Spaces Of Different Sizes Research Articles

SPATIAL COGNITION AND SCALE: A CHILD'S PERSPECTIVE

Scale is an essential component in geographic and spatial cognition. Spatial cognition in spaces of different size, or scale, relies on qualitatively different information. In order to provide empirical evidence for differences between spaces of different size a controlled experiment was conducted comparing a large, environmental space with a small, desktop space. Two groups of children (7 and 9 years of age) and one group of adults participated in the study. Each participant experienced one of the two experimental spaces, all participants completed the same set of tasks. Two location recall tasks were completed, as was a spatial description task. Location recall consisted of learning an array of five objects in one of the two experimental spaces and performing two reconstruction tasks. The first reconstruction task was a ‘landmark free’ location recall task, which required participants to place one of the five objects (arbitrarily chosen) in the location it occupied during the learning episode. This was followed by a ‘relative’ location recall task, which required participants to place as many of the remaining four objects (from the learning episode) back in the experimental space. Both object identity and location recall were recorded over five trials (five distinct arrays of objects). In the second phase of the experiment participants described an array of five objects in the same space in which the reconstruction task had been completed. Participants' use of frames of reference while describing spatial location, orientation and arrangement was recorded to indicate mechanisms for the encoding and recall of spatial location in different size spaces. The availability and use of local and permanent frames of reference appear to facilitate location recall in the absence of proximal landmarks in large spaces. Relative location recall improves with age and is better in large, environmental spaces. This pattern is supported by both increased accuracy in location recall (landmark free recall in particular) and the structure and completeness of verbal descriptions.

Scanning tunneling microscopic and voltammetric studies of the surface structures of an electrochemically activated glassy carbon electrode.

The microscopic surface structures of electrochemically activated glassy carbon have been examined by scanning tunneling microscopy. Experimental results demonstrate that there are two different types of electrode surface sites, corresponding to the bundles and bundle edges of the fibrous graphite microcrystallities. Electrochemical activation results in the formation of new void spaces of different sizes, and the structures are affected by the electrochemical activation procedures employed. The void volume resulting from cyclic polarization is usually smaller than that obtained by potentostatic activation. Electrochemical behaviors of the activated electrode are related to both the new void structures and the size of the electroactive species employed. On the basis of the STM voltammetric results, the microscopic structure of the activated electrode is proposed.

Poisson processes of carbonate accumulation on Paleozoic and Holocene platforms

ABSTRACT Cambro-Ordovician carbonate lithofacies units in the Elbrook and Conococheague formations exposed at Wytheville, Virginia, as well as those in many other Phanerozoic peritidal sequences, exhibit exponential thickness frequency distributions. That is, occurrence frequency decreases exponentially with linear increase in unit thickness. Such distributions are characteristic of waiting times between independent Poisson events. This relative frequency of spaces of different size between horizons of lithologic change is what one would expect if the horizons were distributed randomly throughout carbonate successions. Abundances of different lithologies, both as net stratigraphic thickness and as number of occurrences, also decreases exponentially among successively rare sediment types, with each lithology being about 60% as plentiful as the next more abundant rock type. Relations between net thickness and number of occurrences for each facies define a linear trend coincident with a mean thickness for all Wytheville units of 0.48 m, a relation indicating that thickness distribution is independent of facies type. Similar relations are apparent for the horizontal extent of carbonate sediment bodies from the Holocene Florida-Bahama platform. Areal extents of individual facies units (lithotopes) are described by a frequency distribution in agreement with that anticipated for a population of equidimensional facies elements whose diameter distribution follows an exponential frequency distribution. Although regional gradients in sediment texture and composition are also apparent along most transects from platform margin to interior, such frequency distributions indicate that lateral extents of individual sediment reflect a largely stochastic distribution of facies boundaries across this Holocene surface. Lithotope abundances also yield trends of exponentially decreasing dominance among successively subordinate facies, with each being about 70% as extensive the next more abundant sediment type. Relations between areas and abundances for all lithotopes define a covariant trend corresponding to a mean area of 2.2 103 km2 for all Florida-Bahamas lithotopes. We consider several numerical models of stochastic carbonate accumulation; although not demonstrably unique, scenarios incorporating the sequential superposition of randomly placed coniform lithotopes result in thickness and area frequency distributions that are the same as those observed in ancient and modern platform deposits. Such simulations of Poisson processes of sediment accumulation are in general agreement with stochastic models of lithologic heterogeneity that have been more widely applied to petroleum reservoirs and groundwater aquifers. To the as yet unknown degree that peritidal lithofacies area and thickness are correlated, data from Paleozoic and Holocene platforms suggest that carbonate units should exhibit length/height ratios of approximately 105. Given the decimeter scale over which facies are designated in most Paleozoic peritidal successions, these relations predict mean lateral extents on the order of several tens of kilometers, a value in general agreement with the few data that exist on spatial continuities of peritidal lithotopes in Paleozoic carbonate sequences.

Acrylic resin-fiber composite—part I: The effect of fiber concentration on fracture resistance

This study tested the effect on the fracture resistance of acrylic resin test specimens when different amounts of fibers were incorporated in the resin matrix. The fibers used included glass, carbon, and aramid fibers, with 30 test specimens of each concentration of fibers. Transverse sections of the specimens were studied by scanning electron microscope to establish how the fibers behave in the polymerization process. The results indicated that an increase in the amount of fibers enhanced the fracture resistance of the test specimens ( p < 0.001). The SEM micrographs of transverse sections of test polymerized specimens revealed void spaces of different sizes inside the fiber roving.

Vascular Transformation of Sinuses in Lymph Nodes

Vascular transformation of lymph node sinuses (VTS) is characterized by conversion of nodal sinuses into capillary-like channels, often accompanied by fibrosis. A detailed study of this entity, based on 76 cases, showed that the morphologic spectrum was much broader than that originally described. The vasoproliferative process caused variable expansion of the subcapsular, intermediate, and medullary sinuses of the lymph nodes and involved single or multiple lymph nodes in a diffuse or segmental fashion. The proliferated vessels formed anastomosing narrow clefts, rounded spaces of different sizes, plexiform channels, or solid spindled to plump cellular foci and often were associated with variable degrees of sclerosis. The vascular spaces were empty, filled with lymph-like fluid, congested with blood, or occasionally thrombosed; extravasation of red cells was common. Several patterns were commonly observed in an individual case. Less common features included perivascular fibrin deposition and the presence of eosinophilic globules. Vascular thrombosis was identified only rarely in extranodal vessels available for histologic assessment. The more cellular forms of this vascular transformation may be mistaken for Kaposi's sarcoma, but can be distinguished from it by the pure sinusoidal distribution, a lack of well-formed spindle cell fascicles, the associated fibrosis, the maturation of the spindle cells into well-formed vascular channels toward the capsular aspect, and the failure of this process to involve the capsule itself, which is frequently affected by Kaposi's sarcoma.

Homogeneous and isotropic clouds of membranes in extra dimensions

A model of a homogeneous and isotropic cloud formed by multidimensional membranes evolving in a spacetime with extra dimensions is presented. The dynamical behaviour of homogeneous and isotropic universes with membranes of several dimensions located in extra spaces of different sizes are studied in some detail. Some general features that depend on the relative dimensions involved in these type of universes are found.

Correlation of ultrasound and pathologic findings of placental anomalies in pregnancies with elevated maternal serum α-fetoprotein

Twenty pregnancies with elevated maternal serum α-fetoprotein (MSAFP), a normal fetus and unusual or abnormal placental/cord sonographic features are reported. These include: (A) gigantic enlargement with multiple sonolucent spaces of different size and shape (n = 2; Swiss cheese); (B) placental masses of variable echogenicity (n = 5); (C) cord masses with central echo-dense zone and peripheral hypoechoic areas (n = 2); (D) enlarged placentas with patchy decrease of echogenicity (n = 6; jelly-like); and (E) large sonolucent spaces with turbulent blood flow surrounded by normal placental tissue (n = 5; placental lakes). After delivery, these ultrasound features were compared with pathologic findings. Diffuse mesenchymal hyperplasia of the stem villi were found in the gigantic placentas (n = 2). The placental masses corresponded to chorioangiomas (n = 3), infarct (n = 1) or subamniotic hematoma (n = 1) and the cord masses to angiomyxomas (n = 2). The ‘jelly-like’ placentas were related to subchorial thrombosis (n = 2), massive fibrin deposition (n = 1) or hypertrophy with no obvious abnormalities (n = 3). Large subchorial thrombosis (n = 2), or no obvious abnormalities (n = 3) were observed in placentas with large lakes. These findings suggest that a large range of placental and cord anomalies are associated with elevated MSAFP and are potentially diagnosable by routine sonographic examination at the time of AFP screening.

Profiles of water content and pore size in Sphagnum and peat, and their relation to peat bog ecology

The bog mosses, Sphagnum , form a significant part of the total mass of plants in the world. Their rate of growth depends to a considerable extent on the supply of water to them, and different species occupy characteristic habitats which differ in their ability to supply water. We used the profiles of water content in almost undisturbed cores of two species to infer the size and distribution of spaces around the plants in an attempt to account for the observation that S. papillosum is usually found not far above the water table, while S. capillifolium is usually found on hummocks well above the water table. Profiles of water content were recorded non-destructively from 30 cm diameter cores of Sphagnum and underlying peat, with use of the absorbance of the soft gamma radiation of 241 Am. The distribution of water-fillable spaces of different size was inferred from profiles with the water table at different distances, to a maximum of 150 cm, below the surface. The larger spaces, which are the main path of water transport, are outside the plant cell walls: between leaves and between pendent branches and stems. The mean radius of such spaces around the hummock species S. capillifolium is smaller than that around S. papillosum . For a given depth of water table the water content of the apical tuft of branches, where growth occurs, is greater in the hummock species than it is in the lawn species. Of ecological importance is that, for a given water content in the apex, the water table is at a greater depth below the hummock species than it is below the lawn species. As the water table rises and falls, so the water content of both species shows hysteresis as large as the difference between them. The ecological significance of this and the need for measurements while water is flowing are discussed.

Modifications of the perilacunar walls resulting from the effect of fluoride on osteocytic activity

Modifications of periosteocytic lacunae are commonly observed in fluorosis. Both mottled and enlarged larunae are recognizable in microradiographs. The mottled lacunae have cavities of normal size, ellipsoidal shape and smooth contour. An ill-defined area of hypomineralized matrix is eccentrically disposed around the lacunae and a tangled mass of canaliculi is embedded in the hypomineralized matrix. The ultrastructural study of this area reveals that, in the organic matrix, the collagen fibrils are not closely packed, but separated by spaces of different sizes; there is no morphological evidence of collagen dissolution. Rounded clusters of crystallites are scattered between and on the fibrils. The existence of mottled lacunae is attributed to impaired bone formation, a defect also observed in vitamin-D resistant rickets. Enlarged lacunae are the result of periosteocytic osteolysis. M the microradlographs, they are characterized by their large size, their sharply outlined borders and the fact that they are surrounded by a well mineralized bone matrix. Their large size is confirmed by morphometric study. Electron microscopy, however, reveals that the decalcification front has a rough and irregular contour during periosteocytic osteolysis. When the mineral substance has disappeared, the collagen fibrils swell and are destroyed. The “origin” of the two types of periosteocytic lacunae is discussed with regard to parathyroid hormone level for the enlarged lacunae and to appositional growth rate, quality of organic matrix and evolution of osteoblasts into osteocytes for mottled lacunae.