185 research outputs found
Length scale dependence of dynamical heterogeneity in a colloidal fractal gel
We use time-resolved dynamic light scattering to investigate the slow
dynamics of a colloidal gel. The final decay of the average intensity
autocorrelation function is well described by , with and
decreasing from 1.5 to 1 with increasing . We show that the dynamics is not
due to a continuous ballistic process, as proposed in previous works, but
rather to rare, intermittent rearrangements. We quantify the dynamical
fluctuations resulting from intermittency by means of the variance
of the instantaneous autocorrelation function, the analogous of
the dynamical susceptibility studied in glass formers. The amplitude
of is found to grow linearly with . We propose a simple --yet
general-- model of intermittent dynamics that accounts for the dependence
of both the average correlation functions and .Comment: Revised and improved, to appear in Europhys. Let
Unexpected spatial distribution of bubble rearrangements in coarsening foams
Foams are ideal model systems to study stress-driven dynamics, as
stress-imbalances within the system are continuously generated by the
coarsening process, which unlike thermal fluctuations, can be conveniently
quantified by optical means. However, the high turbidity of foams generally
hinders the detailed study of the temporal and spatial distribution of
rearrangement events, such that definite assessments regarding their
contribution to the overall dynamics could not be made so far. In this paper,
we use novel light scattering techniques to measure the frequency and position
of events within a large sample volume. As recently reported (A. S. Gittings
and D. J. Durian, Phys. Rev. E, 2008, 78, 066313), we find that the foam
dynamics is determined by two distinct processes: intermittent bubble
rearrangements of finite duration and a spatially homogeneous quasicontinuous
process. Our experiments show that the convolution of these two processes
determines the age-dependence of the mean dynamics, such that relations between
intermittent rearrangements and coarsening process can not be established by
considering means. By contrast the use of the recently introduced photon
correlation imaging technique (A. Duri, D. A. Sessoms, V. Trappe, and L.
Cipelletti, Phys. Rev. Lett., 2009, 102, 085702) enables us to assess that the
event frequency is directly determined by the strain-rate imposed by the
coarsening process. Surprisingly, we also find that, although the distribution
of successive events in time is consistent with a random process, the spatial
distribution of successive events is not random: rearrangements are more likely
to occur within a recently rearranged zone. This implies that a topological
rearrangement is likely to lead to an unstable configuration, such that a small
amount of coarsening-induced strain is sufficient to trigger another event
Analisis Rasio untuk Pengukuran Kinerja Keuangan dan Evaluasi Kinerja Keuangan Pemerintah (Studi Kasus Pemerintah Kota Jayapura)
Penelitian ini bertujuan untuk mengetahui kinerja keuangan Pemerintah Kota Jayapura pada tahun 2011 s/d 2017 untuk mengevaluasi kinerja keuangan Pemerintah Kota Jayapura yang dapat menjadi evaluasi untuk meningkatkan kinerja keuangan Pemerintah Kota Jayapura.Berdasarkan hasil Analisis ratio keuangan diperoleh Kontribusi PAD terhadap Penerimaan daerah Kota Jayapura menunjukkan bahwa semakin tinggi kontribusi PAD rata-rata ratio derajat desentralisasi dari tahun 2011s/d 2017 adalah sebesar 11,56 persen. Namun masih dalam kategori rendah sekali. Rasio ketergantungan Pemerintah Kota Jayapura terhadap Pemerintah Pusat semakin menurun tetapi masih dalam kategori tinggi karena masih dominannya pendapatan transfer pusat dalam pendapatan daerah . Rasio kemandirian daerah maka menunjukkan bahwa rasio kemandirian masih rendah sekali dan perlu ada upaya yang dilakukan oleh Pemerintah Kota Jayapura untuk meningkatkan kemandiriannya terhadap penerimaan transfer pusat..Rasio Efektifitas menunjukkan realisasi PAD Kota Jayapura pada tahun 2011 s/d 2017 menunjukkan hasil sangat efektif karena pencapaian realisasi PAD diatas target yang ditetapkan. Rasio efisiensi pemerintah Kota Jayapura masuk dalam kriteria Efisien karena perbandingan antara biaya pemungutan PAD dan realisasi penerimaan PAD tahun 2011 s/d 2017 sebesar 3,21 persen yang masuk dalam kategori Efisien. Kontribusi yang diperoleh dari penerimaan BUMD masih tergolong kecil terhadap Total Penerimaan daerah. Penelitian ini diharapkan Sebagai bahan evaluasi kinerja keuangan bagi Pemerintah Kota Jayapura untuk terus meningkatkan kinerja keuangannya antara lain mengurangi ketergantungan pada transfer pusat dan meningkatkan kemandirian daerah terhadap pemerintah pusat
Unexpected drop of dynamical heterogeneities in colloidal suspensions approaching the jamming transition
As the glass (in molecular fluids\cite{Donth}) or the jamming (in colloids
and grains\cite{LiuNature1998}) transitions are approached, the dynamics slow
down dramatically with no marked structural changes. Dynamical heterogeneity
(DH) plays a crucial role: structural relaxation occurs through correlated
rearrangements of particle ``blobs'' of size
\cite{WeeksScience2000,DauchotPRL2005,Glotzer,Ediger}. On approaching
these transitions, grows in glass-formers\cite{Glotzer,Ediger},
colloids\cite{WeeksScience2000,BerthierScience2005}, and driven granular
materials\cite{KeysNaturePhys2007} alike, strengthening the analogies between
the glass and the jamming transitions. However, little is known yet on the
behavior of DH very close to dynamical arrest. Here, we measure in colloids the
maximum of a ``dynamical susceptibility'', , whose growth is usually
associated to that of \cite{LacevicPRE}. initially increases with
volume fraction , as in\cite{KeysNaturePhys2007}, but strikingly drops
dramatically very close to jamming. We show that this unexpected behavior
results from the competition between the growth of and the reduced
particle displacements associated with rearrangements in very dense
suspensions, unveiling a richer-than-expected scenario.Comment: 1st version originally submitted to Nature Physics. See the Nature
Physics website fro the final, published versio
Resolving long-range spatial correlations in jammed colloidal systems using photon correlation imaging
We introduce a new dynamic light scattering method, termed photon correlation
imaging, which enables us to resolve the dynamics of soft matter in space and
time. We demonstrate photon correlation imaging by investigating the slow
dynamics of a quasi two-dimensional coarsening foam made of highly packed,
deformable bubbles and a rigid gel network formed by dilute, attractive
colloidal particles. We find the dynamics of both systems to be determined by
intermittent rearrangement events. For the foam, the rearrangements extend over
a few bubbles, but a small dynamical correlation is observed up to macroscopic
length scales. For the gel, dynamical correlations extend up to the system
size. These results indicate that dynamical correlations can be extremely
long-ranged in jammed systems and point to the key role of mechanical
properties in determining their nature.Comment: Published version (Phys. Rev. Lett. 102, 085702 (2009)) The Dynamical
Activity Mapsprovided as Supplementary Online Material are also available on
http://w3.lcvn.univ-montp2.fr/~lucacip/dam/movies.ht
Mars Regolith Simulant Ameliorated by Compost as In Situ Cultivation Substrate Improves Lettuce Growth and Nutritional Aspects
Heavy payloads in future shuttle journeys to Mars present limiting factors, making self-sustenance essential for future colonies. Therefore, in situ resources utilization (ISRU) is the path to successful and feasible space voyages. This research frames the concept of planting leafy vegetables on Mars regolith simulant, ameliorating this substrate’s fertility by the addition of organic residues produced in situ. For this purpose, two butterhead lettuce (Lactuca sativa L. var. capitata) cultivars (green and red Salanova®) were chosen to be cultivated in four dierent mixtures of MMS-1 Mojave Mars simulant:compost (0:100, 30:70, 70:30 and 100:0; v:v) in a phytotron open gas exchange growth chamber. The impact of compost rate on both crop performance and the nutritive value of green- and red-pigmented cultivars was assessed. The 30:70 mixture proved to be optimal in terms of crop performance, photosynthetic activity, intrinsic water use eciency and quality traits of lettuce. In particular, red Salanova® showed the best performance in terms of these quality traits, registering 32% more phenolic content in comparison to 100% simulant. Nonetheless, the 70:30 mixture represents a more realistic scenario when taking into consideration the sustainable use of compost as a limited resource in space farming, while still accepting a slight significant decline in yield and quality in comparison to the 30:70 mixture
Ultra-long range correlations of the dynamics of jammed soft matter
We use Photon Correlation Imaging, a recently introduced space-resolved
dynamic light scattering method, to investigate the spatial correlation of the
dynamics of a variety of jammed and glassy soft materials. Strikingly, we find
that in deeply jammed soft materials spatial correlations of the dynamics are
quite generally ultra-long ranged, extending up to the system size, orders of
magnitude larger than any relevant structural length scale, such as the
particle size, or the mesh size for colloidal gel systems. This has to be
contrasted with the case of molecular, colloidal and granular ``supercooled''
fluids, where spatial correlations of the dynamics extend over a few particles
at most. Our findings suggest that ultra long range spatial correlations in the
dynamics of a system are directly related to the origin of elasticity. While
solid-like systems with entropic elasticity exhibit very moderate correlations,
systems with enthalpic elasticity exhibit ultra-long range correlations due to
the effective transmission of strains throughout the contact network.Comment: To appear in Soft Matte
On the rigidity of a hard sphere glass near random close packing
We study theoretically and numerically the microscopic cause of the
mechanical stability of hard sphere glasses near their maximum packing. We show
that, after coarse-graining over time, the hard sphere interaction can be
described by an effective potential which is exactly logarithmic at the random
close packing . This allows to define normal modes, and to apply recent
results valid for elastic networks: mechanical stability is a non-local
property of the packing geometry, and is characterized by some length scale
which diverges at [1, 2]. We compute the scaling of the bulk and
shear moduli near , and speculate on the possible implications of these
results for the glass transition.Comment: 7 pages, 4 figures. Figure 4 had a wrong unit in abscissa, which was
correcte
Dynamic heterogeneities in attractive colloids
We study the formation of a colloidal gel by means of Molecular Dynamics
simulations of a model for colloidal suspensions. A slowing down with gel-like
features is observed at low temperatures and low volume fractions, due to the
formation of persistent structures. We show that at low volume fraction the
dynamic susceptibility, which describes dynamic heterogeneities, exhibits a
large plateau, dominated by clusters of long living bonds. At higher volume
fraction, where the effect of the crowding of the particles starts to be
present, it crosses over towards a regime characterized by a peak. We introduce
a suitable mean cluster size of clusters of monomers connected by "persistent"
bonds which well describes the dynamic susceptibility.Comment: 4 pages, 4 figure
Heterogeneous Dynamics, Marginal Stability and Soft Modes in Hard Sphere Glasses
In a recent publication we established an analogy between the free energy of
a hard sphere system and the energy of an elastic network [1]. This result
enables one to study the free energy landscape of hard spheres, in particular
to define normal modes. In this Letter we use these tools to analyze the
activated transitions between meta-bassins, both in the aging regime deep in
the glass phase and near the glass transition. We observe numerically that
structural relaxation occurs mostly along a very small number of
nearly-unstable extended modes. This number decays for denser packing and is
significantly lowered as the system undergoes the glass transition. This
observation supports that structural relaxation and marginal modes share common
properties. In particular theoretical results [2, 3] show that these modes
extend at least on some length scale where
corresponds to the maximum packing fraction, i.e. the jamming
transition. This prediction is consistent with very recent numerical
observations of sheared systems near the jamming threshold [4], where a similar
exponent is found, and with the commonly observed growth of the rearranging
regions with compression near the glass transition.Comment: 6 pages, improved versio
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