Major Network Components Research Articles

Axial Tubule Junctions Activate Atrial Ca2+ Release Across Species.

Rationale: Recently, abundant axial tubule (AT) membrane structures were identified deep inside atrial myocytes (AMs). Upon excitation, ATs rapidly activate intracellular Ca2+ release and sarcomeric contraction through extensive AT junctions, a cell-specific atrial mechanism. While AT junctions with the sarcoplasmic reticulum contain unusually large clusters of ryanodine receptor 2 (RyR2) Ca2+ release channels in mouse AMs, it remains unclear if similar protein networks and membrane structures exist across species, particularly those relevant for atrial disease modeling.Objective: To examine and quantitatively analyze the architecture of AT membrane structures and associated Ca2+ signaling proteins across species from mouse to human.Methods and Results: We developed superresolution microscopy (nanoscopy) strategies for intact live AMs based on a new custom-made photostable cholesterol dye and immunofluorescence imaging of membraneous structures and membrane proteins in fixed tissue sections from human, porcine, and rodent atria. Consistently, in mouse, rat, and rabbit AMs, intact cell-wide tubule networks continuous with the surface membrane were observed, mainly composed of ATs. Moreover, co-immunofluorescence nanoscopy showed L-type Ca2+ channel clusters adjacent to extensive junctional RyR2 clusters at ATs. However, only junctional RyR2 clusters were highly phosphorylated and may thus prime Ca2+ release at ATs, locally for rapid signal amplification. While the density of the integrated L-type Ca2+ current was similar in human and mouse AMs, the intracellular Ca2+ transient showed quantitative differences. Importantly, local intracellular Ca2+ release from AT junctions occurred through instantaneous action potential propagation via transverse tubules (TTs) from the surface membrane. Hence, sparse TTs were sufficient as electrical conduits for rapid activation of Ca2+ release through ATs. Nanoscopy of atrial tissue sections confirmed abundant ATs as the major network component of AMs, particularly in human atrial tissue sections.Conclusion: AT junctions represent a conserved, cell-specific membrane structure for rapid excitation-contraction coupling throughout a representative spectrum of species including human. Since ATs provide the major excitable membrane network component in AMs, a new model of atrial “super-hub” Ca2+ signaling may apply across biomedically relevant species, opening avenues for future investigations about atrial disease mechanisms and therapeutic targeting.

Mechanics of a two-fiber model with one nested fiber network, as applied to the collagen-fibrin system

The mechanical behavior of collagen-fibrin (col-fib) co-gels is both scientifically interesting and clinically relevant. Collagen-fibrin networks are a staple of tissue engineering research, but the mechanical consequences of changes in co-gel composition have remained difficult to predict or even explain. We previously observed fundamental differences in failure behavior between collagen-rich and fibrin-rich co-gels, suggesting an essential change in how the two components interact as the co-gel’s composition changes.In this work, we explored the hypothesis that the co-gel behavior is due to a lack of percolation by the dilute component. We generated a series of computational models based on interpenetrating fiber networks. In these models, the major network component percolated the model space but the minor component did not, instead occupying a small island embedded within the larger network. Each component was assigned properties based on a fit of single-component gel data. Island size was varied to match the relative concentrations of the two components. The model predicted that networks rich in collagen, the stiffer component, would roughly match pure-collagen gel behavior with little additional stress due to the fibrin, as seen experimentally. For fibrin-rich gels, however, the model predicted a smooth increase in the overall network strength with added collagen, as seen experimentally but not consistent with an additive parallel model. We thus conclude that incomplete percolation by the low-concentration component of a co-gel is a major determinant of its macroscopic properties, especially if the low-concentration component is the stiffer component. Statement of significanceModels for the behavior of fibrous networks have useful applications in many different fields, including polymer science, textiles, and tissue engineering. In addition to being important structural components in soft tissues and blood clots, these protein networks can serve as scaffolds for bioartificial tissues. Thus, their mechanical behavior, especially in co-gels, is both interesting from a materials science standpoint and significant with regard to tissue engineering.

Temperature-induced phase transition in hydrogels of interpenetrating networks poly(N-isopropylmethacrylamide)/poly(N-isopropylacrylamide)

The combination of 1H NMR spectroscopy, DSC, dynamic mechanical spectroscopy, and optical microscopy was used to investigate temperature-induced volume phase transition in hydrogels of interpenetrating networks (IPNs) poly(N-isopropylmethacrylamide)/poly(N-isopropylacrylamide) (PNIPMAm/PNIPAm) with various PNIPMAm content. In these IPNs, both networks are thermosensitive; such systems were not examined so far. All methods showed phase transition starting at 307 K, which is the volume phase transition temperature of PNIPAm, the major network component. Only the sample with the lowest content of PNIPAm (~54 %) shows two-step collapse transition, other samples with higher PNIPAm content show a single transition in NMR and DSC which indicates enhanced mutual entanglement of both components. In all samples, the phase transition results in substantial increase of both components of the shear modulus. Although the properties of all samples change with temperature in similar way, differences in dependence on the PNIPMAm content and the shape of the sample can be seen.

Challenges in Building a Trustworthy Network

An open challenge in trustworthy computing is the development of a trustworthy network since network plays an essential role of current computing infrastructure (e.g., grid computing, cloud computing, etc.). In order to have a trustworthy network, security, privacy, and reliability must be protected on every major network component. For instance, if there is no trusted mechanism to enforce security protection of every data transaction on major network components, a network cannot be relied on performing trustworthy computing. It has been observed that trustworthy network cannot be practically achieved if there is no trusted integration of major network components. In this paper, we discuss the challenges in building a trustworthy network and develop a trustworthy network model that is both scalable and interoperable with existing and future network architectures.

Cooperative networks for the future wireless world

Beyond-3G (B3G) systems have been envisaged as an evolution and convergence of mobile/wireless communication systems and IP technologies to offer a multitude of services over a variety of access technologies. To fulfill the vision, it is necessary to understand the requirements with respect to the support of heterogeneity in network accesses, communication services, mobility, user devices, and so on. Besides, it is equally important to promote the necessary research in networking technology by providing a guiding framework of research areas and technical issues with priority. The new architectures and technologies have to address the fundamental assumptions and requirements that govern the design. All these issues are being tackled by the cooperative network group (CoNet) of WWRF; the group is working on a series of white papers outlining B3G visions and roadmap, architectural principles, research challenges, and candidate approaches. This article outlines the CoNet concept, architectural principles, and guidelines for research into cooperative networks assuming that the B3G systems are built over generic IP networking technologies. The article also presents the key research challenges, research framework, and major network components and technologies. The key points are that the system should be layered on demand, encourage reuse if independent modularized functional blocks, support multiple services and service creation, ensure consistent end-to-end connectivity across different access technologies, and cooperate in terms of network control, operations, and maintenance. The architecture includes the endpoints of communications as part of the communications system, and provides a secure and trusted environment in which network functions are performed; the network should self-organize dynamically. Additionally, the article presents the IST WSI architecture proposed to CoNet as reference model along with some approaches to the outlined research challenges. Finally, this study selects three important network components and technologies (i.e., mobility management, multiple access, and moving networks) in order to provide with answers and possible solutions the research challenges presented in earlier sections.

Experience in designing a TCP/IP based VOD system over a dedicated network

We address the problem of designing a TCP/IP based VOD system over a dedicated network. Despite of the general belief that TCP/IP is not suitable for real-time multimedia applications, after testing in a laboratory environment for one year, we are confident in announcing that our prototype is both efficient and reliable. This success depends on several important factors. First of all, the system operates on a dedicated network in which there exists no other traffic except a small amount of background traffic generated by the Ether Switch, the major network component used by our prototype. Second, the system overhead due to the VOD server and the network adaptor card is minimized. Third, we maximize the disk bandwidth by implementing a proprietary disk file system. Our experiment shows that it requires only about 330 KBytes at the client buffer to smooth packet delay jitters.

Experience in designing a using TCP as transport protocol VOD system over a dedicated network

We address the problem of designing a TCP and IP (TCP/IP) based video on demand (VOD) system over a dedicated network based on standard internet protocols, i.e., transmission control protocol (TCP) and Internet protocol (IP). TCP and IP are usually referred together as TCP/IP. Despite of the general belief that TCP/IP is not suitable for real-time multimedia applications, after testing in a laboratory environment for about one year, we are confident in announcing that our prototype is both efficient and reliable. This success depends on several important factors. First of all, the system operates on a dedicated network in which there exists no other traffic except a light of background traffic generated by the Ether Switch, the major network component used by our prototype. Second, system overhead due to the VOD server and the network adaptor card is minimized. Third, we maximize the disk bandwidth by implementing a proprietary disk file system. Our experiment shows that it requires only about 330 KBytes at the client buffer to smooth packet delay jitters. In our experimental environment, due to resource limitations, up to 40 clients had been tested successfully. By looking at the network bandwidth and CPU utilization, we estimate that a single VOD server should be able to handle more than 40 interactive clients playing MPEG-1 system streams simultaneously.

Network status display system

The paper describes a wide area network monitoring system that displays and records changes in the status of major network components. The system can be accessed by any interactive user on the network to receive the status information or warnings of future service disruption. The information collection techniques used, operator and user interfaces and examples of reports generated are explained, along with some discussion of the practical problems encountered.