U.S. agriculture: challenges for the twenty-first century

Agriculture ; Farm produce ; Exports

Design and Implementation of an IP based authentication mechanism for Open Source Proxy Servers in Interception Mode

Proxy servers are being increasingly deployed at organizations for performance benefits; however, there still exists drawbacks in ease of client authentication in interception proxy mode mainly for Open Source Proxy Servers. Technically, an interception mode is not designed for client authentication, but implementation in certain organizations does require this feature. In this paper, we focus on the World Wide Web, highlight the existing transparent proxy authentication mechanisms, its drawbacks and propose an authentication scheme for transparent proxy users by using external scripts based on the clients Internet Protocol Address. This authentication mechanism has been implemented and verified on Squid-one of the most widely used HTTP Open Source Proxy Server.Comment: 11 pages, Authenticating Clients in Transparent/ Interception Mode, Squid Proxy Serve

Phylogenetic mixtures on a single tree can mimic a tree of another topology

Phylogenetic mixtures model the inhomogeneous molecular evolution commonly observed in data. The performance of phylogenetic reconstruction methods where the underlying data is generated by a mixture model has stimulated considerable recent debate. Much of the controversy stems from simulations of mixture model data on a given tree topology for which reconstruction algorithms output a tree of a different topology; these findings were held up to show the shortcomings of particular tree reconstruction methods. In so doing, the underlying assumption was that mixture model data on one topology can be distinguished from data evolved on an unmixed tree of another topology given enough data and the ``correct'' method. Here we show that this assumption can be false. For biologists our results imply that, for example, the combined data from two genes whose phylogenetic trees differ only in terms of branch lengths can perfectly fit a tree of a different topology

Thermal diffusivity and chaos in metals without quasiparticles

We study the thermal diffusivity $D_T$ in models of metals without quasiparticle excitations (`strange metals'). The many-body quantum chaos and transport properties of such metals can be efficiently described by a holographic representation in a gravitational theory in an emergent curved spacetime with an additional spatial dimension. We find that at generic infra-red fixed points $D_T$ is always related to parameters characterizing many-body quantum chaos: the butterfly velocity $v_B$, and Lyapunov time $\tau_L$ through $D_T \sim v_B^2 \tau_L$. The relationship holds independently of the charge density, periodic potential strength or magnetic field at the fixed point. The generality of this result follows from the observation that the thermal conductivity of strange metals depends only on the metric near the horizon of a black hole in the emergent spacetime, and is otherwise insensitive to the profile of any matter fields.Comment: 27 page