Nonparametric Bayesian hazard rate models based on penalized splines

Extensions of the traditional Cox proportional hazard model, concerning the following features are often desirable in applications: Simultaneous nonparametric estimation of baseline hazard and usual fixed covariate effects, modelling and detection of time-varying covariate effects and nonlinear functional forms of metrical covariates, and inclusion of frailty components. In this paper, we develop Bayesian multiplicative hazard rate models for survival and event history data that can deal with these issues in a flexible and unified framework. Some simpler models, such as piecewise exponential models with a smoothed baseline hazard, are covered as special cases. Embedded in the counting process approach, nonparametric estimation of unknown nonlinear functional effects of time or covariates is based on Bayesian penalized splines. Inference is fully Bayesian and uses recent MCMC sampling schemes. Smoothing parameters are an integral part of the model and are estimated automatically. We investigate performance of our approach through simulation studies, and illustrate it with a real data application

A VHDL-based Modelling Approach for Rapid Functional Simulation and Verification of Adiabatic Circuits

Adiabatic logic is an energy-efficient technique, however, the time required in the design, validation and debugging increases manifold for large-scale adiabatic system designs. In this endeavor, we present a Hardware Description Language (HDL) based modelling approach for 4-phase adiabatic logic design. The paper highlights the drawbacks of the existing approaches and proposes a new approach that captures the timing errors and detects the circuit’s invalid operation due to mutually exclusive inputs being violated. We develop a model library containing the function of the four periods used in the trapezoidal power-clock and the adiabatic logic gates. The validation and verification of the proposed approach were done on the ISO-14443 standard benchmark circuit, a 16-bit Cyclic Redundancy Check (CRC) circuit. The system modelled using HDL shows the timing agreement with the transistor-level SPICE simulations. The novel use of the four periods of a power-clock improves the robustness and reliability for the design and verification of large adiabatic systems

Functional model-based design of embedded systems with UniTi

Advancing the field of embedded systems requires a rigorous approach to their design. This is because embedded systems are complex, diverse and challenging. Although many tools exist, none support the following four essential features: (i) the modelling of multiple domains, (ii) accurate inclusion of time, (iii) mathematical definitions, and (iv) model transformations. In addition, such a tool must underlie a sound design flow that adequately supports the complexity of designing embedded systems.\ud \ud In this thesis we propose a design flow and a modelling and simulation framework called UniTi that manages complexity in a top-down fashion; a problem is split up into sub-problems that are solved individually and then combined. This design flow and framework is based on model-based design, i.e. a single reference model is iteratively and incrementally developed and refined during the design process. Our approach is a functional approach, not only because it is practical and useful, but also because it has a mathematical basis supported by a functional language, i.e. computations are considered as evaluations of mathematical functions.\ud \ud In this work we specialise the design for the application domain of beamforming applications, for which we propose a generic platform. Two adaptive algorithms for tracking are developed in the context of this platform. A tiled reconfigurable architecture is used, as the tiles provide scalability and reconfigurability provides flexibility. The environment and analogue hardware are represented in the continuous time (CT) domain, while digital hardware is represented in the discrete time (DT) domain and software in the dataflow (DF) domain.\ud \ud We formally define the CT, DT, and DF domains for UniTi. It also supports exact time delays in the CT domain by representing signals as functions of time. Model components, represented as signal transformations, are composed using function composition instead of value-passing, with unified sequential, parallel and feedback composition by re-defining the dataflow model to match with CT and DT components and signals. As a consequence, mixed-domain models are executable for simulation. Finally, UniTi provides support for model transformations.\ud \ud The result of this work is a functional model-based design approach for designing, modelling, and simulation of embedded systems

Modelling and Simulation of Fluid Power Systems in ObjectOriented Programming Environment

ABSTRACT The paper deals with principles of computer modelling and simulation of behaviour of fluid power systems in object-oriented programming environment. The approach is based on using multi-pole models and signal-flow graphs of functional elements, that enables methodical, graphical representation of mathematical models of large and complicated chain systems. In this way we can be convinced in the correct composing of models. A high-level programming environment NUT is used as a tool for building modelling and simulation systems. Several modelling and simulation systems have been developed using approach described above. Different simulation tasks have been solved on these modelling systems. Methodology described in the paper has several advantages and novelties

From COTS Simulation Software to an Open-source Platform: A Use Case in the Medical Device Industry

AbstractThe implementation of Discrete Event Simulation (DES) – based decision support tools in complex manufacturing environments could prove of invaluable help to industrial practitioners involved in cross-functional decision processes at multiple hierarchical levels. The increasing number of decision variables, their stochastic nature and the non-linearity of their mutual relationships theoretically make simulation a preferred modelling approach for a great variety of manufacturing systems as strict simplifying assumptions are not necessarily required and the models’ detail level can be tuned according to the analysis purposes. However, recourse to Commercial Off-The-Shelf (COTS) simulation packages to develop and implement simulation-based solutions in real manufacturing environments usually presents significant cost-of-ownership (COO). Along with license costs, modelling flexibility and sustainability represent fundamental issues raised by industrial engineers that adopt COTS simulation packages. In order to promote the use of DES in production related decision making processes and reduce the associated COO for manufacturing companies, an open-source simulation platform, ManPy, has been developed. ManPy consists of a library of DES objects implemented in SimPy. ManPy's scope is to provide modellers with generic, highly customizable open-source simulation objects that can be connected to form a model in the same fashion of COTS simulation packages. ManPy's on-going development is based on guidelines provided by the analysis of real industrial use cases. Specific pilot models developed in SimPy are used to identify new objects and relevant features to be incorporated in ManPy in order to make it a highly flexible simulation tool. In this article, a use case based on a labour intensive serial production line operating in a medical device manufacturing plant is described. Insights for the transition from a COTS simulation model to a specific SimPy model and finally to generic ManPy objects are presented