3,298 research outputs found
Truly On-The-Fly LTL Model Checking
We propose a novel algorithm for automata-based LTL model checking that
interleaves the construction of the generalized B\"{u}chi automaton for the
negation of the formula and the emptiness check. Our algorithm first converts
the LTL formula into a linear weak alternating automaton; configurations of the
alternating automaton correspond to the locations of a generalized B\"{u}chi
automaton, and a variant of Tarjan's algorithm is used to decide the existence
of an accepting run of the product of the transition system and the automaton.
Because we avoid an explicit construction of the B\"{u}chi automaton, our
approach can yield significant improvements in runtime and memory, for large
LTL formulas. The algorithm has been implemented within the SPIN model checker,
and we present experimental results for some benchmark examples
BERT WEAVER: Using WEight AVERaging to enable lifelong learning for transformer-based models in biomedical semantic search engines
Recent developments in transfer learning have boosted the advancements in
natural language processing tasks. The performance is, however, dependent on
high-quality, manually annotated training data. Especially in the biomedical
domain, it has been shown that one training corpus is not enough to learn
generic models that are able to efficiently predict on new data. Therefore, in
order to be used in real world applications state-of-the-art models need the
ability of lifelong learning to improve performance as soon as new data are
available - without the need of re-training the whole model from scratch. We
present WEAVER, a simple, yet efficient post-processing method that infuses old
knowledge into the new model, thereby reducing catastrophic forgetting. We show
that applying WEAVER in a sequential manner results in similar word embedding
distributions as doing a combined training on all data at once, while being
computationally more efficient. Because there is no need of data sharing, the
presented method is also easily applicable to federated learning settings and
can for example be beneficial for the mining of electronic health records from
different clinics
Chandra X-ray Observations of Galaxies in an Off-Center Region of the Coma Cluster
We have performed a pilot Chandra survey of an off-center region of the Coma
cluster to explore the X-ray properties and Luminosity Function of normal
galaxies. We present results on 13 Chandra-detected galaxies with optical
photometric matches, including four spectroscopically-confirmed Coma-member
galaxies. All seven spectroscopically confirmed giant Coma galaxies in this
field have detections or limits consistent with low X-ray to optical flux
ratios (fX/fR < 10^-3). We do not have sufficient numbers of X-ray detected
galaxies to directly measure the galaxy X-ray Luminosity Function (XLF).
However, since we have a well-measured optical LF, we take this low X-ray to
optical flux ratio for the 7 spectroscopically confirmed galaxies to translate
the optical LF to an XLF. We find good agreement with Finoguenov et al. (2004),
indicating that the X-ray emission per unit optical flux per galaxy is
suppressed in clusters of galaxies, but extends this work to a specific
off-center environment in the Coma cluster. Finally, we report the discovery of
a region of diffuse X-ray flux which might correspond to a small group
interacting with the Coma Intra-Cluster Medium (ICM).Comment: Accepted for publication in the Astrophysical Journa
Reservoir Memory Machines as Neural Computers
Differentiable neural computers extend artificial neural networks with an
explicit memory without interference, thus enabling the model to perform
classic computation tasks such as graph traversal. However, such models are
difficult to train, requiring long training times and large datasets. In this
work, we achieve some of the computational capabilities of differentiable
neural computers with a model that can be trained very efficiently, namely an
echo state network with an explicit memory without interference. This extension
enables echo state networks to recognize all regular languages, including those
that contractive echo state networks provably can not recognize. Further, we
demonstrate experimentally that our model performs comparably to its
fully-trained deep version on several typical benchmark tasks for
differentiable neural computers.Comment: In print at the special issue 'New Frontiers in Extremely Efficient
Reservoir Computing' of IEEE TNNL
Band gap engineering by Bi intercalation of graphene on Ir(111)
We report on the structural and electronic properties of a single bismuth
layer intercalated underneath a graphene layer grown on an Ir(111) single
crystal. Scanning tunneling microscopy (STM) reveals a hexagonal surface
structure and a dislocation network upon Bi intercalation, which we attribute
to a Bi structure on the underlying Ir(111)
surface. Ab-initio calculations show that this Bi structure is the most
energetically favorable, and also illustrate that STM measurements are most
sensitive to C atoms in close proximity to intercalated Bi atoms. Additionally,
Bi intercalation induces a band gap (eV) at the Dirac point of
graphene and an overall n-doping (eV), as seen in angular-resolved
photoemission spectroscopy. We attribute the emergence of the band gap to the
dislocation network which forms favorably along certain parts of the moir\'e
structure induced by the graphene/Ir(111) interface.Comment: 5 figure
Olig2 regulates Sox10 expression in oligodendrocyte precursors through an evolutionary conserved distal enhancer
The HMG-domain transcription factor Sox10 is expressed throughout oligodendrocyte development and is an important component of the transcriptional regulatory network in these myelin-forming CNS glia. Of the known Sox10 regulatory regions, only the evolutionary conserved U2 enhancer in the distal 5′-flank of the Sox10 gene exhibits oligodendroglial activity. We found that U2 was active in oligodendrocyte precursors, but not in mature oligodendrocytes. U2 activity also did not mediate the initial Sox10 induction after specification arguing that Sox10 expression during oligodendroglial development depends on the activity of multiple regulatory regions. The oligodendroglial bHLH transcription factor Olig2, but not the closely related Olig1 efficiently activated the U2 enhancer. Olig2 bound U2 directly at several sites including a highly conserved one in the U2 core. Inactivation of this site abolished the oligodendroglial activity of U2 in vivo. In contrast to Olig2, the homeodomain transcription factor Nkx6.2 repressed U2 activity. Repression may involve recruitment of Nkx6.2 to U2 and inactivation of Olig2 and other activators by protein–protein interactions. Considering the selective expression of Nkx6.2 at the time of specification and in differentiated oligodendrocytes, Nkx6.2 may be involved in limiting U2 activity to the precursor stage during oligodendrocyte development
Batch and median neural gas
Neural Gas (NG) constitutes a very robust clustering algorithm given
euclidian data which does not suffer from the problem of local minima like
simple vector quantization, or topological restrictions like the
self-organizing map. Based on the cost function of NG, we introduce a batch
variant of NG which shows much faster convergence and which can be interpreted
as an optimization of the cost function by the Newton method. This formulation
has the additional benefit that, based on the notion of the generalized median
in analogy to Median SOM, a variant for non-vectorial proximity data can be
introduced. We prove convergence of batch and median versions of NG, SOM, and
k-means in a unified formulation, and we investigate the behavior of the
algorithms in several experiments.Comment: In Special Issue after WSOM 05 Conference, 5-8 september, 2005, Pari
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