Numerical investigation of controlling interfacial instabilities in non-standard Hele-Shaw configurations

Viscous fingering experiments in Hele-Shaw cells lead to striking pattern formations which have been the subject of intense focus among the physics and applied mathematics community for many years. In recent times, much attention has been devoted to devising strategies for controlling such patterns and reducing the growth of the interfacial fingers. We continue this research by reporting on numerical simulations, based on the level set method, of a generalised Hele-Shaw model for which the geometry of the Hele-Shaw cell is altered. First, we investigate how imposing constant and time-dependent injection rates in a Hele-Shaw cell that is either standard, tapered or rotating can be used to reduce the development of viscous fingering when an inviscid fluid is injected into a viscous fluid over a finite time period. We perform a series of numerical experiments comparing the effectiveness of each strategy to determine how these non-standard Hele-Shaw configurations influence the morphological features of the inviscid-viscous fluid interface. Tapering plates in either converging or diverging directions leads to reduced metrics of viscous fingering at the final time when compared to the standard parallel configuration, especially with carefully chosen injection rates; for the rotating plate case, the effect is even more dramatic, with sufficiently large rotation rates completely stabilising the interface. Next, we illustrate how the number of non-splitting fingers can be controlled by injecting the inviscid fluid at a time-dependent rate while increasing the gap between the plates. Simulations compare well with previous experimental results for various injection rates and geometric configurations. Further, we demonstrate how the fully nonlinear dynamics of the problem affect the number of fingers that emerge and how well this number agrees with predictions from linear stability analysis

A new morphological marker in Neurospora

A new morphological marker in Neurospor

Speech perception in MRI scanner noise by persons with aphasia

Purpose. To examine reductions in performance on auditory tasks by aphasic and neurologically-intact individuals as a result of concomitant MRI scanner noise. Methods. Four tasks together forming a continuum of linguistic complexity were developed. They included complex-tone pitch discrimination, same/different discrimination of minimal pair syllables, lexical decision, and sentence plausibility. Each task was performed by persons with aphasia (PWA) and by controls. The stimuli were presented in silence and also in the noise recorded from within the bore of a 3T MRI scanner at three signal-to-noise ratios (S/Ns). Results. Across the four tasks, the PWA scored lower than the controls and performance fell as a function of decreased S/N. However, the rate at which performance fell was not different across the two listener groups in any task. Conclusions. Depending upon the relative levels of the signals and noise, the intense noise accompanying MRI scanning has the potential to severely disrupt performance. However, PWA are no more susceptible to the disruptive influence of this noise than are unimpaired individuals usually employed as controls. Thus, fMRI data from aphasic and control individuals may be interpreted without complications associated with large interactions between scanner noise and performance reduction

Instrumentation for the Evaluation of Business Students\u27 Performance in Class Presentations

This paper presents and discusses the use of two instruments that have been developed to provide students with structured and constructive quantitative feedback regarding their performance in class presentations that are frequently required in business school courses. The content of the instruments is described in detail, and suggestions for using and adapting the instruments to maximize student learning are discussed

Delivering Effective Presentations: A Review of Techniques for Enhancing Audience Involvement Reflections on a Lifetime in the Securities Industry

In this paper, the author reviews and discusses the use of several techniques to enhance the impact and interest of presentations delivered to an audience. Attention is given to those steps that can be taken to heighten the audience\u27s sense of involvement and participation in presentations. The rationale underlying the use of each technique is explained and examples of the techniques are provided

Defining a New Type of Organizational Leadership: The Heroic Leader

In this paper the concepts of leadership and heroism are defined, discussed, and compared. The concepts are then integrated to form an orientation toward leadership known as heroic leadership. A model of heroic leadership consisting of five major dimensions including character, work orientation, risk-taking and reward orientation, relating to others, and organizational impact is then presented and discussed. Major sub-elements for each dimension are also identified and examined. The implications for leadership in non-heroic organizational settings are highlighted