Design Flow Methodology for Radiation Hardened by Design CMOS Enclosed-Layout-Transistor-Based Standard-Cell Library

Ionizing radiation degrades the electrical characteristics of MOS devices, reducing their reliability, performance, and lifetime; therefore, hardening techniques are required for the proper functioning of those devices when exposed to harsh environments. Nonetheless, in the context of design flow automation, necessary to synthesize complex digital circuits, there is a lack of reliable foundry-provided Radiation Hardening by Design (RHBD) cell libraries. In this work, a complete RHBD flow methodology employing enclosed-layout transistors (ELTs) and guard rings, transparent to the designer, and fully compatible with commercial CAD tools and standard fabrication processes is presented. The proposed flow includes the automated calculation of the effective aspect ratio of the ELTs for annular and rectangular topologies, and a template proposal for digital cells, as well as series and parallel arrangements. Moreover, calculation of aspect ratio between pull-up and down networks and output buffers sizing using Logical Effort (LE) methodology, i.e., timing optimization accounting for typical commercial digital design constraints, is considered. Test structures, enclosing single n,pMOS devices, series and parallel arrangements, inverter cells, ring oscillators, and output buffers, were fabricated in two different technology nodes (600 nm and 180 nm). The experimental results were compared to SPICE simulations performed using the models here implemented. The results indicate that the flow methodology is feasible to implement and fully compatible with the CAD tools employed for circuit design. Besides, two case studies were first silicon-proven, presenting fully functional behavior under typical conditions.     

Cognitive Radio Networks: Analysis of a Paid-Sharing Approach Based on Admission Control Decisions

Cognitive radio networks have emerged in the last decade as a solution for two problems: spectrum underutilization and spectrum scarcity. The main idea is to manage the radio spectrum more efficiently, where secondary users (SUs) are allowed to exploit the spectrum holes in primary user’s (PUs) frequency bands. We consider a paid-sharing approach where SUs pay for spectrum utilization. A challenging aspect in these mechanisms is how to proceed when a PU needs certain amount of bandwidth and the free capacity is insufficient. We assume a preemptive system where PUs have strict priority over SUs; when a PU arrives to the system and there are not enough free channels to accommodate the new user, one or more SUs will be deallocated. The affected SUs will then be reimbursed, implying some cost for the PUs service provider (SP). This paper bears on the design and analysis of an optimal SU admission control policy; i.e. that maximizes the long-run profit of the SP. We model the optimal revenue problem as a Markov Decision Process and we use dynamic programming and further techniques such as sample-path analysis to characterize properties of the optimal admission control policy. We introduce different changes to one of the best known dynamic programming algorithms incorporating the knowledge of the characterization. In particular, those proposals accelerate the rate of convergence of the algorithm when is applied in the considered context. Our results are validated through numerical examples.     

Effects of a single dose of beetroot juice on cycling time trial performance at ventilatory thresholds intensity in male triathletes

Background

Beetroot juice (BJ) is classified as a high-level supplement for improving sports performance. There is some controversy over the benefits of BJ supplementation for endurance exercise performance, especially when referring to well-trained athletes. This study examines the effects of acute BJ supplementation on cardioventilatory responses, exercise economy/efficiency, slow component of oxygen uptake, time trial performance, blood lactate, energy consumption, and carbohydrate and fat oxidation.

Methods

Twelve well-trained, male triathletes (aged 21–47 yr) were assigned in a randomized, double-blind, crossover design to receive 70 ml of BJ (6.5 mmol NO₃^?) or placebo (PL). Three hours after taking the supplement, participants completed an endurance test on a cycle ergometer at a constant work rate (W) corresponding to first ventilatory threshold (VT1) (30 min) and second ventilatory threshold (VT2) time trial (~?15 min).

Results

Maximal oxygen uptake was 54.78?±?3.13 mL·min^??1·kg^??1, and gross efficiency was >?22% at each load intensity and experimental condition. No significant interaction effect (supplement*intensity) was observed on any of the cardioventilatory variables, efficiency/economy, VT2 time trial, energy expenditure, carbohydrate oxidation and fat oxidation (p?>?0.05).

Conclusion

Our findings do not support an improvement in the variables examined in response to acute BJ supplementation. Probably, higher doses are needed for improving time trial performance in male triathletes during a cycle ergometer test conducted at a load intensity equivalent to the first and second ventilatory threshold.

     

Percentage porosity computation of three-dimensional non-convex porous geometries using the direct Monte Carlo simulation

Engineering with Computers - The pursuit of more representative numerical models for open-cell metallic foams requires the computation of volume and percentage porosity of geometries containing...     

Strategy and algorithms for the parallel solution of the nearest neighborhood problem in shared-memory processors

The neighborhood problem appears in many applications of computational geometry, computational mechanics, etc. In all these situations, the main requirement for a competitive implementation is performance, which can only be attained in modern hardware by exploiting parallelism. However, whereas the performance of serial algorithms is fairly predictable, that of parallel methods depends on delicate issues that have a huge impact (cache memory, cache misses, memory alignment, etc.), but are not easy to control. Even if there is not a simple approach to deal with these factors in shared-memory architectures, it is quite convenient to program parallel algorithms where the data are segregated on a per-thread basis. With this objective in mind, we propose a strategy to develop parallel algorithms based on a two-level design, and apply it to efficiently solve the nearest neighborhood problem. At a higher level, the proposed methods orchestrate the parallel algorithm and split the space into cells stored in a hash table; at the lower level, our methods hold serial search algorithms that are completely agnostic to the high-level counterpart. Using this strategy, we have developed a library combining different serial and parallel algorithms, optimized them, and assessed their performance. The analysis carried out allows to better understand the main bottlenecks in the algorithmic solution of the nearest neighborhood problem and come out with very fast implementations that improve existing available software.

     

The conceptual framing,design and evaluation of device ecologies for collaborative activities

A variety of computing technologies, in addition to the personal computer, are now commonly used in many settings. As networking infrastructures mature, it is increasingly feasible and affordable to consider closer integration and use of these heterogeneous devices in tandem. However, little is known about how best to design or evaluate such ‘device ecologies’; in particular, how best to combine devices to achieve a desired type of collaborative user experience. A central concern is how users switch their attention between devices, to utilize the various elements to best effect. We describe here the development of an ecology of devices for groups of students to use when engaged in collaborative inquiry-learning activities. This included a multi-touch tabletop, laptops, projections, video streams and telephone. In situ studies of students and tutors using it in three different settings showed how individuals and groups switched their foci between the multiple devices. We present our findings, using a novel method for analysing users’ transitions between foci, identifying patterns and emergent characteristics. We then discuss the importance of designing for transitions that enable groups to appropriately utilise an ecology of devices, using the concepts of seams, bridges, niches and focal character.     

Silver nanoparticles from AgNO<Subscript>3</Subscript>–affinin complex synthesized by an ecofriendly route: chitosan-based electrospun composite production

A novel nanofibrous chitosan-based composite containing affinin and silver nanoparticles is obtained by electrospinning. Silver nanoparticles are synthesized by sunlight photoreduction of the metal complex [Ag₂–(affinin)](NO₃)₂ in polymeric solution, via a green one-pot methodology, wherein chitosan and affinin act as reducing, dispersing and stabilizing agent.     

Novel cluster partitioning models for visible light communication networks

Photonic Network Communications - In this paper, we consider the problem of clustering nodes in a wireless visible light communication (VLC) network while simultaneously forming a spanning tree...     

A dynamical system perspective on mathematical programming

We explore how to build a vector field from the various functions involved in a given mathematical programme, and show that equilibria of the corresponding dynamical system are precisely the solutions of the underlying optimality conditions for the original optimization problem. The general situation in which explicit inequality constraints are present is especially interesting as the vector field has to be discontinuous, and so one is led to consider discontinuous dynamical systems and their equilibria.