Results 1  10
of
41
Modelling Concurrency with Partial Orders
, 1986
"... Concurrency has been expressed variously in terms of formal languages (typically via the shuffle operator), partial orders, and temporal logic, inter alia. In this paper we extract from these three approaches a single hybrid approach having a rich language that mixes algebra and logic and having a n ..."
Abstract

Cited by 257 (18 self)
 Add to MetaCart
Concurrency has been expressed variously in terms of formal languages (typically via the shuffle operator), partial orders, and temporal logic, inter alia. In this paper we extract from these three approaches a single hybrid approach having a rich language that mixes algebra and logic and having a natural class of models of concurrent processes. The heart of the approach is a notion of partial string derived from the view of a string as a linearly ordered multiset by relaxing the linearity constraint, thereby permitting partially ordered multisets or pomsets. Just as sets of strings form languages, so do sets of pomsets form processes. We introduce a number of operations useful for specifying concurrent processes and demonstrate their utility on some basic examples. Although none of the operations is particularly oriented to nets it is nevertheless possible to use them to express processes constructed as a net of subprocesses, and more generally as a system consisting of components. Th...
Geometric and physical interpretation of fractional integration and fractional differentiation”, Fractional Calculus and Applied Analysis, vol.5, number 4
, 2002
"... A solution to the more than 300years old problem of geometric and physical interpretation of fractional integration and differentiation (i.e., integration and differentiation of an arbitrary real order) is suggested for the RiemannLiouville fractional integration and differentiation, the Caputo fr ..."
Abstract

Cited by 53 (0 self)
 Add to MetaCart
(Show Context)
A solution to the more than 300years old problem of geometric and physical interpretation of fractional integration and differentiation (i.e., integration and differentiation of an arbitrary real order) is suggested for the RiemannLiouville fractional integration and differentiation, the Caputo fractional differentiation, the Riesz potential, and the Feller potential. It is also generalized for giving a new geometric and physical interpretation of more general convolution integrals of the Volterra type. Besides this, a new physical interpretation is suggested for the Stieltjes integral.
The Proper Treatment of Events
, 2004
"... this paper was developed by Murray Shanahan (building upon earlier work by Kowalski and Sergot [64]) in a series of papers [102], [101], [103] and [100]. Shanahan's discussion of the frame problem and his proposed solution can also be found in the book [104] ..."
Abstract

Cited by 51 (8 self)
 Add to MetaCart
this paper was developed by Murray Shanahan (building upon earlier work by Kowalski and Sergot [64]) in a series of papers [102], [101], [103] and [100]. Shanahan's discussion of the frame problem and his proposed solution can also be found in the book [104]
Timestamp Semantics and Representation
, 1992
"... this paper [Pavise 1982]. In order to simplify the present discussion we shall adopt the Gregorian calendar as our prototypical calendar. Calendar years are typically an integral number of days, yet there are not (currently) an integral number of days in any astronomically computed year. For example ..."
Abstract

Cited by 20 (14 self)
 Add to MetaCart
this paper [Pavise 1982]. In order to simplify the present discussion we shall adopt the Gregorian calendar as our prototypical calendar. Calendar years are typically an integral number of days, yet there are not (currently) an integral number of days in any astronomically computed year. For example, for the Gregorian calendar year 1985, the anomalistic year was 365:259; 641 ephemeris days, the tropical year was in the northern hemisphere's Spring and fast in its Fall; and unpredictable variations, probably caused by differing rates of rotation between the core and the mantle. The gradual slowing of the rate of rotation adds about 1.5 milliseconds to the length of a day (in comparison to other clocks) during a century. The length of a day could fluctuate by 4 milliseconds over the course of a decade due to the unpredictable variations. Finally, seasonal variations can cause changes on the order of 1.2 milliseconds in the length of a day during a year [Howse 1980]. Another factor to consider in making precise sidereal time measurements is polar wander . Polar wander is a slight circular wobble of the Earth around the North/South pole on the order of 8 meters a year. Polar wander shifts an observer's meridian by a fraction each day (recall that the observer's meridian is used to determine when the sidereal and solar days start). The size of the shift depends on the observer's latitude. The family of universal times attempts to correct for these variations. UT0 is the mean solar time for the prime meridian computed by direct astronomical observations. The prime meridian is the 0
An ActorBased Framework For RealTime Coordination
, 1997
"... Programming language research should be driven by the needs of specific application domains, such as realtime embedded systems, multimedia, distributed database management applications, etc. For instance, most often large realtime applications involve distributed and concurrently but asynchronous ..."
Abstract

Cited by 11 (1 self)
 Add to MetaCart
Programming language research should be driven by the needs of specific application domains, such as realtime embedded systems, multimedia, distributed database management applications, etc. For instance, most often large realtime applications involve distributed and concurrently but asynchronously operating devices. The correctness of the integrated systems depends not only on the correct operation of each individual device, but also on the correct coordination among these devices. Furthermore, the correctness of device operation and cooperation requires that both the underlying logical computation be correct and the computation satisfy some notion of quantitative timing requirements. This thesis is a case study for how a language should be designed to suit a specific application domain. Specifically, I have designed RTsynchronizers (Real Time Synchronizers), a highlevel programming language abstraction for specifying realtime coordination constraints between objects in a distrib...
Why the Quantum Must Yield to Gravity
"... After providing an extensive overview of the conceptual elements – such as Einstein’s ‘hole argument ’ – that underpin Penrose’s proposal for gravitationally induced quantum state reduction, the proposal is constructively criticised. Penrose has suggested a mechanism for objective reduction of quan ..."
Abstract

Cited by 9 (1 self)
 Add to MetaCart
(Show Context)
After providing an extensive overview of the conceptual elements – such as Einstein’s ‘hole argument ’ – that underpin Penrose’s proposal for gravitationally induced quantum state reduction, the proposal is constructively criticised. Penrose has suggested a mechanism for objective reduction of quantum states with postulated collapse time τ = ¯h/∆E, where ∆E is an illdefinedness in the gravitational selfenergy stemming from the profound conflict between the principles of superposition and general covariance. Here it is argued that, even if Penrose’s overall conceptual scheme for the breakdown of quantum mechanics is unreservedly accepted, his formula for the collapse time of superpositions reduces to τ → ∞ (∆E → 0) in the strictly Newtonian regime, which is the domain of his proposed experiment to corroborate the effect. A suggestion is made to rectify this situation. In particular, recognising the cogency of Penrose’s reasoning in the domain of full ‘quantum gravity’, it is demonstrated that an appropriate experiment which could in principle corroborate his argued ‘macroscopic ’ breakdown of superpositions is not the one involving nonrotating mass distributions as he has suggested, but a Leggetttype SQUID or BEC
Temporal Logic
 The Blackwell Guide to Philosophical Logic. Blackwell Philosophy Guides (2001
, 1998
"... this paper, section 3, is devoted to a fairly detailed exposition of Prior's basic tense logic; the aim of this is not only to introduce the readers to this particular system, but perhaps even more to acquaint them with the kind of questions that temporal logicians tend to ask. In the sections ..."
Abstract

Cited by 9 (0 self)
 Add to MetaCart
(Show Context)
this paper, section 3, is devoted to a fairly detailed exposition of Prior's basic tense logic; the aim of this is not only to introduce the readers to this particular system, but perhaps even more to acquaint them with the kind of questions that temporal logicians tend to ask. In the sections 4 and 5 we present some extensions and alternatives to this base system. In section 6 we sketch some developments that have taken place over the last ten years or so. Finally, in the epilogue we try to answer the question what Temporal Logic is; this section also contains a short list of monographs surveying the field of temporal logic. 2 Flows of time
MärzkeWheeler coordinates for accelerated observers in special relativity
, 2000
"... Abstract. In special relativity, the definition of coordinate systems adapted to generic accelerated observers is a longstanding problem, which has found unequivocal solutions only for the simplest motions. We show that the MärzkeWheeler construction, an extension of the Einstein synchronization c ..."
Abstract

Cited by 9 (0 self)
 Add to MetaCart
(Show Context)
Abstract. In special relativity, the definition of coordinate systems adapted to generic accelerated observers is a longstanding problem, which has found unequivocal solutions only for the simplest motions. We show that the MärzkeWheeler construction, an extension of the Einstein synchronization convention, produces accelerated systems of coordinates with desirable properties: (a) they reduce to Lorentz coordinates in a neighborhood of the observers ’ worldlines; (b) they index continuously and completely the causal envelope of the worldline (that is, the intersection of its causal past and its causal future: for wellbehaved worldlines, the entire spacetime). In particular, MärzkeWheeler coordinates provide a smooth and consistent foliation of the causal envelope of any accelerated observer into spacelike surfaces. We compare the MärzkeWheeler procedure with other definitions of accelerated coordinates; we examine it in the special case of stationary motions, and we provide explicit coordinate transformations for uniformly accelerated and uniformly rotating observers. Finally, we employ the notion of MärzkeWheeler simultaneity to clarify the relativistic paradox of the twins, by pinpointing the local origin of differential aging. 1.
Timing Analysis of Embedded RealTime Systems
 PhD thesis, UIUC technical reports UIUCDCSR992079 and UILUENG991702., Univ. of Illinois at UrbanaChampaign
, 1999
"... We address the problem of timing constraint derivation and validation for reactive and realtime embedded systems. We assume that such a system is structured into its tasks, and the structure is modeled using a task graph. Our solution uses the timing behavior committed by the environment to the sys ..."
Abstract

Cited by 7 (2 self)
 Add to MetaCart
(Show Context)
We address the problem of timing constraint derivation and validation for reactive and realtime embedded systems. We assume that such a system is structured into its tasks, and the structure is modeled using a task graph. Our solution uses the timing behavior committed by the environment to the system first to derive the timing constraints on the system's internal behavior and then use them to derive and validate the timing constraints on the system's external behavior. Our solution consists of the following contributions: (1) a generalized task graph model and a comprehensive classification of timing constraints, (2) algorithms for derivation and validation of timing constraints of the system modeled in the generalized task graph model, (3) new and improved algorithms for finding the performance of cyclic embedded systems and a comprehensive comparison of the existing algorithms, (4) a general formulation of the problem of debugging timing violations in cyclic embedded systems and it...
On the physical basis of cosmic time
, 805
"... In this manuscript we initiate a systematic examination of the physical basis for the time concept in cosmology. We discuss and defend the idea that the physical basis of the time concept is necessarily related to physical processes which could conceivably take place among the material constituents ..."
Abstract

Cited by 7 (2 self)
 Add to MetaCart
(Show Context)
In this manuscript we initiate a systematic examination of the physical basis for the time concept in cosmology. We discuss and defend the idea that the physical basis of the time concept is necessarily related to physical processes which could conceivably take place among the material constituents available in the universe. As a consequence we motivate the idea that one cannot, in a welldefined manner, speak about time ‘before ’ such physical processes were possible, and in particular, the idea that one cannot speak about a time scale ‘before ’ scalesetting physical processes were possible. It is common practice to link the concept of cosmic time with a spacetime metric set up to describe the universe at large scales, and then define a cosmic time t as what is measured by a comoving standard clock. We want to examine, however, the physical basis for setting up a comoving reference frame and, in particular, what could be meant by a standard clock. For this purpose we introduce the concept of a ‘core ’ of a clock (which, for a standard clock in cosmology, is a scalesetting