356 research outputs found
M/M/1 polling models with two finite queues
Ankara : Department of Industrial Engineering and the Institute of Engineering and Science of Bilkent University, 1995.Thesis (Master's) -- Bilkent University, 1995.Includes bibliographical references leaves 92-95.Polling models are special kinds of queueing models where multiple-customer
type single-stage is considered. In this thesis, first an overview and a classification
of polling models will be given. Then two-costomer one server M /M /l
polling models will be analyzed and the performance of models will be developed
for exhaustive, gated, and G-limited service policies. We give analytical
methods for a special type of polling model where we solve the system to get
mean queue lengths and thruput rates by three methods. The first one is based
on solving the steady state distribution of the Markov Process. The second is
a decompositon aiming to decrease the size of the problem. The third one is
an approximation method that uses the earlier results and it is very accurate.
The thesis will be concluded with possible future extensions.Daşçı, AbdullahM.S
Plethora : a framework for the intelligent control of robotic assembly systems
Plethora : a framework for the intelligent control of robotic assembly system
Analysis of CIM performance using different LAN structures a simulation approach
This research illustrates a systematic procedure for modeling and performance analysis of the integration effect of communication network to the physical system. The concept is to model different layouts of Computer Integration Manufacturing (CIM) using different Local Area Network(LAN) structures. The steps to accomplish this concepts are, a) To determine the performance measures for physical layouts and the communication network, in order to obtain a performance analysis. b) Modeling the physical layout using Promodel simulation package. c) Extracting results from the outcome of the simulation of the physical layout and using this as input to the communication network simulation. d) Modeling the communication network using LNET simulation package. e) Comparing the output of each simulation run and determine which is most acceptable.
Having different performance measures for both physical layout and networks, the proposed research objective is to illustrate the effectiveness of network structures on physical systems performance. Throughput, utilization, and delay are used as measures for both the physical layouts and network structures. Using these measures the optimum layout and network is selected
Election Security Is Harder Than You Think
Recent years have seen the rise of nation-state interference in elections
across the globe, making the ever-present need for more secure elections all
the more dire. While certain common-sense approaches have been a typical
response in the past, e.g. ``don't connect voting machines to the Internet''
and ``use a voting system with a paper trail'', known-good solutions to
improving election security have languished in relative obscurity for decades.
These techniques are only now finally being implemented at scale, and that
implementation has brought the intricacies of sophisticated approaches to
election security into full relief.
This dissertation argues that while approaches to improve election security
like paper ballots and post-election audits seem straightforward, in reality
there are significant practical barriers to sufficient implementation.
Overcoming these barriers is a necessary condition for an election to be
secure, and while doing so is possible, it requires significant refinement of
existing techniques. In order to better understand how election security
technology can be improved, I first develop what it means for an election to be
secure. I then delve into experimental results regarding voter-verified paper,
discussing the challenges presented by paper ballots as well as some strategies
to improve the security they can deliver. I examine the post-election audit
ecosystem and propose a manifest improvement to audit workload analysis
through parallelization. Finally, I show that even when all of these conditions
are met (as in a vote-by-mail scenario), there are still wrinkles that must be
addressed for an election to be truly secure.PHDComputer Science & EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/163272/1/matber_1.pd
Aeronautical Engineering: A continuing bibliography with indexes (supplement 188)
This bibliography lists 477 reports, articles and other documents introduced into the NASA scientific and technical information system in May 1985. The coverage includes documents on the engineering and theoretical aspects of design, construction, evaluation, testing, operation, and performance of aircraft (including aircraft engines) and associated components, equipment and systems
Design and provisioning of WDM networks for traffic grooming
Wavelength Division Multiplexing (WDM) is the most viable technique for utilizing the enormous amounts of bandwidth inherently available in optical fibers. However, the bandwidth offered by a single wavelength in WDM networks is on the order of tens of Gigabits per second, while most of the applications\u27 bandwidth requirements are still subwavelength. Therefore, cost-effective design and provisioning of WDM networks require that traffic from different sessions share bandwidth of a single wavelength by employing electronic multiplexing at higher layers. This is known as traffic grooming. Optical networks supporting traffic grooming are usually designed in a way such that the cost of the higher layer equipment used to support a given traffic matrix is reduced. In this thesis, we propose a number of optimal and heuristic solutions for the design and provisioning of optical networks for traffic grooming with an objective of network cost reduction. In doing so, we address several practical issues. Specifically, we address the design and provisioning of WDM networks on unidirectional and bidirectional rings for arbitrary unicast traffic grooming, and on mesh topologies for arbitrary multipoint traffic grooming. In multipoint traffic grooming, we address both multicast and many-to-one traffic grooming problems. We provide a unified frame work for optimal and approximate network dimensioning and channel provisioning for the generic multicast traffic grooming problem, as well as some variants of the problem. For many-to-one traffic grooming we propose optimal as well as heuristic solutions. Optimal formulations which are inherently non-linear are mapped to an optimal linear formulation. In the heuristic solutions, we employ different problem specific search strategies to explore the solution space. We provide a number of experimental results to show the efficacy of our proposed techniques for the traffic grooming problem in WDM networks
Ultra Low Power Communication Protocols for UWB Impulse Radio Wireless Sensor Networks
This thesis evaluates the potential of Ultra Wideband Impulse Radio for wireless sensor network applications. Wireless sensor networks are collections of small electronic devices composed of one or more sensors to acquire information on their environment, an energy source (typically a battery), a microcontroller to control the measurements, process the information and communicate with its peers, and a radio transceiver to enable these communications. They are used to regularly collect information within their deployment area, often for very long periods of time (up to several years). The large number of devices often considered, as well as the long deployment durations, makes any manual intervention complex and costly. Therefore, these networks must self-configure, and automatically adapt to changes in their electromagnetic environment (channel variations, interferers) and network topology modifications: some nodes may run out of energy, or suffer from a hardware failure. Ultra Wideband Impulse Radio is a novel wireless technology that, thanks to its extremely large bandwidth, is more robust to frequency dependent propagation effects. Its impulsional nature makes it robust to multipath fading, as the short duration of the pulses leads most multipath components to arrive isolated. This technology should also enable high precision ranging through time of flight measurements, and operate at ultra low power levels. The main challenge is to design a system that reaches the same or higher degree of energy savings as existing narrowband systems considering all the protocol layers. As these radios are not yet widely available, the first part of this thesis presents Maximum Pulse Amplitude Estimation, a novel approach to symbol-level modeling of UWB-IR systems that enabled us to implement the first network simulator of devices compatible with the UWB physical layer of the IEEE 802.15.4A standard for wireless sensor networks. In the second part of this thesis, WideMac, a novel ultra low power MAC protocol specifically designed for UWB-IR devices is presented. It uses asynchronous duty cycling of the radio transceiver to minimize the power consumption, combined with periodic beacon emissions so that devices can learn each other's wake-up patterns and exchange packets. After an analytical study of the protocol, the network simulation tool presented in the first part of the thesis is used to evaluate the performance of WideMac in a medical body area network application. It is compared to two narrowband and an FM-UWB solutions. The protocol stack parameters are optimized for each solution, and it is observed that WideMac combined to UWB-IR is a credible technology for such applications. Similar simulations, considering this time a static multi-hop network are performed. It is found that WideMac and UWB-IR perform as well as a mature and highly optimized narrowband solution (based on the WiseMAC ULP MAC protocol), despite the lack of clear channel assessment functionality on the UWB radio. The last part of this thesis studies analytically a dual mode MAC protocol named WideMac-High Availability. It combines the Ultra Low PowerWideMac with the higher performance Aloha protocol, so that ultra low power consumption and hence long deployment times can be combined with high performance low latency communications when required by the application. The potential of this scheme is quantified, and it is proposed to adapt it to narrowband radio transceivers by combining WiseMAC and CSMA under the name WiseMAC-HA
Stability Problems for Stochastic Models: Theory and Applications II
Most papers published in this Special Issue of Mathematics are written by the participants of the XXXVI International Seminar on Stability Problems for Stochastic Models, 2125 June, 2021, Petrozavodsk, Russia. The scope of the seminar embraces the following topics: Limit theorems and stability problems; Asymptotic theory of stochastic processes; Stable distributions and processes; Asymptotic statistics; Discrete probability models; Characterization of probability distributions; Insurance and financial mathematics; Applied statistics; Queueing theory; and other fields. This Special Issue contains 12 papers by specialists who represent 6 countries: Belarus, France, Hungary, India, Italy, and Russia
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