Review of Mechanical Vapour Compression Refrigeration System Part 2: Performance Challenge

Reducing energy consumption and providing high performance for a vapour compression refrigeration system are big challenges that need more attention and investigation. This paper provides an extensive review of experimental and theoretical studies to present the vapour compression refrigeration system and its modifications that can be used to improve system’s performance and reduce its energy consumption. This paper also presents the challenges that can be considered as a gab of research for the future works and investigations. Cooling capacity, refrigerant effect, energy consumption can be improved by using vapour injection technique, natural working fluid, and heat exchanger. Based on the outcome of this paper, vapour injection technique using natural refrigerant such as water can provide ultimate friendly refrigeration system. Future vision for the vapour compression refrigeration system and its new design technique using Computational Fluid Dynamic (CFD) is also considered and presented.

An Analysis of Participation and Performance of 2067 100-km Ultra-Marathons Worldwide

This study aimed to analyze the number of successful finishers and the performance of the athletes in 100-km ultra-marathons worldwide. A total of 2067 100-km ultra-marathon races with 369,969 men and 69,668 women competing between 1960 and 2019 were analyzed, including the number of successful finishers, age, sex, and running speed. The results showed a strong increase in the number of running events as well as a strong increase in the number of participants in the 100-km ultra-marathons worldwide. The performance gap disappeared in athletes older than 60 years. Nevertheless, the running speed of athletes over 70 years has improved every decade. In contrast, the performance gap among the top three athletes remains persistent over all decades (F = 83.4, p < 0.001; pη2 = 0.039). The performance gap between the sexes is not significant in the youngest age groups (20–29 years) and the oldest age groups (>90 years) among recreational athletes and among top-three athletes over 70 years. In summary, especially for older athletes, a 100-km ultra-marathon competition shows an increasing number of opponents and a stronger performance challenge. This will certainly be of interest for coaches and athletes in the future, both from a scientific and sporting point of view.

A Preemptive Priority-Based Data Fragmentation Scheme for Heterogeneous Traffic in Wireless Sensor Networks

Prioritizing the heterogeneous traffic for Wireless Sensor Networks (WSNs) imposes an important performance challenge for Internet of Things (IoT) applications. Most past preemptive MAC schemes are based on scheduling the high priority packets earlier than those of lower priority. However, in a majority of these schemes, high priority traffic must wait for the ongoing transmission of lower priority traffic due to the non-availability of an interruption mechanism. This paper presents the design and high-level implementation details of a fragmentation scheme (FROG-MAC) for heterogeneous traffic in WSN. FROG-MAC aims at guaranteeing quick transmission of high priority/emergency traffic by interrupting ongoing on channel transmissions. High level implementation of FROG-MAC has been developed in MATLAB as a proof of concept. Traffic of two priorities was generated and a single hop star topology of 100 nodes was used for the experiments. Effect of the proposed fragmentation scheme has been evaluated on delay and Packet Drop Ratio (PDR) for both traffic types, by varying the packet size and fragment size. Simulation results have suggested that with the increasing packet size, the delay and PDR increase for both traffic types. When fragmentation was applied, the performance of high priority traffic significantly improved as compared to the low priority for both the parameters, delay and PDR. Furthermore, it has been found that decreasing the fragment size for low priority traffic results in reducing the delay for high priority traffic.

Lean leadership in major projects: from “predict and provide” to “predict and prevent”

PurposeThe purpose of this paper is to understand the context of major projects and their management from an OM perspective; the authors provide a foundation for exploring how the body of work on lean production (the “old” theory) can contribute to the development of major projects (the “new” context). In doing so, it extends the prevailing economic approach to major projects (best described as “predict and provide”) and posits the development of an alternative approach based on extending the lean production logic to this new context (referred to as “predict and prevent”).Design/methodology/approachThe paper investigates the scope for adopting lean practices in context of major project. To this effect the authors review the current state of both lean thinking and major project management, and use “Universal Credit” as an exploratory case study to illustrate and verify the arguments in practice.FindingsTwo main findings are proposed: first, the authors demonstrate the inherent performance challenge of major projects in OM terms, which the authors argue presents significant scope for the application of OM concepts to improve major project performance. Second, using lean thinking as framing, the authors identify three distinct process levels and common wastes in major projects, and identify five principles how lean could improve the delivery of major projects.Research limitations/implicationsMajor projects present an untapped area for OM research; based on the exploratory case the authors propose ways how OM concepts can be applied to this new context. Further research will be needed to validate and generalise.Practical implicationsMajor projects, including organisational transformations, IT-enabled change, major events and large infrastructure projects, constitute a large proportion of economic activity. Despite their prominence, however, they are also commonly associated with low success rates. This paper provides one route for exploring how a successful set of principles could be applied to improving their performance.Originality/valueThis work translates a popular set of ideas from OM to strengthening a relatively neglected context within OM. An agenda for further research is suggested to support the development of this application.