共查询到20条相似文献,搜索用时 15 毫秒
1.
Maria G. Vigliotti Peter G. Harrison 《Electronic Notes in Theoretical Computer Science》2006,164(3):169-186
Mobile Ambients (MA) have acquired a fundamental role in modelling mobility in systems with mobile code and mobile devices, and in computation over administrative domains. We present the stochastic version of Mobile Ambients, called Stochastic Mobile Ambients (SMA), where we extend MA with time and probabilities. Inspired by previous models, PEPA and Sπ, we enhance the prefix of the capabilities with a rate and the ambient with a linear function that operates on the rates of processes executing inside it. The linear functions associated with ambients represent the delays that govern particular administrative domains. We derive performance measures from the labelled transition semantics as in standard models. We also define a strong Markov bisimulation in the style of reduction semantics known as barbed bisimulation. We argue that performance measures are of vital importance in designing any kind of distributed system, and that SMA can be useful in the design of the complicated mobile systems. 相似文献
2.
Iain Phillips Maria Grazia Vigliotti 《Electronic Notes in Theoretical Computer Science》2005,128(2):185
Palamidessi has shown that the π-calculus with mixed choice is powerful enough to solve the leader election problem on a symmetric ring of processes. We show that this is also possible in the calculus of Mobile Ambients (MA), without using communication or restriction. Following Palamidessi's methods, we deduce that there is no encoding satisfying certain conditions from MA into CCS. We also show that the calculus of Boxed Ambients is more expressive than its communication-free fragment. 相似文献
3.
《Theoretical computer science》2004,322(3):477-515
Pure mobile ambients is a process calculus suitable to focus on issues related to mobility, abstracting away from aspects concerning process communication. However, it incorporates name restriction (i.e. the (νn) binder) and ambient movement (i.e. the in and out capabilities) that can be seen as characteristics adapted, or directly borrowed, from the tradition of communication-based process calculi. For this reason, we retain that it is worth to investigate whether or not these features can be removed from pure mobile ambients without losing expressive power.To this aim, we consider two variants of pure mobile ambients which differ in the way infinite processes can be defined; the former exploits process replication, while the latter is more general and permits recursive process definition. We analyse whether or not the elimination of ambient movement and/or name restriction reduces the expressive power of these two calculi, using the decidability of process termination as a yardstick. We prove that name restriction can be removed from both calculi without reducing the expressive power. On the other hand, the elimination of both ambient movement and name restriction strictly reduces the expressive power of both calculi. As far as the elimination of only ambient movement is concerned, we prove an interesting discrimination result: process termination is undecidable under recursive process definition, while it turns out to be decidable under process replication. 相似文献
4.
In the Mobile Ambients of Cardelli and Gordon an ambient is a unit for mobility, which may contain processes (data) and sub-ambients. Since the seminal work of Cardelli and Gordon, several ambient-based calculi have been proposed (Seal, Box-π, Safe Ambients, Secure Safe Ambients, Boxed Ambients), mainly for supporting security. At the operational level these (box- and) ambient-based calculi differ only in the capabilities of processes. We propose a way of extending ambient-based calculi, which embodies two principles: an ambient is a unit for monitoring and coordination, the name of an ambient determines its (monitoring and coordination) policy. More specifically, to each ambient we attach a guardian, which monitors the activity of sub-components (i.e. processes and sub-ambients) and the interaction with the external environment. In our proposal, guardians and processes play a dual role: guardians are centralized entities monitoring and inhibiting actions, while processes are decentralized entities performing actions. We exemplify the use of guardians for enforcing security properties. 相似文献
5.
There are two players on the plane: an invader I with maximal speed v > 1 and a defender D with maximal speed 1. It is shown that the disk of radius rv(v − 1)−1 (where r denotes the ‘destruction radius’ of the defender) is the domain of largest area which can be guarded by the defender. 相似文献
6.
Beg M. Faisal Miller Michael I. Trouvé Alain Younes Laurent 《International Journal of Computer Vision》2005,61(2):139-157
This paper examine the Euler-Lagrange equations for the solution of the large deformation diffeomorphic metric mapping problem studied in Dupuis et al. (1998) and Trouvé (1995) in which two images I
0, I
1 are given and connected via the diffeomorphic change of coordinates I
0○ϕ−1=I
1 where ϕ=Φ1 is the end point at t= 1 of curve Φ
t
, t∈[0, 1] satisfying .Φ
t
=v
t (Φ
t
), t∈ [0,1] with Φ0=id. The variational problem takes the form
where ‖v
t‖
V
is an appropriate Sobolev norm on the velocity field v
t(·), and the second term enforces matching of the images with ‖·‖L
2 representing the squared-error norm.In this paper we derive the Euler-Lagrange equations characterizing the minimizing vector fields v
t, t∈[0, 1] assuming sufficient smoothness of the norm to guarantee existence of solutions in the space of diffeomorphisms. We describe the implementation of the Euler equations using semi-lagrangian method of computing particle flows and show the solutions for various examples. As well, we compute the metric distance on several anatomical configurations as measured by ∫0
1‖v
t‖
V
dt on the geodesic shortest paths. 相似文献
7.
Richard Rebarber 《Systems & Control Letters》1990,14(4)
Let A be a generator of a strongly continuous semigroup of operators, and assume that C and H are operators such that A + CH generates a strongly continuous semigroup SH(t) on X. Let λ0 be a real number in the resolvent set of A, and let ε [−1, 1]. Then there are some fairly unrestrictive conditions under which A+(λ0 − A)CH(λ0 − A)− also generates a strongly continuous semigroup SK(t) on X which has the same exponential growth rate as SH(t). Given an input operator B, we can use this to identify a class of feedback perturbations K such that A + BK generates a strongly continuous semigroup. We can also use this result to identify classes of feedbacks which can and cannot uniformly stabilize a system. For example, we show that if the control on a cantilever beam in the state space H02[0, 1] × L2[0, 1] is a moment force on the free end, then we cannot stabilize the beam with an A−1/2-bounded feedback, but we can find an A−1/4-bounded feedback, for any > 0, which does stabilize the beam. 相似文献
8.
The glassy carbon electrode (GCE) modified with Mo(CN)84−-incorporated-poly(4-vinylpyridine) (PVP/Mo(CN)84−), which has been recently shown to possess several attractive attributes as an efficient electrocatalytic electrode for l-ascorbic acid oxidation and its estimation, is used for l-ascorbic acid estimation directly in orange fruit juice and Celin tablet in a 0.1 M H2SO4 acid solution without any special treatment. Constant potential amperometry at 570 mV (saturated calomel electrode, SCE) in stirred solutions is used for this purpose. A good correlation is attained with the official titrametric method. To understand the possible electrocatalytic reaction mechanism for the electro-oxidation of l-ascorbic acid, calibration graphs over the range 1 × 10−5 to 1 × 10−2 mol dm−3 l-ascorbic acid are compared for the three electrodes, ca. PVP/Mo(CN)84−, undoped PVP, and GCE; the curvature at high ascorbic acid concentration for the PVP/Mo(CN)84− electrode is explained in terms of Michaelis–Menten (MM) saturation kinetics. The apparent MM constant (KM), the maximum catalytic current (iM), the complex decomposition rate constant (kc), and the heterogeneous modified electrode rate constant (k′ME) are calculated from three different approaches. A reasonably high value of ≈1 × 10−2 cm s−1 is obtained for k′ME, indicating efficient l-ascorbic acid mediation at the PVP/Mo(CN)84− electrode, thus accounting for quite a high sensitivity of this modified film electrode compared to several other modified electrodes. 相似文献
9.
Mikkel Bundgaard Thomas Hildebrandt 《Electronic Notes in Theoretical Computer Science》2006,154(2):7-29
Bigraphs have been introduced with the aim to provide a topographical meta-model for mobile, distributed agents that can manipulate their own linkages and nested locations, generalising both characteristics of the π-calculus and the Mobile Ambients calculus. We give the first bigraphical presentation of a non-linear, higher-order process calculus with nested locations, non-linear active process mobility, and local names, the calculus of Higher-Order Mobile Embedded Resources (Homer). The presentation is based on Milner's recent presentation of the λ-calculus in local bigraphs. The combination of non-linear active process mobility and local names requires a new definition of parametric reaction rules and a representation of the location of names. We suggest localised bigraphs as a generalisation of local bigraphs in which links can be further localised. 相似文献
10.
The Ambient Calculus offers many ways in which processes can interact and be observed. In the context of Levi and Sangiorgi's Safe Mobile Ambients (SA), the extra co-capabilities required for interaction complicate the fundamental observations. We show that different formulations of barbs lead to the same barbed congruence. We prove this by following Honda and Yoshida's approach for the π-calculus by defining the insensitive terms of SA. 相似文献
11.
In this paper the quasilinear heat equation with the nonlinear boundary condition is studied. The blow-up rate and existence of a self-similar solution are obtained. It is proved that the rescaled function
v(y,t)=(T−t)1/(2p+α−2)u((T−t)(p−1)/(2p+α−2)y,t),