Multispeed cities and the logistics of living in the Information Age

We now have a wealth of data on how the use of information and digital technologies (ICTs) is unevenly mapped onto different income, gender and ethnic groups. However we remain poorly equipped to understand how ICTs, with their intrinsic abilities to transcend barriers of space and time, relate to the fine grain of people’s lives on the ground in cities and neighbourhoods. ICTs contract space in enabling us to contact distant friends, pick up voice mail and order goods. Mobile phones on the move short-circuit time to an instant. But what are the effects of these space and time manipulations on the actual logistics of our interaction with other people? And what does it mean for people and neighbourhoods who do not have access to ICTs to live in a world that is being restructured to suit those who do? This project helps to fill these and allied gaps in our knowledge by simultaneously examining how ICTs relate to social inequalities through their use in orchestrati! ng the social time-space worlds both of a privileged and of a marginalized neighbourhood in Newcastle upon Tyne. Key Findings • Measures of the “digital divide” based on ICT ownership are inadequate to depict the complex patterns of use and access to a variety of technologies. For example, respondents in the poorer area may not have had access to, say, the Internet nor used online services, but they often relied on neighbours, family or friends to provide access. ICT use is often more collective and collaborative, beyond the household level, which suggests some caution over widely used official, individualistic measures. • In the richer area ICTs formed pervasive infrastructures underpinning everyday life, to such an extent that respondents could not say when they specifically used a technology because it was on all the time. In the poorer area, ICT use tended to be for specific purposes, which were recalled as discrete events marked out by their use of advanced technology. • Research on ICTs can profitably use a conceptual framework which emphasises the way in which interactions that do and do not use ICTs inter-relate to shape the detail of subjects’ everyday life. Such an approach allows research to address the ways in which multiple ICTs are used simultaneously and in subtle and continuous combination. • The relaxing of restrictions imposed by time and space that ICTs can give offers new possibilities for structuring the rhythms of daily life. Crucially, this leads not to a disembedding from local life but to forging new interactions within cities. Other Findings • By having ICTs as an “always on” background, affluent and ICT literate groups benefitted from accelerating lifestyles and mobility patterns and are enabled to cram extremely dense and flexible patterns of transaction, communication and information exchange into the logistical framework of their lives. • ICT use in the more marginalized neighbourhood tended to offer occasional support to existing patterns of everyday life. About the Study The project deployed an innovative cascade of methods to establish how ICT- mediated and place-based activities intersect to define together the logistics of everyday life for the affluent Jesmond and a relatively marginalized “off line” Blakelaw neighbourhood in Newcastle upon Tyne

Noise-Activated Escape from a Sloshing Potential Well

We treat the noise-activated escape from a one-dimensional potential well of an overdamped particle, to which a periodic force of fixed frequency is applied. We determine the boundary layer behavior, and the physically relevant length scales, near the oscillating well top. We show how stochastic behavior near the well top generalizes the behavior first determined by Kramers, in the case without forcing. Both the case when the forcing dies away in the weak noise limit, and the case when it does not, are examined. We also discuss the relevance of various scaling regimes to recent optical trap experiments.Comment: 9 pages, no figures, REVTeX, expanded versio

Quantum Energies of Interfaces

We present a method for computing the one-loop, renormalized quantum energies of symmetrical interfaces of arbitrary dimension and codimension using elementary scattering data. Internal consistency requires finite-energy sum rules relating phase shifts to bound state energies.Comment: 8 pages, 1 figure, minor changes, Phys. Rev. Lett., in prin

Mechanisms of degassing at Nevado del Ruiz volcano, Colombia

Author Posting. © Geological Society, 2003. This article is posted here by permission of Geological Society for personal use, not for redistribution. The definitive version was published in Journal of the Geological Society 160 (2003): 507-521, doi:10.1144/0016-764902-028.Nevado del Ruiz volcano is an andesite stratovolcano located in the northern Andes of Colombia. The volcano erupted on 11 September 1985, 13 November 1985, and 1 September 1989. The last two eruptions emitted juvenile solid material. This paper examines the volatile and light lithophile trace element contents of melt inclusions and matrix glasses from this juvenile material, and proposes a model for degassing within the volcano. Major element distributions in the glasses show two evolutionary trends, with subsidiary points that lie between the two trends. The data suggest the existence of two separate magmas, which have interacted, mingled, and mixed during their ascent and eruption. Water contents in melt inclusions, as determined by secondary ionization mass spectrometric analysis, are generally low, averaging between 1.6 and 3.3 wt.%. Halogen concentrations in the glasses range from 400 to 1200 ppm for fluorine and from 1100 to 1500 ppm for chlorine. Sulphur contents are low, not exceeding 500 ppm, with most glasses containing <200 ppm. Lithium concentrations range from 20 to 40 ppm, beryllium from 1.5 to 2 ppm, and boron exhibits high variability from 30 to 100 ppm. The only significant difference between melt inclusions and matrix glasses is for water, with matrix glasses having significantly lower concentrations (<0.5 wt.%) than the melt inclusions. The generally elevated concentrations of boron in the magma may be a consequence of enrichment in the source region of the magma, i.e. by subduction of altered oceanic crust and/or sediments. Yet the large degree of boron heterogeneity in both melt inclusions and matrix glasses necessitates subsequent addition of boron at shallower depths as well, by the assimilation of crustal sedimentary rocks or by interaction with hydrothermal fluids. Evidence for pre-eruptive magma emplacement at shallow levels is provided by (1) anhydrous mineral assemblages of plagioclase and pyroxene, (2) high silica contents of glasses, and (3) low water contents in melt inclusions. When combined, these observations suggest a period of magma residence at shallow depths, probably <3 km beneath the summit of the volcano. A multistage model of magma transport and degassing involves alternating periods of magma ascent and magma ponding. Initially, volatile-bearing magma ascends from depths of 9–15 km, driven by buoyancy. During decompression, the magma loses gas, particularly CO2 and sulphur. The magma eventually ponds at its neutral buoyancy level. At this point, the gas-saturated magma cools and crystallizes, thereby liberating gas under isobaric conditions. As a result, CO2 is depleted from the magma whereas H2O and SiO2 are enriched. The H2O enrichment is caused by its increased solubility in the magma as CO2 is degassed, whereas SiO2 is enriched by fractional crystallization. The density of the magma decreases as the level of dissolved H2O increases, eventually causing the magma to become buoyant once more and to continue its ascent, either to erupt or to freeze at shallow depths.This work was funded with grants to J.S. by the Natural Sciences and Engineering Research Council of Canada and by the Fonds pour la formation de chercheurs et l’aide a` la recherche (Que´bec)

Coarse-grained simulations of flow-induced nucleation in semi-crystalline polymers

We perform kinetic Monte Carlo simulations of flow-induced nucleation in polymer melts with an algorithm that is tractable even at low undercooling. The configuration of the non-crystallized chains under flow is computed with a recent non-linear tube model. Our simulations predict both enhanced nucleation and the growth of shish-like elongated nuclei for sufficiently fast flows. The simulations predict several experimental phenomena and theoretically justify a previously empirical result for the flow-enhanced nucleation rate. The simulations are highly pertinent to both the fundamental understanding and process modeling of flow-induced crystallization in polymer melts.Comment: 17 pages, 6 eps figure

Inertial Range Scaling, Karman-Howarth Theorem and Intermittency for Forced and Decaying Lagrangian Averaged MHD in 2D

We present an extension of the Karman-Howarth theorem to the Lagrangian averaged magnetohydrodynamic (LAMHD-alpha) equations. The scaling laws resulting as a corollary of this theorem are studied in numerical simulations, as well as the scaling of the longitudinal structure function exponents indicative of intermittency. Numerical simulations for a magnetic Prandtl number equal to unity are presented both for freely decaying and for forced two dimensional MHD turbulence, solving directly the MHD equations, and employing the LAMHD-alpha equations at 1/2 and 1/4 resolution. Linear scaling of the third-order structure function with length is observed. The LAMHD-alpha equations also capture the anomalous scaling of the longitudinal structure function exponents up to order 8.Comment: 34 pages, 7 figures author institution addresses added magnetic Prandtl number stated clearl

The Signature of Primordial Grain Growth in the Polarized Light of the AU Mic Debris Disk

We have used the Hubble Space Telescope/ACS coronagraph to make polarization maps of the AU Mic debris disk. The fractional linear polarization rises monotonically from about 0.05 to 0.4 between 20 and 80 AU. The polarization is perpendicular to the disk, indicating that the scattered light originates from micron sized grains in an optically thin disk. Disk models, which simultaneously fit the surface brightness and polarization, show that the inner disk (< 40-50 AU) is depleted of micron-sized dust by a factor of more than 300, which means that the disk is collision dominated. The grains have high maximum linear polarization and strong forward scattering. Spherical grains composed of conventional materials cannot reproduce these optical properties. A Mie/Maxwell-Garnett analysis implicates highly porous (91-94%) particles. In the inner Solar System, porous particles form in cometary dust, where the sublimation of ices leaves a "bird's nest" of refractory organic and silicate material. In AU Mic, the grain porosity may be primordial, because the dust "birth ring" lies beyond the ice sublimation point. The observed porosities span the range of values implied by laboratory studies of particle coagulation by ballistic cluster-cluster aggregation. To avoid compactification, the upper size limit for the parent bodies is in the decimeter range, in agreement with theoretical predictions based on collisional lifetime arguments. Consequently, AU Mic may exhibit the signature of the primordial agglomeration process whereby interstellar grains first assembled to form macroscopic objects.Comment: 12 pages, 8 figures, ApJ, in pres

Systematics of the Relationship between Vacuum Energy Calculations and Heat Kernel Coefficients

Casimir energy is a nonlocal effect; its magnitude cannot be deduced from heat kernel expansions, even those including the integrated boundary terms. On the other hand, it is known that the divergent terms in the regularized (but not yet renormalized) total vacuum energy are associated with the heat kernel coefficients. Here a recent study of the relations among the eigenvalue density, the heat kernel, and the integral kernel of the operator $e^{-t\sqrt{H}}$ is exploited to characterize this association completely. Various previously isolated observations about the structure of the regularized energy emerge naturally. For over 20 years controversies have persisted stemming from the fact that certain (presumably physically meaningful) terms in the renormalized vacuum energy density in the interior of a cavity become singular at the boundary and correlate to certain divergent terms in the regularized total energy. The point of view of the present paper promises to help resolve these issues.Comment: 19 pages, RevTeX; Discussion section rewritten in response to referees' comments, references added, minor typos correcte