Dynamic sharing of a multiple access channel

In this paper we consider the mutual exclusion problem on a multiple access channel. Mutual exclusion is one of the fundamental problems in distributed computing. In the classic version of this problem, n processes perform a concurrent program which occasionally triggers some of them to use shared resources, such as memory, communication channel, device, etc. The goal is to design a distributed algorithm to control entries and exits to/from the shared resource in such a way that in any time there is at most one process accessing it. We consider both the classic and a slightly weaker version of mutual exclusion, called ep-mutual-exclusion, where for each period of a process staying in the critical section the probability that there is some other process in the critical section is at most ep. We show that there are channel settings, where the classic mutual exclusion is not feasible even for randomized algorithms, while ep-mutual-exclusion is. In more relaxed channel settings, we prove an exponential gap between the makespan complexity of the classic mutual exclusion problem and its weaker ep-exclusion version. We also show how to guarantee fairness of mutual exclusion algorithms, i.e., that each process that wants to enter the critical section will eventually succeed

Distributed Online and Stochastic Queueing on a Multiple Access Channel

We consider the problems of online and stochastic packet queueing in a distributed system of n nodes with queues, where the communication between the nodes is done via a multiple access channel. In the online setting, in each round, an arbitrary number of packets can be injected to nodes’ queues. Two measures of performance are considered: the total number of packets in all queues, called the total load , and the maximum queue size, called the maximum load . We develop a deterministic distributed algorithm that is asymptotically optimal with respect to both complexity measures, in a competitive way. More precisely, the total load of our algorithm is bigger than the total load of any other algorithm, including centralized online solutions, by only an additive term of O ( n 2 ), whereas the maximum queue size of our algorithm is at most n times bigger than the maximum queue size of any other algorithm, with an extra additive O ( n ). The optimality for both measures is justified by proving the corresponding lower bounds, which also separates nearly exponentially distributed solutions from the centralized ones. Next, we show that our algorithm is also stochastically stable for any expected injection rate smaller or equal to 1. This is the first solution to the stochastic queueing problem on a multiple access channel that achieves such stability for the (highest possible) rate equal to 1. </jats:p

Planning of organizational changes

This article examines the importance of planning the activity to the head, especially during periods of active changes of operating principles in all possible company existence stages. A logical link is carried out between specific changes within the selected process: either with related activities or with the whole company structure organization. The author argues that the effective communication should be in the company and outside it to build a successful business.Данная статья показывает важность планирования своей деятельности как руководителя, особенно в периоды проведения активных изменений принципов работы, на всех возможных этапах существования компании, а также проводится логическая связь между конкретными изменениями внутри выбранного процесса не только со смежными направлениями деятельности, но и со организацией структуры компании в целом. Речь также идет о влиянии эффективных коммуникаций, внутри компании и за ее пределами, для построения успешного бизнеса и карьеры менеджера в целом. Данная статья будет полезна для начинающих руководителей всех типов компаний

Production of He-4 and (4) in Pb-Pb collisions at root(NN)-N-S=2.76 TeV at the LHC

Results on the production of He-4 and (4) nuclei in Pb-Pb collisions at root(NN)-N-S = 2.76 TeV in the rapidity range vertical bar y vertical bar <1, using the ALICE detector, are presented in this paper. The rapidity densities corresponding to 0-10% central events are found to be dN/dy4(He) = (0.8 +/- 0.4 (stat) +/- 0.3 (syst)) x 10(-6) and dN/dy4 = (1.1 +/- 0.4 (stat) +/- 0.2 (syst)) x 10(-6), respectively. This is in agreement with the statistical thermal model expectation assuming the same chemical freeze-out temperature (T-chem = 156 MeV) as for light hadrons. The measured ratio of (4)/He-4 is 1.4 +/- 0.8 (stat) +/- 0.5 (syst). (C) 2018 Published by Elsevier B.V.Peer reviewe

6-stroke engine: thermodynamic modelling and design for testing

In the study AVL BOOST™ is used to perform a thermodynamic simulation of a six-stroke engine, being built by a research team based in Saudi Arabia. The six-stroke cycle consists of a standard four-stroke Otto Cycle followed by a heat recovering steam expansion cycle. Water is injected into the hot combustion chamber towards the end of the Otto expansion stroke producing steam, which is used to perform work on a piston. This process produces power using waste heat and therefore increases the overall efficiency of the engine. The Robin EY28D engine, which is a single cylinder, four-stroke, gasoline engine was used for this simulation study. The engine was modelled and converted into six-stroke engine in AVL BOOST. The results show that six-stroke engine is more efficient than four-stroke engine. In six-stroke engine, the engine power is increased by 33.1% and brake specific fuel consumption (BSFC) is decreased by approximately 16%. Where emissions are concerned, Nitrogen Oxide (NOx) emission from six-stroke engine is reduced by 80%, while the Hydrocarbon (HC) emission increases by 85% compared with the original 4-stroke. Moreover, the most efficient camshaft was found and designed according to the most efficient valve profile for this engine, which is combination of 60CA° of valve duration and 10 mm of valve lifting

Solutions in the vehicle suspension

The paper presents a review of the suspension solutions used on the street vehicle up to the now a days, finalising with presentation of their damping characteristics and with evaluation of their advantages or disadvantages. Long time the suspension systems have been dominated by the classic passive suspensions realized with metallic springs, shock absorbers with constant damping coefficients and anti-roll bars, excepting some luxury and sport cars using semi-active and active suspensions. There are presented some semi-active suspension solutions with continuous or discontinuous damping characteristics adjustment and the evolution of the Citroen and other active suspensions. All of them improve in some matter the performances but all of them have not ability to recuperate energy and has auxiliary energy consumption so last period the electromagnetically shock absorbers are researched, the paper presenting some of them. The paper also presents magneto rheological MR damper, solutions for adjustable passive shock absorbers and solutions for passive shock absorbers with variable damping coefficient with the stroke, e.g. Monroe Sensa Trac, Citroën Solution and VZN solution, with their damping characteristics and performances

Elements of the model positioning of aircraft on the apron

The design of airports and the organization of their work requires the recognition of the basic components of the air transport process, consisting of an "aerial" part, including the landing phase and the landing operation itself, as well as take-off, the "ground" part, including the task of taxiing aircraft on apron, ground handling tasks, "terminal" part, including passenger handling tasks. These elements form a cause-and-effect sequence, or a series-parallel structure that determines the quality of services provided by the airport, their efficiency, reliability and price. The article presents the issues of decision support for the operation and maintenance of airport infrastructure and traffic management on the ramp and within the airport, i.e. the operation of allocating aircraft to the gates of "gates" using simulation tools. Aircraft taxiing operations on the tarmac integrate the flight phase (along with its components and its problems, such as arriving and departing sequencing) with the ground handling phase of aircraft and passengers at terminals. The model presented in the article is a single element of a holistic approach to the operation of an airport. The overall model consists of the development of decision models for the organization of aircraft traffic on the apron, algorithms for their solution and the possibility of practical application as a simulation tool for analyzing and assessing aircraft traffic processes in the take-off, taxiing and landing phase. To describe the model, a formal mapping of the structure of the necessary airport elements was proposed. A formal record of boundary conditions and criteria relevant to aircraft allocation processes is presented due to the minimization of travel time of passengers transferring between two aircraft assigned to two different gates. Test results can be used in practice, among others by airspace controllers and airport designers for: analyzing and assessing the possibilities of increasing airport capacity, analyzing and assessing the determination of taxiway lengths, maintaining high safety reserves, etc

Nonsynchronous Rotor Blade Vibrations in Last Stage of 380 MW LP Steam Turbine at Various Condenser Pressures

This paper presents an analysis of nonsynchronous rotor blade vibrations in the last stage of an LP steam turbine at various condenser pressures. The nonlinear least squares Levenberg&ndash;Marquardt method is used in a tip-timing analysis to determine nonsynchronous multimode rotor blade vibrations, which is a novelty. This is done with two sensors in the casing and a once-per-revolution sensor. The accuracy of the nonlinear least squares Levenberg&ndash;Marquardt multimode method is compared with the one-mode linear method. The algorithm is verified by comparing it with one-mode tip-timing methods for synchronous and nonsynchronous vibrations. The analysis shows that the rotor blades vibrate simultaneously with two modes in non-nominal conditions, which is also a novelty. The rotor frequencies are unchanged, although the blade vibration amplitudes vary, depending on the pressure in the condenser. Flutter does not appear in the last stage for the various condenser pressures and powers that were tested