The computational status of physics

According to the Church-Turing Thesis (CTT), effective formal behaviours can be simulated by Turing machines; this has naturally led to speculation that physical systems can also be simulated computationally. But is this wider claim true, or do behaviours exist which are strictly hypercomputational? Several idealised computational models are known which suggest the possibility of hypercomputation, some Newtonian, some based on cosmology, some on quantum theory. While these models’ physicality is debatable, they nonetheless throw into question the validity of extending CTT to include all physical systems. We consider the physicality of hypercomputational behaviour from first principles, by showing that quantum theory can be reformulated in a way that explains why physical behaviours can be regarded as ‘computing something’ in the standard computational state-machine sense. While this does not rule out the physicality of hypercomputation, it strongly limits the forms it can take. Our model also has physical consequences; in particular, the continuity of motion and arrow of time become theorems within the basic model.     

Fuzzy symmetries of point ensembles

The fuzzy symmetry concept developed by us for planar forms (using a Fourier analysis of the form's contour function R(ϕ), [1]) is applied to ensembles of points. We calculate misfit values Δ (inversely proportional to the degree of symmetry) for a form (point ensemble) with respect to arbitrary transformations or even whole symmetry groups. On this basis, symmetry properties of forms lying on a surface within a suitably chosen form space can be illustrated by a misfit landscape. Likewise, a form transition can be characterized by the misfit profile along its trajectory in such a form space. These misfit profiles or landscapes can visualize and quantify hidden symmetry properties of forms.     

Future scientific programming on parallel machines

A language for large scientific applications should facilitate encoding and debugging of programs at the highest level possible. At the same time it should facilitate generation of efficient code for parallel machines. Often these two requirements are conflicting, and trade-offs must be made. Functional and other declarative languages offer relief on both counts. The use of higher-order functions, especially in carried forms, can raise the level of programming dramatically. In addition, such languages often have straightforward operational semantics, thereby providing tremendous opportunities for parallel execution. Programs written in declarative languages thus eliminate the problem of “detecting parallelism.” This paper illustrates programming in one such language, Id Nouveau, and contrasts it with programming in Fortran. Using an excerpt from an application known as Simple, it is shown how a program can be composed in Id Nouveau from small functions that directly relate to the mathematical and physical concepts of the problem. The difficulty of expressing these concepts in Fortran is discussed. Finally, it is shown that by performing simple transformations, such as in-line substitution of functions, the resulting Id Nouveau code becomes as efficient as an equivalent Fortran program written to run efficiently on a parallel machine.     

Eliminating unscalable communication in transaction processing

Multicore hardware demands software parallelism. Transaction processing workloads typically exhibit high concurrency, and, thus, provide ample opportunities for parallel execution. Unfortunately, because of the characteristics of the application, transaction processing systems must moderate and coordinate communication between independent agents; since it is notoriously difficult to implement high performing transaction processing systems that incur no communication whatsoever. As a result, transaction processing systems cannot always convert abundant, even embarrassing, request-level parallelism into execution parallelism due to communication bottlenecks. Transaction processing system designers must therefore find ways to achieve scalability while still allowing communication to occur. To this end, we identify three forms of communication in the system—unbounded, fixed, and cooperative—and argue that only the first type poses a fundamental threat to scalability. The other two types tend not impose obstacles to scalability, though they may reduce single-thread performance. We argue that proper analysis of communication patterns in any software system is a powerful tool for improving the system’s scalability. Then, we present and evaluate under a common framework techniques that attack significant sources of unbounded communication during transaction processing and sketch a solution for those that remain. The solutions we present affect fundamental services of any transaction processing engine, such as locking, logging, physical page accesses, and buffer pool frame accesses. They either reduce such communication through caching, downgrade it to a less-threatening type, or eliminate it completely through system design. We find that the later technique, revisiting the transaction processing architecture, is the most effective. The final design cuts unbounded communication by roughly an order of magnitude compared with the baseline, while exhibiting better scalability on multicore machines.     

The contraction of control implementations

The implementation of a high level language which provides higher control forms such as concurrency and coroutines along with the more traditional recursive procedures is obligated to support all control forms in a reasonably efficient manner. In particular, the implementation of a general purpose language (such as Simula or Ada) should contract gracefully into a scheme incurring overhead approximately the same amount as a simple stack when presented with programs which employ control forms no more general than recursive procedures. This study is a quantitative investigation into the contraction of implementations capable of supporting higher control forms into an environment in which recursive procedures are the most complex control form. A technique called the stack-heap is shown to contract most fully.     

Virtual “Third Places”: A Case Study of Sociability in Massively Multiplayer Games

Georg Simmel [American Journal of Sociology 55:254–261 (1949)] is widely credited as the first scholar to have seriously examined sociability – “the sheer pleasure of the company of others” and the central ingredient in many social forms of recreation and play. Later Ray Oldenburg [The Great Good Place. New York: Marlowe & Company (1989)] extended Simmel’s work by focusing on a certain class of public settings, or “third places,” in which sociability tends to occur, such as, bars, coffee shops, general stores, etc. But while Simmel and Oldenburg describe activities and public spaces in the physical world, their concepts may apply as well to virtual or online worlds. Today Massively Multiplayer Online Games (MMOGs) are extensive, persistent online 3D environments that are populated by hundreds of thousands of players at any given moment. The sociable nature of these online spaces is often used to explain their success: unlike previous video games, MMOGs require players to exchange information and collaborate in real-time to progress in the game. In order to shed light on this issue, we critically examine player-to-player interactions in a popular MMOG (Star Wars Galaxies). Based on several months of ethnographic observations and computerized data collection, we use Oldenburg’s notion of “third places” to evaluate whether or not the social spaces of this virtual world fit existing definitions of sociable environments. We discuss the role online games can play in the formation and maintenance of social capital, what they can teach us about the evolution of sociability in an increasingly digitally connected social world, and what could be done to make such games better social spaces.     

Exploring the viability of walk-sharing in outdoor urban spaces

Pedestrians, while walking alone, feel unsafe and vulnerable in certain outdoor spaces at certain times of the day. This fear of victimisation often leads pedestrians to avail costlier alternatives, such as taking viable detours or abandoning walking altogether and switching to alternative forms of transport. This fear reduces the appeal of walking, the most basic transport mode, and one that is essential for preserving our physical and mental health. In this study, we introduce walk-sharing, a hypothetical buddy-service, which is aimed at encouraging people to choose walking when it is viable, and not pursue alternative modes. In walk-sharing, a potential pedestrian will get matched to another so that they are able to walk together, instead of walking alone, and thus overcome any potential fear that arises out of seemingly unsafe walking environments. To understand whether walk-sharing can be beneficial for the community, this study will outline its core concepts and explore its viability under different plausible scenarios. We use agent-based modelling techniques under synthetic and realistic scenarios to understand the conditions in which walk-sharing will produce acceptable outcomes.     

Enhancing online forms: Use format specifications for fields with format restrictions to help respondents

Field format restrictions are often used in online forms to impose certain formatting and content rules on users, such as minimum password length or date entry format. In this study, the question whether and how format restrictions for fields in online forms should be communicated to Internet users was explored. In an online study with n = 166 participants, four ways to communicate format restrictions were investigated: (1) no visual format restriction, (2) format examples, (3) format specifications, and (4) both format restrictions (examples and specifications). Results show that providing details of any format restriction to users in advance leads to significantly fewer errors and trials. The most efficient way to communicate field format restrictions to users is by stating the imposed rule (format specification). Providing an additional example neither helps nor constrains users.     

CoCONet: A collision-free container-based core optical network

Electrical-to-optical domain conversions and vice versa (denoted by O/E/O conversions) for each hop in optical core transport networks impose considerable capital and financial overhead on the providers. In this paper, we propose a full-mesh topology driven core network with a central scheduler that handles the task of signaling and coordination among slot transmissions for every hop to eliminate such O/E/O conversions. We introduce the concept of a container as a macro data unit that forms a separate layer in the protocol stack above the optical layer. A FAST centralized scheduling algorithm is proposed based on a preemptive scheduling technique that can ensure that there are no collisions between the containers. We also analyze the complexity of this algorithm. Next we design the logical architecture for the core and edge switches following the de facto policy of moving the complexity to the edge. We also designed a hierarchical architecture for the edge switch and provide the respective block diagrams. To get a more concrete design prototype, we further proposed a generic (vendor independent) physical architecture for a single port of the switch considering SONET/SDH on the access side. Moreover, we develop a concise delay model for the containers to analyze the packet arrival process and derive the optimal container size, based on the link speed. Finally, we present some simulation results to study the performance of the algorithms and models proposed in our work.     

Digital twins for collaborative robots: A case study in human-robot interaction

Human-robot collaboration (HRC) can expand the level of automation in areas that have conventionally been difficult to automate such as assembly. However, the need of adaptability and the dynamics of human presence are keeping the full potential of human-robot collaborative systems difficult to achieve. This paper explores the opportunities of using a digital twin to address the complexity of collaborative production systems through an industrial case and a demonstrator. A digital twin, as a virtual counterpart of a physical human-robot assembly system, is built as a ‘front-runner’ for validation and control throughout its design, build and operation. The forms of digital twins along system's life cycle, its building blocks and the potential advantages are presented and discussed. Recommendations for future research and practice in the use of digital twins in the field of cobotics are given.     

A physical hash for preventing and detecting cyber-physical attacks in additive manufacturing systems

Cyber-physical security is a major concern in the modern environment of digital manufacturing, wherein a cyber-attack has the potential to result in the production of defective parts, theft of IP, or damage to infrastructure or the operator have become a real threat that have the potential to create bad parts. Current cyber only solutions are insufficient due to the nature of manufacturing environments where it may not be feasible or even possible to upgrade physical equipment to the most current cyber security standards, necessitating an approach that addresses both the cyber and the physical components. This paper proposes a new method for detecting malicious cyber-physical attacks on additive manufacturing (AM) systems. The method makes use of a physical hash, which links digital data to the manufactured part via a disconnected side-channel measurement system. The disconnection ensures that if the network and/or AM system becomes compromised, the manufacturer can still rely on the measurement system for attack detection. The physical hash ensures protection of the intellectual property (IP) associated with both process and toolpath parameters while also enabling in situ quality assurance. In this paper, the physical hash takes the form of a QR code that contains a hash string of the nominal process parameters and toolpath. It is manufactured alongside the original geometry for the measurement system to scan and compare to the readings from its sensor suite. By taking measurements in situ, the measurement system can detect in real-time if the part being manufactured matches the designer’s specification.In this paper, the overall concept and underlying algorithm of the physical hash is presented. A proof-of-concept validation is realized on a material extrusion AM machine, to demonstrate the ability of a physical hash and in situ monitoring to detect the existence (and absence) of malicious attacks on the STL file, the printing process parameters, and the printing toolpath.     

On the numerical condition of algebraic curves and surfaces 1. Implicit equations

The numerical stability of algebraic curves and surfaces represented by implicit equations is investigated. The condition number at a point of a curve or surface is defined as the ratio of the maximum normal displacement of that point to the relative magnitude ϵ of the random perturbations in the curve or surface coefficients, in the limit ϵ → 0. Closed-form expressions for such condition numbers are presented, and the singular points of implicitly defined curves and surfaces are shown to be inherently ill-conditioned. Condition numbers for curve and surface intersections may be expressed in terms of those of the participant entities at the given point and certain geometric factors determined by the normal directions there. Tangential intersections are also seen to be inherently ill-conditioned. The dependence of condition numbers on the chosen multivariate polynomial basis is then examined. In particular, we compare power expansions about a given center, barycentric Bernstein bases over simplicial domains, and tensor-product Bernstein bases over rectangular domains. Configurations are enumerated in which one of these bases provides better conditioning than another at each point of every curve or surface in a given domain. The subdivision and degree elevation of multivariate Bernstein forms (barycentric or tensor-product) exhibit such behavior.     

Conditional extremals

Imagine that measurements are made at times t ₀ and t ₁ of the trajectory of a physical system whose governing laws are given approximately by a class ${{\mathcal A}}$ of so-called prior vector fields. Because the physical laws are not known precisely, the measurements might not be realised by the integral curve of any prior field. We want to estimate the behaviour of the physical system between times t ₀ and t ₁. This is done by solving a variational problem, yielding so-called conditional extrema which satisfy an Euler?CLagrange equation. Then conservative prior fields on simply-connected Riemannian manifolds are characterised in terms of their conditional extrema. For specific prior fields on space forms, conditional extrema are obtained in terms of the Weierstrass elliptic function. Another class of examples comes from left-invariant prior fields on bi-invariant Lie groups, whose conditional extrema are shown to be right translations of pointwise-products of 1-parameter subgroups.     

Supporting diagrammatic knowledge acquisition: an ontological analysis of Cartesian graphs

Cartesian graphs constitute an important class of knowledge representation devices. As part of a project on diagrammatic knowledge acquisition we have formulated principles that can underpin the construction, interpretation and use of Cartesian graphs in general and in the specific context of knowledge acquisition. Cartesian graphs are distinguished from other forms of representations by the manner in which they use two-dimensional space to encode quantities on interval or ratio scales. An ontological approach to the analysis of graphs was adopted in which a framework for mapping between the EngMath ontology for engineering mathematics and an ontology of visual components of graphs was developed, the GraphRep framework. GraphRep considers the roles of physical dimensions, measurement units, scales of measurement, functional relations amongst quantities and magnitudes in the generation and interpretation of graphs. It provides a topology of standard graphs and rules for the construction of composite graphs. The utility of the framework is demonstrated by using it: (1) to explain why a particular type of complex composite graph is often used for problem solving in thermodynamics; (2) to analyse the limitations of existing software packages for visualizing data, such as spreadsheets, and to suggest the improvements in their design; and (3) to provide constraints and guidelines for the design of procedures and software to support diagrammatic knowledge acquisition with Cartesian graphs.     

Instrumenting Wireless Sensor Networks — A survey on the metrics that matter

Wireless Sensor Networks (WSN) are part of the technical fundament enabling the ‘Internet of Things’ (IoT), where sensing and actuator nodes instantaneously interact with the environment at large. As such they become part of everyday life and drive applications as diverse as medical monitoring, smart homes, smart environment, and smart factories, to name but a few. To acquire data, individual sensors interact with the physical environment by sensing physical phenomena in proximity. The wireless network connectivity is leveraged to collect the raw data or pre-processed events, and to disseminate code, queries or commands. Actuating capabilities facilitate instant interactions with the environment or application processes. Experience on how to operate large scale heterogeneous WSNs in (critical) real-world applications is still scarce, and operational considerations are often an afterthought to WSN deployment. A principled look into the metrics, i.e., a standard or best practice of measurement of the ‘vital’ parameters in WSNs is still missing. In this article, we contribute a survey on the most important metrics to characterize the performance of WSNs. We define an abstract system model for WSNs, take a look on what the WSN community considers ‘metrics that matter’, and categorize the metrics into scopes of relevance. We discuss the properties of the metrics as well as practical aspects on how to obtain and process them. Our survey can serve as a ‘manual’ for implementors and operators of WSNs in the IoT.     

Quality of physical activity of children in exergames: Sequential body movement analysis and its implications for interaction design

Exergames are videogames based on full-body interaction that foster physical exercise during gameplay. Much research has focused on whether exergames foster sufficient physical activity and with which intensity they do so. This is usually measured through energy expenditure and compared to traditional physical activities such as sports or physical education exercises. However, little research has been undertaken on the quality of the physical activity, understood not as how well the movement is done, but as the richness and diversity of physical activity defined by experts, such as diverse types of motor skills (jumps, turns, pivots, manipulative actions, etc) and diverse types of conditioning capabilities (endurance, stretch, general strength, coordination, etc.). Hence, exergames typically address only aerobic (cardiovascular) activity and other types tend to be ignored. In this paper we propose a method for analyzing the types of physical activity (quality) that an exertion interface elicits. We propose this method as an analytical tool which can provide key information to categorize exergames, aid to their design and help designers make sure they achieve game mechanics that elicit the desired types of physical activity. We describe the method through the analysis of two exergames that we developed in the past for our exertion interface for children, called the Interactive Slide. We present the results of a systematic observational method, until now used mainly in sports analysis, which is based on applying sequential body movement analysis to obtain the play characteristics of 48 children. These results -action events and time-based patterns- typify the movement found in the two aforementioned exergames for this platform. We have found significant movement differences between the two, as well as some differences associated to age. Moreover, we show that sequential body movement analysis, which has already been successfully used in the past to analyze sports, can also be effective in analyzing exergames and hence allow grounded discussion on health issues related to their use.     

An Algorithm for Computing a New Normal Form for Dynamical Systems

We propose in this paper a new normal form for dynamical systems or vector fields which improves the classical normal forms in the sense that it is a further reduction of the classical normal forms. We give an algorithm for an effective computation of these normal forms. Our approach is rational in the sense that if the coefficients of the system are in a field K(which, in practice, is Q, R), so is the normal form and all computations are done inK . As a particular case, if the matrix of the linear part is a companion matrix then we reduce the dynamical system to a single differential equation. Our method is applicable for both the nilpotent and the non-nilpotent cases. We have implemented our algorithm in Maple V and obtained many examples of the further reduced normal forms up to some finite order.     

Easy-to-use authoring system for Noh (Japanese traditional) dance animation and its evaluation

Noh is a genre of Japanese traditional theater, a kind of musical drama. Similar to other dance forms, Noh dance (shimai) can also be divided into small, discrete units of motion (shosa). Therefore, if we have a set of motion clips of motion units (shosa), we can synthesize Noh dance animation by composing them in a sequence based on the Noh dance notation (katatsuke). However, it is difficult for researchers and learners of Noh dance to utilize existing animation systems to create such animations. The purpose of this research is to develop an easy-to-use authoring system for Noh dance animation. In this paper, we introduce the design, implementation, and evaluation of our system. To solve the problems of existing animation systems, we employ our smart motion synthesis technique to compose motion units automatically. We improved the motion synthesis method by enhancing the algorithms for detecting body orientation and constraints between the foot and ground to handle Noh dance motions correctly. We classify motion units as either pattern units, which are specific forms of motion, represented as shot motion clips, or locomotion units, generated on the fly to denote movement towards a specific position or direction. To handle locomotion-type motion units, we implemented a module to generate walking motion based on a given path. We created several Noh dance animations using this system, which was evaluated through a series of experiments. We also conducted a user test to determine the usefulness of our system for learners of Noh dance.