2,491 research outputs found
Indentation of ellipsoidal and cylindrical elastic shells
Thin shells are found in nature at scales ranging from viruses to hens’ eggs; the stiffness of such shells is essential for their function. We present the results of numerical simulations and theoretical analyses for the indentation of ellipsoidal and cylindrical elastic shells, considering both pressurized and unpressurized shells. We provide a theoretical foundation for the experimental findings of Lazarus et al. [Phys. Rev. Lett. (submitted)] and for previous work inferring the turgor pressure of bacteria from measurements of their indentation stiffness; we also identify a new regime at large indentation. We show that the indentation stiffness of convex shells is dominated by either the mean or Gaussian curvature of the shell depending on the pressurization and indentation depth. Our results reveal how geometry rules the rigidity of shells
The indentation of pressurized elastic shells: From polymeric capsules to yeast cells
Pressurized elastic capsules arise at scales ranging from the 10 m diameter pressure vessels used to store propane at oil refineries to the microscopic polymeric capsules that may be used in drug delivery. Nature also makes extensive use of pressurized elastic capsules: plant cells, bacteria and fungi have stiff walls, which are subject to an internal turgor pressure. Here we present theoretical, numerical and experimental investigations of the indentation of a linearly elastic shell subject to a constant internal pressure. We show that, unlike unpressurized shells, the relationship between force and displacement demonstrates two linear regimes. We determine analytical expressions for the effective stiffness in each of these regimes in terms of the material properties of the shell and the pressure difference. As a consequence, a single indentation experiment over a range of displacements may be used as a simple assay to determine both the internal pressure and elastic properties of capsules. Our results are relevant for determining the internal pressure in bacterial, fungal or plant cells. As an illustration of this, we apply our results to recent measurements of the stiffness of baker’s yeast and infer from these experiments that the internal osmotic pressure of yeast cells may be regulated in response to changes in the osmotic pressure of the external medium
Wrinkling of pressurized elastic shells
We study the formation of localized structures formed by the point loading of an internally pressurized elastic shell. While unpressurized shells (such as a ping pong ball) buckle into polygonal structures, we show that pressurized shells are subject to a wrinkling instability. We present scaling laws for the critical indentation at which wrinkling occurs and the number of wrinkles formed in terms of the internal pressurization and material properties of the shell. These results are validated by numerical simulations. We show that the evolution of the wrinkle length with increasing indentation can be understood for highly pressurized shells from membrane theory. These results suggest that the position and number of wrinkles may be used in combination to give simple methods for the estimation of the mechanical properties of highly pressurized shells
Triggered qutrits for Quantum Communication protocols
A general protocol in Quantum Information and Communication relies in the
ability of producing, transmitting and reconstructing, in general, qunits. In
this letter we show for the first time the experimental implementation of these
three basic steps on a pure state in a three dimensional space, by means of the
orbital angular momentum of the photons. The reconstruction of the qutrit is
performed with tomographic techniques and a Maximum-Likelihood estimation
method. In this way we also demonstrate that we can perform any transformation
in the three dimensional space
Robust Multi-Partite Multi-Level Quantum Protocols
We present a tripartite three-level state that allows a secret sharing
protocol among the three parties, or a quantum key distribution protocol
between any two parties. The state used in this scheme contains entanglement
even after one system is traced out. We show how to utilize this residual
entanglement for quantum key distribution purposes, and propose a realization
of the scheme using entanglement of orbital angular momentum states of photons.Comment: 9 pages, 2 figure
Experimental Quantum Coin Tossing
In this letter we present the first implementation of a quantum coin tossing
protocol. This protocol belongs to a class of ``two-party'' cryptographic
problems, where the communication partners distrust each other. As with a
number of such two-party protocols, the best implementation of the quantum coin
tossing requires qutrits. In this way, we have also performed the first
complete quantum communication protocol with qutrits. In our experiment the two
partners succeeded to remotely toss a row of coins using photons entangled in
the orbital angular momentum. We also show the experimental bounds of a
possible cheater and the ways of detecting him
Angular Schmidt Modes in Spontaneous Parametric Down-Conversion
We report a proof-of-principle experiment demonstrating that appropriately
chosen set of Hermite-Gaussian modes constitutes a Schmidt decomposition for
transverse momentum states of biphotons generated in the process of spontaneous
parametric down conversion. We experimentally realize projective measurements
in Schmidt basis and observe correlations between appropriate pairs of modes.
We perform tomographical state reconstruction in the Schmidt basis, by direct
measurement of single-photon density matrix eigenvalues.Comment: 5 pages, 4 figure
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