In the contemporary landscape, the escalating deployment of drones across diverse industries has ushered in a consequential concern, including ensuring the security of drone operations. This concern extends to a spectrum of challenges, encompassing collisions with stationary and mobile obstacles and encounters with other drones. Moreover, the inherent limitations of drones, namely constraints on energy consumption, data storage capacity, and processing power, present formidable obstacles in developing collision avoidance algorithms. This review paper explores the challenges of ensuring safe drone operations, focusing on collision avoidance. We explore collision avoidance methods for UAVs from various perspectives, categorizing them into four main groups: obstacle detection and avoidance, collision avoidance algorithms, drone swarm, and path optimization. Additionally, our analysis delves into machine learning techniques, discusses metrics and simulation tools to validate collision avoidance systems, and delineates local and global algorithmic perspectives. Our evaluation reveals significant challenges in current drone collision prevention algorithms. Despite advancements, critical UAV network and communication challenges are often overlooked, prompting a reliance on simulation-based research due to cost and safety concerns. Challenges encompass precise detection of small and moving obstacles, minimizing path deviations at minimal cost, high machine learning and automation expenses, prohibitive costs of real testbeds, limited environmental comprehension, and security apprehensions. By addressing these key areas, future research can advance the field of drone collision avoidance and pave the way for safer and more efficient UAV operations.

To handle task execution, modern supercomputers employ thousands (or millions) of processors. In such supercomputers, task scheduling has a meaningful impression on system performance. To improve efficiency, task scheduling algorithms aim to decrease the volume of communication and the number of message exchanges. These efforts, however, result in other bottlenecks, such as high-link congestion. In addition, the heterogeneity of processors and networks is another major challenge for schedulers. This paper presents a new algorithm for scheduling called Heterogeneity-Aware Task Scheduling (HATS). The proposed algorithm adopts an updated multi-level hyper-graph partitioning approach. It describes a new method of aggregation in the coarsening step that helps to accurately coarsen the hyper-graph of the task model. The Raccoon Optimization algorithm is then used in the initial partitioning phase, and in the un-coarsening phase, a novel refinement procedure optimises the initial partitions. The experiments on this approach showed that, compared to the other well-known algorithms, the proposed method offers better schedules with lower communication volume and imbalance ratio in a shorter time.

Delivering optimum performance on a parallel computer is highly dependant on the efficiency of the scheduling and mapping procedure. If the composition of the parallel application is known a prior, the mapping can be accomplished statically on the compilation time. The mapping algorithm uses the model of the parallel application and maps its tasks to processors in a way to minimize the total execution time. In this article, current modeling approaches have discussed. Later, a new modeling schema named Model of Exascale Message-Passing Programs on Heterogeneous Architectures (MEMPHA) has proposed. A comparative study has been performed between MEMPHA and existing models. To exhibit the efficiency of the MEMPHA, experiments have performed on a set of data-set hypergraphs. The results obtained from the experiments show that deploying the MEMPHA helps to optimize metrics, including the congestion, total communication volume and maximum volume of data being sent or received. These improvements vary from 76 to 1 percent, depending on the metric and benchmark model. Moreover, MEMPHA supports the modeling of applications with multiple producers for a single data transmission, where the rest of the approaches fail.

Web caching plays a key role in delivering web objects to the end-users which is one of the advantages of World Wide Web (WWW). However, the size of the cache is limited which is considered as one of the drawbacks of web caching. Furthermore, retrieving the same web object from the origin server many times consumes the network bandwidth. Moreover, cache pollution is a drawback of traditional web caching policies such as Least Recently Used (LRU) web caching policy where web objects that are stored in the cache are not visited frequently. In this work, new intelligent cooperative web caching approach based on J48 classifier is presented. A simulation is carried out to evaluate the performance of the proposed approach. The results show that the new approach improves the performance of the LRU web caching policy.

Nowadays, the idea of media contents streaming through the Internet has become a very important issue. On the other hand, full caching for media objects is not a practical solution and leads to consume the cache storage in keeping few media objects because of its limited capacity. Furthermore, repeated traffic which is being sent to clients wastes the network bandwidth. Thus, utilizing the bandwidth of the network is considered as an important objective for network administrators. Media objects have some characteristics that have to be considered when a caching algorithm is going to be performed. In this paper, recent approaches that have been proposed for media streams caching in peer-to-peer systems are reviewed.

The results produced by five different MPI benchmark programs on an SGI Altix 3700 are analyzed and compared. There are significant differences in the results for some MPI operations. We investigate the reasons for these discrepancies, which are due to differences in the measurement techniques, implementation details and default configurations of the different benchmarks. The variation in results on the Altix are generally much greater than on a distributed memory machine, due primarily to the ccNUMA architecture and the importance of cache effects, as well as some implementation details of the SGI MPI libraries