Characterization of solar cells by photocurrent spectroscopy and current-voltage characteristics with high spatial resolution.

Spatially resolved photocurrent-spectroscopy and spatially resolved current-voltage characteristics are introduced as new methods to characterize solar cells. A combination of these two methods is shown to localize and characterize deficiencies and structural damages in processed solar cells with high spatial resolution. The local external and internal quantum efficiencies as well as the local characteristic parameters of the p-n junction like the short circuit current, the saturation current, the ideality factor, and the optically induced shunt resistance can be determined quantitatively. Both, a slab of a damaged and an undamaged (GaIn)(NAs) concentrator solar cell, are used as test structures. Upon these test structures domains with a high concentration of impurities in the crystal structure and structural imperfections in the upper contact region are identified and analyzed. Additional numerical simulations prove the reliability and show limits of the methods.

Chlorophyll b is involved in long-wavelength spectral properties of light-harvesting complexes LHC I and LHC II.

Chlorophyll (Chl) molecules attached to plant light-harvesting complexes (LHC) differ in their spectral behavior. While most Chl a and Chl b molecules give rise to absorption bands between 645 nm and 670 nm, some special Chls absorb at wavelengths longer than 700 nm. Among the Chl a/b-antennae of higher plants these are found exclusively in LHC I. In order to assign this special spectral property to one chlorophyll species we reconstituted LHC of both photosystem I (Lhca4) and photosystem II (Lhcb1) with carotenoids and only Chl a or Chl b and analyzed the effect on pigment binding, absorption and fluorescence properties. In both LHCs the Chl-binding sites of the omitted Chl species were occupied by the other species resulting in a constant total number of Chls in these complexes. 77-K spectroscopic measurements demonstrated that omission of Chl b in refolded Lhca4 resulted in a loss of long-wavelength absorption and 730-nm fluorescence emission. In Lhcb1 with only Chl b long-wavelength emission was preserved. These results clearly demonstrate the involvement of Chl b in establishing long-wavelength properties.

Segmental distribution of afferent fibres in the left inferior cardiac nerve of the cat studied by anterograde transport of horseradish peroxidase.

The segmental projection of afferent fibres in the left inferior cardiac nerve of the cat was studied by using the anterograde transport of horseradish peroxidase (HRP). HRP-positive cell bodies were detected in ipsilateral dorsal root ganglia from segments T1 to T7. No labelled neurones were found at segments C8 and T8. The total number of labelled neurones ranged from 157 to 535 neurones in individual experiments. The majority of neurones (70-88%) were localized in the dorsal root ganglia of segments T2-T4. Labelled neurones were oval shaped, and most neurones had a long axis in the range from 20 to 40 microns.

Measurements of cytochrome f and P-700 in intact leaves of Sinapis alba grown under high-light and low-light conditions.

The oxidation and reduction of cytochrome f and P-700 is measured spectrophotometrically in leaves of low-light and high-light plants. After illumination with red light, an induction phenomenon for cytochrome f oxidation is observed which indicates a regulation of photosystem I activity through energy distribution between the pigment systems by the energy state of the membrane. After far-red excitation the reduction of cytochrome f in the dark is much slower in low-light leaves. This shows that cyclic electron transport is not improved in low-light plants under these conditions. P-700 is oxidized on excitation with far-red light. However, with high intensities of far-red light, P-700 is partially reduced again which is due to a low extent of photosystem II excitation with the far-red used in the experiments. The low-light leaves show greater sensitivity of photosystem II to this excitation. The initial rate of the cytochrome f oxidation-rate is the same in low-light and high-light leaves. This shows that several P-700 are connected with only one electron transport chain. The consequences of these results concerning the tripartite concept and the photosynthetic unit are discussed. In the high-light plants the experimental data can be well explained by the tripartite organization of the photosynthetic unit. In low-light plants, however, a multipartite organization has to be postulated. In the partition regions of the grana, several antennae systems I, antennae systems II, and light-harvesting complexes can communicate with one electron transport chain.

The intensification of absorbance changes in leaves by light-dispersion : Differences between high-light and low-light leaves.

In dispersive samples, like leaves, the absorbance of pigments is intensified. The intensification is due to a longer optical path through the dispersive sample. However, in chloroplast suspensions the optical path is not much longer than in clear solutions. The factor of intensification ß (=the lengthening of the optical path) is calculated by comparing the absorbance of leaves and the absorbance of chloroplast suspensions with equal pigment-content. This method also includes the influence of possible sieve effects which could decrease absorbance. The measurements are carried out with high- and low-light leaves of different thickness and pigment content. The intensification of absorbance was 2-2.5 fold. In highlight leaves it was somewhat less than in low-light leaves. The factor ß is better correlated to the pigment content than to the thickness of the leaves. The plot of absorbance versus the pigment content of the leaves shows that ß decreases with increasing pigment content. In contrast, chloroplast suspensions show a linear dependence as expected from Lambert-Beer's law. Thus, in leaves with very low pigment content the absorbance is intensified up to 6 fold while the intensification decreases with increasing absorbance. These results are in good agreement with measurements of Tsel'niker (1975) and with the theoretical predictions of Butler's formula (1960). Absorbance changes due to photooxidation of P-700 and cytochrome f in intact leaves are measured, and ß is used to calculate the amount of the oxidized components. Without correction for ß the values would be much greater than the amount actually present. The corrected data show that between 70 and 90% of the present P-700 and cytochrome f can be photooxidized in the intact leaf.

[Fetal heart rate and Doppler flow parameters in fetal blood vessels--evaluation of 2,517 individual signals]. / Fetale Herzfrequenz und Doppler-Flow-Parameter in fetalen Gefässen--Auswertung von 2517 Einzelsignalen.

Analysis of more than 2500 doppler flow signals in three patients was performed to evaluate the influence of fetal heart rate (fhr) variation on S/D-ratio in fetal vessels. Little differences of S/D-ratio in fetal vessels (descending aorta, umbilical arteries) were detected within the physiological variations of fhr (120-160 bpm) (envelope of regression line -0.007, -0.006). Analysing inter- as well as intraindividual variation only minor effects of fhr alteration can be observed in clinical application of doppler flow velocimetry. Dopplersonographic measurements, however, should be performed for at least a three minute period (for each vessel) to avoid false-positive or false-negative interpretation of short term changes of doppler signals. This is especially important in distressed fetuses.

Cyclic and noncyclic photophosphorylation during the ontogenesis of high-light and low-light leaves of Sinapis alba.

Noncyclic electron transport to ferricyanide and photophosphorylation as well as the methylviologen mediated aerobic and anaerobic photophosphorylation with dichlorophenolindophenol-ascorbate as the electron donor of photosystem I were measured during the development of high-light and low-light adapted leaves of Sinapis alba. Anaerobic methylviologen-catalyzed phosphorylation is more than twice as high as aerobic phosphorylation. The difference between the rates of aerobic and anaerobic phosphorylation is sensitive to dibromothymoquinone. Thus, under anaerobic conditions, methylviologen mediates a cyclic phosphorylation including plastoquinone. All photochemical activities of high-light chloroplasts are about twice as high as that of low-light chloroplasts and show a permanent decline with increasing plant age. The lower activities of low-light chloroplasts correlate with a decrease of electron transport components, such as cytochrome f. This indicates that the number of electron transport chains is decreased under low-light conditions and more chlorophyll molecules interact with one electrontransport chain.

Measurements of manganese in thylakoids of Sinapis alba grown under high-light and low-light conditions.

The manganese content of thylakoids and tissues was measured in leaves grown under high- and low-light conditions. Especially when grown in a nutrient medium enriched in manganese (20 µM), the thylakoids contained large amounts of manganese, which could be removed by EDTA washing without impairment of the Hill reaction. The unremovable content of manganese was almost the same in thylakoids from plants grown in nutrient media of normal (2 µM) and reduced (0.2 µM) manganese content. Up to this limit of manganese content, Hill activity did not seem to be impaired. 1.2 atoms Mn per 100 molecules chlorophyll were found in low-light thylakoids and 1.6 atoms Mn in high-light thylakoids. This is similar to the behaviour of other electron transport components, the number of which is also decreased under low-light conditions. However, the decrease in the manganese content is not as striking as the decrease in, for example, the cytochrome f and ferredoxin content. This may be attributed to an invariable pool of manganese which is not involved in the oxygen evolving system. Alternatively, if all of our measured manganese is involved in electron transport to PS II, this could indicate that in low-light chloroplasts the ratio of PS II/PS I components may be somewhat increased.

Studies on the mechanism of photosystem II photoinhibition I. A two-step degradation of D1-protein.

The role of D1-protein in photoinhibition was examined. Photoinhibition of spinach thylakoids at 20°C caused considerable degradation of D1-protein and a parallel loss of variable fluorescence, QB-independent electron flow and QB-dependent electron flow. The breakdown of D1-protein as well as the loss of variable fluorescence and QB-independent electron flow were largely prevented when thylakoids were photoinhibited at 0°C. The QB-dependent electron flow markedly decreased under the same conditions. This inactivation may represent the primary event in photoinhibition and could be the result of some modification at the QB-site of D1-protein. Evidence for this comes from fluorescence relaxation kinetics following photoinhibition at 0°C which indicate a partial inactivation of QA (-)-reoxidation. These results support the idea of D1-protein breakdown during photoinhibition as a two step process consisting of an initial inactivation at the QB-site of the protein followed by its degradation. The latter is accompanied by the loss of PS II-reaction centre function.

Studies on the mechanism of photosystem II photoinhibition II. The involvement of toxic oxygen species.

In a previous paper it was shown that photoinhibition of reaction centre II of spinach thylakoids was predominantly caused by the degradation of D1-protein. An initial inactivation step at the QB-site was distinguished from its breakdown. The present paper deals with the question as to whether this loss of QB-function is caused by oxygen radical attack. For this purpose the photoinhibition of thylakoids was induced at 20°C in the presence of either superoxide dismutase and catalase or the antioxidants glutathione and ascorbic acid. This resulted in comparable though not total protection of D1-protein, photochemistry and fluorescence from photoinhibition. The combined action of both the enzymatic and the non-enzymatic radical scavenging systems brought about an even more pronounced protective effect against photoinhibition than did either of the two systems singularly at saturating concentrations. The results signify a major contribution of activated oxygen species to the degradation process of D1-protein and the related phenomena of photoinhibition. Thylakoids treated with hydroxyl radicals generated through a Fenton reaction showed a loss of atrazine binding sites, electron transport capacity and variable fluorescence in a similar manner, though not to the same extent, as usually observed following photoinhibitory treatment.

Regulation of the photosynthetic electron transport during dark-light transitions by activation of the ferredoxin-NADP(+)-oxidoreductase in higher plants.

Absorbance changes associated with the oxidation and reduction of cytochrome f belong to the classical observations about the interaction of the two photosystems. A complex induction pattern of cytochrome f oxidation results, if both photosystems are excited simultaneously. This indicates a light-modulated regulation of the photosynthetic electron transport, which we examined for intact biological systems of decreasing complexity. The ferredoxin-NADP(+)-oxidoreductase (FNR) is suggested to be activated by light and inactivated in the dark. This is pointed out by the kinetics of variable fluorescence and by the influence of different artificial electron acceptors on the cytochrome f kinetics. The photoreduction of NADP(+) by carefully prepared thylakoids demonstrates the activation process directly.

Structure and function of ferredoxin-NADP(+)-oxidoreductase.

The redox-enzyme ferredoxin-NADP-oxidoreductase has been shown to be activated by light and inactivated in the dark. This review will summarize recent data concerning the biochemical characterization of the enzyme compared to its in-vivo activation. Further-more the mechanism of this activation process is discussed as a conformational change caused by the light-driven proton gradient.

[Doppler ultrasound in obstetrics--contribution to understanding reverse flow in the umbilical artery]. / Dopplersonographie in der Geburtshilfe--Beitrag zum Verständnis des "Reverse Flow" in der Arteria umbilicalis.

"Reverse Flow" as a Doppler sonographic finding indicates the appearance of retrograde blood flow in the diastolic part of the cardiac cycle. It has so far not been observed in uncomplicated pregnancies and seems to be an indicator of severe deterioration of the foetal condition. Several pathophysiological hypotheses are discussed in this paper on the basis of own results and the findings of other investigators.

[Doppler flow studies (duplex sonography). Differential diagnostic assessment of intrauterine growth retardation and uncertain gestational age]. / Doppler-Flow-Untersuchungen (Duplex-Sonographie). Differentialdiagnostische Abklärung intrauterine Wachstumsretardierung und unsicheres Schwangerschaftsalter.

In 116 patients referred to Heidelberg University Gynecological Clinic because of a discrepancy between calculated and biologically determined gestational age, the suitability of the Doppler Flow examination method (duplex method) for resolving this question was studied. The signals from the fetal descending aorta, the umbilical artery, and from maternal placental vessels were used. An A/B ratio of over 7 in the fetal aorta, an A/B ratio of over 4 in the umbilical artery, and detection of an early diastolic incisure in the so-called arcuate arteries were considered pathologic. The relatively high accuracy of this examination method is expressed by its sensitivity (91%) and likewise high specificity (86%) for this diagnostic question. In view of the predictive value of 88% thus determined, reliable differential diagnostic distinction between intrauterine growth retardation and uncertainty regarding term appears possible. Doppler sonographic examination can be performed without causing any serious discomfort to the patient and within a short period of time. While the number of false-positive results in this study was in any case relatively low (11%), an in-depth analysis showed that an "acute placental insufficiency" had occurred in the peripartum in more than one-half of the cases.

[Reliability of duplex sonography in non-quantitative determination of blood flow in comparison to inductive flow measurement--an in vitro study]. / Verlässlichkeit der Duplex-Sonographie zur nichtquantitativen Messung des Durchflusses im Vergleich zur induktiven Flussmessung--eine in-vitro-Studie.

Using an experimental design permitting generation of a pulsatile "flow-velocity waveform" corresponding to the fetal aortic signal, the influence of measurement depth, the angle between the Doppler beam and the vessel, the high-pass filter and the extent of overlap between the "sample volume" and the vessel cross-section were studied in vitro. The Resistance Index showed the best relation to inductive flow measurement, which was defined as standard. Considering the conditions prevailing during clinical studies, good reliability is likely at angles of between 0 degrees and 60 degrees (120 degrees-180 degrees) over the entire range of measuring depths (4-13 cm) and when using 100-200 Hz high-pass filters. The magnitude and location of the sample volume does not seem to play a decisive role provided a part of it is within the sonographically imaged "vessel" and there is no likelihood of interference from vessels in the immediate vicinity in which blood flow is in the same direction.

Chlorophyll-protein-complexes of thylakoids of wild type and chlorophyll b mutants of Arabidopsis thaliana.

Pigment-protein-complexes of two chlorophyll b deficient mutants of Arabidopsis and from the wild type were separated electrophoretically. Light-harvesting proteins were absent in the chlorophyll b free mutant ch(1) and their amount was reduced in the mutant ch(2) which has a reduced content of chlorophyll b. The ratio of CPa:CP I increased with decreasing chlorophyll b content which indicated that the stoichiometry of photosystem II to photosystem I is not constant.

Chlorophyll-protein-complexes of thylakoids of wild type and chlorophyll b mutants of Arabidopsis thaliana.

Pigment-protein-complexes of two chlorophyll b deficient mutants of Arabidopsis and from the wild type were separated electrophoretically. Light-harvesting proteins were absent in the chlorophyll b free mutant ch(1) and their amount was reduced in the mutant ch(2) which has a reduced content of chlorophyll b. The ratio of CPa:CP I increased with decreasing chlorophyll b content which indicated that the stoichiometry of photosystem II to photosystem I is not constant.

[Doppler ultrasound of fetal blood vessels--optimizing the diagnostic value by a combined diagram]. / Doppler-Sonographie der fetalen Gefässe--Optimierung der Aussagekraft durch ein Kombinationsdiagramm.

The dopplersonographic data of 1926 pregnant women in the 3. trimester of pregnancy was used to evaluate a graphic system for the analysis of A/B-ratio in fetal vessels (pulsed wave duplex system; descending aorta and umbilical arteries). The basis of the newly developed combination diagram were dopplersonographic standard values (single cut off and pregnancy duration related percentiles). One of the results was the fact, that the combined measurement and analysis of both fetal vessels increased the positive predictive value compared to single measurements. The value of dopplersonographic examinations in the aorta was slightly better than those in the umbilical arteries. The combined diagram showed a marked improvement in graphicness, especially in follow-up cases, and a partial improvement in statistical values.

[Evaluation of the antepartum CTG course in cases of highly pathologic Doppler flow findings]. / Auswertung des antepartalen CTG-Verlaufs in Fällen mit hochpathologischen Doppler-Flow-Befunden.

In a group of 79 pregnancies with highly abnormal Doppler-flow findings in foetal vessels the value of antepartal CTG criteria was evaluated in detail. In cases with absent enddiastolic flow (AEDF) the prognostical value was not further increased by antepartal pathological CTG findings. In cases with permanently normal antepartal CTG's, however, foetal outcome was fairly good (median duration of pregnancy 38 + 6 weeks, median foetal birth weight 2,545 grams, arterial pH < 7.20 in 9%). This was true also in the presence of pathological Doppler-flow findings except AEDF. In cases with pathological antepartal CTG findings in the antepartal course of pregnancy the loss of acceleration was most frequent (82%), followed by decreased frequency (53%) or narrowed amplitude (38%) of the foetal heart rate variation. Combination of both methods (Doppler sonography and CTG) is recommended clinically because the rate of uncertain findings can be reduced. Especially in cases with AEDF an active management would be justified before CTG's become pathological.