Reza Ali

Laminar-turbulent boundary-layer transition over a rough rotating disk

Boundary-layer transition over a disk spinning under water is investigated. Transitional Reynolds numbers, Rec, and associated boundary-layer velocity profiles are determined from flow-visualizations and hot-film measurements, respectively. The value of Rec and the velocity profiles are studied as a function of the disk’s surface roughness. It is found that transition over rough disks occurs in a similar fashion to that over smooth disks, i.e., abruptly and axisymmetrically at well-defined radii. Wall roughness has little effect on Rec until a threshold relative roughness is reached. Above the threshold Rec decreases sharply. The decrease is consistent with the drop one expects for our flow for the absolute instability discovered by Lingwood [J. Fluid Mech. 299, 17 (1995); 314, 373 (1996); 331, 405 (1997)]. This indicates that the Lingwood absolute instability may continue to play a major role in the transition process even for large relative roughness.

A coupled drug kinetics-cell cycle model to analyse the response of human cells to intervention by topotecan

A model describing the response of the growth of single human cells in the absence and presence of the anti-cancer agent topotecan (TPT) is presented. The model includes a novel coupling of both the kinetics of TPT and cell cycle responses to the agent. By linking the models in this way, rather than using separate (disjoint) approaches, it is possible to illustrate how the drug perturbs the cell cycle. The model is compared to experimental in vitro cell cycle response data (comprising single cell descriptors for molecular and behavioural events), showing good qualitative agreement for a range of TPT dose levels.

A deterministic model for the sublayer streaks in turbulent boundary layers for application to flow control

We present a relatively simple, deterministic, theoretical model for the sublayer streaks in a turbulent boundary layer based on an analogy with Klebanoff modes. Our approach is to generate the streamwise vortices found in the buffer layer by means of a vorticity source in the form of a fictitious body force. It is found that the strongest streaks correspond to a spanwise wavelength that lies within the range of the experimentally observed values for the statistical mean streak spacing. We also present results showing the effect of streamwise pressure gradient, Reynolds number and wall compliance on the sublayer streaks. The theoretical predictions for the effects of wall compliance on the streak characteristics agree well with experimental data. Our proposed theoretical model for the quasi-periodic bursting cycle is also described, which places the streak modelling in context. The proposed bursting process is as follows: (i) streamwise vortices generate sublayer streaks and other vortical elements generate propagating plane waves, (ii) when the streaks reach a sufficient amplitude, they interact nonlinearly with the plane waves to produce oblique waves that exhibit transient growth, and (iii) the oblique waves interact nonlinearly with the plane wave to generate streamwise vortices; these in turn generate the sublayer streaks and so the cycle is renewed.

Experimental verification of Type-II-eigenmode destabilization in the boundary layer over a compliant rotating disk

Destabilization of the Type-II eigenmode in boundary layers over compliant rotating disks was predicted theoretically by Cooper and Carpenter [J. Fluid Mech. 350, 231 (1997)]. Their results showed that for relatively low levels of compliance the Type-II eigenmode was destabilized, to be stabilized and ultimately eliminated for higher levels of compliance. The goal of the present study was to obtain the first experimental verification of the prediction that the Type-II mode can be destabilized at low levels of compliance. To this end a new type of rotating-disk apparatus was designed and a new type of material was used to produce suitable compliant walls for the experiments. Background noise in the new facility is substantially reduced in comparison with that in facilities used in related previous studies. This enabled the detection of substantially cleaner hot-film signals. Although the mean base flow remained unchanged, noise characteristics have been improved and turbulence intensities are significantly reduced. The measurements reveal not only the comparatively strong signals from the Type-I (cross-flow vortices) instability mode but also clear evidence of the Type-II eigenmode. In agreement with the theory of Cooper and Carpenter the data analysis shows that relatively low levels of wall compliance destabilize the Type-II mode.

Effects of wall compliance on the laminar–turbulent transition of torsional Couette flow

Torsional Couette flow between a rotating disk and a stationary wall is studied experimentally. The surface of the disk is either rigid or covered with a compliant coating. The influence of wall compliance on characteristic flow instabilities and on the laminar–turbulent flow transition is investigated. Data obtained from analysing flow visualizations are discussed. It is found that wall compliance favours two of the three characteristic wave patterns associated with the transition process and broadens the parameter regime in which these patterns are observed. The results for the effects of wall compliance on the third pattern are inconclusive. However, the experiments indicate that the third pattern is not a primary constituent of the laminar–turbulent transition process of torsional Couette flow.

DISTURBANCE DEVELOPMENT IN BOUNDARY LAYERS OVER COMPLIANT SURFACES

Numerical simulation results for the behaviour of disturbances in flows over compliant surfaces are described. Most attention is given to the propagation of Tollmien-Schlichting waves over compliant panels and the self-excited generation of such waves by very short panels. The use of compliant walls to suppress transiently growing forms of boundary-layer disturbance and the effects of surface compliance on the rotating disc boundary layer are also briefly discussed.

A NOVEL INTEGRATIVE BIOINFORMATICS ENVIRONMENT FOR ENCODING AND INTERROGATING TIMELAPSE MICROSCOPY IMAGES

Abstract Image-derived kinetic cell-based assays, where time is the quality parameter, demand unique solutions enabling image encoding and interrogation of spatio-temporal cellular events. Our overall strategy is to derive integrated data mining tools and predictive models capable of producing in-silico cell response fingerprints for use in drug screening, experimental therapeutics and hypothesis-testing for the design of treatment regimens. Critical to realizing this aim is the development of bioinformatics and visualisation tools to address problems of cellular heterogeneity, stochasticity and scaling for the impact of drugs on cell populations and to use these tools in making fundamental advances in our understanding of drug targeting in complex neoplastic systems.

A PK-PD model of cell cycle response to topotecan

Abstract A model describing the response of the growth of single human cells in the absence and presence of the anti-cancer agent, topotecan, is presented. The model is a result of linking the pharmacokinetic (pK) and pharmacodynamic (pD) responses. By linking the models in this way, rather than using separate (static) approaches, it is possible to illustrate how the drug perturbs the cell cycle. The model is validated for a range of drug concentrations with experimental data.

Modelling the Control of Cell Proliferation by An Anti-cancer Agent

A mathematical model has been developed which describes human cell growth in the presence of topotecan (TPT), an anti-cancer agent. Previously, a model was developed for the pharmacokinetics (PK) of TPT; this provided a description of the activity of TPT and the subsequent delivery of the active form to the nuclear DNA target. This model is described briefly in this paper. The development of a new pharmacodynamic (PD) model for cell growth, based on a well-known cell cycle model is then discussed. The linking of the PK model to the PD model is considered with respect to the modulation of cell growth. Our PK — PD model has good agreement with in vitro experimental data. In a clinical context, it is intended that the model will be used for discovering routes for drug resistance and eventually as a tool for improving drug treatments for patients.