Revival of the spin-Peierls transition in Cu_xZn_(1-x)GeO_3 under pressure

Pressure and temperature dependent susceptibility and Raman scattering experiments on single crystalline Cu_xZn_(1-x)GeO_3 have shown an unusually strong increase of the spin-Peierls phase transition temperature upon applying hydrostatic pressure. The large positive pressure coefficient (7.5 K/GPa) - almost twice as large as for the pure compound (4.5 K/GPa) - is interpreted as arising due to an increasing magnetic frustration which decreases the spin-spin correlation length, and thereby weakens the influence of the non-magnetic Zn-substitution.Comment: LaTeX, 15 pages, 5 eps figures, Phys. Rev. B, to appea

Spin-phonon coupled modes in the incommensurate phases of doped CuGeO3_{3}

The doping effect of the folded phonon mode at 98 cm$^{-1}$ was investigated on the Si-doped CuGeO$_3$ by magneto-optical measurements in far-infrared (FIR) region under high magnetic field. The folded phonon mode at 98 cm$^{-1}$ appears not only in the dimerized (D) phase but also in the dimerized-anitiferromagnetic (DAF) phase on the doped CuGeO$_3$. The splitting was observed in the incommensurate (IC) phase and the antiferromagnetically ordered incommensurate (IAF) phase above $H_C$. The split-off branches exhibit different field dependence from that of the pure CuGeO$_3$ in the vicinity of $H_C$, and the discrepancy in the IAF phase is larger than that in the IC phase. It is caused by the interaction between the solitons and the impurities.Comment: 7 pages, 4 figures, resubmitted to Phys. Rev.

Magnon-magnon interactions in the Spin-Peierls compound CuGeO_3

In a magnetic substance the gap in the Raman spectrum, Delta_R, is approximatively twice the value of the neutron scattering gap, Delta_S, if the the magnetic excitations (magnons) are only weakly interacting. But for CuGeO_3 the experimentally observed ratio Delta_R/Delta_S is approximatively 1.49-1.78, indicating attractive magnon-magnon interactions in the quasi-1D Spin-Peierls compound CuGe_3. We present numerical estimates for Delta_R/Delta_S from exact diagonalization studies for finite chains and find agreement with experiment for intermediate values of the frustration parameter alpha. An analysis of the numerical Raman intensity leads us to postulate a continuum of two-magnon bound states in the Spin-Peierls phase. We discuss in detail the numerical method used, the dependence of the results on the model parameters and a novel matrix-element effect due to the dimerization of the Raman-operator in the Spin-Peierls phase.Comment: submitted to PRB, Phys. Rev. B, in pres

Engineering serendipity: high-throughput discovery of materials that resist bacterial attachment

Controlling the colonisation of materials by microorganisms is important in a wide range of industries and clinical settings. To date, the underlying mechanisms that govern the interactions of bacteria with material surfaces remain poorly understood, limiting the ab initio design and engineering of biomaterials to control bacterial attachment. Combinatorial approaches involving high-throughput screening have emerged as key tools for identifying materials to control bacterial attachment. The hundreds of different materials assessed using these methods can be carried out with the aid of computational modelling. This approach can develop an understanding of the rules used to predict bacterial attachment to surfaces of non-toxic synthetic materials. Here we outline our view on the state of this field and the challenges and opportunities in this area for the coming years

Sewage treatment with anammox

Contains fulltext : 84019.pdf (publisher's version ) (Closed access)2 p

Method for the treatment of waste water with sludge granules

The invention relates to a method for the treatment of waste water comprising an organic nutrient. According to the invention, the waste water is in a first step fed to sludge granules, after the supply of the waste water to be treated the sludge granules are fluidised in the presence of an oxygen-comprising gas, and in a third step, the sludge granules are allowed to settle in a settling step. This makes it possible to effectively remove not only organic nutrients but optionally also nitrogen compounds and phosphateApplied Science

Effect of free calcium concentration and ionic strength on alginate fouling in cross-flow membrane filtration

Extracellular polymeric substances (EPS) are generally negatively charged polymers. Membrane fouling in membrane bioreactors (MBRs) by EPS is therefore influenced by the water chemistry of the mixed liquor (calcium concentration, foulant concentration and ionic strength). We used alginate as a model compound to study this fouling in detail. Flux-step experiments were performed with a flat sheet test cell, varying the free calcium concentration, total ionic strength and alginate concentration. There was a strong relation between calcium concentration and fouling rate. An increased ionic strength had no impact on fouling rate in low fouling experiments, but decreased fouling with 66–72% at high fouling conditions. Reversibility of the fouling decreased with increasing calcium concentrations to values as low as 3%. Several fouling mechanisms were identified and the reducing effect of increased ionic strength on alginate fouling was explained by competition for carboxyl groups on the alginate polymer. Further research will focus on the interaction of polysaccharides with other compounds typically present in the MBR supernatant (e.g. proteins, humic acids and sludge particles) and a more detailed analysis of the fouling laye

Reduced inorganic sulfur oxidation supports autotrophic and mixotrophic growth of Magnetospirillum strain J10 and Magnetospirillum gryphiswaldense

Magnetotactic bacteria are present at the oxic-anoxic transition zone where opposing gradients of oxygen and reduced sulfur and iron exist. Growth of non-magnetotactic lithoautotrophic Magnetospirillum strain J10 and its close relative magnetotactic Magnetospirillum gryphiswaldense was characterized in microaerobic continuous culture. Both strains were able to grow in mixotrophic (acetate + sulfide) and autotrophic (sulfide or thiosulfate) conditions. Autotrophically growing cells completely converted sulfide or thiosulfate to sulfate and produced 7.5 g dry weight per mol substrate at a maximum observed growth rate of 0.09 h(-1) for strain J10 and 0.07 h(-1) for M. gryphiswaldense. The respiratory activity for acetate was repressed in autotrophic and also in mixotrophic cultures, suggesting acetate was used as C-source in the latter. We have estimated the proportions of substrate used for assimilatory processes and evaluated the biomass yields per mol dissimilated substrate. The yield for lithoheterotrophic growth using acetate as the C-source was approximately twice the autotrophic growth yield and very similar to the heterotrophic yield, showing the importance of reduced sulfur compounds for growth. In the draft genome sequence of M. gryphiswaldense homologues of genes encoding a partial sulfur-oxidizing (Sox) enzyme system and reverse dissimilatory sulfite reductase (Dsr) were identified, which may be involved in the oxidation of sulfide and thiosulfate. Magnetospirillum gryphiswaldense is the first freshwater magnetotactic species for which autotrophic growth is show

Effect of free calcium concentration and ionic strength on alginate fouling in cross-flow membrane filtration

Extracellular polymeric substances (EPS) are generally negatively charged polymers. Membrane fouling in membrane bioreactors (MBRs) by EPS is therefore influenced by the water chemistry of the mixed liquor (calcium concentration, foulant concentration and ionic strength). We used alginate as a model compound to study this fouling in detail. Flux-step experiments were performed with a flat sheet test cell, varying the free calcium concentration, total ionic strength and alginate concentration. There was a strong relation between calcium concentration and fouling rate. An increased ionic strength had no impact on fouling rate in low fouling experiments, but decreased fouling with 66–72% at high fouling conditions. Reversibility of the fouling decreased with increasing calcium concentrations to values as low as 3%. Several fouling mechanisms were identified and the reducing effect of increased ionic strength on alginate fouling was explained by competition for carboxyl groups on the alginate polymer. Further research will focus on the interaction of polysaccharides with other compounds typically present in the MBR supernatant (e.g. proteins, humic acids and sludge particles) and a more detailed analysis of the fouling laye