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A total of 63 patients with localized hepatic lesions were examined using two and three-dimensional sonography. The tumor volumes were calculated by means of the ellipsoid formula, compared with an experimentally determined reference volume and subsequently differentiated into correct and erroneous measurements according to the WHO criteria for tumor volumes. In a second test series, an analysis of the tumor shapes was carried out using parallel projections. It could be seen that 65% of the erroneous measurements resulted from the use of the ellipsoid formula, a procedure which is used to determine the volume of hepatic lesions. In the third part of this study, it was found that findings which are difficult to measure are frequently not recognized as such by the investigator making use of two-dimensional sonography. As a consequence, the volume measurements of focal hepatic lesions in oncology patients being considered for particular therapies should preferably be carried out with the aid of planimetric measurements rather than with the use of the ellipsoid formula.
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We consider the spatio-temporal dynamics of a spatially-structured generalization of the phytoplankton-zooplankton-fish larvae model system proposed earlier (Biktashev et al., 2003, J. Plankton Res. 5, 21-33; James et al., 2003, Ecol. Model. 160, 77-90). In contrast to Pitchford and Brindley (2001, Bull. Math. Biol. 63, 527-546), who were concerned with small scale patchiness (i.e., 1-10 m), on which the (stochastic) raptorial behaviour of individual larvae is important, we address here the much larger scale 'patchy' problems (i.e., 10-100 km), on which both larvae and plankton may be regarded as passive tracers of the fluid motion, dispersed and mixed by the turbulent diffusion processes. In particular, we study the dependence of the fish recruitment on carrying capacities of the plankton subsystem and on spatio-temporal evolution of that subsystem with respect to the larvae hatching site(s). It is shown that the main features found both in the nonstructured and age-structured spatially uniform models are observed in the spatially structured case, but that spatial effects can significantly modify the overall quantitative outcome. Spatial patterns in the metamorphosed fish distribution are a consequence of quasi-local interaction of larvae with plankton, in which the dispersion of larvae by large scale turbulent eddies plays little part due to the relatively short timescale of the larvae development. As a result, in a strong phyto/zooplankton subsystem, with fast reproduction rate and large carrying capacity of phytoplankton and high conversion ratio of zooplankton, recruitment success depends only on the localization and timing of the hatching with respect to the plankton patches. In a weak phyto/zooplankton system, with slow reproduction rate and small carrying capacity of phytoplankton and low conversion ratio of zooplankton, the larvae may significantly influence the evolution of the plankton patches, which may lead to nontrivial cooperative effects between different patches of larvae. However, in this case, recruitment is very low.
Stable spatially localized structures exist in a wide variety of spatially extended nonlinear systems, including nonlinear optical devices. We study stochastic resonance (SR) in models of optical parametric oscillators in the presence of a spatially uniform time-periodic driving and in a regime where two equivalent states with equal intensity but opposite phase exist. Diffraction and nonlinearity enable the existence of localized states, formed by the locking of kinks and antikinks and displaying spatially damped oscillatory tails (in one dimension) or the stabilization of dark ring cavity solitons (in two dimensions). We show that SR is inhibited at low driving amplitudes by the presence of localized states which obstruct the front motion. For larger driving amplitudes, in the regime where localized states cease to be stable, we observe instead an enhancement of SR.
Spatial reconstruction of anatomic and histologic structures is of increasing importance in biological and medical research. A special kind of disease--hereditary opalescent dentine (HOD)--offered a good chance for the use of a comfortable image-analysis system (IBAS, Kontron) in combination with a special software for three-dimensional reconstruction. New aspects of the morphologic organisation of a key structure of HOD--the giant dentinal canals--could be shown, thus supporting the hypothesis of a vasal origin.
"Using ten Asian megacities as examples, this article discusses a range of megacity characteristics and problems, including population growth, economic structure, spatial strategies, land policy, urban service provision, institutional development, and managerial problems. In spite of major progress in urban service delivery, ineffective land policies and inadequate cost-recovery systems remain serious obstacles. Megacities need and are promoting policentric spatial structures, but implementation lags in many cases. Institutional reforms are needed to cope with the metropolitan region character of megacity growth."
Pigeons (Columba livia) were trained with a spatial structural discrimination, which was based on the spatial relationship among the components of a pattern, and a feature-binding structural discrimination, which was based on how different visual features within a pattern were combined. Neither discrimination was impaired by damage to the hippocampus and area parahippocampalis. The lesions impaired performance on a spatial working memory and a spatial reference memory task in open field. The results indicate an intact hippocampus is not essential for the solution of structural discriminations in pigeons and the hippocampus is important for processing some types of spatial information--that used in navigation, but not other types--that used in spatial structural discriminations.
By using statistics and geostatistics, this paper studied the content and spatial pattern of soil total nitrogen (TN) in a glassland and an arable land of southeast Keerqin sandy land. The TN content in 0-10 cm soil layer of the arable land reclaimed from a glassland 8 years ago was not different from that of the virgin grassland, but the TN content in 10-20 cm soil layer was higher than that in the grassland (P < 0.05). The soil TN storage in the grassland was 262.36 g x hm(-2) higher than that in the arable land, and its spatial pattern was significantly different between arable land and grassland. The heterogeneity and spatial dependence of TN in each soil layer (0-10 cm and 10-20 cm) of the arable land were larger than those of the grassland, and the ranges and fractal dimensions of TN in each soil layer of the arable land were larger than those of the grassland. There existed a clear horizontal spatial structure heterogeneity and spatial distribution pattern in the arable land, while in the grassland, the horizontal spatial structure heterogeneity was very low, and the horizontal spatial distribution pattern was random and uniform. The TN content in the 0-10 cm and 10-20 cm soil layers of the arable land had no difference (P < 0.05), its spatial structure characters had some difference (P < 0.05), and its spatial distribution pattern was very similar (r = 0.683, P < 0.05). The TN content and its spatial structure characters between two soil layers of the grassland had remarkable difference (P < 0.05), but its spatial distribution pattern in the two layers was relatively similar (r = 0.395, P < 0.05). In conclusion, agricultural activity could not only influence soil TN content, but also influence its spatial structure characteristics and spatial distribution pattern. Therefore, our study might promote the further study on the effect of land use change on soil nitrogen distribution pattern and its cycling in ecosystems.
Spatial structure of genetic variation within populations is well measured by statistics based on the distribution of pairs of individual genotypes, and various such statistics have been widely used in experimental studies. However, the problem of uncharacterized correlations among statistics for different alleles has limited the applications of multiallelic, multilocus summary measures, since these had unknown sampling distributions. Usually multiple alleles and/or multiple loci are required in order to precisely measure spatial structures, and to provide precise indirect estimates of the amount of dispersal in samples of reasonable size. This article examines the correlations among pair-wise statistics, including Moran I-statistics and various measures of conditional kinship, for different alleles of a locus. First the correlations are mathematically derived for random spatial distributions, which allow averages over alleles and loci to be used as more powerful yet exact test statistics for the null hypothesis. Then extensive computer simulations are conducted to examine the correlations among values for different alleles under isolation by distance processes. For loci with more than three alleles, the results show that the correlations are remarkably and perhaps surprisingly small, establishing the principle that then alleles behave as nearly independent realizations of space-time stochastic processes. The results also show that the correlations are largely robust with respect to the degree of spatial structure, and they can be used in a straightforward manner to form confidence intervals for averages. The results allow a precise connection between observations in experimental studies and levels of dispersal in theoretical models.
Arabidopsis halleri, a close wild relative of A. thaliana, is a clonal, insect-pollinated herb tolerant to heavy metals (Zn, Pd, Cd) and a hyperaccumulator of Zn and Cd. It is of particular interest in the study of evolutionary processes and phytoremediation. However, little is known about its population gene flow patterns and the structure of its genetic diversity. We used five microsatellite loci to investigate the genetic structure at a fine spatial scale (10 cm to 500 m) in a metallicolous population of A. halleri. We also studied the contributions made by clonal propagation and sexual reproduction (seed and pollen dispersal) to the genetic patterns. Clonal diversity was high (D(G) > 0.9). Clonal spread occurs only at short distances (< 1 m). Both clonal spread and limited dispersal, associated with sexual reproduction, contribute to the significant spatial genetic structure revealed by spatial autocorrelation analysis. The shape of the autocorrelogram suggests that seed dispersal is restricted and pollen flow extensive, which may be related to intense activity by insect pollinators. Clonal spread was more extensive in the lowly polluted zone than in the highly polluted zone. This cannot be interpreted as a strategy for promoting the propagation of adapted genotypes under the harshest ecological constraints (highest heavy metal concentrations). The higher fine-scale spatial genetic structure found in the lowly polluted zone can be ascribed to plant densities that were lower than in the highly polluted zone. No evidence of genetic divergence due to spatial heavy metal heterogeneity was found between lowly and highly polluted zones.