Optimal Tuning of PID Controller using Adaptive Hybrid Particle Swarm Optimization Algorithm Particle swarm optimization (PSO) has proved its ability as an efficient search tool in many optimization problems. However, PSO is easy to be trapped into local minima due to its mechanism in information sharing. Under this circumstance, all the particles could quickly converge to a position by the attraction of the best particle; all particles could hardly be improved. To overcome premature convergence of the standard PSO algorithm, this paper presents an adaptive hybrid PSO, namely (AHPSO) by employing an adaptive mutation operator for local best particles instead of applying the mutation operator to the global best particle as has been done in previous work. The developed algorithm is a new approach which allows the swarm to be more diverse by making better exploration of the local search space instead of global search space investigated by previous researchers. The proposed algorithm holds on the properties of simple structure, fast convergence, and at the same time enhances the variety of the population, and extends the search space. It is applied to self-tuning of proportional-integral-derivative-(PID) controller in the ball and hoop system which represents a system of complex industrial processes. The results are compared with those obtained by applying standard PSO, and adaptive hybrid PSO based on global best particles. It has been shown that the developed AHPSO local best algorithm is faster in convergence and the obtained results are proved to have higher fitness than the other two algorithms. The PID controller was the most popular controller of this century because of its remarkable effectiveness, simplicity of implementation and broad applicability. In practice, it is hard to obtain optimal tuning for PID controller. Most of PID tuning is done manually which is difficult and time consuming. In order to use PID controller better, the optimal tuning of its parameters have become an important research field [1] . People have made lots of research, and proposed some advanced PID control methods, such as expert PID control based on knowledge inference [2] , self-learning PID control based on regulation, neural network PID control based on connection mechanism [3] , and intelligent PID control based on fuzzy logic [4, 5] . Genetic algorithm (GA) has 102 S. Morkos, H. Kamal been applied to self-tuning of PID parameters, too [6] . However, GA has the disadvantages of premature and slow convergence rate, and the need to set up many parameters. Recently, the computational intelligence has proposed particle swarm optimization (PSO) [7, 8] as opened paths to a new generation of advanced process control. The PSO algorithm, proposed by Kennedy and Eberhart [7] in 1995, was an evolution computation technology based on population intelligent methods. In comparison with genetic algorithm, PSO is simple, easy to realize and has very deep intelligent background. It is not only suitable for scientific research, but also suitable for engineering applications in particular. Thus, PSO received widely attentions from evolution computation field and other fields. Now the PSO has become a hotspot of research.. Many efforts on the enhancement of traditional PSO have been proposed, by combining the PSO with other techniques, especially evolutionary computation techniques. The research effort in [9] has developed a hybrid method combining two heuristic optimization techniques, GA and PSO, for the global optimization of multimodal functions. The work in [10] , obtained better results by applying PSO first followed by applying GA in their profiled corrugated horn antenna optimization problem. The effort in [11] has introduced a new integrated genetic swarm optimization algorithm (IGSA), combining the strengths of PSO with GA. It is applied in the tuning of PID controllers for the ball and hoop system. A genetic programming based adaptable evolutionary hybrid particle swarm optimization algorithm, have presented in [12] , for avoiding premature convergence to local minima by the introduction of diversity in the swarm.. In addition to incorporate evolutionary algorithms into PSO, another research trend is to merge evolutionary operators like selection, crossover and mutation to the PSO. By applying selection operation in PSO, the particles with the best performance are copied into the next generation; therefore, PSO can always keep the best performed particles [13] . By applying crossover operation, information can be swapped between two individuals to have the ability to "fly" to the new search area as that in evolutionary programming and GA [14] . Among the three evolutionary operators, the mutation operators are the most commonly applied evolutionary operators in PSO. The purpose of applying mutation to PSO is to increase the diversity of the population and the ability to have the PSO to escape from the local minima. One approach is to mutate PSO parameters such as the position of the best neighborhood, as well as the inertia weight [15] . Another approach is to prevent particles from moving too close to each other so that the diversity could be maintained and therefore escape from being trapped into local minima. In [16] , the particles are relocated when they are too close to each other. In [17] , collision-avoiding mechanisms are designed to prevent particle from colliding with each other and therefore increase the diversity of the population. In [18] , deflection and stretching techniques as well as a repulsion technique are incorporated into the original PSO to avoid particles to move toward the already found global minima, so that the PSO can have more chances to find as many global minima as possible. Chen [19] presented a Gaussian mutation operator with adaptive mutation probability. Wang [20] proposed an adaptive mutation on the basis of average velocity of swarm. Pant [21] used an adaptive Cauchy mutation operator in PSO, which was based on beta distribution. Tang [22] proposed Local Search PSO, namely LSPSO by applying an adaptive mutation operator which dynamically adjusts the step size of local search in terms of the size of current search space in order to improve the global search ability of PSO. He introduced one technique for mutating the global best particle by a value which based on the difference between the maximum and minimum value for each dimension of the search space. However, the results given by LSPSO as well as the standard PSO, PSO with both Gaussian and Cauchy mutation fall into local optima for some types of test functions.. In the present work, a new adaptive hybrid PSO, called AHPSO local best is proposed by applying an adaptive mutation operator, which differs from the above mutation techniques by using three types of mutation operators instead of using one technique. The main idea Optimal Tuning of PID Controller using Adaptive Hybrid Particle Swarm Optimization Algorithm 103 of AHPSO local best is to generate an operator that can adaptively select the most suitable mutation method in each generation according to each stage of the problem. Three types of mutation operators are used in this work, Gaussian, Cauchy, and Levy mutation operators. In the proposed algorithm, the local best particles are to be mutated by the selected mutation operator instead of applying the mutation operator to the global best particle as in the previous literatures. This can be accomplished by searching the neighborhood of the global best particles in each generation, resulting in more exploration of the search space and increasing the diversity of the population and the ability to have the PSO to avoid the local optima. The new developed algorithm is carried out for the optimal tuning of PID controller to the ball and hoop system. The performance of the system is compared with the standard PSO and adaptive PSO using the global best particle. Experimental studies on tuning the parameters of PID controller for the ball and hoop problem show that AHPSO local best performs better than the standard PSO and adaptive PSO based on global best particle search technique. The obtained results have higher fitness and faster convergence. The rest of the paper is organized as follows. Section 2 describes the standard PSO. In Section 3, PSO with adaptive mutation operator is described and the proposed AHPSO local best algorithm is presented in detail. An overview of the control problem which will be solved is provided in Section 4. Experimental results and discussions are presented in Section 5. Finally, Section 6 concludes the whole work. This paper is concerned with developing adaptive operator for the selection of best mutation technique of three investigated mutation techniques: Cauchy, Gaussian, and Levy techniques. Instead of applying single mutation operator, several mutation operators are applied at different stages for best performance. A new particle swarm algorithm based on adaptive mutation operator to local best particles namely AHPSO local best is proposed in this paper. Instead of applying the best mutation operators to the global particle, it is applied to the neighbors' of global best particle. Besides, the paper investigates the use of AHPSO based on local best particles for tuning PID controller parameters for the ball and hoop system and compares the system performance with the standard PSO and AHPSO based on global best particles. The performance of the three algorithms is analyzed based on three performance indices; IAE, ISE, and MSE. Experimental results show the superiority of the AHPSO local search over the other techniques for the optimal tuning of PID controller to the ball and hoop system. Also, it has been shown that the developed algorithm is faster in convergence and gives higher fitness value than the other algorithms, at the same time enhances the variety of the population, and extends the search space. Also, the time response characteristics of the proposed algorithm are better than other techniques. In future research, we intend to apply the technique to different set of practical constrained problems to show the robustness of the technique. Also, comparison of the effectiveness of different mutation operators on particles velocity for different types of problems will be studied.

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Interlayer Bit Allocation for Scalable Video Coding Abstract-In this paper, we present a theoretical analysis of the distortion in multilayer coding structures. Specifically, we analyze the prediction structure used to achieve temporal, spatial, and quality scalability of scalable video coding (SVC) and show that the average peak signal-to-noise ratio (PSNR) of SVC is a weighted combination of the bit rates assigned to all the streams. Our analysis utilizes the end user's preference for certain resolutions. We also propose a rate-distortion (R-D) optimization algorithm and compare its performance with that of a state-of-the-art scalable bit allocation algorithm. The reported experiment results demonstrate that the R-D algorithm significantly outperforms the compared approach in terms of the average PSNR.Index Terms-H.264/SVC, rate allocation, scalable video coding (SVC).

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LTL over Integer Periodicity Constraints Abstract. Periodicity constraints are used in many logical formalisms, in fragments of Presburger LTL, in calendar logics, and in logics for access control, to quote a few examples. In the paper, we introduce the logic PLTL mod , an extension of Linear-Time Temporal Logic LTL with past-time operators whose atomic formulae are defined from a first-order constraint language dealing with periodicity. Although the underlying constraint language is a fragment of Presburger arithmetic shown to admit a pspace-complete satisfiability problem, we establish that PLTL mod model-checking and satisfiability problems remain in pspace as plain LTL (full Presburger LTL is known to be highly undecidable). This is particularly interesting for dealing with periodicity constraints since the language of PLTL mod has a language more concise than existing languages and the temporalization of our first-order language of periodicity constraints has the same worst case complexity as the underlying constraint language. Finally, we show that adding quantification in the logical language provides to PLTL mod , expspace-hard problems. As another application, we establish that the equivalence problem for extended single-string automata, known to express the equality of time granularities, is pspace-complete by designing a reduction from QBF and by using our results for PLTL mod . The paper concludes by presenting a bunch of open problems related to decidability and complexity issues for other fragments of Presburger LTL. We have introduced a first-order theory of periodicity constraints IPC ++ whose satisfiability is pspace-complete and a version of LTL with past whose atomic formulae are constraints from IPC ++ (with comparison of variables at different states). PLTL mod is a very concise logical formalism to deal with periodicity constraints. We have shown that PLTL mod model-checking and satisfiability are pspace-complete and that PLTL ∃ (IPC + ), the fragment PLTL(IPC + ) of PLTL mod extended with the quantifier ∃ has problems in expspace. As an application, we have also proved that the equivalence problem for ESSA introduced in [LM01, Sect. 5] is pspace-complete, even if restricted to two variables.. In Table 1 in the table refers to the decidability status. All undecidability results are consequences of the fact that LTL over the constraint language allowing atomic constraint of the form x = y and x = y + 1 is undecidable by simulation of two-counter machines 1 . Two families of open problems can be distinguished from Table 1: 1. How to deal with the constraint language IPC + {x < y, x = y}? The difficulty with the decidability status of PLTL(IPC + {x < y, x = y}) is that LTL({x < y, x = y}) already characterizes non ω-regular sequences of constraints, see details in [DD03] . 2. How to deal with ↓ in the presence of atomic constraints of the form x = y?. For instance, the decidability status of LTL({x = y}) + ↓ even restricted to formulae with a unique local variable is open. The formula 2 ↓ x ′ =x X2(x = x ′ ) belongs to this language.. 1 For instance, the undecidability of PLTL + ↓({x = y, x < y}) can be shown by adapting the proof of [DD03, Theorem 10.1] with the domain Z, =, succ . We modify the formula ϕ M (used in the proof of [DD03, Theorem 10.1]) encoding the behaviour of the machine M . First, we introduce a new variable z and the formula 2(z < Xz) is a new conjunct of ϕ M . In that way, σ, 0 |= 2(z < Xz) iff σ(0)(z), σ(1)(z), . . . is isomorphic to N. Second, all the variables x occurring in ϕ M are forced to take their values in {σ(i)(z) : i ∈ N}, which can be done with the formula 2(↓ x ′ =x F −1 (z = x ′ ) ∨ F(z = x ′ )). The conjunction of all these formulae is added to ϕ M . Third, we replace every occurrence of succ(X n 1 x 1 , X n 2 x 2 ) in ϕ M stating that the value of x 2 at the n 2 th next state is 1 plus the value of x 1 at the n 1 th next state, by. with Everywhere(ψ) = G −1 (ψ) ∨ 2(ψ). The quantification over Z that allows to express the successor function by means of < is encoded by a quantification over the states, which is fine by the properties satisfied by the interpretation of z. The modified version of ϕ M (with new conjuncts) encodes the behaviour of M , whence the undecidability of PLTL + ↓({x = y, x < y}). The decidability status of LTL + ↓({x = y, x < y}) (no past-time operators) is open.

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Hypothetical in silico model of the early-stage intermediate in protein folding Abstract This paper presents a method for determining the structure of the early stage (ES) intermediate in the multistage protein folding process. ES structure is modeled on the basis of a limited conformational subspace of the Ramachandran plot. The model distinguishes seven structural motifs corresponding to seven local probability maxima within the limited conformational subspace. Three of these are assigned to well-defined secondary structures, while the remaining four are found to represent various types of random coils. The presented heuristic approach also provides insight into the reasons behind incorrect predictions occurring when the folding process depends on external factors (e.g., ligands, ions or other proteins) rather than on the characteristics of the backbone itself. The accuracy of the presented method is estimated at around 48 %. Although the multi-stage nature of protein folding has been confirmed experimentally [1] , experimental research into the structure of early stage intermediates remains scant. In silico models are thus needed to supply adequate starting structures for folding simulations. Several authors have recently presented experimentally determined structures which they claim to correspond to early stage intermediates [2] .. Many traditional in silico structure prediction methods depend on a set of starting structures, subjected to energy minimization algorithms in hope of arriving at the native form of the analyzed protein. Preparation of such starting structures depends on the model in question, with important differences separating Darwinian and Boltzmann-based approaches [3] . The former model relies on preserving structural similarities as the chain undergoes evolutionary, sequential changes, while the latter treats folding as a spontaneous process triggered by the chain's natural propensity to seek out its global free energy minimum. Determining starting structures is much easier in the Darwinian approach due to the existence of protein homologues whose structure is well known. Pasting together structural motifs from sequentially similar fragments yields useful structures which can then be subjected to energy minimization. The Boltzmann approach is far more challenging and typically relies on Monte Carlo simulations to stochastically select Φ and Ψ angles for a given chain. Some Boltzmann algorithms depends on databases which contain data on short peptide fragments (tripeptides or 9-peptides-such as in the Rosetta package [4] ).. The model presented in this paper attempts to simulate early stage intermediates by referring to a limited conformational subspace established within the bounds of the Ramachandran plot [5] . The subspace assumes the form of an elliptical path whose shape and placement are the result of geometric analysis of the polypeptide chain (Fig. 1) . The path traverses all fragments of the map which correspond to specific structural motifs. Assuming that the theoretical model is correct, generation of the early stage intermediate may take on two forms. In the step back procedure the crystalline form undergoes changes intended to reverse the folding process, replacing the values of Φ and Ψ with corresponding pairs of early-stage angles (Φ e and Ψ e ) belonging to the limited conformational subspace. From an algorithmic point of view, each pair of dihedral angles {Φ, Ψ} is matched to a corresponding early-stage pair {Φ e , Ψ e } which lies on the elliptical path and is closest to the original pair (see [5] [6] [7] [8] [9] for a more detailed description of this process and refer to Fig. 1 ). Given this distribution of dihedral angles, the limited conformational subspace is partitioned into seven sections, each centered upon a distinct local probability maximum, labeled A through G. This process established the structural alphabet for the early stage intermediate (Fig. 2) [10] .. Applying the above algorithm to a nonredundant set of proteins produces a contingency table which lists the relations between structural motifs and peptide sequences (in our case, the base sequence is a tetrapeptide fragment). Given the number of possible code variations and structural motifs, the size of the contingency table is 160,000×2401. Each cell lists the probability of encountering a specific structural motif for a given sequence of peptides (see Table 1 ) [10] . The other possible approach, called the step forward model, applies the contingency table directly to assign structural motifs to tetrapeptide fragments within the limited conformational subspace. This paper compares both approaches in order to highlight the most common misconceptions associated with the step forward procedure. The step back algorithm is treated as a baseline when determining the scope of simulation errors and inaccuracies [11] . It should be noted that the limited conformational subspace is-in itself-not a novel concept as theoretical and experimental considerations have led others to suggest similar approaches [12] . The presented derivation based on the geometric model of the polypeptide chain [11] is merely one of many attempts to establish such a subspace.. The effectiveness of the presented early stage intermediate generation method is verified on the basis of a set of protein chains extracted from the Protein Data Bank (PDB). The presented study complements the outcomes of these simulations as a crucial step in the protein folding process [13] . The goal of the early stage analysis step, presented here, is to assess the effectiveness of the proposed model when applied to raw amino acid sequences. This paper shows where the model succeeds and where it fails; it also explains the reasons behind simulation failures (on either stage of the folding process). The main aim of early stage model is to deliver the structural forms for further energy minimization procedures (computational interpretation) and to deliver structural forms which mimic the initial steps of folding process (biological interpretation).

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Large-scale analysis of the evolutionary histories of phosphorylation motifs in the human genome Background: Protein phosphorylation is a post-translational modification that is essential for a wide range of eukaryotic physiological processes, such as transcription, cytoskeletal regulation, cell metabolism, and signal transduction. Although more than 200,000 phosphorylation sites have been reported in the human genome, the physiological roles of most remain unknown. In this study, we provide some useful datasets for the assessment of functional phosphorylation signaling using a comparative genome analysis of phosphorylation motifs.

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Terminating constraint set satisfiability and simplification algorithms for context-dependent overloading Abstract Algorithms for constraint set satisfiability and simplification of Haskell type class constraints are used during type inference in order to allow the inference of more accurate types and to detect ambiguity. Unfortunately, both constraint set satisfiability and simplification are in general undecidable, and the use of these algorithms may cause nontermination of type inference. This paper presents algorithms for these problems that terminate on any given input, based on the use of a criterion that is tested on each recursive step. The use of this criterion eliminates the need of imposing syntactic conditions on Haskell type class and instance declarations in order to guarantee termination of type inference in the presence of multi-parameter type classes, and allows program compilation without the need of compiler flags for lifting such restrictions. Undecidability of the problems implies the existence of instances for which the algorithm incorrectly reports unsatisfiability, but we are not aware of any practical example where this occurs. Haskell's type class system [5, 18] extends the HindleyMilner type system [16] with constrained polymorphic types, in order to support overloading. Type class constraints may occur in types of expressions involving overloaded names (or symbols), and restrict the set of types to which quantified type variables may be instantiated, to those types for which these type constraints are satisfied, according to types of definitions that exist in a relevant context.. A type class declaration specifies the name and parameters of the class, and the principal type of names which can then be overloaded in instance definitions. For example:. class Eq a where (==):: a → a → Bool (/=):: a → a → Bool is a declaration of type class Eq, with parameter a, that specifies the principal types of (==) and (/=). Function (==) has type ∀ a. Eq a ⇒ a → a → Bool, where constraint Eq a indicates that type variable a cannot be instantiated to an arbitrary type, but only to a type that has been defined as an instance of class Eq. An instance of a type class specifies instance types for type class parameters, and gives definitions of the overloaded names specified in the class. The type of each overloaded name in an instance definition is obtained by substituting type class parameters with corresponding instance types. For example, the following instance declarations specify definitions of the equality operator for types Int and for polymorphic lists, respectively: For a base type, like Int, a corresponding predefined operation is provided. The definition of equality for lists of elements of an arbitrary type uses the equality test for elements of this type. Constraint Eq a must be specified as the context for the head Eq [a] of the instance declaration. A context is a set of type class constraints, and constraint π is the head of a qualified constraint P ⇒ π , where P is a set of type class constraints.. As an aside, type classes in Haskell may also contain default definitions of the overloaded names, in order to avoid repeating the same definitions in instances.. Class constraints introduced on the types of overloaded symbols occur also on the types of expressions defined in terms of these symbols. For example, consider the following function that tests list membership:. The principal type of elem is ∀a. Eq a ⇒ a → [a] → Bool. Constraint Eq a occurs in the type of elem due to the use of the equality operator (==) in its definition.. Haskell restricts type classes to have a single parameter but the extension to multi-parameter type classes, called Haskell+mptcs in the sequel, is widely used.. Type inference for constrained type systems rely on constraint set simplification, which, for the case of type classes, essentially amounts to performing (so-called) context reduction. Constraint set simplification yields equivalent constraint sets, and are useful for providing simpler types for expressions. Context reduction simplifies constraints by substituting constraints or removing resolved constraints according to available instance definitions, besides removing duplicate constraints or substituting constraints according to the class hierarchy.. As an example, context Eq[t] is reduced to Eq t, for any type t, in the presence of instance Eq[a] with context Eq a.. Improvement [13] is also a process of simplification of constrained types, but it is of a different nature, and is used in type inference to avoid ambiguity and to infer more informative types. Improvement is fundamentally based on constraint set satisfiability: it is a process of transforming a constraint set P into a constraint set obtained by applying a substitution S to P so that the set of satisfiable instances of P is preserved.. The mechanism of functional dependencies and other alternatives have been proposed to deal with improvement [7, 4, 10, 11, 14] , for detection of ambiguity and for specialization of constrained types in the presence of multi-parameter type classes. We do not discuss improvement specifically in this paper, but focus on constraint set satisfiability, which is only used for the implementation of improvement or any alternative approach.. Unfortunately, both constraint set satisfiability and simplification are in general undecidable problems [6] , and the use of computable functions for solving these problems may cause non-termination of type inference. This paper presents algorithms for constraint set satisfiability and simplification that use a termination criterion which is based on a measure of the sizes of types in type constraints. The sequence of constraints that unify with a constraint axiom in recursive calls of the function that checks satisfiability or simplification of a type constraint is such that either the sizes of types of each constraint in this sequence is decreasing or there exists at least one type parameter position with decreasing size.. The use of this criterion eliminates the need for imposing syntactic conditions on Haskell type class and instance declarations in order to guarantee termination of type inference in the presence of multi-parameter type classes, and allows program compilation without the need of compiler flags for lifting such restrictions.. The use of a termination criterion implies that there exist well-typed programs for which the presented algorithm incorrectly reports unsatisfiability. However, practical examples where this occurs are expected to be very rare. The algorithms have been implemented and tested by using a prototype front-end for Haskell, available at the mptc github repository. The algorithm works as expected when subjected to examples mentioned in the literature, Haskell libraries that use multi-parameter type classes and many tests, including those used by the most commonly used Haskell compiler [19] , GHC, involving all pertinent GHC extensions.. Restrictions imposed on class and instance declarations in Haskell, in Haskell+mptcs and in GHC, and GHC compilation flags used to avoid these restrictions [20] , are summarized in Sect. 2. Section 3 reviews entailment and satisfiability relations on type class constraints. Section 4 gives a definition of a computable function that returns the set of satisfiable substitutions of a given constraint set P, when it terminates. Subsection 4.1 defines a termination criterion and redefines this computable function in order to use this criterion. Section 5 defines a constraint set simplification computable function, based on the same termination criterion. Section 6 concludes. This paper presents a termination criterion and terminating algorithms for constraint simplification and improvement, based on the use of a value that always decreases on each recursive step in these algorithms. The termination criterion defined can be used in any form of constraint simplification and improvement algorithm during type inference. The use of this criterion eliminates the need for imposing syntactic conditions on Haskell type class and instance declarations and the need for using a recursion stack depth limit in order to guarantee termination of type inference in the presence of multi-parameter type classes, in case these syntactic conditions are chosen by programmers not to be enforced.. Since type class constraint satisfiability is in general undecidable, there exist instances of this problem for which the algorithm presented in this paper incorrectly reports unsatisfiability. However, practical examples where this occurs are expected to be very rare. The algorithms have been implemented and used in a prototype front-end for Haskell, available at http://github.com/rodrigogribeiro/mptc. For all examples mentioned in the literature, Haskell libraries that use multi-parameter type classes and tests used by the Haskell GHC compiler, involving all pertinent GHC extensions, the algorithm works as expected without the need for any compilation flag.. In comparison to the use of a recursion depth limit, our approach has the advantage that type-correctness is not implementation dependent (a constraint is or is not satisfiable with respect to a given set of constraint axioms). The use of a recursion depth limit can make a constraint set satisfiable in one implementation and unsatisfiable in another that uses a lower limit. Incorrectly reporting unsatisfiability can occur in both cases, but is expected to be extremely rare with our approach. We are not aware of any practical example where this occurs.. The main disadvantages of our approach are that it is not syntactically possible to characterize such incorrect unsatisfiability cases and it is not very easy for programmers to understand how type class constraints are handled in such a case, if and when it occurs.

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Evaluation on the influence of internet prefix hijacking events The inter-domain routing system based on the BGP protocol is a kernel establishment in the Internet. There have been many incidents of IP prefix hijacking by BGP protocol in the Internet. Attacks may hijack victim's address space to disrupt network services or perpetrate malicious activities such as spamming and DoS attacks without disclosing identity. The relation between prefix hijacking and the Internet hierarchy is presented in this paper. The Internet is classified into three tiers based on the power-law and commercial relations of autonomous systems. The relation between network topology and prefix hijacking influence is presented for all sorts of hijacking events in different layers. The results assert that the hierarchical nature of network influences the prefix hijacking greatly. The inter-domain routing system based on the BGP protocol is a kernel establishment in the Internet. It is not only the basic mechanism of exchanging the reachable information, but also the key way to inter-connect the autonomous systems and establish the policy control in ISPs. Unfortunately, the limited guarantees provided by BGP sometimes contribute to serious instabilities and outages. Prefix hijacking are probably the most straightforward type of BGP attack.. Prefix hijacking is also known as BGP hijacking, because to receive traffic destined to hijacked IP addresses, the attacker has to make those IP addresses known to other parts of the Internet by announcing them through BGP. Because there is no authentication mechanism used in BGP, a misbehaving router can announce routes to any destination prefix on the Internet and even manipulate route attributes in the routing updates it sends to neighboring routers. Taking advantage of this weakness has become the fundamental mechanism for constructing prefix hijack attacks. They occur when an AS announces a route that it does not have, or when an AS originates a prefix that it does not own. In the recent past, there have been many instances of prefix hijacking in the Internet wherein an Autonomous System hijacks routes simply by advertising the corresponding prefixes [1] . On January 22, 2006, a network (AS-27506) wrongly announced the IP prefix 65.173.134.0/24 representing an address block of 224 IP addresses, into the global routing system. This prefix belonged to another network (AS-19758) and because routers do not have a means to accurately verify the legitimate origin of each prefix, they accepted announcements from both the true origin (AS-19758) and the false one (AS-27506), and selected one of them based on the local routing policies and other criteria. As a result, some networks sent for data traffic destined to 65.173.134.0/24, to AS-27506 instead of the true owner.. Irrespective of whether it is caused by a misconfiguration or a malicious entity, the AS that hijacks a prefix can blackhole and intercept all the hijacked traffic and thus, cause a denial-of-service attack or a man-in-the-middle attack against the prefix owner [2, 3] . Because the current BGP protocol implements little authentication and often assumes a high level of trust to its neighbor routers, IP hijacking can easily succeed.. Previous efforts on prefix hijacking are presented from two aspects: hijack prevention and hijack detection. Generally speaking, prefix hijack prevention solutions are based on cryptographic authentications [4] [5] [6] [7] [8] where BGP routers sign and verify the origin AS and AS path of each prefix. While hijack detection mechanisms [9] [10] [11] [12] [13] [14] [15] are provided when a prefix hijack is going to happen which correction steps must follow.. Because there is a lack of a general understanding on the impact of a successful prefix hijack, it is difficult to assess the overall damage once an attack occurs, and to provide guidance to network operators on how to prevent the damage. Ballani et. al. [16] presents a study of Internet prefix hijacking and interception, which analyzes the probability of an AS hijacking the traffic to a prefix from another AS and the proposal of the prefix interception. Lad et. al. [17] estimate the resilience of Prefix hijacks through simulation across the Internet's AS-level topology.. In this paper, we conduct a systematic study on the impaction of prefix hijacks launched at different position in the Internet hierarchy. The Internet is classified into three hierarchies-core layer, forwarding layer and marginal layer based on the power-law and commercial relations between autonomous systems (ASes). Two impaction parameters-affected ASes set Nc and affected paths factor µ, are analyzed for typical nine types of prefix hijacking events in different layers.. The remainder of this paper is organized as follows: The section 2 descripts the hierarchy model of the Internet based on the power-law and relationships between ASes. Based on section 2, section 3 builds the attack model of IP prefix hijacks on a comprehensive attack taxonomy relying on the Internet hierarchy model and BGP protocol policies. The impaction analysis of the prefix hijacks attack is also presented. The related works are discussed in section 4 and section 5 concludes the paper. This paper conducts a systematic study on the impaction prefix hijacks launched at different position in the Internet hierarchy based on the work in Evaluation on the Influence of Internet Prefix Hijacking Events ComSIS Vol. 10, No. 2, Special Issue, April 2013 629 paper [34] . The Internet is classified into three tiers-core layer, forwarding layer and marginal layer based on the power-law and commercial relations between ASes. Two impaction parameters-affected ASes set Nc and affected paths factor µ, are analyzed for the same prefix hijacking events and the covered prefix hijacking events in different layers. We studied nine type hijacking events based on the position of the hijacking ASes and the hijacked ASes.. The study shows that if the AS in the marginal layer being hijacked, the number of the affected nodes is the largest among the three levels. The hijacked AS in the forwarding layer can affect more paths than the core layer or the marginal layer. If the hijacked ASes are in the same level, the hijacking AS in the forwarding layer can affect more nodes than the core layer or the marginal layer, and the higher attacker is in, the larger its influence will be. The sub-prefix hijack can affect more ASes than the same prefix hijack, and the lager sub-prefix range is, the bigger affected path factor µ will be. Various prefix hijack events have been reported to NANOG [23] mailing list from time to time. IETF's rpsec (Routing Protocol Security Requirements) Working Group provides general threat information for routing protocols and in particular BGP security requirements [24] . Recent works [3, 25] give a comprehensive overview on BGP security. The prefix hijacking is one of the key problems being noticed to BGP in these papers.. Previous works on prefix hijacking can be sorted into two categories: hijack prevention and hijack detection. The former one is trying to prevent the hijacking in the protocol mechanism level, and the latter one is trying to find and alert the hijacking event after it happening. The methods can be categorized into two types: cryptography based and non-crypto based.. The cryptography methods, like [4] [5] [6] [27] [28] [29] [30] [31] , imply that BGP routers sign and verify the origin AS and AS path of each prefix. Origin authentication [31] uses trusted database to guarantee that an AS cannot falsely claim to be the rightful owner for an IP prefix. However, the manipulator can still get away with announcing any path that ends at the AS that rightfully owns the victim IP prefix. Secure Origin BGP (soBGP) [30] provides origin authentication as well as a trusted database that guarantees that any announced path physically exists in the AS-level topology of the internetwork. However, a manipulator can still get away with announcing a path that exists but is not actually available. In addition to origin authentication, S-BGP [6] also uses cryptographically-signed routing announcements to provide a property called path verification. It effectively limits a single manipulator to announcing available paths. However, S-BGP does not prevent the manipulator from announcing the shorter, more expensive, provider path, while actually forwarding traffic on the cheaper, longer customer path. In SPV [32] , the originator of a prefix establishes a single root value used to seed the generation of one-time signature structures for each hop in the PATH. However, the security of SPV is in some cases based on probabilistic arguments, which may be acceptable for some constrained environments, and it is unclear whether such arguments will be acceptable in the larger Internet. And it does not provide the requisite security to protect against path modification. In addition to added router workload, these solutions require changes to all router implementations, and some of them also require a public key infrastructure. Due to these obstacles, none of the proposed prevention schemes is expected to see deployment in near future.. The non-crypto methods include [4, 9, 10, 12, 14] . PHAS [10] is predicated on the notion that a prefix owner is the only entity that can differentiate between real routing changes and those that take place as a result of a prefix hijacking attack. And if there are changes to the originator of a route, the owner of that prefix is notified through email. The system is incrementally deployable in that to join the system. A prefix owner need only register with the PHAS server; however, this server is also a single point of failure in the system, and if it is compromised, it could send out numerous false alarms to prefix owners. Additionally, the system relies on the validity of entities registering their prefixes; there is no protection against an adversary making a false registration. Hu and Mao examined prefix hijacking in greater detail and provided a mechanism for detecting prefix hijacking attacks in real time [14] . Their solution is based on fingerprinting techniques for networks and hosts. If there are conflicting origin ASes advertised, which is potential evidence of a prefix hijacking attack, the collected fingerprints are compared against probes sent to all origins. This approach relies on a real-time BGP UPDATE monitor, which sends differentiating probes if prefixes are advertised from multiple locations. The availability of the monitor is critical as, if updates are delayed, the ability to collect measures, such as probing and subsequent decision making, will be compromised. The Whisper protocol [4] is designed to validate the initial source of path information. The protocol seeks to alert network administrators of potential routing inconsistencies. A random value is initially assigned to each prefix by the originator. The value is repeatedly hashed at each hop as it is propagated from AS to AS. if the hash values are the same, then they must have come from the same source. Only the route originator can verify the route because of the non-invertibility of secure hash functions. Thus, the recipient would have to query the originator as to the veracity of the route, which is often outside of the purview of the originator's knowledge. Another recently-proposed alerting system is pretty good BGP (PGBGP) [12] . The key insight in this work is that misconfigurations and prefix hijacking attacks could be mitigated if routers exercise a certain amount of judgement with the routes that they adopt into their routing tables. MyASN[9] is an offline prefix hijack alert service provided by RIPE. A prefix owner registers the valid origin set for a prefix, and MyASN sends an alarm via regular email when any invalid origin AS is observed in BGP routing update.

O O O O O O O O O O B I I O O O B O O O O O O O O O O O O O O B I I O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O B O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O B O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O


The Software Reliability Model Based on Fractals Fractals are mathematical or natural objects that are made of parts similar to the whole in certain ways. In this paper a software reliability forecasting method of software failure is proposed based on predictability of fractal time series. The empirical failure data (three data sets of Musa's) are used to demonstrate the performance of the reliability prediction. Compared with other methods, our method is effective. Software reliability, namely the capability that a given component or system within a specified environment will operate correctly for a specified period of time, has been one of the most important requirements. The important problem of the software reliability models is to calculate and predict the next failure time in advance. It was mainly treated as random and statistical problem. The Jelinski-Moranda model is based on time measurement and maximum likeness estimation. The Kalman filter is an efficient recursive filter that estimates the state of a linear dynamic system from a series of noisy measurements. The ARIMA models are the most general class of models for forecasting a time series which can be stationarized by transformations such as differencing and logging. Recently Bayesian networks, recurrent neural networks, and support vector machine are applied in time series analysis, which afford good results.. The term fractal, which means broken or irregular fragments, was originally coined by Mandelbrot to describe a family of complex shapes that possess an inherent selfsimilarity or self-affinity in their geometrical structure. It belongs to geometrical category. A fractal has a self-similar structure that occurs at different scales. Fractal objects, by definition, contain infinite detail, i.e., they contain the same degree of detail in each part as is contained in the entire object, no matter how many times its sections are enlarged. For example, a small branch of a tree looks like the whole tree due to the existence of branching structures. Fractal objects are self-similar under some changes in scale, either strictly or statistically.. A power law is a relationship between two scalar variables x and y, which can be written as follows: where C is the constant of proportionality and k is the exponent of the power law. Such a power law relationship appears as a straight line on a log-log plot since, taking logs of both sides, the above equation is equivalent to. which has the same form as the equation for a straight line. The equation f (x) = C, x k has a property that relative scale change f (sx)/ f (x) is independent of x. In this sense, f (x) is scale invariant or lacks a characteristic scale. Consequently, f (x) can be related to fractal because of its scale invariance. The k is called Fractal Dimension.. For Strictly Self-Similar Fractal, two scalar variables x and y fit power law strictly described as Eq. (2); for Statistically Self-Similar Fractal, the x and y fit power law statistically and fractal dimension k is slope of linear regression on a log-log plot described as Eq. (2) .. Fractals have been applied to analyze some random events like earthquakes, random walks and Brownian motions etc. Hughes et al. [1] has discovered that there exists interrelationship between random events and fractal. Software failures are also random events and the key of studying fractal is self-similarity. If self-similarity exists in time series then we may investigate the relationship between software failures and fractal.. The outline of this paper is the following: Section 2 presents sliding-window fractal forecasting model of software failure and validates the model through analyzing the empirical failure data. Section 3 concludes this paper and describes the future research. This paper proposes the software reliability model based on fractals to forecasting the next software failure time which almost fit the actual failure time. Studying the empirical data (three data sets of Musa's) and comparison with other models validate our method. Our model is different from existing forecasting approaches for it is based on geometrical notion and method. We will research the mechanism behind fractals further in future work.

O O B O O O B B O O O O O O O O O O O O O O O O O O O O O O B O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O B B O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O B O O O B O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O


Protected control packets to prevent denial of services attacks in IEEE 802.11 wireless networks Denial-of-service (DoS) attack exploits inherent limitation of resources in wireless networks in attempt to overwhelm and exhaust their finite capacity. In wireless networks, clear-text form of control packets (CP) exhibits a security flaw that can be exploited by attackers to render the networks incapable of providing normal services. While these attacks are quite damaging in terms of consuming available processing and bandwidth resources, they are easy to conduct against the wireless networks. In this study, we propose two distinct models to prevent wireless DoS and replay attacks based on trust in CP for IEEE 802.11 wireless networks. The first model is based on original HMAC-SHA1 algorithm and the second one is based on a proposed modified HMAC-SHA1 (M-hmac) algorithm. Both models are implemented and the results are obtained and evaluated based on a number of metrics. The results show that the two models successfully prevent both wireless DoS and replay attacks. In addition, the newly proposed M-hmac algorithm provides better network performance in term of the metrics. There are various types of security protocols in wireless networks that protect data packets during transmission such as WEP, WPA, and 802.11i. Despite providing different levels of security, these security protocols are not able to protect control packets (CP). Consequently, the CP including RTS, CTS, ACK, CF-End, and CF-End-ACK are transmitted in clear-text form. Wireless CPs contain a 2-byte duration field with 32767 μs maximum value used to set the network allocation vector (NAV). The field shows the time that the channel will be kept busy by the originator node. During this time, other nodes are not allowed to transmit and must wait until NAV reaches zero. Because CP are not protected, it is possible for the attackers to generate false CP with large duration values in order to trigger denial-of-service (DoS) attacks. The intention is to overload the target wireless networks and crash the systems by quickly consuming the networks' capacities.. The attackers may continuously transmit false CP to the target wireless network within short intervals. The target network has to accept the false CP because the 802.11 standard does not provide any mechanism to distinguish the true CPs from the false [1] [2] [3] . Reception of large number of false CP within a short time will quickly consume the network resources until the access point (AP) becomes overloaded and crashed. When this happens, the AP has to disconnect all the users who are at the time connected to the network as it comes to a complete halt and shutdown. While these attacks are easy to implement, they have highly negative impact so that completely shut down the wireless networks and significantly degrade the quality of services.. In this study, two distinct models are proposed to distinguish the trust-based CP belonging to the authorized users from the false CP belonging to the attackers. The models enable the recipients to investigate the CP and analyze information contained in their security elements in order to accept trusted CP and discard false CP. The proposed models support all types of CP and are able to prevent both DoS attacks and replay attacks with sufficient level of security.. The remainder of this article is organized as follows. Related studies are discussed in Section 2. Section 3 presents the structures of the two proposed models. Section 4 details out the experimental setup to implement the models. Section 5 presents the experimental results and discussion. Finally, Section 6 concludes the article. The unprotected CP are capable to make the entire wireless networks vulnerable to DoS attacks and result in serious damages in the critical areas where constant availability of the networks, resources, and services is a prime priority. In this study, we proposed two new distinct models, SCP-M and SCP-O, to prevent wireless DoS and replay attacks by protecting the CP. The proposed SCP-M and SCP-O models were evaluated through extensive set of scenarios and experiments. The obtained results proved that while the standard model failed against the attacks, both the proposed models have successfully prevented the wireless DoS and replay attacks. The results also showed that the best performance of the both models is obtained when the RTS/ CTS handshake is disabled. In this case, the performance of the SCP-M and SCP-O models is considerably close to the standard 802.11 model with a negligible security cost. Results of comparison between SCP-M and SCP-O models also proved that by adopting the SCP-M in wireless networks, the network performance is enhanced. This proves that the proposed M-hmac as underlying authentication algorithm of the SCP-M model provides higher efficiency to access to the system resources and services while maintaining a sufficient level of security.

O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


The trade-off between taxi time and fuel consumption in airport ground movement Abstract Environmental impact is a very important agenda item in many sectors nowadays, which the air transportation sector is also trying to reduce as much as possible. One area which has remained relatively unexplored in this context is the ground movement problem for aircraft on the airport's surface. Aircraft have to be routed from a gate to a runway and vice versa and it is still unknown whether fuel burn and environmental impact reductions will best result from purely minimising the taxi times or whether it is also important to avoid multiple acceleration phases. This paper presents a newly developed multi-objective approach for analysing the trade-off between taxi time and fuel consumption during taxiing. The approach consists of a combination of a graph-based routing algorithm and a population adaptive immune algorithm to discover different speed profiles of aircraft. Analysis with data from a European hub airport has highlighted the impressive performance of the new approach. Furthermore, it is shown that the trade-off between taxi time and fuel consumption is very sensitive to the fuel-related objective function which is used. Air transportation is a growing sector and this trend is predicted to continue in future. At the same time, the stakeholders are caring more and more about the environmental impact of the sector. Aircraft ground movement is an operation which is affected a lot by these two conflicting trends. With the increase in aircraft movements, it is likely that hub airports, especially, will form bottlenecks for air transportation. The ground movement problem is thereby key to reducing delays, through increasingly efficient airport operations, linking the runway sequencing, stand holding and gate assignment problems. However, lower accelerations may sometimes be more fuel efficient, even though movement times would be increased. An ambitious goal stated in the report of the High Level Group on Aviation Research for the European Commission attempts to have emission-free aircraft movements when taxiing in the year 2050 (European Commission 2011).. The details of the ground movement problem vary depending upon the aims of the airport but it can be summarised as the problem of producing conflictfree routings for aircraft on the airport's surface, usually from gates/stands to runways and vice versa. A variety of different constraints and objective functions have been used in the past. Previous research on ground movement often focused on minimising the total taxi time (Atkin et al. 2011b; Marín 2006; Pesic et al. 2001; Roling and Visser 2008) or minimising the makespan (the duration from first to last aircraft movement) (García et al. 2005; Herrero et al. 2005) . Multi-objective approaches have also been used. In addition to minimising the total taxi time, penalising deviations from a scheduled time of departure/arrival was also considered (Balakrishnan and Jung 2007; Deau et al. 2009; Smeltink et al. 2004 ) and Gotteland et al. (2003) considered penalising deviations from a departure time interval. Other research has used a weighted linear objective function to simultaneously consider the total routing time, the delays for arrivals and departures, the number of arrivals and take-offs, the worst routing time and the number of controller interventions (Marín and Codina 2008) . Although multi-objective approaches were used, we have not found any research focusing on the integration of objectives related to the environmental impact. A literature review was recently published by Atkin et al. (2010b) , which also highlighted the differences between the existing approaches.. There is little coverage of environmental considerations in taxiing within the previous research. The main focus has been upon stand holding in order to reduce fuel burn (Atkin et al. 2010a (Atkin et al. , 2011a Burgain et al. 2009 ). The assumption made by them was that by reducing the total taxi time, one can simultaneously improve the efficiency of airport operations and reduce the fuel consumption. However, as indicated in Chen and Stewart (2011) , this may not be true for all cases or airports, since the detailed relationship between fuel consumption and the corresponding speed profile was not investigated in previous research. Atkin et al. (2010b) suggested the value of considering speed profiles when routing aircraft to avoid unnecessary fuel burn due to acceleration and declaration. Lesire (2010) applied a postprocessing stage in his routing approach to smoothen the speed profiles. Finally, Chen and Stewart (2011) presented an approach to analyse the trade-off between taxi time and fuel consumption for a single trajectory of an unimpeded aircraft.. In this research, we analyse the trade-off between the total taxi time and the fuel consumption for the conflict-free routing problem for aircraft on an airport's surface. In contrast to the approach of Chen and Stewart (2011) , the interactions between multiple aircraft are considered. These interactions affect the speed profiles of the aircraft involved and massively increase the solution space of the routing approach, hence, a sophisticated new procedure had to be developed to make such an analysis possible.. Section 2 presents the case which was analysed, then the newly developed multi-objective approach for analysing the trade-off between taxi time and fuel consumption is detailed in Section 3. The results of the application of the algorithm to the dataset are then shown in Section 4; before the paper ends with some conclusions in Section 5. The focus of this research is entirely on the ground movement part of the airport operations of aircraft. In doing this, the pushback/landing time of aircraft are as specified by the dataset and assumed to be fixed.. This section first introduces the objective functions, before an overview of the developed integrated procedure is given. Two key elements of the procedure are given in separate sections afterwards.

O O O O O O O O O O B I O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


Probe Trajectory Interpolation for 3D Reconstruction of Freehand Ultrasound Three-dimensional (3D) Freehand ultrasound uses the acquisition of non parallel Bscans localized in 3D by a tracking system (optic, mechanical or magnetic). Using the positions of the irregularly spaced B-scans, a regular 3D lattice volume can be reconstructed, to which conventional 3D computer vision algorithms (registration and segmentation) can be applied. This paper presents a new 3D reconstruction method which explicitly accounts for the probe trajectory. Experiments were conducted on phantom and intra-operative datasets using various probe motion types and varied slice-to-slice B-scan distances. Results suggest that this technique improves on classical methods at the expense of computational time. Ultrasonography has become a very popular medical imaging modality thanks to its low cost, real time image formation capability and non invasive nature. Due to its many attributes, ultrasound has been used in neurosurgery for the last two decades [1] . Several studies demonstrated that ultrasonography can be used in the location of tumors, definition of their margins, differentiation of internal characteristics and detection of brain shift and residual tumoral tissue [2] .. Despite its advantages, the lack of 3D information in traditional 2D ultrasound imaging prevents reproductivity of examinations, longitudinal follow-up and precise quantitative measurements. To overcome these limits and produce a 3D representation of the scanned organs, severals techniques exist: mechanicallyswept acquisitions, freehand imaging [3] , mechanical built-in probes and 2D phased-array probes [4] . The two first approaches are based on the reconstruction of a 3D regular lattice from 2D B-scans and their positions, whereas 3D probes directly acquire 3D images. The main advantages of freehand imaging, compared to other 3D approaches, are flexibility, low cost and large organs examination capabilities. Moreover, compared to 3D probes, the image quality and the field of view are better suited to clinical applications [5, 6] .. Freehand imaging techniques consist of tracking a standard 2D probe by using a 3D localizer (magnetic, mechanical or optic). The tracking system continuously measures the 3D position and orientation of the probe. This 3D position is used for the localization of B-scans in the coordinate system of the localizer. In order to establish the transformation between the B-scan coordinates and the 3D position and orientation of the probe, a calibration procedure is necessary [7, 8] . Calibration is needed to estimate the transformation matrix linking the different coordinate systems (spatial calibration), but also the latency between image and position time stamps (temporal calibration). The localization accuracy of B-scan pixels in the 3D referential system depends on the calibration procedure. A review of calibration techniques is presented in [9] .. To analyze the sequences of B-scans, two types of approaches can be used: the reslicing (without reconstruction) or the true 3D reconstruction including interpolation step. The first is used by the StradX system [10] and enables the analysis of the data without reconstruction. The sequence of B-scans can be arbitrarily resliced and distance/volume measurements are performed without reconstruction. This strategy is very powerful for manual analysis of 3D datasets. However, 3D isotropic reconstruction is still necessary in the clinical context when automatic segmentation or registration procedures are required. The second approach is based on the interpolation of the information within the B-scans to fill a regular 3D lattice thus creating a volumetric reconstruction. Due to the non uniform distribution of the B-scans, this step is acutely expensive with respect to computation time and reconstruction quality: an efficient reconstruction method should not introduce geometrical artifacts, degrade nor distort the images. To resolve this problem several methods were proposed. The most common ones are Pixel Nearest-Neighbor (PNN) [11] , Voxel Nearest-Neighbor (VNN) [10, 12] and Distance-Weighted interpolation (DW) [13, 14] .. Due to its simplicity of implementation and its reduced computation time, the most straightforward reconstruction algorithm is the PNN method. This algorithm is divided into two stages: the bin-filling and the hole-filling [15] . The bin-filling stage consist in searching, for each pixel in every B-scan. The nearest voxel which is filled with the value of the pixel. Secondly, the remaining gaps in the 3D voxel array are filled via a hole-filling method. Usually, the hole-filling method is a local average of filled voxels. Although the PNN method is fast and simple to implement, this approach generates artifacts. Contrary to the PNN method, the VNN approach does not require the holefilling stage because all voxels are filled in one step using the value of the nearest pixel obtained by orthogonal projection on the nearest B-scan. In the DW interpolation approach, each voxel is filled with the weighted average of pixels from the nearest B-scans (see section 2.1 and Fig. 1 for a detailed explanation) . The set of pixels or interpolation kernel is defined either by a spherical neighborhood [13] , or by projection on the two nearest B-scans [14] . Then, all pixel intensities of this set are weighted by the inverse distance to the voxel to calculate voxel intensity. A complete survey of these three methods is presented in [16] . These approaches are designed to reduce computation time, at the cost of a lower reconstruction quality compared to more elaborated methods.. More elaborated methods were recently developed in order to increase the reconstruction quality. Firstly, the registration based approach consists in reconstructing a 3D volume after a non-rigid registration of each successive B-scans. In [17] , a linear interpolation between the two nearest pixels is used to calculate the intensity voxel. This technique is notably used to avoid artifacts due to tissue motion. Some studies focus on the improvement of the interpolation step using radial basis functions (RBF) [16] , weighted Gaussian convolution [6, 18] or Rayleigh model for intensity distribution [19] . Finally, the optimization of the axis orientation and voxel size are discussed in [6] . Nevertheless, the quality improvement obtained with these approaches induces computational burden.. The paper is organized as follows. Section 2 describes the proposed reconstruction method using the 3D probe trajectory (PT) information. Section 3 briefly describes the evaluation framework and compares the proposed method with VNN and DW methods. Finally, in section 4 the advantages and limitations of the PT method are discussed and further improvements are outlined.. X DW ti+1 P robe trajectory Fig. 1 . Illustration of DW and PT principles. The two orthogonal projections for DW interpolation method and the construction of a "virtual" plane π t containing X for PT method. This paper presented a 3D freehand ultrasound reconstruction method explicitly taking into account the probe trajectory information. Through an evaluation framework, it shows that the proposed method performs better than traditional reconstruction approaches (i.e. Voxel Nearest Neighbor and Distance Weighted interpolation) with a reasonable increase of the computation time.. The main limitation of PT method is the assumption of constant probe speed between two slices. Nonetheless, this hypothesis is reasonable when using a decent frame rate (more than 10Hz). Moreover, the direct interpolation of rotation parameters instead of Spherical Linear Interpolation (SLERP) does not introduce artifacts but accelerates the reconstruction process. The evaluation results underline the relevance of probe trajectory information, especially on sequences with low frame rate acquisitions or large distances between two consecutive B-scans. The PT method is a trade-off between reconstruction error and computational time. The results show that the hypothesis of a correlation between the signal structure and the probe trajectory is relevant. Indeed, in practice, the probe trajectory and signal structure are correlated because the medical practitioner tends to follow the structure of interest (see on Fig. 11 ).. The precise localization of anatomy and pathology within the complex 3D geometry of the brain remains one of the major difficulties of neurosurgery. Thus, image-guided neurosurgery (IGNS) is an adequate context to experiment the proposed method because the reconstruction quality is of utmost importance and the time dedicated to image reconstruction is limited. The PT method is thus interesting for applications where an accurate reconstruction is needed in a reasonable time. Further work should be pursued for comparing the PT reconstruction approach with registration based approaches [17] . Registration based approaches avoid artifacts of slice misregistration due to errors in tracking data (i.e. trajectory) and/or tissue deformation. The compensation of tissue motion can be especially interesting in neurosurgery due to the complex problem of soft tissue deformations also known as brainshift. However, since the registration is a computationally expensive process, the benefit for image reconstruction should be studied. Then, our implementation could be largely optimized using graphic library implementation (ex: OpenGL) or grid computation especially for IGNS purpose. Finally, the impact of PT reconstruction on registration (mono and multimodal) to compensate for errors of localization and brainshift needs to be investigated further. Indeed, the current pitfalls of the neuronavigator system are: the errors caused by geometrical distortion in the preoperative images, registration, tracking errors [22] , and brainshift. The reconstructions were performed on a P4 3.2 Ghz with 2Go RAM. In order to only compare interpolation times, the total computational time is divided as follows: L time corresponds to labeling step and I time corresponds to interpolation time. The labeling step consists in constructing the label vector K n for each voxel X (described in 2.3). This work builds on the distance weighted interpolation and proposes to incorporate probe trajectory information. The distance weighted interpolation is first presented in section (2.1). Then, the probe trajectory information is incorporated in section (2.2).

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