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Biomedical subjects

A Wacker

Publications and source records attributed to A Wacker.

At least 19 recordsLinked to original sources
PubMed2001

Dynamic scenarios of multistable switching in semiconductor superlattices.

We analyze the dynamics of charge distributions in weakly coupled, doped, dc voltage biased semiconductor superlattices subject to voltage steps of different sizes. Qualitatively different current responses to voltage switching processes have been observed experimentally. We explain them by invoking distinct scenarios for electric-field domain formation, validated by numerical simulations. Furthermore, we investigate the transient from an unstable to a stable point in the current-voltage characteristics after a steplike or ramplike increase of the external voltage.

Journal Article↗
PubMed2000

[Assessment of teaching at the faculties of medicine in Germany].

BACKGROUND AND OBJECTIVES: The aim of this study was to gather, against the background of a long-discussed deficit in academic teaching, data on the current activities of medical faculties with regard to teaching, and to analyse these findings. Another aim was to obtain suggestions for establishing a consensus on indicators that could be used to assess the quality of teaching. MATERIAL AND METHODS: In March 2000, a written inquiry was addressed to the deans of all 37 medical faculties in Germany. The questionnaire, arranged so that responses could be entered into a data-base, consisted of ten items in three parts. Part 1 concerned the evaluation of teaching, parts 2 and 3 dealt with the place of specific assessment of teaching in the process of choosing lecturers ("habilitation") and appointing senior professors. In addition to providing alternative answers (in some instances, allowing a choice of several alternatives) there was also space for written comments. The answers were analysed by descriptive statistics. RESULTS: All questionnaires were returned in a usable form (response rate 100%). 36 faculties had, at the time of receiving the questionnaire, already instituted teaching assessments, of clinical teaching sessions more often than preclinical ones (97% vs 89%). The most widespread method of assessment consisted of obtaining students' opinion and of using the centralized written examinations of the institute for Medical and Pharmaceutical Examination Questions. In more than half of the faculties (57%) an above-average teaching performance by teachers was acknowledged in special ways (honours/prizes). In 31 faculties (84%) teaching experience counted as an absolute prerequisite for obtaining a lectureship, but as a rule without employing any defined standards. With regard to the selection of senior professors, 27 faculties (73%) explicitly took teaching competence into account. Defined criteria for assessing teaching ability were largely absent. CONCLUSIONS: The assessment of teaching quality can be considered as well established at medical faculties in Germany. However, the methods and models used are highly heterogeneous. Furthermore, numerous activities exist in the various faculties to increase the importance attached to academic teaching. However, despite using diverse indicators of quality, the central problems for assessing teaching ability remain unsolved.

Faculty, Medical↗
PubMed2000

A randomised controlled trial of delayed cord clamping in very low birth weight preterm infants.

UNLABELLED: This study was carried out to assess the feasibility of late cord clamping of 45 s in preterm infants delivered mainly by caesarean section and the effects on postpartal adaptation and anaemia of prematurity. Prior to delivery, 40 infants of < 33 gestational weeks were randomised to either 20 s or 45 s of late cord clamping. After the first shoulder was delivered, oxytocin was given intravenously to the mother in order to enhance placento-fetal transfusion while the infant was held below the level of the placenta. The 20 infants in group 1 (20 s) had a mean birth weight of 1070 g and a mean gestational age of 29 + 4/7 weeks versus 1190 g and 30 weeks in group 2 (45 s). On day 42 of life there were ten infants without transfusions in group 2 versus three in group 1 (P < 0.05). Out of the 20 infants in group 1, 19 and 15/19 in group 2 were delivered by caesarean section. There were no significant differences in Apgar scores, temperature on admission, heart rate, blood pressure and requirements for artificial ventilation. CONCLUSION: Delayed cord clamping of 45 s is feasible and safe in preterm infants below 33 weeks of gestation. It is possible to perform the procedure at caesarean section deliveries and it should be performed whenever possible. It reduces the need for packed red cell transfusions during the first 6 weeks of life.

Anemia, Neonatal↗
PubMed2000

Wave fronts may move upstream in semiconductor superlattices

In weakly coupled, current biased, doped semiconductor superlattices, domain walls may move upstream against the flow of electrons. For appropriate doping values, a domain wall separating two electric-field domains moves downstream below a first critical current, it remains stationary between this value and a second critical current, and then moves upstream above. These conclusions are reached by using a comparison principle to analyze a discrete drift-diffusion model, and validated by numerical simulations. Possible experimental realizations are suggested.

Journal Article↗
PubMed1998

[75 years after Dandy, Fay and Mixter--looking back on the history of neuroendoscopy].

The first neuroendoscopic operation was done in the year 1910 by the urologically practicing doctor Victor Darwin Lespinasse (1878-1946). Lespinasse never published this procedure. He only reported the case in front of a local surgical society. Several years later (1922/23) the first endoscopic operations in the brain were published by three neurological surgeons within one year (Dandy, Fay and Mixter). This 75 year anniversary is the background for the following historical overview.

Endoscopes↗
PubMed1993

[Prognostic indicators of psychogenic diseases in adulthood based on childhood variables].

Using the data of the Mannheim Cohort Projekt (Schepank, 1987, 1990), the authors investigate possible correlations between psychic symptoms in childhood, risk and protective factors with regard to psychogenic disorders in adulthood. For this, the number of symptoms and the "Impairment-Score" as the degree of psychogenic complaints were related to each other by determining Spearmen's rank correlation coefficient. Additionally, the predictive power of these three variables were investigated by means of discriminance analysis. It could be shown, that the severity of psychogenic illness in adulthood increases with the number of childhood symptoms. There was no evidence for the hypothesis of an increasing predictive power for the assembled variables (number of symptoms, risk factors, and protective factors) in comparison with the single variables. The results found are, however, comparable to the data of two prospective longitudinal studies.

Adaptation, Psychological↗
PubMed1980

Enzymatic hypermethylation of DNA in mouse-mouse somatic cell hybrids.

Somatic cell hybrids between mouse L fibroblasts (A9 cells) and Ehrlich ascites tumour cells were constructed by use of poly(ethyleneglycol). The hybrids were selected in hypoxanthine/aminopterin/thymidine medium and morphologically different syncaryons were isolated by a micromanipulation. They were simultaneously analysed for their tumourogeneity, a release of certain proteins into the culture medium, the activity of pyrimidine salvage pathways, and the extent of enzymatic DNA methylation. None of these hybrids gave a rise of tumours if transplanted into DBA/2 mice. Two of the hybrids released a protein immunologically cross-reacting with antibody against C-peptide of human proinsulin. Activities of pyrimidine salvage pathways as measured by incorporation of [14C]deoxycytidine into DNA cytosine and thymine, respectively, are different in the analyzed cells. Enzymatic DNA methylation in somatic cell hybrids was significantly elevated as compared to the parental cell lines.

Animals↗
PubMed1980

Quantitative determination of small amounts of L-penicillamine in D-penicillamine after desulfurization with Raney nickel.

Commercially available D-penicillamine is desulfurized with Raney nickel at room temperature in aqueous solution. L-Valine derived from contaminating L-penicillamine is determined colorimetrically by the amino acid oxidase/peroxidase reaction, using 2,2'-azino-di-[3-ethyl-benz-thiazoline-sulfonate(6)] (ABTS). The procedure assures the quantitation of L-penicillamine contaminating D-penicillamine down to the level of 0.1%.

Drug Contamination↗