Craig White

Body image dimensions and cancer: a heuristic cognitive behavioural model

The term body image has been associated with a multitude of definitions within psychosocial oncology. It is well known that cancer and cancer treatments often have a negative impact on appearance‐related variables. A growing literature has emerged in recent years on the psychological aspects of changed appearance. This work has mainly addressed weight‐related appearance and the psychology of eating disorders. A number of themes have emerged from this work. These themes have been strongly influenced by a cognitive behavioural perspective. There seems, however, to have been few attempts to integrate findings from such work with attempts to understand cancer‐related appearance changes. This paper outlines some of the key developments within body image psychology and suggests a heuristic cognitive behavioural model that could be applied to the assessment, conceptualisation and treatment of body image disturbance among cancer patients. Copyright

Deterministic numerical solutions of the Boltzmann equation using the fast spectral method

The Boltzmann equation describes the dynamics of rarefied gas flows, but the multidimensional nature of its collision operator poses a real challenge for its numerical solution. In this paper, the fast spectral method 36], originally developed by Mouhot and Pareschi for the numerical approximation of the collision operator, is extended to deal with other collision kernels, such as those corresponding to the soft, Lennard-Jones, and rigid attracting potentials. The accuracy of the fast spectral method is checked by comparing our numerical solutions of the space-homogeneous Boltzmann equation with the exact Bobylev-Krook-Wu solutions for a gas of Maxwell molecules. It is found that the accuracy is improved by replacing the trapezoidal rule with Gauss-Legendre quadrature in the calculation of the kernel mode, and the conservation of momentum and energy are ensured by the Lagrangian multiplier method without loss of spectral accuracy. The relax-to-equilibrium processes of different collision kernels with the same value of shear viscosity are then compared; the numerical results indicate that different forms of the collision kernels can be used as long as the shear viscosity (not only the value, but also its temperature dependence) is recovered. An iteration scheme is employed to obtain stationary solutions of the space-inhomogeneous Boltzmann equation, where the numerical errors decay exponentially. Four classical benchmarking problems are investigated: the normal shock wave, and the planar Fourier/Couette/force-driven Poiseuille flows. For normal shock waves, our numerical results are compared with a finite difference solution of the Boltzmann equation for hard sphere molecules, experimental data, and molecular dynamics simulation of argon using the realistic Lennard-Jones potential. For planar Fourier/Couette/force-driven Poiseuille flows, our results are compared with the direct simulation Monte Carlo method. Excellent agreements are observed in all test cases, demonstrating the merit of the fast spectral method as a computationally efficient method for rarefied gas dynamics.

Permeability of Ablative Materials Under Rarefied Gas Conditions

Numerical meshes of both cork and carbon fiber ablative materials in their virgin and pyrolized states, with realistic porosity and tortuosity, have been created from microcomputed tomography scans. The porosity of each material has been calculated from the microcomputed scans and used to extract smaller representative sample volumes to perform numerical simulations on. Direct simulation Monte Carlo simulations of rarefied gas flow through these materials have been performed to find the permeability of each material to argon gas and to a gas mixture. The method has been validated by comparing the measured permeability for a Berea sandstone material with previously published experimental values. For the specific pressure conditions investigated here, the cork-phenolic material becomes around 10 times more permeable after being pyrolized, whereas the carbon-phenolic material only becomes five times more permeable than its virgin form. The permeability to the gas mixture is found to be greater than to argon ...

Thermal rarefied gas flow investigations through micro/nano backward-facing step: Comparison of DSMC and CFD subject to hybrid slip and jump boundary conditions

This paper evaluates the suitability of a newly developed hybrid “Langmuir–Maxwell” and “Langmuir–Smoluchowski” slip/jump boundary conditions in the Navier–Stokes–Fourier equations for nano-/micro-backward-facing step geometry flow which experiences separation and reattachment. Additionally, this paper investigates the effect of different parameters such as step pressure ratio, inflow temperature, and wall temperature on the separation zone in the nano-/micro-step geometry. We chose nitrogen as the working gas and use two direct simulation Monte Carlo (DSMC) solvers to assess the accuracy of the computational fluid dynamics (CFD) solutions. DSMC results showed that the increase of the inlet temperatures extends the length of the separation zone and raises the mass flow rate. The change of pressure ratio does not affect the separation length while the increase of the step wall temperature decreases the length of this zone for both CFD and DSMC results. Compared to the DSMC results, the hybrid slip/jump boundary conditions predict better surface pressure, surface gas temperature, and slip velocity in the separation zone than the standard Maxwell/Smoluchowski boundary conditions.

Effects of curvature on rarefied gas flows between rotating concentric cylinders

The gas flow between two concentric rotating cylinders is considered in order to investigate non-equilibrium effects associated with the Knudsen layers over curved surfaces. We investigate the nonlinear flow physics in the near-wall regions using a new power-law (PL) wall-scaling approach. This PL model incorporates Knudsen layer effects in near-wall regions by taking into account the boundary limiting effects on the molecular free paths. We also report new direct simulation Monte Carlo results covering a wide range of Knudsen numbers and accommodation coefficients, and for various outer-to-inner cylinder radius ratios. Our simulation data are compared with both the classical slip flow theory and the PL model, and we find that non-equilibrium effects are not only dependent on Knudsen number and accommodation coefficient but are also significantly affected by the surface curvature. The relative merits and limitations of both theoretical models are explored with respect to rarefaction and curvature effects. The PL model is able to capture some of the nonlinear trends associated with Knudsen layers up to the early transition flow regime. The present study also illuminates the limitations of classical slip flow theory even in the early slip flow regime for higher curvature test cases, although the model does exhibit good agreement throughout the slip flow regime for lower curvature cases. Torque and velocity profile comparisons also convey that a good prediction of integral flow properties does not necessarily guarantee the accuracy of the theoretical model used, and it is important to demonstrate that field variables are also predicted satisfactorily.

Coherent Rayleigh-Brillouin scattering: influence of the intermolecular potential

The spectrum of the coherent Rayleigh-Brillouin scattering (CRBS) of light by rarefied gas is obtained by solving the Boltzmann equation numerically using the fast spectral method. The influence of the intermolecular potential on the CRBS spectrum is investigated and the accuracy of the prevailing Tenti’s s6 kinetic model is evaluated. Our numerical results show that i) the intermolecular potential has a great influence on CRBS spectrum when the Knudsen number is between 0.05 and 1 and ii) the Tenti’s s6 kinetic model can only predict the line shape accurately for Maxwell gases at small Knudsen numbers.

Accounting for rotational non-equilibrium effects in subsonic DSMC boundary conditions

From study of the kinetic theory of dilute gases, it becomes clear that the subsonic, implicit boundary conditions which are commonly used in direct simulation Monte Carlo simulations of micro-scale channel flows do not take any form of rotational non-equilibrium into account. The consequences of not considering non-equilibration of the rotational mode are discussed and a new form of the boundary conditions which attempt to take this effect into account are proposed. It is shown that for a highly compressible test case involving these implicit boundaries in the literature that a degree of rotational non-equilibrium is present. The changes in the recovered macroscopic properties when the new boundary is applied in the same case include an improved rotational temperature distribution and a slightly lower velocity at the channel exit. A further test case exhibiting no rotational non-equilibrium was performed and it is shown that the macroscopic properties which are recovered are essentially the same for both boundaries. The results indicate that the newly proposed outlet boundary condition increases the range of applicability of these types of boundary conditions, without adding any significant computational expense.

Thermochemistry modelling in an open-source DSMC code

Hypersonic vehicles which typically operate in rarefied gas environments and are subject to extremes of velocity and altitude, so it is important that the aerodynamic and thermal loads on the vehicle are properly characterised if the feasibility of the vehicle design is to be accurately assessed. The vehicle may also encounter gasside chemical reactions that can have a significant influence on aerodynamic performance and vehicle surface heat flux [1]. Numerical models which fail to incorporate such reacting flows miss out on an essential part of the flow physics surrounding the vehicle.

Rarefaction effects in gas flows over curved surfaces

The fundamental test case of gas flow between two concentric rotating cylinders is considered in order to investigate rarefaction effects associated with the Knudsen layers over curved surfaces. We carry out direct simulation Monte Carlo simulations covering a wide range of Knudsen numbers and accommodation coefficients, and for various outer-to-inner cylinder radius ratios. Numerical data is compared with classical slip flow theory and a new power-law (PL) wall scaling model. The PL model incorporates Knudsen layer effects in near-wall regions by taking into account the boundary limiting effects on the molecular free paths. The limitations of both theoretical models are explored with respect to rarefaction and curvature effects. Torque and velocity profile comparisons also convey that mere prediction of integral flow parameters does not guarantee the accuracy of a theoretical model, and that it is important to ensure that prediction of the local flowfield is in agreement with simulation data.

The Effect of Increasing Rarefaction on the Edney Type IV Shock Interaction Problem

Two-dimensional direct simulation Monte Carlo simulations of the Edney Type IV shock interaction problem, where an oblique shock wave generated by a wedge encounters the bow shock from a cylinder, are carried out for three different Knudsen numbers using the dsmcFoam+ code. The numerical results for surface and flow properties are in good agreement with experiment for a Knudsen number of 0.0067. When the degree of rarefaction is increased, the oblique and normal shock waves become more diffuse and the bow shock standoff distance increases. The supersonic jet that forms in the interaction region becomes weaker as the Knudsen number increases and the point at where it impinges on the cylinder surface moves in a clockwise direction due to the jet being turned upward. The location of the peak heat transfer coefficient, peak pressure coefficient, and zero skin friction coefficient on the cylinder surface follow the supersonic jet impingement in a clockwise direction around the cylinder. The peak heat transfer and pressure coefficients decrease with increasing Knudsen number.