2,141 research outputs found
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Determining the effects of aqueous alteration on the distribution of oxygen isotopes in carbonaceous chondrites
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Evolved gas analysis of hydrated phases in Murchison and Orgueil
To better characterise the hydrated minerals in chondrites Evolved Gas Analysis of Murchison, Orgueil and selected minerals has been carried out. Meteorite water release profiles show significant differences to expected reference minerals
Development of a novel 3D simulation modelling system for distributed manufacturing
This paper describes a novel 3D simulation modelling system for supporting our distributed machine design and control paradigm with respect to simulating and emulating machine behaviour on the Internet. The system has been designed and implemented using Java2D and Java3D. An easy assembly concept of drag-and-drop assembly has been realised and implemented by the introduction of new connection features (unified interface assembly features) between two assembly components (modules). The system comprises a hierarchical geometric modeller, a behavioural editor, and two assemblers. During modelling, designers can combine basic modelling primitives with general extrusions and integrate CAD geometric models into simulation models. Each simulation component (module) model can be visualised and animated in VRML browsers.
It is reusable. This makes machine design re-configurable and flexible. A case study example is given to support our conclusions
Resurgent Insurgents:Quantitative Research Into Jihadists Who Get Suspended but Return on Twitter
Jihadists are very active on Twitter but their accounts frequently get suspended. A substantial debate over the effectiveness of suspension has arisen; an important factor is that Jihadists quickly create new accounts, resurging back like a game of whack-a-mole. This causes biases for terrorism and intelligence analysts. Whilst widely acknowledged, little research addresses the problem. In this study we identify resurging Jihadist accounts with novel methods, and provide detailed analysis going beyond previous case-studies. We show that suspension is less disruptive to terrorists than previously thought, whilst the bias and disruption caused to terrorism research has been underestimated
A framework of web-based conceptual design
A web-based conceptual design prototype system is presented. The system consists of four parts which interpret on-line sketches as 2D and 3D geometry, extract 3D hierarchical configurations, allow editing of component behaviours, and produce VRML-based behavioural simulations for design verification and web-based application. In the first part, on-line freehand sketched input is interpreted as 2D and 3D geometry, which geometrically represents conceptual design. The system then infers 3D configuration by analysing 3D modelling history. The configuration is described by a parentâchild hierarchical relationship and relative positions between two geometric components. The positioning information is computed with respect to the VRML97 specification. In order to verify the conceptual design of a product, the behaviours can be specified interactively on different components. Finally, the system creates VRML97 formatted files for behavioural simulation and collaborative design application over the Internet. The paper gives examples of web-based applications. This work forms a part of a research project into the design and establishing of modular machines for automation manufacture. A consortium of leading automotive companies is collaborating on the research project
Muon Capture on the Proton and Deuteron
By measuring the lifetime of the negative muon in pure protium (hydrogen-1),
the MuCap experiment determines the rate of muon capture on the proton, from
which the proton's pseudoscalar coupling g_p may be inferred. A precision of
15% for g_p has been published; this is a step along the way to a goal of 7%.
This coupling can be calculated precisely from heavy baryon chiral perturbation
theory and therefore permits a test of QCD's chiral symmetry. Meanwhile, the
MuSun experiment is in its final design stage; it will measure the rate of muon
capture on the deuteron using a similar technique. This process can be related
through pionless effective field theory and chiral perturbation theory to other
two-nucleon reactions of astrophysical interest, including proton-proton fusion
and deuteron breakup.Comment: Submitted to the proceedings of the 2007 Advanced Studies Institute
on Symmetries and Spin (SPIN-Praha-2007
Quantum-to-classical Transition of Cosmological Perturbations for Non-vacuum Initial States
Transition from quantum to semiclassical behaviour and loss of quantum
coherence for inhomogeneous perturbations generated from a non-vacuum initial
state in the early Universe is considered in the Heisenberg and the
Schr\"odinger representations, as well as using the Wigner function. We show
explicitly that these three approaches lead to the same prediction in the limit
of large squeezing (i.e. when the squeezing parameter ): each
two-modes quantum state (k, -k) of these perturbations is equivalent to a
classical perturbation that has a stochastic amplitude, obeying a non-gaussian
statistics which depends on the initial state, and that belongs to the
quasi-isotropic mode (i.e. it possesses a fixed phase). The Wigner function is
not everywhere positive for any finite , hence its interpretation as a
classical distribution function in phase space is impossible without some
coarse graining procedure. However, this does not affect the transition to
semiclassical behaviour since the Wigner function becomes concentrated near a
classical trajectory in phase space when even without coarse
graining. Deviations of the statistics of the perturbations in real space from
a Gaussian one lie below the cosmic variance level for the N-particles initial
states with N=N(|k|) but may be observable for other initial states without
statistical isotropy or with correlations between different k modes. As a way
to look for this effect, it is proposed to measure the kurtosis of the angular
fluctuations of the cosmic microwave background temperature.Comment: LaTeX (28 pages),+2 eps figure
A conservative control strategy for variable-speed stall-regulated wind turbines
Simulation models of a variable-speed, fixed-pitch wind turbine were investigated to evaluate the feasibility of constraining rotor speed and power output without the benefit of active aerodynamic control devices. A strategy was postulated to control rotational speed by specifying the demanded generator torque. By controlling rotor speed in relation to wind speed, the aerodynamic power extracted by the blades from the wind was manipulated. Specifically, the blades were caused to stall in high winds. In low and moderate winds, the demanded generator torque and the resulting rotor speed were controlled to cause the wind turbine to operate near maximum efficiency. Using the developed models, simulations were conducted of operation in turbulent winds. Results indicated that rotor speed and power output were well regulated. Preliminary investigations of system dynamics showed that, compared to fixed-speed operation, variable-speed operation caused cyclic loading amplitude to be reduced for the turbine blades and low-speed shaft and slightly increased for the tower loads. This result suggests a favorable impact on fatigue life from implementation of the proposed control strategy
Solution of generalized fractional reaction-diffusion equations
This paper deals with the investigation of a closed form solution of a
generalized fractional reaction-diffusion equation. The solution of the
proposed problem is developed in a compact form in terms of the H-function by
the application of direct and inverse Laplace and Fourier transforms.
Fractional order moments and the asymptotic expansion of the solution are also
obtained.Comment: LaTeX, 18 pages, corrected typo
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