43,191 research outputs found
Fault detection in operating helicopter drive train components based on support vector data description
The objective of the paper is to develop a vibration-based automated procedure dealing with early detection of
mechanical degradation of helicopter drive train components using Health and Usage Monitoring Systems (HUMS) data. An anomaly-detection method devoted to the quantification of the degree of deviation of the mechanical state of a component from its nominal condition is developed. This method is based on an Anomaly Score (AS) formed by a combination of a set of statistical features correlated with specific damages, also known as Condition Indicators (CI), thus the operational variability is implicitly included in the model through the CI correlation. The problem of fault detection is then recast as a one-class classification problem in the space spanned by a set of CI, with the aim of a global differentiation between normal and anomalous observations, respectively related to healthy and supposedly faulty components. In this paper, a procedure based on an efficient one-class classification method that does not require any assumption on the data distribution, is used. The core of such an approach is the Support Vector Data Description (SVDD), that allows an efficient data description without the need of a significant amount of statistical data. Several analyses have been carried out in order to validate the proposed procedure, using flight vibration data collected from a H135, formerly known as EC135, servicing helicopter, for which micro-pitting damage on a gear was detected by HUMS and assessed through visual inspection. The capability of the proposed approach of providing better trade-off between false alarm rates and missed detection rates with respect to individual CI and to the AS obtained assuming jointly-Gaussian-distributed CI has been also analysed
Comment on "Sound Modes broadening in Quasicrystals"
Recently de Boissieu et al. proposed an explanation for the broadening of
acoustic modes observed in quasicrystals (QC). It is the transcription of a
well-known model used for glasses. We raise two fundamental objections against
applying it to QC. After the text of the Comment we report the methodology that
has been used to thwart the publication of this Comment, which is perfectly
valid.Comment: 7 pages, 0 Figures, literal citations remove
MDI-QKD: Continuous- versus discrete-variables at metropolitan distances
In a comment, Xu, Curty, Qi, Qian, and Lo claimed that discrete-variable (DV)
measurement device independent (MDI) quantum key distribution (QKD) would
compete with its continuous-variable (CV) counterpart at metropolitan
distances. Actually, Xu et al.'s analysis supports exactly the opposite by
showing that the experimental rate of our CV protocol (achieved with practical
room-temperature devices) remains one order of magnitude higher than their
purely-numerical and over-optimistic extrapolation for qubits, based on
nearly-ideal parameters and cryogenic detectors (unsuitable solutions for a
realistic metropolitan network, which is expected to run on cheap
room-temperature devices, potentially even mobile). The experimental rate of
our protocol (expressed as bits per relay use) is confirmed to be two-three
orders of magnitude higher than the rate of any realistic simulation of
practical DV-MDI-QKD over short-medium distances. Of course this does not mean
that DV-MDI-QKD networks should not be investigated or built, but increasing
their rate is a non-trivial practical problem clearly beyond the analysis of Xu
et al. Finally, in order to clarify the facts, we also refute a series of
incorrect arguments against CV-MDI-QKD and, more generally, CV-QKD, which were
made by Xu et al. with the goal of supporting their thesis.Comment: Updated reply to Xu, Curty, Qi, Qian and Lo (arXiv:1506.04819),
including a point-to-point rebuttal of their new "Appendix E: Addendum
Are You Still There? - A Lightweight Algorithm to Monitor Node Presence in Self-Configuring Networks
This paper is concerned with the analysis and redesign of a distributed algorithm to monitor the availability of nodes in self-configuring networks. The simple scheme to regularly probe a node ¿ "are you still there?" ¿ may easily lead to over- or underloading. The essence of the algorithm is therefore to automatically adapt the probing frequency. We show that a self-adaptive scheme to control the probe load, originally proposed as an extension to the UPnPTM (Universal Plug and Play) standard, leads to an unfair treatment of nodes: some nodes probe fast while others almost starve. An alternative distributed algorithm is proposed that overcomes this problem and that tolerates highly dynamic network topology changes. The algorithm is very simple and can be implemented on large networks of small computing devices such as mobile phones, PDAs, and so on
EEG correlates of social interaction at distance
This study investigated EEG correlates of social interaction at distance between twenty-five pairs of participants who were not connected by any traditional channels of communication. Each session involved the application of 128 stimulations separated by intervals of random duration ranging from 4 to 6 seconds. One of the pair received a one-second stimulation from a light signal produced by an arrangement of red LEDs, and a simultaneous 500 Hz sinusoidal audio signal of the same length. The other member of the pair sat in an isolated sound-proof room, such that any sensory interaction between the pair was impossible. An analysis of the Event-Related Potentials associated with sensory stimulation using traditional averaging methods showed a distinct peak at approximately 300 ms, but only in the EEG activity of subjects who were directly stimulated. However, when a new algorithm was applied to the EEG activity based on the correlation between signals from all active electrodes, a weak but robust response was also detected in the EEG activity of the passive member of the pair, particularly within 9 – 10 Hz in the Alpha range. Using the Bootstrap method and the Monte Carlo emulation, this signal was found to be statistically significant
Hidden scaling patterns and universality in written communication
The temporal statistics exhibited by written correspondence appear to be
media dependent, with features which have so far proven difficult to
characterize. We explain the origin of these difficulties by disentangling the
role of spontaneous activity from decision-based prioritizing processes in
human dynamics, clocking all waiting times through each agent's `proper time'
measured by activity. This unveils the same fundamental patterns in written
communication across all media (letters, email, sms), with response times
displaying truncated power-law behavior and average exponents near -3/2. When
standard time is used, the response time probabilities are theoretically
predicted to exhibit a bi-modal character, which is empirically borne out by
our new years-long data on email. These novel perspectives on the temporal
dynamics of human correspondence should aid in the analysis of interaction
phenomena in general, including resource management, optimal pricing and
routing, information sharing, emergency handling.Comment: 27 pages, 10 figure
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