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First measurement of jet axis decorrelation with photon-tagged jets in pp and PbPb collisions at 5.02 TeV
No full textThe first measurement of the jet axis decorrelation in events with jets recoiling from an isolated photon is presented for lead-lead (PbPb) and proton-proton (pp) collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV. The jet axis decorrelation is the angular difference () between two definitions of the jet axis. This quantity is expected to be sensitive to the scattering of jet constituents in the quark-gluon plasma (QGP). Events which have a leading isolated photon with transverse momentum 60 200 GeV and recoiling jets with 30 100 GeV are selected for the analysis. The PbPb result is reported as a function of collision centrality and compared to pp reference data. Jets with 60 GeV have consistent shapes for pp and PbPb collisions. However, a narrowing is observed for jets with 60 GeV in central PbPb collisions. The results are compared to predictions from the JEWEL, PYQUEN, and HYBRID theoretical models, which include different descriptions of parton energy loss in the QGP
Plasma screening in mid-charged ions observed by K-shell line emission
No full textDense plasma environment affects the electronic structure of ions via variations of the microscopic electrical fields, also known as plasma screening. This effect can be either estimated by simplified analytical models, or by computationally expensive and to date unverified numerical calculations. We have experimentally quantified plasma screening from the energy shifts of the bound-bound transitions in matter driven by the x-ray free electron laser (XFEL). This was enabled by identification of detailed electronic configurations of the observed Kα, Kβ and Kγ lines. This work paves the way for improving plasma screening models including connected effects like ionization potential depression and continuum lowering, which will advance the understanding of atomic physics in the Warm Dense Matter regime
Diagnosing interstellar magnetic turbulence with TeV pulsar halos
No full textInterstellar magnetic field is essential in various astrophysical phenomena and processes. Pulsar halos are a recently discovered class of TeV gamma-ray sources formed by escaping electrons/positrons from pulsars. The morphology of the halo is regulated by the diffusion of those escaping particles, and hence carry information of the interstellar magnetic field. We suggest that the morphology of TeV pulsar halos can be used as a novel probe of the properties of interstellar magnetic field around the pulsar, such as the Alfv\'{e}nic Mach number and the mean direction. We establish a theoretical relation between these quantities and the observational features of the halo's morphology based on the anisotropic diffusion model, and show that how X-ray observations of the pulsar halos can further improve the diagnosis of the magnetic field. Lastly, we try to apply our method to an observed pulsar halo candidate, HESS~J1809-193, as a practical example
On the role of atomic shuffling in the 4O, 4M and 8M martensite structures in Ni-Mn-Sn single crystal
No full textThe crystal structure of a four-layered martensite phase in Ni 50 Mn 37.5 Sn 12.5 single crystal following vari- ous modes of training procedure was examined by high energy synchrotron radiation and high-resolution transmission electron microscopy. Three distinct types of unit cell i.e . 4O, 4M, and 8M were unveiled, de- pending on the mechanical history of the specimen. The most stable phase turned out to be the 4M martensite. Analysis of the intensity of modulation reflections allowed for defining a periodic atomic dis- placement of 0.3497 ˚A. The results support the concept of a periodic atomic shuffling as opposed to the adaptive nanotwining approach
Microstructural evolution in high-temperature direct aging on PBF-LB 15-5PH stainless steel
No full textHigh solidification rates and in situ heat treatments are commonly found in additive manufacturing (AM) ofsteels, resulting in a complex and far-from-equilibrium microstructure. Therefore, standard post-processing heattreatments commonly applied to wrought steels can favor the occurrence of different phenomena and can changethe phase transformation sequence, due to the unique microstructure obtained by powder bed fusion – laserbeam (PBF-LB). This work reports the microstructural evolution of 15-5 precipitation hardening (PH) stainlesssteel manufactured by PBF-LB during direct aging heat treatments at 621 ◦C (AMS H1150 standard condition), aroute used to increase fracture toughness due to the martensite reversion and precipitates coarsening. Thereversion of martensite into a Ni-rich austenite, predicted by kinetic calculations, was confirmed by high-energyX-ray diffraction (HE-XRD), being preferentially nucleated close to the copper-rich precipitates (CRPs), whichcan act as a preferential nucleation site. CRPs presented an oval shape, as confirmed by electronic microscopy(SEM and TEM) and atom probe tomography (APT). Fast Fourier transform (FFT) analysis of high-resolution TEM(HR-TEM) images suggests CRPs still present the metastable untwined 3R-type structure after 8 h, rather than themost stable FCC structure. The presence of retained austenite, inherent to PBF-LB-processed PH steels, affects theCRPs evolution in different phases, and the CRPs themselves act as nucleation sites for Nb(C,N) secondaryprecipitation. These findings emphasize the necessity of microstructure-oriented heat treatment routes to unlockthe full potential of additively manufactured PH stainless steels
Synthese von Goldhydrid bei hohen Drücken und Temperaturen
No full textGold ist ein unreaktives Metall und seine chemische Wechselwirkung mit Wasserstoff wird erst seit Kurzem untersucht. Unter Verwendung verschiedener Kohlenwasserstoffe als Wasserstoffquelle beobachten wir hier die Bildung von festem Goldhydrid in der Diamantstempelzelle, die mit einem Freie-Elektronen-Laser beheizt wird. Bei Drücken oberhalb von 40 GPa und bei Temperaturen in der Nähe des Schmelzpunkts bildet sich eine hexagonale Phase, die einem Hydrid mit der Stöchiometrie entspricht, wobei x mit dem Druck (40 bis 80 GPa) von 0 auf nahezu 1 ansteigt. Es handelt sich um eine Hochtemperaturphase, die sich beim Abkühlen auf 295 K in flächenzentriertes kubisches Gold umwandelt. Begleitende DFT-MD-Simulationen stimmen hervorragend mit den Ergebnissen der Experimente überein und zeigen, dass die Struktur aus einem hexagonal dicht gepackten Goldgitter mit ungeordneten Wasserstoffatomen in den Zwischenräumen besteht. Der Wasserstoff ist superionisch, d.h. er weist eine hohe Diffusionsfähigkeit durch das kristalline Goldgitter auf. Unsere Ergebnisse weisen die erste binäre Verbindung aus Gold und Wasserstoff im festen Zustand nach
Microstructure after quenching and precipitation behavior during tempering in Fe–Cu–Ni–Al steels
No full textThis study investigates the microstructure after quenching and the precipitation behavior during subsequent tempering in Fe-2.5Ni-0.5Al, Fe-2.5Cu, and Fe-2.5Cu-2.5Ni-0.5Al (wt%) steels, with and without Mo additions. All alloys were solution-treated at 900 °C for 60 min, followed by quenching and tempering at 550 °C for up to 40 min. Microstructure and precipitation characteristics were analyzed using microscopy, atom probe tomography, and in situ small-angle X-ray scattering, supported by thermodynamic calculations and continuous cooling transformation diagram simulations. The Fe-Ni-Al steels (with or without Mo) exhibited a ferritic–bainitic microstructure. The Fe-Cu steel was primarily ferritic, while Mo addition promoted a ferritic-bainitic structure. The Fe-Cu-Ni-Al steel displayed a ferritic–martensitic microstructure, which transformed into a fully martensitic structure with Mo addition. During tempering, no precipitates were detected in the Fe-2.5Ni-0.5Al steel, whereas Cu-rich precipitates formed in both Fe-2.5Cu and Fe-2.5Cu-2.5Ni-0.5Al steels. The enhanced bainitic/martensitic transformation induced by Mo addition resulted in a higher dislocation density after quenching, which facilitated Cu precipitate nucleation during tempering. Hybrid Monte Carlo/Molecular Dynamics simulation confirm that Mo alters the matrix distortion in Fe-2.5Cu-2.5Ni-0.5Al steel, a key factor influencing nucleation and precipitation kinetics. Moreover, the addition of Mo reduced precipitate growth and coarsening, contributing to the retention of high hardness after tempering
X-ray reflectivity and fluorescence study of foulant monolayers for prediction of organic fouling and inorganic scaling during membrane filtration
No full textHypothesisOrganic foulants and ions in real feed solutions act synergistically, determining the rates of organic deposition and mineral scaling. We hypothesize that foulant Langmuir monolayers on defined subphases provide predictive model interfaces, in which X-ray reflectivity (XRR) and grazing-incidence X-ray fluorescence (GIXRF) quantify monolayer densification and interfacial ion partitioning that together forecast fouling severity and gypsum scaling.ExperimentsWe formed Langmuir monolayers of bovine serum albumin (BSA), lysozyme (Lys), and humic acid (HA) on water, 150 mM NaCl, and 25 mM CaSO subphases, varying surface pressure from relaxed to collapsed states. XRR yielded electron-density profiles and monolayer density. GIXRF provided interfacial enrichment factors (IEF) for Ca and SO. We correlated these interfacial descriptors with reverse osmosis (RO) tests determining the flux-decline ratio (FDR) and with post-filtration autopsy by SEM, XRD, and FTIR.FindingsIncreasing ionic strength densifies the Lys and HA layers, correlating with higher FDR due to increased deposition of organic foulants; this effect is especially pronounced for HA in the presence of Ca. By contrast, the influence of ionic strength on the BSA layer is moderate. GIXRF analysis shows that the BSA monolayer depletes Ca at the interface (IEF ≈ 0.5), inhibiting gypsum scaling, whereas the HA monolayer enriches Ca (IEF ≈ 3), promoting scaling—findings confirmed in filtration experiments. Overall, this study demonstrates that Langmuir interfacial models, combined with XRR and GIXRF, provide a robust tool for predicting fouling severity and its impact on scaling in complex feed streams, which is critical for water purification technologies
Emission and ESA/GSA thermographic properties of Pr-doped tungstate phosphors under vacuumultraviolet and visible excitation.
No full textThe impact of synchrotron radiation, temperature, and optically active ion concentration on the emission and thermographic properties of Pr3+-doped NaY0.5Gd0.5(WO4)2, NaGd(WO4)2 and NaY(WO4)2 phosphors was investigated. At cryogenic temperature T = 12 K, synchrotron radiation stimulates intense, broad-band O2−–W6+ charge transfer emission within the 350–700 nm spectral region. The VUV-UV excitation processes are characterized by complex effects involving charge transfer phenomena and excitonic transitions. The excitation realized by the ultrashort femtosecond laser pulses was able to recognize and characterize various relaxation dynamics of 3P0/1D2 praseodymium excited states and [WO4]2− luminescence. The effective interionic processes correspond mainly to cross-relaxation channels employing 1D2 praseodymium luminescence levels for all studied tungstate phosphors. Two-band and single-band-ratiometric approaches utilizing thermally coupled 3P0/3P1 levels and GSA/ESA transitions were applied to evaluate the materials under study as potential luminescent thermometers. In particular, the visible emission of praseodymium increased with increasing temperature for the excited state absorption (ESA) process in contrast to ground state absorption (GSA). As a result, effective relative sensitivity reaching above 6% K−1 was determined for the Pr3+-doped solid solution phosphor
Microstructure evolution of underwater welded SUS304 revealed by high-energy synchrotron-XRD
No full textThis study reveals the multiscale microstructure evolution and residual stress distribution of SUS304, which was fabricated by local dry underwater welding (LDUW) with a water depth of 0.2 m and average current of 163 A. By integrating high-energy synchrotron-XRD (HE-SXRD) with microstructural analysis methods (SEM, EBSD, and TEM) and mechanical tests, quantitative correlations between microstructural features (grain size, phase fraction, etc.) and mechanical properties were accurately established. The results demonstrate a gradient microstructure along the path from the base metal (BM) to the heat-affected zone (HAZ) and to the weld metal (WM), the increased grain size (14.6 → 19.6 → 33.3 μm), decreased dislocation density (4.0 → 3.0 → 1.4 × 1013 m-2), and almost increased ferrite fraction (2.8% → 2.5% → 5.6%) were achieved, which was attributed to arc-induced recrystallization and recovery in the local dry cavity despite the rapid underwater cooling. Residual stresses at the weld centre reached maximum 407.2 MPa (longitudinal) and 259.7 MPa (transverse). The weldment exhibited ultimate tensile strength and elongation of 666.7 MPa and 30.7%, respectively, which were lower than that of the BM (816.2 MPa and 56.2%). This mechanical performance decline was caused by the coarse-grained structure, inhomogeneous microstructure, and high residual stress distribution in the underwater weldment, which collectively impaired its ability to undergo coordinated plastic deformation. This work provides a practical guidance for regulating the microstructure and mechanical performance in underwater welding field