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  • 2000-2004  (26)
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  • 11
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 1953-1955 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This work describes near-field investigations of luminescent nanosamples based on monitoring fluorescence due to the enhanced field around a laser-illuminated probe tip. These fluorescence effects are investigated as a function of probe-sample separation, which identify a strong, spatially localized ((approximate)7 nm) enhancement of the incident laser field in the vicinity of the probe tip. From a model fit to the fluorescence data, the localized enhancement of the electric field is estimated to be 〉tenfold, which predicts a significant increase in localized excitation intensity (〉100-fold) for fluorescence imaging of molecular size samples. © 2000 American Institute of Physics.
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  • 12
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Axis formation occurs in plants, as in animals, during early embryogenesis. However, the underlying mechanism is not known. Here we show that the first manifestation of the apical–basal axis in plants, the asymmetric division of the zygote, produces a basal cell that transports and an apical ...
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  • 13
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 5774-5778 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Enhancement γ of the electrical field at the end of a tip relative to the incident field in a focused radiation beam is calculated by the finite-element time-domain (FETD) method. First, the reliability of the FETD method is established by calculating the electric field on simple structures like thin cylinders, spheres, and ellipsoids, and comparing the results with analytical solutions. The calculations on these test structures also reveal that phase retardation effects substantially modify γ when the size of the structure is larger than approximately λ/4, λ being the radiation wavelength. For plasmon resonance, in particular, phase retardation severely reduces the resonance and the expected field enhancement for a gold tip. The small value of γ=4 calculated by FETD is about an order of magnitude smaller than the value found in recent published work. Resonance effects can be recovered for special tips, which have a discontinuity or a different material composition at the end of the tip. Some tuning of the discontinuity dimension is needed to maximize the resonance. Under optimal conditions for plasmon resonance, an enhancement in the electric field of about 50 is calculated at the end of a small gold protrusion mounted on a wider silicon or glass tip. © 2001 American Institute of Physics.
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  • 14
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Single molecule confocal microscopy is used to study fluorescence intermittency of individual ZnS overcoated CdSe quantum dots (QDs) excited at 488 nm. The confocal apparatus permits the distribution of "on" and "off" times (i.e., periods of sustained fluorescence emission and darkness) to be measured over an unprecedentedly large dynamic range (109) of probability densities, with nonexponential behavior in τoff over a 105 range in time scales. In dramatic contrast, these same τoff distributions in all QDs are described with remarkable simplicity over this 109-fold dynamic range by a simple inverse power law, i.e., P(τoff)∝1/τoff1+α. Such inverse power law behavior is a clear signature of distributed kinetics, such as predicted for (i) an exponential distribution of trap depths or (ii) a distribution of tunneling distances between QD core/interface states. This has important statistical implications for all previous studies of fluorescence intermittency in semiconductor QDs and may have broader implications for other systems such as single polymer molecules. © 2000 American Institute of Physics.
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  • 15
    ISSN: 1432-1424
    Keywords: Key words: Ion transport — Cotransport — Erythrocytes — Ionic strength — Intracellular pH
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract. The change of intracellular pH of erythrocytes under different experimental conditions was investigated using the pH-sensitive fluorescent dye BCECF and correlated with (ouabain + bumetanide + EGTA)-insensitive K+ efflux and Cl− loss. When human erythrocytes were suspended in a physiological NaCl solution (pH o = 7.4), the measured pH i was 7.19 ± 0.04 and remained constant for 30 min. When erythrocytes were transferred into a low ionic strength (LIS) solution, an immediate alkalinization increased the pH i to 7.70 ± 0.15, which was followed by a slower cell acidification. The alkalinization of cells in LIS media was ascribed to a band 3 mediated effect since a rapid loss of approximately 80% of intracellular Cl− content was observed, which was sensitive to known anion transport inhibitors. In the case of cellular acidification, a comparison of the calculated H+ influx with the measured unidirectional K+ efflux at different extracellular ionic strengths showed a correlation with a nearly 1:1 stoichiometry. Both fluxes were enhanced by decreasing the ionic strength of the solution resulting in a H+ influx and a K+ efflux in LIS solution of 108.2 ± 20.4 mmol (l cells hr)−1 and 98.7 ± 19.3 mmol (l cells hr)−1, respectively. For bovine and porcine erythrocytes, in LIS media, H+ influx and K+ efflux were of comparable magnitude, but only about 10% of the fluxes observed in human erythrocytes under LIS conditions. Quinacrine, a known inhibitor of the mitochondrial K+(Na+)/H+ exchanger, inhibited the K+ efflux in LIS solution by about 80%. Our results provide evidence for the existence of a K+(Na+)/H+ exchanger in the human erythrocyte membrane.
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  • 16
    ISSN: 1432-2013
    Keywords: Electron microscopy Intracellular pH Monocarboxylate transport Pigment epithelium of eye Proton–lactate cotransport Retinal metabolism Sodium/proton exchange
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract. Monolayer cultures of human fetal retinal pigment epithelial (RPE) cells were examined for ultrastructural characteristics and junctional integrity by means of electron microscopy. Intracellular pH (pHi) and cell volume changes were measured using the fluorescent dye BCECF. The EM studies indicate that the RPE cells preserve in vivo morphology before and after loading with BCECF. Monolayer cultures were placed in a perfusion chamber in which the solution facing the retinal cell membrane could be changed rapidly. Removal of Na+ or the addition of amiloride caused intracellular acidifications. pHi recovery from an NH4 +-induced acid load was blocked by sodium removal or amiloride addition. These results suggest the presence of a Na+–H+ exchange mechanism in the retinal cell membrane. When Cl- was replaced isotonically by lactate or pyruvate the cells acidified. The intracellular acidifications were saturable, reversibly reduced with the inhibitor probenecid (2 mM), and the lactate-induced acidifications were reversibly inhibited by equimolar concentrations of pyruvate. These results indicate the presence of a H+–lactate cotransport mechanism in the retinal membrane. When Cl– was replaced by lactate the cells not only acidified, they also swelled. The data are compatible with water transport induced by the H+–lactate cotransporter.
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  • 17
    ISSN: 1432-2013
    Keywords: Exocytosis Membrane potential
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract. This study aimed to assess the relevance of specific potassium channels, such as inwardly or outwardly rectifying and calcium-regulated potassium channels, to the control of renin secretion. For this purpose we examined the effects of the K+ channel blockers 4-aminopyridine (1 mmol/l), barium (100 µmol/l), tetraethylammonium (2 mmol/l) and apamin (200 nmol/l) on basal renin secretion, on renin secretion stimulated by isoproterenol (10 nmol/l) and on the inhibition of renin secretion by angiotensin II (100–300 pmol/l) in the isolated rat kidney perfused at constant pressure. Whilst all four K+ channel blockers increased renal vascular resistance, only 4-aminopyridine and barium attenuated isoproterenol-stimulated renin secretion in an additive fashion and augmented the inhibitory effect of angiotensin II. These effects of K+ channel blockers were not changed by the L-type calcium channel blocker amlodipine (5 µmol/l), indicating that their effects on renin secretion are not due to voltage-operated calcium influx. Our data, moreover, suggest that potassium efflux from renal juxtaglomerular cells is not important for the inhibitory action of angiotensin II on renin secretion. As a consequence it appears that the membrane potential of renal juxtaglomerular cells per se is relevant to renin secretion such that membrane depolarization inhibits the exocytosis of renin whilst hyperpolarization favors renin secretion. By their activity, potassium channels can contribute to membrane hyperpolarization and thus facilitate renin secretion.
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  • 18
    ISSN: 1439-099X
    Keywords: Schlüsselwörter: Strahlentherapie ; Diarrhö ; Prophylaxe ; Smektit ; Key Words: Radiotherapy ; Diarrhea ; Prophylaxis ; Smectite
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Purpose: Diarrhea and abdominal pain are well-known side effects abdominal or pelvic of radiation therapy that may lead to interruption of treatment in serious cases. In recent trials the silicate smectite has proven a promising drug in the prophylaxis if these adverse events. The presented trial aimed at the verification of earlier studies and the evaluation of a dose-effect relationship. Patients and Methods: Between April 1994 and May 1995, a total of 176 patients obtaining radiotherapy of the pelvis or the abdomen were evaluated in a double-blind, randomized placebo-controlled investigation regarding the prophylactic effect of smectite (= Colina®) against radiotherapy-induced diarrhea. During the whole period of radiotherapy 85 patients obtained 2 × 6 g smectite daily and 91 patients received 2 × 6 g placebo. The primary end point of the analysis was the time to the first appearance of diarrhea (≥ 3 pappy stools). Results: All 176 patients were evaluated according to an intent-to-treat analysis. There was no significant difference between the prophylactic effects of smectite and placebo. For an explorative post-hoc analysis the total study group was split up into 2 subgroups, one with an irradiated small bowel volume ≤ 837.5 ml, the other with a small bowel volume 〉 837,5 ml (median); the analysis indicated that the first subgroup showed a benefit for the smectite-treated patients in contrast to the placebo treatment (32 vs. 18 calendar days to the first appearance of diarrhea). This benefit was statistically not significant. Conclusion: Prophylactic application of smectite during irradiation of the pelvis and the abdomen can delay the development of radiotherapy-induced diarrhea, a statistical significance could not be verified neither in the total study group nor in the post-hoc subgroup analysis.
    Notes: Hintergrund und Ziel: Strahlentherapieinduzierte Diarrhöen und Schmerzen sind bekannte Nebenwirkungen der Becken- und Abdominalbestrahlung und können in schwerwiegenden Fällen zur Unterbrechung der Strahlenbehandlung führen. Das Schichtsilikat Smektit hat sich in den ersten Anwendungsstudien als ein vielversprechendes Therapeutikum zur Prophylaxe dieser Nebenwirkungen erwiesen. Die vorliegende Untersuchung diente der Verifizierung bekannter Studienresultate und der Erarbeitung einer Dosis-Wirkungs-Beziehung. Patienten und Methoden: Zwischen April 1994 und Mai 1995 wurde bei 176 Patienten mit Becken- bzw. Abdominalbestrahlung die prophylaktische Wirkung von Smektit (Handelsname: Colina®) bezüglich radiogener Diarrhöen in einer doppelblinden, randomisierten und plazebokontrollierten Studie untersucht. Während des gesamten Zeitraums der Strahlentherapie erhielten 85 Patienten täglich 2mal 6 g Smektit und 91 Patienten täglich 2mal 6 g von identisch aussehender Plazebosubstanz. Das Hauptzielkriterium der Auswertung war der Zeitraum bis zum Auftreten einer bestrahlungsinduzierten Diarrhö (definiert als ≥ 3 breiige Stühle). Ergebnisse: Alle 176 Patienten wurden in der Intent-to-treat-Analyse ausgewertet. In der Gesamtgruppe zeigten sich keine signifikanten Unterschiede zwischen der prophylaktischen Wirkung von Smektit und Plazebo. Eine explorative Post-hoc-Analyse mit Teilung des Gesamtkollektivs in Subgruppen mit einem bestrahlten Dünndarmvolumen ≤ 837,5 ml bzw. 〉 837,5 ml (Median) deutet im Kollektiv ≤ 837,5 ml an, dass bei gegebener Dosierung ein Vorteil für Smektit gegenüber Plazebo (32 versus 18 Kalendertage bis zum ersten Auftreten einer Diarrhö) besteht; dieser Vorteil ist jedoch statistisch nicht signifikant. Schlussfolgerung: Durch den prophylaktischen Einsatz eines Smektitpräparates als Antidiarrhoikum während einer Bestrahlung des Becken- und Abdominalbereiches kann die Entstehung einer bestrahlungsinduzierten Diarrhö verzögert werden, eine statistische Signifikanz konnte jedoch sowohl im Gesamtkollektiv als auch in einer Post-hoc-Subgruppenanalyse nicht nachgewiesen werden.
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  • 19
    ISSN: 1573-7217
    Keywords: BRCA1 mutation ; breast cancer ; disease-free survival ; overall survival ; pathology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Reports from different countries have been inconclusive in attempting to relate the BRCA1 mutation status to the survival of breast cancer patients. The purpose of this study was to investigate overall and disease-free survival for German hereditary breast cancer patients. Data on clinical outcome and data on age at diagnosis of breast cancer, histology, tumor size, lymph node status, histological grade, and laterality of 36 breast cancer patients from 12 families with a BRCA1 mutation and from one family with strong evidence for linkage to BRCA1 were compared with those of 49 hereditary breast cancer patients from 23 families that did not harbor a BRCA1 mutation. Overall and disease-free survival was estimated for both groups. BRCA1 mutation carriers had a significantly earlier age of diagnosis than non-carriers (p = 0.0001) and more frequently developed contralateral breast cancer (p = 0.04). Also, BRCA1-associated tumors more frequently were of larger size (p = 0.041) and higher grade of malignancy (p = 0.005) than non-BRCA1-associated tumors. Whereas no difference in overall survival was seen, disease-free survival at 10 years differed significantly with 53.3% for BRCA1 mutation carriers and 76% for non- carriers (p = 0.02). However, after stratification for age and in multivariate analysis for mutation status, age, and bilaterality, it was shown that the worse prognosis for BRCA1 mutation carriers disappeared. Our results suggest that the worse prognosis of BRCA1 mutation carriers in terms of disease-free survival may in large part be due to the age of onset of breast cancer in this population. Thus, BRCA1 mutation status does not appear to be an independent prognostic factor.
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  • 20
    ISSN: 1432-1904
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General
    Notes: Abstract  The GPS recorder consists of a GPS receiver board, a logging facility, an antenna, a power supply, a DC-DC converter and a casing. Currently, it has a weight of 33 g. The recorder works reliably with a sampling rate of 1/s and with an operation time of about 3 h, providing time-indexed data on geographic positions and ground speed. The data are downloaded when the animal is recaptured. Prototypes were tested on homing pigeons. The records of complete flight paths with surprising details illustrate the potential of this new method that can be used on a variety of medium-sized and large vertebrates.
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