Estimation of place-to-place migration flows from net migration totals: a minimum information approach

"A truism in demography has been that net migration may be derived from information on gross place-to-place flows, but that gross place-to-place flows cannot be inferred back from information on the net population movements in a system. Some recent work on maximum entropy and minimum information models, however, suggests a possible means for estimating just such as set of place-to-place flows. The net migration constrained model presented here could prove particularly useful for updating detailed migration matrices on the basis of current net migration estimates, and could even provide some clues as to the nature of the still poorly understood relationship between gross and net migration. Performance of the model is demonstrated using flow matrices from the 1960 and 1970 U.S. Censuses.     

Alterations of heme metabolism in lymphocytes and metal content in blood plasma as markers of diesel fuels effects on human organism

Workers in the diesel fuel distribution trade are intensively exposed to fuel vapours. Diesel fuel presents the main source of air pollution by benzene at a marine diesel fuel terminal. Levels of benzene are used to evaluate the external exposure to diesel fuel. Since benzene causes alterations in porphyrin metabolism, and some of these may lead to the generation of tumours, heme synthesis is proposed as a biomarker of early health effects of diesel fuel. A group of 20 workers exposed to diesel fuel and a group of 20 unexposed persons were examined and interviewed using structured questionnaires. The levels of 5-aminolevulinic acid (ALA) and protoporphyrin (PP), activities of ALA synthase and ferrochelatase, as well as levels of PP associated with DNA were determined in lymphocytes spectrophotometrically. Amounts of the metals Cd, Mn, Zn, Cu and Ca were measured in blood plasma by flame atomic absorption spectrometry method. Both ALA and PP levels were significantly increased in marine terminal workers: 3.0 +/- 0.4 vs. 0.8 +/- 0.2 nmol/10(6) lymphocytes: and 511 +/- 164 vs. 389 +/- 77 pmol/10(6) lymphocytes in exposed and control individuals, respectively. ALA-synthase activity was 2.5 fold higher in lymphocytes of workers exposed to diesel fuels (P < 0.01). At the same time ferrochelatase activity was decreased and protoporphyrin level was accordingly elevated. The amount of porphyrin associated with DNA increased 1.4 fold in exposed workers (P = 0.05). Among all investigated metals in blood plasma of exposed workers only zinc levels were statistically significantly increased (P < 0.05). The disturbances of heme metabolism in lymphocytes and zinc level in blood plasma caused by diesel fuel exposure seems to be a useful biomarkers for carcinogenic risk assessment.     

Information,communication and networks in international migration systems

This paper focuses on the role of information and communication in international migration by means of a survey which covers economic and broader perspectives, both at the micro and macro levels. The human capital model of migration is reviewed and the likely impact of recent and anticipated developments in telecommunications technology is noted. The job search model is reformulated in the context of international migration but extensive modification is required to describe the potential sampling of job offers and other informational needs of international migrants. It is argued that spatial selectivity is to a large extent influenced by migration networks in which information flows play a critical role. This is further elucidated by offering an analytical framework based on the systems approach to migration.     

Data Fusion of Fixed Detector and Probe Vehicle Data for Incident Detection

An important feature of many advanced traveler information systems (ATIS) is real-time information about incidents on the street network. This paper describes a system for automatically detecting incidents for such an ATIS developed using artificial neural networks and statistical prediction methods. The system monitors traffic conditions using two types of data: inductive loop detectors (ILDs) and vehicle probes. For both neural network and statistical methods, incident detection is accomplished using two approaches: by processing traffic input data directly and by processing the output of specialized algorithms that detect incidents using information from each data source. Analysis data generated from a simulation of a typical suburban signalized major arterial street are used. Different model configurations are examined and tested to identify the input variables and methods that are the best predictors of incident occurrence. The neural network approaches consistently perform at least as well as the discriminant analysis models, especially when results are adjusted to avoid false alarms.     

A family of spatial interaction models incorporating information flows and choice set constraints applied to U.S. interstate labor flows

"A new family of migration models belonging to the elimination by aspects family is examined, with the spatial interaction model shown to be a special case. The models have simple forms; they incorporate information flow processes and choice set constraints; they are free of problems raised by the Luce Choice Axiom; and are capable of generating intransitive flows. Preliminary calibrations using the Continuous Work History Sample [time] series data indicate that the model fits the migration data well, while providing estimates of interstate job message flows. The preliminary calculations also indicate that care is needed in assuming that destination [attraction] are independent of origins."     

A preliminary investigation of the metal content of certain children's sweet wrappers

An investigation of the lead, cadmium and copper contents of certain sweet wrappers has been carried out in response to a number of reports by other workers on the metal content of American confection wrappers. In this study the wrappers analysed were from some of the most popular sweets consumed by young children in the U.K. This selection was made as it is not uncommon for children to suck the sweet wrappers as well as the sweets contained therein. No significant levels of any of the metals examined were found and it is apparent that no hazard exists from this source at the present time.     

Migration analysis: The role of geographic scale

The purpose of this paper is to empirically evaluate the effect of geographic scale on migration analysis by conducting similar migration studies at two levels of spatial aggregation. The analyses are concerned with the interrelationship between interregional population movement in the U. S. from 1965 to 1970 and various socio-economic, demographic, and environmental factors usually associated with migration. Recognizing the interdependent nature of these relationships, the model is specified as a system of simultaneous equations, and the parameters are estimated using a two stage least squares solution. The results indicate that scale does, in fact, influence the outcome of the analyses such that the effects of migration on regional attractiveness and the conditions under which migration occurs vary from one geographic scale to another.     

Numerical approach of carbon monoxide concentration dispersion in an enclosed garage

This paper draws attention to the lack of information about the carbon monoxide (CO) dispersion in enclosed garages, a typical occupational microenvironment, with high expected CO concentrations, where employees are exposed daily as well as garage users, and refers to the numerical prediction of CO concentration inside the garage. A mathematical model implemented in a general computer code that can provide detailed information on CO concentration as well as air flow field prevailing in three-dimensional enclosed spaces of any geometrical complexity is presented. This model involves the partial differential equations governing CO levels and airflow transfer in large enclosures. For the evaluation of the mathematical model, experimental CO concentrations measured inside are used as input data. This paper refers to a number of simulations where different ventilation rates were examined in order to provide adequate ventilation to dilute indoor CO sources and CO levels. Regarding the airflow patterns it was found that while the ventilation of indoor spaces improved the CO concentration decreased to half the value. The simulation results could be used as a base for ventilation design for enclosed garages, aimed at a proper ventilation system selection for a more healthy and comfortable working microenvironment.     

水源热泵回灌井悬浮颗粒运移和沉积物理特性试验模型研究

 针对地下水源热泵系统阻塞机制研究开发的砂层阻塞模拟试验系统,利用砾石颗粒作为多孔介质,以粉煤灰颗粒作为悬浮物,研究悬浮颗粒在砾石中运移和沉积时相对浓度与孔隙体积的关系。通过试验可知：(1) 在3种不同流速试验条件下,悬浮颗粒在砾石介质中的运移和沉积主要经历了浓度的增加、骤减和平稳段,总体趋势是相同的,主要区别在于浓度的峰值有所不同,流速越大所对应的峰值越大,反之亦然。(2) 给出的渗透率衰减模型对预见试验中悬浮颗粒的迁移所引起的孔隙率下降是有效的。(3) 把理论分析方法同试验曲线比较后发现,余尾效应在本次试验中并没有出现,试验值和理论值具有较好的吻合性。     

Wage returns to interregional mobility among Ph.D graduates: Do occupations matter?

This paper addresses the wage returns to interregional mobility among Italian Ph.D workers. We control for selection bias in both migration and occupation choice by estimating a double sample selection model. While OLS estimates indicate a positive wage premium of mobility across all types of occupations examined, wage equations estimated by correcting for double sample selection evidence a wage penalty for movers within academia, no effects for movers carrying out R&D activities but positive returns if they work within the industry sector. The selection process appears to be stronger when mobility choice is considered in comparison to the choice of occupation.     

Fault tree analysis for integrated and probabilistic risk analysis of drinking water systems

Drinking water systems are vulnerable and subject to a wide range of risks. To avoid sub-optimisation of risk-reduction options, risk analyses need to include the entire drinking water system, from source to tap. Such an integrated approach demands tools that are able to model interactions between different events. Fault tree analysis is a risk estimation tool with the ability to model interactions between events. Using fault tree analysis on an integrated level, a probabilistic risk analysis of a large drinking water system in Sweden was carried out. The primary aims of the study were: (1) to develop a method for integrated and probabilistic risk analysis of entire drinking water systems; and (2) to evaluate the applicability of Customer Minutes Lost (CML) as a measure of risk. The analysis included situations where no water is delivered to the consumer (quantity failure) and situations where water is delivered but does not comply with water quality standards (quality failure). Hard data as well as expert judgements were used to estimate probabilities of events and uncertainties in the estimates. The calculations were performed using Monte Carlo simulations. CML is shown to be a useful measure of risks associated with drinking water systems. The method presented provides information on risk levels, probabilities of failure, failure rates and downtimes of the system. This information is available for the entire system as well as its different sub-systems. Furthermore, the method enables comparison of the results with performance targets and acceptable levels of risk. The method thus facilitates integrated risk analysis and consequently helps decision-makers to minimise sub-optimisation of risk-reduction options.     

Managing Agricultural Pollution Using a Linked Geographical Information System and Non-Point Source Pollution Model

This study documents the development of a link between a geographical information system (GIS) and a non-point source pollution model. The GIS ARC/INFO was linked to the agricultural non-point source pollution model and ORACLE data sources. Application of the system is demonstrated using the Bedford-Ouse catchment as a suitable case study. Water quality impacts are predicted from source data describing topography, soils, land use and river network. The model results were in agreement with observed nitrate concentrations at the catchment outlet, and more appropriate data sources are considered to be the main priority for improving model predictive ability. Management scenarios were established to assess the impact of changing agricultural management practices on predicted water quality. The approach has significant potential for the management of agricultural pollution in the UK.     

International mobility and wages: an analysis of Italian Ph.D. graduates

Following a recent stream of research that focuses on the migration of high-skilled workers, this paper examines the wage performance of two cohorts of Italian Ph.D. graduates associated with international mobility. After controlling for the endogeneity of the migration decision, we find that labor mobility is associated with higher wages and that selection on unobservable traits is essential to address the issue of the returns to migration. Additionally, we do not find evidence of individual heterogeneity in the response of wages to migration. We also show that our results are always confirmed when we include two exclusion restrictions in the empirical model and when we restrict the analysis to different subpopulations.     

Monocyte-macrophage system and polymorphonuclear leukocytes in workers exposed to low levels of metallic mercury

Our previous research (Soleo L, Vacca A, Vimercati L et al. Occup Environ Med 1997;54:437-442) showed a reduction in tumor necrosis factor-alpha (TNF-alpha) serum levels in workers with prolonged exposure to low doses of inorganic mercury, suggesting an in vivo functional defect of the monocyte-macrophage system. On this basis, here we wondered whether workers exposed to lower doses of metallic mercury displayed possible changes in the monocyte-macrophage system. In this particular cohort of workers, we also sought for the effects of the exposure on the polymorphonuclear leukocytes (PMNL) chemotaxis. The monocyte-macrophage system and the natural killer (NK) cells were examined in 19 exposed workers and in 25 unexposed workers, as the control group (controls). Specifically, the circulating monocyte-macrophage cells and their CD13, CD15 and CD33 subsets, serum cytokines (IL-8, GM-CSF and TNF-alpha) and the NK cells were analyzed. In seven exposed and seven controls randomly chosen workers the PMNL chemotaxis was also assessed. The selected indicator of mercury exposure were the levels of mercury in the urine (U-Hg), that was significantly higher in exposed workers than the controls (9.7 +/- 5.5 microg/l and 2.4 +/- 1.2 microg/l, respectively). None of the exposed workers had shown signs of either acute or chronic inorganic mercury toxicity or any form of hypersensitivity. Several immunological variables tested, monocyte-macrophage cells and their subsets, NK cells and serum cytokines overlapped between the exposed and the control workers. When the workers were considered as a whole (exposed plus controls), no correlation was found between current U-Hg and all immunological parameters. However, when exposed workers were studied separately, an inverse correlation was disclosed between cumulative U-Hg and cells (as percentage) expressing the CD13 (r = -0.599; P = 0.007) and CD15 (r = -0.614; P = 0.005) molecules, and NK cells (r = -0.455; P = 0.05). Moreover, a significant impairment in the PMNL chemotaxis (t = 3.70; P = 0.003) was observed in the exposed workers. The results of our study suggest that the exposure to very low levels of metallic mercury led to subtle impairment of circulating monocyte and NK cells (as percentages) according to the increase in U-Hg levels, as well as of the PMNL chemotactic function in this particular group of workers, even though they remain clinically asymptomatic. Therefore, we suggest that impairment of these parameters provide a sensitive indicator of metallic mercury and other chemical contaminants present in the environment.     

Migration in an interregional macroeconometric model of the United States: will net outmigration from the Northeast continue?

"This paper reports on the specification, estimation and simulation of an interregional net migration model of the United States. The model makes use of time series data including, as explanatory variables, wage rates, unemployment rates, and population density. Simulation experiments are undertaken by joining the migration model with a multi-regional macroeconometric model to examine the effect [on] migration patterns of changes in national economic growth. In particular, the net outmigration trends in the Northeast are examined under alternative scenarios including faster national economic growth and a different energy pricing policy."     

Interregional labour migration and real wage disparities: Evidence from Japan

This paper empirically tests the relationships between interregional labour migration and regional real wages based on a multi-region economic geography model, which describes bilateral migration flows. In particular, this paper highlights real wage disparities in the migration analysis. Our empirical methodology contains two steps. First, we structurally estimate a gravity model using manufacturing workers’ migration flows across the 47 Japanese prefectures. Second, using the estimates of the structural parameters, we examine the impact of the real wage on the net migration rate. We find that migrants respond to real wage disparities, rather than to nominal wage disparities.     

A behavioral model of international labor and nonlabor migration: the case of Turkish movements to West Germany, 1960-1986

"In this paper behavioral models of international labor and nonlabor migration are presented. The models are based on the concept of chain migration, where the immigrant stock, differentiated by the duration of stay, induces and directs future migration flows. Three roles of the immigrant stock in inducing the inflow of potential migrants are identified: provider of assimilation aid; transmitter of information; and source of family reunification. Operationalized versions of the models are empirically tested for Turkish labor and nonlabor migration to West Germany, 1960-86. The results support the importance of information for labor migrants, and reunification ties for nonlabor migrants."     

Levels of antimony,arsenic, cadmium,copper, lead,mercury, selenium,silver, tin and zinc in bone tissue of industrially exposed workers

The contents of the elements antimony, arsenic, cadmium, copper, lead, mercury, selenium, silver, tin and zinc in bone tissue from autopsy specimens of the femur of workers who had been exposed to a large number of metals in a smeltery and refinery in Northern Sweden as well as of a control group have been quantitatively assayed.The analytical techniques used were atomic absorption spectrophotometry, neutron activation analysis and particle induced X-ray emission analysis (PIXE) in a proton microprobe. Increased levels of lead in the bone tissue of exposed workers compared to a non-exposed control group were observed. The median level of lead in the group of exposed workers exceeded the corresponding value of the control group about 5 times.Using the proton microprobe in the PIXE-mode, concentration profiles of copper, lead and zinc were examined within the Haversian system of the bone samples.     

The commuting behaviour of self-employed workers: Evidence for Spain

The aim of the paper is to examine the commuting behaviour of self-employed workers in Spain as well as its relationship with satisfaction with jobs and housing. According to our results although conventional estimations indicate that commuting trips are shorter among the self-employed, the differences with employees vanish when the potential endogeneity of self-employment is controlled for. We also show that the job and housing satisfaction levels of the self-employed are less sensitive to commuting than those of employees, and that in fact no significant effect is observed for relevant segments of the former group, what gives partial support to the theoretical model that we propose where imperfect information problems affect the employees but not the self-employed.     

Extremely low frequency-magnetic fields (ELF-EMF) occupational exposure and natural killer activity in peripheral blood lymphocytes

Extremely Low Frequency-Magnetic Fields (ELF-MF) are possible carcinogens to humans and some data suggest that they can act as promoters or progressors. Since NK cells play a major role in the control of cancer development, an adverse effect on ELF-MF on NK function has been hypothesized. We examined NK activity in 52 workers exposed to different levels of ELF-MF in various activities. Individual exposure was monitored during 3 complete work-shifts using personal dosimeters. Environmental exposure was also monitored. ELF-MF levels in the workers were expressed as Time-Weighted Average (TWA) values. NK activity was measured in peripheral blood lymphocytes (PBL). In the whole group the median occupational TWA was 0.21 microT. According to the TWA levels, workers were classified as low exposed (26 subjects, TWA < or =0.2 microT) and higher exposed workers (26 subjects; TWA >0.2 microT). In higher exposed workers, we observed a trend to reduce NK activity compared to low exposed, but the difference was not significant. Then we selected a subgroup of highest exposed workers (12 subjects; TWA >1 microT); no difference was observed between low and highest exposed subjects in the main personal variables. Considering both E:T ratios from 12:1 to 50:1 and Lytic Units, a significant reduction in NK activity was observed in the highest exposed workers compared to the low exposed. Multivariate analysis showed a significant negative correlation between exposure and LU, while no correlation was evidenced with other personal characteristics. ELF-MF are considered possible carcinogens, and existing data suggest that they can act as promoters. Due to the role of NK activity in host defence against cancer, the results obtained in this study in workers exposed to ELF-MF levels exceeding 1 microT are in agreement with this hypothesis, and support the need for further investigation in this field.