Peter Andrew Mataga

Dynamic crack propagation in piezoelectric materials—Part I. Electrode solution

Abstract An analysis is performed for the transient response of a semi-infinite, anti-plane crack propagating in a hexagonal piezoelectric medium. The mixed boundary value problem is solved by transform methods together with the Wiener-Hopf and Cagniard-de Hoop techniques. As a special case, a closed form solution is obtained for constant speed crack propagation under external anti-plane shear loading with the conducting electrode type of electric boundary condition imposed on the crack surface (a second type of boundary condition is considered in Part II of this work). In purely elastic, transversely isotropic elastic solids, there is no antiplane mode surface wave. However, for certain orientations of piezoelectric materials, a surface wave will occur—the BleusteindashGulyaev wave. Since surface wave speeds strongly influence crack propagation, the nature of antiplane dynamic fracture in piezoelectric materials is fundamentally different from that in purely elastic solids, exhibiting many features only associated with the indashplane modes in the elastic case. For a general distribution of crack face tractions, the dynamic stress intensity factor and the dynamic electric displacement intensity factor are derived and discussed in detail for the electrode case. As for inplane elastodynamic fracture, the stress intensity factor and energy release rate go to zero as the crack propagation velocity approaches the surface wave speed. However, the electric displacement intensity does not vanish.

Dynamic crack propagation in piezoelectric materials-Part II. Vacuum solution

Abstract In Part I of this work, antiplane dynamic crack propagation in piezoelectric materials was studied under the condition that crack surfaces behaved as though covered with a conducting electrode. Piezoelectric surface wave phenomena were clearly seen to be critical to the behavior of the moving crack. Closed form results were obtained for stress and electric displacement intensities at the crack tip in the subsonic crack speed range; the major result is that the energy release rate vanishes as the crack speed approaches the surface (Bleustein-Gulyaev) wave speed. In this paper, an alternative assumption is made that between the growing crack surfaces there is a permeable vacuum free space, in which the electrostatic potential is nonzero. By coupling the piezoelectric equations of the solid phase with the electric charge equation in the vacuum region, a closed form solution is again obtained. In contrast to the electrode case of Part I, this case allows both applied charge and applied traction loading. In addition, the work of Part I is extended to examine piezoelectric crack propagation over the full velocity range of subsonic, transonic and supersonic speeds. Several aspects of the results are explored. The energy release rate in this case does not go to zero when the crack propagating velocity approaches the surface wave speed, even if there is only applied traction loading. When the crack exceeds the Bleustein-Gulyaev wave speed, the character of the crack-tip singularities of the physical fields depends on both speed regime and type of loading. At the other extreme, the quasi-static limit of the dynamic solution furnishes a set of new static solutions. The general permeability assumptions made here allow for fully coupled conditions that are ruled out by the a priori interfacial assumptions made in previously published solutions.

Sisl: Several Interfaces, Single Logic

Modern interactive services such as information and e-commerce services are becoming increasingly more flexible in the types of user interfaces they support. These interfaces incorporate automatic speech recognition and natural language understanding and include graphical user interfaces on the desktop and web-based interfaces using applets and HTML forms. To what extent can the user interface software be decoupled from the service logic software (the code that defines the essential function of a service)? Decoupling of user interface from service logic directly impacts the flexibility of services, or how easy they are to modify and extend.To explore these issues, we have developed Sisl, an architecture and domain-specific language for designing and implementing interactive services with multiple user interfaces. A key principle underlying Sisl is that all user interfaces to a service share the same service logic. Sisl provides a clean separation between the service logic and the software for a variety of interfaces, including Java applets, HTML pages, speech-based natural language dialogue, and telephone-based voice access. Sisl uses an event-based model of services that allows service providers to support interchangeable user interfaces (or add new ones) to a single consistent source of service logic and data.As part of a collaboration between research and development, Sisl is being used to prototype a new generation of call processing services for a Lucent Technologies switching product.

A framework for evaluating specification methods for reactive systems: experience report

Numerous formal specification methods for reactive systems have been proposed in the literature. Because the significant differences bet ween the methods are hard to determine, choosing the best method for a particular application can be difficult. We have applied several different methods, including Modechart, VFSM, ESTEREL, Basic LOTOS, Z, SDL and C, to an application problem encountered in the design of software for AT&Ts 5ESS® telephone switching system. We have developed a set of criteria for evaluating and comparing the different specification methods. We argue that the evaluation of a method must take into account not only academic concerns, but also the maturity of the method, its compatibility with the existing software development process and system execution environment, and its suitability for the chosen application domain.

Formal Specification of Telephone Features

A full formal specification of the external behavior of a realistic feature set for ISDN telephones is described. In addition to Plain Old Telephone Service, about ten of the most frequently used features of the 5ESS® switch are specified. The connections model deals with shared and multiple directory numbers and billing.

Speech-enabled services using TelePortal™ software and VoiceXML

TelePortal™ software, which resides on a speech-enabled telephony platform, brings the advantages of the World Wide Web to advanced speech recognition telephone services. In response to an incoming call, this software retrieves a dialogue specification document from a Web server, interprets it to collect input from a caller, and submits the input to a (possibly different) Web server, which processes the input and may continue the call by returning another dialogue specification document. The TelePortal architecture includes a browser (to retrieve and cache Web content), a set of interpreters (to process documents), and a set of platform interfaces (to allow the interpreters to control the speech and telephony resources of the host platform). Using the Web to retrieve dialogue documents and to process the input they collect creates a new business opportunity for network operators and third-party application developers. Interactive voice response (IVR) services, which may be made available from a standard wireline or wireless telephone, are easily programmed using the emerging Voice Extensible Markup Language (VoiceXML∗) standard. TelePortal software is being integrated into several Lucent platforms. We present examples of the new network IVR opportunities that this software provides for one of these — the platform of the intelligent network.

Using Z to specify telephone features

Abstract This paper gives a very brief overview of a formal specification of the behaviour of a set of about 10 realistic features for ISDN telephones. The full specification employs a multiparadigm technique in which partial specifications in different languages are composed, but the focus here is on the use of the Z notation to specify call processing and subscriber database aspects of telephone features. Our experiences with the approach, and with Z in particular, are discussed.

Formal Methods Through Domain Engineering

It is almost an article of faith among advocates of formai methods that the major benefits should be most evident for large, complex software systems — yet there are few examples of the use of formal specification and analysis techniques in such systems. This is in large part because of the lack of attention paid by the formal methods community to the technology transfer process and the realities of large software development.