The Research Space: using the career paths of scholars to predict the evolution of the research output of individuals, institutions, and nations

In recent years scholars have built maps of science by connecting the academic fields that cite each other, are cited together, or that cite a similar literature. But since scholars cannot always publish in the fields they cite, or that cite them, these science maps are only rough proxies for the potential of a scholar, organization, or country, to enter a new academic field. Here we use a large dataset of scholarly publications disambiguated at the individual level to create a map of science-or research space-where links connect pairs of fields based on the probability that an individual has published in both of them. We find that the research space is a significantly more accurate predictor of the fields that individuals and organizations will enter in the future than citation based science maps. At the country level, however, the research space and citations based science maps are equally accurate. These findings show that data on career trajectories-the set of fields that individuals have previously published in-provide more accurate predictors of future research output for more focalized units-such as individuals or organizations-than citation based science maps

Application of image analysis in microecophysiology research : methodology development.

Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1998.Rehabilitation of landfill sites is important for successful land utilization. Revegetation is one key element of the process since it can overcome aesthetic problems. The inimical challenges of landfill leachate and gas are largely responsible for the difficulties associated with the revegetation of completed sites. Many components of landfill leachate can be catabolized by microbial associations thereby reducing their impacts on the environment. The importance of research on interactions between pollutants, microorganisms and soil is its applicability in environmental risk assessment and impact studies of organic pollutants which enter the soil either accidentally or intentionally. The application of image analysis with microscopy techniques to landfill soil-pollution interactions provides a means to study surface microbiology directly and to investigate microbial cells under highly controlled conditions. This research focused on the development of a method to study the real time processes of attachment, establishment, growth and division of microbial cells/associations in site covering soils. Image analysis provides a powerful tool for differential quantification of microbial number, identification of morphotypes and their respective responses to microenvironment changes. This minimal disturbance technique of examining visually complex images utilizes the spatial distributions and metabolic sensitivities of microbial species. It was, therefore, used to examine hexanoic acid catabolizing species, both free-living and in a biofilm, with respect to obviating the threat of hexanoic acid to reclamation strategies. The three sources of inoculum (soil cover, soil from the landfill base liner and municipal refuse) were compared for their ability to provide associations which catabolized the substrate rapidly. During the enrichment programme the inocula were challenged with different concentrations of hexanoic acid, a common landfill intermediate. From the rates at which the substrate was catabolized conclusions were drawn on which concentration of hexanoate facilitated the fastest enrichment. The results of initial batch culture enrichments confirmed that the soil used contained microbial associations capable of catabolizing hexanoic acid at concentrations < 50mM, a key leachate component. Exposing the landfill top soil microorganisms to a progressive increase in hexanoic acid concentration ensured that catabolic populations developed which, in situ, should reduce the phytotoxic threat to plants subsequently grown on the landfill cover. The analysis of surface colonization was simplified by examining the initial growth on newly-exposed surfaces. The microbial associations generated complex images which were visually difficult to quantify. Nevertheless, the dimensional and morphological exclusions which were incorporated in the image analysis software permitted the quantification of selected components of the associations although morphology alone was inadequate to confirm identification. The effects of increasing the dilution rate and substrate concentration on the growth of surface-attached associations in Continuous Culture Microscopy Units (CCMUs) were examined. Of the five dilution rates examined the most extensive biofilm development (9.88 jum2) during the selected time period (72h) resulted at a dilution rate of 0.5h' (at 10mM hexanoic acid). The highest growth (608 microorganisms.field"1) was recorded in the presence of 50mM hexanoic acid (D = 0.5h"1). To ensure that the different morphotypes of the associations were able to multiply under the defined conditions a detailed investigation of the component morphotypes was made. Numerically, after 60h of open culture cultivation in the presence of 50mM hexanoic acid, rods were the predominant bacterial morphotypes (43.74 field'1) in the biofilms. Both rods and cocci were distributed throughout the CCMUs whereas the less numerous fungal hyphae (0.25 field'1) were concentrated near the effluent port. The specific growth rates of the surface-attached associations and the component morphotypes were determined by area (//m2) colonized and number of microorganisms.field"' and compared to aerobic planktonic landfill associations. From area determinations ( > 0.16 h'1) and the number of microorganisms.field"1 10mM hexanoic acid was found to support the highest specific growth rate ( > 0.05 h"1) of the surfaceattached association isolated from municipal refuse. With optical density determinations, the highest specific growth rate (0.01 h'1) was recorded with 25mM hexanoic acid. The surface-attached microbial associations component species determinations by area and number showed that the hyphae had the highest specific growth rate ( > 0.11 h"1). The surface-attached microbial association specific growth rate determinations from the discriminated phase (0.023 h'1), area colonized (0.023 h"1) and number of microorganisms (0.027 h"1) calculated from the results of the component species rather than the association should give more accurate results. The specific growth rate obtained differed depending on the method of determination. Any one of these may be the "correct" answer under the cultivation conditions. Depending on the state (thickness) of the association (free-living, monolayer or thick biofilm) the different monitoring methods may be employed to determine the growth. As a consequence of the results of this study, the kinetics of microbial colonization of surfaces in situ may be subjected to the same degree of mathematical analysis as the kinetics of homogeneous cultures. This type of analysis is needed if quantitative studies of microbial growth are to be extended to surfaces in various natural and artificial environments

Investigations on skeleton completeness for skeleton-based shape matching

Skeleton is an important shape descriptor for deformable shape matching, because it integrates both geometrical and topological features of a shape. As the skeletonisation process often generates redundant skeleton branches that may seriously disturb the skeleton matching and cause high computational complexity, skeleton pruning is required to remove the inaccurate or redundant branches while preserving the essential topology of the original skeleton. However, pruning approaches normally require manual intervention to produce visually complete skeletons. As different people may have different perceptions for identifying visually complete skeletons, it is unclear how much the accuracy of skeleton-based shape matching is influenced by human selection. Moreover, it is also unclear how skeleton completeness impacts the accuracy of skeleton-based shapematching. We investigate here these two questions in a structured way. In addition, we present experimental evidence to show that it is possible to do automatic skeleton pruning while maintaining the matching accuracy by estimating the approximate pruning power of each shape

Fiscal year 1973 scientific and technical reports, articles, papers, and presentations

Formal NASA technical reports, papers published in technical journals, and presentations by MSFC personnel in FY73 are presented. Papers of MSFC contractors are also included

Aerospace Medicine and Biology: A continuing bibliography with indexes, supplement 144

This bibliography lists 257 reports, articles, and other documents introduced into the NASA scientific and technical information system in July 1975

USSR Space Life Sciences Digest, issue 1

The first issue of the bimonthly digest of USSR Space Life Sciences is presented. Abstracts are included for 49 Soviet periodical articles in 19 areas of aerospace medicine and space biology, published in Russian during the first quarter of 1985. Translated introductions and table of contents for nine Russian books on topics related to NASA's life science concerns are presented. Areas covered include: botany, cardiovascular and respiratory systems, cybernetics and biomedical data processing, endocrinology, gastrointestinal system, genetics, group dynamics, habitability and environmental effects, health and medicine, hematology, immunology, life support systems, man machine systems, metabolism, musculoskeletal system, neurophysiology, perception, personnel selection, psychology, radiobiology, reproductive system, and space biology. This issue concentrates on aerospace medicine and space biology

Flow cytometry, fluorescent probes, and flashing bacteria

Key words: fluorescent probes, flow cytometry, CSLM, viability, survival, microbial physiology, lactic acid bacteria, Lactococcus lactis , Lactobacillus plantarum , cheese, milk, probiotic In food industry there is a perceived need for rapid methods for detection and viability assessment of microbes. Fluorescent staining and flow cytometry provide excellent tools for microbial analysis. This thesis describes fluorescent techniques for assessment of the physiological state of lactic acid bacteria.Lysis of lactic acid bacteria plays a crucial role in cheese manufacturing. It is generally considered that lysis results in leakage of intracellular enzymes in the cheese curd and, thus, plays an important role in ripening and flavor formation. Bac Light (Molecular Probes) was applied for monitoring the lysis process of Lactococcus lactis MG1363 in a buffered suspension with high osmolarity to mimic cheese conditions. The Bac Light kit combines the nucleic acid dyes propidium iodide (PI) and SYTO 9. PI is commonly used to determine membrane integrity based on dye exclusion. When used in combination with the permeant SYTO 9, membrane-damaged cells are stained by PI (red) while the intact cells are stained by SYTO 9 (green). Lysis was induced with mutanolysin and followed in time using fluorescence microscopy and flow cytometry. Also, enzyme assays and plate counts were performed. The results demonstrated a transient permeable cell status that has a significant role in the lysis process. Furthermore, permeable cells were demonstrated in ripening cheese with confocal scanning laser microcopy and Bac Light.Viability assessment by conventional plate counting requires long incubation times and provides limited information. Flow cytometric assessment of the viability of lactic acid bacteria was investigated and compared with plate counts. The esterase substrate carboxyfluorescein diacetate (cFDA) and the impermeant nucleic acid dyes PI and TOTO-1 were tested using exponential phase at 70°C heat-killed cultures of a Lactococcus , a Streptococcus , three Lactobacillus , two Leuconostoc , an Enterococcus , and a Pediococcus species. The combination of cFDA and TOTO-1 gave the best results. The intact and membrane-damaged subpopulations were distinguished well. Sorting and plating showed that cFDA stained the culturable and TOTO-1 the nonculturable cells. The assay was applied to cultures exposed to deconjugated bile salts or to hydrochloric acid and results corresponded well with plate counts.Subsequently, flow cytometry with cFDA and TOTO-1 staining was applied to Lactobacillus plantarum WCFS 1 suspended in milk. To facilitate flow cytometry clearing of the milk was required. A procedure based on a milk clearing solution was optimized to increase the signal-to-noise-ratio and flow cytometry enumerations were accurate to a lower limit of 10 5cells/ml.Finally, the novel assay was applied to starter cultures for cheese and yogurt and to the probiotic products Yakult, Mona Vifit, and Orthiflorplus. Flow cytometry in combination with plate counts revealed three populations: culturable cells, cells that are intact and metabolically active but not culturable, and permeabilized cells. The proportions of the populations differed between the tested products.In conclusion, the development of flow cytometry for bacteria is an important asset for microbiological research. The rapid novel methods described in this thesis provide possibilities for examination of fermentation processes and food products