20 research outputs found
Robust Energy Management for Green and Survivable IP Networks
Despite the growing necessity to make Internet greener, it is worth pointing
out that energy-aware strategies to minimize network energy consumption must
not undermine the normal network operation. In particular, two very important
issues that may limit the application of green networking techniques concern,
respectively, network survivability, i.e. the network capability to react to
device failures, and robustness to traffic variations. We propose novel
modelling techniques to minimize the daily energy consumption of IP networks,
while explicitly guaranteeing, in addition to typical QoS requirements, both
network survivability and robustness to traffic variations. The impact of such
limitations on final network consumption is exhaustively investigated. Daily
traffic variations are modelled by dividing a single day into multiple time
intervals (multi-period problem), and network consumption is reduced by putting
to sleep idle line cards and chassis. To preserve network resiliency we
consider two different protection schemes, i.e. dedicated and shared
protection, according to which a backup path is assigned to each demand and a
certain amount of spare capacity has to be available on each link. Robustness
to traffic variations is provided by means of a specific modelling framework
that allows to tune the conservatism degree of the solutions and to take into
account load variations of different magnitude. Furthermore, we impose some
inter-period constraints necessary to guarantee network stability and preserve
the device lifetime. Both exact and heuristic methods are proposed.
Experimentations carried out with realistic networks operated with flow-based
routing protocols (i.e. MPLS) show that significant savings, up to 30%, can be
achieved also when both survivability and robustness are fully guaranteed
Energy management in communication networks: a journey through modelling and optimization glasses
The widespread proliferation of Internet and wireless applications has
produced a significant increase of ICT energy footprint. As a response, in the
last five years, significant efforts have been undertaken to include
energy-awareness into network management. Several green networking frameworks
have been proposed by carefully managing the network routing and the power
state of network devices.
Even though approaches proposed differ based on network technologies and
sleep modes of nodes and interfaces, they all aim at tailoring the active
network resources to the varying traffic needs in order to minimize energy
consumption. From a modeling point of view, this has several commonalities with
classical network design and routing problems, even if with different
objectives and in a dynamic context.
With most researchers focused on addressing the complex and crucial
technological aspects of green networking schemes, there has been so far little
attention on understanding the modeling similarities and differences of
proposed solutions. This paper fills the gap surveying the literature with
optimization modeling glasses, following a tutorial approach that guides
through the different components of the models with a unified symbolism. A
detailed classification of the previous work based on the modeling issues
included is also proposed
The Covering-Assignment Problem for Swarm-powered Ad-hoc Clouds: A Distributed 3D Mapping Use-case
The popularity of drones is rapidly increasing across the different sectors
of the economy. Aerial capabilities and relatively low costs make drones the
perfect solution to improve the efficiency of those operations that are
typically carried out by humans (e.g., building inspection, photo collection).
The potential of drone applications can be pushed even further when they are
operated in fleets and in a fully autonomous manner, acting de facto as a drone
swarm. Besides automating field operations, a drone swarm can serve as an
ad-hoc cloud infrastructure built on top of computing and storage resources
available across the swarm members and other connected elements. Even in the
absence of Internet connectivity, this cloud can serve the workloads generated
by the swarm members themselves, as well as by the field agents operating
within the area of interest. By considering the practical example of a
swarm-powered 3D reconstruction application, we present a new optimization
problem for the efficient generation and execution, on top of swarm-powered
ad-hoc cloud infrastructure, of multi-node computing workloads subject to data
geolocation and clustering constraints. The objective is the minimization of
the overall computing times, including both networking delays caused by the
inter-drone data transmission and computation delays. We prove that the problem
is NP-hard and present two combinatorial formulations to model it.
Computational results on the solution of the formulations show that one of them
can be used to solve, within the configured time-limit, more than 50% of the
considered real-world instances involving up to two hundred images and six
drones
Heuristics for optimizing 3D mapping missions over swarm-powered ad hoc clouds
Drones have been getting more and more popular in many economy sectors. Both
scientific and industrial communities aim at making the impact of drones even
more disruptive by empowering collaborative autonomous behaviors -- also known
as swarming behaviors -- within fleets of multiple drones. In swarming-powered
3D mapping missions, unmanned aerial vehicles typically collect the aerial
pictures of the target area whereas the 3D reconstruction process is performed
in a centralized manner. However, such approaches do not leverage computational
and storage resources from the swarm members.We address the optimization of a
swarm-powered distributed 3D mapping mission for a real-life humanitarian
emergency response application through the exploitation of a swarm-powered ad
hoc cloud. Producing the relevant 3D maps in a timely manner, even when the
cloud connectivity is not available, is crucial to increase the chances of
success of the operation. In this work, we present a mathematical programming
heuristic based on decomposition and a variable neighborhood search heuristic
to minimize the completion time of the 3D reconstruction process necessary in
such missions. Our computational results reveal that the proposed heuristics
either quickly reach optimality or improve the best known solutions for almost
all tested realistic instances comprising up to 1000 images and fifteen drones
Measurement of the very rare decay
The decay K+→π+νν¯
, with a very precisely predicted branching ratio of less than 10−10
,
is among the best processes to reveal indirect effects of new physics.
The NA62 experiment at CERN SPS is designed to study the K+→π+νν¯
decay and to measure its branching ratio using a decay-in-flight technique.
NA62 took data in 2016, 2017 and 2018, reaching the sensitivity of the Standard Model
for the K+→π+νν¯
decay by the analysis of the 2016 and 2017 data,
and providing the most precise measurement of the branching ratio to date
by the analysis of the 2018 data.
This measurement is also used to set limits on BR(K+→π+X
), where X
is a scalar
or pseudo-scalar particle.
The final result of the BR(K+→π+νν¯
) measurement and its interpretation in terms
of the K+→π+X
decay from the analysis of the full 2016-2018 data set is presented, and future plans and prospects are reviewed
Comparative study of dissolved inorganic carbon utilization and photosynthetic responses in Nannochloris (Chlorophyceae) and Nannochloropsis (Eustigmatophyceae) species
5 páginas, 2 figuras, 2 tablas.[EN] Four species of marine microalgae with similar morphology and life cycle, namely Nannochloris atomus Butcher, Nannochloris maculata Butcher, Nannochloropsis gaditana Lubian, and Nannochloropsis oculata (Droop) Hibberd, have been examined with respect to their affinity for different sources of dissolved inorganic carbon. External carbonic anhydrase activity was not found in any of these species, but the cell affinity for dissolved inorganic carbon (DIC) in Nannochloris species was affected by the inhibitor acetazolamide at a concentration of 400 µM. Measurement of photosynthetic rates and CO2 compensation points at different pH values showed that the Nannochloris species had a greater capacity for CO2 rather than HCO3- utilization. In contrast, the observed rates of photosynthetic oxygen evolution in Nannochloropsis species were greater than could be accounted for by the theoretical rate of CO2 supply from the spontaneous dehydration of bicarbonate in the external medium. This indicates that these algae were able to transport bicarbonate across the plasmalemma. Furthermore, the K0.5 (DIC) value at acidic pH showed that Nannochloropsis oculata could also use CO2 as an exogenous carbon source for photosynthesis. Although the species of marine phytoplankton used in this study possess similar morphological characteristics and life cycle, there exist many differences in the mode of inorganic carbon utilization between these microalgae.Key words: Nannochloris, Nannochloropsis, inorganic carbon utilization, bicarbonate transport, CO2 compensation point, photosynthesis.[FR] Les auteurs ont examiné quatre espèces de microalgues marines ayant des morphologies et des cycles vitaux similaires, nommément les Nannochloris atomus Butcher, Nannochloris maculata Butcher, Nannochloropsis gaditana
Lubian et Nannochloropsis oculata (Droop) Hibberd, afin de déterminer leur affinité pour différentes sources de carbone
inorganique dissout. Aucune activité de l'anhydrase carbonique externe n'a pas pu être décelée chez ces espèces, mais
l'affinité des cellules pour le carbone inorganique dissout (DIC) chez les espèces de Nannochloris est affectée par
l'inhibiteur acétazolamide à une concentration de 400 µM. La mesure des taux de photosynthèse et des points de
compensation en CO2 à différentes valeurs de pH montre que les espèces de Nannochloris ont une plus grande capacité d'utilisation du CO2 que du HCO3-. Au contraire, les taux d'évolution de l'oxygène photosynthétique observés chez les espèces de Nannochloropsis sont plus élevés que les valeurs théoriques du taux d'approvisionnement en CO2 provenant de la déshydratation spontanée du bicarbonate dans le milieu externe. Ceci indique que ces algues sont capables de transporter du bicarbonate à travers leur plasmalemme. De plus, la valeur K0.5
(DIC) à pH acide montre que le annochloropsis oculata peut également utiliser le CO2 comme source exogène de carbone pour la photosynthèse. Bien que les espèces de phytoplancton marin utilisées dans cette étude possèdent des caractéristiques morphologiques et des cycles vitaux similaires, il existe plusieurs différences dans les modalités d'utilisation du carbone inorganique dissout entre ces microalgues.This research was supported by a grant from the Spanish Ministry of Education and Science (Project CICYT, AMB94-0684-CO2-01). We also thank Dr. B. Colman for the gas chromatography.Peer reviewe
A robust optimization approach for energy-aware routing in MPLS networks
A robust multi-period model is proposed to minimize the energy consumption of IP networks, while guaranteeing the satisfaction of uncertain traffic demands. Energy savings are achieved by putting into sleep mode cards and chassis. The study of the solution robustness shows that there is a trade-off between energy consumption and the solutions conservatism degree. The model allows this trade-off to be tuned by simply modifying a single parameter per link. The multi-period optimization is constrained by inter-period limitations necessary to guarantee network stability. Both, exact and heuristic methods are proposed. Results show that up to 60% of the energy savings can be achieved for realistic test scenarios in networks operated with flow-based routing protocols (i.e. MPLS) and with a good level of robustness to traffic variations