Finding the Limitations of the Expanded Equivalent Fluid Approximation For Simulating Acoustic Interactions With the Ocean Bottom

Equivalent fluids use complex densities in place of realistic seafloor conditions to simplify simulations of acoustic interaction with the seafloor. This eliminates the computationally intensive attempts to simulate realistic seafloor interactions that include shear waves. A previous method used such equivalent fluids and was found to be accurate only for interaction with low grazing angles and low shear speeds. The current method expands by also parameterizing the speed of sound in the fluid, allowing higher grazing angles and shear speeds to be modeled with equivalent fluids. For a particular window of grazing angle, there are several approaches to determining the complex density and the fluid\u27s speed of sound using this Expanded Equivalent Fluid. By calculating statistics and comparing acoustic simulation results, the approach that most accurately mimics the actual seafloor and the highest window of grazing angle at which the fluid yields respectable results are investigated

National science agency - university collaboration inspires an inquiry-oriented experiment

An initiative involving the University of Technology, Sydney (UTS) and Australia's premier science agency, the Commonwealth Scientific and Industrial Research Agency (CSIRO), connects first year students in a large enrolment physics service subject to research of national standing through a co-developed inquiry-oriented experiment. We describe the background to the initiative which we believe to be the first of its kind, how it was piloted, and our findings from the first running of the experiment with enrolled students. The initiative applies a previously published framework for designing and evaluating new and existing experiments with regard to student engagement and learning, laboratory logistics, and scale. Evidence from focus groups, student surveys, and classroom observations indicates that the experiment is regarded by students as: 1) a worthwhile, very valuable or outstanding learning experience; 2) engaging; and 3) benefitting their learning through group discussions. Student feedback during the development phase highlighted issues to be addressed, including allowing students greater time to design and carry out their own investigations, more explicit assistance for students in the use of supporting technology, and better guidance on the assessed component of the experiment

Accelerated aging-related transcriptome changes in the female prefrontal cortex

Human female life expectancy is higher than that of males. Intriguingly, it has been reported that women display faster rates of age-related cognitive decline and a higher prevalence of Alzheimers disease (AD). To assess the molecular bases of these contradictory trends, we analyzed differences in expression changes with age between adult males and females, in four brain regions. In the superior frontal gyrus (SFG), a part of the prefrontal cortex, we observed manifest differences between the two sexes in the timing of age-related changes, that is, sexual heterochrony. Intriguingly, age-related expression changes predominantly occurred earlier, or at a faster pace, in females compared to men. These changes included decreased energy production and neural function and up-regulation of the immune response, all major features of brain aging. Furthermore, we found that accelerated expression changes in the female SFG correlated with expression changes observed in AD, as well as stress effects in the frontal cortex. Accelerated aging-related changes in the female SFG transcriptome may provide a link between a higher stress exposure or sensitivity in women and the higher prevalence of AD

Operation Moshtarak and the manufacture of credible, “heroic” warfare

Richard Lance Keeble argues that Fleet Street’s coverage of the Afghan conflict has served largely to promote the interests of the military/industrial/media complex – and marginalise the views of the public who have consistently appealed in polls for the troops to be brought back hom

Methods for speeding up the Boundary Element Solution of Acoustic Radiation Problems

Methods for speeding up the boundary element solution of acoustic radiation problems are considered. The methods are based on solving the integral equation formulation of Burton and Miller for the exterior Helmholtz equation over a range of frequencies simultaneously. methods for speeding up the computation of the discrete forms of the integral operators and the solution of the linear systems that arise in the boundary element method are considered. A particular implementation of speed up methods is described. Results from the application of this to test problems are given

Computer memories: the history of computer form

This paper looks at the computer as a truly global form. The similar beige boxes found in offices across the world are analysed from the perspective of design history rather than that of the history of science and technology. Through the exploration of an archive of computer manufacturer's catalogues and concurrent design texts, this paper examines the changes that have occurred in the production and consumption of the computer in the context of the workplace, from its inception as a room-sized mainframe operated through a console of flashing lights, to the personal computer as a 'universal' form, reproduced by many manufacturers. It shows how the computer in the past has been as diverse as any other product, and asks how and why it now appears as a standardised, sanitised object. In doing so our relationship with the office computer, past and present is explored, revealing a complex history of vicissitude.</p

On Convergence and Threshold Properties of Discrete Lotka-Volterra Population Protocols

In this work we focus on a natural class of population protocols whose dynamics are modelled by the discrete version of Lotka-Volterra equations. In such protocols, when an agent $a$ of type (species) $i$ interacts with an agent $b$ of type (species) $j$ with $a$ as the initiator, then $b$'s type becomes $i$ with probability $P\_{ij}$. In such an interaction, we think of $a$ as the predator, $b$ as the prey, and the type of the prey is either converted to that of the predator or stays as is. Such protocols capture the dynamics of some opinion spreading models and generalize the well-known Rock-Paper-Scissors discrete dynamics. We consider the pairwise interactions among agents that are scheduled uniformly at random. We start by considering the convergence time and show that any Lotka-Volterra-type protocol on an $n$-agent population converges to some absorbing state in time polynomial in $n$, w.h.p., when any pair of agents is allowed to interact. By contrast, when the interaction graph is a star, even the Rock-Paper-Scissors protocol requires exponential time to converge. We then study threshold effects exhibited by Lotka-Volterra-type protocols with 3 and more species under interactions between any pair of agents. We start by presenting a simple 4-type protocol in which the probability difference of reaching the two possible absorbing states is strongly amplified by the ratio of the initial populations of the two other types, which are transient, but "control" convergence. We then prove that the Rock-Paper-Scissors protocol reaches each of its three possible absorbing states with almost equal probability, starting from any configuration satisfying some sub-linear lower bound on the initial size of each species. That is, Rock-Paper-Scissors is a realization of a "coin-flip consensus" in a distributed system. Some of our techniques may be of independent value

Factors affecting internal standard selection for quantitative elemental bio-imaging of soft tissues by LA-ICP-MS

Element response variations under different laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) operating conditions were investigated to identify important factors for selecting an internal standard (IS) for quantitative elemental bio-imaging. Analytes covering a range of atomic masses and first ionisation potentials (FIP) were selected to investigate the signal response variation with changes in laser spot diameter, mass bias and cell sampling position. In all cases, an IS improved experimental precision regardless of a close match in element mass or FIP but optimal analyte/IS combinations depended on the difference in masses of the analyte and IS. Particular attention was paid to 13C as this isotope is typically used as an IS in elemental bio-imaging applications. Despite its non-ideal IS characteristics (often different mass and FIP to many analytes), possibility of abundance sensitivity effects and poor signal-to-background ratio, 13C was a suitable IS candidate exhibiting a linear response with respect to the mass ablated, apparent independence from the high abundance of the adjacent 14N mass peak and effective analyte normalisation after background subtraction as long as the 13C signal from the sample was at least 6% of the gross signal. © 2011 The Royal Society of Chemistry

Identifying an Experimental Two-State Hamiltonian to Arbitrary Accuracy

Precision control of a quantum system requires accurate determination of the effective system Hamiltonian. We develop a method for estimating the Hamiltonian parameters for some unknown two-state system and providing uncertainty bounds on these parameters. This method requires only one measurement basis and the ability to initialise the system in some arbitrary state which is not an eigenstate of the Hamiltonian in question. The scaling of the uncertainty is studied for large numbers of measurements and found to be proportional to one on the square-root of the number of measurements.Comment: Minor corrections, Accepted for publication in Physical Review

Variation of theanine, phenolic, and methylxanthine compounds in 21 cultivars of Camellia sinensis harvested in different seasons

This is the first study to use chemometric methods to differentiate among 21 cultivars of Camellia sinensis from China and between leaves harvested at different times of the year using 30 compounds implicated in the taste and quality of tea. Unique patterns of catechin derivatives were observed among cultivars and across harvest seasons. C. sinensis var. pubilimba (You 510) differed from the cultivars of C. sinensis var. sinensis, with higher levels of theobromine, (+)-catechin, gallocatechin, gallocatechin gallate and theasinensin B, and lower levels of (−)-epicatechin, (−)-epigallocatechin (EGC) and (-)-epigallocatechin gallate (EGCG), respectively. Three cultivars of C. sinensis var. sinensis, Fuyun 7, Qiancha 7 and Zijuan contained significantly more caffeoylquinic acids than others cultivars. A Linear Discriminant Analysis model based on the abundance of 12 compounds was able to discriminate amongst all 21 tea cultivars. Harvest time impacted the abundance of EGC, theanine and afzelechin gallate