Search

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

The 1-indenyl (C9H7•) radical, a prototype aromatic and resonantly stabilized free radical carrying a six- and a five-membered ring, has emerged as a fundamental molecular building block of nonplanar polycyclic aromatic hydrocarbons (PAHs) and carbonaceous nanostructures in deep space and combustion systems. However, the underlying formation mechanisms have remained elusive. Here, we reveal an unconventional low-temperature gas-phase formation of 1-indenyl via barrierless ring annulation involving reactions of atomic carbon [C(3P)] with styrene (C6H5C2H3) and propargyl (C3H3•) with phenyl (C6H5•). Macroscopic environments like molecular clouds act as natural low-temperature laboratories, where rapid molecular mass growth to 1-indenyl and subsequently complex PAHs involving vinyl side-chained aromatics and aryl radicals can occur. These reactions may account for the formation of PAHs and their derivatives in the interstellar medium and carbonaceous chondrites and could close the gap of timescales of their production and destruction in our carbonaceous universe.

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

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

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

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

Investigating the temperature and density structures of gas in massive protoclusters is crucial for understanding the chemical properties therein. In this study, we present observations of the continuum and thioformaldehyde (H2CS) lines at 345 GHz of 11 massive protoclusters using the Atacama Large Millimeter/submillimeter Array (ALMA) telescope. High spatial resolution and sensitivity observations have detected 145 continuum cores from the 11 sources. H2CS line transitions are observed in 72 out of 145 cores, including line-rich cores, warm cores and cold cores. The H2 column densities of the 72 cores are estimated from the continuum emission which are larger than the density threshold value for star formation, suggesting that H2CS can be widely distributed in star-forming cores with different physical environments. Rotation temperature and column density of H2CS are derived by use of the XCLASS software. The results show the H2CS abundances increase as temperature rises and higher gas temperatures are usually associated with higher H2CS column densities. The abundances of H2CS are positively correlated with its column density, suggesting that the H2CS abundances are enhanced from cold cores, warm cores to line-rich cores in star forming regions., Comment: 23 pages, 7 figures, 6 tables, accepted by ApJ

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.

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

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

Manganese nodules are a potential source of critical metals such as Cu, Ni, and Co and are widely distributed on the abyssal plains of the global oceans. A polymetallic nodule metallogenic belt with a heterogeneous and spatially clustered nodule distribution was recently discovered in NW Pacific inter-seamount basin (NPIB) areas. However, the geological processes that regulate the nodule occurrence in that region are unresolved. Here, we report on the characteristics of a high-density field of manganese nodules in the abyssal plain north of Suda Seamount. Ship-borne multibeam bathymetric data reveal a typical seamount sector-collapse topography characterized by radial lineaments of debris channels and ridges formed by rapid debris-avalanche flow. Backscatter data linked with underwater observation indicate that manganese nodules are more concentrated (50%–80% areal coverage) along the main body of the debris apron compared to adjacent neighboring areas (<30%). The extremely high concentrations (~80% areal coverage) characterized by overlapping nodules are apparently associated with downslope movement, possibly triggered by block movement along the fault slip plane or by gravity processes. Our results indicate that seamount sector collapse may have provided sufficient nucleus material for nodule growth and contributed to high nodule concentrations locally. The destruction of submarine volcanic edifices is universal, and the debris aprons and plains around such seamounts are potential prospecting areas for manganese nodule resources throughout the NPIB.

Manganese nodules are a potential source of critical metals such as Cu, Ni, and Co and are widely distributed on the abyssal plains of the global oceans. A polymetallic nodule metallogenic belt with a heterogeneous and spatially clustered nodule distribution was recently discovered in NW Pacific inter-seamount basin (NPIB) areas. However, the geological processes that regulate the nodule occurrence in that region are unresolved. Here, we report on the characteristics of a high-density field of manganese nodules in the abyssal plain north of Suda Seamount. Ship-borne multibeam bathymetric data reveal a typical seamount sector-collapse topography characterized by radial lineaments of debris channels and ridges formed by rapid debris-avalanche flow. Backscatter data linked with underwater observation indicate that manganese nodules are more concentrated (50%–80% areal coverage) along the main body of the debris apron compared to adjacent neighboring areas (<30%). The extremely high concentrations (~80% areal coverage) characterized by overlapping nodules are apparently associated with downslope movement, possibly triggered by block movement along the fault slip plane or by gravity processes. Our results indicate that seamount sector collapse may have provided sufficient nucleus material for nodule growth and contributed to high nodule concentrations locally. The destruction of submarine volcanic edifices is universal, and the debris aprons and plains around such seamounts are potential prospecting areas for manganese nodule resources throughout the NPIB.

To study the high-transition dense-gas tracers and their relationships to the star formation of the inner ∼2 kpc circumnuclear region of NGC 253, we present HCN J = 4−3 and HCO+ J = 4−3 maps obtained with the James Clerk Maxwell Telescope. Using the spatially resolved data, we compute the concentration indices r90/r50 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 (fdense, traced by the velocity-integrated-intensity ratios of HCN/CO and HCO+/CO) and the ratio R31 (CO 3–2/1–0) decline towards larger galactocentric distances, but increase with higher star formation rate surface density. The radial variation and the large scatter of fdense and R31 imply distinct physical conditions in different regions of the galactic disc. The relationships of fdense versus Σstellar, and SFEdense versus Σstellar are explored. SFEdense increases with higher Σstellar 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 SFEdense seems to be decreasing with higher fdense 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.

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

To study the high-transition dense-gas tracers and their relationships to the star formation of the inner similar to 2 kpc circumnuclear region of NGC 253, we present HCN J = 4-3 and HCO+ J = 4-3 maps obtained with the James Clerk Maxwell Telescope. Using 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(dense), traced by v the velocity-integrated-intensity ratios of HCN/CO and HCO+/CO) and the ratio R-31 (CO 3-2 / 1 -0) decline towards larger galactocentric distances, but increase with higher star formation rate surface density. The radial variation and the large scatter of f(dense )- dense and R31 imply distinct physical conditions in different regions of the galactic disc. The relationships of f(dense) versus Sigma(stellar) and SFEdense versus Sigma(stellar) are explored. SFEdense increases with higher Sigma(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(dense )seems to be decreasing with higher f(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.

To study the high-transition dense-gas tracers and their relationships to the star formation of the inner similar to 2 kpc circumnuclear region of NGC 253, we present HCN J = 4-3 and HCO+ J = 4-3 maps obtained with the James Clerk Maxwell Telescope. Using 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(dense), traced by v the velocity-integrated-intensity ratios of HCN/CO and HCO+/CO) and the ratio R-31 (CO 3-2 / 1 -0) decline towards larger galactocentric distances, but increase with higher star formation rate surface density. The radial variation and the large scatter of f(dense )- dense and R31 imply distinct physical conditions in different regions of the galactic disc. The relationships of f(dense) versus Sigma(stellar) and SFEdense versus Sigma(stellar) are explored. SFEdense increases with higher Sigma(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(dense )seems to be decreasing with higher f(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.

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

Complex organosilicon molecules are ubiquitous in the circumstellar envelope of the asymptotic giant branch (AGB) star IRC+10216, but their formation mechanisms have remained largely elusive until now. These processes are of fundamental importance in initiating a chain of chemical reactions leading eventually to the formation of organosilicon molecules-among them key precursors to silicon carbide grains-in the circumstellar shell contributing critically to the galactic carbon and silicon budgets with up to 80% of the ejected materials infused into the interstellar medium. Here we demonstrate via a combined experimental, computational, and modeling study that distinct chemistries in the inner and outer envelope of a carbon star can lead to the synthesis of circumstellar silicon tricarbide (c-SiC3) as observed in the circumstellar envelope of IRC+10216. Bimolecular reactions of electronically excited silicon atoms (Si(1D)) with allene (H2CCCH2) and methylacetylene (CH3CCH) initiate the formation of SiC3H2 molecules in the inner envelope. Driven by the stellar wind to the outer envelope, subsequent photodissociation of the SiC3H2 parent operates the synthesis of the c-SiC3 daughter species via dehydrogenation. The facile route to silicon tricarbide via a single neutral-neutral reaction to a hydrogenated parent molecule followed by photochemical processing of this transient to a bare silicon-carbon molecule presents evidence for a shift in currently accepted views of the circumstellar organosilicon chemistry, and provides an explanation for the previously elusive origin of circumstellar organosilicon molecules that can be synthesized in carbon-rich, circumstellar environments.

Complex organosilicon molecules are ubiquitous in the circumstellar envelope of the asymptotic giant branch (AGB) star IRC+10216, but their formation mechanisms have remained largely elusive until now. These processes are of fundamental importance in initiating a chain of chemical reactions leading eventually to the formation of organosilicon molecules-among them key precursors to silicon carbide grains-in the circumstellar shell contributing critically to the galactic carbon and silicon budgets with up to 80% of the ejected materials infused into the interstellar medium. Here we demonstrate via a combined experimental, computational, and modeling study that distinct chemistries in the inner and outer envelope of a carbon star can lead to the synthesis of circumstellar silicon tricarbide (c-SiC3) as observed in the circumstellar envelope of IRC+10216. Bimolecular reactions of electronically excited silicon atoms (Si(1D)) with allene (H2CCCH2) and methylacetylene (CH3CCH) initiate the formation of SiC3H2 molecules in the inner envelope. Driven by the stellar wind to the outer envelope, subsequent photodissociation of the SiC3H2 parent operates the synthesis of the c-SiC3 daughter species via dehydrogenation. The facile route to silicon tricarbide via a single neutral-neutral reaction to a hydrogenated parent molecule followed by photochemical processing of this transient to a bare silicon-carbon molecule presents evidence for a shift in currently accepted views of the circumstellar organosilicon chemistry, and provides an explanation for the previously elusive origin of circumstellar organosilicon molecules that can be synthesized in carbon-rich, circumstellar environments.

Complex organosilicon molecules are ubiquitous in the circumstellar envelope of the asymptotic giant branch (AGB) star IRC+10216, but their formation mechanisms have remained largely elusive until now. These processes are of fundamental importance in initiating a chain of chemical reactions leading eventually to the formation of organosilicon molecules-among them key precursors to silicon carbide grains-in the circumstellar shell contributing critically to the galactic carbon and silicon budgets with up to 80% of the ejected materials infused into the interstellar medium. Here we demonstrate via a combined experimental, computational, and modeling study that distinct chemistries in the inner and outer envelope of a carbon star can lead to the synthesis of circumstellar silicon tricarbide (c-SiC3) as observed in the circumstellar envelope of IRC+10216. Bimolecular reactions of electronically excited silicon atoms (Si(1D)) with allene (H2CCCH2) and methylacetylene (CH3CCH) initiate the formation of SiC3H2 molecules in the inner envelope. Driven by the stellar wind to the outer envelope, subsequent photodissociation of the SiC3H2 parent operates the synthesis of the c-SiC3 daughter species via dehydrogenation. The facile route to silicon tricarbide via a single neutral-neutral reaction to a hydrogenated parent molecule followed by photochemical processing of this transient to a bare silicon-carbon molecule presents evidence for a shift in currently accepted views of the circumstellar organosilicon chemistry, and provides an explanation for the previously elusive origin of circumstellar organosilicon molecules that can be synthesized in carbon-rich, circumstellar environments.

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

The heat treatment process on ADI consists of austenitization, austempering and quenching to room temperature. Finally, ausferritic microstructure and nodule graphite formed in the ADI material. The parameters austempering time and temperature in the heat treatment process directly affect the morphology of ausferritic structure, which furthermore determine the mechanical properties of the material for industrial applications. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), atom probe tomography (APT) and small angle neutron scattering (SANS) investigations were carried out to quantify the relationship between heat treatment parameters and ausferritic microstructure. At the same time, the process of carbon redistribution during the heat treatment has been explored using in-situ synchrotron diffraction and APT. The retained austenite in ausferrite is metastable and transforms into martensite during plastic deformation in a similar process as has been found in TRIP steels. The evolution of the martensite phase fraction as a function of plastic deformation has been quantitatively determined using Rietveld refinement of neutron diffraction data taking into consideration the influence of texture formation. Finally, the martensite volume fraction as a function of plastic strain could be modelled using an shear-intersection mechanism taking into account the content of alloying elements by directly measuring the corresponding martensite-start temperature Ms of the material., Der Wärmebehandlungsprozess bei ADI besteht aus Austenitisierung, Austempern und abschließender Abschreckung auf Raumtemperatur. Im resultierenden ADI-Material bildet sich eine ausferritische Mikrostruktur mit Kugelgraphit aus. Die unterschiedlichen Prozessparameter wie Austemperzeit und -temperatur während der Wärmebehandlung beeinflussen direkt das Gefüge der ausferritischen Mikrotruktur, und darüber hinaus entscheidend die mechanischen Eigenschaften des Materials für die industrielle Anwendungen. Messungen mit Rasterelektronenmikroskopie (SEM), Transmissionselektronenmikroskopie (TEM), Atomsonden-Tomographie (APT) und Kleinwinkelneutronenstreuung (SANS) wurden durchgeführt, um den Einfluss der Wärmebehandlungsparameter auf die sich ausbildende ausferritischer Mikrostruktur zu quantifizieren. Gleichzeitig wurde die Kohlenstoffumverteilung während des Wärmebehandlungsprozesses mit in-situ-Synchrotrondiffraktion und APT untersucht. Der Restaustenit im Ausferrit ist metastabil und wandelt sich bei plastischer Verformung in Martensit um, wie es ähnlich in TRIP-Stählen gefunden wurde. Der Martensitvolumeanteil als eine Funktion der plastischen Dehnung wurde unter Verwendung der Rietveld-Verfeinerung von Neutronendiffraktionsdaten unter Berücksichtigung der Textur quantitativ untersucht. Schließlich konnte der Martensitvolumenanteil als eine Funktion der plastischen Verformung mit Hilfe eines Scherungsmodells simuliert werden. In diesem Modell wurde der Einfluss von Legierungselementen über die direkt messbare Martensitstarttemperatur Ms des Materials berücksichtigt.

The heat treatment process on ADI consists of austenitization, austempering and quenching to room temperature. Finally, ausferritic microstructure and nodule graphite formed in the ADI material. The parameters austempering time and temperature in the heat treatment process directly affect the morphology of ausferritic structure, which furthermore determine the mechanical properties of the material for industrial applications. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), atom probe tomography (APT) and small angle neutron scattering (SANS) investigations were carried out to quantify the relationship between heat treatment parameters and ausferritic microstructure. At the same time, the process of carbon redistribution during the heat treatment has been explored using in-situ synchrotron diffraction and APT. The retained austenite in ausferrite is metastable and transforms into martensite during plastic deformation in a similar process as has been found in TRIP steels. The evolution of the martensite phase fraction as a function of plastic deformation has been quantitatively determined using Rietveld refinement of neutron diffraction data taking into consideration the influence of texture formation. Finally, the martensite volume fraction as a function of plastic strain could be modelled using an shear-intersection mechanism taking into account the content of alloying elements by directly measuring the corresponding martensite-start temperature Ms of the material., Der Wärmebehandlungsprozess bei ADI besteht aus Austenitisierung, Austempern und abschließender Abschreckung auf Raumtemperatur. Im resultierenden ADI-Material bildet sich eine ausferritische Mikrostruktur mit Kugelgraphit aus. Die unterschiedlichen Prozessparameter wie Austemperzeit und -temperatur während der Wärmebehandlung beeinflussen direkt das Gefüge der ausferritischen Mikrotruktur, und darüber hinaus entscheidend die mechanischen Eigenschaften des Materials für die industrielle Anwendungen. Messungen mit Rasterelektronenmikroskopie (SEM), Transmissionselektronenmikroskopie (TEM), Atomsonden-Tomographie (APT) und Kleinwinkelneutronenstreuung (SANS) wurden durchgeführt, um den Einfluss der Wärmebehandlungsparameter auf die sich ausbildende ausferritischer Mikrostruktur zu quantifizieren. Gleichzeitig wurde die Kohlenstoffumverteilung während des Wärmebehandlungsprozesses mit in-situ-Synchrotrondiffraktion und APT untersucht. Der Restaustenit im Ausferrit ist metastabil und wandelt sich bei plastischer Verformung in Martensit um, wie es ähnlich in TRIP-Stählen gefunden wurde. Der Martensitvolumeanteil als eine Funktion der plastischen Dehnung wurde unter Verwendung der Rietveld-Verfeinerung von Neutronendiffraktionsdaten unter Berücksichtigung der Textur quantitativ untersucht. Schließlich konnte der Martensitvolumenanteil als eine Funktion der plastischen Verformung mit Hilfe eines Scherungsmodells simuliert werden. In diesem Modell wurde der Einfluss von Legierungselementen über die direkt messbare Martensitstarttemperatur Ms des Materials berücksichtigt.

Water quality deterioration caused by a wide variety of persistent organic pollutants (POPs) has become a serious concern worldwide. Traditional advanced oxidation process (e.g., Fenton reaction) is often inadequate, unsafe, and require post-treatment to remove residual H2O2. In this context, the bioelectrochemical technology assisted advanced oxidation reactions (namely bio-electro-Fenton system) have found a niche where they can become dominant in the near future, especially for POPs removal. Compared to traditional Electro-Fenton technologies, the bio-Electro-Fenton system greatly reduced the expenses on wastewater treatment in terms of electric energy consumption and operation costs. The bio-electro-Fenton system is becoming a versatile platform technology and offers a new solution for emerging environmental issues related to wastewater treatment. This paper critically reviews the existing literature about the degradation of POPs in bio-electro-Fenton system, especially with respect to the treatment performance associated with reactor design and main operating parameters. The review aims to assist researchers and engineers to gain fundamental understandings and critical view of bio-electro-Fenton system, and hopefully with the knowledge it could bring new opportunities for the future development of this promising wastewater treatment technology.

Aiming at the skew and misalignment between the inner and outer rings of the spindle bearing during the installation process, a new method for detecting the spindle bearing assembly state is proposed combined an improved maximum correlated kurtosis deconvolution (IMCKD) and support vector machine (SVM). The vibration and impulse signals induced by bearing assembly skew or dislocation are quite weak. In this paper, the collected vibration signals were preprocessed by IMCKD algorithm with optimized parameters between the normal and skewed state of the outer rings at first, which aims to deconvolve periodic impulse characteristic and enhance the periodic impulse component from a new assembly spindle vibration signal. Then, wavelet packet decomposition method was adopted to extract the characteristic energy value of different frequency bands, and the eigenvector of the assembly state of the spindle bearing was calculated. Furthermore, the support vector machine classification method is implemented to analyze the eigenvectors under different assembly states. Finally, the proposed method was verified by experimental results. The results show that the IMCKD and SVM methods can effectively detect the bearing assembly skew state of the spindle with an accuracy of more than 95 %.

Water quality deterioration caused by a wide variety of recalcitrant organics and pathogenic microorganisms has become a serious concern worldwide. Bio-electro-Fenton systems have been considered as cost-effective and highly efficient water treatment platform technology. While it has been extensively studied for recalcitrant organics removal, its application potential towards water disinfection (e.g., inactivation of pathogens) is still unknown. This study investigated the inactivation of Escherichia coli in a microbial electrolysis cell based bio-electro-Fenton system (renamed as microbial electrolytic-Fenton cell) with the aim to broad the application of microbial electrochemistry. Results showed that a 4-log reduction of Escherichia coli (107 to hundreds CFU/mL) was achieved with an external applied voltage of 0.2 V, 0.3 mM Fe2+ and cathodic pH of 3.0. However, non-notable inactivation was observed in the control experiments without external voltage or Fe2+ dose. The disinfection effect was enhanced when cathode air flow rate increased from 7 to 41 mL/min and was also in proportion to the increase of Fe2+ concentration from 0.15 to 0.45 mmol/mL. Fatal cell membrane destruction by [rad]OH was identified as one potential mechanism for disinfection. This study successfully demonstrated the feasibility of bio-electro-Fenton process for pathogens inactivation, which offers insight for the future development of sustainable, efficient, and cost-effective biological water treatment technology.

Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) are ubiquitous municipal wastewater pollutants of which several are resistant to degradation in conventional wastewater treatment, and represent a major environmental health concern worldwide. An alternative treatment, the bio-electro-Fenton process, has received increasing attention in past years. In this process the strong oxidant •HO is formed using the electrons derived from bacterial oxidation of organic substrate. In this work, a laboratory scale microbial electrolysis cell based bio-electro-Fenton process was developed for the treatment of four different NSAIDs. The system was demonstrated to remove low concentration NSAIDs from water and wastewater and all tested parameters (cathode pH, cathode air-flow, cathode Fe2+ concentration, applied voltage, NSAIDs concentration and reaction time) were found to affect the apparent first order rate constant and removal efficiency for NSAIDs. Optimum parameter values were found to be pH = 2, Fe+2 = 7.5 mM, air-flow = 8 mL min-1, applied voltage = 0.3 V; the apparent rate constant was higher for higher NSAIDs initial concentration. For reaction times of 5 hours removal efficiencies were 59%-61% for Ketoprofen, 87%-97% for Diclofenac, 80%-86% for Ibuprofen and 75%-81% for Naproxen. Prolonged reaction times lead to substantial increase in removal efficiencies for Ketoprofen and Naproxen. Finally results obtained with real wastewater show lower removal rate constants than with distilled water matrices suggesting interference from wastewater components in the NSAIDs oxidation process. The results offer insight into future developments of an efficient platform for wastewater treatment technology targeting micropollutants.

Bioelektrokemiske systemer (BESs) er opstået som lovende bæredygtig bioteknologi som kan anvendes til at behandle spildevand og samtidig producere værdifulde kemikalier (såsom H2O2, acetat og ethanol). BESs står imidlertid stadig overfor økonomiske og tekniske udfordringer, som kræver betydelig opmærksomhed for at opnå fuldt potentiale i kommerciel skala. Hovedformålet med denne undersøgelse var at forbedre ydeevnen og reducere omkostningerne ved anvendelse af BES teknologier til produktion af kemikalier og fjernelse af forurenende stoffer. For det første, blev et nyt bipolært membran mikrobiel elektrolysecelle (MEC)-Fenton system udviklet til effektiv behandling af anilin-holdigt spildevand. I et sådant system, bliver H2O2 produceret in situ i katoden af MEC, som samtidigt blev brugt som kilde til •OH dannelse som var ansvarlig for nedbrydning af anilin. Anilinen blev effektivt nedbrudt under en påført spænding på 0.5V med anilinen fjernelses effektiviteten af 97.1 ± 1.2%. I øvrigt viste energibalance også at MEC-Fenton system er en lovende teknologi for fjernelse af svært nedbrydelige forurenende stoffer i spildevand. For at reducere forbruget af elektrisk energi blev et hybrid system bestående af MEC og reverse electrodialysis (RED) teknologi udviklet til produktion af værdifulde kemikalier og samtidig spildevandsrensning, som blev benævnt mikrobiel reverse electrodialysis elektrolysecelle (MREC). I MREC, blev et elektrisk potentiale frembragt af eksoelektrogenmikrober og saltkoncentrationsgradient energi mellem havvand og flodvand til at drive H2O2 produktion. Driftsparametre såsom luftstrømningshastighed, pH, katodepotentiale, strømningshastighed af salt og ferskvand blev undersøgt. MREC blev yderligere integreret med Fenton system til fjernelse af vedholdende organiske forurenende stoffer. Dette hybrid system har flere fordele, såsom lavere driftsomkostninger, lavere elektrisk, Bioelectrochemical systems (BESs) have been emerging as promising sustainable biotechnology for wastewater treatment and production of value-added chemicals (such as H2O2, acetate, and ethanol). However, BESs still face economic and technical challenges, which need considerable attention for achieving full potential at commercial scale. The main objective of this study was to improve the performance and reduce the cost of BESs for chemicals production and pollutants removal. Firstly, a novel bipolar membrane microbial electrolysis cell (MEC)-Fenton system was developed for the efficient treatment of aniline wastewater. In such system, H2O2 was in situ generated at the cathode of MEC, which was simultaneously used as a source of •OH for the degradation of aniline. The aniline was effectively degraded under an applied voltage of 0.5 V with aniline removal efficiency of 97.1±1.2%. Moreover, energy balance demonstrated that the MEC-Fenton system is a promising strategy for removal of persistent organic pollutants from wastewater. In order to reduce the consumption of applied voltage, a hybrid system of the MEC and reverse electrodialysis (RED) technology was developed, for value-added chemicals production and wastewater treatment, which was named microbial reverse-electrodialysis electrolysis cell (MREC). In the MREC, electrical potential generated by the exoelectrogenic microbes and salinity-gradient energy between seawater and river water were utilized to drive H2O2 production. Operational parameters such as air flow rate, pH, cathode potential, flow rate of salt and fresh water were investigated. The MREC was further integrated with Fenton system for removal of persistent organic pollutants. This hybrid system has several advantages, such as lower operational costs, lower electrical energy consumption, and higher safety level, which provide an efficient and cost-effective system for

Ammonia monitoring is important to control anaerobic digestion (AD) process due to inhibition effect. Here, an electrolysis cell (EC) was integrated with a complete nitrification reactor as an alternative approach for online monitoring of ammonia during AD processes. The AD effluent was pumped into nitrification reactor to convert ammonia to nitrate, followed by the introduction of nitrate-rich effluent to EC cathode. It was first evaluated with synthetic ammonia-rich digesters and was observed that the current at 5 min were linearly corresponding to the ammonia levels (from 0 to 7.5 mM NH4+-N, R2 = 0.9673). The linear relationship was always observed regardless of different wastewater pH and external voltage. Pre-removal of other electron acceptors from digestate at cathode could eliminate their disturbances to sensor performance. Finally, the accuracy of biosensor was verified with real digestate test. The simple and reliable biosensor showed great promising for online ammonia monitoring of AD processes.

The impact of different anode acclimation methods for enhancing hydrogen production in microbial electrolysis cell (MEC) was investigated in this study. The anodes were first acclimated in microbial fuel cells using acetate, butyrate and corn stalk fermentation effluent (CSFE) as substrate before moving into MECs, respectively. Subsequently, CSFE was used as feedstock in all the three MECs. The maximum hydrogen yield with the anode pre-acclimated with butyrate (5.21 ± 0.24 L H2/L CSFE) was higher than that pre-acclimated with acetate (4.22 ± 0.19 L H2/L CSFE) and CSFE (4.55 ± 0.14 L H2/L CSFE). The current density (480 ± 11 A/m3) and hydrogen production rate (4.52 ± 0.13 m3/m3/d) with the anode pre-acclimated with butyrate were also higher that another two reactors. These results demonstrated that the anode biofilm pre-acclimated with butyrate has significant advantages in CSFE treatment and could improve the performance of hydrogen production in MEC.

Aniline-containing wastewater can cause significant environmental problems and threaten the humans's life. However, rapid degradation of aniline with cost-efficient methods remains a challenge. In this work, a novel microbial electrolysis cell with bipolar membrane was integrated with Fenton reaction (MEC-Fenton) for efficient treatment of real wastewater containing a high concentration (4460 ± 52 mg L−1) of aniline. In this system, H2O2 was in situ electro-synthesized from O2 reduction on the graphite cathode and was simultaneously used as source of radical dotOH for the oxidation of aniline wastewater under an acidic condition maintained by the bipolar membrane. The aniline was effectively degraded following first-order kinetics at a rate constant of 0.0166 h−1 under an applied voltage of 0.5 V. Meanwhile, a total organic carbon (TOC) removal efficiency of 93.1 ± 1.2% was obtained, revealing efficient mineralization of aniline. The applicability of bipolar membrane MEC-Fenton system was successfully demonstrated with actual aniline wastewater. Moreover, energy balance showed that the system could be a promising technology for removal of biorefractory organic pollutants from wastewaters.

Hydrogen peroxide (H2O2) as a strong oxidant, is widely used in various chemical industries and environmental remediation processes. In this study, we developed an innovative method for cost-effective production of H2O2 by using a microbial reverse-electrodialysis electrolysis cell (MREC). In the MREC, electrical potential generated by the exoelectrogens and the salinity-gradient between salt and fresh water were utilized to drive the high-rate H2O2 production. Operational parameters such as air flow rate, pH, cathodic potential, flow rate of salt and fresh water were investigated. The optimal H2O2 production was observed at salt and fresh water flow rate of 0.5 mL min−1, air flow rate of 12–20 mL min−1, cathode potential of −0.485 ± 0.025 V (vs Ag/AgCl). The maximum H2O2 accumulated concentration of 778 ± 11 mg L−1 was obtained at corresponding production rate of 11.5 ± 0.5 mg L−1 h−1. The overall energy input for the synthesis process was 0.45 ± 0.03 kWh kg−1 H2O2. Cathode potential was the key factor for H2O2 production, which was mainly affected by the air flow rate. This work for the first time proved the potential of MREC as an efficient platform technology for simultaneous electrosynthesis of valuable chemicals and utilization of salinity-gradient energy.

Development of sustanaible technologies for treatment of azo dyes containing wastewaters has long been of great interest. In this study, we proposed an innovative concept of using microbial reverse-electrodialysis electrolysis cell (MREC) based Fenton process to treat azo dye wastewater. In such MREC-Fenton integrated process, the production of H2O2 which is the key reactant of fenton-reaction was driven by the electrons harvested from the exoelectrogens and salinity-gradient between sea water and fresh water in MREC. Complete decolorization and mineralization of 400 mg L-1 Orange G was achieved with apparent first order rate constants of 1.15 ± 0.06 and 0.26 ± 0.03 h-1, respectively. Furthermore, the initial concentration of orange G, initial solution pH, catholyte concentration, high and low concentration salt water flow rate and air flow rate were all found to significantly affect the dye degradation. This study provides an efficient and cost-effective system for the degradation of non-biodegradable pollutants.

This study presents an innovative biosensor that was developed on the basis of a microbial electrolysis cell for fast and reliable measurement of volatile fatty acids (VFA) during anaerobic digestion (AD) process. The bio-electrolytic sensor was first tested with synthetic wastewater containing varying concentrations of VFA. A linear correlation (R2 = 0.99) between current densities (0.03 ± 0.01 to 2.43 ± 0.12 A/m2) and VFA concentrations (5–100 mM) was found. The sensor performance was then investigated under different affecting parameters such as the external voltage, VFA composition ratio, and ionic strength. Linear relationship between the current density and VFA concentrations was always observed. Furthermore, the bio-electrolytic sensor proved ability to handle interruptions such as the presence of complex organic matter, anode exposure to oxygen and low pH. Finally, the sensor was applied to monitor VFA concentrations in a lab-scale AD reactor for a month. The VFA measurements from the sensor correlated well with those from GC analysis which proved the accuracy of the system. Since hydrogen was produced in the cathode as byproduct during monitoring, the system could be energy self-sufficient. Considering the high accuracy, short response time, long-term stability and additional benefit of H2 production, this bio-electrolytic sensor could be a simple and cost-effective method for VFA monitoring during AD and other anaerobic processes.

Biogas upgrading to natural gas quality is essential for the efficient use of biogas in various applications. Carbon dioxide (CO2) which constitutes a major part of the biogas is generally removed by physicochemical methods. However, most of the methods are expensive and often present environmental challenges. In this study, an innovative microbial electrolytic system was developed to capture, separate and regenerate CO2 for biogas upgrading without external supply of chemicals, and potentially to treat wastewater. The new system was operated at varied biogas flow rates and external applied voltages. CO2 was effectively separated from the raw biogas and the CH4 content in the outlet reached as high as 97.0±0.2% at the external voltage of 1.2 V and gas flow rate of 19.6 mL/h. Regeneration of CO2 was also achieved in the regeneration chamber with low pH (1.34±0.04). The relatively low electric energy consumption (≤0.15 kWh/m3) along with the H2 production which can contribute to the energy input makes the overall energy need of the system low, and thereby makes the technology promising. This work provides the first attempt for development of a sustainable biogas upgrading technology and potentially expands the application of microbial electrochemical technologies.

Traditional security analyses are often geared towards cryptographic primitives or protocols. Although such analyses are necessary, they cannot address a defender's need for insight into {\em which aspects of a networked system having a significant impact on its security, and how to tune its configurations or parameters so as to improve security}. This question is known to be notoriously difficult to answer, and the state-of-the-art is that we know little about it. Towards ultimately addressing this question, this paper presents a stochastic model for quantifying security of networked systems. The resulting model captures two aspects of a networked system: (1) the strength of deployed security mechanisms such as intrusion detection systems, and (2) the underlying {\em vulnerability graph}, which reflects how attacks may proceed. The resulting model brings the following insights: (1) How should a defender "tune" system configurations (e.g., network topology) so as to improve security? (2) How should a defender "tune" system parameters (e.g., by upgrading which security mechanisms) so as to improve security? (3) Under what conditions is the steady-state number of compromised entities of interest below a given threshold with a high probability? Simulation studies are conducted to confirm the analytic results, and to show the tightness of the bounds of certain important metric that cannot be resolved analytically.

Microbial reverse-electrodialysis electrolysis cell (MREC) as a novel type of microbial electrochemical technologies has been proposed to produce H2 and CH4. In this study, we developed MREC to produce the strong oxidant H2O2. In the MREC, electrical potential generated by the exoelectrogens and the salinity-gradient between sea water and river water were utilized to drive the high-rate H2O2 production without external power supply. Operational parameters such as air flow rate, pH, cathodic potential, flow rate of high and low concentration solution were investigated. The optimal H2O2 production were observed at high and low concentration solution flow rate of 0.5 mL/min, air flow rate of 8-20 mL/min, cathode potential of -0.485 ± 0.025 V (vs Ag/AgCl). Under the optimal conditions, the maximum H2O2 yield of 778 ± 11 mg/L could be obtained. Cathode potential was found as the key factor for H2O2 production, which can be controlled through adjusting the air flow rate without power supply and potentiostat. This study shows for the first time high yield synthesis of H2O2 from oxygen reduction in a microbial electrochemical system without external power supply.

Hydrogen peroxide (H2O2) is widely used in various chemical industries and environmental remediation. Recently, bioelectrochemical systems (BES) have gained increasing attention for synthesizing H2O2 with simultaneous wastewater treatment[1]. However, in order to get high-yield H2O2 requires additional electrical energy to power these BES or control the cathode potential. In this study, we develop an innovative BES called microbial reverse-electrodialysis electrolysis cell (MREC) to produce H2O2 in cathode. In the MREC(See Fig.1), the salinity-gradient energy between seawater and river water can be used to generated renewable eleltrical energy to replace the external power supply[2]. Operational parameters such as air flow rate, pH, cathodic potential, flow rate of high and low concentration NaCl solution in RED were investigated as to improve the H2O2 yield. The optimal parameters for H2O2 production are air gas flow rate of 8-20 ml/min, cathode potential of -0.485 ± 0.025 V vs Ag/AgCl, the corresponding dissolved oxygen is 6.80 ± 0.30 mg/l in catholyte. Under the optimal conditions, a maximum H2O2 yield of 770 ± 18 mg/L could be obtained with corresponding H2O2 production rates of 0.44 ± 0.04 g/m2/h and current density of 1.40 ± 0.13 A/m2. Results indicate the air gas flow rate and cathode potential are the key parameters for H2O2 production in MREC. This study indicate for the first time high yield synthesis of H2O2 from oxygen reduction in BES without external power supply, furthermore, we also discover the cathode potential can be controlled through adjusting the air flow rate without power supply and potentiostat.

The envelopes of AGB stars are irradiated externally by ultraviolet photons; hence, the chemistry is sensitive to the photodissociation of N$_2$ and CO, which are major reservoirs of nitrogen and carbon, respectively. The photodissociation of N$_2$ has recently been quantified by laboratory and theoretical studies. Improvements have also been made for CO photodissociation. For the first time, we use accurate N$_2$ and CO photodissociation rates and shielding functions in a model of the circumstellar envelope of the carbon-rich AGB star, IRC +10216. We use a state-of-the-art chemical model of an AGB envelope, the latest CO and N$_2$ photodissociation data, and a new method for implementing molecular shielding functions in full spherical geometry with isotropic incident radiation. We compare computed column densities and radial distributions of molecules with observations. The transition of N$_2$ $\to$ N (also, CO $\to$ C $\to$ C$^+$) is shifted towards the outer envelope relative to previous models. This leads to different column densities and radial distributions of N-bearing species, especially those species whose formation/destruction processes largely depend on the availability of atomic or molecular nitrogen, for example, C$_n$N ($n$=1, 3, 5), C$_n$N$^-$ ($n$=1, 3, 5), HC$_n$N ($n$=1, 3, 5, 7, 9), H$_2$CN and CH$_2$CN. The chemistry of many species is directly or indirectly affected by the photodissociation of N$_2$ and CO, especially in the outer shell of AGB stars where photodissociation is important. Thus, it is important to include N$_2$ and CO shielding in astrochemical models of AGB envelopes and other irradiated environments. In general, while differences remain between our model of IRC +10216 and the observed molecular column densities, better agreement is found between the calculated and observed radii of peak abundance., Comment: 13 pages, 17 figures, 3 tables. Accepted for publication in Astronomy and Astrophysics

The dynamics of the reaction H + OH $\to$ O (3P) + H2 have been studied in a series of quasi-classical trajectory (QCT) calculations and transition state theory (TST) methods using high quality 3A' and 3A'' potential energy surfaces (PESs). Accurate OH (v, j) state resolved cross sections and rate constants on both potential energy surfaces are presented and fitted for OH at (v = 0, j = 0-16) and (v = 1, j = 0-6). The cross sections were calculated for different collisional energies (Ec), ranging from the threshold energy at each specific rovibrational state up to 1.0 eV with step sizes of 0.1 eV or less. They increase steeply with collision energy when the barrier to reaction can be overcome, after which the cross sections stay nearly constant with energy. State resolved rate constants in the temperature range 200-2500 K are presented based on the cross sections. Total thermal rate constants were calculated by summing the rates for reaction on the 3A' and 3A'' potential energy surfaces weighted by 1/3 and taking into account the thermal populations of the rovibrational states of the OH molecules. It is shown that the improved canonical variational transition (CVT) treatments with the approximation of zero-curvature tunneling (ZCT) or small-curvature tunneling (SCT) produce results more in accord with the QCT results than the TST and CVT methods. The reactions are governed by the direct reaction mechanism. The rate constants for OH in excited vibrational and rotational states are orders of magnitude larger than the thermal rate constants, which needs to be taken into account in astrochemical models., Comment: Current version: 35 pages with 7 figures and 2 tables. Online version: 8 pages, see http://pubs.acs.org/doi/abs/10.1021/jp4068153

The envelopes of AGB stars are irradiated externally by ultraviolet photons; hence, the chemistry is sensitive to the photodissociation of N$_2$ and CO, which are major reservoirs of nitrogen and carbon, respectively. The photodissociation of N$_2$ has recently been quantified by laboratory and theoretical studies. Improvements have also been made for CO photodissociation. For the first time, we use accurate N$_2$ and CO photodissociation rates and shielding functions in a model of the circumstellar envelope of the carbon-rich AGB star, IRC +10216. We use a state-of-the-art chemical model of an AGB envelope, the latest CO and N$_2$ photodissociation data, and a new method for implementing molecular shielding functions in full spherical geometry with isotropic incident radiation. We compare computed column densities and radial distributions of molecules with observations. The transition of N$_2$ $\to$ N (also, CO $\to$ C $\to$ C$^+$) is shifted towards the outer envelope relative to previous models. This leads to different column densities and radial distributions of N-bearing species, especially those species whose formation/destruction processes largely depend on the availability of atomic or molecular nitrogen, for example, C$_n$N ($n$=1, 3, 5), C$_n$N$^-$ ($n$=1, 3, 5), HC$_n$N ($n$=1, 3, 5, 7, 9), H$_2$CN and CH$_2$CN. The chemistry of many species is directly or indirectly affected by the photodissociation of N$_2$ and CO, especially in the outer shell of AGB stars where photodissociation is important. Thus, it is important to include N$_2$ and CO shielding in astrochemical models of AGB envelopes and other irradiated environments. In general, while differences remain between our model of IRC +10216 and the observed molecular column densities, better agreement is found between the calculated and observed radii of peak abundance., Comment: 13 pages, 17 figures, 3 tables. Accepted for publication in Astronomy and Astrophysics

The dynamics of the reaction H + OH $\to$ O (3P) + H2 have been studied in a series of quasi-classical trajectory (QCT) calculations and transition state theory (TST) methods using high quality 3A' and 3A'' potential energy surfaces (PESs). Accurate OH (v, j) state resolved cross sections and rate constants on both potential energy surfaces are presented and fitted for OH at (v = 0, j = 0-16) and (v = 1, j = 0-6). The cross sections were calculated for different collisional energies (Ec), ranging from the threshold energy at each specific rovibrational state up to 1.0 eV with step sizes of 0.1 eV or less. They increase steeply with collision energy when the barrier to reaction can be overcome, after which the cross sections stay nearly constant with energy. State resolved rate constants in the temperature range 200-2500 K are presented based on the cross sections. Total thermal rate constants were calculated by summing the rates for reaction on the 3A' and 3A'' potential energy surfaces weighted by 1/3 and taking into account the thermal populations of the rovibrational states of the OH molecules. It is shown that the improved canonical variational transition (CVT) treatments with the approximation of zero-curvature tunneling (ZCT) or small-curvature tunneling (SCT) produce results more in accord with the QCT results than the TST and CVT methods. The reactions are governed by the direct reaction mechanism. The rate constants for OH in excited vibrational and rotational states are orders of magnitude larger than the thermal rate constants, which needs to be taken into account in astrochemical models., Comment: Current version: 35 pages with 7 figures and 2 tables. Online version: 8 pages, see http://pubs.acs.org/doi/abs/10.1021/jp4068153

Molecular nitrogen is one of the key species in the chemistry of interstellar clouds and protoplanetary disks and the partitioning of nitrogen between N and N2 controls the formation of more complex prebiotic nitrogen-containing species. The aim of this work is to gain a better understanding of the interstellar N2 photodissociation processes based on recent detailed theoretical and experimental work and to provide accurate rates for use in chemical models. We simulated the full high-resolution line-by-line absorption + dissociation spectrum of N2 over the relevant 912-1000 \AA\ wavelength range, by using a quantum-mechanical model which solves the coupled-channels Schr\"odinger equation. The simulated N2 spectra were compared with the absorption spectra of H2, H, CO, and dust to compute photodissociation rates in various radiation fields and shielding functions. The effects of the new rates in interstellar cloud models were illustrated for diffuse and translucent clouds, a dense photon dominated region and a protoplanetary disk., Comment: Online database: http://home.strw.leidenuniv.nl/~ewine/photo

Molecular nitrogen is one of the key species in the chemistry of interstellar clouds and protoplanetary disks and the partitioning of nitrogen between N and N2 controls the formation of more complex prebiotic nitrogen-containing species. The aim of this work is to gain a better understanding of the interstellar N2 photodissociation processes based on recent detailed theoretical and experimental work and to provide accurate rates for use in chemical models. We simulated the full high-resolution line-by-line absorption + dissociation spectrum of N2 over the relevant 912-1000 \AA\ wavelength range, by using a quantum-mechanical model which solves the coupled-channels Schr\"odinger equation. The simulated N2 spectra were compared with the absorption spectra of H2, H, CO, and dust to compute photodissociation rates in various radiation fields and shielding functions. The effects of the new rates in interstellar cloud models were illustrated for diffuse and translucent clouds, a dense photon dominated region and a protoplanetary disk., Comment: Online database: http://home.strw.leidenuniv.nl/~ewine/photo