X-ray absorption near edge spectroscopy of thermochromic phase transition in CuMoO4

Thermochromic phase transition was studied in CuMoO4 using the Cu and Mo K-edge x-ray absorption spec-troscopy in the temperature range of 10-300 K. The hysteretic behavior has been evidenced from the tempera-ture dependence of the pre-edge shoulder intensity at the Mo K-edge, indicating that the transition from brown-ish-red γ-CuMoO4 to green α-CuMoO4 occurs in the temperature range of 230-280 K upon heating, whereas the α-to-γ transition occurs between 200 and 120 K upon cooling. Such behavior of the pre-edge shoulder at the Mo K-edge correlates with the change of molybdenum coordination between distorted tetrahedral in α-CuMoO4 and distorted octahedral in γ-CuMoO4. This result has been supported by ab initio full-multiple-scattering x-ray ab-sorption near edge structure (XANES) calculations.Financial support provided by Scientific Research Project for Students and Young Researchers Nr. SJZ/2017/5 realized at the Institute of Solid State Physics, University of Latvia is greatly acknowledged. The experiment at HASYLAB/DESY was performed within the project I-20160149 EC; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Classical Scalar Fields and the Generalized Second Law

It has been shown that classical non-minimally coupled scalar fields can violate all of the standard energy conditions in general relativity. Violations of the null and averaged null energy conditions obtainable with such fields have been suggested as possible exotic matter candidates required for the maintenance of traversable wormholes. In this paper, we explore the possibility that if such fields exist, they might be used to produce large negative energy fluxes and macroscopic violations of the generalized second law (GSL) of thermodynamics. We find that it appears to be very easy to produce large magnitude negative energy fluxes in flat spacetime. However we also find, somewhat surprisingly, that these same types of fluxes injected into a black hole do {\it not} produce violations of the GSL. This is true even in cases where the flux results in a decrease in the area of the horizon. We demonstrate that two effects are responsible for the rescue of the GSL: the acausal behavior of the horizon and the modification of the usual black hole entropy formula by an additional term which depends on the scalar field.Comment: 25 pages, 2 figures; paper substantially rewritten, major changes in the conclusion

Low Temperature Anharmonicity and Superconductivity in Cuprates

Temperature-dependent X-ray absorption spectra of the hole-doped $La_{2−x}Sr_{x} CuO_{4}$ and electron-doped $Nd_{2−x} Ce _{x} CuO_{4−\delta}$ high-temperature superconductors were investigated above the Cu K absorption edge. We observed strong anharmonicity in the superconductive $CuO_{2}$ plane. For x=0.15 it was shown that part of oxygen ions oscillate in a double-well potential and their vibrations are correlated with the local electron (hole) pair transfer. We suppose that at a low temperature the phase coherence of the local pair movement is determined by the peculiarities of the perovskite-like structure which includes the stiff $CuO_{n}$ (n = 4,6) complexes combined by collective rotational and breathing modes

XAFS and XRD studies of local structure peculiarities in magnetic R2Fe17−xMnxR_{2}Fe_{17−x}Mn_{x} (R=Ce, Lu) intermetallics

The rearrangement of cerium and lutetium local environment in Ce2Fe17−xMnx and Lu2Fe17-xMnx intermetallics vs. Mn concentration and temperature was investigated by means of the extended X-ray absorption fine structure (EXAFS) spectroscopy above K-Ce absorption edge and powder X-ray diffraction. The valence state of Ce in Ce2Fe17−xMnx was also studied by X-ray absorption near-edge structure (XANES) spectroscopy above L3-Ce absorption edge. The correlation between changes in local electronic and crystal structure and the types of magnetic ordering in these compounds is discussed

Effect of Chemical Chaperones on the Stability of Proteins during Heat– or Freeze–Thaw Stress

The importance of studying the structural stability of proteins is determined by the structure–function relationship. Protein stability is influenced by many factors among which are freeze–thaw and thermal stresses. The effect of trehalose, betaine, sorbitol and 2-hydroxypropyl-β-cyclodextrin (HPCD) on the stability and aggregation of bovine liver glutamate dehydrogenase (GDH) upon heating at 50 °C or freeze–thawing was studied by dynamic light scattering, differential scanning calorimetry, analytical ultracentrifugation and circular dichroism spectroscopy. A freeze–thaw cycle resulted in the complete loss of the secondary and tertiary structure, and aggregation of GDH. All the cosolutes suppressed freeze–thaw- and heat-induced aggregation of GDH and increased the protein thermal stability. The effective concentrations of the cosolutes during freeze–thawing were lower than during heating. Sorbitol exhibited the highest anti-aggregation activity under freeze–thaw stress, whereas the most effective agents stabilizing the tertiary structure of GDH were HPCD and betaine. HPCD and trehalose were the most effective agents suppressing GDH thermal aggregation. All the chemical chaperones stabilized various soluble oligomeric forms of GDH against both types of stress. The data on GDH were compared with the effects of the same cosolutes on glycogen phosphorylase b during thermal and freeze–thaw-induced aggregation. This research can find further application in biotechnology and pharmaceutics

Local crystal structure of TiNiCu shape memory alloys

The features of long-range crystal structure and local environment of Ni and Cu atoms in shape memory alloy Ti50Ni25Cu25 are investigated using X-ray diffraction and extended X-ray absorption fine structure spectroscopy (EXAFS) in the temperature range of direct and reverse martensitic transformations. According to XRD study, alloy has the B2 type structure in austenitic phase and B19 type structure (space group Pmmb) in martensitic phase. EXAFS demonstrates the difference between Cu-Ti and Ni-Ti bond lengths ~ 0.09 Å not typical for common TiNi lattice. The static disordering is more significant in the local environment of Ni atoms than in local environment of Cu atoms

“Chemical Metamagnetism”: From Antiferromagnetic PrCo₂P₂ to Ferromagnetic Pr_0.8Eu_0.2Co₂P₂ via Chemical Compression

“Chemical Metamagnetism”: From Antiferromagnetic PrCo₂P₂ to Ferromagnetic Pr_0.8Eu_0.2Co₂P₂ via Chemical Compressio