Abstract: The purpose of this qualitative case study was to explore the asynchronous communication perspectives and experiences of undergraduate students in an online course. Interviews with 22 preservice teachers, student-to-instructor email transcripts, asynchronous discussion transcripts, and two independent reviewers' reviews of the asynchronous discussions were used to collect and analyze the data. The results of this study have implications for the effective design of asynchronous communication, and interaction between student and instructor, between student and student, and between student and content. The results inform researchers and practitioners of the factors, strategies and barriers that need to be taken into account, and suggestions for how to overcome barriers when utilizing asynchronous communication tools for learning. A comprehensive understanding of computer-mediated communication tools and student preferences and experiences can contribute to a knowledge base for effective planning and implementation of successful learning.

Abstract: In this communication, we give an overview of our work on an asynchronous brain-computer interface (where the subject makes self-paced decisions on when to switch from one mental task to the next) that responds every 0.5 s. A local neural classifier tries to recognize three different mental tasks; it may also respond "unknown" for uncertain samples as the classifier has incorporated statistical rejection criteria. We report our experience with 15 subjects. We also briefly describe two brain-actuated applications we have developed: a virtual keyboard and a mobile robot (emulating a motorized wheelchair).

Abstract: In this paper, we consider the diagnosis of asynchronous discrete event systems. We follow a so-called true concurrency approach, in which no global state and no global time is available. Instead, we use only local states in combination with a partial order model of time. Our basic mathematical tool is that of net unfoldings originating from the Petri net research area. This study was motivated by the problem of event correlation in telecommunications network management.

Abstract: We propose an approach to topology control based on the principle of maintaining the number of neighbors of every node equal to or slightly below a specific value k. The approach enforces symmetry on the resulting communication graph, thereby easing the operation of higher layer protocols. To evaluate the performance of our approach, we estimate the value of k that guarantees connectivity of the communication graph with high probability. We then define k-Neigh, a fully distributed, asynchronous, and localized protocol that follows the above approach and uses distance estimation. We prove that k-Neigh terminates at every node after a total of 2n messages have been exchanged (with n nodes in the network) and within strictly bounded time. Finally, we present simulations results which show that our approach is about 20% more energy-efficient than a widely-studied existing protocol.

Abstract: Transferring data between mutually asynchronous clock domains requires safe synchronization. However, the exact nature of synchronization sometimes eludes designers, and as a result synchronization circuits get "optimized" to the point where they do no longer operate correctly. This paper reviews a number of such cases, analyzes the causes of the errors, and offers a correct synchronizer circuit for each case. A correct two flop synchronizer is presented. After discussing cases that avoid synchronization, the following synchronizers are reviewed: one flop, sneaky path, greedy path, wrong protocol, global reset, async clear, DFT leakage, pulse, slow-to-fast, metastability blocker, parallel and shared flop synchronizers.

Abstract: . . . 1. Theories and Methods Technology mediated communication is a fact of life. The human communication apparatus is constrained in several ways. There are limits to the distance at which speech is audible, and visible behaviours such as gesture, gaze or facial expressions are perceivable. Furthermore, these natural communication behaviours are ephemeral and do not persist over time. Given these limitations, we must rely on some form of mediation, if we are to communicate at distance and across time. People have therefore invented technologies that attempt to circumvent these limits to allow remote synchronous communication (e.g. telephone, videoconference) or asynchronous communication (e.g. letters, telegraph, email, fax, voicemail). Understanding the principles that govern mediated communication has important practical implications. Because of the pervasiveness of mediated communication, we need to determine whether, how and why, it differs from face to face communication. If there are differences between mediated and face to face communication, we need to provide guidelines to inform decisions about the circumstances in which it is appropriate to use mediated communication, and the effects of using it in those situations. Systematic insights into mediated communication should also enable us to improve the designs of current and future technologies supporting mediated communication. An understanding of mediated communication should also inform more general theorizing about the psychology of communication. Most current communication theories regard face to face communication as an integrated set of speech, gaze, and gestural behaviours. As we shall see, studies of mediated communication allow us to isolate the individual contribution of different nonverbal behaviours, such as gaze and gesture to communication. They also help to clarify the overall influence of visual information in communication, and the effects of communication interactive processes such as feedback on communication. The structure of the review is as follows. The main part of the review is organized around 3 main theoretical approaches to mediated communication. We first talk about the general characteristics of mediated communication theories, and methods in this area. We then characterize each theory in detail and evaluate the evidence for it. We conclude with a discussion of outstanding practical and theoretical issues.

Abstract: We describe algorithms for two-stage stochastic linear programming with recourse and their implementation on a grid computing platform. In particular, we examine serial and asynchronous versions of the L-shaped method and a trust-region method. The parallel platform of choice is the dynamic, heterogeneous, opportunistic platform provided by the Condor system. The algorithms are of master-worker type (with the workers being used to solve second-stage problems), and the MW runtime support library (which supports master-worker computations) is key to the implementation. Computational results are presented on large sample-average approximations of problems from the literature.

Abstract: In preferred embodiments, a system including a transmitter, a receiver, and a serial link, in which the transmitter is configured to transmit video data, embedded-clock auxiliary data (or auxiliary data derived from embedded-clock auxiliary data), and a video clock over the link to the receiver. The transmitter is configured to extract a sample clock from the auxiliary data without use of a phase-locked loop, and to generate time stamp data in response to the sample clock and the video clock. Typically, the auxiliary data are SPDIF (or other) audio data, and the sample clock changes state in response to codes that occur periodically in the audio data. Other aspects of the invention are a transmitter for use in such a system, a time stamp data generation circuit for use in such a transmitter, and a method for generating time stamp data in response to a stream of embedded-clock auxiliary data and a video clock.

Abstract: The famous Fischer, Lynch, and Paterson impossibility proof shows that it is impossible to solve the consensus problem in a natural model of an asynchronous distributed system if even a single process can fail. Since its publication, two decades of work on fault-tolerant asynchronous consensus algorithms have evaded this impossibility result by using extended models that provide (a) randomization, (b) additional timing assumptions, (c) failure detectors, or (d) stronger synchronization mechanisms than are available in the basic model. Concentrating on the first of these approaches, we illustrate the history and structure of randomized asynchronous consensus protocols by giving detailed descriptions of several such protocols.

Abstract: We study long-running transactions in open component-based distributed applications, such as Web Services platforms. Long-running transactions describe time-extensive activities that involve several distributed components. Henceforth, in case of failure, it is usually not possible to restore the initial state, and firing a compensation process is preferable. Despite the interest of such transactional mechanisms, a formal modeling of them is still lacking. In this paper we address this issue by designing an extension of the asynchronous π-calculus with long-running transactions (and sequences) – the πt -calculus. We study the practice of πt-calculus, by discussing few paradigmatic examples, and its theory, by defining a semantics and providing a correct encoding of πt-calculus into asynchronous π-calculus.

Abstract: A method is provided for transmitting wireless signals in a network comprising a network coordinator and one or more remote devices. The available transmission time is divided into a plurality of superframes, each of which is further divided up into a beacon duration, one or more management time slots, one or more guaranteed time slots, and one or more asynchronous time slots. Each of the management time slots, guaranteed time slots, and asynchronous time slots are assigned to one of the one or more remote devices. The network coordinator sends a beacon to the one or more remote devices during the beacon duration. The device or coordinator assigned to the current guaranteed time slot sends frames of isochronous data in the current guaranteed time slot. The device or coordinator assigned to the current asynchronous time slot sends frames of asynchronous data in the current asynchronous time slot.

Abstract: In this paper we consider the problems faced by an industrial planner who is responsible for the design of real-life asynchronous production lines under stochastic conditions that may be due to breakdowns or random processing times. Based on real-life system data, it is shown that a number of available algorithms for the performance evaluation of a given system configuration as well as an algorithm for determining the optimum buffer configuration can be successfully applied in industrial practice.

Abstract: With increasing integration densities, large chip designs are commonly partitioned into multiple clock domains. While the computation within each individual domain may be synchronous, the interfaces between these domains often use asynchronous methods. One such approach is the STARI technique where a self-timed FIFO compensates for clock-skew between the sender and receiver. We present implementations of STARI where the FIFO consists of a single, handshaking stage. We start with the simplest case where the sender and receiver operate at exactly the same frequency with an unknown skew. We then generalize this design for links with clocks whose frequencies are rational multiples of each other, clocks whose frequencies are closely matched, and arbitrary clocks. We show that in each of these cases, the STARI interface can exploit the stability of typical clocks to achieve low latencies and negligible probabilities of synchronization failure using very simple hardware.

Abstract: Unreliable failure detectors introduced by Chandra and Toueg are abstract mechanisms that provide information on process failures. On the one hand, failure detectors allow to state the minimal requirements on process failures that allow to solve problems that cannot be solved in purely asynchronous systems. But, on the other hand, they cannot be implemented in such systems: their implementation requires that the underlying distributed system be enriched with additional assumptions. The usual failure detector implementations rely on additional synchrony assumptions (e.g., partial synchrony). This paper proposes a new look at the implementation of failure detectors and more specifically at Chandra-Toueg’s failure detectors. The proposed approach does not rely on synchrony assumptions (e.g., it allows the communication delays to always increase). It is based on a query-response mechanism and assumes that the query/response messages exchanged obey a pattern where the responses from some processes to a query arrive among the (n − f ) first ones (n being the total number of processes, f the maximum number of them that can crash, with 1 ≤ f< n). When we consider the particular case f =1 , and the implementation of a failure detector of the class denoted S (the weakest class that allows to solve the consensus problem), the additional assumption the underlying system has to satisfy boils down to a simple channel property, namely, there is eventually a pair of processes (pi ,p j) such that the channel connecting them is never the slowest among the channels connecting pi or pj to the other processes. A probabilistic analysis shows that this requirement is practically met in asynchronous distributed systems.

Abstract: A disaster-tolerant data backup and remote copy system which is implemented as a controller-based replication of one or more LUNs (logical units) between two remotely separated pairs of array controllers connected by redundant links. The system provides a method for allowing a large number of commands to be ‘outstanding’ in transit between local and remote sites while ensuring the proper ordering of commands on remote media during asynchronous or synchronous data replication. In addition, the system provides a mechanism for automatic ‘tuning’ of links based on the distance between the array controllers.

Abstract: We consider the problem of secure leader election and propose two cheat-proof election algorithms: Secure Extrema Finding Algorithm (SEFA) and Secure Preference-based Leader Election Algorithm (SPLEA). Both algorithms assume a synchronous distributed system in which the various rounds of election proceed in a lock-step fashion. SEFA assumes that all elector-nodes share a single common evaluation function that returns the same value at any elector-node when applied to a given candidate-node. When elector-nodes can have different preferences for a candidate-node, the scenario becomes more complicated. Our Secure Preference-based Leader Election Algorithm (SPLEA) deals with this case. Here, individual utility functions at each elector-node determine an elector-node's preference for a given candidate-node. We relax the assumption of a synchronous distributed system in our Asynchronous Extrema Finding Algorithm (AEFA) and also allow the topology to change during the election process. In AEFA, nodes can start the process of election at different times, but eventually after topological changes stop long enough for the algorithm to terminate, all nodes agree on a unique leader. Our algorithm has been proven to be "weakly" self-stabilizing.

Abstract: The objective of this study is to investigate the performances of packet-switching architectures working in a synchronous and asynchronous way; in such architectures, the packet contention is resolved in the wavelength domain and the used wavelength converters are shared. We investigate on the saving of the number of converters that the sharing technique allows to obtain in the synchronous and asynchronous architectures and compare the obtained results. These ones show that when a packet loss probability is fixed, in the synchronous case a greater number of converters is saved. In some cases, the gain is 40% more than the asynchronous case. Furthermore, in the asynchronous case, a more expensive switching matrix is needed. The analysis is performed by introducing analytical and simulation models, and when both unicast and multicast traffic scenarios are considered.

Abstract: Multiple clock domains is one solution to the increasing problem of propagating the clock signal across increasingly larger and faster chips. The ability to independently scale frequency and voltage in each domain creates a powerful means of reducing power dissipation. A multiple clock domain (MCD) microarchitecture, which uses a globally asynchronous, locally synchronous (GALS) clocking style, permits future aggressive frequency increases, maintains a synchronous design methodology, and exploits the trend of making functional blocks more autonomous. In MCD, each processor domain is internally synchronous, but domains operate asynchronously with respect to one another. Designers still apply existing synchronous design techniques to each domain, but global clock skew is no longer a constraint. Moreover, domains can have independent voltage and frequency control, enabling dynamic voltage scaling at the domain level.

Abstract: A system is provided for seamless synchronization through asynchronous integration of Internet content with broadcast content within a portable handheld device (14), such as a remote control or a personal digital assistant (PDA). The handheld device (14) receives program-related data from the television (12) while the user is watching a program. The program-related data places the handheld device (14) in sync with the program the user is watching and augments the user's enjoyment of the program by providing supplemental broadcast information or additional interactive features. The handheld device (14) is also configured to retrieve additional supplemental information from at least one content source distinct from the broadcast source.

Abstract: In recent years, large distributed sensor networks have emerged as a new fast-growing application domain for wireless computing. In this paper, we present a distributed application-layer service for data placement and asynchronous multicast whose purpose is power conservation. Since the dominant traffic in a sensor network is that of data retrieval, (i) caching mutable data at locations that minimize the sum of request and update traffic, and (ii) asynchronously multicasting updates from sensors to observers can significantly reduce the total number of packet transmissions in the network. Our simulation results show that our service subsequently reduces network energy consumption while maintaining the desired data consistency semantics.

Abstract: We study long-running transactions in open component-based distributed applications, such as Web Services platforms. Long-running transactions describe time-extensive activities that involve several distributed components. Henceforth, in case of failure, it is usually not possible to restore the initial state, and firing a compensation process is preferable. Despite the interest of such transactional mechanisms, a formal modeling of them is still lacking. In this paper we address this issue by designing an extension of the asynchronous π-calculus with long-running transactions (and sequences) - the πt-calculus. We study the practice of πt-calculus, by discussing few paradigmatic examples, and its theory, by defining a semantics and providing a correct encoding of πt-calculus into asynchronous π-calculus.

Abstract: Patients' desire for online communication with their health care providers is likely to change the course of both telemedicine and e-health technologies.

Abstract: For a complete network of n processors within which communication lines are private, we show how to achieve concurrently many Byzantine Agreements within constant expected time both on synchronous and asynchronous networks. As an immediate consequence, this provides a solution to the Interactive Consistency problem. Our algorithms tolerate up to (n - 1)/3 faulty processors in both the synchronous and asynchronous cases and are therefore resilient-optimal.In terms of time complexity, our results improve a time bound of O(log n) (for n concurrent agreements) which is immediately implied by the constant expected time Byzantine Agreement of Feldman and Micali (synchronous systems) and of Canetti and Rabin (asynchronous systems). In terms of resiliency, our results improve the resiliency bound of the constant time, O(4√n)-resilient algorithm of Ben-Or.An immediate application of our protocols is a constant expected time simulation of simultaneous broadcast channels over a network with private lines.

Abstract: In a preferred embodiment, the present invention is an asymmetric data processing system (10) having two or more groups of processors that have attributes that are optimized for their assigned functions. A first processor group, which may be SMP (SMP Execution Engine) machines, are responsible for interfacing with applications and/or end users to obtain queries, and for planning query execution. A second processor group consists of many streaming record-oriented processors called Job Processing Units (JPUs), typically arranged as an MPP structure (MPP Execution Engine). The JPUs carry out the bulk of the data processing required to implement the logic of a query, running autonomously and asynchronously from other processors in the system. The JPUs preferably use a multi-tasking operating system that permits multiple tasks to run at a given instant in time, in either an absolute-priority- or a weighted-priority-based demand scheduling environment.

Abstract: A disaster recovery system with sequenced cascaded resynchronization comprises a plurality of data centers and a distributed control system. The individual data centers comprise a communication interface, a data storage, and a controller. The distributed control system is distributed and executable in the controllers of the plurality of data centers, and is capable of coordinating operations via the communication interfaces of the plurality of data centers to resynchronize a plurality of communication links between data center pairs of the plurality of data centers. The communication links including at least one synchronous link and at least one asynchronous link.

Abstract: Technology is starting to influence psychological fields. In particular, computer-mediated communication (CMC) is providing new tools that can be fruitfully applied in psychotherapy. These new technologies do not substitute for traditional techniques and approaches but they could be used as integration in the clinical process, enhancing or making easier particular steps of it. This paper focuses on the concept of e-therapy as a new modality of helping people resolve life and relationship issues. It utilizes the power and convenience of the Internet to allow synchronous and asynchronous communication between patient and therapist. It is important to underline that e-therapy is not an alternative treatment, but a resource that can be added to traditional psychotherapy. The paper also discusses how different forms of CMC can be fruitfully applied in psychology and psychotherapy, by evaluating the effectiveness of them in the clinical practice. To enhance the diffusion of e-therapy, further research is needed...

Abstract: Relative timing (RT) is introduced as a method for asynchronous design Timing requirements of a circuit are made explicit using relative timing Timing can be directly added, removed, and optimized using this style RT synthesis and verification are demonstrated on three example circuits, facilitating transformations from speed-independent circuits to burst-mode and pulse-mode circuits Relative timing enables improved performance, area, power, and functional testability of up to a factor of 3/spl times/ in all three cases This method is the foundation of optimized timed circuit designs used in an industrial test chip, and may be formalized and automated

Abstract: Opinions differ widely as to the type of architecture most suitable for achieving the tremendous performance gains expected with computers built by nanotechnology. In this context little research effort has gone into asynchronous cellular arrays, an architecture that is promising for nanocomputers due to (1) its regular structure of locally interconnected cells, and (2) its asynchronous mode of timing. The first facilitates bottom-up manufacturing techniques like directed self-assembly. The second allows the cells' operations to be timed randomly and independently of each other, mitigating the problems accompanying a central clock, like high power consumption and heat dissipation. The advantages of asynchronous timing notwithstanding, it makes computation less straightforward. Attempts to compute on asynchronous cellular arrays have therefore focused on simulating synchronous operation on them, at the price of more complex cells. Here we advance a more effective approach based on the configuration on an asynchronous cellular array of delay-insensitive circuits, a type of asynchronous circuit that is robust to arbitrary delays in signals. Our results may be a step towards future nanocomputers with a huge number of autonomously operating cells organized in homogeneous arrays that can be programmed by configuring them as delay-insensitive circuits.