Bielefeld University

About: Bielefeld University is a education organization based out in Bielefeld, Nordrhein-Westfalen, Germany. It is known for research contribution in the topics: Population & Quantum chromodynamics. The organization has 10123 authors who have published 26576 publications receiving 728250 citations. The organization is also known as: University of Bielefeld & UNIVERSITAET BIELEFELD.

Quasi-Landau Spectrum of the Chaotic Diamagnetic Hydrogen Atom

Abstract: The highly excited hydrogen atom in static magnetic fields has been in recent years a subject of intense experimental [1–4] and theoretical [4–9] studies which have led to substantial progress in the understanding of this previously unsolved elementary problem. Described by the Hamiltonian (in atomic units) $$H=\frac{1}{2}{{P}^{2}}+\frac{1}{2}\gamma {{L}_{z}}+\frac{1}{8}{{\gamma }^{2}}{{\rho }^{2}}-\frac{1}{\gamma }$$ (1) (cylindrical coordinates, r = (ρ2 + z2)½ field parameter γ = B/Bo with Bo = 2.35 × 105 Tesla) the magnetized atom is of particular interest in the quasiLandau regime of strong mixing of the Coulomb and diamagnetic interactions, i.e. where the two forces are of comparable strength. In this regime the motion of the Rydberg electron becomes classically chaotic [10]. It is this aspect which has recently attracted much attention, as the magnetized atom constitutes an ideal model case for detailed experimental studies of the quantum mechanics of a most simple atomic system in classical chaos.

Characteristic patterns of chronic and dynamic photoinhibition of different functional groups in a Mediterranean ecosystem

Abstract: To analyse characteristic patterns of dynamic and chronic photoinhibition within a plant community, a new technique is proposed, which is based on the long- and short-term recovery time of maximum photochemical efficiency of PSII (F v/F m) after environmental stress. Chronic photoinhibition was determined as a sustainable decrease in predawn F v/F m, occurring during periods of prolonged stress, whereas dynamic photoinhibition was assessed from the fully reversible diurnal decline in F v/F m. Applied to a Mediterranean macchia ecosystem, this definition allowed the characterization of typical annual patterns of chronic and dynamic photoinhibition. Both types of photoinhibition were highest during summer drought. However, differences emerged among the ten dominant macchia species regarding their susceptibility to chronic photoinhibition during different seasons. Chronic and dynamic photoinhibition were dependent on leaf orientation. Semi-deciduous species avoided enhanced chronic photoinhibition through a reduction of excessive light interception by vertical foliage orientation during summer, whereas evergreen sclerophylls did not exhibit pronounced structural photoprotective mechanisms. Chronic and total photoinhibition were significantly correlated with predawn and midday water potentials, respectively, and a grouping of the macchia species into three functional groups is proposed according to this relationship.

Antisense Suppression of 2-Cysteine Peroxiredoxin in Arabidopsis Specifically Enhances the Activities and Expression of Enzymes Associated with Ascorbate Metabolism But Not Glutathione Metabolism

Abstract: The aim of this study was to characterize the effect of decreased 2-cysteine peroxiredoxin (2-CP) on the leaf anti-oxidative system in Arabidopsis. At three stages of leaf development, two lines of transgenic Arabidopsis mutants with decreased contents of chloroplast 2-CP were compared with wild type and a control line transformed with an empty vector. Glutathione contents and redox state were similar in all plants, and no changes in transcript levels for enzymes involved in glutathione metabolism were observed. Transcript levels for chloroplastic glutathione peroxidase were much lower than those for 2-CP, and both cytosolic and chloroplastic glutathione peroxidase were not increased in the mutants. In contrast, the foliar ascorbate pool was more oxidized in the mutants, although the difference decreased with plant age. The activities of thylakoid and stromal ascorbate peroxidase and particularly monodehydroascorbate reductase were increased as were transcripts for these enzymes. No change in dehydroascorbate reductase activity was observed, and effects on transcript abundance for glutathione reductase, catalase, and superoxide dismutase were slight or absent. The results demonstrate that 2-CP forms an integral part of the anti-oxidant network of chloroplasts and is functionally interconnected with other defense systems. Suppression of 2-CP leads to increased expression of other anti-oxidative genes possibly mediated by increased oxidation state of the leaf ascorbate pool.

The Importance of Being Exchanged: [GdIII4MII8(OH)8(L)8(O2CR)8]4+ Clusters for Magnetic Refrigeration

Abstract: One of the most promising applications for molecules built from paramagnetic metal ions is low temperature magnetic refrigeration.[1] Indeed recent studies have suggested that molecular coolers can outperform any conventionally-employed solid-state refrigerant material by orders of magnitude.[2] In order to do so, molecules must possess a combination of a large spin ground state (S), with negligible anisotropy (Dcluster = 0), weak magnetic exchange between the constituent metal ions and a relatively large metal:non-metal mass ratio (i.e. a large magnetic density).[1b] These molecular pre-requisites suggest the use of lanthanide ions and, in particular, the f7 ion Gd3+ in the construction of homoand heterometallic (Gd-3d) clusters, and a sensible starting point is the synthesis of GdIII-CuII clusters since previous studies have shown this combination favours ferromagnetic exchange.[3] Here we introduce a rather remarkable new family of compounds of general formula [Ln4M8(OH)8(L)8(O2CR)8](X)4 in which almost all the constituent parts – the lanthanide ions (Ln3+), the transition metal ions (M2+), the bridging ligand L, the carboxylates and the counter anions (X) can be exchanged. In each case the structure remains essentially the same and this allows for a thorough understanding of the individual contributions to the magneto-caloric effect (MCE). In this communication we describe the three family members [Gd4M8(OH)8(L)8(O2CR)8](ClO4)4 (M = Zn, R = CHMe2, 1; M = Cu, R = CHMe2, 2; M = Ni, R = CH2Me, 3; LH = 2(hydroxymethyl)pyridine) and show how the identity of the transition metal and the sign of the magnetic exchange are vital components to consider when designing molecular coolers. For the sake of brevity we provide a generic structure description, highlighting any differences. The core (Figure 1 shows complex 2) of the molecule consists of a square (or wheel) of four cornersharing {Gd2M2O4} cubanes. The shared corners are the Gd ions which thus themselves form an inner {Gd4} square, each edge of which is occupied by two μ3-OH ions which further bridge to a MII ion. The μ3-L ions chelate the M2+ ions and use their O-arm to further bridge to the second M2+ ion in the same cubane and to one Gd ion. There are two carboxylates per cubane, each μ-bridging across a M2+...Gd square face, alternately above and below the plane of the {Gd4} square.