Apparent Size Research Articles

Native state structural and chemical characterisation of Pickering emulsions: A cryo-electron microscopy study.

Transmission electron microscopy can be used for the characterisation of a wide range of thin specimens, but soft matter and aqueous samples such as gels, nanoparticle dispersions, and emulsions will dry out and collapse under the microscope vacuum, therefore losing information on their native state and ultimately limiting the understanding of the sample. This study examines commonly used techniques in transmission electron microscopy when applied to the characterisation of cryogenically frozen Pickering emulsion samples. Oil-in-water Pickering emulsions stabilised by 3 to 5nm platinum nanoparticles were cryogenically frozen by plunge-freezing into liquid ethane to retain the native structure of the system without inducing crystallisation of the droplet oil cores. A comparison between the droplet morphology following different sample preparation methods has confirmed the effectiveness of using plunge-freezing to prepare these samples. Scanning transmission electron microscopy imaging showed that dry droplets collapse under the microscope vacuum, changing their shape and size (average apparent diameter: ∼342nm) compared to frozen samples (average diameter: ∼183nm). Cryogenic electron tomography was used to collect additional information of the 3D shape and size of the emulsion droplets, and the position of the stabilising nanoparticles relative to the droplet surface. Cryogenic energy dispersive X-ray and electron energy loss spectroscopy were used to successfully obtain elemental data and generate elemental maps to identify the stabilising nanoparticles and the oil phase. Elemental maps generated from spectral data were used in conjunction with electron tomography to obtain 3D information of the oil phase in the emulsion droplets. Beam-induced damage to the ice was the largest limiting factor to the sample characterisation, limiting the effective imaging resolution and signal-to-noise ratio, though careful consideration of the imaging parameters used allowed for the characterisation of the samples presented in this study. Ultimately this study shows that cryo-methods are effective for the representative characterisation of Pickering emulsions.

Apparent Diameters of F- to M-type Main-sequence Stars as Viewed from Habitable Zone Planets

Apparent Diameters of F- to M-type Main-sequence Stars as Viewed from Habitable Zone Planets

Epsilon Canis Majoris: The Brightest Extreme-ultraviolet Source with Surprisingly Low Interstellar Absorption

Abstract The B2 star Epsilon Canis Majoris (ϵ CMa), at parallax distance d = 124 ± 2 pc, dominates the H i photoionization of the Local Interstellar Cloud. At its closer parallax distance compared to previous estimates, ϵ CMa has a 0.9 mag fainter absolute magnitude M V = −3.97 ± 0.04. We combine measurements of distance with the integrated flux f = (41.5 ± 3.3) × 10−6 erg cm−2 s−1 and angular diameter θ d = 0.80 ± 0.05 mas to produce a consistent set of stellar parameters: radius R = 10.7 ± 0.7 R ⊙, mass M = 13.1 ± 2.3 M ⊙, gravity log g = 3.50 ± 0.05 , effective temperature T eff ≈ 21,000 K, and luminosity L ≈ 20,000 L ⊙. These parameters place ϵ CMa outside the β Cephei instability strip, consistent with its observed lack of pulsations. The observed extreme-ultraviolet spectrum yields a hydrogen photoionization rate ΓHI ≈ 10−15 s−1 (at Earth). The total flux decrement factor at the Lyman limit (ΔLL = 5000 ± 500) is a combination of attenuation in the stellar atmosphere (Δstar = 110 ± 10) and interstellar medium (ΔISM = 45 ± 5) with optical depth τ LL = 3.8 ± 0.1. After correcting for interstellar H i column density N HI = (6 ± 1) × 1017cm−2, we find a stellar LyC photon flux ΦLyC ≈ 3000 cm−2 s−1 and ionizing luminosity Q LyC = 1045.7±0.3 photons s−1. The photoionization rate ΓH ≈ (1–2) × 10−14 s−1 at the cloud surface produces an ionization fraction (30%–40%) for total hydrogen density n H = 0.2 cm−3. With its 27.3 ± 0.4 km s−1 heliocentric radial velocity and small proper motion, ϵ CMa passed within 9.3 ± 0.5 pc of the Sun 4.4 Myr ago, with a 180 times higher photoionization rate.

MOA-2022-BLG-033Lb, KMT-2023-BLG-0119Lb, and KMT-2023-BLG-1896Lb: Three low mass-ratio microlensing planets detected through dip signals

We examined the anomalies in the light curves of the lensing events MOA-2022-BLG-033, KMT-2023-BLG-0119, and KMT-2023-BLG-1896. These anomalies share similar traits: they occur near the peak of moderately to highly magnified events and display a distinct short-term dip feature. We conducted detailed modeling of the light curves to uncover the nature of the anomalies. This modeling revealed that all signals originated from planetary companions to the primary lens. The planet-to-host mass ratios are very low: q∼ 7.5 for MOA-2022-BLG-033, $q∼ 3.6 $ for KMT-2023-BLG-0119, and q∼ 6.9 for KMT-2023-BLG-1896. The anomalies occurred as the source passed through the negative deviation region behind the central caustic along the planet-host axis. The solutions are subject to a common inner-outer degeneracy, which results in varying estimations of the projected planet-host separation. For KMT-2023-BLG-1896, although the planetary scenario provides the best explanation for the anomaly, the binary companion scenario is possible. We estimated the physical parameters of the planetary systems through Bayesian analyses based on the lensing observables. While the event timescale was measured for all events, the angular Einstein radius was not measured for any. Additionally, the microlens parallax was measured for MOA-2022-BLG-033. The analysis identifies MOA-2022-BLG-033L as a planetary system with an ice giant with a mass of approximately 12 times that of Earth orbiting an early M dwarf star. The companion of KMT-2023-BLG-1896L is also an ice giant, with a mass of around 16 Earth masses, orbiting a mid-K-type main-sequence star. The companion of KMT-2023-BLG-0119L, which has a mass around that of Saturn, orbits a mid-K-type dwarf star. The lens for MOA-2022-BLG-033 is highly likely to be located in the disk, whereas for the other events the probabilities of the lens being in the disk or the bulge are roughly equal.

Colour Vision Deficits in Children with Amblyopia: Impact of Angular Size of Stimuli on Detection

Colour Vision Deficits in Children with Amblyopia: Impact of Angular Size of Stimuli on Detection

Identifying the most notable events at the first stage of the solar cycle 25

This study documented 359 occurrences during the initial phase of solar cycle 25, spanning from December 2019 to April 2023. These events were the most powerful coronal mass ejections (CMEs). Out of the total of 359 events, four of them did not have any solar flares, whereas the remaining 355 events were linked to solar flares. This study involved the observation and analysis of solar events, which led to the identification of two significant coronal mass ejections that displayed robust shock waves. Both of these events displayed rapid linear velocities and significant angular widths. The coronal mass ejections were accompanied by solar flares that displayed exceptional intensity in the form of X-rays. The shock waves generated during these events provided valuable insights into the dynamics and transmission of coronal mass ejections. These findings enhance our comprehension of the impact of powerful events on the space environment by analyzing the attributes of shock waves.

Pick‐Up ion Distributions in the Inner and Middle Saturnian Magnetosphere

AbstractBased on the entire dataset collected by the Cassini Plasma Spectrometer, we provide a comprehensive picture of the pitch angle (PA) and velocity distributions of pick‐up ions (PUIs) in Saturn's inner and middle magnetosphere. We investigate the dependence of these distributions on Saturnian Local Time and magnetic latitude. We also search for correlations with the signatures of ion cyclotron waves (ICWs) observed by the Cassini magnetometer. Our survey reveals that ion PA distributions have a pancake shape and their full width increases monotonically with magnetic latitude. This increase in angular width is anti‐correlated with the observed amplitudes of ICWs that are generated during the thermalization of the PUI distribution. We find no evidence of the previously observed, non‐monotonic change of wave amplitudes with magnetic latitude mapping into the width of the PA distributions. This suggests that only a small fraction of the energy deposited into the waves is transferred back to the ions to broaden the distribution. We find that the PA scattering time is several times the bounce period, meaning PUIs become PA scattered only after completing several cycles of bounce motion and, hence migrating to higher latitudes by the time they become more isotropic. When moving away from Saturn's magnetic equatorial plane, the observed half‐width of the velocity distributions does not evolve appreciably with latitude and shell value. This behavior changes only outside the orbit of Rhea where the observed velocity distributions begin to broaden due to elevated plasma temperatures.

Supernova remnant candidates discovered by the SARAO MeerKAT Galactic Plane Survey

Context. Sensitive radio continuum data could bring the number of known supernova remnants (SNRs) in the Galaxy more in line with what is expected. Due to confusion in the Galactic plane, however, faint SNRs can be challenging to distinguish from brighter H II regions and filamentary radio emission. Aims. We exploited new 1.3 GHz SARAO MeerKAT Galactic Plane Survey (SMGPS) radio continuum data, which cover 251° ≤ ℓ ≤ 358° and 2° ≤ ℓ ≤ 61° at | b | ≤ 1.5°, to search for SNR candidates in the Milky Way disk. Methods. We also used mid-infrared data from the Spitzer GLIMPSE, Spitzer MIPSGAL, and WISE surveys to help identify SNR candidates. These candidates are sources of extended radio continuum emission that lack mid-infrared counterparts, are not known as H II regions in the WISE Catalog of Galactic H II Regions, and have not been previously identified as SNRs. Results. We locate 237 new Galactic SNR candidates in the SMGPS data. We also identify and confirm the expected radio morphology for 201 objects classified in the literature as SNRs and 130 previously identified SNR candidates. The known and candidate SNRs have similar spatial distributions and angular sizes. Conclusions. The SMGPS data allowed us to identify a large population of SNR candidates that can be confirmed as true SNRs using radio polarization measurements or by deriving radio spectral indices. If the 237 candidates are confirmed as true SNRs, it would approximately double the number of known Galactic SNRs in the survey area, alleviating much of the discrepancy between the known and expected populations.

Broad-angle mid-infrared polarization selectivity assisted by a polarization-sensitive photonic band gap in a one-dimensional photonic crystal comprising single-material hyperbolic metamaterials

In conventional all-dielectric one-dimensional (1-D) photonic crystals (PCs), photonic band gaps (PBGs) move toward shorter wavelength direction for both p- and s-polarizations according to the Bragg condition. Consequently, it is difficult to achieve broad-angle polarization selectivity in all-dielectric 1-D PCs. In this work, we theoretically design a polarization-sensitive PBG in a 1-D PC comprising single-material hyperbolic metamaterials at mid-infrared wavelengths. As the incident angle goes up, the PBG moves toward longer wavelength direction for p-polarization while moves toward shorter wavelength direction for s-polarization. Assisted by the polarization-sensitive feature of the PBG, we achieve broad-angle polarization selectivity at mid-infrared wavelengths. The working angular width of polarization selectivity is up to 31.76°. The maximal polarization selectivity ratio reaches the order of 103. Our work paves an approach, well within the current fabrication techniques, to achieving broad-angle polarization selectivity.

Aircraft Position Estimation Using Deep Convolutional Neural Networks for Low SNR (Signal-to-Noise Ratio) Values.

The safety of the airspace could be improved by the use of visual methods for the detection and tracking of aircraft. However, in the case of the small angular size of airplanes and the high noise level in the image, sufficient use of such methods might be difficult. By using the ConvNN (Convolutional Neural Network), it is possible to obtain a detector that performs the segmentation task for aircraft images that are very small and lost in the background noise. In the learning process, a database of actual aircraft images was used. Using the Monte Carlo method, four types of Max algorithms, i.e., Pixel Value, Min. Pixel Value, and Max. Abs. Pixel Value, were compared with ConvNN's forward architecture. The obtained results showed superior detection with ConvNN. For example, if the standard deviation equals 0.1, it was twice as large. Deep dream analysis for network layers is presented, which shows a preference for images with horizontal contrast lines. The proposed solution uses the processed image values for the tracking process with the raw data using the Track-Before-Detect method.

A mathematical model of plasmin-mediated fibrinolysis of single fibrin fibers.

Fibrinolysis, the plasmin-mediated degradation of the fibrin mesh that stabilizes blood clots, is an important physiological process, and understanding mechanisms underlying lysis is critical for improved stroke treatment. Experimentalists are now able to study lysis on the scale of single fibrin fibers, but mathematical models of lysis continue to focus mostly on fibrin network degradation. Experiments have shown that while some degradation occurs along the length of a fiber, ultimately the fiber is cleaved at a single location. We built a 2-dimensional stochastic model of a fibrin fiber cross-section that uses the Gillespie algorithm to study single fiber lysis initiated by plasmin. We simulated the model over a range of parameter values to learn about patterns and rates of single fiber lysis in various physiological conditions. We also used epifluorescent microscopy to measure the cleavage times of fibrin fibers with different apparent diameters. By comparing our model results to the laboratory experiments, we were able to: 1) suggest value ranges for unknown rate constants(namely that the degradation rate of fibrin by plasmin should be ≤ 10 s-1 and that if plasmin crawls, the rate of crawling should be between 10 s-1 and 60 s-1); 2) estimate the fraction of fibrin within a fiber cross-section that must be degraded for the fiber to cleave in two; and 3) propose that that fraction is higher in thinner fibers and lower in thicker fibers. Collectively, this information provides more details about how fibrin fibers degrade, which can be leveraged in the future for a better understanding of why fibrinolysis is impaired in certain disease states, and could inform intervention strategies.

KMT-2024-BLG-1044L: A sub-Uranus microlensing planet around a host at the star–brown dwarf mass boundary

Aims. We analysed microlensing data to uncover the nature of the anomaly that appeared near the peak of the short-timescale microlensing event KMT-2024-BLG-1044. Despite the anomaly’s brief duration of less than a day, it was densely observed through high-cadence monitoring conducted by the KMTNet survey. Methods. Detailed modelling of the light curve confirmed the planetary origin of the anomaly and revealed two possible solutions, due to an inner–outer degeneracy. The two solutions provide different measured planet parameters: (s, q)inner = [1.0883 ± 0.0027, (3.125 ± 0.248) × 10−4] for the inner solutions and (s, q)outer = [1.0327 ± 0.0054, (3.350 ± 0.316) × 10−4] for the outer solutions. Results. Using Bayesian analysis with constraints provided by the short event timescale (tE ~ 9.1 day) and the small angular Einstein radius (θE ~ 0.16 mas for the inner solution and ~ 0.10 mas for the outer solutio), we determined that the lens is a planetary system consisting of a host near the boundary between a star and a brown dwarf and a planet with a mass lower than that of Uranus. The discovery of the planetary system highlights the crucial role of the microlensing technique in detecting planets that orbit substellar brown dwarfs or very low-mass stars.

First Resolution of Microlensed Images of a Binary-lens Event

We resolve the multiple images of the binary-lens microlensing event ASASSN-22av using the GRAVITY instrument of the Very Large Telescope Interferometer (VLTI). The light curves show weak binary-lens perturbations, complicating the analysis, but the joint modeling with the VLTI data breaks several degeneracies, arriving at a strongly favored solution. Thanks to precise measurements of the angular Einstein radius θ E = 0.724 ± 0.002 mas and microlens parallax, we determine that the lens system consists of two M dwarfs with masses of M 1 = 0.258 ± 0.008 M ⊙ and M 2 = 0.130 ± 0.007 M ⊙, a projected separation of r ⊥ = 6.83 ± 0.31 au, and a distance of D L = 2.29 ± 0.08 kpc. The successful VLTI observations of ASASSN-22av open up a new path for studying intermediate-separation (i.e., a few astronomical units) stellar-mass binaries, including those containing dark compact objects such as neutron stars and stellar-mass black holes.

Cosmography from accurate mass modeling of the lens group SDSS J0100+1818: Five sources at three different redshifts

Systems where multiple sources at different redshifts are strongly lensed by the same deflector allow one to directly investigate the evolution of the angular diameter distances as a function of redshift, and thus to learn about the geometry of the Universe. We present measurements of the values of the total matter density, Ωm, and of the dark energy equation of state parameter, w, through a detailed strong lensing analysis of SDSS J0100+1818, a group-scale system at z = 0.581 with five lensed sources, from z = 1.698 to 4.95. We take advantage of new spectroscopic data from the Multi Unit Spectroscopic Explorer (MUSE) on the Very Large Telescope to securely measure the redshift of 65 sources, including the 5 multiply imaged background sources (lensed into a total of 18 multiple images) and 19 galaxies on the deflector plane, all employed to build robust strong lensing models with the software GLEE. The total mass distribution of the deflector is described in a relatively simple way, and includes an extended halo, the brightest group galaxy (BGG) with a measured stellar velocity dispersion of (380.5 ± 4.4) km s−1, and fainter members. We measure Ωm = 0.14−0.09+0.16 in a flat Λ cold dark matter (CDM) model, and Ωm = 0.19−0.10+0.17 and w = −1.27−0.48+0.43 in a flat wCDM model. Given the presence of different sources angularly close in projection, we quantify through a multiplane approach their impact on the inferred values of the cosmological parameters. We obtain consistent median values, with uncertainties for only Ωm increasing by approximately a factor of 1.5. Thanks to the remarkably wide radial interval where the multiple images are observed, ranging from 15 to 77 kpc from the BGG, we accurately measure the total mass profile and infer the stellar over total mass profile of the deflector. They result in a total mass of (1.55 ± 0.01)×1013 M⊙ within 50 kpc and a stellar over total mass profile decreasing from 45.6−8.3+8.7% at the BGG effective radius to (6.6 ± 1.1)% at R ≈ 77 kpc. Our results confirm that SDSS J0100+1818 is one of the most massive (lens) galaxies known at intermediate redshift and one of the most distant candidate fossil systems. We also show that group-scale systems that act as lenses for ≥3 background sources at different redshifts enable one to estimate the values of the cosmological parameters Ωm and w with an accuracy that is competitive with that obtained from lens galaxy clusters.

ODIN: Identifying Protoclusters and Cosmic Filaments Traced by Lyα-emitting Galaxies

To understand the formation and evolution of massive cosmic structures, studying them at high redshift, in the epoch when they formed the majority of their mass, is essential. The One-hundred-deg2 DECam Imaging in Narrowbands (ODIN) survey is undertaking the widest-area narrowband program to date, to use Lyα-emitting galaxies (LAEs) to trace the large-scale structure (LSS) of the Universe on the scale of 10–100 cMpc at three cosmic epochs. In this work, we present results at z = 3.1 based on early ODIN data in the COSMOS field. We identify protoclusters and cosmic filaments using multiple methods and discuss their strengths and weaknesses. We then compare our observations against the IllustrisTNG suite of cosmological hydrodynamical simulations. The two are in excellent agreement, identifying a similar number and angular size of structures above a specified density threshold. We successfully recover the simulated protoclusters with log(M z=0/M ⊙) ≳ 14.4 in ∼60% of the cases. With these objects, we show that the descendant masses of our observed protoclusters can be estimated purely based on our 2D measurements, finding a median z = 0 mass of ∼1014.5 M ⊙. The lack of information on the radial extent of each protocluster introduces a ∼0.4 dex uncertainty in its descendant mass. Finally, we show that the recovery of the cosmic web in the vicinity of protoclusters is both efficient and accurate. The similarity of our observations and the simulations implies that our structure selection is likewise robust and efficient, demonstrating that LAEs are reliable tracers of the LSS.

Tracking an Eruptive Prominence Using Multiwavelength and Multiview Observations on 2023 March 7

In this paper, we carry out multiwavelength and multiview observations of the prominence eruption, which generated a C2.3 class flare and a coronal mass ejection (CME) on 2023 March 7. For the first time, we apply the revised cone model to three-dimensional reconstruction and tracking of the eruptive prominence for ∼4 hr. The prominence propagates nonradially and makes a detour around the large-scale coronal loops in active region NOAA 13243. The northward deflection angle increases from ∼36° to ∼47° before returning to ∼36° and keeping up. There is no longitudinal deflection throughout the propagation. The angular width of the cone increases from ∼30° and reaches a plateau at ∼37°. The heliocentric distance of the prominence rises from ∼1.1 to ∼10.0 R ☉, and the prominence experiences continuous acceleration (∼51 m s−2) over 2 hr, which is probably related to the magnetic reconnection during the C-class flare. The true speed of the CME front is estimated to be ∼829 km s−1, which is ∼1.2 times larger than that of the CME core (prominence). We conclude that both acceleration and deflection of eruptive prominences in their early lives could be reproduced with the revised cone model.

Limits on Dark Matter Compact Objects implied by Supermagnified Stars in Lensing Clusters

Abstract Supermagnified stars are gravitationally lensed individual stars that are located close to a caustic of a lensing galaxy cluster, and have their flux magnified by a large enough factor (typically ∼ 1000) to make them detectable with present telescopes. The maximum magnification is limited by microlensing caused by intracluster stars or other compact objects, which create a network of corrugated critical lines with an angular width proportional to the surface density of microlenses. We consider a set of 9 cases of supermagnified stars reported in the literature, and derive an upper limit on the surface density of compact objects, such as primordial black holes, that might be present as a fraction of the dark matter in addition to known intracluster stars. Any such additional compact objects would widen the corrugated critical line network and therefore the width of the distribution of supermagnified stars around the modeled critical lines of the lens. We find that any compact objects, including primordial black holes, with masses above ∼10−6 M⊙ (below which the microcaustics are closer together than the typical angular size of supermagnified stars) cannot account for more than ∼ 2% of the dark matter.

Simultaneous two colour intensity interferometry with H.E.S.S.

Abstract In recent years, intensity interferometry has been successfully applied to the Imaging Atmospheric Cherenkov Telescopes H.E.S.S. , MAGIC, and VERITAS. All three telescope systems have proven the feasibility and capability of this method. After our first campaign in 2022, when two of the H.E.S.S. telescopes in Namibia were equipped with our external setup and the angular diameter of two stars was measured, our setup was upgraded for a second campaign in 2023, where the goal is to perform simultaneous two colour measurements. The second campaign not only involves a third equipped telescope, but also each mechanical setup now includes two interference filters at two different wavelengths (375 nm and 470 nm) with a broader bandwidth of 10 nm. This enables having simultaneous two-colour measurements, which yields information about the star’s physical size at different wavelengths. This is the first time that simultaneous dual-waveband intensity interferometry measurements are performed. The angular diameter results of the 4 stars, Mimosa (β Cru), Eta Centauri (η Cen), Nunki (σ Sgr) and Dschubba (δ Sco), are reported, where the effects of limb darkening are also taken into account.

Duration of the recovery phase of sporadic Forbush decreases

A model is proposed to describe the recovery of sporadic Forbush decreases, in which the geometry of the large-scale magnetic field plays a significant role. The dependence of the duration of the recovery of the Forbush decrease on the angular width of the disturbance, the gradient of the solar wind flow velocity, and the heliolongitude of the source of the ejection has been established. The relative contribution of different causes to the duration of recovery varies in events and depends on the parameter values. The modeled duration of the Forbush decrease recovery agrees with the measurements. The model explains the east–west duration asymmetry, consistent with the measurements. Analysis of the observed Forbush decreases using the model shows its applicability. The model can be applied to determine the angular width of an interplanetary coronal mass ejection (a hard-to-determine parameter) using the observed parameters: the duration of the Forbush decrease recovery, the solar wind velocity gradient, and the heliolongitude of the coronal mass ejection source.

Manufacturing of carbon-supported platinum cathodes for proton exchange membrane fuel cell using the doctor blade process: Microstructure and performance

Catalyst layers (CL, the anode and cathode) properties do influence the performance of proton exchange membrane fuel cells (PEMFC). CLs are prepared by depositing an ink made from a catalyst (carbon-supported Pt-based nanoparticles, NPs) and an ionomer in appropriate solvents on a substrate, followed by post-treatment (solvent evaporation, calendaring, hot-pressing). The literature rarely provides details and characterizations about CLs fabrication. This contribution investigates a way to prepare Pt/VC (Pt NPs supported on Vulcan XC72 carbon-black) and Pt/GC (Pt NPs supported on graphitized-carbon-black) PEMFC CLs. The ink formulation, mixing and deposition methods are evaluated and the areal homogeneity/texture of the formed CLs thoroughly characterized by scanning electron microscopy and X-Ray fluorescence. Light-ball-milling mixing enables to prepare homogeneous and agglomerate-free inks without degrading the Pt/C catalysts. The optimal ionomer-to-carbon ratio differs for Pt/GC and Pt/VC CLs; it not only depends on the BET surface area of the carbon substrate and its outer apparent surface (apparent carbon particles diameter), but should also be adapted to physicochemical surface properties of the Pt/C sample. Optimized I/C = 1–1.2 enables to improve the performance of Pt/GC cathodes by ca. 300 % versus I/C = 0.5 (at 80 °C, 80%RH), owing to hugely-depreciated proton-transport-resistance in the CL.