Primary and repeat migration: comparisons of Hispanic, Black and non-Hispanic white migration in the United States

Working PaperRepetitive behavior is widespread in human life. This applies in areas of behaviors that are typically infrequent as well as normative daily routines. Yet, some individual never engage in some behaviors and individuals who initiate particular behaviors differ in the extent to which the behavior is repeated. In demography, one of the areas in which this general principle applies is between prior migration and subsequent migration with prior migrants being much more likely to migrate again than individual who have never migrated are to make a first migration. A major classification that emerged from this research was between primary migration and repeat migration with length of residence as a key consideration for prior migrants. Although a rich body of research emerged on this relationship (Goldstein 1954; DaVanzo and Morrison 1981) little recent research has built on this important area of migration research. Also, while there is an extensive body of research on Hispanic immigrants in the United States there is little research that compares the internal migration of Hispanics with non-Hispanic Whites and Blacks. A common note in the early research on primary and repeat migration was the need to examine the extent to which the relationship held across socioeconomic groups and settings. The main purpose of this research is to examine the extent to which Hispanic, Black and White primary and repeat migration rates differ once other migration related variables are controlled. Data from the National Longitudinal Survey of Youth that began in 1979 are used in the analysis. During the study period the respondents transit the ages during which families and careers are typically launched and when migration rates are high

Political, Economic and Social Dominance of Major Cities in East Asia During the Twentieth Century

One of the greatest shift in human societies has been the change from dispersed settlement patterns toward a complex urban pattern. Prior to the industrialization there were only a few urban places scattered throughout the world and none could compare with numerous cities of today with respect to size and complexity. In recent decades the growth of cities in Asia has been particularly remarkable as there has been an increase in the number of medium sized cities and the growth of a number of mega cities. This urbanization of the worlds population has corresponded with other fundamental changes in human society although the relationship between urbanization and other social changes differ for time periods and regions of the world. Among the other changes were the transition from an agricultural toward a diverse economic structure and tremendous increases in population size along with declines in birth and death rates. Many researchers view these changes as being interlocked in a complex set of reciprocal causal relationship. This paper reviews explanations of urbanization with a focus on the emergence of mega cities and their relationship to smaller cities and to national levels of economic development. Special attention is given to literature on primate cities and to whether such cities hinder economic development for Asian societies

Correlation Between Luminescent Properties and Local Coordination Environment for Erbium Dopant in Yttrium Oxide Nanotubes

The local dopant coordination environment and its effect on the photoluminescent (PL) spectral features of erbium-doped yttrium oxide nanotubes (NTs) were probed by synchrotron-based x-ray diffraction (XRD), x-ray absorption near-edge spectroscopy (XANES), and extended x-ray absorption fine structure (EXAFS). XRD, XANES, and EXAFS data demonstrate that single phase solid solutions of Y (2-x) Erx O3 were formed at 0≤

Understanding the selective etching of electrodeposited ZnO nanorods

ZnO nanotubes were prepared by selective dissolution of electrodeposited nanorods. The effect of solution pH, rod morphology, and chloride ion concentration on the dissolution mechanism was studied. The selective etching was rationalized in terms of the surface energy of the different ZnO crystal faces and reactant diffusion. The nanorod diameter and chloride concentration are the most influential parameters on the dissolution mechanism because they control homogeneous dissolution or selective etching of the (110) and (002) surfaces. Bulk solution pH only has an effect on the rate of dissolution. By accurate control of the dissolution process, the nanomorphology can be tailored, and the formation of rods with a thin diameter (10-20 nm), cavity, or ultra-thin-walled tubes (2-5 nm) can be achieved

Size-Dependent Lattice Structure and Confinement Properties in CsPbI₃ Perovskite Nanocrystals: Negative Surface Energy for Stabilization

CsPbI₃ nanocrystals with narrow size distributions were prepared to study the size-dependent properties. The nanocrystals adopt the perovskite (over the nonperovskite orthorhombic) structure with improved stability over thin-film materials. Among the perovskite phases (cubic α, tetragonal β, and orthorhombic γ), the samples are characterized by the γ phase, rather than α, but may have a size-dependent average tilting between adjacent octahedra. Size-dependent lattice constants systematically vary 3% across the size range, with unit cell volume increasing linearly with the inverse of size to 2.1% for the smallest size. We estimate the surface energy to be from −3.0 to −5.1 eV nm⁻² for ligated CsPbI₃ nanocrystals. Moreover, the size-dependent bandgap is best described using a nonparabolic intermediate confinement model. We experimentally determine the bulk bandgap, effective mass, and exciton binding energy, concluding with variations from the bulk α-phase values. This provides a robust route to understanding γ-phase properties of CsPbI₃

Correlating photovoltaic properties of PTB7-Th:PC71BM blend to photophysics and microstructure as a function of thermal annealing

We acknowledge support from EPSRC (grant number EP/L012294/1) and the European Research Council (grant number 321305). I.D.W.S. also acknowledges a Royal Society Wolfson Research Merit Award. VS acknowledges support from the Office of Naval Research NDSEG fellowship. Research data supporting this paper is available at doi http://dx.doi.org/10.17630/eadf56f3-8c70-47da-ac6d-67f2d78b3f74Selective optimisation of light harvesting materials and interface properties has brought breakthroughs in power conversion efficiency (11-12 %) of organic photovoltaics (OPVs). However to translate this promising efficiency to economically viable applications, long term stability is a fundamental requirement. A number of degradation pathways, both extrinsic and intrinsic, reduce the long term stability of OPVs. Here, the photovoltaic properties of a highly efficient bulk heterojunction PTB7-Th:PC71BM blend were investigated as a function of thermal annealing. The changes in charge generation, separation, and transport due to thermal annealing were measured and related to changes in the microstructure and photovoltaic performance. A 30 % drop in power conversion efficiency of PTB7-Th:PC71BM blends upon thermal annealing at 150 oC was identified as mainly due to morphological instability induced by strong phase separation of donor and acceptor molecules of the blend films. Based on the insight gained from these investigations, enhanced thermal stability was demonstrated by replacing the PC71BM fullerene acceptor with the non-fullerene acceptor ITIC, for which power conversion efficiency dropped only by 9 % upon thermal annealing at 150 oC.PostprintPeer reviewe

Structural and spectral dynamics of single-crystalline Ruddlesden-Popper phase halide perovskite blue light-emitting diodes.

Achieving perovskite-based high-color purity blue-emitting light-emitting diodes (LEDs) is still challenging. Here, we report successful synthesis of a series of blue-emissive two-dimensional Ruddlesden-Popper phase single crystals and their high-color purity blue-emitting LED demonstrations. Although this approach successfully achieves a series of bandgap emissions based on the different layer thicknesses, it still suffers from a conventional temperature-induced device degradation mechanism during high-voltage operations. To understand the underlying mechanism, we further elucidate temperature-induced device degradation by investigating the crystal structural and spectral evolution dynamics via in situ temperature-dependent single-crystal x-ray diffraction, photoluminescence (PL) characterization, and density functional theory calculation. The PL peak becomes asymmetrically broadened with a marked intensity decay, as temperature increases owing to [PbBr6]4- octahedra tilting and the organic chain disordering, which results in bandgap decrease. This study indicates that careful heat management under LED operation is a key factor to maintain the sharp and intense emission