Temporal‐spatial dispersion and stability analysis of finite element method in explicit elastodynamics

This work presents the temporal‐spatial (full) dispersion and stability analysis of plane square linear and biquadratic serendipity finite elements in explicit numerical solution of transient elastodynamic problems. Here, the central difference method, as an explicit time integrator, is exploited. The paper complements and extends the previous work on spatial/grid dispersion analysis of plane square biquadratic serendipity finite elements. We report on a computational strategy for temporal‐spatial dispersion relationships, where eigenfrequencies from grid/spatial dispersion analysis are adjusted to comply with the time integration method. Besides that, an ‘optimal’ lumped mass matrix for the studied finite element types is proposed and investigated. Based on the temporal‐spatial dispersion and stability analysis, relationships suggesting the ‘proper’ choice of mesh size and time step size from knowledge of the loading spectrum are presented. Copyright © 2015 John Wiley & Sons, Ltd.     

Characterization of oxidized cellulose with ultraviolet–visible spectroscopy

This article describes some properties and behavior of oxidized cellulose evaluated with ultraviolet–visible spectroscopy. Newly defined analytical parameters are described. Mechanisms of poly(1,4‐β‐D ‐anhydroglucuronic acid) degradation and destruction are formulated. The feasibility of using the same Staudinger–Mark–Houwink equation to calculate the degree of polymerization of cellulose and the degree of polymerization of oxidized cellulose is demonstrated. Utilization of ultraviolet–visible spectroscopy is shown for the optimization of oxidized cellulose production and aging. Advantages and limitations of this method are discussed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

The last snapshot of natural pelagic fish assemblage in Lake Turkana,Kenya: A hydroacoustic study

A hydroacoustic survey and supplementary gillnet investigation were carried out in the open water of the central part of Lake Turkana in September 2009. Overall acoustic fish density and biomass were assessed as 1381 ind./ha and 30 kg/ha, respectively. The fish density estimate was lower than the results from two previous investigations in the 1970s and 1980s (long-term average 3739 ind./ha), but the biomass remained relatively unchanged (long-term average 25.4 kg/ha). A decreasing gradient in pelagic fish density from the western to eastern shore of the lake was observed. Fish were distributed unevenly within the water column. During the day, a majority of fish aggregated in the mid-water layers (10–12 m below the water surface), creating on echograms the so-called Midwater Scattering Layer. This feature dissipated completely during dusk and the majority of fish occurred in the surface layers at night. These diel vertical fish migrations influenced day and night hydroacoustic estimates of the total fish abundance. Synodontis spp., Lates spp. and Schilbe uranoscopus dominated the catch of both mid-water and bottom gillnets installed in open water areas. Hydrocynus forskalii and Brycinus spp. contributed significantly to the catch of mid-water gillnets while Bagrus bayad and the endemic Haplochromis macconneli occurred only in the catch of the bottom gillnets.     

1D-photonic crystals prepared from the amorphous chalcogenide films

We describe the preparation and optical properties of the 15-layer chalcogenide dielectric mirrors with the first order stop bands in near infrared range. The high refractive index Sb–Se and low refractive index Ge–S layers were deposited on silicon and glass substrates using thermal evaporation method. To centre the stop bands of the prepared chalcogenide mirrors at 1.55 μm, the layer thicknesses, d(Sb–Se) = 117 and d(Ge–S) = 183 nm, were calculated from the quarter wave stack condition. The optical reflectivity measurements revealed the total reflection from the 15-layer chalcogenide mirrors in the range of 1,400–1,600 nm for the unpolarized light with normal incidence. The effect of annealing on the optical properties of the prepared chalcogenide mirrors was studied as well. Using spectral ellipsometry, we examined the angular dependence of the multilayers reflectivity for the light with s- and p-polarization. The preparation of the dielectric mirrors for near infrared region from chalcogenide films seems to be possible exploiting good optical quality of chalcogenide films and their simple deposition.     

Luftionen in Gebäuden – elektroionisches Mikroklima

Air ionization and indoor climate. Positive and negative ions are produced in the air by the impact of the electric field between earth and ionosphere, by UV and cosmic radiation and by so called Lenard effect. The created electrically charged particles (ions) are not stable and join together with neutral atoms and molecules into the complexes of 10 to 30 molecules being already stable and called “lightweight ions” or “aeroions”. In an interior the aeroion creation is impacted by the external walls (classic materials as wood and bricks are optimal), by air‐handling systems (aeroions are discharged at the metal parts of the system), by indoor equipment (e.g., raw wood without surface finish neutralizes a considerable aeroion quantity by its surface) and by human activities: just one smoked cigarette liquidates practically all aeroions in the room. The aeroions are the catalyzers of human body biochemical reactions and affects the nervous system total condition. Finally principles of the most often used ionizers are presented, especially hydrodynamic and with corona charge.     

Effects of monomer impurities on the emulsion polymerization of chloroprene and properties of polychloroprene. II. Effect of monovinylacetylene

The free-radical emulsion polymerization of chloroprene containing monovinylacetylene in concentrations from 0% to 10% has been studied. It was found that in the presence of monovinylacetylene, a polymer with a great gel content, increased values of plasticity, and deteriorated physical and mechanical properties is formed. Monovinylacetylene has been proved to copolymerize with chloroprene under the conditions used. Acetylenic groups remain unchanged in the copolymer; they cause the crosslinking of polychloroprene macromolecules and corresponding changes in polymer properties. Copolymerization reactions of monovinylacetylene with chloroprene together with the crosslinking effect of monovinylacetylene cause a substantial lowering of the crystallization rate of polychloroprene.     

Determination of the density dispersion of suspension poly(vinyl chloride) by the method of kinetic density curves

A new method has been developed for the evaluation and comparison of quality of various types of poly(vinyl chloride) (PVC) powder with respect to their density homogeneity. The method consists in the determination of the dependence of the volume of a specifically heavier fraction of PVC powder on the density or concentration of testing aqueous NaNO₃ solutions after a chosen time of contact between the powder and the testing solutions. Compared with the method of determination of density distribution using densitometric titration, the new method simplifies and extends possibilities of comparison of polymers and improves the density characterization.     

Estimation of the inherent friction factor per main-chain friction unit of liquid low-molecular-weight unsaturated polyesters

The temperature dependence (at 323–443 K) of the zero-shear viscosity η of about 30 nonfractionated samples of an unsaturated polyester (300 < M_n < 1500) was analyzed and the parameters of the Vogel equation describing the η(T) dependence were estimated. Their dependence on the molecular weight is discussed. The inherent friction factor per main-chain friction unit, ξ_o, has been evaluated for 15 < Z_n < 70 (where Z_n is the number-average number of main-chain friction units) and compared with the values available for other polymers.     

Effect of temperature on the solution properties in 2-ethoxyethanol of statistical copolymers of methacrylic acid and methyl methacrylate

Summary The temperature dependence of the second virial coefficient and intrinsic viscosity of statistical copolymers of methyl methacrylate and methacrylic acid in 2-ethoxyethanol was investigated. It was found that the -temperatures of copolymers are outside the temperature range given by the -values for poly(methacrylic acid) and poly(methyl methacrylate). Their dependence on the copolymer composition has a discontinuity. Simple theoretical considerations have shown that this behaviour may be expected with copolymers composed of monomer units dissolving, respectively, with absorption and evolution of heat.