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Sample records for active virtual network

  1. Topological evolution of virtual social networks by modeling social activities

    NASA Astrophysics Data System (ADS)

    Sun, Xin; Dong, Junyu; Tang, Ruichun; Xu, Mantao; Qi, Lin; Cai, Yang

    2015-09-01

    With the development of Internet and wireless communication, virtual social networks are becoming increasingly important in the formation of nowadays' social communities. Topological evolution model is foundational and critical for social network related researches. Up to present most of the related research experiments are carried out on artificial networks, however, a study of incorporating the actual social activities into the network topology model is ignored. This paper first formalizes two mathematical abstract concepts of hobbies search and friend recommendation to model the social actions people exhibit. Then a social activities based topology evolution simulation model is developed to satisfy some well-known properties that have been discovered in real-world social networks. Empirical results show that the proposed topology evolution model has embraced several key network topological properties of concern, which can be envisioned as signatures of real social networks.

  2. Mobile Virtual Private Networking

    NASA Astrophysics Data System (ADS)

    Pulkkis, Göran; Grahn, Kaj; Mårtens, Mathias; Mattsson, Jonny

    Mobile Virtual Private Networking (VPN) solutions based on the Internet Security Protocol (IPSec), Transport Layer Security/Secure Socket Layer (SSL/TLS), Secure Shell (SSH), 3G/GPRS cellular networks, Mobile IP, and the presently experimental Host Identity Protocol (HIP) are described, compared and evaluated. Mobile VPN solutions based on HIP are recommended for future networking because of superior processing efficiency and network capacity demand features. Mobile VPN implementation issues associated with the IP protocol versions IPv4 and IPv6 are also evaluated. Mobile VPN implementation experiences are presented and discussed.

  3. Virtualized Network Control. Final Report

    SciTech Connect

    Ghani, Nasir

    2013-02-01

    This document is the final report for the Virtualized Network Control (VNC) project, which was funded by the United States Department of Energy (DOE) Office of Science. This project was also informally referred to as Advanced Resource Computation for Hybrid Service and TOpology NEtworks (ARCHSTONE). This report provides a summary of the project's activities, tasks, deliverable, and accomplishments. It also provides a summary of the documents, software, and presentations generated as part of this projects activities. Namely, the Appendix contains an archive of the deliverables, documents, and presentations generated a part of this project.

  4. Virtualized Network Control (VNC)

    SciTech Connect

    Lehman, Thomas; Guok, Chin; Ghani, Nasir

    2013-01-31

    The focus of this project was on the development of a "Network Service Plane" as an abstraction model for the control and provisioning of multi-layer networks. The primary motivation for this work were the requirements of next generation networked applications which will need to access advanced networking as a first class resource at the same level as compute and storage resources. A new class of "Intelligent Network Services" were defined in order to facilitate the integration of advanced network services into application specific workflows. This new class of network services are intended to enable real-time interaction between the application co-scheduling algorithms and the network for the purposes of workflow planning, real-time resource availability identification, scheduling, and provisioning actions.

  5. Game-Based Virtual Worlds as Decentralized Virtual Activity Systems

    NASA Astrophysics Data System (ADS)

    Scacchi, Walt

    There is widespread interest in the development and use of decentralized systems and virtual world environments as possible new places for engaging in collaborative work activities. Similarly, there is widespread interest in stimulating new technological innovations that enable people to come together through social networking, file/media sharing, and networked multi-player computer game play. A decentralized virtual activity system (DVAS) is a networked computer supported work/play system whose elements and social activities can be both virtual and decentralized (Scacchi et al. 2008b). Massively multi-player online games (MMOGs) such as World of Warcraft and online virtual worlds such as Second Life are each popular examples of a DVAS. Furthermore, these systems are beginning to be used for research, deve-lopment, and education activities in different science, technology, and engineering domains (Bainbridge 2007, Bohannon et al. 2009; Rieber 2005; Scacchi and Adams 2007; Shaffer 2006), which are also of interest here. This chapter explores two case studies of DVASs developed at the University of California at Irvine that employ game-based virtual worlds to support collaborative work/play activities in different settings. The settings include those that model and simulate practical or imaginative physical worlds in different domains of science, technology, or engineering through alternative virtual worlds where players/workers engage in different kinds of quests or quest-like workflows (Jakobsson 2006).

  6. Network Virtualization - Opportunities and Challenges for Operators

    NASA Astrophysics Data System (ADS)

    Carapinha, Jorge; Feil, Peter; Weissmann, Paul; Thorsteinsson, Saemundur E.; Etemoğlu, Çağrı; Ingþórsson, Ólafur; Çiftçi, Selami; Melo, Márcio

    In the last few years, the concept of network virtualization has gained a lot of attention both from industry and research projects. This paper evaluates the potential of network virtualization from an operator's perspective, with the short-term goal of optimizing service delivery and rollout, and on a longer term as an enabler of technology integration and migration. Based on possible scenarios for implementing and using network virtualization, new business roles and models are examined. Open issues and topics for further evaluation are identified. In summary, the objective is to identify the challenges but also new opportunities for telecom operators raised by network virtualization.

  7. A virtual network computer's optical storage virtualization scheme

    NASA Astrophysics Data System (ADS)

    Wang, Jianzong; Hu, Huaixiang; Wan, Jiguang; Wang, Peng

    2008-12-01

    In this paper, we present the architecture and implementation of a virtual network computers' (VNC) optical storage virtualization scheme called VOSV. Its task is to manage the mapping of virtual optical storage to physical optical storage, a technique known as optical storage virtualization. The design of VOSV aims at the optical storage resources of different clients and servers that have high read-sharing patterns. VOSV uses several schemes such as a two-level Cache mechanism, a VNC server embedded module and the iSCSI protocols to improve the performance. The results measured on the prototype are encouraging, and indicating that VOSV provides the high I/O performance.

  8. Knowledge Searching and Sharing on Virtual Networks.

    ERIC Educational Resources Information Center

    Helokunnas, Tuija; Herrala, Juha

    2001-01-01

    Describes searching and sharing of knowledge on virtual networks, based on experiences gained when hosting virtual knowledge networks at Tampere University of Technology in Finland. Discusses information and knowledge management studies; role of information technology in knowledge searching and sharing; implementation and experiences of the…

  9. Scalable Virtual Network Mapping Algorithm for Internet-Scale Networks

    NASA Astrophysics Data System (ADS)

    Yang, Qiang; Wu, Chunming; Zhang, Min

    The proper allocation of network resources from a common physical substrate to a set of virtual networks (VNs) is one of the key technical challenges of network virtualization. While a variety of state-of-the-art algorithms have been proposed in an attempt to address this issue from different facets, the challenge still remains in the context of large-scale networks as the existing solutions mainly perform in a centralized manner which requires maintaining the overall and up-to-date information of the underlying substrate network. This implies the restricted scalability and computational efficiency when the network scale becomes large. This paper tackles the virtual network mapping problem and proposes a novel hierarchical algorithm in conjunction with a substrate network decomposition approach. By appropriately transforming the underlying substrate network into a collection of sub-networks, the hierarchical virtual network mapping algorithm can be carried out through a global virtual network mapping algorithm (GVNMA) and a local virtual network mapping algorithm (LVNMA) operated in the network central server and within individual sub-networks respectively with their cooperation and coordination as necessary. The proposed algorithm is assessed against the centralized approaches through a set of numerical simulation experiments for a range of network scenarios. The results show that the proposed hierarchical approach can be about 5-20 times faster for VN mapping tasks than conventional centralized approaches with acceptable communication overhead between GVNCA and LVNCA for all examined networks, whilst performs almost as well as the centralized solutions.

  10. VNEC - A Virtual Network Experiment Controller

    NASA Astrophysics Data System (ADS)

    Gagnon, François; Dej, Tomas; Esfandiari, Babak

    This paper presents VNEC, a tool to specify and execute network experiments in a virtual environment. The user first formulates the network topology and then provides the tasks that should be performed by the computers together with their execution. Next, VNEC initializes the environment by powering up and configuring the virtual machines to match the desired network topology. Finally, commands are dispatched to the right virtual machines in the specified order. VNEC provides an environment for several types of research experiments such as virus propagation patterns and reactions of different targets against a given attack.

  11. Efficient algorithms for survivable virtual network embedding

    NASA Astrophysics Data System (ADS)

    Sun, Gang; Yu, Hongfang; Li, Lemin; Anand, Vishal; di, Hao; Gao, Xiujiao

    2010-12-01

    Network Virtualization Technology is serving as an effective method for providing a flexible and highly adaptable shared substrate network to satisfy the diversity of demands. But the problem of efficiently embedding Virtual Network (VN) onto substrate network is intractable since it is NP-hard. How to guarantee survivability of the embedding efficiently is another great challenge. In this paper, we investigate the Survivable Virtual Network Embedding (SVNE) problem and propose two efficient algorithms for solving this problem efficiently. Firstly, we formulate the model with minimum-cost objective of survivable network virtualization problem by Mixed Integer Linear Programming (MILP). We then devise two efficient relaxation-based algorithms for solving survivable virtual network embedding problem: (1) Lagrangian Relaxation based algorithm, called LR-SVNE in this paper; (2) Decomposition based algorithm called DSVNE in this paper. The results of simulation experiments show that these two algorithms both have good performance on time efficiency but LR-SVNE can guarantee the solution converge to optimal one under small scale substrate network.

  12. Virtual atmospheric mercury emission network in China.

    PubMed

    Liang, Sai; Zhang, Chao; Wang, Yafei; Xu, Ming; Liu, Weidong

    2014-01-01

    Top-down analysis of virtual atmospheric mercury emission networks can direct efficient demand-side policy making on mercury reductions. Taking China-the world's top atmospheric mercury emitter-as a case, we identify key contributors to China's atmospheric mercury emissions from both the producer and the consumer perspectives. China totally discharged 794.9 tonnes of atmospheric mercury emissions in 2007. China's production-side control policies should mainly focus on key direct mercury emitters such as Liaoning, Hebei, Shandong, Shanxi, Henan, Hunan, Guizhou, Yunnan, and Inner Mongolia provinces and sectors producing metals, nonmetallic mineral products, and electricity and heat power, while demand-side policies should mainly focus on key underlying drivers of mercury emissions such as Shandong, Jiangsu, Zhejiang, and Guangdong provinces and sectors of construction activities and equipment manufacturing. China's interregional embodied atmospheric mercury flows are generally moving from the inland to the east coast. Beijing-Tianjin (with 4.8 tonnes of net mercury inflows) and South Coast (with 3.3 tonnes of net mercury inflows) are two largest net-inflow regions, while North (with 5.3 tonnes of net mercury outflows) is the largest net-outflow region. We also identify primary supply chains contributing to China's virtual atmospheric mercury emission network, which can be used to trace the transfers of production-side and demand-side policy effects. PMID:24479953

  13. Case study of virtual private network

    NASA Astrophysics Data System (ADS)

    Hernandez, Harold; Chung, Ping-Tsai

    2001-07-01

    In this study, business benefits for this Virtual Private Network (VPN) and protocols, techniques, equipments used in this VPN are reported. In addition, our design experience for fault tolerance, security and network management and administration on this VPN are showed. Finally, the issues for future planning of this VPN is addressed.

  14. Libraries' Place in Virtual Social Networks

    ERIC Educational Resources Information Center

    Mathews, Brian S.

    2007-01-01

    Do libraries belong in the virtual world of social networking? With more than 100 million users, this environment is impossible to ignore. A rising philosophy for libraries, particularly in blog-land, involves the concept of being where the users are. Simply using new media to deliver an old message is not progress. Instead, librarians should…

  15. Spatial Models for Virtual Networks

    NASA Astrophysics Data System (ADS)

    Janssen, Jeannette

    This paper discusses the use of spatial graph models for the analysis of networks that do not have a direct spatial reality, such as web graphs, on-line social networks, or citation graphs. In a spatial graph model, nodes are embedded in a metric space, and link formation depends on the relative position of nodes in the space. It is argued that spatial models form a good basis for link mining: assuming a spatial model, the link information can be used to infer the spatial position of the nodes, and this information can then be used for clustering and recognition of node similarity. This paper gives a survey of spatial graph models, and discusses their suitability for link mining.

  16. Ecological network analysis for a virtual water network.

    PubMed

    Fang, Delin; Chen, Bin

    2015-06-01

    The notions of virtual water flows provide important indicators to manifest the water consumption and allocation between different sectors via product transactions. However, the configuration of virtual water network (VWN) still needs further investigation to identify the water interdependency among different sectors as well as the network efficiency and stability in a socio-economic system. Ecological network analysis is chosen as a useful tool to examine the structure and function of VWN and the interactions among its sectors. A balance analysis of efficiency and redundancy is also conducted to describe the robustness (RVWN) of VWN. Then, network control analysis and network utility analysis are performed to investigate the dominant sectors and pathways for virtual water circulation and the mutual relationships between pairwise sectors. A case study of the Heihe River Basin in China shows that the balance between efficiency and redundancy is situated on the left side of the robustness curve with less efficiency and higher redundancy. The forestation, herding and fishing sectors and industrial sectors are found to be the main controllers. The network tends to be more mutualistic and synergic, though some competitive relationships that weaken the virtual water circulation still exist. PMID:25938930

  17. Management of optical virtual private networks

    NASA Astrophysics Data System (ADS)

    Wu, Jing; Savoie, Michel; Campbell, Scott; Zhang, Hanzi; Figuerola, Sergi

    2007-11-01

    The Layer 1 Virtual Private Network (L1VPN) technology supports multiple user networks over a common carrier transport network. We present an L1VPN management architecture where network providers manage physical network infrastructures, service providers manage L1VPN services by composing individual network resources into L1VPNs, end users invoke L1VPN management services to configure operational L1VPNs. Using a Service-Oriented Architecture (SOA) and Web Services (WS), we implemented an L1VPN management tool, called User Controlled Light Paths (UCLP). Network providers use the tool to partition resources at the L1VPN level by assigning resources, together with the WS based management services for the resources, to service providers. Service providers use the tool to receive resource partitions from multiple network providers and partner service providers. Further resource partitioning or re-grouping can be conducted on the received resources, and leasing or trading resources with partner service providers is supported. After the service providers compose the use scenarios of resources, and make the use scenarios available to the L1VPN end users as WS, the end users reconfigure the L1VPN without intervention of either network or service providers.

  18. A European Languages Virtual Network Proposal

    NASA Astrophysics Data System (ADS)

    García-Peñalvo, Francisco José; González-González, Juan Carlos; Murray, Maria

    ELVIN (European Languages Virtual Network) is a European Union (EU) Lifelong Learning Programme Project aimed at creating an informal social network to support and facilitate language learning. The ELVIN project aims to research and develop the connection between social networks, professional profiles and language learning in an informal educational context. At the core of the ELVIN project, there will be a web 2.0 social networking platform that connects employees/students for language practice based on their own professional/academic needs and abilities, using all relevant technologies. The ELVIN remit involves the examination of both methodological and technological issues inherent in achieving a social-based learning platform that provides the user with their own customized Personal Learning Environment for EU language acquisition. ELVIN started in November 2009 and this paper presents the project aims and objectives as well as the development and implementation of the web platform.

  19. Social Networks in the Virtual Science Laboratory

    SciTech Connect

    Chin, George; Myers, James D.; Hoyt, David W.

    2002-08-01

    Located at the Pacific Northwest National Laboratory (PNNL), the High Field Magnetic Resonance Facility (HFMRF) houses 11 nuclear magnetic resonance (NMR) spectrometers. Additionally, the Virtual Nuclear Magnetic Resonance Facility (VNMRF) provides on-line Internet access to these HFMRF spectrometers. Through the VNMRF and its suite of computer-supported cooperative work (CSCW) tools, researchers may collaboratively set the controls of an NMR spectrometer, execute an NMR experiment, acquire data, analyze results, and communicate with other researchers all from the comforts of their home institutions and their own offices. Virtual science laboratories like the VNMRF promote a compelling vision. Consistent with Wulf's notion of a "collaboratory," a virtual science laboratory is a "'center without walls', in which the nation's researchers can perform their research without regard to geographical location." Such a laboratory strives to provide an open research environment in which scientists from different disciplines may collaborate on advanced research using leading-edge instruments and tools, while reducing the physical, organizational, and political boundaries that confront researchers as they amass their collective skills, capabilities, and brainpower to solve the world's most challenging scientific problems. In this article, we describe the social networks that have emerged from the VNMRF and the impacts and influences that CSCW technologies have had upon those networks. The development of social networks depends on various factors including personal and professional objectives, work functions, organizational roles, and afforded collaborative capabilities. As such, our results serve as a useful point of comparison and contrast in the analysis of social networks and CSCW impacts that evolve from scientific contexts as well as from other collaborative settings such as in business and education.

  20. Survivable virtual optical network embedding with probabilistic network-element failures in elastic optical networks

    NASA Astrophysics Data System (ADS)

    Yang, Hui; Cheng, Lei; Luo, Guangjun; Zhang, Jie; Zhao, Yongli; Ding, Huixia; Zhou, Jing; Wang, Yang

    2015-06-01

    The elastic optical networks can elastically allocate spectrum tailored for various bandwidth requirements. In addition, different virtual optical networks (VONs) formed by different applications or service providers need to be embedded on the common physical optical network, it brings virtual optical network embedding (VONE) problem. There is no precise standard to measure the survivability of VON from the failure probability view and take minimum VON failure probability as an objective in a VONE problem. In this paper, we investigate a survivable VONE problem from a new perspective. Considering probabilistic physical network-element failures, a novel metric, named virtual optical network failure probability (VON-FP), is introduced to evaluate the survivability of VONs in elastic optical networks. Moreover, a failure-probability-aware virtual optical network embedding (FPA-VONE) algorithm is proposed to deploy VONs on the physical network elements with small failure probability, and finally to decrease the VON-FP and enhance the spectrum utilization effectively.

  1. Virtual Networking for Career Development. Trends and Issues Alert.

    ERIC Educational Resources Information Center

    Kerka, Sandra

    The critical career development strategy of networking is being transformed by the Internet into virtual or e-networking. Virtual networking provides these advantages: it eliminates the fear of making initial contact and the stress of first impressions; it overcomes restrictions of location, time, or money; it makes responses faster and easier;…

  2. Building multiservice Internet protocol virtual private networks

    NASA Astrophysics Data System (ADS)

    Cheung, William

    1999-11-01

    Multiservice Internet Protocol-based Virtual Private Networks (MIP- VPNs) with Quality of Service (QoS) are becoming a reality due to the availability of new standards from the Internet Engineering Task Force (IETF). This paper describes how components including security models, IP tunneling protocols, and service differentiation schemes fit together in order to construct such a VPN. First, the concept and rationale of VPN is presented, followed by a discussion of its supporting components. A comparison is made among the various VPN technologies.

  3. A Survey of Middleware for Sensor and Network Virtualization

    PubMed Central

    Khalid, Zubair; Fisal, Norsheila; Rozaini, Mohd.

    2014-01-01

    Wireless Sensor Network (WSN) is leading to a new paradigm of Internet of Everything (IoE). WSNs have a wide range of applications but are usually deployed in a particular application. However, the future of WSNs lies in the aggregation and allocation of resources, serving diverse applications. WSN virtualization by the middleware is an emerging concept that enables aggregation of multiple independent heterogeneous devices, networks, radios and software platforms; and enhancing application development. WSN virtualization, middleware can further be categorized into sensor virtualization and network virtualization. Middleware for WSN virtualization poses several challenges like efficient decoupling of networks, devices and software. In this paper efforts have been put forward to bring an overview of the previous and current middleware designs for WSN virtualization, the design goals, software architectures, abstracted services, testbeds and programming techniques. Furthermore, the paper also presents the proposed model, challenges and future opportunities for further research in the middleware designs for WSN virtualization. PMID:25615737

  4. Link prediction in the network of global virtual water trade

    NASA Astrophysics Data System (ADS)

    Tuninetti, Marta; Tamea, Stefania; Laio, Francesco; Ridolfi, Luca

    2016-04-01

    Through the international food-trade, water resources are 'virtually' transferred from the country of production to the country of consumption. The international food-trade, thus, implies a network of virtual water flows from exporting to importing countries (i.e., nodes). Given the dynamical behavior of the network, where food-trade relations (i.e., links) are created and dismissed every year, link prediction becomes a challenge. In this study, we propose a novel methodology for link prediction in the virtual water network. The model aims at identifying the main factors (among 17 different variables) driving the creation of a food-trade relation between any two countries, along the period between 1986 and 2011. Furthermore, the model can be exploited to investigate the network configuration in the future, under different possible (climatic and demographic) scenarios. The model grounds the existence of a link between any two nodes on the link weight (i.e., the virtual water flow): a link exists when the nodes exchange a minimum (fixed) volume of virtual water. Starting from a set of potential links between any two nodes, we fit the associated virtual water flows (both the real and the null ones) by means of multivariate linear regressions. Then, links with estimated flows higher than a minimum value (i.e., threshold) are considered active-links, while the others are non-active ones. The discrimination between active and non-active links through the threshold introduces an error (called link-prediction error) because some real links are lost (i.e., missed links) and some non-existing links (i.e., spurious links) are inevitably introduced in the network. The major drivers are those significantly minimizing the link-prediction error. Once the structure of the unweighted virtual water network is known, we apply, again, linear regressions to assess the major factors driving the fluxes traded along (modelled) active-links. Results indicate that, on the one hand

  5. Active localization of virtual sounds

    NASA Astrophysics Data System (ADS)

    Loomis, Jack M.; Hebert, C.; Cicinelli, J. G.

    1991-06-01

    We describe a virtual sound display built around a 12 MHz 80286 microcomputer and special purpose analog hardware. The display implements most of the primary cues for sound localization in the ear-level plane. Static information about direction is conveyed by interaural time differences and, for frequencies above 1800 Hz, by head sound shadow (interaural intensity differences) and pinna sound shadow. Static information about distance is conveyed by variation in sound pressure (first power law) for all frequencies, by additional attenuation in the higher frequencies (simulating atmospheric absorption), and by the proportion of direct to reverberant sound. When the user actively locomotes, the changing angular position of the source occasioned by head rotations provides further information about direction and the changing angular velocity produced by head translations (motion parallax) provides further information about distance. Judging both from informal observations by users and from objective data obtained in an experiment on homing to virtual and real sounds, we conclude that simple displays such as this are effective in creating the perception of external sounds to which subjects can home with accuracy and ease.

  6. Active localization of virtual sounds

    NASA Technical Reports Server (NTRS)

    Loomis, Jack M.; Hebert, C.; Cicinelli, J. G.

    1991-01-01

    We describe a virtual sound display built around a 12 MHz 80286 microcomputer and special purpose analog hardware. The display implements most of the primary cues for sound localization in the ear-level plane. Static information about direction is conveyed by interaural time differences and, for frequencies above 1800 Hz, by head sound shadow (interaural intensity differences) and pinna sound shadow. Static information about distance is conveyed by variation in sound pressure (first power law) for all frequencies, by additional attenuation in the higher frequencies (simulating atmospheric absorption), and by the proportion of direct to reverberant sound. When the user actively locomotes, the changing angular position of the source occasioned by head rotations provides further information about direction and the changing angular velocity produced by head translations (motion parallax) provides further information about distance. Judging both from informal observations by users and from objective data obtained in an experiment on homing to virtual and real sounds, we conclude that simple displays such as this are effective in creating the perception of external sounds to which subjects can home with accuracy and ease.

  7. Teaching Network Security in a Virtual Learning Environment

    ERIC Educational Resources Information Center

    Bergstrom, Laura; Grahn, Kaj J.; Karlstrom, Krister; Pulkkis, Goran; Astrom, Peik

    2004-01-01

    This article presents a virtual course with the topic network security. The course has been produced by Arcada Polytechnic as a part of the production team Computer Networks, Telecommunication and Telecommunication Systems in the Finnish Virtual Polytechnic. The article begins with an introduction to the evolution of the information security…

  8. A distributed framework for inter-domain virtual network embedding

    NASA Astrophysics Data System (ADS)

    Wang, Zihua; Han, Yanni; Lin, Tao; Tang, Hui

    2013-03-01

    Network virtualization has been a promising technology for overcoming the Internet impasse. A main challenge in network virtualization is the efficient assignment of virtual resources. Existing work focused on intra-domain solutions whereas inter-domain situation is more practical in realistic setting. In this paper, we present a distributed inter-domain framework for mapping virtual networks to physical networks which can ameliorate the performance of the virtual network embedding. The distributed framework is based on a Multi-agent approach. A set of messages for information exchange is defined. We design different operations and IPTV use scenarios to validate the advantages of our framework. Use cases shows that our framework can solve the inter-domain problem efficiently.

  9. The Virtual Reference Desk: Building a Network of Expertise for America's Schools. White Paper.

    ERIC Educational Resources Information Center

    Lankes, R. David

    This paper presents the Virtual Reference Desk project, its current activities, and a proposed information system architecture to build a human intermediated network of expertise and experience for the K-12 community. The Virtual Reference Desk is a project headed by the ERIC Clearinghouse on Information & Technology and funded by the U.S.…

  10. Propagation of crises in the virtual water trade network

    NASA Astrophysics Data System (ADS)

    Tamea, Stefania; Laio, Francesco; Ridolfi, Luca

    2015-04-01

    The international trade of agricultural goods is associated to the displacement of the water used to produce such goods and embedded in trade as a factor of production. Water virtually exchanged from producing to consuming countries, named virtual water, defines flows across an international network of 'virtual water trade' which enable the assessment of environmental forcings and implications of trade, such as global water savings or country dependencies on foreign water resources. Given the recent expansion of commodity (and virtual water) trade, in both displaced volumes and network structure, concerns have been raised about the exposure to crises of individuals and societies. In fact, if one country had to markedly decrease its export following a socio-economical or environmental crisis, such as a war or a drought, many -if not all- countries would be affected due to a cascade effect within the trade network. The present contribution proposes a mechanistic model describing the propagation of a local crisis into the virtual water trade network, accounting for the network structure and the virtual water balance of all countries. The model, built on data-based assumptions, is tested on the real case study of the Argentinean crisis in 2008-09, when the internal agricultural production (measured as virtual water volume) decreased by 26% and the virtual water export of Argentina dropped accordingly. Crisis propagation and effects on the virtual water trade are correctly captured, showing the way forward to investigations of crises impact and country vulnerability based on the results of the model proposed.

  11. Neural Mechanisms of Hierarchical Planning in a Virtual Subway Network.

    PubMed

    Balaguer, Jan; Spiers, Hugo; Hassabis, Demis; Summerfield, Christopher

    2016-05-18

    Planning allows actions to be structured in pursuit of a future goal. However, in natural environments, planning over multiple possible future states incurs prohibitive computational costs. To represent plans efficiently, states can be clustered hierarchically into "contexts". For example, representing a journey through a subway network as a succession of individual states (stations) is more costly than encoding a sequence of contexts (lines) and context switches (line changes). Here, using functional brain imaging, we asked humans to perform a planning task in a virtual subway network. Behavioral analyses revealed that humans executed a hierarchically organized plan. Brain activity in the dorsomedial prefrontal cortex and premotor cortex scaled with the cost of hierarchical plan representation and unique neural signals in these regions signaled contexts and context switches. These results suggest that humans represent hierarchical plans using a network of caudal prefrontal structures. VIDEO ABSTRACT. PMID:27196978

  12. A virtual water network of the Roman world

    NASA Astrophysics Data System (ADS)

    Dermody, B. J.; van Beek, R. P. H.; Meeks, E.; Klein Goldewijk, K.; Scheidel, W.; van der Velde, Y.; Bierkens, M. F. P.; Wassen, M. J.; Dekker, S. C.

    2014-12-01

    The Romans were perhaps the most impressive exponents of water resource management in preindustrial times with irrigation and virtual water trade facilitating unprecedented urbanization and socioeconomic stability for hundreds of years in a region of highly variable climate. To understand Roman water resource management in response to urbanization and climate variability, a Virtual Water Network of the Roman World was developed. Using this network we find that irrigation and virtual water trade increased Roman resilience to interannual climate variability. However, urbanization arising from virtual water trade likely pushed the Empire closer to the boundary of its water resources, led to an increase in import costs, and eroded its resilience to climate variability in the long term. In addition to improving our understanding of Roman water resource management, our cost-distance-based analysis illuminates how increases in import costs arising from climatic and population pressures are likely to be distributed in the future global virtual water network.

  13. A virtual water network of the Roman world

    NASA Astrophysics Data System (ADS)

    Dermody, B. J.; van Beek, R. P. H.; Meeks, E.; Klein Goldewijk, K.; Scheidel, W.; van der Velde, Y.; Bierkens, M. F. P.; Wassen, M. J.; Dekker, S. C.

    2014-06-01

    The Romans were perhaps the most impressive exponents of water resource management in preindustrial times with irrigation and virtual water trade facilitating unprecedented urbanisation and socioeconomic stability for hundreds of years in a region of highly variable climate. To understand Roman water resource management in response to urbanisation and climate variability, a Virtual Water Network of the Roman World was developed. Using this network we find that irrigation and virtual water trade increased Roman resilience to climate variability in the short term. However, urbanisation arising from virtual water trade likely pushed the Empire closer to the boundary of its water resources, led to an increase in import costs, and reduced its resilience to climate variability in the long-term. In addition to improving our understanding of Roman water resource management, our cost-distance based analysis illuminates how increases in import costs arising from climatic and population pressures are likely to be distributed in the future global virtual water network.

  14. Large-Scale Networked Virtual Environments: Architecture and Applications

    ERIC Educational Resources Information Center

    Lamotte, Wim; Quax, Peter; Flerackers, Eddy

    2008-01-01

    Purpose: Scalability is an important research topic in the context of networked virtual environments (NVEs). This paper aims to describe the ALVIC (Architecture for Large-scale Virtual Interactive Communities) approach to NVE scalability. Design/methodology/approach: The setup and results from two case studies are shown: a 3-D learning environment…

  15. Horizontal protection for multicast optical virtual private networks

    NASA Astrophysics Data System (ADS)

    Peng, Yunfeng; Long, Keping

    2008-11-01

    New concepts of horizontal protection and half-mesh topology for survivability design in multicast optical virtual private networks are presented. All issues mentioned in this paper are expected to form targets for further investigations.

  16. Distributed virtual worlds in high-speed networks

    NASA Astrophysics Data System (ADS)

    Schiffner, Norbert

    1998-09-01

    Recent research efforts have concentrated on determining how the distributed workplace can be transformed into a shared virtual environment. Interaction among people and process virtual worlds has to be provided and improved. To enhance the usability of our virtual collaborative environment we integrated a multicast communication environment. With the availability of global information highways, 3D graphical intercontinental collaboration will become a part of our daily work routine. This paper describes the basics of our network infrastructure and the multicast support. As a proof of concept, a virtual world scenario is also presented in this paper.

  17. An Overview of Methods for Virtual Social Networks Analysis

    NASA Astrophysics Data System (ADS)

    D'Andrea, Alessia; Ferri, Fernando; Grifoni, Patrizia

    The increasing achievement of the Web has led people to exploit collaborative technologies in order to encourage partnerships among different groups. The cooperation can be achieved by Virtual Social Networks that facilitate people's social interaction and enable them to remain in touch with friends exploiting the pervasive nature of information devices and services. The interest in analysing Virtual Social Networks has grown massively in recent years, and it involves researches from different fields. This led to the development of different methods to study relationships between people, groups, organisations- and other knowledge-processing entities on the Web. This chapter classifies these methods in two categories. The first category concerns methods used for the network data collection while the second category deals with methods used for the network data visualisation. The chapter gives an example of application of these methods to analyse the Virtual Social Network LinkedIn.

  18. Research and development of network virtual instrument laboratory

    NASA Astrophysics Data System (ADS)

    Cui, Hongmei; Pei, Xichun; Ma, Hongyue; Ma, Shuoshi

    2006-11-01

    A software platform of the network virtual instrument test laboratory has been developed to realize the network function of the test and signal analysis as well as the share of the hardware based on the data transmission theory and the study of the present technologies of the network virtual instrument. The whole design procedure was also presented in this paper. The main work of the research is as follows. 1. A suitable scheme of the test system with B/S mode and the virtual instrument laboratory with BSDA (Browser/Server/Database/Application) mode was determined. 2. The functions were classified and integrated by adopting the multilayer structure. The application for the virtual instruments running in the client terminal and the network management server managing the multiuser in the test laboratory according to the "Concurrent receival, sequential implementation" strategy in Java as well as the code of the test server application responding the client's requests of test and signal analysis in LabWindows/CVI were developed. As the extending part of network function of the original virtual test and analysis instruments, a software platform of network virtual instrument test laboratory was built as well. 3. The communication of the network data between Java and the LabWindows/CVI was realized. 4. The database was imported to store the data as well as the correlative information acquired by the server and help the network management server to manage the multiuser in the test laboratory. 5. A website embedding Java Applet of virtual instrument laboratory with the on-line help files was designed.

  19. Structure and Controls of the Global Virtual Water Trade Network

    NASA Astrophysics Data System (ADS)

    Suweis, S. S.

    2011-12-01

    Recurrent or ephemeral water shortages are a crucial global challenge, in particular because of their impacts on food production. The global character of this challenge is reflected in the trade among nations of virtual water, i.e. the amount of water used to produce a given commodity. We build, analyze and model the network describing the transfer of virtual water between world nations for staple food products. We find that all the key features of the network are well described by a model, the fitness model, that reproduces both the topological and weighted properties of the global virtual water trade network, by assuming as sole controls each country's gross domestic product and yearly rainfall on agricultural areas. We capture and quantitatively describe the high degree of globalization of water trade and show that a small group of nations play a key role in the connectivity of the network and in the global redistribution of virtual water. Finally, we illustrate examples of prediction of the structure of the network under future political, economic and climatic scenarios, suggesting that the crucial importance of the countries that trade large volumes of water will be strengthened. Our results show the importance of incorporating a network framework in the study of virtual water trades and provide a model to study the structure and resilience of the GVWTN under future scenarios for social, economic and climate change.

  20. Performance analysis of electronic code division multiple access based virtual private networks over passive optical networks

    NASA Astrophysics Data System (ADS)

    Nadarajah, Nishaanthan; Nirmalathas, Ampalavanapillai

    2008-03-01

    A solution for implementing multiple secure virtual private networks over a passive optical network using electronic code division multiple access is proposed and experimentally demonstrated. The multiple virtual private networking capability is experimentally demonstrated with 40 Mb/s data multiplexed with a 640 Mb/s electronic code that is unique to each of the virtual private networks in the passive optical network, and the transmission of the electronically coded data is carried out using Fabry-Perot laser diodes. A theoretical scalability analysis for electronic code division multiple access based virtual private networks over a passive optical network is also carried out to identify the performance limits of the scheme. Several sources of noise such as optical beat interference and multiple access interference that are present in the receiver are considered with different operating system parameters such as transmitted optical power, spectral width of the broadband optical source, and processing gain to study the scalability of the network.

  1. Supplier Selection in Virtual Enterprise Model of Manufacturing Supply Network

    NASA Astrophysics Data System (ADS)

    Kaihara, Toshiya; Opadiji, Jayeola F.

    The market-based approach to manufacturing supply network planning focuses on the competitive attitudes of various enterprises in the network to generate plans that seek to maximize the throughput of the network. It is this competitive behaviour of the member units that we explore in proposing a solution model for a supplier selection problem in convergent manufacturing supply networks. We present a formulation of autonomous units of the network as trading agents in a virtual enterprise network interacting to deliver value to market consumers and discuss the effect of internal and external trading parameters on the selection of suppliers by enterprise units.

  2. Physical environment virtualization for human activities recognition

    NASA Astrophysics Data System (ADS)

    Poshtkar, Azin; Elangovan, Vinayak; Shirkhodaie, Amir; Chan, Alex; Hu, Shuowen

    2015-05-01

    Human activity recognition research relies heavily on extensive datasets to verify and validate performance of activity recognition algorithms. However, obtaining real datasets are expensive and highly time consuming. A physics-based virtual simulation can accelerate the development of context based human activity recognition algorithms and techniques by generating relevant training and testing videos simulating diverse operational scenarios. In this paper, we discuss in detail the requisite capabilities of a virtual environment to aid as a test bed for evaluating and enhancing activity recognition algorithms. To demonstrate the numerous advantages of virtual environment development, a newly developed virtual environment simulation modeling (VESM) environment is presented here to generate calibrated multisource imagery datasets suitable for development and testing of recognition algorithms for context-based human activities. The VESM environment serves as a versatile test bed to generate a vast amount of realistic data for training and testing of sensor processing algorithms. To demonstrate the effectiveness of VESM environment, we present various simulated scenarios and processed results to infer proper semantic annotations from the high fidelity imagery data for human-vehicle activity recognition under different operational contexts.

  3. Evolution of the global virtual water trade network.

    PubMed

    Dalin, Carole; Konar, Megan; Hanasaki, Naota; Rinaldo, Andrea; Rodriguez-Iturbe, Ignacio

    2012-04-17

    Global freshwater resources are under increasing pressure from economic development, population growth, and climate change. The international trade of water-intensive products (e.g., agricultural commodities) or virtual water trade has been suggested as a way to save water globally. We focus on the virtual water trade network associated with international food trade built with annual trade data and annual modeled virtual water content. The evolution of this network from 1986 to 2007 is analyzed and linked to trade policies, socioeconomic circumstances, and agricultural efficiency. We find that the number of trade connections and the volume of water associated with global food trade more than doubled in 22 years. Despite this growth, constant organizational features were observed in the network. However, both regional and national virtual water trade patterns significantly changed. Indeed, Asia increased its virtual water imports by more than 170%, switching from North America to South America as its main partner, whereas North America oriented to a growing intraregional trade. A dramatic rise in China's virtual water imports is associated with its increased soy imports after a domestic policy shift in 2000. Significantly, this shift has led the global soy market to save water on a global scale, but it also relies on expanding soy production in Brazil, which contributes to deforestation in the Amazon. We find that the international food trade has led to enhanced savings in global water resources over time, indicating its growing efficiency in terms of global water use. PMID:22474363

  4. Evolution of the global virtual water trade network

    PubMed Central

    Dalin, Carole; Konar, Megan; Hanasaki, Naota; Rinaldo, Andrea; Rodriguez-Iturbe, Ignacio

    2012-01-01

    Global freshwater resources are under increasing pressure from economic development, population growth, and climate change. The international trade of water-intensive products (e.g., agricultural commodities) or virtual water trade has been suggested as a way to save water globally. We focus on the virtual water trade network associated with international food trade built with annual trade data and annual modeled virtual water content. The evolution of this network from 1986 to 2007 is analyzed and linked to trade policies, socioeconomic circumstances, and agricultural efficiency. We find that the number of trade connections and the volume of water associated with global food trade more than doubled in 22 years. Despite this growth, constant organizational features were observed in the network. However, both regional and national virtual water trade patterns significantly changed. Indeed, Asia increased its virtual water imports by more than 170%, switching from North America to South America as its main partner, whereas North America oriented to a growing intraregional trade. A dramatic rise in China's virtual water imports is associated with its increased soy imports after a domestic policy shift in 2000. Significantly, this shift has led the global soy market to save water on a global scale, but it also relies on expanding soy production in Brazil, which contributes to deforestation in the Amazon. We find that the international food trade has led to enhanced savings in global water resources over time, indicating its growing efficiency in terms of global water use. PMID:22474363

  5. Ubiquitous virtual private network: a solution for WSN seamless integration.

    PubMed

    Villa, David; Moya, Francisco; Villanueva, Félix Jesús; Aceña, Óscar; López, Juan Carlos

    2014-01-01

    Sensor networks are becoming an essential part of ubiquitous systems and applications. However, there are no well-defined protocols or mechanisms to access the sensor network from the enterprise information system. We consider this issue as a heterogeneous network interconnection problem, and as a result, the same concepts may be applied. Specifically, we propose the use of object-oriented middlewares to provide a virtual private network in which all involved elements (sensor nodes or computer applications) will be able to communicate as if all of them were in a single and uniform network. PMID:24399154

  6. Ubiquitous Virtual Private Network: A Solution for WSN Seamless Integration

    PubMed Central

    Villa, David; Moya, Francisco; Villanueva, Félix Jesús; Aceña, Óscar; López, Juan Carlos

    2014-01-01

    Sensor networks are becoming an essential part of ubiquitous systems and applications. However, there are no well-defined protocols or mechanisms to access the sensor network from the enterprise information system. We consider this issue as a heterogeneous network interconnection problem, and as a result, the same concepts may be applied. Specifically, we propose the use of object-oriented middlewares to provide a virtual private network in which all involved elements (sensor nodes or computer applications) will be able to communicate as if all of them were in a single and uniform network. PMID:24399154

  7. Continuity Aware Spectrum Allocation Schemes for Virtual Optical Network Embedding in Elastic Optical Networks

    NASA Astrophysics Data System (ADS)

    Wang, Wei; Zhao, Yongli; He, Ruiying; Yu, Xiaosong; Zhang, Jie; Zheng, Haomian; Lin, Yi; Han, Jianrui

    2016-05-01

    Optical network virtualization has been studied as a promising technique for optical network resources provisioning. In the virtualization context of Elastic Optical Network (EON), Virtual Optical Network Embedding (VONE) is investigated as a key issue for allocating spectrum resources to VON requests. This paper discusses the continuity constraint for the VONE problem in EONs, and presents three continuity-aware spectrum allocation schemes according to strict and relaxed continuity constraints. We have demonstrated the proposed schemes on emulated testbed to verify the feasibility of composing VON with discontiguous spectrum resources. Additionally, the performances of the proposed schemes are compared via simulation in terms of blocking probability, spectrum resource utilization and discontinuity degree.

  8. Self-healing ATM networks based on virtual path concept

    NASA Astrophysics Data System (ADS)

    Kawanura, Ryutaro; Sato, Ken-Ichi; Tokizawa, Ikuo

    1994-01-01

    This paper proposes self-healing network techniques suitable for ATM networks in order to realize a high-reliable B-ISDN. First the characteristic of virtual paths (VP) and their influence on failure restoration are discussed. A high-speed restoration technique which exploits the benefits of VP's is then proposed and described. The technique simplifies the message transmission processes and reduces the number of generated messages by using preassigned backup virtual paths. Next, the scheme used to design the backup VP routes and spare resource distribution for each link is proposed in order to create a network that applies the proposed restoration scheme. Next, self-reconstruction techniques of backup virtual paths are proposed for the realization of a reversionless restoration cycle. Finally, the feasibility of distributed control operation is discussed.

  9. On the temporal variability of the virtual water network

    NASA Astrophysics Data System (ADS)

    Carr, Joel A.; D'Odorico, Paolo; Laio, Francesco; Ridolfi, Luca

    2012-03-01

    Food security strongly depends on how water resources available in a certain region contribute to determine the maximum amount of food that it can produce. Human societies often cope with water scarcity by importing food products from other regions. Thus, the international trade of food commodities is associated with a virtual transfer of water resources from production to consumption regions through a network of trade. Even though global food security increasingly relies on this trade, the spatiotemporal patterns of the virtual water network remain poorly investigated. It is unclear how these patterns are changing over time, whether there is an increase in the interconnectedness of the network, and at what rate the globalization of water resources is occurring. Here we use a rich database of international trade and reconstruct the virtual water network from 1986 through 2008. We find that the total flow has more than doubled, and the number of links has increased by 92% over this time period. The network has become more homogeneous but most of the flow concentrates in few links and hubs, while several countries exhibit only few (and weak) connections. 50% of the global fluxes are carried by 1.1% of the links, and on average 6-8% of the global population controls more than 50% of the net virtual water exports. The network is extremely dynamic and intermittent with only few permanent links, while each year many links are created and dismissed.

  10. Water for food: The global virtual water trade network

    NASA Astrophysics Data System (ADS)

    Konar, M.; Dalin, C.; Suweis, S. S.; Hanasaki, N.; Rinaldo, A.; Rodriguez-Iturbe, I.

    2011-12-01

    We present a novel conceptual framework and methodology for studying virtual water trade. We utilize complex network theory to analyze the structure of the global virtual water trade associated with the international food trade. In the global virtual water trade network, the nations that participate in the international food trade correspond to the nodes, and the links represent the flows of virtual water associated with the trade of food from the country of export to the country of import. We find that the number of trade connections follows an exponential distribution, except for the case of import trade relationships, while the volume of water that each nation trades compares well with a stretched exponential distribution, indicating high heterogeneity of flows between nations. There is a power law relationship between the volume of virtual water traded and the number of trade connections of each nation. Highly connected nations are preferentially linked to poorly connected nations and exhibit low levels of clustering. However, when the volume of virtual water traded is taken into account, this structure breaks down. This indicates a global hierarchy, in which nations that trade large volumes of water are more likely to link to and cluster with other nations that trade large volumes of water, particularly when the direction of trade is considered. Nations that play a critical role in maintaining the global network architecture are highlighted. Our analysis provides the necessary framework for the development of a model of global virtual water trade aimed at applications ranging from network optimization to climate change impact evaluations.

  11. Water for food: The global virtual water trade network

    NASA Astrophysics Data System (ADS)

    Konar, M.; Dalin, C.; Suweis, S.; Hanasaki, N.; Rinaldo, A.; Rodriguez-Iturbe, I.

    2011-05-01

    We present a novel conceptual framework and methodology for studying virtual water trade. We utilize complex network theory to analyze the structure of the global virtual water trade associated with the international food trade. In the global virtual water trade network, the nations that participate in the international food trade correspond to the nodes, and the links represent the flows of virtual water associated with the trade of food from the country of export to the country of import. We find that the number of trade connections follows an exponential distribution, except for the case of import trade relationships, while the volume of water that each nation trades compares well with a stretched exponential distribution, indicating high heterogeneity of flows between nations. There is a power law relationship between the volume of virtual water traded and the number of trade connections of each nation. Highly connected nations are preferentially linked to poorly connected nations and exhibit low levels of clustering. However, when the volume of virtual water traded is taken into account, this structure breaks down. This indicates a global hierarchy, in which nations that trade large volumes of water are more likely to link to and cluster with other nations that trade large volumes of water, particularly when the direction of trade is considered. Nations that play a critical role in maintaining the global network architecture are highlighted. Our analysis provides the necessary framework for the development of a model of global virtual water trade aimed at applications ranging from network optimization to climate change impact evaluations.

  12. Human hippocampal theta activity during virtual navigation.

    PubMed

    Ekstrom, Arne D; Caplan, Jeremy B; Ho, Emily; Shattuck, Kirk; Fried, Itzhak; Kahana, Michael J

    2005-01-01

    This study examines whether 4-8-Hz theta oscillations can be seen in the human hippocampus, and whether these oscillations increase during virtual movement and searching, as they do in rodents. Recordings from both hippocampal and neocortical depth electrodes were analyzed while six epileptic patients played a virtual taxi-driver game. During the game, the patients alternated between searching for passengers, whose locations were random, and delivering them to stores, whose locations remained constant. In both hippocampus and neocortex, theta increased during virtual movement in all phases of the game. Hippocampal and neocortical theta activity were also significantly correlated with each other, but this correlation did not differ between neocortex and hippocampus and within disparate neocortical electrodes. Our findings demonstrate the existence of movement-related theta oscillations in human hippocampus, and suggest that both cortical and hippocampal oscillations play a role in attention and sensorimotor integration. PMID:16114040

  13. Structure and controls of the global virtual water trade network

    NASA Astrophysics Data System (ADS)

    Suweis, S.; Konar, M.; Dalin, C.; Hanasaki, N.; Rinaldo, A.; Rodriguez-Iturbe, I.

    2011-05-01

    Recurrent or ephemeral water shortages are a crucial global challenge, in particular because of their impacts on food production. The global character of this challenge is reflected in the trade among nations of virtual water, i.e., the amount of water used to produce a given commodity. We build, analyze and model the network describing the transfer of virtual water between world nations for staple food products. We find that all the key features of the network are well described by a model that reproduces both the topological and weighted properties of the global virtual water trade network, by assuming as sole controls each country's gross domestic product and yearly rainfall on agricultural areas. We capture and quantitatively describe the high degree of globalization of water trade and show that a small group of nations play a key role in the connectivity of the network and in the global redistribution of virtual water. Finally, we illustrate examples of prediction of the structure of the network under future political, economic and climatic scenarios, suggesting that the crucial importance of the countries that trade large volumes of water will be strengthened.

  14. A survey on virtualization of Wireless Sensor Networks.

    PubMed

    Islam, Md Motaharul; Hassan, Mohammad Mehedi; Lee, Ga-Won; Huh, Eui-Nam

    2012-01-01

    Wireless Sensor Networks (WSNs) are gaining tremendous importance thanks to their broad range of commercial applications such as in smart home automation, health-care and industrial automation. In these applications multi-vendor and heterogeneous sensor nodes are deployed. Due to strict administrative control over the specific WSN domains, communication barriers, conflicting goals and the economic interests of different WSN sensor node vendors, it is difficult to introduce a large scale federated WSN. By allowing heterogeneous sensor nodes in WSNs to coexist on a shared physical sensor substrate, virtualization in sensor network may provide flexibility, cost effective solutions, promote diversity, ensure security and increase manageability. This paper surveys the novel approach of using the large scale federated WSN resources in a sensor virtualization environment. Our focus in this paper is to introduce a few design goals, the challenges and opportunities of research in the field of sensor network virtualization as well as to illustrate a current status of research in this field. This paper also presents a wide array of state-of-the art projects related to sensor network virtualization. PMID:22438759

  15. A Survey on Virtualization of Wireless Sensor Networks

    PubMed Central

    Islam, Md. Motaharul; Hassan, Mohammad Mehedi; Lee, Ga-Won; Huh, Eui-Nam

    2012-01-01

    Wireless Sensor Networks (WSNs) are gaining tremendous importance thanks to their broad range of commercial applications such as in smart home automation, health-care and industrial automation. In these applications multi-vendor and heterogeneous sensor nodes are deployed. Due to strict administrative control over the specific WSN domains, communication barriers, conflicting goals and the economic interests of different WSN sensor node vendors, it is difficult to introduce a large scale federated WSN. By allowing heterogeneous sensor nodes in WSNs to coexist on a shared physical sensor substrate, virtualization in sensor network may provide flexibility, cost effective solutions, promote diversity, ensure security and increase manageability. This paper surveys the novel approach of using the large scale federated WSN resources in a sensor virtualization environment. Our focus in this paper is to introduce a few design goals, the challenges and opportunities of research in the field of sensor network virtualization as well as to illustrate a current status of research in this field. This paper also presents a wide array of state-of-the art projects related to sensor network virtualization. PMID:22438759

  16. Where Social and Professional Networking Meet: The Virtual Association Chapter

    ERIC Educational Resources Information Center

    Noxon, Rose

    2011-01-01

    Online Capella University wanted to sponsor an International Society for Performance Improvement (ISPI) chapter. Using social networking platforms, a new type of chapter was designed. The virtual chapter breaks new ground on more than the chapter's platform; it is also the first university-sponsored chapter and has a unique approach to…

  17. QoS for virtual private networks (VPN) over optical WDM networks

    NASA Astrophysics Data System (ADS)

    Qin, Yang; Sivalingam, Krishna M.; Li, Bo

    2000-09-01

    In this paper, we study the problem of employing virtual private network (VPN) over wavelength division multiplexing networks to facilitate the guarantee of diverse quality of service requirements of different VPNs. A wavelength routed backbone network is considered. A VPN is specified by the desired logical topology and an a priori traffic matrix.

  18. Cyber-Physical System Security With Deceptive Virtual Hosts for Industrial Control Networks

    SciTech Connect

    Vollmer, Todd; Manic, Milos

    2014-05-01

    A challenge facing industrial control network administrators is protecting the typically large number of connected assets for which they are responsible. These cyber devices may be tightly coupled with the physical processes they control and human induced failures risk dire real-world consequences. Dynamic virtual honeypots are effective tools for observing and attracting network intruder activity. This paper presents a design and implementation for self-configuring honeypots that passively examine control system network traffic and actively adapt to the observed environment. In contrast to prior work in the field, six tools were analyzed for suitability of network entity information gathering. Ettercap, an established network security tool not commonly used in this capacity, outperformed the other tools and was chosen for implementation. Utilizing Ettercap XML output, a novel four-step algorithm was developed for autonomous creation and update of a Honeyd configuration. This algorithm was tested on an existing small campus grid and sensor network by execution of a collaborative usage scenario. Automatically created virtual hosts were deployed in concert with an anomaly behavior (AB) system in an attack scenario. Virtual hosts were automatically configured with unique emulated network stack behaviors for 92% of the targeted devices. The AB system alerted on 100% of the monitored emulated devices.

  19. Cyber-Physical System Security With Deceptive Virtual Hosts for Industrial Control Networks

    DOE PAGESBeta

    Vollmer, Todd; Manic, Milos

    2014-05-01

    A challenge facing industrial control network administrators is protecting the typically large number of connected assets for which they are responsible. These cyber devices may be tightly coupled with the physical processes they control and human induced failures risk dire real-world consequences. Dynamic virtual honeypots are effective tools for observing and attracting network intruder activity. This paper presents a design and implementation for self-configuring honeypots that passively examine control system network traffic and actively adapt to the observed environment. In contrast to prior work in the field, six tools were analyzed for suitability of network entity information gathering. Ettercap, anmore » established network security tool not commonly used in this capacity, outperformed the other tools and was chosen for implementation. Utilizing Ettercap XML output, a novel four-step algorithm was developed for autonomous creation and update of a Honeyd configuration. This algorithm was tested on an existing small campus grid and sensor network by execution of a collaborative usage scenario. Automatically created virtual hosts were deployed in concert with an anomaly behavior (AB) system in an attack scenario. Virtual hosts were automatically configured with unique emulated network stack behaviors for 92% of the targeted devices. The AB system alerted on 100% of the monitored emulated devices.« less

  20. Addressing security issues related to virtual institute distributed activities

    NASA Astrophysics Data System (ADS)

    Stytz, Martin R.; Banks, Sheila B.

    2008-03-01

    One issue confounding the development and experimentation of distributed modeling and simulation environments is the inability of the project team to identify and collaborate with resources, both human and technical, from outside the United States. This limitation is especially significant within the human behavior representation area where areas such as cultural effects research and joint command team behavior modeling require the participation of various cultural and national representatives. To address this limitation, as well as other human behavior representation research issues, NATO Research and Technology Organization initiated a project to develop a NATO virtual institute that enables more effective and more collaborative research into human behavior representation. However, in building and operating a virtual institute one of the chief concerns must be the cyber security of the institute. Because the institute "exists" in cyberspace, all of its activities are susceptible to cyberattacks, subterfuge, denial of service and all of the vulnerabilities that networked computers must face. In our opinion, for the concept of virtual institutes to be successful and useful, their operations and services must be protected from the threats in the cyber environment. A key to developing the required protection is the development and promulgation of standards for cyber security. In this paper, we discuss the types of cyber standards that are required, how new internet technologies can be exploited and can benefit the promulgation, development, maintenance, and robustness of the standards. This paper is organized as follows. Section One introduces the concept of the virtual institutes, the expected benefits, and the motivation for our research and for research in this area. Section Two presents background material and a discussion of topics related to VIs, uman behavior and cultural modeling, and network-centric warfare. Section Three contains a discussion of the

  1. Node Splitting for Improved Virtual Network Embedding: A Feasibility Study

    NASA Astrophysics Data System (ADS)

    Ha, Jihun; Park, Yongtae; Kim, Byungjo; Kim, Eunah; Yang, Sunhee; Kim, Hyogon

    When the residual resources on a virtualized substrate network (SN) are insufficient to meet the resource demands from the requested virtual network (VN) at specific locations, we can attempt to accommodate the VN by allocating resources at alternative locations and transparently serve the accesses to the VN by having them internally rerouted to the actually allocated locations. In this letter, we explore the feasibility of nodal resource splitting in such alternative allocation scenarios. We find that in order to facilitate such alternative allocations, we should first define the node-link resource dependencies. Once the dependencies are given, we demonstrate that the splitting can visibly improve the SN utilization and the request rejection rate for VN embedding requests under many network scenarios.

  2. Monitoring Malware Activity on the LAN Network

    NASA Astrophysics Data System (ADS)

    Skrzewski, Mirosław

    Many security related organizations periodically publish current network and systems security information, with the lists of top malware programs. These lists raises the question how these threats spreads out, if the worms (the only threat with own communication abilities) are low or missing on these lists. The paper discuss the research on malware network activity, aimed to deliver the answer to the question, what is the main infection channel of modern malware, done with the usage of virtual honeypot systems on dedicated, unprotected network. Systems setup, network and systems monitoring solutions, results of over three months of network traffic and malware monitoring are presented, along with the proposed answer to our research question.

  3. Dynamics of the global virtual water trade network

    NASA Astrophysics Data System (ADS)

    Dalin, C.; Konar, M.; Hanasaki, N.; Rodriguez-Iturbe, I.

    2011-12-01

    Water resources are under increasing pressure from population growth, socio-economic development and climate change. Since agriculture is by far the most freshwater-consuming process, the international food trade may be a way of transferring water resources to water-scarce countries, and of saving water globally by encouraging trade from water-efficient countries to less water-efficient countries. We applied complex network theory to analyze the dynamics of the global virtual water trade network. Our goal was to assess how the properties of the virtual water trade network changed in time, and how these changes are related to national policies, economic and weather conditions or events. We found that, on average, the number of trade partners of each country in the network doubled from 1986 to 2007, while the volume of water associated with food trade tripled. Despite this growth of the network, we found that the shape of the network properties distributions remained similar: for all years studied, the degree distribution is well fitted by an exponential distribution and the strength distribution compares well with a stretched exponential distribution, indicating high heterogeneity of flows between nations. Other global network structure characteristics, such as the power law relationship between node strength and node degree, dissasortative behavior and weighted rich club phenomenon were also stable through the 22 year-period. However, there are significant changes at the country and link scale of analysis. The USA has remained the world's top exporter of virtual water, while, since 2001, China has been the world's largest virtual water importer, a position formerly occupied by Russia and Japan. The sharp increase in China's virtual water imports is mostly due to its increased soybean imports, following a domestic policy shift regarding the soy trade in 2000 and 2001. Importantly, the food trade has led to enhanced savings in global water resources over the last few

  4. Managing integrated oncology treatment in virtual networks.

    PubMed

    Stanicki, Verena; Becker, Matthias; Böckmann, Britta

    2015-01-01

    Interdisciplinary and intersectoral coordinated healthcare management based on Clinical Practice Guidelines is essential to achieve high quality in oncological networks. The objective of our research project is to create a cookbook, which can be used by oncological networks as a template. The cookbook is based on guideline-compliant care processes. To develop these care processes, the three S3-guidelines breast, colon and prostate carcinoma have been formalized. The thus-obtained platform-independent process fragments were transformed into an underlying metamodel, which is based on HL7 and can be used for modeling clinical pathways. Additional, qualitative guided interviews were chosen to capitalize on the experts' (e.g. chief residents, resident specialists) wide knowledge and experience in oncological health care management. One of these use cases (tumor board scheduling) is developed for a healthcare management platform which is linked to a national electronic case record. The projected result of our approach is a cookbook which shows, how the treatment can be controlled by interdisciplinary and intersectoral care processes in an oncological network. PMID:26063274

  5. Smart Equipment and Virtual Resources trigger Network Principles in Manufacturing

    NASA Astrophysics Data System (ADS)

    Kuehnle, H.

    2014-06-01

    Computing miniaturization and smart devices rapidly change manufacturing. Decentralization and atomisation of resources uncover novel manufacturing behaviour. Virtual representations of units, processes and resources enforce unaccustomed network principles with strategic impact and irrefutable implications on manufacturing. Eventually manufacturing in total might have to be reconsidered. Distributed manufacturing, largely engaging interacting intelligent manufacturing units and decentralized planning, may be regarded as the manufacturing future. Gradually evolving decision procedures clearly illustrate important effects of irreversible shifts of focus towards units' collaboration and interoperability.

  6. The Effect of Social Network Diagrams on a Virtual Network of Practice: A Korean Case

    ERIC Educational Resources Information Center

    Jo, Il-Hyun

    2009-01-01

    This study investigates the effect of the presentation of social network diagrams on virtual team members' interaction behavior via e-mail. E-mail transaction data from 22 software developers in a Korean IT company was analyzed and depicted as diagrams by social network analysis (SNA), and presented to the members as an intervention. Results…

  7. Network worlds : from link analysis to virtual places.

    SciTech Connect

    Joslyn, C.

    2002-01-01

    Significant progress is being made in knowledge systems through recent advances in the science of very large networks. Attention is now turning in many quarters to the potential impact on counter-terrorism methods. After reviewing some of these advances, we will discuss the difference between such 'network analytic' approaches, which focus on large, homogeneous graph strucures, and what we are calling 'link analytic' approaches, which focus on somewhat smaller graphs with heterogeneous link types. We use this venue to begin the process of rigorously defining link analysis methods, especially the concept of chaining of views of multidimensional databases. We conclude with some speculation on potential connections to virtual world architectures.

  8. Constructing Social Networks from Unstructured Group Dialog in Virtual Worlds

    NASA Astrophysics Data System (ADS)

    Shah, Fahad; Sukthankar, Gita

    Virtual worlds and massively multi-player online games are rich sources of information about large-scale teams and groups, offering the tantalizing possibility of harvesting data about group formation, social networks, and network evolution. However these environments lack many of the cues that facilitate natural language processing in other conversational settings and different types of social media. Public chat data often features players who speak simultaneously, use jargon and emoticons, and only erratically adhere to conversational norms. In this paper, we present techniques for inferring the existence of social links from unstructured conversational data collected from groups of participants in the Second Life virtual world. We present an algorithm for addressing this problem, Shallow Semantic Temporal Overlap (SSTO), that combines temporal and language information to create directional links between participants, and a second approach that relies on temporal overlap alone to create undirected links between participants. Relying on temporal overlap is noisy, resulting in a low precision and networks with many extraneous links. In this paper, we demonstrate that we can ameliorate this problem by using network modularity optimization to perform community detection in the noisy networks and severing cross-community links. Although using the content of the communications still results in the best performance, community detection is effective as a noise reduction technique for eliminating the extra links created by temporal overlap alone.

  9. Triadic motifs in the dependence networks of virtual societies.

    PubMed

    Xie, Wen-Jie; Li, Ming-Xia; Jiang, Zhi-Qiang; Zhou, Wei-Xing

    2014-01-01

    In friendship networks, individuals have different numbers of friends, and the closeness or intimacy between an individual and her friends is heterogeneous. Using a statistical filtering method to identify relationships about who depends on whom, we construct dependence networks (which are directed) from weighted friendship networks of avatars in more than two hundred virtual societies of a massively multiplayer online role-playing game (MMORPG). We investigate the evolution of triadic motifs in dependence networks. Several metrics show that the virtual societies evolved through a transient stage in the first two to three weeks and reached a relatively stable stage. We find that the unidirectional loop motif (M9) is underrepresented and does not appear, open motifs are also underrepresented, while other close motifs are overrepresented. We also find that, for most motifs, the overall level difference of the three avatars in the same motif is significantly lower than average, whereas the sum of ranks is only slightly larger than average. Our findings show that avatars' social status plays an important role in the formation of triadic motifs. PMID:24912755

  10. Ecological network analysis on global virtual water trade.

    PubMed

    Yang, Zhifeng; Mao, Xufeng; Zhao, Xu; Chen, Bin

    2012-02-01

    Global water interdependencies are likely to increase with growing virtual water trade. To address the issues of the indirect effects of water trade through the global economic circulation, we use ecological network analysis (ENA) to shed insight into the complicated system interactions. A global model of virtual water flow among agriculture and livestock production trade in 1995-1999 is also built as the basis for network analysis. Control analysis is used to identify the quantitative control or dependency relations. The utility analysis provides more indicators for describing the mutual relationship between two regions/countries by imitating the interactions in the ecosystem and distinguishes the beneficiary and the contributor of virtual water trade system. Results show control and utility relations can well depict the mutual relation in trade system, and direct observable relations differ from integral ones with indirect interactions considered. This paper offers a new way to depict the interrelations between trade components and can serve as a meaningful start as we continue to use ENA in providing more valuable implications for freshwater study on a global scale. PMID:22243129

  11. Name-Based Address Mapping for Virtual Private Networks

    NASA Astrophysics Data System (ADS)

    Surányi, Péter; Shinjo, Yasushi; Kato, Kazuhiko

    IPv4 private addresses are commonly used in local area networks (LANs). With the increasing popularity of virtual private networks (VPNs), it has become common that a user connects to multiple LANs at the same time. However, private address ranges for LANs frequently overlap. In such cases, existing systems do not allow the user to access the resources on all LANs at the same time. In this paper, we propose name-based address mapping for VPNs, a novel method that allows connecting to hosts through multiple VPNs at the same time, even when the address ranges of the VPNs overlap. In name-based address mapping, rather than using the IP addresses used on the LANs (the real addresses), we assign a unique virtual address to each remote host based on its domain name. The local host uses the virtual addresses to communicate with remote hosts. We have implemented name-based address mapping for layer 3 OpenVPN connections on Linux and measured its performance. The communication overhead of our system is less than 1.5% for throughput and less than 0.2ms for each name resolution.

  12. Cortical Spiking Network Interfaced with Virtual Musculoskeletal Arm and Robotic Arm

    PubMed Central

    Dura-Bernal, Salvador; Zhou, Xianlian; Neymotin, Samuel A.; Przekwas, Andrzej; Francis, Joseph T.; Lytton, William W.

    2015-01-01

    Embedding computational models in the physical world is a critical step towards constraining their behavior and building practical applications. Here we aim to drive a realistic musculoskeletal arm model using a biomimetic cortical spiking model, and make a robot arm reproduce the same trajectories in real time. Our cortical model consisted of a 3-layered cortex, composed of several hundred spiking model-neurons, which display physiologically realistic dynamics. We interconnected the cortical model to a two-joint musculoskeletal model of a human arm, with realistic anatomical and biomechanical properties. The virtual arm received muscle excitations from the neuronal model, and fed back proprioceptive information, forming a closed-loop system. The cortical model was trained using spike timing-dependent reinforcement learning to drive the virtual arm in a 2D reaching task. Limb position was used to simultaneously control a robot arm using an improved network interface. Virtual arm muscle activations responded to motoneuron firing rates, with virtual arm muscles lengths encoded via population coding in the proprioceptive population. After training, the virtual arm performed reaching movements which were smoother and more realistic than those obtained using a simplistic arm model. This system provided access to both spiking network properties and to arm biophysical properties, including muscle forces. The use of a musculoskeletal virtual arm and the improved control system allowed the robot arm to perform movements which were smoother than those reported in our previous paper using a simplistic arm. This work provides a novel approach consisting of bidirectionally connecting a cortical model to a realistic virtual arm, and using the system output to drive a robotic arm in real time. Our techniques are applicable to the future development of brain neuroprosthetic control systems, and may enable enhanced brain-machine interfaces with the possibility for finer control of

  13. Cortical Spiking Network Interfaced with Virtual Musculoskeletal Arm and Robotic Arm.

    PubMed

    Dura-Bernal, Salvador; Zhou, Xianlian; Neymotin, Samuel A; Przekwas, Andrzej; Francis, Joseph T; Lytton, William W

    2015-01-01

    Embedding computational models in the physical world is a critical step towards constraining their behavior and building practical applications. Here we aim to drive a realistic musculoskeletal arm model using a biomimetic cortical spiking model, and make a robot arm reproduce the same trajectories in real time. Our cortical model consisted of a 3-layered cortex, composed of several hundred spiking model-neurons, which display physiologically realistic dynamics. We interconnected the cortical model to a two-joint musculoskeletal model of a human arm, with realistic anatomical and biomechanical properties. The virtual arm received muscle excitations from the neuronal model, and fed back proprioceptive information, forming a closed-loop system. The cortical model was trained using spike timing-dependent reinforcement learning to drive the virtual arm in a 2D reaching task. Limb position was used to simultaneously control a robot arm using an improved network interface. Virtual arm muscle activations responded to motoneuron firing rates, with virtual arm muscles lengths encoded via population coding in the proprioceptive population. After training, the virtual arm performed reaching movements which were smoother and more realistic than those obtained using a simplistic arm model. This system provided access to both spiking network properties and to arm biophysical properties, including muscle forces. The use of a musculoskeletal virtual arm and the improved control system allowed the robot arm to perform movements which were smoother than those reported in our previous paper using a simplistic arm. This work provides a novel approach consisting of bidirectionally connecting a cortical model to a realistic virtual arm, and using the system output to drive a robotic arm in real time. Our techniques are applicable to the future development of brain neuroprosthetic control systems, and may enable enhanced brain-machine interfaces with the possibility for finer control of

  14. Temporal dynamics of blue and green virtual water trade networks

    NASA Astrophysics Data System (ADS)

    Konar, M.; Dalin, C.; Hanasaki, N.; Rinaldo, A.; Rodriguez-Iturbe, I.

    2012-12-01

    Global food security increasingly relies on the trade of food commodities. Freshwater resources are essential to agricultural production and are thus embodied in the trade of food commodities, referred to as "virtual water trade." Agricultural production predominantly relies on rainwater (i.e., "green water"), though irrigation (i.e., "blue water") does play an important role. These different sources of water have distinctly different opportunity costs, which may be reflected in the way these resources are traded. Thus, the temporal dynamics of the virtual water trade networks from these distinct water sources require characterization. We find that 42 × 109 m3 blue and 310 × 109 m3 green water was traded in 1986, growing to 78 × 109 m3 blue and 594 × 109 m3 green water traded in 2008. Three nations dominate the export of green water resources: the USA, Argentina, and Brazil. As a country increases its export trade partners it tends to export relatively more blue water. However, as a country increases its import trade partners it does not preferentially import water from a specific source. The amount of virtual water that a country imports by increasing its import trade partners has been decreasing over time, with the exception of the soy trade. Both blue and green virtual water networks are efficient: 119 × 109 m3 blue and 105 × 109 m3 green water were saved in 2008. Importantly, trade has been increasingly saving water over time, due to the intensification of crop trade on more water-efficient links.

  15. Temporal dynamics of blue and green virtual water trade networks

    NASA Astrophysics Data System (ADS)

    Konar, M.; Dalin, C.; Hanasaki, N.; Rinaldo, A.; Rodriguez-Iturbe, I.

    2012-07-01

    Global food security increasingly relies on the trade of food commodities. Freshwater resources are essential to agricultural production and are thus embodied in the trade of food commodities, referred to as "virtual water trade." Agricultural production predominantly relies on rainwater (i.e., "green water"), though irrigation (i.e., "blue water") does play an important role. These different sources of water have distinctly different opportunity costs, which may be reflected in the way these resources are traded. Thus, the temporal dynamics of the virtual water trade networks from these distinct water sources require characterization. We find that 42 × 109 m3 blue and 310 × 109 m3 green water was traded in 1986, growing to 78 × 109 m3 blue and 594 × 109 m3 green water traded in 2008. Three nations dominate the export of green water resources: the USA, Argentina, and Brazil. As a country increases its export trade partners it tends to export relatively more blue water. However, as a country increases its import trade partners it does not preferentially import water from a specific source. The amount of virtual water that a country imports by increasing its import trade partners has been decreasing over time, with the exception of the soy trade. Both blue and green virtual water networks are efficient: 119 × 109 m3 blue and 105 × 109 m3 green water were saved in 2008. Importantly, trade has been increasingly saving water over time, due to the intensification of crop trade on more water-efficient links.

  16. Virtual water trade and country vulnerability: A network perspective

    NASA Astrophysics Data System (ADS)

    Sartori, Martina; Schiavo, Stefano

    2015-04-01

    This work investigates the relationship between countries' participation in virtual water trade and their vulnerability to external shocks from a network perspective. In particular, we investigate whether (i) possible sources of local national crises may interact with the system, propagating through the network and affecting the other countries involved; (ii) the topological characteristics of the international agricultural trade network, translated into virtual water-equivalent flows, may favor countries' vulnerability to external crises. Our work contributes to the debate on the potential merits and risks associated with openness to trade in agricultural and food products. On the one hand, trade helps to ensure that even countries with limited water (and other relevant) resources have access to sufficient food and contribute to the global saving of water. On the other hand, there are fears that openness may increase the vulnerability to external shocks and thus make countries worse off. Here we abstract from political considerations about food sovereignty and independence from imports and focus instead on investigating whether the increased participation in global trade that the world has witnessed in the last 30 years has made the system more susceptible to large shocks. Our analysis reveals that: (i) the probability of larger supply shocks has not increased over time; (ii) the topological characteristics of the VW network are not such as to favor the systemic risk associated with shock propagation; and (iii) higher-order interconnections may reveal further important information about the structure of a network. Regarding the first result, fluctuations in output volumes, among the sources of shock analyzed here, are more likely to generate some instability. The first implication is that, on one side, past national or regional economic crises were not necessarily brought about or strengthened by global trade. The second, more remarkable, implication is that, on

  17. Virtual private networks can provide reliable IT connections.

    PubMed

    Kabachinski, Jeff

    2006-01-01

    A VPN is a private network that uses a public network, such as the Internet, to connect remote sites and users together. Instead of using a dedicated hard-wired connection as in a trusted connection or leased lines, a VPN uses a virtual connection routed through the Internet from the organization's private network to the remote site or employee. Typical VPN services allow for security in terms of data encryption as well as means to authenticate, authorize, and account for all the traffic. VPN services allow the organization to use whatever network operating system they wish as it also encapsulate your data into the protocols needed to transport data across public lines. The intention of this IT World article was to give the reader an introduction to VPNs. Keep in mind that there are no standard models for a VPN. You're likely to come across many vendors presenting the virtues of their VPN applications and devices when you Google "VPN." However the general uses, concepts, and principles outlined here should give you a fighting chance to read through the marketing language in the online ads and "white papers." PMID:16544788

  18. The virtual international day of the midwife: social networking for continuing professional development.

    PubMed

    Stewart, Sarah; Sidebotham, Mary; Davis, Deborah

    2012-09-01

    In order to maintain competence to practice, midwives must become lifelong learners and engage in education and CPD activities. The Virtual International Day of the Midwife event (VIDM) is a free online annual synchronous conference that uses social networking tools to bring midwives together to network, share research and practice information. This paper presents the evaluation based on the 2010 and 2011 events. Participants appreciated the opportunity to be able to network with colleagues in an international context, believed the event provided access to quality material and presenters, and valued the accessibility and availability of the event and resources. Participants suggested that the event could be improved by making the program more accessible, with sessions spread over several days, as opposed to 24 hours; providing information about appropriate netiquette and extensive advertising. Further research is required to investigate how social networking and initiatives such as the VIDM impact on practice in the long term. PMID:22765905

  19. Virtual Network Configuration Management System for Data Center Operations and Management

    NASA Astrophysics Data System (ADS)

    Okita, Hideki; Yoshizawa, Masahiro; Uehara, Keitaro; Mizuno, Kazuhiko; Tarui, Toshiaki; Naono, Ken

    Virtualization technologies are widely deployed in data centers to improve system utilization. However, they increase the workload for operators, who have to manage the structure of virtual networks in data centers. A virtual-network management system which automates the integration of the configurations of the virtual networks is provided. The proposed system collects the configurations from server virtualization platforms and VLAN-supported switches, and integrates these configurations according to a newly developed XML-based management information model for virtual-network configurations. Preliminary evaluations show that the proposed system helps operators by reducing the time to acquire the configurations from devices and correct the inconsistency of operators' configuration management database by about 40 percent. Further, they also show that the proposed system has excellent scalability; the system takes less than 20 minutes to acquire the virtual-network configurations from a large scale network that includes 300 virtual machines. These results imply that the proposed system is effective for improving the configuration management process for virtual networks in data centers.

  20. Enabling distributed simulation multilevel security using virtual machine and virtual private network technology

    NASA Astrophysics Data System (ADS)

    Stytz, Martin R.; Banks, Sheila B.

    2007-04-01

    Increasing the accuracy of the portrayal of all of the elements of a simulation environment has long been a prime goal of the modeling and simulation community; a goal that has remained far out of reach for many reasons. One of the greatest hurdles facing simulation developers in the effort to increase simulation accuracy is the need to segregate information across the entire simulation environment according to access restrictions in order to insure the integrity, security, and reliability requirements imposed on the data. However, this need for segregation does not mean that those with the highest access permissions should be forced to use multiple computers and displays to integrate the information that they need or that intelligent agents should be restricted in their access to the information that they need in order to adequately assist their human operators. In this paper, we present a potential solution to the problem of integrating and segregating data, which is the use of virtual machine and virtual private network technology in order to maintain segregation of data, control access, and control intercommunication.

  1. The Effectiveness of Using Virtual Laboratories to Teach Computer Networking Skills in Zambia

    ERIC Educational Resources Information Center

    Lampi, Evans

    2013-01-01

    The effectiveness of using virtual labs to train students in computer networking skills, when real equipment is limited or unavailable, is uncertain. The purpose of this study was to determine the effectiveness of using virtual labs to train students in the acquisition of computer network configuration and troubleshooting skills. The study was…

  2. Design of virtual private networks (VPNs) over optical wavelength-division-multiplexed (WDM) networks

    NASA Astrophysics Data System (ADS)

    Ramamurthy, Byrav; Ramakrishnan, Ashok

    2000-09-01

    The bandwidth requirements of the Internet are increasing every day and there are newer and more bandwidth-thirsty applications emerging on the horizon. Wavelength division multiplexing (WDM) is the next step towards leveraging the capabilities of the optical fiber, especially for wide-area backbone networks. Virtual private networks are seen as the killer applications of tomorrow, and a great amount of research and development effort is being channeled into finding efficient ways for implementing them. In our work, we introduce the notion of VPNs operating over optical wavelength-routed WDM backbone networks. We formulate the problem of VPN design over optical WDM networks as an integer linear problem. A new method to deal with traffic from diverse VPNs is introduced and its performance analyzed.

  3. Novel Quantum Virtual Private Network Scheme for PON via Quantum Secure Direct Communication

    NASA Astrophysics Data System (ADS)

    Gong, Li-Hua; Liu, Ye; Zhou, Nan-Run

    2013-09-01

    Two quantum secure direct communication (QSDC) protocols with quantum identification (QI) based on passive optical network (PON) architecture are proposed. One QSDC protocol can be implemented between two different optical network units just with simple configurations of PON by optical line terminal when they are in the same virtual private network after optical line terminal performing QI to the optical network units in the given PON architecture. The other QSDC protocol is also implemented between any two legitimated users in the virtual private network but with considerable reduction of workload of the optical line terminal. The security analysis shows that the proposed QSDC schemes with quantum identification are unconditionally secure and allow the legitimate users to exchange their secret information efficiently and to realize a quantum virtual private network in the PON networks ultimately.

  4. A Social Network Analysis of Teaching and Research Collaboration in a Teachers' Virtual Learning Community

    ERIC Educational Resources Information Center

    Lin, Xiaofan; Hu, Xiaoyong; Hu, Qintai; Liu, Zhichun

    2016-01-01

    Analysing the structure of a social network can help us understand the key factors influencing interaction and collaboration in a virtual learning community (VLC). Here, we describe the mechanisms used in social network analysis (SNA) to analyse the social network structure of a VLC for teachers and discuss the relationship between face-to-face…

  5. Teaching Advanced Concepts in Computer Networks: VNUML-UM Virtualization Tool

    ERIC Educational Resources Information Center

    Ruiz-Martinez, A.; Pereniguez-Garcia, F.; Marin-Lopez, R.; Ruiz-Martinez, P. M.; Skarmeta-Gomez, A. F.

    2013-01-01

    In the teaching of computer networks the main problem that arises is the high price and limited number of network devices the students can work with in the laboratories. Nowadays, with virtualization we can overcome this limitation. In this paper, we present a methodology that allows students to learn advanced computer network concepts through…

  6. A Stochastic Algorithm for Generating Realistic Virtual Interstitial Cell of Cajal Networks.

    PubMed

    Gao, Jerry; Sathar, Shameer; O'Grady, Gregory; Archer, Rosalind; Cheng, Leo K

    2015-08-01

    Interstitial cells of Cajal (ICC) play a central role in coordinating normal gastrointestinal (GI) motility. Depletion of ICC numbers and network integrity contributes to major functional GI motility disorders. However, the mechanisms relating ICC structure to GI function and dysfunction remains unclear, partly because there is a lack of large-scale ICC network imaging data across a spectrum of depletion levels to guide models. Experimental imaging of these large-scale networks remains challenging because of technical constraints, and hence, we propose the generation of realistic virtual ICC networks in silico using the single normal equation simulation (SNESIM) algorithm. ICC network imaging data obtained from wild-type (normal) and 5-HT2B serotonin receptor knockout (depleted ICC) mice were used to inform the algorithm, and the virtual networks generated were assessed using ICC network structural metrics and biophysically-based computational modeling. When the virtual networks were compared to the original networks, there was less than 10% error for four out of five structural metrics and all four functional measures. The SNESIM algorithm was then modified to enable the generation of ICC networks across a spectrum of depletion levels, and as a proof-of-concept, virtual networks were successfully generated with a range of structural and functional properties. The SNESIM and modified SNESIM algorithms, therefore, offer an alternative strategy for obtaining the large-scale ICC network imaging data across a spectrum of depletion levels. These models can be applied to accurately inform the physiological consequences of ICC depletion. PMID:25781477

  7. The Virtual Liver Network: systems understanding from bench to bedside.

    PubMed

    Henney, Adriano; Coaker, Hannah

    2014-01-01

    Adriano Henney speaks to Hannah Coaker, Commissioning Editor. After achieving a PhD in medicine and spending many years in academic research in the field of cardiovascular disease, Adriano Henney was recruited by Zeneca Pharmaceuticals from a British Heart Foundation Senior Fellowship, where he led the exploration of new therapeutic approaches in atherosclerosis, specifically focusing on his research interests in vascular biology. Following the merger with Astra to form AstraZeneca, Henney became responsible for exploring strategic improvements to the company's approaches to pharmaceutical target identification and the reduction of attrition in early development, directing projects across research sites and across functional project teams in the USA, Sweden and the UK. This resulted in the creation of a new multidisciplinary department that focused on pathway mapping, modeling and simulation and supporting projects across research and development, which evolved into the establishment of the practice of systems biology within the company. Here, projects prototyped the application of mechanistic disease-modeling approaches in order to support the discovery of innovative new medicines, such as Iressa®. Since leaving AstraZeneca, Henney has continued his interest in systems biology, synthetic biology and systems medicine through his company, Obsidian Biomedical Consulting Ltd. He now directs a major €50 million German national flagship program – the Virtual Liver Network – which is currently the largest systems biology program in Europe. PMID:25574529

  8. Wearable Virtual White Cane Network for navigating people with visual impairment.

    PubMed

    Gao, Yabiao; Chandrawanshi, Rahul; Nau, Amy C; Tse, Zion Tsz Ho

    2015-09-01

    Navigating the world with visual impairments presents inconveniences and safety concerns. Although a traditional white cane is the most commonly used mobility aid due to its low cost and acceptable functionality, electronic traveling aids can provide more functionality as well as additional benefits. The Wearable Virtual Cane Network is an electronic traveling aid that utilizes ultrasound sonar technology to scan the surrounding environment for spatial information. The Wearable Virtual Cane Network is composed of four sensing nodes: one on each of the user's wrists, one on the waist, and one on the ankle. The Wearable Virtual Cane Network employs vibration and sound to communicate object proximity to the user. While conventional navigation devices are typically hand-held and bulky, the hands-free design of our prototype allows the user to perform other tasks while using the Wearable Virtual Cane Network. When the Wearable Virtual Cane Network prototype was tested for distance resolution and range detection limits at various displacements and compared with a traditional white cane, all participants performed significantly above the control bar (p < 4.3 × 10(-5), standard t-test) in distance estimation. Each sensor unit can detect an object with a surface area as small as 1 cm(2) (1 cm × 1 cm) located 70 cm away. Our results showed that the walking speed for an obstacle course was increased by 23% on average when subjects used the Wearable Virtual Cane Network rather than the white cane. The obstacle course experiment also shows that the use of the white cane in combination with the Wearable Virtual Cane Network can significantly improve navigation over using either the white cane or the Wearable Virtual Cane Network alone (p < 0.05, paired t-test). PMID:26334037

  9. Virtual Fiber Networking and Impact of Optical Path Grooming on Creating Efficient Layer One Services

    NASA Astrophysics Data System (ADS)

    Naruse, Fumisato; Yamada, Yoshiyuki; Hasegawa, Hiroshi; Sato, Ken-Ichi

    This paper presents a novel “virtual fiber” network service that exploits wavebands. This service provides virtual direct tunnels that directly convey wavelength paths to connect customer facilities. To improve the resource utilization efficiency of the service, a network design algorithm is developed that can allow intermediate path grooming at limited nodes and can determine the best node location. Numerical experiments demonstrate the effectiveness of the proposed service architecture.

  10. Global TIE: Developing a Virtual Network of Robotic Observatories for K-12 Education

    NASA Astrophysics Data System (ADS)

    Mayo, L. A.; Clark, G.

    2001-11-01

    Astronomy in grades K-12 is traditionally taught (if at all) using textbooks and a few simple hands-on activities. In addition, most students, by High School graduation, will never have even looked through the eyepiece of a telescope. The possibility now exists to establish a network of research grade telescopes, no longer useful to the professional astronomical community, that can be made accessible to schools all across the country through existing IT technologies and applications. These telescopes could provide unparalleled research and educational opportunities for a broad spectrum of K-12 and college students and turns underutilized observatory facilities into valuable, state-of-the-art teaching centers. The NASA-sponsored Telescopes In Education (TIE, http://tie.jpl.nasa.gov) project has been wildly successful in engaging the K-12 education community in real-time, hands-on, interactive astronomy activities. Hundreds of schools in the US, Australia, Canada, England, and Japan have participated in the TIE program, remotely controlling the 24-inch telescope at the Mount Wilson Observatory from their classrooms. In recent years, several (approximately 20 to date) other telescopes have been, or are in the process of being, outfitted for remote use as TIE affiliates. Global TIE integrates these telescopes seamlessly into one virtual observatory and provides the services required to operate this facility, including a scheduling service, tools for data manipulation, an online proposal review environment, an online "Virtual TIE Student Ap J" for publication of results, and access to related educational materials provided by the TIE community. Global TIE provides unparalleled research and educational opportunities for a broad spectrum of K-12 and college students and turns essentially unused observatory facilities into valuable, state-of-the-art teaching centers. This presentation describes the Global TIE Observatory data and organizational systems and details the

  11. Postcolonial Practices for a Global Virtual Group: The Case of the International Network for Learning and Teaching Geography in Higher Education (INLT)

    ERIC Educational Resources Information Center

    Hay, Iain

    2008-01-01

    This paper offers a critical review of the role of the International Network for Learning and Teaching geography in higher education (INLT) in the production of geographical knowledge. Through an examination of the Network's membership and activities, it explores some of the ways in which INLT--as a global virtual group--may be inadvertently…

  12. Virtual terrain: a security-based representation of a computer network

    NASA Astrophysics Data System (ADS)

    Holsopple, Jared; Yang, Shanchieh; Argauer, Brian

    2008-03-01

    Much research has been put forth towards detection, correlating, and prediction of cyber attacks in recent years. As this set of research progresses, there is an increasing need for contextual information of a computer network to provide an accurate situational assessment. Typical approaches adopt contextual information as needed; yet such ad hoc effort may lead to unnecessary or even conflicting features. The concept of virtual terrain is, therefore, developed and investigated in this work. Virtual terrain is a common representation of crucial information about network vulnerabilities, accessibilities, and criticalities. A virtual terrain model encompasses operating systems, firewall rules, running services, missions, user accounts, and network connectivity. It is defined as connected graphs with arc attributes defining dynamic relationships among vertices modeling network entities, such as services, users, and machines. The virtual terrain representation is designed to allow feasible development and maintenance of the model, as well as efficacy in terms of the use of the model. This paper will describe the considerations in developing the virtual terrain schema, exemplary virtual terrain models, and algorithms utilizing the virtual terrain model for situation and threat assessment.

  13. The Virtual Brain: a simulator of primate brain network dynamics.

    PubMed

    Sanz Leon, Paula; Knock, Stuart A; Woodman, M Marmaduke; Domide, Lia; Mersmann, Jochen; McIntosh, Anthony R; Jirsa, Viktor

    2013-01-01

    We present The Virtual Brain (TVB), a neuroinformatics platform for full brain network simulations using biologically realistic connectivity. This simulation environment enables the model-based inference of neurophysiological mechanisms across different brain scales that underlie the generation of macroscopic neuroimaging signals including functional MRI (fMRI), EEG and MEG. Researchers from different backgrounds can benefit from an integrative software platform including a supporting framework for data management (generation, organization, storage, integration and sharing) and a simulation core written in Python. TVB allows the reproduction and evaluation of personalized configurations of the brain by using individual subject data. This personalization facilitates an exploration of the consequences of pathological changes in the system, permitting to investigate potential ways to counteract such unfavorable processes. The architecture of TVB supports interaction with MATLAB packages, for example, the well known Brain Connectivity Toolbox. TVB can be used in a client-server configuration, such that it can be remotely accessed through the Internet thanks to its web-based HTML5, JS, and WebGL graphical user interface. TVB is also accessible as a standalone cross-platform Python library and application, and users can interact with the scientific core through the scripting interface IDLE, enabling easy modeling, development and debugging of the scientific kernel. This second interface makes TVB extensible by combining it with other libraries and modules developed by the Python scientific community. In this article, we describe the theoretical background and foundations that led to the development of TVB, the architecture and features of its major software components as well as potential neuroscience applications. PMID:23781198

  14. The Virtual Brain: a simulator of primate brain network dynamics

    PubMed Central

    Sanz Leon, Paula; Knock, Stuart A.; Woodman, M. Marmaduke; Domide, Lia; Mersmann, Jochen; McIntosh, Anthony R.; Jirsa, Viktor

    2013-01-01

    We present The Virtual Brain (TVB), a neuroinformatics platform for full brain network simulations using biologically realistic connectivity. This simulation environment enables the model-based inference of neurophysiological mechanisms across different brain scales that underlie the generation of macroscopic neuroimaging signals including functional MRI (fMRI), EEG and MEG. Researchers from different backgrounds can benefit from an integrative software platform including a supporting framework for data management (generation, organization, storage, integration and sharing) and a simulation core written in Python. TVB allows the reproduction and evaluation of personalized configurations of the brain by using individual subject data. This personalization facilitates an exploration of the consequences of pathological changes in the system, permitting to investigate potential ways to counteract such unfavorable processes. The architecture of TVB supports interaction with MATLAB packages, for example, the well known Brain Connectivity Toolbox. TVB can be used in a client-server configuration, such that it can be remotely accessed through the Internet thanks to its web-based HTML5, JS, and WebGL graphical user interface. TVB is also accessible as a standalone cross-platform Python library and application, and users can interact with the scientific core through the scripting interface IDLE, enabling easy modeling, development and debugging of the scientific kernel. This second interface makes TVB extensible by combining it with other libraries and modules developed by the Python scientific community. In this article, we describe the theoretical background and foundations that led to the development of TVB, the architecture and features of its major software components as well as potential neuroscience applications. PMID:23781198

  15. Making Wireless Networks Secure for NASA Mission Critical Applications using Virtual Private Network (VPN) Technology

    NASA Technical Reports Server (NTRS)

    Nichols, Kelvin F.; Best, Susan; Schneider, Larry

    2004-01-01

    With so many security issues involved with wireless networks, the technology has not been fully utilized in the area of mission critical applications. These applications would include the areas of telemetry, commanding, voice and video. Wireless networking would allow payload operators the mobility to take computers outside of the control room to their offices and anywhere else in the facility that the wireless network was extended. But the risk is too great of having someone sit just inside of your wireless network coverage and intercept enough of your network traffic to steal proprietary data from a payload experiment or worse yet hack back into your system and do even greater harm by issuing harmful commands. Wired Equivalent Privacy (WEP) is improving but has a ways to go before it can be trusted to protect mission critical data. Today s hackers are becoming more aggressive and innovative, and in order to take advantage of the benefits that wireless networking offer, appropriate security measures need to be in place that will thwart hackers. The Virtual Private Network (VPN) offers a solution to the security problems that have kept wireless networks from being used for mission critical applications. VPN provides a level of encryption that will ensure that data is protected while it is being transmitted over a wireless local area network (IAN). The VPN allows a user to authenticate to the site that the user needs to access. Once this authentication has taken place the network traffic between that site and the user is encapsulated in VPN packets with the Triple Data Encryption Standard (3DES). 3DES is an encryption standard that uses a single secret key to encrypt and decrypt data. The length of the encryption key is 168 bits as opposed to its predecessor DES that has a 56-bit encryption key. Even though 3DES is the common encryption standard for today, the Advance Encryption Standard (AES), which provides even better encryption at a lower cycle cost is growing

  16. Making Wireless Networks Secure for NASA Mission Critical Applications Using Virtual Private Network (VPN) Technology

    NASA Technical Reports Server (NTRS)

    Nichols, Kelvin F.; Best, Susan; Schneider, Larry

    2004-01-01

    With so many security issues involved with wireless networks, the technology has not been fully utilized in the area of mission critical applications. These applications would include the areas of telemetry, commanding, voice and video. Wireless networking would allow payload operators the mobility to take computers outside of the control room to their off ices and anywhere else in the facility that the wireless network was extended. But the risk is too great of having someone sit just inside of your wireless network coverage and intercept enough of your network traffic to steal proprietary data from a payload experiment or worse yet hack back into your system and do even greater harm by issuing harmful commands. Wired Equivalent Privacy (WEP) is improving but has a ways to go before it can be trusted to protect mission critical data. Today s hackers are becoming more aggressive and innovative, and in order to take advantage of the benefits that wireless networking offer, appropriate security measures need to be in place that will thwart hackers. The Virtual Private Network (VPN) offers a solution to the security problems that have kept wireless networks from being used for mission critical applications. VPN provides a level of encryption that will ensure that data is protected while it is being transmitted over a wireless local area network (LAN). The VPN allows a user to authenticate to the site that the user needs to access. Once this authentication has taken place the network traffic between that site and the user is encapsulated in VPN packets with the Triple Data Encryption Standard (3DES). 3DES is an encryption standard that uses a single secret key to encrypt and decrypt data. The length of the encryption key is 168 bits as opposed to its predecessor DES that has a 56-bit encryption key. Even though 3DES is the common encryption standard for today, the Advance Encryption Standard (AES), which provides even better encryption at a lower cycle cost is growing

  17. Links between real and virtual networks: a comparative study of online communities in Japan and Korea.

    PubMed

    Ishii, Kenichi; Ogasahara, Morihiro

    2007-04-01

    The present study explores how online communities affect real-world personal relations based on a cross-cultural survey conducted in Japan and Korea. Findings indicate that the gratifications of online communities moderate the effects of online communities on social participation. Online communities are categorized into a real-group-based community and a virtual-network-based community. The membership of real-group-based online community is positively correlated with social bonding gratification and negatively correlated with information- seeking gratification. Japanese users prefer more virtual-network-based online communities, while their Korean counterparts prefer real-group-based online communities. Korean users are more active in online communities and seek a higher level of socializing gratifications, such as social bonding and making new friends, when compared with their Japanese counterparts. These results indicate that in Korea, personal relations via the online community are closely associated with the real-world personal relations, but this is not the case in Japan. This study suggests that the effects of the Internet are culture-specific and that the online community can serve a different function in different cultural environments. PMID:17474843

  18. Virtual reality interface devices in the reorganization of neural networks in the brain of patients with neurological diseases.

    PubMed

    Gatica-Rojas, Valeska; Méndez-Rebolledo, Guillermo

    2014-04-15

    Two key characteristics of all virtual reality applications are interaction and immersion. Systemic interaction is achieved through a variety of multisensory channels (hearing, sight, touch, and smell), permitting the user to interact with the virtual world in real time. Immersion is the degree to which a person can feel wrapped in the virtual world through a defined interface. Virtual reality interface devices such as the Nintendo® Wii and its peripheral nunchuks-balance board, head mounted displays and joystick allow interaction and immersion in unreal environments created from computer software. Virtual environments are highly interactive, generating great activation of visual, vestibular and proprioceptive systems during the execution of a video game. In addition, they are entertaining and safe for the user. Recently, incorporating therapeutic purposes in virtual reality interface devices has allowed them to be used for the rehabilitation of neurological patients, e.g., balance training in older adults and dynamic stability in healthy participants. The improvements observed in neurological diseases (chronic stroke and cerebral palsy) have been shown by changes in the reorganization of neural networks in patients' brain, along with better hand function and other skills, contributing to their quality of life. The data generated by such studies could substantially contribute to physical rehabilitation strategies. PMID:25206907

  19. Virtual reality interface devices in the reorganization of neural networks in the brain of patients with neurological diseases

    PubMed Central

    Gatica-Rojas, Valeska; Méndez-Rebolledo, Guillermo

    2014-01-01

    Two key characteristics of all virtual reality applications are interaction and immersion. Systemic interaction is achieved through a variety of multisensory channels (hearing, sight, touch, and smell), permitting the user to interact with the virtual world in real time. Immersion is the degree to which a person can feel wrapped in the virtual world through a defined interface. Virtual reality interface devices such as the Nintendo® Wii and its peripheral nunchuks-balance board, head mounted displays and joystick allow interaction and immersion in unreal environments created from computer software. Virtual environments are highly interactive, generating great activation of visual, vestibular and proprioceptive systems during the execution of a video game. In addition, they are entertaining and safe for the user. Recently, incorporating therapeutic purposes in virtual reality interface devices has allowed them to be used for the rehabilitation of neurological patients, e.g., balance training in older adults and dynamic stability in healthy participants. The improvements observed in neurological diseases (chronic stroke and cerebral palsy) have been shown by changes in the reorganization of neural networks in patients’ brain, along with better hand function and other skills, contributing to their quality of life. The data generated by such studies could substantially contribute to physical rehabilitation strategies. PMID:25206907

  20. Fiber networks amplify active stress.

    PubMed

    Ronceray, Pierre; Broedersz, Chase P; Lenz, Martin

    2016-03-15

    Large-scale force generation is essential for biological functions such as cell motility, embryonic development, and muscle contraction. In these processes, forces generated at the molecular level by motor proteins are transmitted by disordered fiber networks, resulting in large-scale active stresses. Although these fiber networks are well characterized macroscopically, this stress generation by microscopic active units is not well understood. Here we theoretically study force transmission in these networks. We find that collective fiber buckling in the vicinity of a local active unit results in a rectification of stress towards strongly amplified isotropic contraction. This stress amplification is reinforced by the networks' disordered nature, but saturates for high densities of active units. Our predictions are quantitatively consistent with experiments on reconstituted tissues and actomyosin networks and shed light on the role of the network microstructure in shaping active stresses in cells and tissue. PMID:26921325

  1. Partially segregated neural networks for spatial and contextual memory in virtual navigation.

    PubMed

    Rauchs, Géraldine; Orban, Pierre; Balteau, Evelyne; Schmidt, Christina; Degueldre, Christian; Luxen, André; Maquet, Pierre; Peigneux, Philippe

    2008-01-01

    Finding our way in a previously learned, ecologically valid environment concurrently involves spatial and contextual cognitive operations. The former process accesses a cognitive map representing the spatial interactions between all paths in the environment. The latter accesses stored associations between landmark objects and their milieu. Here, we aimed at dissociating their neural basis in the context of memory-based virtual navigation. To do so, subjects freely explored a virtual town for 1 h, then were scanned using fMRI while retrieving their way between two locations, under four navigation conditions designed to probe separately or jointly the spatial and contextual memory components. Besides prominent commonalities found in a large hippocampo-neocortical network classically involved in topographical navigation, results yield evidence for a partial dissociation between the brain areas supporting spatial and contextual components of memory-based navigation. Performance-related analyses indicate that hippocampal activity mostly supports the spatial component, whereas parahippocampal activity primarily supports the contextual component. Additionally, the recruitment of contextual memory during navigation was associated with higher frontal, posterior parietal and lateral temporal activity. These results provide evidence for a partial segregation of the neural substrates of two crucial memory components in human navigation, whose combined involvement eventually leads to efficient navigation behavior within a learned environment. PMID:18240326

  2. Multi-flow virtual concatenation triggered by path cascading degree in Flexi-Grid optical networks

    NASA Astrophysics Data System (ADS)

    Yang, Hui; Zhang, Jie; Zhao, Yongli; Wang, Shouyu; Gu, Wanyi; Han, Jianrui; Lin, Yi; Lee, Young

    2013-12-01

    The Flexi-Grid optical networks can elastically allocate spectrum tailored for various bandwidth requirements. In the flexible architecture, routing and spectrum allocation (RSA) is the key problem is to assign spectral resources to accommodate traffic demands. However, spectrum continuity and contiguity constraints in Flexi-Grid optical networks may cause the network fragmentation issue and lead to poor spectrum utilization. In this paper, different from defragmentation methods, we propose multi-flow virtual concatenation (MFVC) in Flexi-Grid optical networks. MFVC can utilize spectral fragments effectively and decrease blocking probability without influencing the already existing active services or wasting additional spectrum resources. We also analyze the feasibility of MFVC and present a MFVC-enabled transponder and control model implementation. For estimating the distribution and size of available fragments on a path in advance, a split-multi-flow RSA heuristic algorithm (SMF) is proposed by introducing path cascading degree (PCD) based triggered mechanism according to the proposed model. Additionally, resource assignment scheme, guard band size, maximum number of split-flow and differential delay constraint are also considered into MFVC and the performances of the proposed algorithm can be demonstrated to improve the spectral utilization and greatly decrease blocking probability through extensive simulations.

  3. Use of the Remote Access Virtual Environment Network (RAVEN) for coordinated IVA-EVA astronaut training and evaluation.

    PubMed

    Cater, J P; Huffman, S D

    1995-01-01

    This paper presents a unique virtual reality training and assessment tool developed under a NASA grant, "Research in Human Factors Aspects of Enhanced Virtual Environments for Extravehicular Activity (EVA) Training and Simulation." The Remote Access Virtual Environment Network (RAVEN) was created to train and evaluate the verbal, mental and physical coordination required between the intravehicular (IVA) astronaut operating the Remote Manipulator System (RMS) arm and the EVA astronaut standing in foot restraints on the end of the RMS. The RAVEN system currently allows the EVA astronaut to approach the Hubble Space Telescope (HST) under control of the IVA astronaut and grasp, remove, and replace the Wide Field Planetary Camera drawer from its location in the HST. Two viewpoints, one stereoscopic and one monoscopic, were created all linked by Ethernet, that provided the two trainees with the appropriate training environments. PMID:11539288

  4. Effects of Collaborative Activities on Group Identity in Virtual World

    ERIC Educational Resources Information Center

    Park, Hyungsung; Seo, Sumin

    2013-01-01

    The purpose of this study was to analyze the effects of collaborative activities on group identity in a virtual world such as "Second Life." To achieve this purpose, this study adopted events that promoted participants' interactions using tools inherent in "Second Life." The interactive tools given to the control group in…

  5. Using Highly Interactive Virtual Environments for Safeguards Activities

    SciTech Connect

    Weil, Bradley S; Alcala, Benjamin S; Alcala, Scott; Eipeldauer, Mary D; Weil, Logan B

    2010-01-01

    Highly interactive virtual environment (HIVE) is a term that refers to interactive educational simulations, serious games and virtual worlds. Studies indicate that learning with the aid of interactive environments produces better retention and depth of knowledge by promoting improved trainee engagement and understanding. Virtual reality or three dimensional (3D) visualization is often used to promote the understanding of something when personal observation, photographs, drawings, and/or sketches are not possible or available. Subjects and situations, either real or hypothetical, can be developed using a 3D model. Models can be tailored to the audience allowing safeguards and security features to be demonstrated for educational purposes in addition to engineering evaluation and performance analysis. Oak Ridge National Laboratory (ORNL) has begun evaluating the feasibility of HIVEs for improving safeguards activities such as training, mission planning, and evaluating worker task performance. This paper will discuss the development workflow of HIVEs and present some recent examples.

  6. Modeling past and future structure of the global virtual water trade network

    NASA Astrophysics Data System (ADS)

    Dalin, C.; Suweis, S.; Konar, M.; Hanasaki, N.; Rodriguez-Iturbe, I.

    2012-12-01

    Climate change and socio-economic development place an increasing pressure on essential natural resources, such as arable land and freshwater. The international food trade can save water globally by redistributing commodities produced relatively more water-efficiently. We focus on the global virtual water trade network associated with international staple food trade from 1986-2008. This study aims to determine which variables control the network's structure and temporal evolution, and to estimate changes in the network under future scenarios. Our fitness model reproduces both the topological and weighted characteristics of the network for the whole period. Undirected and directed network properties are well reproduced in each year, assuming as sole controls each nation's GDP, mean annual rainfall, agricultural area and population. The future structure of the network is estimated using climate and socio-economic projections, showing that volumes of virtual water traded will become increasingly heterogeneous and the importance of dominant importing nations will further strengthen.

  7. Analysis of the social network development of a virtual community for Australian intensive care professionals.

    PubMed

    Rolls, Kaye Denise; Hansen, Margaret; Jackson, Debra; Elliott, Doug

    2014-11-01

    Social media platforms can create virtual communities, enabling healthcare professionals to network with a broad range of colleagues and facilitate knowledge exchange. In 2003, an Australian state health department established an intensive care mailing list to address the professional isolation experienced by senior intensive care nurses. This article describes the social network created within this virtual community by examining how the membership profile evolved from 2003 to 2009. A retrospective descriptive design was used. The data source was a deidentified member database. Since 2003, 1340 healthcare professionals subscribed to the virtual community with 78% of these (n = 1042) still members at the end of 2009. The membership profile has evolved from a single-state nurse-specific network to an Australia-wide multidisciplinary and multiorganizational intensive care network. The uptake and retention of membership by intensive care clinicians indicated that they appeared to value involvement in this virtual community. For healthcare organizations, a virtual community may be a communications option for minimizing professional and organizational barriers and promoting knowledge flow. Further research is, however, required to demonstrate a link between these broader social networks, enabling the exchange of knowledge and improved patient outcomes. PMID:25310223

  8. Enhancing Sensorimotor Activity by Controlling Virtual Objects with Gaze

    PubMed Central

    Modroño, Cristián; Plata-Bello, Julio; Zelaya, Fernando; García, Sofía; Galván, Iván; Marcano, Francisco; Navarrete, Gorka; Casanova, Óscar; Mas, Manuel; González-Mora, José Luis

    2015-01-01

    This fMRI work studies brain activity of healthy volunteers who manipulated a virtual object in the context of a digital game by applying two different control methods: using their right hand or using their gaze. The results show extended activations in sensorimotor areas, not only when participants played in the traditional way (using their hand) but also when they used their gaze to control the virtual object. Furthermore, with the exception of the primary motor cortex, regional motor activity was similar regardless of what the effector was: the arm or the eye. These results have a potential application in the field of the neurorehabilitation as a new approach to generate activation of the sensorimotor system to support the recovery of the motor functions. PMID:25799431

  9. Virtual First Impressions Matter: The Effect of Social Networking Sites on Impression Formation in Virtual Teams

    ERIC Educational Resources Information Center

    Cummings, Jeffrey

    2012-01-01

    The introduction of social media has changed the way individuals communicate and collaborate both within and outside the organization. While social media has the potential to change how organizations interact internally, minimal research has examined the impact this media may have within a virtual team environment. This dissertation examines a…

  10. Virtual interactive simulation and inspection tool (VISIT) Modeling sensor networks in a virtual city

    SciTech Connect

    Moore, D. M.

    2004-01-01

    The U.S. government is currently investigating the deployment of radiation sensor systems to protect cities against nuclear and radiological threats. Due to the high cost of installing such systems, there is a need to analyze the effectiveness of a variety of sensor configurations in detecting such threats before installing such systems in the field. The Virtual Interactive Simulation and Inspection Tool (VISIT) is a computer program developed for various virtual-reality applications in national security programs, and is presently being adapted to test the efficacy of a variety of sensor configurations in a virtual urban environment. The value of a particular sensor configuration will be assessed by running virtual exercises in which a threat team will choose a radiological device and route to a target and a detection team will specify the locations and types of sensors to be placed in the city to attempt detection of the threat prior to it reaching its target. This paper will discuss the VISIT package, its proposed application, and lessons learned from modeling done to date.

  11. SelectAudit: A Secure and Efficient Audit Framework for Networked Virtual Environments

    NASA Astrophysics Data System (ADS)

    Phan, Tuan; Yao, Danfeng (Daphne)

    Networked virtual environments (NVE) refer to the category of distributed applications that allow a large number of distributed users to interact with one or more central servers in a virtual environment setting. Recent studies identify that malicious users may compromise the semantic integrity of NVE applications and violate the semantic rules of the virtual environments without being detected. In this paper, we propose an efficient audit protocol to detect violations of semantic integrity through a probabilistic checking mechanism done by a third-party audit server.

  12. Networked virtual reality for real-time 4D navigation of astrophysical turbulence data

    SciTech Connect

    Hudson, R.; Malagoli, A.

    1996-11-01

    This paper describes a prototype distributed virtual reality system for real-time spatial and temporal navigation of volumetric data generated by simulations of hydrodynamic turbulence on high-performance computers. This system makes use of a virtual environment connected to a scalably parallel computer via a scalably high-speed network. The data are either computed in real-time or precomputed on the parallel computer, then are transferred to the virtual environment where fast volume visualization is accomplished by using sophisticated three-dimensional texture-mapping hardware.

  13. Virtual Spaces and Networks in Geographical Education and Research

    ERIC Educational Resources Information Center

    Chalmers, Lex

    2009-01-01

    This paper relates developments in the use of Internet-based communication technologies to contemporary exchanges of geographical ideas and content. A brief history of the Internet provides the basis for a review of uses of broadband Internet in contemporary Geography. Two themes are explored: the first is the concept of virtual communities of…

  14. Fiber networks amplify active stress

    NASA Astrophysics Data System (ADS)

    Lenz, Martin; Ronceray, Pierre; Broedersz, Chase

    Large-scale force generation is essential for biological functions such as cell motility, embryonic development, and muscle contraction. In these processes, forces generated at the molecular level by motor proteins are transmitted by disordered fiber networks, resulting in large-scale active stresses. While fiber networks are well characterized macroscopically, this stress generation by microscopic active units is not well understood. I will present a comprehensive theoretical study of force transmission in these networks. I will show that the linear, small-force response of the networks is remarkably simple, as the macroscopic active stress depends only on the geometry of the force-exerting unit. In contrast, as non-linear buckling occurs around these units, local active forces are rectified towards isotropic contraction and strongly amplified. This stress amplification is reinforced by the networks' disordered nature, but saturates for high densities of active units. I will show that our predictions are quantitatively consistent with experiments on reconstituted tissues and actomyosin networks, and that they shed light on the role of the network microstructure in shaping active stresses in cells and tissue.

  15. Fast Virtual Stenting with Active Contour Models in Intracranical Aneurysm

    PubMed Central

    Zhong, Jingru; Long, Yunling; Yan, Huagang; Meng, Qianqian; Zhao, Jing; Zhang, Ying; Yang, Xinjian; Li, Haiyun

    2016-01-01

    Intracranial stents are becoming increasingly a useful option in the treatment of intracranial aneurysms (IAs). Image simulation of the releasing stent configuration together with computational fluid dynamics (CFD) simulation prior to intervention will help surgeons optimize intervention scheme. This paper proposed a fast virtual stenting of IAs based on active contour model (ACM) which was able to virtually release stents within any patient-specific shaped vessel and aneurysm models built on real medical image data. In this method, an initial stent mesh was generated along the centerline of the parent artery without the need for registration between the stent contour and the vessel. Additionally, the diameter of the initial stent volumetric mesh was set to the maximum inscribed sphere diameter of the parent artery to improve the stenting accuracy and save computational cost. At last, a novel criterion for terminating virtual stent expanding that was based on the collision detection of the axis aligned bounding boxes was applied, making the stent expansion free of edge effect. The experiment results of the virtual stenting and the corresponding CFD simulations exhibited the efficacy and accuracy of the ACM based method, which are valuable to intervention scheme selection and therapy plan confirmation. PMID:26876026

  16. Vulnerability of countries to food-production crises propagating in the virtual water trade network

    NASA Astrophysics Data System (ADS)

    Tamea, S.; Laio, F.; Ridolfi, L.

    2015-12-01

    In recent years, the international trade of food and agricultural commodities has undergone a marked increase of exchanged volumes and an expansion of the trade network. This globalization of trade has both positive and negative effects, but the interconnectedness and external dependency of countries generate complex dynamics which are often difficult to understand and model. In this study we consider the volume of water used for the production of agricultural commodities, virtually exchanged among countries through commodity trade, i.e. the virtual water trade. Then, we set up a parsimonious mechanistic model describing the propagation, into the global trade network, of food-production crises generated locally by a social, economic or environmental event (such as war, economic crisis, drought, pest). The model, accounting for the network structure and the virtual water balance of all countries, bases on rules derived from observed virtual water flows and on data-based and statistically verified assumption. It is also tested on real case studies that prove its capability to capture the main features of crises propagation. The model is then employed as the basis for the development of an index of country vulnerability, measuring the exposure of countries to crises propagating in the virtual water trade network. Results of the analysis are discussed within the context of socio-economic and environmental conditions of countries, showing that not only water-scarce, but also wealthy and globalized countries, are among the most vulnerable to external crises. The temporal analysis for the period 1986-2011 reveals that the global average vulnerability has strongly increased over time, confirming the increased exposure of countries to external crises which may occur in the virtual water trade network.

  17. METAMORPHOSE VI - the Virtual Institute for artificial electromagnetic materials and metamaterials: origin, mission, and activities

    NASA Astrophysics Data System (ADS)

    Bilotti, Filiberto; Rockstuhl, Carsten; Schuchinsky, Alex; Tretyakov, Sergei

    2014-06-01

    In this paper, we outline the background, mission, and activities of the Virtual Institute for Artificial Electromagnetic Materials and Metamaterials (METAMORPHOSE VI). This international association, founded in the framework of the FP-6 Network of Excellence METAMORPHOSE, aims at promoting and developing research, training, and dissemination activities in the emerging and highly dynamic field of advanced electromagnetic materials and metamaterials at both European and International levels. More than 300 researchers are currently associated with the METAMORPHOSE VI which networks them together in a learnt society. After a brief description of the association and its mission, we present an overview of the activities developed by the METAMORPHOSE VI, with a particular emphasis on the coordination of the European Doctoral Program on Metamaterials (EUPROMETA) and the organization of the International Congress on Advanced Electromagnetic Materials in Microwaves and Optics - metamaterials congress.

  18. Virtual Cortical Resection Reveals Push-Pull Network Control Preceding Seizure Evolution.

    PubMed

    Khambhati, Ankit N; Davis, Kathryn A; Lucas, Timothy H; Litt, Brian; Bassett, Danielle S

    2016-09-01

    In ∼20 million people with drug-resistant epilepsy, focal seizures originating in dysfunctional brain networks will often evolve and spread to surrounding tissue, disrupting function in otherwise normal brain regions. To identify network control mechanisms that regulate seizure spread, we developed a novel tool for pinpointing brain regions that facilitate synchronization in the epileptic network. Our method measures the impact of virtually resecting putative control regions on synchronization in a validated model of the human epileptic network. By applying our technique to time-varying functional networks, we identified brain regions whose topological role is to synchronize or desynchronize the epileptic network. Our results suggest that greater antagonistic push-pull interaction between synchronizing and desynchronizing brain regions better constrains seizure spread. These methods, while applied here to epilepsy, are generalizable to other brain networks and have wide applicability in isolating and mapping functional drivers of brain dynamics in health and disease. PMID:27568515

  19. Virtual Learning Environments as Sociomaterial Agents in the Network of Teaching Practice

    ERIC Educational Resources Information Center

    Johannesen, Monica; Erstad, Ola; Habib, Laurence

    2012-01-01

    This article presents findings related to the sociomaterial agency of educators and their practice in Norwegian education. Using actor-network theory, we ask how Virtual Learning Environments (VLEs) negotiate the agency of educators and how they shape their teaching practice. Since the same kinds of VLE tools have been widely implemented…

  20. Network Analysis of a Virtual Community of Learning of Economics Educators

    ERIC Educational Resources Information Center

    Fontainha, Elsa; Martins, Jorge Tiago; Vasconcelos, Ana Cristina

    2015-01-01

    Introduction: This paper aims at understanding virtual communities of learning in terms of dynamics, types of knowledge shared by participants, and network characteristics such as size, relationships, density, and centrality of participants. It looks at the relationships between these aspects and the evolution of communities of learning. It…

  1. Virtual Oncological Networks--IT Support for an Evidence-based, Oncological Health Care Management.

    PubMed

    Heiden, Katja; Sinha, Monika; Böckmann, Britta

    2015-01-01

    An interdisciplinary and intersectoral coordinated therapy management along Clinical Practice Guidelines can ensure that all patients receive adequate diagnostic, treatment, and supportive services that lead most likely to optimal outcomes. Within the research project "Virtual Oncological Networks", guideline-compliant pathways are defined and enacted within a Health Care Management Platform to support treatment planning and ongoing care of oncological diseases. PMID:26262255

  2. Second Line of Defense Virtual Private Network Guidance for Deployed and New CAS Systems

    SciTech Connect

    Singh, Surya V.; Thronas, Aaron I.

    2010-01-01

    This paper discusses the importance of remote access via virtual private network (VPN) for the Second Line of Defense (SLD) Central Alarm System (CAS) sites, the requirements for maintaining secure channels while using VPN and implementation requirements for current and future sites.

  3. On-demand virtual optical network access using 100 Gb/s Ethernet.

    PubMed

    Ishida, Osamu; Takamichi, Toru; Arai, Sachine; Kawate, Ryusuke; Toyoda, Hidehiro; Morita, Itsuro; Araki, Soichiro; Ichikawa, Toshiyuki; Hoshida, Takeshi; Murai, Hitoshi

    2011-12-12

    Our Terabit LAN initiatives attempt to enhance the scalability and utilization of lambda resources. This paper describes bandwidth-on-demand virtualized 100GE access to WDM networks on a field fiber test-bed using multi-domain optical-path provisioning. PMID:22274022

  4. Investigating Factors Related to Virtual Private Network Adoption in Small Businesses

    ERIC Educational Resources Information Center

    Lederer, Karen

    2012-01-01

    The purpose of this quantitative study was to investigate six factors that may influence adoption of virtual private network (VPN) technologies in small businesses with fewer than 100 employees. Prior research indicated small businesses employing fewer than 100 workers do not adopt VPN technology at the same rate as larger competitors, and the…

  5. Taming Wild Horses: The Need for Virtual Time-based Scheduling of VMs in Network Simulations

    SciTech Connect

    Yoginath, Srikanth B; Perumalla, Kalyan S; Henz, Brian J

    2012-01-01

    The next generation of scalable network simulators employ virtual machines (VMs) to act as high-fidelity models of traffic producer/consumer nodes in simulated networks. However, network simulations could be inaccurate if VMs are not scheduled according to virtual time, especially when many VMs are hosted per simulator core in a multi-core simulator environment. Since VMs are by default free-running, on the outset, it is not clear if, and to what extent, their untamed execution affects the results in simulated scenarios. Here, we provide the first quantitative basis for establishing the need for generalized virtual time scheduling of VMs in network simulators, based on an actual prototyped implementations. To exercise breadth, our system is tested with multiple disparate applications: (a) a set of message passing parallel programs, (b) a computer worm propagation phenomenon, and (c) a mobile ad-hoc wireless network simulation. We define and use error metrics and benchmarks in scaled tests to empirically report the poor match of traditional, fairness-based VM scheduling to VM-based network simulation, and also clearly show the better performance of our simulation-specific scheduler, with up to 64 VMs hosted on a 12-core simulator node.

  6. Quality of service policy control in virtual private networks

    NASA Astrophysics Data System (ADS)

    Yu, Yiqing; Wang, Hongbin; Zhou, Zhi; Zhou, Dongru

    2004-04-01

    This paper studies the QoS of VPN in an environment where the public network prices connection-oriented services based on source, destination and grade of service, and advertises these prices to its VPN customers (users). As different QoS technologies can produce different QoS, there are according different traffic classification rules and priority rules. The internet service provider (ISP) may need to build complex mechanisms separately for each node. In order to reduce the burden of network configuration, we need to design policy control technologies. We considers mainly directory server, policy server, policy manager and policy enforcers. Policy decision point (PDP) decide its control according to policy rules. In network, policy enforce point (PEP) decide its network controlled unit. For InterServ and DiffServ, we will adopt different policy control methods as following: (1) In InterServ, traffic uses resource reservation protocol (RSVP) to guarantee the network resource. (2) In DiffServ, policy server controls the DiffServ code points and per hop behavior (PHB), its PDP distributes information to each network node. Policy server will function as following: information searching; decision mechanism; decision delivering; auto-configuration. In order to prove the effectiveness of QoS policy control, we make the corrective simulation.

  7. Euro-VO-Coordination of virtual observatory activities in Europe

    NASA Astrophysics Data System (ADS)

    Genova, Françoise; Allen, Mark G.; Arviset, Christophe; Lawrence, Andy; Pasian, Fabio; Solano, Enrique; Wambsganss, Joachim

    2015-06-01

    The European Virtual Observatory Euro-VO has been coordinating European VO activities through a series of projects co-funded by the European Commission over the last 15 years. The bulk of VO work in Europe is ensured by the national VO initiatives and those of intergovernmental agencies. VO activities at the European level coordinate the work in support of the three "pillars" of the Virtual Observatory: support to the scientific community, take-up by the data providers, and technological activities. Several Euro-VO projects have also provided direct support to selected developments and prototyping. This paper explains the methodology used by Euro-VO over the years. It summarises the activities which were performed and their evolutions at different stages of the development of the VO, explains the Euro-VO role with respect to the international and national levels of VO activities, details the lessons learnt for best practices for the coordination of the VO building blocks, and the liaison with other European initiatives, documenting the added-value of European coordination. Finally, the current status and next steps of Euro-VO are briefly addressed.

  8. Effects of active navigation on object recognition in virtual environments.

    PubMed

    Hahm, Jinsun; Lee, Kanghee; Lim, Seung-Lark; Kim, Sei-Young; Kim, Hyun-Taek; Lee, Jang-Han

    2007-04-01

    We investigated the importance and efficiency of active and passive exploration on the recognition of objects in a variety of virtual environments (VEs). In this study, 54 participants were randomly allocated into one of active and passive navigation conditions. Active navigation was performed by allowing participants to self-pace and control their own navigation, but passive navigation was conducted by forced navigation. After navigating VEs, participants were asked to recognize the objects that had been in the VEs. Active navigation condition had a significantly higher percentage of hit responses (t (52) = 4.000, p < 0.01), and a significantly lower percentage of miss responses (t (52) = -3.763, p < 0.01) in object recognition than the passive condition. These results suggest that active navigation plays an important role in spatial cognition as well as providing an explanation for the efficiency of learning in a 3D-based program. PMID:17474852

  9. Virtualization in network and servers infrastructure to support dynamic system reconfiguration in ALMA

    NASA Astrophysics Data System (ADS)

    Shen, Tzu-Chiang; Ovando, Nicolás.; Bartsch, Marcelo; Simmond, Max; Vélez, Gastón; Robles, Manuel; Soto, Rubén.; Ibsen, Jorge; Saldias, Christian

    2012-09-01

    ALMA is the first astronomical project being constructed and operated under industrial approach due to the huge amount of elements involved. In order to achieve the maximum through put during the engineering and scientific commissioning phase, several production lines have been established to work in parallel. This decision required modification in the original system architecture in which all the elements are controlled and operated within a unique Standard Test Environment (STE). The advance in the network industry and together with the maturity of virtualization paradigm allows us to provide a solution which can replicate the STE infrastructure without changing their network address definition. This is only possible with Virtual Routing and Forwarding (VRF) and Virtual LAN (VLAN) concepts. The solution allows dynamic reconfiguration of antennas and other hardware across the production lines with minimum time and zero human intervention in the cabling. We also push the virtualization even further, classical rack mount servers are being replaced and consolidated by blade servers. On top of them virtualized server are centrally administrated with VMWare ESX. Hardware costs and system administration effort will be reduced considerably. This mechanism has been established and operated successfully during the last two years. This experience gave us confident to propose a solution to divide the main operation array into subarrays using the same concept which will introduce huge flexibility and efficiency for ALMA operation and eventually may simplify the complexity of ALMA core observing software since there will be no need to deal with subarrays complexity at software level.

  10. Building a sense of virtual community: the role of the features of social networking sites.

    PubMed

    Chen, Chi-Wen; Lin, Chiun-Sin

    2014-07-01

    In recent years, social networking sites have received increased attention because of the potential of this medium to transform business by building virtual communities. However, theoretical and empirical studies investigating how specific features of social networking sites contribute to building a sense of virtual community (SOVC)-an important dimension of a successful virtual community-are rare. Furthermore, SOVC scales have been developed, and research on this issue has been called for, but few studies have heeded this call. On the basis of prior literature, this study proposes that perceptions of the three most salient features of social networking sites-system quality (SQ), information quality (IQ), and social information exchange (SIE)-play a key role in fostering SOVC. In particular, SQ is proposed to increase IQ and SIE, and SIE is proposed to enhance IQ, both of which thereafter build SOVC. The research model was examined in the context of Facebook, one of the most popular social networking sites in the world. We adopted Blanchard's scales to measure SOVC. Data gathered using a Web-based questionnaire, and analyzed with partial least squares, were utilized to test the model. The results demonstrate that SIE, SQ, and IQ are the factors that form SOVC. The findings also suggest that SQ plays a fundamental role in supporting SIE and IQ in social networking sites. Implications for theory, practice, and future research directions are discussed. PMID:24690087

  11. Virtual Wireless Sensor Networks: Adaptive Brain-Inspired Configuration for Internet of Things Applications.

    PubMed

    Toyonaga, Shinya; Kominami, Daichi; Murata, Masayuki

    2016-01-01

    Many researchers are devoting attention to the so-called "Internet of Things" (IoT), and wireless sensor networks (WSNs) are regarded as a critical technology for realizing the communication infrastructure of the future, including the IoT. Against this background, virtualization is a crucial technique for the integration of multiple WSNs. Designing virtualized WSNs for actual environments will require further detailed studies. Within the IoT environment, physical networks can undergo dynamic change, and so, many problems exist that could prevent applications from running without interruption when using the existing approaches. In this paper, we show an overall architecture that is suitable for constructing and running virtual wireless sensor network (VWSN) services within a VWSN topology. Our approach provides users with a reliable VWSN network by assigning redundant resources according to each user's demand and providing a recovery method to incorporate environmental changes. We tested this approach by simulation experiment, with the results showing that the VWSN network is reliable in many cases, although physical deployment of sensor nodes and the modular structure of the VWSN will be quite important to the stability of services within the VWSN topology. PMID:27548177

  12. Traffic routing for multicomputer networks with virtual cut-through capability

    NASA Technical Reports Server (NTRS)

    Kandlur, Dilip D.; Shin, Kang G.

    1992-01-01

    Consideration is given to the problem of selecting routes for interprocess communication in a network with virtual cut-through capability, while balancing the network load and minimizing the number of times that a message gets buffered. An approach is proposed that formulates the route selection problem as a minimization problem with a link cost function that depends upon the traffic through the link. The form of this cost function is derived using the probability of establishing a virtual cut-through route. The route selection problem is shown to be NP-hard, and an algorithm is developed to incrementally reduce the cost by rerouting the traffic. The performance of this algorithm is exemplified by two network topologies: the hypercube and the C-wrapped hexagonal mesh.

  13. Theorizing Network-Centric Activity in Education

    ERIC Educational Resources Information Center

    HaLevi, Andrew

    2011-01-01

    Networks and network-centric activity are increasingly prevalent in schools and school districts. In addition to ubiquitous social network tools like Facebook and Twitter, educational leaders deal with a wide variety of network organizational forms that include professional development, advocacy, informational networks and network-centric reforms.…

  14. Virtual Collaborative Learning Environments for Music: Networked Drumsteps

    ERIC Educational Resources Information Center

    McCarthy, Conor; Bligh, James; Jennings, Kevin; Tangney, Brendan

    2005-01-01

    This paper focuses on a tool for meaningful, collaborative, interaction in a constructionist music composition environment. In particular, it describes the design and implementation of ''Networked DrumSteps'', an application that allows multiple users in different locations to collaborate in the process of music composition, but without the use of…

  15. Virtual History: A Socially Networked Pedagogy of Enlightenment

    ERIC Educational Resources Information Center

    Ellison, Katherine; Matthews, Carol

    2010-01-01

    Background: Twenty-first-century undergraduates often find eighteenth-century culture difficult to access and, influenced by popular assumptions about the period in current media theory, characterise the century as individualist, underestimating the cultural significance of social networking in literary and political history. Purpose: This study…

  16. Active Contraction of Microtubule Networks

    NASA Astrophysics Data System (ADS)

    Foster, Peter; Fürthauer, Sebastian; Shelley, Michael; Needleman, Daniel

    Many cellular processes are driven by cytoskeletal assemblies. It remains unclear how cytoskeletal filaments and motor proteins organize into cellular scale structures and how molecular properties of cytoskeletal components affect the large scale behaviors of these systems. Here we investigate the self-organization of stabilized microtubules in Xenopus oocyte extracts and find that they can form macroscopic networks that spontaneously contract. We propose that these contractions are driven by the clustering of microtubule minus ends by dynein. Based on this idea, we construct an active fluid theory of network contractions which predicts a dependence of the timescale of contraction on initial network geometry, a development of density inhomogeneities during contraction, a constant final network density, and a strong influence of dynein inhibition on the rate of contraction, all in quantitative agreement with experiments. These results demonstrate that the motor-driven clustering of filament ends is a generic mechanism leading to contraction.

  17. Active contraction of microtubule networks.

    PubMed

    Foster, Peter J; Fürthauer, Sebastian; Shelley, Michael J; Needleman, Daniel J

    2015-01-01

    Many cellular processes are driven by cytoskeletal assemblies. It remains unclear how cytoskeletal filaments and motor proteins organize into cellular scale structures and how molecular properties of cytoskeletal components affect the large-scale behaviors of these systems. Here, we investigate the self-organization of stabilized microtubules in Xenopus oocyte extracts and find that they can form macroscopic networks that spontaneously contract. We propose that these contractions are driven by the clustering of microtubule minus ends by dynein. Based on this idea, we construct an active fluid theory of network contractions, which predicts a dependence of the timescale of contraction on initial network geometry, a development of density inhomogeneities during contraction, a constant final network density, and a strong influence of dynein inhibition on the rate of contraction, all in quantitative agreement with experiments. These results demonstrate that the motor-driven clustering of filament ends is a generic mechanism leading to contraction. PMID:26701905

  18. An Intelligent Active Video Surveillance System Based on the Integration of Virtual Neural Sensors and BDI Agents

    NASA Astrophysics Data System (ADS)

    Gregorio, Massimo De

    In this paper we present an intelligent active video surveillance system currently adopted in two different application domains: railway tunnels and outdoor storage areas. The system takes advantages of the integration of Artificial Neural Networks (ANN) and symbolic Artificial Intelligence (AI). This hybrid system is formed by virtual neural sensors (implemented as WiSARD-like systems) and BDI agents. The coupling of virtual neural sensors with symbolic reasoning for interpreting their outputs, makes this approach both very light from a computational and hardware point of view, and rather robust in performances. The system works on different scenarios and in difficult light conditions.

  19. The Potential of Using Virtual Reality Technology in Physical Activity Settings

    ERIC Educational Resources Information Center

    Pasco, Denis

    2013-01-01

    In recent years, virtual reality technology has been successfully used for learning purposes. The purposes of the article are to examine current research on the role of virtual reality in physical activity settings and discuss potential application of using virtual reality technology to enhance learning in physical education. The article starts…

  20. Summarizing scale-free networks based on virtual and real links

    NASA Astrophysics Data System (ADS)

    Bei, Yijun; Lin, Zhen; Chen, Deren

    2016-02-01

    Techniques to summarize and cluster graphs are indispensable to understand the internal characteristics of large complex networks. However, existing methods that analyze graphs mainly focus on aggregating strong-interaction vertices into the same group without considering the node properties, particularly multi-valued attributes. This study aims to develop a unified framework based on the concept of a virtual graph by integrating attributes and structural similarities. We propose a summarizing graph based on virtual and real links (SGVR) approach to aggregate similar nodes in a scale-free graph into k non-overlapping groups based on user-selected attributes considering both virtual links (attributes) and real links (graph structures). An effective data structure called HB-Graph is adopted to adjust the subgroups and optimize the grouping results. Extensive experiments are carried out on actual and synthetic datasets. Results indicate that our proposed method is both effective and efficient.

  1. A new algorithm with coordinated node and link mapping for virtual network embedding based on LP relaxation

    NASA Astrophysics Data System (ADS)

    Gao, Xiujiao; Yu, Hongfang; Anand, Vishal; Sun, Gang; Di, Hao

    2010-12-01

    Network virtualization can help diversify the Internet by supporting multiple virtual network (VN) architectures on a shared substrate. Making efficient use of the underlying substrate network resources requires effective algorithms for virtual network embedding (VNE) that maps each virtual network (VN) to specific nodes and links in the substrate network. In this paper, we formulate the VNE problem as a mixed integer linear program (MILP), and then propose a progressively greedy VNE algorithm (PG-VNE) which has three main improvements over previous approaches. 1) Adding constraints after we relax the MILP to obtain STRICT_LP model which leads to better coordination between the node and link mapping stages, 2) Using the greedy idea to map virtual nodes and 3) Mapping virtual nodes progressively, i.e., mapping virtual nodes one by one. Simulation results show that PG-VNE algorithm realizes close coordination between node and link mapping stages and performs well in terms of revenue, cost and VN request acceptance ratio when compared with the well known D-ViNE and R-ViNE algorithms.

  2. Application of the dynamically allocated virtual clustering management system to emulated tactical network experimentation

    NASA Astrophysics Data System (ADS)

    Marcus, Kelvin

    2014-06-01

    The U.S Army Research Laboratory (ARL) has built a "Network Science Research Lab" to support research that aims to improve their ability to analyze, predict, design, and govern complex systems that interweave the social/cognitive, information, and communication network genres. Researchers at ARL and the Network Science Collaborative Technology Alliance (NS-CTA), a collaborative research alliance funded by ARL, conducted experimentation to determine if automated network monitoring tools and task-aware agents deployed within an emulated tactical wireless network could potentially increase the retrieval of relevant data from heterogeneous distributed information nodes. ARL and NS-CTA required the capability to perform this experimentation over clusters of heterogeneous nodes with emulated wireless tactical networks where each node could contain different operating systems, application sets, and physical hardware attributes. Researchers utilized the Dynamically Allocated Virtual Clustering Management System (DAVC) to address each of the infrastructure support requirements necessary in conducting their experimentation. The DAVC is an experimentation infrastructure that provides the means to dynamically create, deploy, and manage virtual clusters of heterogeneous nodes within a cloud computing environment based upon resource utilization such as CPU load, available RAM and hard disk space. The DAVC uses 802.1Q Virtual LANs (VLANs) to prevent experimentation crosstalk and to allow for complex private networks. Clusters created by the DAVC system can be utilized for software development, experimentation, and integration with existing hardware and software. The goal of this paper is to explore how ARL and the NS-CTA leveraged the DAVC to create, deploy and manage multiple experimentation clusters to support their experimentation goals.

  3. The European Virtual Broadband Seismic Network (VEBSN) and ORFEUS

    NASA Astrophysics Data System (ADS)

    van Eck, Torild; Sleeman, Reinoud; van den, Gert-Jan Hazel; Networks, Contributing

    2010-05-01

    Since 2002 ORFEUS has been coordinating the VEBSN concept, in which (near) real-time data is exchanged between Seismological observatory networks and the Orfeus Data Center (ODC). Seismological observatories in and around Europe have usually as primary objective the monitoring and analysis of current local and regional seismicity and seismic hazard. The data gathered by the observatories is, however, also valuable for fundamental research within global and European scale seismology; and therefore a primary data source for Academic seismological research. Within the VEBSN concept, the ODC provides and improves Quality control procedures for the observatories and the observatories provide real-time data for long-term secure waveform data archives at the ODC accessible for seismological research. In this concept the data remains ownership of the contributing network, while the ODC provides a secure back-up archive of waveform data. By facilitating a few data exchange mechanism with emphasis on SeedLink, the VEBSN strategy also enables observatories to exchange data between each other, thus enhancing the capabilities of the local or regional network and improving its performance for their monitoring and hazard objectives More recently, the ODC has been enlarged into the European Distributed waveform Data Archive (EIDA) in which currently GFZ/GEOFON, INGV and RESIF participate in an effort to extend the accessible waveform archive beyond only the VEBSN data. Currently the VEBSN consists of more then 450 3-component stations, each channel well defined with a full up-to-date SEED volume, providing all relevant metadata for a full reconstruction of the true ground motion. This encompases only about 45% of the operational BB stations in the European-Mediterranean area and our goal is to enlarge this.

  4. Virtual Round Table on ten leading questions for network research

    NASA Astrophysics Data System (ADS)

    2004-03-01

    The following discussion is an edited summary of the public debate started during the conference “Growing Networks and Graphs in Statistical Physics, Finance, Biology and Social Systems” held in Rome in September 2003. Drafts documents were circulated electronically among experts in the field and additions and follow-up to the original discussion have been included. Among the scientists participating to the discussion L.A.N. Amaral, A. Barrat, A.L. Barabasi, G. Caldarelli, P. De Los Rios, A. Erzan, B. Kahng, R. Mantegna, J.F.F. Mendes, R. Pastor-Satorras, A. Vespignani are acknowledged for their contributions and editing.

  5. Virtual optical network provisioning with unified service logic processing model for software-defined multidomain optical networks

    NASA Astrophysics Data System (ADS)

    Zhao, Yongli; Li, Shikun; Song, Yinan; Sun, Ji; Zhang, Jie

    2015-12-01

    Hierarchical control architecture is designed for software-defined multidomain optical networks (SD-MDONs), and a unified service logic processing model (USLPM) is first proposed for various applications. USLPM-based virtual optical network (VON) provisioning process is designed, and two VON mapping algorithms are proposed: random node selection and per controller computation (RNS&PCC) and balanced node selection and hierarchical controller computation (BNS&HCC). Then an SD-MDON testbed is built with OpenFlow extension in order to support optical transport equipment. Finally, VON provisioning service is experimentally demonstrated on the testbed along with performance verification.

  6. Modeling past and future structure of the global virtual water trade network

    NASA Astrophysics Data System (ADS)

    Dalin, C.; Suweis, S.; Konar, M.; Hanasaki, N.; Rodriguez-Iturbe, I.

    2012-12-01

    Climate change and socio-economic development place an increasing pressure on essential natural resources, such as arable land and freshwater. The international food trade can save water globally by redistributing commodities produced relatively more water-efficiently. We focus on the global virtual water trade network associated with international food trade from 1986-2008. This study aims to determine which variables control the network's structure and temporal evolution, and to estimate changes in the network under future scenarios. Our fitness model reproduces both the topological and weighted characteristics of the network for the whole period. Undirected and directed network properties are well reproduced in each year, assuming as sole controls simple national-level variables. The future structure of the network is estimated using climate and socio-economic projections, showing that volumes of virtual water traded will become increasingly heterogeneous and the importance of dominant importing nations will further strengthen. Exceedance probability distribution of the undirected node degree (k, panel a) and strength (s, panel b): comparison of data and model results in 1986, 1992, 2000 and 2008, respectively. The similarity between data and model is confirmed in each year by a Kolgmogorov - Smirnov statistical test, the results of this test are shown in the "KS test'' box.

  7. Virtual reality exposure therapy for active duty soldiers.

    PubMed

    Reger, Greg M; Gahm, Gregory A

    2008-08-01

    Virtual reality exposure (VRE) therapy is a promising treatment for a variety of anxiety disorders and has recently been extended to the treatment of posttraumatic stress disorder (PTSD). In this article, the authors briefly review the rationale for VRE and its key processes. They illustrate the treatment with an active-duty Army soldier diagnosed with combat-related PTSD. Six sessions of VRE were provided using an immersive simulation of a military convoy in Iraq. Self-reported PTSD symptoms and psychological distress were reduced at posttreatment relative to pretreatment reports, as assessed by the PTSD Checklist-Military Version and the Behavior and Symptom Identification Scale-24. The case outcomes parallel those reported in the research with other disorders and suggest the applicability of VRE in treating active duty soldiers with combat-related PTSD. PMID:18612993

  8. Growing a Professional Network to Over 3000 Members in Less Than 4 Years: Evaluation of InspireNet, British Columbia’s Virtual Nursing Health Services Research Network

    PubMed Central

    Atherton, Pat; Borycki, Elizabeth; Mickelson, Grace; Cordeiro, Jennifer; Novak Lauscher, Helen; Black, Agnes

    2014-01-01

    Background Use of Web 2.0 and social media technologies has become a new area of research among health professionals. Much of this work has focused on the use of technologies for health self-management and the ways technologies support communication between care providers and consumers. This paper addresses a new use of technology in providing a platform for health professionals to support professional development, increase knowledge utilization, and promote formal/informal professional communication. Specifically, we report on factors necessary to attract and sustain health professionals’ use of a network designed to increase nurses’ interest in and use of health services research and to support knowledge utilization activities in British Columbia, Canada. Objective “InspireNet”, a virtual professional network for health professionals, is a living laboratory permitting documentation of when and how professionals take up Web 2.0 and social media. Ongoing evaluation documents our experiences in establishing, operating, and evaluating this network. Methods Overall evaluation methods included (1) tracking website use, (2) conducting two member surveys, and (3) soliciting member feedback through focus groups and interviews with those who participated in electronic communities of practice (eCoPs) and other stakeholders. These data have been used to learn about the types of support that seem relevant to network growth. Results Network growth exceeded all expectations. Members engaged with varying aspects of the network’s virtual technologies, such as teams of professionals sharing a common interest, research teams conducting their work, and instructional webinars open to network members. Members used wikis, blogs, and discussion groups to support professional work, as well as a members’ database with contact information and areas of interest. The database is accessed approximately 10 times per day. InspireNet public blog posts are accessed roughly 500 times

  9. The virtual microphone technique in active sound field control systems

    NASA Astrophysics Data System (ADS)

    Lampropoulos, Iraklis E.; Shimizu, Yasushi

    2003-04-01

    Active Sound Field Control (AFC) has been proven very useful in reverberation enhancement applications in large rooms. However, feedback control is required in order to eliminate peaks in the frequency response of the system. The present research closely follows the studies of Shimizu in AFC, in which smoothing of the rooms transfer function is achieved by averaging the impulse responses of multiple microphones. ``The virtual or rotating microphone technique'' reduces the number of microphones in the aforementioned AFC technology, while still achieving the same acoustical effects in the room. After the impulse responses at previously specified pairs of microphone positions are measured, the ratio of transfer functions for every pair is calculated, thus yielding a constant K. Next, microphones are removed and their impulse responses are reproduced by processing the incoming signal of each pair through a convolver, where the computed K constants have been previously stored. Band limiting, windowing and time variance effects are critical factors, in order to reduce incoherence effects and yield reliable approximations of inverse filters and consequently calculations of K. The project is implemented in a church lacking low frequency reverberation for music and makes use of 2 physical and 2 virtual microphones.

  10. Convolutional virtual electric field for image segmentation using active contours.

    PubMed

    Wang, Yuanquan; Zhu, Ce; Zhang, Jiawan; Jian, Yuden

    2014-01-01

    Gradient vector flow (GVF) is an effective external force for active contours; however, it suffers from heavy computation load. The virtual electric field (VEF) model, which can be implemented in real time using fast Fourier transform (FFT), has been proposed later as a remedy for the GVF model. In this work, we present an extension of the VEF model, which is referred to as CONvolutional Virtual Electric Field, CONVEF for short. This proposed CONVEF model takes the VEF model as a convolution operation and employs a modified distance in the convolution kernel. The CONVEF model is also closely related to the vector field convolution (VFC) model. Compared with the GVF, VEF and VFC models, the CONVEF model possesses not only some desirable properties of these models, such as enlarged capture range, u-shape concavity convergence, subject contour convergence and initialization insensitivity, but also some other interesting properties such as G-shape concavity convergence, neighboring objects separation, and noise suppression and simultaneously weak edge preserving. Meanwhile, the CONVEF model can also be implemented in real-time by using FFT. Experimental results illustrate these advantages of the CONVEF model on both synthetic and natural images. PMID:25360586

  11. Principle and verification of novel optical virtual private networks over multiprotocol label switching/optical packet switching networks

    NASA Astrophysics Data System (ADS)

    Zhang, Chongfu; Wang, Zhengsuan; Jin, Wei; Qiu, Kun

    2012-11-01

    A novel realization method of the optical virtual private networks (OVPN) over multiprotocol label switching/optical packet switching (MPLS/OPS) networks is proposed. In this scheme, the introduction of MPLS control plane makes OVPN over OPS networks more reliable and easier; OVPN makes use of the concept of high reconfiguration of light-paths offered by MPLS, to set up secure tunnels of high bandwidth across intelligent OPS networks. Through resource management, the signal mechanism, connection control, and the architecture of the creation and maintenance of OVPN are efficiently realized. We also present an OVPN architecture with two traffic priorities, which is used to analyze the capacity, throughput, delay time of the proposed networks, and the packet loss rate performance of the OVPN over MPLS/OPS networks based on full mesh topology. The results validate the applicability of such reliable connectivity to high quality services in the OVPN over MPLS/OPS networks. Along with the results, the feasibility of the approach as the basis for the next generation networks is demonstrated and discussed.

  12. Virtual prototyping of a semi-active transfemoral prosthetic leg.

    PubMed

    Lui, Zhen Wei; Awad, Mohammed I; Abouhossein, Alireza; Dehghani-Sanij, Abbas A; Messenger, Neil

    2015-05-01

    This article presents a virtual prototyping study of a semi-active lower limb prosthesis to improve the functionality of an amputee during prosthesis-environment interaction for level ground walking. Articulated ankle-foot prosthesis and a single-axis semi-active prosthetic knee with active and passive operating modes were considered. Data for level ground walking were collected using a photogrammetric method in order to develop a base-line simulation model and with the hip kinematics input to verify the proposed design. The simulated results show that the semi-active lower limb prosthesis is able to move efficiently in passive mode, and the activation time of the knee actuator can be reduced by approximately 50%. Therefore, this semi-active system has the potential to reduce the energy consumption of the actuators required during level ground walking and requires less compensation from the amputee due to lower deviation of the vertical excursion of body centre of mass. PMID:25991714

  13. Active Gaming: Is "Virtual" Reality Right for Your Physical Education Program?

    ERIC Educational Resources Information Center

    Hansen, Lisa; Sanders, Stephen W.

    2012-01-01

    Active gaming is growing in popularity and the idea of increasing children's physical activity by using technology is largely accepted by physical educators. Teachers nationwide have been providing active gaming equipment such as virtual bikes, rhythmic dance machines, virtual sporting games, martial arts simulators, balance boards, and other…

  14. Enterprise virtual private network (VPN) with dense wavelength division multiplexing (DWDM) design

    NASA Astrophysics Data System (ADS)

    Carranza, Aparicio

    An innovative computer simulation and modeling tool for metropolitan area optical data communication networks is presented. These models address the unique requirements of Virtual Private Networks for enterprise data centers, which may comprise a mixture of protocols including ESCON, FICON, Fibre Channel, Sysplex protocols (ETR, CLO, ISC); and other links interconnected over dark fiber using Dense Wavelength Division Multiplexing (DWDM). Our models have the capability of designing a network with minimal inputs; to compute optical link budgets; suggest alternative configurations; and also optimize the design based on user-defined performance metrics. The models make use of Time Division Multiplexing (TDM) wherever possible for lower data rate traffics. Simulation results for several configurations are presented and they have been validated by means of experiments conducted on the IBM enterprise network testbed in Poughkeepsie, N.Y.

  15. Interpreting collective neural activity underlying spatial navigation in virtual reality

    NASA Astrophysics Data System (ADS)

    Meshulam, Leenoy; Gauthier, Jeff; Tank, David; Bialek, William

    2015-03-01

    Traditionally, cognitive- demanding processes like spatial navigation were studied by recording the activity of single neurons. However, recent technological progress allows imaging the simultaneous activity of large neuronal populations in awake behaving animals. This progress in experimental work calls for a similar adjustments of the modeling frameworks. To achieve a description of the ``real thermodynamics'' of the neural system, we construct maximum entropy models for optical imaging data taken in vivo, from the hippocampus of mice navigating in a virtual reality environment. This provides a natural extension of statistical mechanics applicable to brain activity, by focusing on the interactions between cells rather than on single cell's activity. We aim to determine how the topology of the energy landscape predicted by the model corresponds to the location of the animal in the environment. Since large subpopulations of the neurons in this area are spatially modulated, we expect the landscape to exhibit a large ``valley'' structure of local minima, corresponding to the animal's position along the environment. Such a finding is especially of interest because the location information emerges solely from the activity patterns that are accessible to the brain.

  16. Case-Based Learning in Virtual Groups--Collaborative Problem Solving Activities and Learning Outcomes in a Virtual Professional Training Course

    ERIC Educational Resources Information Center

    Kopp, Birgitta; Hasenbein, Melanie; Mandl, Heinz

    2014-01-01

    This article analyzes the collaborative problem solving activities and learning outcomes of five groups that worked on two different complex cases in a virtual professional training course. In this asynchronous virtual learning environment, all knowledge management content was delivered virtually and collaboration took place through forums. To…

  17. Active contraction of microtubule networks

    PubMed Central

    Foster, Peter J; Fürthauer, Sebastian; Shelley, Michael J; Needleman, Daniel J

    2015-01-01

    Many cellular processes are driven by cytoskeletal assemblies. It remains unclear how cytoskeletal filaments and motor proteins organize into cellular scale structures and how molecular properties of cytoskeletal components affect the large-scale behaviors of these systems. Here, we investigate the self-organization of stabilized microtubules in Xenopus oocyte extracts and find that they can form macroscopic networks that spontaneously contract. We propose that these contractions are driven by the clustering of microtubule minus ends by dynein. Based on this idea, we construct an active fluid theory of network contractions, which predicts a dependence of the timescale of contraction on initial network geometry, a development of density inhomogeneities during contraction, a constant final network density, and a strong influence of dynein inhibition on the rate of contraction, all in quantitative agreement with experiments. These results demonstrate that the motor-driven clustering of filament ends is a generic mechanism leading to contraction. DOI: http://dx.doi.org/10.7554/eLife.10837.001 PMID:26701905

  18. How Sleep Activates Epileptic Networks?

    PubMed Central

    Halász, Peter

    2013-01-01

    Background. The relationship between sleep and epilepsy has been long ago studied, and several excellent reviews are available. However, recent development in sleep research, the network concept in epilepsy, and the recognition of high frequency oscillations in epilepsy and more new results may put this matter in a new light. Aim. The review address the multifold interrelationships between sleep and epilepsy networks and with networks of cognitive functions. Material and Methods. The work is a conceptual update of the available clinical data and relevant studies. Results and Conclusions. Studies exploring dynamic microstructure of sleep have found important gating mechanisms for epileptic activation. As a general rule interictal epileptic manifestations seem to be linked to the slow oscillations of sleep and especially to the reactive delta bouts characterized by A1 subtype in the CAP system. Important link between epilepsy and sleep is the interference of epileptiform discharges with the plastic functions in NREM sleep. This is the main reason of cognitive impairment in different forms of early epileptic encephalopathies affecting the brain in a special developmental window. The impairment of cognitive functions via sleep is present especially in epileptic networks involving the thalamocortical system and the hippocampocortical memory encoding system. PMID:24159386

  19. Performance analysis of cooperative virtual MIMO systems for wireless sensor networks.

    PubMed

    Rafique, Zimran; Seet, Boon-Chong; Al-Anbuky, Adnan

    2013-01-01

    Multi-Input Multi-Output (MIMO) techniques can be used to increase the data rate for a given bit error rate (BER) and transmission power. Due to the small form factor, energy and processing constraints of wireless sensor nodes, a cooperative Virtual MIMO as opposed to True MIMO system architecture is considered more feasible for wireless sensor network (WSN) applications. Virtual MIMO with Vertical-Bell Labs Layered Space-Time (V-BLAST) multiplexing architecture has been recently established to enhance WSN performance. In this paper, we further investigate the impact of different modulation techniques, and analyze for the first time, the performance of a cooperative Virtual MIMO system based on V-BLAST architecture with multi-carrier modulation techniques. Through analytical models and simulations using real hardware and environment settings, both communication and processing energy consumptions, BER, spectral efficiency, and total time delay of multiple cooperative nodes each with single antenna are evaluated. The results show that cooperative Virtual-MIMO with Binary Phase Shift Keying-Wavelet based Orthogonal Frequency Division Multiplexing (BPSK-WOFDM) modulation is a promising solution for future high data-rate and energy-efficient WSNs. PMID:23760087

  20. Performance Analysis of Cooperative Virtual MIMO Systems for Wireless Sensor Networks

    PubMed Central

    Rafique, Zimran; Seet, Boon-Chong; Al-Anbuky, Adnan

    2013-01-01

    Multi-Input Multi-Output (MIMO) techniques can be used to increase the data rate for a given bit error rate (BER) and transmission power. Due to the small form factor, energy and processing constraints of wireless sensor nodes, a cooperative Virtual MIMO as opposed to True MIMO system architecture is considered more feasible for wireless sensor network (WSN) applications. Virtual MIMO with Vertical-Bell Labs Layered Space-Time (V-BLAST) multiplexing architecture has been recently established to enhance WSN performance. In this paper, we further investigate the impact of different modulation techniques, and analyze for the first time, the performance of a cooperative Virtual MIMO system based on V-BLAST architecture with multi-carrier modulation techniques. Through analytical models and simulations using real hardware and environment settings, both communication and processing energy consumptions, BER, spectral efficiency, and total time delay of multiple cooperative nodes each with single antenna are evaluated. The results show that cooperative Virtual-MIMO with Binary Phase Shift Keying-Wavelet based Orthogonal Frequency Division Multiplexing (BPSK-WOFDM) modulation is a promising solution for future high data-rate and energy-efficient WSNs. PMID:23760087

  1. Virtualization of Event Sources in Wireless Sensor Networks for the Internet of Things

    PubMed Central

    Martínez, Néstor Lucas; Martínez, José-Fernán; Díaz, Vicente Hernández

    2014-01-01

    Wireless Sensor Networks (WSNs) are generally used to collect information from the environment. The gathered data are delivered mainly to sinks or gateways that become the endpoints where applications can retrieve and process such data. However, applications would also expect from a WSN an event-driven operational model, so that they can be notified whenever occur some specific environmental changes instead of continuously analyzing the data provided periodically. In either operational model, WSNs represent a collection of interconnected objects, as outlined by the Internet of Things. Additionally, in order to fulfill the Internet of Things principles, Wireless Sensor Networks must have a virtual representation that allows indirect access to their resources, a model that should also include the virtualization of event sources in a WSN. Thus, in this paper a model for a virtual representation of event sources in a WSN is proposed. They are modeled as internet resources that are accessible by any internet application, following an Internet of Things approach. The model has been tested in a real implementation where a WSN has been deployed in an open neighborhood environment. Different event sources have been identified in the proposed scenario, and they have been represented following the proposed model. PMID:25470489

  2. Virtualization of event sources in wireless sensor networks for the internet of things.

    PubMed

    Lucas Martínez, Néstor; Martínez, José-Fernán; Hernández Díaz, Vicente

    2014-01-01

    Wireless Sensor Networks (WSNs) are generally used to collect information from the environment. The gathered data are delivered mainly to sinks or gateways that become the endpoints where applications can retrieve and process such data. However, applications would also expect from a WSN an event-driven operational model, so that they can be notified whenever occur some specific environmental changes instead of continuously analyzing the data provided periodically. In either operational model, WSNs represent a collection of interconnected objects, as outlined by the Internet of Things. Additionally, in order to fulfill the Internet of Things principles, Wireless Sensor Networks must have a virtual representation that allows indirect access to their resources, a model that should also include the virtualization of event sources in a WSN. Thus, in this paper a model for a virtual representation of event sources in a WSN is proposed. They are modeled as internet resources that are accessible by any internet application, following an Internet of Things approach. The model has been tested in a real implementation where a WSN has been deployed in an open neighborhood environment. Different event sources have been identified in the proposed scenario, and they have been represented following the proposed model. PMID:25470489

  3. Real world navigation independence in the early blind correlates with differential brain activity associated with virtual navigation

    PubMed Central

    Halko, Mark A.; Connors, Erin C.; Sánchez, Jaime; Merabet, Lotfi B.

    2014-01-01

    Navigating is a complex cognitive task that places high demands on spatial abilities, particularly in the absence of sight. Significant advances have been made in identifying the neural correlates associated with various aspects of this skill, however, how the brain is able to navigate in the absence of visual experience remains poorly understood. Furthermore, how neural network activity relates to the wide variability in navigational independence and skill in the blind population is also unknown. Using fMRI, we investigated the neural correlates of audio-based navigation within a large scale, indoor virtual environment in early profoundly blind participants with differing levels of spatial navigation independence (assessed by the Santa Barbara Sense of Direction (SBSoD) scale). Performing path integration tasks in the virtual environment was associated with activation within areas of a core network implicated in navigation. Furthermore, we found a positive relationship between SBSoD scores and activation within right temporal parietal junction (TPJ) during the planning and execution phases of the task. These findings suggest that differential navigational ability in the blind may be related to the utilization of different brain network structures. Further characterization of the factors that influence network activity may have important implications regarding how this skill is taught in the blind community. PMID:24027192

  4. Real world navigation independence in the early blind correlates with differential brain activity associated with virtual navigation.

    PubMed

    Halko, Mark A; Connors, Erin C; Sánchez, Jaime; Merabet, Lotfi B

    2014-06-01

    Navigating is a complex cognitive task that places high demands on spatial abilities, particularly in the absence of sight. Significant advances have been made in identifying the neural correlates associated with various aspects of this skill; however, how the brain is able to navigate in the absence of visual experience remains poorly understood. Furthermore, how neural network activity relates to the wide variability in navigational independence and skill in the blind population is also unknown. Using functional magnetic resonance imaging, we investigated the neural correlates of audio-based navigation within a large scale, indoor virtual environment in early profoundly blind participants with differing levels of spatial navigation independence (assessed by the Santa Barbara Sense of Direction scale). Performing path integration tasks in the virtual environment was associated with activation within areas of a core network implicated in navigation. Furthermore, we found a positive relationship between Santa Barbara Sense of Direction scores and activation within right temporal parietal junction during the planning and execution phases of the task. These findings suggest that differential navigational ability in the blind may be related to the utilization of different brain network structures. Further characterization of the factors that influence network activity may have important implications regarding how this skill is taught in the blind community. PMID:24027192

  5. All-optical virtual private network and ONUs communication in optical OFDM-based PON system.

    PubMed

    Zhang, Chongfu; Huang, Jian; Chen, Chen; Qiu, Kun

    2011-11-21

    We propose and demonstrate a novel scheme, which enables all-optical virtual private network (VPN) and all-optical optical network units (ONUs) inter-communications in optical orthogonal frequency-division multiplexing-based passive optical network (OFDM-PON) system using the subcarrier bands allocation for the first time (to our knowledge). We consider the intra-VPN and inter-VPN communications which correspond to two different cases: VPN communication among ONUs in one group and in different groups. The proposed scheme can provide the enhanced security and a more flexible configuration for VPN users compared to the VPN in WDM-PON or TDM-PON systems. The all-optical VPN and inter-ONU communications at 10-Gbit/s with 16 quadrature amplitude modulation (16 QAM) for the proposed optical OFDM-PON system are demonstrated. These results verify that the proposed scheme is feasible. PMID:22109510

  6. Active Learning through the Use of Virtual Environments

    ERIC Educational Resources Information Center

    Mayrose, James

    2012-01-01

    Immersive Virtual Reality (VR) has seen explosive growth over the last decade. Immersive VR attempts to give users the sensation of being fully immersed in a synthetic environment by providing them with 3D hardware, and allowing them to interact with objects in virtual worlds. The technology is extremely effective for learning and exploration, and…

  7. Global Detection of Live Virtual Machine Migration Based on Cellular Neural Networks

    PubMed Central

    Xie, Kang; Yang, Yixian; Zhang, Ling; Jing, Maohua; Xin, Yang; Li, Zhongxian

    2014-01-01

    In order to meet the demands of operation monitoring of large scale, autoscaling, and heterogeneous virtual resources in the existing cloud computing, a new method of live virtual machine (VM) migration detection algorithm based on the cellular neural networks (CNNs), is presented. Through analyzing the detection process, the parameter relationship of CNN is mapped as an optimization problem, in which improved particle swarm optimization algorithm based on bubble sort is used to solve the problem. Experimental results demonstrate that the proposed method can display the VM migration processing intuitively. Compared with the best fit heuristic algorithm, this approach reduces the processing time, and emerging evidence has indicated that this new approach is affordable to parallelism and analog very large scale integration (VLSI) implementation allowing the VM migration detection to be performed better. PMID:24959631

  8. Global detection of live virtual machine migration based on cellular neural networks.

    PubMed

    Xie, Kang; Yang, Yixian; Zhang, Ling; Jing, Maohua; Xin, Yang; Li, Zhongxian

    2014-01-01

    In order to meet the demands of operation monitoring of large scale, autoscaling, and heterogeneous virtual resources in the existing cloud computing, a new method of live virtual machine (VM) migration detection algorithm based on the cellular neural networks (CNNs), is presented. Through analyzing the detection process, the parameter relationship of CNN is mapped as an optimization problem, in which improved particle swarm optimization algorithm based on bubble sort is used to solve the problem. Experimental results demonstrate that the proposed method can display the VM migration processing intuitively. Compared with the best fit heuristic algorithm, this approach reduces the processing time, and emerging evidence has indicated that this new approach is affordable to parallelism and analog very large scale integration (VLSI) implementation allowing the VM migration detection to be performed better. PMID:24959631

  9. Efficiently Scheduling Multi-core Guest Virtual Machines on Multi-core Hosts in Network Simulation

    SciTech Connect

    Yoginath, Srikanth B; Perumalla, Kalyan S

    2011-01-01

    Virtual machine (VM)-based simulation is a method used by network simulators to incorporate realistic application behaviors by executing actual VMs as high-fidelity surrogates for simulated end-hosts. A critical requirement in such a method is the simulation time-ordered scheduling and execution of the VMs. Prior approaches such as time dilation are less efficient due to the high degree of multiplexing possible when multiple multi-core VMs are simulated on multi-core host systems. We present a new simulation time-ordered scheduler to efficiently schedule multi-core VMs on multi-core real hosts, with a virtual clock realized on each virtual core. The distinguishing features of our approach are: (1) customizable granularity of the VM scheduling time unit on the simulation time axis, (2) ability to take arbitrary leaps in virtual time by VMs to maximize the utilization of host (real) cores when guest virtual cores idle, and (3) empirically determinable optimality in the tradeoff between total execution (real) time and time-ordering accuracy levels. Experiments show that it is possible to get nearly perfect time-ordered execution, with a slight cost in total run time, relative to optimized non-simulation VM schedulers. Interestingly, with our time-ordered scheduler, it is also possible to reduce the time-ordering error from over 50% of non-simulation scheduler to less than 1% realized by our scheduler, with almost the same run time efficiency as that of the highly efficient non-simulation VM schedulers.

  10. Virtual machine-based simulation platform for mobile ad-hoc network-based cyber infrastructure

    DOE PAGESBeta

    Yoginath, Srikanth B.; Perumalla, Kayla S.; Henz, Brian J.

    2015-09-29

    In modeling and simulating complex systems such as mobile ad-hoc networks (MANETs) in de-fense communications, it is a major challenge to reconcile multiple important considerations: the rapidity of unavoidable changes to the software (network layers and applications), the difficulty of modeling the critical, implementation-dependent behavioral effects, the need to sustain larger scale scenarios, and the desire for faster simulations. Here we present our approach in success-fully reconciling them using a virtual time-synchronized virtual machine(VM)-based parallel ex-ecution framework that accurately lifts both the devices as well as the network communications to a virtual time plane while retaining full fidelity. At themore » core of our framework is a scheduling engine that operates at the level of a hypervisor scheduler, offering a unique ability to execute multi-core guest nodes over multi-core host nodes in an accurate, virtual time-synchronized manner. In contrast to other related approaches that suffer from either speed or accuracy issues, our framework provides MANET node-wise scalability, high fidelity of software behaviors, and time-ordering accuracy. The design and development of this framework is presented, and an ac-tual implementation based on the widely used Xen hypervisor system is described. Benchmarks with synthetic and actual applications are used to identify the benefits of our approach. The time inaccuracy of traditional emulation methods is demonstrated, in comparison with the accurate execution of our framework verified by theoretically correct results expected from analytical models of the same scenarios. In the largest high fidelity tests, we are able to perform virtual time-synchronized simulation of 64-node VM-based full-stack, actual software behaviors of MANETs containing a mix of static and mobile (unmanned airborne vehicle) nodes, hosted on a 32-core host, with full fidelity of unmodified ad-hoc routing protocols, unmodified

  11. Virtual machine-based simulation platform for mobile ad-hoc network-based cyber infrastructure

    SciTech Connect

    Yoginath, Srikanth B.; Perumalla, Kayla S.; Henz, Brian J.

    2015-09-29

    In modeling and simulating complex systems such as mobile ad-hoc networks (MANETs) in de-fense communications, it is a major challenge to reconcile multiple important considerations: the rapidity of unavoidable changes to the software (network layers and applications), the difficulty of modeling the critical, implementation-dependent behavioral effects, the need to sustain larger scale scenarios, and the desire for faster simulations. Here we present our approach in success-fully reconciling them using a virtual time-synchronized virtual machine(VM)-based parallel ex-ecution framework that accurately lifts both the devices as well as the network communications to a virtual time plane while retaining full fidelity. At the core of our framework is a scheduling engine that operates at the level of a hypervisor scheduler, offering a unique ability to execute multi-core guest nodes over multi-core host nodes in an accurate, virtual time-synchronized manner. In contrast to other related approaches that suffer from either speed or accuracy issues, our framework provides MANET node-wise scalability, high fidelity of software behaviors, and time-ordering accuracy. The design and development of this framework is presented, and an ac-tual implementation based on the widely used Xen hypervisor system is described. Benchmarks with synthetic and actual applications are used to identify the benefits of our approach. The time inaccuracy of traditional emulation methods is demonstrated, in comparison with the accurate execution of our framework verified by theoretically correct results expected from analytical models of the same scenarios. In the largest high fidelity tests, we are able to perform virtual time-synchronized simulation of 64-node VM-based full-stack, actual software behaviors of MANETs containing a mix of static and mobile (unmanned airborne vehicle) nodes, hosted on a 32-core host, with full fidelity of unmodified ad-hoc routing protocols, unmodified application

  12. Students' Personal Networks in Virtual and Personal Learning Environments: A Case Study in Higher Education Using Learning Analytics Approach

    ERIC Educational Resources Information Center

    Casquero, Oskar; Ovelar, Ramón; Romo, Jesús; Benito, Manuel; Alberdi, Mikel

    2016-01-01

    The main objective of this paper is to analyse the effect of the affordances of a virtual learning environment and a personal learning environment (PLE) in the configuration of the students' personal networks in a higher education context. The results are discussed in light of the adaptation of the students to the learning network made up by two…

  13. Complex networks in brain electrical activity

    NASA Astrophysics Data System (ADS)

    Ray, C.; Ruffini, G.; Marco-Pallarés, J.; Fuentemilla, L.; Grau, C.

    2007-08-01

    This letter reports a method to extract a functional network of the human brain from electroencephalogram measurements. A network analysis was performed on the resultant network and the statistics of the cluster coefficient, node degree, path length, and physical distance of the links, were studied. Even given the low electrode count of the experimental data the method was able to extract networks with network parameters that clearly depend on the type of stimulus presented to the subject. This type of analysis opens a door to studying the cerebral networks underlying brain electrical activity, and links the fields of complex networks and cognitive neuroscience.

  14. Using Virtual Pets to Promote Physical Activity in Children: An Application of the Youth Physical Activity Promotion Model.

    PubMed

    Ahn, Sun Joo Grace; Johnsen, Kyle; Robertson, Tom; Moore, James; Brown, Scott; Marable, Amanda; Basu, Aryabrata

    2015-01-01

    A virtual pet was developed based on the framework of the youth physical activity promotion model and tested as a vehicle for promoting physical activity in children. Children in the treatment group interacted with the virtual pet for three days, setting physical activity goals and teaching tricks to the virtual pet when their goals were met. The virtual pet became more fit and learned more sophisticated tricks as the children achieved activity goals. Children in the control group interacted with a computer system presenting equivalent features but without the virtual pet. Physical activity and goal attainment were evaluated using activity monitors. Results indicated that children in the treatment group engaged in 1.09 more hours of daily physical activity (156% more) than did those in the control group. Physical activity self-efficacy and beliefs served as mediators driving this increase in activity. Children that interacted with the virtual pet also expressed higher intentions than children in the control group to continue physical activity in the future. Theoretical and practical potentials of using a virtual pet to systematically promote physical activity in children are discussed. PMID:26020285

  15. All-optical OFDM network coding scheme for all-optical virtual private communication in PON

    NASA Astrophysics Data System (ADS)

    Li, Lijun; Gu, Rentao; Ji, Yuefeng; Bai, Lin; Huang, Zhitong

    2014-03-01

    A novel optical orthogonal frequency division multiplexing (OFDM) network coding scheme is proposed over passive optical network (PON) system. The proposed scheme for all-optical virtual private network (VPN) does not only improve transmission efficiency, but also realize full-duplex communication mode in a single fiber. Compared with the traditional all-optical VPN architectures, the all-optical OFDM network coding scheme can support higher speed, more flexible bandwidth allocation, and higher spectrum efficiency. In order to reduce the difficulty of alignment for encoding operation between inter-communication traffic, the width of OFDM subcarrier pulse is stretched in our proposed scheme. The feasibility of all-optical OFDM network coding scheme for VPN is verified, and the relevant simulation results show that the full-duplex inter-communication traffic stream can be transmitted successfully. Furthermore, the tolerance of misalignment existing in inter-ONUs traffic is investigated and analyzed for all-optical encoding operation, and the difficulty of pulse alignment is proved to be lower.

  16. Virtual resistive network and conductivity reconstruction with Faradayʼs law

    NASA Astrophysics Data System (ADS)

    Lee, Min Gi; Ko, Min-Su; Kim, Yong-Jung

    2014-12-01

    A network-based conductivity reconstruction method is introduced using the third Maxwell equation, or Faraday's law, for a static case. The usual choice in electrical impedance tomography is the divergence-free equation for the electrical current density. However, if the electrical current density is given, the curl-free equation for the electrical field gives a direct relation between the current and the conductivity and this relation is used in this paper. Mimetic discretization is applied to the equation, which gives the virtual resistive network system. Properties of the numerical schemes introduced are investigated and their advantages over other conductivity reconstruction methods are discussed. Numerically simulated results, with an analysis of noise propagation, are presented.

  17. A metro-access integrated network with all-optical virtual private network function using DPSK/ASK modulation format

    NASA Astrophysics Data System (ADS)

    Tian, Yue; Leng, Lufeng; Su, Yikai

    2008-11-01

    All-optical virtual private network (VPN), which offers dedicated optical channels to connect users within a VPN group, is considered a promising approach to efficient internetworking with low latency and enhanced security implemented in the physical layer. On the other hand, time-division multiplexed (TDM) / wavelength-division multiplexed (WDM) network architecture based on a feeder-ring with access-tree topology, is considered a pragmatic migration scenario from current TDM-PONs to future WDM-PONs and a potential convergence scheme for access and metropolitan networks, due to its efficiently shared hardware and bandwidth resources. All-optical VPN internetworking in such a metro-access integrated structure is expected to cover a wider service area and therefore is highly desirable. In this paper, we present a TDM/WDM metro-access integrated network supporting all-optical VPN internetworking among ONUs in different sub- PONs based on orthogonal differential-phase-shift keying (DPSK) / amplitude-shift keying (ASK) modulation format. In each ONU, no laser but a single Mach-Zehnder modulator (MZM) is needed for the upstream and VPN signal generation, which is cost-effective. Experiments and simulations are performed to verify its feasibility as a potential solution to the future access service.

  18. The photoelectric effect and study of the diffraction of light: Two new experiments in UNILabs virtual and remote laboratories network

    NASA Astrophysics Data System (ADS)

    Pedro Sánchez, Juan; Sáenz, Jacobo; de la Torre, Luis; Carreras, Carmen; Yuste, Manuel; Heradio, Rubén; Dormido, Sebastián

    2016-05-01

    This work describes two experiments: "study of the diffraction of light: Fraunhofer approximation" and "the photoelectric effect". Both of them count with a virtual, simulated, version of the experiment as well as with a real one which can be operated remotely. The two previous virtual and remote labs (built using Easy Java(script) Simulations) are integrated in UNILabs, a network of online interactive laboratories based on the free Learning Management System Moodle. In this web environment, students can find not only the virtual and remote labs but also manuals with related theory, the user interface description for each application, and so on.

  19. Behavioral Intention to Use a Virtual Instrumental Activities of Daily Living System Among People With Stroke

    PubMed Central

    Adams, Richard; White, Marga; Diamond, Paul

    2015-01-01

    OBJECTIVE. The purpose of this study was to investigate the behavioral intention to use (BIU) regarding a virtual system for practicing instrumental activities of daily living (IADLs) among people with stroke. METHOD. Fourteen people who had sustained a stroke used a virtual world–based system over four sessions to participate in virtual occupations of preparing meals and putting away groceries. To investigate intention to use the technology, participants responded to a questionnaire based on the Technology Acceptance Model and were interviewed about the experience. RESULTS. Analysis of questionnaire responses revealed favorable attitudes toward the technology and statistically significant correlations between these attitudes and positive BIU. Analysis of qualitative data revealed four themes to support system use: Use of the affected arm increased, the virtual practice was enjoyable, the technology was user-friendly, and the system reflected real-life activities. CONCLUSION. This study shows that participants reported a positive BIU for the virtual system for practicing IADLs. PMID:25871604

  20. Neural network sensor fusion: Creation of a virtual sensor for cloud-base height estimation

    NASA Astrophysics Data System (ADS)

    Pasika, Hugh Joseph Christopher

    2000-10-01

    Sensor fusion has become a significant area of signal processing research that draws on a variety of tools. Its goals are many, however in this thesis, the creation of a virtual sensor is paramount. In particular, neural networks are used to simulate the output of a LIDAR (LASER. RADAR) that measures cloud-base height. Eye-safe LIDAR is more accurate than the standard tool that would be used for such measurement; the ceilometer. The desire is to make cloud-base height information available at a network of ground-based meteorological stations without actually installing LIDAR sensors. To accomplish this, fifty-seven sensors ranging from multispectral satellite information to standard atmospheric measurements such as temperature and humidity, are fused in what can only be termed as a very complex, nonlinear environment. The result is an accurate prediction of cloud-base height. Thus, a virtual sensor is created. A total of four different learning algorithms were studied; two global and two local. In each case, the very best state-of-the-art learning algorithms have been selected. Local methods investigated are the regularized radial basis function network, and the support vector machine. Global methods include the standard backpropagation with momentum trained multilayer perceptron (used as a benchmark) and the multilayer perceptron trained via the Kalman filter algorithm. While accuracy is the primary concern, computational considerations potentially limit the application of several of the above techniques. Thus, in all cases care was taken to minimize computational cost. For example in the case of the support vector machine, a method of partitioning the problem in order to reduce memory requirements and make the optimization over a large data set feasible was employed and in the Kalman algorithm case, node-decoupling was used to dramatically reduce the number of operations required. Overall, the methods produced somewhat equivalent mean squared errors indicating

  1. On the Role of Hyper-arid Regions within the Virtual Water Trade Network

    NASA Astrophysics Data System (ADS)

    Aggrey, James; Alshamsi, Aamena; Molini, Annalisa

    2016-04-01

    Climate change, economic development, and population growth are bound to increasingly impact global water resources, posing a significant threat to the sustainable development of arid regions, where water consumption highly exceeds the natural carrying capacity, population growth rate is high, and climate variability is going to impact both water consumption and availability. Virtual Water Trade (VWT) - i.e. the international trade network of water-intensive products - has been proposed as a possible solution to optimize the allocation of water resources on the global scale. By increasing food availability and lowering food prices it may in fact help the rapid development of water-scarce regions. The structure of the VWT network has been analyzed by a number of authors both in connection with trade policies, socioeconomic constrains and agricultural efficiency. However a systematic analysis of the structure and the dynamics of the VWT network conditional to aridity, climatic forcing and energy availability, is still missing. Our goal is hence to analyze the role of arid and hyper-arid regions within the VWN under diverse climatic, demographic, and energy constraints with an aim to contribute to the ongoing Energy-Water-Food nexus discussion. In particular, we focus on the hyper-arid lands of the Arabian Peninsula, the role they play in the global network and the assessment of their specific criticalities, as reflected in the VWN resilience.

  2. Virtual war, military revolutions, and networks: a guide through the concepts from an Australian perspective

    NASA Astrophysics Data System (ADS)

    Bowley, Dean K.; Gaertner, Paul S.

    2003-07-01

    In this paper the argument is made that the offensive fire support organisation and doctrine, born of the "indirect fire revolution" of the first world war, is the start point for distributed sensors, shooters and deciders that may be transferred to a joint force; that the culture of directive control and mission orders developed by the German Army in 1918 and then adopted by most western armies is the start point for the culture required to achieve "self synchronisation" and that the network developed for the air defence of carrier battle groups is the start point for developing a networked ground manoeuvre force. We discuss the strategic expectations of network centric warfare, a "virtual war" scenario and the inherent vulnerabilities. The current level of understanding and implementation in specific areas is analysed and lessons for general application are developed and the potential payoff identified. Three broad operational domains are investigated, networked platform versus platform warfare between states, guerrilla/counter-insurfence operations and the emerging domain of "netwars" (terror organisations and criminal gangs).

  3. Quality of Service Control Based on Virtual Private Network Services in a Wide Area Gigabit Ethernet Optical Test Bed

    NASA Astrophysics Data System (ADS)

    Rea, Luca; Pompei, Sergio; Valenti, Alessandro; Matera, Francesco; Zema, Cristiano; Settembre, Marina

    We report an experimental investigation about the Virtual Private LAN Service technique to guarantee the quality of service in the metro/core network and also in the presence of access bandwidth bottleneck. We also show how the virtual private network can be set up for answering to a user request in a very fast way. The tests were performed in a GMPLS test bed with GbE core routers linked with long (tens of kilometers) GbE G.652 fiber links.

  4. Building a Virtual Network in a Community Health Research Training Program

    PubMed Central

    Lau, Francis; Hayward, Robert

    2000-01-01

    Objective: To describe the experiences, lessons, and implications of building a virtual network as part of a two-year community health research training program in a Canadian province. Design: An action research field study in which 25 health professionals from 17 health regions participated in a seven-week training course on health policy, management, economics, research methods, data analysis, and computer technology. The participants then returned to their regions to apply the knowledge in different community health research projects. Ongoing faculty consultations and support were provided as needed. Each participant was given a notebook computer with the necessary software, Internet access, and technical support for two years, to access information resources, engage in group problem solving, share ideas and knowledge, and collaborate on projects. Measurements: Data collected over two years consisted of program documents, records of interviews with participants and staff, meeting notes, computer usage statistics, automated online surveys, computer conference postings, program Web site, and course feedback. The analysis consisted of detailed review and comparison of the data from different sources. NUD*IST was then used to validate earlier study findings. Results: The ten key lessons are that role clarity, technology vision, implementation staging, protected time, just-in-time training, ongoing facilitation, work integration, participatory design, relationship building, and the demonstration of results are essential ingredients for building a successful network. Conclusion: This study provides a descriptive model of the processes involved in developing, in the community health setting, virtual networks that can be used as the basis for future research and as a practical guide for managers. PMID:10887165

  5. Behavioral and Network Origins of Wealth Inequality: Insights from a Virtual World

    PubMed Central

    Fuchs, Benedikt; Thurner, Stefan

    2014-01-01

    Almost universally, wealth is not distributed uniformly within societies or economies. Even though wealth data have been collected in various forms for centuries, the origins for the observed wealth-disparity and social inequality are not yet fully understood. Especially the impact and connections of human behavior on wealth could so far not be inferred from data. Here we study wealth data from the virtual economy of the massive multiplayer online game (MMOG) Pardus. This data not only contains every player's wealth at every point in time, but also all actions over a timespan of almost a decade. We find that wealth distributions in the virtual world are very similar to those in Western countries. In particular we find an approximate exponential distribution for low wealth levels and a power-law tail for high levels. The Gini index is found to be , which is close to the indices of many Western countries. We find that wealth-increase rates depend on the time when players entered the game. Players that entered the game early on tend to have remarkably higher wealth-increase rates than those who joined later. Studying the players' positions within their social networks, we find that the local position in the trade network is most relevant for wealth. Wealthy people have high in- and out-degrees in the trade network, relatively low nearest-neighbor degrees, and low clustering coefficients. Wealthy players have many mutual friendships and are socially well respected by others, but spend more time on business than on socializing. Wealthy players have few personal enemies, but show animosity towards players that behave as public enemies. We find that players that are not organized within social groups are significantly poorer on average. We observe that “political” status and wealth go hand in hand. PMID:25153072

  6. A Novel Clustering Algorithm for Mobile Ad Hoc Networks Based on Determination of Virtual Links' Weight to Increase Network Stability

    PubMed Central

    Karimi, Abbas; Afsharfarnia, Abbas; Zarafshan, Faraneh; Al-Haddad, S. A. R.

    2014-01-01

    The stability of clusters is a serious issue in mobile ad hoc networks. Low stability of clusters may lead to rapid failure of clusters, high energy consumption for reclustering, and decrease in the overall network stability in mobile ad hoc network. In order to improve the stability of clusters, weight-based clustering algorithms are utilized. However, these algorithms only use limited features of the nodes. Thus, they decrease the weight accuracy in determining node's competency and lead to incorrect selection of cluster heads. A new weight-based algorithm presented in this paper not only determines node's weight using its own features, but also considers the direct effect of feature of adjacent nodes. It determines the weight of virtual links between nodes and the effect of the weights on determining node's final weight. By using this strategy, the highest weight is assigned to the best choices for being the cluster heads and the accuracy of nodes selection increases. The performance of new algorithm is analyzed by using computer simulation. The results show that produced clusters have longer lifetime and higher stability. Mathematical simulation shows that this algorithm has high availability in case of failure. PMID:25114965

  7. Evolutionary Approach of Virtual Communities of Practice: A Reflection within a Network of Spanish Rural Schools

    NASA Astrophysics Data System (ADS)

    Frossard, Frédérique; Trifonova, Anna; Barajas Frutos, Mario

    The isolation of rural communities creates special necessities for teachers and students in rural schools. The present article describes "Rural Virtual School", a Virtual Community of Practice (VCoP) in which Spanish teachers of rural schools share learning resources and teaching methodologies through social software applications. The article arrives to an evolutionary model, in which the use of the social software tools evolves together with the needs and the activities of the VCoP through the different stages of its lifetime. Currently, the community has reached a high level of maturity and, in order to keep its momentum, the members intentionally use appropriate technologies specially designed to enhance rich innovative educational approaches, through which they collaboratively generate creative practices.

  8. Stochastic cycle selection in active flow networks.

    PubMed

    Woodhouse, Francis G; Forrow, Aden; Fawcett, Joanna B; Dunkel, Jörn

    2016-07-19

    Active biological flow networks pervade nature and span a wide range of scales, from arterial blood vessels and bronchial mucus transport in humans to bacterial flow through porous media or plasmodial shuttle streaming in slime molds. Despite their ubiquity, little is known about the self-organization principles that govern flow statistics in such nonequilibrium networks. Here we connect concepts from lattice field theory, graph theory, and transition rate theory to understand how topology controls dynamics in a generic model for actively driven flow on a network. Our combined theoretical and numerical analysis identifies symmetry-based rules that make it possible to classify and predict the selection statistics of complex flow cycles from the network topology. The conceptual framework developed here is applicable to a broad class of biological and nonbiological far-from-equilibrium networks, including actively controlled information flows, and establishes a correspondence between active flow networks and generalized ice-type models. PMID:27382186

  9. Virtual Reality: Developing a VR space for Academic activities

    NASA Astrophysics Data System (ADS)

    Kaimaris, D.; Stylianidis, E.; Karanikolas, N.

    2014-05-01

    Virtual reality (VR) is extensively used in various applications; in industry, in academia, in business, and is becoming more and more affordable for end users from the financial point of view. At the same time, in academia and higher education more and more applications are developed, like in medicine, engineering, etc. and students are inquiring to be well-prepared for their professional life after their educational life cycle. Moreover, VR is providing the benefits having the possibility to improve skills but also to understand space as well. This paper presents the methodology used during a course, namely "Geoinformatics applications" at the School of Spatial Planning and Development (Eng.), Aristotle University of Thessaloniki, to create a virtual School space. The course design focuses on the methods and techniques to be used in order to develop the virtual environment. In addition the project aspires to become more and more effective for the students and provide a real virtual environment with useful information not only for the students but also for any citizen interested in the academic life at the School.

  10. Avatars Go to Class: A Virtual Environment Soil Science Activity

    ERIC Educational Resources Information Center

    Mamo, M.; Namuth-Covert, D.; Guru, A.; Nugent, G.; Phillips, L.; Sandall, L.; Kettler, T.; McCallister, D.

    2011-01-01

    Web 2.0 technology is expanding rapidly from social and gaming uses into the educational applications. Specifically, the multi-user virtual environment (MUVE), such as SecondLife, allows educators to fill the gap of first-hand experience by creating simulated realistic evolving problems/games. In a pilot study, a team of educators at the…

  11. Dynamics of active actin networks

    NASA Astrophysics Data System (ADS)

    Koehler, Simone

    2014-03-01

    Local mechanical and structural properties of a eukaryotic cell are determined by its cytoskeleton. To adapt to their environment, cells rely on constant self-organized rearrangement processes of their actin cytoskeleton. To shed light on the principles underlying these dynamic self-organization processes we investigate a minimal reconstituted active system consisting of actin filaments, crosslinking molecules and molecular motor filaments. Using quantitative fluorescence microscopy and image analysis, we show, that these minimal model systems exhibit a generic structure formation mechanism. The competition between force generation by molecular motors and the stabilization of the network by crosslinking proteins results in a highly dynamic reorganization process which is characterized by anomalous transport dynamics with a superdiffusive behavior also found in intracellular dynamics. In vitro, these dynamics are governed by chemical and physical parameters that alter the balance of motor and crosslinking proteins, such as pH. These findings can be expected to have broad implications in our understanding of cytoskeletal regulation in vivo.

  12. Shaping Neuronal Network Activity by Presynaptic Mechanisms

    PubMed Central

    Ashery, Uri

    2015-01-01

    Neuronal microcircuits generate oscillatory activity, which has been linked to basic functions such as sleep, learning and sensorimotor gating. Although synaptic release processes are well known for their ability to shape the interaction between neurons in microcircuits, most computational models do not simulate the synaptic transmission process directly and hence cannot explain how changes in synaptic parameters alter neuronal network activity. In this paper, we present a novel neuronal network model that incorporates presynaptic release mechanisms, such as vesicle pool dynamics and calcium-dependent release probability, to model the spontaneous activity of neuronal networks. The model, which is based on modified leaky integrate-and-fire neurons, generates spontaneous network activity patterns, which are similar to experimental data and robust under changes in the model's primary gain parameters such as excitatory postsynaptic potential and connectivity ratio. Furthermore, it reliably recreates experimental findings and provides mechanistic explanations for data obtained from microelectrode array recordings, such as network burst termination and the effects of pharmacological and genetic manipulations. The model demonstrates how elevated asynchronous release, but not spontaneous release, synchronizes neuronal network activity and reveals that asynchronous release enhances utilization of the recycling vesicle pool to induce the network effect. The model further predicts a positive correlation between vesicle priming at the single-neuron level and burst frequency at the network level; this prediction is supported by experimental findings. Thus, the model is utilized to reveal how synaptic release processes at the neuronal level govern activity patterns and synchronization at the network level. PMID:26372048

  13. Routing and wavelength assignment algorithms for all-optical WDM networks based on virtual multiple self-healing ring architecture

    NASA Astrophysics Data System (ADS)

    Ishikawa, Akio; Kishi, Yoji

    2000-09-01

    This paper newly proposes a self-healing architecture in all- optical WDM networks based on virtual embedded multiple rings (Virtual Multiple Self Healing Rings: VM-SHR). Focusing upon the network design aspect of the proposed architecture, this paper describes design methodologies for VM-SHR networks. For two major problems in all-optical WDM network design, that is, the connection routing and wavelength assignment problems, we first established solution models based on mathematical programming formulation, each of which can be solved by common integer programming algorithms, respectively. In addition, we also developed an efficient heuristic algorithm for the wavelength assignment problem. Their usefulness and performance are demonstrated through the extensive simulation results.

  14. Reliable Geographical Forwarding in Cognitive Radio Sensor Networks Using Virtual Clusters

    PubMed Central

    Zubair, Suleiman; Fisal, Norsheila

    2014-01-01

    The need for implementing reliable data transfer in resource-constrained cognitive radio ad hoc networks is still an open issue in the research community. Although geographical forwarding schemes are characterized by their low overhead and efficiency in reliable data transfer in traditional wireless sensor network, this potential is still yet to be utilized for viable routing options in resource-constrained cognitive radio ad hoc networks in the presence of lossy links. In this paper, a novel geographical forwarding technique that does not restrict the choice of the next hop to the nodes in the selected route is presented. This is achieved by the creation of virtual clusters based on spectrum correlation from which the next hop choice is made based on link quality. The design maximizes the use of idle listening and receiver contention prioritization for energy efficiency, the avoidance of routing hot spots and stability. The validation result, which closely follows the simulation result, shows that the developed scheme can make more advancement to the sink as against the usual decisions of relevant ad hoc on-demand distance vector route select operations, while ensuring channel quality. Further simulation results have shown the enhanced reliability, lower latency and energy efficiency of the presented scheme. PMID:24854362

  15. Network and user interface for PAT DOME virtual motion environment system

    NASA Technical Reports Server (NTRS)

    Worthington, J. W.; Duncan, K. M.; Crosier, W. G.

    1993-01-01

    The Device for Orientation and Motion Environments Preflight Adaptation Trainer (DOME PAT) provides astronauts a virtual microgravity sensory environment designed to help alleviate tye symptoms of space motion sickness (SMS). The system consists of four microcomputers networked to provide real time control, and an image generator (IG) driving a wide angle video display inside a dome structure. The spherical display demands distortion correction. The system is currently being modified with a new graphical user interface (GUI) and a new Silicon Graphics IG. This paper will concentrate on the new GUI and the networking scheme. The new GUI eliminates proprietary graphics hardware and software, and instead makes use of standard and low cost PC video (CGA) and off the shelf software (Microsoft's Quick C). Mouse selection for user input is supported. The new Silicon Graphics IG requires an Ethernet interface. The microcomputer known as the Real Time Controller (RTC), which has overall control of the system and is written in Ada, was modified to use the free public domain NCSA Telnet software for Ethernet communications with the Silicon Graphics IG. The RTC also maintains the original ARCNET communications through Novell Netware IPX with the rest of the system. The Telnet TCP/IP protocol was first used for real-time communication, but because of buffering problems the Telnet datagram (UDP) protocol needed to be implemented. Since the Telnet modules are written in C, the Adap pragma 'Interface' was used to interface with the network calls.

  16. A New Method for Creating Efficient Security Policies in Virtual Private Network

    NASA Astrophysics Data System (ADS)

    Sadeghi, Mohammad Mehdi Gilanian; Mohd Ali, Borhanuddin; Pedram, Hossein; Deghan, Mehdi; Sabaei, Masoud

    One of the most important protocols for implementing tunnels in order to take action of secure virtual private network is IPsec protocol. IPsec policies are used widely in order to limit access to information in security gateways or firewalls. The security treatment, namely (Deny, Allow or Encrypt) is done for outbound as well as inbound traffic by security policies. It is so important that they adjust properly. The current methods for security policies creation as seen in given security requirements are not efficient enough i.e. there are much more created policies than requirements. In this paper, we define a new method to decrease adopted security policies for a specific set of security requirements without any undesirable effect. Our measurement shows that security policies creation will be improved efficiently, and their updating time will be decreased.

  17. The FarNet Journey: Effective Teaching Strategies for Engaging Maori Students on the Virtual Learning Network

    ERIC Educational Resources Information Center

    Barbour, Michael; Bennett, Carolyn

    2013-01-01

    The Virtual Learning Network (VLN) provides schools, particularly those in rural and remote areas, with the opportunity to cooperate to expand curricular offerings for their students. Each school that participates in a VLN cluster contributes at least one course delivered by an e-teacher, allowing member schools access to any course offered…

  18. An Examination of a Virtual Private Network Implementation to Support a Teleworking Initiative: The Marcus Food Company Inc. Case Study

    ERIC Educational Resources Information Center

    Ferguson, Jason W.

    2010-01-01

    In this dissertation, the author examined the capabilities of virtual private networks (VPNs) in supporting teleworking environments for small businesses in the food marketing sector. The goal of this research was to develop an implementation model for small businesses in the food marketing sector that use a VPN solution to support teleworker…

  19. All-optical virtual private network system in OFDM based long-reach PON using RSOA re-modulation technique

    NASA Astrophysics Data System (ADS)

    Kim, Chang-Hun; Jung, Sang-Min; Kang, Su-Min; Han, Sang-Kook

    2015-01-01

    We propose an all-optical virtual private network (VPN) system in an orthogonal frequency division multiplexing (OFDM) based long reach PON (LR-PON). In the optical access network field, technologies based on fundamental upstream (U/S) and downstream (D/S) have been actively researched to accommodate explosion of data capacity. However, data transmission among the end users which is arisen from cloud computing, file-sharing and interactive game takes a large weight inside of internet traffic. Moreover, this traffic is predicted to increase more if Internet of Things (IoT) services are activated. In a conventional PON, VPN data is transmitted through ONU-OLT-ONU via U/S and D/S carriers. It leads to waste of bandwidth and energy due to O-E-O conversion in the OLT and round-trip propagation between OLT and remote node (RN). Also, it causes inevitable load to the OLT for electrical buffer, scheduling and routing. The network inefficiency becomes more critical in a LR-PON which has been researched as an effort to reduce CAPEX and OPEX through metro-access consolidation. In the proposed system, the VPN data is separated from conventional U/S and re-modulated on the D/S carrier by using RSOA in the ONUs to avoid bandwidth consumption of U/S and D/S unlike in previously reported system. Moreover, the transmitted VPN data is re-directed to the ONUs by wavelength selective reflector device in the RN without passing through the OLT. Experimental demonstration for the VPN communication system in an OFDM based LR-PON has been verified.

  20. An Activity Theory Approach to Analyze Barriers to a Virtual Management Information Systems (MIS) Curriculum

    ERIC Educational Resources Information Center

    Jaradat, Suhair; Qablan, Ahmad; Barham, Areej

    2011-01-01

    This paper explains how the activity theory is used as a framework to analyze the barriers to a virtual Management Information Stream (MIS) Curriculum in Jordanian schools, from both the sociocultural and pedagogical perspectives. Taking the activity system as a unit of analysis, this study documents the processes by which activities shape and are…

  1. Interevent time distributions of human multi-level activity in a virtual world

    NASA Astrophysics Data System (ADS)

    Mryglod, O.; Fuchs, B.; Szell, M.; Holovatch, Yu.; Thurner, S.

    2015-02-01

    Studying human behavior in virtual environments provides extraordinary opportunities for a quantitative analysis of social phenomena with levels of accuracy that approach those of the natural sciences. In this paper we use records of player activities in the massive multiplayer online game Pardus over 1238 consecutive days, and analyze dynamical features of sequences of actions of players. We build on previous work where temporal structures of human actions of the same type were quantified, and provide an empirical understanding of human actions of different types. This study of multi-level human activity can be seen as a dynamic counterpart of static multiplex network analysis. We show that the interevent time distributions of actions in the Pardus universe follow highly non-trivial distribution functions, from which we extract action-type specific characteristic 'decay constants'. We discuss characteristic features of interevent time distributions, including periodic patterns on different time scales, bursty dynamics, and various functional forms on different time scales. We comment on gender differences of players in emotional actions, and find that while males and females act similarly when performing some positive actions, females are slightly faster for negative actions. We also observe effects on the age of players: more experienced players are generally faster in making decisions about engaging in and terminating enmity and friendship, respectively.

  2. Competing activation mechanisms in epidemics on networks

    NASA Astrophysics Data System (ADS)

    Castellano, Claudio; Pastor-Satorras, Romualdo

    2012-04-01

    In contrast to previous common wisdom that epidemic activity in heterogeneous networks is dominated by the hubs with the largest number of connections, recent research has pointed out the role that the innermost, dense core of the network plays in sustaining epidemic processes. Here we show that the mechanism responsible of spreading depends on the nature of the process. Epidemics with a transient state are boosted by the innermost core. Contrarily, epidemics allowing a steady state present a dual scenario, where either the hub independently sustains activity and propagates it to the rest of the system, or, alternatively, the innermost network core collectively turns into the active state, maintaining it globally. In uncorrelated networks the former mechanism dominates if the degree distribution decays with an exponent larger than 5/2, and the latter otherwise. Topological correlations, rife in real networks, may perturb this picture, mixing the role of both mechanisms.

  3. Hybrid crosstalk aware Q-Factor analysis for selection of optical virtual private network connection

    NASA Astrophysics Data System (ADS)

    Das, S. K.; Samantray, A. K.; Patra, S. K.

    2016-01-01

    The presence of physical layer impairments (PLIs) in high-speed optical virtual private network (OVPN) over wavelength-division multiplexing/ dense-wavelength division multiplexing network degrades the connection quality (CQ). The quality can be numerically expressed as the quality factor (Q-Factor) of the connection. The CQ can be further affected by the increasing demand of connections and data speed. It is important to have an efficient OVPN control manager (OVPNCM) to maintain the CQ. OVPNCM can ensure better quality of transmission to the OVPN clients. Traditional routing and wavelength assignment (RWA) algorithms have less regards to the PLIs and cannot provide guaranteed OVPN connection (OVPNC) quality. In order to achieve a guaranteed CQ, we proposed a wavelength assignment (WA) scheme and a hybrid crosstalk model based on linear in-band and nonlinear four-wave mixing crosstalk. The performance of the proposed WA scheme with the hybrid crosstalk model is demonstrated. The results show that the proposed hybrid crosstalk model with WA scheme not only provides a guaranteed OVPNC, but also improves the OVPN performance in terms of blocking probability.

  4. A virtual tall tower network for understanding continental sources and sinks of CO2

    SciTech Connect

    Davis, K.J.; Richardson, S.J.; Miles, N.L.

    2007-03-09

    Our understanding of the North American terrestrial carbon cycle is limited by both a lack of continental atmospheric CO2 data, and by a need for methods to interpret these and other continental data with confidence. In response to this challenge a rapid expansion of the N. American carbon cycle observational network is underway. This expansion includes a network of continuous, continental CO2 mixing ratio observations being collected at a subset of AmeriFlux towers. Progress in developing this resource includes instrument development, site installation, calibration and intercalibration efforts, and initiation of a uniform data product. Progess in applying these data include proposed methods for interpreting surface layer measurements in atmospheric inversions (the virtual tall towers approach), examination of coherence patterns in continental mixing ratios in response to weather and climate, and application of these mixing ratio measurements in formal atmospheric inversions. Future work will merge these methods with interpretation of flux towers observations of terrestrial carbon fluxes in an effort to create a single coherent diagnosis of North American terrestrial carbon fluxes over a multi-year period.

  5. Assessing Upper Extremity Motor Function in Practice of Virtual Activities of Daily Living

    PubMed Central

    Adams, Richard J.; Lichter, Matthew D.; Krepkovich, Eileen T.; Ellington, Allison; White, Marga; Diamond, Paul T.

    2015-01-01

    A study was conducted to investigate the criterion validity of measures of upper extremity (UE) motor function derived during practice of virtual activities of daily living (ADLs). Fourteen hemiparetic stroke patients employed a Virtual Occupational Therapy Assistant (VOTA), consisting of a high-fidelity virtual world and a Kinect™ sensor, in four sessions of approximately one hour in duration. An Unscented Kalman Filter-based human motion tracking algorithm estimated UE joint kinematics in real-time during performance of virtual ADL activities, enabling both animation of the user’s avatar and automated generation of metrics related to speed and smoothness of motion. These metrics, aggregated over discrete sub-task elements during performance of virtual ADLs, were compared to scores from an established assessment of UE motor performance, the Wolf Motor Function Test (WMFT). Spearman’s rank correlation analysis indicates a moderate correlation between VOTA-derived metrics and the time-based WMFT assessments, supporting the criterion validity of VOTA measures as a means of tracking patient progress during an UE rehabilitation program that includes practice of virtual ADLs. PMID:25265612

  6. Controlling Contagion Processes in Activity Driven Networks

    NASA Astrophysics Data System (ADS)

    Liu, Suyu; Perra, Nicola; Karsai, Márton; Vespignani, Alessandro

    2014-03-01

    The vast majority of strategies aimed at controlling contagion processes on networks consider the connectivity pattern of the system either quenched or annealed. However, in the real world, many networks are highly dynamical and evolve, in time, concurrently with the contagion process. Here, we derive an analytical framework for the study of control strategies specifically devised for a class of time-varying networks, namely activity-driven networks. We develop a block variable mean-field approach that allows the derivation of the equations describing the coevolution of the contagion process and the network dynamic. We derive the critical immunization threshold and assess the effectiveness of three different control strategies. Finally, we validate the theoretical picture by simulating numerically the spreading process and control strategies in both synthetic networks and a large-scale, real-world, mobile telephone call data set.

  7. Earthquake networks based on similar activity patterns.

    PubMed

    Tenenbaum, Joel N; Havlin, Shlomo; Stanley, H Eugene

    2012-10-01

    Earthquakes are a complex spatiotemporal phenomenon, the underlying mechanism for which is still not fully understood despite decades of research and analysis. We propose and develop a network approach to earthquake events. In this network, a node represents a spatial location while a link between two nodes represents similar activity patterns in the two different locations. The strength of a link is proportional to the strength of the cross correlation in activities of two nodes joined by the link. We apply our network approach to a Japanese earthquake catalog spanning the 14-year period 1985-1998. We find strong links representing large correlations between patterns in locations separated by more than 1000 kilometers, corroborating prior observations that earthquake interactions have no characteristic length scale. We find network characteristics not attributable to chance alone, including a large number of network links, high node assortativity, and strong stability over time. PMID:23214652

  8. Techniques for active embodiment of participants in virtual environments

    SciTech Connect

    Hightower, R.; Stansfield, S.

    1996-03-01

    This paper presents preliminary work in the development of an avatar driver. An avatar is the graphical embodiment of a user in a virtual world. In applications such as small team, close quarters training and mission planning and rehearsal, it is important that the user`s avatar reproduce his or her motions naturally and with high fidelity. This paper presents a set of special purpose algorithms for driving the motion of the avatar with minimal information about the posture and position of the user. These algorithms utilize information about natural human motion and posture to produce solutions quickly and accurately without the need for complex general-purpose kinematics algorithms. Several examples illustrating the successful applications of these techniques are included.

  9. Use of a virtual community to contextualize learning activities.

    PubMed

    Gonzalez, Laura; Fenske, Cynthia L

    2012-01-01

    This article reports the experiences of two schools of nursing using a virtual community (VC) and how integrated teaching strategies were developed, which lessened the gap between didactic and clinical applications. Exemplars for nursing education practice are highlighted. The term context as used in nursing education, means placing the particular concept, topic, or skill in a setting where it is given enhanced meaning to the learner. This strategy allows nursing students to better retain knowledge and apply new concepts. The VC detailed in this article provides students with such context to enhance learning. It also enhances student engagement by adding an additional level of complexity and richness. One advantage of the VC is the ability to present nursing education beyond the acute inpatient care setting. The VC allows students to observe how illness progresses and exacerbations occur. This pedagogical shift moves from content-driven didactic instruction to a learner-centered approach. PMID:22132719

  10. Virtual Reality as a Leisure Activity for Young Adults with Physical and Intellectual Disabilities

    ERIC Educational Resources Information Center

    Yalon-Chamovitz, Shira; Weiss, Patrice L.

    2008-01-01

    Participation in leisure activities is a fundamental human right and an important factor of quality of life. Adults with intellectual disabilities (ID) and physical disabilities often experience limited opportunities to participate in leisure activities, virtual reality (VR) technologies may serve to broaden their repertoire of accessible leisure…

  11. Contradictions between the Virtual and Physical High School Classroom: A Third-Generation Activity Theory Perspective

    ERIC Educational Resources Information Center

    Murphy, Elizabeth; Manzanares, Maria A. Rodriguez

    2008-01-01

    This paper uses a third-generation Activity Theory perspective to gain insight into the contradictions between the activity systems of the physical and virtual high school classroom from the perspective of teachers who had transitioned from one system to the other. Data collection relied on semi-structured interviews conducted with e-teachers as…

  12. Education and Outreach activities in the framework of the Spanish Virtual Observatory

    NASA Astrophysics Data System (ADS)

    Solano, E.; Rodrigo, C.

    2015-05-01

    In this paper we will describe the main education and outreach activities that are being conducted in the framework of the Spanish Virtual Observatory. In particular, we will outline the scientific and technical activities that are being done in collaboration with astronomical amateurs as well as the citizen science project to improve the orbits of near Earth asteroids using archive images.

  13. Understanding Player Activity in a Game-Based Virtual Learning Environment

    ERIC Educational Resources Information Center

    Boyer, David Matthew

    2011-01-01

    This study examines player activity in a game-based virtual learning environment as a means toward evaluating instructional and game design. By determining the goals embedded in project development and the availability and structure of in-game activities, the first part of this research highlights opportunities for players to engage with learning…

  14. Temporal percolation in activity-driven networks

    NASA Astrophysics Data System (ADS)

    Starnini, Michele; Pastor-Satorras, Romualdo

    2014-03-01

    We study the temporal percolation properties of temporal networks by taking as a representative example the recently proposed activity-driven-network model [N. Perra et al., Sci. Rep. 2, 469 (2012), 10.1038/srep00469]. Building upon an analytical framework based on a mapping to hidden variables networks, we provide expressions for the percolation time Tp marking the onset of a giant connected component in the integrated network. In particular, we consider both the generating function formalism, valid for degree-uncorrelated networks, and the general case of networks with degree correlations. We discuss the different limits of the two approaches, indicating the parameter regions where the correlated threshold collapses onto the uncorrelated case. Our analytical predictions are confirmed by numerical simulations of the model. The temporal percolation concept can be fruitfully applied to study epidemic spreading on temporal networks. We show in particular how the susceptible-infected-removed model on an activity-driven network can be mapped to the percolation problem up to a time given by the spreading rate of the epidemic process. This mapping allows us to obtain additional information on this process, not available for previous approaches.

  15. Multi-Hop Link Capacity of Multi-Route Multi-Hop MRC Diversity for a Virtual Cellular Network

    NASA Astrophysics Data System (ADS)

    Daou, Imane; Kudoh, Eisuke; Adachi, Fumiyuki

    In virtual cellular network (VCN), proposed for high-speed mobile communications, the signal transmitted from a mobile terminal is received by some wireless ports distributed in each virtual cell and relayed to the central port that acts as a gateway to the core network. In this paper, we apply the multi-route MHMRC diversity in order to decrease the transmit power and increase the multi-hop link capacity. The transmit power, the interference power and the link capacity are evaluated for DS-CDMA multi-hop VCN by computer simulation. The multi-route MHMRC diversity can be applied to not only DS-CDMA but also other access schemes (i. e. MC-CDMA, OFDM, etc.).

  16. The Convergence of Virtual Reality and Social Networks: Threats to Privacy and Autonomy.

    PubMed

    O'Brolcháin, Fiachra; Jacquemard, Tim; Monaghan, David; O'Connor, Noel; Novitzky, Peter; Gordijn, Bert

    2016-02-01

    The rapid evolution of information, communication and entertainment technologies will transform the lives of citizens and ultimately transform society. This paper focuses on ethical issues associated with the likely convergence of virtual realities (VR) and social networks (SNs), hereafter VRSNs. We examine a scenario in which a significant segment of the world's population has a presence in a VRSN. Given the pace of technological development and the popularity of these new forms of social interaction, this scenario is plausible. However, it brings with it ethical problems. Two central ethical issues are addressed: those of privacy and those of autonomy. VRSNs pose threats to both privacy and autonomy. The threats to privacy can be broadly categorized as threats to informational privacy, threats to physical privacy, and threats to associational privacy. Each of these threats is further subdivided. The threats to autonomy can be broadly categorized as threats to freedom, to knowledge and to authenticity. Again, these three threats are divided into subcategories. Having categorized the main threats posed by VRSNs, a number of recommendations are provided so that policy-makers, developers, and users can make the best possible use of VRSNs. PMID:25552240

  17. An integrated architecture for deploying a virtual private medical network over the web.

    PubMed

    Gritzalis, S; Gritzalis, D; Moulinos, C; Iliadis, J

    2001-01-01

    In this paper we describe a pilot architecture aiming at protecting Web-based medical applications through the development of a virtual private medical network. The basic technology, which is utilized by this integrated architecture, is the Trusted Third Party (TTP). In specific, a TTP is used to generate, distribute, and revoke digital certificates to/from medical practitioners and healthcare organizations wishing to communicate in a secure way. Digital certificates and digital signatures are, in particular, used to provide peer and data origin authentication and access control functionalities. We also propose a logical Public Key Infrastructure (PKI) architecture, which is robust, scalable, and based on standards. This architecture aims at supporting large-scale healthcare applications. It supports openness, scalability, flexibility and extensibility, and can be integrated with existing TTP schemes and infrastructures offering transparency and adequate security. Finally, it is demonstrated that the proposed architecture enjoys all desirable usability characteristics, and meets the set of criteria, which constitutes an applicable framework for the development of trusted medical services over the Web. PMID:11583408

  18. Virtual reality adaptive stimulation of limbic networks in the mental readiness training.

    PubMed

    Cosić, Kresimir; Popović, Sinisa; Kostović, Ivica; Judas, Milos

    2010-01-01

    A significant proportion of severe psychological problems in recent large-scale peacekeeping operations underscores the importance of effective methods for strengthening the stress resilience. Virtual reality (VR) adaptive stimulation, based on the estimation of the participant's emotional state from physiological signals, may enhance the mental readiness training (MRT). Understanding neurobiological mechanisms by which the MRT based on VR adaptive stimulation can affect the resilience to stress is important for practical application in the stress resilience management. After the delivery of a traumatic audio-visual stimulus in the VR, the cascade of events occurs in the brain, which evokes various physiological manifestations. In addition to the "limbic" emotional and visceral brain circuitry, other large-scale sensory, cognitive, and memory brain networks participate with less known impact in this physiological response. The MRT based on VR adaptive stimulation may strengthen the stress resilience through targeted brain-body interactions. Integrated interdisciplinary efforts, which would integrate the brain imaging and the proposed approach, may contribute to clarifying the neurobiological foundation of the resilience to stress. PMID:20543262

  19. The HMO Research Network Virtual Data Warehouse: A Public Data Model to Support Collaboration

    PubMed Central

    Ross, Tyler R.; Ng, Daniel; Brown, Jeffrey S.; Pardee, Roy; Hornbrook, Mark C.; Hart, Gene; Steiner, John F.

    2014-01-01

    The HMO Research Network (HMORN) Virtual Data Warehouse (VDW) is a public, non-proprietary, research-focused data model implemented at 17 health care systems across the United States. The HMORN has created a governance structure and specified policies concerning the VDW’s content, development, implementation, and quality assurance. Data extracted from the VDW have been used by thousands of studies published in peer-reviewed journal articles. Advances in software supporting care delivery and claims processing and the availability of new data sources have greatly expanded the data available for research, but substantially increased the complexity of data management. The VDW data model incorporates software and data advances to ensure that comprehensive, up-to-date data of known quality are available for research. VDW governance works to accommodate new data and system complexities. This article highlights the HMORN VDW data model, its governance principles, data content, and quality assurance procedures. Our goal is to share the VDW data model and its operations to those wishing to implement a distributed interoperable health care data system. PMID:25848584

  20. Spontaneous network activity and synaptic development

    PubMed Central

    Kerschensteiner, Daniel

    2014-01-01

    Throughout development, the nervous system produces patterned spontaneous activity. Research over the last two decades has revealed a core group of mechanisms that mediate spontaneous activity in diverse circuits. Many circuits engage several of these mechanisms sequentially to accommodate developmental changes in connectivity. In addition to shared mechanisms, activity propagates through developing circuits and neuronal pathways (i.e. linked circuits in different brain areas) in stereotypic patterns. Increasing evidence suggests that spontaneous network activity shapes synaptic development in vivo. Variations in activity-dependent plasticity may explain how similar mechanisms and patterns of activity can be employed to establish diverse circuits. Here, I will review common mechanisms and patterns of spontaneous activity in emerging neural networks and discuss recent insights into their contribution to synaptic development. PMID:24280071

  1. An Optimal CDS Construction Algorithm with Activity Scheduling in Ad Hoc Networks.

    PubMed

    Penumalli, Chakradhar; Palanichamy, Yogesh

    2015-01-01

    A new energy efficient optimal Connected Dominating Set (CDS) algorithm with activity scheduling for mobile ad hoc networks (MANETs) is proposed. This algorithm achieves energy efficiency by minimizing the Broadcast Storm Problem [BSP] and at the same time considering the node's remaining energy. The Connected Dominating Set is widely used as a virtual backbone or spine in mobile ad hoc networks [MANETs] or Wireless Sensor Networks [WSN]. The CDS of a graph representing a network has a significant impact on an efficient design of routing protocol in wireless networks. Here the CDS is a distributed algorithm with activity scheduling based on unit disk graph [UDG]. The node's mobility and residual energy (RE) are considered as parameters in the construction of stable optimal energy efficient CDS. The performance is evaluated at various node densities, various transmission ranges, and mobility rates. The theoretical analysis and simulation results of this algorithm are also presented which yield better results. PMID:26221627

  2. An Optimal CDS Construction Algorithm with Activity Scheduling in Ad Hoc Networks

    PubMed Central

    Penumalli, Chakradhar; Palanichamy, Yogesh

    2015-01-01

    A new energy efficient optimal Connected Dominating Set (CDS) algorithm with activity scheduling for mobile ad hoc networks (MANETs) is proposed. This algorithm achieves energy efficiency by minimizing the Broadcast Storm Problem [BSP] and at the same time considering the node's remaining energy. The Connected Dominating Set is widely used as a virtual backbone or spine in mobile ad hoc networks [MANETs] or Wireless Sensor Networks [WSN]. The CDS of a graph representing a network has a significant impact on an efficient design of routing protocol in wireless networks. Here the CDS is a distributed algorithm with activity scheduling based on unit disk graph [UDG]. The node's mobility and residual energy (RE) are considered as parameters in the construction of stable optimal energy efficient CDS. The performance is evaluated at various node densities, various transmission ranges, and mobility rates. The theoretical analysis and simulation results of this algorithm are also presented which yield better results. PMID:26221627

  3. NETWORK ACTIVATION DURING BIMANUAL MOVEMENTS IN HUMANS

    PubMed Central

    Walsh, RR; Small, SL; Chen, EE; Solodkin, A.

    2008-01-01

    The coordination of movement between the upper limbs is a function highly distributed across the animal kingdom. How the central nervous system generates such bilateral, synchronous movements, and how this differs from the generation of unilateral movements, remains uncertain. Electrophysiologic and functional imaging studies support that the activity of many brain regions during bimanual and unimanual movement are quite similar. Thus, the same brain regions (and indeed the same neurons) respond similarly during unimanual and bimanual movements as measured by electrophysiological responses. How then are different motor behaviors generated? To address this question, we studied unimanual and bimanual movements using fMRI and constructed networks of activation using Structural Equation Modeling (SEM). Our results suggest that (1) the dominant hemisphere appears to initiate activity responsible for bimanual movement; (2) activation during bimanual movement does not reflect the sum of right and left unimanual activation; (3) production of unimanual movement involves a network that is distinct from, and not a mirror of, the network for contralateral unimanual movement; and (4) using SEM, it is possible to obtain robust group networks representative of a population and to identify individual networks which can be used to detect subtle differences both between subjects as well as within a single subject over time. In summary, these results highlight a differential role for the dominant and non-dominant hemispheres during bimanual movements, further elaborating the concept of handedness and dominance. This knowledge increases our understanding of cortical motor physiology in health and after neurological damage. PMID:18718872

  4. A Survey of Students' Experiences on Collaborative Virtual Learning Activities Based on Five-Stage Model

    ERIC Educational Resources Information Center

    Karaman, M. Kemal; Özen, Sevil Orhan

    2016-01-01

    In this study, we aimed to design collaborative virtual learning (CVL) activities by using a five-stage model (FSM) and survey of students' experiences. The study group consisted of 14 voluntary students in the Turkish Teaching Department. In this case study, data were collected through observations, recordings in Second Life (SL) and interviews.…

  5. Physics Education Technology (PhET) Virtual Lab Activities for Distance Learning Courses

    NASA Astrophysics Data System (ADS)

    Callaway, Thomas

    2012-03-01

    The Physics Education Technology (PhET) simulations offer a great set of tools to present simulations of physics phenomena in the classroom. This presentation describes the use of PhET to develop virtual lab assignments that supplement hands-on lab activities for a distance learning class in conceptual physics.

  6. OpenSim-Supported Virtual Learning Environment: Transformative Content Representation, Facilitation, and Learning Activities

    ERIC Educational Resources Information Center

    Kim, Heesung; Ke, Fengfeng

    2016-01-01

    The pedagogical and design considerations for the use of a virtual reality (VR) learning environment are important for prospective and current teachers. However, empirical research investigating how preservice teachers interact with transformative content representation, facilitation, and learning activities in a VR educational simulation is still…

  7. Developing Adolescents' Resistance to Sexual Coercion through Role-Playing Activities in a Virtual World

    ERIC Educational Resources Information Center

    McGinn, Marion; Arnedillo-Sánchez, Inmaculada

    2015-01-01

    This paper explores the use of a three dimensional virtual world (3-DVW) to delivery assertiveness training to young adolescents. The case study aims to understand how a sense of presence in VWs facilitates and affect the performance of students role-playing activities to enhance their ability to resist sexual coercion. The results indicate that a…

  8. 3-Dimensional and Interactive Istanbul University Virtual Laboratory Based on Active Learning Methods

    ERIC Educational Resources Information Center

    Ince, Elif; Kirbaslar, Fatma Gulay; Yolcu, Ergun; Aslan, Ayse Esra; Kayacan, Zeynep Cigdem; Alkan Olsson, Johanna; Akbasli, Ayse Ceylan; Aytekin, Mesut; Bauer, Thomas; Charalambis, Dimitris; Gunes, Zeliha Ozsoy; Kandemir, Ceyhan; Sari, Umit; Turkoglu, Suleyman; Yaman, Yavuz; Yolcu, Ozgu

    2014-01-01

    The purpose of this study is to develop a 3-dimensional interactive multi-user and multi-admin IUVIRLAB featuring active learning methods and techniques for university students and to introduce the Virtual Laboratory of Istanbul University and to show effects of IUVIRLAB on students' attitudes on communication skills and IUVIRLAB. Although…

  9. Human Activity Behavior and Gesture Generation in Virtual Worlds for Long- Duration Space Missions. Chapter 8

    NASA Technical Reports Server (NTRS)

    Sierhuis, Maarten; Clancey, William J.; Damer, Bruce; Brodsky, Boris; vanHoff, Ron

    2007-01-01

    A virtual worlds presentation technique with embodied, intelligent agents is being developed as an instructional medium suitable to present in situ training on long term space flight. The system combines a behavioral element based on finite state automata, a behavior based reactive architecture also described as subsumption architecture, and a belief-desire-intention agent structure. These three features are being integrated to describe a Brahms virtual environment model of extravehicular crew activity which could become a basis for procedure training during extended space flight.

  10. Navigated Active Learning in an International Academic Virtual Enterprise

    ERIC Educational Resources Information Center

    Horvath, Imre; Wiersma, Meindert; Duhovnik, Joze; Stroud, Ian

    2004-01-01

    Active learning is an educational paradigm that has been reinvented and methodologically underpinned many times in order to intensify learning in various forms. This paper presents a complex approach to active learning in a design-centred academic course with international participation. Research and design were considered as vehicles of active…

  11. Reconstructing Causal Biological Networks through Active Learning.

    PubMed

    Cho, Hyunghoon; Berger, Bonnie; Peng, Jian

    2016-01-01

    Reverse-engineering of biological networks is a central problem in systems biology. The use of intervention data, such as gene knockouts or knockdowns, is typically used for teasing apart causal relationships among genes. Under time or resource constraints, one needs to carefully choose which intervention experiments to carry out. Previous approaches for selecting most informative interventions have largely been focused on discrete Bayesian networks. However, continuous Bayesian networks are of great practical interest, especially in the study of complex biological systems and their quantitative properties. In this work, we present an efficient, information-theoretic active learning algorithm for Gaussian Bayesian networks (GBNs), which serve as important models for gene regulatory networks. In addition to providing linear-algebraic insights unique to GBNs, leading to significant runtime improvements, we demonstrate the effectiveness of our method on data simulated with GBNs and the DREAM4 network inference challenge data sets. Our method generally leads to faster recovery of underlying network structure and faster convergence to final distribution of confidence scores over candidate graph structures using the full data, in comparison to random selection of intervention experiments. PMID:26930205

  12. Reconstructing Causal Biological Networks through Active Learning

    PubMed Central

    Cho, Hyunghoon; Berger, Bonnie; Peng, Jian

    2016-01-01

    Reverse-engineering of biological networks is a central problem in systems biology. The use of intervention data, such as gene knockouts or knockdowns, is typically used for teasing apart causal relationships among genes. Under time or resource constraints, one needs to carefully choose which intervention experiments to carry out. Previous approaches for selecting most informative interventions have largely been focused on discrete Bayesian networks. However, continuous Bayesian networks are of great practical interest, especially in the study of complex biological systems and their quantitative properties. In this work, we present an efficient, information-theoretic active learning algorithm for Gaussian Bayesian networks (GBNs), which serve as important models for gene regulatory networks. In addition to providing linear-algebraic insights unique to GBNs, leading to significant runtime improvements, we demonstrate the effectiveness of our method on data simulated with GBNs and the DREAM4 network inference challenge data sets. Our method generally leads to faster recovery of underlying network structure and faster convergence to final distribution of confidence scores over candidate graph structures using the full data, in comparison to random selection of intervention experiments. PMID:26930205

  13. Coordinated network activity in the hippocampus.

    PubMed

    Draguhn, Andreas; Keller, Martin; Reichinnek, Susanne

    2014-01-01

    The hippocampus expresses a variety of highly organized network states which bind its individual neurons into collective modes of activity. These patterns go along with characteristic oscillations of extracellular potential known as theta, gamma, and ripple oscillations. Such network oscillations share some important features throughout the entire central nervous system of higher animals: they are restricted to a defined behavioral state, they are mostly generated by subthreshold synaptic activity, and they entrain active neurons to fire action potentials at strictly defined phases of the oscillation cycle, thereby providing a unifying 'zeitgeber' for coordinated multineuronal activity. Recent work from the hippocampus of rodents and humans has revealed how the resulting spatiotemporal patterns support the formation of neuronal assemblies which, in our present understanding, form the neuronal correlate of spatial, declarative, or episodic memories. In this review, we introduce the major types of spatiotemporal activity patterns in the hippocampus, describe the underlying neuronal mechanisms, and illustrate the concept of memory formation within oscillating networks. Research on hippocampus-dependent memory has become a key model system at the interface between cellular and cognitive neurosciences. The next step will be to translate our increasing insight into the mechanisms and systemic functions of neuronal networks into urgently needed new therapeutic strategies. PMID:24777128

  14. "Active" and "passive" learning of three-dimensional object structure within an immersive virtual reality environment.

    PubMed

    James, K H; Humphrey, G K; Vilis, T; Corrie, B; Baddour, R; Goodale, M A

    2002-08-01

    We used a fully immersive virtual reality environment to study whether actively interacting with objects would effect subsequent recognition, when compared with passively observing the same objects. We found that when participants learned object structure by actively rotating the objects, the objects were recognized faster during a subsequent recognition task than when object structure was learned through passive observation. We also found that participants focused their study time during active exploration on a limited number of object views, while ignoring other views. Overall, our results suggest that allowing active exploration of an object during initial learning can facilitate recognition of that object, perhaps owing to the control that the participant has over the object views upon which they can focus. The virtual reality environment is ideal for studying such processes, allowing realistic interaction with objects while maintaining experimenter control. PMID:12395554

  15. It Takes a Virtual Community: Promoting Collaboration through Student Activities

    ERIC Educational Resources Information Center

    Battista, Ludmila; Forrey, Carol; Stevenson, Carolyn

    2008-01-01

    Distance education provides many nontraditional students with the opportunity to pursue a college education not possible through traditional brick and mortar education. Although not meeting face-to-face, student activities help promote a stronger connection between the classroom and university community. This paper will discuss strategies for…

  16. Student Activity and Learning Outcomes in a Virtual Learning Environment

    ERIC Educational Resources Information Center

    Romanov, Kalle; Nevgi, Anne

    2008-01-01

    The aim of the study was to explore the relationship between degree of participation and learning outcomes in an e-learning course on medical informatics. Overall activity in using course materials and degree of participation in the discussion forums of an online course were studied among 39 medical students. Students were able to utilise the…

  17. A mountain environmental virtual observatory (Mountain-EVO) to support participatory monitoring in a network of Andean catchments

    NASA Astrophysics Data System (ADS)

    Buytaert, Wouter; Ochoa Tocachi, Boris; De Bievre, Bert; Zulkafli, Zed

    2015-04-01

    The tropical Andes are a hotspot of environmental change. The combination of dramatic land-use change with global climate change, demographic growth, and increasing water demand is causing extreme pressures on water resources. This is of particular concern to rural upland communities. They are facing a double challenge of maintaining their own livelihoods with dwindling natural resources, and at the same time supporting downstream ecosystem services such as a well buffered stream flow and good water quality. This challenge is complicated further by the acute lack of data on the hydrological functioning of Andean catchments. The factors controlling their hydrological response are extremely variable in space and time, including meteorological forcing, land cover types, soil properties and geology. This makes it very difficult to predict accurately the impact of human activities such as land use, ecosystem management, and watershed investments. Such predictions are essential for policy-making and sustainable ecosystem management. To tackle the issue of hydrological data scarcity in the tropical Andes, an initiative was set up to implement a network of hydrological monitoring of upland catchments in a pairwise fashion. Using a trading-space-for-time approach, the initiative intends to use these data to improve predictions about the impact of land-use changes and other ecosystem management practices on the hydrological response. Currently, over 25 catchments are being monitored for precipitation and streamflow in 9 sites located in Bolivia, Peru, Ecuador, and Venezuela. The sites are supported by local stakeholders and communities in a participatory monitoring scheme that otherwise would be impractical or prohibitively expensive. To overcome the technical challenges of monitoring hydrological variables in remote mountain areas, the initiative has set up a web-based infrastructure to support local technicians and stakeholders. Additionally, using open data standards such

  18. Sloppiness in Spontaneously Active Neuronal Networks

    PubMed Central

    Panas, Dagmara; Amin, Hayder; Maccione, Alessandro; Muthmann, Oliver; van Rossum, Mark; Berdondini, Luca

    2015-01-01

    Various plasticity mechanisms, including experience-dependent, spontaneous, as well as homeostatic ones, continuously remodel neural circuits. Yet, despite fluctuations in the properties of single neurons and synapses, the behavior and function of neuronal assemblies are generally found to be very stable over time. This raises the important question of how plasticity is coordinated across the network. To address this, we investigated the stability of network activity in cultured rat hippocampal neurons recorded with high-density multielectrode arrays over several days. We used parametric models to characterize multineuron activity patterns and analyzed their sensitivity to changes. We found that the models exhibited sloppiness, a property where the model behavior is insensitive to changes in many parameter combinations, but very sensitive to a few. The activity of neurons with sloppy parameters showed faster and larger fluctuations than the activity of a small subset of neurons associated with sensitive parameters. Furthermore, parameter sensitivity was highly correlated with firing rates. Finally, we tested our observations from cell cultures on an in vivo recording from monkey visual cortex and we confirm that spontaneous cortical activity also shows hallmarks of sloppy behavior and firing rate dependence. Our findings suggest that a small subnetwork of highly active and stable neurons supports group stability, and that this endows neuronal networks with the flexibility to continuously remodel without compromising stability and function. PMID:26041916

  19. Virtual Active Touch Using Randomly Patterned Intracortical Microstimulation

    PubMed Central

    O’Doherty, Joseph E.; Lebedev, Mikhail A.; Li, Zheng; Nicolelis, Miguel A.L.

    2012-01-01

    Intracortical microstimulation (ICMS) has promise as a means for delivering somatosensory feedback in neuroprosthetic systems. Various tactile sensations could be encoded by temporal, spatial, or spatiotemporal patterns of ICMS. However, the applicability of temporal patterns of ICMS to artificial tactile sensation during active exploration is unknown, as is the minimum discriminable difference between temporally modulated ICMS patterns. We trained rhesus monkeys in an active exploration task in which they discriminated periodic pulse-trains of ICMS (200 Hz bursts at a 10 Hz secondary frequency) from pulse trains with the same average pulse rate, but distorted periodicity (200 Hz bursts at a variable instantaneous secondary frequency). The statistics of the aperiodic pulse trains were drawn from a gamma distribution with mean inter-burst intervals equal to those of the periodic pulse trains. The monkeys distinguished periodic pulse trains from aperiodic pulse trains with coefficients of variation 0.25 or greater. Reconstruction of movement kinematics, extracted from the activity of neuronal populations recorded in the sensorimotor cortex concurrent with the delivery of ICMS feedback, improved when the recording intervals affected by ICMS artifacts were removed from analysis. These results add to the growing evidence that temporally patterned ICMS can be used to simulate a tactile sense for neuroprosthetic devices. PMID:22207642

  20. QoS differentiation scheme with multiple burst transmission and virtual resource reservation for optical burst switching networks

    NASA Astrophysics Data System (ADS)

    Arakawa, Yutaka; Yamanaka, Naoaki

    2007-08-01

    We propose what we believe to be a new scheme to provide basic quality of service (QoS) in optical burst switching networks. Our proposal consists of multiple burst transmission (MBT) and virtual resource reservation (VRR). With MBT, consecutive bursts headed to the same destination are serially transmitted, and, at the transmission of high-priority bursts, the wavelength resource reserved by the head burst is kept reserving for the following bursts. We call it VRR. Computer simulations show that our proposal offers a larger differentiation of burst loss than the conventional offset-based QoS differentiation scheme. Also, it can improve the burst loss rate of both high-priority and low-priority bursts. Moreover, it can minimize the burst loss rate of high-priority bursts even when the high-priority traffic occupies a large percentage of the network traffic. The proposed scheme can be applied to the future multiservice optical network architecture.

  1. Virtual Congresses

    PubMed Central

    Lecueder, Silvia; Manyari, Dante E.

    2000-01-01

    A new form of scientific medical meeting has emerged in the last few years—the virtual congress. This article describes the general role of computer technologies and the Internet in the development of this new means of scientific communication, by reviewing the history of “cyber sessions” in medical education and the rationale, methods, and initial results of the First Virtual Congress of Cardiology. Instructions on how to participate in this virtual congress, either actively or as an observer, are included. Current advantages and disadvantages of virtual congresses, their impact on the scientific community at large, and future developments and possibilities in this area are discussed. PMID:10641960

  2. Neural networks underlying affective states in a multimodal virtual environment: contributions to boredom

    PubMed Central

    Mathiak, Krystyna A.; Klasen, Martin; Zvyagintsev, Mikhail; Weber, René; Mathiak, Klaus

    2013-01-01

    The interaction of low perceptual stimulation or goal-directed behavior with a negative subjective evaluation may lead to boredom. This contribution to boredom may shed light on its neural correlates, which are poorly characterized so far. A video game served as simulation of free interactive behavior without interruption of the game’s narrative. Thirteen male German volunteers played a first-person shooter game (Tactical Ops: Assault on Terror) during functional magnetic resonance imaging (fMRI). Two independent coders performed the time-based analysis of the audio-visual game content. Boredom was operationalized as interaction of prolonged absence of goal-directed behavior with lowered affect in the Positive and Negative Affect Schedule (PANAS). A decrease of positive affect (PA) correlated with response amplitudes in bilateral insular clusters extending into the amygdala to prolonged inactive phases in a game play and an increase in negative affect (NA) was associated with higher responses in bilateral ventromedial prefrontal cortex (vmPFC). Precuneus and hippocampus responses were negatively correlated with changes in NA. We describe for the first time neural contributions to boredom, using a video game as complex virtual environment. Further our study confirmed that PA and NA are separable constructs, reflected by distinct neural patterns. PA may be associated with afferent limbic activity whereas NA with affective control. PMID:24348366

  3. Virtual Investigations of an Active Deep Sea Volcano

    NASA Astrophysics Data System (ADS)

    Sautter, L.; Taylor, M. M.; Fundis, A.; Kelley, D. S.; Elend, M.

    2013-12-01

    Axial Seamount, located on the Juan de Fuca spreading ridge 300 miles off the Oregon coast, is an active volcano whose summit caldera lies 1500 m beneath the sea surface. Ongoing construction of the Regional Scale Nodes (RSN) cabled observatory by the University of Washington (funded by the NSF Ocean Observatories Initiative) has allowed for exploration of recent lava flows and active hydrothermal vents using HD video mounted on the ROVs, ROPOS and JASON II. College level oceanography/marine geology online laboratory exercises referred to as Online Concept Modules (OCMs) have been created using video and video frame-captured mosaics to promote skill development for characterizing and quantifying deep sea environments. Students proceed at their own pace through a sequence of short movies with which they (a) gain background knowledge, (b) learn skills to identify and classify features or biota within a targeted environment, (c) practice these skills, and (d) use their knowledge and skills to make interpretations regarding the environment. Part (d) serves as the necessary assessment component of the laboratory exercise. Two Axial Seamount-focused OCMs will be presented: 1) Lava Flow Characterization: Identifying a Suitable Cable Route, and 2) Assessing Hydrothermal Vent Communities: Comparisons Among Multiple Sulfide Chimneys.

  4. A Network-Based Multi-Target Computational Estimation Scheme for Anticoagulant Activities of Compounds

    PubMed Central

    Li, Canghai; Chen, Lirong; Song, Jun; Tang, Yalin; Xu, Xiaojie

    2011-01-01

    Background Traditional virtual screening method pays more attention on predicted binding affinity between drug molecule and target related to a certain disease instead of phenotypic data of drug molecule against disease system, as is often less effective on discovery of the drug which is used to treat many types of complex diseases. Virtual screening against a complex disease by general network estimation has become feasible with the development of network biology and system biology. More effective methods of computational estimation for the whole efficacy of a compound in a complex disease system are needed, given the distinct weightiness of the different target in a biological process and the standpoint that partial inhibition of several targets can be more efficient than the complete inhibition of a single target. Methodology We developed a novel approach by integrating the affinity predictions from multi-target docking studies with biological network efficiency analysis to estimate the anticoagulant activities of compounds. From results of network efficiency calculation for human clotting cascade, factor Xa and thrombin were identified as the two most fragile enzymes, while the catalytic reaction mediated by complex IXa:VIIIa and the formation of the complex VIIIa:IXa were recognized as the two most fragile biological matter in the human clotting cascade system. Furthermore, the method which combined network efficiency with molecular docking scores was applied to estimate the anticoagulant activities of a serial of argatroban intermediates and eight natural products respectively. The better correlation (r = 0.671) between the experimental data and the decrease of the network deficiency suggests that the approach could be a promising computational systems biology tool to aid identification of anticoagulant activities of compounds in drug discovery. Conclusions This article proposes a network-based multi-target computational estimation method for

  5. Pathological tau disrupts ongoing network activity.

    PubMed

    Menkes-Caspi, Noa; Yamin, Hagar G; Kellner, Vered; Spires-Jones, Tara L; Cohen, Dana; Stern, Edward A

    2015-03-01

    Pathological tau leads to dementia and neurodegeneration in tauopathies, including Alzheimer's disease. It has been shown to disrupt cellular and synaptic functions, yet its effects on the function of the intact neocortical network remain unknown. Using in vivo intracellular and extracellular recordings, we measured ongoing activity of neocortical pyramidal cells during various arousal states in the rTg4510 mouse model of tauopathy, prior to significant cell death, when only a fraction of the neurons show pathological tau. In transgenic mice, membrane potential oscillations are slower during slow-wave sleep and under anesthesia. Intracellular recordings revealed that these changes are due to longer Down states and state transitions of membrane potentials. Firing rates of transgenic neurons are reduced, and firing patterns within Up states are altered, with longer latencies and inter-spike intervals. By changing the activity patterns of a subpopulation of affected neurons, pathological tau reduces the activity of the neocortical network. PMID:25704951

  6. Networks of Task Co-Activations

    PubMed Central

    Laird, Angela R.; Eickhoff, Simon B.; Rottschy, Claudia; Bzdok, Danilo; Ray, Kimberly L.; Fox, Peter T.

    2013-01-01

    Recent progress in neuroimaging informatics and meta-analytic techniques has enabled a novel domain of human brain connectomics research that focuses on task-dependent co-activation patterns across behavioral tasks and cognitive domains. Here, we review studies utilizing the BrainMap database to investigate data trends in the activation literature using methods such as meta-analytic connectivity modeling (MACM), connectivity-based parcellation (CPB), and independent component analysis (ICA). We give examples of how these methods are being applied to learn more about the functional connectivity of areas such as the amygdala, the default mode network, and visual area V5. Methods for analyzing the behavioral metadata corresponding to regions of interest and to their intrinsically connected networks are described as a tool for local functional decoding. We finally discuss the relation of observed co-activation connectivity results to resting state connectivity patterns, and provide implications for future work in this domain. PMID:23631994

  7. Motor Behavior Activates Bergmann Glial Networks

    PubMed Central

    Nimmerjahn, Axel; Mukamel, Eran A.; Schnitzer, Mark J.

    2010-01-01

    SUMMARY Although it is firmly established neuronal activity is a prime determinant of animal behavior, relationships between astrocytic excitation and animal behavior have remained opaque. Cerebellar Bergmann glia are radial astrocytes that are implicated in motor behavior and exhibit Ca2+-excitation. However, Ca2+-excitation in these cells has not previously been studied in behaving animals. Using two-photon microscopy we found that Bergmann glia exhibit three forms of Ca2+-excitation in awake behaving mice. Two of these are ongoing within the cerebellar vermis. During locomotor performance concerted Ca2+-excitation arises in networks of at least hundreds of Bergmann glia extending across several hundred microns or more. Concerted Ca2+-excitation was abolished by anesthesia or blockade of either neural activity or glutamatergic transmission. Thus, large networks of Bergmann glia can be activated by specific animal behaviors and undergo excitation of sufficient magnitude to potentially initiate macroscopic changes in brain dynamics or blood flow. PMID:19447095

  8. An insulin with the native sequence but virtually no activity.

    PubMed

    Wollmer, A; Gilge, G; Brandenburg, D; Gattner, H G

    1994-03-01

    The B24-B25 peptide bond of insulin was replaced by an ester bond. To our knowledge this is the first replacement of a main chain atom reported for the hormone. It is meant to eliminate a structurally important H-bond between the imino group of B25 and the carbonyl oxygen of A19, and consequently to enhance detachment of the C-terminal B chain from the underlying A chain. On the basis of independent experimental evidence this very conformational change is believed to be a prerequisite for receptor binding. It was thus anticipated that increased flexibility would increase receptor binding and activity. Intriguingly, porcine [B24-B25 CO-O]insulin (depsi-insulin) and likewise [B24-B25 CO-O]des-(B26-B30)insulin-B25-amide (depsi-DPI-amide) were found to be only 3-4% potent. PMID:8011179

  9. Position paper on active countermeasures for computer networks.

    SciTech Connect

    Van Randwyk, Jamie A.

    2003-07-01

    Computer security professionals have used passive network countermeasures for several years in order to secure computer networks. Passive countermeasures such as firewalls and intrusion detection systems are effective but their use alone is not enough to protect a network. Active countermeasures offer new ways of protecting a computer network. Corporations and government entities should adopt active network countermeasures as a means of protecting their computer networks.

  10. From Idea to Virtual Reality: ALADIN - The Adult Learning Documentation and Information Network. Report of a CONFINTEA V Workshop and Its Follow-Up.

    ERIC Educational Resources Information Center

    Giere, Ursula, Ed.; Imel, Susan, Ed.

    This publication contains the story of how the idea for a network conceived through CONFINTEA V became a [virtual] reality in ALADIN, the Adult Learning Documentation and Information Network. Part I contains 15 papers delivered as a part of the CONFINTEA workshop, "Global Community of Adult Learning through Information and Documentation:…

  11. Material Matters for Learning in Virtual Networks: A Case Study of a Professional Learning Programme Hosted in a Google+ Online Community

    ERIC Educational Resources Information Center

    Ackland, Aileen; Swinney, Ann

    2015-01-01

    In this paper, we draw on Actor-Network Theories (ANT) to explore how material components functioned to create gateways and barriers to a virtual learning network in the context of a professional development module in higher education. Students were practitioners engaged in family learning in different professional roles and contexts. The data…

  12. Intruder Activity Analysis under Unreliable Sensor Networks

    SciTech Connect

    Tae-Sic Yoo; Humberto E. Garcia

    2007-09-01

    This paper addresses the problem of counting intruder activities within a monitored domain by a sensor network. The deployed sensors are unreliable. We characterize imperfect sensors with misdetection and false-alarm probabilities. We model intruder activities with Markov Chains. A set of Hidden Markov Models (HMM) models the imperfect sensors and intruder activities to be monitored. A novel sequential change detection/isolation algorithm is developed to detect and isolate a change from an HMM representing no intruder activity to another HMM representing some intruder activities. Procedures for estimating the entry time and the trace of intruder activities are developed. A domain monitoring example is given to illustrate the presented concepts and computational procedures.

  13. The activation of interactive attentional networks.

    PubMed

    Xuan, Bin; Mackie, Melissa-Ann; Spagna, Alfredo; Wu, Tingting; Tian, Yanghua; Hof, Patrick R; Fan, Jin

    2016-04-01

    Attention can be conceptualized as comprising the functions of alerting, orienting, and executive control. Although the independence of these functions has been demonstrated, the neural mechanisms underlying their interactions remain unclear. Using the revised attention network test and functional magnetic resonance imaging, we examined cortical and subcortical activity related to these attentional functions and their interactions. Results showed that areas in the extended frontoparietal network (FPN), including dorsolateral prefrontal cortex, frontal eye fields (FEF), areas near and along the intraparietal sulcus, anterior cingulate and anterior insular cortices, basal ganglia, and thalamus were activated across multiple attentional functions. Specifically, the alerting function was associated with activation in the locus coeruleus (LC) in addition to regions in the FPN. The orienting functions were associated with activation in the superior colliculus (SC) and the FEF. The executive control function was mainly associated with activation of the FPN and cerebellum. The interaction effect of alerting by executive control was also associated with activation of the FPN, while the interaction effect of orienting validity by executive control was mainly associated with the activation in the pulvinar. The current findings demonstrate that cortical and specific subcortical areas play a pivotal role in the implementation of attentional functions and underlie their dynamic interactions. PMID:26794640

  14. On the Resource Efficiency of Virtual Concatenation in SDH/SONET Mesh Transport Networks Bearing Protected Scheduled Connections

    NASA Astrophysics Data System (ADS)

    Kuri, Josu�; Gagnaire, Maurice; Puech, Nicolas

    2005-10-01

    Virtual concatenation (VCAT) is a Synchronous Digital Hierarchy (SDH)/Synchronous Optical Network (SONET) network functionality recently standardized by the International Telecommunication Union Telecommunication Standardization Sector (ITU-T). VCAT provides the flexibility required to efficiently allocate network resources to Ethernet, Fiber Channel (FC), Enterprise System Connection (ESCON), and other important data traffic signals. In this article, we assess the resources' gain provided by VCAT with respect to contiguous concatenation (CCAT) in SDH/SONET mesh transport networks bearing protected scheduled connection demands (SCDs). As explained later, an SCD is a connection demand for which the set-up and tear-down dates are known in advance. We define mathematical models to quantify the add/drop and transmission resources required to instantiate a set of protected SCDs in VCAT-and CCAT-capable networks. Quantification of transmission resources requires a routing and slot assignment (RSA) problem to be solved. We formulate the RSA problem in VCAT-and CCAT-capable networks as two different combinatorial optimization problems: RSA in VCAT-capable networks (RSAv) and RSA in CCAT-capable networks (RSAc), respectively. Protection of the SCDs is considered in the formulations using a shared backup path protection (SBPP) technique. We propose a simulated annealing (SA)-based meta-heuristic algorithm to compute approximate solutions to these problems (i.e., solutions whose cost approximates the cost of the optimal ones). The gain in transmission resources and the cost structure of add/drop resources making VCAT-capable networks more economical are analyzed for different traffic scenarios.

  15. Using the Virtual Design Center

    NASA Astrophysics Data System (ADS)

    Kim, Beaumie

    2006-06-01

    The Virtual Design Center (http://vdc.cet.edu) provides research-based design guidelines for inquiry-based learning activities. The Virtual Design Center also provides educational researchers opportunities to share new knowledge about how practitioners could apply learning theories to learning activities. The participants will be introduced to the six-step process and the various services of the Virtual Design Center. The Virtual Design Center’s process has been tested mostly with NASA-funded projects (NASA Learning Technologies, NASA Explorer Schools Instructional Materials Development Grant program, NASA Digital Learning Network, NASA-sponsored Classroom of the Future, etc.), and we are working to expand its impact beyond the NASA community.

  16. Virtual reality and neuropsychological assessment: The reliability of a virtual kitchen to assess daily-life activities in victims of traumatic brain injury.

    PubMed

    Besnard, Jeremy; Richard, Paul; Banville, Frederic; Nolin, Pierre; Aubin, Ghislaine; Le Gall, Didier; Richard, Isabelle; Allain, Phillippe

    2016-01-01

    Traumatic brain injury (TBI) causes impairments affecting instrumental activities of daily living (IADL). However, few studies have considered virtual reality as an ecologically valid tool for the assessment of IADL in patients who have sustained a TBI. The main objective of the present study was to examine the use of the Nonimmersive Virtual Coffee Task (NI-VCT) for IADL assessment in patients with TBI. We analyzed the performance of 19 adults suffering from TBI and 19 healthy controls (HCs) in the real and virtual tasks of making coffee with a coffee machine, as well as in global IQ and executive functions. Patients performed worse than HCs on both real and virtual tasks and on all tests of executive functions. Correlation analyses revealed that NI-VCT scores were related to scores on the real task. Moreover, regression analyses demonstrated that performance on NI-VCT matched real-task performance. Our results support the idea that the virtual kitchen is a valid tool for IADL assessment in patients who have sustained a TBI. PMID:26569498

  17. Social Networking Sites as Virtual Communities of Practice: A Mixed Method Study

    ERIC Educational Resources Information Center

    Davis, Lorretta J.

    2010-01-01

    Membership in social networking sites is increasing rapidly. Social networking sites serve many purposes including networking, communication, recruitment, and sharing knowledge. Social networking sites, public or private, may be hosted on applications such as Facebook and LinkedIn. As individuals begin to follow and participate in social…

  18. Identification of a Selective G1-Phase Benzimidazolone Inhibitor by a Senescence-Targeted Virtual Screen Using Artificial Neural Networks12

    PubMed Central

    Bilsland, Alan E.; Pugliese, Angelo; Liu, Yu; Revie, John; Burns, Sharon; McCormick, Carol; Cairney, Claire J.; Bower, Justin; Drysdale, Martin; Narita, Masashi; Sadaie, Mahito; Keith, W. Nicol

    2015-01-01

    Cellular senescence is a barrier to tumorigenesis in normal cells, and tumor cells undergo senescence responses to genotoxic stimuli, which is a potential target phenotype for cancer therapy. However, in this setting, mixed-mode responses are common with apoptosis the dominant effect. Hence, more selective senescence inducers are required. Here we report a machine learning–based in silico screen to identify potential senescence agonists. We built profiles of differentially affected biological process networks from expression data obtained under induced telomere dysfunction conditions in colorectal cancer cells and matched these to a panel of 17 protein targets with confirmatory screening data in PubChem. We trained a neural network using 3517 compounds identified as active or inactive against these targets. The resulting classification model was used to screen a virtual library of ~ 2M lead-like compounds. One hundred and forty-seven virtual hits were acquired for validation in growth inhibition and senescence-associated β-galactosidase assays. Among the found hits, a benzimidazolone compound, CB-20903630, had low micromolar IC50 for growth inhibition of HCT116 cells and selectively induced senescence-associated β-galactosidase activity in the entire treated cell population without cytotoxicity or apoptosis induction. Growth suppression was mediated by G1 blockade involving increased p21 expression and suppressed cyclin B1, CDK1, and CDC25C. In addition, the compound inhibited growth of multicellular spheroids and caused severe retardation of population kinetics in long-term treatments. Preliminary structure-activity and structure clustering analyses are reported, and expression analysis of CB-20903630 against other cell cycle suppressor compounds suggested a PI3K/AKT-inhibitor–like profile in normal cells, with different pathways affected in cancer cells. PMID:26476078

  19. Shoulder Kinematics and Spatial Pattern of Trapezius Electromyographic Activity in Real and Virtual Environments

    PubMed Central

    Samani, Afshin; Pontonnier, Charles; Dumont, Georges; Madeleine, Pascal

    2015-01-01

    The design of an industrial workstation tends to include ergonomic assessment steps based on a digital mock-up and a virtual reality setup. Lack of interaction and system fidelity is often reported as a main issue in such virtual reality applications. This limitation is a crucial issue as thorough ergonomic analysis is required for an investigation of the biomechanics. In the current study, we investigated the biomechanical responses of the shoulder joint in a simulated assembly task for comparison with the biomechanical responses in virtual environments. Sixteen male healthy novice subjects performed the task on three different platforms: real (RE), virtual (VE), and virtual environment with force feedback (VEF) with low and high precision demands. The subjects repeated the task 12 times (i.e., 12 cycles). High density electromyography from the upper trapezius and rotation angles of the shoulder joint were recorded and split into the cycles. The angular trajectories and velocity profiles of the shoulder joint angles over a cycle were computed in 3D. The inter-subject similarity in terms of normalized mutual information on kinematics and electromyography was investigated. Compared with RE the task in VE and VEF was characterized by lower kinematic maxima. The inter-subject similarity in RE compared with intra-subject similarity across the platforms was lower in terms of movement trajectories and greater in terms of trapezius muscle activation. The precision demand resulted in lower inter- and intra-subject similarity across platforms. The proposed approach identifies biomechanical differences in the shoulder joint in both VE and VEF compared with the RE platform, but these differences are less marked in VE mostly due to technical limitations of co-localizing the force feedback system in the VEF platform. PMID:25768123

  20. Recurrent network activity drives striatal synaptogenesis.

    PubMed

    Kozorovitskiy, Yevgenia; Saunders, Arpiar; Johnson, Caroline A; Lowell, Bradford B; Sabatini, Bernardo L

    2012-05-31

    Neural activity during development critically shapes postnatal wiring of the mammalian brain. This is best illustrated by the sensory systems, in which the patterned feed-forward excitation provided by sensory organs and experience drives the formation of mature topographic circuits capable of extracting specific features of sensory stimuli. In contrast, little is known about the role of early activity in the development of the basal ganglia, a phylogenetically ancient group of nuclei fundamentally important for complex motor action and reward-based learning. These nuclei lack direct sensory input and are only loosely topographically organized, forming interlocking feed-forward and feed-back inhibitory circuits without laminar structure. Here we use transgenic mice and viral gene transfer methods to modulate neurotransmitter release and neuronal activity in vivo in the developing striatum. We find that the balance of activity between the two inhibitory and antagonist pathways in the striatum regulates excitatory innervation of the basal ganglia during development. These effects indicate that the propagation of activity through a multi-stage network regulates the wiring of the basal ganglia, revealing an important role of positive feedback in driving network maturation. PMID:22660328

  1. Virtual Labs and Virtual Worlds

    NASA Astrophysics Data System (ADS)

    Boehler, Ted

    2006-12-01

    Virtual Labs and Virtual Worlds Coastline Community College has under development several virtual lab simulations and activities that range from biology, to language labs, to virtual discussion environments. Imagine a virtual world that students enter online, by logging onto their computer from home or anywhere they have web access. Upon entering this world they select a personalized identity represented by a digitized character (avatar) that can freely move about, interact with the environment, and communicate with other characters. In these virtual worlds, buildings, gathering places, conference rooms, labs, science rooms, and a variety of other “real world” elements are evident. When characters move about and encounter other people (players) they may freely communicate. They can examine things, manipulate objects, read signs, watch video clips, hear sounds, and jump to other locations. Goals of critical thinking, social interaction, peer collaboration, group support, and enhanced learning can be achieved in surprising new ways with this innovative approach to peer-to-peer communication in a virtual discussion world. In this presentation, short demos will be given of several online learning environments including a virtual biology lab, a marine science module, a Spanish lab, and a virtual discussion world. Coastline College has been a leader in the development of distance learning and media-based education for nearly 30 years and currently offers courses through PDA, Internet, DVD, CD-ROM, TV, and Videoconferencing technologies. Its distance learning program serves over 20,000 students every year. sponsor Jerry Meisner

  2. Extended Virtual Spring Mesh (EVSM): The Distributed Self-Organizing Mobile Ad Hoc Network for Area Exploration

    SciTech Connect

    Kurt Derr

    2011-12-01

    Mobile Ad hoc NETworks (MANETs) are distributed self-organizing networks that can change locations and configure themselves on the fly. This paper focuses on an algorithmic approach for the deployment of a MANET within an enclosed area, such as a building in a disaster scenario, which can provide a robust communication infrastructure for search and rescue operations. While a virtual spring mesh (VSM) algorithm provides scalable, self-organizing, and fault-tolerant capabilities required by aMANET, the VSM lacks the MANET's capabilities of deployment mechanisms for blanket coverage of an area and does not provide an obstacle avoidance mechanism. This paper presents a new technique, an extended VSM (EVSM) algorithm that provides the following novelties: (1) new control laws for exploration and expansion to provide blanket coverage, (2) virtual adaptive springs enabling the mesh to expand as necessary, (3) adapts to communications disturbances by varying the density and movement of mobile nodes, and (4) new metrics to assess the performance of the EVSM algorithm. Simulation results show that EVSM provides up to 16% more coverage and is 3.5 times faster than VSM in environments with eight obstacles.

  3. Virtual Worlds for Virtual Organizing

    NASA Astrophysics Data System (ADS)

    Rhoten, Diana; Lutters, Wayne

    The members and resources of a virtual organization are dispersed across time and space, yet they function as a coherent entity through the use of technologies, networks, and alliances. As virtual organizations proliferate and become increasingly important in society, many may exploit the technical architecture s of virtual worlds, which are the confluence of computer-mediated communication, telepresence, and virtual reality originally created for gaming. A brief socio-technical history describes their early origins and the waves of progress followed by stasis that brought us to the current period of renewed enthusiasm. Examination of contemporary examples demonstrates how three genres of virtual worlds have enabled new arenas for virtual organizing: developer-defined closed worlds, user-modifiable quasi-open worlds, and user-generated open worlds. Among expected future trends are an increase in collaboration born virtually rather than imported from existing organizations, a tension between high-fidelity recreations of the physical world and hyper-stylized imaginations of fantasy worlds, and the growth of specialized worlds optimized for particular sectors, companies, or cultures.

  4. Can simple interactions capture complex features of neural activity underlying behavior in a virtual reality environment?

    NASA Astrophysics Data System (ADS)

    Meshulam, Leenoy; Gauthier, Jeffrey; Brody, Carlos; Tank, David; Bialek, William

    The complex neural interactions which are abundant in most recordings of neural activity are relatively poorly understood. A prime example of such interactions can be found in the in vivo neural activity which underlies complex behaviors of mice, imaged in brain regions such as hippocampus and parietal cortex. Experimental techniques now allow us to accurately follow these neural interactions in the simultaneous activity of large neuronal populations of awake behaving animals. Here, we demonstrate that pairwise maximum entropy models can predict a surprising number of properties of the neural activity. The models, that are constrained with activity rates and interactions between pairs of neurons, are well fit to the activity `states' in the hippocampus and cortex of mice performing cognitive tasks while navigating in a virtual reality environment.

  5. Virtual reality as a leisure activity for young adults with physical and intellectual disabilities.

    PubMed

    Yalon-Chamovitz, Shira; Weiss, Patrice L Tamar

    2008-01-01

    Participation in leisure activities is a fundamental human right and an important factor of quality of life. Adults with intellectual disabilities (ID) and physical disabilities often experience limited opportunities to participate in leisure activities, virtual reality (VR) technologies may serve to broaden their repertoire of accessible leisure activities. Although the use of VR in rehabilitation has grown over the past decade, few applications have been reported for people with ID. Thirty-three men and women with moderate ID and severe cerebral palsy participated in the study. Each participant in the experimental group (n=17) took part in VR activity two to three times weekly for 12 weeks. Virtual games were provided via GestureTek's Gesture Xtreme video capture VR system. The VR-based activities were perceived by the participants to be enjoyable and successful. Moreover, participants demonstrated clear preferences, initiation and learning. They performed consistently and maintained a high level of interest throughout the intervention period. VR appears to provide varied and motivating opportunities for leisure activities among young adults with intellectual and physical disabilities. Its ease of use and adaptability make it a feasible option for this population. PMID:17590313

  6. Performance evaluation of multi-stratum resources optimization with network functions virtualization for cloud-based radio over optical fiber networks.

    PubMed

    Yang, Hui; He, Yongqi; Zhang, Jie; Ji, Yuefeng; Bai, Wei; Lee, Young

    2016-04-18

    Cloud radio access network (C-RAN) has become a promising scenario to accommodate high-performance services with ubiquitous user coverage and real-time cloud computing using cloud BBUs. In our previous work, we implemented cross stratum optimization of optical network and application stratums resources that allows to accommodate the services in optical networks. In view of this, this study extends to consider the multiple dimensional resources optimization of radio, optical and BBU processing in 5G age. We propose a novel multi-stratum resources optimization (MSRO) architecture with network functions virtualization for cloud-based radio over optical fiber networks (C-RoFN) using software defined control. A global evaluation scheme (GES) for MSRO in C-RoFN is introduced based on the proposed architecture. The MSRO can enhance the responsiveness to dynamic end-to-end user demands and globally optimize radio frequency, optical and BBU resources effectively to maximize radio coverage. The efficiency and feasibility of the proposed architecture are experimentally demonstrated on OpenFlow-based enhanced SDN testbed. The performance of GES under heavy traffic load scenario is also quantitatively evaluated based on MSRO architecture in terms of resource occupation rate and path provisioning latency, compared with other provisioning scheme. PMID:27137302

  7. Medicine in long duration space exploration: the role of virtual reality and broad bandwidth telecommunications networks

    NASA Astrophysics Data System (ADS)

    Ross, Muriel D.

    2001-08-01

    Safety of astronauts during long-term space exploration is a priority for NASA. This paper describes efforts to produce Earth-based models for providing expert medical advice when unforeseen medical emergencies occur on spacecraft. These models are Virtual Collaborative Clinics that reach into remote sites using telecommunications and emerging stereo-imaging and sensor technologies.

  8. Impact of a Virtual Clinic in a Paediatric Cardiology Network on Northeast Brazil.

    PubMed

    de Araújo, Juliana Sousa Soares; Dias Filho, Adalberto Vieira; Silva Gomes, Renata Grigório; Regis, Cláudio Teixeira; Rodrigues, Klecida Nunes; Siqueira, Nicoly Negreiros; Albuquerque, Fernanda Cruz de Lira; Mourato, Felipe Alves; Mattos, Sandra da Silva

    2015-01-01

    Introduction. Congenital heart diseases (CHD) affect approximately 1% of live births and is an important cause of neonatal morbidity and mortality. Despite that, there is a shortage of paediatric cardiologists in Brazil, mainly in the northern and northeastern regions. In this context, the implementation of virtual outpatient clinics with the aid of different telemedicine resources may help in the care of children with heart defects. Methods. Patients under 18 years of age treated in virtual outpatient clinics between January 2013 and May 2014 were selected. They were divided into 2 groups: those who had and those who had not undergone a screening process for CHD in the neonatal period. Clinical and demographic characteristics were collected for further statistical analysis. Results. A total of 653 children and teenagers were treated in the virtual outpatient clinics. From these, 229 had undergone a neonatal screening process. Fewer abnormalities were observed on the physical examination of the screened patients. Conclusion. The implementation of pediatric cardiology virtual outpatient clinics can have a positive impact in the care provided to people in areas with lack of skilled professionals. PMID:26265913

  9. Impact of a Virtual Clinic in a Paediatric Cardiology Network on Northeast Brazil

    PubMed Central

    de Araújo, Juliana Sousa Soares; Dias Filho, Adalberto Vieira; Silva Gomes, Renata Grigório; Regis, Cláudio Teixeira; Rodrigues, Klecida Nunes; Siqueira, Nicoly Negreiros; Albuquerque, Fernanda Cruz de Lira; Mourato, Felipe Alves; Mattos, Sandra da Silva

    2015-01-01

    Introduction. Congenital heart diseases (CHD) affect approximately 1% of live births and is an important cause of neonatal morbidity and mortality. Despite that, there is a shortage of paediatric cardiologists in Brazil, mainly in the northern and northeastern regions. In this context, the implementation of virtual outpatient clinics with the aid of different telemedicine resources may help in the care of children with heart defects. Methods. Patients under 18 years of age treated in virtual outpatient clinics between January 2013 and May 2014 were selected. They were divided into 2 groups: those who had and those who had not undergone a screening process for CHD in the neonatal period. Clinical and demographic characteristics were collected for further statistical analysis. Results. A total of 653 children and teenagers were treated in the virtual outpatient clinics. From these, 229 had undergone a neonatal screening process. Fewer abnormalities were observed on the physical examination of the screened patients. Conclusion. The implementation of pediatric cardiology virtual outpatient clinics can have a positive impact in the care provided to people in areas with lack of skilled professionals. PMID:26265913

  10. The Design of the Virtual Company: Synergism of Learning and Working in a Networked Environment.

    ERIC Educational Resources Information Center

    Westera, Wim; Sloep, Peter B.; Gerrissen, Jack F.

    2000-01-01

    Describes the Virtual Company, a learning environment developed by the Open University (Netherlands) that is modeled after real companies to bridge the gap between learning and working by situating learning in a real-life business setting. Discusses problems in higher education, demands of society, and results of a pilot study. (Author/LRW)

  11. To Enhance Collaborative Learning and Practice Network Knowledge with a Virtualization Laboratory and Online Synchronous Discussion

    ERIC Educational Resources Information Center

    Hwang, Wu-Yuin; Kongcharoen, Chaknarin; Ghinea, Gheorghita

    2014-01-01

    Recently, various computer networking courses have included additional laboratory classes in order to enhance students' learning achievement. However, these classes need to establish a suitable laboratory where each student can connect network devices to configure and test functions within different network topologies. In this case, the Linux…

  12. The Virtual Research and Extension Communication Network (VRECN): An Interactive Learning and Communication Network for Research and Extension Personnel. Concept Paper for the Food & Agriculture Organisation of the United Nations (FAO).

    ERIC Educational Resources Information Center

    Richardson, Don

    A Virtual Research and Extension Communication Network (VRECN) is a set of networked electronic tools facilitating improvement in communication processes and information sharing among stakeholders involved in agricultural development. In developing countries, research and extension personnel within a ministry of agriculture, in consultation and…

  13. Performance evaluation of data center service localization based on virtual resource migration in software defined elastic optical network.

    PubMed

    Yang, Hui; Zhang, Jie; Ji, Yuefeng; Tan, Yuanlong; Lin, Yi; Han, Jianrui; Lee, Young

    2015-09-01

    Data center interconnection with elastic optical network is a promising scenario to meet the high burstiness and high-bandwidth requirements of data center services. In our previous work, we implemented cross stratum optimization of optical network and application stratums resources that allows to accommodate data center services. In view of this, this study extends the data center resources to user side to enhance the end-to-end quality of service. We propose a novel data center service localization (DCSL) architecture based on virtual resource migration in software defined elastic data center optical network. A migration evaluation scheme (MES) is introduced for DCSL based on the proposed architecture. The DCSL can enhance the responsiveness to the dynamic end-to-end data center demands, and effectively reduce the blocking probability to globally optimize optical network and application resources. The overall feasibility and efficiency of the proposed architecture are experimentally verified on the control plane of our OpenFlow-based enhanced SDN testbed. The performance of MES scheme under heavy traffic load scenario is also quantitatively evaluated based on DCSL architecture in terms of path blocking probability, provisioning latency and resource utilization, compared with other provisioning scheme. PMID:26368410

  14. Seismic active control by neural networks.

    SciTech Connect

    Tang, Y.

    1998-01-01

    A study on the application of artificial neural networks (ANNs) to activate structural control under seismic loads is carried out. The structure considered is a single-degree-of-freedom (SDF) system with an active bracing device. The control force is computed by a trained neural network. The feed-forward neural network architecture and an adaptive back-propagation training algorithm is used in the study. The neural net is trained to reproduce the function that represents the response-excitation relationship of the SDF system under seismic loads. The input-output training patterns are generated randomly. In the back-propagation training algorithm, the learning rate is determined by ensuring the decrease of the error function at each epoch. The computer program implemented is validated by solving the classification of the XOR problem. Then, the trained ANN is used to compute the control force according to the control strategy. If the control force exceeds the actuator's capacity limit, it is set equal to that limit. The concept of the control strategy employed herein is to apply the control force at every time step to cancel the system velocity induced at the preceding time step so that the gradual rhythmic buildup of the response is destroyed. The ground motions considered in the numerical example are the 1940 El Centro earthquake and the 1979 Imperial Valley earthquake in California. The system responses with and without the control are calculated and compared. The feasibility and potential of applying ANNs to seismic active control is asserted by the promising results obtained from the numerical examples studied.

  15. Seismic active control by neutral networks

    SciTech Connect

    Tang, Yu

    1995-12-31

    A study on the application of artificial neural networks (ANNs) to active structural control under seismic loads is carried out. The structure considered is a single-degree-of-freedom (SDF) system with an active bracing device. The control force is computed by a trained neural network. The feedforward neural network architecture and an adaptive backpropagation training algorithm is used in the study. The neural net is trained to reproduce the function that represents the response-excitation relationship of the SDF system under seismic loads. The input-output training patterns are generated randomly. In the backpropagation training algorithm, the learning rate is determined by ensuring the decrease of the error function at each epoch. The computer program implemented is validated by solving the classification of the XOR problem. Then, the trained ANN is used to compute the control force according to the control strategy. If the control force exceeds the actuator`s capacity limit, it is set equal to that limit. The concept of the control strategy employed herein is to apply the control force at every time step to cancel the system velocity induced at the preceding time step so that the gradual rhythmic buildup of the response is destroyed. The ground motions considered in the numerical example are the 1940 El Centro earthquake and the 1979 Imperial Valley earthquake in California. The system responses with and without the control are calculated and compared. The feasibility and potential of applying ANNs to seismic active control is asserted by the promising results obtained from the numerical examples studied.

  16. Active structural acoustic control of a smart cylindrical shell using a virtual microphone

    NASA Astrophysics Data System (ADS)

    Loghmani, Ali; Danesh, Mohammad; Kwak, Moon K.; Keshmiri, Mehdi

    2016-04-01

    This paper investigates the active structural acoustic control of sound radiated from a smart cylindrical shell. The cylinder is equipped with piezoelectric sensors and actuators to estimate and control the sound pressure that radiates from the smart shell. This estimated pressure is referred to as a virtual microphone, and it can be used in control systems instead of actual microphones to attenuate noise due to structural vibrations. To this end, the dynamic model for the smart cylinder is derived using the extended Hamilton’s principle, the Sanders shell theory and the assumed mode method. The simplified Kirchhoff-Helmholtz integral estimates the far-field sound pressure radiating from the baffled cylindrical shell. A modified higher harmonic controller that can cope with a harmonic disturbance is designed and experimentally evaluated. The experimental tests were carried out on a baffled cylindrical aluminum shell in an anechoic chamber. The frequency response for the theoretical virtual microphone and the experimental actual microphone are in good agreement with each other, and the results show the effectiveness of the designed virtual microphone and controller in attenuating the radiated sound.

  17. Illusion-related brain activations: a new virtual reality mirror box system for use during functional magnetic resonance imaging.

    PubMed

    Diers, Martin; Kamping, Sandra; Kirsch, Pinar; Rance, Mariela; Bekrater-Bodmann, Robin; Foell, Jens; Trojan, Joerg; Fuchs, Xaver; Bach, Felix; Maaß, Heiko; Cakmak, Hüseyin; Flor, Herta

    2015-01-12

    Extended viewing of movements of one's intact limb in a mirror as well as motor imagery have been shown to decrease pain in persons with phantom limb pain or complex regional pain syndrome and to increase the movement ability in hemiparesis following stroke. In addition, mirrored movements differentially activate sensorimotor cortex in amputees with and without phantom limb pain. However, using a so-called mirror box has technical limitations, some of which can be overcome by virtual reality applications. We developed a virtual reality mirror box application and evaluated its comparability to a classical mirror box setup. We applied both paradigms to 20 healthy controls and analyzed vividness and authenticity of the illusion as well as brain activation patterns. In both conditions, subjects reported similar intensities for the sensation that movements of the virtual left hand felt as if they were executed by their own left hand. We found activation in the primary sensorimotor cortex contralateral to the actual movement, with stronger activation for the virtual reality 'mirror box' compared to the classical mirror box condition, as well as activation in the primary sensorimotor cortex contralateral to the mirrored/virtual movement. We conclude that a virtual reality application of the mirror box is viable and that it might be useful for future research. PMID:25446453

  18. Carnegie Mellon's STUDIO for Creative Inquiry [and] The Interdisciplinary Teaching Network (ITeN) [and] Interactive Fiction [and] The Networked Virtual Art Museum.

    ERIC Educational Resources Information Center

    Holden, Lynn; And Others

    1992-01-01

    Explains the STUDIO for Creative Inquiry, an interdisciplinary center at Carnegie Mellon University that supports experimental activities in the arts, and its Interdisciplinary Teaching Network. Three STUDIO projects are described: the Ancient Egypt Prototype application of the network; an interactive fiction system based on artificial…

  19. Medicine in long duration space exploration: the role of virtual reality and broad bandwidth telecommunications networks

    NASA Technical Reports Server (NTRS)

    Ross, M. D.

    2001-01-01

    Safety of astronauts during long-term space exploration is a priority for NASA. This paper describes efforts to produce Earth-based models for providing expert medical advice when unforeseen medical emergencies occur on spacecraft. These models are Virtual Collaborative Clinics that reach into remote sites using telecommunications and emerging stereo-imaging and sensor technologies. c 2001. Elsevier Science Ltd. All rights reserved.

  20. Deep Neural Networks with Multistate Activation Functions

    PubMed Central

    Cai, Chenghao; Xu, Yanyan; Ke, Dengfeng; Su, Kaile

    2015-01-01

    We propose multistate activation functions (MSAFs) for deep neural networks (DNNs). These MSAFs are new kinds of activation functions which are capable of representing more than two states, including the N-order MSAFs and the symmetrical MSAF. DNNs with these MSAFs can be trained via conventional Stochastic Gradient Descent (SGD) as well as mean-normalised SGD. We also discuss how these MSAFs perform when used to resolve classification problems. Experimental results on the TIMIT corpus reveal that, on speech recognition tasks, DNNs with MSAFs perform better than the conventional DNNs, getting a relative improvement of 5.60% on phoneme error rates. Further experiments also reveal that mean-normalised SGD facilitates the training processes of DNNs with MSAFs, especially when being with large training sets. The models can also be directly trained without pretraining when the training set is sufficiently large, which results in a considerable relative improvement of 5.82% on word error rates. PMID:26448739

  1. Sum Product Networks for Activity Recognition.

    PubMed

    Amer, Mohamed R; Todorovic, Sinisa

    2016-04-01

    This paper addresses detection and localization of human activities in videos. We focus on activities that may have variable spatiotemporal arrangements of parts, and numbers of actors. Such activities are represented by a sum-product network (SPN). A product node in SPN represents a particular arrangement of parts, and a sum node represents alternative arrangements. The sums and products are hierarchically organized, and grounded onto space-time windows covering the video. The windows provide evidence about the activity classes based on the Counting Grid (CG) model of visual words. This evidence is propagated bottom-up and top-down to parse the SPN graph for the explanation of the video. The node connectivity and model parameters of SPN and CG are jointly learned under two settings, weakly supervised, and supervised. For evaluation, we use our new Volleyball dataset, along with the benchmark datasets VIRAT, UT-Interactions, KTH, and TRECVID MED 2011. Our video classification and activity localization are superior to those of the state of the art on these datasets. PMID:26390445

  2. Fractal Patterns of Neural Activity Exist within the Suprachiasmatic Nucleus and Require Extrinsic Network Interactions

    PubMed Central

    Hu, Kun; Meijer, Johanna H.; Shea, Steven A.; vanderLeest, Henk Tjebbe; Pittman-Polletta, Benjamin; Houben, Thijs; van Oosterhout, Floor; Deboer, Tom; Scheer, Frank A. J. L.

    2012-01-01

    The mammalian central circadian pacemaker (the suprachiasmatic nucleus, SCN) contains thousands of neurons that are coupled through a complex network of interactions. In addition to the established role of the SCN in generating rhythms of ∼24 hours in many physiological functions, the SCN was recently shown to be necessary for normal self-similar/fractal organization of motor activity and heart rate over a wide range of time scales—from minutes to 24 hours. To test whether the neural network within the SCN is sufficient to generate such fractal patterns, we studied multi-unit neural activity of in vivo and in vitro SCNs in rodents. In vivo SCN-neural activity exhibited fractal patterns that are virtually identical in mice and rats and are similar to those in motor activity at time scales from minutes up to 10 hours. In addition, these patterns remained unchanged when the main afferent signal to the SCN, namely light, was removed. However, the fractal patterns of SCN-neural activity are not autonomous within the SCN as these patterns completely broke down in the isolated in vitro SCN despite persistence of circadian rhythmicity. Thus, SCN-neural activity is fractal in the intact organism and these fractal patterns require network interactions between the SCN and extra-SCN nodes. Such a fractal control network could underlie the fractal regulation observed in many physiological functions that involve the SCN, including motor control and heart rate regulation. PMID:23185285

  3. Effectiveness of virtual reality exposure therapy for active duty soldiers in a military mental health clinic.

    PubMed

    Reger, Greg M; Holloway, Kevin M; Candy, Colette; Rothbaum, Barbara O; Difede, JoAnn; Rizzo, Albert A; Gahm, Gregory A

    2011-02-01

    Exposure therapy is an evidence-based treatment for posttraumatic stress disorder (PTSD), but research evaluating its effectiveness with active duty service members is limited. This report examines the effectiveness of virtual reality exposure therapy (VRE) for active duty soldiers (N = 24) seeking treatment following a deployment to Iraq or Afghanistan. Relative to their pretreatment self-reported symptoms on the PTSD Checklist, Military Version (M = 60.92; SD = 11.03), patients reported a significant reduction at posttreatment (M = 47.08; SD = 12.70; p < .001). Sixty-two percent of patients (n = 15) reported a reliable change of 11 points or more. This study supports the effectiveness of exposure therapy for active duty soldiers and extends previous research on VRE to this population. PMID:21294166

  4. Enabled scalable and privacy wavelength division multiplexing-radio over fiber system based on optical virtual private networks

    NASA Astrophysics Data System (ADS)

    Zhang, Qiaoyan; Zhang, Chongfu; Jin, Wei; Qiu, Kun

    2014-06-01

    A new wavelength division multiplexing (WDM)-based radio over fiber (RoF) system is proposed for optical virtual private network (OVPN) communication between inter-base stations (inter-BSs) or intra-BSs, using four-wave mixing (FWM) in a semiconductor optical amplifier as well as wavelength reflection of fiber Bragg gratings. By establishing inter-BSs and intra-BSs OVPN link of a 60-GHz WDM-RoF system, the private channels for the communication of end users under different BSs of sub-RoFs can be provided. In our scheme, 58 and 60-GHz millimeter waves are used to carry OVPN data and downstream data, respectively. Furthermore, the scalability of the proposed system is improved by the integration of an RoF system, WDM, and FWM. The simulation results successfully verify the feasibility of our proposed scheme.

  5. Recent work on network application layer: MioNet, the virtual workplace for small businesses

    NASA Astrophysics Data System (ADS)

    Hesselink, Lambertus; Rizal, Dharmarus; Bjornson, Eric; Miller, Brian; Chan, Keith

    2005-11-01

    Small businesses must be extremely efficient and smartly leverage their resources, suppliers, and partners to successfully compete with larger firms. A successful small business requires a set of companies with interlocking business relationships that are dynamic and needs-based. There has been no software solution that creates a secure and flexible way to efficiently connect small business computer-based employees and partners. In this invited paper, we discuss MioNet, a secure and powerful data management platform which may provide millions of small businesses with a virtual workplace and help them to succeed.

  6. VObs.it, the Italian contribution to the international Virtual Observatory-History, activities, strategy

    NASA Astrophysics Data System (ADS)

    Pasian, F.

    2015-06-01

    The origins of the Italian contribution to the international Virtual Observatory (VO) were mainly tied to the definition and implementation of a Data Grid using Grid standards. From there on, by means of a step-wise evolution, activities started including the implementation of VO-aware tools and facilities, or the production of services accessing data archives in ways compliant to the international VO standards. An important activity the Italian VO community has carried out is the dissemination of the VO capabilities to professionals, students and amateurs: in particular, an important and maybe unique success has been bringing to the classrooms the VO, and using it as a powerful tool to teach astronomy at all levels, from junior high school to undergraduate courses. Lately, there has been also direct involvement of the Italian community in the definition of standards and services within the framework of the International Virtual Observatory Alliance (IVOA), and participation and leadership in the IVOA Working Groups. Along this path, the national funding for these activities has been rather low, although essential to carry the activities on. There were no bursts of funding to allow a quick rise in activities leading to the fast realisation of tools and systems. Rather, the manpower involved in VObs.it has been always fairly low but steady. In the view of managing a national VO initiative with a low budget, strategic choices were made to exploit the available resources and to guarantee a constant background activity, mainly geared at providing services to the community, development in lower-priority VO areas, dissemination and support.

  7. Brain activity in goal-directed movements in a real compared to a virtual environment using the Nintendo Wii.

    PubMed

    Baumeister, Jochen; Reinecke, Kirsten; Cordes, Marjolijn; Lerch, Christiane; Weiss, Michael

    2010-08-30

    Low budget virtual environments like the Nintendo Wii increased in popularity and may play a role in motor learning related to sports and exercise. But nothing was known about the comparability of cortical activity of motor tasks in real and virtual environments. The aim of the study was to examine cortical differences between real and Wii based virtual sports performances using the golf putt as a model. Ten male golfers (26.0 +/- 0.7 years; 81.8 +/- 5.6 kg; 184.5 +/- 6.0 cm; handicap 30.0+/-10.0; 2.9+/-1.0 years of golf experience) were asked to putt for 3 min in random order in the real and the virtual Wii condition. A rest in sitting position (3 min) followed each performance. The score and cortical activity (EEG) were recorded continuously. The participants performed with a significant better score in the real condition (p < or = 0.01). Compared to virtual putting Theta spectral power showed a significant increase during real performance at F3 and F4 (p < or = 0.05). Significantly increased Alpha-2 power was demonstrated during real putting compared to the virtual putting performance at P3 (p < or = 0.05). The findings suggested that putting performance and brain activity was influenced by the choice of a real or virtual environment. The results were discussed based on the concept of the working memory where increased frontal Theta power indicated higher focused attention and higher Alpha-2 power was inversely related to the quantity of sensory information processing in the real putting compared to the virtual condition. PMID:20600604

  8. How Older Adults Use Virtual Personal Learning Networks to Support Informal, Self-Directed Lifelong Learning Goals: A Research Program Description

    ERIC Educational Resources Information Center

    Morrison, Dirk

    2015-01-01

    This short paper will describe the details of a SSHRC/IDG-funded research program currently underway (2015-2016) that will investigate how older adults (65+) use Web 2.0 tools and Internet-based resources to establish and expand their virtual personal learning networks (PLNs) for the purposes of enriching their expertise and knowledge within the…

  9. Aircraft panel with sensorless active sound power reduction capabilities through virtual mechanical impedances

    NASA Astrophysics Data System (ADS)

    Boulandet, R.; Michau, M.; Micheau, P.; Berry, A.

    2016-01-01

    This paper deals with an active structural acoustic control approach to reduce the transmission of tonal noise in aircraft cabins. The focus is on the practical implementation of the virtual mechanical impedances method by using sensoriactuators instead of conventional control units composed of separate sensors and actuators. The experimental setup includes two sensoriactuators developed from the electrodynamic inertial exciter and distributed over an aircraft trim panel which is subject to a time-harmonic diffuse sound field. The target mechanical impedances are first defined by solving a linear optimization problem from sound power measurements before being applied to the test panel using a complex envelope controller. Measured data are compared to results obtained with sensor-actuator pairs consisting of an accelerometer and an inertial exciter, particularly as regards sound power reduction. It is shown that the two types of control unit provide similar performance, and that here virtual impedance control stands apart from conventional active damping. In particular, it is clear from this study that extra vibrational energy must be provided by the actuators for optimal sound power reduction, mainly due to the high structural damping in the aircraft trim panel. Concluding remarks on the benefits of using these electrodynamic sensoriactuators to control tonal disturbances are also provided.

  10. The effect of virtual reality-based eccentric training on lower extremity muscle activation and balance in stroke patients.

    PubMed

    Park, Seung Kyu; Yang, Dae Jung; Uhm, Yo Han; Heo, Jae Won; Kim, Je Ho

    2016-07-01

    [Purpose] The purpose of this study was to examine the effect of virtual reality-based eccentric training on lower extremity muscle activity and balance in stroke patients. [Subjects and Methods] Thirty stroke patients participated, with 15 patients allotted to each of two eccentric training groups: one using a slow velocity (group I) and one using a fast velocity (group II). The virtual reality-based eccentric training was performed by the patients for 30 minutes once a day, 5 days a week, for 8 weeks using an Eccentron system. Surface electromyography was used to measure the lower extremity muscle activity, while a BioRescue was used to measure balancing ability. [Results] A significant difference in lower extremity muscle activation and balance ability was observed in group I compared with group II. [Conclusion] This study showed that virtual reality-based eccentric training using a slow velocity is effective for improving lower extremity muscle activity and balance in stroke patients. PMID:27512263

  11. The effect of virtual reality-based eccentric training on lower extremity muscle activation and balance in stroke patients

    PubMed Central

    Park, Seung Kyu; Yang, Dae Jung; Uhm, Yo Han; Heo, Jae Won; Kim, Je Ho

    2016-01-01

    [Purpose] The purpose of this study was to examine the effect of virtual reality-based eccentric training on lower extremity muscle activity and balance in stroke patients. [Subjects and Methods] Thirty stroke patients participated, with 15 patients allotted to each of two eccentric training groups: one using a slow velocity (group I) and one using a fast velocity (group II). The virtual reality-based eccentric training was performed by the patients for 30 minutes once a day, 5 days a week, for 8 weeks using an Eccentron system. Surface electromyography was used to measure the lower extremity muscle activity, while a BioRescue was used to measure balancing ability. [Results] A significant difference in lower extremity muscle activation and balance ability was observed in group I compared with group II. [Conclusion] This study showed that virtual reality-based eccentric training using a slow velocity is effective for improving lower extremity muscle activity and balance in stroke patients. PMID:27512263

  12. Dynamics of Actively Driven Crosslinked Microtubule Networks

    NASA Astrophysics Data System (ADS)

    Yadav, Vikrant; Stanhope, Kasimira; Evans, Arthur A.; Ross, Jennifer L.

    We have designed a model experiment to explore dynamics of crosslinked active microtubule clusters crosslinked with MAP65. Microtubule clusters are allowed to settle on a slide coated with kinesin-1 molecular motors, which move microtubules. We systematically tune either concentration of cross linkers bound to microtubule (ρc) or the global concentration of microtubules (ρMT) . We quantified the shape of the cluster by measuring the standard deviation (σ) of the cluster outline. At low ρMTor ρc the network is in an expanding state. At higher ρMTor ρc expansion slows down, reaches zero at a critical density, and become negative indicating contraction. Further increase of ρMTor ρc halts any kind of dynamics. The ρMT-ρc phase space shows distinct regions of extensile, contractile and static regimes. We model these results using active hydrodynamic theory. Microtubules are modeled as active rods whereas effect of crosslinkers is modeled using a collision term that prefers anti-parallel alignment of microtubules. A linearized analysis of hydrodynamic equation predicts existence of density driven expanding, contracting, and static phases for microtubule clusters.

  13. A Virtual Screening Approach For Identifying Plants with Anti H5N1 Neuraminidase Activity

    PubMed Central

    2016-01-01

    Recent outbreaks of highly pathogenic and occasional drug-resistant influenza strains have highlighted the need to develop novel anti-influenza therapeutics. Here, we report computational and experimental efforts to identify influenza neuraminidase inhibitors from among the 3000 natural compounds in the Malaysian-Plants Natural-Product (NADI) database. These 3000 compounds were first docked into the neuraminidase active site. The five plants with the largest number of top predicted ligands were selected for experimental evaluation. Twelve specific compounds isolated from these five plants were shown to inhibit neuraminidase, including two compounds with IC50 values less than 92 μM. Furthermore, four of the 12 isolated compounds had also been identified in the top 100 compounds from the virtual screen. Together, these results suggest an effective new approach for identifying bioactive plant species that will further the identification of new pharmacologically active compounds from diverse natural-product resources. PMID:25555059

  14. A virtual screening approach for identifying plants with anti H5N1 neuraminidase activity.

    PubMed

    Ikram, Nur Kusaira Khairul; Durrant, Jacob D; Muchtaridi, Muchtaridi; Zalaludin, Ayunni Salihah; Purwitasari, Neny; Mohamed, Nornisah; Rahim, Aisyah Saad Abdul; Lam, Chan Kit; Normi, Yahaya M; Rahman, Noorsaadah Abd; Amaro, Rommie E; Wahab, Habibah A

    2015-02-23

    Recent outbreaks of highly pathogenic and occasional drug-resistant influenza strains have highlighted the need to develop novel anti-influenza therapeutics. Here, we report computational and experimental efforts to identify influenza neuraminidase inhibitors from among the 3000 natural compounds in the Malaysian-Plants Natural-Product (NADI) database. These 3000 compounds were first docked into the neuraminidase active site. The five plants with the largest number of top predicted ligands were selected for experimental evaluation. Twelve specific compounds isolated from these five plants were shown to inhibit neuraminidase, including two compounds with IC50 values less than 92 μM. Furthermore, four of the 12 isolated compounds had also been identified in the top 100 compounds from the virtual screen. Together, these results suggest an effective new approach for identifying bioactive plant species that will further the identification of new pharmacologically active compounds from diverse natural-product resources. PMID:25555059

  15. Active route learning in virtual environments: disentangling movement control from intention, instruction specificity, and navigation control.

    PubMed

    von Stülpnagel, Rul; Steffens, Melanie C

    2013-09-01

    Active navigation research examines how physiological and psychological involvement in navigation benefits spatial learning. However, existing conceptualizations of active navigation comprise separable, distinct factors. This research disentangles the contributions of movement control (i.e., self-contained vs. observed movement) as a central factor from learning intention (Experiment 1), instruction specificity and instruction control (Experiment 2), as well as navigation control (Experiment 3) to spatial learning in virtual environments. We tested the effects of these factors on landmark recognition (landmark knowledge), tour-integration and route navigation (route knowledge). Our findings suggest that movement control leads to robust advantages in landmark knowledge as compared to observed movement. Advantages in route knowledge do not depend on learning intention, but on the need to elaborate spatial information. Whenever the necessary level of elaboration is assured for observed movement, too, the development of route knowledge is not inferior to that for self-contained movement. PMID:22922991

  16. Discovery of KDM5A inhibitors: Homology modeling, virtual screening and structure-activity relationship analysis.

    PubMed

    Wu, Xiaoai; Fang, Zhen; Yang, Bo; Zhong, Lei; Yang, Qiuyuan; Zhang, Chunhui; Huang, Shenzhen; Xiang, Rong; Suzuki, Takayoshi; Li, Lin-Li; Yang, Sheng-Yong

    2016-05-01

    Herein we report the discovery of a series of new KDM5A inhibitors. A three-dimensional (3D) structure model of KDM5A jumonji domain was firstly established based on homology modeling. Molecular docking-based virtual screening was then performed against commercial chemical databases. A number of hit compounds were retrieved. Further structural optimization and structure-activity relationship (SAR) analysis were carried out to the most active hit compound, 9 (IC50: 2.3μM), which led to the discovery of several new KDM5A inhibitors. Among them, compound 15e is the most potent one with an IC50 value of 0.22μM against KDM5A. This compound showed good selectivity for KDM5A and considerable ability to suppress the demethylation of H3K4me3 in intact cells. Compound 15e could be taken as a good lead compound for further studies. PMID:27020306

  17. A robotic system to train activities of daily living in a virtual environment.

    PubMed

    Guidali, Marco; Duschau-Wicke, Alexander; Broggi, Simon; Klamroth-Marganska, Verena; Nef, Tobias; Riener, Robert

    2011-10-01

    In the past decade, several arm rehabilitation robots have been developed to assist neurological patients during therapy. Early devices were limited in their number of degrees of freedom and range of motion, whereas newer robots such as the ARMin robot can support the entire arm. Often, these devices are combined with virtual environments to integrate motivating game-like scenarios. Several studies have shown a positive effect of game-playing on therapy outcome by increasing motivation. In addition, we assume that practicing highly functional movements can further enhance therapy outcome by facilitating the transfer of motor abilities acquired in therapy to daily life. Therefore, we present a rehabilitation system that enables the training of activities of daily living (ADL) with the support of an assistive robot. Important ADL tasks have been identified and implemented in a virtual environment. A patient-cooperative control strategy with adaptable freedom in timing and space was developed to assist the patient during the task. The technical feasibility and usability of the system was evaluated with seven healthy subjects and three chronic stroke patients. PMID:21796422

  18. Inter-BSs virtual private network for privacy and security enhanced 60 GHz radio-over-fiber system

    NASA Astrophysics Data System (ADS)

    Zhang, Chongfu; Chen, Chen; Zhang, Wei; Jin, Wei; Qiu, Kun; Li, Changchun; Jiang, Ning

    2013-06-01

    A novel inter-basestations (inter-BSs) based virtual private network (VPN) for the privacy and security enhanced 60 GHz radio-over-fiber (RoF) system using optical code-division multiplexing (OCDM) is proposed and demonstrated experimentally. By establishing inter-BSs VPN overlaying the network structure of a 60 GHz RoF system, the express and private paths for the communication of end-users under different BSs can be offered. In order to effectively establish the inter-BSs VPN, the OCDM encoding/decoding technology is employed in the RoF system. In each BS, a 58 GHz millimeter-wave (MMW) is used as the inter-BSs VPN channel, while a 60 GHz MMW is used as the common central station (CS)-BSs communication channel. The optical carriers used for the downlink, uplink and VPN link transmissions are all simultaneously generated in a lightwave-centralized CS, by utilizing four-wave mixing (FWM) effect in a semiconductor optical amplifier (SOA). The obtained results properly verify the feasibility of our proposed configuration of the inter-BSs VPN in the 60 GHz RoF system.

  19. Web-Based Virtual Patients in Nursing Education: Development and Validation of Theory-Anchored Design and Activity Models

    PubMed Central

    2014-01-01

    Background Research has shown that nursing students find it difficult to translate and apply their theoretical knowledge in a clinical context. Virtual patients (VPs) have been proposed as a learning activity that can support nursing students in their learning of scientific knowledge and help them integrate theory and practice. Although VPs are increasingly used in health care education, they still lack a systematic consistency that would allow their reuse outside of their original context. There is therefore a need to develop a model for the development and implementation of VPs in nursing education. Objective The aim of this study was to develop and evaluate a virtual patient model optimized to the learning and assessment needs in nursing education. Methods The process of modeling started by reviewing theoretical frameworks reported in the literature and used by practitioners when designing learning and assessment activities. The Outcome-Present State Test (OPT) model was chosen as the theoretical framework. The model was then, in an iterative manner, developed and optimized to the affordances of virtual patients. Content validation was performed with faculty both in terms of the relevance of the chosen theories but also its applicability in nursing education. The virtual patient nursing model was then instantiated in two VPs. The students’ perceived usefulness of the VPs was investigated using a questionnaire. The result was analyzed using descriptive statistics. Results A virtual patient Nursing Design Model (vpNDM) composed of three layers was developed. Layer 1 contains the patient story and ways of interacting with the data, Layer 2 includes aspects of the iterative process of clinical reasoning, and finally Layer 3 includes measurable outcomes. A virtual patient Nursing Activity Model (vpNAM) was also developed as a guide when creating VP-centric learning activities. The students perceived the global linear VPs as a relevant learning activity for the

  20. Network Patch Cables Demystified: A Super Activity for Computer Networking Technology

    ERIC Educational Resources Information Center

    Brown, Douglas L.

    2004-01-01

    This article de-mystifies network patch cable secrets so that people can connect their computers and transfer those pesky files--without screaming at the cables. It describes a network cabling activity that can offer students a great hands-on opportunity for working with the tools, techniques, and media used in computer networking. Since the…

  1. Prefrontal Cortex Activation Upon a Demanding Virtual Hand-Controlled Task: A New Frontier for Neuroergonomics.

    PubMed

    Carrieri, Marika; Petracca, Andrea; Lancia, Stefania; Basso Moro, Sara; Brigadoi, Sabrina; Spezialetti, Matteo; Ferrari, Marco; Placidi, Giuseppe; Quaresima, Valentina

    2016-01-01

    Functional near-infrared spectroscopy (fNIRS) is a non-invasive vascular-based functional neuroimaging technology that can assess, simultaneously from multiple cortical areas, concentration changes in oxygenated-deoxygenated hemoglobin at the level of the cortical microcirculation blood vessels. fNIRS, with its high degree of ecological validity and its very limited requirement of physical constraints to subjects, could represent a valid tool for monitoring cortical responses in the research field of neuroergonomics. In virtual reality (VR) real situations can be replicated with greater control than those obtainable in the real world. Therefore, VR is the ideal setting where studies about neuroergonomics applications can be performed. The aim of the present study was to investigate, by a 20-channel fNIRS system, the dorsolateral/ventrolateral prefrontal cortex (DLPFC/VLPFC) in subjects while performing a demanding VR hand-controlled task (HCT). Considering the complexity of the HCT, its execution should require the attentional resources allocation and the integration of different executive functions. The HCT simulates the interaction with a real, remotely-driven, system operating in a critical environment. The hand movements were captured by a high spatial and temporal resolution 3-dimensional (3D) hand-sensing device, the LEAP motion controller, a gesture-based control interface that could be used in VR for tele-operated applications. Fifteen University students were asked to guide, with their right hand/forearm, a virtual ball (VB) over a virtual route (VROU) reproducing a 42 m narrow road including some critical points. The subjects tried to travel as long as possible without making VB fall. The distance traveled by the guided VB was 70.2 ± 37.2 m. The less skilled subjects failed several times in guiding the VB over the VROU. Nevertheless, a bilateral VLPFC activation, in response to the HCT execution, was observed in all the subjects. No correlation was found

  2. Prefrontal Cortex Activation Upon a Demanding Virtual Hand-Controlled Task: A New Frontier for Neuroergonomics

    PubMed Central

    Carrieri, Marika; Petracca, Andrea; Lancia, Stefania; Basso Moro, Sara; Brigadoi, Sabrina; Spezialetti, Matteo; Ferrari, Marco; Placidi, Giuseppe; Quaresima, Valentina

    2016-01-01

    Functional near-infrared spectroscopy (fNIRS) is a non-invasive vascular-based functional neuroimaging technology that can assess, simultaneously from multiple cortical areas, concentration changes in oxygenated-deoxygenated hemoglobin at the level of the cortical microcirculation blood vessels. fNIRS, with its high degree of ecological validity and its very limited requirement of physical constraints to subjects, could represent a valid tool for monitoring cortical responses in the research field of neuroergonomics. In virtual reality (VR) real situations can be replicated with greater control than those obtainable in the real world. Therefore, VR is the ideal setting where studies about neuroergonomics applications can be performed. The aim of the present study was to investigate, by a 20-channel fNIRS system, the dorsolateral/ventrolateral prefrontal cortex (DLPFC/VLPFC) in subjects while performing a demanding VR hand-controlled task (HCT). Considering the complexity of the HCT, its execution should require the attentional resources allocation and the integration of different executive functions. The HCT simulates the interaction with a real, remotely-driven, system operating in a critical environment. The hand movements were captured by a high spatial and temporal resolution 3-dimensional (3D) hand-sensing device, the LEAP motion controller, a gesture-based control interface that could be used in VR for tele-operated applications. Fifteen University students were asked to guide, with their right hand/forearm, a virtual ball (VB) over a virtual route (VROU) reproducing a 42 m narrow road including some critical points. The subjects tried to travel as long as possible without making VB fall. The distance traveled by the guided VB was 70.2 ± 37.2 m. The less skilled subjects failed several times in guiding the VB over the VROU. Nevertheless, a bilateral VLPFC activation, in response to the HCT execution, was observed in all the subjects. No correlation was found

  3. Competition and cooperation between active intra-network and passive extra-network transport processes

    PubMed Central

    Maruyama, Dan; Zochowski, Michal

    2014-01-01

    Many networks are embedded in physical space and often interact with it. This interaction can be exemplified through constraints exerted on network topology, or through interactions of processes defined on a network with those that are linked to the space that the network is embedded within, leading to complex dynamics. Here we discuss an example of such an interaction in which a signaling agent is actively transported through the network edges and, at the same time, spreads passively through space due to diffusion. We show that these two processes cooperate or compete depending on the network topology leading to complex dynamics. PMID:24920178

  4. Virtual Screening Analysis and In-vitro Xanthine Oxidase Inhibitory Activity of Some Commercially Available Flavonoids.

    PubMed

    Umamaheswari, Muthuswamy; Madeswaran, Arumugam; Asokkumar, Kuppusamy

    2013-01-01

    Allopurinol, the xanthine oxidase inhibitor, is the only drug available for the treatment of gout. We examined the xanthine oxidase inhibitory activity of some commercially available flavonoids such asepigallocatechin, acacatechin, myricetin, naringenin, daidzein and glycitein by virtual screening and in-vitro studies. The interacting residues within the complex model and their contact types were identified. The virtual screening analysis were carried out using AutoDock 4.2 and in-vitro xanthine oxidase inhibitory activity was carried out using xanthine as the substrate. In addition, enzyme kinetics was performed using LineweaverBurkplot analysis. Allopurinol, a known xanthine oxidase inhibitor was used as the standard. The docking energy ofglycitein was found to be -8.49 kcal/mol which was less than that of the standard (-4.47 kcal/ mol). All the selected flavonoids were found to exhibit lower binding energy (-8.08 to -6.03 kcal/ mol) than allopurinol. The docking results confirm that flavonoids showed greater inhibition of xanthine oxidase due to their active binding sites and lesser binding energies compared to allopurinol. This may be attributed to the presence of benzopyran ring in the flavonoids. In the xanthine oxidase assay, IC50 value of glycitein was found to be 12±0.86 μg/mL, whereas that of allopurinol was 24±0.28 μg/mL. All the remaining compounds exhibited IC50 values ranging between 22±0.64 to 62±1.18 μg/mL. In the enzyme kinetic studies, flavonoids showed competitive type of enzyme inhibition. It can be concluded that flavonoids could be a promising remedy for the treatment of gout and related inflammatory disorders. Further in-vivo studies are required to develop potential compounds with lesser side effects. PMID:24250638

  5. Virtual Screening Analysis and In-vitro Xanthine Oxidase Inhibitory Activity of Some Commercially Available Flavonoids

    PubMed Central

    Umamaheswari, Muthuswamy; Madeswaran, Arumugam; Asokkumar, Kuppusamy

    2013-01-01

    Allopurinol, the xanthine oxidase inhibitor, is the only drug available for the treatment of gout. We examined the xanthine oxidase inhibitory activity of some commercially available flavonoids such asepigallocatechin, acacatechin, myricetin, naringenin, daidzein and glycitein by virtual screening and in-vitro studies. The interacting residues within the complex model and their contact types were identified. The virtual screening analysis were carried out using AutoDock 4.2 and in-vitro xanthine oxidase inhibitory activity was carried out using xanthine as the substrate. In addition, enzyme kinetics was performed using LineweaverBurkplot analysis. Allopurinol, a known xanthine oxidase inhibitor was used as the standard. The docking energy ofglycitein was found to be -8.49 kcal/mol which was less than that of the standard (-4.47 kcal/ mol). All the selected flavonoids were found to exhibit lower binding energy (-8.08 to -6.03 kcal/ mol) than allopurinol. The docking results confirm that flavonoids showed greater inhibition of xanthine oxidase due to their active binding sites and lesser binding energies compared to allopurinol. This may be attributed to the presence of benzopyran ring in the flavonoids. In the xanthine oxidase assay, IC50 value of glycitein was found to be 12±0.86 μg/mL, whereas that of allopurinol was 24±0.28 μg/mL. All the remaining compounds exhibited IC50 values ranging between 22±0.64 to 62±1.18 μg/mL. In the enzyme kinetic studies, flavonoids showed competitive type of enzyme inhibition. It can be concluded that flavonoids could be a promising remedy for the treatment of gout and related inflammatory disorders. Further in-vivo studies are required to develop potential compounds with lesser side effects. PMID:24250638

  6. Virtualization and Programming Support for Video Sensor Networks with Application to Wireless and Physical Security

    NASA Astrophysics Data System (ADS)

    Bestavros, Azer; Ocean, Michael J.

    Network Security Systems are heavily anchored in the digital plane of "cyber space" and hence cannot be used effectively to derive the physical identity of an intruder in order to prevent further malicious wireless broadcasts (i.e., escorting an intruder off the premises based on physical evidence). Embedded Sensor Networks (SNs) can be used to bridge the gap between digital and physical security planes, and thus can provide reciprocal benefit to security tasks on both planes. Toward that end, we present our experience integrating wireless networking security services into snBench (the Sensor Network workBench). snBench provides an extensible framework that enables the rapid development and automated deployment of SN applications on a shared, embedded sensing and actuation infrastructure. snBench's extensible architecture allows an engineer to quickly integrate new sensing and response capabilities into the snBench framework, while high-level languages, compilers and execution environments allow novice SN programmers to compose SN service logic, unaware of the lower-level components on which their services rely. Concrete examples are provided to illustrate the power and potential of Wireless Security Services that span both the physical and digital plane.

  7. Virtual Red Light Districts: Detecting Covert Networks and Sex Trafficking Circuits in the U.S.

    ERIC Educational Resources Information Center

    Ibanez, Michelle

    2015-01-01

    The United States is the second leading destination country for sex trafficking in the world. Increased effort to understand patterns of sex trafficking within the U.S. is imperative to combatting this issue. Covert networks are increasingly using information and communication technologies (ICTs) to extend their operations. Due to the increase in…

  8. Using Virtualization and Automatic Evaluation: Adapting Network Services Management Courses to the EHEA

    ERIC Educational Resources Information Center

    Ros, S.; Robles-Gomez, A.; Hernandez, R.; Caminero, A. C.; Pastor, R.

    2012-01-01

    This paper outlines the adaptation of a course on the management of network services in operating systems, called NetServicesOS, to the context of the new European Higher Education Area (EHEA). NetServicesOS is a mandatory course in one of the official graduate programs in the Faculty of Computer Science at the Universidad Nacional de Educacion a…

  9. Virtual Social Network Communities: An Investigation of Language Learners' Development of Sociopragmatic Awareness and Multiliteracy Skills

    ERIC Educational Resources Information Center

    Blattner, Geraldine; Fiori, Melissa

    2011-01-01

    Although often neglected in language textbooks and classrooms, sociopragmatic and multiliteracy skills are crucial elements in language learning that language educators should not disregard. This article investigates whether a social networking community (SNC) website such as Facebook can be exploited in the context of an intermediate foreign…

  10. Online Social Networks That Connect Users to Physical Activity Partners: A Review and Descriptive Analysis

    PubMed Central

    Passarella, Ralph Joseph; Appel, Lawrence J

    2014-01-01

    Background The US Centers for Disease Control and Prevention have identified a lack of encouragement, support, or companionship from family and friends as a major barrier to physical activity. To overcome this barrier, online social networks are now actively leveraging principles of companion social support in novel ways. Objective The aim was to evaluate the functionality, features, and usability of existing online social networks which seek to increase physical activity and fitness among users by connecting them to physical activity partners, not just online, but also face-to-face. Methods In September 2012, we used 3 major databases to identify the website addresses for relevant online social networks. We conducted a Google search using 8 unique keyword combinations: the common keyword “find” coupled with 1 of 4 prefix terms “health,” “fitness,” “workout,” or “physical” coupled with 1 of 2 stem terms “activity partners” or “activity buddies.” We also searched 2 prominent technology start-up news sites, TechCrunch and Y Combinator, using 2 unique keyword combinations: the common keyword “find” coupled with 1 of 2 stem terms “activity partners” and “activity buddies.” Sites were defined as online social health activity networks if they had the ability to (1) actively find physical activity partners or activities for the user, (2) offer dynamic, real-time tracking or sharing of social activities, and (3) provide virtual profiles to users. We excluded from our analysis sites that were not Web-based, publicly available, in English, or free. Results Of the 360 initial search results, we identified 13 websites that met our complete criteria of an online social health activity network. Features such as physical activity creation (13/13, 100%) and private messaging (12/13, 92%) appeared almost universally among these websites. However, integration with Web 2.0 technologies such as Facebook and Twitter (9/13, 69%) and the option of

  11. Virtual Manufacturing Techniques Designed and Applied to Manufacturing Activities in the Manufacturing Integration and Technology Branch

    NASA Technical Reports Server (NTRS)

    Shearrow, Charles A.

    1999-01-01

    One of the identified goals of EM3 is to implement virtual manufacturing by the time the year 2000 has ended. To realize this goal of a true virtual manufacturing enterprise the initial development of a machinability database and the infrastructure must be completed. This will consist of the containment of the existing EM-NET problems and developing machine, tooling, and common materials databases. To integrate the virtual manufacturing enterprise with normal day to day operations the development of a parallel virtual manufacturing machinability database, virtual manufacturing database, virtual manufacturing paradigm, implementation/integration procedure, and testable verification models must be constructed. Common and virtual machinability databases will include the four distinct areas of machine tools, available tooling, common machine tool loads, and a materials database. The machine tools database will include the machine envelope, special machine attachments, tooling capacity, location within NASA-JSC or with a contractor, and availability/scheduling. The tooling database will include available standard tooling, custom in-house tooling, tool properties, and availability. The common materials database will include materials thickness ranges, strengths, types, and their availability. The virtual manufacturing databases will consist of virtual machines and virtual tooling directly related to the common and machinability databases. The items to be completed are the design and construction of the machinability databases, virtual manufacturing paradigm for NASA-JSC, implementation timeline, VNC model of one bridge mill and troubleshoot existing software and hardware problems with EN4NET. The final step of this virtual manufacturing project will be to integrate other production sites into the databases bringing JSC's EM3 into a position of becoming a clearing house for NASA's digital manufacturing needs creating a true virtual manufacturing enterprise.

  12. Identities in flux: cognitive network activation in times of change.

    PubMed

    Menon, Tanya; Smith, Edward Bishop

    2014-05-01

    Using a dynamic cognitive model, we experimentally test two competing hypotheses that link identity and cognitive network activation during times of change. On one hand, affirming people's sense of power might give them confidence to think beyond the densest subsections of their social networks. Alternatively, if such power affirmations conflict with people's more stable status characteristics, this could create tension, deterring people from considering their networks' diversity. We test these competing hypotheses experimentally by priming people at varying levels of status with power (high/low) and asking them to report their social networks. We show that confirming identity-not affirming power-cognitively prepares people to broaden their social networks when the world is changing around them. The emotional signature of having a confirmed identity is feeling comfortable and in control, which mediates network activation. We suggest that stable, confirmed identities are the foundation from which people can exhibit greater network responsiveness. PMID:24576631

  13. Use of Virtual Patients in an Advanced Therapeutics Pharmacy Course to Promote Active, Patient-Centered Learning

    PubMed Central

    Mohammad, Rima A.; Benedict, Neal

    2014-01-01

    Objective. To assess student satisfaction and learning of course objectives following the integration of virtual patient cases designed to promote active, patient-centered learning in an advanced therapeutics pharmacy course. Design. A dynamic virtual patient platform that incorporated a branched-narrative, decision-making teaching model was used in an advanced therapeutics course to supplement lecture content. Assessment. Presimulation and postsimulation tests were used to assess student learning. The use of virtual patients significantly enhanced student learning for both higher- and lower-level test questions (p<0.001 and p=0.01, respectively). Students agreed or strongly agreed that the virtual patient cases provided an effective way to learn (72%), were enjoyable (69%), and were appropriate in content (80%), and that more should be incorporated (59%). Conclusion. The use of virtual patients in an advanced therapeutics practicum effectively promoted active, patient-centered learning; engaged students in an interactive and dynamic educational technology; encouraged teamwork; enhanced higher-level student learning; and improved student satisfaction in the course. PMID:25147397

  14. Age and active navigation effects on episodic memory: A virtual reality study.

    PubMed

    Sauzéon, Hélène; N'Kaoua, Bernard; Arvind Pala, Prashant; Taillade, Mathieu; Guitton, Pascal

    2016-02-01

    We investigated the navigation-related age effects on learning, proactive interference semantic clustering, recognition hits, and false recognitions in a naturalistic situation using a virtual apartment-based task. We also examined the neuropsychological correlates (executive functioning [EF] and episodic memory) of navigation-related age effects on memory. Younger and older adults either actively navigated or passively followed the computer-guided tour of an apartment. The results indicated that active navigation increased recognition hits compared with passive navigation, but it did not influence other memory measures (learning, proactive interference, and semantic clustering) to a similar extent in either age group. Furthermore, active navigation helped to reduce false recognitions in younger adults but increased those made by older adults. This differential effect of active navigation for younger and older adults was accounted for by EF score. Like for the subject-performed task effects, the effects from the navigation manipulation were well accounted for by item-specific/relational processing distinction, and they were also consistent with a source monitoring deficit in older adults. PMID:26756717

  15. Molecular Fingerprint-based Artificial Neural Networks QSAR for Ligand Biological Activity Predictions

    PubMed Central

    Myint, Kyaw-Zeyar; Wang, Lirong; Tong, Qin; Xie, Xiang-Qun

    2012-01-01

    In this manuscript, we have reported a novel 2D fingerprint-based artificial neural network QSAR (FANN-QSAR) method in order to effectively predict biological activities of structurally diverse chemical ligands. Three different types of fingerprints, namely ECFP6, FP2 and MACCS, were used in FANN-QSAR algorithm development, and FANN-QSAR models were compared to known 3D and 2D QSAR methods using five data sets previously reported. In addition, the derived models were used to predict GPCR cannabinoid ligand binding affinities using our manually curated cannabinoid ligand database containing 1699 structurally diverse compounds with reported cannabinoid receptor subtype CB2 activities. To demonstrate its useful applications, the established FANN-QSAR algorithm was used as a virtual screening tool to search a large NCI compound database for lead cannabinoid compounds and we have discovered several compounds with good CB2 binding affinities ranging from 6.70 nM to 3.75 μM. To the best of our knowledge, this is the first report for a fingerprint-based neural network approach validated with a successful virtual screening application in identifying lead compounds. The studies proved that the FANN-QSAR method is a useful approach to predict bioactivities or properties of ligands and to find novel lead compounds for drug discovery research. PMID:22937990

  16. Virtual colonoscopy

    MedlinePlus

    Colonoscopy - virtual; CT colonography; Computed tomographic colonography; Colography - virtual ... Virtual colonoscopy is different from regular colonoscopy . Regular colonoscopy uses a long, lighted tool called a colonoscope that is ...

  17. Competing dynamic phases of active polymer networks

    NASA Astrophysics Data System (ADS)

    Freedman, Simon; Banerjee, Shiladitya; Dinner, Aaron R.

    Recent experiments on in-vitro reconstituted assemblies of F-actin, myosin-II motors, and cross-linking proteins show that tuning local network properties can changes the fundamental biomechanical behavior of the system. For example, by varying cross-linker density and actin bundle rigidity, one can switch between contractile networks useful for reshaping cells, polarity sorted networks ideal for directed molecular transport, and frustrated networks with robust structural properties. To efficiently investigate the dynamic phases of actomyosin networks, we developed a coarse grained non-equilibrium molecular dynamics simulation of model semiflexible filaments, molecular motors, and cross-linkers with phenomenologically defined interactions. The simulation's accuracy was verified by benchmarking the mechanical properties of its individual components and collective behavior against experimental results at the molecular and network scales. By adjusting the model's parameters, we can reproduce the qualitative phases observed in experiment and predict the protein characteristics where phase crossovers could occur in collective network dynamics. Our model provides a framework for understanding cells' multiple uses of actomyosin networks and their applicability in materials research. Supported by the Department of Defense (DoD) through the National Defense Science & Engineering Graduate Fellowship (NDSEG) Program.

  18. Brain Network Activity in Monolingual and Bilingual Older Adults

    PubMed Central

    Grady, Cheryl L.; Luk, Gigi; Craik, Fergus I.M.; Bialystok, Ellen

    2016-01-01

    Bilingual older adults typically have better performance on tasks of executive control (EC) than do their monolingual peers, but differences in brain activity due to language experience are not well understood. Based on studies showing a relation between the dynamic range of brain network activity and performance on EC tasks, we hypothesized that life-long bilingual older adults would show increased functional connectivity relative to monolinguals in networks related to EC. We assessed intrinsic functional connectivity and modulation of activity in task vs. fixation periods in two brain networks that are active when EC is engaged, the frontoparietal control network (FPC) and the salience network (SLN). We also examined the default mode network (DMN), which influences behavior through reduced activity during tasks. We found stronger intrinsic functional connectivity in the FPC and DMN in bilinguals than in monolinguals. Although there were no group differences in the modulation of activity across tasks and fixation, bilinguals showed stronger correlations than monolinguals between intrinsic connectivity in the FPC and task-related increases of activity in prefrontal and parietal regions. This bilingual difference in network connectivity suggests that language experience begun in childhood and continued throughout adulthood influences brain networks in ways that may provide benefits in later life. PMID:25445783

  19. Virtual platform for power and security analysis of wireless sensor network

    NASA Astrophysics Data System (ADS)

    Diaz, A.; Gonzalez-Bayon, J.; González de Aledo Marugán, P.; Sanchez, P.

    2013-05-01

    Wireless Sensor Networks (WSNs) include low-power and low-cost devices (nodes) with demanding power requirements (long autonomous lifetime). The nodes have to use the available battery carefully and avoid expensive computations or radio transmissions. Therefore, effective simulation mechanisms that allow the developer to obtain estimations at the early stages of the WSN design, prior to deployment, are necessary. Power consumption is not the only important concern in this design but security is becoming a real problem too, since some WSNs process sensitive data. Thus, it is necessary to ensure that the processed data are tamper-proof. This paper proposes a framework for network simulation and embedded SW performance analysis that focuses not only on time and power estimation but also on two new metrics: the "entropy security-oriented metric" provides information about the security encryption used in WSN transmissions and the "heterogeneity metric" provides information to help avoid "replication attacks". All this information will aid in the whole WSN deployment design, providing useful metrics about power and security.

  20. Virtual reality training improves balance function

    PubMed Central

    Mao, Yurong; Chen, Peiming; Li, Le; Huang, Dongfeng

    2014-01-01

    Virtual reality is a new technology that simulates a three-dimensional virtual world on a computer and enables the generation of visual, audio, and haptic feedback for the full immersion of users. Users can interact with and observe objects in three-dimensional visual space without limitation. At present, virtual reality training has been widely used in rehabilitation therapy for balance dysfunction. This paper summarizes related articles and other articles suggesting that virtual reality training can improve balance dysfunction in patients after neurological diseases. When patients perform virtual reality training, the prefrontal, parietal cortical areas and other motor cortical networks are activated. These activations may be involved in the reconstruction of neurons in the cerebral cortex. Growing evidence from clinical studies reveals that virtual reality training improves the neurological function of patients with spinal cord injury, cerebral palsy and other neurological impairments. These findings suggest that virtual reality training can activate the cerebral cortex and improve the spatial orientation capacity of patients, thus facilitating the cortex to control balance and increase motion function. PMID:25368651

  1. Effect of Modeling-Based Activities Developed Using Virtual Environments and Concrete Objects on Spatial Thinking and Mental Rotation Skills

    ERIC Educational Resources Information Center

    Yurt, Eyup; Sunbul, Ali Murat

    2012-01-01

    In this study, the effect of modeling based activities using virtual environments and concrete objects on spatial thinking and mental rotation skills was investigated. The study was designed as a pretest-posttest model with a control group, which is one of the experimental research models. The study was carried out on sixth grade students…

  2. The Effects of Activity and Gain Based Virtual Material on Student's Success, Permanency and Attitudes towards Science Lesson

    ERIC Educational Resources Information Center

    Tas, Erol

    2015-01-01

    The main objective of this study is to research the effects of a student gains and activity based virtual material on students' success, permanence and attitudes towards science lesson, developed for science and technology lesson 6th grade "Systems in our body" unit. The study, which had a quasi-experimental design, was conducted with…

  3. Neural network with formed dynamics of activity

    SciTech Connect

    Dunin-Barkovskii, V.L.; Osovets, N.B.

    1995-03-01

    The problem of developing a neural network with a given pattern of the state sequence is considered. A neural network structure and an algorithm, of forming its bond matrix which lead to an approximate but robust solution of the problem are proposed and discussed. Limiting characteristics of the serviceability of the proposed structure are studied. Various methods of visualizing dynamic processes in a neural network are compared. Possible applications of the results obtained for interpretation of neurophysiological data and in neuroinformatics systems are discussed.

  4. The salience network causally influences default mode network activity during moral reasoning

    PubMed Central

    Wilson, Stephen M.; D’Esposito, Mark; Kayser, Andrew S.; Grossman, Scott N.; Poorzand, Pardis; Seeley, William W.; Miller, Bruce L.; Rankin, Katherine P.

    2013-01-01

    Large-scale brain networks are integral to the coordination of human behaviour, and their anatomy provides insights into the clinical presentation and progression of neurodegenerative illnesses such as Alzheimer’s disease, which targets the default mode network, and behavioural variant frontotemporal dementia, which targets a more anterior salience network. Although the default mode network is recruited when healthy subjects deliberate about ‘personal’ moral dilemmas, patients with Alzheimer’s disease give normal responses to these dilemmas whereas patients with behavioural variant frontotemporal dementia give abnormal responses to these dilemmas. We hypothesized that this apparent discrepancy between activation- and patient-based studies of moral reasoning might reflect a modulatory role for the salience network in regulating default mode network activation. Using functional magnetic resonance imaging to characterize network activity of patients with behavioural variant frontotemporal dementia and healthy control subjects, we present four converging lines of evidence supporting a causal influence from the salience network to the default mode network during moral reasoning. First, as previously reported, the default mode network is recruited when healthy subjects deliberate about ‘personal’ moral dilemmas, but patients with behavioural variant frontotemporal dementia producing atrophy in the salience network give abnormally utilitarian responses to these dilemmas. Second, patients with behavioural variant frontotemporal dementia have reduced recruitment of the default mode network compared with healthy control subjects when deliberating about these dilemmas. Third, a Granger causality analysis of functional neuroimaging data from healthy control subjects demonstrates directed functional connectivity from nodes of the salience network to nodes of the default mode network during moral reasoning. Fourth, this Granger causal influence is diminished in

  5. Virtual Worlds? "Outlook Good"

    ERIC Educational Resources Information Center

    Kelton, AJ

    2008-01-01

    Many people believed that virtual worlds would end up like the eight-track audiotape: a memory of something no longer used (or useful). Yet today there are hundreds of higher education institutions represented in three-dimensional (3D) virtual worlds such as Active Worlds and Second Life. The movement toward the virtual realm as a viable teaching…

  6. Acoustic Emission Source Location in Unidirectional Carbon-Fibre-Reinforced Plastic Plates Using Virtually Trained Artificial Neural Networks

    SciTech Connect

    Caprino, G.; Lopresto, V.; Leone, C.; Papa, I.

    2010-06-02

    Acoustic emission source location in a unidirectional carbon-fibre-reinforced plastic plate was attempted employing Artificial Neural Network (ANN) technology. The acoustic emission events were produced by a lead break, and the response wave received by piezoelectric sensors, type VS150-M resonant at 150 kHz. The waves were detected by a Vallen AMSY4 eight-channel instrumentation. The time of arrival, determined through the conventional threshold crossing technique, was used to measure the dependence of wave velocity on fibre orientation. A simple empirical formula, relying on classical lamination and suggested by wave propagation theory, was able to accurately model the experimental trend. Based on the formula, virtual training and testing data sets were generated for the case of a plate monitored by three transducers, and adopted to select two potentially effective ANN architectures. For final validation, experimental tests were carried out, positioning the source at predetermined points evenly distributed within the plate area. A very satisfactory correlation was found between the actual source locations and the ANN predictions.

  7. Investigation of frame mode unification and virtual channel multiplexing based on the multilayered satellite network OISLs interface

    NASA Astrophysics Data System (ADS)

    Deng, Boyu; Zhao, Shanghong; Li, Yongjun; Zhang, Xiwen; Cheng, Zhen

    2015-12-01

    In a multi-layered optical satellite network, a standardized data transmission is a reliable guarantee to efficiently process and transfer multi-service data for the space link. The transmission frame reframing unit (TFRU) is proposed to solve the problem of different service data having low transmission efficiency in the laser link. The TFRU uses a virtual channel (VC) technology to unify the format and rate of transmitted data using second encapsulation and VC scheduling for the service data. The Priority VC schedule algorithm is proposed to further improve multiplex efficiency. According to the principle of TFRU encapsulation and arrival rate of service data, the frame dynamic priority is defined by the VC priority and frame criticality. Furthermore, the Priority VC schedule specific method is provided. The simulation results show that the throughput increases to 3.0546 M, and the scheduling time delay reduces to 0.9183 s. Thus, the system performance has been greatly enhanced. The cache demands are satisfied because the laser terminal data transmission rate is larger than the sum of all service data rates. Using the dynamic schedule generated TFRU frames, the priority algorithm based on the TFRU ensures frame scheduling fairness in each VC.

  8. Generating Coherent Patterns of Activity from Chaotic Neural Networks

    PubMed Central

    Sussillo, David; Abbott, L. F.

    2009-01-01

    Neural circuits display complex activity patterns both spontaneously and when responding to a stimulus or generating a motor output. How are these two forms of activity related? We develop a procedure called FORCE learning for modifying synaptic strengths either external to or within a model neural network to change chaotic spontaneous activity into a wide variety of desired activity patterns. FORCE learning works even though the networks we train are spontaneously chaotic and we leave feedback loops intact and unclamped during learning. Using this approach, we construct networks that produce a wide variety of complex output patterns, input-output transformations that require memory, multiple outputs that can be switched by control inputs, and motor patterns matching human motion capture data. Our results reproduce data on pre-movement activity in motor and premotor cortex, and suggest that synaptic plasticity may be a more rapid and powerful modulator of network activity than generally appreciated. PMID:19709635

  9. Google matrix of the world network of economic activities

    NASA Astrophysics Data System (ADS)

    Kandiah, Vivek; Escaith, Hubert; Shepelyansky, Dima L.

    2015-07-01

    Using the new data from the OECD-WTO world network of economic activities we construct the Google matrix G of this directed network and perform its detailed analysis. The network contains 58 countries and 37 activity sectors for years 1995 and 2008. The construction of G, based on Markov chain transitions, treats all countries on equal democratic grounds while the contribution of activity sectors is proportional to their exchange monetary volume. The Google matrix analysis allows to obtain reliable ranking of countries and activity sectors and to determine the sensitivity of CheiRank-PageRank commercial balance of countries in respect to price variations and labor cost in various countries. We demonstrate that the developed approach takes into account multiplicity of network links with economy interactions between countries and activity sectors thus being more efficient compared to the usual export-import analysis. The spectrum and eigenstates of G are also analyzed being related to specific activity communities of countries.

  10. The Impact of Student Activity in a Virtual Learning Environment on Their Final Mark

    ERIC Educational Resources Information Center

    Mogus, Ana M.; Djurdjevic, Ivana; Suvak, Nenad

    2012-01-01

    By studying the use of a virtual learning environment, many have focused on automatically logged web data in order to detect factors that enhance students' use of the virtual learning environment and that may impact their productive and efficient learning via this means. Following their footsteps, the aim of this research is to examine data…

  11. IHY activities in Mexico and the Virtual Earth-Sun Observatory (VESO)

    NASA Astrophysics Data System (ADS)

    Gonzalez-Esparza, Americo; Francisco Valdes-Galicia, Jose; Cifuentes-Nava, Gerardo; Cordero, Guadalupe; Caballero-Lopez, Rogelio A.; Hernández-Quintero, Esteban; Lara, Alejandro

    We present a report on the IHY activities in Mexico in 2007. These activities were coordinated by the Instituto de Geofisica of the Universidad Nacional Autonoma de Mexico (UNAM) which include three international scientific conferences, a Latin American space physics school, outreach activities in some cities in the country, and two museum exhibitions. As a part of the scientific projects we developed the Virtual Earth-Sun Observatory (VESO) located at the web site http://www.veso.unam.mx. This site shows a real time integrated database obtained from four instruments of the Instituto de Geofisica-UNAM studying Sun-Earth connection phenomena. (1) The Solar Radio Interferometer (RIS, Radio Interfeŕmetro Solar) measures the o lower solar atmosphere radiation at 7.5 GHz, revealing microwave bursts associated with solar activity. (2) The Mexican Array Radio Telescope (MEXART, Observatorio de Centelleo Interplanetario de Coeneo) will detect solar wind large-scale disturbances between Sun and Earth (e.g., Interplanetary counterparts of Coronal Mass Ejections (ICMES) and Stream Interaction Regions (SIR)) employing the interplanetary scintillation technique (IPS) operating at 140 MHz. (3) The Cosmic Ray Observatory (RC) detects high energy galactic particles, whose flow is affected by magnetic disturbances in the solar wind, and (4) the Teoloyucan Geomagnetic Observatory (TEO) measures the variations in the Earth's magnetic field. The VESO instruments provide data from four different points of the complex chain of the solar terrestrial relations and will allow the study of intense solar events causing geomagnetic activity. The VESO project is part of the celebration of the International Heliophysical Year (IHY) and the Electronic Geophysical Year (EGY) in Mexico.

  12. Impact of Network Activity Levels on the Performance of Passive Network Service Dependency Discovery

    SciTech Connect

    Carroll, Thomas E.; Chikkagoudar, Satish; Arthur-Durett, Kristine M.

    2015-11-02

    Network services often do not operate alone, but instead, depend on other services distributed throughout a network to correctly function. If a service fails, is disrupted, or degraded, it is likely to impair other services. The web of dependencies can be surprisingly complex---especially within a large enterprise network---and evolve with time. Acquiring, maintaining, and understanding dependency knowledge is critical for many network management and cyber defense activities. While automation can improve situation awareness for network operators and cyber practitioners, poor detection accuracy reduces their confidence and can complicate their roles. In this paper we rigorously study the effects of network activity levels on the detection accuracy of passive network-based service dependency discovery methods. The accuracy of all except for one method was inversely proportional to network activity levels. Our proposed cross correlation method was particularly robust to the influence of network activity. The proposed experimental treatment will further advance a more scientific evaluation of methods and provide the ability to determine their operational boundaries.

  13. A four-dimensional virtual hand brain–machine interface using active dimension selection

    NASA Astrophysics Data System (ADS)

    Rouse, Adam G.

    2016-06-01

    Objective. Brain–machine interfaces (BMI) traditionally rely on a fixed, linear transformation from neural signals to an output state-space. In this study, the assumption that a BMI must control a fixed, orthogonal basis set was challenged and a novel active dimension selection (ADS) decoder was explored. Approach. ADS utilizes a two stage decoder by using neural signals to both (i) select an active dimension being controlled and (ii) control the velocity along the selected dimension. ADS decoding was tested in a monkey using 16 single units from premotor and primary motor cortex to successfully control a virtual hand avatar to move to eight different postures. Main results. Following training with the ADS decoder to control 2, 3, and then 4 dimensions, each emulating a grasp shape of the hand, performance reached 93% correct with a bit rate of 2.4 bits s‑1 for eight targets. Selection of eight targets using ADS control was more efficient, as measured by bit rate, than either full four-dimensional control or computer assisted one-dimensional control. Significance. ADS decoding allows a user to quickly and efficiently select different hand postures. This novel decoding scheme represents a potential method to reduce the complexity of high-dimension BMI control of the hand.

  14. Gender differences in EEG coherent activity before and after training navigation skills in virtual environments.

    PubMed

    Ramos-Loyo, J; Sanchez-Loyo, L M

    2011-01-01

    Gender differences in electroencephalographic activity (EEG) changes during navigation task performance after training were assessed in young adults. Female and male subjects were matched on initial navigation performance. EEG recordings were obtained while subjects navigated in an immersive virtual environment without visual cues, before and after a navigational skills training (9 sessions). In spite of task performance was similar in both groups, females showed higher theta band coherent activity between frontal and parietal and frontal and central regions than males before training. Correlation in theta band between fronto-central, fronto-parietal, and centro-parietal regions was enhanced in the left hemisphere for females but in the right hemisphere for males after training. Females also demonstrated a decreased in correlation in theta band over the right hemisphere between centro-parietal regions, whereas males demonstrated a similar effect over the left hemisphere. Navigation training seems to promote fronto-central-parietal synchronization in both genders but in different hemisphere. These results are interpreted as reflecting verbal-analytical working memory functions in females and global-spatial working memory mode in males. PMID:22332431

  15. Coalitions and networks: facilitating global physical activity promotion.

    PubMed

    Matsudo, Sandra Mahecha; Matsudo, Victor Rodrigues

    2006-01-01

    This article aims to synthesise the experience of coalitions and networks working for physical activity promotion. By introducing the concept of partnerships, especially within the Brazilian context, the authors outline the factors that comprise a successful partnership, describing key elements, such as, financing, membership and methods of empowerment. Agita São Paulo, the Physical Activity Network of the Americas-RAFA-PANA and Agita Mundo are used as examples. The article shows that local, national and global programmes, partnerships and networks at all levels are essential to guarantee the success of physical activity promotion as a public health strategy. PMID:17017291

  16. Botulinum Toxin Suppression of CNS Network Activity In Vitro

    PubMed Central

    Pancrazio, Joseph J.; Gopal, Kamakshi; Keefer, Edward W.; Gross, Guenter W.

    2014-01-01

    The botulinum toxins are potent agents which disrupt synaptic transmission. While the standard method for BoNT detection and quantification is based on the mouse lethality assay, we have examined whether alterations in cultured neuronal network activity can be used to detect the functional effects of BoNT. Murine spinal cord and frontal cortex networks cultured on substrate integrated microelectrode arrays allowed monitoring of spontaneous spike and burst activity with exposure to BoNT serotype A (BoNT-A). Exposure to BoNT-A inhibited spike activity in cultured neuronal networks where, after a delay due to toxin internalization, the rate of activity loss depended on toxin concentration. Over a 30 hr exposure to BoNT-A, the minimum concentration detected was 2 ng/mL, a level consistent with mouse lethality studies. A small proportion of spinal cord networks, but not frontal cortex networks, showed a transient increase in spike and burst activity with exposure to BoNT-A, an effect likely due to preferential inhibition of inhibitory synapses expressed in this tissue. Lastly, prior exposure to human-derived antisera containing neutralizing antibodies prevented BoNT-A induced inhibition of network spike activity. These observations suggest that the extracellular recording from cultured neuronal networks can be used to detect and quantify functional BoNT effects. PMID:24688538

  17. Botulinum toxin suppression of CNS network activity in vitro.

    PubMed

    Pancrazio, Joseph J; Gopal, Kamakshi; Keefer, Edward W; Gross, Guenter W

    2014-01-01

    The botulinum toxins are potent agents which disrupt synaptic transmission. While the standard method for BoNT detection and quantification is based on the mouse lethality assay, we have examined whether alterations in cultured neuronal network activity can be used to detect the functional effects of BoNT. Murine spinal cord and frontal cortex networks cultured on substrate integrated microelectrode arrays allowed monitoring of spontaneous spike and burst activity with exposure to BoNT serotype A (BoNT-A). Exposure to BoNT-A inhibited spike activity in cultured neuronal networks where, after a delay due to toxin internalization, the rate of activity loss depended on toxin concentration. Over a 30 hr exposure to BoNT-A, the minimum concentration detected was 2 ng/mL, a level consistent with mouse lethality studies. A small proportion of spinal cord networks, but not frontal cortex networks, showed a transient increase in spike and burst activity with exposure to BoNT-A, an effect likely due to preferential inhibition of inhibitory synapses expressed in this tissue. Lastly, prior exposure to human-derived antisera containing neutralizing antibodies prevented BoNT-A induced inhibition of network spike activity. These observations suggest that the extracellular recording from cultured neuronal networks can be used to detect and quantify functional BoNT effects. PMID:24688538

  18. Detecting eavesdropping activity in fiber optic networks

    NASA Astrophysics Data System (ADS)

    MacDonald, Gregory G.

    The secure transmission of data is critical to governments, military organizations, financial institutions, health care providers and other enterprises. The primary method of securing in-transit data is though data encryption. A number of encryption methods exist but the fundamental approach is to assume an eavesdropper has access to the encrypted message but does not have the computing capability to decrypt the message in a timely fashion. Essentially, the strength of security depends on the complexity of the encryption method and the resources available to the eavesdropper. The development of future technologies, most notably quantum computers and quantum computing, is often cited as a direct threat to traditional encryption schemes. It seems reasonable that additional effort should be placed on prohibiting the eavesdropper from coming into possession of the encrypted message in the first place. One strategy for denying possession of the encrypted message is to secure the physical layer of the communications path. Because the majority of transmitted information is over fiber-optic networks, it seems appropriate to consider ways of enhancing the integrity and security of the fiber-based physical layer. The purpose of this research is to investigate the properties of light, as they are manifested in single mode fiber, as a means of insuring the integrity and security of the physical layer of a fiber-optic based communication link. Specifically, the approach focuses on the behavior of polarization in single mode fiber, as it is shown to be especially sensitive to fiber geometry. Fiber geometry is necessarily modified during the placement of optical taps. The problem of detecting activity associated with the placement of an optical tap is herein approached as a supervised machine learning anomaly identification task. The inputs include raw polarization measurements along with additional features derived from various visualizations of the raw data (the inputs are

  19. Observations on Electronic Networks: Appropriate Activities for Learning.

    ERIC Educational Resources Information Center

    Levin, James A.; And Others

    1989-01-01

    Discussion of the use of electronic networks for learning activities highlights the Noon Observation Project in which students in various locations measured the length of a noontime shadow to determine the earth's circumference. Electronic pen pals are discussed, and the roles of the network and of the class are described. (LRW)

  20. The Global Space Geodesy Network: Activities Underway

    NASA Astrophysics Data System (ADS)

    Pearlman, Michael R.; Ipatov, Alexander; Long, James; Ma, Chopo; Merkowitz, Stephen; Neilan, Ruth; Noll, Carey; Pavlis, Erricos; Shargorodsky, Victor; Stowers, David; Wetzel, Scott

    2014-05-01

    Several initiatives are underway that should make substantial improvement over the next decade to the international space geodesy network as the international community works toward the GGOS 2020 goal of 32 globally distributed Core Sites with co-located VLBI, SLR, GNSS and DORIS. The Russian Space Agency and the Russian Academy of Sciences are moving forward with an implementation of six additional SLR systems and a number of GNSS receivers to sites outside Russia to expand GNSS tracking and support GGOS. The NASA Space Geodesy program has completed its prototype development phase and is now embarking on an implementation phase that is planning for deployment of 6 - 10 core sites in key geographic locations to support the global network. Additional sites are in the process of implementation in Europe and Asia. Site evaluation studies are in progress, looking at some new potential sites and there are ongoing discussions for partnership arrangements with interested agencies for new sites in South America and Africa. Work continues on the site layout design to avoid RF interference issues among co-located instruments and with external communications and media system. The placement of new and upgraded sites is guided by appropriate Observing System Simulation Experiments (OSSEs) conducted under the support of the interested international agencies. The results will help optimize the global distribution of core geodetic observatories and they will lead to the improvement of the data products from the future network. During this effort it is also recognized that co-located sites with less than the full core complement will continue to play an important and critical role in filling out the global network and strengthening the connection among the techniques. This talk will give an update on the current state of expansion of the global network and the projection for the network configuration that we forecast over the next 10 years.

  1. Ecological Validity of Virtual Reality Daily Living Activities Screening for Early Dementia: Longitudinal Study

    PubMed Central

    Schlee, Winfried; Tsolaki, Magda; Müri, René; Mosimann, Urs; Nef, Tobias

    2013-01-01

    Background Dementia is a multifaceted disorder that impairs cognitive functions, such as memory, language, and executive functions necessary to plan, organize, and prioritize tasks required for goal-directed behaviors. In most cases, individuals with dementia experience difficulties interacting with physical and social environments. The purpose of this study was to establish ecological validity and initial construct validity of a fire evacuation Virtual Reality Day-Out Task (VR-DOT) environment based on performance profiles as a screening tool for early dementia. Objective The objectives were (1) to examine the relationships among the performances of 3 groups of participants in the VR-DOT and traditional neuropsychological tests employed to assess executive functions, and (2) to compare the performance of participants with mild Alzheimer’s-type dementia (AD) to those with amnestic single-domain mild cognitive impairment (MCI) and healthy controls in the VR-DOT and traditional neuropsychological tests used to assess executive functions. We hypothesized that the 2 cognitively impaired groups would have distinct performance profiles and show significantly impaired independent functioning in ADL compared to the healthy controls. Methods The study population included 3 groups: 72 healthy control elderly participants, 65 amnestic MCI participants, and 68 mild AD participants. A natural user interface framework based on a fire evacuation VR-DOT environment was used for assessing physical and cognitive abilities of seniors over 3 years. VR-DOT focuses on the subtle errors and patterns in performing everyday activities and has the advantage of not depending on a subjective rating of an individual person. We further assessed functional capacity by both neuropsychological tests (including measures of attention, memory, working memory, executive functions, language, and depression). We also evaluated performance in finger tapping, grip strength, stride length, gait speed

  2. Active Sampling in Evolving Neural Networks.

    ERIC Educational Resources Information Center

    Parisi, Domenico

    1997-01-01

    Comments on Raftopoulos article (PS 528 649) on facilitative effect of cognitive limitation in development and connectionist models. Argues that the use of neural networks within an "Artificial Life" perspective can more effectively contribute to the study of the role of cognitive limitations in development and their genetic basis than can using…

  3. Ligand Biological Activity Predictions Using Fingerprint-Based Artificial Neural Networks (FANN-QSAR)

    PubMed Central

    Myint, Kyaw Z.; Xie, Xiang-Qun

    2015-01-01

    This chapter focuses on the fingerprint-based artificial neural networks QSAR (FANN-QSAR) approach to predict biological activities of structurally diverse compounds. Three types of fingerprints, namely ECFP6, FP2, and MACCS, were used as inputs to train the FANN-QSAR models. The results were benchmarked against known 2D and 3D QSAR methods, and the derived models were used to predict cannabinoid (CB) ligand binding activities as a case study. In addition, the FANN-QSAR model was used as a virtual screening tool to search a large NCI compound database for lead cannabinoid compounds. We discovered several compounds with good CB2 binding affinities ranging from 6.70 nM to 3.75 μM. The studies proved that the FANN-QSAR method is a useful approach to predict bioactivities or properties of ligands and to find novel lead compounds for drug discovery research. PMID:25502380

  4. Distal gap junctions and active dendrites can tune network dynamics.

    PubMed

    Saraga, Fernanda; Ng, Leo; Skinner, Frances K

    2006-03-01

    Gap junctions allow direct electrical communication between CNS neurons. From theoretical and modeling studies, it is well known that although gap junctions can act to synchronize network output, they can also give rise to many other dynamic patterns including antiphase and other phase-locked states. The particular network pattern that arises depends on cellular, intrinsic properties that affect firing frequencies as well as the strength and location of the gap junctions. Interneurons or GABAergic neurons in hippocampus are diverse in their cellular characteristics and have been shown to have active dendrites. Furthermore, parvalbumin-positive GABAergic neurons, also known as basket cells, can contact one another via gap junctions on their distal dendrites. Using two-cell network models, we explore how distal electrical connections affect network output. We build multi-compartment models of hippocampal basket cells using NEURON and endow them with varying amounts of active dendrites. Two-cell networks of these model cells as well as reduced versions are explored. The relationship between intrinsic frequency and the level of active dendrites allows us to define three regions based on what sort of network dynamics occur with distal gap junction coupling. Weak coupling theory is used to predict the delineation of these regions as well as examination of phase response curves and distal dendritic polarization levels. We find that a nonmonotonic dependence of network dynamic characteristics (phase lags) on gap junction conductance occurs. This suggests that distal electrical coupling and active dendrite levels can control how sensitive network dynamics are to gap junction modulation. With the extended geometry, gap junctions located at more distal locations must have larger conductances for pure synchrony to occur. Furthermore, based on simulations with heterogeneous networks, it may be that one requires active dendrites if phase-locking is to occur in networks formed

  5. Computer Simulator of Glycine Receptor Activity: A New Window into a Virtual World.

    PubMed

    Boronovsky, S E; Nartsissov, Y R

    2016-07-01

    Our study reports computer software that simulates the work of a single glycine receptor (GlyR). GlyRs have been found in various types of tissues, but their most important role seems to be in neurons, where they hyperpolarise membranes by opening chloride transmembrane channels. The software is based on a combination of two blocks. One block describes the Brownian dynamics of charged particle motion in a dielectric medium, and the other block determines the probability and timing of receptor activation. Using this software, the voltage-current dependencies and time curves of the transmembrane current were obtained. The mean value of the simulated anion current (4.5 ± 0.3 pA) is in good agreement with measured values under identical conditions ([Formula: see text] pA). It was shown that there is a condition under which the GlyR anion channel remains active despite a negligible chloride gradient. Virtual experiments allow evaluation of the value of half maximal effective concentration (EC[Formula: see text]) of the GlyR ([Formula: see text] [Formula: see text]M) and confirm that this receptor activates according to a mechanism involving three ligand binding sites. The advantage of the model is the ability to adjust parameters to the precise demands of experimental researchers. Moreover, the introduced algorithm has low computational power demands; therefore, it can be used as a research tool for assistance with structural experiments and applied aspects of neurophysiology. PMID:27412156

  6. Virtual Screening of compounds from Tabernaemontana divaricata for potential anti-bacterial activity

    PubMed Central

    Gogoi, Rashmi Rekha; Gogoi, Dhrubajyoti; Bezbaruah, Rajib Lochan

    2014-01-01

    Virtual Screening and Molecular Docking analysis for Tabernaemontana divaricata derived 66 Law Molecular Weight Compounds (LMW) was conducted and to identified and predicted novel molecules as a inhibitor of Streptococcus pneumonia. The investigation has revealed several compounds with optimum binding towards Penicillin-binding proteins, Sialidases, Aspartate betasemialdehide dehydrogenase cell membrane protein of Streptococcus pneumonia. Docking results were computed in term of binding energy, ligand efficiency and number of hydrogen bonding. Apparicine (-5.14), 5-Hydroxyvoaphylline (-4.78), Voacangine (-4.7), 19-Hydroxycoronaridine (-4.44) and Coronaridine (-4.72) are identified as most suitable to bind with N-acetylglucosamine-1- phosphate uridyltransferase receptor. Ervaticine (-6.33), Ibogamine (-6.15), Methylvoaphylline (-5.74) and Coronaridine hydroxyindolenine (-5.32) has showed novel binding against the penicillin-binding proteins. Ervaticine (-6.42), 5-oxo-11-hydroxy voaphylline (-6.18), Conolobine B (-6.02) has found optimum binding against the active site of NanB sialidase of Streptococcus pneumonia. The compounds 3S-Cyanocoronaridine (-6.71), 19-Epivoacristine (-5.48) and Ervaticine(-5.45) interacting with aspartate beta-semialdehide and found suitable with least docking score. PMID:24748755

  7. Virtual Screening of compounds from Tabernaemontana divaricata for potential anti-bacterial activity.

    PubMed

    Gogoi, Rashmi Rekha; Gogoi, Dhrubajyoti; Bezbaruah, Rajib Lochan

    2014-01-01

    Virtual Screening and Molecular Docking analysis for Tabernaemontana divaricata derived 66 Law Molecular Weight Compounds (LMW) was conducted and to identified and predicted novel molecules as a inhibitor of Streptococcus pneumonia. The investigation has revealed several compounds with optimum binding towards Penicillin-binding proteins, Sialidases, Aspartate betasemialdehide dehydrogenase cell membrane protein of Streptococcus pneumonia. Docking results were computed in term of binding energy, ligand efficiency and number of hydrogen bonding. Apparicine (-5.14), 5-Hydroxyvoaphylline (-4.78), Voacangine (-4.7), 19-Hydroxycoronaridine (-4.44) and Coronaridine (-4.72) are identified as most suitable to bind with N-acetylglucosamine-1- phosphate uridyltransferase receptor. Ervaticine (-6.33), Ibogamine (-6.15), Methylvoaphylline (-5.74) and Coronaridine hydroxyindolenine (-5.32) has showed novel binding against the penicillin-binding proteins. Ervaticine (-6.42), 5-oxo-11-hydroxy voaphylline (-6.18), Conolobine B (-6.02) has found optimum binding against the active site of NanB sialidase of Streptococcus pneumonia. The compounds 3S-Cyanocoronaridine (-6.71), 19-Epivoacristine (-5.48) and Ervaticine(-5.45) interacting with aspartate beta-semialdehide and found suitable with least docking score. PMID:24748755

  8. Trainable structure-activity relationship model for virtual screening of CYP3A4 inhibition.

    PubMed

    Didziapetris, Remigijus; Dapkunas, Justas; Sazonovas, Andrius; Japertas, Pranas

    2010-11-01

    A new structure-activity relationship model predicting the probability for a compound to inhibit human cytochrome P450 3A4 has been developed using data for >800 compounds from various literature sources and tested on PubChem screening data. Novel GALAS (Global, Adjusted Locally According to Similarity) modeling methodology has been used, which is a combination of baseline global QSAR model and local similarity based corrections. GALAS modeling method allows forecasting the reliability of prediction thus defining the model applicability domain. For compounds within this domain the statistical results of the final model approach the data consistency between experimental data from literature and PubChem datasets with the overall accuracy of 89%. However, the original model is applicable only for less than a half of PubChem database. Since the similarity correction procedure of GALAS modeling method allows straightforward model training, the possibility to expand the applicability domain has been investigated. Experimental data from PubChem dataset served as an example of in-house high-throughput screening data. The model successfully adapted itself to both data classified using the same and different IC₅₀ threshold compared with the training set. In addition, adjustment of the CYP3A4 inhibition model to compounds with a novel chemical scaffold has been demonstrated. The reported GALAS model is proposed as a useful tool for virtual screening of compounds for possible drug-drug interactions even prior to the actual synthesis. PMID:20814717

  9. Epidemic spreading and immunization in node-activity networks

    NASA Astrophysics Data System (ADS)

    Wu, Qingchu; Chen, Shufang

    2015-09-01

    In this paper, we study the epidemic spreading in node-activity networks, where an individual participates in social networks with a certain rate h. There are two cases for h: the state-independent case and the state-dependent case. We investigate the epidemic threshold as a function of h compared to the static network. Our results suggest the epidemic threshold cannot be exactly predicted by using the analysis approach in the static network. In addition, we further propose a local information-based immunization protocol on node-activity networks. Simulation analysis shows that the immunization can not only eliminate the infectious disease, but also change the epidemic threshold via increasing the immunization parameter.

  10. A comparison of older adults' subjective experiences with virtual and real environments during dynamic balance activities.

    PubMed

    Proffitt, Rachel; Lange, Belinda; Chen, Christina; Winstein, Carolee

    2015-01-01

    The purpose of this study was to explore the subjective experience of older adults interacting with both virtual and real environments. Thirty healthy older adults engaged with real and virtual tasks of similar motor demands: reaching to a target in standing and stepping stance. Immersive tendencies and absorption scales were administered before the session. Game engagement and experience questionnaires were completed after each task, followed by a semistructured interview at the end of the testing session. Data were analyzed respectively using paired t tests and grounded theory methodology. Participants preferred the virtual task over the real task. They also reported an increase in presence and absorption with the virtual task, describing an external focus of attention. Findings will be used to inform future development of appropriate game-based balance training applications that could be embedded in the home or community settings as part of evidence-based fall prevention programs. PMID:24334299

  11. A comparison of older adults' subjective experience with virtual and real environments during dynamic balance activities

    PubMed Central

    Proffitt, Rachel; Lange, Belinda; Chen, Christina; Winstein, Carolee

    2014-01-01

    The purpose of this study was to explore the subjective experience of older adults interacting with both virtual and real environments. Thirty healthy older adults engaged with real and virtual tasks of similar motor demands: reaching to a target in standing and stepping stance. Immersive tendencies and absorption scales were administered before the session. Game engagement and experience questionnaires were completed after each task, followed by a semi-structured interview at the end of the testing session. Data were analyzed respectively using paired t-tests and grounded theory methodology. Participants preferred the virtual task over the real task. They also reported an increase in presence and absorption with the virtual task, describing an external focus of attention. Findings will be used to inform future development of appropriate game-based balance training applications that could be embedded in the home or community settings as part of evidence-based fall prevention programs. PMID:24334299

  12. Active system area networks for data intensive computations. Final report

    SciTech Connect

    2002-04-01

    The goal of the Active System Area Networks (ASAN) project is to develop hardware and software technologies for the implementation of active system area networks (ASANs). The use of the term ''active'' refers to the ability of the network interfaces to perform application-specific as well as system level computations in addition to their traditional role of data transfer. This project adopts the view that the network infrastructure should be an active computational entity capable of supporting certain classes of computations that would otherwise be performed on the host CPUs. The result is a unique network-wide programming model where computations are dynamically placed within the host CPUs or the NIs depending upon the quality of service demands and network/CPU resource availability. The projects seeks to demonstrate that such an approach is a better match for data intensive network-based applications and that the advent of low-cost powerful embedded processors and configurable hardware makes such an approach economically viable and desirable.

  13. Virtual Goods Recommendations in Virtual Worlds

    PubMed Central

    Chen, Kuan-Yu; Liao, Hsiu-Yu; Chen, Jyun-Hung; Liu, Duen-Ren

    2015-01-01

    Virtual worlds (VWs) are computer-simulated environments which allow users to create their own virtual character as an avatar. With the rapidly growing user volume in VWs, platform providers launch virtual goods in haste and stampede users to increase sales revenue. However, the rapidity of development incurs virtual unrelated items which will be difficult to remarket. It not only wastes virtual global companies' intelligence resources, but also makes it difficult for users to find suitable virtual goods fit for their virtual home in daily virtual life. In the VWs, users decorate their houses, visit others' homes, create families, host parties, and so forth. Users establish their social life circles through these activities. This research proposes a novel virtual goods recommendation method based on these social interactions. The contact strength and contact influence result from interactions with social neighbors and influence users' buying intention. Our research highlights the importance of social interactions in virtual goods recommendation. The experiment's data were retrieved from an online VW platform, and the results show that the proposed method, considering social interactions and social life circle, has better performance than existing recommendation methods. PMID:25834837

  14. Tuning of temporo-occipital activity by frontal oscillations during virtual mirror exposure causes erroneous self-recognition.

    PubMed

    Serino, Andrea; Sforza, Anna Laura; Kanayama, Noriaki; van Elk, Michiel; Kaliuzhna, Mariia; Herbelin, Bruno; Blanke, Olaf

    2015-10-01

    Self-face recognition, a hallmark of self-awareness, depends on 'off-line' stored information about one's face and 'on-line' multisensory-motor face-related cues. The brain mechanisms of how on-line sensory-motor processes affect off-line neural self-face representations are unknown. This study used 3D virtual reality to create a 'virtual mirror' in which participants saw an avatar's face moving synchronously with their own face movements. Electroencephalographic (EEG) analysis during virtual mirror exposure revealed mu oscillations in sensory-motor cortex signalling on-line congruency between the avatar's and participants' movements. After such exposure and compatible with a change in their off-line self-face representation, participants were more prone to recognize the avatar's face as their own, and this was also reflected in the activation of face-specific regions in the inferotemporal cortex. Further EEG analysis showed that the on-line sensory-motor effects during virtual mirror exposure caused these off-line visual effects, revealing the brain mechanisms that maintain a coherent self-representation, despite our continuously changing appearance. PMID:26215485

  15. Systematic fluctuation expansion for neural network activity equations

    PubMed Central

    Buice, Michael A.; Cowan, Jack D.; Chow, Carson C.

    2009-01-01

    Population rate or activity equations are the foundation of a common approach to modeling for neural networks. These equations provide mean field dynamics for the firing rate or activity of neurons within a network given some connectivity. The shortcoming of these equations is that they take into account only the average firing rate while leaving out higher order statistics like correlations between firing. A stochastic theory of neural networks which includes statistics at all orders was recently formulated. We describe how this theory yields a systematic extension to population rate equations by introducing equations for correlations and appropriate coupling terms. Each level of the approximation yields closed equations, i.e. they depend only upon the mean and specific correlations of interest, without an ad hoc criterion for doing so. We show in an example of an all-to-all connected network how our system of generalized activity equations captures phenomena missed by the mean field rate equations alone. PMID:19852585

  16. Activator-inhibitor systems on heterogeneous ecological networks

    NASA Astrophysics Data System (ADS)

    Nicolaides, C.; Cueto-Felgueroso, L.; Juanes, R.

    2012-12-01

    The consideration of activator-inhibitor systems as complex networks has broadened our knowledge of non-equilibrium reaction-diffusion processes in heterogeneous systems. For example, the Turing mechanism represents a classical model for the formation of self-organized spatial structures in non-equilibrium activator-inhibitor systems. The study of Turing patterns in networks with heterogeneous connectivity has revealed that, contrary to other models and systems, the segregation process takes place mainly in vertices of low degree. In this paper, we study the formation of vegetation patterns in semiarid ecosystems from the perspective of a heterogeneous interacting ecological network. The structure of ecological networks yields fundamental insight into the ecosystem self-organization. Using simple rules for the short-range activation and global inhibition, we reconstruct the observed power-law distribution of vegetation patch size that has been observed in semiarid ecosystems like the Kalahari transect.

  17. Decorrelation of Neural-Network Activity by Inhibitory Feedback

    PubMed Central

    Einevoll, Gaute T.; Diesmann, Markus

    2012-01-01

    Correlations in spike-train ensembles can seriously impair the encoding of information by their spatio-temporal structure. An inevitable source of correlation in finite neural networks is common presynaptic input to pairs of neurons. Recent studies demonstrate that spike correlations in recurrent neural networks are considerably smaller than expected based on the amount of shared presynaptic input. Here, we explain this observation by means of a linear network model and simulations of networks of leaky integrate-and-fire neurons. We show that inhibitory feedback efficiently suppresses pairwise correlations and, hence, population-rate fluctuations, thereby assigning inhibitory neurons the new role of active decorrelation. We quantify this decorrelation by comparing the responses of the intact recurrent network (feedback system) and systems where the statistics of the feedback channel is perturbed (feedforward system). Manipulations of the feedback statistics can lead to a significant increase in the power and coherence of the population response. In particular, neglecting correlations within the ensemble of feedback channels or between the external stimulus and the feedback amplifies population-rate fluctuations by orders of magnitude. The fluctuation suppression in homogeneous inhibitory networks is explained by a negative feedback loop in the one-dimensional dynamics of the compound activity. Similarly, a change of coordinates exposes an effective negative feedback loop in the compound dynamics of stable excitatory-inhibitory networks. The suppression of input correlations in finite networks is explained by the population averaged correlations in the linear network model: In purely inhibitory networks, shared-input correlations are canceled by negative spike-train correlations. In excitatory-inhibitory networks, spike-train correlations are typically positive. Here, the suppression of input correlations is not a result of the mere existence of correlations between

  18. Turing patterns in network-organized activator-inhibitor systems

    NASA Astrophysics Data System (ADS)

    Nakao, Hiroya; Mikhailov, Alexander S.

    2010-07-01

    Turing instability in activator-inhibitor systems provides a paradigm of non-equilibrium self-organization; it has been extensively investigated for biological and chemical processes. Turing instability should also be possible in networks, and general mathematical methods for its treatment have been formulated previously. However, only examples of regular lattices and small networks were explicitly considered. Here we study Turing patterns in large random networks, which reveal striking differences from the classical behaviour. The initial linear instability leads to spontaneous differentiation of the network nodes into activator-rich and activator-poor groups. The emerging Turing patterns become furthermore strongly reshaped at the subsequent nonlinear stage. Multiple coexisting stationary states and hysteresis effects are observed. This peculiar behaviour can be understood in the framework of a mean-field theory. Our results offer a new perspective on self-organization phenomena in systems organized as complex networks. Potential applications include ecological metapopulations, synthetic ecosystems, cellular networks of early biological morphogenesis, and networks of coupled chemical nanoreactors.

  19. Connectivity, excitability and activity patterns in neuronal networks

    NASA Astrophysics Data System (ADS)

    le Feber, Joost; Stoyanova, Irina I.; Chiappalone, Michela

    2014-06-01

    Extremely synchronized firing patterns such as those observed in brain diseases like epilepsy may result from excessive network excitability. Although network excitability is closely related to (excitatory) connectivity, a direct measure for network excitability remains unavailable. Several methods currently exist for estimating network connectivity, most of which are related to cross-correlation. An example is the conditional firing probability (CFP) analysis which calculates the pairwise probability (CFPi,j) that electrode j records an action potential at time t = τ, given that electrode i recorded a spike at t = 0. However, electrode i often records multiple spikes within the analysis interval, and CFP values are biased by the on-going dynamic state of the network. Here we show that in a linear approximation this bias may be removed by deconvoluting CFPi,j with the autocorrelation of i (i.e. CFPi,i), to obtain the single pulse response (SPRi,j)—the average response at electrode j to a single spike at electrode i. Thus, in a linear system SPRs would be independent of the dynamic network state. Nonlinear components of synaptic transmission, such as facilitation and short term depression, will however still affect SPRs. Therefore SPRs provide a clean measure of network excitability. We used carbachol and ghrelin to moderately activate cultured cortical networks to affect their dynamic state. Both neuromodulators transformed the bursting firing patterns of the isolated networks into more dispersed firing. We show that the influence of the dynamic state on SPRs is much smaller than the effect on CFPs, but not zero. The remaining difference reflects the alteration in network excitability. We conclude that SPRs are less contaminated by the dynamic network state and that mild excitation may decrease network excitability, possibly through short term synaptic depression.

  20. Stimulus information stored in lasting active and hidden network states is destroyed by network bursts.

    PubMed

    Dranias, Mark R; Westover, M Brandon; Cash, Sidney; VanDongen, Antonius M J

    2015-01-01

    In both humans and animals brief synchronizing bursts of epileptiform activity known as interictal epileptiform discharges (IEDs) can, even in the absence of overt seizures, cause transient cognitive impairments (TCI) that include problems with perception or short-term memory. While no evidence from single units is available, it has been assumed that IEDs destroy information represented in neuronal networks. Cultured neuronal networks are a model for generic cortical microcircuits, and their spontaneous activity is characterized by the presence of synchronized network bursts (SNBs), which share a number of properties with IEDs, including the high degree of synchronization and their spontaneous occurrence in the absence of an external stimulus. As a model approach to understanding the processes underlying IEDs, optogenetic stimulation and multielectrode array (MEA) recordings of cultured neuronal networks were used to study whether stimulus information represented in these networks survives SNBs. When such networks are optically stimulated they encode and maintain stimulus information for as long as one second. Experiments involved recording the network response to a single stimulus and trials where two different stimuli were presented sequentially, akin to a paired pulse trial. We broke the sequential stimulus trials into encoding, delay and readout phases and found that regardless of which phase the SNB occurs, stimulus-specific information was impaired. SNBs were observed to increase the mean network firing rate, but this did not translate monotonically into increases in network entropy. It was found that the more excitable a network, the more stereotyped its response was during a network burst. These measurements speak to whether SNBs are capable of transmitting information in addition to blocking it. These results are consistent with previous reports and provide baseline predictions concerning the neural mechanisms by which IEDs might cause TCI. PMID:25755638

  1. Stimulus information stored in lasting active and hidden network states is destroyed by network bursts

    PubMed Central

    Dranias, Mark R.; Westover, M. Brandon; Cash, Sidney; VanDongen, Antonius M. J.

    2015-01-01

    In both humans and animals brief synchronizing bursts of epileptiform activity known as interictal epileptiform discharges (IEDs) can, even in the absence of overt seizures, cause transient cognitive impairments (TCI) that include problems with perception or short-term memory. While no evidence from single units is available, it has been assumed that IEDs destroy information represented in neuronal networks. Cultured neuronal networks are a model for generic cortical microcircuits, and their spontaneous activity is characterized by the presence of synchronized network bursts (SNBs), which share a number of properties with IEDs, including the high degree of synchronization and their spontaneous occurrence in the absence of an external stimulus. As a model approach to understanding the processes underlying IEDs, optogenetic stimulation and multielectrode array (MEA) recordings of cultured neuronal networks were used to study whether stimulus information represented in these networks survives SNBs. When such networks are optically stimulated they encode and maintain stimulus information for as long as one second. Experiments involved recording the network response to a single stimulus and trials where two different stimuli were presented sequentially, akin to a paired pulse trial. We broke the sequential stimulus trials into encoding, delay and readout phases and found that regardless of which phase the SNB occurs, stimulus-specific information was impaired. SNBs were observed to increase the mean network firing rate, but this did not translate monotonically into increases in network entropy. It was found that the more excitable a network, the more stereotyped its response was during a network burst. These measurements speak to whether SNBs are capable of transmitting information in addition to blocking it. These results are consistent with previous reports and provide baseline predictions concerning the neural mechanisms by which IEDs might cause TCI. PMID:25755638

  2. A neural networks study of quinone compounds with trypanocidal activity.

    PubMed

    de Molfetta, Fábio Alberto; Angelotti, Wagner Fernando Delfino; Romero, Roseli Aparecida Francelin; Montanari, Carlos Alberto; da Silva, Albérico Borges Ferreira

    2008-10-01

    This work investigates neural network models for predicting the trypanocidal activity of 28 quinone compounds. Artificial neural networks (ANN), such as multilayer perceptrons (MLP) and Kohonen models, were employed with the aim of modeling the nonlinear relationship between quantum and molecular descriptors and trypanocidal activity. The calculated descriptors and the principal components were used as input to train neural network models to verify the behavior of the nets. The best model for both network models (MLP and Kohonen) was obtained with four descriptors as input. The descriptors were T5 (torsion angle), QTS1 (sum of absolute values of the atomic charges), VOLS2 (volume of the substituent at region B) and HOMO-1 (energy of the molecular orbital below HOMO). These descriptors provide information on the kind of interaction that occurs between the compounds and the biological receptor. Both neural network models used here can predict the trypanocidal activity of the quinone compounds with good agreement, with low errors in the testing set and a high correctness rate. Thanks to the nonlinear model obtained from the neural network models, we can conclude that electronic and structural properties are important factors in the interaction between quinone compounds that exhibit trypanocidal activity and their biological receptors. The final ANN models should be useful in the design of novel trypanocidal quinones having improved potency. PMID:18629551

  3. Probing mechanics and activity of cytoskeletal networks using carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Fakhri, Nikta

    2013-03-01

    We use single-walled carbon nanotubes (SWNTs) as multi-scale micro-probes to monitor transport and fluctuations in cytoskeletal networks. SWNTs are nanometer-diameter hollow carbon filaments with micrometer lengths and a tunable bending stiffness. Their persistence length varies between 20-100 microns. We study the motion of individual SWNTs in reconstituted actin networks by near-infrared fluorescence microscopy. At long times, SWNTs reptate through the networks. At short times, SWNTs sample the spectrum of thermal fluctuations in the networks. We can calculate complex shear moduli from recorded fluctuations and observe power-law scaling in equilibrium actin networks. In the non-equilibrium cytoskeleton of cells we have targeted SWNTs to kinesin motors and thereby to their microtubule tracks. We observe both transport along the tracks as well as active fluctuations of the tracks themselves. Human Frontier Science Program Cross-Disciplinary Fellow

  4. Chronic electrical stimulation homeostatically decreases spontaneous activity, but paradoxically increases evoked network activity

    PubMed Central

    Goel, Anubhuti

    2013-01-01

    Neural dynamics generated within cortical networks play a fundamental role in brain function. However, the learning rules that allow recurrent networks to generate functional dynamic regimes, and the degree to which these regimes are themselves plastic, are not known. In this study we examined plasticity of network dynamics in cortical organotypic slices in response to chronic changes in activity. Studies have typically manipulated network activity pharmacologically; we used chronic electrical stimulation to increase activity in in vitro cortical circuits in a more physiological manner. Slices were stimulated with “implanted” electrodes for 4 days. Chronic electrical stimulation or treatment with bicuculline decreased spontaneous activity as predicted by homeostatic learning rules. Paradoxically, however, whereas bicuculline decreased evoked network activity, chronic stimulation actually increased the likelihood that evoked stimulation elicited polysynaptic activity, despite a decrease in evoked monosynaptic strength. Furthermore, there was an inverse correlation between spontaneous and evoked activity, suggesting a homeostatic tradeoff between spontaneous and evoked activity. Within-slice experiments revealed that cells close to the stimulated electrode exhibited more evoked polysynaptic activity and less spontaneous activity than cells close to a control electrode. Collectively, our results establish that chronic stimulation changes the dynamic regimes of networks. In vitro studies of homeostatic plasticity typically lack any external input, and thus neurons must rely on “spontaneous” activity to reach homeostatic “set points.” However, in the presence of external input we propose that homeostatic learning rules seem to shift networks from spontaneous to evoked regimes. PMID:23324317

  5. Virtual versus Physical Channel for Sex Networking in Men Having Sex with Men of Sauna Customers in the City of Hong Kong

    PubMed Central

    Lee, Shui-Shan; Lam, Agnes N. S.; Lee, Chi-Kei; Wong, Ngai-Sze

    2012-01-01

    Background Advances in communication technology may affect networking pattern, thereby influencing the dynamics of sex partnership. The aim of the study is to explore the impacts of partner sourcing through internet and related channels on exposure risk to sexually transmitted infections (STI) including HIV. Methods Using venue-based sampling, a cross-sectional questionnaire survey was conducted at saunas frequented by men having sex with men (MSM) in Hong Kong. Comparison was made between MSM sourcing partners through physical venues alone versus concomitant users of physical and virtual channels, the latter referring to internet and smart-phone applications, using bivariate logistic regression. Results Over a 7-week study period, 299 MSM were recruited from 9 saunas. Three main types of sex partners were distinguished: steady (46.8%), regular (26.4%) and casual (96.0%) partners. Users of sauna (n = 78) were compared with concomitant users of saunas and virtual channels (n = 179) for partner sourcing. Sauna-visiting virtual channel users were younger and inclined to use selected physical venues for sourcing partners. Smart-phone users (n = 90) were not different from other internet-users in terms of age, education level and single/mixed self-identified body appearance. Classifying respondents into high risk and low risk MSM by their frequency of condom use, concomitant use of both sauna and virtual channels accounted for a higher proportion in the high risk category (71.6% vs. 58.2%, OR = 1.81, p<0.05). In virtual channel users, partner sourcing through smart-phone was not associated with a higher practice of unprotected sex. Conclusion MSM sauna customers commonly use virtual channels for sex partner sourcing. Unprotected sex is more prevalent in sauna customers who use virtual channel for sex partner sourcing. While the popularity of smart-phone is rising, its use is not associated with increased behavioural risk for HIV/STI transmission. PMID

  6. Adaptation and growth of tomato cells on the herbicide 2,6-dichlorobenzonitrile leads to production of unique cell walls virtually lacking a cellulose-xyloglucan network

    SciTech Connect

    Shedletzky, E.; Shmuel, M. ); Delmer, D.P. Michigan State Univ., East Lansing, MI ); Lamport, D.T.A. )

    1990-11-01

    Suspension-cultured cells of tomato (Lycopersicon esculentum VF 36) have been adapted to growth on high concentrations of 2,6-dichlorobenzonitrile, an herbicide which inhibits cellulose biosynthesis. The mechanism of adaptation appears to rest largely on the ability of these cells to divide and expand in the virtual absence of a cellulose-xyloglucan network. Walls of adapted cells growing on 2,6-dichlorobenzonitrile also differ from nonadapted cells by having reduced levels of hydroxyproline in protein, both in bound and salt-elutable form, and in having a much higher proportion of homogalacturonan and rhamnogalacturonan-like polymers. Most of these latter polymers are apparently cross-linked in the wall via phenolic-ester and/or phenolic ether linkages, and these polymers appear to represent the major load-bearing network in these unusual cell walls. The surprising finding that plant cells can survive in the virtual absence of a major load-bearing network in their primary cell walls indicates that plants possess remarkable flexibility for tolerating changes in wall composition.

  7. Using W-phase for regional source inversion: An application to the data from the virtual seismic network in the Western Pacific region

    NASA Astrophysics Data System (ADS)

    Liang, W.; Zhao, L.; Chen, P.; Yu, Y.; Liu, C.; Huang, B.; Kanamori, H.

    2009-12-01

    The W-phase inversion has been proven to be an efficient way to determine the magnitude and source mechanism of large earthquakes for tsunami warning purposes (Kanamori and Rivera, 2008). The Institute of Earth Sciences has exchanged seismic data in a real-time manner with other agencies in surrounding countries, including Japan, Vietnam, and Malaysia, to form a virtual seismic network in the western Pacific region. Any local organization may issue an earthquake report with its own data acquisition system individually. With the hypocentral information provided, we are able to apply this new technique to invert the data from this virtual regional network for the source mechanisms of large earthquakes which occurred on the major convergent plate boundary zones within 2-30 degrees. In this case, the W-phase will be completely retrieved in 1.5-12.5 minutes. To evaluate the reliability of inversion with this network geometry, we invert waveforms of scenario earthquakes synthesized by normal mode summation method. A series of examples were then studied to compare the difference between our results and the global CMT solutions. We hope this practical application will contribute to the tsunami mitigation and seismic hazard assessment in the Western Pacific and Southern Asia regions.

  8. Performance evaluation of multi-stratum resources integration based on network function virtualization in software defined elastic data center optical interconnect.

    PubMed

    Yang, Hui; Zhang, Jie; Ji, Yuefeng; Tian, Rui; Han, Jianrui; Lee, Young

    2015-11-30

    Data center interconnect with elastic optical network is a promising scenario to meet the high burstiness and high-bandwidth requirements of data center services. In our previous work, we implemented multi-stratum resilience between IP and elastic optical networks that allows to accommodate data center services. In view of this, this study extends to consider the resource integration by breaking the limit of network device, which can enhance the resource utilization. We propose a novel multi-stratum resources integration (MSRI) architecture based on network function virtualization in software defined elastic data center optical interconnect. A resource integrated mapping (RIM) scheme for MSRI is introduced in the proposed architecture. The MSRI can accommodate the data center services with resources integration when the single function or resource is relatively scarce to provision the services, and enhance globally integrated optimization of optical network and application resources. The overall feasibility and efficiency of the proposed architecture are experimentally verified on the control plane of OpenFlow-based enhanced software defined networking (eSDN) testbed. The performance of RIM scheme under heavy traffic load scenario is also quantitatively evaluated based on MSRI architecture in terms of path blocking probability, provisioning latency and resource utilization, compared with other provisioning schemes. PMID:26698748

  9. Virtual colonoscopy

    MedlinePlus

    Colonoscopy - virtual; CT colonography; Computed tomographic colonography; Colography - virtual ... standards for gastroenterologists for performing and interpreting diagnostic computed tomography colonography: 2011 update. Gastroenterology . 2011;141:2240-2266. ...

  10. Pattern Formation on Networks: from Localised Activity to Turing Patterns

    PubMed Central

    McCullen, Nick; Wagenknecht, Thomas

    2016-01-01

    Networks of interactions between competing species are used to model many complex systems, such as in genetics, evolutionary biology or sociology and knowledge of the patterns of activity they can exhibit is important for understanding their behaviour. The emergence of patterns on complex networks with reaction-diffusion dynamics is studied here, where node dynamics interact via diffusion via the network edges. Through the application of a generalisation of dynamical systems analysis this work reveals a fundamental connection between small-scale modes of activity on networks and localised pattern formation seen throughout science, such as solitons, breathers and localised buckling. The connection between solutions with a single and small numbers of activated nodes and the fully developed system-scale patterns are investigated computationally using numerical continuation methods. These techniques are also used to help reveal a much larger portion of of the full number of solutions that exist in the system at different parameter values. The importance of network structure is also highlighted, with a key role being played by nodes with a certain so-called optimal degree, on which the interaction between the reaction kinetics and the network structure organise the behaviour of the system. PMID:27273339

  11. Pattern Formation on Networks: from Localised Activity to Turing Patterns

    NASA Astrophysics Data System (ADS)

    McCullen, Nick; Wagenknecht, Thomas

    2016-06-01

    Networks of interactions between competing species are used to model many complex systems, such as in genetics, evolutionary biology or sociology and knowledge of the patterns of activity they can exhibit is important for understanding their behaviour. The emergence of patterns on complex networks with reaction-diffusion dynamics is studied here, where node dynamics interact via diffusion via the network edges. Through the application of a generalisation of dynamical systems analysis this work reveals a fundamental connection between small-scale modes of activity on networks and localised pattern formation seen throughout science, such as solitons, breathers and localised buckling. The connection between solutions with a single and small numbers of activated nodes and the fully developed system-scale patterns are investigated computationally using numerical continuation methods. These techniques are also used to help reveal a much larger portion of of the full number of solutions that exist in the system at different parameter values. The importance of network structure is also highlighted, with a key role being played by nodes with a certain so-called optimal degree, on which the interaction between the reaction kinetics and the network structure organise the behaviour of the system.

  12. Pattern Formation on Networks: from Localised Activity to Turing Patterns.

    PubMed

    McCullen, Nick; Wagenknecht, Thomas

    2016-01-01

    Networks of interactions between competing species are used to model many complex systems, such as in genetics, evolutionary biology or sociology and knowledge of the patterns of activity they can exhibit is important for understanding their behaviour. The emergence of patterns on complex networks with reaction-diffusion dynamics is studied here, where node dynamics interact via diffusion via the network edges. Through the application of a generalisation of dynamical systems analysis this work reveals a fundamental connection between small-scale modes of activity on networks and localised pattern formation seen throughout science, such as solitons, breathers and localised buckling. The connection between solutions with a single and small numbers of activated nodes and the fully developed system-scale patterns are investigated computationally using numerical continuation methods. These techniques are also used to help reveal a much larger portion of of the full number of solutions that exist in the system at different parameter values. The importance of network structure is also highlighted, with a key role being played by nodes with a certain so-called optimal degree, on which the interaction between the reaction kinetics and the network structure organise the behaviour of the system. PMID:27273339

  13. Recent evolution of China's virtual water trade: analysis of selected crops and considerations for policy

    NASA Astrophysics Data System (ADS)

    Shi, J.; Liu, J.; Pinter, L.

    2014-04-01

    China has dramatically increased its virtual water import over recent years. Many studies have focused on the quantity of traded virtual water, but very few go into analysing geographic distribution and the properties of China's virtual water trade network. This paper provides a calculation and analysis of the crop-related virtual water trade network of China based on 27 major primary crops between 1986 and 2009. The results show that China is a net importer of virtual water from water-abundant areas of North America and South America, and a net virtual water exporter to water-stressed areas of Asia, Africa, and Europe. Virtual water import is far larger than virtual water export, and in both import and export a small number of trade partners control the supply chain. Grain crops are the major contributors to virtual water trade, and among grain crops, soybeans, mostly imported from the US, Brazil and Argentina, are the most significant. In order to mitigate water scarcity and secure the food supply, virtual water should actively be incorporated into national water management strategies. And the sources of virtual water import need to be further diversified to reduce supply chain risks and increase resilience.

  14. Collective versus hub activation of epidemic phases on networks

    NASA Astrophysics Data System (ADS)

    Ferreira, Silvio C.; Sander, Renan S.; Pastor-Satorras, Romualdo

    2016-03-01

    We consider a general criterion to discern the nature of the threshold in epidemic models on scale-free (SF) networks. Comparing the epidemic lifespan of the nodes with largest degrees with the infection time between them, we propose a general dual scenario, in which the epidemic transition is either ruled by a hub activation process, leading to a null threshold in the thermodynamic limit, or given by a collective activation process, corresponding to a standard phase transition with a finite threshold. We validate the proposed criterion applying it to different epidemic models, with waning immunity or heterogeneous infection rates in both synthetic and real SF networks. In particular, a waning immunity, irrespective of its strength, leads to collective activation with finite threshold in scale-free networks with large degree exponent, at odds with canonical theoretical approaches.

  15. Correlated gene expression supports synchronous activity in brain networks

    PubMed Central

    Richiardi, Jonas; Altmann, Andre; Milazzo, Anna-Clare; Chang, Catie; Chakravarty, M. Mallar; Banaschewski, Tobias; Barker, Gareth J.; Bokde, Arun L.W.; Bromberg, Uli; Büchel, Christian; Conrod, Patricia; Fauth-Bühler, Mira; Flor, Herta; Frouin, Vincent; Gallinat, Jürgen; Garavan, Hugh; Gowland, Penny; Heinz, Andreas; Lemaître, Hervé; Mann, Karl F.; Martinot, Jean-Luc; Nees, Frauke; Paus, Tomáš; Pausova, Zdenka; Rietschel, Marcella; Robbins, Trevor W.; Smolka, Michael N.; Spanagel, Rainer; Ströhle, Andreas; Schumann, Gunter; Hawrylycz, Mike; Poline, Jean-Baptiste; Greicius, Michael D.

    2016-01-01

    During rest, brain activity is synchronized between different regions widely distributed throughout the brain, forming functional networks. However, the molecular mechanisms supporting functional connectivity remain undefined. We show that functional brain networks defined with resting-state functional magnetic resonance imaging can be recapitulated by using measures of correlated gene expression in a post mortem brain tissue data set. The set of 136 genes we identify is significantly enriched for ion channels. Polymorphisms in this set of genes significantly affect resting-state functional connectivity in a large sample of healthy adolescents. Expression levels of these genes are also significantly associated with axonal connectivity in the mouse. The results provide convergent, multimodal evidence that resting-state functional networks correlate with the orchestrated activity of dozens of genes linked to ion channel activity and synaptic function. PMID:26068849

  16. Non-equilibrium States of Active Filament Networks

    NASA Astrophysics Data System (ADS)

    Blackwell, Robert A.; Betterton, Meredith D.; Sweezy, Oliver M.; Glaser, Matthew A.

    2014-03-01

    Active networks of filamentous proteins and crosslinking motor proteins play a critical role in many cellular processes. Among the most important active networks is the mitotic spindle, an assembly of microtubules and crosslinking motor proteins that forms during cell division and that ultimately separates chromosomes into two daughter cells. To evolve a better understanding of spindle formation, structure, and dynamics, we have developed course-grained models of active networks composed of filaments, modeled as hard spherocylinders, in diffusive equilibrium with a reservoir of crosslinking motors, modeled as Hookean springs that can adsorb to microtubules and translocate at finite velocity along the microtubule axis. We explore the phase diagram and other characteristics of this model in two and three dimensions as a function of filament packing fraction, and of crosslink concentration, velocity, and adsorption and desorption rates. We observe a variety of interesting emergent behaviors including sorting of filaments into polar domains, generation of extensile stress, and superdiffusive transport. DMR-0820579

  17. Passive vs. active virtual reality learning: the effects on short- and long-term memory of anatomical structures.

    PubMed

    Phelps, Andrew; Fritchle, Alicia; Hoffman, Helene

    2004-01-01

    This pilot study compares the differences in learning outcomes when students are presented with either an active (student-centered) or passive (teacher-centered) virtual reality-based anatomy lesson. The "active" lesson used UCSD's Anatomic VisualizeR and enabled students to interact with 3D models and control presentation of learning materials. The "passive" lesson used a digital recording of an anatomical expert's tour of the same VR lesson played back as a QuickTime movie. Subsequent examination of the recall and retention of the studied anatomic objects were comparable in both groups. Issues underlying these results are discussed. PMID:15544293

  18. Control of a virtual vehicle influences postural activity and motion sickness.

    PubMed

    Dong, Xiao; Yoshida, Ken; Stoffregen, Thomas A

    2011-06-01

    Everyday experience suggests that drivers are less susceptible to motion sickness than passengers. In the context of inertial motion (i.e., physical displacement), this effect has been confirmed in laboratory research using whole body motion devices. We asked whether a similar effect would occur in the context of simulated vehicles in a visual virtual environment. We used a yoked control design in which one member of each pair of participants played a driving video game (i.e., drove a virtual automobile). A recording of that performance was viewed (in a separate session) by the other member of the pair. Thus, the two members of each pair were exposed to identical visual motion stimuli, but the risk of behavioral contagion was minimized. Participants who drove the virtual vehicle (drivers) were less likely to report motion sickness than participants who viewed game recordings (passengers). Data on head and torso movement revealed that drivers tended to move more than passengers, and that the movements of drivers were more predictable than the movements of passengers. Before the onset of subjective symptoms of motion sickness movement differed between participants who (later) reported motion sickness and those who did not, consistent with a prediction of the postural instability theory of motion sickness. The results confirm that control is an important factor in the etiology of motion sickness and extend this finding to the control of noninertial virtual vehicles. PMID:21604911

  19. Analysing the Suitability of Virtual Worlds for Direct Instruction and Individual Learning Activities

    ERIC Educational Resources Information Center

    Zarraonandia, Telmo; Francese, Rita; Passero, Ignazio; Diaz, Paloma; Tortora, Genoveffa

    2014-01-01

    Despite several researchers reporting evidence that 3D Virtual Worlds can be used to effectively support educational processes in recent years, the integration of this technology in real learning processes is not as commonplace as in other educational technologies. Instructional designers have to balance the cost associated with the development of…

  20. Coordinating Computing, Network and Archiving activities within INAF

    NASA Astrophysics Data System (ADS)

    Pasian, F.; Bodo, G.; Fini, L.; Garilli, B.; Longo, G.; Massimino, P.; Nanni, M.; Smareglia, R.

    When INAF was reformed, it was decided to create a `Computing, Network and Archives Service' within the Projects Department, in order to coordinate all computer-related activities and to properly harmonize management and development policies in the field. A `Computing, Network and Archives Committee' was immediately nominated for the duration of one year to cope with the immediate needs. The Committee has the task of identifying and making operational strategies to coordinate activities in the areas of interest, improving service to all users, implementing synergies and economies, while guaranteeing a single INAF contact point for all external institutions working in the field.

  1. Fast transient networks in spontaneous human brain activity

    PubMed Central

    Baker, Adam P; Brookes, Matthew J; Rezek, Iead A; Smith, Stephen M; Behrens, Timothy; Probert Smith, Penny J; Woolrich, Mark

    2014-01-01

    To provide an effective substrate for cognitive processes, functional brain networks should be able to reorganize and coordinate on a sub-second temporal scale. We used magnetoencephalography recordings of spontaneous activity to characterize whole-brain functional connectivity dynamics at high temporal resolution. Using a novel approach that identifies the points in time at which unique patterns of activity recur, we reveal transient (100–200 ms) brain states with spatial topographies similar to those of well-known resting state networks. By assessing temporal changes in the occurrence of these states, we demonstrate that within-network functional connectivity is underpinned by coordinated neuronal dynamics that fluctuate much more rapidly than has previously been shown. We further evaluate cross-network interactions, and show that anticorrelation between the default mode network and parietal regions of the dorsal attention network is consistent with an inability of the system to transition directly between two transient brain states. DOI: http://dx.doi.org/10.7554/eLife.01867.001 PMID:24668169

  2. BRAIN NETWORKS. Correlated gene expression supports synchronous activity in brain networks.

    PubMed

    Richiardi, Jonas; Altmann, Andre; Milazzo, Anna-Clare; Chang, Catie; Chakravarty, M Mallar; Banaschewski, Tobias; Barker, Gareth J; Bokde, Arun L W; Bromberg, Uli; Büchel, Christian; Conrod, Patricia; Fauth-Bühler, Mira; Flor, Herta; Frouin, Vincent; Gallinat, Jürgen; Garavan, Hugh; Gowland, Penny; Heinz, Andreas; Lemaître, Hervé; Mann, Karl F; Martinot, Jean-Luc; Nees, Frauke; Paus, Tomáš; Pausova, Zdenka; Rietschel, Marcella; Robbins, Trevor W; Smolka, Michael N; Spanagel, Rainer; Ströhle, Andreas; Schumann, Gunter; Hawrylycz, Mike; Poline, Jean-Baptiste; Greicius, Michael D

    2015-06-12

    During rest, brain activity is synchronized between different regions widely distributed throughout the brain, forming functional networks. However, the molecular mechanisms supporting functional connectivity remain undefined. We show that functional brain networks defined with resting-state functional magnetic resonance imaging can be recapitulated by using measures of correlated gene expression in a post mortem brain tissue data set. The set of 136 genes we identify is significantly enriched for ion channels. Polymorphisms in this set of genes significantly affect resting-state functional connectivity in a large sample of healthy adolescents. Expression levels of these genes are also significantly associated with axonal connectivity in the mouse. The results provide convergent, multimodal evidence that resting-state functional networks correlate with the orchestrated activity of dozens of genes linked to ion channel activity and synaptic function. PMID:26068849

  3. Assessing capacity and disease burden in a virtual network of New York City primary care providers following Hurricane Sandy.

    PubMed

    Sebek, Kimberly; Jacobson, Laura; Wang, Jason; Newton-Dame, Remle; Singer, Jesse

    2014-08-01

    Urban contexts introduce unique challenges that must be addressed to ensure that areas of high population density can function when disasters occur. The ability to generate useful data to guide decision-making is critical in this context. Widespread adoption of electronic health record (EHR) systems in recent years has created electronic data sources and networks that may play an important role in public health surveillance efforts, including in post-disaster situations. The Primary Care Information Project (PCIP) at the New York City Department of Health and Mental Hygiene has partnered with local clinicians to establish an electronic data system, and this network provides infrastructure to support primary care surveillance activities in New York City. After Hurricane Sandy, PCIP generated several sets of data to contribute to the city's efforts to assess the impact of the storm, including daily connectivity data to establish practice operations, data to examine patterns of primary care utilization in severely affected and less affected areas, and data on the frequency of respiratory infection diagnosis in the primary care setting. Daily patient visit data from three heavily affected neighborhoods showed the health department where primary care capacity was most affected in the weeks following Sandy. Overall transmission data showed that practices in less affected areas were quicker to return to normal reporting patterns, while those in more affected areas did not resume normal data transmissions for a few months. Rates of bronchitis increased after Sandy compared to the two prior years; while this was most likely attributable to a more severe flu season, it demonstrates the capacity of primary care networks to pick up on these types of post-emergency trends. Hurricane Sandy was the first disaster situation where PCIP was asked to assess public health impact, generating information that could contribute to aid and recovery efforts. This experience allowed us to

  4. Slowing of Hippocampal Activity Correlates with Cognitive Decline in Early Onset Alzheimer's Disease. An MEG Study with Virtual Electrodes.

    PubMed

    Engels, Marjolein M A; Hillebrand, Arjan; van der Flier, Wiesje M; Stam, Cornelis J; Scheltens, Philip; van Straaten, Elisabeth C W

    2016-01-01

    Pathology in Alzheimer's disease (AD) starts in the entorhinal cortex and hippocampus. Because of their deep location, activity from these areas is difficult to record with conventional electro- or magnetoencephalography (EEG/MEG). The purpose of this study was to explore hippocampal activity in AD patients and healthy controls using "virtual MEG electrodes". We used resting-state MEG recordings from 27 early onset AD patients [age 60.6 ± 5.4, 12 females, mini-mental state examination (MMSE) range: 19-28] and 26 cognitively healthy age- and gender-matched controls (age 61.8 ± 5.5, 14 females). Activity was reconstructed using beamformer-based virtual electrodes for 78 cortical regions and 6 hippocampal regions. Group differences in peak frequency and relative power in six frequency bands were identified using permutation testing. For the patients, spearman correlations between the MMSE scores and peak frequency or relative power were calculated. Moreover, receiver operator characteristic curves were plotted to estimate the diagnostic accuracy. We found a lower hippocampal peak frequency in AD compared to controls, which, in the patients, correlated positively with MMSE [r(25) = 0.61; p < 0.01] whereas hippocampal relative theta power correlated negatively with MMSE [r(25) = -0.54; p < 0.01]. Cortical peak frequency was also lower in AD in association areas. Furthermore, cortical peak frequency correlated positively with MMSE [r(25) = 0.43; p < 0.05]. In line with this finding, relative theta power was higher in AD across the cortex, and relative alpha and beta power was lower in more circumscribed areas. The average cortical relative theta power was the best discriminator between AD and controls (sensitivity 82%; specificity 81%). Using beamformer-based virtual electrodes, we were able to detect hippocampal activity in AD. In AD, this hippocampal activity is slowed, and correlates better with cognition than the (slowed) activity in cortical areas. On the other

  5. Network effect of knowledge spillover: Scale-free networks stimulate R&D activities and accelerate economic growth

    NASA Astrophysics Data System (ADS)

    Konno, Tomohiko

    2016-09-01

    We study how knowledge spillover networks affect research and development (R&D) activities and economic growth. For this purpose, we extend a Schumpeterian growth model to the one on networks that depict the knowledge spillover relationships of R&D. We show that scale-free networks stimulate R&D activities and accelerate economic growth.

  6. Persistent Activity in Neural Networks with Dynamic Synapses

    PubMed Central

    Barak, Omri; Tsodyks, Misha

    2007-01-01

    Persistent activity states (attractors), observed in several neocortical areas after the removal of a sensory stimulus, are believed to be the neuronal basis of working memory. One of the possible mechanisms that can underlie persistent activity is recurrent excitation mediated by intracortical synaptic connections. A recent experimental study revealed that connections between pyramidal cells in prefrontal cortex exhibit various degrees of synaptic depression and facilitation. Here we analyze the effect of synaptic dynamics on the emergence and persistence of attractor states in interconnected neural networks. We show that different combinations of synaptic depression and facilitation result in qualitatively different network dynamics with respect to the emergence of the attractor states. This analysis raises the possibility that the framework of attractor neural networks can be extended to represent time-dependent stimuli. PMID:17319739

  7. Patterns of Neural Activity in Networks with Complex Connectivity

    NASA Astrophysics Data System (ADS)

    Solla, Sara A.

    2008-03-01

    An understanding of emergent dynamics on complex networks requires investigating the interplay between the intrinsic dynamics of the node elements and the connectivity of the network in which they are embedded. In order to address some of these questions in a specific scenario of relevance to the dynamical states of neural ensembles, we have studied the collective behavior of excitable model neurons in a network with small-world topology. The small-world network has local lattice order, but includes a number of randomly placed connections that may provide connectivity shortcuts. This topology bears a schematic resemblance to the connectivity of the cerebral cortex, in which neurons are most strongly coupled to nearby cells within fifty to a hundred micrometers, but also make projections to cells millimeters away. We find that the dynamics of this small-world network of excitable neurons depend mostly on both the density of shortcuts and the delay associated with neuronal projections. In the regime of low shortcut density, the system exhibits persistent activity in the form of propagating waves, which annihilate upon collision and are spawned anew via the re-injection of activity through shortcut connections. As the density of shortcuts reaches a critical value, the system undergoes a transition to failure. The critical shortcut density results from matching the time associated with a recurrent path through the network to an intrinsic recovery time of the individual neurons. Furthermore, if the delay associated with neuronal interactions is sufficiently long, activity reemerges above the critical density of shortcuts. The activity in this regime exhibits long, chaotic transients composed of noisy, large-amplitude population bursts.

  8. Impact of Network Activity on the Spread of Infectious Diseases through the German Pig Trade Network

    PubMed Central

    Lebl, Karin; Lentz, Hartmut H. K.; Pinior, Beate; Selhorst, Thomas

    2016-01-01

    The trade of livestock is an important and growing economic sector, but it is also a major factor in the spread of diseases. The spreading of diseases in a trade network is likely to be influenced by how often existing trade connections are active. The activity α is defined as the mean frequency of occurrences of existing trade links, thus 0 < α ≤ 1. The observed German pig trade network had an activity of α = 0.11, thus each existing trade connection between two farms was, on average, active at about 10% of the time during the observation period 2008–2009. The aim of this study is to analyze how changes in the activity level of the German pig trade network influence the probability of disease outbreaks, size, and duration of epidemics for different disease transmission probabilities. Thus, we want to investigate the question, whether it makes a difference for a hypothetical spread of an animal disease to transport many animals at the same time or few animals at many times. A SIR model was used to simulate the spread of a disease within the German pig trade network. Our results show that for transmission probabilities <1, the outbreak probability increases in the case of a decreased frequency of animal transports, peaking range of α from 0.05 to 0.1. However, for the final outbreak size, we find that a threshold exists such that finite outbreaks occur only above a critical value of α, which is ~0.1, and therefore in proximity of the observed activity level. Thus, although the outbreak probability increased when decreasing α, these outbreaks affect only a small number of farms. The duration of the epidemic peaks at an activity level in the range of α = 0.2–0.3. Additionally, the results of our simulations show that even small changes in the activity level of the German pig trade network would have dramatic effects on outbreak probability, outbreak size, and epidemic duration. Thus, we can conclude and recommend that the network activity

  9. Homeostatic Activity-Dependent Tuning of Recurrent Networks for Robust Propagation of Activity

    PubMed Central

    Evers, Jan Felix; Eglen, Stephen J.

    2016-01-01

    Developing neuronal networks display spontaneous bursts of action potentials that are necessary for circuit organization and tuning. While spontaneous activity has been shown to instruct map formation in sensory circuits, it is unknown whether it plays a role in the organization of motor networks that produce rhythmic output. Using computational modeling, we investigate how recurrent networks of excitatory and inhibitory neuronal populations assemble to produce robust patterns of unidirectional and precisely timed propagating activity during organism locomotion. One example is provided by the motor network in Drosophila larvae, which generates propagating peristaltic waves of muscle contractions during crawling. We examine two activity-dependent models, which tune weak network connectivity based on spontaneous activity patterns: a Hebbian model, where coincident activity in neighboring populations strengthens connections between them; and a homeostatic model, where connections are homeostatically regulated to maintain a constant level of excitatory activity based on spontaneous input. The homeostatic model successfully tunes network connectivity to generate robust activity patterns with appropriate timing relationships between neighboring populations. These timing relationships can be modulated by the properties of spontaneous activity, suggesting its instructive role for generating functional variability in network output. In contrast, the Hebbian model fails to produce the tight timing relationships between neighboring populations required for unidirectional activity propagation, even when additional assumptions are imposed to constrain synaptic growth. These results argue that homeostatic mechanisms are more likely than Hebbian mechanisms to tune weak connectivity based on spontaneous input in a recurrent network for rhythm generation and robust activity propagation. SIGNIFICANCE STATEMENT How are neural circuits organized and tuned to maintain stable function

  10. Citation Networks as Indicators of Journalism Research Activity.

    ERIC Educational Resources Information Center

    Tankard, James W.; And Others

    1984-01-01

    Reviews citation networks and discovers that the six major areas of activity in mass communication research are (1) television and politics, (2) sociological studies of journalists, (3) agenda setting, (4) the effects of mass communication, (5) the credibility of various news media, and (6) the characteristics of users and nonusers of mass media.…

  11. Kainate-induced network activity in the anterior cingulate cortex.

    PubMed

    Shinozaki, R; Hojo, Y; Mukai, H; Hashizume, M; Murakoshi, T

    2016-06-14

    Anterior cingulate cortex (ACC) plays a pivotal role in higher order processing of cognition, attention and emotion. The network oscillation is considered an essential means for integration of these CNS functions. The oscillation power and coherence among related areas are often dis-regulated in several psychiatric and pathological conditions with a hemispheric asymmetric manner. Here we describe the network-based activity of field potentials recorded from the superficial layer of the mouse ACC in vitro using submerged type recordings. A short activation by kainic acid administration to the preparation induced populational activities ranging over several frequency bands including theta (3-8Hz), alpha (8-12Hz), beta (13-30Hz), low gamma (30-50Hz) and high gamma (50-80Hz). These responses were repeatable and totally abolished by tetrodotoxin, and greatly diminished by inhibitors of ionotropic and metabotropic glutamate receptors, GABAA receptor or gap-junctions. These observations suggest that the kainate-induced network activity can be a useful model of the network oscillation in the ACC circuit. PMID:26993576

  12. California Health Services/Educational Activities. Consortium Network.

    ERIC Educational Resources Information Center

    White, Charles H.

    Profiles are presented of each of the 10 consortia that make up the California Health Services/Education Activities (HS/EA) network (new relationships between educational facilities where health care manpower is trained in the community settings where they practice). The first part of the booklet is a comparative analysis of (1) Area Health…

  13. The Use of Virtual Learning Environment (VLE) and Social Network Site (SNS) Hosted Forums in Higher Education: A Preliminary Examination

    ERIC Educational Resources Information Center

    Hollyhead, Andrew; Edwards, David J.; Holt, Gary D.

    2012-01-01

    Grounded theory is used to examine the role and application of both educator-led and student-led forums within a virtual learning environment (VLE) of a higher education institution (HEI). The study reports experiences and perceptions of academics in two faculties (business and technology) in the HEI who use both asynchronous VLE forums and social…

  14. Building a Collaborative Network To Support Michigan Community Colleges in a Global Market. Michigan Community College Virtual Learning Collaborative.

    ERIC Educational Resources Information Center

    Michigan Community Coll. Association, Lansing.

    This report describes the Michigan Community College Virtual Learning Collaborative (MCCVLC), an innovative educational environment that provides learners access to high-quality courses through a variety of technologies. The following describe the collaborative's guiding principles: (1) faculty and staff at all Michigan community colleges will…

  15. Photonic network R and D activities in Japan

    NASA Astrophysics Data System (ADS)

    Kitayama, Ken-ichi; Miki, Tetsuya; Morioka, Toshio; Tsushima, Hideaki; Koga, Masafumi; Mori, Kazuyuki; Araki, Soichiro; Sato, Ken-ichi; Onaka, Hiroshi; Namiki, Shu; Aovama, Tomonori

    2005-11-01

    R and D activities on photonic networks in Japan are presented. First, milestones in current, ongoing R and D programs supported by Japanese government agencies are introduced, including long-distance and WDM fiber transmission, wavelength routing, optical burst switching, and control plane technology for IP backbone networks. Their goal was set to evolve a legacy telecommunications network to IP over WDM networks by introducing technologies for WDM and wavelength routing. We then discuss the perspectives of so-called PHASE II R and D programs for photonic networks over the next five years until 2010, by focusing on the report which has been recently issued by the Photonic Internet Forum (PIF), a consortium that has major carriers, telecom vendors, and Japanese academics as members. The PHASE II R and D programs should serve to establish a photonic platform to provide abundant bandwidth on demand, at any time on a real-time basis through the customer's initiative, to promote bandwidth-rich applications, such as grid computing, real-time digital-cinema streaming, medical and educational applications, and network storage in e-commerce.

  16. Detection of interplanetary activity using artificial neural networks

    NASA Astrophysics Data System (ADS)

    Gothoskar, Pradeep; Khobragade, Shyam

    1995-12-01

    Early detection of interplanetary activity is important when attempting to associate, with better accuracy, interplanetary phenomena with solar activity and geomagnetic disturbances. However, for a large number of interplanetary observations to be done every day, extensive data analysis is required, leading to a delay in the detection of transient interplanetary activity. In particular, the interplanetary scintillation (IPS) observations done with Ooty Radio Telescope (ORT) need extensive human effort to reduce the data and to model, often subjectively, the scintillation power spectra. We have implemented an artificial neural network (ANN) to detect interplanetary activity using the power spectrum scintillation. The ANN was trained to detect the disturbed power spectra, used as an indicator of the interplanetary activity, and to recognize normal and strong scattering spectra from a large data base of IPS spectra. The coincidence efficiency of classification by the network compared with the experts' judgement to detect the normal, disturbed and strong scattering spectra was found to be greater than 80 per cent. The neural network, when applied during the IPS mapping programme to provide early indication of interplanetary activity, would significantly help the ongoing efforts to predict geomagnetic disturbances.

  17. Design and implementation of dynamic hybrid Honeypot network

    NASA Astrophysics Data System (ADS)

    Qiao, Peili; Hu, Shan-Shan; Zhai, Ji-Qiang

    2013-05-01

    The method of constructing a dynamic and self-adaptive virtual network is suggested to puzzle adversaries, delay and divert attacks, exhaust attacker resources and collect attacking information. The concepts of Honeypot and Honeyd, which is the frame of virtual Honeypot are introduced. The techniques of network scanning including active fingerprint recognition are analyzed. Dynamic virtual network system is designed and implemented. A virtual network similar to real network topology is built according to the collected messages from real environments in this system. By doing this, the system can perplex the attackers when Hackers attack and can further analyze and research the attacks. The tests to this system prove that this design can successfully simulate real network environment and can be used in network security analysis.

  18. Virtual Worlds for Educators

    ERIC Educational Resources Information Center

    Dembo, Steve

    2008-01-01

    This article describes an online experience that has not only created a fantasy world for the general public but has enabled some tech-savvy educators to create virtual educational opportunities. Second Life, or SL, is a 3-D Internet-based virtual world created by Linden Lab and populated by nearly 1,000,000 active users worldwide since 2003.…

  19. Optimal active power dispatch by network flow approach

    SciTech Connect

    Carvalho, M.F. ); Soares, S.; Ohishi, T. )

    1988-11-01

    In this paper the optimal active power dispatch problem is formulated as a nonlinear capacitated network flow problem with additional linear constraints. Transmission flow limits and both Kirchhoff's laws are taken into account. The problem is solved by a Generalized Upper Bounding technique that takes advantage of the network flow structure of the problem. The new approach has potential applications on power systems problems such as economic dispatch, load supplying capability, minimum load shedding, and generation-transmission reliability. The paper also reviews the use of transportation models for power system analysis. A detailed illustrative example is presented.

  20. Enhanced activation of motor execution networks using action observation combined with imagination of lower limb movements.

    PubMed

    Villiger, Michael; Estévez, Natalia; Hepp-Reymond, Marie-Claude; Kiper, Daniel; Kollias, Spyros S; Eng, Kynan; Hotz-Boendermaker, Sabina

    2013-01-01

    The combination of first-person observation and motor imagery, i.e. first-person observation of limbs with online motor imagination, is commonly used in interactive 3D computer gaming and in some movie scenes. These scenarios are designed to induce a cognitive process in which a subject imagines himself/herself acting as the agent in the displayed movement situation. Despite the ubiquity of this type of interaction and its therapeutic potential, its relationship to passive observation and imitation during observation has not been directly studied using an interactive paradigm. In the present study we show activation resulting from observation, coupled with online imagination and with online imitation of a goal-directed lower limb movement using functional MRI (fMRI) in a mixed block/event-related design. Healthy volunteers viewed a video (first-person perspective) of a foot kicking a ball. They were instructed to observe-only the action (O), observe and simultaneously imagine performing the action (O-MI), or imitate the action (O-IMIT). We found that when O-MI was compared to O, activation was enhanced in the ventralpremotor cortex bilaterally, left inferior parietal lobule and left insula. The O-MI and O-IMIT conditions shared many activation foci in motor relevant areas as confirmed by conjunction analysis. These results show that (i) combining observation with motor imagery (O-MI) enhances activation compared to observation-only (O) in the relevant foot motor network and in regions responsible for attention, for control of goal-directed movements and for the awareness of causing an action, and (ii) it is possible to extensively activate the motor execution network using O-MI, even in the absence of overt movement. Our results may have implications for the development of novel virtual reality interactions for neurorehabilitation interventions and other applications involving training of motor tasks. PMID:24015241

  1. Enhanced Activation of Motor Execution Networks Using Action Observation Combined with Imagination of Lower Limb Movements

    PubMed Central

    Villiger, Michael; Estévez, Natalia; Hepp-Reymond, Marie-Claude; Kiper, Daniel; Kollias, Spyros S.; Eng, Kynan; Hotz-Boendermaker, Sabina

    2013-01-01

    The combination of first-person observation and motor imagery, i.e. first-person observation of limbs with online motor imagination, is commonly used in interactive 3D computer gaming and in some movie scenes. These scenarios are designed to induce a cognitive process in which a subject imagines himself/herself acting as the agent in the displayed movement situation. Despite the ubiquity of this type of interaction and its therapeutic potential, its relationship to passive observation and imitation during observation has not been directly studied using an interactive paradigm. In the present study we show activation resulting from observation, coupled with online imagination and with online imitation of a goal-directed lower limb movement using functional MRI (fMRI) in a mixed block/event-related design. Healthy volunteers viewed a video (first-person perspective) of a foot kicking a ball. They were instructed to observe-only the action (O), observe and simultaneously imagine performing the action (O-MI), or imitate the action (O-IMIT). We found that when O-MI was compared to O, activation was enhanced in the ventralpremotor cortex bilaterally, left inferior parietal lobule and left insula. The O-MI and O-IMIT conditions shared many activation foci in motor relevant areas as confirmed by conjunction analysis. These results show that (i) combining observation with motor imagery (O-MI) enhances activation compared to observation-only (O) in the relevant foot motor network and in regions responsible for attention, for control of goal-directed movements and for the awareness of causing an action, and (ii) it is possible to extensively activate the motor execution network using O-MI, even in the absence of overt movement. Our results may have implications for the development of novel virtual reality interactions for neurorehabilitation interventions and other applications involving training of motor tasks. PMID:24015241

  2. Meditation leads to reduced default mode network activity beyond an active task.

    PubMed

    Garrison, Kathleen A; Zeffiro, Thomas A; Scheinost, Dustin; Constable, R Todd; Brewer, Judson A

    2015-09-01

    Meditation has been associated with relatively reduced activity in the default mode network, a brain network implicated in self-related thinking and mind wandering. However, previous imaging studies have typically compared meditation to rest, despite other studies having reported differences in brain activation patterns between meditators and controls at rest. Moreover, rest is associated with a range of brain activation patterns across individuals that has only recently begun to be better characterized. Therefore, in this study we compared meditation to another active cognitive task, both to replicate the findings that meditation is associated with relatively reduced default mode network activity and to extend these findings by testing whether default mode activity was reduced during meditation, beyond the typical reductions observed during effortful tasks. In addition, prior studies had used small groups, whereas in the present study we tested these hypotheses in a larger group. The results indicated that meditation is associated with reduced activations in the default mode network, relative to an active task, for meditators as compared to controls. Regions of the default mode network showing a Group × Task interaction included the posterior cingulate/precuneus and anterior cingulate cortex. These findings replicate and extend prior work indicating that the suppression of default mode processing may represent a central neural process in long-term meditation, and they suggest that meditation leads to relatively reduced default mode processing beyond that observed during another active cognitive task. PMID:25904238

  3. Reactivation of visual-evoked activity in human cortical networks.

    PubMed

    Chelaru, Mircea I; Hansen, Bryan J; Tandon, Nitin; Conner, Chris R; Szukalski, Susann; Slater, Jeremy D; Kalamangalam, Giridhar P; Dragoi, Valentin

    2016-06-01

    In the absence of sensory input, neuronal networks are far from being silent. Whether spontaneous changes in ongoing activity reflect previous sensory experience or stochastic fluctuations in brain activity is not well understood. Here we demonstrate reactivation of stimulus-evoked activity that is distributed across large areas in the human brain. We performed simultaneous electrocorticography recordings from occipital, parietal, temporal, and frontal areas in awake humans in the presence and absence of sensory stimulation. We found that, in the absence of visual input, repeated exposure to brief natural movies induces robust stimulus-specific reactivation at individual recording sites. The reactivation sites were characterized by greater global connectivity compared with those sites that did not exhibit reactivation. Our results indicate a surprising degree of short-term plasticity across multiple networks in the human brain as a result of repeated exposure to unattended information. PMID:26984423

  4. Mind in the Gap Between Neural and Social Networks - Cyberspace and Virtual Reality in Psychiatry and Healthcare.

    PubMed

    Šendula-Jengić, Vesna; Šendula-Pavelić, Martina; Hodak, Jelena

    2016-06-01

    In terms of health and healthcare cyberspace and virtual reality can be used differently and for different purposes and consequently create different outcomes. The three main areas which we shall discuss here are: 1) cyberspace as provider of health information and self-help resources, since the anonymity cyberspace provides is particularly important in the highly stigmatized field of psychiatry where a large number of people never seek professional help, which in turn negatively affects not only the person in question, but the family and ultimately the society (work efficiency, disability-adjusted life year - DALY, etc.), 2) cyberspace and virtual reality (VR) as cause of psychopathology, starting from violent behaviour, to addictive behaviour and other, 3) and finally cyberspace and VR as providers of efficient professional therapy in the field of psychiatry. PMID:27287782

  5. Dynamical state of the network determines the efficacy of single neuron properties in shaping the network activity

    PubMed Central

    Sahasranamam, Ajith; Vlachos, Ioannis; Aertsen, Ad; Kumar, Arvind

    2016-01-01

    Spike patterns are among the most common electrophysiological descriptors of neuron types. Surprisingly, it is not clear how the diversity in firing patterns of the neurons in a network affects its activity dynamics. Here, we introduce the state-dependent stochastic bursting neuron model allowing for a change in its firing patterns independent of changes in its input-output firing rate relationship. Using this model, we show that the effect of single neuron spiking on the network dynamics is contingent on the network activity state. While spike bursting can both generate and disrupt oscillations, these patterns are ineffective in large regions of the network state space in changing the network activity qualitatively. Finally, we show that when single-neuron properties are made dependent on the population activity, a hysteresis like dynamics emerges. This novel phenomenon has important implications for determining the network response to time-varying inputs and for the network sensitivity at different operating points. PMID:27212008

  6. Dynamical state of the network determines the efficacy of single neuron properties in shaping the network activity.

    PubMed

    Sahasranamam, Ajith; Vlachos, Ioannis; Aertsen, Ad; Kumar, Arvind

    2016-01-01

    Spike patterns are among the most common electrophysiological descriptors of neuron types. Surprisingly, it is not clear how the diversity in firing patterns of the neurons in a network affects its activity dynamics. Here, we introduce the state-dependent stochastic bursting neuron model allowing for a change in its firing patterns independent of changes in its input-output firing rate relationship. Using this model, we show that the effect of single neuron spiking on the network dynamics is contingent on the network activity state. While spike bursting can both generate and disrupt oscillations, these patterns are ineffective in large regions of the network state space in changing the network activity qualitatively. Finally, we show that when single-neuron properties are made dependent on the population activity, a hysteresis like dynamics emerges. This novel phenomenon has important implications for determining the network response to time-varying inputs and for the network sensitivity at different operating points. PMID:27212008

  7. Optimal stimulus scheduling for active estimation of evoked brain networks

    NASA Astrophysics Data System (ADS)

    Kafashan, MohammadMehdi; Ching, ShiNung

    2015-12-01

    Objective. We consider the problem of optimal probing to learn connections in an evoked dynamic network. Such a network, in which each edge measures an input-output relationship between sites in sensor/actuator-space, is relevant to emerging applications in neural mapping and neural connectivity estimation. Approach. We show that the problem of scheduling nodes to a probe (i.e., stimulate) amounts to a problem of optimal sensor scheduling. Main results. By formulating the evoked network in state-space, we show that the solution to the greedy probing strategy has a convenient form and, under certain conditions, is optimal over a finite horizon. We adopt an expectation maximization technique to update the state-space parameters in an online fashion and demonstrate the efficacy of the overall approach in a series of detailed numerical examples. Significance. The proposed method provides a principled means to actively probe time-varying connections in neuronal networks. The overall method can be implemented in real time and is particularly well-suited to applications in stimulation-based cortical mapping in which the underlying network dynamics are changing over time.

  8. 3D Actin Network Centerline Extraction with Multiple Active Contours

    PubMed Central

    Xu, Ting; Vavylonis, Dimitrios; Huang, Xiaolei

    2013-01-01

    Fluorescence microscopy is frequently used to study two and three dimensional network structures formed by cytoskeletal polymer fibers such as actin filaments and actin cables. While these cytoskeletal structures are often dilute enough to allow imaging of individual filaments or bundles of them, quantitative analysis of these images is challenging. To facilitate quantitative, reproducible and objective analysis of the image data, we propose a semi-automated method to extract actin networks and retrieve their topology in 3D. Our method uses multiple Stretching Open Active Contours (SOACs) that are automatically initialized at image intensity ridges and then evolve along the centerlines of filaments in the network. SOACs can merge, stop at junctions, and reconfigure with others to allow smooth crossing at junctions of filaments. The proposed approach is generally applicable to images of curvilinear networks with low SNR. We demonstrate its potential by extracting the centerlines of synthetic meshwork images, actin networks in 2D Total Internal Reflection Fluorescence Microscopy images, and 3D actin cable meshworks of live fission yeast cells imaged by spinning disk confocal microscopy. Quantitative evaluation of the method using synthetic images shows that for images with SNR above 5.0, the average vertex error measured by the distance between our result and ground truth is 1 voxel, and the average Hausdorff distance is below 10 voxels. PMID:24316442

  9. 3D Filament Network Segmentation with Multiple Active Contours

    NASA Astrophysics Data System (ADS)

    Xu, Ting; Vavylonis, Dimitrios; Huang, Xiaolei

    2014-03-01

    Fluorescence microscopy is frequently used to study two and three dimensional network structures formed by cytoskeletal polymer fibers such as actin filaments and microtubules. While these cytoskeletal structures are often dilute enough to allow imaging of individual filaments or bundles of them, quantitative analysis of these images is challenging. To facilitate quantitative, reproducible and objective analysis of the image data, we developed a semi-automated method to extract actin networks and retrieve their topology in 3D. Our method uses multiple Stretching Open Active Contours (SOACs) that are automatically initialized at image intensity ridges and then evolve along the centerlines of filaments in the network. SOACs can merge, stop at junctions, and reconfigure with others to allow smooth crossing at junctions of filaments. The proposed approach is generally applicable to images of curvilinear networks with low SNR. We demonstrate its potential by extracting the centerlines of synthetic meshwork images, actin networks in 2D TIRF Microscopy images, and 3D actin cable meshworks of live fission yeast cells imaged by spinning disk confocal microscopy.

  10. Sensorimotor Training in Virtual Reality: A Review

    PubMed Central

    Adamovich, Sergei V.; Fluet, Gerard G.; Tunik, Eugene; Merians, Alma S.

    2010-01-01

    Recent experimental evidence suggests that rapid advancement of virtual reality (VR) technologies has great potential for the development of novel strategies for sensorimotor training in neurorehabilitation. We discuss what the adaptive and engaging virtual environments can provide for massive and intensive sensorimotor stimulation needed to induce brain reorganization. Second, discrepancies between the veridical and virtual feedback can be introduced in VR to facilitate activation of targeted brain networks, which in turn can potentially speed up the recovery process. Here we review the existing experimental evidence regarding the beneficial effects of training in virtual environments on the recovery of function in the areas of gait, upper extremity function and balance, in various patient populations. We also discuss possible mechanisms underlying these effects. We feel that future research in the area of virtual rehabilitation should follow several important paths. Imaging studies to evaluate the effects of sensory manipulation on brain activation patterns and the effect of various training parameters on long term changes in brain function are needed to guide future clinical inquiry. Larger clinical studies are also needed to establish the efficacy of sensorimotor rehabilitation using VR approaches in various clinical populations and most importantly, to identify VR training parameters that are associated with optimal transfer into real-world functional improvements. PMID:19713617

  11. CRAFFT: An Activity Prediction Model based on Bayesian Networks

    PubMed Central

    Nazerfard, Ehsan; Cook, Diane J.

    2014-01-01

    Recent advances in the areas of pervasive computing, data mining, and machine learning offer unique opportunities to provide health monitoring and assistance for individuals facing difficulties to live independently in their homes. Several components have to work together to provide health monitoring for smart home residents including, but not limited to, activity recognition, activity discovery, activity prediction, and prompting system. Compared to the significant research done to discover and recognize activities, less attention has been given to predict the future activities that the resident is likely to perform. Activity prediction components can play a major role in design of a smart home. For instance, by taking advantage of an activity prediction module, a smart home can learn context-aware rules to prompt individuals to initiate important activities. In this paper, we propose an activity prediction model using Bayesian networks together with a novel two-step inference process to predict both the next activity features and the next activity label. We also propose an approach to predict the start time of the next activity which is based on modeling the relative start time of the predicted activity using the continuous normal distribution and outlier detection. To validate our proposed models, we used real data collected from physical smart environments. PMID:25937847

  12. COMMUNICATION: Neuron network activity scales exponentially with synapse density

    NASA Astrophysics Data System (ADS)

    Brewer, G. J.; Boehler, M. D.; Pearson, R. A.; DeMaris, A. A.; Ide, A. N.; Wheeler, B. C.

    2009-02-01

    Neuronal network output in the cortex as a function of synapse density during development has not been explicitly determined. Synaptic scaling in cortical brain networks seems to alter excitatory and inhibitory synaptic inputs to produce a representative rate of synaptic output. Here, we cultured rat hippocampal neurons over a three-week period to correlate synapse density with the increase in spontaneous spiking activity. We followed the network development as synapse formation and spike rate in two serum-free media optimized for either (a) neuron survival (Neurobasal/B27) or (b) spike rate (NbActiv4). We found that while synaptophysin synapse density increased linearly with development, spike rates increased exponentially in developing neuronal networks. Synaptic receptor components NR1, GluR1 and GABA-A also increase linearly but with more excitatory receptors than inhibitory. These results suggest that the brain's information processing capability gains more from increasing connectivity of the processing units than increasing processing units, much as Internet information flow increases much faster than the linear number of nodes and connections.

  13. History and geography of virtual water trade

    NASA Astrophysics Data System (ADS)

    Carr, J. A.; D'Odorico, P.; Laio, F.; Ridolfi, L.

    2012-12-01

    The global trade of goods is associated with a virtual transfer of the water required for their production. The way changes in trade affect the virtual redistribution of freshwater resources has been recently documented through the analysis of the virtual water network. It is, however, unclear how these changes are contributed by different types of products and regions of the world. Here we show how the global patterns of virtual water transport are contributed by the trade of different commodity types, including plant, animal, luxury (e.g., coffee, tea, and alcohol), and other products (non-edible plant and animal products typically used for manufacturing). Major contributors to the virtual water network exhibit different trade patterns with regard to these commodity types with the net importers of virtual water relying on the supply of virtual water from a small percentage of the global population. Discrepancies exist among the different commodity networks. Surprisingly, while the total virtual water flux through the network has increased between 1986 and 2008, the global proportions associated with the four commodity groups have remained relatively stable. Here we discuss some major changes in the global patterns of virtual water trade with a focus on the increase in regional dependencies on foreign virtual water. The increase in virtual water trade and the percentage of the total virtual water flux in the network corresponding to plant, animals, luxury, and other commodities.

  14. Broken Detailed Balance of Filament Dynamics in Active Networks

    NASA Astrophysics Data System (ADS)

    Gladrow, J.; Fakhri, N.; MacKintosh, F. C.; Schmidt, C. F.; Broedersz, C. P.

    2016-06-01

    Myosin motor proteins drive vigorous steady-state fluctuations in the actin cytoskeleton of cells. Endogenous embedded semiflexible filaments such as microtubules, or added filaments such as single-walled carbon nanotubes are used as novel tools to noninvasively track equilibrium and nonequilibrium fluctuations in such biopolymer networks. Here, we analytically calculate shape fluctuations of semiflexible probe filaments in a viscoelastic environment, driven out of equilibrium by motor activity. Transverse bending fluctuations of the probe filaments can be decomposed into dynamic normal modes. We find that these modes no longer evolve independently under nonequilibrium driving. This effective mode coupling results in nonzero circulatory currents in a conformational phase space, reflecting a violation of detailed balance. We present predictions for the characteristic frequencies associated with these currents and investigate how the temporal signatures of motor activity determine mode correlations, which we find to be consistent with recent experiments on microtubules embedded in cytoskeletal networks.

  15. Broken Detailed Balance of Filament Dynamics in Active Networks.

    PubMed

    Gladrow, J; Fakhri, N; MacKintosh, F C; Schmidt, C F; Broedersz, C P

    2016-06-17

    Myosin motor proteins drive vigorous steady-state fluctuations in the actin cytoskeleton of cells. Endogenous embedded semiflexible filaments such as microtubules, or added filaments such as single-walled carbon nanotubes are used as novel tools to noninvasively track equilibrium and nonequilibrium fluctuations in such biopolymer networks. Here, we analytically calculate shape fluctuations of semiflexible probe filaments in a viscoelastic environment, driven out of equilibrium by motor activity. Transverse bending fluctuations of the probe filaments can be decomposed into dynamic normal modes. We find that these modes no longer evolve independently under nonequilibrium driving. This effective mode coupling results in nonzero circulatory currents in a conformational phase space, reflecting a violation of detailed balance. We present predictions for the characteristic frequencies associated with these currents and investigate how the temporal signatures of motor activity determine mode correlations, which we find to be consistent with recent experiments on microtubules embedded in cytoskeletal networks. PMID:27367410

  16. Active transport and cluster formation on 2D networks.

    PubMed

    Greulich, P; Santen, L

    2010-06-01

    We introduce a model for active transport on inhomogeneous networks embedded in a diffusive environment which is motivated by vesicular transport on actin filaments. In the presence of a hard-core interaction, particle clusters are observed that exhibit an algebraically decaying distribution in a large parameter regime, indicating the existence of clusters on all scales. The scale-free behavior can be understood by a mechanism promoting preferential attachment of particles to large clusters. The results are compared with a diffusion-limited aggregation model and active transport on a regular network. For both models we observe aggregation of particles to clusters which are characterized by a finite size scale if the relevant time scales and particle densities are considered. PMID:20556462

  17. Time-resolved microrheology of actively remodeling actomyosin networks

    NASA Astrophysics Data System (ADS)

    Silva, Marina Soares e.; Stuhrmann, Björn; Betz, Timo; Koenderink, Gijsje H.

    2014-07-01

    Living cells constitute an extraordinary state of matter since they are inherently out of thermal equilibrium due to internal metabolic processes. Indeed, measurements of particle motion in the cytoplasm of animal cells have revealed clear signatures of nonthermal fluctuations superposed on passive thermal motion. However, it has been difficult to pinpoint the exact molecular origin of this activity. Here, we employ time-resolved microrheology based on particle tracking to measure nonequilibrium fluctuations produced by myosin motor proteins in a minimal model system composed of purified actin filaments and myosin motors. We show that the motors generate spatially heterogeneous contractile fluctuations, which become less frequent with time as a consequence of motor-driven network remodeling. We analyze the particle tracking data on different length scales, combining particle image velocimetry, an ensemble analysis of the particle trajectories, and finally a kymograph analysis of individual particle trajectories to quantify the length and time scales associated with active particle displacements. All analyses show clear signatures of nonequilibrium activity: the particles exhibit random motion with an enhanced amplitude compared to passive samples, and they exhibit sporadic contractile fluctuations with ballistic motion over large (up to 30 μm) distances. This nonequilibrium activity diminishes with sample age, even though the adenosine triphosphate level is held constant. We propose that network coarsening concentrates motors in large clusters and depletes them from the network, thus reducing the occurrence of contractile fluctuations. Our data provide valuable insight into the physical processes underlying stress generation within motor-driven actin networks and the analysis framework may prove useful for future microrheology studies in cells and model organisms.

  18. Soil water and carbon management for agricultural resilience in a key node in the global virtual water trade network: Mato Grosso, Brazil

    NASA Astrophysics Data System (ADS)

    Johnson, M. S.; Speratti, A. B.; Lathuilliere, M. J.; Dalmagro, H. J.; Couto, E. G.

    2015-12-01

    The Amazon region is globally connected through agricultural exports, with the Brazilian state of Mato Grosso in particular emerging as a key node in the global virtual water trade network in recent years, based largely on rainfed agriculture. The anticipated growth in the world's population suggests that virtual water trade will only become more important to global food security. In this presentation we will evaluate strategies for improving the resilience of rainfed agriculture in the region, particularly for the nearly 12 million hectares of sandy soil with low water holding capacity within Mato Grosso that has largely been converted to agricultural use. We will review land use change trajectories and present results from soil water balance modeling and carbon fluxes for a range of future scenarios, including continued agricultural extensification, potential strategies for agricultural intensification, and novel water and carbon management strategies including biochar use in sandy soils to improve soil water holding capacities and soil carbon sequestration. We will also consider the role that irrigation might play in the future in the Amazon for improving agricultural resilience to climate change and feedbacks between irrigation and land use change pressures, noting that groundwater resources in the region are presently among the least exploited on the planet.

  19. Ultrananocrystalline diamond thin films functionalized with therapeutically active collagen networks.

    SciTech Connect

    Huang, H.; Chen, M.; Bruno, P.; Lam, R.; Robinson, E.; Gruen, D.; Ho, D.; Materials Science Division; Northwestern Univ.

    2009-01-01

    The fabrication of biologically amenable interfaces in medicine bridges translational technologies with their surrounding biological environment. Functionalized nanomaterials catalyze this coalescence through the creation of biomimetic and active substrates upon which a spectrum of therapeutic elements can be delivered to adherent cells to address biomolecular processes in cancer, inflammation, etc. Here, we demonstrate the robust functionalization of ultrananocrystalline diamond (UNCD) with type I collagen and dexamethasone (Dex), an anti-inflammatory drug, to fabricate a hybrid therapeutically active substrate for localized drug delivery. UNCD oxidation coupled with a pH-mediated collagen adsorption process generated a comprehensive interface between the two materials, and subsequent Dex integration, activity, and elution were confirmed through inflammatory gene expression assays. These studies confer a translational relevance to the biofunctionalized UNCD in its role as an active therapeutic network for potent regulation of cellular activity toward applications in nanomedicine.

  20. Energy-aware Activity Classification using Wearable Sensor Networks.

    PubMed

    Dong, Bo; Montoye, Alexander; Moore, Rebecca; Pfeiffer, Karin; Biswas, Subir

    2013-05-29

    This paper presents implementation details, system characterization, and the performance of a wearable sensor network that was designed for human activity analysis. Specific machine learning mechanisms are implemented for recognizing a target set of activities with both out-of-body and on-body processing arrangements. Impacts of energy consumption by the on-body sensors are analyzed in terms of activity detection accuracy for out-of-body processing. Impacts of limited processing abilities for the on-body scenario are also characterized in terms of detection accuracy, by varying the background processing load in the sensor units. Impacts of varying number of sensors in terms of activity classification accuracy are also evaluated. Through a rigorous systems study, it is shown that an efficient human activity analytics system can be designed and operated even under energy and processing constraints of tiny on-body wearable sensors. PMID:25075266

  1. Meditation leads to reduced default mode network activity beyond an active task

    PubMed Central

    Garrison, Kathleen A.; Zeffiro, Thomas A.; Scheinost, Dustin; Constable, R. Todd; Brewer, Judson A.

    2015-01-01

    Meditation has been associated with relatively reduced activity in the default mode network, a brain network implicated in self-related thinking and mind wandering. However, previous imaging studies have typically compared meditation to rest despite other studies reporting differences in brain activation patterns between meditators and controls at rest. Moreover, rest is associated with a range of brain activation patterns across individuals that has only recently begun to be better characterized. Therefore, this study compared meditation to another active cognitive task, both to replicate findings that meditation is associated with relatively reduced default mode network activity, and to extend these findings by testing whether default mode activity was reduced during meditation beyond the typical reductions observed during effortful tasks. In addition, prior studies have used small groups, whereas the current study tested these hypotheses in a larger group. Results indicate that meditation is associated with reduced activations in the default mode network relative to an active task in meditators compared to controls. Regions of the default mode showing a group by task interaction include the posterior cingulate/precuneus and anterior cingulate cortex. These findings replicate and extend prior work indicating that suppression of default mode processing may represent a central neural process in long-term meditation, and suggest that meditation leads to relatively reduced default mode processing beyond that observed during another active cognitive task. PMID:25904238

  2. Out of Class--Out of Mind? The Use of a Virtual Learning Environment to Encourage Student Engagement in Out of Class Activities

    ERIC Educational Resources Information Center

    Leese, Maggie

    2009-01-01

    With increasing student numbers and a diverse student body, it is crucial to consider a range of methods to engage students in learning and teaching activities. This project was used to encourage 1st-year undergraduate students to engage in out of class activities between taught sessions. The project used a virtual learning environment (VLE) known…

  3. Network feedback regulates motor output across a range of modulatory neuron activity.

    PubMed

    Spencer, Robert M; Blitz, Dawn M

    2016-06-01

    Modulatory projection neurons alter network neuron synaptic and intrinsic properties to elicit multiple different outputs. Sensory and other inputs elicit a range of modulatory neuron activity that is further shaped by network feedback, yet little is known regarding how the impact of network feedback on modulatory neurons regulates network output across a physiological range of modulatory neuron activity. Identified network neurons, a fully described connectome, and a well-characterized, identified modulatory projection neuron enabled us to address this issue in the crab (Cancer borealis) stomatogastric nervous system. The modulatory neuron modulatory commissural neuron 1 (MCN1) activates and modulates two networks that generate rhythms via different cellular mechanisms and at distinct frequencies. MCN1 is activated at rates of 5-35 Hz in vivo and in vitro. Additionally, network feedback elicits MCN1 activity time-locked to motor activity. We asked how network activation, rhythm speed, and neuron activity levels are regulated by the presence or absence of network feedback across a physiological range of MCN1 activity rates. There were both similarities and differences in responses of the two networks to MCN1 activity. Many parameters in both networks were sensitive to network feedback effects on MCN1 activity. However, for most parameters, MCN1 activity rate did not determine the extent to which network output was altered by the addition of network feedback. These data demonstrate that the influence of network feedback on modulatory neuron activity is an important determinant of network output and feedback can be effective in shaping network output regardless of the extent of network modulation. PMID:27030739

  4. A neural network model for olfactory glomerular activity prediction

    NASA Astrophysics Data System (ADS)

    Soh, Zu; Tsuji, Toshio; Takiguchi, Noboru; Ohtake, Hisao

    2012-12-01

    Recently, the importance of odors and methods for their evaluation have seen increased emphasis, especially in the fragrance and food industries. Although odors can be characterized by their odorant components, their chemical information cannot be directly related to the flavors we perceive. Biological research has revealed that neuronal activity related to glomeruli (which form part of the olfactory system) is closely connected to odor qualities. Here we report on a neural network model of the olfactory system that can predict glomerular activity from odorant molecule structures. We also report on the learning and prediction ability of the proposed model.

  5. A study of epidemic spreading on activity-driven networks

    NASA Astrophysics Data System (ADS)

    Zou, Yijiang; Deng, Weibing; Li, Wei; Cai, Xu

    2016-03-01

    The epidemic spreading was explored on activity-driven networks (ADNs), accounting for the study of dynamics both on and of the ADN. By employing the susceptible-infected-susceptible (SIS) model, two aspects were considered: (1) the infection rate of susceptible agent (depending on the number of its infected neighbors) evolves due to the temporal structure of ADN, rather than being a constant number; (2) the susceptible and infected agents generate unequal links while being activated, namely, the susceptible agent gets few contacts with others in order to protect itself. Results show that, in both cases, the larger epidemic threshold and smaller outbreak size were obtained.

  6. System Management Software for Virtual Environments

    SciTech Connect

    Vallee, Geoffroy R; Naughton, III, Thomas J; Scott, Stephen L

    2007-01-01

    Recently there has been an increased interest in the use of system-level virtualization using mature solutions such as Xen, QEMU, or VMWare. These virtualization platforms are being used in distributed and parallel environments including high performance computing. The use of virtual machines within such environments introduces new challenges to system management. These include tedious tasks such as deploying para-virtualized host operating systems to support virtual machine execution or virtual overlay networks to connect these virtual machines. Additionally, there is the problem of machine definition and deployment, which is complicated by differentiation in the underlying virtualization technology. This paper discusses tools for the deployment and management of both host operating systems and virtual machines in clusters. We begin with an overview of system-level virtualization and move on to a description of tools that we have developed to aid with these environments. These tools extend prior work in the area of cluster installation, configuration and management.

  7. Tera-node Network Technology (TASK 4) Network Infrastructure Activities (NIA) final report

    SciTech Connect

    Postel, John; Bannister, Joe

    2000-03-15

    The TNT project developed software technologies in scalable personal telecommunications (SPT), Reservation Protocol 2 (RSVP2), Scalable Computing Infrastructure (SCOPE), and Network Infrastructure Activities (NIA). SPT = developed many innovative protocols to support the use of videoconferencing applications on the Internet. RSVP2 = developed a new reference model and further standardization of RSVP. SCOPE = developed dynamic resource discovery techniques and distributed directory services in support of resource allocation for large distributed systems and computations. NIA = provided policy, operational, and support to the transitioning Internet.

  8. Active defense scheme against DDoS based on mobile agent and network control in network confrontation

    NASA Astrophysics Data System (ADS)

    Luo, Rong; Li, Junshan; Ye, Xia; Wang, Rui

    2013-03-01

    In order to effective defend DDoS attacks in network confrontation, an active defense scheme against DDoS is built based on Mobile Agent and network control. A distributed collaborative active defense model is constructed by using mobile agent technology and encapsulating a variety of DDoS defense techniques. Meanwhile the network control theory is applied to establish a network confrontation's control model for DDoS to control the active defense process. It provides a new idea to solve the DDoS problem.

  9. Taurine activates GABAergic networks in the neocortex of immature mice

    PubMed Central

    Sava, Bogdan A.; Chen, Rongqing; Sun, Haiyan; Luhmann, Heiko J.; Kilb, Werner

    2014-01-01

    Although it has been suggested that taurine is the main endogenous neurotransmitter acting on glycine receptors, the implications of glycine receptor-mediated taurine actions on immature neocortical networks have not been addressed yet. To investigate the influence of taurine on the excitability of neuronal networks in the immature neocortex, we performed whole-cell patch-clamp recordings from visually identified pyramidal neurons and interneurons in coronal slices from C57Bl/6 and GAD67-green fluorescent protein (GFP) transgenic mice (postnatal days 2–4). In 46% of the pyramidal neurons bath-application of taurine at concentrations ≥ 300 μM significantly enhanced the frequency of postsynaptic currents (PSCs) by 744.3 ± 93.8% (n = 120 cells). This taurine-induced increase of PSC frequency was abolished by 0.2 μM tetrodotoxin (TTX), 1 μM strychnine or 3 μM gabazine, but was unaffected by the glutamatergic antagonists 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and (±) R(-)-3-(2-carboxypiperazine-4-yl)-propyl-1-phosphonic acid (CPP), suggesting that taurine specifically activates GABAergic network activity projecting to pyramidal neurons. Cell-attached recordings revealed that taurine enhanced the frequency of action potentials (APs) in pyramidal neurons, indicating an excitatory action of the GABAergic PSCs. In order to identify the presynaptic targets of taurine we demonstrate that bath application of taurine induced in GAD67-GFP labeled interneurons an inward current that is mainly mediated by glycine receptors and can generate APs in these cells. We conclude from these results that taurine can enhance network excitability in the immature neocortex by selectively activating GABAergic interneurons via interactions with glycine receptors. PMID:24550782

  10. Virtual Libraries: Service Realities.

    ERIC Educational Resources Information Center

    Novak, Jan

    This paper discusses client service issues to be considered when transitioning to a virtual library situation. Themes related to the transitional nature of society in the knowledge era are presented, including: paradox and a contradictory nature; blurring of boundaries; networks, systems, and holistic thinking; process/not product, becoming/not…

  11. Creating a virtual community of practice to investigate legitimate peripheral participation by African American middle school girls in science activities

    NASA Astrophysics Data System (ADS)

    Edwards, Leslie D.

    How do teenage girls develop an interest in science? What kinds of opportunities can science teachers present to female students that support their engagement with learning science? I studied one aspect of this issue by focusing on ways students could use science to enhance or gain identities that they (probably) already valued. To do that I created technology-rich activities and experiences for an after school class in science and technology for middle school girls who lived in a low socio-economic urban neighborhood. These activities and experiences were designed to create a virtual community of practice whose members used science in diverse ways. Student interest was made evident in their responses to the activities. Four conclusions emerged. (1) Opportunities to learn about the lives and work of admired African American business women interested students in learning by linking it to their middle-class aspirations and their interest in things that money and status can buy. (2) Opportunities to learn about the lives and work of African American women experts in science in a classroom context where students then practiced similar kinds of actual scientific tasks engaged students in relations of legitimate peripheral participation in a virtual and diverse community of practice focused on science which was created in the after-school classes. (3) Opportunities where students used science to show off for family, friends, and supporters of the after-school program, identities they valued, interested them enough that they engaged in long-term science and technology projects that required lots of revisions. (4) In response to the opportunities presented, new and enhanced identities developed around becoming a better student or becoming some kind of scientist.

  12. The contribution of raised intraneuronal chloride to epileptic network activity.

    PubMed

    Alfonsa, Hannah; Merricks, Edward M; Codadu, Neela K; Cunningham, Mark O; Deisseroth, Karl; Racca, Claudia; Trevelyan, Andrew J

    2015-05-20

    Altered inhibitory function is an important facet of epileptic pathology. A key concept is that GABAergic activity can become excitatory if intraneuronal chloride rises. However, it has proved difficult to separate the role of raised chloride from other contributory factors in complex network phenomena, such as epileptic pathology. Therefore, we asked what patterns of activity are associated with chloride dysregulation by making novel use of Halorhodopsin to load clusters of mouse pyramidal cells artificially with Cl(-). Brief (1-10 s) activation of Halorhodopsin caused substantial positive shifts in the GABAergic reversal potential that were proportional to the charge transfer during the illumination and in adult neocortical pyramidal neurons decayed with a time constant of τ = 8.0 ± 2.8s. At the network level, these positive shifts in EGABA produced a transient rise in network excitability, with many distinctive features of epileptic foci, including high-frequency oscillations with evidence of out-of-phase firing (Ibarz et al., 2010). We show how such firing patterns can arise from quite small shifts in the mean intracellular Cl(-) level, within heterogeneous neuronal populations. Notably, however, chloride loading by itself did not trigger full ictal events, even with additional electrical stimulation to the underlying white matter. In contrast, when performed in combination with low, subepileptic levels of 4-aminopyridine, Halorhodopsin activation rapidly induced full ictal activity. These results suggest that chloride loading has at most an adjunctive role in ictogenesis. Our simulations also show how chloride loading can affect the jitter of action potential timing associated with imminent recruitment to an ictal event (Netoff and Schiff, 2002). PMID:25995461

  13. The Contribution of Raised Intraneuronal Chloride to Epileptic Network Activity

    PubMed Central

    Alfonsa, Hannah; Merricks, Edward M.; Codadu, Neela K.; Cunningham, Mark O.; Deisseroth, Karl; Racca, Claudia

    2015-01-01

    Altered inhibitory function is an important facet of epileptic pathology. A key concept is that GABAergic activity can become excitatory if intraneuronal chloride rises. However, it has proved difficult to separate the role of raised chloride from other contributory factors in complex network phenomena, such as epileptic pathology. Therefore, we asked what patterns of activity are associated with chloride dysregulation by making novel use of Halorhodopsin to load clusters of mouse pyramidal cells artificially with Cl−. Brief (1–10 s) activation of Halorhodopsin caused substantial positive shifts in the GABAergic reversal potential that were proportional to the charge transfer during the illumination and in adult neocortical pyramidal neurons decayed with a time constant of τ = 8.0 ± 2.8s. At the network level, these positive shifts in EGABA produced a transient rise in network excitability, with many distinctive features of epileptic foci, including high-frequency oscillations with evidence of out-of-phase firing (Ibarz et al., 2010). We show how such firing patterns can arise from quite small shifts in the mean intracellular Cl− level, within heterogeneous neuronal populations. Notably, however, chloride loading by itself did not trigger full ictal events, even with additional electrical stimulation to the underlying white matter. In contrast, when performed in combination with low, subepileptic levels of 4-aminopyridine, Halorhodopsin activation rapidly induced full ictal activity. These results suggest that chloride loading has at most an adjunctive role in ictogenesis. Our simulations also show how chloride loading can affect the jitter of action potential timing associated with imminent recruitment to an ictal event (Netoff and Schiff, 2002). PMID:25995461

  14. Robust synchronisation tracking control of networked Euler-Lagrange systems using reference trajectory estimation based on virtual double-integrators

    NASA Astrophysics Data System (ADS)

    Yang, Zi-Jiang; Qin, Pan

    2016-07-01

    This paper considers the problem of distributed synchronisation tracking control of multiple Euler-Lagrange systems on a directed graph which contains a spanning tree with the leader node being the root. To design the high performance distributed controllers, a virtual double-integrator is introduced in each agent and is controlled by a virtual distributed linear high-gain synchronisation tracking controller, so that the position and velocity of each agent track those of the reference trajectory with arbitrarily short transient time and small ultimate tracking error. Then taking the double-integrator's position and velocity as the estimates of those of the reference trajectory, in each generalised coordinate of each Euler-Lagrange agent, a local controller with a disturbance observer and a sliding mode control term is designed, to suppress the mutual interactions among the agents and the modelling uncertainties. The boundedness of the overall signals and the synchronisation tracking control performance are analysed, and the conditions for guaranteed control performance are clarified. Simulation examples are provided to demonstrate the performance of the distributed controllers.

  15. Active multi-point microrheology of cytoskeletal networks

    PubMed Central

    Paust, Tobias; Mertens, Lina Katinka; Martin, Ines; Beil, Michael; Walther, Paul; Schimmel, Thomas; Marti, Othmar

    2016-01-01

    Summary Active microrheology is a valuable tool to determine viscoelastic properties of polymer networks. Observing the response of the beads to the excitation of a reference leads to dynamic and morphological information of the material. In this work we present an expansion of the well-known active two-point microrheology. By measuring the response of multiple particles in a viscoelastic medium in response to the excitation of a reference particle, we are able to determine the force propagation in the polymer network. For this purpose a lock-in technique is established that allows for extraction of the periodical motion of embedded beads. To exert a sinusoidal motion onto the reference bead an optical tweezers setup in combination with a microscope is used to investigate the motion of the response beads. From the lock-in data the so called transfer tensor can be calculated, which is a direct measure for the ability of the network to transmit mechanical forces. We also take a closer look at the influence of noise on lock-in measurements and state some simple rules for improving the signal-to-noise ratio. PMID:27335739

  16. Innovation diffusion on time-varying activity driven networks

    NASA Astrophysics Data System (ADS)

    Rizzo, Alessandro; Porfiri, Maurizio

    2016-01-01

    Since its introduction in the 1960s, the theory of innovation diffusion has contributed to the advancement of several research fields, such as marketing management and consumer behavior. The 1969 seminal paper by Bass [F.M. Bass, Manag. Sci. 15, 215 (1969)] introduced a model of product growth for consumer durables, which has been extensively used to predict innovation diffusion across a range of applications. Here, we propose a novel approach to study innovation diffusion, where interactions among individuals are mediated by the dynamics of a time-varying network. Our approach is based on the Bass' model, and overcomes key limitations of previous studies, which assumed timescale separation between the individual dynamics and the evolution of the connectivity patterns. Thus, we do not hypothesize homogeneous mixing among individuals or the existence of a fixed interaction network. We formulate our approach in the framework of activity driven networks to enable the analysis of the concurrent evolution of the interaction and individual dynamics. Numerical simulations offer a systematic analysis of the model behavior and highlight the role of individual activity on market penetration when targeted advertisement campaigns are designed, or a competition between two different products takes place.

  17. Extraction of Multilayered Social Networks from Activity Data

    PubMed Central

    Bródka, Piotr; Kazienko, Przemysław; Gaworecki, Jarosław

    2014-01-01

    The data gathered in all kinds of web-based systems, which enable users to interact with each other, provides an opportunity to extract social networks that consist of people and relationships between them. The emerging structures are very complex due to the number and type of discovered connections. In web-based systems, the characteristic element of each interaction between users is that there is always an object that serves as a communication medium. This can be, for example, an e-mail sent from one user to another or post at the forum authored by one user and commented on by others. Based on these objects and activities that users perform towards them, different kinds of relationships can be identified and extracted. Additional challenge arises from the fact that hierarchies can exist between objects; for example, a forum consists of one or more groups of topics, and each of them contains topics that finally include posts. In this paper, we propose a new method for creation of multilayered social network based on the data about users activities towards different types of objects between which the hierarchy exists. Due to the flattening, preprocessing procedure of new layers and new relationships in the multilayered social network can be identified and analysed. PMID:25105159

  18. Unconscious activation of the prefrontal no-go network.

    PubMed

    van Gaal, Simon; Ridderinkhof, K Richard; Scholte, H Steven; Lamme, Victor A F

    2010-03-17

    Cognitive control processes involving prefrontal cortex allow humans to overrule and inhibit habitual responses to optimize performance in new and challenging situations, and traditional views hold that cognitive control is tightly linked with consciousness. We used functional magnetic resonance imaging to investigate to what extent unconscious "no-go" stimuli are capable of reaching cortical areas involved in inhibitory control, particularly the inferior frontal cortex (IFC) and the pre-supplementary motor area (pre-SMA). Participants performed a go/no-go task that included conscious (weakly masked) no-go trials, unconscious (strongly masked) no-go trials, as well as go trials. Replicating typical neuroimaging findings, response inhibition on conscious no-go stimuli was associated with a (mostly right-lateralized) frontoparietal "inhibition network." Here, we demonstrate, however, that an unconscious no-go stimulus also can activate prefrontal control networks, most prominently the IFC and the pre-SMA. Moreover, if it does so, it brings about a substantial slowdown in the speed of responding, as if participants attempted to inhibit their response but just failed to withhold it completely. Interestingly, overall activation in this "unconscious inhibition network" correlated positively with the amount of slowdown triggered by unconscious no-go stimuli. In addition, neural differences between conscious and unconscious control are revealed. These results expand our understanding of the limits and depths of unconscious information processing in the human brain and demonstrate that prefrontal cognitive control functions are not exclusively influenced by conscious information. PMID:20237284

  19. Application of neural networks to seismic active control

    SciTech Connect

    Tang, Yu

    1995-07-01

    An exploratory study on seismic active control using an artificial neural network (ANN) is presented in which a singledegree-of-freedom (SDF) structural system is controlled by a trained neural network. A feed-forward neural network and the backpropagation training method are used in the study. In backpropagation training, the learning rate is determined by ensuring the decrease of the error function at each training cycle. The training patterns for the neural net are generated randomly. Then, the trained ANN is used to compute the control force according to the control algorithm. The control strategy proposed herein is to apply the control force at every time step to destroy the build-up of the system response. The ground motions considered in the simulations are the N21E and N69W components of the Lake Hughes No. 12 record that occurred in the San Fernando Valley in California on February 9, 1971. Significant reduction of the structural response by one order of magnitude is observed. Also, it is shown that the proposed control strategy has the ability to reduce the peak that occurs during the first few cycles of the time history. These promising results assert the potential of applying ANNs to active structural control under seismic loads.

  20. Trust Building in Virtual Communities

    NASA Astrophysics Data System (ADS)

    Mezgár, István

    By using different types of communication networks various groups of people can come together according to their private or business interest forming a Virtual Community. In these communities cooperation and collaboration plays an important role. As trust is the base of all human interactions this fact is even more valid in case of virtual communities. According to different experiments the level of trust in virtual communities is highly influenced by the way/mode of communication and by the duration of contact. The paper discusses the ways of trust building focusing on communication technologies and security aspects in virtual communities.

  1. Platelet Serotonin Transporter Function Predicts Default-Mode Network Activity

    PubMed Central

    Kasess, Christian H.; Meyer, Bernhard M.; Hofmaier, Tina; Diers, Kersten; Bartova, Lucie; Pail, Gerald; Huf, Wolfgang; Uzelac, Zeljko; Hartinger, Beate; Kalcher, Klaudius; Perkmann, Thomas; Haslacher, Helmuth; Meyer-Lindenberg, Andreas; Kasper, Siegfried; Freissmuth, Michael; Windischberger, Christian; Willeit, Matthäus; Lanzenberger, Rupert; Esterbauer, Harald; Brocke, Burkhard; Moser, Ewald; Sitte, Harald H.; Pezawas, Lukas

    2014-01-01

    Background The serotonin transporter (5-HTT) is abundantly expressed in humans by the serotonin transporter gene SLC6A4 and removes serotonin (5-HT) from extracellular space. A blood-brain relationship between platelet and synaptosomal 5-HT reuptake has been suggested, but it is unknown today, if platelet 5-HT uptake can predict neural activation of human brain networks that are known to be under serotonergic influence. Methods A functional magnetic resonance study was performed in 48 healthy subjects and maximal 5-HT uptake velocity (Vmax) was assessed in blood platelets. We used a mixed-effects multilevel analysis technique (MEMA) to test for linear relationships between whole-brain, blood-oxygen-level dependent (BOLD) activity and platelet Vmax. Results The present study demonstrates that increases in platelet Vmax significantly predict default-mode network (DMN) suppression in healthy subjects independent of genetic variation within SLC6A4. Furthermore, functional connectivity analyses indicate that platelet Vmax is related to global DMN activation and not intrinsic DMN connectivity. Conclusion This study provides evidence that platelet Vmax predicts global DMN activation changes in healthy subjects. Given previous reports on platelet-synaptosomal Vmax coupling, results further suggest an important role of neuronal 5-HT reuptake in DMN regulation. PMID:24667541

  2. Social status modulates neural activity in the mentalizing network

    PubMed Central

    Muscatell, Keely A.; Morelli, Sylvia A.; Falk, Emily B.; Way, Baldwin M.; Pfeifer, Jennifer H.; Galinsky, Adam D.; Lieberman, Matthew D.; Dapretto, Mirella; Eisenberger, Naomi I.

    2013-01-01

    The current research explored the neural mechanisms linking social status to perceptions of the social world. Two fMRI studies provide converging evidence that individuals lower in social status are more likely to engage neural circuitry often involved in ‘mentalizing’ or thinking about others' thoughts and feelings. Study 1 found that college students' perception of their social status in the university community was related to neural activity in the mentalizing network (e.g., DMPFC, MPFC, precuneus/PCC) while encoding social information, with lower social status predicting greater neural activity in this network. Study 2 demonstrated that socioeconomic status, an objective indicator of global standing, predicted adolescents' neural activity during the processing of threatening faces, with individuals lower in social status displaying greater activity in the DMPFC, previously associated with mentalizing, and the amygdala, previously associated with emotion/salience processing. These studies demonstrate that social status is fundamentally and neurocognitively linked to how people process and navigate their social worlds. PMID:22289808

  3. Different brain correlates for watching real and virtual hand actions.

    PubMed

    Perani, D; Fazio, F; Borghese, N A; Tettamanti, M; Ferrari, S; Decety, J; Gilardi, M C

    2001-09-01

    We investigated whether observation of actions reproduced in three-dimensional virtual reality would engage perceptual and visuomotor brain processes different from those induced by the observation of real hand actions. Participants were asked to passively observe grasping actions of geometrical objects made by a real hand or by hand reconstructions of different quality in 3D virtual reality as well as on a 2D TV screen. We found that only real actions in natural environment activated a visuospatial network including the right posterior parietal cortex. Observation of virtual-reality hand actions engaged prevalent visual perceptual processes within lateral and mesial occipital regions. Thus, only perception of actions in reality maps onto existing action representations, whereas virtual-reality conditions do not access the full motor knowledge available to the central nervous system. PMID:11506547

  4. Temporary seismic networks on active volcanoes of Kamchatka (Russia)

    NASA Astrophysics Data System (ADS)

    Jakovlev, Andrey; Koulakov, Ivan; Abkadyrov, Ilyas; Shapiro, Nikolay; Kuznetsov, Pavel; Deev, Evgeny; Gordeev, Evgeny; Chebrov, Viktor

    2016-04-01

    We present details of four field campaigns carried out on different volcanoes of Kamchatka in 2012-2015. Each campaign was performed in three main steps: (i) installation of the temporary network of seismic stations; (ii) autonomous continuous registration of three component seismic signal; (III) taking off the network and downloading the registered data. During the first campaign started in September 2012, 11 temporary stations were installed over the Avacha group of volcanoes located 30 km north to Petropavlovsk-Kamchatsky in addition to the seven permanent stations operated by the Kamchatkan Branch of the Geophysical Survey (KBGS). Unfortunately, with this temporary network we faced with two obstacles. The first problem was the small amount of local earthquakes, which were detected during operation time. The second problem was an unexpected stop of several stations only 40 days after deployment. Nevertheless, after taking off the network in August 2013, the collected data appeared to be suitable for analysis using ambient noise. The second campaign was conducted in period from August 2013 to August 2014. In framework of the campaign, 21 temporary stations were installed over Gorely volcano, located 70 km south to Petropavlovsk-Kamchatsky. Just in time of the network deployment, Gorely Volcano became very seismically active - every day occurred more than 100 events. Therefore, we obtain very good dataset with information about thousands of local events, which could be used for any type of seismological analysis. The third campaign started in August 2014. Within this campaign, we have installed 19 temporary seismic stations over Tolbachik volcano, located on the south side of the Klyuchevskoy volcano group. In the same time on Tolbachik volcano were installed four temporary stations and several permanent stations operated by the KBGS. All stations were taking off in July 2015. As result, we have collected a large dataset, which is now under preliminary analysis

  5. Open challenges in structure-based virtual screening: Receptor modeling, target flexibility consideration and active site water molecules description.

    PubMed

    Spyrakis, Francesca; Cavasotto, Claudio N

    2015-10-01

    Structure-based virtual screening is currently an established tool in drug lead discovery projects. Although in the last years the field saw an impressive progress in terms of algorithm development, computational performance, and retrospective and prospective applications in ligand identification, there are still long-standing challenges where further improvement is needed. In this review, we consider the conceptual frame, state-of-the-art and recent developments of three critical "structural" issues in structure-based drug lead discovery: the use of homology modeling to accurately model the binding site when no experimental structures are available, the necessity of accounting for the dynamics of intrinsically flexible systems as proteins, and the importance of considering active site water molecules in lead identification and optimization campaigns. PMID:26271444

  6. Integrated virtual screening for the identification of novel and selective peroxisome proliferator-activated receptor (PPAR) scaffolds.

    PubMed

    Nevin, Daniel K; Peters, Martin B; Carta, Giorgio; Fayne, Darren; Lloyd, David G

    2012-06-14

    We describe a fully customizable and integrated target-specific "tiered" virtual screening approach tailored to identifying and characterizing novel peroxisome proliferator activated receptor γ (PPARγ) scaffolds. Built on structure- and ligand-based computational techniques, a consensus protocol was developed for use in the virtual screening of chemical databases, focused toward retrieval of novel bioactive chemical scaffolds for PPARγ. Consequent from application, three novel PPAR scaffolds displaying distinct chemotypes have been identified, namely, 5-(4-(benzyloxy)-3-chlorobenzylidene)dihydro-2-thioxopyrimidine-4,6(1H,5H)-dione (MDG 548), 3-((4-bromophenoxy)methyl)-N-(4-nitro-1H-pyrazol-1-yl)benzamide (MDG 559), and ethyl 2-[3-hydroxy-5-(5-methyl-2-furyl)-2-oxo-4-(2-thienylcarbonyl)-2,5-dihydro-1H-pyrrol-1-yl]-4-methyl-1,3-thiazole-5-carboxylate (MDG 582). Fluorescence polarization(FP) and time resolved fluorescence resonance energy transfer (TR-FRET) show that these compounds display high affinity competitive binding to the PPARγ-LBD (EC(50) of 215 nM to 5.45 μM). Consequent characterization by a TR-FRET activation reporter assay demonstrated agonism of PPARγ by all three compounds (EC(50) of 467-594 nM). Additionally, differential PPAR isotype specificity was demonstrated through assay against PPARα and PPARδ subtypes. This work showcases the ability of target specific "tiered screen" protocols to successfully identify novel scaffolds of individual receptor subtypes with greater efficacy than isolated screening methods. PMID:22582973

  7. Modulation of cortical activity in 2D versus 3D virtual reality environments: an EEG study.

    PubMed

    Slobounov, Semyon M; Ray, William; Johnson, Brian; Slobounov, Elena; Newell, Karl M

    2015-03-01

    There is a growing empirical evidence that virtual reality (VR) is valuable for education, training, entertaining and medical rehabilitation due to its capacity to represent real-life events and situations. However, the neural mechanisms underlying behavioral confounds in VR environments are still poorly understood. In two experiments, we examined the effect of fully immersive 3D stereoscopic presentations and less immersive 2D VR environments on brain functions and behavioral outcomes. In Experiment 1 we examined behavioral and neural underpinnings of spatial navigation tasks using electroencephalography (EEG). In Experiment 2, we examined EEG correlates of postural stability and balance. Our major findings showed that fully immersive 3D VR induced a higher subjective sense of presence along with enhanced success rate of spatial navigation compared to 2D. In Experiment 1 power of frontal midline EEG (FM-theta) was significantly higher during the encoding phase of route presentation in the 3D VR. In Experiment 2, the 3D VR resulted in greater postural instability and modulation of EEG patterns as a function of 3D versus 2D environments. The findings support the inference that the fully immersive 3D enriched-environment requires allocation of more brain and sensory resources for cognitive/motor control during both tasks than 2D presentations. This is further evidence that 3D VR tasks using EEG may be a promising approach for performance enhancement and potential applications in clinical/rehabilitation settings. PMID:25448267

  8. Pre-stimulus BOLD-network activation modulates EEG spectral activity during working memory retention.

    PubMed

    Kottlow, Mara; Schlaepfer, Anthony; Baenninger, Anja; Michels, Lars; Brandeis, Daniel; Koenig, Thomas

    2015-01-01

    Working memory (WM) processes depend on our momentary mental state and therefore exhibit considerable fluctuations. Here, we investigate the interplay of task-preparatory and task-related brain activity as represented by pre-stimulus BOLD-fluctuations and spectral EEG from the retention periods of a visual WM task. Visual WM is used to maintain sensory information in the brain enabling the performance of cognitive operations and is associated with mental health. We tested 22 subjects simultaneously with EEG and fMRI while performing a visuo-verbal Sternberg task with two different loads, allowing for the temporal separation of preparation, encoding, retention and retrieval periods. Four temporally coherent networks (TCNs)-the default mode network (DMN), the dorsal attention, the right and the left WM network-were extracted from the continuous BOLD data by means of a group ICA. Subsequently, the modulatory effect of these networks' pre-stimulus activation upon retention-related EEG activity in the theta, alpha, and beta frequencies was analyzed. The obtained results are informative in the context of state-dependent information processing. We were able to replicate two well-known load-dependent effects: the frontal-midline theta increase during the task and the decrease of pre-stimulus DMN activity. As our main finding, these two measures seem to depend on each other as the significant negative correlations at frontal-midline channels suggested. Thus, suppressed pre-stimulus DMN levels facilitated later task related frontal midline theta increases. In general, based on previous findings that neuronal coupling in different frequency bands may underlie distinct functions in WM retention, our results suggest that processes reflected by spectral oscillations during retention seem not only to be "online" synchronized with activity in different attention-related networks but are also modulated by activity in these networks during preparation intervals. PMID:25999828

  9. Wireless sensor networks for active vibration control in automobile structures

    NASA Astrophysics Data System (ADS)

    Mieyeville, Fabien; Ichchou, Mohamed; Scorletti, Gérard; Navarro, David; Du, Wan

    2012-07-01

    Wireless sensor networks (WSNs) are nowadays widely used in monitoring and tracking applications. This paper presents the feasibility of using WSNs in active vibration control strategies. The method employed here involves active-structural acoustic control using piezoelectric sensors distributed on a car structure. This system aims at being merged with a WSN whose head node collects data and processes control laws so as to command piezoelectric actuators wisely placed on the structure. We will study the feasibility of implementing WSNs in active vibration control and introduce a complete design methodology to optimize hardware/software and control law synergy in mechatronic systems. A design space exploration will be conducted so as to identify the best WSN platform and the resulting impact on control.

  10. Fast Booting Many Similar Virtual Machines

    NASA Astrophysics Data System (ADS)

    Wang, Xiaolin; Wang, Zhenlin; Liang, Shuang; Zhang, Zhengyi; Luo, Yingwei; Li, Xiaoming

    Virtual Machines have been commonly used for server consolidation in data centers, network classrooms, and cloud computing environments. Although booting up a virtual machine takes much less time than booting up a physical computer, booting up multiple virtual machines on a single physical server still takes a lot of time. We propose a method to speed up the booting process when a set of similar virtual machines share a snapshot enabled storage. Our method exploits massive memory page sharing stemming from the reads to common disk blocks by these virtual machines. Our experiments show that the second virtual machine may reduce the booting time by half.

  11. GeoMapApp Learning Activities: A Virtual Lab Environment for Student-Centred Engagement with Geoscience Data

    NASA Astrophysics Data System (ADS)

    Kluge, S.; Goodwillie, A. M.

    2012-12-01

    As STEM learning requirements enter the mainstream, there is benefit to providing the tools necessary for students to engage with research-quality geoscience data in a cutting-edge, easy-to-use map-based interface. Funded with an NSF GeoEd award, GeoMapApp Learning Activities ( http://serc.carleton.edu/geomapapp/collection.html ) are being created to help in that endeavour. GeoMapApp Learning Activities offer step-by-step instructions within a guided inquiry approach that enables students to dictate the pace of learning. Based upon GeoMapApp (http://www.geomapapp.org), a free, easy-to-use map-based data exploration and visualisation tool, each activity furnishes the educator with an efficient package of downloadable documents. This includes step-by-step student instructions and answer sheet; an educator's annotated worksheet containing teaching tips, additional content and suggestions for further work; and, quizzes for use before and after the activity to assess learning. Examples of activities so far created involve calculation and analysis of the rate of seafloor spreading; compilation of present-day evidence for huge ancient landslides on the seafloor around the Hawaiian islands; a study of radiometrically-dated volcanic rocks to help understand the concept of hotspots; and, the optimisation of contours as a means to aid visualisation of 3-D data sets on a computer screen. The activities are designed for students at the introductory undergraduate, community college and high school levels, and present a virtual lab-like environment to expose students to content and concepts typically found in those educational settings. The activities can be used in the classroom or out of class, and their guided nature means that the requirement for teacher intervention is reduced thus allowing students to spend more time analysing and understanding geoscience data, content and concepts. Each activity is freely available through the SERC-Carleton web site.

  12. A semi-immersive virtual reality incremental swing balance task activates prefrontal cortex: a functional near-infrared spectroscopy study.

    PubMed

    Basso Moro, Sara; Bisconti, Silvia; Muthalib, Makii; Spezialetti, Matteo; Cutini, Simone; Ferrari, Marco; Placidi, Giuseppe; Quaresima, Valentina

    2014-01-15

    Previous functional near-infrared spectroscopy (fNIRS) studies indicated that the prefrontal cortex (PFC) is involved in the maintenance of the postural balance after external perturbations. So far, no studies have been conducted to investigate the PFC hemodynamic response to virtual reality (VR) tasks that could be adopted in the field of functional neurorehabilitation. The aim of this fNIRS study was to assess PFC oxygenation response during an incremental and a control swing balance task (ISBT and CSBT, respectively) in a semi-immersive VR environment driven by a depth-sensing camera. It was hypothesized that: i) the PFC would be bilaterally activated in response to the increase of the ISBT difficulty, as this cortical region is involved in the allocation of attentional resources to maintain postural control; and ii) the PFC activation would be greater in the right than in the left hemisphere considering its dominance for visual control of body balance. To verify these hypotheses, 16 healthy male subjects were requested to stand barefoot while watching a 3 dimensional virtual representation of themselves projected onto a screen. They were asked to maintain their equilibrium on a virtual blue swing board susceptible to external destabilizing perturbations (i.e., randomizing the forward-backward direction of the impressed pulse force) during a 3-min ISBT (performed at four levels of difficulty) or during a 3-min CSBT (performed constantly at the lowest level of difficulty of the ISBT). The center of mass (COM), at each frame, was calculated and projected on the floor. When the subjects were unable to maintain the COM over the board, this became red (error). After each error, the time required to bring back the COM on the board was calculated (returning time). An eight-channel continuous wave fNIRS system was employed for measuring oxygenation changes (oxygenated-hemoglobin, O2Hb; deoxygenated-hemoglobin, HHb) related to the PFC activation (Brodmann Areas 10, 11

  13. Environmental Monitoring Networks Optimization Using Advanced Active Learning Algorithms

    NASA Astrophysics Data System (ADS)

    Kanevski, Mikhail; Volpi, Michele; Copa, Loris

    2010-05-01

    The problem of environmental monitoring networks optimization (MNO) belongs to one of the basic and fundamental tasks in spatio-temporal data collection, analysis, and modeling. There are several approaches to this problem, which can be considered as a design or redesign of monitoring network by applying some optimization criteria. The most developed and widespread methods are based on geostatistics (family of kriging models, conditional stochastic simulations). In geostatistics the variance is mainly used as an optimization criterion which has some advantages and drawbacks. In the present research we study an application of advanced techniques following from the statistical learning theory (SLT) - support vector machines (SVM) and the optimization of monitoring networks when dealing with a classification problem (data are discrete values/classes: hydrogeological units, soil types, pollution decision levels, etc.) is considered. SVM is a universal nonlinear modeling tool for classification problems in high dimensional spaces. The SVM solution is maximizing the decision boundary between classes and has a good generalization property for noisy data. The sparse solution of SVM is based on support vectors - data which contribute to the solution with nonzero weights. Fundamentally the MNO for classification problems can be considered as a task of selecting new measurement points which increase the quality of spatial classification and reduce the testing error (error on new independent measurements). In SLT this is a typical problem of active learning - a selection of the new unlabelled points which efficiently reduce the testing error. A classical approach (margin sampling) to active learning is to sample the points closest to the classification boundary. This solution is suboptimal when points (or generally the dataset) are redundant for the same class. In the present research we propose and study two new advanced methods of active learning adapted to the solution of

  14. Temporal dynamics of spontaneous MEG activity in brain networks.

    PubMed

    de Pasquale, Francesco; Della Penna, Stefania; Snyder, Abraham Z; Lewis, Christopher; Mantini, Dante; Marzetti, Laura; Belardinelli, Paolo; Ciancetta, Luca; Pizzella, Vittorio; Romani, Gian Luca; Corbetta, Maurizio

    2010-03-30

    Functional MRI (fMRI) studies have shown that low-frequency (<0.1 Hz) spontaneous fluctuations of the blood oxygenation level dependent (BOLD) signal during restful wakefulness are coherent within distributed large-scale cortical and subcortical networks (resting state networks, RSNs). The neuronal mechanisms underlying RSNs remain poorly understood. Here, we describe magnetoencephalographic correspondents of two well-characterized RSNs: the dorsal attention and the default mode networks. Seed-based correlation mapping was performed using time-dependent MEG power reconstructed at each voxel within the brain. The topography of RSNs computed on the basis of extended (5 min) epochs was similar to that observed with fMRI but confined to the same hemisphere as the seed region. Analyses taking into account the nonstationarity of MEG activity showed transient formation of more complete RSNs, including nodes in the contralateral hemisphere. Spectral analysis indicated that RSNs manifest in MEG as synchronous modulation of band-limited power primarily within the theta, alpha, and beta bands-that is, in frequencies slower than those associated with the local electrophysiological correlates of event-related BOLD responses. PMID:20304792

  15. Social Protocols for Agile Virtual Teams

    NASA Astrophysics Data System (ADS)

    Picard, Willy

    Despite many works on collaborative networked organizations (CNOs), CSCW, groupware, workflow systems and social networks, computer support for virtual teams is still insufficient, especially support for agility, i.e. the capability of virtual team members to rapidly and cost efficiently adapt the way they interact to changes. In this paper, requirements for computer support for agile virtual teams are presented. Next, an extension of the concept of social protocol is proposed as a novel model supporting agile interactions within virtual teams. The extended concept of social protocol consists of an extended social network and a workflow model.

  16. New GPS Network on the Active Fault System in Taiwan

    NASA Astrophysics Data System (ADS)

    Hou, C.; Chen, Y.; Hu, J.; Lin, C.; Chen, C.; Wang, J.; Chung, L.; Chung, W.; Hsieh, C.; Chen, Y.

    2004-12-01

    According to the historical records, disastrous earthquakes occurred in Taiwan were caused by reactivations of active faults. In last century, there were five with the surface rupture: 1906 Meishan Eq. (the Meishan F.), 1935 Hsihchu Eq. (the Shihtan and the Tuntzuchiao F.), 1946 Hsinhua Eq. (Hsinhua F.), 1951 Hualien-Taitung Eq. (Longitudinal Valley F.), and 1999 Chi-Chi Eq. (the Chelungpu F.). In order to identify earthquake associated surface rupture and further to mitigate potential hazards, the investigation and monitoring on the active fault system are of great urgency. Central Geological Survey (CGS) of Taiwan is currently executing a 5-year (2002-2006) project, integrating geological and geodetic data to better characterize short-term and long-term spatial and temporal variations in deformation across major already-known active faults of Taiwan. For the former, we use field survey, drilling, geophysical exploration, and trenching to recognize the long-term slip rate and recurrence interval of each fault. For the latter, we deploy near-fault campaign-style GPS and leveling monitoring networks. Here we further combine the result of other GPS networks including continuous-mode. This project is actually concentrated on fault-specific investigation.. Until Dec. 2004, we have set up 756 GPS stations and 27 precise leveling lines including 1024 leveling benchmarks. For the purpose of understanding temporal variability and receive continuous record, the CGS began to deploy 6~10 new GPS stations of continuous mode since 2004. Upon the completion of the geodetic project, we are supposed to provide information on short-term slip rates of major active faults. By integrating other geological datasets we will also evaluate the short-term and long-term behavior of the active faults, and further offer insight into spatial and temporal variability in deformation processes.

  17. Functional Language Networks in Sedentary and Physically Active Older Adults

    PubMed Central

    Zlatar, Zvinka Z.; Towler, Stephen; McGregor, Keith M.; Dzierzewski, Joseph M.; Bauer, Andrew; Phan, Stephanie; Cohen, Matthew; Marsiske, Michael; Manini, Todd M.; Crosson, Bruce

    2013-01-01

    Functional magnetic resonance imaging (fMRI) studies have identified consistent age-related changes during various cognitive tasks, such that older individuals display more positive and less negative task-related activity than young adults. Recently, evidence shows that chronic physical exercise may alter aging-related changes in brain activity; however, the effect of exercise has not been studied for the neural substrates of language function. Additionally, the potential mechanisms by which aging alters neural recruitment remain understudied. To address these points, the present study enrolled elderly adults who were either sedentary or physically active to characterize the neural correlates of language function during semantic fluency between these groups in comparison to a young adult sample. Participants underwent fMRI during semantic fluency and transcranial magnetic stimulation to collect the ipsilateral silent period, a measure of interhemispheric inhibition. Results indicated that sedentary older adults displayed reductions in negative task-related activity compared to the active old group in areas of the attention network. Longer interhemispheric inhibition was associated with more negative task-related activity in the right and left posterior perisylvian cortex, suggesting that sedentary aging may result in losses in task facilitatory cortical inhibition. However, these losses may be mitigated by regular engagement in physical exercise. PMID:23458438

  18. Metropolitian area network services comprised of virtual local area networks running over hybrid fiber-coax and asynchronous transfer mode technologies

    NASA Astrophysics Data System (ADS)

    Biedron, William S.

    1995-11-01

    Since 1990 there has been a rapid increase in the demand for communication services, especially local and wide area network (LAN/WAN) oriented services. With the introduction of the DFB laser transmitter, hybrid-fiber-coax (HFC) cable plant designs, ATM transport technologies and rf modems, new LAN/WAN services can now be defined and marketed to residential and business customers over existing cable TV systems. The term metropolitan area network (MAN) can be used to describe this overall network. This paper discusses the technical components needed to provision these services as well as provides some perspectives on integration issues. Architecture at the headend and in the backbone is discussed, as well as specific service definitions and the technology issues associated with each. The TCP/IP protocol is suggested as a primary protocol to be used throughout the MAN.

  19. Recent evolution of China's virtual water trade: analysis of selected crops and considerations for policy

    NASA Astrophysics Data System (ADS)

    Shi, J.; Liu, J.; Pinter, L.

    2013-09-01

    China has dramatically increased its virtual water import unconsciously for recent years. Many studies have focused on the quantity of traded virtual water but very few go into analysing geographic distribution and the properties of China's virtual water trade network. This paper provides a calculation and analysis of the crop-related virtual water trade network of China based on 27 major primary crops between 1986 and 2009. The results show that China is a net importer of virtual water from water-abundant areas of North and South America, and a net virtual water exporter to water-stressed areas of Asia, Africa, and Europe. Virtual water import is far larger than virtual water export and in both import and export a small number of trade partners control the supply chain. Grain crops are the major contributors to virtual water trade, and among grain crops soybeans, mostly imported from the US, Brazil and Argentina are the most significant. As crop yield and crop water productivity in North and South America are generally higher than those in Asia and Africa, the effect of China's crop-related virtual water trade positively contributes to optimizing crop water use efficiency at the global scale. In order to mitigate water scarcity and secure the food supply, virtual water should be actively incorporated into national water management strategies. From the national perspective, China should reduce the export and increase the import of water-intensive crops. But the sources of virtual water import need to be further diversified to reduce supply chain risks and increase resilience.

  20. The Pragmatics of Virtual Worlds for K-12 Educators: Investigating the Affordances and Constraints of "Active Worlds" and "Second Life" with K-12 In-Service Teachers

    ERIC Educational Resources Information Center

    Dickey, Michele D.

    2011-01-01

    The purpose of this study is to address the pragmatics of integrating virtual worlds for teaching and learning for K-12 education. Specifically this qualitative investigation focuses on a reflective dialogue gathered from a group of K-12 (primary and secondary school) educators about their experiences using both "Active Worlds Educational…

  1. Are All Hands-On Activities Equally Effective? Effect of Using Plastic Models, Organ Dissections, and Virtual Dissections on Student Learning and Perceptions

    ERIC Educational Resources Information Center

    Lombardi, Sara A.; Hicks, Reimi E.; Thompson, Katerina V.; Marbach-Ad, Gili

    2014-01-01

    This study investigated the impact of three commonly used cardiovascular model-assisted activities on student learning and student attitudes and perspectives about science. College students enrolled in a Human Anatomy and Physiology course were randomly assigned to one of three experimental groups (organ dissections, virtual dissections, or…

  2. From Physical Benchmarks to Mental Benchmarks: A Four Dimensions Dynamic Model to Assure the Quality of Instructional Activities in Electronic and Virtual Learning Environments

    ERIC Educational Resources Information Center

    Ahmed Abdelaziz, Hamdy

    2013-01-01

    The objective of this paper was to develop a four dimensions dynamic model for designing instructional activities appropriate to electronic and virtual learning environments. The suggested model is guided by learning principles of cognitivism, constructivism, and connectivism learning theories in order to help online learners to build and acquire…

  3. A Preliminary Study of Functional Brain Activation among Marijuana Users during Performance of a Virtual Water Maze Task

    PubMed Central

    Sneider, Jennifer Tropp; Gruber, Staci A.; Rogowska, Jadwiga; Silveri, Marisa M.; Yurgelun-Todd, Deborah A.

    2013-01-01

    Numerous studies have reported neurocognitive impairments associated with chronic marijuana use. Given that the hippocampus contains a high density of cannabinoid receptors, hippocampal-mediated cognitive functions, including visuospatial memory, may have increased vulnerability to chronic marijuana use. Thus, the current study examined brain activation during the performance of a virtual analogue of the classic Morris water maze task in 10 chronic marijuana (MJ) users compared to 18 nonusing (NU) comparison subjects. Imaging data were acquired using blood oxygen level-dependent (BOLD) functional MRI at 3.0 Tesla during retrieval (hidden platform) and motor control (visible platform) conditions. While task performance on learning trials was similar between groups, MJ users demonstrated a deficit in memory retrieval. For BOLD fMRI data, NU subjects exhibited greater activation in the right parahippocampal gyrus and cingulate gyrus compared to the MJ group for the Retrieval-Motor Control contrast (NU > MJ). These findings suggest that hypoactivation in MJ users may be due to differences in the efficient utilization of neuronal resources during the retrieval of memory. Given the paucity of data on visuospatial memory function in MJ users, these findings may help elucidate the neurobiological effects of marijuana on brain activation during memory retrieval. PMID:23951549

  4. A preliminary study of functional brain activation among marijuana users during performance of a virtual water maze task.

    PubMed

    Sneider, Jennifer Tropp; Gruber, Staci A; Rogowska, Jadwiga; Silveri, Marisa M; Yurgelun-Todd, Deborah A

    2013-01-01

    Numerous studies have reported neurocognitive impairments associated with chronic marijuana use. Given that the hippocampus contains a high density of cannabinoid receptors, hippocampal-mediated cognitive functions, including visuospatial memory, may have increased vulnerability to chronic marijuana use. Thus, the current study examined brain activation during the performance of a virtual analogue of the classic Morris water maze task in 10 chronic marijuana (MJ) users compared to 18 non-using (NU) comparison subjects. Imaging data were acquired using blood oxygen-level dependent (BOLD) functional MRI at 3.0 Tesla during retrieval (hidden platform) and motor control (visible platform) conditions. While task performance on learning trials was similar between groups, MJ users demonstrated a deficit in memory retrieval. For BOLD fMRI data, NU subjects exhibited greater activation in the right parahippocampal gyrus and cingulate gyrus compared to the MJ group for the Retrieval - Motor control contrast (NU > MJ). These findings suggest that hypoactivation in MJ users may be due to differences in the efficient utilization of neuronal resources during the retrieval of memory. Given the paucity of data on visuospatial memory function in MJ users, these findings may help elucidate the neurobiological effects of marijuana on brain activation during memory retrieval. PMID:23951549

  5. Virtual Laboratories and Virtual Worlds

    NASA Astrophysics Data System (ADS)

    Hut, Piet

    2008-05-01

    Since we cannot put stars in a laboratory, astrophysicists had to wait till the invention of computers before becoming laboratory scientists. For half a century now, we have been conducting experiments in our virtual laboratories. However, we ourselves have remained behind the keyboard, with the screen of the monitor separating us from the world we are simulating. Recently, 3D on-line technology, developed first for games but now deployed in virtual worlds like Second Life, is beginning to make it possible for astrophysicists to enter their virtual labs themselves, in virtual form as avatars. This has several advantages, from new possibilities to explore the results of the simulations to a shared presence in a virtual lab with remote collaborators on different continents. I will report my experiences with the use of Qwaq Forums, a virtual world developed by a new company (see http://www.qwaq.com).

  6. Pre-stimulus BOLD-network activation modulates EEG spectral activity during working memory retention

    PubMed Central

    Kottlow, Mara; Schlaepfer, Anthony; Baenninger, Anja; Michels, Lars; Brandeis, Daniel; Koenig, Thomas

    2015-01-01

    Working memory (WM) processes depend on our momentary mental state and therefore exhibit considerable fluctuations. Here, we investigate the interplay of task-preparatory and task-related brain activity as represented by pre-stimulus BOLD-fluctuations and spectral EEG from the retention periods of a visual WM task. Visual WM is used to maintain sensory information in the brain enabling the performance of cognitive operations and is associated with mental health. We tested 22 subjects simultaneously with EEG and fMRI while performing a visuo-verbal Sternberg task with two different loads, allowing for the temporal separation of preparation, encoding, retention and retrieval periods. Four temporally coherent networks (TCNs)—the default mode network (DMN), the dorsal attention, the right and the left WM network—were extracted from the continuous BOLD data by means of a group ICA. Subsequently, the modulatory effect of these networks' pre-stimulus activation upon retention-related EEG activity in the theta, alpha, and beta frequencies was analyzed. The obtained results are informative in the context of state-dependent information processing. We were able to replicate two well-known load-dependent effects: the frontal-midline theta increase during the task and the decrease of pre-stimulus DMN activity. As our main finding, these two measures seem to depend on each other as the significant negative correlations at frontal-midline channels suggested. Thus, suppressed pre-stimulus DMN levels facilitated later task related frontal midline theta increases. In general, based on previous findings that neuronal coupling in different frequency bands may underlie distinct functions in WM retention, our results suggest that processes reflected by spectral oscillations during retention seem not only to be “online” synchronized with activity in different attention-related networks but are also modulated by activity in these networks during preparation intervals. PMID

  7. Stock price change rate prediction by utilizing social network activities.

    PubMed

    Deng, Shangkun; Mitsubuchi, Takashi; Sakurai, Akito

    2014-01-01

    Predicting stock price change rates for providing valuable information to investors is a challenging task. Individual participants may express their opinions in social network service (SNS) before or after their transactions in the market; we hypothesize that stock price change rate is better predicted by a function of social network service activities and technical indicators than by a function of just stock market activities. The hypothesis is tested by accuracy of predictions as well as performance of simulated trading because success or failure of prediction is better measured by profits or losses the investors gain or suffer. In this paper, we propose a hybrid model that combines multiple kernel learning (MKL) and genetic algorithm (GA). MKL is adopted to optimize the stock price change rate prediction models that are expressed in a multiple kernel linear function of different types of features extracted from different sources. GA is used to optimize the trading rules used in the simulated trading by fusing the return predictions and values of three well-known overbought and oversold technical indicators. Accumulated return and Sharpe ratio were used to test the goodness of performance of the simulated trading. Experimental results show that our proposed model performed better than other models including ones using state of the art techniques. PMID:24790586

  8. Stock Price Change Rate Prediction by Utilizing Social Network Activities

    PubMed Central

    Mitsubuchi, Takashi; Sakurai, Akito

    2014-01-01

    Predicting stock price change rates for providing valuable information to investors is a challenging task. Individual participants may express their opinions in social network service (SNS) before or after their transactions in the market; we hypothesize that stock price change rate is better predicted by a function of social network service activities and technical indicators than by a function of just stock market activities. The hypothesis is tested by accuracy of predictions as well as performance of simulated trading because success or failure of prediction is better measured by profits or losses the investors gain or suffer. In this paper, we propose a hybrid model that combines multiple kernel learning (MKL) and genetic algorithm (GA). MKL is adopted to optimize the stock price change rate prediction models that are expressed in a multiple kernel linear function of different types of features extracted from different sources. GA is used to optimize the trading rules used in the simulated trading by fusing the return predictions and values of three well-known overbought and oversold technical indicators. Accumulated return and Sharpe ratio were used to test the goodness of performance of the simulated trading. Experimental results show that our proposed model performed better than other models including ones using state of the art techniques. PMID:24790586

  9. In vitro neuronal network activity in NMDA receptor encephalitis

    PubMed Central

    2013-01-01

    Background Anti-NMDA-encephalitis is caused by antibodies against the N-methyl-D-aspartate receptor (NMDAR) and characterized by a severe encephalopathy with psychosis, epileptic seizures and autonomic disturbances. It predominantly occurs in young women and is associated in 59% with an ovarian teratoma. Results We describe effects of cerebrospinal fluid (CSF) from an anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis patient on in vitro neuronal network activity (ivNNA). In vitro NNA of dissociated primary rat cortical populations was recorded by the microelectrode array (MEA) system. The 23-year old patient was severely affected but showed an excellent recovery following multimodal immunomodulatory therapy and removal of an ovarian teratoma. Patient CSF (pCSF) taken during the initial weeks after disease onset suppressed global spike- and burst rates of ivNNA in contrast to pCSF sampled after clinical recovery and decrease of NMDAR antibody titers. The synchrony of pCSF-affected ivNNA remained unaltered during the course of the disease. Conclusion Patient CSF directly suppresses global activity of neuronal networks recorded by the MEA system. In contrast, pCSF did not regulate the synchrony of ivNNA suggesting that NMDAR antibodies selectively regulate distinct parameters of ivNNA while sparing their functional connectivity. Thus, assessing ivNNA could represent a new technique to evaluate functional consequences of autoimmune encephalitis-related CSF changes. PMID:23379293

  10. Photonic Network R&D Activities in Japan-Current Activities and Future Perspectives

    NASA Astrophysics Data System (ADS)

    Kitayama, Ken-Ichi; Miki, Tetsuya; Morioka, Toshio; Tsushima, Hideaki; Koga, Masafumi; Mori, Kazuyuki; Araki, Soichiro; Sato, Ken-Ichi; Onaka, Hiroshi; Namiki, Shu; Aoyama, Tomonori

    2005-10-01

    R&D activities on photonic networks in Japan are presented. First, milestones in current ongoing R&D programs supported by Japanese government agencies are introduced, including long-distance and wavelength division multiplexing (WDM) fiber transmission, wavelength routing, optical burst switching (OBS), and control-plane technology for IP backbone networks. Their goal was set to evolve a legacy telecommunications network to IP-over-WDM networks by introducing technologies for WDM and wavelength routing. We then discuss the perspectives of so-called PHASE II R&D programs for photonic networks over the next 5 years until 2010, by focusing on the report that has been recently issued by the Photonic Internet Forum (PIF), a consortium that has major carriers, telecom vendors, and Japanese academics as members. The PHASE II R&D programs should serve to establish a photonic platform to provide abundant bandwidth on demand, at any time on a real-time basis, through the customer's initiative to promote bandwidth-rich applications, such as grid computing, real-time digital-cinema streaming, medical and educational applications, and network storage in e-commerce.

  11. GAIA - A Virtual Auroral Observatory

    NASA Astrophysics Data System (ADS)

    Donovan, E.; Spanswick, E.; Syrj M; Marple, S.; Jackel, B.; Kauristie, K.; Honary, F.; Mende, S.; Weatherwax, A.; Moen, J.; Sandahl, I.

    2005-12-01

    Advancements in computer, communications, and instrument technologies have spawned an explosion of activity in ground-based geospace observations. There is increasing interest in the development of virtual observatories as we approach the International Polar and Heliosphysical Years and the electronic Geophysical Year, and are faced with burgeoning data sets from arrays of different instrument types the world over. We are developing a virtual observatory for dealing with data from geospace optical and riometer systems. While these two classes of instruments are very different in their observational technique, they are close relatives in what they observe, which is primarily auroral precipitation. The GAIA (Global Auroral Imaging Access) Project is a network-based set of tools for browsing summary data from All-Sky Imagers (ASIs), Meridian Scanning Photometers (MSPs), and riometers worldwide, and that provides indexes for direct access to data at PI institutes. This program is the virtual observatory component of the IPY Auroral Optical Network (AON) and GLORIA (Global Riometer Imaging Array) projects, and falls under the ICESTAR IPY grouping. As well, GAIA is being developed so as to be fully consistent with the data policies described in the `Declaration of the eGY'. We demonstrate the GAIA concept with ASI data from Canada and Finland, MSP data from Canada, and riometer data from Canada and Scandinavia. We explore the requirements that such a system must meet in order to be successful, which include ease of use, credit to data providers, ability for data providers to monitor usage, and reliance on software rather than hardware. The latter is consistent with our concept of a summary data set consisting of keograms, time series, and thumbnail images, a fully peer to peer data access system, and a relational data base that allows for easy grouping of and linkages between data. We describe how we are ensuring that GAIA is compatible with larger efforts such as SPIDR

  12. Virtually Possible

    ERIC Educational Resources Information Center

    Mellon, Ericka

    2011-01-01

    Diane Lewis began building her popular virtual education program in a storage closet. The drab room, just big enough to squeeze in a tiny table, was her office at the headquarters of Seminole County (Florida) Public Schools. She had a computer and a small staff of temporary workers. Lewis, who managed to open two successful virtual schools for…

  13. Active Learning: A Small Group Histology Laboratory Exercise in a Whole Class Setting Utilizing Virtual Slides and Peer Education

    ERIC Educational Resources Information Center

    Bloodgood, Robert A.

    2012-01-01

    Histology laboratory instruction is moving away from the sole use of the traditional combination of light microscopes and glass slides in favor of virtual microscopy and virtual slides. At the same time, medical curricula are changing so as to reduce scheduled time for basic science instruction as well as focusing on student-centered learning…

  14. Virtual Worlds, Virtual Literacy: An Educational Exploration

    ERIC Educational Resources Information Center

    Stoerger, Sharon

    2008-01-01

    Virtual worlds enable students to learn through seeing, knowing, and doing within visually rich and mentally engaging spaces. Rather than reading about events, students become part of the events through the adoption of a pre-set persona. Along with visual feedback that guides the players' activities and the development of visual skills, visual…

  15. Detection of silent cells, synchronization and modulatory activity in developing cellular networks.

    PubMed

    Hjorth, Johannes J J; Dawitz, Julia; Kroon, Tim; Pires, Johny; Dassen, Valerie J; Berkhout, Janna A; Emperador Melero, Javier; Nadadhur, Aish G; Alevra, Mihai; Toonen, Ruud F; Heine, Vivi M; Mansvelder, Huibert D; Meredith, Rhiannon M

    2016-04-01

    Developing networks in the immature nervous system and in cellular cultures are characterized by waves of synchronous activity in restricted clusters of cells. Synchronized activity in immature networks is proposed to regulate many different developmental processes, from neuron growth and cell migration, to the refinement of synapses, topographic maps, and the mature composition of ion channels. These emergent activity patterns are not present in all cells simultaneously within the network and more immature "silent" cells, potentially correlated with the presence of silent synapses, are prominent in different networks during early developmental periods. Many current network analyses for detection of synchronous cellular activity utilize activity-based pixel correlations to identify cellular-based regions of interest (ROIs) and coincident cell activity. However, using activity-based correlations, these methods first underestimate or ignore the inactive silent cells within the developing network and second, are difficult to apply within cell-dense regions commonly found in developing brain networks. In addition, previous methods may ignore ROIs within a network that shows transient activity patterns comprising both inactive and active periods. We developed analysis software to semi-automatically detect cells within developing neuronal networks that were imaged using calcium-sensitive reporter dyes. Using an iterative threshold, modulation of activity was tracked within individual cells across the network. The distribution pattern of both inactive and active, including synchronous cells, could be determined based on distance measures to neighboring cells and according to different anatomical layers. PMID:26097169

  16. A virtual lymph node model to dissect the requirements for T-cell activation by synapses and kinapses

    PubMed Central

    Moreau, Hélène D; Bogle, Gib; Bousso, Philippe

    2016-01-01

    The initiation of T-cell responses in lymph nodes requires T cells to integrate signals delivered by dendritic cells (DCs) during long-lasting contacts (synapses) or more transient interactions (kinapses). However, it remains extremely challenging to understand how a specific sequence of contacts established by T cells ultimately dictates T-cell fate. Here, we have coupled a computational model of T-cell migration and interactions with DCs with a real-time, flow cytometry-like representation of T-cell activation. In this model, low-affinity peptides trigger T-cell proliferation through kinapses but we show that this process is only effective under conditions of high DC densities and prolonged antigen availability. By contrast, high-affinity peptides favor synapse formation and a vigorous proliferation under a wide range of antigen presentation conditions. In line with the predictions, decreasing the DC density in vivo selectively abolished proliferation induced by the low-affinity peptide. Finally, our results suggest that T cells possess a biochemical memory of previous stimulations of at least 1–2 days. We propose that the stability of T-cell–DC interactions, apart from their signaling potency, profoundly influences the robustness of T-cell activation. By offering the ability to control parameters that are difficult to manipulate experimentally, the virtual lymph node model provides new possibilities to tackle the fundamental mechanisms that regulate T-cell responses elicited by infections or vaccines. PMID:27089942

  17. A virtual lymph node model to dissect the requirements for T-cell activation by synapses and kinapses.

    PubMed

    Moreau, Hélène D; Bogle, Gib; Bousso, Philippe

    2016-08-01

    The initiation of T-cell responses in lymph nodes requires T cells to integrate signals delivered by dendritic cells (DCs) during long-lasting contacts (synapses) or more transient interactions (kinapses). However, it remains extremely challenging to understand how a specific sequence of contacts established by T cells ultimately dictates T-cell fate. Here, we have coupled a computational model of T-cell migration and interactions with DCs with a real-time, flow cytometry-like representation of T-cell activation. In this model, low-affinity peptides trigger T-cell proliferation through kinapses but we show that this process is only effective under conditions of high DC densities and prolonged antigen availability. By contrast, high-affinity peptides favor synapse formation and a vigorous proliferation under a wide range of antigen presentation conditions. In line with the predictions, decreasing the DC density in vivo selectively abolished proliferation induced by the low-affinity peptide. Finally, our results suggest that T cells possess a biochemical memory of previous stimulations of at least 1-2 days. We propose that the stability of T-cell-DC interactions, apart from their signaling potency, profoundly influences the robustness of T-cell activation. By offering the ability to control parameters that are difficult to manipulate experimentally, the virtual lymph node model provides new possibilities to tackle the fundamental mechanisms that regulate T-cell responses elicited by infections or vaccines. PMID:27089942

  18. Self-organization of synchronous activity propagation in neuronal networks driven by local excitation.

    PubMed

    Bayati, Mehdi; Valizadeh, Alireza; Abbassian, Abdolhossein; Cheng, Sen

    2015-01-01

    Many experimental and theoretical studies have suggested that the reliable propagation of synchronous neural activity is crucial for neural information processing. The propagation of synchronous firing activity in so-called synfire chains has been studied extensively in feed-forward networks of spiking neurons. However, it remains unclear how such neural activity could emerge in recurrent neuronal networks through synaptic plasticity. In this study, we investigate whether local excitation, i.e., neurons that fire at a higher frequency than the other, spontaneously active neurons in the network, can shape a network to allow for synchronous activity propagation. We use two-dimensional, locally connected and heterogeneous neuronal networks with spike-timing dependent plasticity (STDP). We find that, in our model, local excitation drives profound network changes within seconds. In the emergent network, neural activity propagates synchronously through the network. This activity originates from the site of the local excitation and propagates through the network. The synchronous activity propagation persists, even when the local excitation is removed, since it derives from the synaptic weight matrix. Importantly, once this connectivity is established it remains stable even in the presence of spontaneous activity. Our results suggest that synfire-chain-like activity can emerge in a relatively simple way in realistic neural networks by locally exciting the desired origin of the neuronal sequence. PMID:26089794

  19. Enabling New and More Transparent Science via DataONE—a Virtual Data Observation Network for Earth (Invited)

    NASA Astrophysics Data System (ADS)

    Michener, W.

    2010-12-01

    Addressing grand environmental science challenges requires unprecedented access to easily understood data that cross the breadth of temporal, spatial, and thematic scales. From a scientist’s perspective, the big challenges lie in discovering the relevant data, dealing with extreme data heterogeneity, and converting data to information and knowledge. Addressing these challenges requires new approaches for managing, preserving, analyzing, and sharing data. DataONE is designed to be the foundation of new innovative environmental research that addresses questions of relevance to science and society. DataONE will ensure preservation and access to multi-scale, multi-discipline, and multi-national data. Operationally, DataONE encompasses a distributed global network of Member Nodes (i.e., data repositories) that provide open and persistent access to well-described and easily discovered Earth observational data. In addition, a smaller number of Coordinating Nodes (i.e., metadata repositories and service centers) support network-wide services such as data replication and access to an array of enabling tools. DataONE’s objectives are to: make biological data available from the genome to the ecosystem; make environmental data available from atmospheric, ecological, hydrological, and oceanographic sources; provide secure and long-term preservation and access; and engage scientists, land-managers, policy makers, students, educators, and the public through logical access and intuitive visualizations. The foundation for excellence of DataONE is the established collaboration among participating organizations that have multi-decade expertise in a wide range of fields that includes: existing archive initiatives, libraries, environmental observing systems and research networks, data and information management, science synthesis centers, and professional societies. DataONE is a means to serve a broad range of science domains directly and indirectly through interoperability with

  20. The Interactive, Virtual Management Information Systems (MIS) Classroom: Creating an Active Learning Environment on the Internet.

    ERIC Educational Resources Information Center

    Abraham, Thomas

    This paper describes the creation of an active learning environment within an Internet-based course in the School of Business, Government and Technology at Kean University (New Jersey). The introductory Management Information Systems (MIS) course is an elective that has become increasingly popular with junior and senior business majors. The main…

  1. Virtual Satellite

    NASA Technical Reports Server (NTRS)

    Hammrs, Stephan R.

    2008-01-01

    Virtual Satellite (VirtualSat) is a computer program that creates an environment that facilitates the development, verification, and validation of flight software for a single spacecraft or for multiple spacecraft flying in formation. In this environment, enhanced functionality and autonomy of navigation, guidance, and control systems of a spacecraft are provided by a virtual satellite that is, a computational model that simulates the dynamic behavior of the spacecraft. Within this environment, it is possible to execute any associated software, the development of which could benefit from knowledge of, and possible interaction (typically, exchange of data) with, the virtual satellite. Examples of associated software include programs for simulating spacecraft power and thermal- management systems. This environment is independent of the flight hardware that will eventually host the flight software, making it possible to develop the software simultaneously with, or even before, the hardware is delivered. Optionally, by use of interfaces included in VirtualSat, hardware can be used instead of simulated. The flight software, coded in the C or C++ programming language, is compilable and loadable into VirtualSat without any special modifications. Thus, VirtualSat can serve as a relatively inexpensive software test-bed for development test, integration, and post-launch maintenance of spacecraft flight software.

  2. Virtual seminars

    NASA Astrophysics Data System (ADS)

    Nelson, H. Roice

    1997-06-01

    A virtual seminar (SM) is an economic and effective instructional tool for teaching students who are at a distance from their instructor. Like conventional class room teaching, a virtual seminar requires an instructor, a student, and a method of communication. Teleconferencing, video conferencing, intranets and the Internet give learners in a Virtual Seminar the ability to interact immediately with their mentors and receive real and relevant answers. This paper shows how industry and academia can benefit from using methods developed and experience gained in presenting the first virtual seminars to academic and petroleum industry participants in mid-1996. The information explosion in industry means that business or technical information is worthless until it is assimilated into a corporate knowledge management system. A search for specific information often turns into a filtering exercise or an attempt to find patterns and classify retrieved material. In the setting of an interactive corporate information system, virtual seminars meet the need for a productive new relationship between creative people and the flux of corporate knowledge. Experience shows that it is more efficient to circulate timesensitive and confidential information electronically through a virtual seminar. Automating the classification of information and removing that task from the usual work load creates an electronic corporate memory and enhances the value of the knowledge to both users and a corporation. Catalogued benchmarks, best-practice standards, and Knowledge Maps (SM) of experience serve as key aids to communicating knowledge through virtual seminars and converting that knowledge into a profit-making asset.

  3. Virtual Machine Logbook - Enabling virtualization for ATLAS

    NASA Astrophysics Data System (ADS)

    Yao, Yushu; Calafiura, Paolo; Poffet, Julien; Cavalli, Andrea; Leggett, Charles; Frédéric, Bapst

    2010-04-01

    ATLAS software has been developed mostly on CERN linux cluster lxplus or on similar facilities at the experiment Tier 1 centers. The fast rise of virtualization technology has the potential to change this model, turning every laptop or desktop into an ATLAS analysis platform. In the context of the CernVM project we are developing a suite of tools and CernVM plug-in extensions to promote the use of virtualization for ATLAS analysis and software development. The Virtual Machine Logbook (VML), in particular, is an application to organize work of physicists on multiple projects, logging their progress, and speeding up "context switches" from one project to another. An important feature of VML is the ability to share with a single "click" the status of a given project with other colleagues. VML builds upon the save and restore capabilities of mainstream virtualization software like VMware, and provides a technology-independent client interface to them. A lot of emphasis in the design and implementation has gone into optimizing the save and restore process to makepractical to store many VML entries on a typical laptop disk or to share a VML entry over the network. At the same time, taking advantage of CernVM's plugin capabilities, we are extending the CernVM platform to help increase the usability of ATLAS software. For example, we added the ability to start the ATLAS event display on any computer running CernVM simply by clicking a button in a web browser. We want to integrate seamlessly VML with CernVM unique file system design to distribute efficiently ATLAS software on every physicist computer. The CernVM File System (CVMFS) download files on-demand via HTTP, and cache it locally for future use. This reduces by one order of magnitude the download sizes, making practical for a developer to work with multiple software releases on a virtual machine.

  4. Water flow based geometric active deformable model for road network

    NASA Astrophysics Data System (ADS)

    Leninisha, Shanmugam; Vani, Kaliaperumal

    2015-04-01

    A width and color based geometric active deformable model is proposed for road network extraction from remote sensing images with minimal human interception. Orientation and width of road are computed from a single manual seed point, from which the propagation starts both right and left hand directions of the starting point, which extracts the interconnected road network from the aerial or high spatial resolution satellite image automatically. Here the propagation (like water flow in canal with defined boundary) is restricted with color and width of the road. Road extraction is done for linear, curvilinear (U shape and S shape) roads first, irrespective of width and color. Then, this algorithm is improved to extract road with junctions in a shape of L, T and X along with center line. Roads with small break or disconnected roads are also extracts by a modified version of this same algorithm. This methodology is tested and evaluated with various remote sensing images. The experimental results show that the proposed method is efficient and extracting roads accurately with less computation time. However, in complex urban areas, the identification accuracy declines due to the various sizes of obstacles, over bridges, multilane etc.

  5. A Virtual Tour of Virtual Schools.

    ERIC Educational Resources Information Center

    Joiner, Lottie L.

    2002-01-01

    Briefly describes the eight virtual schools in the United States: Kentucky Virtual High School; Illinois Virtual High School; Florida Virtual School; CCS Web Academy in Fayetteville, North Carolina; The Virtual High School in Hudson, Massachusetts; Basehor-Linwood Virtual Charter School in Kansas; Monte Vista Online Academy in Colorado; and…

  6. Virtual machine performance benchmarking.

    PubMed

    Langer, Steve G; French, Todd

    2011-10-01

    The attractions of virtual computing are many: reduced costs, reduced resources and simplified maintenance. Any one of these would be compelling for a medical imaging professional attempting to support a complex practice on limited resources in an era of ever tightened reimbursement. In particular, the ability to run multiple operating systems optimized for different tasks (computational image processing on Linux versus office tasks on Microsoft operating systems) on a single physical machine is compelling. However, there are also potential drawbacks. High performance requirements need to be carefully considered if they are to be executed in an environment where the running software has to execute through multiple layers of device drivers before reaching the real disk or network interface. Our lab has attempted to gain insight into the impact of virtualization on performance by benchmarking the following metrics on both physical and virtual platforms: local memory and disk bandwidth, network bandwidth, and integer and floating point performance. The virtual performance metrics are compared to baseline performance on "bare metal." The results are complex, and indeed somewhat surprising. PMID:21207096

  7. Enzymatic activity preservation through entrapment within degradable hydrogel networks

    NASA Astrophysics Data System (ADS)

    Mariani, Angela Marie

    This dissertation aimed to design and develop a "biogel;" a reproducible, abiotic, and biocompatible polymer hydrogel matrix, that prolongs enzymatic stability allowing for rapid production of biomolecules. The researched entrapment method preserves enzyme activity within an amicable environment while resisting activity reduction in the presence of increased pH environmental challenges. These biogels can be used in a number of applications including repeated production of small molecules and in biosensors. Five main objectives were accomplished: 1) Biogels capable of maintaining enzymatic functionality post-entrapment procedures were fabricated; 2) Biogel activity dependence on crosslinker type and crosslink density was determined; 3) Biogel composition effects on sustained activity after storage were compared; 4) Biogel activity dependence on charged monomer moieties was evaluated, and 5) Combined optimization knowledge gained from the first four objectives was utilized to determine the protection of enzymes within hydrogels when challenged with an increased pH above 8. Biogels were fabricated by entrapping β-galactosidase (lactase) enzyme within acrylamide (ACR) gels crosslinked with poly(ethylene glycol) diacrylate (PEGDA, degradable through hydrolysis) or N,N'-methylenebisacrylamide (BIS, non-degradable). Initial hydrogel entrapment reduced activity to 40% in ACR/PEGDA gels, compared to a 75% reduction in initial activity of ACR/BIS biogels. Once entrapped, these enzymes resist activity reduction in the presence of environmental challenges, such as altering the pH from 7 to above 8. When biogels were challenged at a pH of 8, activity retention positively correlated to PEGDA crosslinker density; increasing from 48% to 91% retention in 30 to 40 mole % PEGDA biogels as compared to solution based control which retained only 23%. Retention of activity when perturbed from pH 7 is advantageous for biogel applications including the repeated production of desired small

  8. Natural lecithin promotes neural network complexity and activity.

    PubMed

    Latifi, Shahrzad; Tamayol, Ali; Habibey, Rouhollah; Sabzevari, Reza; Kahn, Cyril; Geny, David; Eftekharpour, Eftekhar; Annabi, Nasim; Blau, Axel; Linder, Michel; Arab-Tehrany, Elmira

    2016-01-01

    Phospholipids in the brain cell membranes contain different polyunsaturated fatty acids (PUFAs), which are critical to nervous system function and structure. In particular, brain function critically depends on the uptake of the so-called "essential" fatty acids such as omega-3 (n-3) and omega-6 (n-6) PUFAs that cannot be readily synthesized by the human body. We extracted natural lecithin rich in various PUFAs from a marine source and transformed it into nanoliposomes. These nanoliposomes increased neurite outgrowth, network complexity and neural activity of cortical rat neurons in vitro. We also observed an upregulation of synapsin I (SYN1), which supports the positive role of lecithin in synaptogenesis, synaptic development and maturation. These findings suggest that lecithin nanoliposomes enhance neuronal development, which may have an impact on devising new lecithin delivery strategies for therapeutic applications. PMID:27228907

  9. Natural lecithin promotes neural network complexity and activity

    PubMed Central

    Latifi, Shahrzad; Tamayol, Ali; Habibey, Rouhollah; Sabzevari, Reza; Kahn, Cyril; Geny, David; Eftekharpour, Eftekhar; Annabi, Nasim; Blau, Axel; Linder, Michel; Arab-Tehrany, Elmira

    2016-01-01

    Phospholipids in the brain cell membranes contain different polyunsaturated fatty acids (PUFAs), which are critical to nervous system function and structure. In particular, brain function critically depends on the uptake of the so-called “essential” fatty acids such as omega-3 (n-3) and omega-6 (n-6) PUFAs that cannot be readily synthesized by the human body. We extracted natural lecithin rich in various PUFAs from a marine source and transformed it into nanoliposomes. These nanoliposomes increased neurite outgrowth, network complexity and neural activity of cortical rat neurons in vitro. We also observed an upregulation of synapsin I (SYN1), which supports the positive role of lecithin in synaptogenesis, synaptic development and maturation. These findings suggest that lecithin nanoliposomes enhance neuronal development, which may have an impact on devising new lecithin delivery strategies for therapeutic applications. PMID:27228907

  10. Epidemic process on activity-driven modular networks

    NASA Astrophysics Data System (ADS)

    Han, Dun; Sun, Mei; Li, Dandan

    2015-08-01

    In this paper, we propose two novel models of epidemic spreading by considering the activity-driven and the network modular. Firstly, we consider the susceptible-infected-susceptible (SIS) contagion model and derive analytically the epidemic threshold. The results indicate that the epidemic threshold only involves with the value of the spread rate and the recovery rate. In addition, the asymptotic refractory density of infected nodes in the different communities exhibits different trends with the change of the modularity-factor. Then, the infected-driven vaccination model is presented. Simulation results illustrate that the final density of vaccination will increase with the increase of the response strength of vaccination. Moreover, the final infected density in the original-infected-community shows different trends with the change of the response strength of vaccination and the spreading rate. The infected-driven vaccination is a good way to control the epidemic spreading.

  11. Antituberculosis Activity of the Molecular Libraries Screening Center Network Library

    PubMed Central

    MADDRY, JOSEPH A.; ANANTHAN, SUBRAMANIAM; GOLDMAN, ROBERT C.; HOBRATH, JUDITH V.; KWONG, CECIL D.; MADDOX, CLINTON; RASMUSSEN, LYNN; REYNOLDS, ROBERT C.; SECRIST, JOHN A.; SOSA, MELINDA I.; WHITE, E. LUCILE; ZHANG, WEI

    2009-01-01

    SUMMARY There is an urgent need for the discovery and development of new antitubercular agents that target novel biochemical pathways and treat drug-resistant forms of the disease. One approach to addressing this need is through high-throughput screening of drug-like small molecule libraries against the whole bacterium in order to identify a variety of new, active scaffolds that will stimulate additional biological research and drug discovery. Through the Molecular Libraries Screening Center Network, the NIAID Tuberculosis Antimicrobial Acquisition and Coordinating Facility tested a 215,110-compound library against M. tuberculosis strain H37Rv. A medicinal chemistry survey of the results from the screening campaign is reported herein. PMID:19783214

  12. Early network activity propagates bidirectionally between hippocampus and cortex.

    PubMed

    Barger, Zeke; Easton, Curtis R; Neuzil, Kevin E; Moody, William J

    2016-06-01

    Spontaneous activity in the developing brain helps refine neuronal connections before the arrival of sensory-driven neuronal activity. In mouse neocortex during the first postnatal week, waves of spontaneous activity originating from pacemaker regions in the septal nucleus and piriform cortex propagate through the neocortex. Using high-speed Ca(2+) imaging to resolve the spatiotemporal dynamics of wave propagation in parasagittal mouse brain slices, we show that the hippocampus can act as an additional source of neocortical waves. Some waves that originate in the hippocampus remain restricted to that structure, while others pause at the hippocampus-neocortex boundary and then propagate into the neocortex. Blocking GABAergic neurotransmission decreases the likelihood of wave propagation into neocortex, whereas blocking glutamatergic neurotransmission eliminates spontaneous and evoked hippocampal waves. A subset of hippocampal and cortical waves trigger Ca(2+) waves in astrocytic networks after a brief delay. Hippocampal waves accompanied by Ca(2+) elevation in astrocytes are more likely to propagate into the neocortex. Finally, we show that two structures in our preparation that initiate waves-the hippocampus and the piriform cortex-can be electrically stimulated to initiate propagating waves at lower thresholds than the neocortex, indicating that the intrinsic circuit properties of those regions are responsible for their pacemaker function. © 2015 Wiley Periodicals, Inc. Develop Neurobiol 76: 661-672, 2016. PMID:26385616

  13. Active colonization dynamics and diversity patterns are influenced by dendritic network connectivity and species interactions

    PubMed Central

    Seymour, Mathew; Altermatt, Florian

    2014-01-01

    Habitat network connectivity influences colonization dynamics, species invasions, and biodiversity patterns. Recent theoretical work suggests dendritic networks, such as those found in rivers, alter expectations regarding colonization and dispersal dynamics compared with other network types. As many native and non-native species are spreading along river networks, this may have important ecological implications. However, experimental studies testing the effects of network structure on colonization and diversity patterns are scarce. Up to now, experimental studies have only considered networks where sites are connected with small corridors, or dispersal was experimentally controlled, which eliminates possible effects of species interactions on colonization dynamics. Here, we tested the effect of network connectivity and species interactions on colonization dynamics using continuous linear and dendritic (i.e., river-like) networks, which allow for active dispersal. We used a set of six protist species and one rotifer species in linear and dendritic microcosm networks. At the start of the experiment, we introduced species, either singularly or as a community within the networks. Species subsequently actively colonized the networks. We periodically measured densities of species throughout the networks over 2 weeks to track community dynamics, colonization, and diversity patterns. We found that colonization of dendritic networks was faster compared with colonization of linear networks, which resulted in higher local mean species richness in dendritic networks. Initially, community similarity was also greater in dendritic networks compared with linear networks, but this effect vanished over time. The presence of species interactions increased community evenness over time, compared with extrapolations from single-species setups. Our experimental findings confirm previous theoretical work and show that network connectivity, species-specific dispersal ability, and species

  14. Size-dependent regulation of synchronized activity in living neuronal networks

    NASA Astrophysics Data System (ADS)

    Yamamoto, Hideaki; Kubota, Shigeru; Chida, Yudai; Morita, Mayu; Moriya, Satoshi; Akima, Hisanao; Sato, Shigeo; Hirano-Iwata, Ayumi; Tanii, Takashi; Niwano, Michio

    2016-07-01

    We study the effect of network size on synchronized activity in living neuronal networks. Dissociated cortical neurons form synaptic connections in culture and generate synchronized spontaneous activity within 10 days in vitro. Using micropatterned surfaces to extrinsically control the size of neuronal networks, we show that synchronized activity can emerge in a network as small as 12 cells. Furthermore, a detailed comparison of small (˜20 cells), medium (˜100 cells), and large (˜400 cells) networks reveal that synchronized activity becomes destabilized in the small networks. A computational modeling of neural activity is then employed to explore the underlying mechanism responsible for the size effect. We find that the generation and maintenance of the synchronized activity can be minimally described by: (1) the stochastic firing of each neuron in the network, (2) enhancement in the network activity in a positive feedback loop of excitatory synapses, and (3) Ca-dependent suppression of bursting activity. The model further shows that the decrease in total synaptic input to a neuron that drives the positive feedback amplification of correlated activity is a key factor underlying the destabilization of synchrony in smaller networks. Spontaneous neural activity plays a critical role in cortical information processing, and our work constructively clarifies an aspect of the structural basis behind this.

  15. Size-dependent regulation of synchronized activity in living neuronal networks.

    PubMed

    Yamamoto, Hideaki; Kubota, Shigeru; Chida, Yudai; Morita, Mayu; Moriya, Satoshi; Akima, Hisanao; Sato, Shigeo; Hirano-Iwata, Ayumi; Tanii, Takashi; Niwano, Michio

    2016-07-01

    We study the effect of network size on synchronized activity in living neuronal networks. Dissociated cortical neurons form synaptic connections in culture and generate synchronized spontaneous activity within 10 days in vitro. Using micropatterned surfaces to extrinsically control the size of neuronal networks, we show that synchronized activity can emerge in a network as small as 12 cells. Furthermore, a detailed comparison of small (∼20 cells), medium (∼100 cells), and large (∼400 cells) networks reveal that synchronized activity becomes destabilized in the small networks. A computational modeling of neural activity is then employed to explore the underlying mechanism responsible for the size effect. We find that the generation and maintenance of the synchronized activity can be minimally described by: (1) the stochastic firing of each neuron in the network, (2) enhancement in the network activity in a positive feedback loop of excitatory synapses, and (3) Ca-dependent suppression of bursting activity. The model further shows that the decrease in total synaptic input to a neuron that drives the positive feedback amplification of correlated activity is a key factor underlying the destabilization of synchrony in smaller networks. Spontaneous neural activity plays a critical role in cortical information processing, and our work constructively clarifies an aspect of the structural basis behind this. PMID:27575164

  16. Computational reverse chemical ecology: Virtual screening and predicting behaviorally active semiochemicals for Bactrocera dorsalis

    PubMed Central

    2014-01-01

    Background Semiochemical is a generic term used for a chemical substance that influences the behaviour of an organism. It is a common term used in the field of chemical ecology to encompass pheromones, allomones, kairomones, attractants and repellents. Insects have mastered the art of using semiochemicals as communication signals and rely on them to find mates, host or habitat. This dependency of insects on semiochemicals has allowed chemical ecologists to develop environment friendly pest management strategies. However, discovering semiochemicals is a laborious process that involves a plethora of behavioural and analytical techniques, making it expansively time consuming. Recently, reverse chemical ecology approach using odorant binding proteins (OBPs) as target for elucidating behaviourally active compounds is gaining eminence. In this scenario, we describe a “computational reverse chemical ecology” approach for rapid screening of potential semiochemicals. Results We illustrate the high prediction accuracy of our computational method. We screened 25 semiochemicals for their binding potential to a GOBP of B. dorsalis using molecular docking (in silico) and molecular dynamics. Parallely, compounds were subjected to fluorescent quenching assays (Experimental). The correlation between in silico and experimental data were significant (r2 = 0.9408; P < 0.0001). Further, predicted compounds were subjected to behavioral bioassays and were found to be highly attractive to insects. Conclusions The present study provides a unique methodology for rapid screening and predicting behaviorally active semiochemicals. This methodology may be developed as a viable approach for prospecting active semiochemicals for pest control, which otherwise is a laborious process. PMID:24640964

  17. The Virtual Environmental Microbiology Center - A Social Network for Enhanced Communication between Water Researchers and Policy Makers

    EPA Science Inventory

    Effective communication within and between organizations involved in research and policy making activities is essential. Sharing information across organizational and geographic boundaries can also facilitate coordination and collaboration, promote a better understanding of tech...

  18. Resting-state fMRI activity predicts unsupervised learning and memory in an immersive virtual reality environment.

    PubMed

    Wong, Chi Wah; Olafsson, Valur; Plank, Markus; Snider, Joseph; Halgren, Eric; Poizner, Howard; Liu, Thomas T

    2014-01-01

    In the real world, learning often proceeds in an unsupervised manner without explicit instructions or feedback. In this study, we employed an experimental paradigm in which subjects explored an immersive virtual reality environment on each of two days. On day 1, subjects implicitly learned the location of 39 objects in an unsupervised fashion. On day 2, the locations of some of the objects were changed, and object location recall performance was assessed and found to vary across subjects. As prior work had shown that functional magnetic resonance imaging (fMRI) measures of resting-state brain activity can predict various measures of brain performance across individuals, we examined whether resting-state fMRI measures could be used to predict object location recall performance. We found a significant correlation between performance and the variability of the resting-state fMRI signal in the basal ganglia, hippocampus, amygdala, thalamus, insula, and regions in the frontal and temporal lobes, regions important for spatial exploration, learning, memory, and decision making. In addition, performance was significantly correlated with resting-state fMRI connectivity between the left caudate and the right fusiform gyrus, lateral occipital complex, and superior temporal gyrus. Given the basal ganglia's role in exploration, these findings suggest that tighter integration of the brain systems responsible for exploration and visuospatial processing may be critical for learning in a complex environment. PMID:25286145

  19. Resting-State fMRI Activity Predicts Unsupervised Learning and Memory in an Immersive Virtual Reality Environment

    PubMed Central

    Wong, Chi Wah; Olafsson, Valur; Plank, Markus; Snider, Joseph; Halgren, Eric; Poizner, Howard; Liu, Thomas T.

    2014-01-01

    In the real world, learning often proceeds in an unsupervised manner without explicit instructions or feedback. In this study, we employed an experimental paradigm in which subjects explored an immersive virtual reality environment on each of two days. On day 1, subjects implicitly learned the location of 39 objects in an unsupervised fashion. On day 2, the locations of some of the objects were changed, and object location recall performance was assessed and found to vary across subjects. As prior work had shown that functional magnetic resonance imaging (fMRI) measures of resting-state brain activity can predict various measures of brain performance across individuals, we examined whether resting-state fMRI measures could be used to predict object location recall performance. We found a significant correlation between performance and the variability of the resting-state fMRI signal in the basal ganglia, hippocampus, amygdala, thalamus, insula, and regions in the frontal and temporal lobes, regions important for spatial exploration, learning, memory, and decision making. In addition, performance was significantly correlated with resting-state fMRI connectivity between the left caudate and the right fusiform gyrus, lateral occipital complex, and superior temporal gyrus. Given the basal ganglia's role in exploration, these findings suggest that tighter integration of the brain systems responsible for exploration and visuospatial processing may be critical for learning in a complex environment. PMID:25286145

  20. A local active noise control system based on a virtual-microphone technique for railway sleeping vehicle applications

    NASA Astrophysics Data System (ADS)

    Diaz, J.; Egaña, J. M.; Viñolas, J.

    2006-11-01

    Low-frequency broadband noise generated on a railway vehicle by the wheel-rail interaction could be a big annoyance for passengers in sleeping cars. Low-frequency acoustic radiation is extremely difficult to attenuate by using passive devices. In this article, an active noise control (ANC) technique has been proposed for this purpose. A three-dimensional cabin was built in the laboratory to carry out the experiments. The proposed scheme is based on a Filtered-X Least Mean Square (FXLMS) control algorithm, particularised for a virtual-microphone technique. Control algorithms were designed with the Matlab-Simulink tool, and the Real Time Windows Target toolbox of Matlab was used to run in real time the ANC system. Referring to the results, different simulations and experimental performances were analysed to enlarge the silence zone around the passenger's ear zone and along the bed headboard. Attenuations of up to 20 and 15 dB(A) (re:20 μPa) were achieved at the passenger's ear in simulations and in experimental results, respectively.