SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Symmetric relation

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This note looks into the reasons why earlier reports may have arrived at differing conclusions about pigeons' capacity to categorize bilaterally symmetric and asymmetric visual patterns. Attention is drawn to pigeons' comparatively superior visual flicker resolution and superior visual linear acuity by reporting results of two ad-hoc experiments. This circumstance turns out to constrain conclusions drawn by earlier symmetry-asymmetry studies that used computer-generated patterns displayed on cathode ray tube monitors as these suffered from pictorial distortions. Additionally one of the studies involved patterns of inconsistent symmetry at global and local levels. A smaller-scale experiment using slide-projected unequivocal symmetric and asymmetric patterns yielded results compatible with the supposition that pigeons are capable of a symmetry-asymmetry categorization. The possibility that an artfactual cue may have inadvertently accentuated this capability in an earlier own experiment is considered.

Concepts: Symmetry, Experiment, Logic, Categorization, Aesthetics, Symmetric relation, Cathode ray tube, Cathode ray

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Diffusion MRI allows us to make inferences on the structural organisation of the brain by mapping water diffusion to white matter microstructure. However, such a mapping is generally ill-defined; for instance, diffusion measurements are antipodally symmetric (diffusion along x and -x are equal), whereas the distribution of fibre orientations within a voxel is generally not symmetric. Therefore, different sub-voxel patterns such as crossing, fanning, or sharp bending, cannot be distinguished by fitting a voxel-wise model to the signal. However, asymmetric fibre patterns can potentially be distinguished once spatial information from neighbouring voxels is taken into account. We propose a neighbourhood-constrained spherical deconvolution approach that is capable of inferring asymmetric fibre orientation distributions (A-fods). Importantly, we further design and implement a tractography algorithm that utilises the estimated A-fods, since the commonly used streamline tractography paradigm cannot directly take advantage of the new information. We assess performance using ultra-high resolution histology data where we can compare true orientation distributions against sub-voxel fibre patterns estimated from down-sampled data. Finally, we explore the benefits of A-fods-based tractography using in vivo data by evaluating agreement of tractography predictions with connectivity estimates made using different in-vivo modalities. The proposed approach can reliably estimate complex fibre patterns such as sharp bending and fanning, which voxel-wise approaches cannot estimate. Moreover, histology-based and in-vivo results show that the new framework allows more accurate tractography and reconstruction of maps quantifying (symmetric and asymmetric) fibre complexity.

Concepts: Statistics, Mathematics, In vivo, Magnetic resonance imaging, Logic, Voxel, Analogy, Symmetric relation

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The bony structures of the face provide the framework upon which the soft-tissue envelope rests, such that facial symmetry and proportionality usually depend upon the morphological patterns and anthropometrical measurements of a symmetrical skull. Facial bony pillars are dynamic and variable according to the demands placed upon them, as well as gender and aging differences. Thus, a more profound knowledge of facial supporting pillars and their dynamic behavior by physicians who practice minimally cosmetic procedures would allow for a more natural approach to facial beautification. It would help them to rebalance age-related and asymmetric congenital imperfections, and minimize any harmful stigma associated with bad cosmetic practice.

J Drugs Dermatol. 2018;17(4):466-470.

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Concepts: Symmetry, Group, According to Jim, Face, Aesthetics, Asymmetry, Beauty, Symmetric relation

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The fragmentation of doubly and triply charged mercury clusters is theoretically studied to analyze an experiment performed by Katakuse’s group at Osaka University [T. Satoh et al., J. Mass Spectrom. Soc. Jpn. 51, 391 (2003)]. The fission barrier is calculated using a liquid-drop model proposed by Echt et al. In the decay of doubly charged clusters, the barrier height is found to take the minimum value for nearly symmetric fission. On the other hand, in the decay of triply charged clusters, the barrier is the lowest for strongly asymmetric fission. These results well explain the product size distribution observed in the experiment. The appearance size for multiply charged clusters measured in the experiment is found to be the size where the fission barrier is equal to the monomer evaporation energy. These findings provide evidence that small mercury clusters behave like van der Waals clusters in the process of fragmentation.

Concepts: Mass, Van der Waals force, Group, Equals sign, Equality, The Barrier, Symmetric relation, Osaka

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Healthcare-associated infections (HAIs) affect millions of patients every year. Pathogen transmission via fomites and healthcare workers (HCWs) contribute to the persistence of HAIs in hospitals. A critical parameter needed to assess risk of environmental transmission is the pathogen transfer efficiency between fomites and fingers. Recent studies have shown that pathogen transfer is not symmetric. In this study,we evaluated how the commonly used assumption of symmetry in transfer efficiency changes the dynamics of pathogen movement between patients and rooms and the exposures to uncolonized patients.

Concepts: Health care provider, Patient, Symmetry, Educational psychology, Group theory, Aesthetics, Asymmetry, Symmetric relation

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Electrophysiological studies of symmetry have found a difference wave termed the Sustained Posterior Negativity (SPN) related to the presence of symmetry. Yet the extent to which the SPN is modulated by luminance-polarity and colour content is unknown. Here we examine how luminance-polarity distribution across the symmetry axis, grouping by luminance polarity, and the number of colours in the stimuli, modulate the SPN. Stimuli were dot patterns arranged either symmetrically or quasi-randomly. There were several arrangements: ‘segregated’-symmetric dots were of one polarity and random dots of the other; ‘unsegregated’-symmetric dots were of both polarities in equal proportions; ‘anti-symmetric’-dots were of opposite polarity across the symmetry axis; ‘polarity-grouped anti-symmetric’-as anti-symmetric but with half the pattern of one polarity and the other opposite; multi-colour symmetric patterns made of either two, three and four colours. We found that the SPN is: reduced by the amount of position-symmetry, sensitive to luminance-polarity mismatch across the symmetry axis and not modulated by the number of colours in the stimuli. Our results show that the sustained nature of the SPN coincides with the late onset of a topographic microstate sensitive to symmetry. These findings emphasise the importance of not only position symmetry, but also luminance polarity matching across the symmetry axis.

Concepts: Symmetry, Color, Dots, Symmetry group, Rotational symmetry, Point groups in three dimensions, Reflection symmetry, Symmetric relation

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The experimental analysis of derived stimulus relations is a critical research area. A training-then-testing preparation nearly always is used to study derived relations. In the training phase, participants learn the relevant baseline discriminations via differential consequences (e.g., AB and AC relations). In the testing phase, they are presented with probe trials in the absence of differential consequences (e.g., BA and CA symmetry trials and BC and CB equivalence trials). High accuracy levels sometimes are observed from the start of testing such that it is unclear whether the participants learned these relations before testing. The present experiment reports data from a novel preparation that monitors the development of derived relations as trained relations are acquired. Three college students were presented with both training trials (AB, AC) and testing trials (BA, CA, BC, CB) in every session from the start of experimentation. Each participant learned each of the six discriminations by the end of experimentation. Most importantly, they learned the trained and symmetrical relations in close temporal proximity and the equivalence relations only after learning the symmetrical relations. These results are consistent with several findings demonstrating disparities between learning different forms of derived relational responding. The results validate the utility of the present preparation in the experimental analysis of derived relational learning.

Concepts: Skill, Experiment, Hypothesis, Learning, Developmental psychology, Knowledge, Symmetric relation, Group action

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We study the symmetric properties of waveguide modes in presence of gain/losses, anisotropy/bianisotropy, or continuous/discrete rotational symmetry. We provide a comprehensive approach to identity the modal symmetry by constructing a 4 × 4 waveguide Hamiltonian and searching the symmetric operation in association with the corresponding waveguides. We classify the chiral/time reversal/parity/parity time/rotational symmetry for different waveguides, and provide the criterion for the aforementioned symmetry operations. Lastly, we provide examples to illustrate how the symmetry operations can be used to classify the modal properties from the symmetric relation between modal profiles of several different waveguides.

Concepts: Angular momentum, Symmetry, Group, Rotational symmetry, Point groups in three dimensions, Symmetric relation, Symmetry combinations, Antisymmetric relation

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It has previously been reported that individuals prefer figures from which they can extract shapes via illusory contours (Kanisza figures) over figures in which this is not possible. However, based on the past research in this area, it is not possible to distinguish the influence of illusory contour perception from other factors such as the symmetry, familiarity, prototypicality, and nameability of the perceived shape. Here, we investigate the influence of illusory contours in the absence of these confounding variables by measuring participants' aesthetic/liking ratings for symmetric Kanisza figures and for unfamiliar and asymmetric Kanisza figures. Results show that illusory contours do indeed influence preference above and beyond any effects of these other factors. (PsycINFO Database Record

Concepts: Cognition, Geometry, Group, Binary relation, Gestalt psychology, Symmetric relation

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We study the symmetry properties in the dynamics of quantum correlations for two-qubit systems in one-sided noisy channels, with respect to a switch in the location of noise from one qubit to the other. We consider four different channel types, namely depolarizing, amplitude damping, bit-flip, and bit-phase-flip channel, and identify the classes of initial states leading to symmetric decay of entanglement, non-locality and discord. Our results show that the symmetric decay of quantum correlations is not directly linked to the presence or absence of symmetry in the initial state, while it does depend on the type of correlation considered as well as on the type of noise. We prove that asymmetric decay can be used to infer, in certain cases, characteristic properties of the channel. We also show that the location of noise may lead to dramatic changes in the persistence of phenomena such as entanglement sudden death and time-invariant discord.

Concepts: Group theory, Typography, Matrix, Quantum entanglement, Symmetric relation