fish nurseries worldwide. Block netting in intertidal mangrove creeks at HW revealed the overwhelming significance of the factors tide and time of day and their combinations (spring tide at dusk and dawn, neap tide at midday and midnight) in structuring fish assemblages. In contrast to neap tide and daylight when nekton catches were poorest, spring tide and darkness produced the most complex fish assemblage structure when abundant species occurred with increased proportions and more rare species entered. Intertidal fish were juveniles or adults of small species, or juveniles of larger species. Stomach analyses of fish showed that the intertidal movements are usually feeding migrations. Fish were concentrated in the subtidal sections at LW. Pioneer studies with a 200 kHz split-beam sonar beaming horizontally and vertically in a large mangrove channel, revealed that the entire fish community rode the first flood rise to achieve upstream transport and to enter the intertidal zone. Despite low Secchi depths, diel changes in vertical distribution were apparent when fish exploited the water column only at night. The four-eyed fish Anableps anableps entered the intertidal creeks rapidly with the first flood rise. They fed in the submerged mangrove at HW and returned gradually after the ebb current maximum to concentrate again in the subtidal parts of the main channel at LW. The combination of high inundation at daylight (spring tide-dawn) provided optimum foraging conditions for A. anableps while darkness and low inundation was linked to poorest foraging conditions (neap tide-night). The mangrove zooplankton was dominated by copepods. Zooplankton densities were higher at spring than at neap tide. In contrast to the number of zooplankton species, the densities were lowest at HW and highest at LW. Obviously, the temporal variations in abundance of fish and zooplankton are synchronized by the tide

Urban characteristics attributable to density-driven tie formation

Motivated by empirical evidence on the interplay between geography, population density and societal interaction, we propose a generative process for the evolution of social structure in cities. Our analytical and simulation results predict both super-linear scaling of social tie density and information flow as a function of the population. We demonstrate that our model provides a robust and accurate fit for the dependency of city characteristics with city size, ranging from individual-level dyadic interactions (number of acquaintances, volume of communication) to population-level variables (contagious disease rates, patenting activity, economic productivity and crime) without the need to appeal to modularity, specialization, or hierarchy.Comment: Early version of this paper was presented in NetSci 2012 as a contributed talk in June 2012. An improved version of this paper is published in Nature Communications in June 2013. It has 14 pages and 5 figure

Explaining family cohesion in an immigration context: patterns of intergenerational relationship quality among young adult Turks and their parents

This exploratory study examines patterns of intergenerational relationships among Turkish migrants in Germany. The aims are (1) to follow-up recent research on relationship types and extent it to migrant families, (2) to contrast patterns among migrants with those associated with non-immigrant Germans, and (3) to analyse the impact of migration-related stressors. We use data from the Germany’s new Family Panel pairfam and a complementary survey on Turkish citizens. Descriptive comparisons indicate the high empirical relevance of all expected patterns, with a slightly higher prevalence of amicable and ambivalent relations, and a somewhat lower prevalence of disharmonious and detached ones among the immigrant community in comparison to the German population. Contrasting the theoretically derived hypotheses, regression analyses reveal the low impact of migration-related variables. Neither discrimination experiences nor acculturation levels seem to affect family ties. In line with the hypothesis, cultural retention in terms of Turkish language skills seems to positively affect the child-father relationship. Results are discussed with regard to family support resources in young and later life

Black-Scholes and Monetary Black Holes

The Black-Scholes formula is fundamental to modeling carried out in the financial world. Black-Scholes presents investment bankers a method of evaluating a stock in order to know how much to charge for a premium when dealing with options; a way of selling and/or buying securities at a predetermined time in the future. Understanding how Black-Scholes and options theory work relies on understanding probability, statistics, and Brownian motion. these tools make it possible for Black-Scholes to do its dirty work

Life satisfaction of migrants, stayers and returnees: reaping the fruits of migration in old age?

This paper evaluates the effects of migration on life satisfaction in later life. We compare the life satisfaction of older migrants with that of non-migrants and return migrants, of a similar age and originating from the same regions in Turkey. Turks constitute one of the largest migrant groups in Europe, and the growing population of older Turkish migrants display greater risks of loneliness and material disadvantage compared to native-born populations in Europe. However, compared to their non-migrant peers from the country of origin, older migrants may experience gains from migration that are reflected in their life satisfaction. Using the 2000 Families study, a large survey of Turkish migrants from the peak labour migration period and their non-migrant comparators, we investigate whether life satisfaction of migrants and stayers differs and the possible causes of any differences. We find that both migrants and return migrants experience higher life satisfaction in old age than stayers. However, the gap cannot be explained by the classical determinants of life satisfaction such as income, health, partner and friends, or religiosity, nor by the better outcomes of the migrants’ children. We discuss possible reasons for this migration satisfaction advantag

Optimal Permutation Routing for Low-dimensional Hypercubes

We consider the offline problem of routing a permutation of tokens on the nodes of a d-dimensional hypercube, under a queueless MIMD communication model (under the constraints that each hypercube edge may only communicate one token per communication step, and each node may only be occupied by a single token between communication steps). For a d-dimensional hypercube, it is easy to see that d communication steps are necessary. We develop a theory of “separability ” which enables an analytical proof that d steps suffice for the case d = 3, and facilitates an experimental verification that d steps suffice for d = 4. This result improves the upper bound for the number of communication steps required to route an arbitrary permutation on arbitrarily large hypercubes to 2d − 4. We also find an interesting side-result, that the number of possible communication steps in a d-dimensional hypercube is the same as the number of perfect matchings in a (d + 1)-dimensional hypercube, a combinatorial quantity for which there is no closed-form expression. Finally we present some experimental observations which may lead to a proof of a more general result for arbitrarily large dimension d. 2

Influence of disorder and interfaces on the electronic and magnetic properties of Heusler systems

Anhand von Mössbauer-spektroskopischen Untersuchungen von Fe3Si-Filmen auf GaAs(100) und MgO(100) konnte nachgewiesen werden, dass das Wachstum von Fe3Si auf GaAs(100) durch eine Interdiffusion von Ga/As-Atomen gestört wird. Die Verwendung einer 3 nm dicken MgO-Tunnelbarriere auf der GaAs-Oberfläche unterdrückt diese Interdiffusion deutlich und ermöglicht so ein epitaktisches Filmwachstum von Fe3Si. Ein Vergleich der Röntgenabsorptionsuntersuchungen mit DFT-Rechnungen offenbart die Beiträge der verschiedenen Fe-Untergitter zum XAS und XMCD. Eine Berücksichtigung von Unordnung durch Ga/As-Atome in DFT-Rechnungen zeigt nur eine geringe Abnahme der Spinpolarisation von Fe3Si, so dass das System Fe3Si/GaAs(100) weiterhin ein interessanter Kandidat für spintronische Anwendungen ist. Für die Gemische Co2MnSi und Co2FeSi konnte der Einfluss der 3d-Übergangsmetalle Mn/Fe auf die Hybridisierung durch Röntgenabsorption und DFT-Rechnungen bestimmt werden. Eine tiefenselektive Untersuchung der elektronischen Struktur von Mn in Co2MnSi an einer MgO-Grenzschicht lässt einen Anstieg der Anzahl unbesetzter d-Zustände vermuten und weist somit auf eine MnSi-Terminierung hin. An nicht-stöchiometrischen Co2FeSi-Gemischen konnte eine Magnetfeldabhängigkeit der elektronischen Struktur von Co und Fe in Si-reichem Co2FeSi beobachtet werden. Dies könnte ein Hinweis auf magnetostriktive Effekte in diesem Gemisch sein. Des Weiteren wurde das Heusler-Gemisch Ni51.6Mn32.9Sn15.5 in dieser Arbeit untersucht, das ein Formgedächtnismetall darstellt und einen deutlichen inversen magnetokalorischen Effekt zeigt. In dieser Arbeit lag der Schwerpunkt auf den elementspezifischen magnetischen Eigenschaften von Ni und Mn. Für Mn wurde ein starker Anstieg des Verhältnisses von Bahn- zu Spinmoment ml/mS beobachtet. Während dieses Verhältnis in der Austenitphase 5% beträgt, steigt es in der Martensitphase auf 13.5% an. Gleichzeitig weist Ni einen nahezu konstanten Wert von ml/mS von 28% auf. Legt man in der Martensitphase ein Magnetfeld von 3 T an, so lässt sich der Wert des Verhältnisses von ml/mS für beide Elemente reduzieren, was auf einen feldinduzierten inversen Martensitübergang (FIRMT) hinweist.A Mössbauer-spectroscopic investigation of Fe3Si films on GaAs(100) and MgO(100) revealed a disordered growth mode of Fe3Si on GaAs(100), which is caused by an interdiffusion of Ga/As atoms. Implementing a 3 nm thick MgO tunnelbarrier on the GaAs surface inhibits the interdiffusion and enables an epitaxial film growth of Fe3Si. By comparing experimental X-ray absorption measurements with DFT calculations we are able to resolve the contribution of the different Fe sublattices to the XAS and XMCD signal. Taking into account atomic disorder arising from Ga/As atoms within DFT calculation yields a small reduction of the spin polarization of Fe3Si, indicating that the system Fe3Si/GaAs(100) still is an interesting candidate for spintronic applications. For the Heusler compounds Co2MnSi and Co2FeSi the influence of the 3d transition metals Mn/Fe on the hybridization was determined by X-ray absorption and DFT calculations. A depth-selective study of the electronic structure of Mn in Co2MnSi at the vicinity to a MgO tunnelbarrier indicates an increased number of unoccupied d states referring a MnSi terminated interface. For non-stochiometric Co2FeSi compounds a dependence of the electronic structure of Co and Fe from the external magnetic field was observed. This points to magnetostrictive effects in this compound. Furthermore, the Heusler compound Ni51.6Mn32.9Sn15.5 was studied in this work. The compound is a shape memory alloy exhibiting a large inverse magnetocaloric effect. In this work the focus was put on the element-specific magnetic properties of Ni and Mn. For Mn a strong increase of the ratio of orbital to spin magnetic moment ml/mS was observed. In the austenite phase this ratio accounts for 5%, whereas in the martensite this value becomes 13.5%. For Ni ml/mS remains almost constant at 28%. Applying a magnetic field of 3 T in the martensite phase leads to a reduction of ml/mS for both elements, indicating a field-induced reverse martensitic transition (FIRMT)

Modeling rates of change in individuals and populations

Thesis (Ph. D.)--Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, 2013.Cataloged from PDF version of thesis.Includes bibliographical references (p. 81-84).This thesis develops methodologies to measure rates of change in individual human behavior, and to capture statistical regularities in change at the population level, in three pieces: i) a model of individual rate of change as a function of search and finite resources, ii) a structural model of population level change in urban economies, and iii) a statistical test for the deviation from a null model of rank chum of items in a distribution. First, two new measures of human mobility and search behavior are defined: exploration and turnover. Exploration is the rate at which new locations are searched by an individual, and turnover is the rate at which his portfolio of visited locations changes. Contrary to expectation, exploration is open-ended for almost all individuals. A present a baseline model is developed for change (or churn) in human systems, relating rate of exploration to rate of turnover. This model recasts the neutral or random drift mechanism for population-level behavior, and distinguishes exploration due to optimization, from exploration due to a taste for variety. A relationship between the latter and income is shown. Second, there exist regular relationships in the economic structure of cities, with important similarities to ecosystems. Third, a new statistical test is developed for distinguishing random from directed churn in rank ordered systems. With a better understanding of rates of change, we can better predict where people will go, the probability of their meeting, and the expected change of a system over time. More broadly, these findings propose a new way of thinking about individual and system-level behavior: as characterized by predictable rates of innovation and change.by Coco Krumme.Ph.D