104 research outputs found
Resilient Cloud Network Mapping with Virtualized BBU Placement for Cloud-RAN
No full textCloud Radio Access Network (C-RAN) will improve mobile radio coordination and resource efficiency by allowing baseband processing unit (BBU) functions to be virtualized and centralized, i.e., deployed in a BBU hotel. We consider a BBU hoteling scheme based on the concept of access cloud network (ACN). An ACN consists of virtualized BBUs (vBBUs) placed in metro cloud data centers (metro DCs). A vBBU is connected to a set of remote radio heads (RRHs). ACN resiliency against network and processing failures is critical for C-RAN deployments. Hence, in this study, we propose three protection approaches: 1+1 ACN protection, 1+1 ACN and vBBU protection, and partial ACN protection. Simulation results show that both 1+1 ACN and 1+1 ACN and vBBU protection requires large capacity for backup to provide 100% survivability for singlelink and single-DC failures. As a result, we suggest a partial ACN protection approach which provides degraded services with only 8% additional network resources.</p
Load balancing and latency reduction in multi-user CoMP over TWDM-VPONs
No full textIn emerging cellular systems, optical fronthaul is expected to play a major role to support many control operations, e.g., Coordinated Multipoint (CoMP). CoMP is a promising technique for interference mitigation as it can transform interfing signals into joint transmission (reception) in which signals from adjacent cell sites are simultaneously transmitted (received) to (from) mobile terminals. But the exchange of information required by CoMP demands high flexibility and capacity. This paper proposes a new architecture for supporting CoMP operations in emerging cellular systems. It is based on a time-and-wavelength-division-multiplexed passive optical network (TWDM-PON) fronthaul, using virtualized base stations and a cloud radio access network (C-RAN) architecture. We also propose techniques to distribute the load on controllers to minimize the coordination delay. Results show that, for a typical setting, our methods can save up to 37% on the time required to distribute channel state information among multiple base stations
Disaster-Survivable Cloud-Network Mapping
No full textCloud-computing services are provided to consumers through a network of servers and network equipment. Cloud-network (CN) providers virtualize resources [ e. g., virtual machine (VM) and virtual network (VN)] for efficient and secure resource allocation. Disasters are one of the worst threats for CNs as they can cause massive disruptions and CN disconnection. A disaster may also induce post-disaster correlated, cascading failures which can disconnect more CNs. Survivable virtual-network embedding (SVNE) approaches have been studied to protect VNs against single physical-link/-node and dual physical-link failures in communication infrastructure, but massive disruptions due to a disaster and their consequences can make SVNE approaches insufficient to guarantee cloud-computing survivability. In this work, we study the problem of survivable CN mapping from disaster. We consider risk assessment, VM backup location, and post-disaster survivability to reduce the risk of failure and probability of CN disconnection and the penalty paid by operators due to loss of capacity. We formulate the proposed approach as an integer linear program and study two scenarios: a natural disaster, e. g., earthquake and a human-made disaster, e. g., weapons-of-mass-destruction attack. Our illustrative examples show that our approach reduces the risk of CN disconnection and penalty up to 90% compared with a baseline CN mapping approach and increases the CN survivability up to 100% in both scenarios
Disaster-resilient virtual-network mapping and adaptation in optical networks
No full textToday's Internet applications include grid- and cloud-computing services which can be implemented by mapping virtual networks (VNs) over physical infrastructure such as an optical network. VN mapping is a resource-allocation problem where fractions of the resources (e.g., bandwidth and processing) in the physical infrastructure (e.g., optical network and servers/data-centers) are provisioned for specific applications. Researchers have been studying the survivable VN mapping (SVNM) problem against physical-infrastructure failures (typically by deterministic failure models), because this type of failure may disconnect one or more VNs, and/or reduce their capacities. However, disasters can cause multiple link/node failures which may disconnect many VNs and dramatically increase the post-disaster vulnerability to correlated cascading failures. Hence, we investigate the disaster-resilient and post-disaster- survivable VN mapping problem using a probabilistic model to reduce the expected VN disconnections and capacity loss, while providing an adaptation to minimize VN disconnections by any postdisaster single-physical-link failure. We model the problem as an integer linear program (ILP). Numerical examples show that our approach reduces VN disconnections and the expected capacity loss after a disaster.</p
The hydrocyclone for separating light dispersions
No full textVarious new hydrocyclone designs developed by the author for
separating light dispersions from heavier carrying fluids are demonstrated and
their relative efficiencies compared using dispersions of plastic powders in water
and suitable non-dimensional equivalence relations. Detailed measurements of
the flow structure with in these hydrocyclones that have aided design work are also
discussed.
The mixture entering the cylindrical hydrocyclone body
tangentially generates a vortex and due to the centrifugal acceleration in this
vortex the less dense particles migrate towards the axis forming a core. This is
then removed through an axially placed outlet in the upstream end wall of the hydrocyclone
with 5-10% of the total through flow while the remaining particle depleted stream
passes out of the downstream end.
The work investigates the effects upon hydrocyclone
performance of changes in total flow rate, mode of operation, and geometry by
comparing particle concentrations in influent and effluent and the probability
of separation of individual particles, which is calculated from input and
output drop size spectra. From a flow of 60 L/min through an efficient
hydrocyclone of diameter 30 mm with a total head loss of 3.2 bar, it is found
that for particles with a relative differential density of 0.1 in water at 50°C,
99% at 50 µm are separated while 80% are separated at 17 µm and 50% separation
occurs at less than 10 µm.
Measurements of the flow structure within the hydrocyclones
have been made using a Laser Doppler Anemometer and from radial profiles of
axial and tangential velocities particle trajectories have been calculated.
With the application of the hydrocyclone for use with other
mixtures and dispersions in mind, an equivalence relation dependent upon
hydrocyclone Reynolds number is employed by which hydrocyclone performance may
be predicted from standard experimental results. The validity of this
relationship is demonstrated by comparing results from similar geometry
hydrocyclones over a range of sizes with different dispersions and changes in
medium viscosity by using water at various temperatures.</p
Contracting arrangements in agribusiness procurement practices in South Africa
No full textContracting arrangements in agribusiness procurement practices in South AfricaProcurement, contracting, agro-processing,
Efficient sentinel surveillance strategies for preventing epidemics on networks
No full textSurveillance plays a crucial role in preventing emerging infectious diseases from becoming epidemic. In circumstances where it is possible to monitor the infection status of certain people, transport hubs, or hospitals, early detection of the disease allows interventions to be implemented before most of the damage can occur, or at least its impact can be mitigated. This paper addresses the question of which nodes we should select in a network of individuals susceptible to some infectious disease in order to minimize the number of casualties. By simulating disease outbreaks on a collection of empirical and synthetic networks we show that the best strategy depends on topological characteristics of the network. For highly modular or spatially embedded networks it is better to place the sentinels on nodes distributed across different regions. However, if the degree heterogeneity is high, then a strategy that targets network hubs is preferred. We further consider the consequences of having an incomplete sample of the network and demonstrate that the value of new information diminishes as more data is collected. Finally we find further marginal improvements using two heuristics informed by known results in graph theory that exploit the fragmented structure of sparse network data. © 2019 Colman et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
Complex scale-free networks with tunable power-law exponent and clustering
No full textThis article is made available through the Brunel Open Access Publishing Fund. It is distributed under a Creative Commons License (http://creativecommons.org/licenses/by/3.0/). Copyright @ 2013 Elsevier B.V.We introduce a network evolution process motivated by the network of citations in the scientific literature. In each iteration of the process a node is born and directed links are created from the new node to a set of target nodes already in the network. This set includes mm “ambassador” nodes and ll of each ambassador’s descendants where mm and ll are random variables selected from any choice of distributions plpl and qmqm. The process mimics the tendency of authors to cite varying numbers of papers included in the bibliographies of the other papers they cite. We show that the degree distributions of the networks generated after a large number of iterations are scale-free and derive an expression for the power-law exponent. In a particular case of the model where the number of ambassadors is always the constant mm and the number of selected descendants from each ambassador is the constant ll, the power-law exponent is (2l+1)/l(2l+1)/l. For this example we derive expressions for the degree distribution and clustering coefficient in terms of ll and mm. We conclude that the proposed model can be tuned to have the same power law exponent and clustering coefficient of a broad range of the scale-free distributions that have been studied empirically.EPSR
Copper metabolism and gut morphology in rainbow trout (Oncorhynchus mykiss) during chronic sublethal dietary copper exposure
No full textJuvenile rainbow trout (Oncorhynchus mykiss) were exposed to 11 (control), 300 (medium), and 1000 mug Cu.g(1) (high) (as CuSO(4)5H(2)O) in the diet for 28 days at a daily ration of 4% wet body weight, with a background waterborne Cu concentration of 3 mug.L-1. There was no effect of dietary Cu on growth, condition factor, or food conversion efficiency. Whole-body Cu content increased continuously over the exposure period in all groups and was twofold and fourfold higher than controls at day 28 for the medium- and high-Cu diets, respectively. Copper accumulated mainly in liver and gut tissue, with the latter stabilizing by day 14. Accumulation also occurred in gill, kidney, and carcass. Plasma Cu concentration was not different from the controls whereas Cu in bile was greatly elevated, an indication of increased hepatobiliary excretion. Dietary Cu pre-exposure decreased the uptake of waterborne Cu across the gills, providing the first evidence of homeostatic interaction between the two routes of uptake. Electron microscopic observations of the midintestine revealed numerous mitochondria, lysosomes, lamellated bodies, and extensive lamellar processes in the enterocytes. Apoptosis, mitosis, and eosinophilic granule cells were more apparent in Cu-exposed fish.PT: J; CR: BERNTSSEN MHG, 1999, AQUAT TOXICOL, V46, P87 CAMPBELL HA, 1999, AQUAT TOXICOL, V46, P177 COLMAN JR, 1979, SCANNING ELECT MICRO, V11, P801 CRESPO S, 1986, J FISH BIOL, V28, P68 DALLINGER R, 1985, OECOLOGIA, V67, P82 DALLINGER R, 1987, OECOLOGIA, V73, P91 EZEASOR DN, 1980, J FISH BIOL, V17, P529 FARAG AM, 1994, ENVIRON TOXICOL CHEM, V13, P2021 GATLIN DM, 1986, AQUACULTURE, V54, P277 GROSELL M, 2000, IN PRESS AM J PHYSL GROSELL MH, 1997, AQUAT TOXICOL, V38, P257 GROSELL MH, 1998, AQUAT TOXICOL, V40, P275 GUASTADISEGNI C, 1999, J TOXICOL ENV HEAL A, V57, P415 HANDY RD, 1992, ARCH ENVIRON CON TOX, V22, P74 HANDY RD, 1993, AQUAT TOXICOL, V27, P1 HANDY RD, 1996, TOXICOLOGY AQUATIC P, P29 HANDY RD, 1999, AQUAT TOXICOL, V47, P23 HUGHES GM, 1984, FISH PHYSIOL, V10, P1 JULSHAMN K, 1988, AQUACULTURE, V73, P143 LANNO RP, 1985, AQUACULTURE, V49, P257 LANNO RP, 1987, AQUAT TOXICOL, V10, P251 LULLMANNRAUCH R, 1979, LYSOSOMES APPLIED BI, V6, P49 MACRAE RK, 1999, ENVIRON TOXICOL CHEM, V18, P1180 MARR JCA, 1996, AQUAT TOXICOL, V36, P17 MCDONALD DG, 1993, FISH ECOPHYSIOLOGY, P270 MILLER PA, 1993, CAN J FISH AQUAT SCI, V50, P1683 MOUNT DR, 1994, ENVIRON TOXICOL CHEM, V13, P2031 MURAI T, 1981, AQUACULTURE, V22, P352 NONNOTTE L, 1986, CELL TISSUE RES, V243, P619 OGINO C, 1980, NIPPON SUISAN GAKK, V46, P455 TAYLOR LN, 2000, ENVIRON TOXICOL CHEM, V19, P2298 WEIS P, 1986, ENVIRON HEALTH PERSP, V65, P167 WOLF K, 1963, PROGRE FISH CULT, V25, P135 WOOD CM, 1992, AQUAT TOXICOL, V22, P239 WOODWARD DF, 1994, T AM FISH SOC, V123, P51 WOODWARD DF, 1995, CAN J FISH AQUAT SCI, V52, P1994; NR: 36; TC: 24; J9: CAN J FISHERIES AQUAT SCI; PG: 13; GA: 399WRSource type: Electronic(1
Structure and dynamics of evolving complex networks
No full textThis thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel UniversityThe analysis of large disordered complex networks has recently received enormous attention motivated by both academic and commercial interest. The most important results in this discipline have come from the analysis of stochastic models which mimic the growth and evolution of real networks as they change over time. The purpose of this thesis is to introduce various novel processes which dictate the development of a network on a small scale, and use techniques learned from statistical physics to derive the dynamical and structural properties of the network on the macroscopic scale. We introduce each model as a set of mechanisms determining how a network changes over a small period in time, from these rules we derive several topological
properties of the network after many iterations, most notably the degree distribution. 1. In the rst mechanism, nodes are introduced and linked to older nodes in the network in such a way as to create triangles and maintain a high level of clustering. The mechanism resembles the growth of a citation network and we demonstrate analytically that the mechanism introduced su ces to explain the power-law form commonly found in citation distributions. 2. The second mechanism involves edge rewiring processes - detaching one end of an edge and reattaching it, either to a random node anywhere in the network or to one selected locally. 3. We analyse a variety of processes based around a novel fragmentation mechanism. 4. The nal model concerns the problem of nding the electrical resistance across a network. The network grows as a random tree, as it grows the distribution of resistance converges towards a steady state solution. We nd an application of the relatively recent concept of a random Fibonacci sequence in deriving the rate of convergence of the mean.EPSR
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