Raman spectroscopy of K x Co2-y Se2 single crystals near the ferromagnet-paramagnet transition.

Polarized Raman scattering spectra of the K x Co2-y Se2 single crystals reveal the presence of two phonon modes, assigned as of the A 1g and B 1g symmetry. The absence of additional modes excludes the possibility of vacancy ordering, unlike in K x Fe2-y Se2. The ferromagnetic (FM) phase transition at [Formula: see text] K leaves a clear fingerprint on the temperature dependence of the Raman mode energy and linewidth. For [Formula: see text] the temperature dependence looks conventional, driven by the thermal expansion and anharmonicity. The Raman modes are rather broad due to the electron-phonon coupling increased by the disorder and spin fluctuation effects. In the FM phase the phonon frequency of both modes increases, while an opposite trend is seen in their linewidth: the A 1g mode narrows in the FM phase, whereas the B 1g mode broadens. We argue that the large asymmetry and anomalous frequency shift of the B 1g mode is due to the coupling of spin fluctuations and vibration. Our density functional theory (DFT) calculations for the phonon frequencies agree rather well with the Raman measurements, with some discrepancy being expected since the DFT calculations neglect the spin fluctuations.

Evidence of superconductivity-induced phonon spectra renormalization in alkali-doped iron selenides.

Polarized Raman scattering spectra of superconducting K(x)Fe(2-y)Se2 and non-superconducting K0.8Fe1.8Co0.2Se2 single crystals were measured in the temperature range from 10 K up to 300 K. Two Raman active modes from the I4/mmm phase and seven from the I4/m phase are observed in the frequency range from 150 to 325 cm(-1) in both compounds, suggesting that the K0.8Fe1.8Co0.2Se2 single crystal also has a two-phase nature. The temperature dependence of the Raman mode energy is analyzed in terms of lattice thermal expansion and phonon-phonon interaction. The temperature dependence of the Raman mode linewidth is dominated by temperature-induced anharmonic effects. It is shown that the change in Raman mode energy with temperature is dominantly driven by thermal expansion of the crystal lattice. An abrupt change of the A1g mode energy near T(C) was observed in K(x)Fe(2-y) Se2, whereas it is absent in non-superconducting K0.8Fe1.8Co0.2Se2. Phonon energy hardening at low temperatures in the superconducting sample is a consequence of superconductivity-induced redistribution of the electronic states below the critical temperature.

C-reactive protein as an early predictor for anastomotic leakage in elective abdominal surgery.

BACKGROUND: Anastomotic leakage (AL) represents a serious complication after abdominal surgery. Therefore, it is important to detect it early before it becomes clinically apparent. The predictive value of C-reactive protein (CRP) as a marker of infective postoperative complications, particularly in the form of anastomotic leakage, has been investigated by several authors with promising results. The aim of this study was to evaluate the diagnostic accuracy of C-reactive protein in predicting anastomotic leakage. METHODS: The serum CRP level, white blood cell (WBC) count, and body temperature (BT) of 156 patients who underwent elective abdominal surgery with primary anastomosis were monitored daily until postoperative day (POD) 7. We recorded all postoperative complications and analyzed the data. Diagnostic accuracy of CRP with regard to development of AL was assessed by receiver operating characteristic curve analysis. RESULTS: Fifteen patients (9.6 %) developed anastomotic leakage. CRP was significantly higher every day during the first 7 postoperative days in patients who developed AL compared with those patients who did not develop complications, whereas the WBC count and BT were not. A CRP cutoff value of 135 mg/l on POD 3 yielded a sensitivity of 73 %, a specificity of 73 %, and a negative predictive value of 95.4 % for the detection of AL. CONCLUSIONS: According to our results, values of CRP less than 135 mg/l on POD 3 may contribute to a safe discharge from hospital. Patients with CRP values higher than 135 mg/l on POD 3 require prolonged hospitalization and an intensive search for infective complications, particularly AL.

Structural characterization of self-assembled ZnO nanoparticles obtained by the sol-gel method from Zn(CH3COO)2·2H2O.

Zinc oxide nanopowders were synthesized by the sol-gel method from an ethanol solution of zinc acetate dihydrate. Detailed structural and microstructural investigations were carried out using x-ray diffraction, Raman spectroscopy, thermogravimetric and differential thermal analyses, as well as high-resolution transmission electron microscopy (TEM) and field-emission scanning electron microscopy. The intermediate compound of the reaction was layered zinc hydroxide acetate that further transforms into hexagonally shaped ZnO crystalline nanoplates (d(m) = 4 nm), which aggregate into larger spherical particles. According to the TEM analysis the ZnO nanoparticles were self-assembled into larger particles with the same orientation, i.e. aligned lattice planes of the particles. A further solvothermal treatment resulted in hexagonal, prismatic ZnO mesocrystals.