ABSTRACT
Using archival data from Suzaku, XMM–Newton, and NuSTAR, nine representative ultra-luminous X-ray sources (ULXs) in nearby galaxies were studied. Their X-ray spectra were all reproduced with ...a multicolour disc emission model plus its Comptonization. However, the spectral shapes of individual sources changed systematically depending on the luminosity, and defined three typical spectral states. These states differ either in the ratio between the Comptonizing electron temperature and the innermost disc temperature, or in the product of Compton y-parameter and fraction of the Comptonized disc photons. The luminosity range at which a particular state emerges was found to scatter by a factor of up to 16 among the eight ULXs. By further assuming that the spectral state is uniquely determined by the Eddington ratio, the sample ULXs are inferred to exhibit a similar scatter in their masses. This gives a model-independent support to the interpretation of ULXs in terms of relatively massive black holes. None of the spectra showed noticeable local structures. Especially, no Fe K-shell absorption/emission lines were detected, with upper limits of 30–40 eV in equivalent width from the brightest three among the sample: NGC 1313 X-1, Holmberg IX X-1, and IC 342 X-1. These properties disfavour ordinary mass accretion from a massive companion star, and suggest direct Bondi–Hoyle accretion from dense parts of the interstellar medium.
Relativistic Runaway Electrons Avalanches (RREAs) development depends on the applied electric field and the environment's air density. This dependency controls the RREA exponential growth length ...scale. The RREA development affects the bremsstrahlung excess occurring due to the passage of charged particles through the thundercloud's electric fields, the gamma‐ray glow. We used Monte Carlo simulations to develop an empirical model showing the RREA behavior in a realistic atmospheric density profile. The new formulation shows how the density variation modulates the electron population under electric field strengths near the RREA electric field threshold. The model limits the initial RREA altitude range as a function of the electric field strength. The new model is valid between ∼0.6 and ∼18 km, covering the relevant heights to investigate the generation of ground‐detected gamma‐ray glows.
Plain Language Summary
Thunderclouds are energy sources for trespassing charged particles from cosmic rays. This extra energy gain may induce electron avalanches, known as Relativistic Runaway Electron Avalanches (RREAs), resulting in an enhanced gamma‐ray flux via bremsstrahlung, the gamma‐ray glow. Recent studies relate this enhancement to electric field strengths close to the RREA requirement. The atmospheric density variations affect avalanche development by modifying the RREA requirement, resulting in isolated avalanches by imposing limits to the avalanche's initial altitude. We show how RREAs develop in a realistic atmospheric density profile. We present a modification on the characteristic avalanche length under this condition. The initial avalanche altitude is crucial because it completely modifies the density profile trespassed by a downward electron shower. Finally, we discuss the consequences of isolated RREAs for high‐energy emissions and show that the electric field strength constrains the possible initial altitudes for the gamma‐ray glow.
Key Points
A new empirical model quantifies how electron avalanches vanish because of atmospheric density variations with ∼10% accuracy
The model limits the initial altitude of electron avalanche development for electric field strengths near the avalanche threshold
We narrow the possible gamma‐ray glow source height range with the new model which is valid through ∼0.6–18 km
During a winter thunderstorm on 24 November 2017, a strong burst of gamma rays with energies up to ∼10 MeV was detected coincident with a lightning discharge, by scintillation detectors installed at ...the Kashiwazaki-Kariwa Nuclear Power Station at sea level in Japan. The burst had a subsecond duration, which is suggestive of photoneutron production. The leading part of the burst was resolved into four intense gamma-ray bunches, each coincident with a low-frequency radio pulse. These bunches were separated by 0.7-1.5 ms, with a duration of ≪1 ms each. Thus, the present burst may be considered as a "downward" terrestrial gamma-ray flash (TGF), which is analogous to upgoing TGFs observed from space. Although the scintillation detectors were heavily saturated by these bunches, the total dose associated with them was successfully measured by ionization chambers, employed by nine monitoring posts surrounding the power plant. From this information and Monte Carlo simulations, the present downward TGF is suggested to have taken place at an altitude of 2500±500 m, involving 8_{-4}^{+8}×10^{18} avalanche electrons with energies above 1 MeV. This number is comparable to those in upgoing TGFs.
Real-space observations in the middle stage of spinodal decomposition have not been achieved because of the small sizes and unclear interfaces of the phases. Here, we performed in situ real-space ...experiments with heating to quantitatively reveal the local dynamics and structures of a calcium aluminosilicate glass in the middle stage of spinodal decomposition by scanning transmission electron microscopy. This glass separate into CaO–Al2O3–SiO2 phase and SiO2 phases. The observations revealed that the CaO–Al2O3–SiO2 phases with low Ca concentrations behaved as if they were in the middle stage, whereas the CaO–Al2O3–SiO2 phases with high Ca concentrations coarsened as if they were in the final stage. This coexistence of stages suggested that the behaviors of the phases depend not only on time, but also on their local relative concentrations. Differing from the well-known final stage of spinodal decomposition, the phases with relatively high Ca concentrations in the middle stage showed peculiar directional migration guided by the phases with relatively low Ca concentrations. These findings have not been observed before and thus have the potential to provide a new way to control the phase-separated structure.
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Objective and Background
Human periodontal ligament mesenchymal stem cells (hPDLMSCs) are reported to be responsible for homeostasis and regeneration of periodontal tissue. Although hPDLMSCs are ...commonly cultured in monolayers, monolayer cultures have been reported as inferior to 3‐dimensional cultures such as spheroids, which are spherical clusters of cells formed by self‐assembly. The aim of this study was to examine the osteogenic phenotype of spheroids of hPDLMSCs, compared with monolayer cultures of hPDLMSC, in vitro and in vivo.
Material and Methods
Spheroids were formed using microwell chips that were tagged with polyethylene glycol. Mesenchymal stem cell (MSC) markers in hPDLMSC spheroids were examined by flow cytometer. Real‐time polymerase chain reaction analysis was examined to measure the expressions of stemness markers and osteogenesis‐related genes in monolayer and spheroid‐cultured hPDLMSCs. Immunofluorescence analysis was performed to confirm protein expressions of stemness markers in PDLMSC spheroids. Nodule formation assay, alkaline phosphatase (ALP) activity assay and transplantation assay in a mouse calvarial defect model were performed to confirm the osteogenic potential of hPDLMSC spheroids. To elucidate the mechanism of spheroid culture enhanced osteogenesis in hPDLMSCs with osteoinductive medium (OIM), a small interfering RNA (siRNA) assay targeted with secreted frizzled‐related protein 3 (SFRP3) was examined. The levels of SFRP3 expression in monolayer and spheroid‐cultured hPDLMSCs with OIM were measured by real‐time polymerase chain reaction and western blotting analysis. ALP gene expression and ALP activity were examined in SFRP3‐deficient hPDLMSC spheroids.
Results
The hPDLMSC spheroids expressed MSC markers, which were similar to hPDLMSCs grown in monolayer cultures. Intriguingly, the protein and mRNA expressions of transcription factors that regulate “stemness” were significantly increased in hPDLMSC spheroids, compared with hPDLMSCs in monolayer cultures. Nodule formation by hPDLMSCs was significantly increased in spheroid cultures grown with OIM, compared with monolayer‐cultured hPDLMSCs. ALP activity and expression of osteogenesis‐related genes were also significantly enhanced in hPDLMSC spheroids, compared with monolayer cultures. Treatment with hPDLMSC spheroids significantly enhanced new bone formation in a murine calvarial defect model, compared with hPDLMSCs in monolayer culture. Finally, to elucidate mechanisms by which spheroid culture enhances ALP activation in hPDLMSCs grown with OIM, an siRNA assay was used to manipulate expression of SFRP3, a Wnt signaling antagonist. Knockdown of SFRP3 suppressed ALP gene expression in hPDLMSCs grown in OIM; further, it suppressed ALP activity in spheroid culture. These data suggest that the enhancement of osteogenic potential in hPDLMSC spheroids is regulated through SFRP3‐mediated ALP activation.
Conclusion
Spheroid cultures of hPDLMSCs may be a novel and useful tool in regenerative medicine.
The purpose of the present study was to ascertain whether increase in step frequency at a given velocity during running reduces the lower extremity loading variables, which is associated with tibial ...stress fracture in runner. We hypothesized that the lower extremity loading variables at a given speed would be minimized at around +15% f step. 10 male subjects were asked to run at 2.5 m/s on a treadmill-mounted force platform. 5 step frequencies were controlled using a metronome: the preferred, below preferred (-15 and -30%) and above preferred (+15 and +30%). From the vertical ground reaction force, we measured following lower extremity loading variables; vertical impact peak (VIP), vertical instantaneous loading rate (VILR) and vertical average loading rate (VALR). We found that there were significant differences in lower extremity loading variables among 5 step frequency conditions. Furthermore, quadratic regression analyses revealed that the minimum loading variable frequencies were 17.25, 17.55, and 18.07% of preferred step frequency for VIP, VILR and VIAR, respectively. Thus, adopting a step frequency greater than one's preferred may be practical in reducing the risk of developing a tibial stress fracture by decreasing lower extremity loading variables.
Magnetars are a special type of neutron stars, considered to have extreme dipole magnetic fields reaching approximately 10(exp 11) T. The magnetar 4U 0142þ61, one of the prototypes of this class, was ...studied in broadband x rays (0.5-70 keV) with the Suzaku observatory. In hard x rays (15-40 keV), its 8.69 sec pulsations suffered slow phase modulations by +/- 0.7 sec, with a period of approximately 15 h. When this effect is interpreted as free precession of the neutron star, the object is inferred to deviate from spherical symmetry by approximately 1.6 x 10(epx -4) in its moments of inertia. This deformation, when ascribed to magnetic pressure, suggest a strong toroidal magnetic field, approximately 10(exp 12) T, residing inside the object. This provides one of the first observational approaches towards toroidal magnetic fields of magnetars.
•Diffractions are used to determine local thickness and composition.•Electron diffractions ranging from 0 to 130 mrad were obtained by 4D-STEM.•Experiment and simulated diffractions are ...compared.•This method reduces the electron dose to 1/10 or less compared with EELS.
The nanometer-scale spatial distributions of local thickness or composition of noncrystalline materials are generally measured by spectroscopy with scanning transmission electron microscopy (STEM). Since spectroscopy requires a high electron dose and causes irradiation damage, alternative non-spectroscopic methods are required to measure the local thickness or composition of electron-sensitive noncrystalline materials. Here, we focus on the radial distribution function (RDF) of the electron diffraction of non-crystalline materials. We confirm that the RDF of the electron diffraction obtained by simulation contains information on the thickness and composition. Next, we demonstrate the determination of both thickness and composition from experimentally obtained RDFs. Although some constraints are required, we determine the local thickness and composition of a BaO-SiO2 glass sample by comparing the RDFs of diffraction measured by a high-speed pixelated detector with those of the simulated diffractions. Collaterally, this determination method can improve the quality of STEM images.
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