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U Rabe

Publications and source records attributed to U Rabe.

8 recordsLinked to original sources
PubMed2002

Evaluation of the contact resonance frequencies in atomic force microscopy as a method for surface characterisation (invited).

The combination of ultrasound with atomic force microscopy (AFM) opens the high lateral resolution of scanning probe techniques in the nanometer range to ultrasonics. One possible method is to observe the resonance frequencies of the AFM sensors under different tip-sample interaction conditions. AFM sensors can be regarded as small flexible beams. Their lowest flexural and torsional resonance frequencies are usually found to be in a range between several kHz and several MHz depending on their exact geometrical shape. When the sensor tip is in a repulsive elastic contact with a sample surface, the local indentation modulus can be determined by the contact resonance technique. Contact resonances in the ultrasonic frequency range can also be used to improve the image contrast in other dynamic techniques as, for example, in the so-called piezo-mode. Here, an alternating electric field is applied between a conducting cantilever and a piezoelectric sample. Via the inverse piezoelectric effect, the sample surface is set into vibration. This excitation is localised around the contact area formed by the sensor tip and the sample surface. We show applications of the contact resonance technique to piezoelectric ceramics.

Journal Article↗
PubMed2001

Flow cytometric analysis of mitogen-induced activation of rainbow trout (Oncorhynchus mykiss) peripheral blood leucocytes.

Proliferation of rainbow trout peripheral blood leucocytes in vitro is usually assessed by measuring incorporated tritiated thymidine. In this report we monitored the in vitro proliferative response to the mitogen Concanavalin A (Con A) by means of flow cytometry (FCM) and 3H-thymidine incorporation. When analysed by FCM, blood leucocytes displayed two main cell populations with distinct forward and side scatter (FSC/SSC) characteristics: lymphocytes with low FSC/SSC values and non-lymphoid leucocytes (NLL) with increased FSC/SSC values. The nature of these cell types were confirmed by microscopy. Interestingly, the FSC/SSC pattern of lymphocytes remained unchanged after in vitro stimulation with Con A, whereas cells from the NLL population showed a marked shift towards increased FSC values. In stimulated cultures, the increase of FSC values of the NLL population significantly correlated with contemporarily measured 3H-thymidine incorporation (r = 0.7, P < 0.001). The mitogenic response of blood leucocytes originating from different individual fish varied over wide ranges. It was found to be related to the numbers of NLL present in the leucocyte sample. The present results show that qualitative and quantitative FCM analysis of morphological parameters (FSC/SSC) of blood leucocytes makes it possible to discriminate between leucocyte populations of the rainbow trout and to monitor cell proliferation experiments.

Animals↗
PubMed2000

Quantitative determination of contact stiffness using atomic force acoustic microscopy

Atomic force acoustic microscopy is a near-field technique which combines the ability of ultrasonics to image elastic properties with the high lateral resolution of scanning probe microscopes. We present a technique to measure the contact stiffness and the Young's modulus of sample surfaces quantitatively, with a resolution of approximately 20 nm, exploiting the contact resonance frequencies of standard cantilevers used in atomic force microscopy. The Young's modulus of nanocrystalline ferrite films has been measured as a function of oxidation temperature. Furthermore, images showing the domain structure of piezoelectric lead zirconate titanate ceramics have been taken.

Journal Article↗
PubMed1989

[Clinical studies of the effect of physical training therapy on oxygen absorption and pulmonary artery pressure in persons with chronic obstructive lung diseases].

Twenty patients with chronic obstructive bronchitis were submitted to a 6-week rehabilitation program including bicycle training, breathing exercise, inhalation, massage, short wave therapy and others. Before and after 6-week training we investigated ventilatory and blood gas parameters and pulmonary artery pressure at rest and during exercise. There was no change in the oxygen uptake on the same exercise stage. We found an insignificant decrease of the pulmonary artery pressure at rest and during exercise. The physical training has no negative influence on the behaviour of pulmonary pressure. We stated a good effect of physical conditioning on the systemic circulation. The working capacity of all patients improved at the end of the training period.

Adult↗
PubMed1984

Evaluation of alpha-tocopherol antioxidant activity in microsomal lipid peroxidation as detected by low-level chemiluminescence.

The significance of microsomal vitamin E in protecting against the free-radical process of lipid peroxidation was evaluated with the low-level-chemiluminescence technique in microsomal fractions from vitamin E-deficient and control rats. The induction period that normally precedes the ascorbate/ADP/Fe3+-induced lipid peroxidation was taken as reflecting the microsomal vitamin E content and was found to be 5-6-fold decreased in microsomal fractions from vitamin E-deficient rats. Supplementation of microsomal fractions from vitamin E-deficient rats with exogenous vitamin E partially restores the induction period observed in that from control rats. The decrease in chemiluminescence intensity and the increase in the induction period both correlate linearly with the amount of vitamin E added. However, the efficiency of exogenous vitamin E is about 50-fold lower than that exerted by the naturally occurring vitamin E in microsomal membranes. These observations are discussed in terms of the process of re-incorporation of vitamin E into membranes, the experimental model for lipid peroxidation selected, and the method to evaluate lipid peroxidation, namely low-level chemiluminescence.

Animals↗
PubMed1981

Peroxisomal fatty acid oxidation as detected by H2O2 production in intact perfused rat liver.

1. H2O2 formation associated with the metabolism of added fatty acids was quantitatively determined in isolated haemoglobin-free perfused rat liver (non-recirculating system) by two different methods. 2. Organ spectrophotometry of catalase Compound I [Sies & Chance (1970) FEBS Lett. 11, 172-176] was used to detect H2O2 formation (a) by steady-state titration with added hydrogen donor, methanol or (b) by comparison of fatty-acid responses with those of the calibration compound, urate. 3. In the use of the peroxidatic reaction of catalase, [14C]methanol was added as hydrogen donor at an optimal concentration of 1 mM in the presence of 0.2 mM-L-methionine, and 14CO2 production rates were determined. 4. Results obtained by the different methods were similar. 5. The yield of H2O2 formation, expressed as the rate of H2O2 formation in relation to the rate of fatty-acid supply, was less than 1.0 in all cases, indicating that, regardless of chain length, less than one acetyl unit was formed per mol of added fatty acid by the peroxisomal system. In particular, the standard substrate used with isolated peroxisomal preparations (C16:0 fatty acid) gave low yield (close to zero). Long-chain monounsaturated fatty acids exhibit a relatively high yield of H2O2 formation. 6. The hypolipidaemic agent bezafibrate led to slightly increased yields for most of the acids tested, but the yield with oleate was decreased to one-half the original yield. 7. It is concluded that in the intact isolated perfused rat liver the assayable capacity for peroxisomal beta-oxidation is used to only a minor degree. However, the observed rates of H2O2 production with fatty acids can account for a considerable share of the endogenous H2O2 production found in the intact animal.

Animals↗