Effect Of Segment Size Research Articles

Phase unwrapping for large depth-of-field 3D laser holographic interferometry measurement of laterally discontinuous surfaces

A phase unwrapping method is developed to mathematically increase the depth-of-field for the 3D optical measurement of objects with laterally discontinuous surfaces, which contain disconnected high aspect ratio regions. This method is applied for laser holographic interferometry precision measurements. The phase wrap identification at boundary pixels, masking and recovery, dynamic segmentation and phase adjustment are developed to overcome the divergence problem in phase unwrapping of laterally discontinuous surfaces. An automotive automatic transmission valve body is applied as an example to demonstrate the developed method. Experimental results demonstrate that the proposed methods can efficiently unwrap the phase to increase the depth-of-field for laterally discontinuous surfaces. Effects of segment size and width of overlapped regions on the computational efficiency are investigated.

Euclidean Cues versus Affine or Projective Invariants in the Visual Perception of Three-Dimensional Distances

Lappin and Fuqua (1983 Science221 480 – 482) reported accurate measurement of three-dimensional (3-D) distances and suggested that performance was based on structural invariance of patterns undergoing perspective transformations. We wanted to replicate their basic findings and test specific hypotheses about the use of Euclidean cues versus affine or projective invariants. The displays consisted of orthographic and perspective projections of three collinear dots rotating rigidly around a fixed centre in a plane slanted 45° in depth. Observers were asked to decide whether the middle of the three dots was exactly centred in 3-D space between the other two dots. The visible rotation segments were 120°, 160°, or 200° and the displacements were 2%, 4%, or 6%. Although our untrained observers performed more poorly overall than Lappin's well-practiced observers, two main results were replicated. First, there was no effect of segment size, which suggests that Euclidean cues were not used. Second, there was no difference between orthographic and perspective displays, which suggests that the invariants used must be projective, not affine. Additional experiments will be performed to investigate the relative importance of invariants such as cross ratios, which are based on the positions of the dots within each time frame, versus invariants of the conic sections, which are based on the elliptic traces of the dots formed over time.

Population Biology of the Clonal Moss Hylocomium Splendens in Norwegian Boreal Spruce Forests. II. Effects of Density

1 Hylocomium splendens is a perennial clonal moss in which new modules may emerge annually by ramification of the current mature segment or by regeneration, the time-delayed development from dormant buds. Demographic information on 14 776 growing points was obtained by following 119 Norwegian boreal spruce forest populations for 5 years. The dry weight of each mature segment was estimated from morphological field measurements. 2 The mean size of mature segments was positively correlated with the density (cover) of the bryophyte layer; a density increase from 0 to 100% was associated with a doubling in mean size. This relationship is attributed to the improved moisture conditions, and hence to prolonged periods with positive net photosynthesis, in dense stands. Mean size was not significantly related to the density of Hylocomium splendens growing points, suggesting that interactions in bryophyte stands are mainly with neighbours regardless of species. 3 The frequency of regeneration declined with increasing density, notably when the effects of segment size were corrected for. Negative density-dependence of regeneration is considered to be due to reduction of light-induced bud initiation in dense stands. 4 The size-corrected mortality (termination and loss) rate was not related to density. Danger of burial in the moss carpet, causing about one tenth of all terminations and losses, increased strongly with density and affected c. 5% of all growing points at high densities. 5 At high densities, Hylocomium splendens populations are not regulated by a negative relationship between size and density, but by a combination of reduced branching (ramification and regeneration) and increased danger of burial in the bryophyte carpet. However, such high densities are infrequent in the forest floor (affecting less than 10% of the area investigated). It is suggested that differences in history due to finescale disturbance and microenvironmental variation are reflected in size differences of individual Hylocomium splendens segments, and that this is the major factor that keeps boreal forest bryophyte populations at low densities.

Word recognition with forced serial processing: Effects of segment size and temporal order variation

Serial processing was forced by displaying words one letter or letter cluster at a time. Letters or clusters appeared in adjacent spatial positions and in rapid sequence, followed immediately by a mask. Under these conditions, there was a sharp increase in the percentage of words correctly identified as the size of the letter clusters presented in series increased. In a control condition without masking, designed to permit parallel processing across clusters, words were identified near-perfectly, regardless of the size of the clusters displayed. Words displayed one letter at a time without masking were identified fairly well even when letters were presented in random order. The results are interpreted as evidence that skilled readers tend to process letters within words in parallel.

Effect of segment size and polydispersity on the properties of polyurethane block polymers

The dynamic-mechanical and thermal scanning behaviour of a series of specially synthesized linear segmented polyurethanes is presented. These materials possess a well defined segment molecular weight and molecular weight distribution and no possibility of intermolecular hydrogen bonding. The dynamic-mechanical transitions observed are assigned to specific molecular motions and the effect of segment size and molecular weight distribution is described. The results are explained in terms of hard segment domain perfection. Differential scanning calorimetry (d.s.c.) curves of annealed samples indicate that domain morphology may be affected by thermal treatment. A comparison of dynamic mechanical and d.s.c. results to hydrogen-bonded polyurethanes is made.