Underurbanisation and the zero urban growth hypothesis: diverted migration in Albania

The author challenges the hypothesis "that the mode of production accounts for the specific forms of urbanisation under socialism and the slow urban growth observed...[and emphasizes instead] the effects of planning in the traditionally organised command economy." It is suggested that strict migration policy is a pivotal factor in achieving zero urban growth. "A case study focusing on patterns of diverted migration and the growth of non-urban settlements on the outskirts of the Albanian capital, Tirana, illustrates how the proposed explanations may help to re-interpret the particulars of urbanisation under orthodox socialist rule."     

The assumption of equilibrium in models of migration

In recent articles Evans (1990) and Harrigan and McGregor (1993) (hereafter HM) scrutinized the equilibrium model of migration presented in a 1989 paper by Schachter and Althaus. This model used standard microeconomics to analyze gross interregional migration flows based on the assumption that gross flows are in approximate equilibrium. HM criticized the model as theoretically untenable, while Evans summoned empirical as well as theoretical objections. HM claimed that equilibrium of gross migration flows could be ruled out on theoretical grounds. They argued that the absence of net migration requires that either all regions have equal populations or that unsustainable regional migration propensities must obtain. In fact some moves are inter- and other are intraregional. It does not follow, however, that the number of interregional migrants will be larger for the more populous region. Alternatively, a country could be divided into a large number of small regions that have equal populations. With uniform propensities to move, each of these analytical regions would experience in equilibrium zero net migration. Hence, the condition that net migration equal zero is entirely consistent with unequal distributions of population across regions. The criticisms of Evans were based both on flawed reasoning and on misinterpretation of the results of a number of econometric studies. His reasoning assumed that the existence of demand shifts as found by Goldfarb and Yezer (1987) and Topel (1986) invalidated the equilibrium model. The equilibrium never really obtains exactly, but economic modeling of migration properly begins with a simple equilibrium model of the system. A careful reading of the papers Evans cited in support of his position showed that in fact they affirmed rather than denied the appropriateness of equilibrium modeling. Zero net migration together with nonzero gross migration are not theoretically incompatible with regional heterogeneity of population, wages, or amenities.     

A general equilibrium analysis of rural-urban migration under uncertainty

ABSTRACT. This paper analyzes the implications of an exogenous shift in relative prices for an economy that suffers from urban unemployment, as well as uncertainty, in the agricultural sector. Among other things, we show that with agricultural uncertainty, an exogenous shift in relative prices will lower agricultural profit. This result is in sharp contrast with the conventional case of risk-neutrality or certainty where agricultural profit is unaffected by changes in the terms of trade.     

Incorporating the effects of spatial structure in discrete choice models of migration

Discrete-choice theory and logit models are evaluated for their usefulness in analyzing migration patterns in a zonal system. The authors "argue that spatial effects and more specifically the relative location of zones are not taken into account in such analyses. We, therefore, introduce a measure of spatial structure and advocate its usage as a predictor of migration in such models. In an example of intrametropolitan migration in Toronto [Canada], we demonstrate that this variable is not only significant but also it improves the performance of all the other variables with the greatest impact on the distance between zones. In addition, inclusion of this variable improves the overall performance of the model in terms of residuals."     

A note on specification of climate variables in models of population migration

"In the literature on population migration, increasing attention has been devoted to quality-of-life factors. Measures of temperature (as proxies for climate) have frequently been employed in empirical work regarding the determinants of population migration decisions. A wide range of such specifications have been used, most of which imply restrictions on the preferences of migrants. In this paper, a variety of temperature variable specifications are analyzed and interpreted. Statistical tests for nested and nonnested hypotheses are used to compare and choose among the various specifications." The model is used to analyze interstate migration in the 48 contiguous states of the United States for the period 1975-1980.     

On the role of amenities in models of migration and regional development

"The role of location-specific amenities in human migration decisions, and subsequently regional development, is explored. A framework is developed which motivates a new assessment of existing alternative models of regional development, indicating the need for additional modeling efforts which focus upon amenities as critical elements in such analyses. The approach hinges upon the notion that amenity values are capitalized into wages, rents, or other local prices. This process of capitalization enables researchers to explore the implicit value that society places upon amenities, which can then be used in assessing future regional-development trends in a more comprehensive manner."     

Numerical models of petroleum migration via buoyancy-driven porosity waves in viscously deformable sediments

The apparent ability of petroleum to migrate rapidly through low permeability sediments in sedimentary basins has led to many questions about the manner of its transport. One possible explanation is suggested from observations of the compaction of viscously deformable porous media. These systems have been found in some cases to give rise to regions of locally elevated liquid fraction, in the form of fluid‐filled porosity waves that can ascend at rates much greater than that of the background flow. Previous research on the phenomenon has focused on its implications for magma transport, but recognition of the fact that the compaction of viscous porous media can take place in sedimentary basins has suggested the possibility that porosity waves could similarly be important for hydrocarbon transport. The purpose of the present study was to test this hypothesis by quantifying the transport that would occur as the result of porosity waves initiated during the conversion of kerogen to petroleum. A one‐dimensional numerical model was constructed solving equations for the mechanics of viscous compaction and for the kinetics of reactions describing the formation of petroleum from kerogen. The results showed that porosity waves would develop readily in viscously deformable regions of sedimentary basins, but would not necessarily provide enhanced transport over that of the background flow regime. In order for the waves to achieve this enhanced transport, they must develop high amplitudes, i.e. high porosities relative to the background porous medium. To achieve the high wave amplitudes, the background porosity must be very low in absolute terms. In addition, high kerogen contents are needed in the source layer, and the source layer needs to be buried rapidly to a high temperature region of the oil window. Considerable uncertainty exists as to the value of the matrix shear viscosity of sediments in basins. However, the wave volumetric transport capacity was not found to be significantly altered as a result of variations in the value of this parameter. The physical form of the waves was strongly altered by the matrix shear viscosity, with higher values leading to lower amplitudes and generation frequency, but higher wavelengths. Thus the waves become less recognizable physically at higher values of the matrix shear viscosity. As the waves ascend to higher stratigraphic levels, where the porosity is higher, they gradually lose their physical definition and become absorbed into the background.     

Voters on the move: The political effectiveness of migration and its effects on state partisan composition

Recent population forecasts issued by the U.S. Census Bureau suggest that by 2030 Sunbelt migration could result in two-thirds of all Americans living in the South and West. What's more, 30% of all Americans could live in California, Texas, and Florida (U.S. Census Bureau, 2005). Regardless of whether such high levels of continued Sunbelt migration occur or other patterns emerge, population movement will have electoral implications as the composition of migration streams change the balance of party identifiers at both origins and destinations. To illustrate how migration streams can exhibit very different levels of ‘political effectiveness,’ this research substantively addresses three key issues under-examined in the current literature: 1) the ability of migration to both reinforce and dilute party strength, 2) the changes in partisanship at the origin and destination of migration streams effected through processes analogous to ‘packing’ and ‘cracking’ in electoral redistricting literature, and 3) the importance of migration selectivity. This research uses an innovative, albeit far-from-precision method to suggest how recent U.S. migration trends may portend changes in Republican and Democratic partisanship. Using 2000 Presidential election exit polls by state, along with 1995–2000 PUMS migration data, individual party identification is inferred from individual migrant characteristics. This research calls attention to and argues for research to address the highly complex relationships of migration with electoral geographies.     

Ancient Iberian horses: a method to recover DNA from archaeological samples buried under sub-optimal conditions for preservation

Existing methods to extract, amplify, and sequence ancient DNA (aDNA) from horse bone and teeth were optimized to recover DNA from a depositional environment of highly permeable acidic soil. DNA was successfully retrieved using 0.10g of bone powder from horse (Equus sp.) remains dating to 25 K years utilizing the methods optimized for this archaeological material. The genetic analyses were performed in a facility that is dedicated to ancient DNA research (Paleo-DNA Laboratory, Thunder Bay, ON, Canada) and has not been previously used to analyse modern or ancient horse DNA. Research was replicated to obtain reliable sequencing results for six samples from the Iberian Peninsula that were consistent with published sequences of Equus caballus. The archaeological sequence data obtained support hypotheses that promote the significance that the Iberian Peninsula has had to the multi-focal centres of origin for horse domestication and distribution of modern horse breeds. The data presented may provide evidence of the existence of an Iberian refugium for Equus during the last glacial period, 10 K years BP. Further molecular data analyses will enhance the ideas presented by this data and our understanding of horse domestication and phylogeny. The optimization of molecular techniques to successfully obtain DNA using minimally destructive, cosmetically sensitive techniques from archaeological remains endeavours to foster further cooperation between museums and researchers.     

On the structure and circulation of the polar thermosphere under magnetically quiet conditions

A theoretical study is presented bearing on the thermospheric circulation and composition at polar latitudes. The observed motions and density perturbations in N₂, O and He have signatures which may be understood in terms of two different source mechanisms. We consider electric field momentum coupling and Joule heating as well as interactions between both processes. A spectral model in terms of vector spherical harmonics (with magnetic coordinates) is used, delineating the diurnal and mean (time independent) components. The important non-linearities are evaluated in configuration space. The electric field model of Volland and the global average density and temperature variations of Hedin (MSIS) are adopted as input. Our analysis leads to the following conclusions. (1) The vortex type double cell polar circulation (zonal wave number m = 1) is primarily driven by collisional momentum transfer from electric field induced ion convection. (2) Because of the thermospheric low pass filter, a large time independent component (zonal wave number m = 0) is produced by Joule heating; the heavier species (N₂) being concentrated where the lighter ones (O, He) are depleted, and vice versa due to wind induced diffusion (3) The electric field driven vortex circulation redistributes the mass and energy in the time independent density and temperature variations (from Joule heating), producing primarily diurnal variations (m = 1) in the temperature and composition near the pole and at auroral latitudes, again the heavier and lighter species varying out of phase. The above results are in substantial agreement with observations. It is worth noting that momentum rectification associated with the diurnally varying electric field and conductivity induces a weak zonally symmetric (single cell) prograde polar vortex. However, this motion is partially compensated by a retrograde vortex from geostrophic balance due to Joule heating, which dominates near the pole. These motions are small compared with the diurnally varying component in the polar circulation.     

Scottish emigration in the 1980s: a migration channels approach to the study of skilled international migration

"British emigration is now dominated by skilled transient movements rather than traditional settler emigration movements. This switch requires new frameworks for migration analysis. A migration channels approach is advocated with attention focused on the roles of the internal labour markets of multi-national companies, international recruitment agencies and international skill transfers by small- and intermediate-sized companies in moulding contemporary skilled migration. The migration processes which have emerged in relation to the operation of these three channels can be differentiated in terms of migrant characteristics, the status of migration contracts and patterns of movement. The regional dimension is highlighted in this article by contrasting the experience of recent Scottish emigration with that of the South-East of England. Three data sources (the International Passenger Survey, the results of a survey questionnaire, and company case study material) are employed to illustrate the nature of Britain's main migration channels. It is argued that the three channels are responsible for a selective structuring of the British migration system."     

In the Valley of the Sweet Mother: Gendered metaphors,domestic lives and reproduction under a Brazilian state mining company

Metaphors have been studied by feminist geographers as examples of both power over and empowerment by women. In this article, the author takes three gendered metaphors used by people in the Brazilian mining town of Itabira as starting points to enlarge a discussion of the mining economy's effects on women's lives. One, the 'sweet mother,' describes the company's reskilling and cultural education of male workers from the 1940s to the early 1980s. Second, women react to these strategies with a contending image of the company as 'the rival.' Finally, the phase of company downsizing has created a new metaphor: 'the stepmother.' These metaphors elucidate ways that public and private spaces become intertwined in three moments of the state mining company's life: its arrival in the region in the mid-1940s; its expansion from the 1960s to the 1980s; and its restructuring in the last 10 years. The author suggests that women's ironic rewriting of the foundational metaphor of 'sweet mother' is central to their reconceptualization of economic change under the company. The alternative metaphors also reflect women's changing views on motherhood, sexuality and family partnership.     

The direction of migration: a dynamic general equilibrium model

A two-sector dynamic general equilibrium model is developed "to investigate the direction of migration in response to differing demographic and consumption demand behavior, as well as variations in production conditions." The model, which involves a rural sector and an urban sector, incorporates "returns to scale and the natural rate of sectoral population growth as important determinants of the direction of migration, in addition to price and income elasticities, and the sectoral technical change rate with which...previous studies dealt."     

新课程下教师课程意识的提升

课程意识是教师对正在实施的课程系统的认识以及即将实施的课程进行的规划。新课程所倡导的课程功能的六大转变以及提出的新课程理念的努力践行要求教师树立并提升课程意识;教师的课程意识对于提高教师的专业化程度,促进教师的专业发展有着重要的作用和意义。