Population Redistribution Research Articles

Dynamic Competition between Catch and Slip Bonds in Selectins Bound to Ligands

Atomic force measurements of unbinding rates (or off-rates) of ligands bound to a class of cell adhesion molecules from the selectin family show a transition from catch to slip bonds as the value of external force (f) is increased. At low forces (<10 pN), the unbinding rates decrease (catch regime), while, at high forces, the rates increase in accord with the Bell model (slip regime). The energy landscape underlying the catch-slip transition can be captured by a two-state model that considers the possibility of redistribution of population from the force-free bound state to the force-stabilized bound state. The excellent agreement between theory and experiments is used to extract the parameters characterizing the energy landscape of the complex by fitting the calculated curves to lifetime data (obtained at constant f) for the monomeric form of PSGL-1 (sPSGL-1). We used the constant force parameters to predict the distributions of unbinding times and unbinding forces as a function of the loading rate. The general two-state model, which also correctly predicts the absence of catch bonds in the binding of antibodies to selectins, is used to resolve the energy landscape parameters characterizing adhesive interactions of P- and L-selectins with physiological ligands such as sPSGL-1 and endoglycan and antibodies such as G1 and DREG56. Despite high sequence similarity, the underlying shapes of the energy landscape of P-selectin and L-selectin interacting with sPSGL-1 are markedly different. The underlying energy landscape of the selectin cell adhesion complex is sensitive to the nature of the ligand. The unified description of selectins bound to physiological ligands and antibodies in conjunction with experimental data can be used to extract the key parameters that describe the dynamics of cell adhesion complexes.

Decentralization of the Nation's Main Street: New Coastal-Proximity-Based Portrayals of Population Distribution in the United States, 1950–2000

Almost half a century has passed since Jean Gottmann coined the term “Megalopolis” in reference to the almost continuously urbanized stretch of land spanning the East Coast of the United States from southern New Hampshire to northern Virginia. Because a disproportionate concentration of population resided in this Megalopolis, the northeastern core enjoyed an economic and cultural supremacy, and he termed the Megalopolis “The Main Street of the Nation.” By the later 1960s and 1970s, however, population migration patterns began to reflect the influence exerted by the emergence of a second national core centered on the large metropolitan areas along the Pacific Coast, especially those of the Los Angeles and Bay Area conurbations in California. Although of different character, this burgeoning concentration of population, economic activity, and cultural influence may reflect the development of a West Coast Megalopolis that could soon rival the original Megalopolis of the Northeastern Corridor. Today, the U.S. population distribution is largely a bicoastal one. This article documents the emergence of this bicoastal population distribution. Using historical census data and GIS technology, we present a number of novel ways to graphically portray and examine this population redistribution phenomenon. The United States is not unique in witnessing an increasing share of its inhabitants clustering in coastal zones. Current critical policy concerns about the worldwide vulnerability of coastal populations have focused the need for better coastal population estimates and better mapping methods for portraying population redistribution trends.

Normal-mode coupling of rare-earth-metal ions in a crystal to a macroscopic optical cavity mode

We demonstrated coupling of rare-earth-metal ions in a crystal to a macroscopic cavity mode by observing optical bistability and normal-mode peaks due to sweeping-laser-induced population redistribution of the ions. The experimentally evaluated coupling constant between the individual ions and the single cavity mode is $15\phantom{\rule{0.3em}{0ex}}\mathrm{kHz}$, which is comparable with or larger than the dissipation of the ions and will exceed the cavity dissipation with a narrowing of the mode waist of the cavity to the wavelength. The results advance the application of a coupled system of rare-earth-metal ions in a crystal and an optical cavity for quantum information processing.

Investigation of KRb and Rb2 formed on cold helium nanodroplets

KRb and Rb2 dimers are formed on cold helium nanodroplets. Laser excitation and emission spectra from the transition (1)3Πg–3Σu+ of Rb2 and the transition (2)3Π–3Σ+ of KRb have been measured. A thorough analysis of the emission, which takes place after desorption of the dimers from the surface of the helium cluster, has been performed. It allows us to determine the redistribution of vibrational population on the droplet surface. A comparison of the experimental spectra with simulations, obtained with the potential energy curves and dipole moments calculated by Aymar and Dulieu, allows a test of the accuracy of the ab initio potentials.

Ionization and plasma formation in high n cold Rydberg samples

The experiments reported here show that the dipole-dipole interaction, the fundamental interaction between the cold Rydberg atoms, is the dominant initial ionization mechanism for evolution from a frozen Rydberg gas into a plasma. The study also indicates that plasma formation follows a path of initial ionization, redistribution of Rydberg population to higher angular momentum states, and rapid avalanche ionization due to electron-Rydberg collisions.

Geografia dos fluxos populacionais segundo níveis de escolaridade dos migrantes

A REESTRUTURAÇÃO produtiva induziu novos contornos na redistribuição espacial das atividades econômicas, que, por sua vez, influencia a redistribuição espacial da população brasileira. Este artigo procura identificar os padrões espaciais dos fluxos migratórios do país, tentando relacioná-los aos novos requisitos locacionais decorrentes da desconcentração da atividade econômica e interurbana. Para tal, foram delimitadas as principais redes migratórias do Brasil, tanto da população mais escolarizada quanto daquela menos escolarizada. As evidências apontam para uma maior regionalização dos fluxos populacionais, principalmente em relação às redes dos migrantes mais escolarizados. Concomitantemente, aqueles movimentos migratórios de mais longa distância, que caracterizavam os períodos de ocupação da fronteira agrícola-mineral e de mão-de-obra com baixa qualificação para as regiões industriais, experimentaram notório enfraquecimento.

On the influence of magnetic fields on level populations

The influence of magnetic fields on the energy level populations of atoms is firstly studied by analysing the Stokes profiles of Fe I 6302.5 forming in the solar magnetized atmosphere, with the aid of a departure factor defined to evaluate the deviation from the normal Boltzmann distribution without a magnetic field. This factor is directly related to the ratio of line-source function to the continuum one. The relationship between the departure and the magnetic field reveals an effect that the magnetic field induces an exponential increase in the level population of the lower level of Fe I 6302.5 (Lande factor g = 2.5) with the field strength. This indicates that the magnetic field can cause the redistribution of populations of those levels whose Land e factors are non-zero. Therefore, this effect should be included in the calculation of the statistical equilibrium. Secondly, an experiment utilizing the Hg5461 line in the laboratory on the Earth is carried out to reveal that the exponential relation is independent of variations in temperature, and the excitation is completely magneto-induced. Finally, the exponential relation is explained by taking account of the magnetic energy in the Boltzmann distribution.

Peri-rural Populations in Search of Territory

In the last 30 years increasing numbers of city dwellers have chosen to go and live in the countryside. This housing migration has led to a social redefinition of country living. It has reinforced the individualisation of lifestyles, thus contributing to a social and spatial redistribution of rural populations. Our article aims to analyse how rural residents of all origins relate to their environment and particularly to the different places they frequent. Concentrating on the material and symbolic investments made by families residing in a village located near Toulouse, we aimed to clarify the processes of territorialisation at play and thus to raise anew question of the relations between city and countryside. E ver since the French population census of 1975, housing migrations of city dwellers to the countryside have consistently increased. This movement can be explained by the fact that rural areas afford people the opportunity of acquiring their own property with a garden ‐ a recreational place for adults and children alike ‐ at a lower cost than in the city. Families maintain that in the countryside they have found an environment close to nature, free from pollution and urban stress, while retaining easy access to urban services, thanks to the improvement of transport infrastructure. These migrations have led to a significant social diversification of the urban exodus, and, consequently, to an important remodelling of the rural areas that have become home to former urban residents (Kayser 1993). Yet this generalisation conceals notable differences between places and between people living in the same place. In view of such complexity, this study aims to understand and describe different types of territoriality by analysing the material, emotional and social relationships that the families develop in their daily living environment (Kaufmann 2004). We chose a socio-anthropological approach, as it enabled us to analyse the diversity of practices and to account for individuals’ relations with each other in face-to-face contacts or social distance from each other. This approach also enabled us to show that such practices are indicators of social relations between families and their neighbourhood, while taking into account the history of the different places and the successive waves of migration to them (Auge 1992). Similarly, spatial mobilities are

Quantum chemical topology description of the hydrogen transfer between the ethynyl radical and ammonia (C 2H [rad] + NH 3) – The electron localization function study

The topological analysis of the Electron Localization Function (ELF) has been carried out for the hydrogen abstraction pathway between ethynyl radical (HCC ) and ammonia (NH 3). The IRC path, minima (HCC⋯HNH 2, HCCH⋯NH 2) and transition structure have been calculated at the UB3LYP/6-311++G(2d, 2p) computational level. The ‘closed-shell’ and ‘spin-polarized’ formula of ELF are used for an analysis. A detailed study of the topology of ELF (the basin population and spin density redistribution) shows that the reaction consists of three main steps distinguished on the IRC path. First, the N–H bond in ammonia is broken, then the hydrogen atom with a population of ca. 0.7 e is transferred and finally the C–H bond in acetylene is formed. It is interesting to note that all chemically important changes occur after the transition state.

Observing angular precession of a Rydberg wave packet due to spin-orbit coupling by orthogonally polarized weak half-cycle pulses

We investigate the response of an $np$ Rydberg wave packet to orthogonally polarized weak half-cycle pulses (HCPs) over the course of its field-free evolution. The population redistribution from $p$ to $s$ states is highly sensitive to the polarization of the HCP and changes with the precession of the electron orbits due to the spin-orbit coupling. We obtain the selection rules and give an intuitive classical interpretation of angular momentum redistribution by a HCP.

Broadband Cavity Ringdown Spectroscopy for Sensitive and Rapid Molecular Detection

We demonstrate highly efficient cavity ringdown spectroscopy in which a broad-bandwidth optical frequency comb is coherently coupled to a high-finesse optical cavity that acts as the sample chamber. 125,000 optical comb components, each coupled into a specific longitudinal cavity mode, undergo ringdown decays when the cavity input is shut off. Sensitive intracavity absorption information is simultaneously available across 100 nanometers in the visible and near-infrared spectral regions. Real-time, quantitative measurements were made of the trace presence, the transition strengths and linewidths, and the population redistributions due to collisions and the temperature changes for molecules such as C2H2, O2, H2O, and NH3.

DETECTING AN ORIENTATION COMPONENT IN ANIMAL PATHS WHEN THE PREFERRED DIRECTION IS INDIVIDUAL-DEPENDENT

An orientation component leads to directionally biased paths, with major consequences in animal population redistribution. Classical orientation analyses, which focus on the overall direction of motion, are useless for detecting such a component when the preferred direction is not common to the whole population, but differs from one path to another. In-depth path analyses are required in this case. They consist of determining whether paths are more suitably represented as biased or unbiased random walks. The answer is not easy because most animals' paths show some forward persistence propensity that acts as a purely local directional bias and, hence, blurs the possible occurrence of an additional, consistent bias in a preferred direction. I highlight the key differences between biased and unbiased random walks and the different ways orientation mechanisms can generate a consistent directional bias. I then examine the strength and weakness of the available methods likely to detect it. Finally, I introduce a new procedure based on the backward evolution of the beeline distance, from the end of the path, which might correspond to a goal toward which the animal orients itself, to each of the animal's preceding locations. This new procedure proves to be very efficient, as it requires only a small sample of short paths for detecting a possible orientation component.

Multiphoton transitions between energy levels in a phase-biased Cooper-pair box

We investigated both theoretically and experimentally dynamic features of a phase-biased charge qubit consisting of a single-Cooper-pair transistor closed by a superconducting loop. The effective inductance of the qubit was probed by a high-quality tank circuit. In the presence of a microwave power, with a frequency of the order of the qubit energy level separation, an alteration of the qubit inductance was observed. We demonstrate that this effect is caused by the redistribution of the qubit level population. The excitation of the qubit by one-, two-, and three-photon processes was detected. Quantitative agreement between theory and experimental data was found.

日本における都市圏の人口規模と都市圏内の人口分布の変動との関係―郊外の多様性に着目した分析―

日本における都市圏の人口規模と都市圏内の人口分布の変動との関係―郊外の多様性に着目した分析―

Changes in number of population, households and population density in Tutin area

The position in the peripheral, mountainous part of Serbia, made Tutin area isolated for a long time. The continual decrease of the number of inhabitants is the result of the weak economic development, of the decrease of the natural growth and emigration. The process of population redistribution is the result of the increase of urban and the decrease of rural population. There is a great number of rural inhabitants, and a great number of small settlements of scattered and spilled type. The changes of population number also influenced the changes of the number of households their structure, as well as the population density. Stopping of the further decrease of population is possible by developing economic branches based on the natural resources of the territory, infrastructure, small economy and tourism.

Expansão urbana nas grandes metrópoles: o significado das migrações intrametropolitanas e da mobilidade pendular na reprodução da pobreza

O objetivo primeiro deste artigo é analisar a simultaneidade do processo de urbanização e de concentração da população urbana nos grandes aglomerados metropolitanos na segunda metade do século passado no Brasil. Como decorrência, também será estudado o processo de redistribuição da população dentro dos aglomerados na perspectiva da metropolização da pobreza, tendo como referência a Região Metropolitana de Belo Horizonte.

Temporal and spatial variation in age-specific net migration in the United States

As fertility differences in the United States diminish, population redistribution trends are increasingly dependent on migration. This research used newly developed county-level age-specific net migration estimates for the 1990s, supplemented with longitudinal age-specific migration data spanning the prior 40 years, to ascertain whether there are clear longitudinal trends in age-specific net migration and to determine if there is spatial clustering in the migration patterns. The analysis confirmed the continuation into the 1990s of distinct net migration "signature patterns" for most types of counties, although there was temporal variation in the overall volume of migration across the five decades. A spatial autocorrelation analysis revealed large, geographically contiguous regions of net in-migration (in particular, Florida and the Southwest) and geographically contiguous regions of net out-migration (the Great Plains, in particular) that persisted over time. Yet the patterns of spatial concentration and fragmentation over time in these migration data demonstrate the relevance of this "neighborhood" approach to understanding spatiotemporal change in migration.

Population distribution and redistribution of the baby-boom cohort in the United States: Recent trends and implications

Over 70 million people were born into the baby-boom cohort between 1946 and 1964. Over 65 million of these individuals are presently alive, and thus the cohort continues to exert a powerful influence on regional population change in the United States. In this article, we examine the recent and current geographic distribution of the baby-boom cohort. In 1990, the members of the cohort comprised a particularly high proportion of the population in a small number of dynamic metropolitan areas. We also highlight the recent migration trends exhibited by this cohort; these trends are potentially important early indicators of the retirement-related migration patterns that the cohort might follow. The spatial redistribution of the cohort has many implications, including potentially significant consequences for intergenerational relationships and caregiving. Also highlighted in the article are the temporal and geographical implications for intergenerational caregiving. There has been much attention given to the "sandwich" generation, with its members having dual caregiving responsibilities to both parents and children. A more appropriate designation may be the "stretched" generation, because caregiving seems to extend over a long period. In particular, many members of the baby-boom cohort are beginning to care for their aging parents just as they finish child rearing.

Post-Socialist Restructuring and Population Redistribution in Hungary*

Abstract This research focuses on pathways by which national level macro-social transformations are transmitted to local communities. Our case is Hungary where we examine the relationship between post-socialist economic restructuring, widespread industrial dislocations, and urban-rural migration. Using secondary data from the Hungarian Central Statistical Office (KSH) and survey data from a study of 49 villages in 4 distinct rural regions, we demonstrate that post-socialist population deconcentration involved both suburbanization and net movement to villages, especially villages that are located relatively close to cities. Contrary to our expectations, movement to villages was from nearby settlements, not from large industrial centers. Moreover, migrants to villages were substantially better off than longer term village residents in terms of their human capital and attachment to the labor force. Consequently, post-socialist population deconcentration is not contributing to rural poverty as feared by some scholars.

Diode laser measurements of the Ar 3p54s1 excited states in an inductively coupled RF plasma

Diode laser absorption spectroscopy has been used to study the four lowest energy excited states of atomic argon (1s2–1s5) arising from the 3p54s1 electronic configuration and produced in an inductively coupled RF discharge. Three of the states (1s2, 1s4 and 1s5) were detected using wavelength modulation spectroscopy with diode laser radiation in the wavelength range 425–430 nm, obtained by frequency doubling the output of a near infrared diode laser in a KNbO3 crystal. The 1s3 state was probed using direct absorption spectroscopy with the fundamental output of a diode laser operating at 795 nm. The 1s5 state dominates the total population of this manifold with a proportion of around 48%, which is essentially independent of plasma power and pressure. Translational temperatures varied with power but were essentially pressure independent. For example, at 20 mTorr total pressure and 400 W applied power, the temperature was found to be 384 ±15 K. The variations in concentrations of all four 1sn states with plasma power and pressure are reported and suggests that a statistical equilibrium between them has been established. The results are rationalized by utilizing a simple kinetic model, to determine the dominant production (electron impact excitation from the ground state) and loss (intra-manifold quenching and radiative decay) processes. Fast redistribution of population in the states, mainly via electron impact excitation to higher lying electronic states and subsequent radiative decay back down, in combination with modified radiative rates for the two radiative states as a consequence of radiation imprisonment, can partially account for the observed relative trends.