Search

We present high-spatial-resolution (0.7 to 1.0 arcsec) submillimeter observations of continuum and molecular lines of CH3OCHO, CH3OCH3, and H2CCO toward 11 high-mass star-forming regions using the Atacama Large Millimetre/submillimetre Array (ALMA). A total of 19 separate cores from 9 high-mass star-forming regions are found to be line-rich, including high-, intermediate-, and low-mass line-rich cores. The three molecules are detected in these line-rich cores. We map the emission of CH3OCHO, CH3OCH3, and H2CCO in 9 high-mass star-forming regions. The spatial distribution of the three molecules is very similar and concentrated in the areas of intense continuum emission. We also calculate the rotation temperatures, column densities, and abundances of CH3OCHO, CH3OCH3, and H2CCO under the local thermodynamic equilibrium (LTE) assumption. The abundances relative to H2 and CH3OH, and line widths of the three molecules are significantly correlated. The abundances relative to H2, temperatures and line widths of the three molecules tend to be higher in cores with higher mass and outflows detected. The possible chemical links of the three molecules are discussed., Comment: 35 pages, 9 figures

We used the Five-hundred-meter Aperture Spherical radio Telescope (FAST) to search for the molecular emissions in the L-band between 1.0 and 1.5 GHz toward four comets, C/2020 F3 (NEOWISE), C/2020 R4 (ATLAS), C/2021 A1 (Leonard), and 67P/Churyumov-Gerasimenko during or after their perihelion passages. Thousands of molecular transition lines fall in this low-frequency range, many attributed to complex organic or prebiotic molecules. We conducted a blind search for the possible molecular lines in this frequency range in those comets and could not identify clear signals of molecular emissions in the data. Although several molecules have been detected at high frequencies of great than 100 GHz in comets, our results confirm that it is challenging to detect molecular transitions in the L-band frequency ranges. The non-detection of L-band molecular lines in the cometary environment could rule out the possibility of unusually strong lines, which could be caused by the masers or non-LTE effects. Although the line strengths are predicted to be weak, for FAST, using the ultra-wide bandwidth receiver and improving the radio frequency interference environments would enhance the detectability of those molecular transitions at low frequencies in the future., Comment: 14 pages, 6 figures, 6 tables, accepted for publication in RAA

Aminoacetonitrile (AAN), also known as glycinenitrile, has been suggested as a possible precursor of glycine and adenine in the interstellar medium. Here we present the chemical modeling of AAN and its isomers in hot cores using the three-phase chemical model NAUTILUS with the addition of over 300 chemical reactions of the three AAN isomers and related species. Our models predicted a peak gas phase abundance of AAN reaching the order of 10-8, which is consistent with observation towards Sgr B2(N). Regarding the reaction pathways of AAN and its isomers, we found that AAN is primarily formed via free radical reactions on grain surfaces during the early evolutionary stages. Subsequently, it is thermally desorbed into the gas phase as the temperature rises and is then destroyed by positive ions and radicals in gas phase. The isomers of AAN are formed through the hydrogenation reaction of CH3NCN on the grain surface and via electron recombination reactions of ion C2H5N2+ in gas phase. We speculate that there is a possibility for NCCN and AAN to react with each other, eventually leading to the formation of adenine in hot cores. However, further investigation is required to understand the efficiency of grain surfaces in adenine formation, through theoretical calculations or laboratory experiments in future research., Comment: 15 pages,8 figures,5 tables,accepted for publication in MNRAS

Spatial optimal responses to both inlet disturbances and harmonic external forcing for hypersonic flows over a blunt cone at nonzero angles of attack are obtained by efficiently solving the direct-adjoint equations with a parabolic approach. In either case, the most amplified disturbances initially take the form of localized streamwise vortices on the windward side and will undergo a two-stage evolution process when propagating downstream: they first experience a substantial algebraic growth by exploiting the Orr and lift-up mechanisms, and then smoothly transition to a quasi exponential-growth stage driven by the crossflow-instability mechanism, accompanied by an azimuthal advection of the disturbance structure towards the leeward side. The algebraic-growth phase is most receptive to the external forcing, whereas the exponential-growth stage relies on the disturbance frequency and can be significantly strengthened by increasing the angle of attack. The wavemaker delineating the structural sensitivity region for the optimal gain is shown to lie on the windward side immediately downstream of the inlet, implying a potent control strategy. Additionally, considerable non-modal growth is also observed for broadband high-frequency disturbances residing in the entropy layer.

Aromatic molecules represent fundamental building blocks in prebiotic chemistry and are contemplated as vital precursors to DNA and RNA nitrogen bases. However, despite the identification of some 300 molecules in extraterrestrial environments, the pathways to pyridine (C5H5N), pyridinyl (C5H4N), and (iso)quinoline (C9H7N) the simplest representative of mono and bicyclic aromatic molecule carrying nitrogen are elusive. Here, we afford compelling evidence on the gas phase formation of methylene amidogen (H2CN) and cyanomethyl (H2CCN) radicals via molecular beam studies and electronic structure calculations. The modeling of the chemistries of Taurus Molecular Cloud (TMC 1) and Titans atmosphere contemplates a complex chain of reactions synthesizing pyridine, pyridinyl, and (iso)quinoline from H2CN and H2CCN at levels of up to 75%. This study affords unique entry points to precursors of DNA and RNA nitrogen bases in hydrocarbon rich extraterrestrial environments thus changing the way we think about the origin of prebiotic molecules in our Galaxy., Comment: Main paper and supplementary information file

Sulfur chemistry in the formation process of low-mass stars and planets remains poorly understood. The protoplanetary disks (PPDs) are the birthplace of planets and its distinctive environment provides an intriguing platform for investigating models of sulfur chemistry. We analyzed the ALMA observations of CS 7-6 transitions in the HD 163296 disk and perform astrochemical modeling to explore its sulfur chemistry. We simulated the distribution of sulfur-containing molecules and compared it with observationally deduced fractional column densities. We have found that the simulated column density of CS is consistent with the observationally deduced fractional column densities, while the simulated column density of C$_2$S is lower than the observationally deduced upper limits on column densities. This results indicate that we have a good understanding of the chemical properties of CS and C$_2$S in the disk. We also investigated the influence of the C/O ratio on sulfur-containing molecules and found that the column densities of SO, SO$_2$, and H$_2$S near the central star are dependent on the C/O ratio. Additionally, we found that the $N$[CS]/$N$[SO] ratio can serve as a promising indicator of the disk's C/O ratio in the HD 163296. Overall, the disk of HD 163296 provides a favorable environment for the detection of sulfur-containing molecules., Comment: 16 pages, 7 figures

We present an unbiased $\lambda$ 3 mm spectral line survey (between 84.5 and 115.8 GHz), conducted by the Purple Mountain Observatory 13.7 meter radio telescope, together with updated modeling results, towards the carbon-rich Asymptotic Giant Branch star, IRC+10216 (CW Leo). A total of 75 spectral lines (96 transitions) are detected, and identified to arise from 19 molecules: C$_2$H, $l$-C$_3$H, C$_4$H, CN, C$_3$N, HC$_3$N, HC$_5$N, HCN, HNC, CH$_3$CN, MgNC, CO, $c$-C$_3$H$_2$, SiC$_2$, SiO, SiS, CS, C$_2$S, C$_3$S, and their isotopologues. Among them, one molecular emission line (H$^{13}$CCCN $J=13-12$) is discovered in IRC+10216 for the first time. The excitation temperature, column density, and fractional abundance of the detected species are deduced by assuming they are in local thermodynamic equilibrium. In addition, the isotopic ratios of [$^{12}$C]/[$^{13}$C], [$^{32}$S]/[$^{34}$S], [$^{28}$Si]/[$^{29}$Si], and [$^{12}$C$^{34}$S]/[$^{13}$C$^{32}$S] are obtained and found to be consistent with previous studies. Finally, we summarize all of the 106 species detected in IRC+10216 to date with their observed and modeled column densities for the convenience of future studies., Comment: 71 pages, 39 figures, 10 tables. Accepted for publication in ApJS

Organic features lead to two distinct types of Class 0/I low-mass protostars: hot corino sources, and warm carbon-chain chemistry (WCCC) sources. Some observations suggest that the chemical variations between WCCC sources and hot corino sources are associated with local environments, as well as the luminosity of protostars. We conducted gas-grain chemical simulation in collapsing protostellar cores, and found that the fiducial model predicts abundant carbon-chain molecules and COMs, and reproduces WCCC and hot corino chemistry in the hybrid source L483. By changing values of some physical parameters, including the visual extinction of ambient clouds ($A_{\rm V}^{\rm amb}$), the cosmic-ray ionization rate ($\zeta$), the maximum temperature during the warm-up phase ($T_{\rm max}$), and the contraction timescale of protostars ($t_{\rm cont}$), we found that UV photons and cosmic rays can boost WCCC features by accelerating the dissociation of CO and CH$_4$ molecules. On the other hand, UV photons can weaken the hot corino chemistry by photodissociation reactions, while the dependence of hot corino chemistry on cosmic rays is relatively complex. The $T_{\rm max}$ does not affect WCCC features, while it can influence hot corino chemistry by changing the effective duration of two-body surface reactions for most COMs. The long $t_{\rm cont}$ can boost WCCC and hot corino chemistry, by prolonging the effective duration of WCCC reactions in the gas phase and surface formation reactions for COMs, respectively. Subsequently, we ran a model with different physical parameters to reproduce scarce COMs in prototypical WCCC sources. The scarcity of COMs in prototypical WCCC sources can be explained by insufficient dust temperature in the inner envelopes to activate hot corino chemistry. Meanwhile, the High $\zeta$ and the long $t_{\rm cont}$ favors the explanation for scarce COMs in these sources., Comment: Accepted for publication in A&A, 18 pages, 10 figures

We present ALMA sub-arcsecond-resolution observations of both continuum and molecular lines at 345 GHz towards the massive star-forming region IRAS 16351-4722 (hereafter I16351). A total of 12 dust cores were detected based on high spatial resolution observations of the continuum. Among them, a high-mass core (11.6 Msun) and a low-mass core (1.7 Msun) show abundant molecular line emissions. 164 molecular transitions from 29 species and 104 molecular transitions from 25 species are identified in the high-mass and low-mass cores, respectively. Complex organic molecules (COMs) such as CH3OH, CH3OCHO, CH3OCH3, C2H5OH, and C2H5CN are detected in the two cores. Under the assumption of local thermodynamic equilibrium (LTE), rotational temperatures and column densities of the COMs are derived with the XCLASS software. The maximum rotation temperature values in the low-mass core and the high-mass core were found to be approximately 130 K and 198 K, respectively. Additionally, the line widths in the high-mass core are larger than those in the low-mass one. Abundant complex organic molecular line transitions, high gas temperatures, and smaller line widths indicate the presence of a low-mass line-rich core in the massive star formation region for the first time, while the high-mass line-rich core shows hot core property. When comparing the molecular abundances of CH3OH, CH3OCHO, CH3OCH3 and C2H5OH of the two cores with other hot cores and hot corinos reported in the literature, we further confirm that both a hot core and a low-mass line-rich core are simultaneously detected in I16351., Comment: 22 pages, 5 figures, 5 tables, 70 references, accepted by ApJ

Fullerenes, including C60, C70, and C60+, are widespread in space through their characteristic infrared vibrational features (C60+ also reveals its presence in the interstellar medium through its electronic transitions) and offer great insights into the carbon chemistry and stellar evolution. The potential existence of fullerene-related species in space has long been speculated and recently put forward by a set of laboratory experiments of C60+, C60H+, C60O+, C60OH+, C70H+, and [C60-Metal]+ complexes. The advent of the James Webb Space Telescope (JWST) provides a unique opportunity to search for these fullerene-related species in space. To facilitate JWST search, analysis, and interpretation, an accurate knowledge of their vibrational properties is essential. Here, we compile a VibFullerene database and conduct a systematic theoretical study on those species. We derive a set of range-specific scaling factors for vibrational frequencies, to account for the deficiency of density functional theory calculations in predicting the accurate frequencies. Scaling factors with low root-mean-square and median errors for the frequencies are obtained, and their performance is evaluated, from which the best-performing methods are recommended for calculating the infrared spectra of fullerene derivatives which balance the accuracy and computational cost. Finally, the recommended vibrational frequencies and intensities of fullerene derivatives are presented for future JWST detection., Comment: 19 pages, 8 figures, 5 tables. Accepted for publication in MNRAS

Whether SiC$_2$ is a parent species, that is formed in the photosphere or as a by-product of high-temperature dust formation, or a daughter species, formed in a chemistry driven by the photodestruction of parent species in the outer envelope, has been debated for a long time. Here, we analyze the ALMA observations of four SiC$_2$ transitions in the CSEs of three C-rich AGB stars (AI Vol, II Lup, and RAFGL 4211), and found that SiC$_2$ exhibits an annular, shell-like distribution in these targets, suggesting that SiC$_2$ can be a daughter species in the CSEs of carbon-rich AGB stars. The results can provide important references for future chemical models., Comment: Accepted in Frontiers in Astronomy and Space Sciences

Large language models have exhibited exceptional performance on various Natural Language Processing (NLP) tasks, leveraging techniques such as the pre-training, and instruction fine-tuning. Despite these advances, their effectiveness in medical applications is limited, due to challenges such as factual inaccuracies, reasoning abilities, and lack grounding in real-world experience. In this study, we present ClinicalGPT, a language model explicitly designed and optimized for clinical scenarios. By incorporating extensive and diverse real-world data, such as medical records, domain-specific knowledge, and multi-round dialogue consultations in the training process, ClinicalGPT is better prepared to handle multiple clinical task. Furthermore, we introduce a comprehensive evaluation framework that includes medical knowledge question-answering, medical exams, patient consultations, and diagnostic analysis of medical records. Our results demonstrate that ClinicalGPT significantly outperforms other models in these tasks, highlighting the effectiveness of our approach in adapting large language models to the critical domain of healthcare.

Dendritic microstructures are frequently observed in as-solidified refractory high-entropy alloys (RHEAs), and their homogenization typically requires a long-term heat treatment at extremely high temperatures. High-pressure torsion (HPT) has been shown to be capable of mixing immiscible systems at room temperature, and therefore represents a promising technique for homogenizing dendritic RHEAs. In this work, the as-solidified RHEA MoNbTaTiVZr was processed up to 40 revolutions by HPT. It was found that the dendritic microstructure was eliminated, resulting in a chemical homogeneity at a von Mises equivalent shear strain of about 400. The study of deformation mechanism showed an initial strain localization, followed by a co-deformation of the dendritic and interdendritic regions. In the co-deformation step, the Zr-rich interdendritic region gradually disappeared. The deformation-induced mixing also led to the formation of an ultra-fine grained (UFG) microstructure, exhibiting a grain size of approximately 50 nm. The microhardness increased from 500 HV in the as-solidified to 675 HV in the homogenized UFG state. The underlying mechanisms responsible for the microhardness enhancement, such as grain refinement and solid solution strengthening, were also discussed.

We investigated the chemical evolutions of gas phase and grain surface species across the Taurus molecular cloud-1 (TMC-1) filament from translucent phase to dense phase. By comparing observations with modeling results from an up-to-date chemical network, we examined the conversion processes for the carbon-, oxygen-, nitrogen- and sulfur-bearing species, i.e.from their initial atomic form to their main molecular reservoir form both in the gas phase and on the grain surface. The conversion processes were found to depend on the species and A$_V$. The effect of initial carbon to oxygen elemental abundances ratio (C/O) by varying O on the chemistry was explored, and an initial carbon elemental abundance of 2.5 $\times$ 10$^{-4}$ and a C/O ratio of 0.5 could best reproduce the abundances of most observed molecules at TMC-1 CP, where more than 90 molecules have been identified. Based on the TMC-1 condition, we predicted a varied grain ice composition during the evolutions of molecular clouds, with H$_2$O ice as the dominant ice composition at A$_V$ $>$ 4 mag, CO$_2$ ice as the dominant ice composition at A$_V$ $<$ 4 mag, while CO ice severely decreased at A$_V$ around 4--5 mag., Comment: 25 pages, 11 figures, accepted for publication in ApJ

At low temperatures (10 K), hydrogen atoms can diffuse quickly on grain ice mantles and frequently encounter hydrogen molecules, which cover a notable fraction of grain surface. The desorption energy of H atoms on H2 substrates is much less than that on water ice. The H atom encounter desorption mechanism is adopted to study the enhanced desorption of H atoms on H2 substrates. Using a small reaction network, we show that the steady-state surface H abundances predicted by the rate equation model that includes H atom encounter desorption agree reasonably well with the results from the more rigorous microscopic Monte Carlo method. For a full gas-grain model, H atom encounter desorption can reduce surface H abundances. Therefore, if a model adopts the encounter desorption of H atoms, it becomes more difficult for hydrogenation products such as methanol to form, but it is easier for C, O and N atoms to bond with each other on grain surfaces., Comment: 11 pages, 6 figures, Accepted for publication in Research in Astronomy and Astrophysics (RAA)

To study the high-transition dense-gas tracers and their relationships to the star formation of the inner $\sim$ 2 kpc circumnuclear region of NGC253, we present HCN $J=4-3$ and HCO$^+ J=4-3$ maps obtained with the James Clerk Maxwell Telescope (JCMT). With the spatially resolved data, we compute the concentration indices $r_{90}/r_{50}$ for the different tracers. HCN and HCO$^+$ 4-3 emission features tend to be centrally concentrated, which is in contrast to the shallower distribution of CO 1-0 and the stellar component. The dense-gas fraction ($f_\text{dense}$, traced by the velocity-integrated-intensity ratios of HCN/CO and HCO$^+$/CO) and the ratio $R_\text{31}$ (CO 3-2/1-0) decline towards larger galactocentric distances, but increase with higher SFR surface density. The radial variation and the large scatter of $f_\text{dense}$ and $R_\text{31}$ imply distinct physical conditions in different regions of the galactic disc. The relationships of $f_\text{dense}$ versus $\Sigma_\text{stellar}$, and SFE$_\text{dense}$ versus $\Sigma_\text{stellar}$ are explored. SFE$_\text{dense}$ increases with higher $\Sigma_\text{stellar}$ in this galaxy, which is inconsistent with previous work that used HCN 1-0 data. This implies that existing stellar components might have different effects on the high-$J$ HCN and HCO$^+$ than their low-$J$ emission. We also find that SFE$_\text{dense}$ seems to be decreasing with higher $f_\text{dense}$, which is consistent with previous works, and it suggests that the ability of the dense gas to form stars diminishes when the average density of the gas increases. This is expected in a scenario where only the regions with high-density contrast collapse and form stars., Comment: accepted to MNRAS

We describe a new approach for managing aleatoric uncertainty in the Reinforcement Learning (RL) paradigm. Instead of selecting actions according to a single statistic, we propose a distributional method based on the second-order stochastic dominance (SSD) relation. This compares the inherent dispersion of random returns induced by actions, producing a more comprehensive and robust evaluation of the environment's uncertainty. The necessary conditions for SSD require estimators to predict accurate second moments. To accommodate this, we map the distributional RL problem to a Wasserstein gradient flow, treating the distributional Bellman residual as a potential energy functional. We propose a particle-based algorithm for which we prove optimality and convergence. Our experiments characterize the algorithm performance and demonstrate how uncertainty and performance are better balanced using an \textsc{ssd} policy than with other risk measures., Comment: Accepted to the 2020 International Conference on Machine Learning