Three dimensional water vapour visualization in porous packing by near-infrared diffuse transmittance tomography

Near-infrared diffuse tomography was used in order to observe dynamic behaviour of flowing gases by measuring the 3D distributions of composition and temperature in a weakly scattering packed bed reactor, subject to wall effects and non-isothermal conditions. The technique was applied to the vapour phase hydrogen isotopic exchange reaction in a hydrophobic packing of low aspect ratio made of platinum on styrene divinyl benzene sulphonate copolymer resin. The results of tomography revealed uneven temperature and composition maps of water and deuterated water vapours in the core-packed bed and in the vicinity of the wall owing to flow maldistribution. The dynamic lag between the near-wall water vapour and deuterated water vapour compositions were observed suggesting that the convective transfer which was significant near the wall at the start, owing to high porosity, was also effective at large conversions.

On the mobility of a one-dimensional damped Frenkel-Kontorova chain: Commensurate versus incommensurate

The mobility of a one-dimensional damped Frenkel-Kontorova chain under a de driving force is studied numerically and analytically For the commensurate case, the particles in the chain me synchronized st high driving force. For the incommensurate chain, a single mode solution dominates st high mobility regime. We are able to calculate the mobilities for both the cases analytically, and a good agreement with numerical results is found. The mobility hysteresis for the incommensurate chain is explained by the existence of two branches of physical solutions, and transitions occur when one of them breaks up.

Lateral electron transport in high-intensity laser-irradiated foils diagnosed by ion emission

An experimental investigation of lateral electron transport in thin metallic foil targets irradiated by ultraintense (>= 10(19) W/cm(2)) laser pulses is reported. Two-dimensional spatially resolved ion emission measurements are used to quantify electric-field generation resulting from electron transport. The measurement of large electric fields (similar to 0.1 TV/m) millimeters from the laser focus reveals that lateral energy transport continues long after the laser pulse has decayed. Numerical simulations confirm a very strong enhancement of electron density and electric field at the edges of the target.

Asymptotic layer-type model of high pressure direct current glow discharge in electronegative gases

Here a self-consistent one-dimensional continuum model is presented for a narrow gap plane-parallel dc glow discharge. The governing equations consist of continuity and momentum equations for positive and negative ions and electrons coupled with Poisson's equation. A singular perturbation method is developed for the analysis of high pressure dc glow discharge. The kinetic processes of the ionization, electron attachment, and ion-ion recombination are included in the model. Explicit results are obtained for the asymptotic limits: delta=(r(D)/L)(2)--> 0, omega=(r(S)/L)(2)--> 0, where r(D) is the Debye radius, r(S) is recombination length, and L is the gap length. The discharge gap divides naturally into four layers with multiple space scales: anode fall region, positive column, transitional region, cathode fall region and diffusion layer adjacent to the cathode surface, its formation is discussed. The effects of the gas pressure, gap spacing and dc voltage on the electrical properties of the layers and its dimension are investigated. (C) 2000 American Institute of Physics. [S0021-8979(00)00813-6].

High-Order Harmonics from Bow Wave Caustics Driven by a High-Intensity Laser

We propose a new mechanism of high-order harmonic generation during an interaction of a high-intensity laser pulse with underdense plasma. A tightly focused laser pulse creates a cavity in plasma pushing electrons aside and exciting the wake wave and the bow wave. At the joint of the cavity wall and the bow wave boundary, an annular spike of electron density is formed. This spike surrounds the cavity and moves together with the laser pulse. Collective motion of electrons in the spike driven by the laser field generates high-order harmonics. A strong localization of the electron spike, its robustness to oscillations imposed by the laser field and, consequently, its ability to produce high-order harmonics is explained by catastrophe theory. The proposed mechanism explains the experimental observations of high-order harmonics with the 9 TW J-KAREN laser (JAEA, Japan) and the 120 TW Astra Gemini laser (CLF RAL, UK) [A. S. Pirozhkov, et al., arXiv:1004.4514 (2010); A. S. Pirozhkov et al, AIP Proceedings, this volume]. The theory is corroborated by high-resolution two- and three-dimensional particle-in-cell simulations.

Three-dimensional delayed-detonation models with nucleosynthesis for type ia supernovae

We present results for a suite of 14 three-dimensional, high-resolution hydrodynamical simulations of delayed-detonation models of Type Ia supernova (SN Ia) explosions. This model suite comprises the first set of three-dimensional SN Ia simulations with detailed isotopic yield information. As such, it may serve as a data base for Chandrasekhar-mass delayed-detonation model nucleosynthetic yields and for deriving synthetic observables such as spectra and light curves. We employ aphysically motivated, stochastic model based on turbulent velocity fluctuations and fuel density to calculate in situ the deflagration-to-detonation transition probabilities. To obtain different strengths of the deflagration phase and thereby different degrees of pre-expansion, we have chosen a sequence of initial models with 1, 3, 5, 10, 20, 40, 100, 150, 200, 300 and 1600 (two different realizations) ignition kernels in a hydrostatic white dwarf with a central density of 2.9 × 10 g cm, as well as one high central density (5.5 × 10 g cm) and one low central density (1.0 × 10 g cm) rendition of the 100 ignition kernel configuration. For each simulation, we determined detailed nucleosynthetic yields by postprocessing10 tracer particles with a 384 nuclide reaction network. All delayed-detonation models result in explosions unbinding thewhite dwarf, producing a range of 56Ni masses from 0.32 to 1.11M. As a general trend, the models predict that the stableneutron-rich iron-group isotopes are not found at the lowest velocities, but rather at intermediate velocities (~3000×10 000 km s) in a shell surrounding a Ni-rich core. The models further predict relatively low-velocity oxygen and carbon, with typical minimum velocities around 4000 and 10 000 km s, respectively. © 2012 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.

Modification of the formation of high-Mach number electrostatic shock-like structures by the ion acoustic instability

The formation of unmagnetized electrostatic shock-like structures with a high Mach number is examined with one- and two-dimensional particle-in-cell (PIC) simulations. The structures are generated through the collision of two identical plasma clouds, which consist of equally hot electrons and ions with a mass ratio of 250. The Mach number of the collision speed with respect to the initial ion acoustic speed of the plasma is set to 4.6. This high Mach number delays the formation of such structures by tens of inverse ion plasma frequencies. A pair of stable shock-like structures is observed after this time in the 1D simulation, which gradually evolve into electrostatic shocks. The ion acoustic instability, which can develop in the 2D simulation but not in the 1D one, competes with the nonlinear process that gives rise to these structures. The oblique ion acoustic waves fragment their electric field. The transition layer, across which the bulk of the ions change their speed, widens and their speed change is reduced. Double layer-shock hybrid structures develop.

Defining Target Volumes for Stereotactic Ablative Radiotherapy of Early-stage Lung Tumours:A Comparison of Three-dimensional F-fluorodeoxyglucose Positron Emission Tomography and Four-dimensional Computed Tomography

Aims: High local control rates are achieved in stage I lung cancer using stereotactic ablative radiotherapy. Target delineation is commonly based on four-dimensional computed tomography (CT) scans. Target volumes defined by positron emission tomography/computed tomography (PET/CT) are compared with those defined by four-dimensional CT and conventional ('three-dimensional') F-fluorodeoxyglucose (F-FDG) PET/CT. Materials and methods: For 16 stage I non-small cell lung cancer tumours, six approaches for deriving PET target volumes were evaluated: manual contouring, standardised uptake value (SUV) absolute threshold of 2.5, 35% of maximum SUV (35%SUV), 41% of SUV (41%SUV) and two different source to background ratio techniques (SBR-1 and SBR-2). PET-derived target volumes were compared with the internal target volume (ITV) from the modified maximum intensity projection (MIP ITV). Volumetric and positional correlation was assessed using the Dice similarity coefficient (DSC). Results: PET-based target volumes did not correspond to four-dimensional CT-based target volumes. The mean DSC relative to MIP ITV were: PET manual = 0.64, SUV2.5 = 0.64, 35%SUV = 0.63, 41%SUV = 0.57. SBR-1 = 0.52, SBR-2 = 0.49. PET-based target volumes were smaller than corresponding MIP ITVs. Conclusions: Conventional three-dimensional F-FDG PET-derived target volumes for lung stereotactic ablative radiotherapy did not correspond well with those derived from four-dimensional CT, including those in routine clinical use (MIP ITV). Caution is required in using three-dimensional PET for motion encompassing target volume delineation. © 2012 The Royal College of Radiologists.

Defining target volumes for stereotactic ablative radiotherapy of early-stage lung tumours: a comparison of three-dimensional 18F-fluorodeoxyglucose positron emission tomography and four-dimensional computed tomography.:PETCT versus 4DCT for SABR in Early Stage NSCLC

AIMS: High local control rates are achieved in stage I lung cancer using
stereotactic ablative radiotherapy. Target delineation is commonly based on
four-dimensional computed tomography (CT) scans. Target volumes defined by
positron emission tomography/computed tomography (PET/CT) are compared with those defined by four-dimensional CT and conventional ('three-dimensional')
(18)F-fluorodeoxyglucose ((18)F-FDG) PET/CT.

MATERIALS AND METHODS: For 16 stage I non-small cell lung cancer tumours, six
approaches for deriving PET target volumes were evaluated: manual contouring,
standardised uptake value (SUV) absolute threshold of 2.5, 35% of maximum SUV
(35%SUV(MAX)), 41% of SUV(MAX) (41%SUV(MAX)) and two different source to
background ratio techniques (SBR-1 and SBR-2). PET-derived target volumes were compared with the internal target volume (ITV) from the modified maximum
intensity projection (MIP(MOD) ITV). Volumetric and positional correlation was
assessed using the Dice similarity coefficient (DSC).

RESULTS: PET-based target volumes did not correspond to four-dimensional CT-based target volumes. The mean DSC relative to MIP(MOD) ITV were: PET manual = 0.64, SUV2.5 = 0.64, 35%SUV(MAX) = 0.63, 41%SUV(MAX) = 0.57. SBR-1 = 0.52, SBR-2 =0.49. PET-based target volumes were smaller than corresponding MIP ITVs.

CONCLUSIONS: Conventional three-dimensional (18)F-FDG PET-derived target volumes for lung stereotactic ablative radiotherapy did not correspond well with those derived from four-dimensional CT, including those in routine clinical use
(MIP(MOD) ITV). Caution is required in using three-dimensional PET for motion
encompassing target volume delineation.

Analysis of the compressive behaviour of the three-dimensional printed porous titanium for dental implants using a modified cellular solid model

A set of cylindrical porous titanium test samples were produced using the three-dimensional printing and sintering method with samples sintered at 900 °C, 1000 °C, 1100 °C, 1200 °C or 1300 °C. Following compression testing, it was apparent that the stress-strain curves were similar in shape to the curves that represent cellular solids. This is despite a relative density twice as high as what is considered the threshold for defining a cellular solid. As final sintering temperature increased, the compressive behaviour developed from being elastic-brittle to elastic-plastic and while Young's modulus remained fairly constant in the region of 1.5 GPa, there was a corresponding increase in 0.2% proof stress of approximately 40-80 MPa. The cellular solid model consists of two equations that predict Young's modulus and yield or proof stress. By fitting to experimental data and consideration of porous morphology, appropriate changes to the geometry constants allow modification of the current models to predict with better accuracy the behaviour of porous materials with higher relative densities (lower porosity).

A Two Dimensional Experimental Investigation of Slamming of an Oscillating Wave Surge Converter

This paper describes a series of experiments undertaken to investigate the slamming of an Oscillating Wave Surge Converter in extreme sea states. These two-dimensional experiments were undertaken in the Wave Flume at Ecole Centrale Marseille. Images from a high speed camera are used to identify the physics of the slamming process. A single pressure sensor is used to record the characteristic of the pressure. Finally numerical results are compared to the output from the experiments.

Coherently Opening a High-Q Cavity

We propose a general framework to effectively `open' a high-Q resonator, that is, to release the quantum state initially prepared in it in the form of a traveling electromagnetic wave. This is achieved by employing a mediating mode that scatters coherently the radiation from the resonator into a one-dimensional continuum of modes such as a waveguide. The same mechanism may be used to `feed' a desired quantum field to an initially empty cavity. Switching between an `open' and `closed' resonator may then be obtained by controlling either the detuning of the scatterer or the amount of time it spends in the resonator. First, we introduce the model in its general form, identifying (i) the traveling mode that optimally retains the full quantum information of the resonator field and (ii) a suitable figure of merit that we study analytically in terms of the system parameters. Then, we discuss two feasible implementations based on ensembles of two-level atoms interacting with cavity fields. In addition, we discuss how to integrate traditional cavity QED in our proposal using three-level atoms.

Synthetic light curves and spectra for three-dimensional delayed-detonation models of type ia supernovae

In a companion paper, Seitenzahl et al. have presented a set of three-dimensional delayed detonation models for thermonuclear explosions of near-Chandrasekhar-mass white dwarfs (WDs). Here,we present multidimensional radiative transfer simulations that provide synthetic light curves and spectra for those models. The model sequence explores both changes in the strength of the deflagration phase (which is controlled by the ignition configuration in our models) and the WD central density. In agreement with previous studies, we find that the strength of the deflagration significantly affects the explosion and the observables. Variations in the central density also have an influence on both brightness and colour, but overall it is a secondary parameter in our set of models. In many respects, the models yield a good match to the observed properties of normal Type Ia supernovae (SNe Ia): peak brightness, rise/decline time-scales and synthetic spectra are all in reasonable agreement. There are, however, several differences. In particular, the models are systematically too red around maximum light, manifest spectral line velocities that are a little too high and yield I-band light curves that do not match observations. Although some of these discrepancies may simply relate to approximations made in the modelling, some pose real challenges to the models. If viewed as a complete sequence, our models do not reproduce the observed light-curve width- luminosity relation (WLR) of SNe Ia: all our models show rather similar B-band decline rates, irrespective of peak brightness. This suggests that simple variations in the strength of the deflagration phase in Chandrasekhar-mass deflagration-to-detonation models do not readily explain the observed diversity of normal SNe Ia. This may imply that some other parameter within the Chandrasekhar-mass paradigm is key to the WLR, or that a substantial fraction of normal SNe Ia arise from an alternative explosion scenario.

Two-dimensional images of dissolved sulfide and metals in anoxic sediments by a novel diffusive gradients in thin film probe and optical scanning techniques

A novel diffusive gradients in thin film probe developed comprises diffusive gel layer of silver iodide (AgI) and a back-up Microchelex resin gel layer. 2D high-resolution images of sulfide and trace metals were determined respectively on the AgI gel by densitometric analysis and on the Microchelex resin layer with laser-ablation-inductively-coupled plasma mass spectrometry (LA-ICP-MS).We investigated the validity of the analytical procedures used for the determination of sulfide and trace metals. We found low relative standard deviations on replicate measurements, linear trace-metal calibration curves between the LA-ICP-MS signal and the true trace-metal concentration in the resin gel, and a good agreement of the sulfide results obtained with the AgI resin gel and with other analytical methods. The method was applied on anoxic sediment pore waters in an estuarine and marine system. Simultaneous remobilization of sulfide and trace metals was observed in the marine sediment.

Optimizing geometric accuracy of four dimensional CT scans acquired using the wall and couch mounted Varian Real-Time Position Management camera systems

Objective:

The aim of this study was to identify sources of anatomical misrepresentation due to the location of camera mounting, tumour motion velocity and image processing artefacts in order to optimise the 4DCT scan protocol and improve geometrical-temporal accuracy.

A phantom with an imaging insert was driven with a sinusoidal superior-inferior motion of varying amplitude and period for 4DCT scanning. The length of a high density cube within the insert was measured using treatment planning software to determine the accuracy of its spatial representation. Scan parameters were varied including the tube rotation period and the cine time between reconstructed images. A CT image quality phantom was used to measure various image quality signatures under the scan parameters tested.

No significant difference in spatial accuracy was found for 4DCT scans carried out using the wall mounted or couch mounted camera for sinusoidal target motion. Greater spatial accuracy was found for 4DCT scans carried out using a tube rotation speed of 0.5s rather than 1.0s. The reduction in image quality when using a faster rotation speed was not enough to require an increase in patient dose.

4DCT accuracy may be increased by optimising scan parameters, including choosing faster tube rotation speeds. Peak misidentification in the recorded breathing trace leads to spatial artefacts and this risk can be reduced by using a couch mounted infrared camera.

This study explicitly shows that 4DCT scan accuracy is improved by scanning with a faster CT tube rotation speed.