31 research outputs found
Topological phonon modes in filamentous structures
Topological phonon modes are robust vibrations localized at the edges of
special structures. Their existence is determined by the bulk properties of the
structures and, as such, the topological phonon modes are stable to changes
occurring at the edges. The first class of topological phonons was recently
found in 2-dimensional structures similar to that of Microtubules. The present
work introduces another class of topological phonons, this time occurring in
quasi one-dimensional filamentous structures with inversion symmetry. The
phenomenon is exemplified using a structure inspired from that of actin
Microfilaments, present in most live cells. The system discussed here is
probably the simplest structure that supports topological phonon modes, a fact
that allows detailed analysis in both time and frequency domains. We advance
the hypothesis that the topological phonon modes are ubiquitous in the
biological world and that living organisms make use of them during various
processes.Comment: accepted for publication (Phys. Rev. E
Dimension-Free Empirical Entropy Estimation
We seek an entropy estimator for discrete distributions with fully empirical
accuracy bounds. As stated, this goal is infeasible without some prior
assumptions on the distribution. We discover that a certain information moment
assumption renders the problem feasible. We argue that the moment assumption is
natural and, in some sense, {\em minimalistic} -- weaker than finite support or
tail decay conditions. Under the moment assumption, we provide the first
finite-sample entropy estimates for infinite alphabets, nearly recovering the
known minimax rates. Moreover, we demonstrate that our empirical bounds are
significantly sharper than the state-of-the-art bounds, for various natural
distributions and non-trivial sample regimes. Along the way, we give a
dimension-free analogue of the Cover-Thomas result on entropy continuity (with
respect to total variation distance) for finite alphabets, which may be of
independent interest. Additionally, we resolve all of the open problems posed
by J\"urgensen and Matthews, 2010
Inducing isotropic growth in multidimensional cesium lead halide perovskite nanocrystals
A new twoâstep synthetic protocol to yield monodisperse spherical zeroâdimensional (0D) Cs4PbX6 nanocrystals (NCs) and threeâdimensional (3D) CsPbX3 NCs is described. The first step of the reaction involves the colloidal synthesis of spherical PbX2 seed NCs, which are subsequently converted to Cs4PbX6 and CsPbX3 NCs through hot injection of a Cs precursor at the desired reaction temperatures. By employing less reactive Pb and halide precursors, the reaction time was extended from several seconds to about five minutes, thereby allowing greater control during the crystallization and growth stages. The adjustment of halide ratios allows color tuning over a wide spectral range (411â669â
nm) for CsPbX3 NCs, with high photoluminescence quantum yields (6â65â%) and narrow emission line widths (ca. 13â30â
nm). We envisage our spherical NCs to become a starting point for shell growth (e.g., ZnS, CdS, PbS) by overcoming the difficulty of shell growth around thermodynamically unfavorable (i.e., high surface free energy) cuboidâshaped NCs.NRF (Natl Research Foundation, Sâpore)MOE (Min. of Education, Sâpore