11,222 research outputs found
Dynamical behavior of a complex fluid near an out-of-equilibrium transition: approaching simple rheological chaos
We report here an extensive study of sustained oscillations of the viscosity
of a complex fluid near an out-of-equilibrium transition. Using well defined
protocols, we perform rheological measurements of the onion texture near a
layering transition in a Couette flow. This complex fluid exhibits sustained
oscillations of the viscosity, on a large time scale (500s) at controlled
stress. These oscillations are directly correlated to an oscillating
microstrutural change of the texture of the fluid. We observe a great diversity
of dynamical behavior and we show that there is a coupling with spatial effects
in the gradient v direction. This is in agreement with a carefull analysis of
the temporal series of the viscosity with the dynamical system theory. This
analysis indicates that the observed dynamical responses do not strictly
correspond to 3-dimensional chaotic states, probably because some
spatio-temporal effects are present and are likely to play an important role.Comment: submitted to Phys. Rev.
Investigation of Metal and Organic Contaminant Distributions and Sedimentation Rates in Backwater Lakes along the Illinois River
Systematic sub-sampling of sediment cores in sections of uniform thickness is necessary
in order to evaluate historic changes in sediment quality, to determine the vertical extent
of contamination, and to measure sedimentation rates. With these objectives in mind,
fourteen sediment cores were collected during March 2002 using the Illinois State Water
Survey vibracorer. Concentrations of metals and total organic carbon were measured
using standard techniques. Concentrations of chlorinated pesticides, phenolic compounds,
polycyclic aromatic hydrocarbons (PAHs), and polychlorinated biphenyls (PCBs) were
measured by gas chromatography/mass spectrometry (GC-MS). The concentrations of
chlorinated pesticides, phenolic compounds and polychlorinated biphenyls (PCBs) were
below the method detection limit in all sediment samples analyzed. However, there was
a wide range in concentrations of polycyclic aromatic hydrocarbons (PAHs) which were
detected in all sediment samples. Also, a wide range of metal concentrations was noted
in the sediments evaluated. Lower concentrations of metals were found in the upper 0.5
m of sediment but concentrations were elevated at depths ranging from 1.0 m to 1.5 m.
Sedimentation rates were estimated using cesium-137 radiometric dating on 14
vibracores. Sedimentation rates range from < 0.1 to 1.9 cm/yr, with an average of 0.9
cm/yr. These rates are comparable to those reported in previous studies.Illinois Sustainable Technology Centerpublished or submitted for publicationis peer reviewe
Maintaining efficiency while integrating entrants from lower-performing groups: an experimental study
Efficiently growing a group or firm often requires integration of individuals from lower-performing entities. We explore the effectiveness of two policies intended to facilitate such integration, using a laboratory experiment that models production as a coordination game with Pareto-ranked equilibria. We initially create an efficient group and an inefficient one. We then allow individuals to move into the high-performing group and vary by treatment whether movement is unrestricted, limited to one entrant per period, or subject to an entry exam. We include two additional treatments that combine the two restrictions in different ways to help understand why the institutions are effective in maintaining coordination. We find that both restrictions work to maintain efficient coordination but they are effective for different reasons.Growth, entry, coordination, experiments
CLEAR: Covariant LEAst-square Re-fitting with applications to image restoration
In this paper, we propose a new framework to remove parts of the systematic
errors affecting popular restoration algorithms, with a special focus for image
processing tasks. Generalizing ideas that emerged for regularization,
we develop an approach re-fitting the results of standard methods towards the
input data. Total variation regularizations and non-local means are special
cases of interest. We identify important covariant information that should be
preserved by the re-fitting method, and emphasize the importance of preserving
the Jacobian (w.r.t. the observed signal) of the original estimator. Then, we
provide an approach that has a "twicing" flavor and allows re-fitting the
restored signal by adding back a local affine transformation of the residual
term. We illustrate the benefits of our method on numerical simulations for
image restoration tasks
Mobilizing Public Will For Social Change
Examines the theory and strategies of "public will" campaigns and offers tangible criteria for their evaluation. It provides a rich inventory of strategies for use in mobilizing the public will through an integration of models of agenda building, social problem construction, issues management, social movements, media advocacy, and social capital. In addition, the paper provides cases and examples of public will campaigns directed at various social problems, along with criteria for evaluating these campaigns at various stages of a social problem's life cycle
Asteroseismology of Massive Stars : Some Words of Caution
Although playing a key role in the understanding of the supernova phenomenon,
the evolution of massive stars still suffers from uncertainties in their
structure, even during their "quiet" main sequence phase and later on during
their subgiant and helium burning phases. What is the extent of the mixed
central region? In the local mixing length theory (LMLT) frame, are there
structural differences using Schwarzschild or Ledoux convection criterion?
Where are located the convective zone boundaries? Are there intermediate
convection zones during MS and post-MS phase, and what is their extent and
location? We discuss these points and show how asteroseismology could bring
some light on these questions.Comment: 10 pages, 5 figures, IAU Symposium 307, New windows on massive stars:
asteroseismology, interferometry, and spectropolarimetry, G. Meynet, C.
Georgy, J.H. Groh & Ph. Stee, ed
Can an underestimation of opacity explain B-type pulsators in the SMC?
Slowly Pulsating B and Cephei are mechanism driven pulsating
B stars. That mechanism works since a peak in the opacity due to a
high number of atomic transitions from iron-group elements occurs in the area
of . Theoretical results predict very few SPBs and no
Cep to be encountered in low metallicity environments such as the Small
Magellanic Cloud. However recent variability surveys of B stars in the SMC
reported the detection of a significant number of SPB and Cep
candidates. Though the iron content plays a major role in the excitation of
Cep and SPB pulsations, the chemical mixture representative of the SMC
B stars such as recently derived does not leave room for a significant increase
of the iron abundance in these stars. Whilst abundance of iron-group elements
seems reliable, is the opacity in the iron-group elements bump underestimated?
We determine how the opacity profile in B-type stars should change to excite
SPB and Cep pulsations in early-type stars of the SMC.Comment: 5 pages, 7 figures, to appear under electronic form in : Proceedings
of the 4th HELAS International Conference: Seismological Challenges for
Stellar Structur
Intermediate range chemical ordering of cations in simple molten alkali halides
The presence of first sharp diffraction peaks in the partial structure
factors is investigated in computer simulations of molten mixtures of alkali
halides. An intermediate range ordering appears for the Li+ ions only, which is
associated with clustering of this species and is not reflected in the
arrangement of other ions. This ordering is surprising in view of the
simplicity of the interionic interactions in alkali halides. The clustering
reflects an incomplete mixing of the various species on a local length scale,
which can be demonstrated by studying the complementary sub-space of cations in
the corresponding pure alkali halides by means of a void analysis.Comment: 5 pages, 5 figure
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