Fluctuations of DNA mobility in nanofluidic entropic traps

We studied the mobility of DNA molecules driven by an electric field through a nanofluidic device containing a periodic array of deep and shallow regions termed entropic traps. The mobility of a group of DNA molecules was measured by fluorescent video microscopy. Since the depth of a shallow region is smaller than the DNA equilibrium size, DNA molecules are trapped for a characteristic time and must compress themselves to traverse the boundary between deep and shallow regions. Consistent with previous experimental results, we observed a nonlinear relationship between the mobility and electric field strength, and that longer DNA molecules have larger mobility. In repeated measurements under seemingly identical conditions, we measured fluctuations in the mobility significantly larger than expected from statistical variation. The variation was more pronounced for lower electric field strengths where the trapping time is considerable relative to the drift time. To determine the origin of these fluctuations, we investigated the dependence of the mobility on several variables: DNA concentration, ionic strength of the solvent, fluorescent dye staining ratio, electroosmotic flow, and electric field strength. The mobility fluctuations were moderately enhanced in conditions of reduced ionic strength and electroosmotic flow.     

Problem Interpretation and Resolution via Visual Stimuli: The Use of ‘Mood Boards’ in Design Education

This paper defines and discusses ‘mood boards’– those assemblages of images and, less frequently, objects, which are used to assist analysis, creativity and idea development in design activity. There is need for discussion since little published information currently exists to guide students and tutors. The paper proposes that mood boards can assist problem finding as well as problem solving. Primarily, mood boards provide a mechanism for students and practising designers to respond to perceptions about the brief, the problem as it emerges and the ideas as they develop. The construction of mood boards potentially stimulates the perception and interpretation of more ephemeral phenomena such as colour, texture, form, image and status. They are, like Debono's lateral thinking techniques, partly responses to an inner dialogue and partly provocation to become engaged in such a dialogue. Examples are drawn from recent work in the field of industrial design at Loughborough University.