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To counteract the dynamic deterioration of digitized chaotic systems, we propose a mathematical model for generating ${n}$ -D non-degenerate hyperchaotic systems (NHS) with ${n}$ positive Lyapunov exponents (LEs) and complex dynamic behaviors. In this brief, we analyze the internal relations among the coefficients, eigenvalues, and singular values of a circulant matrix. Based on singular value decomposition, the ${n}$ -D NHS can be constructed by presetting a conjugate symmetric vector, with a theoretical proof provided. The LEs of the ${n}$ -D NHS can be adjusted arbitrarily by changing a preconfigured eigenvalue vector. We demonstrate the feasibility and efficacy of the proposed scheme with two examples, a 4-D NHS and a 5-D NHS. Based on the 5-D NHS, we design a simple pseudorandom number generator (PRNG) with desirable statistical properties. The proposed NHS model has fewer control coefficients, making it suitable for applications in IoT security and lightweight chaotic cryptography.

Currently, low-dimensional chaotic maps have many disadvantages, such as narrow chaotic regions, numerous cycle windows, and weak chaotic representations. Based on this issue, an n -dimensional non-degenerate chaotic system (n D - NDCS) is constructed. By setting the control parameters of the system, we can obtain dimensionally adjustable non-degenerate chaotic systems with desired Lyapunov exponents. Compared with existing methods, the proposed n D - NDCS has a simple structure with few control parameters, which is suitable for resource-constrained scenarios, such as small embedded devices and mobile devices. To demonstrate the practicality of the proposed method, we construct a 3D - NDCS and a 4D - NDCS as two examples. Performance evaluations show better randomness and complexity than other methods in terms of sample entropy, permutation entropy and other indicators. Since both chaotic systems can produce pseudo-random sequences with sensitive initial values and strong randomness, we further design an efficient pseudo-random number generator (PRNG) on the FPGA. The experiment results show that the proposed PRNG occupies merely 3.13 % of the effective resources of the target FPGA. In addition, the throughput of the PRNG which obtained from post-processing is up to 15 Gb/s, and successfully passed the NIST SP800-22 test. Finally, an FPGA-based hardware implementation platform is developed to realize the proposed PRNG. [ABSTRACT FROM AUTHOR]

Adaptive feeding is a strategy used by many organisms to maintain growth and reproduction success while encountering varying feeding conditions. Oysters are sessile benthic and non‐siphon filter feeders. Oysters are well adapted to modify the ambient microenvironment through their pumping behavior and particle selection activity. Rejection of unsuitable food particulates bound in pseudofeces via ejection events are an integral part of oyster feeding during which oysters produced strong flow opposite to their inhalant feeding flow. The strong opposite pulsatile flow during the ejection event inevitably disrupts the oyster's normal feeding cycle, but how oysters restart their feeding and allocate their energy consumption during an ejection event has not been investigated. The present study used particle image velocimetry (PIV) to examine the impact of ejection events on the feeding of the American oyster, Crassostrea virginica. The strong pulsatile flow resulting from pseudofecal ejection altered the external flow fields by moving water away from the shell. The initial feeding zone after pseudofecal ejection was relatively narrow, possessed a low pulsatile flow, and did not exploit the full flow field. The feeding zone gradually expanded as the pulsatile flow weakened. The strong shear rate at the stable feeding zone then sustained the feeding flow that facilitated oyster feeding. Furthermore, the volumetric fluxes often increased after the ejection event, suggesting increase in feeding efficiency after ejection events. These PIV studies provide new insight on the interactions between feeding oysters and the surrounding physical environment at small yet ecologically relevant scales.

To enhance interfacial properties of carbon fiber/epoxy composites, a facile and effective process was developed to fabricate three-dimensional interconnected nanosheet architecture by in situ growing Ni(OH)2nanosheets on carbon fibers (CFs). Scanning electron microcopy clearly revealed that the nanostructured Ni(OH)2nanosheets were uniformly grown on carbon fibers, which could play as nanocontainers of the epoxy matrix when fracture occurred. To explore the mechanical interlocking of composites, energy-dispersive spectrometry mapping scanning was performed to explore the penetration transition layer. The interfacial shear strength improved up to 82.1% compared with untreated composites, and the optimal interlaminar shear strength of composites reached up to 93.9 MPa. According to the test results, it is reasonable to consider that this new effective and low-cost strategy could effectively improve the interfacial properties of CF/epoxy composites and could be a good candidate for potential large-scale industrial application.

The cross-sectional micrograph, microhardness profile, and microstructures of the resistance spot-weld (RSW) for QP980 steel are shown to reveal the effects of the content and tempering of the martensite in the fusion zone (FZ) and the heat-affected zone (HAZ) on the microhardness profile of the RSW. It is indicated that the transient peak temperature above the critical temperature during the welding thermal cycle induces the significant variations of material and mechanical properties in the FZ and HAZ. The quasi-static uniaxial compression stress-strain curve of the FZ martensite in the RSW for QP980 steel is obtained with digital image correlation (DIC) and compared with that of two micropillars of martensite phase in the base material (BM) of the RSW for QP980 steel which was given by Srivastava et al. It is attributed to the welding thermal cycle different from QP980 steel heat treatment that the flow stress of the FZ martensite in the RSW is higher than that of the martensite phase in the BM. The dynamic uniaxial compression experiments for the FZ martensite in the RSW for QP980 steel are performed on a modified split Hopkinson pressure bar (SHPB), in which the reflected and transmitted waves are improved. A dynamic compression constitutive equation is presented by analyzing the results of the quasi-static and dynamic uniaxial compression experiments. A Swift law for martensite phase is extended to high strain rates to describe the weak strain-rate dependence of the dynamic compression behaviors of the FZ martensite in the RSW for QP980 steel.

Lyapunov exponents (LEs) characterize the average exponential rate of convergence or divergence between adjacent orbits in phase space. Thus, the number of positive LEs can reflect the complexity of chaotic systems from a certain point of view. To resist the dynamic degradation of digital chaos, we propose a novel universal method that is based on QR decomposition for constructing non-degenerate hyperchaotic maps. A large number of positive LEs can be generated to increase the complexity of chaotic systems. Furthermore, we construct a 4-D discrete non-degenerate hyperchaotic map as an example to demonstrate the adaptability and efficacy of the proposed scheme. For the proposed method, the related control parameters can not only effectively adjust Lyapunov exponents, but also carry out chaotic regulation on the discrete map, such as amplitude control and offset boosting. In addition, a pseudorandom number generator (PRNG) is designed with desirable statistical properties. Then, a microcontroller-based platform was developed to implement the proposed chaotic map. This study is interesting and has a potential for real-world applications, such as secure communication and cryptography. [ABSTRACT FROM AUTHOR]

Digital chaotic maps are severely hampered by the finite calculation accuracy of the hardware device that is used to implement them, and their applications in cryptography and information assurance are seriously degraded. To resolve this issue, we put forward a universal iterative model to construct non-degenerate polynomial chaotic maps with any desired number of positive Lyapunov exponents. In addition, we innovatively propose the geometric control methods of polynomial chaotic maps, including amplitude control, offset boosting, plane rotation, shape control, and combined regulation. Furthermore, to assess the effectiveness and feasibility of the proposed method, a microcontroller-based platform was developed to demonstrate the hardware implementation and geometric control of the proposed polynomial chaotic map. Finally, a PRNG is constructed by interval quantization. Numerical experiments are performed to verify the desirable statistical properties of the PRNG in terms of local weak random test, discrete Fourier transform test, linear complexity and NIST SP800-22 test. [ABSTRACT FROM AUTHOR]

In this work, cloud point-TiO2/sepiolite composites–octyl alcohol extraction combined with UV–vis spectrometry was applied to analyze nickel in real samples. Trace nickel was separated and preconcentrated with PAN as chelating agent, and TiO2/sepiolite composites—octylphenoxypolyethoxyethanol (TX-114)—octyl alcohol as extraction agent. Factors influencing extraction efficiency, such as concentrations of TX-114 and octanol, type of the desorption on the extraction system, concentration of chelating agent, pH, incubation temperature, incubation time and conditions of phase separation were investigated and optimized systematically. The results showed that TiO2/sepiolite composites exert significant effects on the extraction efficiency; especially nickel concentration is very low. Under the optimal conditions, the absorbance signal is linear with nickel concentration in the range of 0.02–3 mg L−1and the detection limit was 5 μg L−1. The developed method was successfully applied to the determination of nickel in natural products of Baisha green tea and coconut water in Hainan.

To analyze the periodic distribution and state-mapping structures of high-dimensional digital chaotic systems in fixed-point arithmetic domain. A chaotic cycle-finding algorithm (CCFA) can be designed to precisely calculate the period length of the orbit of digital chaos under different finite calculation accuracy. Furthermore, to test the versatility and effectiveness of our proposed algorithm, the periodic distribution and security of the digital Sprott D system are analyzed in detail. Numerical simulation results show that the chaotic system have potential security risks, such as short period and low sequence complexity. In addition, we put forward a new resistance method based on automatic cycle detection and random jump of chaotic trajectories for the objective of enhancing the dynamical properties of high-dimensional digital chaotic systems. This scheme can construct a new chaotic model with many desirable properties, such as long period, high state-space utilization, low autocorrelation, and good ergodicity. [ABSTRACT FROM AUTHOR]

Due to the limited machine word length of hardware devices, the dynamics of digital chaotic systems will degenerate. To combat this issue, we proposed a universal method that is based on singular value decomposition (SVD), which can reversely construct non-degenerate hyperchaotic systems with any desired number of positive Lyapunov exponents by controlling pre-specified singular values. To assess the practicability and effectiveness of the method, we construct a 6-dimensional non-degenerate hyperchaotic system as an example. Furthermore, based on the hyperchaotic system, a pseudorandom number generator (PRNG) with desirable statistical characteristics is designed for image encryption. Numerical simulations were performed to evaluate the security of the image encryption algorithm in terms of histogram, information entropy, differential attack test, etc. The proposed non-degenerate hyperchaotic system can be effectively applied in the field of multimedia data encryption and information security. [ABSTRACT FROM AUTHOR]

The present study compared 68Ga-FAPI and 18F-FDG PET/CT in a patient with GSRCC (gastric signet-ring cell carcinoma). In this case, 68Ga-FAPI PET/CT shows much higher tumor-to-background contrast of primary tumor and reveals more metastatic lesions than 18F-FDG PET/CT. This case demonstrates that 68Ga-FAPI PET/CT outperforms 18F-FDG in identifying both primary and metastatic lesions in GSRCC.

To investigate the possibility that natural medicines affect lipid metabolism by regulating lipoprotein lipase (LPL) expression, a green fluorescent protein (GFP) gene was constructed downstream of the peroxisome proliferator response element (PPRE) and the constructed plasmid was microinjected into Xenopusoocytes to establish a PPRE regulatory reporter system. Using this system, hawthorn flavonoids were quickly selected from a panel of natural medicines and found to up-regulate GFP expression by an effect on PPRE. To confirm the effect of hawthorn flavonoids, we treated mice orally with water (control), hawthorn flavonoids, and pioglitazone and measured the LPL levels in serum, adipose tissue, and muscle by an enzyme-linked immunosorbent assay. The serum LPL levels were no different from the controls after treatment with either hawthorn flavonoids or pioglitazone, but LPL increased significantly in muscular tissues and decreased in adipose tissues. These results demonstrate that hawthorn flavonoids meditate LPL expression in mice with tissue-specific differences. A novel PPRE regulatory report system was established for rapid and effective selection and evaluation of LPL-mediating drugs.