Dr Bjorn Ruffer

Dr Bjorn Ruffer

Lecturer

School of Mathematical and Physical Sciences (Mathematics)

Career Summary

Biography

Dr Rüffer graduated with a Master of Science in Mathematics from the University of Warwick, UK in 2004 and with a PhD in applied mathematics from the University of Bremen, Germany in 2007. 

In Bremen, Dr Rüffer was a member of the Collaborative Research Centre 637 “Autonomous Cooperating Logistic Processes — A paradigm shift and its limitations” from September 2004 to September 2007. From October 2007 to June 2009 he was a member of the Signal Processing Microelectronics (SPM) group and the School of Electrical Engineering and Computer Science at the University of Newcastle, Australia. From July 2009 to January 2011 he was a Research Fellow within the Department of Electrical and Electronic Engineering at the University of Melbourne, Australia. In early 2010 he has undertaken a three months research fellowship at the Kyushu Institute of Technology, Japan, under the auspices of the Japan Society for the Promotion of Science (JSPS). From February 2011 to February 2015 he was an "Akademischer Rat auf Zeit" (assistant professor) with the Institute of Electrical Engineering at the University of Paderborn, Germany. In the summer term of 2014 he was a visiting professor at the University of Passau, Germany.

In March 2015 he joined the School of Mathematical & Physical Sciences with the University of Newcastle, Australia as a lecturer in applied mathematics.
 
Research Expertise
Dr Rüffer's research focuses on the qualitative theory of dynamical and control systems, in particular robust stability. Well-recognised contributions include results on the stability of arbitrarily many interconnected, heterogeneous systems in the input-to-state stability framework. His interests further include synchronisation and consensus problems, all aspects of Lyapunov theory, as well as positive and monotone systems.

Teaching Expertise
Dr Rüffer has a teaching track record spanning more than a decade. He has taught at five different universities, covering subjects from mathematics as well as electrical engineering, and reaching students in a wide range of degree programs.

Administrative Expertise
Dr Rüffer has filled a number of administrative roles in the past, both at the university/discipline level as well as for the research community. Past roles include student advisor in an industrial engineering discipline, head of departmental computer labs, and member of various standing boards of examiners. Currently Dr Rüffer is an associate editor for Systems & Control Letters and serves on a number of programme committees for international conferences.

Collaborations
Dr Rüffer has past and ongoing collaborations with research partners in Australia, France, Germany, Iran, Israel, Japan, Russia, Sweden, the Netherlands, the United Kingdom, and the United States.

Qualifications

  • PhD, University of Bremen - Germany
  • Master of Science, University of Warwick - England

Keywords

  • Control Theory
  • Differential Equations
  • Dynamical Systems
  • Mathematical Systems Theory
  • Mathematics
  • Networks of dynamical systems
  • Stability Theory

Languages

  • German (Fluent)

Fields of Research

Code Description Percentage
010109 Ordinary Differential Equations, Difference Equations and Dynamical Systems 35
010203 Calculus of Variations, Systems Theory and Control Theory 50
010204 Dynamical Systems in Applications 15

Professional Experience

UON Appointment

Title Organisation / Department
Lecturer University of Newcastle
School of Mathematical and Physical Sciences
Australia

Academic appointment

Dates Title Organisation / Department
1/04/2014 - 1/09/2014 Visiting Professor University of Passau
Faculty of Computer Science and Mathematics
Germany
1/01/2012 -  Editorial Board International Symposium on Mathematical Theory of Networks and Systems / Member of the international programme committee
Australia
1/01/2012 -  Editorial Board International Symposium on Positive Systems / Member of the international programme committee
Australia
1/02/2011 - 1/02/2015 Assistant Professor (Akademischer Rat) University of Paderborn
Faculty of Electrical Engineering, Computer Science, and Mathematics
Germany
1/01/2010 -  Editorial Board Systems & Control Letters / Associate Editor
Australia
1/07/2009 - 1/01/2011 Senior Research Fellow The University of Melbourne
Department of Electrical and Electronic Engineering
Australia
1/01/2008 -  Membership American Mathematical Society
United States
1/01/2008 -  Membership Institute of Electrical and Electronics Engineers
United States
1/10/2007 - 1/06/2009 Senior Research Associate University of Newcastle
School of Electrical Engineering and Computing
Australia
1/09/2004 - 1/09/2007 Research Associate University of Bremen
Faculty of Mathematics and Computer Science
Germany
1/01/2002 -  Membership German Mathematicians Association
Germany

Teaching

Code Course Role Duration
MATH1110 Mathematics 1
The University of Newcastle - Faculty of Science and IT

Covers the parts of calculus and algebra which have proved fundamental to all of mathematics and its applications. It is the first of a pair of courses, MATH1110 and MATH1120, designed to cover a range of mathematical topics of importance to students in the Sciences, Engineering or Commerce.

In algebra, students learn concepts and symbolic manipulation when calculating with large numbers of variables. In calculus, they learn concepts used when working with continuously changing variables. Both ways of thinking are essential in the mathematics met by students in the Sciences, Engineering and Commerce.

Lecturer 1/03/2015 - 5/06/2015
MATH2310 Calculus of Science and Engineering
The University of Newcastle - Faculty of Science and IT

Provides the essential mathematical techniques of Physical Science and Engineering. These are the methods of Multivariable Calculus and Differential Equations. Multivariable Calculus involves a study of the differential and integral calculus of functions of two or more variables. In particular it covers introductory material on the differential calculus of scalar and vector fields, and the integral calculus of scalar and vector functions. Differential Equations arise from mathematical models of physical processes. Also includes the study of the main analytical and numerical methods for obtaining solutions to first and second order differential equations. The course also introduces students to the use of mathematical software in the investigation of problems in multivariable calculus and differential equations.

Lecturer 27/07/2015 - 6/11/2015
MATH3700 Advanced Differential Equations
The University of Newcastle - Faculty of Science and IT

This course introduces students to the modern theory and methods of ordinary and partial differential equations. It builds on the classical foundations of differential equations studied in second year. Ordinary and partial differential equations form an essential part of the mathematical background required for engineering and the physical sciences. A large number of real-life problems can be modelled using differential equations, making the subject one of the most widely applicable areas of mathematics. The course concentrates on some fundamental analytical and numerical methods for applied differential equations arising from the mathematical modelling of physical, chemical and biological systems.

Lecturer 27/07/2015 - 6/11/2015
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Publications

For publications that are currently unpublished or in-press, details are shown in italics.

Highlighted Publications

Year Citation Altmetrics Link
2010 Ruffer BS, Kellett CM, Weller SR, 'Connection between cooperative positive systems and integral input-to-state stability of large-scale systems', Automatica, 46 1019-1027 (2010) [C1]
DOI 10.1016/j.automatica.2010.03.012
Citations Scopus - 35Web of Science - 30
Co-authors Steven Weller, Chris Kellett
2010 Ruffer BS, 'Monotone inequalities, dynamical systems, and paths in the positive orthant of Euclidean n-space', Positivity, 14 257-283 (2010) [C1]
DOI 10.1007/s11117-009-0016-5
Citations Scopus - 37Web of Science - 30

Chapter (1 outputs)

Year Citation Altmetrics Link
2007 Scholz-Reiter B, Wirth F, Freitag M, Dashkovskiy S, Jagalski T, De Beer C, Ruffer BS, 'Mathematical models of autonomous logistic processes', Understanding Autonomous Cooperation and Control in Logistics: The Impact of Autonomy on Management, Information, Communication and Material Flow, Springer, Berlin Heidelberg 121-138 (2007)
DOI 10.1007/978-3-540-47450-0_9
Citations Scopus - 2

Journal article (17 outputs)

Year Citation Altmetrics Link
2015 Dirr G, Ito H, Rantzer A, Rueffer BS, 'SEPARABLE LYAPUNOV FUNCTIONS FOR MONOTONE SYSTEMS: CONSTRUCTIONS AND LIMITATIONS', DISCRETE AND CONTINUOUS DYNAMICAL SYSTEMS-SERIES B, 20 2497-2526 (2015) [C1]
DOI 10.3934/dcdsb.2015.20.2497
Citations Scopus - 12Web of Science - 6
2014 Ruffer BS, 'Input-to-state stability for discrete-time monotone systems', Proceedings of the 21st International Symposium om Mathematics Theory of Networks and Systems (MTNS), 96-102 (2014)
2013 Ruffer BS, Van De Wouw N, Mueller M, 'Convergent systems vs. incremental stability', Systems and Control Letters, 62 277-285 (2013)
DOI 10.1016/j.sysconle.2012.11.015
Citations Scopus - 34Web of Science - 26
2013 Ito H, Jiang Z-P, Dashkovskiy SN, Ruffer BS, 'Robust stability of networks of iISS systems: Construction of sum-type Lyapunov functions', IEEE Transactions on Automatic Control, 58 1192-1207 (2013)
DOI 10.1109/TAC.2012.2231552
Citations Scopus - 35Web of Science - 31
2012 Dashkovskiy SN, Jiang ZP, Ruffer BS, 'Special issue on robust stability and control of large-scale nonlinear systems', Mathematics of Control, Signals, and Systems, 24 1-2 (2012)
DOI 10.1007/s00498-012-0083-1
Citations Scopus - 1Web of Science - 3
2011 Ruffer BS, 'Discussion on: "On a small gain theorem for ISS networks in dissipative lyapunov form"', European Journal of Control, 17 366-367 (2011)
2011 Rüffer BS, Wirth FR, 'Stability verification for monotone systems using homotopy algorithms', Numerical Algorithms, 58 529-543 (2011)

A monotone self-mapping of the nonnegative orthant induces a monotone discrete-time dynamical system which evolves on the same orthant. If with respect to this system the origin i... [more]

A monotone self-mapping of the nonnegative orthant induces a monotone discrete-time dynamical system which evolves on the same orthant. If with respect to this system the origin is attractive then there must exist points whose image under the monotone map is strictly smaller than the original point, in the component-wise partial ordering. Here it is shown how such points can be found numerically, leading to a recipe to compute order intervals that are contained in the region of attraction and where the monotone map acts essentially as a contraction. An important application is the numerical verification of so-called generalized small-gain conditions that appear in the stability theory of large-scale systems. © 2011 Springer Science+Business Media, LLC.

DOI 10.1007/s11075-011-9468-3
Citations Scopus - 5Web of Science - 3
2010 Ruffer BS, Kellett CM, Dower PM, Weller SR, 'Belief propagation as a dynamical system: The linear case and open problems', IET Control Theory and Applications, 4 1188-1200 (2010) [C1]
DOI 10.1049/iet-cta.2009.0233
Citations Scopus - 6Web of Science - 4
Co-authors Steven Weller, Chris Kellett
2010 Ruffer BS, Sailer R, Wirth FR, 'Comments on "A Multichannel IOS Small Gain Theorem for Systems With Multiple Time-Varying Communication Delays', IEEE Transactions on Automatic Control, 55 1722-1725 (2010)
DOI 10.1109/TAC.2010.2048938
Citations Scopus - 5Web of Science - 5
2010 Dashkovskiy SN, Ruffer BS, 'Local ISS of large-scale interconnections and estimates for stability regions', Systems and Control Letters, 59 241-247 (2010)
DOI 10.1016/j.sysconle.2010.02.001
Citations Scopus - 23Web of Science - 18
2010 Dashkovskiy SN, Ruffer BS, Wirth FR, 'Small gain theorems for large scale systems and construction of ISS Lyapunov functions', SIAM Journal on Control and Optimization, 48 4089-4118 (2010)
DOI 10.1137/090746483
Citations Scopus - 149Web of Science - 128
2010 Ruffer BS, Kellett CM, Weller SR, 'Connection between cooperative positive systems and integral input-to-state stability of large-scale systems', Automatica, 46 1019-1027 (2010) [C1]
DOI 10.1016/j.automatica.2010.03.012
Citations Scopus - 35Web of Science - 30
Co-authors Steven Weller, Chris Kellett
2010 Ruffer BS, 'Small-Gain Conditions and the Comparison Principle', IEEE TRANSACTIONS ON AUTOMATIC CONTROL, 55 1732-1736 (2010)
DOI 10.1109/TAC.2010.2048053
Citations Scopus - 17Web of Science - 15
2010 Ruffer BS, 'Monotone inequalities, dynamical systems, and paths in the positive orthant of Euclidean n-space', Positivity, 14 257-283 (2010) [C1]
DOI 10.1007/s11117-009-0016-5
Citations Scopus - 37Web of Science - 30
2007 Dashkovskiy S, Ruffer BS, Wirth FR, 'An ISS small gain theorem for general networks', Mathematics of Control, Signals, and Systems, 19 93-122 (2007)
DOI 10.1007/s00498-007-0014-8
Citations Scopus - 180Web of Science - 155
2007 Rekersbrink H, Ruffer BS, Wenning BL, Scholz-Reiter B, Gorg C, 'Routing in dynamischen netzen', Logistik Management, 9 25-36 (2007)
2006 Scholz-Reiter B, Wirth FR, Freitag M, Dashkovskiy SN, Jagalski T, de Beer C, Ruffer BS, 'Some remarks on the stability of production networks', Operations Research Proceedings, 2005 91-96 (2006)
Show 14 more journal articles

Conference (28 outputs)

Year Citation Altmetrics Link
2017 Rüffer BS, 'Nonlinear left and right eigenvectors for max-preserving maps' (2017) [E1]
DOI 10.1007/978-3-319-54211-9_18
2016 Tran DN, Rüffer BS, Kellett CM, 'Incremental stability properties for discrete-time systems', 2016 IEEE 55th Conference on Decision and Control, CDC 2016 (2016) [E1]
DOI 10.1109/CDC.2016.7798314
Co-authors Chris Kellett
2016 Fernando DAIP, Ruffer B, 'A preliminary model for understanding how life experiences generate human emotions and behavioural responses', Neural Information Processing. 23rd International Conference, ICONIP 2016 (2016) [E1]
DOI 10.1007/978-3-319-46675-0_30
2015 Ruffer BS, Ito H, 'Sum-separable Lyapunov functions for networks of ISS systems: A gain function approach', Proceedings of the IEEE Conference on Decision and Control (2015) [E1]
DOI 10.1109/CDC.2015.7402475
Citations Scopus - 1
2014 Noroozi N, Ruffer BS, 'Non-conservative dissipativity and small-gain theory for ISS networks', Proceedings of the IEEE Conference on Decision and Control (2014)

© 2014 IEEE.This paper addresses input-to-state stability (ISS) analysis for discrete-time systems using the notion of finite-step ISS Lyapunov functions. Here, finite-step Lyapu... [more]

© 2014 IEEE.This paper addresses input-to-state stability (ISS) analysis for discrete-time systems using the notion of finite-step ISS Lyapunov functions. Here, finite-step Lyapunov functions are energy functions that decay after a fixed but finite number of steps, rather than at every time step. We establish non-conservative dissipativity and small-gain conditions for ISS of networks of discrete-time systems, by generalizing results in [1] and [2] to the case of ISS. The effectiveness of the results is illustrated through two examples.

DOI 10.1109/CDC.2014.7039872
Citations Scopus - 1Web of Science - 1
2014 Ito H, Ruffer BS, Rantzer A, 'Max- and sum-separable Lyapunov functions for monotone systems and their level sets', Proceedings of the IEEE Conference on Decision and Control (2014)

© 2014 IEEE.For interconnected systems and systems of large size, aggregating information of subsystems studied individually is useful for addressing the overall stability. In th... [more]

© 2014 IEEE.For interconnected systems and systems of large size, aggregating information of subsystems studied individually is useful for addressing the overall stability. In the Lyapunov-based analysis, summation and maximization of separately constructed functions are two typical approaches in such a philosophy. This paper focuses on monotone systems which are common in control applications and elucidates some fundamental limitations of max-separable Lyapunov functions in estimating domains of attractions. This paper presents several methods of constructing sum- and max-separable Lyapunov functions for second order monotone systems, and some comparative discussions are given through illustrative examples.

DOI 10.1109/CDC.2014.7039750
Citations Scopus - 6Web of Science - 3
2013 Pogromsky AY, Matveev AS, Chaillet A, Ruffer BS, 'Input-dependent stability analysis of systems with saturation in feedback', Proceedings of the IEEE Conference on Decision and Control (2013)
DOI 10.1109/CDC.2013.6760820
Citations Scopus - 2
2013 Chaillet A, Pogromsky AY, Ruffer BS, 'A Razumikhin approach for the incremental stability of delayed nonlinear systems', Proceedings of the IEEE Conference on Decision and Control (2013)
DOI 10.1109/CDC.2013.6760110
Citations Scopus - 4Web of Science - 4
2013 Rantzer A, Ruffer BS, Dirr G, 'Separable Lyapunov functions for monotone systems', Proceedings of the IEEE Conference on Decision and Control (2013)
DOI 10.1109/CDC.2013.6760604
Citations Scopus - 8Web of Science - 3
2013 Ito H, Ruffer BS, 'A two-phase approach to stability of networks given in iISS framework: Utilization of a matrix-like criterion', Proceedings of the American Control Conference (2013)

This article is concerned with global asymptotic stability (GAS) of dynamical networks. The case when subsystems are integral input-to-state stable (iISS) has been recognized as n... [more]

This article is concerned with global asymptotic stability (GAS) of dynamical networks. The case when subsystems are integral input-to-state stable (iISS) has been recognized as notoriously difficult to deal with in the literature. In fact, the lack of energy dissipation for large input denies direct application of the small-gain argument for input-to-state stable (ISS) subsystems. Here for networks consisting of iISS subsystems it is demonstrated that a two-phase approach allows us to make use of the ISS small-gain argument by separating a trajectory into a transient and a subsequent ISS-like phase. In contrast to the previous iISS results, the two-phase approach immediately leads to a sufficiency criterion for GAS of general nonlinear networks, which is given in a matrix-like form (order condition). © 2013 AACC American Automatic Control Council.

2012 Ruffer BS, Van De Wouw N, Mueller M, 'From convergent dynamics to incremental stability', Proceedings of the IEEE Conference on Decision and Control (2012)
DOI 10.1109/CDC.2012.6425916
Citations Scopus - 1
2012 Ito H, Jiang Z-P, Dashkovskiy SN, Rüffer BS, 'A cyclic small-gain condition and an equivalent matrix-like criterion for iISS networks', Proceedings of the IEEE Conference on Decision and Control (2012)
DOI 10.1109/CDC.2012.6426994
2012 Dashkovskiy SN, Ruffer BS, Wirth FR, 'Small gain theorems for large scale systems and construction of ISS Lyapunov functions', Proceedings of the IEEE Conference on Decision and Control (2012)
DOI 10.1109/CDC.2012.6426856
2011 Ito H, Jiang Z-P, Dashkovskiy SN, Ruffer BS, 'A small-gain theorem and construction of sum-type Lyapunov functions for networks of iISS systems', Proceedings of the American Control Conference (2011)
Citations Scopus - 8
2010 Ruffer BS, Ito H, Dower PM, 'Computing asymptotic gains of large-scale interconnections', Proceedings of the IEEE Conference on Decision and Control (2010)
DOI 10.1109/CDC.2010.5717387
Citations Scopus - 4Web of Science - 3
2010 Ruffer BS, Dower PM, Ito H, 'Computational comparison principles for large-scale system stability analysis', Proceedings of the 10th SICE Annual Conference on Control Systems (2010)
2010 Ruffer BS, Kellett CM, Dower PM, 'On copositive Lyapunov functions for a class of monotone systems', Proceedings of the 19th International Symposium on Mathematics Theory Networks Systems (MTNS) (2010)
2010 Ruffer BS, Dower PM, Kellett CM, Weller SR, 'On robust stability of the Belief Propagation Algorithm for LDPC decoding', Proceedings of the 19th International Symposium on Mathematics Theory Networks Systems (MTNS) (2010)
2009 Ruffer BS, Kellett CM, Weller SR, 'Integral input-to-state stability of interconnected iISS systems by means of a lower-dimensional comparison system', Proceedings of the 48th IEEE Conference on Decision and Control, 2009 held jointly with the 2009 28th Chinese Control Conference, CDC/CCC 2009 (2009) [E1]
DOI 10.1109/cdc.2009.5400344
Citations Scopus - 3Web of Science - 1
Co-authors Steven Weller, Chris Kellett
2008 Dashkovskiy SN, Ruffer BS, Wirth FR, 'Stability of autonomous vehicle formations using an ISS small-gain theorem for networks', PAMM: Proceedings in Applied Mathematics and Mechanics (2008) [E3]
DOI 10.1002/pamm.200810911
2008 Dashkovskiy SN, Ruffer BS, Wirth FR, 'Applications of the general Lyapunov ISS small-gain theorem for networks', Proceedings of the 47th IEEE Conference on Decision and Control (2008) [E1]
DOI 10.1109/cdc.2008.4739299
Citations Scopus - 7Web of Science - 2
2008 Dashkovskiy SN, Ruffer BS, Wirth FR, 'Application of small gain type theorems in logistics of autonomous processes', Proceedings of the 1st International Conference on Dynamics in Logistics, (2008)
2008 Dashkovskiy SN, Ruffer BS, Wirth FR, 'Stability of interconnections of ISS systems', Proceedings of the 8th SICE Annual Conference on Control Systems (2008)
2007 Dashkovskiy SN, Ruffer BS, Wirth FR, 'Numerical verification of local input-to-state stability for large networks', PROCEEDINGS OF THE 46TH IEEE CONFERENCE ON DECISION AND CONTROL, VOLS 1-14 (2007)
Citations Scopus - 13
2007 Dashkovskiy SN, Ruffer BS, Wirth FR, 'A Lyapunov ISS small-gain theorem for strongly connected networks', IFAC Proceedings Volumes (IFAC-PapersOnline) (2007)
2006 Dashkovskiy SN, Ruffer BS, Wirth FR, 'Discrete time monotone systems: Criteria for global asymptotic stability and applications', Proceedings of the 17th International Symposium on Mathematical Theory of Networks and Systems (MTNS) (2006)
2006 Dashkovskiy SN, Ruffer BS, Wirth FR, 'On the construction of ISS Lyapunov functions for networks of ISS systems', Proceedings of the 17th International Symposium on Mathematical Theory of Networks and Systems (MTNS) (2006)
2005 Dashkovskiy S, Ruffer BS, Wirth FR, 'A small-gain type stability criterion for large scale networks of ISS systems', Proceedings of the 44th IEEE Conference on Decision and Control, and the European Control Conference, CDC-ECC '05 (2005)
DOI 10.1109/CDC.2005.1583060
Citations Scopus - 21Web of Science - 8
Show 25 more conferences

Report (2 outputs)

Year Citation Altmetrics Link
2008 Ruffer BS, Kellett CM, 'Implementing the Belief Propagation Algorithm in MATLAB', Department of Electrical Engineering and Computer Science, University of Newcastle (2008)
2006 Dashkovskiy SN, Ruffer BS, 'Construction of ISS Lyapunov functions for networks', ZeTeM, Universitat Bremen, Germany (2006)

Thesis / Dissertation (1 outputs)

Year Citation Altmetrics Link
2007 Ruffer BS, Monotone dynamical systems, graphs, and stability of large-scale inter- connected systems, Universitat Bremen, Germany (2007)
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Research Supervision

Number of supervisions

Completed0
Current2

Total current UON EFTSL

PhD0.75

Current Supervision

Commenced Level of Study Research Title Program Supervisor Type
2017 PhD A Post-Keynesian SFC Model of GFC and Secular Stagnation PhD (Economics), Faculty of Business and Law, The University of Newcastle Co-Supervisor
2015 PhD Nonlinear Model Predictive Path Following Control for Model Robot PhD (Electrical Engineering), Faculty of Engineering and Built Environment, The University of Newcastle Co-Supervisor
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Research Collaborations

The map is a representation of a researchers co-authorship with collaborators across the globe. The map displays the number of publications against a country, where there is at least one co-author based in that country. Data is sourced from the University of Newcastle research publication management system (NURO) and may not fully represent the authors complete body of work.

Country Count of Publications
Germany 25
Australia 15
Japan 8
Netherlands 4
United States 4
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Dr Bjorn Ruffer

Position

Lecturer
School of Mathematical and Physical Sciences
Faculty of Science

Focus area

Mathematics

Contact Details

Email bjorn.ruffer@newcastle.edu.au
Phone (02) 491 38169
Fax (02) 492 16898
Links Google+
Personal webpage

Office

Room V227
Building Mathematics Building
Location Callaghan
University Drive
Callaghan, NSW 2308
Australia
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