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Abstract The interaction between phonons and 4f electrons, which is forming a new quantum state (quasi-bound state) beyond Born-Oppenheimer approximation, is very prominent and lattice dynamics plays here a key role. There is only a small number of compounds in which the experimental observation suggest such a scenario. One of these compounds is CePd2Al2. Here the study of phonon dispersion curves of (Ce,La)Pd2Al2 at 1.5, 7.5, 80 and 300 K is presented. The inelastic X-ray scattering technique was used for mapping the phonon modes at X and Z points as well as in Λ and Δ directions, where the symmetry analysis of phonon modes was performed. The measured spectra are compared with the theoretical calculation, showing very good agreement. The measurements were performed in several Brillouin zones allowing the reconstruction of phonon dispersion curves. The results are discussed with respect to the magneto-elastic interaction and are compared with other cerium compounds. The phonon mode symmetry A1g was found to be unaffected by the interaction, which is in contrast to previous assumptions.

We report an experimental observation of mesoscopic fluctuations underlying the thermodynamic anomalies of ambient liquid water. The combination of two sound-velocity-measurement methods with largely different frequencies, namely inelastic x-ray scattering (IXS) in the terahertz band and ultrasonic (US) in the megahertz band, allows us to investigate a relaxation phenomenon that has a characteristic frequency between the two aforementioned frequencies. We performed IXS measurements to obtain the IXS sound velocity of liquid water from the ambient conditions to the supercritical region of liquid–gas phase transition (LGT) and compared the results with the US sound velocity reported in the literature. We found that the ratio of the sound velocities, S_{f}, which corresponds to the relaxation strength, obtained using these two methods exhibits a simple but significant change. Two distinct rises were observed in the high- and low-temperature regions, implying that two relaxation phenomena exist. In the high-temperature region, a peak was observed near the LGT critical ridge line, which was linked to changes in the magnitude of density fluctuation and isochoric and isobaric-specific heat capacities. This result indicates that the high-temperature relaxation originates from the LGT critical fluctuation, proving that this method is effective for observing such mesoscopic fluctuations. Meanwhile, in the low-temperature region, S_{f} increased from 550 K toward the low-temperature region and reached a high value, attaining the “fast sound” state under ambient conditions. This result indicates that another mechanism of relaxation exists, which causes the sound velocity anomaly, including the “fast sound” phenomenon of liquid water under ambient conditions. The change in S_{f} in the low-temperature region is linked to the change in the isochoric heat capacity, which identified that this relaxation causes the well-known heat capacity anomaly of liquid water. This low-temperature relaxation corresponds to the critical fluctuation of the liquid–liquid phase transition (LLT) that is speculated to exist in the supercooled region. In this study, both LGT and LLT critical fluctuations were observed, and the relationship between thermodynamics and the critical fluctuations was comprehensively discussed by analyzing the similarities and differences between the two phase transitions.

Abstract The longitudinal sound velocity (V P ) and the density (ρ) of wüstite, FeO, were measured at pressures of up to 112.3 GPa and temperatures of up to 1700 K using both inelastic X-ray scattering and X-ray diffraction combined with a laser-heated diamond-anvil cell. The linear relationship between V P and ρ, Birch’s law, for wüstite can be expressed as V P = 1.55 (1) × ρ [g/cm3] − 2.03 (8) [km/s] at 300 K and V P = 1.61 (1) × ρ [kg/m3] − 2.82 (10) [km/s] at 1700 K. The sound velocity of wüstite is significantly lower than that of bridgmanite and ferropericlase under lower mantle conditions. In other words, the existence of wüstite in the lower mantle can efficiently decrease the seismic velocity. Considering its slow velocity and several mechanisms for the formation of FeO-rich regions at the core–mantle boundary, we confirm earlier suggestions indicating that wüstite enrichment at the bottom of the Earth’s mantle may contribute to the formation of denser ultra-low velocity zones.

Abstract Background Representation learning provides new and powerful graph analytical approaches and tools for the highly valued data science challenge of mining knowledge graphs. Since previous graph analytical methods have mostly focused on homogeneous graphs, an important current challenge is extending this methodology for richly heterogeneous graphs and knowledge domains. The biomedical sciences are such a domain, reflecting the complexity of biology, with entities such as genes, proteins, drugs, diseases, and phenotypes, and relationships such as gene co-expression, biochemical regulation, and biomolecular inhibition or activation. Therefore, the semantics of edges and nodes are critical for representation learning and knowledge discovery in real world biomedical problems. Results In this paper, we propose the edge2vec model, which represents graphs considering edge semantics. An edge-type transition matrix is trained by an Expectation-Maximization approach, and a stochastic gradient descent model is employed to learn node embedding on a heterogeneous graph via the trained transition matrix. edge2vec is validated on three biomedical domain tasks: biomedical entity classification, compound-gene bioactivity prediction, and biomedical information retrieval. Results show that by considering edge-types into node embedding learning in heterogeneous graphs, edge2vec significantly outperforms state-of-the-art models on all three tasks. Conclusions We propose this method for its added value relative to existing graph analytical methodology, and in the real world context of biomedical knowledge discovery applicability.

Inelastic x-ray scattering measurements using high-pressure apparatus were carried out for liquid Te up to 1673 K above the boiling point at the normal pressure. We could obtain the dynamic structure factor S(Q,E) of good quality at 1.8 ≤ Q ≤ 22 nm−1. Although the excitation energies of the acoustic mode are fluctuating more at lower temperatures, we found that the dynamical sound speed at 1.8 and 2.1 nm−1 becomes fast with increasing temperature from 773 to 923 K, similarly to the temperature dependence of ultrasonic sound speed in liquid Te. Despite this unusual temperature dependence at the lowest Q, the sound speed at higher Q is consistent with those obtained by the previous inelastic neutron and x-ray scattering studies, in which the dynamical sound just slows down with increasing temperature. The present results may be correlated with the temperature-driven semiconductor-metal transition in liquid Te, and if so, it is inferred that a domain size of inhomogeneity induced with the transition is comparable to the wave length corresponding to the lowest Q. Keywords: Inelastic x-ray scattering, Atomic dynamics, Collective mode, Semiconductor-metal transition, Liquid chalcogen

Synchrotron X-ray diffraction measurements on a single crystal of Ca5Ir3O12 were performed to clarify the details of the superlattice reflections characterized by q = ð1=3; 1=3; 1=3Þ. A search for superlattice reflections in a wide reciprocal space was performed using an imaging plate, and it was confirmed that there were no superlattice reflections at other than q = ð1=3; 1=3; 1=3Þ. From the extinction rule of the superlattice reflections, the space group of the crystal structure below 105K was found to be R3. The details of the superlattice reflections at specific q were investigated using a fourcircle diffractometer. The temperature dependence of the integrated intensity at several q confirms that the order parameter of the phase transition of Ca5Ir3O12 at 105K belongs to an A2 irreducible representation in the point group C3v from the discussion based on the Landau theory of phase transitions. The basis function of the A2 irreducible representation, which is a rotation around the c-axis, corresponds to an electric toroidal dipole. [ABSTRACT FROM AUTHOR]