We present the a-calculus, a calculus of communicating systems in which one can naturally express processes which have changing structure. Not only may the component agents of a system be arbitrarily linked, but a communication between neighbours may carry information which changes that linkage. The calculus is an extension of the process algebra CCS, following work by Engberg and Nielsen, who added mobility to CCS while preserving its algebraic properties. The rr-calculus gains simplicity by removing all distinction between variables and constants; communication links are identified by names, and computation is represented purely as the communication of names across links. After an illustrated description of how the n-calculus generalises conventional process algebras in treating mobility, several examples exploiting mobility are given in some detail. The important examples are the encoding into the n-calculus of higher-order functions (the I-calculus and combinatory algebra), the transmission of processes as values, and the representation of data structures as processes. The paper continues by presenting the algebraic theory of strong bisimilarity and strong equivalence, including a new notion of equivalence indexed by distinctions-i.e., assumptions of inequality among names. These theories are based upon a semantics in terms of a labeled transition system and a notion of strong bisimulation, both of which are expounded in detail in a companion paper. We also report briefly on work-in-progress based upon the corresponding notion of weak bisimulation, in which internal actions cannot be observed. 0 1992 Academic Press, Inc.

A calculus of mobile processes, II

Long viewed as a topic in classical physics, ferroelectricity can be described by a quantum mechanical ab initio theory. Thin-film nanoscale device structures integrated onto Si chips have made inroads into the semiconductor industry. Recent prototype applications include ultrafast switching, cheap room-temperature magnetic-field detectors, piezoelectric nanotubes for microfluidic systems, electrocaloric coolers for computers, phased-array radar, and three-dimensional trenched capacitors for dynamic random access memories. Terabit-per-square-inch ferroelectric arrays of lead zirconate titanate have been reported on Pt nanowire interconnects and nanorings with 5-nanometer diameters. Finally, electron emission from ferroelectrics yields cheap, high-power microwave devices and miniature x-ray and neutron sources.

http://science.sciencemag.org/content/sci/315/5814/954.full.pdf

Applications of Modern Ferroelectrics

Software architectures shift the focus of developers from lines-of-code to coarser-grained architectural elements and their overall interconnection structure. Architecture description languages (ADLs) have been proposed as modeling notations to support architecture-based development. There is, however, little consensus in the research community on what is an ADL, what aspects of an architecture should be modeled in an ADL, and which of several possible ADLs is best suited for a particular problem. Furthermore, the distinction is rarely made between ADLs on one hand and formal specification, module interconnection, simulation and programming languages on the other. This paper attempts to provide an answer to these questions. It motivates and presents a definition and a classification framework for ADLs. The utility of the definition is demonstrated by using it to differentiate ADLs from other modeling notations. The framework is used to classify and compare several existing ADLs, enabling us, in the process, to identify key properties of ADLs. The comparison highlights areas where existing ADLs provide extensive support and those in which they are deficient, suggesting a research agenda for the future.

/pdf/a-classification-and-comparison-framework-for-software-3so7xapmcq.pdf

A classification and comparison framework for software architecture description languages

This is the second of two papers in which we present the rc-calculus, a calculus of mobile processes. The companion paper (Milner, Parrow, and Walker, 1989a) contains an introduction to the calculus through a sequence of examples, together with statements of many results about it. The purpose of the present paper is to provide a detailed presentation of some of the theory of the calculus developed to date, and in particular to establish most of the results stated in the companion paper. Once the motivation and intuition for the n-calculus are understood, with the help of the companion paper, the present paper serves as a self-contained development of the theory. To achieve this we have found it necessary to repeat some material from the companion paper. Section 1 contains a description of the syntax of agents and a discursive presentation of the transitional semantics. In Section 2 we present and motivate the definitions of strong bisimulation and strong bisimilarity, strong equivalence, and a useful family of indexed equivalences. Section 3 contains a series of properties of strong bisimilarity, while properties of

A Calculus of Mobile Processes - Part II

From the Publisher:
Since the introduction of Hoares' Communicating Sequential Processes notation, powerful new tools have transformed CSP into a practical way of describing industrial-sized problems. This book gives you the fundamental grasp of CSP concepts you'll need to take advantage of those tools.Part I provides a detailed foundation for working with CSP, using as little mathematics as possible. It introduces the ideas behind operational, denotational and algebraic models of CSP. Parts II and III go into greater detail about theory and practice. Topics include: parallel operators, hiding and renaming, piping and enslavement, buffers and communication, termination and sequencing, and semantic theory. Three detailed practical case studies are also presented.For anyone interested in modeling sequential processes.

/pdf/the-theory-and-practice-of-concurrency-1kzi2sg7cs.pdf

The Theory and Practice of Concurrency

Transparent piezoelectrics are highly desirable for numerous hybrid ultrasound–optical devices ranging from photoacoustic imaging transducers to transparent actuators for haptic applications1–7. However, it is challenging to achieve high piezoelectricity and perfect transparency simultaneously because most high-performance piezoelectrics are ferroelectrics that contain high-density light-scattering domain walls. Here, through a combination of phase-field simulations and experiments, we demonstrate a relatively simple method of using an alternating-current electric field to engineer the domain structures of originally opaque rhombohedral Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) crystals to simultaneously generate near-perfect transparency, an ultrahigh piezoelectric coefficient d33 (greater than 2,100 picocoulombs per newton), an excellent electromechanical coupling factor k33 (about 94 per cent) and a large electro-optical coefficient γ33 (approximately 220 picometres per volt), which is far beyond the performance of the commonly used transparent ferroelectric crystal LiNbO3. We find that increasing the domain size leads to a higher d33 value for the [001]-oriented rhombohedral PMN-PT crystals, challenging the conventional wisdom that decreasing the domain size always results in higher piezoelectricity8–10. This work presents a paradigm for achieving high transparency and piezoelectricity by ferroelectric domain engineering, and we expect the transparent ferroelectric crystals reported here to provide a route to a wide range of hybrid device applications, such as medical imaging, self-energy-harvesting touch screens and invisible robotic devices. The use of alternating-current electric fields to control domain size in ferroelectric crystals affords excellent transparency, piezoelectricity and birefringence.

/pdf/transparent-ferroelectric-crystals-with-ultrahigh-jt7u0amv1l.pdf

Transparent ferroelectric crystals with ultrahigh piezoelectricity

The aqueous crystallization-driven sphere-to-rod transition of poly(lactide)-b-poly(acrylic acid), PLA-b-PAA block copolymers, with a short homochiral PLA core forming block and a 10 times longer (in terms of degree of polymerization) PAA corona forming block is presented. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) is utilized to follow the kinetics of the transition and wide angle X-ray diffraction (WAXD) to confirm the correlation between degree of crystallinity and morphology. Studies at different concentrations and solvent mixtures provide valuable information regarding the nucleation and growth mechanism of the system, showing that the micelle dynamics are a key aspect of the assembly process. Furthermore, the in situ crystallization-driven cylinder formation during the acrylate ester hydrolysis reaction is demonstrated. Finally, we report that the micelle morphology can be switched between cylinders and spheres by facilitating or blocking the crystallization of the core block, demonstrating a simple method to control the morphology of the resultant assembly.

Crystallization-driven sphere-to-rod transition of poly(lactide)-b-poly(acrylic acid) diblock copolymers: mechanism and kinetics

It has been well documented that single-crystal stable-temperature (ST)-cut quartz substrates can horizontally align single-walled carbon nanotubes (SWNTs) along the x direction ([100]) during catalyzed chemical vapor deposition. It has been suggested that alignment is due to either surface-guided growth along step edges and/or lattice directions, although recent atomic force microscopy (AFM) evidence suggests the latter is more appropriate [Liu, et al. J. Am. Chem. Soc. 2008, 130, 5428]. In light of this we explore the growth mechanism on single-crystal quartz in more detail, focusing particularly on the crystallography of the alignment surface and the effects of annealing treatments. X-ray diffraction (XRD) studies enable us to identify, for the first time, the crystallographic plane of ST-cut quartz as (0111), with a surface normal lying close to [121], which is 42.5° from the y axis ([010]). For this plane, formulation of both crystallographic orientation and polar diagrams, the latter which reveals ...

David Walker

Papers

A calculus of mobile processes, II

A Calculus of Mobile Processes - Part II

Transparent ferroelectric crystals with ultrahigh piezoelectricity

Crystallization-driven sphere-to-rod transition of poly(lactide)-b-poly(acrylic acid) diblock copolymers: mechanism and kinetics

Horizontal Alignment of Chemical Vapor-Deposited SWNTs on Single-Crystal Quartz Surfaces: Further Evidence for Epitaxial Alignment