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Multi-objective intelligent optimization design of a bioinspired spider-web microchannel heat sink
No full textWith the rapid increase in chip computing power, the heat flux density has sharply increased, becoming one of the bottlenecks restricting chip performance. This study presents a synergistic approach to thermal management by integrating a bioinspired spider-web microchannel heat sink with intelligent optimization. A multi-objective particle swarm optimization algorithm was employed to systematically optimize channel geometry, maximizing heat transfer while minimizing pressure loss. The TOPSIS-based decision-making identified an optimal solution that increases the convective heat transfer coefficient by 35.2% while reducing pressure loss by 8.3%. And, this advantage is particularly evident at 320 W/cm2, with a maximum temperature reduction of 9.68 K. It means that the proposed structure significantly enhances both thermal and hydraulic performance compared to conventional designs, with improvements becoming more pronounced under increasing heat flux. Finally, the diamond/copper composite material was used to prepare the microchannel heat sink, and the heat dissipation performance of the designed biomimetic heat sink was verified by loop test. This work demonstrates the strong potential of combining bioinspired design with intelligent optimization for advanced thermal management in high-heat-flux applications
Cosmic Vine: High abundance of massive galaxies and dark matter halos in a forming cluster at
No full textThe Cosmic Vine is a massive protocluster at z = 3.44 in the JWST CEERS field, offering an ideal laboratory for studying the early phases of cluster formation. Using the data from the DAWN JWST Archive, we conducted a comprehensive study on the large-scale structure, stellar mass function (SMF), quiescent members, and dark matter halos in the Cosmic Vine. First, we spectroscopically confirmed 136 galaxies in the Vine at z ≈ 3.44, along with an additional 47 galaxies belonging to a diffuse foreground structure at z ≈ 3.34, which we dubbed the Leaf. We identified four subgroups comprising the Cosmic Vine and two subgroups within the Leaf. Second, we identified 11 quiescent members with log(M*/M⊙) = 9.5 − 11.0, the largest sample of quiescent galaxies in overdense environments at z > 3, which gives an enhanced quiescent galaxy number density ∼1 − 2 × 10−4 cMpc−3 that is two to three times above the field level at log(M*/M⊙) > 10. Notably, these quiescent members form a tight red sequence on the colour-magnitude diagram, making it one of the earliest red sequences known to date. Third, by constructing the SMFs for both star-forming and quiescent members, we find that both SMFs are top-heavy, with a significantly enhanced quiescent fraction at log(M*/M⊙) > 10.5 compared to field counterparts. The stellar mass–size analysis reveals that star-forming members are more compact at higher masses than their field counterparts. Finally, we estimated a halo mass of log(Mh/M⊙) = 13.2 ± 0.3 for the protocluster core and log(Mh/M⊙) = 11.9 − 12.4 for satellite subgroups. The phase-space analysis indicates that three subgroups are likely infalling to the core. This work reveals a high abundance of massive galaxies and dark matter halos in this forming cluster, demonstrating the accelerated assembly of massive galaxies in massive halos when the Universe was less than 2 billion years old
A clustering-based search for substructures in the Galactic plane and bulge using RR Lyrae stars as tracers
No full textContext. Although many globular clusters (GCs) have been identified in the Galaxy, their population is estimated to be incomplete, especially in regions with significant crowding and/or interstellar extinction, such as the Galactic bulge and plane. RR Lyrae stars, as bright standard candles and tracers of old populations, hold immense potential in the search for GCs in these regions. Furthermore, large catalogs of RR Lyrae stars in these areas have become available in recent years.
Aims. We aim to build a sample of RR Lyrae stars with six-dimensional information (three-dimensional positions, proper motions, and metallicities) in the Galactic plane and bulge, and to exploit it with a hierarchical clustering algorithm to search for new Galactic substructures.
Methods. We build a sample of fundamental-mode RR Lyrae (RRab) stars in the Galactic plane and bulge with positions, distances, proper motions, and photometric metallicity estimates, using data from the Gaia and VVV surveys. Using a clustering algorithm calibrated to optimize the recovery of GCs, we form groups of RRab stars with similar positions in the six-dimensional space studied. Finally, to identify the most promising RRab groups among the many artifacts produced by the clustering algorithm, we compare their properties with those of known GCs.
Results. We find many RRab groups associated with known Galactic GCs. Additionally, we estimate the first RR Lyrae-based distances for the GCs BH 140 and NGC 5986, further constraining their positions in the Milky Way. We detect small groups of two to three RRab stars, located at distances of up to ∼ 25 kpc, that are not associated with any known GC, but exhibit GC-like distributions across all six parameters analyzed. Several of these groups – mostly pairs – are found toward the Galactic bulge, but have distinct proper motions or distances, indicating that they may not belong to the bulge population.
Conclusions. By exploiting an RRab sample in the Galactic plane and bulge with a hierarchical clustering algorithm, we identify dozens of groups displaying GC-like properties, which are excellent candidates for further follow-up observations. Furthermore, future radial velocity measurements could evaluate if the RRab members of our groups are truly moving together
Polycyclic aromatic hydrocarbon spectral diversity in NGC 7027 and the evolution of aromatic carriers
No full textPolycyclic aromatic hydrocarbons (PAHs) constitute a significant fraction of the Universe's carbon budget, playing a key role in the cosmic carbon cycle and dominating the mid-infrared spectra of astrophysical environments in which they reside. Although PAHs are known to form in the circumstellar envelopes of post-asymptotic giant branch stars, their formation and evolution are still not well understood.
We aim to understand how pristine complex hydrocarbons and PAHs in circumstellar environments transition to the PAHs observed in the interstellar medium.
The mid-infrared PAH spectra (5-18 of the planetary nebula, NGC 7027, were investigated using spectral cubes from JWST MIRI-MRS.
We report the first detection of spatially resolved variations of the PAH spectral profiles across class ļassA, ļassAB, and ļassB in all major PAH bands (6.2, 7.7, 8.6, and 11.2 within a single source, NGC 7027. These variations are linked to morphological structures within NGC 7027. Clear correlations are revealed between the 6.2, 7.7, and 8.6 features, where the red components (6.26, 7.8, and 8.65 exhibit a strong correlation and the same is found for the blue components of the 6.2 and 7.7 features (6.205 and 7.6 The blue component of the 8.6 feature (8.56 appears to be independent of the other components. We link this behavior to differences in the molecular structure of their PAH subpopulations. Decomposition of the 11.2 band confirms two previously identified components, with the broader 11.25 component attributed to emission from very small grains or PAH clusters rather than PAH emission.
We show that PAH profile classes generally vary with proximity to the central star's UV radiation field, suggesting class ļassB PAHs represent more processed species while class ļassA PAHs remain relatively pristine, challenging current notions on the spectral evolution of PAHs
High-resolution X-ray spectroscopy of Cen X-3 with XMM-Newton
No full textThe spectral analysis of two observations of the high-mass X-ray binary system Cen X-3 is presented. In particular, it is focused on the eclipse and out-of-eclipse spectra in order to compare the properties of the environment around the compact object. XMM-Newton
The high-resolution spectra obtained from the reflection grating spectrometer on board were analysed, with a focus on studying eclipse and out-of-eclipse spectra separately. Several continuum models were explored in , for which we studied the properties of emitting and absorbing matter depending on the emission and absorption lines identified in the spectra. XMM-Newton SPEX
It was found that the X-ray continuum is heavily absorbed by a neutral gas and photoionised matter. Emission lines from Si , Mg , Mg , and Ne were detected in the eclipse spectrum; in particular, H-like lines of Mg and Ne with a significance of gtrsim5, σ in the eclipse spectrum and ∼ 3, σ in the out-of-eclipse spectrum. However, in the out-of-eclipse spectrum any absorption lines were detected with a significance of less than 2, σ. RGS light curve showed dips in the out-of-eclipse spectrum that are not due to an increase in the column absorption but that may be produced by instabilities in the accretion stream. On the other hand, the level of counts above 20 Å, was compatible with the X-ray background. A simple local continuum model was used to describe the He-like triplet of Ne and the derived values of v xii xi x and ratio parameters pointed out that the UV photospheric field should be important at the line production site and an electron density greater than 10^12 cm -3 . As a consequence, a hybrid plasma may be present in the binary system
Formation of black holes from He stars
No full textMassive He stars are potential candidates of type Ib/c supernova (SN) progenitors. Understanding their final fates remains a key issue in astrophysics. In this work, we investigate the evolution of He stars with initial masses from to , focusing on the presupernova (pre-SN) core structures to assess their explodability. Our simulations indicate that the final core structure is determined by the CO core mass and the central ^ 12 C $ mass fraction at the end of core He burning, affecting the properties of central C-burning and the locations of convective shells. The location of the last convective C-burning shell sets the mass of the C-free core, constraining the iron core mass and compactness. We found that the final compactness and iron core mass exhibit non-monotonic behavior with initial mass, suggesting that the boundary between neutron star and black hole formation is not a simple mass threshold. This is due to core C/Ne burning becoming neutrino dominated. This process drives stronger core contraction, ultimately increasing the iron core mass and the final compactness. In contrast, earlier core Ne/O/Si ignition and shell mergers inhibit core contraction, reducing both the iron core mass and final compactness. We also discuss the effects of metallicity and overshooting on the pre-SN core structure. These factors potentially affect the explodability of progenitors
Modelling solar radial velocities and photometric variability with SOAP
No full textStellar activity remains one of the main limitations in the detection of Earth-like planets using radial velocity (RV) measurements. The Sun, as the only star for which surface features can be spatially resolved, offers a unique testbed for studying the impact of active regions on RV and photometric variability.
Using (Spot Oscillation And Planet), we modelled solar RV and photometric variability induced by spots and faculae over long timescales. Our goal is to verify whether present-day, state-of-the-art models of the cross-correlation function correctly reproduce the observed variability. Moreover, we aim to assess how the choice of input data and identification technique influences the agreement between simulated and observed signals. SOAPv4
To simulate solar RV and photometric time series, we first identified active regions in SDO images. This was done using mathematical morphological transforms applied to SDO/HMI and AIA images. Mathematical morphological identification was validated against other state-of-the-art identification methods. Using these inputs, we ran to simulate solar RVs and photometry, and we validated the results with HARPS-N RV observations, as well as with VIRGO/SPM photometric measurements. SOAPv4
The simulations that use mathematical morphological identification achieved the best match with the observed RV time series, yielding residuals with a measured standard deviation of sim0.91 m/s. Other state-of-the-art methods produced higher filling factors and, consequently, larger discrepancies. The photometric simulations reproduced the overall variability trends.
We demonstrate that mathematical morphological transforms accurately identify solar active regions. Using these inputs, reproduces the observed solar RV variability with a measured standard deviation of the residuals of sim0.91 m/s. Photometric simulations capture the overall variability trends, confirming that can reliably model the impact of both spots and faculae on solar RVs and photometry. SOAPv4 SOA
Magnetic plasmoid explosions in the context of magnetar giant flares and fast radio bursts
No full textMagnetar flares are highly energetic and rare events in which intense X and γ-ray emission is released from strongly magnetised neutron stars. The events are also accompanied by mass ejection from the neutron star. Fast radio bursts are short and intense pulses of coherent radio emission. Their large dispersion measures support an extragalactic origin. While their exact origin still remains elusive, a substantial number of models associates them with strong magnetic field and high-energy relativistic plasma found in the vicinity of magnetars. There is growing evidence that some fast radio bursts are associated with flare-type events from magnetars.
We provide a set of configurations describing a relativistic, spherical, magnetic plasmoid explosion. We proceed by solving the equations of relativistic magnetohydrodynamics for a system that expands while maintaining its internal equilibrium.
We employed a semi-analytical approach to solve the equations of relativistic magnetohydrodynamics. We assumed self-similarity in time and radius, axial symmetry, and separation of variables in the spherical and polar angle coordinate. This allowed us to reduce the problem to solving a set of ordinary differential equations.
We find the interdependent relation between pressure, mass density, Lorentz factor, and magnetic field that determines the detailed properties of the solutions. A dichotomy of solutions exists that correspond to higher and lower density and thermal pressure compared to the external one. For stronger toroidal magnetic fields, the maximum permitted expansion velocity becomes lower than the weaker toroidal fields. For a given ratio of the toroidal to the poloidal field, the inclusion of pressure and mass density leads to either a higher expansion velocity when the density and pressure are lower in regions with a higher magnetic flux or to a lower expansion velocity when the pressure and mass density are higher in regions with a higher magnetic flux.
These solution classes can be applied to magnetar giant flares and fast radio bursts. Those that corresponding to overdensities and higher pressure can be associated with magnetar flares, and those corresponding to underdensities can be relevant to fast radio bursts that correspond to magnetically dominated events with low mass loading
Characterization of nata de soya electrolyte membrane as a capacitor separator using (NH₄)₂SO₄
No full textTempeh and tofu production continues to grow rapidly in Indonesia. This means that the volume of liquid waste is also increasing dramatically. The problem is that most of this waste is disposed of in the environment and has the potential to pollute nature. In this study, Nata de Soya was used as a capacitor separator after undergoing a soaking process. This material was soaked for 30 minutes in an ammonium sulfate ((NH₄)₂SO₄) electrolyte solution. Researchers tested four different concentration levels, namely 22.5%, 25%, 27.5%, and 30%, to see how it performed. Characterization was performed using Cyclic Voltammetry (CV) to measure its specific capacitance and Electrochemical Impedance Spectroscopy (EIS) to measure the level of ionic conductivity. The test results show that increasing the electrolyte concentration has a positive effect on performance. After 30 minutes of soaking, the 30% concentration sample showed the highest capacitance compared to other samples, at 13.35 F/g, and also had the highest ionic conductivity, at 0.382 S/m. Based on these results, Nata de Soya membranes treated with varying electrolyte concentrations, including the 30% sample, show potential to be further explored as separator materials for environmentally friendly energy storage applications
Turbostratic graphene formation by flash joule heating: A comprehensive characterization study
No full textGraphene is a technologically important two-dimensional carbon material due to its exceptional electrical conductivity, mechanical strength, and potential for energy storage applications. However, conventional graphene synthesis methods often encounter challenges related to scalability, structural control, and environmental sustainability. Flash Joule Heating (FJH) provides an alternative approach that enables high-temperature conversion of carbon-based materials through a simplified process. In this study, turbostratic graphene was synthesized from a mixture of commercial graphite and acetylene black (AB) using FJH method. Raman spectroscopy revealed an increased intensity ratio of the D to G band ID/IG indicating a higher density of structural defects, while the intensity ratio of the 2D to G band ID/IG confirmed the presence of few-layer graphene. X-ray diffraction (XRD) analysis showed rotational disorder of graphene layers, characteristic of turbostratic stacking. While Scanning Electron Microscopy (SEM) images revealed the transformation of compact graphite particles into fractured and thinner structures. The addition of AB increased defect density and influenced the structural and electrical-related properties of the resulting material. These results demonstrate that FJH enables the direct conversion of commercial graphite into turbostratic graphene through an efficient and environmentally sustainable route with promising potential for energy storage applications