Structure of cellulose and microcrystalline cellulose from various wood species, cotton and flax studied by X-ray scattering

The structure of microcrystalline cellulose (MCC) made by mild acid hydrolysis from cotton linter, flax fibres and sulphite or kraft cooked wood pulp was studied and compared with the structure of the starting materials. Crystallinities and the length and the width of the cellulose crystallites were determined by wide-angle X-ray scattering and the packing and the cross-sectional shape of the microfibrils were determined by small-angle X-ray scattering. The morphological differences were studied by scanning electron microscopy. A model for the changes in microfibrillar structure between native materials, pulp and MCC samples was proposed. The results indicated that from softwood or hardwood pulp, flax cellulose and cotton linter MCC with very similar nanostructures were obtained with small changes in reaction conditions. The crystallinity of MCC samples was 54–65%. The width and the length of the cellulose crystallites increased when MCC was made. For example, between cotton and cotton MCC the width increased from 7.1 nm to 8.8 nm and the length increased from 17.7 nm to 30.4 nm. However, the longest crystallites were found in native spruce wood (35–36 nm).     

Synthesis of novel deuterium labelled derivatives of N-alkylated polyamines

Novel di-, tetra- and octadeuterated derivatives of mono-N-alkylated diaminopropanes, spermidines, spermines, symmetrically bis-N-alkylated spermines and unsymmetrically bis-N-alkylated spermines were synthesized. Deuterium labels were introduced into the RHNCH₂CH₂CN intermediate either by exchanging the protons next to the nitrile group under basic conditions with D₂O-EtOD mixture or/and by reducing the nitrile group to a CD₂-NH₂ fragment with LiAlD₄.     

Lebesgue type decompositions for nonnegative forms

A nonnegative form on a complex linear space is decomposed with respect to another nonnegative form : it has a Lebesgue decomposition into an almost dominated form and a singular form. The part which is almost dominated is the largest form majorized by which is almost dominated by . The construction of the Lebesgue decomposition only involves notions from the complex linear space. An important ingredient in the construction is the new concept of the parallel sum of forms. By means of Hilbert space techniques the almost dominated and the singular parts are identified with the regular and a singular parts of the form. This decomposition addresses a problem posed by B. Simon. The Lebesgue decomposition of a pair of finite measures corresponds to the present decomposition of the forms which are induced by the measures. T. Ando's decomposition of a nonnegative bounded linear operator in a Hilbert space with respect to another nonnegative bounded linear operator is a consequence. It is shown that the decomposition of positive definite kernels involving families of forms also belongs to the present context. The Lebesgue decomposition is an example of a Lebesgue type decomposition, i.e., any decomposition into an almost dominated and a singular part. There is a necessary and sufficient condition for a Lebesgue type decomposition to be unique. This condition is inspired by the work of Ando concerning uniqueness questions.     

Glucomannan composite films with cellulose nanowhiskers

Spruce galactoglucomannans (GGM) and konjac glucomannan (KGM) were mixed with cellulose nanowhiskers (CNW) to form composite films. Remarkable effects of CNW on the appearance of the films were detected when viewed with regular and polarizing optical microscopes and with a scanning electron microscope. Addition of CNW to KGM-based films induced the formation of fiberlike structures with lengths of several millimeters. In GGM-based films, rodlike structures with lengths of several tens of micrometers were formed. The degree of crystallinity of mannan in the plasticized KGM-based films increased slightly when CNW were added, from 25 to 30%. The tensile strength of the KGM-based films not containing glycerol increased with increasing CNW content from 57 to 74 MPa, but that of glycerol-plasticized KGM and GGM films was not affected. Interestingly, the notable differences in the film structure did not appear to be related to the thermal properties of the films.     

Solid-state shifts in the L3M4,5M4,5 Auger spectra of the elements Cu TO Se

The kinetic-energy shifts between atomic and solid-state L₃M_4,5M_4,5 Auger electron spectra of Cu, Zn, Ga, Ge, As, and Se are determined with the aid of semiempirically calculated atomic and experimental solid-state Auger energies. The shift values are calculated by applying the thermochemical model to the Auger process. Good agreement is found between the calculated and experimental values.     

Taylor expansion of the accumulated rounding error

The article describes analytic and algorithmic methods for determining the coefficients of the Taylor expansion of an accumulated rounding error with respect to the local rounding errors, and hence determining the influence of the local errors on the accumulated error. Second and higher order coefficients are also discussed, and some possible methods of reducing the extensive storage requirements are analyzed.     

Adduct formed by chromium trioxide and zwitterionic quinolinic acid

Chromium trioxide forms an adduct with zwitterionic quinolinic acid. The structure of the product was found to be (quinolinium-3-carboxylato-O)trioxidochromium(VI), determined by single-crystal X-ray diffraction methods. To evaluate the bonding properties of the compound, its structure was optimized at the B3LYP/6-311G* level of theory. The electronic characteristics were investigated by topological methods applied to the total charge density in various model compounds including the title compound, title compound with a HF molecule presenting a hydrogen bonding and anionic moiety. Calculated aromaticity indices indicate that the quinolinic rings tend to conserve their degree of aromaticity against hydrogen bonding. However, when there is hydrogen bonding involving an N-H bond or when the quinolinium zwitterion is deprotonated, there are clear changes in the interaction between chromium trioxide and the quinolinic moiety.      

Enhanced vertical confinement in angled-wall slot waveguides

Optical confinement in slot waveguides with angled sidewalls is studied. Improved vertical optical confinement is observed. Different mode solvers are compared in the modeling of slot waveguides with varying sidewall angles. The finite element method was found best suitable for this task. The effect of the slot waveguide geometry on the vertical optical confinement is studied. The reduced effective mode area is beneficial in all-optical applications due to enhancement of nonlinear effects in the waveguide.     

Method to determine critical current of poorly cooled short sample

Superconducting wire characterization can fail owing to many reasons. For example, unintentional sample heating may distort voltage–current-data, i.e. decrease the critical current and increase the n-value. This occurs rarely if a sample is immersed into liquid cryogen, but in conduction cooled measurements, constant sample temperature is difficult to achieve. Ohmic losses are generated at current contacts as well as inside the sample even at subcritical currents. Most of these losses can be extracted using a well designed sample holder, but in any case, significant amount of heat is generated rapidly when critical current is approached and overstepped, especially if n-value is low. Then, heat has no time to conduct away, and thus, the sample will warm up distorting the measurement. In this paper, we present a computational post-processing method to reduce the effect of heating on measured voltage–current characteristics. Simulations are performed for a Bi-2223/Ag tape, but the model can be applied to any other superconductor as well.