Sub-Wavelength Profile 2-D Leaky-Wave Antennas With Two Periodic Layers

A fast and accurate analysis and synthesis technique for high-gain sub-wavelength 2-D Fabry-Perot leaky-wave antennas (LWA) consisting of two periodic metallodielectric arrays over a ground plane is presented. Full-wave method of moments (MoM) together with reciprocity is employed for the estimation of the near fields upon plane wave illumination and the extraction of the radiation patterns of the LWA. This yields a fast and rigorous tool for the characterisation of this type of antennas. A thorough convergence study for different antenna designs is presented and the operation principles of these antennas as well as the radiation characteristics are discussed. Moreover, design guidelines to tailor the antenna profile, the dimensions of the arrays as well as the antenna directivity and bandwidth are provided. A study on the radiation efficiency for antennas with different profiles is also presented and the trade off between directivity and radiation bandwidth is discussed. Numerical examples are given throughout to demonstrate the technique. A finite size antenna model is simulated using commercial software (CST Microstripes 2009) which validates the technique.

Impact of gate-source/drain channel architecture on the performance of an operational transconductance amplifier (OTA)

In this work, we report on the significance of gate-source/drain extension region (also known as underlap design) optimization in double gate (DG) FETs to improve the performance of an operational transconductance amplifier (OTA). It is demonstrated that high values of intrinsic voltage gain (A(VO_OTA)) > 55 dB and unity gain frequency (f(T_OTA)) similar to 57 GHz in a folded cascode OTA can be achieved with gate-underlap channel design in 60 nm DG MOSFETs. These values correspond to 15 dB improvement in A(VO_OTA) and three fold enhancement in f(T_OTA) over a conventional non-underlap design. OTA performance based on underlap single gate SOI MOSFETs realized in ultra-thin body (UTB) and ultra-thin body BOX (UTBB) technologies is also evaluated. A(VO_OTA) values exhibited by a DG MOSFET-based OTA are 1.3-1.6 times higher as compared to a conventional UTB/UTBB single gate OTA. f(T_OTA) values for DG OTA are 10 GHz higher for UTB OTAs whereas a twofold improvement is observed with respect to UTBB OTAs. The simultaneous improvement in A(VO_OTA) and f(T_OTA) highlights the usefulness of underlap channel architecture in improving gain-bandwidth trade-off in analog circuit design. Underlap channel OTAs demonstrate high degree of tolerance to misalignment/oversize between front and back gates without compromising the performance, thus relaxing crucial process/technology-dependent parameters to achieve 'idealized' DG MOSFETs. Results show that underlap OTAs designed with a spacer-to-straggle (s/sigma) ratio of 3.2 and operated below a bias current (IBIAS) of 80 mu A demonstrate optimum performance. The present work provides new opportunities for realizing future ultra-wide band OTA design with underlap DG MOSFETs.

Near-field enhancement for infrared sensor applications

A detailed investigation on planar two dimensional metallodielectric dipole arrays with enhanced near-fields for sensing applications was carried out. Two approaches for enhancing the near-fields and increasing the quality factor were studied. The reactive power stored in the vicinity of the array at resonance increases rapidly with increasing periodicity. Higher quality factors are produced as a result. The excitation of the odd mode in the presence of a perturbation gives rise to a sharp resonance with near-field enhanced by at least an order of magnitude compared to unperturbed arrays. The trade-off between near-field enhancement and thermal losses was also studied, and the effect of supporting dielectric layers on thermal losses and quality factors were examined. Secondary transmissions due to the dielectric alone were found to enhance and reduce cyclically the quality factor as a function of the thickness of the dielectric material. The performance of a perturbed frequency selective surface in sensing nearby materials was investigated. Finally, unperturbed and perturbed arrays working at infrared frequencies were demonstrated experimentally. (C) 2011 Society of Photo-Optical Instrumentation Engineers (SPIE). [DOI: 10.1117/1.3604785]

Dynamic Linear Precoding for the Exploitation of Known Interference in MIMO Broadcast Systems

This paper introduces a novel channel inversion (CI) precoding scheme for the downlink of phase shift keying (PSK)-based multiple input multiple output (MIMO) systems. In contrast to common practice where knowledge of the interference is used to eliminate it, the main idea proposed here is to use this knowledge to glean benefit from the interference. It will be shown that the system performance can be enhanced by exploiting some of the existent inter-channel interference (ICI). This is achieved by applying partial channel inversion such that the constructive part of ICI is preserved and exploited while the destructive part is eliminated by means of CI precoding. By doing so, the effective signal to interference-plus-noise ratio (SINR) delivered to the mobile unit (MU) receivers is enhanced without the need to invest additional transmitted signal power at the MIMO base station (BS). It is shown that the trade-off to this benefit is a minor increase in the complexity of the BS processing. The presented theoretical analysis and simulations demonstrate that due to the SINR enhancement, significant performance and throughput gains are offered by the proposed MIMO precoding technique compared to its conventional counterparts.

Mixed radix Reed-Muller expansions

The choice of radix is crucial for multi-valued logic synthesis. Practical examples, however, reveal that it is not always possible to find the optimal radix when taking into consideration actual physical parameters of multi-valued operations. In other words, each radix has its advantages and disadvantages. Our proposal is to synthesise logic in different radices, so it may benefit from their combination. The theory presented in this paper is based on Reed-Muller expansions over Galois field arithmetic. The work aims to firstly estimate the potential of the new approach and to secondly analyse its impact on circuit parameters down to the level of physical gates. The presented theory has been applied to real-life examples focusing on cryptographic circuits where Galois Fields find frequent application. The benchmark results show the approach creates a new dimension for the trade-off between circuit parameters and provides information on how the implemented functions are related to different radices.

Fairness Metrics for Multi-Threaded Processors

Multi-threaded processors execute multiple threads concurrently in order to increase overall throughput. It is well documented that multi-threading affects per-thread performance but, more importantly, some threads are affected more than others. This is especially troublesome for multi-programmed workloads. Fairness metrics measure whether all threads are affected equally. However defining equal treatment is not straightforward. Several fairness metrics for multi-threaded processors have been utilized in the literature, although there does not seem to be a consensus on what metric does the best job of measuring fairness. This paper reviews the prevalent fairness metrics and analyzes their main properties. Each metric strikes a different trade-off between fairness in the strict sense and throughput. We categorize the metrics with respect to this property. Based on experimental data for SMT processors, we suggest using the minimum fairness metric in order to balance fairness and throughput.

Fetch Gating Control through Speculative Instruction Window Weighting

In a dynamic reordering superscalar processor, the front-end fetches instructions and places them in the issue queue. Instructions are then issued by the back-end execution core. Till recently, the front-end was designed to maximize performance without considering energy consumption. The front-end fetches instructions as fast as it can until it is stalled by a filled issue queue or some other blocking structure. This approach wastes energy: (i) speculative execution causes many wrong-path instructions to be fetched and executed, and (ii) back-end execution rate is usually less than its peak rate, but front-end structures are dimensioned to sustained peak performance. Dynamically reducing the front-end instruction rate and the active size of front-end structure (e.g. issue queue) is a required performance-energy trade-off. Techniques proposed in the literature attack only one of these effects.
In previous work, we have proposed Speculative Instruction Window Weighting (SIWW) [21], a fetch gating technique that allows to address both fetch gating and instruction issue queue dynamic sizing. SIWW computes a global weight on the set of inflight instructions. This weight depends on the number and types of inflight instructions (non-branches, high confidence or low confidence branches, ...). The front-end instruction rate can be continuously adapted based on this weight. This paper extends the analysis of SIWW performed in previous work. It shows that SIWW performs better than previously proposed fetch gating techniques and that SIWW allows to dynamically adapt the size of the active instruction queue.

Security scanning at 94GHz - art. no. 62110C

It is well known that millimetre waves can pass through clothing. In short range applications such as in the scanning of people for security purposes, operating at W band can be an advantage. The size of the equipment is decreased when compared to operation at Ka band and the equipments have similar performance.

In this paper a W band mechanically scanned imager designed for imaging weapons and contraband hidden under clothing is discussed. This imager is based on a modified folded conical scan technology previously reported. In this design an additional optical element is added to give a Cassegrain configuration in image space. This increases the effective focal length and enables improved sampling of the image and provides more space for the receivers. This imager is constructed from low cost materials such as polystyrene, polythene and printed circuit board materials. The trade off between image spatial resolution and thermal sensitivity is discussed.

Animal group forces resulting from predator avoidance and competition minimization

A new model to explain animal spacing, based on a trade-off between foraging efficiency and predation risk, is derived from biological principles. The model is able to explain not only the general tendency for animal groups to form, but some of the attributes of real groups. These include the independence of mean animal spacing from group population, the observed variation of animal spacing with resource availability and also with the probability of predation, and the decline in group stability with group size. The appearance of "neutral zones" within which animals are not motivated to adjust their relative positions is also explained. The model assumes that animals try to minimize a cost potential combining the loss of intake rate due to foraging interference and the risk from exposure to predators. The cost potential describes a hypothetical field giving rise to apparent attractive and repulsive forces between animals. Biologically based functions are given for the decline in interference cost and increase in the cost of predation risk with increasing animal separation. Predation risk is calculated from the probabilities of predator attack and predator detection as they vary with distance. Using example functions for these probabilities and foraging interference, we calculate the minimum cost potential for regular lattice arrangements of animals before generalizing to finite-sized groups and random arrangements of animals, showing optimal geometries in each case and describing how potentials vary with animal spacing. (C) 1999 Academic Press.</p>

Real-life Social Attention in Children with Autism Spectrum Disorders

Autism is a neuro-developmental disorder defined by atypical social behaviour, of which atypical social attention behaviours are among the earliest clinical markers (Volkmar et al., 1997). Eye tracking studies using still images and movie clips have provided a method for the precise quantification of atypical social attention in ASD. This is generally characterised by diminished viewing of the most socially pertinent regions (eyes), and increased viewing of less socially informative regions (body, background, objects) (Klin et al., 2002; Riby & Hancock, 2008, 2009). Ecological validity within eye tracking studies has become an increasingly important issue. As of yet, however, little is known about the precise nature of the atypicalities of social attention in ASD in real-life. Objectives: To capture and quantify gaze patterns for children with an ASD within a real life setting, compared to two Typically Developing (TD) comparison groups. Methods: Nine children with an ASD were compared to two age matched TD groups – a verbal (N=9) and a non-verbal (N=9) comparison group. A real-life scenario was created involving an experimenter posing as a magician, and consisted of 3 segments: a conversation segment; a magic trick segment; and a puppet segment. The first segment explored children’s attentional preferences during a real-life conversation; the magic trick segment explored children’s use of the eyes as a communicative cue, and the puppet segment explored attention capture. Finally, part of the puppet section explored children’s use of facial information in response to an unexpected event. Results: The most striking difference between the groups was the diminished viewing of the eyes by the ASD group in comparison to both control groups. This was found particularly during the conversation segment, but also during the magic trick segment, and during the puppet segment. When in conversation, participants with ASD were found to spend a greater proportion time looking off-screen, in comparison to TD participants. There was also a tendency for the ASD group to spend a greater proportion of time looking to the mouth of the experimenter. During the magic trick segment, despite the fact that the eyes were not predictive of a correct location, both TD comparison groups continued to use the eyes as a communicative cue, whereas the ASD group did not. In the puppet segment, all three groups spent a similar amount of time looking between the puppet and regions of the experimenter’s face. However, in response to an unexpected event, the ASD group were significantly slower to fixate back on the experimenter’s face. Conclusions: The results demonstrate the reduced salience of socially pertinent information for children with ASD in real life, and they provide support for the findings from previous eye tracking studies involving scene viewing. However, the results also highlight a pattern looking off-screen for both the TD and ASD groups. This eye movement behaviour is likely to be associated specifically with real-life interaction, as it has functional relevance (Doherty-Sneddon et al., 2002). However, the fact that it is significantly increased in the ASD group has implications for their understanding of real life social interactions.

Freshwater pearl mussels show plasticity of responses to different predation risks but also show consistent individual differences in responsiveness

Animals often show behavioural plasticity with respect to predation risk but also show behavioural syndromes in terms of consistency of responses to different stimuli. We examine these features in the freshwater pearl mussel. These bivalves often aggregate presumably to reduce predation risk to each individual. Predation risk, however, will be higher in the presence of predator cues. Here we use dimming light, vibration and touch as novel stimuli to examine the trade-off between motivation to feed and motivation to avoid predation. We present two experiments that each use three sequential novel stimuli to cause the mussels to close their valves and hence cease feeding. We find that mussels within a group showed shorter closure times than solitary mussels, consistent with decreased vulnerability to predation in group-living individuals. Mussels exposed to the odour of a predatory crayfish showed longer closures than control mussels, highlighting the predator assessment abilities of this species. However, individuals showed significant consistency in their closure responses across the trial series, in line with behavioural syndrome theory. Our results show that bivalves trade-off feeding and predator avoidance according to predation risk but the degree to which this is achieved is constrained by behavioural consistency. © 2011 Elsevier B.V.

Advantages and limitations of navigation-based multicriteria optimization (MCO) for localized prostate cancer IMRT planning

Efficacy of inverse planning is becoming increasingly important for advanced radiotherapy techniques. This study's aims were to validate multicriteria optimization (MCO) in RayStation (v2.4, RaySearch Laboratories, Sweden) against standard intensity-modulated radiation therapy (IMRT) optimization in Oncentra (v4.1, Nucletron BV, the Netherlands) and characterize dose differences due to conversion of navigated MCO plans into deliverable multileaf collimator apertures. Step-and-shoot IMRT plans were created for 10 patients with localized prostate cancer using both standard optimization and MCO. Acceptable standard IMRT plans with minimal average rectal dose were chosen for comparison with deliverable MCO plans. The trade-off was, for the MCO plans, managed through a user interface that permits continuous navigation between fluence-based plans. Navigated MCO plans were made deliverable at incremental steps along a trajectory between maximal target homogeneity and maximal rectal sparing. Dosimetric differences between navigated and deliverable MCO plans were also quantified. MCO plans, chosen as acceptable under navigated and deliverable conditions resulted in similar rectal sparing compared with standard optimization (33.7 ± 1.8Gy vs 35.5 ± 4.2Gy, p = 0.117). The dose differences between navigated and deliverable MCO plans increased as higher priority was placed on rectal avoidance. If the best possible deliverable MCO was chosen, a significant reduction in rectal dose was observed in comparison with standard optimization (30.6 ± 1.4Gy vs 35.5 ± 4.2Gy, p = 0.047). Improvements were, however, to some extent, at the expense of less conformal dose distributions, which resulted in significantly higher doses to the bladder for 2 of the 3 tolerance levels. In conclusion, similar IMRT plans can be created for patients with prostate cancer using MCO compared with standard optimization. Limitations exist within MCO regarding conversion of navigated plans to deliverable apertures, particularly for plans that emphasize avoidance of critical structures. Minimizing these differences would result in better quality treatments for patients with prostate cancer who were treated with radiotherapy using MCO plans.

Integrating allowable design strains in composites with whole life value

Fibre-Reinforced Plastics (FRPs) have been used in civil aerospace vehicles for decades. The current state-of-the-art in airframe design and manufacture results in approximately half the airframe mass attributable to FRP materials. The continual increase in the use of FRP materials over metallic alloys is attributable to the material's superior specific strength and stiffness, fatigue performance and corrosion resistance. However, the full potential of these materials has yet to be exploited as analysis methods to predict physical failure with equal accuracy and robustness are not yet available. The result is a conservative approach to design, but one that can bring benefit via increased inspection intervals and reduced cost over the vehicle life. The challenge is that the methods used in practice are based on empirical tests and real relationships and drivers are difficult to see in this complex process and so the trade-off decision is challenging and uncertain. The aim of this feasibility study was to scope a viable process which could help develop some rules and relationships based on the fundamental mechanics of composite material and the economics of production and operation, which would enhance understanding of the role and impact of design allowables across the life of a composite structure.

Model checking support for conflict resolution in multiple non-functional concern management

When implementing autonomic management of multiple non-functional concerns a trade-off must be found between the ability to develop independently management of the individual concerns (following the separation of concerns principle) and the detection and resolution of conflicts that may arise when combining the independently developed management code. Here we discuss strategies to establish this trade-off and introduce a model checking based methodology aimed at simplifying the discovery and handling of conflicts arising from deployment-within the same parallel application-of independently developed management policies. Preliminary results are shown demonstrating the feasibility of the approach.

Monte Carlo calculations of quantum yield in inhomogeneous PtSi/p-Si Schottky barriers

Monte Carlo calculations of quantum yield in PtSi/p-Si infrared detectors are carried out taking into account the presence of a spatially distributed barrier potential. In the 1-4 mu m wavelength range it is found that the spatial inhomogeneity of the barrier has no significant effect on the overall device photoresponse. However, above lambda = 4.0 mu m and particularly as the cut-off wavelength (lambda approximate to 5.5 mu m) is approached, these calculations reveal a difference between the homogeneous and inhomogeneous barrier photoresponse which becomes increasingly significant and exceeds 50% at lambda = 5.3 mu m. It is, in fact, the inhomogeneous barrier which displays an increased photoyield, a feature that is confirmed by approximate analytical calculations assuming a symmetric Gaussian spatial distribution of the barrier. Furthermore, the importance of the silicide layer thickness in optimizing device efficiency is underlined as a trade-off between maximizing light absorption in the silicide layer and optimizing the internal yield. The results presented here address important features which determine the photoyield of PtSi/Si Schottky diodes at energies below the Si absorption edge and just above the Schottky barrier height in particular.