Thomas Mestl - Academia.edu (original) (raw)

Papers by Thomas Mestl

Proceedings of the 10th Annual Joint Conference, 2010

Page 1. A Mathematical Framework for Modeling and Analyzing Migration Time Feng Luan Dept. of Com... more Page 1. A Mathematical Framework for Modeling and Analyzing Migration Time Feng Luan Dept. of Computer and Information Science, Norwegian University of Science and Technology, Trondheim, Norway +47 735 91457 luan@idi.ntnu.no Mads Nygård Dept. ...

Communications in Computer and Information Science, 2010

Migration is the most common preservation strategy in long-term digital preservation systems. It ... more Migration is the most common preservation strategy in long-term digital preservation systems. It relays old digital objects from one technique to another. A prerequisite for a successful migration is the availability of migration metadata, which provide enough background information to preserved digital objects. Without the migration metadata, the migration may not be possible, but also the digital object’s consistency may be violated. It is therefore recognized that the migration metadata are essential but surprisingly no requirements on these migration metadata seem to be available. In this paper, quality requirements of such migration metadata are derived from common preservation metadata schemas. The completeness and the usefulness of these quality requirements are validated by a case study. The final results show that the quality requirements can actually improve the workflow of a migration procedure. In addition, they can be used to improve metadata schemas and thereby decrease the risks in future migrations. Finally, six improvement suggestions for preservation systems are derived from our analysis of the quality requirements.

WMU Journal of Maritime Affairs, 2015

ABSTRACT In the years to come, the maritime industry will have to improve its energy efficiency a... more ABSTRACT In the years to come, the maritime industry will have to improve its energy efficiency and soften its environmental footprint to meet higher energy prices and more stringent regulations. Shipowners, managers, and operators are often reluctant in installing new technologies even though they may already have successfully been applied in other industries. By analyzing historical data for the adoption of steel hull and diesel engine technology in the worldwide fleet, we find an indication that dissemination of new technologies happens in a step-like manner. That is, the underlying dynamics does not change continuously but rather abruptly. We argue that this phenomenon could be explained by the fact that any new technology has to function within given structures in a given context; if not, structures will act as barriers. We provide a new explanatory model where the concept of structures is central, i.e., tangible or intangible constructs, usually human made, in the form of infrastructure, regulations, competence, norms, behavior, etc. Constructs can limit (barriers) or support (enablers) a new technology. Once the structures and/or the (new) technology (which itself is a structure) are adapted to each other, they have an enabling effect and thereby change the underlying dynamics in a stepwise way. We support our view by comparing the proposed concept with other published approaches on technology adoption.

Proceedings of the 10th annual joint conference on Digital libraries - JCDL '10, 2010

Page 1. A Mathematical Framework for Modeling and Analyzing Migration Time Feng Luan Dept. of Com... more Page 1. A Mathematical Framework for Modeling and Analyzing Migration Time Feng Luan Dept. of Computer and Information Science, Norwegian University of Science and Technology, Trondheim, Norway +47 735 91457 luan@idi.ntnu.no Mads Nygård Dept. ...

Physical Review Letters, 1997

A class of differential equations, which captures the logical structure of discrete time logical ... more A class of differential equations, which captures the logical structure of discrete time logical switching networks composed of many elements, displays deterministic chaos if each element has many inputs. Statistical features of the dynamics are approximated by using a mean field Langevin-type equation with a random telegraph signal as a stochastic forcing function, and also by considering a random walk on an N-dimensional hypercube. [S0031-9007(97)03599-0] PACS numbers: 05.45. + b, 05.40. + j, 05.50. + q,

Physica D: Nonlinear Phenomena, 1996

Neural and gene networks are often modeled by differential equations. If the continuous threshold... more Neural and gene networks are often modeled by differential equations. If the continuous threshold functions in the differential equations are replaced by step functions, the equations become piecewise linear (PL equations). The flow through the state space is represented schematically by paths and directed graphs on an n-dimensional hypercube. Closed pathways, called cycles, may/effect periodic orbits with associated fixed points in a chosen Poincar6 section. A return map in the Poincar6 section can be constructed by the composition of fractional linear maps. The stable and unstable manifolds of the fixed points can be determined analytically. These methods allow us to analyze the dynamics in higher-dimensional networks as exemplified by a four-dimensional network that displays chaotic behavior. The three-dimensional Poincar6 map is projected to a two-dimensional plane. This much simpler piecewise linear two-dimensional map conserves the important qualitative features of the flow.

Journal of Theoretical Biology, 1995

This paper presents a mathematical framework for describing and analysing gene regulatory network... more This paper presents a mathematical framework for describing and analysing gene regulatory networks by autonomous differential equations. It represents an improvement on existing frameworks in that it may handle a wider range of gene regulatory mechanisms. Gene regulatory networks are frequently threshold-dominated, i.e. genes are activated only when the concentration of certain gene products lie between definite thresholds. Here, the concept of regulatory domain is introduced to describe these regions in the phase space. To each regulatory domain is associated an indicator function whose value is 1 inside and 0 outside the domain. The indicator functions thus reflect the logical structure of the network. The sharp borders between the regulatory domains may be smoothed by replacing the logical step functions by continuous sigmoids or so-called logoid functions. A logoid function coincides with the step function outside a narrow interval around the threshold, and rises continuously from 0 to 1 inside it. Using logoids, the task of finding steady states is considerably simplified. A list of regions in phase space comprising all steady states lying close to a threshold is obtained by examining a certain type of matrix called the Logoid-Jacobian. In addition, this matrix leads to the conditions necessary for stability of the steady states. External signals may be conveniently incorporated in the form of Boolean variables. Thus the framework is well suited for studying gene regulatory networks both in single cells and multicellular systems.

Journal of Mathematical Biology, 1998

A wide range of complex systems appear to have switch-like interactions, i.e. below (or above) a ... more A wide range of complex systems appear to have switch-like interactions, i.e. below (or above) a certain threshold x has no or little influence on y, while above (or below) this threshold the effect of x on y saturates rapidly to a constant level. Switching functions are frequently described by sigmoid functions or combinations of these. Within the context of ordinary differential equations we present a very general methodological basis for designing and analysing models involving complicated switching functions together with any other non-linearities. A procedure to determine position and stability properties of all stationary points lying close to a threshold for one or several variables, so-called singular stationary points, is developed. Such points may represent homeostatic states in models, and are therefore of considerable interest. The analysis provides a profound insight into the generic effects of steep sigmoid interactions on the dynamics around homeostatic points. It leads to qualitative as well as quantitative predictions without using advanced mathematical methods. Thus, it may have an important heuristic function in connection with numerical simulations aimed at unfolding the predictive potential of realistic models.

Journal of Biological Systems, 1995

By fairly simple considerations of stability and multistationarity in nonlinear systems of first ... more By fairly simple considerations of stability and multistationarity in nonlinear systems of first order differential equations it is shown that under quite mild restrictions a negative feedback loop is a necessary condition for stability, and that a positive feedback loop is a necessary condition for multistationarity.

Journal of Biological Systems, 1995

A new method for analysing stationary states in complex differential equation systems when the in... more A new method for analysing stationary states in complex differential equation systems when the interaction terms contain sigmoid functions is presented. Originally aimed at simplifying the analysis of certain gene regulatory networks, the method is applicable to models comprising a wide range of sigmoid functions. The basic idea is to analyse the limiting case when the sigmoids approach the step function, and consider sigmoids with finite steepness as a perturbation. After a brief presentation the method is applied to a model for a herbivore feeding on two competing autotrophs. Analytical expresssions for the stationary points in the step function limit are given, and their dependence on the parameter values is analysed and interpreted.

Environmental Science & Technology, 2013

On January 1st, 2012, the maximum limit for sulfur concentration in marine fuels on the high seas... more On January 1st, 2012, the maximum limit for sulfur concentration in marine fuels on the high seas was lowered from 4.50% to 3.50% by the International Maritime Organization (IMO). It was one of a series of planned steps toward reducing the negative environmental and health impacts of international shipping. This study investigates the effectiveness of the IMO regulation in reducing global sulfur emissions. We found a reduction in global average sulfur concentration of only 0.07% points from 2011 to 2012. On the positive side, we also found that only 2.3% of the bunkerings were noncompliant in 2012, that is, exceeded the new 3.50% sulfur concentration cap. The analysis furthermore suggests that compliance with the new regulation is achieved by blending high sulfur fuel with lower sulfur fuel, rather than by removing high sulfur fuel from the market or removing the excess sulfur. The main conclusion is that the regulation has been effective in reducing the maximum sulfur concentration but has not been very effective in reducing the average sulfur concentration. Thus, the regulation may have resulted in local environmental benefits but has not resulted in global benefits with respect to global sulfur emissions from international shipping.

Benchmarking: An International Journal, 2012

ABSTRACT Purpose – The purpose of this paper is to construct a realistic best practice benchmark ... more ABSTRACT Purpose – The purpose of this paper is to construct a realistic best practice benchmark and develop a methodology for comparison of individual suppliers of marine bunker fuel. As is well-known in this trade, unfair business behaviors in the bunker fuel market are not uncommon, resulting in financial losses for the buyers. Design/methodology/approach – Establishing a best practice will naturally involve some degree of subjectivity as there is not an a priori correct answer to this problem. Using the concept of membership functions from fuzzy set theory, a score can be derived from a best practice benchmark histogram. The main advantages of this method are its relative independence both of sample size and of the underlying distribution, as well as being computationally very efficient. Findings – The authors' methodology turns out to be more powerful than standard descriptive statistics, as it is less sensitive to outliers and is well suited for small datasets and even single numbers. When applied to data for all suppliers worldwide, it is shown that the number of good suppliers is actually much lower than might be expected. Practical implications – Bunker fuel is a major expense for ship owners, and can easily reach $30 million/year for a single container ship. There is, therefore, a considerable interest in the market for benchmarking of individual fuel suppliers. The authors' methodology is also applicable to other quality-related fuel parameters. Originality/value – To the best of the authors' knowledge, this is the first attempt to benchmark actors in the marine bunker fuel industry and to quantify their behaviors.

Dynamics and Stability of Systems, 1995

Motivated by the periodic behaviour of regulatory networks within cell biology and neurology, we ... more Motivated by the periodic behaviour of regulatory networks within cell biology and neurology, we have studied the periodic solutions of piecewise-linear, first- order differential equations with identical relative decay rates. The flow of the solution trajectories can be represented qualitatively by a directed graph. By examining the cycles in this graph and solving the eigenvalue problem for corresponding mapping matrices,

Dynamics and Stability of Systems, 1994

A new method to investigate asymptotic properties of linear differential equations with strong th... more A new method to investigate asymptotic properties of linear differential equations with strong threshold and switching effects is presented. The method is applied to systems of equations of the form dx/dt = F(x) - yx, where y = constant and the dependence of F on x is mediated by sigmoid functions. Using a special sigmoid function called a logoid, which

Environmental Science & Technology, 2013

On January 1st, 2012, the maximum limit for sulfur concentration in marine fuels on the high seas... more On January 1st, 2012, the maximum limit for sulfur concentration in marine fuels on the high seas was lowered from 4.50% to 3.50% by the International Maritime Organization (IMO). It was one of a series of planned steps toward reducing the negative environmental and health impacts of international shipping. This study investigates the effectiveness of the IMO regulation in reducing global sulfur emissions. We found a reduction in global average sulfur concentration of only 0.07% points from 2011 to 2012. On the positive side, we also found that only 2.3% of the bunkerings were noncompliant in 2012, that is, exceeded the new 3.50% sulfur concentration cap. The analysis furthermore suggests that compliance with the new regulation is achieved by blending high sulfur fuel with lower sulfur fuel, rather than by removing high sulfur fuel from the market or removing the excess sulfur. The main conclusion is that the regulation has been effective in reducing the maximum sulfur concentration but has not been very effective in reducing the average sulfur concentration. Thus, the regulation may have resulted in local environmental benefits but has not resulted in global benefits with respect to global sulfur emissions from international shipping.

TransNav, the International Journal on Marine Navigation and Safety of Sea Transportation, 2016

Benchmarking: An International Journal, 2012

ABSTRACT Purpose – The purpose of this paper is to construct a realistic best practice benchmark ... more ABSTRACT Purpose – The purpose of this paper is to construct a realistic best practice benchmark and develop a methodology for comparison of individual suppliers of marine bunker fuel. As is well-known in this trade, unfair business behaviors in the bunker fuel market are not uncommon, resulting in financial losses for the buyers. Design/methodology/approach – Establishing a best practice will naturally involve some degree of subjectivity as there is not an a priori correct answer to this problem. Using the concept of membership functions from fuzzy set theory, a score can be derived from a best practice benchmark histogram. The main advantages of this method are its relative independence both of sample size and of the underlying distribution, as well as being computationally very efficient. Findings – The authors' methodology turns out to be more powerful than standard descriptive statistics, as it is less sensitive to outliers and is well suited for small datasets and even single numbers. When applied to data for all suppliers worldwide, it is shown that the number of good suppliers is actually much lower than might be expected. Practical implications – Bunker fuel is a major expense for ship owners, and can easily reach $30 million/year for a single container ship. There is, therefore, a considerable interest in the market for benchmarking of individual fuel suppliers. The authors' methodology is also applicable to other quality-related fuel parameters. Originality/value – To the best of the authors' knowledge, this is the first attempt to benchmark actors in the marine bunker fuel industry and to quantify their behaviors.

Environmental Science Technology, May 28, 2013

On January 1st, 2012, the maximum limit for sulfur concentration in marine fuels on the high seas... more On January 1st, 2012, the maximum limit for sulfur concentration in marine fuels on the high seas was lowered from 4.50% to 3.50% by the International Maritime Organization (IMO). It was one of a series of planned steps toward reducing the negative environmental and health impacts of international shipping. This study investigates the effectiveness of the IMO regulation in reducing global sulfur emissions. We found a reduction in global average sulfur concentration of only 0.07% points from 2011 to 2012. On the positive side, we also found that only 2.3% of the bunkerings were noncompliant in 2012, that is, exceeded the new 3.50% sulfur concentration cap. The analysis furthermore suggests that compliance with the new regulation is achieved by blending high sulfur fuel with lower sulfur fuel, rather than by removing high sulfur fuel from the market or removing the excess sulfur. The main conclusion is that the regulation has been effective in reducing the maximum sulfur concentration but has not been very effective in reducing the average sulfur concentration. Thus, the regulation may have resulted in local environmental benefits but has not resulted in global benefits with respect to global sulfur emissions from international shipping.

Proceedings of the 10th Annual Joint Conference, 2010

Page 1. A Mathematical Framework for Modeling and Analyzing Migration Time Feng Luan Dept. of Com... more Page 1. A Mathematical Framework for Modeling and Analyzing Migration Time Feng Luan Dept. of Computer and Information Science, Norwegian University of Science and Technology, Trondheim, Norway +47 735 91457 luan@idi.ntnu.no Mads Nygård Dept. ...

Communications in Computer and Information Science, 2010

Migration is the most common preservation strategy in long-term digital preservation systems. It ... more Migration is the most common preservation strategy in long-term digital preservation systems. It relays old digital objects from one technique to another. A prerequisite for a successful migration is the availability of migration metadata, which provide enough background information to preserved digital objects. Without the migration metadata, the migration may not be possible, but also the digital object’s consistency may be violated. It is therefore recognized that the migration metadata are essential but surprisingly no requirements on these migration metadata seem to be available. In this paper, quality requirements of such migration metadata are derived from common preservation metadata schemas. The completeness and the usefulness of these quality requirements are validated by a case study. The final results show that the quality requirements can actually improve the workflow of a migration procedure. In addition, they can be used to improve metadata schemas and thereby decrease the risks in future migrations. Finally, six improvement suggestions for preservation systems are derived from our analysis of the quality requirements.

WMU Journal of Maritime Affairs, 2015

ABSTRACT In the years to come, the maritime industry will have to improve its energy efficiency a... more ABSTRACT In the years to come, the maritime industry will have to improve its energy efficiency and soften its environmental footprint to meet higher energy prices and more stringent regulations. Shipowners, managers, and operators are often reluctant in installing new technologies even though they may already have successfully been applied in other industries. By analyzing historical data for the adoption of steel hull and diesel engine technology in the worldwide fleet, we find an indication that dissemination of new technologies happens in a step-like manner. That is, the underlying dynamics does not change continuously but rather abruptly. We argue that this phenomenon could be explained by the fact that any new technology has to function within given structures in a given context; if not, structures will act as barriers. We provide a new explanatory model where the concept of structures is central, i.e., tangible or intangible constructs, usually human made, in the form of infrastructure, regulations, competence, norms, behavior, etc. Constructs can limit (barriers) or support (enablers) a new technology. Once the structures and/or the (new) technology (which itself is a structure) are adapted to each other, they have an enabling effect and thereby change the underlying dynamics in a stepwise way. We support our view by comparing the proposed concept with other published approaches on technology adoption.

Proceedings of the 10th annual joint conference on Digital libraries - JCDL '10, 2010

Page 1. A Mathematical Framework for Modeling and Analyzing Migration Time Feng Luan Dept. of Com... more Page 1. A Mathematical Framework for Modeling and Analyzing Migration Time Feng Luan Dept. of Computer and Information Science, Norwegian University of Science and Technology, Trondheim, Norway +47 735 91457 luan@idi.ntnu.no Mads Nygård Dept. ...

Physical Review Letters, 1997

A class of differential equations, which captures the logical structure of discrete time logical ... more A class of differential equations, which captures the logical structure of discrete time logical switching networks composed of many elements, displays deterministic chaos if each element has many inputs. Statistical features of the dynamics are approximated by using a mean field Langevin-type equation with a random telegraph signal as a stochastic forcing function, and also by considering a random walk on an N-dimensional hypercube. [S0031-9007(97)03599-0] PACS numbers: 05.45. + b, 05.40. + j, 05.50. + q,

Physica D: Nonlinear Phenomena, 1996

Neural and gene networks are often modeled by differential equations. If the continuous threshold... more Neural and gene networks are often modeled by differential equations. If the continuous threshold functions in the differential equations are replaced by step functions, the equations become piecewise linear (PL equations). The flow through the state space is represented schematically by paths and directed graphs on an n-dimensional hypercube. Closed pathways, called cycles, may/effect periodic orbits with associated fixed points in a chosen Poincar6 section. A return map in the Poincar6 section can be constructed by the composition of fractional linear maps. The stable and unstable manifolds of the fixed points can be determined analytically. These methods allow us to analyze the dynamics in higher-dimensional networks as exemplified by a four-dimensional network that displays chaotic behavior. The three-dimensional Poincar6 map is projected to a two-dimensional plane. This much simpler piecewise linear two-dimensional map conserves the important qualitative features of the flow.

Journal of Theoretical Biology, 1995

This paper presents a mathematical framework for describing and analysing gene regulatory network... more This paper presents a mathematical framework for describing and analysing gene regulatory networks by autonomous differential equations. It represents an improvement on existing frameworks in that it may handle a wider range of gene regulatory mechanisms. Gene regulatory networks are frequently threshold-dominated, i.e. genes are activated only when the concentration of certain gene products lie between definite thresholds. Here, the concept of regulatory domain is introduced to describe these regions in the phase space. To each regulatory domain is associated an indicator function whose value is 1 inside and 0 outside the domain. The indicator functions thus reflect the logical structure of the network. The sharp borders between the regulatory domains may be smoothed by replacing the logical step functions by continuous sigmoids or so-called logoid functions. A logoid function coincides with the step function outside a narrow interval around the threshold, and rises continuously from 0 to 1 inside it. Using logoids, the task of finding steady states is considerably simplified. A list of regions in phase space comprising all steady states lying close to a threshold is obtained by examining a certain type of matrix called the Logoid-Jacobian. In addition, this matrix leads to the conditions necessary for stability of the steady states. External signals may be conveniently incorporated in the form of Boolean variables. Thus the framework is well suited for studying gene regulatory networks both in single cells and multicellular systems.

Journal of Mathematical Biology, 1998

A wide range of complex systems appear to have switch-like interactions, i.e. below (or above) a ... more A wide range of complex systems appear to have switch-like interactions, i.e. below (or above) a certain threshold x has no or little influence on y, while above (or below) this threshold the effect of x on y saturates rapidly to a constant level. Switching functions are frequently described by sigmoid functions or combinations of these. Within the context of ordinary differential equations we present a very general methodological basis for designing and analysing models involving complicated switching functions together with any other non-linearities. A procedure to determine position and stability properties of all stationary points lying close to a threshold for one or several variables, so-called singular stationary points, is developed. Such points may represent homeostatic states in models, and are therefore of considerable interest. The analysis provides a profound insight into the generic effects of steep sigmoid interactions on the dynamics around homeostatic points. It leads to qualitative as well as quantitative predictions without using advanced mathematical methods. Thus, it may have an important heuristic function in connection with numerical simulations aimed at unfolding the predictive potential of realistic models.

Journal of Biological Systems, 1995

By fairly simple considerations of stability and multistationarity in nonlinear systems of first ... more By fairly simple considerations of stability and multistationarity in nonlinear systems of first order differential equations it is shown that under quite mild restrictions a negative feedback loop is a necessary condition for stability, and that a positive feedback loop is a necessary condition for multistationarity.

Journal of Biological Systems, 1995

A new method for analysing stationary states in complex differential equation systems when the in... more A new method for analysing stationary states in complex differential equation systems when the interaction terms contain sigmoid functions is presented. Originally aimed at simplifying the analysis of certain gene regulatory networks, the method is applicable to models comprising a wide range of sigmoid functions. The basic idea is to analyse the limiting case when the sigmoids approach the step function, and consider sigmoids with finite steepness as a perturbation. After a brief presentation the method is applied to a model for a herbivore feeding on two competing autotrophs. Analytical expresssions for the stationary points in the step function limit are given, and their dependence on the parameter values is analysed and interpreted.

Environmental Science & Technology, 2013

On January 1st, 2012, the maximum limit for sulfur concentration in marine fuels on the high seas... more On January 1st, 2012, the maximum limit for sulfur concentration in marine fuels on the high seas was lowered from 4.50% to 3.50% by the International Maritime Organization (IMO). It was one of a series of planned steps toward reducing the negative environmental and health impacts of international shipping. This study investigates the effectiveness of the IMO regulation in reducing global sulfur emissions. We found a reduction in global average sulfur concentration of only 0.07% points from 2011 to 2012. On the positive side, we also found that only 2.3% of the bunkerings were noncompliant in 2012, that is, exceeded the new 3.50% sulfur concentration cap. The analysis furthermore suggests that compliance with the new regulation is achieved by blending high sulfur fuel with lower sulfur fuel, rather than by removing high sulfur fuel from the market or removing the excess sulfur. The main conclusion is that the regulation has been effective in reducing the maximum sulfur concentration but has not been very effective in reducing the average sulfur concentration. Thus, the regulation may have resulted in local environmental benefits but has not resulted in global benefits with respect to global sulfur emissions from international shipping.

Benchmarking: An International Journal, 2012

ABSTRACT Purpose – The purpose of this paper is to construct a realistic best practice benchmark ... more ABSTRACT Purpose – The purpose of this paper is to construct a realistic best practice benchmark and develop a methodology for comparison of individual suppliers of marine bunker fuel. As is well-known in this trade, unfair business behaviors in the bunker fuel market are not uncommon, resulting in financial losses for the buyers. Design/methodology/approach – Establishing a best practice will naturally involve some degree of subjectivity as there is not an a priori correct answer to this problem. Using the concept of membership functions from fuzzy set theory, a score can be derived from a best practice benchmark histogram. The main advantages of this method are its relative independence both of sample size and of the underlying distribution, as well as being computationally very efficient. Findings – The authors' methodology turns out to be more powerful than standard descriptive statistics, as it is less sensitive to outliers and is well suited for small datasets and even single numbers. When applied to data for all suppliers worldwide, it is shown that the number of good suppliers is actually much lower than might be expected. Practical implications – Bunker fuel is a major expense for ship owners, and can easily reach $30 million/year for a single container ship. There is, therefore, a considerable interest in the market for benchmarking of individual fuel suppliers. The authors' methodology is also applicable to other quality-related fuel parameters. Originality/value – To the best of the authors' knowledge, this is the first attempt to benchmark actors in the marine bunker fuel industry and to quantify their behaviors.

Dynamics and Stability of Systems, 1995

Motivated by the periodic behaviour of regulatory networks within cell biology and neurology, we ... more Motivated by the periodic behaviour of regulatory networks within cell biology and neurology, we have studied the periodic solutions of piecewise-linear, first- order differential equations with identical relative decay rates. The flow of the solution trajectories can be represented qualitatively by a directed graph. By examining the cycles in this graph and solving the eigenvalue problem for corresponding mapping matrices,

Dynamics and Stability of Systems, 1994

A new method to investigate asymptotic properties of linear differential equations with strong th... more A new method to investigate asymptotic properties of linear differential equations with strong threshold and switching effects is presented. The method is applied to systems of equations of the form dx/dt = F(x) - yx, where y = constant and the dependence of F on x is mediated by sigmoid functions. Using a special sigmoid function called a logoid, which

Environmental Science & Technology, 2013

On January 1st, 2012, the maximum limit for sulfur concentration in marine fuels on the high seas... more On January 1st, 2012, the maximum limit for sulfur concentration in marine fuels on the high seas was lowered from 4.50% to 3.50% by the International Maritime Organization (IMO). It was one of a series of planned steps toward reducing the negative environmental and health impacts of international shipping. This study investigates the effectiveness of the IMO regulation in reducing global sulfur emissions. We found a reduction in global average sulfur concentration of only 0.07% points from 2011 to 2012. On the positive side, we also found that only 2.3% of the bunkerings were noncompliant in 2012, that is, exceeded the new 3.50% sulfur concentration cap. The analysis furthermore suggests that compliance with the new regulation is achieved by blending high sulfur fuel with lower sulfur fuel, rather than by removing high sulfur fuel from the market or removing the excess sulfur. The main conclusion is that the regulation has been effective in reducing the maximum sulfur concentration but has not been very effective in reducing the average sulfur concentration. Thus, the regulation may have resulted in local environmental benefits but has not resulted in global benefits with respect to global sulfur emissions from international shipping.

TransNav, the International Journal on Marine Navigation and Safety of Sea Transportation, 2016

Benchmarking: An International Journal, 2012

ABSTRACT Purpose – The purpose of this paper is to construct a realistic best practice benchmark ... more ABSTRACT Purpose – The purpose of this paper is to construct a realistic best practice benchmark and develop a methodology for comparison of individual suppliers of marine bunker fuel. As is well-known in this trade, unfair business behaviors in the bunker fuel market are not uncommon, resulting in financial losses for the buyers. Design/methodology/approach – Establishing a best practice will naturally involve some degree of subjectivity as there is not an a priori correct answer to this problem. Using the concept of membership functions from fuzzy set theory, a score can be derived from a best practice benchmark histogram. The main advantages of this method are its relative independence both of sample size and of the underlying distribution, as well as being computationally very efficient. Findings – The authors' methodology turns out to be more powerful than standard descriptive statistics, as it is less sensitive to outliers and is well suited for small datasets and even single numbers. When applied to data for all suppliers worldwide, it is shown that the number of good suppliers is actually much lower than might be expected. Practical implications – Bunker fuel is a major expense for ship owners, and can easily reach $30 million/year for a single container ship. There is, therefore, a considerable interest in the market for benchmarking of individual fuel suppliers. The authors' methodology is also applicable to other quality-related fuel parameters. Originality/value – To the best of the authors' knowledge, this is the first attempt to benchmark actors in the marine bunker fuel industry and to quantify their behaviors.

Environmental Science Technology, May 28, 2013

On January 1st, 2012, the maximum limit for sulfur concentration in marine fuels on the high seas... more On January 1st, 2012, the maximum limit for sulfur concentration in marine fuels on the high seas was lowered from 4.50% to 3.50% by the International Maritime Organization (IMO). It was one of a series of planned steps toward reducing the negative environmental and health impacts of international shipping. This study investigates the effectiveness of the IMO regulation in reducing global sulfur emissions. We found a reduction in global average sulfur concentration of only 0.07% points from 2011 to 2012. On the positive side, we also found that only 2.3% of the bunkerings were noncompliant in 2012, that is, exceeded the new 3.50% sulfur concentration cap. The analysis furthermore suggests that compliance with the new regulation is achieved by blending high sulfur fuel with lower sulfur fuel, rather than by removing high sulfur fuel from the market or removing the excess sulfur. The main conclusion is that the regulation has been effective in reducing the maximum sulfur concentration but has not been very effective in reducing the average sulfur concentration. Thus, the regulation may have resulted in local environmental benefits but has not resulted in global benefits with respect to global sulfur emissions from international shipping.