1,016 research outputs found
Reparameterized Variational Rejection Sampling
Traditional approaches to variational inference rely on parametric families
of variational distributions, with the choice of family playing a critical role
in determining the accuracy of the resulting posterior approximation. Simple
mean-field families often lead to poor approximations, while rich families of
distributions like normalizing flows can be difficult to optimize and usually
do not incorporate the known structure of the target distribution due to their
black-box nature. To expand the space of flexible variational families, we
revisit Variational Rejection Sampling (VRS) [Grover et al., 2018], which
combines a parametric proposal distribution with rejection sampling to define a
rich non-parametric family of distributions that explicitly utilizes the known
target distribution. By introducing a low-variance reparameterized gradient
estimator for the parameters of the proposal distribution, we make VRS an
attractive inference strategy for models with continuous latent variables. We
argue theoretically and demonstrate empirically that the resulting
method--Reparameterized Variational Rejection Sampling (RVRS)--offers an
attractive trade-off between computational cost and inference fidelity. In
experiments we show that our method performs well in practice and that it is
well-suited for black-box inference, especially for models with local latent
variables.Comment: 26 pages & 10 figure
On Uncertainty Calibration and Selective Generation in Probabilistic Neural Summarization: A Benchmark Study
Modern deep models for summarization attains impressive benchmark
performance, but they are prone to generating miscalibrated predictive
uncertainty. This means that they assign high confidence to low-quality
predictions, leading to compromised reliability and trustworthiness in
real-world applications. Probabilistic deep learning methods are common
solutions to the miscalibration problem. However, their relative effectiveness
in complex autoregressive summarization tasks are not well-understood. In this
work, we thoroughly investigate different state-of-the-art probabilistic
methods' effectiveness in improving the uncertainty quality of the neural
summarization models, across three large-scale benchmarks with varying
difficulty. We show that the probabilistic methods consistently improve the
model's generation and uncertainty quality, leading to improved selective
generation performance (i.e., abstaining from low-quality summaries) in
practice. We also reveal notable failure patterns of probabilistic methods
widely-adopted in NLP community (e.g., Deep Ensemble and Monte Carlo Dropout),
cautioning the importance of choosing appropriate method for the data setting
The Effect of ENSO on Hydrological Structure and Environment in the South Central Coast – Vietnam
ENSO (El Niño-Southern Oscillation) phenomena have impacted on the hydrodynamic regime and environmental factors of the tropical ocean in general. In case of Vietnamese South-Central Waters, impacts of ENSO only focused on issues of changing seasonal wind, seawater temperature anomalies, changing of water masses as the air-sea interaction. Based on several data sets collecting in the period of 2003-2017, new finding of seawater temperature, salinity and environmental factors was identified in the water masses of Vietnamese South-Central Waters. The highest salinity was 35.4 ‰. During the El Nino event, increasing water temperature and salinity caused to move the deeper water masses to be closer to the sea surface than that initial depth in the neutral period. During the La Nina event, the temperature of most water masses reduced by 0.1-3°C, and then these water masses could be affected to the deeper layer. During the phase from strong ENSO event towards the neutral time, nutrient salts of the 4 water masses were lower concentration in the neutral year, causing the lack of phosphorus in sea surface water masses
Solution structures of all parallel-stranded monomeric and dimeric G-quadruplex scaffolds of the human c-kit2 promoter
Previous studies have demonstrated that nuclease hypersensitivity regions of several proto-oncogenic DNA promoters, situated upstream of transcription start sites, contain guanine-rich tracts that form intramolecular G-quadruplexes stabilized by stacked G•G•G•G tetrads in monovalent cation solution. The human c-kit oncogenic promoter, an important target in the treatment of gastrointestinal tumors, contains two such stretches of guanine-rich tracts, designated c-kit1 and c-kit2. Our previous nuclear magnetic resonance (NMR)-based studies reported on the novel G-quadruplex scaffold of the c-kit1 promoter in K+-containing solution, where we showed for the first time that even an isolated guanine was involved in G-tetrad formation. These NMR-based studies are now extended to the c-kit2 promoter, which adopts two distinct all-parallel-stranded conformations in slow exchange, one of which forms a monomeric G-quadruplex (form-I) in 20 mM K+-containing solution and the other a novel dimeric G-quadruplex (form-II) in 100 mM K+-containing solution. The c-kit2 promoter dimeric form-II G-quadruplex adopts an unprecedented all-parallel-stranded topology where individual c-kit2 promoter strands span a pair of three-G-tetrad-layer-containing all-parallel-stranded G-quadruplexes aligned in a 3′ to 5′-end orientation, with stacking continuity between G-quadruplexes mediated by a sandwiched A•A non-canonical pair. We propose that strand exchange during recombination events within guanine-rich segments, could potentially be mediated by a synapsis intermediate involving an intergenic parallel-stranded dimeric G-quadruplex
Rapid onset of collectivity in the vicinity of 78Ni
gamma-rays following the B and B-n decay of the very neutron rich 84Ga
produced by photo-fission of 238U have been studied at the newly built ISOL
facility of IPN Orsay: ALTO. Two activities were observed and assigned to two
B-decaying states: 84gGa, I = (0\^-) and 84mGa, I = (3\^-, 4\^-). Excitation
energies of the 2+1 and 4+1 excited states of 84Ge were measured at E(2+1) =
624.3 keV and E(4+1) = 1670.1 keV. Comparison with HFB+GCM calculations allows
to establish the collective character of this nucleus indicating a substantial
N=50 core polarization. The excitation energy of the 1/2+1 state in 83Ga known
to carry a large part of the neutron 3s1/2 strength was measured at 247.8keV.
Altogether these data allow to confirm the new single particle state ordering
which appears immediately after the double Z=28 and N=50 shell closure and to
designate 78Ni as a fragile and easily polarized doubly-magic core.Comment: 4 pages, ReVTe
PSSA- INTERNATIONAL SOLUTION TO PROTECT THE BIODIVERSITY IN HA LONG BAY - CAT BA MARINE AREA
A Particularly Sensitive Sea Area (PSSA) is an important management tool for biodiversity protection of a marine area. At the time of designation of a Particularly Sensitive Sea Area, an associated protective measure, which meets the requirements of the appropriate legal instrument establishing such measure, must have been approved or adopted by IMO to prevent, reduce, or eliminate the threat or identified vulnerability. Information on each of the Particularly Sensitive Sea Areas (PSSAs) that has been designated by IMO is available on the nautical chart. The Vietnam’s coastal zones and islands are the isolated oceanic habitat of extremely rich marine life in very good condition which is important to the maintenance and dispersal of the marine life of the western tropical Pacific. Vietnam coastal areas are very high risk areas affected by maritime activities, particularly international shipping, therefore in the future identification of some Particularly Sensitive Sea Areas (PSSAs) is necessary. The first Particularly Sensitive Sea Area for Vietnam in Ha Long - Cat Ba was initially proposed in this paper
Simple top-down preparation of magnetic BiGdFeTiO nanoparticles by ultrasonication of multiferroic bulk material
We present a simple technique to synthesize ultrafine nanoparticles directly
from bulk multiferroic perovskite powder. The starting materials, which were
ceramic pellets of the nominal compositions of
BiGdFeTiO (x = 0.00-0.20), were prepared
initially by a solid state reaction technique, then ground into
micrometer-sized powders and mixed with isopropanol or water in an ultrasonic
bath. The particle size was studied as a function of sonication time with
transmission electron microscopic imaging and electron diffraction that
confirmed the formation of a large fraction of single-crystalline nanoparticles
with a mean size of 11-13 nm. A significant improvement in the magnetic
behavior of BiGdFeTiO nanoparticles compared to
their bulk counterparts was observed at room temperature. This sonication
technique may be considered as a simple and promising route to prepare
ultrafine nanoparticles for functional applications.Comment: 7 pages, 5 figure
A thermodynamic overview of naturally occurring intramolecular DNA quadruplexes
Loop length and its composition are important for the structural and functional versatility of quadruplexes. To date studies on the loops have mainly concerned model sequences compared with naturally occurring quadruplex sequences which have diverse loop lengths and compositions. Herein, we have characterized 36 quadruplex-forming sequences from the promoter regions of various proto-oncogenes using CD, UV and native gel electrophoresis. We examined folding topologies and determined the thermodynamic profile for quadruplexes varying in total loop length (5–18 bases) and composition. We found that naturally occurring quadruplexes have variable thermodynamic stabilities (ΔG37) ranging from −1.7 to −15.6 kcal/mol. Overall, our results suggest that both loop length and its composition affect quadruplex structure and thermodynamics, thus making it difficult to draw generalized correlations between loop length and thermodynamic stability. Additionally, we compared the thermodynamic stability of quadruplexes and their respective duplexes to understand quadruplex–duplex competition. Our findings invoke a discussion on whether biological function is associated with quadruplexes with lower thermodynamic stability which undergo facile formation and disruption, or by quadruplexes with high thermodynamic stability
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