Replication and differentiation of spots in a class of reaction–diffusion equations are studied by extending the Gray–Scott model with self-replicating spots so that it includes many chemical species. By examining many possible reaction networks, the behavior of this model is categorized into three types: replication of homogeneous fixed spots, replication of oscillatory spots, and differentiat...

In Flanders, approximately 1014 accident locations are currently considered as ‘dangerous’. These ‘dangerous’ accident sites or ‘black spots’ are selected by means of their historic accident data for the period 1997-1999. More specifically; a combination of weighting values, respectively 1 for each light injury, 3 for each serious injury and 5 for each deadly injury (1_3_5), is used to rank and...

Psychophysical evidence is given for the existence of two distinct systems in human vision: a fast, sign-invariant system concerned with extracting contours and a slower, sign-sensitive system concerned with assigning surface color. A class of stimuli we developed seems to selectively activate the fast, contour system. This stimulus is formed by adjacent fields of black and white spots, which f...

Pigmented Bowen's disease is rare, though more prevalent in men. It presents as a well-delineated plaque in areas unexposed to sun. There are reports of association with seborrheic keratosis, solar lentigo or exuberant pigmentation of genital and intertriginous regions. A specific dermoscopy finding is the presence of brown or gray dots in regular arrangement and coiled or dotted vessels. Thus,...

Actin networks in certain single-celled organisms exhibit a complex pattern-forming dynamics that starts with the appearance of static spots of actin on the cell cortex. Spots soon become mobile, executing persistent random walks, and eventually give rise to traveling waves of actin. Here we describe a possible physical mechanism for this distinctive set of dynamic transformations, by equipping...

We describe a simple way to generate a wide-area high-resolution focus grid by in-line holography and study the factors that impacts its quality. In our holographic recording setup, the reference beam was the direct transmission of the incoming collimated laser beam through a mask coating with thin metal film, and the sample beam was the transmission of the laser through small apertures fabrica...

A series of Astatotilapia burtoni photographs were used to investigate the ontogenetic development of male egg-spots, a putative evolutionary key innovation of haplochromine cichlids. Four stages of egg-spot development were defined and all males had developed true egg-spots (stage 4) before reaching a standard length of 25 mm. Raising condition only slightly influenced the timing of the first ...