Resource retrial queue with two orbits and negative customers

In this paper, a multi-server retrial queue with two orbits is considered. There are two arrival processes of positive customers (with two types of customers) and one process of negative customers. Every positive customer requires some amount of resource whose total capacity is limited in the system. The service time does not depend on the customer’s resource requirement and is exponentially distributed with parameters depending on the customer’s type. If there is not enough amount of resource for the arriving customer, the customer goes to one of the two orbits, according to his type. The duration of the customer delay in the orbit is exponentially distributed. A negative customer removes all the customers that are served during his arrival and leaves the system. The objects of the study are the number of customers in each orbit and the number of customers of each type being served in the stationary regime. The method of asymptotic analysis under the long delay of the customers in the orbits is applied for the study. Numerical analysis of the obtained results is performed to show the influence of the system parameters on its performance measure

Effects of pot fishing on the physical condition of snow crab (Chionoecetes opilio) and southern Tanner crab (Chionoecetes bairdi)

The effects of commercial fishing with crab pots on the physical condition of the snow crab (Chionoecetes opilio) and southern Tanner crab (C. bairdi) were investigated in the Bering Sea and in Russian waters of the Sea of Okhotsk. In crabs that were subjected to pot hauling, the presence of gas embolism and the deformation of gill lamellae were found in histopathological investigations. Crab vitality, which was characterized subjectively through observation of behavioral responses, depended on not only the number of pot hauls but also the time between hauls. Immediately after repeated pot hauls at short time intervals (≤3 days), we observed a rapid decline in vitality of crabs. When hauling intervals were increased to >3 days, the condition of crabs did not significantly change. After repeated pot hauls, concentration of the respiratory pigment hemocyanin ([Hc]) was often lower in the hemolymph of crabs than in the hemolymph of freshly caught animals. Our research indicated that changes in [Hc] in crabs after repeated pot hauls were caused by the effects of decompression and not by starvation of crabs in pots or exposure of crabs to air. We suggest that the decrease in [Hc] in hemolymph of snow and southern Tanner crabs was a response to the adverse effects of decompression and air-bubble disease. The decrease in [Hc] in affected crabs may be a result of mechanisms that regulate internal pressure in damaged gills to optimize respiratory circulation

Multi-service resource queue with the multy-component Poisson arrivals

In many papers devoted to telecommunication systems, multiservice queueing models with heterogeneous customer arrivals are given. As a rule, there is streaming traffic, corresponding to the audio and video conference, and elastic traffic, corresponding to the data and file transmission. Different types of traffic require different quality of service, therefore the multi-service systems are also differentiated service systems. Such papers are aimed at developing a framework for estimating the quality of service indicators in new generation multi-service networks. This paper considers a multiservice resource queueing system with three Poisson arrivals, one of which is splitting. The equation for the probabilities distribution of the total resource amounts on the system blocks is compiling by the dynamic screening method, and using the characteristic function of the stationary distribution, the solution is obtaining. The numerical characteristics of the system performance are obtained by the method of moments using characteristic function. A numerical example shows that arrivals intensity growing increases optimal total resource amounts on system blocks in the system with limited resources, and the splitting arrivals affect the correlation between total resource amounts

Efficacy of targeted screening for familial hypercholesterolemia in children and adults aged <44 years: retrospective, prospective observational study

BACKGROUND: Considering the high cardiovascular risk in patients with familial hypercholesterolemia (FH), early diagnosis and treatment are the basis for the prevention of vascular accidents. In the absence of universal screening, the results of more targeted diagnostics are of interest — the search for lipid metabolism disorders in young relatives of patients with atherosclerotic vascular diseases. OBJECTIVE: To determine the effectiveness of targeted screening for identifying patients with FH, which will justify its widespread use in clinical practice. MATERIALS AND METHODS: At the start of the observational study, 584 patients were identified from the vascular centers of the Krasnoyarsk Regional Hospital, Krasnoyarsk Interdistrict Clinical Hospital No. 20 named after. I.S. Berzon, who had lipid profile data and early cardiovascular events (all forms of coronary heart diseases), including reconstructive vascular interventions up to 55 years in men and up to 60 years in women in the case of first-degree relatives and up to 50 years in second-degree relatives. The study examined patients’ relatives aged 44 years. To diagnose FH in participants aged 16 years, the scale developed by a network of Dutch lipid clinics was used; in participants aged 16 years, the S. Broome criteria were used. Targeted screening and lipid parameters in individuals with probable, possible, and definite FH were analyzed. Data processing was performed using Microsoft Excel and Statistica v. 12.0 (USA). Parametric (calculation of the median and 25th and 75th quartiles) and nonparametric (statistical significance of differences was determined using the Mann–Whitney and χ2 tests) methods were used. RESULTS: The study examined 70 children and 104 adults aged 44 years whose first- and/or second-degree relatives suffered premature vascular events. In the general group of participants, 42 (24.14%) patients had FH (of which 18 were 17 years old) and 37 (21.2%) had hyperlipoproteinemia (a). Definite FH was documented in 16 (9.1%) patients, probable in another 16, and possible in 9. Hyperlipoproteinemia (a) was found in 37 (21.2% of general group) patients, including 12 children (17.1% of pediatric group). CONCLUSION: Not more than 30% of the population are aware of the hereditary nature of lipid metabolism disorders and atherosclerotic diseases. Targeted screening is the least expensive and most effective tool for identifying patients with FH and hyperdipoproteinemia (a)

Mathematical model of call center in the form of multi-server queueing system

The paper considers the model of a call center in the form of a multi-server queueing system with Poisson arrivals and an unlimited waiting area. In the model under consideration, incoming calls do not differ in terms of service conditions, requested service, and interarrival periods. It is assumed that an incoming call can use any free server and they are all identical in terms of capabilities and quality. The goal problem is to find the stationary distribution of the number of calls in the system for an arbitrary recurrent service. This will allow us to evaluate the performance measures of such systems and solve various optimization problems for them. Considering models with non-exponential service times provides solutions for a wide class of mathematical models, making the results more adequate for real call centers. The solution is based on the approximation of the given distribution function of the service time by the hyperexponential distribution function. Therefore, first, the problem of studying a system with hyperexponential service is solved using the matrix-geometric method. Further, on the basis of this result, an approximation of the stationary distribution of the number of calls in a multi-server system with an arbitrary distribution function of the service time is constructed. Various issues in the application of this approximation are considered, and its accuracy is analyzed based on comparison with the known analytical result for a particular case, as well as with the results of the simulation

Asymptotic diffusion analysis of an retrial queueing system M/M/1 with impatient calls

In the paper, the retrial queueing system of M/M/1 type with input Poison flow of events and impatient calls is considered. The service time, delay time of calls in the orbit and the impatience time of calls in the orbit have exponential distribution. Asymptotic diffusion analysis method is proposed for the solving problem of finding distribution of the number of calls in the orbit under a long delay of calls in orbit and long time patience of calls in the orbit condition

Resource QS with the requests duplication at the second phase and renewal arrival process

In this paper, a resource queueing system with renewal arrival process, arbitrary service time distribution and requests duplication at the second phase is considered. In more detail, we apply the dynamic screening method to obtain the asymptotic expression for the stationary probability distribution of the total amount of occupied resource in the system. Finally, we verify the goodness of the obtained Gaussian approximation by means of discrete event simulation

Asymptotic stationary probability distribution of total amount of physics experimental data

A mathematical model has been constructed for processing of physics experimental data in the form of a twophas

Asymptotic analysis of resource heterogeneous QS (MMPP + 2M)(2,ν)/GI(2)/∞ under equivalently increasing service time

We consider a resource heterogeneous queuing system with a flexible two-node request-response facility. Each node has a certain resource capacity for service (buffer space) and hence a potential to respond to an incoming demand that generates a request for the provision of some random amount of resources for some random time. The request flows are steady-state Poisson flows of varying intensity. If it is required to use the resources of both nodes to serve a request, then it is assumed that the moments of arrival of such requests form an MMPP flow with a division into two different types of requests. A distinctive feature of the systems under consideration is that the resource is released in the same amount as requested. To construct a multidimensional Markov process, we use the method of introducing an additional variable and dynamic probabilities. The problem of analyzing the total amount of resources occupied by each type is solved provided that the request servicing intensity is much lower than the incoming flow intensity and assuming that the servers have unlimited resources

Highly Stable Supramolecular Donor–Acceptor Complexes Involving a Bis(18-Crown-6)azobenzene as Weak Donor: Structure–Property Relationships

The physicochemical properties of highly stable supramolecular donor–acceptor (D–A) complexes of a bis(18-crown-6)azobenzene (weak π-donor) with a series of bis(ammonioalkyl) derivatives of viologen-like molecules (π-acceptors) in acetonitrile were studied using cyclic voltammetry, UV–vis absorption spectroscopy, 1H NMR spectroscopy, and density functional theory (DFT) calculations. The crystalline structures of the bis(crown)azobenzene and its complex with a bis(ammoniopropyl) derivative of 2,7-diazapyrene were determined by X-ray diffraction analysis. In solution, all of the supramolecular D–A complexes studied have a pseudocyclic structure owing to ditopic coordination of the ammonium groups of the acceptor to the crown ether moieties of the donor. These complexes show somewhat lower stability as compared with the previously studied complexes of the related derivative of stilbene (strong π-donor), which is explained by the relatively weak intermolecular charge-transfer (CT) interactions. Time-dependent DFT calculations predict that the low-energy CT transition in the D–A complex of the bis(crown)azobenzene with a bis(ammoniopropyl) derivative of 4,4′-bipyridine lies between the local ππ* and nπ* transitions of the azobenzene. The absorption band associated with the CT transition is indiscernible in the spectrum since it is overlapped with broad and more intense ππ* and nπ* bands. It was found that the E → Z photoisomerization quantum yield of the bis(crown)azobenzene decreases by almost an order of magnitude upon the complexation with the 4,4′-bipyridine derivative. This effect was tentatively attributed to the intermolecular electron transfer that occurs in the 1ππ* excited state of the azobenzene and competes with the 1ππ* → 1nπ* internal conversion