1,721,098 research outputs found
Towards a non-intrusive recognition of anomalous system behavior in data centers
No full textIn this paper we propose a monitoring system of a data center that is able to infer when the data center is getting into an anomalous behavior by analyzing the power consumption at each server and the data center network traffic. The monitoring system is non-intrusive in the sense that there is no need to install software on the data center servers. The monitoring architecture embeds two Elman Recurrent Networks (RNNs) to predict power consumed by each data center component starting from data center network traffic and viceversa. Results obtained along six mounts of experiments, within a data center, show that the architecture is able to classify anomalous system behaviors and normal ones by analyzing the error between the actual values of power consumption and network traffic and the ones inferred by the two RNNs
A proactive Q-learning approach for autoscaling heterogeneous cloud servers
No full textCloud providers offer different physical or virtual machine (VM) types that have different computational power and cost. Choosing the right configuration in a such heterogeneous environment able to sustain a workload while minimising costs is a challenging key aspect. Furthermore, turning-on/off a VM does not come for free, but introduce a reconfiguration overhead that might bring additional costs (e.g. time for moving to the new state and wasted resources for reconfiguration process). In this paper, we aim to find at run time a configuration s.t. (i) is able to sustain an input workload, (ii) does not over-provide resources, and that (iii) is as close as possible to the current one, to minimise the number of involved VMs in the reconfiguration, and thus, minimise the reconfiguration overhead. We propose here a Q-Learning approach to automatically learn the best policy to move from a configuration to another according to a predicted workload. We defined two reward functions which respectively look for (i) a configuration which perfectly fits the requested workload and (ii) a configuration which arrives close to the requested workload, to minimise the reconfiguration overhead. We compared the results with the two reward functions in term of average number of VMs involved in a reconfiguration and we show as with the first reward function we need to change in average 2.3 VM/reconfiguration while with the second reward function we can reduce such number up to 1 VM per reconfiguration with some over-provisioning.</p
Effects of antenna orientation on 3-D ground penetrating radar surveys: an archaeological perspective
No full textThis paper investigates the impact that the GPR antenna orientation, or survey direction, has
on migrated image resulting from 3-D georadar acquisitions carried out on heterogeneous
and anisotropic subsurface. This feature is related to the directional dependency of wave
propagation effects, such as dispersion, absorption, depolarization, and scattering phenomena.
We provide a proof of this with two field examples, demonstrating that a 3-D survey performed
along a single direction could bringweak results in terms of target detection and reconstruction.
To overcome this risk, we show the improvements that the combination of GPR 3-D data
acquired along different directions on the same area can obtain: an enhancement of target
detection probability and the practical advantage for the end-user of looking through a single
image. Further on, we develop a stacking scheme that employs a threshold associated with
amplitude comparison to adaptively handle the combination of georadar data volumes
Combining orthogonal polarization for elongated target detection with GPR
Full text linkFor an accurate imaging of ground penetrating radar data the polarization characteristics of
the propagating electromagnetic (EM) wavefield and wave amplitude variations with antenna
pattern orientation must be taken into account. For objects that show some directionality
feature and cylindrical shape any misalignment between transmitter and target can strongly
modify the polarization state of the backscattered wavefield, thus conditioning the detection
capability of the system. Hints on the depolarization can be used to design the optimal GPR
antenna survey to avoid omissions and pitfalls during data processing.
This research addresses the issue of elongated target detection through a multi azimuth
(or multi polarization) approach based on the combination of mutually orthogonal GPR data.
Results from the analysis of the formal scattering problem demonstrate how this strategy can
reach a scalar formulation of the scattering matrix and achieve a rotational invariant quantity.
The effectiveness of the algorithm is then evaluated with a detailed field example showing
results closely proximal to those obtained under the optimal alignment condition: detection is
significantly improved and the risk of target missing is reduce
Utilities detection through the sum of orthogonal polarization in 3D georadar surveys
Full text linkGround penetrating radar (GPR) is widely used in subsurface investigations for extracting the position
and the route followed by the utility, an issue that gains more and more importance when
considering the cost related to trench damage and disruptions. However, it has been noted that
various targets of GPR surveys, especially linear and elongated targets, have polarization-dependent
scattering characteristics. This implies that the visibility of a subsurface scatterer in the acquired
data depends on the used antenna configuration and its orientation with respect to the feature to be
imaged.
Furthermore, wave attributes could be modified by the surrounding soil anisotropy and heterogeneity
degree. As the GPR antennas are composed of directional dipoles, any changes in the
propagation plane of the returning wave affects the recording of GPR data.
This work presents an approach based on a combination of mutually orthogonal GPR 3D data
volumes through which polarization issues can be overcome, ensuring target detection even when
the position and material are adverse. The strategy is evaluated through two field examples: in
homogeneous soil this technique fully recovers the polarization mismatch, providing results that are
closely similar to the ones that would be obtained with the optimal configuration; in heterogeneous
environments it overcomes the wavelet alteration, depolarization included, strongly enhancing the
signal to noise ratio and improving target reconstruction
Significance of GPR polarisation for improving target detection and characterisation
Full text linkThis paper focuses on the application of ground penetrating radar (GPR) technique for
civil engineering purposes, addressing the issues related to wave polarisation and
antennas geometry. Even if polarisation of GPR signal is often an underestimated
feature during data analysis and post processing, detection or avoidance of a specific
target can be managed handling its polarimetric response. This opportunity is of high
importance in this field of application, where the mixture of target with different
polarimetric response is a commonly encountered situation. To provide an insight of
this, two multicomponent GPR surveys have been performed: a first survey to show the
effect of antenna-target mutual alignment variation and a second experiment in which
the benefits of acquiring with different antenna arrangements are clearly evident.
Because each antenna arrangement is sensitive towards different features of the
received wavefield, this strategy is able to discriminate targets depending on their
geometrical shape, thus delivering better detailed image of the acquired area
Influence of internal structure on landmine radar signatures
Full text linkCheap and easy to use, landmines are among the favourite weapons in civil wars and wars of insurgency and are used by governments and guerrillas alike. These 'eternal sentinels' stand guard long after the conflicts have ended and kill and maim without mercy or discrimination. Therefore, there is a pressing need to remove these devices and to clear the contaminated land. As many landmines have low metal content they are difficult to detect using traditional techniques such as metal detectors, hence Ground Penetrating Radar (GPR) is an attractive tool in landmine clearance. Many investigations of landmine detection using GPR make use of surrogate landmine targets, since real landmines are difficult to obtain. This paper investigates the importance of the fidelity of such surrogates in terms of their external design, internal structure and explosive content
An architecture for enabling log-based resolution of disputes in multi-party transactions
No full textWe are witnessing an ongoing global trend towards the automation of almost any transaction through the employment of some Internet-based mean. Furthermore, the large spread of cloud computing and the massive emergence of the software as a service (Saas) paradigm have unveiled many opportunities to combine distinct services, provided by different parties, to establish higher level and more advanced services, that can be offered to end users and enterprises. Business-to-business (B2B) integration and third-party authorization (i.e., using standards like OAuth) are examples of processes requiring more parties to interact each other to deliver some desired functionality. These kinds of interactions mostly consist of transactions and are usually regulated by some agreement which defines the obligations that involved parties have to comply with. In case one of the parties claims a violation of some clause of such agreement, disputes can occur if the party accused of the infraction refuses to recognize its fault. Moreover, in case of auditing, for convenience reasons a party may deny to have taken part in a given transaction, or may forge historical records related to that transaction.
Solutions based on a trusted third party (TTP) have drawbacks: high overhead due to the involvement of an additional party, possible fees to pay for each transaction, and the risks stemming from having to blindly trust another party. If it were possible to only base on transaction logs to sort disputes out, then it would be feasible to get rid of any TTP and related shortcomings.
In this paper we propose an architecture, and an algorithm to execute in such architecture, aimed at providing strong guarantees on the integrity of transaction logs, so that they can be certified and used as unquestionable proofs when controversies arise. The solution we suggest includes three steps: (i) identification of the monitoring points where to produce the logs during transaction execution, (ii) an agreement among involved parties on produced logs, and (iii) persistence of the hashes of these logs in a blockchain-based storage. As a case study, we describe an instantiation of such architecture for federations of clouds
Sparse Ground Penetrating Radar Acquisition: Implication for Buried Landmine Localization and Reconstruction
No full textThe effectiveness of the ground penetrating radar (GPR) imaging process and its capability of correctly reconstructing buried objects is strictly bounded to a correct acquisition strategy, both in terms of data density and regularity. In some GPR applications, such as landmine detection, these requirements may not be fulfiled due to logistical limitations and environmental obstacles. In the light of autonomous platform, possibly driven by a positioning device, the knowledge of the maximum affordable grid irregularity is essential. This experimental work, employing a data set acquired at a landmine test site, provides a demonstration that the same information content could be maintained even with a sparser data grid, compared to the commonly adopted requirements, mitigating the pressing demand for a precise samples positioning
Masonry texture reconstruction for building seismic assessment: Practical evaluation and potentials of Ground Penetrating Radar methodology
No full textWithin the context of masonry texture identification and geometrical reconstruction, Ground Penetrating Radar (GPR) could emerge as an effective survey method, due to its high-resolution, scalable and non-destructive approach. This study has methodologically assessed operational advantages and weaknesses of the methodology when implemented for a seismic assessment purpose. In particular, the scope was to examine acquisition and post-processing strategies that could reliably highlight the presence or absence of specific construction features on which to develop a quantitative indication of the quality of the masonry. For this purpose, a high frequency 3D GPR acquisition on a plastered masonry wall incorporating different brick geometries, has been carried out. The acquisition was made along two different survey directions and analysing unfocussed and migrated radar slices. Thanks to a favourable antenna pattern alignment and achieved resolution enhancement, the focussed GPR data collected along the vertical mortar joints orientation have proven to be able to properly reconstruct the wall texture, providing therefore detailed and crucial information on its geometrical appearance
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