2,279 research outputs found
Mixed-mode cyclic debonding of adhesively bonded composite joints
A combined experimental-analytical investigation to characterize the cyclic failure mechanism of a simple composite-to-composite bonded joint is conducted. The cracked lap shear (CLS) specimens of graphite/epoxy adherend bonded with EC-3445 adhesive are tested under combined mode 1 and 2 loading. In all specimens tested, fatigue failure occurs in the form of cyclic debonding. The cyclic debond growth rates are measured. The finite element analysis is employed to compute the mode 1, mode 2, and total strain energy release rates (i.e., GI, GII, and GT). A wide range of mixed-mode loading, i.e., GI/GII ranging from 0.03 to 0.38, is obtained. The total strain energy release rate, G sub T, appeared to be the driving parameter for cyclic debonding in the tested composite bonded system
Abundances of Suprathermal Heavy Ions in CIRs during the Minimum of Solar Cycle 23
In this paper we examine the elemental composition of the 0.1-1 MeV/nucleon
interplanetary heavy ions from H to Fe in corotating interaction regions (CIRs)
measured by the SIT (Suprathermal Ion Telescope) instrument. We use
observations taken on board the STEREO spacecraft from January 2007 through
December 2010, which included the unusually long solar minimum following solar
cycle 23. During this period instruments on STEREO observed more than 50 CIR
events making it possible to investigate CIR ion abundances during solar
minimum conditions with unprecedented high statistics. The observations reveal
annual variations of relative ion abundances in the CIRs during the 2007-2008
period as indicated by the He/H, He/O and Fe/O elemental ratios. We discuss
possible causes of the variability in terms of the helium focusing cone passage
and heliolatitude dependence. The year 2009 was very quiet in CIR event
activity. In 2010 the elemental composition in CIRs were influenced by sporadic
solar energetic particle (SEP) events. The 2010 He/H and He/O abundance ratios
in CIRs show large event to event variations with values resembling the
SEP-like composition. This finding points out that the suprathermal SEPs could
be the source population for CIR acceleration.Comment: accepted for publication in Solar Physic
Interaction of mixed mode loading on cyclic debonding in adhesively bonded composite joints
A combined experimental and analytical investigation of an adhesively-bonded composite joint was conducted to characterize the fracture mode dependence of cyclic debonding. The system studied consisted of graphite/epoxy adherends bonded with EC 3445 adhesive. Several types of specimens are tested which provide the cyclic debond growth rate measurements under various load conditions: mode 1, mixed mode 1 to 2, and mostly mode 2. This study shows that the total strain-energy-release rate is the governing factor for cyclic debonding
3He-rich SEP Events Observed by STEREO-A
Using the SIT (Suprathermal Ion Telescope) instrument on STEREO-A we have
examined the abundance of the rare isotope 3He during the rising activity phase
of solar cycle 24 between January 2010 and December 2011. We have identified
six solar energetic particle (SEP) events with enormous abundance enhancements
of 3He (3He/4He >1). The events were short lasting, typically ~0.5-1 day and
most of them occurred in association with high-speed solar wind streams and
corotating interaction regions. With one exception the events were not
associated with ~100 keV solar electron intensity increases. The events showed
also enhanced NeS/O and Fe/O ratios. The solar images indicate that the events
were generally associated with the active regions located near a coronal hole.Comment: accepted for publication in AIP Conference Proceedings for
'Thirteenth International Solar Wind Conference
Multi-Spacecraft Observations of Recurrent 3He-Rich Solar Energetic Particles
We study the origin of 3He-rich solar energetic particles (<1 MeV/nucleon)
that are observed consecutively on STEREO-B, ACE, and STEREO-A spacecraft when
they are separated in heliolongitude by more than 90{\deg}. The 3He-rich period
on STEREO-B and STEREO-A commences on 2011 July 1 and 2011 July 16,
respectively. The ACE 3He-rich period consists of two sub-events starting on
2011 July 7 and 2011 July 9. We associate the STEREO-B July 1 and ACE July 7
3He-rich events with the same sizeable active region producing X-ray flares
accompanied by prompt electron events, when it was near the west solar limb as
seen from the respective spacecraft. The ACE July 9 and STEREO-A July 16 events
were dispersionless with enormous 3He enrichment, lacking solar energetic
electrons and occurring in corotating interaction regions. We associate these
events with a small, recently emerged active region near the border of a
low-latitude coronal hole that produced numerous jet-like emissions temporally
correlated with type III radio bursts. For the first time we present
observations of 1) solar regions with long-lasting conditions for 3He
acceleration and 2) solar energetic 3He that is temporary
confined/re-accelerated in interplanetary space.Comment: accepted for publication in The Astrophysical Journa
Kernel Spectral Clustering and applications
In this chapter we review the main literature related to kernel spectral
clustering (KSC), an approach to clustering cast within a kernel-based
optimization setting. KSC represents a least-squares support vector machine
based formulation of spectral clustering described by a weighted kernel PCA
objective. Just as in the classifier case, the binary clustering model is
expressed by a hyperplane in a high dimensional space induced by a kernel. In
addition, the multi-way clustering can be obtained by combining a set of binary
decision functions via an Error Correcting Output Codes (ECOC) encoding scheme.
Because of its model-based nature, the KSC method encompasses three main steps:
training, validation, testing. In the validation stage model selection is
performed to obtain tuning parameters, like the number of clusters present in
the data. This is a major advantage compared to classical spectral clustering
where the determination of the clustering parameters is unclear and relies on
heuristics. Once a KSC model is trained on a small subset of the entire data,
it is able to generalize well to unseen test points. Beyond the basic
formulation, sparse KSC algorithms based on the Incomplete Cholesky
Decomposition (ICD) and , , Group Lasso regularization are
reviewed. In that respect, we show how it is possible to handle large scale
data. Also, two possible ways to perform hierarchical clustering and a soft
clustering method are presented. Finally, real-world applications such as image
segmentation, power load time-series clustering, document clustering and big
data learning are considered.Comment: chapter contribution to the book "Unsupervised Learning Algorithms
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