2,326 research outputs found
Multiplicative LSTM for sequence modelling
We introduce multiplicative LSTM (mLSTM), a recurrent neural network
architecture for sequence modelling that combines the long short-term memory
(LSTM) and multiplicative recurrent neural network architectures. mLSTM is
characterised by its ability to have different recurrent transition functions
for each possible input, which we argue makes it more expressive for
autoregressive density estimation. We demonstrate empirically that mLSTM
outperforms standard LSTM and its deep variants for a range of character level
language modelling tasks. In this version of the paper, we regularise mLSTM to
achieve 1.27 bits/char on text8 and 1.24 bits/char on Hutter Prize. We also
apply a purely byte-level mLSTM on the WikiText-2 dataset to achieve a
character level entropy of 1.26 bits/char, corresponding to a word level
perplexity of 88.8, which is comparable to word level LSTMs regularised in
similar ways on the same task
Evaluation of the capability of the simulated dual energy X-ray absorptiometry-based two-dimensional finite element models for predicting vertebral failure loads
Prediction of the vertebral failure load is of great importance for the prevention and early treatment of bone fracture. However, an efficient and effective method for accurately predicting the failure load of vertebral bones is still lacking. The aim of the present study was to evaluate the capability of the simulated dual energy X-ray absorptiometry (DXA)-based finite element (FE) model for predicting vertebral failure loads. Thirteen dissected spinal segments (T11/T12/L1) were scanned using a HR-pQCT scanner and then were mechanically tested until failure. The subject-specific three-dimensional (3D) and two-dimensional (2D) FE models of T12 were generated from the HR-pQCT scanner and the simulated DXA images, respectively. Additionally, the areal bone mineral density (aBMD) and areal bone mineral content (aBMC) of T12 were calculated. The failure loads predicted by the simulated DXA-based 2D FE models were more moderately correlated with the experimental failure loads (R  = 0.66) than the aBMC (R  = 0.61) and aBMD (R  = 0.56). The 2D FE models were slightly outperformed by the HR-pQCT-based 3D FE models (R  = 0.71). The present study demonstrated that the simulated DXA-based 2D FE model has better capability for predicting the vertebral failure loads than the densitometric measurements but is outperformed by the 3D FE model. The 2D FE model is more suitable for clinical use due to the low radiation dose and low cost, but it remains to be validated by further in vitro and in vivo studies. [Abstract copyright: Copyright © 2019. Published by Elsevier Ltd.
De Sitter Vacua from Heterotic M-Theory
It is shown how metastable de Sitter vacua might arise from heterotic
M-theory. The balancing of its two non-perturbative effects, open membrane
instantons against gaugino condensation on the hidden boundary, which act with
opposing forces on the interval length, is used to stabilize the orbifold
modulus (dilaton) and other moduli. The non-perturbative effects break
supersymmetry spontaneously through F-terms which leads to a positive vacuum
energy density. In contrast to the situation for the weakly coupled heterotic
string, the charged scalar matter fields receive non-vanishing vacuum
expectation values and therefore masses in a phenomenologically relevant
regime. It is important that in order to obtain these de Sitter vacua we are
not relying on exotic effects or fine-tuning of parameters. Vacua with more
realistic supersymmetry breaking scales and gravitino masses are obtained by
breaking the hidden gauge group down to groups of smaller rank. Also
small values for the open membrane instanton Pfaffian are favored in this
respect. Finally we outline how the incorporation of additional flux
superpotentials can be used to stabilize the remaining moduli.Comment: 45 pages, 5 figures, typos correcte
Radio Continuum Jet in NGC 7479
The barred galaxy NGC 7479 hosts a remarkable jet-like radio continuum
feature: bright, 12-kpc long in projection, and hosting an aligned magnetic
field. The degree of polarization is 6%-8% along the jet, and remarkably
constant, which is consistent with helical field models. The radio brightness
of the jet suggests strong interaction with the ISM and hence a location near
the disk plane. We observed NGC 7479 at four wavelengths with the VLA and
Effelsberg radio telescopes. The equipartition strength is 35-40 micro-G for
the total and >10 micro-G for the ordered magnetic field in the jet. The jet
acts as a bright, polarized background. Faraday rotation between 3.5 and 6 cm
and depolarization between 6 and 22 cm can be explained by magneto-ionic gas in
front of the jet, with thermal electron densities of ~0.06 cm**(-3) in the bar
and ~0.03 cm**(-3) outside the bar. The regular magnetic field along the bar
points toward the nucleus on both sides. The regular field in the disk reveals
multiple reversals, probably consisting of field loops stretched by a shearing
gas flow in the bar. The projection of the jet bending in the sky plane is in
the sense opposite to that of the underlying stellar and gaseous spiral
structure. The bending in 3-D is most easily explained as a precessing jet,
with an age less than 10**6 years. Our observations are consistent with very
recent triggering, possibly by a minor merger. NGC 7479 provides a unique
opportunity to study interaction-triggered 15-kpc scale radio jets within a
spiral galaxy.Comment: 18 pages, 21 figures, accepted for publication in the Astrophysical
Journa
M-Theory Inflation from Multi M5-Brane Dynamics
We derive inflation from M-theory on S^1/Z_2 via the non-perturbative
dynamics of N M5-branes. The open membrane instanton interactions between the
M5-branes give rise to exponential potentials which are too steep for inflation
individually but lead to inflation when combined together. The resulting type
of inflation, known as assisted inflation, facilitates considerably the
requirement of having all moduli, except the inflaton, stabilized at the
beginning of inflation. During inflation the distances between the M5-branes,
which correspond to the inflatons, grow until they reach the size of the
S^1/Z_2 orbifold. At this stage the M5-branes will reheat the universe by
dissolving into the boundaries through small instanton transitions. Further
flux and non-perturbative contributions become important at this late stage,
bringing inflation to an end and stabilizing the moduli. We find that with
moderate values for N, one obtains both a sufficient amount of e-foldings and
the right size for the spectral index.Comment: 30 pages, 3 figures; v3: one comment and refs adde
Reducing Annotation Need in Self-Explanatory Models for Lung Nodule Diagnosis
Feature-based self-explanatory methods explain their classification in terms
of human-understandable features. In the medical imaging community, this
semantic matching of clinical knowledge adds significantly to the
trustworthiness of the AI. However, the cost of additional annotation of
features remains a pressing issue. We address this problem by proposing
cRedAnno, a data-/annotation-efficient self-explanatory approach for lung
nodule diagnosis. cRedAnno considerably reduces the annotation need by
introducing self-supervised contrastive learning to alleviate the burden of
learning most parameters from annotation, replacing end-to-end training with
two-stage training. When training with hundreds of nodule samples and only 1%
of their annotations, cRedAnno achieves competitive accuracy in predicting
malignancy, meanwhile significantly surpassing most previous works in
predicting nodule attributes. Visualisation of the learned space further
indicates that the correlation between the clustering of malignancy and nodule
attributes coincides with clinical knowledge. Our complete code is open-source
available: https://github.com/diku-dk/credanno.Comment: 10 pages, 4 figures, 2 table
Simulations of the Origin and Fate of the Galactic Center Cloud G2
We investigate the origin and fate of the recently discovered gas cloud G2
close to the Galactic Center. Our hydrodynamical simulations focussing on the
dynamical evolution of the cloud in combination with currently available
observations favor two scenarios: a Compact Cloud which started around the year
1995 and a Spherical Shell of gas, with an apocenter distance within the
disk(s) of young stars and a radius of a few times the size of the Compact
Cloud. The former is able to explain the detected signal of G2 in the
position-velocity diagram of the Br gamma emission of the year 2008.5 and
2011.5 data. The latter can account for both, G2's signal as well as the
fainter extended tail-like structure G2t seen at larger distances from the
black hole and smaller velocities. In contrast, gas stripped from a compact
cloud by hydrodynamical interactions is not able to explain the location of the
detected G2t emission in the observed position-velocity diagrams. This favors
the Spherical Shell Scenario and might be a severe problem for the Compact
Cloud as well as the so-called Compact Source Scenario. From these first
idealized simulations we expect a roughly constant feeding of the supermassive
black hole through a nozzle-like structure over a long period, starting shortly
after the closest approach in 2013.51 for the Compact Cloud. If the matter
accretes in the hot accretion mode, we do not expect a significant boost of the
current activity of Sgr A* for the Compact Cloud model, but a boost of the
average infrared and X-ray luminosity by roughly a factor of 80 for the
Spherical Shell scenario with order of magnitude variations on a timescale of a
few months. The near-future evolution of the cloud will be a sensitive probe of
the conditions of the gas distribution in the milli-parsec environment of the
massive black hole in the Galactic Center.Comment: 16 pages, 16 figures, accepted by Ap
Yeast Protein Interactome Topology Provides Framework for Coordinated-Functionality
The architecture of the network of protein-protein physical interactions in
Saccharomyces cerevisiae is exposed through the combination of two
complementary theoretical network measures, betweenness centrality and
`Q-modularity'. The yeast interactome is characterized by well-defined
topological modules connected via a small number of inter-module protein
interactions. Should such topological inter-module connections turn out to
constitute a form of functional coordination between the modules, we speculate
that this coordination is occurring typically in a pair-wise fashion, rather
than by way of high-degree hub proteins responsible for coordinating multiple
modules. The unique non-hub-centric hierarchical organization of the
interactome is not reproduced by gene duplication-and-divergence stochastic
growth models that disregard global selective pressures.Comment: Final, revised version. 13 pages. Please see Nucleic Acids open
access article for higher resolution figure
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