13888487
Hierarchical finite state machines with multiple concurrency models
This paper studies the semantics of hierarchical finite state machines (FSM's) that are composed using various concurrency models, particularly dataflow, discrete-events, and synchronous/reactive modeling. It is argued that all three combinations are useful, and that the concurrency model can be selected independently of the decision to use hierarchical FSM's. In contrast, most formalisms that combine FSM's with concurrency models, such as statecharts (and its variants) and hybrid systems, tightly integrate the FSM semantics with the concurrency semantics. An implementation that supports three combinations is described.
858750
Operational Semantics of Hybrid Systems
Hybrid systems are heterogeneous systems that include continuous-time (CT) subsystems interacting with discrete-event (DE) subsystems. They are effective models for physical systems interacting with software or experiencing discrete mode changes. 
This dissertation discusses an interpretation of hybrid systems as executable programs written in a programming language with a hybrid system semantics. The semantic properties of such a programming language affect our ability to understand, execute, and analyze a hybrid system model. This dissertation focuses on a few semantic issues that come in defining such a programming language, such as the interpretation of discontinuities in CT signals and simultaneous discrete events in DE signals, liveness property, and the consequences of numerical ODE solver techniques. 
The interactions between CT and DE subsystems and between DE subsystems themselves are captured by discontinuities in continuous-time signals and simultaneous discrete events in discrete-event signals. In order to precisely represent them in compute execution results, a two-dimension domain, called "super-dense time," is used as the domain for defining signals. This domain allows a signal to have multiple values at the same time point while keeping the values ordered. 
CT and DE subsystems are modeled as actors, which are functions that map a set of signals to another set of signals. In this way, a hybrid system model is just a network of actors interacting via signals. We can always transform a network of actors into a composite actor with feedback, where the function of the composition actor is the composition of functions of the component actors. The least fixed point solution to the function of the composite actor, which is a set of signals, gives the denotational semantics of the hybrid system model. 
The operational semantics takes the denotational semantics as a mathematical foundation and defines a set of rules for evaluating actors such that the least fixed point solution can be constructed. Rather than constructing the whole signals, the operational semantics only computes a discrete subset of the signals called a discrete representation of the signals. The constructive procedure is formalized with the Abstract State Machine semantics, where a hybrid system is treated as a state transition system and the rules specify how state transformations are performed. 
This operational semantics supports heterogeneous and hierarchical composition of different models of computation, such as CT, DE, finite state machines, and synchronous languages, and modular execution of the composition as a whole. This ability makes it easy to jointly model and design software controlled systems. 
The operational semantics proposed in this dissertation has been implemented in HyVisual, which is a software tool for modeling and simulating hybrid systems. HyVisual is part of the Ptolemy II software framework, which is available in open-source form at http://ptolemy.org.
36039309
Consistency in Dataflow Graphs
Analytical properties of programming languages with dataflow graph semantics are discussed. It is shown that one of the most serious problems with these languages is that subtle inconsistencies between parts of the dataflow graph can be inadvertently created. These inconsistencies can lead to deadlock, or in the case of nonterminating programs, to unbounded memory requirements. Consistency is defined to mean that the same number of tokens is consumed as produced on any arc, in the long run. A token-flow model is developed for testing for inconsistency. The method is a generalization of consistency checks for synchronous dataflow (SDF) graphs. The token-flow model is compared to similar tests applied to hybrid dynamical systems. It is argued that dataflow semantics make steady-state analysis possible, leading to a simpler method in most cases. >
5648139
The problem with threads
For concurrent programming to become mainstream, we must discard threads as a programming model. Nondeterminism should be judiciously and carefully introduced where needed, and it should be explicit in programs. In general-purpose software engineering practice, we have reached a point where one approach to concurrent programming dominates all others namely, threads, sequential processes that share memory. They represent a key concurrency model supported by modern computers, programming languages, and operating systems. In scientific computing, where performance requirements have long demanded concurrent programming, data-parallel language extensions and message-passing libraries such as PVM, MPI, and OpenMP dominate over threads for concurrent programming. Computer architectures intended for scientific computing often differ significantly from so-called general-purpose architectures.
36370882
Multi-agent Based Hybrid System for Dynamic Web-Content Adaptation
Context-aware adaptation service is rapidly becoming an important issue. This service overcomes the limitations of wireless devices and maintains adequate service levels in changing environments. The majority of existing studies concentrate on adaptation modules on the client, proxy, or server. These existing studies thus suffer from the problem of having the workload concentrated on a single system. This means that increasing the number of users increases the response time of a user’s request. In this paper, the adaptation module is dispersed and arranged over the client, proxy, and server. The module monitors the context of each system and creates a dispersed adaptation system, optimized for efficient operation. Through this method, faster adaptation work is made possible, even when the number of users increases, and the dividing workload makes more stable system operation possible. In order to evaluate the proposed system, a prototype is constructed and dispersed operations are tested using multimedia content, simulating server overload and comparing the response times and system stability with existing server based adaptation systems. The effectiveness of the system is confirmed through the results.
821388
Subvarieties of the Variety Generated by the Five-element Brandt Semigroup
All subvarieties of the variety B2 generated by the five-element Brandt semigroup are characterized. Based on this characterization, an algorithm is provided that decides if a finite set of identities defines, within B2, a finitely generated subvariety.
19038002
Computational Experience of an Interior-Point Algorithm in a Parallel Branch-and-Cut Framework
An interior-point algorithm within a branch-and-bound framework for solving nonlinear mixed integer programs is described. In contrast to solving the relaxation to optimality at each tree node, the relaxation is only solved to near-optimality. Analogous to using advanced bases for warmstart solutions in the case of linear MIP, a \dynamic" collection of warmstart vectors is kept. Computational results on various classes of nonlinear mixed integer programs are presented.
7621577
Towards a quantitative analysis of audio scrolling interfaces
We present the results of a user study inspired by previous work in document navigation comparing rate and position control for navigating an audio timeline. Although interfaces for controlling playback speed (rate) are favored over playback position, we found that position control is, on average, 15-19% faster than rate control when searching for targets 90 to 100 seconds away in the audio timeline. Additional studies are being planned to further characterize audio scrolling performance with position and rate controls.
7551391
The Role of Time in Engineering Computer Music Systems
Discussion of time in interactive computer music systems engineering has been largely limited to data acquisition rates and latency. Since music is an inherently time-based medium, we believe that time plays a more important role in both the usability and implementation of these systems. In this paper, we present a time design space, which we use to expose some of the challenges of developing computer music systems with time-based interaction. We describe and analyze the time-related issues we encountered whilst designing and building a series of interactive music exhibits that fall into this design space. These issues often occur because of the varying and sometimes conflicting conceptual models of time in the three domains of user, application (music), and engineering. We present some of our latest work in conducting gesture interpretation and frameworks for digital audio, which attempt to analyze and address these conflicts in temporal conceptual models.