Retrial BMAP/PH/N Queueing System with a Threshold-Dependent Inter-Retrial Time Distribution

In this paper, we study a multi-server queueing system with retrials and an infinite orbit. The arrival of primary customers is described by a batch Markovian arrival process (BMAP), and the service times have a phase-type (PH) distribution. Previously, in the literature, such a system was mainly considered under the strict assumption that the intervals between the repeated attempts from the orbit have an exponential distribution. Only a few publications dealt with retrial queueing systems with non-exponential inter-retrial times. These publications assumed either the rate of retrials is constant regardless of the number of customers in the orbit or this rate is constant when the number of orbital customers exceeds a certain threshold. Such assumptions essentially simplify the mathematical analysis of the system, but do not reflect the nature of the majority of real-life retrial processes. The main feature of the model under study is that we considered the classical retrial strategy under which the retrial rate is proportional to the number of orbital customers. However, in this case, the assumption of the non-exponential distribution of inter-retrial times leads to insurmountable computational difficulties. To overcome these difficulties, we supposed that inter-retrial times have a phase-type distribution if the number of customers in the orbit is less than or equal to some non-negative integer (threshold) and have an exponential distribution in the contrary case. By appropriately choosing the threshold, one can obtain a sufficiently accurate approximation of the system with a PH distribution of the inter-retrial times. Thus, the model under study takes into account the realistic nature of the retrial process and, at the same time, does not resort to restrictions such as a constant retrial rate or to rough truncation methods often applied to the analysis of retrial queueing systems with an infinite orbit. We describe the behavior of the system by a multi-dimensional Markov chain, derive the stability condition, and calculate the steady-state distribution and the main performance indicators of the system. We made sure numerically that there was a reasonable value of the threshold under which our model can be served as a good approximation of the BMAP/PH/N queueing system with the PH distribution of inter-retrial times. We also numerically compared the system under consideration with the corresponding queueing system having exponentially distributed inter-retrial times and saw that the latter is a poor approximation of the system with the PH distribution of inter-retrial times. We present a number of illustrative numerical examples to analyze the behavior of the system performance indicators depending on the system parameters, the variance of inter-retrial times, and the correlation in the input flow.

Implementing E-Commerce from Logistic Perspective: Literature Review and Methodological Framework

E-commerce is always more diffused as a selling channel around the whole world market, and its importance has increased and continues to increase with the COVID-19 pandemic emergency. It provides enterprises a lot of opportunities, as the importance of physical stores to sell goods is bypassed. However, it has also changed the role of logistics in the supply chain. For this reason, this work aims to identify the main logistics research areas related to e-commerce implementation and the factors and key performance indicators, which should be taken into account for each logistics research area, with particular attention to sustainable aspects. For doing this, a structured and comprehensive literature analysis is carried out. Keywords associated with e-commerce and logistics areas are matched to identify the most interesting works related to its implementation. From the analysis, five main research areas are identified: Supply Chain Network Design (SCND); Outbound Logistics (OL); Reverse Logistics (RL); Warehousing (WR); and IT and data management (E-IT). For each area, key factors, strategies and performance indicators have been identified. Finally, a methodological framework that summarizes the results of the analysis is presented; this is a useful tool for managers to implement or expand their e-commerce business. Many works are focused on one research area, carrying out critical factors, models, and methods to implement that topic. Instead, the methodological framework presented here summarizes multiple research areas from a logistic point of view, identifying for each one input and output variables and how they influence each other.

Improving the Methodology for Assessing the Effectiveness of Economic Entities in Modern Conditions

Modern conditions impose special requirements to the assessment of economic entities. Efficiency is an important parameter of the activity of any business. The present research involved a critical analysis of standard methods for assessing the effectiveness of both domestic and foreign practices. The analysis revealed a need to apply new approaches to business efficiency assessment because the standard approach is not systematic and its indicators repeat themselves. The article offers a new conceptual methodological approach to understanding the term efficiency. The new methodological concept is hybrid in nature and includes classical economic, financial, and institutional methods. It also adopts some methods and approaches from management and natural sciences. The authors built a comprehensive model for assessing the effectiveness of an economic entity in modern conditions. It is based on the idea that the optimal methods are those that do not use relative indicators. This model includes three levels of indicators: standard, qualitative, and synergistic. The new approach is systemic and corresponds to modern economic environment, which resolves the issue of relative performance indicators.

Influences of Engaging in a Participatory Monitoring and Evaluation Process on Stakeholder Perceptions of Key Performance Indicators for Trails

Trail use is growing globally. Managers confront the classic dilemma of protecting ecological integrity and providing enriching experiences. They concomitantly face the imperative for sustainability—contemporarily characterized by complexity, uncertainty, conflict, and change. Heightened levels of visitation are cause for immense concerns due to adverse impacts to the environment as well as visitor experiences. COVID-19 exacerbates these challenges as heightened levels of visitation are occurring, while managers simultaneously face decreases in conservation funding, and restrictions on protected area operations. Participatory monitoring and evaluation (PM&E) is an emerging in- novation to collaboratively address social-ecological challenges, such as issues as- sociated with trail use. This research is concerned with exploring the influences of engaging in a PM&E process on stakeholder perceptions of key performance indicators (KPIs) for trails. This study compares stakeholder perceptions of KPIs for trails before and after a PM&E workshop at the Niagara Glen Nature Reserve in Ontario, Canada. Results show that PM&E can facilitate consensus among stakeholders regarding the overall goals of management and associated KPIs for environmental management planning. Stakeholders were shown to experience a real change in their perceptions of KPIs. The PM&E process studied show that participants became more conscious of the wider social realities as well as their perceptions of trail management. The study has important implications for managers concerned with trails and sustainability, including building consensus among key stakeholders to reach management goals, enhancing localized decision making, and building capacity for management towards sustainability. Trails, as well as the wider community can ultimately benefit from participatory approaches to environmental management. Consensus-building through PM&E works to enhance decisions that account for a diversity of perspectives. Stakeholder participation in trail management increases the likelihood that local needs and priorities are met, while allowing stakeholders to build capacity and learn to effectively manage their environments. Furthermore, positive perceptions from being meaningfully involved in PM&E can ensure the support of constituents, which is imperative for the long-term success of management planning.

Efficiency of Municipal Self-Government Bodies in the Kemerovo Region (Kuzbass)

The author reviewed domestic and foreign publications that feature various methods of assessing the performance of municipal authorities, which is the most important criterion for determining the well-being of population. The article introduces an authentic method that relies on the analysis of performance indicators based on the predominance of the achieved values over the average converted values. The method makes it possible to quantify and interpret the level of the so-called "administrative rationality" of municipal self-government bodies. It converts the values of indicators into coefficients (dominance and achievement), elements, and integral values of efficiency. The transformed values are then systematized in the context of economy (assets, budget, wages, etc.) and social components (transport accessibility, land, population, housing, communal services, etc.). A comparative analysis determined the following effective municipal districts of the Kemerovo region: Prokopyevsk, Kemerovo, Novokuznetsk, Yaya, Leninsk-Kuznetsky, and Izhmorka. The new method provides a transparent and objective assessment of municipal management.

Photodetectors Based on Micro-nano Structure Material

Photodetectors converting optical signals into electrical signals have been widely utilized and have received more and more attention in scientific research and industrial fields including optical interconnection, optical communication, and environmental monitoring. Herein, we summarize the latest development of photodetectors with different micro-nano structures and different materials and the performance indicators of photodetectors. Several photodetectors, such as flexible, ultraviolet two-dimensional (2D) microscale, and dual-band photodetectors, are listed in this minireview. Meanwhile, the current bottleneck and future development prospects of the photodetector are discussed.

Investigating the Electrocoagulation Treatment of Landfill Leachate by Iron/Graphite Electrodes: Process Parameters and Efficacy Assessment

Electrocoagulation is a widely used method for treating leachate since it is cost effective and eco-friendly. In the present study, the electrocoagulation process was employed to remove chemical oxygen demand (COD), NH4+, total dissolved solids (TDS), total suspended solids (TSS), turbidity, and color from landfill leachate. At first, lime was used as a pretreatment, then the Fe/Gr and Ti/PbO2/steel electrodes were used, and the optimum electrode was selected. Afterwards, the effects of some variables, including pH, current density, temperature, the inter-electrode distance, and the type of electrolyte were investigated. Results showed that COD, NH4+, TSS, TDS, electrical conductivity (EC), turbidity, color, and pH of effluent pretreatment chemical reached 22,371, 385, 884, 21,820 (mg/L), 13.8 (ms/cm3), 1355 (NTU), 8500 (TCU) and 10, respectively (the removal efficiency was 0, 20.37, 32.4, 61.99, 59.18, and 56.6 percent). With the Fe/Gr electrode, the optimal condition was observed as follows: pH of 7.5, current density of 64 mA/cm2, inter-electrode distance was equal to 1.5 cm, temperature at 20 °C, and retention time 2–4 h. Overall, the electrocoagulation with the Fe/Gr electrode was a suitable technology for landfill leachate treatment due to its effectiveness for the removal of both COD and NH4+, with advantageous performance indicators.