Elastic-plastic finite-element analyses of thermally cycled double-edge wedge specimens

Elastic-plastic stress-strain analyses were performed for double-edge wedge specimens subjected to thermal cycling in fluidized beds at 316 and 1088 C. Four cases involving different nickel-base alloys (IN 100, Mar M-200, NASA TAZ-8A, and Rene 80) were analyzed by using the MARC nonlinear, finite element computer program. Elastic solutions from MARC showed good agreement with previously reported solutions obtained by using the NASTRAN and ISO3DQ computer programs. Equivalent total strain ranges at the critical locations calculated by elastic analyses agreed within 3 percent with those calculated from elastic-plastic analyses. The elastic analyses always resulted in compressive mean stresses at the critical locations. However, elastic-plastic analyses showed tensile mean stresses for two of the four alloys and an increase in the compressive mean stress for the highest plastic strain case

Materials constitutive models for nonlinear analysis of thermally cycled structures

Effects of inelastic materials models on computed stress-strain solutions for thermally loaded structures were studied by performing nonlinear (elastoplastic creep) and elastic structural analyses on a prismatic, double edge wedge specimen of IN 100 alloy that was subjected to thermal cycling in fluidized beds. Four incremental plasticity creep models (isotropic, kinematic, combined isotropic kinematic, and combined plus transient creep) were exercised for the problem by using the MARC nonlinear, finite element computer program. Maximum total strain ranges computed from the elastic and nonlinear analyses agreed within 5 percent. Mean cyclic stresses, inelastic strain ranges, and inelastic work were significantly affected by the choice of inelastic constitutive model. The computing time per cycle for the nonlinear analyses was more than five times that required for the elastic analysis

Effects of Vascular Nitric Oxide Bioactivity and Vascular Ageing on Arterial Blood Pressure and Flow Waveforms

Analysis of blood pressure and flow waveforms may lead to improved diagnosis of arterial dysfunction and disease. This thesis describes experiments to investigate the characteristic alteration of peripheral waveforms produced by stimulated release of vascular nitric oxide (an effect that is attenuated by endothelial dysfunction) and the changes that occur with age. In vivo experiments were conducted in anaesthetised rabbits and in vitro experiments employed a polyurethane model of the human aorta and its principal branches. Blood pressure, blood flow, pulse wave velocities and vessel diameter were recorded in the rabbit abdominal aorta. Equivalent recordings were obtained from the model aorta. Data were analysed in the time domain using wave intensity analysis after separation of reservoir (Windkessel) pressure and wave pressure. Effects of acetylcholine (Ach) and NG-nitro-L-arginine methyl ester (L-NAME) were investigated in vivo. Ach (which promotes endothelial production of nitric oxide) increased wave reflection, whilst L-NAME (which inhibits nitric oxide production) decreased it. These trends were opposite to the expected ones, and do not account for the established effects of nitric oxide on peripheral arterial waveforms. Further work is required to investigate these contradictions. Arterial stiffening in immature and mature rabbits was attempted by supplementing their diet with fructose. Fructose is known to form advanced glycation end-products in arterial walls and hence to stiffen arteries. Unexpectedly, fructose did not affect haemodynamic function. However, immature control rabbits had markedly reduced aortic wave reflection compared to mature control rabbits, indicating that the former have arterial impedances that are better matched for incident wave propagation. Wrapping the model aorta in Clingfilm was used to simulate age- or drug-induced stiffening of the aorta in vivo. Increased pulse pressure was observed, resembling the isolated systolic hypertension prevalent in aged populations. The model has potential for modelling haemodynamic function in health and disease

VisGenome: visualization of single and comparative genome representations

VisGenome visualizes single and comparative representations for the rat, the mouse and the human chromosomes at different levels of detail. The tool offers smooth zooming and panning which is more flexible than seen in other browsers. It presents information available in Ensembl for single chromosomes, as well as homologies (orthologue predictions including ortholog one2one, apparent ortholog one2one, ortholog many2many) for any two chromosomes from different species. The application can query supporting data from Ensembl by invoking a link in a browser

Integrated maneuvering and life support system simulation Final report

Integrated maneuvering and life support system simulatio

The emergence of coherence in complex networks of heterogeneous dynamical systems

We present a general theory for the onset of coherence in collections of heterogeneous maps interacting via a complex connection network. Our method allows the dynamics of the individual uncoupled systems to be either chaotic or periodic, and applies generally to networks for which the number of connections per node is large. We find that the critical coupling strength at which a transition to synchrony takes place depends separately on the dynamics of the individual uncoupled systems and on the largest eigenvalue of the adjacency matrix of the coupling network. Our theory directly generalizes the Kuramoto model of equal strength, all-to-all coupled phase oscillators to the case of oscillators with more realistic dynamics coupled via a large heterogeneous network.Comment: 4 pages, 1 figure. Published versio

Parametric Feedback Resonance in Chaotic Systems

If one changes the control parameter of a chaotic system proportionally to the distance between an arbitrary point on the strange attractor and the actual trajectory, the lifetime τ of the most stable unstable periodic orbit in the vicinity of this point starts to diverge with a power law. The volume in parameter space where τ becomes infinite is finite and from its nonfractal boundaries one can determine directly the local Liapunov exponents. The experimental applicability of the method is demonstrated for two coupled diode resonators

Appraisals of previous maths experiences play an important role in maths anxiety

Maths anxiety affects many people, from young children through to older adults. Whilst there has been debate concerning the developmental trajectory of maths anxiety and negative maths attitudes, little attention has been given to the role of appraisals of previous maths experiences. We surveyed 308 adults (mean age = 27.56 years, SD = 11.25) and assessed self-reported measures of maths anxiety, mathematical resilience, maths attitudes, and appraisal of previous maths experiences. As hypothesised, all variables were found to be interrelated. Maths anxiety was significantly negatively related to appraisal of previous maths experiences, mathematical resilience and maths attitudes. Moreover, appraisal of previous maths experiences was shown to mediate the relations between i) maths anxiety and maths attitudes, and ii) mathematical resilience and maths attitudes. The findings demonstrate the importance of considering current appraisals of previous maths experiences and are consistent with an interpretation account of maths anxiety. This may help inform cognitive based interventions that focus on one’s interpretation of past events to support current and future maths learning and engagement

Effects of horizontal vibration on hopper flows of granular materials

The current experiments investigate the discharge of glass spheres in a planar wedge-shaped hopper (45 degree sidewalls) that is vibrated hoizontally. When the hopper is discharged without vibration, the discharge occurs as a funnel flow, with the material exiting the central region of the hopper and stagnant material along the sides. With horizontal vibration, the discharge rate increases with the velocity of vibration as compared with the discharge rate without vibration. For a certain range of acceleration parameters (20-30 Hz and accelerations greater than about 1 g), the discharge of the material occurs in an inverted-funnel pattern, with the material along the sides exiting first, followed by the material in the core; the free surface shows a peak at the center of the hopper with the free surface particles avalanching from the center toward the sides. During the deceleration phase of a vibration cycle, particles all along the trailing or low-pressure wall separate from the surface and fall under gravity for a short period before reconnecting the hopper. For lower frequencies (5 and 10 Hz), the free surface remains horizontal and the material appears to discharge uniformly from the hopper

Effects of Horizontal Vibration on Hopper Flows of Granular Material

This study experimentally examines the flow of glass spheres in a wedge-shaped hopper that is vibrated hoizontally. When the hopper is discharged without vibration, discharge occurs as a funnel flow, with the material exiting the central region of the hopper and stagnant material along the sides. With vibration, the discharge of the material occurs in reverse, with the material along the sides exiting first, followed by the material in the central region. These patterns are observed with flow visualization and high-speed photography. The study also includes measurements of the discharge rate, which increases with the amplitude of the velocity of vibration