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Chemical study of two starless cores in the B213/L1495 filament
No full textContext. The chemical evolution of pre-stellar cores during their transition to a protostellar stage is not yet fully understood. Detailed chemical characterizations of these sources are needed to better define their chemistry during star formation.
Aims. Our goal is to characterize the chemistry of the starless cores C2 and C16 in the B213/L1495 filament of the Taurus Molecular Cloud, and to understand how it relates to the environmental conditions and the evolutionary state of the cores.
Methods. We made use of two complete spectral surveys at 7 mm of these sources, carried out using the Yebes 40-m telescope. Derived molecular abundances were compared with those of other sources in different evolutionary stages and with values computed by chemical models.
Results. Including isotopologs, 22 molecules were detected in B213-C2, and 25 in B213-C16. The derived rotational temperatures have values of between ∼5 K and ∼9 K. A comparison of the two sources shows lower abundances in C2, except for l-C3H and HOCO+, which have similar values in both cores. Model results indicate that both cores are best fit assuming early-time chemistry, and point to C2 being in a more advanced evolutionary stage, as it presents a higher molecular hydrogen density and sulfur depletion, and a lower cosmic-ray ionization rate. Our chemical modeling successfully accounts for the abundances of most molecules, including complex organic molecules and long cyanopolynes (HC5N, HC7N), but fails to reproduce those of the carbon chains CCS and C3O.
Conclusions. Chemical differences between C2 and C16 could stem from the evolutionary stage of the cores, with C2 being closer to the pre-stellar phase. Both cores are better fit assuming early-time chemistry of t ~ 0.1 Myr. The more intense UV radiation in the northern region of B213 could account for the high abundances of l-C3H and HOCO+ in C2
Comparing simulated and observed particle energy distributions through magnetic reconnection in Earth’s magnetotail
No full textContext. Magnetic reconnection is an explosive process that accelerates particles to high energies in Earth’s magnetosphere, offering a unique natural laboratory to study this phenomenon.
Aims. This study investigates how well data-driven fully kinetic simulations can reproduce the ion and electron energy distributions observed during a reconnection event by the Magnetospheric Multiscale (MMS) mission.
Methods. We performed fully kinetic 2D simulations initialized with plasma parameters derived from the MMS event and compared the resulting ion and electron energy distributions with observations. Key numerical and physical parameters were systematically varied to assess their influence on the resulting particle spectra.
Results. The simulations capture the overall shape and evolution of nonthermal energy distributions for both species, but generally underestimate the very high-energy tail of the electron spectrum. Variations in numerical parameters have negligible effects on the resulting spectra, while the initial upstream temperatures instead play a more pronounced role in reproducing the observed distributions.
Conclusions. We present a novel analysis of data-driven fully kinetic simulations of MR, showing that key aspects of particle acceleration can be captured, while also highlighting the limitations of 2D simulations and the need for more realistic (e.g., 3D) setups to reproduce the observed particle energization accurately
Nutritional quality of proteins from major oilseeds – a review
No full textDriven by the ongoing dietary transition in Western countries, numerous research studies focus on new sustainable plant-based sources. Oilseeds, known for their high lipid and protein content, represent a promising option. This review focuses on the protein quality of oilseeds and their potential to meet population wide nutritional needs. Although the nutritional value of the protein of oilseeds is generally lower than that of animal proteins, due to deficiencies in certain indispensable amino acids (particularly lysine) and reduced digestibility, several strategies can enhance their value. Combining oilseeds with legumes to achieve complementary amino acid profiles, processing techniques such as dehulling and oil extraction, as well as bioprocesses (fermentation/germination), all contribute to improved protein quality. Moreover, oilseeds provide bioactive peptides and polyunsaturated fatty acids which often exhibit anti-inflammatory and/or pro-anabolic effects. In conclusion, oilseeds are valuable sources of both protein and lipids, and current dietary guidelines support increased consumption of these seeds among the general population
Exploring the interplay between molecular and ionized gas in H
No full textContext. Massive stars strongly impact their natal environments and influence subsequent star formation through feedback mechanisms such as shocks, outflows, and radiation. H I
The Nucleated Atomistic Grain Growth Simulator (NAGGS): application to the size-dependent structural and physical properties of nanosilicate dust
No full textContext. The essential physics of dust grains are typically rationalised using phenomenological approaches, often assuming highly simplified grain morphologies. Such descriptions are necessary if the underlying microscopic details are unknown or too complex to model. For small nanosized dust particles, these constraints can be overcome by atomistic simulations that can provide realistic detailed grain models.
Aims. We show how atomistic forcefield-based simulations can be harnessed to: (i) model the growth of structurally realistic nanograins, and (ii) calculate a range of astrophysically relevant physicochemical properties directly from the growing grains.
Methods. We report the Nucleated Atomistic Grain Growth Simulator (NAGGS) as a new tool to model the growth of realistic nanosized dust grains through the progressive accretion of monomers onto a nucleated seed. NAGGS can be used with open source molecular dynamics codes, allowing for the modelling of grains that have different chemical compositions and are grown under a range of astrophysical conditions.
Results. To demonstrate how NAGGS works, we use it to produce 40 nanosilicate grain models with diameters of ∼3.5 nm and consisting of ∼1500 atoms. We consider Mg-rich olivinic and pyroxenic grains, and growth under two circumstellar dust-producing conditions. We calculate properties from the atomistically detailed nanograin structures (e.g. morphology, surface area, density, dipole moments) with respect to the size, chemical composition, and growth temperature of the grains.
Conclusions. Our simulations reveal detailed new insights into the complex interacting degrees of freedom during grain growth and how they affect the resultant physicochemical properties. For example, we find that surface roughness depends on the Mg:Si ratio during growth. We also find that nanosilicates have very high dipole moments, which depend on the growth temperature. Such findings could have important consequences (e.g. astrochemistry, microwave emission). In summary, our bottom-up physically motivated approach offers a detailed understanding of nanograins that could help in both interpreting observations and improving dust models
Zero modes and geometric phase for 2D Weyl fermions on Lifshitz backgrounds
No full textHere we investigate analytical properties of Weyl fermions in (2+1)-dimensional Lifshitz spacetimes. In particular, we are interested in obtaining geometric phases and verifying the existence of well-behaved fermionic zero modes. Using the Dirac phase method, we show how geometric phases naturally arise from the coupling between the fermionic fields and the Lifshitz geometry. We also present exact solutions of the zero modes by rewriting the Weyl equation as a system of supersymmetric equations
A review on the stability of magnetorheological materials
No full textMagnetorheological materials, as a type of intelligent controllable material, have broad application prospects in the engineering field. However, stability issues (such as sedimentation, particle agglomeration, and extreme temperature adaptability) severely limit the practical application of magnetorheological materials. In this paper, the research progress on the stability of magnetorheological materials was summarized and categorized, and analyzed from three aspects: material systems, testing methods, and improvement strategies. First, the compositional characteristics and stability challenges of magnetorheological materials with different matrix morphologies were compared, and it was pointed out that sedimentation issues in magnetorheological fluids and particle migration issues in magnetorheological elastomers are key research focuses. Second, the currently available stability testing methods were summarized, including sedimentation observation, particle concentration testing, redispersibility testing, and temperature stability testing, and the applicable scenarios, advantages and disadvantages of different methods are discussed. Third, the technical measures to enhance stability were discussed in detail, such as additive optimization (surfactants, thixotropic agents, nanoparticles, etc.), magnetic particle surface modification (polymer coating, composite structure design, etc.), and matrix carrier modification (magnetic matrix carriers, fluid-solid carrier conversion, etc.), and the enhancement mechanisms and characteristics of different methods were compared. Finally, current research limitations in terms of performance trade-offs and long-term reliability were identified, and future directions such as smart responsive materials and standardized testing were proposed. This study provides theoretical references and technical guidance for the stability design and engineering applications of magnetorheological materials
Tunable modulation frequency in photo-acoustic spectroscopy towards precise discrimination of resonant modes in nanostructures on absorbing substrates
No full textScattering-free assessment of resonantly absorbed electromagnetic field is highly important in nano-photonics and plasmonics: nanostructures and metamaterials can be tailored to optimize absorption for applications spanning from solar cells to efficient gas sensing. Photo-acoustic technique converts absorption-induced periodic heating in an acoustic signal, giving powerful means of characterizing absorption in scattering-free and non-destructive way. In this work, we use a widely tunable laser and tunable modulation frequency to perform photo-acoustic experiment on nanowire ensembles. We study absorption in two samples: semiconductor and semiconductor-plasmonic nanowires, both vertically standing on absorbing substrates. Increasing the modulation frequency from 54 Hz to 1225 Hz leads to the sharpening of the resonant nanowire response in the near-infrared range. Moreover, in the hybrid sample, the asymmetric Au layer leads to extrinsic chiral response in the whole wavelength range
Vacuum ultraviolet photochemistry of CS
No full textContext. The evolution of sulphur-bearing species in the interstellar medium remains to be understood. One hypothesis that addresses the sulphur depletion issue postulates that sulphur-bearing molecules are present in interstellar ices, such as CS2. The evolution of CS2 under interstellar conditions has not yet been fully studied.
Aims. We performed experimental studies on the vacuum ultraviolet (VUV) photochemistry of CS2 with H2 under simulated interstellar conditions.
Methods. Gas mixtures of CS2 in either H2 or D2 with a relative proportion of 1:1000 were deposited on a gold substrate at 3.5 K. The matrices were irradiated with a VUV lamp, and the formed species were followed at 3.5 K by IR spectroscopy. Temperature programmed desorption (TPD) was also performed to probe desorbing species using quadrupolar mass spectrometry.
Results. The formation of CH4 (or CD4 with D2) and CS was detected by IR spectroscopy at 3.5 K. A slower formation kinetics of CD4 compared to CH4 is observed. No S-H bond formation was detected at 3.5 K, whereas the thermal desorption of H2S/D2S, CH3SH/CD3SD, and CH4/CD4 occurred during TPD. The desorption of S, S2, and S3 was not detected.
Conclusions. We conclude that the photo-dissociation channel CS2 C + S2 initiates the formation of CH4/CD4 via several reaction steps between the carbon atom and the H2/D2 matrix: C + 3H2/3D2 → CH4/CD4 + 2H/2D. We propose that the H/D generated by this reaction scheme induces the hydrogenation of the remaining sulphur-bearing species (S2, CS, S, and/or CS2) during TPD to form H2S/D2S and CH3SH/CD3SD. As no S-H bonds are detected at 3.5 K, the reactions H2 + X, where X = CS, S, and S2 in ground or excited states, do not seem to be effective. The astronomical relevance of these reaction channels is discussed
Euclid preparation. LXXXVIII. 3D reconstruction of the cosmic web with Euclid Deep spectroscopic samples
No full textThe ongoing Euclid mission is aimed at measuring spectroscopic redshifts for approximately two million galaxies using the , ^ line emission detected in near-infrared slitless spectroscopic data from the Euclid Deep Fields, leveraging both the red and blue grisms. These measurements will reach a flux limit of 5 , , ^ 10^ -17 ̊m erg ̊m cm -2 ̊m s -1 in the redshift range 0.4<z<1.8, paving the way to numerous scientific investigations involving galaxy evolution, extending well beyond the mission's core objectives. The achieved luminosity depth will lead to a sufficiently high sampling, enabling the reconstruction of the large-scale galaxy environment. Here, we assess the quality of the reconstruction of the galaxy cosmic web environment with the expected spectroscopic dataset in Euclid Deep Fields. The analysis was carried out on the Flagship and galaxy mock catalogues. The quality of the reconstruction was first evaluated using simple geometrical and topological statistics measured on the cosmic web network; namely, the length of filaments, the area of walls, the volume of voids, and its connectivity and multiplicity. We then quantified how accurately gradients in galaxy properties can be recovered, with respect to the distance from filaments. As expected, the small-scale redshift-space distortions, such as Fingers of God (FoG) effects, have a strong impact on filament lengths and connectivity; however, they can be mitigated by compressing galaxy groups identified with an anisotropic group finder prior to a skeleton extraction. The cosmic web reconstruction is biased when relying solely on emitters. This limitation can be mitigated by applying stellar mass weighting during the cosmic web reconstruction. However, this approach introduces non-trivial biases that need to be accounted for when comparing to theoretical predictions. Redshift uncertainties pose the greatest challenge in recovering the expected dependence of galaxy properties, although the well-established stellar mass transverse gradients towards filaments can still be observed to a lesser extent