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J Stelzer

Publications and source records attributed to J Stelzer.

7 recordsLinked to original sources
PubMed2001

Motion, creation, and annihilation of disclinations in multidomain structured nematic liquid crystal cells.

We study dynamical processes in a multidomain (MD) structured nematic liquid crystal cell with a particular emphasis on the motion, creation, and annihilation of disclinations. In the MD cell right- and left-handed director helices alternate due to a special choice of the director pretilt angles at the surfaces. As a result, a net of twist disclinations occurs. We have implemented a numerical algorithm based on a pure rotational dynamics of the director field to monitor the motion of the defect lines during the switching process, i.e., when an electric voltage is applied to or removed from the cell. We demonstrate that the total light transmission vs time is not affected by the presence of the defects compared to a conventional twisted nematic cell. If the pretilt angles at the surfaces are sufficiently small, the twisting sense of one species of helices is reversed and a configuration free of defects occurs. On the other hand, for an applied voltage twist disclinations close to the surface have to exist. Therefore, defect lines are created or they annihilate during the switching process. We investigate these situations in detail and reveal the underlying mechanisms.

Journal Article↗
PubMed2001

Numerical study of surface-induced reorientation and smectic layering in a nematic liquid crystal.

Surface-induced profiles of both nematic and smectic order parameters in a nematic liquid crystal, ranging from an orienting substrate to "infinity," were evaluated numerically on the basis of an extended Landau theory. In order to obtain a smooth behavior of the solutions at "infinity," a boundary energy functional was derived by linearizing the Landau energy around its equilibrium solutions. We find that the intrinsic wave number of the smectic structure, which plays the role of a coupling between nematic and smectic order, strongly influences the director reorientation. Whereas the smectic order is rapidly decaying when moving away from the surface, the uniaxial nematic order parameter shows an oscillatory behavior close to the substrate, accompanied by a nonzero local biaxiality.

Journal Article↗
PubMed1995

Problem solving, stress, and coping in adolescent suicide attempts.

Twenty adolescents who had made suicide attempts were compared with 20 nonpsychiatric control subjects on measures of problem solving, stress, and coping. The suicidal group did not show evidence of "rigid" thinking or of deficits in the ability to generate solutions to standardized interpersonal problems. However, they did report recent histories of more severe life stress and had inaccurate appraisal of the extent to which stressful events could be controlled. Although suicidal patients were able to generate as many adaptive strategies as control subjects for coping with their own most severe recent real-life stressor, they actually used fewer. They were also more likely to identify maladaptive behaviors as ways of coping. These findings support a transactional model of adolescent suicidal behavior, whereby inaccuracies in the appraisal aspects of problem solving (but not in the solution-generation aspects) in the face of high life stress lead to a reduction in the use of adaptive efforts to cope.

Adaptation, Psychological↗
PubMed1988

[Autologous retransfusion of washed erythrocytes in transurethral resection of prostatic adenomas. Preliminary report].

Red blood cells were concentrated from the irrigation fluid used during prostatic resection in 30 patients by means of a cell saver system. The resulting units of packed red cells were analysed for quality and possible contamination. Average blood loss during the procedure was 645 ml, and an average of 580 ml of packed red cells was harvested and retransfused in 25 patients. Retransfusion was well tolerated and no adverse reactions were seen. Our positive clinical experience with the method and the ease of application suggest that it can probably be recommended as a routine procedure during transurethral resection of the prostate.

Aged↗