Inspection of fine wires simplified by capillary tube wire holder

Capillary tube wire holder provides a mount for fine wires for photomicrographs. The holder is mounted in a stainless steel tube and cast in a transparent casting material. It protects and permits easy location of the wire

Self-scaled barriers for irreducible symmetric cones

Self-scaled barrier functions are fundamental objects in the theory of interior-point methods for linear optimization over symmetric cones, of which linear and semidefinite programming are special cases. We are classifying all self-scaled barriers over irreducible symmetric cones and show that these functions are merely homothetic transformations of the universal barrier function. Together with a decomposition theorem for self-scaled barriers this concludes the algebraic classification theory of these functions. After introducing the reader to the concepts relevant to the problem and tracing the history of the subject, we start by deriving our result from first principles in the important special case of semidefinite programming. We then generalise these arguments to irreducible symmetric cones by invoking results from the theory of Euclidean Jordan algebras.Comment: 12 page

Simultaneous Perturbation Algorithms for Batch Off-Policy Search

We propose novel policy search algorithms in the context of off-policy, batch mode reinforcement learning (RL) with continuous state and action spaces. Given a batch collection of trajectories, we perform off-line policy evaluation using an algorithm similar to that by [Fonteneau et al., 2010]. Using this Monte-Carlo like policy evaluator, we perform policy search in a class of parameterized policies. We propose both first order policy gradient and second order policy Newton algorithms. All our algorithms incorporate simultaneous perturbation estimates for the gradient as well as the Hessian of the cost-to-go vector, since the latter is unknown and only biased estimates are available. We demonstrate their practicality on a simple 1-dimensional continuous state space problem

Landscape Predictions from Cosmological Vacuum Selection

In BP models with hundreds of fluxes, we compute the effects of cosmological dynamics on the probability distribution of landscape vacua. Starting from generic initial conditions, we find that most fluxes are dynamically driven into a different and much narrower range of values than expected from landscape statistics alone. Hence, cosmological evolution will access only a tiny fraction of the vacua with small cosmological constant. This leads to a host of sharp predictions. Unlike other approaches to eternal inflation, the holographic measure employed here does not lead to "staggering", an excessive spread of probabilities that would doom the string landscape as a solution to the cosmological constant problem.Comment: 15 pages, 6 figures, v4 prd format, minor editin

Tensor Microwave Background Fluctuations for Large Multipole Order

We present approximate formulas for the tensor BB, EE, TT, and TE multipole coefficients for large multipole order l. The error in using the approximate formula for the BB multipole coefficients is less than cosmic variance for l>10. These approximate formulas make various qualitative properties of the calculated multipole coefficients transparent: specifically, they show that, whatever values are chosen for cosmological parameters, the tensor EE multipole coefficients will always be larger than the BB coefficients for all l>15, and that these coefficients will approach each other for l<<100. These approximations also make clear how these multipole coefficients depend on cosmological parameters.Comment: 19 pages, 9 figures, accepted for publication in Phys. Rev. D, references and comments on earlier work on the subject added, cosmetic modification of figure

Adhesion between a viscoelastic material and a solid surface

In this paper, we present a qualitative analysis of the dissipative processes during the failure of the interface between a viscoelastic polymer and a solid surface. We reassess the "viscoelastic trumpet" model [P.-G. de Gennes, C. R. Acad. Sci. Paris, 307, 1949 (1988)], and show that, for a crosslinked polymer, the interface toughness G(V) starts from a relatively low value, G_0, due to local processes near the fracture tip, and rises up to a maximum of order $G_0 (\mu_{\infty}/\mu_0)$ (where $\mu_0$ and $\mu_{\infty}$ stand for the elastic modulus of the material, respectively at low and high strain frequencies). This enhancement of fracture energy is due to far-field viscous dissipation in the bulk material, and begins for peel-rates V much lower than previously thought. For a polymer melt, the adhesion energy is predicted to scale as 1/V. In the second part of this paper, we compare some of our theoretical predictions with experimental results about the viscoelastic adhesion between a polydimethylsiloxane polymer melt and a glass surface. In particular, the expected dependence of the fracture energy versus separation rate is confirmed by the experimental data, and the observed changes in the concavity of the crack profile are in good agreement with our simple model.Comment: Revised version to appear in Macromolecule

Dewetting on porous media with aspiration

We consider a porous solid covered with a water film (or with a drop) in situations where the liquid is pumped in, either spontaneously (if the porous medium is hydrophilic) or mechanically (by an external pump). The dynamics of dewetting is then strongly modified. We analyse a few major examples: a) horizontal films, which break at a certain critical thickness, b) the "modified Landau-Levich problem" where a porous plate moves up from a bath and carries a film: aspiration towards the plate limits the height H reached by the film, c) certain situation where the hysteresis of contact angles is important.Comment: Revised version: The analysis of the 'modified Landau-Levich problem' (section 3) has been significantly revised. It is now treated as a singular perturbation problem (using boundary-layer techniques), leading to a more accurate physical pictur