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  <front>
    <journal-meta />
    <article-meta>
      <title-group>
        <article-title>Connector and Provincial Hub Dichotomy in Scientific Collaborations Identified by Reinforcement Learning Algorithm⋆</article-title>
      </title-group>
      <contrib-group>
        <contrib contrib-type="author">
          <string-name>Feifan Liu</string-name>
          <xref ref-type="aff" rid="aff0">0</xref>
          <xref ref-type="aff" rid="aff1">1</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Shuang Zhang</string-name>
          <xref ref-type="aff" rid="aff1">1</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Haoxiang Xia</string-name>
          <xref ref-type="aff" rid="aff0">0</xref>
          <xref ref-type="aff" rid="aff1">1</xref>
        </contrib>
        <aff id="aff0">
          <label>0</label>
          <institution>Institute for Advanced Intelligence, Dalian University of Technology</institution>
          ,
          <addr-line>No.2 Linggong Road, Dalian, 116024, Liaoning</addr-line>
          ,
          <country country="CN">China</country>
        </aff>
        <aff id="aff1">
          <label>1</label>
          <institution>Institute of Systems Engineering, Dalian University of Technology</institution>
          ,
          <addr-line>No.2 Linggong Road, Dalian, 116024, Liaoning</addr-line>
          ,
          <country country="CN">China</country>
        </aff>
      </contrib-group>
      <abstract>
        <p>Scientific problem-solving relies on efective organizational patterns of research collaboration. To recognize the more complex crosscommunity collaboration patterns of researchers in modern science, this study probes the central core structure of co-authorship networks at the mesoscale, aiming at understanding the emerging structural characteristics and functional performance of the efectiveness of complex research and innovation systems. Taking the field of physics as an example, combining the deep reinforcement learning pretraining model with the hub role information of the complex network, this study identifies both the provincial hub and global connector hub and the emergence of multi-core structures at the mesoscopic level of the scientific collaboration network. The existence of the multi-core structure reflects the spontaneous formation of "local centrality and global decentrality" in the scientific collaboration system, which makes the knowledge creation system economical at the structural level and eficient in the functions of global collaboration and knowledge difusion. Through an analysis of the structural and functional characteristics and mesoscale collaborative organizational structures of researchers, this study enhances comprehension and insights into the inherent factors propelling scientific development and the dynamics of collective knowledge creation. The findings contribute valuable perspectives for the establishment of inclusive scientific research management policies, fostering a more sophisticated scientific research and innovation system.</p>
      </abstract>
      <kwd-group>
        <kwd>eol&gt;Scientific collaborative behavior</kwd>
        <kwd>complex network analysis</kwd>
        <kwd>deep reinforcement learning</kwd>
        <kwd>hub role identification</kwd>
      </kwd-group>
    </article-meta>
  </front>
  <body>
    <sec id="sec-1">
      <title>1. Introduction</title>
      <p>
        The scientific research and innovation system embodies a
form of "collective intelligence," where individual scholars
possessing specialized knowledge and intellectual
capacity collaboratively tackle intricate real-world challenges
through self-organizing coordination, thereby propelling
the advancement of knowledge domains [
        <xref ref-type="bibr" rid="ref1">1</xref>
        ]. Within this
context, the scientific collaboration network constitutes a
fundamental component of the overall innovation
framework, embodying the interactive and cooperative dynamics
among researchers [
        <xref ref-type="bibr" rid="ref2 ref3 ref4 ref5">2, 3, 4, 5</xref>
        ]. Ongoing development in
knowledge engineering and the science of science discipline
center on unraveling the nature of collective collaborative
behavior, uncovering emergent collaborative patterns, and
elucidating the underlying mechanisms driving knowledge
creation system [
        <xref ref-type="bibr" rid="ref6 ref7 ref8 ref9">6, 7, 8, 9</xref>
        ].
      </p>
      <p>
        Existing studies has demonstrated that co-authorship
networks typically exhibit typical heterogeneity, confirming
that these networks feature a high degree of uneven
distribution in connectivity [
        <xref ref-type="bibr" rid="ref10 ref11 ref12">10, 11, 12</xref>
        ]. This implies that scientists
with extensive social ties wield significant influence over
the network as a whole, often engaging preferentially in
collaborations with other highly influential peers, thus giving
rise to the formation of "rich clubs" [
        <xref ref-type="bibr" rid="ref13 ref14">13, 14</xref>
        ].
      </p>
      <p>Despite this, the investigation into the diversity of pivotal
actors within expansive scientific collaboration networks
remains underexplored, particularly concerning the
identiifcation of mesoscale core structures that bolster global
eficiency within large-scale social systems. There is a dearth
of research addressing how researchers with varying levels
of social capital or difering types of social linkages
contribute to the social division of cognitive labor in scientific
communities.</p>
      <p>
        This study aims to address these pressing issues by
identifying and examining multi-core structures within
coauthorship networks using a mesoscopic lens that taps into
the inherent community structure. Leveraging a pre-trained
reinforcement learning algorithm[
        <xref ref-type="bibr" rid="ref15">15</xref>
        ], it focuses on
identifying key players within the co-authorship milieu. By
combining the complex network topology theory, the study
distinguishes between provincial hub scientists—those
central within their respective communities—and connector
hub scientists who bridge diferent communities. Moreover,
it delves deeper to discern and analyze the multifaceted
clublike properties and functions of members within these two
core structural typologies. The results of this study promise
to enrich our comprehension of the intricate collaborative
patterns in a large-scale social innovation ecosystem.
      </p>
    </sec>
    <sec id="sec-2">
      <title>2. Dataset</title>
      <p>
        This study focuses on the field of physics. We use the
scientific publications in the journals of the American Physical
Society (APS) from the period 1985 to 2009 [
        <xref ref-type="bibr" rid="ref16">16</xref>
        ]. After the
necessary pre-processing procedure, the dataset finally
contains 104,484 researchers and their 848,231 edges established
by coauthorship relations.
      </p>
    </sec>
    <sec id="sec-3">
      <title>3. Results</title>
      <p>In this study, we propose an interpretable framework to
detect and analyze crucial core structures within large-scale
co-authorship networks, integrating previously mentioned
research concepts alongside club structure detection
algorithms. This approach involves applying a second-stage
"key player" detection algorithm, which ranks nodes in the
co-authorship network based on their "criticality."</p>
      <p>As depicted in Figure 1a-c, the network resilience
experiment shows the significance of the key members detected
using the deep reinforcement learning algorithm. Figure 1a
illustrates the ratio of the maximum connected subgraph
size to the potential maximum size after systematically
removing nodes according to their ranked criticality. The
sheer size and complexity of the entire co-authorship
network make visualizing it challenging. Therefore, Figures
1bc present embeddings of the co-authorship network graphs
between select communities (7, 10, and 14) to exemplify the
influence of key members on the network’s architecture.
The findings reveal that eliminating just the top 28% of key
members causes a near-total collapse of the network,
reducing the maximum connected subgraph size to almost zero.
These results suggest a three-phase impact of key members
on the overall network resilience. From Figures 1b-c, it
becomes evident that the "key members" recognized by the
deep reinforcement learning algorithm play a significantly
more pivotal role in maintaining the network structure
compared to randomly chosen nodes.</p>
      <p>
        To assess the overlap between the "key members" and the
"pivotal players" in the co-authorship network and verify
if they support one another, the study conducts statistical
analyses. Given that real-world networks tend to display
hierarchical modularity [
        <xref ref-type="bibr" rid="ref17 ref18">17, 18</xref>
        ], we calculate the modularity
of each collaborative community, partitioning them further
into sub-communities using a co-authorship network
community detection algorithm [
        <xref ref-type="bibr" rid="ref19">19</xref>
        ]. We then identify "pivotal"
roles within these sub-communities. With an average
modularity of around 0.71 across the 20 sub-communities, this
suggests a prevalent hierarchical modular organization
pattern within the co-authorship network.
      </p>
      <p>Moreover, the multi-scale hierarchical modular structure
observed in the co-authorship network reflects the
inherent hierarchical structure of domain knowledge. Research
directions, topics, subfields, and disciplines compose the
knowledge hierarchy in a discipline, and researchers
adaptively form co-authorships that embed research problems
within diferent knowledge system scales.</p>
      <p>Figure 1d presents the variation of club coeficients within
the sub-communities of the multi-scale physical domain as
a function of the proportion of deleted nodes (f). It
demonstrates that each sub-community contains both global
connector hubs and local provincial hubs, with global connector
hubs exhibiting a stronger cohesive core structure relative
to provincial hubs from the complex network system view.</p>
      <p>Figures 1e-f summarize the density and number
distribution of "pivotal role" members in the "key member" sequence
groups. Key observations include: 1) A significant majority
of globally and locally pivotal members are concentrated
in the initial sequence subgroups of "key members." This
indicates that the higher the criticality rank, the greater
the proportion of "pivotal role" members. 2) There is a
descending order correlation between the criticality of "pivotal
role" member classification. 3) Nodes with high degree are
more critical and occur in larger numbers across both the
global collaborative communities and the sub-communities,
demonstrating a consistent pattern in terms of importance
and centrality within the network structure.</p>
    </sec>
    <sec id="sec-4">
      <title>4. Discussion and Conclusion</title>
      <p>Scientific collaborative behavior is a cornerstone of
largescale knowledge exploration among researchers and
significantly influences their academic productivity and impact.
Co-authorship networks serve as a primary analytical tool
for deciphering collaboration patterns among researchers
within a knowledge landscape. As network science theories
and methodologies have evolved, so too has the examination
of co-authorship networks’ macroscopic and mesoscopic
attributes, including scale-free, small-world, modularity, and
club structures. While the modularity-based and collective
collaboration aspects of these networks have received
substantial attention, the in-depth analysis of core structures
within co-authorship networks from the modularization and
collaboration perspective remains an open issue.</p>
      <p>
        Recent research has demonstrated that mesoscopic core
structures have indeed been detected and studied in various
domains like biology, transportation, and power systems
[
        <xref ref-type="bibr" rid="ref20 ref21 ref22">20, 21, 22</xref>
        ], playing a pivotal role in global information
integration and subsystem coordination. This study extends
this line of inquiry by exploring the existence of similar
mesoscopic core structures in co-authorship networks and
analyzing their associated network structural traits and
functional implications.
      </p>
      <p>By harnessing the interpretability of complex topology
theory and the representational power of deep learning
techniques, this study introduces an interpretable
framework to identify and analyze the key cohesive structures
in co-authorship networks. The study reveals the
coexistence of two distinct core structures: local provincial hubs
that primarily consolidate community members with sparse
interconnections among themselves, and global connector
hubs that act as bridges between researchers across diferent
research areas within the collaborative community,
maintaining tight interconnections.</p>
      <p>These two types of hubs exhibit minimal overlap and
possess unique network structural characteristics, exerting
varying degrees of influence on other network members.
The provincial hubs demonstrate a star-shaped, centralized
structure, whereas the connector hubs showcase a flatter
and less centralized pattern of close collaborations.</p>
      <p>The coexistence of local centrality and global
decentralization in co-authorship networks reflects a delicate balance
between cost-efectiveness, stability, and flexibility within
the large-scale researcher-driven knowledge exploration
process. Future research aims to delve into the potential
universal patterns of scientific meso-core structures across
various disciplines and career stages, drawing upon
comprehensive academic datasets covering multiple fields and
historical periods.</p>
    </sec>
    <sec id="sec-5">
      <title>Acknowledgments</title>
      <p>This work is supported by the National Natural Science
Foundation of China (Grant No.71871042 and 72371052).</p>
    </sec>
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