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On the departure process of a leaky bucket system with long-range dependent input traffic 总被引:2,自引:0,他引:2
Due to the strong experimental evidence that the traffic to be offered to future broadband networks will display long-range
dependence, it is important to study the possible implications that such traffic may have for the design and performance of
these networks. In particular, an important question is whether the offered traffic preserves its long-range dependent nature
after passing through a policing mechanism at the interface of the network. One of the proposed solutions for flow control
in the context of the emerging ATM standard is the so-called leaky bucket scheme. In this paper we consider a leaky bucket
system with long-range dependent input traffic. We adopt the following popular model for long-range dependent traffic: Time
is discrete. At each unit time a random number of sessions is initiated, having the distribution of a Poisson random variable
with mean λ. Each of these sessions has a random duration τ, where the integer random variable τ has finite mean, infinite
variance, and a regularly varying tail, i.e., P(τ >К) ~ К-Lα
L(К), where 1 < α < 2 L(·) is a slowly varying function. Once a session is initiated, it generates one cell at each unit of time until its termination.
We examine the departure process of the leaky bucket policing mechanism driven by such an arrival process, and show that it
too is long-range dependent for any token buffer size and any - finite or infinite - cell buffer size. Moreover, upper and
lower bounds for the covariance sequence of the output process are established. The above results demonstrate that long-range
dependence cannot be removed by the kinds of flow control schemes that are currently being envisioned for broadband networks.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
3.
Caitlin E. Karver Eric S. Molina Erin T. Economos Jonathan C. Fuentes Socrates M. Kaitson Samuel Kogan 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(2):101-105
Electrophilic trisubstituted ethylenes, halogen ring-substituted methyl 2-cyano-3-phenyl-2-propenoates, RPhCH=C(CN)CO2CH3 (where R is 3-Br-4-CH3O, 5-Br-2-CH3O, 2-F-5-CH3, 2-F-6-CH3, 4-F-3-CH3, 4-F-3-PhO, 2-F-5-I, 2-F-6-I, 2-F3C, 4-F3C) were prepared and copolymerized with styrene. The monomers were synthesized by the piperidine catalyzed Knoevenagel condensation of ring-substituted benzaldehydes and methyl cyanoacetate, and characterized by CHN analysis, IR, 1H and 13C-NMR. All the ethylenes were copolymerized with styrene (M1) in solution with radical initiation (ABCN) at 70°C. The compositions of the copolymers were calculated from nitrogen analysis and the structures were analyzed by IR, 1H and 13C-NMR. The order of relative reactivity (1/r 1) for the monomers is 2-F-5-CH3 (6.4) > 4-F-3-PhO (5.6) > 4-F3C (4.8) > 3-Br-4-CH3O (3.7) > 2-F-5-I (3.6) > 2-F3C (2.2) > 2-F-6-I (2.1) > 5-Br-2-CH3O (1.9) > 4-F-3-CH3 (1.8) > 2-F-6-CH3 (1.2). Relatively high T g of the copolymers in comparison with that of polystyrene indicates a decrease in chain mobility of the copolymer due to the high dipolar character of the trisubstituted ethylene monomer unit. Decomposition of the copolymers in nitrogen occurred in two steps, first in the 200-500°C range with residue (2–21% wt), which then decomposed in the 500–800°C range. 相似文献
4.
Lewis Acid Catalyzed Condensation–Cyclization Cascade: Direct Synthesis of Di/Trifluoromethyl‐1,2,3,4‐tetrahydroquinazolines
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Prof. Dr. G. K. Surya Prakash Dr. Attila Papp Socrates B. Munoz Nathan May John‐Paul Jones Prof. Dr. Ralf Haiges Prof. Dr. Pierre Mothé Esteves Dr. Thomas Mathew 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(28):10170-10178
Condensed heterocycles such as quinazolines constitute the framework of many promising drugs. The great impact of the dramatic fluorine effect in pharmaceuticals prompted a great surge in the quest for fluorinated drug design resulting in over 20 % fluorine‐containing drugs in the market today. Therefore, finding an efficient and cost‐effective method for the direct synthesis of fluorine‐tagged quinazoline systems is of great significance in the pharmaceutical arena. For the first time, a one‐pot sequential condensation–cyclization reaction to form selectively the difluoro/trifluoromethylated tetrahydroquinazolines from simple components difluoro/trifluoroacetaldehyde hemiacetal and aromatic amines is reported. Our recent studies using difluoro/trifluoroacetaldehyde hemiacetal as simple and elegant difluoro/trifluoromethyl synthons and metal triflates such as gallium triflate as safe and stable Lewis acid catalysts led us to this direct synthesis protocol for the expedient and convenient synthesis of fluorinated quinazolines. DFT calculations at PCM/B3LYP/6‐31++G** were carried out for evaluating a possible reaction mechanism for this cyclization. According to the DFT calculations, product stereochemistry is thermodynamically driven, favoring the cis isomer as the major product, which is also confirmed experimentally. 相似文献
5.
Daniel A. Krzyzanowski Socrates Kypreos Leonardo Barreto 《Computational Management Science》2008,5(3):207-231
Steadily growing prices of oil and emissions coming from conventional vehicles, might force a switch to an alternative and
less polluting fuel in the coming future. In this article we analyze the potential influence of selected factors for successful
market penetration of hydrogen fuel cell vehicles in hydrogen based private transportation economy. Using a world scale, full
energy system, bottom-up, optimization model (Global MARKAL Model—GMM) we address the possibility of supporting the fuel cell
vehicle technology to become competitive in the markets. In a series of optimizations we evaluate the potential influence
of governmental supports and the internalization of externalities related to CO2 and local pollution emissions originating from the transportation sector, as well as preferential crediting options and demonstration
projects promoting fuel cell vehicles. The results suggest that the crucial element is the price of fuel cells and their further
potential to reduce costs. This reduction of costs may be triggered by governmental support such as direct subsidies to fuel
cells, preferential crediting options for the buildup of hydrogen infrastructure as well as penalization of emitters of CO2 and/or local pollutants. 相似文献
6.
Petros Giastas Athanasios Papakyriakou George Tsafaras Socrates J. Tzartos Marios Zouridakis 《Molecules (Basel, Switzerland)》2022,27(14)
The β3 subunit of nicotinic acetylcholine receptors (nAChRs) participates in heteropentameric assemblies with some α and other β neuronal subunits forming a plethora of various subtypes, differing in their electrophysiological and pharmacological properties. While β3 has for several years been considered an accessory subunit without direct participation in the formation of functional binding sites, recent electrophysiology data have disputed this notion and indicated the presence of a functional (+) side on the extracellular domain (ECD) of β3. In this study, we present the 2.4 Å resolution crystal structure of the monomeric β3 ECD, which revealed rather distinctive loop C features as compared to those of α nAChR subunits, leading to intramolecular stereochemical hindrance of the binding site cavity. Vigorous molecular dynamics simulations in the context of full length pentameric β3-containing nAChRs, while not excluding the possibility of a β3 (+) binding site, demonstrate that this site cannot efficiently accommodate the agonist nicotine. From the structural perspective, our results endorse the accessory rather than functional role of the β3 nAChR subunit, in accordance with earlier functional studies on β3-containing nAChRs. 相似文献
7.
Xanath Ispizua-Rodriguez Dr. Socrates B. Munoz Dr. Vinayak Krishnamurti Dr. Thomas Mathew Prof. Dr. G. K. S. Prakash 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(64):15908-15913
A simple and straightforward approach to the synthesis of trifluoromethyl and difluoromethyl ketones from widely available carboxylic acids is disclosed. The transformation utilizes an acyloxyphosphonium ion as the active electrophile, conveniently generated in situ from the carboxylic acid substrate by using commodity chemicals. The utility of the reaction system is exemplified by its chemoselectivity, with tolerance to a variety of important functional groups. The late-stage functionalization of carboxylic acid active pharmaceutical ingredients and pharmaceutically relevant compounds is also discussed. 相似文献
8.
A modified excess Gibbs energy model which is based on the local composition concept and assigns a single energy parameter per pair of components, is incorporated into the GE—EoS thermodynamic formalism for vapor-liquid equilibrium (VLE) calculations of simple and complex refrigerant mixtures. One temperature set of data close to 273 K is used to obtain the model's parameters, which are used to extrapolate the VLE at other temperatures and pressures. A one-parameter form of the model based on the Wong-Sandler mixing rule is presented for several simple systems. The physical significance of the model's energy parameter is connected to the preference of the mixture for like to unlike interactions. The model is applied for VLE predictions of the ternary system R14-R23-R13, and the results are compared to calculations using the 3PWS model [H. Orbey. S.I. Sandler, Ind. Eng. Chem. Res. 34 (1995) 2520–2525] and the van der Waals mixing rule. Modelling of a few complex systems with only three data points given at each temperature is shown with a two parameter version of our model on the basis of the Huron-Vidal mixing rule. 相似文献
9.
Socrates Kypreos 《Computational Management Science》2008,5(1-2):141-170
Policies may help to keep the anthropogenic temperature change below some critical temperature thresholds. We apply MERGE
in a probabilistic risk assessment framework to assess the risk of action versus inaction on climate change. The method applied
gives a probabilistic assessment of the associated economic costs and levels of carbon-values and emissions reduction, as
well as the needed technological change to restructure the energy system. The study suggests that a set of low-carbon and
carbon-free technologies has to be developed and diffused around the world in order to reduce the risk of serious, adverse
climate change. Eventually, a mass deployment of biomass farming technologies for bio-fuels and/or hydrogen production, in
conjunction with carbon capture and sequestration options, are needed to satisfy the EU threshold of 2°C average atmospheric
temperature rise above the pre-industrial temperature levels by the year 2100. However, because this temperature threshold
represents a severe target, the global “willingness-to-pay” (WTP) must be significantly improved in relation with present
attitudes. 相似文献
10.
Cañete SJ Zhang Z Kong L Schlegel VL Plantz BA Dowben PA Lai RY 《Chemical communications (Cambridge, England)》2011,47(43):11918-11920
We report, for the first time, the application of synchrotron FTIR microspectroscopy to determine the spatial distribution of methylene blue conjugated onto a self-assembled monolayer surface via Sharpless "click" chemistry. 相似文献