bluuebunny/crossref_metadata_2025 huggingface dataset:
Designing a Module on Stuttering and Cluttering: A Guide for Speech-Language Pathology Educators
Authors: Connery Amy , Shé Caitríona Ní
Published: February 2024

Purpose:

Due to the scope of practice of speech-language pathology (SLP) expanding considerably in recent times, there is reduced emphasis on certain communication conditions within the curricula of SLP university programs. Stuttering and cluttering are neglected components of such curricula, despite the complex clinical skill set required to work with these client groups. Evaluation of the content and quality of modules on stuttering and cluttering is warranted to ensure that SLP students are graduating with adequate competence and confidence for supporting people with these conditions. This tutorial, based on a review of the literature, aims to provide guidance to educators who are designing or revising such modules.

Method:

The All Ireland Society for Higher Education (AISHE) model for module design provides a practical and theoretically underpinned guide to educators in higher education on the design of a new module or the review of an existing one. The model's seven key components are discussed, and their application to a module on stuttering and cluttering is outlined.

Results:

The AISHE model provides a systematic and user-friendly approach to module design in SLP university programs. It supports educators who are designing a new module or revising a module currently being taught on stuttering and cluttering.

Conclusions:

Educators are encouraged to familiarize themselves with the seven components of the AISHE model and to use it as a tool to design or revise modules on stuttering and cluttering. This will ensure that SLP students are graduating with increased competence and confidence in working with these client groups.
Physics‐informed surrogates for electromagnetic dynamics using Transformers and graph neural networks
Authors: Noakoasteen O. , Christodoulou C. , Peng Z. , Goudos S. K.
Published: February 2024

A novel use case for two data‐driven models, namely, a Transformer and a convolutional graph neural network (CGNN) is proposed. The authors propose to use these models for emulating the dynamics of electromagnetic (EM) propagation and scattering. The Transformer translates a past sequence into a future sequence by constructing representations from the past and using it to predict the future, taking all of its own previous predictions as input at each step of prediction. The CGNN updates the current state of attribute vectors of each node by passing it information (messages) from all of its neighbouring nodes. We train these models with FDTD simulations of plane waves propagating and scattering from PEC objects. The authors demonstrate that, within the bounds of computational resources, the Transformer can be utilised as a surrogate for EM dynamics, providing 14× speed‐up, while the CGNN can be utilised as a next‐frame predictor, providing 9× speed‐up. When comparing the accuracy of these two models with the authors’ previously developed Encoder‐Recurrent‐Decoder (ERD) model, it is observed that the error for both the Transformer and the CGNN remains within the same bound for the ERD model. To the best of the authors’ knowledge, this work is the first to utilise the Transformer as a surrogate for EM dynamics.
Machine learning applications in studies of the physical properties of active galactic nuclei based on photometric observations
Authors: Mechbal Sarah , Ackermann Markus , Kowalski Marek
Published: February 2024

Context. We investigate the physical nature of active galactic nuclei (AGNs) using machine learning (ML) tools.

Aims. We show that the redshift, z, bolometric luminosity, LBol, central mass of the supermassive black hole (SMBH), MBH, Eddington ratio, λEdd, and AGN class (obscured or unobscured) can be reconstructed through multi-wavelength photometric observations only.

Methods. We trained a random forest regressor (RFR) ML-model on 7616 spectroscopically observed AGNs from the SPIDERS-AGN survey, which had previously been cross-matched with soft X-ray observations (from ROSAT or XMM), WISE mid-infrared photometry, and optical photometry from SDSS ugriz filters. We built a catalog of 21 050 AGNs that were subsequently reconstructed with the trained RFR; for 9687 sources, we found archival redshift measurements. All AGNs were classified as either type 1 or type 2 using a random forest classifier (RFC) algorithm on a subset of known sources. All known photometric measurement uncertainties were incorporated via a simulation-based approach.

Results. We present the reconstructed catalog of 21 050 AGNs with redshifts ranging from 0 < z < 2.5. We determined z estimations for 11 363 new sources, with both accuracy and outlier rates within 2%. The distinction between type 1 or type 2 AGNs could be identified with respective efficiencies of 94% and 89%. The estimated obscuration level, a proxy for AGN classification, of all sources is given in the dataset. The LBol, MBH, and λEdd values are given for 21 050 new sources with their estimated error. These results have been made publicly available.

Conclusions. The release of this catalog will advance AGN studies by presenting key parameters of the accretion history of 6 dex in luminosity over a wide range of z. Similar applications of ML techniques using photometric data only will be essential in the future, with large datasets from eROSITA, JSWT, and the VRO poised to be released in the next decade.
Measurement of the size of the gamma-ray source in blazar B0218+357 based on microlensing at the 100 GeV energy band
Authors: Vovk Ie. , Neronov A.
Published: February 2024

Context.Observations of the effect of microlensing in gravitationally lensed quasars can be used to study the structure of active galactic nuclei on distance scales down to the sizes of a supermassive black hole’s powering source activity.

Aims.We searched for a microlensing effect in the signal from a gravitationally lensed blazar, B0218+357, in a very-high-energyγ-ray band.

Methods.We combined observations of a bright flare of the source in 2014 by theFermiLarge Area Telescope and MAGIC telescopes in the 0.1 − 300 GeV and 65 − 175 GeV energy ranges, respectively. Using the time-delayed leading and trailing signals from two gravitationally lensed images of the source, we measured the magnification factor at the moment of the flare. We used the scaling of the maximal magnification factor with the source size to constrain the size of theγ-ray emission region in the wide 0.1 − 175 GeV energy range.

Results.The magnification factor in the very-high-energy band that we derived from our comparison ofFermi/LAT and MAGIC data isμVHE = 25−17+38, which is substantially larger than the factor found in the radio band. This suggests one of the source images is strongly affected by microlensing at the moment of the flare. Assuming that the microlensing is produced by a stellar mass object in the lens galaxy, we constrained the size of the emission region in theE > 100 GeV band to beRVHE = 6.6−5.6+69 × 1014 cm. We note that the spectrum of the microlensed source was unusually hard at the moment of the flare, and we speculate that this hardening may be due to the energy-dependent microlensing effect. This interpretation suggests that the source size decreases with energy in the entire 0.1 − 175 GeV energy range we studied.
Curves of growth for transiting exocomets: Application to Fe II lines in the β Pictoris system
Authors: Vrignaud T. , Lecavelier des Etangs A. , Kiefer F. , Lagrange A.-M. , Hébrard G. , Strøm P. A. , Vidal-Madjar A.
Published: February 2024

Using transit spectroscopy, exocomets are routinely observed in the young planetary system of β Pic. However, despite more than 35 yr of observations, we still have very little information on the physical properties and almost no information on the abundances of the gaseous clouds surrounding the comets’ nuclei, the difficulty being the conversion of the observed absorption profiles into column density measurements. Here, we present a new method to interpret the exocomet absorptions observed in β Pic spectrum and link them to the physical properties of the transiting cometary tails (e.g. size, temperature, and column density). We show that the absorption depth of a comet in a set of lines arising from similar excitation levels of a given chemical species follows a simple curve as a function of g·f, where f is the line oscillator strength and g its lower level multiplicity. This curve is the analogue of the curve of growth for interstellar absorption lines, where equivalent widths are replaced by absorption depths. To fit this exocomet curve of growth, we introduced a model where the cometary absorption is produced by a homogeneous cloud, covering only a limited fraction of the stellar disc. This model is defined by two parameters: α, characterising the size of the cloud relative to the star, and β, related to the optical depth of the absorbing gas. This model was tested on two comets observed with the Hubble Space Telescope in December 1997 and October 2018, in a set of lines of ionised iron (Fe II) at 2750 Å. The measured absorption depths are found to satisfactory match the two-parameter curve of growth model, indicating that both comets cover roughly 40% of the stellar disc (α = 0.4) and have optical thicknesses close to unity in those lines (β ~ 1). Then, we show that if we consider a set of lines arising from a wider range of energy levels, the absorbing species seems to be populated at thermodynamical equilibrium, causing the cometary absorption to follow a curve of growth as a function of g f ⋅ e−El/kBT (where T is the temperature of the absorbing medium). For the comet observed on December 6, 1997, we derive a temperature of T = 10 500 ± 500 K and a total Fe II column density of NFeII = (1.11 ± 0.09) × 1015 cm−2. By considering the departure from the Boltzmann distribution of the highest excited energy levels (El ~ 25 000 cm−1), we also estimate an electronic density of ne ≈ (3 ± 1) × 107 cm−3.
A distinct radial acceleration relation across the brightest cluster galaxies and galaxy clusters
Authors: Tian Yong , Ko Chung-Ming , Li Pengfei , McGaugh Stacy , Poblete Shemile L.
Published: February 2024

Recent studies reveal a radial acceleration relation (RAR) in galaxies, which illustrates a tight empirical correlation connecting the observational acceleration and the baryonic acceleration with a characteristic acceleration scale. However, a distinct RAR has been revealed on brightest cluster galaxy (BCG) cluster scales with a seventeen-times-larger acceleration scale due to the gravitational lensing effect. In this work, we systematically explore the acceleration and mass correlations between dynamical and baryonic components in 50 BCGs. To investigate the dynamical RAR in BCGs, we derived their dynamical accelerations from the stellar kinematics using the Jeans equation through Abel inversion and adopted the baryonic mass from Sloan Digital Sky Survey photometry. We explored the spatially resolved kinematic profiles with the largest integral field spectroscopy (IFS) data collected by the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey. Our results demonstrate that the dynamical RAR in BCGs is consistent with the lensing RAR on BCG-cluster scales as well as a larger acceleration scale. This finding may imply that BCGs and galaxy clusters have fundamental differences from field galaxies. We also find a mass correlation, but it is less tight than the acceleration correlation.
New insight on the nature of cosmic reionizers from the CEERS survey
Authors: Mascia S. , Pentericci L. , Calabrò A. , Santini P. , Napolitano L. , Arrabal Haro P. , Castellano M. , Dickinson M. , Ocvirk P. , Lewis J. S. W. , Amorín R. , Bagley M. , Bhatawdekar R. , Cleri N. J. , Costantin L. , Dekel A. , Finkelstein S. L. , Fontana A. , Giavalisco M. , Grogin N. A. , Hathi N. P. , Hirschmann M. , Holwerda B. W. , Jung I. , Kartaltepe J. S. , Koekemoer A. M. , Lucas R. A. , Papovich C. , Pérez-González P. G. , Pirzkal N. , Trump J. R. , Wilkins S. M. , Yung L. Y. A.
Published: February 2024

The Epoch of Reionization (EoR) began when galaxies grew in abundance and luminosity, so their escaping Lyman continuum (LyC) radiation started ionizing the surrounding neutral intergalactic medium (IGM). Despite significant recent progress, the nature and role of cosmic reionizers are still unclear: in order to define them, it would be necessary to directly measure their LyC escape fraction (fesc). However, this is impossible during the EoR due to the opacity of the IGM. Consequently, many efforts at low and intermediate redshift have been made to determine measurable indirect indicators in high-redshift galaxies so that their fesc can be predicted. This work presents the analysis of the indirect indicators of 62 spectroscopically confirmed star-forming galaxies at 6 ≤ z ≤ 9 from the Cosmic Evolution Early Release Science (CEERS) survey, combined with 12 sources with public data from other JWST-ERS campaigns. From the NIRCam and NIRSpec observations, we measured their physical and spectroscopic properties. We discovered that on average 6 < z < 9 star-forming galaxies are compact in the rest-frame UV (re ∼ 0.4 kpc), are blue sources (UV-β slope ∼ − 2.17), and have a predicted fesc of about 0.13. A comparison of our results to models and predictions as well as an estimation of the ionizing budget suggests that low-mass galaxies with UV magnitudes fainter than M1500 = −18 that we currently do not characterize with JWST observations probably played a key role in the process of reionization.
Investigating black hole accretion disks as potential polluter sources for the formation of enriched stars in globular clusters
Authors: Fréour Laurane , Zocchi Alice , van de Ven Glenn , Pancino Elena
Published: February 2024

Accretion disks surrounding stellar mass black holes have been suggested as potential locations for the nucleosynthesis of light elements, which are our primary observational discriminant of multiple stellar populations within globular clusters. The population of enriched stars in globular clusters are enhanced in 14N, 23Na, and sometimes in 27Al and/or in 39K. In this study, our aim is to investigate the feasibility of initiating nucleosynthesis for these four elements in black hole accretion disks, considering various internal parameters such as the temperature of the gas and timescale of the accretion. To achieve this, we employed a 132-species reaction network. We used the slim disk model, suitable for the Super-Eddington mass accretion rate and for geometrically and optically thick disks. We explored the conditions related to the mass, mass accretion rate, viscosity, and radius of the black hole-accretion disk system that would allow for the creation of 14N, 23Na, 27Al, and 39K before the gas is accreted onto the central object. This happens when the nucleosynthesis timescale is shorter than the viscous timescale. Our findings reveal that there is no region in the parameter space where the formation of 23Na can occur and only a very limited region where the formation of 14N, 27Al, and 39K is plausible. Specifically, this occurs for black holes with masses lower than 10 solar masses (m < 10 M⊙), with a preference toward even lower mass values (m < 1 M⊙) and extremely low viscosity parameters (α < 10−3). Such values are highly unlikely based on current observations of stellar mass black holes. However, such low mass black holes could actually exist in the early universe, as so-called primordial black holes. In conclusion, our study suggests that the nucleosynthesis within black hole accretion disks of elements of interest for the multiple stellar populations, namely, 14N, 23Na, 27Al, and 39K is improbable, but not impossible, using the slim disk model. Future gravitational wave missions will help constrain the existence of tiny and light black holes.
Super-early JWST galaxies, outflows, and Lyαvisibility in the Epoch of Reionization
Authors: Ferrara A.
Published: February 2024

The overabundance of super-early (redshiftz > 10) luminous (MUV < −20) blue galaxies detected by JWST has been explained as being due to negligible dust attenuation in these systems. We show that this model correctly reproduces the UV luminosity function atz > 10 and the star formation rate (SFR) density evolution. The model also predicts, in agreement with data, that the cosmic specific SFR (sSFR) grows as sSFR ∝ (1 + z)3/2. Atz ≃ 10, the cosmic sSFR crosses the critical value sSFR⋆ = 25 Gyr−1, and approximately 45% of the galaxies become super-Eddington, driving outflows reaching velocities of ≈830(ϵ⋆/fM)1/2km s−1, whereϵ⋆andfMare the star formation efficiency and fraction of the halo gas expelled in the outflow, respectively. This prediction is consistent with the outflow velocities measured in 12 super-Eddington galaxies of the JWST/JADES sample. Such outflows clear the dust, thus boosting the galaxy luminosity. They also dramatically enhance the visibility of the Lyαline fromz > 10 galaxies by introducing a velocity offset. The observed Lyαproperties in GN-z11 (z = 10.6) are simultaneously recovered by the outflow model if logNHI ≃ 20.1, implying that the outflow is largely ionized. We make analogous predictions for the Lyαvisibility of other super-early galaxies, and we compare the model with Lyαsurveys atz > 7, finding that essentially all super-Eddington (sub-Eddington) galaxies are (not) detected in Lyα. Finally, the sSFR positively correlates with the LyC escape fraction, as outflows carve ionized transparent channels through which LyC photons leak.
Rotation of ZZ Ceti stars as seen by TESS
Authors: Bognár Zsófia , Sódor Ádám
Published: February 2024

Context. Knowing the rotation rates and masses of white dwarf stars is an important step towards characterising the angular momentum transport mechanism in their progenitors, and coupling the cores of red giants to their envelopes. However, deriving these rotation rates is not an easy task. One can use the rotational broadening of spectral lines, but there is another way to gather reliable information on the stellar rotation periods of pulsators: through studying the splitting effect of rotation on oscillation frequencies.

Aims. We aim to derive stellar rotation periods in the TESS sample for as many white dwarf pulsators as possible.

Methods. We rely on light-curve analysis of the TESS observations, and search for closely spaced frequency multiplets that could be rotationally split pulsation modes. We work with triplet frequencies, even if one or two triplet components are only marginally detectable. We also utilise ground-based observations available from the literature in an attempt to confirm the presence of several triplets.

Results. We successfully identified rotationally split multiplets and derived rotation rates for 14 stars. The fastest rotators we identified have rotation periods of 6.6–10.0 h. The majority of the pulsators rotate with periods of 11.9–47.5 h, while we derived 85.5 and 93.2 h periods for the slowest rotators. In addition to providing stellar mass estimations, our results confirm previous findings that larger-mass WDs rotate faster than their lower-mass counterparts. We determine the rotation periods of four stars for the first time.
Forming localized dust concentrations in a dust ring: DM Tau case study
Authors: Liu Hauyu Baobab , Muto Takayuki , Konishi Mihoko , Chung Chia-Ying , Hashimoto Jun , Doi Kiyoaki , Dong Ruobing , Kudo Tomoyuki , Hasegawa Yasuhiro , Terada Yuka , Kataoka Akimasa
Published: February 2024

Context. Previous high-angular-resolution 225 GHz (~1.3 mm) continuum observations of the transitional disk DM Tau have resolved an outer ring at 20–120 au radii that is weakly azimuthally asymmetric.

Aims. We aim to examine dust growth and filtration in the outer ring of DM Tau.

Methods. We performed ~0″.06 (~8.7 au) resolution Karl G. Jansky Very Large Array (JVLA) 40–48 GHz (~7 mm; Q band) continuum observations, along with complementary observations at lower frequencies. In addition, we analyzed the archival JVLA observations undertaken since 2010.

Results. Intriguingly, the Q band image resolved the azimuthally highly asymmetric, knotty dust emission sources close to the inner edge of the outer ring. Fitting the 8–700 GHz spectral energy distribution (SED) with two dust components indicates that the maximum grain size (amax) in these knotty dust emission sources is likely ≳300 µm, whereas it is ≳50 µm in the rest of the ring. These results may be explained by a trapping of inwardly migrating “grown” dust close to the ring inner edge. The exact mechanism for developing the azimuthal asymmetry has not yet been identified, which may be due to planet-disk interaction that might also be responsible for the creation of the dust cavity and pressure bump. Otherwise, it may be due to the fluid instabilities and vortex formation as a result of shear motions. Finally, we remark that the asymmetries in DM Tau are difficult to diagnose from the ≳225 GHz observations, owing to a high optical depth at the ring. In other words, the apparent symmetric or asymmetric morphology of the transitional disks may be related to the optical depths of those disks at the observing frequency.
Detection of a cyclotron line in the Be X-ray pulsar IGR J06074+2205
Authors: Roy Kinjal , Sharma Rahul , Manikantan Hemanth , Paul Biswajit
Published: February 2024

Context. IGR J0607.4+2205 is a transient Be X-ray binary discovered two decades ago. IGR J0607.4+2205 underwent an outburst in 2023 during which it was observed twice with NuSTAR.

Aims. The main goal of this work is to model the broadband X-ray spectrum of IGR J0607.4+2205 during the outburst and to study the variations of the spectral and timing features at different intensities.

Methods. We extracted the light curve and spectrum of the source from the two NuSTAR observations carried out during the recent outburst in the energy range of 3−78 keV. We used the epoch folding technique to find pulsation from the source and to study the changes in emission characteristics from the source with energy across an order of magnitude variation in source luminosity.

Results. IGR J0607.4+2205 shows pulsations with a period of ∼347.6 s during both the observations, with a pulse fraction of ≥50%. The broadband spectrum of the source was modelled using a power-law continuum with a high-energy cutoff. During the first observation, a cyclotron absorption line at ∼51 keV was also present in the source with an optical depth of ∼1.3. However, no cyclotron line feature was detected in the second observation when the source was an order of magnitude fainter. Additionally, soft excess was detected in the second observation, which was modelled with a black body component emerging from close to the neutron star (NS).

Conclusions. We report the first ever detection of a cyclotron line in the broadband spectrum of IGR J0607.4+2205 centred at 51 ± 1 keV. The magnetic field strength of the NS is estimated to be ∼4 × 1012 G from the centroid energy of the absorption line. A significant change is observed in the pulse profile with luminosity during the decay of the outburst, indicating an associated change in the beaming pattern.
The Role of Mesons in Light-by-Light Scattering at Low Transverse Momentum
Authors: Jucha Paweł , Kłusek-Gawenda Mariola
Published: February 2024

Abstract. Light-by-Light scattering involves the interaction of two strong elec tromagnetic fields, resulting in the emission of two photons. In the next years, the ALICE 3 experiment is going to measure photons in the transverse mo mentum range pt = 1 - 50 MeV and 100 - 5000 MeV, which have not been investigated so far. Moving to a lower range of pt imposes a consideration of low-energy meson resonances which decay into two-photon channel. Further more, experimental possibilities to investigate the VDM-Regge mechanism are discussed. The role of the vertical background in light-by-light scattering mea surements is also shown.
Properties of the Tcc(3875)+ and the Tcc (3875)− states in nuclear matter
Authors: Montesinos Víctor , Albaladejo Miguel , Nieves Juan , Tolos Laura
Published: February 2024

Abstract. Since its first detection, the interesting properties of the Tcc(3875)+ have made it to be one of the most prominent tetraquark-like states up to date. In this work we present a joint analysis of the T+cc and its charge-conjugated partner in a dense nuclear medium. We start by considering both states as purely isoscalar D* D and D¯*D¯ S -wave bound states, respectively. We use previous results for the in-medium D, D¯*D¯, D* and D* spectral functions to determine the modified two-meson amplitudes. We find important changes in the in-medium mass and width of both tetraquark-like resonances, which become more visible when increasing the nuclear density and molecular probabilities. The experimental confirmation of the found distinctive patterns will support the existence of molecular components in the T+cc and T-c¯c¯ wave functions.
μJ-level normal-dispersion fiber optical chirped-pulse parametric oscillator
Authors: Guezennec Tristan , Idlahcen Saïd , Cervera Armand , Hanzard Pierre-Henry , Landais David , Provino Laurent , Haboucha Adil , Godin Thomas , Hideur Ammar
Published: February 2024

We demonstrate the generation of broadband tunable and synchronized pulses exceeding the microjoule level using the new concept of Fiber Optical Parametric Chirped-Pulse Oscillation (FOPCPO). The oscillator is based on a collapsed-ends photonic crystal fiber pumped in the normal dispersion regime by an ytterbium fiber laser delivering highly-chirped pulses. The experimental results are compared with the results of numerical simulations and highlight that the feedback ratio appears as a key parameter for optimizing the system’s efficiency and dynamics.
Exploring the complex dynamics of a diffusive epidemic model: Stability and bifurcation analysis
Authors: Acharya Sattwika , Kumar Upadhyay Ranjit , Mondal Bapin
Published: February 2024

The recent pandemic has highlighted the need to understand how we resist infections and their causes, which may differ from the ways we often think about treating epidemic diseases. The current study presents an improved version of the susceptible-infected-recovered (SIR) epidemic model, to better comprehend the community’s overall dynamics of diseases, involving numerous infectious agents. The model deals with a non-monotone incidence rate that exhibits psychological or inhibitory influence and a saturation treatment rate. It has been identified that depending on the measure of medical resources and the effectiveness of their supply, the model exposes both forward and backward bifurcations where two endemic equilibria coexist with infection-free equilibrium. The model also experiences local and global bifurcations of codimension two, including saddle-node, Hopf, and Bogdanov–Takens bifurcations. Additionally, the stability of equilibrium points is investigated. For a spatially extended SIR model system, we have shown that cross-diffusion allows S and I populations to coexist in a habitat. Also, the Turing instability requirements and Turing bifurcation regime are derived. The relationship between distinct role-playing model parameters and various pattern formations like spot and stripe patterns is validated by carrying out in-depth numerical simulations. The findings in the vicinity of the endemic equilibrium solution demonstrate the significance of positive and negative valued cross-diffusion coefficients in regulating the genesis of spatial patterns in susceptible as well as diseased individuals. The discussion of the findings of epidemiological ramifications concludes the manuscript.
Measurement of mix at the fuel–ablator interface in indirectly driven capsule implosions on the National Ignition Facility
Authors: Hall G. N. , Weber C. R. , Smalyuk V. A. , Landen O. L. , Trosseille C. , Pak A. , Hartouni E. , Marley E. , Ebert T. , Bradley D. K. , Hsing W. , Tommasini R. , Izumi N. , Pape S. Le , Divol L. , Krauland C. M. , Thompson N. , Casco E. R. , Ayers M. J. , Nagel S. R. , Carpenter A. C. , Hurd E. R. , Dayton M. S. , Engelhorn K. , Holder J. P.
Published: February 2024

The interface between the capsule ablator and fuel ice layer is susceptible to hydrodynamic instabilities. The subsequent mixing of hot ablator material into the ice reduces fuel compression at stagnation and is a candidate for reduced capsule performance. The ability to diagnose ice–ablator mix is critical to understanding and improving stability at this interface. Combining the crystal backlighter imager with the single line of sight camera on the National Ignition Facility (NIF) allows direct measurement of ice–ablator mix by providing multiple quasi-monochromatic radiographs of layered capsule implosions per experiment with high spatial (∼12 μm) and temporal (∼35 ps) resolution. The narrow bandwidth of this diagnostic platform allows radiography of the inner edge of the capsule limb close to stagnation without capsule self-emission contaminating the data and removes opacity uncertainties typically associated with the spectral content of the radiograph. Analysis of radiographic data via a parameterized forward-fitting Abel inversion technique provides measurements of the distribution of mix mass inwards from the ice–ablator interface. The sensitivity of this mix measurement technique was demonstrated by applying it to layered experiments in which the stability of the ice–ablator interface was expected to vary significantly. Additional experiments suggest that high-density carbon capsules that employ a buried-layer dopant profile suffer from mixing at the innermost doped–undoped interface. Data from these experiments suggest that opacity models used in hydrodynamic simulations of NIF experiments can potentially over-predict the opacity of doped capsules. LLNL-JRNL-850535-DRAFT.
Electrolyte gated graphene terahertz amplitude modulators
Authors: Sarfraz Syed Muhammad Abouzar , Di Gaspare Alessandra , Vitiello Miriam Serena , Scamarcio Gaetano
Published: February 2024

Active manipulation of the amplitude of terahertz (THz) frequency waves, through electrical tuning, is key for next-generation THz imaging and essential for unlocking strategic applications, from wireless communication to quantum technologies. Here, we demonstrate high-performance THz amplitude modulators based on an electrolyte-gated single-layer graphene. Broadband modulation in the 1.5–6 THz range is achieved by optimizing the electric field coupling by carefully controlling the spacer thickness in a quarter-wavelength cavity structure, with a maximum modulation depth of 40% at around 2 THz. Raman characterization confirms a Fermi-level tuning of 0.39 eV via electrolyte gating of graphene. A test 2 × 2 modulator array with independent control of sub-millimeter regions is then developed and tested, with no crosstalk between pixels. The reported results highlight the potential of electrolyte-gated graphene for efficient THz modulation. The single-chip design offers compactness and ease of integration with other electronic components, making it a promising platform for THz spatial light modulators and adaptive optical components.
Extra invariant and plasma inhomogeneity to improve zonal flow
Authors: Balk Alexander M.
Published: February 2024

Zonal flows are known to diminish turbulent transport in magnetic fusion. Interestingly, there is an adiabatic invariant that implies the emergence of zonal flow. This paper shows that if this invariant is decreasing (due to some external factors), then the emerging zonal flow is better. It is also shown that the plasma inhomogeneity can lead to the decrease in the adiabatic invariant. A simple condition for such decrease is found.
Estimates of global recycling coefficients for LTX-β discharges
Authors: Maan A. , Boyle D. P. , Majeski R. , Wilkie G. J. , Francisquez M. , Banerjee S. , Kaita R. , Maingi R. , LeBlanc B. P. , Abe S. , Jung E. , Perez E. , Capecchi W. , Ostrowski E. T. , Elliott D. B. , Hansen C. , Kubota S. , Soukhanovskii V. , Zakharov L.
Published: February 2024

We report the first observation of global recycling coefficient R near 0.5 in the Lithium Tokamak eXperiment-β (LTX-β), significantly below the minimum R previously reported in other devices. In a series of experiments with varied Li wall conditioning, estimates of the recycling coefficient have been made using a Lyman-α array and DEGAS2 modeling. A progressive reduction in Lyman-α emission with increased lithium and an increase in edge electron temperature are observed. It is also observed that with increasing Li coating thickness, the effective particle confinement time τp* is reduced and approaches TRANSP calculated energy confinement time (τE), with τp* near τE,TRANSP for the lowest recycling coefficients. Edge temperatures approaching core plasma temperatures, first reported in LTX, can now be directly connected to estimates of the recycling coefficient and qualitatively agree with previous UEDGE simulations. The particle flux to the limiting surfaces appears to be significantly reduced in comparison with fluid scrape-off layer (SOL) models, indicating that a large fraction of the SOL ions are mirror trapped. SOL collisionality drops more than an order of magnitude below the banana regime boundary, indicating the importance of kinetic effects. Full-f 1x2v gyrokinetic simulations of SOL field lines with the GKEYLL code indicate that the fraction of ions trapped along field lines increases as collisionality drops, as a result of increased lithium evaporation.
Emergence of crack tip plasticity in semi-brittle α-Fe
Authors: Suzudo T. , Ebihara K. , Tsuru T. , Mori H.
Published: February 2024

Fractures in body-centered-cubic metals and alloys below the ductile-to-brittle transition temperature are brittle. This is theoretically explained by the notion that the critical stress intensity factor of a given crack front for brittle fracture is smaller than that for plastic deformation; hence, brittle fracture is selected over plastic deformation. Although this view is true from a macroscopic perspective, such a fracture is always accompanied by small-scale plastic deformation near the crack tip, that is, crack tip plasticity. This paper investigates the origin of this plasticity using atomistic modeling with the machine learning interatomic potential of α-Fe. Some plastic modes are activated by rapid crack propagation, whereas no plasticity is activated when the crack tips are gradually fractured. The group of activated atoms dynamically caused by brittle crack propagation was identified as the precursor of plasticity.
Hydrodynamic benefits of passive flexibility in a self-propelled oscillatory ray
Authors: Jeong Young Dal , Lee Jae Hwa
Published: February 2024

In the present study, numerical simulations are conducted to investigate the hydrodynamic benefits of a self-propelled oscillatory ray with passive flexibility compared to those with active flexibility. For the active flexibility case, the prescribed motion is applied to the entire surface of the ray. On the other hand, for the passive flexibility case, the motion of the leading edges is only prescribed, whereas that of the rest parts is determined by the interaction with the surrounding fluid. The cruising speed and input power of the ray with passive flexibility increase as the horizontal bending rigidity decreases, and its propulsive efficiency is maximized at a specific horizontal bending rigidity. Compared to the active flexibility case, the propulsive performance of the oscillatory ray with passive flexibility is improved by not only enhanced circulation and added-mass effects but also by the favorable repartition of the resultant force caused by a large deflection angle. Strong vortical structures induced by a large deformation over the entire region of the fin generate strong negative pressure on the forward side of the overall surface, even near the central body (i.e., increased circulation effect). Furthermore, the positive pressure on the backward side increases in the passive flexibility case due to high fin acceleration caused by more intense oscillating motions (i.e., increased added-mass effect). When the oscillating frequency and the Reynolds number vary, the performance of the ray with passive flexibility is confirmed to be higher than that with active flexibility.
Palladium at high pressure and high temperature: A combined experimental and theoretical study
Authors: Baty S. R. , Burakovsky L. , Luscher D. J. , Anzellini S. , Errandonea D.
Published: February 2024

Palladium is one of the most important technological materials, yet its phase diagram remains poorly understood. At ambient conditions, its solid phase is face-centered cubic (fcc). However, another solid phase of Pd, body-centered cubic (bcc), was very recently predicted in two independent theoretical studies to occur at high pressures and temperatures. In this work, we report an experimental study on the room-temperature equation of state (EOS) of Pd to a pressure of 80 GPa, as well as a theoretical study on the phase diagram of Pd including both fcc-Pd and bcc-Pd. Our theoretical approach consists in ab initio quantum molecular dynamics (QMD) simulations based on the Z methodology which combines both direct Z method for the simulation of melting curves and inverse Z method for the calculation of solid–solid phase transition boundaries. We obtain the melting curves of both fcc-Pd and bcc-Pd and an equation for the fcc–bcc solid–solid phase transition boundary as well as the thermal EOS of Pd which is in agreement with experimental data and QMD simulations. We uncover the presence of another solid phase of Pd on its phase diagram, namely, random hexagonal close-packed (rhcp), and estimate the location of the rhcp-bcc solid–solid phase transition boundary and the rhcp–fcc–bcc triple point. We also discuss the topological similarity of the phase diagrams of palladium and silver, the neighbor of Pd in the periodic table. We argue that Pd is a reliable standard for shock-compression studies and present the analytic model of its principal Hugoniot in a wide pressure range.
Including the parallel mass flow in calculating the steady-state solutions and stability of the momentum balance equations for a quasisymmetric stellarator
Authors: Michaelides D. N. , Talmadge J. N.
Published: February 2024

The Helically Symmetric Experiment (HSX) is a quasisymmetric stellarator with minimal parallel viscous damping in a helical direction. The parallel flow (Vǁ) along the magnetic field is similarly weakly damped by viscosity. In this paper, the self-consistent steady-state parallel and poloidal momentum balance equations are used to show that a large Vǁ on the order of the ion thermal velocity can increase the ion resonant radial electric field (Er) beyond the value calculated using the typical approximation that Vǁ is zero. By altering the damping of Vǁ, either by degrading the quasisymmetry or varying the neutral density, the ion resonant Er can shift in a controllable fashion. It is shown explicitly that there exist stable and unstable steady-state solutions in the two-dimensional space of Vǁ and Er. A stability analysis of each solution is performed by calculating the eigenvalues and eigenvectors of the Jacobian. The unstable solution corresponds to a saddle point in which the eigenvalues have opposite signs. The analysis leads to the conclusion that unstable solutions occur when the derivative of the total poloidal damping with respect to Er is positive. A hysteresis in Er and Vǁ is observed when the radial current density is linearly increased to a maximum and then decreased back to zero. Jumps in the radial electric field and the parallel flow are observed as the radial current density drives the evolution from one stable point to the next. This result is similar to experimental data observed on several devices.
Simulation of dust grain charging under hypervelocity impact plasma environment
Authors: Zhou Xiao-jun , Chen Xiao-wei
Published: February 2024

Dust plasma readily forms during hypervelocity impact, which serves as a source of plasma macroscopic charge separation and strong electromagnetic fields. In this study, we examine the dynamic evolution of surface charging of aluminum dust grains with micrometer or submicrometer sizes in a hypervelocity impact plasma environment based on the theory of orbital motion limited. As dust grains traverse the expanding plasma, plasma density and temperature decrease with increasing distance from the impact point. This leads to longer relaxation times for charging equilibrium (ranging from picoseconds to microseconds) and reduced equilibrium charges. The model incorporates thermionic and secondary electron emission effects on dust grain charging processes while also examining the impacts of five heating and cooling mechanisms on the thermal equilibrium temperatures of dust grains. Near the impact point, thermal equilibrium temperatures exceed aluminum's boiling point, which results in phase transition ablation processes. As dust grain temperatures increase, thermionic emission currents may dominate charging dynamics and influence final equilibrium charge numbers. High-temperature dust grains tend to acquire positive charges. Moreover, we observe that the radius of dust grains considerably affects charging processes, and smaller grain radii correspond to low equilibrium charges and longer relaxation times.
Molecular dynamics informed calibration of crystal plasticity critical shear stresses for the mesoscopic mechanical modeling of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) single crystal
Authors: Lafourcade P. , Maillet J.-B. , Bruzy N. , Denoual C.
Published: February 2024

An extension of a constitutive law for 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) is proposed with a focus on the calibration of a crystal plasticity law. TATB, a highly anisotropic energetic molecular crystal used in explosive formulations, can be subjected to high-pressure and high-temperature conditions, either under high strain-rate deformation or shock loading. The existing thermodynamically consistent model, fully informed by molecular dynamics (MD) simulations, includes nonlinear elasticity as well as a phase-field by reaction pathway formalism under large strain for the modeling of TATB behavior upon pressure as well as its well-known twinning–buckling deformation mechanism. However, it has been observed that TATB single crystal can accommodate large deformations through dislocation-mediated plasticity, a feature not included in the mesoscale model. In the present work, we take advantage of the microscopic flow surface, previously computed through MD calculations, to calibrate a crystal plasticity law, extending the capability of the continuum model currently limited to low velocity impacts and moderate strain rate. Indeed, the microscopic flow surface, defined as a 3D stress-at-first-defect-nucleation contains all information about TATB single crystal mechanical response under directional shear loading, including twinning, buckling, and plastic events. The calibration process uses differential evolution optimization to calibrate TATB basal and transverse slip systems critical stresses to reproduce the microscopic flow surface. Finally, the response of a TATB single crystal to directional loading is investigated in order to evaluate the new model.
Influence of oxygen content on the properties of In2(OxS1−x)3 used as buffer material in Cu(In,Ga)Se2 solar cells
Authors: Ghorbani Elaheh , Jin Xiaowei , Perera Delwin , Schneider Reinhard , Gerthsen Dagmar , Hariskos Dimitrios , Menner Richard , Witte Wolfram , Albe Karsten
Published: February 2024

We investigate magnetron-sputtered In2(OxS1−x)3 compounds acting as an alternative buffer system to the solution-grown CdS or Zn(O,S) buffer layers in Cu(In,Ga)Se2 (CIGS) thin-film solar cells. The influence of the oxygen content on the solar cell performance, microstructure of the mixed systems, bandgap, and band offsets to CIGS is investigated experimentally and also characterized by calculations based on density functional theory. Samples in a series with different chemical compositions ranging from In2S3 to In2O3 are either directly deposited from ceramic targets or from a pure In2S3 target by reactive sputtering by adding O2 in the Ar sputtering gas. The binary compounds In2S3 and In2O3 sputtered at 220 °C substrate temperature from ceramic targets exhibit a crystalline structure, whereas the ternary In2(O,S)3 compounds are either nanocrystalline in the case of In2(O0.25S0.75)3 or amorphous for In2(O0.5S0.5)3 and In2(O0.75S0.25)3. For [O]/([O] + [S]) ratios above 0.25, the cell efficiencies decrease drastically, mainly due to lower open-circuit voltages (VOC). This behavior can be explained by an increase of the negative conduction band offset between the CIGS absorber and the oxygen-rich In2(OxS1−x)3 or In2O3 buffer, resulting in pronounced VOC losses. Adding oxygen to In2S3 with optical bandgap energies of around 2 eV results in a bowing of the values to below 2 eV and finally reaching values of around 2.7 eV for In2O3 if an indirect band transition is assumed. In summary, our results reveal that pronounced oxygen incorporation in In2S3 is not beneficial in terms of CIGS device efficiency because oxygen is electronically inactive and poorly miscible.
Hyperfine-resolved rotational spectroscopy of HCNH+
Authors: Silva Weslley G. D. P. , Bonah Luis , Schmid Philipp C. , Schlemmer Stephan , Asvany Oskar
Published: February 2024

The rotational spectrum of the molecular ion HCNH+ is revisited using double-resonance spectroscopy in an ion trap apparatus, with six transitions measured between 74 and 445 GHz. Due to the cryogenic temperature of the trap, the hyperfine splittings caused by the 14N quadrupolar nucleus were resolved for transitions up to J = 4 ← 3, allowing for a refinement of the spectroscopic parameters previously reported, especially the quadrupole coupling constant eQq.
Development of a universal method for vibrational analysis of the terminal alkyne C≡C stretch
Authors: Streu Kristina , Hunsberger Sara , Patel Jeanette , Wan Xiang , Daly Clyde A.
Published: February 2024

The terminal alkyne C≡C stretch has a large Raman scattering cross section in the “silent” region for biomolecules. This has led to many Raman tag and probe studies using this moiety to study biomolecular systems. A computational investigation of these systems is vital to aid in the interpretation of these results. In this work, we develop a method for computing terminal alkyne vibrational frequencies and isotropic transition polarizabilities that can easily and accurately be applied to any terminal alkyne molecule. We apply the discrete variable representation method to a localized version of the C≡C stretch normal mode. The errors of (1) vibrational localization to the terminal alkyne moiety, (2) anharmonic normal mode isolation, and (3) discretization of the Born–Oppenheimer potential energy surface are quantified and found to be generally small and cancel each other. This results in a method with low error compared to other anharmonic vibrational methods like second-order vibrational perturbation theory and to experiments. Several density functionals are tested using the method, and TPSS-D3, an inexpensive nonempirical density functional with dispersion corrections, is found to perform surprisingly well. Diffuse basis functions are found to be important for the accuracy of computed frequencies. Finally, the computation of vibrational properties like isotropic transition polarizabilities and the universality of the localized normal mode for terminal alkynes are demonstrated.