Oxygen reduction via grain boundary transport in thin film platinum electrodes on yttria stabilized zirconia.

Model-type sputter deposited platinum microelectrodes with different grain sizes were investigated on single crystalline yttria stabilized zirconia (YSZ) by means of impedance spectroscopy. Measurements on single platinum microelectrodes could be continuously performed for > 100 h and from 250 to 800 °C without losing contact. From the temperature dependence, two parallel reaction pathways for oxygen reduction could be identified. Above 450 °C, a surface path with a rate determining step located at the three phase boundary is predominant. Its polarization resistance is independent of the Pt grain size and exhibits an activation energy of ca. 1.8 eV. In the low temperature regime (< 450 °C) a bulk path through Pt was verified, with an electrode polarization resistance depending on the Pt grain size. This resistance is only slightly thermally activated and the rate limiting step is most probably oxygen diffusion along Pt grain boundaries.

A novel approach for analyzing electrochemical properties of mixed conducting solid oxide fuel cell anode materials by impedance spectroscopy.

For application of acceptor-doped mixed conducting oxides as solid oxide fuel cell (SOFC) anodes, high electrochemical surface activity as well as acceptable electronic and ionic conductivity are crucial. In a reducing atmosphere, particularly the electronic conductivity of acceptor-doped oxides can become rather low and the resulting complex interplay of electrochemical reactions and charge transport processes makes a mechanistic interpretation of impedance measurements very complicated. In order to determine all relevant resistive and capacitive contributions of mixed conducting electrodes in a reducing atmosphere, a novel electrode design and impedance-based analysis technique is therefore introduced. Two interdigitating metallic current collectors are placed in a microelectrode, which allows in-plane measurements within the electrode as well as electrochemical measurements versus a counter electrode. Equivalent circuit models for quantifying the spectra of both measurement modes are developed and applied to simultaneously fit both spectra, using the same parameter set. In this manner, the electronic and ionic conductivity of the material as well as the area-specific resistance of the surface reaction and the chemical capacitance can be determined on a single microelectrode in a H2-H2O atmosphere. The applicability of this new tool was demonstrated in SrTi0.7Fe0.3O(3-δ) (STFO) thin film microelectrodes, deposited on single-crystalline yttria-stabilized zirconia (YSZ) substrates. All materials parameters that contribute to the polarization resistance of STFO electrodes in a reducing atmosphere could thus be quantified.

Intensity- and frequency-specific effects of transcranial alternating current stimulation are explained by network dynamics.

Transcranial alternating current stimulation (tACS) can be used to non-invasively entrain neural activity, and thereby cause changes in local neural oscillatory power. Despite an increased use in cognitive and clinical neuroscience, the fundamental mechanisms of tACS are still not fully understood. Here, we develop a computational neuronal network model of two-compartment pyramidal neurons and inhibitory interneurons which mimic the local cortical circuits. We model tACS with electric field strengths that are achievable in human applications. We then simulate intrinsic network activity and measure neural entrainment to investigate how tACS modulates ongoing endogenous oscillations. First, we show that intensity-specific effects of tACS are non-linear. At low intensities (<0.3 mV/mm), tACS desynchronizes neural firing relative to the endogenous oscillations. At higher intensities (>0.3 mV/mm), neurons are entrained to the exogenous electric field. We then further explore the stimulation parameter space and find that entrainment of ongoing cortical oscillations also depends on frequency by following an Arnold tongue. Moreover, neuronal networks can amplify the tACS induced entrainment via excitation-inhibition balance. Our model shows that pyramidal neurons are directly entrained by the exogenous electric field and drive the inhibitory neurons. Our findings can thus provide a mechanistic framework for understanding the intensity- and frequency- specific effects of oscillating electric fields on neuronal networks. This is crucial for rational parameters selection for tACS in cognitive studies and clinical applications.

Induced neural phase precession through exogeneous electric fields.

The gradual shifting of preferred neural spiking relative to local field potentials (LFPs), known as phase precession, plays a prominent role in neural coding. Correlations between the phase precession and behavior have been observed throughout various brain regions. As such, phase precession is suggested to be a global neural mechanism that promotes local neuroplasticity. However, causal evidence and neuroplastic mechanisms of phase precession are lacking so far. Here we show a causal link between LFP dynamics and phase precession. In three experiments, we modulated LFPs in humans, a non-human primate, and computational models using alternating current stimulation. We show that continuous stimulation of motor cortex oscillations in humans lead to a gradual phase shift of maximal corticospinal excitability by ~90°. Further, exogenous alternating current stimulation induced phase precession in a subset of entrained neurons (~30%) in the non-human primate. Multiscale modeling of realistic neural circuits suggests that alternating current stimulation-induced phase precession is driven by NMDA-mediated synaptic plasticity. Altogether, the three experiments provide mechanistic and causal evidence for phase precession as a global neocortical process. Alternating current-induced phase precession and consequently synaptic plasticity is crucial for the development of novel therapeutic neuromodulation methods.

Combining electrochemical and quantitative elemental analysis to investigate the sulfur poisoning process of ceria thin film fuel electrodes.

This work deals with the effect of sulfur incorporation into model-type GDC thin films on their in-plane ionic conductivity. By means of impedance measurements, a strongly deteriorating effect on the grain boundary conductivity was confirmed, which additionally depends on the applied electrochemical polarisation. To quantify the total amount of sulfur incorporated into GDC thin films, online-laser ablation of solids in liquid (online-LASIL) was used as a novel solid sampling strategy. Online-LASIL combines several advantages of conventional sample introduction systems and enables the detection of S as a minor component in a very limited sample system (in the present case 35 µg total sample mass). To reach the requested sensitivity for S detection using an inductively coupled plasma-mass spectrometer (ICP-MS), the reaction cell of the quadrupole instrument was used and the parameters for the mass shift reaction with O2 were optimised. The combination of electrical and quantitative analytical results allows the identification of a potential sulfur incorporation pathway, which very likely proceeds along GDC grain boundaries with oxysulfide formation as the main driver of ion transport degradation. Depending on the applied cathodic bias, the measured amount of sulfur would be equivalent to 1-4 lattice constants of GDC transformed into an oxysulfide phase at the material's grain boundaries.

Quantitative imaging of structured complex metal oxide thin films using online-LASIL-ICP-MS.

Online-laser ablation of solids in liquid (online-LASIL) coupled with ICP-MS detection was used as a new sampling strategy for the analysis of complex metal oxide (CMO) thin films. The in-house built and optimized online-LASIL ablation cell provides the unique possibility to correlate the signal intensities with the spatial origin of the signal at the sample. For that purpose a particle transport with as little particle dispersion as possible is crucial. To demonstrate the 2D imaging capability of this technique, geometrically structured samples with varying composition were prepared by pulsed laser deposition (PLD) and ion beam etching procedures. These thin films with a thickness of 220 nm were spatially resolved analysed. As a result, 2D intensity maps obtained by online-LASIL can be reported for the first time. Additionally a new approach for simultaneous online quantification was developed by adopting the standard addition concept allowing to correct for instrumental drifts of long time measurements.

The PTPN22gain-of-function+1858T(+) genotypes correlate with low IL-2 expression in thymomas and predispose to myasthenia gravis.

Protein tyrosine phosphatase, non-receptor type 22 (PTPN22) inhibits T-cell activation and interleukin-2 (IL-2) production. The PTPN22(gain-of-function)+1858T(+) genotypes predispose to multiple autoimmune diseases, including early-onset (non-thymomatous) myasthenia gravis (MG). The disease association and the requirement of IL-2/IL-2 receptor signaling for intrathymic, negative T-cell selection have suggested that these genotypes may weaken T-cell receptor (TCR) signaling and impair the deletion of autoreactive T cells. Evidence for this hypothesis is missing. Thymoma-associated MG, which depends on intratumorous generation and export of mature autoreactive CD4(+) T cells, is a model of autoimmunity because of central tolerance failure. Here, we analyzed the PTPN22 +1858C/T single nucleotide polymorphism in 426 German Caucasian individuals, including 125 thymoma patients (79 with MG), and investigated intratumorous IL-2 expression levels. Unlike two previous studies on French and Swedish patients, we found strong association of PTPN22 +1858T(+) genotypes not only with early-onset MG (P=0.00034) but also with thymoma-associated MG (P=0.0028). IL-2 expression in thymomas with PTPN22 +1858T(+) genotypes (P=0.028) was lower, implying weaker TCR signaling. We conclude that the PTPN22(gain-of-function) variant biases towards MG in a subgroup of thymoma patients possibly by impeding central tolerance induction.

Autologous blood donor screening indicated a lower prevalence of viral hepatitis in East vs West Germany: epidemiological benefit from established health resources.

Prevalence data concerning viral hepatitis and human immunodeficiency virus (HIV) in the general population are usually scarce. We aimed for a large cohort representative of the general population that required little funding. Autologous blood donors are relatively representative of the general population, and are tested for viral hepatitis and HIV in many countries. However, frequently these data are not captured for epidemiologic purposes. We analysed data from well over 35,000 autologous blood donors as recorded in 21 different transfusion centres for anti-hepatitis C virus (HCV), HBsAg and anti-HIV, as well as TPHA if available. We found a lower prevalence of hepatitis B virus and HCV in East vs West Germany, 0.2%vs 0.32% and 0.16%vs 0.32% respectively, which confirms earlier data in smaller cohorts, thus supporting the value of our approach. HIV was too rare to disclose significant differences, 0.01%vs 0.02%. TPHA was higher in East (0.34%) vs West Germany (0.29%) without significant differences. HCV was more frequent in women vs men. Transfusion institutes managing autologous blood donations should be used as a resource for epidemiological data relating to viral hepatitis and HIV, if such testing is performed routinely. This approach generates data relating to the general population with special emphasis on undiagnosed cases.

[Autologous serum and alternative blood products for the treatment of ocular surface disorders]. / Eigenserum und alternative Blutprodukte zur Behandlung von Augenoberflächenerkrankungen.

Eye drops made from autologous serum have been increasingly used in the past decade to treat ocular surface disorders such as persistent epithelial defects and dry eye. Due to biologically active ingredients such as growth factors, vitamins, and nutrients, they can be used to lubricate the ocular surface and support epithelial wound healing. According to current legal requirements, they can be dispensed only for outpatient treatment if the producer has obtained a license from the appropriate local authorities. Therefore, the production and dispensing of autologous serum eye drops in Germany is currently limited to a very few institutions and their patients. We review the current evidence on the use of serum eye drops, recommend a standard protocol for their production, and describe a number of recently emerging alternative blood products for the treatment of ocular surface diseases along with their potential advantages and limitations.

Changes in plasminogen activator activity and plasmin inhibition in the pig during experimental hypovolaemia.

A markedly decreased plasminogen activator activity (PAA) was seen in lung, heart and kidney after experimental hypovolemia in the pig. In 2 of 12 cases, an increased PAA was found in liver and spleen. In skeletal muscle, skin, sciatic nerve and in 10 of 12 cases in liver and spleen PAA was unchanged. A slightly increased plasmin inhibition was noted only in the lung. These changes in tissue PAA were reflected by an increase in the PAA of euglobulin fractions concomitant with a decrease in antiplasmin activity in the blood samples obtained during the bleeding experiments.

Anesthesiology and intensive care during epilepsy surgery in children and adolescents.

Thus far there are no known studies of the management of anesthesiology and intensive care in cases of implantation of subdural plates for the purpose of determining the epileptogenic areal and of subsequent epilepsy surgery. Such operative measures are still considered too risky, especially in the case of small children. The authors report on cases of 45 children and adolescents who underwent this kind of surgery between December 1992 and December 1997 in Gilead hospital. In order to judge the anesthesiological risk the children were divided into three age groups: A, 1-5 years (n = 12); B, 6-11 years (n = 14); C, 12-18 years (n = 19). In none of these groups were there complications which in retrospect would have shed a negative light on the operation.

[Mechanical strain in the forearm bones]. / Mechanisch Dehnungen am Unterarmskelett.

Knowledge of the physiologic distribution of strain in bone is essential for a successful osteosynthesis by means of compression plate. This method guarantees optimum stability if the plate acts as a tension band. If the side of tensile stresses varies within the bone, strain may not only occur on the side of the plate but also on the opposite cortex. In such cases the distribution of pressure in the fracture gap is of special importance. For determining the distribution of strain on the radius, it is necessary to examine the forces caused by the flexor- and extensor muscles of the wrist and fingers. Additional forces come also from flexor- and extensor muscles of the elbow. The frame formed by the bow-shaped radius and the ulna is of further importance for the distribution of strain. Kind and amount of tension is fundamentally influenced by forearm rotation. Anatomic studies on post-mortem specimens showed how the direction of muscle action to wrist and fingers changed in relation to the position of a plate fixed to the proximal shaft of the radius. This already demonstrates possible variations in the bending forces caused by forearm rotation. An analysis of the distribution of strain in the forearm bones was carried out on a biomechanical model using strain gauges. This method allows the simulation of strain to the skeleton caused by muscle force and the influence of load. The distribution of strain can be studied on the same model in various different positions of elbow and forearm. Six muscles and two muscle groups were simulated by means of wire pulls with calibrated strain gauges; these muscles and muscle groups act, on account of the physiological cross section and their position, as bending forces to the forearm bones in a dorsovolar plane. The tensile force on radius and ulna were each controlled by three strain gauges in four sections. The characteristic quantities of these sections were determined by evaluation of the appropriate computertomograms. With the aid of three strain gauges per section it was possible to assess the strain at any one desired point. Distribution of strain was determined by pull to each "muscle" in the extreme position of forearm rotation and three different positions of flexion to the elbow. The tensile force was expressed on graphs as muscle tension of 2 kp/cm2 per cross section (ill. 6 to 12).(ABSTRACT TRUNCATED AT 400 WORDS)

[Vascular and capsule-band reconstruction following knee joint dislocation]. / Gefäss- und Kapsel-Band-Rekonstruktion nach Kniegelenksluxation.

This is a report about bilateral dislocations of the knee joints in one patient with arterial and venous stop because of endothelial lesions and thrombosis of the popliteal vessels on both sides. After reconstruction of circulation by means of vena saphena, the disrupted knee ligaments were also sutured. Large ventral exposure of the knee joint is recommended for both reconstruction of vessels and ligaments.

[Treatment results of late surgery in subcutaneous ruptures of the Achilles tendon]. / Behandlungsergebnisse verspätet operierter subkutaner Achillessehnenrisse.

15 patients with neglected subcutaneous ruptures of the tendo Achilles where operated at an average interval of 7 weeks after the accident. Up to 7 weeks after the rupture direct suture was possible, when the scar tissue was not removed. After a longer interval additional reinforcement of the suture or plastic repair was necessary. As immobilisation a low leg cast for 6 weeks is sufficient. Weight bearing is permitted after wound healing. Late results on 11 patients showed in all of them a loss of muscle strength of at least 10% as compared to the other leg. Also limitations of motion of the ankle joint is to be expected. 3 patients had infections. The use of non absorbable suture material is not to be recommended. The "pen-box operation" (Griffelschachtelplastik) leads to less devascularisation of the material then other methods with twisting a flap from the proximal tendon-stump for 180 degrees (Umkipp-Plastik).

[Open craniocerebral lesion due to perforation with a pneumatic pike-driver (author's transl)]. / Ungewöhnlicher Fall einer Gehirnverletzung durch Nageleinschuss aus einem Druckluftnagler.

The article reports on a patient with an open craniocerebral lesion due to a pneumatic pike-driver. The unusual type of injury without any neurological symptoms will be discussed. In spite of participation of the ventricle-system there was no infection up to the fifth month.

[New classification of epiphyseal-plate injuries with regard to therapy and prognosis (author's transl)]. / Klassifikationsvorschlag für Epiphysenfugen-verletzungen im Hinblick auf Therapie und Prognose.

In this report a new simple classification of epiphyseal-plate injuries with regard to therapy and prognosis is pointed out. The classification can be used for each epiphysis and will be demonstrated on the injuries of the distal lower leg. Type I: There is complete separation of the epiphysis from the metaphysis without and with a metaphyseal fragment. The prognosis for growth is excellent after conservative or operative treatment. Type II: The fracture which is intraarticular (epiphyseal fragment) and the fracture across the full thickness of the epiphyseal plate and through a portion of the metaphysis needs accurate reduction. The prognosis for growth is good only after open operation. Type III: This relatively uncommon injury results from a very severe crushing force applied through the epiphysis to one area of the epiphyseal plate. The prognosis in this type is decidedly poor. The need for regular follow-up observation in these cases is obvious. At the end the good results of 40 patients after epiphyseal-plate injuries of the distal lower leg are presented.

Subintimal revascularization of chronic iliac artery occlusions using a reentry-catheter.

PURPOSE: To demonstrate the value of a Reentry-Catheter for true lumen access after subintimal revascularization of chronic iliac artery occlusions. MATERIALS AND METHODS: Subintimal revascularization was performed in 5 patients (mean age: 67 ± 12 years; female: 3, male: 2) with total iliac artery occlusion (TASC B to D), but without gaining access to the true lumen distal to the occlusion. Subsequently, a Reentry-Catheter was used to establish reentry and a new subintimal tract. Patients were followed up after 6, 12 and 24 months for clinical re-evaluation to determine the Rutherford score and the ankle brachial index (ABI). In addition, duplex ultrasound was performed to evaluate vessel patency. RESULTS: The primary technical success rate was 100 %. In all cases angioplasty was followed by stent placement to establish the subintimal tract. The mean Rutherford score decreased from 3.6 ± 0.9 to 0.33 ± 0.57 after 24 months, while the ABI increased from 0.67 ± 0.06 to 1.2 ± 0. Vessel patency was observed in all patients available for follow-up examinations. CONCLUSION: The Reentry-Catheter reliably allowed access to the true lumen after subintimal revascularization of occluded iliac arteries. Results in this small patient cohort showed a significant reduction in the Rutherford score, increase in the ABI, and a good patency rate after two years.