Hub Structure Research Articles

Small‐world properties of nonlinear brain activity in schizophrenia

A disturbance in the interactions between distributed cortical regions may underlie the cognitive and perceptual dysfunction associated with schizophrenia. In this article, nonlinear measures of cortical interactions and graph-theoretical metrics of network topography are combined to investigate this schizophrenia "disconnection hypothesis." This is achieved by analyzing the spatiotemporal structure of resting state scalp EEG data previously acquired from 40 young subjects with a recent first episode of schizophrenia and 40 healthy matched controls. In each subject, a method of mapping the topography of nonlinear interactions between cortical regions was applied to a widely distributed array of these data. The resulting nonlinear correlation matrices were converted to weighted graphs. The path length (a measure of large-scale network integration), clustering coefficient (a measure of "cliquishness"), and hub structure of these graphs were used as metrics of the underlying brain network activity. The graphs of both groups exhibited high levels of local clustering combined with comparatively short path lengths--features consistent with a "small-world" topology--as well as the presence of strong, central hubs. The graphs in the schizophrenia group displayed lower clustering and shorter path lengths in comparison to the healthy group. Whilst still "small-world," these effects are consistent with a subtle randomization in the underlying network architecture--likely associated with a greater number of links connecting disparate clusters. This randomization may underlie the cognitive disturbances characteristic of schizophrenia.

E-Work based collaborative optimization approach for strategic logistic network design problem

We propose a collaborative e-Work based optimization approach for assisting the strategic logistic network design problem, which considers fleet design and customer clustering decisions. Normally, fleet design and customer clustering decisions are made by mid-level logistics managers while network design decision is made independently by high-level logistics managers. In the proposed approach, strategic distribution network design is modeled as a Facility Location Problem, considering long term inventory control decisions. On the other hand, tactical fleet design and customer clustering decisions are modeled based on a Hub and Spoke cost structure. An e-Work based heuristic approach is proposed to solve collaboratively the network design problem at strategic and tactical levels. The collaborative solution approach results from a particular sequential decomposition of the problem, similarly to traditional location–allocation heuristics, modeling an information sharing strategy between decision makers involved at each organizational level. A numerical application of the approach with real data based instances shows significant benefits, when compared to a non-collaborative independent optimization, where the hierarchical levels share no dynamic information and base their decisions on static and independent optimization models. These results show evidence of the advantage of the e-collaborative approach to deal with logistic decisions at different hierarchical levels, organizational units, or companies, compared to non-integrated non-linear mixed integer programming models.

Motivating proactive subsidiary innovation: Agent-based theory and socialization models in global R&D

Abstract An integration of agency theory and socialization models is developed and used to explain the types of governance and organizational structures associated with self-initiated subsidiary innovation. This theorizing suggests that: 1) The hub structure is the greatest user of behavior-based contracting and engenders the fewest self-initiated innovations; 2) The federation structure is the greatest user of outcome-based contracting and engenders the most self-initiated innovations, but these are primarily oriented to business level strategy rather than corporate; and, 3) The network structure is the greatest user of goal internalization and is the strongest generator of self-initiated innovations which are oriented to corporate-level strategy. The empirical evidence from extant studies of other researchers in the field is consistent with these propositions. Implications for management practice, research and theory are discussed in the paper.

Global maritime networks: The case of Maersk

Two contrasting approaches to the provision of maritime services are frequently presented: one based on direct port to port services, the other characterised by a hub and spoke network. We demonstrate there is no contradiction between these two models, that in fact they are complementary. Integrating direct services with a hub structure is necessary for assuring a wider geographical coverage. The complementarity is explained by analysing the world’s largest container shipping line, Maersk, which over the last 30 years has created a global shipping network.

Tetrameric Hub Structure of Postsynaptic Scaffolding Protein Homer

Homer is a crucial postsynaptic scaffolding protein involved in both maintenance and activity-induced plasticity of the synapse. However, its quaternary structure has yet to be determined. We conducted a series of biophysical experiments that provide the first evidence that Homer forms a tetramer via its coiled-coil domain, in which all subunits are aligned in parallel orientation. To test the importance of the tetrameric structure for functionality, we engineered dimeric and tetrameric Homer by deleting a part of coiled-coil domain or replacing it with artificially engineered dimeric or tetrameric coiled-coil domain from a yeast protein. The structure-activity relationship was determined by assaying cocluster formation with its ligand in heterologous cells, distribution in dendritic spines, and turnover rate of protein exist in dendritic spines. Our results provide the first insight into the structure of native Homer protein as a tetramer and the functional significance conferred by that structure.

Hierarchical network structure as seen in container shipping liner services in the Caribbean Basin

This paper concerns the network structure of container shipping services in the Caribbean Basin. It investigates Robinson’s (1998) concept of hierarchical networks in container shipping in which the higher the order of the network the fewer the ports and the fewer the connections among those ports. Three networks are defined based on the geographical reach of the carriers’ services: Intra-Basin, Americas’ region, and Inter-Oceanic. All three networks are quite similar, although there are differences in the number of ports served and the number of services and linkages among the ports of each net. Each net has a high degree of redundancy. Almost 40 per cent of the 88 ports in the basin belong to all three nets. It is not true that the higher the order the network, where order is defined by the geographical scale of service, the fewer ports and the fewer linkages. Defining hierarchical structure is elusive. Even the hub and spoke service structure is not immediately obvious.

Physical Topology Design for Survivable Routing of Logical Rings in WDM-Based Networks

In a wavelength-division multiplexed (WDM)-based network, a single physical link failure may correspond to multiple logical link failures. As a result, two-connected logical topologies, such as rings routed on a WDM physical topology, may become disconnected after a single physical link failure. We consider the design of physical topologies that ensure logical rings can be embedded in a survivable manner. This is of particular interest in metropolitan area networks, where logical rings are in practice almost exclusively employed for providing protection against link failures. First, we develop necessary conditions for the physical topology to be able to embed all logical rings in a survivable manner. We then use these conditions to provide tight bounds on the number of physical links that an N-node physical topology must have in order to support all logical rings for different sizes K. We show that when K/spl ges/4 the physical topology must have at least 4N/3 links, and that when K/spl ges/6 the physical topology must have at least 3N/2 links. Subsequently, we generalize this bound for all K/spl ges/4. When K/spl ges/N-2, we show that the physical topology must have at least 2N-4 links. Finally, we design physical topologies that meet the above bounds for both K=4 and K=N-2. Specifically, our physical topology for embedding (N-2)-node rings has a dual hub structure and is able to embed all rings of size less than N-1 in a survivable manner. We also provide a simple extension to this topology that addresses rings of size K=N-1 and rings of size K=N for N odd. We observe that designing the physical topology for supporting all logical rings in a survivable manner does not use significantly more physical links than a design that only supports a small number of logical rings. Hence, our approach of designing physical topologies that can be used to embed all possible ring logical topologies does not lead to a significant overdesign of the physical topology.

Reciprocal State and Local Airport Spending Spillovers and Symmetric Responses to Cuts and Increases in Federal Airport Grants

How states and localities react to federal airport grant cuts is a question of increasing importance, especially in light of recent congressional funding reauthorization debates. This study finds that states and localities behave in the way public finance theory predicts. The magnitude of an airport spending change is the same (but in opposite directions) for a cut and an increase in airport grants. Thus, the flypaper effect operates in both directions. Spillovers arising from airport spending are also considered. With the hub and spoke structure of the U.S. air transportation system, a spending increase on airports experiencing major time delays confers spillover benefits on individuals in other states in the form of travel time savings from decreased congestion. These spillovers are reciprocal. There is significant evidence of such interdependencies, and an individual state raises airport spending by between 50 and 60 cents when other states increase airport spending by 1 dollar.

BLISS/S: a new method for two-level structural optimization

The paper describes a two-level method for structural optimization for a minimum weight under the local strength and displacement constraints. The method divides the optimization task into separate optimizations of the individual substructures (in the extreme, the individual components) coordinated by the assembled structure optimization. The substructure optimizations use local cross-sections as design variables and satisfy the highly nonlinear local constraints of strength and buckling. The design variables in the assembled structure optimization govern the structure overall shape and handle the displacement constraints. The assembled structure objective function is the objective in each of the above optimizations. The substructure optimizations are linked to the assembled structure optimization by the sensitivity derivatives. The method was derived from a previously reported two-level optimization method for engineering systems, e.g. aerospace vehicles, that comprise interacting modules to be optimized independently, coordination provided by a system-level optimization. This scheme was adapted to structural optimization by treating each substructure as a module in a system, and using the standard finite element analysis as the system analysis. A numerical example, a hub structure framework, is provided to show the new method agreement with a standard, no-decomposition optimization. The new method advantage lies primarily in the autonomy of the individual substructure optimization that enables concurrency of execution to compress the overall task elapsed time. The advantage increases with the magnitude of that task.

The Japanese software industry: the ‘hub structure’ approach

The Japanese software industry is a paradox, at once highly productive and yet unsuccessful. What does this contrast suggest? This paper provides an analysis of the overall structure of the industry. Its user-driven nature, that is the role played by the large users of software as compared to the roles of independent software houses, is shown to be an important factor. The paper demonstrates that when information technologies are introduced, sustaining shopfloor usability, rather than stressing technological innovation, is Japan's most salient characteristic. The structure explains the fact that the Japanese software industry is characterized by a high degree of customized software and that the efficiency gains can be obtained by software factories in several of the large computer-related companies. However, the structure of the Japanese software industry has inhibited the development of packaged software and also the evolution of innovative independent software houses. With the current trend in the computer industry towards down-sizing and open systems, the structure of the Japanese software industry presents critical weaknesses.

Batching and Scheduling in FMS Hubs: Flow Time Considerations

Many flexible manufacturing systems (FMS) involve complex queueing networks in the processing of lots (jobs) in a production facility. In particular, the feedback of lots to a common, multipurpose workstation, or hub, processing different tasks for the same lot at various points in the production process, can create serious scheduling problems. This paper models the hub structure and presents some results for dual measures of flow time in the facility, namely, total flow time required for a fixed number of lots (or makespan), and average flow time for all lots (or average completion time). The flow time performance is a function of different batch sizes and priority scheduling rules for lots arriving at the hub. The results can be used to establish strategies for batching and scheduling lots according to adjustments in the importance of the cycle time versus the work-in-process (WIP) tradeoff. Extensions of the results to more general production facilities are also discussed.

大手スーパー自社配送センターの立地と配送構造 関東地方の事例

The purpose of this paper is to analyse the location of delivery centres of major supermarkets and the areal structure of their delivery networks. Three major supermarkets i. e, Daiei, Seiyu, Jusco and their affiliated firms, were chosen as objects of the investigation. The three companies established more delivery centres in the Kanto area than in other areas of Japan.The results of the analysis are summarized as follows:1) In the Kanto area, most of the delivery centres were established in the 1980s. Seiyu built a delivery center there in 1969, but Daiei and Jusco did not build centres there until the early 1980s. From the middle of the 1980s. the three companies established more delivery centres in the Kanto area. These delivery centres were all smaller than the ones previously established.2) In the early 1980s, a hub and spoke delivery structure was evident in the Daiei and Seiyu groups, whose new stores were concentrated in the southern Kanto area. A bipolar delivery structure became evident in the Jusco group, whose new store locations were split between the southern and northern Kanto areas.3) From the middle to the end of the 1980s, each supermarket established several delivery centres that were small in size and served a small area within the range of the larger delivery areas. A bipolar delivery structure was noticeable in the Daiei and Seiyu groups, and a multipolar delivery structure became evident in the Jusco group. This transformation may have resulted from each supermarket company emphasizing the importance of store delivery. In addition, this multipolar delivery structure developed due to the increase in the number of widely dispersed retail stores for each of the three corporate groups.4) Between the Dahei and Seiyu groups, in which a bipolar delivery networks is currently noticeable, the delivery time for each store is different. In the Daiei group, the delivery area is divided within city areas such as Tokyo and Yokohama, in which traffic can be heavy, so there is a large number of stores with a short delivery time. In the Seiyu group, there is only a small number of stores that have a short delivery time. This is because the Seiyu group has a large delivery centre serving a large area where is heavy traffic. and the smaller regional delivery centres serve larger areas compared to the Daiei and Jusco groups. In conclusion, the location of delivery centres and delivery area boundaries, as delivery area size, have a great influence on delivery time.

Composite issues in rotor hub structure design

While the use of composites in rotor hubs has produced many benefits, it has also revealed weaknesses in application. In order to design a structurally efficient composite hub, weakness issues in structures and materials need to be addressed. This paper discusses the structural and material aspects of these issues.

Genetic control of bacteriophage T4 baseplate morphogenesis: III. Formation of the central plug and overall assembly pathway

Cells infected with bacteriophage T4 amber mutants defective in any of seven baseplate genes (5, 25, 26, 51, 27, 28 and 29) are unable to form functional baseplates because of a defect in the assembly of the central part of the baseplate. Upon mixing concentrated extracts of such mutant-infected cells, complete baseplates, and subsequently, viable phage, assemble in vitro. By characterizing the in vitro assembly activity of the precursor complexes accumulating in the mutant-infected cells, we have been able to define the gene product interactions in morphogenesis. The pathway for the interaction of the six gene products which form the central part of the baseplate is as follows: the gene 29 protein is acted upon by the gene 26 and 28 products, yielding a 7 S precursor. The action of the gene 51 product converts this to a 14 S complex. Independently, the gene 27 and gene 5 products assemble into a 12 S complex. This 12 S 5+:27+ complex then combines with the 14 S 29+:28+:26+:51+ complex to form the final 22 S complex. This structure probably represents the hexameric central plug or hub of the baseplate. A number of the proteins probably act catalytically and are not present in the final complex. Three of the gene products gp29, gp5, and gp27† are incorporated into the complex. These results taken together with those of the previous papers show that the overall pathway for the morphogenesis of the T4 baseplate represents the aggregation of six 15 S arm complexes around a central 22 S hub structure. Two more gene products add to the outer face of the baseplate, and two other gene products to the inner face, only after an hexagonal structure has organized. Five of the six genes specifying hub proteins are contiguous on the phage chromosome. Similarly, six of the seven genes specifying “arm” proteins are contiguous on the chromosome. The odd gene in each set maps at one end of the opposite cluster. As a result of these experiments, we can now define the complete pathway for the interactions of 22 T4 gene products involved in the morphogenesis of the phage tail. The sequential nature of this pathway is striking; proteins only interact with each other if one member has already been incorporated into a growing structure. Thus, the regulation of assembly appears to be entirely at the level of protein-protein interactions, and the genetic control of this particular morphogenetic process operates at the level of primary protein sequence specification.

Month in the Patent Office

A piston‐and‐cylinder friction type vibration damper 16 is disposed between each pair of adjacent rotor blades 10 of a helicopter rotor. There is no damper provided at the drag hinge 14 between each blade 10 and the hub structure 13 of the rotor. The damper 16 comprises a scrubbing action with vibration damping and it provides constant damping for normal blade‐to‐blade oscillations and an increased degree of damping when abnormal oscillations take place. As shown in fig. 1, the damper provides resistance to compression movements only. Another damper is described which is double‐acting.