A short range many-body potential for modelling bcc metals

The problem considered is the fitting of a many-body interaction potential to bulk crystal data. A parameterisation of the potential is assumed which is based on physical considerations. The free parameters are determined by using global optimization to perform a least squares fit, to a large number of crystal properties. This has been achieved for body centered cubic (bcc) materials. The approach adopted here fits the bcc crystal structure, as the preferred minimum energy configuration for tungsten, and also fits the dimer energetics and the elastic properties of crystalline tungsten.     

Strong interaction effects in the 2p-1s transition in pionic neon

We present experimental results for the 2p-1s transition energy and the natural line-width of the 1s state in pionic neon. The line width ifΓ=14.5 ± 3.0 keV is in substantial agreement with semiphenomenological low-energy pion-nucleus interaction theories in the region A ≈ 20.     

Alcaloides steroidiques—LII Alcaloides du buxus balearica Willd.: Cycloprotobuxine-D, buxamine-E, buxaminol-E, N-isobutyryl-baleabuxidine-F, N-benzoyl-baleabuxidine-F, baleabuxoxazine-C, N-isobutyryl-baleabuxidienine-F, N-benzoyl-baleabuxidienine-F, N-isobutyryl-baleabuxaline-F

The following alkaloides have been extracted from the leaves of Buxus balearica Willd.: cyclomicrophylline-B, cycloprotobuxines A, C and D, baleabuxine (N-isobutyryl-baleabuxine-F), buxamine-E and buxaminol-E (already reported), N-isobutyryl- and N-benzoyl-baleabuxidine-F, baleabuxoxazine-C, N-isobutyryl- and N-benzoyl-baleabuxidienine-F, N-isobutyryl-baleabuxaline-F, the structures of which are proposed. The stereochemistry of baleabuxidines and baleabuxoxazines is established on the base of chemical correlations between these two groups and cyclomicrophyllines.     

Broadly tunable femtosecond solid-state laser sources

The techniques of coupled-cavity modelocking and self-modelocking in which intensity-induced nonlinear effects are exploited have been reviewed for broad-band gain media. Particular emphases have been placed upon the archetypical colour-centre and titanium-sapphire laser configurations in which these techniques were first demonstrated and subsequent refinements are set in context. A femtosecond optical parametric oscillator pumped by a self-mode-locked titanium-sapphire laser has also been described as an exemplar of a practical means of extending the source tunability into the mid-infrared spectral region.     

Search for low-lying resonances in electron scattering by atomic hydrogen

Measurements of the transmission of an energy-selected electron beam through atomic hydrogen fail to indicate any resonance below 9·5-eV electron energy. The negative result contradicts recent suggestions by Rudkjøbing and by Van Rensbergenthat some diffuse interstellar absorption bands might be attributable to preionizing transitions in the hydrogen negative ion. A bulk of reliable theoretical data, however, justifies our finding.     

Observation of long-range compositional fluctuations in glasses: implications for atomic and electronic structure

Experimental evidence for long-range compositional fluctuations in glasses is given. The implications for electronic structure and stoichiometry-induced structural variations are analyzed. These fluctuations were discovered by examining the spatial dependence of inner shell near-edge absorption spectra obtained using a 50nm diameter probe. This spectroscopy is sensitive to both angular and distance correlations in bonding. Comparisons with spectra from compositionally equivalent crystals, and multiple-scattering calculations which include core-hole effects are used to analyze the data.     

Tomographic femtosecond x-ray diffractive imaging

A method is proposed for obtaining three simultaneous projections of a target from a single radiation pulse, which also allows the relative orientation of successive targets to be determined. The method has application to femtosecond x-ray diffraction, and does not require solution of the phase problem. We show that the principal axes of a compact charge-density distribution can be obtained from projections of its autocorrelation function, which is directly accessible in diffraction experiments. The results may have more general application to time resolved tomographic pump-probe experiments and time-series imaging.     

A comparative study of energy consumption and physical properties of microfibrillated cellulose produced by different processing methods

Microfibrillated celluloses (MFCs) with diameters predominantly in the range of 10–100 nm liberated from larger plant-based fibers have garnered much attention for the use in composites, coatings, and films due to large specific surface areas, renewability, and unique mechanical properties. Energy consumption during production is an important aspect in the determination of the “green” nature of these MFC-based materials. Bleached and unbleached hardwood pulp samples were processed by homogenization, microfluidization, and micro-grinding, to determine the effect of processing on microfibril and film properties, relative to energy consumption. Processing with these different methods affected the specific surface area of the MFCs, and the film characteristics such as opacity, roughness, density, water interaction properties, and tensile properties. Apparent film densities were approximately 900 kg/m³ for all samples and the specific surface area of the processed materials ranged from approximately 30 to 70 m²/g for bleached hardwood and 50 to 110 m²/g for unbleached hardwood. The microfluidizer resulted in films with higher tensile indices than both micro-grinding and homogenization (148 Nm/g vs. 105 Nm/g and 109 Nm/g, respectively for unbleached hardwood). Microfluidization and micro-grinding resulted in films with higher toughness values than homogenization and required less energy to obtain these properties, offering promise for producing MFC materials with lower energy input. It was also determined that a refining pretreatment required for microfluidization or homogenization can be reduced or eliminated when producing MFCs with the micro-grinder. A summary of the fiber and mechanical energy costs for different fibers and processing conditions with economic potential is presented.