440 research outputs found
The Mass Fractionation of Helium in the Escaping Atmosphere of HD 209458b
The absorption signals of metastable He in HD 209458b and several other
exoplanets can be explained via escaping atmosphere model with a subsolar He/H
ratio. The low abundance of helium can be a result of planet formation if there
is a small amount of helium in their primordial atmosphere. However, another
possibility is that the low He/H ratio is caused by the process of mass
fractionation of helium in the atmosphere. In order to investigate the effect
of the fractionation in the hydrogen-helium atmosphere, we developed a
self-consistent multi-fluid 1D hydrodynamic model based on the well-known
open-source MHD code PLUTO. Our simulations show that a lower He/H ratio can be
produced spontaneously in the multi-fluid model. We further modeled the
transmission spectra of He 10830 lines for HD 209458b in a broad parameter
space. The transmission spectrum of the observation can be fitted in the
condition of 1.80 times the X-ray and extreme-ultraviolet flux of the quiet
Sun. Meanwhile, the ratio of the escaping flux of helium to hydrogen,
, is 0.039. Our results indicate that the mass fractionation of
helium to hydrogen can naturally interpret the low He/H ratio required by the
observation. Thus, in the escaping atmosphere of HD 209458b, decreasing the
abundance of helium in the atmosphere is not needed even if its He abundance is
similar to that of the Sun. The simulation presented in this work hints that in
the escaping atmosphere, mass fractionation can also occur on other exoplanets,
which needs to be explored further.Comment: Accepted by Ap
Modeling H and He 10830 transmission spectrum of WASP-52b
Escaping atmosphere has been detected by the excess absorption of Ly,
H and He triplet (10830) lines. Simultaneously modeling the
absorption of the H and He 10830 lines can provide useful constraints
about the exoplanetary atmosphere. In this paper, we use a hydrodynamic model
combined with a non-local thermodynamic model and a new Monte Carlo simulation
model to obtain the H(2) and He(2S) populations. The Monte Carlo
simulations of Ly radiative transfer are performed with assumptions of
a spherical stellar Ly radiation and a spherical planetary atmosphere,
for the first time, to calculate the Ly mean intensity distribution
inside the planetary atmosphere, necessary in estimating the H(2) population.
We model the transmission spectra of the H and He 10830 lines
simultaneously in hot Jupiter WASP-52b. We find that models with many different
H/He ratios can reproduce the H observations well if the host star has
(1) a high X-ray/extreme ultraviolet (XUV) flux () and a
relatively low X-ray fraction in XUV radiation (), or (2) a low
and a high . The simulations of He 10830
triplet suggest that a high H/He ratio ( 98/2) is required to fit the
observation. The models that fit both lines well confine to be
about 0.5 times the fiducial value and to have a value around 0.3.
The models also suggest that hydrogen and helium originate from the escaping
atmosphere, and the mass-loss rate is about 2.8 g s.Comment: Accepted for publication in ApJ, 48 page
Lightweight photovoltaic composite structure on stratospheric airships
A semirigid solar array is an efficient energy system on the surface of stratospheric airships for utilizing the solar energy, which we believe that it has succeeded in providing some impressive results for conceptual design. This paper developed a lightweight photovoltaic composite structure (LPCS) according to the characteristics of the stratospheric airship capsule. In order to improve the flexibility of the solar cell, we studied the mechanical properties in the different thicknesses of the honeycomb core for LPCS by FEM software and three-point bending test, and we also launched experiments to measure the temperature difference between upper and lower surfaces of the LPCS test samples under different solar radiation flux conditions. The experimental data were examined to evaluate the mechanical properties and thermal insulation performances of LPCS. Considering the quality of the whole structure, the paper finally comes up with the conclusion of the optimal thickness of the honeycomb core with further detailed descriptions
Deep Imaging of the HCG 95 Field.I.Ultra-diffuse Galaxies
We present a detection of 89 candidates of ultra-diffuse galaxies (UDGs) in a
4.9 degree field centered on the Hickson Compact Group 95 (HCG 95) using
deep - and -band images taken with the Chinese Near Object Survey
Telescope. This field contains one rich galaxy cluster (Abell 2588 at
=0.199) and two poor clusters (Pegasus I at =0.013 and Pegasus II at
=0.040). The 89 candidates are likely associated with the two poor clusters,
giving about 50 60 true UDGs with a half-light radius kpc
and a central surface brightness mag arcsec. Deep
'-band images are available for 84 of the 89 galaxies from the Dark Energy
Camera Legacy Survey (DECaLS), confirming that these galaxies have an extremely
low central surface brightness. Moreover, our UDG candidates are spread over a
wide range in color, and 26% are as blue as normal star-forming
galaxies, which is suggestive of young UDGs that are still in formation.
Interestingly, we find that one UDG linked with HCG 95 is a gas-rich galaxy
with H I mass detected by the Very Large Array,
and has a stellar mass of . This
indicates that UDGs at least partially overlap with the population of nearly
dark galaxies found in deep H I surveys. Our results show that the high
abundance of blue UDGs in the HCG 95 field is favored by the environment of
poor galaxy clusters residing in H I-rich large-scale structures.Comment: Published in Ap
Nitrogen mass transfer and surface layer formation during the active screen plasma nitriding of austenitic stainless steels
Assessing public perception and willingness to pay for renewable energy in Pakistan through the theory of planned behavior
With growing urbanization and increasing world population, energy demand also increases. A significant portion of the world’s energy comes from fossil fuels, and these sources of energy are declining rapidly at the current consumption rate. There are also growing environmental concerns on the use of fossil fuels increasing greenhouse gas emissions. In this regard, renewable energy (RE) shows promising solutions which are both sustainable and environmentally friendly. Developed countries and leading organizations are investing heavily in the RE sector. However, the developing world has anxieties over social acceptability and people’s willingness to pay for renewable energy. This study is conducted in Pakistan to understand the public perception and willingness to pay. The Theory of Planned Behavior (TPB) was utilized with background factors such as awareness, perceived advantages, perceived challenges, and moral obligations to examine its influence on people’s willingness to pay. In addition to this, the study also assessed the indirect effects of background factors (awareness, perceived advantages, and perceived challenges) on willingness to pay through public attitude. Furthermore, the indirect relationship between background factors (awareness and moral obligation) and willingness to pay through subjective norms was also examined. A total of 512 samples were gathered from participants and were analyzed through partial least square–structural equation modeling (PLS-SEM) and SPSS. The study findings are very interesting and back up our hypotheses that the background factors (awareness, perceived advantages, and perceived challenges) are positively associated with public attitude and have an indirect effect on willingness to pay through public attitude. Similarly, variables such as awareness and moral obligation are negatively and positively associated with subjective norms, respectively. However, the variables, awareness and moral obligation, have no indirect relationship with willingness to pay through subjective norms. Additionally, the study reveals that the components (attitude and perceived behavior control) of TPB have a significantly positive effect on willingness to pay. The study also concludes that the participants having formal education and knowledge about climate change and renewable energy are inclined toward green energy and are willing to pay, and they are hardly influenced by others' opinions. Furthermore, the study also provides insights for policymakers, suggestions, and recommendations for the future
HanoiT: Enhancing Context-aware Translation via Selective Context
Context-aware neural machine translation aims to use the document-level
context to improve translation quality. However, not all words in the context
are helpful. The irrelevant or trivial words may bring some noise and distract
the model from learning the relationship between the current sentence and the
auxiliary context. To mitigate this problem, we propose a novel end-to-end
encoder-decoder model with a layer-wise selection mechanism to sift and refine
the long document context. To verify the effectiveness of our method, extensive
experiments and extra quantitative analysis are conducted on four
document-level machine translation benchmarks. The experimental results
demonstrate that our model significantly outperforms previous models on all
datasets via the soft selection mechanism
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