Two-dimensional type I quadratic spatial solitons in KNbO(3) near noncritical phase matching

Experiments on the properties of quadratic, two-dimensional spatial soliton properties in KNbO(3) near and at noncritical phase matching (NCPM) are reported. The NCPM geometry leads to unique features such as a large angular bandwidth for soliton generation, weak dependence of soliton composition on intensity and incidence angle, and unique multisoliton-generation properties.     

On Asymptotic Properties of a Strongly Nonlinear Differential Equation

The paper describes asymptotic properties of a strongly nonlinear system . The existence of an n/2 parametric family of solutions tending to zero is proved. Conditions posed on the system try to be independent of its linear approximation.     

Determining the resonance frequencies of forced vibrations of turbogenerators with foundations

The model method for determination of dynamic properties of framed foundations on plastic scale models is elaborated. Position shifting of resonance peaks has been found by evaluation of different response curves, measured on models. Theoretical and experimental analysis of forced vibrations of complex damped mechanical system with several degrees of freedom has shown that resonance peaks, measured at different points of the same system, correspond to various frequencies of exciting force. To locate eigen frequencies and dangerous resonances from results of measurements, it is necessary to plot the envelope of the set of curves and to determine the positions of its peaks, or, at least, to find the concentration of resonance maxima of all individual curves.     

Taking one charge off a two-dimensional Wigner crystal

A planar array of identical charges at vanishing temperature forms a Wigner crystal with hexagonal symmetry. We take off one (reference) charge in a perpendicular direction, hold it fixed, and search for the ground state of the whole system. The planar projection of the reference charge should then evolve from a sixfold coordination (centre of a hexagon) for small distances to a threefold arrangement (centre of a triangle), at large distances d from the plane. The aim of this paper is to describe the corresponding non-trivial lattice transformation. For that purpose, two numerical methods (direct energy minimisation and Monte Carlo simulations), together with an analytical treatment, are presented. Our results indicate that the d = 0 and d → ∞ limiting cases extend for finite values of d from the respective starting points into two sequences of stable states, with intersecting energies at some value d_t; beyond this value the branches continue as metastable states.     

Intensification of heat transfer in a liquid film evaporator

Influence of the heat exchanger shape on the heat transfer efficiency investigated. Heat transfer efficiency of two vertical pipe-in-pipe heat exchangers, one with a straight wall and the other with a twisted wall were compared. Both heat exchangers worked on the principle of liquid falling film. Electric transformer oil was used as the heated liquid and water vapor at atmospheric pressure was used as the heating agent. Oil was just heated, not evaporated during the experiments. Oil inlet and outlet temperature were measured at six different oil mass flows. Heat flux and heat flux density in the straight- and twisted-wall heat exchangers were compared. Mathematical model was built to verify the possibility of the oil outlet temperature prediction.     

Measurement of critical heat flux conditions under vacuum

Determination of optimum conditions for waste oil (used motor oils, transformer oils) regeneration using vacuum distillation was attempted including the search for the optimum temperature difference between the heating surface and the boiling point of the liquid. Optimum temperature allowed the distillation equipment to operate at maximum performance. Equipment suitable for the measurement of boiling curves under atmospheric pressure and vacuum conditions was assembled. These curves were used to determine the optimum temperature difference of various substances including waste oils. Properties of pure substances, for example water, ethanol, hexane, heptane, isooctane, decane, or dodecane, were measured with this equipment under atmospheric pressure. Results of various liquids measurements under vacuum and atmospheric pressure are presented.     

Self-Associating Polymers Chitosan and Hyaluronan for Constructing Composite Membranes as Skin-Wound Dressings Carrying Therapeutics

Chitosan, industrially acquired by the alkaline N-deacetylation of chitin, belongs to β-N-acetyl-glucosamine polymers. Another β-polymer is hyaluronan. Chitosan, a biodegradable, non-toxic, bacteriostatic, and fungistatic biopolymer, has numerous applications in medicine. Hyaluronan, one of the major structural components of the extracellular matrix in vertebrate tissues, is broadly exploited in medicine as well. This review summarizes that these two biopolymers have a mutual impact on skin wound healing as skin wound dressings and carriers of remedies.     

Low uncertainty determination of manganese and vanadium in environmental and biological reference materials by instrumental neutron activation analysis

The elements Mn and V were determined by INAA in about 5 mg and 100 mg aliquots of NIST SRM 1648 to elucidate discrepancies between our previous results for the 0.5 mg to 15 mg aliquots and the NIST certified and/or information values. Simultaneously, other NIST SRMs 1633a, 2704, and BCR CRMs 038, 101 and 143 were also analyzed. Special attention was given to evaluating and minimizing uncertainties of all steps of analysis. Our results compared very well with the respective certified and/or information values (if available) of all SRMs and CRMs studied, except for NIST SRM 1648. For this SRM we have found significantly lower results than the NIST values which suggests that the NIST values are positively biased by about 10%. A new value for V in BCR CRM 143 was also obtained.     

Untersuchung von Eisen(III)-phosphiten im Hinblick auf die Wasserstoffbindungen

Iron(III) phosphites, vic. Fe₂(HPO₃)₃·9 H₂O, FeH₃P₂O₆·3 H₂O, FeH₆P₃O₉·H₂O and Fe₄H₃₃P₁₅O₄₅·6 H₂O were studied by means of powder X-ray, thermographic, IR and UV spectroscopy methods and by measurement of magnetic susceptibility. From the results obtained, and from analogy with phosphites studied earlier, the following structural model can be proposed: in the compounds studied, every iron atom is surrounded by six oxygen atoms of the water molecules and phosphite or, polyorthophosphite anions which form a weak ligand field of approximately octahedral symmetry. In Fe₂(HPO₃)₃·9 H₂O, symmetry of the anion is decreased from the point group C_3v to the C_s group. This anion is characterised by two bonding distances between phosphorus and oxygen atoms,r _PO=1,46 Å andr _{PO 2}=1,50 Å, the respective force constants beingK _PO=8.7 mdyn/Å andK _PO2=7.1 mdyn/Å. Three types of hydrogen bonds occur in the crystal lattices of the compounds studied. The weakest bond (bond lengthr=2.86–2.88 Å, bond energyE=4.6–5.0 kcal/bond) is formed between molecules of hydrate water, its energy approaching that of the hydrogen bond in liquid water. The stronger hydrogen bond (r=2.67–2.70 Å,E=5.7 to 8.0 kcal/bond) is found between water molecules and phosphite or polyorthophosphite anions. The strongest hydrogen bond (r=2.55–2.64 Å) is formed by polyorthophosphite anions, linking hydroxyl groups to oxygen atoms bound to different phosphorus atoms.     

Hydrogen photoevolution on InGaP polycrystalline and tandem-type electrodes

We report on preparation of p-In_1−x Ga _x P polycrystalline, p-In_0.5 Ga_0.5P/p-GaAs, and p-In_0.5 Ga_0.5P/n-GaAs/n-InP tandem-type cathodes. The photovoltaic efficiency of InGaP tandem type epitaxial electrodes is two times higher than that of polycrystalline photocathodes. The most significant advantage of epitaxial electrodes is in their markedly better corrosion resistance in comparison with polycrystalline photocatodes. Presented at the 1st Czech-Chinese Workshop “Advanced Materials for Optoelectronics”, Prague, Czech Republic, June 13–17, 1998.