Joint Encryption and Compression-Based Watermarking Technique for Security of Digital Documents

Recently, due to the increase in popularity of the Internet, the problem of digital data security over the Internet is increasing at a phenomenal rate. Watermarking is used for various notable applications to secure digital data from unauthorized individuals. To achieve this, in this article, we propose a joint encryption then-compression based watermarking technique for digital document security. This technique offers a tool for confidentiality, copyright protection, and strong compression performance of the system. The proposed method involves three major steps as follows: (1) embedding of multiple watermarks through non-sub-sampled contourlet transform, redundant discrete wavelet transform, and singular value decomposition; (2) encryption and compression via SHA-256 and Lempel Ziv Welch (LZW), respectively; and (3) extraction/recovery of multiple watermarks from the possibly distorted cover image. The performance estimations are carried out on various images at different attacks, and the efficiency of the system is determined in terms of peak signal-to-noise ratio (PSNR) and normalized correlation (NC), structural similarity index measure (SSIM), number of changing pixel rate (NPCR), unified averaged changed intensity (UACI), and compression ratio (CR). Furthermore, the comparative analysis of the proposed system with similar schemes indicates its superiority to them.

Effects of intermittent pneumatic compression on femoral vein peak venous velocity during active ankle exercise

Introduction: The risk of developing deep vein thrombosis (DVT) is high even after the period of bed rest following major general surgery including total joint arthroplasty (TJA). Mobile intermittent pneumatic compression (IPC) devices allow the application of IPC during postoperative exercise. Although ambulation included ankle movement, no reports have been made regarding the effects of IPC during exercise, including active ankle exercise (AAE), on venous flow. This study was performed to examine whether using a mobile IPC device can effectively augment the AAE-induced increase in peak velocity (PV). Methods: PV was measured by Doppler ultrasonography in the superficial femoral vein at rest, during AAE alone, during IPC alone, and during AAE with IPC in 20 healthy subjects in the sitting position. PV in AAE with IPC was measured with a mobile IPC device during AAE in the strong compression phase. AAE was interrupted from the end of the strong compression phase to minimize lower limb fatigue. Results: AAE with IPC (76.2 cm/s [95%CI, 69.0–83.4]) resulted in a significant increase in PV compared to either AAE or IPC alone (47.1 cm/s [95%CI, 38.7–55.6], p < 0.001 and 48.1 cm/s [95%CI, 43.7–52.4], p < 0.001, respectively). Discussion: Reduced calf muscle pump activity due to the decline in ambulation ability reduced venous flow. Therefore, use of a mobile IPC device during postoperative rehabilitation in hospital and activity including self-training in an inpatient ward may promote venous flow compared to postoperative exercise without IPC. Conclusion: Use of a mobile IPC device significantly increased the PV during AAE, and simultaneous AAE with IPC could be useful evidence for the prevention of DVT in clinical settings, including after TJA.

Shake table test of RC walls' coupling provided by slabs

When designed to the seismic load effects, reinforced concrete walls connected by slabs without coupling beams are usually considered cantilever walls. Several recent studies indicated that slabs themselves could provide strong coupling in some cases, and the walls could respond differently from cantilever walls. To study the slab-to-wall piers interaction, a shake table test of the half-scale three-story specimen was conducted within HORIZON 2020 SERA-TA project. The specimen consisted of four rectangular walls linked by three slabs. It was subjected to a series of seismic excitations of increasing intensity. In the last three tests, the nonlinear response of the slabs and wall piers was observed. At the strong seismic excitations, one pier was subjected to strong tensile, while the adjacent pier was subjected to strong compression forces. The crack pattern of piers was asymmetric and different from the cross-shaped damage pattern, typical for cantilever walls. The coupling of wall piers provided by slabs was considerably stronger than it was expected. The share of the overturning moment resisted by the frame action induced by the slabs was more than 50%. All slabs were fully activated and significantly damaged. Their damage was primarily flexural. The effective width of slabs was equal to their total width.

Dynamics and fragmentation of small inextensible fibres in turbulence

The fragmentation of small, brittle, flexible, inextensible fibres is investigated in a fully developed, homogeneous, isotropic turbulent flow. Such small fibres spend most of their time fully stretched and their dynamics follows that of stiff rods. They can then break through tensile failure, i.e. when the tension is higher than a given threshold. Fibres bend when experiencing a strong compression. During these rare and intermittent buckling events, they can break under flexural failure, i.e. when the curvature exceeds a threshold. Fine-scale massive simulations of both the fluid flow and the fibre dynamics are performed to provide statistics on these two fragmentation processes. This gives ingredients for the development of accurate macroscopic models, namely the fragmentation rate and daughter-size distributions, which can be used to predict the time evolution of the fibre size distribution. Evidence is provided for the generic nature of turbulent fragmentation and of the resulting population dynamics. It is indeed shown that the statistics of break-up is fully determined by the probability distribution of Lagrangian fluid velocity gradients. This approach singles out that the only relevant dimensionless parameter is a local flexibility which balances flow stretching to the fibre elastic forces. This article is part of the theme issue ‘Fluid dynamics, soft matter and complex systems: recent results and new methods’.

Implanted β-Tricalcium Phosphate Blocks Can Function as a Placeholder in Recurrent Giant Cell Tumor of Bone

The giant cell tumor of bone (GCTB) is a locally aggressive tumor. Reconstruction methods using β-tricalcium phosphate (β-TCP) blocks with strong compression resistance in and around the knee joint for GCTB have been reported. Among six cases of GCTB treated using this method, two recurrent cases revealed osteolysis, predominantly within the β-TCP block based on plain radiographs or computed tomography, while remodeled host bones were preserved. Implanted β-TCP blocks can function as a placeholder to preserve host bone in recurrent cases, leading to a higher probability of joint preservation.

Reply to the ‘Comment on “Pressure enhancement in carbon nanopores: a major confinement effect”’ by D. van Dijk, Phys. Chem. Chem. Phys., 2020, 22, DOI: 10.1039/C9CP02890K

By calculating the unique effective tangential pressure and discussing recent evidence from experiment and simulations, we show that the high pressure and strong compression in adsorbed layers for wetting systems on carbon are significant.

Safe Conditions for Conducting Tests Using Ballistic Facilities

Understanding the physical and thermomechanical response of materials subjected to intense dynamic loading is a significant challenge that has a practical implication for modern engineering. Shock compression followed by expansion precipitates both reversible and irreversible physical and mechanical processes in the material. These processes include strong compression in solids, high heating rates, phase transformations, electronic structure change, work hardening, spalling. Methods and devices for producing intense shock loads can be subdivided into several groups. Presently, in worldwide practice, gun type launchers have gained the widest acceptance in studying dynamic compressibility, strength characteristics, and spallatation phenomena in laboratory conditions. In this type of facility, the launched body moves in a tube under the force of a compressed gas. The facilities differ depending on the gas used and the method of its compression. Specific features of the facilities impose certain limitations on the registration and format of the tests. Examples of determining the boundary between the interior and exterior ballistics, the influence of the launched body supporting elements and the conditions of safe testing at high-speed entry in fuel are considered in this work.