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Single Pair (single + pair)
Selected AbstractsIndividuation of pairs of objects in infancyDEVELOPMENTAL SCIENCE, Issue 4 2007Alan M. Leslie Looking-time studies examined whether 11-month-old infants can individuate two pairs of objects using only shape information. In order to test individuation, the object pairs were presented sequentially. Infants were familiarized either with the sequential pairs, disk-triangle/disk-triangle (XY/XY), whose shapes differed within but not across pairs, or with the sequential pairs, disk-disk/triangle-triangle (XX/YY), whose shapes differed across but not within pairs. The XY/XY presentation looked to adults like a single pair of objects presented repeatedly, whereas the XX/YY presentation looked like different pairs of objects. Following familiarization to these displays, infants were given a series of test trials in which the screen was removed, revealing two pairs of objects in one of two outcomes, XYXY or XXYY. On the first test trial, infants familiarized with the identical pairs (XY/XY) apparently expected a single pair to be revealed because they looked longer than infants familiarized with the distinct pairs (XX/YY). Infants who had seen the distinct pairs apparently expected a double pair outcome. A second experiment showed outcomes of a single XY pair. This outcome is unexpected for XX/YY-familiarized infants but expected for XY/XY-familiarized infants, the reverse of Experiment 1. This time looking times were longer for XX/YY infants. Eleven-month-olds appear to be able to represent not just individual objects but also pairs of objects. These results suggest that if they can group the objects into sets, infants may be able to track more objects than their numerosity limit or available working memory slots would normally allow. We suggest possible small exact numerosity representations that would allow tracking of such sets. [source] Ultrastructural and immunocytochemical observations of the nervous systems of three macrodasyidan gastrotrichsACTA ZOOLOGICA, Issue 3 2003R. Hochberg Abstract The nervous systems of three macrodasyidan gastrotrichs, Dactylopodola baltica, Macrodasys caudatus and Dolichodasys elongatus, were investigated using immunocytochemistry and electron microscopy. Labelling of neural structures against serotonin revealed the presence of two pairs of cerebral cells, a dorsal cerebral connective, and paired ventral nerve cords in D. baltica. In M. caudatus and D. elongatus serotonin immunoreactivity was present in a single pair of dorsal cerebral cells and the ventral nerve cords; the dorsal connective of D. elongatus was also immunoreactive to serotonin and acetylated ,-tubulin. The presence of paired, serotonin-like immunoreactive cells in D. baltica and other species may represent the plesiomorphic condition in Macrodasyida. The fine structure of the photoreceptors in D. baltica was also investigated to explore the potential ground pattern for eyes in the Macrodasyida. The pigmented photoreceptors of D. baltica contain a unicellular pigment cup, sheath cell and sensory receptor. The pigment cup contains numerous osmiophilic granules that presumably function to shield the eyes from downwelling light in the red part of the spectrum. Projecting into the pigment cup and sheath cell are numerous microvilli from a bipolar sensory cell. A single sensory cell may represent the plesiomorphic condition in Macrodasyida, with multiplication of sensory cells representative of more derived taxa. [source] Material stiffness, branching pattern and soil matric potential affect the pullout resistance of model root systemsEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 6 2007S. B. Mickovski Summary Understanding of the detailed mechanisms of how roots anchor in and reinforce soil is complicated by the variability and complexity of both materials. This study controlled material stiffness and architecture of root analogues, by using rubber and wood, and also employed real willow root segments, to investigate the effect on pullout resistance in wet and air-dry sand. The architecture of model roots included either no laterals (tap-root) or a single pair at two different locations (herringbone and dichotomous). During pullout tests, data on load and displacement were recorded. These studies were combined with Particle Image Velocimetry (PIV) image analysis of the model root-soil system at a transparent interface during pullout to increase understanding of mechanical interactions along the root. Model rubber roots with small stiffness had increasing pullout resistance as the branching and the depth of the lateral roots increased. Similarly, with the stiff wooden root models, the models with lateral roots embedded deeper showed greatest resistance. PIV showed that rubber model roots mobilized their interface shear strength progressively whilst rigid roots mobilized it equally and more rapidly over the whole root length. Soil water suction increased the pullout resistance of the roots by increasing the effective stress and soil strength. Separate pullout tests conducted on willow root samples embedded in sand showed similar behaviour to the rigid model roots. These tests also demonstrated the effect of the root curvature and rough interface on the maximum pullout resistance. [source] Information rate bounds in common-mode aided wireline communicationsEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 5 2006Thomas Magesacher Communication over the copper twisted-pair channel is performed by transmitting and receiving differential-mode (DM) signals. In this paper, we extend the conventional DM receiver scheme by incorporating the common-mode (CM) signal, which is strongly correlated with the DM signal and can be extracted at the end of every wire pair. The wireline channel, including the CM receive signal, is modelled as a Gaussian vector (multiple-input multiple-output) channel with memory and an arbitrary number of disturbers that introduce interference which can be correlated both temporally and spatially. We investigate the potential of CM-aided reception in terms of information rate for single-user digital subscriber line systems (xDSL) operating on a single pair. Numerical results of information rate calculations using measured channel data are presented. The achievable information rate of the twisted-pair channel when incorporating the CM signal in practically relevant example scenarios can exceed the information rate of the conventional DM channel by a factor of up to two. Copyright © 2005 AEIT. [source] MINIMAL SELFING, FEW CLONES, AND NO AMONG-HOST GENETIC STRUCTURE IN A HERMAPHRODITIC PARASITE WITH ASEXUAL LARVAL PROPAGATIONEVOLUTION, Issue 3 2006Charles D. Criscione Abstract Little is known about actual mating systems in natural populations of parasites or about what constitutes the limits of a parasite deme. These parameters are interesting because they affect levels of genetic diversity, opportunities for local adaptation, and other evolutionary processes. We expect that transmission dynamics and the distribution of parasites among hosts should have a large effect on mating systems and demic structure, but currently we have mostly speculation and very few data. For example, infrapopulations (all the parasites in a single host) should behave as demes if parasite offspring are transmitted as a clump from host to host over several generations. However, if offspring are well mixed, then the parasite component population (all the parasites among a host population) would function as the deme. Similarly, low mean intensities or a high proportion of worms in single infections should increase the selfing rate. For species having an asexual amplification stage, transmission between intermediate and definitive (final) hosts will control the variance in clonal reproductive success, which in turn could have a large influence on effective sizes and rates of inbreeding. We examined demic structure, selfing rates, and the variance in clonal reproductive success in natural populations of Plagioporus shawi, a hermaphroditic trematode that parasitizes salmon. Overall levels of genetic diversity were very high. An a posteriori inference of population structure overwhelmingly supports the component population as the deme, rather than individual infrapopulations. Only a single pair of 597 adult individuals was identified as clones. Thus, the variance in clonal reproductive success was almost zero. Despite being hermaphroditic, P. shawi appears to be almost entirely outcrossing. Genetic estimates of selfing (<5%) were in accordance with the proportion of parasites from single infections. Thus, it appears that individual flukes outcross whenever possible and only resort to selfing when alone. Finally, our data support the hypothesis that aquatic transmission and the use of several intermediate hosts promotes high genetic diversity and well-mixed infrapopulations. [source] EVOLUTION OF SUBTERRANEAN DIVING BEETLES (COLEOPTERA: DYTISCIDAE HYDROPORINI, BIDESSINI) IN THE ARID ZONE OF AUSTRALIAEVOLUTION, Issue 12 2003Remko Leys Abstract Calcrete aquifers in arid inland Australia have recently been found to contain the world's most diverse assemblage of subterranean diving beetles (Coleoptera: Dytiscidae). In this study we test whether the adaptive shift hypothesis (ASH) or the climatic relict hypothesis (CRH) is the most likely mode of evolution for the Australian subterranean diving beetles by using a phylogeny based on two sequenced fragments of mitochondrial genes (CO1 and 16S-tRNA-ND1) and linearized using a relaxed molecular clock method. Most individual calcrete aquifers contain an assemblage of diving beetle species of distantly related lineages and/or a single pair of sister species that significantly differ in size and morphology. Evolutionary transitions from surface to subterranean life took place in a relatively small time frame between nine and four million years ago. Most of the variation in divergence times of the sympatric sister species is explained by the variation in latitude of the localities, which correlates with the onset of aridity from the north to the south and with an aridity maximum in the Early Pliocene (five mya). We conclude that individual calcrete aquifers were colonized by several distantly related diving beetle lineages. Several lines of evidence from molecular clock analyses support the CRH, indicating that all evolutionary transitions took place during the Late Miocene and Early Pliocene as a result of aridification. [source] Musculature of Notholca acuminata (Rotifera: Ploima: Brachionidae) revealed by confocal scanning laser microscopyINVERTEBRATE BIOLOGY, Issue 3 2003Martin V. Sørensen Abstract. The body-wall and visceral musculature of Notholca acuminata was visualized using phalloidin-linked fluorescent dye under confocal laser scanning microscopy. The body-wall musculature includes dorsal, lateral, and ventral pairs of longitudinally oriented body retractor muscles, two pairs of head retractors, three pairs of incomplete circular muscles, which are modified into dorso-ventral muscles, and a single pair of dorsolateral muscles. The visceral musculature consists of a complex of thick muscles associated with the mastax, as well as several sets of delicate fibers associated with the corona, stomach, gut, and cloaca, including thin longitudinal gut fibers and viscero-cloacal fibers, never before reported in other species of rotifers. The dorsal, lateral, and ventral retractor muscles and the incomplete circular muscles associated with the body wall appear to be apomorphies for the Rotifera. Muscle-revealing staining shows promise for providing additional information on previously unrecognized complexity in rotifer musculature that will be useful in functional morphology and phylogenetic analyses. [source] Refining the stress-gradient hypothesis for competition and facilitation in plant communitiesJOURNAL OF ECOLOGY, Issue 2 2009Fernando T. Maestre Summary 1The stress-gradient hypothesis (SGH) predicts that the frequency of facilitative and competitive interactions will vary inversely across abiotic stress gradients, with facilitation being more common in conditions of high abiotic stress relative to more benign abiotic conditions. With notable exceptions, most tests of the SGH have studied the interaction between a single pair or a few pairs of species, and thus have evaluated shifts in the magnitude and direction of pair-wise interactions along stress gradients, rather than shifts in the general frequency of interactions. 2The SGH has been supported by numerous studies in many ecosystems, has provided a crucial foundation for studying the interplay between facilitation and competition in plant communities, and has a high heuristic value. However, recent empirical research indicates that factors like the variation among species and the nature of the stress gradient studied add complexity not considered in the SGH, creating an opportunity to extend the SGH's general conceptual framework. 3We suggest that one approach for extending the SGH framework is to differentiate between the original idea of how ,common' interactions might be along stress gradients and the ubiquitous empirical approach of studying shifts in the strength of pair-wise interactions. Furthermore, by explicitly considering the life history of the interacting species (relative tolerance to stress vs. competitive ability) and the characteristics of the stress factor (resource vs. non-resource) we may be able to greatly refine specific predictions relevant to the SGH. 4We propose that the general pattern predicted by the SGH would hold more frequently for some combinations of life histories and stress factor, particularly when the benefactor and beneficiary species are mostly competitive and stress-tolerant, respectively. However, we also predict that other combinations are likely to yield different results. For example, the effect of neighbours can be negative at both ends of the stress gradient when both interacting species have similar ,competitive' or ,stress-tolerant' life histories and the abiotic stress gradient is driven by a resource (e.g. water). 5Synthesis. The extension of the SGH presented here provides specific and testable hypotheses to foster research and helps to reconcile potential discrepancies among previous studies. It represents an important step in incorporating the complexity and species-specificity of potential outcomes into models and theories addressing how plant,plant interactions change along stress gradients. [source] Highly variable microsatellite loci for studies of introduced populations of the small Indian mongoose (Herpestes javanicus)MOLECULAR ECOLOGY RESOURCES, Issue 4 2002C.-G. Thulin Abstract During their introduction, non-native species typically undergo founder events that reduce genetic variation. To allow a high-resolution genetic investigation of introduced populations of the small Indian mongoose (Herpestes javanicus), we developed primers for nine variable microsatellite loci. Their applicability was assessed in 10 mongooses from the large Fijian population, which originated from a single pair from Calcutta, India. The number of alleles ranged from two to five per locus, possibly as a result of preservation of initial variability and in situ mutations during the rapid population expansion after introduction. [source] Discovering robust protein biomarkers for disease from relative expression reversals in 2-D DIGE data.PROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 8 2007Troy J. Anderson Abstract This study assesses the ability of a novel family of machine learning algorithms to identify changes in relative protein expression levels, measured using 2-D DIGE data, which support accurate class prediction. The analysis was done using a training set of 36 total cellular lysates comprised of six normal and three cancer biological replicates (the remaining are technical replicates) and a validation set of four normal and two cancer samples. Protein samples were separated by 2-D DIGE and expression was quantified using DeCyder-2D Differential Analysis Software. The relative expression reversal (RER) classifier correctly classified 9/9 training biological samples (p<0.022) as estimated using a modified version of leave one out cross validation and 6/6 validation samples. The classification rule involved comparison of expression levels for a single pair of protein spots, tropomyosin isoforms and ,-enolase, both of which have prior association as potential biomarkers in cancer. The data was also analyzed using algorithms similar to those found in the extended data analysis package of DeCyder software. We propose that by accounting for sources of within- and between-gel variation, RER classifiers applied to 2-D DIGE data provide a useful approach for identifying biomarkers that discriminate among protein samples of interest. [source] The Optimisation of Drying Schedules for Pinus radiata Sapwood BoardsASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2004T.A.G. Langrish Optimal drying schedules have been predicted for the drying of Pinus radiata sapwood from an initial moisture content of 140% over a drying time of twenty-four hours for 50mm-thick boards. Initially, a single pair of dry and wet-bulb temperatures (108d,C. 60d,C) over the full time period is estimated to keep the total tangential strain under 50% of the predicted limiting failure value. However, after twelve hours drying, more severe conditions may be used, with the final moisture content predicted to be reduced from 8.2% for a constant set of conditions throughout the schedule (108d,C, 60d,C) to 2.4% when the dry-bulb temperature is raised from 108d,C to 122d,C after twelve hours. It is also possible to use a linearly increasing dry-bulb temperature after twelve hours, rising from 108d,C to 155d,C at the end of drying with a predicted final moisture content of 0.2%. However, to reduce the moisture content to only 10%, there is little difference between the ramped and two-step schedules, both yielding a total drying time of eighteen hours. The two-step schedule would be the easier to in practice. [source] Surface images of the short period contact binary AE PheASTRONOMISCHE NACHRICHTEN, Issue 3 2004J. R. Barnes Abstract We present high resolution Doppler images of the short period (P = 0.362 d) contact binary AE Phe. Using least squares deconvolution, we make use of the information content of the several thousand lines in each échelle spectrum to obtain the necessary S/N and time resolution required to resolve individual starspot features. A single pair of rotationally broadened profiles (free of sidelobes due to blending) with a typical S/N of 3000 - 4000 per spectrum is thus obtained. With 300 sec exposures we achieve a cadence of 350 sec which is equivalent to sampling the rotation phase every 4°. We derive images for four nights of data which reveal starspots at most latitudes on both components of the common envelope system. Individual starspots evolve significantly on very short timescales, of order one day; significantly faster than the week timescales found on active single stars and the Sun. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The Mystery of Perpendicular Fivefold Axes and the Fourth Dimension in Intermetallic StructuresCHEMISTRY - A EUROPEAN JOURNAL, Issue 13 2008Robert Abstract The structures of eight related known intermetallic structure types are the impetus to this paper: Li21Si5, Mg44Rh7, Zn13(Fe,Ni)2, Mg6Pd, Na6Tl, Zn91Ir11, Li13Na29Ba19, and Al69Ta39. All belong to the F3m space group, have roughly 400 atoms in their cubic unit cells, are built up at least partially from the ,-brass structure, and exhibit pseudo-tenfold symmetric diffraction patterns. These pseudo-tenfold axes lie in the ,1,1,0, directions, and thus present a paradox. The ,1,1,0, set is comprised of three pairs of perpendicular directions. Yet no 3D point group contains a single pair of perpendicular fivefold axes (by Friedel's Law, a fivefold axis leads to a tenfold diffraction pattern). The current work seeks to resolve this paradox. Its resolution is based on the largest of all 4D Platonic solids, the 600-cell. We first review the 600-cell, building an intuition discussing 4D polyhedroids (4D polytopes). We then show that the positions of common atoms in the F3m structures lie close to the positions of vertices in a 3D projection of the 600-cell. For this purpose, we develop a projection method that we call intermediate projection. The introduction of the 600-cell resolves the above paradox. This 4D Platonic solid contains numerous orthogonal fivefold rotations. The six fivefold directions that are best preserved after projection prove to lie along the ,1,1,0, directions of the F3m structures. Finally, this paper shows that at certain ideal projected cluster sizes related to one another by the golden mean (,=(1+,5)/2), constructive interference leading to tenfold diffraction patterns is optimized. It is these optimal values that predominate in actual F3m structures. Explicit comparison of experimental cluster sizes and theoretically derived cluster sizes shows a clear correspondence, both for isolated and crystalline pairs of projected 600-cells. [source] Rust of flax and linseed caused by Melampsora liniMOLECULAR PLANT PATHOLOGY, Issue 4 2007GREGORY J. LAWRENCE SUMMARY Melampsora lini, while of economic importance as the causal agent of rust disease of flax and linseed, has for several decades been the ,model' rust species with respect to genetic studies of avirulence/virulence. Studies by Harold Flor demonstrated that single pairs of allelic genes determine the avirulence/virulence phenotype on host lines with particular resistance genes and led him to propose his famous ,gene-for-gene' hypothesis. Flor's inheritance studies, together with those subsequently carried out by others, also revealed that, in some cases, an inhibitor gene pair and an avirulence/virulence gene pair interact to determine the infection outcome on host lines with particular resistance genes. Recently, avirulence/virulence genes at four loci, AvrL567, AvrM, AvrP4 and AvrP/AvrP123, have been cloned. All encode novel, small, secreted proteins that are recognized inside plant cells. Yeast two-hybrid studies have shown that the AvrL567 proteins interact directly with the resistance gene protein. The molecular basis of Flor's gene-for-gene relationship has now been elucidated for six interacting gene pairs: those involving resistance genes L5, L6, L7, M, P and P2, where both the resistance gene and the corresponding avirulence gene have been cloned. In other inheritance studies it has been shown that M. lini does not possess a (+) and (,) mating system, but may possess a two factor system. Double-stranded (ds) RNA molecules occur in many strains of M. lini: examination of the progeny of one strain that possesses 11 dsRNA molecules revealed that they fall into three transmission units, designated L, A and B. The L unit consists of a single large dsRNA of 5.2 kbp while the A and B units each consist of five dsRNAs in the size range 1.1,2.8 kbp. The three units have different sexual and asexual transmission characteristics. The L unit is encapsidated in a virus-like particle, whereas the other units are not encapsidated. The population and coevolutionary aspects of M. lini on a wild, native Australian host species, Linum marginale, have been extensively investigated. A recent molecular analysis revealed that the M. lini isolates from L. marginale fall into two distinct lineages, one of which is apparently hybrid between two diverse genomes. Isolates in this lineage are largely fixed for heterozygosity, which suggests that sexual recombination does not occur in this lineage. [source] | |||||||||||||