BackgroundPontocerebellar hypoplasia type 6 (PCH6) is a mitochondrial disease caused by mutations in the RARS2 gene. RARS2 encodes mitochondrial arginyl transfer RNA synthetase, an enzyme involved in mitochondrial protein translation. A total of 27 patients from 14 families have been reported so far. Characteristic clinical features comprise neonatal lactic acidosis, severe encephalopathy, intractable seizures, feeding problems and profound developmental delay. Most patients show typical neuroradiologic abnormalities including cerebellar hypoplasia and progressive pontocerebellar atrophy.MethodsWe describe the clinical, biochemical and molecular features of 2 siblings with a novel homozygous mutation in RARS2. Both patients presented neonatally with lactic acidosis. While the older sibling had severe neurological symptoms with microcephaly, seizures and developmental delay, the younger patient was still neurologically asymptomatic at the age of 2 months.ResultsMRI studies in both children lacked pontocerebellar involvement. The expression of the OXPHOS complex proteins was decreased in both patients, whereas oxygen consumption was increased.ConclusionsCharacteristic neuroradiological abnormalities of PCH6 such as vermis and cerebellar hypoplasia and progressive pontocerebellar atrophy may be missing in patients with RARS2 mutations. RARS2 testing should therefore also be performed in patients without pontocerebellar hypoplasia but otherwise typical clinical symptoms.
The anodic oxidation behavior of niobium has been investigated under nearly industrial conditions. High porosity sintered bodies as well as flat niobium sheets were anodized between 20-100 V in 1 wt % aqueous solution of o-phosphoric acid at 65°C, applying current densities between 0.01 and 0.067 mA/cm 2 . During formation at constant current, changes in the rate of voltage increase has been observed. Stopping oxidation at such changes in the V(t) curve, the electrical properties, surface composition and in-depth homogeneity of the oxide was analyzed. The formed oxide layers have also been investigated after a heat-treatment in vacuum and in air. Based on the measured composition profiles, the role of the solid suboxide phases ͓Nb͑O͒, NbO, NbO 2 ] in the oxide growth and in the annealing could be clarified.The Nb/Nb 2 O 5 system is a candidate to replace the widely used Ta/Ta 2 O 5 system in solid electrolyte capacitors in some applications. 1-5 Advantages of the Nb/Nb 2 O 5 system are the high dielectric permittivity 6 ( r Ϸ 42) of Nb 2 O 5 , the relatively low price of niobium, and the vastness of niobium reserves. 7 However, some properties of niobium, like its high oxygen absorbing capacity, 2,8 strong chemical affinity to oxygen, carbon, and nitrogen, 2 as well as the existence of its suboxides, NbO 2 , NbO, and Nb͑O͒ beside the desirable Nb 2 O 5 , makes this system hard to handle. [8][9][10][11]12 Nevertheless, the usage of Nb as anode material is feasible considering the following facts. ͑i͒ The stable working voltage of this system is significantly lower than that of the Ta/Ta 2 O 5 system, 6 because the r value of Nb 2 O 5 is higher. This lower electrical field in the oxide leads to the same ionic current. ͑ii͒ The maximum working temperature of the system is 125°C, which is lower than that of the Ta/Ta 2 O 5 system ͑typically 150°C͒. Therefore, despite the problems mentioned, the Nb/Nb 2 O 5 based capacitors are reliable and stable devices. 13 The anodization of niobium has been widely studied 6,14-18 at the basic research level. This process proved to be basically similar to the anodization of tantalum. The investigation of the effect of heattreatment is important, as it causes changes in the capacity ͑C͒ and leakage current of the capacitors. The thermal stability of the Ta/Ta 2 O 5 system has been widely studied. [19][20][21][22][23][24][25] The capacity of such systems changes after heat-treatment due to the incorporation of O from the oxide into the Ta metal. A change in the structure of the oxide layer was found by X-ray diffraction ͑XRD͒. 21 Smith and Tripp 26 have extended their studies onto the anodically oxidized Nb/Nb 2 O 5 system. The effect of annealing was much more pronounced than in the Ta/Ta 2 O 5 system. The microphysical properties and structure of various niobium oxides are described in detail. 27 Grundner and Halbritter 28 have investigated the heattreatment induced transformation of the chemical structure of various thin film oxides ͑grown both anodically and thermally͒. Like Hahn...
The replacement of the anode material in tantalum capacitors by a new generation of high CV niobium powders offers the possibility to get an economical alternative to tantalum for a wide range of applications. Due to the high CV potential of niobium powder there is also an alternative to low voltage aluminum electrolytic capacitors. We developed a new niobium capacitor which shows stable electrical values. By optimizing the structure of the dielectric and the cathodic layers as well as the process parameters we gained a capacitor which can be used up to105 °C. Electrical characteristics and lifetest behavior of niobium capacitors out of 100 k–150 k CV/g powder will be discussed.
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