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1

Directed network modules  

NASA Astrophysics Data System (ADS)

A search technique locating network modules, i.e. internally densely connected groups of nodes in directed networks is introduced by extending the clique percolation method originally proposed for undirected networks. After giving a suitable definition for directed modules we investigate their percolation transition in the Erdos Rényi graph both analytically and numerically. We also analyse four real-world directed networks, including Google's own web-pages, an email network, a word association graph and the transcriptional regulatory network of the yeast Saccharomyces cerevisiae. The obtained directed modules are validated by additional information available for the nodes. We find that directed modules of real-world graphs inherently overlap and the investigated networks can be classified into two major groups in terms of the overlaps between the modules. Accordingly, in the word-association network and Google's web-pages, overlaps are likely to contain in-hubs, whereas the modules in the email and transcriptional regulatory network tend to overlap via out-hubs.

Palla, Gergely; Farkas, Illés J.; Pollner, Péter; Derényi, Imre; Vicsek, Tamás

2007-06-01

2

Centrality properties of directed module members in social networks  

NASA Astrophysics Data System (ADS)

Several recent studies of complex networks have suggested algorithms for locating network communities, also called modules or clusters, which are mostly defined as groups of nodes with dense internal connections. Along with the rapid development of these clustering techniques, the ability of revealing overlaps between communities has become very important as well. An efficient search technique for locating overlapping modules is provided by the Clique Percolation Method (CPM) and its extension to directed graphs, the CPMd algorithm. Here we investigate the centrality properties of directed module members in social networks obtained from e-mail exchanges and from sociometric questionnaires. Our results indicate that nodes in the overlaps between modules play a central role in the studied systems. Furthermore, the two different types of networks show interesting differences in the relation between the centrality measures and the role of the nodes in the directed modules.

Pollner, Péter; Palla, Gergely; Ábel, Dániel; Vicsek, András; Farkas, Illés J.; Derényi, Imre; Vicsek, Tamás

2008-08-01

3

Sequence dependence of phase-induced intensity noise in optical networks that employ direct modulation  

NASA Astrophysics Data System (ADS)

Phase-induced intensity noise in optical networks that employ directly modulated laser sources is observed to be bit-sequence dependent. This dependence is explained by optical frequency variations that are due to the heating history of the laser chip and is accurately modeled. This effect may permit suppression of phase-induced intensity noise in many types of fiber system with multipaths.

Tur, M.; Legg, P. J.; Shabeer, M.; Andonovic, I.

1995-02-01

4

Direct-Sequence Spread-Spectrum Modulation for Utility Packet Transmission in Underwater Acoustic Communication Networks  

NASA Astrophysics Data System (ADS)

This thesis investigates the feasibility and performance of using Direct-Sequence Spread-Spectrum (DSSS) modulation for utility-packet transmission in Seaweb underwater wireless acoustic communications networks, Seaweb networks require robust channel-tolerant utility packets having a low probability of detection (LPD) and allowing for multi-user access, MATLAB code simulated the DSSS transmitter and receiver structures and a modeled channel impulse response represented the underwater environment, The specific modulation scheme implemented is direct-sequence, differentially encoded binary phase-shift keying (DS-DBPSK) with quadrature spreading, Performance is examined using Monte Carlo simulation Bit error rates and packet error rates for various signal-to-noise ratios and channel conditions are presented and the use of a RAKE receiver, forward error-correction coding and symbol interleaving are examined for improving system performance.

Duke, Peter S.

2002-09-01

5

Module bay with directed flow  

DOEpatents

A module bay requires less cleanroom airflow. A shaped gas inlet passage can allow cleanroom air into the module bay with flow velocity preferentially directed toward contaminant rich portions of a processing module in the module bay. Preferential gas flow direction can more efficiently purge contaminants from appropriate portions of the module bay, allowing a reduced cleanroom air flow rate for contaminant removal. A shelf extending from an air inlet slit in one wall of a module bay can direct air flowing therethrough toward contaminant-rich portions of the module bay, such as a junction between a lid and base of a processing module.

Torczynski, John R. (Albuquerque, NM)

2001-02-27

6

Weighted network modules  

NASA Astrophysics Data System (ADS)

The inclusion of link weights into the analysis of network properties allows a deeper insight into the (often overlapping) modular structure of real-world webs. We introduce a clustering algorithm clique percolation method with weights (CPMw) for weighted networks based on the concept of percolating k-cliques with high enough intensity. The algorithm allows overlaps between the modules. First, we give detailed analytical and numerical results about the critical point of weighted k-clique percolation on (weighted) Erdos Rényi graphs. Then, for a scientist collaboration web and a stock correlation graph we compute three-link weight correlations and with the CPMw the weighted modules. After reshuffling link weights in both networks and computing the same quantities for the randomized control graphs as well, we show that groups of three or more strong links prefer to cluster together in both original graphs.

Farkas, Illés; Ábel, Dániel; Palla, Gergely; Vicsek, Tamás

2007-06-01

7

Clustering signatures classify directed networks  

NASA Astrophysics Data System (ADS)

We use a clustering signature, based on a recently introduced generalization of the clustering coefficient to directed networks, to analyze 16 directed real-world networks of five different types: social networks, genetic transcription networks, word adjacency networks, food webs, and electric circuits. We show that these five classes of networks are cleanly separated in the space of clustering signatures due to the statistical properties of their local neighborhoods, demonstrating the usefulness of clustering signatures as a classifier of directed networks.

Ahnert, S. E.; Fink, T. M. A.

2008-09-01

8

Dynamic behaviors in directed networks  

SciTech Connect

Motivated by the abundance of directed synaptic couplings in a real biological neuronal network, we investigate the synchronization behavior of the Hodgkin-Huxley model in a directed network. We start from the standard model of the Watts-Strogatz undirected network and then change undirected edges to directed arcs with a given probability, still preserving the connectivity of the network. A generalized clustering coefficient for directed networks is defined and used to investigate the interplay between the synchronization behavior and underlying structural properties of directed networks. We observe that the directedness of complex networks plays an important role in emerging dynamical behaviors, which is also confirmed by a numerical study of the sociological game theoretic voter model on directed networks.

Park, Sung Min [Center of Complex Systems, Samsung Economic Research Institute, Seoul 140-702 (Korea, Republic of); Kim, Beom Jun [Department of Physics, BK21 Physics Research Division, and Institute of Basic Science, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of)

2006-08-15

9

Directions in active networks  

Microsoft Academic Search

Active networks represent a significant step in the evolution of packet-switched networks, from traditional packet-forwarding engines to more general functionality supporting dynamic control and modification of network behavior. However, the phrase “active network” means different things to different people. This article introduces a model and nomenclature for talking about active networks, describes some possible approaches in terms of that nomenclature,

K. L. Calvert; S. Bhattacharjee; E. Zegura; J. Sterbenz

1998-01-01

10

Epidemic threshold in directed networks  

NASA Astrophysics Data System (ADS)

Epidemics have so far been mostly studied in undirected networks. However, many real-world networks, such as the online social network Twitter and the world wide web, on which information, emotion, or malware spreads, are directed networks, composed of both unidirectional links and bidirectional links. We define the directionality ? as the percentage of unidirectional links. The epidemic threshold ?c for the susceptible-infected-susceptible (SIS) epidemic is lower bounded by 1/?1 in directed networks, where ?1, also called the spectral radius, is the largest eigenvalue of the adjacency matrix. In this work, we propose two algorithms to generate directed networks with a given directionality ?. The effect of ? on the spectral radius ?1, principal eigenvector x1, spectral gap (?1-?2), and algebraic connectivity ?N-1 is studied. Important findings are that the spectral radius ?1 decreases with the directionality ?, whereas the spectral gap and the algebraic connectivity increase with the directionality ?. The extent of the decrease of the spectral radius depends on both the degree distribution and the degree-degree correlation ?D. Hence, in directed networks, the epidemic threshold is larger and a random walk converges to its steady state faster than that in undirected networks with the same degree distribution.

Li, Cong; Wang, Huijuan; Van Mieghem, Piet

2013-12-01

11

A mean field neural network for hierarchical module placement  

NASA Technical Reports Server (NTRS)

This paper proposes a mean field neural network for the two-dimensional module placement problem. An efficient coding scheme with only O(N log N) neurons is employed where N is the number of modules. The neurons are evolved in groups of N in log N iteration steps such that the circuit is recursively partitioned in alternating vertical and horizontal directions. In our simulations, the network was able to find optimal solutions to all test problems with up to 128 modules.

Unaltuna, M. Kemal; Pitchumani, Vijay

1992-01-01

12

Sampling properties of directed networks  

NASA Astrophysics Data System (ADS)

For many real-world networks only a small “sampled” version of the original network may be investigated; those results are then used to draw conclusions about the actual system. Variants of breadth-first search (BFS) sampling, which are based on epidemic processes, are widely used. Although it is well established that BFS sampling fails, in most cases, to capture the IN component(s) of directed networks, a description of the effects of BFS sampling on other topological properties is all but absent from the literature. To systematically study the effects of sampling biases on directed networks, we compare BFS sampling to random sampling on complete large-scale directed networks. We present new results and a thorough analysis of the topological properties of seven complete directed networks (prior to sampling), including three versions of Wikipedia, three different sources of sampled World Wide Web data, and an Internet-based social network. We detail the differences that sampling method and coverage can make to the structural properties of sampled versions of these seven networks. Most notably, we find that sampling method and coverage affect both the bow-tie structure and the number and structure of strongly connected components in sampled networks. In addition, at a low sampling coverage (i.e., less than 40%), the values of average degree, variance of out-degree, degree autocorrelation, and link reciprocity are overestimated by 30% or more in BFS-sampled networks and only attain values within 10% of the corresponding values in the complete networks when sampling coverage is in excess of 65%. These results may cause us to rethink what we know about the structure, function, and evolution of real-world directed networks.

Son, S.-W.; Christensen, C.; Bizhani, G.; Foster, D. V.; Grassberger, P.; Paczuski, M.

2012-10-01

13

Sampling properties of directed networks.  

PubMed

For many real-world networks only a small "sampled" version of the original network may be investigated; those results are then used to draw conclusions about the actual system. Variants of breadth-first search (BFS) sampling, which are based on epidemic processes, are widely used. Although it is well established that BFS sampling fails, in most cases, to capture the IN component(s) of directed networks, a description of the effects of BFS sampling on other topological properties is all but absent from the literature. To systematically study the effects of sampling biases on directed networks, we compare BFS sampling to random sampling on complete large-scale directed networks. We present new results and a thorough analysis of the topological properties of seven complete directed networks (prior to sampling), including three versions of Wikipedia, three different sources of sampled World Wide Web data, and an Internet-based social network. We detail the differences that sampling method and coverage can make to the structural properties of sampled versions of these seven networks. Most notably, we find that sampling method and coverage affect both the bow-tie structure and the number and structure of strongly connected components in sampled networks. In addition, at a low sampling coverage (i.e., less than 40%), the values of average degree, variance of out-degree, degree autocorrelation, and link reciprocity are overestimated by 30% or more in BFS-sampled networks and only attain values within 10% of the corresponding values in the complete networks when sampling coverage is in excess of 65%. These results may cause us to rethink what we know about the structure, function, and evolution of real-world directed networks. PMID:23214649

Son, S-W; Christensen, C; Bizhani, G; Foster, D V; Grassberger, P; Paczuski, M

2012-10-01

14

System control network for multiple processor modules  

SciTech Connect

This patent describes, in a network of multiple units of processors and digital modules, a control network system for providing direct communication capability between any two digital units in the network designated as a transmitting unit and a receiving unit. The system comprises: (a) processor means wherein each processor means includes a maintenance processor means for interfacing the processor means to a system network bus means, the maintenance processor means including: means to generate a LOCK signal; means to generate an address signal to indicate presence of address data; means to generate a strobe when transmitting and an acknowledge signal when receiving; (b) network bus means connecting each maintenance processor means to every other maintenance processor means, the network bus means including: a first set of bit lines for transferring data bits from the transmitting unit to the receiving unit; and a second bit line for carrying a LOCK signal to hold the network bus means available for exclusive use of the unit originating the LOCK signal, the LOCK signal originated by the transmitting unit.

Whittaker, B.E.; Jeppensen, J.H.; Beale, A.W.

1987-04-14

15

Distributed Pulse Forming Network for Magnetic Modulator.  

National Technical Information Service (NTIS)

A pulse forming network with distributed inductance and capacitance is disclosed for use in a magnetic modulator. The magnetic modulator has a magnetic core with a primary winding and a secondary winding around it. The pulse forming network includes an in...

M. Weiner J. L. Carter R. J. Youmans

1984-01-01

16

Notational usage modulates attention networks in binumerates  

PubMed Central

Multicultural environments require learning multiple number notations wherein some are encountered more frequently than others. This leads to differences in exposure and consequently differences in usage between notations. We find that differential notational usage imposes a significant neurocognitive load on number processing. Despite simultaneous acquisition, twenty four adult binumerates, familiar with two positional writing systems namely Hindu Nagari digits and Hindu Arabic digits, reported significantly lower preference and usage for Nagari as compared to Arabic. Twenty-four participants showed significantly increased reaction times and reduced accuracy while performing magnitude comparison tasks in Nagari with respect to Arabic. Functional magnetic resonance imaging revealed that processing Nagari elicited significantly greater activity in number processing and attention networks. A direct subtraction of networks for Nagari and Arabic notations revealed a neural circuit comprising of bilateral Intra-parietal Sulcus (IPS), Inferior and Mid Frontal Gyri, Fusiform Gyrus and the Anterior Cingulate Cortex (FDR p < 0.005). Additionally, whole brain correlation analysis showed that activity in the left inferior parietal region was modulated by task performance in Nagari. We attribute the increased activation in Nagari to increased task difficulty due to infrequent exposure and usage. Our results reiterate the role of left IPS in modulating performance in numeric tasks and highlight the role of the attention network for monitoring symbolic notation mode in binumerates.

Koul, Atesh; Tyagi, Vaibhav; Singh, Nandini C.

2014-01-01

17

Modulation for emergent networks: serotonin and dopamine.  

PubMed

In autonomous learning, value-sensitive experiences can improve the efficiency of learning. A learning network needs be motivated so that the limited computational resources and the limited lifetime are devoted to events that are of high value for the agent to compete in its environment. The neuromodulatory system of the brain is mainly responsible for developing such a motivation system. Although reinforcement learning has been extensively studied, many existing models are symbolic whose internal nodes or modules have preset meanings. Neural networks have been used to automatically generate internal emergent representations. However, modeling an emergent motivational system for neural networks is still a great challenge. By emergent, we mean that the internal representations emerge autonomously through interactions with the external environments. This work proposes a generic emergent modulatory system for emergent networks, which includes two subsystems - the serotonin system and the dopamine system. The former signals a large class of stimuli that are intrinsically aversive (e.g., stress or pain). The latter signals a large class of stimuli that are intrinsically appetitive (e.g., pleasure or sweet). We experimented with this motivational system for two settings. The first is a visual recognition setting to investigate how such a system can learn through interactions with a teacher, who does not directly give answers, but only punishments and rewards. The second is a setting for wandering in the presence of a friend and a foe. PMID:23294763

Weng, Juyang; Paslaski, Stephen; Daly, James; VanDam, Courtland; Brown, Jacob

2013-05-01

18

Modafinil modulation of the default mode network  

Microsoft Academic Search

Rationale  The default mode network (DMN) is a functional network which is implicated in a range of cognitive processes. This network\\u000a is proposed to consist of hubs located in the ventromedial prefrontal cortex (vmPFC), posterior cingulate\\/retrosplenial cortex\\u000a (PCC\\/rSpl), and inferior parietal lobule (IPL), with other midline cortical and temporal lobe nodes connected to these hubs.\\u000a How this network is modulated by

Michael J. Minzenberg; Jong H. Yoon; Cameron S. Carter

2011-01-01

19

Network modulation during complex syntactic processing.  

PubMed

Complex sentence processing is supported by a left-lateralized neural network including inferior frontal cortex and posterior superior temporal cortex. This study investigates the pattern of connectivity and information flow within this network. We used fMRI BOLD data derived from 12 healthy participants reported in an earlier study (Thompson, C. K., Den Ouden, D. B., Bonakdarpour, B., Garibaldi, K., & Parrish, T. B. (2010b). Neural plasticity and treatment-induced recovery of sentence processing in agrammatism. Neuropsychologia, 48(11), 3211-3227) to identify activation peaks associated with object-cleft over syntactically less complex subject-cleft processing. Directed Partial Correlation Analysis was conducted on time series extracted from participant-specific activation peaks and showed evidence of functional connectivity between four regions, linearly between premotor cortex, inferior frontal gyrus, posterior superior temporal sulcus and anterior middle temporal gyrus. This pattern served as the basis for Dynamic Causal Modeling of networks with a driving input to posterior superior temporal cortex, which likely supports thematic role assignment, and networks with a driving input to inferior frontal cortex, a core region associated with syntactic computation. The optimal model was determined through both frequentist and Bayesian Model Selection and turned out to reflect a network with a primary drive from inferior frontal cortex and modulation of the connection between inferior frontal cortex and posterior superior temporal cortex by complex sentence processing. The winning model also showed a substantive role for a feedback mechanism from posterior superior temporal cortex back to inferior frontal cortex. We suggest that complex syntactic processing is driven by word-order analysis, supported by inferior frontal cortex, in an interactive relation with posterior superior temporal cortex, which supports verb argument structure processing. PMID:21820518

den Ouden, Dirk-Bart; Saur, Dorothee; Mader, Wolfgang; Schelter, Björn; Lukic, Sladjana; Wali, Eisha; Timmer, Jens; Thompson, Cynthia K

2012-01-01

20

A direct density modulation cathode in magnetron  

SciTech Connect

A direct Density Modulation Cathode (DMC) in magnetron is proposed in this paper. By removing the velocity modulation process, electron spokes corresponding to the dominant operating mode can be quickly formed when the DMC is used. Based on theoretical analysis, particle-in-cell simulations and experimental investigations are carried out for demonstration. The final results show that compared with conventional solid cathode and transparent cathode, the DMC can increase 68% and even 146% of relative microwave widths, respectively.

Li, Wei; Zhang, Jun; Liu, Yong-gui; Yang, Han-wu; Shu, Ting [College of Optoelectronic Science and Engineering, National University of Defense Technology, Changsha, Hunan 410073 (China)] [College of Optoelectronic Science and Engineering, National University of Defense Technology, Changsha, Hunan 410073 (China)

2013-09-15

21

Coarse graining for synchronization in directed networks  

NASA Astrophysics Data System (ADS)

Coarse-graining model is a promising way to analyze and visualize large-scale networks. The coarse-grained networks are required to preserve statistical properties as well as the dynamic behaviors of the initial networks. Some methods have been proposed and found effective in undirected networks, while the study on coarse-graining directed networks lacks of consideration. In this paper we proposed a path-based coarse-graining (PCG) method to coarse grain the directed networks. Performing the linear stability analysis of synchronization and numerical simulation of the Kuramoto model on four kinds of directed networks, including tree networks and variants of Barabási-Albert networks, Watts-Strogatz networks, and Erdös-Rényi networks, we find our method can effectively preserve the network synchronizability.

Zeng, An; Lü, Linyuan

2011-05-01

22

Percolation in directed scale-free networks  

Microsoft Academic Search

Many complex networks in nature have directed links, a property that affects the network's navigability and large-scale topology. Here we study the percolation properties of such directed scale-free networks with correlated in and out degree distributions. We derive a phase diagram that indicates the existence of three regimes, determined by the values of the degree exponents. In the first regime

N. Schwartz; R. Cohen; D. Ben-Avraham; A.-L. Barabási; S. Havlin

2002-01-01

23

Downhole drilling network using burst modulation techniques  

DOEpatents

A downhole drilling system is disclosed in one aspect of the present invention as including a drill string and a transmission line integrated into the drill string. Multiple network nodes are installed at selected intervals along the drill string and are adapted to communicate with one another through the transmission line. In order to efficiently allocate the available bandwidth, the network nodes are configured to use any of numerous burst modulation techniques to transmit data.

Hall; David R. (Provo, UT), Fox; Joe (Spanish Fork, UT)

2007-04-03

24

Network community structure detection for directional neural networks inferred from multichannel multisubject EEG data.  

PubMed

In many neuroscience applications, one is interested in identifying the functional brain modules from multichannel, multiple subject neuroimaging data. However, most of the existing network community structure detection algorithms are limited to single undirected networks and cannot reveal the common community structure for a collection of directed networks. In this paper, we propose a community detection algorithm for weighted asymmetric (directed) networks representing the effective connectivity in the brain. Moreover, the issue of finding a common community structure across subjects is addressed by maximizing the total modularity of the group. Finally, the proposed community detection algorithm is applied to multichannel multisubject electroencephalogram data. PMID:24956610

Liu, Ying; Moser, Jason; Aviyente, Selin

2014-07-01

25

Optimization of directional antenna network topology in Airborne Networks  

Microsoft Academic Search

Future IP-based Airborne Networks, important components in net-centric military communications, are envisioned to consist of a persistent backbone core network and dynamic tactical edge networks. The backbone would consist of quasi-stable platforms equipped with multiple high-capacity directional wireless links. The tactical edge networks would consist of highly dynamic platforms such as fighter jets equipped with omni-directional wireless links, and these

G. Hadynski; S. B. Lee; G. Rajappan; R. Sundaram; X. Wang; F. Zhou

2010-01-01

26

Module Placement Based on Resistive Network Optimization  

Microsoft Academic Search

A new constructive placement and partitioning method based on resistive network optimization is proposed. The objective function used is the sum of the squared wire length. The method has the feature which includes fixed modules in the formulation. The overall algorithm comprises the following subprograms: optimization, scaling, relaxation, partitioning and assignment. The method is efficient because it takes advantage of

Chung-kuan Cheng; Ernest S. Kuh

1984-01-01

27

Uncovering the overlapping modules of complex networks  

NASA Astrophysics Data System (ADS)

Many complex systems in nature and society can be described in terms of networks capturing the intricate web of connections among the units they are made of. A fundamental question of great current interest is how to interpret the global organisation of such networks as the coexistence of their structural sub-units (called modules, communities, clusters, etc) associated with more highly interconnected parts. Identifying these unknown building blocks (e.g., functionally related proteins, industrial sectors, groups of people) is crucial to the understanding of the structural and functional properties of networks. The existing deterministic methods used for large data sets find separated modules, while most of the actual networks are made of highly overlapping cohesive groups of nodes. Here we introduce an approach to analyse the main statistical features of the interwoven sets of overlapping communities making a much needed step towards the uncovering of the modular structure of complex systems. After defining a set of new characteristic quantities for their statistics, we apply an efficient technique to explore overlapping communities on a large scale. We find that overlaps are indeed very significant, and the distributions we introduce reveal novel universal features of networks. Our studies of collaboration, word association, and protein interaction graphs demonstrate that the web of modules has highly non-trivial correlations and specific scaling properties.

Vicsek, Tamas

2006-03-01

28

Dynamics and Directionality in Complex Networks  

NASA Astrophysics Data System (ADS)

We investigate how we can improve the synchronizability of complex networks simply by changing the link direction while conserving the local link weights and topology. Performing the linear stability analysis of synchronization and numerical simulation of the Kuramoto model in the directed networks, we find that while a random assignment of link directions generally weakens the degree of synchronization, a properly organized directionality can systematically enhance the network synchronization. In this respect, we suggest a simple method of changing the link direction according to the larger residual degree starting from small residual degree nodes. This result provides plausible applications to control the synchronizability of systems in various fields.

Son, Seung-Woo; Kim, Beom Jun; Hong, Hyunsuk; Jeong, Hawoong

2009-11-01

29

Network management, status and directions  

SciTech Connect

It has been said that the network is the system''. This implies providing levels of service, reliability, predictability and availability that are commensurate with or better than those that individual computers provide today. To provide this requires integrated network management for interconnected networks of heterogeneous devices covering both the local campus and across the world and spanning many administrative domains. This talk will review the status of existing tools to address management for networks. It draws on experience from both within and outside the HEP community.

Cottrell, R.L.A.; Streater, T.C.

1992-09-01

30

Network management, status and directions  

SciTech Connect

It has been said that the ``network is the system``. This implies providing levels of service, reliability, predictability and availability that are commensurate with or better than those that individual computers provide today. To provide this requires integrated network management for interconnected networks of heterogeneous devices covering both the local campus and across the world and spanning many administrative domains. This talk will review the status of existing tools to address management for networks. It draws on experience from both within and outside the HEP community.

Cottrell, R.L.A.; Streater, T.C.

1992-09-01

31

Performances of a new directional optical module  

NASA Astrophysics Data System (ADS)

The goal of the future KM3NeT neutrino telescope in the Mediterranean Sea is the investigation of the high energy component of the cosmic neutrino spectrum: a promising tool to better understand the mechanisms that generate extreme energy cosmic rays. Neutrino energy and direction will be reconstructed using the Cherenkov light produced in water by neutrino induced muons. In the framework of the EU funded KM3NeT Design Study, a new design for a large (10?) 4-anode photomultiplier has been developed. A prototype manufactured by Hamamatsu has been integrated into a spherical glass pressure-resistant optical module. It will be used for the first time to detect the direction of the detected Cherenkov light at one of the candidate site for KM3NeT, near Capo Passero in Sicily. The photocathode surface in these optical modules has been effectively divided into four quadrants by a pair of crescent shaped mirrors embedded in the optical gel linking the photomultiplier to the glass sphere. A series of measurements was performed at the testing facility of the NEMO group in Genova. The light collection and the angular response of the prototype have been studied, to have a complete characterisation and allow a comparison with previous models. The results of tests of the optical module are presented here.

Bersani, Andrea

2011-01-01

32

Packaging issues related to network access modules  

NASA Astrophysics Data System (ADS)

WDM networks offer potentially increased bandwidth and functionality when compared to single wavelength ones, with applications ranging from straightforward capacity enhancement through to switched virtual dark fiber carrying disparate traffic to the customers' premises. However, to be implemented in the ground, these optical networks have to offer cost effective solutions to the users. This means that WDM equipment must be built small, rugged with low power consumption and high functional density. The NAM (network access module) developed by the ONTC, makes extensive use of array electronics, optoelectronics and optoelectronic integrated circuits (OEICs) and illustrates such system integration. But high level integration and high functional density bring new challenges in packaging together with the difficulty of managing crosstalk. In this paper we describe the network access module, detail some of the key packaging technologies and discuss alternative integration approaches which are explored as part of another collaboration project called Rozinante. To conclude, some applications using the NAM are proposed which show the key role of this network element in building reconfigurable optical networks.

Dreze, Cecile

1997-01-01

33

Weakly explosive percolation in directed networks  

NASA Astrophysics Data System (ADS)

Percolation, the formation of a macroscopic connected component, is a key feature in the description of complex networks. The dynamical properties of a variety of systems can be understood in terms of percolation, including the robustness of power grids and information networks, the spreading of epidemics and forest fires, and the stability of gene regulatory networks. Recent studies have shown that if network edges are added “competitively” in undirected networks, the onset of percolation is abrupt or “explosive.” The unusual qualitative features of this phase transition have been the subject of much recent attention. Here we generalize this previously studied network growth process from undirected networks to directed networks and use finite-size scaling theory to find several scaling exponents. We find that this process is also characterized by a very rapid growth in the giant component, but that this growth is not as sudden as in undirected networks.

Squires, Shane; Sytwu, Katherine; Alcala, Diego; Antonsen, Thomas M.; Ott, Edward; Girvan, Michelle

2013-05-01

34

Weakly explosive percolation in directed networks.  

PubMed

Percolation, the formation of a macroscopic connected component, is a key feature in the description of complex networks. The dynamical properties of a variety of systems can be understood in terms of percolation, including the robustness of power grids and information networks, the spreading of epidemics and forest fires, and the stability of gene regulatory networks. Recent studies have shown that if network edges are added "competitively" in undirected networks, the onset of percolation is abrupt or "explosive." The unusual qualitative features of this phase transition have been the subject of much recent attention. Here we generalize this previously studied network growth process from undirected networks to directed networks and use finite-size scaling theory to find several scaling exponents. We find that this process is also characterized by a very rapid growth in the giant component, but that this growth is not as sudden as in undirected networks. PMID:23767507

Squires, Shane; Sytwu, Katherine; Alcala, Diego; Antonsen, Thomas M; Ott, Edward; Girvan, Michelle

2013-05-01

35

Transmission line directional protection using neural networks and filtering algorithms  

NASA Astrophysics Data System (ADS)

Power transmission lines are the vital links in power systems providing the essential continuity of service from generating plants to the end users. To maintain stability in a power system it is imperative that any fault in the transmission system be identified by protective relays and the faulted line be isolated from the network with minimal delay. Faults on transmission lines need to be detected, classified and cleared as fast as possible. Moreover, the fault direction should be identified. Development of different modules of a transmission line protective relaying system is outlined in this dissertation. Different modules such as fault direction identification, fault detection and phase selection modules are designed, implemented and tested. Neural network technique is employed to design the transmission line fault direction identification module. Different neural network structures are used and four different directional modules are proposed. A new high speed algorithm, based on impedance measurement is proposed for fault detection and phase selection. Adaptive features are also added to the proposed relaying modules to enable them to track the changing operation conditions of the system. Off-line studies are performed with the proposed relaying modules on a simulated power system model. The system is subjected to different types of disturbances while it is operating at different operating conditions, and the performance of the proposed modules is evaluated. The results obtained indicate that the proposed relaying modules perform rapidly and correctly for different system conditions. The relaying algorithm has been implemented on a digital signal processor board. Using a power system model consisting of a micro-alternator connected to a constant voltage system extensive experimental studies are conducted and the performance of the relaying algorithm is investigated. The performance of the proposed modules is investigated further using recorded fault data from a high voltage power system. In this way, the performance of the newly designed relaying modules can be further verified in a more realistic environment. Results using various recorded field data are presented. The results presented in this dissertation confirm the feasibility of the proposed relaying modules.

Sanaye-Pasand, Majid

36

Parsimonious Module Inference in Large Networks  

NASA Astrophysics Data System (ADS)

We investigate the detectability of modules in large networks when the number of modules is not known in advance. We employ the minimum description length principle which seeks to minimize the total amount of information required to describe the network, and avoid overfitting. According to this criterion, we obtain general bounds on the detectability of any prescribed block structure, given the number of nodes and edges in the sampled network. We also obtain that the maximum number of detectable blocks scales as N, where N is the number of nodes in the network, for a fixed average degree ?k?. We also show that the simplicity of the minimum description length approach yields an efficient multilevel Monte Carlo inference algorithm with a complexity of O(?Nlog?N), if the number of blocks is unknown, and O(?N) if it is known, where ? is the mixing time of the Markov chain. We illustrate the application of the method on a large network of actors and films with over 106 edges, and a dissortative, bipartite block structure.

Peixoto, Tiago P.

2013-04-01

37

On Functional Module Detection in Metabolic Networks  

PubMed Central

Functional modules of metabolic networks are essential for understanding the metabolism of an organism as a whole. With the vast amount of experimental data and the construction of complex and large-scale, often genome-wide, models, the computer-aided identification of functional modules becomes more and more important. Since steady states play a key role in biology, many methods have been developed in that context, for example, elementary flux modes, extreme pathways, transition invariants and place invariants. Metabolic networks can be studied also from the point of view of graph theory, and algorithms for graph decomposition have been applied for the identification of functional modules. A prominent and currently intensively discussed field of methods in graph theory addresses the Q-modularity. In this paper, we recall known concepts of module detection based on the steady-state assumption, focusing on transition-invariants (elementary modes) and their computation as minimal solutions of systems of Diophantine equations. We present the Fourier-Motzkin algorithm in detail. Afterwards, we introduce the Q-modularity as an example for a useful non-steady-state method and its application to metabolic networks. To illustrate and discuss the concepts of invariants and Q-modularity, we apply a part of the central carbon metabolism in potato tubers (Solanum tuberosum) as running example. The intention of the paper is to give a compact presentation of known steady-state concepts from a graph-theoretical viewpoint in the context of network decomposition and reduction and to introduce the application of Q-modularity to metabolic Petri net models.

Koch, Ina; Ackermann, Jorg

2013-01-01

38

Multi-directed Eulerian growing networks  

NASA Astrophysics Data System (ADS)

We introduce and analyze a model of a multi-directed Eulerian network, that is a directed and weighted network where a path exists that passes through all the edges of the network once and only once. Networks of this type can be used to describe information networks such as human language or DNA chains. We are able to calculate the strength and degree distribution in this network and find that they both exhibit a power law with an exponent between 2 and 3. We then analyze the behavior of the accelerated version of the model and find that the strength distribution has a double slope power-law behavior. Finally we introduce a non-Eulerian version of the model and find that the statistical topological properties remain unchanged. Our analytical results are compared with numerical simulations.

Masucci, A. P.; Rodgers, G. J.

2007-12-01

39

Direct characterization of linear-optical networks.  

PubMed

We introduce an efficient method for fully characterizing multimode linear-optical networks. Our approach requires only a standard laser source and intensity measurements to directly and uniquely determine all moduli and non-trivial phases of the matrix describing a network. We experimentally demonstrate the characterization of a 6×6 fiber-optic network and independently verify the results via nonclassical two-photon interference. PMID:23736598

Rahimi-Keshari, Saleh; Broome, Matthew A; Fickler, Robert; Fedrizzi, Alessandro; Ralph, Timothy C; White, Andrew G

2013-06-01

40

Gene-module level analysis: Identification to Networks and Dynamics  

PubMed Central

Summary Nature exhibits modular design in biological systems. Gene-module level analysis is based on this module concept, aiming to understand biological network design and systems behavior in disease and development by emphasizing on modules of genes rather than individual genes. Module-level analysis has been extensively applied in genome wide level analysis, exploring the organization of biological systems from identifying modules to reconstructing module networks and analyzing module dynamics. Such module-level perspective provides a high level representation of the regulatory scenario and design of biological systems, promising to revolutionize our view of systems biology, genetic engineering as well as disease mechanisms and molecular medicine.

Wang, Xuewei; Dalkic, Ertugrul; Wu, Ming; Chan, Christina

2008-01-01

41

NRC TLD Direct Radiation Monitoring Network.  

National Technical Information Service (NTIS)

This report provides the status and results of the NRC Thermoluminescent Dosimeter (TLD) Direct Radiation Monitoring Network. It presents the radiation levels measured in the vicinity of 55 NRC-licensed facility sites throughout the country for the first ...

L. K. Cohen M. J. Slobodien

1982-01-01

42

Dynamics-based centrality for directed networks.  

PubMed

Determining the relative importance of nodes in directed networks is important in, for example, ranking websites, publications, and sports teams, and for understanding signal flows in systems biology. A prevailing centrality measure in this respect is the PageRank. In this work, we focus on another class of centrality derived from the Laplacian of the network. We extend the Laplacian-based centrality, which has mainly been applied to strongly connected networks, to the case of general directed networks such that we can quantitatively compare arbitrary nodes. Toward this end, we adopt the idea used in the PageRank to introduce global connectivity between all the pairs of nodes with a certain strength. Numerical simulations are carried out on some networks. We also offer interpretations of the Laplacian-based centrality for general directed networks in terms of various dynamical and structural properties of networks. Importantly, the Laplacian-based centrality defined as the stationary density of the continuous-time random walk with random jumps is shown to be equivalent to the absorption probability of the random walk with sinks at each node but without random jumps. Similarly, the proposed centrality represents the importance of nodes in dynamics on the original network supplied with sinks but not with random jumps. PMID:21230545

Masuda, Naoki; Kori, Hiroshi

2010-11-01

43

Dynamics-based centrality for directed networks  

NASA Astrophysics Data System (ADS)

Determining the relative importance of nodes in directed networks is important in, for example, ranking websites, publications, and sports teams, and for understanding signal flows in systems biology. A prevailing centrality measure in this respect is the PageRank. In this work, we focus on another class of centrality derived from the Laplacian of the network. We extend the Laplacian-based centrality, which has mainly been applied to strongly connected networks, to the case of general directed networks such that we can quantitatively compare arbitrary nodes. Toward this end, we adopt the idea used in the PageRank to introduce global connectivity between all the pairs of nodes with a certain strength. Numerical simulations are carried out on some networks. We also offer interpretations of the Laplacian-based centrality for general directed networks in terms of various dynamical and structural properties of networks. Importantly, the Laplacian-based centrality defined as the stationary density of the continuous-time random walk with random jumps is shown to be equivalent to the absorption probability of the random walk with sinks at each node but without random jumps. Similarly, the proposed centrality represents the importance of nodes in dynamics on the original network supplied with sinks but not with random jumps.

Masuda, Naoki; Kori, Hiroshi

2010-11-01

44

Predicting network instabilities in mobile directional wireless networks  

NASA Astrophysics Data System (ADS)

We have been investigating the dynamics of molecular systems as analogies for directional wireless networks. This has provided significant insight into reconfigurations of mobile wireless networks using directional point-to-point links (e.g. free-space optics or radio frequency). In this effort, we conceptualize the network as a giant molecule comprised of atoms that exert forces (attraction and repulsion) that stretch and relax the corresponding links. We monitor second-order variations of a potential energy function to gain an improved understanding of the large dimensionality of the optimized reconfiguration for network topology management. Ultimately, we envision this approach will allow for the prediction of two distinct events: 1) localized link failures and 2) catastrophic network events such as a partition. Our results show the detection of localized link failures and the availability for resource allocation more than one minute ahead of the failure (due to known events such as range and antenna blockage) with <80% accuracy.

Coleman, David M.; Milner, Stuart D.; Davis, Christopher C.

2013-09-01

45

Direct digital modulation system for LLRF  

NASA Astrophysics Data System (ADS)

Stability and precision of signal controlling particle accelerator is very complex problem. Most sophisticated analog design of vector modulator sometimes cannot provide signal with satisfying parameters. This paper present possible future solution using less components than analog vector modulator. There are described two options, one is digital vector modulation with analog upconversion and second one is full digital synthesis.

Tarnowski, Szymon; Piotrowski, Adam; Napieralski, Andrzej

2008-01-01

46

Direct modulation at L-band using a quadrature modulator with feedback  

NASA Technical Reports Server (NTRS)

This paper describes how a high quality modulated signal can be generated directly at the frequency of transmission, using a standard quadrature modulator and other commercially-available, low-cost building blocks. The method uses a feedback technique for automatic correction of carrier leakage, differential gain and phase mismatch errors in the quadrature modulator, and other building blocks, by providing guidance to the digital baseband portion of the modulator. Experimental results are presented for direct modulation at 1.65 GHz.

Datta, Ravi; Crozier, Stewart N.

1995-01-01

47

Data reliability in complex directed networks  

NASA Astrophysics Data System (ADS)

The availability of data from many different sources and fields of science has made it possible to map out an increasing number of networks of contacts and interactions. However, quantifying how reliable these data are remains an open problem. From Biology to Sociology and Economics, the identification of false and missing positives has become a problem that calls for a solution. In this work we extend one of the newest, best performing models—due to Guimerá and Sales-Pardo in 2009—to directed networks. The new methodology is able to identify missing and spurious directed interactions with more precision than previous approaches, which renders it particularly useful for analyzing data reliability in systems like trophic webs, gene regulatory networks, communication patterns and several social systems. We also show, using real-world networks, how the method can be employed to help search for new interactions in an efficient way.

Sanz, Joaquín; Cozzo, Emanuele; Moreno, Yamir

2013-12-01

48

A Constructive RBF Neural Network for Estimating the Probability of Defects in Software Modules  

Microsoft Academic Search

Much of the current research in software defect prediction focuses on building classifiers to predict only whether a software module is fault-prone or not. Using these techniques, the effort to test the software is directed at modules that are labelled as fault-prone by the classifier. This paper introduces a novel algorithm based on constructive RBF neural networks aimed at predicting

Miguel E. R. Bezerra; Adriano L. I. Oliveira; Silvio R. L. Meira

2007-01-01

49

Directional borehole radar with dipole antenna array using optical modulators  

Microsoft Academic Search

In this paper, we describe a directional borehole radar comprising a dipole antenna array with an optical modulator capable of determining the position of targets in three dimensions (3-D). Optical modulators using a Mach-Zehnder interferometer are used to transform electrical signals into optical signals at the feeding points of the dipole antennas. The advantages of using these modulators are that

Satoshi Ebihara

2004-01-01

50

Clustering and community detection in directed networks: A survey  

NASA Astrophysics Data System (ADS)

Networks (or graphs) appear as dominant structures in diverse domains, including sociology, biology, neuroscience and computer science. In most of the aforementioned cases graphs are directed - in the sense that there is directionality on the edges, making the semantics of the edges nonsymmetric as the source node transmits some property to the target one but not vice versa. An interesting feature that real networks present is the clustering or community structure property, under which the graph topology is organized into modules commonly called communities or clusters. The essence here is that nodes of the same community are highly similar while on the contrary, nodes across communities present low similarity. Revealing the underlying community structure of directed complex networks has become a crucial and interdisciplinary topic with a plethora of relevant application domains. Therefore, naturally there is a recent wealth of research production in the area of mining directed graphs - with clustering being the primary method sought and the primary tool for community detection and evaluation. The goal of this paper is to offer an in-depth comparative review of the methods presented so far for clustering directed networks along with the relevant necessary methodological background and also related applications. The survey commences by offering a concise review of the fundamental concepts and methodological base on which graph clustering algorithms capitalize on. Then we present the relevant work along two orthogonal classifications. The first one is mostly concerned with the methodological principles of the clustering algorithms, while the second one approaches the methods from the viewpoint regarding the properties of a good cluster in a directed network. Further, we present methods and metrics for evaluating graph clustering results, demonstrate interesting application domains and provide promising future research directions.

Malliaros, Fragkiskos D.; Vazirgiannis, Michalis

2013-12-01

51

Optical waveform generation using a directly modulated laser  

NASA Astrophysics Data System (ADS)

The capability of a directly modulated laser (DML) can be dramatically enhanced through precise control of the drive current waveform based on digital signal processing (DSP) and a digital-to-analog convertor (DAC). In this paper, a novel method to pre-compensate fiber dispersion for metro and regional networks is described for a bit rate of 10.709 Gb/s using a DML. A look-up table (LUT) for the drive current is optimized for dispersion mitigation. The entries of the LUT are determined based on the effects of the DML adiabatic and transient chirp on pulse propagation, the nonlinear mapping between the input current and the output optical power, and the bandwidth of the DML package. A DAC operating at 2 samples per bit (21.418 GSa/s with 6 bit resolution) converts the digital samples at the output of the LUT to an analog current waveform driving the DML. Experimental results for a bit rate of 10.709 Gb/s and on-off keying demonstrate a transmission reach of 252 km using a DML intended for 2.5 Gb/s operation and 608 km using a chirp managed laser intended for 10 Gb/s operation. Using this approach (DSP + DAC), the generation of 10.709 Gb/s differential phase shift keying (DPSK) and 56 Gb/s 16-ary quadrature amplitude modulation, sub-carrier multiplexed (QAM SCM) optical signals using the direct modulation of a passive feedback laser is also presented. 6-bit DACs operating at sampling rates of 21.418 GSa/s and 28 GSa/s, respectively, was used to generate the requisite analog current waveform.

Cartledge, John C.; Karar, Abdullah S.; Roberts, Kim

2013-10-01

52

Gaussian Networks for Direct Adaptive Control  

Microsoft Academic Search

A direct adaptive tracking control architecture is proposed and evaluated for a class of continuous-time nonlinear dynamic systems for which an explicit linear parameterization of the uncertainty in the dynamics is either unknown or impossible. The architecture employs a network of gausian radial basis functions to adaptively compensate for the plant nonlinearities. Under mild assumptions about the degree of smoothness

Robert M. Sanner; Jean-Jacques E. Slotine

1991-01-01

53

Vesicles modulate an actin network for asymmetric spindle positioning  

PubMed Central

Actin networks drive many essential cellular processes, including cell migration, cytokinesis and tissue morphogenesis. But how cells organize and regulate dynamic actin networks that consist of long, unbranched actin filaments is only poorly understood. This study in mouse oocytes reveals that cells can use vesicles as adaptable, motorized network nodes to regulate the dynamics and density of intracellular actin networks. In particular, Rab11a-positive vesicles drive the network dynamics in a myosin-Vb-dependent manner, and modulate the network density by sequestering and clustering the network’s actin nucleators. We also report a simple way by which networks of different densities can be generated, namely by adjusting the number and volume of vesicles in the cell. This vesicle-based mechanism of actin network modulation is essential for asymmetric positioning of the meiotic spindle in mouse oocytes, a vital step in the development of a fertilizable egg in mammals.

Holubcova, Zuzana; Howard, Gillian; Schuh, Melina

2013-01-01

54

Topology-Aware Modulation and Error-Correction Coding for Cooperative Networks  

Microsoft Academic Search

User cooperation in wireless networks is inherently a cross-layer optimization problem. We identify a new direction for cooperative communications: i.e., in addition to the point-to-point communication channel between the transmitter and the receiver, the communication configuration should take the network topology into account. In this paper, we first propose a network modulation (NM) design that can transmit bits with different

Zhe Yang; Lin Cai; Yuanqian Luo; Jianping Pan

2012-01-01

55

Identification of directed interactions in networks.  

PubMed

Multichannel data collection in the neurosciences is routine and has necessitated the development of methods to identify the direction of interactions among processes. The most widely used approach for detecting these interactions in such data is based on autoregressive models of stochastic processes, although some work has raised the possibility of serious difficulties with this approach. This article demonstrates that these difficulties are present and that they are intrinsic features of the autoregressive method. Here, we introduce a new method taking into account unobserved processes and based on coherence. Two examples of three-process networks are used to demonstrate that although coherence measures are intrinsically non-directional, a particular network configuration will be associated with a particular set of coherences. These coherences may not specify the network uniquely, but in principle will specify all network configurations consistent with their values and will also specify the relationships among the unobserved processes. Moreover, when new information becomes available, the values of the measures of association already in place do not change, but the relationships among the unobserved processes may become further resolved. PMID:21678101

Lindsay, K A; Rosenberg, J R

2011-06-01

56

Serotonin modulation of cortical neurons and networks.  

PubMed

The serotonergic pathways originating in the dorsal and median raphe nuclei (DR and MnR, respectively) are critically involved in cortical function. Serotonin (5-HT), acting on postsynaptic and presynaptic receptors, is involved in cognition, mood, impulse control and motor functions by (1) modulating the activity of different neuronal types, and (2) varying the release of other neurotransmitters, such as glutamate, GABA, acetylcholine and dopamine. Also, 5-HT seems to play an important role in cortical development. Of all cortical regions, the frontal lobe is the area most enriched in serotonergic axons and 5-HT receptors. 5-HT and selective receptor agonists modulate the excitability of cortical neurons and their discharge rate through the activation of several receptor subtypes, of which the 5-HT1A, 5-HT1B, 5-HT2A, and 5-HT3 subtypes play a major role. Little is known, however, on the role of other excitatory receptors moderately expressed in cortical areas, such as 5-HT2C, 5-HT4, 5-HT6, and 5-HT7. In vitro and in vivo studies suggest that 5-HT1A and 5-HT2A receptors are key players and exert opposite effects on the activity of pyramidal neurons in the medial prefrontal cortex (mPFC). The activation of 5-HT1A receptors in mPFC hyperpolarizes pyramidal neurons whereas that of 5-HT2A receptors results in neuronal depolarization, reduction of the afterhyperpolarization and increase of excitatory postsynaptic currents (EPSCs) and of discharge rate. 5-HT can also stimulate excitatory (5-HT2A and 5-HT3) and inhibitory (5-HT1A) receptors in GABA interneurons to modulate synaptic GABA inputs onto pyramidal neurons. Likewise, the pharmacological manipulation of various 5-HT receptors alters oscillatory activity in PFC, suggesting that 5-HT is also involved in the control of cortical network activity. A better understanding of the actions of 5-HT in PFC may help to develop treatments for mood and cognitive disorders associated with an abnormal function of the frontal lobe. PMID:23626526

Celada, Pau; Puig, M Victoria; Artigas, Francesc

2013-01-01

57

Decreased Default Mode Neural Network Modulation with Age in Schizophrenia  

PubMed Central

Objective Previous studies have shown that patients with schizophrenia have less modulation of the task-positive and default mode networks of the brain during novelty detection. To date, the relationship between network modulation and age has not been assessed in patients with a long duration of illness. Method Seventeen patients with schizophrenia with a minimum disorder duration of 15 years and 28 age-matched healthy controls from the Mind Clinical Imaging Consortium database completed the auditory oddball discrimination task. Independent component analysis identified temporally cohesive but spatially distributed neural networks. This study examined whether age was associated with modulation of executive control and default mode networks during novelty detection in the patient and control groups. Analyses also tested whether duration of illness, chlorpromazine equivalents and symptoms were predictive of network modulation in the patient group. Results The modulation for the anterior default mode network had a main effect by group (F1, 41 = 7.17, p = 0.011) and an interaction of group and age (F1, 41 = 6.92, p = 0.012). Older patients with schizophrenia tended to have less negative modulation of the anterior default mode network with age. Exploratory analyses revealed patients with schizophrenia had less positive modulation of the task-positive network than healthy controls (F1, 43 = 4.01, p = 0.052). Conclusions Decreased negative modulation of the anterior default mode network occurs late in the disease course of schizophrenia. This may be related to inability of older patients to allocate attentional resources away from task-irrelevant stimuli in the environment.

Abbott, Christopher; Kim, Dae Il; Sponheim, Scott; Bustillo, Juan; Calhoun, Vince D.

2010-01-01

58

Spatiotemporal positioning of multipotent modules in diverse biological networks.  

PubMed

A biological network exhibits a modular organization. The modular structure dependent on functional module is of great significance in understanding the organization and dynamics of network functions. A huge variety of module identification methods as well as approaches to analyze modularity and dynamics of the inter- and intra-module interactions have emerged recently, but they are facing unexpected challenges in further practical applications. Here, we discuss recent progress in understanding how such a modular network can be deconstructed spatiotemporally. We focus particularly on elucidating how various deciphering mechanisms operate to ensure precise module identification and assembly. In this case, a system-level understanding of the entire mechanism of module construction is within reach, with important implications for reasonable perspectives in both constructing a modular analysis framework and deconstructing different modular hierarchical structures. PMID:24413666

Chen, Yinying; Wang, Zhong; Wang, Yongyan

2014-07-01

59

Direct modulation of lanthanide emission at sub-lifetime scales.  

PubMed

The long lifetime of lanthanide emitters can present a challenge for conventional pump-based modulation schemes, where the maximum switching speed is limited by the decay time of the excited state. However, spontaneous emission can also be controlled through the local optical environment. Here, we demonstrate a direct modulation scheme enabled by dynamic control of the local density of optical states (LDOS). Specifically, we exploit the LDOS differences between electric and magnetic dipole transitions near a metal mirror and demonstrate that rapid nanometer-scale mirror displacements can modulate the emission spectra of trivalent europium ions within their excited state lifetime. The dynamic LDOS modulation presented here can be readily extended to faster optical modulation schemes and applied to other long-lived emitters to control the direction, polarization, and spectrum of spontaneous emission at sublifetime scales. PMID:23597062

Karaveli, Sinan; Weinstein, Aaron J; Zia, Rashid

2013-05-01

60

Community Landscapes: An Integrative Approach to Determine Overlapping Network Module Hierarchy, Identify Key Nodes and Predict Network Dynamics  

PubMed Central

Background Network communities help the functional organization and evolution of complex networks. However, the development of a method, which is both fast and accurate, provides modular overlaps and partitions of a heterogeneous network, has proven to be rather difficult. Methodology/Principal Findings Here we introduce the novel concept of ModuLand, an integrative method family determining overlapping network modules as hills of an influence function-based, centrality-type community landscape, and including several widely used modularization methods as special cases. As various adaptations of the method family, we developed several algorithms, which provide an efficient analysis of weighted and directed networks, and (1) determine pervasively overlapping modules with high resolution; (2) uncover a detailed hierarchical network structure allowing an efficient, zoom-in analysis of large networks; (3) allow the determination of key network nodes and (4) help to predict network dynamics. Conclusions/Significance The concept opens a wide range of possibilities to develop new approaches and applications including network routing, classification, comparison and prediction.

Kovacs, Istvan A.; Palotai, Robin; Szalay, Mate S.; Csermely, Peter

2010-01-01

61

Research on High Frequency direct Modulation of laser light source  

NASA Astrophysics Data System (ADS)

A kind of Laser source with ATC, APC,ACC and modulation interface is introduced, we use the sine electric signal to complete direct modulation, the sine electric signal‘s frequency change from 50 MHz to 200 MHz,and the period is 0.5ms,then we use New focus 1161Photodetector which frequency response is 1 GHz to detect the output modulated light signal, the modulated light signal‘s frequency change from 50 MHz to 200 MHz, contrast with the electric signal, analyzing the factors which influence the light signal‘s modulation depth, through adjusting laser‘s output power and electric signal‘s peak, the light signal‘s modulation depth can reach 33% at last. Click here and insert your abstract text.

Jinjun, Lu; Shuai, Sun; Xiaochuan, Guo

62

Millimetre Wave Transmit and Receive Module for Broadband Mesh Networks  

Microsoft Academic Search

The development of Mesh (multipoint to multipoint) technology for broadband wireless access networks has brought a need for high performance low cost millimeter wave transmit and receive modules (TRMs). This paper describes the design and realization of millimetric TRMs suitable for such applications. The module is based on commercially available MMICs with a number of key design features introduced as

N. Watson; C. Caddick; T. Gokdemir; E. Bayar

2001-01-01

63

Development of an optical neural network module  

Microsoft Academic Search

The main features of artificial neural networks are the large number of nonlinear processing elements and the massively parallel interconnections among them. Many researchers have studied the hardware required for artificial neural networks and the software for such highly parallel co mputations. In terms of the hardware, two different ap- proaches have been proposed: VLSI-based neural networks and optical neural

Toyohiko Yatagai

1994-01-01

64

Direct digital RF synthesis and modulation for MSAT mobile applications  

NASA Technical Reports Server (NTRS)

A practical method of performing direct digital RF synthesis using the Hilbert transform single sideband (SSB) technique is described. It is also shown that amplitude and phase modulation can be achieved directly at L-band with frequency stability and spurii performance exceeding stringent MSAT system requirements.

Crozier, Stewart; Datta, Ravi; Sydor, John

1993-01-01

65

Module detection in complex networks using integer optimisation  

Microsoft Academic Search

BACKGROUND: The detection of modules or community structure is widely used to reveal the underlying properties of complex networks in biology, as well as physical and social sciences. Since the adoption of modularity as a measure of network topological properties, several methodologies for the discovery of community structure based on modularity maximisation have been developed. However, satisfactory partitions of large

Gang Xu; Laura Bennett; Lazaros G Papageorgiou; Sophia Tsoka

2010-01-01

66

Direct ink writing of microvascular networks  

NASA Astrophysics Data System (ADS)

Nature is replete with examples of embedded microvascular systems that enable efficient fluid flow and distribution for autonomic healing, cooling, and energy harvesting. The ability to incorporate microvascular networks in functional materials systems is therefore both scientifically and technologically important. In this PhD thesis, the direct-write assembly of planar and 3D biomimetic microvascular networks within polymer and hydrogel matrices is demonstrated. In addition, the influence of network design of fluid transport efficiency is characterized. Planar microvascular networks composed of periodic lattices of uniformal microchannels and hierarchical, branching architectures are constructed by direct-write assembly of a fugitive organic ink. Several advancements are required to facilitate their patterning, including pressure valving, dual ink printing, and dynamic pressure variation to allow tunable control of ink deposition. The hydraulic conductance is measured using a high pressure flow meter as a function of network design. For a constant vascular volume and areal coverage, 2- and 4-generation branched architectures that obey Murray's Law exhibited the highest hydraulic conductivity. These experimental observations are in good agreement with predictions made by analytic models. 3D microvascular networks are fabricated by omnidirectional printing a fugitive organic ink into a photopolymerizable hydrogel matrix that is capped with fluid filler of nearly identical composition. Using this approach, 3D networks of arbitrary design can be patterned. After ink deposition is complete, the matrix and fluid filler are chemically cross-linked via UV irradiation, and the ink is removed by liquefication. Aqueous solutions composed of a triblock copolymer of polyethylene oxide (PEO)-polypropylene oxide (PPO)-PEO constitute the materials system of choice due to their thermal- and concentration-dependent phase behavior. Specifically, the fugitive ink consists of a 23 w/w% PEO-PPO-PEO (Pluronic F127) solution, while matrix (25 w/w%) and fluid filler (20 w/w%) are composed of an acrylate-modified form of the Pluronic F127 that can be subsequently photopolymerized. The ink and matrix concentrations exceed the critical micelle concentration (CMC) of 22 w/w% and thus reside in a physical gel state. At their respective concentrations, they possess an elastic plateau modulus G' > 104 Pa needed for ink filament formation, shape retention, and support during the printing process. By contrast, the fluid filler is formulated below the CMC to facilitate its flow into void spaces created as the nozzle translates through the matrix during printing. After printing is completed, photopolymerization is carried out to yield a chemically cross-linked matrix from which the fugitive ink is removed leaving behind the desired 3D microvascular network. Due to the potential application of 3D microvasularized hydrogels in tissue engineering, dye diffusion through the cured Pluronic F127-diacrylate matrix is investigated via fluorescent microscopy. Image analysis is used to extract diffusion profiles of the dye as a function of time. Extraction of the 1-D Gaussian fitting parameters is used to determine the spatial peak variance sigma2 and plotted as a function of time to determine the dye diffusivity.

Wu, Willie

67

Network connectivity during mergers and growth: optimizing the addition of a module.  

PubMed

The principal eigenvalue ? of a network's adjacency matrix often determines dynamics on the network (e.g., in synchronization and spreading processes) and some of its structural properties (e.g., robustness against failure or attack) and is therefore a good indicator for how "strongly" a network is connected. We study how ? is modified by the addition of a module, or community, which has broad applications, ranging from those involving a single modification (e.g., introduction of a drug into a biological process) to those involving repeated additions (e.g., power-grid and transit development). We describe how to optimally connect the module to the network to either maximize or minimize the shift in ?, noting several applications of directing dynamics on networks. PMID:21797446

Taylor, Dane; Restrepo, Juan G

2011-06-01

68

eXamine: Exploring annotated modules in networks  

PubMed Central

Background Biological networks have a growing importance for the interpretation of high-throughput “omics” data. Integrative network analysis makes use of statistical and combinatorial methods to extract smaller subnetwork modules, and performs enrichment analysis to annotate the modules with ontology terms or other available knowledge. This process results in an annotated module, which retains the original network structure and includes enrichment information as a set system. A major bottleneck is a lack of tools that allow exploring both network structure of extracted modules and its annotations. Results This paper presents a visual analysis approach that targets small modules with many set-based annotations, and which displays the annotations as contours on top of a node-link diagram. We introduce an extension of self-organizing maps to lay out nodes, links, and contours in a unified way. An implementation of this approach is freely available as the Cytoscape app eXamine Conclusions eXamine accurately conveys small and annotated modules consisting of several dozens of proteins and annotations. We demonstrate that eXamine facilitates the interpretation of integrative network analysis results in a guided case study. This study has resulted in a novel biological insight regarding the virally-encoded G-protein coupled receptor US28.

2014-01-01

69

Identification of Unstable Network Modules Reveals Disease Modules Associated with the Progression of Alzheimer's Disease  

PubMed Central

Alzheimer’s disease (AD), the most common cause of dementia, is associated with aging, and it leads to neuron death. Deposits of amyloid ? and aberrantly phosphorylated tau protein are known as pathological hallmarks of AD, but the underlying mechanisms have not yet been revealed. A high-throughput gene expression analysis previously showed that differentially expressed genes accompanying the progression of AD were more down-regulated than up-regulated in the later stages of AD. This suggested that the molecular networks and their constituent modules collapsed along with AD progression. In this study, by using gene expression profiles and protein interaction networks (PINs), we identified the PINs expressed in three brain regions: the entorhinal cortex (EC), hippocampus (HIP) and superior frontal gyrus (SFG). Dividing the expressed PINs into modules, we examined the stability of the modules with AD progression and with normal aging. We found that in the AD modules, the constituent proteins, interactions and cellular functions were not maintained between consecutive stages through all brain regions. Interestingly, the modules were collapsed with AD progression, specifically in the EC region. By identifying the modules that were affected by AD pathology, we found the transcriptional regulation-associated modules that interact with the proteasome-associated module via UCHL5 hub protein, which is a deubiquitinating enzyme. Considering PINs as a system made of network modules, we found that the modules relevant to the transcriptional regulation are disrupted in the EC region, which affects the ubiquitin-proteasome system.

Kikuchi, Masataka; Ogishima, Soichi; Miyamoto, Tadashi; Miyashita, Akinori; Kuwano, Ryozo; Nakaya, Jun; Tanaka, Hiroshi

2013-01-01

70

New simple feed network for an array module of four microstrip elements  

NASA Technical Reports Server (NTRS)

A simple microstripline feed network for an array module comprising four microstrip elements is described. The advantages and disadvantages of the network are discussed as well as a theoretical explanation for the radiation characteristics of array modules using the network.

Oberhart, M. L.; Lo, Y. T.; Lee, R. Q. H.

1987-01-01

71

New simple feed network for an array module of four microstrip elements  

NASA Astrophysics Data System (ADS)

A simple microstripline feed network for an array module comprising four microstrip elements is described. The advantages and disadvantages of the network are discussed as well as a theoretical explanation for the radiation characteristics of array modules using the network.

Oberhart, M. L.; Lo, Y. T.; Lee, R. Q. H.

1987-04-01

72

Direct frequency modulation in AlGaAs semiconductor lasers  

Microsoft Academic Search

A theoretical and experimental study is presented of direct FM characteristics in three AlGaAs lasers: (1) a channeled-substrate planar (CSP) laser; (2) a buried-heterostructure laser; and (3) a transverse-junction-stripe (TJS) laser. It is determined that, while FM response in the low-modulation frequency region from zero to 10 MHz gradually decreases with modulation frequency due to thermal effects, FM response in

S. Kobayashi; Y. Yamamoto; T. Kimura; M. Ito

1982-01-01

73

Identifying protein complexes and functional modules--from static PPI networks to dynamic PPI networks.  

PubMed

Cellular processes are typically carried out by protein complexes and functional modules. Identifying them plays an important role for our attempt to reveal principles of cellular organizations and functions. In this article, we review computational algorithms for identifying protein complexes and/or functional modules from protein-protein interaction (PPI) networks. We first describe issues and pitfalls when interpreting PPI networks. Then based on types of data used and main ideas involved, we briefly describe protein complex and/or functional module identification algorithms in four categories: (i) those based on topological structures of unweighted PPI networks; (ii) those based on characters of weighted PPI networks; (iii) those based on multiple data integrations; and (iv) those based on dynamic PPI networks. The PPI networks are modelled increasingly precise when integrating more types of data, and the study of protein complexes would benefit by shifting from static to dynamic PPI networks. PMID:23780996

Chen, Bolin; Fan, Weiwei; Liu, Juan; Wu, Fang-Xiang

2014-03-01

74

Directly modulated lasers for high speed optical transmission  

NASA Astrophysics Data System (ADS)

Directly modulated lasers (DML) have been widely used in data rate at 2.5 Gb/s and below. The advantages of its simplicity and cost effectiveness have attracted considerable amount of effort in developing DMLs for higher data rate optical transmission systems, especially for short reach applications. The major issue is semiconductor laser's intrinsic modulation bandwidth and the amplitude modulation induced frequency chirp at high speed of 10 Gb/s and beyond. In this paper, we first briefly review the advancement of directly modulated lasers at 10 Gb/s and above. We then present our work on the investigation of using 10 Gb/s directly modulated laser in multiple amplified spans of a typical metro system. The experimental results show that 10 Gb/s DML may have potential to be a cost-effective option for a typical 100GHz spacing DWDM, 6x80km metro link over standard single-mode fiber. The DML performance will also be compared to conventional Mach-Zehnder modulator-based transmitter.

Du, Mei; Grüner-Nielsen, Lars

2007-11-01

75

Inverter power module with distributed support for direct substrate cooling  

DOEpatents

Systems and/or methods are provided for an inverter power module with distributed support for direct substrate cooling. An inverter module comprises a power electronic substrate. A first support frame is adapted to house the power electronic substrate and has a first region adapted to allow direct cooling of the power electronic substrate. A gasket is interposed between the power electronic substrate and the first support frame. The gasket is configured to provide a seal between the first region and the power electronic substrate. A second support frame is adapted to house the power electronic substrate and joined to the first support frame to form the seal.

Miller, David Harold (San Pedro, CA); Korich, Mark D. (Chino Hills, CA); Ward, Terence G. (Redondo Beach, CA); Mann, Brooks S. (Redondo Beach, CA)

2012-08-21

76

Spread of infectious diseases in directed and modular metapopulation networks.  

PubMed

We consider epidemics in metapopulations on different network topologies. Recent work on epidemics on networks has focused on epidemics of humans. In this work we present a model for epidemics on directed networks, which are found, for example, in the livestock trade. We show that the direction of edges and the modular structure of networks have an impact on the outbreak size and the time of the outbreak peak. In some circumstances, the outbreak size in directed networks can even be larger than in undirected systems. The results presented here could be useful for decision-making processes in directed modular systems. PMID:23005166

Lentz, Hartmut H K; Selhorst, Thomas; Sokolov, Igor M

2012-06-01

77

Erbium-doped optical amplifiers in amorphous zirconia and relative phase in the directional coupler modulator  

NASA Astrophysics Data System (ADS)

Optical modulators, amplifiers and couplers are key components of optical communications systems, enabling signal generation, routing, conditioning and transmission over long distances. This work details the investigation of three aspects of these devices: Erbium-doped waveguide amplifiers in amorphous zirconia, directional coupler modulators with linear intensity response, and the theory and design of optical directional coupler devices. The attainment of large gain and wide bandwidth in Erbium-doped waveguide amplifiers requires a host material that offers a high degree of optical activity, as well as broad spectral luminescence. In the first part of this work, the optical characteristics of Erbium-doped, ion-beam sputtered amorphous zirconia (ZrO2/SiO2) have been examined in these respects, and optical amplifiers have been developed. The second part of this work involves the development of linear-response optical modulators for analog systems. Such devices are of interest for a variety of applications including microwave distribution networks, phased-array radar, test equipment and sensors, in which linearity is important for system performance. This work has studied the use of optical phase shifts in the directional coupler modulator to provide linear intensity modulation, and used them to demonstrate one of the most efficient linear modulator designs to date. The final portion of this work deals with the theory and design of directional coupler devices, relevant to a wide range of optical components including modulators, filters, dispersion compensators and tunable lasers. The coupled-mode equations describing the directional coupler have been reformulated in such a way as to reveal the strong relationship between power transfer and the phase of the optical fields. This has also been used to produce a graphical chart, which plots field progression in the directional coupler, and allows these devices to be designed in a more intuitive manner than traditional numerical techniques.

Schermer, Ross Timothy

78

Nonlinear distortion reduction in directly modulated semiconductor laser using feedforward linearisation  

Microsoft Academic Search

This paper outlines an approach to optical feedforward linearisation technique to reduce nonlinear distortion generated by a directly modulated semiconductor laser diode for Wireless Local Area Network (WLAN) operating in the Industrial Scientific -Medical (ISM) band 2.4 GHz (IEEE802.11b) for Radio over Fibre (RoF). Various linearization techniques are reviewed. Results with feedforward linearis ation have shown over 10 dB reduction

T Ismail; A J Seeds

79

Network-dependent modulation of brain activity during sleep.  

PubMed

Brain activity dynamically changes even during sleep. A line of neuroimaging studies has reported changes in functional connectivity and regional activity across different sleep stages such as slow-wave sleep (SWS) and rapid-eye-movement (REM) sleep. However, it remains unclear whether and how the large-scale network activity of human brains changes within a given sleep stage. Here, we investigated modulation of network activity within sleep stages by applying the pairwise maximum entropy model to brain activity obtained by functional magnetic resonance imaging from sleeping healthy subjects. We found that the brain activity of individual brain regions and functional interactions between pairs of regions significantly increased in the default-mode network during SWS and decreased during REM sleep. In contrast, the network activity of the fronto-parietal and sensory-motor networks showed the opposite pattern. Furthermore, in the three networks, the amount of the activity changes throughout REM sleep was negatively correlated with that throughout SWS. The present findings suggest that the brain activity is dynamically modulated even in a sleep stage and that the pattern of modulation depends on the type of the large-scale brain networks. PMID:24814208

Watanabe, Takamitsu; Kan, Shigeyuki; Koike, Takahiko; Misaki, Masaya; Konishi, Seiki; Miyauchi, Satoru; Miyahsita, Yasushi; Masuda, Naoki

2014-09-01

80

Protein complexes and functional modules in molecular networks.  

PubMed

Proteins, nucleic acids, and small molecules form a dense network of molecular interactions in a cell. Molecules are nodes of this network, and the interactions between them are edges. The architecture of molecular networks can reveal important principles of cellular organization and function, similarly to the way that protein structure tells us about the function and organization of a protein. Computational analysis of molecular networks has been primarily concerned with node degree [Wagner, A. & Fell, D. A. (2001) Proc. R. Soc. London Ser. B 268, 1803-1810; Jeong, H., Tombor, B., Albert, R., Oltvai, Z. N. & Barabasi, A. L. (2000) Nature 407, 651-654] or degree correlation [Maslov, S. & Sneppen, K. (2002) Science 296, 910-913], and hence focused on single/two-body properties of these networks. Here, by analyzing the multibody structure of the network of protein-protein interactions, we discovered molecular modules that are densely connected within themselves but sparsely connected with the rest of the network. Comparison with experimental data and functional annotation of genes showed two types of modules: (i) protein complexes (splicing machinery, transcription factors, etc.) and (ii) dynamic functional units (signaling cascades, cell-cycle regulation, etc.). Discovered modules are highly statistically significant, as is evident from comparison with random graphs, and are robust to noise in the data. Our results provide strong support for the network modularity principle introduced by Hartwell et al. [Hartwell, L. H., Hopfield, J. J., Leibler, S. & Murray, A. W. (1999) Nature 402, C47-C52], suggesting that found modules constitute the "building blocks" of molecular networks. PMID:14517352

Spirin, Victor; Mirny, Leonid A

2003-10-14

81

Direct modulation of excited state quantum dot lasers  

NASA Astrophysics Data System (ADS)

The use of the excited state quantum dot lasers for high speed direct modulation is proposed and demonstrated. A direct comparison of lasers utilizing the ground state and excited state from the same laser material reveals a factor of two increase in the K-factor limited bandwidth. This is attributed to an increase in the saturated gain and reduced carrier scattering time of the excited state compared to the ground state.

Stevens, B. J.; Childs, D. T. D.; Shahid, H.; Hogg, R. A.

2009-08-01

82

Module Network Inference from a Cancer Gene Expression Data Set Identifies MicroRNA Regulated Modules  

PubMed Central

Background MicroRNAs (miRNAs) are small RNAs that recognize and regulate mRNA target genes. Multiple lines of evidence indicate that they are key regulators of numerous critical functions in development and disease, including cancer. However, defining the place and function of miRNAs in complex regulatory networks is not straightforward. Systems approaches, like the inference of a module network from expression data, can help to achieve this goal. Methodology/Principal Findings During the last decade, much progress has been made in the development of robust and powerful module network inference algorithms. In this study, we analyze and assess experimentally a module network inferred from both miRNA and mRNA expression data, using our recently developed module network inference algorithm based on probabilistic optimization techniques. We show that several miRNAs are predicted as statistically significant regulators for various modules of tightly co-expressed genes. A detailed analysis of three of those modules demonstrates that the specific assignment of miRNAs is functionally coherent and supported by literature. We further designed a set of experiments to test the assignment of miR-200a as the top regulator of a small module of nine genes. The results strongly suggest that miR-200a is regulating the module genes via the transcription factor ZEB1. Interestingly, this module is most likely involved in epithelial homeostasis and its dysregulation might contribute to the malignant process in cancer cells. Conclusions/Significance Our results show that a robust module network analysis of expression data can provide novel insights of miRNA function in important cellular processes. Such a computational approach, starting from expression data alone, can be helpful in the process of identifying the function of miRNAs by suggesting modules of co-expressed genes in which they play a regulatory role. As shown in this study, those modules can then be tested experimentally to further investigate and refine the function of the miRNA in the regulatory network.

Bonnet, Eric; Tatari, Marianthi; Joshi, Anagha; Michoel, Tom; Marchal, Kathleen; Berx, Geert; Van de Peer, Yves

2010-01-01

83

Characteristics of directly modulated ROF link for wireless access  

Microsoft Academic Search

The radio-over-fiber (ROF) link is of much interest to provide broadband wireless access. In this paper, we discuss some characteristics of a directly modulated ROF link in CDMA and FDMA environments. These RF measurement results show that, though the ROF link has adequate bandwidth to support several radio channels, nonlinear distortion and power loss, mainly due to electrical to optical

Xavier N. Fernando; Abu B. Sesay

2004-01-01

84

Noradrenergic modulation of cortical networks engaged in visuomotor processing.  

PubMed

Both animal and human data suggest that stimulation of the noradrenergic system may influence neuronal excitability in regions engaged in sensory processing and visuospatial attention. We tested the hypothesis that the neural mechanisms subserving motor performance in tasks relying on the visuomotor control of goal-directed hand movements might be modulated by noradrenergic influences. Healthy subjects were stimulated using the selective noradrenaline reuptake inhibitor reboxetine (RBX) in a placebo-controlled crossover design. Functional magnetic resonance imaging and dynamic causal modeling (DCM) were used to assess drug-related changes in blood oxygen level-dependent activity and interregional connectivity while subjects performed a joystick task requiring goal-directed movements. Improved task performance under RBX was associated with increased activity in right visual, intraparietal and superior frontal cortex (premotor/frontal eye field). DCM revealed that the neuronal coupling among these regions was significantly enhanced when subjects were stimulated with RBX. Concurrently, right intraparietal cortex and right superior frontal cortex exerted a stronger driving influence on visuomotor areas of the left hemisphere, including SMA and M1. These effects were independent from task difficulty. The data suggest that stimulating noradrenergic mechanisms may rearrange the functional network architecture within and across the hemispheres, for example, by synaptic gating, thereby optimizing motor behavior. PMID:19687293

Grefkes, Christian; Wang, Ling E; Eickhoff, Simon B; Fink, Gereon R

2010-04-01

85

Genetic programming: building nanobrains with genetically programmed neural network modules  

Microsoft Academic Search

The author extends ideas concerning the programming methodology called genetic programming, which is the application of the genetic algorithm to the evolution of the signs and weights of fully (self-) connected neural network modules which perform some time-(in)dependent function (e.g. walking, oscillating, etc.) in an optimal manner. Genetically programmed neural net (GenNet) modules are of two types, functional and control.

Hugo de Garis

1990-01-01

86

Constructing module maps for integrated analysis of heterogeneous biological networks  

PubMed Central

Improved methods for integrated analysis of heterogeneous large-scale omic data are direly needed. Here, we take a network-based approach to this challenge. Given two networks, representing different types of gene interactions, we construct a map of linked modules, where modules are genes strongly connected in the first network and links represent strong inter-module connections in the second. We develop novel algorithms that considerably outperform prior art on simulated and real data from three distinct domains. First, by analyzing protein–protein interactions and negative genetic interactions in yeast, we discover epistatic relations among protein complexes. Second, we analyze protein–protein interactions and DNA damage-specific positive genetic interactions in yeast and reveal functional rewiring among protein complexes, suggesting novel mechanisms of DNA damage response. Finally, using transcriptomes of non–small-cell lung cancer patients, we analyze networks of global co-expression and disease-dependent differential co-expression and identify a sharp drop in correlation between two modules of immune activation processes, with possible microRNA control. Our study demonstrates that module maps are a powerful tool for deeper analysis of heterogeneous high-throughput omic data.

Amar, David; Shamir, Ron

2014-01-01

87

Deciphering early development of complex diseases by progressive module network.  

PubMed

There is no effective cure nowadays for many complex diseases, and thus it is crucial to detect and further treat diseases in earlier stages. Generally, the development and progression of complex diseases include three stages: normal stage, pre-disease stage, and disease stage. For diagnosis and treatment, it is necessary to reveal dynamical organizations of molecular modules during the early development of the disease from the pre-disease stage to the disease stage. Thus, we develop a new framework, i.e. we identify the modules presenting at the pre-disease stage (pre-disease module) based on dynamical network biomarkers (DNBs), detect the modules observed at the advanced stage (disease-responsive module) by cross-tissue gene expression analysis, and finally find the modules related to early development (progressive module) by progressive module network (PMN). As an application example, we used this new method to analyze the gene expression data for NOD mouse model of Type 1 diabetes mellitus (T1DM). After the comprehensive comparison with the previously reported milestone molecules, we found by PMN: (1) the critical transition point was identified and confirmed by the tissue-specific modules or DNBs relevant to the pre-disease stage, which is considered as an earlier event during disease development and progression; (2) several key tissues-common modules related to the disease stage were significantly enriched on known T1DM associated genes with the rewired association networks, which are marks of later events during T1DM development and progression; (3) the tissue-specific modules associated with early development revealed several common essential progressive genes, and a few of pathways representing the effect of environmental factors during the early T1DM development. Totally, we developed a new method to detect the critical stage and the key modules during the disease occurrence and progression, and show that the pre-disease modules can serve as warning signals for the pre-disease state (e.g. T1DM early diagnosis) whereas the progressive modules can be used as the therapy targets for the disease state (e.g. advanced T1DM), which were also validated by experimental data. PMID:24561825

Zeng, Tao; Zhang, Chuan-chao; Zhang, Wanwei; Liu, Rui; Liu, Juan; Chen, Luonan

2014-06-01

88

Nicotinic modulation of intrinsic brain networks in schizophrenia.  

PubMed

The nicotinic receptor is a promising drug target currently being investigated for the treatment of cognitive symptoms in schizophrenia. A key step in this process is the development of noninvasive functional neuroimaging biomarkers that can be used to determine if nicotinic agents are eliciting their targeted biological effect, ideally through modulation of a fundamental aspect of neuronal function. To that end, neuroimaging researchers are beginning to understand how nicotinic modulation affects "intrinsic" brain networks to elicit potentially therapeutic effects. An intrinsic network is a functionally and (often) structurally connected network of brain areas whose activity reflects a fundamental neurobiological organizational principle of the brain. This review summarizes findings of the effects of nicotinic drugs on three topics related to intrinsic brain network activity: (1) the default mode network, a group of brain areas for which activity is maximal at rest and reduced during cognitive tasks, (2) the salience network, which integrates incoming sensory data with prior internal representations to guide future actions and change predictive values, and (3) multi-scale complex network dynamics, which describe these brain's ability to efficiency integrate information while preserving local functional specialization. These early findings can be used to inform future neuroimaging studies that examine the network effects of nicotinic agents. PMID:23796751

Smucny, Jason; Tregellas, Jason

2013-10-15

89

A Survey of Wormhole Routing Techniques in Direct Networks  

Microsoft Academic Search

Efficient routing of messages is critical to the performance of direct network systems.The popular wormhole routing technique faces several challenges - particularly flow control and deadlock avoidance

Lionel M. Ni; Philip K. Mckinley

1993-01-01

90

Investigation of direct integrated optics modulators. [applicable to data preprocessors  

NASA Technical Reports Server (NTRS)

Direct modulation techniques applicable to integrated optics data preprocessors were investigated. Several methods of modulating a coherent optical beam by interaction with an incoherent beam were studied. It was decided to investigate photon induced conductivity changes in thin semiconductor cladding layers on optical waveguides. Preliminary calculations indicate significant changes can be produced in the phase shift in a propagating wave when the conductivity is changed by ten percent or more. Experimental devices to verify these predicted phase changes and experiments designed to prove the concept are described.

Batchman, T. E.

1980-01-01

91

Seed selection strategy in global network alignment without destroying the entire structures of functional modules  

PubMed Central

Background Network alignment is one of the most common biological network comparison methods. Aligning protein-protein interaction (PPI) networks of different species is of great important to detect evolutionary conserved pathways or protein complexes across species through the identification of conserved interactions, and to improve our insight into biological systems. Global network alignment (GNA) problem is NP-complete, for which only heuristic methods have been proposed so far. Generally, the current GNA methods fall into global heuristic seed-and-extend approaches. These methods can not get the best overall consistent alignment between networks for the opinionated local seed. Furthermore These methods are lost in maximizing the number of aligned edges between two networks without considering the original structures of functional modules. Methods We present a novel seed selection strategy for global network alignment by constructing the pairs of hub nodes of networks to be aligned into multiple seeds. Beginning from every hub seed and using the membership similarity of nodes to quantify to what extent the nodes can participate in functional modules associated with current seed topologically we align the networks by modules. By this way we can maintain the functional modules are not damaged during the heuristic alignment process. And our method is efficient in resolving the fatal problem of most conventional algorithms that the initialization selected seeds have a direct influence on the alignment result. The similarity measures between network nodes (e.g., proteins) include sequence similarity, centrality similarity, and dynamic membership similarity and our algorithm can be called Multiple Hubs-based Alignment (MHA). Results When applying our seed selection strategy to several pairs of real PPI networks, it is observed that our method is working to strike a balance, extending the conserved interactions while maintaining the functional modules unchanged. In the case study, we assess the effectiveness of MHA on the alignment of the yeast and fly PPI networks. Our method outperforms state-of-the-art algorithms at detecting conserved functional modules and retrieves in particular 86% more conserved interactions than IsoRank. Conclusions We believe that our seed selection strategy will lead us to obtain more topologically and biologically similar alignment result. And it can be used as the reference and complement of other heuristic methods to seek more meaningful alignment results.

2012-01-01

92

Controllability and observability analysis for vertex domination centrality in directed networks.  

PubMed

Topological centrality is a significant measure for characterising the relative importance of a node in a complex network. For directed networks that model dynamic processes, however, it is of more practical importance to quantify a vertex's ability to dominate (control or observe) the state of other vertices. In this paper, based on the determination of controllable and observable subspaces under the global minimum-cost condition, we introduce a novel direction-specific index, domination centrality, to assess the intervention capabilities of vertices in a directed network. Statistical studies demonstrate that the domination centrality is, to a great extent, encoded by the underlying network's degree distribution and that most network positions through which one can intervene in a system are vertices with high domination centrality rather than network hubs. To analyse the interaction and functional dependence between vertices when they are used to dominate a network, we define the domination similarity and detect significant functional modules in glossary and metabolic networks through clustering analysis. The experimental results provide strong evidence that our indices are effective and practical in accurately depicting the structure of directed networks. PMID:24954137

Wang, Bingbo; Gao, Lin; Gao, Yong; Deng, Yue; Wang, Yu

2014-01-01

93

Controllability and observability analysis for vertex domination centrality in directed networks  

PubMed Central

Topological centrality is a significant measure for characterising the relative importance of a node in a complex network. For directed networks that model dynamic processes, however, it is of more practical importance to quantify a vertex's ability to dominate (control or observe) the state of other vertices. In this paper, based on the determination of controllable and observable subspaces under the global minimum-cost condition, we introduce a novel direction-specific index, domination centrality, to assess the intervention capabilities of vertices in a directed network. Statistical studies demonstrate that the domination centrality is, to a great extent, encoded by the underlying network's degree distribution and that most network positions through which one can intervene in a system are vertices with high domination centrality rather than network hubs. To analyse the interaction and functional dependence between vertices when they are used to dominate a network, we define the domination similarity and detect significant functional modules in glossary and metabolic networks through clustering analysis. The experimental results provide strong evidence that our indices are effective and practical in accurately depicting the structure of directed networks.

Wang, Bingbo; Gao, Lin; Gao, Yong; Deng, Yue; Wang, Yu

2014-01-01

94

Remote Synchronization Reveals Network Symmetries and Functional Modules  

NASA Astrophysics Data System (ADS)

We study a Kuramoto model in which the oscillators are associated with the nodes of a complex network and the interactions include a phase frustration, thus preventing full synchronization. The system organizes into a regime of remote synchronization where pairs of nodes with the same network symmetry are fully synchronized, despite their distance on the graph. We provide analytical arguments to explain this result, and we show how the frustration parameter affects the distribution of phases. An application to brain networks suggests that anatomical symmetry plays a role in neural synchronization by determining correlated functional modules across distant locations.

Nicosia, Vincenzo; Valencia, Miguel; Chavez, Mario; Díaz-Guilera, Albert; Latora, Vito

2013-04-01

95

Adaptive modulation and MIMO coding for broadband wireless data networks  

Microsoft Academic Search

Link adaptation techniques, where the modulation, coding rate, and\\/or other signal transmission parameters are dynamically adapted to the changing channel conditions, have emerged as powerful tools for increasing the data rate and spectral efficiency of wireless data-centric networks. While there has been significant progress on understanding the theoretical aspects of time adaptation in LA protocols, new challenges surface when dynamic

Severine Catreux; Vinko Erceg; David Gesbert

2002-01-01

96

Detection of functional modules from protein interaction networks.  

PubMed

Complex cellular processes are modular and are accomplished by the concerted action of functional modules (Ravasz et al., Science 2002;297:1551-1555; Hartwell et al., Nature 1999;402:C47-52). These modules encompass groups of genes or proteins involved in common elementary biological functions. One important and largely unsolved goal of functional genomics is the identification of functional modules from genomewide information, such as transcription profiles or protein interactions. To cope with the ever-increasing volume and complexity of protein interaction data (Bader et al., Nucleic Acids Res 2001;29:242-245; Xenarios et al., Nucleic Acids Res 2002;30:303-305), new automated approaches for pattern discovery in these densely connected interaction networks are required (Ravasz et al., Science 2002;297:1551-1555; Bader and Hogue, Nat Biotechnol 2002;20:991-997; Snel et al., Proc Natl Acad Sci USA 2002;99:5890-5895). In this study, we successfully isolate 1046 functional modules from the known protein interaction network of Saccharomyces cerevisiae involving 8046 individual pair-wise interactions by using an entirely automated and unsupervised graph clustering algorithm. This systems biology approach is able to detect many well-known protein complexes or biological processes, without reference to any additional information. We use an extensive statistical validation procedure to establish the biological significance of the detected modules and explore this complex, hierarchical network of modular interactions from which pathways can be inferred. PMID:14705023

Pereira-Leal, Jose B; Enright, Anton J; Ouzounis, Christos A

2004-01-01

97

Stability of bi-directional cooperative relay networks  

Microsoft Academic Search

We consider a pair of nodes who wish to communicate with each other via intermediate relays. In this bi-directional network with stochastic flows, we develop the throughput optimal control policy, i.e., a policy that stabilizes the network whenever the arrival rates are within the region established. We investigate the effect of implementing different practical transmission protocols and network coding. The

E. N. Ciftcioglu; A. Yener; R. Berry

2008-01-01

98

Modulation of behavioral networks by selective interneuronal inactivation.  

PubMed

Gamma-aminobutyric acid (GABA)-ergic disturbances are hallmark features of schizophrenia and other neuropsychiatric disorders and encompass multiple interneuronal cell types. Using bacterial artificial chromosome-driven, miRNA silencing technology we generated transgenic mouse lines that suppress glutamic acid decarboxylase 1 (GAD1) in either cholecystokinin (CCK)- or neuropeptide Y (NPY)-expressing interneurons. In situ lipidomic and proteomic analyses on brain tissue sections revealed distinct, brain region-specific profiles in each transgenic line. Behavioral analyses revealed that suppression of GAD1 in CCK+ interneurons resulted in locomotor and olfactory sensory changes, whereas suppression in NPY+ interneurons affected anxiety-related behaviors and social interaction. Both transgenic mouse lines had altered sensitivity to amphetamine albeit in opposite directions. Together, these data argue that reduced GAD1 expression leads to altered molecular and behavioral profiles in a cell type-dependent manner, and that these subpopulations of interneurons are strong and opposing modulators of dopamine system function. Furthermore, our findings also support the hypothesis that neuronal networks are differentially controlled by diverse inhibitory subnetworks. PMID:24322205

Schmidt, M J; Horvath, S; Ebert, P; Norris, J L; Seeley, E H; Brown, J; Gellert, L; Everheart, M; Garbett, K A; Grice, T W; Caprioli, R M; Mirnics, K

2014-05-01

99

Adaptive Cluster Synchronization of Directed Complex Networks with Time Delays  

PubMed Central

This paper studied the cluster synchronization of directed complex networks with time delays. It is different from undirected networks, the coupling configuration matrix of directed networks cannot be assumed as symmetric or irreducible. In order to achieve cluster synchronization, this paper uses an adaptive controller on each node and an adaptive feedback strategy on the nodes which in-degree is zero. Numerical example is provided to show the effectiveness of main theory. This method is also effective when the number of clusters is unknown. Thus, it can be used in the community recognizing of directed complex networks.

Liu, Heng; Wang, Xingyuan; Tan, Guozhen

2014-01-01

100

Directions in Packet Classification for Network Processors  

Microsoft Academic Search

To classify a packet as belonging to a flow often requires network systems—such as routers and firewalls—to maintain large data structures and perform several memory accesses. Network processors, on the other hand, are generally configured with only a small amount of memory with limited access bandwidth. Hence, a key challenge is to design packet classification algorithms that can be implemented

Michael E. Kounavis; Alok Kumar; Harrick Vin; Raj Yavatkar; Andrew T. Campbell

101

Directions in Packet Classification for Network Processors  

Microsoft Academic Search

Abstract--To classify a packet as belonging to a flow often requires network systems, such as routers and firewalls, to maintain large data structures and perform several memory accesses. Network processors, on the other hand, are generally configured with only a small amount of memory with limited access bandwidth. Hence, a key challenge is to design packet classification algorithms that can

M. E. Kounavis; A. Kumar; H. Vin; R. Yavatkar; A. T. Campbell

2003-01-01

102

Energy Efficient Communications in Ad Hoc Networks Using Directional Antennas  

Microsoft Academic Search

Directional antennas can be useful in significantly increasing node and network lifetime in wireless ad hoc networks. In order to utilize directional antennas, an algorithm is needed that will enable nodes to point their antennas to the right place at the right time. In this paper we present an energy-efficient routing and scheduling algorithm that coordinates transmissions in ad hoc

Akis Spyropoulos; Cauligi S. Raghavendra

2002-01-01

103

Multi-agent coordination in directed moving neighbourhood random networks  

NASA Astrophysics Data System (ADS)

This paper considers the consensus problem of dynamical multiple agents that communicate via a directed moving neighbourhood random network. Each agent performs random walk on a weighted directed network. Agents interact with each other through random unidirectional information flow when they coincide in the underlying network at a given instant. For such a framework, we present sufficient conditions for almost sure asymptotic consensus. Numerical examples are taken to show the effectiveness of the obtained results.

Shang, Yi-Lun

2010-07-01

104

Transmission scheduling in ad hoc networks with directional antennas  

Microsoft Academic Search

Directional antennas can adaptively select radio signals of interest in specific directions, while filtering out unwanted interference from other directions. Although a couple of medium access protocols based on random access schemes have been proposed for networks with directional antennas, they suffer from high probability of collisions because of their dependence on omnidirectional mode for the transmission or reception of

Lichun Bao; J. J. Garcia-Luna-Aceves

2002-01-01

105

Directionality of real world networks as predicted by path length in directed and undirected graphs  

NASA Astrophysics Data System (ADS)

Many real world networks either support ordered processes, or are actually representations of such processes. However, the same networks contain large strong connectivity components and long circles, which hide a possible inherent order, since each vertex can be reached from each vertex in a directed path. Thus, the presence of an inherent directionality in networks may be hidden. We here discuss a possible definition of such a directionality and propose a method to detect it. Several common algorithms, such as the betweenness centrality or the degree, measure various aspects of centrality in networks. However, they do not address directly the issue of inherent directionality. The goal of the algorithm discussed here is the detection of global directionality in directed networks. Such an algorithm is essential to detangle complex networks into ordered process. We show that indeed the vast majority of measured real world networks have a clear directionality. Moreover, this directionality can be used to classify vertices in these networks from sources to sinks. Such an algorithm can be highly useful in order to extract a meaning from large interaction networks assembled in many domains.

Rosen, Yonatan; Louzoun, Yoram

2014-05-01

106

Acupuncture modulates the neuro-endocrine-immune network.  

PubMed

As a nonspecific physical stimulation, the effect of acupuncture on diseases is produced by motivating the inherent regulatory system in the body, having the characteristics of whole regulation, dual directional regulation, etc. Modern scientific researches show that body's inherent regulatory system is neuro-endocrine-immune (NEI) network. Hence, we speculate that the regulatory effect of acupuncture may be produced through its regulation of NEI network. In this article, we reviewed the recent researches about acupuncture's effect on the NEI network, to find out the evidence of acupuncture adjusting NEI network and provide some evidences for revealing the mechanism of acupuncture. PMID:24106314

Ding, S S; Hong, S H; Wang, C; Guo, Y; Wang, Z K; Xu, Y

2014-05-01

107

Modulation of protein release from photocrosslinked networks by gelatin microparticles.  

PubMed

Injectable delivery systems are attractive as vehicles for localized delivery of therapeutics especially in the context of regenerative medicine. In this study, photocrosslinked polyanhydride (PA) networks were modified by incorporation of microparticles to modulate long-term delivery of macromolecules. The in vitro release of two model proteins (horseradish peroxidase (HRP) and bovine serum albumin labeled with fluorescein isothiocyanate (FITC-BSA)) were evaluated from networks composed of sebacic acid dimethacrylate (MSA), 1,6-bis-carboxyphenoxyhexane dimethacrylate (MCPH), poly(ethylene glycol) diacrylate (PEGDA), and calcium carbonate (CaCO3), supplemented with gelatin microparticles or sodium chloride crystals. Prior to incorporation into the networks, proteins were formulated into granules by dilution with a cyclodextrin excipient and gelatin-based wet-granulation. Protein release was modulated by incorporation of microparticles into photocrosslinked PA networks, presumably by enabling aqueous channels through the matrix. Furthermore, a dual release system has been demonstrated by incorporation of protein in both the PA matrix and the gelatin microparticles. These results suggest that microparticle incorporation into the photocrosslinked PA system may be a useful strategy to modulate protein release in injectable delivery systems for the long-term delivery of macromolecules. These composites present an interesting class of materials for bone regeneration applications. PMID:18565702

Weiner, Ashley A; Moore, Marc C; Walker, Amanda H; Shastri, V Prasad

2008-08-01

108

Sigma-delta cellular neural network for 2D modulation.  

PubMed

Although sigma-delta modulation is widely used for analog-to-digital (A/D) converters, sigma-delta concepts are only for 1D signals. Signal processing in the digital domain is extremely useful for 2D signals such as used in image processing, medical imaging, ultrasound imaging, and so on. The intricate task that provides true 2D sigma-delta modulation is feasible in the spatial domain sigma-delta modulation using the discrete-time cellular neural network (DT-CNN) with a C-template. In the proposed architecture, the A-template is used for a digital-to-analog converter (DAC), the C-template works as an integrator, and the nonlinear output function is used for the bilevel output. In addition, due to the cellular neural network (CNN) characteristics, each pixel of an image corresponds to a cell of a CNN, and each cell is connected spatially by the A-template. Therefore, the proposed system can be thought of as a very large-scale and super-parallel sigma-delta modulator. Moreover, the spatio-temporal dynamics is designed to obtain an optimal reconstruction signal. The experimental results show the excellent reconstruction performance and capabilities of the CNN as a sigma-delta modulator. PMID:18215502

Aomori, Hisashi; Otake, Tsuyoshi; Takahashi, Nobuaki; Tanaka, Mamoru

2008-01-01

109

Nicotinic modulation of neuronal networks: from receptors to cognition  

Microsoft Academic Search

Rationale  Nicotine affects many aspects of human cognition, including attention and memory. Activation of nicotinic acetylcholine receptors\\u000a (nAChRs) in neuronal networks modulates activity and information processing during cognitive tasks, which can be observed\\u000a in electroencephalograms (EEGs) and functional magnetic resonance imaging studies.\\u000a \\u000a \\u000a \\u000a Objectives  In this review, we will address aspects of nAChR functioning as well as synaptic and cellular modulation important for

Huibert D. Mansvelder; Karlijn I. van Aerde; Jonathan J. Couey; Arjen B. Brussaard

2006-01-01

110

Detecting modulated lasers in the battlefield and determining their direction  

NASA Astrophysics Data System (ADS)

Many different lasers are deployed in the battlefield for range finding, target designation, communications, dazzle, location of targets, munitions guidance, and destruction. Laser warning devices on military systems detect and identify lasers striking them in order to assess their threat level and plan avoidance or retaliation. Types of lasers and their characteristics are discussed: power, frequency, coherence, bandwidth, direction, pulse length and modulation. We describe three approaches for laser warning devices from which specific cases may be tailored: simultaneous estimation of direction and wavelength with a grating, wavefront direction only estimation for low light levels with lenses, absolute simultaneous wavelength only estimation with a Fizeau interferometer. We investigate the feasibility and compare the suitability of these approaches for different applications.

McAulay, Alastair D.

2009-05-01

111

Smelling directions: Olfaction modulates ambiguous visual motion perception  

PubMed Central

Senses of smells are often accompanied by simultaneous visual sensations. Previous studies have documented enhanced olfactory performance with concurrent presence of congruent color- or shape- related visual cues, and facilitated visual object perception when congruent smells are simultaneously present. These visual object-olfaction interactions suggest the existences of couplings between the olfactory pathway and the visual ventral processing stream. However, it is not known if olfaction can modulate visual motion perception, a function that is related to the visual dorsal stream. We tested this possibility by examining the influence of olfactory cues on the perceptions of ambiguous visual motion signals. We showed that, after introducing an association between motion directions and olfactory cues, olfaction could indeed bias ambiguous visual motion perceptions. Our result that olfaction modulates visual motion processing adds to the current knowledge of cross-modal interactions and implies a possible functional linkage between the olfactory system and the visual dorsal pathway.

Kuang, Shenbing; Zhang, Tao

2014-01-01

112

Enabling Technologies for Direct Detection Optical Phase Modulation Formats  

NASA Astrophysics Data System (ADS)

Phase modulation formats are believed to be one of the key enabling techniques for next generation high speed long haul fiber-optic communication systems due to the following main advantages: (1) with a balanced detection, a better receiver sensitivity over conventional intensity modulation formats, e.g., a ˜3-dB sensitivity improvement using differential phase shift keying (DPSK) and a ˜1.3-dB sensitivity improvement using differential quadrature phase shift keying (DQPSK); (2) excellent robustness against fiber nonlinearities; (3) high spectrum efficiency when using multilevel phase modulation formats, such as DQPSK. As the information is encoded in the phase of the optical field, the phase modulation formats are sensitive to the phase-related impairments and the deterioration induced in the phase-intensity conversion. This consequently creates new challenging issues. The research objective of this thesis is to depict some of the challenging issues and provide possible solutions. The first challenge is the cross-phase modulation (XPM) penalty for the phase modulated channels co-propagating with the intensity modulated channels. The penalty comes from the pattern dependent intensity fluctuations of the neighboring intensity modulated channels being converted into phase noise in the phase modulation channels. We propose a model to theoretically analyze the XPM penalty dependence on the walk off effect. From this model, we suggest that using fibers with large local dispersion or intentionally introducing some residual dispersion per span would help mitigate the XPM penalty. The second challenge is the polarization dependent frequency shift (PDf) induced penalty during the phase-intensity conversion. The direct detection DPSK is usually demodulated in a Mach-Zehnder delay interferometer (DI). The polarization dependence of DI introduces a PDf causing a frequency offset between the laser's frequency and the transmissivity peak of DI, degrading the demodulated DPSK signal. We found that PDf ratio, defined as PDf/FSR, plays a predominant role in determining the performance of the demodulator. We further investigate on the PDf induced penalty for a 40-GHz DPSK demodulator on a 40-Gb/s return-to-zero (RZ)-DPSK signal to study PDf incurred optical filtering effect and spectrum distortion. Degradation for the RZ signal has been found in the presence the PDf. The third challenge is fiber dispersion induced inter-symbol interference for the phase modulated signals. Traditionally the dispersion is compensated using dispersion compensation fibers (DCF). Recently emerged electronic dispersion compensation (EDC) not only avoids the attenuation that would be introduced by DCF, but also is capable of simultaneously compensating the chromatic dispersion (CD) and polarization mode dispersion (PMD). We investigate on EDC's CD and PMD compensation capabilities for the direct detection return-to-zero (NRZ)-DPSK signal. The simulation results show that around 300-ps/nm CD and 10-ps differential group delay (DGD) can be compensated by employing EDC. However, compared with the on-off keying (OOK) signal, the EDC is actually less effective with the DPSK signal. The investigation is extended to the RZ-DPSK signal and found out the decision feedback equalizer (DFE) exhibits better performance with the RZ-DPSK signal.

Xu, Xian

113

Link module for a downhole drilling network  

DOEpatents

A repeater is disclosed in one embodiment of the present invention as including a cylindrical housing, characterized by a proximal end and a distal end, and having a substantially cylindrical wall, the cylindrical wall defining a central bore passing therethrough. The cylindrical housing is formed to define at least one recess in the cylindrical wall, into which a repeater is inserted. The cylindrical housing also includes an annular recess formed into at least one of the proximal end and the distal end. An annular transmission element, operably connected to the repeater, is located in the annular recess. In selected embodiments, the annular transmission element inductively converts electrical energy to magnetic energy. In other embodiments, the annular transmission element includes an electrical contact to transmit electrical energy directly to another contact.

Hall, David R. (Provo, UT); Fox, Joe (Provo, UT)

2007-05-29

114

Task induced modulation of neural oscillations in electrophysiological brain networks.  

PubMed

In recent years, one of the most important findings in systems neuroscience has been the identification of large scale distributed brain networks. These networks support healthy brain function and are perturbed in a number of neurological disorders (e.g. schizophrenia). Their study is therefore an important and evolving focus for neuroscience research. The majority of network studies are conducted using functional magnetic resonance imaging (fMRI) which relies on changes in blood oxygenation induced by neural activity. However recently, a small number of studies have begun to elucidate the electrical origin of fMRI networks by searching for correlations between neural oscillatory signals from spatially separate brain areas in magnetoencephalography (MEG) data. Here we advance this research area. We introduce two methodological extensions to previous independent component analysis (ICA) approaches to MEG network characterisation: 1) we show how to derive pan-spectral networks that combine independent components computed within individual frequency bands. 2) We show how to measure the temporal evolution of each network with millisecond temporal resolution. We apply our approach to ~10h of MEG data recorded in 28 experimental sessions during 3 separate cognitive tasks showing that a number of networks could be identified and were robust across time, task, subject and recording session. Further, we show that neural oscillations in those networks are modulated by memory load, and task relevance. This study furthers recent findings on electrodynamic brain networks and paves the way for future clinical studies in patients in which abnormal connectivity is thought to underlie core symptoms. PMID:22906787

Brookes, M J; Liddle, E B; Hale, J R; Woolrich, M W; Luckhoo, H; Liddle, P F; Morris, P G

2012-12-01

115

Modulation format identification in heterogeneous fiber-optic networks using artificial neural networks.  

PubMed

We propose a simple and cost-effective technique for modulation format identification (MFI) in next-generation heterogeneous fiber-optic networks using an artificial neural network (ANN) trained with the features extracted from the asynchronous amplitude histograms (AAHs). Results of numerical simulations conducted for six different widely-used modulation formats at various data rates demonstrate that the proposed technique can effectively classify all these modulation formats with an overall estimation accuracy of 99.6% and also in the presence of various link impairments. The proposed technique employs extremely simple hardware and digital signal processing (DSP) to enable MFI and can also be applied for the identification of other modulation formats at different data rates without necessitating hardware changes. PMID:22714229

Khan, Faisal Nadeem; Zhou, Yudi; Lau, Alan Pak Tao; Lu, Chao

2012-05-21

116

System architecture directions for networked sensors  

Microsoft Academic Search

Technological progress in integrated, low-power, CMOS communication devices and sensors makes a rich design space of networked sensors viable. They can be deeply embedded in the physical world and spread throughout our environment like smart dust. The missing elements are an overall system architecture and a methodology for systematic advance. To this end, we identify key requirements, develop a small

Jason L. Hill; Robert Szewczyk; Alec Woo; Seth Hollar; David E. Culler; Kristofer S. J. Pister

2000-01-01

117

Identifying functional modules in interaction networks through overlapping Markov clustering  

PubMed Central

Motivation: In recent years, Markov clustering (MCL) has emerged as an effective algorithm for clustering biological networks—for instance clustering protein–protein interaction (PPI) networks to identify functional modules. However, a limitation of MCL and its variants (e.g. regularized MCL) is that it only supports hard clustering often leading to an impedance mismatch given that there is often a significant overlap of proteins across functional modules. Results: In this article, we seek to redress this limitation. We propose a soft variation of Regularized MCL (R-MCL) based on the idea of iteratively (re-)executing R-MCL while ensuring that multiple executions do not always converge to the same clustering result thus allowing for highly overlapped clusters. The resulting algorithm, denoted soft regularized Markov clustering, is shown to outperform a range of extant state-of-the-art approaches in terms of accuracy of identifying functional modules on three real PPI networks. Availability: All data and codes are freely available upon request. Contact: srini@cse.ohio-state.edu Supplementary Information: Supplementary data are available at Bioinformatics online.

Shih, Yu-Keng; Parthasarathy, Srinivasan

2012-01-01

118

Connection cube modules for optical backplanes and fiber networks.  

PubMed

A modular free-space optical system, called the connection cube, for connecting arrays of electro-optic transceivers and fiber-array connectors is presented. The connection cube module provides bidirectional data transfer between four processing nodes on a cube face and can be used as a basic building block for optical backplanes and interconnect networks. An experimental system for connecting four processing nodes is presented and used to examine alignment and packaging issues. An analysis of the dimensional requirements and scaling capability for systems based on this module is conducted. This analysis shows that, when the connection cube module is adapted to vertical-cavity surface-emitting-laser-based point-to-point fiber-array links currently under development, it can connect up to 14 processing nodes with an aggregate data transfer capacity of 112 Gbits/s with 19.6-W power consumption. PMID:18259270

Kostuk, R K; Ramsey, D L; Kim, T J

1997-07-10

119

Errorless and errorful learning modulated by transcranial direct current stimulation  

PubMed Central

Background Errorless learning is advantageous over trial and error learning (errorful learning) as errors are avoided during learning resulting in increased memory performance. Errorful learning challenges the executive control system of memory processes as the erroneous items compete with the correct items during retrieval. The left dorsolateral prefrontal cortex (DLPFC) is a core region involved in this executive control system. Transcranial direct current stimulation (tDCS) can modify the excitability of underlying brain functioning. Results In a single blinded tDCS study one group of young healthy participants received anodal and another group cathodal tDCS of the left DLPFC each compared to sham stimulation. Participants had to learn words in an errorless and an errorful manner using a word stem completion paradigm. The results showed that errorless compared to errorful learning had a profound effect on the memory performance in terms of quality. Anodal stimulation of the left DLPFC did not modulate the memory performance following errorless or errorful learning. By contrast, cathodal stimulation hampered memory performance after errorful learning compared to sham, whereas there was no modulation after errorless learning. Conclusions Concluding, the study further supports the advantages of errorless learning over errorful learning. Moreover, cathodal stimulation of the left DLPFC hampered memory performance following the conflict-inducing errorful learning as compared to no modulation after errorless learning emphasizing the importance of the left DLPFC in executive control of memory.

2011-01-01

120

System characteristics of direct modulated and externally modulated RF fiber-optic links  

Microsoft Academic Search

RF fiber-optic links have numerous applications to microwave systems. To fully exploit their usefulness, and RF system designer must understand their properties in terms of the performance parameters that are used to describe the terminal properties of other RF components such as loss, signal-to-noise, linearity, and dynamics. This review paper details the performance of direct and external modulation fiber-optic links

W. E. Stephens; T. R. Joseph

1987-01-01

121

Network deconvolution as a general method to distinguish direct dependencies in networks  

PubMed Central

Recognizing direct relationships between variables connected in a network is a pervasive problem in biological, social and information sciences as correlation-based networks contain numerous indirect relationships. Here we present a general method for inferring direct effects from an observed correlation matrix containing both direct and indirect effects. We formulate the problem as the inverse of network convolution, and introduce an algorithm that removes the combined effect of all indirect paths of arbitrary length in a closed-form solution by exploiting eigen-decomposition and infinite-series sums. We demonstrate the effectiveness of our approach in several network applications: distinguishing direct targets in gene expression regulatory networks; recognizing directly-interacting amino-acid residues for protein structure prediction from sequence alignments; and distinguishing strong collaborations in co-authorship social networks using connectivity information alone.

Feizi, Soheil; Marbach, Daniel; Medard, Muriel; Kellis, Manolis

2013-01-01

122

The IRIS Network of Excellence: Future Directions in Interactive Storytelling  

NASA Astrophysics Data System (ADS)

The IRIS Network of Excellence started its work in January 2009. In this paper we highlight some new research directions developing within the network: one is revisiting narrative formalisation through the use of Linear Logic and the other is challenging the conventional framework of basing Interactive Storytelling on computer graphics to explore the content-based recombination of video sequences.

Cavazza, Marc; Champagnat, Ronan; Leonardi, Riccardo

123

Optical modulation of astrocyte network using ultrashort pulsed laser  

NASA Astrophysics Data System (ADS)

Astrocyte, the most abundant cell type in the central nervous system, has been one of major topics in neuroscience. Even though many tools have been developed for the analysis of astrocyte function, there has been no adequate tool that can modulates astrocyte network without pharmaceutical or genetic interventions. Here we found that ultrashort pulsed laser stimulation can induce label-free activation of astrocytes as well as apoptotic-like cell death in a dose-dependent manner. Upon irradiation with high intensity pulsed lasers, the irradiated cells with short exposure time showed very rapid mitochondria fragmentation, membrane blebbing and cytoskeletal retraction. We applied this technique to investigate in vivo function of astrocyte network in the CNS: in the aspect of neurovascular coupling and blood-brain barrier. We propose that this noninvasive technique can be widely applied for in vivo study of complex cellular network.

Yoon, Jonghee; Ku, Taeyun; Chong, Kyuha; Ryu, Seung-Wook; Choi, Chulhee

2012-02-01

124

Epidemic dynamics on semi-directed complex networks.  

PubMed

In this paper an SIS model for epidemic spreading on semi-directed networks is established, which can be used to examine and compare the impact of undirected and directed contacts on disease spread. The model is analyzed for the case of uncorrelated semi-directed networks, and the basic reproduction number R0 is obtained analytically. We verify that the R0 contains the outbreak threshold on undirected networks and directed networks as special cases. It is proved that if R0<1 then the disease-free equilibrium is globally asymptotically stable, otherwise the disease-free equilibrium is unstable and the unique endemic equilibrium exists, which is globally asymptotically stable. Finally the numerical simulations holds for these analytical results are given. PMID:24140877

Zhang, Xiaoguang; Sun, Gui-Quan; Zhu, Yu-Xiao; Ma, Junling; Jin, Zhen

2013-12-01

125

Hopfield Network Approach to Direct Adaptive Control of Nonlinear Systems.  

National Technical Information Service (NTIS)

An automatic control system capable of controlling an unknown nonlinear system is designed using a direct adaptive control scheme, implemented with a Hopfield network. The application of this method to an arbitrary system is discussed in detail and three ...

R. S. Starsman

1991-01-01

126

High-speed transmission of adaptively modulated optical OFDM signals over multimode fibers using directly Modulated DFBs  

Microsoft Academic Search

A novel optical signal modulation concept of adaptively modulated optical orthogonal frequency division multiplexing (AMOOFDM) is proposed, and a comprehensive theoretical model of AMOOFDM modems is developed. Numerical simulations of the transmission performance of the AMOOFDM signals are undertaken in unamplified multimode fiber (MMF)-based links using directly modulated distributed feedback (DFB) lasers (DMLs). It is shown that 28 Gb\\/s over

J. M. Tang; K. Alan Shore

2006-01-01

127

Bidirectional Quantum Secure Direct Communication Network Protocol with Hyperentanglement  

NASA Astrophysics Data System (ADS)

We propose a bidirectional quantum secure direct communication (QSDC) network protocol with the hyperentanglment in both the spatial-mode ad the polarization degrees of freedom of photon pairs which can in principle be produced with a beta barium borate crystal. The secret message can be encoded on the photon pairs with unitary operations in these two degrees of freedom independently. Compared with other QSDC network protocols, our QSDC network protocol has a higher capacity as each photon pair can carry 4 bits of information. Also, we discuss the security of our QSDC network protocol and its feasibility with current techniques.

Gu, Bin; Huang, Yu-Gai; Fang, Xia; Chen, Yu-Lin

2011-10-01

128

Evolutionary dynamics and fixation probabilities in directed networks  

NASA Astrophysics Data System (ADS)

In this paper, we investigate the evolutionary dynamics in directed and/or weighted networks. We study the fixation probability of a mutant in finite populations in stochastic voter-type dynamics for several update rules. The fixation probability is defined as the probability of a newly introduced mutant in a wild-type population taking over the entire population. In contrast to the case of undirected and unweighted networks, the fixation probability of a mutant in directed networks is characterized not only by the degree of the node that the mutant initially invades but also by the global structure of networks. Consequently, the gross connectivity of networks such as small-world property or modularity has a major impact on the fixation probability.

Masuda, Naoki; Ohtsuki, Hisashi

2009-03-01

129

Serotonin targets inhibitory synapses to induce modulation of network functions  

PubMed Central

The cellular effects of serotonin (5-HT), a neuromodulator with widespread influences in the central nervous system, have been investigated. Despite detailed knowledge about the molecular biology of cellular signalling, it is not possible to anticipate the responses of neuronal networks to a global action of 5-HT. Heterogeneous expression of various subtypes of serotonin receptors (5-HTR) in a variety of neurons differently equipped with cell-specific transmitter receptors and ion channel assemblies can provoke diverse cellular reactions resulting in various forms of network adjustment and, hence, motor behaviour. Using the respiratory network as a model for reciprocal synaptic inhibition, we demonstrate that 5-HT1AR modulation primarily affects inhibition through glycinergic synapses. Potentiation of glycinergic inhibition of both excitatory and inhibitory neurons induces a functional reorganization of the network leading to a characteristic change of motor output. The changes in network operation are robust and help to overcome opiate-induced respiratory depression. Hence, 5-HT1AR activation stabilizes the rhythmicity of breathing during opiate medication of pain.

Manzke, Till; Dutschmann, Mathias; Schlaf, Gerald; Morschel, Michael; Koch, Uwe R.; Ponimaskin, Evgeni; Bidon, Olivier; Lalley, Peter M.; Richter, Diethelm W.

2009-01-01

130

Space station common module network topology and hardware development  

NASA Technical Reports Server (NTRS)

Conceptual space station common module power management and distribution (SSM/PMAD) network layouts and detailed network evaluations were developed. Individual pieces of hardware to be developed for the SSM/PMAD test bed were identified. A technology assessment was developed to identify pieces of equipment requiring development effort. Equipment lists were developed from the previously selected network schematics. Additionally, functional requirements for the network equipment as well as other requirements which affected the suitability of specific items for use on the Space Station Program were identified. Assembly requirements were derived based on the SSM/PMAD developed requirements and on the selected SSM/PMAD network concepts. Basic requirements and simplified design block diagrams are included. DC remote power controllers were successfully integrated into the DC Marshall Space Flight Center breadboard. Two DC remote power controller (RPC) boards experienced mechanical failure of UES 706 stud-mounted diodes during mechanical installation of the boards into the system. These broken diodes caused input to output shorting of the RPC's. The UES 706 diodes were replaced on these RPC's which eliminated the problem. The DC RPC's as existing in the present breadboard configuration do not provide ground fault protection because the RPC was designed to only switch the hot side current. If ground fault protection were to be implemented, it would be necessary to design the system so the RPC switched both the hot and the return sides of power.

Anderson, P.; Braunagel, L.; Chwirka, S.; Fishman, M.; Freeman, K.; Eason, D.; Landis, D.; Lech, L.; Martin, J.; Mccorkle, J.

1990-01-01

131

Genome evolution reveals biochemical networks and functional modules.  

PubMed

The analysis of completely sequenced genomes uncovers an astonishing variability between species in terms of gene content and order. During genome history, the genes are frequently rear-ranged, duplicated, lost, or transferred horizontally between genomes. These events appear to be stochastic, yet they are under selective constraints resulting from the functional interactions between genes. These genomic constraints form the basis for a variety of techniques that employ systematic genome comparisons to predict functional associations among genes. The most powerful techniques to date are based on conserved gene neighborhood, gene fusion events, and common phylogenetic distributions of gene families. Here we show that these techniques, if integrated quantitatively and applied to a sufficiently large number of genomes, have reached a resolution which allows the characterization of function at a higher level than that of the individual gene: global modularity becomes detectable in a functional protein network. In Escherichia coli, the predicted modules can be bench-marked by comparison to known metabolic pathways. We found as many as 74% of the known metabolic enzymes clustering together in modules, with an average pathway specificity of at least 84%. The modules extend beyond metabolism, and have led to hundreds of reliable functional predictions both at the protein and pathway level. The results indicate that modularity in protein networks is intrinsically encoded in present-day genomes. PMID:14673105

von Mering, Christian; Zdobnov, Evgeny M; Tsoka, Sophia; Ciccarelli, Francesca D; Pereira-Leal, Jose B; Ouzounis, Christos A; Bork, Peer

2003-12-23

132

Predictive Direct Power Control of Three-Phase Pulsewidth Modulation (PWM) Rectifier Using Space-Vector Modulation (SVM)  

Microsoft Academic Search

In this paper, we present a direct power control (DPC) of three-phase pulsewidth modulation rectifier with constant switching frequency using space-vector modulation (SVM). The developed DPC scheme is based on the predictive control strategy to achieve direct control of instantaneous active and reactive power of the converter. For this purpose, at the beginning of each switching period, the required rectifier

Abdelouahab Bouafia; Jean-Paul Gaubert; Fateh Krim

2010-01-01

133

Capacity bounds for ad-hoc networks using directional antennas  

Microsoft Academic Search

Directional antennas can be useful in significantly increasing the capacity of wireless ad hoc networks. With directional antennas, independent communications between nodes can occur in parallel, even if the nodes are within range of each other. However, mutual interference by simultaneous transmissions limits the maximum number of such concurrent communications. Furthermore, it poses bounds on the amount of capacity gain

Akis Spyropoulos; Cauligi S. Raghavendra

2003-01-01

134

Symbol-level random network coded cooperation with hierarchical modulation in relay communication  

Microsoft Academic Search

In order to effectively minimize packet error rate in error prone wireless networks, a novel cooperative communication strategy jointly using symbol-level random network coding and hierarchical modulation is proposed in this paper. The source broadcasts random network coded symbols with hierarchical modulation to the relays and the destination. In following time slots, the relays, which have successfully decoded the original

Ronny Yongho Kim; Young Yong Kim

2009-01-01

135

Motion words selectively modulate direction discrimination sensitivity for threshold motion  

PubMed Central

Can speech selectively modulate the sensitivity of a sensory system so that, in the presence of a suitable linguistic context, the discrimination of certain perceptual features becomes more or less likely? In this study, participants heard upward or downward motion words followed by a single visual field of random dots moving upwards or downwards. The time interval between the onsets of the auditory and the visual stimuli was varied parametrically. Motion direction could be either discriminable (suprathreshold motion) or non-discriminable (threshold motion). Participants had to judge whether the dots were moving upward or downward. Results show a double dissociation between discrimination sensitivity (d?) and reaction times depending on whether vertical motion was above or at threshold. With suprathreshold motion, responses were faster for congruent directions of words and dots, but sensitivity was equal across conditions. With threshold motion, sensitivity was higher for congruent directions of words and dots, but responses were equally fast across conditions. The observed differences in sensitivity and response times were largest when the dots appeared 450 ms after word onset, that is, consistently with electrophysiology, at the time the up/down semantics of the word had become available. These data suggest that word meanings can alter the balance between signal and noise within the visual system and affect the perception of low-level sensory features.

Pavan, Andrea; Skujevskis, Maris; Baggio, Giosue

2013-01-01

136

Chirped laser dispersion spectroscopy using a directly modulated quantum cascade laser  

NASA Astrophysics Data System (ADS)

Chirped laser dispersion spectroscopy (CLaDS) utilizing direct modulation of a quantum cascade laser (QCL) is presented. By controlling the laser bias nearly single- and dual-sideband CLaDS operation can be realized in an extremely simplified optical setup with no external optical modulators. Capability of direct single-sideband modulation is a unique feature of QCLs that exhibit a low linewidth enhancement factor. The developed analytical model shows excellent agreement with the experimental, directly modulated CLaDS spectra. This method overcomes major technical limitations of mid-infrared CLaDS systems by allowing significantly higher modulation frequencies and eliminating optical fringes introduced by external modulators.

Hangauer, Andreas; Spinner, Georg; Nikodem, Michal; Wysocki, Gerard

2013-11-01

137

Oriented modulation for watermarking in direct binary search halftone images.  

PubMed

In this paper, a halftoning-based watermarking method is presented. This method enables high pixel-depth watermark embedding, while maintaining high image quality. This technique is capable of embedding watermarks with pixel depths up to 3 bits without causing prominent degradation to the image quality. To achieve high image quality, the parallel oriented high-efficient direct binary search (DBS) halftoning is selected to be integrated with the proposed orientation modulation (OM) method. The OM method utilizes different halftone texture orientations to carry different watermark data. In the decoder, the least-mean-square-trained filters are applied for feature extraction from watermarked images in the frequency domain, and the naïve Bayes classifier is used to analyze the extracted features and ultimately to decode the watermark data. Experimental results show that the DBS-based OM encoding method maintains a high degree of image quality and realizes the processing efficiency and robustness to be adapted in printing applications. PMID:22581134

Guo, Jing-Ming; Su, Chang-Cheng; Liu, Yun-Fu; Lee, Hua; Lee, Jiann-Der

2012-09-01

138

Optical filtering in directly modulated/detected OOFDM systems.  

PubMed

This work presents a theoretical investigation on the performance of directly modulated/detected (DM/DD) optical orthogonal frequency division multiplexed (OOFDM) systems subject to optical filtering. The impact of both linear and nonlinear distortion effects are taken into account to calculate the effective signal-to-noise ratio of each subcarrier. These results are then employed to optimize the design parameters of two simple optical filtering structures: a Mach Zehnder interferometer and a uniform fiber Bragg grating, leading to a significant optical power budget improvement given by 3.3 and 3dB, respectively. These can be further increased to 5.5 and 4.2dB respectively when balanced detection configurations are employed. We find as well that this improvement is highly dependent on the clipping ratio. PMID:24514636

Sánchez, C; Ortega, B; Wei, J L; Capmany, J

2013-12-16

139

How familiarization and repetition modulate the picture naming network.  

PubMed

A common strategy to reveal the components of the speech production network is to use psycholinguistic manipulations previously tested in behavioral protocols. This often disregards how implementation aspects that are nonessential for interpreting behavior may affect the neural response. We compared the electrophysiological (EEG) signature of two popular picture naming protocols involving either unfamiliar pictures without repetitions or repeated familiar pictures. We observed significant semantic interference effects in behavior but not in the EEG, contrary to some previous findings. Remarkably, the two protocols elicited clearly distinct EEG responses. These were not due to naming latency differences nor did they reflect a homogeneous modulation of amplitude over the trial time-window. The effect of protocol is attributed to the familiarization induced by the first encounter with the materials. Picture naming processes can be substantially modulated by specific protocol requirements controlled by familiarity and, to a much lesser degree, the repetition of materials. PMID:24785306

Llorens, Anaïs; Trébuchon, Agnès; Riès, Stéphanie; Liégeois-Chauvel, Catherine; Alario, F-Xavier

2014-06-01

140

Sinusoidal modulation control method in a chaotic neural network  

NASA Astrophysics Data System (ADS)

Chaotic neural networks (CNNs) have chaotic dynamic associative memory properties: The memory states appear non-periodically, and cannot be converged to a stored pattern. Thus, it is necessary to control chaos in a CNN in order to recognize associative memory. In this paper, a novel control method, the sinusoidal modulation control method, has been proposed to control chaos in a CNN. In this method, a sinusoidal wave simplified from brain waves is used as a control signal to modulate a parameter of the CNN. The simulation results demonstrate the effectiveness of this control method. The controlled CNN can be applied to information processing. Moreover, the method provides a way to associate brain waves by controlling CNNs.

Zhang, Qihanyue; Xie, Xiaoping; Zhu, Ping; Chen, Hongping; He, Guoguang

2014-08-01

141

Network deconvolution as a general method to distinguish direct dependencies in networks.  

PubMed

Recognizing direct relationships between variables connected in a network is a pervasive problem in biological, social and information sciences as correlation-based networks contain numerous indirect relationships. Here we present a general method for inferring direct effects from an observed correlation matrix containing both direct and indirect effects. We formulate the problem as the inverse of network convolution, and introduce an algorithm that removes the combined effect of all indirect paths of arbitrary length in a closed-form solution by exploiting eigen-decomposition and infinite-series sums. We demonstrate the effectiveness of our approach in several network applications: distinguishing direct targets in gene expression regulatory networks; recognizing directly interacting amino-acid residues for protein structure prediction from sequence alignments; and distinguishing strong collaborations in co-authorship social networks using connectivity information alone. In addition to its theoretical impact as a foundational graph theoretic tool, our results suggest network deconvolution is widely applicable for computing direct dependencies in network science across diverse disciplines. PMID:23851448

Feizi, Soheil; Marbach, Daniel; Médard, Muriel; Kellis, Manolis

2013-08-01

142

IEEE1451-based smart module for in-vehicle networking systems of intelligent vehicles  

Microsoft Academic Search

As vehicles become intelligent for the convenience and safety of drivers, in-vehicle networking (IVN) systems and smart modules are essential components of intelligent vehicles. However, there are obstacles for the wide acceptance of smart modules. First, there exist numerous IVN protocols that a smart module should be able to support. Second, the whole smart module has to be replaced when

Kyung Chang Lee; Man Ho Kim; Suk Lee; Hong Hee Lee

2004-01-01

143

Interarrival times of message propagation on directed networks  

NASA Astrophysics Data System (ADS)

One of the challenges in fighting cybercrime is to understand the dynamics of message propagation on botnets, networks of infected computers used to send viruses, unsolicited commercial emails (SPAM) or denial of service attacks. We map this problem to the propagation of multiple random walkers on directed networks and we evaluate the interarrival time distribution between successive walkers arriving at a target. We show that the temporal organization of this process, which models information propagation on unstructured peer to peer networks, has the same features as SPAM reaching a single user. We study the behavior of the message interarrival time distribution on three different network topologies using two different rules for sending messages. In all networks the propagation is not a pure Poisson process. It shows universal features on Poissonian networks and a more complex behavior on scale free networks. Results open the possibility to indirectly learn about the process of sending messages on networks with unknown topologies, by studying interarrival times at any node of the network.

Mihaljev, Tamara; de Arcangelis, Lucilla; Herrmann, Hans J.

2011-08-01

144

Interarrival times of message propagation on directed networks.  

PubMed

One of the challenges in fighting cybercrime is to understand the dynamics of message propagation on botnets, networks of infected computers used to send viruses, unsolicited commercial emails (SPAM) or denial of service attacks. We map this problem to the propagation of multiple random walkers on directed networks and we evaluate the interarrival time distribution between successive walkers arriving at a target. We show that the temporal organization of this process, which models information propagation on unstructured peer to peer networks, has the same features as SPAM reaching a single user. We study the behavior of the message interarrival time distribution on three different network topologies using two different rules for sending messages. In all networks the propagation is not a pure Poisson process. It shows universal features on Poissonian networks and a more complex behavior on scale free networks. Results open the possibility to indirectly learn about the process of sending messages on networks with unknown topologies, by studying interarrival times at any node of the network. PMID:21929069

Mihaljev, Tamara; de Arcangelis, Lucilla; Herrmann, Hans J

2011-08-01

145

Modulated scale-free network in Euclidean space.  

PubMed

A random network is grown by introducing at unit rate randomly selected nodes on the Euclidean space. A node is randomly connected to its ith predecessor of degree k(i) with a directed link of length l using a probability proportional to k(i)l(alpha). Our numerical study indicates that the network is scale free for all values of alpha>alpha(c) and the degree distribution decays stretched exponentially for the other values of alpha. The link length distribution follows a power law: D(l) approximately l(delta), where delta is calculated exactly for the whole range of values of alpha. PMID:12513354

Manna, S S; Sen, Parongama

2002-12-01

146

Modulated scale-free network in Euclidean space  

NASA Astrophysics Data System (ADS)

A random network is grown by introducing at unit rate randomly selected nodes on the Euclidean space. A node is randomly connected to its ith predecessor of degree ki with a directed link of length l using a probability proportional to kil?. Our numerical study indicates that the network is scale free for all values of ?>?c and the degree distribution decays stretched exponentially for the other values of ?. The link length distribution follows a power law: D(l)~l?, where ? is calculated exactly for the whole range of values of ?.

Manna, S. S.; Sen, Parongama

2002-12-01

147

A comparison of the functional modules identified from time course and static PPI network data  

PubMed Central

Background Cellular systems are highly dynamic and responsive to cues from the environment. Cellular function and response patterns to external stimuli are regulated by biological networks. A protein-protein interaction (PPI) network with static connectivity is dynamic in the sense that the nodes implement so-called functional activities that evolve in time. The shift from static to dynamic network analysis is essential for further understanding of molecular systems. Results In this paper, Time Course Protein Interaction Networks (TC-PINs) are reconstructed by incorporating time series gene expression into PPI networks. Then, a clustering algorithm is used to create functional modules from three kinds of networks: the TC-PINs, a static PPI network and a pseudorandom network. For the functional modules from the TC-PINs, repetitive modules and modules contained within bigger modules are removed. Finally, matching and GO enrichment analyses are performed to compare the functional modules detected from those networks. Conclusions The comparative analyses show that the functional modules from the TC-PINs have much more significant biological meaning than those from static PPI networks. Moreover, it implies that many studies on static PPI networks can be done on the TC-PINs and accordingly, the experimental results are much more satisfactory. The 36 PPI networks corresponding to 36 time points, identified as part of this study, and other materials are available at http://bioinfo.csu.edu.cn/txw/TC-PINs.

2011-01-01

148

Formation and dynamics of modules in a dual-tasking multilayer feed-forward neural network  

NASA Astrophysics Data System (ADS)

We study a feed-forward neural network for two independent function approximation tasks. Upon training, two modules are automatically formed in the hidden layers, each handling one of the tasks predominantly. We demonstrate that the sizes of the modules can be dynamically driven by varying the complexities of the tasks. The network serves as a simple example of an artificial neural network with an adaptable modular structure. This study was motivated by related dynamical nature of modules in animal brains.

Lam, Chi-Hang; Shin, F. G.

1998-09-01

149

Construction principles for highly synchronizable sparse directed networks  

NASA Astrophysics Data System (ADS)

In this Letter sparse directed interaction networks of heterogeneous Kuramoto oscillators that give rise to enhanced synchronization properties are generated and analyzed. The particular networks, which allow for the transition to full synchronization for the smallest coupling strength, i.e., optimal networks, are found to be very homogeneous in the in-degree distribution, but exhibit very skewed out-degree distributions. Various correlations between in- and out-degree structure, oscillator heterogeneity and component structure, which are linked to an enhanced synchronizability, are discussed.

Brede, Markus

2008-08-01

150

Degree and Weighted Properties of the Directed China Railway Network  

NASA Astrophysics Data System (ADS)

As well known, many real complex systems are directed and weighted ones. For understanding the topology structure of the directed China Railway Network (CRN) further, we analyze the degree properties of the directed CRN and propose a new method to measure the weight of station (i.e., the utilized efficiency of station) in CRN according to how CRN works really. Rigorous analysis of the existing CRN data shows that the CRN is an assortative network with scale-free degree distribution in space L. On the other hand, the cumulative distribution of station's relative weight, the cumulative distribution of the shortest path length between stations, and the relationship between relative weight and in-(out-)degree have been studied. Our present work provides a new perspective to define the weight of transport complex network, which will be helpful for studying the dynamics of CRN.

Guo, Long; Cai, Xu

151

Revealing the Hidden Relationship by Sparse Modules in Complex Networks with a Large-Scale Analysis  

PubMed Central

One of the remarkable features of networks is module that can provide useful insights into not only network organizations but also functional behaviors between their components. Comprehensive efforts have been devoted to investigating cohesive modules in the past decade. However, it is still not clear whether there are important structural characteristics of the nodes that do not belong to any cohesive module. In order to answer this question, we performed a large-scale analysis on 25 complex networks with different types and scales using our recently developed BTS (bintree seeking) algorithm, which is able to detect both cohesive and sparse modules in the network. Our results reveal that the sparse modules composed by the cohesively isolated nodes widely co-exist with the cohesive modules. Detailed analysis shows that both types of modules provide better characterization for the division of a network into functional units than merely cohesive modules, because the sparse modules possibly re-organize the nodes in the so-called cohesive modules, which lack obvious modular significance, into meaningful groups. Compared with cohesive modules, the sizes of sparse ones are generally smaller. Sparse modules are also found to have preferences in social and biological networks than others.

Jiao, Qing-Ju; Huang, Yan; Liu, Wei; Wang, Xiao-Fan; Chen, Xiao-Shuang; Shen, Hong-Bin

2013-01-01

152

Direct Adaptive Aircraft Control Using Dynamic Cell Structure Neural Networks  

NASA Technical Reports Server (NTRS)

A Dynamic Cell Structure (DCS) Neural Network was developed which learns topology representing networks (TRNS) of F-15 aircraft aerodynamic stability and control derivatives. The network is integrated into a direct adaptive tracking controller. The combination produces a robust adaptive architecture capable of handling multiple accident and off- nominal flight scenarios. This paper describes the DCS network and modifications to the parameter estimation procedure. The work represents one step towards an integrated real-time reconfiguration control architecture for rapid prototyping of new aircraft designs. Performance was evaluated using three off-line benchmarks and on-line nonlinear Virtual Reality simulation. Flight control was evaluated under scenarios including differential stabilator lock, soft sensor failure, control and stability derivative variations, and air turbulence.

Jorgensen, Charles C.

1997-01-01

153

Irreversible bimolecular chemical reactions on directed scale-free networks.  

PubMed

Kinetics of irreversible bimolecular chemical reactions A+A?0 and A+B?0 on directed scale-free networks with the in-degree distribution P(in)(k)?k(-?)(in) and the out-degree distribution P(out)(?)??(-?)(out) are investigated. Since the correlation between k and ? of each node generally exists in directed networks, we control the correlation (k?) with the probability r?[0,1] by two different algorithms for the construction of the directed networks, i.e., the so-called k and ? algorithms. For r=1, the k algorithm gives (k?)=(k(2)), whereas the ? algorithm gives (k?)=(?(2). For r=0, (k?)=(k)(?) for both algorithms. The kinetics of both reactions are analyzed using heterogeneous mean-field (HMF) theory and Monte Carlo simulations. The density of particles (?) algebraically decays in time t as ?(t)?t(-?). The kinetics of both reactions are determined by the same rate equation, d?/dt=a?(2)+b?(?-1), apart from coefficients. The exponent ? is determined by the algorithm: ?=?(in) for the k algorithm (r?0) and ?=?(min) for the ? algorithm (r>0), where ?(min) is the smaller exponent between ?(in) and ?(out). For ?>3, one observes the ordinary mean-field kinetics, ??1/t (?=1). In contrast, for ?<3, ?(t) anomalously decays with ?=1/(?-2). The HMF predictions are confirmed by the simulations on quenched directed networks. PMID:24229156

Kwon, Sungchul; Kim, Yup

2013-10-01

154

Irreversible bimolecular chemical reactions on directed scale-free networks  

NASA Astrophysics Data System (ADS)

Kinetics of irreversible bimolecular chemical reactions A+A?0 and A+B?0 on directed scale-free networks with the in-degree distribution Pin(k)˜k-?in and the out-degree distribution Pout(?)˜?-?out are investigated. Since the correlation between k and ? of each node generally exists in directed networks, we control the correlation with the probability r?[0,1] by two different algorithms for the construction of the directed networks, i.e., the so-called k and ? algorithms. For r=1, the k algorithm gives =, whereas the ? algorithm gives =. For r=0, = for both algorithms. The kinetics of both reactions are analyzed using heterogeneous mean-field (HMF) theory and Monte Carlo simulations. The density of particles (?) algebraically decays in time t as ?(t)˜t-?. The kinetics of both reactions are determined by the same rate equation, d?/dt=a?2+b??-1, apart from coefficients. The exponent ? is determined by the algorithm: ?=?in for the k algorithm (r?0) and ?=?min for the ? algorithm (r>0), where ?min is the smaller exponent between ?in and ?out. For ?>3, one observes the ordinary mean-field kinetics, ?˜1/t (?=1). In contrast, for ?<3, ?(t) anomalously decays with ?=1/(?-2). The HMF predictions are confirmed by the simulations on quenched directed networks.

Kwon, Sungchul; Kim, Yup

2013-10-01

155

Semantic Networks as Means for Goal-Directed Formative Feedback  

Microsoft Academic Search

Kalz, M., Berlanga, A., Van Rosmalen, P., Stoyanov, S., Van Bruggen, J., & Koper, R. (2009). Semantic Networks as Means for Goal Directed Formative Feedback. In V. Hornung-Prähauser & M. Luckmann (Eds.), Kreativität und Innovationskompetenz im digitalen Netz - Creativity and Innovation Competencies in the Web, Sammlung von ausgewählten Fach- und Praxisbeiträgen der 5. EduMedia Fachtagung 2009 (pp. 88-95). Mai,

Marco Kalz; Adriana J. Berlanga; Peter Van Rosmalen; Slavi Stoyanov; Jan Van Bruggen; Rob Koper

2009-01-01

156

Coverage directed test generation for functional verification using bayesian networks  

Microsoft Academic Search

Functional verification is widely acknowledged as the bottleneck in the hardware design cycle. This paper addresses one of the main challenges of simulation based verification (or dynamic verification), by providing a new approach for Coverage Directed Test Generation (CDG). This approach is based on Bayesian networks and computer learning techniques. It provides an efficient way for closing a feedback loop

Shai Fine; Avi Ziv

2003-01-01

157

Quetiapine modulates functional connectivity in brain aggression networks.  

PubMed

Aggressive behavior is associated with dysfunctions in an affective regulation network encompassing amygdala and prefrontal areas such as orbitofrontal (OFC), anterior cingulate (ACC), and dorsolateral prefrontal cortex (DLPFC). In particular, prefrontal regions have been postulated to control amygdala activity by inhibitory projections, and this process may be disrupted in aggressive individuals. The atypical antipsychotic quetiapine successfully attenuates aggressive behavior in various disorders; the underlying neural processes, however, are unknown. A strengthened functional coupling in the prefrontal-amygdala system may account for these anti-aggressive effects. An inhibition of this network has been reported for virtual aggression in violent video games as well. However, there have been so far no in-vivo observations of pharmacological influences on corticolimbic projections during human aggressive behavior. In a double-blind, placebo-controlled study, quetiapine and placebo were administered for three successive days prior to an fMRI experiment. In this experiment, functional brain connectivity was assessed during virtual aggressive behavior in a violent video game and an aggression-free control task in a non-violent modification. Quetiapine increased the functional connectivity of ACC and DLPFC with the amygdala during virtual aggression, whereas OFC-amygdala coupling was attenuated. These effects were observed neither for placebo nor for the non-violent control. These results demonstrate for the first time a pharmacological modification of aggression-related human brain networks in a naturalistic setting. The violence-specific modulation of prefrontal-amygdala networks appears to control aggressive behavior and provides a neurobiological model for the anti-aggressive effects of quetiapine. PMID:23501053

Klasen, Martin; Zvyagintsev, Mikhail; Schwenzer, Michael; Mathiak, Krystyna A; Sarkheil, Pegah; Weber, René; Mathiak, Klaus

2013-07-15

158

Low-frequency analog signal distribution on digital photonic networks by optical delta-sigma modulation  

NASA Astrophysics Data System (ADS)

We propose a delta-sigma modulation scheme for low- and medium-frequency signal transmission in a digital photonic network system. A 10-Gb/s-class optical transceiver with a delta-sigma modulator utilized as a high-speed analog-to-digital converter (ADC) provides a binary optical signal. On the signal reception side, a low-cost and slow-speed photonic receiver directly converts the binary signal into an analog signal at frequencies from several hundreds of kilohertz several tens of megahertz. Further, by using a clock and data recovery circuit at the receiver to reduce jitters, the single-sideband phase noise of the generated signals can be significantly reduced.

Kanno, Atsushi; Kawanishi, Tetsuya

2013-12-01

159

Self-organizing task modules and explicit coordinate systems in a neural network model for 3-D saccades.  

PubMed

The goal of this study was to train an artificial neural network to generate accurate saccades in Listing's plane and then determine how the hidden units performed the visuomotor transformation. A three-layer neural network was successfully trained, using back-prop, to take in oculocentric retinal error vectors and three-dimensional eye orientation and to generate the correct head-centric motor error vector within Listing's plane. Analysis of the hidden layer of trained networks showed that explicit representations of desired target direction and eye orientation were not employed. Instead, the hidden-layer units consistently divided themselves into four parallel modules: a dominant "vector-propagation" class (approximately 50% of units) with similar visual and motor tuning but negligible position sensitivity and three classes with specific spatial relations between position, visual, and motor tuning. Surprisingly, the vector-propagation units, and only these, formed a highly precise and consistent orthogonal coordinate system aligned with Listing's plane. Selective "lesions" confirmed that the vector-propagation module provided the main drive for saccade magnitude and direction, whereas a balance between activity in the other modules was required for the correct eye-position modulation. Thus, contrary to popular expectation, error-driven learning in itself was sufficient to produce a "neural" algorithm with discrete functional modules and explicit coordinate systems, much like those observed in the real saccade generator. PMID:11361255

Smith, M A; Crawford, J D

2001-01-01

160

Dopaminergic modulation of the default mode network in Parkinson's disease.  

PubMed

Default mode network (DMN) is characterized by a deactivation of several cortical areas (including medial prefrontal cortex and posterior cingulate cortex) during goal-directed experimental tasks. Few findings are reported on DMN and the involvement of dopaminergic medication on this network in Parkinson's disease (PD). To evaluate the effect of levodopa on DMN deactivation, we conducted a randomized, crossover, placebo-controlled experiment consisting of two fMRI assessments in fourteen non-demented, non-depressed PD patients compared to thirteen healthy volunteers. They received either acute doses of levodopa or placebo in two fMRI sessions. Brain deactivation was evaluated during a facial emotion recognition task. While the control subjects showed a classical brain deactivation pattern during the emotional task, the PD patients taking placebo only deactivated the ventral medial prefrontal cortex. Patients failed to deactivate the posterior midline and lateral parts of DMN network. After levodopa administration, this network was restored conjointly with the improvement of motor dysfunction in PD patients. The levodopa effect on DMN is probably the consequence of a beneficial dopamine (DA) medication effect which leads to a fine tuning of the dopamine level in the motor part of striatum, resulting to a global improvement of physical state of PD patients and consequently an increased attentional resource to external stimuli. The absence of medial prefrontal deactivation impairment may suggest a preserved mesocortical DA system in these patients. PMID:20674286

Delaveau, Pauline; Salgado-Pineda, Pilar; Fossati, Philippe; Witjas, Tatiana; Azulay, Jean-Philippe; Blin, Olivier

2010-11-01

161

Heterogeneous optical networking using orthogonal OAM multimode modulation  

NASA Astrophysics Data System (ADS)

In order to solve capacity and energy-efficiency problems of future Internet technologies simultaneously, in this paper, we propose the use of energy-efficient N-dimensional (ND) orbital angular momentum (OAM) coded-modulation. The energy-efficient signal constellation is obtained by employing the energy-efficient signal constellation design algorithm. This scheme can achieve beyond 100 Gb/s transmission while employing the state-of-the-art 10 Gb/s technology. The proposed scheme significantly outperforms conventional M-ary PAM. The proposed scheme represents a promising candidate for indoor optical wireless communication, terrestrial free-space optical (FSO) communication, data center applications and can be used as enabling technology for heterogeneous optical networking, thanks to its transparency to both free-space optical and few-mode/multimode fiber links.

Djordjevic, Ivan B.; Anguita, Jaime

2012-10-01

162

Proposal of radio modulation level controlled VPC is ATM networks and its call blocking improvement  

Microsoft Academic Search

This paper proposes radio modulation controlled level VPC in ATM networks. This technique combines the modulation level controlled radio (MLCR) and virtual path capacity control (VPC) method. The traffic fluctuation can be absorbed flexibly when applying the MLCR system to the radio channel of ATM networks which consist of wired and radio channels. We theoretically analyze the call blocking probability

Masahiro Nishi; Katsutoshi Tsukamoto; Minoru Okada; Shozo Komaki

1996-01-01

163

Unbiased degree-preserving randomization of directed binary networks  

NASA Astrophysics Data System (ADS)

Randomizing networks using a naive “accept-all” edge-swap algorithm is generally biased. Building on recent results for nondirected graphs, we construct an ergodic detailed balance Markov chain with nontrivial acceptance probabilities for directed graphs, which converges to a strictly uniform measure and is based on edge swaps that conserve all in and out degrees. The acceptance probabilities can also be generalized to define Markov chains that target any alternative desired measure on the space of directed graphs in order to generate graphs with more sophisticated topological features. This is demonstrated by defining a process tailored to the production of directed graphs with specified degree-degree correlation functions. The theory is implemented numerically and tested on synthetic and biological network examples.

Roberts, E. S.; Coolen, A. C. C.

2012-04-01

164

Allosteric Modulators for the Treatment of Schizophrenia: Targeting Glutamatergic Networks  

PubMed Central

Schizophrenia is a highly debilitating mental disorder which afflicts approximately 1% of the global population. Cognitive and negative deficits account for the lifelong disability associated with schizophrenia, whose symptoms are not effectively addressed by current treatments. New medicines are needed to treat these aspects of the disease. Neurodevelopmental, neuropathological, genetic, and behavioral pharmacological data indicate that schizophrenia stems from a dysfunction of glutamate synaptic transmission, particularly in frontal cortical networks. A number of novel pre- and postsynaptic mechanisms affecting glutamatergic synaptic transmission have emerged as viable targets for schizophrenia. While developing orthosteric glutamatergic agents for these targets has proven extremely difficult, targeting allosteric sites of these targets has emerged as a promising alternative. From a medicinal chemistry perspective, allosteric sites provide an opportunity of finding agents with better drug-like properties and greater target specificity. Furthermore, allosteric modulators are better suited to maintaining the highly precise temporal and spatial aspects of glutamatergic synaptic transmission. Herein, we review neuropathological and genomic/genetic evidence underscoring the importance of glutamate synaptic dysfunction in the etiology of schizophrenia and make a case for allosteric targets for therapeutic intervention. We review progress in identifying allosteric modulators of AMPA receptors, NMDA receptors, and metabotropic glutamate receptors, all with the aim of restoring physiological glutamatergic synaptic transmission. Challenges remain given the complexity of schizophrenia and the difficulty in studying cognition in animals and humans. Nonetheless, important compounds have emerged from these efforts and promising preclinical and variable clinical validation has been achieved.

Menniti, Frank S.; Lindsley, Craig W.; Conn, P. Jeffrey; Pandit, Jayvardhan; Zagouras, Panayiotis; Volkmann, Robert A.

2013-01-01

165

Early fragmentation in the adaptive voter model on directed networks.  

PubMed

We consider voter dynamics on a directed adaptive network with fixed out-degree distribution. A transition between an active phase and a fragmented phase is observed. This transition is similar to the undirected case if the networks are sufficiently dense and have a narrow out-degree distribution. However, if a significant number of nodes with low out degree is present, then fragmentation can occur even far below the estimated critical point due to the formation of self-stabilizing structures that nucleate fragmentation. This process may be relevant for fragmentation in current political opinion formation processes. PMID:22680538

Zschaler, Gerd; Böhme, Gesa A; Seißinger, Michael; Huepe, Cristián; Gross, Thilo

2012-04-01

166

A Rule-based Detection of Functional Modules in Protein-Protein Interaction Networks  

Microsoft Academic Search

In the protein-protein interaction (PPI) network there are many functional modules, each involving several protein interactions to perform discrete functions. Pathways and protein complexes are the examples of the functional modules. In this paper, we propose a rule-based method for detecting the modules. The rule is expressed in terms of triples and operators between the triples. The former represents conceptual

Jongmin Park; Jaehun Choi; Jaedong Yang; Soo-Jun Park

2006-01-01

167

Detecting functional modules in the yeast protein-protein interaction network  

Microsoft Academic Search

Motivation: Identification of functional modules in protein interaction networksis a first step in understanding the organization anddynamics of cell functions. To ensure that the identified modules are biologically meaningful, network-partitioning algorithms should take into account notonlytopologicalfeaturesbutalsofunctionalrelationships,andiden- tified modules should be rigorously validated. Results: In this study we first integrate proteomics and microarray datasets and represent the yeast protein-protein interaction network

Jingchun Chen; Bo Yuan

2006-01-01

168

Evaluation of 4-Gbit\\/s optical fiber transmission distance with direct and external modulation  

Microsoft Academic Search

Transmission characteristics for a recently modulated measured distributed-feedbacked (DFB) laser and an externally modulated DFB laser using a Ti:LiNbO3, Mach-Zehnder modulator at 4 Gb\\/s are discussed. The transmission characteristics are estimated by an advanced eye-pattern analysis method. The maximum measured fiber dispersion with a directly modulated laser is 100 to 140 ps\\/nm when the chirp power penalty is 1 dB.

Tadashi Okiyama; Hiroshi Nishimoto; Izumi Yokota; Takashi Touge

1988-01-01

169

An analytic and experimental comparison of direct and external modulation in analog fiber-optic links  

Microsoft Academic Search

Analytic lumped-element small-signal models of directly and externally modulated analog fiber-optic links are derived. Incremental modulation efficiency is defined and used to compare the performances of these modulation techniques. In experiments to optimize link RF-to-RF gain and noise figure, the measurements obtained agreed with calculations to within ≈1 dB. The externally modulated link was operated with two different impedance matching

G. E. Betts; L. M. Johnson

1990-01-01

170

Nonlinear dynamics in directly modulated semiconductor ring lasers  

NASA Astrophysics Data System (ADS)

In this paper, we have theoretically studied the dynamical behavior of current modulated semiconductor ring lasers (SRLs). As we vary the amplitude and frequency of the modulation around a fixed bias current, difference dynamical states including periodic, quasi-periodic and chaotic states are found. As in other single mode semiconductor lasers, the modal intensities in an SRL present chaotic behavior for driving frequencies comparable to the relaxation oscillation frequency. In this regime the two counter-propagating modes vary in phase. However, for modulation frequencies significantly lower than the relaxation oscillation frequency, we reveal the existence of chaotic oscillations where the two counter-propagating modes are in anti-phase.

Kingni, S. Takougang; Van der Sande, G.; Gelens, L.; Danckaert, J.

2012-05-01

171

C-element: A New Clustering Algorithm to Find High Quality Functional Modules in PPI Networks  

PubMed Central

Graph clustering algorithms are widely used in the analysis of biological networks. Extracting functional modules in protein-protein interaction (PPI) networks is one such use. Most clustering algorithms whose focuses are on finding functional modules try either to find a clique like sub networks or to grow clusters starting from vertices with high degrees as seeds. These algorithms do not make any difference between a biological network and any other networks. In the current research, we present a new procedure to find functional modules in PPI networks. Our main idea is to model a biological concept and to use this concept for finding good functional modules in PPI networks. In order to evaluate the quality of the obtained clusters, we compared the results of our algorithm with those of some other widely used clustering algorithms on three high throughput PPI networks from Sacchromyces Cerevisiae, Homo sapiens and Caenorhabditis elegans as well as on some tissue specific networks. Gene Ontology (GO) analyses were used to compare the results of different algorithms. Each algorithm's result was then compared with GO-term derived functional modules. We also analyzed the effect of using tissue specific networks on the quality of the obtained clusters. The experimental results indicate that the new algorithm outperforms most of the others, and this improvement is more significant when tissue specific networks are used.

Ghasemi, Mahdieh; Rahgozar, Maseud; Bidkhori, Gholamreza; Masoudi-Nejad, Ali

2013-01-01

172

C-element: a new clustering algorithm to find high quality functional modules in PPI networks.  

PubMed

Graph clustering algorithms are widely used in the analysis of biological networks. Extracting functional modules in protein-protein interaction (PPI) networks is one such use. Most clustering algorithms whose focuses are on finding functional modules try either to find a clique like sub networks or to grow clusters starting from vertices with high degrees as seeds. These algorithms do not make any difference between a biological network and any other networks. In the current research, we present a new procedure to find functional modules in PPI networks. Our main idea is to model a biological concept and to use this concept for finding good functional modules in PPI networks. In order to evaluate the quality of the obtained clusters, we compared the results of our algorithm with those of some other widely used clustering algorithms on three high throughput PPI networks from Sacchromyces Cerevisiae, Homo sapiens and Caenorhabditis elegans as well as on some tissue specific networks. Gene Ontology (GO) analyses were used to compare the results of different algorithms. Each algorithm's result was then compared with GO-term derived functional modules. We also analyzed the effect of using tissue specific networks on the quality of the obtained clusters. The experimental results indicate that the new algorithm outperforms most of the others, and this improvement is more significant when tissue specific networks are used. PMID:24039752

Ghasemi, Mahdieh; Rahgozar, Maseud; Bidkhori, Gholamreza; Masoudi-Nejad, Ali

2013-01-01

173

A Control Plane Architecture for Mobile Free Space Optical Network and Directional RF MANETs  

Microsoft Academic Search

As the traffic demands for tactical military operations increase and operational scenarios depend increasingly on robust, high speed inter-domain communication and inter-theater data transfer, military networks will likely rely on directional networking technologies. Networks with free space optical (FSO) and directional RF links provide higher data rates, secure operation, and frequency reuse. Forming and maintaining the network with directional links

Anurag Dwivedi; Daniel J. Tebben; Harshavardhana Paramasiviah; A. Roger Hammons; Robert A. Nichols

2007-01-01

174

A theoretical and experimental comparison of directly and externally modulated fiber-optic links  

Microsoft Academic Search

Analytic models of directly and externally modulated fiber-optic links were derived and experimentally confirmed. The models were used to optimize the operating parameters of fiber-optic links. Experimental measurements on these optimized links indicated net incremental link power gains of +3 dB for direct modulation and +11 dB for external modulation. The implications of these optimizations for other measures of link

L. M. Johnson; G. E. Betts

1989-01-01

175

Identifying Modules in Complex Networks by a Graph-Theoretical Method and Its Application in Protein Interaction Networks  

NASA Astrophysics Data System (ADS)

Detecting community structure/modules in complex networks recently attracts increasing attention from various fields including mathematics, physics and biology. In this paper, we propose a method based on graph-theoretical clustering for identifying modularity structure in complex networks. Compared with the existing algorithms, this method, based on minimum spanning tree, has several advantages. For example, unlike many algorithms, this method is deterministic and not sensitive to the initialization. In addition, the method does not require a prior knowledge about the number of the modules. It can easily obtain the number of clusters by analyzing the edge weight distribution of minimum spanning tree. Moreover, this algorithm has computational compexity of polynomial-time with low order and can be used to deal with large-scale networks. Experimental results show that our method produces good results for real networks and can also uncover meaningful functional modules in protein interaction networks.

Wang, Rui-Sheng; Zhang, Shihua; Zhang, Xiang-Sun; Chen, Luonan

176

DTN-based free-space optical and directional RF networks  

Microsoft Academic Search

With the growth in demand for capacity from users in wireless networks and the scarcity of available RF spectrum, directional networks are expected to provide effective solutions. Directional RF antennas offer increased capacity over omni-directional antenna networks and some emerging highly-directional networks like free-space optical communication (FSOC) systems will be an important part of future networking infrastructures. The ability to

Robert A. Nichols; A. Roger Hammons Jr

2008-01-01

177

40-Gb/s directly-modulated photonic crystal lasers under optical injection-locking  

NASA Astrophysics Data System (ADS)

CMOS integrated circuits (IC) usually requires high data bandwidth for off-chip input/output (I/O) data transport with sufficiently low power consumption in order to overcome pin-count limitation. In order to meet future requirements of photonic network interconnect, we propose an optical output device based on an optical injection-locked photonic crystal (PhC) laser to realize low-power and high-speed off-chip interconnects. This device enables ultralow-power operation and is suitable for highly integrated photonic circuits because of its strong light-matter interaction in the PhC nanocavity and ultra-compact size. High-speed operation is achieved by using the optical injection-locking (OIL) technique, which has been shown as an effective means to enhance modulation bandwidth beyond the relaxation resonance frequency limit. In this paper, we report experimental results of the OIL-PhC laser under various injection conditions and also demonstrate 40-Gb/s large-signal direct modulation with an ultralow energy consumption of 6.6 fJ/bit.

Chen, Chin-Hui; Takeda, Koji; Shinya, Akihiko; Nozaki, Kengo; Sato, Tomonari; Kawaguchi, Yoshihiro; Notomi, Masaya; Matsuo, Shinji

2011-08-01

178

Integrated Brain Circuits: Astrocytic Networks Modulate Neuronal Activity and Behavior  

PubMed Central

The past decade has seen an explosion of research on roles of neuron-astrocyte interactions in the control of brain function. We highlight recent studies performed on the tripartite synapse, the structure consisting of pre- and postsynaptic elements of the synapse and an associated astrocytic process. Astrocytes respond to neuronal activity and neuro-transmitters, through the activation of metabotropic receptors, and can release the gliotransmitters ATP, D-serine, and glutamate, which act on neurons. Astrocyte-derived ATP modulates synaptic transmission, either directly or through its metabolic product adenosine. D-serine modulates NMDA receptor function, whereas glia-derived glutamate can play important roles in relapse following withdrawal from drugs of abuse. Cell type–specific molecular genetics has allowed a new level of examination of the function of astrocytes in brain function and has revealed an important role of these glial cells that is mediated by adenosine accumulation in the control of sleep and in cognitive impairments that follow sleep deprivation.

Halassa, Michael M.; Haydon, Philip G.

2011-01-01

179

Direct DPSK modulation of chirp-managed laser as cost-effective downstream transmitter for symmetrical 10-Gbit/s WDM PONs.  

PubMed

This paper proposes the use of chirp-managed lasers (CML) as cost-effective downstream (DS) transmitters for next generation access networks. As the laser bandwidth is as high as 10 GHz, the CML could be directly modulated at 10 Gbit/s for downstream transmission in future wavelength division multiplexing passive optical networks (WDM PON). The laser adiabatic chirp, which is the main drawback limiting the transmission performance of directly modulated lasers, is now utilized to generate phase-shift keying (PSK) modulation format by direct modulation. At the user premise, the wavelength reuse technique based on reflective colorless upstream transmitter is applied. The optical network unit (ONU) reflects and orthogonally remodulates the received light with upstream data. A full-duplex transmission with symmetrical 10-Gbit/s bandwidth is demonstrated. Bit-error-rate measurement showed that optical power budgets of 29 dB at BER of 10(-9) or of 36 dB at BER of 10(-3) could be obtained with direct phase-shift-keying modulation of CML which proves that the proposed solution is a viable candidate for future WDM-PONs. PMID:23262890

Le, Quang Trung; Emsia, Ali; Briggmann, Dieter; Küppers, Franko

2012-12-10

180

A new kind of node centrality in directed weighted networks based on the demands of network clients  

NASA Astrophysics Data System (ADS)

To reveal the correlation between the demands of network clients and the safety and robustness of real-world networks, we propose client demand centrality (CDC) in order to quantify the contributions of nodes in the transportation processes in directed weighted networks. CDC is defined by incorporating not only the topology and dynamics of the network but also the demands of network clients. The centrality measures node potential to ensure acceptable and successful transportation for clients and does quite well in distinguishing the roles of different nodes in the network. Simulation results show that node CDC has Gaussian distributions in directed networks with different link weight distributions, and the expected value of the Gaussian distribution increases from negative to positive with a decrease of the client demand. In particular, for directed scale-free networks with the scale-free link weight distribution, the network CDC is only correlated with the degree structure of the network when the client demand is large.

Ma, Lili; Jiang, Xin; Zhang, Zhanli; Tang, Shaoting; Zheng, Zhiming

2011-08-01

181

Standard Chinese: A Modular Approach. Student Workbook. Module 3: Money; Module 4: Directions.  

ERIC Educational Resources Information Center

Texts in spoken Standard Chinese were developed to improve and update Chinese materials and to reflect current usage in Beijing and Taipei. The focus is on communicating in Chinese in practical situations. The overall course is organized into 10 situational modules, student workbooks, and resource modules. This workbook covers the money and…

Defense Language Inst., Monterey, CA.

182

Integrated Module and Gene-Specific Regulatory Inference Implicates Upstream Signaling Networks  

PubMed Central

Regulatory networks that control gene expression are important in diverse biological contexts including stress response and development. Each gene's regulatory program is determined by module-level regulation (e.g. co-regulation via the same signaling system), as well as gene-specific determinants that can fine-tune expression. We present a novel approach, Modular regulatory network learning with per gene information (MERLIN), that infers regulatory programs for individual genes while probabilistically constraining these programs to reveal module-level organization of regulatory networks. Using edge-, regulator- and module-based comparisons of simulated networks of known ground truth, we find MERLIN reconstructs regulatory programs of individual genes as well or better than existing approaches of network reconstruction, while additionally identifying modular organization of the regulatory networks. We use MERLIN to dissect global transcriptional behavior in two biological contexts: yeast stress response and human embryonic stem cell differentiation. Regulatory modules inferred by MERLIN capture co-regulatory relationships between signaling proteins and downstream transcription factors thereby revealing the upstream signaling systems controlling transcriptional responses. The inferred networks are enriched for regulators with genetic or physical interactions, supporting the inference, and identify modules of functionally related genes bound by the same transcriptional regulators. Our method combines the strengths of per-gene and per-module methods to reveal new insights into transcriptional regulation in stress and development.

Roy, Sushmita; Lagree, Stephen; Hou, Zhonggang; Thomson, James A.; Stewart, Ron; Gasch, Audrey P.

2013-01-01

183

Low chirp observed in directly modulated quantum dot lasers  

Microsoft Academic Search

We have examined the dynamic properties of high-aspect-ratio InAs-quantum-dot (QD) lasers at room temperature. A novel characteristic of low chirp in the lasing wavelength under 1-GHz current modulation was found in the quantum dot lasers. This is more than one order of magnitude less than the typical chirp (0.2-nm) found in a conventional quantum well laser that we used as

Hideaki Saito; Kenichi Nishi; Akio Kamei; Shigeo Sugou

2000-01-01

184

Direct inversion methods for spectral amplitude modulation of femtosecond pulses.  

PubMed

In the present work, we applied an amplitude-spatial light modulator to shape the spectral amplitude of femtosecond pulses in a single step, without an iterative algorithm, by using an inversion method defined as the generalized retardance function. Additionally, we also present a single step method to shape the intensity profile defined as the influence matrix. Numerical and experimental results are presented for both methods. PMID:24784591

Delgado-Aguillón, Jesús; Garduño-Mejía, Jesús; López-Téllez, Juan Manuel; Bruce, Neil C; Rosete-Aguilar, Martha; Román-Moreno, Carlos Jesús; Ortega-Martínez, Roberto

2014-04-01

185

Asymptotic theory of instabilities in directly modulated semiconductor lasers  

Microsoft Academic Search

Summary form only given. High-speed modulation of laser diodes is important for realizing large-capacity information transmission and ultrafast optical-processing systems. Recently a great deal of interest has been generated by the potential to use lasers running in chaotic regime as the carriers of information in a secure chaotic communication scheme. We have undertaken analytical and numerical calculations in the framework

C. Mayol; S. I. Turovets; R. Toral; C. R. Mirasso; L. Pesquera

2000-01-01

186

Ultrafast direct modulation of a single-mode photonic crystal nanocavity light-emitting diode  

Microsoft Academic Search

Low-power and electrically controlled optical sources are vital for next generation optical interconnect systems to meet strict energy demands. Current optical transmitters consisting of high-threshold lasers plus external modulators consume far too much power to be competitive with future electrical interconnects. Here we demonstrate a directly modulated photonic crystal nanocavity light-emitting diode (LED) with 10 GHz modulation speed and less

Gary Shambat; Bryan Ellis; Arka Majumdar; Jan Petykiewicz; Marie A. Mayer; Tomas Sarmiento; James Harris; Eugene E. Haller; Jelena Vu?kovi?

2011-01-01

187

Identification of susceptibility modules for coronary artery disease using a genome wide integrated network analysis.  

PubMed

Although recent genome-wide association studies (GWAS) have identified a handful of variants with best significance for coronary artery disease (CAD), it remains a challenge to summarize the underlying biological information from the abundant genotyping data. Here, we propose an integrated network analysis that effectively combines GWAS genotyping dataset, protein-protein interaction (PPI) database, literature and pathway annotation information. This three-step approach was illustrated for a comprehensive network analysis of CAD as the following. First, a network was constructed from PPI database and CAD seed genes mined from the available literatures. Then, susceptibility network modules were captured from the results of gene-based association tests. Finally, susceptibility modules were annotated with potential mechanisms for CAD via the KEGG pathway database. Our network analysis identified four susceptibility modules for CAD including a complex module that consisted of 15 functional inter-connected sub-modules, AGPAT3-AGPAT4-PPAP2B module, ITGA11-ITGB1 module and EMCN-SELL module. MAPK10 and COL4A2 among the top-scored focal adhesion pathway related module were the most significant genes (MAPK10: OR=32.5, P=3.5 × 10(-11); COL4A2: OR=2.7, P=2.8 × 10(-10)). The significance of the two genes were further validated by other two gene-based association tests (MAPK10: P=0.009 and 0.007; COL4A2: P=0.001 and 0.023) and another independent GWAS dataset (MAPK10: P=0.001; COL4A2: P=0.0004). Furthermore, 34 out of 44 previously reported CAD susceptibility genes were captured by our CAD PPI network and 17 of them were also significant genes. The susceptibility modules identified in our study might provide novel clues for the clarification of CAD pathogenesis in the future. PMID:23994195

Duan, Shiwei; Luo, Xuhong; Dong, Changzheng

2013-12-01

188

Signal to Noise Ratios of Pulsed and Sinewave Modulated Direct Detection Lidar for IPDA Measurements  

NASA Technical Reports Server (NTRS)

The signal-to-noise ratios have been derived for IPDA lidar using a direct detection receiver for both pulsed and sinewave laser modulation techniques, and the results and laboratory measurements are presented

Sun, Xiaoli; Abshire, James B.

2011-01-01

189

Direct modulation of semiconductor lasers at f>10 GHz by low-temperature operation  

SciTech Connect

Using a 175-..mu..m-long buried-heterostructure laser fabricated on a semi-insulating substrate operating at -50 /sup 0/C, a direct amplitude modulation bandwidth in excess of 10 GHz has been achieved.

Lau, K.Y.; Harder, C.; Yariv, A.

1984-02-01

190

Myosin lever arm directs collective motion on cellular actin network.  

PubMed

The molecular motor myosin teams up to drive muscle contraction, membrane traffic, and cell division in biological cells. Myosin function in cells emerges from the interaction of multiple motors tethered to a scaffold, with surrounding actin filaments organized into 3D networks. Despite the importance of myosin function, the influence of intermotor interactions on collective motion remains poorly understood. In this study, we used precisely engineered myosin assemblies to examine emergence in collective myosin movement. We report that tethering multiple myosin VI motors, but not myosin V motors, modifies their movement trajectories on keratocyte actin networks. Single myosin V and VI dimers display similar skewed trajectories, albeit in opposite directions, when traversing the keratocyte actin network. In contrast, tethering myosin VI motors, but not myosin V motors, progressively straightens the trajectories with increasing myosin number. Trajectory shape of multimotor scaffolds positively correlates with the stiffness of the myosin lever arm. Swapping the flexible myosin VI lever arm for the relatively rigid myosin V lever increases trajectory skewness, and vice versa. A simplified model of coupled motor movement demonstrates that the differences in flexural rigidity of the two myosin lever arms is sufficient to account for the differences in observed behavior of groups of myosin V and VI motors. In accordance with this model trajectory, shapes for scaffolds containing both myosin V and VI are dominated by the myosin with a stiffer lever arm. Our findings suggest that structural features unique to each myosin type may confer selective advantages in cellular functions. PMID:24591646

Hariadi, Rizal F; Cale, Mario; Sivaramakrishnan, Sivaraj

2014-03-18

191

A 0.7-3 GHz GaAs QPSK\\/QAM direct modulator  

Microsoft Academic Search

A single chip I\\/Q direct modulator for use in digital radio links is presented. This device translates directly the phase and quadrature baseband signals to a microwave frequency that can be chosen between 700 MHz and 3 GHz avoiding the use of IF circuits. It is able to generate any type of digital modulation as QPSK, n-PSK, n-QAM, GMSK, etc.,

Angel Boveda; J. I. Alonso

1993-01-01

192

Design of an LTCC integrated tri-band direct conversion receiver front-end module  

Microsoft Academic Search

This paper presents the results of a front-end receiver module integrating GSM\\/DCS\\/PCS band select functions and a direct conversion IC on a low temperature cofired ceramic (LTCC) substrate. The front-end-module (FEM) integrated a SP3T GaAs PHEMT switch for band selection, three SAW filters for pre-selection, and a direct conversion IC for down conversion of the RF signal. Integrated passives included

R. Lucero; A. Pavio; D. Penunuri; J. Bost

2002-01-01

193

Modulation of cortical-subcortical networks in Parkinson's disease by applied field effects  

PubMed Central

Studies suggest that endogenous field effects may play a role in neuronal oscillations and communication. Non-invasive transcranial electrical stimulation with low-intensity currents can also have direct effects on the underlying cortex as well as distant network effects. While Parkinson’s disease (PD) is amenable to invasive neuromodulation in the basal ganglia by deep brain stimulation (DBS), techniques of non-invasive neuromodulation like transcranial direct current stimulation (tDCS) and transcranial alternating current stimulation (tACS) are being investigated as possible therapies. tDCS and tACS have the potential to influence the abnormal cortical-subcortical network activity that occurs in PD through sub-threshold changes in cortical excitability or through entrainment or disruption of ongoing rhythmic cortical activity. This may allow for the targeting of specific features of the disease involving abnormal oscillatory activity, as well as the enhancement of potential cortical compensation for basal ganglia dysfunction and modulation of cortical plasticity in neurorehabilitation. However, little is currently known about how cortical stimulation will affect subcortical structures, the size of any effect, and the factors of stimulation that will influence these effects.

Hess, Christopher W.

2013-01-01

194

Constraint-based Approach to Discovery of Inter Module Dependencies in Modular Bayesian Networks  

Microsoft Academic Search

This paper introduces an information theoretic ap- proach to verification of modular causal probabilistic models. We assume systems which are gradually ex- tended by adding new functional modules, each hav- ing a limited domain knowledge captured by a local Bayesian network. Different modules originate fromin- dependent design processes. We assume that the local models are correct, which, however does not

Patrick De Oude; Gregor Pavlin

2009-01-01

195

A novel functional module detection algorithm for protein-protein interaction networks  

Microsoft Academic Search

BACKGROUND: The sparse connectivity of protein-protein interaction data sets makes identification of functional modules challenging. The purpose of this study is to critically evaluate a novel clustering technique for clustering and detecting functional modules in protein-protein interaction networks, termed STM. RESULTS: STM selects representative proteins for each cluster and iteratively refines clusters based on a combination of the signal transduced

Woochang Hwang; Young-rae Cho; Aidong Zhang; Murali Ramanathan

2006-01-01

196

Wavelength channel data rewrite using saturated SOA modulator for WDM networks with centralized light sources  

Microsoft Academic Search

This paper describes a method for realizing the efficient utilization of wavelength resources in wavelength-division multiplexing networks with centralized light sources. Using a deeply saturated semiconductor optical amplifier (SOA) modulator located in a remote node (RN), we erase the data on a downstream signal with a low extinction ratio and modulate it with new data to generate an upstream signal.

Hiroki Takesue; Toshihiko Sugie

2003-01-01

197

Network based elucidation of drug response: from modulators to targets  

PubMed Central

Network-based drug discovery aims at harnessing the power of networks to investigate the mechanism of action of existing drugs, or new molecules, in order to identify innovative therapeutic treatments. In this review, we describe some of the most recent advances in the field of network pharmacology, starting with approaches relying on computational models of transcriptional networks, then moving to protein and signaling network models and concluding with “drug networks”. These networks are derived from different sources of experimental data, or literature-based analysis, and provide a complementary view of drug mode of action. Molecular and drug networks are powerful integrated computational and experimental approaches that will likely speed up and improve the drug discovery process, once fully integrated into the academic and industrial drug discovery pipeline.

2013-01-01

198

Community analysis in directed networks: In-, out-, and pseudocommunities  

NASA Astrophysics Data System (ADS)

When analyzing important classes of complex interconnected systems, link directionality can hardly be neglected if a precise and effective picture of the structure and function of the system is needed. If community analysis is performed, the notion of "community" itself is called into question, since the property of having a comparatively looser external connectivity could refer to the inbound or outbound links only or to both categories. In this paper, we introduce the notions of in-, out-, and in-/out-community in order to correctly classify the directedness of the interaction of a subnetwork with the rest of the system. Furthermore, we extend the scope of community analysis by introducing the notions of in-, out-, and in-/out-pseudocommunity. They are subnetworks having strong internal connectivity but also important interactions with the rest of the system, the latter taking place by means of a minority of its nodes only. The various types of (pseudo-)communities are qualified and distinguished by a suitable set of indicators and, on a given network, they can be discovered by using a "local" searching algorithm. The application to a broad set of benchmark networks and real-world examples proves that the proposed approach is able to effectively disclose the different types of structures above defined and to usefully classify the directionality of their interactions with the rest of the system.

Landi, Pietro; Piccardi, Carlo

2014-01-01

199

Analysis of Synchronization Between Two Modules of Pulse Neural Networks with Excitatory and Inhibitory Connections  

Microsoft Academic Search

To study the synchronized oscillations among distant neurons in the visual cortex, the synchronization be- tween two modules of pulse neural networks was ana- lyzed using the phase response function. It was found that the inter-module connections from excitatory to excitatory ensembles tend to stabilize the anti-phase synchronization, and that the inter-module connections from excitatory to inhibitory ensembles tend to

Takashi Kanamaru

2006-01-01

200

Protein complexes and functional modules in molecular networks  

Microsoft Academic Search

Proteins, nucleic acids, and small molecules form a dense network of molecular interactions in a cell. Molecules are nodes of this network, and the interactions between them are edges. The architecture of molecular networks can reveal important principles of cellular organization and function, similarly to the way that protein structure tells us about the function and organization of a protein.

Victor Spirin; Leonid A. Mirny

2003-01-01

201

Graph Partitioning Method for Functional Module Detections of Protein Interaction Network  

Microsoft Academic Search

Study on topology structure of protein interaction network has been suggested as a potential effort to discover biological functions and cellular mechanisms at systems level. In this work, we introduced a graph partitioning method to partition protein interaction network into several clusters of interacting proteins that share similar functions called functional modules. Our proposed method encompasses three major steps which

Afnizanfaizal Abdullah; Safaai Deris; Siti Zaiton Mohd Hashim; Hamimah Mohd Jamil

2009-01-01

202

Effect of Modulated Alternating and Direct Current Iontophoresis on Transdermal Delivery of Lidocaine Hydrochloride  

PubMed Central

The objective of this study was to investigate the iontophoretic delivery of lidocaine hydrochloride through porcine skin and to compare the effects of modulated alternating and direct current iontophoresis. Continuous and modulated iontophoresis was applied for one hour and two hours (0-1?h and 4-5th?h) using a 1%?w/v solution of lidocaine hydrochloride. Tape stripping was done to quantify the amount of drug permeated into stratum corneum and skin extraction studies were performed to determine the amount of drug in stripped skin. Receptor was sampled and analyzed over predefined time periods. The amount of lidocaine delivered across porcine skin after modulated direct current iontophoresis for 2?h was 1069.87 ± 120.03??g/sq·cm compared to 744.81 ± 125.41??g/sq·cm after modulated alternating current iontophoresis for 2?h. Modulated direct current iontophoresis also enhanced lidocaine delivery by twelvefold compared to passive delivery as 91.27 ± 18.71??g/sq·cm of lidocaine was delivered after passive delivery. Modulated iontophoresis enhanced the delivery of lidocaine hydrochloride across porcine skin compared to the passive delivery. Modulated alternating current iontophoresis for duration of 2?h at frequency of 1?kHz was found to be comparable to the continuous direct current iontophoresis for 1?h.

Banga, Ajay K.

2014-01-01

203

ModuleRole: A Tool for Modulization, Role Determination and Visualization in Protein-Protein Interaction Networks  

PubMed Central

Rapidly increasing amounts of (physical and genetic) protein-protein interaction (PPI) data are produced by various high-throughput techniques, and interpretation of these data remains a major challenge. In order to gain insight into the organization and structure of the resultant large complex networks formed by interacting molecules, using simulated annealing, a method based on the node connectivity, we developed ModuleRole, a user-friendly web server tool which finds modules in PPI network and defines the roles for every node, and produces files for visualization in Cytoscape and Pajek. For given proteins, it analyzes the PPI network from BioGRID database, finds and visualizes the modules these proteins form, and then defines the role every node plays in this network, based on two topological parameters Participation Coefficient and Z-score. This is the first program which provides interactive and very friendly interface for biologists to find and visualize modules and roles of proteins in PPI network. It can be tested online at the website http://www.bioinfo.org/modulerole/index.php, which is free and open to all users and there is no login requirement, with demo data provided by “User Guide” in the menu Help. Non-server application of this program is considered for high-throughput data with more than 200 nodes or user’s own interaction datasets. Users are able to bookmark the web link to the result page and access at a later time. As an interactive and highly customizable application, ModuleRole requires no expert knowledge in graph theory on the user side and can be used in both Linux and Windows system, thus a very useful tool for biologist to analyze and visualize PPI networks from databases such as BioGRID. Availability ModuleRole is implemented in Java and C, and is freely available at http://www.bioinfo.org/modulerole/index.php. Supplementary information (user guide, demo data) is also available at this website. API for ModuleRole used for this program can be obtained upon request.

Li, GuiPeng; Li, Ming; Zhang, YiWei; Wang, Dong; Li, Rong; Guimera, Roger; Gao, Juntao Tony; Zhang, Michael Q.

2014-01-01

204

Infant-Directed Speech Is Modulated by Infant Feedback  

ERIC Educational Resources Information Center

When mothers engage in infant-directed (ID) speech, their voices change in a number of characteristic ways, including adopting a higher overall pitch. Studies have examined these acoustical cues and have tested infants' preferences for ID speech. However, little is known about how these cues change with maternal sensitivity to infant feedback in…

Smith, Nicholas A.; Trainor, Laurel J.

2008-01-01

205

Identification of responsive gene modules by network-based gene clustering and extending: application to inflammation and angiogenesis  

Microsoft Academic Search

BACKGROUND: Cell responses to environmental stimuli are usually organized as relatively separate responsive gene modules at the molecular level. Identification of responsive gene modules rather than individual differentially expressed (DE) genes will provide important information about the underlying molecular mechanisms. Most of current methods formulate module identification as an optimization problem: find the active sub-networks in the genome-wide gene network

Jin Gu; Yang Chen; Shao Li; Yanda Li

2010-01-01

206

Functional Influence-Based Approach to Identify Overlapping Modules in Biological Networks  

Microsoft Academic Search

\\u000a The inherent, dynamic, and structural behaviors of complex biological networks in a topological perspective have been widely\\u000a studied recently. These studies have attempted to discover hidden functional knowledge on a system level since biological\\u000a networks provide insights into the underlying mechanisms of biological processes and molecular functions within a cell. Functional\\u000a modules can be identified from biological networks as a

Young-Rae Cho; Aidong Zhang

207

Power consumption and throughput in mobile ad hoc networks using directional antennas  

Microsoft Academic Search

We present medium access control (MAC) protocols for mobile ad hoc networks that utilize directional antennas. The use of directional antennas in place of traditional omnidirectional antennas reduces interference and thereby improves the throughput performance of the network. An additional advantage of using directional antennas is due to its higher gain from its directivity, which can be utilized to reduce

Asis Nasipuri; Kai Li; Uma Reddy Sappidi

2002-01-01

208

Semantic integration to identify overlapping functional modules in protein interaction networks  

PubMed Central

Background The systematic analysis of protein-protein interactions can enable a better understanding of cellular organization, processes and functions. Functional modules can be identified from the protein interaction networks derived from experimental data sets. However, these analyses are challenging because of the presence of unreliable interactions and the complex connectivity of the network. The integration of protein-protein interactions with the data from other sources can be leveraged for improving the effectiveness of functional module detection algorithms. Results We have developed novel metrics, called semantic similarity and semantic interactivity, which use Gene Ontology (GO) annotations to measure the reliability of protein-protein interactions. The protein interaction networks can be converted into a weighted graph representation by assigning the reliability values to each interaction as a weight. We presented a flow-based modularization algorithm to efficiently identify overlapping modules in the weighted interaction networks. The experimental results show that the semantic similarity and semantic interactivity of interacting pairs were positively correlated with functional co-occurrence. The effectiveness of the algorithm for identifying modules was evaluated using functional categories from the MIPS database. We demonstrated that our algorithm had higher accuracy compared to other competing approaches. Conclusion The integration of protein interaction networks with GO annotation data and the capability of detecting overlapping modules substantially improve the accuracy of module identification.

Cho, Young-Rae; Hwang, Woochang; Ramanathan, Murali; Zhang, Aidong

2007-01-01

209

Identifying Modules in Complex Networks by a Graph-Theoretical Method and Its Application in Protein Interaction Networks  

Microsoft Academic Search

Detecting community structure\\/modules in complex networks recently attracts increasing attention from various fields including\\u000a mathematics, physics and biology. In this paper, we propose a method based on graph-theoretical clustering for identifying\\u000a modularity structure in complex networks. Compared with the existing algorithms, this method, based on minimum spanning tree,\\u000a has several advantages. For example, unlike many algorithms, this method is deterministic

Rui-Sheng Wang; Shihua Zhang; Xiang-Sun Zhang; Luonan Chen

2007-01-01

210

Reconstructing differentially co-expressed gene modules and regulatory networks of soybean cells  

PubMed Central

Background Current experimental evidence indicates that functionally related genes show coordinated expression in order to perform their cellular functions. In this way, the cell transcriptional machinery can respond optimally to internal or external stimuli. This provides a research opportunity to identify and study co-expressed gene modules whose transcription is controlled by shared gene regulatory networks. Results We developed and integrated a set of computational methods of differential gene expression analysis, gene clustering, gene network inference, gene function prediction, and DNA motif identification to automatically identify differentially co-expressed gene modules, reconstruct their regulatory networks, and validate their correctness. We tested the methods using microarray data derived from soybean cells grown under various stress conditions. Our methods were able to identify 42 coherent gene modules within which average gene expression correlation coefficients are greater than 0.8 and reconstruct their putative regulatory networks. A total of 32 modules and their regulatory networks were further validated by the coherence of predicted gene functions and the consistency of putative transcription factor binding motifs. Approximately half of the 32 modules were partially supported by the literature, which demonstrates that the bioinformatic methods used can help elucidate the molecular responses of soybean cells upon various environmental stresses. Conclusions The bioinformatics methods and genome-wide data sources for gene expression, clustering, regulation, and function analysis were integrated seamlessly into one modular protocol to systematically analyze and infer modules and networks from only differential expression genes in soybean cells grown under stress conditions. Our approach appears to effectively reduce the complexity of the problem, and is sufficiently robust and accurate to generate a rather complete and detailed view of putative soybean gene transcription logic potentially underlying the responses to the various environmental challenges. The same automated method can also be applied to reconstruct differentially co-expressed gene modules and their regulatory networks from gene expression data of any other transcriptome.

2012-01-01

211

Fabricating fiber Bragg gratings using phase modulated direct UV writing  

NASA Astrophysics Data System (ADS)

The authors present a direct UV writing approach to fabricate fiber Bragg gratings (FBGs) and gratings in photolithographic waveguides. The technique uses two coherent UV beams, which are focused to a small spot (~7?m diameter) at the point at which they overlap. The resulting interference pattern at the foci consists of fringes which are used to define several grating planes per exposure, giving greater design flexibility and a significantly larger accessible spectral range compared to traditional approaches. The typical index contrast during grating fabrication is observed to be 4.7×10-3, at writing speeds of 8 mm/min.

Holmes, C.; Sima, C.; Mennea, P. L.; Carpenter, L. G.; Gates, J. C.; Smith, P. G. R.

2014-03-01

212

Control of bistability in a directly modulated semiconductor laser using delayed optoelectronic feedback  

Microsoft Academic Search

We show numerically that direct delayed optoelectronic feedback can suppress hysteresis and bistability in a directly modulated semiconductor laser. The simulation of a laser with feedback is performed for a considerable range of feedback strengths and delays and the corresponding values for the areas of the hysteresis loops are calculated. It is shown that the hysteresis loop completely vanishes for

S. Rajesh; V. M. Nandakumaran

2006-01-01

213

Using directed phylogenetic networks to retrace species dispersal history.  

PubMed

Methods designed for inferring phylogenetic trees have been widely applied to reconstruct biogeographic history. Because traditional phylogenetic methods used in biogeographic reconstruction are based on trees rather than networks, they follow the strict assumption in which dispersal among geographical units have occurred on the basis of single dispersal routes across regions and are, therefore, incapable of modelling multiple alternative dispersal scenarios. The goal of this study is to describe a new method that allows for retracing species dispersal by means of directed phylogenetic networks obtained using a horizontal gene transfer (HGT) detection method as well as to draw parallels between the processes of HGT and biogeographic reconstruction. In our case study, we reconstructed the biogeographic history of the postglacial dispersal of freshwater fishes in the Ontario province of Canada. This case study demonstrated the utility and robustness of the new method, indicating that the most important events were south-to-north dispersal patterns, as one would expect, with secondary faunal interchange among regions. Finally, we showed how our method can be used to explore additional questions regarding the commonalities in dispersal history patterns and phylogenetic similarities among species. PMID:22491069

Layeghifard, Mehdi; Peres-Neto, Pedro R; Makarenkov, Vladimir

2012-07-01

214

A 45nm low-power SAW-less WCDMA transmit modulator using direct quadrature voltage modulation  

Microsoft Academic Search

To address the low-noise low-power requirement of the WCDMA transmitter this paper describes an innovative approach using direct quadrature voltage modulation via a passive voltage mixer driven by a 25%-duty-cycle LO. As shown in Fig. 6.5.2, first the IF l\\/Q voltage inputs are filtered by the passive LPF to lower the far-out noise. By switching on\\/off the transistors M1 to

Xin He; Jan van Sinderen

2009-01-01

215

Cartography of complex networks: modules and universal roles  

Microsoft Academic Search

Integrative approaches to the study of complex systems demand that one knows the manner in which the parts comprising the system are connected. The structure of the complex network defining the interactions provides insight into the function and evolution of the components of the system. Unfortunately, the large size and intricacy of these networks implies that such insight is usually

Roger Guimerà; Luís A Nunes Amaral

2005-01-01

216

Spatially resolved non-invasive chemical stimulation for modulation of signalling in reconstructed neuronal networks  

PubMed Central

Functional coupling of reconstructed neuronal networks with microelectronic circuits has potential for the development of bioelectronic devices, pharmacological assays and medical engineering. Modulation of the signal processing properties of on-chip reconstructed neuronal networks is an important aspect in such applications. It may be achieved by controlling the biochemical environment, preferably with cellular resolution. In this work, we attempt to design cell–cell and cell–medium interactions in confined geometries with the aim to manipulate non-invasively the activity pattern of an individual neuron in neuronal networks for long-term modulation. Therefore, we have developed a biohybrid system in which neuronal networks are reconstructed on microstructured silicon chips and interfaced to a microfluidic system. A high degree of geometrical control over the network architecture and alignment of the network with the substrate features has been achieved by means of aligned microcontact printing. Localized non-invasive on-chip chemical stimulation of micropatterned rat cortical neurons within a network has been demonstrated with an excitatory neurotransmitter glutamate. Our system will be useful for the investigation of the influence of localized chemical gradients on network formation and long-term modulation.

Mourzina, Yulia; Steffen, Alfred; Kaliaguine, Dmitri; Wolfrum, Bernhard; Schulte, Petra; Bocker-Meffert, Simone; Offenhausser, Andreas

2005-01-01

217

Efficient and accurate greedy search methods for mining functional modules in protein interaction networks  

PubMed Central

Background Most computational algorithms mainly focus on detecting highly connected subgraphs in PPI networks as protein complexes but ignore their inherent organization. Furthermore, many of these algorithms are computationally expensive. However, recent analysis indicates that experimentally detected protein complexes generally contain Core/attachment structures. Methods In this paper, a Greedy Search Method based on Core-Attachment structure (GSM-CA) is proposed. The GSM-CA method detects densely connected regions in large protein-protein interaction networks based on the edge weight and two criteria for determining core nodes and attachment nodes. The GSM-CA method improves the prediction accuracy compared to other similar module detection approaches, however it is computationally expensive. Many module detection approaches are based on the traditional hierarchical methods, which is also computationally inefficient because the hierarchical tree structure produced by these approaches cannot provide adequate information to identify whether a network belongs to a module structure or not. In order to speed up the computational process, the Greedy Search Method based on Fast Clustering (GSM-FC) is proposed in this work. The edge weight based GSM-FC method uses a greedy procedure to traverse all edges just once to separate the network into the suitable set of modules. Results The proposed methods are applied to the protein interaction network of S. cerevisiae. Experimental results indicate that many significant functional modules are detected, most of which match the known complexes. Results also demonstrate that the GSM-FC algorithm is faster and more accurate as compared to other competing algorithms. Conclusions Based on the new edge weight definition, the proposed algorithm takes advantages of the greedy search procedure to separate the network into the suitable set of modules. Experimental analysis shows that the identified modules are statistically significant. The algorithm can reduce the computational time significantly while keeping high prediction accuracy.

2012-01-01

218

Identification of functional hubs and modules by converting interactome networks into hierarchical ordering of proteins  

PubMed Central

Background Protein-protein interactions play a key role in biological processes of proteins within a cell. Recent high-throughput techniques have generated protein-protein interaction data in a genome-scale. A wide range of computational approaches have been applied to interactome network analysis for uncovering functional organizations and pathways. However, they have been challenged because ofcomplex connectivity. It has been investigated that protein interaction networks are typically characterized by intrinsic topological features: high modularity and hub-oriented structure. Elucidating the structural roles of modules and hubs is a critical step in complex interactome network analysis. Results We propose a novel approach to convert the complex structure of an interactome network into hierarchical ordering of proteins. This algorithm measures functional similarity between proteins based on the path strength model, and reveals a hub-oriented tree structure hidden in the complex network. We score hub confidence and identify functional modules in the tree structure of proteins, retrieved by our algorithm. Our experimental results in the yeast protein interactome network demonstrate that the selected hubs are essential proteins for performing functions. In network topology, they have a role in bridging different functional modules. Furthermore, our approach has high accuracy in identifying functional modules hierarchically distributed. Conclusions Decomposing, converting, and synthesizing complex interaction networks are fundamental tasks for modeling their structural behaviors. In this study, we systematically analyzed complex interactome network structures for retrievingfunctional information. Unlike previous hierarchical clustering methods, this approach dynamically explores the hierarchical structure of proteins in a global view. It is well-applicable to the interactome networks in high-level organisms because of its efficiency and scalability.

2010-01-01

219

Electroptic Polymer Linear Modulators Based on Multiple-Domain Y-Fed Directional Coupler  

Microsoft Academic Search

We developed an analytical method to optimize the design of Y-fed direction couplers at large modulation depth from 10% to 50%. Simulation results indicate that three and four-domain devices can obtain 45 dB higher distortion suppression than two-domain devices, which can potentially achieve 120 dB spurious free dynamic range. We also experimentally demonstrated that the two-domain electrooptic modulator obtained 94

Xiaolong Wang; Boem-Suk Lee; Che-Yun Lin; Dechang An; Ray T. Chen

2010-01-01

220

Social network modulation of reward-related signals  

PubMed Central

Everyday goals and experiences are often shared with others who may hold different places within our social networks. We investigated whether the experience of sharing a reward differs with respect to social network. Twenty human participants played a card guessing game for shared monetary outcomes with three partners: a computer, a confederate (out-of-network), and a friend (in-network). Participants subjectively rated the experience of sharing a reward more positively with their friend than the other partners. Neuroimaging results support participants’ subjective reports, as ventral striatal BOLD responses were more robust when sharing monetary gains with a friend, as compared to with the confederate or computer, suggesting a higher value for sharing with an in-network partner. Interestingly, ratings of social closeness co-varied with this activity, resulting in a significant partner × closeness interaction: exploratory analysis showed that only participants reporting higher levels of closeness demonstrated partner-related differences in striatal BOLD response. These results suggest that reward valuation in social contexts is sensitive to distinctions of social network, such that sharing positive experiences with in-network others may carry higher value.

Fareri, Dominic S.; Niznikiewicz, Michael A.; Lee, Victoria K.; Delgado, Mauricio R.

2012-01-01

221

An overlapping module identification method in protein-protein interaction networks  

PubMed Central

Background Previous studies have shown modular structures in PPI (protein-protein interaction) networks. More recently, many genome and metagenome investigations have focused on identifying modules in PPI networks. However, most of the existing methods are insufficient when applied to networks with overlapping modular structures. In our study, we describe a novel overlapping module identification method (OMIM) to address this problem. Results Our method is an agglomerative clustering method merging modules according to their contributions to modularity. Nodes that have positive effects on more than two modules are defined as overlapping parts. As well, we designed de-noising steps based on a clustering coefficient and hub finding steps based on nodal weight. Conclusions The low computational complexity and few control parameters prove that our method is suitable for large scale PPI network analysis. First, we verified OMIM on a small artificial word association network which was able to provide us with a comprehensive evaluation. Then experiments on real PPI networks from the MIPS Saccharomyces Cerevisiae dataset were carried out. The results show that OMIM outperforms several other popular methods in identifying high quality modular structures.

2012-01-01

222

Network modulation following sham surgery in Parkinson's disease  

PubMed Central

Patient responses to placebo and sham effects are a major obstacle to the development of therapies for brain disorders, including Parkinson’s disease (PD). Here, we used functional brain imaging and network analysis to study the circuitry underlying placebo effects in PD subjects randomized to sham surgery as part of a double-blind gene therapy trial. Metabolic imaging was performed prior to randomization, then again at 6 and 12 months after sham surgery. In this cohort, the sham response was associated with the expression of a distinct cerebello-limbic circuit. The expression of this network increased consistently in patients blinded to treatment and correlated with independent clinical ratings. Once patients were unblinded, network expression declined toward baseline levels. Analogous network alterations were not seen with open-label levodopa treatment or during disease progression. Furthermore, sham outcomes in blinded patients correlated with baseline network expression, suggesting the potential use of this quantitative measure to identify “sham-susceptible” subjects before randomization. Indeed, Monte Carlo simulations revealed that a priori exclusion of such individuals substantially lowers the number of randomized participants needed to demonstrate treatment efficacy. Individualized subject selection based on a predetermined network criterion may therefore limit the need for sham interventions in future clinical trials.

Ko, Ji Hyun; Feigin, Andrew; Mattis, Paul J.; Tang, Chris C.; Ma, Yilong; Dhawan, Vijay; During, Matthew J.; Kaplitt, Michael G.; Eidelberg, David

2014-01-01

223

LLL Octopus Network: Some Lessons and Future Directions.  

National Technical Information Service (NTIS)

The Octopus network, designed and developed by the Lawrence Livermore Laboratory, is a pioneering, high-performance, local computer network. Several lessons derived from the 14 years of experience in the evolution of Octopus are described, and some of the...

R. W. Watson

1978-01-01

224

CATV/radio-on-fiber transport system based on direct modulation  

NASA Astrophysics Data System (ADS)

A directly modulated CATV/radio-on-fiber (ROF) transport system based on external light injection technique, optical single sideband (SSB) filter, and RF amplifier predistorter is proposed and demonstrated. To the best of my knowledge, it is the first time to transmit CATV and ROF signals simultaneously in a directly modulated form. Good performances of carrier-to-noise ratio (CNR), composite second order (CSO) and composite triple beat (CTB) were obtained for CATV band; and low third order intermodulation distortion to carrier ratio (IMD 3/C), and bit error rate (BER) values were achieved for ROF application.

Tzeng, Shah-Jye

2006-03-01

225

W-band Communication System with Direct Frequency Shift Keying Modulation to Phase-locked Oscillator  

NASA Astrophysics Data System (ADS)

Based on the theory of phase-locked loop, the analysis and simulation of direct frequency shift keying to phase-locked oscillator is presented. Then, a W-band digital communication system is developed, in which the millimeter wave phase-locked oscillator of the transmitter is modulated directly by 15grades 2048 kbit/s signal. The results of the experiment in the field show that the phase-locked loop has little influence on the modulating signal. It is a good way to simplify the transmitter configuration and suitable for high bit rate communication.

Zhang, Yonghong; Fan, Yong; Wu, Zhengde; Tang, Xiaohong

2008-05-01

226

A phase-modulated direct-detection fiber optical CATV transport system  

NASA Astrophysics Data System (ADS)

A fiber optical CATV transport system based on phase modulation (PM) and direct-detection schemes to reduce noise and distortion induced by systems is proposed and experimentally demonstrated. The architecture of the proposed systems is simplified by the fiber-dispersion-induced PM-to-intensity modulation (IM) conversion technique. As a result, the optical signal is detected directly by a photodiode (PD), without using the sophisticated and expensive delay interferometer (DI). Impressive performances of carrier-to-noise ratio (CNR), composite second-order (CSO), and composite triple beat (CTB) were obtained in our proposed systems over a 100-km single-mode fiber (SMF) transport.

Chen, Chia-Yi; Lu, Hai-Han; Lin, Chun-Yu; Wu, Kuan-Hung; Jhang, Tai-Wei; Ying, Cheng-Ling

2014-05-01

227

A directionality based location discovery scheme for wireless sensor networks  

Microsoft Academic Search

A sensor network is a large ad hoc network of densely distributed sensors that are equipped with low power wireless transceivers. Such networks can be applied for cooperative signal detection, monitoring, and tracking, and are especially useful for applications in remote or hazardous locations. This paper addresses the problem of location discovery at the sensor nodes, which is one of

Asis Nasipuri; Kai Li

2002-01-01

228

Membrane properties of striatal direct and indirect pathway neurons in mouse and rat slices and their modulation by dopamine.  

PubMed

D1 and D2 receptor expressing striatal medium spiny neurons (MSNs) are ascribed to striatonigral ("direct") and striatopallidal ("indirect") pathways, respectively, that are believed to function antagonistically in motor control. Glutamatergic synaptic transmission onto the two types is differentially affected by Dopamine (DA), however, less is known about the effects on MSN intrinsic electrical properties. Using patch clamp recordings, we comprehensively characterized the two pathways in rats and mice, and investigated their DA modulation. We identified the direct pathway by retrograde labeling in rats, and in mice we used transgenic animals in which EGFP is expressed in D1 MSNs. MSNs were subjected to a series of current injections to pinpoint differences between the populations, and in mice also following bath application of DA. In both animal models, most electrical properties were similar, however, membrane excitability as measured by step and ramp current injections consistently differed, with direct pathway MSNs being less excitable than their counterparts. DA had opposite effects on excitability of D1 and D2 MSNs, counteracting the initial differences. Pronounced changes in AP shape were seen in D2 MSNs. In direct pathway MSNs, excitability increased across experimental conditions and parameters, and also when applying DA or the D1 agonist SKF-81297 in presence of blockers of cholinergic, GABAergic, and glutamatergic receptors. Thus, DA induced changes in excitability were D1 R mediated and intrinsic to direct pathway MSNs, and not a secondary network effect of altered synaptic transmission. DAergic modulation of intrinsic properties therefore acts in a synergistic manner with previously reported effects of DA on afferent synaptic transmission and dendritic processing, supporting the antagonistic model for direct vs. indirect striatal pathway function. PMID:23469183

Planert, Henrike; Berger, Thomas K; Silberberg, Gilad

2013-01-01

229

Multicarrier modulation and cooperative communication in multihop cognitive radio networks  

Microsoft Academic Search

For high-data-rate wireless communication systems, two major issues are the underutilization of limited available radio spectrum and the effect of channel fading. Using dynamic spectrum access, cognitive radio can improve spectrum utilization. Almost all proposed CR systems are based on multicarrier modulation since multiple users can access the MCM systems by allocating subcarriers. Generally, MCM mainly includes two different schemes,

Tao Luo; Fei Lin; Tao Jiang; Mohsen Guizani; Wen Chen

2011-01-01

230

The segment polarity network is a robust developmental module  

NASA Astrophysics Data System (ADS)

All insects possess homologous segments, but segment specification differs radically among insect orders. In Drosophila, maternal morphogens control the patterned activation of gap genes, which encode transcriptional regulators that shape the patterned expression of pair-rule genes. This patterning cascade takes place before cellularization. Pair-rule gene products subsequently `imprint' segment polarity genes with reiterated patterns, thus defining the primordial segments. This mechanism must be greatly modified in insect groups in which many segments emerge only after cellularization. In beetles and parasitic wasps, for instance, pair-rule homologues are expressed in patterns consistent with roles during segmentation, but these patterns emerge within cellular fields. In contrast, although in locusts pair-rule homologues may not control segmentation, some segment polarity genes and their interactions are conserved. Perhaps segmentation is modular, with each module autonomously expressing a characteristic intrinsic behaviour in response to transient stimuli. If so, evolution could rearrange inputs to modules without changing their intrinsic behaviours. Here we suggest, using computer simulations, that the Drosophila segment polarity genes constitute such a module, and that this module is resistant to variations in the kinetic constants that govern its behaviour.

von Dassow, George; Meir, Eli; Munro, Edwin M.; Odell, Garrett M.

2000-07-01

231

Genetic modules and networks for behavior: lessons from Drosophila.  

PubMed

Behaviors are quantitative traits determined through actions of multiple genes and subject to genome-environment interactions. Early studies concentrated on analyzing the effects of single genes on behaviors, often generating views of simplified linear genetic pathways. The genome era has generated a profound paradigm shift enabling us to identify all the genes that contribute to expression of a behavioral phenotype, to investigate how they are organized as functional ensembles and to begin to identify polymorphisms that contribute to phenotypic variation and are targets for natural selection. Recent studies show that the genetic architecture of behavior is determined by dynamic and plastic modular networks of pleiotropic genes and that the behavioral phenotype manifests itself as an emergent property of such networks. Such networks are exquisitely sensitive to genetic background and sex effects. This review describes how Drosophila can serve as a model for uncovering fundamental principles of the genetic architecture of behavior. PMID:15551265

Anholt, Robert R H

2004-12-01

232

Highly spectrum efficient OFDM\\/PDM wireless networks by using optical SSB modulation  

Microsoft Academic Search

Optical frequency division multiplexing (OFDM) wireless access network using optical single-sideband modulation is proposed, which allows to deliver different wireless signals from a central station to each base station over an optical fiber network. The optical single-sideband (SSB) OFDM can achieve the highest spectrum efficiency of 0.25 b\\/s\\/Hz. A 0.25 b\\/s\\/Hz has been experimentally verified by the error-free transport of

Ken-Ichi Kitayama

1998-01-01

233

The PlaNet-OTN module: A double layer design tool for optical transport networks  

Microsoft Academic Search

PlaNet is a multilayer network planning tool designed and developed at the University of Texas at Dallas. This paper illustrates some of the features of PlaNet-OTN, one of the modules available in the PlaNet tool. PlaNet-OTN can be used to design and plan an optical transport network (OTN), which is comprised of two layers: wavelength division multiplexing (WDM) layer, which

Limin Tang; S. Billenahalli; Wanjun Huang; M. Razo; A. Sivasankaran; H. Vardhan; P. Monti; M. Tacca; A. Fumagalli

2009-01-01

234

Development of high-speed directly modulated DFB and DBR lasers with surface gratings  

NASA Astrophysics Data System (ADS)

The conventional distributed feedback and distributed Bragg reflector edge-emitting lasers employ buried gratings, which require two or more epitaxial growth steps. By using lateral corrugations of the ridge-waveguide as surface gratings the epitaxial overgrowth is avoided, reducing the fabrication complexity, increasing the yield and reducing the fabrication cost. The surface gratings are applicable to different materials, including Al-containing ones and can be easily integrated in complex device structures and photonic circuits. Single-contact and multiple contact edge-emitting lasers with laterally-corrugated ridge waveguide gratings have been developed both on GaAs and InP substrates with the aim to exploit the photon-photon resonance in order to extend their direct modulation bandwidth. The paper reports on the characteristics of such surface-grating-based lasers emitting both at 1.3 and 1.55 ?m and presents the photon-photon resonance extended small-signal modulation bandwidth (> 20 GHz) achieved with a 1.6 mm long single-contact device under direct modulation. Similarly structured devices, with shorter lengths are expected to exceed 40 GHz small-signal modulation bandwidth under direct modulation.

Dumitrescu, M.; Telkkälä, J.; Karinen, J.; Viheriälä, J.; Laakso, A.; Afzal, S.; Reithmaier, J.-P.; Kamp, M.; Melanen, P.; Uusimaa, P.; Bardella, P.; Vallone, M.; Montrosset, I.; Parillaud, O.; Krakowski, M.; Gready, D.; Eisenstein, G.; Sek, G.

2011-02-01

235

Optical Systems With High-Order DPSK and Star QAM Modulation Based on Interferometric Direct Detection  

NASA Astrophysics Data System (ADS)

Increased interest in novel modulation formats for optical transmission has come up in recent years. Receivers with interferometric direct detection can be used to detect arbitrary modulation formats with differentially encoded phases as differential phase-shift keying (DPSK) and differentially phase-encoded star-shaped quadrature amplitude modulation (Star QAM). In this paper, two novel 16-ary modulation formats, which are the 16DPSK and the Star 16QAM (ASK-8DPSK), are characterized for optical transmission for the first time. To be able to identify clear performance tendencies for high-order optical modulation, the novel formats are compared to a wide range of already investigated formats by conducting comprehensive calculations in a uniform simulation environment. The influence of different transmitter structures and decision schemes is considered, and all the systems are characterized with respect to the optical signal-to-noise ratio requirements, dispersion tolerance, and self-phase-modulation (SPM) performance for nonreturn-to-zero (NRZ) and RZ pulse shapes. Moreover, an inherent problem of Star QAM transmission concerning SPM is illustrated, and compensation techniques are examined. The results give a substantial insight into the properties of high-order optical modulation formats.

Seimetz, Matthias; Noelle, Markus; Patzak, Erwin

2007-06-01

236

Controlling the likelihood of rogue waves in an optically injected semiconductor laser via direct current modulation  

NASA Astrophysics Data System (ADS)

Extreme and rare events are nowadays the object of intensive research. Rogue waves are extreme waves that appear suddenly in many natural systems, even in apparently calm situations. Here we study numerically the rogue wave dynamics in an optically injected semiconductor laser with external periodic forcing that is implemented via direct modulation of the laser pump current. In the region of optical injection parameters where the laser intensity is chaotic and occasional ultrahigh pulses occur, our aim is to control the system by applying a weak modulation. We find that for an adequate range of frequency and amplitude parameters, the modulation can completely suppress the extreme pulses. We also show that the interplay between modulation and an external source of noise can significantly modify their probability of occurrence. These results can motivate a range of experimental and theoretical investigations in other natural systems.

Perrone, S.; Vilaseca, R.; Zamora-Munt, J.; Masoller, C.

2014-03-01

237

Quantitative orientation-independent differential interference contrast microscope with fast switching shear direction and bias modulation.  

PubMed

We describe a quantitative orientation-independent differential interference contrast (DIC) microscope, which allows bias retardation to be modulated and shear directions to be switched rapidly without any mechanical movement. The shear direction is switched by a regular liquid-crystal cell sandwiched between two standard DIC prisms. Another liquid-crystal cell modulates the bias. Techniques for measuring parameters of DIC prisms and calibrating the bias are shown. Two sets of raw DIC images with the orthogonal shear directions are captured within 1 s. Then the quantitative image of optical path gradient distribution within a thin optical section is computed. The gradient data are used to obtain a quantitative distribution of the optical path, which represents the refractive index gradient or height distribution. Computing enhanced regular DIC images with any desired shear direction is also possible. PMID:23595339

Shribak, Michael

2013-04-01

238

Quantitative orientation-independent DIC microscope with fast switching shear direction and bias modulation  

PubMed Central

We describe quantitative orientation-independent differential interference contrast (OI-DIC) microscope, which allows the bias retardation to be modulated and shear directions to be switched rapidly without any mechanically moving. The shear direction is switched by regular liquid crystal cell sandwiched between two standard DIC prisms. Another liquid crystal cell modulates the bias. Techniques for measuring parameters of DIC prisms and calibrating the bias are shown. Two sets of raw DIC images with the orthogonal shear directions are captured within a second. Then the quantitative image of optical path gradient distribution within a thin optical section is computed. The gradient data are used to obtain quantitative distribution of optical path, which represents refractive index gradient or height distribution. Computing enhanced regular DIC images with any desired shear direction is also possible.

Shribak, Michael

2013-01-01

239

Lateralized alpha-band cortical networks regulate volitional modulation of beta-band sensorimotor oscillations.  

PubMed

Sensorimotor rhythms (SMRs) are oscillatory brain activities in the ?- and ?-bands across the sensorimotor regions of the brain. Each frequency band has its own specific function. The ?-band oscillations are closely related to intrinsic cortical networks, whereas oscillations in the ?-band are relevant for the information transfer between the cortex and periphery, as well as for visual and proprioceptive feedback. This study aimed to investigate the interaction between these two frequency bands, under the premise that the regional modulation of ?-band power is linked to a cortical network in the ?-band. We therefore designed a procedure to maximize the modulation of ?-band activity over the sensorimotor cortex by combining kinesthetic motor-imagery with closed-loop haptic feedback. The cortical network activity during this procedure was estimated via the phase slope index in electroencephalographic recordings. Analysis of effective connectivity within the ?-band network revealed an information flow between the precentral (premotor and primary motor), postcentral (primary somatosensory) and parietal cortical areas. The range of ?-modulation was connected to a reduction of an ipsilateral sensorimotor and parietal ?-network and, consequently, to a lateralization of this network to the contralateral side. These results showed that regional sensorimotor oscillatory activity in the ?-band was regulated by cortical coupling of distant areas in the ?-band. PMID:24121086

Vukeli?, Mathias; Bauer, Robert; Naros, Georgios; Naros, Ilias; Braun, Christoph; Gharabaghi, Alireza

2014-02-15

240

Morphology effect on the light scattering and dynamic response of polymer network liquid crystal phase modulator.  

PubMed

Polymer network liquid crystal (PNLC) was one of the most potential liquid crystal for submillisecond response phase modulation, which was possible to be applied in submillisecond response phase only spatial light modulator. But until now the light scattering when liquid crystal director was reoriented by external electric field limited its phase modulation application. Dynamic response of phase change when high voltage was applied was also not elucidated. The mechanism that determines the light scattering was studied by analyzing the polymer network morphology by SEM method. Samples were prepared by varying the polymerization temperature, UV curing intensity and polymerization time. The morphology effect on the dynamic response of phase change was studied, in which high voltage was usually applied and electro-striction effect was often induced. The experimental results indicate that the polymer network morphology was mainly characterized by cross linked single fibrils, cross linked fibril bundles or even both. Although the formation of fibril bundle usually induced large light scattering, such a polymer network could endure higher voltage. In contrast, although the formation of cross linked single fibrils induced small light scattering, such a polymer network cannot endure higher voltage. There is a tradeoff between the light scattering and high voltage endurance. The electro-optical properties such as threshold voltage and response time were taken to verify our conclusion. For future application, the monomer molecular structure, the liquid crystal solvent and the polymerization conditions should be optimized to generate optimal polymer network morphology. PMID:24977571

Xiangjie, Zhao; Cangli, Liu; Jiazhu, Duan; Jiancheng, Zeng; Dayong, Zhang; Yongquan, Luo

2014-06-16

241

A digital receiver module with direct data acquisition for magnetic resonance imaging systems.  

PubMed

A digital receiver module for magnetic resonance imaging (MRI) with detailed hardware implementations is presented. The module is based on a direct sampling scheme using the latest mixed-signal circuit design techniques. A single field-programmable gate array chip is employed to perform software-based digital down conversion for radio frequency signals. The modular architecture of the receiver allows multiple acquisition channels to be implemented on a highly integrated printed circuit board. To maintain the phase coherence of the receiver and the exciter in the context of direct sampling, an effective phase synchronization method was proposed to achieve a phase deviation as small as 0.09°. The performance of the described receiver module was verified in the experiments for both low- and high-field (0.5 T and 1.5 T) MRI scanners and was compared to a modern commercial MRI receiver system. PMID:23126784

Tang, Weinan; Sun, Hongyu; Wang, Weimin

2012-10-01

242

Modeling of CIR-driven modulations of galactic cosmic ray intensity obtained by the Muon detector network  

NASA Astrophysics Data System (ADS)

The solar wind modulates Galactic Cosmic Ray (GCR) intensity. Modulations with a time scale of several days are mainly caused by Coronal Mass Ejections (CME) and solar wind stream interaction regions. The modulation caused by CME is called Forbush decrease (FD). The modulation that occurs at intervals of 27 days associated with Co-rotating Interaction Regions (CIR) is called recurrent storm. It has been considered that the mechanism of FD consists of two different processes as follows. (i) A turbulent region of solar wind magnetic field behind an interplanetary shock prevents incursion of GCR particles (shock effect). (ii) An interplanetary magnetic flux rope that has a low GCR density passes near the Earth (ejecta effect). A gradient of GCR density which is caused by an ejecta generates the flow of GCR called the B x grad n drift anisotropy. Therefore, the directional anisotropy of GCR intensity can be measured with ground-based observations [Bieber and Evenson, 1998]. Kuwabara et al. [2004] have established a model for reproducing both the temporal variations of isotropic intensity and the anisotropy of GCR measured by the Muon detector network. The shape of the GCR low density region inside ejecta is modeled with a cylinder. Since the CIR-driven GCR decrease accompanied by the directional anisotropy can be observed by the Muon detector network, it is expected that a low density region of GCR exists in the CIR structure. The mechanism of CIR-driven GCR decrease is still an open question. Using the data obtained by satellite observations, Richardson et al. [1996] investigated the relationship between the start time of GCR intensity decrease and the solar wind structure. They suggested that a turbulent region of solar wind magnetic field takes an important role in understanding the mechanism of modulation caused by CIR. However some problems are left. For example, the start time of GCR intensity decrease does not always correspond to the turbulent region of magnetic field. With these backgrounds, we assume a slab shape for the low density region caused by CIR and construct a model for reproducing temporal variations of isotropic intensity and the anisotropy of GCR measured by the Muon detector network. Details of this model will be reported. We will also discuss a relationship between the deduced low density region of GCR and the solar wind structure on the basis of some event studies of CIR- driven GCR modulations.

Okazaki, Y.; Fukunishi, H.; Munakata, K.

2006-12-01

243

Urban road network evolution mechanism based on the ‘direction preferred connection’ and ‘degree constraint’  

NASA Astrophysics Data System (ADS)

The urban road network is a complex system that exhibits the properties of self-organization and emergence. Recent theoretical and empirical studies have mainly focused on the structural properties of the urban road networks. This research concentrates on some important parameters such as degree, average degree, meshedness coefficient, betweeness, etc. These parameters of the real road network exhibit specific statistical properties. Some studies show that perhaps these specific statistical properties are caused by a compromise mechanism of the formation of a minimum spanning tree and the greedy triangulation. Inspired by these results, we propose a principle to construct the network (we call it a MG network in this paper) whose structure is located between the minimum spanning tree and the greedy triangulation at first. The structural properties of the MG network are analyzed. We find the formation mechanism of the MG network cannot explain the urban road network evolution well. Then, based on the formation mechanism of the MG network, we add the ‘direction preferred connection’ and ‘degree constraint’ principles to the urban road network evolution simulation process. The result of the simulation network turns out to be a planar network that is in accordance with reality. Compared with the real road network’s structural properties, we find the simulation results are so consistent with it. It indicates the validation of the model and also demonstrates perhaps the ‘direction preferred connection’ and ‘degree constraint’ principle can explain the urban road network evolution better.

Yuan, PengCheng; Juan, ZhiCai

2013-10-01

244

Assessing the functional coherence of modules found in multiple-evidence networks from Arabidopsis  

PubMed Central

Background Combining multiple evidence-types from different information sources has the potential to reveal new relationships in biological systems. The integrated information can be represented as a relationship network, and clustering the network can suggest possible functional modules. The value of such modules for gaining insight into the underlying biological processes depends on their functional coherence. The challenges that we wish to address are to define and quantify the functional coherence of modules in relationship networks, so that they can be used to infer function of as yet unannotated proteins, to discover previously unknown roles of proteins in diseases as well as for better understanding of the regulation and interrelationship between different elements of complex biological systems. Results We have defined the functional coherence of modules with respect to the Gene Ontology (GO) by considering two complementary aspects: (i) the fragmentation of the GO functional categories into the different modules and (ii) the most representative functions of the modules. We have proposed a set of metrics to evaluate these two aspects and demonstrated their utility in Arabidopsis thaliana. We selected 2355 proteins for which experimentally established protein-protein interaction (PPI) data were available. From these we have constructed five relationship networks, four based on single types of data: PPI, co-expression, co-occurrence of protein names in scientific literature abstracts and sequence similarity and a fifth one combining these four evidence types. The ability of these networks to suggest biologically meaningful grouping of proteins was explored by applying Markov clustering and then by measuring the functional coherence of the clusters. Conclusions Relationship networks integrating multiple evidence-types are biologically informative and allow more proteins to be assigned to a putative functional module. Using additional evidence types concentrates the functional annotations in a smaller number of modules without unduly compromising their consistency. These results indicate that integration of more data sources improves the ability to uncover functional association between proteins, both by allowing more proteins to be linked and producing a network where modular structure more closely reflects the hierarchy in the gene ontology.

2011-01-01

245

Observation of a time modulated muon flux in the direction of Cygnus X-3  

Microsoft Academic Search

The analysis of angular and phase distribution is reported for high energy muons recorded in the NUSEX nucleon decay detector, located in the Mont Blanc tunnel at a depth of about 5000 hg of standard rock. Evidence is found for a signal correlated to the direction and time modulation of Cygnus X-3.

G. Battistoni; E. Bellotti; C. Bloise; G. Bologna; P. Campana; C. Castagnoli; A. Castellina; V. Chiarella; A. Ciocio; Donald C Cundy; B. D'Ettorre-Piazzoli; Ettore Fiorini; P. Galeotti; Enzo Iarocci; C. Liguori; G. Mannocchi; G P Murtas; P. Negri; G. Nicoletti; P. Picchi; M. Price; Antonio Pullia; S. Ragazzi; M. Rollier; O. Saavedra; L. Satta; P. Serri; S. Vernetto; L. Zanotti

1985-01-01

246

Effect of modulation format and jamming spectrum on performance of direct sequence spread spectrum systems  

NASA Technical Reports Server (NTRS)

The processing gain of a direct sequence spread spectrum system is approximately the ratio of the spreading code chip rate to the data rate. This paper provides a more accurate understanding of the performance of such systems as a function of the modulation scheme and jammer characteristics.

Levitt, B. K.

1980-01-01

247

Suppression of chaos in a directly modulated semiconductor laser with delayed optoelectronic feedback  

Microsoft Academic Search

The effect of delayed optoelectronic feedback on a directly modulated InGaAsP laser diode is numerically studied. It is found that a complete elimination of the previously observed period doubling, chaos and formation of pulses with double peak structure is possible by the feedback with small delays. Bifurcation diagrams and time series plots are used to characterize the chaotic and periodic

S. Rajesh; V. M. Nandakumaran

2003-01-01

248

Analysis of protein-protein interaction network and functional modules on primary osteoporosis  

PubMed Central

Background Primary osteoporosis is an age-related disease, and the main cause of this disease is the failure of bone homeostasis. Previous studies have shown that primary osteoporosis is associated with gene mutations. To explore the functional modules of the PPI (protein-protein interaction) network of differentially expressed genes (DEGs), and the related pathways participating in primary osteoporosis. Methods The gene expression profile of primary osteoporosis GSE35956 was downloaded from the GEO (Gene Expression Omnibus) database and included five MSC (mesenchymal stem cell) specimens of normal osseous tissue and five MSC specimens of osteoporosis. The DEGs between the two types of MSC specimens were identified by the samr package in R language. In addition, the functions and pathways of DEGs were enriched. Then the DEGs were mapped to String to acquire PPI pairs and the PPI network was constructed with by these PPI pairs. Topological properties of the network were calculated by Network Analyzer, and modules in the network were screened by Cluster ONE software. Subsequently, the fronting five modules whose P-value was less than 1.0e-05 were identified and function analysis was conducted. Results A total of 797 genes were filtered as DEGs from these ten specimens of GSE35956 with 660 up-regulated genes and 137 down-regulated genes. Meanwhile, up-regulated DEGs were mainly enriched in functions and pathways related to cell cycle and DNA replication. Furthermore, there were 4,135 PPI pairs and 377 nodes in the PPI network. Four modules were enriched in different pathways, including cell cycle and DNA replication pathway in module 2. Conclusions In this paper, we explored the genes and pathways involved in primary osteoporosis based on gene expression profiles, and the present findings have the potential to be used clinically for the future treatment of primary osteoporosis.

2014-01-01

249

Neural network decision directed edge-adaptive Kalman filter for image estimation  

Microsoft Academic Search

A neural network-based scheme for decision directed edge- adaptive Kalman filtering is introduced in this work. A backpropagation neural network makes the decisions about the orientation of the edges based on the information in a window centered at the current pixel being processed. Then based upon the neural network output an appropriate image model which closely matches the local statistics

Mahmood R. Azimi-sadjadi; Rongrui Xiong; Xi Yu

1999-01-01

250

A testbed to emulate next-generation directional RF and free-space optical tactical networks  

Microsoft Academic Search

The tactical edge network emulation tool (TENET) hardware integration system (THIS) is designed to characterize higher layer responses to the dynamic physical layer topology of a tactical network utilizing directional communication links. THIS emulates the mobile, tactical, network environment using the hardware in a static infrastructure. MATLAB-based tools implement the TENET emulation to simulate mobility induced link fragility, and the

William M. Turner; Daniel J. Tebben; Jason R. Madsen; Anurag Dwivedi

2009-01-01

251

Identifying directed links in large scale functional networks: application to brain fMRI  

Microsoft Academic Search

BACKGROUND: Biological experiments increasingly yield data representing large ensembles of interacting variables, making the application of advanced analytical tools a forbidding task. We present a method to extract networks of correlated activity, specifically from functional MRI data, such that: (a) network nodes represent voxels, and (b) the network links can be directed or undirected, representing temporal relationships between the nodes.

Guillermo A Cecchi; A Ravishankar Rao; Maria V Centeno; Marwan Baliki; A Vania Apkarian; Dante R Chialvo

2007-01-01

252

Direct imaging of fluctuations in a cross-linked biopolymer network  

NASA Astrophysics Data System (ADS)

Cross-linked networks are ubiquitous in synthetic and biological polymer systems, such as rubbers and cytoskeletons. To model cross-linked networks, several theories have been developed on the basis of different assumptions as to fluctuations in the networks. Here we put these theories to direct test. This talk will describe direct single-molecule imaging of the dynamic fluctuations of junction points in a cross-linked semiflexible polymer (F-actin) network. The actin filaments are cross linked by biotin/avidin. The junction points are selectively labeled to allow nm spatial imaging resolution. The surprising results point to limitations of the prevailing network models.

Wang, Bo; Jiang, Lingxiang; Tsang, Boyce; Granick, Steve

2013-03-01

253

Digital quadrature amplitude modulation with optimized non-rectangular constellations for 100 Gb/s transmission by a directly-modulated laser.  

PubMed

We study the performance of novel quadrature amplitude modulation (QAM) constellations for 100 Gb/s transmission by a directly-modulated laser. Due to the strong nonlinearity of a directly-modulated laser, rectangular constellations suffer a large penalty from their regular spacing between symbols. We present a method for synthesizing irregular constellations which position symbols more efficiently. We will demonstrate the improved performance of these novel constellations over the conventional rectangular constellation as well as the superior performance achievable with digital QAM compared to optimally bit-loaded discrete-multitone modulation. PMID:24921784

Ling, William A; Lyubomirsky, Ilya; Solgaard, Olav

2014-05-01

254

Temperature monitoring in wireless sensor network using Zigbee transceiver module  

Microsoft Academic Search

In this paper, we are using the features and technology of wireless sensor networks such as distributed and self-organization to build temperature monitoring system, which can monitor the temperature of bus bar junction in real time to prevent fire and other accidents. This system applies ZigBee communication protocol and uses the IC-CC2500, 2.4GHz(ISM) as RF transceiver. It has the characteristics

Rajesh Singh; Shailesh Mishra

2010-01-01

255

Automatic Multi-Module Neural Network Evolution in an Artificial Brain  

Microsoft Academic Search

A major problem in artificial brain building is the au- tomatic construction and training of multi-module systems of neural networks. For example, consider a biological hu- man brain, which has millions of neural nets. If an artificial brain is to have similar complexity, it is unrealistic to re- quire that the training data set for each neural net must be

Jonathan Dinerstein; Nelson Dinerstein; Hugo De Garis

2003-01-01

256

Broad band RF module of millimeter wave radar network for airport FOD detection system  

Microsoft Academic Search

Foreign Objects and Debris (FODs) must be removed from runways. With the necessity of automatic continuous survey, we are investigating a new FOD detection system based on a millimeter wave radar network. This paper describes the concept of this FOD detection system and the Radio Frequency (RF) module for this application. In order to minimize cost and size, we installed

Naruto Yonemoto; Akiko Kohmura; Shunichi Futatsumori; Tetsuji Uebo; Alexandre Saillard

2009-01-01

257

Task difficulty modulates young-old differences in network expression.  

PubMed

The extent of task-related fMRI activation can vary as a function of task difficulty. Also the efficiency or capacity of the brain networks underlying task performance can change with aging. We asked whether the expression of a network underlying task performance would differ as a function of task demand in old and young individuals. 26 younger and 23 older healthy adults performed a delayed item recognition task that used the response signal method to parametrically manipulate the extrinsic difficulty of the task by imposing five different deadlines for recognition response. Both age groups showed a speed-accuracy trade-off, but the younger group achieved greater discriminability at the longer deadlines. We identified a spatial pattern of fMRI activation during the probe phase whose expression increased as the response deadline shortened and the task became more difficult. This pattern was expressed to a greater degree by the old group at the long deadlines, when the task was easiest. By contrast, this pattern was expressed to a greater degree by the younger group at the short deadlines, when the task was hardest. This suggests reduced efficiency and capacity of this network in older subjects. These findings suggest that neuroimaging studies comparing task-related activation across groups with different cognitive abilities must be interpreted in light of the relative difficulty of the task for each group. PMID:22197699

Stern, Yaakov; Rakitin, Brian C; Habeck, Christian; Gazes, Yunglin; Steffener, Jason; Kumar, Arjun; Reuben, Aaron

2012-01-30

258

Networked Automotive Cyber Physical Systems: Applications, Challenges and Research Directions  

Microsoft Academic Search

Next-generation Automotive Cyber Physical Systems (CPS) are expected to be networked in the wireless domain. It is not un-reasonable to envisage thousands of automobiles with appropriate sensing, actuation and communication ability to network themselves wirelessly in the cyber world. A wide spectrum of applications are possible in this domain. In this article, we highlight three canonical applications, while illustrating their

Sriram Chellappan; Sanjay Kumar Madria

259

Security-aware routing and localization for a directional mission critical network  

Microsoft Academic Search

There has been recent interest in the development of untethered sensor nodes that communicate directionally via free space optical communications for mission critical settings in which high-speed link guarantees in hostile environments are needed. Directional wireless optical sensor networks have the potential to provide gigabits per second speeds for relatively low power consumption enabling bursty traffic and longer network lifetimes.

Unoma Ndili Okorafor; Deepa Kundur

2010-01-01

260

A Distance-Based Directional Broadcast Protocol for Urban Vehicular Ad Hoc Network  

Microsoft Academic Search

The topology of a vehicular ad hoc network (VANET) changes rapidly due to high-speed movement of vehicles, so traditional mobile ad hoc network (MANET) broadcast protocol may not work efficiently in VANET. This paper proposes a distance-based broadcast protocol called Efficient Directional Broadcast (EDB) for VANET using directional antennas. In EDB, only the furthest receiver is responsible to forward the

Da Li; Hongyu Huang; Xu Li; Minglu Li; Feilong Tang

2007-01-01

261

Power-aware ad hoc networks with directional antennas: Models and analysis  

Microsoft Academic Search

Directional antennas offer numerous benefits for wireless ad hoc networks, such as extended communication range, better spatial reuse, improved capacity and suppressed interference. In this work, we study analytically the benefits of transmission power control on throughput and energy consumption in a uniformly distributed power-aware ad hoc network where nodes are equipped with directional antennas. We construct an interference model

Basel Alawieh; Chadi Assi; Hussein T. Mouftah

2009-01-01

262

Distributed Correlative Power Control Schemes for Mobile Ad hoc Networks Using Directional Antennas  

Microsoft Academic Search

Medium access control (MAC) protocols simultaneously integrating transmission power (TP) control with directional antennas have the potential to enhance both energy savings and capacity throughput in wireless multihop Mobile Ad hoc NETworks (MANETs). In this paper, we present a model to calculate future interference in networks with directional antennas, and based on this model, we derive some relations that should

Basel Alawieh; Chadi M. Assi; Wessam Ajib

2008-01-01

263

Spectral properties of the Google matrix of the World Wide Web and other directed networks  

NASA Astrophysics Data System (ADS)

We study numerically the spectrum and eigenstate properties of the Google matrix of various examples of directed networks such as vocabulary networks of dictionaries and university World Wide Web networks. The spectra have gapless structure in the vicinity of the maximal eigenvalue for Google damping parameter ? equal to unity. The vocabulary networks have relatively homogeneous spectral density, while university networks have pronounced spectral structures which change from one university to another, reflecting specific properties of the networks. We also determine specific properties of eigenstates of the Google matrix, including the PageRank. The fidelity of the PageRank is proposed as a characterization of its stability.

Georgeot, Bertrand; Giraud, Olivier; Shepelyansky, Dima L.

2010-05-01

264

Angular MAC: a framework for directional antennas in wireless mesh networks  

Microsoft Academic Search

Capacity of wireless mesh networks can be enhanced through the use of smart directional antennas, which not only enable nodes\\u000a to have high quality links but also increase network throughput by allowing spatial reuse. This paper proposes a new MAC protocol\\u000a and framework, called Angular MAC (ANMAC) that enables directional antennas in wireless mesh networks. The protocols and algorithms\\u000a of

Erdem Ulukan; Özgür Gürbüz

2008-01-01

265

Modulation of cortical activity as a result of voluntary postural sway direction: an EEG study.  

PubMed

There is increasing evidence demonstrating the role of the cerebral cortex in human postural control. Modulation of EEG both in voltage and frequency domains has been observed preceding and following self-paced postural movements and those induced by external perturbations. The current study set out to provide additional evidence regarding the role of cerebral cortex in human postural control by specifically examining modulation of EEG as a function of postural sway direction. Twelve neurologically normal subjects were instructed to produce self-paced voluntary postural sways in the anterior-posterior (AP) and medial-lateral (ML) directions. The center of pressure dynamics and EEG both in voltage and frequency domains were extracted by averaging and Morlet wavelet techniques, respectively. The amplitude of movement-related cortical potentials (MRCP) was significantly higher preceding ML sways. Also, time-frequency wavelet coefficients (TF) indicated differential modulation of EEG within alpha, beta and gamma bands as a function of voluntary postural sway direction. Thus, ML sway appear to be more difficult and energy demanding tasks than the AP sway as reflected in differential modulation of EEG. These results are discussed within the conceptual framework of differential patterns of brain activation as a result of postural task complexity. PMID:18639613

Slobounov, Semyon; Hallett, Mark; Cao, Cheng; Newell, Karl

2008-09-19

266

MORAL ENHANCEMENT VIA DIRECT EMOTION MODULATION: A REPLY TO JOHN HARRIS  

PubMed Central

Some argue that humans should enhance their moral capacities by adopting institutions that facilitate morally good motives and behaviour. I have defended a parallel claim: that we could permissibly use biomedical technologies to enhance our moral capacities, for example by attenuating certain counter-moral emotions. John Harris has recently responded to my argument by raising three concerns about the direct modulation of emotions as a means to moral enhancement. He argues (1) that such means will be relatively ineffective in bringing about moral improvements, (2) that direct modulation of emotions would invariably come at an unacceptable cost to our freedom, and (3) that we might end up modulating emotions in ways that actually lead to moral decline. In this article I outline some counter-intuitive potential implications of Harris' claims. I then respond individually to his three concerns, arguing that they license only the very weak conclusion that moral enhancement via direct emotion modulation is sometimes impermissible. However I acknowledge that his third concern might, with further argument, be developed into a more troubling objection to such enhancements.

Douglas, Thomas

2013-01-01

267

Active modulation of wavelength and radiation direction of fluorescence via liquid crystal-tuned surface plasmons  

NASA Astrophysics Data System (ADS)

Plasmonic elements which can tune light in micro-nano dimension have attracted much attention nowadays. However, available approaches for externally manipulating surface plasmons (SPs) are still in great demand. Here, we described an effective approach to modulate SPs by voltage signal. Through adding a liquid crystal cell with a dye layer to the Kretschmann configuration, the wavelength and the radiation direction of the fluorescence of dye can be modulated continuously and reversibly by changing applied voltages. This design has great application potentials in the development of tunable luminescent devices and smart plasmonic elements.

Li, Haibo; Xu, Shuping; Gu, Yuejiao; Wang, Kai; Xu, Weiqing

2013-02-01

268

Some implications of TCM for optical direct-detection channels. [trellis coded modulation  

NASA Technical Reports Server (NTRS)

Consideration is given to the optical direct-detection channel, and it is shown how simple trellis-coded modulation (TCM) can be used to improve performance or increase throughput (in bits per second) without bandwidth expansion or performance loss. In fact, a modest performance gain can be achieved. Although the approach can be used with other signal constellations, the authors concentrate on signals derived from the pulse-position modulation (PPM) format by allowing overlap. Theoretical motivation for using this signal set, known as overlapping PPM (OPPM), was recently given by David and Kaplan (1984), who showed a capacity gain when overlap is introduced.

Georghiades, Costas N.

1989-01-01

269

Ion transport membrane module and vessel system with directed internal gas flow  

DOEpatents

An ion transport membrane system comprising (a) a pressure vessel having an interior, an inlet adapted to introduce gas into the interior of the vessel, an outlet adapted to withdraw gas from the interior of the vessel, and an axis; (b) a plurality of planar ion transport membrane modules disposed in the interior of the pressure vessel and arranged in series, each membrane module comprising mixed metal oxide ceramic material and having an interior region and an exterior region; and (c) one or more gas flow control partitions disposed in the interior of the pressure vessel and adapted to change a direction of gas flow within the vessel.

Holmes, Michael Jerome (Thompson, ND); Ohrn, Theodore R. (Alliance, OH); Chen, Christopher Ming-Poh (Allentown, PA)

2010-02-09

270

Influences of impedance matching network on pulse-modulated radio frequency atmospheric pressure glow discharges  

NASA Astrophysics Data System (ADS)

Pulse-modulated RF atmospheric pressure glow discharges (APDGs) were investigated in recent years to reduce the thermal accumulation and extend the operation region of the stable alpha glow mode. Different pulse-modulated voltage and current waveforms were acquired in previous experiments, but no attention was paid to the interpretation. We investigated this issue and associated phenomenon via positive and negative feedback effects derived from varying the series capacitor in the inversely L-shaped matching network used in our pulse-modulated RF APGD source. The evolutions of pulse-modulated RF waveforms were found to be associated with the feedback region and the pulsed plasma absorbed RF power. In the positive feedback region, pulse-modulated RF APGDs are relatively stable. In the negative feedback region, wide spikes as well as undershoots occur in RF voltage and current waveforms and the plasma absorbed RF power. In case of a high RF power discharge with a low modulation frequency, the pulse-modulated RF APGD is extinguished and re-ignited due to the enhanced undershoot during the initial pulse phase. The pulse-modulated RF APGD can transit from positive to negative feedback region in a range of series capacitance. Experimental results are discussed by the aid of equivalent circuit, negative and positive feedback effects.

Huo, W. G.; Xu, K.; Sun, B.; Ding, Z. F.

2012-08-01

271

Evidence for a cognitive control network for goal-directed attention in simple sustained attention.  

PubMed

The deterioration of performance over time is characteristic for sustained attention tasks. This so-called "performance decrement" is measured by the increase of reaction time (RT) over time. Some behavioural and neurobiological mechanisms of this phenomenon are not yet fully understood. Behaviourally, we examined the increase of RT over time and the inter-individual differences of this performance decrement. On the neurophysiological level, we investigated the task-relevant brain areas where neural activity was modulated by RT and searched for brain areas involved in good performance (i.e. participants with no or moderate performance decrement) as compared to poor performance (i.e. participants with a steep performance decrement). For this purpose, 20 healthy, young subjects performed a carefully designed task for simple sustained attention, namely a low-demanding version of the Rapid Visual Information Processing task. We employed a rapid event-related functional magnetic resonance imaging (fMRI) design. The behavioural results showed a significant increase of RT over time in the whole group, and also revealed that some participants were not as prone to the performance decrement as others. The latter was statistically significant comparing good versus poor performers. Moreover, high BOLD-responses were linked to longer RTs in a task-relevant bilateral fronto-cingulate-insular-parietal network. Among these regions, good performance was associated with significantly higher RT-BOLD correlations in the pre-supplementary motor area (pre-SMA). We concluded that the task-relevant bilateral fronto-cingulate-insular-parietal network was a cognitive control network responsible for goal-directed attention. The pre-SMA in particular might be associated with the performance decrement insofar that good performers could sustain activity in this brain region in order to monitor performance declines and adjust behavioural output. PMID:23262174

Hilti, Caroline C; Jann, Kay; Heinemann, Doerthe; Federspiel, Andrea; Dierks, Thomas; Seifritz, Erich; Cattapan-Ludewig, Katja

2013-03-01

272

Feature-based attention modulates direction-selective hemodynamic activity within human MT.  

PubMed

Attending to the spatial location or to nonspatial features of a stimulus modulates neural activity in cortical areas that process its perceptual attributes. The feature-based attentional selection of the direction of a moving stimulus is associated with increased firing of individual neurons tuned to the direction of the movement in area V5/MT, while responses of neurons tuned to opposite directions are suppressed. However, it is not known how these multiplicatively scaled responses of individual neurons tuned to different motion-directions are integrated at the population level, in order to facilitate the processing of stimuli that match the perceptual goals. Using functional magnetic resonance imaging (fMRI) the present study revealed that attending to the movement direction of a dot field enhances the response in a number of areas including the human MT region (hMT) as a function of the coherence of the stimulus. Attending the opposite direction, however, lead to a suppressed response in hMT that was inversely correlated with stimulus-coherence. These findings demonstrate that the multiplicative scaling of single-neuron responses by feature-based attention results in an enhanced direction-selective population response within those cortical modules that processes the physical attributes of the attended stimuli. Our results provide strong support for the validity of the "feature similarity gain model" on the integrated population response as quantified by parametric fMRI in humans. PMID:21305663

Stoppel, Christian Michael; Boehler, Carsten Nicolas; Strumpf, Hendrik; Heinze, Hans-Jochen; Noesselt, Toemme; Hopf, Jens-Max; Schoenfeld, Mircea Ariel

2011-12-01

273

Asymmetric friction of nonmotor MAPs can lead to their directional motion in active microtubule networks.  

PubMed

Diverse cellular processes require microtubules to be organized into distinct structures, such as asters or bundles. Within these dynamic motifs, microtubule-associated proteins (MAPs) are frequently under load, but how force modulates these proteins' function is poorly understood. Here, we combine optical trapping with TIRF-based microscopy to measure the force dependence of microtubule interaction for three nonmotor MAPs (NuMA, PRC1, and EB1) required for cell division. We find that frictional forces increase nonlinearly with MAP velocity across microtubules and depend on filament polarity, with NuMA's friction being lower when moving toward minus ends, EB1's lower toward plus ends, and PRC1's exhibiting no directional preference. Mathematical models predict, and experiments confirm, that MAPs with asymmetric friction can move directionally within actively moving microtubule pairs they crosslink. Our findings reveal how nonmotor MAPs can generate frictional resistance in dynamic cytoskeletal networks via micromechanical adaptations whose anisotropy may be optimized for MAP localization and function within cellular structures. PMID:24725408

Forth, Scott; Hsia, Kuo-Chiang; Shimamoto, Yuta; Kapoor, Tarun M

2014-04-10

274

Coordinated Directional Medium Access Control in a Wireless Network.  

National Technical Information Service (NTIS)

A method of simultaneously transmitting and receiving multiple data packets over wireless channels among the nodes of a wireless network is provided. The method includes automatically selecting a master sending node and corresponding master receiving node...

D. O. Wu J. Wang Y. M. Fang

2005-01-01

275

Shaping Embodied Neural Networks for Adaptive Goal-directed Behavior  

PubMed Central

The acts of learning and memory are thought to emerge from the modifications of synaptic connections between neurons, as guided by sensory feedback during behavior. However, much is unknown about how such synaptic processes can sculpt and are sculpted by neuronal population dynamics and an interaction with the environment. Here, we embodied a simulated network, inspired by dissociated cortical neuronal cultures, with an artificial animal (an animat) through a sensory-motor loop consisting of structured stimuli, detailed activity metrics incorporating spatial information, and an adaptive training algorithm that takes advantage of spike timing dependent plasticity. By using our design, we demonstrated that the network was capable of learning associations between multiple sensory inputs and motor outputs, and the animat was able to adapt to a new sensory mapping to restore its goal behavior: move toward and stay within a user-defined area. We further showed that successful learning required proper selections of stimuli to encode sensory inputs and a variety of training stimuli with adaptive selection contingent on the animat's behavior. We also found that an individual network had the flexibility to achieve different multi-task goals, and the same goal behavior could be exhibited with different sets of network synaptic strengths. While lacking the characteristic layered structure of in vivo cortical tissue, the biologically inspired simulated networks could tune their activity in behaviorally relevant manners, demonstrating that leaky integrate-and-fire neural networks have an innate ability to process information. This closed-loop hybrid system is a useful tool to study the network properties intermediating synaptic plasticity and behavioral adaptation. The training algorithm provides a stepping stone towards designing future control systems, whether with artificial neural networks or biological animats themselves.

Chao, Zenas C.; Bakkum, Douglas J.; Potter, Steve M.

2008-01-01

276

Shaping embodied neural networks for adaptive goal-directed behavior.  

PubMed

The acts of learning and memory are thought to emerge from the modifications of synaptic connections between neurons, as guided by sensory feedback during behavior. However, much is unknown about how such synaptic processes can sculpt and are sculpted by neuronal population dynamics and an interaction with the environment. Here, we embodied a simulated network, inspired by dissociated cortical neuronal cultures, with an artificial animal (an animat) through a sensory-motor loop consisting of structured stimuli, detailed activity metrics incorporating spatial information, and an adaptive training algorithm that takes advantage of spike timing dependent plasticity. By using our design, we demonstrated that the network was capable of learning associations between multiple sensory inputs and motor outputs, and the animat was able to adapt to a new sensory mapping to restore its goal behavior: move toward and stay within a user-defined area. We further showed that successful learning required proper selections of stimuli to encode sensory inputs and a variety of training stimuli with adaptive selection contingent on the animat's behavior. We also found that an individual network had the flexibility to achieve different multi-task goals, and the same goal behavior could be exhibited with different sets of network synaptic strengths. While lacking the characteristic layered structure of in vivo cortical tissue, the biologically inspired simulated networks could tune their activity in behaviorally relevant manners, demonstrating that leaky integrate-and-fire neural networks have an innate ability to process information. This closed-loop hybrid system is a useful tool to study the network properties intermediating synaptic plasticity and behavioral adaptation. The training algorithm provides a stepping stone towards designing future control systems, whether with artificial neural networks or biological animats themselves. PMID:18369432

Chao, Zenas C; Bakkum, Douglas J; Potter, Steve M

2008-03-01

277

Effect of gravitational focusing on annual modulation in dark-matter direct-detection experiments.  

PubMed

The scattering rate in dark-matter direct-detection experiments should modulate annually due to Earth's orbit around the Sun. The rate is typically thought to be extremized around June 1, when the relative velocity of Earth with respect to the dark-matter wind is maximal. We point out that gravitational focusing can alter this modulation phase. Unbound dark-matter particles are focused by the Sun's gravitational potential, affecting their phase-space density in the lab frame. Gravitational focusing can result in a significant overall shift in the annual-modulation phase, which is most relevant for dark matter with low scattering speeds. The induced phase shift for light O(10)??GeV dark matter may also be significant, depending on the threshold energy of the experiment. PMID:24483881

Lee, Samuel K; Lisanti, Mariangela; Peter, Annika H G; Safdi, Benjamin R

2014-01-10

278

Directional MAC Approach for Wireless Body Area Networks  

PubMed Central

Wireless Body Area Networks (WBANs) designed for medical, sports, and entertainment applications, have drawn the attention of academia and industry alike. A WBAN is a special purpose network, designed to operate autonomously to connect various medical sensors and appliances, located inside and/or outside of a human body. This network enables physicians to remotely monitor vital signs of patients and provide real time feedback for medical diagnosis and consultations. The WBAN system can offer two significant advantages: patient mobility due to their use of portable monitoring devices and a location independent monitoring facility. With its appealing dimensions, it brings about a new set of challenges, which we do not normally consider in such small sensor networks. It requires a scalable network in terms of heterogeneous data traffic, low power consumption of sensor nodes, integration in and around the body networking and coexistence. This work presents a medium access control protocol for WBAN which tries to overcome the aforementioned challenges. We consider the use of multiple beam adaptive arrays (MBAA) at BAN Coordinator (BAN_C) node. When used as a BAN_C, an MBAA can successfully receive two or more overlapping packets at the same time. Each beam captures a different packet by automatically pointing its pattern toward one packet while annulling other contending packets. This paper describes how an MBAA can be integrated into a single hope star topology as a BAN_C. Simulation results show the performance of our proposed protocol.

Hussain, Md. Asdaque; Alam, Md. Nasre; Kwak, Kyung Sup

2011-01-01

279

Throughput enhancement of direct-sequence spread-spectrum packet radio networks by adaptive power control  

NASA Astrophysics Data System (ADS)

The performance of direct-sequence spread-spectrum packet radio networks in the presence of the near/far problem is investigated. It is found that the maximum throughput of the network suffers degradation due to the near/far problem. However, analysis also shows that, under high traffic conditions, a network with the near/far problem delivers higher throughput than another without the near/far problem. This suggests that the direct-sequence spread-spectrum packet radio network with the near/far problem retains stability for heavier traffic conditions. Following these findings, a new adaptive power control scheme is suggested to enhance network throughput under both low and heavy traffic conditions. The mean and variance of the packet delay are derived and network stability and deadlock avoidance issues are discussed. The impact of channel fading on the network behavior is also studied in this paper.

Sheikh, Asrar; Yao, Yu-Dong; Cheng, Shixing

1994-02-01

280

Global analysis of the human pathophenotypic similarity gene network merges disease module components.  

PubMed

The molecular complexity of genetic diseases requires novel approaches to break it down into coherent biological modules. For this purpose, many disease network models have been created and analyzed. We highlight two of them, "the human diseases networks" (HDN) and "the orphan disease networks" (ODN). However, in these models, each single node represents one disease or an ambiguous group of diseases. In these cases, the notion of diseases as unique entities reduces the usefulness of network-based methods. We hypothesize that using the clinical features (pathophenotypes) to define pathophenotypic connections between disease-causing genes improve our understanding of the molecular events originated by genetic disturbances. For this, we have built a pathophenotypic similarity gene network (PSGN) and compared it with the unipartite projections (based on gene-to-gene edges) similar to those used in previous network models (HDN and ODN). Unlike these disease network models, the PSGN uses semantic similarities. This pathophenotypic similarity has been calculated by comparing pathophenotypic annotations of genes (human abnormalities of HPO terms) in the "Human Phenotype Ontology". The resulting network contains 1075 genes (nodes) and 26197 significant pathophenotypic similarities (edges). A global analysis of this network reveals: unnoticed pairs of genes showing significant pathophenotypic similarity, a biological meaningful re-arrangement of the pathological relationships between genes, correlations of biochemical interactions with higher similarity scores and functional biases in metabolic and essential genes toward the pathophenotypic specificity and the pleiotropy, respectively. Additionally, pathophenotypic similarities and metabolic interactions of genes associated with maple syrup urine disease (MSUD) have been used to merge into a coherent pathological module.Our results indicate that pathophenotypes contribute to identify underlying co-dependencies among disease-causing genes that are useful to describe disease modularity. PMID:23437198

Reyes-Palomares, Armando; Rodríguez-López, Rocío; Ranea, Juan A G; Sánchez Jiménez, Francisca; Medina, Miguel Angel

2013-01-01

281

Dopamine: a parallel pathway for the modulation of spinal locomotor networks  

PubMed Central

The spinal cord contains networks of neurons that can produce locomotor patterns. To readily respond to environmental conditions, these networks must be flexible yet at the same time robust. Neuromodulators play a key role in contributing to network flexibility in a variety of invertebrate and vertebrate networks. For example, neuromodulators contribute to altering intrinsic properties and synaptic weights that, in extreme cases, can lead to neurons switching between networks. Here we focus on the role of dopamine in the control of stepping networks in the spinal cord. We first review the role of dopamine in modulating rhythmic activity in the stomatogastric ganglion (STG) and the leech, since work from these preparations provides a foundation to understand its role in vertebrate systems. We then move to a discussion of dopamine’s role in modulation of swimming in aquatic species such as the larval xenopus, lamprey and zebrafish. The control of terrestrial walking in vertebrates by dopamine is less studied and we review current evidence in mammals with a focus on rodent species. We discuss data suggesting that the source of dopamine within the spinal cord is mainly from the A11 area of the diencephalon, and then turn to a discussion of dopamine’s role in modulating walking patterns from both in vivo and in vitro preparations. Similar to the descending serotonergic system, the dopaminergic system may serve as a potential target to promote recovery of locomotor function following spinal cord injury (SCI); evidence suggests that dopaminergic agonists can promote recovery of function following SCI. We discuss pharmacogenetic and optogenetic approaches that could be deployed in SCI and their potential tractability. Throughout the review we draw parallels with both noradrenergic and serotonergic modulatory effects on spinal cord networks. In all likelihood, a complementary monoaminergic enhancement strategy should be deployed following SCI.

Sharples, Simon A.; Koblinger, Kathrin; Humphreys, Jennifer M.; Whelan, Patrick J.

2014-01-01

282

Discrimination of Direction in Fast Frequency-Modulated Tones by Rats  

PubMed Central

Fast frequency modulations (FM) are an essential part of species-specific auditory signals in animals as well as in human speech. Major parameters characterizing non-periodic frequency modulations are the direction of frequency change in the FM sweep (upward/downward) and the sweep speed, i.e., the speed of frequency change. While it is well established that both parameters are represented in the mammalian central auditory pathway, their importance at the perceptual level in animals is unclear. We determined the ability of rats to discriminate between upward and downward modulated FM-tones as a function of sweep speed in a two-alternative-forced-choice-paradigm. Directional discrimination in logarithmic FM-sweeps was reduced with increasing sweep speed between 20 and 1,000 octaves/s following a psychometric function. Average threshold sweep speed for FM directional discrimination was 96 octaves/s. This upper limit of perceptual FM discrimination fits well the upper limit of preferred sweep speeds in auditory neurons and the upper limit of neuronal direction selectivity in the rat auditory cortex and midbrain, as it is found in the literature. Influences of additional stimulus parameters on FM discrimination were determined using an adaptive testing-procedure for efficient threshold estimation based on a maximum likelihood approach. Directional discrimination improved with extended FM sweep range between two and five octaves. Discrimination performance declined with increasing lower frequency boundary of FM sweeps, showing an especially strong deterioration when the boundary was raised from 2 to 4 kHz. This deterioration corresponds to a frequency-dependent decline in direction selectivity of FM-encoding neurons in the rat auditory cortex, as described in the literature. Taken together, by investigating directional discrimination of FM sweeps in the rat we found characteristics at the perceptual level that can be related to several aspects of FM encoding in the central auditory pathway.

King, Isabella; Felsheim, Christian; Ostwald, Joachim; von der Behrens, Wolfger

2006-01-01

283

On the design and performance of TDBC-based bi-directional network beamforming  

Microsoft Academic Search

We study and compare the performance of two bi-directional relay network beamforming schemes, namely time division broadcast channel (TDBC) strategy and multiple access broadcast channel (MABC) strategy, under joint optimal power control and beamforming design. Under the presence of a direct link between the two transceivers, we first design the optimal TDBC-based bi-directional network beamformer to minimize the total power

Mohammad Zaeri-Amirani; Shahram Shahbazpanahi; Min Dong

2011-01-01

284

Network Discovery Pipeline Elucidates Conserved Time-of-Day-Specific cis-Regulatory Modules  

PubMed Central

Correct daily phasing of transcription confers an adaptive advantage to almost all organisms, including higher plants. In this study, we describe a hypothesis-driven network discovery pipeline that identifies biologically relevant patterns in genome-scale data. To demonstrate its utility, we analyzed a comprehensive matrix of time courses interrogating the nuclear transcriptome of Arabidopsis thaliana plants grown under different thermocycles, photocycles, and circadian conditions. We show that 89% of Arabidopsis transcripts cycle in at least one condition and that most genes have peak expression at a particular time of day, which shifts depending on the environment. Thermocycles alone can drive at least half of all transcripts critical for synchronizing internal processes such as cell cycle and protein synthesis. We identified at least three distinct transcription modules controlling phase-specific expression, including a new midnight specific module, PBX/TBX/SBX. We validated the network discovery pipeline, as well as the midnight specific module, by demonstrating that the PBX element was sufficient to drive diurnal and circadian condition-dependent expression. Moreover, we show that the three transcription modules are conserved across Arabidopsis, poplar, and rice. These results confirm the complex interplay between thermocycles, photocycles, and the circadian clock on the daily transcription program, and provide a comprehensive view of the conserved genomic targets for a transcriptional network key to successful adaptation.

McEntee, Connor; Byer, Amanda; Trout, Jonathan D; Hazen, Samuel P; Shen, Rongkun; Priest, Henry D; Sullivan, Christopher M; Givan, Scott A; Yanovsky, Marcelo; Hong, Fangxin; Kay, Steve A; Chory, Joanne

2008-01-01

285

Performance of a FPGA-based Direct Digitising Signal Measurement module for MIT  

NASA Astrophysics Data System (ADS)

A novel MIT Direct Digitising Signal Measurement (DDSM) module has been developed aiming to replace the centralised NI PXI system and PC processing of the Cardiff Mk2 MIT system, thus offering potentially faster measurement cycles. The proposed module replaces the signal acquisition and offers local processing. The core of the system is a Xilinx Spartan-3 FPGA, paired with a dual 14-bit ADC capable of 120 MS/s. The FPGA provides a flexible and fast platform for data acquisition and processing. The phase is measured using a two channel phase sensitive detection via I/Q demodulation. Built-in averaging reduces the data to a single signal period of 12 samples before multiplying and accumulating the data with the I/Q signals. The system provides the I/Q values for both channels directly, eliminating the long download and processing times required by the centralised NI PXI system currently used in the Cardiff Mk2 MIT system. The module acquires both the measurement and the reference signal and has a phase noise as low as 7.5m° using a measurement time constant of 6ms. The phase drift over 6 hours is considerable at 119m°. Details of the module, circuits and algorithms employed are provided as are the results of the performance measurements.

Patz, R.; Watson, S.; Ktistis, C.; Hamsch, M.; Peyton, A. J.

2010-04-01

286

Directly phase-modulation-mode-locked doubly-resonant optical parametric oscillator.  

PubMed

We present results on direct mode-locking of a doubly-resonant optical parametric oscillator (DRO) using an electro-optic phase modulator with low resonant frequency of 80 MHz as the single mode-locking element. Pumped by a cw laser at 532 nm and based on MgO:sPPLT as the nonlinear material, the DRO generates 533 ps pulses at 80 MHz and 471 ps pulses at 160 MHz. Stable train of mode-locked pulses is obtained at a modulation depth of 1.83 radians when the modulation frequency is precisely tuned and the cavity length is carefully adjusted. The effects of frequency detuning, modulation depth, input laser pump power, crystal temperature and position of modulator inside the cavity, on pulse duration and repetition rate have been studied. Operating at degeneracy, under mode-locked condition, the signal-idler spectrum exhibits a bandwidth of ~31 nm, and the spectrum has been investigated for different phase-matching temperatures. Mode-locked operation has been confirmed by second-harmonic-generation of the DRO output in a ?-BaB?O? crystal, where a 4 times enhancement in green power is observed compared to cw operation. PMID:24104250

Devi, Kavita; Kumar, S Chaitanya; Ebrahim-Zadeh, M

2013-10-01

287

A direct torque control scheme for permanent magnet synchronous motors based on space vector modulation  

NASA Astrophysics Data System (ADS)

In order to solve the problem of direct torque control (DTC) for permanent magnet synchronous motor (PMSM) related to the flux and the torque ripple and the uncertainty of switching frequency, A novel direct torque control system based on space vector modulation(SVM-DTC) for permanent magnet synchronous motor was proposed. In this method flux and torque are controlled through stator voltage components in stator flux linkage coordinate axes and space vector modulation is used to control inverters. Therefore, the errors of torque and flux linkage could be compensated accurately. The whole system has only one easily adjustable PI adjuster and needs no high for hardware and easy for realize. The simulation results verify the feasibility of this method, reduction of the flux and the torque ripple, and the good performance of DTC.

Su, Xiao-hui; Xu, Shu-Ping

2013-03-01

288

Current-mode implementation of processing modules in ART-based neural networks  

NASA Astrophysics Data System (ADS)

This paper describes implementation of neural network processing layers using basic current-mode operating modules. The research work has been focused on the implementation of neural networks based on the Adaptive Resonance Theory, developed by S. Grossberg and G.A. Carpenter. The ART-based neural network whose operating modules have been choosen for development is the one called MART, proposed by F. Delgado, because of its complex architecture, auto--adaptive self-learning process, able to discard unmeaningful cathegories. Our presentation starts introducing the behaviour of MART with an analysis of its structure. The development described by this research work is focused on the monochannel block included in the main signal processing part of the MART neural network. The description of the computing algorithm of the layers inside a monochannel block are also provided in order to show what operational current-mode modules are needed (multiplier, divider, square-rooter, adder, substractor, absolute value, maximum and minimum evaluator...). Descriptions at schematic and layout levels of all the processing layers are given. All of them have been designed using AMS 0.35 micron technology with a supply voltage of 3.3 volts. The modules are designed to deal with input currents in the range of 20 to 50 microamps, showing a lineal behaviour and an output error of less than 10%, which is good enough for neural signal processing systems. The maximum frecuency of operation is around 200 kHz. Simulation results are included to show that the operation performed by the hardware designed matches the behaviour described by the MART neural network. For testing purposes we show the design of a monochannel block hardware implementation restricted to five inputs and three cathegories.

Lopez-Alcantud, Jose-Alejandro; Hauer, Hans; Diaz-Madrid, Jose-Angel; Ruiz-Merino, Ramon

2003-04-01

289

Sex-Specific Modulation of Gene Expression Networks in Murine Hypothalamus  

PubMed Central

The hypothalamus contains nuclei and cell populations that are critical in reproduction and that differ significantly between the sexes in structure and function. To examine the molecular and genetic basis for these differences, we quantified gene expression in the hypothalamus of 39 pairs of adult male and female mice belonging to the BXD strains. This experimental design enabled us to define hypothalamic gene coexpression networks and provided robust estimates of absolute expression differences. As expected, sex has the strongest effect on the expression of genes on the X and Y chromosomes (e.g., Uty, Xist, Kdm6a). Transcripts associated with the endocrine system and neuropeptide signaling also differ significantly. Sex-differentiated transcripts often have well delimited expression within specific hypothalamic nuclei that have roles in reproduction. For instance, the estrogen receptor (Esr1) and neurokinin B (Tac2) genes have intense expression in the medial preoptic and arcuate nuclei and comparatively high expression in females. Despite the strong effect of sex on single transcripts, the global pattern of covariance among transcripts is well preserved, and consequently, males and females have well matched coexpression modules. However, there are sex-specific hub genes in functionally equivalent modules. For example, only in males is the Y-linked gene, Uty, a highly connected transcript in a network that regulates chromatin modification and gene transcription. In females, the X chromosome paralog, Kdm6a, takes the place of Uty in the same network. We also find significant effect of sex on genetic regulation and the same network in males and females can be associated with markedly different regulatory loci. With the exception of a few sex-specific modules, our analysis reveals a system in which sets of functionally related transcripts are organized into stable sex-independent networks that are controlled at a higher level by sex-specific modulators.

Mozhui, Khyobeni; Lu, Lu; Armstrong, William E.; Williams, Robert W.

2012-01-01

290

Direct gigabit modulation of injection lasers--Structure-dependent speed limitations  

Microsoft Academic Search

Samples of a large variety of quaternary 1.3- and 1.5-?m injection lasers were directly modulated at bit rates up to 2 Gbit\\/s using a drive circuit known to have a flat response up to speeds more than twice this high. The resulting optical signals were detected and analyzed for eye degradation and bit error rates. It was found that some

RICHARD A. LINKE

1984-01-01

291

Direct-Sequence Spread Spectrum with DPSK Modulation and Diversity for Indoor Wireless Communications  

Microsoft Academic Search

Direct-sequence spread spectrum with differential phase shift-keying (DPSK) modulation and code-division multiple-access is a promising approach for wireless communications in an indoor environment, which is characterized in this paper by a Rayleigh-fading multipath channel. In this study, we consider two specific channel models having different path-delay distributions and average path power profiles. A star configuration, in which each user exercises

MOHSEN KAVEHRAD; BHASKAR RAMAMURTHI

1987-01-01

292

Suppression of chaos in a directly modulated semiconductor laser with delayed optoelectronic feedback  

NASA Astrophysics Data System (ADS)

The effect of delayed optoelectronic feedback on a directly modulated InGaAsP laser diode is numerically studied. It is found that a complete elimination of the previously observed period doubling, chaos and formation of pulses with double peak structure is possible by the feedback with small delays. Bifurcation diagrams and time series plots are used to characterize the chaotic and periodic states of the laser.

Rajesh, S.; Nandakumaran, V. M.

2003-12-01

293

Achievable information rate for outdoor free space optical communication with intensity modulation and direct detection  

Microsoft Academic Search

This work investigates the achievable information rate with the state-of-the-art turbo coding and intensity modulation\\/direct detection for outdoor long-distance free-space optic (FSO) communications. The channel under weak atmospheric turbulence is modeled as a log-normal intensity fading channel where on-off keying makes it look asymmetric. While no effort is made to spectrally match the code to the asymmetry of the channel,

Jing Li; Murat Uysal

2003-01-01

294

Direct modulation and mode locking of 1.3 mum quantum dot lasers  

Microsoft Academic Search

We report 7 GHz cut-off frequency, 2.5 and 5 Gb s-1 eye pattern measurements upon direct modulation of 1.3 mum quantum dot lasers grown without incorporating phosphorus in the layers. Passive mode-locking is achieved from very low frequencies up to 50 GHz and hybrid mode-locking is achieved up to 20 GHz. The minimum pulse width of the Fourier-limited pulses at

M. Kuntz; G. Fiol; M. Lämmlin; D. Bimberg; M. G. Thompson; K. T. Tan; C. Marinelli; A. Wonfor; R. Sellin; R. V. Penty; I. H. White; V. M. Ustinov; A. E. Zhukov; Yu M. Shernyakov; A. R. Kovsh; N. N. Ledentsov; C. Schubert; V. Marembert

2004-01-01

295

Wireless Multimedia Sensor Networks: current trends and future directions.  

PubMed

Wireless Multimedia Sensor Networks (WMSNs) have emerged and shifted the focus from the typical scalar wireless sensor networks to networks with multimedia devices that are capable to retrieve video, audio, images, as well as scalar sensor data. WMSNs are able to deliver multimedia content due to the availability of inexpensive CMOS cameras and microphones coupled with the significant progress in distributed signal processing and multimedia source coding techniques. In this paper, we outline the design challenges of WMSNs, give a comprehensive discussion of the proposed architectures, algorithms and protocols for the different layers of the communication protocol stack for WMSNs, and evaluate the existing WMSN hardware and testbeds. The paper will give the reader a clear view of the state of the art at all aspects of this research area, and shed the light on its main current challenges and future trends. We also hope it will foster discussions and new research ideas among its researchers. PMID:22163571

Almalkawi, Islam T; Zapata, Manel Guerrero; Al-Karaki, Jamal N; Morillo-Pozo, Julian

2010-01-01

296

Wireless Multimedia Sensor Networks: Current Trends and Future Directions  

PubMed Central

Wireless Multimedia Sensor Networks (WMSNs) have emerged and shifted the focus from the typical scalar wireless sensor networks to networks with multimedia devices that are capable to retrieve video, audio, images, as well as scalar sensor data. WMSNs are able to deliver multimedia content due to the availability of inexpensive CMOS cameras and microphones coupled with the significant progress in distributed signal processing and multimedia source coding techniques. In this paper, we outline the design challenges of WMSNs, give a comprehensive discussion of the proposed architectures, algorithms and protocols for the different layers of the communication protocol stack for WMSNs, and evaluate the existing WMSN hardware and testbeds. The paper will give the reader a clear view of the state of the art at all aspects of this research area, and shed the light on its main current challenges and future trends. We also hope it will foster discussions and new research ideas among its researchers.

Almalkawi, Islam T.; Zapata, Manel Guerrero; Al-Karaki, Jamal N.; Morillo-Pozo, Julian

2010-01-01

297

Adaptation to mirror-reversed vision is based on directionally tuned modules.  

PubMed

Sensorimotor adaptation to rotated visual feedback is thought to be achieved by directionally tuned modules. Here we scrutinize whether adaptation to reversed vision utilizes similar mechanisms. Specifically, we hypothesize that adaptive transfer to unpracticed target directions is determined by the superposition of neighboring modules. One group of subjects adapted to a left-right reversal of visual feedback, which requires a 180°, ±90°, or no change of response direction, depending on target position. Two groups of control subjects adapted to a 180° and to a 90° rotation of visual feedback. We found that adaptation to a left-right reversal is less efficient than adaptation to rotations requiring the same adaptive change, and attribute this decrement to an overlap of neighboring modules. We further found that transfer to unpracticed targets is well predicted by a simple Gaussian model. From this we conclude that adaptation to a left-right reversal emerges in a regional and interdependent fashion, and can be modeled as overlapping Gaussian tuned processes. PMID:21764164

Werner, Susen

2012-02-01

298

Phosphorylation-directed antibodies in high-flux screens for compounds that modulate signal transduction.  

PubMed

Synthetic tyrosine phosphopeptides were used to generate antibodies that recognize phosphotyrosine in the context of a defined sequence of flanking amino acids. Using phosphopeptide immunogens derived from regulatory or signal-generating motifs, "phosphorylation-directed antibodies" can be targeted to specific growth factor receptors or signal-generating proteins. In his paper, we show how phosphorylation-directed antibodies can be used in a colorimetric, high-throughput screen for drugs that modulate the function of specific growth factor receptors or signal-generating proteins. PMID:9298221

Alberta, J A; Stiles, C D

1997-09-01

299

Multi-user bidirectional communication using isochronal synchronisation of array of chaotic directly modulated semiconductor lasers  

NASA Astrophysics Data System (ADS)

Isochronal synchronisation between the elements of an array of three mutually coupled directly modulated semiconductor lasers is utilized for the purpose of simultaneous bidirectional secure communication. Chaotic synchronisation is achieved by adding the coupling signal to the self feedback signal provided to each element of the array. A symmetric coupling is effective in inducing synchronisation between the elements of the array. This coupling scheme provides a direct link between every pair of elements thus making the method suitable for simultaneous bidirectional communication between them. Both analog and digital messages are successfully encrypted and decrypted simultaneously by each element of the array.

Krishna, Bindu M.; John, Manu P.; Nandakumaran, V. M.

2010-04-01

300

ABC and IFC: Modules Detection Method for PPI Network  

PubMed Central

Many clustering algorithms are unable to solve the clustering problem of protein-protein interaction (PPI) networks effectively. A novel clustering model which combines the optimization mechanism of artificial bee colony (ABC) with the fuzzy membership matrix is proposed in this paper. The proposed ABC-IFC clustering model contains two parts: searching for the optimum cluster centers using ABC mechanism and forming clusters using intuitionistic fuzzy clustering (IFC) method. Firstly, the cluster centers are set randomly and the initial clustering results are obtained by using fuzzy membership matrix. Then the cluster centers are updated through different functions of bees in ABC algorithm; then the clustering result is obtained through IFC method based on the new optimized cluster center. To illustrate its performance, the ABC-IFC method is compared with the traditional fuzzy C-means clustering and IFC method. The experimental results on MIPS dataset show that the proposed ABC-IFC method not only gets improved in terms of several commonly used evaluation criteria such as precision, recall, and P value, but also obtains a better clustering result.

Lei, Xiujuan; Tian, Jianfang

2014-01-01

301

Opportunistic mechanisms for IEEE 802.11 networks using directional antennas  

Microsoft Academic Search

Directional antennas have been introduced to improve the performance of 802.11 based wireless networks. Station equipped with directional antennas can beamform data in a specific direction. However, IEEE 802.11 is developed with omni-directional antennas in mind. Thus, deploying IEEE 802.11 in a directional antenna environment leads stations to be conservative in blocking their own transmissions in favor of the ongoing

Tamer Nadeem

2009-01-01

302

Implementing direct, spatially isolated problems on transputer networks  

NASA Technical Reports Server (NTRS)

Parametric studies were performed on transputer networks of up to 40 processors to determine how to implement and maximize the performance of the solution of problems where no processor-to-processor data transfer is required for the problem solution (spatially isolated). Two types of problems are investigated a computationally intensive problem where the solution required the transmission of 160 bytes of data through the parallel network, and a communication intensive example that required the transmission of 3 Mbytes of data through the network. This data consists of solutions being sent back to the host processor and not intermediate results for another processor to work on. Studies were performed on both integer and floating-point transputers. The latter features an on-chip floating-point math unit and offers approximately an order of magnitude performance increase over the integer transputer on real valued computations. The results indicate that a minimum amount of work is required on each node per communication to achieve high network speedups (efficiencies). The floating-point processor requires approximately an order of magnitude more work per communication than the integer processor because of the floating-point unit's increased computing capacity.

Ellis, Graham K.

1988-01-01

303

Survivin, cancer networks and pathway-directed drug discovery  

Microsoft Academic Search

Although there is no shortage of potential targets for cancer therapeutics, we know of only a handful of molecules that are differentially expressed in cancer and intersect multiple pathways required for tumour maintenance. Survivin embodies these properties, and orchestrates integrated cellular networks that are essential for tumour cell proliferation and viability. Pursuing the nodal functions of survivin in cancer might

Dario C. Altieri

2008-01-01

304

Neural network surface acoustic wave RF signal processor for digital modulation recognition.  

PubMed

An architecture of a surface acoustic wave (SAW) processor based on an artificial neural network is proposed for an automatic recognition of different types of digital passband modulation. Three feed-forward networks are trained to recognize filtered and unfiltered binary phase shift keying (BPSK) and quadrature phase shift keying (QPSK) signals, as well as unfiltered BPSK, QPSK, and 16 quadrature amplitude (16QAM) signals. Performance of the processor in the presence of additive white Gaussian noise (AWGN) is simulated. The influence of second-order effects in SAW devices, phase, and amplitude errors on the performance of the processor also is studied. PMID:12243579

Kavalov, Dimitar; Kalinin, Victor

2002-09-01

305

Modeling and Analysis of Power-Aware Ad hoc Networks with Directional Antennas  

Microsoft Academic Search

In this work, we study analytically the benefits of transmission power control on throughput and energy consumption in a uniformly distributed power-aware ad hoc networks where nodes are equipped with directional antennas. We construct an interference model for directional antenna based on a honey grid model to calculate the maximum interference. We further derive a directional collision avoidance model and

Bassel Alawieh; Chadi Assi

2007-01-01

306

Extending the direct laser modulation bandwidth by exploiting the photon-photon resonance: modeling, simulations and experiments  

NASA Astrophysics Data System (ADS)

The direct laser modulation bandwidth can be extended substantially by introducing a supplementary photon-photon resonance (PPR) at a higher frequency than the carrier-photon resonance (CPR). The paper presents a modified rate equation model that takes into account the PPR by treating the longitudinal confinement factor as a dynamic variable. The conditions required for obtaining a strong PPR and an enhancement of the small-signal modulation bandwidth are analyzed and experimental results confirming the model are presented. Since the small-signal modulation bandwidth may not be indicative of the large-signal modulation capability, particularly in case of a small-signal modulation response with substantial variations across the bandwidth, we have also analyzed the influence of the PPR-enhanced small-signal modulation response shape on the large-signal modulation capability as well as the methods that can be employed to flatten the small-signal modulation transfer function between the CPR and PPR.

Dumitrescu, M.; Laakso, A.; Viheriala, J.; Kamp, M.; Bardella, P.; Eisenstein, G.

2013-03-01

307

Early appraisal of the fixation probability in directed networks  

NASA Astrophysics Data System (ADS)

In evolutionary dynamics, the probability that a mutation spreads through the whole population, having arisen from a single individual, is known as the fixation probability. In general, it is not possible to find the fixation probability analytically given the mutant’s fitness and the topological constraints that govern the spread of the mutation, so one resorts to simulations instead. Depending on the topology in use, a great number of evolutionary steps may be needed in each of the simulation events, particularly in those that end with the population containing mutants only. We introduce two techniques to accelerate the determination of the fixation probability. The first one skips all evolutionary steps in which the number of mutants does not change and thereby reduces the number of steps per simulation event considerably. This technique is computationally advantageous for some of the so-called layered networks. The second technique, which is not restricted to layered networks, consists of aborting any simulation event in which the number of mutants has grown beyond a certain threshold value and counting that event as having led to a total spread of the mutation. For advantageous mutations in large populations and regardless of the network’s topology, we demonstrate, both analytically and by means of simulations, that using a threshold of about [N/(r-1)]1/4 mutants, where N is the number of simulation events and r is the ratio of the mutants’ fitness to that of the remainder of the population, leads to an estimate of the fixation probability that deviates in no significant way from that obtained from the full-fledged simulations. We have observed speedups of two orders of magnitude for layered networks with 10000 nodes.

Barbosa, Valmir C.; Donangelo, Raul; Souza, Sergio R.

2010-10-01

308

Research on the electric power grid vulnerability under the directed-weighted topological model based on Complex Network Theory  

Microsoft Academic Search

The vulnerability of electric power grid under the topological model is analyzed based on Complex Network Theory in this paper. And a directed-weighted topological model based on the P-Q networks decomposition is proposed. Firstly the electric power network topological model is decomposed into active and reactive networks ones. Then the direction and weight of line, which is according to the

Zhenbo Wei; Junyong Liu

2010-01-01

309

A novel prediction methodology for detecting failures and instabilities in directional wireless networks  

NASA Astrophysics Data System (ADS)

Even though advances in wireless technology have yielded lower power consumption, higher data rates, and numerous other improvements, the ability to develop a proactive strategy towards handling degradations and failures in directional wireless networks has evaded the research community. In this paper, we introduce a methodology using an analogy to molecular systems in which a directional wireless network utilizing free space optical (FSO) or RF links is modeled as a molecule whose links can grow/retract similarly to bonds. A normal mode analysis (NMA) is performed to identify link instabilities (degradations and failures) and an N-dimensional potential energy surface (PES) is derived with respect to network and environmental parameters to aide in the detection of when a new topology is available ahead of the topology computation stage. Together, the NMA and PES form a basis for a proactive network methodology aimed at improving performance in directional wireless networks.

Coleman, David M.; Milner, Stuart D.; Davis, Christopher C.

2012-10-01

310

The Myth of Spatial Reuse with Directional Antennas in Indoor Wireless Networks  

NASA Astrophysics Data System (ADS)

Interference among co-channel users is a fundamental problem in wireless networks, which prevents nearby links from operating concurrently. Directional antennas allow the radiation patterns of wireless transmitters to be shaped to form directed beams. Conventionally, such beams are assumed to improve the spatial reuse (i.e. concurrency) in indoor wireless networks. In this paper, we use experiments in an indoor office setting of Wifi Access points equipped with directional antennas, to study their potential for interference mitigation and spatial reuse. In contrast to conventional wisdom, we observe that the interference mitigation benefits of directional antennas are minimal. On analyzing our experimental traces we observe that directional links do not reduce interference to nearby links due to the lack of signal confinement due to indoor multipath fading. We then use the insights derived from our study to develop an alternative approach that provides better interference reduction in indoor networks compared to directional links.

Lakshmanan, Sriram; Sundaresan, Karthikeyan; Rangarajan, Sampath; Sivakumar, Raghupathy

311

Comparison of Modules of Wild Type and Mutant Huntingtin and TP53 Protein Interaction Networks: Implications in Biological Processes and Functions  

PubMed Central

Disease-causing mutations usually change the interacting partners of mutant proteins. In this article, we propose that the biological consequences of mutation are directly related to the alteration of corresponding protein protein interaction networks (PPIN). Mutation of Huntingtin (HTT) which causes Huntington's disease (HD) and mutations to TP53 which is associated with different cancers are studied as two example cases. We construct the PPIN of wild type and mutant proteins separately and identify the structural modules of each of the networks. The functional role of these modules are then assessed by Gene Ontology (GO) enrichment analysis for biological processes (BPs). We find that a large number of significantly enriched () GO terms in mutant PPIN were absent in the wild type PPIN indicating the gain of BPs due to mutation. Similarly some of the GO terms enriched in wild type PPIN cease to exist in the modules of mutant PPIN, representing the loss. GO terms common in modules of mutant and wild type networks indicate both loss and gain of BPs. We further assign relevant biological function(s) to each module by classifying the enriched GO terms associated with it. It turns out that most of these biological functions in HTT networks are already known to be altered in HD and those of TP53 networks are altered in cancers. We argue that gain of BPs, and the corresponding biological functions, are due to new interacting partners acquired by mutant proteins. The methodology we adopt here could be applied to genetic diseases where mutations alter the ability of the protein to interact with other proteins.

Basu, Mahashweta; Bhattacharyya, Nitai P.; Mohanty, Pradeep K.

2013-01-01

312

A wideband radiometer module for an unamplified direct detection scalable W-band imaging array  

NASA Astrophysics Data System (ADS)

A W-band unamplified direct detection radiometer module is described that provides a wideband response and is scalable to large arrays. The radiometer design is intended to provide sufficient sensitivity for millimeter wave imaging applications with a goal of 2K noise equivalent temperature difference (NETD) at a 30 Hz frame rate. This effort leverages previously reported device scaling to increase sensitivity. We present a radiometer module designed for 60 GHz RF bandwidth that utilizes HRL's antimonide-based backward tunnel diode. An impedance matching circuit with on- and off-chip elements, as well as ridged waveguide, provides a wideband match to the detectors. Modules were designed with two different microwave substrates: 125 micron thick quartz and 100 micron thick alumina. flip-chip bonding of the detectors is amenable to automated pick-and-place for high volume manufacturing. The modular nature of the array approach allows large arrays to be manufactured in a straightforward manner. We present the design approach along with both electromagnetic simulations and measured performance of the modules. This work was supported by phase II of DARPA's MIATA program.

Schaffner, James H.; Lynch, Jonathan J.; Guinn, Keith V.; Schulman, Joel N.; Moyer, Harris P.; Bowen, Ross; Musni, Marcel

2008-05-01

313

A neural network approach to off-line signature verification using directional PDF  

Microsoft Academic Search

A neural network approach is proposed to build the first stage of an Automatic Handwritten Signature Verification System. The directional Probability Density Function was used as a global shape factor and its discriminating power was enhanced by reducing its cardinality via filtering. Various experimental protocols were used to implement the backpropagation network (BPN) classifier. A comparison, on the same database

Jean-pierre Drouhard; Robert Sabourin; Mario Godbout

1996-01-01

314

NETWORK REPRESENTATION AND SHORTEST PATH REFLECTING THE RAMP ENTRY OR EXIT DIRECTION LIMITATION  

Microsoft Academic Search

There are some ramp entry or exit direction limitations on networks. This kind of limitation is represented by successive passage prohibition (SPP). It indicates that the vehicles cannot successively pass two links with SPP attributes. However, the shortest-path tree sometimes cannot be expressed with a simple tree when a network having this limitation is represented with single nodes. In such

Kazutaka TAKAO; Tohru HIGASHI; Koji YASUDA; Yasuo ASAKURA

315

An Efficient Localization Based on Directional Antenna for Wireless Sensor Networks (WSN's)  

Microsoft Academic Search

In this paper we have introduced an algorithm for localization in wireless sensor network (WSN) with the help of directional antenna. Location of each node in a wireless sensor network play an important role after tracing or event detection on a particular node. Manually configuration of location about each node in wireless sensor environment is not feasible at the time

Dileep Kumar; Shirshu Varma

2009-01-01

316

A 50-kW Module Power Station of Directly Solar-Pumped Iodine Laser  

NASA Technical Reports Server (NTRS)

The conceptual design of a 50 kW Directly Solar-Pumped Iodine Laser (DSPIL) module was developed for a space-based power station which transmits its coherent-beam power to users such as the moon, Martian rovers, or other satellites with large (greater than 25 kW) electric power requirements. Integration of multiple modules would provide an amount of power that exceeds the power of a single module by combining and directing the coherent beams to the user's receiver. The model developed for the DSPIL system conservatively predicts the laser output power (50 kW) that appears much less than the laser output (93 kW) obtained from the gain volume ratio extrapolation of experimental data. The difference in laser outputs may be attributed to reflector configurations adopted in both design and experiment. Even though the photon absorption by multiple reflections in experimental cavity setup was more efficient, the maximum secondary absorption amounts to be only 24.7 percent of the primary. However, the gain volume ratio shows 86 percent more power output than theoretical estimation that is roughly 60 percent more than the contribution by the secondary absorption. Such a difference indicates that the theoretical model adopted in the study underestimates the overall performance of the DSPIL. This fact may tolerate more flexible and radical selection of design parameters than used in this design study. The design achieves an overall specific power of approximately 5 W/kg and total mass of 10 metric tons.

Choi, S. H.; Lee, J. H.; Meador, W. E.; Conway, E. J.

1997-01-01

317

KATP-channels in beta-cells in tissue slices are directly modulated by millimolar ATP.  

PubMed

In pancreatic beta-cells, inhibition of K(ATP)-channels plays a pivotal role in signal transduction of glucose-induced insulin release. However, the extreme sensitivity of K(ATP)-channels to its ligand ATP as found in inside-out patches is not directly compatible with modulation of these channels at physiological [ATP](i). We studied K(ATP)-channel sensitivity to ATP in beta-cells in dispersed culture and in fresh pancreatic tissue slices. Physiological [ATP](i) blocks more than 99% of K(ATP)-channels in cultured beta-cells, while only 90% in beta-cells in slices, indicating reduced sensitivity to ATP in the fresh slices. Applying cytosolic factors like ADP, phosphatidylinositol-4,5-bisphosphate (PIP(2)) or oleoyl-CoA did not restore the K(ATP)-channel sensitivity in cultured beta-cells. Our data suggest that interaction between SUR1 and Kir6.2 subunit of the K(ATP)-channel could be a factor in sensitivity modulation. Tissue slices are the first beta-cell preparation to study direct K(ATP)-channel modulation by physiological [ATP](i). PMID:15664451

Speier, S; Yang, S-B; Sroka, K; Rose, T; Rupnik, M

2005-01-31

318

Cancer core modules identification through genomic and transcriptomic changes correlation detection at network level  

PubMed Central

Background Identification of driver mutations among numerous genomic alternations remains a critical challenge to the elucidation of the underlying mechanisms of cancer. Because driver mutations by definition are associated with a greater number of cancer phenotypes compared to other mutations, we hypothesized that driver mutations could more easily be identified once the genotype-phenotype correlations are detected across tumor samples. Results In this study, we describe a novel network analysis to identify the driver mutation through integrating both cancer genomes and transcriptomes. Our method successfully identified a significant genotype-phenotype change correlation in all six solid tumor types and revealed core modules that contain both significantly enriched somatic mutations and aberrant expression changes specific to tumor development. Moreover, we found that the majority of these core modules contained well known cancer driver mutations, and that their mutated genes tended to occur at hub genes with central regulatory roles. In these mutated genes, the majority were cancer-type specific and exhibited a closer relationship within the same cancer type rather than across cancer types. The remaining mutated genes that exist in multiple cancer types led to two cancer type clusters, one cluster consisted of three neural derived or related cancer types, and the other cluster consisted of two adenoma cancer types. Conclusions Our approach can successfully identify the candidate drivers from the core modules. Comprehensive network analysis on the core modules potentially provides critical insights into convergent cancer development in different organs.

2012-01-01

319

Soft-Input Soft-Output Modules for the Construction and Distributed Iterative Decoding of Code Networks  

NASA Technical Reports Server (NTRS)

Soft-input soft-output building blocks (modules) are presented to construct and iteratively decode in a distributed fashion code networks, a new concept that includes, and generalizes, various forms of concatenated coding schemes.

Benedetto, S.; Divsalar, D.; Montorsi, G.; Pollara, F.

1998-01-01

320

Performance evaluation of ePTFE and PVDF flat-sheet module direct contact membrane distillation.  

PubMed

This paper reports experiments using a flat-sheet module with 0.18 approximately 0.45 microm ePTFE (expanded polytetrafluoroethylene) and PVDF (polyvinylidene fluoride) membranes to show the effects of membrane properties, salt concentration and fluid hydrodynamics on the permeate flux and salt rejection of DCMD (direct contact membrane distillation). A theoretical prediction of the permeate flux was carried out, and was in close agreement with the experimental results. In addition, the energy integration of the process was also analyzed in order to evaluate module design to increase energy efficiency. According to the simulated results of the energy integration design, a combination of simultaneous cooling of the permeate stream and an additional heat exchanger to lower the temperature of the permeate stream not only enhances the MD flux, but also reduces energy consumption. PMID:20651439

Chuang, Ching-Jung; Tung, Kuo-Lun; Fan, Yang-Hsiang; Ho, Chii-Dong; Huang, James

2010-01-01

321

Direct CATV modulation and phase remodulated radio-over-fiber transport system.  

PubMed

A novel transport system, with directly modulating community antenna television (CATV) signal downstream and phase-remodulating radio-over-fiber (ROF) signal upstream, is proposed and experimentally demonstrated. By modulating multi-carriers CATV signal in amplitude domain and ROF signal in phase domain, a single optical wavelength is able to serve these two applications simultaneous. To be the first system of communicating CATV signal downstream and phase remodulating radio signal upstream, the performances of transmitting CATV and radio signals over 20 km single-mode fiber (SMF) were experimentally verified. Good performances of carrier-to-noise ratio (CNR), composite second-order (CSO), and composite triple beat (CTB) were obtained for CATV applications as well as high extinction ration (ER) and low bit error rate (BER) values were measured for ROF transmission. PMID:20588884

Lin, Wen-Yi; Chang, Ching-Hung; Peng, Peng-Chun; Lu, Hai-Han; Huang, Ching-Hsiu

2010-05-10

322

Technical evaluation of a USSC Integrated/Direct Mount PV Roofing Module system at NREL  

SciTech Connect

The results of a 16 month technical evaluation performed on a nominal 1 kW{sub ac} utility-interconnect amorphous silicon PV system deployed at the National Renewable Energy Laboratory`s PV outdoor test site are given here. The system employs 64 prototype United Solar Systems Corp. Integrated/Direct Mount PV Roofing Modules mounted on simulated attic/roof structures. In this paper we show that the PV array fill factor has been relatively stable with respect to time and that the seasonal variations in performance can be largely attributed to seasonal variations in current. We also show that in determining the summer and winter ac power output, the summation of the manufacturer-supplied module peak powers at STC for a similarly located and configured a-Si PV array should be derated by factors of approximately of 0.83 and 0.78 for summer and winter operation, respectively.

Strand, T.; Hansen, R.; Mrig, L.

1995-05-01

323

Unilateral deafness in children affects development of multi-modal modulation and default mode networks  

PubMed Central

Monaural auditory input due to congenital or acquired unilateral hearing loss (UHL) may have neurobiological effects on the developing brain. Using functional magnetic resonance imaging (fMRI), we investigated the effect of UHL on the development of functional brain networks used for cross-modal processing. Children ages 7–12 with moderate or greater unilateral hearing loss of sensorineural origin (UHL-SN; N = 21) and normal-hearing controls (N = 23) performed an fMRI-compatible adaptation of the Token Test involving listening to a sentence such as “touched the small green circle and the large blue square” and simultaneously viewing an arrow touching colored shapes on a video. Children with right or severe-to-profound UHL-SN displayed smaller activation in a region encompassing the right inferior temporal, middle temporal, and middle occipital gyrus (BA 19/37/39), evidencing differences due to monaural hearing in cross-modal modulation of the visual processing pathway. Children with UHL-SN displayed increased activation in the left posterior superior temporal gyrus, likely the result either of more effortful low-level processing of auditory stimuli or differences in cross-modal modulation of the auditory processing pathway. Additionally, children with UHL-SN displayed reduced deactivation of anterior and posterior regions of the default mode network. Results suggest that monaural hearing affects the development of brain networks related to cross-modal sensory processing and the regulation of the default network during processing of spoken language.

Schmithorst, Vincent J.; Plante, Elena; Holland, Scott

2014-01-01

324

Unilateral deafness in children affects development of multi-modal modulation and default mode networks.  

PubMed

Monaural auditory input due to congenital or acquired unilateral hearing loss (UHL) may have neurobiological effects on the developing brain. Using functional magnetic resonance imaging (fMRI), we investigated the effect of UHL on the development of functional brain networks used for cross-modal processing. Children ages 7-12 with moderate or greater unilateral hearing loss of sensorineural origin (UHL-SN; N = 21) and normal-hearing controls (N = 23) performed an fMRI-compatible adaptation of the Token Test involving listening to a sentence such as "touched the small green circle and the large blue square" and simultaneously viewing an arrow touching colored shapes on a video. Children with right or severe-to-profound UHL-SN displayed smaller activation in a region encompassing the right inferior temporal, middle temporal, and middle occipital gyrus (BA 19/37/39), evidencing differences due to monaural hearing in cross-modal modulation of the visual processing pathway. Children with UHL-SN displayed increased activation in the left posterior superior temporal gyrus, likely the result either of more effortful low-level processing of auditory stimuli or differences in cross-modal modulation of the auditory processing pathway. Additionally, children with UHL-SN displayed reduced deactivation of anterior and posterior regions of the default mode network. Results suggest that monaural hearing affects the development of brain networks related to cross-modal sensory processing and the regulation of the default network during processing of spoken language. PMID:24723873

Schmithorst, Vincent J; Plante, Elena; Holland, Scott

2014-01-01

325

Evolutionary developmental transcriptomics reveals a gene network module regulating interspecific diversity in plant leaf shape  

PubMed Central

Despite a long-standing interest in the genetic basis of morphological diversity, the molecular mechanisms that give rise to developmental variation are incompletely understood. Here, we use comparative transcriptomics coupled with the construction of gene coexpression networks to predict a gene regulatory network (GRN) for leaf development in tomato and two related wild species with strikingly different leaf morphologies. The core network in the leaf developmental GRN contains regulators of leaf morphology that function in global cell proliferation with peripheral gene network modules (GNMs). The BLADE-ON-PETIOLE (BOP) transcription factor in one GNM controls the core network by altering effective concentration of the KNOTTED-like HOMEOBOX gene product. Comparative network analysis and experimental perturbations of BOP levels suggest that variation in BOP expression could explain the diversity in leaf complexity among these species through dynamic rewiring of interactions in the GRN. The peripheral location of the BOP-containing GNM in the leaf developmental GRN and the phenotypic mimics of evolutionary diversity caused by alteration in BOP levels identify a key role for this GNM in canalizing the leaf morphospace by modifying the maturation schedule of leaves to create morphological diversity.

Ichihashi, Yasunori; Aguilar-Martinez, Jose Antonio; Farhi, Moran; Chitwood, Daniel H.; Kumar, Ravi; Millon, Lee V.; Peng, Jie; Maloof, Julin N.; Sinha, Neelima R.

2014-01-01

326

Evolutionary developmental transcriptomics reveals a gene network module regulating interspecific diversity in plant leaf shape.  

PubMed

Despite a long-standing interest in the genetic basis of morphological diversity, the molecular mechanisms that give rise to developmental variation are incompletely understood. Here, we use comparative transcriptomics coupled with the construction of gene coexpression networks to predict a gene regulatory network (GRN) for leaf development in tomato and two related wild species with strikingly different leaf morphologies. The core network in the leaf developmental GRN contains regulators of leaf morphology that function in global cell proliferation with peripheral gene network modules (GNMs). The BLADE-ON-PETIOLE (BOP) transcription factor in one GNM controls the core network by altering effective concentration of the KNOTTED-like HOMEOBOX gene product. Comparative network analysis and experimental perturbations of BOP levels suggest that variation in BOP expression could explain the diversity in leaf complexity among these species through dynamic rewiring of interactions in the GRN. The peripheral location of the BOP-containing GNM in the leaf developmental GRN and the phenotypic mimics of evolutionary diversity caused by alteration in BOP levels identify a key role for this GNM in canalizing the leaf morphospace by modifying the maturation schedule of leaves to create morphological diversity. PMID:24927584

Ichihashi, Yasunori; Aguilar-Martínez, José Antonio; Farhi, Moran; Chitwood, Daniel H; Kumar, Ravi; Millon, Lee V; Peng, Jie; Maloof, Julin N; Sinha, Neelima R

2014-06-24

327

Analysis and Enhancements for IEEE 802.11 Networks Using Directional Antenna With Opportunistic Mechanisms  

Microsoft Academic Search

Directional antennas are introduced to improve the performance of IEEE 802.11-based wireless networks by allowing stations equipped with directional antennas to beam the data in a specific direction. Since IEEE 802.11 has been developed with omni antennas in mind, deploying IEEE 802.11 in a directional antenna environment leads stations to be conservative in blocking their own transmissions in favor of

Tamer Nadeem

2010-01-01

328

Directed clustering coefficient as a measure of systemic risk in complex banking networks  

NASA Astrophysics Data System (ADS)

Recent literature has focused on the study of systemic risk in complex networks. It is clear now, after the crisis of 2008, that the aggregate behavior of the interaction among agents is not straightforward and it is very difficult to predict. Contributing to this debate, this paper shows that the directed clustering coefficient may be used as a measure of systemic risk in complex networks. Furthermore, using data from the Brazilian interbank network, we show that the directed clustering coefficient is negatively correlated with domestic interest rates.

Tabak, Benjamin M.; Takami, Marcelo; Rocha, Jadson M. C.; Cajueiro, Daniel O.; Souza, Sergio R. S.

2014-01-01

329

Moral judgment modulation by disgust is bi-directionally moderated by individual sensitivity.  

PubMed

Modern theories of moral judgment predict that both conscious reasoning and unconscious emotional influences affect the way people decide about right and wrong. In a series of experiments, we tested the effect of subliminal and conscious priming of disgust facial expressions on moral dilemmas. "Trolley-car"-type scenarios were used, with subjects rating how acceptable they found the utilitarian course of action to be. On average, subliminal priming of disgust facial expressions resulted in higher rates of utilitarian judgments compared to neutral facial expressions. Further, in replication, we found that individual change in moral acceptability ratings due to disgust priming was modulated by individual sensitivity to disgust, revealing a bi-directional function. Our second replication extended this result to show that the function held for both subliminally and consciously presented stimuli. Combined across these experiments, we show a reliable bi-directional function, with presentation of disgust expression primes to individuals with higher disgust sensitivity resulting in more utilitarian judgments (i.e., number-based) and presentations to individuals with lower sensitivity resulting in more deontological judgments (i.e., rules-based). Our results may reconcile previous conflicting reports of disgust modulation of moral judgment by modeling how individual sensitivity to disgust determines the direction and degree of this effect. PMID:24639665

Ong, How Hwee; Mullette-Gillman, O'Dhaniel A; Kwok, Kenneth; Lim, Julian

2014-01-01

330

Two cascaded SOAs used as intensity modulators for adaptively modulated optical OFDM signals in optical access networks.  

PubMed

Detailed theoretical and numerical investigations of the transmission performance of adaptively modulated optical orthogonal frequency division multiplexed (AMOOFDM) signals are undertaken, for the first time, in optical amplification and chromatic dispersion (CD) compensation free single mode fiber (SMF) intensity-modulated and direct-detection (IMDD) systems using two cascaded semiconductor optical amplifiers in a counterpropagating configuration as an intensity modulator (TC-SOA-CC-IM). A theoretical model describing the characteristics of this configuration is developed. Extensive performance comparisons are also made between the TC-SOA-CC and the single SOA intensity modulators. It is shown that, the TC-SOA-CC reaches its strongly saturated region using a lower input optical power much faster than the single SOA resulting in significantly reduced effective carrier lifetime and thus wide TC-SOA-CC bandwidths. It is shown that at low input optical power, we can increase the signal line rate almost 115% which will be more than twice the transmission performance offered by single SOA. In addition, the TC-SOA-CC-IM is capable of supporting signal line rates higher than corresponding to the SOA-IM by using 10dB lower input optical powers. For long transmission distance, the TC-SOA-CC-IM has much stronger CD compensation capability compared to the SOA-IM. In addition the use of TC-SOA-CC-IM is more effective regarding the capability to benefit from the CD compensation for shorter distances starting at 60km SMF, whilst for the SOA-IM starting at 90km. PMID:24977835

Hamié, Ali; Hamzé, Mohamad; Taki, Haidar; Makouk, Layaly; Sharaiha, Ammar; Alaeddine, Ali; Al Housseini, Ali; Giacoumidis, Elias; Tang, J M

2014-06-30

331

A new direction-sensitive optical module for deep-sea neutrino telescopy  

NASA Astrophysics Data System (ADS)

Within the KM3NeT framework, the NEMO (NEutrino Mediterranean Observatory) project is studying new technologies for a km3-scale neutrino telescope in the Mediterranean Sea. The telescope goal will be the investigation of the high-energy component of the cosmic neutrino spectrum: a promising tool to better understand the mechanisms that originate extreme-energy cosmic rays. Neutrino energy and direction will be reconstructed using the Cherenkov light produced in water by muons coming from neutrino interactions. Two prototypes of a new large-area (10 in.) 4-anode photomultipliers, manufactured by Hamamatsu at the request of the NEMO Collaboration, have been extensively studied. These tubes will be integrated into spherical glass pressure-resistant optical modules and used for the first time to detect the direction of the detected Cherenkov light at the NEMO deep-sea (3600 m) site near Capo Passero in Sicily. The photocathode surface in these optical modules will be effectively divided into four quadrants by a pair of crescent-shaped mirrors embedded in the optical gel linking the PMT to the glass pressure sphere. A series of measurements was performed at the testing facility of the NEMO group at the INFN Sezione di Catania. The single photoelectron peak, the transit time spread, the gain and the cross-talk of the prototype have been studied, to have a complete characterization and make feasible a comparison with previous models. The first prototype of direction-sensitive optical module has been assembled and tested with a dedicated experimental setup at the INFN Sezione di Genova. First results of tests of the prototype are presented.

Brunoldi, Marco

2009-10-01

332

A 45nm WCDMA transmitter using direct quadrature voltage modulator with high oversampling digital front-end  

Microsoft Academic Search

A 45 nm WCDMA transmitter using a direct quadrature voltage modulator with high oversampling digital front-end is described. The highly digitized transmitter realizes modulation in the voltage domain. Delivering 1 dBm WCDMA output power, the transmitter achieves -158 dBc\\/Hz noise and 2% EVM, while consuming 30 mW including the digital front-end.

Xin He; Jan van Sinderen; Robert Rutten

2010-01-01

333

Constructivist Instructional Design and Development of a Networked Learning Skills (NICLS) Module for Continuing Professional Education Distance Learning.  

ERIC Educational Resources Information Center

This paper proposes an instructional systems design (ISD) approach for the design and development of a basic Networked Information and Communication Literacy Skills (NICLS) module. It concentrates on the design and development of a NICLS core skills pre-module for the Master of Arts in Information Technology Management (MA ITM) program at the…

Nunes, J. M. Baptista; McPherson, M.; Rico, M.

334

Data Rewrite of Wavelength Channel Using Saturated SOA Modulator for WDM Metro\\/Access Networks with Centralized Light Sources  

Microsoft Academic Search

We propose a simple wavelength reuse technique for WDM metro\\/access networks with centralized light sources. Using a deeply saturated SOA modulator located in a remote node, we erase the data on a low-extinction-ratio downstream signal and modulate it with new data to generate an upstream signal.

H. Takesue; T. Sugie

2002-01-01

335

Networks of genes modulating the pleiotropic drug response in Saccharomyces cerevisiae.  

PubMed

The pleiotropic drug response (PDR) or multidrug resistance (MDR) are cellular defence mechanisms present in all species to deal with potential toxicity from environmental small molecule toxins or bioactives. The rapid induction of MDR by xenobiotics in mammalian cells and PDR in budding yeast (S. cerevisiae) has been well studied but how pathway specificity is achieved across different structural classes of xenobiotics is not well understood. As a novel approach to this problem we investigated the genome-wide network of genes modulating the yeast PDR. Fluorescently-tagged ABC pumps Pdr5p-GFP and Yor1p-GFP were used as real-time reporters for the Pdr1p/Pdr3p controlled response. Using the yeast non-essential gene deletion set fifty-four gene deletions that suppressed up-regulation of reporter fluorescence to the cell surface in the presence of atorvastatin were identified by high content confocal automated microscopy. Secondary validation using spot dilution assays to known PDR substrates and Western blot assays of Pdr5p expression confirmed 26 genes able to modulate the PDR phenotype. By analysis of network connectivity, an additional 10 genes that fell below the primary screen cut-off were predicted to be involved in PDR and confirmed as above. The PDR modulating genes taken together were enriched in signalling (Rho-GTPase, MAPK), Mediator complexes, and chromatin modification (subunits of ADA and SAGA complexes). Many of the gene deletions cause extra sensitivity in ?pdr1?pdr3 strains strongly suggesting that there are alternative pathways to upregulate PDR, independently of Pdr1p/Pdr3p. We present here the first high-content microscopy screening for PDR modulators, and identify genes that are previously unsuspected regulators of PDR apparently contributing via network interactions. PMID:24201294

Yibmantasiri, Ploi; Bircham, Peter W; Maass, David R; Bellows, David S; Atkinson, Paul H

2014-01-01

336

Modulation of Deoxysugar Transfer by the Elloramycin Glycosyltransferase ElmGT through Site-Directed Mutagenesis?  

PubMed Central

The glycosyltransferase ElmGT from Streptomyces olivaceus is involved in the biosynthesis of the antitumor drug elloramycin, and it has been shown to possess a broad deoxysugar recognition pattern, being able to transfer different l- and d-deoxysugars to 8-demethyl-tetracenomycin C, the elloramycin aglycone. Site-directed mutagenesis in residues L309 and N312, located in the ?/?/? motif within the nucleoside diphosphate-sugar binding region, can be used to modulate the substrate flexibility of ElmGT, making it more precise for transfer of specific deoxysugars.

Ramos, Angelina; Olano, Carlos; Brana, Alfredo F.; Mendez, Carmen; Salas, Jose A.

2009-01-01

337

Random networks of cross-linked directed polymers.  

PubMed

We explore the effect of random permanent cross-links on a system of directed polymers confined between two planes with their end points free to slide on them. We treat the cross-links as quenched disorder and we use a semimicroscopic replica field theory to study the structure and elasticity of this system. Upon increasing the cross-link density, we get a continuous gelation transition signaled by the emergence of a finite in-plane localization length. The distribution of localization length turns out to depend on the height along the preferred direction of the directed polymers. The gelation transition also gives rise to a finite in-plane shear modulus which we calculate and turns out to be universal, i.e., independent of the energy and length scales of the polymers and the cross-links. Using a symmetry argument, we show that cross-links of negligible extent along the preferred axis of the directed polymers do not cause any renormalization to the tilt modulus of the uncross-linked system. PMID:20365585

Ulrich, Stephan; Zippelius, Annette; Benetatos, Panayotis

2010-02-01

338

Adaptive MAC protocol for UAV communication networks using directional antennas  

Microsoft Academic Search

Unmanned aerial vehicle (UAV) has been used recently a lot in military applications as well as in civilian. It shows great advantages and importance in the search and rescue, real-time surveillance, reconnaissance operations, traffic monitoring, hazardous site inspection and range extension. Moreover, UAVs are suited for situations that are too dangerous for direct human monitoring. In general, UAVs have the

Abdel Ilah Alshbatat; Liang Dong

2010-01-01

339

Medical applications of wireless sensor networks - current status and future directions.  

PubMed

In recent years a significant development of BASN (Body Area Sensor Networks) as a special subclass of WSN (Wireless Sensor Networks) has emerged. These networks have enabled a rapid development of telemedicine systems, which provide remote monitoring of patients and their vital parameters. The article gives a short overview of the BASN networks. Furthermore, a general system architecture of telemedicine systems is proposed. The proposed architecture includes a local sensory area, a communication network area and an institutional network area. It also provides the security and privacy of patient-related data. Furthermore, the article surveys some existing telemedicine systems. Finally, some current problems are explained and the directions for the future development of the telemedicine systems are given. PMID:22634904

Grgi?, Krešimir; Zagar, Drago; Križanovi?, Višnja

2012-02-01

340

Direct learning of sparse changes in markov networks by density ratio estimation.  

PubMed

We propose a new method for detecting changes in Markov network structure between two sets of samples. Instead of naively fitting two Markov network models separately to the two data sets and figuring out their difference, we directly learn the network structure change by estimating the ratio of Markov network models. This density-ratio formulation naturally allows us to introduce sparsity in the network structure change, which highly contributes to enhancing interpretability. Furthermore, computation of the normalization term, a critical bottleneck of the naive approach, can be remarkably mitigated. We also give the dual formulation of the optimization problem, which further reduces the computation cost for large-scale Markov networks. Through experiments, we demonstrate the usefulness of our method. PMID:24684449

Liu, Song; Quinn, John A; Gutmann, Michael U; Suzuki, Taiji; Sugiyama, Masashi

2014-06-01

341

Directional Bias and Pheromone for Discovery and Coverage on Networks  

SciTech Connect

Natural multi-agent systems often rely on “correlated random walks” (random walks that are biased toward a current heading) to distribute their agents over a space (e.g., for foraging, search, etc.). Our contribution involves creation of a new movement and pheromone model that applies the concept of heading bias in random walks to a multi-agent, digital-ants system designed for cyber-security monitoring. We examine the relative performance effects of both pheromone and heading bias on speed of discovery of a target and search-area coverage in a two-dimensional network layout. We found that heading bias was unexpectedly helpful in reducing search time and that it was more influential than pheromone for improving coverage. We conclude that while pheromone is very important for rapid discovery, heading bias can also greatly improve both performance metrics.

Fink, Glenn A.; Berenhaut, Kenneth S.; Oehmen, Christopher S.

2012-09-11

342

Direct solutions of sparse network equations by optimally ordered triangular factorization  

Microsoft Academic Search

Matrix inversion is very inefficient for computing direct solutions of the large sparse systems of linear equations that arise in many network problems. Optimally ordered triangular factorization of sparse matrices is more efficient and offers other important computational advantages in some applications. With this method, direct solutions are computed from sparse matrix factors instead of from a full inverse matrix,

W. F. Tinney; J. W. Walker

1967-01-01

343

Medium Access Control Protocols using Directional Antennas in Ad Hoc Networks  

Microsoft Academic Search

Using directional antennas can be beneficial for wireless ad hoc networks consisting of a collection of wireless hosts. To best utilize di- rectional antennas, a suitable Medium Access Control (MAC) protocol must be designed. Current MAC protocols, such as the IEEE 802.11 standard, do not benefit when using directional antennas, because these protocols have been designed for omnidirectional antennas. In

Young-bae Ko; Vinaychandra Shankarkumar; Nitin H. Vaidya

2000-01-01

344

Medium Access Control Protocols Using Directional Antennas in Ad Hoc Networks  

Microsoft Academic Search

Using directional antennas can be beneficial for wireless adhoc networks consisting of a collection of wireless hosts. To best utilize directionalantennas, a suitable Medium Access Control (MAC) protocol mustbe designed. Current MAC protocols, such as the IEEE 802.11 standard, donot benefit when using directional antennas, because these protocols havebeen designed for omnidirectional antennas. In this paper, we attempt todesign new

Young-bae Ko; Vinaychandra Shankarkumar

1999-01-01

345

Fuzzy Direct Torque Controlled Drive for Permanent Magnet Synchronous Motor Based on Neural Networks  

Microsoft Academic Search

For permanent magnet synchronous motor (PMSM) direct torque controlled (DTC) drive, stator resistance variation and conventional hysteresis controller will bring high flux linkage and torque ripples inevitably. In order to solve this problem, the implementation of fuzzy direct torque controlled drive for permanent magnet synchronous based on neural networks is presented, which replaces the conventional hysteresis controller with fuzzy controller

Xianqing Cao; Chunhua Zang; Liping Fan

2006-01-01

346

Identification of responsive gene modules by network-based gene clustering and extending: application to inflammation and angiogenesis  

PubMed Central

Background Cell responses to environmental stimuli are usually organized as relatively separate responsive gene modules at the molecular level. Identification of responsive gene modules rather than individual differentially expressed (DE) genes will provide important information about the underlying molecular mechanisms. Most of current methods formulate module identification as an optimization problem: find the active sub-networks in the genome-wide gene network by maximizing the objective function considering the gene differential expression and/or the gene-gene co-expression information. Here we presented a new formulation of this task: a group of closely-connected and co-expressed DE genes in the gene network are regarded as the signatures of the underlying responsive gene modules; the modules can be identified by finding the signatures and then recovering the "missing parts" by adding the intermediate genes that connect the DE genes in the gene network. Results ClustEx, a two-step method based on the new formulation, was developed and applied to identify the responsive gene modules of human umbilical vein endothelial cells (HUVECs) in inflammation and angiogenesis models by integrating the time-course microarray data and genome-wide PPI data. It shows better performance than several available module identification tools by testing on the reference responsive gene sets. Gene set analysis of KEGG pathways, GO terms and microRNAs (miRNAs) target gene sets further supports the ClustEx predictions. Conclusion Taking the closely-connected and co-expressed DE genes in the condition-specific gene network as the signatures of the underlying responsive gene modules provides a new strategy to solve the module identification problem. The identified responsive gene modules of HUVECs and the corresponding enriched pathways/miRNAs provide useful resources for understanding the inflammatory and angiogenic responses of vascular systems.

2010-01-01

347

Calaxin drives sperm chemotaxis by Ca2+-mediated direct modulation of a dynein motor  

PubMed Central

Sperm chemotaxis occurs widely in animals and plants and plays an important role in the success of fertilization. Several studies have recently demonstrated that Ca2+ influx through specific Ca2+ channels is a prerequisite for sperm chemotactic movement. However, the regulator that modulates flagellar movement in response to Ca2+ is unknown. Here we show that a neuronal calcium sensor, calaxin, directly acts on outer-arm dynein and regulates specific flagellar movement during sperm chemotaxis. Calaxin inhibition resulted in significant loss of sperm chemotactic movement, despite normal increases in intracellular calcium concentration. Using a demembranated sperm model, we demonstrate that calaxin is essential for generation and propagation of Ca2+-induced asymmetric flagellar bending. An in vitro motility assay revealed that calaxin directly suppressed the velocity of microtubule sliding by outer-arm dynein at high Ca2+ concentrations. This study describes the missing link between chemoattractant-mediated Ca2+ signaling and motor-driven microtubule sliding during sperm chemotaxis.

Mizuno, Katsutoshi; Shiba, Kogiku; Okai, Masahiko; Takahashi, Yusuke; Shitaka, Yuji; Oiwa, Kazuhiro; Tanokura, Masaru; Inaba, Kazuo

2012-01-01

348

AMBIENT: Active Modules for Bipartite Networks - using high-throughput transcriptomic data to dissect metabolic response  

PubMed Central

Background With the continued proliferation of high-throughput biological experiments, there is a pressing need for tools to integrate the data produced in ways that produce biologically meaningful conclusions. Many microarray studies have analysed transcriptomic data from a pathway perspective, for instance by testing for KEGG pathway enrichment in sets of upregulated genes. However, the increasing availability of species-specific metabolic models provides the opportunity to analyse these data in a more objective, system-wide manner. Results Here we introduce ambient (Active Modules for Bipartite Networks), a simulated annealing approach to the discovery of metabolic subnetworks (modules) that are significantly affected by a given genetic or environmental change. The metabolic modules returned by ambient are connected parts of the bipartite network that change coherently between conditions, providing a more detailed view of metabolic changes than standard approaches based on pathway enrichment. Conclusions ambient is an effective and flexible tool for the analysis of high-throughput data in a metabolic context. The same approach can be applied to any system in which reactions (or metabolites) can be assigned a score based on some biological observation, without the limitation of predefined pathways. A Python implementation of ambient is available at http://www.theosysbio.bio.ic.ac.uk/ambient.

2013-01-01

349

Directionality in hyperbrain networks discriminates between leaders and followers in guitar duets.  

PubMed

To investigate whether directionality in hyperbrain networks reflects different roles during interpersonal action coordination (IAC), we recorded EEG data from pairs of guitarists playing together as musical leaders versus followers. We used an asymmetric index of in-phase synchronization to analyze hyperbrain networks of directed functional connectivity in the alpha and beta frequency ranges for time segments around coordinated play onsets. After exploring the small-world characteristics of the networks at different thresholds, we examined the directed connection strengths within and between brains. As predicted, we found evidence suggesting that the musical roles of leader and follower are associated with different patterns of directed between-brain couplings. The functional significance of these differences for IAC requires further study. PMID:23761745

Sänger, Johanna; Müller, Viktor; Lindenberger, Ulman

2013-01-01

350

Patterns of vegetation biodiversity: the roles of dispersal directionality and river network structure.  

PubMed

This paper investigates the importance of dispersal directionality and river network structure to biodiversity patterns. Our model results suggest that dispersal directionality plays a crucial role in determining biodiversity patterns, even more so than dispersal rates. Dispersal directionality heterogenizes the spatial distribution of abundance, which results in higher extinction rates of rare species and higher beta diversity. It induces a few species with very high abundances at the expense of many species with intermediate abundances, thereby lowering alpha and gamma diversities. The river network structure also increases beta diversity, i.e., more heterogeneous ecosystems, in comparison to typical two-dimensional landscapes. We find that the interplay between the dispersal directionality and network topology has important consequences on relative species abundance patterns and the distribution of alpha diversity. PMID:18343409

Muneepeerakul, Rachata; Bertuzzo, Enrico; Rinaldo, Andrea; Rodriguez-Iturbe, Ignacio

2008-05-21

351

The anticonvulsant stiripentol acts directly on the GABAA receptor as a positive allosteric modulator  

PubMed Central

SUMMARY Stiripentol(STP) has been used as co-therapy for treatment of epilepsy for many years. Its mechanism of action has long been considered to be indirect, as it inhibits the enzymes responsible for metabolism of other anticonvulsant agents. However, a recent report suggested that STP might also act at the neuronal level, increasing inhibitory GABAergic neurotransmission. We examined the effect of STP on the functional properties of recombinant GABAA receptors (GABARs) and found that it was a positive allosteric modulator of these ion channels. Its activity showed some dependence on subunit composition, with greater potentiation of ?3-containing receptors and reduced potentiation when the ?1 or ? subunits were present. STP caused a leftward shift in the GABA concentration-response relationship, but did not increase the peak response of the receptors to a maximal GABA concentration. Although STP shares some functional characteristics with the neurosteroids, its activity was not inhibited by a neurosteroid site antagonist and was unaffected by a mutation in the ?3 subunit that reduced positive modulation by neurosteroids. The differential effect of STP on ?1- and ?2/?3-containing receptors was not altered by mutations within the second transmembrane domain that affect modulation by loreclezole. These findings suggest that STP acts as a direct allosteric modulator of the GABAR at a site distinct from many commonly used anti-convulsant, sedative and anxiolytic drugs. Its higher activity at ?3-containing receptors as well as its activity at ?-containing receptors may provide a unique opportunity to target selected populations of GABARs.

Fisher, Janet L.

2009-01-01

352

Characterizing system dynamics with a weighted and directed network constructed from time series data  

NASA Astrophysics Data System (ADS)

In this work, we propose a novel method to transform a time series into a weighted and directed network. For a given time series, we first generate a set of segments via a sliding window, and then use a doubly symbolic scheme to characterize every windowed segment by combining absolute amplitude information with an ordinal pattern characterization. Based on this construction, a network can be directly constructed from the given time series: segments corresponding to different symbol-pairs are mapped to network nodes and the temporal succession between nodes is represented by directed links. With this conversion, dynamics underlying the time series has been encoded into the network structure. We illustrate the potential of our networks with a well-studied dynamical model as a benchmark example. Results show that network measures for characterizing global properties can detect the dynamical transitions in the underlying system. Moreover, we employ a random walk algorithm to sample loops in our networks, and find that time series with different dynamics exhibits distinct cycle structure. That is, the relative prevalence of loops with different lengths can be used to identify the underlying dynamics.

Sun, Xiaoran; Small, Michael; Zhao, Yi; Xue, Xiaoping

2014-06-01

353

Directional virtual carrier sensing for directional antennas in mobile ad hoc networks  

Microsoft Academic Search

This paper presents a new carrier sensing mechanism called DVCS (Directional Virtual Carrier Sensing) for wireless communication using directional antennas. DVCS does not require specific antenna configurations or external devices. Instead it only needs information on AOA (Angle of Arrival) and antenna gain for each signal from the underlying physical device, both of which are commonly used for the adaptation

Mineo Takai; Jay Martin; Rajive Bagrodia; Aifeng Ren

2002-01-01

354

Fiber-Optic Transceiver Module for High-Speed Intrasatellite Networks  

NASA Astrophysics Data System (ADS)

High-speed intrasatellite networks are needed to interconnect units such as synthetic aperture radars, high-resolution cameras, and fast image-compression processors that produce data beyond gigabits per second. We have developed a fiber-optic link, named SpaceFibre, which operates up to 3.125 Gb/s and is compatible with the existing SpaceWire network. The link provides symmetrical, bidirectional, full-duplex, and point-to-point communication. It employs 850-nm vertical-cavity surface emitting lasers, radiation-hardened laser-optimized 50/125 µm graded-index fibers, and GaAs p-i-n photo diodes. The transceiver electronics is realized using a multilayer-ceramic-substrate technology that enables the passive alignment of optical fibers to active devices. The SpaceFibre link demonstrator was tested to transfer data at 2.5 Gb/s over 100 m with a bit error rate of less than 1.3 · 10-14. Fiber-pigtailed modules were stressed with temperature variations from -40 °C to +85 °C, vibrations up to 30 g, and mechanical shocks up to 3900 g. The test results of 20 modules show that the SpaceFibre link is a promising candidate for the upcoming high-speed intrasatellite networks.

Heikkinen, Veli; Alajoki, Teemu; Juntunen, Eveliina; Karppinen, Mikko; Kautio, Kari; Mäkinen, Jukka-Tapani; Ollila, Jyrki; Tanskanen, Antti; Toivonen, Jaakko; Casey, Rory; Scott, Shane; Pintzka, Wilhelm; Thériault, Sylvain; McKenzie, Iain

2007-05-01

355

Carboxylated and uncarboxylated forms of osteocalcin directly modulate the glucose transport system and inflammation in adipocytes.  

PubMed

Osteocalcin is secreted by osteoblasts and improves insulin sensitivity in vivo, although mechanisms remain unclear. We tested the hypothesis that osteocalcin directly modulates cell biology in insulin-targeted peripheral tissues. In L-6 myocytes, osteocalcin stimulated glucose transport both in the absence (basal) and presence of insulin. Similarly, in primary cultured adipocytes, both carboxylated and uncarboxylated osteocalcin increased basal and insulin-stimulated glucose transport as well as insulin sensitivity. Osteocalcin also increased basal and insulin-stimulated glucose oxidation, though there was no effect on fatty acid synthesis or lipolysis. In primary-cultured adipocytes, both forms of osteocalcin suppressed secretion of tumor necrosis factor alpha into the media; however, only carboxylated osteocalcin suppressed interleukin 6 release, and neither form of osteocalcin modulated monocyte chemoattractant protein-1 secretion. Both carboxylated and uncarboxylated osteocalcin increased secretion of adiponectin and the anti-inflammatory cytokine interleukin 10. In conclusion, both carboxylated and uncarboxylated osteocalcin directly increase glucose transport in adipocytes and muscle cells, while suppressing proinflammatory cytokine secretion and stimulating interleukin 10 and adiponectin release. Thus, these results provide a mechanism for the insulin-sensitizing effects of osteocalcin and help elucidate the role that bone plays in regulating systemic metabolism. PMID:24554534

Hill, H S; Grams, J; Walton, R G; Liu, J; Moellering, D R; Garvey, W T

2014-05-01

356

Performance of motor imagery brain-computer interface based on anodal transcranial direct current stimulation modulation.  

PubMed

Voluntarily modulating neural activity plays a key role in brain-computer interface (BCI). In general, the self-regulated neural activation patterns are used in the current BCI systems involving the repetitive trainings with feedback for an attempt to achieve a high-quality control performance. With the limitation posed by the training procedure in most BCI studies, the present work aims to investigate whether directly modulating the neural activity by using an external method could facilitate the BCI control. We designed an experimental paradigm that combines anodal transcranial direct current stimulation (tDCS) with a motor imagery (MI)-based feedback EEG BCI system. Thirty-two young and healthy human subjects were randomly assigned to the real and sham stimulation groups to evaluate the effect of tDCS-induced EEG pattern changes on BCI classification accuracy. Results showed that the anodal tDCS obviously induces sensorimotor rhythm (SMR)-related event-related desynchronization (ERD) pattern changes in the upper-mu (10-14 Hz) and beta (14-26 Hz) rhythm components. Both the online and offline BCI classification results demonstrate that the enhancing ERD patterns could conditionally improve BCI performance. This pilot study suggests that the tDCS is a promising method to help the users to develop reliable BCI control strategy in a relatively short time. PMID:23475381

Wei, Pengfei; He, Wei; Zhou, Yi; Wang, Liping

2013-05-01

357

Modulation of Cortical Activity by Transcranial Direct Current Stimulation in Patients with Affective Disorder  

PubMed Central

Transcranial direct current stimulation (tDCS) has been shown to have antidepressant efficacy in patients experiencing a major depressive episode, but little is known about the underlying neurophysiology. The purpose of our study was to investigate the acute effects of tDCS on cortical activity using electroencephalography (EEG) in patients with an affective disorder. Eighteen patients diagnosed with an affective disorder and experiencing a depressive episode participated in a sham-controlled study of tDCS, each receiving a session of active (2 mA for 20 minutes) and sham tDCS to the left dorsolateral prefrontal cortex (DLPFC). The effects of tDCS on EEG activity were assessed after each session using event-related potentials (ERP) and measurement of spectral activity during a visual working memory (VWM) task. We observed task and intervention dependent effects on both ERPs and task-related alpha and theta activity, where active compared to sham stimulation resulted in a significant reduction in the N2 amplitude and reduced theta activity over frontal areas during memory retrieval. In summary a single session of anodal tDCS stimulation to the left DLPFC during a major depressive episode resulted in modulated brain activity evident in task-related EEG. Effects on the N2 and frontal theta activity likely reflect modulated activity in the medial frontal cortex and hence indicate that the after-effects of tDCS extend beyond the direct focal effects to the left DLPFC.

Powell, Tamara Y.; Boonstra, Tjeerd W.; Martin, Donel M.; Loo, Colleen K.; Breakspear, Michael

2014-01-01

358

RadSensor: Xray Detection by Direct Modulation of an Optical Probe Beam  

SciTech Connect

We present a new x-ray detection technique based on optical measurement of the effects of x-ray absorption and electron hole pair creation in a direct band-gap semiconductor. The electron-hole pairs create a frequency dependent shift in optical refractive index and absorption. This is sensed by simultaneously directing an optical carrier beam through the same volume of semiconducting medium that has experienced an xray induced modulation in the electron-hole population. If the operating wavelength of the optical carrier beam is chosen to be close to the semiconductor band-edge, the optical carrier will be modulated significantly in phase and amplitude. This approach should be simultaneously capable of very high sensitivity and excellent temporal response, even in the difficult high-energy xray regime. At xray photon energies near 10 keV and higher, we believe that sub-picosecond temporal responses are possible with near single xray photon sensitivity. The approach also allows for the convenient and EMI robust transport of high-bandwidth information via fiber optics. Furthermore, the technology can be scaled to imaging applications. The basic physics of the detector, implementation considerations, and preliminary experimental data are presented and discussed.

Lowry, M E; Bennett, C V; Vernon, S P; Bond, T; Welty, R; Behymer, E; Petersen, H; Krey, A; Stewart, R; Kobayashi, N P; Sperry, V; Stephan, P; Reinhardt, C; Simpson, S; Stratton, P; Bionta, R; McKernan, M; Ables, E; Ott, L; Bond, S; Ayers, J.; Landen, O L; Bell, P M

2003-08-01

359

Effect of Sintering Temperature on Electrical Properties of Chip on Glass Module with Direct Printing Method  

NASA Astrophysics Data System (ADS)

In order to apply the direct printing method to the fabrication of chip on glass (COG) modules, we examined that the effect of the sintering temperature on the electrical properties of a COG module with direct printing method. Firstly, we fabricated an Ag conductive circuit on a glass substrate by the screen-printing method. To investigate its the effect on the electrical properties of the circuit, it was sintered at various temperatures, such as 150, 200, 250, and 300 °C for 30 min. Subsequently, we conducted Au electro-plating for the fabrication of a Si dummy chip. Finally, the flip-chip bonding process was conducted using anisotropic conductive film (ACF). The printed Ag circuits were well formed on the quartz substrate without any shorts or remarkable changes compared with the initial design. The electrical properties of the printed Ag circuits improved with increasing sintering temperature. The conductive particles in the ACF were well deformed in between the Au bumps and printed Ag pads after the bonding process. The four-point probe method was employed to measure the connection resistance of the joints constructed with the Au bumps on the Si chip and printed Ag circuit on the quartz substrate. The resistances of the interconnections drastically decreased with increasing sintering temperature, i.e., subsequently converged from 11.8 ? to 7.36 m?.

Lee, Young-Chul; Kim, Yongil; Jung, Seung-Boo

2012-09-01

360

Plasmonic modulator utilizing three parallel metal-dielectric-metal waveguide directional coupler and elasto-optic effects  

NASA Astrophysics Data System (ADS)

We report, for the first time, on the design of a plasmonic modulator working on the principle of the elasto-optic effects in a directional coupling structure, utilizing three parallel metal-dielectric-metal waveguides. We propose to achieve the active switching of the power propagation using the elasto-optic effect and optimize the extinction ratio of the optical modulation. The device is characterized and numerically analyzed using the finite-element-method at the wavelengths of 1.55 ?m. For the modulator length of 2.33 ?m, the extinction ratio of the modulation is nearly 14 dB, and the calculated attenuation loss is 4.5 dB. The calculated driving voltage is 4.8 V for the given modulator. The effect of the applied voltage on the modulation is also analyzed.

Dwivedi, Ram Prakash; Lee, Hyun-Shik; Song, Jun-Hwa; An, Shinmo; Lee, El-Hang

2011-03-01

361

Task-related concurrent but opposite modulations of overlapping functional networks as revealed by spatial ICA.  

PubMed

Animal studies indicate that different functional networks (FNs), each with a unique timecourse, may overlap at common brain regions. For understanding how different FNs overlap in the human brain and how the timecourses of overlapping FNs are modulated by cognitive tasks, we applied spatial independent component analysis (sICA) to functional magnetic resonance imaging (fMRI) data. These data were acquired from healthy participants while they performed a visual task with parametric loads of attention and working memory. sICA identified a total of 14 FNs, and they showed different extents of overlap at a majority of brain regions exhibiting any functional activity. More FNs overlapped at the higher-order association cortex including the anterior and posterior cingulate, precuneus, insula, and lateral and medial frontoparietal cortices (FPCs) than at the primary sensorimotor cortex. Furthermore, overlapping FNs exhibited concurrent but different task-related modulations of timecourses. FNs showing task-related up- vs. down-modulation of timecourses overlapped at both the lateral and medial FPCs and subcortical structures including the thalamus, striatum, and midbrain ventral tegmental area (VTA). Such task-related, concurrent, but opposite changes in timecourses in the same brain regions may not be detected by current analyses based on General-Linear-Model (GLM). The present findings indicate that multiple cognitive processes may associate with common brain regions and exhibit simultaneous but different modulations in timecourses during cognitive tasks. PMID:23611864

Xu, Jiansong; Zhang, Sheng; Calhoun, Vince D; Monterosso, John; Li, Chiang-Shan R; Worhunsky, Patrick D; Stevens, Michael; Pearlson, Godfrey D; Potenza, Marc N

2013-10-01

362

Implementation of accelerometer sensor module and fall detection monitoring system based on wireless sensor network.  

PubMed

This research implements wireless accelerometer sensor module and algorithm to determine wearer's posture, activity and fall. Wireless accelerometer sensor module uses ADXL202, 2-axis accelerometer sensor (Analog Device). And using wireless RF module, this module measures accelerometer signal and shows the signal at ;Acceloger' viewer program in PC. ADL algorithm determines posture, activity and fall that activity is determined by AC component of accelerometer signal and posture is determined by DC component of accelerometer signal. Those activity and posture include standing, sitting, lying, walking, running, etc. By the experiment for 30 subjects, the performance of implemented algorithm was assessed, and detection rate for postures, motions and subjects was calculated. Lastly, using wireless sensor network in experimental space, subject's postures, motions and fall monitoring system was implemented. By the simulation experiment for 30 subjects, 4 kinds of activity, 3 times, fall detection rate was calculated. In conclusion, this system can be application to patients and elders for activity monitoring and fall detection and also sports athletes' exercise measurement and pattern analysis. And it can be expected to common person's exercise training and just plaything for entertainment. PMID:18002455

Lee, Youngbum; Kim, Jinkwon; Son, Muntak; Lee, Myoungho

2007-01-01

363

Towards the identification of protein complexes and functional modules by integrating PPI network and gene expression data  

PubMed Central

Background Identification of protein complexes and functional modules from protein-protein interaction (PPI) networks is crucial to understanding the principles of cellular organization and predicting protein functions. In the past few years, many computational methods have been proposed. However, most of them considered the PPI networks as static graphs and overlooked the dynamics inherent within these networks. Moreover, few of them can distinguish between protein complexes and functional modules. Results In this paper, a new framework is proposed to distinguish between protein complexes and functional modules by integrating gene expression data into protein-protein interaction (PPI) data. A series of time-sequenced subnetworks (TSNs) is constructed according to the time that the interactions were activated. The algorithm TSN-PCD was then developed to identify protein complexes from these TSNs. As protein complexes are significantly related to functional modules, a new algorithm DFM-CIN is proposed to discover functional modules based on the identified complexes. The experimental results show that the combination of temporal gene expression data with PPI data contributes to identifying protein complexes more precisely. A quantitative comparison based on f-measure reveals that our algorithm TSN-PCD outperforms the other previous protein complex discovery algorithms. Furthermore, we evaluate the identified functional modules by using “Biological Process” annotated in GO (Gene Ontology). The validation shows that the identified functional modules are statistically significant in terms of “Biological Process”. More importantly, the relationship between protein complexes and functional modules are studied. Conclusions The proposed framework based on the integration of PPI data and gene expression data makes it possible to identify protein complexes and functional modules more effectively. Moveover, the proposed new framework and algorithms can distinguish between protein complexes and functional modules. Our findings suggest that functional modules are closely related to protein complexes and a functional module may consist of one or multiple protein complexes. The program is available at http://netlab.csu.edu.cn/bioinfomatics/limin/DFM-CIN/index.html.

2012-01-01

364

Water distribution system vulnerability analysis using weighted and directed network models  

NASA Astrophysics Data System (ADS)

The reliability and robustness against failures of networked water distribution systems are central tenets of water supply system design and operation. The ability of such networks to continue to supply water when components are damaged or fail is dependent on the connectivity of the network and the role and location of the individual components. This paper employs a set of advanced network analysis techniques to study the connectivity of water distribution systems, its relationship with system robustness, and susceptibility to damage. Water distribution systems are modeled as weighted and directed networks by using the physical and hydraulic attributes of system components. A selection of descriptive measurements is utilized to quantify the structural properties of benchmark systems at both local (component) and global (network) scales. Moreover, a novel measure of component criticality, the demand-adjusted entropic degree, is proposed to support identification of critical nodes and their ranking according to failure impacts. The application and value of this metric is demonstrated through two case study networks in the USA and UK. Discussion focuses on the potential for gradual evolution of abstract graph-based tools and techniques to more practical network analysis methods, where a theoretical framework for the analysis of robustness and vulnerability of water distribution networks to better support planning and management decisions is presented.

Yazdani, Alireza; Jeffrey, Paul

2012-06-01

365

Posterior Association Networks and Functional Modules Inferred from Rich Phenotypes of Gene Perturbations  

PubMed Central

Combinatorial gene perturbations provide rich information for a systematic exploration of genetic interactions. Despite successful applications to bacteria and yeast, the scalability of this approach remains a major challenge for higher organisms such as humans. Here, we report a novel experimental and computational framework to efficiently address this challenge by limiting the ‘search space’ for important genetic interactions. We propose to integrate rich phenotypes of multiple single gene perturbations to robustly predict functional modules, which can subsequently be subjected to further experimental investigations such as combinatorial gene silencing. We present posterior association networks (PANs) to predict functional interactions between genes estimated using a Bayesian mixture modelling approach. The major advantage of this approach over conventional hypothesis tests is that prior knowledge can be incorporated to enhance predictive power. We demonstrate in a simulation study and on biological data, that integrating complementary information greatly improves prediction accuracy. To search for significant modules, we perform hierarchical clustering with multiscale bootstrap resampling. We demonstrate the power of the proposed methodologies in applications to Ewing's sarcoma and human adult stem cells using publicly available and custom generated data, respectively. In the former application, we identify a gene module including many confirmed and highly promising therapeutic targets. Genes in the module are also significantly overrepresented in signalling pathways that are known to be critical for proliferation of Ewing's sarcoma cells. In the latter application, we predict a functional network of chromatin factors controlling epidermal stem cell fate. Further examinations using ChIP-seq, ChIP-qPCR and RT-qPCR reveal that the basis of their genetic interactions may arise from transcriptional cross regulation. A Bioconductor package implementing PAN is freely available online at http://bioconductor.org/packages/release/bioc/html/PANR.html.

Wang, Xin; Castro, Mauro A.

2012-01-01

366

Single-chip fully integrated direct-modulation CMOS RF transmitters for short-range wireless applications.  

PubMed

Ultra-low power radio frequency (RF) transceivers used in short-range application such as wireless sensor networks (WSNs) require efficient, reliable and fully integrated transmitter architectures with minimal building blocks. This paper presents the design, implementation and performance evaluation of single-chip, fully integrated 2.4 GHz and 433 MHz RF transmitters using direct-modulation power voltage-controlled oscillators (PVCOs) in addition to a 2.0 GHz phase-locked loop (PLL) based transmitter. All three RF transmitters have been fabricated in a standard mixed-signal CMOS 0.18 µm technology. Measurement results of the 2.4 GHz transmitter show an improvement in drain efficiency from 27% to 36%. The 2.4 GHz and 433 MHz transmitters deliver an output power of 8 dBm with a phase noise of -122 dBc/Hz at 1 MHz offset, while drawing 15.4 mA of current and an output power of 6.5 dBm with a phase noise of -120 dBc/Hz at 1 MHz offset, while drawing 20.8 mA of current from 1.5 V power supplies, respectively. The PLL transmitter delivers an output power of 9 mW with a locking range of 128 MHz and consumes 26 mA from 1.8 V power supply. The experimental results demonstrate that the RF transmitters can be efficiently used in low power WSN applications. PMID:23917260

El-Desouki, Munir M; Qasim, Syed Manzoor; BenSaleh, Mohammed; Deen, M Jamal

2013-01-01

367

Single-Chip Fully Integrated Direct-Modulation CMOS RF Transmitters for Short-Range Wireless Applications  

PubMed Central

Ultra-low power radio frequency (RF) transceivers used in short-range application such as wireless sensor networks (WSNs) require efficient, reliable and fully integrated transmitter architectures with minimal building blocks. This paper presents the design, implementation and performance evaluation of single-chip, fully integrated 2.4 GHz and 433 MHz RF transmitters using direct-modulation power voltage-controlled oscillators (PVCOs) in addition to a 2.0 GHz phase-locked loop (PLL) based transmitter. All three RF transmitters have been fabricated in a standard mixed-signal CMOS 0.18 ?m technology. Measurement results of the 2.4 GHz transmitter show an improvement in drain efficiency from 27% to 36%. The 2.4 GHz and 433 MHz transmitters deliver an output power of 8 dBm with a phase noise of ?122 dBc/Hz at 1 MHz offset, while drawing 15.4 mA of current and an output power of 6.5 dBm with a phase noise of ?120 dBc/Hz at 1 MHz offset, while drawing 20.8 mA of current from 1.5 V power supplies, respectively. The PLL transmitter delivers an output power of 9 mW with a locking range of 128 MHz and consumes 26 mA from 1.8 V power supply. The experimental results demonstrate that the RF transmitters can be efficiently used in low power WSN applications.

El-Desouki, Munir M.; Qasim, Syed Manzoor; BenSaleh, Mohammed; Deen, M. Jamal

2013-01-01

368

Direct-DMC for AQM computational complexity reduction in TCP\\/IP networks  

Microsoft Academic Search

Active queue management (AQM) mechanisms are designed to provide better support for end-to-end congestion control mechanisms of transmission control protocol (TCP) in TCP\\/IP networks. This paper introduces direct dynamic matrix control (D-DMC) as a new AQM method in dynamic TCP networks. Ability of the controller in handling system delay along with its simplicity and low computational loads makes D-DMC a

Sarah Ostadabbas; Mohammad Haeri

2007-01-01

369

Reconstructing Cortical Networks: Case of Directed Graphs with High Level of Reciprocity  

Microsoft Academic Search

\\u000a The problem of prediction of yet uncharted connections in the large scale network of the cerebral cortex is addressed. Our\\u000a approach was determined by the fact that the cortical network is highly reciprocal although directed, i.e. the input and output\\u000a connection patterns of vertices are slightly different. In order to solve the problem of predicting missing connections in\\u000a the cerebral

Tamás Nepusz; László Négyessy; Gábor Tusnády; Fülöp Bazsó

370

Rapid and Continuous Modulation of Hippocampal Network State during Exploration of New Places  

PubMed Central

Hippocampal information processing is often described as two-state, with a place cell state during movement and a reactivation state during stillness. Relatively little is known about how the network transitions between these different patterns of activity during exploration. Here we show that hippocampal network changes quickly and continuously as animals explore and become familiar with initially novel places. We measured the relationship between moment-by-moment changes in behavior and information flow through hippocampal output area CA1 in rats. We examined local field potential (LFP) patterns, evoked potentials and ensemble spiking and found evidence suggestive of a smooth transition from strong CA3 drive of CA1 activity at low speeds to entorhinal cortical drive of CA1 activity at higher speeds. These changes occurred with changes in behavior on a timescale of less than a second, suggesting a continuous modulation of information processing in the hippocampal circuit as a function of behavioral state.

Karlsson, Mattias P.; Frank, Loren M.

2013-01-01

371

Robustness and epistasis in the C. elegans vulval signaling network revealed by pathway dosage modulation.  

PubMed

Biological systems may perform reproducibly to generate invariant outcomes, despite external or internal noise. One example is the C. elegans vulva, in which the final cell fate pattern is remarkably robust. Although this system has been extensively studied and the molecular network underlying cell fate specification is well understood, very little is known in quantitative terms. Here, through pathway dosage modulation and single molecule fluorescence in situ hybridization, we show that the system can tolerate a 4-fold variation in genetic dose of the upstream signaling molecule LIN-3/epidermal growth factor (EGF) without phenotypic change in cell fate pattern. Furthermore, through tissue-specific dosage perturbations of the EGF and Notch pathways, we determine the first-appearing patterning errors. Finally, by combining different doses of both pathways, we explore how quantitative pathway interactions influence system behavior. Our results highlight the feasibility and significance of launching experimental studies of robustness and quantitative network analysis in genetically tractable, multicellular eukaryotes. PMID:23328399

Barkoulas, Michalis; van Zon, Jeroen S; Milloz, Josselin; van Oudenaarden, Alexander; Félix, Marie-Anne

2013-01-14

372

Rapid decision threshold modulation by reward rate in a neural network  

PubMed Central

Optimal performance in two-alternative, free response decision making tasks can be achieved by the drift-diffusion model of decision making - which can be implemented in a neural network - as long as the threshold parameter of that model can be adapted to different task conditions. Evidence exists that people seek to maximize reward in such tasks by modulating response thresholds. However, few models have been proposed for threshold adaptation, and none have been implemented using neurally plausible mechanisms. Here we propose a neural network that adapts thresholds in order to maximize reward rate. The model makes predictions regarding optimal performance and provides a benchmark against which actual performance can be compared, as well as testable predictions about the way in which reward rate may be encoded by neural mechanisms.

Simen, Patrick; Cohen, Jonathan D.; Holmes, Philip

2006-01-01

373

Epidemic spreading in annealed directed networks: Susceptible-infected-susceptible model and contact process  

NASA Astrophysics Data System (ADS)

We investigate epidemic spreading in annealed directed scale-free networks with the in-degree (k) distribution Pin(k)˜k-?in and the out-degree (?) distribution, Pout(?)˜?-?out. The correlation of each node on the networks is controlled by the probability r(0?r?1) in two different algorithms, the so-called k and ? algorithms. For r=1, the k algorithm gives =, whereas the ? algorithm gives =. For r=0, = for both algorithms. As the prototype of epidemic spreading, the susceptible-infected-susceptible model and contact process on the networks are analyzed using the heterogeneous mean-field theory and Monte Carlo simulations. The directedness of links and the correlation of the network are found to play important roles in the spreading, so that critical behaviors of both models are distinct from those on undirected scale-free networks.

Kwon, Sungchul; Kim, Yup

2013-01-01

374

Epidemic spreading in annealed directed networks: susceptible-infected-susceptible model and contact process.  

PubMed

We investigate epidemic spreading in annealed directed scale-free networks with the in-degree (k) distribution P(in)(k)~k(-?(in)) and the out-degree (?) distribution, P(out)(?)~?(-?(out)). The correlation of each node on the networks is controlled by the probability r(0?r?1) in two different algorithms, the so-called k and ? algorithms. For r=1, the k algorithm gives =, whereas the ? algorithm gives =. For r=0, = for both algorithms. As the prototype of epidemic spreading, the susceptible-infected-susceptible model and contact process on the networks are analyzed using the heterogeneous mean-field theory and Monte Carlo simulations. The directedness of links and the correlation of the network are found to play important roles in the spreading, so that critical behaviors of both models are distinct from those on undirected scale-free networks. PMID:23410394

Kwon, Sungchul; Kim, Yup

2013-01-01

375

Extrasynaptic Neurotransmission in the Modulation of Brain Function. Focus on the Striatal Neuronal-Glial Networks  

PubMed Central

Extrasynaptic neurotransmission is an important short distance form of volume transmission (VT) and describes the extracellular diffusion of transmitters and modulators after synaptic spillover or extrasynaptic release in the local circuit regions binding to and activating mainly extrasynaptic neuronal and glial receptors in the neuroglial networks of the brain. Receptor-receptor interactions in G protein-coupled receptor (GPCR) heteromers play a major role, on dendritic spines and nerve terminals including glutamate synapses, in the integrative processes of the extrasynaptic signaling. Heteromeric complexes between GPCR and ion-channel receptors play a special role in the integration of the synaptic and extrasynaptic signals. Changes in extracellular concentrations of the classical synaptic neurotransmitters glutamate and GABA found with microdialysis is likely an expression of the activity of the neuron-astrocyte unit of the brain and can be used as an index of VT-mediated actions of these two neurotransmitters in the brain. Thus, the activity of neurons may be functionally linked to the activity of astrocytes, which may release glutamate and GABA to the extracellular space where extrasynaptic glutamate and GABA receptors do exist. Wiring transmission (WT) and VT are fundamental properties of all neurons of the CNS but the balance between WT and VT varies from one nerve cell population to the other. The focus is on the striatal cellular networks, and the WT and VT and their integration via receptor heteromers are described in the GABA projection neurons, the glutamate, dopamine, 5-hydroxytryptamine (5-HT) and histamine striatal afferents, the cholinergic interneurons, and different types of GABA interneurons. In addition, the role in these networks of VT signaling of the energy-dependent modulator adenosine and of endocannabinoids mainly formed in the striatal projection neurons will be underlined to understand the communication in the striatal cellular networks.

Fuxe, Kjell; Borroto-Escuela, Dasiel O.; Romero-Fernandez, Wilber; Diaz-Cabiale, Zaida; Rivera, Alicia; Ferraro, Luca; Tanganelli, Sergio; Tarakanov, Alexander O.; Garriga, Pere; Narvaez, Jose Angel; Ciruela, Francisco; Guescini, Michele; Agnati, Luigi F.

2012-01-01

376

Bi-directional astrocytic regulation of neuronal activity within a network  

PubMed Central

The concept of a tripartite synapse holds that astrocytes can affect both the pre- and post-synaptic compartments through the Ca2+-dependent release of gliotransmitters. Because astrocytic Ca2+ transients usually last for a few seconds, we assumed that astrocytic regulation of synaptic transmission may also occur on the scale of seconds. Here, we considered the basic physiological functions of tripartite synapses and investigated astrocytic regulation at the level of neural network activity. The firing dynamics of individual neurons in a spontaneous firing network was described by the Hodgkin–Huxley model. The neurons received excitatory synaptic input driven by the Poisson spike train with variable frequency. The mean field concentration of the released neurotransmitter was used to describe the presynaptic dynamics. The amplitudes of the excitatory postsynaptic currents (PSCs) obeyed the gamma distribution law. In our model, astrocytes depressed the presynaptic release and enhanced the PSCs. As a result, low frequency synaptic input was suppressed while high frequency input was amplified. The analysis of the neuron spiking frequency as an indicator of network activity revealed that tripartite synaptic transmission dramatically changed the local network operation compared to bipartite synapses. Specifically, the astrocytes supported homeostatic regulation of the network activity by increasing or decreasing firing of the neurons. Thus, the astrocyte activation may modulate a transition of neural network into bistable regime of activity with two stable firing levels and spontaneous transitions between them.

Gordleeva, S. Yu; Stasenko, S. V.; Semyanov, A. V.; Dityatev, A. E.; Kazantsev, V. B.

2012-01-01

377

Exploration and modulation of brain network interactions with noninvasive brain stimulation in combination with neuroimaging.  

PubMed

Much recent work in systems neuroscience has focused on how dynamic interactions between different cortical regions underlie complex brain functions such as motor coordination, language and emotional regulation. Various studies using neuroimaging and neurophysiologic techniques have suggested that in many neuropsychiatric disorders, these dynamic brain networks are dysregulated. Here we review the utility of combined noninvasive brain stimulation and neuroimaging approaches towards greater understanding of dynamic brain networks in health and disease. Brain stimulation techniques, such as transcranial magnetic stimulation and transcranial direct current stimulation, use electromagnetic principles to alter brain activity noninvasively, and induce focal but also network effects beyond the stimulation site. When combined with brain imaging techniques such as functional magnetic resonance imaging, positron emission tomography and electroencephalography, these brain stimulation techniques enable a causal assessment of the interaction between different network components, and their respective functional roles. The same techniques can also be applied to explore hypotheses regarding the changes in functional connectivity that occur during task performance and in various disease states such as stroke, depression and schizophrenia. Finally, in diseases characterized by pathologic alterations in either the excitability within a single region or in the activity of distributed networks, such techniques provide a potential mechanism to alter cortical network function and architectures in a beneficial manner. PMID:22429242

Shafi, Mouhsin M; Westover, M Brandon; Fox, Michael D; Pascual-Leone, Alvaro

2012-03-01

378

Modulation of amplitude and latency of motor evoked potential by direction of transcranial magnetic stimulation  

NASA Astrophysics Data System (ADS)

The present study analyzed the effects of monophasic magnetic stimulation to the motor cortex. The effects of magnetic stimulation were evaluated by analyzing the motor evoked potentials (MEPs). The amplitude and latency of MEPs on the abductor pollicis brevis muscle were used to evaluate the effects of repetitive magnetic stimulation. A figure eight-shaped flat coil was used to stimulate the region over the primary motor cortex. The intensity of magnetic stimulation was 120% of the resting motor threshold, and the frequency of magnetic stimulation was 0.1 Hz. In addition, the direction of the current in the brain was posterior-anterior (PA) or anterior-posterior (AP). The latency of MEP was compared with PA and AP on initial magnetic stimulation. The results demonstrated that a stimulus in the AP direction increased the latency of the MEP by approximately 2.5 ms. MEP amplitude was also compared with PA and AP during 60 magnetic stimulations. The results showed that a stimulus in the PA direction gradually increased the amplitude of the MEP. However, a stimulus in the AP direction did not modulate the MEP amplitude. The average MEP amplitude induced from every 10 magnetic pulses was normalized by the average amplitude of the first 10 stimuli. These results demonstrated that the normalized MEP amplitude increased up to approximately 150%. In terms of pyramidal neuron indirect waves (I waves), magnetic stimulation inducing current flowing backward to the anterior preferentially elicited an I1 wave, and current flowing forward to the posterior elicited an I3 wave. It has been reported that the latency of the I3 wave is approximately 2.5 ms longer than the I1 wave elicitation, so the resulting difference in latency may be caused by this phenomenon. It has also been reported that there is no alteration of MEP amplitude at a frequency of 0.1 Hz. However, this study suggested that the modulation of MEP amplitude depends on stimulation strength and stimulation direction.

Sato, Aya; Torii, Tetsuya; Iwahashi, Masakuni; Itoh, Yuji; Iramina, Keiji

2014-05-01

379

Fast changes in direction during human locomotion are executed by impulsive activation of motor modules.  

PubMed

This study investigated the modular control of complex locomotor tasks that require fast changes in direction, i.e., cutting manoeuvres. It was hypothesized that such tasks are accomplished by an impulsive (burst-like) activation of a few motor modules, as observed during walking and running. It was further hypothesized that the performance in cutting manoeuvres would be associated to the relative timing of the activation impulses. Twenty-two healthy men performed 90° side-step cutting manoeuvres while electromyography (EMG) activity from 16 muscles of the supporting limb and trunk, kinematics, and ground reaction forces were recorded. Motor modules and their respective temporal activations were extracted from the EMG signals by non-negative matrix factorization. The kinematic analysis provided the velocity of the centre of mass and the external work absorbed during the load acceptance (negative work, external work during absorption (W-Abs)) and propulsion phases (positive work, external work during propulsion (W-Prp)) of the cutting manoeuvres. Five motor modules explained the EMG activity of all muscles and were driven in an impulsive way, with timing related to the initial contact (M2), load acceptance (M3), and propulsion (M4). The variability in timing between impulses across subjects was greater for cutting manoeuvres than for running. The timing difference between M2 and M3 in the cutting manoeuvres was significantly associated to W-Abs (r(2)=0.45) whereas the timing between M3 and M4 was associated to W-Prp (r(2)=0.43). These results suggest that complex locomotor tasks can be achieved by impulsive activation of muscle groups, and that performance is associated to the specific timing of the activation impulses. PMID:23085217

Oliveira, A S; Silva, P B; Lund, M E; Kersting, U G; Farina, D

2013-01-01

380

Transcranial direct-current stimulation modulates synaptic mechanisms involved in associative learning in behaving rabbits  

PubMed Central

Transcranial direct-current stimulation (tDCS) is a noninvasive brain stimulation technique that has been successfully applied for modulation of cortical excitability. tDCS is capable of inducing changes in neuronal membrane potentials in a polarity-dependent manner. When tDCS is of sufficient length, synaptically driven after-effects are induced. The mechanisms underlying these after-effects are largely unknown, and there is a compelling need for animal models to test the immediate effects and after-effects induced by tDCS in different cortical areas and evaluate the implications in complex cerebral processes. Here we show in behaving rabbits that tDCS applied over the somatosensory cortex modulates cortical processes consequent to localized stimulation of the whisker pad or of the corresponding area of the ventroposterior medial (VPM) thalamic nucleus. With longer stimulation periods, poststimulation effects were observed in the somatosensory cortex only after cathodal tDCS. Consistent with the polarity-specific effects, the acquisition of classical eyeblink conditioning was potentiated or depressed by the simultaneous application of anodal or cathodal tDCS, respectively, when stimulation of the whisker pad was used as conditioned stimulus, suggesting that tDCS modulates the sensory perception process necessary for associative learning. We also studied the putative mechanisms underlying immediate effects and after-effects of tDCS observed in the somatosensory cortex. Results when pairs of pulses applied to the thalamic VPM nucleus (mediating sensory input) during anodal and cathodal tDCS suggest that tDCS modifies thalamocortical synapses at presynaptic sites. Finally, we show that blocking the activation of adenosine A1 receptors prevents the long-term depression (LTD) evoked in the somatosensory cortex after cathodal tDCS.

Marquez-Ruiz, Javier; Leal-Campanario, Rocio; Sanchez-Campusano, Raudel; Molaee-Ardekani, Behnam; Wendling, Fabrice; Miranda, Pedro C.; Ruffini, Giulio; Gruart, Agnes; Delgado-Garcia, Jose Maria

2012-01-01

381

Sliding mode controller based on fuzzy neural network optimization for direct torque controlled PMSM  

Microsoft Academic Search

A sliding mode controller for permanent magnet synchronous machine (PMSM) is investigated in this paper, in which direct torque control (DTC) concept, variable structure control and space vector modulation (SVM) are integrated to achieve high performance. It features in very low flux and torque ripple, strong robustness and fixed switching frequency. Then, an FNN is investigated to optimize the control

Hongkui Li; Qinlin Wang

2010-01-01

382

?FosB differentially modulates nucleus accumbens direct and indirect pathway function.  

PubMed

Synaptic modifications in nucleus accumbens (NAc) medium spiny neurons (MSNs) play a key role in adaptive and pathological reward-dependent learning, including maladaptive responses involved in drug addiction. NAc MSNs participate in two parallel circuits, direct and indirect pathways that subserve distinct behavioral functions. Modification of NAc MSN synapses may occur in part via changes in the transcriptional potential of certain genes in a cell type–specific manner. The transcription factor ?FosB is one of the key proteins implicated in the gene expression changes in NAc caused by drugs of abuse, yet its effects on synaptic function in NAc MSNs are unknown. Here, we demonstrate that overexpression of ?FosB decreased excitatory synaptic strength and likely increased silent synapses onto D1 dopamine receptor–expressing direct pathway MSNs in both the NAc shell and core. In contrast, ?FosB likely decreased silent synapses onto NAc shell, but not core, D2 dopamine receptor–expressing indirect pathway MSNs. Analysis of NAc MSN dendritic spine morphology revealed that ?FosB increased the density of immature spines in D1 direct but not D2 indirect pathway MSNs. To determine the behavioral consequences of cell type-specific actions of ?FosB, we selectively overexpressed ?FosB in D1 direct or D2 indirect MSNs in NAc in vivo and found that direct (but not indirect) pathway MSN expression enhances behavioral responses to cocaine. These results reveal that ?FosB in NAc differentially modulates synaptic properties and reward-related behaviors in a cell type- and subregion-specific fashion. PMID:23319622

Grueter, Brad A; Robison, Alfred J; Neve, Rachael L; Nestler, Eric J; Malenka, Robert C

2013-01-29

383

Direct acceleration of electrons by a circular polarized laser pulse with phase modulation  

NASA Astrophysics Data System (ADS)

Electron acceleration by transversely echelon phase-modulated (EPM) circularly polarized (CP) intense laser pulse is investigated. Solution of the relativistic electron equations of motion shows that the CP EPM light wave structure can disrupt the harmonic response of a trapped electron not only in the transverse direction but also in the direction of laser propagation. In each laser cycle, there can be a net gain in the electron's transverse momentum, which is promptly converted into the forward direction by the Lorentz force. As a result, the electron can be trapped and accelerated in the favorable phase of the laser for a rather long time. Its momentum gain then accumulates and can eventually reach high levels. It is also found that with the CP EPM laser, the net acceleration of the electron is not sensitive to its initial position and velocity relative to the phase of the laser fields, so that such a laser can also be useful for accelerating thermal electron bunches to high energies.

Zhu, Lun-Wu; Sheng, Zheng-Mao; Yu, M. Y.

2013-11-01

384

Direct acceleration of electrons by a circular polarized laser pulse with phase modulation  

SciTech Connect

Electron acceleration by transversely echelon phase-modulated (EPM) circularly polarized (CP) intense laser pulse is investigated. Solution of the relativistic electron equations of motion shows that the CP EPM light wave structure can disrupt the harmonic response of a trapped electron not only in the transverse direction but also in the direction of laser propagation. In each laser cycle, there can be a net gain in the electron's transverse momentum, which is promptly converted into the forward direction by the Lorentz force. As a result, the electron can be trapped and accelerated in the favorable phase of the laser for a rather long time. Its momentum gain then accumulates and can eventually reach high levels. It is also found that with the CP EPM laser, the net acceleration of the electron is not sensitive to its initial position and velocity relative to the phase of the laser fields, so that such a laser can also be useful for accelerating thermal electron bunches to high energies.

Zhu, Lun-Wu [Department of Physics, Institute for Fusion Theory and Simulation, Zhejiang University, Hangzhou 310027 (China) [Department of Physics, Institute for Fusion Theory and Simulation, Zhejiang University, Hangzhou 310027 (China); Department of Science, Zhejiang University of Science and Technology, Hangzhou 310023 (China); Sheng, Zheng-Mao; Yu, M. Y. [Department of Physics, Institute for Fusion Theory and Simulation, Zhejiang University, Hangzhou 310027 (China)] [Department of Physics, Institute for Fusion Theory and Simulation, Zhejiang University, Hangzhou 310027 (China)

2013-11-15

385

Positive cloud-to-ground lightning detection by a direction-finder network  

NASA Technical Reports Server (NTRS)

Consideration is given to the ability of an automatic direction-finder network to identify cloud-to-ground flashes that effectively lower positive charge to the ground (+CG flashes). Records from an extremely low frequency system are examined to determine whether or not 340 +CG flashes detected by the network have coincident waveforms characteristic of +CG flashes. It is found that false detection in the system is negligible for +CG flashes with range-normalized amplitudes of at least 50 direction-finder units. Also, it is shown that no more than about 15 percent of the +CG flashes detected by the system at smaller amplitudes are false detections.

Macgorman, Donald R.; Taylor, William L.

1989-01-01

386

Transcranial direct current stimulation of the prefrontal cortex: a means to modulate fear memories.  

PubMed

Targeting memory processes by noninvasive interventions is a potential gateway to modulate fear memories as shown by animal and human studies in recent years. Modulation of fear memories by noninvasive brain stimulation techniques might be an attractive approach, which, however, has not been examined so far. We investigated the effect of transcranial direct current stimulation (tDCS) applied to the right dorsolateral prefrontal cortex and left supraorbital region on fear memories in humans. Seventy-four young, healthy individuals were assigned randomly to two groups, which underwent fear conditioning with mild electric stimuli paired with a visual stimulus. Twenty-four hours later, both groups were shown a reminder of the conditioned fearful stimulus. Shortly thereafter, they received either tDCS (right prefrontal - anodal, left supraorbital - cathodal) for 20 min at 1 mA current intensity or sham stimulation. A day later, fear responses of both groups were compared by monitoring skin conductance. On day 3, during fear response assessment, the tDCS group had a significantly (P<0.05) higher mean skin conductance in comparison with the sham group. These results suggest that tDCS (right prefrontal - anodal, left supraorbital - cathodal) enhanced fear memories, possibly by influencing the prefrontal cortex-amygdala circuit underlying the memory for fear. PMID:24384505

Mungee, Aditya; Kazzer, Philipp; Feeser, Melanie; Nitsche, Michael A; Schiller, Daniela; Bajbouj, Malek

2014-05-01

387

Analytical formulation of directly modulated OOFDM signals transmitted over an IM/DD dispersive link.  

PubMed

We provide an analytical study on the propagation effects of a directly modulated OOFDM signal through a dispersive fiber and subsequent photo-detection. The analysis includes the effects of the laser operation point and the interplay between chromatic dispersion and laser chirp. The final expression allows to understand the physics behind the transmission of a multi-carrier signal in the presence of residual frequency modulation and the description of the induced intermodulation distortion gives us a detailed insight into the diferent intermodulation products which impair the recovered signal at the receiver-end side. Numerical comparisons between transmission simulations results and those provided by evaluating the expression obtained are carried out for different laser operation points. Results obtained by changing the fiber length, laser parameters and using single mode fiber with negative and positive dispersion are calculated in order to demonstrate the validity and versatility of the theory provided in this paper. Therefore, a novel analytical formulation is presented as a versatile tool for the description and study of IM/DD OOFDM systems with variable design parameters. PMID:23546148

Sánchez, C; Ortega, B; Wei, J L; Tang, J; Capmany, J

2013-03-25

388

Theoretical foundation of the controlling UEP method for direct transient-stability analysis of network-preserving power system models  

Microsoft Academic Search

The controlling unstable equilibrium point (CUEP) method developed for the traditional network-reduction power-system (transient-stability) model requires some modification for direct stability analysis of the network-preserving power system model. This is mainly due to the peculiar nonlinear jump behaviors occurring in network-preserving power system model. An extended CUEP method suitable for direct stability analysis of network-preserving models is developed. The extended

Yun Zou; Ming-Hui Yin; Hsiao-Dong Chiang

2003-01-01

389

Node-weighted measures for complex networks with directed and weighted edges for studying atmospheric moisture recycling  

NASA Astrophysics Data System (ADS)

In many real-world networks, nodes represents agents of different sizes or importance. However, the sizes of the node are rarely taken into account in networks analysis, inducing bias in network measures and confusion in their interpretation. Recently, a new axiomatic scheme of node-weighted network measures have been suggested for networks with undirected and unweighted edges. However, many real-world systems are best represented by complex networks which have directed and/or weighted edges. Here, we extend this approach and suggest node-centrality measures for the networks with directed and/or weighted edges and weighted nodes. We apply these measures on a artificial spatially embedded network and a real-world moisture recycling network. We show that these measures improve the representation of the underlying physical systems and can be used for any types of complex networks.

Zemp, Delphine; Wiedermann, Marc; Donges, Jonathan; Schleussner, Carl-Friedrich; Rammig, Anja

2014-05-01

390

Bidirectional direct modulation CATV and phase remodulation radio-over-fiber transport systems.  

PubMed

A bidirectional lightwave transport system employing direct modulation CATV and phase remodulation radio-over-fiber (ROF) signals in two-way transmission is proposed and experimentally demonstrated. To be the first system of reusing the phase of the transmitting lightwave with multi-carrier analog CATV signal, the transmission performances of CATV and ROF signals are investigated in bidirectional way, with the help of optical band-pass filters (OBPFs) at the receiving sites. Through a serious investigation, the transmitting light sources are successfully remodulated with RF signals for transmission. Brilliant transmission performances of composite second-order (CSO), composite triple-beat (CTB), and bit error rate (BER) were obtained; accompanied with acceptable carrier-to-noise ratio (CNR) value. This proposed system reveals a prominent one with economy and convenience to be installed. PMID:21164956

Tsai, Wen-Shing; Ma, Hsien-Li; Lu, Hai-Han; Lin, Ying-Pyng; Chen, Hung-Yi; Yan, Shr-Chi

2010-12-01

391

Multi-Pulse Pulse-Position-Modulation Signaling for Optical Communication with Direct Detection  

NASA Astrophysics Data System (ADS)

A modification of the traditional pulse-position modulation (PPM) scheme typically employed on the optical direct-detection channel is proposed that allows for significantly improved information throughput and bandwidth advantage. The scheme sends a multitude (K) of pulses per symbol interval and as such provides a signal constellation whose size, for a given number of pulse slots (M), varies as M^K (for large M) rather than linearly with M, as is the case for conventional PPM. Maximum performance improvement is obtained for deep-space optical communications applications, where narrow high-peak-power transmitted pulses offer significant advantages in terms of detection probabilities and background suppression capabilities at the receiver.

Simon, M. K.; Vilnrotter, V. A.

2003-11-01

392

Pharmacological modulation of cortical excitability shifts induced by transcranial direct current stimulation in humans  

PubMed Central

Transcranial direct current stimulation (tDCS) of the human motor cortex results in polarity-specific shifts of cortical excitability during and after stimulation. Anodal tDCS enhances and cathodal stimulation reduces excitability. Animal experiments have demonstrated that the effect of anodal tDCS is caused by neuronal depolarisation, while cathodal tDCS hyperpolarises cortical neurones. However, not much is known about the ion channels and receptors involved in these effects. Thus, the impact of the sodium channel blocker carbamazepine, the calcium channel blocker flunarizine and the NMDA receptor antagonist dextromethorphane on tDCS-elicited motor cortical excitability changes of healthy human subjects were tested. tDCS-protocols inducing excitability alterations (1) only during tDCS and (2) eliciting long-lasting after-effects were applied after drug administration. Carbamazepine selectively eliminated the excitability enhancement induced by anodal stimulation during and after tDCS. Flunarizine resulted in similar changes. Antagonising NMDA receptors did not alter current-generated excitability changes during a short stimulation, which elicits no after-effects, but prevented the induction of long-lasting after-effects independent of their direction. These results suggest that, like in other animals, cortical excitability shifts induced during tDCS in humans also depend on membrane polarisation, thus modulating the conductance of sodium and calcium channels. Moreover, they suggest that the after-effects may be NMDA receptor dependent. Since NMDA receptors are involved in neuroplastic changes, the results suggest a possible application of tDCS in the modulation or induction of these processes in a clinical setting. The selective elimination of tDCS-driven excitability enhancements by carbamazepine proposes a role for this drug in focussing the effects of cathodal tDCS, which may have important future clinical applications.

Nitsche, M A; Fricke, K; Henschke, U; Schlitterlau, A; Liebetanz, D; Lang, N; Henning, S; Tergau, F; Paulus, W

2003-01-01

393

Octopamine modulates activity of neural networks in the honey bee antennal lobe.  

PubMed

Neuronal plasticity allows an animal to respond to environmental changes by modulating its response to stimuli. In the honey bee (Apis mellifera), the biogenic amine octopamine plays a crucial role in appetitive odor learning, but little is known about how octopamine affects the brain. We investigated its effect in the antennal lobe, the first olfactory center in the brain, using calcium imaging to record background activity and odor responses before and after octopamine application. We show that octopamine increases background activity in olfactory output neurons, while reducing average calcium levels. Odor responses were modulated both upwards and downwards, with more odor response increases in glomeruli with negative or weak odor responses. Importantly, the octopamine effect was variable across glomeruli, odorants, odorant concentrations and animals, suggesting that the octopaminergic network is shaped by plasticity depending on an individual animal's history and possibly other factors. Using RNA interference, we show that the octopamine receptor AmOA1 (homolog of the Drosophila OAMB receptor) is involved in the octopamine effect. We propose a network model in which octopamine receptors are plastic in their density and located on a subpopulation of inhibitory neurons in a disinhibitory pathway. This would improve odor-coding of behaviorally relevant, previously experienced odors. PMID:23681219

Rein, Julia; Mustard, Julie A; Strauch, Martin; Smith, Brian H; Galizia, C Giovanni

2013-11-01

394

Emergence of complex computational structures from chaotic neural networks through reward-modulated Hebbian learning.  

PubMed

This paper addresses the question how generic microcircuits of neurons in different parts of the cortex can attain and maintain different computational specializations. We show that if stochastic variations in the dynamics of local microcircuits are correlated with signals related to functional improvements of the brain (e.g. in the control of behavior), the computational operation of these microcircuits can become optimized for specific tasks such as the generation of specific periodic signals and task-dependent routing of information. Furthermore, we show that working memory can autonomously emerge through reward-modulated Hebbian learning, if needed for specific tasks. Altogether, our results suggest that reward-modulated synaptic plasticity can not only optimize the network parameters for specific computational tasks, but also initiate a functional rewiring that re-programs microcircuits, thereby generating diverse computational functions in different generic cortical microcircuits. On a more general level, this work provides a new perspective for a standard model for computations in generic cortical microcircuits (liquid computing model). It shows that the arguably most problematic assumption of this model, the postulate of a teacher that trains neural readouts through supervised learning, can be eliminated. We show that generic networks of neurons can learn numerous biologically relevant computations through trial and error. PMID:23146969

Hoerzer, Gregor M; Legenstein, Robert; Maass, Wolfgang

2014-03-01

395

Dopaminergic Modulation of Corticostriatal Responses in Medium Spiny Projection Neurons from Direct and Indirect Pathways  

PubMed Central

Suprathreshold corticostriatal responses recorded from medium spiny neurons (MSNs) from the direct and indirect pathways of the basal ganglia are different. Their differences readily distinguish D1- and D2-type receptor expressing MSNs in both bacterial artificial chromosome-transgenic mice and their control littermates as well as in rats: indirect pathway neurons are more excitable than direct pathway neurons revealing autoregenerative spikes underlying their spike trains, whereas direct pathway neurons exhibit more prolonged plateau potentials and spike trains. SFK 81297, a selective agonist for D1-class receptors enhanced corticostriatal responses in direct pathway neurons, while quinelorane, a selective agonist for D2-class receptors reduced orthodromic and autoregenerative responses in indirect pathway neurons thus making both neuron classes similarly excitable. Because dopaminergic postsynaptic actions target CaV1 (L) class voltage-gated calcium channels in MSNs, we hypothesized that these channels are involved and can explain a part of the dopaminergic actions on corticostriatal integration. Both 2.5??M nicardipine and 400?nM calciseptine, selective CaV1 channel blockers, reduced corticostriatal responses in both D1- and D2-receptor expressing neurons, respectively. A previous blockade of CaV1 channels occluded the actions of dopamine agonists in both neuronal classes. In contrast, a CaV1 (L) channel activator, 2.5??M Bay K 8644, enhanced corticostriatal responses in neurons from both pathways. It is concluded that CaV1 intrinsic currents mediate a part of the dopaminergic modulation during orthodromic synaptic integration of cortical inputs in both classes of MSNs.

Flores-Barrera, Eden; Vizcarra-Chacon, Bianca J.; Bargas, Jose; Tapia, Dagoberto; Galarraga, Elvira

2011-01-01

396

Effects of ?-opioid receptor modulation on the hippocampal network activity of sharp wave and ripples  

PubMed Central

Background and Purpose Hippocampus-dependent memory involves the activity of sharp wave ripples (SWRs), which are thought to participate in the process of memory consolidation. The hippocampus contains high levels of endogenous opioids and of ?-opioid receptors (MORs). Here, we have assessed the role of MOR agonists in the modulation of SWRs. Experimental Approach Using recordings of extracellular potentials from the CA1 field of rat hippocampal slices, we examined the pharmacological actions of morphine, DAMGO and fentanyl on SWRs and on network excitability and paired-pulse inhibition. Key Results All three MOR agonists (1 nM–10 ?M) significantly increased the amplitude of sharp waves and the occurrence of SWR sequences, but reduced the initiation of episodes of SWRs. Fentanyl was most potent in producing these effects and morphine the least. Interestingly, although SWRs were reduced by relatively high concentrations (?100 nM) of all agonists, they were significantly enhanced by very low concentrations of morphine (5–10 nM). Morphine and DAMGO at moderate-to-high concentrations increased network excitability and reduced inhibition. Furthermore, DAMGO suppressed inhibition more readily than it increased excitation, whereas morphine suppressed inhibition only at high concentrations. These drug effects were reversed by the MOR antagonists naloxone and CTOP. Conclusions and Implications We found that the SWRs were significantly modulated by three MOR agonists and that the SWRs were very sensitive to subtle changes in the excitation/inhibition balance induced by MOR agonists. Such modulation might underlie the effects of these agonists on hippocampus-dependent memory.

Giannopoulos, Panagiotis; Papatheodoropoulos, Costas

2013-01-01

397

1.25Gb\\/s bidirectional transceiver module using 1.5%-? silica directional coupler-type WDM  

Microsoft Academic Search

A 1.5%-? silica directional coupler-type wavelength-division multiplexer dividing 1310\\/1550-nm wavelength bands was used to develop a bidirectional optical transceiver module. The active devices such as a spot-size converted Fabry-Pe´rot laser diode and waveguide photodetectors were hybridly integrated on a silica-terraced planar lightwave circuit platform. As main performances of the module, the clear eye pattern and the minimum receiver sensitivity of

Young-Tak Han; Yoon-Jung Park; Sang-Ho Park; Jang-Uk Shin; Duk-Jun Kim; Sung-Woong Park; Sun-Ho Song; Kang-Yong Jung; Deug-Ju Lee; Wol-Yon Hwang; Hee-Kyung Sung

2005-01-01

398

Chirp reduction of directly modulated semiconductor lasers at 10 Gb\\/s by strong CW light injection  

Microsoft Academic Search

The influence of strong light injection on the reduction of the dynamical linewidth broadening of directly current-modulated semiconductor lasers at high bit rates is theoretically investigated and experimentally verified for 10 Gb\\/s NRZ pseudorandom modulation with a large current swing of 40 mA pp. Significant chirp reduction and single-mode operation are observed for bulk DFB, quantum well DFB lasers at

Stefan Mohrdiek; Herbert Burkhard; Herbert Walter

1994-01-01

399

A wearable sensor module with a neural-network-based activity classification algorithm for daily energy expenditure estimation.  

PubMed

This paper presents a wearable module and neural-network-based activity classification algorithm for energy expenditure estimation. The purpose of our design is first to categorize physical activities with similar intensity levels, and then to construct energy expenditure regression (EER) models using neural networks in order to optimize the estimation performance. The classification of physical activities for EER model construction is based on the acceleration and ECG signal data collected by wearable sensor modules developed by our research lab. The proposed algorithm consists of procedures for data collection, data preprocessing, activity classification, feature selection, and construction of EER models using neural networks. In order to reduce the computational load and achieve satisfactory estimation performance, we employed sequential forward and backward search strategies for feature selection. Two representative neural networks, a radial basis function network (RBFN) and a generalized regression neural network (GRNN), were employed as EER models for performance comparisons. Our experimental results have successfully validated the effectiveness of our wearable sensor module and its neural-network-based activity classification algorithm for energy expenditure estimation. In addition, our results demonstrate the superior performance of GRNN as compared to RBFN. PMID:22875251

Lin, Che-Wei; Yang, Ya-Ting C; Wang, Jeen-Shing; Yang, Yi-Ching

2012-09-01

400

Evolution of ethnocentrism on undirected and directed Barabási-Albert networks  

NASA Astrophysics Data System (ADS)

Using Monte Carlo simulations, we study the evolution of contingent cooperation and ethnocentrism in the one-shot game. Interactions and reproduction among computational agents are simulated on undirected and directed Barabási-Albert (BA) networks. We first replicate the Hammond-Axelrod model of in-group favoritism on a square lattice and then generalize this model on undirected and directed BA networks for both asexual and sexual reproduction cases. Our simulations demonstrate that irrespective of the mode of reproduction, the ethnocentric strategy becomes common even though cooperation is individually costly and mechanisms such as reciprocity or conformity are absent. Moreover, our results indicate that the spread of favoritism towards similar others highly depends on the network topology and the associated heterogeneity of the studied population.

Lima, F. W. S.; Hadzibeganovic, Tarik; Stauffer, Dietrich

2009-12-01

401

Space direction-finding technique of forward/backward linear prediction based on neural networks  

NASA Astrophysics Data System (ADS)

Based on linear plan neural network, this paper provides the method of detecting space direction by forward/backward linear prediction. The first step of this method is to turn the solution in complex field of forward/backward linear prediction coefficients to the solution in real field. Then we come to the realization by use of linear plan neural network which has been supplied by Tank and Hopfield. Because this network can come to a dynamic balance within several hundreds ns, it provides a new way for the realization of real time detecting direction in forward/backward linear forecast space. It is demonstrated by computer simulation that this method is better than traditional Burg algorithm, so it is practicable.

Wan, Jianwei; Wang, Ling; Huang, Fukan; Zhou, Liangzhu; Zhao, YangXi

1997-04-01

402

Identifying influential nodes in large-scale directed networks: the role of clustering.  

PubMed

Identifying influential nodes in very large-scale directed networks is a big challenge relevant to disparate applications, such as accelerating information propagation, controlling rumors and diseases, designing search engines, and understanding hierarchical organization of social and biological networks. Known methods range from node centralities, such as degree, closeness and betweenness, to diffusion-based processes, like PageRank and LeaderRank. Some of these methods already take into account the influences of a node's neighbors but do not directly make use of the interactions among it's neighbors. Local clustering is known to have negative impacts on the information spreading. We further show empirically that it also plays a negative role in generating local connections. Inspired by these facts, we propose a local ranking algorithm named ClusterRank, which takes into account not only the number of neighbors and the neighbors' influences, but also the clustering coefficient. Subject to the susceptible-infected-recovered (SIR) spreading model with constant infectivity, experimental results on two directed networks, a social network extracted from delicious.com and a large-scale short-message communication network, demonstrate that the ClusterRank outperforms some benchmark algorithms such as PageRank and LeaderRank. Furthermore, ClusterRank can also be applied to undirected networks where the superiority of ClusterRank is significant compared with degree centrality and k-core decomposition. In addition, ClusterRank, only making use of local information, is much more efficient than global methods: It takes only 191 seconds for a network with about [Formula: see text] nodes, more than 15 times faster than PageRank. PMID:24204833

Chen, Duan-Bing; Gao, Hui; Lü, Linyuan; Zhou, Tao

2013-01-01

403

Estimating the 3D pore size distribution of biopolymer networks from directionally biased data.  

PubMed

The pore size of biopolymer networks governs their mechanical properties and strongly impacts the behavior of embedded cells. Confocal reflection microscopy and second harmonic generation microscopy are widely used to image biopolymer networks; however, both techniques fail to resolve vertically oriented fibers. Here, we describe how such directionally biased data can be used to estimate the network pore size. We first determine the distribution of distances from random points in the fluid phase to the nearest fiber. This distribution follows a Rayleigh distribution, regardless of isotropy and data bias, and is fully described by a single parameter--the characteristic pore size of the network. The bias of the pore size estimate due to the missing fibers can be corrected by multiplication with the square root of the visible network fraction. We experimentally verify the validity of this approach by comparing our estimates with data obtained using confocal fluorescence microscopy, which represents the full structure of the network. As an important application, we investigate the pore size dependence of collagen and fibrin networks on protein concentration. We find that the pore size decreases with the square root of the concentration, consistent with a total fiber length that scales linearly with concentration. PMID:24209841

Lang, Nadine R; Münster, Stefan; Metzner, Claus; Krauss, Patrick; Schürmann, Sebastian; Lange, Janina; Aifantis, Katerina E; Friedrich, Oliver; Fabry, Ben

2013-11-01

404

Metabolomic correlation-network modules in Arabidopsis based on a graph-clustering approach  

PubMed Central

Background Deciphering the metabolome is essential for a better understanding of the cellular metabolism as a system. Typical metabolomics data show a few but significant correlations among metabolite levels when data sampling is repeated across individuals grown under strictly controlled conditions. Although several studies have assessed topologies in metabolomic correlation networks, it remains unclear whether highly connected metabolites in these networks have specific functions in known tissue- and/or genotype-dependent biochemical pathways. Results In our study of metabolite profiles we subjected root tissues to gas chromatography-time-of-flight/mass spectrometry (GC-TOF/MS) and used published information on the aerial parts of 3 Arabidopsis genotypes, Col-0 wild-type, methionine over-accumulation 1 (mto1), and transparent testa4 (tt4) to compare systematically the metabolomic correlations in samples of roots and aerial parts. We then applied graph clustering to the constructed correlation networks to extract densely connected metabolites and evaluated the clusters by biochemical-pathway enrichment analysis. We found that the number of significant correlations varied by tissue and genotype and that the obtained clusters were significantly enriched for metabolites included in biochemical pathways. Conclusions We demonstrate that the graph-clustering approach identifies tissue- and/or genotype-dependent metabolomic clusters related to the biochemical pathway. Metabolomic correlations complement information about changes in mean metabolite levels and may help to elucidate the organization of metabolically functional modules.

2011-01-01

405

Reduced-order modelling of biochemical networks: application to the GTPase-cycle signalling module  

PubMed Central

Biochemical systems embed complex networks and hence development and analysis of their detailed models pose a challenge for computation. Coarse-grained biochemical models, called reduced-order models (ROMs), consisting of essential biochemical mechanisms are more useful for computational analysis and for studying important features of a biochemical network. The authors present a novel method to model-reduction by identifying potentially important parameters using multidimensional sensitivity analysis. A ROM is generated for the GTPase-cycle module of m1 muscarinic acetylcholine receptor, Gq, and regulator of G-protein signalling 4 (a GTPase-activating protein or GAP) starting from a detailed model of 48 reactions. The resulting ROM has only 17 reactions. The ROM suggested that complexes of G-protein coupled receptor (GPCR) and GAP – which were proposed in the detailed model as a hypothesis – are required to fit the experimental data. Models previously published in the literature are also simulated and compared with the ROM. Through this comparison, a minimal ROM, that also requires complexes of GPCR and GAP, with just 15 parameters is generated. The proposed reduced-order modelling methodology is scalable to larger networks and provides a general framework for the reduction of models of biochemical systems.

Maurya, M.R.; Bornheimer, S.J.; Venkatasubramanian, V.; Subramaniam, S.

2011-01-01

406

CO2 directly modulates connexin 26 by formation of carbamate bridges between subunits  

PubMed Central

Homeostatic regulation of the partial pressure of CO2 (PCO2) is vital for life. Sensing of pH has been proposed as a sufficient proxy for determination of PCO2 and direct CO2-sensing largely discounted. Here we show that connexin 26 (Cx26) hemichannels, causally linked to respiratory chemosensitivity, are directly modulated by CO2. A ‘carbamylation motif’, present in CO2-sensitive connexins (Cx26, Cx30, Cx32) but absent from a CO2-insensitive connexin (Cx31), comprises Lys125 and four further amino acids that orient Lys125 towards Arg104 of the adjacent subunit of the connexin hexamer. Introducing the carbamylation motif into Cx31 created a mutant hemichannel (mCx31) that was opened by increases in PCO2. Mutation of the carbamylation motif in Cx26 and mCx31 destroyed CO2 sensitivity. Course-grained computational modelling of Cx26 demonstrated that the proposed carbamate bridge between Lys125 and Arg104 biases the hemichannel to the open state. Carbamylation of Cx26 introduces a new transduction principle for physiological sensing of CO2. DOI: http://dx.doi.org/10.7554/eLife.01213.001

Meigh, Louise; Greenhalgh, Sophie A; Rodgers, Thomas L; Cann, Martin J; Roper, David I; Dale, Nicholas

2013-01-01

407

Rab GTPases-cargo direct interactions: fine modulators of intracellular trafficking.  

PubMed

Rab proteins are a large family of monomeric GTPases that comprise about 70 members. These proteins cycle from a GDP-bound to a GTP-bound state and are considered molecular switches of membrane traffic. Indeed, they control several steps of vesicular trafficking such as vesicle formation, vesicle movement on actin and tubulin cytoskeletal tracks, vesicle tethering, docking and fusion to the target compartment. Accordingly, Rab proteins are considered key factors in vesicular trafficking as they have a fundamental role in specifying identity and routing of vesicles and organelles. Given their role in membrane traffic, it is not surprising that Rab proteins control the cellular fate of several membrane molecules such as signal transduction receptors and ion channels, being thus fundamental for their correct function. However, much evidence of interaction of a number of Rab proteins with cargo has been reported, raising the question of the functional meaning of these interactions. Indeed, Rab proteins have been demonstrated to directly interact with several membrane proteins, such as signaling receptors, immunoglobulin receptors, integrins and ion channels. Growing evidence indicates that, through interactions with Rab proteins, cargos directly control their own fate. Furthermore, often a cargo protein has the ability to interact with more than one Rab and/or with the same Rab in different activation states. This review focuses on these interactions highlighting their role in modulating cargo's trafficking and functions. PMID:23558751

Aloisi, Anna Laura; Bucci, Cecilia

2013-07-01

408

Topology formation for tactical networks with directional RF and free-space optical links  

Microsoft Academic Search

This work addresses the graph theoretical under-pinning of forming a topology during the deployment of directional RF or free space optical (FSO) based tactical networks. The objective is to construct a topology that not only has a good reliability, but also supports the maximal delivery of traffic. Given the fact that each node has a limited number of transceivers, the

Kyle Guan; Reza Ghanadan; Kevin McNeil; Srikanta Kumar

2008-01-01

409

Modeling of a Direct Expansion Solar Assisted Heat Pump Using Artificial Neural Networks  

Microsoft Academic Search

This study presents the applicability of artificial neural networks (ANNs) to model a direct expansion solar assisted heat pump (DXSAHP). The experiments were conducted to determine the effects of solar intensity under the meteorological conditions of Calicut, India. The parameters such as coefficient of performance, compressor pressure ratio, air temperature at condenser outlet, and solar energy input ratio predicted from

M. Mohanraj; S. Jayaraj; C. Muraleedharan

2008-01-01

410

Improved Direct Power Control of a DFIG-Based Wind Turbine During Network Unbalance  

Microsoft Academic Search

This paper proposes an improved coordinate direct power control (DPC) strategy for the doubly fed induction generator (DFIG) and the grid side converter (GSC) of a wind power generation system under unbalanced network conditions. Two improved DPC schemes for the DFIG and the GSC are presented, respectively. The DPC for DFIG is to eliminate the torque and stator reactive power

Peng Zhou; Yikang He; Dan Sun

2009-01-01