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

MORMON AND NONMORMON MIGRATION IN AND OUT OF UTAH'

Migration plays a key role in the maintenanc

Tuning the bandgap of Cs2AgBiBr6 through dilute tin alloying.

The promise of lead halide hybrid perovskites for optoelectronic applications makes finding less-toxic alternatives a priority. The double perovskite Cs2AgBiBr6 (1) represents one such alternative, offering long carrier lifetimes and greater stability under ambient conditions. However, the large and indirect 1.95 eV bandgap hinders its potential as a solar absorber. Here we report that alloying crystals of 1 with up to 1 atom% Sn results in a bandgap reduction of up to ca. 0.5 eV while maintaining low toxicity. Crystals can be alloyed with up to 1 atom% Sn and the predominant substitution pathway appears to be a ∼2 : 1 substitution of Sn2+ and Sn4+ for Ag+ and Bi3+, respectively, with Ag+ vacancies providing charge compensation. Spincoated films of 1 accommodate a higher Sn loading, up to 4 atom% Sn, where we see mostly Sn2+ substitution for both Ag+ and Bi3+. Density functional theory (DFT) calculations ascribe the bandgap redshift to the introduction of Sn impurity bands below the conduction band minimum of the host lattice. Using optical absorption spectroscopy, photothermal deflection spectroscopy, X-ray absorption spectroscopy, 119Sn NMR, redox titration, single-crystal and powder X-ray diffraction, multiple elemental analysis and imaging techniques, and DFT calculations, we provide a detailed analysis of the Sn content and oxidation state, dominant substitution sites, and charge-compensating defects in Sn-alloyed Cs2AgBiBr6 (1:Sn) crystals and films. An understanding of heterovalent alloying in halide double perovskites opens the door to a wider breadth of potential alloying agents for manipulating their band structures in a predictable manner

Structural origin of gap states in semicrystalline polymers and the implications for charge transport

We quantify the degree of disorder in the {\pi}-{\pi} stacking direction of crystallites of a high performing semicrystalline semiconducting polymer with advanced X-ray lineshape analysis. Using first principles calculations, we obtain the density of states of a system of {\pi}-{\pi} stacked polymer chains with increasing amounts of paracrystalline disorder. We find that for an aligned film of PBTTT the paracrystalline disorder is 7.3%. This type of disorder induces a tail of trap states with a breadth of ~100 meV as determined through calculation. This finding agrees with previous device modeling and provides physical justification for the mobility edge model.Comment: Text and figures are unchanged in the new version of the file. The only modification is the addition of a funding source to the acknowledgment

Tuning Charge Transport in Solution-Sheared Organic Semiconductors Using Lattice Strain

Circuits based on organic semiconductors are being actively explored for flexible, transparent and low-cost electronic applications. But to realize such applications, the charge carrier mobilities of solution-processed organic semiconductors must be improved. For inorganic semiconductors, a general method of increasing charge carrier mobility is to introduce strain within the crystal lattice. Here we describe a solution-processing technique for organic semiconductors in which lattice strain is used to increase charge carrier mobilities by introducing greater electron orbital overlap between the component molecules. For organic semiconductors, the spacing between cofacially stacked, conjugated backbones (the π–π stacking distance) greatly influences electron orbital overlap and therefore mobility. Using our method to incrementally introduce lattice strain, we alter the π–π stacking distance of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) from 3.33Å to 3.08 Å. We believe that 3.08Å is the shortest π–π stacking distance that has been achieved in an organic semiconductor crystal lattice (although a π–π distance of 3.04Å has been achieved through intramolecular bonding). The positive charge carrier (hole) mobility in TIPS-pentacene transistors increased from $0.8 cm^2 V^{−1} s^{−1}$ for unstrained films to a high mobility of $4.6 cm^2 V^{−1} s^{−1}$ for a strained film. Using solution processing to modify molecular packing through lattice strain should aid the development of high-performance, low-cost organic semiconducting devices.Chemistry and Chemical Biolog

Effects of Odd–Even Side Chain Length of Alkyl-Substituted Diphenylbithiophenes on First Monolayer Thin Film Packing Structure

Because of their preferential two-dimensional layer-by-layer growth in thin films, 5,5′bis(4-alkylphenyl)-2,2′-bithiophenes (P2TPs) are model compounds for studying the effects of systematic chemical structure variations on thin-film structure and morphology, which in turn, impact the charge transport in organic field-effect transistors. For the first time, we observed, by grazing incidence X-ray diffraction (GIXD), a strong change in molecular tilt angle in a monolayer of P2TP, depending on whether the alkyl chain on the P2TP molecules was of odd or even length. The monolayers were deposited on densely packed ultrasmooth self-assembled alkane silane modified $SiO_2$ surfaces. Our work shows that a subtle change in molecular structure can have a significant impact on the molecular packing structure in thin film, which in turn, will have a strong impact on charge transport of organic semiconductors. This was verified by quantum-chemical calculations that predict a corresponding odd–even effect in the strength of the intermolecular electronic coupling.Chemistry and Chemical BiologyEngineering and Applied Science

Effects of Molecular Structure and Packing Order on the Stretchability of Semicrystalline Conjugated Poly(Tetrathienoacene-diketopyrrolopyrrole) Polymers

The design of polymer semiconductors possessing high charge transport performance, coupled with good ductility, remains a challenge. Understanding the distribution and behavior of both crystalline domains and amorphous regions in conjugated polymer films, upon an applied stress, shall provide general guiding principles to design stretchable organic semiconductors. Structure–property relationships (especially in both side chain and backbone engineering) are investigated for a series of poly(tetrathienoacene-diketopyrrolopyrrole) polymers. It is observed that the fused thiophene diketopyrrolopyrrole-based polymer, when incorporated with branched side chains and an additional thiophene spacer in the backbone, exhibits improved mechanical endurance and, in addition, does not show crack propagation until 40% strain. Furthermore, this polymer exhibits a hole mobility of 0.1 cm2 V−1 s−1 even at 100% strain or after recovered from strain, which reveals prominent continuity and viscoelasticity of the polymer thin film. It is also observed that the molecular packing orientations (either edge-on or face-on) significantly affect the mechanical compliance of the polymer films. The improved stretchability of the polymers is attributed to both the presence of soft amorphous regions and the intrinsic packing arrangement of its crystalline domains

Spectroscopic and Mechanistic Studies of Heterodimetallic Forms of Metallo-β-lactamase NDM-1

In an effort to characterize the roles of each metal ion in metallo-β-lactamase NDM-1, heterodimetallic analogues (CoCo-, ZnCo-, and CoCd-) of the enzyme were generated and characterized. UV–vis, 1H NMR, EPR, and EXAFS spectroscopies were used to confirm the fidelity of the metal substitutions, including the presence of a homogeneous, heterodimetallic cluster, with a single-atom bridge. This marks the first preparation of a metallo-β-lactamase selectively substituted with a paramagnetic metal ion, Co(II), either in the Zn1 (CoCd-NDM-1) or in the Zn2 site (ZnCo-NDM-1), as well as both (CoCo-NDM-1). We then used these metal-substituted forms of the enzyme to probe the reaction mechanism, using steady-state and stopped-flow kinetics, stopped-flow fluorescence, and rapid-freeze-quench EPR. Both metal sites show significant effects on the kinetic constants, and both paramagnetic variants (CoCd- and ZnCo-NDM-1) showed significant structural changes on reaction with substrate. These changes are discussed in terms of a minimal kinetic mechanism that incorporates all of the data

Intentional creation of carbon-rich dark earth soils in the Amazon

Fertile soil known as Amazonian dark earth is central to the debate over the size and ecological impact of ancient human populations in the Amazon. Dark earth is typically associated with human occupation, but it is uncertain whether it was created intentionally. Dark earth may also be a substantial carbon sink, but its spatial extent and carbon inventory are unknown. We demonstrate spatial and compositional similarities between ancient and modern dark earth and document modern Indigenous practices that enrich soil, which we use to propose a model for the formation of ancient dark earth. This comparison suggests that ancient Amazonians managed soil to improve fertility and increase crop productivity. These practices also sequestered and stored carbon in the soil for centuries, and we show that some ancient sites contain as much carbon as the above-ground rainforest biomass. Our results demonstrate the intentional creation of dark earth and highlight the value of Indigenous knowledge for sustainable rainforest management