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Asymmetric Pattern (asymmetric + pattern)
Selected AbstractsDevelopment of the proepicardium in Xenopus laevisDEVELOPMENTAL DYNAMICS, Issue 10 2008Maike Jahr Abstract The proepicardium (PE) is an embryonic progenitor cell population, which provides the epicardium, the majority of the cardiac interstitium, the coronary vasculature and possibly some cardiomyocytes. Recent studies have documented (1) the presence of bilaterally paired PE anlagen in several vertebrates, and (2) species-specific differences in the fate of the left and right PE anlagen. Here, we document PE development in Xenopus laevis (stages 37,46). The PE appears at stage 41 in the form of a cone-shaped accumulation of mesothelial cells covering the pericardial surface of the right horn of the sinus venosus. No such structure appears on the left sinus horn. At the end of stage 41, the tip of the PE establishes a firm contact with the developing ventricle. A secondary tissue bridge is established facilitating the transfer of PE cells to the heart. During stages 41,46, this tissue bridge is visible in vivo through the transparent body wall. Corresponding to the morphological data, the PE marker gene Tbx18 is expressed only on the right sinus horn suggesting a right-sided origin of the PE. Left,right lineage tracing has confirmed this idea. These results show that Xenopus PE development proceeds in a bilaterally asymmetric pattern as previously observed in chicks. We speculate that asymmetric PE development is controlled by signals from left,right signaling pathways and that the PE is an indicator for right-sidedness in Xenopus embryos. Xenopus might be a good model to uncover the role of left,right signaling pathways in the control of asymmetric PE development. Developmental Dynamics 237:3088,3096, 2008. © 2008 Wiley-Liss, Inc. [source] Household demand analysis of organic and conventional fluid milk in the United States based on the 2004 Nielsen Homescan panelAGRIBUSINESS : AN INTERNATIONAL JOURNAL, Issue 3 2010Pedro A. Alviola IV Using the 2004 AC Nielsen panel consisting of over 38,000 households, the authors ascertain the influence of selected demographic variables associated with the purchase of organic fluid milk through the estimation of a probit model. From the use of the Heckman two-step procedure, they also calculate own-price, cross-price, and income elasticities by estimating demand relationships for both organic and conventional milk. They find that demographic factors play a crucial role in the household choice of purchasing organic milk. Furthermore, households are more sensitive to own-price changes in the case of organic milk versus conventional milk. Evidence from estimated cross-price elasticities indicates that organic and conventional milk are substitutes. However, quantities purchased of organic milk are more sensitive to changes in prices of conventional milk than vice versa. Consequently, an asymmetric pattern exists with regard to the substitution patterns of the respective milk types. Moreover, evidence indicates that organic milk is responsive to income changes, but conventional milk is not responsive to income changes. Finally, a 1% increase in the price of organic milk reduces total milk sales by 0.20%, but a 1% increase in the price of conventional milk raises total milk sales by 0.31%. [EconLit citations: C25, D12]. © 2010 Wiley Periodicals, Inc. [source] Monetary integration in the ex-Soviet Union: A ,union of four'?*THE ECONOMICS OF TRANSITION, Issue 1 2006Vladimir Chaplygin F02; F15; E58 Abstract The governments of four ex-Soviet countries recently discussed forming a currency union. To examine the economic feasibility of this proposition, we use conventional techniques and show that the arrangement is likely to find it difficult to handle the lack of structural symmetry, the asymmetric pattern of shocks, and the lack of market flexibility among the potential participants. Moreover, the union would be a unilateral one. It would require an unusual degree of political commitment to survive. Nonetheless, there are some subtleties in the timing and pattern of mutual dependence between Russia and Kazakhstan, and to a lesser extent in Belarus, which may reduce the strain from a currency union in those countries. Otherwise, the black market will have to provide the necessary market flexibility. [source] Drainage patterns and tectonic forcing: a model study for the Swiss AlpsBASIN RESEARCH, Issue 2 2001A. Kühni ABSTRACT A linear surface process model is used to examine the effect of different patterns of rock uplift on the evolution of the drainage network of the Swiss Alps. An asymmetric pattern of tectonic forcing simulates a phase of rapid retrothrusting in the south of the Swiss Alps (,Lepontine'-type uplift). A domal pattern of tectonic forcing in the north of the model orogen simulates the phase of the formation of the ,Aar massif', an external basement uplift in the frontal part of the orogenic wedge (,Aar'-type uplift). Model runs using the ,Lepontine'-type uplift pattern result in a model mountain chain with a water divide in the zone of maximum uplift and orogen-normal rivers. Model runs examining the effect of ,Lepontine'-type uplift followed by ,Aar'-type uplift show that the initially formed orogen-normal river system and the water divide are both very stable and hardly affected by the additional uplift. This indifference to changes in tectonic forcing is mainly due to the requirement of a high model erosion capacity for the river systems in order to reproduce the exhumation data (high-grade rocks in the south of the Swiss Alps point to removal of a wedge-shaped nappe stack with a maximum thickness of about 25 km). The model behaviour is in agreement with the ancestral drainage pattern of the Alps in Oligocene and Miocene times and with the modern pattern observed in the Coast Range of British Columbia; in both cases river incision occurred across a zone of rapid uplift in the lower course of the rivers. The model behaviour does not, however, explain the modern drainage pattern in the Alps with its orogen-parallel rivers. When the model system is forced to develop two locally independent main water divides (simultaneous ,Lepontine'- and ,Aar'-type uplift), a zone of reduced erosional potential forms between the two divides. As a consequence, the divides approach each other and eventually merge. The new water divide remains fixed in space independent of the two persisting uplift maxima. The model results suggest that spatial and temporal changes in tectonic forcing alone cannot produce the change from the orogen-normal drainage pattern of the Swiss Alps in Oligocene,Miocene times to the orogen-parallel drainage observed in the Swiss Alps today. [source] Institutional Trading and Price MomentumINTERNATIONAL REVIEW OF FINANCE, Issue 1-2 2008CHIH-HSIEN JERRY YU ABSTRACT This paper aims to explore the effect of institutional trading on the two asymmetric phenomena found by Lee and Swaminathan: (1) asymmetric price momentum: price momentum is more pronounced among high-turnover stocks; (2) asymmetric return phenomenon: low-turnover stocks tend to outperform high-turnover stocks. Lee and Swaminathan use a ,momentum life cycle' to explain the asymmetric momentum effect while attributing the asymmetric return phenomenon to the analysts' overestimating (underestimating) the future profitability of high (low)-turnover firms. However, it essentially needs trading activity to induce both of the above asymmetric results. Because institutional investors exhibit a momentum trading pattern and the trading behavior of institutional investors may have a huge impact on the movement of stock prices, institutional trading may be one of the major driving forces leading to both of the above asymmetric patterns. The empirical results show that, first of all, after controlling for the turnover, the price momentum is still more pronounced among stocks with higher institutional ownership, while high-turnover stocks no longer exhibit a pronounced momentum effect after controlling for the institutional ownership. Furthermore, stocks with higher institutional ownership have better return performance in any of the turnover groups. While low-turnover stocks still outperform high-turnover stocks after controlling for the institutional ownership level, for some winner stocks this is no longer true. The results suggest that the asymmetric momentum effect is not induced by a stock's turnover, but rather it is driven by institutional trading. Turnover is only a proxy for institutional trading. That is, turnover per se has no economic significance in such a momentum phenomenon. [source] The role of visible persistence for perception of visual bilateral symmetry1JAPANESE PSYCHOLOGICAL RESEARCH, Issue 4 2005RYOSUKE NIIMI Abstract:, Although the detection of visual bilateral symmetry has been claimed to be highly efficient, the possible involvement and function of visual memory in such efficient mechanisms has rarely been examined. We hypothesized that symmetry perception is rapid, as it can be achieved from rapidly decaying information of visible persistence. To test this hypothesis, we employed a temporal integration paradigm. A symmetric dot pattern was randomly divided into two asymmetric patterns and presented successively with a blank screen presented between patterns. Observers could detect symmetry when the two patterns were presented close in time (Experiment 1), indicating that observers perceived symmetry presumably utilizing visible persistence. In addition, the inverse-intensity effect of visible persistence (Di Lollo & Bischof, 1995) was evident in our temporal integration task of symmetry (Experiment 2). The results of the current study clearly demonstrate that the detection of symmetry can be achieved based on the visible persistence. The large capacity and high spatial precision of visible persistence might be adequate for the rapid and spatially global encoding of visual symmetry. [source] Geological history and within-island diversity: a debris avalanche and the Tenerife lizard Gallotia gallotiMOLECULAR ECOLOGY, Issue 12 2006RICHARD P. BROWN Abstract Several processes have been described that could explain geographical variation and speciation within small islands, including fragmentation of populations through volcanic eruptions. Massive landslides, or debris avalanches, could cause similar effects. Here we analyse the potential impact of the 0.8 million-year-ago (Ma) Güimar valley debris avalanche on the phylogeography of the lizard Gallotia galloti on the Canary Island of Tenerife. Distributions of mitochondrial DNA lineages (based on cytochrome b sequences) were analysed on a 60-km southeastern coast transect centred on this area. Three main clades were detected, which can be divided into northern (one clade) and southern (two clades) groups that introgress across the valley. Maximum-likelihood estimates of migration rates (scaled for mutation rate) revealed highly asymmetric patterns, indicating that long-term gene flow into this region from both the northern and the southern populations greatly exceeded that in the opposite directions, consistent with recolonization of the area. The ancestral Tenerife node on the G. galloti tree is estimated at 0.80 Ma, matching closely with the geological estimate for the debris avalanche. Morphological variation (body dimensions and scalation) was also analysed and indicated a stepped cline in female scalation across the valley, although the patterns for male scalation and male and female body dimensions were not as clear. Together these findings provide support for the hypothesis that the debris avalanche has shaped the phylogeography of G. galloti and may even have been a primary cause of the within-island cladogenesis through population fragmentation and isolation. Current estimates of timing of island unification mean that the original hypothesis that within-island diversity is explained by the secondary contact of populations from the two ancient precursor islands of Teno and Anaga is less plausible for this and some other Tenerife species. Large-scale landslides have occurred on many volcanic islands, and so may have been instrumental in shaping within-island diversities. [source] Variability of Broca's area homologue in African great apes: Implications for language evolutionTHE ANATOMICAL RECORD : ADVANCES IN INTEGRATIVE ANATOMY AND EVOLUTIONARY BIOLOGY, Issue 2 2003Chet C. Sherwood Abstract The cortical circuits subserving neural processing of human language are localized to the inferior frontal operculum and the posterior perisylvian region. Functional language dominance has been related to anatomical asymmetry of Broca's area and the planum temporale. The evolutionary history of these asymmetric patterns, however, remains obscure. Although testing of hypotheses about the evolution of language areas requires comparison to homologous regions in the brains of our closest living relatives, the great apes, to date little is known about normal interindividual variation of these regions in this group. Here we focus on Brodmann's area 44 in African great apes (Pan troglodytes and Gorilla gorilla). This area corresponds to the pars opercularis of the inferior frontal gyrus (IFG), and has been shown to exhibit both gross and cytoarchitectural asymmetries in humans. We calculated frequencies of sulcal variations and mapped the distribution of cytoarchitectural area 44 to determine whether its boundaries occurred at consistent macrostructural landmarks. A considerable amount of variation was found in the distribution of the inferior frontal sulci among great ape brains. The inferior precentral sulcus in particular was often bifurcated, which made it impossible to determine the posterior boundary of the pars opercularis. In addition, the distribution of Brodmann's area 44 showed very little correspondence to surface anatomy. We conclude that gross morphologic patterns do not offer substantive landmarks for the measurement of Brodmann's area 44 in great apes. Whether or not Broca's area homologue of great apes exhibits humanlike asymmetry can only be resolved through further analyses of microstructural components. Anat Rec Part A 271A:276,285, 2003. © 2003 Wiley-Liss, Inc. [source] | |||||||||||||