Science.gov

Sample records for migration modelagem numerica

  1. Modelagem do vento e da fotosfera de AG Carinae

    NASA Astrophysics Data System (ADS)

    Groh, J. H.; Damineli, A.

    2003-08-01

    A trajetória evolutiva das estrelas de alta massa depende fortemente de suas taxas de perda de massa. Apesar do rápido progresso no estudo destas estrelas, a taxa de perda de massa e outros parâmetros físicos básicos, como a temperatura superficial e a velocidade terminal do vento ainda não estão bem determinados. Isto ocorre devido à presença de ventos irregulares, rápidos e fortes ao redor destas estrelas, tornando a interpretação dos seus espectros uma tarefa difícil. Assim, a modelagem do vento e da fotosfera dessas estrelas está sendo cada vez mais usada para obter tais parâmetros a partir dos espectros. O aumento da taxa de perda de massa durante a fase LBV (Variáveis Luminosas Azuis), comparado com outros tipos de estrelas, tem sido atribuído a instabilidades do tipo S Doradus. Dispomos de uma base de dados espectroscópicos cobrindo 22 anos de observações de AG Carinae, incluindo um ciclo S Doradus completo, com espectros CCD em alta resolução na faixa óptica e infravermelha. Utilizamos o programa desenvolvido por Schmutz (1997) para uma análise preliminar desse ciclo, obtendo a taxa de perda de massa a partir da linha do Ha. Não existe uma correlação clara da taxa de perda de massa com mudanças da temperatura efetiva, do raio da estrela e do fluxo na banda V. A estrela atingiu seu mínimo fotométrico (raio mínimo) em 1990 e o máximo fotométrico (raio máximo) em 1995, enquanto que o fluxo máximo da linha do Ha ocorreu em 1996. Além disso a taxa de perda de massa não segue esse ciclo, contrariamente às idéias correntes. Para fazer um modelo mais realista estamos usando o programa CMFGEN (Hillier & Miller), que trata a fotosfera e o vento estelar de forma consistente, considerando a radiação fora do equilíbrio termodinâmico (NLTE) e com blanketting total de linhas. Simulamos o espectro de AG Carinae em duas épocas extremas do ciclo S Dor para testar os resultados obtidos com o modelo mais simplificado.

  2. Return migration.

    PubMed

    Gmelch, G

    1980-01-01

    The author reviews the findings of the growing literature on return migration. Topics covered include typologies of return migrants, reasons for return, adaptation and readjustment of returnees, and the impact of return migration on the migrants' home societies. The focus of the study is on international return migration, migration to Northern Europe and northeastern North America, and return migration to the southern and eastern fringes of Europe and the Caribbean

  3. Cell Migration

    PubMed Central

    Trepat, Xavier; Chen, Zaozao; Jacobson, Ken

    2015-01-01

    Cell migration is fundamental to establishing and maintaining the proper organization of multicellular organisms. Morphogenesis can be viewed as a consequence, in part, of cell locomotion, from large-scale migrations of epithelial sheets during gastrulation, to the movement of individual cells during development of the nervous system. In an adult organism, cell migration is essential for proper immune response, wound repair, and tissue homeostasis, while aberrant cell migration is found in various pathologies. Indeed, as our knowledge of migration increases, we can look forward to, for example, abating the spread of highly malignant cancer cells, retarding the invasion of white cells in the inflammatory process, or enhancing the healing of wounds. This article is organized in two main sections. The first section is devoted to the single-cell migrating in isolation such as occurs when leukocytes migrate during the immune response or when fibroblasts squeeze through connective tissue. The second section is devoted to cells collectively migrating as part of multicellular clusters or sheets. This second type of migration is prevalent in development, wound healing, and in some forms of cancer metastasis. PMID:23720251

  4. [Internal migration].

    PubMed

    Borisovna, L

    1991-06-01

    Very few studies have been conducted that truly permit explanation of internal migration and it repercussions on social and economic structure. It is clear however that a profound knowledge of the determinants and consequences of internal migration will be required as a basis for economic policy decisions that advance the goal of improving the level of living of the population. the basic supposition of most studies of the relationship of population and development is that socioeconomic development conditions demographic dynamics. The process of development in Mexico, which can be characterized by great heterogeneity, consequently produces great regional disparities. At the national level various studies have estimated the volume of internal migration in Mexico, but they have usually been limited to interstate migration because the main source of data, the census, is classified by states. But given the great heterogeneity within states in all the elements related to internal migration, it is clear that studies of internal migration within states are also needed. Such studies are almost nonexistent because of their technical difficulty. National level studies show that interstate migration increased significantly between 1940-80. The proportion of Mexicans living outside their states of birth increased by 558% in those years, compared to the 342% increase in the total Mexican population. Although Puebla has a high rate of increase, migration has kept it below Mexico's national growth rate. Migration between Puebla and other states and within Puebla has led to an increasing unevenness of spatial distribution. Between 1970-80, 57 of Puebla's municipios had growth rates above the state average of 2.8%/year, 6 had growth rates equal to the average, and 129 had growth rates that were below the average but not negative. 25 states with negative growth rates that were considered strongly expulsive. In 1980, 51.7% of the population was concentrated in the 57 municipios

  5. Migration Theories

    NASA Astrophysics Data System (ADS)

    Crida, Aurélien

    2015-08-01

    The great variety of the architectures of the extra-solar planetary systems has revealed the fundamental role played by planetary migration: the interactions between the planets and the gaseous disk in which they form leads to a modification of their orbits. Here, I will review the basic processes and the most recent results in this area.Planets up to ~50 Earth masses are prone to so-called type I migration.I will describe the processes at play, namely the Lindblad and corotation torques, and explain how the total torque depends on the planet mass and the local disk structure. Application to realistic disks shows one or two sweet spot(s) for outward migration of planets roughly between 5 and 30 Earth masses around the snowline ; this is confirmed by dedicated 3D numerical simulations. This has strong consequences on the formation of hot Super-Earths or mini-Neptunes.For smaller mass planets, it has been recently proposed that the heating of the neighboring gas by the luminous planet can lead to a positive torque, hence promoting outward migration. On the other hand, if the planet is not a heat source, a cold finger appears, whose resulting torque is negative. Applications of these two recent results should be discussed.Giant planets open gaps in the proto-planetary disk, and then are supposedly subject to type II migration, following the viscous accretion of the disk. This standard picture has been questioned recently, as gas appears to drift through the gap. Although the gap opening process is well understood in 2D for a planet on a fixed orbit, recent results on 3D simulations or migrating planets make the picture more accurate.Our ever better understanding of planet-disk interactions is of crucial importance as the statistics on extra solar systems keep growing and the results of these interactions are now imaged.

  6. [Theories on migration and migration policy].

    PubMed

    Waldrauch, H

    1995-01-01

    "In its first part the article gives a short historical overview of theories on migration.... The author tries to clarify the term[s]...'migration policy' and...'migration' itself and assesses the usefulness of various migration typologies. The final chapter analyses determinants and trends of migration policies in Europe in the 1990s: the continuing pressures for migration in developing countries, the end of numerous barriers to emigration, the revival of nationalistic concepts of immigration and exclusionary tendencies founded on culturalistic arguments, the process of harmonizing control mechanisms in the European Union, and the influence of international human rights declarations on the formulation of migration policies." (SUMMARY IN ENG AND FRE)

  7. Internationalization and migration pressure.

    PubMed

    Kultalahti, O

    1994-01-01

    The author first develops the concept of migration pressure, which is defined as the growth in the number of people wishing to migrate and the barriers preventing them from so doing. Both macro- and micro-level factors affecting migration pressure are identified. Historical trends in migration pressure in Finland are then discussed. The author then applies this concept to the analysis of current Finnish migration trends. The primary focus is on international migration.

  8. Return migration to Italy and labour migration.

    PubMed

    Calvaruso, C

    1983-01-01

    The problems caused by large-scale return migration to Italy in recent years are considered. The importance of the additional skills and capital acquired by these migrants while abroad is stressed. Extensive data on the volume of return migration in the 1970s are included.

  9. Population, migration and urbanization.

    PubMed

    1982-06-01

    Despite recent estimates that natural increase is becoming a more important component of urban growth than rural urban transfer (excess of inmigrants over outmigrants), the share of migration in the total population growth has been consistently increasing in both developed and developing countries. From a demographic perspective, the migration process involves 3 elements: an area of origin which the mover leaves and where he or she is considered an outmigrant; the destination or place of inmigration; and the period over which migration is measured. The 2 basic types of migration are internal and international. Internal migration consists of rural to urban migration, urban to urban migration, rural to rural migration, and urban to rural migration. Among these 4 types of migration various patterns or processes are followed. Migration may be direct when the migrant moves directly from the village to the city and stays there permanently. It can be circular migration, meaning that the migrant moves to the city when it is not planting season and returns to the village when he is needed on the farm. In stage migration the migrant makes a series of moves, each to a city closer to the largest or fastest growing city. Temporary migration may be 1 time or cyclical. The most dominant pattern of internal migration is rural urban. The contribution of migration to urbanization is evident. For example, the rapid urbanization and increase in urban growth from 1960-70 in the Republic of Korea can be attributed to net migration. In Asia the largest component of the population movement consists of individuals and groups moving from 1 rural location to another. Recently, because urban centers could no longer absorb the growing number of migrants from other places, there has been increased interest in the urban to rural population redistribution. This reverse migration also has come about due to slower rates of employment growth in the urban centers and improved economic opportunities

  10. Migration and Adult Education

    ERIC Educational Resources Information Center

    Gois, William

    2007-01-01

    The objective of this paper is to highlight the role of adult education as a tool in addressing labour migration issues, specifically those concerning the protection of migrant workers' rights and the transformation of the impact of migration into positive holistic developmental gains. The view of labour migration as a means to forge the economic…

  11. Aquaporins and cell migration.

    PubMed

    Papadopoulos, M C; Saadoun, S; Verkman, A S

    2008-07-01

    Aquaporin (AQP) water channels are expressed primarily in cell plasma membranes. In this paper, we review recent evidence that AQPs facilitate cell migration. AQP-dependent cell migration has been found in a variety of cell types in vitro and in mice in vivo. AQP1 deletion reduces endothelial cell migration, limiting tumor angiogenesis and growth. AQP4 deletion slows the migration of reactive astrocytes, impairing glial scarring after brain stab injury. AQP1-expressing tumor cells have enhanced metastatic potential and local infiltration. Impaired cell migration has also been seen in AQP1-deficient proximal tubule epithelial cells, and AQP3-deficient corneal epithelial cells, enterocytes, and skin keratinocytes. The mechanisms by which AQPs enhance cell migration are under investigation. We propose that, as a consequence of actin polymerization/depolymerization and transmembrane ionic fluxes, the cytoplasm adjacent to the leading edge of migrating cells undergoes rapid changes in osmolality. AQPs could thus facilitate osmotic water flow across the plasma membrane in cell protrusions that form during migration. AQP-dependent cell migration has potentially broad implications in angiogenesis, tumor metastasis, wound healing, glial scarring, and other events requiring rapid, directed cell movement. AQP inhibitors may thus have therapeutic potential in modulating these events, such as slowing tumor growth and spread, and reducing glial scarring after injury to allow neuronal regeneration. PMID:17968585

  12. Migration to Windows NT.

    ERIC Educational Resources Information Center

    Doles, Daniel T.

    In the constantly changing world of technology, migration is not only inevitable but many times necessary for survival, especially when the end result is simplicity for both users and IT support staff. This paper describes the migration at Franklin College (Indiana). It discusses the reasons for selecting Windows NT, the steps taken to complete…

  13. The Future of Migration.

    ERIC Educational Resources Information Center

    Organisation for Economic Cooperation and Development, Paris (France).

    This book comprises papers delivered at a conference of National Experts on Migration. The principle objective of the conference was twofold: to examine significant trends that will affect the future of migration in countries in the Organization for Economic Co-operation and Development (OCED), and to identify the relevant issues that will have to…

  14. The Great Migration.

    ERIC Educational Resources Information Center

    Trotter, Joe William, Jr.

    2002-01-01

    Describes the migration of African Americans in the United States and the reasons why African Americans migrated from the south. Focuses on issues, such as the effect of World War I, the opportunities offered in the north, and the emergence of a black industrial working class. (CMK)

  15. Migration and Environmental Hazards

    PubMed Central

    Hunter, Lori M.

    2011-01-01

    Losses due to natural hazards (e.g., earthquakes, hurricanes) and technological hazards (e.g., nuclear waste facilities, chemical spills) are both on the rise. One response to hazard-related losses is migration, with this paper offering a review of research examining the association between migration and environmental hazards. Using examples from both developed and developing regional contexts, the overview demonstrates that the association between migration and environmental hazards varies by setting, hazard types, and household characteristics. In many cases, however, results demonstrate that environmental factors play a role in shaping migration decisions, particularly among those most vulnerable. Research also suggests that risk perception acts as a mediating factor. Classic migration theory is reviewed to offer a foundation for examination of these associations. PMID:21886366

  16. Migration and Environmental Hazards.

    PubMed

    Hunter, Lori M

    2005-03-01

    Losses due to natural hazards (e.g., earthquakes, hurricanes) and technological hazards (e.g., nuclear waste facilities, chemical spills) are both on the rise. One response to hazard-related losses is migration, with this paper offering a review of research examining the association between migration and environmental hazards. Using examples from both developed and developing regional contexts, the overview demonstrates that the association between migration and environmental hazards varies by setting, hazard types, and household characteristics. In many cases, however, results demonstrate that environmental factors play a role in shaping migration decisions, particularly among those most vulnerable. Research also suggests that risk perception acts as a mediating factor. Classic migration theory is reviewed to offer a foundation for examination of these associations.

  17. Migration of health workers.

    PubMed

    Buchan, James

    2008-01-01

    The discussion and debate stimulated by these papers focused across a range of issues but there were four main areas of questioning: "measuring" and monitoring migration (issues related to comparability, completeness and accuracy of data sets on human resources); the impact of migration of health workers on health systems; the motivations of individual health workers to migrate (the "push" and "pull" factors) and the effect of policies designed either to reduce migration (e.g "self ufficiency") or to stimulate it (e.g active international recruitment). It was recognised that there was a critical need to examine migratory flows within the broader context of all health care labour market dynamics within a country, that increasing migration of health workers was an inevitable consequence of globalisation, and that there was a critical need to improve monitoring so as to better inform policy formulation and policy testing in this area. PMID:18561695

  18. Migration of health workers.

    PubMed

    Buchan, James

    2008-01-01

    The discussion and debate stimulated by these papers focused across a range of issues but there were four main areas of questioning: "measuring" and monitoring migration (issues related to comparability, completeness and accuracy of data sets on human resources); the impact of migration of health workers on health systems; the motivations of individual health workers to migrate (the "push" and "pull" factors) and the effect of policies designed either to reduce migration (e.g "self ufficiency") or to stimulate it (e.g active international recruitment). It was recognised that there was a critical need to examine migratory flows within the broader context of all health care labour market dynamics within a country, that increasing migration of health workers was an inevitable consequence of globalisation, and that there was a critical need to improve monitoring so as to better inform policy formulation and policy testing in this area.

  19. On marriage and migration.

    PubMed

    Stark, O

    1988-09-01

    Marriage, migration, and related phenomena such as marital stability, fertility, and investment in human capital may be better explained by studying marriage and migration jointly. This paper examines the role of migration in obtaining joint labor market and marriage market equilibrium. When broadly interpreted, marriage and migration share a number of common features. Both involve search and its resolution (pairing of mates in the former and matching of labor and firms in the latter). In both cases, success in finding a partner is sensitive to the availability of partners and to the distribution of their endowments and traits. Almost always, and along with separation and divorce, marriage mandates spatial relocation which may translate into migration. Both involve a movement that is associated with adjustment costs from 1 state into another. The decisions to enter marriage and undertake employment or the decisions to divorce and quit a job depend on exogenous parameters, some of which are determined by the marriage market and the labor market. Since both marriage and divorce take place in the context of broadly defined markets, they may and often are analyzed applying market concepts, theorems, and solutions. Yet the authors could not pinpoint 1 single, systematic attempt that checks through the interactions between marriage and migration, so this paper attempts to rectify this state of research. Essentially, this paper 1) discusses individual decision making pending possible migration prior to or following marriage, 2) examines whether it is easier for a married couple or a single person to migrate, and 3) considers whether marriage dissolution could cause migration when marriage is the only reason that has kept a spouse from moving. This integrated research agenda for both marriage and migration can delineate interesting new implications to examine.

  20. [Determinants of migration to Warsaw].

    PubMed

    Kucinski, K; Rakowski, W

    1990-01-01

    The authors examine trends and determinants of internal migration to Warsaw, Poland. Consideration is given to occupational and socioeconomic status of migrants, rural-urban migration, and effects of migration on marriage. (SUMMARY IN ENG AND RUS)

  1. Neuronal migration illuminated

    PubMed Central

    Trivedi, Niraj

    2011-01-01

    During vertebrate brain development, migration of neurons from the germinal zones to their final laminar positions is essential to establish functional neural circuits.1–3 Whereas key insights into neuronal migration initially came from landmark studies identifying the genes mutated in human cortical malformations,4 cell biology has recently greatly advanced our understanding of how cytoskeletal proteins and molecular motors drive the morphogenic cell movements that build the developing brain. This Commentary & View reviews recent studies examining the role of the molecular motors during neuronal migration and critically examines current models of acto-myosin function in the two-step neuronal migration cycle. Given the apparent emerging diversity of neuronal sub-type cytoskeletal organizations, we propose that two approaches must be taken to resolve differences between the current migration models: the mechanisms of radial and tangential migration must be compared, and the loci of tension generation, migration substrates and sites of adhesion dynamics must be precisely examined in an integrated manner. PMID:20935494

  2. Migration without migraines

    SciTech Connect

    Lines, L.; Burton, A.; Lu, H.X.

    1994-12-31

    Accurate velocity models are a necessity for reliable migration results. Velocity analysis generally involves the use of methods such as normal moveout analysis (NMO), seismic traveltime tomography, or iterative prestack migration. These techniques can be effective, and each has its own advantage or disadvantage. Conventional NMO methods are relatively inexpensive but basically require simplifying assumptions about geology. Tomography is a more general method but requires traveltime interpretation of prestack data. Iterative prestack depth migration is very general but is computationally expensive. In some cases, there is the opportunity to estimate vertical velocities by use of well information. The well information can be used to optimize poststack migrations, thereby eliminating some of the time and expense of iterative prestack migration. The optimized poststack migration procedure defined here computes the velocity model which minimizes the depth differences between seismic images and formation depths at the well by using a least squares inversion method. The optimization methods described in this paper will hopefully produce ``migrations without migraines.``

  3. Women in migration.

    PubMed

    Morokvasic, M

    1984-01-01

    This special issue reflects the belated but growing scholarly appreciation of the specificity and importance of women in migration. Aside from the sheer numerical significance of female migration documented in this issue, women migrants encounter problems and make special contributions which render comprehension of their specificity critical to an understanding of international migration in general. In an introductory essay, Morokvasic surveys the state of knowledge concerning women in migration. The focus then shifts, in Part II, to regional and national case studies which collectively elucidate the multifaceted dimensions of the women in migration research issue through time and space. In Part III, an international comparison of female immigrants and their labor market characteristics reveals striking similarities but also important differences. The US Canada and Australia can be discretely compared through 5 census-based quantitative analyses. The role of migrant women in the labor market is also the theme of Part IV. But the 5 studies comprising this section are based on survey research or on discernible global trends in migration and employment. Part V is devoted to the theme of female rural to urban migration in the Third World.

  4. Labor migration in Asia.

    PubMed

    Martin, P L

    1991-01-01

    "A recent conference sponsored by the United Nations Center for Regional Development (UNCRD) in Nagoya, Japan examined the growing importance of labor migration for four major Asian labor importers (Japan, Hong Kong, Malaysia, and Singapore) and five major labor exporters (Bangladesh, Korea, Pakistan, Philippines, and Thailand).... The conference concluded that international labor migration would increase within Asia because the tight labor markets and rising wages which have stimulated Japanese investment in other Asian nations, for example, have not been sufficient to eliminate migration push and pull forces...."

  5. Indonesia's migration transition.

    PubMed

    Hugo, G

    1995-01-01

    This article describes population movements in Indonesia in the context of rapid and marked social and economic change. Foreign investment in Indonesia is increasing, and global mass media is available to many households. Agriculture is being commercialized, and structural shifts are occurring in the economy. Educational levels are increasing, and women's role and status are shifting. Population migration has increased over the decades, both short and long distance, permanent and temporary, legal and illegal, and migration to and between urban areas. This article focuses specifically on rural-to-urban migration and international migration. Population settlements are dense in the agriculturally rich inner areas of Java, Bali, and Madura. Although the rate of growth of the gross domestic product was 6.8% annually during 1969-94, the World Bank ranked Indonesia as a low-income economy in 1992 because of the large population size. Income per capita is US $670. Indonesia is becoming a large exporter of labor to the Middle East, particularly women. The predominance of women as overseas contract workers is changing women's role and status in the family and is controversial due to the cases of mistreatment. Malaysia's high economic growth rate of over 8% per year means an additional 1.3 million foreign workers and technicians are needed. During the 1980s urban growth increased at a very rapid rate. Urban growth tended to occur along corridors and major transportation routes around urban areas. It is posited that most of the urban growth is due to rural-to-urban migration. Data limitations prevent an exact determination of the extent of rural-to-urban migration. More women are estimated to be involved in movements to cities during the 1980s compared to the 1970s. Recruiters and middlemen have played an important role in rural-to-urban migration and international migration. PMID:12347370

  6. Migration and malaria.

    PubMed

    Jitthai, Nigoon

    2013-01-01

    Migration is an important global issue as poorly managed migration can result in a diversity of problems, including an increase in the transmission of diseases such as malaria. There is evidence to suggest that malaria is no longer a forest-dependent disease and may largely be affected by population movements, mostly to agricultural areas. While internal and transnational migration has different legal implications in most countries, both types of migration occur for the same reasons; economic and/ or safety. Although migration in itself is not a definitive risk for malaria, several factors can put, migrants and local communities alike, in vulnerable situations. In particular, infrastructure and rural development, deforestation for logging and economic farming, political movements, and natural disasters are some of the major factors that push and pull people in and out of malaria-endemic areas. Therefore, understanding the changing socio-environmental situation as well as population movements and their associated risks for malaria infection, is critical for malaria control, containment, and elimination. Efforts to address these issues should include advocacy, mapping exercises and expanded/ strengthened surveillance to also include migrant health information systems. Malaria related information, prevention measures, and early diagnosis and appropriate treatment should be made easily accessible for migrants regardless of their migration status; not only to ensure that they are equipped with appropriate knowledge and devices to protect themselves, but also to ensure that they are properly diagnosed and treated, to prevent further transmission, and to ensure that they are captured by the surveillance system. PMID:24159832

  7. Timescales of DNAPL migration

    NASA Astrophysics Data System (ADS)

    Kueper, B.; Gerhard, J.; Reynolds, D.

    2003-04-01

    Dense, non-aqueous phase liquids such as chlorinated solvents, PCB oils, creosote, and coal tar are common soil and groundwater contaminants at sites throughout the world. Current source zone remediation approaches typically assume that the residual and pooled DNAPL of interest is no longer migrating. The motivation for partial mass removal from a DNAPL source zone varies from site to site, but is often motivated by the belief that mass removal will lead to shorter steady-state plumes, shorter longevity of the source zone, and possibly aquifer restoration in a reasonable period of time. This talk addresses the issue of DNAPL migration timescales, and illustrates that certain types of DNAPL in certain geological environments are likely still migrating at some sites. The implication of this is that remedial strategies may need to be aimed at source zone stabilization in the short term, not partial mass removal for the reasons outlined above. The timescales of DNAPL migration at a site are influenced by many factors, including fluid properties, capillary properties, relative permeability characteristics, boundary conditions, and the volume and nature of release. Accurate prediction of DNAPL migration timescales requires a model that properly accounts for both the entry and terminal pressures in the capillary pressure -- saturation constitutive relationship, and properly accounts for relative permeability characteristics. This talk will address the above issues, and will present the results of laboratory experiments and numerical simulations to illustrate the timescale of DNAPL migration in a variety of environments including fractured rock, fractured clay, and unconsolidated porous media.

  8. Human rights and migration policies.

    PubMed

    Marmora, L

    1990-01-01

    This paper concerns the history of migration, migration policies, and the rights of migrants in Latin America from 1500 to the present. In the first part of the article, the author identifies and discusses the basic rights of migrants. In the second part, migration policies, migration flows, and the treatment of migrants are examined over time.

  9. Environmental concerns and international migration.

    PubMed

    Hugo, G

    1996-01-01

    "This article focuses on international migration occurring as a result of environmental changes and processes. It briefly reviews attempts to conceptualize environment-related migration and then considers the extent to which environmental factors have been and may be significant in initiating migration. Following is an examination of migration as an independent variable in the migration-environment relationship. Finally, ethical and policy dimensions are addressed."

  10. Environmental concerns and international migration.

    PubMed

    Hugo, G

    1996-01-01

    "This article focuses on international migration occurring as a result of environmental changes and processes. It briefly reviews attempts to conceptualize environment-related migration and then considers the extent to which environmental factors have been and may be significant in initiating migration. Following is an examination of migration as an independent variable in the migration-environment relationship. Finally, ethical and policy dimensions are addressed." PMID:12291410

  11. Biometrics and international migration.

    PubMed

    Redpath, Jillyanne

    2007-01-01

    This paper will focus on the impact of the rapid expansion in the use of biometric systems in migration management on the rights of individuals; it seeks to highlight legal issues for consideration in implementing such systems, taking as the starting point that the security interests of the state and the rights of the individual are not, and should not be, mutually exclusive. The first part of this paper briefly describes the type of biometric applications available, how biometric systems function, and those used in migration management. The second part examines the potential offered by biometrics for greater security in migration management, and focuses on developments in the use of biometrics as a result of September 11. The third part discusses the impact of the use of biometrics in the management of migration on the individual's right to privacy and ability to move freely and lawfully. The paper highlights the increasing need for domestic and international frameworks to govern the use of biometric applications in the migration/security context, and proposes a number of issues that such frameworks could address. PMID:17536151

  12. Migration from Packaging Materials

    NASA Astrophysics Data System (ADS)

    Meulenaer, B. De

    Various chemical compounds can be present in foodstuffs which may induce health problems in humans. The origin of these compounds can be very diverse. Mathematical modeling can sometimes be used to predict the concentration of these chemicals in the food. Particularly for compounds which are produced in the food during, e.g., processing and for compounds which migrate from a food contact material this technique can be very fruitful. For the former type of compounds, classical chemical kinetics can be applied. In this contribution, the modeling of the migration from polymeric food contact materials is considered. This migration phenomenon can be modeled mathematically since the physical processes which govern this process are very well studied and understood. Therefore, initially some of these fundamentals will be discussed in more detail.

  13. More myths of migration.

    PubMed

    Basch, L; Lerner, G

    1986-01-01

    This paper discusses some of the myths of migration. The 5 myths presented are: 1) racism has little to do with the causes of migration and does not necessarily impede the adjustment or success of migrants; 2) in areas where there is a strong feminist movement and trade unions, migrant women receive their support and can count on the solidarity of these organizations; 3) transnational corporations are positive forces in the developing countries where they operate--not only do they provide these states with new sources of capital, but they also impart new industrial skills to the labor force; 4) migration today is essentially short-term in nature--it therefore does not have a strong impact on family life; and 5) most migrants cluster together in ethnic enclaves which provide a strong source of support and diminish dislocation inherent in the migrant process.

  14. [Migration, climate and health].

    PubMed

    Tellier, Siri; Carballo, Manuel; Calballo, Manuel

    2009-10-26

    Many tentative connections have been postulated between migration and climate. This article points to rural-urban migration, particularly into low elevation urban slums prone to flooding as an issue needing urgent attention by health professionals. It also notes the no-man's land in which environmental refugees find themselves and the consequences this may have. Finally, it points to the urgent need to reform health systems in both developing and developed countries to adapt to rapidly changing disease patterns and to become more responsive to them.

  15. What's driving migration?

    PubMed

    Kane, H

    1995-01-01

    During the 1990s investment in prevention of international or internal migration declined, and crisis intervention increased. The budgets of the UN High Commissioner for Refugees and the UN Development Program remained about the same. The operating assumption is that war, persecution, famine, and environmental and social disintegration are inevitable. Future efforts should be directed to stabilizing populations through investment in sanitation, public health, preventive medicine, land tenure, environmental protection, and literacy. Forces pushing migration are likely to increase in the future. Forces include depletion of natural resources, income disparities, population pressure, and political disruption. The causes of migration are not constant. In the past, migration occurred during conquests, settlement, intermarriage, or religious conversion and was a collective movement. Current migration involves mass movement of individuals and the struggle to survive. There is new pressure to leave poor squatter settlements and the scarcities in land, water, and food. The slave trade between the 1500s and the 1800s linked continents, and only 2-3 million voluntarily crossed national borders. Involuntary migration began in the early 1800s when European feudal systems were in a decline, and people sought freedom. Official refugees, who satisfy the strict 1951 UN definition, increased from 15 million in 1980 to 23 million in 1990 but remained a small proportion of international migrants. Much of the mass movement occurs between developing countries. Migration to developed countries is accompanied by growing intolerance, which is misinformed. China practices a form of "population transfer" in Tibet in order to dilute Tibetan nationalism. Colonization of countries is a new less expensive form of control over territory. Eviction of minorities is another popular strategy in Iraq. Public works projects supported by foreign aid displace millions annually. War and civil conflicts

  16. Migration strategies of insects.

    PubMed

    Dingle, H

    1972-03-24

    Physiological and ecological results from a variety of species are consistent with what seem to be valid general statements concerning insect migration. These are as follows: (i)During migration locomotory functions are enhanced and vegetative functions such as feeding and reproduction are suppressed. (ii) Migration usually occurs prereproductively in the life of the adult insect (the oogenesis-flight syndrome). (iii)Since migrant individuals are usually prereproductive, their reproductive values, and hence colonizing abilities, are at or near maximum. (iv) Migrants usually reside in temporary habitats. (v)Migrants have a high potential for population increase, r, which is also advantageous for colonizers. (vi)Both the physiological and ecological parameters of migration are modifiable by environmental factors (that is, phenotypically modifiable)to suit the prevailing conditions. Taken together, these criteria establish a comprehensive theory and adumbrate the basic strategy for migrant insects. This basic strategy is modified to suit the ecological requirements of individual species. Comparative studies of these modifications are of considerable theoretical and practical interest, the more so since most economically important insects are migrants. No satisfactory general statements can as yet be made with respect to the genotype and migration. Certainly we expect colonizing populiations to possess genotypes favoring a high r, but genotypic variation in r depends on the heritabilities of life table statistics, and such measurements are yet to be made (10, 53). The fact that flight duration can be increased by appropriate selection in Oncopeltus fasciatus, and the demonstration of additive genetic variance for this trait in Lygaeus kalmii, suggest that heritability studies of migratory behavior would also be worth pursuing. Most interesting of course, will be possible genetic correlations between migration and life history parameters. Also, migration often

  17. [Migration and health].

    PubMed

    Litvinjenko, S

    1997-01-01

    In the last decades of this century we are witnesses of frequent crises in different parts of the world produced by internal disturbance and wars. These crises, together with natural disasters, poverty and hunger, follow the history of mankind often forcing huge population groups to leave their homes. The harmful health consequences are among negative effects of migrations. While stable populations have well-tried routines for maintaining health, migrations mean abandoning such support systems. The increased exposure to harmful factors contributes more to the bad health condition of the migrant population. Setting of newcomers and local people together in the same homes, reduction in food and heating resources, drug shortage as well as importation of new infectious agents, may also endanger health of the native population. These observations have also been confirmed by Yugoslav experience. Depending on the fact whether a migration is elemental or organized i.e. dependent on its place in the large scale between these two extreme endpoints, the size of risk is also dependent on the consequences and degree of their difficulty. Mass health disturbances occur during migrations of the population from war regions, migrations from areas of natural disasters, mass pilgrimage, migrations of seasonal workers and migrations of armies during wars. However, even in these difficult times and conditions, a good organization can contribute to the mitigation of harmful consequences caused by these migrations. For instance, in 1942 there was an epidemic of typhus fever in Bosnia when many refugees crossed the Drina river on the way to Serbia escaping from Ustasha terrorism. At the Serbian side there were checkpoints where the refugees could taka a bath and where their laundry and clothing were depediculated with dry air, and after a two-week quarantine they could continue to Serbian provinces without making new foci of typhus fever. The most vulnerable and numerous group of refugees

  18. Method of migrating seismic records

    DOEpatents

    Ober, Curtis C.; Romero, Louis A.; Ghiglia, Dennis C.

    2000-01-01

    The present invention provides a method of migrating seismic records that retains the information in the seismic records and allows migration with significant reductions in computing cost. The present invention comprises phase encoding seismic records and combining the encoded seismic records before migration. Phase encoding can minimize the effect of unwanted cross terms while still allowing significant reductions in the cost to migrate a number of seismic records.

  19. The commercialization of migration.

    PubMed

    Abrera-mangahas, M A

    1989-01-01

    International migration is not new to the Philippines. In the recent outflow of contract workers to the Middle East, there is a shift from individual and family initiated migrations to the more organized, highly commercial variety. While profit-taking intermediaries have played some role in the past, the increase in the number and influence of these intermediaries has altered the story of migration decision-making. In 1975, the signing of the bilateral labor agreement between the governments of Iran and the Philippines signalled the rising demand for Filipino contract workers. From 1970 to 1975, the number of Asian migrant workers in the Gulf countries rose from about 120,000 to 370,000. These figures rose dramatically to 3.3 million in 1985. The growing share of organized and commercialized migration has altered migration decision making. Primarily, intermediaries are able to broaden access to foreign job and high wage opportunities. Commercialization effectively raises the transaction costs for contract migration. Studies on recruitment costs and fees show that self-solicited foreign employment costs less than employment obtained through recruitment agents and intermediaries. The difference in the 2 prices is due, not only to overhead costs of intermediation, but more importantly to the rent exacted by agents from having job information and placement rights. In the Philippines in October 1987 the average placement fee was P8000, greatly exceeding the mandated maximum fee level of P5000. This average is understated because the computation includes the 17% who do not pay any fees. The widespread and popular view of recruitment intermediaries is negative, dominated by images of abuses and victims. Private intermediaries and the government bureaucracy need each other. Intermediaries need government; their consistent demand for incentives and protection is indicative. On the other hand, government expands its supervision of control of overseas employment via the

  20. [Return migrations in the Italian migration system: a reexamination].

    PubMed

    Bonifazi, C; Heins, F

    1996-06-01

    The authors discuss trends in return migration in Italy, with a focus on regional differences. "On a regional level, the effects of return migration are very much connected with socio-economic structure. Only highly developed and autonomous regions can absorb productive investments and changes brought about by return migration. Several southern regions--especially those with greater migration experience--have shown in the last decades a very poor socio-economic development." The study is concerned with both internal and international migration. (SUMMARY IN ENG AND FRE)

  1. Forced Migration: Refugee Populations

    PubMed Central

    Boyle, Joyceen S.

    2015-01-01

    Undocumented migration is a global phenomenon that manifests in various contexts. This article describes the impact of the movement of large numbers of people in several African countries, producing a unique type of migrant—the refugee. We describe issues that refugee movements create on fragile health care systems, situations that precipitate refugee movements, certain human rights violations that are of particular concern such as gender based violence (GBV) and child soldiers, and lastly, implications for nursing practice and policy. We use examples from several countries in Sub-Saharan Africa, including the Democratic Republic of the Congo, Rwanda, Liberia, Sierra Leone, and Mozambique. Drawing on key documents from the United Nations High Commissioner for Refugees, current literature, as well as the international experience of the authors, this article presents an overview of forced migration and discusses opportunities for nurses to impact research, practice and policy related to refugee health. PMID:25645484

  2. Migration with fiscal externalities.

    PubMed

    Hercowitz, Z; Pines, D

    1991-11-01

    "This paper analyses the distribution of a country's population among regions when migration involves fiscal externalities. The main question addressed is whether a decentralized decision making [by] regional governments can produce an optimal population distribution...or a centralized intervention is indispensable, as argued before in the literature.... It turns out that, while with costless mobility the fiscal externality is fully internalized by voluntary interregional transfers, with costly mobility, centrally coordinated transfers still remain indispensable for achieving the socially optimal allocation."

  3. IAPs and cell migration.

    PubMed

    Dubrez, Laurence; Rajalingam, Krishnaraj

    2015-03-01

    Inhibitors of apoptosis (IAPs) constitute a family of cell signaling regulators controlling several fundamental biological processes such as innate immunity, inflammation, cell death, cell proliferation, and cell differentiation. Increasing evidence from in vivo and in vitro studies indicate a function for IAPs in the modulation of invasive and migratory properties of cells. Here, we present and discuss the mechanisms whereby IAPs can control cell migration.

  4. Migration and stratification

    PubMed Central

    Jasso, Guillermina

    2011-01-01

    Migration and stratification are increasingly intertwined. One day soon it will be impossible to understand one without the other. Both focus on life chances. Stratification is about differential life chances - who gets what and why - and migration is about improving life chances - getting more of the good things of life. To examine the interconnections of migration and stratification, we address a mix of old and new questions, carrying out analyses newly enabled by a unique new data set on recent legal immigrants to the United States (the New Immigrant Survey). We look at immigrant processing and lost documents, depression due to the visa process, presentation of self, the race-ethnic composition of an immigrant cohort (made possible by the data for the first time since 1961), black immigration from Africa and the Americas, skin-color diversity among couples formed by U.S. citizen sponsors and immigrant spouses, and English fluency among children age 8–12 and their immigrant parents. We find, inter alia, that children of previously illegal parents are especially more likely to be fluent in English, that native-born U.S. citizen women tend to marry darker, that immigrant applicants who go through the visa process while already in the United States are more likely to have their documents lost and to suffer visa depression, and that immigration, by introducing accomplished black immigrants from Africa (notably via the visa lottery), threatens to overturn racial and skin color associations with skill. Our analyses show the mutual embeddedness of migration and stratification in the unfolding of the immigrants' and their children's life chances and the impacts on the stratification structure of the United States. PMID:26321771

  5. Pathologic tooth migration.

    PubMed

    Brunsvold, Michael A

    2005-06-01

    Pathologic tooth migration (PTM) is a common complication of moderate to severe periodontitis and is often the motivation for patients to seek periodontal therapy. In this review of the literature, available information concerning prevalence, etiology, treatment, and prevention of pathologic tooth migration is summarized. Prevalence of PTM among periodontal patients has been reported to range from 30.03% to 55.8%. A survey of the literature regarding chief complaints of periodontal patients support these high prevalence findings. The etiology of PTM appears to be multifactorial. Periodontal bone loss appears to be a major factor in the etiology of PTM. Many aspects of occlusion can contribute to abnormal migration of teeth, and more than one of those factors may be present in an individual patient. Soft tissue forces of the tongue, cheeks, and lips are known to cause tooth movement and in some situations can cause PTM. Also considered important in the etiology of PTM is pressure produced from inflammatory tissues within periodontal pockets. Because extrusion is a common form of PTM, clinical observations support the theory that eruption forces sometimes play a role in the etiology of PTM. Many oral habits have been associated with PTM which are often difficult for the therapist to detect. Most cases of severe PTM require a team approach to achieve success. Periodontal, orthodontic, and prosthodontic treatment are often required. Many patient variables enter into the selection of treatment for PTM. In early stages of PTM, spontaneous correction of migrated teeth sometimes occurs after periodontal therapy. Light intrusive forces are used successfully to treat extrusion and flaring forms of PTM. Based on the literature reviewed, it appears that many cases of PTM could be prevented through the early diagnosis and treatment of periodontal disease, occlusal contributing factors, gingival enlargement, and oral habits. PMID:15948679

  6. Gender and Migration from Albania

    PubMed Central

    STECKLOV, GUY; CARLETTO, CALOGERO; AZZARRI, CARLO; DAVIS, BENJAMIN

    2010-01-01

    This article examines the dynamics and causes of the shift in the gender composition of migration, and more particularly, in women’s access to migration opportunities and decision-making. Our analysis focuses on Albania, a natural laboratory for studying international migration where out-migration was essentially nonexistent from the end of World War II to the end of the 1980s. Interest in the Albanian case is heightened because of the complex layers of inequality existing at the time when migration began: relatively low levels of inequality within the labor market and educational system—a product of the Communist era—while household relations remained heavily steeped in tradition and patriarchy. We use micro-level data from the Albania 2005 Living Standards Measurement Study, including migration histories for family members since migration began. Based on discrete-time hazard models, the analysis shows a dramatic increase in male migration and a gradual and uneven expansion of the female proportion of this international migration. Female migration, which is shown to be strongly associated with education, wealth, and social capital, appears responsive to economic incentives and constraints. Using information on the dependency of female migration to the household demographic structure as well as the sensitivity of female migration to household-level shocks, we show how household-level constraints and incentives affect male and female migration differently. Throughout this period, however, women’s migration behavior appears more directly aligned with household-level factors, and there is little evidence to suggest that increased female migration signals rising behavioral independence among Albanian women. PMID:21308565

  7. Conservation physiology of animal migration.

    PubMed

    Lennox, Robert J; Chapman, Jacqueline M; Souliere, Christopher M; Tudorache, Christian; Wikelski, Martin; Metcalfe, Julian D; Cooke, Steven J

    2016-01-01

    Migration is a widespread phenomenon among many taxa. This complex behaviour enables animals to exploit many temporally productive and spatially discrete habitats to accrue various fitness benefits (e.g. growth, reproduction, predator avoidance). Human activities and global environmental change represent potential threats to migrating animals (from individuals to species), and research is underway to understand mechanisms that control migration and how migration responds to modern challenges. Focusing on behavioural and physiological aspects of migration can help to provide better understanding, management and conservation of migratory populations. Here, we highlight different physiological, behavioural and biomechanical aspects of animal migration that will help us to understand how migratory animals interact with current and future anthropogenic threats. We are in the early stages of a changing planet, and our understanding of how physiology is linked to the persistence of migratory animals is still developing; therefore, we regard the following questions as being central to the conservation physiology of animal migrations. Will climate change influence the energetic costs of migration? Will shifting temperatures change the annual clocks of migrating animals? Will anthropogenic influences have an effect on orientation during migration? Will increased anthropogenic alteration of migration stopover sites/migration corridors affect the stress physiology of migrating animals? Can physiological knowledge be used to identify strategies for facilitating the movement of animals? Our synthesis reveals that given the inherent challenges of migration, additional stressors derived from altered environments (e.g. climate change, physical habitat alteration, light pollution) or interaction with human infrastructure (e.g. wind or hydrokinetic turbines, dams) or activities (e.g. fisheries) could lead to long-term changes to migratory phenotypes. However, uncertainty remains

  8. Conservation physiology of animal migration

    PubMed Central

    Lennox, Robert J.; Chapman, Jacqueline M.; Souliere, Christopher M.; Tudorache, Christian; Wikelski, Martin; Metcalfe, Julian D.; Cooke, Steven J.

    2016-01-01

    Migration is a widespread phenomenon among many taxa. This complex behaviour enables animals to exploit many temporally productive and spatially discrete habitats to accrue various fitness benefits (e.g. growth, reproduction, predator avoidance). Human activities and global environmental change represent potential threats to migrating animals (from individuals to species), and research is underway to understand mechanisms that control migration and how migration responds to modern challenges. Focusing on behavioural and physiological aspects of migration can help to provide better understanding, management and conservation of migratory populations. Here, we highlight different physiological, behavioural and biomechanical aspects of animal migration that will help us to understand how migratory animals interact with current and future anthropogenic threats. We are in the early stages of a changing planet, and our understanding of how physiology is linked to the persistence of migratory animals is still developing; therefore, we regard the following questions as being central to the conservation physiology of animal migrations. Will climate change influence the energetic costs of migration? Will shifting temperatures change the annual clocks of migrating animals? Will anthropogenic influences have an effect on orientation during migration? Will increased anthropogenic alteration of migration stopover sites/migration corridors affect the stress physiology of migrating animals? Can physiological knowledge be used to identify strategies for facilitating the movement of animals? Our synthesis reveals that given the inherent challenges of migration, additional stressors derived from altered environments (e.g. climate change, physical habitat alteration, light pollution) or interaction with human infrastructure (e.g. wind or hydrokinetic turbines, dams) or activities (e.g. fisheries) could lead to long-term changes to migratory phenotypes. However, uncertainty remains

  9. Conservation physiology of animal migration.

    PubMed

    Lennox, Robert J; Chapman, Jacqueline M; Souliere, Christopher M; Tudorache, Christian; Wikelski, Martin; Metcalfe, Julian D; Cooke, Steven J

    2016-01-01

    Migration is a widespread phenomenon among many taxa. This complex behaviour enables animals to exploit many temporally productive and spatially discrete habitats to accrue various fitness benefits (e.g. growth, reproduction, predator avoidance). Human activities and global environmental change represent potential threats to migrating animals (from individuals to species), and research is underway to understand mechanisms that control migration and how migration responds to modern challenges. Focusing on behavioural and physiological aspects of migration can help to provide better understanding, management and conservation of migratory populations. Here, we highlight different physiological, behavioural and biomechanical aspects of animal migration that will help us to understand how migratory animals interact with current and future anthropogenic threats. We are in the early stages of a changing planet, and our understanding of how physiology is linked to the persistence of migratory animals is still developing; therefore, we regard the following questions as being central to the conservation physiology of animal migrations. Will climate change influence the energetic costs of migration? Will shifting temperatures change the annual clocks of migrating animals? Will anthropogenic influences have an effect on orientation during migration? Will increased anthropogenic alteration of migration stopover sites/migration corridors affect the stress physiology of migrating animals? Can physiological knowledge be used to identify strategies for facilitating the movement of animals? Our synthesis reveals that given the inherent challenges of migration, additional stressors derived from altered environments (e.g. climate change, physical habitat alteration, light pollution) or interaction with human infrastructure (e.g. wind or hydrokinetic turbines, dams) or activities (e.g. fisheries) could lead to long-term changes to migratory phenotypes. However, uncertainty remains

  10. Gender and migration from Albania.

    PubMed

    Stecklov, Guy; Carletto, Calogero; Azzarri, Carlo; Davis, Benjamin

    2010-11-01

    This article examines the dynamics and causes of the shift in the gender composition of migration, and more particularly, in women's access to migration opportunities and decision-making. Our analysis focuses on Albania, a natural laboratory for studying international migration where out-migration was essentially nonexistent from the end of World War II to the end of the 1980s. Interest in the Albanian case is heightened because of the complex layers of inequality existing at the time when migration began: relatively low levels of inequality within the labor market and educational system-a product of the Communist era-while household relations remained heavily steeped in tradition and patriarchy. We use micro-level data from the Albania 2005 Living Standards Measurement Study, including migration histories for family members since migration began. Based on discrete-time hazard models, the analysis shows a dramatic increase in male migration and a gradual and uneven expansion of the female proportion of this international migration. Female migration, which is shown to be strongly associated with education, wealth, and social capital, appears responsive to economic incentives and constraints. Using information on the dependency of female migration to the household demographic structure as well as the sensitivity of female migration to household-level shocks, we show how household-level constraints and incentives affect male and female migration differently. Throughout this period, however, women's migration behavior appears more directly aligned with household-level factors, and there is little evidence to suggest that increased female migration signals rising behavioral independence among Albanian women.

  11. Hydrodynamics of pronuclear migration

    NASA Astrophysics Data System (ADS)

    Nazockdast, Ehssan; Needleman, Daniel; Shelley, Michael

    2014-11-01

    Microtubule (MT) filaments play a key role in many processes involved in cell devision including spindle formation, chromosome segregation, and pronuclear positioning. We present a direct numerical technique to simulate MT dynamics in such processes. Our method includes hydrodynamically mediated interactions between MTs and other cytoskeletal objects, using singularity methods for Stokes flow. Long-ranged many-body hydrodynamic interactions are computed using a highly efficient and scalable fast multipole method, enabling the simulation of thousands of MTs. Our simulation method also takes into account the flexibility of MTs using Euler-Bernoulli beam theory as well as their dynamic instability. Using this technique, we simulate pronuclear migration in single-celled Caenorhabditis elegans embryos. Two different positioning mechanisms, based on the interactions of MTs with the motor proteins and the cell cortex, are explored: cytoplasmic pulling and cortical pushing. We find that although the pronuclear complex migrates towards the center of the cell in both models, the generated cytoplasmic flows are fundamentally different. This suggest that cytoplasmic flow visualization during pronuclear migration can be utilized to differentiate between the two mechanisms.

  12. Population, desertification, and migration.

    PubMed

    Westing, A H

    1994-01-01

    When an imbalance develops between population numbers and the carrying capacity of the land, the persons thereby displaced are referred to as environmental refugees. The utilization of the land beyond sustainability leads to land degradation and ultimately, desertification. The social and political impacts of long-term environmental migration can be distinguished: a) at the site of origin of the displaced persons by the residual population; b) at rural sites of destination within the nation between the new arrivals and preestablished populations; c) in the cities within the nation; d) in the nonindustrialized foreign countries; and e) in the industrialized foreign countries. In the event that an area which had previously been devoted to pastoralism is converted to agriculture, the displaced pastoralists might respond through armed rebellion. In some instances, the disenchanted urban squatters become a politically restive and even a destabilizing force, as occurred in Sudan in the 1980s, especially in Khartoum and Port Sudan. The foreign countries to which many of the displaced persons are migrating are subjected to increasing levels of migrant-induced economic, cultural, and political strains. The growing problems associated with south-to-north migration across the Mediterranean Sea have recently led France, Italy, Portugal, and Spain to enter into a consultative arrangement with Algeria, Libya, Mauritania, Morocco, and Tunisia. All foreign aid to the nonindustrialized countries that attempts to ameliorate the problem of desertification must adopt integrated approaches that: a) address population issues; b) support environmental education; c) provide for the protection of biodiversity; d) encourage participatory forms of local and national government; e) provide opportunities for income generation outside the livestock sector; and f) foster political security and facilitate ecogeographical (subregional) cooperation.

  13. ILO - International Migration Programme.

    PubMed

    Boudraa, Miriam

    2011-01-01

    In a wide International Context characterised not only by the economical development but also by the social, cultural, political and individual development, we witness more and more to a exchange between the developed and the developing countries, which can be translated especially in the migration of the work force. In theory, all countries are either countries of origin either countries of transit or destination, and they are all responsible for the rights of migrant workers by promoting the rights, by monitoring and by preventing the abusive conditions. The process of migration of the workforce can be divided into three stages: the first coincides with the period prior to departure, the second is represented by the aftermath of the departure and the period of stay in the country of destination, the third stage corresponds to the return in the country of origin. The workers must be protected throughout this process by the international organizations that perform the catalytic role of communication and exchange between countries, for the only purpose of protecting the rights of immigrant and/or immigrants workers. The responsibility for the protection of workers is divided among the various players in the International Labour Organisation. Every country has to apply measures according to the international standards regarding workers' rights, standards that guide the various countries in the formulation and implementation of their policies and legislation. These standards are suggested by International Conventions, the ILO Conventions and other international instruments such as the human rights instrument. There has been a big step forward once the ILO Fundamental Conventions and Conventions on Migrant Workers where implemented and this implementation represented the use of the Guidelines "ILO Multilateral Framework on Labour Migration".

  14. ILO - International Migration Programme.

    PubMed

    Boudraa, Miriam

    2011-01-01

    In a wide International Context characterised not only by the economical development but also by the social, cultural, political and individual development, we witness more and more to a exchange between the developed and the developing countries, which can be translated especially in the migration of the work force. In theory, all countries are either countries of origin either countries of transit or destination, and they are all responsible for the rights of migrant workers by promoting the rights, by monitoring and by preventing the abusive conditions. The process of migration of the workforce can be divided into three stages: the first coincides with the period prior to departure, the second is represented by the aftermath of the departure and the period of stay in the country of destination, the third stage corresponds to the return in the country of origin. The workers must be protected throughout this process by the international organizations that perform the catalytic role of communication and exchange between countries, for the only purpose of protecting the rights of immigrant and/or immigrants workers. The responsibility for the protection of workers is divided among the various players in the International Labour Organisation. Every country has to apply measures according to the international standards regarding workers' rights, standards that guide the various countries in the formulation and implementation of their policies and legislation. These standards are suggested by International Conventions, the ILO Conventions and other international instruments such as the human rights instrument. There has been a big step forward once the ILO Fundamental Conventions and Conventions on Migrant Workers where implemented and this implementation represented the use of the Guidelines "ILO Multilateral Framework on Labour Migration". PMID:22073693

  15. Physical view on migration modes

    PubMed Central

    Mierke, Claudia Tanja

    2015-01-01

    Cellular motility is essential for many processes such as embryonic development, wound healing processes, tissue assembly and regeneration, immune cell trafficing and diseases such as cancer. The migration efficiency and the migratory potential depend on the type of migration mode. The previously established migration modes such as epithelial (non-migratory) and mesenchymal (migratory) as well as amoeboid (squeezing motility) relay mainly on phenomenological criteria such as cell morphology and molecular biological criteria such as gene expression. However, the physical view on the migration modes is still not well understood. As the process of malignant cancer progression such as metastasis depends on the migration of single cancer cells and their migration mode, this review focuses on the different migration strategies and discusses which mechanical prerequisites are necessary to perform a special migration mode through a 3-dimensional microenvironment. In particular, this review discusses how cells can distinguish and finally switch between the migration modes and what impact do the physical properties of cells and their microenvironment have on the transition between the novel migration modes such as blebbing and protrusive motility. PMID:26192136

  16. Migration of Asteroidal Dust

    NASA Technical Reports Server (NTRS)

    Ipatov, S. I.; Mather, J. C.

    2003-01-01

    Using the Bulirsh Stoer method of integration, we investigated the migration of dust particles under the gravitational influence of all planets, radiation pressure, Poynting Robertson drag and solar wind drag for equal to 0.01, 0.05, 0.1, 0.25, and 0.4. For silicate particles such values of correspond to diameters equal to about 40, 9, 4, 2, and 1 microns, respectively [1]. The relative error per integration step was taken to be less than 10sup-8. Initial orbits of the particles were close to the orbits of the first numbered mainbelt asteroids.

  17. Process migration in UNIX environments

    NASA Technical Reports Server (NTRS)

    Lu, Chin; Liu, J. W. S.

    1988-01-01

    To support process migration in UNIX environments, the main problem is how to encapsulate the location dependent features of the system in such a way that a host independent virtual environment is maintained by the migration handlers on the behalf of each migrated process. An object-oriented approach is used to describe the interaction between a process and its environment. More specifically, environmental objects were introduced in UNIX systems to carry out the user-environment interaction. The implementation of the migration handlers is based on both the state consistency criterion and the property consistency criterion.

  18. Kirchhoff migration without phases

    NASA Astrophysics Data System (ADS)

    Bardsley, Patrick; Guevara Vasquez, Fernando

    2016-10-01

    We present a simple, frequency domain, preprocessing step to Kirchhoff migration that allows the method to image scatterers when the wave field phase information is lost at the receivers, and only intensities are measured. The resulting imaging method does not require knowing the phases of the probing field or manipulating the phase of the wave field at the receivers. In a regime where the scattered field is small compared to the probing field, the problem of recovering the full-waveform scattered field from intensity data can be formulated as an embarrassingly simple least-squares problem. Although this only recovers the projection (on a known subspace) of the full-waveform scattered field, we show that, for high frequencies, this projection gives Kirchhoff images asymptotically identical to the images obtained with full waveform data. Our method can also be used when the source is modulated by a Gaussian process and autocorrelations are measured at an array of receivers.

  19. Chandra Contaminant Migration Model

    NASA Technical Reports Server (NTRS)

    Swartz, Douglas A.; O'Dell, Steve L.

    2014-01-01

    High volatility cleans OBFs and low volatility produces a high build-up at OBF centers; only a narrow (factor of 2 or less) volatility range produces the observed spatial pattern. Simulations predict less accumulation above outer S-array CCDs; this may explain, in part, gratings/imaging C/MnL discrepancies. Simulations produce a change in center accumulation due solely to DH heater ON/OFF temperature change; but a 2nd contaminant and perhaps a change in source rate is also required. Emissivity E may depend on thickness; another model parameter. Additional physics, e.g., surface migration, is not warranted at this time. At t approx. 14 yrs, model produced 0.22 grams of contaminant, 0.085 grams remaining within ACIS cavity; 7 percent (6mg) on OBFs.

  20. Migration and women's health.

    PubMed

    Adanu, Richard M K; Johnson, Timothy R B

    2009-08-01

    Women have been migrating at similar rates to men for the past 40 years, and comprised about half of all migrants in 2005. Women and children are most affected by displacement as a result of wars and human trafficking. In some cases, the health of female migrants is improved via integration into better health systems in the host country. More often, however, the health of female migrants is affected negatively. Women are doubly disadvantaged because they are discriminated against as women and as migrants. Female migrants are also highly vulnerable to acts of sexual abuse, rape, and violence. This is especially true for women in refugee camps, whose reproductive health needs are often overlooked. To improve the health of female migrants it is important to develop and implement policies that recognize and insist on the respect of the rights of migrants. PMID:19539929

  1. Migration issues important -- Mongolia.

    PubMed

    1999-01-01

    Migration and urbanization are issues that require increasing attention in Mongolia. Mr. Sodov Sonin, Minister of Health and Social Welfare, stated at the Forum that fertility has declined, but mortality, in particular the mortality of children and mothers, is still too high. In addition, there is a significant gap between the knowledge of and behaviors concerning reproductive health, which is one of the causes of the country's high abortion rates. However, on the positive side, literacy is high among women--70% of the students in Mongolia's higher educational institutions are female and the State recognizes equal rights for women. Moreover, programs that promote health and education, including the National Program on Reproductive Health, are being implemented; but despite all these, Mongolia still lacks the human and financial resources to implement the ICPD Program of Action satisfactorily. The country also needs dramatic changes in mind-set and in terms of capacity building, given its ongoing socioeconomic transition. PMID:12295512

  2. Cohort Size Effects and Migration.

    ERIC Educational Resources Information Center

    Wilson, Franklin D.

    1983-01-01

    Explores whether changes in the size of cohorts entering the labor force affected the propensity within the U.S. labor force to migrate and socioeconomic circumstances of migrants at destination within 1965-76. Suggests that a significant reduction in the volume of migration among members of the baby boom cohort was the primary adjustment…

  3. Migration in asymmetric, random environments

    NASA Astrophysics Data System (ADS)

    Deem, Michael; Wang, Dong

    Migration is a key mechanism for expansion of communities. As a population migrates, it experiences a changing environment. In heterogeneous environments, rapid adaption is key to the evolutionary success of the population. In the case of human migration, environmental heterogeneity is naturally asymmetric in the North-South and East-West directions. We here consider migration in random, asymmetric, modularly correlated environments. Knowledge about the environment determines the fitness of each individual. We find that the speed of migration is proportional to the inverse of environmental change, and in particular we find that North-South migration rates are lower than East-West migration rates. Fast communication within the population of pieces of knowledge between individuals, similar to horizontal gene transfer in genetic systems, can help to spread beneficial knowledge among individuals. We show that increased modularity of the relation between knowledge and fitness enhances the rate of evolution. We investigate the relation between optimal information exchange rate and modularity of the dependence of fitness on knowledge. These results for the dependence of migration rate on heterogeneity, asymmetry, and modularity are consistent with existing archaeological facts.

  4. Africa: Setting for Human Migration

    ERIC Educational Resources Information Center

    Buuba, Babacar Diop

    2007-01-01

    Analysis of African migrations can help to understand prehistoric, historical, ancient modern and contemporaneous migrations. Movements of populations were and continue to be so intense that, for some analysts, they constitute one of the dominant trends of the history and destiny of the very old continent. African and non-African states, whether…

  5. Merlin's wizardry guides cohesive migration.

    PubMed

    Zoch, Ansgar; Morrison, Helen

    2015-03-01

    Cells often migrate in tightly connected groups with coordinated movement and polarity. The collective migration of epithelial cell sheets is now shown to be mediated by a signalling axis that involves the merlin tumour-suppressor protein, the tight-junction-associated angiomotin-Rich1 complex and the Rac1 small GTPase. PMID:25720961

  6. Migrating thermospheric tides

    NASA Astrophysics Data System (ADS)

    Hagan, M. E.; Roble, R. G.; Hackney, J.

    2001-07-01

    The capabilities of the global-scale wave model (GSWM) [Hagan et al., 1995, 1999] are extended to include migrating thermospheric solar tides. The GSWM thermospheric tidal forcing parameterization is based on neutral gas heating calculated from first principles in the National Center for Atmospheric Research (NCAR) thermosphere/ionosphere electrodynamics general circulation model (TIE-GCM). This is the first time that a physics-based thermospheric forcing scheme has been used in a model like GSWM. Previous two-dimensional steady state linear tidal models used exospheric temperature measurements to calibrate upper atmospheric tidal forcing. New GSWM results illustrate thermospheric tidal responses that are largely consistent with tides in the TIE-GCM. Diurnal temperature amplitudes increase with increasing solar activity, but there is no analogous diurnal wind response. The thermospheric semidiurnal tide is much weaker than the diurnal tide. Semidiurnal temperature perturbations peak in the lower thermosphere where the semidiurnal forcing maximizes. The new in situ results must be combined with the GSWM upward propagating tide in the lower thermosphere, because the upward propagating components dominate the semidiurnal response throughout the region and the diurnal response below ˜130 km. In situ forcing accounts for most of the diurnal response aloft. Our preliminary evaluation of the GSWM thermospheric predictions is inconclusive. More extensive evaluations are necessary to make a firm assessment of whether the model captures the salient features of the seasonal and solar cycle variability of thermospheric tides.

  7. Neuritin 1 promotes neuronal migration.

    PubMed

    Zito, Arianna; Cartelli, Daniele; Cappelletti, Graziella; Cariboni, Anna; Andrews, William; Parnavelas, John; Poletti, Angelo; Galbiati, Mariarita

    2014-01-01

    Neuritin 1 (Nrn1 or cpg15-1) is an activity-dependent protein involved in synaptic plasticity during brain development, a process that relies upon neuronal migration. By analyzing Nrn1 expression, we found that it is highly expressed in a mouse model of migrating immortalized neurons (GN11 cells), but not in a mouse model of non-migrating neurons (GT1-7 cells). We thus hypothesized that Nrn1 might control neuronal migration. By using complementary assays, as Boyden's microchemotaxis, scratch-wounding and live cell imaging, we found that GN11 cell migration is enhanced when Nrn1 is overexpressed and decreased when Nrn1 is silenced. The effects of Nrn1 in promoting neuronal migration have been then confirmed ex vivo, on rat cortical interneurons, by Boyden chamber assays and focal electroporation of acute embryonic brain slices. Furthermore, we found that Nrn1 level modulation affects GN11 cell morphology. The process is also paralleled by Nrn1-induced α-tubulin post-translational modifications, a well-recognized marker of microtubule stability. Altogether, the data demonstrate a novel function of Nrn1 in promoting migration of neuronal cells and indicate that Nrn1 levels impact on microtubule stability. PMID:23212301

  8. Vulnerable to HIV / AIDS. Migration.

    PubMed

    Fernandez, I

    1998-01-01

    This special report discusses the impact of globalization, patterns of migration in Southeast Asia, gender issues in migration, the links between migration and HIV/AIDS, and spatial mobility and social networks. Migrants are particularly marginalized in countries that blame migrants for transmission of infectious and communicable diseases and other social ills. Effective control of HIV/AIDS among migrant and native populations requires a multisectoral approach. Programs should critically review the privatization of health care services and challenge economic models that polarize the rich and the poor, men and women, North and South, and migrant and native. Programs should recognize the equality between locals and migrants in receipt of health services. Countermeasures should have input from migrants in order to reduce the conditions that increase vulnerability to HIV/AIDS. Gender-oriented research is needed to understand women's role in migration. Rapid assessment has obscured the human dimension of migrants' vulnerability to HIV. Condom promotion is not enough. Migration is a major consequence of globalization, which holds the promise, real or imagined, of prosperity for all. Mass migration can be fueled by explosive regional developments. In Southeast Asia, migration has been part of the process of economic development. The potential to emigrate increases with greater per capita income. "Tiger" economies have been labor importers. Safe sex is not practiced in many Asian countries because risk is not taken seriously. Migrants tend to be used as economic tools, without consideration of social adjustment and sex behavior among singles.

  9. Migration of dispersive GPR data

    USGS Publications Warehouse

    Powers, M.H.; Oden, C.P.; ,

    2004-01-01

    Electrical conductivity and dielectric and magnetic relaxation phenomena cause electromagnetic propagation to be dispersive in earth materials. Both velocity and attenuation may vary with frequency, depending on the frequency content of the propagating energy and the nature of the relaxation phenomena. A minor amount of velocity dispersion is associated with high attenuation. For this reason, measuring effects of velocity dispersion in ground penetrating radar (GPR) data is difficult. With a dispersive forward model, GPR responses to propagation through materials with known frequency-dependent properties have been created. These responses are used as test data for migration algorithms that have been modified to handle specific aspects of dispersive media. When either Stolt or Gazdag migration methods are modified to correct for just velocity dispersion, the results are little changed from standard migration. For nondispersive propagating wavefield data, like deep seismic, ensuring correct phase summation in a migration algorithm is more important than correctly handling amplitude. However, the results of migrating model responses to dispersive media with modified algorithms indicate that, in this case, correcting for frequency-dependent amplitude loss has a much greater effect on the result than correcting for proper phase summation. A modified migration is only effective when it includes attenuation recovery, performing deconvolution and migration simultaneously.

  10. Population commission discusses international migration.

    PubMed

    1997-01-01

    At the 30th session of the Commission on Population and Development during February 24-28, 1997, international migration was the main topic, with special linkages between migration and development and on gender issues and the family. New and emerging issues were also considered. Members stressed the need for more reliable data on migration, the direction of migrants flows, and the characteristics of migrants. The Commission requested a task force on basic social services to hold a technical symposium of experts on international migration in 1998. Its chair, Dr. Nafis Sadik, said that migration issues should based on the reality of choice not on coercive measures or quotas. Almost half of the migrants globally are women. The Commission was given a new impetus by the International Conference on Population and Development held at Cairo in 1994. Migration pressures intensified in the second half of the 1980s and in the early 1990s, creating areas of concern: the negative impact of short-term migration on working conditions in host countries; migration pressures emanating from climatic change; the protection of migrant women and their children; the right of receiving countries to regulate access to their territory; the adverse consequences of forced migration; the situation of persons whose asylum claims have been rejected; the trafficking in women and children, prostitution and coercive adoption; and the sudden and massive arrival of refugees in need of international protection. The 1998 session of the Commission will feature the theme of health and mortality, with special emphasis on the linkages between health and development and on gender and age.

  11. NASTRAN migration to UNIX

    NASA Technical Reports Server (NTRS)

    Chan, Gordon C.; Turner, Horace Q.

    1990-01-01

    COSMIC/NASTRAN, as it is supported and maintained by COSMIC, runs on four main-frame computers - CDC, VAX, IBM and UNIVAC. COSMIC/NASTRAN on other computers, such as CRAY, AMDAHL, PRIME, CONVEX, etc., is available commercially from a number of third party organizations. All these computers, with their own one-of-a-kind operating systems, make NASTRAN machine dependent. The job control language (JCL), the file management, and the program execution procedure of these computers are vastly different, although 95 percent of NASTRAN source code was written in standard ANSI FORTRAN 77. The advantage of the UNIX operating system is that it has no machine boundary. UNIX is becoming widely used in many workstations, mini's, super-PC's, and even some main-frame computers. NASTRAN for the UNIX operating system is definitely the way to go in the future, and makes NASTRAN available to a host of computers, big and small. Since 1985, many NASTRAN improvements and enhancements were made to conform to the ANSI FORTRAN 77 standards. A major UNIX migration effort was incorporated into COSMIC NASTRAN 1990 release. As a pioneer work for the UNIX environment, a version of COSMIC 89 NASTRAN was officially released in October 1989 for DEC ULTRIX VAXstation 3100 (with VMS extensions). A COSMIC 90 NASTRAN version for DEC ULTRIX DECstation 3100 (with RISC) is planned for April 1990 release. Both workstations are UNIX based computers. The COSMIC 90 NASTRAN will be made available on a TK50 tape for the DEC ULTRIX workstations. Previously in 1988, an 88 NASTRAN version was tested successfully on a SiliconGraphics workstation.

  12. [Oxyuriasis and prehistoric migrations].

    PubMed

    Araújo, A; Ferreira, L F

    1995-01-01

    Parasite findings in archeological material have made it possible to trace the dispersion of infectious agents and their human hosts in ancient times. These findings allow us to re-examine theories proposed at the beginning of the century concerning transpacific contacts that Asian populations may have had with South America. This has been the case, for example, with hookworm eggs found in archeological material dating up to 7,000 years before present. Because of the increase in scientific production in this area, it has now become necessary to undertake syntheses that assess the state of the art and propose workable paleoepidemological models of the prehistoric dispersion of human parasitoses. Based on findings of Enterobius vermicularis eggs in archeological material in the Americas, the present study is an effort in this direction. Unlike the hookworm, the pinworm does not require a soil cycle in order to be transmitted from one host to another, thereby meaning that its persistence in a given human population does not depend on climatic conditions. Thus, it could have been brought from the old to the new continent, possibly by human migrations across the Bering Strait. This may explain the greater geographical dispersion and dissemination of these findings in North America from 10,000 yrs B.P. till today. In South America, on the other hand, archeological findings have only confirmed existence of Enterobius vermicularis eggs within the Andean region, with findings located specifically in Chile and northern Argentina. Although a large number of samples have been examined, no such eggs have been found in coprolites in Brazil. The paper discusses models that account for the known distribution of this parasitosis in prehistoric populations. PMID:11625244

  13. Nonequilibrium migration in human history.

    PubMed Central

    Wakeley, J

    1999-01-01

    A nonequilibrium migration model is proposed and applied to genetic data from humans. The model assumes symmetric migration among all possible pairs of demes and that the number of demes is large. With these assumptions it is straightforward to allow for changes in demography, and here a single abrupt change is considered. Under the model this change is identical to a change in the ancestral effective population size and might be caused by changes in deme size, in the number of demes, or in the migration rate. Expressions for the expected numbers of sites segregating at particular frequencies in a multideme sample are derived. A maximum-likelihood analysis of independent polymorphic restriction sites in humans reveals a decrease in effective size. This is consistent with a change in the rates of migration among human subpopulations from ancient low levels to present high ones. PMID:10581291

  14. Correctness criteria for process migration

    NASA Technical Reports Server (NTRS)

    Lu, Chin; Liu, J. W. S.

    1987-01-01

    Two correctness criteria, the state consistency criterion and the property consistency criterion for process migration are discussed. The state machine approach is used to model the interactions between a user process and its environment. These criteria are defined in terms of the model. The idea of environment view was introduced to distinguish what a user process observes about its environment from what its environment state really is and argue that a consistent view of the environment must be maintained for every migrating process.

  15. Homeward bound: Yemeni return migration.

    PubMed

    Colton, N A

    1993-01-01

    The author discusses the return migration of Yemenis from Saudi Arabia during the period 1970-1989. "Through the use of original, empirical data collected in Yemen, this article sheds light on who these returning migrants are, where they have come from, and what sort of future awaits them.... The survey conducted on return migration was administered in the winter and spring of 1989 in a region of North Yemen called al-Hujariyya."

  16. Radar studies of bird migration

    NASA Technical Reports Server (NTRS)

    Williams, T. C.; Williams, J. M.

    1974-01-01

    Observations of bird migration with NASA radars were made at Wallops Island, Va. Simultaneous observations were made at a number of radar sites in the North Atlantic Ocean in an effort to discover what happened to those birds that were observed leaving the coast of North America headed toward Bermuda, the Caribbean and South America. Transatlantic migration, utilizing observations from a large number of radars is discussed. Detailed studies of bird movements at Wallops Island are presented.

  17. Distance and Intrastate College Student Migration

    ERIC Educational Resources Information Center

    Alm, James; Winters, John V.

    2009-01-01

    Most studies of student migration focus on "interstate" migration of college students, largely because the aggregate data typically used are limited in geographic specificity to states. However, interstate migration is only a small part of the total student migration. Public institutions generally get most of their students from within their…

  18. Rural-Urban Migration in Colombia.

    ERIC Educational Resources Information Center

    Schultz, T. Paul

    The rural-urban migration pattern in Colombia during the last 25 years has resulted in a population increase in urban areas from 30 to 52 percent of the total population. This study explores the causes of internal migration. Migration rates are estimated for various groups in the population to clarify who migrates and to where. A model of…

  19. [On the theoretical basis of migration research].

    PubMed

    Soderling, I

    1980-01-01

    A critique of current theories of migration is first presented. The author suggests that a variety of theories is needed to explain different types of migration. The model used to study internal migration at the Institute of Migration in Turku, Finland, is then described. (summary in ENG) PMID:12265094

  20. International migration: a global challenge.

    PubMed

    Martin, P; Widgren, J

    1996-04-01

    Trends in international migration are presented in this multiregional analysis. Seven of the world's wealthiest countries have about 33% of the world's migrant population, but under 16% of the total world population. Population growth in these countries is substantially affected by the migrant population. The migration challenge is external and internal. The external challenge is to balance the need for foreign labor and the commitment to human rights for those migrants seeking economic opportunity and political freedom. The internal challenge is to assure the social adjustment of immigrants and their children and to integrate them into society as citizens and future leaders. Why people cross national borders and how migration flows are likely to evolve over the next decades are explained. This report also presents some ways that countries can manage migration or reduce the pressures which force people to migrate. It is recommended that receiving nations control immigration by accelerating global economic growth and reducing wars and human rights violations. This report examines the impact of immigration on international trade, aid, and direct intervention policies. Although migration is one of the most important international economic issues, it is not coordinated by an international group. The European experience indicates that it is not easy to secure international cooperation on issues that affect national sovereignty. It is suggested that countries desiring control of their borders should remember that most people never cross national borders to live or work in another country, that 50% of the world's migrants move among developing countries, and that countries can shift from being emigration to immigration countries. The author suggests that sustained reductions in migration pressure are a better alternative than the "quick fixes" that may invite the very much feared mass and unpredictable movements.

  1. International migration: a global challenge.

    PubMed

    Martin, P; Widgren, J

    1996-04-01

    Trends in international migration are presented in this multiregional analysis. Seven of the world's wealthiest countries have about 33% of the world's migrant population, but under 16% of the total world population. Population growth in these countries is substantially affected by the migrant population. The migration challenge is external and internal. The external challenge is to balance the need for foreign labor and the commitment to human rights for those migrants seeking economic opportunity and political freedom. The internal challenge is to assure the social adjustment of immigrants and their children and to integrate them into society as citizens and future leaders. Why people cross national borders and how migration flows are likely to evolve over the next decades are explained. This report also presents some ways that countries can manage migration or reduce the pressures which force people to migrate. It is recommended that receiving nations control immigration by accelerating global economic growth and reducing wars and human rights violations. This report examines the impact of immigration on international trade, aid, and direct intervention policies. Although migration is one of the most important international economic issues, it is not coordinated by an international group. The European experience indicates that it is not easy to secure international cooperation on issues that affect national sovereignty. It is suggested that countries desiring control of their borders should remember that most people never cross national borders to live or work in another country, that 50% of the world's migrants move among developing countries, and that countries can shift from being emigration to immigration countries. The author suggests that sustained reductions in migration pressure are a better alternative than the "quick fixes" that may invite the very much feared mass and unpredictable movements. PMID:12320315

  2. Seasonal Survival Probabilities Suggest Low Migration Mortality in Migrating Bats

    PubMed Central

    Giavi, Simone; Moretti, Marco; Bontadina, Fabio; Zambelli, Nicola; Schaub, Michael

    2014-01-01

    Migration is adaptive if survival benefits are larger than costs of residency. Many aspects of bat migration ecology such as migratory costs, stopover site use and fidelity are largely unknown. Since many migrating bats are endangered, such information is urgently needed to promote conservation. We selected the migrating Leisler's bat (Nyctalus leisleri) as model species and collected capture-recapture data in southern Switzerland year round during 6 years. We estimated seasonal survival and site fidelity with Cormack-Jolly-Seber models that accounted for the presence of transients fitted with Bayesian methods and assessed differences between sexes and seasons. Activity peaked in autumn and spring, whereas very few individuals were caught during summer. We hypothesize that the study site is a migratory stopover site used during fall and spring migration for most individuals, but there is also evidence for wintering. Additionally, we found strong clues for mating during fall. Summer survival that included two major migratory journeys was identical to winter survival in males and slightly higher in females, suggesting that the migratory journeys did not bear significant costs in terms of survival. Transience probability was in both seasons higher in males than in females. Our results suggest that, similarly to birds, Leisler's bat also use stopover sites during migration with high site fidelity. In contrast to most birds, the stopover site was also used for mating and migratory costs in terms of survival seemed to be low. Transients' analyses highlighted strong individual variation in site use which makes particularly challenging the study and modelling of their populations as well as their conservation. PMID:24454906

  3. Seasonal survival probabilities suggest low migration mortality in migrating bats.

    PubMed

    Giavi, Simone; Moretti, Marco; Bontadina, Fabio; Zambelli, Nicola; Schaub, Michael

    2014-01-01

    Migration is adaptive if survival benefits are larger than costs of residency. Many aspects of bat migration ecology such as migratory costs, stopover site use and fidelity are largely unknown. Since many migrating bats are endangered, such information is urgently needed to promote conservation. We selected the migrating Leisler's bat (Nyctalus leisleri) as model species and collected capture-recapture data in southern Switzerland year round during 6 years. We estimated seasonal survival and site fidelity with Cormack-Jolly-Seber models that accounted for the presence of transients fitted with Bayesian methods and assessed differences between sexes and seasons. Activity peaked in autumn and spring, whereas very few individuals were caught during summer. We hypothesize that the study site is a migratory stopover site used during fall and spring migration for most individuals, but there is also evidence for wintering. Additionally, we found strong clues for mating during fall. Summer survival that included two major migratory journeys was identical to winter survival in males and slightly higher in females, suggesting that the migratory journeys did not bear significant costs in terms of survival. Transience probability was in both seasons higher in males than in females. Our results suggest that, similarly to birds, Leisler's bat also use stopover sites during migration with high site fidelity. In contrast to most birds, the stopover site was also used for mating and migratory costs in terms of survival seemed to be low. Transients' analyses highlighted strong individual variation in site use which makes particularly challenging the study and modelling of their populations as well as their conservation.

  4. Thread Migration in the Presence of Pointers

    NASA Technical Reports Server (NTRS)

    Cronk, David; Haines, Matthew; Mehrotra, Piyush

    1996-01-01

    Dynamic migration of lightweight threads supports both data locality and load balancing. However, migrating threads that contain pointers referencing data in both the stack and heap remains an open problem. In this paper we describe a technique by which threads with pointers referencing both stack and non-shared heap data can be migrated such that the pointers remain valid after migration. As a result, threads containing pointers can now be migrated between processors in a homogeneous distributed memory environment.

  5. Ethical concerns in nurse migration.

    PubMed

    McElmurry, Beverly J; Solheim, Karen; Kishi, Rieko; Coffia, Marcia A; Woith, Wendy; Janepanish, Poolsuk

    2006-01-01

    International nurse migration is natural and to be expected. Recently, however, those who have fostered nurse migration believe that it will solve nursing shortages in developed countries and offer nurse migrants better working conditions and an improved quality of life. Whether natural or manipulated, migration flow patterns largely occur from developing to developed countries. In this article, nurse migration is examined using primary health care (PHC) as an ethical framework. The unmanaged flow of nurse migrants from developing to developed countries is inconsistent with "health for all" principles. Removing key health personnel from countries experiencing resource shortages is contrary to PHC equity. Often, nurse migrants are placed in vulnerable, inequitable work roles, and employing nurse migrants fails to address basic causes of nurse shortages in developed countries, such as dissatisfaction with work conditions and decreased funding for academic settings. Nurse migration policies and procedures can be developed to satisfy PHC ethics criteria if they (1) leave developing countries enhanced rather than depleted, (2) contribute to country health outcomes consistent with essential care for all people, (3) are based on community participation, (4) address common nursing labor issues, and (5) involve equitable and clear financial arrangements. PMID:16873045

  6. Sedimentary record of erg migration

    SciTech Connect

    Porter, M.L.

    1986-06-01

    The sedimentary record of erg (eolian sand sea) migration consists of an idealized threefold division of sand-sea facies sequences. The basal division, here termed the fore-erg, is composed of a hierarchy of eolian sand bodies contained within sediments of the flanking depositional environment. The fore-erg represents the downwind, leading edge of the erg and records the onset of eolian sedimentation. Basin subsidence coupled with erg migration places the medial division, termed the central erg, over the fore-erg strata. Eolian influence on regional sedimentation patterns is greatest in the central erg, and most of the sand transported and deposited in the erg is contained within this region. Reduction in sand supply and continued erg migration will cover the central-erg deposits with a veneer of back-erg deposits. This upper division of the erg facies sequence resembles closely the fore-erg region. Back-erg deposits may be thin due to limited eolian influence on sedimentation or incomplete erg migration, or they may be completely absent because of great susceptibility to postdepositional erosion. Tectonic, climatic, and eustatic influences on sand-sea deposition will produce distinctive variations or modifications of the idealized erg facies sequence. The resulting variants in the sedimentary record of erg migration are illustrated with ancient examples from western North America, Europe, southern Africa, and South America. 38 references, 2 figures, 2 tables.

  7. Controlled-aperture wave-equation migration

    SciTech Connect

    Huang, L.; Fehler, Michael C.; Sun, H.; Li, Z.

    2003-01-01

    We present a controlled-aperture wave-equation migration method that no1 only can reduce migration artiracts due to limited recording aperlurcs and determine image weights to balance the efl'ects of limited-aperture illumination, but also can improve thc migration accuracy by reducing the slowness perturbations within thc controlled migration regions. The method consists of two steps: migration aperture scan and controlled-aperture migration. Migration apertures for a sparse distribution of shots arc determined using wave-equation migration, and those for the other shots are obtained by interpolation. During the final controlled-aperture niigration step, we can select a reference slowness in c;ontrollecl regions of the slowness model to reduce slowncss perturbations, and consequently increase the accuracy of wave-equation migration inel hods that makc use of reference slownesses. In addition, the computation in the space domain during wavefield downward continuation is needed to be conducted only within the controlled apertures and therefore, the computational cost of controlled-aperture migration step (without including migration aperture scan) is less than the corresponding uncontrolled-aperture migration. Finally, we can use the efficient split-step Fourier approach for migration-aperture scan, then use other, more accurate though more expensive, wave-equation migration methods to perform thc final controlled-apertio.ee migration to produce the most accurate image.

  8. Neurobiology of Monarch Butterfly Migration.

    PubMed

    Reppert, Steven M; Guerra, Patrick A; Merlin, Christine

    2016-01-01

    Studies of the migration of the eastern North American monarch butterfly (Danaus plexippus) have revealed mechanisms behind its navigation. The main orientation mechanism uses a time-compensated sun compass during both the migration south and the remigration north. Daylight cues, such as the sun itself and polarized light, are processed through both eyes and integrated through intricate circuitry in the brain's central complex, the presumed site of the sun compass. Monarch circadian clocks have a distinct molecular mechanism, and those that reside in the antennae provide time compensation. Recent evidence shows that migrants can also use a light-dependent inclination magnetic compass for orientation in the absence of directional daylight cues. The monarch genome has been sequenced, and genetic strategies using nuclease-based technologies have been developed to edit specific genes. The monarch butterfly has emerged as a model system to study the neural, molecular, and genetic basis of long-distance animal migration. PMID:26473314

  9. Focus: Asian migration to Canada.

    PubMed

    Kobayashi, A

    1988-01-01

    This collection of 5 short essays on Asian migration to Canada focuses on the relationships between individual migrants and their social contexts, both Asian and Canadian. Papers by Anderson and Kobayashi adopt research perspectives of outsider and insider, respectively. Vibert provides a historical overview against which the substantive issues introduced in the other 3 papers can be understood, and he illustrates the links between circumstances of migration and the larger issues by which the course of Canadian social progress has been steered. Mercer provides an introduction to issues that dominate the agenda of contemporary research, to show that Canadian communities of Asian heritage continue to grow in size, diversity, and complexity, as they become more established on the Canadian landscape. This collection is as much about the geography of racism as it is about migration.

  10. Neocortical neurogenesis and neuronal migration

    PubMed Central

    Tan, Xin; Shi, Song-Hai

    2012-01-01

    The neocortex, the evolutionarily newest part of the cerebral cortex, controls nearly all aspects of behavior, including perception, language and decision-making. It contains an immense number of neurons that can be broadly divided into two groups, excitatory neurons and inhibitory interneurons. These neurons are predominantly produced through extensive progenitor cell divisions during the embryonic stages. Moreover, they are not randomly dispersed, but spatially organized into horizontal layers that are essential for neocortex function. The formation of this laminar structure requires exquisite control of neuronal migration from their birthplace to their final destination. Extensive research over the past decade has greatly advanced our understanding of the production and migration of both excitatory neurons and inhibitory interneurons in the developing neocortex. In this review, we aim to give an overview on the molecular and cellular processes of neocortical neurogenesis and neuronal migration. PMID:24014417

  11. Migration, refugees, and health risks.

    PubMed Central

    Carballo, M.; Nerukar, A.

    2001-01-01

    Migration both voluntary and forced is increasing all over the world. People are moving in larger numbers faster and further than at any other time in history. This is happening at a time when many countries are ill-prepared to deal with a changing demography and when policies and attitudes to population movement and immigration are hardening. The health implications of this are many, and, in some cases, illness and death rates associated with migration are exacerbated by a lack of policies needed to make migration a healthy and socially productive process. From a public health point of view, this is having and will continue to have serious ramifications for the people that move, the family they leave behind, and the communities that host the newcomers. PMID:11485671

  12. Migration, refugees, and health risks.

    PubMed

    Carballo, M; Nerukar, A

    2001-01-01

    Migration both voluntary and forced is increasing all over the world. People are moving in larger numbers faster and further than at any other time in history. This is happening at a time when many countries are ill-prepared to deal with a changing demography and when policies and attitudes to population movement and immigration are hardening. The health implications of this are many, and, in some cases, illness and death rates associated with migration are exacerbated by a lack of policies needed to make migration a healthy and socially productive process. From a public health point of view, this is having and will continue to have serious ramifications for the people that move, the family they leave behind, and the communities that host the newcomers.

  13. Climate Migration and Moral Responsibility

    PubMed Central

    Nawrotzki, Raphael

    2016-01-01

    Even though anthropogenic climate change is largely caused by industrialized nations, its burden is distributed unevenly with poor developing countries suffering the most. A common response to livelihood insecurities and destruction is migration. Using Peter Singer’s “historical principle” this paper argues that a morally just evaluation requires taking causality between climate change and migration under consideration. The historical principle is employed to emphasize shortcomings in commonly made philosophical arguments to oppose immigration. The article concludes that none of these arguments is able to override the moral responsibility of industrialized countries to compensate for harms that their actions have caused.

  14. The migration transition in Malaysia.

    PubMed

    Lim, L L

    1996-01-01

    "Exploring the unique experience of migration transition in Malaysia, this paper identifies the turning points in relation to the level and nature of economic and labor market developments in Malaysia. Examining the development dynamics that mark the passage from exporting labor to depending on foreign labor, the paper concludes that such dynamics are influenced not only by economic but also sociocultural, demographic and policy factors. Several lessons from the Malaysian experience are drawn at the end to be utilized by other countries that still have to reach the turning points of the migration transition." PMID:12320775

  15. Rural migration in southern Nevada

    SciTech Connect

    Mosser, D.; Soden, D.L.

    1993-08-01

    This study reviews the history of migration in two rural counties in Southern Nevada. It is part of a larger study about the impact of a proposed high-level nuclear waste repository on in- and out-migration patterns in the state. The historical record suggests a boom and bust economic cycle has predominated in the region for the past century creating conditions that should be taken into account by decision makers when ascertaining the long-term impacts of the proposed repository.

  16. Climate Migration and Moral Responsibility

    PubMed Central

    Nawrotzki, Raphael

    2016-01-01

    Even though anthropogenic climate change is largely caused by industrialized nations, its burden is distributed unevenly with poor developing countries suffering the most. A common response to livelihood insecurities and destruction is migration. Using Peter Singer’s “historical principle” this paper argues that a morally just evaluation requires taking causality between climate change and migration under consideration. The historical principle is employed to emphasize shortcomings in commonly made philosophical arguments to oppose immigration. The article concludes that none of these arguments is able to override the moral responsibility of industrialized countries to compensate for harms that their actions have caused. PMID:27668124

  17. [Family reunification, family-formation migration, and return migration of Turks and Moroccans].

    PubMed

    De Beer, J; Kuijper, H; Noordam, R

    1991-01-01

    The authors analyze migration patterns to the Netherlands from Turkey and Morocco for the period 1977-1989. Three distinct phases emerge: labor migration, family-reunification migration, and family-formation migration. The rise in migration from Turkey and Morocco during the second half of the 1980s is attributed to family-formation migration, which is defined as a member of the second generation marrying a partner from the country of origin. (SUMMARY IN ENG)

  18. Migration cost externality and interregional equilibrium.

    PubMed

    Shin, C

    1994-01-01

    "This paper will investigate the characteristics of population allocation between two regions in the presence of migration cost. It will also examine both populations and the non-migration range of the initial population in which migration does not occur, in social optimum and market equilibrium with central government intervention, to reveal migration cost externality, and to propose a remedy for it." The author finds that "migration cost gives the social planner an additional burden of population reallocation, and it has an important effect upon an individual's decisions on migration in a decentralized market mechanism."

  19. Zebrafish germ cells: motility and guided migration.

    PubMed

    Paksa, Azadeh; Raz, Erez

    2015-10-01

    In the course of embryonic development, the process of cell migration is critical for establishment of the embryonic body plan, for morphogenesis and for organ function. Investigating the molecular mechanisms underlying cell migration is thus crucial for understanding developmental processes and clinical conditions resulting from abnormal cell migration such as cancer metastasis. The long-range migration of primordial germ cells toward the region at which the gonad develops occurs in embryos of various species and thus constitutes a useful in vivo model for single-cell migration. Recent studies employing zebrafish embryos have greatly contributed to the understanding of the mechanisms facilitating the migration of these cells en route to their target.

  20. A Discrete Cell Migration Model

    SciTech Connect

    Nutaro, James J; Kruse, Kara L; Ward, Richard C; O'Quinn, Elizabeth; Woerner, Matthew M; Beckerman, Barbara G

    2007-01-01

    Migration of vascular smooth muscle cells is a fundamental process in the development of intimal hyperplasia, a precursor to development of cardiovascular disease and a potential response to injury of an arterial wall. Boyden chamber experiments are used to quantify the motion of cell populations in response to a chemoattractant gradient (i.e., cell chemotaxis). We are developing a mathematical model of cell migration within the Boyden chamber, while simultaneously conducting experiments to obtain parameter values for the migration process. In the future, the model and parameters will be used as building blocks for a detailed model of the process that causes intimal hyperplasia. The cell migration model presented in this paper is based on the notion of a cell as a moving sensor that responds to an evolving chemoattractant gradient. We compare the results of our three-dimensional hybrid model with results from a one-dimensional continuum model. Some preliminary experimental data that is being used to refine the model is also presented.

  1. Externality, migration, and urban crises.

    PubMed

    Kanemoto, Y

    1980-01-01

    The author analyzes a special aspect of the short-run dynamics of an urban area which arises when there is a contrast between different types of households. The possibility of cumulative or catastrophic processes because of migration by poor families and then by rich families in or out of an urban area is discussed

  2. The OECD and International Migration.

    ERIC Educational Resources Information Center

    Organisation for Economic Cooperation and Development, Paris (France).

    The document focuses on various aspects of the social, economic, and policy implications of migration in Europe based on the actions undertaken by the Organization for Economic Cooperation and Development (OECD). A discussion of issues which may remedy the disequilibrium between the relative portions of the factors of production is presented: (1)…

  3. Migration and circulation in Ecuador.

    PubMed

    Brea, J A

    1991-01-01

    "This study investigates labor mobility in Ecuador as a function of the socioeconomic structure of places and personal attributes of migrants and circulators (short-term movers).... Particular attention is given to the role of agrarian change in altering established migration and circulation patterns." The author finds that "circulation may significantly alter family organization and the role of women in many Ecuadorian communities."

  4. Les questions de migrations internationales

    NASA Astrophysics Data System (ADS)

    Samman, Mouna Liliane

    1993-03-01

    International migrations have growing implications for both countries of origin and countries of destination. In the latter, the presence of foreigners and of members of their families today creates problems of integration, causes argument and brings mounting xenophobia. Paralleling political, economic and social measures taken by public authorities to respond to these difficulties, education needs to assist in defusing the resulting social tensions by preparing the minds of learners and helping to develop new attitudes. In particular, when educational programmes address questions of international migration, these should be treated in the framework of historical evolution so that their real significance and their true temporal and spatial dimensions become apparent. It is also important that the growing interdependence between countries should be made plain, that national history should be placed in its international context, and that the true consequences of these developments should be made clear. In this context, learners need to be acquainted with Human Rights, thereby stressing universal moral values and the role of the individual. Lastly, questions relating to international migration are usually presented in the media in a selective and partial manner, and the young people who take in this information often accept the hasty judgments which are made of situations as proven facts. This is why all teaching about international migration needs to be considered or reconsidered in the light of the complementary or competing actions of the media.

  5. Youth Migration from Rural Areas.

    ERIC Educational Resources Information Center

    Haller, Emil J.; Monk, David H.

    The persistent net loss of young people from rural areas has potentially contradictory implications for educational policy. Believing that youth migration to urban areas is inevitable, one school board might feel obligated to prepare students for urban jobs. Another board might view such actions as community suicide and attempt to slow…

  6. Job Migration: A Collaborative Effort

    ERIC Educational Resources Information Center

    Wagoner, Cynthia L.

    2012-01-01

    Music teachers often change jobs several times during their careers. Reasons for job changes vary, but regardless, these changes bring a different set of challenges. Sharing knowledge and learning are part and parcel of collaboration. So what if, as education professionals, music teachers decided to collaborate during job migrations? For all music…

  7. [Haitian migration to Santo Domingo].

    PubMed

    Latortue, P R

    1985-01-01

    This work examines the history of Haitian migration to the Dominican Republic, the central role of Haitian migration in Dominican society, working conditions of Haitian migrants in the Dominican Republic, and the relationship of the migration to economic development on the island of Hispaniola. Lack of data, the difficulty of measuring illegal movement, and the problem of defining Haitians in Santo Domingo have impeded understanding of migration to the Dominican Republic. It is believed by many authorities that Haitian migration to Santo Domingo is considerable and perhaps exceeds that to the US. Haitian migration to the Dominican Republic began after 1915 with the fall of the Haitian president, a worsening of economic conditions partly caused by stagnation in the agricultural sector, and the newly dominant role of the US in Haitian economic affairs. The Great Depression of the 1930s was a direct antecedent of the massacre of Haitians by Dominican police in which some 30 thousand persons were killed; the economic recession of the early 1980s has also caused an outburst of antiHaitian feeling in the Dominican Republic although 80% of laborers in the sugar industry are Haitians. Sugar is extremely important to the Dominican economy: in 1974, sugar covered 12% of cultivated land, produced 40% of foreign exchange earnings, and was responsable for 21% of taxable income. Dominicans however refuse to work in sugar plantations under the current technological. conditions and wage system. Although the government periodically demands the Dominicanization of the sugar work force, no such changes have been made. Sugar will probably continue to play a decisive role in the generation of foreign exchange despite introduction of more technologically advanced sectors which benefit from better prices in the international market. Possibilities of mechanizing sugar production in the Dominican Republic appear remote, and failure to modernize an important sector of the economy has

  8. [Haitian migration to Santo Domingo].

    PubMed

    Latortue, P R

    1985-01-01

    This work examines the history of Haitian migration to the Dominican Republic, the central role of Haitian migration in Dominican society, working conditions of Haitian migrants in the Dominican Republic, and the relationship of the migration to economic development on the island of Hispaniola. Lack of data, the difficulty of measuring illegal movement, and the problem of defining Haitians in Santo Domingo have impeded understanding of migration to the Dominican Republic. It is believed by many authorities that Haitian migration to Santo Domingo is considerable and perhaps exceeds that to the US. Haitian migration to the Dominican Republic began after 1915 with the fall of the Haitian president, a worsening of economic conditions partly caused by stagnation in the agricultural sector, and the newly dominant role of the US in Haitian economic affairs. The Great Depression of the 1930s was a direct antecedent of the massacre of Haitians by Dominican police in which some 30 thousand persons were killed; the economic recession of the early 1980s has also caused an outburst of antiHaitian feeling in the Dominican Republic although 80% of laborers in the sugar industry are Haitians. Sugar is extremely important to the Dominican economy: in 1974, sugar covered 12% of cultivated land, produced 40% of foreign exchange earnings, and was responsable for 21% of taxable income. Dominicans however refuse to work in sugar plantations under the current technological. conditions and wage system. Although the government periodically demands the Dominicanization of the sugar work force, no such changes have been made. Sugar will probably continue to play a decisive role in the generation of foreign exchange despite introduction of more technologically advanced sectors which benefit from better prices in the international market. Possibilities of mechanizing sugar production in the Dominican Republic appear remote, and failure to modernize an important sector of the economy has

  9. [Agricultural migration has changed face].

    PubMed

    Ouedraogo, D

    1991-04-01

    Movements related to colonization of new lands for cultivation or pasturing have constituted the dominant form of migration in the Sahel countries since the colonial period. the relative importance of such movements declined with the development of labor migration, but geographic mobility continues to be an integral part of Sahel life. A principal strategy during crises of agricultural production was the vast movement of population toward new lands, but such movements had little macroeconomic or macrosocial importance given the low population density and technical development of the time; the family subsistence enterprise was merely displaced. The artificial division into separate countries in the colonial era brought some control of migratory movements, and especially those across international borders, but such migrations increased again after independence and especially during the prolonged drought. Rural migration has been encouraged by development of transportation and communication facilities and by progress in controlling endemic diseases such as river blindness and sleeping sickness. Contemporary migration differs fundamentally from agricultural migration of the past. Migration has become, in addition to a survival strategy, a strategy of economic and social advancement. The change of residence is often accompanied by a restructuring of economic activities and substantial increases in the household's resources. Migrants attempt to produce enough for their own consumption, with some left for sale. They may also take on secondary employment, especially in the dry season: sale of firewood, petty trading, artisanal production. Spontaneous population movements seem to benefit the migrants, improving family and national agricultural production and contributing to a better distribution of rural population, but they have a high social and ecological cost and should receive more attention from planners and researchers in the context of the current campaign against

  10. The circular migration of smallholders in Kenya.

    PubMed

    Bigsten, A

    1996-01-01

    Circular migration is a central phenomenon in the lives of smallholders in East Africa. Many migration decisions are not individual decisions, but rather household decisions in which the household allocates its labor force among activities to maximize household utility. A probit model which incorporates circular migration and takes into account contacts, information, and indivisibilities is used to analyze migration among 763 farm households in the Central and Nyanza provinces of Kenya. Study data are from a 1982 survey. The pull of high urban wages appears to be a far more important determinant of migration decision outcomes than the push of land scarcity, while a strong local nonagricultural economy does not seem to restrict migration. Networks of personal contacts were found to be highly significant determinants of migration. These findings suggest that rural development will probably not reduce the flow of migration.

  11. Individual Decisions to Migrate During Civil Conflict

    PubMed Central

    Bohra-Mishra, Pratikshya; Massey, Douglas S.

    2012-01-01

    The existing literature on forced migration limits our understanding of how violence affects migration to competing destinations. This article adds to the literature on forced migration by studying how armed violence during a period of civil conflict in south-central Nepal influenced the likelihood of local, internal, and international migration. We find that violence has a nonlinear effect on migration, such that low to moderate levels of violence reduce the odds of movement, but when violence reaches high levels, the odds of movement increase. We also find that the effect of violence on mobility increases as the distance of the move increases. When we consider the influence of violence on microlevel decision-making, we find that the effects of individual and household-level determinants were mostly consistent with hypotheses derived from contemporary theories of voluntary migration and that no predictor of migration influenced the decision to migrate differently in the presence of violence. PMID:21541805

  12. Migration policies and return migration with particular reference to Yugoslavia.

    PubMed

    Chepulis, R L

    1981-09-01

    "The essay analyses some of the most recent migratory trends in Europe in the light of labour turnover, integration and assimilation. The author states that [since] World War II the expansion of the European and international capitalistic system has encouraged or discouraged, according to the various circumstances, the transferral of workers to different countries. "Particular attention has been given to the case of Yugoslavia. The changing of its migration policies has often coincided with the different modalities of flows." (summary in FRE)

  13. [Urban employment and internal migration in Peru].

    PubMed

    Cotlear, D

    1984-06-01

    The relationship between internal migration and employment problems in Peru is examined. The author argues that regional differences in income distribution are the primary causes of migration, particularly to urban areas. A model of the migration process is developed and tested using data from official sources, surveys, and the published literature. PMID:12313840

  14. [Urban employment and internal migration in Peru].

    PubMed

    Cotlear, D

    1984-06-01

    The relationship between internal migration and employment problems in Peru is examined. The author argues that regional differences in income distribution are the primary causes of migration, particularly to urban areas. A model of the migration process is developed and tested using data from official sources, surveys, and the published literature.

  15. Japanese Migration and the Americas: An Introduction to the Study of Migration.

    ERIC Educational Resources Information Center

    Mukai, Gary; Brunette, Rachel

    This curriculum module introduces students to the study of migration, including a brief overview of some categories of migration and reasons why people migrate. As a case study, the module uses the Japanese migration experience in the United States, Peru, Brazil, Canada, Mexico, Argentina, Bolivia, and Paraguay. The module introduces students to…

  16. Nuclide-migration field experiments

    SciTech Connect

    Erdal, B.R.; Wolfsberg, K.; Johnstone, J.K.; Erickson, K.L.; Friedman, A.M.; Fried, S.; Hines, J.J.

    1981-03-01

    When considering groundwater flow and radionuclide retention in the complex flow systems that can occur in geologic formations, one has a serious problem in determining if laboratory studies are being performed under conditions appropriate to natural systems. This document is the project plan for a program designed to begin to address these problems. The project is being carried out jointly by the Los Alamos National Laboratory, Sandia National Laboratories, and Argonne National Laboratory. The work has three principal objectives: (1) to develop the experimental, instrumental, and safety techniques necessary to conduct controlled, small-scale radionuclide migration field experiments, including those involving actinides; (2) to use these techniques to define radionuclide migration through rock by performing generic, at-depth experiments under closely monitored conditions; and (3) to determine whether available lithologic, geochemical, and hydrologic properties together with existing or developing transport models are sufficient and appropriate to describe real field conditions.

  17. Neural crest migration: trailblazing ahead

    PubMed Central

    McLennan, Rebecca

    2015-01-01

    Embryonic cell migration patterns are amazingly complex in the timing and spatial distribution of cells throughout the vertebrate landscape. However, advances in in vivo visualization, cell interrogation, and computational modeling are extracting critical features that underlie the mechanistic nature of these patterns. The focus of this review highlights recent advances in the study of the highly invasive neural crest cells and their migratory patterns during embryonic development. We discuss these advances within three major themes and include a description of computational models that have emerged to more rapidly integrate and test hypothetical mechanisms of neural crest migration. We conclude with technological advances that promise to reveal new insights and help translate results to human neural crest-related birth defects and metastatic cancer. PMID:25705385

  18. China: surplus labour and migration.

    PubMed

    Banister, J; Taylor, J R

    1989-12-01

    Surplus labor force and migration trends in China are examined, with emphasis on the impact of underemployment in rural areas. "Government policy encourages surplus labourers to transfer out of crop farming into agricultural sidelines or non-agricultural work. Peasants are urged to stay where they are, shifting jobs without shifting location; however, many rural areas are poorly endowed for providing alternative employment, so their surplus workers must also leave the village to find work. Many do not formally migrate, but rather move on a seasonal basis or set up 'temporary' residence in an urban place. This 'floating' population has been escalating rapidly in recent years....[The authors argue] that China's cities and towns can absorb millions of surplus labourers from rural areas each year, to the mutual benefit of sending and receiving areas." PMID:12342630

  19. Physicists' Forced Migrations under Hitler

    NASA Astrophysics Data System (ADS)

    Beyerchen, Alan

    2011-03-01

    When the Nazis came to power in early 1933 they initiated formal and informal measures that forced Jews and political opponents from public institutions such as universities. Some physicists retired and others went into industry, but most emigrated. International communication and contact made emigration a viable option despite the desperate economic times in the Great Depression. Another wave of emigrations followed the annexation of Austria in 1938. Individual cases as well as general patterns of migration and adaptation to new environments will be examined in this presentation. One important result of the forced migrations was that many of the physicists expelled under Hitler played important roles in strengthening physics elsewhere, often on the Allied side in World War II.

  20. Incentives and disincentives: international migration.

    PubMed

    Bhagwati, J N

    1984-01-01

    International migration is largely controlled by disincentives, or quotas, on immigration rather than checks on emigrations. Societies generally feel they have a right to exclude others from their boundaries, but they also usually feel that they do not have a right to control emigration. The single-planetary approach holds that people have the right to live wherever they like on the planet, and the cosmopolitan-utilitarian approach believes the same for reasons of world efficiency. The current feeling that societies have the right to exclude others may be explained best by territoriality in human animals. People also believe that their culture will be diluted if too many outsiders enter. In many cases, immigration systems cannot really control immigration, as in the cases of long landlocked borders between the US and Mexico and between Bangladesh and Assam. Immigration systems also contain legal loopholes. For example, in the US it is easier to get a student visa and convert to immigrant status than to gain immigrant status directly. Loopholes lead to plugs, which lead in turn to more loopholes. An upsurge in requests for political asylum followed increased restrictions on immigration in Western Europe. The US has investigated foreign aid and foreign investments to Mexico and Haiti to curb the flow of illegal migrants. The author suggests that foreign investments may lead to more migration because of the creation of a new proletariat used to the ways of developed countries. An estimate of what would happen if all immigration control were removed worldwide concludes that efficiency and income distribution would improve worldwide. Most migration from developing to developed countries currently consists of the migration of skilled professionals, the brain drain. The author proposes a tax on these professionals to be paid to the country of origin to compensate them for the loss in education and training. The author summarizes the differences between the West German

  1. 3D grain boundary migration

    NASA Astrophysics Data System (ADS)

    Becker, J. K.; Bons, P. D.

    2009-04-01

    Microstructures of rocks play an important role in determining rheological properties and help to reveal the processes that lead to their formation. Some of these processes change the microstructure significantly and may thus have the opposite effect in obliterating any fabrics indicative of the previous history of the rocks. One of these processes is grain boundary migration (GBM). During static recrystallisation, GBM may produce a foam texture that completely overprints a pre-existing grain boundary network and GBM actively influences the rheology of a rock, via its influence on grain size and lattice defect concentration. We here present a new numerical simulation software that is capable of simulating a whole range of processes on the grain scale (it is not limited to grain boundary migration). The software is polyhedron-based, meaning that each grain (or phase) is represented by a polyhedron that has discrete boundaries. The boundary (the shell) of the polyhedron is defined by a set of facets which in turn is defined by a set of vertices. Each structural entity (polyhedron, facets and vertices) can have an unlimited number of parameters (depending on the process to be modeled) such as surface energy, concentration, etc. which can be used to calculate changes of the microstructre. We use the processes of grain boundary migration of a "regular" and a partially molten rock to demonstrate the software. Since this software is 3D, the formation of melt networks in a partially molten rock can also be studied. The interconnected melt network is of fundamental importance for melt segregation and migration in the crust and mantle and can help to understand the core-mantle differentiation of large terrestrial planets.

  2. Incentives and disincentives: international migration.

    PubMed

    Bhagwati, J N

    1984-01-01

    International migration is largely controlled by disincentives, or quotas, on immigration rather than checks on emigrations. Societies generally feel they have a right to exclude others from their boundaries, but they also usually feel that they do not have a right to control emigration. The single-planetary approach holds that people have the right to live wherever they like on the planet, and the cosmopolitan-utilitarian approach believes the same for reasons of world efficiency. The current feeling that societies have the right to exclude others may be explained best by territoriality in human animals. People also believe that their culture will be diluted if too many outsiders enter. In many cases, immigration systems cannot really control immigration, as in the cases of long landlocked borders between the US and Mexico and between Bangladesh and Assam. Immigration systems also contain legal loopholes. For example, in the US it is easier to get a student visa and convert to immigrant status than to gain immigrant status directly. Loopholes lead to plugs, which lead in turn to more loopholes. An upsurge in requests for political asylum followed increased restrictions on immigration in Western Europe. The US has investigated foreign aid and foreign investments to Mexico and Haiti to curb the flow of illegal migrants. The author suggests that foreign investments may lead to more migration because of the creation of a new proletariat used to the ways of developed countries. An estimate of what would happen if all immigration control were removed worldwide concludes that efficiency and income distribution would improve worldwide. Most migration from developing to developed countries currently consists of the migration of skilled professionals, the brain drain. The author proposes a tax on these professionals to be paid to the country of origin to compensate them for the loss in education and training. The author summarizes the differences between the West German

  3. Population forecasting with endogenous migration: an application to trans-Tasman migration.

    PubMed

    Gorbey, S; James, D; Poot, J

    1999-04-01

    "This article focuses on forecasting migration between Australia and New Zealand (trans-Tasman migration), which is largely visa-free and therefore resembles internal migration. Net trans-Tasman migration is a major component of New Zealand population change and is embedded in this article in a Bayesian or unrestricted vector autoregression (VAR) model, which includes foreign and domestic economic variables. When time series of net migration are available, this approach provides a useful input into forecasting population growth in the short run in the absence of major policy changes. This conclusion applies equally to interregional migration and to unrestricted international migration between economically integrated nations."

  4. Lessons from the motorized migrations

    USGS Publications Warehouse

    Ellis, D.H.; Gee, G.F.; Clegg, K.R.; Duff, J.W.; Lishman, W.A.; Sladen, William J. L.

    2001-01-01

    Ten experiments have been conducted to determine if cranes can be led on migration and if those so trained will repeat migrations on their own. Results have been mixed as we have experienced the mishaps common to pilot studies. Nevertheless, we have learned many valuable lessons. Chief among these are that cranes can be led long distances behind motorized craft (air and ground), and those led over most or the entire route will return north come spring and south in fall to and from the general area of training. However, they will follow their own route. Groups transported south and flown at intervals along the route will migrate but often miss target termini. If certain protocol restrictions are followed, it is possible to make the trained cranes wild, however, the most practical way of so doing is to introduce them into a flock of wild cranes. We project that it is possible to create or restore wild migratory flocks of cranes by first leading small groups from chosen northern to southern termini.

  5. International migration statistics in Mexico.

    PubMed

    Garcia Y Griego, M

    1987-01-01

    During the past decade, Mexico has experienced both large-scale emigration directly, mostly to the US, and the mass immigration of Central American refugees. The implementation of the US Immigration and Control Act of 1986 and the possible escalation of armed conflicts in Central America may result in expanded inflows either of returning citizens or of new refugee waves. To develop appropriate policy responses, Mexico needs reliable information on international migration flows. This research note reviews available sources of that information--arrival and departure statistics, population censuses, refugee censuses, and survey data--and concludes that most of them are relatively weak. Currently, the published data on entries and departures provide little information on the demographic impact of legal migration, although they suggest that the inflow of foreigners is small. The census corroborates such findings, but it yields inadequate demographic detail. The movement of Mexican nationals, on the other hand, is poorly reflected by both sources. The void they leave has been palliated somewhat by surveys, but the only nationally representative survey on emigration was carried out in the late 1970s and might be a less than ideal basis for current policy formulation. It is hoped that as the relevance of international migration becomes more evident, steps towards the improvement of existing statistical systems may be undertaken. In the absence of such measures, policy-makers and researchers will have to continue relying on ad hoc surveys to answer the most pressing questions on the subject. PMID:12280914

  6. SUPER-ECCENTRIC MIGRATING JUPITERS

    SciTech Connect

    Socrates, Aristotle; Katz, Boaz; Dong Subo; Tremaine, Scott

    2012-05-10

    An important class of formation theories for hot Jupiters involves the excitation of extreme orbital eccentricity (e = 0.99 or even larger) followed by tidal dissipation at periastron passage that eventually circularizes the planetary orbit at a period less than 10 days. In a steady state, this mechanism requires the existence of a significant population of super-eccentric (e > 0.9) migrating Jupiters with long orbital periods and periastron distances of only a few stellar radii. For these super-eccentric planets, the periastron is fixed due to conservation of orbital angular momentum and the energy dissipated per orbit is constant, implying that the rate of change in semi-major axis a is a-dot {proportional_to}a{sup 1/2} and consequently the number distribution satisfies dN/d log a{proportional_to}a{sup 1/2}. If this formation process produces most hot Jupiters, Kepler should detect several super-eccentric migrating progenitors of hot Jupiters, allowing for a test of high-eccentricity migration scenarios.

  7. Transplantation stimulates interstitial cell migration in hydra

    SciTech Connect

    Fujisawa, T.; David, C.N.; Bosch, T.C. )

    1990-04-01

    Migration of interstitial cells and nerve cell precursors was analyzed in Hydra magnipapillata and Hydra vulgaris (formerly Hydra attenuata). Axial grafts were made between ({sup 3}H)thymidine-labeled donor and unlabeled host tissue. Migration of labeled cells into the unlabeled half was followed for 4 days. The results indicate that the rate of migration was initially high and then slowed on Days 2-4. Regrafting fresh donor tissue on Days 2-4 maintained high levels of migration. Thus, migration appears to be stimulated by the grafting procedure itself.

  8. Managing international migration: past, present, and future trends and issues.

    PubMed

    Hammar, T

    1991-01-01

    The author provides a brief overview of current international migration trends. Aspects considered include economic motives for migration, refugee migration, migration policies and human rights, and political factors. Comments by Jean-Yves Carlier are included (pp. 192-3).

  9. Trends in return migration to the South.

    PubMed

    Long, L H; Hansen, K A

    1975-11-01

    The rate of return migration to the South rose by nearly 19 percent between the late 1950's and the late 1960's and was an important factor in changing the South's overall migration pattern. But an increase in the rate of return migration was somewhat less important in changing Southern migration than (1) a decline in the rate of out-migration of native Southerners and (2) an increase in the rate at which non-Southern-born persons move to the South. The probability of former migrants returning to the South was over four times greater for whites than for blacks in the 1955-1960 period and three and one-fourth times greater in the 1965-1970 period. Since 1970 the rate of return migration has apparently continued to rise at a faster rate for blacks, but the black rate of return migration is still below the white rate.

  10. An economic analysis of migration in Mexico.

    PubMed

    Greenwood, M J; Ladman, J R

    1978-07-01

    This paper analyzes internal migration in Mexico over the 1960-70 period. A model of the determinants of migration is specified and estimated for aggregated interstate migration flows. Results show that distance serves as a significant deterrent to migration, that higher destination earning levels are attractive to migrants, and that regions with high unemployment rates experience lower rates of inmigration. An unanticipated finding is that regions with higher earning levels have greater rates of outmigration. The data are disaggregated to examine separate migration relationships for each state. The results are that distance is a lesser deterrent for those migrants with more accessible alternatives, that higher earning levels reduce the deterring effects of distance, and that regions with higher earning levels have lower associated elasticities of migration. It is concluded that economic factors have played a crucial role in internal migration and thus in the changing occupational and geographic structure of the Mexican labor force. PMID:12265626

  11. An economic analysis of migration in Mexico.

    PubMed

    Greenwood, M J; Ladman, J R

    1978-07-01

    This paper analyzes internal migration in Mexico over the 1960-70 period. A model of the determinants of migration is specified and estimated for aggregated interstate migration flows. Results show that distance serves as a significant deterrent to migration, that higher destination earning levels are attractive to migrants, and that regions with high unemployment rates experience lower rates of inmigration. An unanticipated finding is that regions with higher earning levels have greater rates of outmigration. The data are disaggregated to examine separate migration relationships for each state. The results are that distance is a lesser deterrent for those migrants with more accessible alternatives, that higher earning levels reduce the deterring effects of distance, and that regions with higher earning levels have lower associated elasticities of migration. It is concluded that economic factors have played a crucial role in internal migration and thus in the changing occupational and geographic structure of the Mexican labor force.

  12. Social Physics and China's Population Migration

    NASA Astrophysics Data System (ADS)

    Wang, Yun-Lin; Li, Ding

    Based on the social physics theory, this paper analyzes the economic disparities between different regions in China, and contributes a conceptual model of population migration among eastern, central, western and north-eastern regions. The national 1% population sample investigation data is adopted to build a network of inter-provincial population migration, and the population migration network is analyzed with social network analysis. The results are shown that there is a very strong correlation between migrant population and economy disparity in China, and the migration with obviously geographical characteristics. The eastern region is the main areas for migration-inflow; the central region is the main areas of migration-outflow; the western region is relatively “locked-up”, with a little of population flow; and the migration of the northeast is mainly within its own regional territory.

  13. Philippine migration policy: dilemmas of a crisis.

    PubMed

    Battistella, G

    1999-04-01

    Philippine migration policy is traced from the early 1970s to the present. The main migration trends in the 1990s are described. An assessment is made of the efficacy and appropriateness of present migration policy in light of the economic crisis. A regional approach to migration policy is necessary in order to encourage placing migration as a greater priority on national agendas and in bilateral agreements. In the Philippines, migrants are considered better paid workers, which diminishes their importance as a legislative or program priority. Santo Tomas (1998) conducted an empirical assessment of migration policies in the Philippines, but refinement is needed. Although migration is a transnational experience, there is little dialogue and cooperation among countries. Philippine migration policy defines its role as an information resource for migrants. Policy shifted from labor export to migrant management in the public and private sectors. Predeparture information program studies are recommending a multi-stage process that would involve all appropriate parties. There is talk of including migration information in the education curriculum. There are a variety of agendas, competing interests, and information resources between migration networks and officiating agencies. The Asian financial crisis may have a mild impact, but there are still issues of reintegration, protection, and employment conditions

  14. Clandestine labor migration to Taiwan.

    PubMed

    Tsay, C

    1992-01-01

    "Illegal migration to Taiwan is a recent phenomenon but with a rapid rate of increase. Most illegal foreign workers enter on visitor's visas and overstay. This paper's detailed analysis of official data reveals that Malaysia, Philippines, Indonesia and Thailand are the major sources, providing a stock of mostly male workers numbering around 40,000. Sociodemographic and attitudinal changes among Taiwanese workers coupled with labor shortages in low-skilled jobs are pressuring the Taiwanese government to formulate plans for a systematic importation of foreign labor." PMID:12285774

  15. Seismic Imaging Processing and Migration

    2000-06-26

    Salvo is a 3D, finite difference, prestack, depth migration code for parallel computers. It is also capable of processing 2D and poststack data. The code requires as input a seismic dataset, a velocity model and a file of parameters that allows the user to select various options. The code uses this information to produce a seismic image. Some of the options available to the user include the application of various filters and imaging conditions. Themore » code also incorporates phase encoding (patent applied for) to process multiple shots simultaneously.« less

  16. Savings, remittances, and return migration.

    PubMed

    Merkle, L; Zimmermann, K F

    1992-01-01

    "We use a data set of immigrants to West Germany to simultaneously study both savings and remittances which we relate to individual characteristics, economic variables, migration experiences and remigration plans. Section 2 discusses the basic hypotheses and explains the data. Section 3 presents the empirical study and Section 4 summarizes." The results suggest that "savings and remittances of migrants can be well explained by remigration plans and economic as well as demographic variables. However, the planned future duration of residence in Germany has a negative and significant effect only on remittances."

  17. Asian student migration to Australia.

    PubMed

    Shu, J; Hawthorne, L

    1996-01-01

    "This paper presents an overview of Asian student migration to Australia, together with an analysis of political and educational aspects of the overseas student programme. It focuses on some significant consequences of this flow for Australia. The characteristics of key student groups are contrasted to provide some perspective of the diversity of historical and cultural backgrounds, with the source countries of Malaysia, Indonesia and PRC [China] selected as case studies. Since the issue of PRC students in Australia has attracted considerable public attention and policy consideration, particular focus is placed on their experience." (SUMMARY IN FRE AND SPA)

  18. Clandestine labor migration to Taiwan.

    PubMed

    Tsay, C

    1992-01-01

    "Illegal migration to Taiwan is a recent phenomenon but with a rapid rate of increase. Most illegal foreign workers enter on visitor's visas and overstay. This paper's detailed analysis of official data reveals that Malaysia, Philippines, Indonesia and Thailand are the major sources, providing a stock of mostly male workers numbering around 40,000. Sociodemographic and attitudinal changes among Taiwanese workers coupled with labor shortages in low-skilled jobs are pressuring the Taiwanese government to formulate plans for a systematic importation of foreign labor."

  19. Migration timing and its determinants for nocturnal migratory birds during autumn migration.

    PubMed

    La Sorte, Frank A; Hochachka, Wesley M; Farnsworth, Andrew; Sheldon, Daniel; Fink, Daniel; Geevarghese, Jeffrey; Winner, Kevin; Van Doren, Benjamin M; Kelling, Steve

    2015-09-01

    1. Migration is a common strategy used by birds that breed in seasonal environments, and multiple environmental and biological factors determine the timing of migration. How these factors operate in combination during autumn migration, which is considered to be under weaker time constraints relative to spring migration, is not clear. 2. Here, we examine the patterns and determinants of migration timing for nocturnal migrants during autumn migration in the north-eastern USA using nocturnal reflectivity data from 12 weather surveillance radar stations and modelled diurnal probability of occurrence for 142 species of nocturnal migrants. We first model the capacity of seasonal atmospheric conditions (wind and precipitation) and ecological productivity (vegetation greenness) to predict autumn migration intensity. We then test predictions, formulated under optimal migration theory, on how migration timing should be related to assemblage-level estimates of body size and total migration distance within the context of dietary guild (insectivore and omnivore) and level of dietary plasticity during autumn migration. 3. Our results indicate seasonal declines in ecological productivity delineate the beginning and end of peak migration, whose intensity is best predicted by the velocity of winds at migration altitudes. Insectivorous migrants departed earlier in the season and, consistent with our predictions, large-bodied and long-distance insectivorous migrants departed the earliest. Contrary to our predictions, large-bodied and some long-distance omnivorous migrants departed later in the season, patterns that were replicated in part by insectivorous migrants that displayed dietary plasticity during autumn migration. 4. Our findings indicate migration timing in the region is dictated by optimality strategies, modified based on the breadth and flexibility of migrant's foraging diets, with declining ecological productivity defining possible resource thresholds during which

  20. Migrational Instabilities in Particle Suspensions

    NASA Technical Reports Server (NTRS)

    Goddard, Joe D.

    1996-01-01

    This work deals with an instability arising from the shear-induced migration of particles in dense suspensions coupled with a dependence of viscosity on particle concentration. The analysis summarized here treats the inertialess (Re = O) linear stability of homogeneous simple shear flows for a Stokesian suspension model of the type proposed by Leighton and Acrivos (1987). Depending on the importance of shear-induced migration relative to concentration-driven diffusion, this model admits short-wave instability arising from wave-vector stretching by the base flow and evolving into particle-depleted shear bands. Moreover, this instability in the time-dependent problem corresponds to loss of ellipticity in the associated static problem (Re = O, Pe = O). While the isotropic version of the Leighton-Acrivos model is found to be stable with their experimentally determined parameters for simple shear, it is known that the stable model does not give a good quantitative description of particle clustering in the core of pipe flow (Nott and Brady 1994). This leads to the conjecture that an appropriate variant on the above model could explain such clustering as a two-phase bifurcation in the base flow.

  1. Endocannabinoid signalling in neuronal migration.

    PubMed

    Zhou, Ya; Falenta, Katarzyna; Lalli, Giovanna

    2014-02-01

    The endocannabinoid (eCB) system consists of several endogenous lipids, their target CB1 and CB2 receptors and enzymes responsible for their synthesis and degradation. The most abundant eCB in the central nervous system (CNS), 2-arachidonoyl glycerol (2-AG), triggers a broad range of signalling events by acting on CB1, the most abundant G protein-coupled receptor in the CNS. The eCB system regulates many physiological processes including neurogenesis, axon guidance and synaptic plasticity. Recent studies have highlighted an additional important role for eCB signalling in neuronal migration, which is crucial to achieve the complex architecture and efficient wiring of the CNS. Indeed, eCB signalling controls migration both pre- and post-natally, regulating interneuron positioning in the developing cortex and hippocampus and the polarised motility of stem cell-derived neuroblasts. While these effects may contribute to cognitive deficits associated with cannabis consumption, they also provide potential opportunities for endogenous stem cell-based neuroregenerative strategies.

  2. Globalisation and international migration in Asia.

    PubMed

    Hugo, G

    1998-03-01

    "The present paper attempts to summarise the major contemporary trends in international migration in Asia and how this is related to the rapid demographic transition occurring across most of the region. The diversity of types of mobility is one of the striking features of Asian international migration and developments in each major type [are] discussed in the paper. It is then argued that there are elements within the Asian migration system that give it a momentum which to some extent operates outside of the influence of economic and political trends. Finally some emerging issues in Asian international migration are briefly addressed. These include the scale and effects of remittances, the feminisation of migration, undocumented migration, increasing government involvement and brain drain issues." (EXCERPT) PMID:12293967

  3. Measuring spatial focusing in a migration system.

    PubMed

    Plane, D A; Mulligan, G F

    1997-05-01

    Equality indexes used in other geographical contexts may be used to gauge the degree of spatial focusing in an entire migration system or within the gross in- and out-migration fields of specific regions. They provide useful indicators of overall shifts in the patterns of interregional migration and can help give insight into the population redistributive roles played by specific regions. Perhaps the most common equality index used to measure income distribution is the Gini coefficient, yet it appears almost never to have been applied in migration research. In this paper we set forth a variety of Gini indexes to be used for different migration analyses and illustrate their application with recent data on U.S. interstate movements. We argue that the Gini index provides some singularly useful insights that differ from those afforded by other measures more commonly found to date in the migration analyst's tool kit.

  4. Regional interdependence and migration in Asia.

    PubMed

    Kim, W B

    1995-01-01

    "The 1980s witnessed increasing regional interdependence in Asia through trade and investment. Increasing flows of labor within the region, however, raise questions about three important issues: (1) the assumption that trade, investment and aid will eventually mitigate migration pressure in source countries and the effectiveness of migration policies based on that assumption; (2) whether increasing regional interdependence stimulates or deters migration; [and] (3) the effect of rising interdependence on the political and international relations aspects of migration. As a partial attempt to address these questions, this article examines the regional pattern of economic interdependence by utilizing information concerning trade, investment and migration flows. The concept of interdependence/dependence is discussed within a political context, focusing on migration and policy responses to it. Observations are made on the implications for regional stability and development."

  5. Multiscale Cues Drive Collective Cell Migration

    NASA Astrophysics Data System (ADS)

    Nam, Ki-Hwan; Kim, Peter; Wood, David K.; Kwon, Sunghoon; Provenzano, Paolo P.; Kim, Deok-Ho

    2016-07-01

    To investigate complex biophysical relationships driving directed cell migration, we developed a biomimetic platform that allows perturbation of microscale geometric constraints with concomitant nanoscale contact guidance architectures. This permits us to elucidate the influence, and parse out the relative contribution, of multiscale features, and define how these physical inputs are jointly processed with oncogenic signaling. We demonstrate that collective cell migration is profoundly enhanced by the addition of contract guidance cues when not otherwise constrained. However, while nanoscale cues promoted migration in all cases, microscale directed migration cues are dominant as the geometric constraint narrows, a behavior that is well explained by stochastic diffusion anisotropy modeling. Further, oncogene activation (i.e. mutant PIK3CA) resulted in profoundly increased migration where extracellular multiscale directed migration cues and intrinsic signaling synergistically conspire to greatly outperform normal cells or any extracellular guidance cues in isolation.

  6. Multiscale Cues Drive Collective Cell Migration

    PubMed Central

    Nam, Ki-Hwan; Kim, Peter; Wood, David K.; Kwon, Sunghoon; Provenzano, Paolo P.; Kim, Deok-Ho

    2016-01-01

    To investigate complex biophysical relationships driving directed cell migration, we developed a biomimetic platform that allows perturbation of microscale geometric constraints with concomitant nanoscale contact guidance architectures. This permits us to elucidate the influence, and parse out the relative contribution, of multiscale features, and define how these physical inputs are jointly processed with oncogenic signaling. We demonstrate that collective cell migration is profoundly enhanced by the addition of contract guidance cues when not otherwise constrained. However, while nanoscale cues promoted migration in all cases, microscale directed migration cues are dominant as the geometric constraint narrows, a behavior that is well explained by stochastic diffusion anisotropy modeling. Further, oncogene activation (i.e. mutant PIK3CA) resulted in profoundly increased migration where extracellular multiscale directed migration cues and intrinsic signaling synergistically conspire to greatly outperform normal cells or any extracellular guidance cues in isolation. PMID:27460294

  7. Globalisation and international migration in Asia.

    PubMed

    Hugo, G

    1998-03-01

    "The present paper attempts to summarise the major contemporary trends in international migration in Asia and how this is related to the rapid demographic transition occurring across most of the region. The diversity of types of mobility is one of the striking features of Asian international migration and developments in each major type [are] discussed in the paper. It is then argued that there are elements within the Asian migration system that give it a momentum which to some extent operates outside of the influence of economic and political trends. Finally some emerging issues in Asian international migration are briefly addressed. These include the scale and effects of remittances, the feminisation of migration, undocumented migration, increasing government involvement and brain drain issues." (EXCERPT)

  8. Characterization of Collective Cell Migration Dynamics

    NASA Astrophysics Data System (ADS)

    Lee, Rachel; Yue, Haicen; Rappel, Wouter-Jan; Losert, Wolfgang

    2015-03-01

    During cancer progression, tumor cells invade the surrounding tissue and migrate throughout the body, forming clinically dangerous secondary tumors. This metastatic process begins when cells leave the primary tumor, either as individual cells or collectively migrating groups. Here we present data on the migration dynamics of epithelial sheets composed of many cells. Using quantitative image analysis techniques, we are able to extract motion information from time-lapse images of cell lines with varying malignancy. Adapting metrics originally used to study fluid flows we are able to characterize the migration dynamics of these cell lines. By describing the migration dynamics in great detail, we are able to make a clear comparison of our results to a simulation of collective cell migration. Specifically, we explore whether leader cells are required to describe our expanding sheets of cells and whether the answer depends on individual cell activity.

  9. Rho GTPase signalling in cell migration

    PubMed Central

    Ridley, Anne J

    2015-01-01

    Cells migrate in multiple different ways depending on their environment, which includes the extracellular matrix composition, interactions with other cells, and chemical stimuli. For all types of cell migration, Rho GTPases play a central role, although the relative contribution of each Rho GTPase depends on the environment and cell type. Here, I review recent advances in our understanding of how Rho GTPases contribute to different types of migration, comparing lamellipodium-driven versus bleb-driven migration modes. I also describe how cells migrate across the endothelium. In addition to Rho, Rac and Cdc42, which are well known to regulate migration, I discuss the roles of other less-well characterized members of the Rho family. PMID:26363959

  10. Neuronal migration on laminin in vitro.

    PubMed

    Liang, S; Crutcher, K A

    1992-03-20

    Chick sympathetic (E-9) or telencephalic (E-7) neurons were cultured at low density on poly-DL-ornithine (PORN), poly-L-lysine (POLS), laminin or laminin-covered PORN or POLS and monitored with time-lapse videomicroscopy. Neurons migrated on laminin, or laminin-covered PORN or POLS, but not on PORN or POLS alone. Neuronal migration did not involve interactions with other cells indicating that neurons are capable of independent migration when exposed to a laminin substrate.

  11. Neuronal migration on laminin in vitro.

    PubMed

    Liang, S; Crutcher, K A

    1992-03-20

    Chick sympathetic (E-9) or telencephalic (E-7) neurons were cultured at low density on poly-DL-ornithine (PORN), poly-L-lysine (POLS), laminin or laminin-covered PORN or POLS and monitored with time-lapse videomicroscopy. Neurons migrated on laminin, or laminin-covered PORN or POLS, but not on PORN or POLS alone. Neuronal migration did not involve interactions with other cells indicating that neurons are capable of independent migration when exposed to a laminin substrate. PMID:1600626

  12. Motorized Migrations: the Future or Mere Fantasy?

    USGS Publications Warehouse

    Ellis, D.H.; Sladen, William J. L.; Lishman, W.A.; Clegg, K.R.; Duff, J.W.; Gee, G.F.; Lewis, J.C.

    2003-01-01

    In 15 experiments from 1993-2002, we led cranes, geese, or swans on their first southward migration with either ultralight aircraft or vehicles on the ground. These experiments reveal that large birds can be readily trained to follow and most will return north (and south) in subsequent migrations unassisted. These techniques can now be used to teach birds new (or forgotten) migration paths. Although we are constantly improving our training techniques, we now have an operational program that can be broadly applied to those species where juveniles learn migration routes from their parents.

  13. A vascular perspective on neuronal migration.

    PubMed

    Segarra, Marta; Kirchmaier, Bettina C; Acker-Palmer, Amparo

    2015-11-01

    During CNS development and adult neurogenesis, immature neurons travel from the germinal zones towards their final destination using cellular substrates for their migration. Classically, radial glia and neuronal axons have been shown to act as physical scaffolds to support neuroblast locomotion in processes known as gliophilic and neurophilic migration, respectively (Hatten, 1999; Marin and Rubenstein, 2003; Rakic, 2003). In adulthood, long distance neuronal migration occurs in a glial-independent manner since radial glia cells differentiate into astrocytes after birth. A series of studies highlight a novel mode of neuronal migration that uses blood vessels as scaffolds, the so-called vasophilic migration. This migration mode allows neuroblast navigation in physiological and also pathological conditions, such as neuronal precursor migration after ischemic stroke or cerebral invasion of glioma tumor cells. Here we review the current knowledge about how vessels pave the path for migrating neurons and how trophic factors derived by glio-vascular structures guide neuronal migration both during physiological as well as pathological processes.

  14. In-migration in Madhya Pradesh.

    PubMed

    Gupta, M P; Sharma, S

    1994-01-01

    "The aim of this paper is to analyse the expectancy of in-migration in the districts of Madhya Pradesh State [India, using the 1981 census.].... The percentage of in-migration in Madhya Pradesh from rural areas is very high (84.83), in comparison to the urban areas (15.17). The influences of industrialisation, urbanisation and facilities of higher education on in-migration has been analysed and found significant. The Chhattisgarh Basin and Malwa Plateau are the regions where the expectancy and actual in-migration are high." PMID:12295161

  15. Animal migration and infectious disease risk.

    PubMed

    Altizer, Sonia; Bartel, Rebecca; Han, Barbara A

    2011-01-21

    Animal migrations are often spectacular, and migratory species harbor zoonotic pathogens of importance to humans. Animal migrations are expected to enhance the global spread of pathogens and facilitate cross-species transmission. This does happen, but new research has also shown that migration allows hosts to escape from infected habitats, reduces disease levels when infected animals do not migrate successfully, and may lead to the evolution of less-virulent pathogens. Migratory demands can also reduce immune function, with consequences for host susceptibility and mortality. Studies of pathogen dynamics in migratory species and how these will respond to global change are urgently needed to predict future disease risks for wildlife and humans alike.

  16. Multiregional estimation of gross internal migration flows.

    PubMed

    Foot, D K; Milne, W J

    1989-01-01

    "A multiregional model of gross internal migration flows is presented in this article. The interdependence of economic factors across all regions is recognized by imposing a non-stochastic adding-up constraint that requires total inmigration to equal total outmigration in each time period. An iterated system estimation technique is used to obtain asymptotically consistent and efficient parameter estimates. The model is estimated for gross migration flows among the Canadian provinces over the period 1962-86 and then is used to examine the likelihood of a wash-out effect in net migration models. The results indicate that previous approaches that use net migration equations may not always be empirically justified."

  17. Factors controlling cardiac neural crest cell migration

    PubMed Central

    Hutson, Mary R

    2010-01-01

    Cardiac neural crest cells originate as part of the postotic caudal rhombencephalic neural crest stream. Ectomesenchymal cells in this stream migrate to the circumpharyngeal ridge and then into the caudal pharyngeal arches where they condense to form first a sheath and then the smooth muscle tunics of the persisting pharyngeal arch arteries. A subset of the cells continues migrating into the cardiac outflow tract where they will condense to form the aorticopulmonary septum. Cell signaling, extracellular matrix and cell-cell contacts are all critical for the initial migration, pauses, continued migration and condensation of these cells. This Review elucidates what is currently known about these factors. PMID:20890117

  18. From migration to settlement: the pathways, migration modes and dynamics of neurons in the developing brain.

    PubMed

    Hatanaka, Yumiko; Zhu, Yan; Torigoe, Makio; Kita, Yoshiaki; Murakami, Fujio

    2016-01-01

    Neuronal migration is crucial for the construction of the nervous system. To reach their correct destination, migrating neurons choose pathways using physical substrates and chemical cues of either diffusible or non-diffusible nature. Migrating neurons extend a leading and a trailing process. The leading process, which extends in the direction of migration, determines navigation, in particular when a neuron changes its direction of migration. While most neurons simply migrate radially, certain neurons switch their mode of migration between radial and tangential, with the latter allowing migration to destinations far from the neurons' site of generation. Consequently, neurons with distinct origins are intermingled, which results in intricate neuronal architectures and connectivities and provides an important basis for higher brain function. The trailing process, in contrast, contributes to the late stage of development by turning into the axon, thus contributing to the formation of neuronal circuits.

  19. From migration to settlement: the pathways, migration modes and dynamics of neurons in the developing brain

    PubMed Central

    HATANAKA, Yumiko; ZHU, Yan; TORIGOE, Makio; KITA, Yoshiaki; MURAKAMI, Fujio

    2016-01-01

    Neuronal migration is crucial for the construction of the nervous system. To reach their correct destination, migrating neurons choose pathways using physical substrates and chemical cues of either diffusible or non-diffusible nature. Migrating neurons extend a leading and a trailing process. The leading process, which extends in the direction of migration, determines navigation, in particular when a neuron changes its direction of migration. While most neurons simply migrate radially, certain neurons switch their mode of migration between radial and tangential, with the latter allowing migration to destinations far from the neurons’ site of generation. Consequently, neurons with distinct origins are intermingled, which results in intricate neuronal architectures and connectivities and provides an important basis for higher brain function. The trailing process, in contrast, contributes to the late stage of development by turning into the axon, thus contributing to the formation of neuronal circuits. PMID:26755396

  20. Migration delays caused by anthropogenic barriers: modeling dams, temperature, and success on migrating salmon smolts

    USGS Publications Warehouse

    Marschall, Elizabeth A.; Mather, Martha E.; Parrish, Donna; Allison, Gary W.; McMenemy, James R.

    2011-01-01

    Disruption to migration is a growing problem for conservation and restoration of animal populations. Anthropogenic barriers along migration paths can delay or prolong migrations, which may result in a mismatch with migration-timing adaptations. To understand the interaction of dams (as barriers along a migration path), seasonally changing environmental conditions, timing of Atlantic salmon (Salmo salar) downstream migration, and ultimate migration success, we used 10 years of river temperature and discharge data as a template upon which we simulated downstream movement of salmon. Atlantic salmon is a cool-water species whose downstream migrating smolts must complete migration before river temperatures become too warm. We found that dams had a local effect on survival as well as a survival effect that was spatially and temporally removed from the encounter with the dam. While smolts are delayed by dams, temperatures downstream can reach lethal or near-lethal temperatures; as a result, the match between completion of migration and the window of appropriate migration conditions can be disrupted. The strength of this spatially and temporally removed effect is at least comparable to the local effects of dams in determining smolt migration success in the presence of dams. We also considered smolts from different tributaries, varying in distance from the river mouth, to assess the potential importance of locally adapted migration timing on the effect of barriers. Migration-initiation temperature affected modeled smolt survival differentially across tributaries, with the success of smolts from upstream tributaries being much more variable across years than that of smolts with a shorter distance to travel. As a whole, these results point to the importance of broadening our spatial and temporal view when managing migrating populations. We must consider not only how many individuals never make it across migration barriers, but also the spatially and temporally removed

  1. Migration delays caused by anthropogenic barriers: Modeling dams, temperature, and success of migrating salmon smolts

    USGS Publications Warehouse

    Marschall, E.A.; Mather, M. E.; Parrish, D.L.; Allison, G.W.; McMenemy, J.R.

    2011-01-01

    Disruption to migration is a growing problem for conservation and restoration of animal populations. Anthropogenic barriers along migration paths can delay or prolong migrations, which may result in a mismatch with migration-timing adaptations. To understand the interaction of dams (as barriers along a migration path), seasonally changing environmental conditions, timing of Atlantic salmon (Salmo salar) downstream migration, and ultimate migration success, we used 10 years of river temperature and discharge data as a template upon which we simulated downstream movement of salmon. Atlantic salmon is a cool-water species whose downstream migrating smolts must complete migration before river temperatures become too warm. We found that dams had a local effect on survival as well as a survival effect that was spatially and temporally removed from the encounter with the dam. While smolts are delayed by dams, temperatures downstream can reach lethal or near-lethal temperatures;as a result, the match between completion of migration and the window of appropriate migration conditions can be disrupted. The strength of this spatially and temporally removed effect is at least comparable to the local effects of dams in determining smolt migration success in the presence of dams. We also considered smolts from different tributaries, varying in distance from the river mouth, to assess the potential importance of locally adapted migration timing on the effect of barriers. Migration-initiation temperature affected modeled smolt survival differentially across tributaries, with the success of smolts from upstream tributaries being much more variable across years than that of smolts with a shorter distance to travel. As a whole, these results point to the importance of broadening our spatial and temporal view when managing migrating populations. We must consider not only how many individuals never make it across migration barriers, but also the spatially and temporally removed

  2. Multi Layer Contaminant Migration Model

    1999-07-28

    This computer software augments and enhances certain calculation included in the previously copyrighted Vadose Zone Contaminant Migration Model. The computational method used in this model recognizes the heterogenous nature of the soils and attempts to account for the variability by using four separate layers to simulate the flow of water through the vadose zone. Therefore, the pore-water velocity calculated by the code will be different than the previous model because it accounts for a widermore » variety of soil properties encountered in the vadose zone. This model also performs an additional screening step than in the previous model. In this model the higher value of two different types of Soil Screening Levels are compared to soil concentrations of contaminants. If the contaminant concentration exceeds the highest of two SSLs, then that contaminant is listed. This is consistent with USEPA's Soil Screening Guidance.« less

  3. Acoustic tracking of migrating salmon.

    PubMed

    Kupilik, Matthew J; Petersen, Todd

    2014-10-01

    Annual salmon migrations vary significantly in annual return numbers from year to year. In order to determine when a species' sustainable return size has been met, a method for counting and sizing the spawning animals is required. This project implements a probability hypothesis density tracker on data from a dual frequency identification sonar to automate the process of counting and sizing the fish crossing an insonified area. Data processing on the sonar data creates intensity images from which possible fish locations can be extracted using image processing. These locations become the input to the tracker. The probability hypothesis density tracker then solves the multiple target tracking problem and creates fish tracks from which length information is calculated using image segmentation. The algorithm is tested on data from the 2010 salmon run on the Kenai river in Alaska and compares favorably with statistical models from sub-sampling and manual measurements.

  4. Determinants of the Egyptian labour migration.

    PubMed

    Kandil, M; Metwally, M

    1992-03-01

    The objective is to summarize the pattern of Egyptian migration to Arab oil-producing countries (AOPC), to review some factors that are important determinants of labor movement based on theory, and to empirically model the migration rate to AOPC and to Saudi Arabia. Factors are differentiated as to their relative importance. Push factors are the low wages, high inflation rate, and high population density in Egypt; pull factors are higher wages. It is predicted that an increase in income from destination countries has a significant positive impact on the migration rate. An increase in population density stimulates migration. An increase in inflation acts to increase out-migration with a 2-year lag, which accommodates departure preparation. Egypt's experience with labor migration is described for the pre-oil boom, and the post-oil boom. Several estimates of labor migration are given. Government policy toward migration is positive. Theory postulates migration to be determined by differences in the availability of labor, labor rewards between destination and origin, and the cost of migration. In the empirical model, push factors are population density, the current inflation rate, and the ratio of income/capita in AOPC to Egypt. The results indicate that the ratio of income/capita had a strong pull impact and population density had a strong push impact. The inflation rate has a positive impact with a lag estimated at 2 years. Prior to the Camp David Accord, there was a significant decrease in the number of Egyptian migrants due to political tension. The findings support the classical theory of factor mobility. The consequences of migration on the Egyptian economy have been adverse. Future models should disaggregate data because chronic shortages exist in some parts of the labor market. Manpower needs assessment would be helpful for policy makers.

  5. Migration for Labor, Migration for Love: Marriage and Family Formation across Borders.

    ERIC Educational Resources Information Center

    Sinke, Suzanne

    1999-01-01

    Addresses how marriage and migration interacted using migration to the United States as an example; the key variables determining this relationship were demographics, legal policies, cultural perceptions, and information and technology. Maintains that the influence of an international marriage market affected the migration decisions of women who…

  6. Recovery Migration After Hurricanes Katrina and Rita: Spatial Concentration and Intensification in the Migration System.

    PubMed

    Curtis, Katherine J; Fussell, Elizabeth; DeWaard, Jack

    2015-08-01

    Changes in the human migration systems of the Gulf of Mexico coastline counties affected by Hurricanes Katrina and Rita provide an example of how climate change may affect coastal populations. Crude climate change models predict a mass migration of "climate refugees," but an emerging literature on environmental migration suggests that most migration will be short-distance and short-duration within existing migration systems, with implications for the population recovery of disaster-stricken places. In this research, we derive a series of hypotheses on recovery migration predicting how the migration system of hurricane-affected coastline counties in the Gulf of Mexico was likely to have changed between the pre-disaster and the recovery periods. We test these hypotheses using data from the Internal Revenue Service on annual county-level migration flows, comparing the recovery period migration system (2007-2009) with the pre-disaster period (1999-2004). By observing county-to-county ties and flows, we find that recovery migration was strong: the migration system of the disaster-affected coastline counties became more spatially concentrated, while flows within it intensified and became more urbanized. Our analysis demonstrates how migration systems are likely to be affected by the more intense and frequent storms anticipated by climate change scenarios, with implications for the population recovery of disaster-affected places.

  7. Recovery Migration After Hurricanes Katrina and Rita: Spatial Concentration and Intensification in the Migration System.

    PubMed

    Curtis, Katherine J; Fussell, Elizabeth; DeWaard, Jack

    2015-08-01

    Changes in the human migration systems of the Gulf of Mexico coastline counties affected by Hurricanes Katrina and Rita provide an example of how climate change may affect coastal populations. Crude climate change models predict a mass migration of "climate refugees," but an emerging literature on environmental migration suggests that most migration will be short-distance and short-duration within existing migration systems, with implications for the population recovery of disaster-stricken places. In this research, we derive a series of hypotheses on recovery migration predicting how the migration system of hurricane-affected coastline counties in the Gulf of Mexico was likely to have changed between the pre-disaster and the recovery periods. We test these hypotheses using data from the Internal Revenue Service on annual county-level migration flows, comparing the recovery period migration system (2007-2009) with the pre-disaster period (1999-2004). By observing county-to-county ties and flows, we find that recovery migration was strong: the migration system of the disaster-affected coastline counties became more spatially concentrated, while flows within it intensified and became more urbanized. Our analysis demonstrates how migration systems are likely to be affected by the more intense and frequent storms anticipated by climate change scenarios, with implications for the population recovery of disaster-affected places. PMID:26084982

  8. Recovery Migration after Hurricanes Katrina and Rita: Spatial Concentration and Intensification in the Migration System

    PubMed Central

    Fussell, Elizabeth; DeWaard, Jack

    2015-01-01

    Changes in the human migration systems of Hurricane Katrina- and Rita-affected Gulf of Mexico coastline counties provide an example of how climate change may affect coastal populations. Crude climate change models predict a mass migration of “climate refugees,” but an emerging literature on environmental migration suggests most migration will be short-distance and short-duration within existing migration systems, with implications for the population recovery of disaster-struck places. In this research, we derive a series of hypotheses on recovery migration predicting how the migration system of hurricane-affected coastline counties in the Gulf of Mexico was likely to have changed between the pre-disaster and the recovery periods. We test these hypotheses using data from the Internal Revenue Service on annual county-level migration flows, comparing the recovery period migration system (2007–2009) to the pre-disaster period (1999–2004). By observing county-to-county ties and flows we find that recovery migration was strong, as the migration system of the disaster-affected coastline counties became more spatially concentrated while flows within it intensified and became more urbanized. Our analysis demonstrates how migration systems are likely to be affected by the more intense and frequent storms anticipated by climate change scenarios with implications for the population recovery of disaster-affected places. PMID:26084982

  9. Spatiotemporal isoscapes for migration research

    NASA Astrophysics Data System (ADS)

    Bowen, G. J.; Hobson, K. A.; Wassenaar, L.; Zhang, T.

    2011-12-01

    Light stable isotope tracers have become a popular and widely used source of information on the regional to continental scale migration patterns of many animal groups. This work is founded on a quantitative understanding of the spatial distribution of environmental isotopes (isoscapes) that are assimilated in animal tissues, providing a basis for assigning animals to locations or regions based on retrospective analysis of their tissues. To date, almost all studies have developed interpretations on climatological, or 'static', isoscapes, because in most cases data and models allowing accurate estimation of isotope distributions for specific calendar years or seasons have not been available. This situation creates a disconnect between the timescales of biological samples and environmental isoscapes, which is limiting in many systems that exhibit a high degree of temporal variability. We report here on new analyses characterizing temporal variation in environmental water (H and O) isotope ratios and testing our ability to accurately model short-term (individual months and seasons) water isoscapes using existing datasets. We implement the resulting data products in a case study using previously published data from monarch butterfly wing keratin and compare the accuracy and sensitivity of Bayesian geographic assignments for these samples using different climatological and time-specific isoscapes. Combined with a continued emphasis on environmental isotope monitoring, the modeling tools used here should support continued improvement in the precision and accuracy of geographic assignments. The data and data analysis methods have been implemented in the IsoMAP web portal and are freely available to the migration research community in support of their research.

  10. Curvature capillary migration of microspheres.

    PubMed

    Sharifi-Mood, Nima; Liu, Iris B; Stebe, Kathleen J

    2015-09-14

    We address the question: how does capillarity propel microspheres along curvature gradients? For a particle on a fluid interface, there are two conditions that can apply at the three phase contact line: either the contact line adopts an equilibrium contact angle, or it can be pinned by kinetic trapping, e.g. at chemical heterogeneities, asperities, or other pinning sites on the particle surface. We formulate the curvature capillary energy for both scenarios for particles smaller than the capillary length and far from any pinning boundaries. The scale and range of the distortion made by the particle are set by the particle radius; we use singular perturbation methods to find the distortions and to rigorously evaluate the associated capillary energies. For particles with equilibrium contact angles, contrary to the literature, we find that the capillary energy is negligible, with the first contribution bounded to fourth order in the product of the particle radius and the deviatoric curvature of the host interface. For pinned contact lines, we find curvature capillary energies that are finite, with a functional form investigated previously by us for disks and microcylinders on curved interfaces. In experiments, we show microspheres migrate along deterministic trajectories toward regions of maximum deviatoric curvature with curvature capillary energies ranging from 6 × 10(3)-5 × 10(4)kBT. These data agree with the curvature capillary energy for the case of pinned contact lines. The underlying physics of this migration is a coupling of the interface deviatoric curvature with the quadrupolar mode of nanometric disturbances in the interface owing to the particle's contact line undulations. This work is an example of the major implications of nanometric roughness and contact line pinning for colloidal dynamics.

  11. Modeling Leaking Gas Plume Migration

    SciTech Connect

    Silin, Dmitriy; Patzek, Tad; Benson, Sally M.

    2007-08-20

    In this study, we obtain simple estimates of 1-D plume propagation velocity taking into account the density and viscosity contrast between CO{sub 2} and brine. Application of the Buckley-Leverett model to describe buoyancy-driven countercurrent flow of two immiscible phases leads to a transparent theory predicting the evolution of the plume. We obtain that the plume does not migrate upward like a gas bubble in bulk water. Rather, it stretches upward until it reaches a seal or until the fluids become immobile. A simple formula requiring no complex numerical calculations describes the velocity of plume propagation. This solution is a simplification of a more comprehensive theory of countercurrent plume migration that does not lend itself to a simple analytical solution (Silin et al., 2006). The range of applicability of the simplified solution is assessed and provided. This work is motivated by the growing interest in injecting carbon dioxide into deep geological formations as a means of avoiding its atmospheric emissions and consequent global warming. One of the potential problems associated with the geologic method of sequestration is leakage of CO{sub 2} from the underground storage reservoir into sources of drinking water. Ideally, the injected green-house gases will stay in the injection zone for a geologically long time and eventually will dissolve in the formation brine and remain trapped by mineralization. However, naturally present or inadvertently created conduits in the cap rock may result in a gas leak from primary storage. Even in supercritical state, the carbon dioxide viscosity and density are lower than those of the indigenous formation brine. Therefore, buoyancy will tend to drive the CO{sub 2} upward unless it is trapped beneath a low permeability seal. Theoretical and experimental studies of buoyancy-driven supercritical CO{sub 2} flow, including estimation of time scales associated with plume evolution, are critical for developing technology

  12. The Psychology of Puerto Rican Migration.

    ERIC Educational Resources Information Center

    Prewitt Diaz, Joseph O.

    The psychology of the Puerto Rican migrant to the United States mainland is explored. Puerto Ricans have been migrating to the U.S. mainland and returning to Puerto Rico for more than 125 years, and, in fact, approximately 57% of all Puerto Ricans have migrated at one time or another. The migrant experience, including the circular migration…

  13. Intraperitoneal stone migration during percutaneos nephrolithotomy.

    PubMed

    Diri, Akif; Karakan, Tolga; Resorlu, Mustafa; Kabar, Mucahit; Germiyanoglu, Cankon

    2014-12-01

    Percutaneos nephrolithotomy (PNL) is the standard care for renal stones larger than 2 cm. The procedure has some major and minor complications. Renal pelvis laceration and stone migration to the retroperitoneum is one of the rare condition. We report the first case of intraperitoneal stone migration during PNL. PMID:25641455

  14. Migration--Not Just for Ducks.

    ERIC Educational Resources Information Center

    Simpson, Carol

    1999-01-01

    Discusses the planning process for migrating to a new library media center automation system, including identification of the need to migrate, solicitation of stakeholder support, enumeration of required attributes of a new system, writing the Request for Proposal (RFP), and maximizing vendor demonstrations. (MES)

  15. Endogenous timing factors in bird migration

    NASA Technical Reports Server (NTRS)

    Gwinner, E. G.

    1972-01-01

    Several species of warbler birds were observed in an effort to determine what initiates and terminates migration. Environmental and endogenous timing mechanisms were analyzed. The results indicate that endogenous stimuli are dominant factors for bird migration especially for long distances. It was concluded that environmental factors act as an assist mechanism.

  16. Migration and Recognition of Diplomas in Sweden

    ERIC Educational Resources Information Center

    Dingu-Kyrklund, Elena

    2005-01-01

    Trans-national migration is now a global phenomenon, affecting an increasing amount of persons, many of whom have already completed a form of higher education in their country of origin or earlier residence at the time of migration. There is consequently a need to evaluate foreign degrees and assess migrants' professional competence beyond their…

  17. The Global Village: Migration and Education.

    ERIC Educational Resources Information Center

    Bhavnagri, Navaz Peshotan

    2001-01-01

    Introduces this special issue on migration and education, describing the common underlying organizational framework for articles in this issue. Presents five common content strands regarding global immigration and schooling, including multiple reasons for migration, initial marginalization of immigrant groups, gaining resilience from support…

  18. Parental Migration and Children's Outcomes in Romania

    ERIC Educational Resources Information Center

    Robila, Mihaela

    2011-01-01

    Although Eastern European migration has increased greatly, the research on its impact on children and families has been limited. In this study I examined the impact of parental economic migration on children psychosocial and academic outcomes in Romania, one of largest Eastern European migrant sending country. Surveys were conducted with 382…

  19. Migrations toward Western Europe: trends, outlook, policies.

    PubMed

    Gomel, G

    1992-01-01

    Recent trends in international migration affecting Europe are reviewed. The author notes that since the 1970s, the pressure from migrants has shifted from northern to southern Europe. He concludes that the focus of future trends will be the Mediterranean region from northern Africa to southern Europe. The possible effect on migration of aid policies to developing countries is considered.

  20. Rearrangement of sulfonamidyl radicals with hydrogen migration

    SciTech Connect

    Troyanskii, E.I.; Lazareva, M.I.; Nikishin, G.I.

    1987-01-20

    One-step outlying oxidative chlorination of alkanesulfonamides by the action of the Na/sub 2/S/sub 2/O/sub 8/-CuCl/sub 2/ system via intermediate sulfonamidyl radicals gives 3- and 4-chloroalkanesulfonamides. Rearrangements of sulfonamidyl radicals with H atom migration from the sulfonyl segment predominates over rearrangement with H atom migration from the amide segment.

  1. Cuba's Exiles: Portrait of a Refugee Migration.

    ERIC Educational Resources Information Center

    Pedraza-Bailey, Sylvia

    1985-01-01

    Argues that to understand the changing social characteristics of Cuban exiles over 20 years of migration, one must understand the changing phases of the Cuban revolution. Explores Egon F. Kunz's theoretical framework for refugee migration in relation to Cuban exodus data. (GC)

  2. Migration and Life of Hispanics in Utah.

    ERIC Educational Resources Information Center

    Gallenstein, Nancy L.

    This paper presents a historical and cultural overview of the migration and life of Hispanics in Utah and identifies three themes: search for a better life, need for and acquisition of a sense of belonging, and substance of the Hispanic people. Over the past 4 centuries, Hispanics have migrated to Utah from New Mexico, Mexico, and Central and…

  3. Rethinking international migration: a review and critique.

    PubMed

    Papademetriou, D G

    1983-01-01

    A new style of international migration, temporary and often illegal immigration in order to work, began to emerge after World War II. Many countries initiated immigration policies that gave the appearance of control, while their back doors remained open and, possibly, unclosable. In the US, it is slowly becoming obvious that foreign workers cannot be used as a temporary labor force at will. 2 usual theories of migration are the classical and the conflicts schools. The classical school presents migration as a rational, economic act that leads to economic adjustment between sending and receiving countries. The conflict school, often Marxist, views migration as an unequal process that leads to the inclusion of developing countries into the world capitalist system and to a widenin gap between rich and poor countries. The convergence of these 2 theories leads to the idea that although migration may be a survival strategy of individuals and households, it is also determined by a country's integration in the world economic system. The author reviews several books on immigration theory, which appreciate the complexity and worldwide character of migration; indicate that migration patterns are persistent; and support the view that migration is an economic, social, and political problem; and recommend that policies must be integrated and address the entire issue. PMID:12280186

  4. College and University Student Migration: The Case of Virginia.

    ERIC Educational Resources Information Center

    Lankford, Francis G., Jr.; Taylor, Alton L.

    1971-01-01

    The migration patterns of college and university students in Virginia are described in relation to other states, public and private institutions, male and female students, student educational level, the migration deficit, and future migration patterns. Based on 1968 statistics the out-migration of Virginia students exceeds the in-migration of…

  5. Undocumented migration in response to climate change

    PubMed Central

    Riosmena, Fernando; Hunter, Lori M.; Runfola, Daniel M.

    2016-01-01

    In the face of climate change induced economic uncertainty, households may employ migration as an adaptation strategy to diversify their livelihood portfolio through remittances. However, it is unclear whether such climate migration will be documented or undocumented. In this study we combine detailed migration histories with daily temperature and precipitation information for 214 weather stations to investigate whether climate change more strongly impacts undocumented or documented migration from 68 rural Mexican municipalities to the U.S. during the years 1986–1999. We employ two measures of climate change, the warm spell duration index (WSDI) and the precipitation during extremely wet days (R99PTOT). Results from multi-level event-history models demonstrate that climate-related international migration from rural Mexico was predominantly undocumented. We conclude that programs to facilitate climate change adaptation in rural Mexico may be more effective in reducing undocumented border crossings than increased border fortification. PMID:27570840

  6. Ethnic return migration: an Estonian case.

    PubMed

    Kulu, H

    1998-01-01

    "This article examines return migration during the post World War 2 period of descendants of Estonians who emigrated to Russia at the end of the nineteenth and at the beginning of the twentieth century" The focus is on changing migration patterns over time. "The behavioural norm of Estonians born in the 1910s-1920s has been return migration to Estonia, while the migration behaviour of the 1930s-1940s and the 1950s-1960s generations can be characterized by urbanization in West Siberia. The results give reason to assume that ethnic return migration over a long period depends neither directly nor indirectly on momentary environmental changes, but rather on changes in people's values, habits, identity etc., which in the case of an ethnic minority living outside its historical homeland may be followed generation by generation." (EXCERPT)

  7. CLASSIFICATION AND BEHAVIOR OF MEANDER MIGRATION.

    USGS Publications Warehouse

    Martin, Edward H.; Shen, Hsieh W.; Glover, J. Ed

    1986-01-01

    Meander migrations on the Mississippi River between Cairo, Illinois and Baton Rouge, Louisiana for the time period between the years 1765 and 1930 were classified into six categories based on the nature of channel movements. During the time period between 1765 and 1900, man's disturbance on this river reach was relatively minor. This study was mainly based on measurements taken in the years 1765, 1825, 1887 and 1930. The six categories of meander migration were: downstream limb migration, downstream limb rotation, mainly upstream limb migration, upstream limb rotation, pure translation and pure expansion. It was determined that over 60% of future meander migrations could be predicted from the characteristics of each individual initial channel pattern.

  8. Migration, remittances, and inequality: estimating the net effects of migration on income distribution.

    PubMed

    Barham, B; Boucher, S

    1998-04-01

    "This paper examines the net effects of migration and remittances on income distribution. Potential home earnings of migrants are imputed, as are the earnings of non-migrants in migrant households, in order to construct no-migration counterfactuals to compare with the observed income distribution including remittances. The earnings functions used to impute migrant home earnings are estimated from observations on non-migrants in a selection-corrected estimation framework which incorporates migration choice and labor-force participation decisions. For a sample of households in Bluefields, Nicaragua, migration and remittances increase income inequality when compared with the no-migration counterfactual."

  9. The multiple faces of leukocyte interstitial migration

    PubMed Central

    Lämmermann, Tim; Germain, Ronald N.

    2014-01-01

    Spatiotemporal control of leukocyte dynamics within tissues is critical for successful innate and adaptive immune responses. Homeostatic trafficking and coordinated infiltration into and within sites of inflammation and infection rely on signaling in response to extracellular cues that in turn controls a variety of intracellular protein networks regulating leukocyte motility, migration, chemotaxis, positioning, and cell–cell interaction. In contrast to mesenchymal cells, leukocytes migrate in an amoeboid fashion by rapid cycles of actin polymerization and actomyosin contraction, and their migration in tissues is generally referred to as low adhesive and nonproteolytic. The interplay of actin network expansion, contraction, and adhesion shapes the exact mode of amoeboid migration, and in this review, we explore how leukocyte subsets potentially harness the same basic biomechanical mechanisms in a cell-type-specific manner. Most of our detailed understanding of these processes derives from in vitro migration studies in three-dimensional gels and confined spaces that mimic geometrical aspects of physiological tissues. We summarize these in vitro results and then critically compare them to data from intravital imaging of leukocyte interstitial migration in mouse tissues. We outline the technical challenges of obtaining conclusive mechanistic results from intravital studies, discuss leukocyte migration strategies in vivo, and present examples of mode switching during physiological interstitial migration. These findings are also placed in the context of leukocyte migration defects in primary immunodeficiencies. This overview of both in vitro and in vivo studies highlights recent progress in understanding the molecular and biophysical mechanisms that shape robust leukocyte migration responses in physiologically complex and heterogeneous environments. PMID:24573488

  10. The mixed effects of migration: community-level migration and birthweight in Mexico.

    PubMed

    Hamilton, Erin R; Choi, Kate H

    2015-05-01

    Research on the relationship between migration and infant health in Mexico finds that migration has mixed impacts on the risk of low birthweight (LBW). Whereas the departure and absence of household and community members are harmful, remittances are beneficial. We extend this work by considering a different measure of infant health in addition to LBW: macrosomia (i.e., heavy birthweight), which is associated with infant, child, and maternal morbidities but has a different social risk profile from LBW. We link the 2008 and 2009 Mexican birth certificates with community data from the 2000 Mexican census to analyze the association between various dimensions of community-level migration (i.e., rates of out-migration, receipt of remittances, and return migration) and the risk of LBW and macrosomia. We examine this association using two sets of models which differ in the extent to which they account for endogeneity. We find that the health impacts of migration differ depending not only on the dimension of migration, but also on the measure of health, and that they are robust to potential sources of endogeneity. Whereas community remittances and return migration are associated with lower risk of LBW, they are associated with increased risk of macrosomia. By contrast, out-migration is associated with increased risk of LBW and lower risk of macrosomia. Our analysis of endogeneity suggests that bias resulting from unmeasured differences between communities with different levels of migration may result in an underestimate of the impacts of community migration on birthweight.

  11. Long-run migration incentives and migration effects: the case of different fertility rates.

    PubMed

    Meier, V

    1994-05-01

    "In this paper the direction of the long-run migration incentive in the presence of closed borders and the long-run welfare effects of a regime change from 'autarky' to 'free permanent migration' are studied. A difference in birth-country specific fertility rates is treated as the final cause for the creation of migration incentives in a two-country model where the standard overlapping-generations framework is used.... Opening the borders for permanent migration can always lead to the equalization of labour force growth rates. A continuum of such equilibria with migration does exist, but the application of the concept of migration-stability, introduced in this paper, gives reason to the suspicion that free migration can also lead to a collapse of the emigration country's economy." (SUMMARY IN GER) PMID:12291063

  12. [Migration patterns in eastern Indonesia].

    PubMed

    Bandiyono, S

    1991-06-01

    The date of Indonesia's 1985 intercensal survey showed interprovincial migration towards the eastern part of the country due to transmigration programs as well as to a higher rate of migration among better educated people. The population of the southeastern and western islands was 2,720,000 in 1980 vs. 2,990,000 in 1985, population density per square km was 148, and the rate of growth from 1971-80 was 2.36% vs. 1.91% from 1980-85. The inhabitants of the southeastern and eastern islands numbered 2,740,000 in 1980 vs. 3,060,000 in 1985, density was 64, and the rate of growth from 1971-80 was 1.95% vs. 2.26% from 1980-85. East Timor's population numbered 630,000 in 1985 with a density of 42 and a growth rate of 2.58% in the period of 1980-85. The population of North Celebes was 2,120,000 in 1980 and 2,310,000 in 1985 with a density of 122 and a growth rate of 2.31% from 1971-80 and 1.8% from 1980-85. Middle Celebes numbered 1,280,000 in 1989 and 1,510,000 in 1985 with a density of 22 and a growth rate of 3.86% from 1971-80 and 3.22% from 1980-85. South Celebes had 6,060,000 people in 1980 and 6.610,000 in 1985 with a density of 91 and a growth rate of 1.74% from 1971-80 and 1.74% from 1980-85. Southeast Celebes had a population of 940,000 in 1980 vs. 1,120,000 in 1985 with a density of 40 and a growth rate of 3.09% from 1971-80 and 3.51% from 1980-85. THe Mollucas totalled 1,410,000 in 1980 and 1.610,000 in 1985 with a density of 22 and growth rate of 2.88% from 1971-80 and 2.66% from 1980-85. Iran and Jaya numbered 1,170,000 in 1980 and 1,370,000 in 1985 with a density of 3 and growth rate of 2.67% from 1971-80 and 3.15% from 1980-85. The whole of eastern Indonesia had a population of 18,440,000 in 1980 and 21,210,000 in 1985 with a density of 62 and growth rate of 2.89% from 1971-80 and 2.83 from 1980-85. The movement of people from the southern part of Celebes was the most massive interprovincial migration in eastern Indonesia.

  13. Nanoclay migration from food packaging materials.

    PubMed

    Echegoyen, Yolanda; Rodríguez, Silvia; Nerín, Cristina

    2016-01-01

    A recent trend is to use nanocomposites materials for food-packaging applications. Different kinds of nanoparticles are incorporated into the polymers to improve their characteristics, and, among them, nanoclay is used to improve their barrier properties to gases. In this work, the results of migration studies with different food simulants (ethanol 10% and acetic acid 3%), temperatures and times (40 ºC for 10 days and 70 ºC for 2 h) from two commercialised LDPE nanocomposite bags are presented. The migration solutions thus obtained were analysed by ICP-MS to evaluate the amount of aluminium which migrated into the solutions both in dissolved form and as a part of nanoparticles. Aluminium migration was observed for both samples with a maximum migration value of 51.65 ng cm(-)(2) for the Aisaika bags and 24.14 ng cm(-)(2) for the Debbie Meyer bags. The presence of spikes working in single-particle mode using ICP-MS indicated that part of this aluminium was present as nanoparticles. The size and morphology of the nanoclay, in both the original material and the migration solutions, was studied by scanning electron microscopy coupled to energy-dispersive X-ray diffraction (SEM-EDX). In this manner, nanoparticles of different morphologies and sizes were found to migrate into the food simulants. PMID:26751017

  14. Migration of Airway Smooth Muscle Cells

    PubMed Central

    Gerthoffer, William T.

    2008-01-01

    Migration of smooth muscle cells is a process fundamental to development of hollow organs, including blood vessels and the airways. Migration is also thought to be part of the response to tissue injury. It has also been suggested to contribute to airways remodeling triggered by chronic inflammation. In both nonmuscle and smooth muscle cells numerous external signaling molecules and internal signal transduction pathways contribute to cell migration. The review includes evidence for the functional significance of airway smooth muscle migration, a summary of promigratory and antimigratory agents, and summaries of important signaling pathways mediating migration. Important signaling pathways and effector proteins described include small G proteins, phosphatidylinositol 3-kinases (PI3-K), Rho activated protein kinase (ROCK), p21-activated protein kinases (PAK), Src family tyrosine kinases, and mitogen-activated protein kinases (MAPK). These signaling modules control multiple critical effector proteins including actin nucleating, capping and severing proteins, myosin motors, and proteins that remodel microtubules. Actin filament remodeling, focal contact remodeling and propulsive force of molecular motors are all coordinated to move cells along gradients of chemical cues, matrix adhesiveness, or matrix stiffness. Airway smooth muscle cell migration can be modulated in vitro by drugs commonly used in pulmonary medicine including β-adrenergic agonists and corticosteroids. Future studies of airway smooth muscle cell migration may uncover novel targets for drugs aimed at modifying airway remodeling. PMID:18094091

  15. Migration and mental health: An interface

    PubMed Central

    Virupaksha, H. G.; Kumar, Ashok; Nirmala, Bergai Parthsarathy

    2014-01-01

    Migration is a universal phenomenon, which existed with the subsistence of the human beings on earth. People migrate from one place to another for several reasons, but the goal or main reason behind changing the residence would be improving their living conditions or to escape from debts and poverty. Migration is also a social phenomenon which influences human life and the environment around. Hence, migration has a great impact on any geographical area and it is known as one of the three basic components of population growth of any particular region (the other two are, mortality and fertility). Migration involves certain phases to go through; hence, it is a process. Many times, lack of preparedness, difficulties in adjusting to the new environment, the complexity of the local system, language difficulties, cultural disparities and adverse experiences would cause distress to the migrants. Moreover subsequently it has a negative impact on mental well-being of such population. Due to globalization, modernization, improved technologies and developments in all the sectors, the migration and its impact on human well-being is a contemporary issue; hence, here is an attempt to understand the migration and its impact on the mental health of the migrants based on the studies conducted around. PMID:25097389

  16. New directions for migration policy in Europe.

    PubMed Central

    Laczko, Frank

    2002-01-01

    There is a growing debate about the future direction of migration policy in Europe. After nearly 30 years of pursuing restrictive immigration and asylum policies, many European Union (EU) governments are beginning to re-assess their migration policies and to call for a new approach. For the first time in many years, several EU governments have begun to talk again about the benefits of labour migration and, even more significantly, have even begun to take action to recruit more migrants, especially skilled workers. This paper looks at the background to current calls for a new approach to migration in Europe and public reaction to these new initiatives. It first describes recent trends in migration in Europe and then briefly considers the demographic case for more migration. This is followed by a brief outline of some of the measures being considered by European governments to promote selective labour migration. The remainder of the paper is devoted to a discussion of some of the implications of this change in policy, focusing on two main issues: the likely consequences for sending countries, and the implications for the fight against the smuggling and trafficking of people. PMID:12028795

  17. Migration and Development: A Theoretical Perspective 1

    PubMed Central

    De Haas, Hein

    2010-01-01

    The debate on migration and development has swung back and forth like a pendulum, from developmentalist optimism in the 1950s and 1960s, to neo‐Marxist pessimism over the 1970s and 1980s, towards more optimistic views in the 1990s and 2000s. This paper argues how such discursive shifts in the migration and development debate should be primarily seen as part of more general paradigm shifts in social and development theory. However, the classical opposition between pessimistic and optimistic views is challenged by empirical evidence pointing to the heterogeneity of migration impacts. By integrating and amending insights from the new economics of labor migration, livelihood perspectives in development studies and transnational perspectives in migration studies – which share several though as yet unobserved conceptual parallels – this paper elaborates the contours of a conceptual framework that simultaneously integrates agency and structure perspectives and is therefore able to account for the heterogeneous nature of migration‐development interactions. The resulting perspective reveals the naivety of recent views celebrating migration as self‐help development “from below”. These views are largely ideologically driven and shift the attention away from structural constraints and the vital role of states in shaping favorable conditions for positive development impacts of migration to occur. PMID:26900199

  18. New directions for migration policy in Europe.

    PubMed

    Laczko, Frank

    2002-04-29

    There is a growing debate about the future direction of migration policy in Europe. After nearly 30 years of pursuing restrictive immigration and asylum policies, many European Union (EU) governments are beginning to re-assess their migration policies and to call for a new approach. For the first time in many years, several EU governments have begun to talk again about the benefits of labour migration and, even more significantly, have even begun to take action to recruit more migrants, especially skilled workers. This paper looks at the background to current calls for a new approach to migration in Europe and public reaction to these new initiatives. It first describes recent trends in migration in Europe and then briefly considers the demographic case for more migration. This is followed by a brief outline of some of the measures being considered by European governments to promote selective labour migration. The remainder of the paper is devoted to a discussion of some of the implications of this change in policy, focusing on two main issues: the likely consequences for sending countries, and the implications for the fight against the smuggling and trafficking of people.

  19. DO GIANT PLANETS SURVIVE TYPE II MIGRATION?

    SciTech Connect

    Hasegawa, Yasuhiro; Ida, Shigeru E-mail: ida@geo.titech.ac.jp

    2013-09-10

    Planetary migration is one of the most serious problems to systematically understand the observations of exoplanets. We clarify that the theoretically predicted type II, migration (like type I migration) is too fast, by developing detailed analytical arguments in which the timescale of type II migration is compared with the disk lifetime. In the disk-dominated regime, the type II migration timescale is characterized by a local viscous diffusion timescale, while the disk lifetime is characterized by a global diffusion timescale that is much longer than the local one. Even in the planet-dominated regime where the inertia of the planet mass reduces the migration speed, the timescale is still shorter than the disk lifetime except in the final disk evolution stage where the total disk mass decays below the planet mass. This suggests that most giant planets plunge into the central stars within the disk lifetime, and it contradicts the exoplanet observations that gas giants are piled up at r {approx}> 1 AU. We examine additional processes that may arise in protoplanetary disks: dead zones, photoevaporation of gas, and gas flow across a gap formed by a type II migrator. Although they make the type II migration timescale closer to the disk lifetime, we show that none of them can act as an effective barrier for rapid type II migration with the current knowledge of these processes. We point out that gas flow across a gap and the fraction of the flow accreted onto the planets are uncertain and they may have the potential to solve the problem. Much more detailed investigation for each process may be needed to explain the observed distribution of gas giants in extrasolar planetary systems.

  20. Modification of meander migration by bank failures

    NASA Astrophysics Data System (ADS)

    Motta, D.; Langendoen, E. J.; Abad, J. D.; García, M. H.

    2014-05-01

    Meander migration and planform evolution depend on the resistance to erosion of the floodplain materials. To date, research to quantify meandering river adjustment has largely focused on resistance to erosion properties that vary horizontally. This paper evaluates the combined effect of horizontal and vertical floodplain material heterogeneity on meander migration by simulating fluvial erosion and cantilever and planar bank mass failure processes responsible for bank retreat. The impact of stream bank failures on meander migration is conceptualized in our RVR Meander model through a bank armoring factor associated with the dynamics of slump blocks produced by cantilever and planar failures. Simulation periods smaller than the time to cutoff are considered, such that all planform complexity is caused by bank erosion processes and floodplain heterogeneity and not by cutoff dynamics. Cantilever failure continuously affects meander migration, because it is primarily controlled by the fluvial erosion at the bank toe. Hence, it impacts migration rates and meander shapes through the horizontal and vertical distribution of erodibility of floodplain materials. Planar failures are more episodic. However, in floodplain areas characterized by less cohesive materials, they can affect meander evolution in a sustained way and produce preferential migration patterns. Model results show that besides the hydrodynamics, bed morphology and horizontal floodplain heterogeneity, floodplain stratigraphy can significantly affect meander evolution, both in terms of migration rates and planform shapes. Specifically, downstream meander migration can either increase or decrease with respect to the case of a homogeneous floodplain; lateral migration generally decreases as result of bank protection due to slump blocks; and the effect on bend skewness depends on the location and volumes of failed bank material caused by cantilever and planar failures along the bends, with possible achievement of

  1. Nonmonotonic effects of migration in subdivided populations.

    PubMed

    Lombardo, Pierangelo; Gambassi, Andrea; Dall'Asta, Luca

    2014-04-11

    The influence of migration on the stochastic dynamics of subdivided populations is still an open issue in various evolutionary models. Here, we develop a self-consistent mean-field-like method in order to determine the effects of migration on relevant nonequilibrium properties, such as the mean fixation time. If evolution strongly favors coexistence of species (e.g., balancing selection), the mean fixation time develops an unexpected minimum as a function of the migration rate. Our analysis hinges only on the presence of a separation of time scales between local and global dynamics, and therefore, it carries over to other nonequilibrium processes in physics, biology, ecology, and social sciences. PMID:24766019

  2. Probabilistic population projections with migration uncertainty

    PubMed Central

    Azose, Jonathan J.; Ševčíková, Hana; Raftery, Adrian E.

    2016-01-01

    We produce probabilistic projections of population for all countries based on probabilistic projections of fertility, mortality, and migration. We compare our projections to those from the United Nations’ Probabilistic Population Projections, which uses similar methods for fertility and mortality but deterministic migration projections. We find that uncertainty in migration projection is a substantial contributor to uncertainty in population projections for many countries. Prediction intervals for the populations of Northern America and Europe are over 70% wider, whereas prediction intervals for the populations of Africa, Asia, and the world as a whole are nearly unchanged. Out-of-sample validation shows that the model is reasonably well calibrated. PMID:27217571

  3. Return migration, uncertainty and precautionary savings.

    PubMed

    Dustmann, C

    1997-04-01

    "This paper presents a life-cycle model where migrants determine re-migration and consumption simultaneously in a stochastic environment. Whether precautionary savings of migrants are above or below those of natives is ambiguous in general--the sign depends on the risk in host- and home-country labor markets and on the correlation of labor market shocks. Furthermore, the effect of an uncertain environment on migration and re-migration plans cannot be unambiguously signed for the general case. It depends on the size of the wage differential as well as the relative risk the migrant exhibits in the two labor markets."

  4. Urban squatting and migration in Peninsular Malaysia.

    PubMed

    Johnstone, M

    1983-01-01

    "This article examines some of the links between the phenomena of urban migration and squatter settlements in the Third World city. This will be done by demonstrating that both are outcomes of fundamental social and political forces that have operated on these societies. Migration and squatting are placed in a context of the historical processes that led to the uneven development of Malaysia. The article offers some explanation for the origin of the inequalities observed in spatial structures--in this case urban housing--by focusing on one of the contributory factors, namely migration."

  5. Migration, development and remittances in rural Mexico.

    PubMed

    Rubenstein, H

    1992-06-01

    The argument is that remittances to Mexico from migrants in the US contribute to household prosperity and lessen the balance of payments problem. The purpose of this article is to provide an overview of the incentives and constraints to development and individual economic well-being in rural Mexico. Examination is made of the financial amount of remittances, the use of remittances, the impact on development of remittances, models of migration, and migration historically. The viewpoint is that migration satisfies labor needs in developed countries to the detriment of underdeveloped countries. $2 billion a year are sent by illegal migrants from the US to Mexico. This sum is 4 times the net earning of Mexico's tourist trade. 21.1% of the Mexican population depend in part on money sent from the US. 79% of illegal migrants remitted money to relatives in Jalisco state. 70% of migrant families receive $170/month. In Guadalupe, 73% of families depended on migrant income. In Villa Guerrero, 50% of households depended on migrant income. Migrant income supported 1 out of 5 households in Mexico. Money is usually spent of household subsistence items. Sometimes money is also spent on community religious festivals, marriage ceremonies, and education of children or improved living conditions. Examples are given of money being used for investment in land and livestock. Migration affects community solidarity, and comparative ethic, and the influence on others to migrate. Employment opportunities are not expanded and cottage and community industries are threatened. Land purchases did not result in land improvements. Migration models are deficient. There is a macro/micro dichotomy. The push-and-pull system is not controllable by individual migrants. The migration remittance model is a product of unequal development and a mechanism feeding migration. Mexican migration has occurred since the 1880's; seasonal migration was encouraged. There was coercion to return to Mexico after the

  6. Particle migration rates in a Couette apparatus.

    SciTech Connect

    Christensen, David.; Hsiao, Shih-Chun; Altobelli, Stephen A.; Ingber, Marc Stuart; Mondy, Lisa Ann

    2005-02-01

    Bulk migration of particles towards regions of lower shear occurs in suspensions of neutrally buoyant spheres in Newtonian fluids undergoing creeping flow in the annular region between two rotating, coaxial cylinders (a wide-gap Couette). For a monomodal suspension of spheres in a viscous fluid, dimensional analysis indicates that the rate of migration at a given concentration should scale with the square of the sphere radius. However, a previous experimental study showed that the rate of migration of spherical particles at 50% volume concentration actually scaled with the sphere radius to approximately the 2.9 power.

  7. Particle migration rates in a Couette apparatus.

    SciTech Connect

    Hsiao, Shih-Chun; Altobelli, Stephen A.; Ingber, Marc Stuart; Mondy, Lisa Ann; Christensen, D.

    2003-07-01

    Bulk migration of particles towards regions of lower shear occurs in suspensions of neutrally buoyant spheres in Newtonian fluids undergoing creeping flow in the annular region between two rotating, coaxial cylinders (a wide-gap Couette). For a monomodal suspension of spheres in a viscous fluid, dimensional analysis indicates that the rate of migration at a given concentration should scale with the square of the sphere radius. However, a previous experimental study showed that the rate of migration of spherical particles at 50% volume concentration actually scaled with the sphere radius to approximately the 2.9 power.

  8. Polish migration policies: challenges and dilemmas.

    PubMed

    Bernatowicz, A

    1992-01-01

    Following a brief historical overview of Polish migration policies and trends, current post-Communism migration is examined. The focus is on "two...types of Polish emigration.... The first, continuing over the last two decades, is temporary labor emigration, when emigres spend two to three years (especially overseas) or a few months (in Western Europe) working outside of Poland. The second model of movement of Poles abroad is short-term private business excursions to different regions of Europe and Asia." The author examines "which migration policies will be beneficial to Poland's political and economic systems, as the country enters a new phase of development." PMID:12317548

  9. Nonmonotonic Effects of Migration in Subdivided Populations

    NASA Astrophysics Data System (ADS)

    Lombardo, Pierangelo; Gambassi, Andrea; Dall'Asta, Luca

    2014-04-01

    The influence of migration on the stochastic dynamics of subdivided populations is still an open issue in various evolutionary models. Here, we develop a self-consistent mean-field-like method in order to determine the effects of migration on relevant nonequilibrium properties, such as the mean fixation time. If evolution strongly favors coexistence of species (e.g., balancing selection), the mean fixation time develops an unexpected minimum as a function of the migration rate. Our analysis hinges only on the presence of a separation of time scales between local and global dynamics, and therefore, it carries over to other nonequilibrium processes in physics, biology, ecology, and social sciences.

  10. Cyclin D1 functions in cell migration.

    PubMed

    Li, Zhiping; Wang, Chenguang; Prendergast, George C; Pestell, Richard G

    2006-11-01

    Cell migration is essential for developmental morphogenesis, tissue repair, and tumor metastasis. A recent study reveals that cyclin D1 acts to promote cell migration by inhibiting Rho/ROCK signaling and expression of thrombospondin-1 (TSP-1), an extracellular matrix protein that regulates cell migration in many settings including cancer. Given the frequent overexpression of cyclin D1 in cancer cells, due to its upregulation by Ras, Rho, Src, and other genes that drive malignant development, the new findings suggest that cyclin D1 may have a central role in mediating invasion and metastasis of cancer cells by controlling Rho/ROCK signaling and matrix deposition of TSP-1.

  11. International labor migration through multinational enterprises.

    PubMed

    Tzeng, R

    1995-01-01

    "This research studies international migration of company transferees. The main purposes are to address how their individual characteristics have influences on their overseas assignment and what kinds of migration patterns are created by the multinational business enterprises. U.S. firms in Taiwan are the primary study focus. By using both quantitative and qualitative data, the results show that although an overseas appointment is mainly based on individual competence, nationality, ethnicity and gender also play crucial roles. And multinationals are important channels for sustainable, return and circular migration."

  12. The cost of migration: spoonbills suffer higher mortality during trans-Saharan spring migrations only

    PubMed Central

    Lok, Tamar; Overdijk, Otto; Piersma, Theunis

    2015-01-01

    Explanations for the wide variety of seasonal migration patterns of animals all carry the assumption that migration is costly and that this cost increases with migration distance. Although in some studies, the relationships between migration distance and breeding success or annual survival are established, none has investigated whether mortality during the actual migration increases with migration distance. Here, we compared seasonal survival between Eurasian spoonbills (Platalea leucorodia leucorodia) that breed in The Netherlands and migrate different distances (ca 1000, 2000 and 4500 km) to winter in France, Iberia and Mauritania, respectively. On the basis of resightings of individually marked birds throughout the year between 2005 and 2012, we show that summer, autumn and winter survival were very high and independent of migration distance, whereas mortality during spring migration was much higher (18%) for the birds that wintered in Mauritania, compared with those flying only as far as France (5%) or Iberia (6%). As such, this study is the first to show empirical evidence for increased mortality during some long migrations, likely driven by the presence of a physical barrier (the Sahara desert) in combination with suboptimal fuelling and unfavourable weather conditions en route. PMID:25589489

  13. Characterizing the International Migration Barriers with a Probabilistic Multilateral Migration Model

    NASA Astrophysics Data System (ADS)

    Li, Xiaomeng; Xu, Hongzhong; Chen, Jiawei; Chen, Qinghua; Zhang, Jiang; di, Zengru

    2016-09-01

    Human migration is responsible for forming modern civilization and has had an important influence on the development of various countries. There are many issues worth researching, and “the reason to move” is the most basic one. The concept of migration cost in the classical self-selection theory, which was introduced by Roy and Borjas, is useful. However, migration cost cannot address global migration because of the limitations of deterministic and bilateral choice. Following the idea of migration cost, this paper developed a new probabilistic multilateral migration model by introducing the Boltzmann factor from statistical physics. After characterizing the underlying mechanism or driving force of human mobility, we reveal some interesting facts that have provided a deeper understanding of international migration, such as the negative correlation between migration costs for emigrants and immigrants and a global classification with clear regional and economic characteristics, based on clustering of migration cost vectors. In addition, we deconstruct the migration barriers using regression analysis and find that the influencing factors are complicated but can be partly (12.5%) described by several macro indexes, such as the GDP growth of the destination country, the GNI per capita and the HDI of both the source and destination countries.

  14. The cost of migration: spoonbills suffer higher mortality during trans-Saharan spring migrations only.

    PubMed

    Lok, Tamar; Overdijk, Otto; Piersma, Theunis

    2015-01-01

    Explanations for the wide variety of seasonal migration patterns of animals all carry the assumption that migration is costly and that this cost increases with migration distance. Although in some studies, the relationships between migration distance and breeding success or annual survival are established, none has investigated whether mortality during the actual migration increases with migration distance. Here, we compared seasonal survival between Eurasian spoonbills (Platalea leucorodia leucorodia) that breed in The Netherlands and migrate different distances (ca 1000, 2000 and 4500 km) to winter in France, Iberia and Mauritania, respectively. On the basis of resightings of individually marked birds throughout the year between 2005 and 2012, we show that summer, autumn and winter survival were very high and independent of migration distance, whereas mortality during spring migration was much higher (18%) for the birds that wintered in Mauritania, compared with those flying only as far as France (5%) or Iberia (6%). As such, this study is the first to show empirical evidence for increased mortality during some long migrations, likely driven by the presence of a physical barrier (the Sahara desert) in combination with suboptimal fuelling and unfavourable weather conditions en route.

  15. Characterizing the International Migration Barriers with a Probabilistic Multilateral Migration Model.

    PubMed

    Li, Xiaomeng; Xu, Hongzhong; Chen, Jiawei; Chen, Qinghua; Zhang, Jiang; Di, Zengru

    2016-01-01

    Human migration is responsible for forming modern civilization and has had an important influence on the development of various countries. There are many issues worth researching, and "the reason to move" is the most basic one. The concept of migration cost in the classical self-selection theory, which was introduced by Roy and Borjas, is useful. However, migration cost cannot address global migration because of the limitations of deterministic and bilateral choice. Following the idea of migration cost, this paper developed a new probabilistic multilateral migration model by introducing the Boltzmann factor from statistical physics. After characterizing the underlying mechanism or driving force of human mobility, we reveal some interesting facts that have provided a deeper understanding of international migration, such as the negative correlation between migration costs for emigrants and immigrants and a global classification with clear regional and economic characteristics, based on clustering of migration cost vectors. In addition, we deconstruct the migration barriers using regression analysis and find that the influencing factors are complicated but can be partly (12.5%) described by several macro indexes, such as the GDP growth of the destination country, the GNI per capita and the HDI of both the source and destination countries. PMID:27597319

  16. Tungsten Cluster Migration on Nanoparticles: Minimum Energy Pathway and Migration Mechanism

    SciTech Connect

    Chen, Dong; Hu, Wangyu; Gao, Fei; Deng, Huiqiu; Sun, Lixian

    2011-03-02

    Transition state searches have been employed to investigate the migration mechanisms of W clusters on W nanoparticles, and to determine the corresponding migration energies for the possible migration paths of these clusters. The tungsten clusters containing up to four adatoms are found to prefer 2D-compact structures with relatively low binding energies. The effect of interface and vertex regions on the migration behavior of the clusters is significantly strong, as compared to that of nanoparticle size. The migration mechanisms are quite different when the clusters are located at the center of the nanoparticle and near the interface or vertex areas. Near the interfaces and vertex areas, the substrate atoms tend to participate in the migration processes of the clusters, and can join the adatoms to form a larger cluster or lead to the dissociation of a cluster via the exchange mechanism, which results in the adatom crossing the facets. The lowest energy paths are used to be determined the energy barriers for W cluster migrations (from 1- to 4-atoms) on the facets, edges and vertex regions. The calculated energy barriers for the trimers suggest that the concerted migration is more probable than the successive jumping of a single adatom in the clusters. In addition, it of interest to note that the dimer shearing is a dominant migration mechanism for the tetramer, but needs to overcome a relatively higher migration energy than other clusters.

  17. Characterizing the International Migration Barriers with a Probabilistic Multilateral Migration Model.

    PubMed

    Li, Xiaomeng; Xu, Hongzhong; Chen, Jiawei; Chen, Qinghua; Zhang, Jiang; Di, Zengru

    2016-01-01

    Human migration is responsible for forming modern civilization and has had an important influence on the development of various countries. There are many issues worth researching, and "the reason to move" is the most basic one. The concept of migration cost in the classical self-selection theory, which was introduced by Roy and Borjas, is useful. However, migration cost cannot address global migration because of the limitations of deterministic and bilateral choice. Following the idea of migration cost, this paper developed a new probabilistic multilateral migration model by introducing the Boltzmann factor from statistical physics. After characterizing the underlying mechanism or driving force of human mobility, we reveal some interesting facts that have provided a deeper understanding of international migration, such as the negative correlation between migration costs for emigrants and immigrants and a global classification with clear regional and economic characteristics, based on clustering of migration cost vectors. In addition, we deconstruct the migration barriers using regression analysis and find that the influencing factors are complicated but can be partly (12.5%) described by several macro indexes, such as the GDP growth of the destination country, the GNI per capita and the HDI of both the source and destination countries.

  18. Characterizing the International Migration Barriers with a Probabilistic Multilateral Migration Model

    PubMed Central

    Li, Xiaomeng; Xu, Hongzhong; Chen, Jiawei; Chen, Qinghua; Zhang, Jiang; Di, Zengru

    2016-01-01

    Human migration is responsible for forming modern civilization and has had an important influence on the development of various countries. There are many issues worth researching, and “the reason to move” is the most basic one. The concept of migration cost in the classical self-selection theory, which was introduced by Roy and Borjas, is useful. However, migration cost cannot address global migration because of the limitations of deterministic and bilateral choice. Following the idea of migration cost, this paper developed a new probabilistic multilateral migration model by introducing the Boltzmann factor from statistical physics. After characterizing the underlying mechanism or driving force of human mobility, we reveal some interesting facts that have provided a deeper understanding of international migration, such as the negative correlation between migration costs for emigrants and immigrants and a global classification with clear regional and economic characteristics, based on clustering of migration cost vectors. In addition, we deconstruct the migration barriers using regression analysis and find that the influencing factors are complicated but can be partly (12.5%) described by several macro indexes, such as the GDP growth of the destination country, the GNI per capita and the HDI of both the source and destination countries. PMID:27597319

  19. Hydrogen migration in polycrystalline silicon

    SciTech Connect

    Nickel, N.H.; Jackson, W.B.; Walker, J.

    1996-03-01

    Hydrogen migration in solid-state crystallized and low-pressure chemical-vapor-deposited (LPCVD) polycrystalline silicon (poly-Si) was investigated by deuterium diffusion experiments. The concentration profiles of deuterium, introduced into the poly-Si samples either from a remote D plasma or from a deuterated amorphous-silicon layer, were measured as a function of time and temperature. At high deuterium concentrations the diffusion was dispersive depending on exposure time. The dispersion is consistent with multiple trapping within a distribution of hopping barriers. The data can be explained by a two-level model used to explain diffusion in hydrogenated amorphous silicon. The energy difference between the transport level and the deuterium chemical potential was found to be about 1.2{endash}1.3 eV. The shallow levels for hydrogen trapping are about 0.5 eV below the transport level, while the deep levels are about 1.5{endash}1.7 eV below. The hydrogen chemical potential {mu}{sub H} decreases as the temperature increases. At lower concentrations, {mu}{sub H} was found to depend markedly on the method used to prepare the poly-Si, a result due in part to the dependence of crystallite size on the deposition process. Clear evidence for deuterium deep traps was found only in the solid-state crystallized material. The LPCVD-grown poly-Si, with columnar grains extending through the film thickness, displayed little evidence of deep trapping, and exhibited enhanced D diffusion. Many concentration profiles in the columnar LPCVD material indicated complex diffusion behavior, perhaps reflecting spatial variations of trap densities, complex formation, and/or multiple transport paths. Many aspects of the diffusion in poly-Si are consistent with diffusion data obtained in amorphous silicon. {copyright} {ital 1996 The American Physical Society.}

  20. International nurse migration: lessons from the Philippines.

    PubMed

    Brush, Barbara L; Sochalski, Julie

    2007-02-01

    Developed countries facing nursing shortages have increasingly turned to aggressive foreign nurse recruitment, primarily from developing nations, to offset their lagging domestic nurse supplies and meet growing health care demands. Few donor nations are prepared to manage the loss of their nurse workforce to migration. The sole country with an explicit nurse export policy and the world's leading donor of nurse labor - the Philippines - is itself facing serious provider maldistribution and countrywide health disparities. Examining the historical roots of Philippines nurse migration provides lessons from which other nurse exporting countries may learn. The authors discuss factors that have predicated nurse migration and policies that have eased the way. Furthermore, the authors analyze how various stakeholders influence migratory patterns, the implications of migration for nurses and the public in their care, and the challenges that future social policy and political systems face in addressing global health issues engendered by unfettered recruitment of nurses and other health workers.

  1. Individuality in bird migration: routes and timing.

    PubMed

    Vardanis, Yannis; Klaassen, Raymond H G; Strandberg, Roine; Alerstam, Thomas

    2011-08-23

    The exploration of animal migration has entered a new era with individual-based tracking during multiple years. Here, we investigated repeated migratory journeys of a long-distance migrating bird, the marsh harrier Circus aeruginosus, in order to analyse the variation within and between individuals with respect to routes and timing. We found that there was a stronger individual repeatability in time than in space. Thus, the annual timing of migration varied much less between repeated journeys of the same individual than between different individuals, while there was considerable variation in the routes of the same individual on repeated journeys. The overall contrast in repeatability between time and space was unexpected and may be owing to strong endogenous control of timing, while short-term variation in environmental conditions (weather and habitat) might promote route flexibility. The individual variation in migration routes indicates that the birds navigate mainly by other means than detailed route recapitulation based on landmark recognition.

  2. [Migration behavior and toxicology of methyltin stabilizers].

    PubMed

    Uhde, W J; Woggon, H

    1977-01-01

    With a view to studying the possible use of methyltin compounds as PVC stabilizers in food industry, the authors elaborated a method for the thin-layer chromatographic and subsequent spectrophotometric or polarographic determination of mono-, di- and trimethyltin compounds in the stabilizer and after migration. Monmethyltin compounds are determined spectrophotometrically after reaction with quercetin. Dimethyltin compounds are incinerated by the wet method using sulphuric and nitric acids, and inorganic tin is then estimated polarographically. Prior to identification trimethyltin compounds must be converted into dimethyltin compounds by ultraviolet irradiation or by treatment with triethylamine and bromine. Corresponding to the different conditions of use, the authors investigated the migration of the methyltin stabilizer from PVC into distilled water, 3% acetic acid, 20% alcohol, 50% alcohol und Fettsimulans HB 307. They stated that its tendency to migration into foods is not greater than that of the octyltin stabilizer. The experimentally obtained migration values are discussed in connexion with toxicological data.

  3. Urbanism, Migration, and Tolerance: A Reassessment.

    ERIC Educational Resources Information Center

    Wilson, Thomas C.

    1991-01-01

    Urbanism's impact on the personality may be stronger than previously thought. Finds that urban residence has a strong positive effect on tolerance. Migration also promotes tolerance, regardless of the size of the destination community. (DM)

  4. Migration and relationship power among Mexican women.

    PubMed

    Parrado, Emilio A; Flippen, Chenoa A; McQuiston, Chris

    2005-05-01

    Our study drew on original data collected in Durham, NC, and four sending communities in Mexico to examine differences in women's relationship power that are associated with migration and residence in the United States. We analyzed the personal, relationship, and social resources that condition the association between migration and women's power and the usefulness of the Relationship Control Scale (RCS) for capturing these effects. We found support for perspectives that emphasize that migration may simultaneously mitigate and reinforce gender inequities. Relative to their nonmigrant peers, Mexican women in the United States average higher emotional consonance with their partners, but lower relationship control and sexual negotiation power. Methodologically, we found that the RCS is internally valid and useful for measuring the impact of resources on women's power. However, the scale appears to combine diverse dimensions of relationship power that were differentially related to migration in our study. PMID:15986990

  5. Religiosity and Migration Aspirations among Mexican Youth

    PubMed Central

    Marsiglia, Flavio Francisco; Ayers, Stephanie L.

    2014-01-01

    International migration has become an important topic of discussion from a policy and humanitarian perspective. Part of the debate includes a renewed interest in understanding the factors that influence decisions about migration to the US among Mexican youth still residing in their country of origin. The purpose of this study was to advance knowledge specifically about internal and external religiosity and their influence on youths' migration aspirations. The data for this study were collected in 2007 from students enrolled in an alternative high school program located in the state of Guanajuato, Mexico. The findings indicated that as external religiosity increases, the desire to work or live in the USA decreases. Furthermore, as internal religiosity increases, the desire to work or live in the USA and plans to migrate increase. The results are interpreted and discussed in light of previous research on religious and cultural norm adherence. PMID:25663825

  6. The dynamics of health and return migration.

    PubMed

    Davies, Anita A; Borland, Rosilyne M; Blake, Carolyn; West, Haley E

    2011-06-01

    The increasing importance and complexity of migration globally also implies a global increase in return migration, and thus an increased interest in the health of returning migrants. The health of returning migrants is impacted by the cumulative exposure to social determinants and risk factors of health during the migration process, during the return movement, and following return. Circular migration often occurs among the diaspora, which can result in the transfer of knowledge and skills that contribute to development, including health system strengthening. Migrants with dual nationality often return to countries with better health services than their country of origin when they are sick and can not get care at home. To maintain and improve the health of returning migrants, multi-sectoral policies at global and national levels should facilitate access to appropriate and equitable health services, social services, and continuity of care across and within borders.

  7. International nurse migration: lessons from the Philippines.

    PubMed

    Brush, Barbara L; Sochalski, Julie

    2007-02-01

    Developed countries facing nursing shortages have increasingly turned to aggressive foreign nurse recruitment, primarily from developing nations, to offset their lagging domestic nurse supplies and meet growing health care demands. Few donor nations are prepared to manage the loss of their nurse workforce to migration. The sole country with an explicit nurse export policy and the world's leading donor of nurse labor - the Philippines - is itself facing serious provider maldistribution and countrywide health disparities. Examining the historical roots of Philippines nurse migration provides lessons from which other nurse exporting countries may learn. The authors discuss factors that have predicated nurse migration and policies that have eased the way. Furthermore, the authors analyze how various stakeholders influence migratory patterns, the implications of migration for nurses and the public in their care, and the challenges that future social policy and political systems face in addressing global health issues engendered by unfettered recruitment of nurses and other health workers. PMID:17470770

  8. Modulation of Neuronal Migration by NMDA Receptors

    NASA Astrophysics Data System (ADS)

    Komuro, Hitoshi; Rakic, Pasko

    1993-04-01

    The N-methyl-D-aspartate (NMDA) subtype of the glutamate receptor is essential for neuronal differentiation and establishment or elimination of synapses in a developing brain. The activity of the NMDA receptor has now been shown to also regulate the migration of granule cells in slice preparations of the developing mouse cerebellum. First, blockade of NMDA receptors by specific antagonists resulted in the curtailment of cell migration. Second, enhancement of NMDA receptor activity by the removal of magnesium or by the application of glycine increased the rate of cell movement. Third, increase of endogenous extracellular glutamate by inhibition of its uptake accelerated the rate of cell migration. These results suggest that NMDA receptors may play an early role in the regulation of calcium-dependent cell migration before neurons reach their targets and form synaptic contacts.

  9. Opportunistic migration in spatial evolutionary games.

    PubMed

    Buesser, Pierre; Tomassini, Marco; Antonioni, Alberto

    2013-10-01

    We study evolutionary games in a spatial diluted grid environment in which agents strategically interact locally but can also opportunistically move to other positions within a given migration radius. Using the imitation of the best rule for strategy revision, it is shown that cooperation may evolve and be stable in the Prisoner's Dilemma game space for several migration distances but only for small game interaction radius while the Stag Hunt class of games become fully cooperative. We also show that only a few trials are needed for cooperation to evolve, i.e., searching costs are not an issue. When the stochastic Fermi strategy update protocol is used cooperation cannot evolve in the Prisoner's Dilemma if the selection intensity is high in spite of opportunistic migration. However, when imitation becomes more random, fully or partially cooperative states are reached in all games for all migration distances tested and for short to intermediate interaction radii. PMID:24229225

  10. Opportunistic migration in spatial evolutionary games

    NASA Astrophysics Data System (ADS)

    Buesser, Pierre; Tomassini, Marco; Antonioni, Alberto

    2013-10-01

    We study evolutionary games in a spatial diluted grid environment in which agents strategically interact locally but can also opportunistically move to other positions within a given migration radius. Using the imitation of the best rule for strategy revision, it is shown that cooperation may evolve and be stable in the Prisoner's Dilemma game space for several migration distances but only for small game interaction radius while the Stag Hunt class of games become fully cooperative. We also show that only a few trials are needed for cooperation to evolve, i.e., searching costs are not an issue. When the stochastic Fermi strategy update protocol is used cooperation cannot evolve in the Prisoner's Dilemma if the selection intensity is high in spite of opportunistic migration. However, when imitation becomes more random, fully or partially cooperative states are reached in all games for all migration distances tested and for short to intermediate interaction radii.

  11. Bird Migration Echoes Observed by Polarimetric Radar

    NASA Astrophysics Data System (ADS)

    Minda, Haruya; Furuzawa, Fumie A.; Satoh, Shinsuke; Nakamura, Kenji

    A C-band polarimetric radar on Okinawa Island successfully observed large-scale bird migrations over the western Pacific Ocean. The birds generated interesting polarimetric signatures. This paper describes the signatures and speculates bird behavior.

  12. Grain-boundary migration in KCl bicrystals

    NASA Technical Reports Server (NTRS)

    Gibbon, C. F.

    1968-01-01

    Boundary migration in melt-grown bicrystals of KCl containing pure twist boundaries was investigated. The experiments involve the use of bicrystal specimens in the shape of right-triangular prisms with the boundary parallel to one side.

  13. Implication of Migration Pattern For Critical Parameters

    NASA Astrophysics Data System (ADS)

    Wu, Y.; Rundle, J. B.

    2012-12-01

    Seismicity migration has been shown by improved pattern informatics (PI) method in retrospective studies. The retrospective studies also show that the migration patterns are dependent on the tectonic setting and parameters used in statistical calculation. For the purpose of a forecast, the critical parameters for a specified efficient forecast period have to be learned. In this study we propose that a forecast and its critical parameters, that is, the magnitude and precursory time, can be learned from a series of empirical migration patterns. We also make the forecast with half year of efficient forecast period for three densely populated seismic regions in Taiwan, Japan, and California based on the migration patterns. The seismic catalog in each region was cut in depth according to the seismogenic layer. Considering the activity of seismicity, the cut magnitudes Mc are given at 3.0, 3.5, and 4.0. The magnitude Mt of the target events are 5.0, 5.5, and 6.0, but the eventual magnitude of the event which can be forecast was determined by the performance of the migration pattern. We calculate the migration pattern with different cut magnitudes and time parameters and count the number of migration hotspots Nhs and the number of hit hotspots Nhit; the migration hotspots means the grids which seismicity migrate toward and the hit hotspots are the migration hotspots with M>Mt target events occurred in the following efficient time on them. The performance of the migration pattern depends both on the ratio of the number of hit hotspots Nhit to the number of target event Nevent which occurred in the following efficient time and the ratio Nhit/Nhs. Giving the criteria of the performance that highest Nhit/Nhs with Nhit/Nevent=1, we obtained the critical parameters for each region. In western Taiwan, the M>=5 events can be forecast using earthquakes with cut magnitude 4.0 and the total precursory time could be about 2.5 years. In Kanto region, the M>=5 events can be forecast

  14. Migration and Marriage: Modeling the Joint Process

    PubMed Central

    Jang, Joy Bohyun; Casterline, John B; Snyder, Anastasia

    2016-01-01

    Background Previous research on inter-relations between migration and marriage has relied on overly simplistic assumptions about the structure of dependency between the two events. However, there is good reason to posit that each of the two transitions has an impact on the likelihood of the other, and that unobserved common factors may affect both migration and marriage, leading to a distorted impression of the causal impact of one on the other. Objective We will investigate relationships between migration and marriage in the United States using data from the National Longitudinal Survey of Youth 1979. We allow for inter-dependency between the two events and examine whether unobserved common factors affect the estimates of both migration and marriage. Methods We estimate a multi-process model in which migration and marriage are considered simultaneously in regression analysis and there is allowance for correlation between disturbances; the latter feature accounts for possible endogeneity between shared unobserved determinants. The model also includes random effects for persons, exploiting the fact that many people experience both events multiple times throughout their lives. Results Unobserved factors appear to significantly influence both migration and marriage, resulting in upward bias in estimates of the effects of each on the other when these shared common factors are not accounted for. Estimates from the multi-process model indicate that marriage significantly increases the hazard of migration while migration does not affect the hazard of marriage. Conclusions Omitting inter-dependency between life course events can lead to a mistaken impression of the direct effects of certain features of each event on the other. PMID:27182198

  15. Multicore Considerations for Legacy Flight Software Migration

    NASA Technical Reports Server (NTRS)

    Vines, Kenneth; Day, Len

    2013-01-01

    In this paper we will discuss potential benefits and pitfalls when considering a migration from an existing single core code base to a multicore processor implementation. The results of this study present options that should be considered before migrating fault managers, device handlers and tasks with time-constrained requirements to a multicore flight software environment. Possible future multicore test bed demonstrations are also discussed.

  16. Visualizing Human Migration Trhough Space and Time

    NASA Astrophysics Data System (ADS)

    Zambotti, G.; Guan, W.; Gest, J.

    2015-07-01

    Human migration has been an important activity in human societies since antiquity. Since 1890, approximately three percent of the world's population has lived outside of their country of origin. As globalization intensifies in the modern era, human migration persists even as governments seek to more stringently regulate flows. Understanding this phenomenon, its causes, processes and impacts often starts from measuring and visualizing its spatiotemporal patterns. This study builds a generic online platform for users to interactively visualize human migration through space and time. This entails quickly ingesting human migration data in plain text or tabular format; matching the records with pre-established geographic features such as administrative polygons; symbolizing the migration flow by circular arcs of varying color and weight based on the flow attributes; connecting the centroids of the origin and destination polygons; and allowing the user to select either an origin or a destination feature to display all flows in or out of that feature through time. The method was first developed using ArcGIS Server for world-wide cross-country migration, and later applied to visualizing domestic migration patterns within China between provinces, and between states in the United States, all through multiple years. The technical challenges of this study include simplifying the shapes of features to enhance user interaction, rendering performance and application scalability; enabling the temporal renderers to provide time-based rendering of features and the flow among them; and developing a responsive web design (RWD) application to provide an optimal viewing experience. The platform is available online for the public to use, and the methodology is easily adoptable to visualizing any flow, not only human migration but also the flow of goods, capital, disease, ideology, etc., between multiple origins and destinations across space and time.

  17. Irish return migration in the nineteenth century.

    PubMed

    Hart, M

    1985-01-01

    This study is concerned with return migration to Ireland from the United States during the nineteenth century. The author first notes that the rate of return migration was relatively low. Reasons for returning are then considered, including inheritance and poor health. Data on 671 Irish returnees from passenger lists of ships arriving in the United Kingdom from the United States between 1858 and 1867 are analyzed with regard to sex, marital status, age, occupations, and impact of returnees.

  18. Nocturnal bird migration in opaque clouds

    NASA Technical Reports Server (NTRS)

    Griffin, D. R.

    1972-01-01

    The use of a tracking radar to measure the flight paths of migrating birds on nights with opaque clouds is discussed. The effects of wind and lack of visual references are examined. The limitations of the radar observations are described, and samples of tracks obtained during radar observations are included. It is concluded that nonvisual mechanisms of orientation make it possible for birds to migrate in opaque clouds, but the exact nature of the sensory information cannot be determined by radar observations.

  19. African return migration: past, present, and future.

    PubMed

    Gregory, J W; Piche, V

    1983-01-01

    The various forms of return migration in Africa in the twentieth century are first examined, and the factors affecting them are discussed. The authors then consider the value of the household, rather than the individual, as the unit of analysis. Return migration is also analyzed in terms of the linking role it plays between Africa's capitalist and non-capitalist countries. Finally, alternative future trends in the circulatory flow of African labor are considered.

  20. Gendered Patterns of Migration in Rural South Africa.

    PubMed

    Camlin, Carol S; Snow, Rachel C; Hosegood, Victoria

    2014-08-01

    Gender is increasingly recognized as fundamental to understanding migration processes, causes and consequences. In South Africa, it is intrinsic to the social transformations fueling high levels of internal migration and complex forms of mobility. While female migration in Africa has often been characterized as less prevalent than male migration, and primarily related to marriage, in South Africa a feminization of internal migration is underway, fueled by women's increasing labor market participation. In this paper, we report sex differences in patterns, trends and determinants of internal migration based on data collected in a demographic surveillance system between 2001 and 2006 in rural KwaZulu-Natal. We show that women were somewhat more likely than men to undertake any migration, but sex differences in migration trends differed by migration flow, with women more likely to migrate into the area than men, and men more likely to out-migrate. Out-migration was suppressed by marriage particularly for women, but most women were not married; both men's and women's out-migrations were undertaken mainly for purposes of employment. Over half of female out-migrations (versus 35% of male out-migrations) were to nearby rural areas. The findings highlight the high mobility of this population and the extent to which gender is intimately related to the processes determining migration. We consider the implications of these findings for the measurement of migration and mobility, in particular for health and social policy and research among highly mobile populations in southern Africa.

  1. Entropy measures of collective cell migration

    NASA Astrophysics Data System (ADS)

    Whitby, Ariadne; Parrinello, Simona; Faisal, Aldo

    2015-03-01

    Collective cell migration is a critical process during tissue formation and repair. To this end there is a need to develop tools to quantitatively measure the dynamics of collective cell migration obtained from microscopy data. Drawing on statistical physics we use entropy of velocity fields derived from dense optic flow to quantitatively measure collective migration. Using peripheral nerve repair after injury as experimental system, we study how Schwann cells, guided by fibroblasts, migrate in cord-like structures across the cut, paving a highway for neurons. This process of emergence of organised behaviour is key for successful repair, yet the emergence of leader cells and transition from a random to ordered state is not understood. We find fibroblasts induce correlated directionality in migrating Schwann cells as measured by a decrease in the entropy of motion vector. We show our method is robust with respect to image resolution in time and space, giving a principled assessment of how various molecular mechanisms affect macroscopic features of collective cell migration. Finally, the generality of our method allows us to process both simulated cell movement and microscopic data, enabling principled fitting and comparison of in silico to in vitro. ICCS, Imperial College London & MRC Clinical Sciences Centre.

  2. Satellite And Propeller Migration In Saturn's Rings

    NASA Astrophysics Data System (ADS)

    Crida, Aurelien; Charnoz, S.; Papaloizou, J.; Salmon, J.

    2009-09-01

    Saturn's rings host satellites like Pan and Daphnis, and smaller bodies like the recently discovered propellers (Tiscareno et al. 2006). These bodies interact gravitationally with the rings. Actually, the resulting perturbations on the ring system have revealed the presence of embedded objects (the Encke and Keeler gaps associated with Pan and Daphnis respectively, the little two-folded structures called propellers tracing the scattering of ring particles by some embedded small objects). Reciprocally, the rings must act on the embedded bodies, leading to their migration. Here, we study how the standard theory of planetary migration applies in Saturn's ring, where the pressure is negligible in contrast with standard protoplanetary disks. Pan and Daphnis should be in standard type II migration, governed by the global disk evolution. Therefore, their presence and position provide constraints on the history of the A-ring, which can be studied using numerical simulations of disk-satellite interactions. The propellers are fully embedded in the disc, and therefore should be subject to type I migration. The simple impulse approximation used by Lin and Papaloi zou (1979) to derive the one-sided torque is particularly suited to this case. Refining their calculation, taking density variations into account, and discussing the possibility for these bodies to enter the type III, runaway regime of migration, we aim at estimating a possible migration rate for these propellers, to be compared to the system life time.

  3. On determinants of migration in West Bengal.

    PubMed

    Roy, N C

    1987-10-01

    The migration flow to West Bengal from different parts of the Indian subcontinent is an old phenomenon which can be traced to the beginning of the 19th century when the process of industrialization began in the areas comprising the present West Bengal. As West Bengal gradually industrialized and urbanized, the migration flow which was an equiliberating process up to 1947 turned into a stagnating mechanism in the economic sphere. This paper attempts to treat the causative process generating migration flows into West Bengal. Some popular hypotheses are tested, and their inadequacies in the case of migration in West Bengal are shown. Then a variable incorporating the expected long-run socioeconomic condition of West Bengal vis-a-vis the states/countries belonging to the migration universe of West Bengal was constructed, and this expectational variable appears to have more explanatory power than the observed income differential. Barring the political factor which played the central role in the case of immigration from Bangladesh, the determinants can be ranked in order of importance as 1) linguistic distance, 2) expected socioeconomic condition, and 3) physical distance. The limitation of the framework used is the scaling of linguistic distance and the inability to treat the political variable in a causal matrix of migration.

  4. Integrating meteorology into research on migration.

    PubMed

    Shamoun-Baranes, Judy; Bouten, Willem; van Loon, E Emiel

    2010-09-01

    Atmospheric dynamics strongly influence the migration of flying organisms. They affect, among others, the onset, duration and cost of migration, migratory routes, stop-over decisions, and flight speeds en-route. Animals move through a heterogeneous environment and have to react to atmospheric dynamics at different spatial and temporal scales. Integrating meteorology into research on migration is not only challenging but it is also important, especially when trying to understand the variability of the various aspects of migratory behavior observed in nature. In this article, we give an overview of some different modeling approaches and we show how these have been incorporated into migration research. We provide a more detailed description of the development and application of two dynamic, individual-based models, one for waders and one for soaring migrants, as examples of how and why to integrate meteorology into research on migration. We use these models to help understand underlying mechanisms of individual response to atmospheric conditions en-route and to explain emergent patterns. This type of models can be used to study the impact of variability in atmospheric dynamics on migration along a migratory trajectory, between seasons and between years. We conclude by providing some basic guidelines to help researchers towards finding the right modeling approach and the meteorological data needed to integrate meteorology into their own research. PMID:20811515

  5. Effect of Migration on Population Dynamics

    NASA Astrophysics Data System (ADS)

    Magdoń, Maria S.

    Computer studies of evolution in migrating population are presented. The model is based on the Penna model. Migration for better living conditions does influence population dynamics in different locations. Examples of different scenarios of preferences to live in bigger or smaller populations (or environmental capacity, or living space available) are discussed. In the limiting case of low migration intensity, each location evolves independently according to its local rules and conditions, as expected. With increasing migration, the population distribution between locations changes, including the critical behavior of extinction of population for some locations for a specific set of the rules. Then, the deserted location may become populated again if the migration is still increasing as result of a pressure to move. The present version is devoted to the migration controlled exclusively by environmental factors, yet the model is primarily designed to describe both inherited mutations on environmental factors and can be used to study the effect of different races mixing, or recovery of environmental capacity of the fields when chasing 2 flocks of geese in a cyclic manner across 3 fields.

  6. Integrating meteorology into research on migration.

    PubMed

    Shamoun-Baranes, Judy; Bouten, Willem; van Loon, E Emiel

    2010-09-01

    Atmospheric dynamics strongly influence the migration of flying organisms. They affect, among others, the onset, duration and cost of migration, migratory routes, stop-over decisions, and flight speeds en-route. Animals move through a heterogeneous environment and have to react to atmospheric dynamics at different spatial and temporal scales. Integrating meteorology into research on migration is not only challenging but it is also important, especially when trying to understand the variability of the various aspects of migratory behavior observed in nature. In this article, we give an overview of some different modeling approaches and we show how these have been incorporated into migration research. We provide a more detailed description of the development and application of two dynamic, individual-based models, one for waders and one for soaring migrants, as examples of how and why to integrate meteorology into research on migration. We use these models to help understand underlying mechanisms of individual response to atmospheric conditions en-route and to explain emergent patterns. This type of models can be used to study the impact of variability in atmospheric dynamics on migration along a migratory trajectory, between seasons and between years. We conclude by providing some basic guidelines to help researchers towards finding the right modeling approach and the meteorological data needed to integrate meteorology into their own research.

  7. Cell migration in the postnatal subventricular zone.

    PubMed

    Menezes, J R L; Marins, M; Alves, J A J; Froes, M M; Hedin-Pereira, C

    2002-12-01

    New neurons are constantly added to the olfactory bulb of rodents from birth to adulthood. This accretion is not only dependent on sustained neurogenesis, but also on the migration of neuroblasts and immature neurons from the cortical and striatal subventricular zone (SVZ) to the olfactory bulb. Migration along this long tangential pathway, known as the rostral migratory stream (RMS), is in many ways opposite to the classical radial migration of immature neurons: it is faster, spans a longer distance, does not require radial glial guidance, and is not limited to postmitotic neurons. In recent years many molecules have been found to be expressed specifically in this pathway and to directly affect this migration. Soluble factors with inhibitory, attractive and inductive roles in migration have been described, as well as molecules mediating cell-to-cell and cell-substrate interactions. However, it is still unclear how the various molecules and cells interact to account for the special migratory behavior in the RMS. Here we will propose some candidate mechanisms for roles in initiating and stopping SVZ/RMS migration.

  8. Integrating Meteorology into Research on Migration

    PubMed Central

    Shamoun-Baranes, Judy; Bouten, Willem; van Loon, E. Emiel

    2010-01-01

    Atmospheric dynamics strongly influence the migration of flying organisms. They affect, among others, the onset, duration and cost of migration, migratory routes, stop-over decisions, and flight speeds en-route. Animals move through a heterogeneous environment and have to react to atmospheric dynamics at different spatial and temporal scales. Integrating meteorology into research on migration is not only challenging but it is also important, especially when trying to understand the variability of the various aspects of migratory behavior observed in nature. In this article, we give an overview of some different modeling approaches and we show how these have been incorporated into migration research. We provide a more detailed description of the development and application of two dynamic, individual-based models, one for waders and one for soaring migrants, as examples of how and why to integrate meteorology into research on migration. We use these models to help understand underlying mechanisms of individual response to atmospheric conditions en-route and to explain emergent patterns. This type of models can be used to study the impact of variability in atmospheric dynamics on migration along a migratory trajectory, between seasons and between years. We conclude by providing some basic guidelines to help researchers towards finding the right modeling approach and the meteorological data needed to integrate meteorology into their own research. PMID:20811515

  9. On determinants of migration in West Bengal.

    PubMed

    Roy, N C

    1987-10-01

    The migration flow to West Bengal from different parts of the Indian subcontinent is an old phenomenon which can be traced to the beginning of the 19th century when the process of industrialization began in the areas comprising the present West Bengal. As West Bengal gradually industrialized and urbanized, the migration flow which was an equiliberating process up to 1947 turned into a stagnating mechanism in the economic sphere. This paper attempts to treat the causative process generating migration flows into West Bengal. Some popular hypotheses are tested, and their inadequacies in the case of migration in West Bengal are shown. Then a variable incorporating the expected long-run socioeconomic condition of West Bengal vis-a-vis the states/countries belonging to the migration universe of West Bengal was constructed, and this expectational variable appears to have more explanatory power than the observed income differential. Barring the political factor which played the central role in the case of immigration from Bangladesh, the determinants can be ranked in order of importance as 1) linguistic distance, 2) expected socioeconomic condition, and 3) physical distance. The limitation of the framework used is the scaling of linguistic distance and the inability to treat the political variable in a causal matrix of migration. PMID:12281036

  10. Husbands’ Labour Migration and Wives’ Autonomy

    PubMed Central

    Yabiku, Scott T.; Agadjanian, Victor; Sevoyan, Arusyak

    2010-01-01

    Labour migration leads to significant changes in origin areas. The separation of migrants from the family unit, whether it is nuclear or extended, has profound implications for family organization and for individual family members. We examined the relationship between men’s labour migration and the decision-making autonomy of women who stay behind. The data for our analyses came from a 2006 survey of 1680 married women from 56 rural villages in southern Mozambique. We find that both men’s cumulative migration history and current migration status are positively associated with women’s autonomy. The results suggest that the impact of men’s labour migration on women’s autonomy may persist even after the man’s return. Three intervening factors — women’s employment outside the home, lower fertility, and residential independence from extended family members—did not fully mediate the effects of men’s labour migration. This is consistent with a “direct” impact of men’s absence on women’s autonomy. PMID:20865630

  11. Changes in leucocyte migration after renal transplantation

    PubMed Central

    Smith, M. G. M.; Eddleston, A. L. W. F.; Dominguez, J. A.; Evans, D. B.; Bewick, M.; Williams, Roger

    1969-01-01

    The leucocyte migration test, an in-vitro measure of cellular immunity, has been used to follow the changes in cell-mediated hypersensitivity to kidney and histocompatibility antigens in three patients after renal transplantation. Inhibition of leucocyte migration, indicating strong sensitization to the antigens used, occurred in each patient, starting five to seven days after transplantation. Satisfactory renal function had not been established in any of the patients at this time. In one case inhibition of leucocyte migration persisted almost continuously until the 24th day and was associated with poor renal function proved histologically to be due to rejection. Treatment with increased dosage of prednisone was associated with a rapid reversion to normal of the migration index and improvement in renal function. Later, inhibition of migration occurred again, and shortly afterwards the graft ceased to function. In the other two cases the migration index became normal without alteration in immunosuppressive therapy and a satisfactory diuresis followed. It is suggested that this simple test should prove useful in the specific diagnosis of rejection and in control of immunosuppressive therapy. ImagesFig. 3Fig. 4 PMID:4899455

  12. Pushing the Pace of Tree Species Migration

    PubMed Central

    Lazarus, Eli D.; McGill, Brian J.

    2014-01-01

    Plants and animals have responded to past climate changes by migrating with habitable environments, sometimes shifting the boundaries of their geographic ranges by tens of kilometers per year or more. Species migrating in response to present climate conditions, however, must contend with landscapes fragmented by anthropogenic disturbance. We consider this problem in the context of wind-dispersed tree species. Mechanisms of long-distance seed dispersal make these species capable of rapid migration rates. Models of species-front migration suggest that even tree species with the capacity for long-distance dispersal will be unable to keep pace with future spatial changes in temperature gradients, exclusive of habitat fragmentation effects. Here we present a numerical model that captures the salient dynamics of migration by long-distance dispersal for a generic tree species. We then use the model to explore the possible effects of assisted colonization within a fragmented landscape under a simulated tree-planting scheme. Our results suggest that an assisted-colonization program could accelerate species-front migration rates enough to match the speed of climate change, but such a program would involve an environmental-sustainability intervention at a massive scale. PMID:25162663

  13. Centrosome Positioning in 1D Cell Migration

    NASA Astrophysics Data System (ADS)

    Adlerz, Katrina; Aranda-Espinoza, Helim

    During cell migration, the positioning of the centrosome and nucleus define a cell's polarity. For a cell migrating on a two-dimensional substrate the centrosome is positioned in front of the nucleus. Under one-dimensional confinement, however, the centrosome is positioned behind the nucleus in 60% of cells. It is known that the centrosome is positioned by CDC42 and dynein for cells moving on a 2D substrate in a wound-healing assay. It is currently unknown, however, if this is also true for cells moving under 1D confinement, where the centrosome position is often reversed. Therefore, centrosome positioning was studied in cells migrating under 1D confinement, which mimics cells migrating through 3D matrices. 3 to 5 μm fibronectin lines were stamped onto a glass substrate and cells with fluorescently labeled nuclei and centrosomes migrated on the lines. Our results show that when a cell changes directions the centrosome position is maintained. That is, when the centrosome is between the nucleus and the cell's trailing edge and the cell changes direction, the centrosome will be translocated across the nucleus to the back of the cell again. A dynein inhibitor did have an influence on centrosome positioning in 1D migration and change of directions.

  14. Hierarchically organized migration fields: the application of higher order factor analysis to population migration tables.

    PubMed

    Clayton, C

    1982-07-01

    "The structure of human geographical systems is often of a hierarchical nature. Population migration systems can usefully be conceptualized as a series of hierarchically related levels of migration fields: the fields at one level nesting within the fields at the next higher level. Such migration fields and the relationships between different levels can be extracted from large population migration origin-destination matrices with the aid of higher order factor analysis." A case study of the western United States illustrating the application of higher order factor analysis to large interaction matrices is presented.

  15. Migration and risk: net migration in marginal ecosystems and hazardous areas

    NASA Astrophysics Data System (ADS)

    de Sherbinin, Alex; Levy, Marc; Adamo, Susana; MacManus, Kytt; Yetman, Greg; Mara, Valentina; Razafindrazay, Liana; Goodrich, Benjamin; Srebotnjak, Tanja; Aichele, Cody; Pistolesi, Linda

    2012-12-01

    The potential for altered ecosystems and extreme weather events in the context of climate change has raised questions concerning the role that migration plays in either increasing or reducing risks to society. Using modeled data on net migration over three decades from 1970 to 2000, we identify sensitive ecosystems and regions at high risk of climate hazards that have seen high levels of net in-migration and out-migration over the time period. This paper provides a literature review on migration related to ecosystems, briefly describes the methodology used to develop the estimates of net migration, then uses those data to describe the patterns of net migration for various ecosystems and high risk regions. The study finds that negative net migration generally occurs over large areas, reflecting its largely rural character, whereas areas of positive net migration are typically smaller, reflecting its largely urban character. The countries with largest population such as China and India tend to drive global results for all the ecosystems found in those countries. Results suggest that from 1970 to 2000, migrants in developing countries have tended to move out of marginal dryland and mountain ecosystems and out of drought-prone areas, and have moved towards coastal ecosystems and areas that are prone to floods and cyclones. For North America results are reversed for dryland and mountain ecosystems, which saw large net influxes of population in the period of record. Uncertainties and potential sources of error in these estimates are addressed.

  16. Conceptualising Irish rural youth migration: a biographical approach.

    PubMed

    Ni Laoire, C

    2000-01-01

    This paper explores the usefulness of a biographical approach in studying Irish rural youth migration. There have been calls recently for an approach to migration study that involves conceptualizing migration as part of individual biographies as well as social structures. However, there is little research that explicitly adopts a biographical approach. This paper presents the theoretical underpinnings, methodological issues and findings of a recent study that was guided by the principles of a biographical approach to migration. The study was an exploration of life-path formation among Irish rural youth from the 1970s to the 1990s. The paper focuses on the three key elements of a biographical approach to migration, and relates them to Irish rural youth migration. Firstly, migration is considered as part of an individual's biography, and the methodological implications of this are explored. Secondly, it is argued, drawing on the research in Ireland, that migration decision-making is a multilayered process. In the case of Irish rural youth migration, a biographical approach highlights the complexity of migration decision-making, revealing the tensions and struggles that lie behind each move, and thus raises questions over the tendency towards simplification of the migration process. Finally, it is argued that migration is a cultural phenomenon, but that this assertion needs careful qualification. This paper problematizes the role of culture in migration processes by untangling the systems of competing discourses of migration that underlie societal norms regarding migration, thereby challenging the view of migration as "normal" for particular societies or cultures.

  17. Social Dynamics of Return Migration to Puerto Rico.

    ERIC Educational Resources Information Center

    de Cintron, Celia Fernandez; Vales, Pedro A.

    The sociological elements associated with the process of return migration such as the motivations responsible for, or associated not only with return migration but with the migration process in general, are addressed in this investigation. Among the questions that guide the research problem are the following: the meaning of migration and of return…

  18. Residence and Migration of College Students. Working Paper Series.

    ERIC Educational Resources Information Center

    Christal, Melodie E.

    Results from the National Center for Education Statistics' (NCES) 1979 Residence and Migration survey that are particularly relevant to higher education policy issues are discussed. Data are provided on the rankings of states by net in-migration and net out-migration of first-time freshmen, and the net migration of first-time freshmen,…

  19. History of migration studies in biological anthropology.

    PubMed

    Mascie-Taylor, C G Nicholas; Little, Michael A

    2004-01-01

    The earliest studies of human biological factors in migration in which a clear research design was employed date back to the early 20th century in the United States. Maurice Fishberg's study of Jewish migrants, published in 1905, antedated the classic study of Franz Boas initiated in 1908. There have been two main approaches. The first approach examined the impact of migration in relation to changing environment and the importance of environmental plasticity. For example, Fishberg reported that migrants had offspring different in stature from themselves and with differences thought to be due to improvements in the environment, although some selection of genetically determined traits was suggested. Subsequently, a number of research designs have been used, ranging from Boas's simple design of sedente (nonmigrant) adults and children compared with first- and second-generation migrants; Shapiro's extension of this study in Japanese migrants to Hawai'i; Goldstein's four-fold comparison of Mexican sedentes and their offspring in Mexico, and migrants to the USA and their offspring in the USA; and Lasker's extension of Goldstein's Mexican study by including comparison of sedentes with returning emigrants. More sophisticated designs were used by Harrison and Baker in examining altitude effects and changes in subsistence and lifestyle during the 1960s through to the 1980s. The second approach has focused on the effect of migration on gene flow. For example, the clinal variation of ABO blood groups in Europe and Australia is generally purported to result from past migration, although increasing random migration for blood groups is likely to eliminate clinal variation. Migration has usually been considered from a spatial (geographic) perspective, but more recent studies have also investigated the impact of social or occupational movement (social mobility) alone, or in combination with geographic migration, and tested whether such movements are selective or random for a number

  20. Neptune's Orbital Migration Was Grainy, Not Smooth

    NASA Astrophysics Data System (ADS)

    Nesvorný, David; Vokrouhlický, David

    2016-07-01

    The Kuiper Belt is a population of icy bodies beyond the orbit of Neptune. The complex orbital structure of the Kuiper Belt, including several categories of objects inside and outside of resonances with Neptune, emerged as a result of Neptune’s migration into an outer planetesimal disk. An outstanding problem with the existing migration models is that they invariably predict excessively large resonant populations, while observations show that the non-resonant orbits are in fact common (e.g., the main belt population is ≃2-4 times larger than Plutinos in the 3:2 resonance). Here we show that this problem can be resolved if it is assumed that Neptune’s migration was grainy, as expected from scattering encounters of Neptune with massive planetesimals. The grainy migration acts to destabilize resonant bodies with large libration amplitudes, a fraction of which ends up on stable non-resonant orbits. Thus, the non-resonant-to-resonant ratio obtained with the grainy migration is higher, up to ˜10 times higher for the range of parameters investigated here, than in a model with smooth migration. In addition, the grainy migration leads to a narrower distribution of the libration amplitudes in the 3:2 resonance. The best fit to observations is obtained when it is assumed that the outer planetesimal disk below 30 au contained 1000-4000 Plutos. We estimate that the combined mass of Pluto-class objects in the original disk represented 10%-40% of the estimated disk mass ({M}{{disk}}≃ 20 {M}{{Earth}}). This constraint can be used to better understand the accretion processes in the outer solar system.

  1. Neptune's Orbital Migration Was Grainy, Not Smooth

    NASA Astrophysics Data System (ADS)

    Nesvorný, David; Vokrouhlický, David

    2016-07-01

    The Kuiper Belt is a population of icy bodies beyond the orbit of Neptune. The complex orbital structure of the Kuiper Belt, including several categories of objects inside and outside of resonances with Neptune, emerged as a result of Neptune’s migration into an outer planetesimal disk. An outstanding problem with the existing migration models is that they invariably predict excessively large resonant populations, while observations show that the non-resonant orbits are in fact common (e.g., the main belt population is ≃2–4 times larger than Plutinos in the 3:2 resonance). Here we show that this problem can be resolved if it is assumed that Neptune’s migration was grainy, as expected from scattering encounters of Neptune with massive planetesimals. The grainy migration acts to destabilize resonant bodies with large libration amplitudes, a fraction of which ends up on stable non-resonant orbits. Thus, the non-resonant-to-resonant ratio obtained with the grainy migration is higher, up to ˜10 times higher for the range of parameters investigated here, than in a model with smooth migration. In addition, the grainy migration leads to a narrower distribution of the libration amplitudes in the 3:2 resonance. The best fit to observations is obtained when it is assumed that the outer planetesimal disk below 30 au contained 1000–4000 Plutos. We estimate that the combined mass of Pluto-class objects in the original disk represented 10%–40% of the estimated disk mass ({M}{{disk}}≃ 20 {M}{{Earth}}). This constraint can be used to better understand the accretion processes in the outer solar system.

  2. History of migration studies in biological anthropology.

    PubMed

    Mascie-Taylor, C G Nicholas; Little, Michael A

    2004-01-01

    The earliest studies of human biological factors in migration in which a clear research design was employed date back to the early 20th century in the United States. Maurice Fishberg's study of Jewish migrants, published in 1905, antedated the classic study of Franz Boas initiated in 1908. There have been two main approaches. The first approach examined the impact of migration in relation to changing environment and the importance of environmental plasticity. For example, Fishberg reported that migrants had offspring different in stature from themselves and with differences thought to be due to improvements in the environment, although some selection of genetically determined traits was suggested. Subsequently, a number of research designs have been used, ranging from Boas's simple design of sedente (nonmigrant) adults and children compared with first- and second-generation migrants; Shapiro's extension of this study in Japanese migrants to Hawai'i; Goldstein's four-fold comparison of Mexican sedentes and their offspring in Mexico, and migrants to the USA and their offspring in the USA; and Lasker's extension of Goldstein's Mexican study by including comparison of sedentes with returning emigrants. More sophisticated designs were used by Harrison and Baker in examining altitude effects and changes in subsistence and lifestyle during the 1960s through to the 1980s. The second approach has focused on the effect of migration on gene flow. For example, the clinal variation of ABO blood groups in Europe and Australia is generally purported to result from past migration, although increasing random migration for blood groups is likely to eliminate clinal variation. Migration has usually been considered from a spatial (geographic) perspective, but more recent studies have also investigated the impact of social or occupational movement (social mobility) alone, or in combination with geographic migration, and tested whether such movements are selective or random for a number

  3. Migration in Vulnerable Deltas: A Research Strategy

    NASA Astrophysics Data System (ADS)

    Hutton, C.; Nicholls, R. J.; Allan, A.

    2015-12-01

    C. Hutton1, & R. J. Nicholls1, , 1 University of Southampton, University Road, Southampton, Hampshire, United Kingdom, SO17 1BJ. cwh@geodata. soton.ac.ukAbstractGlobally, deltas contain 500 million people and with rising sea levels often linked to large number of forced migrants are expected in the coming century. However, migration is already a major process in deltas, such as the growth of major cities such as Dhaka and Kolkata. Climate and environmental change interacts with a range of catchment and delta level drivers, which encompass a nexus of sea-level rise, storms, freshwater and sediment supply from the catchment, land degradation, subsidence, agricultural loss and socio-economic stresses. DECCMA (Deltas, Vulnerability and Climate Change: Migration and Adaptation/CARRIA) is investigating migration in the Ganges-Brahmaputra-Meghna (GBM), Mahanadi and Volta Deltas, including the influence of climate change. The research will explore migration from a range of perspectives including governance and stakeholder analysis, demographic analysis, household surveys of sending and receiving areas, macro-economic analysis, and hazards and hotspot analysis both historically and into the future. Migration under climate change will depend on other adaptation in the deltas and this will be examined. Collectively, integrated analysis will be developed to examine migration, other adaptation and development pathways with a particular focus on the implications for the poorest. This will require the development of input scenarios, including expert-derived exogenous scenarios (e.g., climate change) and endogenous scenarios of the delta developed in a participatory manner. This applied research will facilitate decision support methods for the development of deltas under climate change, with a focus on migration and other adaptation strategies.

  4. MIGRATION OF SMALL MOONS IN SATURN's RINGS

    SciTech Connect

    Bromley, Benjamin C.; Kenyon, Scott J. E-mail: skenyon@cfa.harvard.edu

    2013-02-20

    The motions of small moons through Saturn's rings provide excellent tests of radial migration models. In theory, torque exchange between these moons and ring particles leads to radial drift. We predict that moons with Hill radii r {sub H} {approx} 2-24 km should migrate through the A ring in 1000 yr. In this size range, moons orbiting in an empty gap or in a full ring eventually migrate at the same rate. Smaller moons or moonlets-such as the propellers-are trapped by diffusion of disk material into corotating orbits, creating inertial drag. Larger moons-such as Pan or Atlas-do not migrate because of their own inertia. Fast migration of 2-24 km moons should eliminate intermediate-size bodies from the A ring and may be responsible for the observed large-radius cutoff of r {sub H} {approx} 1-2 km in the size distribution of the A ring's propeller moonlets. Although the presence of Daphnis (r {sub H} Almost-Equal-To 5 km) inside the Keeler gap challenges this scenario, numerical simulations demonstrate that orbital resonances and stirring by distant, larger moons (e.g., Mimas) may be important factors. For Daphnis, stirring by distant moons seems the most promising mechanism to halt fast migration. Alternatively, Daphnis may be a recent addition to the ring that is settling into a low inclination orbit in {approx}10{sup 3} yr prior to a phase of rapid migration. We provide predictions of observational constraints required to discriminate among possible scenarios for Daphnis.

  5. TOWARD CHEMICAL CONSTRAINTS ON HOT JUPITER MIGRATION

    SciTech Connect

    Madhusudhan, Nikku; Amin, Mustafa A.; Kennedy, Grant M.

    2014-10-10

    The origin of hot Jupiters—gas giant exoplanets orbiting very close to their host stars—is a long-standing puzzle. Planet formation theories suggest that such planets are unlikely to have formed in situ but instead may have formed at large orbital separations beyond the snow line and migrated inward to their present orbits. Two competing hypotheses suggest that the planets migrated either through interaction with the protoplanetary disk during their formation, or by disk-free mechanisms such as gravitational interactions with a third body. Observations of eccentricities and spin-orbit misalignments of hot Jupiter systems have been unable to differentiate between the two hypotheses. In the present work, we suggest that chemical depletions in hot Jupiter atmospheres might be able to constrain their migration mechanisms. We find that sub-solar carbon and oxygen abundances in Jovian-mass hot Jupiters around Sun-like stars are hard to explain by disk migration. Instead, such abundances are more readily explained by giant planets forming at large orbital separations, either by core accretion or gravitational instability, and migrating to close-in orbits via disk-free mechanisms involving dynamical encounters. Such planets also contain solar or super-solar C/O ratios. On the contrary, hot Jupiters with super-solar O and C abundances can be explained by a variety of formation-migration pathways which, however, lead to solar or sub-solar C/O ratios. Current estimates of low oxygen abundances in hot Jupiter atmospheres may be indicative of disk-free migration mechanisms. We discuss open questions in this area which future studies will need to investigate.

  6. Endothelial cells enhance migration of meniscus cells

    PubMed Central

    Yuan, Xiaoning; Eng, George M.; Arkonac, Derya E.; Chao, Pen-hsiu Grace; Vunjak-Novakovic, Gordana

    2014-01-01

    Objective To study the interactions between vascular endothelial cells and meniscal fibrochondrocytes from the inner avascular and outer vascular regions of the meniscus, and identify angiogenic factors that enhance cell migration and integrative repair. Methods Bovine meniscal fibrochondrocytes (bMFCs) from the inner and outer regions of meniscus were cultured for seven days with and without human umbilical vein endothelial cells (HUVECs) in a micropatterned three-dimensional hydrogel system for cell migration. Angiogenic factors secreted by HUVECs were probed for their role in paracrine mechanisms governing bMFC migration, and applied to a full-thickness defect model of meniscal repair in explants from the inner and outer regions over four weeks. Results Endothelial cells enhanced migration of inner and outer bMFCs in the micropatterned system via endothelin-1 (ET-1) signaling. Supplementation of ET-1 significantly enhanced integration strength of full-thickness defects in inner and outer explants, and cell migration at the macro-scale, compared to controls without ET-1 treatment. Conclusion We report for the first time that bMFCs from both the avascular and vascular regions respond to the presence of endothelial cells with increased migration. Paracrine signaling by endothelial cells regulates the bMFCs differentially by region, but we identify ET-1 as an angiogenic factor that stimulates migration of inner and outer cells at the micro-scale, and integrative repair of inner and outer explants at the macro-scale. These findings reveal the regional interactions between vasculature and MFCs, and suggest ET-1 as a potential new treatment modality for avascular meniscal injuries, in order to prevent the development of osteoarthritis. PMID:25307081

  7. Chemistry and biology of the compounds that modulate cell migration.

    PubMed

    Tashiro, Etsu; Imoto, Masaya

    2016-03-01

    Cell migration is a fundamental step for embryonic development, wound repair, immune responses, and tumor cell invasion and metastasis. Extensive studies have attempted to reveal the molecular mechanisms behind cell migration; however, they remain largely unclear. Bioactive compounds that modulate cell migration show promise as not only extremely powerful tools for studying the mechanisms behind cell migration but also as drug seeds for chemotherapy against tumor metastasis. Therefore, we have screened cell migration inhibitors and analyzed their mechanisms for the inhibition of cell migration. In this mini-review, we introduce our chemical and biological studies of three cell migration inhibitors: moverastin, UTKO1, and BU-4664L.

  8. East-West migration in Europe: can migration theories help estimate the numbers?

    PubMed

    Oberg, S; Wils, A B

    1992-01-01

    "In this article, we discuss the types of scientific knowledge that could be used to estimate migration flows." Theories from the disciplines of economics, geography, geopolitics, sociology, demography, econometrics, and history are reviewed. The authors find that "each field provides a partial explanation of...migration flows." The geographical focus is on Europe. PMID:12286068

  9. Recovery Migration to the City of New Orleans after Hurricane Katrina: A Migration Systems Approach

    PubMed Central

    Fussell, Elizabeth; Curtis, Katherine J.; DeWaard, Jack

    2014-01-01

    Hurricane Katrina’s effect on the population of the City of New Orleans provides a model of how severe weather events, which are likely to increase in frequency and strength as the climate warms, might affect other large coastal cities. Our research focuses on changes in the migration system – defined as the system of ties between Orleans Parish and all other U.S. counties – between the pre-disaster (1999–2004) and recovery (2007–2009) periods. Using Internal Revenue Service county-to-county migration flow data, we find that in the recovery period Orleans Parish increased the number of migration ties with and received larger migration flows from nearby counties in the Gulf of Mexico coastal region, thereby spatially concentrating and intensifying the in-migration dimension of this predominantly urban system, while the out-migration dimension contracted and had smaller flows. We interpret these changes as the migration system relying on its strongest ties to nearby and less damaged counties to generate recovery in-migration. PMID:24729651

  10. Recovery Migration to the City of New Orleans after Hurricane Katrina: A Migration Systems Approach.

    PubMed

    Fussell, Elizabeth; Curtis, Katherine J; Dewaard, Jack

    2014-03-01

    Hurricane Katrina's effect on the population of the City of New Orleans provides a model of how severe weather events, which are likely to increase in frequency and strength as the climate warms, might affect other large coastal cities. Our research focuses on changes in the migration system - defined as the system of ties between Orleans Parish and all other U.S. counties - between the pre-disaster (1999-2004) and recovery (2007-2009) periods. Using Internal Revenue Service county-to-county migration flow data, we find that in the recovery period Orleans Parish increased the number of migration ties with and received larger migration flows from nearby counties in the Gulf of Mexico coastal region, thereby spatially concentrating and intensifying the in-migration dimension of this predominantly urban system, while the out-migration dimension contracted and had smaller flows. We interpret these changes as the migration system relying on its strongest ties to nearby and less damaged counties to generate recovery in-migration. PMID:24729651

  11. East-West migration in Europe: can migration theories help estimate the numbers?

    PubMed

    Oberg, S; Wils, A B

    1992-01-01

    "In this article, we discuss the types of scientific knowledge that could be used to estimate migration flows." Theories from the disciplines of economics, geography, geopolitics, sociology, demography, econometrics, and history are reviewed. The authors find that "each field provides a partial explanation of...migration flows." The geographical focus is on Europe.

  12. Emergence of oligarchy in collective cell migration

    NASA Astrophysics Data System (ADS)

    Schumacher, Linus; Maini, Philip; Baker, Ruth

    Identifying the principles of collective cell migration has the potential to help prevent birth defects, improve regenerative therapies and develop model systems for cancer metastasis. In collaboration with experimental biologists, we use computational simulations of a hybrid model, comprising individual-based stochastic cell movement coupled to a reaction-diffusion equation for a chemoattractant, to explore the role of cell specialisation in the guidance of collective cell migration. In the neural crest, an important migratory cell population in vertebrate embryo development, we present evidence that just a few cells are guiding group migration in a cell-induced chemoattractant gradient that determines the switch between ``leader'' and ``follower'' behaviour in individual cells. This leads us to more generally consider under what conditions cell specialisation might become advantageous for collective migration. Alternatively, individual cell responses to locally different microenvironmental conditions could create the (artefactual) appearance of heterogeneity in a population of otherwise identical cellular agents. We explore these questions using a self-propelled particle model as a minimal description for collective cell migration in two and three dimensions.

  13. Migration of helium-pair in metals

    NASA Astrophysics Data System (ADS)

    Cao, J. L.; Geng, W. T.

    2016-09-01

    We have carried out a first-principles density functional theory investigation into the migration of both a single interstitial He and an interstitial He-pair in Fe, Mo, W, Cu, Pd, and Pt. We find the migration trajectories and barriers are determined predominantly by low-energy He-pair configurations which depend mainly on the energy state of a single He in different interstices. The migration barrier for a He-pair in bcc metals is always slightly higher than for a single He. Configurations of a He-pair in fcc metals are very complicated, due to the existence of interstitial sites with nearly identical energy for a single He. The migration barrier for a He-pair is slightly lower than (in Cu), or similar to (in Pd and Pt) a single He. The collective migrations of a He-pair are ensured by strong Hesbnd He interactions with strength-versus-distance forms resembling chemical bonds and can be described with Morse potentials.

  14. Migration behavior of pronghorn in southeastern Idaho

    SciTech Connect

    Hoskinson, R.L.; Tester, J.R.

    1980-01-01

    Fifty-four pronghorn (Antilocapra americana) were radio-collared out of 232 captured on 3 winter ranges in southeastern Idaho. Radioed pronghorn were followed for up to 21 months each, from December 1975 through August 1977. Winter home ranges showed a difference (P < 0.005) in size among valleys the 1st winter and were different in size and location within valleys between years. Snow covered the ground 1 week earlier and lasted 3 weeks longer in 1975 to 1976 than in 1976 to 1977. Spring migration began more than 1 month earlier in 1977 than 1976, and appeared related to loss of snow cover on the winter ranges in both years. Distances that pronghorn migrated in spring 1976 were different among valleys (P < 0.05) but directions were, in general, upward to areas near the heads of the valleys. Summer home ranges of all radioed pronghorn averaged 2033 +- 322 (SE) ha. Yearlings wandered during summer and their home ranges were 2 to 5 times as large as ranges of adults. Fall migration in 1976 began after 1 October and was not prompted by snowfall. Percent moisture in vegetation is suggested as a stimulus for onset of fall migration, and snowfall is suggested as a factor influencing distance migrated and location of winter.

  15. A Missing Element in Migration Theories

    PubMed Central

    Massey, Douglas S.

    2016-01-01

    From the mid-1950s through the mid1980s, migration between Mexico and the United States constituted a stable system whose contours were shaped by social and economic conditions well-theorized by prevailing models of migration. It evolved as a mostly circular movement of male workers going to a handful of U.S. states in response to changing conditions of labor supply and demand north and south of the border, relative wages prevailing in each nation, market failures and structural economic changes in Mexico, and the expansion of migrant networks following processes specified by neoclassical economics, segmented labor market theory, the new economics of labor migration, social capital theory, world systems theory, and theoretical models of state behavior. After 1986, however, the migration system was radically transformed, with the net rate of migration increasing sharply as movement shifted from a circular flow of male workers going a limited set of destinations to a nationwide population of settled families. This transformation stemmed from a dynamic process that occurred in the public arena to bring about an unprecedented militarization of the Mexico-U.S. border, and not because of shifts in social, economic, or political factors specified in prevailing theories. In this paper I draw on earlier work to describe that dynamic process and demonstrate its consequences, underscoring the need for greater theoretical attention to the self-interested actions of politicians, pundits, and bureaucrats who benefit from the social construction and political manufacture of immigration crises when none really exist. PMID:27398085

  16. The Malaysian state's response to migration.

    PubMed

    Pillai, P

    1999-04-01

    This paper aims to provide a profile of migration trends in Malaysia since 1970 and to analyze public policy on migration in the context of economic growth and the labor market. The discussion centers on the impact of the Asian financial crisis. There is long history of immigration to Malaysia. The development strategy of the 1970s and 1980s was to create more jobs and restructure employment to meet equity goals. Labor shortages on plantations and construction booms led to a more organized, sustained effort to import labor. Recession in the mid-1980s led to unemployment, but many Malaysians were unwilling to work on plantations, in construction, or in low paying jobs. Economic growth during 1987-96 was very high, and labor shortages spread to service and manufacturing sectors. Migration policy has shifted over the decades. Both the market and the government's promotion of export-based industrialization require access to low cost migrant labor. Public and official recognition of the large number of migrants was not made until 1995. The financial crisis in 1998 led to enforcement of a new migration policy on illegal migrants and greater outflow of migrants. The economic crisis has increased job and income inequities in the region; this encourages continued migration. It is argued that it would be best for Malaysia to maximize short-term gains while minimizing long-term economic, social, and political costs.

  17. Acanthamoeba Migration in an Electric Field

    PubMed Central

    Rudell, Jolene Chang; Gao, Jing; Sun, Yuxin; Sun, Yaohui; Chodosh, James; Schwab, Ivan; Zhao, Min

    2013-01-01

    Purpose. We investigated the in vitro response of Acanthamoeba trophozoites to electric fields (EFs). Methods. Acanthamoeba castellanii were exposed to varying strengths of an EF. During EF exposure, cell migration was monitored using an inverted microscope equipped with a CCD camera and the SimplePCI 5.3 imaging system to capture time-lapse images. The migration of A. castellanii trophozoites was analyzed and quantified with ImageJ software. For analysis of cell migration in a three-dimensional culture system, Acanthamoeba trophozoites were cultured in agar, exposed to an EF, digitally video recorded, and analyzed at various Z focal planes. Results. Acanthamoeba trophozoites move at random in the absence of an EF, but move directionally in response to an EF. Directedness in the absence of an EF is 0.08 ± 0.01, while in 1200 mV/mm EF, directedness is significantly higher at −0.65 ± 0.01 (P < 0.001). We find that the trophozoite migration response is voltage-dependent, with higher directionality with higher voltage application. Acanthamoeba move directionally in a three-dimensional (3D) agar system as well when exposed to an EF. Conclusions. Acanthamoeba trophozoites move directionally in response to an EF in a two-dimensional and 3D culture system. Acanthamoeba trophozoite migration is also voltage-dependent, with increased directionality with increasing voltage. This may provide new treatment modalities for Acanthamoeba keratitis. PMID:23716626

  18. Stochastic Migration in a Dissipating Disk

    NASA Astrophysics Data System (ADS)

    Mills, Sean; Fabrycky, Daniel C.

    2016-10-01

    It is yet unclear whether the majority of planets formed in situ in their presently observed locations or if they formed distant from their current locations and migrated through the gas and dust protoplanetary disk extant early in their host star's lifetime. Migration simulations generally produce an abundance of planets near mean motion resonances (MMRs); however, statistical analysis of the observed population of exoplanets shows only a very modest enhancement of planets near MMRs and a large number in a continuum of period ratios. It has previously been suggested that migration through a turbulent, dissipating disk may disrupt the resonances formed via migration and approximately reproduce the period ratios of pairs of planets observed in planets observed by Kepler. Here we expand on this analysis to include more realistic dissipation and turbulence parameterizations and compare the results of our simulations to the architectures of higher multiplicity systems observed by Kepler as well as individual planet pairs. We thus place tighter constraints on the turbulence and dissipation properties of disks during planet formation and migration.

  19. Analytical fundamentals of migration in reflection seismics

    NASA Astrophysics Data System (ADS)

    Ray, Arnab K.

    2016-06-01

    We consider migration in reflection seismics from a completely analytical perspective. We review the basic geometrical ray-path approach to understanding the subject of migration, and discuss the limitations of this method. We stress the importance of the linear differential wave equation in migration. We also review briefly how a wavefield, travelling with a constant velocity, is extrapolated from the differential wave equation, with the aid of Fourier transforms. Then we present a non-numerical treatment by which we derive an asymptotic solution for both the amplitude and the phase of a planar subsurface wavefield that has a vertical velocity variation. This treatment entails the application of the Wentzel-Kramers-Brillouin approximation, whose self-consistency can be established due to a very slow logarithmic variation of the velocity in the vertical direction, a feature that holds more firmly at increasingly greater subsurface depths. For a planar subsurface wavefield, we also demonstrate an equivalence between two apparently different migration algorithms, namely, the constant-velocity Stolt Migration algorithm and the stationary-phase approximation method.

  20. The Malaysian state's response to migration.

    PubMed

    Pillai, P

    1999-04-01

    This paper aims to provide a profile of migration trends in Malaysia since 1970 and to analyze public policy on migration in the context of economic growth and the labor market. The discussion centers on the impact of the Asian financial crisis. There is long history of immigration to Malaysia. The development strategy of the 1970s and 1980s was to create more jobs and restructure employment to meet equity goals. Labor shortages on plantations and construction booms led to a more organized, sustained effort to import labor. Recession in the mid-1980s led to unemployment, but many Malaysians were unwilling to work on plantations, in construction, or in low paying jobs. Economic growth during 1987-96 was very high, and labor shortages spread to service and manufacturing sectors. Migration policy has shifted over the decades. Both the market and the government's promotion of export-based industrialization require access to low cost migrant labor. Public and official recognition of the large number of migrants was not made until 1995. The financial crisis in 1998 led to enforcement of a new migration policy on illegal migrants and greater outflow of migrants. The economic crisis has increased job and income inequities in the region; this encourages continued migration. It is argued that it would be best for Malaysia to maximize short-term gains while minimizing long-term economic, social, and political costs. PMID:12295145

  1. International migration network: Topology and modeling

    NASA Astrophysics Data System (ADS)

    Fagiolo, Giorgio; Mastrorillo, Marina

    2013-07-01

    This paper studies international migration from a complex-network perspective. We define the international migration network (IMN) as the weighted-directed graph where nodes are world countries and links account for the stock of migrants originated in a given country and living in another country at a given point in time. We characterize the binary and weighted architecture of the network and its evolution over time in the period 1960-2000. We find that the IMN is organized around a modular structure with a small-world binary pattern displaying disassortativity and high clustering, with power-law distributed weighted-network statistics. We also show that a parsimonious gravity model of migration can account for most of observed IMN topological structure. Overall, our results suggest that socioeconomic, geographical, and political factors are more important than local-network properties in shaping the structure of the IMN.

  2. Psychosis and migration: does a correlation exist?

    PubMed

    Mandaglio, Chiara; Maierà, Enza

    2014-11-01

    The mental health of migrants is considered today one of the major problems of individual and public health. Unlike other European countries, such as England and France, where migration is linked to a colonial past, Italy has only recently found itself faced with a tumultuous transformation of identity, becoming from a country of emigration, an immigration country. In light of all this, this work stems from the need to shed light on the relationship between social integration and development of psychiatric disorders in migrants, with particular attention to the correlation between migration and psychotic pathology. Finally, the elaboration of various issues related to the migration process will be dealt with, placing the priority on investigating the greater psychiatric morbidity in migrants compared with natives. PMID:25413526

  3. The internal dynamics of international migration systems.

    PubMed

    Waldorf, B

    1996-04-01

    "In this paper I provide a conceptualization of international migration networks, which can be used to identify and integrate the internal components of migration systems, and formalize the relationships in an analytic model of the internal network dynamic. With the use of the operationalized model, and microlevel and macrolevel data for guestworkers in Germany during the period 1970 to 1989, we can empirically test the relative influence of internal network variables versus external forces on the attraction of immigrants over time. The empirical results suggest that--as the system matures--network variables have an increasing impact on the attraction of immigrants, while the impact of economic factors declines. The research is concluded with a series of simulations that further highlight the internal dynamic of international migration systems."

  4. Migration of historical earthquakes in California

    USGS Publications Warehouse

    King, C.-Y.; Ma, Z.

    1988-01-01

    Most large earthquakes of magnitude ???6.0 in California during 1852-1987 appear to show a southeast-to-northwest tendency of epicenter migration. This finding is consistent with earlier findings of Savage (1971) for a relatively few large earthquakes along the west coast of North America, and of Wood and Allen (1973) for smaller events along the San Andreas fault in central California. The average speed of migration is approximately 130 km/yr, which is within the range of speeds observed for other major seismic zones in the world. The epicenter migration in California may be the result of some small but broad-scaled episodic strain changes associated with creep waves induced by magma injections at the East Pacific Rise and propagating northwestwardly along a broad transform boundary between the Pacific and North American plates at subseismogenic depths as proposed by Savage (1971). ?? 1988 Birkha??user Verlag.

  5. Reducing PICC migrations and improving patient outcomes.

    PubMed

    Elen Hughes, Meinir

    Inadvertent migration of central venous catheters can lead to several issues including delayed therapy and clinical morbidities such as thrombosis. Peripherally inserted central catheters (PICCs) are particularly at risk of movement. An innovative new device which allows anchorage of the catheter has proved very successful in the minimisation of catheter migration. The SecurAcath device incorporates a small blunt anchor which lies beneath the skin in order to secure the catheter in place and prevent inadvertent movement. An evaluation of 31 patients with a SecurAcath device in situ to secure a PICC found only one case of insignificant catheter migration. Some initial problems with infection and pain were encountered and interventions were put in place to minimise their incidence. SecurAcath removal proved to be the most significant challenge but this can be overcome with suitable guidance and training.

  6. Cadmium migration in aerospace nickel cadmium cells

    NASA Technical Reports Server (NTRS)

    Mcdermott, P. P.

    1976-01-01

    The effects of temperature, the nature of separator material, charge and discharge, carbonate contamination, and the mode of storage are studied with respect to the migration of active material from the negative toward the positive plate. A theoretical model is proposed which takes into account the solubility of cadmium in various concentrations of hydroxide and carbonate at different temperatures, the generation of the cadmiate ion, Cd(OH)3(-), during discharge, the migration of the cadmiate ion and particulate Cd(OH)2 due to electrophoretic effects and the movement of electrolyte in and out of the negative plate and, finally, the recrystallization of cadmiate ion in the separator as Cd(OH)2. Application of the theoretical model to observations of cadmium migration in cycled cells is also discussed.

  7. Migration of historical earthquakes in California

    NASA Astrophysics Data System (ADS)

    King, Chi-Yu; Ma, Zongjin

    1988-12-01

    Most large earthquakes of magnitude ≥6.0 in California during 1852 1987 appear to show a southeast-to-northwest tendency of epicenter migration. This finding is consistent with earlier findings of Savage (1971) for a relatively few large earthquakes along the west coast of North America, and of Wood and Allen (1973) for smaller events along the San Andreas fault in central California. The average speed of migration is approximately 130 km/yr, which is within the range of speeds observed for other major seismic zones in the world. The epicenter migration in California may be the result of some small but broad-scaled episodic strain changes associated with creep waves induced by magma injections at the East Pacific Rise and propagating northwestwardly along a broad transform boundary between the Pacific and North American plates at subseismogenic depths as proposed by Savage (1971).

  8. Migration and sensory evaluation of irradiated polymers

    NASA Astrophysics Data System (ADS)

    Stoffers, Niels H.; Linssen, Jozef P. H.; Franz, Roland; Welle, Frank

    2004-09-01

    The effects on ionising irradiation on polymer additives, monomers and polymers themselves have been investigated. Changes of initial concentrations of certain additives and monomers, a change in their specific migration as well as sensory changes of the polymers were examined. Polymer stabilizers such as Irganox 1076 and Irgafos 168 used in polyethylene were found to be degraded by ionising radiation. Decreased concentrations of stabilisers in polyolefins led to lower specific migration, however, not to lower overall migration into food simulants. Irganox 1076 levels in polystyrene did not change up to irradiation doses of 54 kGy. Sensory properties of LDPE, HDPE, PA6 and PA12 worsened, while sensory properties of PS improved with increasing irradiation doses.

  9. Transcrystalline melt migration and Earth's mantle.

    PubMed

    Schiano, Pierre; Provost, Ariel; Clocchiatti, Roberto; Faure, François

    2006-11-10

    Plate tectonics and volcanism involve the formation, migration, and interaction of magma and gas. Experiments show that melt inclusions subjected to a thermal gradient migrate through olivine crystals, under the kinetic control of crystal-melt interface mechanisms. Exsolved gas bubbles remain fixed and eventually separate from the melt. Scaled to thermal gradients in Earth's mantle and geological times, our results account for the grain-scale segregation of primitive melts, reinterpret CO2-rich fluid inclusions as escaped from melt, and question the existence of a free, deeply percolating fluid phase. Melt migration experiments also allow us to quantify crystal growth kinetics at very low undercoolings in conditions appropriate to many natural systems.

  10. [Migrations forced by violence: the Colombian case].

    PubMed

    Builes, Gloria Marcela Gómez; Arias, Gilberto Mauricio Astaiza; Minayo, Maria Cecília de Souza

    2008-01-01

    The human migrations have been one of the motors in the history of humanity. During the twentieth century, internal forced displacement has been an important component of the migration processes in the world. Colombia, a paradigm for this phenomenon, is a country with more than three and a half million people displaced over the last 25 years by force of the violence resulting from an internal armed conflict. Besides the socio-demographic effects in the reconfiguration of the cities, this problem affects the human condition of the victims deteriorating their health and quality of life. This article aims to show the general panorama of migrations forced by violence in the world and to analyze the peculiarities of this phenomenon in the Colombian case. We conclude that forced displacement is a serious violation of human rights producing a human drama by exposing the affected individuals and communities to vulnerability and a deep deterioration of their quality of life and health. PMID:18813665

  11. [Migrations forced by violence: the Colombian case].

    PubMed

    Builes, Gloria Marcela Gómez; Arias, Gilberto Mauricio Astaiza; Minayo, Maria Cecília de Souza

    2008-01-01

    The human migrations have been one of the motors in the history of humanity. During the twentieth century, internal forced displacement has been an important component of the migration processes in the world. Colombia, a paradigm for this phenomenon, is a country with more than three and a half million people displaced over the last 25 years by force of the violence resulting from an internal armed conflict. Besides the socio-demographic effects in the reconfiguration of the cities, this problem affects the human condition of the victims deteriorating their health and quality of life. This article aims to show the general panorama of migrations forced by violence in the world and to analyze the peculiarities of this phenomenon in the Colombian case. We conclude that forced displacement is a serious violation of human rights producing a human drama by exposing the affected individuals and communities to vulnerability and a deep deterioration of their quality of life and health.

  12. Migration and the family: the female perspective.

    PubMed

    Zlotnik, H

    1995-01-01

    "This article shows that a family perspective is especially important for the analysis of female migration because: (1) women are major participants in 'family migration' as defined by governments and, although they benefit from family reunification provisions, they are also constrained by them; (2) migrant women are important economic actors and their participation in economic activity is closely related to the needs of their families, so that the choices that migrant women make regarding work cannot be understood without taking into account the situation of their families and women's roles within them; (3) women are increasingly becoming migrant workers in order to improve the economic status of their families; and (4) women rely on their families to provide various types of support that both make migration possible and condition its outcome. A review of the literature provides evidence supporting each of these observations."

  13. Chemical speciation of radionuclides migrating in groundwaters

    SciTech Connect

    Robertson, D.; Schilk, A.; Abel, K.; Lepel, E.; Thomas, C.; Pratt, S.; Cooper, E.; Hartwig, P.; Killey, R.

    1994-04-01

    In order to more accurately predict the rates and mechanisms of radionuclide migration from low-level waste disposal facilities via groundwater transport, ongoing studies are being conducted at field sites at Chalk River Laboratories to identify and characterize the chemical speciation of mobile, long-lived radionuclides migrating in groundwaters. Large-volume water sampling techniques are being utilized to separate and concentrate radionuclides into particular, cationic, anionic, and nonionic chemical forms. Most radionuclides are migrating as soluble, anionic species that appear to be predominantly organoradionuclide complexes. Laboratory studies utilizing anion exchange chromatography have separated several anionically complexed radionuclides, e.g., {sup 60}Co and {sup 106}Ru, into a number of specific compounds or groups of compounds. Further identification of the anionic organoradionuclide complexes is planned utilizing high resolution mass spectrometry. Large-volume ultra-filtration experiments are characterizing the particulate forms of radionuclides being transported in these groundwaters.

  14. Modernization, migration and obesity among Samoan adults.

    PubMed

    Bindon, J R; Baker, P T

    1985-01-01

    Modernization and migration have biological as well as social effects on people. In this study, 2657 Samoan adults from Western Samoa, American Samoa and Hawaii were surveyed in an attempt to examine the relationships between modernization, migration and obesity. The Samoan men showed an increase in the frequency of obesity with increasing modernity of residence or occupation. While the women in American Samoa had the highest frequency of obesity of any subsample, Samoan women also demonstrated a pattern of higher adiposity in more modern jobs. Young women tended to show a negative relationship between obesity frequency and education, with college-educated women having the lowest average levels of adiposity. Time since migration to Hawaii was not found to exert a major effect on frequency of obesity.

  15. Oceanic migration and spawning of anguillid eels.

    PubMed

    Tsukamoto, K

    2009-06-01

    Many aspects of the life histories of anguillid eels have been revealed in recent decades, but the spawning migrations of their silver eels in the open ocean still remains poorly understood. This paper overviews what is known about the migration and spawning of anguillid species in the ocean. The factors that determine exactly when anguillid eels will begin their migrations are not known, although environmental influences such as lunar cycle, rainfall and river discharge seem to affect their patterns of movement as they migrate towards the ocean. Once in the ocean on their way to the spawning area, silver eels probably migrate in the upper few hundred metres, while reproductive maturation continues. Although involvement of a magnetic sense or olfactory cues seems probable, how they navigate or what routes they take are still a matter of speculation. There are few landmarks in the open ocean to define their spawning areas, other than oceanographic or geological features such as oceanic fronts or seamounts in some cases. Spawning of silver eels in the ocean has never been observed, but artificially matured eels of several species have exhibited similar spawning behaviours in the laboratory. Recent collections of mature adults and newly spawned preleptocephali in the spawning area of the Japanese eel Anguilla japonica have shown that spawning occurs during new moon periods in the North Equatorial Current region near the West Mariana Ridge. These data, however, show that the latitude of the spawning events can change among months and years depending on oceanographic conditions. Changes in spawning location of this and other anguillid species may affect their larval transport and survival, and appear to have the potential to influence recruitment success. A greater understanding of the spawning migration and the choice of spawning locations by silver eels is needed to help conserve declining anguillid species.

  16. Cell density determines epithelial migration in culture.

    PubMed Central

    Rosen, P; Misfeldt, D S

    1980-01-01

    The dog kidney epithelial cell line (MDCK) has been shown to exhibit a density-correlated inhibition of growth at approxmately 6.6 X 10(5) cells per cm2. When a confluent monolayer at its maximal density was wounded by removal of a wide swath of cells, migration of the cell sheet into the denuded area occurred. Precise measurements of the rate of migration for 5 day showed that the cells accelerated at a uniform rate of 0.24 micrometer . hr-2 and, by extrapolation, possessed an apparent initial velocity of 2.8 micrometer . hr-1 at the time of wounding. The apparent initial velocity was considered to be the result of a brief (< 10 hr) and rapid acceleration dependent on cell density. To verify this, wounds were made at different densities below the maximum. In these experiments, the cells did not migrate until a "threshold" density of 2.0 X 10(5) cells per cm2 was reached regardless of the density at the time of wounding. At the threshold density, the cell sheet began to accelerate at the previously measured rate (0.24 micrometer . hr-2). Any increase in density by cell division was balanced by cell migration, so that the same threshold density was maintained by the migrating cells. Each migrating cell sustained the movement of the cell sheet at a constant rate of acceleration. It is proposed that an acceleration is, in general, characteristic of the vectorial movement of an epithelial cell sheet. Images PMID:6933523

  17. Oceanic migration and spawning of anguillid eels.

    PubMed

    Tsukamoto, K

    2009-06-01

    Many aspects of the life histories of anguillid eels have been revealed in recent decades, but the spawning migrations of their silver eels in the open ocean still remains poorly understood. This paper overviews what is known about the migration and spawning of anguillid species in the ocean. The factors that determine exactly when anguillid eels will begin their migrations are not known, although environmental influences such as lunar cycle, rainfall and river discharge seem to affect their patterns of movement as they migrate towards the ocean. Once in the ocean on their way to the spawning area, silver eels probably migrate in the upper few hundred metres, while reproductive maturation continues. Although involvement of a magnetic sense or olfactory cues seems probable, how they navigate or what routes they take are still a matter of speculation. There are few landmarks in the open ocean to define their spawning areas, other than oceanographic or geological features such as oceanic fronts or seamounts in some cases. Spawning of silver eels in the ocean has never been observed, but artificially matured eels of several species have exhibited similar spawning behaviours in the laboratory. Recent collections of mature adults and newly spawned preleptocephali in the spawning area of the Japanese eel Anguilla japonica have shown that spawning occurs during new moon periods in the North Equatorial Current region near the West Mariana Ridge. These data, however, show that the latitude of the spawning events can change among months and years depending on oceanographic conditions. Changes in spawning location of this and other anguillid species may affect their larval transport and survival, and appear to have the potential to influence recruitment success. A greater understanding of the spawning migration and the choice of spawning locations by silver eels is needed to help conserve declining anguillid species. PMID:20735675

  18. Female urbanward migration and human resource issues.

    PubMed

    Zosa-feranil, I

    1990-01-01

    Of those migrating to urban centers in the Philippines, a disproportionate number of them are young females, most of whom end up working in the service sector. Between 1975-80, 1.3 million people migrated to urban centers, 56% of whom were females. Furthermore, a 1980 census indicates that 13% of all urban migrants were females age 15-19, and almost 1/4 of them were women in their 20s. Figures also show that single females make up a substantial portion of the urban migrants. Compared to the men migrating into the cities, the female urban migrants had lower educational attainments. Many of uneducated migrants do not integrate as easily, and are relegated to the periphery of urban centers. The search for employment serves as the driving force for urban migration, and in fact, the level of female participation in the workforce is high. But while male migrants work mostly as craftsmen or in the production sector, most female migrants work in the service sector. This category includes domestic workers, laundry women, cooks and waitresses, hospitality girls, and prostitutes. Generally attracting single, young females, the service sector has easy entry, which helps explain the high rate of female employment. The author explains that this trend is cause for concern, considering that the number of people involved is large, that the service sector provides low earning, and that it lends itself to the exploitation of the workers. Nonetheless, the author says that the migration pattern might only be transitory, and the urban migration might be a liberating process for women, but explains that further research is needed concerning the upward mobility of urban migrants.

  19. A polar system of intercontinental bird migration.

    PubMed

    Alerstam, Thomas; Bäckman, Johan; Gudmundsson, Gudmundur A; Hedenström, Anders; Henningsson, Sara S; Karlsson, Håkan; Rosén, Mikael; Strandberg, Roine

    2007-10-22

    Studies of bird migration in the Beringia region of Alaska and eastern Siberia are of special interest for revealing the importance of bird migration between Eurasia and North America, for evaluating orientation principles used by the birds at polar latitudes and for understanding the evolutionary implications of intercontinental migratory connectivity among birds as well as their parasites. We used tracking radar placed onboard the ice-breaker Oden to register bird migratory flights from 30 July to 19 August 2005 and we encountered extensive bird migration in the whole Beringia range from latitude 64 degrees N in Bering Strait up to latitude 75 degrees N far north of Wrangel Island, with eastward flights making up 79% of all track directions. The results from Beringia were used in combination with radar studies from the Arctic Ocean north of Siberia and in the Beaufort Sea to make a reconstruction of a major Siberian-American bird migration system in a wide Arctic sector between longitudes 110 degrees E and 130 degrees W, spanning one-third of the entire circumpolar circle. This system was estimated to involve more than 2 million birds, mainly shorebirds, terns and skuas, flying across the Arctic Ocean at mean altitudes exceeding 1 km (maximum altitudes 3-5 km). Great circle orientation provided a significantly better fit with observed flight directions at 20 different sites and areas than constant geographical compass orientation. The long flights over the sea spanned 40-80 degrees of longitude, corresponding to distances and durations of 1400-2600 km and 26-48 hours, respectively. The birds continued from this eastward migration system over the Arctic Ocean into several different flyway systems at the American continents and the Pacific Ocean. Minimization of distances between tundra breeding sectors and northerly stopover sites, in combination with the Beringia glacial refugium and colonization history, seemed to be important for the evolution of this major

  20. A polar system of intercontinental bird migration.

    PubMed

    Alerstam, Thomas; Bäckman, Johan; Gudmundsson, Gudmundur A; Hedenström, Anders; Henningsson, Sara S; Karlsson, Håkan; Rosén, Mikael; Strandberg, Roine

    2007-10-22

    Studies of bird migration in the Beringia region of Alaska and eastern Siberia are of special interest for revealing the importance of bird migration between Eurasia and North America, for evaluating orientation principles used by the birds at polar latitudes and for understanding the evolutionary implications of intercontinental migratory connectivity among birds as well as their parasites. We used tracking radar placed onboard the ice-breaker Oden to register bird migratory flights from 30 July to 19 August 2005 and we encountered extensive bird migration in the whole Beringia range from latitude 64 degrees N in Bering Strait up to latitude 75 degrees N far north of Wrangel Island, with eastward flights making up 79% of all track directions. The results from Beringia were used in combination with radar studies from the Arctic Ocean north of Siberia and in the Beaufort Sea to make a reconstruction of a major Siberian-American bird migration system in a wide Arctic sector between longitudes 110 degrees E and 130 degrees W, spanning one-third of the entire circumpolar circle. This system was estimated to involve more than 2 million birds, mainly shorebirds, terns and skuas, flying across the Arctic Ocean at mean altitudes exceeding 1 km (maximum altitudes 3-5 km). Great circle orientation provided a significantly better fit with observed flight directions at 20 different sites and areas than constant geographical compass orientation. The long flights over the sea spanned 40-80 degrees of longitude, corresponding to distances and durations of 1400-2600 km and 26-48 hours, respectively. The birds continued from this eastward migration system over the Arctic Ocean into several different flyway systems at the American continents and the Pacific Ocean. Minimization of distances between tundra breeding sectors and northerly stopover sites, in combination with the Beringia glacial refugium and colonization history, seemed to be important for the evolution of this major

  1. Roaming yuppies: Hong Kong migration to Australia.

    PubMed

    Wong, S

    1994-01-01

    "Hong Kong has been the top source for Asian migration to Australia in recent years. The majority of the Hong Kong migrants are young, educated professionals. Using survey data conducted in Hong Kong on emigration tendencies, this article analyzes why they are leaving Hong Kong, what attracts them to Australia, and what impact this influx has on Australian society. It is speculated that this movement may create an enduring change in the identity of emigrant Hong Kongers and have a wider significance in the contradictory currents of geopolitics and geoeconomics which are simultaneously encouraging and resisting migration." PMID:12289778

  2. Stretch due to Penile Prosthesis Reservoir Migration

    PubMed Central

    Baten, E.; Vandewalle, T.; van Renterghem, K.

    2016-01-01

    A 43-year old patient presented to the emergency department with stretch, due to impossible deflation of the penile prosthesis, 4 years after successful implant. A CT-scan showed migration of the reservoir to the left rectus abdominis muscle. Refilling of the reservoir was inhibited by muscular compression, causing stretch. Removal and replacement of the reservoir was performed, after which the prosthesis was well-functioning again. Migration of the penile prosthesis reservoir is extremely rare but can cause several complications, such as stretch. PMID:26793592

  3. Roaming yuppies: Hong Kong migration to Australia.

    PubMed

    Wong, S

    1994-01-01

    "Hong Kong has been the top source for Asian migration to Australia in recent years. The majority of the Hong Kong migrants are young, educated professionals. Using survey data conducted in Hong Kong on emigration tendencies, this article analyzes why they are leaving Hong Kong, what attracts them to Australia, and what impact this influx has on Australian society. It is speculated that this movement may create an enduring change in the identity of emigrant Hong Kongers and have a wider significance in the contradictory currents of geopolitics and geoeconomics which are simultaneously encouraging and resisting migration."

  4. Migration and health: fact, fiction, art, politics

    PubMed Central

    Tam, Clarence C

    2006-01-01

    The recent Immigration Bill debate in the United States Congress has again re-ignited the polemic regarding immigration policy. In this essay, I argue that disputes surrounding the legality of migrant workers highlight chronic, underlying problems related to factors that drive migration. The public health field, although concerned primarily with addressing the health needs of migrant populations, cannot remain disengaged from the wider debates about migration. The health needs of migrants, although in themselves important, are merely symptoms of deeper structural process that are intrinsically linked to equity and human rights, and simply focusing on health issues will be insufficient to address these societal pathologies. PMID:17014732

  5. Mechanism for diffusion induced grain boundary migration

    SciTech Connect

    Balluffi, R.W.; Cahn, J.W.

    1980-08-01

    Grain boundaries are found to migrate under certain conditions when solute atoms are diffused along them. This phenomenon, termed diffusion induced grain boundary migration (DIGM), has now been found in six systems. The observed phenomenon and empirical data are used to discard certain concepts for the driving force and the mechanism. A mechanism is proposed in which differences in the diffusion coefficients of the diffusing species along the grain boundary cause a self-sustaining climb of grain boundary dislocations and motion of their associated grain boundary steps.

  6. The Geography of Undocumented Mexican Migration

    PubMed Central

    Massey, Douglas S.; Rugh, Jacob S.; Pren, Karen A.

    2010-01-01

    Using data from Mexico’s Matrícula Consular program, we analyze the geographic organization of undocumented Mexican migration to the United States. We show that emigration has moved beyond its historical origins in west-central Mexico into the central region and, to a lesser extent, the southeast and border regions. In the United States, traditional gateways continue to dominate, but a variety of new destinations have emerged. California, in particular, has lost its overwhelming dominance. Although the geographic structure of Mexico-U.S. migration is relatively stable, it has nonetheless continued to evolve and change over time. PMID:20814589

  7. [Migration of young people in Burkina].

    PubMed

    Boutillier, J; Quesnel, A; Vaugelade, J

    1985-01-01

    Migration patterns in Burkina Faso, contributing factors, and migrant characteristics are examined. Data are from published literature for the years 1969-1973. Net emigration from Burkina Faso, primarily to the Ivory Coast and Ghana, is shown to be the predominant trend. The migrant population consists largely of men aged 15-30 from the rural Mossi regions. The socioeconomic context contributing to the observed emigration and the benefits to the communities of origin as a result of these movements are considered. The impact of return migration on agricultural development is discussed. PMID:12267600

  8. Stretch due to Penile Prosthesis Reservoir Migration.

    PubMed

    Baten, E; Vandewalle, T; van Renterghem, K

    2016-03-01

    A 43-year old patient presented to the emergency department with stretch, due to impossible deflation of the penile prosthesis, 4 years after successful implant. A CT-scan showed migration of the reservoir to the left rectus abdominis muscle. Refilling of the reservoir was inhibited by muscular compression, causing stretch. Removal and replacement of the reservoir was performed, after which the prosthesis was well-functioning again. Migration of the penile prosthesis reservoir is extremely rare but can cause several complications, such as stretch.

  9. Climate change-related migration and infectious disease

    PubMed Central

    McMichael, Celia

    2015-01-01

    Anthropogenic climate change will have significant impacts on both human migration and population health, including infectious disease. It will amplify and alter migration pathways, and will contribute to the changing ecology and transmission dynamics of infectious disease. However there has been limited consideration of the intersections between migration and health in the context of a changing climate. This article argues that climate-change related migration - in conjunction with other drivers of migration – will contribute to changing profiles of infectious disease. It considers infectious disease risks for different climate-related migration pathways, including: forced displacement, slow-onset migration particularly to urban-poor areas, planned resettlement, and labor migration associated with climate change adaptation initiatives. Migration can reduce vulnerability to climate change, but it is critical to better understand and respond to health impacts – including infectious diseases - for migrant populations and host communities. PMID:26151221

  10. Climate change-related migration and infectious disease.

    PubMed

    McMichael, Celia

    2015-01-01

    Anthropogenic climate change will have significant impacts on both human migration and population health, including infectious disease. It will amplify and alter migration pathways, and will contribute to the changing ecology and transmission dynamics of infectious disease. However there has been limited consideration of the intersections between migration and health in the context of a changing climate. This article argues that climate-change related migration - in conjunction with other drivers of migration - will contribute to changing profiles of infectious disease. It considers infectious disease risks for different climate-related migration pathways, including: forced displacement, slow-onset migration particularly to urban-poor areas, planned resettlement, and labor migration associated with climate change adaptation initiatives. Migration can reduce vulnerability to climate change, but it is critical to better understand and respond to health impacts - including infectious diseases - for migrant populations and host communities.

  11. Migration efficiency ratios and the optimal distribution of population.

    PubMed

    Gallaway, L; Vedder, R

    1985-01-01

    The authors present a theoretical description of the migration process and criticize the conventional interpretation of the migration efficiency ratio, which is defined as the ratio of the net number of moves of individuals between areas to the gross number of moves that take place. "The conventional interpretation of the migration efficiency ratio is that the closer it lies to zero the less efficient the migration process....However, [the authors] feel that this is a somewhat misleading conception of the notion of efficiency in migration in that it emphasizes the physical efficiency of the migration process rather than focusing on the contribution of migration to a socially efficient allocation of population. Thus, to redirect attention, [they] have chosen to judge migration efficiency on the basis of its contribution to producing an equilibrium population distribution." The focus is on internal migration.

  12. Reinventing US Internal Migration Studies in the Age of International Migration

    PubMed Central

    Ellis, Mark

    2014-01-01

    I argue that researchers have sidelined attention to issues raised by US internal migration as they shifted focus to the questions posed by the post-1960s rise in US immigration. In this paper, I offer some reasons about why immigration has garnered more attention and why there needs to be greater consideration of US internal migration and its significant and myriad social, economic, political, and cultural impacts. I offer three ideas for motivating more research into US internal geographic mobility that would foreground its empirical and conceptual connections to international migration. First, there should be more work on linked migration systems investigating the connections between internal and international flows. Second, the questions asked about immigrant social, cultural, and economic impacts and adaptations in host societies should also be asked about internal migrants. Third, and more generally, migration researchers should jettison the assumption that the national scale is the pre-eminent delimiter of migration types and processes. Some groups can move easily across borders; others are constrained in their moves within countries. These subnational scales and constraints will become more visible if migration research decentres the national from its theory and empirics. PMID:24839406

  13. Reinventing US Internal Migration Studies in the Age of International Migration.

    PubMed

    Ellis, Mark

    2012-03-01

    I argue that researchers have sidelined attention to issues raised by US internal migration as they shifted focus to the questions posed by the post-1960s rise in US immigration. In this paper, I offer some reasons about why immigration has garnered more attention and why there needs to be greater consideration of US internal migration and its significant and myriad social, economic, political, and cultural impacts. I offer three ideas for motivating more research into US internal geographic mobility that would foreground its empirical and conceptual connections to international migration. First, there should be more work on linked migration systems investigating the connections between internal and international flows. Second, the questions asked about immigrant social, cultural, and economic impacts and adaptations in host societies should also be asked about internal migrants. Third, and more generally, migration researchers should jettison the assumption that the national scale is the pre-eminent delimiter of migration types and processes. Some groups can move easily across borders; others are constrained in their moves within countries. These subnational scales and constraints will become more visible if migration research decentres the national from its theory and empirics. PMID:24839406

  14. Migration as family strategy: rural-urban labor migration in India during the twentieth century.

    PubMed

    De Haan, A

    1997-01-01

    "The article analyzes the role of families in processes of rural-urban migration in India in the twentieth century. It shows that the continuous circular form of this migration should be explained as a consequence of rural family strategies. Already established kinship relations or marriage opportunities in the future act as a centripetal force, drawing the labor migrants back to their communities time and again. In addition, the article shows how labor migration is informed by economic and cultural considerations which determine the socioeconomic behavior of men and women." PMID:12293228

  15. Migration and coherency stacking of the Friendswood reverse VSP data

    SciTech Connect

    Nemeth, T.

    1994-12-31

    In this paper the author applies processing methods to reverse VSP data: iterative conjugate gradient migration and coherency stacking. Iterative conjugate gradient migration helps to eliminate the migration artifacts and produce a reflectivity distribution which is consistent with the observed seismogram. The second method, coherent stacking, helps to coherently stack the prestack migrated sections to produce a more highly resolved composite migrated section. Numerical results show that these procedures are capable of eliminating a fault-like artifact from the conventionally processed VSP migrated section.

  16. International Student Migration: Outcomes and Implications

    ERIC Educational Resources Information Center

    McGill, Jenny

    2013-01-01

    The present study examined the possible correlation between six life circumstances of international students (N = 124) admitted entry into the United States for the purpose of academic study and their geographic choice of location upon graduation. This paper improves upon the current literature by offering actual migration outcomes (rather than…

  17. The Singapore state's response to migration.

    PubMed

    Yap, M T

    1999-04-01

    Migration trends in Singapore are traced since 1819. Immigration has been encouraged to advance economic development. Local and international factors fuel migration to Singapore. Singapore depends upon foreign labor. Population growth has been mainly due to migration from China, India, Malaysia, and countries surrounding Singapore. Independence in 1965 led to policies aimed at controlling high population growth. Policies became pronatalist after 1987. Foreigners in 1998 were over 18% of the total population, which was six times the number in 1970. About 2000 Singaporeans per year emigrated during the 1990s. Singapore is encouraging overseas industrial development. In 1997, the Prime Minister called for recruitment of foreign talent in order to meet the challenges of an increasingly globalized world, low fertility, and an aging society. Economic planners recommend short-term migration of unskilled foreign workers who would be a revolving pool to fill jobs natives do not want. Singapore is promoting arts and culture in order to keep people in Singapore. The government has issued assurances that natives will have first priority on jobs, education, and training. Singapore's ability to absorb workers will depend upon its economic performance.

  18. [Dentists' workforce in Hungary and international migration].

    PubMed

    Balázs, Péter

    2012-06-01

    In Hungary, cross-national migration in dental care was performed rather by patients from abroad instead of the domestic dentists' migration for working abroad. Actually, this tacitly realized and so-called dental tourism experienced two basic changes. The National Medical Tourism Ltd. arranged the First Conference for Development of Dental Tourism on 21 April 2011. Hungary's prime minister addressed the meeting and finally signed an agreement with the organizing Ltd. about governmental financial support for development of dental tourism. On the other hand, Germany and Austria deleted all restrictions against the free cross-national workforce migration since 1 May this year. For understanding and prognosis of dentists' future migration, it is inevitable to collect and analyse relevant data of the previous years. This study is presenting data obtained from January 1, 2006 to December 31, 2010. According to the net outcome, the dentists' human resource system was balanced down to the end of 2010. However, this state is unsure even for the near future, thus preventing the deficit of dentists all necessary measures must be taken to keep up the present level of the domestic dentral service.

  19. Seismic velocity estimation from time migration

    NASA Astrophysics Data System (ADS)

    Cameron, M. K.; Fomel, S. B.; Sethian, J. A.

    2007-08-01

    We address the problem of estimating seismic velocities inside the Earth which is necessary for obtaining seismic images in regular Cartesian coordinates. The main goals are to develop algorithms to convert time-migration velocities to true seismic velocities, and to convert time-migrated images to depth images in regular Cartesian coordinates. Our main results are three-fold. First, we establish a theoretical relation between the true seismic velocities and the 'time-migration velocities' using the paraxial ray tracing. Second, we formulate an appropriate inverse problem describing the relation between time-migration velocities and depth velocities, and show that this problem is mathematically ill posed, i.e., unstable to small perturbations. Third, we develop numerical algorithms to solve regularized versions of these equations which can be used to recover smoothed velocity variations. Our algorithms consist of efficient time-to-depth conversion algorithms, based on Dijkstra-like fast marching methods, as well as level set and ray tracing algorithms for transforming Dix velocities into seismic velocities. Our algorithms are applied to both two-dimensional and three-dimensional problems, and we test them on a collection of both synthetic examples and field data.

  20. PROTOPLANETARY DISK RESONANCES AND TYPE I MIGRATION

    SciTech Connect

    Tsang, David

    2011-11-10

    Waves reflected by the inner edge of a protoplanetary disk are shown to significantly modify Type I migration, even allowing the trapping of planets near the inner disk edge for small planets in a range of disk parameters. This may inform the distribution of planets close to their central stars, as observed recently by the Kepler mission.

  1. Labor Migration by Russian Young People

    ERIC Educational Resources Information Center

    Man'shin, R. V.; Timoshenko, O. V.; Pis'mennaia, E. E.

    2009-01-01

    Russia's young people have become active participants in processes of migration. After the fall of the USSR, young people began to travel outside Russia in substantially greater numbers. At the present time, young Russians can be found in all kinds of regions and countries of the world. They are getting an education in foreign universities and…

  2. Transnationalism, Migration and Emotions: Implications for Education

    ERIC Educational Resources Information Center

    Zembylas, Michalinos

    2012-01-01

    This article is concerned with the emotional dynamics of transnationalism and migration and the impact on education. This impact is discussed in terms of how the movement of people involves complex emotional processes that have important consequences for educational policy, practice and research. The purpose of the author is to theorise how…

  3. Indigenous Youth Migration and Language Contact

    ERIC Educational Resources Information Center

    Wyman, Leisy T.

    2013-01-01

    Few studies ethnographically detail how Indigenous young people's mobility intersects with sociolinguistic transformation in an interconnected world. Drawing on a decade-long study of youth and language contact, I analyze Yup'ik young people's migration in relation to emerging language ideologies and patterns of language use in "Piniq,"…

  4. Migrating Professional Knowledge: Progressions, Regressions, and Dislocations

    ERIC Educational Resources Information Center

    Slade, Bonnie L.

    2015-01-01

    Drawing on practice-based learning theory, this chapter examines issues pertaining to the deskilling of immigrant professionals in Canada. It argues that adult educators need to have an awareness of transnational migration dynamics and work in meaningful ways to keep immigrant professionals connected to professional knowledge practices.

  5. A Radical Break: Restraining Neutrophil Migration.

    PubMed

    Renkawitz, Jörg; Sixt, Michael

    2016-09-12

    When neutrophils infiltrate a site of inflammation, they have to stop at the right place to exert their effector function. In this issue of Developmental Cell, Wang et al. (2016) show that neutrophils sense reactive oxygen species via the TRPM2 channel to arrest migration at their target site. PMID:27623379

  6. Life Earnings and Rural-Urban Migration

    ERIC Educational Resources Information Center

    Lucas, Robert E., Jr.

    2004-01-01

    This paper is a theoretical study of rural-urban migration--urbanization--as it has occurred in many low-income economies in the postwar period. This process is viewed as a transfer of labor from a traditional, land-intensive technology to a human capital-intensive technology with an unending potential for growth. The model emphasizes the role of…

  7. International migration, international relations and foreign policy.

    PubMed

    Mitchell, C

    1989-01-01

    Recent literature on migration, international relations, and foreign policy is reviewed in this article, stressing applications of global systems paradigms, studies of state entry and exit rules, and anatomies of domestic policy-setting processes on migration. After a concise assessment of the contemporary theory of global political economy, the paper argues for seeking mid-range generalizations on the international relations of migration. It also suggests that analysis begin with the policy-setting processes of the state. Especially through the use of comparative perspectives available from domestic policy making studies and from the field of international comparative public policy, this approach offers the opportunity to fix empirically the political roles of transnational social forces, which often present themselves as participants in domestic policy contests. Promising future directions in the study of state-to-state relations are also evaluated, with the anticipation that verifying regional or other intermediate patterns of world migration politics may contribute to more general theories of international political economy.

  8. Resonant Removal of Exomoons during Planetary Migration

    NASA Astrophysics Data System (ADS)

    Spalding, Christopher; Batygin, Konstantin; Adams, Fred C.

    2016-01-01

    Jupiter and Saturn play host to an impressive array of satellites, making it reasonable to suspect that similar systems of moons might exist around giant extrasolar planets. Furthermore, a significant population of such planets is known to reside at distances of several Astronomical Units (AU), leading to speculation that some moons thereof might support liquid water on their surfaces. However, giant planets are thought to undergo inward migration within their natal protoplanetary disks, suggesting that gas giants currently occupying their host star’s habitable zone formed farther out. Here we show that when a moon-hosting planet undergoes inward migration, dynamical interactions may naturally destroy the moon through capture into a so-called evection resonance. Within this resonance, the lunar orbit’s eccentricity grows until the moon eventually collides with the planet. Our work suggests that moons orbiting within about ∼10 planetary radii are susceptible to this mechanism, with the exact number dependent on the planetary mass, oblateness, and physical size. Whether moons survive or not is critically related to where the planet began its inward migration, as well as the character of interlunar perturbations. For example, a Jupiter-like planet currently residing at 1 AU could lose moons if it formed beyond ∼5 AU. Cumulatively, we suggest that an observational census of exomoons could potentially inform us on the extent of inward planetary migration, for which no reliable observational proxy currently exists.

  9. Migration and the Earnings of Hispanic Men.

    ERIC Educational Resources Information Center

    Tienda, Marta; Wilson, Franklin D.

    1992-01-01

    Investigates the relationship between geographic mobility and earnings of Hispanic-American and white men using the 1980 Public Use Sample from the U.S. Census. Economic returns to migration are negligible for both Hispanic-American men and white men. Among Hispanic Americans, the earnings determination process is roughly similar for movers and…

  10. Migration Patterns and Language Maintenance in Paraguay.

    ERIC Educational Resources Information Center

    Gynan, Shaw N.

    1998-01-01

    Discusses migration patterns and language maintenance in Paraguay, where the majority of the population are speakers of Guarani, an indigenous South American language. Careful examination of Paraguayan census data reveals that Spanish-Guarani bilingualism is not nearly as widespread as claimed. (Author/VWL)

  11. Migration from Print to Online Use.

    ERIC Educational Resources Information Center

    Trubkin, Leone

    1980-01-01

    Examines the economic effects on information-producing companies of user migration from print to online information services. Three reasons are cited for the transition to online: (1) inflation, (2) new technology, and (3) database enhancement. Cost graphs and responses to questionnaires supplement the discussion. (SW)

  12. Rural to Urban Migration: A Colombian Case.

    ERIC Educational Resources Information Center

    Flinn, William L.

    This report examines reasons for movement of farmers to urban areas in an effort to determine whether migration is of an unselective nature or based on a selective process with regard to education, sex, age, and other factors. The investigation focuses on a specific case study in which the following aspects are discussed: (1) background…

  13. Migration Processes and Mechanisms of Youth Socialization.

    ERIC Educational Resources Information Center

    Mitev, Peter-Emil

    The dramatic changes in Bulgaria's agriculture, labor structure, and demography caused by the establishment of socialism in the country in the mid-1940s have resulted in changing mechanisms of youth socialization. Industrialization and agricultural consolidation precipitated a rural-urban migration boom and a resulting higher education level,…

  14. Effects of Photoevaporation on Planet Migration

    NASA Astrophysics Data System (ADS)

    Wise, Alexander; Dodson-Robinson, Sarah E.

    2015-01-01

    The final locations of planets may be influenced by turning points in their migration tracks called 'planet traps' (Hasegawa & Pudritz 2013, 2014). We explore a new planet trap caused by photoevaporation of a protoplanetary disk. Near the end of the lifetime of the gas disk, photoevaporation rates on the inner disk begin to exceed viscous accretion rates, initially resulting in a gap being formed at ~1 AU. Disk material inside the gap is quickly drained and then the gap widens until the gas disk is entirely blown away. Using a combination of analytical calculations and numerical simulations, we show that the variations of disk density resulting from this process affect the migration tracks of planets. In particular, the initial photoevaporative gap at ~1 AU stops planets from migrating inward from the gap for tens of thousands of years, until photoevaporation disperses the remaining disk and the planets lose their primary source of migration. This process may explain the apparent pileup of exoplanets at ~1 AU.

  15. Young People and Migration from Contemporary Poland

    ERIC Educational Resources Information Center

    White, Anne

    2010-01-01

    Young Polish migrants to the UK are often portrayed as being highly educated and mobile: willing nomads who are privileged to be able to take advantage of new opportunities for travel and work abroad offered by European Union membership. However, there are also less well-educated young people who adopt migration as a livelihood strategy in…

  16. Migration, Sociolinguistic Scale, and Educational Reproduction

    ERIC Educational Resources Information Center

    Collins, James

    2012-01-01

    Migration-based language pluralism and globalized identity conflicts pose challenges for educational research and linguistic anthropology, in particular, how we think about education and social inequality. This article proposes new conceptual tools, drawn from linguistic anthropology as well as world systems theory, for analyzing the role of…

  17. Analysis of Winds in Extreme Bird Migrations

    NASA Astrophysics Data System (ADS)

    Chapman, W.; Mills, C. M.; Gill, R. E.; Douglas, D.; Walsh, J. E.

    2013-12-01

    Bar-tailed Godwits feed in the nutrient-rich mud flats of western Alaska during the summer prior to attempting an extreme, non-stop migration of ~10,000 km lasting up to ten days and nights between late August and October to the Southern Hemisphere. In-situ measurements indicate that the birds make use of episodic near-surface tailwinds (north/northeast winds) on the backsides of low-pressure systems passing through the Gulf of Alaska to facilitate their trip. Projections of future climate from GCMs indicate northward shifts in these low-pressure systems, likely making a trip that already pushes the physical limits of these birds (in the present climate) more arduous. A generalized tailwind index is created in order to quantify the near-surface winds experienced during a typical migration season, providing clarity on the frequency and duration of beneficial tailwind episodes and facilitating comparison between present climate and paleoclimate scenarios. A comparison of our tailwind index to in-situ measurements verifies that the birds generally depart Alaska at advantageous times. Examination of past climate for possible alternate migration pathways provides useful information concerning the future of these birds. Spatial patterns of future wind and storm track shifts are consistent with more difficult migrations during the next century.

  18. Intercultural Communication and the Challenges of Migration

    ERIC Educational Resources Information Center

    Verschueren, Jef

    2008-01-01

    This paper discusses some basic properties of intercultural communication (treated from the point of view of linguistic pragmatics as fundamentally similar to any other form of communication, and emphasising the need to move radically away from any essentialist substantiation of "culture") against the background of contexts of migration. Three…

  19. The migration of nurses: trends and policies.

    PubMed Central

    Buchan, James; Sochalski, Julie

    2004-01-01

    This paper examines the policy context of the rise in the international mobility and migration of nurses. It describes the profile of the migration of nurses and the policy context governing the international recruitment of nurses to five countries: Australia, Ireland, Norway, the United Kingdom, and the United States. We also examine the policy challenges for workforce planning and the design of health systems infrastructure. Data are derived from registries of professional nurses, censuses, interviews with key informants, case studies in source and destination countries, focus groups, and empirical modelling to examine the patterns and implications of the movement of nurses across borders. The flow of nurses to these destination countries has risen, in some cases quite substantially. Recruitment from lower-middle income countries and low-income countries, as defined by The World Bank, dominate trends in nurse migration to the United Kingdom, Ireland, and the United States, while Norway and Australia, primarily register nurses from other high-income countries. Inadequate data systems in many countries prevent effective monitoring of these workforce flows. Policy options to manage nurse migration include: improving working conditions in both source and destination countries, instituting multilateral agreements to manage the flow more effectively, and developing compensation arrangements between source and destination countries. Recommendations for enhancements to workforce data systems are provided. PMID:15375448

  20. Factors influencing phototaxis in nocturnal migrating birds.

    PubMed

    Zhao, Xuebing; Chen, Mingyan; Wu, Zhaolu; Wang, Zijiang

    2014-12-01

    Many migratory bird species fly during the night (nocturnal migrants) and have been shown to display some phototaxis to artificial light. During 2006 to 2009, we investigated phototaxis in nocturnal migrants at Jinshan Yakou in Xinping County (N23°56', E101°30'; 2400 m above sea-level), and at the Niaowang Mountain in Funing County (N23°30', E105°35'; 1400 m above sea-level), both in the Yunnan Province of Southwest China. A total of 5069 birds, representing 129 species, were captured by mist-netting and artificial light. The extent of phototaxis effect on bird migration was examined during all four seasons, three phases of the moon, and under two weather conditions (mist and wind). Data were statistically analyzed to determine the extent to which these factors may impact phototaxis of nocturnal migrants. The results point to phototaxis in birds migrating in the spring and autumn, especially in the autumn. Furthermore, migrating birds were more readily attracted to artificial lights during nights with little moonlight, mist, and a headwind. Regardless of the initial orientation in which birds flew, either following the wind or against the wind, birds would always fly against the wind when flying towards the light. This study broadens our understanding of the nocturnal bird migration, potentially resulting in improved bird ringing practices, increased awareness, and better policies regarding bird protection.

  1. Hispanics Find Jobs that Shift Migration

    ERIC Educational Resources Information Center

    Gilroy, Marilyn

    2007-01-01

    Economic opportunity, the force that has driven population shifts for years, is changing the face of migration as Hispanics move into parts of the nation beyond border states and traditional ports of entry. North Carolina, Tennessee, Georgia, and Indiana are experiencing a steady growth in Hispanic population. In addition, West Virginia, Ohio, and…

  2. Retirement Migration and Interstate Income Transfers.

    ERIC Educational Resources Information Center

    Longino, Charles F., Jr.; Crown, William H.

    1990-01-01

    Examined transfer of income from state to state as result of elderly migration. Data from 1980 census microdata files revealed that billions of dollars are transferred between states each year. Used 1980-81 Consumer Expenditure Interview Survey to estimate consumption patterns of typical migrant household. Findings are discussed in context of…

  3. The future scenario for international labour migration.

    PubMed

    Tassello, G

    1989-01-01

    The study of migration helps us to grasp the social evolution and the political and economic strategies required to meet the new economic trends. The issue of permanent or temporary migration, long debated in the 1960s, now tends to disappear. Migrants are compared more to commuters on the international labor markets. Besides the economic out-migration flows, there are also the refugee migrations or the ever present phenomenon of persons uprooted from their home country as a result of natural disasters and famine. The worldwide economic crisis in the 1970s, the recession affecting some industrialized countries which used to be traditional labor-importing countries have barred many potential immigrant workers from entering these countries. If, on 1 hand, the persistent high rate of unemployment due to the transformation of industry and the computerization process has caused the dismissal of numerous unskilled--mainly immigrants--on the other hand, it has created the exigency of highly qualified personnel. The children of the indigenous population are therefore favored because of their better scholastic training. A 2nd generation is now condemned to remain marginal even though they have been brought up to the ideals of social improvement and integration into higher standards of living. A highly dissatisfied category of young people is now an integral part of many labor-importing countries. Many industrial countries are flirting with zero population growth. Considering the demographic, economic, social, and political imbalances which exist and tend to grow, the world now has all the prerequisites for huge and prolonged migration flows originating from the South and moving almost exclusively toward the megacities and the industrial countries in the North. As long as technological as well as social inequalities persist, inner and international migration flows will continue. It is evident that the aim of many highly industrialized countries is the total ceasing of all

  4. Changing Migration Patterns Within the United States. Resource Papers for College Geography No. 77-2.

    ERIC Educational Resources Information Center

    Roseman, Curtis C.

    In this study migration is examined as a component of population change. Decisions involved in migration are discussed. Source of migration data are suggested. Generalized in-migration and out-migration fields are described. Migration patterns before 1975 and recent migration patterns are examined and decisions underlying the latter are analyzed.…

  5. DIRECTLY IMAGING TIDALLY POWERED MIGRATING JUPITERS

    SciTech Connect

    Dong Subo; Katz, Boaz; Socrates, Aristotle

    2013-01-10

    Upcoming direct-imaging experiments may detect a new class of long-period, highly luminous, tidally powered extrasolar gas giants. Even though they are hosted by {approx} Gyr-'old' main-sequence stars, they can be as 'hot' as young Jupiters at {approx}100 Myr, the prime targets of direct-imaging surveys. They are on years-long orbits and presently migrating to 'feed' the 'hot Jupiters'. They are expected from 'high-e' migration mechanisms, in which Jupiters are excited to highly eccentric orbits and then shrink semimajor axis by a factor of {approx}10-100 due to tidal dissipation at close periastron passages. The dissipated orbital energy is converted to heat, and if it is deposited deep enough into the atmosphere, the planet likely radiates steadily at luminosity L {approx} 100-1000 L{sub Jup}(2 Multiplication-Sign 10{sup -7}-2 Multiplication-Sign 10{sup -6} L{sub Sun }) during a typical {approx} Gyr migration timescale. Their large orbital separations and expected high planet-to-star flux ratios in IR make them potentially accessible to high-contrast imaging instruments on 10 m class telescopes. {approx}10 such planets are expected to exist around FGK dwarfs within {approx}50 pc. Long-period radial velocity planets are viable candidates, and the highly eccentric planet HD 20782b at maximum angular separation {approx}0.''08 is a promising candidate. Directly imaging these tidally powered Jupiters would enable a direct test of high-e migration mechanisms. Once detected, the luminosity would provide a direct measurement of the migration rate, and together with mass (and possibly radius) estimate, they would serve as a laboratory to study planetary spectral formation and tidal physics.

  6. Social effects of migration in receiving countries.

    PubMed

    Ohndorf, W

    1989-06-01

    This paper examines the impact of post-1945 migration into Western, Middle, and Northern Europe from Southern Europe, Turkey, and Northern Africa, and migration to the traditional immigration countries by Asian and Latin American immigrants, on the social structures of receiving countries. Between 1955 and 1974, 1) traditional migration to the US and Australia became less important for European countries while traditional receiving countries accepted many immigrants from developing countries; and 2) rapid economic revival in Western and Northern Europe caused a considerable labor shortage which was filled by migrant workers especially from Southern Europe, Turkey, and Northern Africa, who stayed only until they reached their economic goals. Since 1974, job vacancies have declined and unemployment has soared. This employment crisis caused some migrants 1) to return to their countries of origin, 2) to bring the rest of their families to the receiving country, or 3) to lengthen their stay considerably. The number of refugees has also significantly increased since the mid-970s, as has the number of illegal migrants. After the mid-1970s, Europe began to experience integration problems. The different aspects of the impact of migration on social structures include 1) improvement of the housing situation for foreigners, 2) teaching migrants the language of the receiving country, 3) solving the unemployment problem of unskilled migrants, 4) improvement of educational and vocational qualifications of 2nd generation migrants, 5) development of programs to help unemployed wives of migrants to learn the language and meet indigenous women, 6) encouraging migrants to maintain their cultural identity and assisting them with reintegration if they return to their original country, 7) coping with the problems of refugees, and 8) solving the problems of illegal migration. Almost all receiving countries now severely restrict further immigration. [Those policies should result in

  7. Poleward migration of eddy driven jets

    NASA Astrophysics Data System (ADS)

    Chemke, Rei; Kaspi, Yohai

    2014-05-01

    There are observational evidence for a poleward migration of temporal anomalies of zonal winds in the upper troposphere. We show that such poleward migration can be due to poleward migration of eddy-driven jets; In fact, any eddy driven baroclinic jet should propagate poleward over time due to the variation of baroclinicity across the jet due to the sphericity of the planet. We demonstrate this using a high resolution idealized GCM where we examine the eddy driven jets over a wide range of rotation rates (up to 24 times the rotation rate of Earth). Unlike Earth-like rotation rates, where the eddy driven jet and the subtropical jet usually merge, at higher rotation rates the eddy driven jets are clearly separated from the subtropical jet and migrate poleward, while the subtropical jets remain in a constant latitude over time. The poleward drift is caused because measures of baroclinicity, such as Eady growth rate and supercriticality have a poleward bias due to the variation of the Coriolis parameter across the jet. This results in a poleward biased eddy momentum flux convergence relative to the mean jet, which overtime deflects the jet poleward. This is demonstrated systematically over the series of numerical simulations we present. As the rotation rate increases, and more (narrower) jets emerge the migration rate becomes smaller due to less eddy momentum flux convergence over the narrower baroclinic zones. This mechanism is consistent with eddy life cycle studies, which show the effects of sphericity on eddy propagation. In addition, we suggest scaling for the meridional scale of the jets and their spacing as function of the planetary rotation rate and latitude.

  8. Computational aspects of Gaussian beam migration

    SciTech Connect

    Hale, D.

    1992-01-01

    The computational efficiency of Gaussian beam migration depends on the solution of two problems: (1) computation of complex-valued beam times and amplitudes in Cartesian (x,z) coordinates, and (2) limiting computations to only those (x,z) coordinates within a region where beam amplitudes are significant. The first problem can be reduced to a particular instance of a class of closest-point problems in computational geometry, for which efficient solutions, such as the Delaunay triangulation, are well known. Delaunay triangulation of sampled points along a ray enables the efficient location of that point on the raypath that is closest to any point (x,z) at which beam times and amplitudes are required. Although Delaunay triangulation provides an efficient solution to this closest point problem, a simpler solution, also presented in this paper, may be sufficient and more easily extended for use in 3-D Gaussian beam migration. The second problem is easily solved by decomposing the subsurface image into a coarse grid of square cells. Within each cell, simple and efficient loops over (x,z) coordinates may be used. Because the region in which beam amplitudes are significant may be difficult to represent with simple loops over (x,z) coordinates, I use recursion to move from cell to cell, until entire region defined by the beam has been covered. Benchmark tests of a computer program implementing these solutions suggest that the cost of Gaussian hewn migration is comparable to that of migration via explicit depth extrapolation in the frequency-space domain. For the data sizes and computer programs tested here, the explicit method was faster. However, as data size was increased, the computation time for Gaussian beam migration grew more slowly than that for the explicit method.

  9. Computational aspects of Gaussian beam migration

    SciTech Connect

    Hale, D.

    1992-08-01

    The computational efficiency of Gaussian beam migration depends on the solution of two problems: (1) computation of complex-valued beam times and amplitudes in Cartesian (x,z) coordinates, and (2) limiting computations to only those (x,z) coordinates within a region where beam amplitudes are significant. The first problem can be reduced to a particular instance of a class of closest-point problems in computational geometry, for which efficient solutions, such as the Delaunay triangulation, are well known. Delaunay triangulation of sampled points along a ray enables the efficient location of that point on the raypath that is closest to any point (x,z) at which beam times and amplitudes are required. Although Delaunay triangulation provides an efficient solution to this closest point problem, a simpler solution, also presented in this paper, may be sufficient and more easily extended for use in 3-D Gaussian beam migration. The second problem is easily solved by decomposing the subsurface image into a coarse grid of square cells. Within each cell, simple and efficient loops over (x,z) coordinates may be used. Because the region in which beam amplitudes are significant may be difficult to represent with simple loops over (x,z) coordinates, I use recursion to move from cell to cell, until entire region defined by the beam has been covered. Benchmark tests of a computer program implementing these solutions suggest that the cost of Gaussian hewn migration is comparable to that of migration via explicit depth extrapolation in the frequency-space domain. For the data sizes and computer programs tested here, the explicit method was faster. However, as data size was increased, the computation time for Gaussian beam migration grew more slowly than that for the explicit method.

  10. Schwann cells promote endothelial cell migration

    PubMed Central

    Ramos, Tiago; Ahmed, Maqsood; Wieringa, Paul; Moroni, Lorenzo

    2015-01-01

    Directed cell migration is a crucial orchestrated process in embryonic development, wound healing, and immune response. The underlying substrate can provide physical and/or chemical cues that promote directed cell migration. Here, using electrospinning we developed substrates of aligned poly(lactic-co-glycolic acid) nanofibres to study the influence of glial cells on endothelial cells (ECs) in a 3-dimensional (3D) co-culture model. ECs build blood vessels and regulate their plasticity in coordination with neurons. Likewise, neurons construct nerves and regulate their circuits in coordination with ECs. In our model, the neuro-vascular cross-talk was assessed using a direct co-culture model of human umbilical vein endothelial cells (HUVECs) and rat Schwann cells (rSCs). The effect of rSCs on ECs behavior was demonstrated by earlier and higher velocity values and genetic expression profiles different of those of HUVECs when seeded alone. We observed 2 different gene expression trends in the co-culture models: (i) a later gene expression of angiogenic factors, such as interleukin-8 (IL-8) and vascular endothelial growth factor (VEGF), and (ii) an higher gene expression of genes involved in actin filaments rearrangement, such as focal adhesion kinase (FAK), Mitogen-activated protein kinase-activated protein kinase 13 (MAPKAPK13), Vinculin (VCL), and Profilin (PROF). These results suggested that the higher ECs migration is mainly due to proteins involved in the actin filaments rearrangement and in the directed cell migration rather than the effect of angiogenic factors. This co-culture model provides an approach to enlighten the neurovascular interactions, with particular focus on endothelial cell migration. PMID:26491999

  11. Gendered Patterns of Migration in Rural South Africa

    PubMed Central

    Camlin, Carol S.; Snow, Rachel C.; Hosegood, Victoria

    2013-01-01

    Gender is increasingly recognized as fundamental to understanding migration processes, causes and consequences. In South Africa, it is intrinsic to the social transformations fueling high levels of internal migration and complex forms of mobility. While female migration in Africa has often been characterized as less prevalent than male migration, and primarily related to marriage, in South Africa a feminization of internal migration is underway, fueled by women’s increasing labor market participation. In this paper, we report sex differences in patterns, trends and determinants of internal migration based on data collected in a demographic surveillance system between 2001 and 2006 in rural KwaZulu-Natal. We show that women were somewhat more likely than men to undertake any migration, but sex differences in migration trends differed by migration flow, with women more likely to migrate into the area than men, and men more likely to out-migrate. Out-migration was suppressed by marriage particularly for women, but most women were not married; both men’s and women’s out-migrations were undertaken mainly for purposes of employment. Over half of female out-migrations (versus 35% of male out-migrations) were to nearby rural areas. The findings highlight the high mobility of this population and the extent to which gender is intimately related to the processes determining migration. We consider the implications of these findings for the measurement of migration and mobility, in particular for health and social policy and research among highly mobile populations in southern Africa. PMID:25332690

  12. Seasonal migration as a substitute for, or precursor to, permanent migration.

    PubMed

    McHugh, K E

    1990-06-01

    Seasonal migration to national amenity areas is a major form of cyclical migration in the United States. This article examines conditions under which seasonal movement serves as a substitute for, or precursor to, permanent migration among winter visitors to recreational vehicle (RV) parks in the Phoenix, Arizona area. Ties to the home community, ties to the seasonal residence, demographic characteristics, and commitment to a mobile lifestyle are specified as determinants of expectations of moving to Phoenix on a permanent basis. The model is tested using survey data for a sample of 1,001 winter visitors in Phoenix RV parks. Results of a discriminant analysis indicate that place ties and position in the life cycle condition expectations of permanently migrating to a seasonal residence.

  13. Proactive Process-Level Live Migration and Back Migration in HPC Environments

    SciTech Connect

    Wang, Chao; Mueller, Frank; Engelmann, Christian; Scott, Stephen L

    2012-01-01

    As the number of nodes in high-performance computing environments keeps increasing, faults are becoming common place. Reactive fault tolerance (FT) often does not scale due to massive I/O requirements and relies on manual job resubmission. This work complements reactive with proactive FT at the process level. Through health monitoring, a subset of node failures can be anticipated when one's health deteriorates. A novel process-level live migration mechanism supports continued execution of applications during much of process migration. This scheme is integrated into an MPI execution environment to transparently sustain health-inflicted node failures, which eradicates the need to restart and requeue MPI jobs. Experiments indicate that 1-6.5 s of prior warning are required to successfully trigger live process migration while similar operating system virtualization mechanisms require 13-24 s. This self-healing approach complements reactive FT by nearly cutting the number of checkpoints in half when 70% of the faults are handled proactively. The work also provides a novel back migration approach to eliminate load imbalance or bottlenecks caused by migrated tasks. Experiments indicate the larger the amount of outstanding execution, the higher the benefit due to back migration.

  14. All across Africa: highly individual migration routes of Eleonora's falcon

    PubMed Central

    Gschweng, Marion; Kalko, Elisabeth K.V; Querner, Ulrich; Fiedler, Wolfgang; Berthold, Peter

    2008-01-01

    Eleonora's falcon (Falco eleonorae) is a rare raptor species that delays its breeding period until late summer to feed its young with passerines at the peak of autumn migration. Since the 1950s, this slender winged falcon has been believed to migrate along a historical route via the Red Sea to its main wintering area in Madagascar. In our study, we used satellite telemetry to investigate the real migration route of Eleonora's falcons and found that the species displayed a highly individual migration pattern. Furthermore, juvenile falcons migrated via West Africa to Madagascar and two juveniles could be tracked during spring migration and to their summering areas in East and West Africa. As juveniles migrated independently of adults, we discuss inherited navigation strategies forming part of a complex navigation system. We propose the idea of an orientation mechanism that naive falcons could apply during their long-distance migration towards their faraway wintering area located in the open ocean. PMID:18765348

  15. All across Africa: highly individual migration routes of Eleonora's falcon.

    PubMed

    Gschweng, Marion; Kalko, Elisabeth K V; Querner, Ulrich; Fiedler, Wolfgang; Berthold, Peter

    2008-12-22

    Eleonora's falcon (Falco eleonorae) is a rare raptor species that delays its breeding period until late summer to feed its young with passerines at the peak of autumn migration. Since the 1950s, this slender winged falcon has been believed to migrate along a historical route via the Red Sea to its main wintering area in Madagascar. In our study, we used satellite telemetry to investigate the real migration route of Eleonora's falcons and found that the species displayed a highly individual migration pattern. Furthermore, juvenile falcons migrated via West Africa to Madagascar and two juveniles could be tracked during spring migration and to their summering areas in East and West Africa. As juveniles migrated independently of adults, we discuss inherited navigation strategies forming part of a complex navigation system. We propose the idea of an orientation mechanism that naive falcons could apply during their long-distance migration towards their faraway wintering area located in the open ocean.

  16. Soil Quality and Human Migration in Kenya and Uganda

    PubMed Central

    Gray, Clark L.

    2011-01-01

    Soil degradation is widely considered to be a key factor undermining agricultural livelihoods in the developing world and contributing to rural out-migration. To date, however, few quantitative studies have examined the effects of soil characteristics on human migration or other social outcomes for potentially vulnerable households. This study takes advantage of a unique longitudinal survey dataset from Kenya and Uganda containing information on household-level soil properties to investigate the effects of soil quality on population mobility. Random effects multinomial logit models are used to test for effects of soil quality on both temporary and permanent migration while accounting for a variety of potential confounders. The analysis reveals that soil quality significantly reduces migration in Kenya, particularly for temporary labor migration, but marginally increases migration in Uganda. These findings are consistent with several previous studies in showing that adverse environmental conditions tend to increase migration but not universally, contrary to common assumptions about environmentally-induced migration. PMID:22016577

  17. Migration in far west Nepal: intergenerational linkages between internal and international migration of rural-to-urban migrants.

    PubMed

    Poertner, Ephraim; Junginger, Mathias; Müller-Böker, Ulrike

    2011-01-01

    In Nepal, international labor migration to India and overseas, as well as internal migration to the rural Nepalese lowlands, is of high socioeconomic significance. Scholarly debates about migration in Nepal have gradually shifted from an economic to a more holistic perspective, also incorporating social dimensions. However, little evidence has been generated about internal migration to urban destinations and the potential linkages between international and internal migration. This article draws on Bourdieu's “Theory of Practice” and sees migration as a social practice. Accordingly, migration practice is regarded as a strategy social agents apply to increase or transfer capitals and ultimately secure or improve their social position. Evidence for this argument is based on a qualitative case study of rural to urban migrants in Far West Nepal conducted in July and August 2009. The study at hand addresses linkages between internal and international migration practices and provides insight about a social stratum that is often neglected in migration research: the middle class and, more precisely, government employees. The authors show that social relations are crucial for channeling internal migration to a specific destination. Furthermore, they unveil how internal migration is connected to the international labor migration of former generations. Finally, the authors examine how migration strategies adopted over generations create multi-local social networks rooted in the family's place of origin.

  18. [Toward an explanation of migration patterns in Upper Volta].

    PubMed

    Piche, V; Gregory, J; Coulibaly, S

    1980-01-01

    The authors analyze the causes and consequences of internal and international migration in Upper Volta from the colonial period to the present. The effects on migration of taxes, military recruitment, forced labor, and the creation of a monetary system are discussed. In the second part of the paper, data from 1974-1975 national migration survey are used to examine migratory movements during the period 1969-1973. Hypotheses that could account for these migration patterns are suggested (SUMMARY IN ENG)

  19. Final Report: Migration Mechanisms for Large-scale Parallel Applications

    SciTech Connect

    Jason Nieh

    2009-10-30

    Process migration is the ability to transfer a process from one machine to another. It is a useful facility in distributed computing environments, especially as computing devices become more pervasive and Internet access becomes more ubiquitous. The potential benefits of process migration, among others, are fault resilience by migrating processes off of faulty hosts, data access locality by migrating processes closer to the data, better system response time by migrating processes closer to users, dynamic load balancing by migrating processes to less loaded hosts, and improved service availability and administration by migrating processes before host maintenance so that applications can continue to run with minimal downtime. Although process migration provides substantial potential benefits and many approaches have been considered, achieving transparent process migration functionality has been difficult in practice. To address this problem, our work has designed, implemented, and evaluated new and powerful transparent process checkpoint-restart and migration mechanisms for desktop, server, and parallel applications that operate across heterogeneous cluster and mobile computing environments. A key aspect of this work has been to introduce lightweight operating system virtualization to provide processes with private, virtual namespaces that decouple and isolate processes from dependencies on the host operating system instance. This decoupling enables processes to be transparently checkpointed and migrated without modifying, recompiling, or relinking applications or the operating system. Building on this lightweight operating system virtualization approach, we have developed novel technologies that enable (1) coordinated, consistent checkpoint-restart and migration of multiple processes, (2) fast checkpointing of process and file system state to enable restart of multiple parallel execution environments and time travel, (3) process migration across heterogeneous

  20. Control of cortical neuronal migration by glutamate and GABA

    PubMed Central

    Luhmann, Heiko J.; Fukuda, A.; Kilb, W.

    2015-01-01

    Neuronal migration in the cortex is controlled by the paracrine action of the classical neurotransmitters glutamate and GABA. Glutamate controls radial migration of pyramidal neurons by acting primarily on NMDA receptors and regulates tangential migration of inhibitory interneurons by activating non-NMDA and NMDA receptors. GABA, acting on ionotropic GABAA-rho and GABAA receptors, has a dichotomic action on radially migrating neurons by acting as a GO signal in lower layers and as a STOP signal in upper cortical plate (CP), respectively. Metabotropic GABAB receptors promote radial migration into the CP and tangential migration of interneurons. Besides GABA, the endogenous GABAergic agonist taurine is a relevant agonist controlling radial migration. To a smaller extent glycine receptor activation can also influence radial and tangential migration. Activation of glutamate and GABA receptors causes increases in intracellular Ca2+ transients, which promote neuronal migration by acting on the cytoskeleton. Pharmacological or genetic manipulation of glutamate or GABA receptors during early corticogenesis induce heterotopic cell clusters in upper layers and loss of cortical lamination, i.e., neuronal migration disorders which can be associated with neurological or neuropsychiatric diseases. The pivotal role of NMDA and ionotropic GABA receptors in cortical neuronal migration is of major clinical relevance, since a number of drugs acting on these receptors (e.g., anti-epileptics, anesthetics, alcohol) may disturb the normal migration pattern when present during early corticogenesis. PMID:25688185

  1. Control of cortical neuronal migration by glutamate and GABA.

    PubMed

    Luhmann, Heiko J; Fukuda, A; Kilb, W

    2015-01-01

    Neuronal migration in the cortex is controlled by the paracrine action of the classical neurotransmitters glutamate and GABA. Glutamate controls radial migration of pyramidal neurons by acting primarily on NMDA receptors and regulates tangential migration of inhibitory interneurons by activating non-NMDA and NMDA receptors. GABA, acting on ionotropic GABAA-rho and GABAA receptors, has a dichotomic action on radially migrating neurons by acting as a GO signal in lower layers and as a STOP signal in upper cortical plate (CP), respectively. Metabotropic GABAB receptors promote radial migration into the CP and tangential migration of interneurons. Besides GABA, the endogenous GABAergic agonist taurine is a relevant agonist controlling radial migration. To a smaller extent glycine receptor activation can also influence radial and tangential migration. Activation of glutamate and GABA receptors causes increases in intracellular Ca(2+) transients, which promote neuronal migration by acting on the cytoskeleton. Pharmacological or genetic manipulation of glutamate or GABA receptors during early corticogenesis induce heterotopic cell clusters in upper layers and loss of cortical lamination, i.e., neuronal migration disorders which can be associated with neurological or neuropsychiatric diseases. The pivotal role of NMDA and ionotropic GABA receptors in cortical neuronal migration is of major clinical relevance, since a number of drugs acting on these receptors (e.g., anti-epileptics, anesthetics, alcohol) may disturb the normal migration pattern when present during early corticogenesis.

  2. MIGRATION OF COLLEGE AND UNIVERSITY STUDENTS, STATE OF WASHINGTON.

    ERIC Educational Resources Information Center

    GOSSMAN, CHARLES S.; AND OTHERS

    TWO GENERAL ASPECTS OF COLLEGE AND UNIVERSITY STUDENT MIGRATION AS IT RELATES TO THE STATE OF WASHINGTON ARE DISCUSSED. THE FIRST ASPECT INCLUDES ANALYSIS OF MIGRATION PATTERNS IN ACCORDANCE WITH ENROLLMENT CATEGORIES AND TYPES OF INSTITUTIONS, DIFFERENTIAL VOLUMES AND PATTERNS OF MIGRATION FOR SPECIFIC COLLEGES AND UNIVERSITIES IN THE STATE, AND…

  3. Evolution of migration rate in a spatially realistic metapopulation model.

    PubMed

    Heino, M; Hanski, I

    2001-05-01

    We use an individual-based, spatially realistic metapopulation model to study the evolution of migration rate. We first explore the consequences of habitat change in hypothetical patch networks on a regular lattice. If the primary consequence of habitat change is an increase in local extinction risk as a result of decreased local population sizes, migration rate increases. A nonmonotonic response, with migration rate decreasing at high extinction rate, was obtained only by assuming very frequent catastrophes. If the quality of the matrix habitat deteriorates, leading to increased mortality during migration, the evolutionary response is more complex. As long as habitat patch occupancy does not decrease markedly with increased migration mortality, reduced migration rate evolves. However, once mortality becomes so high that empty patches remain uncolonized for a long time, evolution tends to increase migration rate, which may lead to an "evolutionary rescue" in a fragmented landscape. Kin competition has a quantitative effect on the evolution of migration rate in our model, but these patterns in the evolution of migration rate appear to be primarily caused by spatiotemporal variation in fitness and mortality during migration. We apply the model to real habitat patch networks occupied by two checkerspot butterfly (Melitaea) species, for which sufficient data are available to estimate rigorously most of the model parameters. The model-predicted migration rate is not significantly different from the empirically observed one. Regional variation in patch areas and connectivities leads to regional variation in the optimal migration rate, predictions that can be tested empirically. PMID:18707258

  4. The Monetary Rewards of Migration Within the U.S.

    ERIC Educational Resources Information Center

    Wertheimer, Richard F., II

    This study focuses on the economic benefits derived by the migrant from migration. The report presents a methodology for computing monetary benefits, an estimate of these benefits, and implications of the findings for public policy. Included are a discussion of domestic migration and public policy, an economic theory of migration, an explanation…

  5. Internal Migration and Citizenship Education in China's Shenzhen City

    ERIC Educational Resources Information Center

    Ye, Wangbei

    2016-01-01

    Migration's influences on citizenship education were widely discussed in the literature. However, most studies were based on international migration that drew experience from, for example, North America and Europe. Less attention was paid to internal migration or developing areas. This article takes China as an example, which is a country that has…

  6. Women in Migration: A Third World Focus. Summary.

    ERIC Educational Resources Information Center

    International Center for Research on Women, Washington, DC.

    A study of women in migration in Third World countries since 1960 reveals that, contrary to assumptions, more women are migrating autonomously from rural to urban areas in an often unsuccessful effort to improve their economic status. The results of the study of migration patterns in Africa, Asia, Central America, South America, and the Middle…

  7. Autofocus correction of excessive migration in synthetic aperture radar images.

    SciTech Connect

    Doerry, Armin Walter

    2004-09-01

    When residual range migration due to either real or apparent motion errors exceeds the range resolution, conventional autofocus algorithms fail. A new migration-correction autofocus algorithm has been developed that estimates the migration and applies phase and frequency corrections to properly focus the image.

  8. 3 CFR - Unexpected Urgent Refugee and Migration Needs

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 3 The President 1 2013-01-01 2013-01-01 false Unexpected Urgent Refugee and Migration Needs... Unexpected Urgent Refugee and Migration Needs Memorandum for the Secretary of State By the authority vested...) of the Migration and Refugee Assistance Act of 1962 (the “Act”), as amended, (22 U.S.C....

  9. The spring migration of adult North American Ospreys

    USGS Publications Warehouse

    Martell, Mark S.; Bierregaard, Richard O.; Washburn, Brian E.; Elliott, John E.; Henny, Charles J.; Kennedy, Robert S.; MacLeod, Iain

    2014-01-01

    Most North American Ospreys (Pandion haliaetus) are migratory, breeding in northern latitudes and migrating long distances to and from their wintering grounds in the tropics. Although fall migration patterns of North American Ospreys have been described and studied, very little has been published about the spring migration of these birds. We used satellite telemetry to: (1) determine the characteristics (timing, duration, migratory routes) of spring migrations of Ospreys; (2) determine if differences in spring migration patterns existed between sexes and among three breeding populations (east coast, midwestern, and western); and (3) compare consecutive fall and spring migrations of individual Ospreys. The median dates for departure from the wintering grounds and arrival on the breeding grounds did not differ significantly between adult male and female Ospreys. Compared to their fall migrations, all male and all east coast Ospreys spent fewer days on migration, fewer days in stopover periods along the migration route, traveled shorter distances overall, and traveled farther (on average) each day during spring. In contrast, fall and spring migration characteristics of all female and western Ospreys were similar. Our findings suggest that, although sex and breeding location might influence the spring migration strategy used by individual Ospreys, both males and females minimize the time spent on migration to ensure a timely arrival on the breeding grounds to establish or defend a nesting territory.

  10. Romanians Abroad: A Snapshot of Highly Skilled Migration

    ERIC Educational Resources Information Center

    Ferro, Anna

    2004-01-01

    This paper is about the experience of labour migration among skilled Romanians, mainly Information Technology workers and highly qualified researchers. It is based on a questionnaire survey where, among other elements, the researcher investigated the push-pull aspects of qualified migration and the strategies of labour migration. This paper…

  11. Bat predation on nocturnally migrating birds.

    PubMed

    Ibáñez, C; Juste, J; García-Mudarra, J L; Agirre-Mendi, P T

    2001-08-14

    Bat predation on birds is a very rare phenomenon in nature. Most documented reports of bird-eating bats refer to tropical bats that occasionally capture resting birds. Millions of small birds concentrate and cross over the world's temperate regions during migration, mainly at night, but no nocturnal predators are known to benefit from this enormous food resource. An analysis of 14,000 fecal pellets of the greater noctule bat (Nyctalus lasiopterus) reveals that this species captures and eats large numbers of migrating passerines, making it the only bat species so far known that regularly preys on birds. The echolocation characteristics and wing morphology of this species strongly suggest that it captures birds in flight.

  12. A magnetic compass aids monarch butterfly migration

    PubMed Central

    Guerra, Patrick A; Gegear, Robert J; Reppert, Steven M

    2014-01-01

    Convincing evidence that migrant monarch butterflies (Danaus plexippus) use a magnetic compass to aid their fall migration has been lacking from the spectacular navigational capabilities of this species. Here we use flight simulator studies to show that migrants indeed possess an inclination magnetic compass to help direct their flight equatorward in the fall. The use of this inclination compass is light-dependent utilizing ultraviolet-A/blue light between 380 and 420 nm. Notably, the significance of light <420 nm for inclination compass function was not considered in previous monarch studies. The antennae are important for the inclination compass because they appear to contain light-sensitive magnetosensors. For migratory monarchs, the inclination compass may serve as an important orientation mechanism when directional daylight cues are unavailable and may also augment time-compensated sun compass orientation for appropriate directionality throughout the migration. PMID:24960099

  13. A magnetic compass aids monarch butterfly migration.

    PubMed

    Guerra, Patrick A; Gegear, Robert J; Reppert, Steven M

    2014-01-01

    Convincing evidence that migrant monarch butterflies (Danaus plexippus) use a magnetic compass to aid their fall migration has been lacking from the spectacular navigational capabilities of this species. Here we use flight simulator studies to show that migrants indeed possess an inclination magnetic compass to help direct their flight equatorward in the fall. The use of this inclination compass is light-dependent utilizing ultraviolet-A/blue light between 380 and 420 nm. Notably, the significance of light <420 nm for inclination compass function was not considered in previous monarch studies. The antennae are important for the inclination compass because they appear to contain light-sensitive magnetosensors. For migratory monarchs, the inclination compass may serve as an important orientation mechanism when directional daylight cues are unavailable and may also augment time-compensated sun compass orientation for appropriate directionality throughout the migration. PMID:24960099

  14. Migration, remittances, livelihood trajectories, and social resilience.

    PubMed

    Adger, W Neil; Kelly, P Mick; Winkels, Alexandra; Huy, Luong Quang; Locke, Catherine

    2002-06-01

    We argue that all aspects of demographic change, including migration, impact on the social resilience of individuals and communities, as well as on the sustainability of the underlying resource base. Social resilience is the ability to cope with and adapt to environmental and social change mediated through appropriate institutions. We investigate one aspect of the relationship between demographic change, social resilience, and sustainable development in contemporary coastal Vietnam: the effects of migration and remittances on resource-dependent communities in population source areas. We find, using longitudinal data on livelihood sources, that emigration and remittances have offsetting effects on resilience within an evolving social and political context. Emigration is occurring concurrently with, not driving, the expansion of unsustainable coastal aquaculture. Increasing economic inequality also undermines social resilience. At the same time diversification and increasing income levels are beneficial for resilience. PMID:12174607

  15. Forced migration, adolescence, and identity formation.

    PubMed

    Anagnostopoulos, Dimitris C; Vlassopoulos, Maria; Lazaratou, Helen

    2006-09-01

    Adolescence is a complex biopsychosocial phenomenon. All the inner-subjective changes in adolescents take place within the context of a specific social environment, which offers the necessary ideological setting that adolescents must confront in the course of their identity formation. Forced migration creates conditions under which the adolescent Ego may be traumatized more easily, resulting in the development of defensive mechanisms, which may interfere with the natural process of identity formation. The aim of this paper is to investigate how a traumatic situation such as forced migration may affect the mechanisms of identity formation in adolescence. For this purpose, clinical material, consisting of two cases of psychoanalytical psychotherapy of adolescents who were forced to immigrate to Greece, is presented and discussed in a psychoanalytical theoretical framework, along with the historical-sociological background.

  16. Primordial Germ Cell Specification and Migration

    PubMed Central

    Marlow, Florence

    2015-01-01

    Primordial germ cells are the progenitor cells that give rise to the gametes. In some animals, the germline is induced by zygotic transcription factors, whereas in others, primordial germ cell specification occurs via inheritance of maternally provided gene products known as germ plasm. Once specified, the primordial germ cells of some animals must acquire motility and migrate to the gonad in order to survive. In all animals examined, perinuclear structures called germ granules form within germ cells. This review focuses on some of the recent studies, conducted by several groups using diverse systems, from invertebrates to vertebrates, which have provided mechanistic insight into the molecular regulation of germ cell specification and migration. PMID:26918157

  17. Using magnetic tape technology for data migration

    NASA Technical Reports Server (NTRS)

    Therrien, David; Cheung, Yim-Ling

    1993-01-01

    Magnetic tape and optical disk library units (jukeboxes) are satisfying the demand for high-capacity cost-effective storage. The choice between optical disk and magnetic tape technology must take into account the cost limitations as well as the performance and reliability requirements of the user environment. Library units require data management software in order to function in an automated and user-transparent way. The most common data management applications are backup and recovery, data migration, and archiving. The medium access patterns that these applications create will be described. Since the most user visible application is data migration, a queue simulator was developed to model its performance against a variety of library units. The major subject of this paper is the design and implementation of this simulator as well as some simulation results. The relative cost and reliability of magnetic tape versus optical disk library units is presented for completeness.

  18. Bat predation on nocturnally migrating birds

    PubMed Central

    Ibáñez, Carlos; Juste, Javier; García-Mudarra, Juan L.; Agirre-Mendi, Pablo T.

    2001-01-01

    Bat predation on birds is a very rare phenomenon in nature. Most documented reports of bird-eating bats refer to tropical bats that occasionally capture resting birds. Millions of small birds concentrate and cross over the world's temperate regions during migration, mainly at night, but no nocturnal predators are known to benefit from this enormous food resource. An analysis of 14,000 fecal pellets of the greater noctule bat (Nyctalus lasiopterus) reveals that this species captures and eats large numbers of migrating passerines, making it the only bat species so far known that regularly preys on birds. The echolocation characteristics and wing morphology of this species strongly suggest that it captures birds in flight. PMID:11493689

  19. Investigating Delamination Migration in Composite Tape Laminates

    NASA Technical Reports Server (NTRS)

    Ratcliffe, James G.; DeCarvalho, Nelson V.

    2014-01-01

    A modification to a recently developed test specimen designed to investigate migration of a delamination between neighboring ply interfaces in tape laminates is presented. The specimen is a cross-ply laminated beam consisting of 40 plies with a polytetrafluoroethylene insert spanning part way along its length. The insert is located between a lower 0-degree ply (specimen length direction) and a stack of four 90-degree plies (specimen width direction). The modification involved a stacking sequence that promotes stable delamination growth prior to migration, and included a relocation of the insert from the specimen midplane to the interface between plies 14 and 15. Specimens were clamped at both ends onto a rigid baseplate and loaded on their upper surface via a piano hinge assembly, resulting in a predominantly flexural loading condition. Tests were conducted with the load-application point positioned at various locations along a specimen's span. This position affected the sequence of damage events during a test.

  20. [Marriage structure of Yakut populations: migrations].

    PubMed

    Kucher, A I; Danilova, A L; Koneva, L A; Nogovitsina, A N

    2010-05-01

    Rural and urban settlements of the Republic of Sakha (Yakutia) are characterized by intense marriage migrations: both indigenous residents of different uluses (districts) of the republic (7-30%) and migrants from outside Yakutia (7-29%) contract marriages in five administrative centers analyzed in this respect. All the populations studied are characterized by a wide geographic range of the birthplaces of persons contracted marriages there (from 14 to 24 uluses of Yakutia), without any predominant migration flow from one district to another. The proportion of homolocal marriages among indigenous ethnic groups (Evenks, Evens, and Yukagirs) is as high as 75-100%; this proportion among Yakuts varies from 26 to 68%; heterolocal marriages are more characteristic of Russian immigrants (41-95%). Positive assortative marriages among persons with the same birthplaces have been found in all populations except for Momsky ulus. PMID:20583606

  1. Bursts of activity in collective cell migration

    PubMed Central

    Chepizhko, Oleksandr; Giampietro, Costanza; Mastrapasqua, Eleonora; Nourazar, Mehdi; Ascagni, Miriam; Sugni, Michela; Fascio, Umberto; Leggio, Livio; Malinverno, Chiara; Scita, Giorgio; Santucci, Stéphane; Alava, Mikko J.; Zapperi, Stefano; La Porta, Caterina A. M.

    2016-01-01

    Dense monolayers of living cells display intriguing relaxation dynamics, reminiscent of soft and glassy materials close to the jamming transition, and migrate collectively when space is available, as in wound healing or in cancer invasion. Here we show that collective cell migration occurs in bursts that are similar to those recorded in the propagation of cracks, fluid fronts in porous media, and ferromagnetic domain walls. In analogy with these systems, the distribution of activity bursts displays scaling laws that are universal in different cell types and for cells moving on different substrates. The main features of the invasion dynamics are quantitatively captured by a model of interacting active particles moving in a disordered landscape. Our results illustrate that collective motion of living cells is analogous to the corresponding dynamics in driven, but inanimate, systems. PMID:27681632

  2. [Regional migrating osteoporosis - a case report].

    PubMed

    Zofková, I; Hrbáč, J; Dostál, J; Sprindrich, J

    2013-09-01

    Regional migrating osteoporosis (RMO) was observed in young man with episodes of bone pain in bearing joints, which migrated from hip to leg and subsequently to knee on the unilateral side. Dynamic scintigraphy (SPECT) carried out during relapse of pain demonstrated increased accumulation of radioizotope in Lisfrank joint, distal epiphysis of femur and proximal epiphysis of tibia on the unilateral side due to hyperperfusion and high metabolic turnover in these regions of the skeleton. Dia-gnosis of RMO was confirmed by magnetic resonance (MRI), which showed bone marrow edema of corresponding regions. Although RMO is relatively benign disease with spontaneous remissions, infection etiology or the more serious avascular necrosis should be taken into account. PMID:24073956

  3. Forced migration, adolescence, and identity formation.

    PubMed

    Anagnostopoulos, Dimitris C; Vlassopoulos, Maria; Lazaratou, Helen

    2006-09-01

    Adolescence is a complex biopsychosocial phenomenon. All the inner-subjective changes in adolescents take place within the context of a specific social environment, which offers the necessary ideological setting that adolescents must confront in the course of their identity formation. Forced migration creates conditions under which the adolescent Ego may be traumatized more easily, resulting in the development of defensive mechanisms, which may interfere with the natural process of identity formation. The aim of this paper is to investigate how a traumatic situation such as forced migration may affect the mechanisms of identity formation in adolescence. For this purpose, clinical material, consisting of two cases of psychoanalytical psychotherapy of adolescents who were forced to immigrate to Greece, is presented and discussed in a psychoanalytical theoretical framework, along with the historical-sociological background. PMID:16964539

  4. Navigational Mechanisms of Migrating Monarch Butterflies

    PubMed Central

    Reppert, Steven M.; Gegear, Robert J.; Merlin, Christine

    2010-01-01

    Recent studies of the iconic fall migration of monarch butterflies have illuminated the mechanisms behind the navigation south, using a time-compensated sun compass. Skylight cues, such as the sun itself and polarized light, are processed through both eyes and likely integrated in the brain’s central complex, the presumed site of the sun compass. Time compensation is provided by circadian clocks that have a distinctive molecular mechanism and that reside in the antennae. Monarchs may also use a magnetic compass, because they possess two cryptochromes that have the molecular capability for light-dependent magnetoreception. Multiple genomic approaches are being utilized to ultimately identify navigation genes. Monarch butterflies are thus emerging as an excellent model organism to study the molecular and neural basis of long-distance migration. PMID:20627420

  5. Networking galore: intermediate filaments and cell migration.

    PubMed

    Chung, Byung-Min; Rotty, Jeremy D; Coulombe, Pierre A

    2013-10-01

    Intermediate filaments (IFs) are assembled from a diverse group of evolutionarily conserved proteins and are specified in a tissue-dependent, cell type-dependent, and context-dependent fashion in the body. IFs are involved in multiple cellular processes that are crucial for the maintenance of cell and tissue integrity and the response and adaptation to various stresses, as conveyed by the broad array of crippling clinical disorders caused by inherited mutations in IF coding sequences. Accordingly, the expression, assembly, and organization of IFs are tightly regulated. Migration is a fitting example of a cell-based phenomenon in which IFs participate as both effectors and regulators. With a particular focus on vimentin and keratin, we here review how the contributions of IFs to the cell's mechanical properties, to cytoarchitecture and adhesion, and to regulatory pathways collectively exert a significant impact on cell migration.

  6. Moisture Migration in Stored Granular Materials

    NASA Astrophysics Data System (ADS)

    Avila-Acevedo, J. G.; Tsotsas, E.

    2010-05-01

    Thermally-driven moisture migration during the storage of polycarbonate pellets in a cylindrical silo is investigated in the present work. The bed of pellets is assumed as saturated porous medium with hygroscopic activity at a uniform initial temperature. The side wall of the cylinder undergoes a change to a low temperature while the ends of the packed cylinder are considered to be insulated. A mathematical model for the transient transport of heat and moisture is developed, where the Darcy law is assumed for the flow, the Boussinesq approximation is used for accounting density variations and the adsorption equilibrium of moisture is considered as a linear relationship to the relative humidity. The dimension analysis of the model and its numerical solution allow for the identification of the mechanisms responsible for moisture migration and for the prediction of moisture maldristibution.

  7. Subgaleal migration of a ventriculoperitoneal shunt.

    PubMed

    Al Hinai, Qasim S; Pawar, Sanjay J; Sharma, Rewati Raman; Devadas, R V

    2006-07-01

    Blockage of a ventriculoperitoneal (VP) shunt is very common. Here, we describe an unusual case of shunt blockage in an infant. He was shunted for hydrocephalus associated with a Dandy-Walker malformation diagnosed at birth. At surgery, the entire VP shunt was found to have migrated into the subgaleal space, which clinically presented as shunt obstruction. We suggest techniques to avoid this rare, but preventable, complication of shunt surgery.

  8. Women and migration: a public health issue.

    PubMed

    Carballo, M; Grocutt, M; Hadzihasanovic, A

    1996-01-01

    The need to migrate is usually a function of the complex interaction of economic, social, familial and political factors. Among the most important, however, are the denial of access to education, employment, goods and services and the lack of respect for basic human rights. Because in many societies women are marginalized from these rights, migration to more economically and educationally open societies can often help improve their personal situation and their professional opportunities. On the other hand, because the status of women is usually linked to their role and status within the family and is defined in relationship to their male partners, migration can place women in situations where they experience stress and anxiety due to the loss of their traditional social entourage and environment. Their social integration in new settings may be equally limited by their initial lack of education and occupational experience. The higher vulnerability of women to sexual abuse and violence also places them at risk of STDs, including HIV, and a range of post-traumatic stress disorders associated with sexual violence. Their reproductive health needs often go unnoticed and unprotected even in well organized refugee and migrant situations, and the insensitivity of health staff to the needs of women is often more pronounced in refugee and migrant contexts than it is in general. Health monitoring of women in all migration-related situations has to be given greater priority. Similarly, much more attention at a health policy level is called for if the rights of women refugees and migrants are to be protected, and their contribution to health and social development is to be acknowledged and promoted.

  9. Return migration to Scotland: some direct evidence.

    PubMed

    Gordon, I

    1982-04-01

    The author presents a critique of a paper by Bell and Kirwan in which they contend that the probability of return migration will tend to be equal for Scottish migrants to England and Wales and for English or Welsh migrants to Scotland. In the present article, comparable data for the United States and Scotland are evaluated, and comments are presented on the regression equations used. A reply by Bell and Kirwan is also included (pp. 135-6).

  10. Women and migration: a public health issue.

    PubMed

    Carballo, M; Grocutt, M; Hadzihasanovic, A

    1996-01-01

    The need to migrate is usually a function of the complex interaction of economic, social, familial and political factors. Among the most important, however, are the denial of access to education, employment, goods and services and the lack of respect for basic human rights. Because in many societies women are marginalized from these rights, migration to more economically and educationally open societies can often help improve their personal situation and their professional opportunities. On the other hand, because the status of women is usually linked to their role and status within the family and is defined in relationship to their male partners, migration can place women in situations where they experience stress and anxiety due to the loss of their traditional social entourage and environment. Their social integration in new settings may be equally limited by their initial lack of education and occupational experience. The higher vulnerability of women to sexual abuse and violence also places them at risk of STDs, including HIV, and a range of post-traumatic stress disorders associated with sexual violence. Their reproductive health needs often go unnoticed and unprotected even in well organized refugee and migrant situations, and the insensitivity of health staff to the needs of women is often more pronounced in refugee and migrant contexts than it is in general. Health monitoring of women in all migration-related situations has to be given greater priority. Similarly, much more attention at a health policy level is called for if the rights of women refugees and migrants are to be protected, and their contribution to health and social development is to be acknowledged and promoted. PMID:9050196

  11. Elderly migration and development in small communities.

    PubMed

    Rowles, G D; Watkins, J F

    1993-01-01

    "This paper develops a conceptual model of the process of community change [in the United States] in response to elderly inmigration. Analysis of intra-regional variation in elderly migration patterns in Appalachia, and synthesis of an emergent literature on the benefits and costs of attracting elderly migrants, serve as a backdrop for case studies, based on field observations and interviews, of three contrasting Appalachian communities at different stages of development as retirement destinations."

  12. Managing international migration in developing countries.

    PubMed

    Farrag, M

    1997-01-01

    This article summarizes the findings of 180 participants from 57 governments attending the UN's International Office of Migration's (IOM) Migration Seminar in April 1997 in Geneva. The teams of researchers represented the four developing world regions: sub-Saharan Africa; South Asia; the Arab Region; and Mexico, Central America, and the Caribbean. The seminar was part of IOM's research project on emigration dynamics in developing countries, which was begun in 1993. Researchers shared a common conceptual framework, which recognized the changing socioeconomic, sociopolitical, demographic, and ecological conditions in each country and subregion, the role of networks between people in sending and receiving countries, and the nature of entry restrictions. The research and workshop aimed to help policymakers in developed and developing countries. Conference delegates found the research framework acceptable despite the differences between regions and countries. Conference delegates agreed that the IOM research project was a unique forum for exchange of information and experience between sending and receiving countries. Many participants wanted IOM to provide technical assistance that would help countries manage migration. Delegates strongly desired international commitments to human rights for migrants. Delegates wanted better information exchanges, particularly interchanges of experience on policy measures among Governments, and the stronger inclusion of migrants in management. Returning migrants needed assistance with reintegration. The delegates made 12 recommendations about establishment of an effective system of information exchange, research on emigration dynamics and return migration, development of measures for managing flows that respect existing employment structures, new agreements, and reliable information for migrants on living conditions in host countries. PMID:12348081

  13. Temporal patterns in adult salmon migration timing across southeast Alaska.

    PubMed

    Kovach, Ryan P; Ellison, Stephen C; Pyare, Sanjay; Tallmon, David A

    2015-05-01

    Pacific salmon migration timing can drive population productivity, ecosystem dynamics, and human harvest. Nevertheless, little is known about long-term variation in salmon migration timing for multiple species across broad regions. We used long-term data for five Pacific salmon species throughout rapidly warming southeast Alaska to describe long-term changes in salmon migration timing, interannual phenological synchrony, relationships between climatic variation and migratory timing, and to test whether long-term changes in migration timing are related to glaciation in headwater streams. Temporal changes in the median date of salmon migration timing varied widely across species. Most sockeye populations are migrating later over time (11 of 14), but pink, chum, and especially coho populations are migrating earlier than they did historically (16 of 19 combined). Temporal trends in duration and interannual variation in migration timing were highly variable across species and populations. The greatest temporal shifts in the median date of migration timing were correlated with decreases in the duration of migration timing, suggestive of a loss of phenotypic variation due to natural selection. Pairwise interannual correlations in migration timing varied widely but were generally positive, providing evidence for weak region-wide phenological synchrony. This synchrony is likely a function of climatic variation, as interannual variation in migration timing was related to climatic phenomenon operating at large- (Pacific decadal oscillation), moderate- (sea surface temperature), and local-scales (precipitation). Surprisingly, the presence or the absence of glaciers within a watershed was unrelated to long-term shifts in phenology. Overall, there was extensive heterogeneity in long-term patterns of migration timing throughout this climatically and geographically complex region, highlighting that future climatic change will likely have widely divergent impacts on salmon

  14. Temporal patterns in adult salmon migration timing across southeast Alaska

    USGS Publications Warehouse

    Kovach, Ryan P.; Ellison, Stephen; Pyare, Sanjay; Tallmon, David

    2015-01-01

    Pacific salmon migration timing can drive population productivity, ecosystem dynamics, and human harvest. Nevertheless, little is known about long-term variation in salmon migration timing for multiple species across broad regions. We used long-term data for five Pacific salmon species throughout rapidly warming southeast Alaska to describe long-term changes in salmon migration timing, interannual phenological synchrony, relationships between climatic variation and migratory timing, and to test whether long-term changes in migration timing are related to glaciation in headwater streams. Temporal changes in the median date of salmon migration timing varied widely across species. Most sockeye populations are migrating later over time (11 of 14), but pink, chum, and especially coho populations are migrating earlier than they did historically (16 of 19 combined). Temporal trends in duration and interannual variation in migration timing were highly variable across species and populations. The greatest temporal shifts in the median date of migration timing were correlated with decreases in the duration of migration timing, suggestive of a loss of phenotypic variation due to natural selection. Pairwise interannual correlations in migration timing varied widely but were generally positive, providing evidence for weak region-wide phenological synchrony. This synchrony is likely a function of climatic variation, as interannual variation in migration timing was related to climatic phenomenon operating at large- (Pacific decadal oscillation), moderate- (sea surface temperature), and local-scales (precipitation). Surprisingly, the presence or the absence of glaciers within a watershed was unrelated to long-term shifts in phenology. Overall, there was extensive heterogeneity in long-term patterns of migration timing throughout this climatically and geographically complex region, highlighting that future climatic change will likely have widely divergent impacts on salmon

  15. Temporal patterns in adult salmon migration timing across southeast Alaska.

    PubMed

    Kovach, Ryan P; Ellison, Stephen C; Pyare, Sanjay; Tallmon, David A

    2015-05-01

    Pacific salmon migration timing can drive population productivity, ecosystem dynamics, and human harvest. Nevertheless, little is known about long-term variation in salmon migration timing for multiple species across broad regions. We used long-term data for five Pacific salmon species throughout rapidly warming southeast Alaska to describe long-term changes in salmon migration timing, interannual phenological synchrony, relationships between climatic variation and migratory timing, and to test whether long-term changes in migration timing are related to glaciation in headwater streams. Temporal changes in the median date of salmon migration timing varied widely across species. Most sockeye populations are migrating later over time (11 of 14), but pink, chum, and especially coho populations are migrating earlier than they did historically (16 of 19 combined). Temporal trends in duration and interannual variation in migration timing were highly variable across species and populations. The greatest temporal shifts in the median date of migration timing were correlated with decreases in the duration of migration timing, suggestive of a loss of phenotypic variation due to natural selection. Pairwise interannual correlations in migration timing varied widely but were generally positive, providing evidence for weak region-wide phenological synchrony. This synchrony is likely a function of climatic variation, as interannual variation in migration timing was related to climatic phenomenon operating at large- (Pacific decadal oscillation), moderate- (sea surface temperature), and local-scales (precipitation). Surprisingly, the presence or the absence of glaciers within a watershed was unrelated to long-term shifts in phenology. Overall, there was extensive heterogeneity in long-term patterns of migration timing throughout this climatically and geographically complex region, highlighting that future climatic change will likely have widely divergent impacts on salmon

  16. Altitudinal migration in bats: evidence, patterns, and drivers.

    PubMed

    McGuire, Liam P; Boyle, W Alice

    2013-11-01

    Altitudinal migrations are common in all major vertebrate and some invertebrate lineages. Such migrations have important implications for the basic and applied ecology of animals making these movements. The idea that bats make altitudinal migrations has been suggested for nearly a century. However, studies documenting the existence and causes of altitudinal bat migrations are scarce, and are frequently published in the 'grey' literature. For the first time, we comprehensively review the evidence supporting the existence of altitudinal bat migrations worldwide, describe basic patterns of migration in temperate and tropical regions, and articulate and propose tests of hypotheses potentially explaining these migrations. We compiled a list of 50 studies indicative of altitudinal bat migration in 61 species (five families) from 21 countries (four continents). The temporal and spatial patterns of these migrations grouped biogeographically. Temperate bats generally exhibit sex-biased migrations with females inhabiting lower elevations than males during reproductive periods. Although there is less information on tropical bat migration, few studies report sex-biased migration. We compiled hypotheses proposed in the bat and (more extensive) avian literature to provide a list of hypotheses potentially explaining altitudinal bat migrations. These hypotheses rely upon temporal availability of (and competition for) food resources, spatial distribution of geomorphological features suitable for hibernation, sex-related differences in the use of torpor, mating opportunities, and climatic factors that impose direct physiological challenges to survival or that restrict the ability to forage. A more thorough description of the migration patterns of most species will be required to distinguish effectively among these hypotheses. We identify research avenues that would broaden our understanding of bat migration patterns and provide critical information required for effective

  17. Return Migration to Mexico: Does Health Matter?

    PubMed

    Arenas, Erika; Goldman, Noreen; Pebley, Anne R; Teruel, Graciela

    2015-12-01

    We use data from three rounds of the Mexican Family Life Survey to examine whether migrants in the United States returning to Mexico in the period 2005-2012 have worse health than those remaining in the United States. Despite extensive interest by demographers in health-related selection, this has been a neglected area of study in the literature on U.S.-Mexico migration, and the few results to date have been contradictory and inconclusive. Using five self-reported health variables collected while migrants resided in the United States and subsequent migration history, we find direct evidence of higher probabilities of return migration for Mexican migrants in poor health as well as lower probabilities of return for migrants with improving health. These findings are robust to the inclusion of potential confounders reflecting the migrants' demographic characteristics, economic situation, family ties, and origin and destination characteristics. We anticipate that in the coming decade, health may become an even more salient issue in migrants' decisions about returning to Mexico, given the recent expansion in access to health insurance in Mexico. PMID:26385111

  18. Impact of jamming on collective cell migration

    NASA Astrophysics Data System (ADS)

    Nnetu, Kenechukwu David; Knorr, Melanie; Pawlizak, Steve; Fuhs, Thomas; Zink, Mareike; KäS, Josef A.

    2012-02-01

    Multi-cellular migration plays an important role in physiological processes such as embryogenesis, cancer metastasis and tissue repair. During migration, single cells undergo cycles of extension, adhesion and retraction resulting in morphological changes. In a confluent monolayer, there are inter-cellular interactions and crowding, however, the impact of these interactions on the dynamics and elasticity of the monolayer at the multi-cellular and single cell level is not well understood. Here we study the dynamics of a confluent epithelial monolayer by simultaneously measuring cell motion at the multi-cellular and single cell level for various cell densities and tensile elasticity. At the multi-cellular level, the system exhibited spatial kinetic transitions from isotropic to anisotropic migration on long times and the velocity of the monolayer decreased with increasing cell density. Moreover, the dynamics was spatially and temporally heterogeneous. Interestingly, the dynamics was also heterogeneous in wound-healing assays and the correlation length was fitted by compressed exponential. On the single cell scale, we observed transient caging effects with increasing cage rearrangement times as the system age due to an increase in density. Also, the density dependent elastic modulus of the monolayer scaled as a weak power law. Together, these findings suggest that caging effects at the single cell level initiates a slow and heterogeneous dynamics at the multi-cellular level which is similar to the glassy dynamics of deformable colloidal systems.

  19. Migration waves to the Baltic Sea region.

    PubMed

    Lappalainen, T; Laitinen, V; Salmela, E; Andersen, P; Huoponen, K; Savontaus, M-L; Lahermo, P

    2008-05-01

    In this study, the population history of the Baltic Sea region, known to be affected by a variety of migrations and genetic barriers, was analyzed using both mitochondrial DNA and Y-chromosomal data. Over 1200 samples from Finland, Sweden, Karelia, Estonia, Setoland, Latvia and Lithuania were genotyped for 18 Y-chromosomal biallelic polymorphisms and 9 STRs, in addition to analyzing 17 coding region polymorphisms and the HVS1 region from the mtDNA. It was shown that the populations surrounding the Baltic Sea are genetically similar, which suggests that it has been an important route not only for cultural transmission but also for population migration. However, many of the migrations affecting the area from Central Europe, the Volga-Ural region and from Slavic populations have had a quantitatively different impact on the populations, and, furthermore, the effects of genetic drift have increased the differences between populations especially in the north. The possible explanations for the high frequencies of several haplogroups with an origin in the Iberian refugia (H1, U5b, I1a) are also discussed. PMID:18294359

  20. Visualizing T Cell Migration in situ

    PubMed Central

    Benechet, Alexandre P.; Menon, Manisha; Khanna, Kamal M.

    2014-01-01

    Mounting a protective immune response is critically dependent on the orchestrated movement of cells within lymphoid tissues. The structure of secondary lymphoid organs regulates immune responses by promoting optimal cell–cell and cell–extracellular matrix interactions. Naïve T cells are initially activated by antigen presenting cells in secondary lymphoid organs. Following priming, effector T cells migrate to the site of infection to exert their functions. Majority of the effector cells die while a small population of antigen-specific T cells persists as memory cells in distinct anatomical locations. The persistence and location of memory cells in lymphoid and non-lymphoid tissues is critical to protect the host from re-infection. The localization of memory T cells is carefully regulated by several factors including the highly organized secondary lymphoid structure, the cellular expression of chemokine receptors and compartmentalized secretion of their cognate ligands. This balance between the anatomy and the ordered expression of cell surface and soluble proteins regulates the subtle choreography of T cell migration. In recent years, our understanding of cellular dynamics of T cells has been advanced by the development of new imaging techniques allowing in situ visualization of T cell responses. Here, we review the past and more recent studies that have utilized sophisticated imaging technologies to investigate the migration dynamics of naïve, effector, and memory T cells. PMID:25120547

  1. Migration-induced architectures of planetary systems.

    PubMed

    Szuszkiewicz, Ewa; Podlewska-Gaca, Edyta

    2012-06-01

    The recent increase in number of known multi-planet systems gives a unique opportunity to study the processes responsible for planetary formation and evolution. Special attention is given to the occurrence of mean-motion resonances, because they carry important information about the history of the planetary systems. At the early stages of the evolution, when planets are still embedded in a gaseous disc, the tidal interactions between the disc and planets cause the planetary orbital migration. The convergent differential migration of two planets embedded in a gaseous disc may result in the capture into a mean-motion resonance. The orbital migration taking place during the early phases of the planetary system formation may play an important role in shaping stable planetary configurations. An understanding of this stage of the evolution will provide insight on the most frequently formed architectures, which in turn are relevant for determining the planet habitability. The aim of this paper is to present the observational properties of these planetary systems which contain confirmed or suspected resonant configurations. A complete list of known systems with such configurations is given. This list will be kept by us updated from now on and it will be a valuable reference for studying the dynamics of extrasolar systems and testing theoretical predictions concerned with the origin and the evolution of planets, which are the most plausible places for existence and development of life.

  2. PROTOPLANETARY MIGRATION IN TURBULENT ISOTHERMAL DISKS

    SciTech Connect

    Baruteau, C.; Lin, D. N. C. E-mail: lin@ucolick.or

    2010-02-01

    In order to reproduce the statistical properties of the observed exoplanets, population synthesis models have shown that the migration of protoplanets should be significantly slowed down, and that processes stalling migration should be at work. Much current theoretical efforts have thus been dedicated to find physical effects that slow down, halt or even reverse migration. Many of these studies rely on the horseshoe drag, whose long-term evolution (saturated or not) is intimately related to the disk viscosity in laminar disk models. We investigate how the horseshoe drag exerted on a low-mass planet is altered by a more realistic treatment of the turbulence in protoplanetary disks. Two-dimensional hydrodynamic simulations are performed with a turbulence model that reproduces the main turbulence properties of three-dimensional magnetohydrodynamic calculations. We find that the horseshoe drag can remain unsaturated on the long term, depending on the turbulence strength. We show that the desaturation of the horseshoe drag by turbulence can be modeled by vortensity diffusion across the time-averaged planet's horseshoe region. At low-turbulence, the running-time-averaged torque is in good agreement with the total torque obtained for an equivalent laminar model, with a similar vortensity diffusion coefficient. At high turbulence, differences arise due to the time evolution of the averaged density profile with turbulence.

  3. Return Migration to Mexico: Does Health Matter?

    PubMed

    Arenas, Erika; Goldman, Noreen; Pebley, Anne R; Teruel, Graciela

    2015-12-01

    We use data from three rounds of the Mexican Family Life Survey to examine whether migrants in the United States returning to Mexico in the period 2005-2012 have worse health than those remaining in the United States. Despite extensive interest by demographers in health-related selection, this has been a neglected area of study in the literature on U.S.-Mexico migration, and the few results to date have been contradictory and inconclusive. Using five self-reported health variables collected while migrants resided in the United States and subsequent migration history, we find direct evidence of higher probabilities of return migration for Mexican migrants in poor health as well as lower probabilities of return for migrants with improving health. These findings are robust to the inclusion of potential confounders reflecting the migrants' demographic characteristics, economic situation, family ties, and origin and destination characteristics. We anticipate that in the coming decade, health may become an even more salient issue in migrants' decisions about returning to Mexico, given the recent expansion in access to health insurance in Mexico.

  4. Migration-induced architectures of planetary systems.

    PubMed

    Szuszkiewicz, Ewa; Podlewska-Gaca, Edyta

    2012-06-01

    The recent increase in number of known multi-planet systems gives a unique opportunity to study the processes responsible for planetary formation and evolution. Special attention is given to the occurrence of mean-motion resonances, because they carry important information about the history of the planetary systems. At the early stages of the evolution, when planets are still embedded in a gaseous disc, the tidal interactions between the disc and planets cause the planetary orbital migration. The convergent differential migration of two planets embedded in a gaseous disc may result in the capture into a mean-motion resonance. The orbital migration taking place during the early phases of the planetary system formation may play an important role in shaping stable planetary configurations. An understanding of this stage of the evolution will provide insight on the most frequently formed architectures, which in turn are relevant for determining the planet habitability. The aim of this paper is to present the observational properties of these planetary systems which contain confirmed or suspected resonant configurations. A complete list of known systems with such configurations is given. This list will be kept by us updated from now on and it will be a valuable reference for studying the dynamics of extrasolar systems and testing theoretical predictions concerned with the origin and the evolution of planets, which are the most plausible places for existence and development of life. PMID:22684330

  5. Limits to Chemically Guided Multicellular Migration

    NASA Astrophysics Data System (ADS)

    Varennes, Julien; Han, Bumsoo; Mugler, Andrew

    Collective cell migration in response to a chemical cue requires both multicellular sensing of chemical gradients and coordinated mechanical action. Examples from morphogenesis and cancer metastasis demonstrate that clusters of migratory cells are extremely sensitive, responding to gradients of less than 1% difference in chemical concentration across a cell body. While the limits to multicellular sensing are becoming known, the ensuing consequences for coherent migration remain poorly understood. We develop a model of multicellular sensing and migration based on the cellular Potts model. Multicellular sensing of noisy chemical gradients is modeled as a process of local excitation and global inhibition (LEGI) among communicating cells. The output of the sensing process is coupled to individual cells' polarization to model migratory behavior. We find that larger clusters of cells detect the gradient direction with higher precision and thus achieve stronger polarization bias. At the same time, larger clusters are also accompanied by less coherent collective motion. The trade-off between these two effects leads to an optimally efficient cluster size. We discuss how our results relate to cancer metastasis.

  6. Internal migration of people in Nepal.

    PubMed

    Shrestha, M N

    1979-07-01

    The Kingdom of Nepal is divided geographically into 3 distinct regions: the Mountain, the Hill, and the Plain. The average rate of population growth from 1961 to 1971 was 2.1%, but recent data suggest that it has now increased to 2.5%. 94% of the labor force is employed in agriculture. With the present rate of internal migration the Plain Region will be supporting approximately 35% of the total population (excluding the population immigrating from other countries) in 1981, and 39% in 1991. If the same migration pattern continues, the population distribution among the geographic regions will stabilize around 95% in the Plain, 4% in the Hill, and 1% in the Mountain. Such an unequal distribution of population will inevitably produce a tremendous stress on the physical environment as well as on the political, social, and economic system of the country. Soil erosion, landslides, floods, and a lowering of the water table in the Hill have resulted; the fertility of the soil has been depleted, if not exhausted. In view of these facts, the author recommends large-scale concurrent programs: 1) to introduce afforestation and horticulture in the Hill; 2) to improve agriculture; 3) to establish small-scale rural industries in order to release people from the agricultural sector; 4) to restrict migration and the family size through proper corrective feedbacks; and 5) to raise the people's awareness and participation in environmental conservation. PMID:12336155

  7. Helicobacter pylori Sequences Reflect Past Human Migrations.

    PubMed

    Moodley, Y; Linz, B

    2009-01-01

    The long association between the stomach bacterium Helicobacter pylori and humans, in combination with its predominantly within-family transmission route and its exceptionally high DNA sequence diversity, make this bacterium a reliable marker for discerning both recent and ancient human population movements. As much of the diversity in H. pylori sequences is generated by recombination and mutation on a local scale, the partitioning of H. pylori sequences from a large globally distributed data set into six geographic populations enabled the detection of recent ( < 500 years) human population movements including the European colonial expansion and the slave trade. The further separation of bacterial populations into distinct sub-populations traced prehistoric population movements like the settlement of the Americas by Asians across the Bering Strait and the Bantu migrations in Africa. The ability to deduce ancestral population structure from modern sequences was a key development that allowed the detection of zones of admixture, such as Europe, and the inference of multiple migration waves into these zones. The significantly similar global population structure of both H. pylori and humans confirmed not only an evolutionary time-scale association between host and parasite, but also that humans had carried H. pylori in their stomachs on their migrations out of Africa. PMID:19696494

  8. Family migration and the economic status of women in Malaysia.

    PubMed

    Chattopadhyay, A

    1997-01-01

    "The impact of family migration on women's economic position in a developing country setting is an area that has received relatively little research attention. Incorporating a lifetime perspective, this study makes use of the retrospective migration histories of husbands and wives from the second round of the Malaysian Family Life Survey to estimate how joint migration with the husband affects women's socioeconomic achievement. The findings show that family migration depresses the chances of working, but it does not significantly reduce socioeconomic attainment of those who do work. However, when a woman migrates with her husband she does forgo the substantial advantage she could have derived had she moved alone." PMID:12292875

  9. Family migration and the economic status of women in Malaysia.

    PubMed

    Chattopadhyay, A

    1997-01-01

    "The impact of family migration on women's economic position in a developing country setting is an area that has received relatively little research attention. Incorporating a lifetime perspective, this study makes use of the retrospective migration histories of husbands and wives from the second round of the Malaysian Family Life Survey to estimate how joint migration with the husband affects women's socioeconomic achievement. The findings show that family migration depresses the chances of working, but it does not significantly reduce socioeconomic attainment of those who do work. However, when a woman migrates with her husband she does forgo the substantial advantage she could have derived had she moved alone."

  10. Mechanisms guiding primordial germ cell migration: strategies from different organisms

    PubMed Central

    Richardson, Brian E.; Lehmann, Ruth

    2015-01-01

    Preface The regulated migration of cells is essential for development and tissue homeostasis, and aberrant cell migration can lead to an impaired immune response and the progression of cancer. Primordial germ cells (PGCs), precursors to sperm and eggs, have to migrate across the embryo to reach somatic gonadal precursors (SGPs) and fulfill their function. Studies of model organisms have revealed that, despite important differences, several features of PGC migration are conserved. PGCs require both an intrinsic motility program and external guidance cues to survive and successfully migrate. Proper guidance involves both attractive and repulsive cues mediated by protein and lipid signalling. PMID:20027186

  11. Coping with uncertainty: Nutrient deficiencies motivate insect migration at a cost to immunity

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Migration is often associated with movement away from areas with depleted nutrients or other resources, and yet migration itself is energetically demanding. Migrating Mormon crickets Anabrus simplex (Orthoptera: Tettigoniidae) lack nutrients, and supplementation of deficient nutrients slows migrator...

  12. Planet Migration Via Numerous Stochastic Scattering Events

    NASA Astrophysics Data System (ADS)

    Hahn, J. M.; Malhotra, R.

    2000-05-01

    Gravitational scattering of a planetesimal disk by recently-formed giant planets may have caused a significant readjustment of planetary orbits. Indeed, an early epoch of planet-migration is often invoked to explain the resonant structure observed in the Kuiper Belt. Had Neptune's orbit smoothly expanded outwards about 7 AU, its 3:2 mean-motion resonance would have swept across much of the early Belt, simultaneously capturing Kuiper Belt Objects (KBOs) and exciting their eccentricities (Malhotra 1993, 1995). However it should be recognized that planet-migration via gravitational scattering is a stochastic process. To effect this in our planet-migration simulations we add some random jitter to the torque that drives Neptune's outward expansion. This jitter is parameterized by σ , which is the standard-deviation of the planet-migration torque in units of the time-averaged torque. Larger σ increases Neptune's to-and-fro motion as its orbit expands. We are investigating whether this jitter can account for the e and i excitation observed in the Kuiper Belt. A system of four migrating giant-planets plus numerous massless KBOs has been evolved for various values of σ . We find that the Kuiper Belt's resonance structure can be preserved despite a surprisingly large amount of jitter. For instance, simulations with 0 ≲ σ ≲ 10 are largely indistinct due to the very efficient capture of KBOs at resonances. However runs with larger jitter, 25 ≲ σ ≲ 75, have reduced capture efficiencies. This allows for the development of a stirred up `classical disk' as particles have their eccentricities pumped up as they slip through the 2:1 resonance. Substantial inclinations of i 10o are also excited at the 3:2 resonance. Although a higher jitter of σ = 100 results in a Kuiper Belt that is depleted interior to a = 45 AU, inefficient capture still occurs at Neptune's 2:1 resonance. Further comparisons between model and observed endstates will be presented at conference time.

  13. A new era in Australian migration policy.

    PubMed

    Birrell, R

    1984-01-01

    The discussion traces the evolution of Australian migration policy since 1975, arguing that the primary factor shaping policy has been interparty competition for influence within Australia's ethnic communities. Since late 1975 when the Liberal/National Country Party (LibNCP) Conservative Government returned to power, Australian immigration policy has moved in different directions from the previous post World War II experience. The demographic implications have been profound. In 1975 the LibNCP government returned to office committed to restoring an active migration program. By 1980-81 it had largely succeeded in this numerical goal. Australia's migration growth rate at .82% of the total population exceeded almost all other Western society. What was new, in comparison to previous policy, was the migrant selection system and source countries. By the time the government lost office in March 1983, family reunion had become the major migration program souce and Asia was rapidly becoming the dominant place of migrant origin. This emphasis on family reunion was not intended by government immigration planners but was a product of domestic political change and resultant new influences over migration policy. As to the increasing Asian component, it has mainly been an unintended consequence of the expansion in the family reunion program. Although the liberalization of family reunion eligibility has largely been designed to appease the major Southern European ethnic communities, few applications have been forthcoming from these countries. Asian applicants have been numerous. Labor government policy since March 1983 has shown remarkable continuity with that of the LibNCP both in its selection system and in the size of the migrant intake. The motivation for the commitment to immigration derived first from longstanding traditions within the Australian business community that Australia's economic growth and dynamism depended on rapid population growth. More specifically there

  14. Seasonal changes in the altitudinal distribution of nocturnally migrating birds during autumn migration.

    PubMed

    La Sorte, Frank A; Hochachka, Wesley M; Farnsworth, Andrew; Sheldon, Daniel; Van Doren, Benjamin M; Fink, Daniel; Kelling, Steve

    2015-12-01

    Wind plays a significant role in the flight altitudes selected by nocturnally migrating birds. At mid-latitudes in the Northern Hemisphere, atmospheric conditions are dictated by the polar-front jet stream, whose amplitude increases in the autumn. One consequence for migratory birds is that the region's prevailing westerly winds become progressively stronger at higher migration altitudes. We expect this seasonality in wind speed to result in migrants occupying progressively lower flight altitudes, which we test using density estimates of nocturnal migrants at 100 m altitudinal intervals from 12 weather surveillance radar stations located in the northeastern USA. Contrary to our expectations, median migration altitudes deviated little across the season, and the variance was lower during the middle of the season and higher during the beginning and especially the end of the season. Early-season migrants included small- to intermediate-sized long-distance migrants in the orders Charadriiformes and Passeriformes, and late-season migrants included large-bodied and intermediate-distance migrants in the order Anseriformes. Therefore, seasonality in the composition of migratory species, and related variation in migration strategies and behaviours, resulted in a convex-concave bounded distribution of migration altitudes. Our results provide a basis for assessing the implications for migratory bird populations of changes in mid-latitude atmospheric conditions probably occurring under global climate change. PMID:27019724

  15. Seasonal changes in the altitudinal distribution of nocturnally migrating birds during autumn migration

    PubMed Central

    La Sorte, Frank A.; Hochachka, Wesley M.; Farnsworth, Andrew; Sheldon, Daniel; Van Doren, Benjamin M.; Fink, Daniel; Kelling, Steve

    2015-01-01

    Wind plays a significant role in the flight altitudes selected by nocturnally migrating birds. At mid-latitudes in the Northern Hemisphere, atmospheric conditions are dictated by the polar-front jet stream, whose amplitude increases in the autumn. One consequence for migratory birds is that the region’s prevailing westerly winds become progressively stronger at higher migration altitudes. We expect this seasonality in wind speed to result in migrants occupying progressively lower flight altitudes, which we test using density estimates of nocturnal migrants at 100 m altitudinal intervals from 12 weather surveillance radar stations located in the northeastern USA. Contrary to our expectations, median migration altitudes deviated little across the season, and the variance was lower during the middle of the season and higher during the beginning and especially the end of the season. Early-season migrants included small- to intermediate-sized long-distance migrants in the orders Charadriiformes and Passeriformes, and late-season migrants included large-bodied and intermediate-distance migrants in the order Anseriformes. Therefore, seasonality in the composition of migratory species, and related variation in migration strategies and behaviours, resulted in a convex–concave bounded distribution of migration altitudes. Our results provide a basis for assessing the implications for migratory bird populations of changes in mid-latitude atmospheric conditions probably occurring under global climate change. PMID:27019724

  16. Do Social Casino Gamers Migrate to Online Gambling? An Assessment of Migration Rate and Potential Predictors.

    PubMed

    Kim, Hyoun S; Wohl, Michael J A; Salmon, Melissa M; Gupta, Rina; Derevensky, Jeffrey

    2015-12-01

    Social casino games (i.e., free-to-play online gambling games) are enjoyed by millions of players worldwide on a daily basis. Despite being free to play, social casino games share many similarities to traditional casino games. As such, concerns have been raised as to whether social casino games influences the migration to online gambling among people who have not engaged in such activity (see Griffiths in World Online Gambl 9:12-13, 2010). To date, however, no empirical research has assessed this possibility. Thus, the purpose of the present research was to assess the extent to which social casino gamers migrate to online gambling and potential predictors (time spent on social casino games, skill building, enhancement and micro-transactions) of such migration. To this end, social casino gamers who never gambled online (N = 409) completed a questionnaire battery assessing our variables of interest and were re-contacted 6-months later to see if they had engaged in online gambling during the intervening months. Approximately 26% of social casino gamers reported having migrated to online gambling. Importantly, engagement in micro-transactions was the only unique predictor of migration from social casino gaming to online gambling. The implications for the potential harms associated with social casino gaming are discussed.

  17. Do Social Casino Gamers Migrate to Online Gambling? An Assessment of Migration Rate and Potential Predictors.

    PubMed

    Kim, Hyoun S; Wohl, Michael J A; Salmon, Melissa M; Gupta, Rina; Derevensky, Jeffrey

    2015-12-01

    Social casino games (i.e., free-to-play online gambling games) are enjoyed by millions of players worldwide on a daily basis. Despite being free to play, social casino games share many similarities to traditional casino games. As such, concerns have been raised as to whether social casino games influences the migration to online gambling among people who have not engaged in such activity (see Griffiths in World Online Gambl 9:12-13, 2010). To date, however, no empirical research has assessed this possibility. Thus, the purpose of the present research was to assess the extent to which social casino gamers migrate to online gambling and potential predictors (time spent on social casino games, skill building, enhancement and micro-transactions) of such migration. To this end, social casino gamers who never gambled online (N = 409) completed a questionnaire battery assessing our variables of interest and were re-contacted 6-months later to see if they had engaged in online gambling during the intervening months. Approximately 26% of social casino gamers reported having migrated to online gambling. Importantly, engagement in micro-transactions was the only unique predictor of migration from social casino gaming to online gambling. The implications for the potential harms associated with social casino gaming are discussed. PMID:25410278

  18. Examining Pre-migration Health Among Filipino Nurses.

    PubMed

    de Castro, A B; Gee, Gilbert; Fujishiro, Kaori; Rue, Tessa

    2015-12-01

    The healthy immigrant hypothesis asserts that immigrants arrive in the receiving country healthier than same race/ethnic counterparts born there. Contemporary research, however, has not evaluated pre-migration health among migrants, nor has explicitly considered comparisons with non-migrants in the country of origin. Pre-migration health was examined among 621 Filipino nurses, including self-reported physical health, mental health, health behaviors, and social stress. Measures were compared by intention to migrate and also tested as predictors of actual migration using time-to-event analysis. Nurses intending to migrate had higher proportion of depression and reported higher general perceived stress compared to those not. Predictors of actual migration included age, mentally unhealthy days, social strain, and social support. Physical health and health behavior measures had no association with migration intention or actual migration. Findings suggest that, relative to those not intending to migrate, nurses intending to migrate have worse mental health status and social stress; and, do not have a physical health advantage. Future research must span the pre- to post-migration continuum to better understand the impact of moving from one country to another on health and well-being.

  19. MIGRATION OF PLANETS EMBEDDED IN A CIRCUMSTELLAR DISK

    SciTech Connect

    Bromley, Benjamin C.; Kenyon, Scott J. E-mail: skenyon@cfa.harvard.edu

    2011-07-01

    Planetary migration poses a serious challenge to theories of planet formation. In gaseous and planetesimal disks, migration can remove planets as quickly as they form. To explore migration in a planetesimal disk, we combine analytic and numerical approaches. After deriving general analytic migration rates for isolated planets, we use N-body simulations to confirm these results for fast and slow migration modes. Migration rates scale as m{sup -1} (for massive planets) and (1 + (e{sub H}/3){sup 3}){sup -1}, where m is the mass of a planet and e{sub H} is the eccentricity of the background planetesimals in Hill units. When multiple planets stir the disk, our simulations yield the new result that large-scale migration ceases. Thus, growing planets do not migrate through planetesimal disks. To extend these results to migration in gaseous disks, we compare physical interactions and rates. Although migration through a gaseous disk is an important issue for the formation of gas giants, we conclude that migration has little impact on the formation of terrestrial planets.

  20. The effect of radial migration on galactic disks

    SciTech Connect

    Vera-Ciro, Carlos; D'Onghia, Elena; Navarro, Julio; Abadi, Mario

    2014-10-20

    We study the radial migration of stars driven by recurring multi-arm spiral features in an exponential disk embedded in a dark matter halo. The spiral perturbations redistribute angular momentum within the disk and lead to substantial radial displacements of individual stars, in a manner that largely preserves the circularity of their orbits and that results, after 5 Gyr (∼40 full rotations at the disk scale length), in little radial heating and no appreciable changes to the vertical or radial structure of the disk. Our results clarify a number of issues related to the spatial distribution and kinematics of migrators. In particular, we find that migrators are a heavily biased subset of stars with preferentially low vertical velocity dispersions. This 'provenance bias' for migrators is not surprising in hindsight, for stars with small vertical excursions spend more time near the disk plane, and thus respond more readily to non-axisymmetric perturbations. We also find that the vertical velocity dispersion of outward migrators always decreases, whereas the opposite holds for inward migrators. To first order, newly arrived migrators simply replace stars that have migrated off to other radii, thus inheriting the vertical bias of the latter. Extreme migrators might therefore be recognized, if present, by the unexpectedly small amplitude of their vertical excursions. Our results show that migration, understood as changes in angular momentum that preserve circularity, can strongly affect the thin disk, but cast doubts on models that envision the Galactic thick disk as a relic of radial migration.

  1. Underground radionuclide migration at the Nevada Test Site

    SciTech Connect

    Nimz, G.J. ); Thompson, J.L. )

    1992-06-22

    This document reviews results from a number of studies concerning underground migration of radionuclides from nuclear test cavities at the Nevada Test Site (NTS). Discussed are all cases known to the Department of Energy's Hydrology and Radionuclide Migration Program where radionuclides have been detected outside of the immediate vicinity of nuclear test cavities that are identifiable as the-source of the nuclides, as well as cases where radionuclides might have been expected and were intentionally sought but not fixed. There are nine locations where source-identifiable radionuclide migration has been detected, one where migration was purposely induced by pumping, and three where migration might be expected but was not found. In five of the nine cases of non-induced migration, the inferred migration mechanism is prompt fracture injection during detonation. In the other four cases, the inferred migration mechanism is water movement. In only a few of the reviewed cases can the actual migration mechanism be stated with confidence, and the attempt has been made to indicate the level of confidence for each case. References are cited where more information may be obtained. As an aid to future study, this document concludes with a brief discussion of the aspects of radionuclide migration that, as the present review indicates, are not yet understood. A course of action is suggested that would produce a better understanding of the phenomenon of radionuclide migration.

  2. A case for internal migration policy in India.

    PubMed

    Ram, S

    1993-01-01

    Migration helps to minimize regional, socioeconomic, and cultural disparities, and is considered to be an integral component of the development process. Migration helps to diffuse development, technology, and innovations from more developed areas or cities to rural or less developed areas. Little attention, however, has been paid to migration policy in India. Most studies on migration in India either describe the patterns of migration or analyze reasons for the moves. This paper discusses why migration takes place, what are the consequences of migration, whether India has a migration policy, whether India needs a migration policy, and what type of policy is required. The development and entrenchment of urban slums in India is related to the country's lack of migration policy. A two-pronged policy on migration is thus proposed which would ensure employment opportunities and an improved standard of living in rural areas, while taking into account the planning of cities and city surroundings. Rural areas and small towns need to be provided with more employment opportunities, financial and technological support to process raw materials, infrastructure for agricultural service centers, better education and other facilities to improve local living standards, and the diffusion of industries from big cities to district headquarters and medium-size towns. Commensurate efforts should be made in urban centers to prevent the future development of slums.

  3. Seismic velocity estimation from time migration

    NASA Astrophysics Data System (ADS)

    Cameron, Maria Kourkina

    This is concerned with imaging and wave propagation in nonhomogeneous media, and includes a collection of computational techniques, such as level set methods with material transport, Dijkstra-like Hamilton-Jacobi solvers for first arrival Eikonal equations and techniques for data smoothing. The theoretical components include aspects of seismic ray theory, and the results rely on careful comparison with experiment and incorporation as input into large production-style geophysical processing codes. Producing an accurate image of the Earth's interior is a challenging aspect of oil recovery and earthquake analysis. The ultimate computational goal, which is to accurately produce a detailed interior map of the Earth's makeup on the basis of external soundings and measurements, is currently out of reach for several reasons. First, although vast amounts of data have been obtained in some regions, this has not been done uniformly, and the data contain noise and artifacts. Simply sifting through the data is a massive computational job. Second, the fundamental inverse problem, namely to deduce the local sound speeds of the earth that give rise to measured reflected signals, is exceedingly difficult: shadow zones and complex structures can make for ill-posed problems, and require vast computational resources. Nonetheless, seismic imaging is a crucial part of the oil and gas industry. Typically, one makes assumptions about the earth's substructure (such as laterally homogeneous layering), and then uses this model as input to an iterative procedure to build perturbations that more closely satisfy the measured data. Such models often break down when the material substructure is significantly complex: not surprisingly, this is often where the most interesting geological features lie. Data often come in a particular, somewhat non-physical coordinate system, known as time migration coordinates. The construction of substructure models from these data is less and less reliable as the

  4. Seismic velocity estimation from time migration

    SciTech Connect

    Cameron, Maria Kourkina

    2007-01-01

    This is concerned with imaging and wave propagation in nonhomogeneous media, and includes a collection of computational techniques, such as level set methods with material transport, Dijkstra-like Hamilton-Jacobi solvers for first arrival Eikonal equations and techniques for data smoothing. The theoretical components include aspects of seismic ray theory, and the results rely on careful comparison with experiment and incorporation as input into large production-style geophysical processing codes. Producing an accurate image of the Earth's interior is a challenging aspect of oil recovery and earthquake analysis. The ultimate computational goal, which is to accurately produce a detailed interior map of the Earth's makeup on the basis of external soundings and measurements, is currently out of reach for several reasons. First, although vast amounts of data have been obtained in some regions, this has not been done uniformly, and the data contain noise and artifacts. Simply sifting through the data is a massive computational job. Second, the fundamental inverse problem, namely to deduce the local sound speeds of the earth that give rise to measured reacted signals, is exceedingly difficult: shadow zones and complex structures can make for ill-posed problems, and require vast computational resources. Nonetheless, seismic imaging is a crucial part of the oil and gas industry. Typically, one makes assumptions about the earth's substructure (such as laterally homogeneous layering), and then uses this model as input to an iterative procedure to build perturbations that more closely satisfy the measured data. Such models often break down when the material substructure is significantly complex: not surprisingly, this is often where the most interesting geological features lie. Data often come in a particular, somewhat non-physical coordinate system, known as time migration coordinates. The construction of substructure models from these data is less and less reliable as the

  5. Transnational nurse migration: future directions for medical anthropological research.

    PubMed

    Prescott, Megan; Nichter, Mark

    2014-04-01

    Transnational nurse migration is a serious global health issue in which inequitably distributed shortages hinder health and development goals. This article selectively reviews the literature on nurse migration that has emerged from nursing, health planning, and the social sciences and offers productive directions for future anthropological research. The literature on global nurse migration has largely focused on push/pull economic logic and the concept of brain drain to understand the causes and effects of nurse migration. These concepts obscure political-economic, historical, and cultural factors that pattern nurse migration and influence the complex effects of nurse migration. Global nurse care chain analysis helps illuminate the numerous nodes in the production and migration of nurses, and management of this transnational process. Examples are provided from the Philippines and India to illustrate ways in which this analysis may be deepened, refined and rendered more critical by anthropological research.

  6. Taking Aim at Moving Targets in Computational Cell Migration.

    PubMed

    Masuzzo, Paola; Van Troys, Marleen; Ampe, Christophe; Martens, Lennart

    2016-02-01

    Cell migration is central to the development and maintenance of multicellular organisms. Fundamental understanding of cell migration can, for example, direct novel therapeutic strategies to control invasive tumor cells. However, the study of cell migration yields an overabundance of experimental data that require demanding processing and analysis for results extraction. Computational methods and tools have therefore become essential in the quantification and modeling of cell migration data. We review computational approaches for the key tasks in the quantification of in vitro cell migration: image pre-processing, motion estimation and feature extraction. Moreover, we summarize the current state-of-the-art for in silico modeling of cell migration. Finally, we provide a list of available software tools for cell migration to assist researchers in choosing the most appropriate solution for their needs.

  7. Trade, aid and migrations: some basic policy issues.

    PubMed

    Faini, R; Venturini, A

    1993-04-01

    The link between trade policy and international migration is explored using data from the United States and Europe. "We conclude that restrictive trade policies in industrialised countries have most likely added to migration pressures. We then turn to the broader question of the effects of income growth in the sending countries on the propensity to migrate. We argue that, in relatively poor countries, an increase in income will be associated with higher migration flows. For middle income countries, however, income growth will lead to lower migrations. In the medium run, therefore, the relationship between development levels, as measured by GDP per capita, and the propensity to migrate follows an inverse-U pattern. Econometric analysis of aggregate migration flows from Southern Europe provides considerable support for such conjecture."

  8. Flight mode affects allometry of migration range in birds.

    PubMed

    Watanabe, Yuuki Y

    2016-08-01

    Billions of birds migrate to exploit seasonally available resources. The ranges of migration vary greatly among species, but the underlying mechanisms are poorly understood. I hypothesise that flight mode (flapping or soaring) and body mass affect migration range through their influence on flight energetics. Here, I compiled the tracks of migratory birds (196 species, weighing 12-10 350 g) recorded by electronic tags in the last few decades. In flapping birds, migration ranges decreased with body mass, as predicted from rapidly increasing flight cost with increasing body mass. The species with higher aspect ratio and lower wing loading had larger migration ranges. In soaring birds, migration ranges were mass-independent and larger than those of flapping birds, reflecting their low flight costs irrespective of body mass. This study demonstrates that many animal-tracking studies are now available to explore the general patterns and the underlying mechanisms of animal migration.

  9. Flow induced migration in polymer melts – Theory and simulation

    SciTech Connect

    Dorgan, John Robert Rorrer, Nicholas Andrew

    2015-04-28

    Flow induced migration, whereby polymer melts are fractionated by molecular weight across a flow field, represents a significant complication in the processing of polymer melts. Despite its long history, such phenomena remain relatively poorly understood. Here a simple analytical theory is presented which predicts the phenomena based on well-established principles of non-equilibrium thermodynamics. It is unambiguously shown that for purely viscous materials, a gradient in shear rate is needed to drive migration; for purely viscometric flows no migration is expected. Molecular scale simulations of flow migration effects in dense polymer melts are also presented. In shear flow the melts exhibit similar behavior as the quiescent case; a constant shear rate across the gap does not induce chain length based migration. In comparison, parabolic flow causes profound migration for both unentangled and entangled melts. These findings are consistent with the analytical theory. The picture that emerges is consistent with flow induced migration mechanisms predominating over competing chain degradation mechanisms.

  10. Synthetic seismic monitoring using reverse-time migration and Kirchhoff migration for CO2 sequestration in Korea

    NASA Astrophysics Data System (ADS)

    Kim, W.; Kim, Y.; Min, D.; Oh, J.; Huh, C.; Kang, S.

    2012-12-01

    During last two decades, CO2 sequestration in the subsurface has been extensively studied and progressed as a direct tool to reduce CO2 emission. Commercial projects such as Sleipner, In Salah and Weyburn that inject more than one million tons of CO2 per year are operated actively as well as test projects such as Ketzin to study the behavior of CO2 and the monitoring techniques. Korea also began the CCS (CO2 capture and storage) project. One of the prospects for CO2 sequestration in Korea is the southwestern continental margin of Ulleung basin. To monitor the behavior of CO2 underground for the evaluation of stability and safety, several geophysical monitoring techniques should be applied. Among various geophysical monitoring techniques, seismic survey is considered as the most effective tool. To verify CO2 migration in the subsurface more effectively, seismic numerical simulation is an essential process. Furthermore, the efficiency of the seismic migration techniques should be investigated for various cases because numerical seismic simulation and migration test help us accurately interpret CO2 migration. In this study, we apply the reverse-time migration and Kirchhoff migration to synthetic seismic monitoring data generated for the simplified model based on the geological structures of Ulleung basin in Korea. Synthetic seismic monitoring data are generated for various cases of CO2 migration in the subsurface. From the seismic migration images, we can investigate CO2 diffusion patterns indirectly. From seismic monitoring simulation, it is noted that while the reverse-time migration generates clear subsurface images when subsurface structures are steeply dipping, Kirchhoff migration has an advantage in imaging horizontal-layered structures such as depositional sediments appearing in the continental shelf. The reverse-time migration and Kirchhoff migration present reliable subsurface images for the potential site characterized by stratigraphical traps. In case of

  11. Chemical migration by contact metamorphism between pegmatite and country rocks: natural analogs for radionuclide migration

    SciTech Connect

    Laul, J.C.; Walker, R.J.; Shearer, C.K.; Papike, J.J.; Simon, S.B.

    1984-01-01

    Comparison of trace element signatures of country rocks as a function of distance from the contact with two pegmatites, Tin Mountain and Etta, in the Black Hills of South Dakota, suggests that some elements such as K, Li, Rb, Cs, As, Sb, Zn and Pb, have migrated to distances of 4 to 40 meters during contact metamorphism. The relative degree of migration varies depending on the element. On the other hand, there is virtually no migration of rare earth elements (REE), Al, Sc, Cr, Hf, U, and Th. Biotite and muscovite are effective trace element traps for Li, Rb, and Cs. Biotite has a greater affinity for Rb, Cs and Li than muscovite. 9 references, 5 figures, 1 table.

  12. Pre-migration Trauma Exposure and Psychological Distress for Asian American Immigrants: Linking the Pre- and Post-migration Contexts.

    PubMed

    Li, Miao; Anderson, James G

    2016-08-01

    Drawing on the life course perspective and the assumptive world theory, this paper examines whether pre-migration trauma exposure is associated with psychological distress through post-migration perceived discrimination for Asian American immigrants. The study is based on cross-sectional data from the National Latino and Asian American Study (N = 1639). Structural equation model is used to estimate the relationship between pre-migration trauma, post-migration perceived discrimination, and psychological distress. Additional models are estimated to explore possible variations across ethnic groups as well as across different types of pre-migration trauma experience. Pre-migration trauma exposure is associated with higher levels of psychological distress, both directly and indirectly through higher level of perceived discrimination, even after controlling for demographic/acculturative factors and post-migration trauma exposure. This pattern holds for the following sub-types of pre-migration trauma: political trauma, crime victimization, physical violence, accidental trauma, and relational trauma. Multi-group analyses show that this pattern holds for all Asian immigrant subgroups except the Vietnamese. Studies of immigrant mental health primarily focus on post-migration stressors. Few studies have considered the link between pre- and post-migration contexts in assessing mental health outcomes. The study illustrates the usefulness of bridging the pre- and post-migration context in identifying the mental health risks along the immigrant life course.

  13. Migration check tool: automatic plan verification following treatment management systems upgrade and database migration.

    PubMed

    Hadley, Scott W; White, Dale; Chen, Xiaoping; Moran, Jean M; Keranen, Wayne M

    2013-01-01

    Software upgrades of the treatment management system (TMS) sometimes require that all data be migrated from one version of the database to another. It is necessary to verify that the data are correctly migrated to assure patient safety. It is impossible to verify by hand the thousands of parameters that go into each patient's radiation therapy treatment plan. Repeating pretreatment QA is costly, time-consuming, and may be inadequate in detecting errors that are introduced during the migration. In this work we investigate the use of an automatic Plan Comparison Tool to verify that plan data have been correctly migrated to a new version of a TMS database from an older version. We developed software to query and compare treatment plans between different versions of the TMS. The same plan in the two TMS systems are translated into an XML schema. A plan comparison module takes the two XML schemas as input and reports any differences in parameters between the two versions of the same plan by applying a schema mapping. A console application is used to query the database to obtain a list of active or in-preparation plans to be tested. It then runs in batch mode to compare all the plans, and a report of success or failure of the comparison is saved for review. This software tool was used as part of software upgrade and database migration from Varian's Aria 8.9 to Aria 11 TMS. Parameters were compared for 358 treatment plans in 89 minutes. This direct comparison of all plan parameters in the migrated TMS against the previous TMS surpasses current QA methods that relied on repeating pretreatment QA measurements or labor-intensive and fallible hand comparisons. PMID:24257281

  14. Migration check tool: automatic plan verification following treatment management systems upgrade and database migration.

    PubMed

    Hadley, Scott W; White, Dale; Chen, Xiaoping; Moran, Jean M; Keranen, Wayne M

    2013-11-04

    Software upgrades of the treatment management system (TMS) sometimes require that all data be migrated from one version of the database to another. It is necessary to verify that the data are correctly migrated to assure patient safety. It is impossible to verify by hand the thousands of parameters that go into each patient's radiation therapy treatment plan. Repeating pretreatment QA is costly, time-consuming, and may be inadequate in detecting errors that are introduced during the migration. In this work we investigate the use of an automatic Plan Comparison Tool to verify that plan data have been correctly migrated to a new version of a TMS database from an older version. We developed software to query and compare treatment plans between different versions of the TMS. The same plan in the two TMS systems are translated into an XML schema. A plan comparison module takes the two XML schemas as input and reports any differences in parameters between the two versions of the same plan by applying a schema mapping. A console application is used to query the database to obtain a list of active or in-preparation plans to be tested. It then runs in batch mode to compare all the plans, and a report of success or failure of the comparison is saved for review. This software tool was used as part of software upgrade and database migration from Varian's Aria 8.9 to Aria 11 TMS. Parameters were compared for 358 treatment plans in 89 minutes. This direct comparison of all plan parameters in the migrated TMS against the previous TMS surpasses current QA methods that relied on repeating pretreatment QA measurements or labor-intensive and fallible hand comparisons.

  15. Labour migration and rural development in Egypt. A study of return migration in six villages.

    PubMed

    Reichert, C

    1993-01-01

    An analysis of the impact of labor migration on social change in 6 rural villages (Shanawan and Kafr Shanawan north of Cairo, Kafr Yusuf and Tambul el Kubra near Simbalaween, and Abu Girg and Bani Walims in Minya governate) in Egypt was conducted in 1987-88. Since the 1991 Gulf war, the political environment, the labor markets, and the structure of migration opportunities have changed. An estimated 5% of rural households might have been directly affected by migrants' departure from Kuwait and Iraq. Data collection involved a household census survey of 8620 households, of which 2483 were migrants, including 1765 return migrants. A sample of return migrant (639) was interviewed about their migration experiences. Participant observation was also conducted among migrants and nonmigrants, and case studies were developed. Villages were demographically and socioeconomically very different; migration ranged from 18.5-434.2%. Structural change was measured on a scale of 1 to 6 in terms of population size, literacy of household heads, share of agricultural occupations, share of new red brick houses, and availability of infrastructural or institutional facilities. The probability of having a household with a migrant member increased with the rural character of the village. Landholdings or other major household variables were unrelated to migration. Rural outmigration was almost exclusively male, the average age was 29.6 years, and the average stay was 2.6 years. Migration destination was specific to individuals but affected by occupation and family or village resources. Professionals were overrepresented in Saudi Arabia, and farm and unskilled laborers or the unemployed were overrepresented in Iraq. Remittances from international migration have contributed along with the economic reforms of Sadat to new, private initiatives from all strata in rural society. 74.3% of returnees stated that improvement in income and living standards was the motivation for migration; many motives

  16. Some issues in Middle Eastern international migration.

    PubMed

    Sirageldin, I

    1983-01-01

    2 controversial issues related to the consequences of Middle Eastern international migration were examined: its effect on the development policies of the labor importing countries with a special reference to the case of Kuwait; and its effect on the growth potential of the labor exporting countries with special reference to recent development in Egypt's agricultural reproductivity. A preliminary note comments on the analytical nature of international labor migration in the Middle East and on the public view of emigrants as export commodities. The basic parameters of a desired population parity are interrelated. It is possible to influence the labor ratio (R2) as well as the nonKuwait crude labor participation rate (R3) through a migration policy. Thus, given a policy objective of some desired balance stated in trms of 1 or more of the identified parameters, it is possible to analyze the consequences of alternative migration strategies. It is important to consider the role of relative productivity (R6). An attempt to change R6 has implications for both the design of a migration policy and a national policy of human capital formation. Other factors may not be immediately related to a migration policy. The question then is whether these ratios are sensitive to policy intervention. In a simulation exercise it was assumed that the Kuwaiti crude labor force participation rate (R4) will increase by 13% during a period of 10 years. R4 increases if relatively more people work. Women are 1 segment of the labor force that is not adequately represented, partly because of traditions, lack of skills, and the presence of high fertility. None of these can change in the short run without an active policy of social reform. Yet, the assumption seems to be in the right direction. A policy that attempts to reduce R4 through increasing fertility in Kuwait is clearly against the tide. In sum, the labor importing countries faced with recent unfavorable demographic realities will actively

  17. Some issues in Middle Eastern international migration.

    PubMed

    Sirageldin, I

    1983-01-01

    2 controversial issues related to the consequences of Middle Eastern international migration were examined: its effect on the development policies of the labor importing countries with a special reference to the case of Kuwait; and its effect on the growth potential of the labor exporting countries with special reference to recent development in Egypt's agricultural reproductivity. A preliminary note comments on the analytical nature of international labor migration in the Middle East and on the public view of emigrants as export commodities. The basic parameters of a desired population parity are interrelated. It is possible to influence the labor ratio (R2) as well as the nonKuwait crude labor participation rate (R3) through a migration policy. Thus, given a policy objective of some desired balance stated in trms of 1 or more of the identified parameters, it is possible to analyze the consequences of alternative migration strategies. It is important to consider the role of relative productivity (R6). An attempt to change R6 has implications for both the design of a migration policy and a national policy of human capital formation. Other factors may not be immediately related to a migration policy. The question then is whether these ratios are sensitive to policy intervention. In a simulation exercise it was assumed that the Kuwaiti crude labor force participation rate (R4) will increase by 13% during a period of 10 years. R4 increases if relatively more people work. Women are 1 segment of the labor force that is not adequately represented, partly because of traditions, lack of skills, and the presence of high fertility. None of these can change in the short run without an active policy of social reform. Yet, the assumption seems to be in the right direction. A policy that attempts to reduce R4 through increasing fertility in Kuwait is clearly against the tide. In sum, the labor importing countries faced with recent unfavorable demographic realities will actively

  18. Noble gas fractionation during subsurface gas migration

    NASA Astrophysics Data System (ADS)

    Sathaye, Kiran J.; Larson, Toti E.; Hesse, Marc A.

    2016-09-01

    Environmental monitoring of shale gas production and geological carbon dioxide (CO2) storage requires identification of subsurface gas sources. Noble gases provide a powerful tool to distinguish different sources if the modifications of the gas composition during transport can be accounted for. Despite the recognition of compositional changes due to gas migration in the subsurface, the interpretation of geochemical data relies largely on zero-dimensional mixing and fractionation models. Here we present two-phase flow column experiments that demonstrate these changes. Water containing a dissolved noble gas is displaced by gas comprised of CO2 and argon. We observe a characteristic pattern of initial co-enrichment of noble gases from both phases in banks at the gas front, followed by a depletion of the dissolved noble gas. The enrichment of the co-injected noble gas is due to the dissolution of the more soluble major gas component, while the enrichment of the dissolved noble gas is due to stripping from the groundwater. These processes amount to chromatographic separations that occur during two-phase flow and can be predicted by the theory of gas injection. This theory provides a mechanistic basis for noble gas fractionation during gas migration and improves our ability to identify subsurface gas sources after post-genetic modification. Finally, we show that compositional changes due to two-phase flow can qualitatively explain the spatial compositional trends observed within the Bravo Dome natural CO2 reservoir and some regional compositional trends observed in drinking water wells overlying the Marcellus and Barnett shale regions. In both cases, only the migration of a gas with constant source composition is required, rather than multi-stage mixing and fractionation models previously proposed.

  19. [The migration policy of the Ivory Coast].

    PubMed

    Brou, K; Charbit, Y

    1994-01-01

    Migration policies adopted by the Ivory Coast at independence were essentially a continuation of colonial policies aimed at providing manpower for the coffee and cacao plantations of the south, whose exports were to form the basis of the national development strategy. Instead of forced labor, the government facilitated installation of migrants in agricultural areas by means of laws assuring their access to lands not currently in use. Massive immigration of workers resulted in an age and sex distribution favorable to the needs of the plantation economy. The concentration of development efforts in the forest zone of the south, including Abidjan, encouraged thousands of workers from the savannah to migrate south in search of higher incomes and better living conditions. Bilateral accords with the former Upper Volta and with France and multilateral accords with the Economic Community of the West African states regulated the migratory movement. The Ivory Coast's migration policy succeeded in populating the forest zone and permitted the Ivory Coast to construct a powerful economy. But the policy produced sometimes violent opposition among natives overwhelmed by foreigners in search of lands. The loss of labor force in the savannah threatened the nation's food supply and demographic balance. In the forest zone itself, many of the immigrant workers left the plantations to seek greater success in the cities, swelling the ranks of the urban unemployed and leaving much of the rural area short of labor. In prosperous times, when prices for southern goods were high, the system worked reasonably well. When economic conditions worsened, the inefficiency of the policy became clear. At those times the international conventions failed to control the influx because of the conflicting interests of the countries. Ethnic and regional tensions mounted, the rural exodus continued despite attempts to encourage regional development, and conflicts over land tenure intensified.

  20. Cyclic motor activity; migrating motor complex: 1985.

    PubMed

    Sarna, S K

    1985-10-01

    Most of the gastrointestinal tract and the biliary tract have a cyclic motor activity. The electric counterpart of this motor activity is called cyclic myoelectric activity. A typical motor cycle in the LES, stomach, and small intestine is composed of a quiescent state, followed by progressively increasing amplitude and frequency of contractions culminating in a state of maximal contractile activity. The colonic motor cycle has only the quiescent and the contractile states. In the small intestine, these motor complexes migrate in an aborad direction, and in the colon in both orad and aborad directions. The mechanisms of initiation and migration of these complexes are best understood in the small intestine. Both the initiation and migration of these complexes seem to be controlled by enteric neural mechanisms. The functions of the enteric mechanisms may be modulated by the central nervous system and by circulating endogenous substances. The mechanisms of initiation of these complexes are not completely understood in the rest of the gastrointestinal tract and in the biliary tract. The physiologic function of these motor complexes that occur only after several hours of fast in the upper gastrointestinal tract of nonruminants may be to clean the digestive tract of residual food, secretions, and cellular debris. This function is aided by a coordinated secretion of enzymes, acid, and bicarbonate. In ruminants, phase III activity is associated with the distal propulsion of ingested food. The function of colonic motor complexes that are not coordinated with the cyclic motor activities of the rest of the gastrointestinal tract may be only to move contents back and forth for optimal absorption. PMID:3896912

  1. Indonesia's great frontier and migration policy.

    PubMed

    Maloney, C

    1987-01-01

    The population of Indonesia is 175 million, of which 65% live in Java. Java has only 7% of the land area, causing a population density of 2,000/square mile. This has lead the government to introduce a policy of transmigration which encourages people to move from Java to the larger outer islands. In the last 35 years 4.3 million people have moved from Java to Sumatra, Borneo, Celebes, and Irian Jaya. The total area of Indonesia stretches over 3,200 miles and has 16,000 islands of which 1,000 are inhabited. It has vast resources of oil, lumber, rubber, tin, palm oil, copra, coffee, tea, pepper, cloves, nutmeg, and quinine. Indonesia is also rich in minerals, including coal, bauxite, iron ore, and gold. Even with a national family planning program, population growth has reached 2.1% a year. 3 other islands that people are induced to move from are Madura, Bali, and Lombok, although their population densities are less then Java. The small islands near Singapore are being developed and Batam will be a free port to compete with Hong Kong. The most intense migration has been to Kalimantan (Borneo) which has 4 provinces. The migration policy began in 1905 and by 1930 100,000 people, had moved to other islands; 600,000 people were relocated to plantations in Java for labor needs. In 1979-84, a more ambitious program costing 2.3 billion moved 1.5 million people. In the most recent 1984-89 plan, a goal of 3.1 million were to be relocated but due to budgetary restrictions only 150,000 families have moved. The main social issue addresses the domination of other people by Javanese, not only in numbers but cultural differences. Some observers say the real reason for migration is political in ensuring the boundaries and geographic integrity of Indonesia. PMID:12316071

  2. Lymphocyte migration patterns in organ allograft recipients.

    PubMed

    Kupiec-Weglinski, J W; Tilney, N L

    1989-04-01

    A central tenet of immunology is the observation, made 30 years ago, that lymphocytes recirculate continuously between peripheral blood and lymphoid tissues. In recent years, the subject of lymphocyte migration, both under physiological conditions and in states of alloresponsiveness, has become more enigmatic. It lies outside most current topics of immunological investigations, labelling and tracing techniques are problematic, and many experimental findings are phenomenological and difficult to interpret. Indeed, our overall knowledge of the functional differences between the various host lymphoid compartments and their constituent cell populations remains rudimentary. However, as understanding increases regarding the host immunological events responding to an antigenic stimulus such as a graft, with growing definition of the distinctive and interconnecting roles of lymphocyte subpopulations and their products acting on each other to produce graft destruction, the conceptual importance of lymphocyte migration again is becoming obvious. This role includes many facets of immunity such as the effects of antigen specificity, immunologic memory, differential behavior of recirculating or sessile populations, and local and systemic contact between antigen and effector cells. It has become evident that lymphocytes migrate in a non-random and highly dynamic fashion determined by a range of specific and non-specific factors; in the setting of organ transplantation, patterns are profoundly affected by the interrelated cellular and humoral components of the immunological cascade which may lead either to graft rejection or to its prolongation in untreated and immunologically modified recipients, respectively. Thus, the traffic of lymphocytes throughout host lymphoid and non-lymphoid compartments and their activity within these compartments should be considered an integral part of the host immunomodulation triggered by transplantation of histoincompatible tissue. Gradual filling

  3. A modeling of buoyant gas plume migration

    SciTech Connect

    Silin, D.; Patzek, T.; Benson, S.M.

    2008-12-01

    This work is motivated by the growing interest in injecting carbon dioxide into deep geological formations as a means of avoiding its atmospheric emissions and consequent global warming. Ideally, the injected greenhouse gas stays in the injection zone for a geologic time, eventually dissolves in the formation brine and remains trapped by mineralization. However, one of the potential problems associated with the geologic method of sequestration is that naturally present or inadvertently created conduits in the cap rock may result in a gas leakage from primary storage. Even in a supercritical state, the carbon dioxide viscosity and density are lower than those of the formation brine. Buoyancy tends to drive the leaked CO{sub 2} plume upward. Theoretical and experimental studies of buoyancy-driven supercritical CO{sub 2} flow, including estimation of time scales associated with plume evolution and migration, are critical for developing technology, monitoring policy, and regulations for safe carbon dioxide geologic sequestration. In this study, we obtain simple estimates of vertical plume propagation velocity taking into account the density and viscosity contrast between CO{sub 2} and brine. We describe buoyancy-driven countercurrent flow of two immiscible phases by a Buckley-Leverett type model. The model predicts that a plume of supercritical carbon dioxide in a homogeneous water-saturated porous medium does not migrate upward like a bubble in bulk water. Rather, it spreads upward until it reaches a seal or until it becomes immobile. A simple formula requiring no complex numerical calculations describes the velocity of plume propagation. This solution is a simplification of a more comprehensive theory of countercurrent plume migration (Silin et al., 2007). In a layered reservoir, the simplified solution predicts a slower plume front propagation relative to a homogeneous formation with the same harmonic mean permeability. In contrast, the model yields much higher

  4. Social effects of migration in receiving countries.

    PubMed

    Bergman, E

    1989-06-01

    Using a theoretical approach, this paper discusses the treatment of different aspects of the social effects of migration in receiving countries which centers around key issues such as ethnicity, discrimination, and the impact of general policy measures upon ethnic relations. Countries may be classified with respect to relations between ethnic groups in the following ways: 1) those that are either plural or multi-ethnic, 2) those consisting of mainly immigrants and their offspring, 3) those that have a fairly homogenous population and ethnic minorities resulting from post-war immigration, and 4) those that have a fairly homogenous population and 1 or more native minorities. International migration requires nations to formulate immigration, immigrant, and ethnic relations policies. Ethnic conflict often stems from a situation of need within competition for such facilities as education, housing, and employment. The underlying factors are mostly economic. The unequal distribution of influence and resources can be reduced by government policies designed to redistribute such influence and resources, and by providing better opportunities for individuals to gain influence and resources. Policy measures in the fields of general economic policy, labor market policy, housing policy, social policy, and educational policy probably affect ethnic relations more deeply than measures in the field of ethnic relations policy. Discrimination on ethnic, racial, or similar grounds is against the constitution of many countries. However, many difficulties arise in trying to use anti-discrimination laws in practice. Ethnicity is probably the most widespread cause of conflict in the world. The ethnic homogeneity of many countries has been reduced by the immigration of new ethnic elements. Can truly multicultural societies emerge from international migration? 3 possibilities exist: 1) unitary social systems will prevail where they 1st existed, 2) ethnic groups may segregate from each other

  5. Droplet migration characteristics in confined oscillatory microflows.

    PubMed

    Chaudhury, Kaustav; Mandal, Shubhadeep; Chakraborty, Suman

    2016-02-01

    We analyze the migration characteristics of a droplet in an oscillatory flow field in a parallel plate microconfinement. Using phase field formalism, we capture the dynamical evolution of the droplet over a wide range of the frequency of the imposed oscillation in the flow field, drop size relative to the channel gap, and the capillary number. The latter two factors imply the contribution of droplet deformability, commonly considered in the study of droplet migration under steady shear flow conditions. We show that the imposed oscillation brings an additional time complexity in the droplet movement, realized through temporally varying drop shape, flow direction, and the inertial response of the droplet. As a consequence, we observe a spatially complicated pathway of the droplet along the transverse direction, in sharp contrast to the smooth migration under a similar yet steady shear flow condition. Intuitively, the longitudinal component of the droplet movement is in tandem with the flow continuity and evolves with time at the same frequency as that of the imposed oscillation, although with an amplitude decreasing with the frequency. The time complexity of the transverse component of the movement pattern, however, cannot be rationalized through such intuitive arguments. Towards bringing out the underlying physics, we further endeavor in a reciprocal identity based analysis. Following this approach, we unveil the time complexities of the droplet movement, which appear to be sufficient to rationalize the complex movement patterns observed through the comprehensive simulation studies. These results can be of profound importance in designing droplet based microfluidic systems in an oscillatory flow environment.

  6. Migration for employment among the Arab countries.

    PubMed

    Birks, S; Sinclair, C

    1979-10-01

    The large-scale recent migrations from Arab countries for jobs in the Persian Gulf and Libya are examined with analyses of the problems from the perspectives of both the importing and the exporting countries. In 1975 there were more than 2.5 million Arab workers living in Arab states other than their own, about 1/2 of whom were employed. Since that time the numbers have increased by about 9% annually; an estimated 1,570,000 Arab workers were living abroad in early 1979. It is estimated that another 975,000 non-Arab migrant workers were employed within the Arab world in January 1979, a total of over 2,500,000 migrants for employment in the Arab Near East. The sheer volume of this migration for employment and its relative importance within the labor markets of the Arab world, the impact that migration for employment has upon economic development, and the mutual independence among countries that labor exporting and importing brings about have made migrant labor movements a leading issue in the Near East. Focus is on the distribution of wealth in the Near East, population and workforce in the Arab states, economic development of the capital-rich and the capital-poor states, the international transfers of labor, and impacts on the labor-supply countries. The impacts of an emigrant workforce vary considerably with the conditions in the different exporting countries. Some of these effects are highlighted by citing examples from Egypt, Jordan, the Yemen and Sudan. PMID:12336017

  7. The CHESHIRE Migration Experiment A Summary Report

    SciTech Connect

    David A. Sawyer; Joseph L. Thompson; David K. Smith

    1999-10-01

    The CHESHIRE nuclear weapon test was detonated in 1976 in fractured volcanic rock at the Nevada Test Site (NTS). This testis representative of many other high-yield tests conducted below the water table in the Pahute Mesa area of the NTS. Since 1976 we have been studying the movement of test-related radionuclides within a few hundred meters of the explosion cavity. CHESHIRE is the only nuclear test characterized before, immediately after, and for decades following the detonation and provides data on both the prompt and long-term dispersal of radionuclides after an underground nuclear test. For this reason it is a unique field-scale transport experiment. Solid and fluid samples were collected from a drill back hole extending into and through the cavity in order to measure the initial distributions of radionuclides after the detonation. We subsequently pumped and sampled water from the cavity region and from a hydraulically transmissive zone about 400 m higher in the collapse chimney. A satellite well was also drilled 380 m down gradient from CHESHIRE and intercepted radionuclides (including tritium in high concentration) being transported through transmissive aquifers. Studies of radionuclide migration at CHESHIRE documented for the first time at the NTS the transport of relatively insoluble radionuclides (e.g., europium isotopes) with colloids moving in the groundwater. Water was pumped again from the cavity and chimney horizons in 1998 in order to observe the evolution of the hydrologic source term after several decades. Recent comprehensive studies of the geology and hydrology at the CHESHIRE site have improved predictions of radionuclide migration in the context of a regional groundwater flow model. This report provides unclassified data and describes a conceptual model for radionuclide migration associated with a nuclear test that is applicable to other tests on Pahute Mesa similar in yield, hydrogeologic setting, and age.

  8. Droplet migration in emulsion systems measured using MR methods.

    PubMed

    Hollingsworth, K G; Johns, M L

    2006-04-15

    The migration of emulsion droplets under shear flow remains a largely unexplored area of study, despite the existence of an extensive literature on the analogous problem of solid particle migration. A novel methodology is presented to track the shear-induced migration of emulsion droplets based on magnetic resonance imaging (MRI). The work is in three parts: first, single droplets of one Newtonian fluid are suspended in a second Newtonian fluid (water in silicone oil (PDMS)) and are tracked as they migrate within a Couette cell; second, the migration of emulsion droplets in Poiseuille flow is considered; third, water-in-silicone oil emulsions are sheared in a Couette cell. The effect of (a) rotational speed of the Couette, (b) the continuous phase viscosity, and (c) the droplet phase concentration are considered. The equilibrium extent of migration and rate of migration increase with rotational speed for two different emulsion systems and increased continuous phase viscosity, leads to a greater equilibrium extent of migration. The relationship between the droplet phase concentration and migration is however complex. These results for semi-concentrated emulsion systems and wide-gap Couette cells are not well described by existing models of emulsion droplet migration. PMID:16257005

  9. A probe into reasons for international migration in Fujian Province.

    PubMed

    Zhu, G

    1990-01-01

    In this paper, the author discusses the extent of international migration from China's Fujian Province and considers the reasons behind the migration. The most recent estimates place China's overseas population at 22.1 million, 19 million (88%) of which are concentrated in Southeast Asia. According to the author's calculations, at least 7 million of the Chinese overseas population are of Fujian descent. Indonesia alone holds some 3.3 million Fujianese. Malaysia, Singapore, and the Philippines account for most of the remaining Fujianese overseas population. Having established the extent of international migration from the Fujian Province, the author attempts to establish the reasons behind it. The author first considers the historical origins of Fujianese international migration, from its early states (end century B.C.-17th century) to modern times *18-early 20th century) to the current period (1949-present). The author then examines the reasons behind the migration, primarily the social environment and individual behavior. Finally, the author provides categories of international migration, stressing that these categories often overlap or coincide. Most of the early migration was "spontaneous" -- essentially, an unplanned occurrence. During the modern period, most migration was "forced" by the contract labor system instituted by colonialists. Political and social upheaval also prompted "provoked" international migration. And following the Chinese Revolution, "free" migration allowed many to return home or to join relative abroad.

  10. Convergence of broad-scale migration strategies in terrestrial birds.

    PubMed

    La Sorte, Frank A; Fink, Daniel; Hochachka, Wesley M; Kelling, Steve

    2016-01-27

    Migration is a common strategy used by birds that breed in seasonal environments. Selection for greater migration efficiency is likely to be stronger for terrestrial species whose migration strategies require non-stop transoceanic crossings. If multiple species use the same transoceanic flyway, then we expect the migration strategies of these species to converge geographically towards the most optimal solution. We test this by examining population-level migration trajectories within the Western Hemisphere for 118 migratory species using occurrence information from eBird. Geographical convergence of migration strategies was evident within specific terrestrial regions where geomorphological features such as mountains or isthmuses constrained overland migration. Convergence was also evident for transoceanic migrants that crossed the Gulf of Mexico or Atlantic Ocean. Here, annual population-level movements were characterized by clockwise looped trajectories, which resulted in faster but more circuitous journeys in the spring and more direct journeys in the autumn. These findings suggest that the unique constraints and requirements associated with transoceanic migration have promoted the spatial convergence of migration strategies. The combination of seasonal atmospheric and environmental conditions that has facilitated the use of similar broad-scale migration strategies may be especially prone to disruption under climate and land-use change.

  11. A probe into reasons for international migration in Fujian Province.

    PubMed

    Zhu, G

    1990-01-01

    In this paper, the author discusses the extent of international migration from China's Fujian Province and considers the reasons behind the migration. The most recent estimates place China's overseas population at 22.1 million, 19 million (88%) of which are concentrated in Southeast Asia. According to the author's calculations, at least 7 million of the Chinese overseas population are of Fujian descent. Indonesia alone holds some 3.3 million Fujianese. Malaysia, Singapore, and the Philippines account for most of the remaining Fujianese overseas population. Having established the extent of international migration from the Fujian Province, the author attempts to establish the reasons behind it. The author first considers the historical origins of Fujianese international migration, from its early states (end century B.C.-17th century) to modern times *18-early 20th century) to the current period (1949-present). The author then examines the reasons behind the migration, primarily the social environment and individual behavior. Finally, the author provides categories of international migration, stressing that these categories often overlap or coincide. Most of the early migration was "spontaneous" -- essentially, an unplanned occurrence. During the modern period, most migration was "forced" by the contract labor system instituted by colonialists. Political and social upheaval also prompted "provoked" international migration. And following the Chinese Revolution, "free" migration allowed many to return home or to join relative abroad. PMID:12284987

  12. Modeling of Carbon Migration During JET Injection Experiments

    SciTech Connect

    Strachan, J. D.; Likonen, J.; Coad, P.; Rubel, M.; Widdowson, A.; Airila, M.; Andrew, P.; Brezinsek, S.; Corrigan, G.; Esser, H. G.; Jachmich, S.; Kallenbach, A.; Kirschner, A.; Kreter, A.; Matthews, G. F.; Philipps, V.; Pitts, R. A.; Spence, J.; Stamp, M.; Wiesen, S.

    2008-10-15

    JET has performed two dedicated carbon migration experiments on the final run day of separate campaigns (2001 and 2004) using {sup 13}CH{sub 4} methane injected into repeated discharges. The EDGE2D/NIMBUS code modelled the carbon migration in both experiments. This paper describes this modelling and identifies a number of important migration pathways: (1) deposition and erosion near the injection location, (2) migration through the main chamber SOL, (3) migration through the private flux region aided by E x B drifts, and (4) neutral migration originating near the strike points. In H-Mode, type I ELMs are calculated to influence the migration by enhancing erosion during the ELM peak and increasing the long-range migration immediately following the ELM. The erosion/re-deposition cycle along the outer target leads to a multistep migration of {sup 13}C towards the separatrix which is called 'walking'. This walking created carbon neutrals at the outer strike point and led to {sup 13}C deposition in the private flux region. Although several migration pathways have been identified, quantitative analyses are hindered by experimental uncertainty in divertor leakage, and the lack of measurements at locations such as gaps and shadowed regions.

  13. Migration and development: a critical relationship.

    PubMed

    Appleyard, R T

    1992-01-01

    "Wide income differentials, the threat of increased illegal immigration from developing countries, and sub-replacement fertility in the developed countries are some reasons for the recent reassessment of the relationship between migration and development.... The model presented in this article proposes different roles for permanent immigrants, contract workers, professional transients, illegal migrants and others according to the stages of modernization of the sending and receiving countries. The model was found consistent with the experiences of Mauritius, Seychelles, Singapore and, to a lesser extent, Malaysia."

  14. Migration and development: a critical relationship.

    PubMed

    Appleyard, R T

    1992-01-01

    "Wide income differentials, the threat of increased illegal immigration from developing countries, and sub-replacement fertility in the developed countries are some reasons for the recent reassessment of the relationship between migration and development.... The model presented in this article proposes different roles for permanent immigrants, contract workers, professional transients, illegal migrants and others according to the stages of modernization of the sending and receiving countries. The model was found consistent with the experiences of Mauritius, Seychelles, Singapore and, to a lesser extent, Malaysia." PMID:12317235

  15. Income inequality and urban/rural migration.

    PubMed

    Slottje, D J; Hayes, K J

    1987-01-01

    "The purpose of this paper is to examine some of the consequences of [U.S.] migration trends from 1970-1980, focusing on the relationship of income inequality within a state with population shifts within and across states. Furthermore, we wish to determine if the movement of wealth and the changing employment opportunities [have] had any effect on the distribution of income within the four census regions and for urban and rural populations across all fifty states." Data are from the 1970 and 1980 censuses.

  16. International labor migration and external debt.

    PubMed

    Bustamante, J A

    1987-01-01

    The prevailing Mexican and US definitions of undocumented migration are poles apart. The US views it as a criminal problem. Mexicans view the undocumented migrants as actors in an economic game in which the rules are extremely disadvantageous to these migrants. Migrants themselves and their communities view the undocumented as a positive element. It is necessary to move toward a bilateral focus and bilateral negotiation on the issue of migratory workers. This proposal derives from several assumptions: 1) the external debt is a bilateral or multilateral issue, 2) it is important to avoid forcing debtor countries to choose between stimulating economic growth or making payment on their foreign debt, 3) prevailing public opinion in the US favors halting undocumented migration, 4) the US views the migration of undocumented Mexicans as the result of forces endogenous to Mexico and exogenous to the US, 5) the US views both Mexico's ability to make payment on its external debt and to halt emigration as tied to the Mexican government's ability or inability to reconcile political stability with scarce monetary resources, and 6) political instability in Mexico could augment emigration to the US and undermine Mexico's ability to address its foreign debt. The following proposal suggests means to link negotiation on the external debt to that of undocumented migration: 1) The Mexican government could reach an accord with the US to channel a portion of the actual interest on the external debt as a fund to be invested in Mexico to construct a system of labor intensive agroindustrial productive units designed to attract former or potential migratory workers; 2) the total amount of these funds would be deducted from interest payments on the principal of the actual external debt and redefined as an ad hoc loan to Mexico to finance these production units; 3) part of the production from these units would be incorporated into ongoing US food relief and food assistance programs; 4) the

  17. Overcoming Migration during Giant Planet Formation

    NASA Astrophysics Data System (ADS)

    Thommes, Edward W.; Nilsson, Leif; Murray, Norman

    2007-02-01

    In the core accretion model, gas giant formation is a race between growth and migration; for a core to become a Jovian planet, it must accrete its envelope before it spirals into the host star. We use a multizone numerical model to extend our previous investigation of the ``window of opportunity'' for gas giant formation within a disk. When the collision cross section enhancement due to core atmospheres is taken into account, we find that a broad range of protoplanetary disks possess such a window.

  18. Modelling granite migration by mesoscale pervasive flow

    NASA Astrophysics Data System (ADS)

    Leitch, A. M.; Weinberg, R. F.

    2002-06-01

    Mesoscale pervasive magma migration leads to granite injection complexes, common in hot crustal terranes. Pervasive migration is limited by magma freezing when intruding cold country rock. Here, we explore numerically the feedback mechanism between magma intrusion and heating of the country rock, which allows younger intrusive batches to reach increasingly shallower/cooler levels. This process relies on the higher solidus temperature of a rock compared to that of its melt, once melt is segregated. We define the 'free-ride layer' as the region above the melt source, where magma may freely migrate because rock temperature is above melt solidus. The top of the free-ride layer, which corresponds to the melt solidus ( TS) isotherm, is at the 'limiting depth', zS. After magma passes through the free-ride layer, the magma 'front' is always at the limiting depth. We modeled the thickening and heating of the crust above the source as melt at its liquidus ( TL) intrudes it pervasively from below. We found that: (a) magma quickly warms crust below zS to about TL, forming a step in temperature at zS; (b) the front ( zS) moves up through the crust as more magma is intruded; (c) as magma is emplaced at the front, a mingled layer of about half magma half crust forms below it, so that the total rise of the front corresponds approximately to half of the thickness of magma added to the free-ride layer; (d) the rate of rise of the front depends on the temperature difference between crust and TL, and slows down as the magma front rises; (e) for most reasonable intrusion rates and volumes, the crust above zS feels little influence of the intrusion, because the diffusion time scale is much smaller than the rise rate of the front. In summary, pervasive migration is an efficient way of heating the lower to middle crust, and can result in an injection complex several kilometers thick, consisting of about half magma and half original crust.

  19. A note on the microeconomics of migration.

    PubMed

    Stahl, K

    1983-11-01

    "The purpose of this note is to demonstrate in a simple model that an individual's migration from a small town to a large city may be rationalized purely by a consumption motive, rather than the motive of obtaining a higher income. More specifically, it is shown that in a large city an individual may derive a higher utility from spending a given amount of income than in a small town." A formal model is first developed that includes the principal forces at work and is then illustrated using a graphic example. The theoretical and empirical issues raised are considered in the concluding section. PMID:12312600

  20. [Migration: theoretical universe and research issues].

    PubMed

    Arguello, O

    1981-04-01

    The author constructs a model of a theoretical universe that integrates the various phenomena present in the migratory process. The model is based on a global conceptualization of migration that considers economic, cultural, political, psychological, and social factors. Various theoretical approaches used in Latin American social science research are discussed and evaluated. The relationships between migratory processes and factors including the size and structure of the agricultural sector, technological development, the social organization of agricultural production, family structure, ethnicity, and cultural, political, and psychological influences are analyzed. PMID:12336939

  1. International labor migration and external debt.

    PubMed

    Bustamante, J A

    1987-01-01

    The prevailing Mexican and US definitions of undocumented migration are poles apart. The US views it as a criminal problem. Mexicans view the undocumented migrants as actors in an economic game in which the rules are extremely disadvantageous to these migrants. Migrants themselves and their communities view the undocumented as a positive element. It is necessary to move toward a bilateral focus and bilateral negotiation on the issue of migratory workers. This proposal derives from several assumptions: 1) the external debt is a bilateral or multilateral issue, 2) it is important to avoid forcing debtor countries to choose between stimulating economic growth or making payment on their foreign debt, 3) prevailing public opinion in the US favors halting undocumented migration, 4) the US views the migration of undocumented Mexicans as the result of forces endogenous to Mexico and exogenous to the US, 5) the US views both Mexico's ability to make payment on its external debt and to halt emigration as tied to the Mexican government's ability or inability to reconcile political stability with scarce monetary resources, and 6) political instability in Mexico could augment emigration to the US and undermine Mexico's ability to address its foreign debt. The following proposal suggests means to link negotiation on the external debt to that of undocumented migration: 1) The Mexican government could reach an accord with the US to channel a portion of the actual interest on the external debt as a fund to be invested in Mexico to construct a system of labor intensive agroindustrial productive units designed to attract former or potential migratory workers; 2) the total amount of these funds would be deducted from interest payments on the principal of the actual external debt and redefined as an ad hoc loan to Mexico to finance these production units; 3) part of the production from these units would be incorporated into ongoing US food relief and food assistance programs; 4) the

  2. International migration and development in Mexican communities.

    PubMed

    Durand, J; Kandel, W; Parrado, E A; Massey, D S

    1996-05-01

    The theoretical and empirical literature generally regards international migration as producing a cycle of dependency and stunted development in sending communities. Most migrants' earnings are spent on consumption; few funds are channeled into productive investment. We argue that this view is misleading because it ignores the conditions under which productive investment is likely to be possible and profitable. We analyze the determinants of migrants' savings and remittance decisions, using variables defined at the individual, household, community, and macroeconomic levels. We identify the conditions under which U.S. earnings are repatriated to Mexico as remittances and savings, and indicate the factors leading to their productive investment.

  3. Contractile forces in tumor cell migration.

    PubMed

    Mierke, Claudia Tanja; Rösel, Daniel; Fabry, Ben; Brábek, Jan

    2008-09-01

    Cancer is a deadly disease primarily because of the ability of tumor cells to spread from the primary tumor, to invade into the connective tissue, and to form metastases at distant sites. In contrast to cell migration on a planar surface where large cell tractions and contractile forces are not essential, tractions and forces are thought to be crucial for overcoming the resistance and steric hindrance of a dense three-dimensional connective tissue matrix. In this review, we describe recently developed biophysical tools, including 2-D and 3-D traction microscopy to measure contractile forces of cells. We discuss evidence indicating that tumor cell invasiveness is associated with increased contractile force generation.

  4. Intermetropolitan migration and quality of life.

    PubMed

    Porell, F W

    1982-05-01

    The aim of this paper is to assess the relative importance of economic and quality of life (QOL) factors as determinants of inter-metropolitan migration in the United States. The study is based on the generalized systemic gravity model of Alonso and on data from a sample of 25 SMSAs over the period 1965-1970. "The most striking feature of the empirical results is the apparent lack of importance of origin economic and QOL factors as determinants of outmigration.... On the other hand, the empirical results suggest both economic and QOL factors to be significant determinants of inmigration."

  5. Terahertz reflection imaging using Kirchhoff migration.

    PubMed

    Dorney, T D; Johnson, J L; Van Rudd, J; Baraniuk, R G; Symes, W W; Mittleman, D M

    2001-10-01

    We describe a new imaging method that uses single-cycle pulses of terahertz (THz) radiation. This technique emulates data-collection and image-processing procedures developed for geophysical prospecting and is made possible by the availability of fiber-coupled THz receiver antennas. We use a simple migration procedure to solve the inverse problem; this permits us to reconstruct the location and shape of targets. These results demonstrate the feasibility of the THz system as a test-bed for the exploration of new seismic processing methods involving complex model systems. PMID:18049652

  6. Regolith migration and sorting on asteroid Itokawa.

    PubMed

    Miyamoto, Hideaki; Yano, Hajime; Scheeres, Daniel J; Abe, Shinsuke; Barnouin-Jha, Olivier; Cheng, Andrew F; Demura, Hirohide; Gaskell, Robert W; Hirata, Naru; Ishiguro, Masateru; Michikami, Tatsuhiro; Nakamura, Akiko M; Nakamura, Ryosuke; Saito, Jun; Sasaki, Sho

    2007-05-18

    High-resolution images of the surface of asteroid Itokawa from the Hayabusa mission reveal it to be covered with unconsolidated millimeter-sized and larger gravels. Locations and morphologic characteristics of this gravel indicate that Itokawa has experienced considerable vibrations, which have triggered global-scale granular processes in its dry, vacuum, microgravity environment. These processes likely include granular convection, landslide-like granular migrations, and particle sorting, resulting in the segregation of the fine gravels into areas of potential lows. Granular processes become major resurfacing processes because of Itokawa's small size, implying that they can occur on other small asteroids should those have regolith. PMID:17446355

  7. Fat, moisture, and ethanol migration through chocolates and confectionary coatings.

    PubMed

    Ghosh, V; Ziegler, G R; Anantheswaran, R C

    2002-01-01

    The migration of fat, moisture, and ethanol is a common problem with chocolate-coated confectionery products. Migration of one of these components into the coating leads to visual and sensory defects such as sugar or fat bloom, making the product unacceptable to the consumer. The migration rate depends on the structure and composition of the coating. The migration of each of these species can be slowed to a certain extent by proper tempering of the coating, because proper tempering will give a structure that resists migration. In the continuous lipid phase, these chemical species migrate mainly through the liquid portion. Thus, the migration rate depends on the amount of liquid oil present in the product. Migration can be delayed either by reducing the liquid fat content or by immobilizing the liquid phase. The actual mechanisms for the migration processes are speculative, and a more thorough understanding is necessary to better abate quality deterioration. Armed with this understanding, a manufacturer would know a priori the effect of changing the ingredient or process. A few methods for control have been suggested, but have found limited application. Mathematical models have been proposed to predict the migration behavior, but their application is hindered because of the simplified assumptions employed. There is a need for developing better models that combine mass transfer with the phase behavior to be able to accurately predict the migration process. This review discusses the current understanding of fat, moisture, and ethanol migration through chocolate coatings and also includes a brief description of the theoretical aspects governing migration.

  8. Concrete Property and Radionuclide Migration Tests

    SciTech Connect

    Wellman, Dawn M.; Mattigod, Shas V.; Powers, Laura; Parker, Kent E.; Clayton, Libby N.; Wood, Marcus I.

    2008-10-01

    The Waste Management Project provides safe, compliant, and cost-effective waste management services for the Hanford Site and the DOE Complex. Part of theses services includes safe disposal of LLW and MLLW at the Hanford Low-Level Waste Burial Grounds (LLBG) in accordance with the requirements listed in DOE Order 435.1, Radioactive Waste Management. To partially satisfy these requirements, a Performance Assessment (PA) analyses were completed and approved. DOE Order 435.1 also requires that continuing data collection be conducted to enhance confidence in the critical assumptions used in these analyses to characterize the operational features of the disposal facility that are relied upon to satisfy the performance objectives identified in the Order. One critical assumption is that concrete will frequently be used as waste form or container material to control and minimize the release of radionuclide constituents in waste into the surrounding environment. Data was collected to (1) quantify radionuclide migration through concrete materials similar to those used to encapsulate waste in the LLBG, (2) measure the properties of the concrete materials, especially those likely to influence radionuclide migration, and (3) quantify the stability of U-bearing solid phases of limited solubility in concrete.

  9. Global solidarity, migration and global health inequity.

    PubMed

    Eckenwiler, Lisa; Straehle, Christine; Chung, Ryoa

    2012-09-01

    The grounds for global solidarity have been theorized and conceptualized in recent years, and many have argued that we need a global concept of solidarity. But the question remains: what can motivate efforts of the international community and nation-states? Our focus is the grounding of solidarity with respect to global inequities in health. We explore what considerations could motivate acts of global solidarity in the specific context of health migration, and sketch briefly what form this kind of solidarity could take. First, we argue that the only plausible conceptualization of persons highlights their interdependence. We draw upon a conception of persons as 'ecological subjects' and from there illustrate what such a conception implies with the example of nurses migrating from low and middle-income countries to more affluent ones. Next, we address potential critics who might counter any such understanding of current international politics with a reference to real-politik and the insights of realist international political theory. We argue that national governments--while not always or even often motivated by moral reasons alone--may nevertheless be motivated to acts of global solidarity by prudential arguments. Solidarity then need not be, as many argue, a function of charitable inclination, or emergent from an acknowledgment of injustice suffered, but may in fact serve national and transnational interests. We conclude on a positive note: global solidarity may be conceptualized to helpfully address global health inequity, to the extent that personal and transnational interdependence are enough to motivate national governments into action.

  10. Understanding oceanic migrations with intrinsic biogeochemical markers.

    PubMed

    Ramos, Raül; González-Solís, Jacob; Croxall, John P; Oro, Daniel; Ruiz, Xavier

    2009-01-01

    Migratory marine vertebrates move annually across remote oceanic water masses crossing international borders. Many anthropogenic threats such as overfishing, bycatch, pollution or global warming put millions of marine migrants at risk especially during their long-distance movements. Therefore, precise knowledge about these migratory movements to understand where and when these animals are more exposed to human impacts is vital for addressing marine conservation issues. Because electronic tracking devices suffer from several constraints, mainly logistical and financial, there is emerging interest in finding appropriate intrinsic markers, such as the chemical composition of inert tissues, to study long-distance migrations and identify wintering sites. Here, using tracked pelagic seabirds and some of their own feathers which were known to be grown at different places and times within the annual cycle, we proved the value of biogeochemical analyses of inert tissue as tracers of marine movements and habitat use. Analyses of feathers grown in summer showed that both stable isotope signatures and element concentrations can signal the origin of breeding birds feeding in distinct water masses. However, only stable isotopes signalled water masses used during winter because elements mainly accumulated during the long breeding period are incorporated into feathers grown in both summer and winter. Our findings shed new light on the simple and effective assignment of marine organisms to distinct oceanic areas, providing new opportunities to study unknown migration patterns of secretive species, including in relation to human-induced mortality on specific populations in the marine environment. PMID:19623244

  11. Understanding oceanic migrations with intrinsic biogeochemical markers.

    PubMed

    Ramos, Raül; González-Solís, Jacob; Croxall, John P; Oro, Daniel; Ruiz, Xavier

    2009-07-22

    Migratory marine vertebrates move annually across remote oceanic water masses crossing international borders. Many anthropogenic threats such as overfishing, bycatch, pollution or global warming put millions of marine migrants at risk especially during their long-distance movements. Therefore, precise knowledge about these migratory movements to understand where and when these animals are more exposed to human impacts is vital for addressing marine conservation issues. Because electronic tracking devices suffer from several constraints, mainly logistical and financial, there is emerging interest in finding appropriate intrinsic markers, such as the chemical composition of inert tissues, to study long-distance migrations and identify wintering sites. Here, using tracked pelagic seabirds and some of their own feathers which were known to be grown at different places and times within the annual cycle, we proved the value of biogeochemical analyses of inert tissue as tracers of marine movements and habitat use. Analyses of feathers grown in summer showed that both stable isotope signatures and element concentrations can signal the origin of breeding birds feeding in distinct water masses. However, only stable isotopes signalled water masses used during winter because elements mainly accumulated during the long breeding period are incorporated into feathers grown in both summer and winter. Our findings shed new light on the simple and effective assignment of marine organisms to distinct oceanic areas, providing new opportunities to study unknown migration patterns of secretive species, including in relation to human-induced mortality on specific populations in the marine environment.

  12. Influence of electric field on cellular migration

    NASA Astrophysics Data System (ADS)

    Guido, Isabella; Bodenschatz, Eberhard

    Cells have the ability to detect continuous current electric fields (EFs) and respond to them with a directed migratory movement. Dictyostelium discoideum (D.d.) cells, a key model organism for the study of eukaryotic chemotaxis, orient and migrate toward the cathode under the influence of an EF. The underlying sensing mechanism and whether it is shared by the chemotactic response pathway remains unknown. Whereas genes and proteins that mediate the electric sensing as well as that define the migration direction have been previously investigated in D.d. cells, a deeper knowledge about the cellular kinematic effects caused by the EF is still lacking. Here we show that besides triggering a directional bias the electric field influences the cellular kinematics by accelerating the movement of cells along their path. We found that the migratory velocity of the cells in an EF increases linearly with the exposure time. Through the analysis of the PI3K and Phg2 distribution in the cytosol and of the cellular adherence to the substrate we aim at elucidating whereas this speed up effect in the electric field is due to either a molecular signalling or the interaction with the substrate. This work is part of the MaxSynBio Consortium which is jointly funded by the Federal Ministry of Education and Research of Germany and the Max Planck Society.

  13. Caesium-137 migration in Hungarian soils.

    PubMed

    Szerbin, P; Koblinger-Bokori, E; Koblinger, L; Végvári, I; Ugron, A

    1999-03-01

    Distribution of 137Cs activity concentration has been measured in soils from 19 Hungarian counties. The levels of soil contamination in Hungary after the Chernobyl fallout are sufficient to study the vertical distribution of the 137Cs under natural conditions. Samples were taken layer by layer on plain, grassy and uncultivated fields down to a depth of 20 cm. The results show that radiocaesium migrates very slowly in the soils investigated. The 137Cs concentration peaks in almost all of the soils remain in the top 5 cm layer, but the distribution patterns are different. Variations in diffusion, sorption-desorption, and complexing processes, plant uptake and plant- and animal-originated mechanical changes result in the formation of site-specific radionuclide distribution profiles. On the basis of the experimental data a model has been developed for the long-term prediction of the 137Cs migration. By application of an applied diffusion-convection model the results can be well fitted, the initial deposition can be calculated and the data can be used for the long-term prediction of the 137Cs distribution profile.

  14. Type II Migration and Giant Planet Survival

    NASA Technical Reports Server (NTRS)

    Ward, William R.

    2003-01-01

    Type II migration, in which a newly formed large planet opens a gap in its precursor circumstellar nebula and subsequently evolves with it, has been implicated as a delivery mechanism responsible for close stellar companions. Large scale migration is possible in a viscously spreading disk of surface density sigma (r,t) when most of it is sacrificed to the primary in order to promote a small portion of the disk to much higher angular momentum orbits. Embedded planets generally follow its evolution unless their own angular momentum is comparable to that of the disk. The fraction of the starting disk mass, M (sub d) = 2pi integral rsigma(r,0)dr, that is consumed by the star depends on the distance at which material escapes the disk's outer boundary. If the disk is allowed to expand indefinitely, virtually all of the disk will fall into the primary in order to send a vanishingly small portion to infinity. For such a case, it is difficult to explain the survival of any giant planets, including Jupiter and Saturn. Realistically, however, there are processes that could truncate a disk at a finite distance, r(sub d). Recent numerical modeling has illustrated that planets can survive in this case. We show here that much of these results can be understood by simple conservation arguments.

  15. Cell migration during heart regeneration in zebrafish.

    PubMed

    Tahara, Naoyuki; Brush, Michael; Kawakami, Yasuhiko

    2016-07-01

    Zebrafish possess the remarkable ability to regenerate injured hearts as adults, which contrasts the very limited ability in mammals. Although very limited, mammalian hearts do in fact have measurable levels of cardiomyocyte regeneration. Therefore, elucidating mechanisms of zebrafish heart regeneration would provide information of naturally occurring regeneration to potentially apply to mammalian studies, in addition to addressing this biologically interesting phenomenon in itself. Studies over the past 13 years have identified processes and mechanisms of heart regeneration in zebrafish. After heart injury, pre-existing cardiomyocytes dedifferentiate, enter the cell cycle, and repair the injured myocardium. This process requires interaction with epicardial cells, endocardial cells, and vascular endothelial cells. Epicardial cells envelope the heart, while endocardial cells make up the inner lining of the heart. They provide paracrine signals to cardiomyocytes to regenerate the injured myocardium, which is vascularized during heart regeneration. In addition, accumulating results suggest that local migration of these major cardiac cell types have roles in heart regeneration. In this review, we summarize the characteristics of various heart injury methods used in the research community and regeneration of the major cardiac cell types. Then, we discuss local migration of these cardiac cell types and immune cells during heart regeneration. Developmental Dynamics 245:774-787, 2016. © 2016 Wiley Periodicals, Inc. PMID:27085002

  16. Modeling of migrating grains on asteroid's surface

    NASA Astrophysics Data System (ADS)

    Yu, Yang; Baoyin, Hexi

    2015-01-01

    We present a numerical method based on the polyhedral data of asteroid shape for simulation of individual grain's dynamics around the asteroid surface, with application to migration of regolith material on specific asteroid. Surface gravitational attraction and potential are computed using polyhedral method with a correction on possible singularities; asteroid surface is approximated with continuous quartic Bézier patches based on the division of polyhedral mesh, which provides sufficient geometrical information for the simulation. Orbital motion and surface motion are processed separately by checking if the particle touches or leaves the surface. Collisions are treated as instantaneous point-contact events with the local quartic curved surface. The subpoint is recorded throughout the process to track the ID of the particle. We provide full description of this method including very detailed treatments in numeric. Several basic tests are conducted to examine the performance of this method, and the potential application of this method is also discussed. The test results of seismic regolith migration on crater walls show consistent conclusions with former investigation.

  17. Globalization of leptospirosis through travel and migration.

    PubMed

    Bandara, Medhani; Ananda, Mahesha; Wickramage, Kolitha; Berger, Elisabeth; Agampodi, Suneth

    2014-08-12

    Leptospirosis remains the most widespread zoonotic disease in the world, commonly found in tropical or temperate climates. While previous studies have offered insight into intra-national and intra-regional transmission, few have analyzed transmission across international borders. Our review aimed at examining the impact of human travel and migration on the re-emergence of Leptospirosis. Results suggest that alongside regional environmental and occupational exposure, international travel now constitute a major independent risk factor for disease acquisition. Contribution of travel associated leptospirosis to total caseload is as high as 41.7% in some countries. In countries where longitudinal data is available, a clear increase of proportion of travel-associated leptospirosis over the time is noted. Reporting patterns is clearly showing a gross underestimation of this disease due to lack of diagnostic facilities. The rise in global travel and eco-tourism has led to dramatic changes in the epidemiology of Leptospirosis. We explore the obstacles to prevention, screening and diagnosis of Leptopirosis in health systems of endemic countries and of the returning migrant or traveler. We highlight the need for developing guidelines and preventive strategies of Leptospirosis related to travel and migration, including enhancing awareness of the disease among health professionals in high-income countries.

  18. Philopatry and migration of Pacific white sharks

    PubMed Central

    Jorgensen, Salvador J.; Reeb, Carol A.; Chapple, Taylor K.; Anderson, Scot; Perle, Christopher; Van Sommeran, Sean R.; Fritz-Cope, Callaghan; Brown, Adam C.; Klimley, A. Peter; Block, Barbara A.

    2010-01-01

    Advances in electronic tagging and genetic research are making it possible to discern population structure for pelagic marine predators once thought to be panmictic. However, reconciling migration patterns and gene flow to define the resolution of discrete population management units remains a major challenge, and a vital conservation priority for threatened species such as oceanic sharks. Many such species have been flagged for international protection, yet effective population assessments and management actions are hindered by lack of knowledge about the geographical extent and size of distinct populations. Combining satellite tagging, passive acoustic monitoring and genetics, we reveal how eastern Pacific white sharks (Carcharodon carcharias) adhere to a highly predictable migratory cycle. Individuals persistently return to the same network of coastal hotspots following distant oceanic migrations and comprise a population genetically distinct from previously identified phylogenetic clades. We hypothesize that this strong homing behaviour has maintained the separation of a northeastern Pacific population following a historical introduction from Australia/New Zealand migrants during the Late Pleistocene. Concordance between contemporary movement and genetic divergence based on mitochondrial DNA demonstrates a demographically independent management unit not previously recognized. This population's fidelity to discrete and predictable locations offers clear population assessment, monitoring and management options. PMID:19889703

  19. Globalization of leptospirosis through travel and migration

    PubMed Central

    2014-01-01

    Leptospirosis remains the most widespread zoonotic disease in the world, commonly found in tropical or temperate climates. While previous studies have offered insight into intra-national and intra-regional transmission, few have analyzed transmission across international borders. Our review aimed at examining the impact of human travel and migration on the re-emergence of Leptospirosis. Results suggest that alongside regional environmental and occupational exposure, international travel now constitute a major independent risk factor for disease acquisition. Contribution of travel associated leptospirosis to total caseload is as high as 41.7% in some countries. In countries where longitudinal data is available, a clear increase of proportion of travel-associated leptospirosis over the time is noted. Reporting patterns is clearly showing a gross underestimation of this disease due to lack of diagnostic facilities. The rise in global travel and eco-tourism has led to dramatic changes in the epidemiology of Leptospirosis. We explore the obstacles to prevention, screening and diagnosis of Leptopirosis in health systems of endemic countries and of the returning migrant or traveler. We highlight the need for developing guidelines and preventive strategies of Leptospirosis related to travel and migration, including enhancing awareness of the disease among health professionals in high-income countries. PMID:25112368

  20. Capturing migration phenology of terrestrial wildlife using camera traps

    USGS Publications Warehouse

    Tape, Ken D.; Gustine, David D.

    2014-01-01

    Remote photography, using camera traps, can be an effective and noninvasive tool for capturing the migration phenology of terrestrial wildlife. We deployed 14 digital cameras along a 104-kilometer longitudinal transect to record the spring migrations of caribou (Rangifer tarandus) and ptarmigan (Lagopus spp.) in the Alaskan Arctic. The cameras recorded images at 15-minute intervals, producing approximately 40,000 images, including 6685 caribou observations and 5329 ptarmigan observations. The northward caribou migration was evident because the median caribou observation (i.e., herd median) occurred later with increasing latitude; average caribou migration speed also increased with latitude (r2 = .91). Except at the northernmost latitude, a northward ptarmigan migration was similarly evident (r2 = .93). Future applications of this method could be used to examine the conditions proximate to animal movement, such as habitat or snow cover, that may influence migration phenology.

  1. Energetic and biomechanical constraints on animal migration distance.

    PubMed

    Hein, Andrew M; Hou, Chen; Gillooly, James F

    2012-02-01

    Animal migration is one of the great wonders of nature, but the factors that determine how far migrants travel remain poorly understood. We present a new quantitative model of animal migration and use it to describe the maximum migration distance of walking, swimming and flying migrants. The model combines biomechanics and metabolic scaling to show how maximum migration distance is constrained by body size for each mode of travel. The model also indicates that the number of body lengths travelled by walking and swimming migrants should be approximately invariant of body size. Data from over 200 species of migratory birds, mammals, fish, and invertebrates support the central conclusion of the model - that body size drives variation in maximum migration distance among species through its effects on metabolism and the cost of locomotion. The model provides a new tool to enhance general understanding of the ecology and evolution of migration. PMID:22093885

  2. Oligodendrocyte precursors migrate along vasculature in the developing nervous system.

    PubMed

    Tsai, Hui-Hsin; Niu, Jianqin; Munji, Roeben; Davalos, Dimitrios; Chang, Junlei; Zhang, Haijing; Tien, An-Chi; Kuo, Calvin J; Chan, Jonah R; Daneman, Richard; Fancy, Stephen P J

    2016-01-22

    Oligodendrocytes myelinate axons in the central nervous system and develop from oligodendrocyte precursor cells (OPCs) that must first migrate extensively during brain and spinal cord development. We show that OPCs require the vasculature as a physical substrate for migration. We observed that OPCs of the embryonic mouse brain and spinal cord, as well as the human cortex, emerge from progenitor domains and associate with the abluminal endothelial surface of nearby blood vessels. Migrating OPCs crawl along and jump between vessels. OPC migration in vivo was disrupted in mice with defective vascular architecture but was normal in mice lacking pericytes. Thus, physical interactions with the vascular endothelium are required for OPC migration. We identify Wnt-Cxcr4 (chemokine receptor 4) signaling in regulation of OPC-endothelial interactions and propose that this signaling coordinates OPC migration with differentiation. PMID:26798014

  3. Migration of nurses in Australia: where and why?

    PubMed

    Ohr, Se Ok; Parker, Vicki; Jeong, Sarah; Joyce, Terry

    2010-01-01

    The Australian health care workforce has benefited from an increasing migration of nurses over the past decades. The nursing profession is the largest single health profession, making up over half of the Australian health care workforce. Migration ofnurses into the Australian nursing workforce impacts significantly on the size ofthe workforce and the capacity to provide health care to the Australian multicultural community. Migration of nurses plays an important role in providing a solution to the ongoing challenges of workforce attraction and retention, hence an understanding of the factors contributing to nurse migration is important. This paper will critically analyse factors reported to impact on migration of nurses to Australia, in particular in relation to: (1) globalisation; (2) Australian society and nursing workforce; and (3) personal reasons. The current and potential implications of nurse migration are not limited to the Australian health care workforce, but also extend to political, socioeconomic and other aspects in Australia. PMID:21133293

  4. [Migration: A neglected dimension of inequalities in health?].

    PubMed

    Razum, Oliver; Karrasch, Laura; Spallek, Jacob

    2016-02-01

    Over the past 70 years, several million people have immigrated into Germany-from different countries of origin and for different reasons. The categories used by society to label immigrants ("guest workers", "persons with a migration background") have changed over time. This change has occurred in parallel with changes in the societal attitude towards immigrants and in their legal position. There is unequivocal evidence that the forms that migration takes, in addition to the societal responses towards immigrants, have an effect on their health. The spectrum of migration to Germany is likely to remain fluent because of the continuing process of globalization; also, societal responses to migration will change over time. Thus, migration will continue to pose challenges to society and to health. Only through continuous attentiveness will it be possible to identify, and then avoid or reduce, health disadvantages faced by persons with a migration background.

  5. Interprovincial migration and suicide in Canada, 1971-78.

    PubMed

    Trovato, F

    1986-01-01

    This study corroborates the findings by Stack (1980) on the relationship between interstate migration and suicide. The present application is to Canada during the early and later parts of the 1970s decade. Strong support for a migration effect emerges, thus supporting the culture shock hypothesis that because migration involves the concomitant processes of severing important social ties with the origin, and adjusting to a new environment, Provinces characterized by high rates of migration will experience high rates of suicide. It is found that while a province's percentage of the population who have received university education is negatively related to suicide, the main effect of migration acts to raise the odds of suicide, but this effect is lower in magnitude than the education measure. A one percent gain in the education index would have served to lower the suicide rate by 1.3%, while a similar change in migration would increase the rate of suicide by .67%.

  6. Migration costs drive convergence of threshold traits for migratory tactics.

    PubMed

    Sahashi, Genki; Morita, Kentaro

    2013-12-22

    Partial migration of some, but not all, members of a population is a common form of migration. We evaluated how migration costs influence which members migrate in 10 populations of two salmonid species. The migratory patterns of both species were evaluated based on the size at maturity for resident males, which is the threshold trait that determines the migratory tactics used within a population. In both species, this size was smaller in males located further from the sea, where migration costs are presumably higher. Moreover, the threshold sizes at maturity in males were correlated between both species. Our results suggest that migration costs are a significant convergent selective force on migratory tactics and life-history traits in nature.

  7. Energetic and biomechanical constraints on animal migration distance.

    PubMed

    Hein, Andrew M; Hou, Chen; Gillooly, James F

    2012-02-01

    Animal migration is one of the great wonders of nature, but the factors that determine how far migrants travel remain poorly understood. We present a new quantitative model of animal migration and use it to describe the maximum migration distance of walking, swimming and flying migrants. The model combines biomechanics and metabolic scaling to show how maximum migration distance is constrained by body size for each mode of travel. The model also indicates that the number of body lengths travelled by walking and swimming migrants should be approximately invariant of body size. Data from over 200 species of migratory birds, mammals, fish, and invertebrates support the central conclusion of the model - that body size drives variation in maximum migration distance among species through its effects on metabolism and the cost of locomotion. The model provides a new tool to enhance general understanding of the ecology and evolution of migration.

  8. Snow goose migration phenology is related to extratropical storm climate

    NASA Astrophysics Data System (ADS)

    Smith, T. J.; Hayden, B. P.

    1984-09-01

    The phenologies of autumn and spring migrations by greater snow geese ( Anser caerulescens atlantica) are shown to be statistically independent. Spring and fall migration phenologies are demonstrated to be significantly related to synoptic scale atmospheric circulation systems (extratropical storms) rather than a factor such as temperature. Interannual variation in the timing of migratory movements by snow geese reflect interannual variation in the climatology of extratropical storms. Early fall migration is significantly related to an increased frequency of cyclonic disturbances off the United States east and gulf coasts. Years in which autumn migration is delayed occur when the Atlantic coast storm track is displaced northward. Late spring migrations are related to extratropical storms being more frequent over the Great Plains, along the gulf coast, and over the northern Gulf of Mexico. Increased cyclone activity through the Ohio River valley and over the Great Lakes tends to advance the onset of spring migrations.

  9. Migrating Oligodendrocyte Progenitor Cells Swell Prior to Soma Dislocation

    PubMed Central

    Happel, Patrick; Möller, Kerstin; Schwering, Nina K.; Dietzel, Irmgard D.

    2013-01-01

    The migration of oligodendrocyte progenitor cells (OPCs) to the white matter is an indispensable requirement for an intact brain function. The mechanism of cell migration in general is not yet completely understood. Nevertheless, evidence is accumulating that besides the coordinated rearrangement of the cytoskeleton, a finetuned interplay of ion and water fluxes across the cell membrane is essential for cell migration. One part of a general hypothesis is that a local volume increase towards the direction of movement triggers a mechano-activated calcium influx that regulates various procedures at the rear end of a migrating cell. Here, we investigated cell volume changes of migrating OPCs using scanning ion conductance microscopy. We found that during accelerated migration OPCs undergo an increase in the frontal cell body volume. These findings are supplemented with time lapse calcium imaging data that hint an increase in calcium content the frontal part of the cell soma. PMID:23657670

  10. The two cultures of health worker migration: a Pacific perspective.

    PubMed

    Connell, John

    2014-09-01

    Migration of health workers from relatively poor countries has been sustained for more than half a century. The rationale for migration has been linked to numerous factors relating to the economies and health systems of source and destination countries. The contemporary migration of health workers is also embedded in a longstanding and intensifying culture of migration, centred on the livelihoods of extended households, and a medical culture that is oriented to superior technology and advanced skills. This dual culture is particularly evident in small island states in the Pacific, but is apparent in other significant migrant source countries in the Caribbean, Sub-Saharan Africa and Asia. Family expectations of the benefits of migration indicate that regulating the migration and attrition of health workers necessitates more complex policies beyond those evident within health care systems alone.

  11. Migration of nurses in Australia: where and why?

    PubMed

    Ohr, Se Ok; Parker, Vicki; Jeong, Sarah; Joyce, Terry

    2010-01-01

    The Australian health care workforce has benefited from an increasing migration of nurses over the past decades. The nursing profession is the largest single health profession, making up over half of the Australian health care workforce. Migration ofnurses into the Australian nursing workforce impacts significantly on the size ofthe workforce and the capacity to provide health care to the Australian multicultural community. Migration of nurses plays an important role in providing a solution to the ongoing challenges of workforce attraction and retention, hence an understanding of the factors contributing to nurse migration is important. This paper will critically analyse factors reported to impact on migration of nurses to Australia, in particular in relation to: (1) globalisation; (2) Australian society and nursing workforce; and (3) personal reasons. The current and potential implications of nurse migration are not limited to the Australian health care workforce, but also extend to political, socioeconomic and other aspects in Australia.

  12. Oligodendrocyte precursors migrate along vasculature in the developing nervous system.

    PubMed

    Tsai, Hui-Hsin; Niu, Jianqin; Munji, Roeben; Davalos, Dimitrios; Chang, Junlei; Zhang, Haijing; Tien, An-Chi; Kuo, Calvin J; Chan, Jonah R; Daneman, Richard; Fancy, Stephen P J

    2016-01-22

    Oligodendrocytes myelinate axons in the central nervous system and develop from oligodendrocyte precursor cells (OPCs) that must first migrate extensively during brain and spinal cord development. We show that OPCs require the vasculature as a physical substrate for migration. We observed that OPCs of the embryonic mouse brain and spinal cord, as well as the human cortex, emerge from progenitor domains and associate with the abluminal endothelial surface of nearby blood vessels. Migrating OPCs crawl along and jump between vessels. OPC migration in vivo was disrupted in mice with defective vascular architecture but was normal in mice lacking pericytes. Thus, physical interactions with the vascular endothelium are required for OPC migration. We identify Wnt-Cxcr4 (chemokine receptor 4) signaling in regulation of OPC-endothelial interactions and propose that this signaling coordinates OPC migration with differentiation.

  13. [Inter-Arab migration and development].

    PubMed

    Fergany, N

    1985-01-01

    This paper argues that interArab migration has weakened the potential for development in the region due to the specific characteristics of the migration and its extremely high level in the past decade. Data on migratory streams is inadequate concerning the volume of migrants, their characteristics, and their impact on socioeconomic structures in the Arab region. In the 1970s, the Arab region was increasingly polarized into oil exporting countries experiencing a massive increase in revenues and nonexporters which have become increasingly impoverished. A World Bank team estimated that, assuming rapid growth, the number of migrant workers in the principal oil-exporting countries would double between 1975-85 from 1.6 to 3.5 million, while the proportion Arab would decline from 65 to 55%. The total foreign population was expected to increase from 3 million in 1975 to 10 million in 1985, representing an increase from 25 to 40% of the total population of those receiving countries. The impact of emigration on the countries of origin was greater than the mere numbers of migrants would suggest, because most migrants tended to be working age men from the most dynamic population sectors, because of the large volume of nonmigrants dependent on the migrants' incomes, because of the large number of persons directly and indirectly involved in migration over time as a consequence of the constant turnover, and because of the macroeconomic effects of massive migration on the local economies. Mechanisms of selection in the countries of employment coupled with the rigidity of educational systems in the countries of origin result in shortages of qualified and sometimes even of unskilled labor in the countries of origin, leading to reduced productivity. Remissions are often viewed as beneficial for the country of origin, but in fact they encourage consumption of imported goods while entire sectors of the domestic economy stagnate or deteriorate. Remissions depend on economic activity of

  14. Scattering and; Delay, Scale, and Sum Migration

    SciTech Connect

    Lehman, S K

    2011-07-06

    How do we see? What is the mechanism? Consider standing in an open field on a clear sunny day. In the field are a yellow dog and a blue ball. From a wave-based remote sensing point of view the sun is a source of radiation. It is a broadband electromagnetic source which, for the purposes of this introduction, only the visible spectrum is considered (approximately 390 to 750 nanometers or 400 to 769 TeraHertz). The source emits an incident field into the known background environment which, for this example, is free space. The incident field propagates until it strikes an object or target, either the yellow dog or the blue ball. The interaction of the incident field with an object results in a scattered field. The scattered field arises from a mis-match between the background refractive index, considered to be unity, and the scattering object refractive index ('yellow' for the case of the dog, and 'blue' for the ball). This is also known as an impedance mis-match. The scattering objects are referred to as secondary sources of radiation, that radiation being the scattered field which propagates until it is measured by the two receivers known as 'eyes'. The eyes focus the measured scattered field to form images which are processed by the 'wetware' of the brain for detection, identification, and localization. When time series representations of the measured scattered field are available, the image forming focusing process can be mathematically modeled by delayed, scaled, and summed migration. This concept of optical propagation, scattering, and focusing have one-to-one equivalents in the acoustic realm. This document is intended to present the basic concepts of scalar scattering and migration used in wide band wave-based remote sensing and imaging. The terms beamforming and (delayed, scaled, and summed) migration are used interchangeably but are to be distinguished from the narrow band (frequency domain) beamforming to determine the direction of arrival of a signal, and

  15. Diel Migrations of Microorganisms within a Benthic, Hypersaline Mat Community

    PubMed Central

    Garcia-Pichel, Ferran; Mechling, Margaret; Castenholz, Richard W.

    1994-01-01

    We studied the diel migrations of several species of microorganisms in a hypersaline, layered microbial mat. The migrations were quantified by repeated coring of the mat with glass capillary tubes. The resulting minicores were microscopically analyzed by using bright-field and epifluorescence (visible and infrared) microscopy to determine depths of coherent layers and were later dissected to determine direct microscopic counts of microorganisms. Microelectrode measurements of oxygen concentration, fiber optic microprobe measurements of light penetration within the mat, and incident irradiance measurements accompanied the minicore sampling. In addition, pigment content, photosynthesis and irradiance responses, the capacity for anoxygenic photosynthesis, and gliding speeds were determined for the migrating cyanobacteria. Heavily pigmented Oscillatoria sp. and Spirulina cf. subsalsa migrated downward into the mat during the early morning and remained deep until dusk, when upward migration occurred. The mean depth of the migration (not more than 0.4 to 0.5 mm) was directly correlated with the incident irradiance over the mat surface. We estimated that light intensity at the upper boundary of the migrating cyanobacteria was attenuated to such an extent that photoinhibition was effectively avoided but that intensities which saturated photosynthesis were maintained through most of the daylight hours. Light was a cue of paramount importance in triggering and modulating the migration of the cyanobacteria, even though the migrating phenomenon could not be explained solely in terms of a light response. We failed to detect diel migration patterns for other cyanobacterial species and filamentous anoxyphotobacteria. The sulfide-oxidizing bacterium Beggiatoa sp. migrated as a band that followed low oxygen concentrations within the mat during daylight hours. During the nighttime, part of this population migrated toward the mat surface, but a significant proportion remained deep

  16. [Export agriculture, class formation, and migration in the Dominican Republic].

    PubMed

    Bray, D

    1985-01-01

    The relationships among export agriculture, class formation, and migration in the Dominican Republic are analyzed. The author discusses the impact of successive strategies of economic development on internal migration and on international migration, primarily to the United States. The transition from subsistence agriculture to export agriculture and the consequent differentiation of classes are examined. Implications for economic development in the Dominican Republic and for U.S. labor policy are considered.

  17. A dynamic analysis of net migration and state employment change.

    PubMed

    Gruidl, J S; Pulver, G C

    1991-01-01

    "The dynamic relationship of net migration and employment change is examined for ten selected states of the U.S. using a multivariate time series approach--a vector autoregression (VAR) model. Granger causality tests and dynamic multipliers provide information on the dynamic process. The results suggest a state-level process in which employment change occurs first, and net migration follows with a lag. The procedure appears promising in investigating the timing of net migration and regional employment change."

  18. [The sociology of migration in Greece since 1960].

    PubMed

    Moussourou, L M

    1984-01-01

    The sociological literature concerning international migration from Greece since 1960 is reviewed. The author suggests that a Marxist approach to the analysis of European migration is likely to be more useful than a country-oriented study: using this approach, migration can be analyzed in the context of the relationship between industrialized countries in the center receiving migrants and nonindustrialized countries on the periphery that send migrants. (SUMMARY IN ENG) PMID:12267759

  19. Cerebellar granule cell migration and the effects of alcohol.

    PubMed

    Jiang, Yulan; Kumada, Tatsuro; Cameron, D Bryant; Komuro, Hitoshi

    2008-01-01

    In the developing brain the majority of neurons migrate from their birthplace to their final destination. This active movement is essential for the formation of cortical layers and nuclei. The impairment of migration does not affect the viability of neurons but often results in abnormal differentiation. The proper migration of neurons requires the orchestrated activities of multiple cellular and molecular events, such as pathway selection, the activation of specific receptors and channels, and the assembly and disassembly of cytoskeletal components. The migration of neurons is very vulnerable to exposure to environmental toxins, such as alcohol. In this article, we will focus on recent developments in the migration of cerebellar granule cells. First, we will describe when, where and how granule cells migrate through different cortical layers to reach their final destination. Second, we will present how internal programs control the sequential changes in granule cell migration. Third, we will review the roles of external guidance cues and transmembrane signals in granule cell migration. Finally, we will reveal mechanisms by which alcohol exposure impairs granule cell migration. PMID:18075250

  20. Texture sensing of cytoskeletal dynamics in cell migration

    NASA Astrophysics Data System (ADS)

    Das, Satarupa; Lee, Rachel; Hourwitz, Matthew J.; Sun, Xiaoyu; Parent, Carole; Fourkas, John T.; Losert, Wolfgang

    Migrating cells can be directed towards a target by gradients in properties such as chemical concentration or mechanical properties of the surrounding microenvironment. In previous studies we have shown that micro/nanotopographical features on scales comparable to those of natural collagen fibers can guide fast migrating amoeboid cells by aligning actin polymerization waves to such nanostructures. We find that actin microfilaments and microtubules are aligned along the nanoridge topographies, modulating overall cell polarity and directional migration in epithelial cells. This work shows that topographic features on a biologically relevant length scale can modulate migration outcomes by affecting the texture sensing property of the cytoskeleton.