Remote fluorescence imaging of dynamic concentration profiles with micrometer resolution using a coherent optical fiber bundle

Dynamic concentration profiles within the diffusion layer of an electrode were imaged in situ using fluorescence detection through a multichannel imaging fiber. In this work, a coherent optical fiber bundle is positioned orthogonal to the surface of an electrode and is used to report spatial and temporal micrometric changes in the fluorescence intensity of an initial fluorescent species. The fluorescence signal is directly related to the local concentration of a redox fluorescent reagent, which is electrochemically modulated by the electrode. Fluorescence images are collected through the optical fiber bundle during the oxidation of tris(2,2'-bipyridine)ruthenium(II) to ruthenium(III) at a diffusion-limited rate and allow the concentration profiles of Ru(II) reagent to be monitored in situ as a function of time. Tris(2,2'-bipyridine)ruthenium(II) is excited at 485 nm and emits fluorescence at 605 nm, whereas the Ru(III) oxidation state is not fluorescent. Our experiments emphasize the influence of two parameters on the micrometer spatial resolution: the numerical aperture of optical fibers within the bundle and the Ru(II) bulk concentration. The extent of the volume probed by each individual fiber of the bundle is discussed qualitatively in terms of a primary inner-filter effect and refractive index gradient. Experimentally measured fluorescence intensity profiles were found to be in very good agreement with concentration profiles predicted upon considering planar diffusion and thus validate the concept of this new application of imaging fibers. The originality of this remote approach is to provide a global view of the entire diffusion layer at a given time through one single image and to allow the time expansion of the diffusion layer to be followed quantitatively in real time.     

Loss measurements in stress-induced optical waveguides fabricated by an embossing process

Stress-induced light guides have been fabricated by an embossing process. The results of detailed loss measurements show that these waveguides can exhibit low optical attenuation.     

Flora und ?sung auf Wild?ckern der Feldflur in Niedersachsen

Zusammenfassung Um die Frage nach dem ökologischen Nutzen einjähriger Wildäcker der Feldflur zu klären, wurden auf 68 Standorten im Tief- und Bergland Niedersachsens während der Vegetationsperiode 2002 die Ansaaten und Pflanzenarten erfasst (letztere vegetationskundlich nachBraun-Blanquet). Jeder Wildacker unterliegt einer individuellen Anbaupraxis; jeder zweite (darunter 26 Stillegungsflächen) besitzt eine andere Einsaat. Das Spektrum der wildwachsenden Pflanzenarten vermittelt zwischen Ackerwildkraut-Gesellschaften und Ruderalen Beifußfluren und ist durch hohe Bauwerte Mehrjähriger gekennzeichnet. Die Artenzahl variiert von 12–63; im Mittel rund 40, im Diepholz-Nienburger Raum 24 Arten. 40% der Wildäcker beherbergen mindestens eine von 17 Arten der Roten Liste. Dabei sind individuenreiche Populationen die Ausnahme und nur auf Standorten mit langer Ackernutzung zu finden. Die quantitative Erfassung der von Rehwild und Feldhase verbissenen Pflanzenarten (Individuenzahl) sowie die Feststellung der pflanzenartspezifischen Äsungspräferenz (Anteil Äcker, wo Art beäst im Verhältnis zur Zahl, wo Art auftrat) ergab 23 Kultur- und 67 Wildpflanzenarten. Süßgräser, aromatische und niederliegende Pflanzenarten werden weniger angenommen; hochwüchsige, milchsaftführende und saftige bevorzugt, vor allem die Rauhe Gänsedistel (Sonchus asper L.ssp. asper). Je artenreicher der Wildacker, desto mehr Arten beäst das Wild. Die wildwachsende Flora der Wildäcker erfüllt damit eine obligate Funktion im sommerlichen Nahrungsspektrum. Eine Deckung von Kulturpflanzen über 80% führt dagegen zur Abnahme der Äsung sowie tendenziell auch zum Rückgang von Roten-Liste-Arten. Durch die regelmäßige Bestellung ackerfähiger Grenzertragsstandorte mit Feldfrüchten tragen Wildäcker zum Schutz erhaltenswerter Segetalvegetation bei, deren Restitution in Fällen kleiner Populationsgrößen der beteiligten Arten dringend geboten ist. Zur Ausschöpfung des natürlichen Standortpotentials wird ein Pilotprojekt Ausgleichsmaßnahme Wildäsungsfläche angeregt.Eingesetzt wurde ein Druckkostenzuschuß des Hessischen Ministeriums für Umwelt, Ländlichen Raum und Verbraucherschutz, für dessen Gewährung verbindlich gedankt wird. - Die Schriftleitung     

The impact of mental fatigue on exploration in a complex computer task: rigidity and loss of systematic strategies

We investigated the impact of mental fatigue on exploration in a complex computer task. The exploration behavior of participants who underwent a fatigue manipulation (N = 36) was compared with that of a control (nonfatigued) group (N = 32). A distinction was also made between participants with high or low levels of general computer experience. Results showed that fatigued participants used significantly less systematic exploration and made more errors than did nonfatigued participants. Fatigued participants with low computer experience also showed significantly more rigid behavior than did the other participants. No differences were found on the number of subtasks solved. Compared with low-experience participants, highly experienced participants showed significantly more systematic exploration, less unsystematic trial and error, solved more subtasks, and made fewer errors (marginally significant p = .056). Findings were interpreted as the result of reduced task engagement under fatigue and reduced involvement of executive control on behavior. Actual or potential applications of this research include guidelines to prevent detrimental effects of mental fatigue on exploration behavior.     

Fourier-transform infrared spectra of fatty acid salts—Kinetics of high-oleic sunflower oil saponification

Sodium, lithium, and calcium soaps obtained by saponification of high-oleic sunflower oil were studied by Fourier-transform infrared spectroscopy. Spectra of crude mixtures containing soap, glycerin, residual alkali, and triacylglycerols were compared to those of pure soaps obtained from fatty acids. The infrared spectra of crude soaps showed the same characteristic bands as pure ones. The absorption bands of asymmetric (ω₂) and symmetric (ω₁) stretching vibrations of the carboxylate group indicated that the metal-oxygen bonds of these soaps had an ionic character whose strength differed from one cationic counterion to another. Once the characteristic absorption bands of the soaps were assigned, a kinetics study of saponification was performed. Saponification by sodium, anhydrous lithium, and calcium hydroxides was an autocatalytic reaction, characterized by an S-shaped kinetics curve, whereas saponification by aqueous lithium hydroxide was stoichiometric. The structure of the metal-oxygen bond played a role in the kinetic mechanisms.     

Prion diseases: from molecular biology to intervention strategies

Prion diseases are fatal neurodegenerative infectious disorders for which no therapeutic or prophylactic regimens exist. Understanding the molecular process of conformational conversion of the cellular prion protein (PrP(c)) into its pathological isoform (PrP(Sc)) will be necessary to devise effective antiprion strategies. In recent years, new findings in the cell biology of PrP(c), in the molecular pathogenesis of PrP(Sc), and in the cellular quality control mechanisms involved in these scenarios have accumulated. A function of the prion protein in signalling, the possible impact of the proteasome, and aggresomes as intracellular waste deposits have been described. Here, important pathogenetic similarities with the more frequent neurodegenerative disorders are evident. The need for therapeutic, postexposure, and prophylactic possibilities was drastically illustrated by the emergence of variant Creutzfeldt-Jakob disease (vCJD), a new human prion disease caused by bovine spongiform encephalopathy (BSE) derived prions. Although prion infectivity in humans is usually restricted to the central nervous system, in vCJD patients prions are present in the lympho-reticular system, posing a theoretical risk of accidental human-to-human transmission. A variety of chemical antiprion substances have been reported in in vitro and cell culture based assays or in animal studies. Occasionally, they have also made their way into the first human trials. In addition, various promising interference strategies have been devised in transgenic models, although they are usually hard to transfer into nontransgenic in vivo situations. New findings in the fields of peripheral prion pathogenesis and immune system involvement fuelled the search for antiprion strategies formerly considered to be entirely impossible. This opened the door towards classical immunological interference techniques. Remarkably, passive and even active vaccination approaches now seem to be realistic goals.     

Intercellular Transport of Nanomaterials is Mediated by Membrane Nanotubes In Vivo

So‐called membrane nanotubes are cellular protrusions between cells whose functions include cell communication, environmental sampling, and protein transfer. It has been previously reported that systemically administered carboxyl‐modified quantum dots (cQDs) are rapidly taken up by perivascular macrophages in skeletal muscle of healthy mice. Expanding these studies, it is found, by means of in vivo fluorescence microscopy on the mouse cremaster muscle, rapid uptake of cQDs not only by perivascular macrophages but also by tissue‐resident cells, which are localized more than 100 μm distant from the closest vessel. Confocal microscopy on muscle tissue, immunostained for the membrane dye DiI, reveals the presence of continuous membranous structures between MHC‐II‐positive, F4/80‐positive cells. These structures contain microtubules, components of the cytoskeleton, which clearly colocalize with cQDs. The cQDs are exclusively found inside endosomal vesicles. Most importantly, by using in vivo fluorescence microscopy, this study detected fast (0.8 μm s^?1, mean velocity), bidirectional movement of cQDs in such structures, indicating transport of cQD‐containing vesicles along microtubule tracks by the action of molecular motors. The findings are the first to demonstrate membrane nanotube function in vivo and they suggest a previously unknown route for the distribution of nanomaterials in tissue.     

How hypertext fosters children’s knowledge acquisition: The roles of text structure and graphical overview

Children in primary and secondary school are asked to go on the Internet for school purposes while research on hypertext has scarcely investigated how children process and learn from hypertext. We therefore examined how hypertext influences children’s knowledge acquisition from expository text. A group of 71 Dutch children (13 years old) from one secondary school for pre-university education participated in the study. In a within-subjects design with four conditions, we compared: regular linear text, regular text with overview, hypertext, and hypertext with overview. Children’s (a) navigation (i.e., reading time and navigation pattern) and (b) learning (i.e., multiple choice knowledge questions and mind maps) was measured. Although reading times did not differ, the children navigated less linearly in both hypertext conditions than in the regular text with overview condition. The four types of text led to the same deep understanding as measured on the text base level. Analyses of the mind maps, however, showed the children to construct richer situation models after reading hypertext or hypertext with an overview relative to regular linear text and regular text with overview. We therefore conclude that hypertext fosters a deeper level of information processing when appropriately designed relative to regular linear text.