bluuebunny/crossref_metadata_2025 huggingface dataset:
The Galactic bulge exploration
Authors: Prudil Z. , Kunder A. , Dékány I. , Koch-Hansen A. J.
Published: April 2024

We present a new set of period–absolute magnitude–metallicity (PMZ) relations for single-mode RR Lyrae stars calibrated for the optical GBP, V, G, GRP, near-infrared I, J, H, and Ks passbands. We compiled a large dataset (over 100 objects) of fundamental and first-overtone RR Lyrae pulsators consisting of mean intensity magnitudes, reddenings, pulsation properties, iron abundances, and parallaxes measured by the Gaia astrometric satellite in its third data release. Our newly calibrated PMZ relations encapsulate the most up-to-date ingredients in terms of both data and methodology. They are intended to be used in conjunction with large photometric surveys targeting the Galactic bulge, including the Optical Gravitational Lensing Experiment (OGLE), the Vista Variables in the Vía Láctea Survey (VVV), and the Gaia catalog. In addition, our Bayesian probabilistic approach provides accurate uncertainty estimates of the predicted absolute magnitudes of individual RR Lyrae stars. Our derived PMZ relations provide consistent results when compared to benchmark distances to globular clusters NGC 6121 (also known as M 4), NGC 5139 (also known as omega Cen), and Large and Small Magellanic Clouds, which are stellar systems rich in RR Lyrae stars. Lastly, our Ks-band PMZ relations match well with the previously published PMZ relations based on Gaia data and accurately predict the distance toward the prototype of this class of variables, the eponymic RR Lyr itself.
Determining the time before or after a galaxy merger event
Authors: Pearson W. J. , Rodriguez-Gomez V. , Kruk S. , Margalef-Bentabol B.
Published: April 2024

Aims.This work aims to reproduce the time before or after a merger event of merging galaxies from the IllustrisTNG cosmological simulation using machine learning.

Methods.Images of merging galaxies were created in theu,g,r, andibands from IllustrisTNG. The merger times were determined using the time difference between the last simulation snapshot where the merging galaxies were tracked as two galaxies and the first snapshot where the merging galaxies were tracked as a single galaxy. This time was then further refined using simple gravity simulations. These data were then used to train a residual network (ResNet50), a Swin Transformer (Swin), a convolutional neural network (CNN), and an autoencoder (using a single latent neuron) to reproduce the merger time. The full latent space of the autoencoder was also studied to see if it reproduces the merger time better than the other methods. This was done by reducing the latent space dimensions using Isomap, linear discriminant analysis (LDA), neighbourhood components analysis, sparse random projection, truncated singular value decomposition, and uniform manifold approximation and projection.

Results.The CNN is the best of all the neural networks. The performance of the autoencoder was close to the CNN, with Swin close behind the autoencoder. ResNet50 performed the worst. The LDA dimensionality reduction performed the best of the six methods used. The exploration of the full latent space produced worse results than the single latent neuron of the autoencoder. For the test data set, we found a median error of 190 Myr, comparable to the time separation between snapshots in IllustrisTNG. Galaxies more than ≈625 Myr before a merger have poorly recovered merger times, as well as galaxies more than ≈125 Myr after a merger event.
NELIOTA: New results and updated statistics after 6.5 years of lunar impact flashes monitoring
Authors: Liakos A. , Bonanos A. Z. , Xilouris E. M. , Koschny D. , Bellas-Velidis I. , Boumis P. , Maroussis A. , Moissl R.
Published: April 2024

We present results of the Near-Earth objects Lunar Impacts and Optical TrAnsients (NELIOTA) campaign for lunar impact flashes observed with the 1.2 m Kryoneri telescope. From August 2019 to August 2023, we report 113 validated and 70 suspected flashes. For the validated flashes, we calculate the physical parameters (masses, radii) of the corresponding projectiles, the temperatures developed during the impacts, and the expected crater sizes. For the multiframe flashes, we present light curves and thermal evolution plots. Using the whole sample of NELIOTA that encompasses 192 validated flashes in total from 2017, the statistics of the physical parameters of the meteoroids, the peak temperatures of the impacts, and the expected crater sizes has been updated. Using this large sample, empirical relations correlating the luminous energies per photometric band were derived and used to roughly estimate the parameters of 92 suspected flashes of the NELIOTA archive. For a typical value of the luminous efficiency, we found that the majority (>75%) of the impacting meteoroids have masses between 1 and 200 g, radii between 0.5 and 3 cm and produced craters up to 3.5 m. 85% of the peak temperatures of the impacts range between 2000 and 4500 K. Statistics regarding the magnitude decline and the cooling rates of the multiframe flashes are also presented. The recalculation of the appearance frequency of meteoroids (lying within the aforementioned ranges of physical parameters) on the Moon yields that the total lunar surface is bombarded with 7.4 sporadic meteoroids per hour and up to 12.6 meteoroids per hour when the Earth-Moon system passes through a strong meteoroid stream. By extrapolating these rates on Earth, the respective rates for various distances from its surface are calculated and used to estimate the probability of an impact of a meteoroid with a hypothetical infrastructure on the Moon, or with a satellite orbiting Earth for various impact surfaces and duration times of the missions.
Solar photospheric spectrum microvariability
Authors: Dravins Dainis , Ludwig Hans-Günter
Published: April 2024

Context. The search for small exoplanets around solar-type stars is limited by stellar physical variability, such as a jittering in the apparent photospheric radial velocity. While chromospheric variability has been aptly studied, challenges remain for the observation, modeling. and understanding the much smaller fluctuations in photospheric spectral line strengths, shapes, and shifts.

Aims. Extreme-precision radial-velocity spectrometers allow for highly precise stellar spectroscopy and time series of the Sun (seen as a star) enable the monitoring of its photospheric variability. Understanding such microvariability through hydrodynamic 3D models would require diagnostics from different categories of well-defined photospheric lines with specific formation conditions. Fluctuations in their line strengths may indeed be correlated with radial-velocity excursions and prove useful in identifying observable proxies for their monitoring.

Methods. From three years of HARPS-N observations of the Sun-as-a-star at λ/Δλ ∼ 100 000, we selected 1000 low-noise spectra and measured line absorption in Fe I, Fe II, Mg I, Mn I, Hα, Hβ, Hγ, Na I, and the G-band. We examined their variations and likely atmospheric origins, also with respect to simultaneously measured chromospheric emission and apparent radial velocity.

Results. Systematic line-strength variability is seen, largely shadowing the solar-cycle evolution of Ca II H & K emission, but to smaller extents (typically on a sub-percent level). Among iron lines, the greatest amplitudes have been seen for Fe II in the blue, while the trends change sign among strong lines in the green Mg I triplet and between Balmer lines. Variations in the G-band core are greater than of the full G-band, in line with theoretical predictions. No variation is detected in the semi-forbidden Mg Iλ 457.1 nm. Hyperfine split Mn I behaves largely similar to Fe I. For lines at longer wavelengths, telluric absorption limits the achievable precision.

Conclusions. Microvariability in the solar photospheric spectrum displays systematic signatures among various features. These measure values that are different than the classical Ca II H & K index, while still reflecting a strong influence from magnetic regions. Although unprecedented precision can be achieved from radial-velocity spectrometers, current resolutions are not adequate to reveal changes in detailed line shapes; in addition, their photometric calibration is not perfect. A forthcoming priority will be to model microvariability in solar magnetic regions, which could also provide desired specifications for future instrumentation toward exoEarth detections.
Radiographers’ attitudes toward the principles of patient radiation protection in the Souss Massa region of Morocco
Authors: El Fahssi M. , Semghouli S. , Amaoui B. , Elkhalladi J. , Çaoui M , Jroundi L.
Published: April 2024

Introduction: Radiographers play a vital role in patient radiation protection. Their training, supervision, and involvement in radiation protection programmes require greater attention from all stakeholders.  Methods: This cross-sectional study was conducted between March and August 2023 to assess Radiographers’ attitudes toward the principles of patient radiation protection in the Souss Massa region of Morocco. An anonymous questionnaire containing 22 questions was sent to 80 radiographers practicing in the Sous Massa region. Results: 67.5% of the radiographers confirmed that they did not use a guide to radiological procedures. 85% of them confirmed that they had checked for the possibility of pregnancy each time a woman of childbearing age was involved in a conventional X-ray, compared with 97.5% who checked for the possibility of pregnancy in a CT scan. 97.5 % of our participants said that they automatically (without medical advice) repeated the X-ray examination if the image was not interpretable. 90% of radiographers said that they did not report parameters for dose estimation for each conventional X-ray examination, and 72.5% did not report data for dose estimation for CT-scan examinations. The results showed no association between gender and professional experience on the one hand and radiographers’ practices on the other. Nevertheless, there is an association between the workplace and certain radiographers’ practices, indicating the lack of a regional strategy aimed at standardizing procedures and radiation protection practices at the level of all radiology departments. Conclusion: It is vital to launch a patient dose management program in the Souss Massa region and campaigns to raise radiographers’ awareness of recommended patient radiation protection practices.
La rationalisation de la radioprotection à l’époque des pionniers du nucléaire
Authors: Portelli A.
Published: April 2024

Le centre nucléaire de Marcoule, mis en service en 1955 par le CEA, accueille les premiers réacteurs français de dimension industrielle. Leur exploitation pose un immense défi en matière de sécurité radiologique, auquel répond la création du Service de Protection contre les Radiations (SPR). Ce dernier rationalise la radioprotection et élabore sa doctrine en même temps qu’il développe ses moyens de contrôle et de surveillance. Conscient de l’ampleur de sa mission, le SPR cherche à réduire sa tâche en promouvant la contribution active du personnel à sa propre protection. Pour ce faire, il développe un programme d’éducation en matière de risque radioactif. Celui-ci est destiné aux agents de Marcoule, mais aussi au grand public, parmi lequel sont recrutés les travailleurs du nucléaire. Ce programme éducatif, illustré par le dessinateur Jacques Castan, participe ainsi de l’effort de rationalisation de la radioprotection entrepris par le SPR.
Arterielle Hypertonie bei Hämodialysepatient*innen
Authors: Haag Stefanie
Published: April 2024

In den USA versterben ca. 50 % der HD-Patient*innen (HD: Hämodialyse) an einer kardiovaskulären (CV) Ursache. Arterielle Hypertonie (aHT) wird bei > 80 % der Erkrankten beobachtet. Die Pathophysiologie ist multifaktoriell und beinhaltet die Volumenüberladung, arterielle Steifigkeit, erhöhte Aktivität des sympathischen Nervensystems und des Renin-Angiotensin-Aldosteron-Systems (RAAS), endotheliale Dysfunktion und Verwendung von Erythropoese stimulierenden Agenzien (ESA). Die Autoren geben in diesem Review einen Überblick über die Definition, Diagnose und Behandlung der aHT.
Aktuelle immunsuppressive Therapie bei hochimmunisierten Nierentransplantatempfängerinnen und -empfängern und/oder positivem Crossmatch
Authors: Thorban Stefan , Matevossian Edouard
Published: April 2024

Fast 30 % aller Patientinnen und Patienten auf der Warteliste für eine Nierentransplantation (NTx) sind hochimmunisiert, wobei > 50 % panelreaktive Antikörper (cPRA) von > 80 % vorweisen. Nach Daten von Eurotransplant fallen bereits 30 % der sensibilisierten Patienten in die hochsensibilisierte Kategorie mit einem cPRA von > 85 %. Präformierte donorspezifische Antikörper (DSA) und das damit verbundene Risiko einer antikörpergesteuerten Abstoßung (AMR) nach einer NTx stellen schwerwiegende Probleme für Nierentransplantatempfänger dar. Die Chance, ein Nierentransplantat über einen Wartelistenplatz zu erhalten, ist hierdurch fast ausgeschlossen und die Prognose für ein langjähriges Transplantatüberleben ungünstig.
Antikoagulation bei abnormer Nierenfunktion oder Dialyse
Authors: Brandenburg Vincent , Henrik Heine Gunnar
Published: April 2024

Patienten mit Vorhofflimmern (VHF) und erhöhtem Risiko für Schlaganfall und systemische Embolie (SSE) sind mit CKD G1–3 (CKD: „chronic kidney disease“) klare Kandidaten für eine Therapie mit neuen orale Antikoagulanzien (NOAK). Patienten mit VHF und erhöhtem SSE-Risiko sind mit CKD 4 wahrscheinlich gute Kandidaten für eine NOAK-Therapie; Vitamin-K-Antagonisten (VKA) sind hier formal kontraindiziert. Keine Art der oralen Antikoagulation (OAK) ist bei Dialysepatienten in Europa explizit zugelassen. Es ist unklar, ob Dialysepatienten von irgendeiner OAK hinsichtlich ischämischem Schlaganfallrisiko und Mortalität bei akzeptablem Blutungsrisiko profitieren. Die Therapie mit einem NOAK ist auch bei Dialyse möglich. Eine Aufklärung über den Off-Label-Gebrauch sollte erfolgen. Die Studie VALKYRIE deutet an, dass eine Rivaroxaban-Therapie (10 mg/d) bei Dialysepatienten eine höhere Effektivität und Sicherheit hat als eine VKA-Therapie. Die Implantation eines LAA-Okkluders kann eine recht sichere und effektive Alternative zur OAK bei Dialysepatienten sein. Hierzu sollte eine Entscheidung durch ein Behandlungsteam gesucht werden.
Erster Schritt Blankoverordnung
Authors: Pintarelli-Rauschenbach Manuela
Published: April 2024

Der Start der Blankoverordnung im Praxisalltag steht kurz bevor. Im März 2024 wird noch mit Hochdruck an
der Vereinbarung gearbeitet und eine Einigung in Kürze erwartet: Auf eine Regelung für den
Geltungsbereich Schulter hatten sich die Vertragspartner bereits vor dem Redaktionsschluss dieser Ausgabe
geeinigt. Ab ► Seite 14 erläutern wir die klaren Vorteile der Blankoverordnung. Wir betrachten sie
als einen ersten Schritt, der uns mehr Autonomie in der Therapiewahl erlaubt und unseren Beruf
attraktiver macht.
A versatile photon counting system with active afterpulse suppression for free-running negative-feedback avalanche diodes
Authors: Sultana Nigar , Bourgoin Jean-Philippe , Kuntz Katanya B. , Jennewein Thomas
Published: April 2024

InGaAs/InP-based negative-feedback avalanche diodes (NFADs) have been demonstrated to be an excellent option for photon detection at telecom wavelengths in quantum communication applications, where photon arrival times are random. However, it is well-known that the operation of NFADs at low temperatures (193 K or below) is crucial to minimize the effects of afterpulsing and high dark count rates (DCRs). In this work, we present a new versatile readout electronics system with active afterpulse suppression that also offers flexible cooling options. Through the characterization of two NFAD detectors from Princeton Lightwave, Inc. and a thorough evaluation of our electronics’ performance under various operating conditions, we demonstrate the effectiveness of this readout system in improving the performance of NFAD-based photon detectors. At the optimal bias for NFADs, our electronics were able to significantly reduce the afterpulsing probability by a factor of 200 for dead times ranging from 5 to 20 µs following each detection event. This helps to keep the total DCRs at around 100 counts per second or less for a 20 µs hold-off time. The versatility of our detection system makes NFADs a cost-effective alternative to more complex detectors, such as superconducting nanowire single-photon detectors, in the research of long-distance quantum communications and low-noise single photon detectors at telecommunication wavelengths.
Spectral characterization of an SPDC source with a fast broadband spectrometer
Authors: Farella Brianna , Medwig Gregory , Abrahao Raphael A. , Nomerotski Andrei
Published: April 2024

Knowing the properties of single photons produced in a Spontaneous Parametric Down-Conversion (SPDC) source can be crucial for specific applications and uses. In particular, the spectral properties are of key relevance. Here, we investigate a commercial SPDC source using our fast broadband spectrometer. Our analysis is a valid method for other SPDC sources, as well as other single-photon generation techniques, thus providing a good example of how to use this spectrometer design. We calibrate the spectrometer using known lines of the argon emission spectrum. We show that the two down-converted photons from the SPDC source have different spectral properties depending on the pump power, and under which condition we measured spectrally similar down-converted photons. Finally, we were able to reconstruct and investigate the spectral information for the pump photon.
Isometric spectral subtriples
Authors: Watcharangkool A. , Sucpikarnon W. , Bertozzini P.
Published: April 2024

We investigate the notion of subsystem in the framework of spectral triple as a generalized notion of noncommutative submanifold. In the case of manifolds, we consider several conditions on Dirac operators which turn embedded submanifolds into isometric submanifolds. We then suggest a definition of spectral subtriple based on the notion of submanifold algebra and the already existing notions of Riemannian, isometric, and totally geodesic morphisms. We have shown that our definitions work at least in some relevant almost commutative examples.
PIC simulations of the competition between backward and forward stimulated Raman side scatter in ignition-scale direct-drive coronal conditions
Authors: Wang Q. , Xiao C. Z. , Xie Y. , Cai H. B. , Chen J. , Liu Z. J. , Cao L. H. , Zheng C. Y. , Liu C. S. , Rozmus W. , Myatt J. F. , He X. T.
Published: April 2024

The competition between forward stimulated Raman side scatter (FSRSS) and backward stimulated Raman side scatter (BSRSS) is investigated in inhomogeneous plasma using particle-in-cell (PIC) simulations. Experimental observations at the National Ignition Facility have demonstrated the significance of stimulated Raman side scatter or backscatter instability compared to two-plasmon-decay under ignition-scale conditions for various laser beam geometries. Side scatter refers to the geometry where the Raman scattered light is generated in a direction perpendicular to the local density gradient. For an obliquely incident pump, the scattered light can either copropagate (FSRSS) or counter propagate (BSRSS) with respect to the pump. Under ignition-scale conditions, linear analysis shows that both BSRSS and FSRSS are absolutely unstable (temporally growing) at higher densities (ne∼0.2 nc), whereas at lower densities (ne∼0.1 nc), BSRSS becomes convective with substantial gain, while FSRSS remains absolute. Two-dimensional PIC simulations demonstrate that the competition between BSRSS and FSRSS is sensitive to the density. BSRSS tends to dominate at higher densities, while FSRSS becomes dominant at lower densities. At moderate densities (ne∼0.15 nc), FSRSS and BSRSS coexist. Furthermore, an increase in laser intensity leads to enhanced electron trapping, which kinetically strengths and then saturates BSRSS in the lower density region.
Enhancing torsional sampling using fully adaptive simulated tempering
Authors: Suruzhon Miroslav , Abdel-Maksoud Khaled , Bodnarchuk Michael S. , Ciancetta Antonella , Wall Ian D. , Essex Jonathan W.
Published: April 2024

Enhanced sampling algorithms are indispensable when working with highly disconnected multimodal distributions. An important application of these is the conformational exploration of particular internal degrees of freedom of molecular systems. However, despite the existence of many commonly used enhanced sampling algorithms to explore these internal motions, they often rely on system-dependent parameters, which negatively impact efficiency and reproducibility. Here, we present fully adaptive simulated tempering (FAST), a variation of the irreversible simulated tempering algorithm, which continuously optimizes the number, parameters, and weights of intermediate distributions to achieve maximally fast traversal over a space defined by the change in a predefined thermodynamic control variable such as temperature or an alchemical smoothing parameter. This work builds on a number of previously published methods, such as sequential Monte Carlo, and introduces a novel parameter optimization procedure that can, in principle, be used in any expanded ensemble algorithms. This method is validated by being applied on a number of different molecular systems with high torsional kinetic barriers. We also consider two different soft-core potentials during the interpolation procedure and compare their performance. We conclude that FAST is a highly efficient algorithm, which improves simulation reproducibility and can be successfully used in a variety of settings with the same initial hyperparameters.
Slice emittance measurements using a slit-grid system and a fast wall-current monitor
Authors: Togawa Kazuaki
Published: April 2024

The time evolution of beam properties in an electron bunch with the duration of a nanosecond was measured with a time resolution of several tens of picoseconds. A combination of horizontal and vertical slits cuts the beamlet from the original beam, with the current waveform of the beamlet measured using a fast wall-current monitor. The reconstruction of the waveform data obtained by scanning these two slits over the entire beam area provided the time evolution of the spatial profile. A similar measurement using two horizontal (vertical) slits separated by a certain distance also provides the time evolution of the phase–space profile. Using this method, the initial beam extracted from the CeB6 thermionic electron gun of the x-ray free-electron laser (XFEL) SACLA was evaluated. Although the slice emittance in the bunch was measured to be constant, the centroid of the spatial profile moved in the transverse direction by a few hundred micrometers in the 0.6 ns flat-top region. This movement arises from the temporal variation in the rectangular high-voltage pulse of the beam chopper and can cause an increase in the projected emittance. These measurements are important for evaluating the conditions of the initial beam emitted from the cathode and processed downstream of the gun. Hence, the proposed diagnostic system will play an important role in developing an extremely low-emittance electron beam or an artificial electron beam with a multi-bunch or micro-bunch structure that enhances the brightness of the XFEL light.
Electron density measurements in low-pressure plasmas using cutoff probes and comparison with hairpin and Langmuir probes
Authors: Mishra Himanshu , Tuharin Kostyantyn , Turek Zdeněk , Tichý Milan , Kudrna Pavel
Published: April 2024

We present a comparative study of electron density obtained in a low-temperature plasma by the cutoff probe and compare the results with data from both the hairpin and the Langmuir probes. The measurements with different probes were conducted in a DC discharge generated by an iron hollow cathode under identical experimental conditions. This comparative analysis provides insight into the reliability and consistency of electron density measurements across different probe types in this specific experimental setup. The information acquired from the cutoff and hairpin probes enables electron density measurements within the frequency range limitations of the instruments. Measurements of electron density are performed in a mixture of argon and oxygen at a low pressure of 5 Pa, in dependence on the discharge current and Ar:O2 mixture ratio. A qualitative discussion of the obtained results is provided.
Magnetic properties of Fe56Pd44−xGdx thin films
Authors: Sahari Mohamed Abdennour , Olivetti Elena Sonia , Magni Alessandro , Fiore Gianluca , Boudissa Mokhtar , Tiberto Paola , Bahamida Saida , Coïsson Marco
Published: April 2024

In this paper, we have studied the effect on the structure and magnetic properties of partial Pd substitution by Gd in Fe–Pd thin films of nominal composition Fe56Pd44−xGdx (x = 1, 3, 5, and 7), deposited onto Si(100) and Si(100)/SiO2 substrates by thermal evaporation. Several techniques contribute to the characterization of their microstructure and magnetic properties, such as x-ray diffraction (XRD), scanning electron microscopy, alternating gradient field magnetometry, and magnetic force microscopy (MFM). X-ray diffraction shows that the as-deposited films are either amorphous or contain a disordered FePd phase, depending on the film thickness. The transformation of disordered fcc-FePd into ordered fct-FePd has been induced by a heat treatment at 530 °C for 4 h. The addition of gadolinium leads to a reduction in the coercivity as a consequence of the emergence of soft phases and of the progressive reduction of the fct-FePd phase, which is primarily responsible for the observed maze magnetic domains. The exchange coupling between the soft phase and the hard fct-FePd phase is demonstrated by first-order reversal curves (FORCs).
Computational analysis of a dense granular system driven by a propagating shock wave in an Eulerian–Eulerian framework
Authors: Lai S. , Rao Y. , Wang H.
Published: April 2024

Numerical simulations using an Eulerian–Eulerian approach are performed to investigate the problem of a dense granular bed driven by a propagating shock wave with special emphasis on the particle-phase behavior. Validation of the granular model based on the kinetic theory of granular flow is performed by comparing the simulation results with experimental data on the shock-particle curtain interaction by Ling et al. [Phys. Fluids 24, 113301 (2012)]. Then, simulations of a Mach-1.92 shock propagating into an infinite-long granular system are tested, where the particle diameter, density, and volume fraction are 115 μm, 2520 kg/m3, and 21%, respectively. The simulations demonstrate that as the gas-phase shock interacts with the granular system, a reflected shock, a contact surface, and a transmitted shock wave form instantly. Meanwhile, a dilute region, a densely packed region, and an “excitation and relaxation” region behind the granular shock are observed. The physics of the granular shock structures are elucidated through an evaluation of forces and pseudo-thermal energy (PTE) fluctuations. It is shown that the combination of a positive drag force and Archimedes force are responsible for the particle motion, while the intergranular stress has a negative contribution in most of the region. The PTE is generated in the initial stage owing to the velocity slip (ϕslip) then dissipates primarily due to particle inelastic collisions (−γ̇l) until particles reach an equilibrium state in the later stages. Finally, the effects of particle parameters including the initial particle packing (αs) and the coefficient of restitution (e) are elucidated and discussed. The results show that the particle concentration greatly affects the granular shock velocity, and as the collisions become less ideal, particle clusters are observed in the dilute region.
Numerical study on the influence of turbine swirl on exhaust system
Authors: Hou Shengwen , Wang Qiang , Hu Haiyang , Fan Chang , Li Sichen
Published: April 2024

This article employed numerical methods to investigate the aerodynamic, thermal, and infrared characteristics of last-stage turbine swirl on a two-dimensional convergent divergent (2D-CD) exhaust system with an afterburner under varying bypass ratios. The research results indicate that the swirl diminishes the thrust coefficient and flow coefficient of the 2D-CD exhaust system with an afterburner. At a bypass ratio of 0.2, the thrust coefficient and flow coefficient decrease by 0.65% and 1.07%, respectively. When the bypass ratio is relatively small, the swirl flow leads to a decrease in the temperature of the afterburner heat shield. Conversely, when the bypass ratio is relatively large, the opposite occurs. The maximum temperature of the heat shield increases by up to 7.2% (bypass ratio = 0.35), while the average temperature decreases by up to 7.1% (bypass ratio = 0.2). The swirl causes an increase in the temperature of the divergent section heat shield, with the most significant deterioration observed at a bypass ratio of 0.25, resulting in a maximum temperature increase in 12.2%. Swirling flow shortens the length of the jet flow, and as the bypass ratio reduces, this attenuation effect becomes more pronounced. When the bypass ratio is 0.2, the length of the core area decreases by 40.3%, and the infrared intensity of the narrow-side jet flow decreases by 12.5%. Overall, on the XOY detection plane, the maximum decrease in infrared intensity is 11.5%, and the maximum increase is 11.7%. On the XOZ detection plane, the maximum decrease in infrared intensity is 15.9%, and the maximum increase is 5.7%.
On the nature of thermal transport in organic/inorganic nanolaminates
Authors: Khadka Rajan , Keblinski Pawel
Published: April 2024

Using non-equilibrium molecular dynamics simulations, we investigate thermal transport in organic/inorganic Au/molecular nanolayer (MNL) nanolaminate. We examine the tunability of thermal conductivity via interfacial bonding by (i) homogeneous change of bonding strength and heterogeneous change of (ii) bond density and (iii) molecular coverage at the interface. By comparing the thermal conductivity of the nanolaminates with the interfacial thermal conductance of corresponding individual interfaces, we conclude that phenomenologically the thermal conductivity can be predicted from independent interfacial resistors connected in a series model, particularly at higher temperatures. However, interfacial thermal conductance shows a moderate increase with temperature, whereas the thermal conductivity of Au/MNL nanolaminates shows the opposite effect. We elucidate this apparent contradiction via phonon wave packet simulations at individual and multiple interface structures.
A personal perspective of the present status and future challenges facing thermal reaction rate theory
Authors: Pollak Eli
Published: April 2024

Reaction rate theory has been at the center of physical chemistry for well over one hundred years. The evolution of the theory is not only of historical interest. Reliable and accurate computation of reaction rates remains a challenge to this very day, especially in view of the development of quantum chemistry methods, which predict the relevant force fields. It is still not possible to compute the numerically exact rate on the fly when the system has more than at most a few dozen anharmonic degrees of freedom, so one must consider various approximate methods, not only from the practical point of view of constructing numerical algorithms but also on conceptual and formal levels. In this Perspective, I present some of the recent analytical results concerning leading order terms in an ℏ2m series expansion of the exact rate and their implications on various approximate theories. A second aspect has to do with the crossover temperature between tunneling and thermal activation. Using a uniform semiclassical transmission probability rather than the “primitive” semiclassical theory leads to the conclusion that there is no divergence problem associated with a “crossover temperature.” If one defines a semiclassical crossover temperature as the point at which the tunneling energy of the instanton equals the barrier height, then it is a factor of two higher than its previous estimate based on the “primitive” semiclassical approximation. In the low temperature tunneling regime, the uniform semiclassical theory as well as the “primitive” semiclassical theory were based on the classical Euclidean action of a periodic orbit on the inverted potential. The uniform semiclassical theory wrongly predicts that the “half-point,” which is the energy at which the transmission probability equals 1/2, for any barrier potential, is always the barrier energy. We describe here how augmenting the Euclidean action with constant terms of order ℏ2 can significantly improve the accuracy of the semiclassical theory and correct this deficiency. This also leads to a deep connection with and improvement of vibrational perturbation theory. The uniform semiclassical theory also enables an extension of the quantum version of Kramers’ turnover theory to temperatures below the “crossover temperature.” The implications of these recent advances on various approximate methods used to date are discussed at length, leading to the conclusion that reaction rate theory will continue to challenge us both on conceptual and practical levels for years to come.
Potential energy landscape of a flexible water model: Equation of state, configurational entropy, and Adam–Gibbs relationship
Authors: Eltareb Ali , Lopez Gustavo E. , Giovambattista Nicolas
Published: April 2024

The potential energy landscape (PEL) formalism is a tool within statistical mechanics that has been used in the past to calculate the equation of states (EOS) of classical rigid model liquids at low temperatures, where computer simulations may be challenging. In this work, we use classical molecular dynamics (MD) simulations and the PEL formalism to calculate the EOS of the flexible q-TIP4P/F water model. This model exhibits a liquid–liquid critical point (LLCP) in the supercooled regime, at (Pc = 150 MPa, Tc = 190 K, and ρc = 1.04 g/cm3) [using the reaction field technique]. The PEL-EOS of q-TIP4P/F water and the corresponding location of the LLCP are in very good agreement with the MD simulations. We show that the PEL of q-TIP4P/F water is Gaussian, which allows us to calculate the configurational entropy of the system, Sconf. The Sconf of q-TIP4P/F water is surprisingly similar to that reported previously for rigid water models, suggesting that intramolecular flexibility does not necessarily add roughness to the PEL. We also show that the Adam–Gibbs relation, which relates the diffusion coefficient D with Sconf, holds for the flexible q-TIP4P/F water model. Overall, our results indicate that the PEL formalism can be used to study molecular systems that include molecular flexibility, the common case in standard force fields. This is not trivial since the introduction of large bending/stretching mode frequencies is problematic in classical statistical mechanics. For example, as shown previously, we find that such high frequencies lead to unphysical (negative) entropy for q-TIP4P/F water when using classical statistical mechanics (yet, the PEL formalism can be applied successfully).
Energy transfer in the spatial evolution of double-wave-group focusing
Authors: Zhou Binzhen , Ding Kanglixi , Xiao Yi , Wang Lei , Tang Tianning
Published: April 2024

The linear superposition of the individual wave groups underestimates the bimodal waves, as it overlooks the interactions between these wave groups, which is thought to be connected to the generation of extreme waves. Continuing our previous work [Zhou et al., “Experimental study on the interactions between wave groups in double-wave-group focusing,” Phys. Fluids 35(3), 037118 (2023)], the energy transfer in the spatial evolution of double-wave-group focusing is highlighted based on a fully nonlinear numerical wave tank with the high-order spectral method. The findings reveal that a sea state with a narrower intermodal distance or an uneven distribution of the bimodal spectrum tends to induce larger waves. The third-order nonlinear interaction is primarily triggered by the transient wave focusing, as opposed to a prolonged evolution like the behavior of even-order components. The configurations of the sea state exert varying impacts on the evolution of harmonical energy, with the most potent nonlinearity observed away from the actual focused position, the nonlinear energy amplified relative to the initial state, and the energy redistributed after wave focus. The study also uncovers that during the wave focus and defocus process, waves experience an irreversible energy exchange, with frequencies shifting from higher to lower, likely due to second-order harmonics. These discoveries broaden our comprehension of the nonlinear characteristics inherent in the interaction between the swell and wind-sea waves.
Large eddy simulations of turbulent pipe flows at moderate Reynolds numbers
Authors: Garg Himani , Wang Lei , Andersson Martin , Fureby Christer
Published: April 2024

Wall-bounded turbulence is relevant for many engineering and natural science applications, yet there are still aspects of its underlying physics that are not fully understood, particularly at high Reynolds numbers. In this study, we investigate fully developed turbulent pipe flows at moderate-to-high friction velocity Reynolds numbers (361≤Reτ≤2000), corresponding to bulk velocity-based Reynolds numbers of 11 700≤Reb≤82 500, using wall-modeled large eddy simulations (LES) in OpenFOAM. A grid convergence study is performed for Reτ=361, followed by an investigation of the accuracy of various subgrid-scale stress models for the same Reynolds number. Results show that the wall-adapting local eddy (WALE) model performs well compared to experiments and direct numerical simulations, while one-equation eddy-viscosity model and Smagorinsky are too dissipative. LES utilizing WALE is then performed for four different Reynolds numbers with gradually refined grids, revealing excellent agreement with DNS data in the outer region. However, a significant deviation from DNS data is observed in the sub-viscous layer region, indicating the need for further mesh refinement in the wall-normal direction to accurately capture the smallest-scale motions' behavior. Additional mesh sensitivity analysis uncovered that, as the Reτ value rises, it becomes crucial for a grid to adhere to the condition of Δx+≤20−25 and Δz+≤10 in order to precisely capture substantial large and small-scale fluctuations. Overall, the WALE model enables accurate numerical simulations of high-Reynolds number, wall-bounded flows at a fraction of the computational cost required for temporal and spatial resolution of the inner layer.
Ultrasound enhanced diffusion in hydrogels: An experimental and non-equilibrium molecular dynamics study
Authors: Price Sebastian E. N. , Einen Caroline , Moultos Othonas A. , Vlugt Thijs J. H. , Davies Catharina de Lange , Eiser Erika , Lervik Anders
Published: April 2024

Focused ultrasound has experimentally been found to enhance the diffusion of nanoparticles; our aim with this work is to study this effect closer using both experiments and non-equilibrium molecular dynamics. Measurements from single particle tracking of 40 nm polystyrene nanoparticles in an agarose hydrogel with and without focused ultrasound are presented and compared with a previous experimental study using 100 nm polystyrene nanoparticles. In both cases, we observed an increase in the mean square displacement during focused ultrasound treatment. We developed a coarse-grained non-equilibrium molecular dynamics model with an implicit solvent to investigate the increase in the mean square displacement and its frequency and amplitude dependencies. This model consists of polymer fibers and two sizes of nanoparticles, and the effect of the focused ultrasound was modeled as an external oscillating force field. A comparison between the simulation and experimental results shows similar mean square displacement trends, suggesting that the particle velocity is a significant contributor to the observed ultrasound-enhanced mean square displacement. The resulting diffusion coefficients from the model are compared to the diffusion equation for a two-time continuous time random walk. The model is found to have the same frequency dependency. At lower particle velocity amplitude values, the model has a quadratic relation with the particle velocity amplitude as described by the two-time continuous time random walk derived diffusion equation, but at higher amplitudes, the model deviates, and its diffusion coefficient reaches the non-hindered diffusion coefficient. This observation suggests that at higher ultrasound intensities in hydrogels, the non-hindered diffusion coefficient can be used.
Magnetization control of the critical current in a S-(S/F)-S superconducting switch
Authors: Kammermeier Lukas , Scheer Elke
Published: April 2024

We show the control of the critical current Ic of a superconductor–superconductor/ferromagnet–superconductor [S-(S/F)-S] type switch by the magnetization state of the F. The inverse proximity effect of a S/F bilayer is used to define the weak link and hence the maximum critical current of the junction. The magnetization of the F lead is set by an external magnetic field. We show that the critical current in zero field depends on the remanent magnetization state via stray-field effects and thereby allows for a post-manufacturing control of the junction's properties, in particular the tunability between a maximal critical current and a full suppression of Ic without applying a persistent magnetic field. We propose a simplified model based on the relative orientation of magnetic domains that explains our findings qualitatively.
Investigation of chemically treated jute/kenaf/glass fiber with TiO2 nano-filler for tensile and impact characteristics
Authors: Jothi Arunachalam S. , Saravanan R. , Sathish T. , Haider Sajjad , Giri Jayant
Published: April 2024

The essential objective of this work was to investigate the effect of silane treatment on the tensile and impact strength of composites made of jute/kenaf/glass fibers with the TiO2 nano-filler. This study also sought to optimize the factors connected with this treatment method. To develop and evaluate trials, the researchers used Response Surface Methodology (RSM) with central composite designs, emphasizing the optimization of silane concentration, immersion time, and nano-filler content. The researchers were able to effectively create quadratic models to forecast the tensile and impact strengths of the nano-composite throughout the silane treatment procedure. The adjustment of silane concentration, immersion duration, and nano-filler content discovered the best conditions for obtaining maximum tensile strength. The optimal values for silane concentration and immersion time have been identified to be 15 wt. % and 30 min, respectively. Considering these conditions, the composite’s tensile strength increased by 32.13% and its impact strength improved by 8.34% above the lowest values achieved from RSM optimization. The results demonstrate the practical value of silane treatment, notably in boosting tensile and impact strengths while enhancing interfacial adhesive among natural fibers and polymer matrices.
Lamb survival and weight at marking may be reduced in ewes lambing on forage oats after grazing lucerne during late pregnancy
Authors: Robertson Susan M. , Morton Walter , Friend Michael A. , Allworth Bruce , Bhanugopan Marie
Published: April 2024

Context Grazing of cereal forage crops is perceived as a risk for increased perinatal lamb mortality. Aims This study evaluated whether grazing oat forage during late pregnancy and/or the lambing period increased lamb mortality compared with grazing a legume (lucerne)-based pasture. Methods Merino ewes (n = 636) were allocated to two replicates of two litter sizes (singles or twins), which grazed the following three forage treatments: either legume-based pasture or oat forage (Avena sativa) from 42 days before and throughout a 4-week lambing period, or a legume-based pasture until 9–12 days pre-lambing before grazing oats throughout the lambing period. All groups were offered a calcium, magnesium and sodium mineral supplement to reduce the risk of deficiency. Key results Lamb survival to marking was similar for ewes grazing legumes (84.2 ± 1.94%) or oat forage (78.5 ± 1.94%) throughout, but was reduced (P = 0.022) for ewes that grazed oats only during the lambing period (71.0 ± 1.94%) compared with those that remained on legumes. The latter was associated with a greater (P = 0.016) loss of condition score in the ewes. The weight of lambs at marking age was 2 kg higher (P ≤ 0.05) when grazed on legume-based pasture during the 4 week lambing period rather than oats. Minimal ewe mortality (0.47%) occurred, no metabolic disease was observed and few ewes (1.3%) required assistance at parturition. None of the sampled ewes was subclinically deficient in calcium or magnesium. Conclusions The study indicates lamb survival was not reduced by grazing oats for an extended period throughout late pregnancy and lambing. Further research is required to determine whether the recorded reduction in lamb survival from grazing oats only during lambing occurs consistently. Implications Ewes may safely graze oat forage throughout late pregnancy and lambing when offered a calcium, magnesium and salt supplement, without this increasing perinatal lamb mortality relative to a legume-based pasture, but there may be a penalty in lamb growth rates and loss of ewe condition, and lamb survival may be reduced with an abrupt change to oats for the lambing period.
Time-modulated near-field radiative heat transfer
Authors: Yu Renwen , Fan Shanhui
Published: April 2024

Near-field radiative heat transfer has recently attracted increasing interests for its applications in energy technologies, such as thermophotovoltaics. Existing works, however, are restricted to time-independent systems. Here, we explore near-field radiative heat transfer between two bodies under time modulation by developing a rigorous fluctuational electrodynamics formalism. We demonstrate that time modulation can result in the enhancement, suppression, elimination, or reversal of radiative heat flow between the two bodies, and can be used to create a radiative thermal diode with an infinite contrast ratio, as well as a near-field radiative heat engine that pumps heat from the cold to the hot bodies. The formalism reveals a fundamental symmetry relation in the radiative heat transfer coefficients that underlies these effects. Our results indicate the significant capabilities of time modulation for managing nanoscale radiative heat flow.
Degrees of disagreement and reliability of information sources in pro- and anti-vaccination comments on
Facebook
Authors: Kotwica Dorota , Albelda Marco Marta
Published: April 2024

During the COVID-19 vaccination campaign, the Spanish Ministry of Health shared informative posts on platforms
like Facebook, sparking heated debates. This paper utilizes a custom corpus of Facebook comments with evidential elements to
explore the disagreement and confrontation in online comments from pro- and anti-vaccine advocates. The study also analyses the
types of evidence employed by posters to support their positions, revealing potential hierarchies of information sources in terms
of reliability and validity.

Findings indicate that anti-vaccine advocates (i) engage in stronger disagreement than vaccine supporters; (ii)
use disqualification and hostile speech acts slightly more; and (iii) employ more impolite strategies. Moreover, the study shows
differences between these two user groups with regard to the sources of the information they chose to use: anti-vaccine posters
employ a higher percentage of more objective types of evidence, while pro-vaccine posters resort to evidence based on more
subjective, and personal sources.