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PubMed1988

African migration decision-making process.

Factors affecting the decision to migrate in Africa are reviewed. The author concludes that most migration studies have focused on the individual migrant, whereas migration decision-making in Africa is affected primarily by "the social institutions at local and household levels. Patterns of migration are influenced by the economic and social trends which developed especially since the colonial era." The importance of extended family relationships, agrarian change, forced migration, and restrictive migration policies indicate a need to take a macrolevel approach to the study of African migration.

Africa↗
PubMed1990

Population structure analysis using polygenic traits: estimation of migration matrices.

Many studies of subdivided populations have attempted to determine the underlying migration rates that generate observed patterns of genetic differentiation. Most previous analyses have yielded only qualitative inferences about migration. In this paper I present a new method for estimating the full migration matrix from information on polygenic trait variation. The method employs multivariate quantitative genetic theory to provide a matrix formulation of the expected covariance structure in multigenerational subdivided populations for which information is available at different points in the life cycle. I develop a restricted maximum likelihood technique (REML) to take account of this additional life-cycle information and to estimate both the migration matrix and the ratio of effective population size to census size. To make the problem computationally tractable, the migration matrix is modeled as a log-linear function of a few covariates, such as subdivision size and geographic distance. I apply the technique to data on dermatoglyphic ridge counts for 1015 individuals of the Jirel population of east Nepal, considering two different age cohorts. In the adult cohort (individuals over 21 years of age) I examine data by both birthplace and residence and for the subadult cohort (under 21 years of age), by birthplace. Results from the REML technique reveal that the best-fitting migration model is a finite island model with an estimated endemicity of 0.730 +/- 0.105 and an estimated ratio of effective size to census size of 0.287 +/- 0.095. Both estimates are reasonable given known demographic data. In addition, Fst values predicted by the migration model are concordant with REML estimates obtained directly from the dermatoglyphic variation.

Adolescent↗
PubMed1978

[Use of 51Cr-labelled macrophages for the objective evaluation of macrophage migration inhibition].

A possibility of using 51Cr-labeld macrophages migrating from the capillaries and lysed with sodium dodecyl sulfate for objective and quantitative assessment of the results of macrophage migration inhibition (MMI) microassay was demonstrated on the basis of correlation analysis of the experimental data. Migration area and sensitivity of 51Cr-labeled macrophages to the action of the factor of migration inhibition were found not to differ from those of unlabeled macrophages. In the assessment of the absolute macrophage migration values and its reduction under the action of the factor of migration inhibition formed in the H-2 system, and also of the specificity of this reduction there was revealed a high correlation between the migration area and the value of the migrant cell label.

Animals↗
PubMed1993

International labour migration in the Asian-Pacific region: patterns, policies and economic implications.

"This paper reviews the literature on international labour migration from and within the Asian-Pacific region. It deals with patterns and characteristics of migration flows, government policies towards labour migration, and economic implications of labour migration for both labour-exporting and importing countries in the region. The indications are that, despite gradual slowing down of labour flows to the western industrial countries and the Middle East, labour migration will continue to be a major economic influence on surplus-labour countries in the region. As an integral part of the growth dynamism in the region, labour migration has now begun to take on a regional dimension, with immense implications for the process of industrial restructuring in high growth economies and the changing pattern of economic interdependence among countries."

Asia↗
PubMed1995

Theories of international labor migration: an overview.

"Emigration pressures are primarily the result of increasing inequalities between countries which, in turn, are the result of factors internal to less developed countries and their relations with developed countries. Both micro (neoclassical) and macrostructural theories of migration are reviewed. It is argued that the neoclassical theory of migration is often unjustly criticized and is sufficiently robust to incorporate those structural considerations which are at the core of macrostructural theories. Moreover, the neoclassical theory, with slight modification, can incorporate the ¿new economics of migration.' The major empirical problem confronting models of international labor migration is that migration flows are constrained by immigration policy. This policy, in turn, is influenced by various special interest groups. The direction and form of migration flows is conditioned by contemporary and historical relationships between source and destination countries."

Demography↗
PubMed1995

Regional interdependence and migration in Asia.

"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."

Asia↗
PubMed1996

A comparative study of Caribbean return migration from Britain and France: towards a context-dependent explanation.

"The currently dominant element in the labour migration from the Caribbean to Britain and France is a return flow of migrants. This paper focuses on the migrations from the Commonwealth and the French Caribbean to Britain and France respectively. While these migrations are historically similar in origin, subsequent differences in the colonial and immigration policies of Britain and France have resulted in divergent migration trends and experiences. New sources of data are drawn on in this comparative study of return migration to the Caribbean, providing up-to-date information on the size and demographic characteristics of the returnee populations. Equally important to this study is the section of the migrant population who are likely to remain in Europe. The authors argue that a comprehensive model of labour migration would need to incorporate the non-return situation in its dynamic entirety."

Americas↗
PubMed1990

Migration in a small semiperiphery: the movement of Puerto Ricans and Dominicans.

"This article argues that the semiperipheral development of Puerto Rico since around 1975 has led to the creation of a relative labor surplus in the formal sectors of the economy while at the same time increasing the demand for cheap labor in the informal service sector. Thus, Puerto Ricans leave their country in search of good jobs in the United States while Dominicans migrate to Puerto Rico and find work in the informal sector. The return migration of Puerto Ricans has also been significant, but is due to their strong national culture, rather than economic reasons. The article concludes that migration to and from Puerto Rico is of a semiperipheral type because it combines characteristics of migration previously described as 'migration from the periphery to the center' and 'migration within the periphery.' A precise definition of the semiperipheral characteristics of Puerto Rico is given."

Americas↗
PubMed1982

The structural correlates of metropolitan migration: 1970-1975.

This study is concerned with the debate over the supremacy of organizational versus environmental models for explaining population change within the context of metropolitan-nonmetropolitan turnaround migration. A sample of U.S. metropolitan areas is classified by a migration typology that considers sign changes or consistencies in rates of net migration between the 1960s and 1970s. "Four categories result and organizational, environmental and technological data are analyzed utilizing ridge regression with interaction terms to ascertain whether structural differences among migration categories exist." The study shows that organizational factors are more relevant for urban areas experiencing in-migration, and environmental factors are more relevant for those experiencing out-migration.

Americas↗
PubMed1996

Stimulation of glioma-cell migration by laminin and inhibition by anti-alpha3 and anti-beta1 integrin antibodies.

An induction of laminin in the confrontation zone between tumor cells and normal brain tissue has been observed in our model systems in vivo and in vitro. In order to study the effects of ECM components on glioma-cell migration and invasion, we have used 2 lacZ-transfected glioma cell lines, AN1/lacZ and U-251 /lacZ. Cell migration from multicellular spheroids was studied using different types of media: DMEM with 10% serum, Ultra Culture medium, and filtrated DMEM with serum in which the protein fraction > 100 kDa had been removed by ultrafiltration. Laminin, fibronectin and collagen type-IV were individually added to the different media, and cell migration from the spheroids was studied. The results show that cell migration in both cell lines, was stimulated by laminin and fibronectin. Collagen type-IV stimulated only cell migration of U-251/lacZ cells. Scanning electron microscopy revealed an extensive change in cell shape as a result of laminin stimulation. Flowcytometric studies showed that both AN1/lacZ and U-251/lacZ strongly express the alpha3 beta1 integrin receptor, which can bind to several ECM components (laminin, fibronectin, collagen). Immunofluorescence microscopy demonstrated that the same integrin sub-units were expressed in multicellular spheroids. When monoclonal antibodies to alpha3 and beta1 were added to the laminin-stimulated cultures, cell migration was significantly reduced. This indicates that the alpha3 beta1 integrin receptor plays an important role during glioma-cell migration.

Antigens, CD↗
PubMed2002

The effect of migration during the divergence.

The mean and variance of the number of nucleotide differences were obtained when the ancestral population diverged with migration. The number of nucleotide differences obtained indicates that not only the migration rate but also the period of migration has influence on a population structure. According to the migration rate and the period of migration, populations behave approximately as a single unit, diverged and isolated populations, two populations under equilibrium, or none of them. When sigma m(t) is about one, the variance of the number of nucleotide differences becomes large, where sigma m(t) is the sum of the migration rate for the period of migration. The distribution of the estimated divergence time was also obtained using computer simulations. It was found that the divergence time can be explained by sigma m(t). That is, the divergence time is mostly estimated as the time when sigma m(t) is less than 1.

Animal Migration↗
PubMed1982

On the relation between origin income and migration.

"While traditional migration theory suggests that the rate of migration is negatively related to income at the origin, many empirical studies of aggregate migration yield a non-significant or even a positive relation. This paper utilizes a simplified model of migration to demonstrate that one possible reason for such results is the imperfect capital market facing migrants. Higher average income at the origin may imply a higher number of individuals who have the cash resources to finance migration, thus generating a positive relation between regional income and migration. The conclusions suggest the use of non-linear specifications in empirical migration studies."

Demography↗
PubMed1989

Regional adjustment and migration flows in Canada, 1971 to 1981.

"The primary purpose of this paper is to consider and test for various interlinkages between migration flows, and also between migration and employment change. Three types of migration flows are distinguished: domestic in-migration and out-migration, and net international migration. The three migration equations are embedded in a model of regional adjustment that also includes regional employment and wage changes as endogenous variables. The data base utilizes Canadian census statistics for 1971 and 1981 in a cross-section analysis with 183 regions represented by counties, or their equivalents. The empirical performance of the various interlinkages is broadly in line with expectations, but the results raise some important questions about interpretation."

Americas↗
PubMed2003

Transmural migration of gastrostomy tube retention discs.

BACKGROUND: Accidental dislodgment is one of the most frequent causes of avoidable cost and consternation related to gastrostomy tubes. The Sacks-Vine gastrostomy tube, inserted in an antegrade fashion by a percutaneous technique, is extremely stable due to the construction of its disc retention device. However, transmural migration of the retention disc is a known severe delayed complication associated with this tube. OBJECTIVE: To review the presentation, diagnosis, and treatment of transmural migration of gastrostomy retention discs, to propose a mechanism for the progressive development of this complication, and to recommend a method for preventing its occurrence. MATERIALS AND METHODS: From January 1991 to October 1999, pediatric interventional radiologists at two children's hospitals performed 300 antegrade gastrostomy and gastrojejunostomy primary insertion procedures. A "push-pull" variation of the antegrade approach used for 44 of these insertions is excluded from further analysis. Of the remaining 256 procedures, 5 boys and 3 girls with a mean age of 5.1 years (range 0.8-19 years) were identified from review of the prospectively gathered procedural database with significant complications related to the disc retention component of their gastrostomy tubes. A retrospective analysis was conducted of their medical records, diagnostic imaging, and interventional and surgical findings. RESULTS: Transmural migration was diagnosed on average 36 months after insertion (16-48 months). The diagnosis was made incidentally during endoscopy (n=1) or fluoroscopy (n=5) in six asymptomatic patients, and during barium enema to explore feculent vomiting and halitosis in two symptomatic patients. Migration of the retention disc fell along a continuum from intramural (n=4) to transmural and intracolonic (n=4), with gastric mucosal erosion, extensive granulation and inflammation in all eight patients. Although there was no evidence of free air in any patient, a gastrocolic fistula was demonstrated in four patients and a gastrocolocutaneous fistula in two of four patients with complete transmural migration. Surgical resection of the disc, gastrostomy, and fistula repair if needed was successfully performed in all patients. CONCLUSIONS: Gastrostomy tubes with an internal retention disc are at risk for progressive disc migration into and through the gastric wall, resulting in irretrievable fixation and potential fistula formation. This severe delayed complication results from prolonged traction on the retention disc. Transmural migration may be avoided through improved tube care education, daily disc mobilization, and earlier disc retrieval.

Adolescent↗
PubMed2005

Meta-ecosystems and biological energy transport from ocean to coast: the ecological importance of herring migration.

Ecosystems are not closed, but receive resource subsidies from other ecosystems. Energy, material and organisms are moved between systems by physical vectors, but migrating animals also transport resources between systems. We report on large scale energy transport from ocean to coast by a migrating fish population, the Norwegian spring-spawning (NSS) herring Clupea harengus. We observe a rapid body mass increase during parts of the annual, oceanic feeding migration and we use a bioenergetics model to quantify energy consumption. The model predicts strong seasonal variation in food consumption with a marked peak in late May to July. The copepod Calanus finmarchicus is the most important prey and 23 x 10(6) tones (wet weight) of C. finmarchicus is consumed annually. The annual consumption-biomass ratio is 5.2. During the feeding migration 17% of consumed energy is converted to body mass. The biomass transported to the coast and left as reproductive output is estimated from gonad weight and is about 1.3 x 10(6) tones for the current population. This transport is to our knowledge the world's largest flux of energy caused by a single population. We demonstrate marked temporal variation in transport during the last century and discuss the effects of NSS herring in the ocean, as a major consumer, and at the coast, where eggs and larvae are important for coastal predators. In particular, we suggest that the rapid decline of lobster Homarus gammarus landings in Western Norway during the 1960s was related to the collapse of NSS herring. We also discuss spatial variation in energy transport caused by changed migration patterns. Both climate and fisheries probably triggered historical changes in the migration patterns of NSS herring. New migration routes emerge at the level of individuals, which in turn determines where resources are gathered and delivered, and therefore, how meta-ecosystems function.

Animal Migration↗
PubMed1993

Improved rapid photometric assay for quantitative measurement of PMN migration.

We developed an improved quantitative method to measure in vitro polymorphonuclear leukocyte (PMN) migration using an assembly consisting of a 96-well chamber, polycarbonate filter membrane, and a 96-well microtiter plate. The convenience in setup and counting of migrated cells using this method allows processing of 80 samples and 16 controls in a short assay time of only 2 h. The peroxidase contained in PMNs was used as a marker enzyme to determine the number of migrated cells. Peroxidase released from lysed migrated cells was detected with an enzymatic method utilizing o-dianisidine as substrate. Photometric measurement was performed with a conventional microtiter plate reader at a wavelength of 405 nm. Optical density readings obtained using the enzymatic assay correlated with the number of migrated cells in a linear fashion up to 1 x 10(5) cells/well. The sensitivity of the enzymatic assay was sufficient to determine cell counts as low as 500 PMNs. PMNs lost no measurable amounts of peroxidase during the migration assay when ZAS was used as the chemoattractant. A calibration method was developed to make corrections for variations in the peroxidase content of different cell preparations and changes in the peroxidase content of cells exposed to the chemoattractant. High speed, convenient handling, and the use of standard laboratory equipment result in low cost per assay and make this migration assay ideally suited to research and clinical applications.

Cell Migration Inhibition↗
PubMed1993

Leu-enkephalin modulates the migration inhibition of mouse splenocytes induced by cAMP-elevating agents.

The ability of Leu-enkephalin (LENK) to alter random migration of mouse spleen cells was tested in vitro and in vivo. Incubation of the cells with LENK (10(-14) M-10(-7) M) for 1 h at 37 degrees C suppressed the migration. The dose-response was irregular, showing two peaks in the physiological concentration range: 10(-10) M, and 10(-13)-10(-14) M. Intraperitoneal (i.p.) injection of LENK (7.5 mg/kg body wt) depressed the migratory capacity of the splenocytes harvested 2 and 24 h later. In contrast to the inhibitory effect of LENK on the migration of native cells, its effect on cells pretreated with the cAMP-elevating agents theophylline, 3-isobutyl-1-methyl-xanthine (IBMX) and forskolin was predominantly a stimulatory one. The addition of LENK resulted in attenuation or even full reversion of the migration-inhibition caused by those agents. Occasionally, potentiation of the suppression was also observed. There was no discrimination between the phosphodiesterase (PDE) inhibitors IBMX and theophylline, and the adenylate cyclase activator forskolin. Specificity of LENK effects was tested by using naloxone (10(-6) M), an opioid-receptor antagonist. Migration-inhibition induced by LENK was reversed in about two-thirds of the experiments. In contrast, migration-inhibition induced by cAMP-elevating agents, could not be reversed by naloxone. Naloxone itself was not inert, usually suppressing the locomotor ability of splenocytes. The data suggest that LENK-induced modulation of cell migration is (at least partly) mediated via opioid receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

1-Methyl-3-isobutylxanthine↗
PubMed2005

A novel approach to prevent repeated catheter migration in a patient with a baclofen pump: a case report.

We report a novel solution to a problem of repeated catheter migration that may aid others caring for patients with catheter migration problems. Catheter migration is a frequently reported complication of intrathecal drug delivery systems. We report on an ambulatory patient with a baclofen pump for control of spasticity due to cerebral palsy and dystonia; the patient suffered repeated episodes of catheter migration. The ultimate solution to the migrations was to place a pediatric pump in the lower thoracic, paraspinal region with the catheter entering the thoracic spine directly adjacent to the pump, thereby minimizing the differential motion between the pump and the spine, which was thought to be the cause of the repeated migration. This solution has not been previously described. Paraspinal pump placement may eliminate repeated catheter migration for patients with intrathecal drug pumps.

Adult↗