Ken Duffy, M.A., Ph.D. Hamilton Institute NUI Maynooth. E-mail: ken.duffy@nuim.ie. Phone: +353 1 708 6796.

Research

I'm an applied mathematician whose main research interests are in applied probability and stochastic modelling.
I have a penchant for interdisciplinary applications within communication networks, immunology and finance.
I am a member of the Institute's Applied Probability Group and the principle investigator, with David Malone
as co-PI, on the Science Foundation Ireland Research Frontiers Grant ENEF530.

Drafts

• Most likely paths to error when estimating the mean of a reflected random walk.
  Ken R. Duffy and Sean P. Meyn.
  
• Estimating Loynes' exponent.
  Ken R. Duffy and Sean P. Meyn.
  
• Mean field Markov models of wireless local area networks.
  Ken R. Duffy.
  
• Sample path large deviations for order statistics.
  Ken R. Duffy, Claudio Macci and Giovanni Luca Torrisi.
  
• On the validity of IEEE 802.11 MAC modeling hypotheses.
  K. D. Huang, Ken R. Duffy and David Malone.
  

Journal papers by subject (by year)
Applied Probability and Stochastic Processes; Communication Networks;
Finance; Queueing Systems; Immunology.

On the large deviations of a class of modulated additive processes.
Ken R. Duffy, Claudio Macci and Giovanni Luca Torrisi.
ESAIM: Probability and Statistics, in press.
• The large deviation principle for the on/off Weibull sojourn process.
  Ken R. Duffy and Artem Sapozhnikov.
  Journal of Applied Probability, 45 (1), 107-117, 2008.
• Ambiguities in estimates of critical exponents for long-range dependent processes.
  Ken Duffy, Christopher King and David Malone.
  Physica A, 377 (1), 43-52, 2007.
• Some remarks on LD plots for heavy-tailed traffic.
  David Malone, Ken Duffy and Christopher King.
  ACM SIGCOMM Computer Communications Review, 37 (1), 41-42, 2007.
• How to estimate a cumulative process's rate-function.
  Ken Duffy and Anthony P. Metcalfe.
  Journal of Applied Probability 42 (4), 1044-1052, 2005.
• The large deviations of estimating rate-functions.
  Ken Duffy and Anthony P. Metcalfe.
  Journal of Applied Probability 42 (1), 267-274, 2005.
• Some useful functions for functional large deviations.
  Ken Duffy and Mark Rodgers-Lee.
  Stochastics and Stochastics Reports 76 (3), 267-279, 2004.
• On Knuth's generalization of Banach's matchbox problem.
  Ken Duffy and W. M. B. Dukes.
  Mathematical Proceedings of the Royal Irish Academy 104A, 107-118, 2004.
• Logarithmic asymptotics for the supremum of a stochastic process.
  Ken Duffy, John T. Lewis and Wayne G. Sullivan.
  Annals of Applied Probability 13:2, 430-445, 2003.
• Distribution-free confidence intervals for measurements of effective bandwidth.
  Laszlo Gyorfi, Andras Racz, Ken Duffy, John T. Lewis and Fergal Toomey.
  Journal of Applied Probability 37:1, 224-235, 2000.
  

• Log-convexity of rate region in 802.11e WLANs.
  Douglas J. Leith, Vijay G. Subramanian and Ken R. Duffy.
  IEEE Communications Letters, 14 (1), 57-59, 2010.
• Existence and uniqueness of fair rate allocations in lossy wireless networks.
  Vijay G. Subramanian, Ken R. Duffy and Douglas J. Leith.
  IEEE Transactions on Wireless Communications, 8 (7), 3401-3406, 2009.
• On a buffering hypothesis in 802.11 analytic models.
  K. D. Huang and Ken R. Duffy
  IEEE Communications Letters, 13 (5), 312-314, 2009.
• Complexity analysis of a decentralised graph colouring algorithm.
  Ken R. Duffy, Neil O'Connell and Artem Sapozhnikov.
  Information Processing Letters, 107 (2), 60-63, 2008.
• Modeling the impact of buffering on 802.11.
  Ken Duffy and Ayalvadi J. Ganesh.
  IEEE Communications Letters, 11 (2), 219-221, 2007.
• Modeling the 802.11 distributed coordination function in non-saturated heterogeneous conditions.
  David Malone, Ken Duffy and Douglas J. Leith.
  IEEE/ACM Transactions on Networking, 15 (1), 159-172, 2007.
• Modeling 802.11 Mesh Networks.
  Ken Duffy, Douglas J. Leith, Tianji Li and David Malone.
  IEEE Communications Letters 10 (8), 635-637, 2006.
• Modeling the 802.11 distributed coordination function in non-saturated conditions.
  Ken Duffy, David Malone and Douglas J. Leith.
  IEEE Communications Letters, 9 (8), 715-717, 2005.

• Loss aversion, large deviation preferences and optimal portfolio weights for some classes of return processes.
  Ken Duffy, Olena Lobunets and Yuri Suhov.
  Physica A, 378 (2), 408-422, 2007.

• Logarithmic asymptotics for a single-server processing distinguishable sources.
  Ken R. Duffy and David Malone.
  Mathematical Methods of Operations Research, 68 (3), 509-537, 2008.
• Using estimated entropy in a queueing system with dynamic routing.
  Ken Duffy, Eugene A. Pechersky, Yuri M. Suhov and Nikita D. Vvedenskaya.
  Markov Processes and Related Fields, 13 (1-2), 57-84, 2007.
• Logarithmic asymptotics for unserved messages at a FIFO.
  Ken Duffy and Wayne G. Sullivan.
  Markov Processes and Related Fields 10 (1), 175-189, 2004.

• A minimum of two distinct heritable factors are required to explain correlation structures in proliferating lymphocytes.
  John F. Markham, Cameron J. Wellard, Edwin D. Hawkins, Ken R. Duffy and Philip D. Hodgkin.
  Journal of the Royal Society Interface, in press.
  The data used in this study is available for download from the Hodgkin Lab at WEHI.
  The published version of this article, which is more elegantly typeset, is freely available from the Royal Society.
• On the impact of correlation between collaterally consanguineous cells on lymphocyte population dynamics.
  Ken R. Duffy and Vijay G. Subramanian.
  Journal of Mathematical Biology, 59 (2), 255-285, 2009.
• Determining the expected variability of immune responses using the Cyton Model.
  Vijay G. Subramanian, Ken R. Duffy, Marian L. Turner and Philip D. Hodgkin.
  Journal of Mathematical Biology, 56 (6), 861-892, 2008.

Conference papers (all communications networks)

• Investigating the validity of IEEE 802.11 MAC modeling hypotheses.
  K. D. Huang, Ken R. Duffy, David Malone and Douglas J. Leith.
  IEEE PIMRC 15-18th September 2008, Cannes, France.
• Improving fairness in multi-hop mesh networks using 802.11e.
  Ken Duffy, Douglas J. Leith, Tianji Li and David Malone.
  Resource Allocation in Wireless Networks, 3rd April 2006, Boston, USA.
• Modeling 802.11e for data traffic parameter design.
  Peter Clifford, Ken Duffy, John Foy, Douglas J. Leith and David Malone.
  WiOPT 2006, 28-37, 3rd-7th April 2006, Boston, USA.
• Modelling 802.11 wireless links.
  Ken Duffy, David Malone and Douglas J. Leith.
  IEEE Conference on Decision and Control, 6952 - 6957, 12th-15th December 2005, Seville, Spain.
• On improving voice capacity in 802.11 infrastructure networks.
  Peter Clifford, Ken Duffy, Douglas J. Leith and David Malone.
  IEEE WirelessCom, 214 - 219, 13th-16th June 2005, Maui, Hawaii, USA.
• Modeling the 802.11 distributed coordination function with heterogeneous finite load.
  David Malone, Ken Duffy and Douglas J. Leith.
  Resource Allocation in Wireless Networks, 3rd April 2005, Trento, Italy.

• Modelling and simulation analysis of the 802.11/802.11e MAC layers.
  Qiang Ni, David Malone, Peter Clifford, Ken Duffy, Douglas Leith and Tianji Li.
  Advances in Wireless Networks: Performance Modelling, Analysis and Enhancement,
  Nova Science Publishers, edited by Geyong Min, Yi Pan and Pingzhi Fan, 2007.

Other articles

• John T. Lewis (1932-2004).
  Ken Duffy and Joe Pule.
  Markov Processes and Related Fields, 13 (1-2), 3-19, 2007.

• Science Foundation Ireland Research Frontiners Programme,
  "Using 802.11 medium access control layer measurements to understand and improve network performance",
  PI (with David Malone as co-PI), €150k, 2007-2010.
• Science Foundation Ireland Short-term Travel Fellowship
  "Mathematical modelling of lymphocyte proliferation and differentiation during an adaptive immune response",
  €8k, to visit Philip Hodgkin at the Walter and Eliza Hall Institute of Medical Research, 2009.
• Science Foundation Ireland Investigator Award,
  "Resource Allocation in WLANs",
  Doug Leith as PI, co-PI with responsibility for €368k of €5.9M total, 2004-2008.

Current grad-students

• Minyu Fang.
• Kaidi Huang.

Past grad-students

• Anthony Paul Metcalfe, M.Sc. Mathematics (University of Dublin), 2004.
  The large deviations of estimating rate-functions.
  
• Mark Rodgers-Lee, M.Sc. Mathematics (University of Dublin), 2003.
  The large deviations of random time-changes in a metric topology.
  

Oddities

I have had the unusual honour of having acknowledgements in at least six diverse places.

1. Christopher Fuchs thanks me for teaching him about magnalium in his article "On the Quantumness of a Hilbert Space", Quantum Information, Statistics, Probability: Dedicated to Alexander S. Holevo on the Occasion of His 60th Birthday, edited by O. Hirota (Rinton Press, Princeton, NJ, 2004).
2. In their O'Reilly book IPv6 Network Administration, the authors, Niall Murphy and David Malone, say the following: "Ken Duffy managed to resist the temptation to edit our manuscript, and we can only admire his restraint."
3. My academic grand-nephew, Stephen Wills of UCC's Mathematics department, thanks me for facilitating corrections to his paper "On the generators of operator Markovian cocycles", Markov Processes and Related Fields 13 (2007), 191-211.
4. In his CUP Monograph Control Techniques for Complex Networks, Sean Meyn thanks me for graphs generated by code that I wrote while attending a meeting organised by Serguei Foss, Takis Konstantopoulos and Stan Zachary.
5. In their forthcoming article "Large deviation results on some estimators for stationary Gaussian processes", to appear in Statistics, Claudio Macci and Lea Petrella thank me for illustrating to them results from the literature on semi-exponential distributions.
6. In their article "A single-cell pedigree analysis of alternative stochastic lymphocyte fates", Proceedings of the National Academy of Sciences 11, 106(32), 13457-13462, E. D. Hawkins, J. F. Markham, L. P. McGuinness and P. D. Hodgkin thank me, along with others, for critical reading of the manuscript and helpful suggestions.