Subspace identification of MIMO LPV systems using a periodic scheduling sequence

A novel subspace identification method is presented which is able to reconstruct the deterministic part of a multivariable state-space LPV system with affine parameter dependence, in the presence of process and output noise. It is assumed that the identification data is generated with the scheduling variable varying periodically during the course of the identification experiment. This allows to use methods from LTI subspace identification to determine the column space of the time-varying observability matrices. It is shown that the crucial step in determining the original LPV system is to ensure the obtained observability matrices are defined with respect to the same state basis. Once the LPV model has been identified, it is valid for other nonperiodic scheduling sequences as well.     

Effect of Microstructure on the Tribological and Mechanical Properties of CuO-Doped 3Y-TZP Ceramics

Dense 8 mol% CuO-doped 3Y-TZP ceramics were prepared by pressureless sintering for 8 h at 1500° and 1550°C, respectively. Transmission electron spectroscopy revealed that the ceramic sintered at 1500°C exhibits grain boundaries free of any amorphous phase, while crystalline copper-oxide grains were found in the zirconia matrix, whereas the sample sintered at 1550°C contains a Cu-rich amorphous grain boundary layer. The tribological behavior of these materials was tested under dry-sliding conditions using a pin-on-disk tribometer. The material sintered at 1500°C showed self-lubrication resulting in a low coefficient of friction ( f ) of 0.2–0.3 and a low specific wear rate ( k ) ≪ 10⁻⁶ mm³·(N·m)⁻¹. In contrast, the material sintered at 1550°C showed poor tribological behavior ( f =0.8–0.9; k ≫ 10⁻⁶ mm³·(N·m)⁻¹ under the same conditions. The difference in the tribological behavior of these two materials was interpreted on the basis of mechanical properties and microstructural characteristics.     

Clinical evaluation of ultra-high-field MRI for three-dimensional visualisation of tumour size in uveal melanoma patients,with direct relevance to treatment planning

Objectives

To assess the tumour dimensions in uveal melanoma patients using 7-T ocular MRI and compare these values with conventional ultrasound imaging to provide improved information for treatment options.

Materials and methods

Ten uveal melanoma patients were examined on a 7-T MRI system using a custom-built eye coil and dedicated 3D scan sequences to minimise eye-motion-induced image artefacts. The maximum tumour prominence was estimated from the three-dimensional images and compared with the standard clinical evaluation from 2D ultrasound images.

Results

The MRI protocols resulted in high-resolution motion-free images of the eye in which the tumour and surrounding tissues could clearly be discriminated. For eight of the ten patients the MR images showed a slightly different value of tumour prominence (average 1.0 mm difference) compared to the ultrasound measurements, which can be attributed to the oblique cuts through the tumour made by the ultrasound. For two of these patients the more accurate results from the MR images changed the treatment plan, with the smaller tumour dimensions making them eligible for eye-preserving therapy.

Conclusion

High-field ocular MRI can yield a more accurate measurement of the tumour dimensions than conventional ultrasound, which can result in significant changes in the prescribed treatment.

     

Hot Chips Turns 20 [Guest editors' introduction]

The five papers in this special issue are extended versions of papers presented at the Hot Chips conference in August 1008.     

Store Atomicity for Transactional Memory

We extend the notion of Store Atomicity [Arvind and Jan-Willem Maessen. Memory model = instruction reordering + store atomicity. In ISCA '06: Proceedings of the 33rd annual International Symposium on Computer Architecture, 2006] to a system with atomic transactional memory. This gives a fine-grained graph-based framework for defining and reasoning about transactional memory consistency. The memory model is defined in terms of thread-local Instruction Reordering axioms and Store Atomicity, which describes inter-thread communication via memory. A memory model with Store Atomicity is serializable: there is a unique global interleaving of all operations which respects the reordering rules and serializes all the operations in a transaction together. We extend Store Atomicity to capture this ordering requirement by requiring dependencies which cross a transaction boundary to point in to the initiating instruction or out from the committing instruction. We sketch a weaker definition of transactional serialization which accounts for the ability to interleave transactional operations which touch disjoint memory. We give a procedure for enumerating the behaviors of a transactional program—noting that a safe enumeration procedure permits only one transaction to read from memory at a time. We show that more realistic models of transactional execution require speculative execution. We define the conditions under which speculation must be rolled back, and give criteria to identify which instructions must be rolled back in these cases.     

Influence of core stiffness on the behavior of tall timber buildings subjected to wind loads

This study analyzes the feasibility of the use of cross-laminated timber (CLT) as a load-bearing structural element in a 40-story building based on Chinese design requirements. The proposed design of the high-rise concrete–CLT building utilizes the core–outrigger system. Concrete is used for the central core and outriggers, and CLT is used for the rest of the structure of the building. Finite element models with different types of connections were developed using SAP2000 to analyze the lateral behavior of the building under wind action. The finite element models with rigid connections deduce the wind load distributions on individual structural elements, which determine the total number and the stiffness of fasteners of the CLT panels. Accordingly, spring links with equivalent stiffness that simulate the mechanical fasteners were employed in SAP2000. The results indicate that CLT increases the lateral flexibility of the building. A closed concrete core was substituted by two half cores to measure the requirement of the maximum lateral deflection. However, the acceleration at the building top still exceeded the limitation prescribed in Chinese Code JGJ 3–2010 owing to the lightweight of CLT and decreased stiffness of the hybrid building. To restrict this top acceleration within the limit, further approaches to increase the stiffness in the weak direction of the building are required. Methods such as the modification of the floor layout, increase in the thickness of walls, and addition of extra damping capacity should be considered and verified in the future.     

Evaluating expectations about negative emotional states of aggressive boys using Bayesian model selection.

Researchers often have expectations about the research outcomes in regard to inequality constraints between, e.g., group means. Consider the example of researchers who investigated the effects of inducing a negative emotional state in aggressive boys. It was expected that highly aggressive boys would, on average, score higher on aggressive responses toward other peers than moderately aggressive boys, who would in turn score higher than nonaggressive boys. In most cases, null hypothesis testing is used to evaluate such hypotheses. We show, however, that hypotheses formulated using inequality constraints between the group means are generally not evaluated properly. The wrong hypotheses are tested, i.e.. the null hypothesis that group means are equal. In this article, we propose an innovative solution to these above-mentioned issues using Bayesian model selection, which we illustrate using a case study. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Nitric oxide in cerebral ischemic neurodegeneration and excitotoxicity

The observation that the free radical nitric oxide (NO) acts as a cell signaling molecule in key physiological processes such as regulation of blood pressure and immunological host-defense responses is probably one of the most important and exciting findings made in biology in the last decade. Likewise, in the brain NO has been implicated in a number of fundamental processes, including memory formation, sexual behavior and the control of cerebral blood flow. This has radically altered the accepted dogma of brain physiology and has placed NO at the center stage of neuroscience research. Evidence suggests that some of the actions of NO in the brain may be intimately linked to those of the classic excitatory neurotransmitter glutamate. The historical view that aberrations in glutamate signal transduction may underlie central neurodegeneration following, for example, cerebral ischemia, has implicated NO, by default, as a potential mediator of neuronal death. Indeed, with the advent of potent and specific compounds that interact with NO synthesizing (NOS) enzymes and with the NO signaling cascade, there is now ample evidence to suggest that NO can mediate neurodegeneration, although its involvement is paradoxical. Its cerebrovascular effects may act to limit ischemic damage by preserving tissue perfusion and preventing platelet aggregation, while NO produced in the parenchyma, either directly following the ischemic insult or at a later stage as part of a neuroinflammatory response, may be deleterious to the outcome of ischemia. Nonetheless, significant efforts are made into the potential therapeutic use of chemical NO donors and specific NOS inhibitors in the treatment of cerebral ischemia and other central neurodegenerative disorders. Here, the latest concepts and developments in our understanding of the role of NO in cerebral ischemic neurodegeneration are discussed.