University of Fribourg

About: University of Fribourg is a education organization based out in Fribourg, Freiburg, Switzerland. It is known for research contribution in the topics: Population & Context (language use). The organization has 6040 authors who have published 14975 publications receiving 542500 citations. The organization is also known as: UNIFR & Universität Freiburg.

Direct measurement of the electronic spin diffusion length in a fully functional organic spin valve by low-energy muon spin rotation.

Abstract: Electronic devices that use the spin degree of freedom hold unique prospects for future technology. The performance of these 'spintronic' devices relies heavily on the efficient transfer of spin polarization across different layers and interfaces. This complex transfer process depends on individual material properties and also, most importantly, on the structural and electronic properties of the interfaces between the different materials and defects that are common to real devices. Knowledge of these factors is especially important for the relatively new field of organic spintronics, where there is a severe lack of suitable experimental techniques that can yield depth-resolved information about the spin polarization of charge carriers within buried layers of real devices. Here, we present a new depth-resolved technique for measuring the spin polarization of current-injected electrons in an organic spin valve and find the temperature dependence of the measured spin diffusion length is correlated with the device magnetoresistance.

Photonic Wires of Nanometric Dimensions. Electronic Energy Transfer in Rigid Rodlike Ru(bpy)32+-(ph)n-Os(bpy)32+ Compounds (ph = 1,4-Phenylene; n = 3, 5, 7)

Abstract: We have synthesized nine rodlike compounds of nanometric dimension with general formula [M(bpy)3-(ph)n-M‘(bpy)3]4+ (M = M‘ = Ru(II); M = M‘ = Os(II); M = Ru(II), M‘ = Os(II); bpy = 2,2‘-bipyridine; ph = 1,4-phenylene; n = 3, 5, 7; the central phenylene unit bears two alkyl chains for solubility reasons; the metal-to metal distance is 4.2 nm for the longest spacer). The absorption spectra and the luminescence properties (emission spectra, quantum yields, and excited-state lifetimes) of the nine dinuclear complexes have been investigated in acetonitrile solution at 293 K and in butyronitrile rigid matrix at 77 K. The results obtained have been compared with those found for the separated chromophoric units ([Ru(bpy)3]2+, [Os(bpy)3]2+, and oligophenylene derivatives). The absorption spectrum of each dinuclear complex is essentially equal to the sum of the spectra of the component species, showing that intercomponent electronic interactions are weak. In the homodinuclear compounds, the strong fluorescence of t...

Developmental origin of wiring specificity in the olfactory system of Drosophila

Abstract: In both insects and mammals, olfactory receptor neurons (ORNs) expressing specific olfactory receptors converge their axons onto specific glomeruli, creating a spatial map in the brain. We have previously shown that second order projection neurons (PNs) in Drosophila are prespecified by lineage and birth order to send their dendrites to one of ∼50 glomeruli in the antennal lobe. How can a given class of ORN axons match up with a given class of PN dendrites? Here, we examine the cellular and developmental events that lead to this wiring specificity. We find that, before ORN axon arrival, PN dendrites have already created a prototypic map that resembles the adult glomerular map, by virtue of their selective dendritic localization. Positional cues that create this prototypic dendritic map do not appear to be either from the residual larval olfactory system or from glial processes within the antennal lobe. We propose instead that this prototypic map might originate from both patterning information external to the developing antennal lobe and interactions among PN dendrites.

Phosphorus and nitrogen regulate arbuscular mycorrhizal symbiosis in petunia hybrida

Abstract: Phosphorus and nitrogen are essential nutrient elements that are needed by plants in large amounts. The arbuscular mycorrhizal symbiosis between plants and soil fungi improves phosphorus and nitrogen acquisition under limiting conditions. On the other hand, these nutrients influence root colonization by mycorrhizal fungi and symbiotic functioning. This represents a feedback mechanism that allows plants to control the fungal symbiont depending on nutrient requirements and supply. Elevated phosphorus supply has previously been shown to exert strong inhibition of arbuscular mycorrhizal development. Here, we address to what extent inhibition by phosphorus is influenced by other nutritional pathways in the interaction between Petunia hybrida and R. irregularis. We show that phosphorus and nitrogen are the major nutritional determinants of the interaction. Interestingly, the symbiosis-promoting effect of nitrogen starvation dominantly overruled the suppressive effect of high phosphorus nutrition onto arbuscular mycorrhiza, suggesting that plants promote the symbiosis as long as they are limited by one of the two major nutrients. Our results also show that in a given pair of symbiotic partners (Petunia hybrida and R. irregularis), the entire range from mutually symbiotic to parasitic can be observed depending on the nutritional conditions. Taken together, these results reveal complex nutritional feedback mechanisms in the control of root colonization by arbuscular mycorrhizal fungi.

Body composition phenotypes in pathways to obesity and the metabolic syndrome.

Abstract: Dynamic changes in body weight have long been recognized as important indicators of risk for debilitating diseases. While weight loss or impaired growth can lead to muscle wastage, as well as to susceptibility to infections and organ dysfunctions, the development of excess fat predisposes to type 2 diabetes and cardiovascular diseases, with insulin resistance as a central feature of the disease entities of the metabolic syndrome. Although widely used as the phenotypic expression of adiposity in population and gene-search studies, body mass index (BMI), that is, weight/height(2) (H(2)), which was developed as an operational definition for classifying both obesity and malnutrition, has considerable limitations in delineating fat mass (FM) from fat-free mass (FFM), in particular at the individual level. After an examination of these limitations within the constraints of the BMI-FM% relationship, this paper reviews recent advances in concepts about health risks related to body composition phenotypes, which center upon (i) the partitioning of BMI into an FM index (FM/H(2)) and an FFM index (FFM/H(2)), (ii) the partitioning of FFM into organ mass and skeletal muscle mass, (iii) the anatomical partitioning of FM into hazardous fat and protective fat and (iv) the interplay between adipose tissue expandability and ectopic fat deposition within or around organs/tissues that constitute the lean body mass. These concepts about body composition phenotypes and health risks are reviewed in the light of race/ethnic variability in metabolic susceptibility to obesity and the metabolic syndrome.