138 research outputs found
Statistical mechanics of thin spherical shells
We explore how thermal fluctuations affect the mechanics of thin amorphous
spherical shells. In flat membranes with a shear modulus, thermal fluctuations
increase the bending rigidity and reduce the in-plane elastic moduli in a
scale-dependent fashion. This is still true for spherical shells. However, the
additional coupling between the shell curvature, the local in-plane stretching
modes and the local out-of-plane undulations, leads to novel phenomena. In
spherical shells thermal fluctuations produce a radius-dependent negative
effective surface tension, equivalent to applying an inward external pressure.
By adapting renormalization group calculations to allow for a spherical
background curvature, we show that while small spherical shells are stable,
sufficiently large shells are crushed by this thermally generated "pressure".
Such shells can be stabilized by an outward osmotic pressure, but the effective
shell size grows non-linearly with increasing outward pressure, with the same
universal power law exponent that characterizes the response of fluctuating
flat membranes to a uniform tension.Comment: 16 pages, 6 figure
Phase behavior and morphology of multicomponent liquid mixtures
Multicomponent systems are ubiquitous in nature and industry. While the
physics of few-component liquid mixtures (i.e., binary and ternary ones) is
well-understood and routinely taught in undergraduate courses, the
thermodynamic and kinetic properties of -component mixtures with have
remained relatively unexplored. An example of such a mixture is provided by the
intracellular fluid, in which protein-rich droplets phase separate into
distinct membraneless organelles. In this work, we investigate equilibrium
phase behavior and morphology of -component liquid mixtures within the
Flory-Huggins theory of regular solutions. In order to determine the number of
coexisting phases and their compositions, we developed a new algorithm for
constructing complete phase diagrams, based on numerical convexification of the
discretized free energy landscape. Together with a Cahn-Hilliard approach for
kinetics, we employ this method to study mixtures with and
components. We report on both the coarsening behavior of such systems, as well
as the resulting morphologies in three spatial dimensions. We discuss how the
number of coexisting phases and their compositions can be extracted with
Principal Component Analysis (PCA) and K-Means clustering algorithms. Finally,
we discuss how one can reverse engineer the interaction parameters and volume
fractions of components in order to achieve a range of desired packing
structures, such as nested `Russian dolls' and encapsulated Janus droplets.Comment: 16 pages, 11 figures + hyperlinks to 7 video
Thermal Excitations of Warped Membranes
We explore thermal fluctuations of thin planar membranes with a frozen spatially varying background metric and a shear modulus. We focus on a special class of D-dimensional “warped membranes” embedded in a d-dimensional space with d≥D+1 and a preferred height profile characterized by quenched random Gaussian variables , , in Fourier space with zero mean and a power-law variance . The case D=2, d=3, with could be realized by flash-polymerizing lyotropic smectic liquid crystals. For the elastic constants are nontrivially renormalized and become scale dependent. Via a self-consistent screening approximation we find that the renormalized bending rigidity increases for small wave vectors q as , while the in-hyperplane elastic constants decrease according to . The quenched background metric is relevant (irrelevant) for warped membranes characterized by exponent , where is the scaling exponent for tethered surfaces with a flat background metric, and the scaling exponents are related through .Molecular and Cellular BiologyPhysic
Mechanical Properties of Warped Membranes
We explore how a frozen background metric affects the mechanical properties of planar membranes with a shear modulus. We focus on a special class of “warped membranes” with a preferred random height profile characterized by random Gaussian variables h(q) in Fourier space with zero mean and variance and show that in the linear response regime the mechanical properties depend dramatically on the system size L for . Membranes with could be produced by flash polymerization of lyotropic smectic liquid crystals. Via a self-consistent screening approximation we find that the renormalized bending rigidity increases as for membranes of size L, while the Young and shear moduli decrease according to resulting in a universal Poisson ratio. Numerical results show good agreement with analytically determined exponents.Molecular and Cellular BiologyPhysic
Grundy dominating sequences and zero forcing sets
In a graph a sequence of vertices is Grundy
dominating if for all we have and is Grundy total dominating if for all
we have .
The length of the longest Grundy (total) dominating sequence has
been studied by several authors. In this paper we introduce two
similar concepts when the requirement on the neighborhoods is
changed to or
. In the former case we
establish a strong connection to the zero forcing number of a graph,
while we determine the complexity of the decision problem in the
latter case. We also study the relationships among the four
concepts, and discuss their computational complexities
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