Search Results (57)

Hypereutectic Al-Si alloys containing primary Si exhibit unique material properties that make them suitable for various industrial applications. Understanding the characteristics of primary Si is crucial for predicting the effect of solidification conditions on the microstructure of these alloys. This paper presents a comprehensive characterisation study of primary Si in hypereutectic alloys. This study provides a detailed analysis of the size, distribution, and morphology of primary Si, providing valuable insights into the alloy structure, mechanical properties, and even the performance of the production process. The effect of forced melt flow by a rotating magnetic field (RMF) and solid/liquid front velocity on the size and morphology of primary Si in a hypereutectic Al-18 wt.% Si alloy was investigated. The purpose of using the RMF technique during the solidification process of Al-Si alloys is to enhance the alloy’s microstructure by inducing electromagnetic stirring. The hypereutectic samples were solidified at five different front velocities (0.02, 0.04, 0.08, 0.2, and 0.4 mm/s), under an average temperature gradient (G) of 8 K/mm, in a crystalliser equipped with an RMF inductor. Each sample was divided into two parts: the first solidified without stirring, while the second underwent electromagnetic stirring using RMF at an induction (B) of 7.2 mT. The results revealed that increasing the front velocity during solidification refined the primary Si in stirred and non-stirred parts. In non-stirred parts, it decreased dendritic forms and increased star-like Si, while polyhedral shapes remained nearly constant. Stirred parts showed stable Si morphology across velocities. Higher velocities also promoted equiaxed over elongated Si forms in both parts. Full article

The choice of constellations largely affects the performance of both wireless and optical communications. To address increasing capacity requirements, constellation shaping, especially for high-order modulations, is imperative in high-speed coherent communication systems. This paper, thus, proposes novel mutual information neural estimation (MINE)-based geometric, probabilistic, and joint constellation shaping schemes, i.e., the MINE-GCS, MINE-PCS, and MINE-JCS, to maximize mutual information (MI) via emerging deep learning (DL) techniques. Innovatively, we first introduce the MINE module to effectively estimate and maximize MI through backpropagation, without clear knowledge of the channel state information. Then, we train encoder and probability generator networks with different signal-to-noise ratios to optimize the distribution locations and probabilities of the points, respectively. Note that MINE transforms the precise MI calculation problem into a parameter optimization problem. Our MINE-based schemes only optimize the transmitter end, and avoid the computational and structural complexity in traditional shaping. All the designs were verified through simulations as having superior performance for MI, among which the MINE-JCS undoubtedly performed the best for additive white Gaussian noise, compared to the unshaped QAMs and even the end-to-end training and other DL-based joint shaping schemes. For example, the low-order 8-ary MINE-GCS could achieve an MI gain of about 0.1 bits/symbol compared to the unshaped Star-8QAM. It is worth emphasizing that our proposed schemes achieve a balance between implementation complexity and MI performance, and they are expected to be applied in various practical scenarios with different noise and fading levels in the future. Full article

Recent studies have focused on how spinning black holes (BHs) within a binary system containing a strongly magnetized neutron star, then immersed in external magnetic fields, can acquire charge through mechanisms like the Wald process and how this charge could power pulsar-like electromagnetic radiation. Those objects called “Black hole pulsar” mimic the behaviour of a traditional pulsar, and they can generate electromagnetic fields, such as magnetic dipoles. Charged particles within an accretion disk around the black hole would then be influenced not only by the gravitational forces but also by electromagnetic forces, leading to different geometries and dynamics. In this context, we focus here on the interplay of the magnetic dipole and the accretion disk. We construct the equilibrium structures of non-conducting charged perfect fluids orbiting Kerr black holes under the influence of a dipole magnetic field aligned with the rotation axis of the BH. The dynamics of the accretion disk in such a system are shaped by a complex interplay between the non-uniform, non-Keplerian angular momentum distribution, the black hole’s induced magnetic dipole, and the fluid’s charge. We show how these factors jointly influence key properties of the disk, such as its geometry, aspect ratio, size, and rest mass density. Full article

Spatial distribution is a critical factor influencing the success or failure of hotel management. This study examines the spatial distribution patterns of foreign star-rated hotels in China from 2000 to 2015 based on 27 typical city cases, using global and local spatial autocorrelation methods within GIS spatial analysis. The research explores the evolution of these patterns, analyzes key characteristics, and combines these insights with a stepwise regression method. Pearson correlation analysis is used to identify factors that influence the evolution of the spatial pattern. This study reveals that, first, the Z-value of global spatial autocorrelation of foreign star-rated hotels in China decreases from 2.38 to 1.63, indicating that the spatial distribution of foreign star-rated hotels in China has shifted from imbalanced to balanced, transitioning from economically developed regions such as areas with overseas Chinese populations, provincial capitals, and municipalities directly under central government control, toward tourist cities. Second, star-rated hotels hold a critical position within the spatial pattern, highlighting their central role in shaping the hospitality landscape. Third, the spatial distribution of foreign star-rated hotels is primarily influenced by the number of inbound tourists, followed by the presence of scenic spots rated 4A and above. The influence of other factors is found to be less significant. Fourth, the correlation coefficient between tourism demand and foreign star-rated hotels increased by 0.004, whereas the correlation coefficient between tourism supply and foreign star-rated hotels decreased by 0.036, indicating that market factors are playing an increasingly important role in shaping the evolution of foreign star-rated hotels in China, reflecting broader market dynamics. This study provides practical guidance for local Chinese hotels facing competition from foreign-funded establishments and offers theoretical insight into the strategic implementation of transnational operations. It points out the expansion direction of local Chinese hotels across different developmental stages. Full article

The stellar initial mass function (IMF) represents a fundamental quantity in astrophysics and cosmology describing the mass distribution of stars from low mass all the way up to massive and very massive stars. It is intimately linked to a wide variety of topics, including stellar and binary evolution, galaxy evolution, chemical enrichment, and cosmological reionization. Nonetheless, the IMF still remains highly uncertain. In this work, we aim to determine the IMF with a novel approach based on the observed rates of transients of stellar origin. We parametrize the IMF with a simple but flexible Larson shape, and insert it into a parametric model for the cosmic UV luminosity density, local stellar mass density, type Ia supernova (SN Ia), core-collapse supernova (CCSN), and long gamma-ray burst (LGRB) rates as a function of redshift. We constrain our free parameters by matching the model predictions to a set of empirical determinations for the corresponding quantities via a Bayesian Markov Chain Monte Carlo method. Remarkably, we are able to provide an independent IMF determination with a characteristic mass $m_c=0.{10}_{-0.08}^{+0.24}{\mathrm{M}}_{\odot }$ and high-mass slope $\xi =-2.{53}_{-0.27}^{+0.24}$ that are in accordance with the widely used IMF parameterizations (e.g., Salpeter, Kroupa, Chabrier). Moreover, the adoption of an up-to-date recipe for the cosmic metallicity evolution allows us to constrain the maximum metallicity of LGRB progenitors to $Z_{max}=0.{12}_{-0.05}^{+0.29}{\mathrm{Z}}_{\odot }$. We also find which progenitor fraction actually leads to SN Ia or LGRB emission (e.g., due to binary interaction or jet-launching conditions), put constraints on the CCSN and LGRB progenitor mass ranges, and test the IMF universality. These results show the potential of this kind of approach for studying the IMF, its putative evolution with the galactic environment and cosmic history, and the properties of SN Ia, CCSN, and LGRB progenitors, especially considering the wealth of data incoming in the future. Full article

The mitochondrial cytochrome c oxidase subunit I (COI) genes of six endangered goose breeds (Xupu, Yangjiang, Yan, Wuzong, Baizi, and Lingxian) were sequenced and compared to assess the genetic diversity of endangered goose breeds. By constructing phylogenetic trees and evolutionary maps of genetic relationships, the affinities and degrees of genetic variations among the six different breeds were revealed. A total of 92 polymorphic sites were detected in the 741 bp sequence of the mtDNA COI gene after shear correction, and the GC content of the processed sequence (51.11%) was higher than that of the AT content (48.89%). The polymorphic loci within the populations of five of the six breeds (Xupu, Yangjiang, Yan, Baizi, and Lingxian) were more than 10, the haplotype diversity > 0.5, and the nucleotide diversity (Pi) > 0.005, with the Baizi geese being the exception. A total of 35 haplotypes were detected based on nucleotide variation among sequences, and the goose breed haplotypes showed a central star-shaped dispersion; the FST values were −0.03781 to 0.02645, The greatest genetic differentiation (FST = 0.02645) was observed in Yan and Wuzong breeds. The most frequent genetic exchange (Nm > 15.00) was between the Wuzong and Yangjiang geese. An analysis of molecular variance showed that the population genetic variation mainly came from within the population; the base mismatch differential distribution analysis of the goose breeds and the Tajima’s D and Fu’s Fs neutral detection of the historical occurrence dynamics of their populations were negative (p > 0.10). The distribution curve of the base mismatches showed a multimodal peak, which indicated that the population tended to be stabilised. These results provide important genetic information for the conservation and management of endangered goose breeds and a scientific basis for the development of effective conservation strategies. Full article

Barred galaxies constitute about two-thirds of observed disc galaxies. Bars affect not only the mass distribution of gas and stars but also that of the dark matter. An elongation of the inner dark matter halo is known as the halo bar. We aim to characterize the structure of the halo bars, with the goal of correlating them with the properties of the stellar bars. We use a suite of simulated galaxies with various bar strengths, including gas and star formation. We quantify the strengths, shapes, and densities of these simulated stellar bars. We carry out numerical experiments with frozen and analytic potentials in order to understand the role played by a live responsive stellar bar. We find that the halo bar generally follows the trends of the disc bar. The strengths of the halo and stellar bars are tightly correlated. Stronger bars induce a slight increase in dark matter density within the inner halo. Numerical experiments show that a non-responsive frozen stellar bar would be capable of inducing a dark matter bar, but it would be weaker than the live case by a factor of roughly two. Full article

This review aims to highlight the most recent advances in the field of the synthesis of branched copolymers and nanogels using reversible addition-fragmentation chain transfer (RAFT) polymerization. RAFT polymerization is a reversible deactivation radical polymerization technique (RDRP) that has gained tremendous attention due to its versatility, compatibility with a plethora of functional monomers, and mild polymerization conditions. These parameters lead to final polymers with good control over the molar mass and narrow molar mass distributions. Branched polymers can be defined as the incorporation of secondary polymer chains to a primary backbone, resulting in a wide range of complex macromolecular architectures, like star-shaped, graft, and hyperbranched polymers and nanogels. These subcategories will be discussed in detail in this review in terms of synthesis routes and properties, mainly in solutions. Full article

Ocypode Weber, 1795 (Brachyura: Ocypodidae) is popularly known as ghost crab, and encompasses 21 valid species, including Ocypode quadrata (Fabricius, 1787). This species has wide distribution along the Atlantic coast of America, from the USA (Massachusetts) to Brazil (Rio Grande do Sul), Central America, and Antilles. Such distribution, along with some biological characteristics of its life cycle and the presence of geographic barriers, could lead to genetic structuring. Herein, we evaluate the hypothesis of the presence of geographic barriers using COI and 16S partial gene fragments. The Maximum Likelihood tree suggests the monophyly of O. quadrata, while the values of intraspecific genetic distance along with the star-shaped haplotype network suggested a lack of genetic structure in Brazilian, Panama, and French Guiana populations, probably caused by larval dispersion. USA and Mexico populations may be a new lineage, but we cannot say it with few sequences and with no morphological characters. Full article

The star-shaped trans-shipment network causes the retailer’s bargaining power to be different, which leads to the misalignment of trans-shipment profit. Aimed at this, we take retailers and the trans-shipment paths as the nodes and edges of the trans-shipment network. Based on this, we model the multilateral negotiations between the central retailer and the local retailer and adopt the Generalized Nash Bargaining game to derive the optimal solution of the value function for the incomplete trans-shipment network under the bargaining mechanism. Furthermore, we reveal the convexity of the optimal trans-shipment value function and give the condition that the allocation of the bargaining mechanism is in the core. Based on this, we introduce the concept of pairwise Nash equilibrium and show the star-shaped trans-shipment network is the optimal endogenous formation of the trans-shipment network. In practice, the central retailer should introduce as many local retailers as possible to join this trans-shipment alliance, which will achieve Pareto improvement. Meanwhile, the central retailer should order as many as possible. Finally, it is more appropriate to establish a star-shaped trans-shipment network when one retailer has stronger negotiation power compared to other retailers in a distribution system, which not only ensures the stability of the allocation of trans-shipment profits but also the stability of the trans-shipment network. Full article

The sea star Patiria pectinifera (Asteroidea; Asterinidae; homotypic synonym: Asterina pectinifera; Muller & Troschel, 1842) is widely distributed in the coastal regions of the Seas of East Asia and the northern Pacific Ocean. Here, a de novo genome sequence of P. pectinifera as a reference for fundamental and applied research was constructed by employing a combination of long-read Oxford Nanopore Technology (ONT) PromethION, short-read Illumina platforms, and 10 × Genomics. The draft genome of P. pectinifera, containing 13,848,344 and 156,878,348 contigs from ONT and Illumina platforms, respectively, was obtained. Assembly with CANU resulted in 2262 contigs with an N50 length of 367 kb. Finally, ARCS + LINKS assembly combined these contigs into 328 scaffolds, totaling 499 Mb with an N50 length of 2 Mbp. The estimated genome size by GenomeScope analysis was 461 Mb. BUSCO analysis indicated that 930 (97.5%) of the expected genes were found in the assembly, with 889 (93.2%) being single-copy and 41 (4.3%) duplicated after searching against the metazoan database. Annotation, utilizing sequences obtained from Illumina RNA-Seq and Pacific Biosciences Iso-Seq, led to the identification of 22,367 protein-coding genes. When examining the orthologous relationship of P. pectinifera against the scaffolds of the common sea star Patiria miniata, high contiguity was observed. Annotation of repeat elements highlighted an enrichment of 1,121,079 transposable elements, constituting 47% of the genome, suggesting their potential role in shaping the genome structure of P. pectinifera. This de novo genome assembly is expected to be a valuable resource for future studies, providing insight into the developmental, environmental, and ecological aspects of P. pectinifera biology. Full article

Onboard scientific cameras are reused in attitude determination to meet the sub-arcsecond attitude determination accuracy requirements of microsatellites. This approach does not require an additional payload for microsatellites. It involves reusing high-quality optical lenses from the scientific camera and utilizing the peripheral high-quality imaging areas of its square-shaped detector. Separate detectors are placed within these areas as attitude determination detectors to obtain star patterns for closed-loop attitude determination, thereby achieving high-precision attitude determination for microsatellites. The star patterns obtained using this method may pose specific issues due to the relative positions of stars. Through an analysis of the theoretical model that examines the relationship between attitude determination accuracy and the main influencing factors, it is indicated that guide star distribution is one of the main, complex factors determining attitude determination accuracy. A further simulation analysis was conducted on the specific impact of two guide star distribution characteristics—namely, the coverage of guide stars in the attitude determination areas and the proportion of the average field of view occupied by the guide star triangles to the total field of view of the attitude determination areas—on attitude determination accuracy. This study concludes that when the measurement error of the guide stars is bigger than the attitude determination accuracy requirement for its area configuration, four attitude determination areas should be configured. Four attitude determination areas should be prioritized when the measurement error is equal to or smaller than the attitude determination accuracy requirement, followed by the option to configure three attitude determination areas or two symmetric attitude determination areas. When selecting guide stars for star pattern recognition, the guide stars should cover the attitude determination areas as much as possible, and guide stars with a higher proportion of the average field of view occupied by the guide star triangles to the total field of view should be chosen. Finally, experimental validation was conducted using star patterns from dense star fields and sparse star fields. The research results provide an important reference for the optimization of attitude determination area configuration, navigation star catalog construction, and star pattern recognition algorithm research for microsatellites equipped with scientific cameras. Full article

This study explores the synthesis, characterization, and application of a heterofunctional initiator derived from 2-hydroxypropyl cyclodextrin (HP-β-CD), having eight bromoester groups and thirteen hydroxyl groups allowing the synthesis of mikto-arm star-shaped polymers. The bromoesterification of HP-β-CD was achieved using α-bromoisobutyryl bromide as the acylation reagent, modifying the cyclodextrin (CD) molecule as confirmed by electrospray ionization mass spectrometry (ESI-MS), nuclear magnetic resonance (NMR), attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy analysis, and differential scanning calorimetry (DSC) thermograms. The initiator’s effectiveness was further demonstrated by obtaining star-comb and mikto-arm polymers via an enzymatically assisted atom transfer radical polymerization (ATRP) method and subsequent ring-opening polymerization (ROP). The ATR polymerization quality and control depended on the type of monomer and was optimized by the way of introducing the initiator into the reaction mixture. In the case of ATRP, high conversion rates for poly(ethylene oxide) methyl ether methacrylate (OEOMA), with molecular weights (Mn) of 500 g/mol and 300 g/mol, were achieved. The molecular weight distribution of the obtained polymers remained in the range of 1.23–1.75. The obtained star-comb polymers were characterized by different arm lengths. Unreacted hydroxyl groups in the core of exemplary star-comb polymers were utilized in the ROP of ε-caprolactone (CL) to obtain a hydrophilic mikto-arm polymer. Cloud point temperature (T_CP) values of the synthesized polymers increased with arm length, indicating the polymers’ reduced hydrophobicity and enhanced solvation by water. Atomic force microscopy (AFM) analysis revealed the ability of the star-comb polymers to create fractals. The study elucidates advancements in the synthesis and utilization of hydrophilic sugar-based initiators for enzymatically assisted ATRP in an aqueous solution for obtaining complex star-comb polymers in a controlled manner. Full article

Sea stars are a diverse and important component of the Southern Ocean benthos. However, scarce information is available regarding their diversity, distribution, evolution, and taxonomic uncertainties persist for multiple taxa. The Magellanic Region (south of Chile) remains under-sampled despite its pivotal location for species distribution and diversity, being located at the crossroad of three ocean basins. In this study, we assessed the biodiversity of coastal Magellanic sea stars and their affinities with other oceanic bioregions. An integrative approach combining morphological identification with DNA barcoding was implemented to highlight taxonomic discrepancies such as suspected synonymy and unrecognised diversity. Firstly, we identified a total of 15 species from the coastal Magellanic Region and reported the occurrence of Cycethra frigida Koehler, 1917 for the first time in this region. The distribution of these 15 species ranged from only in South America to circumpolar, bipolar, or possibly cosmopolitan. Secondly, we highlighted possible synonymy in two species pairs within the genera Anasterias and Odontaster. This preliminary biodiversity assessment forms an important baseline for monitoring and conservation purposes, especially in the face of distribution shifts as a response to climate change and the increased presence of invasive species. Developmental mode has previously been suggested to be important in shaping biogeographical patterns. However, developmental mode was insufficient to explain the observed patterns, and other factors (e.g., physiological constraints, competition, bathymetrical range, and the possibility of passively rafting on kelp) are suggested to be at least equally important. Finally, an increase in barcoding effort is needed to better capture phylogeographic patterns for each species, both by increasing the number of specimens investigated and by covering a broader geographical range. Full article

Pneumatic tires are used in diverse industries. However, their design is difficult, as it relies on the knowledge of experienced designers. In this paper, we generate images of non-pneumatic tire designs with patterns based on shapes and lines for different generative adversarial network (GAN) models and test the performance of the models. Using OpenCV, 2000 training images were generated, corresponding to spoke, curve, triangle, and honeycomb non-pneumatic tires. The images created for training were used after removing highly similar images by applying mean squared error (MSE) and structural similarity index (SSIM). To identify the best model for generating patterns of regularly shaped non-pneumatic tires, GAN, deep convolutional generative adversarial network (DCGAN), StarGAN v2, StyleGAN v2-ADA, and ProjectedGAN were compared and analyzed. In the qualitative evaluation, the GAN, DCGAN, StarGAN v2, and StyleGAN v2-ADA models distorted the circle shape and did not maintain a consistent pattern, but ProjectedGAN retained consistency in the circle, and the pattern was less distorted than in the other GAN models. When evaluating quantitative metrics, ProjectedGAN performed the best among several techniques when the difference between the generated and actual image distributions was measured. Full article