191 research outputs found
GrOVe: Ownership Verification of Graph Neural Networks using Embeddings
Graph neural networks (GNNs) have emerged as a state-of-the-art approach to
model and draw inferences from large scale graph-structured data in various
application settings such as social networking. The primary goal of a GNN is to
learn an embedding for each graph node in a dataset that encodes both the node
features and the local graph structure around the node. Embeddings generated by
a GNN for a graph node are unique to that GNN. Prior work has shown that GNNs
are prone to model extraction attacks. Model extraction attacks and defenses
have been explored extensively in other non-graph settings. While detecting or
preventing model extraction appears to be difficult, deterring them via
effective ownership verification techniques offer a potential defense. In
non-graph settings, fingerprinting models, or the data used to build them, have
shown to be a promising approach toward ownership verification. We present
GrOVe, a state-of-the-art GNN model fingerprinting scheme that, given a target
model and a suspect model, can reliably determine if the suspect model was
trained independently of the target model or if it is a surrogate of the target
model obtained via model extraction. We show that GrOVe can distinguish between
surrogate and independent models even when the independent model uses the same
training dataset and architecture as the original target model. Using six
benchmark datasets and three model architectures, we show that consistently
achieves low false-positive and false-negative rates. We demonstrate that is
robust against known fingerprint evasion techniques while remaining
computationally efficient.Comment: 11 pages, 5 figure
A supernova remnant coincident with the slow X-ray pulsar AX J1845-0258
We report on Very Large Array observations in the direction of the
recently-discovered slow X-ray pulsar AX J1845-0258. In the resulting images,
we find a 5-arcmin shell of radio emission; the shell is linearly polarized
with a non-thermal spectral index. We class this source as a previously
unidentified, young (< 8000 yr), supernova remnant (SNR), G29.6+0.1, which we
propose is physically associated with AX J1845-0258. The young age of G29.6+0.1
is then consistent with the interpretation that anomalous X-ray pulsars (AXPs)
are isolated, highly magnetized neutron stars ("magnetars"). Three of the six
known AXPs can now be associated with SNRs; we conclude that AXPs are young
(~<10 000 yr) objects, and that they are produced in at least 5% of
core-collapse supernovae.Comment: 4 pages, 1 embedded EPS file, uses emulateapj.sty. Accepted to ApJ
Letter
Optical and Infrared Observations of SGR 1806-20
The soft gamma-ray repeater (SGR) 180620 is associated with the
center-brightened non-thermal nebula G~10.00.3, thought to be a plerion. As
in other plerions, a steady \Xray\ source, AX~1805.72025, has been detected
coincident with the peak of the nebular radio emission. Vasisht et al.\ have
shown that the radio peak has a core-jet appearance, and argue that the core
marks the true position of the SGR. At optical wavelengths, we detect three
objects in the vicinity of the radio core. Only for the star closest to the
core, barely visible in the optical but bright in the infrared (mag.),
the reddening is consistent with the high extinction (mag.) that
has been inferred for AX~1805.72025. From the absence of CO band absorption,
we infer that the spectral type of this star is earlier than late~G/early~K.
The large extinction probably arises in a molecular cloud located at a distance
of 6kpc, which means that the star, just like AX~1805.72025, is in or
behind this cloud. This implies that the star is a supergiant. Since
supergiants are rare, a chance coincidence with the compact radio core is very
unlikely. To our knowledge, there are only three other examples of luminous
stars embedded in non-thermal radio nebulae, SS~433, \mbox{Cir X-1} and
G~70.7+1.2. Given this and the low coincidence probability, we suggest that the
bright star is physically associated with SGR~180620, making it the first
stellar identification of a high-energy transient.Comment: 7 pages, AASTeX (needs LaTeX style files aaspptwo.sty and epsf.sty,
plus PostScript figure). In case of problems, contact [email protected]
Apolipoprotein C3 SstI polymorphism and triglyceride levels in Asian Indians
BACKGROUND: A close association between Sst I polymorphism in the 3' untranslated region of the apolipoproteinC3 (APOC3) gene and levels of plasma triglycerides (TG) had been reported by different investigators. Hypertriglyceridemia(HTG) is a known risk factor for coronary artery disease (CAD) in the context of Asian Indians. We conducted a study on the relationship between APOC3 SstI polymorphism (S1S1, S1S2 and S2S2 genotypes) and plasma TG levels in a group of 139 male healthy volunteers from Northern India. METHODS: DNA samples were analyzed by polymerase chain reaction (PCR) followed by SstI digestion. Digested PCR products were run on 3% agarose gel and visualized by ethidium bromide staining. RESULTS: Rare S2 allele was highly prevalent in our study population (0.313) as compared to the Caucasians (0.00â0.11). The genotypic distribution was in agreement with Hardy-Weinberg equilibrium. S2 allele was almost two times more prevalent in the HTG group (N = 34) as compared to NTG group (N = 105) (p = 0.001). Multiple logistic regression revealed S1S2 individuals had age-adjusted odds ratio of 2.43 (95%CI = 0.99â6.01, p = 0.054) and S2S2 had 9.9 (95%CI = 2.66â37.29, p = 0.0006) for developing HTG in comparison to S1S1 genotype. CONCLUSIONS: Our study shows a significant association between rare S2 allele and HTG in Asian Indians
Early phases of different types of isolated neutron star
Two Galactic isolated strong X-ray pulsars seem to be in the densest
environments compared to other types of Galactic pulsar. X-ray pulsar
J1846-0258 can be in an early phase of anomalous X-ray pulsars and soft gamma
repeaters if its average braking index is ~1.8-2.0. X-ray pulsar J1811-1925
must have a very large average braking index (n~11) if this pulsar was formed
by SN 386AD. This X-ray pulsar can be in an early phase of evolution of the
radio pulsars located in the region P~50-150 ms and \.{P}~10
s/s of the P-\.{P} diagram. X-ray/radio pulsar J0540-69 seems to be evolving in
the direction to the dim isolated thermal neutron star region on the P-\.{P}
diagram. Possible progenitors of different types of neutron star are also
discussed.Comment: to appear in the International Journal of Modern Physics
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