163,483 research outputs found
Fast and flexible selection with a single switch
Selection methods that require only a single-switch input, such as a button
click or blink, are potentially useful for individuals with motor impairments,
mobile technology users, and individuals wishing to transmit information
securely. We present a single-switch selection method, "Nomon," that is general
and efficient. Existing single-switch selection methods require selectable
options to be arranged in ways that limit potential applications. By contrast,
traditional operating systems, web browsers, and free-form applications (such
as drawing) place options at arbitrary points on the screen. Nomon, however,
has the flexibility to select any point on a screen. Nomon adapts automatically
to an individual's clicking ability; it allows a person who clicks precisely to
make a selection quickly and allows a person who clicks imprecisely more time
to make a selection without error. Nomon reaps gains in information rate by
allowing the specification of beliefs (priors) about option selection
probabilities and by avoiding tree-based selection schemes in favor of direct
(posterior) inference. We have developed both a Nomon-based writing application
and a drawing application. To evaluate Nomon's performance, we compared the
writing application with a popular existing method for single-switch writing
(row-column scanning). Novice users wrote 35% faster with the Nomon interface
than with the scanning interface. An experienced user (author TB, with > 10
hours practice) wrote at speeds of 9.3 words per minute with Nomon, using 1.2
clicks per character and making no errors in the final text.Comment: 14 pages, 5 figures, 1 table, presented at NIPS 2009 Mini-symposi
Pharmacological Fingerprints of Contextual Uncertainty
Successful interaction with the environment requires flexible updating of our beliefs about the world. By estimating the likelihood of future events, it is possible to prepare appropriate actions in advance and execute fast, accurate motor responses. According to theoretical proposals, agents track the variability arising from changing environments by computing various forms of uncertainty. Several neuromodulators have been linked to uncertainty signalling, but comprehensive empirical characterisation of their relative contributions to perceptual belief updating, and to the selection of motor responses, is lacking. Here we assess the roles of noradrenaline, acetylcholine, and dopamine within a single, unified computational framework of uncertainty. Using pharmacological interventions in a sample of 128 healthy human volunteers and a hierarchical Bayesian learning model, we characterise the influences of noradrenergic, cholinergic, and dopaminergic receptor antagonism on individual computations of uncertainty during a probabilistic serial reaction time task. We propose that noradrenaline influences learning of uncertain events arising from unexpected changes in the environment. In contrast, acetylcholine balances attribution of uncertainty to chance fluctuations within an environmental context, defined by a stable set of probabilistic associations, or to gross environmental violations following a contextual switch. Dopamine supports the use of uncertainty representations to engender fast, adaptive responses. \ua9 2016 Marshall et al
Traffic Management Applications for Stateful SDN Data Plane
The successful OpenFlow approach to Software Defined Networking (SDN) allows
network programmability through a central controller able to orchestrate a set
of dumb switches. However, the simple match/action abstraction of OpenFlow
switches constrains the evolution of the forwarding rules to be fully managed
by the controller. This can be particularly limiting for a number of
applications that are affected by the delay of the slow control path, like
traffic management applications. Some recent proposals are pushing toward an
evolution of the OpenFlow abstraction to enable the evolution of forwarding
policies directly in the data plane based on state machines and local events.
In this paper, we present two traffic management applications that exploit a
stateful data plane and their prototype implementation based on OpenState, an
OpenFlow evolution that we recently proposed.Comment: 6 pages, 9 figure
A Supervisor for Control of Mode-switch Process
Many processes operate only around a limited number of operation points. In order to have adequate control around each operation point, and adaptive controller could be used. When the operation point changes often, a large number of parameters would have to be adapted over and over again. This makes application of conventional adaptive control unattractive, which is more suited for processes with slowly changing parameters. Furthermore, continuous adaptation is not always needed or desired. An extension of adaptive control is presented, in which for each operation point the process behaviour can be stored in a memory, retrieved from it and evaluated. These functions are co-ordinated by a ¿supervisor¿. This concept is referred to as a supervisor for control of mode-switch processes. It leads to an adaptive control structure which quickly adjusts the controller parameters based on retrieval of old information, without the need to fully relearn each time. This approach has been tested on experimental set-ups of a flexible beam and of a flexible two-link robot arm, but it is directly applicable to other processes, for instance, in the (petro) chemical industry
Reduced Switching Connectivity for Large Scale Antenna Selection
In this paper, we explore reduced-connectivity radio frequency (RF) switching
networks for reducing the analog hardware complexity and switching power losses
in antenna selection (AS) systems. In particular, we analyze different hardware
architectures for implementing the RF switching matrices required in AS designs
with a reduced number of RF chains. We explicitly show that fully-flexible
switching matrices, which facilitate the selection of any possible subset of
antennas and attain the maximum theoretical sum rates of AS, present numerous
drawbacks such as the introduction of significant insertion losses,
particularly pronounced in massive multiple-input multiple-output (MIMO)
systems. Since these disadvantages make fully-flexible switching suboptimal in
the energy efficiency sense, we further consider partially-connected switching
networks as an alternative switching architecture with reduced hardware
complexity, which we characterize in this work. In this context, we also
analyze the impact of reduced switching connectivity on the analog hardware and
digital signal processing of AS schemes that rely on channel power information.
Overall, the analytical and simulation results shown in this paper demonstrate
that partially-connected switching maximizes the energy efficiency of massive
MIMO systems for a reduced number of RF chains, while fully-flexible switching
offers sub-optimal energy efficiency benefits due to its significant switching
power losses.Comment: 14 pages, 11 figure
On-board processing architectures for satellite B-ISDN services
Onboard baseband processing architectures for future satellite broadband integrated services digital networks (B-ISDN's) are addressed. To assess the feasibility of implementing satellite B-ISDN services, critical design issues, such as B-ISDN traffic characteristics, transmission link design, and a trade-off between onboard circuit and fast packet switching, are analyzed. Examples of the two types of switching mechanisms and potential onboard network control functions are presented. A sample network architecture is also included to illustrate a potential onboard processing system
Current and Nascent SETI Instruments
Here we describe our ongoing efforts to develop high-performance and
sensitive instrumentation for use in the search for extra-terrestrial
intelligence (SETI). These efforts include our recently deployed Search for
Extraterrestrial Emissions from Nearby Developed Intelligent Populations
Spectrometer (SERENDIP V.v) and two instruments currently under development;
the Heterogeneous Radio SETI Spectrometer (HRSS) for SETI observations in the
radio spectrum and the Optical SETI Fast Photometer (OSFP) for SETI
observations in the optical band. We will discuss the basic SERENDIP V.v
instrument design and initial analysis methodology, along with instrument
architectures and observation strategies for OSFP and HRSS. In addition, we
will demonstrate how these instruments may be built using low-cost, modular
components and programmed and operated by students using common languages, e.g.
ANSI C.Comment: 12 pages, 5 figures, Original version appears as Chapter 2 in "The
Proceedings of SETI Sessions at the 2010 Astrobiology Science Conference:
Communication with Extraterrestrial Intelligence (CETI)," Douglas A. Vakoch,
Edito
Separation Framework: An Enabler for Cooperative and D2D Communication for Future 5G Networks
Soaring capacity and coverage demands dictate that future cellular networks
need to soon migrate towards ultra-dense networks. However, network
densification comes with a host of challenges that include compromised energy
efficiency, complex interference management, cumbersome mobility management,
burdensome signaling overheads and higher backhaul costs. Interestingly, most
of the problems, that beleaguer network densification, stem from legacy
networks' one common feature i.e., tight coupling between the control and data
planes regardless of their degree of heterogeneity and cell density.
Consequently, in wake of 5G, control and data planes separation architecture
(SARC) has recently been conceived as a promising paradigm that has potential
to address most of aforementioned challenges. In this article, we review
various proposals that have been presented in literature so far to enable SARC.
More specifically, we analyze how and to what degree various SARC proposals
address the four main challenges in network densification namely: energy
efficiency, system level capacity maximization, interference management and
mobility management. We then focus on two salient features of future cellular
networks that have not yet been adapted in legacy networks at wide scale and
thus remain a hallmark of 5G, i.e., coordinated multipoint (CoMP), and
device-to-device (D2D) communications. After providing necessary background on
CoMP and D2D, we analyze how SARC can particularly act as a major enabler for
CoMP and D2D in context of 5G. This article thus serves as both a tutorial as
well as an up to date survey on SARC, CoMP and D2D. Most importantly, the
article provides an extensive outlook of challenges and opportunities that lie
at the crossroads of these three mutually entangled emerging technologies.Comment: 28 pages, 11 figures, IEEE Communications Surveys & Tutorials 201
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