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Open access

H. Danninger, G. Leitner and Ch. Gierl-Mayer

Abstract

In situ characterization of the sintering process is a difficult task, in particular for systems without pronounced dimensional changes. Dilatometry is not too helpful in those cases, and therefore other properties have to be recorded. In the present study, sintering of ferrous powder compacts was studied in situ by measuring the thermal diffusivity a using a laser flash apparatus. This property is a measure to characterise the heat flow through a material; it depends on the contact area between the particles and thus reveals their change during sintering. It is shown that the change of a during sintering of ferrous compacts is much less pronounced than in the case of cemented carbides which is not surprising when regarding the widely differing porosity changes. The results are however in good agreement with expectations when considering some experimental limitations. The trend for the thermal conductivity λ. which can be calculated from a, the specific heat and the density, is in good agreement with that found for the electrical conductivity, both properties being linked through Wiedemann-Franz’ law.

Open access

M Haas, P Schröder, D Komoßa, H Sandermann and RG May

Abstract

The metabolism of the plant growth regulator maleic hydrazide (MH) has been studied in sterile cell suspension cultures of tobacco, soybean, maize and wheat under standardized conditions. Maleic hydrazide was converted to its O-b -D-glucoside in yields between 9.0 % (tobacco) 15.0 % (soybean), 5.1 % (maize) and 2.2 % (wheat) respectively. This glucoside was completely cleaved under simulated conditions (pH 1, 37°C, 24 h) of a ruminant stomach. From these results it is concluded that MH-O-b-D-glucoside (MHG) belongs to a small group of acid-labile pesticide conjugates (11). The participation of a glucosyltransferase (GT) (EC 2.4.1-) in this conjugation reaction of MH was demonstrated in vitro for the first time. In addition, up to 18 % of the applied maleic hydrazide became associated with nonextractable residues (NER) in soybean, whereas in tobacco only 0.2 % could be detected in this fraction. The residue from soybean cells was solubilized only to a low degree (about 3 %) under simulated stomach conditions, but up to 20 % by the white rot fungus Phanerochaetechrysosporium.

Open access

V. Vassileva, H. Danninger, S. Strobl, Ch. Gierl-Mayer, R. de Oro Calderon and H. Hutter

Abstract

Boron has been known to activate densification during sintering of ferrous powder compacts, though with risk of embrittlement. In the present study, specimens Fe-B and Fe-C-B prepared from standard atomized iron powder with addition of ferroboron Fe-21%B were sintered in different atmospheres, and the resulting microstructures and properties were studied. It showed that the activating effect of boron is observed during sintering in argon and in hydrogen while sintering in N2 containing atmospheres results in rapid deactivation of boron, through formation of stable BN. In hydrogen atmosphere, surface deboronizing was observed to considerable depth. Ar is chemically inert, but Ar trapped inside closed pores tends to inhibit further densification. The impact energy data indicated that the embrittling effect of boron is enhanced significantly by presence of carbon. In the fracture surfaces, transgranular cleavage fracture can be observed both at very low and high impact energy values.

Open access

Mihaela Opris, Anca Sglimbea, Anca Maier, A. Bardas, Voichita Sirbu and H. Suciu

Abstract

Constrictive pericarditis is an uncommon condition, often of unknown etiology. The diagnosis of constrictive pericarditis can be difficult and is often delayed, because the signs and symptoms of this disease can be falsely attributed to other causes. We report the case of a 62-year-old woman presented with a one year history of progressively worsening dyspnea, peripheral oedema, prominent jugular distension, hepatomegaly, ascites. The patient is known with a history of effusive pericarditis. Blood test showed a normal white cell count, anaemia, raised CRP. Chest X-Ray shows a normal sized heart and without calcification of the pericardium. The echocardiographic exam showed septal bounce-abrupt transient rightward movement, left, right ventricular size decreased-heart tubularin shape, mild atrial enlargement, IVC plethoric and unresponsive to respiration, hepatic veins dilated. Doppler echocardiographic findings were consistent with constrictive pericarditis. Cardiac catheterization showed elevation and equalization of diastolic filling pressures, and dips and plateau configuration of ventricular pressure during diastole (square root sign). Based on these results pericardiectomy was necessary. Constrictive pericarditis was also confirmed at the time of surgery. The pericardium was found with thickening of up to 30 mm in some areas. Histopathological exam showed fibrosis and calcification within the pericardium with no evidence of malignancy or tuberculosis. The patient was discharged 10 days later. At 3 months she had no significant symptoms. Diagnosis of constrictive pericarditis remains challenging. Constrictive pericarditis should be suspected in patients with clinical features of right-sides heart failure. Echocardiography and cardiac catheterisation are important investigation in diagnosis of constrictive pericarditis and avoiding unnecessary treatments.

Open access

Heike Faßbender and Julius Mayer

Abstract

The fully adaptive rational global Arnoldi method (AIRGA) for the modelorder reduction of second-order multi-input multi-output systems with proportional damping is revisited. The method automatically generates a reduced system approximating the transfer function. It is based on a moment-matching approach. The expansion points are determined iteratively. The reduced order and the number of moments matched per expansion point are determined adaptively using a heuristic based on an error estimation. A revised moment error expression is presented as well as some related findings.

Open access

B. Üregen, C. Gierl-Mayer and H. Danninger

Abstract

Phosphorus as an alloy element is quite common in powder metallurgy, the contents industrially used being markedly higher than those present in wrought steels. In this study, the influence of phosphorus addition through different P carriers was investigated. PM steels of the type Fe-0.7%C-x%P (x = 0.0 … 0.8%) were manufactured by pressing and sintering in H2. It showed that Fe3P is the best phosphorus carrier, resulting in fine and regular microstructure and in high impact energy data at 0.3 … 0.45%P while red P and also Fe2P showed a tendency to agglomeration, with resulting secondary porosity. At high P levels the mechanical properties tend to drop, for the tensile strength at P > 0.60%P while for the impact energy the threshold is 0.45%P. The dimensional behaviour of Fe-C-P can be related to PM aluminium alloys, expansion by transient liquid phase being followed by shrinkage by persistent liquid phase, at least at higher temperatures. In contrast to the dimensional behaviour, degassing and reduction is hardly affected by the phosphorus content.

Open access

H. May, R. Palka, P. Paplicki, S. Szkolny and W.-R. Canders

Modified concept of permanent magnet excited synchronous machines with improved high-speed features

Permanent magnet (PM) excited synchronous machines used in modern drives for electro-mobiles suffer in high speed regions from the limited battery-voltage. The field weakening requires designing machines with reduced power conversion properties or increasing the size of the power converter. A new concept of such a machine features PM excitation, single-tooth winding and an additional circumferential excitation coil fixed on the stator in the axial center of the machine. By the appropriate feeding of this coil, the amplitude of the voltage effective excitation field can be varied from zero to values above those of the conventional PM-machines. The capability of reducing the excitation field to zero is an important safety aspect in case of failing of the feeding convertor.

Open access

IA Nechifor-Boila, H Suciu, Loghin Andrada, Borda Angela, A Maier, Martha Orsolya and C Chibelean

Abstract

Surgery for renal cell carcinomas with tumor thrombus extending in the Inferior Vena Cava (IVC) can be particularly challenging, especially in the retrohepatic and intraatrial situations (T3b and T3c). Classically, these tumors require the intraoperative use of cardio-pulmonary by-pass (CPB) and deep hypothermic circulatory arrest (DHCA), that can result in specific complications (stroke, platelet dysfunction), with increased postoperative morbidity rates.

In urological practice, a particular IVC preparation method is currently in use, allowing full control both upon the IVC and its tributaries. It is derived from the “piggy-back” liver transplantation technique and implies the resection of all hepatic ligaments, leaving the hepatic vascular connections intact. This procedure is joined by a form of veno-venous bypass (between the right atrium and the infrarenal IVC) that allows a constant central venous pressure (by assuring blood return), with less bleeding and without the need for CPB and DHCA (avoiding, in this way, their inherent complications). All in all, these recently-introduced procedures can offer better thrombus control, improved oncologic outcomes and smaller complication rates. We aim to present a case of borderline T3b/T3c renal tumor that was successfully treated in our university center using these techniques.

Open access

Stela Mariana Al Hussein, F. Buicu, Dalila Maier, H. Al Hussein, Adriana Ciurba, Hamida Al Hussein and Maria Titica Dogaru

Abstract

Objectives: The aim of this study was to compare the efficacy and tolerability of 20% trichloroacetic acid (TCA) peel with 15% azelaic acid gel, a standard antiacne topical treatment.

Materials and methods: 51 patients aged between 16-40 years, with mild and moderate acne, were randomized into two groups. Before the treatment were investigated the patients clinical features and hygienic habits, the previous antiacne treatments and feed-back to them. No cases under treatment with contraceptive pills or antiacne medication that could interfere with the results, were included. For a period of eight weeks, 27 patients (group A) were treated with 15% azelaic acid gel, twice daily, and 24 patients (group B) underwent four sessions of 20% TCA peels, at 14 days interval. The efficacy was evaluated by acne lesions counting, at baseline and at 8 weeks. Adverse effects incidence (erythema, local skin irritation), as well as the satisfaction degree of patients, were investigated.

Results: Was observed a mean reduction in the number of acne lesions of 32,36% for the group A and 69,36% for the group B. There was no statistically significant difference between the average number of acne lesions before treatment between the two groups. The mean number of acne lesions after the treatment was significantly different (p<0,0001), 20% TCA peels showed superior results than 15% azelaic acid gel. Additionally, 96% of patients who underwent TCA peels were very satisfied with the results obtained.

Conclusions: TCA peel is an efficient and well tolerated method for the treatment of acne vulgaris.