Unreliable Retrial Queues in a Random Environment

This dissertation investigates stability conditions and approximate steady-state performance measures for unreliable, single-server retrial queues operating in a randomly evolving environment. In such systems, arriving customers that find the server busy or failed join a retrial queue from which they attempt to regain access to the server at random intervals. Such models are useful for the performance evaluation of communications and computer networks which are characterized by time-varying arrival, service and failure rates. To model this time-varying behavior, we study systems whose parameters are modulated by a finite Markov process. Two distinct cases are analyzed. The first considers systems with Markov-modulated arrival, service, retrial, failure and repair rates assuming all interevent and service times are exponentially distributed. The joint process of the orbit size, environment state, and server status is shown to be a tri-layered, level-dependent quasi-birth-and-death (LDQBD) process, and we provide a necessary and sufficient condition for the positive recurrence of LDQBDs using classical techniques. Moreover, we apply efficient numerical algorithms, designed to exploit the matrix-geometric structure of the model, to compute the approximate steady-state orbit size distribution and mean congestion and delay measures. The second case assumes that customers bring generally distributed service requirements while all other processes are identical to the first case. We show that the joint process of orbit size, environment state and server status is a level-dependent, M/G/1-type stochastic process. By employing regenerative theory, and exploiting the M/G/1-type structure, we derive a necessary and sufficient condition for stability of the system. Finally, for the exponential model, we illustrate how the main results may be used to simultaneously select mean time customers spend in orbit, subject to bound and stability constraints

Using Simulation to Model Time Utilization of Army Recruiters

It is a well-known fact Army recruiters work very long hours in a demanding environment. In many cases, recruiting stations are geographically isolated from military bases, with recruiters often tolerating a high cost of living, crime, and other such adverse conditions that characterize the communities they work in. The job itself demands self-starting, motivated individuals with a wide range of skills, from street-savvy to salesmanship, in order to succeed. A number of factors in recent years have made military recruiting more difficult, which include scandals involving highly-placed soldiers and changes in attitudes towards military service among eligible men and women. A recent mission increase has exacerbated this problem even further for the many recruiters who must shoulder this burden. Unlike previous studies which have concentrated on the effects of advertisements and other determinants of enlistments in the Army, this study instead focuses on the individual recruiters themselves, with the ultimate purpose of defining the relationship between the various recruiter tasks and the end product - qualified Army recruits. The key step towards the accomplishment of this goal was the determination of which factors influence recruiter effectiveness. In the course of developing a model and subsequent computer simulation of the recruiting process, a thorough process flow description of the major recruiter tasks was generated. Task completion times were estimated on the basis of empirical studies of actual recruiting stations in anticipation of their use as model input parameters. All of this information was then incorporated into working Simprocess and ModSim computer simulations of a single recruiting station with an arbitrary number of recruiters

Do EVA ™ Adopters Outperform their Industry Peers? Evidence from Security Analyst Earnings Forecasts

The purpose of the present study is to re-examine the link between EVA ™ adoption and firm performance, using security analyst earnings forecasts. These forecasts, we argue, function as a proxy for firm performance that usefully supplements other accounting and stock market measures. We begin by reviewing some of the literature on EVA™, noting claims for strengths and weaknesses of that performance measure and management system. We then make the case for why security analyst earnings forecasts are a useful performance measure for testing the performance effects of EVA TM adoption. We test our hypothesis using Stern Stewart\u27s sample of firms in 1997

A regeneração florestal afeta a fauna de tripes fungívoros (Insecta: Thysanoptera) na Mata Atlântica

Forest regeneration can affect the soil-dwelling insect fauna by promoting an increase in tree diversity and accelerating the accumulation of litter biomass in this environment. This study evaluated the effect of forest regeneration of Atlantic Forest fragments on the fungus-feeding thrips community. In each fragment, two treatments were selected: (i) intermediate successional stage (ISS) and (ii) early successional stage (ESS). Each treatment had three transects, each one with 10 sampling units, comprising 240 sampling units. We sampled 221 adult thrips, 135 individuals in the ISS, and 86 individuals in the ESS. We found 35 Thysanoptera species in 15 genera, all of them belonging to Phlaeothripidae. Abundance, richness, and Shannon’s diversity were higher in the ISS than in the ESS. The low number of individuals and high species richness suggests a remarkable distribution of thrips fauna in the litter. Although some taxa were more related to ISS, species composition structure did not differ between successional stages. Our study indicates that the fungivorous thrips fauna associated with litter was affected by the different natural regeneration states, suggesting that these fungivorous insects are sensitive to different successional stages.  A regeneração florestal pode afetar a fauna de insetos que habitam o solo, ao promover um aumento na diversidade de árvores e acelerar o acúmulo de biomassa da serapilheira nesse ambiente. O objetivo deste estudo foi avaliar o efeito da regeneração florestal de fragmentos da Mata Atlântica na comunidade de tripes fungívoros. Em cada fragmento, foram selecionados dois tratamentos: (i) estágio sucessional intermediário e (ii) estágio sucessional inicial. Cada tratamento compreendeu três transectos, cada um com 10 unidades amostrais, totalizando 240 unidades amostrais. Foram amostrados 221 tripes adultos, 135 nas áreas de sucessão intermediária e 86 indivíduos nas áreas de sucessão inicial.  Encontramos 35 espécies de Thysanoptera em 15 gêneros, todos pertencentes à família Phlaeothripidae. Abundância, riqueza e diversidade de Shannon foram maiores em locais de sucessão intermediária. Esse baixo número de indivíduos e a alta riqueza de espécies sugerem uma distribuição notável da fauna de tripes na serapilheira. Embora alguns táxons estivessem mais relacionados ao estágio intermediário de sucessão, a estrutura de composição das espécies não diferiu entre os tratamentos. Nosso estudo indica que a fauna de tripes fungívoros associada à serapilheira foi afetada pelos diferentes estados de regeneração natural, sugerindo que esses insetos são sensíveis a diferentes estágios sucessionais

On the development of a technological solution for long-term preservation of the commercial qualities in live oysters

The Pacific Oyster has adapted well to the southern Brazilian environmental conditions, where the combination of factors allows harvest in less than eight months. Although convenient for most of the year, it is during summer that water temperature can exceed 30 ºC, a summer condition that leads to high mortality rates. According to the literature, if spawning is not triggered, a substantial reduction in mortality can be achieved. Studies previously presented at CYTEF 2020 showed that confining oysters at temperatures close to those of basal metabolism can inhibit the effects of gametogenesis. Further research was conducted in order to verify the possible outcomes of long term confinement of late autumn harvested oysters, presenting high glycogen reserves. This article reports the experimental results of those tests, regarding the preservation of quality attributes and the reduction of mortality rates, when confining oysters under temperatures similar to those of basal metabolism regime

Effect of Epidemic Interference on the Performance of M-ASK, M-PSK and M-QAM Modulation Schemes

This article presents a study on the performance of different digital modulation systems in the presence of epidemic interference. This type of interference is caused by the fast increase in the number of users in a system at a given time. The epidemic interference can be modeled as a non-stationary stochastic process, which presents random power levels over time. In a previous work, the authors assessed the effect of the epidemic interference on the performance of BPSK, QPSK, and M-QAM systems. The present paper extends the previous results for MASK and M-PSK systems. Furthermore, numerical results from Monte Carlo simulations are presented for all evaluated digital modulation systems

The Association between Childhood Obesity and Cardiovascular Changes in 10 Years Using Special Data Science Analysis

The increasing prevalence of overweight and obesity is a worldwide problem, with several well-known consequences that might start to develop early in life during childhood. The present research based on data from children that have been followed since birth in a previously established cohort study (Generation XXI, Porto, Portugal), taking advantage of State-of-the-Art (SoA) data science techniques and methods, including Neural Architecture Search (NAS), explainable Artificial Intelligence (XAI), and Deep Learning (DL), aimed to explore the hidden value of data, namely on electrocardiogram (ECG) records performed during follow-up visits. The combination of these techniques allowed us to clarify subtle cardiovascular changes already present at 10 years of age, which are evident from ECG analysis and probably induced by the presence of obesity. The proposed novel combination of new methodologies and techniques is discussed, as well as their applicability in other health domains.João Rala Cordeiro received support from Fundação para a Ciência e Tecnologia (PhD Research Scholarship reference 2020.07443.BD)

Ciência, cognição e informação na operacionalização da gestão participativa da água no Brasil

A aprovação da Lei da Água no Brasil (Lei nº 9.433/97) não garantiu a sua operacionalização, incluindo o princípio da gestão participativa nas instâncias dos organismos de bacia (Comitês de Bacia Hidrográfica). Este trabalho aborda a importância da consideração conjunta de conhecimentos científicos e vivenciais, bem como da organização de uma sociedade da informação em rede, para a viabilização deste processo. Aspectos como capacitação dos decisores, visão sistêmica, subjetividade, valores, percepções, atitudes, ética e diálogo são alguns dos elementos cognitivos abordados e considerados estratégicos para o sucesso da gestão participativa. O trabalho visa levantar reflexões sobre o papel do conhecimento e sobre a relevância da integração de qualidades individuais na busca de processos decisórios eficientes. A pesquisa foi realizada como parte do processo de doutoramento no Centro de Desenvolvimento Sustentável/UnB