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Complex Sequence (complex + sequence)
Selected AbstractsMajor muscle systems in the larval caenogastropod, Ilyanassa obsoleta, display different patterns of developmentJOURNAL OF MORPHOLOGY, Issue 10 2009Carol C.E. Evans Abstract This study describes the anatomical and developmental aspects of muscular development from the early embryo to competent larval stage in the gastropod Ilyanassa obsoleta. Staining of F-actin revealed differential spatial and temporal patterns of several muscles. In particular, two major muscles, the larval retractor and pedal retractor muscles originate independently and display distinct developmental patterns similar to observations in other gastropod species. Additionally, together with the larval retractor muscle, the accessory larval muscle developed in the embryo at the trochophore stage. Therefore, both these muscles develop prior to ontogenetic torsion. The pedal retractor muscle marked the most abundant growth in the mid veliger stage. Also during the middle stage, the metapodial retractor muscle and opercular retractor muscle grew concurrently with development of the foot. We show evidence that juvenile muscles, such as the buccal mass muscle and siphon muscle develop initially during the late veliger stage. Collectively, these findings substantiate that larval myogenesis involves a complex sequence of events that appear evolutionary conserved within the gastropods, and set the stage for future studies using this model species to address issues concerning the evolution and eventual fates of larval musculature in molluscs. J. Morphol., 2009. © 2009 Wiley-Liss, Inc. [source] A resorbable porous ceramic composite bone graft substitute in a rabbit metaphyseal defect modelJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 4 2003W. R. Walsh The success of converted corals as a bone graft substitute relies on a complex sequence of events of vascular ingrowth, differentiation of osteoprogenitor cells, bone remodeling and graft resorption occurring together with host bone ingrowth into and onto the porous coralline microstructure or voids left behind during resorption. This study examined the resorption rates and bone infiltration into a family of resorbable porous ceramic placed bilaterally in critical sized defects in the tibial metaphyseal,diaphyseal of rabbits. The ceramics are made resorbable by partially converting the calcium carbonate of corals to form a hydroxyapatite (HA) layer on all surfaces. Attempts have been made to control the resorption rate of the implant by varying the HA thickness. New bone was observed at the periosteal and endosteal cortices, which flowed into the centre of the defect supporting the osteoconductive nature of partially converted corals. The combination of an HA layer and calcium carbonate core provides a composite bone graft substitute for new tissue integration. The HA-calcium carbonate composite demonstrated an initial resorption of the inner calcium carbonate phase but the overall implant resorption and bone ingrowth behaviour did not differ with HA thickness. © 2003 Orthopaedic Research Society. Published by Elsevier Science Ltd. All rights reserved. [source] Striatal synaptic plasticity: Implications for motor learning and Parkinson's diseaseMOVEMENT DISORDERS, Issue 4 2005Antonio Pisani MD Abstract Changing the strength of synaptic connections between neurons is widely assumed to be the mechanism by which memory traces are encoded and stored in the central nervous system. Plastic changes appear to follow a regional specialization and underlie the specific type of memory mediated by the brain area in which plasticity occurs. Thus, long-term changes occurring at excitatory corticostriatal synapses should be critically involved in motor learning. Indeed, repetitive stimulation of the corticostriatal pathway can cause either a long-lasting increase or an enduring decrease in synaptic strength, respectively referred to as long-term potentiation (LTP), and long-term depression, both requiring a complex sequence of biochemical events. Once established, LTP can be reversed to control levels by a low-frequency stimulation protocol, an active phenomenon defined "synaptic depotentiation," required to erase redundant information. In the 6-hydroxydopamine rat model of Parkinson's disease (PD), striatal synaptic plasticity has been shown to be impaired, although chronic treatment with levodopa was able to restore it. Of interest, a consistent number of L -dopa,treated animals developed involuntary movements, resembling human dyskinesias. Strikingly, electrophysiological recordings from the dyskinetic group of rats demonstrated a selective impairment of synaptic depotentiation. This survey will provide an overview of plastic changes occurring at striatal synapses. The potential relevance of these findings in the control of motor function and in the pathogenesis both of PD and L -dopa,induced motor complications will be discussed. © 2005 Movement Disorder Society [source] Wavelet analysis and the governing dynamics of a large-amplitude mesoscale gravity-wave event along the East Coast of the United StatesTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 577 2001Fuqing Zhang Abstract Detailed diagnostic analyses are performed upon a mesoscale numerical simulation of a well-observed gravity-wave event that occurred on 4 January 1994 along the East Coast of the United States. The value of using wavelet analysis to investigate the evolving gravity-wave structure and of using potential vorticity (PV) inversion to study the nature of the flow imbalance in the wave generation region is demonstrated. The cross-stream Lagrangian Rossby number, the residual in the nonlinear balance equation, and the unbalanced geopotential-height field obtained from PV inversion are each evaluated for their usefulness in diagnosing the flow imbalance. All of these fields showed clear evidence of strong imbalance associated with a middle-to-upper tropospheric jet streak, and tropopause fold upstream of the large-amplitude gravity wave several hours before the wave became apparent at the surface. Analysis indicates that a train of gravity waves was continuously generated by geostrophic adjustment in the exit region of the unbalanced upper-level jet streak as it approached the inflection axis in the height field immediately downstream of the maximum imbalance associated with the tropopause fold. A split front in the middle troposphere, characterized by the advance of the dry conveyor belt above the warm front, was overtaken by one of these propagating waves. During this merger process, a resonant interaction resulted, which promoted the rapid amplification and scale contraction of both the incipient wave (nonlinear wave development) and the split front (frontogenesis). The gravity wave and front aloft became inseparable following this merger. The situation became even more complex within a few hours as the vertical motion enhanced by this front-wave interaction acted upon a saturated, potentially unstable layer to produce elevated moist convection. An analysis of the temporal changes in the vertical profile of wave energy flux suggests that moist convective downdraughts efficiently transported the wave energy from the midlevels downward beneath the warm-front surface, where the wave became ducted. However, pure ducting was not sufficient for maintaining and amplifying the waves; rather, wave-CISK (Conditional Instability of the Second Kind) was crucial. This complex sequence of nonlinear interactions produced a long-lived, large-amplitude gravity wave that created hazardous winter weather and disrupted society over a broad and highly populated area. Although gravity waves with similar appearance to this large-amplitude wave of depression occasionally have been seen in other strong cyclogenesis cases involving a jet streak ahead of the upper-level trough axis, it is unknown whether other such events share this same sequence of interactions. [source] A spectral method for on-line computation of the harmonics of symmetrical components in induction machinesEUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 3 2005T. Assaf Abstract This paper describes a procedure for the on-line computation of the harmonics of symmetrical components for voltages, currents and impedances in working induction machines. The algorithm used to compute these components is based on the discrete Fourier transform (DFT) of complex sequences. An experimental test-bed with a 0.12,kW star-connected induction motor has been used to test the procedure. The stability of the numerical results is verified to show the performance of the proposed method. Copyright © 2005 John Wiley & Sons, Ltd. [source] Scaffolding Imitation in Capoeira: Physical Education and Enculturation in an Afro-Brazilian ArtAMERICAN ANTHROPOLOGIST, Issue 2 2008GREG DOWNEY ABSTRACT, Imitation plays a crucial role in apprenticeship in the Afro-Brazilian performance genre capoeira, as in many skills across cultures. In this article, I examine the interactional dynamics of imitative pedagogy in capoeira to better understand physical education as a form of bodily enculturation. The ability to learn through imitation is widely considered a hallmark of our species. Imitative ability, however, is a social accomplishment rather than a capacity of the learner in isolation. Human models often provide assistance to novices seeking to imitate, including a variety of forms of what educational theorists call "scaffolding," which are astutely structured to a novice's ability, perceptions, and even neurology. Scaffolding techniques vary. I here examine how instructors reduce students' degrees of movement freedom, reorient their model in perceptual space, and parse complex sequences into component gestures. Close analysis of pedagogical interaction highlights the divergence between forms of instruction and practical skills being taught. [source] Speed, Accuracy, and Serial Order in Sequence ProductionCOGNITIVE SCIENCE - A MULTIDISCIPLINARY JOURNAL, Issue 1 2007Peter Q. Pfordresher The production of complex sequences like music or speech requires the rapid and temporally precise production of events (e.g., notes and chords), often at fast rates. Memory retrieval in these circumstances may rely on the simultaneous activation of both the current event and the surrounding context (Lashley, 1951). We describe an extension to a model of incremental retrieval in sequence production (Palmer & Pfordresher, 2003) that incorporates this logic to predict overall error rates and speed,accuracy trade-offs, as well as types of serial ordering errors. The model,assumes that retrieval of the current event is influenced by activations of surrounding events. Activations of surrounding events increase over time, such that both the accessibility of distant events and overall accuracy increases at slower production rates. The model's predictions were tested in an experiment in which pianists performed unfamiliar music at 8 different tempi. Model fits to speed,accuracy data and to serial ordering errors support model predictions. Parameter fits to individual data further suggest that working memory contributes to the retrieval of serial order and overall accuracy is influenced in addition by motor dexterity and domain-specific skill. [source] | ||||||||||