Why you can't build an arbiter

Caption title.Includes bibliographical references (p. 9-11).Supported by the Army Research Office and the Center for Intelligent Control Systems. DAAL03-92-G-0164 DAAL03-92-G-0115Michael S. Branicky

On the unavoidability of metastable behaviour. (Computing science notes

Abstract The unavoidability of metastable behaviour in digital circuit-components like flipflops, arbiters and synchronisers is based on the assumption that the point representing such systems in phase space follows a trajectory which depends continuously on initial conditions. The validity of this assumption is well-established for existing implementations, and claimed for all implementations that are possible according to the classical laws of physics. In this paper we argue that the validity of the continuity assumption for quantum mechanical systems is an open question

Hardware synthesis for asynchronous communications mechanisms

Asynchronous data communication mechanisms (ACMs) have been extensively studied as data connectors between independently timed concurrent processes. In this work an automatic method for synthesis of re-reading ACMs is introduced. This method is is oriented to the generation of hardware artifacts. The behavior of re-reading ACMs is formally defined and the correctness properties are discussed. Then it is shown how to generate the ACMs specifications and how they can be translated into a proper hardware implementation. Verilog has been used as the target language to describe the hardware being synthesized.Peer ReviewedPostprint (published version

Store-and-forward CDC packet transmission in digital systems

Data transmission across clock domains is a major point of interest by ASIC designers as a limited bandwidth can be responsible for a processing power bottleneck that affects the entire system. Clock domain crossing is inherently expensive in terms of area and latency as it requires overcoming issues related to the physical nature of integrated circuit latches, in particular metastability. These issues are dangerous as they do not manifest in RTL simulation. Due to this, designers often opt for generic data synchronisation solutions that are not fully suited to the nature of the data being transferred.This dissertation presents a clock domain crossing mechanism that allows two clock domains to share a common memory to transfer packet-based data. The mechanism consists in a memory controller that coordinates commands from a push (write) domain and a pop (read) domain.The main objective of the memory controller project consists in the implementation of efficient synchronisation methods in order to eliminate the need for separate synchronisation and storage memories. In essence, the controller is an extension of an asynchronous FIFO controller with added functionality, supporting multiple virtual FIFOs and variable length data packets

A theory of delay-insensitive systems

xiii+134hlm.;24c

Forty years of antiprotons

The discovery of the antiproton some 40 years ago and the almost synchronous fall of parity (P) and charge conjugation (C) symmetries were soon followed by the realization that CPT rather than C invariance is the fundamental symmetry connecting matter and antimatter, and that consequently any measurement of the antiproton ' s properties can be interpreted as a test of that symmetry. It is the latter view of the antiproton, as an object of study in its own right, rather than as a means to such other ends as the production of gauge bosons and meson resonances, that is presented here. The authors review the technical steps that have led from the handful of antiprotons observed by Chamberlain, Segre, Wiegand, and Ypsilantis to the intense, high-quality beams available today and show how the state of rest and isolation required for high precision high-quality beams available today and show how the state of rest and isolation required for high precision measurements of their properties can be achieved by confining them in electromagnetic traps or in their microscopic counterparts, exotic atoms. The test bench role of antiprotons and antihydrogen atoms for both CPT symmetry and the gravitational weak equivalence principle is discussed, and the body of experimental results obtained since 1955 critically reviewed from this standpoint. Future experiments are then discussed in the light of the closure of the CERN Low Energy Antiproton Ring (LEAR), its replacement in 1999 by the Antiproton Decelerator (AD), and the likely antiproton source at the Japan Hadron Facility

Tune-out measurement in lukewarm lithium with phase-patterned atom interferometry

Atom interferometry deploys atoms as sensors, delivering precision measurements that span the gamut of physics. Laser-cooled samples simplify uniform detection strategies and allow meticulous control over degrees of freedom and systematic effects. Advanced cooling and interferometry techniques do apply readily to a few atomic species, but they leave behind a large class of species otherwise suited for precision sensing. This thesis describes atom interferometry with a sample of lukewarm $^7$Li, near the Doppler temperature. High thermal speeds demand rapid atom optics and complicate detection. We nevertheless develop interferometer techniques that considerably relax cooling requirements, including a recoil-sensitive scheme capable of measuring the fine-structure constant that takes advantage of $^7$Li's low mass. We also establish a phase-patterning protocol to inscribe and sense spatially-varying phases with matter-wave interferometers whose sample sizes exceed the arm separation. Phase patterning forms the basis of the first precision measurement of $^7$Li's red tune-out wavelength, the wavelength where AC Stark shifts from the $D$-line transitions cancel and the polarizability vanishes. Our measurement registers a 3-$\sigma$ tension with \emph{ab initio} atomic theory regarding the tensor-shifted tune-out wavelength and a 2-$\sigma$ tension regarding the size of the tensor shift, but agrees with theory regarding the scalar tune-out wavelength. These results motivate further work on lithium's polarizability, enable direct measurements of hyperpolarizability, and empower an assortment of future applications of phase patterning in matter-wave interferometry

Speculations

From the Editorial Introduction: "Since I am convinced that nobody reads editorials I will keep my remarks brief. Putting together the inaugural issue of Speculations has been an unusual experience. It has depended on the collusion of fellow speculative types, the help of many anonymous reviewers, the endless patience of designer Thomas Gokey, and more hours than someone in the final year of their PhD should ever spend on a project. Looking over the final product I think it has all been worth it. This is the first journal dedicated to speculative realism and despite the obscurity of that term I think we all understand it as a handy label under which weird realists, continental metaphysicians, object oriented ontologists, transcendental realists, vitalists, and Lovecraftians can unite. This is also, perhaps, the first time a journal can boast that each contributor is also a blogger. This is the reason why Speculations could only ever be an online, open-access journal. …

Towards an uncausal practice of visual communication

This practice-based PhD introduces the concept of uncausality as both method and methodology to uncover potentialities for action and thought beyond habitual patterns of causality and experience. The concept derives from an investigation of asemic writing’s paradoxical dynamic, also referred to as ‘asemic effect’. Asemic writing’s formal and gestural resemblance to conventional writing evokes expectations of legibility and semantic meaning. At the same time, any effort to retrieve meaning remains unsuccessful. The asemic effect is detached from its immediate context and explored to offer a dynamic that is divergent from the ‘causal pleasure’ of human-computer interaction. The direct and predictable causality between human action and computer reaction not only appeals to, but also consolidates the human being in their position as the all-knowing agent in the face of an increasingly complex world. This thesis critiques the emphasis on pleasure, power and control that confines human thought and action to the comfortable, protected realm of the already known, hindering any venture into the unknown. The concept of uncausality taps into the potential of an encounter with the unknown, the nonsensical and the dissonant. The contemporary condition that asks humans to revaluate their habitual ways of being underlines the urgency for such an exploration. While this research originates from a practice of visual communication with a focus on interactive type design, it follows a transdisciplinary methodology, after Guattari, to weave a heterogeneous net of connections across disciplines and modes of research. It draws on the philosophical explorations of Deleuze and Guattari, their own sources and thinkers who followed them. This research engages in a practice and process of programming visually abstract real-time human-computer interfaces to explore, test and expand on the concept of uncausality. The iterative nature of the process of programming becomes an entry point to create, and encounter, a continuous mutation of the relation between cause and effect, action and reaction. The practice, conscious of the symbiotic relationship between culture and technology, explores an approach to interactivity that maintains human action and thought in a state of physical and intellectual tension. Introducing the concept of uncausality, this research hopes to invigorate practices that keep the human mind elastic in a confrontation with a changing world