Development of Hot Equal Channel Angular Processing (ECAP) consolidation technique in the production of Boron Carbide(B4C)-Reinforced Aluminium Chip (AA6061)-based composite

The production of metal matrix composites (MMCs) through recycled materials is a cost-saving process. However, the improvement of the mechanical and physical properties is another challenge to be concerned. In this study, recycled aluminium 6061 (AA6061) chips reinforced with different volumetric fractions of boron carbide (B4C) were produced through hot equal channel angular processing (ECAP). Response surface methodology (RSM) was carried out to investigate the dependent response (compressive strength) with independent parameters such as different volumetric fractions (5-15%) of added contents of B4C and preheating temperature (450 – 550°C). Also, the number of passes were examined to check the effect on the mechanical and physical properties of the developed recycled AA6061/B4C composite. The results show that maximum compressive strength and hardness of recycled AA6061/B4C were 59.2 MPa and 69 HV respectively at 5% of B4C contents. Likewise, the density and number of pores increased, which were confirmed through scanning electron microscope (SEM) and atomic force microscopes (AFM) analysis. However, the number of passes enhanced the mechanical and physical properties of the recycled AA6061/B4C composite. Therefore, the maximum compressive strength and hardness achieved were 158 MPa and 74.95 HV for the 4th pass. Moreover, the physical properties of recycled AA6061/B4C composite become denser of 2.62 g/cm3 at the 1st pass and 2.67 g/cm3 for the 4th pass. Thus, it can be concluded that the B4C volumetric fraction and number of passes have a significant effect on recycled AA6061 chips

Hot extrusion followed by a hot ecap consolidation combined technique in the production of Boron Carbide (B4C) reinforced with aluminium chips (AA6061) composite

A new and promising MMC approach to the reduction of pollution, greenhouse effects, and emissions is to develop a technology related to materials composite forming. Hot extrusion followed by hot ECAP is a combination of solid-state recycling method (direct recycling) that consists of chip preparations, cold compaction, and hot extrusion, followed by the ECAP process. The developed process is used to consolidate the chips for direct chip recycling purposes without the remelting phase. In this study, finished or semi-finished products from B4C-reinforced particles and AA6061 aluminium chips were produced. The samples made by hot extrusion were compared with samples obtained from hot extrusion followed by the hot ECAP process in terms of mechanical properties. Additional plastic deformation by hot ECAP after hot extrusion significantly increased the mechanical properties of the MMC compared with the samples obtained from the hot extrusion only. The density and microstructure of the samples were also determined

Localizatation estimation usign the technique of multi-sequence positioning

Wireless sensor networks (WSN) have been considered as promising tools for many location dependent applications such as area surveillance, search and rescue, mobile tracking and navigation, etc. In addition, the geographic information of sensor nodes can be critical for improving network management, topology planning, packet routing and security. Although localization plays an important role in all those systems, itself is a challenging problem due to extremely limited resources available at each low-cost sensor node. This study is focusing on using a distribution-based estimation method. The reason for selecting this method because it is considered an energy saving effort comparing to costly centralized localization scheme. The scope of the estimation in localization of sensor nodes is a Multi-Sequence Positioning (MSP) method that can be applied for a large-scale network in order to achieve accurate distance estimation in sensor deployments where the source of event has a line-of-sight to all sensors. The MATLAB is the programming will be used in the study. This is conceived as an extension of existing WSN programming frameworks. The evaluation was carried based on the error resulted from location estimation scenario compared to the current localization technique of Received Signal Strength (RSS) and the Time of Arrival (TOA). The result showed that MSP showed more efficiently in short and long range as compared to TOA. However, RSS proven to perform better than MSP in long range estimation. This was reasoned to different functional related measures in which RSS is usually perceive less obstruction and shielding of satellite signals whereas MSP can be effected by cellular networks in which it limited by the cell size

Effect of angiotensin-converting enzyme inhibitor and angiotensin receptor blocker initiation on organ support-free days in patients hospitalized with COVID-19

IMPORTANCE Overactivation of the renin-angiotensin system (RAS) may contribute to poor clinical outcomes in patients with COVID-19. Objective To determine whether angiotensin-converting enzyme (ACE) inhibitor or angiotensin receptor blocker (ARB) initiation improves outcomes in patients hospitalized for COVID-19. DESIGN, SETTING, AND PARTICIPANTS In an ongoing, adaptive platform randomized clinical trial, 721 critically ill and 58 non–critically ill hospitalized adults were randomized to receive an RAS inhibitor or control between March 16, 2021, and February 25, 2022, at 69 sites in 7 countries (final follow-up on June 1, 2022). INTERVENTIONS Patients were randomized to receive open-label initiation of an ACE inhibitor (n = 257), ARB (n = 248), ARB in combination with DMX-200 (a chemokine receptor-2 inhibitor; n = 10), or no RAS inhibitor (control; n = 264) for up to 10 days. MAIN OUTCOMES AND MEASURES The primary outcome was organ support–free days, a composite of hospital survival and days alive without cardiovascular or respiratory organ support through 21 days. The primary analysis was a bayesian cumulative logistic model. Odds ratios (ORs) greater than 1 represent improved outcomes. RESULTS On February 25, 2022, enrollment was discontinued due to safety concerns. Among 679 critically ill patients with available primary outcome data, the median age was 56 years and 239 participants (35.2%) were women. Median (IQR) organ support–free days among critically ill patients was 10 (–1 to 16) in the ACE inhibitor group (n = 231), 8 (–1 to 17) in the ARB group (n = 217), and 12 (0 to 17) in the control group (n = 231) (median adjusted odds ratios of 0.77 [95% bayesian credible interval, 0.58-1.06] for improvement for ACE inhibitor and 0.76 [95% credible interval, 0.56-1.05] for ARB compared with control). The posterior probabilities that ACE inhibitors and ARBs worsened organ support–free days compared with control were 94.9% and 95.4%, respectively. Hospital survival occurred in 166 of 231 critically ill participants (71.9%) in the ACE inhibitor group, 152 of 217 (70.0%) in the ARB group, and 182 of 231 (78.8%) in the control group (posterior probabilities that ACE inhibitor and ARB worsened hospital survival compared with control were 95.3% and 98.1%, respectively). CONCLUSIONS AND RELEVANCE In this trial, among critically ill adults with COVID-19, initiation of an ACE inhibitor or ARB did not improve, and likely worsened, clinical outcomes. TRIAL REGISTRATION ClinicalTrials.gov Identifier: NCT0273570

Enhancing the scalability of heterogeneous MANET routing protocols

Ad hoc networks consist of a set of de-centralised end-user nodes which perform routing in a distributed manner over the wireless medium. This distinct feature of these networks has created a number of new and challenging research issues in the wireless data networking paradigm. One such issue is routing, which has consequently received significant attention in particular, the problem of creating routing protocols that scale well in large networks. This has led to the proposition of various categories of routing protocols. These routing protocols have been classified into three classes according to the strategies for discovering and maintaining routes: proactive, reactive, and hybrid. Each routing protocol reacts differently to node mobility and density. On-demand routing protocols have the potential to provide scalable information delivery in large ad hoc networks. The novelty of these protocols is in their approach to route discovery, where a route is determined only when it is required by initiating a route discovery procedure. Much of the research in this area has focused on reducing the route discovery overhead when prior knowledge of the destination is available at the source or by routing through stable links. Hence, many of the protocols proposed to date still resort to flooding the network when prior knowledge about the destination is un-available. In addition, the issue of node heterogeneity is not considered in current MANET routing protocols. Although most current MANET routing protocols assume homogeneous networking conditions where all nodes have the same capabilities and resources, in practice MANETs may consist of heterogeneous nodes that have diverse capabilities and resources, for example military (battlefield) networks and rescue operations systems. Homogeneous networks are easy to model and analyse, but tend to exhibit poor scalability compared with heterogeneous networks. Therefore, scalability and heterogeneity in MANETs are issues that significantly affect the performance of routing protocols. Hence, this dissertation examines the scalability properties of ad hoc routing protocols in homogeneous and heterogeneous MANETs. The research begins with a review of the scalability characteristics of several different classes of routing protocols. This is followed by an extensive study of the performance of current on-demand routing protocols in heterogeneous networks that consist of different nodes with different resources. The study shows that while all protocols perform reasonably well in homogeneous networking conditions, their performance suffer significantly over heterogeneous networks. This dissertation presents two scalable routing protocols. The first is proposed to improve scalability of homogeneous ad hoc networks when there is no prior knowledge about the destination. This protocol is called On-demand Tree-based Routing Protocol (OTRP) . It combines the idea of hop-by-hop routing (as used by Ad-hoc On-Demand Distance Vector (AODV) with an efficient route discovery algorithm called Tree-based Optimised Flooding (TOF) . In this protocol, route discovery overheads are minimised by selectively flooding the network through a limited set of nodes, referred to as branching nodes. The key factors governing the performance of OTRP are theoretically analysed and evaluated, including the number of branch nodes, location of branching nodes and number of Route REQuest (RREQ) retries. It was found that the performance of OTRP (evaluated using a variety of well-known metrics) improves as the number of branching nodes increases and the number of consumed RREQ retries is reduced. Additionally, theoretical analysis and simulation results shows that OTRP outperforms AODV, Dynamic MANET On-demand (DYMO) , and Optimised Link State Routing (OLSR) with reduced overheads as the number of nodes and traffic load increases. The second protocol is On-demand Tree-based Routing Protocol Heterogeneity-Aware (OTRP_HA) . It utilises node heterogeneity and optimises route discovery to reduce overheads while ensuring connectivity between different types of nodes with different interfaces. A node heterogeneity model is developed which can be used to describe common types of node heterogeneity. Nodes in this model are identified by: number of radio interfaces, types of interfaces, and types of power that provides energy for nodes. A strategy called Location-Based Utilisation (LBU) is then introduced to detect unidirectional links and resolve them in a timely fashion. This strategy is based on utilising locations of nodes to filter and cache incoming RREQ packets to find reliable paths to the destination when unidirectional links exist. This strategy is evaluated by applying it on top of ADOV and OTRP. Simulation results show that LBU outperforms existing strategies in homogeneous and heterogeneous MANETs. Finally, a new approach to route discovery is proposed based on the node heterogeneity model. Each node makes its own decision as to whether or not to participate in the route discovery process according to its location, local density, and available resources. This route discovery strategy is combined with LBU. Theoretical analysis and simulation results show that OTRP_HA outperforms OTRP and AODV while reducing overhead as a the number of nodes and traffic volume increase, while also further prolonging the lifetime of batterypowered single-interface nodes when compared to AODV

Scalability of MANET Routing Protocols for Heterogeneous and Homogenous Networks

In Mobile Ad hoc Network (MANET), mobility, traffic and node density are main network conditions that significantly affect the performance of routing protocols. Much of the previous researches in MANET routing have focused on developing strategies, which suit one specific networking scenario. Therefore, there is no existing protocol that can work well in all different networking scenarios. This paper reviews characteristics of each different classes of routing protocols. Moreover, most of current routing protocols assume homogeneous networking conditions where all nodes have the same capabilities and resources. Although homogenous networks are easy to model and analysis, they exhibits poor scalability compared with heterogeneous networks that consist of different nodes with different resources. This paper presents extensive studies simulations for DSR, AODV, LAR1, FSR and WRP in homogenous and heterogeneous networks. The results showed that these which all protocols perform reasonably well in homogenous networking conditions, their performance suffer significantly over heterogonous networks

Routing Metric for Multi-interface and Power-Aware Nodes in Heterogenous MANETs

This paper presents heterogeneity ratio (HR) as a new routing metric for heterogeneous MANETs. This metric is the ratio of number of powerful nodes to hop count that is used to select the best path to destination. Node heterogeneity is modeled in terms of: types and number of different interfaces, power, and transmission ranges. Our proposed routing metric is based on developing route discovery algorithm that is implemented on the top of on-demand tree-based routing protocol (OTRP)[2] to accommodate nodes heterogeneity. Simulation results show that using HR with OTRP heterogeneity aware outperforms other metrics like minimal hop count and maximal number of powerful nodes

On optimising route discovery in absence of previous route information in MANETs

This paper present a new routing protocol for Ad hoc networks, called On-demand Tree-based Routing Protocol (OTRP). This protocol combines the idea of hop-by-hop routing such as AODV with an efficient route discovery algorithm called Tree-based Optimized Flooding (TOF) to improve scalability of Ad hoc networks when there is no previous knowledge about the destination. To achieve this in OTRP, route discovery overheads are minimized by selectively flooding the network through a limited set of nodes, referred to as branching-nodes. The theoretical analysis and simulation results showed that OTRP outperforms AODV, DYMO, and OLSR and it reduces overheads as number of nodes and traffic increase

Effects of Preheating Temperature on Deformed AA6061 Aluminium Properties of Hot Equal Channel Angular Pressing (ECAP) by Using Deform-3D Software

In this paper, the deformation characteristics of engineering AA6061 aluminium in the Equal Channel Angular Pressing (ECAP) are performed using the deformed 3D software. This study is designed to use 0.01 friction, 80,000 number of elements, and 450C, 500C, 550C preheating temperature. The study investigates the effects of die factors such as ECAP outer or inner ingles, die displacement, strength coefficient applied punch force, strain homogeneity, and strain distribution. Moreover, the hot ECAP die factors have played an essential role in the magnitude of material effective strain. On the one hand, decreasing die angles leads to imposing more strain with higher punch force on the workpiece, which results in more homogeneity of the processed materials. On the other hand, stress distribution mainly occurs at the die corner of the die, raising the temperature gradient. In comparison mechanical and physical properties which show an important agreement to support the importance of temperature processing gradient investigations. The study confirms that preheating temperature and friction values play a significant role in hot ECAP materials forming and die safety