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Relativistic reflection features are commonly observed in the X-ray spectra of accreting black holes. In the presence of high quality data and with the correct astrophysical model, X-ray reflection spectroscopy can be quite a powerful tool to probe the strong gravity region, study the morphology of the accreting matter, measure black hole spins, and possibly test Einstein’s theory of general relativity in the strong field regime. In the last decade, there has been significant progress in the development of the analysis of these features, thanks to more sophisticated astrophysical models and new observational facilities. Here we review the state-of-the-art in relativistic reflection modeling, listing assumptions and simplifications that may affect, at some level, the final measurements and may be investigated better in the future. We review black hole spin measurements and the most recent efforts to use X-ray reflection spectroscopy for testing fundamental physics.

Polyamorphic transitions driven by high-energy mechanical milling (nanomilling) are studied in thioarsenide As4Sen-type glassy alloys obtained by melt quenching deviated from arsenic triselenide As2Se3 stoichiometry towards tetraarsenic pentaselenide (g-As4Se5) and tetraarsenic tetraselenide (g-As4Se4). This employs a multiexperimental approach based on powder X-ray diffraction (XRD) analysis complemented by thermophysical heat transfer, micro-Raman scattering (micro-RS) spectroscopy, and revised positron annihilation lifetime (PAL) analysis. Microstructure scenarios of these nanomilling-driven transformations in arsenoselenides are identified by quantum-chemical modeling using the authorized modeling code CINCA (the Cation Interlinked Network Cluster Approach). A straightforward interpretation of a medium-range structure response of a nanomilling-driven polyamorphism in the arsenoselenides is developed within the modified microcrystalline model. Within this model, the diffuse peak-halos arrangement in the XRD patterning is treated as a superposition of the Bragg-diffraction contribution from inter-planar correlations supplemented by the Ehrenfest-diffraction contribution from inter-atomic (inter-molecular) correlations related to derivatives of network As2Se3-type and molecular As4Se4-type conformations. Changes in the medium-range structure of examined glassy arsenoselenides subjected to nanomilling occur as an interplay between disrupted intermediate-range ordering and enhanced extended-range ordering. The domination of network-forming conformations in arsenoselenides deviated from As2Se3 stoichiometry (such as g-As4Se5) results in rather slight changes in their calorimetric heat-transfer and micro-RS responses. At the atomic-deficient level probed by PAL spectroscopy, these changes are accompanied by reduced positron trapping rate of agglomerated multiatomic vacancies and vacancy-type clusters in an amorphous As-Se network. Under an increase in As content beyond the g-As4Se5 composition approaching g-As4Se4, nanomilling-driven polyamorphic transitions, which can be classified as reamorphization (amorphous I-to-amorphous II) phase transitions, are essentially enhanced due to the higher molecularity of these glassy alloys enriched in thioarsenide-type As4Se4 cage-like molecular entities and their low-order network-forming derivatives.

Binary AsxSe100−x alloys from the border of a glass-forming region (65 < x < 70) subjected to nanomilling in dry and dry–wet modes are characterized by the XRPD, micro-Raman scattering (micro-RS) and revised positron annihilation lifetime (PAL) methods complemented by a disproportionality analysis using the quantum–chemical cluster modeling approach. These alloys are examined with respect to tetra-arsenic biselenide As4Se2 stoichiometry, realized in glassy g-As65Se35, glassy–crystalline g/c-As67Se33 and glassy–crystalline g/c-As70Se30. From the XRPD results, the number of rhombohedral As and cubic arsenolite As2O3 phases in As-Se alloys increases after nanomilling, especially in the wet mode realized in a PVP water solution. Nanomilling-driven amorphization and reamorphization transformations in these alloys are identified by an analysis of diffuse peak halos in their XRPD patterning, showing the interplay between the levels of a medium-range structure (disruption of the intermediate-range ordering at the cost of an extended-range one). From the micro-RS spectroscopy results, these alloys are stabilized by molecular thioarsenides As4Sen (n = 3, 4), regardless of their phase composition, remnants of thioarsenide molecules destructed under nanomilling being reincorporated into a glass network undergoing a polyamorphic transition. From the PAL spectroscopy results, volumetric changes in the wet-milled alloys with respect to the dry-milled ones are identified as resulting from a direct conversion of the bound positron–electron (Ps, positronium) states in the positron traps. Ps-hosting holes in the PVP medium appear instead of positron traps, with ~0.36–0.38 ns lifetimes ascribed to multivacancies in the As-Se matrix. The superposition of PAL spectrum peaks and tails for pelletized PVP, unmilled, dry-milled, and dry–wet-milled As-Se samples shows a spectacular smoothly decaying trend. The microstructure scenarios of the spontaneous (under quenching) and activated (under nanomilling) decomposition of principal network clusters in As4Se2-bearing arsenoselenides are recognized. Over-constrained As6·(2/3) ring-like network clusters acting as pre-cursors of the rhombohedral As phase are the main products of this decomposition. Two spontaneous processes for creating thioarsenides with crystalline counterparts explain the location of the glass-forming border in an As-Se system near the As4Se2 composition, while an activated decomposition process for creating layered As2Se3 structures is responsible for the nanomilling-driven molecular-to-network transition.

Active galactic nuclei (AGNs), either radio-quiet or radio-loud, had never been observed in X-ray polarized light until the advent of the Imaging X-ray Polarimetry Explorer (IXPE) in the end of 2021. This satellite opened a new observational window for studying supermassive black holes and their complex environment. In this regard, radio-quiet AGNs are probably better targets than radio-loud objects to probe accretion processes due to the lack of synchrotron emission from jets that can dilute the polarized signal from the central engine. Their relatively clean environment not only allows to detect and measure the X-ray polarization originating from the hot corona responsible for X-ray emission, but also to assess the geometry of the media immediately surrounding the supermassive black hole. Such geometrical measurements work just as well for characterizing the corona morphology in pole-on AGNs as it does for determining the three-dimensional shape of the circumnuclear cold obscurer (the so-called torus) in edge-on AGNs. In this review paper, we will return to each of the observations made by IXPE so far in the field of radio-quiet AGNs and highlight the fundamental contribution of X-ray polarimetry to our understanding of how light is emitted and how matter is shaped around supermassive black holes.

Accreting stellar-mass black holes represent unique laboratories for studying matter and radiation under the influence of extreme gravity. They are highly variable sources going through different accretion states, showing various components in their X-ray spectra from the thermal emission of the accretion disc dominating in the soft state to the up-scattered Comptonisation component from an X-ray corona in the hard state. X-ray polarisation measurements are particularly sensitive to the geometry of the X-ray scatterings and can thus constrain the orientation and relative positions of the innermost components of these systems. The IXPE mission has observed about a dozen stellar-mass black holes with masses up to 20 solar masses in X-ray binaries with different orientations and in various accretion states. The low-inclination sources in soft states have shown a low fraction of polarisation. On the other hand, several sources in soft and hard states have revealed X-ray polarisation higher than expected, which poses significant challenges for theoretical interpretation, with 4U 1630–47 being one of the most puzzling sources. IXPE has measured the spin of three black holes via the measurement of their polarisation properties in the soft emission state. In each of the three cases, the new results agree with the constraints from the spectral observations. The polarisation observations of the black hole X-ray transient Swift J1727.8–1613 across its entire outburst has revealed that the soft-state polarisation is much weaker than the hard-state polarisation. Remarkably, the observations furthermore show that the polarisation of the bright hard state and that of the 100 times less luminous dim hard state are identical within the accuracy of the measurement. For sources with a radio jet, the electric field polarisation tends to align with the radio jet, indicating the equatorial geometry of the X-ray corona, e.g., in the case of Cyg X–1. In the unique case of Cyg X–3, where the polarisation is perpendicular to the radio jet, the IXPE observations reveal the presence and geometry of obscuring material hiding this object from our direct view. The polarisation measurements acquired by the IXPE mission during its first 2.5 years have provided unprecedented insights into the geometry and physical processes of accreting stellar-mass black holes, challenging existing theoretical models and offering new avenues for understanding these extreme systems.

In this paper, the authors argue that video games offer unique and pervasive opportunities for children to develop social dispositions that are necessary to succeed in the 21st century. To this end, they discuss the design of TavCats—a virtual role-playing game that aimed to engage children (ages 9 to 13) in understanding, acting upon, and coming to value being caring and compassionate. The authors' discussion takes the form of a design narrative through which they explain the connections between their theoretical commitments and design decisions. Specifically, they review four design elements they utilized in their design work: identity claims, boundary objects, profession trajectories, and cyclic gameplay. The authors briefly share their observations from a pilot study with children in an afterschool setting to illustrate how their design work might be realized in the world. They conclude their paper with a discussion of the implications of their work for designing educational video games for supporting social dispositions as well as academic learning, and future directions.

Impact of nanosized oxide particles of titania (titanium dioxide, rutile) and silica–titania fumed compound on structure relaxation processes in nanocomposites of an orthophtalic unsaturated styrene cross-linked polyester resin has been experimentally studied using the thermal desorption mass spectroscopy, the dielectric spectroscopy, and the positron annihilation lifetime spectroscopy. All the nanocomposites showed unmonotonous variations in the thermal resistance, the dielectric permittivity and losses, and the annihilation rates for both positrons and ortho-positronium atoms with increasing filler’s loading. The nanoparticle-loading effects can be explained on the assumption that the oxide particles embedded into a cross-linked polyester resin induce rearrangements in its structure. Several mechanisms of particle–polymer interface interaction compete simultaneously and thus promote the alterations in molecular structure of the nanocomposites. The mechanisms may include both chemical and electrostatic fastening of polyester chains and styrene cross-links to the active surface sites, the destruction of the styrene cross-links, and redistribution of electron density in polymers. The features of the loading effects observed in the different nanocomposites can be ascribed to distinctions in both of active surface sites and intrinsic dielectric properties of the filling oxide particles.

The water-vapor sorption processes in nanoporous MgO-Al 2 O 3 ceramics are studied with positron annihilation lifetime (PAL) spectroscopy employing positron trapping and positronium (Ps)-decaying modes. It is demonstrated that the longest-lived components in the four-term reconstructed PAL spectra with characteristic lifetimes near 2 and 60–70 ns can be, respectively, attributed to ortho-positronium (o-Ps) traps in nanopores with 0.3- and 1.5–1.8-nm radii. The first o-Ps decaying process includes “pick-off” annihilation in the “bubbles” of liquid water, while the second is based on o-Ps interaction with physisorbed water molecules at the walls of the pores. In addition, the water vapor modifies structural defects located at the grain boundaries in a vicinity of pores, this process being accompanied by void fragmentation during water adsorption and agglomeration during water desorption after drying.

This study used innovative assessment practices to obtain and document broad learning outcomes for a 15-hour game-based curriculum in Quest Atlantis, a multiuser virtual environment that supports school-based participation in socio scientific inquiry in ecological sciences. Design-based methods were used to refine and align the enactment of virtual narrative and scientific investigations to a challenging problem solving assessment and indirectly to achievement test items that were independent of the curriculum. In study one, one-sixth grade teacher used the curriculum in two of his classes and obtained larger gains in understanding and achievement than his two other classes, which used an expository text to learn the same concepts and skills. Further treatment refinements were carried out, and two forms of virtual formative feedback were introduced. In study two, the same teacher used the curriculum in all four of his classes; the revised curriculum resulted in even larger gains in understanding and achievement. Gains averaged 1.1 SD and 0.4 SD, respectively, with greater gains shown for students who engaged more with formative feedback. Principles for assessing designs and designing assessments in virtual environments are presented.

The amorphization is studied in mechanically activated β-As 4 S 4 using high-energy ball milling in a dry mode with 100–600 min −1 rotational speeds, employing complementary methods of X-ray powder diffraction (XRPD) related to the first sharp diffraction peak, positron annihilation lifetime (PAL) spectroscopy, and ab initio quantum-chemical simulation within cation-interlinking network cluster approach (CINCA). The amorphous substance appeared under milling in addition to nanostructurized β-As 4 S 4 shows character XRPD halos parameterized as extrapolation of the FSDPs, proper to near-stoichiometric amorphous As–S alloys. The structural network of amorphized arsenicals is assumed as built of randomly packed multifold cycle-type entities proper to As 4 S 4 network. The depressing and time-enhancing tendency in the PAL spectrum peak is direct indicative of milling-driven amorphization, associated with free-volume evolution of interrelated positron- and Ps-trapping sites. At lower speeds (200–500 min −1 ), these changes include Ps-to-positron trapping conversion, but they attain an opposite direction at higher speed (600 min −1 ) due to consolidation of β-As 4 S 4 crystallites. In respect of CINCA modeling, the effect of high-energy milling is identified as destruction–polymerization action on monomer cage-type As 4 S 4 molecules and existing amorphous phase, transforming them to amorphous network of triple-broken As 4 S 4 derivatives. These findings testify in a favor of “shell” kinetic model of solid-state amorphization, the amorphous phase continuously generated under speed-increased milling being identified as compositionally authentic to arsenic monosulfide, different in medium range ordering from stoichiometric As 2 S 3 .