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We propose a new, principled approach to adaptive heap sizing based on control theory. We review current state-of-the-art heap sizing mechanisms, as deployed in Jikes RVM and HotSpot. We then formulate heap sizing as a control problem, apply and tune a standard controller algorithm, and evaluate its performance on a set of well-known benchmarks. We find our controller adapts the heap size more responsively than existing mechanisms. This responsiveness allows tighter virtual machine memory footprints while preserving target application throughput, which is ideal for both embedded and utility computing domains. In short, we argue that formal, systematic approaches to memory management should be replacing ad-hoc heuristics as the discipline matures.

The Terahertz (THz) frequency band has traditionally been of interest for the past 30 years in astronomy. However, recent advancements in technology in this band have sparked interest in other applications such as security. The THz frequency band is specially suited to this task, given that it has the penetration aspects of higher frequencies without the harmful ionizing effects. Although the area of airport security systems has seen new developments in hardware and commercial products, it is still largely underdeveloped in terms of efficient software. There are two potential considerations for efficiency in this area: personal privacy and detection speed. Both are addressed in our research.

Special approaches unique to the waveband are required for the modelling of terahertz optical systems. Ray tracing is inadequate because in typical instruments the propagating beams are not very many wavelengths in diameter and a "quasi-optical" approach is required in which Fresnel diffraction effects can be efficiently and accurately simulated. Typically, it is also necessary to be able to simulate the coupling of quasi-optical beams to feed antenna structures to predict optical performance. In many systems the beams can be considered to be coherent and their propagation through a beam guide consisting of re-focussing elements can be efficiently modelled using modal analysis, especially useful for quick design purposes, beam control and optimisation. This modal approach has been extended to allow for aberrations and truncation particularly relevant in compact mirror based systems. At the same time physical optics, although computationally intensive, is also a useful tool when detailed analysis is required, particularly for providing crosspolarisation information and high accuracy far-field beam patterns from large reflecting antennas, for example. However, modal analysis in general is a very powerful tool, which enables one also to understand issues associated with throughput when partially coherent systems are being considered. This is important for the efficient optical modelling of large arrays systems now being developed for next generation astronomical instrumentation. In the presentation, we will discuss these issues and present examples from real instrumentation. We also summarise our continuing work on the development of computationally efficient modelling tools for fast quasi-optical design and analysis.

We report on efficient CAD software (MODAL) that we are developing to specifically model long wavelength systems. Beam mode analysis which includes both aberration and truncation scattering using fast SVD methods allows sufficiently accurate and computationally highly efficient representations of a propagating beam for real time design feedback purposes.

The aim of long wavelength analysis is to understand the unique behaviour of terahertz (300 (iHz - 30 THz) quasi- optical s)stems, and since most THz systems have small Fresnel numbers, a modal approach to analysis is appropriate. In this paper in particular we discuss the extension of a powerful approach based on Singular Value Decomposition (SVD) [1] fir improving the efficiency of the application of Gaussian Beam Mode Analysis ((iBMA) to complex optical systems. We compare the efficiency of the SVD approach with the overlap integral approach, and also validate the technique by comparison with test cases computed using physical optics code. This work was inspired by the need for efficient numerical schemes as part of the development of a soft-ware package for quasi-optical analysis and design of terahertz systems at NUT Maynooth (MODAL).

Optical design in the terahertz (THz) waveband suffers from a lack of dedicated software tools for modelling the range of electromagnetic and quasi-optical propagation conditions encountered in typical systems. Optical engineers are forced to use packages written for very different wavelength systems and there is often a lack of confidence in the results because of possible inappropriate underlying physical models. In this paper we describe the analytical techniques and dedicated CAD software tools (MODAL1) that we are developing for long-wavelength design and analysis in the THz waveband. Our basic approach to modelling long-wavelength propagation is the application of modal analysis appropriate to the problem under investigation2,3. We have extended this to include the efficient description of common off-axis (tilted) components such as simple curved reflectors4. In earlier research we have investigated the conditions under which approximate methods (ray tracing, paraxial modes) can provide extremely efficient and accurate solutions and situations where a more rigorous approach is required5,6. As a rigorous model of electromagnetic wave propagation, physical optics can be used to characterize complete systems to high accuracy. However, the straightforward approach is computationally intensive and, therefore, not suitable for the initial design or preliminary analysis of large multi-element optical systems. In order to improve the computational efficiency of the usual PO approach we have developed fast physical optics software, initially for the analysis of the ESA PLANCK system7. The MODAL code is modular and multi-platform, and different propagation models can be used within the same framework. Distributed parallel computing enables significant reduction of the time needed to perform the calculations. We present the new software and analyses of the QuaD8 and Herschel (HIFI)9 telescope systems.