The generalised discrete algebraic Riccati equation in linear-quadratic optimal control

This paper investigates the properties of the solutions of the generalised discrete algebraic Riccati equation arising from the classic infinite-horizon linear quadratic (LQ) control problem. In particular, a geometric analysis is used to study the relationship existing between the solutions of the generalised Riccati equation and the output-nulling subspaces of the underlying system and the corresponding reachability subspaces. This analysis reveals the presence of a subspace that plays an important role in the solution of the related optimal control problem, which is reflected in the generalised eigenstructure of the corresponding extended symplectic pencil. In establishing the main results of this paper, several ancillary problems on the discrete Lyapunov equation and spectral factorisation are also addressed and solved.     

Analytical and graphical design of lead–lag compensators

In this article an approach based on inversion formulae is used for the design of lead–lag compensators which satisfy frequency domain specifications on phase margin, gain margin and phase (or gain) crossover frequency. An analytical and graphical procedure for the compensator design on the Nyquist and Nichols planes is presented with some numerical examples.     

Shock absorption performance of a motorbike helmet with honeycomb reinforced liner

The enhancement of the energy absorption properties of motorbike helmets could significantly improve the safety of riders. This study reports a novel concept of helmet design, which consists in the use of aluminium honeycomb as reinforcement material of the helmet liner. A modified version of a commercial helmet is presented, in which aluminium honeycombs are used in the energy absorbing liner. The ECE 22.05 standard tests were performed on both the prototype helmets and their commercial counterparts (presenting same dimensions, geometry, material properties and weight), and the dynamic responses were compared. The results showed that the prototype helmets provided better protection to the head from impacts against the kerbstone anvil. More limited improvements were also observed in some of the impacts on flat anvil, although other results indicated to some extent the limitations of the strategy adopted in our research.     

Correlation between microhardness and optical anisotropies and crystallinity in lamellar regenerated cellulose

An experimental study about the effect of the crystallinity on the birefringence and microhardness of regenerated cellulose tubular films is reported. The degrees of crystallinity of samples varied between 0.53 and 0.66. It was demonstrated that for the polymeric films studied there was an excellent agreement between crystallinity and optical and microhardness anisotropies, showing that micro-indentation hardness, scarcely used but rapid and nondestructive, is a suitable technique for characterizing the degree of order in this polymer.     

Application of near (NIR) infrared and mid (MIR) infrared spectroscopy as a rapid tool to classify extra virgin olive oil on the basis of fruity attribute intensity

A sensory analysis of 112 virgin olive oils was performed by a fully trained taste panel. The samples were divided in “defective” and “not defective” on the basis of their olfactory attributes. Then, the “not defective” samples were classified into “low”, “medium” and “high” according to the fruity aroma intensity perceived by assessors. All samples were also analysed by FT-NIR and FT-IR spectroscopy and processed by classification methods (LDA and SIMCA). The results showed that NIR and MIR spectroscopy coupled with statistical methods are an interesting technique compared with traditional sensory assessment in classifying olive oil samples on the basis of the fruity attribute. The prediction rate varied between 71.6% and 100%, as average value. The spectroscopic methods, combined with chemometric strategies, could represent a reliable, cheap and fast classification tool, able to draw a complete fingerprint of a food product, describing its intrinsic quality attributes, that include its sensory attributes.     

Prediction of air and steam leak rate through cracked reinforced concrete panels

The leak rate prediction of air and steam through a cracked concrete wall is an extremely important issue in assessing the safety of a nuclear reactor containment building. Such a problem requires a multidisciplinary approach involving both the non-linear analysis of the structure, and the thermodynamics aspects related to the flow of a gas through a conduit. In the present paper, some of the available leak rate evaluation formulae are reviewed, and an application to the prediction of the leak rate of either dry air or air+steam mixture through a cracked concrete panel is presented. Finally, in order to validate the numerical procedure herein adopted and to give some indication on the relative merit of the different leak rate formulae considered, the results of the numerical application are compared against leak rate values measured during an experimental test carried out at the ISMES laboratory.     

Closed-Form Solution for System Availability Distribution

Highly reliable systems with long mission time, that can tolerate no down time, have motivated the study of system reliability. The emergence of fault-tolerant computing systems, where small down times may be tolerable, and preventive and corrective maintenance permitted, motivates a revisit to measures like mean availability. Vendors of computer systems are being required to specify the level of availability that will be met by their systems over a finite time interval, and pay a penalty for non-compliance. Since no closed-form solution has been reported in the literature, numerical approaches have often been used to compute systems availability over a finite time, even for simple Markov models. We report a Laplace transform solution for the distribution of availability over a finite interval, for a semi-Markov model. The transform of the distribution is analytically inverted to obtain a closed-form solution for the corresponding Markov model.     

Nitric oxide synthase activity in human squamous cell carcinoma of the head and neck

A continuous fluorometric assay for tryptophan hydroxylase activity based on the different spectral characteristics of tryptophan and 5-hydroxytryptophan is presented. Hydroxylation of tryptophan at the 5-position results in a large increase in the fluorescence of the molecule. The assay selectively monitors the fluorescence yield of 5-hydroxytryptophan by exciting the reaction mix at 300 nm. The rate of increase of the emission signal was found to be directly proportional to the enzyme concentration. Inner filter effects due to quinonoid dihydropterin accumulation were eliminated by the inclusion of a thiol reductant. Activity measured using this assay method was found to be the same as that determined by established discontinuous HPLC assay methods. The application of the assay to routine activity measurements and to steady-state determinations with the substrates tryptophan and tetrahydropterin is described.     

Strong normalization property for second order linear logic

The paper contains the first complete proof of strong normalization (SN) for full second order linear logic (LL): Girard’s original proof uses a standardization theorem which is not proven. We introduce sliced pure structures (sps), a very general version of Girard’s proof-nets, and we apply to sps Gandy’s method to infer SN from weak normalization (WN). We prove a standardization theorem for sps: if WN without erasing steps holds for an sps, then it enjoys SN. A key step in our proof of standardization is a confluence theorem for sps obtained by using only a very weak form of correctness, namely acyclicity slice by slice. We conclude by showing how standardization for sps allows to prove SN of LL, using as usual Girard’s reducibility candidates.