15,973 research outputs found
Durability testing at one atmosphere of advanced catalysts and catalyst supports for automotive gas turbine engine combustors, part 1
The durability of catalysts and catalyst supports in a combustion environment was experimentally demonstrated. A test of 1000 hours duration was completed with two catalysts, using diesel fuel and operating at catalytically supported thermal combustion conditions. The performance of the catalysts was determined by monitoring emissions throughout the test, and by examining the physical condition of the catalyst core at the conclusion of the test. The test catalysts proved to be capable of low emissions operation after 1000 hours diesel aging, with no apparent physical degradation of the catalyst support
Product-form solutions for integrated services packet networks and cloud computing systems
We iteratively derive the product-form solutions of stationary distributions
of priority multiclass queueing networks with multi-sever stations. The
networks are Markovian with exponential interarrival and service time
distributions. These solutions can be used to conduct performance analysis or
as comparison criteria for approximation and simulation studies of large scale
networks with multi-processor shared-memory switches and cloud computing
systems with parallel-server stations. Numerical comparisons with existing
Brownian approximating model are provided to indicate the effectiveness of our
algorithm.Comment: 26 pages, 3 figures, short conference version is reported at MICAI
200
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Survey of traffic control schemes and error control schemes for ATM networks
Among the techniques proposed for B-ISDN transfer mode, ATM concept is considered to be the most promising transfer technique because of its flexibility and efficiency. This paper surveys and reviews a number of topics related to ATM networks. Those topics cover congestion control, provision of multiple classes of traffic, and error control. Due to the nature of ATM networks, those issues are far more challenging than in conventional networks. Sorne of the more promising solutions to those issues are surveyed, and the corresponding results on performance are summarized. Future research problems in ATM protocol aspect are also presented
Pendekatan konstruktif dalam inovasi pengajaran dan pembelajaran Bahasa Melayu di Kolej Vokasional
Pendekatan konstruktif adalah pendekatan pengajaran dan pembelajaran yang
berpusatkan pelajar manakala inovasi pengajaran pula dikaitkan dengan kaedah
pengajaran yang terbaru demi mengukuhkan pemahaman pelajar. Pembelajaran
berasaskan pendekatan konstruktif merupakan elemen yang penting dan perlu
difahami oleh guru-guru bagi memantapkan proses pengajaran dan pembelajaran
sesuai dengan peredaran masa dan menjayakan proses tranformasi pendidikan
negara. Objektif kajian ini dijalankan untuk mengenal pasti pemahaman guru-guru
bahasa Melayu berkaitan inovasi, mengenal pasti perbezaan yang wujud antara guru
lelaki dan guru perempuan dalam mengamalkan inovasi, pengkaji juga melihat
adakah wujud perbezaan antara guru baru dan guru yang sudah berpengalaman
dalam aspek mengaplikasikan inovasi serta mengenal pasti kekangan-kekangan yang
dialami oleh para guru untuk mengaplikasikan inovasi di sekolah. Seramai 63 orang
guru bahasa Melayu dari lapan buah kolej vokasional telah dipilih sebagai responden
dalam kajian ini. Data dianalisis menggunakan perisian Winsteps 3.69.1.11 dengan
pendekatan Model Pengukuran Rasch. Hasil analisis menunjukkan bahawa guru�guru bahasa Melayu memahami kepentingan inovasi dalam pengajaran dan
pembelajaran. Hasil kajian juga menunjukkan guru-guru perempuan lebih banyak
menerapkan unsur inovasi dalam pengajaran berbanding guru lelaki. Walaupun
begitu, aspek pengalaman tidak menunjukkan perbezaan dari segi pengamalan
inovasi sama ada guru baru ataupun guru yang sudah berpengalaman. Pengkaji juga
mengenal pasti beberapa kekangan yang dialami oleh guru-guru untuk mengamalkan
inovasi ini. Sebagai langkah untuk menangani masalah berkenaan, beberapa
cadangan telah dikemukakan oleh pengkaji bagi memastikan guru-guru dapat
merealisasikan proses pengajaran berkesan dengan penerapan inovasi mengikut
model pendekatan konstruktif. Pengkaji berharap, kajian ini dapat dijadikan sebagai
satu panduan kepada pelaksana kurikulum bagi memastikan budaya inovasi sentiasa
menjadi amalan dalam kalangan guru demi mengangkat profesionalisme guru di
Malaysia
Design and evaluation of a connection management mechanism for an ATM-based connectionless service
The Asynchronous Transfer Mode (ATM) has been developed as a connection-oriented technique for the transfer of fixed-size cells over high-speed networks. Many applications, however, require a connectionless network service. In order to provide such a technique, one can built a connectionless service on top of the connection-oriented service. In doing so, the issue of connection management comes into play. In this paper we propose a new connection management mechanism that provides for low bandwidth usage (as compared to a permanent connection) and low delays (as compared to a connection-per-packet approach). We model the new mechanism under two workload scenarios: an ordinary Poisson process and an interrupted Poisson process. We use Markovian techniques as well as matrix-geometric methods to evaluate the new connection management mechanism. From the evaluations it turns out that the proposed mechanism is superior to older approaches (which can be seen as limiting cases)
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Apparatus and method for congestion control in high speed networks
An adjustable bit rate (ABR) feedback control scheme is provided where the effects of multiloop delays and high priority traffic transmission are built into the control model. The data traffic is filtered by a low pass filter. Then, the low frequency bandwidth of the filtered traffic is measured and compared to a predetermined threshold. If the measured value exceeds the threshold, the ABR traffic flow is reduced. If the measured value is less than the threshold, the ABR traffic flow is increased. In addition, a General Prediction Control (GPC) method may be applied to the control model for optimal performance. An object of the invention is to minimize the unused link capacity subject to no congestion, where the ABR traffic is adapted to the low frequency variation of high priority traffic flow for high efficiency.Board of Regents, University of Texas Syste
Low Cost Quality of Service Multicast Routing in High Speed Networks
Many of the services envisaged for high speed networks, such as B-ISDN/ATM, will support real-time applications with large numbers of users. Examples of these types of application range from those used by closed groups, such as private video meetings or conferences, where all participants must be known to the sender, to applications used by open groups, such as video lectures, where partcipants need not be known by the sender. These types of application will require high volumes of network resources in addition to the real-time delay constraints on data delivery. For these reasons, several multicast routing heuristics have been proposed to support both interactive and distribution multimedia services, in high speed networks. The objective of such heuristics is to minimise the multicast tree cost while maintaining a real-time bound on delay. Previous evaluation work has compared the relative average performance of some of these heuristics and concludes that they are generally efficient, although some perform better for small multicast groups and others perform better for larger groups. Firstly, we present a detailed analysis and evaluation of some of these heuristics which illustrates that in some situations their average performance is reversed; a heuristic that in general produces efficient solutions for small multicasts may sometimes produce a more efficient solution for a particular large multicast, in a specific network. Also, in a limited number of cases using Dijkstra's algorithm produces the best result. We conclude that the efficiency of a heuristic solution depends on the topology of both the network and the multicast, and that it is difficult to predict. Because of this unpredictability we propose the integration of two heuristics with Dijkstra's shortest path tree algorithm to produce a hybrid that consistently generates efficient multicast solutions for all possible multicast groups in any network. These heuristics are based on Dijkstra's algorithm which maintains acceptable time complexity for the hybrid, and they rarely produce inefficient solutions for the same network/multicast. The resulting performance attained is generally good and in the rare worst cases is that of the shortest path tree. The performance of our hybrid is supported by our evaluation results. Secondly, we examine the stability of multicast trees where multicast group membership is dynamic. We conclude that, in general, the more efficient the solution of a heuristic is, the less stable the multicast tree will be as multicast group membership changes. For this reason, while the hybrid solution we propose might be suitable for use with closed user group multicasts, which are likely to be stable, we need a different approach for open user group multicasting, where group membership may be highly volatile. We propose an extension to an existing heuristic that ensures multicast tree stability where multicast group membership is dynamic. Although this extension decreases the efficiency of the heuristics solutions, its performance is significantly better than that of the worst case, a shortest path tree. Finally, we consider how we might apply the hybrid and the extended heuristic in current and future multicast routing protocols for the Internet and for ATM Networks.
ATMSeer: Increasing Transparency and Controllability in Automated Machine Learning
To relieve the pain of manually selecting machine learning algorithms and
tuning hyperparameters, automated machine learning (AutoML) methods have been
developed to automatically search for good models. Due to the huge model search
space, it is impossible to try all models. Users tend to distrust automatic
results and increase the search budget as much as they can, thereby undermining
the efficiency of AutoML. To address these issues, we design and implement
ATMSeer, an interactive visualization tool that supports users in refining the
search space of AutoML and analyzing the results. To guide the design of
ATMSeer, we derive a workflow of using AutoML based on interviews with machine
learning experts. A multi-granularity visualization is proposed to enable users
to monitor the AutoML process, analyze the searched models, and refine the
search space in real time. We demonstrate the utility and usability of ATMSeer
through two case studies, expert interviews, and a user study with 13 end
users.Comment: Published in the ACM Conference on Human Factors in Computing Systems
(CHI), 2019, Glasgow, Scotland U
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