Analysis and optimisation of a M/M/1/WV queue with Bernoulli schedule vacation interruption and customer’s impatience

In this investigation, we establish a steady-state solution of an infinite-space single-server Markovian queueing system with working vacation (WV), Bernoulli schedule vacation interruption, and impatient customers. Once the system becomes empty, the server leaves the system and takes a vacation with probability p or a working vacation with probability 1 − p, where 0 ≤ p ≤ 1. The working vacation period is interrupted if the system is non empty at a service completion epoch and the server resumes its regular service period with probability 1 − q or carries on with the working vacation with probability q. During vacation and working vacation periods, the customers may be impatient and leave the system. We use a probability generating function technique to obtain the expected number of customers and other system characteristics. Stochastic decomposition of the queueing model is given. Then, a cost function is constructed by considering different cost elements of the system states, in order to determine the optimal values of the service rate during regular busy period, simultaneously, to minimize the total expected cost per unit time by using a quadratic fit search method (QFSM). Further, by taking illustration, numerical experiment is performed to validate the analytical results and to examine the impact of different parameters on the system characteristics.

Performance Analysis of Retrial Queueing Model with Working Vacation, Interruption, Waiting Server, Breakdown and Repair

In this present paper, an M/M/1 retrial queueing model with a waiting server subject to breakdown and repair under working vacation, vacation interruption is considered. Customers are served at a slow rate during the working vacation period, and the server may undergo breakdowns from a normal busy state. The customer has to wait in orbit for the service until the server gets repaired. Steady-state solutions are obtained using the probability generating function technique. Probabilities of different server states and some other performance measures of the system are developed. The variation in mean orbit size, availability of the server, and server state probabilities are plotted for different values of breakdown parameter and repair rate with the help of MATLAB software. Finally, cost optimization of the system is also discussed, and the optimal value of the slow service rate for the model is obtained.

Body Composition Adaptations Throughout an Elite Circus Student-Artist Training Season

The purpose of this study was to perform a longitudinal assessment of body composition of circus student-artists in an elite 3-year college training program. Ninety-two student-artists participated (age = 20.39 ± 2.42 years; height = 170.01 ± 8.01 cm; mass = 66.48 ± 11.07 kg; 36% female and 64% male), representing 92% of the student population. Body composi- tion was assessed using multi-frequency bioelectrical impedance at four strategic time points throughout the training year to evaluate changes over the two semesters (September to December and January to April) and winter vacation (December to January). Workloads were subjectively assessed using ratings of perceived exer- tion (RPE). Averaged over the academic terms, fat mass was 11.5 ± 4.8%, muscle mass was 50.2 ± 3.4%, and body mass index was 22.9 ± 2.2. Males and females differed significantly across all absolute and relative body composition variables. Muscle mass increased (semester one, +1.0%, p < 0.001; semester two, +0.4%, p < 0.05) while fat mass decreased during each semester (semester one, -1.6%, p < 0.001; semester two, -0.6%, p < 0.05) co-varying with changes in RPE (semester one, +2.3, p < 0.05; semester two, +1.7, p < 0.05). During the winter vacation period, percent fat mass increased (males, +1.0%; females, +2.0%) and percent muscle mass decreased (males, -0.6%; females, -0.9%). Discipline-specific differences in body composition were also detected, and significant differences were observed between student-artists grouped by years in school. Over the training year, there was a positive adaptation for muscle and fat mass despite the negative adaptation experienced during the winter vacation period.

Effects of white-tailed deer habitat use preferences on southern cattle fever tick eradication: simulating impact on “pasture vacation” strategies

Background Rhipicephalus (Boophilus) annulatus and Rhipicephalus (Boophilus) microplus (southern cattle fever tick; SCFT), collectively known as cattle-fever ticks (CFTs), are vectors of protozoal parasites (Babesia bigemina and Babesia bovis) that cause bovine babesiosis (also known as cattle fever). One traditional strategy for CFT eradication involves the implementation of a “pasture vacation,” which involves removing cattle (Bos taurus) from an infested pasture for an extended period of time. However, vacated pastures are often inhabited by wildlife hosts, such as white-tailed deer (WTD; Odocoileus virginianus), which can serve as alternate hosts for questing CFTs. We hypothesized that the distribution of host-seeking larvae among habitat types post-pasture vacation would reflect habitat use patterns of WTD, and in turn, affect the subsequent rate of pasture infestation by CFT. Methods We adapted a spatially explicit, individual-based model to simulate interactions among SCFT, cattle, and WTD as a tool to investigate the potential effects of WTD habitat use preferences on the efficacy of a pasture vacation. We parameterized the model to represent conditions typical of rangelands in south Texas, USA, simulated a 1-year pasture vacation under different assumptions regarding WTD habitat use preferences, and summarized effects on efficacy through (1) time post-vacation to reach 100% of pre-vacation densities of host-seeking larvae, and (2) the ecological conditions that resulted in the lowest host-seeking larval densities following pasture vacation. Results Larval densities at the landscape scale varied seasonally in a similar manner over the entire simulation period, regardless of WTD habitat use preferences. Following the removal of cattle, larval densities declined sharply to < 100 larvae/ha. Following the return of cattle, larval densities increased to > 60% of pre-vacation densities ≈ 21 weeks post-vacation, and reached pre-vacation levels in less than a year. Trends in larval densities in different habitat types paralleled those at the landscape scale over the entire simulation period, but differed quantitatively from one another during the pasture vacation. Relative larval densities (highest to lowest) shifted from (1) wood/shrub, (2) grass, (3) mixed-brush during the pre-vacation period to (1) mixed-brush, (2) wood/shrub, (3) grass or (1) wood/shrub, (2) mixed-brush, (3) grass during the post-vacation period, depending on WTD habitat use preferences. Conclusions By monitoring WTD-driven shifts in distributions of SCFT host-seeking larvae among habitat types during simulated pasture vacation experiments, we were able to identify potential SCFT refugia from which recrudescence of infestations could originate. Such information could inform timely applications of acaricides to specific refugia habitats immediately prior to the termination of pasture vacations.

Big Five traits as Predictors of Perceived Stressfulness of the COVID-19 Pandemic

This study examined the Big Five personality traits as predictors of individual differences and changes in the perceived stressfulness of the COVID-19 pandemic in Germany between early April 2020 and early September 2020. This timeframe includes the first national “lockdown,” the period of “easing” of restrictions, and the summer vacation period. Data were collected from n = 588 full-time employees, who provided baseline data on their personality traits in early December 2019, and then later provided data on perceived stressfulness of the COVID-19 pandemic at five time points, spanning six months. Consistent with expectations based on event and transition theories, results showed that, on average, perceived stressfulness declined between early April 2020 and early September 2020. Moreover, this effect was stronger between early April 2020 and early July 2020. Hypotheses based on the differential reactivity model of personality and stress were partially supported. Emotional stability was associated with lower, and extraversion associated with higher, average levels of perceived stressfulness. Finally, extraversion was associated with increases (i.e., positive trajectories) in perceived stressfulness between early April 2020 and early July 2020 and decreases (i.e., negative trajectories) in perceived stressfulness between early July 2020 and early September 2020.

ON MARKOVIAN QUEUES WITH SINGLE WORKING VACATION AND BERNOULLI INTERRUPTIONS

This paper considers the customers’ equilibrium and socially optimal joining–balking behavior in a single-server Markovian queue with a single working vacation and Bernoulli interruptions. The model is motivated by practical service systems where the service rate can be adjusted according to whether or not the system is empty. Specifically, we focus on a single-server queue in which the server's service rate is reduced from a regular to a lower one when the system becomes empty. This lower rate period is called a working vacation for the server which may represent that part of the service facility is under a maintenance process or works on other non-queueing job, or simply for saving the energy (for a machine server case). In this paper, we assume that the working vacation period is terminated after a random period or with probability p after serving a customer in a non-empty system. Such a system is called a queue with single working vacation and Bernoulli interruptions. Customers are strategic and can make choice of joining or balking based on different levels of system information. We consider four scenarios: fully observable, almost observable, almost unobservable, and fully unobservable queue cases. Under a reward-cost structure, we analyze the customer's equilibrium and social-optimal strategies. In addition, the effects of system parameters on optimal strategies are illustrated by numerical examples.

Analysis of stress level and recovery of formative football coaches. Case studies (Análisis del nivel de estrés y recuperación de los entrenadores de fútbol formativo. Estudios de caso)

This study aimed to monitor and compare the levels of stress and recovery in elite football coaches of youth teams at different moments of one sports season. A descriptive study with longitudinal characteristics was conducted. Twenty-six coaches (37.60±7.37 years old) with experience time (7.20±5.37 years) from the categories U-15, U-17 and U-20 of the main Brazilian elite football teams were evaluated. The coaches filled out the demographic data questionnaire and the RESTQ-Coach in three periods of the sports season: vacation, training and competition. The stress levels were higher in competition periods, as well as during training moments, compared to the vacation period. The recovery levels showed a decrease in the competition period compared to the vacation period. The stress values were not higher than the recovery values of the coaches evaluated at different times of the sports season. Stress and recovery levels oscillate during a sports season. However, recovery levels have remained higher than stress. It seems that the elite football coaches are adapted and support the work pressures to which they are submitted in the sports context over one season. Resumen. El objetivo de este estudio era identificar y comparar los niveles de estrés y recuperación de los entrenadores de fútbol de élite de los equipos juveniles en diferentes momentos de una temporada deportiva. Se realizó un estudio descriptivo con características longitudinales. Se evaluaron 26 entrenadores (37,60±7,37 años) con tiempo de experiencia (7,20±5,37 años) de las categorías sub-15, sub-17 y sub-20 de los principales equipos de fútbol de élite de Brasil. Los entrenadores rellenaron el cuestionario de datos demográficos y el RESTQ-Coach en tres periodos de la temporada deportiva: vacaciones, entrenamiento y competición. Los niveles de estrés fueron más altos en los períodos de competición, así como en los momentos de entrenamiento, en comparación con el período de vacaciones. Los niveles de recuperación mostraron una disminución en el período de competición en comparación con el período de vacaciones. Los valores de estrés no fueron superiores a los valores de recuperación de los entrenadores evaluados en diferentes momentos de la temporada deportiva. Los niveles de estrés y recuperación oscilan durante la temporada deportiva. Sin embargo, los niveles de recuperación se han mantenido más altos que el estrés. Parece que los entrenadores de fútbol de élite están adaptados y soportan las presiones laborales a las que están sometidos en el contexto deportivo durante una temporada.

ORGANIZATION OF REHABILITATION AND PSYCHOLOGICAL SUPPORT IN A HEALTH CAMP CHILDREN AFTER SEVERE DISEASES

The issue of organizing recreation, health improvement and employment of children and ado-lescents during the vacation period is always in the focus of attention of educational, social medical organiza-tions, government bodies of the constituent entities of the Russian Federation. The life activity of the children's camp is a whole system in which the possibilities of improving physical and psychological health are laid, value orientations are formed, and the creative abilities of children are developed. Special or inclusive shifts are organized for children with disabilities with the aim of their social rehabilitation. The article reveals the possibilities of psychological and pedagogical support and support of such children during their holidays on the example of the activities of the Sheredar Children's Health and Rehabilitation Center.

A Cross-Regional Analysis of the COVID-19 Spread during the 2020 Italian Vacation Period: Results from Three Computational Models Are Compared

On 21 February 2020, a violent COVID-19 outbreak, which was initially concentrated in Lombardy before infecting some surrounding regions exploded in Italy. Shortly after, on 9 March, the Italian Government imposed severe restrictions on its citizens, including a ban on traveling to other parts of the country. No travel, no virus spread. Many regions, such as those in southern Italy, were spared. Then, in June 2020, under pressure for the economy to reopen, many lockdown measures were relaxed, including the ban on interregional travel. As a result, the virus traveled for hundreds of kilometers, from north to south, with the effect that areas without infections, receiving visitors from infected areas, became infected. This resulted in a sharp increase in the number of infected people; i.e., the daily count of new positive cases, when comparing measurements from the beginning of July to those from at the middle of September, rose significantly in almost all the Italian regions. Upon confirmation of the effect of Italian domestic tourism on the virus spread, three computational models of increasing complexity (linear, negative binomial regression, and cognitive) have been compared in this study, with the aim of identifying the one that better correlates the relationship between Italian tourist flows during the summer of 2020 and the resurgence of COVID-19 cases across the country. Results show that the cognitive model has more potential than the others, yet has relevant limitations. The models should be considered as a relevant starting point for the study of this phenomenon, even if there is still room to further develop them up to a point where they become able to capture all the various and complex spread patterns of this disease.