Symmetry Of Pattern Research Articles

Influence of characteristic parameters on the tribological properties of vein-bionic textured cylindrical roller thrust bearings

In this research, three types of vein-bionic texture patterns inspired by five kinds of leaves (Forsythia, Clausena lansium, Ash, Pipal, and Apricot) were designed and fabricated on the raceways of the shaft washers of cylindrical roller thrust bearings (CRTBs) through a fiber laser marking system. A vertical universal wear test rig was used to obtain the coefficient of friction (COF) of bearings under starved lubrication, with a customized tribo-pair. The wear losses of the shaft washers and the worn surfaces were characterized. The influence of different veins (chief, primary, secondary) and vein-structure characteristics (pattern symmetry, number of veins) on the tribological behavior of vein-bionic textured CRTBs is investigated and discussed. The results show that the original vein-bionic (V) pattern inspired by the Ash has the best friction-reducing performance, while the texture with the no-chief vein (NC) obtained by Clausena lansium has the best wear resistance. The chief vein mainly contributes to the low friction by enhancing the secondary lubrication effect and facilitating the formation of a protective nylon film. A reasonable mechanism for improving the tribological properties of resulting textures is proposed.

Overlapping Neural Responses to Reflectional Symmetry and Glass Patterns Revealed by an ERP Priming Paradigm

The extrastriate visual cortex is activated by visual regularity and generates an ERP known as the sustained posterior negativity (SPN). Spatial filter models offer a biologically plausible account of regularity detection based on the spectral properties of an image. These models are specific to reflection and therefore imply that reflectional symmetry and Glass patterns are coded by different neural populations. We utilised the SPN priming effect to probe representational overlap between reflection and Glass patterns. For each trial, participants were presented with a rapid succession of three patterns. In the Repeated condition, three reflections or three Glass patterns were presented. In the Changing condition, patterns alternated between reflection and Glass patterns. An increase in SPN amplitude (priming) was observed in both the Repeated and Changing conditions. Results indicate a greater representational overlap in the brain between reflection and Glass patterns than predicted by spatial filter models.

Strain engineering of the magnetic anisotropy and magnetic moment in NdFeO3 epitaxial thin films

Strain engineering is a powerful mean for tuning the various functionalities of ABO3 perovskite oxide thin films. Rare-earth orthoferrite RFeO3 materials such as NdFeO3 (NFO) are of prime interest because of their intriguing magnetic properties as well as their technological potential applications especially as thin films. Here, using a large set of complementary and advanced techniques, we show that NFO epitaxial thin films, successfully grown by pulsed laser deposition on (001)-SrTiO3, show a strong magnetic anisotropy below a critical thickness tc of 54 nm, associated with the occurrence of structural modifications related to symmetry and domain pattern changes. By varying the tensile misfit strain through the decrease of film thickness below tc, the amplitudes of in and out-of-plane magnetization can be continuously tuned while their ratio stays constant. Furthermore, different low-temperature magnetic behaviors are evidenced for strained and relaxed films, suggesting that the strain-induced structural state impacts the magnetic phase stability.

Identify Patterns in Online Bin Packing Problem: An Adaptive Pattern-Based Algorithm

Bin packing is a typical optimization problem with many real-world application scenarios. In the online bin packing problem, a sequence of items is revealed one at a time, and each item must be packed into a bin immediately after its arrival. Inspired by duality in optimization, we proposed pattern-based adaptive heuristics for the online bin packing problem. The idea is to predict the distribution of items based on packed items, and to apply this information in packing future arrival items in order to handle uncertainty in online bin packing. A pattern in bin packing is a combination of items that can be packed into a single bin. Patterns selected according to past items are adopted and periodically updated in scheduling future items in the algorithm. Symmetry in patterns and the stability of patterns in the online bin packing problem are discussed. We have implemented the algorithm and compared it with the Best-Fit in a series of experiments with various distribution of items to show its effectiveness.

From Chaos to Ordering: New Studies in the Shannon Entropy of 2D Patterns.

Properties of the Voronoi tessellations arising from random 2D distribution points are reported. We applied an iterative procedure to the Voronoi diagrams generated by a set of points randomly placed on the plane. The procedure implied dividing the edges of Voronoi cells into equal or random parts. The dividing points were then used to construct the following Voronoi diagram. Repeating this procedure led to a surprising effect of the positional ordering of Voronoi cells, reminiscent of the formation of lamellae and spherulites in linear semi-crystalline polymers and metallic glasses. Thus, we can conclude that by applying even a simple set of rules to a random set of seeds, we can introduce order into an initially disordered system. At the same time, the Shannon (Voronoi) entropy showed a tendency to attain values that are typical for completely random patterns; thus, the Shannon (Voronoi) entropy does not distinguish the short-range ordering. The Shannon entropy and the continuous measure of symmetry of the patterns demonstrated the distinct asymptotic behavior, while approaching the close saturation values with the increase in the number of iteration steps. The Shannon entropy grew with the number of iterations, whereas the continuous measure of symmetry of the same patterns demonstrated the opposite asymptotic behavior. The Shannon (Voronoi) entropy is not an unambiguous measure of order in the 2D patterns. The more symmetrical patterns may demonstrate the higher values of the Shannon entropy.

Diffraction enhancement of symmetry and modular structures.

Diffraction enhancement of symmetry (DES) is the phenomenon according to which the symmetry of the diffraction pattern of a crystal can be higher than the point symmetry of the structure that has produced it. The most well known example is that of Friedel's law, which is however violated in the presence of resonant scattering. This phenomenon is addressed in monoarchetypal modular structures and it is shown that a sufficient condition for DES is that both the module and the family of stacking vectors are invariant under an isometry that is not a symmetry operation for the structure. In general, DES is still observed in the presence of significant resonant scattering. The example of SiC polytypes, where the phenomenon has been confirmed experimentally, is studied in detail but the conclusions depend only on the symmetry of the layer and on the stacking vectors: the same applies therefore to all compounds sharing these features, like ZnS.

Seven-month-old infants detect symmetrical structures in multi-featured abstract visual patterns.

The present study investigated 7-month-old infants’ ability to perceive structural symmetry in mosaic-like abstract visual patterns. We examined infants’ (n = 98) spontaneous looking behaviour to mosaic-like sequences with symmetrical and asymmetrical structures. Sequences were composed of square tiles from two categories that differed in their colour scheme and internal shape. We manipulated sequence length (3 or 5 tiles) and abstractness of the symmetry (token vs. category level). The 7-month-olds discriminated structurally symmetrical from asymmetrical mosaics in the first half of the test phase (first 8 trials). Sequence length, level of symmetry, or number of unique tiles per sequence did not significantly modulate infants’ looking behaviour. These results suggest that very young infants detect differences in structural symmetry in multi-featured visual patterns.

A transparent ultra-broadband microwave absorber based on flexible multilayer structure

In this work, a transparent ultra-broadband microwave absorber (MA) based on flexible multilayer structure was demonstrated. The designed resonant structure consists of a resistive film pattern of indium tin oxide (ITO) on a flexible substrate PET. By adjusting the size of the resonant layer ITO pattern and the array position arrangement, an ultra-broadband absorption of over 90% is achieved in the frequency range 8.6–75.8 GHz, with a relative absorption bandwidth of 159%. At the same time, the transparent flexible medium polydimethy-lsiloxane (PDMS) and PET substrate are used to obtain good optical transmittance. Due to the quadruple symmetry of the resistive film resonance pattern, MA shows high polarization insensitivity. For TE and TM polarised waves, the proposed MA can maintain an absorption rate greater than 80% as the angle of incidence is increased to 40°. The current distribution of each resonant layer at strong resonant frequency is simulated and analysed to determine the absorption mechanism of MA. A sample consisting of 11 × 11 cells was produced and the experimental measurements were in general consistent with the numerical simulation results. Due to its ultra-wideband absorption characteristics and wide incident angle stability, it has potential application value in the fields of radar stealth system and transparent electromagnetic shielding.

Spontaneous symmetry breaking in ride-sharing adoption dynamics

Symmetry breaking ubiquitously occurs across complex systems, from phase transition in statistical physics to self-organized lane formation in pedestrian dynamics. Here, we uncover spontaneous symmetry breaking in a simple model of ride-sharing adoption. We analyze how collective interactions among ride-sharing users to avoid detours in shared rides give rise to spontaneous symmetry breaking and pattern formation in the adoption dynamics. These dynamics result in bistability of high homogeneous and partial heterogeneous adoption states, potentially limiting the population-wide adoption of ride sharing. Our results provide a framework to understand real-world adoption patterns of ride sharing in complex urban settings and support the (re)design of ride-sharing services and incentives for sustainable shared mobility.

Learning the crystal structure genome for property classification

Materials property predictions have improved from advances in machine learning algorithms, delivering materials discoveries and novel insights through data-driven models of structure-property relationships. Nearly all available models rely on featurization of materials composition, however, whether the exclusive use of structural knowledge in such models has the capacity to make comparable predictions remains unknown. Here we employ a deep neural network model to decode structure-property relationships in crystalline materials without explicitly considering chemical compositions. The focus is on classification of crystal systems, mechanical elasticity, electronic band gap, and phase stability. Our model utilizes a three-dimensional (3D) momentum space representation of structure from elastic x-ray scattering theory that exhibits rotation and permutation invariance. We perform novel ablation studies to help interpret the model performance by perturbing the physically meaningful input features (i.e., the diffraction patterns) instead of tuning the architecture of the learning model as in conventional ablation methods. We find that the spatial symmetry of the 3D diffraction patterns, which reflects crystalline symmetry operations, is more important than the diffraction intensities contained within for the model to make a successful classification. Our work showcases the potential of using statistical learning models to help understand materials physics, rather than performing predictive and generative tasks as in most materials informatics research. We also argue that learning the crystal structure genome in a chemistry-agnostic manner demonstrates that some crystal structures inherently host high propensities for optimal materials properties, which enables the decoupling of structure and composition for future codesign of multifunctionality.

Tessellations on bidimensional materials based on Phthalocyanine and applications: a review

In this review, we explore the bidimensional materials based on phthalocyanine molecules. The phthalocyanine molecule is used as a brick for the construction of new bidimensional materials. In particular, the phthalocyanine molecules can be placed at each vertex or sharing edges to form tessellations. The tessellations available are constrained to the four-fold type of the phthalocyanine molecules and can be a mix of several polygons to increase the number of possibilities. Computationally, the popular tessellations used are the Archimedean tiling, but many others expect to be discovered and well-studied. Different tessellations will provide new symmetric systems to explore. Each new symmetry pattern will modify the physical and chemical properties of the new bi-dimensional material. These new materials present many exciting applications as capture and storage of greenhouse gases and molecular electronic devices. In the present review, we summarized some of these tessellations and the many applications that they can have.

Preferred Spin Excitations in the Bilayer Iron-Based Superconductor CaK(Fe_{0.96}Ni_{0.04})_{4}As_{4} with Spin-Vortex Crystal Order.

Spin-orbit coupling (SOC) is a key to understand the magnetically driven superconductivity in iron-based superconductors, where both local and itinerant electrons are present and the orbital angular momentum is not completely quenched. Here, we report a neutron scattering study on the bilayer compound CaK(Fe_{0.96}Ni_{0.04})_{4}As_{4} with superconductivity coexisting with a noncollinear spin-vortex crystal magnetic order that preserves the tetragonal symmetry of the Fe-Fe plane. In the superconducting state, two spin resonance modes with odd and even L symmetries due to the bilayer coupling are found similar to the undoped compound CaKFe_{4}As_{4} but at lower energies. Polarization analysis reveals that the odd mode is c-axis polarized, and the low-energy spin anisotropy can persist to the paramagnetic phase at high temperature, which closely resembles other systems with in-plane collinear and c-axis biaxial magnetic orders. These results provide the missing piece of the puzzle on the SOC effect in iron-pnictide superconductors, and also establish a common picture of c-axis preferred magnetic excitations below T_{c} regardless of the details of magnetic pattern or lattice symmetry.

Strides to Achieve a Stable Symmetry Index During Running.

The quality of running mechanics is often characterized by limb pattern symmetry and used to support clinical decisions throughout the rehabilitation of lower-extremity injuries. It is valuable to ensure that gait analyses provide stable measures while not asking an individual to complete an excessive number of running strides. The present study aimed to determine the minimum number of strides required to establish a stable mean symmetry index (SMSI) of discrete-level measures of spatiotemporal parameters, joint kinematics, and joint kinetics. Further, the study aimed to determine if differences occurred between random and consecutive strides for directional and absolute symmetry indices. Descriptive laboratory study. A sequential average was used to determine how many strides were required to achieve a SMSI within a 60-second trial. Multiple 2-factor repeated-measure analysis of variances were used to determine if differences between bins of strides and symmetry calculations were significantly different. A median SMSI was achieved in 15 strides for all biomechanical variables. There were no significant differences (P > .05) found between consecutive and random bins of 15 strides within a 60-second trial. Although there were significant differences between symmetry calculation values for most variables (P < .05), there appeared to be no systematic difference between the numbers of strides required for stable symmetry for either index. As 15 strides were sufficient to achieve a SMSI during running, a continued emphasis should be placed on the number of strides collected when examining interlimb symmetry.

Locomotion asymmetry in young Standardbred trotters in training and links to future racing career

This study evaluated whether front and hind limb symmetry patterns observed from 1.5 through 3 years of age in Standardbred trotters in training affect racing activity at older age. The hypothesis tested was that asymmetries observed during this period are linked to reduced number of lifetime races and low earnings. Sixteen Standardbreds were subjected to a controlled training and dietary programme from the age of 1.5 years until December as 3-year-olds (P1) and then continued their career with other trainers. On 17 occasions during P1, locomotion asymmetry (vector sum) in front and hind limbs during trot in hand was recorded with a sensor-based system. By 10 years of age, data on lifetime number of races and earnings of the horses were obtained from the Swedish Trotting Association. Horses were divided in groups based on the number of lifetime races performed, i.e. more or less than the median of the cohort born the same year. Mean asymmetry levels did not differ between horses performing more or less lifetime races than the cohort median. However, horses that showed the poorest lifetime race activity showed elevated hind limb asymmetry in August at the age of 3 years, compared to horses with more races (group &lt;median: 9±6 mm vs group &gt;median: 6±2 mm (P=0.02)). There were no correlations between individual mean and peak asymmetries and lifetime earnings. It is concluded that locomotion symmetry observed during trot in hand at the age of 1.5-year-olds to December as 3-year-olds was not a simple and straight-forward predictor of future racing career. However, hind limb asymmetries of around 10 mm in the late season as 3-year-olds could be a warning of impaired future performance.

Rule Similarity and Axis Symmetry Patterns in Young Patients with Bilateral Astigmatism.

To report rule similarity and axis symmetry patterns in young subjects with bilateral astigmatism. The cross-sectional study was conducted at Al-Shifa Trust Eye Hospital, Rawalpindi, Pakistan, from October 1, 2018, to March 31, 2019, and comprised diagnosed cases of bilateral astigmatism of either gender aged 15-45 years. After giving detailed ophthalmic history, all the participants underwent autorefraction followed by subjective refraction. Based on refractive status, rule similarity was categorised as isorule or anisorule, while axis symmetry was categorised as direct or mirror. Data was analysed using SPSS 20. Of the 204 participants, 128(62.7%) were males and 76(37.3%) were females. The overall mean age was 26.64±8.44 years. Isorule astigmatism was present in 169(82.8%) participants, while 125(61.3%) had a mirror pattern of axis symmetry. Under the mirror and direct symmetry models, the medians of absolute difference in the axis of fellow eyes were 10 and 5 degrees respectively from exact symmetry. No significant association of rule similarity or symmetry of axis was found with age or gender (p>0.05), while significant association was found between rule similarity and type of astigmatism (p<0.001). Bilateral astigmatism of isorule category was found in majority of the participants, while mirror symmetry of the axis was more common than direct symmetry.

Infrared thermography as an adjunctive tool for detection of femoral arterial thrombosis after cardiac catheterization: A prospective, pilot study.

To assess the utility of infrared thermography (IRT), to map skin temperature, in the detection of femoral arterial (FA) thrombosis after cardiac catheterization. Ultrasound is a validated method for thrombus detection but is generally reserved as a confirmatory test for clinical suspicion due to various constraints. Prospective study of infants and children undergoing cardiac catheterization via FA access, comparing IRT and pulse examination. The thermograms, displayed in a color map with each pixel representing a temperature, were examined by qualitative assessment of symmetry in thermal patterns and quantitative image analysis with abnormal thermographic asymmetry defined as a difference of >10% between limbs. In the 20 children enrolled, excellent agreement was found between the two methods with a Kappa value of 0.89. The median thermographic asymmetry in the nine children with pulse loss was 36 (13-76)%. Using receiver operating characteristicanalysis, the asymmetrical pattern of ≥18% between limbs predicted the need for anticoagulation with a sensitivity of 100% and specificity of 89%. The area under the curve was 0.97 (95% confidence interval: 0.95-1). Children with absent pulse requiring anticoagulation showed a slower recovery in thermal asymmetry compared to those with a reduced pulse. By qualitative IRT assessment, all children with absent pulse requiring anticoagulation were correctly identified by 10 independent assessors. This pilot study showed that IRT is feasible and reliable as an adjunctive tool for thrombus detection postcatheterization and treatment monitoring. Specific advantages of IRT include portability, affordability, and contactless image acquisition.

An Alternative Low-Cost Embedded NILM System for Household Energy Conservation with a Low Sampling Rate

The measurement of the energy consumption of electrical appliances, where the meter is installed at a single point on the main input circuit of the building, is called non-intrusive load monitoring (NILM). The NILM method can distinguish the loads that are currently active and break down how the loads consume electricity. A microcontroller with embedded software was selected to read the data into the NILM method process at a low sampling rate every 1 s or 1 Hz. The measured data and the data obtained by the NILM algorithm were displayed via an internet platform. This article presents an alternative low-cost embedded NILM system for household energy conservation with a low sampling rate, which could identify electrical appliances such as an air conditioner, refrigerator, television, electric kettle, electric iron, microwave oven, rice cooker, and washing machine. Four features of symmetry pattern were extracted, containing information on the value of active power change, the value of reactive power change, the number of intersection points between the active power data and the reference line, and an estimation of an equation for the starting characteristics of the electrical equipment. The proposed NILM system was tested in a selected test house that used a single-phase power system. A typical meter was also installed to compare the results with the proposed NILM. The validity of the tests was checked for 1 month in 3 houses to analyze the results. The proposed method was able to detect 91.3% of total events. The accuracy of the average ability of the system to disaggregate devices was 0.897. The accuracy value for total power consumption was 0.927. The continuous data recording of the NILM method provides information on the behavior of electrical appliances that can be used for maintenance and warnings.

Shannon (Information) Measures of Symmetry for 1D and 2D Shapes and Patterns

In this paper, informational (Shannon) measures of symmetry are introduced and analyzed for patterns built of 1D and 2D shapes. The informational measure of symmetry Hsym(G) characterizes the averaged uncertainty in the presence of symmetry elements from group G in a given pattern, whereas the Shannon-like measure of symmetry Ωsym(G) quantifies the averaged uncertainty of the appearance of shapes possessing a total of n elements of symmetry belonging to group G in a given pattern. Hsym(G1)=Ωsym(G1)=0 for the patterns built of irregular, non-symmetric shapes, where G1 is the identity element of the symmetry group. Both informational measures of symmetry are intensive parameters of the pattern and do not depend on the number of shapes, their size, and the entire area of the pattern. They are also insensitive to the long-range order (translational symmetry) inherent for the pattern. Additionally, informational measures of symmetry of fractal patterns are addressed, the mixed patterns including curves and shapes are considered, the time evolution of Shannon measures of symmetry are examined, the close-packed and dispersed 2D patterns are analyzed, and an application of the suggested measures of symmetry for the analysis of the chemical reaction is demonstrated.

The chronometry of symmetry detection in the lateral occipital (LO) cortex

The lateral occipital cortex (LO) has been shown to code the presence of both vertical and horizontal visual symmetry in dot patterns. However, the specific time window at which LO is causally involved in symmetry encoding has not been investigated. This was assessed using a chronometric transcranial magnetic stimulation (TMS) approach. Participants were presented with a series of dot configurations and instructed to judge whether they were symmetric along the vertical axis or not while receiving a double pulse of TMS over either the right LO (rLO) or the vertex (baseline) at different time windows (ranging from 50 ms to 290 ms from stimulus onset). We found that TMS delivered over the rLO significantly decreased participants’ accuracy in discriminating symmetric from non-symmetric patterns when TMS was applied between 130 ms and 250 ms from stimulus onset, suggesting that LO is causally involved in symmetry perception within this time window. These findings confirm and extend prior neuroimaging and ERP evidence by demonstrating not only that LO is causally involved in symmetry encoding but also that its contribution occurs in a relatively large temporal window, at least in tasks requiring fast discrimination of mirror symmetry in briefly (75 ms) presented patterns as in our study.

Effects of scanning strategies on residual stress and deformation by high-power direct energy deposition: Island size and laser jump strategy between islands

The path-dependent residual stress and deformation are two critical defects of the parts fabricated by direct energy deposition (DED). The optimal design of the scanning strategy is an important method for controlling the residual stress and deformation. In this paper, a thermo-mechanical finite element model based on the modified flash heat method was developed to simulate the high-power DED process. The effects of the island size and the laser jump strategy between islands were investigated on the residual stress and deformation in the high-power DED component. The dependence of residual deformation on the laser jump strategy between islands was discussed. An evaluation method for the laser jump strategy was proposed. Finally, we carried out experiments for the validation. The results show that the z-direction maximum residual deformation decreases by 17.3%. The ratio of the area with high residual von Mises stress decreases from 93.1% to 5.1% when the island size decreases from 160 mm to 20 mm. We found that different laser jump strategies between islands lead to significant differences in residual deformation. Increasing the laser jump distance between islands plays a vital role in reducing the residual deformation. The dual-diagonal symmetry pattern and the “least” heat influence pattern lead to minimum residual deformation. The superposition and offset of the deformation caused by the mechanical interaction between islands have a remarkable effect on the history of the deformation in the DED process. The proposed evaluation method is reliable for designing or optimizing the laser jump strategy between islands. The optimal design idea of the laser jump strategy between islands is to adopt the large laser jump distance between islands while reducing the number of adjacent islands when depositing a new island. This work provides important insights for the scanning path planning of large parts built by high-power DED.