Conductivity and magnetoresistance of La0.7Ce0.3MnO(3-δ) thin films under photoexcitation.

La0.7Ce0.3MnO3 thin films of different thicknesses, degrees of CeO2-phase segregation and oxygen deficiency, grown on SrTiO3 single crystal substrates, were comparatively investigated with respect to both their spectral and temperature-dependent photoconductivity (PC) and their magnetoresistance (MR) behaviour under photoexcitation. While as-grown films were insensitive to optical excitation, oxygen reduction appeared to be an effective way to decrease the film resistance, but the film thickness was found to play a minor role. However, from the evaluation of the spectral behaviour of the PC and the comparison of the MR of the LCeMO/substrate-samples with a bare substrate under illumination we find that the photoconductivity data reflects not only contributions from (i) photogenerated charge carriers in the film and (ii) carriers injected from the photoconductive substrate (as concluded from earlier works), but also (iii) a decisive parallel photoconduction in the SrTiO3 substrate. Furthermore--also by analyzing the MR characteristics--the unexpected occurence of a strong electroresistive effect in the sample with the highest degree of CeO2 segregation and oxygen deficiency could be attributed to the electroresistance of the SrTiO3 substrate as well. The results suggest a critical reconsideration and possibly a reinterpretation of several previous photoconductivity and electroresistance investigations of manganite thin films on SrTiO3.

The Mn(2+)/Mn(3+) state of La0.7Ce0.3MnO3 by oxygen reduction and photodoping.

Films of cerium-doped LaMnO3, which has been intensively discussed as an electron-doped counterpart to hole-doped mixed-valence lanthanum manganites during the past decade, were analyzed by x-ray photoemission spectroscopy with respect to their manganese valence under photoexcitation. The comparative analysis of the Mn 3s exchange splitting of La0.7Ce0.3MnO3 (LCeMO) films in the dark and under illumination clearly shows that both oxygen reduction and illumination are able to decrease the Mn valence towards a mixed 2+/3+ state, independently of the film thickness and the degree of CeO2 segregation. Charge-injection from the photoconductive SrTiO3 substrate into the Mn eg band with carrier lifetimes in the range of tens of seconds and intrinsic generation of electron-hole pairs within the films are discussed as two possible sources of the Mn valence shift and the subsequent electron doping.

Electric field assisted charge carrier photogeneration in poly(spirobifluorene-co-benzothiadiazole).

The dynamics of charge carrier generation in poly(spirobifluorene-co-benzothiadiazole) was investigated by electric field-induced fluorescence quenching and differential absorption measurements. Three different time domains of carrier generation have been identified: an ultrafast phase, a subnanosecond phase, and an entire lifetime phase. The charge generation efficiencies during the first and second phases were found to be almost independent of temperature, being about 25% and 10%, respectively, at an applied electric field of 1.3×10(6) V/cm, while the generation efficiency during the third phase increases from 2% at 80 K to 10% at room temperature. The results of transient spectroscopy measurements and quantum chemical calculations suggest an intramolecular charge transfer for about 1 ps from the alkoxy-substituted fluorene side group to the benzothiadiazole subunit of the main chain. The formation and evolution of the resulting charge transfer states determine the way of charge carrier generation.

Large photoconductivity of oxygen-deficient La(0.7)Ca(0.3)MnO(3)/SrTiO(3) heterostructures.

The electrical resistance of stoichiometric and oxygen-deficient epitaxial 10 nm thick La(0.7)Ca(0.3)MnO(3) thin films on SrTiO(3) under photoexcitation covering the visible to the ultraviolet range has been investigated systematically as a function of illumination intensity, wavelength and temperature. In contrast to as-prepared films, the oxygen-deficient samples exhibit large photoconductivity of several orders of magnitude at low temperatures. By our detailed comparative analysis of the electrical conductivity of the film/substrate heterostructure and the bare substrate we are able to elucidate contributions of both carrier generation in the film and carrier injection from the substrate to the observed effect.

Método alternativo para a determinaçäo da concentraçäo espermática / Alternative method to determination of spermatic concentration

No presente trabalho, os autores descrevem um método alternativo para determinar a concentraçäo espermática. Baseia-se na medida da altura do precipitado de células, obtido por centrifugaçäo, em tubo apropriado

Mechanism of action of Moraxella bovis hemolysin.

Bovine erythrocytes (RBCs) exposed to Moraxella bovis culture supernatants exhibited rapid leakage of intracellular K+ (95% in 10 min), slower cell swelling (1.20-fold increase in mean corpuscular volume in 20 min), and subsequent lysis (76% leakage of hemoglobin in 25 min). Incubation media made hypertonic by the addition of 75 mM carbohydrates with molecular diameters of 0.72 to 1.32 nm prevented hemolysin-induced RBC swelling, but incubation media made hypertonic by the addition of carbohydrates with molecular diameters of less than 0.72 nm did not protect against hemolysin-induced RBC swelling. Raffinose (75 mM; molecular diameter, 1.14 nm) did not block hemolysin-induced K+ leakage but did block hemolysis. These findings support the hypothesis that hemolysin-induced lysis occurs by colloid-osmotic swelling and are compatible with M. bovis hemolysin acting as a pore-forming cytolysin. Assuming that M. bovis hemolysin acts as a transmembrane molecular sieve, then the functional size of the hemolysin transmembrane pores in bovine RBCs is approximately 0.9 nm, the molecular size of sucrose. Hemolytic activity was inhibited by the Ca2+ chelator ethylene glycol-bis (beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA), but hemolysin-induced K+ leakage was not affected by EGTA.

Menstrual cyclic thrombocytopenia.

We studied three patients with cyclic thrombocytopenia which occurred in phase with the menstrual cycle. The platelet count in each patient reached a nadir of 5-20 x 10(9)/l at the onset of menses. Thrombocytopenia was associated with bruising, epistaxis and menorrhagia and was followed 5-14 d later by normal or elevated platelet counts (up to 900 x 10(9)/l). Repeat bone marrow examinations performed at the time of reduced platelet counts showed megakaryocytic hyperplasia. 111In-platelet-disappearance from the circulation was measured in one patient; T50, time to half activity, was shortened to 0.7 d during the period of thrombocytopenia and was prolonged to 3.2 d when the platelet count increased (normal platelet T50 is about 4.8 d). In two of three patients platelet-associated anti-glycoprotein Ib autoantibodies were present and remained elevated despite normalization of the platelet count. In both of two patients the decrease in platelet count at the onset of menses was associated with an increase in the expression of monocyte Fc gamma receptors. Based on the reported capacity of oestrogenic hormones to modulate macrophage Fc gamma receptor expression, we propose that hormonal changes during the menstrual cycle may alter the Fc gamma receptor-mediated clearance of antibody-coated platelets by macrophages, modulate platelet survival, and cause cyclic thrombocytopenia.

Severe transient pancytopenia associated with procainamide ingestion.

A 73-year-old woman was found to have clinically significant pancytopenia in association with procainamide hydrochloride ingestion. The syndrome, resembling systemic lupus erythematosus, which has been reported to develop in patients treated with this agent, is characterized by mild to moderate anemia and mild to moderate granulocytopenia. Severe granulocytopenia in patients taking procainamide and unrelated to a lupus syndrome has not previously been reported in association with significant thrombocytopenia. The clinical severity of this patient's presentation, suggesting an aleukemic leukemia, and its complete remission after cessation of procainamide administration occasional this report.