146 research outputs found
Alien Registration- Jodrey, Charles E. (Andover, Oxford County)
https://digitalmaine.com/alien_docs/12590/thumbnail.jp
Alien Registration- Jodrey, Clarence H. (Lewiston, Androscoggin County)
https://digitalmaine.com/alien_docs/28831/thumbnail.jp
Is Random Close Packing of Spheres Well Defined?
Despite its long history, there are many fundamental issues concerning random
packings of spheres that remain elusive, including a precise definition of
random close packing (RCP). We argue that the current picture of RCP cannot be
made mathematically precise and support this conclusion via a molecular
dynamics study of hard spheres using the Lubachevsky-Stillinger compression
algorithm. We suggest that this impasse can be broken by introducing the new
concept of a maximally random jammed state, which can be made precise.Comment: 6 pages total, 2 figure
A first-order phase transition at the random close packing of hard spheres
Randomly packing spheres of equal size into a container consistently results
in a static configuration with a density of ~64%. The ubiquity of random close
packing (RCP) rather than the optimal crystalline array at 74% begs the
question of the physical law behind this empirically deduced state. Indeed,
there is no signature of any macroscopic quantity with a discontinuity
associated with the observed packing limit. Here we show that RCP can be
interpreted as a manifestation of a thermodynamic singularity, which defines it
as the "freezing point" in a first-order phase transition between ordered and
disordered packing phases. Despite the athermal nature of granular matter, we
show the thermodynamic character of the transition in that it is accompanied by
sharp discontinuities in volume and entropy. This occurs at a critical
compactivity, which is the intensive variable that plays the role of
temperature in granular matter. Our results predict the experimental conditions
necessary for the formation of a jammed crystal by calculating an analogue of
the "entropy of fusion". This approach is useful since it maps
out-of-equilibrium problems in complex systems onto simpler established
frameworks in statistical mechanics.Comment: 33 pages, 10 figure
Structural transitions in granular packs: statistical mechanics and statistical geometry investigations
We investigate equal spheres packings generated from several experiments and
from a large number of different numerical simulations. The structural
organization of these disordered packings is studied in terms of the network of
common neighbours. This geometrical analysis reveals sharp changes in the
network's clustering occurring at the packing fractions (fraction of volume
occupied by the spheres respect to the total volume, ) corresponding to
the so called Random Loose Packing limit (RLP, ) and Random
Close Packing limit (RCP, ). At these packing fractions we
also observe abrupt changes in the fluctuations of the portion of free volume
around each sphere. We analyze such fluctuations by means of a statistical
mechanics approach and we show that these anomalies are associated to sharp
variations in a generalized thermodynamical variable which is the analogous for
these a-thermal systems to the specific heat in thermal systems.Comment: 7 pages, 6 figure
Combined Molecular Algorithms for the Generation, Equilibration and Topological Analysis of Entangled Polymers: Methodology and Performance
We review the methodology, algorithmic implementation and performance characteristics of a hierarchical modeling scheme for the generation, equilibration and topological analysis of polymer systems at various levels of molecular description: from atomistic polyethylene samples to random packings of freely-jointed chains of tangent hard spheres of uniform size. Our analysis focuses on hitherto less discussed algorithmic details of the implementation of both, the Monte Carlo (MC) procedure for the system generation and equilibration, and a postprocessing step, where we identify the underlying topological structure of the simulated systems in the form of primitive paths. In order to demonstrate our arguments, we study how molecular length and packing density (volume fraction) affect the performance of the MC scheme built around chain-connectivity altering moves. In parallel, we quantify the effect of finite system size, of polydispersity, and of the definition of the number of entanglements (and related entanglement molecular weight) on the results about the primitive path network. Along these lines we approve main concepts which had been previously proposed in the literature
STUDIES ON SHELL FORMATION. III. MEASUREMENT OF CALCIUM DEPOSITION IN SHELL AND CALCIUM TURNOVER IN MANTLE TISSUE USING THE MANTLE-SHELL PREPARATION AND Ca45
Volume: 104Start Page: 398End Page: 40
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