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S Scheidl

Publications and source records attributed to S Scheidl.

11 recordsLinked to original sources
PubMed2006

Spin-wave dispersion in orbitally ordered La1/2Sr3/2MnO4.

The magnon dispersion in the charge, orbital, and spin ordered phase in La1/2Sr3/2MnO4 has been studied by means of inelastic neutron scattering. We find excellent agreement with a magnetic interaction model based on the CE-type superstructure. The magnetic excitations are dominated by ferromagnetic exchange parameters revealing a nearly one-dimensional character at high energies. The strong ferromagnetic interaction in the charge or orbital ordered phase appears to be essential for the capability of manganites to switch between metallic and insulating phases.

Journal Article↗
PubMed2005

Rectification in Luttinger liquids.

We investigate the rectification of an ac bias in Luttinger liquids in the presence of an asymmetric potential (the ratchet effect). We show that a strong repulsive electron interaction enhances the ratchet current in comparison with Fermi-liquid systems, and the dc I-V curve is strongly asymmetric in the low-voltage regime even for a weak asymmetric potential. At higher voltages the ratchet current exhibits an oscillatory voltage dependence.

Journal Article↗
PubMed2001

Sufentanil potentiates the inhibitory effect of epinephrine on intestinal motility.

OBJECTIVE: The aim of our study was to evaluate the effect of the combination of different catecholamines and sufentanil on peristalsis of the isolated guinea pig small bowel in vitro. DESIGN: In vitro study on excised guinea pig small-bowel segments (8-10 segments per substance tested). SETTING: Laboratory for experimental studies at the University. SUBJECTS: Isolated guinea pig small-bowel segments. INTERVENTIONS: Excised segments of guinea pig small bowel were mounted in a tissue bath (37 degrees C) in Tyrode's solution and bubbled with carbogen (95% O2/5% CO2). The lumina were perfused with Tyrode's solution at 0.5 ml/min. The test drugs (epinephrine, norepinephrine, dobutamine, sufentanil, and a combination of these catecholamines with sufentanil) were added to the tissue bath and peristalsis recorded via changes in the intraluminal pressure. One-way and two-way ANOVA were used for statistical analysis. MEASUREMENTS AND RESULTS: All the tested substances, both individually and in combination, inhibited intestinal peristalsis in a dose-dependent manner. High doses resulted in a complete blockade of peristalsis. Preexposure of the segments to sufentanil at 0.1 nM barely influenced the effects of the catecholamines on peristalsis. However, sufentanil at 0.3 nM enhanced the antiperistaltic activity of epinephrine in a supraadditive manner, whereas the effect on norepinephrine and dobutamine was less pronounced. CONCLUSIONS: Our experimental data suggest that the combination of epinephrine and sufentanil might be the worst choice for the intensive care setting. This is due to its pronounced inhibitory effect on peristalsis in vitro at moderate and higher concentrations.

Adrenergic Agents↗
PubMed2000

Low potential of dobutamine and dopexamine to block intestinal peristalsis as compared with other catecholamines.

OBJECTIVE: Catecholamines are frequently used in critically ill patients to restore stable hemodynamics and to improve organ perfusion. One effect of short-term or long-term administration of catecholamines may be inhibition of propulsive motility in the intestine. We therefore analyzed the effect of dopexamine, dobutamine, and dopamine on ileal peristalsis and compared their action with that of epinephrine and norepinephrine, which have long been known to suppress intestinal peristalsis. DESIGN: In vitro study on excised guinea pig ileum segments. SETTING: Laboratory for experimental studies at the University. SUBJECTS: Isolated guinea pig ileum. INTERVENTIONS: Segments of ileum excised from guinea pigs were mounted in a tissue bath in Krebs-Henseleit solution and bubbled with 95% oxygen/5% CO2. Luminal perfusion with the same solution was performed at a rate of 0.35 mL/min. The bath temperature was kept at 36.5 degrees C. Peristalsis was recorded via changes in the intraluminal pressure. The drugs under investigation (dopamine, epinephrine, norepinephrine, dobutamine, and dopexamine) were added to the tissue bath. MEASUREMENTS AND MAIN RESULTS: Low concentrations of each catecholamine, except epinephrine, caused a decrease in the pressure threshold, which reflects a stimulatory effect on peristalsis. Higher catecholamine concentrations caused a concentration-related increase in the threshold, cumulating in a complete block of peristalsis. The rank order of inhibitory potency was epinephrine > norepinephrine > dopamine > dobutamine approximately dopexamine. Dobutamine and dopexamine were about 500-fold less active than epinephrine in suppressing peristalsis. CONCLUSIONS: This study shows that dobutamine and dopexamine have the least potential to block propulsive motility in the intestine, whereas epinephrine demonstrates the most adverse inhibitory effect. Because at low concentrations dobutamine and dopexamine even stimulate peristalsis, these drugs appear to be superior compared with other catecholamines with regard to their direct effects on intestinal motility.

Adrenergic beta-Agonists↗