Characteristic analysis of the fractional-order hyperchaotic complex system and its image encryption application

Color image encryption using non-dominated sorting genetic algorithm with local chaotic search based 5D chaotic map

The one-dimensional (2D) chaotic encryption algorithm has good encryption performance. For its properties, such as the excellent complexity, pseudo-randomness, and sensitivity to the initial value of the chaotic sequence. However, compared with other methods, its biggest drawback is that the key space is too small. To address these problems, in this study, the authors introduce an improved 2D logistic sine chaotic map (2D-LSMM). A novel image encryption scheme based on dynamic DNA sequences encryption and improved 2D-LSMM is presented. The logistic map is used to control the input of the sine map. And the encoding and operation rules of DNA sequences are determined by 2D-LSMM chaotic sequences. By implementing dynamic DNA sequence encryption, the encryption process becomes more complicated and harder to be attacked. Simulation experimental results and security analysis show that the authors’ encryption scheme not only achieves proper encryption but can also resist different attacks.

https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/iet-ipr.2019.1340

Novel image encryption by combining dynamic DNA sequence encryption and the improved 2D logistic sine map

In recent years, many image encryption approaches have been proposed on the basis of chaotic maps. The various types of chaotic maps such as one-dimensional and multi-dimensional have been used to generate the secret keys. Chaotic maps require some parameters and value assignment to these parameters is very crucial. Because, poor value assignments may make the chaotic map un-chaotic. Therefore, hyper-parameter tuning of chaotic maps is required. Recently, meta-heuristic based image encryption approaches have been designed by researchers to resolve this issue. However, the majority of the techniques suffer from poor computational speed and stuck in local optima problems. Therefore, in this study, a strength Pareto evolutionary algorithm-II based meta-heuristic approach is proposed to tune the hyper-parameters of the four-dimensional chaotic map. The proposed approach is also implemented in a parallel fashion to enhance the computational speed. The effectiveness of the proposed approach is evaluated through extensive experiments. Comparative analyses show that the proposed approach outperforms the competitive approaches in terms of entropy, NPCR, UACI, and PSNR by 0.9834 , 1.0728 , 0.9134 , and 0.8971 % , respectively.

https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/iet-ipr.2019.0587

Parallel strength Pareto evolutionary algorithm-II based image encryption

A novel image encryption algorithm based on SPWLCM and DNA coding

Chaotic mapping has been widely used in image encryption given the unpredictability, ergodicity, and sensitivity of parameters and initial values and the high correspondence with cryptography. The logistic map has the disadvantages of uneven distribution, low security, and small parameter space. In order to overcome these disadvantages, in this article, a new chaotic map based on a real-time variable logistic map with a randomly selected decimal is proposed. Furthermore, this chaotic mapping is applied to image encryption. Several simulation experiments show that the new encryption algorithm can obtain a safely encrypted image at a minimal time complexity.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/iet-ipr.2018.5900

Novel image encryption algorithm based on improved logistic map

Tidal flat system is composed of multiple sub-scale geomorphological units. We found a new mesoscale geomorphological unit on sand-mud mixed intertidal zone along China coast, which was defined as hummocky patches. Hummock patches are most developed in middle tidal flat, with horizontal magnitude of 10–20 m and vertical magnitude of ∼15 cm. Hummocky patches significantly influence local sediment transport, thus affect morphological evolution of tidal flats. In order to understand the formation and development mechanisms of hummocky patches, we collected hydrodynamics, topography, sediment properties, and substrate erosion thresholds data through an in-situ field observation covering a spring-neap tidal cycle over an accretional intertidal flat in Jiangsu, China. We found that sediment characteristics including sorting coefficient (σ: measuring the uniformity of sediment particles) and silt/clay/organic matter/water content are essentially different between hummocky patches and nearby seabed, which leads to spatially varied substrate erosion resistance. The measured erosion thresholds for patches are two times higher comparing to surrounding seabed sediment, which provides foundation for the formation of hummocky patches. Under the impact of periodical tidal currents and waves, surrounding seabed experiences considerably more erosion than patch area, which finally develops to hummocky patches. Therefore, hydrodynamic forces drive the formation and development of patches. The erosion resistance of patches decreases vertically from seabed surface to sublayer, causing initial erosion in the lower sublayer, followed by a mass collapse of the seabed surface layer. Hummocky patches are commonly found in middle tidal zone and their sizes decrease to the shore as tidal currents and waves attenuate with shoreward propagation. Hummocky patches have distinct seasonal variations, which only appear in summer and autumn when wind waves are comparatively lower than winter and spring. We infer the reason is that the strong hydrodynamics caused by winter storms cause larger bottom shear stress than the erosion threshold of hummocky patches, leading to destruction of hummocky patches and a smooth tidal flat surface. This study shed new insight on the knowledge of mesoscale geomorphological units and their formation and development in intertidal flats, which provides crucial information for developing more realistic tidal flat sediment transport and morphological models.

/pdf/the-hummocky-patches-and-associated-sediment-dynamics-over-1xgwy699.pdf

The Hummocky Patches and Associated Sediment Dynamics Over an Accretional Intertidal Flat

In estuarine environments, tidal variation affects turbulence and associated sediment transport processes near the bed. In situ turbulence and sediment data from the benthic boundary layer of the subaqueous Yangtze delta were collected over tidal cycles and are used to gain new insights into turbulence structure and sediment mobility in the benthic boundary layer. Our analysis reveals that turbulent kinetic energy production was balanced by dissipation during flood, while during ebb an imbalance was found (dissipation > production) attributed to turbulence advection. Quadrant analysis showed a tidal variability of the four quadrants with ejections (E) and sweeps (S) being the dominant and equal contributors to Reynolds stress and sediment resuspension. Increased dissipation due to TKE advection during ebb coincides with an increase in the timeshare of inward- and outward-interaction events, resulting in a higher Reynolds stress contribution from ejections and sweeps. The contribution of outward (O) and inward (I) -interactions to sediment resuspension was found to be negligible. For characterizing turbulence intermittency, frequency, duration, strength, and intensity of quadrant events are introduced. The frequency and duration of outward (O) and inward (I) -interactions controlled bursts were 1/3∼1/2 that of the ejections (E) and sweeps (S)-controlled ones which lead to them having limited effects on Reynolds stress. By comparing with the settling velocity, the results show that vertical sediment transport is mainly controlled by ejection and sweep events. Inward- and outward-interaction appears to be more important for fine material with settling velocities of the order of 1 mm/s. 

Renzhi Li

Papers

Novel image encryption algorithm based on improved logistic map

The Hummocky Patches and Associated Sediment Dynamics Over an Accretional Intertidal Flat

Turbulence structure and burst events observed in a tidally induced bottom boundary layer

An unrealised project? —Isaiah Berlin and the philosophy of history