New synthesis route and magnetic structure of Tm2Mn2O7 pyrochlore.

In this work, we present a new chemical route to synthesize Tm2Mn2O7 pyrochlore, which a compound that is thermodynamically unstable at ambient pressure. Differently from the reported in the past high-pressure synthesis of the same compound applying oxides as starting materials, we have obtained a pure Tm2Mn2O7 phase by a converting TmMnO3 at 1100 °C and an oxygen pressure of 1300 bar. The studies of Tm2Mn2O7 performed by a high-resolution neutron powder diffraction have shown that a pure pyrochlore cubic phase Tm2Mn2O7 (space group Fd3¯m) have been obtained. Upon cooling below 25 K, there is a transition to a ferromagnetically (FM) ordered phase observed with an additional antiferromagnetic (AFM) canting, suggesting a lowering of the initial cubic crystal symmetry. The magnetic transition is accompanied by a small but very visible magnetostriction effect. Using symmetry analysis, we have found a solution for the AFM structure in the maximal Shubnikov subgroup I41/am'd'.

Critical current oscillations in the intrinsic hybrid vortex state of SmFeAs(O,F).

In layered superconductors the order parameter may be modulated within the unit cell, leading to nontrivial modifications of the vortex core if the interlayer coherence length ξ(c)(T) is comparable to the interlayer spacing. In the iron pnictide SmFeAs(O,F) (T(c)≈50 K) this occurs below a crossover temperature T(⋆)≈41 K, which separates two regimes of vortices: anisotropic Abrikosov-like at high and Josephson-like at low temperatures. Yet in the transition region around T(⋆), hybrid vortices between these two characteristics appear. Only in this region around T(⋆) and for magnetic fields well aligned with the FeAs layers, we observe oscillations of the c-axis critical current j(c)(H) periodic in 1/sqrt[H] due to a delicate balance of intervortex forces and interaction with the layered potential. j(c)(H) shows pronounced maxima when a hexagonal vortex lattice is commensurate with the underlying crystal structure. The narrow temperature window in which oscillations are observed suggests a significant suppression of the order parameter between the superconducting layers in SmFeAs(O,F), despite its low coherence length anisotropy (γ(ξ)≈3-5).

Transition from slow Abrikosov to fast moving Josephson vortices in iron pnictide superconductors.

Iron pnictides are layered high T(c) superconductors with moderate material anisotropy and thus Abrikosov vortices are expected in the mixed state. Yet, we have discovered a distinct change in the nature of the vortices from Abrikosov-like to Josephson-like in the pnictide superconductor SmFeAs(O,F) with T(c)~48-50 K on cooling below a temperature T*~41-42 K, despite its moderate electronic anisotropy γ~4-6. This transition is hallmarked by a sharp drop in the critical current and accordingly a jump in the flux-flow voltage in a magnetic field precisely aligned along the FeAs layers, indicative of highly mobile vortices. T* coincides well with the temperature where the coherence length ξ(c) perpendicular to the layers matches half of the FeAs-layer spacing. For fields slightly out-of-plane (> 0.1°- 0.15°) the vortices are completely immobilized as well-pinned Abrikosov segments are introduced when the vortex crosses the FeAs layers. We interpret these findings as a transition from well-pinned, slow moving Abrikosov vortices at high temperatures to weakly pinned, fast flowing Josephson vortices at low temperatures. This vortex dynamics could become technologically relevant as superconducting applications will always operate deep in the Josephson regime.

High magnetic-field scales and critical currents in SmFeAs(O, F) crystals.

With the discovery of new superconducting materials, such as the iron pnictides, exploring their potential for applications is one of the foremost tasks. Even if the critical temperature T(c) is high, intrinsic electronic properties might render applications difficult, particularly if extreme electronic anisotropy prevents effective pinning of vortices and thus severely limits the critical current density, a problem well known for cuprates. Although many questions concerning microscopic electronic properties of the iron pnictides have been successfully addressed and estimates point to a very high upper critical field, their application potential is less clear. Thus, we focus here on the critical currents, their anisotropy and the onset of electrical dissipation in high magnetic fields up to 65 T. Our detailed study of the transport properties of SmFeAsO(0.7)F(0.25) single crystals reveals a promising combination of high (>2 x 10(6) A cm(-2)) and nearly isotropic critical current densities along all crystal directions. This favourable intragrain current transport in SmFeAs(O, F), which shows the highest T(c) of 54 K at ambient pressure, is a crucial requirement for possible applications. Essential in these experiments are four-probe measurements on focused-ion-beam-cut single crystals with a sub-square-micrometre cross-section, with current along and perpendicular to the crystallographic c axis.

Dynastab S: A new concept for high energy fractures of the distal tibia.

Background. High energy fractures of the distal tibia ("pylon fractures") usually result in severe reduction of the range of motion of the superior ankle joint. If there is severe soft tissue trauma coexisting with the fractures, the possibilities for surgical treatment are limited. Our study examined the suitability of the DYNASTAB S external fixator (for ankle joint stabilization). Material and methods. We studied 25 adult patients (15 men, 10 women), treated from April 2001 to March 2003, to whom the DYNASTAB-S stabilizer was applied for an average of 10.5 weeks. Results. In all patients bone union was achieved, with a good range of motion in the talo-crural joint. All patients tolerated the applied treatment well. The average hospital stay was 9 days. There were 2 cases of transient inflammatory reaction of the skin around the screws, and 1 case of algodystrophy syndrome, which resolved after physical treatment combined with pharmacotherapy. Conclusions. The Dynastab S external fixator is very successful in the treatment of fractures with poor prognosis in traditional methods of conservative and surgical treatment, providing bone union and good functional efficiency of the superior ankle joint. The use of the mechanical joint imitating the movement of the injured ankle joint allows for early joint rehabilitation without loss of stability of the fracture. Adaptation of the device to the operated limb is excellent. The Dynastab S external fixator can be recommended for wider use in the treatment of pylon fractures.

The new concept of the monitoring and appraisal of bone union inflexibility of fractures treated by Dynastab DK external fixator.

Background. This work focuses on problems of heuristic techniques based on artificial intelligence. Mainly about artificial non-linear and multilayer neurons, which were used to estimate the bone union fractures treatment process using orthopaedic stabilizers Dynastab DK. Material and methods. The author utilizes computer software based on multilayer neuronal network systems, which allows to predict the curve of the bone union at early stages of therapy. The training of the neural net has been made on fifty six cases of bone fracture which has been cured by the Dynastab stabilizers DK. Using such trained net, seventeen fractures of long bones shafts were being examined on strength and prediction of the bone union as well. Results. Analyzing results, it should be underlined that mechanical properties of the bone union in the slot of fracture are changing in nonlinear way in function of time. Especially, major changes were observed during the forth month of the fracture treatment. There is strong correlation between measure number two and measure number six. Measure number two is more strict and in the matter of fact it refers to flexion, as well as the measure number six, to compression of the bone in the fracture slot. Conclusions. Consequently, deflection loads are especially hazardous for healing bone. The very strong correlation between real curves and predicted curves shows the correctness of the neuronal model.

[External fixation of fractures using Dysnastab-S stabilizers for massive ankle fractures of tibial bone epiphyseal articulations ]. / Zewnetrzne zespolenie odlamów przy uzyciu stabilizatora Dynastab-S (skok) w zlozonych zlamaniach stawowych nasady dalszej kosci piszczelowej.

Massive ankle fractures lead to joint stiffness and resulting decrease in range of motion. This can be avoided by functional treatment. In cases where severe soft tissue trauma coexists with bone fractures surgical treatment is limited and external fixation is the method of choice. Modern external fixation technique allows for stabilisation and maintaining range of motion in the affected joint. This paper presents the results of application of the Dynastab-S external fixator. The construction of this fixator allows dorsal and plantar, reducing postraumatic joint stiffness. It also allows appropriate insight into soft tissues and debridement of devitalised tissues as well as their forthcoming surgical reconstruction. In our material (27 cases) treated with the Dynastab-S fixator for an average of 16 weeks a satisfactory bone healing process in all cases was noted. Appropriate function of the extremity was maintained, with comparable plantar flexion to the contralateral, not affected joint. Only in one case post operative treatment was complicated by algodystrophy. Our observations showed that implementation of modern external stabilisation techniques leads to appropriate fracture healing with full function of the inferior extremity.

MgNB(9), a new magnesium nitridoboride.

The structure of a new magnesium nitridoboride, MgNB(9), has been refined from single-crystal X-ray data. The Mg and N atoms lie on sites with crystallographic 3m symmetry. The structure consists of two layers alternating along the c axis. The NB(6) layer, with B(12) icosahedra, has the C(2)B(13) structure type. Within this layer, boron icosahedra are bonded to N atoms, each coordinating to three boron polyhedra. Another MgB(3) layer, with B(6) octahedra, does not belong to any known structure type. The boron icosahedra and octahedra are connected to each other, thus forming a three-dimensional boron framework.