[en] Polycrystalline samples of RO_1-xF_xFeAs(0≤x≤0.25) were prepared in a two step method, similar described by Zhu et al. In the first step FeAs is prepared which is milled afterwards. In the second step the FeAs powder is mixed together with rare-earth-oxides, -fluorides and -pure element powders and pressed into pellets under a well defined pressure. Then, the samples were heated in an evacuated silica tube at 940 C and 1150 C. The composition of the samples and particularly the fluorine content was determined by wavelength-dispersive X-ray spectroscopy (WDX) in the electron microscope. The polycrystalline samples consist of the RO_1-xF_xFeAs phase mainly, only small amount of RO_yF_z and FeAs are found. We find that the measured fluorine content can deviate from the initial weight. In the lanthanum compound LaO_1-xF_xFeAs, e.g., we found a good agreement mainly for x>0.05, but the fluorine hardly goes into the sample for x<0.05. For the samarium compound again we measure less fluorine in the sample as weighted for all fluorine contents. These measured values are taken into account when drawing the electronic phase diagrams of LaO_1-xF_xFeAs and SmO_1-xF_xFeAs. Furthermore, we studied which preparation steps are crucial for the fluorine incorporation.

[en] LaFeAsO_1-xF_x thin films were deposited successfully on (001)-oriented LaAlO₃ and MgO substrates from stoichiometric LaFeAsO_1-xF_x polycrystalline targets with fluorine concentrations up to x=0.25 by pulsed laser deposition (PLD). Room temperature deposition and post annealing yield films with a pronounced c-axis texture and a strong biaxial in-plane orientation. Transport measurements show metallic resistance and onset of superconductivity at 11 K. μ₀H_c2(T) was determined by resistive measurements and yield μ₀H_c2 values of 3 T at 3.6 K for the perpendicular field direction and 6 T at 6.4 K for the parallel field direction to the sample surface.

[en] We present ⁷⁵As Nuclear Magnetic Resonance (NMR) measurements on the iron-based superconductor LaO_1-xF_xFeAs with 0 ≤ x ≤ 0.1, covering a broad range of the phase diagram from magnetically-ordered to optimally-doped superconducting samples. For underdoped samples (x=0.05,x=0.075) the ⁷⁵As NMR spin-lattice relaxation rate (T₁T)^-1 shows a Curie-Weiss-like increase at intermediate temperatures, indicating the slowing down of spin fluctuations. However, a simple Curie-Weiss fit fails to describe (T₁T)^-1(T) above 250 K and the occurrence of a peak in (T₁T)^-1 slightly above T_c. Instead, the data can be well described by considering a BPP-model for fluctuating magnetic fields in combination with a doping-independent linear temperature dependence at high temperature. At optimal doping (x=0.1) spin fluctuations are suppressed and only the linear contribution to (T₁T)^-1 is left. This stands in contrast to other pnictides, such as Ba(Fe_1-xCo_xAs)₂ and Ba(FeAs_1-xP_x)₂. Our analysis is consistent with charge carrier localization in underdoped LaO_1-xF_xFeAs as seen by means of resistivity measurements.

[en] Background. The sphenoid sinus is a frequent target of paranasal sinus surgery. Because of the high risk of injuring the surrounding structures (e.g. internal carotid artery, optical nerve) a preoperative imaging is absolutely necessary. Purpose. To analyze the possibilities of cone-beam computed tomography (CBCT), which is especially quite a new technique in ENT, in the evaluation of the sphenoid sinus, its surrounding structures, and the corresponding anatomical variations. Material and Methods. This was a retrospective, single-centre study of 580 patients (1160 sides = cases). The Accu-I-Tomo-F17 was used. Pneumatization of sphenoid sinus, course of internal artery, course of optical nerve, and dehiscence of the bony canals were evaluated. Results. In the case of pneumatization a type I (completely missing or minimal sphenoid sinus) was found in two patients (0.3%), type II (posterior wall of sphenoid sinus is in front of the anterior wall of the sella) in 38 patients (6.6%), type III (posterior wall is between anterior and posterior wall of sella) in 332 patients (57,2%), type IVa (posterior wall is behind the posterior wall of sella without air dorsal the sella) in 104 patients (17.9%), and type IVb (similar to type IVa but with air dorsal the sella) in 104 patients (17.9%). In 1025 cases (89.5%) a smooth course of the internal carotid artery was found whereas a free course could be detected in 120 cases (10.5%). Defects of the bony canal of the optical nerve were found in 16.7% and of the internal carotid artery in 2.7% of the cases. The optical nerve showed a free course through the sphenoid in 151 cases (13.7%) and a smooth course in 1007 cases (87.0%). Conclusion. CBCT could evaluate all relevant anatomic structures and answer the questions of different anatomical variants. A modified classification of the pneumatization of the sphenoid sinus could be described. Frequencies of anatomical variations are in accordance with the current literature of CT research

[en] We report a study on electrical resistivity, thermoelectric power, Hall effect and Nernst coefficient of polycrystalline LaFeAsO_1-xF_x in the temperature range 5-300 K and magnetic field 14 T. We show the evolution of transport properties with electron doping (F content x=0,0.05,0.1). The parent compound undergoes two phase transitions at the temperature around 150 K: magnetic to antiferromagnetically ordered spin density wave state and structural - from tetragonal to orthorombic crystal structure. The presence of phase transitions gives rise to changes in charge carrier scattering processes, which is reflected as profound anomalies in investigated transport properties. In the superconducting samples these two transitions are not present, nevertheless in the underdoped compound (x=0.05) we observe features reminiscent of the transitions, in particular change of slope in electrical resistivity and Nernst signal. We discuss the possibility of presence of spin fluctuations, which lead to formation of SDW state in parent compound and to anomalies in transport properties in underdoped superconducting samples. At the same time the optimally doped sample (x=0.1) does not show any of these characteristic features.

[en] We have performed ⁷⁵As, ¹³⁹La, and ⁵⁷Fe Nuclear Magnetic Resonance (NMR) measurements on the new LaO_1-xF_xFeAs superconductor. For x=0.1, NMR on all three nuclei shows that the local electronic susceptibility increases with increasing temperature in the normal state. The scaling of all NMR shifts with respect to the macroscopic susceptibility indicates a single spin liquid. Relaxation measurements exhibit a similar temperature-dependence for (T₁T)^-1, and suggest that the dynamical susceptibility changes uniformly in q space with varying temperature. For x=0.05, in the underdoped regime, we find a Curie Weiss like increase of (T₁T)^-1 at low temperatures, indicating the onset of local moment fluctuations.

[en] We assessed the results of self-expanding metallic stent insertion into benign proximal tracheal stenosis in patients not appropriate or unfit for surgical repair. Proximal benign tracheal stenoses had occurred in 11 patients (7 men, 4 women, mean age 68.8 years) after long-time intubation (n = 6), tracheostomy (n = 4), or chondropathia (n = 1). Fourteen self-expanding nitinol stents were placed in the patients under general anesthesia with endoscopical and fluoroscopical guidance. Stent insertion was successful in all cases and led to immediate relief of the morphological and functional airway obstruction. No immediate complications were noted. During the mean follow-up period of 67.5 weeks we observed one recurrent dyspnea 3 months after implantation and granuloma formation at the stent insertion site in another patient. Both complications were successfully treated with additional stent insertion in one case and laser resection of granulomas in the other. Self-expanding nitinol stents should be considered for the treatment of benign proximal tracheal obstruction in selected patients for whom surgical repair is contraindicated

[en] The discovery of a new class of superconducting materials, ReFeAsO_1-xF_x, stirred up the scientific community. Here we report the Gd³⁺ high field ESR study of differently doped (La,Gd)FeAsO_1-xF_x compounds. In lightly Gd-doped LaFeAsO samples the SDW transition yields line-broadening at the transition temperature, the SDW transition is then suppressed upon F-doping. In the dense compound, GdFeAsO, with SDW transition around 140 K, the Gd-ESR was also studied. With 15% F-doping superconductivity appears at ∝ 21 K. The SDW and SC transitions are clearly seen in ESR and in μ SR as well. Surprisingly the reminiscence of the SDW transition of the undoped material (GdFeAsO) was identified in the doped (15% F) compound at lower temperature (∝ 80 K). This indicates the importance of the the interplay between superconductivity and magnetism in oxypnictides.

[en] We summarize our Nuclear Magnetic Resonance (NMR) and Nuclear Quadrupole Resonance (NQR) results on the new iron arsenide superconductor LaO_1-xF_xFeAs in the normal state, and show new NMR data in the superconducting state. Beyond early evidence of nodes and spin-singlet pairing[2], we find evidence of a deviation of the T³ behaviour of the spin lattice relaxation rate, 1/T₁, at temperatures significantly below T_c, which would agree with the suggested extended s-wave symmetry. The deviation of the T³ behaviour is induced by the pair breaking effect of impurities. Different amounts of impurities would lead to different temperature dependences of 1/T₁, which would allow to differentiate between d-wave and extended s-wave symmetries.

[en] Polycrystalline samples from the REOFeAs system were studied by means of electrical resistivity, thermal conductivity and thermoelectric power in temperature range 5-300 K. All investigated compounds undergo a magnetic and a structural phase transition around 150 K, which lead to profound anomalies in electrical, thermal and thermoelectric properties. We present the influence of substituting rare earth elements for La ion on the low temperature thermopower data. We discuss also the strong impact of magnetic field (B=14 T) on thermoelectric properties.