Robust adaptive cruise control of high speed trains

The cruise control problem of high speed trains in the presence of unknown parameters and external disturbances is considered. In particular a Lyapunov-based robust adaptive controller is presented to achieve asymptotic tracking and disturbance rejection. The system under consideration is nonlinear, MIMO and non-minimum phase. To deal with the limitations arising from the unstable zero-dynamics we do an output redefinition such that the zero-dynamics with respect to new outputs becomes stable. Rigorous stability analyses are presented which establish the boundedness of all the internal states and simultaneously asymptotic stability of the tracking error dynamics. The results are presented for two common configurations of high speed trains, i.e. the DD and PPD designs, based on the multi-body model and are verified by several numerical simulations.     

Central sleep apnoea in Arnold-Chiari malformation: evidence of pathophysiological heterogeneity

We report on the case of two young patients with type I Arnold-Chiari malformation (ACM), as revealed by a central sleep apnoea (CSA) syndrome without any other neurological defect. Case 1 was a 14-yr-old male patient, who developed severe alveolar hypoventilation and needed long-term mechanical ventilation via a tracheostomy. Case 2 was a 39-yr-old male patient, who developed features suggestive of sleep apnoea and responded to nasal continuous positive airway pressure ventilation despite the central type of apnoeas. These two cases illustrate the different pathophysiological mechanisms involved in CSA, namely a blunted chemical drive (in hypercapnic patients) and an increased chemical drive, which destabilizes the breathing pattern during sleep (in normo/hypocapnic patients). Central sleep apnoea can be the initial manifestation of Arnold-Chiari malformation and can lead to a life-threatening condition.     

Heat Transfer Analysis of a Microspherical Particle in the Slip Flow Regime by Considering Variable Properties

In order to investigate how far the temperature-dependent fluid properties and characteristic length influence the drag coefficient and the heat flux, a three-dimensional simulation study for a slip flow around an unconfined microspherical particle has been performed. Gas properties such as density, viscosity, conductivity, and mean free path were assumed to vary with temperature. Slip velocity and temperature jump at the gas particle interface were both treated numerically by imposition of the slip boundary conditions. The effects of variable gas properties and Knudsen number on momentum and heat transfer were also taken into account. It was concluded that for microflows with high heat transfer rates, the constant fluid properties approximation is very crude. In addition, the slip velocity and temperature jump affect the heat transfer in opposite ways: a large slip on the wall increases the convection along the surface, whereas a large temperature jump decreases the heat transfer by reducing the temperature gradient at the wall. Therefore, neglecting temperature jump will result in the overestimation of the heat transfer coefficient.     

Microstructure of polycrystalline Fe<Subscript>82</Subscript>Ga<Subscript>18</Subscript> sample with solidification texture

Main attention of this paper was devoted to studying the effect of solidification texture on microstructure (phase constituents, grain morphology, and magnetic domain structure) of polycrystalline Fe₈₂Ga₁₈ sample. The alloy was melted using button arc melting and solidified in water-cooled copper mold. Optical microscope (OM) results confirm the development of large columnar grains in the solidification microstructure. Phase constitution and magnetic domain structures of the sample were studied by X-ray diffraction (XRD) and magnetic force microscopy (MFM). Results show a single-phase solid solution with an A2 structure for the sample which consists of regularly aligned magnetic domains. Although some maze-like subdomains are found in few regions, well-aligned stripe-like domains are predominant patterns in the sample. It demonstrates the high dependence of grain morphology and magnetic domain structure upon a preferred crystallographic direction during solidification.     

Multicomponent oxide composites for carriers in catalytic applications

Binary, ternary, and quaternary composite oxides of rare earths (La and Ce) with one or more of aluminum, magnesium, and zirconium, prepared by coprecipitation are studied. Potential use is carrier in steam or dry reforming of hydrocarbons and ethanol. Individual components influence specific surface area, porosity, acidity, hydrothermal stability, and oxygen storage capacity (OSC) differently. Interaction effects between components further influence these properties resulting in unexpected trends. Alumina and magnesia form solid solutions with zirconia until 650℃. Magnesia imparts better hydrothermal stability to zirconia. Aluminum and magnesium form MgAl₂O₄ spinel in ternary composites. Specific surface area varies linearly with alumina content. Alumina influences porosity, whereas magnesia influences pore diameter. The composites are mesoporous. Only binary composites present unimodal, pore size distribution. Composites containing alumina present type H2 isotherms while the remaining composites present H3 type isotherms. OSC increases over ZrO₂/CeO₂ 5.7 to 15.3 molar. Magnesia and alumina affect microstructure and hydrothermal stability in contrasting ways. Thermogravimetry indicates that ternary composites of zirconia with alumina or magnesia form through oxolation. Surface hydroxyls with varying acidity are seen by FTIR in as synthesized samples. Magnesia and zirconia influence acidity in opposite ways, which impacts deactivation in the decomposition of 2-methyl-3-butyn-2-ol.     

Heat extraction methods from salinity-gradient solar ponds and introduction of a novel system of heat extraction for improved efficiency

Heat has generally been successfully extracted from the lower convective zone (LCZ) of solar ponds by two main methods. In the first, hot brine from the LCZ is circulated through an external heat exchanger, as tested and demonstrated in El Paso and elsewhere. In the second method, a heat transfer fluid circulates in a closed cycle through an in-pond heat exchanger, as used in the Pyramid Hill solar pond, in Victoria, Australia. Based on the experiences at the El Paso and Pyramid Hill solar ponds, the technical specifications, material selection, stability control, clarity maintenance, salt management and operating strategies are presented. A novel method of extracting heat from a solar pond is to draw the heat from the gradient layer. This method is analysed theoretically and results of an experimental investigation at Bundoora East, RMIT, are presented. An in-pond heat exchanger made of polyethylene pipe has been used to extract heat for over 2 months. Results indicate that heat extraction from the gradient layer increases the overall energy efficiency of the solar pond by up to 55%, compared with conventional method of heat extraction solely from the LCZ. The experimental results are compared with the theoretical analysis. A close agreement has been found. From this small-scale experimental study, convection currents were found to be localised only and the density profiles were unaffected. An experimental study using an external heat exchanger for brine extraction and re-injection at different levels within the gradient layer still needs to be conducted to determine the effect of the heat extraction from the non-convective zone (NCZ) on the stability of the salinity gradient (both vertically and horizontally) and an economic analysis needs to be conducted to determine the economic gains from increased thermal efficiency.     

The conundrum of research productivity: a study on sociologists in Italy

This paper aims to understand the influence of institutional and organisational embeddedness on research productivity of Italian sociologists. We looked at all records published by Italian sociologists in Scopus from 1973 to 2016 and reconstructed their co-authorship patterns. We built an individual productivity index by considering the number and type of records, the impact factor of journals in which these records were published and each record’s citations. We found that sociologists who co-authored more frequently with international authors were more productive and that having a stable group of co-authors had a positive effect on the number of publications but not on citations. We found that organisational embeddedness has a positive effect on productivity at the group level (i.e., sociologists working in the same institute), less at the individual level. We did not found any effect of the scientific disciplinary sectors, which are extremely influential administratively and politically for promotion and career in Italy. With all caveats due to several limitations of our analysis, our findings suggest that internationalisation and certain context-specific organisational settings could promote scientist productivity .     

Factors Controlling Gully Advancement and Models Evaluation (Hableh Rood Basin,Iran)

Gully erosion is one of the most complicated and destructive forms of water erosion. In order to prevent this erosion, the important factors controlling gully heads must be understood. This paper examines gully head advancement in the Hableh Rood Basin, Iran by (1) observing gully head advance between 1957 and 2005 using field studies, aerial photography and GIS analysis and: (2) applying and evaluating widely used experimental models including the, Thompson (Trans ASAE 7(1):54–55, 1964), SCS (I) and SCS (II) models, for estimating migrating headcuts over the study period. The results showed that the highest mean gully advancement (0.26 m year^− 1) took place during the 1956–1967 period, with most gullies having lower and steady headcut retreat rates between 1967–2000 (0.21 m year^− 1) and 2000–2005 (0.15 m year^− 1). This suggests that the majority of gullies in the study area were still in the early stages of formation in the first study period and their formation may be linked to land use or climatic changes pre 1956. Analysis of the correlation between environmental characteristics of the study area and gully advancement indicated that the upslope area of head cuts and soluble mineral content of the soil were the two most important factors influencing the spatial and temporal variation of gully longitudinal development. Results of multiple regression revealed that the simple relation including upslope area and soluble minerals can explain 93% of total variance and relatively reflects the effects of runoff and waterfall process for headcut retreat. Application of statistical error analysis to evaluate the four gully advancement models showed that in comparison to other models, the second model of SCS has more reliable results for predicting longitudinal gully advancement in this study area and other similar regions. However, this study indicates that future modelling in the region should consider the role of soil soluble mineral content in predicting gully advancement.     

Investigation on the Collapse Behavior of Diagonal Stiffened Composite Plate Girders Subjected to Shear Loading

In this study, a new analytical method is presented to estimate the shear capacity of diagonally stiffened steel–concrete composite plate girders. This method is formulated based on tension field action in steel girder web and failure mechanism of concrete slab deck. To validate the accuracy of the proposed method, the obtained results are compared with three-dimensional finite element analysis of composite plate girders with different configuration of stiffeners. The results of analytical and numerical investigations indicate that the proposed method can accurately estimate the ultimate shear capacity of composite plate girders. In addition, it is shown that the diagonal stiffeners on one hand can reduce the buckling effects of shear panel of girders and on the other hand can increase the strength of elastic shear buckling and ultimate shear capacity of girders well in comparison with the unstiffened thin steel plate girders.