Построение и анализ модели воспроизведения каналов вещательного телевидения в Р2Р сети

In this paper, we introduce a closed queueing network model with a single customer to analyze the behavior of a peer in P2P streaming systems. Then we use the passage to the limit when the number of peers approaches infinity in a closed queueing network model with limited population to analytically study the performance of multi-channel P2P streaming systems with the isolated channel (ISO) streaming design. The product-form solution for steady state probabilities and the expressions for the probability of universal streaming for a channel were derived. Some calculations for both models (when the number of peers is limited and when the number of peers approaches infinity) were conducted.В статье построена вероятностная модель просмотра каналов вещательного телевидения пользователями одноранговой сети (от англ. peer-to-peer, P2P - равный к равному). Поведение отдельного пользователя представлено в терминах замкнутой экспоненциальной сети массового обслуживания. Стационарное распределение вероятностей состояний модели функционирования P2PTV-сети представлено в мультипликативном виде по числу телеканалов и числу пользователей системы. С учётом популярности телеканалов получены формулы для анализа основного показателя качества функционирования P2PTV-сети на уровне пользователя (QoE, Quality of Experience) - вероятности всеобщей передачи (от англ. universal streaming), т.е. качественного приёма видеопотока всеми пользователями

Nitrite in Organ Protection

In the last decade, the nitrate-nitrite-nitric oxide (NO) pathway has emerged to therapeutical importance. Modulation of endogenous nitrate and nitrite levels with the subsequent S-nitros(yl)ation of the downstream signalling cascade open the way for novel cytoprotective strategies. In the following we summarize the actual literature and give a short overview on the potential of nitrite in organ protection

К анализу характеристик интерференции взаимодействующих устройств в сетях беспроводной связи

The distinctive features of fifth generation (5G) mobile networks are the support of technologies for Internet of Things (IoT) network connectivity and direct device-to-device (D2D) communications, including support for wireless connections during the mobility of devices. The key indicators of the effectiveness of the 5G network are energy efficiency, reliability, and network capacity. The quality of service provisioning in the 5G network is determined by the quality of data transmission on the radio channel between the mobile subscribers, one of the important factors of which is the interference created by the subscribers transmitting data over the same or neighboring radio frequencies. In the paper, an analytical review devoted to the methods of interference analysis in wireless networks with D2D technology both for the case of fixed interacting subscribers and for the case of moving subscribers was conducted. The performance metric of interference characterization is the signal-to-interference ratio (SIR) that relates the level of the useful signal to the level of the background interference, i.e. the SIR ratio is the proportion between the received modulated carrier power and the received co-channel cross-talk power from other transmitters than the useful signal. The analysis of SIR for fixed transmitters and receivers is based on stochastic geometry methods that allow for a given location of interacting devices or for a given distance distribution between the devices and the density of the devices within the coverage area to estimate the SIR at an arbitrary receiver. The methods can be used by the radio resource allocation scheduler to assess the possibility of establishing a new transmitter-receiver connection and to assign a radio frequency for it by taking into account the known properties of already established connections of the associated pairs over the coverage area. In case of moving devices, the value of SIR is variable due to a change in inter-device distances. The goal of the paper is to propose an approach to the analysis of interference characteristics when the trajectories of mobile devices are given by certain kinetic equations. One of the SIR characteristics in this case is the distribution of time interval of connection unavailability caused by the drop of SIR below a predetermined threshold. Also, a research problem for the case of moving devices is to develop a recommendation on the choice of the movement model from the known random walk models for further interference characterization. © Copyright 2017 for the individual papers by the papers' authors.Отличительными особенностями сетей мобильной связи пятого поколения (5G) являются поддержка технологий Интернета вещей (Internet of Things, IoT) и прямого взаимодействия устройств (device-to-device communications, D2D), включая организацию соединений в процессе перемещения беспроводных устройств на местности. Ключевыми показателями эффективности сети 5G являются энергоэффективность, надежность и пропускная способность сети. Качество предоставления услуг в сети 5G определяется качеством передачи данных по радиоканалу между мобильными абонентами, одним из важных показателей которого является интерференция, создаваемая абонентами, передающими данные на одной и той же или близких радиочастотах. В статье проведен аналитический обзор методов исследования интерференции в беспроводных сетях с технологией D2D как для случая фиксированных взаимодействующих абонентов, так и для случая движущихся абонентов. Метрикой характеристик качества передачи данных в радиканале является отношение сигнал/интерференция (signal-to-interference ratio, SIR), которое связывает уровень полезного сигнала на приемнике с уровнем фоновых помех, и является отношением между мощностью сигнала, принимаемого от ассоциированного передатчика, и суммарной мощностью сигналов от интерферирующих передатчиков, работающих на той же радиочастоте. Анализ SIR для случая фиксированных передатчиков и приемников основан на методах стохастической геометрии, которые позволяют оценить эту характеристику для заданного расположения взаимодействующих устройств или для заданного распределения расстояний между устройствами и плотности устройств в пределах зоны покрытия. Эти методы могут использоваться планировщиком распределения радиоресурсов для оценки возможности установления нового соединения «передатчик–приемник» и присвоения ему радиочастоты с учетом уже установленных соединений для ассоциированных пар устройств в зоне обслуживания. В случае движущихся устройств значение SIR становится переменным из-за изменения расстояний между устройствами. Цель работы — предложить подход к анализу характеристик интерференции, когда траектории мобильных устройств задаются некоторыми кинетическими уравнениями. Одной из характеристик SIR в этом случае является распределение временного интервала недоступности соединения, вызванной падением SIR ниже заданного порогового значения. Кроме того, в работе для случая движущихся устройств предложены рекомендации по выбору модели движения из известных моделей случайного блуждания для дальнейшего исследования характеристик интерференции

Non-enzymatic nitric oxide synthesis in biological systems

AbstractNitric oxide (NO) is an important regulator of a variety of biological functions, and also has a role in the pathogenesis of cellular injury. It had been generally accepted that NO is solely generated in biological tissues by specific nitric oxide synthases (NOS) which metabolize arginine to citrulline with the formation of NO. However, NO can also be generated in tissues by either direct disproportionation or reduction of nitrite to NO under the acidic and highly reduced conditions which occur in disease states, such as ischemia. This NO formation is not blocked by NOS inhibitors and with long periods of ischemia progressing to necrosis, this mechanism of NO formation predominates. In postischemic tissues, NOS-independent NO generation has been observed to result in cellular injury with a loss of organ function. The kinetics and magnitude of nitrite disproportionation have been recently characterized and the corresponding rate law of NO formation derived. It was observed that the generation and accumulation of NO from typical nitrite concentrations found in biological tissues increases 100-fold when the pH falls from 7.4 to 5.5. It was also observed that ischemic cardiac tissue contains reducing equivalents which reduce nitrite to NO, further increasing the rate of NO formation more than 40-fold. Under these conditions, the magnitude of enzyme-independent NO generation exceeds that which can be generated by tissue concentrations of NOS. The existence of this enzyme-independent mechanism of NO formation has important implications in our understanding of the pathogenesis and treatment of tissue injury

Pathways of Microcirculatory Endothelial Dysfunction in Obstructive Sleep Apnea: A Comprehensive Ex Vivo Evaluation in Human Tissue.

BackgroundThe mechanism and markers of cardiovascular disease (CVD) in obstructive sleep apnea (OSA) remain unknown. The microcirculation is the site of early changes in OSA patients who are free of CVD risk.MethodsPatients with newly diagnosed moderate to severe OSA (n = 7) were studied before and 12 weeks after intensive treatment with continuous positive airway pressure (CPAP), along with weight and age matched controls (n = 7). Microcirculatory vessels were isolated from gluteal biopsies and changes in critical functional genes were measured.ResultsThe following genes changed after 12 weeks of intensive CPAP therapy in the microcirculatory vessels: angiotensin receptor type 1 (AGTR-1) (11.6 (3.4) to 6 (0.8); P = 0.019); NADPH oxidase (NOX4) (0.85 (0.02) to 0.79 (0.11); P = 0.016); and dimethylarginine dimethylaminohydrolase (DDAH 1) (1 (0.31) to 0.55 (0.1); P = 0.028). Despite decreased nitric oxide (NO) availability as measured indirectly through brachial artery flow-mediated dilation, endothelial NO synthase (NOS3) did not change with CPAP. Other disease markers of OSA that changed with treatment in the microcirculation were endothelin, hypoxia inducible factor 1a, nuclear factor kappa B, interleukin-8, and interleukin-6.ConclusionsIn this ex vivo evaluation of the microcirculation of patients with OSA and no CVD risk, several pathways of CVD were activated supporting that OSA independently induces microcirculatory endothelial dysfunction and serving as disease-specific markers for future pharmacological targeting of OSA-related CVD risk. The findings support the role of renin-angiotensin activation and endothelial oxidative stress in the decreased microcirculatory NO availability in OSA

Poly-arginine conjugated triarylmethyl radical as intracellular spin label

Stable triarylmethyl radicals are ideal spin labels used for biomedical electron paramagnetic resonance applications. Previously reported structures exhibit polar charged functions for water solubilization preventing them from crossing the cell membrane. We report the synthesis of a triarylmethyl radical conjugated to poly-arginine peptide allowing intracellular delivery the paramagnetic label