Determinants of intraregional migration in Sub-Saharan Africa 1980-2000

Despite great accomplishments in the migration literature, the determinants of South-South migration remain poorly understood. In an attempt to fill this gap, this paper formulates and tests an empirical model for intraregional migration in sub-Saharan Africa within an extended human capital framework, taking into account spatial interaction. Using bilateral panel data between 1980 and 2000, we find that intraregional migration on the subcontinent is predominantly driven by economic opportunities and sociopolitics in the host country, facilitated by geographical proximity. The role played by network effects and environmental conditions is also apparent. Finally, origin and destination spatial dependence should definitely not be ignored

The Effect of Expected Income on Individual Migration Decisions

The paper develops a tractable econometric model of optimal migration, focusing on expected income as the main economic influence on migration. The model improves on previous work in two respects: it covers optimal sequences of location decisions (rather than a single once-for-all choice), and it allows for many alternative location choices. The model is estimated using panel data from the NLSY on white males with a high school education. Our main conclusion is that interstate migration decisions are influenced to a substantial extent by income prospects. The results suggest that the link between income and migration decisions is driven both by geographic differences in mean wages and by a tendency to move in search of a better locational match when the income realization in the current location is unfavorable.

Physical phenomena in containerless glass processing

Experiments were conducted on bubble migration in rotating liquid bodies contained in a sphere. Experiments were initiated on the migration of a drop in a slightly less dense continuous phase contained in a rotating sphere. A refined apparatus for the study of thermocapillar flow in a glass melt was built, and data were acquired on surface velocities in the melt. Similar data also were obtained from an ambient temperature fluid model. The data were analyzed and correlated with the aid of theory. Data were obtained on flow velocities in a pendant drop heated from above. The motion in this system was driven principally by thermocapillarity. An apparatus was designed for the study of volatilization from a glass melt

Poverty Traps, Distance, and Diversity: The Migration Connection

Within-country ethnic diversity in high-wage immigrant nations is driven by long distance migration. This paper documents the migration-diversity connection for the first global century before 1914 and the second global century after 1950. It distinguishes between ethnic diversity among the foreign-born, between the foreign-born and native-born and for total populations using country-of-birth data. It exploits the polarization index made popular in the recent diversity-growth debate and exploits an emigration life cycle model to predict the connection. It also shows how policy matters.

Non-Markovian data-driven modeling of single-cell motility

Trajectories of human breast cancer cells moving on one-dimensional circular tracks are modeled by thenon-Markovian version of the Langevin equation that includes an arbitrary memory function. When averagedover cells, the velocity distribution exhibits spurious non-Gaussian behavior, while single cells are characterizedby Gaussian velocity distributions. Accordingly, the data are described by a linear memory model whichincludes different random walk models that were previously used to account for various aspects of cell motilitysuch as migratory persistence, non-Markovian effects, colored noise, and anomalous diffusion. The memoryfunction is extracted from the trajectory data without restrictions or assumptions, thus making our approachtruly data driven, and is used for unbiased single-cell comparison. The cell memory displays time-delayedsingle-exponential negative friction, which clearly distinguishes cell motion from the simple persistent randomwalk model and suggests a regulatory feedback mechanism that controls cell migration. Based on the extractedmemory function we formulate a generalized exactly solvable cell migration model which indicates thatnegative friction generates cell persistence over long timescales. The nonequilibrium character of cell motionis investigated by mapping the non-Markovian Langevin equation with memory onto a Markovian model thatinvolves a hidden degree of freedom and is equivalent to the underdamped active Ornstein-Uhlenbeck process

WAGE GAPS AND MIGRANTION COSTS: AN ANALYSIS FROM SIMULATION DATA

Borjas (1987, 1991 and 1994) developed the self-selection theory, applying Roy’s model (1951) to migration studies. He establishes that the characteristics of migrants in terms of skills and abilities are driven by wage distribution differences between the host country and home. In this regard, when the country of origin has higher relative returns for skills and more disperse income distribution, a negative selection of migrants is generated, and vice versa. A great deal of literature has studied Self-selection model to analyse how wage distribution influences migrants’ decisions, leading to consistent and inconsistent results. Given the conflicting results in the literature, this paper examines how migration costs and wage differences influence self-selection patterns –i.e. skills in terms of schooling levels. Taking into account that self-selection can not be studied systematically by means of standard data sources because of the lack of data, we propose an analytical model based on the individual investment decision theory (Human Capital theory), applying simulated data by Monte-Carlo method. The theory of individual investment decisions allows us to analyze self-selection patterns across differences in wages and economic conditions at home and in host countries and to introduce uncertainty using a stochastic framework. An empirical application for long-distant migrations –from Ecuador to Spain– is implemented. Our findings show that migrants are positively selected on observable skills between Spain and Ecuador, considering both constant direct migration costs and constant direct migration costs-plus-variable opportunity migration costs. Secondary data from official sources confirm this tendency.

A Global Plate Model Including Lithospheric Deformation Along Major Rifts and Orogens Since the Triassic

Global deep‐time plate motion models have traditionally followed a classical rigid plate approach, even though plate deformation is known to be significant. Here we present a global Mesozoic–Cenozoic deforming plate motion model that captures the progressive extension of all continental margins since the initiation of rifting within Pangea at ~240 Ma. The model also includes major failed continental rifts and compressional deformation along collision zones. The outlines and timing of regional deformation episodes are reconstructed from a wealth of published regional tectonic models and associated geological and geophysical data. We reconstruct absolute plate motions in a mantle reference frame with a joint global inversion using hot spot tracks for the last 80 million years and minimizing global trench migration velocities and net lithospheric rotation. In our optimized model, net rotation is consistently below 0.2°/Myr, and trench migration scatter is substantially reduced. Distributed plate deformation reaches a Mesozoic peak of 30 × 106 km2 in the Late Jurassic (~160–155 Ma), driven by a vast network of rift systems. After a mid‐Cretaceous drop in deformation, it reaches a high of 48 x 106 km2 in the Late Eocene (~35 Ma), driven by the progressive growth of plate collisions and the formation of new rift systems. About a third of the continental crustal area has been deformed since 240 Ma, partitioned roughly into 65% extension and 35% compression. This community plate model provides a framework for building detailed regional deforming plate networks and form a constraint for models of basin evolution and the plate‐mantle system

Migration-Based Seismic Trace Interpolation of Sparse Converted Phase Micro-Seismic Data

Multi-component elastic seismic data collected at large offsets have the potential to be used in micro seismic imaging and monitoring. However, types of receiver surface deployments used for micro-seismic monitoring are generally very sparse, and thus the data used for imaging from these receivers cause receiver-migration-operator artifacts that severely contaminate the shallow part of the image. In this study, we present a data-driven method that alleviates these imaging artifacts. The method is based on converted-phase elastic seismic migration and de-migration. We show that despite the spatial aliasing of the recorded data, we are able to suppress the receiver migration-operator artifacts and reconstruct the shallow part of the image. The merit of this approach is that it is elastic, fully data-driven (i.e, independent of source parameters), and does not suffer from migration operator source aliasing, when a small number of shots or micro-seismic events are used. We present a derivation of the method and test it with a synthetic model and a field data set from a geothermal reservoir with abundant natural and induced seismicity