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Current Search:
All of 'Hamilton' and 'Institute' in all fields;
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Displaying Results 1 - 25 of 338 on page 1 of 14
Marked
Mark
Max-min Fairness in 802.11 Mesh Networks
(2010)
Leith, Douglas J. ; Cao, Qizhi,; Subramanian, Vijay G.
Max-min Fairness in 802.11 Mesh Networks
(2010)
Leith, Douglas J. ; Cao, Qizhi,; Subramanian, Vijay G.
Abstract:
In this paper we build upon the recent observation that the 802.11 rate region is log-convex and, for the first time, characterise max-min fair rate allocations for a large class of 802.11 wireless mesh networks.
http://eprints.nuim.ie/2202/
Marked
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Estimating Link Quality in 802.11 WLANs
(2007)
Giustiniano, Domenico ; Malone, David; Leith, Douglas J. ; Papagiannaki, Konstantina
Estimating Link Quality in 802.11 WLANs
(2007)
Giustiniano, Domenico ; Malone, David; Leith, Douglas J. ; Papagiannaki, Konstantina
Abstract:
We propose a powerful new MAC/PHY cross-layer approach to estimating link quality in 802.11WLANs. Unlike previous approaches, we explicitly classify channel impairments into noise-related losses, collision induced losses, hidden-node losses and 802.11 impairments caused by exposed nodes and capture effects. Our approach distinguishes among these different types of impairments without requiring any modification to the 802.11 protocol and provides separate quantitative measures of the severity of each one. Our approach is suited to implementation on commodity hardware and we demonstrate both a prototype implementation and experimental assessments.
http://eprints.nuim.ie/2215/
Marked
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Proportional Fair Coding for Wireless Mesh Networks
(2011)
Premkumar, K.; Chen, Xiaomin; Leith, Douglas J.
Proportional Fair Coding for Wireless Mesh Networks
(2011)
Premkumar, K.; Chen, Xiaomin; Leith, Douglas J.
Abstract:
We consider multi–hop wireless networks carrying unicast flows for multiple users. Each flow has a specified delay deadline, and the lossy wireless links are modelled as binary symmetric channels (BSCs). Since transmission time, also called airtime, on the links is shared amongst flows, increasing the airtime for one flow comes at the cost of reducing the airtime available to other flows sharing the same link. We derive the joint allocation of flow airtimes and coding rates that achieves the proportionally fair throughput allocation. This utility optimisation problem is non–convex, and one of the technical contributions of this paper is to show that the proportional fair utility optimisation can nevertheless be decomposed into a sequence of convex optimisation problems. The solution to this sequence of convex problems is the unique solution to the original non–convex optimisation. Surprisingly, this solution can be written in an explicit form that yields considerable insight into th...
http://eprints.nuim.ie/3631/
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Utility Optimal Coding for Packet Transmission over Wireless Networks – Part II: Networks of Packet Erasure Channels
(2011)
Premkumar, K.; Chen, Xiaomin; Leith, Douglas J.
Utility Optimal Coding for Packet Transmission over Wireless Networks – Part II: Networks of Packet Erasure Channels
(2011)
Premkumar, K.; Chen, Xiaomin; Leith, Douglas J.
Abstract:
We define a class of multi–hop erasure networks that approximates a wireless multi–hop network. The network carries unicast flows for multiple users, and each information packet within a flow is required to be decoded at the flow destination within a specified delay deadline. The allocation of coding rates amongst flows/users is constrained by network capacity. We propose a proportional fair transmission scheme that maximises the sum utility of flow throughputs. This is achieved by jointly optimising the packet coding rates and the allocation of bits of coded packets across transmission slots.
http://eprints.nuim.ie/3630/
Marked
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Utility Optimal Coding for Packet Transmission over Wireless Networks – Part I: Networks of Binary Symmetric Channels
(2011)
Premkumar, K.; Chen, Xiaomin; Leith, Douglas J.
Utility Optimal Coding for Packet Transmission over Wireless Networks – Part I: Networks of Binary Symmetric Channels
(2011)
Premkumar, K.; Chen, Xiaomin; Leith, Douglas J.
Abstract:
We consider multi–hop networks comprising Binary Symmetric Channels (BSCs). The network carries unicast flows for multiple users. The utility of the network is the sum of the utilities of the flows, where the utility of each flow is a concave function of its throughput. Given that the network capacity is shared by the flows, there is a contention for network resources like coding rate (at the physical layer), scheduling time (at the MAC layer), etc., among the flows. We propose a proportional fair transmission scheme that maximises the sum utility of flow throughputs subject to the rate and the scheduling constraints. This is achieved by jointly optimising the packet coding rates of all the flows through the network.
http://eprints.nuim.ie/3629/
Marked
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Young People and Crime: Research, Policy and Practice
(2007)
Lalor, Kevin; Ryan, Fergus; Seymour, Mairead; Hamilton, Clarie
Young People and Crime: Research, Policy and Practice
(2007)
Lalor, Kevin; Ryan, Fergus; Seymour, Mairead; Hamilton, Clarie
Abstract:
<p>These are the full proceedings of a two day National conference on Young people and Crime, hosted by the Centre for Social and Educational Research.</p>
http://arrow.dit.ie/csercon/2
Marked
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Engineering of a Single Alkaline Fuel Cell Part II: Long Term Operation in Air
(2009)
Blackledge, Jonathan; Coyle, Eugene; Kennedy, David; Schmidt-Walter, Heinz; Kohnke, Han...
Engineering of a Single Alkaline Fuel Cell Part II: Long Term Operation in Air
(2009)
Blackledge, Jonathan; Coyle, Eugene; Kennedy, David; Schmidt-Walter, Heinz; Kohnke, Hans; Sauer, Gerhard; Schudt, Steffen; Hamilton, James; Brunton, James
Abstract:
<p>Research into renewable energy sources has previously lacked sufficient investment. However, emphasis has now shifted and funding is being made available in a proactive manner by various governments eager to encourage renewable energy technology and reduce carbon taxes. Fuel Cells offer a realistic, sustainable and clean alternative energy option for stationary and mobile applications. Hydrogen and fuel cell technologies are recognised by many as possible long term energy solutions, but to-date, have failed to make an impact on the energy market. This is due to a number of key reasons, some of which include efficiency, scale, accessories and power output. For example, applying fuel cells to small telecommunication components requires the applications of Micro and Nanotechnology, which have yet to be perfected to make them long lasting and cost effective. This paper focuses on the design, engineering and development of a new Alkaline Fuel Cell outlining its capabilities and ...
http://arrow.dit.ie/engscheleart2/22
Marked
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Engineering of a Single Alkaline Fuel Cell Part I: Construction of a Test Bed
(2009)
Blackledge, Jonathan; Brunton, James; Coyle, Eugene; Kennedy, David; Schmidt-Walter, He...
Engineering of a Single Alkaline Fuel Cell Part I: Construction of a Test Bed
(2009)
Blackledge, Jonathan; Brunton, James; Coyle, Eugene; Kennedy, David; Schmidt-Walter, Heinz; Kohnke, Hans; Sauer, Gerhard; Schudt, Steffen; Hamilton, James
Abstract:
<p>Fuel Cells offer a realistic, sustainable and clean alternative energy option for stationary and mobile applications. Hydrogen and fuel cell technologies are recognised by many as possible long term energy solutions, but to-date have failed to make an impact on the energy market. This is due to a number of key reasons, some of which include, efficiency, scale, accessories and power output. Applying fuel cells to small telecommunication components requires the applications of Micro and Nanotechnology, which have yet to be perfected to make them long lasting and cost effective. This paper outlines the reasons for commercialisation of fuel cells and supports the argument that utilising hydrogen technology should be done in an environmentally friendly manner from the offset to prevent further damage to the environment. In particular, the paper focuses on the research, design and development of a Single Alkaline Fuel Cell Test Bed and outlines the AFC's capabilities and lim...
http://arrow.dit.ie/engscheleart2/21
Marked
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Learning Theories and Higher Education
(2004)
Ashworth, Frank; Brennan, Gabriel; Egan, Kathy; Hamilton, Ron; Sáenz, Olalla
Learning Theories and Higher Education
(2004)
Ashworth, Frank; Brennan, Gabriel; Egan, Kathy; Hamilton, Ron; Sáenz, Olalla
Abstract:
<p>This paper offers a number of materials and resources which may be used as teaching aids for introduction-level courses in learning theories, especially those in higher education. The materials were developed during our participation in a postgraduate diploma module on the psychology of learning and learning theories in 2004, as part of the diploma in third-level learning and teaching at the DIT Learning and Teaching Centre.</p>
http://arrow.dit.ie/engscheleart/4
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The Life and Times of Young People on Remand: Recommendations for Future Policy in Ireland
(2007)
Freeman, Sinead
The Life and Times of Young People on Remand: Recommendations for Future Policy in Ireland
(2007)
Freeman, Sinead
Abstract:
The remand population of children and young people continues to rise in Ireland. Despite this growth, little is known about their experiences on remand. This paper focuses on such experiences from the perspective of the young prisoners. It is based on 62 semi-structured interviews conducted with young males and females aged 16 to 21 years on remand in St. Patrick’s Institution, Cloverhill Remand Prison and the Dόchas Centre, Mountjoy Prison. The paper highlights how young people who have yet to be found guilty are frequently detained for long periods in prison and are exposed to punitive conditions. The findings have important implications for policy in Ireland particularly in light of the principles of the Children Act, 2001 which state that young people should only be detained in custody for the shortest amount of time possible and as a measure of last resort. The paper seeks to make an important contribution to the criminology field by providing a critical analysis of the pro...
http://arrow.dit.ie/aaschsslcon/3
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Booklet of Selected Theses from the MA in Criminology, MA in Law, and MA in Child, Family and Community Studies 2007- 2009.
(2010)
Lalor, Kevin; Hamilton, Claire; Ryan, Fergus; McCarthy, Brian
Booklet of Selected Theses from the MA in Criminology, MA in Law, and MA in Child, Family and Community Studies 2007- 2009.
(2010)
Lalor, Kevin; Hamilton, Claire; Ryan, Fergus; McCarthy, Brian
http://arrow.dit.ie/aaschssldis/24
Marked
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Firm Growth as a Research Issue
(2004)
Cooney, Thomas M; Malinen, Pasi
Firm Growth as a Research Issue
(2004)
Cooney, Thomas M; Malinen, Pasi
Abstract:
<p>A key issue of debate regarding small firms over the past two decades has focused on the ability of small firms to engender growth, particularly fast-growth firms. Many commentators believe that it is a minimal group of enterprises germinating rapidly that provide the real jobs and therefore, that it is these firms which policy makers should be converging upon. But how can small businesses be transformed into fast-growth firms? As Tuck and Hamilton (1993) noted, despite the magnitude of research on small firms, especially regarding growth, researchers are still uncertain why some firms grow and others do not when originating from similar circumstances.</p>
http://arrow.dit.ie/buschmarart/45
Marked
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In Blue Sea or Sky
(2003)
Doris, Cliona
In Blue Sea or Sky
(2003)
Doris, Cliona
Abstract:
<p>Clíona Doris performs contemporary harp music from Britain and Ireland. The CD includes world premiere recordings of works by two of Ireland's major compositional voices, Brian Boydell and Ian Wilson, as well as Benjamin Britten's Suite for Harp, and music by William Mathias and Sir Hamilton Harty.</p>
http://arrow.dit.ie/aaconmusaud/24
Marked
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In Blue Sea or Sky
(2003)
Doris, Cliona
In Blue Sea or Sky
(2003)
Doris, Cliona
Abstract:
<p>Cliona Doris performs contemporary harp music from Britain and Ireland. The CD includes world premier recordings of works by two of Ireland's major compositional voices, Brian Boydell and Ian Wilson, as well as Benjamin Britten's Suite for Harp, and music by William Mathias and Sir Hamilton Harty.</p>
http://arrow.dit.ie/musrec/1013/thumbnail.jpg
http://arrow.dit.ie/musrec/12
Marked
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Experimental evaluation of TCP protocols for high-speed networks
(2007)
Li, Yee-Ting; Leith, Douglas J. ; Shorten, Robert N.
Experimental evaluation of TCP protocols for high-speed networks
(2007)
Li, Yee-Ting; Leith, Douglas J. ; Shorten, Robert N.
Abstract:
In this paper, we present experimental results evaluating the performance of the scalable-TCP, HS-TCP, BIC-TCP, FAST-TCP, and H-TCP proposals in a series of benchmark tests. In summary, we find that both Scalable-TCP and FAST-TCP consistently exhibit substantial unfairness, even when competing flows share identical network path characteristics. Scalable-TCP, HS-TCP, FAST-TCP, and BIC-TCP all exhibit much greater RTT unfairness than does standard TCP, to the extent that long RTT flows may be completely starved of bandwidth. Scalable-TCP, HS-TCP, and BIC-TCP all exhibit slow convergence and sustained unfairness following changes in network conditions such as the start-up of a new flow. FAST-TCP exhibits complex convergence behavior.
http://eprints.nuim.ie/1726/
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On queue provisioning, network efficiency and the Transmission Control Protocol
(2007)
Shorten, Robert; Leith, Douglas J.
On queue provisioning, network efficiency and the Transmission Control Protocol
(2007)
Shorten, Robert; Leith, Douglas J.
Abstract:
In this paper we propose a sender side modification to TCP to accommodate small network buffers. We exploit the fact that the manner in which network buffers are provisioned is intimately related to the manner in which TCP operates. However, rather than designing buffers to accommodate the TCP AIMD algorithm, as is the traditional approach in network design, we suggest simple modifications to the AIMD algorithm to accommodate buffers of any size in the network. We demonstrate that networks with small buffers can be designed that transport TCP traffic in an efficient manner while retaining fairness and friendliness with standard TCP traffic.
http://eprints.nuim.ie/1680/
Marked
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A Positive Systems Model of TCP-Like Congestion Control: Asymptotic Results.
(2006)
Shorten, Robert; Wirth, Fabian; Leith , Douglas
A Positive Systems Model of TCP-Like Congestion Control: Asymptotic Results.
(2006)
Shorten, Robert; Wirth, Fabian; Leith , Douglas
Abstract:
Abstract—We study communication networks that employ drop-tail queueing and Additive-Increase Multiplicative-Decrease (AIMD) congestion control algorithms. It is shown that the theory of nonnegative matrices may be employed to model such networks. In particular, important network properties, such as: 1) fairness; 2) rate of convergence; and 3) throughput, can be characterized by certain nonnegative matrices. We demonstrate that these results can be used to develop tools for analyzing the behavior of AIMD communication networks. The accuracy of the models is demonstrated by several NS studies.
http://eprints.nuim.ie/1764/
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Modeling the 802.11 distributed coordination function in nonsaturated heterogeneous conditions
(2007)
Malone, David; Duffy, Ken; Leith, Doug
Modeling the 802.11 distributed coordination function in nonsaturated heterogeneous conditions
(2007)
Malone, David; Duffy, Ken; Leith, Doug
Abstract:
Analysis of the 802.11 CSMA/CA mechanism has received considerable attention recently. Bianchi presented an analytic model under a saturated traffic assumption. Bianchi's model is accurate, but typical network conditions are nonsaturated and heterogeneous. We present an extension of his model to a nonsaturated environment. The model's predictions, validated against simulation, accurately capture many interesting features of nonsaturated operation. For example, the model predicts that peak throughput occurs prior to saturation. Our model allows stations to have different traffic arrival rates, enabling us to address the question of fairness between competing flows. Although we use a specific arrival process, it encompasses a wide range of interesting traffic types including, in particular, VoIP.
http://eprints.nuim.ie/1514/
Marked
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Active alignment for two-beam interferometers
(2006)
Kalamatianos, Dimitrios; Wellstead, Peter
Active alignment for two-beam interferometers
(2006)
Kalamatianos, Dimitrios; Wellstead, Peter
Abstract:
An active control system is described for the automatic alignment of the mirrors in a two-beam interferometer. From an initial unaligned position the active control system determines the degree of misalignment and adjusts the relative mirror positions accordingly. An embodiment of the system is described for a Michelson interferometer in which one of the mirrors is mounted upon three piezoelectric transducers PZT arranged so that they can both tilt and retard the mirror. Laser sources and corresponding photodetectors are also incorporated such that a control system can use the PZT actuators to produce a series of mirror movements relative to the fixed mirror and give a set of two-dimensional diffraction patterns one for each of the laser photodetectors. Amplitude and phase information is extracted from these patterns which enables the control system to align the mirrors such that the diffraction pattern maxima is at the center of the instrument central photodetector. In a further st...
http://eprints.nuim.ie/942/
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A Plea for More Theory in Molecular Biology
(2006)
Wolkenhauer, O.; Mesarovic, M.; Wellstead, P.
A Plea for More Theory in Molecular Biology
(2006)
Wolkenhauer, O.; Mesarovic, M.; Wellstead, P.
Abstract:
The integrationist principles of systems theory have proven hugely successful in the physical sciences and engineering. It is an underlying assumption made in the systems approach to biology that they can also be used to understand biological phenomena at the level of an entire organism or organ. Within this holistic vision, the vastmajority of systems biology research projects investigate phenomena at the level of the cell, with the belief that unifying principles established at the most basic level can establish a framework within which we may understand phenomena at higher levels of organization. In this spirit, and to use a celestial analogy, if a disease effecting an organ or entire body is our universe of discourse, then the cell is the star we gaze at. In building an understanding of disease and the effect of drugs, systems biology makes an implicit assumption about direct causal entailment between cell function and physiology. A skeptic might argue that this is about the sam...
http://eprints.nuim.ie/943/
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Aggregation with fragment retransmission for very high-speed WLANs
(2009)
Li, Tianji; Ni, Qiang; Malone, David; Leith , Douglas; Turletti, Thierry; Xiao, Yang
Aggregation with fragment retransmission for very high-speed WLANs
(2009)
Li, Tianji; Ni, Qiang; Malone, David; Leith , Douglas; Turletti, Thierry; Xiao, Yang
Abstract:
In upcoming very high-speed WLANs the physical layer (PHY) rate may reach 600 Mbps. To achieve high efficiency at the medium access control (MAC) layer, we identify fundamental properties that must be satisfied by any CSMA/CA based MAC layer and develop a novel scheme called Aggregation with Fragment Retransmission (AFR). In the AFR scheme, multiple packets are aggregated into and transmitted in a single large frame. If errors happen during the transmission, only the corrupted fragments of the large frame are retransmitted. An analytic model is developed to evaluate the throughput and delay performance of AFR over a noisy channel, and to compare AFR with competing schemes in the literature. Optimal frame and fragment sizes are calculated using this model. Transmission delays are minimised by using a zero-waiting mechanism where frames are transmitted immediately once the MAC wins a transmission opportunity. We prove that zero waiting can achieve maximum throughput. As a complement t...
http://eprints.nuim.ie/1202/
Marked
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Logarithmic asymptotics for the supremum of a stochastic process
(2003)
Duffy, Ken; Lewis, John T.; Sullivan, Wayne G.
Logarithmic asymptotics for the supremum of a stochastic process
(2003)
Duffy, Ken; Lewis, John T.; Sullivan, Wayne G.
Abstract:
Logarithmic asymptotics are proved for the tail of the supremum of a stochastic process, under the assumption that the process satisfies a restricted large deviation principle on regularly varying scales. The formula for the rate of decay of the tail of the supremum, in terms of the underlying rate function, agrees with that stated by Duffield and O’Connell [Math. Proc. Cambridge Philos. Soc. (1995) 118 363–374]. The rate function of the process is not assumed to be convex. A number of queueing examples are presented which include applications to Gaussian processes and Weibull sojourn sources.
http://eprints.nuim.ie/1823/
Marked
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Gain-Scheduled Control: Relaxing Slow Variation Requirements by Velocity-Based Design
(2000)
Leith, Douglas J. ; Leithead, William E.
Gain-Scheduled Control: Relaxing Slow Variation Requirements by Velocity-Based Design
(2000)
Leith, Douglas J. ; Leithead, William E.
Abstract:
This paper investigates the application of the gain-scheduling approach to flight control tasks where the conditions required by conventional techniques need not be satisfied. The conditions required by conventional techniques are progressively relaxed and the design of gain-scheduled controllers under a range of conditions is addressed. In particular, the paper considers gain-scheduled control design in situations where the vehicle is manoeuvring aggressively far from equilibrium, the airspeed need not be slowly varying and/or scheduling on the instantaneous incidence angle is required.
http://eprints.nuim.ie/1835/
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A Spectrum of Colors: Investigating the Temporal Frequency Characteristics of the Human Visual System Using a System Identification Approach
(2006)
Lalor, Edmund C.; Reilly, Richard B.; Pearlmutter, Barak A.; Foxe, John J.
A Spectrum of Colors: Investigating the Temporal Frequency Characteristics of the Human Visual System Using a System Identification Approach
(2006)
Lalor, Edmund C.; Reilly, Richard B.; Pearlmutter, Barak A.; Foxe, John J.
Abstract:
Noise input signals are commonly used in both linear and nonlinear system identification of physiological systems. This method can be applied to electrophysiological analysis of the human visual system by controlling the modulation of the contrast of a checkerboard stimulus using a pre-computed noise waveform. In this study we describe how one can obtain an estimate of the linear impulse response of the visual system using noise waveforms. Furthermore, we examine the impulse responses obtained using noise signals with different frequency characteristics, in an attempt to investigate the temporal frequency characteristics of the human visual system. We show that noise signals with frequency content greater than 15 Hz are more effective at evoking these responses than those with little or no power at high frequencies.
http://eprints.nuim.ie/2048/
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Subject-Independent Magnetoencephalographic Source Localization by a Multilayer Perceptron
(2003)
Sung, C. Jun; Pearlmutter, Barak A.
Subject-Independent Magnetoencephalographic Source Localization by a Multilayer Perceptron
(2003)
Sung, C. Jun; Pearlmutter, Barak A.
Abstract:
We describe a system that localizes a single dipole to reasonable accuracy from noisy magnetoencephalographic (MEG) measurements in real time. At its core is a multilayer perceptron (MLP) trained to map sensor signals and head position to dipole location. Including head position overcomes the previous need to retrain the MLP for each subject and session. The training dataset was generated by mapping randomly chosen dipoles and head positions through an analytic model and adding noise from real MEG recordings. After training, a localization took 0.7 ms with an average error of 0.90 cm. A few iterations of a Levenberg-Marquardt routine using the MLP’s output as its initial guess took 15 ms and improved the accuracy to 0.53 cm, only slightly above the statistical limits on accuracy imposed by the noise. We applied these methods to localize single dipole sources from MEG components isolated by blind source separation and compared the estimated locations to those generated by standard ma...
http://eprints.nuim.ie/2050/
Displaying Results 1 - 25 of 338 on page 1 of 14
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