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The role of attentional mechanisms in memory search was investigated in 2 experiments. In Experiment 1, an abrupt-onset cue was a valid or invalid predictor of a spatially displaced memory probe in a memory search paradigm. The 2 conditions differed only in terms of the duration of the memory probe: either 200 ms or an unlimited duration until the subject's response. We found that memory probe duration had little impact on memory search, as revealed by the slope across memory set size, although an invalid prior cue slowed responding by increasing the intercept by about 70 ms. In Experiment 2, costs and benefits of valid and invalid cues were assessed by inclusion of a neutral condition. Both costs and benefits were found, with effects again localized in the intercept of the memory search functions. A simple model was proposed that estimated 2 attentional transit times, 1 to the abrupt-onset cue and 1 activated after disengagement from an invalid location. We address whether the rapid examination of the contents of working memory should be considered an encapsulated process, unperturbed by abrupt-onset events that delay but do not otherwise disturb the resulting search., The present study extends our earlier analysis (Homa, Newton, Terry, Schafer, & Richter, 2007) of the roles of attentional cues in the Sternberg (1966) paradigm. In our earlier study, we [...]

A version of the input-to-output stability (IOS) small gain theorem is derived for interconnections where the subsystems communicate asynchronously over multiple channels, and the communication is subject to multiple time-varying possibly unbounded communication delays. It is shown that a "multi-dimensional" version of the small gain condition guarantees the stability of the interconnection of IOS subsystems under certain mild assumptions imposed on communication process. The fulfillment of these assumptions does not depend on characteristics of the communication channels, but can always be guaranteed by implementation of certain features of the underlying communication protocol. This result is applicable to a wide range of dynamical systems whose parts communicate over networks, such as Internet-based teleoperators. Index Terms--Networked control systems, small-gain condition, stability, time-varying communication delays.

We introduce the continuous time asynchronous channel as a model for time jitter in a communication system with no common clock between the transmitter and the receiver. We have obtained a simple characterization for an optimal zero-error self-synchronizable code for the asynchronous channel. The capacity of this channel is determined by both a combinatorial approach and a probabilistic approach. Our results unveil the somewhat surprising fact that it is not necessary for the receiver clock to resynchronize with the transmitter clock within a fixed maximum time in order to achieve reliable communication. This means that no upper limit should be imposed on the run lengths of the self-synchronization code as in the case of run-length limited (RLL) codes which are commonly used in magnetic recording. Index Terms--Asynchronous channel, magnetic recording, run-length limited (RLL) codes, self-synchronizable codes, synchronization, time jitter.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.comnet.2008.08.023 Byline: Jehn-Ruey Jiang Keywords: Mobile ad hoc network (MANET); Asynchronous power-saving algorithm; Optimal quorum system Abstract: Quorum systems satisfying the rotation closure property can be used to realize asynchronous power-saving algorithms for mobile ad hoc networks. The FPP, grid, cyclic, torus and e-torus quorum systems can provide the algorithms with the lowest or near lowest active ratios since they have the optimal or near optimal quorum sizes. The algorithms guarantee that a node can sense the status of every neighbor by receiving one or more beacons from it within a round of beacon intervals. Traditionally, the smallest quorum overlap size (SQOS) and the maximum quorum overlap separation (MQOS) are used to measure the neighbor sensibility. However, it is difficult to differentiate the quorum systems by SQOS and MQOS since most of them have the same SQOS and MQOS values. In this paper, the expected quorum overlap size (EQOS) is proposed as an average-case neighbor sensibility measurement. We can easily judge the goodness of quorum systems by EQOS since they have different EQOS values. Larger than one EQOS values are desirable. Observing quorum systems are of EQOS values far larger than one, we are inspired to devise a new quorum system, called the fraction torus (f-torus) quorum system, for the construction of flexible mobility-adaptive power-saving algorithms. The f-torus quorum system can further reduce the active ratio to save energy by shrinking the quorum size, while still keeping the EQOS larger than one. We derive EQOS values for all the above-mentioned quorum systems by analysis and simulation experiments. As we will show, the EQOS analysis and simulation results coincide very closely. Author Affiliation: Department of Computer Science and Information Engineering, National Central University, No. 300, Jhongda Road, Jhongli 32001, Taiwan, ROC Article History: Received 9 March 2008; Revised 23 June 2008; Accepted 24 August 2008 Article Note: (miscellaneous) Responsible Editor: E. Chong

Dual-modular-redundancy (DMR) architectures use duplication and self-voting asynchronous circuits to mitigate single event transients (SETs). The area and performance of DMR circuitry is evaluated against conventional triple-modular-redundancy (TMR) logic. Benchmark ASIC circuits designed with DMR logic show a 10-24% area improvement for flip-flop designs, and a 33 % improvement for latch designs. Index Terms--Asynchronous circuits, combinational logic, sequential logic, single event effects.

1 Introduction With the proliferation of portable computing platforms and small wireless devices, ad hoc wireless networks have received more and more attention as a means of data communication among […], Power-saving is a critical issue for all kinds of portable devices. The power-saving mode of IEEE 802.11 is designed for a single-hop (or fully connected) ad hoc network and is not applicable for multi-hop ad hoc networks. In this paper, we propose an asynchronous power-saving protocol for mobile ad hoc networks (MANETs) with unpredictable mobility and multi-hop communication. Neighbors that wish to communicate estimate the relative phase difference between their sleep/awake cycles. A station uses this phase information for transmitting the pending traffic. Stations can also increase their awake period for transmitting the data and to reduce latency for delay sensitive flows. Simulation studies indicate that the proposed asynchronous protocol is quite effective under various traffic characteristics and loads; energy saving can be as high as 70%, while the packet delivery ratio is comparable to networks without power management. Key words: 802.11, ad-hoc networks, clock synchronization, scalability

The design of a 4-bit asynchronous RSFQ/RSFQ-AT microprocessor which reduces the complexity of global clock distribution, clock view and considerations for clock jitter is described.

This article contends that there is a growing interest in the theory and practice of Distance Learning (DL). The article presents a DL application in a public/nonprofit administration curriculum. A description of the major DL platforms is made including the author's use of the WebCT and Yahoo groups platforms. Moreover, the article examines the many technological and behavioral challenges of DL. It is argued that in meeting such challenges, the higher education community must find ways to invest and support flexible platforms that support all faculty. Until such solutions are found, DL may never reach its fullest potential. Keywords: distance learning, synchronous communication, asynchronous communication, message board, critical thinking

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.comnet.2006.02.005 Byline: Shay Kutten (a), David Peleg (b) Keywords: Peer-to-peer; Topology changes; Topology knowledge loss; Distributed algorithms; Asynchronous networks Abstract: The resource discovery problem arises in the context of peer to peer (P2P) networks, where at any point of time a peer may be placed at or removed from any location over a general purpose network (e.g., an Internet site). A node (peer) can communicate with another node directly if and only if it knows a certain routing information to that other node. Hence, a critical task is for the peers to convey this routing information to each other. The problem was formalized by Harchol-Balter et al. and the specific P2P application they had in mind was the logical networks G.sub.0 of servers placed by Akamai at various Internet sites. The routing information needed for a node to reach another peer is that peer's identifier (e.g., IP address). A logical directed edge represents the fact that the peer at the tail of the edge knows the IP address of the one at its head. The problem is to compute the connected components in the underlying graph of G.sub.0 (namely, the undirected graph obtained from G.sub.0 by removing edge directionality). A number of algorithms were developed in Harchol-Balter et al. for this problem in the model of a synchronous network over a weakly connected directed graph. That is, the assumption was that some clock delivers pulses to every node every time unit at the same time, and a message delivery takes one time unit. The best of these algorithms was randomized. Subsequently, a deterministic algorithm for the problem on synchronous networks with improved complexity was presented in a paper by Kutten et al. The current paper extends the deterministic algorithm of Kutten et al. to the environment of asynchronous networks, where no clock pulses are assumed, and the message delivery time may vary and is not known. We managed to maintain complexities similar to those of the synchronous algorithm of Kutten et al. (translated to the asynchronous model). These are lower than the complexities that would be needed to synchronize the system. The main technical difficulty in a directed, weakly connected system is to ensure that nodes take steps that are consistent with each other, even if their knowledge about each other is not symmetric. Here, this task is further complicated by the fact that there is no timeout mechanism (which does exist in synchronous systems) to assist in ensuring consistency. In particular, as opposed to the case in synchronous systems, an asynchronous algorithm cannot first transform every directed edge to be bidirectional and second, apply an algorithm for bidirectional graph. Thus, our result takes another step towards representing the actual setting in a realistic manner. Author Affiliation: (a) Faculty of Industrial Engineering and Management, The Technion, Haifa 32000, Israel (b) Department of Computer Science and Applied Mathematics, The Weizmann Institute, Rehovot 76100, Israel Article History: Received 3 February 2004; Revised 14 October 2005; Accepted 22 February 2006 Article Note: (footnote) [star] A preliminary version of this paper appeared in the Proceedings of the 21st IEEE Symposium on Reliable Distributed Systems (SRDS'02), October 13-16, 2002, Osaka University, Suita, Japan., [star][star] May this paper serve as a modest tribute to the memory of Daniel Lewin, a co-author of a previous paper on the subject, who died tragically on September 11th, 2001.

A new fully asynchronous algorithm is presented, where pixels can compute their local data in parallel and independently from one another, requiring only a unique final global synchronization point. Several configurations of the algorithm-architecture are explored, simulated and validated using a 'SystemC' model, which reveals an image segmentation rate up to 66,000 QCIF images/sec.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.comnet.2005.09.032 Byline: V. Vidhyashankar (a), B.S. Manoj (b), C. Siva Ram Murthy (c) Keywords: Asynchronous ad hoc wireless networks; Time sensitive traffic; End-to-end reservation; Reservation slot positioning; Hybrid wireless mesh networks Abstract: Heterogeneous multihop wireless networks such as wireless mesh networks consist of a set of resource-constrained mobile nodes that want to communicate with each other and a set of fixed relay nodes that are equipped with better resources and help in relaying data to the mobile nodes. Supporting real-time traffic in wireless mesh networks is considered as a challenging problem. In a synchronous or asynchronous slotted environment, the position of reservation slots at every link of an end-to-end path influences the end-to-end delay. The major contributions of this paper are the following: (i) an on-demand QoS routing protocol for asynchronous single channel wireless mesh networks, (ii) three heuristics for the slot allocation and positioning process in such networks, and (iii) the adaptations of slot allocation and positioning strategies for taking advantage of the recovery capacity effect of batteries of the mobile nodes. The heuristics we propose are the Early Fit Reservation (EFR), Minimum Bandwidth Reservation (MBR), and the Position-based Hybrid Reservation (PHR). The EFR heuristic reserves bandwidth at the first available slot on every link on a link-by-link basis in the forward path. The MBR heuristic allocates bandwidth on the links in the increasing order of bandwidth and the PHR heuristic assigns bandwidth for every link at a position which is proportional to its location in the path. Recent studies on chemical battery characteristics show that a pulsed current discharge can extend the battery life compared to a continuous discharge. We have also adapted the basic slot allocation strategies, that are aimed at maximizing system throughput, to take benefit of the pulsed discharge model. The adapted heuristics are designed to provide an extended battery life and hence reduce the number of battery recharges. Simulation studies show that EFR performs better in terms of delay characteristics, whereas PHR and MBR provide better system throughput in terms of call acceptance rate. The adapted heuristics are found to be performing better in terms of the number of deaths of mobile nodes and the average number of path breaks. Author Affiliation: (a) Department of Computer Science, Cornell University, Ithaca, NY 14853, USA (b) Department of Electrical and Computer Engineering, University of California San Diego, San Diego, CA 92093, USA (c) Department of Computer Science and Engineering, Indian Institute of Technology, Madras, Chennai 600 036, India Article History: Received 17 October 2004; Revised 15 July 2005; Accepted 26 September 2005 Article Note: (miscellaneous) Responsible Editor: E. Gregori

The combination of a time-free assumption on the message pattern with a synchrony assumption on process speed and message delay is investigated. Results show that both types of assumptions can be combined to obtain a hybrid eventual leader protocol.

In this paper, we consider a point-to-point communication network of discrete memoryless channels. In the network, there are a source node and possibly more than one sink node. Information is generated at the source node and is multicast to each sink node. We allow a node to encode its received information before loading it onto an outgoing channel, where the channels are independent of each other. We also allow the nodes to pass along messages asynchronously. In this paper, we characterize the admissibility of single-source multi-sink communication networks. Our result can be regarded as a network generalization of Shannon's result that feedback does not increase the capacity of a discrete memoryless channels (DMCs), and it implies a separation theorem for network coding and channel coding in such a communication network. Index Terms--Channel coding, feedback, network coding, separation theorem.

This paper gives a formulation of the basins of fixed point states of fully asynchronous discrete-time discrete-state dynamic networks. That formulation provides two advantages. The first one is to point out the different behaviors between synchronous and asynchronous modes and the second one is to allow us to easily deduce an algorithm which determines the behavior of a network for a given initialization. In the context of this study, we consider networks of a large number of neurons (or units, processors, etc.), whose dynamic is fully asynchronous with overlapping updates . We suppose that the neurons take a finite number of discrete states and that the updating scheme is discrete in time. We make no hypothesis on the activation functions of the nodes, so that the dynamic of the network may have multiple cycles and/or basins. Our results are illustrated on a simple example of a fully asynchronous Hopfield neural network. Index Terms--Asynchronism, Hopfield networks, networks dynamic.

A resource dilemma is a circumstance in which an aggregate of people share a slowly replenishing resource pool out of which each person can harvest a significant amount. Resource dilemmas normally make salient an allocation norm of equality in harvests among aggregate members. When asymmetry among aggregate members exists in terms of either access to the resource pool or reward for harvest, the equity allocation norm becomes equally relevant. In this study, groups experienced an experimental simulation of a resource dilemma under either symmetric, asymmetric harvest limit, or asymmetric reward conditions. Groups in the asymmetric conditions were more likely to choose explicitly to follow an allocation norm, and groups that chose to follow a norm had a far more task-oriented discussion and positive perceptions of their experience than groups that did not make an explicit choice. Neither experimental condition nor explicit norm choice revealed a discernible impact on harvesting. Keywords: small group discussion; resource dilemma; asymmetry; social norm

The asymmetrical half-bridge (AHB) topology discussed in this paper is one of the complementary driven pulse-width modulated converter topologies, which presents an inherent zero-voltage switching (ZVS) capability. In the previous work, the ideal operation of the converter and the ZVS realization process have been analyzed. However, the influence of the circuit parasitics on the output voltage drop and the design constraints of the circuit parameters to ensure the ZVS operation have not been investigated. The minimum load needed to ensure the ZVS operation is also not readily available. This paper presents a detailed and practical design for a 1-MHz AHB converter. A revised voltage transfer ratio of the converter is derived considering the influence of circuit parasitics and the ZVS transition. Two circuit parameters responsible for maintaining the ZVS operation are the transformer leakage inductance and the interlock delay time between the gate signals of two switches. A design method of the two parameters is proposed, which can ensure the ZVS transition. The possible ZVS range of the load variation is also investigated. A 50-W AHB converter with 1-MHz switching frequency was constructed, and a maximum efficiency of 91% was achieved. Index Terms--Asymmetrical half-bridge (AHB) topology, pulse-width modulated (PWM), zero-voltage switching (ZVS).

The problem of controlling a finite-state asynchronous sequential machine is examined. Main consideration is given to input/output control, where access to the state of the machine is not available. The objective is to use output feedback to control the machine so as to match a prescribed model. It is shown that necessary and sufficient conditions for the existence of appropriate controllers can be stated in terms of a simple F comparison of two numerical matrices. Whenever controllers exist, algorithms for their design are outlined. Index Terms--Asynchronous sequential machines, model matching, observers, output feedback, separation principle.

An optimized asynchronous self-timing scheme that will simplify and speed up the design of large digital circuits is presented. The way by which design methodology introduced with this asynchronous self-timing scheme can simplify the design of automated CAD tools for RSFQ-AT is shown.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.compeleceng.2005.01.001 Byline: Abdulhamit Subasi (a), Etem Koklukaya (b) Abstract: Performance of ATM networks depends on switch performance and architecture. This paper presents a simulation study of a new dynamic allocation of input buffer space in ATM switching elements. The switching elements are composed of input and output buffers which are used to store received and forwarded cells, respectively. Efficient and fair use of buffer space in an ATM switch is essential to gain high throughput and low cell loss performance from the network. In this paper, input buffer space of each switching element is allocated dynamically as a function of traffic load. A shared buffer pool is provided with threshold-based virtual partition among input ports, which supplies the necessary input buffer space as required by each input port. The system behaviour under varying traffic loads has investigated using a simulation program. Also, a comparison with a static allocation scheme shows that the threshold based dynamic buffer allocation scheme ensures an increased network throughput and a fair share of the buffer space even under bursty loading conditions. Author Affiliation: (a) Department of Electrical and Electronics Engineering, KahramanmaraA Sutcu A[degrees]mam University, 46100 KahramanmaraA, Turkey (b) Department of Electrical and Electronics Engineering, Sakarya University, 54187 Sakarya, Turkey

A theoretical algorithm and its practical version are introduced to perform a decentralized detection of the global convergence of parallel asynchronous iterative algorithms. It is proved that even if the algorithm is completely decentralized, the detection of global convergence is achieved on one processor under the classical conditions.

There was generally a significant relationship between the hypothesized mediators and perceived learning for online courses. Studies indicate that outcomes of online courses improved when professors structured them to support the growth of a learning community, by being available online to interact with students, and by using collaborative learning strategies.

In recent years, wireless asynchronous transfer mode networks have become popular and are in widespread use for supporting various types of data transmission. To minimize the cost in setting up routes and to meet the QoS constraint in time-sensitive traffic, in addition to bandwidth capacity, this paper focuses on the optimization of the number of shared links to reduce the call-blocking rate and the handoff failure rate for intercell roaming. The average longest path length and the average of the average path length of the constructed multicast trees are shown to be stable when the network load becomes heavy. Keywords: Asynchronous transfer mode; Multicast; Migration; Wireless; Handoff

Study conducted on the flow assignment problem in fibre optic based Asynchronous transfer mode networks is presented.

The Kaufman-Roberts multirate recurrence equation is converted to a functional equation subject to a single step parameter d, which defines the state-dependent recurrence depth of the multirate model, d is verified to be the joint solution of two moment-generating functions. In contrast to the multirate transform domain solution, the characteristic function of the functional model may be inverted explicitly. But this inverse is scaled by d and yields a new state-dependent probability density based on two types of scaled Gamma functions. They uniformly cover wide areas of continuous states, capacities C, and demands. A two-moments series expansion of d in the transform domain signifies that it models the effective bitrate of the multirate connections under progress within a complete sharing mode of C. Selected case studies show very good agreements to the exact Kaufman-Roberts' state probabilities and to the high accurate Mitra-Morrison's tail probabilities. Further partial sharing mode investigations include an efficient approximation for connection admission controls by trunk reservation covering partial and full fairness. The resulting state and tail probabilities deviate only slightly from Roberts' approximations of the past. All solutions achieve time complexities of O(1) per state, which amount to O(SC) with iterative multirate recurrence solutions for S service classes. Index Terms--asynchronous transfer mode (ATM), multimedia systems, multirate traffic engineering, universal mobile telecommunications system (UMTS).

We consider networks of a large number of neurons (or units, processors, ...), whose dynamics are fully asynchronous with overlapping updating. We suppose that the neurons take a finite number of states (discrete states), and that the updating scheme is discrete in time. We make no hypotheses on the activation function of the neurons; the networks may have multiple cycles and basins. We derive conditions on the initialization of the networks, which ensures convergence to fixed points only. Application to a fully asynchronous Hopfield neural network allows us to validate our study. Index Terms--Asynchronism, dynamic neural networks, stability.

We introduce the class of hysteretic linear-threshold (HLT) logic functions as a novel extension of linear threshold logic, and prove their general applicability for constructing state-holding Boolean functions. We then demonstrate a fusion of HLT logic with the quasi-delay insensitive style of asynchronous circuit design, complete with logical design examples. Future research directions are also identified. Index Terms--Asynchronous VLSI, digital logic, hysteresis, linear-threshold logic, quasi-delay insensitive (QDI).