Space Priority Research Articles

Solid Oxide Fuel Based Auxiliary Power Unit for Regional Jets: Design and Mission Simulation With Different Cell Geometries

Although it accounts for only 4.2% of the total global warming potential, the concern today is that aviation generated CO2 is projected to grow to approximately 5.7% by 2050. Aviation emissions are growing faster than any other sector and they risk undermining the progress achieved through emission cuts in other areas of the economy. Rapidly emerging hydrogen and fuel-cell-based technologies could be developed for future replacement of on-board electrical systems in “more-electric” or “all-electric” aircrafts. Primary advantages of deploying these technologies are low emissions and low noise (important features for commuter airplanes, which takeoff and land in urban areas). Solid oxide fuel-cell (SOFC) systems could result advantageous for some aeronautical applications due to their capability of accepting hydrocarbons and high energy-density fuels. Moreover they are suitable for operating in combined-heat-and-power configurations, recovering heat from the high-temperature exhaust gases, which could be used to supply thermal loads therefore reducing the electric power requested by the aircraft. ENFICA-FC is a project selected by the European Commission in the Aeronautics and Space priority of the Sixth Framework Programme (FP6) and led by Politecnico di Torino, in Turin, Italy. One of the objectives of the project is to carry out a feasibility study on a more-electric intercity aircraft (regional jet: 32 seats). After the characterization of the power consumption of electrical and nonelectrical loads, and the definition of a mission profile, the design of the SOFC-based energy system as well as the simulation of a complete mission is performed hypothesizing different system configurations. The simulation concerns both the stack (current and current density, cell and stack voltage, etc.) and the balance-of-plant (air compressor power, gross stack power, system efficiency, etc.). The obtained results are analyzed and discussed.

Ten new and emerging trends in residential group living environments

Residential styled environments for physically challenged people with neuro disabilities are rapidly replacing the standard institutional skilled nursing home. Ten trends are described that utilize residential design approaches to the physical environment while relying on home-care style methods for service delivery. Combined these two forces create powerful differentiators which make group residential settings more friendly and humane. Northern European, as well as, US best practices and prototypes are described that combine housing with services in a range of contexts. The success of northern Europeans in promulgating models of aging-in-place that keep those at risk more independent in the community or within family settings are remarkable. Topics like the impact of small group living clusters, interior design treatments, access to landscape gardens, life skill management methods, movement systems for circulation and exercise, shared space priorities, unit design trends and innovative care giving techniques are introduced. The focus of the article is on specific practices gleaned from cultures and exemplars that appear to increase autonomy, independence and privacy for those who are threatened because of their disabilities with the loss of these lifestyle attributes. Promising concepts of service organization and community outreach are combined with detailed recommendations that address the need for lift technology and safety features in bathrooms and kitchens.

Analysis of discrete-time space priority queue with fuzzy threshold

In this paper, we develop a discrete-time queueing model of fuzzythreshold-based space priority buffer management and study itsperformance under realistic conditions. It applies a matrix-analyticapproach to analyze the relevant performance measure, including thepacket loss probability of high-priority traffic and the packet lossprobability of low-priority traffic. Intuitively, the fuzzythreshold adapts well to different input traffic conditions andpacket loss rate requirements of high-priority packet, yielding alower packet loss probability for low-priority packet.

Astronomers unveil wish list

Roadmap sets out Europe's space priorities.

Акмеологические характеристики профессионального самоотношения женщин-руководителей

In professional women-heads’ work the knowledge of a person about self and development of subjective control makes the great value (W. James, G. Midd, E. Erikson, K. Rogers, S. R. Panteleev, V.V. Stolin, R. Bern, E. Bern, G. Rotter, T.N. Sherbakova, A.A. Rean, P.K. Vlasov, G.S. Nikiforova). The system of personal self-attitudes mediates subjective interpretation of own experience and external effect, perception of self and world around, determines pros- pects of own development and prospects of relations with the world. An adequate self-estimation allows a woman-head to place correctly priorities in professional field and interpersonal space.

New Methodology for Optimizing Transit Priority at the Network Level

A new methodology for optimizing transit road space priority at the network level is proposed. Transit vehicles carry large numbers of passengers within congested road space efficiently. This aids justification of transit priority. Almost all studies that have investigated transit priority lanes focus at a link or an arterial road level, and no study has investigated road space allocation for priority from a network perspective. The aim of the proposed approach is to find the optimum combination of exclusive lanes in an existing operational transport network. Mode share is assumed variable, and an assignment is performed for both private and transit traffic. The problem is formulated by using bilevel programming, which minimizes the total travel time. The approach is applied to an example network and the results are discussed. The approach can identify the optimal combination of transit priority lanes and achieve the global optimum of the objective function. Areas for further development are discussed.

Analysis of M/M/1 queueing system with two priority classes

The present paper investigates the two-class priority M/M/1 queueing system, where the prioritized first class customers are served under first-come , first served (FCFS) preemptive resume discipline and have finite room capacity. The second class customers have infinite waiting space and low priority i.e. during the service of a low priority customer, if a high priority customer joins the system, then the low priority customer’s service is interrupted and will be resumed again when there is no high priority customer present in the system. Our aim is to get explicit expressions for the generating functions of the steady state probabilities in terms of Chebyshev’s polynomial of second kind have obtained. A recursive method is employed to solve the steady-state equations governing the model. Moreover, the expressions for the mean queue length, the marginal distributions of high and low priority customers are also given. The derivation is based only on the general structure of the system and the generating function involved, and thus is simpler than previous methods. We examine the effect of number of high priority customers, input and output rates on the average queue lengths of low and high priority classes by looking at a numerical illustration.

Smaller State Perspectives on the Future of Space Governance

Current debates over impending developments in military and civilian uses of space raise deeper questions of how the expanding human presence in space over the next century might unfold. Appreciating the full range of challenges and opportunities posed by this uncertain future requires exploring all scenarios and perspectives comprehensively. As a contribution to such analysis, this article draws insights from the outlooks of smaller states toward national and global space priorities. The first two sections summarize and contrast United States and Canadian policy trajectories and dispositions in their respective space programs. The third section assesses how differences in smaller state perspectives can contribute to developing an analytically rigorous concept of space power. The fourth section then examines how juxtaposing alternative scenarios for the long-term development of human space presence, consistent with power-based theory, offers a stronger foundation for explaining and assessing current conditions than does making limiting assumptions of inevitable future trajectories. The article concludes that more inclusive analysis of serious future possibilities also enables more complete assessment of current space security challenges.

Space priority queue with fuzzy set threshold

In this paper, we develop a queueing model of fuzzy threshold-based space priority buffer management and study its performance under realistic conditions. It applies a matrix-analytic approach to analyze the relevant performance measure, including the packet loss probability of high-priority traffic and the packet loss probability of low-priority traffic. Based on the proposed framework, we explore the properties of the fuzzy threshold-based space priority buffer management scheme. Numerical results reveal that the fixed threshold scheme, through its abrupt nature, causes a relatively higher low-priority packet drop. Intuitively, the fuzzy threshold adapts well to different input traffic conditions and packet loss rate requirements of high-priority packet, yielding a lower packet loss probability for low-priority packet.

Loss behavior in space priority queue with batch Markovian arrival process — continuous-time case

This paper applies a matrix-analytic approach to analyze both the long-term and the short-term loss behaviors of a queue with space priority scheme. Five related performance measures are derived from conditional statistics, including the long-term high-priority and low-priority packet loss probabilities, and the three short-term measures — the average length of a critical period, the average length of a non-critical period, and the conditional high-priority packet loss probability during a critical period. The overall complexity of computing these performance measures is of the order O ( K 2 m 1 3 m 2 3 σ 3 ) , where m 1 , m 2 are the numbers of phases of the underlying Markovian structures for the high-priority and the low-priority packet arrival processes respectively and σ is the number of phases of the phase-type server.

ATM 노드를 위한 WCSFQ-유사 공간 우선순위 정책의 성능분석

ATM과 IP 망에서 혼잡발생시 높은 우선순위를 가진 패킷은 낮은 우선순위를 가진 패킷에 비해 영향을 적게 받도록 설계되어야 한다. 이러한 문제 해결을 위해, 본 논문에서는 기존 If 망에서 사용되는 가중치 CSFQ(Weighted Core-Stateless Fair Queueing)를 ATM 노드의 공간 우선순위(space priority) 정책에 적용하였다. 성능분석을 위해 임계치(threshold)를 갖는 MMPP/D/1/K 큐잉모델의 트래픽 클래스별 셀 손실률을 유도하고 그 결과를 논하였다. 분석결과를 통해 가중치 CSFQ 기법이 ATM 혹은 IP 노드에서 차별화된 서비스 제공에 매우 유용함을 보였다. In ATM and W networks, high Priority Packets should be selectively favored over low Priority Packets in case of congestion. For this purpose, we introduce a space priority policy for ATM nodes in this paper which is very similar to the weighted core-stateless fair queueing(WCSFQ) in IP nodes. We also analyze the loss probabilities for different classes of cells for MMPP/D/1/K with a threshold level, and discuss the numerical results. The numerical results illustrate that the WCSFQ scheme can be used to support the differentiated services in ATM or IP nodes.

Capacity and flow assignment issues in MPLS networks

AbstractMPLS technology enables IP networks to accept the challenge raised by emerging communication paradigms. This paper describes a nonlinear model with path capacity as design variables and space priority as constraints. The analysis shows that the close‐form solution exists if traffic flows are allocated by an independent protocol. Copyright © 2003 John Wiley &Sons, Ltd.

Entropy maximisation and open queueing networks with priorities and blocking

A review is carried out on the characterisation and algorithmic implementation of an extended product-form approximation, based on the principle of maximum entropy (ME), for a wide class of arbitrary finite capacity open queueing network models (QNMs) with service and space priorities. A single server finite capacity GE/GE/1/ N queue with R ( R>1) distinct priority classes, compound Poisson arrival processes (CPPs) with geometrically distributed batches and generalised exponential (GE) service times is analysed via entropy maximisation, subject to suitable GE-type queueing theoretic constraints, under preemptive resume (PR) and head-of-line (HOL) scheduling rules combined with complete buffer sharing (CBS) and partial buffer sharing (PBS) management schemes stipulating a sequence of buffer thresholds { N=( N 1,…, N R ),0< N i ≤ N i−1 , i=2,…, R}. The GE/GE/1/ N queue is utilised, in conjunction with GE-type first two moment flow approximation formulae, as a cost-effective building block towards the establishment of a generic ME queue-by-queue decomposition algorithm for arbitrary open QNMs with space and service priorities under repetitive service blocking with random destination (RS-RD). Typical numerical results are included to illustrate the credibility of the ME algorithm against simulation for various network topologies and define experimentally pessimistic GE-type performance bounds. Remarks on the extensions of the ME algorithm to other types of blocking mechanisms, such as repetitive service blocking with fixed destination (RS-FD) and blocking-after-service (BAS), are included.

Performance analysis of an ATM MUX with a new space priority mechanism under ON-OFF arrival processes

We propose a new space priority mechanism, and analyze its performance in a single Constant Bit Rate (CBR) server. The arrival process is derived from the superposition of two types of traffics, each in turn results from the superposition of homogeneous ON-OFF sources that can be approximated by means of a two-state Markov Modulated Poisson Process (MMPP). The buffer mechanism enables the Asynchronous Transfer Mode (ATM) layer to adapt the quality of the cell transfer to the Quality of Service (QoS) requirements and to improve the utilization of network resources. This is achieved by “Selective-Delaying and Pushing-In” (SDPI) cells according to the class they belong to. The scheme is applicable to schedule delay-tolerant non-real time traffic and delay-sensitive real time traffic. Analytical expressions for various performance parameters and numerical results are obtained. Simulation results in term of cell loss probability conform with our numerical analysis.

Efficient buffer sharing in shared memory ATM systems with space priority traffic

In this letter we study the problem of the optimal design of buffer management policies within the class of pushout and expelling policies for a shared memory asynchronous transfer mode (ATM) switch or demultiplexer fed by traffic containing two different space priorities. A numerical study of the optimal policies for small buffer sizes is used to help design heuristics applicable to large buffer sizes. Simulation studies for large buffer systems are then presented.

Loss behavior in space priority queue with batch Markovian arrival process — discrete-time case

This paper applies matrix-analytic approach to the examination of the loss behavior of a space priority queue. In addition to the evaluation of the long-term high-priority and low-priority packet loss probabilities, we examine the bursty nature of packet losses by means of conditional statistics with respect to critical and non-critical periods that occur in an alternating manner. The critical period corresponds to having more than a certain number of packets in the buffer; non-critical corresponds to the opposite. Hence there is a threshold buffer level that splits the state space into two. By such a state-space decomposition, two hypothesized Markov chains are devised to describe the alternating renewal process. The distributions of various absorbing times in the two hypothesized Markov chains are derived to compute the average durations of the two periods and the conditional high-priority packet loss probability encountered during a critical period. These performance measures greatly assist the space priority mechanism for determining a proper threshold. The overall complexity of computing these performance measures is of the order O( K 2 m 1 3 m 2 3), where K is the buffer capacity, and m 1 and m 2 are the numbers of phases of the underlying Markovian structures for the high-priority and low-priority packet arrival processes, respectively. Thus the results obtained are computationally tractable and numerical results show that, by choosing a proper threshold, a space priority queue not only can maintain the quality of service for the high-priority traffic but also can provide the near-optimum utilization of the capacity for the low-priority traffic.

Computer simulation for the evaluation of static and dynamic priority schemes in an ATM multiplexer with multimedia traffic

This paper is concerned with the evaluation of static and dynamic priority schemes for ATM multiplexers using digital computer simulation and has three main parts. The first provides a basic computer simulation model of an ATM multiplexer with multimedia traffic streams that enables investigation of static and dynamic priority schemes. The second part uses the simulation model to study such schemes. The third part investigates combined dynamic space and dynamic time priorities to provide better performance for ATM multiplexers in comparison to using dynamic time priority only. Copyright © 1999 John Wiley & Sons, Ltd.

Queueing analysis of explicit priority assignment buffer access scheme for ATM networks

The recommended implementation of two quality of service bearer services in ATM networks has generated considerable work on the analysis of implicit policy assignment space priority control buffer access schemes. Since then, there has been more interest directed towards explicit policy assignment space priority schemes because of their increased efficiency and flexibility over implicit assignment schemes. This paper considers an explicit policy assignment space priority control scheme employing the partial buffer sharing buffer access mechanism. Cell loss probabilities are derived for a traffic model consisting of two source classes. Each source class consists of bursty traffic generated by a multiple number of three-state discrete-time Markov sources. The dependence of cell loss probabilities on traffic load and burstiness characteristics, as well as system parameters such as buffer size and buffer sharing thresholds, is examined.

A new buffer management scheme for hierarchical shared memory switches

We study a multistage hierarchical asynchronous transfer mode (ATM) switch in which each switching element has its own local cell buffer memory that is shared among all its output ports. We propose a novel buffer management technique called delayed pushout that combines a pushout mechanism (for sharing memory efficiently among queues within the same switching element) and a backpressure mechanism (for sharing memory across switch stages). The backpressure component has a threshold to restrict the amount of sharing between stages. A synergy emerges when pushout, backpressure, and this threshold are all employed together. Using a computer simulation of the switch under symmetric but bursty traffic, we study delayed pushout as well as several simpler pushout and backpressure schemes under a wide range of loads. At every load level, we find that the delayed pushout scheme has a lower cell loss rate than its competitors. Finally, we show how delayed pushout can be extended to share buffer space between traffic classes with different space priorities.

ATM switch with multimedia traffic priority control

AbstractIn this paper, a novel ATM switch with a dynamic multimedia traffic priority control scheme (HQMS: Hybrid combination of Queue Length Threshold and Minimum Laxity Threshold Scheme) is proposed. The ATM switch has the same basic topology as the Knockout switch, but employs a simpler N×L concentration scheme, which takes into account cells belonging to different priority levels. The structure of the switch supports two priority mechanisms. The first one is called priority discarding and acts as a local congestion control scheme within the switch fabric satisfying different cell loss requirements of different ATM traffic classes. The second one is called priority scheduling and uses two priority methods: a space priority method used for the control of the buffer space when an overflow condition occurs andor when the expiration of the maximum admissible delay of the delay sensitive cells takes place and the service priority method which assigns transmission priorities to the buffered cells. A hardware implementation of the two priority mechanisms of the HQMS is presented. The performance of the switch has been studied by simulation, considering three ATM classes (video, data, voice) with different source models. The results have shown that for a large range of traffic load, the proposed HQMS satisfies the loss and delay requirements of the three classes.