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2.
Duminda Wijesekera Jaideep Srivastava Anil Nerode Mark Foresti 《Multimedia Systems》1999,7(6):486-499
Perception of multimedia quality, specified by quality-of-service (QoS) metrics, can be used by system designers to optimize
customer satisfaction within resource bounds enforced by general-purpose computing platforms. Media losses, rate variations
and transient synchronization losses have been suspected to affect human perception of multimedia quality. This paper presents
metrics to measure such defects, and results of a series of user experiments that justify such speculations. Results of the
study provide bounds on losses, rate variations and transient synchronization losses as a function of user satisfaction, in
the form of Likert values. It is shown how these results can be used by algorithm designers of underlying multimedia systems. 相似文献
3.
Reaction Kinetics and Coking Behavior for Furan Deoxygenation via Catalytic Pyrolysis Using Methane 下载免费PDF全文
The effective deoxygenation of oxygenates remains a major challenge that needs to be overcome for industrial‐scale conversion of biomass to fuels. Present technology uses expensive gaseous hydrogen for deoxygenation. This work looks at the possibility of using methane or natural gas as an alternative for the deoxygenation process. Catalytic pyrolysis studies were carried out using furan as the model oxygenate in the presence of methane in a fixed‐bed reactor over 5 % Ni/HZSM‐5 as catalyst. The effects of temperature and space velocity on the catalyst activity, reaction kinetics, and deactivation behavior were studied. It was found that the deoxygenation of furan was first and second order with respect to furan and methane concentration, respectively. Deactivation studies suggested that catalyst deactivation takes place through poisoning, fouling, and sintering. 相似文献
4.
We have studied the electronic characteristics of multilayer epitaxial graphene under a perpendicularly applied electric bias. Ultraviolet photoemission spectroscopy measurements reveal that there is notable variation of the electronic density-of-states in valence bands near the Fermi level. Evolution of the electronic structure of graphite and rotational-stacked multilayer epitaxial graphene as a function of the applied electric bias is investigated using first-principles density-functional theory including interlayer van der Waals interactions. The experimental and theoretical results demonstrate that the tailoring of electronic band structure correlates with the interlayer coupling tuned by the applied bias. The implications of controllable electronic structure of rotationally fault-stacked epitaxial graphene grown on the C-face of SiC for future device applications are discussed. 相似文献
5.
We present a self-consistent ab initio simulation method to calculate coherent quantum transport through a molecule connected to metal electrodes in the linear-response regime. Density-functional theory (DFT) is applied to the metal-molecule-metal system. The molecule and the metal electrodes are treated on the same footing as one extended molecule. The Full Approximation Scheme (FAS) nonlinear multigrid technique is used to accelerate convergence in a nonorthogonal localized orbital basis. The Landauer formula is employed to calculate the current with the transmission function obtained from a Green's function calculation. The current-voltage characteristics of a benzene-1,4-dithiolate (BDT) extended molecule are studied as an example, and our results are compared to other theoretical calculations. We also show that a recently formulated constrained-current formalism is invariant to a reversal in the imposed current. Hence, the predicted voltage drop must be zero. This suggests the theory must be modified to properly treat possible nonlinearities in the nonzero current case 相似文献
6.
Detecting VoIP Floods Using the Hellinger Distance 总被引:1,自引:0,他引:1
Sengar H. Haining Wang Wijesekera D. Jajodia S. 《Parallel and Distributed Systems, IEEE Transactions on》2008,19(6):794-805
Voice over IP (VoIP), also known as Internet telephony, is gaining market share rapidly and now competes favorably as one of the visible applications of the Internet. Nevertheless, being an application running over the TCP/IP suite, it is susceptible to flooding attacks. If flooded, as a time-sensitive service, VoIP may show noticeable service degradation and even encounter sudden service disruptions. Because multiple protocols are involved in a VoIP service and most of them are susceptible to flooding, an effective solution must be able to detect and overcome hybrid floods. As a solution, we offer the VoIP flooding detection system (vFDS)-an online statistical anomaly detection framework that generates alerts based on abnormal variations in a selected hybrid collection of traffic flows. It does so by viewing collections of related packet streams as evolving probability distributions and measuring abnormal variations in their relationships based on the Hellinger distance-a measure of variability between two probability distributions. Experimental results show that vFDS is fast and accurate in detecting flooding attacks, without noticeably increasing call setup times or introducing jitter into the voice streams. 相似文献
7.
Raymond A. Paul Jaideep Srivastava Duminda Wijesekera 《Annals of Software Engineering》1999,8(1-4):289-311
As information services become increasingly ubiquitous, and are being charged for, users are demanding the ability to choose
the quality of an information service based on its cost. In this environment, delivering the right information to the right
user at the right time, and with appropriate quality, is the challenge. In addition, resource optimizations must be performed
to the degree possible. In this paper we introduce the concept of information quality based system evaluation. The key contribution
is a framework in which user/application needs for information quality can be quantified in terms of rigorously defined metrics,
existing systems can be evaluated against these metrics, and the tradeoffs between information quality and its cost of provisioning
can be examined. Further, this provides an approach to developing information quality aware policies and mechanisms for the
system. This framework has been partially validated by applying it to the provisioning of continuous media services, i.e.,
audio and video, in a distributed environment. This paper presents the case study in detail. Finally, the paper outlines a
research program in the area of information quality based system evaluation.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
8.
Quality of service (QoS) metrics for continuous media 总被引:1,自引:0,他引:1
This paper presents quality of service (QoS) metrics for continuity and synchronization specifications in continuous media (CM). Proposed metrics specify continuity and synchronization, with tolerable limits on average and bursty defaults from perfect continuity, timing and synchronization constraints. These metrics can be used in a distributed environment for resource allocation. Continuity specification of a CM stream consists of its sequencing, display rate and drift profiles. The sequencing profile of a CM stream consists of tolerable aggregate and consecutive frame miss ratios. Rate profiles specify the average rendition rate and its variation. Given a rate profile, the ideal time unit for frame display is determined as an offset from the beginning of the stream. Drift profile specifies the average and bursty deviation of schedules for frames from such fixed points in time. Synchronization requirements of a collection of CM streams are specified by mixing, rate and synchronization drift profiles. Mixing profiles specify vectors of frames that can be displayed simultaneously. They consist of average and bursty losses of synchronization. Rate profiles consist of average rates and permissible deviations thereof. Synchronization drift profiles specify permissible aggregate and bursty time drifts between schedules of simultaneously displayable frames. It is shown that rate profiles of a collection of synchronized streams is definable in terms of rate profiles of its component streams. It is also shown that mixing and drift profiles of a collection of streams are non-definable in terms of sequencing and drift profiles of its constituents. An important consequence of the mutual independence of synchronization and continuity specification is that, in a general purpose platform with limited resources, synchronized display of CM streams may require QoS tradeoffs. An algorithm that makes such tradeoffs is presented as a proof of applicability of our metrics in a realistic environment. 相似文献
9.
10.
Duminda A. Gunawardena 《Chemical Engineering Communications》2013,200(8):1115-1124
Deoxygenation, or removal of oxygen from oxygenates, is an important element in the hydrocarbon fuel production process from biorenewable substrates. A thermodynamic equilibrium analysis gives valuable insights on the theoretical limits of desired products when a substrate is reacted under a given set of conditions. Here we report the equilibrium composition of glucose-to-hydrocarbon system by minimizing the total Gibbs energy of the system. The system was treated as a mixture of 11 components comprised of C6H6, C7H8, C8H10 (ethyl benzene), C8H10 (xylenes), C6H5 –OH, CH4, H2O, C, CO2, CO, and H2. Equilibrium compositions of each species were analyzed between temperatures 300 and 1500 K and pressures 0–15 atm. It was observed that at high temperature, CO and H2 dominate the equilibrium mixture with mole fractions of 0.597 and 0.587 respectively. At low temperatures the equilibrium mixture is dominated by CH4, CO2, H2O, and carbon. The aromatic hydrocarbon composition observed at thermodynamic equilibrium was extremely small. 相似文献