The Pleiotropic Effects of Beneficial Mutations of Adapted Escherichia coli Populations

Mutations that improve fitness in one environment can often be beneficial, deleterious, or neutral in alternative environments. When a single mutation effects fitness in multiple environments, it is said to be a pleiotropic, which can have important consequences for niche specialization, niche expansion, speciation, and even extinction in the face of environmental change. While previous studies have revealed that pleiotropy is nearly universal, the role of adaptive history in the spectrum of pleiotropic effects has yet to undergo detailed experimental observation. Using experimental evolution we gathered beneficial mutations in a previously adapted strain of Escherichia coli growing in the same common substrate over hundreds of generations. We then tested the effects of these mutations in multiple alternative environments and compared their fitness to the ancestor. We found that the magnitude of the effects correlates positively with the similarity of resources to glucose, indicating that selective history has an influence in the distribution of beneficial mutations. These findings broaden our understanding of the effects of history on pleiotropy, and may provide answers into how evolution in a constant environment influences ecological niche formation and constraint

Origami building blocks: generic and special 4-vertices

Four rigid panels connected by hinges that meet at a point form a 4-vertex, the fundamental building block of origami metamaterials. Here we show how the geometry of 4-vertices, given by the sector angles of each plate, affects their folding behavior. For generic vertices, we distinguish three vertex types and two subtypes. We establish relationships based on the relative sizes of the sector angles to determine which folds can fully close and the possible mountain-valley assignments. Next, we consider what occurs when sector angles or sums thereof are set equal, which results in 16 special vertex types. One of these, flat-foldable vertices, has been studied extensively, but we show that a wide variety of qualitatively different folding motions exist for the other 15 special and 3 generic types. Our work establishes a straightforward set of rules for understanding the folding motion of both generic and special 4-vertices and serves as a roadmap for designing origami metamaterials.Comment: 8 pages, 9 figure

Cross-Correlating Probes of Primordial Gravitational Waves

One of the most promising ways of detecting primordial gravitational waves generated during inflation is to observe B-modes of polarization, generated by Thomson scattering after reionization, in the cosmic microwave background (CMB). Large scale foregrounds though are expected to be a major systematic issue, so -- in the event of a tentative detection -- an independent confirmation of large scale gravitational waves would be most welcome. Previous authors have suggested searching for the analogous mode of cosmic shear in weak lensing surveys but have shown that the signal to noise of this mode is marginal at best. This argument is reconsidered here, accounting for the cross-correlations of the polarization and lensing B-modes. A lensing survey can potentially strengthen the argument for a detection of primordial gravitational waves, although it is unlikely to help constrain the amplitude of the signal.Comment: 13 pages, 8 figure

Addressing Function Approximation Error in Actor-Critic Methods

In value-based reinforcement learning methods such as deep Q-learning, function approximation errors are known to lead to overestimated value estimates and suboptimal policies. We show that this problem persists in an actor-critic setting and propose novel mechanisms to minimize its effects on both the actor and the critic. Our algorithm builds on Double Q-learning, by taking the minimum value between a pair of critics to limit overestimation. We draw the connection between target networks and overestimation bias, and suggest delaying policy updates to reduce per-update error and further improve performance. We evaluate our method on the suite of OpenAI gym tasks, outperforming the state of the art in every environment tested.Comment: Accepted at ICML 201

A Computable General Equilibrium (CGE) Analysis of the Impact of an Oil Price Increase in South Africa

Following recent international oil price increases, there has been considerable interest in how this external factor can affect the South African economy. This paper reports results from a computable general equilibrium (CGE) analysis of an increase (up to 30 per cent) in international oil prices. Background information is provided, which puts the magnitude of the price variations in historical context. We describe the procedure used to adjust the social accounting matrix (SAM), which is used to calibrate the model, to account explicitly for crude oil. Then, the effects of the crude oil price increase are traced through the economy, from markets, industries through to factors, households and the government. Predictably, the shock hurts the economy: a 20 per cent increase results in a drop in GDP of 1 per cent. It is found that the major impact is to be found in the petroleum industry itself, whereas the effects on liquid fuel dependent industries such as transport is not as large as may be supposed. In agriculture, it is found that the depreciating currency has a positive effect, offsetting most of the negative effects of higher petroleum prices, particularly in export-oriented areas. In a long-term scenario, capital and skilled labour becomes mobile, and the results suggest that such reallocation may not be to the overall advantage of the economy.Resource /Energy Economics and Policy,

A fully dynamical simulation of central nuclear collisions

We present a fully dynamical simulation of central nuclear collisions around mid-rapidity at LHC energies. Unlike previous treatments, we simulate all phases of the collision, including the equilibration of the system. For the simulation, we use numerical relativity solutions to AdS/CFT for the pre-equilibrium stage, viscous hydrodynamics for the plasma equilibrium stage and kinetic theory for the low density hadronic stage. Our pre-equilibrium stage provides initial conditions for hydrodynamics, resulting in sizable radial flow. The resulting light particle spectra reproduce the measurements from the ALICE experiment at all transverse momenta.Comment: 4 pages, 6 figures; v2: minor changes; v3: major changes, including a new section comparing to free streaming, matches published versio

Coupled-mode analysis of fiber-optic add drop filters for dense wavelength-division multiplexing

We present a coupled-mode theory of fiber-optic add drop filters, which involve directional coupling between two fibers combined with fiber Bragg gratings defined inside the coupling region. The analysis self-consistently accounts for both the directional and the reflection coupling, and the propagation constants and structure of the supermodes of the combined structure are derived. We present a detailed analysis of a filter design based on identical fibers. The calculated device parameters satisfy the requirements for dense wavelength-division multiplexing applications

CCi digital futures 2014: the Internet in Australia

This report presents findings from the third survey of the Australian component of the World Internet Project. The survey was conducted in late 2013. This research is a project of the ARC Centre of Excellence for Creative Industries and Innovation at the Swinburne Institute for Social Research, Swinburne University of Technology. This report provides an overview of the study, presenting a broad picture of the Internet in Australia, with comparisons to our earlier 2007, 2009 and 2013 studies, and to the international findings of our partners in the World Internet Project. At the end of each section we have added some further analysis, examining aspects of the Australian data in more detail, and providing some international context using results from the findings of our international research partners. &nbsp

On the proof of some theorem on locally nilpotent subgroups in division rings

In Hai-Thin (2009), there is a theorem, stating that every locally nilpotent subnormal subgroup in a division ring $D$ is central (see Hai-Thin (2009, Th. 2.2)). Unfortunately, there is some mistake in the proof of this theorem. In this note we give the another proof of this theorem.Comment: 3 page