Development and characterizations of graded porous titanium scaffolds via selective laser melting for orthopedics applications

To improve the treatment effect of bone defect repair, titanium scaffolds having graded structures with porosities of 78.8%, 70.8%, 62.6%, and 54.4% (denoted as P1, P2, P3, and P4, respectively) were designed and fabricated by selective laser melting. The manufacturability, microstructure, mechanical properties, and permeability were investigated theoretically and experimentally. Simulation results showed that the maximum von Mises stress and permeability were in the range of 569.1–1469.0 MPa and (21.7–54.6)×10−9 m2 respectively. Thereinto, P3 and P4 exhibited lower maximum von Mises stress, meaning a higher strength. The microstructure of fabricated scaffolds with P3 and P4 consisted of martensitic α′ phase. The yield strength and elastic modulus were 185.3-250.8 MPa and 6.1-9.7 GPa, respectively. Compared with the scaffold with P3, the scaffold with P4 exhibited higher yield strength and a more matched elastic modulus to cortical bone, and its permeability (18.6×10−9 m2) was within the range of permeability of human bone. Comprehensively, the scaffold with P4 is a promising candidate for bone defect reconstructions

An intelligent channel assignment algorithm for cognitive radio networks using a tree-centric approach in IoT

Cognitive radio network (CRN) is getting growing interest of the researchers due to its wide applicability for spectrum sharing with massive number of active devices in Internet of Things (IoT). In existing schemes, a large part of the spectrum may remain underutilized which was assigned to service providers as primary users (PU). Secondary user (SU) may be the alternative to use the spectrum. The main challenge is that SU keeps on sending the packets in an incremental manner until a free channel is found in real conditions. It results in excessive communication and packet loss. This paper presents an efficient tree-centric approach where a centralized base-station maintains a tree of available channels and intelligently allocate to the SUs as per the real-time availability of channels. It analyzes for the effective usage of these channels by the SUs. It also manages the authenticated SUs to avoid any interference due to the hidden node problem. A number of extensive simulations are performed using network simulator. The existing instantaneous approaches require 10 to 12 attempts to send request for acquiring free channel with an average delay of 315 ms, the Hybrid-P1 and Hybrid-P2 approaches consumed 4 requests each with a delay of 128 ms to 135 ms. Our proposed CDC mechanism achieves a channel access mostly in 1 to 2 requests with an average delay of about 72 ms. Results are extracted from the trace files that prove the dominance of proposed scheme

A secure and privacy preserved data aggregation scheme in IoMT

The Internet of Things (IoT) is a network of intelligent devices especially in healthcare-based systems. Internet of Medical Things (IoMT) uses wearable sensors to collect data and transmit to central repositories. The security and privacy of healthcare data is a challenging task. The aim of the study is to provide a secure data sharing mechanism. The existing studies provide secure data sharing schemes but still have limitations in terms of hiding the patient identify in the messages exchanged to upload the data on central repositories. This paper presents a Secure Aggregated Data Collection and Transmission (SADCT) that provides anonymity for the identities of patient's mobile device and the intermediate fog nodes. Our system involves an authenticated server for node registration and authentication by saving security credentials. The proposed scheme presents the novel data aggregation algorithm at the mobile device, and the data extraction algorithm at the fog node. The work is validated through extensive simulations in NS along with a security analysis. Results prove the supremacy of SADCT in terms of energy consumption, storage, communication, and computational costs