Schmelzen und Behandeln von Metallen und Legierungen im Vakuum

The growing demands for better quality of metallic materials can only be met by the application of vacuum during the production of these metals and alloys and their field of application.     

Step response analysis of phosphoric acid fuel cell (PAFC) cathode through a transient model

Transient state response analysis of phosphoric acid fuel cell (PAFC) cathode is important to understand various competitive processes like diffusion, reaction and product back diffusion occurring at various layers of the composite cathode. A two-dimensional unsteady state model for simulating PAFC cathode is developed as an extension of the previously developed steady-state model [S. Roy Choudhury, M.B. Deshmukh, R. Rengaswamy, A two-dimensional steady-state model for phosphoric acid fuel cells (PAFC), J. Power sources 112 (2002) 137–152]. The transient model is solved to study the impact of various parameters such as Tafel slope, diffusivity etc on the step response of the fuel cell. The effect of partial pressure variation in bulk gas for large sized PAFC cathode is also analysed. Trend analysis based on the model output is also experimentally verified using a small unit cell setup. The effect of various parameters on the settling time of the cathode, as revealed in this study, suggests possible development of a diagnostic tool employing such transient model.     

Barrier properties of poly(vinyl alcohol) membranes containing carbon nanotubes or activated carbon

Carbon nanotube addition has been shown to improve the mechanical properties of some polymers. Because of their unique adsorptive properties, carbon nanotubes may also improve the barrier performance of polymers used in contaminant containment. This study compares the barrier performance of poly(vinyl alcohol) (PVA) membranes containing single-walled carbon nanotubes (SWCNTs) to that for PVA containing powdered activated carbon (PAC). Raw and surface-functionalized versions of each sorbent were tested for their abilities to adsorb 1,2,4-trichlorobenzene and Cu(2+), representing the important hydrophobic organic and heavy metal contaminant classes, as they diffused across the PVA. In both cases, PAC (for 1,2,4-trichlorobenzene) and functionalized PAC (for Cu(2+)) outperformed SWCNTs on a per mass basis by trapping more of the contaminants within the barrier membrane. Kinetics of sorption are important in evaluating barrier properties, and poor performance of SWCNT-containing membranes as 1,2,4-TCB barriers is attributed to kinetic limitations.     

Effect of Cerium Doping on Microstructure and Dielectric Properties of BaTiO3 Ceramics

A solid state reaction method was used to synthesize barium titanate (BT) and barium cerium titanate (BCT) ceramics at sintering temperature of 1473 K for 4 h. The effect of cerium (Ce) on the structure, microstructure and dielectric properties of BCT was investigated. The scanning electron microscopy (SEM) investigations revealed that the grain size increases with increasing Ce content. The X-ray diffraction (XRD) patterns showed mostly the BT phase, where the lattice parameter decreased with the addition of Ce. The temperature dependence of dielectric constant showed decrease in the phase transition temperature with higher Ce content. The dielectric constant decreased slightly with increasing frequency. The direct current (dc) density-voltage characteristics of the ceramics showed ohmic behavior for both the BT and BCT. As the temperature increased, the dc resistivity of the ceramics decreased. The activation energy increased with increasing Ce content.     

Organic and Inorganic Blocking Layers for Solution‐Processed Colloidal PbSe Nanocrystal Infrared Photodetectors

A PbSe solution‐processed nanocrystal‐based infrared photodetector incorporating carrier blocking layers is demonstrated, and significant reduction of dark current is achieved. Detectivity values close to 10¹² Jones are achieved by using poly[(9,9′‐dioctylfluorenyl‐2,7‐diyl)‐co‐(4,4′‐(N‐(4‐sec‐butyl))diphenylamine)] (TFB) and ZnO nanocrystals (NC) as the electron blocker and hole blocker, respectively. An improvement in lifetime is also observed in the devices with the ZnO NCs hole blocking layer.     

Metabolism and pharmacokinetics of 1-(2''-trimethylacetoxyethyl)-2-ethyl-3-hydroxypyridin-4-one (CP117) in the rat

A modified endoscopic technique for anterior cruciate ligament (ACL) reconstruction using an autologous patellar tendon graft is described using the early results for 120 patients. A special technique using an oscillating hollow saw allows for the rapid and standardized harvest of cylindrical bone plugs, ensuring safe and adequate femoral press-fit fixation. The complications encountered included one fracture of a bone back on plugging in as well as two cases with revision procedures for interference screw fixation due to insufficient femoral anchorage. Within the framework of a prospective study, all 120 patients underwent a control arthroscopy after the first postoperative year showing viable and mechanically stable grafts in 64 (53.3%) of the patients. In 44 patients (36.7%), viable though somewhat lax grafts were found, whereas the remaining 12 patients (10%) only showed insufficient tissue residues. All of these cases were the result of a ventral misplacement of the femoral insertion site representing the primary complication of transtibial technique. The results of the control arthroscopies showed a highly significant correlation with the clinical results for the IKDC score obtained in a follow-up after an average 29 (18 to 36) months. The results for stability according to the IKDC rating scale showed a normal or near-normal knee function in 76.7%. With regard to the subjective results in the IKDC rating scale, 83.3% of the patients (n = 100) assessed their knee function as normal or almost normal. The location and positioning of the femoral and tibial tunnel were evaluated in an exact radiographic evaluation showing an "ideal position" of the graft in only 94 cases (78.3%). Statistically, a significant correlation of stability with the femoral fixation site could be shown.     

Phonon dispersion relations and densities of states in La2CuO4 and La2NiO4

Rigid-ion model calculations of phonon dispersion relations, densities of states and partial densities of states of the highT _c superconductor La₂CuO₄ and its isostructural compound La₂NiO₄ have been carried out both in the tetragonal and orthorhombic phases of La₂CuO₄ and the tetragonal phase of La₂NiO₄. The calculations are in fair agreement with reported experiments. The computed phonon dispersion in the tetragonal phase of La₂CuO₄ reproduces the soft mode behaviour for the lowest Σ₄ TO branch which is found to harden in the orthorhombic phase, consistent with experimental data.     

The effect of priming with vecuronium and rocuronium on young and elderly patients

The priming principle consists of administering a subparalyzing dose of nondepolarizing neuromuscular blocking drug 3-6 min before giving a second dose for tracheal intubation. This study was performed to observe the effects of priming doses of vecuronium and rocuronium on pulmonary function tests and muscular weaknesses in young (25-35 yr of age) and elderly (65-73 yr of age) patients. Ten young and 10 elderly patients were each placed in vecuronium and rocuronium groups. Oxygen saturation and train-of-four (TOF) ratio were determined, and pulmonary function tests were performed. Then 20% of the 95% effective dose (ED95) of the muscle relaxants was given intravenously. All tests were performed again 4 min after vecuronium and 3 min after rocuronium. Other signs of muscular weaknesses were also recorded. Elderly patients showed more signs of muscle weakness in both groups. The TOF ratio was 0.77 and 0.79 in the elderly rocuronium and vecuronium groups, respectively, and 0.89 and 0.90 in the young rocuronium and vecuronium groups, respectively. Dynamic spirometry revealed decreases in forced expiratory volume in 1 s and forced vital capacity in both groups, and no significant changes in peak expiratory flow rate. The expiratory reserve volume was reduced more in the elderly groups. Oxygen saturation decreased in both groups. We conclude that oxygen saturation, pulmonary function, and muscle strength decrease more in the elderly than in their younger counterparts from priming doses of vecuronium or rocuronium. IMPLICATIONS: The priming principle consists of giving a subparalyzing dose of muscle relaxant 3-6 min before giving a second dose for tracheal intubation. We found that priming doses of vecuronium and rocuronium produced greater decreases in oxygen saturation and pulmonary function in the elderly (aged 65-73 yr) than their younger (aged 25-35 yr) counterparts. Priming may not be a safe approach in elderly patients.     

Epidemiological studies of blood groups in the district of Bankura with special reference to tribals

Distribution of ABO blood groups was studied in 4301 subjects, both tribals and non-tribals of the district of Bankura in West Bengal. It was observed that group 'O' blood was found in most cases and group 'AB' was seen in least number of cases. It was also found that there was no significant difference in distribution of blood groups between the tribals and non-tribals.