1,284 research outputs found
Novel Features Arising in the Maximally Random Jammed Packings of Superballs
Dense random packings of hard particles are useful models of granular media
and are closely related to the structure of nonequilibrium low-temperature
amorphous phases of matter. Most work has been done for random jammed packings
of spheres, and it is only recently that corresponding packings of nonspherical
particles (e.g., ellipsoids) have received attention. Here we report a study of
the maximally random jammed (MRJ) packings of binary superdisks and
monodispersed superballs whose shapes are defined by |x_1|^2p+...+|x_2|^2p<=1
with d = 2 and 3, respectively, where p is the deformation parameter with
values in the interval (0, infinity). We find that the MRJ densities of such
packings increase dramatically and nonanalytically as one moves away from the
circular-disk and sphere point. Moreover, the disordered packings are
hypostatic and the local arrangements of particles are necessarily nontrivially
correlated to achieve jamming. We term such correlated structures "nongeneric".
The degree of "nongenericity" of the packings is quantitatively characterized
by determining the fraction of local coordination structures in which the
central particles have fewer contacting neighbors than average. We also show
that such seemingly special packing configurations are counterintuitively not
rare. As the anisotropy of the particles increases, the fraction of rattlers
decreases while the minimal orientational order increases. These novel
characteristics result from the unique rotational symmetry breaking manner of
the particles.Comment: 20 pages, 8 figure
Controlling the Short-Range Order and Packing Densities of Many-Particle Systems
Questions surrounding the spatial disposition of particles in various
condensed-matter systems continue to pose many theoretical challenges. This
paper explores the geometric availability of amorphous many-particle
configurations that conform to a given pair correlation function g(r). Such a
study is required to observe the basic constraints of non-negativity for g(r)
as well as for its structure factor S(k). The hard sphere case receives special
attention, to help identify what qualitative features play significant roles in
determining upper limits to maximum amorphous packing densities. For that
purpose, a five-parameter test family of g's has been considered, which
incorporates the known features of core exclusion, contact pairs, and damped
oscillatory short-range order beyond contact. Numerical optimization over this
five-parameter set produces a maximum-packing value for the fraction of covered
volume, and about 5.8 for the mean contact number, both of which are within the
range of previous experimental and simulational packing results. However, the
corresponding maximum-density g(r) and S(k) display some unexpected
characteristics. A byproduct of our investigation is a lower bound on the
maximum density for random sphere packings in dimensions, which is sharper
than a well-known lower bound for regular lattice packings for d >= 3.Comment: Appeared in Journal of Physical Chemistry B, vol. 106, 8354 (2002).
Note Errata for the journal article concerning typographical errors in Eq.
(11) can be found at http://cherrypit.princeton.edu/papers.html However, the
current draft on Cond-Mat (posted on August 8, 2002) is correct
Hyperuniformity, quasi-long-range correlations, and void-space constraints in maximally random jammed particle packings. II. Anisotropy in particle shape
We extend the results from the first part of this series of two papers by
examining hyperuniformity in heterogeneous media composed of impenetrable
anisotropic inclusions. Specifically, we consider maximally random jammed
packings of hard ellipses and superdisks and show that these systems both
possess vanishing infinite-wavelength local-volume-fraction fluctuations and
quasi-long-range pair correlations. Our results suggest a strong generalization
of a conjecture by Torquato and Stillinger [Phys. Rev. E. 68, 041113 (2003)],
namely that all strictly jammed saturated packings of hard particles, including
those with size- and shape-distributions, are hyperuniform with signature
quasi-long-range correlations. We show that our arguments concerning the
constrained distribution of the void space in MRJ packings directly extend to
hard ellipse and superdisk packings, thereby providing a direct structural
explanation for the appearance of hyperuniformity and quasi-long-range
correlations in these systems. Additionally, we examine general heterogeneous
media with anisotropic inclusions and show for the first time that one can
decorate a periodic point pattern to obtain a hard-particle system that is not
hyperuniform with respect to local-volume-fraction fluctuations. This apparent
discrepancy can also be rationalized by appealing to the irregular distribution
of the void space arising from the anisotropic shapes of the particles. Our
work suggests the intriguing possibility that the MRJ states of hard particles
share certain universal features independent of the local properties of the
packings, including the packing fraction and average contact number per
particle.Comment: 29 pages, 9 figure
Hyperuniformity and its Generalizations
Disordered many-particle hyperuniform systems are exotic amorphous states
characterized by anomalous suppression of large-scale density fluctuations.
Here we substantially broaden the hyperuniformity concept along four different
directions. This includes generalizations to treat fluctuations in the
interfacial area in heterogeneous media and surface-area driven evolving
microstructures, random scalar fields, divergence-free random vector fields, as
well as statistically anisotropic many-particle systems and two-phase media.
Interfacial-area fluctuations play a major role in characterizing the
microstructure of two-phase systems , physical properties that intimately
depend on the geometry of the interface, and evolving two-phase microstructures
that depend on interfacial energies (e.g., spinodal decomposition). In the
instances of divergence-free random vector fields and statistically anisotropic
structures, we show that the standard definition of hyperuniformity must be
generalized such that it accounts for the dependence of the relevant spectral
functions on the direction in which the origin in Fourier space
(nonanalyticities at the origin). Using this analysis, we place some well-known
energy spectra from the theory of isotropic turbulence in the context of this
generalization of hyperuniformity. We show that there exist many-particle
ground-state configurations in which directional hyperuniformity imparts exotic
anisotropic physical properties (e.g., elastic, optical and acoustic
characteristics) to these states of matter. Such tunablity could have
technological relevance for manipulating light and sound waves in ways
heretofore not thought possible. We show that disordered many-particle systems
that respond to external fields (e.g., magnetic and electric fields) are a
natural class of materials to look for directional hyperuniformity.Comment: In pres
Robust Algorithm to Generate a Diverse Class of Dense Disordered and Ordered Sphere Packings via Linear Programming
We have formulated the problem of generating periodic dense paritcle packings
as an optimization problem called the Adaptive Shrinking Cell (ASC) formulation
[S. Torquato and Y. Jiao, Phys. Rev. E {\bf 80}, 041104 (2009)]. Because the
objective function and impenetrability constraints can be exactly linearized
for sphere packings with a size distribution in -dimensional Euclidean space
, it is most suitable and natural to solve the corresponding ASC
optimization problem using sequential linear programming (SLP) techniques. We
implement an SLP solution to produce robustly a wide spectrum of jammed sphere
packings in for and with a diversity of disorder
and densities up to the maximally densities. This deterministic algorithm can
produce a broad range of inherent structures besides the usual disordered ones
with very small computational cost by tuning the radius of the {\it influence
sphere}. In three dimensions, we show that it can produce with high probability
a variety of strictly jammed packings with a packing density anywhere in the
wide range . We also apply the algorithm to generate various
disordered packings as well as the maximally dense packings for
and 6. Compared to the LS procedure, our SLP protocol is able to ensure that
the final packings are truly jammed, produces disordered jammed packings with
anomalously low densities, and is appreciably more robust and computationally
faster at generating maximally dense packings, especially as the space
dimension increases.Comment: 34 pages, 6 figure
Basic Understanding of Condensed Phases of Matter via Packing Models
Packing problems have been a source of fascination for millenia and their
study has produced a rich literature that spans numerous disciplines.
Investigations of hard-particle packing models have provided basic insights
into the structure and bulk properties of condensed phases of matter, including
low-temperature states (e.g., molecular and colloidal liquids, crystals and
glasses), multiphase heterogeneous media, granular media, and biological
systems. The densest packings are of great interest in pure mathematics,
including discrete geometry and number theory. This perspective reviews
pertinent theoretical and computational literature concerning the equilibrium,
metastable and nonequilibrium packings of hard-particle packings in various
Euclidean space dimensions. In the case of jammed packings, emphasis will be
placed on the "geometric-structure" approach, which provides a powerful and
unified means to quantitatively characterize individual packings via jamming
categories and "order" maps. It incorporates extremal jammed states, including
the densest packings, maximally random jammed states, and lowest-density jammed
structures. Packings of identical spheres, spheres with a size distribution,
and nonspherical particles are also surveyed. We close this review by
identifying challenges and open questions for future research.Comment: 33 pages, 20 figures, Invited "Perspective" submitted to the Journal
of Chemical Physics. arXiv admin note: text overlap with arXiv:1008.298
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