Showing papers by "Emory University published in 1984"

Persistence in models of three interacting predator-prey populations

Abstract: This paper considers a class of deterministic models of three interacting populations with a view towards determining when all of the populations persist. In analytical terms persistence means that liminft→∞x(t)> 0 for each population x(t); in geometric terms, that each trajectory of the modeling system of differential equations is eventually bounded away from the coordinate planes. The class of systems considered allows three level food webs, two competing predators feeding on a single prey, or a single predator feeding on two competing prey populations. As a corollary to the last case it is shown that the addition of a predator can lead to persistence of a three population system where, without a predator, the two competing populations on the lower trophic level would have only one survivor. The basic models are of Kolmogorov type, and the results improve several previous theorems on persistence.

Dynamic Scaling for Aggregation of Clusters

Abstract: The model of cluster growth by diffusion-limited aggregation of clusters is studied in two dimensions and the cluster size distribution ${n}_{s}(t)$ is determined as a function of the cluster size $s$ and the time $t$. A dynamic scaling function of the form ${n}_{s}(t)\ensuremath{\sim}{t}^{\ensuremath{-}w}{s}^{\ensuremath{-}\ensuremath{\tau}}f(\frac{s}{{t}^{z}})$ is proposed and is shown to lead to the scaling relation $w=(2\ensuremath{-}\ensuremath{\tau})z$ among the critical exponents. The simulation results support this scaling law.

Oxidative stress on lens and cataract formation: role of light and oxygen.

Abstract: The mechanism of oxidative damage to the lens through intraocular photochemical generation of superoxide and its derivatization to other oxidants such as singlet oxygen, hydroxyl radical and hydrogen peroxide has been studied. Rat lenses when organ cultured aerobically in TC 199 containing additional amounts of riboflavin were damaged as demonstrated by an inhibition of the uptake of Rb 86 against a concentration gradient. The pump was not affected by light if the culture was conducted in the basal TC 199. However, light was observed to induce significant peroxidative degradation of the tissue lipids even in the basal medium, the degradation being indicated by the formation of malonaldehyde. Both the inhibition of the pump as well as the peroxidative degradation of the tissue lipids, were attenuated considerably by scavengers of superoxide and hydrogen peroxide. In addition, the lipid degradation was prevented by vitamins C and E. The results suggest that the photodynamic injury to the lens cation pump as well as to membrane lipids is incumbent upon an initial generation of superoxide and its derivatization to other oxidants. Thus, the ocular lens is susceptible to oxidative insult and physiological damage through photocatalytic generation of various oxygen radicals. Large concentrations of ascorbic acid in the aqueous humor seems to be able to provide significant protection against such an insult. Thus, this may be one of the functions of high concentration of ascorbic acid in the aqueous humor. The implication of oxidative stress has also been examined in the genesis of cataracts in vivo. Treatment with vitamin E of the Emory mouse led to a decrease in the rate of cataract progression suggesting that at least in some instances an oxidative stress could participate in the formation of cataracts. Oxygen radicals may inflict damage at multifarious biochemical sites. Human lens lipids were also shown to have an absorption maxima at 239 nm indicating their susceptibility to oxidative degradation. In addition the lipid extract has fluorescence similar to that of lipofuscins. The levels of MDA were higher in the brunescent cataracts as compared to that in the nonbrunescent cataracts. The implications of oxidative stress towards the genesis of cataracts in humans is being explored further.

Risk of side branch occlusion during coronary angioplasty.

Abstract: To assess the risk of side branch occlusion during percutaneous transluminal coronary angioplasty (PTCA), 600 consecutive procedures were analyzed. On the basis of pre-PTCA angiograms of 557 patients in whom the balloon was actually inflated, 365 side branches in 302 patients (54% of patients) were deemed in jeopardy. A total of 122 side branches in 102 patients (18%) originated from the lesion segment itself, i.e., their take-off was narrowed (Group I, 33% of side branches at risk), whereas 243 side branches in 214 patients (38%) originated from the immediate vicinity of the stenosis in a way that they were subjected to temporary occlusion during balloon dilatation (Group II, 67% of side branches at risk). Patency of side branches was determined by consensus of 2 observers. Criteria for occlusion were disappearance, filling by collaterals, or stagnation of flow. After PTCA, 20 of 365 side branches (5%) were occluded and associated with chest pain in 5 patients, creatine kinase increase in 6, left anterior hemiblock, septal Q waves and transient atrial fibrillation in 1 and non-sustained ventricular tachycardia in 1 of the 20 patients. Exercise tolerance did not decrease. No local predilection for side branch occlusion was evident. Seventeen of 122 side branches (14%) occluded in Group I, compared with 3 of 243 (1%) in Group II (p less than 0.001). Thus, more than half of the patients who underwent PTCA had side branches at risk for iatrogenic occlusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Dendritic and axonal organization of mitral and tufted cells in the rat olfactory bulb.

Abstract: The output cells of the main olfactory bulb, the mitral and tufted cells, can be categorized into subclasses on the basis of their intrabulbar dendritic and axonal characteristics. Their form was studied in rats following labeling by iontophoretic injection of horseradish peroxidase into the external plexiform layer (EPL). The fact that these extracellular injections labeled small numbers of neurons permitted reconstruction of individual cells. The injection depth within the EPL determined the type of cells labeled. Secondary dendrites of each cell type lay in one of three partially overlapping zones in the EPL. The deepest zone contained the secondary dendrites of one group of mitral cells (Type I), which had the deepest and longest dendrites of the output cells. An intermediate zone of the EPL contained the secondary dendrites of middle tufted and a second class of mitral cells (Type II). The superficial zone, adjacent to the glomerular layer, contained the relatively short, asymmetric dendritic fields of external tufted cells. The few labeled internal tufted cells had secondary dendrites in either the intermediate or deep zones. Every cell type, except the Type I mitral cells, had axon collaterals in the internal plexiform and upper granule cell layers. No cell types had axons re-entering the EPL. These results for output cells combined with our previous observations on granule cells point to a functional sublaminar organization of the EPL that has not previously been proposed.

The incidence of occult metastases for cancer of the oral tongue and floor of the mouth: treatment rationale.

Abstract: One hundred thirty-six surgical cases of squamous cell carcinoma of the oral tongue and floor of the mouth at the Emory University Hospitals were reviewed for the incidence of occult metastases. Thirty-five percent of the T1 T2 lesions of the anterior tongue had occult metastases. The figure was 31.5% for similarly staged lesions of the floor of the mouth. The presence of regional metastases resulted in a 2-year determinate survival rate of 37% and 32% for patients with oral tongue and floor of the mouth lesions, respectively. The poor prognosis in the study for delayed cervical metastases and the high incidence of occult cervical metastases have led the authors to propose a more aggressive therapy for the clinically negative necks in these two sites of squamous cell carcinoma of the oral cavity.

Pattern Formation in Diffusion-Limited Aggregation

Abstract: The diffusion-limited-aggregation model is generalized in order to take into account the surface effects playing an essential role during most of the growth processes. With variation of a parameter of the model the geometry of the clusters generated in the Monte Carlo simulations gradually changes from the randomly branched diffusion-limited-aggregation clusters into compact, nearly regular, snowflakelike patterns. The deposition of particles along a line results in patterns similar to those observed in the experiments on directional solidification.

Crevicular fluid prostaglandin E levels as a measure of the periodontal disease status of adult and juvenile periodontitis patients

Abstract: The measurement of crevicular fluid PGE (CF-PGE) as an indicator of periodontal disease status was investigated. The association between CF-PGE levels and the PGE content of the adjacent periodontal tissues was found to be highly significant (P=5.3 × 10−6). The high correlation (r=0.925) between the log CF-PGE level and the tissue PGE concentration indicates that CF levels can be used to reliably predict tissue levels. The CF-PGE measurements at each periodontal site were found to be highly reproducible. Samples from adult and juvenile periodontitis patients demonstrated that the mean CF-PGE levels were correlated with disease severity, as determined by mean attachment loss. The mean CF-PGE level in juvenile periodontitis patients was almost three-fold higher than that present in adult periodontitis (144.0 ± 28.0 ng/ml vs 57.5 ± 8.7 ng/ml, mean ± S.E., significant at P = 0.002). The use of CF-PGE concentrations as an indicator of disease activity (i.e. longitudinal attachment loss) cannot be demonstrated by this cross-sectional study. However, the CF-PGE measurement has been demonstrated to be a non-invasive, sensitive, reproducible, and reliable reflection of tissue levels of PGE2. The association of increasing levels of CF-PGE with increased severity and aggressiveness of disease is consistent with PGE as an inflammatory mediator of tissue destruction.

Compartmentalization of single muscle units in cat lateral gastrocnemius

Abstract: The distribution of muscle fibers in single muscle units in cat lateral gastrocnemius (LG) muscle was analyzed using the method of glycogen depletion. Single, type FF motor units in LG were identified by stimulation of dissected ventral rootlets and then activated to produce depletion of glycogen in their innervated muscle fibers. Serial histological sections were made of the entire triceps surae muscles and then reacted for the demonstration of glycogen. Projected tracings of the sections were used to compare the distribution of glycogen depleted muscle fibers to the heads of the LG muscle. Results of analysis of single muscle units indicate that the muscle fibers innervated by single cat LG type FF motor units are distributed to the same regions of muscle which are innervated by primary branches of the nerve to the LG muscle. The single units are thus compartmentalized. These results support the hypothesis that each of the neuromuscular compartments of LG contains a unique population of motor units. It is suggested that compartmentalization of muscles about primary branches of their muscle nerves may from a major organizational principle in the design of skeletal muscles.

Sizes, laminar and topographic origins of cortical projections to the major divisions of the red nucleus in the monkey.

Abstract: The retrograde transport of horseradish peroxidase was used to study the topographic and laminar origins of the cortical projections to the parvocellular and the magnocellular divisions of the red nucleus in Macaca mulatto and Macaca fascicularis. Approximately 90% of the corticorubral projection is directed to the parvocellular division of the nucleus. Corticoparvocellular division of the nucleus. Corticoparvocellular (CRp) neurons are pyramidally shaped, are smaller in size than corticospinal neurons, and are more numerous. They are found principally in sublamina Va of cytoarchitectonic areas 4 and 6, and in moderate quantities in sublamina Vb of posterior area 8 and area 5. In areas 4 and 6, the cells are grouped in clusters of three to 15 neurons each and are arranged in cellular bands of varying rostrocaudal thickness which course mediolaterally. With respect functionally define zones, CRp neurons are found through the supplementary motor area and the precentral motor cortex. In addition, they are found in parts of area 5, 6, and 24 that project to these cortical motor areas, and that are thought to have “premotor” or movement programmming functions. The corticomagnocellular (CRm) projection arises principally from cells in sublamina Vb of the precentral arm and leg areas (area 4), and from adjacent parts of posterior area 6. CRm cells are pyramidally shaped and their size distribution is bimodal, with peaks that correspond, respectively, to the modal diameters of CRp and of corticospinal neurons. These result and those of previous studies that CRm neurons are involved principally in the control of hand and foot movements, with little effect on proximal musculature. The massive CRp projection, however, is clearly part of a large cerebrocerebellar communications system, with motor and/or movement programming functions that have yet to be clearly defined.

Interpreting Harry Bahrick's discovery: what confers immunity against forgetting?

Abstract: L'interpretation des donnees de Bahrick (1984) sur la retention de l'espagnol appris a l'ecole et sa theorie du stockage permanent («permastore») sont critiquees par reference a une hypothese de reconstruction

On the Use of Verbal Reports in Reading Research

Abstract: In 1917, E. L. Thorndike focused attention on the processes, particularly the reasoning processes, involved in reading. More than 50 years later, following the hiatus imposed by behaviorism, Simons (1971) reemphasized that research should focus more on the reading process than on the product of reading if progress were to be made toward understanding the nature of comprehension. However, observing and understanding the comprehension process seems more easily proposed than actualized. We have generally inferred the process from products, such as differential performance on different comprehension questions, perhaps collected under different conditions. Researchers interested in studying the cognitive processes involved in reading have recently shown interest in the use of verbal reports to gather data on aspects of the reading process (Bridge & Winograd, 1982; Brown & Day, 1983; Garner, 1982; Johnston & Afflerbach, 1983; Kavale & Schreiner, 1979; Marr, 1983; Olshavsky, 1976-77). This interest is actually a continuation of the long, if sporadic, history of verbal report data in reading research (Huey, 1908; McCallister, 1930; Piekarz, 1954; Strang, 1964, 1970). Verbal reporting, especially introspection, had been an important component of psychological investigation, including reading research, prior to the rise of behaviorism

The adjuvant activity of nonionic block polymer surfactants. II. Antibody formation and inflammation related to the structure of triblock and octablock copolymers.

Abstract: We tested the ability of 17 surface-active agents to enhance antibody formation and inflammation. The surfactants were all block copolymers of hydrophilic polyoxyethylene (POE) and hydrophobic polyoxypropylene (POP), which differed in m.w. and mode of linkage of POP to POE. Mice were injected in each rear footpad with 1.25 mg of each surfactant with 25 micrograms of bovine serum albumin in an oil-in-water emulsion. Each agent produced a distinct pattern of immune response and inflammation. Preparations that are large and insoluble with the POE chains flanking the POP chains were very effective adjuvants for increasing antibody formation. They also activated complement and induced the release of chemotactic factors from serum. Increasing the percent of POE decreased adjuvant activity and inflammation. Decreasing the m.w. of the molecules while maintaining the proportions of POP and POE decreased the adjuvant activity and increased inflammation. Preparations synthesized in the reverse order, with the POP flanking POE, tended to induce granulomas instead of antibody. These data demonstrate that block copolymer surfactants have a spectrum of biologic activities that depend on the size and arrangement of their constituent parts. We suggest that much of the activity of these agents derives from their ability to form adsorptive surfaces similar to those of a mycobacterial glycolipid, quartz, and monosodium urate.

Black Children's Race Awareness, Racial Attitudes and Self-Concept: A Reinterpretation.

Abstract: Results of a study of 130 black preschool children support the previous research finding that black preschoolers show majority group racial attitudes. Eighty percent of the sample obtained positive self-concept scores, while demonstrating pro-white biased cultural values on a racial attitude and preference measure. This significant finding is contrary to previous theorizing and consistent with recent data for a Southern sample (Spencer, 1982a). Few studies have empirically questioned this relationship, assuming less positive self-concepts of black children who have consistently shown pro-white cultural values. Race awareness affected majority group-preferenced racial attitudes. Results suggest that black preschool children effectively compartmentalize personal identity (i.e. self-concept) from knowledge of racial evaluations.

Structural studies on the lipid A component of enterobacterial lipopolysaccharides by laser desorption mass spectrometry. Location of acyl groups at the lipid A backbone.

Abstract: In the present paper laser desorption mass spectrometry (LDMS) was applied to dephosphorylated free lipid A preparations obtained from lipopolysaccharides of Re mutants of Salmonella minnesota, Escherichia coli and Proteus mirabilis. The purpose of this study was to elucidate the location of (R)-3-hydroxytetradecanoic acid and 3-O-acylated (R)-3-hydroxytetradecanoic acid residues which are bound to amino and hydroxyl groups of the glucosamine disaccharide backbone of lipid A. Based on the previous finding from biochemical analyses that the amino group of the nonreducing glucosamine residue (GlcN II) of the backbone carries, in S. minnesota and E. coli, 3-dodecanoyloxytetradecanoic acid and, in P. mirabilis, 3-tetradecanoyloxytetradecanoic acid, a self-consistent interpretation of the LDMS was possible. It was found that: (a) in all three lipids A GlcN II is, besides the amide-linked 3-acyloxyacyl residue, substituted by ester-linked 3-tetradecanoyloxytetradecanoic acid; (b) the reducing glucosamine (GlcN I) is substituted by ester-linked 3-hydroxytetradecanoic acid; (c) the amino group of GlcN I carries a 3-hydroxytetradecanoic acid which is non-acylated in E. coli and which is partially acylated by hexadecanoic acid in S. minnesota and P. mirabilis. In lipids A which were obtained from the P. mirabilis Re mutant grown at low temperature (12°C) LDMS analysis revealed that specifically the one fatty acid bound to the 3-hydroxyl group of amide-linked 3-hydroxytetradecanoic acid at GlcN II is positionally replaced by Δ9-hexadecenoic acid (palmitoleic acid). It appears, therefore, that enterobacterial lipids A resemble each other in that the 3-hydroxyl groups of the two 3-hydroxytetradecanoic acid residues linked to GlcN II are fully acylated, while those of the two 3-hydroxytetradecanoic acid groups attached to GlcN I are free or only partially substituted.