Star-shaped Research Articles

Mechanical properties of a hybrid auxetic metamaterial and metastructure system

We propose in this work an innovative hybrid auxetic metamaterial with a centersymmetric unit cell and tessellation topology similar to the one provided by the missing rib configuration. The tessellation proposed is applied to different core unit cells (star shape, cross-chiral shape with same dimensions, and reentrant). The effects of the geometric parameters of the cells on the in-plane mechanical properties of this hybrid auxetic metamaterial system are investigated via finite elements (FEMs). Representative unit cells (RUCs) with optimal mechanical behaviors are identified; those configurations exhibit the larger negative Poisson’s ratios and enhanced specific moduli. Designs related to two groups of auxetic metastructures with cylindric and cubic shapes are then developed based on the optimized RUCs along x and y directions. The equivalent mechanical performance of these metastructures under internal pressure is evaluated from a numerical standpoint. Auxetic cylindrical metastructures can be tailored by adjusting the number of the optimized RUCs along the circumferential and longitudinal directions, together with the geometric parameters of the optimized RUC itself. These hybrid auxetic metamaterials and metastructures provide the potential for multifunctional applications in biomechanics, flexible electronics, and aerospace.

Biocompatibility of New SiO2 Anti‐Bacterial Material Synthesized by Sol–Gel Route

AbstractSilica material is prepared through sol–gel route using tetramethylorthosilicate as alkoxide precursor. The material is characterized by Fourier transformed InfraRed spectroscopy, and its amorphous state is ascertained by X‐ray powder diffraction (XRD). The SiO2 sol–gel bio‐glass shows antibacterial activity towards the Gram‐negative Escherichia coli with a clear halo zone diameter. Furthermore, in order to assess biocompatibility, a primary fibroblast cell line is seeded on biomaterial fragments, sterilized, and directly introduced inside the culture dishes. To show the relations between biomaterial‐cultured cells, a morphological study is performed by light microscopy during all the incubation time and finally the cultures are stopped after 7, 14, and 21 days of incubation. A suitable biocompatibility of the SiO2 sol–gel bio‐glass is observed. In fact, cells maintained their conventional star shape and the monolayer stratified at the dish bottom show only minimal disruption in the biomaterial‐rubbing points, without any other morphological alteration.

Clinical Course of Terminal Ileal Ulcers Observed Incidentally During Colonoscopy.

Cecal intubation is essential during colonoscopy, and observation of the terminal ileum is performed in most clinical practices. However, data on terminal ileal (TI) ulcers observed incidentally during colonoscopy are rare. We aimed to identify the characteristics and clinical course of TI ulcers observed incidentally during colonoscopy. Between January 2008 and December 2018, medical records from multi-centers reporting asymptomatic subjects who underwent biopsy on TI ulcers during colonoscopy were retrospectively reviewed. The characteristics of endoscopic findings and clinical course of TI ulcers were analyzed, and the factors affecting the clinical course of TI ulcers were evaluated. The median follow-up durations from first to second colonoscopy and from second to third colonoscopy were 20months (interquartile range, 12-36) and 24months (interquartile range, 12-34), respectively. A total of 134 subjects were included in the analysis. The histopathologic findings of TI ulcers were mostly chronic or active ileitis/inflammation (92.7%). On the second colonoscopy, 59 (44.0%) patients had no ulcers, 38 (28.4%) showed a decrease in size or number, and 37 (27.6%) patients showed no change in ulcers. Among 62 subjects who underwent a third colonoscopy, 14 (10.4%) had decreased size or number, 10 (7.5%) had no ulcer change, and two (1.5%) had increased ulcer size or number. In multivariate logistic regression analysis, a star shape was the only factor affecting continuation without improvement of incidental TI ulcers. Most TI ulcers observed incidentally showed no unusual findings on biopsy and improved on follow-up colonoscopy without treatment.

Evolutionary analysis of SARS-CoV-2 spike protein for its different clades.

The spike protein of severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) has become the main target for antiviral and vaccine development. Despite its relevance, e information is scarse about its evolutionary traces. The aim of this study was to investigate the diversification patterns of the spike for each clade of SARS‐CoV‐2 through different approaches. Two thousand and one hundred sequences representing the seven clades of the SARS‐CoV‐2 were included. Patterns of genetic diversifications and nucleotide evolutionary rate were estimated for the spike genomic region. The haplotype networks showed a star shape, where multiple haplotypes with few nucleotide differences diverge from a common ancestor. Four hundred seventy‐nine different haplotypes were defined in the seven analyzed clades. The main haplotype, named Hap‐1, was the most frequent for clades G (54%), GH (54%), and GR (56%) and a different haplotype (named Hap‐252) was the most important for clades L (63.3%), O (39.7%), S (51.7%), and V (70%). The evolutionary rate for the spike protein was estimated as 1.08 × 10−3 nucleotide substitutions/site/year. Moreover, the nucleotide evolutionary rate after nine months of the pandemic was similar for each clade. In conclusion, the present evolutionary analysis is relevant as the spike protein of SARS‐CoV‐2 is the target for most therapeutic candidates; besides, changes in this protein could have consequences on viral transmission, response to antivirals and efficacy of vaccines. Moreover, the evolutionary characterization of clades improves knowledge of SARS‐CoV‐2 and deserves to be assessed in more detail as re‐infection by different phylogenetic clades has been reported.

Effect of Sulfurization Temperature on RF Sputtered MoS2 Thin Film

Molybdenum disulfide (MoS2) is one among the transition-metal dichalcogenide (TMD) family which exhibits exotic physical properties at their mono-layer limit. We report a facile way to fabricate stoichiometric, crystalline and star shaped MoS2 film. In this work, ultra-thin MoS2 films were fabricated by two step process (i) RF sputtering of MoS2 target followed by (ii) sulfurization to improve stoichiometry and crystallinity. In order to study the effect of sulfurization temperature on sputtered MoS2, sulfurization has been performed at five different temperatures - 700, 750, 775, 800 and 825°C. Surface morphology of as sputtered and sulfurized MoS2 films were characterized using optical and scanning electron microscopes. Crystallinity and layer thickness of the fabricated MoS2 films were estimated by using Laser Raman spectroscopy. These results confirm that as sputtered MoS2 films are discontinuous, amorphous in nature and it crystalizes into a layered structure during sulfurization at temperature ≥ 750°C. It was observed that at sulfurization temperature of 800°C, the nucleated crystallites well grown into a star shaped crystalline MoS2 with their thickness vary between 2 and 3 mono-layers. These star shapes can provide more surface area/edges that can be exploited to enhance the efficiency of gas sensors.

RBF collocation and hybrid-LHI methods for Stokes systems and its application to controllability problems

The purpose of this article is to introduce radial basis function (RBF) methods for solving both direct Stokes equations and controllability problems for the Stokes system with few internal scalar controls. In both cases, Dirichlet or Navier-slip boundary conditions are considered. We introduce two radial basis function solvers, one global and the other local, to solve Stokes equations. These methods are used to discretize the primal and adjoint systems related to the controllability problems. Both techniques are based on divergence-free global RBFs. A global colocation technique based on Div-free inverse multi-quadrics is formulated and analyzed. A generalization of scalar hybrid kernels to a vector divergence-free hybrid RBFs setting is defined. Based on these kernels, the local Hermite interpolation (LHI) method in vector form is introduced. Due to the properties of the hybrid kernel, we show that due to the properties of the hybrid kernel this local method, can reduce up to double precision, the value of the condition number of the local Gram matrices. Simultaneously, it is proved that the real components of the eigenvalues corresponding to the global LHI matrix are negative and that consequently backward difference formulas are stable for time integration. The conjugate gradient algorithm is adapted to the radial basis function setting to solve the controllability problems. Several benchmarks problems in two dimensions with a non-convex domain (a star shape) are numerically solved by these RBFs methods to display and compare their feasibility. The solutions to these problems are also implemented by finite element techniques to study their relative performance.

Security analysis of image CAPTCHA using a mask R-CNN-based attack model

The CAPTCHAs are attacked by automated programs to break their underlying design principle. Therefore, analysing the robustness of CAPTCHA is the critical requirement. Recently, a neural style transfer-based image CAPTCHA called style area CAPTCHA (SACAPTCHA) has been reported. Though the security of SACAPTCHA is evaluated on R-CNN and FCN attack models using accuracy metrics, they are ineffective to analyse its robustness. Therefore, we propose a mask R-CNN-based attack model to critically analyse the robustness of SACAPTCHA. The proposed model performs a shape-wise analysis to test the usability of different shapes and quantifies the model performance using the F1-score. The simulation results show the highest F1 score of 0.962 and 0.828 for star and circle shapes in dataset-1 and dataset-2 respectively. The results show that model prediction is independent of the regularities of the shape. The observations prove that SACAPTCHA is vulnerable to object detection attack even after using irregular shapes.

An analytical investigation on helix concrete

Abstract Helix concrete consists of twisted steel wires of star shape and size approximately 1 mm2 areas with 25 mm, 35 mm, 50 mm, 65 mm & 80 mm long added to cement concrete. Replacing the rebar to some extent is to achieve higher crack resistance and structural strength throughout the concrete mass in all directions. In the present research, the analytical studies have been carried-out using MSC Nastran. The analytical studies have been carried-out on star cross sections of helix. It was observed that the shape and number of twists of steel wires maximizes the bond between the steel and cement based concrete matrix. Helix steel wire, with its twisted profile is a more superior reinforcement and is a substantial improvement over fibers of any time. When concrete is stressed or bent the fibers which are straight will slide out smoothly with minimal possible friction, so the force required to pullout is generally small. Adding deformation like a hooked end or corrugations adds friction and increases pullout force substantially.

Astigmatic hybrid SU(2) vector vortex beams: towards versatile structures in longitudinally variant polarized optics.

Structured light with more controllable degrees-of-freedom (DoFs) is an exciting topic with versatile applications. In contrast to conventional vector vortex beams (VVBs) with two DoFs of orbital angular momentum (OAM) and polarization, a hybrid ray-wave structure was recently proposed [Optica 7(7), 820-831 (2020)], which simultaneously manifests multiple DoFs such as ray trajectory, coherent state phase, trajectory combination, besides OAM and polarization. Here we further generalize this exotic structure as the astigmatic hybrid VVB by hatching a new DoF of astigmatic degree. Importantly, the transverse topology varies with propagation, e.g. a linearly distributed hybrid trajectory pattern can topologically evolve to a circularly polygonal star shape, where the number of singularity changes from zero to multiple in a single beam. The propagation-dependent evolution can be easily controlled by the astigmatic degree, including as a vector vortex state such that different astigmatic trajectories have different polarizations. We experimentally generate such beams from a simple laser with a special astigmatic conversion by combined spherical and cylindrical lenses, and the results agree well with our theoretical simulation. With our new structured light, the propagation-multiplexing multi-DoF patterns can be controlled in a single beam, which can largely extend related applications such as high-dimensional large-capacity optical communication, laser machining, and particle trapping.

Form Follows Content: An Empirical Study on Symbol-Content (In)Congruences in Thematic Maps

Through signs and symbols, maps represent geographic space in a generalized and abstracted way. Cartographic research is, therefore, concerned with establishing a mutually shared set of signs and semiotic rules to communicate geospatial information successfully. While cartographers generally strive for cognitively congruent maps, empirical research has only started to explore the different facets and levels of correspondences between external cartographic representations and processes of human cognition. This research, therefore, draws attention to the principle of contextual congruence to study the correspondences between shape symbols and different geospatial content. An empirical study was carried out to explore the (in)congruence of cartographic point symbols with respect to positive, neutral, and negative geospatial topics in monothematic maps. In an online survey, 72 thematic maps (i.e., 12 map topics × 6 symbols) were evaluated by 116 participants in a between-groups design. The point symbols comprised five symmetric shapes (i.e., Circle, Triangle, Square, Rhomb, Star) and one Asymmetric Star shape. The study revealed detailed symbol-content congruences for each map topic as well as on an aggregated level, i.e., by positive, neutral, and negative topic clusters. Asymmetric Star symbols generally showed to be highly incongruent with positive and neutral topics, while highly congruent with negative map topics. Symmetric shapes, on the other hand, emerged to be of high congruence with positive and neutral map topics, whilst incongruent with negative topics. As the meaning of point symbols showed to be susceptible to context, the findings lead to the conclusion that cognitively congruent maps require profound context-specific considerations when designing and employing map symbols.

The isodominism class of the graphs

In this paper, the new concept [Formula: see text]-isodominism between two graphs is introduced, where [Formula: see text] is a positive integer. The [Formula: see text]-isodominism is a pair of the graph isomorphism which depends on the smallest [Formula: see text]-dominating sets. By this tool, a graph with one vertex, complete graphs, wheels and stars are in the same [Formula: see text]-isodominism class. Furthermore, some results about the [Formula: see text]-isodominism classes of paths, cycles and star polygon are presented.

The in-plane stretching and compression mechanics of Negative Poisson’s ratio structures: Concave hexagon, star shape, and their combination

Negative Poisson’s ratio structure is one of the international research hotspots, but there are still few reports on negative Poisson’s ratio combination structure. In this paper, two single cell structures (concave hexagonal structure and star shape structure) with connection beam and three nine-grid combination structures (X-type, H-type, Sd-type) were designed. To obtain the negative Poisson’s ratio mechanics, based on the Euler beam theory, the theoretical calculation method of single cell structure was established. By comparing the critical force, the sequence of bending and stretching/compression deformation was discussed. The mechanical properties of multi-cell structures were predicted by adopting the mixed law. The results show that the main deformation of the designed structures are bending, and the instability buckling occurs during compression. It is proved that the mechanical properties of multi-cell structures can be characterized by its single cell structure. The combination structure integrates the negative Poisson’s ratio mechanical properties of different single cell structures. An important application is that the mechanical properties of combination structures can be obtained by changing the proportion of single cell structures without changing the structure size.

Folic Acid-Functionalized Composite Scaffolds of Gelatin and Gold Nanoparticles for Photothermal Ablation of Breast Cancer Cells.

Photothermal therapy (PTT) has been developed as a useful therapeutic method for cancer treatment. Localization of PTT agents in cancer sites and targeting capacity are required to further increase therapeutic efficacy. In this study, gold nanoparticles (AuNPs) and gelatin were functionalized with folic acid (FA) and hybridized to prepare FA-functionalized gelatin–AuNPs composite scaffolds. AuNPs with rod and star shapes of three sizes (40, 70, and 110 nm) were used for the hybridization to investigate the influence of AuNPs shape and size. The composite scaffolds showed porous structures with good interconnectivity. Modification with FA increased capture capacity of the composite scaffolds. Hybridization with AuNPs rendered the composite scaffold a good photothermal conversion property under near-infrared (NIR) laser irradiation. Temperature change during laser irradiation increased with the laser power intensity and irradiation time. The shape and size of AuNPs also affected their photothermal conversion property. The composite scaffold of gold nanorods 70 (FA-G/R70) had the highest photothermal conversion capacity. Breast cancer cells cultured in the FA-G/R70 composite scaffold were killed under NIR laser irradiation. Mouse subcutaneous implantation further demonstrated the excellent photothermal ablation capability of FA-G/R70 composite scaffold to breast cancer cells. The FA-functionalized composite scaffolds were demonstrated a high potential for local PPT of breast cancer.

Effects of pore geometry on the natural convective heat transmission in a porous cavity: a lattice Boltzmann simulation

In this study, a two-dimensional investigation on natural convection inside a porous cavity at pore-scale is performed using the lattice Boltzmann method with the focus on the effects of pores geometry. The model is independent of the shape, density, porosity, and arrangements of the pores, because the image of the porous cavity is binarized and given to the code as input. The influences of pores geometry, Rayleigh number, porosity, and pore/liquid thermal diffusivity ratio are studied. A D2Q9 multi-relaxation time and a D2Q9 single-relaxation time lattice Boltzmann model are used for the flow and energy equations, respectively, with two separate distribution functions approach. For this purpose, pores with square, circular, and star shapes are considered. The Rayleigh number is varied in the range of 103 to 106 for three different porosity values (0.43, 0.71, 0.85) and pore/liquid thermal diffusivity ratios of 6, 70, and 788, with water and air as working fluids. Local variations of hot wall Nusselt number revealed that the star, circular, and square pores have the highest peak values of the local Nusselt number, respectively. By contrast, the lowest local values occur in the porous cavity with circular pores. In the examined porous media, the maximum increase in the hot wall averaged Nusselt number is equal to 24.3% occurring at $$\varepsilon = 0.71$$ , when pores are varied from circular to star shapes at $${\text{Ra}} = 10^{4}$$ . Moreover, using the star pores with a porosity value of 0.43, the averaged Nusselt number on the hot wall is increased by 184.46% compared to the empty cavity at $${\text{Ra}} = 10^{3}$$ . Besides, it is shown that increasing the thermal diffusivity ratio higher than 70 has little effect on the hot wall averaged Nusselt number.

Influence of Heterogeneity on the Chiral Expression of Star-Shaped Conjugated Polymers

In this report, the influence of heterogeneity on the chiral expression of star-shaped conjugated polymers is investigated. For this purpose, two heterogeneous star-shaped conjugated polymers, i.e....

Telescope performance real-time monitoring based on machine learning

ABSTRACT In astronomy, the demand for high-resolution imaging and high-efficiency observation requires telescopes that are maintained at peak performance. To improve telescope performance, it is useful to conduct real-time monitoring of the telescope status and detailed recordings of the operational data of the telescope. In this paper, we provide a method based on machine learning to monitor the telescope performance in real-time. First, we use picture features and the random forest algorithm to select normal pictures captured by the acquisition camera or science camera. Next, we cut out the source image of the picture and use convolutional neural networks to recognize star shapes. Finally, we monitor the telescope performance based on the relationship between the source image shape and telescope performance. Through this method, we achieve high-performance real-time monitoring with the Large Sky Area Multi-Object Fibre Spectroscopic Telescope, including guiding system performance, focal surface defocus, submirror performance, and active optics system performance. The ultimate performance detection accuracy can reach up to 96.7 per cent.

Existence, Uniqueness and Stabilization of Solutions of a Generalized Telegraph Equation on Star Shaped Networks

The existence, uniqueness, strong and exponential stability of a generalized telegraph equation set on one dimensional star shaped networks are established. It is assumed that a dissipative boundary condition is applied at all the external vertices and an improved Kirchhoff law at the common internal vertex is considered. First, using a general criteria of Arendt-Batty (see Arendt and Batty in Trans. Am. Math. Soc. 306(2):837–852, 1988), combined with a new uniqueness result, we prove that our system is strongly stable. Next, using a frequency domain approach, combined with a multiplier technique and the construction of a new multiplier satisfying some ordinary differential inequalities, we show that the energy of the system decays exponentially to zero.

Triaxially deformed freely precessing neutron stars: continuous electromagnetic and gravitational radiation

ABSTRACT The shape of a neutron star (NS) is closely linked to its internal structure and the equation of state of supranuclear matters. A rapidly rotating, asymmetric NS in the Milky Way undergoes free precession, making it a potential source for multimessenger observation. The free precession could manifest in (i) the spectra of continuous gravitational waves (GWs) in the kilohertz (kHz) band for ground-based GW detectors, and (ii) the timing behaviour and pulse-profile characteristics if the NS is monitored as a pulsar with radio and/or X-ray telescopes. We extend previous work and investigate in great detail the free precession of a triaxially deformed NS with analytical and numerical approaches. In particular, its associated continuous GWs and pulse signals are derived. Explicit examples are illustrated for the continuous GWs, as well as timing residuals in both time and frequency domains. These results are ready to be used for future multimessenger observation of triaxially deformed freely precessing NSs, in order to extract scientific implication as much as possible.

Origin of Irregular Star Polygons in Ground Projection Plans of Muqarnas

Many muqarnas contain star polygons in their ground projection plans. Such star polygons usually have equal edge lengths. In this study, the geometric background of irregular star polygons with unequal edge lengths, observed in some ground projection plans of muqarnas, was investigated. The plan of the muqarnas at the main gate of the Atik Valide Mosque was examined according to the theoretical framework of shape grammars. As a result of the case study, it was concluded that ellipse grids were used to form the layout of the ground projection plan of muqarnas. It was shown that stars placed in the areas formed by the intersections of the ellipse grid formed irregular polygons naturally. In addition, a parametric 3D geometry of muqarnas was obtained by considering a geometric decomposition of the analysed ground projection plan of muqarnas.

Applying Linear Regression to Estimate Weight of Non Axi-Symmetric fruit

Weight is an important parameter in fruits’ quality identification. Measuring fruits’ weight using scale is tedious since fruits must be taken from tree and placed on contact to scale. Many researches have proposed non-contact estimation methods of fruits’ weight using 2D images. The studies were commonly applied in axi-symmetric fruits, such oranges. In this paper, an algorithm to estimate weight of non axi-symmetric fruit is developed. It used a Linear Regression rather than geometric-based methods as proposed by other researches. The non axi-symmetric fruits chosen was star fruits. It is a challenging fruits since its basic shape is not round but irregular star shape. The estimation used pixel count from one-view image of the fruits’ projection as feature. The proposed method has RMSE of 16.322 Gram and MAPE of 7.089% compare to the expected weights. It also has high Coefficient of Determination, R^2, 0.8829 compare to the weight scale measurement.