Bigdata-based investigation of heterogeneous migration and population distribution

Human mobility is very important in understanding complex social and economic systems. With massive empirical datasets from the China Household Finance Survey and the National Statistics in the UK, we construct a migration probability matrix, and analyze the heterogeneous migration patterns. We then develop a random walk model to dynamically simulate the population distribution. In the stationary state, the resulting population distribution is in good agreement with the real statistical data. For comparison, simulations with an optimized gravity model and other datasets such as the census data in China are also performed. Further, the model simulation is applied to predict the demographic trend with different education levels. Our method could be generally extended to other real communities and internet worlds.

Multi-Population Parallel Wolf Pack Algorithm for Task Assignment of UAV Swarm

The effectiveness of the Wolf Pack Algorithm (WPA) in high-dimensional discrete optimization problems has been verified in previous studies; however, it usually takes too long to obtain the best solution. This paper proposes the Multi-Population Parallel Wolf Pack Algorithm (MPPWPA), in which the size of the wolf population is reduced by dividing the population into multiple sub-populations that optimize independently at the same time. Using the approximate average division method, the population is divided into multiple equal mass sub-populations whose better individuals constitute an elite sub-population. Through the elite-mass population distribution, those better individuals are optimized twice by the elite sub-population and mass sub-populations, which can accelerate the convergence. In order to maintain the population diversity, population pretreatment is proposed. The sub-populations migrate according to a constant migration probability and the migration of sub-populations are equivalent to the re-division of the confluent population. Finally, the proposed algorithm is carried out in a synchronous parallel system. Through the simulation experiments on the task assignment of the UAV swarm in three scenarios whose dimensions of solution space are 8, 30 and 150, the MPPWPA is verified as being effective in improving the optimization performance.

A Collision Avoidance Method for Intelligent Ship Based on the Improved Bacterial Foraging Optimization Algorithm

The bacterial foraging optimization algorithm (BFOA) is an intelligent population optimization algorithm widely used in collision avoidance problems; however, the BFOA is inappropriate for the intelligent ship collision avoidance planning with high safety requirements because BFOA converges slowly, optimizes inaccurately, and has low stability. To fix the above shortcomings of BFOA, an autonomous collision avoidance algorithm based on the improved bacterial foraging optimization algorithm (IBFOA) is demonstrated in this paper. An adaptive diminishing fractal dimension chemotactic step length is designed to replace the fixed step length to achieve the adaptive step length adjustment, an optimal swimming search method is proposed to solve the invalid searching and repeated searching problems of the traditional BFOA, and the adaptive migration probability is developed to take the place of the fixed migration probability to prevent elite individuals from being lost in BOFA. The simulation of benchmark tests shows that the IBFOA has a better convergence speed, optimized accuracy, and higher stability; according to a collision avoidance simulation of intelligent ships which applies the IBFOA, it can realize the autonomous collision avoidance of intelligent ships in dynamic obstacles environment is quick and safe. This research can also be used for intelligent collision avoidance of automatic driving ships.

Small thrombus size, thrombus composition, and poor collaterals predict pre-interventional thrombus migration

BackgroundDifferent imaging characteristics such as clot burden score, collaterals, and pre-interventional thrombus migration are associated with functional outcome in patients with acute ischemic stroke. Moreover, histological thrombus composition is associated with pre-interventional thrombus migration. We hypothesized that smaller clots may more likely migrate and that collateral status in ischemic stroke patients may mediate this tendency of the clot to migrate.MethodsIn this prospective cohort of consecutive ischemic stroke patients, clot burden scores and collateral scores were rated and the retrieved thrombi were histologically analyzed. We then investigated the relationship between clot burden score, probability for thrombus migration, and collateral scores using mediation analysis.Results163 patients are included of which 36 (22.1%) had a clot migration. Probability of thrombus migration was significantly associated with lower collateral scores (P<0.01), higher clot burden scores (P<0.01), shorter thrombi (P<0.01), and higher RBC count (P<0.01). In the mediator pathway, higher collateral scores were significantly associated with higher clot burden scores (P<0.01) and younger age (P=0.029). The total effect of an increase in clot burden score by one grade on thrombus migration is composed of the direct effect (+18%, P<0.01) and the collateral score-mediated indirect effect (−5%, P<0.01).ConclusionsSmaller, erythrocyte-rich thrombi tend to migrate more often. Good collaterals seem to have a considerable effect on limiting migration. This supports the hypothesis that larger clots have stronger adherence with the vessel wall and that good collaterals increase the counter pressure distal of the clot.

Modeling long lifespans in eusocial insect populations

Along with division of labour, and life-history complexities, a characteristic of eusocial insect societies is the greatly extended lifespan for queens. The colony structure reduces the extrinsic mortality of the queen, and according to classical evolutionary theories of ageing, this greatly increases the lifespan. We explore the relationship between the evolution of longevity and the evolution of eusociality by introducing age-structure into a previously proposed evolutionary model and also define an associated agent-based model. A set of three population structures are defined: (i) solitary with all reproductive individuals, (ii) monogynous eusocial with a single queen, and (iii) polygynous eusocial, with multiple queens.In order to compare the relative fitnesses we compete all possible pairs of these strategies as well as all three together, analysing the effects of parameters such as the probability of progeny migration, group benefits, and extrinsic mortality on the evolution of long lifespans. Simulations suggest that long lifespans appear to evolve only in eusocial populations, and further, that long lifespans enlarge the region of parameter space where eusociality evolves. When all three population strategies compete, the agent-based simulations indicate that solitary strategies are largely confined to shorter lifespans. For long lifespan strategies the solitary behaviour results only for extreme (very low or very high) migration probability. For median and small values of migration probability, the polygynous eusocial and monogynous eusocial strategies give advantage to the population respectively. For a given migration probability, with an increase in lifespan, the dominant strategy changes from solitary to polygynous to monogynous eusociality. The evolution of a long lifespan is thus closely linked to the evolution of eusociality, and our results are in accord with the observation that the breeding female in monogynous eusocial species has a longer lifespan than those in solitary or polygynous eusocial species.

The Effect of Information Opacity and Accounting Irregularities on Personal Lending Relationships: Evidence from Lender and Manager Co-Migration

ABSTRACT We examine how personal lending relationships between lenders and managers are affected by information and accounting environments of borrowing firms. We address this question by exploring whether, following managerial turnover, lenders migrate with the manager from the firm where a relationship developed (origin firm) to the manager's new firm (destination firm). We find that the opacity of the external information environment of the destination firm significantly increases the probability of lenders' co-migration, while accounting irregularities at both the destination and origin firms decrease it. We also show that co-migration is affected by a lender's monitoring efficiency. A lender's monitoring efficiency increases its co-migration probability when a manager moves to an opaque firm, but not when she moves to a transparent one. When the destination or origin firm experiences accounting irregularities, even lenders with strong monitoring capabilities are mostly reluctant to continue their relationship with a migrating manager.

¿Los cubanos se autoseleccionan en su emigración? De Cuba a Estados Unidos / Do Cubans select themselves in their migration? From Cuba to the United States

ABSTRACTThe aim of this paper is to study the educational self-selection problem of Cuban migrants to the United States. For the analysis, we specify and estimate a binary logit model to analyze the observable covariates that explain migration probability. The data used in the study came from the United States Census of Population and Housing of 2010, and from the Cuba Census of Population and Housing of 2002. The results indicate that education, age and occupational covariates explain migration probability. Moreover, there is a positive educational self-selection problem, that is, migrate those people with more educational level. The principal contribution of this paper is demonstrate that a high level educational increases the probability to emigrate.RESUMENEn este artículo se analiza el problema de la autoselección educativa de los emigrantes cubanos a Estados Unidos. Para el análisis hemos especificado y estimado un modelo logit binario a fin de identificar las variables obser-vables que influyen en la probabilidad de emigrar. Los datos utilizados provienen del Censo de Población y Vivienda de Estados Unidos del año 2010 y del Censo de Población y Vivienda de Cuba del año 2002. Los resultados indican que las variables educación, edad y categoría ocupacional explican la probabilidad de emigrar. Además, se produce una autose-lección positiva en cuanto al nivel educativo de los individuos, es decir, emigran los que más años de educación poseen. La principal aportación de este artículo consiste en demostrar que un alto nivel de educación incrementa la probabilidad de emigrar de los cubanos.