Velocity field in a twin-screw extruder

Velocity measurements inside the screw channels of a co-rotating, self-wiping, twin-screw extruder were carried out. A laser Doppler anemometer (LDA) system was used to measure tangential and axial velocity components in the translational region of one of the screws of a twin-screw extruder. The velocity measurements were carried out using heavy corn syrup at different screw speeds and for two forwards conveying elements differing in their pitch. It was found that velocity profiles in the translational region were substantially affected by the pitch of the screw element, however, screw speed (30–90 r.p.m.) did not have a significant effect on the shape of the velocity profiles. The range of velocity values in a 14 mm pitch screw element was wider than that in a 28 mm pitch screw element. Experimentally measured velocity profiles were compared with predictions of a one-dimensional model, which showed that the model underpredicted the velocity values, for the 14 mm pitch element.     

Mass-transport enhancement in regions bounded by rigid walls

The mass transport into a fluid bounded by stationary rigid walls in the limit of large Péclet number, Pe, is examined analytically. Two model systems are considered in detail: a stationary cavity and a model involving two concentric rotating cylinders. A macroscopic gradient is imposed between the top and bottom surfaces. It is demonstrated that mass transport into the fluid is enhanced owing to a recirculation zone which is connected to the solid boundary through a boundary layer of thickness O(Pe ^–1/3) in which cross-stream molecular diffusion is balanced by convection. The associated enhancement is large and scales as Pe ^1/3. Our asymptotic analysis is found to be in good agreement with numerical solutions of the full transport equation.     

Wave dynamics on a thin-liquid film falling down a heated wall

The dynamics of a thin liquid film falling down a uniformly heated wall is studied. The model introduced by Kalliadasis et al. [J. Fluid Mech. 475 (2003) 377] for the same problem is revisited and its deficiencies, namely the prediction of a critical Reynolds number with 20% error, cured. For the energy equation a high-order Galerkin projection in terms of polynomial test functions is developed. It is shown that not only does this more refined formulation correct the critical Reynolds number, but it also gives, with an appropriate expansion close to criticality, the long-wave theory. Bifurcation diagrams for permanent solitary waves are constructed and compared with the solution branches obtained from different models. It is shown that, in all cases, the long-wave theory exhibits limit points and branch multiplicity, while the other models predict the continuing existence of solitary waves. Time-dependent computations show that the free surface and interfacial temperature approach a train of coherent structures that resemble the infinite-domain stationary solitary pulses.     

A computational model for RNA multiple structural alignment

This paper addresses the problem of aligning multiple sequences of noncoding RNA (ncRNA) genes. We approach this problem with the biologically motivated paradigm that scoring of ncRNA alignments should be based primarily on secondary structure rather than nucleotide conservation. We introduce a novel graph theoretic model (NLG) for analyzing algorithms based on this approach, prove that the RNA multiple alignment problem is NP-Complete in this model, and present a polynomial time algorithm that approximates the optimal structure of size S   within a factor of O(log²S)$\mathrm{O}({\log }^{2}S)$.     

Novel Imatinib Derivatives with Altered Specificity between Bcr–Abl and FMS,KIT, and PDGF Receptors

Imatinib is a clinically important ATP analogue inhibitor that targets the tyrosine kinase domain of the intracellular Abl kinase and the PDGF receptor family. Imatinib has revolutionised the treatment of chronic myeloid leukaemia, which is caused by the oncogene Bcr–Abl and certain solid tumours that harbor oncogenic mutations of the PDGF receptor family. As a leading kinase inhibitor, imatinib also provides an excellent model system to investigate how changes in drug design impact biological activity, which is an important consideration for rational drug design. Herein we report a new series of imatinib derivatives that in general have greater activity against the family of PDGF receptors and poorer activity against Abl, as a result of modifications of the phenyl and N‐methylpiperazine rings. These new compounds provide a platform for further drug development against the therapeutically important PDGF receptor family and they also provide insight into the engineering of drugs with altered biological activity.     

Influence of gravity on the spreading of two-dimensional droplets over topographical substrates

The influence of gravity on the motion of a two-dimensional droplet of a partially wetting fluid over a topographical substrate is considered. The spreading dynamics is modeled under the assumption of small contact angles in which case the long-wave expansion in the Stokes-flow regime can be employed to derive a single equation for the evolution of the droplet thickness. The relative importance of gravity to capillarity in the equation is measured by the Bond number which is taken to be low to moderate. In this regime, the flow in the vicinity of the contact line is matched asymptotically through a singular perturbation approach to the flow in the bulk of the droplet to yield a set of coupled integrodifferential equations for the location of the two droplet fronts. The matching procedure is verified through direct comparisons with numerical solutions to the full problem. The equations obtained by asymptotic matching are analyzed in the phase plane and the effects of Bond number on the droplet dynamics and its equilibria are scrutinized.     

Flame quenching through endothermic reaction

A laminar premixed flame model is considered in which there is a second-order branching reaction coupled with an endothermic decay of a chemical inhibitor. An analysis, based on high activation energies for the reactions, is performed and two distinct cases are found. These depend on dimensionless parameters representing the loss of heat relative to its production, , and the consumption of inhibitor relative to that of fuel, . With 1, extinction is achieved through a saddle-node bifurcation at a critical value of . For , no extinction is found though considerable reductions in wave speed over the adiabatic limit are seen. The asymptotic results are compared with numerical simulations of an initial-value problem for the model.