1,484 research outputs found
Crystallisation in a granular material
The athermal and dissipative nature of packings of grains is still challenging our understanding of their compaction
as well as their crystallisation. For instance, some beads poured in a container get jammed in random disordered con gurations,
which cannot be denser than 64%, the random closed packing (RCP) limit. Remarkably it has been suggested that the
RCP bound is saturated with dense patterns of beads aggregated into polytetrahedral structures. Yet when a suitable vibration
is applied, a packing of beads might start to order and some regular patterns appear.
We present new experiments on the crystallisation of the packing of beads. By extending tapping techniques, we have
obtained packings with volume fractions Ï ranging from the RCP to the crystal (Ï = 0.74). Computing tomography has been
used to scan the internal structure of large packings (â200,000 beads). Voronoi and Delaunay space partitions on the grain
centres were performed to characterise the structural rearrangements during the crystallisation. This allows us to describe
statistical properties of the local volume uctuations and the evolution of the densest patterns of beads.
In terms of statistical description, a parameter based on the volume uctuations discloses different regimes during the
transition. In terms of geometry, we con rm that polytetrahedral dense clusters are ubiquitous at the RCP. We describe some
intrinsic features of these clusters such as rings of tetrahedra and show how they disappear as the crystal grows.
This experiment enlightens how an athermal system jammed in a complex frustrated con guration is gradually converted
into a periodic crystal
Current State of Strain in the Central Cascadia Margin Derived from Changes in Distance between GPS Stations
Using continuously operating Global Positioning Stations in the Pacific Northwest of the United States, over 100 station-station baseline length changes were determined along seven West-East transects, two North-South transects and in three localized areas to determine both the average annual strains over the past several years, and the variation in strain over the central Cascadia convergent margin. The North-South transects (composed of multiple baselines) show shortening. Along West-East transects some baselines show shortening and others extension. The direction of the principle strains calculated for two areas 100 km from the deformation front are close to per-pendicular to the deformation front. The North-South strains are 10?8 a?1, which is an order-of-magnitude less than the West-East strains (10?7 a?1). Along several West-East transects, the magnitude of the strain increases away from the deformation front. All West-East transects showed a change in strain 250 km inland from deformation front
Proximal Records of Paleotsunami Runup in Barrage Creek Floodplains from Late-Holocene Great Earthquakes in the Central Cascadia Suduction Zone, Oregon, USA
Tholins as Coloring Agents on Outer Solar System Bodies
The red colors of many solid bodies in outer Solar System may be caused by tholins, which are refractory organic complexes, incorporated in their surface materials. Tholins synthesized in the laboratory are shown to match the colors of these bodies when their optical properties are used in rigorous scattering models. We review recent successes in modeling the spectra of icy outer Solar System bodies with tholins as the coloring agents. New work on the systematic laboratory synthesis and analysis of tholins made by cold plasma discharge in mixtures of gaseous CH4/N2 shows that the composition of the tholin depends strongly on the pressure in the reaction chamber, and only weakly on the mixing fraction of CH4 relative to N2. In tholins made at high pressure (e.g., 23 hPa) the abundance of aliphatic hydrocarbons is greater and the abundance of aromatic hydrocarbons is less than in tholins made at low pressure (e.g., 0.13 hPa). Tholins made at low deposition pressures show a greater abundance of N-H bonds
The Spectrum of Pluto, 0.40 - 0.93 m I. Secular and longitudinal distribution of ices and complex organics
Context. During the last 30 years the surface of Pluto has been
characterized, and its variability has been monitored, through continuous
near-infrared spectroscopic observations. But in the visible range only few
data are available. Aims. The aim of this work is to define the Pluto's
relative reflectance in the visible range to characterize the different
components of its surface, and to provide ground based observations in support
of the New Horizons mission. Methods. We observed Pluto on six nights between
May and July 2014, with the imager/spectrograph ACAM at the William Herschel
Telescope (La Palma, Spain). The six spectra obtained cover a whole rotation of
Pluto (Prot = 6.4 days). For all the spectra we computed the spectral slope and
the depth of the absorption bands of methane ice between 0.62 and 0.90 m.
To search for shifts of the center of the methane bands, associated with
dilution of CH4 in N2, we compared the bands with reflectances of pure methane
ice. Results. All the new spectra show the methane ice absorption bands between
0.62 and 0.90 m. The computation of the depth of the band at 0.62 m
in the new spectra of Pluto, and in the spectra of Makemake and Eris from the
literature, allowed us to estimate the Lambert coefficient at this wavelength,
at a temperature of 30 K and 40 K, never measured before. All the detected
bands are blue shifted, with minimum shifts in correspondence with the regions
where the abundance of methane is higher. This could be indicative of a
dilution of CH4:N2 more saturated in CH4. The longitudinal and secular
variations of the parameters measured in the spectra are in accordance with
results previously reported in the literature and with the distribution of the
dark and bright material that show the Pluto's albedo maps from New Horizons.Comment: This manuscript may change and improve during the reviewing process.
The data reduction and calibration is reliable and has been checked
independently using different reduction approaches. The data will be made
publicily available when the paper is accepted. If you need them before,
please, contact the autho
Secular evolution of a satellite by tidal effect. Application to Triton
Some of the satellites in the Solar System, including the Moon, appear to
have been captured from heliocentric orbits at some point in their past, and
then have evolved to the present configurations. The exact process of how this
trapping occurred is unknown, but the dissociation of a planetesimal binary in
the gravitational field of the planet, gas drag, or a massive collision seem to
be the best candidates. However, all these mechanisms leave the satellites in
elliptical orbits that need to be damped to the present almost circular ones.
Here we give a complete description of the secular tidal evolution of a
satellite just after entering a bounding state with the planet. In particular,
we take into account the spin evolution of the satellite, which has often been
assumed synchronous in previous studies. We apply our model to Triton and
successfully explain some geophysical properties of this satellite, as well as
the main dynamical features observed for the Neptunian system.Comment: 4 pages, 1 figur
The paradox of tenant empowerment: regulatory and liberatory possibilities
Tenant empowerment has traditionally been regarded as a means of realising democratic ideals: a quantitative increase in influence and control, which thereby enables "subjects" to acquire the fundamental properties of "citizens". By contrast governmentality, as derived from the work of Michel Foucault, offers a more critical appraisal of the concept of empowerment by highlighting how it is itself a mode of subjection and a means of regulating human conduct towards particular ends. Drawing on particular data about how housing governance has changed in Glasgow following its 2003 stock transfer, this paper adopts the insights of governmentality to illustrate how the political ambition of "community ownership" has been realized through the mobilization and shaping of active tenant involvement in the local decision making process. In addition, it also traces the tensions and conflict inherent in the reconfiguration of power relations post-transfer for "subjects" do not necessarily conform to the plans of those that seek to govern them
Post-Foucauldian governmentality: what does it offer critical social policy analysis?
This article considers the theoretical perspective of post-Foucauldian governmentality, especially the insights and challenges it poses for applied researchers within the critical social policy tradition. The article firstly examines the analytical strengths of this approach to understanding power and rule in contemporary society, before moving on to consider its limitations for social policy. It concludes by arguing that these insights can be retained, and some of the weaknesses overcome, by adopting a ârealist governmentalityâ approach (Stenson 2005, 2008). This advocates combining traditional discursive analysis with more ethnographic methods in order to render visible the concrete activity of governing, and unravel the messiness, complexity and unintended consequences involved in the struggles around subjectivity
Fatally Flawed? : Discursive Evidence from the Movement to Establish Lesbian Studies Programs
While related areas such as Queer Studies and Sexuality Studies have become established as disciplinary formations in North American and British universities, Lesbian Studies has not. This article reports on an analysis of key publications by critics and advocates of Lesbian Studies to explore the possibility that Lesbian Studies was flawed in ways that account for its non-emergence. Charges against Lesbian Studies include naĂŻve essentialism, white middle-classness, separatism, and paranoia. Discourse analysis of books by Lesbian Studies advocates examines evidence of each of these qualities and concludes that Lesbian Studies was above all too lesbian to be successfully integrated into the enduringly heteropatriarchal institution of universities.University of Winnipeghttp://journals.sagepub.com/doi/10.1177/095935351037018
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