419,981 research outputs found
Probabilistic Anomaly Detection in Natural Gas Time Series Data
This paper introduces a probabilistic approach to anomaly detection, specifically in natural gas time series data. In the natural gas field, there are various types of anomalies, each of which is induced by a range of causes and sources. The causes of a set of anomalies are examined and categorized, and a Bayesian maximum likelihood classifier learns the temporal structures of known anomalies. Given previously unseen time series data, the system detects anomalies using a linear regression model with weather inputs, after which the anomalies are tested for false positives and classified using a Bayesian classifier. The method can also identify anomalies of an unknown origin. Thus, the likelihood of a data point being anomalous is given for anomalies of both known and unknown origins. This probabilistic anomaly detection method is tested on a reported natural gas consumption data set
The applicability of the T/S method to geopotential anomaly computations in the Northeast Atlantic
Methods are tested for computing geopotential anomalies from temperature data in the
subtropical Northeast Atlantic. Mean temperature-salinity, salinity-depth and
density-depth relationships are determined for 3 x 3° squares, using hydrographie data
from World Oceanographie Data Centre A. Geopotential anomalies computed from
observed temperatures and salinities from these mean relationships are compared with
anomalies from the original temperature and salinity data. For 0-500 dbar, geopotential
anomalies can be weil approximated, and the methods also work reasonably weil for
0-1000 dbar. The approximation is poor for 0-2000 dbar. Appropriate methods for
obtaining the best results in each 3 x 3° square are specified. The method is applied to
a particular subset of the data
Deep learning for inferring cause of data anomalies
Daily operation of a large-scale experiment is a resource consuming task,
particularly from perspectives of routine data quality monitoring. Typically,
data comes from different sub-detectors and the global quality of data depends
on the combinatorial performance of each of them. In this paper, the problem of
identifying channels in which anomalies occurred is considered. We introduce a
generic deep learning model and prove that, under reasonable assumptions, the
model learns to identify 'channels' which are affected by an anomaly. Such
model could be used for data quality manager cross-check and assistance and
identifying good channels in anomalous data samples. The main novelty of the
method is that the model does not require ground truth labels for each channel,
only global flag is used. This effectively distinguishes the model from
classical classification methods. Being applied to CMS data collected in the
year 2010, this approach proves its ability to decompose anomaly by separate
channels.Comment: Presented at ACAT 2017 conference, Seattle, US
On the anomalies in the latest LHCb data
Depending on the assumptions on the power corrections to the exclusive b -> s
l+ l- decays, the latest data of the LHCb collaboration - based on the 3 fb^-1
data set and on two different experimental analysis methods - still shows some
tensions with the SM predictions. We present a detailed analysis of the
theoretical inputs and various global fits to all the available b -> s l+ l-
data. This constitutes the first global analysis of the new data of the LHCb
collaboration based on the hypothesis that these tensions can be at least
partially explained by new physics contributions. In our model-independent
analysis we present one-, two-, four-, and also five-dimensional global fits in
the space of Wilson coefficients to all available b -> s l+ l- data. We also
compare the two different experimental LHCb analyses of the angular observables
in B -> K* mu+ mu-. We explicitly analyse the dependence of our results on the
assumptions about power corrections, but also on the errors present in the form
factor calculations. Moreover, based on our new global fits we present
predictions for ratios of observables which may show a sign of lepton
non-universality. Their measurements would crosscheck the LHCb result on the
ratio R_K = BR(B+ -> K+ mu+ mu-) / BR(B+ -> K+ e+ e-) in the low-q^2 region
which deviates from the SM prediction by 2.6 sigma.Comment: 41 pages, 24 figures. v2: references and comment on 1006.4945
[hep-ph] adde
Alignment and signed-intensity anomalies in WMAP data
Significant alignment and signed-intensity anomalies of local features of the
cosmic microwave background (CMB) are detected on the three-year WMAP data,
through a decomposition of the signal with steerable wavelets on the sphere.
Firstly, an alignment analysis identifies two mean preferred planes in the sky,
both with normal axes close to the CMB dipole axis. The first plane is defined
by the directions toward which local CMB features are anomalously aligned. A
mean preferred axis is also identified in this plane, located very close to the
ecliptic poles axis. The second plane is defined by the directions anomalously
avoided by local CMB features. This alignment anomaly provides further insight
on recent results (Wiaux et al. 2006). Secondly, a signed-intensity analysis
identifies three mean preferred directions in the southern galactic hemisphere
with anomalously high or low temperature of local CMB features: a cold spot
essentially identified with a known cold spot (Vielva et al. 2004), a second
cold spot lying very close to the southern end of the CMB dipole axis, and a
hot spot lying close to the southern end of the ecliptic poles axis. In both
analyses, the anomalies are observed at wavelet scales corresponding to angular
sizes around 10 degress on the celestial sphere, with global significance
levels around 1%. Further investigation reveals that the alignment and
signed-intensity anomalies are only very partially related. Instrumental noise,
foreground emissions, as well as some form of other systematics, are strongly
rejected as possible origins of the detections. An explanation might still be
envisaged in terms of a global violation of the isotropy of the Universe,
inducing an intrinsic statistical anisotropy of the CMB.Comment: 12 pages, 7 figures. Accepted for publication in MNRAS. Small changes
made (including the new subsection 3.4) to match the final versio
Data Imputation through the Identification of Local Anomalies
We introduce a comprehensive and statistical framework in a model free
setting for a complete treatment of localized data corruptions due to severe
noise sources, e.g., an occluder in the case of a visual recording. Within this
framework, we propose i) a novel algorithm to efficiently separate, i.e.,
detect and localize, possible corruptions from a given suspicious data instance
and ii) a Maximum A Posteriori (MAP) estimator to impute the corrupted data. As
a generalization to Euclidean distance, we also propose a novel distance
measure, which is based on the ranked deviations among the data attributes and
empirically shown to be superior in separating the corruptions. Our algorithm
first splits the suspicious instance into parts through a binary partitioning
tree in the space of data attributes and iteratively tests those parts to
detect local anomalies using the nominal statistics extracted from an
uncorrupted (clean) reference data set. Once each part is labeled as anomalous
vs normal, the corresponding binary patterns over this tree that characterize
corruptions are identified and the affected attributes are imputed. Under a
certain conditional independency structure assumed for the binary patterns, we
analytically show that the false alarm rate of the introduced algorithm in
detecting the corruptions is independent of the data and can be directly set
without any parameter tuning. The proposed framework is tested over several
well-known machine learning data sets with synthetically generated corruptions;
and experimentally shown to produce remarkable improvements in terms of
classification purposes with strong corruption separation capabilities. Our
experiments also indicate that the proposed algorithms outperform the typical
approaches and are robust to varying training phase conditions
On estimating gravity anomalies from gradiometer data
The Gravsat-gradiometer mission involves flying a gradiometer on a gravity satellite (Gravsat) which is in a low, polar, and circular orbit. Results are presented of a numerical simulation of the mission which demonstrates that, if the satellite is in a 250-km orbit, 3- and 5-degree gravity anomalies may be estimated with accuracies of 0.03 and 0.01 mm/square second (3 and 1 mgal), respectively. At an altitude of 350 km, the results are 0.07 and 0.025 mm.square second (7 and 2.5 mgal), respectively. These results assume a rotating type gradiometer with a 0.1 -etvos unit accuracy. The results can readily be scaled to reflect another accuracy level
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