Self-selection patterns in Mexico-U.S. migration: the role of migration networks

This paper examines the role of migration networks in determining self-selection patterns of Mexico-U.S. migration. We first present a simple theoretical framework showing how such networks impact on migration incentives at different education levels and, consequently, how they are likely to affect the expected skill composition of migration. Using survey data from Mexico, we then show that the probability of migration is increasing with education in communities with low migrant networks, but decreasing with education in communities with high migrant networks. This is consistent with positive self-selection of migrants being driven by high migration costs, as advocated by Chiquiar and Hanson (2005), and with negative self-selection of migrants being driven by lower returns to education in the U.S. than in Mexico, as advocated by Borjas (1987)

Can migration reduce educational attainments? depressing evidence from Mexico

This paper examines the impact of migration on educational attainments in rural Mexico. Using historical migration rates by state to instrument for current migration, we find evidence of a significant negative effect of migration on schooling attendance and attainments of 12 to 18 year-old boys and of 16 to 18 year-old girls. IV-Censored Ordered Probit results show that living in a migrant household lowers the chances of boys completing junior high-school and of boys and girls completing high-school. The negative effect of migration on schooling is somewhat mitigated for younger girls with low educated mothers, which is consistent with remittances relaxing credit constraints on education investment for the very poor. However, for the majority of rural Mexican children, family migration depresses educational attainment. Comparison of the marginal effects of migration on school attendance and on participation to other activities shows that the observed decrease in schooling of 16 to 18 year olds is accounted for by current migration of boys and increases in housework for girls

Rastersondenmikroskopie mit Hochfrequenzsignalen

Diese Arbeit beschäftigt sich mit der Entwicklung und Verbesserung von Rastersondenmikroskopen durch den Anschluß eines Signalpfades für hochfrequente Wechselfelder (ca. 1 GHz). Dabei entstanden sowohl ein Hochfrequenzrastertunnelmikroskop (HF-STM), als auch ein Hochfrequenzkapazitätsmikroskop (HF-SCM). Das gemeinsame Funktionsprinzip dieser Mikroskope besteht in der Nutzung der Nahfeldwechselwirkungszone als Mischer für die hochfrequenten Signale. Dabei entstehen aus den Eingangssignalen neue Signale anderer Frequenz, die verstärkt und detektiert werden. Beim HF-STM werden diese Signale durch die Nichtlinearität der statischen Strom-Spannungskennlinie des Tunnelsüberganges hervorgerufen. Hieraus ergeben sich zwei neue Nutzungsmöglichkeiten im Vergleich zum herkömmlichen STM: Erstens lassen sich durch Vergleich mit den gleichzeitig aufgenommenen topographischen Bildern elektronische von topographischen Gegebenheiten unterscheiden. Zweitens ist ein Betrieb des HF-STM's auf leitenden Oberflächen möglich, zu denen jedoch keine leitende Verbindung besteht, wie beispielsweise Metallinseln auf einem Nichtleiter-geträgerten Katalysator. Im Falle des HF-SCMs konnte gezeigt werden, daß die detektierten Signale durch die Nichtlinearität der Kapazitäts-Spannungskennlinie des von Spitze und Substrat gebildeten MOS-Kondensators entstehen. Das Mikroskop läßt sich verwenden, um Schwankungen der Oxidschichtdicke oder laterale Dotierprofile in Halbleiterstrukturen abzubilden. Gegenüber dem herkömmlichen SCM bietet die Methode den Vorteil der freien Wahl der Arbeitsfrequenz, wodurch zusätzlich frequenzabhängige Messungen möglich werden.This work concerns the developement and improvement of scanning probe microscopes by connecting a high frequency signal path (approx. 1 GHz) to the tip of the microscope. This allowed the construction of both, a high frequency scanning tunneling microscope (HF-STM) as well as a high frequency scanning capacity microscope (HF-SCM). The common priciple of the microscopes is the use of the nearfield zone as a mixing device for the high frequency signals. From the input signals new signals at other frequencies are generated, amplified and detected. In case of the HF-STM these signals are caused by the nonlinear current-voltage characteristics of the tunneling junction. The principle permits two new applications: First the comparison between conventional STM-pictures with the newly generated pictures of the same area allows to differantiate between topographic and electronic features of the surface. Second, the new method allows the imaging of conducting surfaces, even if there is no direct conducting conection. An example would be the imaging of metal clusters embedded in a nonconducting surface. In case of the HF-SCM it could be demonstrated that the detected signals are caused by the the nonlinear capacity-voltage dependence of the MOS-capacitor, formed by the substrate and the conducting tip. The microscope can be used to image changes of the oxide layer thicknes or lateral doping profiles in semicoductor devices. In comparison with the conventional SCM the new device is not restricted to one frequency and can therefore be used to carry out frequency-dependent measurements

Growing Scale-Free Networks with Tunable Clustering

We extend the standard scale-free network model to include a ``triad formation step''. We analyze the geometric properties of networks generated by this algorithm both analytically and by numerical calculations, and find that our model possesses the same characteristics as the standard scale-free networks like the power-law degree distribution and the small average geodesic length, but with the high-clustering at the same time. In our model, the clustering coefficient is also shown to be tunable simply by changing a control parameter - the average number of triad formation trials per time step.Comment: Accepted for publication in Phys. Rev.

Stepwise disarmament and sudden destruction in a two-person game: a research tool

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66968/2/10.1177_002200276400800104.pd

Interlayer Registry Determines the Sliding Potential of Layered Metal Dichalcogenides: The case of 2H-MoS2

We provide a simple and intuitive explanation for the interlayer sliding energy landscape of metal dichalcogenides. Based on the recently introduced registry index (RI) concept, we define a purely geometrical parameter which quantifies the degree of interlayer commensurability in the layered phase of molybdenum disulphide (2HMoS2). A direct relation between the sliding energy landscape and the corresponding interlayer registry surface of 2H-MoS2 is discovered thus marking the registry index as a computationally efficient means for studying the tribology of complex nanoscale material interfaces in the wearless friction regime.Comment: 13 pages, 7 figure

An analysis of integrative outcomes in the Dayton peace negotiations

The nature of the negotiated outcomes of the eight issues of the Dayton Peace Agreement was studied in terms of their integrative and distributive aspects. in cases where integrative elements were Sound, further analysis was conducted by concentrating on Pruitt's five types of integrative solutions: expanding the pie, cost cutting, non-specific compensation, logrolling, and bridging. The results showed that real world international negotiations can arrive at integrative agreements even when they involve redistribution of resources tin this case the redistribution of former Yugoslavia). Another conclusion was that an agreement can consist of several distributive outcomes and several integrative outcomes produced by different kinds of mechanisms. Similarly, in single issues more than one mechanism can be used simultaneously. Some distributive bargaining was needed in order to determine how much compensation was required. Finally, each integrative formula had some distributive aspects as well

On population abundance and niche structure

Recent published evidence indicates a negative correlation between density of populations and the distance of their environments to a suitably defined ‘niche centroid’. This empirical observation lacks theoretical grounds. We provide a theoretical underpinning for the empirical relationship between population density and position in niche space, and use this framework to understand the circumstances under which the relationship will fail. We propose a metapopulation model for the area of distribution, as a system of ordinary differential equations coupled with a dispersal kernel. We present an analytical approximation to the solution of the system as well as R code to solve the full model numerically. We use this tool to analyze various scenarios and assumptions. General and realistic demographic assumptions imply a good correlation between position in niche space and population abundance. Factors that modify this correlation are: transitory states, a heterogeneous spatial structure of suitability, and Allee effects. We also explain why the raw output of the niche modeling algorithm MaxEnt is not a good predictor of environmental suitability. Our results elucidate the empirical results for spatial patterns of population size in niche terms, and provide a theoretical basis for a structured theory of the niche

Managing action research: the PEArL framework

The difficulty of managing and validating Action Research field studies has been widely discussed. Several different approaches to Action Research have emerged, and one of the most widely used models is Checkland’s FMA model, where a framework is provided to facilitate interested individuals in ‘recovering’ the route of the inquiry. In this paper, I argue that the FMA model is a valuable tool for planning the application of theoretical ideas in a practical situation, but that, as a guide to Action Research, it still fails to provide a sense of the manner in which an inquiry is undertaken. The PEArL mnemonic has been previously offered as a guide to facilitate researchers, participants, and those interested in gaining an appreciation of the manner in which an inquiry is conducted. In this paper, it is argued that applying the PEArL elements does not provide insight into the dynamic nature of collaborative inquiry. In order to gain a sense of the manner in which an inquiry was undertaken it is necessary to apply the PEArL mnemonic alongside a framework that facilitates the flow of the action research cycle. To illustrate the framework, an Action Research field study is described that was undertaken with residents and key workers in a shelter for the homeless, where the aim was to create a shared understanding of complex needs and support requirements