Photoelectrochemical production of hydrogen from p-type transition metal phosphides

We present a photoelectrochemical investigation of a number of p-conducting transition metal phosphide semiconductors MeP₂ (Me = Cu, Zn, Cd). The series MeP₂ can be divided into two subgroups. The first of these consists (e.g.) of the monoclinic compounds CuP₂ and β-ZnP₂, which appear ideally suited for photovoltaic applications, due to their bandgaps close to 1.4 eV. The quantum yield of a β-ZnP₂ single crystal electrode, in 1 M Na₂SO₄ at pH 2.5, is above 60% for the polarization Ec in a large portion of the visible and near infrared spectrum.

The second class of materials are the tetragonal modifications -ZnP₂ and CdP₂. Their bandgaps are near 2.1 and 2 eV, respectively. The quantum yield of -ZnP₂ is above 70% for photon energies above 2.7 eV.

A general feature of all these materials is the high energy of the conduction band, or conversely, the negative position of the flatband potential V_fb on the electrochemical scale. From the Mott-Schottky data for β-ZnP₂, it follows, that V_fb = 0.11 ± 0.02 V_SCE in 1 M Na₂SO₄, at pH 2.5. Photo-assisted electrolysis requires thus a rather large bias. On the other hand, hydrogen evolution can be very efficient in the presence of an electron donor. This is demonstrated with RuO₂-loaded -ZnP₂ particles in an electrolyte containing EDTA. Due to the negative V_fb these materials could also be ideal candidates for other important redox reactions, such as CO₂ reduction.     

An atomic force microscope tip designed to measure time-varying nanomechanical forces

Tapping-mode atomic force microscopy (AFM), in which the vibrating tip periodically approaches, interacts and retracts from the sample surface, is the most common AFM imaging method. The tip experiences attractive and repulsive forces that depend on the chemical and mechanical properties of the sample, yet conventional AFM tips are limited in their ability to resolve these time-varying forces. We have created a specially designed cantilever tip that allows these interaction forces to be measured with good (sub-microsecond) temporal resolution and material properties to be determined and mapped in detail with nanoscale spatial resolution. Mechanical measurements based on these force waveforms are provided at a rate of 4 kHz. The forces and contact areas encountered in these measurements are orders of magnitude smaller than conventional indentation and AFM-based indentation techniques that typically provide data rates around 1 Hz. We use this tool to quantify and map nanomechanical changes in a binary polymer blend in the vicinity of its glass transition.     

Mueller matrix measurements of algae with different shape and size distributions

The full Mueller matrix was measured to obtain the polarization state of the scattered light for a variety of algae with different shapes, wall compositions, sizes, and refractive indices. The experimental setup was a multiple laser Mueller matrix ellipsometer, by which measurements were performed for scattering angles from 16° to 160° sampled at every second degree for wavelengths of 473?nm and 532?nm. Previously, the polarization of light scattered from microalgae was investigated only for a few species, and the Mueller matrix was found to have little variation between the species. In our work a total of 11 algal species were investigated, representing diatoms, dinoflagellates, coccolithophorids, green algae, and a cryptophyte. The selection of species was made to obtain high variability in shape, size, cell wall, and refractive index. As in previous investigations, very small variations were found between species for most of the Mueller matrix elements, but noticeable variations were found for M(11), (M(12)+M(21))/2 and (M(33)+M(44))/2.     

Staphylococcus aureus and Streptococcus dysgalactiae in Norwegian herds after introduction of selective dry cow therapy and teat dipping

The objective was to promote a reduction in the prevalence of Staphylococcus aureus and Streptococcus dysgalactiae after 2 years of selective dry cow therapies and teat dipping/external teat sealant implementation. Three different dry cow treatments, one long-acting and two short-acting penicillin-based products were tested at herd level together with a negative control teat dipping group, an iodine teat dipping group and DryFlextrade mark, an external teat sealant. The regimes were independently randomly allocated to 178 dairy herds. Yearly bacteriological quarter milk samples were collected from all cows at the beginning of the trial, after 1 year and 2 years. At herd level, a total of 15% of the herds showed no Staphylococcus aureus isolates after 2 years, compared with 5% at the beginning. The distribution of Streptococcus dysgalactiae infected herds remained the same after 2 years. At cow level, there were no significant differences in the reduction of Staph. aureus between the different dry cow therapies and teat dipping regimes. But there was a significant reduction of Str. dysgalactiae in the iodine teat dipping group compared with Dryflextrade mark and the negative control group. The proportional rate of Staph. aureus positive quarters was reduced from 65.9% to 54.9% after 2 years. As for Str. dysgalactiae, an increase was observed from 14.2% to 15.2%.     

Applying power quality characteristics of wind turbines for assessing impact on voltage quality

Injection of wind power into an electric grid affects the voltage quality. As the voltage quality must be within certain limits to comply with utility requirements, the effect should be assessed prior to installation. To assess the effect, knowledge about the electrical characteristics of the wind turbines is needed or else the result could easily be an inappropriate design of the grid connection. The electrical characteristics of wind turbines are manufacturer‐specific but not site‐specific. This means that, having the actual parameter values for a specific wind turbine, the expected impact of the wind turbine type on voltage quality when deployed at a specific site, possibly as a group of wind turbines, can be calculated. The methodology for this is explained and illustrated by case studies considering a 5 × 750 kW wind farm on a 22 kV distribution feeder. The detailed analysis suggests that the wind farm capacity can be operated at the grid without causing unacceptable voltage quality. For comparison, a simplified design criterion is considered assuming that the wind farm is only allowed to cause a voltage increment of 1%. According to this criterion, only a very limited wind power capacity would be allowed. Measurements confirm, however, the suggestion of the detailed analysis, and it is concluded that a simplified design criterion such as the ‘1% rule’ should not be used for dimensioning the grid connection of wind farms. Rather, this article suggests a systematic approach including assessment of slow voltage variations, flicker, voltage dips and harmonics, possibly supported by more detailed analyses, e.g. system stability if the wind farm is large or the grid is very weak, and impact on grid frequency in systems where wind power covers a high fraction of the load, i.e. most relevant for isolated systems. Copyright © 2002 John Wiley & Sons, Ltd.     

Modelling natural drying efficiency in covered and uncovered piles of whole broadleaf trees for energy use

Small dimensions regenerated forests are considered a useful fuel resource for small local heat plants in Norway, since it is not relevant for the timber industry. Most small heat plants built so far are constructed for moisture contents of about 35% on wet basis. Therefore, the material must be dried. Because artificial drying induces additional costs, storing the material in piles roadside as whole trees until desired moisture content is obtained is considered beneficial. Traditionally, leaf seasoning has been considered an efficient method. To increase the understanding of these processes, a study on drying whole trees in piles has been accomplished at three different locations with different climatic conditions. The study focuses on the following explanatory variables: harvesting season, location, climatic conditions, position in the pile, tree species, and relative crown length. The effect of covering the piles in order to reduce the moisture uptake during winter was also studied. Models, estimating the moisture content with time profiles, were developed.During spring and summer the moisture content was reduced to approximately 35% also when the material was harvested in the autumn the year before. The climatic conditions were important for the drying result, but drying was effective also in the moist climate in western Norway. Covering the dry piles before the winter was important in order to maintain the requested moisture content. The effect of covering the material harvested in autumn was limited.     

Structural investigation of a high-affinity MnII binding site in the hammerhead ribozyme by EPR spectroscopy and DFT calculations. Effects of neomycin B on metal-ion binding

Electron paramagnetic resonance spectroscopy and density functional theory methods were used to study the structure of a single, high-affinity Mn(II) binding site in the hammerhead ribozyme. This binding site exhibits a dissociation constant Ke of 4.4 microM in buffer solutions containing 1 M NaCl, as shown by titrations monitored by continuous wave (cw) EPR. A combination of electron spin echo envelope modulation (ESEEM) and hyperfine sublevel correlation (HYSCORE) experiments revealed that the paramagnetic manganese(II) ion in this binding site is coupled to a single nitrogen atom with a quadrupole coupling constant kappa of 0.7 MHz, an asymmetry parameter eta of 0.4, and an isotropic hyperfine coupling constant of Aiso(14N)=2.3 MHz. All three EPR parameters are sensitive to the arrangement of the Mn(II) ligand sphere and can therefore be used to determine the structure of the binding site. A possible location for this binding site may be at the G10.1, A9 site found to be occupied by Mn(II) in crystals (MacKay et al., Nature 1994, 372, 68 and Scott et al., Science 1996, 274, 2065). To determine whether the structure of the binding site is the same in frozen solution, we performed DFT calculations for the EPR parameters, based on the structure of the Mn(II) site in the crystal. Computations with the BHPW91 density function in combination with a 9s7p4d basis set for the manganese(II) center and the Iglo-II basis set for all other atoms yielded values of kappa(14N)=+0.80 MHz, eta=0.324, and Aiso(14N)=+2.7 MHz, in excellent agreement with the experimentally obtained EPR parameters, which suggests that the binding site found in the crystal and in frozen solution are the same. In addition, we demonstrated by EPR that Mn(II) is released from this site upon binding of the aminoglycoside antibiotic neomycin B (Kd=1.2 microM) to the hammerhead ribozyme. Neomycin B has previously been shown to inhibit the catalytic activity of this ribozyme (Uhlenbeck et al., Biochemistry 1995, 34, 11 186).     

预变形结合人工时效对Al-Mg-Si合金力学性能的影响

研究预变形结合人工时效处理对AA6060铝合金强度和韧性的影响。对经过均匀化热处理和挤压加工的AA6060铝合金进行固溶处理,然后对材料实施0-10%的预变形并再进行时效处理或者在人工时效过程中进行同步变形。通过对不同时效处理后的合金的显微硬度和拉伸性能分析,发现预变形对材料的时效行为和力学性能有显著影响,它可以使合金的时效速度明显加快。比较预变形和同步变形对人工时效的影响发现,同步变形结合人工时效可以使该合金在更短的时间内得到更好的力学性能。对两种变形对时效行为的影响机理进行了探讨。     

Calcium alginate gel fibers: Influence of alginate source and gel structure on fiber strength

The low-deformation extension modulus was measured for Ca–alginate gel fibers prepared from alginates of different compositions and molecular weights. The modulus showed an increase with increasing molecular weight for alginates of the same composition and sequence parameters. Fibers prepared with an inhomogeneous polymer concentration profile showed higher moduli than did fibers with a homogeneous polymer concentration profile. The higher modulus observed for fiber prepared from an alginate with low Ca²⁺ affinity is tentatively explained as resulting from a higher degree of polymer chain alignment. © 1994 John Wiley & Sons, Inc.     

Ein Übergang aus der Strychnin- in die Heteroyohimban-Reihe der Indolalkaloide durch oxidative Umlagerung von Isostrychninsäure

A Transformation from the strychnine into the Heteroyohimbane Series of the Indole Alkaloids by Oxidative Rearrangement of Isostrychnic Acid By peroxyacid oxidation of isostrychnic acid there are formed, together with the amine oxide of base 2 , three isomeric lactone bases, C₂₁H₂₀N₂O₄, which are formulated as 3–5. Reduction of the isatogen 5 leads to ring opening on both sides of the indole nitrogen ( 6, 7 ), and hydrochloric acid introduces a chloro atom in p-position to the nitrogen ( 9 ). – Both tautomeric forms of 2 can be fixed by reduction to 8 and 10 , respectively. – The lactone ring of 2 is hydrolyzed by hot dilute hydrochloric acid, followed by rearrangement to the heteroyohimbane type indoloquinolizidine 12 . Compound 12 , featuring as keto-enol and amino acid, can be reduced and cyclised with mineral acid to the lactone 14 (two diasteroisomers) serving for X-ray structural analysis. Treatment of 12 with acetic anhydride afforded the lactone 20 by rearrangement of the double bonds. Further hydrogenation products of 12 are described ( 15 , 16 , 18 ) and their spectra, including mass and CD spectra, are discussed. Biochemical implications are referred, too.