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We present the results of two 2.3 μm near-infrared (NIR) radial velocity (RV) surveys to detect exoplanets around 36 nearby and young M dwarfs. We use the CSHELL spectrograph (R ~ 46,000) at the NASA InfraRed Telescope Facility (IRTF), combined with an isotopic methane absorption gas cell for common optical path relative wavelength calibration. We have developed a sophisticated RV forward modeling code that accounts for fringing and other instrumental artifacts present in the spectra. With a spectral grasp of only 5 nm, we are able to reach long-term radial velocity dispersions of ~20–30 m s−1 on our survey targets.
Growth kinetics, mechanisms, and material quality in GaN epitaxial lateral over-growth (ELO) were examined using a single mask of systematically varied patterns. A 2-D gas phase reaction/diffusion model describes how transport of the Ga precursor to the growth surface enhances the lateral rate in the early stages of growth. In agreement with SEM studies of truncated growth runs, the model also predicts the dramatic decrease in the lateral rate that occurs as GaN over-growth reduces the exposed area of the mask. At the point of convergence, a step-flow coalescence mechanism is observed to fill in the area between lateral growth-fronts. This alternative growth mode in which a secondary growth of GaN is nucleated along a single convergence line, may be responsible for producing smooth films observed to have uniform cathodoluminescence (CL) when using 1μm nucleation zones. Although emission is comprised of both UV (∼365nm) and yellow (∼550nm) components, the spectra suggest these films have reduced concentrations of threading dislocations normally associated with non-radiative recombination centers and defects known to accompany growth-front convergence lines.
We report the growth and characterization of quaternary AlGaInN. A combination of photoluminescence (PL), high-resolution x-ray diffraction (XRD), and Rutherford backscattering spectrometry (RBS) characterizations enables us to explore the contours of constant- PL peak energy and lattice parameter as functions of the quaternary compositions. The observation of room temperature PL emission at 351nm (with 20% Al and 5% In) renders initial evidence that the quaternary could be used to provide confinement for GaInN (and possibly GaN). AlGaInN/GaInN MQW heterostructures have been grown; both XRD and PL measurements suggest the possibility of incorporating this quaternary into optoelectronic devices.
We are all products of human migration. Some of us migrated during our lifetimes from one part of the world to another, and had to learn different cultures, languages, diets, and systems of education. Others have parents who were forcibly relocated at different times, particularly during World War II and its sequelae, and experienced displaced persons camps, disease, and violence, and were uprooted to various corners of the world, such as the Americas and Australia. Yet others have ancestors who migrated hundreds or thousands of years ago and have lived in relatively undisturbed households for many generations. Finally, some people originated in Africa and migrated within the continent or were forcibly relocated by wars and the slave trade.
The authors of this volume are migrants and describe the human condition from their unique migratory experiences. Each author has a complex personal history of migration, often occurring in different generations, cultural traditions, and languages. All of the authors currently residing in the Americas are either recent migrants or have descended from ancestors who relocated to the Americas generations ago. Several of the authors have experienced extensive migration and relocation within their lifetimes, as the following examples show.
With its rich archaeological and historical record, Peru offers an exceptional opportunity for the study of human migration. While Amazonia comprises nearly 60% of the country’s national territory, most studies of Peru’s human populations have emphasized the Andean highlands. The selva baja, or lowland tropical forested region of Peru’s Lower Huallaga Valley, is particularly important for genetic studies on migration. A geographically significant crossroads of migration, the Lower Huallaga Valley is characterized by its degree of ethnic diversity among both indigenous and immigrant populations. Despite centuries of colonization, many contemporary indigenous societies reside in the selva baja region surrounding the city of Yurimaguas, including: Quechua-speaking populations (Kichwa Lamista, Kichwa del Pastaza); Jibaroan speakers (Achuar, Awajun, Kandozi, Wampis, and Jibaro); Tupi-Guarani speakers (Kukama-Kukamira); Cahuapanan speakers (Shawi and Shiwilu); Arawakan speakers (Chamicuro); and the Urarina (linguistic isolate).
In light of the region’s recent pattern of urbanization, this study evaluates the genetic consequences of migration using mitochondrial DNA (mtDNA) to characterize the maternal genetic structure of residents of the “new urban settlements” (or barriadas) enveloping Yurimaguas, one of the selva baja’s principal cities (Dean and Silverstein, 2011). Maternal markers were used to infer prominent source population and/or pattern of migration into the provincial capital city of Yurimaguas by comparing the focus sample with others from South America. By estimating the proportion of non-native maternal admixture and establishing estimates of a past population reduction we provide novel insights for understanding the effects of human migration in the Lower Huallaga Valley.
Migration has a deep history, dating back to the very origins of our species. An evolutionary perspective suggests that an activity as deeply rooted and ubiquitous as migration must be imbedded in our human nature and genes. Thus, the social and cultural factors involved in migration are intertwined within our human biology. Not only are ecological factors such as climate important in the economic push/pull factors that social scientists consider to underlie decisions about migration, but there may be individual variation in our genomes that lead to a propensity to migrating in the first place (see the chapter by Ben Campbell and Lindsay Barone on the variation in dopamine receptors and its association with migration out of Africa).
Furthermore, far from being simply the bearer of ideas and institutions, as sociologists might have it, or job skills and economic goods as the economists may emphasize, migrants represent bodies that carry an imprint of their original surroundings. These include the transmission of disease vectors as well as physiological and behavioral traits that can influence chronic diseases, especially metabolic conditions associated with eating and activity and mental illness (see the chapter by M. J. Mosher on potential epigenetic effects associated with dietary changes in migrant populations). These imprints also include more behavioral and evolutionary factors such as fertility and fecundity patterns that have important demographic consequences in the migrant’s new home.
Migration is a widespread human activity dating back to the origin of our species. Advances in genetic sequencing have greatly increased our ability to track prehistoric and historic population movements and allowed migration to be described both as a biological and socioeconomic process. Presenting the latest research, Causes and Consequences of Human Migration provides an evolutionary perspective on human migration past and present. Crawford and Campbell have brought together leading thinkers who provide examples from different world regions, using historical, demographic and genetic methodologies, and integrating archaeological, genetic and historical evidence to reconstruct large-scale population movements in each region. Other chapters discuss established questions such as the Basque origins and the Caribbean slave trade. More recent evidence on migration in ancient and present day Mexico is also presented. Pitched at a graduate audience, this book will appeal to anyone with an interest in human population movements.
This chapter provides a broad overview of migration, its history and causes, as well as its geographic and genetic influences on two human groups living in radically different areas of the world – the Caribbean and Aleutian Islands. Prehistoric colonization and settlement by both Garifuna and Aleuts, severely disrupted by forced relocation from outside (British, Russian, or American) during the eighteenth and nineteenth centuries, resulted in substantial cultural and genetic transformations in both groups. The Garifuna forced migration stimulated a unique evolutionary success story along the coast of Central America, while the Aleut populations experienced highly asymmetric patterns of gene flow from Russian colonists and Scandinavian and British fishermen.
What is migration?
Migration is the relocation of people from one geographical region of the world to another region. Movements of culturally and/or linguistically homogeneous migrants were traditionally termed diasporas (Brubaker, 2005). For example, the dispersion of Jews from the Middle East into Babylonia in the sixth century BC, followed by further migrations into Europe and Asia, has been characterized as the Jewish diaspora. The terminology was further broadened to include other forced movements and population relocations, such as the African diaspora (Alpers, 2001). These migrations result in the fission of the parental populations, founder effects, reproductive isolation, exposure of genomes to new environments, and gene flow – if the region was previously inhabited.