A Passage Through Science: Crossing Disciplinary Boundaries.

ABSTRACT

A METHODOLOGY IS PRESENTED FOR CREATING pathways through the scientific literature following strong co-citation links. A specific path is described starting in economics and ending in astrophysics traversing 331 documents. Special attention is given to where the path crosses disciplinary boundaries and how analogy can be used to model the thought processes involved in such transitions. Implications of information pathways for retrieval, the unity of science, discovery, epistemology, and evaluation are discussed.

INFORMATION RETRIEVAL AND INFORMATION TRANSITIONS

A great deal of information science is concerned with retrieving all the documents from a database that precisely match a user's query. In this magic bullet model of information retrieval, the documents retrieved will ideally be homogeneous in character. Such an ideal is, of course, rarely achieved. In practice, a wide array of documents of varying relevance is retrieved, resembling more an ecology of information than a uniform set.

Less often under consideration is how to understand the diversity and breadth of information that most queries generate, how one topic relates to another, or the transitions from one document to another. Questions such as these naturally arise for large samples of documents and especially multidisciplinary databases. For example, a user interested in a topic such as asthma might retrieve a large number of hits and find that some deal with treatment options, age factors, psychological aspects, hereditary tendencies, environmental factors, and so on. The question is how to make sense of this diversity.

One reason questions of subject diversity do not come up more often is the tacit assumption that topics or subjects are relatively isolated and distinct from one another, each representing a more or less separate homogeneous entity. Another reason is the assumption that users' information needs are simple and highly specific. This contrasts with the view that information seeking is more like a gradually unfolding discovery process in which the initial query is only the first step in a long journey, each step depending on what came before (Kuhlthau, 1999).

INFORMATION TRANSITIONS AND THE UNITY OF SCIENCE

Earlier discussions of the unity of science (Neurath, 1938) or its modern incarnation in E. O. Wilson's (1998) consilience, view scientific knowledge as an interconnected fabric of fields and disciplines. In the sociology of science, it is commonplace to say that a great deal of scientific and technological innovation takes place at the boundaries between disciplines (Lemaine et al., 1976) or by individuals who have crossed from one field to another. Cross-fertilization of fields is another term for this, when an idea in one field finds fertile ground in a neighboring field (Crane, 1972). Information scientists have begun to explore these issues by attempting to find unconnected subject areas which, if connected, might yield new discoveries (Swanson & Smalheiser, 1997). Attempts to visualize information spaces also address subject connections since a visualization must depict the relationships among diverse sets of documents (White & McCain, 1997). It seems likely that future information retrieval systems based on the visual paradigm will have the equivalent of road signs telling the user what direction to travel to reach a particular topic.

CITATIONS AND THE STRUCTURE OF SCIENCE

One of the best ways of studying the connectedness of information is to use reference or citation links. While connections can also be established by shared vocabulary or indexing terms, a citation link represents a more direct author-selected dependency. By taking a wide-ranging sample of documents across many fields, the unity of scientific information can be examined from a global perspective.

Vannevar Bush's (1945) idea of associative information trails is a natural consequence of the unity of science and the connectedness of knowledge. Hummon and Doreian (1989) attempted to demonstrate this on a small scale by finding a critical path through a DNA citation network. Path analysis has more recently been undertaken for documents in the area of hypertext research using author co-citations (Chen & Carr, 1999).

Taking citation links as the basis of a structural analysis of science, it is natural to suppose that it would be possible to travel from any topic or field to any other (Small, 1999) just as in the world of the Internet we might follow a series of hypertext links to reach any desired Web site. In the abstract, this is equivalent to traversing a network, but there is no guarantee the structure is in fact connected. In science, citations are very unevenly distributed, concentrating in narrowly defined pockets which correspond roughly to specialties or invisible colleges of researchers (Small & Griffith, 1974). The boundaries of these regions of high density are not well defined, however. Yet the most interesting links in the chain from one end of science to the other are those which cross disciplinary boundaries. Interdisciplinary links represent a kind of intellectual leap from one domain to another.

In the world of citation analysis, strong links can be established by frequent patterns of co-citation (Small, 1973) or bibliographic coupling (Kessler, 1963). Co-citation links are a second order form of citation linkage that depends on the joint citing of two earlier documents by later documents. Unlike direct citation links, co-citations are nondirectional and can be weighted by frequency of occurrence. By simple "thresholding," it is possible to identify regions of high co-citation density. Thresholding is in fact equivalent to the method of clustering called "single-linkage" (Hartigan, 1975).

In a map based on co-citation clusters, an interdisciplinary link can occur when an author co-cites across the boundary of two disciplinary clusters. If the author cites predominantly into one cluster, as is often the case, the interdisciplinary co-citation reaches out beyond the author's home cluster (see Figure 1). This reaching out or stretching can import or export methods, ideas, models, or empirical results from the author's field to the other field. This is an act requiring a broad awareness of literature plus the creative imagination to see how the outside information fits with the author's problem domain. The author of such a paper is going out on a limb to integrate ideas from another discipline.

[Figure 1 ILLUSTRATION OMITTED]

The objective of the present study is to examine the nature of the connections that tie the scientific literature together, focusing particularly on links crossing disciplinary boundaries. The question is whether interdisciplinary transitions are gradual or abrupt or based on shared features, analogies, creative insights, or perhaps even questionable assumptions--in short, how far the author had to stretch to make the connection. In another sense it is an examination of the creative process of moving from one domain of knowledge to another. If citation relationships capture authors' decisions or selections on what documents are relevant to a problem, paths that follow citation links may in some sense capture steps in problem-solving behavior, logical thinking, or intuition.

INFORMATION PATHWAYS

The basic requirement of a pathway through science is that the linked objects form a chain of significant connections. Ideally each connection represents a relationship whose logic can be determined by some form of content analysis. In an abstract sense, an information pathway could be defined as a sequence or succession of information objects or events (documents, descriptors, topics) such that each object along the path bears some kind of relationship to the objects that precede it. Of course, the zero order case is a random path or walk in which there is no relationship, or at least an arbitrary one, between successive objects. Order can be imposed on this succession by introducing various types of formal restrictions. For example, a path through scientific papers might be required to follow citation or co-citation links or other form of document association. Other types of restrictions are whether to allow the repetition of objects along the path, whether the path is exhaustive or complete--that is, all objects must be visited--or whether the path is to be as short as possible (Harary, 1972). Optimal paths of various kinds can be defined such as the shortest path that visits all nodes in the network, called the "traveling salesman" problem (Simon, 1969).

Due to the complexity of the citation graph, it is impossible to create a nonrepeating, linear path through all of science, touching all papers only once if the path is constrained to follow specific links. Only the simplest of graph structures would allow this. However, nonrepeating sequences of objects can be formed by relaxing the requirement that each document must be linked to its predecessor. The depth- or breadth-first search techniques are effective when a complete tour of objects is desired that remains as coherent as possible (Sedgewick, 1983). The depth-first search was used to transform a co-citation graph for a cancer research area into a linear narrative (Small, 1986).

Linear nonrepetitive paths necessarily exist through a network connecting any two arbitrarily selected points, provided of course the graph is connected and contains no unreachable subcomponents (Hillier & Lieberman, 1967). This is the type of path illustrated below. The path should follow strong links but need not be the shortest path. Shortest paths are reminiscent of the small world experiments in sociology (Milgram, 1967; Garfield, 1981; Kochen, 1989) where the smallest number of intervening acquaintances between two arbitrarily selected individuals is sought. In the citation world, short paths might arise, for example, if a paper in astrophysics cites a paper in sociology. Such paths, though occasionally seen, are not the norm and usually are idiosyncratic and have low frequency. More interesting are paths that follow links established by multiple authors and hence represent a consensus or congruence of opinion. These might be called high frequency or well traveled paths.

CO-CITATION MAPPING METHODS

The creation of pathways through science begins with a hierarchical clustering of highly cited papers in which co-citation serves as the measure of association between papers (Small, 1999). This is carried out in a series of iterations until as much as possible of the corpus of scientific literature can be amalgamated into a single hierarchical structure several levels deep. The number of levels required depends on the number of starting documents which in turn depends on the thresholds set for defining what is considered highly cited. A fractional citation counting method is used to ensure that papers are sampled across the various disciplines of science without biasing the selection to fields that inherently cite more than others (Small & Sweeney, 1985). In addition, an integer citation count threshold is used to avoid selection of infrequently cited papers.

In clustering an annual multidisciplinary database, several iterations of clustering are required to build up an overall structure. The output of each iteration becomes the input to the next, and residual co-citation links are recalculated to refer to the clustered objects at each step. At the end of the process, what is left are large-scale aggregates connected by rather weak links. These weak links make the macro-structure somewhat unstable over time, but they represent boundary-spanning events of considerable interest.

An integral part of the clustering process is creation of a spatial arrangement of the objects at each level or iteration. This is achieved by a geometric triangulation procedure that converts each link into a distance measure (Lee et al., 1977). The unit of distance is called the Garfield and is given by the formula:

Distance A-B = (1 - similarity)/(1 - similarity threshold) Similarity = co-cites A-B/sqrt (cites A* cites B)

Note: When the similarity is equal to the similarity threshold, the distance is equal to one Garfield--the distance associated with the weakest link on the map.

The positioning of objects is accomplished by taking the two strongest links (shortest distances) for each object to be added to the map (Small, 1997). After each cluster is configured by triangulating on the strongest links, the structures are integrated hierarchically. This involves expanding the higher level objects and translating the coordinates of lower level objects so that they fit into them. In two dimensions, objects are represented as circles whether they are clusters or documents and, because the structure is hierarchical, the larger circles contain smaller circles, the smallest ones being the documents themselves. In three dimensions, circles become spheres containing smaller spheres.

THE 1996 MAP OF SCIENCE

The procedure for generating the science map for 1996 was similar to that used for a 1995 map (Small, 1999). An integer citation threshold of six (6) and a fractional threshold of 1.0 were set to select papers cited in the 1996 Science Citation Index[R] (SCI) file. The cited references were restricted to publication dates in a fifteen-year period 1982 to 1996. Only the results for the main cluster hierarchy will be presented here. These are the papers included in the largest hierarchical grouping. Table 1 shows the number of clusters and documents for each of the five levels. Thus 39,964 highly cited documents are contained in 4,723 level 1 clusters containing two or more documents. The 4,723 clusters are in turn contained in 757 level 2 clusters, which aggregate to form 159 level 3 objects. These form 43 level 4 clusters, which amalgamate to a single group of 43 level 4 clusters at level 5, including all lower level clusters.

Table 1. OBJECTS IN THE MAIN CLUSTER HIERARCHY

Level   Number of   Number of     Mean      Mean
        Clusters     Objects    Objects   Documents

1        4,723       39,964        8.5          8.5
2          757        4,723        6.2         52.8
3          159          757        4.8        251.3
4           43          159        3.7        929.4
5            1           43       43.0     39,964.0

The map of science for 1996 (see Figure 2) is a linked structure of disciplines and research areas similar to those obtained for earlier annual files of the SCL The map is predominantly linear in its progression from social science, biomedicine, chemistry, to physics. The social science areas are situated at the lower right and physics areas are in the upper left, although there is no significance to this general orientation. Neuroscience is situated above psychology and economics, and above neuroscience is a large central biomedical region. To the left and closely allied with biomedicine is protein chemistry and above it general chemistry. Ecology is situated to the left of chemistry and geoscience is to its left. Geoscience is just below physics, and above physics are surface science, materials, and optics. Computer science is at the social science/medicine pole of the map, linked to imaging and neural networks.

[Figure 2 ILLUSTRATION OMITTED]

A PATH FROM ECONOMICS TO PHYSICS

A path through science was generated by selecting starting and destination fields from among the forty-four high level clusters. To illustrate as wide a range of topics as possible, economics, shown at the lower right of Figure 2, was selected as the starting area and physics at the upper left was selected as the destination. Not only were these fields at opposite ends of the map, but they seemed at opposite intellectual poles--one in the worldly realm of human behavior the other in the extra-terrestrial. Specific papers within these regions were not specified, so the path algorithm was required only to find one beginning and one ending paper within each region.

The cluster hierarchy greatly simplifies finding strongly linked paths because the relatively few large-scale objects at the higher levels of aggregation can be traversed before descending to lower level objects, making the process one of gradually emerging detail and avoiding combinatorial complexity. The approach is to move down the hierarchy one level at a time. The path through the largest scale objects of course must begin and end with the starting and destination points. Among the objects at a given level, a minimal spanning tree is formed using the strongest co-citation links. A high level path is formed by navigating only those branches of the tree necessary to connect the starting and destination nodes. Then, moving down to the next level, for each successive pair of large-scale objects along this path, a pair of lower level objects is found that are most strongly linked by co-citation. This lower level pair thus links the larger objects. This defines starting and ending points within each large-scale object that can be navigated using the minimal spanning tree approach. Hence the process proceeds by alternating between finding paths through objects at some level and finding pairs of lower level objects spanning the higher-level object path. This continues until the document level is reached and a complete document pathway is formed.

Thus, the two kinds of path-forming processes are: (1) finding a sequence of lower level objects within a higher level object, and (2) finding the most strongly linked lower level objects within two adjacent higherlevel objects. The two modes of traversal might be termed stepping and jumping, the one akin to stepping from stone to stone along a garden path, the other like jumping from one path to another. These are illustrated in Figure 3. The "jumps," of course, can involve traversing more weakly connected or distant objects and may entail larger shifts in subject matter while the "steps" are more strongly linked and closer in topic.

[Figure 3 ILLUSTRATION OMITTED]

Table 2 gives the number of objects from each level touched by the completed path from economics to physics. Clearly the number of objects in the path decreases as the level increases, while the percentage of total objects increases. A total of 331 documents make up the final path corresponding to 330 transitions (either steps or jumps) from beginning to end. Table 3 shows how the transitions from object to object are distributed for each of the levels. For the document and first levels, there are about two steps for every jump. For higher levels (except the highest) there are about equal numbers of jumps and steps. Note that the sum of jumps and steps for a given level must equal the number of jumps at the next lower level.

Table 2. OBJECTS IN THE PATH

Level     Number     Percentage
        of Objects    of Total

Docs       331           0.8
1          121           2.6
2           42           5.5
3           23          14.5
4           11          25.6

Table 3. PATH STATISTICS

 Level                                                 Mean
Document   Jumps   Steps   Transitions   Objects   Co-citations

            120     210        330         331         14.7
   1         41      79        120         121         11.5
   2         22      19         41          42         10.8
   3         10      12         22          23          6.0
   4          0      10         10          11          7.9

It is also possible to compute the mean document co-citation strengths for transitions from object to object. The last column of Table 3 shows these mean values for steps (excluding jumps) between objects of each level. Mean co-citation strength diminishes with increasing level (except for the third and fourth levels), indicating that the larger aggregates are bound by weaker document co-citation links than the smaller aggregates. This is to be expected since ties are stronger at the local level.

DESCRIPTION OF THE PATH FROM ECONOMICS TO ASTROPHYSICS

The dotted line on Figure 2 shows how the path connects the highest level objects on the map of science. The path traverses the broad areas of economics, psychology, neuroscience, biomedicine, proteins, chemistry, ecology, geoscience, surface science, optics, and physics. Within economics, the starting point is a paper entitled "Making Fast Strategic Decisions in High-Velocity Environments." From here the path makes a transition from economics to psychology and moves into the psychology of work teams. The last paper in the path is a physics paper entitled "Wave Function of the Universe." Just prior to reaching this physics destination, the path traverses the topic of quantum field theory. The 331 documents comprising the full path are given in the Appendix. Headings interspersed in this list show the major subdivisions by cluster and subcluster, and the indentation of the heading indicates the hierarchical level of the subdivision.

Another way to view the progression from economics to physics is to plot co-citation frequency as a function of the position on the path (Figure 4). The number of co-citations is counted for each successive pair of documents. The figure is labeled with the subject matter of the highest level objects, indicating the points of transition between each by arrows along the vertical axis. The highest co-citation rates are concentrated in biomedicine, neuroscience, and proteins. High co-citation rates are sometimes correlated with subject matter. For example, within neuroscience, high rates are observed in the section dealing with nitric oxide as a neuronal messenger, and in surface science, for the topic of quantum dots. The steep spikes occasionally emerging above the terrain indicate the linking of highly cited technique papers.

[Figure 4 ILLUSTRATION OMITTED]

A detailed interpretation of the entire path will not be attempted here. However, discussion of fifty or so documents comprising the psychology section should suffice to give a general flavor. The starting paper on decision making leads to the psychology of work teams and team leadership. Work teams then move to the more general concept of groups and differences in male and female participation. This leads to gender stereotypes and a focus on category-based versus individual impression formation. The role of memory in judgment emerges from this and how expectations interact with memory. Memory of persons gives way to attribution of cause and effect and causal thinking. The role of positive and negative events on thinking leads to perceptions of one's own health. Negative feelings on health then progress to measuring affect, and in turn to scales for assessing depression. Measuring depression links to treatments for depression and recurrent depression. Rapid cycling emerges from recurrent depression, then progressing to bipolar disorder. Expressed emotion is a common diagnostic method for both bipolar disorder and schizophrenia, which is the next topic. Drug treatment of schizophrenia moves to studies of cerebral blood flow, eventually ending up in the field of neuroscience with the study of the normal brain.

The above description exemplifies many of the types of shifts seen in the path as a whole: movement from the specific to the general, from the normal to the abnormal, from the aggregate to the disaggregate, the macro to the micro, and so on. But these shifts do not tell the whole story. For example, the gradual transition from studies of thinking to studies of depression is particularly striking. It appears to be mediated by the perception of well-being and specifically negative thinking and emotion regarding one's health. Health complaints are, in effect, generalized to adverse emotional states that then progress to depression or anxiety.

Table 4 summarizes the path in terms of the main subtopics visited and the corresponding range of documents traversed. The subtopic list corresponds to divisions at clustering levels below the fourth level, and the intent was to break the path into segments of approximately equal length. The document ranges correspond to the numbering scheme in the Appendix. The approximate nature of the boundaries established by clustering are evident in the case of geoscience and its transition to surface science. Some solid-state topics, such as the equation of state for solids and ab-initio molecular dynamics, have been incorporated into geoscience that might more logically have been assigned to surface science. Despite this boundary question, the topics progress from one to another in a logical and regular manner.

Table 4. TOPICS ALONG THE PATH

Level 4 Cluster   Subtopic (Levels 3 - 1)        Document Range

Economics         Decision making                         1
Psychology        Social groups                      2 - 17
                  Well-being                        18 - 25
                  Depression                        26 - 37
                  Expressed emotion                 38 - 42
                  Schizophrenia                     43 - 51
Neuroscience      Visual cortex                     52 - 65
                  Thalamic neurons                  67 - 72
                  Synaptic transmission             78 - 86
                  Nitric-oxide messenger            88 - 101
Biomedicine       Nuclear factor kappa-B           102 - 104
                  Tumor necrosis factor            105 - 108
                  Interleukin                      109 - 114
                  Drug resistant HIV               115 - 128
Proteins          Protein structure                130 - 135
Chemistry         Metallocene catalysis            137 - 140
                  Khand reaction                   141 - 146
                  Palladium catalysis              147 - 154
                  Asymmetric catalysis             156 - 168
                  Porphyrins                       169 - 189
Ecology           Atmospheric [CO.sub.2]           193 - 216
                  Models of biosphere              217 - 227
Geoscience        Climate cycles                   228 - 237
                  Earth's geoid                    238 - 248
                  Earth's mantle                   250 - 253
                  Seismic velocity                 256 - 258
                  Equation of state for solids     263 - 266
                  Ab-initio molecular dynamics     269 - 273
Surface science   Diamond surface                  274 - 281
                  Epitaxial surface growth         282 - 295
                  Quantum dots                     296 - 302
Optics            Quantum wells                    303 - 322
                  Quantum field theory             323 - 330
Physics           Astrophysics                           331

The sequence of research areas reflects a plausible scenario for interweaving the scientific fabric. From the broadest perspective there is the progression from human to biological to physical sciences. Moving down a level, there is a progression of general themes. Starting with social groups, the progression is to individual behavior. Normal behavior leads to considerations of abnormal behavior. In trying to understand the basic biology of abnormal behavior, the path leads back to study of the normal brain in neuroscience. Within the nervous system, the level of the neuron is reached, at which point chemical neurotransmitters enter the picture. This biochemical level moves from the nervous system to the immune system and immune disease. The attempt to understand the biochemistry of AIDS leads to structural analysis of biochemical molecules and to chemistry in general. The traversal of chemistry follows catalytic processes and ends up with photosynthesis, which leads in turn to considerations of the earth's atmosphere. Climate studies follow, and we land back on the earth's crust and the physical processes that govern the earth's mantle. Moving down to the atomic level for understanding solids, the focus turns to the surfaces of solids. Descending to yet finer scales, quantum phenomena are encountered and their abstract mathematical treatment, leading finally to theories of the universe as a whole within the field of astrophysics.

The most striking aspect of this broad brush discussion of main themes is how the focus alternates from large to small scale, from the group to the individual, from diseases to molecules, from molecules to the atmosphere, from the earth back down to the atomic and quantum levels, and finally up again to the universe. But, to understand the logic behind these shifts in topic, it is necessary to consider transitions at the document to document level.

UNDERSTANDING TRANSITIONS BETWEEN DISCIPLINES

A proper analysis of the nature of the topic transitions would require a content analysis of the co-citation passages for pairs of documents along the path. However, a first order approximation to understanding the nature of the transitions can be based on a close examination of the titles of the linked documents. Many of the transitions resemble what might be called substitution around a stable point of reference in which one aspect or theme changes while another remains constant. The following cases illustrate this principle using some of the main disciplinary transitions along the path.

The transition from psychology to neuroscience starts with the study of patterns of cerebral blood flow in schizophrenia using positron emission tomography (PET). PET can also be used to study willed action and word usage in the normal prefrontal cortex. Schizophrenia then leads to the study of the normal human cortex via the reference point provided by the PET technique, and a normal activity is substituted for the abnormal condition.

The transition from neuroscience to immunology involves going from the neuronal messenger nitric oxide to HIV. The common link is a substance that appears to play a role in controlling their biochemistry. Nitric oxide in the nervous system is synthesized by the nitric oxide synthase gene, and the encoding of the gene is induced by a substance called nuclear factor kappa-B. This substance also plays a role in the immune system where it can activate HIV. Thus the topic transition occurs around a point of reference provided by the substance nuclear factor Kappa-B with HIV activation being substituted for the stimulation of the nitric-oxide gene.

In the transition from biomedicine to biochemistry, the topic moves from the study of biologically important proteins, in particular DNA-polymerase, to the use of computer plotting methods, such as molscript or electron density mapping, to study protein structure. Here the reference point is the protein molecule, while biological function of the molecule is exchanged for the physical depiction of its structure.

The transition from protein structure to chemistry proper is more subtle but seems to hinge on the structural specificity of catalytic reactions. The study of molecular structure by x-ray diffraction thus leads to the mechanism of catalytic reactions. The point of reference is molecular structure itself, and the study of catalytic reactions replaces the methodology of x-ray diffraction.

The transition from chemistry to ecology is simpler and involves going from the study of artificial photosynthesis to natural photosynthesis in bacteria, photosynthesis being the common thread. From ecology to geoscience involves going from the development of meteorological models of general atmospheric circulation to the study of climate changes over long periods of time. Climate is the common thread, and historical cycles substitute for model building. Hence, each of the interdisciplinary transitions seems to involve a common thread and a substitution.

CONCLUSION

Examination of these major topic shifts suggests that some general principles may be at work. Since the transitions are brought about by the behavior of the co-citing authors, understanding these patterns will ultimately involve an examination of creative information seeking by authors and, in particular, how authors in one field reach out for information in another field. Based on this preliminary content analysis, it is possible to identify some possible mechanisms and strategies authors use to bridge information gaps.

First, there is the mechanism of extending a topic with a gradual shift in its scope. For example, in psychology, negative affect was extended to depression and hence to rapid mood cycling and bipolar disorder. Extending can also be literal, importing a concept or method into another domain without modification, as in the case of PET in the transition from psychology to neuroscience. Extension provides the common point of reference in many of the interdisciplinary transitions. The second mechanism is the substitution of one entity for another. This was seen in many of the cross-disciplinary transitions--e.g., the HIV substitution for nitric oxide in going from neuroscience to biomedicine.

The joint operation of extension and substitution might be seen as a simple kind of progression by analogy in which "A is to B as B is to C" where B is the common thread or point of reference. True analogies of the form "A is to B as C is to D" are also possible and could emerge, for example, if an extension of topic B transformed it into a distinct entity D. True analogies are also more tenuous than extension with substitution. It is tempting to postulate that the author first sees the possibility of a link up with another domain as a true analogy but, as his or her thinking firms up, there is a realization that B and D can be made equivalent in some sense, perhaps by transforming one into the other by logical extension. Thus the concrete transition emerges from the initial glimmer of an analogy.

It seems plausible that the creative use of information involves some form of thinking by analogy and the recognition of similar structures in disparate domains. Returning to the retrieval example at the beginning of this article, it would be as if we were to take two apparently unrelated items from a search output and ask subjects to think of ways the two items might be related or brought into a common framework. If a path-finding algorithm were in place within the retrieval system, then a document path between them could be generated. This might reveal new ways that seemingly unrelated pieces of information can be related and thereby provide creative insights, new hypotheses, or perhaps even aid in discovery. It also suggests that the ability of users to see the relevance of apparently nonrelevant pieces of information is a key step in the discovery process. Path-finding techniques might offer a new approach to revealing such hidden or potential relevance.

EPISTEMOLOGY AND THE UNITY OF SCIENCE

In addition to information discovery, path creation might have application to the evaluation of information and to an epistemological warrant for science. There appears to be a movement in philosophy toward making scientific belief more a function of group than individual cognition (Schmitt, 1994). It seems reasonable to postulate that the unity and coherence of science, and therefore the existence of pathways, is related to the solidity of the scientific findings (Small, 1998). This is based on the notion that of all the documents vying for attention, the most promising ones are those most closely tied to the existing body of strongly verified knowledge (Stent, 1972). Assuming that it were possible to identify a core of strongly verified documents in science, an attempt could be made to connect any new document to the verified core by a pathfinding algorithm.

A text with connections to strongly confirmed or verified knowledge would deserve more serious attention than one without such connections. Texts lacking connections would be treated with greater caution and skepticism. Topic connections may offer a way of evaluating uncontrolled information sources on the Web (Kleinberg, 1998). Grafton (1997) points out, however, the mere existence of linkages or the quoting of sources does not guarantee truth or objectivity. Thus the nature as well as number of links is critical, and the existence of a path could only be considered an indicator, not an infallible guide.

While this article has focused on linear paths that connect arbitrarily selected beginning and ending documents, other kinds of paths may also be of interest, particularly those that provide a complete tour of the network. Complete paths, if properly constructed, could provide a comprehensive review of a subject area and ultimately an excursion through the entire fabric of science. A promising approach for achieving this is the identification of the longest linear routes through the minimal spanning tree representation for each cluster, to preserve, as far as possible, a coherent sequential flow of ideas. This could be coupled with a breadth-first search on the tree to explore side branches, much as one would digress from a main topic. Since the structure is hierarchical, this process could progress down the hierarchy until the document level is reached, piecing together the document sequences like strands of DNA. The final result would be a linear ordering of all the documents in the structure, a kind of complete genome sequence of science.

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Small, H. (1986). The synthesis of specialty narratives from co-citation clusters. Journal of the American Society for Information Science, 37(3), 97-110.

Small, H. (1997). Update on science mapping: Creating large document spaces. Scientometrics, 38(2), 275-293.

Small, H. (1998). Citations and consilience in science. Scientometrics, 43(1), 143-148. Small, H. (1999). Visualizing science by citation mapping. Journal of the American Society for Information Science, 50(9), 799-813.

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APPENDIX

DOCUMENT PATH FROM ECONOMICS TO PHYSICS

ECONOMICS

1 EISENHARDT KM,ACAD MGMT J,vol 0032,page 0543,1989,cites=33,MAKING FAST STRATEGIC DECISIONS INHIGH-VELOCITY ENVIRONMENTS

PSYCHOLOGY

SOCIAL GROUPS

2 GERSICK CJG,ACAD MGMT J,vol 0031,page 0009,1988,cites= 12,TIME AND TRANSITION IN WORK TEAMS - TOWARD A NEW MODEL OF GROUP DEVELOPMENT

3 SUNDSTROM E,AM PSYCHOL,vol 0045,page 0120,1990,cites= 17,WORK TEAMS-APPLICATIONS AND EFFECTIVENESS

4 MANZ CC,ADM SCI QUA,vol 0032,page 0106,1987,cites= 11,LEADING WORKERS TO LEAD THEMSELVES - THE EXTERNAL LEADERSHIP OF SELF-MANAGING WORK TEAMS

5 WHEELAN SA,SEX ROLES,vol 0027,page 0001,1992,cites= 6,DIFFERENCES IN MALE AND FEMALE PATTERNS OF COMMUNICATION IN GROUPS - A METHODOLOGICAL ARTIFACT

6 WOOD W,PSYCHOL B,vol 0102,page 0053,1987,cites= 8,META-ANALYTIC REVIEW OF SEX-DIFFERENCES IN GROUP-PERFORMANCE

7 EAGLY AH,J PERS SOC,vol 0060,page 0685,1991,cites= 15,GENDER AND THE EMERGENCE OF LEADERS - A METAANALYSIS

8 EAGLY AH,PSYCHOL B,vol 0108,page 0233,1990,cites= 23,GENDER AND LEADERSHIP-STYLE - A METAANALYSIS

9 EAGLY AH,J PERS SOC,vol 0046,page 0735,1984,cites= 17,GENDER STEREOTYPES STEM FROM THE DISTRIBUTION OF WOMEN AND MEN INTO SOCIAL ROLES

10 FISKE ST, ADV EXP SOC,vol 0023,page 0001,1990,cites= 53,A CONTINUUM OF IMPRESSION-FORMATION, FROM CATEGORY-BASED TO INDIVIDUATING PROCESSES - INFLUENCES OF INFORMATION AND MOTIVATION ON ATTENTION AND INTERPRETATION

11 SRULL TK,PSYCHOL REV,vol 0096,page 0058,1989,cites= 30,PERSON MEMORY AND JUDGMENT

12 STANGOR C,PSYCHOL B,vol 0111,page 0042,1992,cites= 20,MEMORY FOR EXPECTANCY-CONGRUENT AND EXPECTANCY-INCONGRUENT INFORMATION - A REVIEW OF THE SOCIAL AND SOCIAL DEVELOPMENTAL LITERATURES

13 SRULL TK,J EXP PSY L,vol 0011,page 0316,1985,cites= 14,ASSOCIATIVE STORAGE AND RETRIEVAL-PROCESSES IN PERSON MEMORY

14 HASTIE R,J PERS SOC,vol 0046,page 0044,1984,cites= 19,CAUSES AND EFFECTS OF CAUSAL ATTRIBUTION

15 WEINER B,PSYCHOL B,vol 0097,page 0074,1985,cites= 15,SPONTANEOUS CAUSAL THINKING

16 ROESE NJ,J PERS SOC,vol 0066,page 0805,1994,cites= 7,THE FUNCTIONAL BASIS OF COUNTERFACTUALTHINKING

17 TAYLOR SE,PSYCHOL B,vol 0110,page 0067,1991,cites= 29,ASYMMETRICAL EFFECTS OF POSITIVE AND NEGATIVE EVENTS - THE MOBILIZATION MINIMIZATION HYPOTHESIS

WELL-BEING

18 TAYLOR SE,PSYCHOL B,vol 0103,page 0193,1988,cites= 114,ILLUSION AND WELL-BEING - A SOCIAL PSYCHOLOGICAL PERSPECTIVE ON MENTAL-HEALTH

19 SCHEIER MF,HEALTH PSYC, vol 0004,page 0219,1985,cites= 78,OPTIMISM, COPING, AND HEALTH - ASSESSMENT AND IMPLICATIONS OF GENERALIZED OUTCOME EXPECTANCIES

20 WATSON D,PSYCHOL REV, vol 0096,page 0234,1989,cites= 77,HEALTH COMPLAINTS, STRESS, AND DISTRESS - EXPLORING THE CENTRAL ROLE OF NEGATIVE AFFECTIVITY

21 WATSON D,PSYCHOL B,vol 0096,page 0465,1984,cites= 97,NEGATIVE AFFECTIVITY-THE DISPOSITION TO EXPERIENCE AVERSIVE EMOTIONAL STATES

22 WATSON D,PSYCHOL B,vol 0098,page 0219,1985,cites= 80,TOWARD A CONSENSUAL STRUCTURE OF MOOD

23 WATSON D,J PERS SOC,vol 0054,page 1063,1988,cites= 116,DEVELOPMENT AND VALIDATION OF BRIEF MEASURES OF POSITIVE AND NEGATIVE AFFECT - THE PANAS SCALES

24 CLARK LA,J ABN PSYCH,vol 0100,page 0316,1991,cites= 41,TRIPARTITE MODEL OF ANXIETYAND DEPRESSION - PSYCHOMETRIC EVIDENCE AND TAXONOMIC IMPLICATIONS

25 BECK AT,CLIN PSYCH,vol 0008,page 0077,1988,cites= 134,PSYCHOMETRIC PROPERTIES OF THE BECK DEPRESSION INVENTORY - 25 YEARS OF EVALUATION

DEPRESSION

26 ELKIN I,ARCH G PSYC,vol 0046,page 0971,1989,cites= 75,NATIONAL-INSTITUTE -OF-MENTAL-HEALTH TREATMENT OF DEPRESSION COLLABORATIVE RESEARCH-PROGRAM - GENERAL EFFECTIVENESS OF TREATMENTS

27 BELSHER G,PSYCHOL B,vol 0104,page 0084,1988,cites= 13,RELAPSE AFTER RECOVERY FROM UNIPOLAR DEPRESSION - A CRITICAL-REVIEW

28 KELLER MB,J AM MED A,vol 0250,page 3299,1983,cites= 15,PREDICTORS OF RELAPSE IN MAJOR DEPRESSIVE DISORDER

29 KELLER MB,ARCH G PSYC,vol 0049,page 0809,1992,cites= 31,TIME TO RECOVERY, CHRONICITY, AND LEVELS OF PSYCHOPATHOLOGY IN MAJOR DEPRESSION - A 5-YEAR PROSPECTIVE FOLLOW-UP OF 431 SUBJECTS

30 FRANK E,ARCH G PSYC,vol 0047,page 1093,1990,cites= 46,3-YEAR OUTCOMES FOR MAINTENANCE THERAPIES IN RECURRENT DEPRESSION

31 PRIEN RF, ARCH G PSYC,vol 0041,page 1096,1984,cites= 33,DRUG-THERAPY IN THE PREVENTION OF RECURRENCES IN UNIPOLAR AND BIPOLAR AFFECTIVEDISORDERS - REPORT OF THE NIMH COLLABORATIVE STUDY-GROUP COMPARING LITHIUM-CARBONATE, IMIPRAMINE, AND A LITHIUM-CARBONATE IMIPRAMINE COMBINATION

32 CORYELL W,ARCH G PSYC,vol 0049,page 0126,1992,cites= 13,RAPIDLY CYCLING AFFECTIVE-DISORDER - DEMOGRAPHICS, DIAGNOSIS, FAMILY HISTORY, AND COURSE

33 BAUER MS,AM J PSYCHI,vol 0151,page 0506,1994,cites= 13,MULTISITE DATA REANALYSIS OF THE VALIDITY OF RAPID-CYCLING AS A COURSE MODIFIER FOR BIPOLAR DISORDER IN DSM-IV

34 WEHR TA,AM J PSYCHI,vol 0144,page 1403,1987,cites= 19,CAN ANTIDEPRESSANTS CAUSE MANIA AND WORSEN THE COURSE OF AFFECTIVE-ILLNESS

35 PEET M,BRJ PSYCHI,vol 0164,page 0549,1994,cites= 14,INDUCTION OF MANIA WITH SELECTIVE SEROTONIN REUPTAKE INHIBITORS AND TRICYCLIC ANTIDEPRESSANTS

36 SACHS GS,J CLIN PSY, vol 0055,page 0391,1994,cites= 15,A DOUBLE-BLIND TRIAL OF BUPROPION VERSUS DESIPRAMINE FOR BIPOLAR DEPRESSION

37 GELENBERG AJ,N ENGJ MED,vol 0321,page 1489,1989,cites= 22,COMPARISON OF STANDARD AND LOW SERUM LEVELS OF LITHIUM FOR MAINTENANCE TREATMENT OF BIPOLAR DISORDER

EXPRESSED EMOTION

38 MIKLOWITZ DJ,ARCH G PSYC,vol 0045,page 0225,1988,cites= 20,FAMILY FACTORS AND THE COURSE OF BIPOLAR AFFECTIVE-DISORDER

39 HOOLEY JM,BR J PSYCHI,vol 0148,page 0642,1986,cites= 18,LEVELS OF EXPRESSED EMOTION AND RELAPSE IN DEPRESSED-PATIENTS

40 KAVANAGH DJ,BR J PSYCHI,vol 0160,page 0601,1992,cites= 32,RECENT DEVELOPMENTS IN EXPRESSED EMOTION AND SCHIZOPHRENIA

41 TARRIER N,BR J PSYCHI,vol 0153,page 0532,1988,cites= 22,THE COMMUNITY MANAGEMENT OF SCHIZOPHRENIA - A CONTROLLED TRIAL OF A BEHAVIORAL INTERVENTION WITH FAMILIES TO REDUCE RELAPSE

42 HOGARTY GE,ARCH G PSYC,vol 0043,page 0633,1986,cites= 36,FAMILY PSYCHOEDUCATION, SOCIAL SKILLS TRAINING, AND MAINTENANCE CHEMOTHERAPY IN THE AFTERCARE TREATMENT OF SCHIZOPHRENIA. 1. ONE-YEAR EFFECTS OF A CONTROLLED-STUDY ON RELAPSE AND EXPRESSED EMOTION

SCHIZOPHRENIA

43 HOGARTY GE,ARCH G PSYC,vol 0045,page 0797,1988,cites= 18,DOSE OF FLUPHENAZINE, FAMILIALEXPRESSED EMOTION, AND OUTCOME IN SCHIZOPHRENIA - RESULTS OF A 2-YEAR CONTROLLED-STUDY

44 MARDER SR,ARCH G PSYC,vol 0044,page 0518,1987,cites= 14,LOW-DOSE AND CONVENTIONAL-DOSE MAINTENANCE THERAPY WITH FLUPHENAZINE DECANOATE - 2-YEAR OUTCOME

45 BALDESSARINI RJ,ARCH G PSYC,vol 0045,page 0079,1988,cites= 34,SIGNIFICANCE OF NEUROLEPTIC DOSE AND PLASMA-LEVEL IN THE PHARMACOLOGICAL TREATMENT OF PSYCHOSES

46 MARDER SR,AM J PSYCHI,vol 0151,page 0825,1994,cites= 92,RISPERIDONE IN THE TREATMENT OF SCHIZOPHRENIA

47 KANE J,ARCH G PSYC,vol 0045,page 0789,1988,cites= 184,CLOZAPINE FOR THE TREATMENT-RESISTANT SCHIZOPHRENIC - A DOUBLE-BLIND COMPARISON WITH CHLORPROMAZINE

48 CARPENTER WT,AM J PSYCHI,vol 0145,page 0578,1988,cites= 52,DEFICIT AND NONDEFICIT FORMS OF SCHIZOPHRENIA - THE CONCEPT

49 MCGLASHAN TH,ARCH G PSYC,vol 0049,page 0063,1992,cites= 20,THE POSITIVE-NEGATIVE DISTINCTION IN SCHIZOPHRENIA - REVIEW OF NATURALHISTORY VALIDATORS

50 LIDDLE PF,BR J PSYCHI,vol 0151,page 0145,1987,cites= 47,THE SYMPTOMS OF CHRONIC-SCHIZOPHRENIA - A RE-EXAMINATION OF THE POSITIVE-NEGATIVE DICHOTOMY

51 LIDDLE PF,BR J PSYCHI,vol 0160,page 0179,1992,cites= 67,PATTERNS OF CEREBRAL BLOOD-FLOW IN SCHIZOPHRENIA NEUROSCIENCE

VISUAL CORTEX

52 FRITH CD,P ROY SOC B,vol 0244,page 0241,1991,cites= 58,WILLED ACTION AND THE PREFRONTAL CORTEX IN MAN - A STUDY WITH PET

53 PETERSEN SE,NATURE,vol 0331,page 0585,1988,cites= 108,POSITRON EMISSION TOMOGRAPHIC STUDIES OF THE CORTICAL ANATOMY OF SINGLEWORD PROCESSING

54 FRISTON KJ,J CEREBR B,vol 0011 ,page 0690,1991,cites= 123,COMPARING FUNCTIONAL %PET [is less than] IMAGES - THE ASSESSMENT OF SIGNIFICANT CHANGE

55 WATSONJDG,CEREB CORT,vol 0003,page 0079,1993,cites= 53,AREA-V5 OF THE HUMAN BRAIN - EVIDENCE FROM A COMBINED STUDY USING POSITRON EMISSION TOMOGRAPHY AND MAGNETIC-RESONANCE-IMAGING

56 ZEKI S,J NEUROSC,vol 0011,page 0641,1991,cites= 55,A DIRECT DEMONSTRATION OF FUNCTIONAL SPECIALIZATION IN HUMAN VISUAL-CORTEX

57 CORBETTA M,J NEUROSC,vol 0011,page 2383,1991,cites= 57,SELECTIVE AND DIVIDED ATTENTION DURING VISUAL DISCRIMINATIONS OF SHAPE, COLOR, AND SPEED - FUNCTIONAL-ANATOMY BY POSITRON EMISSION TOMOGRAPHY

58 ZEKI S,NATURE,vol 0335,page 0311,1988,cites= 44,THE FUNCTIONAL LOGIC OF CORTICAL CONNECTIONS

59 LIVINGSTONE M,SCIENCE,vol 0240,page 0740,1988,cites= 84,SEGREGATION OF FORM, COLOR, MOVEMENT, AND DEPTH - ANATOMY, PHYSIOLOGY, AND PERCEPTION

60 LIVINGSTONE MS,J NEUROSC,vol 0004,page 0309,1984,cites= 51,ANATOMYAND PHYSIOLOGY OF A COLOR SYSTEM IN THE PRIMATE VISUAL-CORTEX

61 TSO DY,J NEUROSC,vol 0008,page 1712,1988,cites= 29,THE ORGANIZATION OF CHROMATIC AND SPATIAL INTERACTIONS IN THE PRIMATE STRIATE CORTEX

62 LIVINGSTONE MS,J NEUROSC,vol 0004,page 2830,1984,cites= 15,SPECIFICITY OF INTRINSIC CONNECTIONS IN PRIMATE PRIMARY VISUAL-CORTEX

63 MCGUIRE BA,J COMP NEUR,vol 0305,page 0370,1991,cites= 26,TARGETS OF HORIZONTAL CONNECTIONS IN MACAQUE PRIMARY VISUAL-CORTEX

64 GILBERT CD,J NEUROSC,vol 0009,page 2432,1989,cites= 39,COLUMNAR SPECIFICITY OF INTRINSIC HORIZONTAL AND CORTICOCORTICAL CONNECTIONS IN CAT VISUAL-CORTEX

65 TSO DY,J NEUROSC, vol 0006,page 1160,1986,cites= 39,RELATIONSHIPS BETWEEN HORIZONTAL INTERACTIONS AND FUNCTIONAL ARCHITECTURE IN CAT STRIATE CORTEX AS REVEALED BY CROSS-CORRELATION ANALYSIS

66 GRAY CM,NATURE,vol 0338,page 0334,1989,cites= 90,OSCILLATORY RESPONSES IN CAT VISUAL-CORTEX EXHIBIT INTER-COLUMNAR SYNCHRONIZATION WHICH REFLECTS GLOBAL STIMULUS PROPERTIES

THALAMIC NEURONS

67 STERIADE M,SCIENCE,vol 0262,page 0679,1993,cites= 86,THALAMOCORTICAL OSCILLATIONS IN THE SLEEPING AND AROUSED BRAIN

68 VONKROSIGK M,SCIENCE,vol 0261,page 0361,1993,cites= 33,CELLULAR MECHANISMS OF A SYNCHRONIZED OSCILLATION IN THE THALAMUS

69 JAHNSEN H,J PHYSL LON,vol 0349,page 0205,1984,cites= 39, ELECTROPHYSIOLOGICAL PROPERTIES OF GUINEA-PIG THALAMIC NEURONS - AN INVITRO STUDY

70 MCCORMICK DA,J PHYSL LON,vol 0431,page 0291,1990,cites= 48,PROPERTIES OF A HYPERPOLARIZATION-ACTIVATED CATION CURRENT AND ITS ROLE IN RHYTHMIC OSCILLATION IN THALAMIC RELAY NEURONS

71 MAYER ML,J PHYSL LON,vol 0340,page 0019,1983,cites= 21,A VOLTAGE-CLAMP ANALYSIS OF INWARD%ANOMALOUS [is less than] RECTIFICATION IN MOUSE SPINAL SENSORY GANGLION NEURONS

72 HALLIWELL JV,BRAIN RES,vol 0250,page 0071,1982,cites= 45,VOLTAGE-CLAMP ANALYSIS OF MUSCARINIC EXCITATION IN HIPPOCAMPAL-NEURONS

73 LANCASTER B,J NEURPHYSL,vol 0055,page 1268,1986,cites= 31,CALCIUM-DEPENDENT CURRENT GENERATING THE AFTERHYPERPOLARIZATION OF HIPPOCAMPAL-NEURONS

74 MADISON DV,J PHYSL LON,vol 0354,page 0319,1984,cites= 27,CONTROL OF THE REPETITIVE DISCHARGE OF RAT CAI PYRAMIDAL NEURONS INVITRO

75 STUART GJ,NATURE,vol 0367,page 0069,1994,cites= 72,ACTIVE PROPAGATION OF SOMATIC ACTIONPOTENTIALS INTO NEOCORTICAL PYRAMIDAL CELL DENDRITES

76 EDWARDS FA,PFLUG ARCH,vol 0414,page 0600,1989,cites= 97,A THIN SLICE PREPARATION FOR PATCH CLAMP RECORDINGS FROM NEURONS OF THE MAMMALIAN CENTRAL NERVOUS-SYSTEM

77 BLANTON MG,J NEUROSC M,vol 0030,page 0203,1989,cites= 96,WHOLE CELL RECORDING FROM NEURONS IN SLICES OF REPTILIAN AND MAMMALIAN CEREBRAL-CORTEX

SYNAPTIC TRANSMISSION

78 EDWARDS FA,J PHYSL LON,vol 0430,page 0213,1090,cites= 37,QUANTAL ANALYSIS OF INHIBITORY SYNAPTIC TRANSMISSION IN THE DENTATE GYRUS OF RAT HIPPOCAMPAL SLICES - A PATCH-CLAMP STUDY

79 BEKKERS JM,P NAS US,vol 0087,page 5359,1990,cites= 29,ORIGIN OF VARIABILITY IN QUANTAL SIZE IN CULTURED HIPPOCAMPAL-NEURONS AND HIPPOCAMPAL SLICES

80 FABER DS,SCIENCE,vol 0258,page 1494,1992,cites= 23,INTRINSIC QUANTAL VARIABILITY DUE TO STOCHASTIC PROPERTIES OF RECEPTOR-TRANSMITTER INTERACTIONS

81 BARBOUR B,NEURON,vol 0012,page 1331,1994,cites= 27,PROLONGED PRESENCE OF GLUTAMATE DURING EXCITATORY SYNAPTIC TRANSMISSION TO CEREBELLAR PURKINJE-CELLS

82 TRUSSELL LO,NEURON,vol 0010,page 1185,1993,cites= 30,DESENSITIZATION OF AMPA RECEPTORS UPON MULTIQUANTAL NEUROTRANSMITTER RELEASE

83 TRUSSELL LO,NEURON,vol 0003,page 0209,1989,cites= 29,GLUTAMATE RECEPTOR DESENSITIZATION AND ITS ROLE IN SYNAPTIC TRANSMISSION

84 YAMADA KA,J NEUROSC,vol 0013,page 3904,1993,cites= 43, BENZOTHIADIAZIDES INHIBIT RAPID GLUTAMATERECEPTOR DESENSITIZATION AND ENHANCE GLUTAMATERGIC SYNAPTIC CURRENTS

85 PARTIN KM,NEURON,vol 0011,page 1069,1993,cites= 37,SELECTIVE MODULATION OF DESENSITIZATION AT AMPA VERSUS KAINATE RECEPTORS BY CYCLOTHIAZIDE AND CONCANAVALIN-A

86 HOLLMANN M,ANN R NEUR,vol 0017,page 0031,1994,cites= 233,CLONED GLUTAMATE RECEPTORS

87 CHOI DW,NEURON,vol 0001,page 0623,1988,cites= 259,GLUTAMATE NEUROTOXICITY AND DISEASES OF THE NERVOUS-SYSTEM

NITRIC-OXIDE MESSENGER

88 DAWSON VL,P NAS US,vol 0088,page 6368,1991,cites= 199,NITRIC-OXIDE MEDIATES GLUTAMATE NEUROTOXICITY IN PRIMARY CORTICAL CULTURES

89 GARTHWAITE J,TRENDS NEUR,vol 0014,page 0060,1991,cites= 206,GLUTAMATE, NITRIC-OXIDE AND CELL CELL SIGNALING IN THE NERVOUS-SYSTEM

90 BREDT DS,NEURON,vol 0008,page 0003,1992,cites= 171,NITRIC-OXIDE, A NOVEL NEURONAL MESSENGER

91 DAWSON TM,P NAS US,vol 0088,page 7797,1991,cites= 197,NITRIC-OXIDE SYNTHASE AND NEURONAL NADPH DIAPHORASE ARE IDENTICAL IN BRAIN AND PERIPHERAL-TISSUES

92 HOPE BT,P NAS US,vol 0088,page 2811,1991,cites: 198,NEURONAL NADPH DIAPHORASE IS A NITRIC-OXIDE SYNTHASE

93 BREDT DS,NATURE,vol 0351,page 0714,1991,cites= 183,CLONED AND EXPRESSED NITRIC-OXIDE SYNTHASE STRUCTURALLY RESEMBLES CYTOCHROME-P-450 REDUCTASE

94 LAMAS S,P NAS US,vol 0089,page 6348,1992,cites= 93,ENDOTHELIAL NITRICOXIDE SYNTHASE - MOLECULARCLONING AND CHARACTERIZATION OF A DISTINCT CONSTITUTIVE ENZYME ISOFORM

95 JANSSENS SP,J BIOL CHEM,vol 0267,page 4519,1992,cites= 65,CLONING AND EXPRESSION OF A CDNA-ENCODING HUMAN ENDOTHELIUM-DERIVED RELAXING FACTOR NITRIC-OXIDE SYNTHASE

96 NAKANE M,FEBS LETTER,vol 0316,page 0175,1993,cites= 53,CLONED HUMAN BRAIN NITRIC-OXIDE SYNTHASE IS HIGHLY EXPRESSED IN SKELETAL-MUSCLE

97 GELLER DA,P NAS US,vol 0090,page 3491,1993,cites= 118,MOLECULAR-CLONING AND EXPRESSION OF INDUCIBLE NITRIC-OXIDE SYNTHASE FROM HUMAN HEPATOCYTES

98 CHARTRAIN NA,J BIOL CHEM,vol 0269,page 6765,1994,cites= 49, MOLECULAR-CLONING, STRUCTURE, AND CHROMOSOMAL LOCALIZATION OF THE HUMAN INDUCIBLE NITRIC-OXIDE SYNTHASE GENE

99 LOWENSTEIN CJ,P NAS US,vol 0090,page 9730,1993,cites= 70,MACROPHAGE NITRIC-OXIDE SYNTHASE GENE - 2 UPSTREAM REGIONS MEDIATE INDUCTION BY INTERFERON-GAMMA AND LIPOPOLYSACCHARIDE

100 XIE QW,J EXP MED,vol 0177,page 1779,1993,cites= 81,PROMOTER OF THE MOUSE GENE ENCODING CALCIUMINDEPENDENT NITRIC-OXIDE SYNTHASE CONFERS INDUCIBILITY BY INTERFERON-GAMMA AND BACTERIAL LIPOPOLYSACCHARIDE

101 XIE QW,J BIOL CHEM,vol 0269,page 4705,1994,cites= 82,ROLE OF TRANSCRIPTION FACTOR NF-KAPPA-B/REL IN INDUCTION OF NITRIC-OXIDE SYNTHASE

BIOMEDICINE

NUCLEAR FACTOR KAPPA-B

102 SCHRECK R,J EXP MED,vol 0175,page l181,1992,cites= 101,DITHIOCARBAMATES AS POTENT INHIBITORS OF NUCLEAR FACTOR KAPPA-B ACTIVATION IN INTACT-CELLS

103 SCHRECK R,EMBO J,vol 0010,page 2247,1991,cites= 256,REACTIVE OXYGEN INTERMEDIATES AS APPARENTLY WIDELY USED MESSENGERS IN THE ACTIVATION OF THE NF-KAPPA-B TRANSCRIPTION FACTOR AND HIV-1

104 BAEUERLE PA,ANN R IMMUN,vol 0012,page 0141,1994, cites= 221 ,FUNCTION AMD ACTIVATION OF NF-KAPPA-B IN THE IMMUNE-SYSTEM

TUMOR NECROSIS FACTOR

105 OSBORN L,P NAS US,vol 0086,page 2336,1989,cites= 98,TUMOR NECROSIS FACTOR-ALPHA AND INTERLEUKIN-1 STIMULATE THE HUMAN IMMUNODEFICIENCY VIRUS ENHANCER BY ACTIVATION OF THE NUCLEAR FACTOR KAPPA-B

106 POLI G,P NAS US,vol 0087,page 0782,1990,cites= 36,TUMOR NECROSIS FACTOR-ALPHA FUNCTIONS IN AN AUTOCRINE MANNER IN THE INDUCTION OF HUMAN IMMUNODEFICIENCY VIRUS EXPRESSION

107 POLI G,J EXP MED,vol 0172,page 0151,1990,cites= 37,INTERLEUKIN-6 INDUCES HUMAN-IMMUNODEFICIENCY-VIRUS EXPRESSION IN INFECTED MONOCYTIC CELLS ALONE AND IN SYNERGY WITH TUMOR NECROSIS FACTOR-ALPHA BY TRANSCRIPTIONAL AND POSTTRANSCRIPTIONAL MECHANISMS

108 BREEN EC,J IMMUNOL,vol 0144,page 0480,1990,cites= 39,INFECTION WITH HIV IS ASSOCIATED WITH ELEVATED IL-6 LEVELS AND PRODUCTION

INTERLEUKIN

109 CLERICI M,SCIENCE,vol 0262,page 1721,1993,cites= 69,RESTORATION OF HIVSPECIFIC CELL-MEDIATED IMMUNE-RESPONSES BY INTERLEUKIN-12 IN-VITRO

110 CHEHIMI J,J EXP MED,vol 0179,page 1361,1994,cites= 57,IMPAIRED INTERLEUKIN-12 PRODUCTION IN HUMAN IMMUNODEFICIENCY VIRUS-INFECTED PATIENTS

111 CLERICI M,J CLIN INV, vol 0091,page 0759,1993,cites= 56,CHANGES IN INTERLEUKIN-2 AND INTERLEUKIN-4 PRODUCTION IN ASYMPTOMATIC, HUMAN IMMUNODEFICIENCY VIRUS-SEROPOSITIVE INDIVIDUALS

112 GRAZIOSI C,SCIENCE,vol 0265,page 0248,1994,cites= 64,LACK OF EVIDENCE FOR THE DICHOTOMY OF T%H [is less than] I AND T%H [is less than] 2 PREDOMINANCE IN HIV-INFECTED INDIVIDUALS

113 MAGGI E,SCIENCE,vol 0265,page 0244,1994,cites= 67,ABILITY OF HIV TO PROMOTE A T%H [is less than] 1 TO T%H [is less than] 0 SHIFT AND TO REPLICATE PREFERENTIALLY IN T%H [is less than] 2 AND T%H [is less than] 0 CELLS

114 CLERICI M,IMMUNOL TOD,vol 0014,page 0107,1993,cites= 159,A T%H [is less than] 1-*T%H [is less than] 2 SWITCH IS A CRITICAL STEP IN THE ETIOLOGY OF HIV-INFECTION

DRUG RESISTANT HIV

115 PANTALEO G,NATURE,vol 0362,page 0355,1993,cites= 204,HIV-INFECTION IS ACTIVE AND PROGRESSIVE IN LYMPHOID-TISSUE DURING THE CLINICALLY LATENT STAGE OF DISEASE

116 HO DD,NATURE,vol 0373,page 0123,1995,cites= 421,RAPID TURNOVER OF PLASMA VIRIONS AND CD4 LYMPHOCYTES IN HIV-1 INFECTION

117 MELLORS JW,ANN INT MED,vol 0122,page 0573,1995,cites= 101,QUANTITATION OF HIV-1 RNA IN PLASMA PREDICTS OUTCOME AFTER SEROCONVERSION

118 OBRIEN WA,N ENGJ MED,vol 0334,page 0426,1996,cites= 49,CHANGES IN PLASMA HIV-1 RNA AND CD4+ LYMPHOCYTE COUNTS AND THE RISK OF PROGRESSION TO AIDS

119 ERON JJ,N ENGJ MED,vol 0333,page 1662,1995,cites= 49,TREATMENT WITH LAMIVUDINE, ZIDOVUDINE, OR BOTH IN HIV-POSITIVE PATIENTS WITH 200 TO 500 CD4+ CELLS PER CUBIC MILLIMETER

120 SCHUURMAN R,J INFEC DIS,vol 0171,page 1411,1995,cites= 38,RAPID CHANGES IN HUMANIMMUNODEFICIENCY-VIRUS TYPE-1 RNA LOAD AND APPEARANCE OF DRUGRESISTANT VIRUS POPULATIONS IN PERSONS TREATED WITH LAMIVUDINE %3TC [is less than]

121 TISDALE M,P NAS US,vol 0090,page 5653,1993,cites= 64,RAPID INVITRO SELECTION OF HUMANIMMUNODEFICIENCY-VIRUS TYPE-1 RESISTANT TO 3$-THIACYTIDINE INHIBITORS DUE TO A MUTATION IN THE YMDD REGION OF REVERSE-TRANSCRIPTASE

122 STCLAIR MH,SCIENCE,vol 0253,page 1557,1991 ,cites= 70,RESISTANCE TO DDI AND SENSITIVITY TO AZT INDUCED BYA MUTATION IN HIV-1 REVERSE-TRANSCRIPTASE

123 LARDER BA, SCIENCE,vol 0246,page 1155,1989,cites= 87,MULTIPLE MUTATIONS IN HIV-1 REVERSE-TRANSCRIPTASE CONFER HIGH-LEVEL RESISTANCE TO ZIDOVUDINE %AZT [is less than]

124 KOHLSTAEDT LA,SCIENCE,vol 0256,page 1783,1992,cites= 141,CRYSTAL-STRUCTURE AT 3.5 ANGSTROM RESOLUTION OF HIV-1 REVERSE-TRANSCRIPTASE COMPLEXED WITH AN INHIBITOR

125 SAWAYA MR,SCIENCE,vol 0264,page 1930,1994,cites= 41 ,CRYSTAL-STRUCTURE OF RAT DNA-POLYMERASE-BETA - EVIDENCE FOR A COMMON POLYMERASE MECHANISM

126 OLLIS DL,NATURE,vol 0313,page 0762,1985,cites= 52,STRUCTURE OF LARGE FRAGMENT OF ESCHERICHIACOLI DNA-POLYMERASE-I COMPLEXED WITH DTMP

127 BEESE LS,SCIENCE,vol 0260,page 0352,1993,cites= 35,STRUCTURE OF DNAPOLYMERASE-I KLENOW FRAGMENT BOUND TO DUPLEX DNA

128 JOYCE CM,ANN R BIOCH,vol 0063,page 0777,1994,cites= 46,FUNCTION AND STRUCTURE RELATIONSHIPS IN DNA-POLYMERASES

PROTEINS

PROTEIN STRUCTURE

129 BEESE LS,EMBO J,vol 0010,page 0025,1991,cites= 59,STRUCTURAL BASIS FOR THE 3$-5$ EXONUCLEASE ACTIVITY OF ESCHERICHIA-COLI DNA-POLYMERASE-I - A 2 METAL-ION MECHANISM

130 KRAULIS PJ,J APPL CRYS,vol 0024,page 0946,1991,cites= 807,MOLSCRIPT - A PROGRAM TO PRODUCE BOTH DETAILED AND SCHEMATIC PLOTS OF PROTEIN STRUCTURES

131 JONES TA,ACT CRYST A,vol 0047,page 0110,1991,cites= 391,IMPROVED METHODS FOR BUILDING PROTEIN MODELS IN ELECTRON-DENSITY MAPS AND THE LOCATION OF ERRORS IN THESE MODELS

132 TRONRUD DE,ACT CRYST A,vol 0043,page 0489,1987,cites= 79,AN EFFICIENT GENERAL-PURPOSE LEAST-SQUARES REFINEMENT PROGRAM FOR MACROMOLECULAR STRUCTURES

133 JONES TA,METH ENZYM,vol 0115,page 0157,1985,cites= 95,INTERACTIVE COMPUTER-GRAPHICS - FRODO

134 KABSCH W,J APPL CRYS,vol 0021,page 0067,1988,cites= 39,AUTOMATIC-INDEXING OF ROTATION DIFFRACTION PATTERNS

135 KABSCH W,J APPL CRYS,vol 0021,page 0916,1988,cites= 145,EVALUATION OF SINGLE-CRYSTAL X-RAY-DIFFRACTION DATA FROM A POSITION-SENSITIVE DETECTOR

CHEMISTRY

136 SHELDRICK GM,ACT CRYST A,vol 0046,page 0467,1990,cites= 970,PHASE ANNEALING IN SHELX-90 - DIRECT METHODS FOR LARGER STRUCTURES

METALLOCENE CATALYSTS

137 BRINTZINGER HH,ANGEW CHEM,vol 0034,page 1143,1995,cites= 77,STEREOSPECIFIC OLEFIN POLYMERIZATION WITH CHIRAL METALLOCENE CATALYSTS

138 MOHRING PCJ ORGMET CH,vol 0479,page 0001,1994,cites= 45,HOMOGENEOUS GROUP-4 METALLOCENE ZIEGLER-NATTA CATALYSTS - THE INFLUENCE OF CYCLOPENTADIENYL-RING SUBSTITUENTS

139 MARKS TJ,ACC CHEM RE,vol 0025,page 0057,1992,cites= 22,SURFACE-BOUND METAL HYDROCARBYLS - ORGANOMETALLIC CONNECTIONS BETWEEN HETEROGENEOUS AND HOMOGENEOUS CATALYSIS

140 JORDAN RF,ADV ORGMET,vol 0032,page 0325,1991,cites= 43,CHEMISTRY OF CATIONIC DICYCLOPENTADIENYL GROUP-4 METAL ALKYL COMPLEXES

KHAND REACTION

141 BUCHWALD SL,CHEM REV,vol 0088,page 1047,1988,cites= 35,GROUP-4 METAL-COMPLEXES OF BENZYNES, CYCLOALKYNES, ACYCLIC ALKYNES, AND ALKENES

142 URABE H,TETRAHEDR L,vol 0036,page 4261,1995,cites= 14,SYNTHETIC APPLICATION OF TITANABICYCLES GENERATED FROM 1,6-DIENES OR 1,7-DIENES, ENYNES, AND DIYNES AND %ETA%2 [is less than]-PROPENE [is less than] TI%O-I-P [is less than] %2 [is less than]

143 BERK SC,J AM CHEM S,vol 0116,page 8593,1994,cites= 17,DEVELOPMENT OF A TITANOCENE-CATALYZED ENYNE CYCLIZATION ISOCYANIDE INSERTION REACTION

144 JEONG NJ AM CHEM S,vol 0116,page 3159,1994,cites= 16,CATALYTIC VERSION OF THE INTRAMOLECULAR PAUSON-KHAND REACTION

145 PAUSON PL,TETRAHEDRON,vol 0041,page 5855,1985,cites= 23,THE KHAND REACTION - A CONVENIENT AND GENERAL-ROUTE TO A WIDE-RANGE OF CYCLOPENTENONE DERIVATIVES

146 SHAMBAYATI S,TETRAHEDR L,vol 0031,page 5289,1990,cites= 14,N-OXIDE PROMOTED PAUSON-KHAND CYCLIZATIONS AT ROOM-TEMPERATURE

PALLADIUM CATALYSIS

147 OPPOLZER W,ANGEW CHEM,vol 0028,page 0038,1989,cites= 17,INTRAMOLECULAR, STOICHIOMETRIC %LI, MG, ZN [is less than] AND CATALYTIC %NI, PD, PT [is less than] METALLO-ENE REACTIONS IN ORGANIC-SYNTHESIS

148 TROST BM,ACC CHEM RE,vol 0023,page 0034,1990,cites= 21,PALLADIUM-CATALYZED CYCLOISOMERIZATIONS OF ENYNES AND RELATED REACTIONS

149 TROST BMJ AM CHEM S,vol 0116,page 4255,1994,cites= 18,PD-CATALYZED CYCLOISOMERIZATION TO 1,2- DIALKYLIDENECYCLOALKANES .1.

150 TROST BM,J AM CHEM S,vol 0116,page 4268,1994,cites= 13,PD-CATALYZED CYCLOISOMERIZATION TO 1,2- DIALKYLIDENECYCLOALKANES .2. ALTERNATIVE CATALYST SYSTEM

151 TROST BMJ AM CHEM S,vol 0115,page 9421,1993,cites= 16,PALLADIUM-CATALYZED CYCLIZATIONS OF POLYENYNES - A PALLADIUM ZIPPER

152 OVERMAN LE,J AM CHEM S,vol 0115,page 2042,1993,cites= 8,1ST TOTAL SYNTHESIS OF SCOPADULCIC ACID-B

153 GRIGG R,TETRAHEDR L,vol 0031,page 1343,1990,cites= 14,PALLADIUM-CATALYZED POLYCYCLISATION-ANION CAPTURE PROCESSES

154 HECK RF,ORG REACT,vol 0027,page 0345,1982,cites= 64,PALLADIUM-CATALYZED VINYLATION OF ORGANIC HALIDES

155 STILLE JK,ANGEW CHEM,vol 0025,page 0508,1986,cites= 132,THE PALLADIUM-CATALYZED CROSS-COUPLING REACTIONS OF ORGANOTIN REAGENTS WITH ORGANIC ELECTROPHILES

ASYMMETRIC CATALYSIS

156 TSUJI J,TETRAHEDRON,vol 0042,page 4361,1986,cites= 25,NEW GENERAL SYNTHETIC METHODS INVOLVING PI-ALLYLPALLADIUM COMPLEXES AS INTERMEDIATES AND NEUTRAL REACTION CONDITIONS

157 CONSIGLIO G,CHEM REV, vol 0089,page 0257,1989,cites= 36, ENANTIOSELECTIVE HOMOGENEOUS CATALYSIS INVOLVING TRANSITION-METAL ALLYL INTERMEDIATES

158 BROWN JM,TETRAHEDRON,vol 0050,page 4493,1994,cites= 30,MECHANISTIC AND SYNTHETIC STUDIES IN CATALYTIC ALLYLIC ALKYLATION WITH PALLADIUM COMPLEXES OF 1-% 2-DIPHENYLPHOSPHINO -1- NAPHTHYL [is less than] ISOQUINOLINE

159 SPRINZ J,TETRAHEDR L,vol 0035,page 1523,1994,cites= 35,CATALYSIS OF ALLYLIC SUBSTITUTIONS BY PD COMPLEXES OF OXAZOLINES CONTAINING AN ADDITIONAL P, S, OR SE CENTER - X-RAY CRYSTAL-STRUCTURES AND SOLUTION STRUCTURES OF CHIRAL PI-ALLYL PALLADIUM COMPLEXES OF PHOSPHINOARYLOXAZOLINES

160 LEUTENEGGER U,TETRAHEDRON,vol 0048,page 2143,1992,cites= 27,5 -AZA-SEMICORRINS - A NEW CLASS OF BIDENTATE NITROGEN LIGANDS FOR ENANTIOSELECTIVE CATALYSIS

161 PFALTZ A,ACC CHEM RE,vol 0026,page 0339,1993,cites= 51,CHIRAL SEMICORRINS AND RELATED NITROGEN-HETEROCYCLES AS LIGANDS IN ASYMMETRIC CATALYSIS

162 BOLM C,ANGEW CHEM,vol 0030,page 0542,1991,cites= 15,BIS%4,5 -DIHYDROOXAZOLYL [is less than] DERIVATIVES IN ASYMMETRIC CATALYSIS

163 HELMCHEN G,SYNLETT,vol ,page 0257,1991,cites= 16,C-2 SYMMETRICAL BIOXAZOLINES AND BITHIAZOLINES AS NEW CHIRAL LIGANDS FOR METALION CATALYZED ASYMMETRIC SYNTHESES - ASYMMETRIC HYDROSILYLATION

164 LOWENTHAL RE,TETRAHEDR L,vol 0031,page 6005,1990,cites= 35,ASYMMETRIC CATALYTIC CYCLOPROPANATION OF OLEFINS - BIS-OXAZOLINE COPPER-COMPLEXES

165 EVANS DA,J AM CHEM S,vol 0113,page 0726,1991,cites= 44,BIS%OXAZOLINES [is less than] AS CHIRAL LIGANDS IN METAL-CATALYZED ASYMMETRIC REACTIONS - CATALYTIC, ASYMMETRIC CYCLOPROPANATION OF OLEFINS

166 LOWENTHAL RE,TETRAHEDR L,vol 0032,page 7373,1991,cites= 22,ASYMMETRIC COPPER-CATALYZED CYCLOPROPANATION OF TRISUBSTITUTED AND UNSYMMETRICAL, CIS-1,2-DISUBSTITUTED OLEFINS - MODIFIED BISOXAZOLINE LIGANDS

167 EVANS DA,J AM CHEM S,vol 0115,page 5328,1993,cites= 35,BIS% OXAZOLINE [is less than] COPPER-COMPLEXES AS CHIRAL CATALYSTS FOR THE ENANTIOSELECTIVE AZIRIDINATION OF OLEFINS

168 LI ZJ AM CHEM S,vol 0115,page 5326,1993,cites= 29,ASYMMETRIC ALKENE AZIRIDINATION WITH READILY AVAILABLE CHIRAL DIIMINE-BASED CATALYSTS

PORPHYRINS

169 JACOBSEN EN,J AM CHEM S,vol 0113,page 7063,1991,cites= 46,HIGHLY ENANTIOSELECTIVE EPOXIDATION CATALYSTS DERIVED FROM 1,2-DIAMINOCYCLOHEXANE

170 PALUCKI M,J AM CHEM S,vol 0116,page 9333,1994,cites= 20,HIGHLY ENANTIOSELECTIVE, LOW-TEMPERATURE EPOXIDATION OF STYRENE

171 GROVES JT,J AM CHEM S,vol 0105,page 5791,1983,cites= 22,CATALYTIC ASYMMETRIC EPOXIDATIONS WITH CHIRAL IRON PORPHYRINS

172 COLLMAN JP, SCIENCE,vol 0261,page 1404,1993,cites= 37,REGIOSELECTIVE AND ENANTIOSELECTIVE EPOXIDATION CATALYZED BY METALLOPORPHYRINS

173 MEUNIER B,CHEM REV,vol 0092,page 1411,1992,cites= 94, METALLOPORPHYRINS AS VERSATILE CATALYSTS FOR OXIDATION REACTIONS AND OXIDATIVE DNA CLEAVAGE

174 TRAYLOR PS,J CHEM S CH,vol ,page 0279,1984,cites= 23,STERICALLY PROTECTED HEMINS WITH ELECTRONEGATIVE SUBSTITUENTS - EFFICIENT CATALYSTS FOR HYDROXYLATION AND EPOXIDATION

175 TRAYLOR TG,INORG CHEM,vol 0026,page 1338,1987,cites= 23,PERHALOGENATED TETRAPHENYLHEMINS - STABLE CATALYSTS OF HIGH TURNOVER CATALYTIC HYDROXYLATIONS

176 TRAYLOR TG,J AM CHEM S,vol 0114,page 1308,1992,cites= 19,ALIPHATIC HYDROXYLATION CATALYZED BY IRON%III [is less than] PORPHYRINS

177 RENAUD JP,J CHEM S CH,vol ,page 0888,1985,cites= 10,A VERY EFFICIENT SYSTEM FOR ALKENE EPOXIDATION BY HYDROGEN-PEROXIDE - CATALYSIS BY MANGANESE-PORPHYRINS IN THE PRESENCE OF IMIDAZOLE

178 HOFFMANN P,B S CHIM FR,vol 0129,page 0085,1992,cites= 13,PREPARATION AND CATALYTIC ACTIVITIES OF THE MANGANESE AND IRON DERIVATIVES OF BR8TMP AND CL12TMP, 2 ROBUST PORPHYRIN LIGANDS OBTAINED BY HALOGENATION OF TETRAMESITYLPORPHYRIN

179 LINDSEY JS,J ORG CHEM,vol 0054, page 0828, 1989, cites= 44, INVESTIGATION OF THE SYNTHESIS OF ORTHO-SUBSTITUTED TETRAPHENYLPORPHYRINS

180 LINDSEY JS,J ORG CHEM,vol 0052,page 0827,1987,cites= 42,ROTHEMUND AND ADLER-LONGO REACTIONS REVISITED - SYNTHESIS OF TETRAPHENYLPORPHYRINS UNDER EQUILIBRIUM CONDITIONS

181 LINDSEY JS,TETRAHEDRON,vol 0050,page 8941,1994,cites= 14,PORPHYRIN BUILDING-BLOCKS FOR MODULAR CONSTRUCTION OF BIOORGANIC MODEL SYSTEMS

182 SETH J,J AM CHEM S,vol 0116,page 0578,1994,cites= 24,INVESTIGATION OF ELECTRONIC COMMUNICATION IN MULTI-PORPHYRIN LIGHT-HARVESTING ARRAYS

183 WAGNER RW,J AM CHEM S,vol 0116,page 9759,1994,cites= 34,A MOLECULAR PHOTONIC WIRE

184 PRATHAPAN S,J AM CHEM S,vol 0115,page 7519,1993,cites= 25,BUILDING-BLOCK SYNTHESIS OF PORPHYRIN LIGHT-HARVESTING ARRAYS

185 SESSLER JL,J AM CHEM S,vol 0115,page 4618,1993,cites= 23,ELECTRONIC-ENERGY MIGRATION AND TRAPPING IN QUINONE-SUBSTITUTED, PHENYLLINKED DIMERIC AND TRIMERIC PORPHYRINS

186 OSUKA A,J AM CHEM S,vol 0115,page 4577,1993,cites= 17,1,2-PHENYLENE -BRIDGED DIPORPHYRIN LINKED WITH PORPHYRIN MONOMER AND PYROMELLITIMIDE AS A MODEL FOR A PHOTOSYNTHETIC REACTION CENTER - SYNTHESIS AND PHOTOINDUCED CHARGE SEPARATION

187 JOHNSON DG,J AM CHEM S,vol 0115,page 5692,1993,cites= 15,PHOTOCHEMICAL ELECTRON-TRANSFER IN CHLOROPHYLL PORPHYRIN QUINONE TRIADS - THE ROLE OF THE PORPHYRIN-BRIDGING MOLECULE

188 GUST D,ACC CHEM RE,vol 0026,page 0198,1993,cites= 50,MOLECULAR MIMICRY OF PHOTOSYNTHETIC ENERGY AND ELECTRON-TRANSFER

189 WASIELEWSKI MR,CHEM REV,vol 0092,page 0435,1992,cites= 118,PHOTOINDUCED ELECTRON-TRANSFER IN SUPRAMOLECULAR SYSTEMS FOR ARTIFICIAL PHOTOSYNTHESIS

ECOLOGY

190 MCDERMOTT G,NATURE,vol 0374,page 0517,1995,cites= 123, CRYSTAL-STRUCTURE OF AN INTEGRAL MEMBRANE LIGHT-HARVESTING COMPLEX FROM PHOTOSYNTHETIC BACTERIA

191 KUHLBRANDT W,NATURE,vol 0367,page 0614,1994,cites= 93,ATOMIC MODEL OF PLANT LIGHT-HARVESTING COMPLEX BY ELECTRON CRYSTALLOGRAPHY

192 DEMMIGADAMS B,