Critical behavior of sandpile models with sticky grains

We revisit the question whether the critical behavior of sandpile models with sticky grains is in the directed percolation universality class. Our earlier theoretical arguments in favor, supported by evidence from numerical simulations [P.K. Mohanty, D. Dhar, Phys. Rev. Lett. 89 (2002) 104303], have been disputed by Bonachela et al. [Phys. Rev. E 74 (2006) 050102] for sandpiles with no preferred direction. We discuss possible reasons for the discrepancy. Our new results of longer simulations of the one-dimensional undirected model fully support our earlier conclusions.     

Magnetocrystalline anisotropy in RAu2Ge2 (R = La, Ce and Pr) single crystals

Anisotropic magnetic properties of single crystalline RAu₂Ge₂ (R=La, Ce and Pr) compounds are reported. LaAu₂Ge₂ exhibits a Pauli-paramagnetic behaviour whereas CeAu₂Ge₂ and PrAu₂Ge₂ show an antiferromagnetic ordering with Nèel temperatures T_N = 13.5 and 9 K, respectively. The anisotropic magnetic response of Ce and Pr compounds establishes [0 0 1] as the easy axis of magnetization and a sharp spin-flip type metamagnetic transition is observed in the magnetic isotherms with H // [0 0 1]. The transport and magnetotransport behaviour of these compounds, in particular LaAu₂Ge₂, indicate an anisotropic Fermi surface. The magnetoresistivity of CeAu₂Ge₂ apparently reveals the presence of a residual Kondo interaction. A crystal electric field analysis of the anisotropic susceptibility in conjunction with the experimentally inferred Schottky heat capacity enables us to propose a crystal electric field level scheme for Ce and Pr compounds. For CeAu₂Ge₂ our values are in excellent agreement with the previous reports on neutron diffraction. The heat capacity data in LaAu₂Ge₂ show clearly the existence of Einstein contribution to the heat capacity.     

Fabrication of high aluminium containing rare-earth doped fiber without core-clad interface defects

The unwanted core-clad interface defect generation and related scattering loss in rare-earth doped optical fibers containing Al-oxide is up to now an unsolved problem as it cannot be avoided without modifying fiber design or composition. Here a simple technique is proposed to eliminate the problem without affecting fiber parameters. The method comprises addition of fumed silica in appropriate amount under dispersed condition to the soaking solution containing Al and rare-earth salts during the solution impregnation stage. This facilitates the networking between Al₂O₃ and SiO₂ during sintering. The method leads to an improvement in optical properties of the fibers and enables doping of high concentration of Al-oxide even in presence of GeO₂ in the core.     

Germanium microsphere high-Q resonator

In this Letter, the fabrication and characterization of a microsphere resonator from the semiconductor germanium is demonstrated. Whispering gallery modes are excited in a 46 μm diameter germanium microsphere resonator using evanescent coupling from a tapered silica optical fiber with a waist diameter of 2 μm. Resonances with Q factors as high as 3.8×10(4) at wavelengths near 2 μm are observed. Because of their ultrahigh optical nonlinearities and extremely broad transparency window, germanium microsphere resonators offer the potential for optical processing devices, in particular at long wavelengths, such as around 2 μm.     

Anisotropic magnetic properties and superzone gap formation in CeGe single crystal

Single crystals of CeGe and its non-magnetic analog LaGe have been grown by the Czochralski method. The CeGe compound crystallizes in the orthorhombic FeB-type crystal structure with the space group Pnma (#62). The anisotropic magnetic properties have been investigated for well oriented single crystals by measuring the magnetic susceptibility, electrical resistivity and heat capacity. It has been found that CeGe orders antiferromagnetically at 10.5?K. Both transport and magnetic studies have revealed large anisotropy, reflecting the orthorhombic crystal structure. The magnetization data at 1.8?K reveal metamagnetic transitions along the [010] direction at 4.8 and 6.4?T and along the [100] direction at a critical field of 10.7?T, while the magnetization along the [001] direction increases linearly without any anomaly up to a field of 16?T. From the magnetic susceptibility and the magnetization measurements it has been found that the [010] direction is the easy axis of magnetization. The electrical resistivity along the three crystallographic directions exhibits an upturn at T(N), indicating superzone gap formation below T(N) in this compound. We have performed crystal electric field analysis on the magnetic susceptibility and the heat capacity data and found that the ground state is a doublet, and the energies of splitting from the ground state to the first and second excited doublet states were estimated to be 39 and 111?K, respectively.     

Fabrication of wood-inspired high-performance composites through fermentation routes

In this paper, we developed a microbial route to fabricate wood-inspired biomimetic composites comparable to natural wood. Focusing on the chemical composition of woody biomass, we performed in situ bioprocessing of bacterial cellulose (BC) imbibed in modified cationic lignin (Catlig), which exhibited significant bioactivity in improving the microbial growth dynamics. The structural and morphological characteristics were enhanced by the formation of hydrophobic and electrostatic interactions between BC and Catlig during biosynthesis. Microbially derived BC/Catlig composites exhibited enhanced thermal stability and crystallinity, with oriented cellulose fibers. The tensile properties, toughness, and specific strength of BC/Catlig composites were comparable to those of a heavy wood species (Zelkova serrata) under hydrated conditions and synthetic soft materials.

Graphic abstract

     

[4 + 2]-Cycloadditionen mit inversem Elektronenbedarf,XVII. Oxepin und 2,7-Dimethyloxepin als Dienophile bei Diels-Alder-Cycloadditionen mit inversem Elektronenbedarf

[4 + 2] Cycloadditions with Inverse Electron Demand, XVII. Oxepin and 2,7-Dimethyloxepin as Dienophiles in Diels-Alder Cycloadditions with Inverse Electron Demand The cycloaddition reactions of oxepin ( 1 ) with the tetrazine 3 and the triazine 12 yield the dihydrooxepino[4,5-d]pyridazine 5 and the oxepino[4,5-c]pyridine 13 , resp., via [2 + 4] cycloaddition as well as the phthalazine 9 and the isoquinoline 14 , resp., most probably via [6 + 4] cycloaddition. On the contrary, 2,7-dimethyloxepin ( 15 ) only gives the products 16 and 20 , which result from [2 + 4] cycloaddition. Oxidation of 16 by silver(I) oxide leads to the oxepino[4,5-d]pyridazine 17 , which as well as 20 in hydrochloric acid rearranges to the pseudoazulenes 19 and 21 , resp.