Comparison of Alternative ACD Models via Density and Interval Forecasts: Evidence from the Australian Stock Market

In this paper a number of alternative ACD models are compared using a sample of data for three major companies traded on the Australian Stock Exchange. The comparison is performed by employing the methodology for evaluating density and interval forecasts, developed by Diebold, Gunther and Tay (1998) and Christoffersen (1998), respectively. Our main finding is that the generalized gamma and log-normal distributions for the error terms have similar performance and perform better that the exponential and Weibull distributions. Additionally, there seems to be no substantial difference between the standard ACD specification of Engle and Russel (1998) and the log-ACD specification of Bauwens and Giot (2000).ACD models, Density forecasts Acknowledgements: This paper forms part of an ARC Linkage Grant research project, ÃModelling stock market liquidity in Australia and the Asia Pacific RegionÓ. We are grateful to the Australian Research Council for financial support. The financial data has been graciously provided by the Securities Research Institute (SIRCA) which is our industry partner.

An investigation on vibration-based damage detection in circular plates

This study aims at the development of vibration-based health monitoring (VHM) methodology for thin circular plates. The possibility of using the first several natural frequencies of a circular plate for damage detection purposes is investigated first. The study then suggests a damage detection method, which considers a vibrating plate as a dynamic system and uses its time domain response represented in a new phase (state) space to extract damage sensitive characteristics. The paper introduces the idea of using large amplitude vibrations and nonlinear time series analysis for damage detection purposes. The suggested damage detection approach explores the possibility to use certain characteristics of the distribution of phase space points on the attractor of the system. It studies the histograms of this distribution and attempts to extract damage sensitive features. Three damage features are suggested and they are shown to detect damage at a rather low level using a finite element model of the plate. The method suggested is rather generic and permits development and application to more complex structures and real data

Forebrain dopamine receptors in cognitive, memory and learning processes

Neurons that utilize dopamine (DA) as a neurotransmitter have attracted great interest because of their involvement in the behavioral, endocrine and descending control of major brain functions. DA is known to exert its physiological effects on target neurons through D1-like (D1 and D5) and D2-like (D2, D3 and D4) receptor subtypes. To better understand the DA modulation of brain functions, the distribution and cellular localization of D1 and D2 DA receptors in the rat forebrain is reviewed, and their possible role in cognitive aspects of behavior is discussed. In general, DA receptors are differentially expressed and mostly distributed in different target fields of DA neurons. Both D1 and D2 receptor gene products are found in the cerebral cortex, basal ganglia and hippocampal formation, albeit in different cell groups or neuronal subpopulations, whereas D3 receptors are mainly located in limbic regions. In the cortex, mRNA signals are seen in all the areas and cortical layers except layer I. In the striatum, the most intense signal is found in the caudate-putamen, nucleus accumbens and olfactory tubercle where a large number of cells are strongly labeled for D1 and D2. In the globus pallidus only scattered D2 mRNA-containing cells are present. In contrast, no D1 or D2 messages can be seen in the ventral pallidum. In the basal forebrain, mRNA encoding the D1 receptor is detected in the islands of Calleja. The medial and lateral septal nuclei show a low D2 signal. In the amygdaloid nuclear complex, the strongest D1 receptor message is observed in the basomedial and basolateral nuclei. Conversely, the highest density of D2 mRNA-expressing cells is revealed in the central nucleus. Moderately labeled for D1 and D2 cells are scattered throughout the anterior and posterior subdivisions of the bed nucleus of stria terminalis, and within all subfields of the hippocampal formation and dentate granule cell layer. Differential regional and cellular distribution of DA receptors in the forebrain provides anatomical evidence for an area-specific regulation of the DAergic neurotransmission. It can be inferred that DA facilitates learning, memory and cognition processes via activation of both the D1 and D2 receptors.Biomedical Reviews 2005; 16: 59-75

Postnatal development of the afferent innervation of the mammalian cochlea

The adult mammalian cochlea receives dual afferent innervation: the inner hair cells (IHCs) are innervated exclusively by type I spiral ganglion neurons (SGNs), whereas the outer hair cells (OHCs) are innervated by type II SGNs. We have characterized the reorganization and morphology of this dual afferent innervation pattern as it is established in the developing rat cochlea. Before the cochlear afferent innervation reaches a mature configuration, there is an initial mismatch, where both populations of SGNs innervate both types of sensory hair cells: during the first postnatal week in the rat cochlea, type I SGN innervation is eliminated from the OHC and type II SGN innervation is eliminated from the IHC. This reorganization occurs during the first two postnatal weeks just before the onset of hearing. Our data reveal distinct phases in the development of the afferent innervation of the organ of Corti: neurite refinement, with a formation of the outer spiral bundles innervating outer hair cells; neurite retraction and synaptic pruning to eliminate type I SGN innervation of OHCs, while retaining their supply to IHCs. Such a reorganization also makes the cochlea a model system for studying CNS synapse development, plasticity and elimination. The present article summarizes the recent progress in our understanding of the afferent innervation of the cochlea.Biomedical Reviews 2012; 23: 37-52

Morphology of the rat carotid body

The carotid body (CB) is the main peripheral arterial chemoreceptor that registers the levels of pO2, pCO2 and pH in the blood and responds to their changes by regulating breathing. It is strategically located in the bifurcation region of each common carotid artery. The organ consists of "glomera" composed of two cell types, glomus and sustentacular cells, interspersed by blood vessels and nerve bundles, and separated by connective tissue. The neuron-like glomus or type I cells contain numerous cytoplasmic organelles and dense-cored vesicles that store and release neurotransmitters. They form both conventional chemical and electrical synapses between each other and are contacted by peripheral nerve endings of petrosal ganglion afferent neurons. The glial-like sustentacular or type II cells sustain physiologic neurogenesis in the adult CB and are thus supposed to be progenitor cells. This new source of adult stem cells may be potentially useful for tissue repair after injury or for cell therapy against neurodegenerative diseases. The CB is a highly vascularized organ and its intraorgan hemodynamics possibly plays a role in the process of chemoreception. There is also evidence that chronic hypoxia induces marked morphological and neurochemical changes within the CB but the detailed molecular mechanisms by which these affect the hypoxic chemosensitivity still remain to be elucidated. Dysregulation of the CB function is implicated in various physiological and pathophysiological conditions, including ventilatory altitude acclimatization and sleep-disordered breathing. Knowledge of the morphological and functional aspects of the CB will contribute to our better understanding of respiratory homeostasis in health and disease.Biomedical Reviews 2011; 22: 41-55

Postnatal development of the inner ear efferent innervation in mammals

Efferent innervation of the inner ear is extensively studied but the whole model revealing the development of efferent synapses is not clear yet. In mammals the lateral and medial olivocochlear systems are known as the source of efferent fibers. The lateral olivocochlear system innervates the ipsilateral cochlea, terminating on the dendrites beneath the inner hair cells (IHCs), the dendrites being spiral ganglion neuron compounds. The medial olivocochlear system is involved in forming synapses directly on the outer hair cells (OHCs). To reach the final targets efferent axons use the afferent fibers as a scaffold. Efferent synaptogenesis occurs just before the onset of hearing. At P0 in rats we observed synaptic-like contacts lacking typical features. At P3 the synapses were immature. At P4-P5 efferent contacts with IHCs were clearly defined. At P6-P7 the efferent terminals were larger with distinct synaptic vesicles. During maturation, at P8-P10, the number of efferent synapses at the base of the ICHs reduced alongside with a decrease in the synaptic cisternae. After P12 efferent terminals formed axodendritic synapses below IHCs and large axosomatic synapses on OHCs. The innervation of OHCs underwent two stages, i.e. transitional with simultaneous innervation of IHCs and OHCs and a final OHC-targeted innervation. These results support the idea for a waiting period of efferent innervation before its final establishment in adult organ of Corti. We also summarize the role of neurotrophic factors, specific neurotransmitter systems, their receptors and transporters for refinement of cochlear efferent innervation.Biomedical Reviews 2013; 24: 33-48

Modelling Intra-day Seasonality and Forecasting Densities in Financial Duration Data

In this paper we model intra-daily seasonality in the shape of the residual distribution of the standard ACD model, which is estimated using diurnally (seasonally) adjusted duration data. Specifically, for two of the three companies in our sample, the shapes of the residual distribution for periods corresponding to the mornings and afternoons in a trading day are virtually identical, and are different from the shape of the residual distribution corresponding to the lunch time period. As a next step, we investigate whether the observed seasonality can explain the bias in density and interval ACD model forecasts, which are popular tools for econometric model evaluation and comparison.ACD models, Daily Seasonality, Density forecasts Acknowledgements: The authors are most grateful to a referee for helpful comments and suggestions. This paper forms part of an ARC Linkage Grant research project, entitled ÃModelling stock market liquidity in Australia and the Asia Pacific RegionÓ. We are grateful to the Australian Research Council for financial support. The financial data has been kindly provided by the Industry Partner, the Securities Research Institute (SIRCA).

Bi-Legendrian manifolds and paracontact geometry

We study the interplays between paracontact geometry and the theory of bi-Legendrian manifolds. We interpret the bi-Legendrian connection of a bi-Legendrian manifold M as the paracontact connection of a canonical paracontact structure induced on M and then we discuss many consequences of this result both for bi-Legendrian and for paracontact manifolds. Finally new classes of examples of paracontact manifolds are presented.Comment: to appear in Int. J. Geom. Meth. Mod. Phy