2,668 research outputs found
Robust statistical methods for automated outlier detection
The computational challenge of automating outlier, or blunder point, detection in radio metric data requires the use of nonstandard statistical methods because the outliers have a deleterious effect on standard least squares methods. The particular nonstandard methods most applicable to the task are the robust statistical techniques that have undergone intense development since the 1960s. These new methods are by design more resistant to the effects of outliers than standard methods. Because the topic may be unfamiliar, a brief introduction to the philosophy and methods of robust statistics is presented. Then the application of these methods to the automated outlier detection problem is detailed for some specific examples encountered in practice
Hubble Space Telescope Weak-lensing Study of the Galaxy Cluster XMMU J2235.3-2557 at z=1.4: A Surprisingly Massive Galaxy Cluster when the Universe is One-third of its Current Age
We present a weak-lensing analysis of the z=1.4 galaxy cluster XMMU
J2235.3-2557, based on deep Advanced Camera for Surveys images. Despite the
observational challenge set by the high redshift of the lens, we detect a
substantial lensing signal at the >~ 8 sigma level. This clear detection is
enabled in part by the high mass of the cluster, which is verified by our both
parametric and non-parametric estimation of the cluster mass. Assuming that the
cluster follows a Navarro-Frenk-White mass profile, we estimate that the
projected mass of the cluster within r=1 Mpc is (8.5+-1.7) x 10^14 solar mass,
where the error bar includes the statistical uncertainty of the shear profile,
the effect of possible interloping background structures, the scatter in
concentration parameter, and the error in our estimation of the mean redshift
of the background galaxies. The high X-ray temperature 8.6_{-1.2}^{+1.3} keV of
the cluster recently measured with Chandra is consistent with this high lensing
mass. When we adopt the 1-sigma lower limit as a mass threshold and use the
cosmological parameters favored by the Wilkinson Microwave Anisotropy Probe
5-year (WMAP5) result, the expected number of similarly massive clusters at z
>~ 1.4 in the 11 square degree survey is N ~ 0.005. Therefore, the discovery of
the cluster within the survey volume is a rare event with a probability < 1%,
and may open new scenarios in our current understanding of cluster formation
within the standard cosmological model.Comment: Accepted to ApJ for publication. 40 pages and 14 figure
Querying Streaming System Monitoring Data for Enterprise System Anomaly Detection
The need for countering Advanced Persistent Threat (APT) attacks has led to
the solutions that ubiquitously monitor system activities in each enterprise
host, and perform timely abnormal system behavior detection over the stream of
monitoring data. However, existing stream-based solutions lack explicit
language constructs for expressing anomaly models that capture abnormal system
behaviors, thus facing challenges in incorporating expert knowledge to perform
timely anomaly detection over the large-scale monitoring data. To address these
limitations, we build SAQL, a novel stream-based query system that takes as
input, a real-time event feed aggregated from multiple hosts in an enterprise,
and provides an anomaly query engine that queries the event feed to identify
abnormal behaviors based on the specified anomaly models. SAQL provides a
domain-specific query language, Stream-based Anomaly Query Language (SAQL),
that uniquely integrates critical primitives for expressing major types of
anomaly models. In the demo, we aim to show the complete usage scenario of SAQL
by (1) performing an APT attack in a controlled environment, and (2) using SAQL
to detect the abnormal behaviors in real time by querying the collected stream
of system monitoring data that contains the attack traces. The audience will
have the option to interact with the system and detect the attack footprints in
real time via issuing queries and checking the query results through a
command-line UI.Comment: Accepted paper at ICDE 2020 demonstrations track. arXiv admin note:
text overlap with arXiv:1806.0933
Principal Component Analysis of the Time- and Position-Dependent Point Spread Function of the Advanced Camera for Surveys
We describe the time- and position-dependent point spread function (PSF)
variation of the Wide Field Channel (WFC) of the Advanced Camera for Surveys
(ACS) with the principal component analysis (PCA) technique. The time-dependent
change is caused by the temporal variation of the focus whereas the
position-dependent PSF variation in ACS/WFC at a given focus is mainly the
result of changes in aberrations and charge diffusion across the detector,
which appear as position-dependent changes in elongation of the astigmatic core
and blurring of the PSF, respectively. Using >400 archival images of star
cluster fields, we construct a ACS PSF library covering diverse environments of
the observations (e.g., focus values). We find that interpolation of a
small number () of principal components or ``eigen-PSFs'' per exposure
can robustly reproduce the observed variation of the ellipticity and size of
the PSF. Our primary interest in this investigation is the application of this
PSF library to precision weak-lensing analyses, where accurate knowledge of the
instrument's PSF is crucial. However, the high-fidelity of the model judged
from the nice agreement with observed PSFs suggests that the model is
potentially also useful in other applications such as crowded field stellar
photometry, galaxy profile fitting, AGN studies, etc., which similarly demand a
fair knowledge of the PSFs at objects' locations. Our PSF models, applicable to
any WFC image rectified with the Lanczos3 kernel, are publicly available.Comment: Accepted to PASP. To appear in December issue. Figures are degraded
to meet the size limit. High-resolution version can be downloaded at
http://acs.pha.jhu.edu/~mkjee/acs_psf/acspsf.pd
Fecal microbiota transplantation as an alternative treatment for infection and inflammation
Our intestinal microbiota comprises 100 trillion bacteria, exceeding our own eukaryotic cells. While the microbiota has incredible health benefits, changes in the normal flora caused by inflammation, antibiotics or diet can negatively impact health and may contribute to diseases such as inflammatory bowel disease (IBD) and obesity. Using healthy microbiota to treat individuals with intestinal disease is not a new idea and fecal microbiota transplantation (FMT) has been used as a successful therapy in patients suffering from Clostridium difficile infection. Currently FMT is being considered as a treatment for patients with IBD. This editorial will discuss the history of FMT and implications for treatment of other inflammatory intestinal diseases
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Visualization Tools for Design Support in SFF 437
When considering the use of SFF, there are many questions a designer might ask. What model orientation should be used, will the model have adequate aesthetic and functional properties, is the STL file suitable for transfer to the SFF machine? These questions could be answered by a comprehensive design support system for SFF. This paper addresses a number of components for such a system that can be met through the use of visualization tools. These include: 1. Visualization of surface roughness 2. Visualization of characteristic features (e.g. surface macro-texture) 3. Visual simulation of fabrication Example applications of these tools are presented together with a status review of their implementation to date. It is envisaged that these tools will be incorporated into an already existing network-based preprocessor used for visualization, repair and slicing of STL files. The direction of future work is also discussed which will include the visual representation of functionally graded materials (connected with FEM results).Mechanical Engineerin
A Safety Case Pattern for Model-Based Development Approach
In this paper, a safety case pattern is introduced to facilitate the presentation of a correctness argument for a system implemented using formal methods in the development process. We took advantage of our experience in constructing a safety case for the Patient Controlled Analgesic (PCA) infusion pump, to define this safety case pattern. The proposed pattern is appropriate to be instantiated within the safety cases constructed for systems that are developed by applying model-based approaches
Star Formation Histories in a Cluster Environment at z~0.84
We present a spectrophotometric analysis of galaxies belonging to the
dynamically young, massive cluster RX J0152.7-1357 at z~0.84, aimed at
understanding the effects of the cluster environment on the star formation
history (SFH) of cluster galaxies and the assembly of the red-sequence (RS). We
use VLT/FORS spectroscopy, ACS/WFC optical and NTT/SofI near-IR data to
characterize SFHs as a function of color, luminosity, morphology, stellar mass,
and local environment from a sample of 134 spectroscopic members. In order to
increase the signal-to-noise, individual galaxy spectra are stacked according
to these properties. Moreover, the D4000, Balmer, CN3883, Fe4383 and C4668
indices are also quantified. The SFH analysis shows that galaxies in the blue
faint-end of the RS have on average younger stars (Delta t ~ 2 Gyr) than those
in the red bright-end. We also found, for a given luminosity range, differences
in age (Delta t ~ 0.5 - 1.3 Gyr) as a function of color, indicating that the
intrinsic scatter of the RS may be due to age variations. Passive galaxies in
the blue faint-end of the RS are preferentially located in the low density
areas of the cluster, likely being objects entering the RS from the "blue
cloud". It is likely that the quenching of the star formation of these RS
galaxies is due to interaction with the intracluster medium. Furthermore, the
SFH of galaxies in the RS as a function of stellar mass reveals signatures of
"downsizing" in the overall cluster.Comment: 36 pages, 5 tables, 14 figures. Accepted for publication in The
Astrophysical Journa
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